Minggu, 02 September 2018

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                         Hasil gambar untuk usa flag selenium      Gambar terkait

                  Hasil gambar untuk digital selenium electronic clock  Hasil gambar untuk digital selenium electronic clock

                      Analogs of Basic Electronic Circuit Elements in a Free-Space Atom         

                                                                     CHIP 


Electronics is based on the manipulation of electrons, possibly enhanced by exploiting internal structure associated with spin (spintronics). Atomtronics seeks do the same with neutral atoms. The more complex internal structure of atoms makes the possibilities of such an architecture far richer than its electronic analog. Recently, persistent currents of superfluid neutral atoms have been created in ring circuits, which are close analogs to superconducting circuits. There have also been efforts towards developing analogs to active electronic circuit elements such as diodes and transistors. Any usable neutral atom circuit, however, will need analogs to the most basic electronic elements – resistors (R), capacitors (C) and inductors (L). Using a two-dimensional (2D) optical dipole potentialto generate what we call free-space atom chips, we have created and characterized a neutral-atom RLC circuit. We show that the resistance is analogous to ballistic (Sharvin) resistance in metals, the inductance is analogous to kinetic inductance in superconductors, and the capacitance is analogous to the quantum capacitance in nanoscale devices,.
A 2D neutral atom analog to an electronic RLC circuit can be realized with a classical ideal gas using two containers of areas A1 and A2 connected by a channel. In an electronic capacitor, a charge imbalance (Q) between two conductors produces a potential difference (ΔV). When a resistor connects the two conductors, electrons flow to eliminate the charge imbalance, causing ΔV to vanish. In our system, a number imbalance (N) between the two containers produces a chemical potential difference (Δμ). When a channel connects the two containers, atoms flow to eliminate the number imbalance, causing Δμ to vanish. To complete this analogy, we define a chemical capacitance,
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with SI units of 1/J and with the same form as the electronic capacitance C = QV.
The chemical potential of a 2D ideal gas is the change in free energy associated with changing the number of particles in the system,
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where k is Boltzmann's constant, h Planck's constant, T the temperature, n the 2D number density and m the mass of a particle in the gas. To determine the capacitance, we start by assuming the two chambers to be in equilibrium, with equal temperatures and equal densities, N1e/A1 = N2e/A2 = ne. Moving a small number of particles N fromA1 to A2 leads to an imbalance in the densities so that n1 = (N1e − N)/A1 and n2 = (N2e + N)/A2. Subtractingequation (2) with n1 from equation (2) with n2 leads to
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This linear approximation is valid for N ≪ N1e and N2e. The experiment we describe below is within this limit. Combining equations (1) and (4) leads to an expression for the neutral-atom chemical capacitance,
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where An external file that holds a picture, illustration, etc.
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When a channel is opened between the chambers, it acts as a resistor and an inductor. To determine the values ofR and L, we examine the flow dynamics of the system. In a 2D ideal gas, the effusion rate F of atoms out of either container is given by
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where Ai is the area of the container and w is the width of the channel. The total rate of change in atom number in container 1 can then be written as
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where the second term on the right hand side of the equation, representing the rate that atoms enter container 1 due to leaving container 2, is evaluated at a time Δt earlier. This delay is due to the finite velocity of the atoms traversing the channel. We approximate this delay time using the average transverse velocity of an atom in the channel,
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where l is the length of the channel. When we combine equations (58), and linearly expand the terms in equation (7) involving Δt, the result is analogous to Kirchhoff's law applied to a series RLC circuit,
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with chemical resistance and inductance given by
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with SI units of J · s and J · s2 respectively. Here,
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is the average 2D momentum of the particles in one container. We dropped a second term in the resistance that is only significant when the channel represents a large portion of the entire area of the system. At this point the small N approximation breaks down, thus the second term is negligible when equation (9) is valid.
The chemical capacitance, resistance and inductance each have specific electronic analogs. Our capacitance results from the shift in chemical potential due to transfer of particles, the same effect that causes the quantum capacitance in nanostructures,. For 2D quantum dots with areas A1 and A2, the quantum capacitance is given by
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where εF is the Fermi energy of the gas. This is similar to equation (5), with an electrical factor of e2 and the thermal energy replaced by the 2D Fermi energy. It is interesting to note that taking An external file that holds a picture, illustration, etc.
Object name is srep01034-m16.jpg in equation (12) does not yield the correct classical limit of the quantum capacitance, which is equation (5).
In electronics, a point junction smaller than the mean free path of the electrons creates what is known as the Sharvin resistance. This arises purely from the ballistic motion of the electrons because there is no scattering of electrons in the point junction itself. For a 2D electronic system the Sharvin resistance is given by
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where An external file that holds a picture, illustration, etc.
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There is an inductance in electronic systems, the kinetic inductance, that arises due to the kinetic energy associated with current flow in a wire,
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Again, this shares the same form as our chemical inductance, differing by a factor of e2 and a numerical factor.
The methods that we used to calculate the capacitance and resistance of classical ideal gas circuit elements can be extended to other atomic systems such as degenerate Fermi gases and Bose-Einstein condensates. To define the chemical capacitance, all that is needed is the dependence of the chemical potential on atom number. The momentum distribution of the sample determines the effusion rate, which leads directly to the chemical resistance. Table 1 summarizes these results for 2D and 3D non-interacting classical gases, non-interacting degenerate Fermi gases, and BECs. The BEC cases are derived using the Gross-Pitaevskii (GP) equations for hard-wall containers in the Thomas-Fermi limit. In this case it is not sufficient to describe the system as consisting of point particles with classical trajectories, which is needed to derive the resistance, thus this is omitted. The 2D Fermi gas capacitance formula is exact. The classical gas and the 3D Fermi gas capacitances are all the first-order terms in Taylor series expansions.

Table 1

Summary of chemical capacitances and resistances for various systems. In the 2D systems, An external file that holds a picture, illustration, etc.
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CcRc
2D3D2D3D
Classical
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Fermi T = 0
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BEC (GP)
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Results

To realize a classical ideal gas neutral atom capacitor, we begin with a sample of 87Rb atoms, cooled and confined using a magneto-optical trap (MOT). This MOT is created inside of a free-space atom chip that consists of two circular containers separated by a rectangular channel. The method used for creating this potential is discussed in the methods section. At time t = 0, the atoms are released from the MOT after a final cooling stage, and allowed to flow between the containers for a variable amount of time, after which a fluorescence image is taken of the atoms. We directly image the gas flow between the containers with this setup. The evolution of this system can be seen in figure 1. We point out that the arrangement employed is similar to that used in atom-optics billiards where a circular potential is known to lead to ”regular” dynamics, which would affect the effusion rate in our experiment. In our case however, the container walls are not smooth, as discussed in the methods. Because of this the atom-wall collisions are not always specular, leading to ergodic dynamics, thus our use of equation (6) is valid. Figure 2shows the decay of the normalized number imbalance N/Ne as a function of time for several channel widths, as well as the solution to the RLC differential equation for the parameters used. The only fit parameter for the RLC solution is the initial atom number imbalance.



Capacitor Discharge.
Images of a discharging atom capacitor with a channel width of 340 μm. The atoms are loaded into the right container and released from the MOT at t = 0 ms. The images are snapshots at 5 ms intervals, starting at t = 5 ms (viewed left to right, top to bottom). Each frame is the average of eight individual experimental runs, and is scaled independently of the other frames.



Comparison of experimental data to analytic solution.
The points indicate the experimental data and the solid lines represent the relevant RLC solution. The black line is for a channel width of 240 μm, the red 384 μm, and the green 576 μm. From equations (5,10), the RC time constant, An external file that holds a picture, illustration, etc.
Object name is srep01034-m18.jpg, can be calculated for each of these systems to be 34, 21 and 14 ms respectively. The diameter of each container is 600 μm. For each experimental data point, 8 individual runs were averaged. The error bars are the standard deviation of the mean.

Discussion

For channels up to approximately half the width of the containers, the data and theory agree well. For channels that approach the width of the containers (green plot in figure 2), the assumption of local equilibrium is no longer valid, and good agreement is not expected, and indeed is not seen. The nature of the disagreement appears to be inductive, showing a significant overshoot. This however, is not the inductance we derive, which is too small to account for this phenomenon.
We have experimentally demonstrated atomtronic capacitors and resistors, and shown how to construct an atomtronic inductor, all on a free-space atom chip defined using 2D optical dipole potentials. These basic linear devices are necessary for biasing active devices, and are also essential for constructing oscillators and filters. Integration into systems such as loops containing BECs, atomtronic Josephson junctions based on BECs, BEC analogs of SQUIDs, and atomtronic batteries, diodes and transistors, is made much more simple through the flexibility of our atom-chip technique.

Methods

To create the trap geometry that was necessary to carry out this experiment, we used what we call free-space atom chips, which are a type of crossed optical dipole trap. We use a sheet dipole trap to confine the atoms to a 2D plane. On top of this, we project an arbitrary 2D optical dipole potential to create the geometry necessary for the experiment. In this particular experiment, the sheet trap was a blue-detuned, repulsive beam confining the atoms from below, with gravity confining them from above.
In the plane, we create our arbitrary 2D pattern using a generalized phase contrast approach. This scheme is shown in figure 3 a). A phase pattern is imprinted onto an input TEM00 beam and sent through a 4-f imaging system. We used a 2D spatial light modulator (SLM) to imprint the pattern. At the Fourier plane, there is a phase-contrast filter that shifts the phase of the lowest spatial frequencies, which exist near the optical axis, by π relative to the remaining spatial frequencies of the beam. The two parts of the beam interfere in the output plane to produce an intensity profile that mirrors the input phase mask. This plane is imaged onto the sheet potential, effectively etching the sheet to create our free-space atom chip. The intensity profile for one of our capacitor potentials is shown in figure 3 b). This method, with the use of the computer-addressable SLM, allows us to create and easily modify the confining potential used in the experiment. This ability was integral to this experiment as it allowed us to easily adjust the channel width. Because of the pixelazation of our SLM, the walls of our containers are rough on the order of 10 μm.

Phase-Contrast imaging system with typical output.
a) A basic phase-contrast imaging system with input phase mask, phase-contrast filter, and 4-f lens arrangement, and b) a typical output pattern used to create blue-detuned optical dipole potentials for an atom capacitor. The blue (white) areas correspond to light (absence of light).
In the experiment, the atoms start with a temperature of approximately 40 μK. The potential height of the container walls is approximately 60 μK. Since there is a significant population of atoms in the thermal distribution with an energy that can escape the trap, there is a truncated velocity distribution in the sample. The number density of the atoms in this experiment is not high enough for rethermalization to occur. Time-of-flight expansion experiments have shown that the truncated distribution is well approximated by a thermal distribution at a temperature of about 20 μK, which is the temperature used in the analytical RLC plots in figure 3. The potential height of the sheet below the atoms is approximately 500 μK, which is effectively infinite when compared to our atom temperatures.
The images were taken by switching on the original near-resonant MOT light for 100 μs, and collecting the light scattered by the atoms using a single lens, one-to-one imaging system with the image plane on the sensor of our camera. A background image was then subtracted to obtain the final image for any one shot. Eight individual runs were then averaged together for each frame of figure 1. To count the atom number difference plotted in figure 2, each imaged was masked off to count the number of atoms in either the left or right container. The error bars in this plot are the standard deviation in the mean for this measurement for the eight runs. Each image was taken after a short (2 ms) time-of-flight for technical reasons. 

                                         XO___XO  What is Selenium?

the chemical element of atomic number 34, a gray crystalline nonmetal with semiconducting properties.

                       



          Early Components — Rectifiers 

Converting ac to dc has been accomplished by several different types of rectifiers through the years. Here are a few of the more common types of rectifiers used in the past 100 years.


    Mercury arc rectifiers
Mercury arc rectifiers, also known as "Cooper Hewitt Rectifiers" were used in the early 20th century before the use of semiconductors to convert alternating current to direct current in high-voltage and -current applications. Constructed of glass for low-power applications and steel tanks for higher-power applications, Mercury Arc rectifiers work on the principle that an arc of electricity between an anode and a pool of mercury will only pass current in one direction. It was not uncommon to have a glass mercury arc rectifier with several anodes for higher-power applications that resembled a large glass octopus.
Today these large odd-shaped tubes are sought after by vacuum tube collectors. Unfortunately since they contain mercury, they are considered hazardous material and should not be shipped by common carrier or the U.S. Mail. The large amount of liquid mercury in these rectifiers has lead to many of them being recycled, further reducing the number that turn up for collectors. Today expect to pay $50 to $150 for a two anode rectifier and several hundred dollars for mercury arc rectifiers with more than two anodes. It's not very likely, but if you are looking to add one to a collection, you might find one in your local area, so proper packing and shipping won't be a concern and additional cost.

The Raytheon BH vacuum tube rectifier
In the second half of the 1920s, Raytheon developed the BH rectifier tube. Its primary purpose was to supply enough power to convert the new household 110-V ac current from a lighting circuit into the two or three different voltages needed to replace the costly batteries in most early battery powered home radios. Containing two cathodes in fireproof sleeves, the BH tube was able to supply enough power in a package the size of a standard radio tube without frequent burn out. The BH rectifier tube also had a consistent voltage drop, which meant the associated power supply circuits needed less filtering and voltage regulation.

 
A Raytheon BH Tube Rectifier.
The BH tube was used extensively in radio battery eliminators through the second half of the 1920s. A BH tube is easily recognized by its mushroom-shaped anode inside the top of the tube.
Typical construction of a BH tube rectifier.

Since the BH tube was primarily used in battery eliminators and not the radio itself, the BH tube is harder to find. The current demand for the BH tube is primarily for use in restoring a 1920s battery eliminator or as a display item in a vacuum tube collection. Even though these are less common, they usually sell for $10 to $25 in good working condition.

Tungar bulbs
Tungar bulbs were half-wave rectifiers and commonly used in battery chargers, carbon-arc lamps, early high-power speaker systems, and other industrial applications. The "Tungar" name is derived from the tungsten filament and argon gas used in these early rectifiers. The term "bulb" most likely comes from the large-diameter screw-type base many had.

The Tungar bulb rectifier
Tungar bulbs were still used up to the 1970s in stage lighting. Today they are easy to find, so their value is not great. Typical prices range from $25 to $40 for nice collector examples with their original porcelain sockets, but Tungar bulbs in working condition may sometimes be found for as little as $15 to $20.


The Number 80 vacuum tube
The 80 vacuum tube is a full-wave rectifier. This type of four-pin glass rectifier tube appeared around 1926. Like the BH tube, the 80's early development was driven by the implementation of electricity in the home and increasing demand for home radios that could run off the new ac electric light wiring.
A common #80 vacuum tube.
The 80 was most commonly used in home radios and tube amplifiers in the 1930s. Different manufactures numbered their 80 as 280, UX280 and other numbers. This was the most common type of rectifier vacuum tube and was used in millions of radios up to the 1940s, when it was replaced by updated versions based on the same design. Today an unused (new-old stock) or tested number 80 vacuum tube sells for between $12 and $25.

Selenium rectifiers
One of the more interesting rectifiers was used after World War II. Developed in the 1930s, the selenium rectifier contained a stack of several steel or aluminum plates coated with bismuth or nickel, with a thicker layer of selenium and a halogen element added. Each plate could typically withstand 20 to 22 reverse volts and the voltage rating was easily increased by adding additional plates to the stack at the time of production. Selenium rectifiers were more efficient than vacuum tubes but unfortunately, they had a shorter usable lifespan and could not be easily replaced by the end user. By the 1970s they were replaced by the smaller, more efficient and reliable silicon diode, which was much cheaper to manufacture.

Selenium Rectifiers voltage rating was increased by adding plates.

Selenium rectifiers today have little or no value to a collector or equipment restorer. I have seen selenium rectifiers rebuilt by inserting a diode inside to maintain the original look but most restorers and service technicians today simply replace them with a modern rectifier.

                         

                         Atomtronics 

Atomtronics is an emerging sub-field of ultracold atomic physics which encompasses a broad range of topics featuring guided atomic matter waves. The systems typically include components analogous to those found in electronic or optical systems, such as beam splitters and transistors. Applications range from studies of fundamental physics to the development of practical devices.

 

Etymology

Atomtronics is a contraction of "atom" and "electronics", in reference to the creation of atomic analogues of electronic components, such as transistors and diodes, and also electronic materials such as semiconductors.[1] The field itself has considerable overlap with atom optics and quantum simulation, and is not strictly limited to the development of electronic-like components.

Methodology

Three major elements are required for an atomtronic circuit. The first is a Bose-Einstein condensate, which is needed for its coherent and superfluid properties, although an ultracold Fermi gas may also be used for certain applications. The second is a tailored trapping potential, which can be generated optically, magnetically, or using a combination of both. The final element is a method to induce movement of atoms within the potential, which can be achieved in a number of ways. For example, a transistor-like atomtronic circuit may be realized by a ring-shaped trap divided into two by two moveable weak barriers, with the two separate parts of the ring acting as the drain and the source, and the barriers acting as the gate. As the barriers move, atoms flow from the source to the drain.

Applications

The field of atomtronics is still very young. Any schemes realized thus far are proof-of-principle. Applications include:
Obstacles to the development of practical sensing devices are largely due to the technical challenges of creating Bose-Einstein condensates, as they require bulky lab-based setups not easily suitable for transportation, although creating portable experimental setups is an active area of research.
     
                 

                              Robotics


  
Robotics is an interdisciplinary branch of engineering and science that includes mechanical engineering, electronics engineering, computer science, and others. Robotics deals with the design, construction, operation, and use of robots, as well as computer systems for their control, sensory feedback, and information processing.
These technologies are used to develop machines that can substitute for humans and replicate human actions. Robots can be used in any situation and for any purpose, but today many are used in dangerous environments (including bomb detection and deactivation), manufacturing processes, or where humans cannot survive. Robots can take on any form but some are made to resemble humans in appearance. This is said to help in the acceptance of a robot in certain replicative behaviors usually performed by people. Such robots attempt to replicate walking, lifting, speech, cognition, and basically anything a human can do. Many of today's robots are inspired by nature, contributing to the field of bio-inspired robotics.
The concept of creating machines that can operate autonomously dates back to classical times, but research into the functionality and potential uses of robots did not grow substantially until the 20th century.[1] Throughout history, it has been frequently assumed that robots will one day be able to mimic human behavior and manage tasks in a human-like fashion. Today, robotics is a rapidly growing field, as technological advances continue; researching, designing, and building new robots serve various practical purposes, whether domestically, commercially, or militarily. Many robots are built to do jobs that are hazardous to people such as defusing bombs, finding survivors in unstable ruins, and exploring mines and shipwrecks. Robotics is also used in STEM (science, technology, engineering, and mathematics) as a teaching aid.
Robotics is a branch of engineering that involves the conception, design, manufacture, and operation of robots. This field overlaps with electronics, computer science, artificial intelligence, mechatronics, nanotechnology and bioengineering 

Robotic aspects

Mechanical construction
Electrical aspect
A level of programming
There are many types of robots; they are used in many different environments and for many different uses, although being very diverse in application and form they all share three basic similarities when it comes to their construction:
  1. Robots all have some kind of mechanical construction, a frame, form or shape designed to achieve a particular task. For example, a robot designed to travel across heavy dirt or mud, might use caterpillar tracks. The mechanical aspect is mostly the creator's solution to completing the assigned task and dealing with the physics of the environment around it. Form follows function.
  2. Robots have electrical components which power and control the machinery. For example, the robot with caterpillar tracks would need some kind of power to move the tracker treads. That power comes in the form of electricity, which will have to travel through a wire and originate from a battery, a basic electrical circuit. Even petrol powered machines that get their power mainly from petrol still require an electric current to start the combustion process which is why most petrol powered machines like cars, have batteries. The electrical aspect of robots is used for movement (through motors), sensing (where electrical signals are used to measure things like heat, sound, position, and energy status) and operation (robots need some level of electrical energy supplied to their motors and sensors in order to activate and perform basic operations)
  3. All robots contain some level of computer programming code. A program is how a robot decides when or how to do something. In the caterpillar track example, a robot that needs to move across a muddy road may have the correct mechanical construction and receive the correct amount of power from its battery, but would not go anywhere without a program telling it to move. Programs are the core essence of a robot, it could have excellent mechanical and electrical construction, but if its program is poorly constructed its performance will be very poor (or it may not perform at all). There are three different types of robotic programs: remote control, artificial intelligence and hybrid. A robot with remote control programing has a preexisting set of commands that it will only perform if and when it receives a signal from a control source, typically a human being with a remote control. It is perhaps more appropriate to view devices controlled primarily by human commands as falling in the discipline of automation rather than robotics. Robots that use artificial intelligence interact with their environment on their own without a control source, and can determine reactions to objects and problems they encounter using their preexisting programming. Hybrid is a form of programming that incorporates both AI and RC functions.

Applications

As more and more robots are designed for specific tasks this method of classification becomes more relevant. For example, many robots are designed for assembly work, which may not be readily adaptable for other applications. They are termed as "assembly robots". For seam welding, some suppliers provide complete welding systems with the robot i.e. the welding equipment along with other material handling facilities like turntables etc. as an integrated unit. Such an integrated robotic system is called a "welding robot" even though its discrete manipulator unit could be adapted to a variety of tasks. Some robots are specifically designed for heavy load manipulation, and are labelled as "heavy duty robots".
Current and potential applications include:
  • Military robots
  • Caterpillar plans to develop remote controlled machines and expects to develop fully autonomous heavy robots by 2021.[19] Some cranes already are remote controlled.
  • It was demonstrated that a robot can perform a herding[20] task.
  • Robots are increasingly used in manufacturing (since the 1960s). In the auto industry, they can amount for more than half of the "labor". There are even "lights off" factories such as an IBM keyboard manufacturing factory in Texas that is 100% automated.[21]
  • Robots such as HOSPI[22] are used as couriers in hospitals (hospital robot). Other hospital tasks performed by robots are receptionists, guides and porters helpers.[23]
  • Robots can serve as waiters[24][25] and cooks,[26] also at home. Boris is a robot that can load a dishwasher.[27] Rotimatic is a robotics kitchen appliance that cooks flatbreads automatically.[28]
  • Robot combat for sport – hobby or sport event where two or more robots fight in an arena to disable each other. This has developed from a hobby in the 1990s to several TV series worldwide.
  • Cleanup of contaminated areas, such as toxic waste or nuclear facilities.[29]
  • Agricultural robots (AgRobots[30][31]).
  • Domestic robots, cleaning and caring for the elderly
  • Medical robots performing low-invasive surgery
  • Household robots with full use.
  • Nanorobots
  • Swarm robotics

Components

Power source

At present, mostly (lead–acid) batteries are used as a power source. Many different types of batteries can be used as a power source for robots. They range from lead–acid batteries, which are safe and have relatively long shelf lives but are rather heavy compared to silver–cadmium batteries that are much smaller in volume and are currently much more expensive. Designing a battery-powered robot needs to take into account factors such as safety, cycle lifetime and weight. Generators, often some type of internal combustion engine, can also be used. However, such designs are often mechanically complex and need a fuel, require heat dissipation and are relatively heavy. A tether connecting the robot to a power supply would remove the power supply from the robot entirely. This has the advantage of saving weight and space by moving all power generation and storage components elsewhere. However, this design does come with the drawback of constantly having a cable connected to the robot, which can be difficult to manage.[32] Potential power sources could be:

Actuation

A robotic leg powered by air muscles
Actuators are the "muscles" of a robot, the parts which convert stored energy into movement. By far the most popular actuators are electric motors that rotate a wheel or gear, and linear actuators that control industrial robots in factories. There are some recent advances in alternative types of actuators, powered by electricity, chemicals, or compressed air.

Electric motors

The vast majority of robots use electric motors, often brushed and brushless DC motors in portable robots or AC motors in industrial robots and CNC machines. These motors are often preferred in systems with lighter loads, and where the predominant form of motion is rotational.

Linear actuators

Various types of linear actuators move in and out instead of by spinning, and often have quicker direction changes, particularly when very large forces are needed such as with industrial robotics. They are typically powered by compressed and oxidized air (pneumatic actuator) or an oil (hydraulic actuator).

Series elastic actuators

A flexure is designed as part of the motor actuator, to improve safety and provide robust force control, energy efficiency, shock absorption (mechanical filtering) while reducing excessive wear on the transmission and other mechanical components. The resultant lower reflected inertia can improve safety when a robot is interacting with humans or during collisions. It has been used in various robots, particularly advanced manufacturing robots and[33] walking humanoid robots.[34]

Air muscles

Pneumatic artificial muscles, also known as air muscles, are special tubes that expand(typically up to 40%) when air is forced inside them. They are used in some robot applications.

Muscle wire

Muscle wire, also known as shape memory alloy, Nitinol® or Flexinol® wire, is a material which contracts (under 5%) when electricity is applied. They have been used for some small robot applications.

Electroactive polymers

EAPs or EPAMs are a new plastic material that can contract substantially (up to 380% activation strain) from electricity, and have been used in facial muscles and arms of humanoid robots,[40] and to enable new robots to float,[41] fly, swim or walk.[42]

Piezo motors


Recent alternatives to DC motors are piezo motors or ultrasonic motors. These work on a fundamentally different principle, whereby tiny piezoceramic elements, vibrating many thousands of times per second, cause linear or rotary motion. There are different mechanisms of operation; one type uses the vibration of the piezo elements to step the motor in a circle or a straight line.[43] Another type uses the piezo elements to cause a nut to vibrate or to drive a screw. The advantages of these motors are nanometer resolution, speed, and available force for their size.[44] These motors are already available commercially, and being used on some robots.[45][46]

Elastic nanotubes

Elastic nanotubes are a promising artificial muscle technology in early-stage experimental development. The absence of defects in carbon nanotubes enables these filaments to deform elastically by several percent, with energy storage levels of perhaps 10 J/cm3 for metal nanotubes. Human biceps could be replaced with an 8 mm diameter wire of this material. Such compact "muscle" might allow future robots to outrun and outjump humans.[47]

Sensing

Sensors allow robots to receive information about a certain measurement of the environment, or internal components. This is essential for robots to perform their tasks, and act upon any changes in the environment to calculate the appropriate response. They are used for various forms of measurements, to give the robots warnings about safety or malfunctions, and to provide real-time information of the task it is performing.

Touch

Current robotic and prosthetic hands receive far less tactile information than the human hand. Recent research has developed a tactile sensor array that mimics the mechanical properties and touch receptors of human fingertips.[48][49] The sensor array is constructed as a rigid core surrounded by conductive fluid contained by an elastomeric skin. Electrodes are mounted on the surface of the rigid core and are connected to an impedance-measuring device within the core. When the artificial skin touches an object the fluid path around the electrodes is deformed, producing impedance changes that map the forces received from the object. The researchers expect that an important function of such artificial fingertips will be adjusting robotic grip on held objects.
Scientists from several European countries and Israel developed a prosthetic hand in 2009, called SmartHand, which functions like a real one—allowing patients to write with it, type on a keyboard, play piano and perform other fine movements. The prosthesis has sensors which enable the patient to sense real feeling in its fingertips.[50]

Vision


Computer vision is the science and technology of machines that see. As a scientific discipline, computer vision is concerned with the theory behind artificial systems that extract information from images. The image data can take many forms, such as video sequences and views from cameras.
In most practical computer vision applications, the computers are pre-programmed to solve a particular task, but methods based on learning are now becoming increasingly common.
Computer vision systems rely on image sensors which detect electromagnetic radiation which is typically in the form of either visible light or infra-red light. The sensors are designed using solid-state physics. The process by which light propagates and reflects off surfaces is explained using optics. Sophisticated image sensors even require quantum mechanics to provide a complete understanding of the image formation process. Robots can also be equipped with multiple vision sensors to be better able to compute the sense of depth in the environment. Like human eyes, robots' "eyes" must also be able to focus on a particular area of interest, and also adjust to variations in light intensities.
There is a subfield within computer vision where artificial systems are designed to mimic the processing and behavior of biological system, at different levels of complexity. Also, some of the learning-based methods developed within computer vision have their background in biology.

Other

Other common forms of sensing in robotics use lidar, radar, and sonar.

Manipulation

KUKA industrial robot operating in a foundry
Puma, one of the first industrial robots
Baxter, a modern and versatile industrial robot developed by Rodney Brooks
Robots need to manipulate objects; pick up, modify, destroy, or otherwise have an effect. Thus the "hands" of a robot are often referred to as end effectors,[51] while the "arm" is referred to as a manipulator.[52] Most robot arms have replaceable effectors, each allowing them to perform some small range of tasks. Some have a fixed manipulator which cannot be replaced, while a few have one very general purpose manipulator, for example, a humanoid hand.[53] Learning how to manipulate a robot often requires a close feedback between human to the robot, although there are several methods for remote manipulation of robots.[54]

Mechanical grippers

One of the most common effectors is the gripper. In its simplest manifestation, it consists of just two fingers which can open and close to pick up and let go of a range of small objects. Fingers can for example, be made of a chain with a metal wire run through it.[55] Hands that resemble and work more like a human hand include the Shadow Hand and the Robonaut hand.[56] Hands that are of a mid-level complexity include the Delft hand.[57][58] Mechanical grippers can come in various types, including friction and encompassing jaws. Friction jaws use all the force of the gripper to hold the object in place using friction. Encompassing jaws cradle the object in place, using less friction.

Vacuum grippers

Vacuum grippers are very simple astrictive[59] devices that can hold very large loads provided the prehension surface is smooth enough to ensure suction.
Pick and place robots for electronic components and for large objects like car windscreens, often use very simple vacuum grippers.

General purpose effectors

Some advanced robots are beginning to use fully humanoid hands, like the Shadow Hand, MANUS,[60] and the Schunk hand.[61] These are highly dexterous manipulators, with as many as 20 degrees of freedom and hundreds of tactile sensors.[62]

Locomotion

Rolling robots

Segway in the Robot museum in Nagoya
For simplicity, most mobile robots have four wheels or a number of continuous tracks. Some researchers have tried to create more complex wheeled robots with only one or two wheels. These can have certain advantages such as greater efficiency and reduced parts, as well as allowing a robot to navigate in confined places that a four-wheeled robot would not be able to.
Two-wheeled balancing robots
Balancing robots generally use a gyroscope to detect how much a robot is falling and then drive the wheels proportionally in the same direction, to counterbalance the fall at hundreds of times per second, based on the dynamics of an inverted pendulum.[63] Many different balancing robots have been designed.[64] While the Segway is not commonly thought of as a robot, it can be thought of as a component of a robot, when used as such Segway refer to them as RMP (Robotic Mobility Platform). An example of this use has been as NASA's Robonaut that has been mounted on a Segway.[65]
One-wheeled balancing robots
A one-wheeled balancing robot is an extension of a two-wheeled balancing robot so that it can move in any 2D direction using a round ball as its only wheel. Several one-wheeled balancing robots have been designed recently, such as Carnegie Mellon University's "Ballbot" that is the approximate height and width of a person, and Tohoku Gakuin University's "BallIP".[66] Because of the long, thin shape and ability to maneuver in tight spaces, they have the potential to function better than other robots in environments with people.[67]
Spherical orb robots
Several attempts have been made in robots that are completely inside a spherical ball, either by spinning a weight inside the ball,[68][69] or by rotating the outer shells of the sphere.[70][71] These have also been referred to as an orb bot[72] or a ball bot.[73][74]
Six-wheeled robots
Using six wheels instead of four wheels can give better traction or grip in outdoor terrain such as on rocky dirt or grass.
Tracked robots
Tank tracks provide even more traction than a six-wheeled robot. Tracked wheels behave as if they were made of hundreds of wheels, therefore are very common for outdoor and military robots, where the robot must drive on very rough terrain. However, they are difficult to use indoors such as on carpets and smooth floors. Examples include NASA's Urban Robot "Urbie".[75]

Walking applied to robots

Walking is a difficult and dynamic problem to solve. Several robots have been made which can walk reliably on two legs, however, none have yet been made which are as robust as a human. There has been much study on human inspired walking, such as AMBER lab which was established in 2008 by the Mechanical Engineering Department at Texas A&M University.[76] Many other robots have been built that walk on more than two legs, due to these robots being significantly easier to construct.[77][78] Walking robots can be used for uneven terrains, which would provide better mobility and energy efficiency than other locomotion methods. Hybrids too have been proposed in movies such as I, Robot, where they walk on two legs and switch to four (arms+legs) when going to a sprint. Typically, robots on two legs can walk well on flat floors and can occasionally walk up stairs. None can walk over rocky, uneven terrain. Some of the methods which have been tried are:
ZMP technique
The zero moment point (ZMP) is the algorithm used by robots such as Honda's ASIMO. The robot's onboard computer tries to keep the total inertial forces (the combination of Earth's gravity and the acceleration and deceleration of walking), exactly opposed by the floor reaction force (the force of the floor pushing back on the robot's foot). In this way, the two forces cancel out, leaving no moment (force causing the robot to rotate and fall over).[79] However, this is not exactly how a human walks, and the difference is obvious to human observers, some of whom have pointed out that ASIMO walks as if it needs the lavatory.[80][81][82] ASIMO's walking algorithm is not static, and some dynamic balancing is used (see below). However, it still requires a smooth surface to walk on.
Hopping
Several robots, built in the 1980s by Marc Raibert at the MIT Leg Laboratory, successfully demonstrated very dynamic walking. Initially, a robot with only one leg, and a very small foot could stay upright simply by hopping. The movement is the same as that of a person on a pogo stick. As the robot falls to one side, it would jump slightly in that direction, in order to catch itself.[83] Soon, the algorithm was generalised to two and four legs. A bipedal robot was demonstrated running and even performing somersaults.[84] A quadruped was also demonstrated which could trot, run, pace, and bound.[85] For a full list of these robots, see the MIT Leg Lab Robots page.[86]
Dynamic balancing (controlled falling)
A more advanced way for a robot to walk is by using a dynamic balancing algorithm, which is potentially more robust than the Zero Moment Point technique, as it constantly monitors the robot's motion, and places the feet in order to maintain stability.[87] This technique was recently demonstrated by Anybots' Dexter Robot,[88] which is so stable, it can even jump.[89] Another example is the TU Delft Flame.
Passive dynamics
Perhaps the most promising approach utilizes passive dynamics where the momentum of swinging limbs is used for greater efficiency. It has been shown that totally unpowered humanoid mechanisms can walk down a gentle slope, using only gravity to propel themselves. Using this technique, a robot need only supply a small amount of motor power to walk along a flat surface or a little more to walk up a hill. This technique promises to make walking robots at least ten times more efficient than ZMP walkers, like ASIMO.[90][91]

Other methods of locomotion

Flying
Two robot snakes. Left one has 64 motors (with 2 degrees of freedom per segment), the right one 10.
A modern passenger airliner is essentially a flying robot, with two humans to manage it. The autopilot can control the plane for each stage of the journey, including takeoff, normal flight, and even landing.[92] Other flying robots are uninhabited and are known as unmanned aerial vehicles (UAVs). They can be smaller and lighter without a human pilot on board, and fly into dangerous territory for military surveillance missions. Some can even fire on targets under command. UAVs are also being developed which can fire on targets automatically, without the need for a command from a human. Other flying robots include cruise missiles, the Entomopter, and the Epson micro helicopter robot. Robots such as the Air Penguin, Air Ray, and Air Jelly have lighter-than-air bodies, propelled by paddles, and guided by sonar.
Snaking
Several snake robots have been successfully developed. Mimicking the way real snakes move, these robots can navigate very confined spaces, meaning they may one day be used to search for people trapped in collapsed buildings.[93] The Japanese ACM-R5 snake robot[94] can even navigate both on land and in water.[95]
Skating
A small number of skating robots have been developed, one of which is a multi-mode walking and skating device. It has four legs, with unpowered wheels, which can either step or roll.[96] Another robot, Plen, can use a miniature skateboard or roller-skates, and skate across a desktop.[97]
Capuchin, a climbing robot
Climbing
Several different approaches have been used to develop robots that have the ability to climb vertical surfaces. One approach mimics the movements of a human climber on a wall with protrusions; adjusting the center of mass and moving each limb in turn to gain leverage. An example of this is Capuchin,[98] built by Dr. Ruixiang Zhang at Stanford University, California. Another approach uses the specialized toe pad method of wall-climbing geckoes, which can run on smooth surfaces such as vertical glass. Examples of this approach include Wallbot[99] and Stickybot.[100] China's Technology Daily reported on November 15, 2008, that Dr. Li Hiu Yeung and his research group of New Concept Aircraft (Zhuhai) Co., Ltd. had successfully developed a bionic gecko robot named "Speedy Freelander". According to Dr. Li, the gecko robot could rapidly climb up and down a variety of building walls, navigate through ground and wall fissures, and walk upside-down on the ceiling. It was also able to adapt to the surfaces of smooth glass, rough, sticky or dusty walls as well as various types of metallic materials. It could also identify and circumvent obstacles automatically. Its flexibility and speed were comparable to a natural gecko. A third approach is to mimic the motion of a snake climbing a pole.[citation needed].
Swimming (Piscine)
It is calculated that when swimming some fish can achieve a propulsive efficiency greater than 90%.[101] Furthermore, they can accelerate and maneuver far better than any man-made boat or submarine, and produce less noise and water disturbance. Therefore, many researchers studying underwater robots would like to copy this type of locomotion.[102] Notable examples are the Essex University Computer Science Robotic Fish G9,[103] and the Robot Tuna built by the Institute of Field Robotics, to analyze and mathematically model thunniform motion.[104] The Aqua Penguin,[105] designed and built by Festo of Germany, copies the streamlined shape and propulsion by front "flippers" of penguins. Festo have also built the Aqua Ray and Aqua Jelly, which emulate the locomotion of manta ray, and jellyfish, respectively.
Robotic Fish: iSplash-II
In 2014 iSplash-II was developed by PhD student Richard James Clapham and Prof. Huosheng Hu at Essex University. It was the first robotic fish capable of outperforming real carangiform fish in terms of average maximum velocity (measured in body lengths/ second) and endurance, the duration that top speed is maintained.[106] This build attained swimming speeds of 11.6BL/s (i.e. 3.7 m/s).[107] The first build, iSplash-I (2014) was the first robotic platform to apply a full-body length carangiform swimming motion which was found to increase swimming speed by 27% over the traditional approach of a posterior confined waveform.[108]
Sailing
The autonomous sailboat robot Vaimos
Sailboat robots have also been developed in order to make measurements at the surface of the ocean. A typical sailboat robot is Vaimos[109] built by IFREMER and ENSTA-Bretagne. Since the propulsion of sailboat robots uses the wind, the energy of the batteries is only used for the computer, for the communication and for the actuators (to tune the rudder and the sail). If the robot is equipped with solar panels, the robot could theoretically navigate forever. The two main competitions of sailboat robots are WRSC, which takes place every year in Europe, and Sailbot.

Environmental interaction and navigation

Radar, GPS, and lidar, are all combined to provide proper navigation and obstacle avoidance (vehicle developed for 2007 DARPA Urban Challenge)
Though a significant percentage of robots in commission today are either human controlled or operate in a static environment, there is an increasing interest in robots that can operate autonomously in a dynamic environment. These robots require some combination of navigation hardware and software in order to traverse their environment. In particular, unforeseen events (e.g. people and other obstacles that are not stationary) can cause problems or collisions. Some highly advanced robots such as ASIMO and Meinü robot have particularly good robot navigation hardware and software. Also, self-controlled cars, Ernst Dickmanns' driverless car, and the entries in the DARPA Grand Challenge, are capable of sensing the environment well and subsequently making navigational decisions based on this information. Most of these robots employ a GPS navigation device with waypoints, along with radar, sometimes combined with other sensory data such as lidar, video cameras, and inertial guidance systems for better navigation between waypoints.

Human-robot interaction

Kismet can produce a range of facial expressions.
The state of the art in sensory intelligence for robots will have to progress through several orders of magnitude if we want the robots working in our homes to go beyond vacuum-cleaning the floors. If robots are to work effectively in homes and other non-industrial environments, the way they are instructed to perform their jobs, and especially how they will be told to stop will be of critical importance. The people who interact with them may have little or no training in robotics, and so any interface will need to be extremely intuitive. Science fiction authors also typically assume that robots will eventually be capable of communicating with humans through speech, gestures, and facial expressions, rather than a command-line interface. Although speech would be the most natural way for the human to communicate, it is unnatural for the robot. It will probably be a long time before robots interact as naturally as the fictional C-3PO, or Data of Star Trek, Next Generation.

Speech recognition

Interpreting the continuous flow of sounds coming from a human, in real time, is a difficult task for a computer, mostly because of the great variability of speech.[110] The same word, spoken by the same person may sound different depending on local acoustics, volume, the previous word, whether or not the speaker has a cold, etc.. It becomes even harder when the speaker has a different accent.[111] Nevertheless, great strides have been made in the field since Davis, Biddulph, and Balashek designed the first "voice input system" which recognized "ten digits spoken by a single user with 100% accuracy" in 1952.[112] Currently, the best systems can recognize continuous, natural speech, up to 160 words per minute, with an accuracy of 95%.[113]

Robotic voice

Other hurdles exist when allowing the robot to use voice for interacting with humans. For social reasons, synthetic voice proves suboptimal as a communication medium,[114] making it necessary to develop the emotional component of robotic voice through various techniques.

Gestures

One can imagine, in the future, explaining to a robot chef how to make a pastry, or asking directions from a robot police officer. In both of these cases, making hand gestures would aid the verbal descriptions. In the first case, the robot would be recognizing gestures made by the human, and perhaps repeating them for confirmation. In the second case, the robot police officer would gesture to indicate "down the road, then turn right". It is likely that gestures will make up a part of the interaction between humans and robots.[117] A great many systems have been developed to recognize human hand gestures.[118]

Facial expression

Facial expressions can provide rapid feedback on the progress of a dialog between two humans, and soon may be able to do the same for humans and robots. Robotic faces have been constructed by Hanson Robotics using their elastic polymer called Frubber, allowing a large number of facial expressions due to the elasticity of the rubber facial coating and embedded subsurface motors (servos).[119] The coating and servos are built on a metal skull. A robot should know how to approach a human, judging by their facial expression and body language. Whether the person is happy, frightened, or crazy-looking affects the type of interaction expected of the robot. Likewise, robots like Kismet and the more recent addition, Nexi[120] can produce a range of facial expressions, allowing it to have meaningful social exchanges with humans.[121]

Artificial emotions

Artificial emotions can also be generated, composed of a sequence of facial expressions and/or gestures. As can be seen from the movie Final Fantasy: The Spirits Within, the programming of these artificial emotions is complex and requires a large amount of human observation. To simplify this programming in the movie, presets were created together with a special software program. This decreased the amount of time needed to make the film. These presets could possibly be transferred for use in real-life robots.

Personality

Many of the robots of science fiction have a personality, something which may or may not be desirable in the commercial robots of the future.[122] Nevertheless, researchers are trying to create robots which appear to have a personality:[123][124] i.e. they use sounds, facial expressions, and body language to try to convey an internal state, which may be joy, sadness, or fear. One commercial example is Pleo, a toy robot dinosaur, which can exhibit several apparent emotions.[125]

Social Intelligence

The Socially Intelligent Machines Lab of the Georgia Institute of Technology researches new concepts of guided teaching interaction with robots. The aim of the projects is a social robot that learns task and goals from human demonstrations without prior knowledge of high-level concepts. These new concepts are grounded from low-level continuous sensor data through unsupervised learning, and task goals are subsequently learned using a Bayesian approach. These concepts can be used to transfer knowledge to future tasks, resulting in faster learning of those tasks. The results are demonstrated by the robot Curi who can scoop some pasta from a pot onto a plate and serve the sauce on top.[126]

Control

Puppet Magnus, a robot-manipulated marionette with complex control systems
RuBot II can resolve manually Rubik cubes
The mechanical structure of a robot must be controlled to perform tasks. The control of a robot involves three distinct phases – perception, processing, and action (robotic paradigms). Sensors give information about the environment or the robot itself (e.g. the position of its joints or its end effector). This information is then processed to be stored or transmitted and to calculate the appropriate signals to the actuators (motors) which move the mechanical.
The processing phase can range in complexity. At a reactive level, it may translate raw sensor information directly into actuator commands. Sensor fusion may first be used to estimate parameters of interest (e.g. the position of the robot's gripper) from noisy sensor data. An immediate task (such as moving the gripper in a certain direction) is inferred from these estimates. Techniques from control theory convert the task into commands that drive the actuators.
At longer time scales or with more sophisticated tasks, the robot may need to build and reason with a "cognitive" model. Cognitive models try to represent the robot, the world, and how they interact. Pattern recognition and computer vision can be used to track objects. Mapping techniques can be used to build maps of the world. Finally, motion planning and other artificial intelligence techniques may be used to figure out how to act. For example, a planner may figure out how to achieve a task without hitting obstacles, falling over, etc.

Autonomy levels

TOPIO, a humanoid robot, played ping pong at Tokyo IREX 2009.[127]
Control systems may also have varying levels of autonomy.
  1. Direct interaction is used for haptic or teleoperated devices, and the human has nearly complete control over the robot's motion.
  2. Operator-assist modes have the operator commanding medium-to-high-level tasks, with the robot automatically figuring out how to achieve them.
  3. An autonomous robot may go without human interaction for extended periods of time . Higher levels of autonomy do not necessarily require more complex cognitive capabilities. For example, robots in assembly plants are completely autonomous but operate in a fixed pattern.
Another classification takes into account the interaction between human control and the machine motions.
  1. Teleoperation. A human controls each movement, each machine actuator change is specified by the operator.
  2. Supervisory. A human specifies general moves or position changes and the machine decides specific movements of its actuators.
  3. Task-level autonomy. The operator specifies only the task and the robot manages itself to complete it.
  4. Full autonomy. The machine will create and complete all its tasks without human interaction.

Research

Much of the research in robotics focuses not on specific industrial tasks, but on investigations into new types of robots, alternative ways to think about or design robots, and new ways to manufacture them. Other investigations, such as MIT's cyberflora project, are almost wholly academic.
A first particular new innovation in robot design is the open sourcing of robot-projects. To describe the level of advancement of a robot, the term "Generation Robots" can be used. This term is coined by Professor Hans Moravec, Principal Research Scientist at the Carnegie Mellon University Robotics Institute in describing the near future evolution of robot technology. First generation robots, Moravec predicted in 1997, should have an intellectual capacity comparable to perhaps a lizard and should become available by 2010. Because the first generation robot would be incapable of learning, however, Moravec predicts that the second generation robot would be an improvement over the first and become available by 2020, with the intelligence maybe comparable to that of a mouse. The third generation robot should have the intelligence comparable to that of a monkey. Though fourth generation robots, robots with human intelligence, professor Moravec predicts, would become possible, he does not predict this happening before around 2040 or 2050.[128]
The second is evolutionary robots. This is a methodology that uses evolutionary computation to help design robots, especially the body form, or motion and behavior controllers. In a similar way to natural evolution, a large population of robots is allowed to compete in some way, or their ability to perform a task is measured using a fitness function. Those that perform worst are removed from the population and replaced by a new set, which have new behaviors based on those of the winners. Over time the population improves, and eventually a satisfactory robot may appear. This happens without any direct programming of the robots by the researchers. Researchers use this method both to create better robots,[129] and to explore the nature of evolution.[130] Because the process often requires many generations of robots to be simulated,[131] this technique may be run entirely or mostly in simulation, using a robot simulator software package, then tested on real robots once the evolved algorithms are good enough.[132] Currently, there are about 10 million industrial robots toiling around the world, and Japan is the top country having high density of utilizing robots in its manufacturing industry.[citation needed]

Dynamics and kinematics

External video
How the BB-8 Sphero Toy Works
The study of motion can be divided into kinematics and dynamics.[133] Direct kinematics refers to the calculation of end effector position, orientation, velocity, and acceleration when the corresponding joint values are known. Inverse kinematics refers to the opposite case in which required joint values are calculated for given end effector values, as done in path planning. Some special aspects of kinematics include handling of redundancy (different possibilities of performing the same movement), collision avoidance, and singularity avoidance. Once all relevant positions, velocities, and accelerations have been calculated using kinematics, methods from the field of dynamics are used to study the effect of forces upon these movements. Direct dynamics refers to the calculation of accelerations in the robot once the applied forces are known. Direct dynamics is used in computer simulations of the robot. Inverse dynamics refers to the calculation of the actuator forces necessary to create a prescribed end-effector acceleration. This information can be used to improve the control algorithms of a robot.
In each area mentioned above, researchers strive to develop new concepts and strategies, improve existing ones, and improve the interaction between these areas. To do this, criteria for "optimal" performance and ways to optimize design, structure, and control of robots must be developed and implemented.

Bionics and biomimetics

Bionics and biomimetics apply the physiology and methods of locomotion of animals to the design of robots. For example, the design of BionicKangaroo was based on the way kangaroos jump.

Education and training

The SCORBOT-ER 4u educational robot
Robotics engineers design robots, maintain them, develop new applications for them, and conduct research to expand the potential of robotics.[134] Robots have become a popular educational tool in some middle and high schools, particularly in parts of the USA,[135] as well as in numerous youth summer camps, raising interest in programming, artificial intelligence, and robotics among students. First-year computer science courses at some universities now include programming of a robot in addition to traditional software engineering-based coursework.[54]

Career training

Universities offer bachelors, masters, and doctoral degrees in the field of robotics.[136] Vocational schools offer robotics training aimed at careers in robotics.

Certification

The Robotics Certification Standards Alliance (RCSA) is an international robotics certification authority that confers various industry- and educational-related robotics certifications.

Summer robotics camp

Several national summer camp programs include robotics as part of their core curriculum. In addition, youth summer robotics programs are frequently offered by celebrated museums and institutions.

Robotics competitions

There are lots of competitions all around the globe. One of the most important competitions is the FLL or FIRST Lego League. The idea of this specific competition is that kids start developing knowledge and getting into robotics while playing with Legos since they are 9 years old. This competition is associated with Ni or National Instruments.

Robotics afterschool programs

Many schools across the country are beginning to add robotics programs to their after school curriculum. Some major programs for afterschool robotics include FIRST Robotics Competition, Botball and B.E.S.T. Robotics.[137] Robotics competitions often include aspects of business and marketing as well as engineering and design.
The Lego company began a program for children to learn and get excited about robotics at a young age.[138]

Employment

A robot technician builds small all-terrain robots. (Courtesy: MobileRobots Inc)
Robotics is an essential component in many modern manufacturing environments. As factories increase their use of robots, the number of robotics–related jobs grow and have been observed to be steadily rising.[139] The employment of robots in industries has increased productivity and efficiency savings and is typically seen as a long term investment for benefactors. A paper by Michael Osborne and Carl Benedikt Frey found that 47 per cent of US jobs are at risk to automation "over some unspecified number of years".[140] These claims have been criticized on the ground that social policy, not AI, causes unemployment

Occupational safety and health implications

A discussion paper drawn up by EU-OSHA highlights how the spread of robotics presents both opportunities and challenges for occupational safety and health (OSH).[142]
The greatest OSH benefits stemming from the wider use of robotics should be substitution for people working in unhealthy or dangerous environments. In space, defence, security, or the nuclear industry, but also in logistics, maintenance, and inspection, autonomous robots are particularly useful in replacing human workers performing dirty, dull or unsafe tasks, thus avoiding workers' exposures to hazardous agents and conditions and reducing physical, ergonomic and psychosocial risks. For example, robots are already used to perform repetitive and monotonous tasks, to handle radioactive material or to work in explosive atmospheres. In the future, many other highly repetitive, risky or unpleasant tasks will be performed by robots in a variety of sectors like agriculture, construction, transport, healthcare, firefighting or cleaning services.[143]
Despite these advances, there are certain skills to which humans will be better suited than machines for some time to come and the question is how to achieve the best combination of human and robot skills. The advantages of robotics include heavy-duty jobs with precision and repeatability, whereas the advantages of humans include creativity, decision-making, flexibility and adaptability. This need to combine optimal skills has resulted in collaborative robots and humans sharing a common workspace more closely and led to the development of new approaches and standards to guarantee the safety of the "man-robot merger". Some European countries are including robotics in their national programmes and trying to promote a safe and flexible co-operation between robots and operators to achieve better productivity. For example, the German Federal Institute for Occupational Safety and Health (BAuA) organises annual workshops on the topic "human-robot collaboration".
In future, co-operation between robots and humans will be diversified, with robots increasing their autonomy and human-robot collaboration reaching completely new forms. Current approaches and technical standards aiming to protect employees from the risk of working with collaborative robots will have to be revised.



                                    XO__XO DW DW Interior of SUN

How can the sun produce so much energy over such a long timelink to a key question

Key points: Source of energy of the sun; how the energy gets to the surface; hydrostatic equilibrium
By 1900, scientists had realized that:
a. chemical processes like burning could produce energy at the sun's rate only for about 3 million years
b. gravitational shrinkage would not produce energy at a constant enough rate -- changes would be evident over only a few million years
Explaining how the sun could produce so much energy required advances in physics!

Einstein and Special Relativity

Recall Einstein's relation between mass and energy:
E = mc2 (E = energy in watts m = mass in kilograms c = speed of light in meters/sec)
Mass and energy are equivalent and can be converted into each other. In the 1930s, astronomers realized that Einstein's Theory held the key to how the sun and stars produce their energy:
What actually happens to make the energy of the sun?
animation of the critical steps in the p-p chain Hydrogen fusion, often called the proton-proton chain, combines hydrogen nuclei into helium ones inside the sun. In addition to producing light in the form of gamma-rays, other particles such as neutrinos are produced (see below). When 4 atoms of hydrogen are converted into one atom of helium, a small portion of the mass is converted to energy. Using this process, a star can produce large amounts of energy for a long time.buttonbook.jpg (10323 bytes)This is an example of nuclear fusion.(From Nick Strobel, www.astronomynotes.com ) (Deuterium is an "isotope" of hydrogenbuttonbook.jpg (10323 bytes))
reactions in proton-proton fusion chain A summary of how it works, showing all the reactions and how long it takes for them to occur, is to the left. (From U. Tenn Ast  162, http://csep10.phys.utk.edu/astr162/lect/energy/ppchain.html)
In stars more massive than the sun, another reaction chain can be important in converting hydrogen to helium. In it, carbon, nitrogen, and oxygen isotopes are critical links although the final mix of isotopes is not modified. In analogy with terminology in chemistry, they are called catalysts. The reaction chain is the "C-N-O cycle".

Why doesn't this happen on Earth?

For two H nuclei, protons, to collide hard enough to overcome their natural electrical repulsion, they must be moving very fast.
==> need very high temperatures
animation: fusion is impossible at low temperatures animation: fusion becomes possible at the high nuclear speeds due to high temperature
(From Nick Strobel, www.astronomynotes.com)
To have enough collisions to generate significant energy requires high density
==> reactions can occur only in the centers of massive objects like stars or (at least so far) in special machines where they can be sustained for only a very short time because the energy released disrupts the continuing reaction
Only about 10% of the mass of the sun has temperatures and pressures sufficiently high for nuclear reactions to occur.
cutaway of the sun
The core of the sun, where
the fusion takes place, is
overlaid by a huge amount
of hot hydrogen and helium
gas.
(From MSFC,

Nonetheless, we can study the reactions in the core by detecting neutrinos from the sun.

neutrinos are made when two protons fuse Neutrinos react extremely weakly with other forms of matter. They can escape from the center of the sun virtually unimpeded and they carry away about 2% of the energy from the fusion reactions occurring there. (From Nick Strobel.www.astronomynotes.com.)
Neutrinos are NOT electromagnetic radiation or matter. They are another type of fundamental particle, similar to photons, but also different from them in some important ways such as their ability to travel through matter without interacting, so they can emerge from the center of the sunbuttonex.jpg (1228 bytes).

Neutrino Detectors

Because neutrinos emerge from the very center of the sun, measuring how many of them escape should allow us to probe our understanding of the reactions taking place there! Although neutrino detectors have found fewer neutrinos than expected, we think it is the neutrino physics that was wrong and that our models for the interior of the sun are very accurate.
How does the rest of the energy escape from the center of the sun?



There are two zones with different types of energy transport: the radiative zone and the convective one.




Cutaway of the sun
sun-core.gif (74725 bytes) Well inside the sun, the gas is so hot it is fully ionized (electrons are all stripped from the atom nuclei), so the atoms are poorly absorbing and the energy is carried by gamma rays that bounce their way off the free electrons. This region is called the radiative zone; within it, there are no large-scale gas motions. About 85% of the way out, the temperature drops to where electrons are retained in atoms and the gas atoms absorb the energy efficiently. The gas gets so hot it expands and rises convectively toward the surface in large-scale blobs. The energy is carried across this "convective zone" by this "boiling" of gas. (From H. Haubold and A. M.Mathai, Encyclopedia of Planetary Sciences, (Page 786 - 794), 1997 Chapman & Hall,  http://www.seas.columbia.edu/~ah297/un-esa/sun/sun-chapter1.html)
convect31.gif (1622306 bytes) The final stage in the convection is the granules, which are just hot gas rising to the surface. This simulation shows the process. (Adapted by G. Rieke from A. Malagoli, http://planetscapes.com/solar/cap/misc/convect3.htm)
grancutaway.jpg (159287 bytes) Energy rises to the surface as gas wells up in the cores of the granules, and cool gas sinks around their edges (From Pat Hall, http://www.yorku.ca/phall/P1070W05/L21/sec3.html.).
The motions from convection drive a lot of the magnetic behavior such as sun spots. The convection results in electric currents of protons and electrons that produce the strong surface magnetic fields and drive the surface activity.
Diagram of magnetic fields on the surface of the sun Electrically charged particles follow the magnetic field. Where the fields are strong, they suppress convection and reduce the flow of heat, creating a relatively cool region that appears as a sunspot. Charged gas atoms and molecules follow the field lines that connect north and south poles, creating arcs and loops far above the solar surface. {From The Essential Cosmic Perspective, by Bennett et al.)

Why the Sun is so Stable

So long as adequate amounts of hydrogen remain in the sun's core, it will continue to produce energy at nearly the current rate.
sunpulse.gif (147086 bytes) The sun's output is so stable (variations of less than a percent) because of hydrostatic equilibrium. The outward pressure of hot gas comprising the sun exactly balances the force of gravity which tries to make the sun grow smaller.buttonbook.jpg (10323 bytes)In the stars like the sun, when the star shrinks the core pressure and temperature increase and that increases the pressure, resisting the shrinkage. When the star swells, the core pressure and temperature drop and reduce the pressure, and gravity makes the star stop swelling. (animation by G. Rieke)
If the sun produced energy more rapidly in its core, it would be hotter. Then the pressure would increase and the core would expand. The larger, lower density core would have fewer proton-proton collisions, reducing the rate of reactions, and causing the production of energy to decrease. Thus, the energy output is self-regulating.
animation of hydrostatic equilibrium The structure of the sun adjusts until the gravitational "pull" towards its center is just balanced by the "push" of the gas pressure outward. Fortunately, this results in a very stable state, called hydrostatic equilibrium.


At the center of our solar system is an enormous nuclear generator. The Earth revolves around this massive body at an average distance of 93 million miles (149.6 million kilometers). It's a star we call the sun. The sun provides us with the energy necessary for life. But could scientists create a miniaturized version here on Earth?
It's not just possible -- it's already been done. If you think of a star as a nuclear fusion machine, mankind has duplicated the nature of stars on Earth. But this revelation has qualifiers. The examples of fusion here on Earth are on a small scale and last for just a few seconds at most.

                         Solar interior

How can the sun produce so much energy?  
Although the sun is so far away from the earth, its continuous emission of light and heat enables living things to sustain and evolve on earth for billions of years. The sun is a huge volume of gases that are mostly hydrogen. The massive hydrogen provides billion of years of incessant fuel for solar nuclear fusion to continuously produce a huge amount of energy.
What is nuclear fusion? 
Nucleus fusion is also called the nucleosynthesis or thermonuclear reaction. It is a process of nuclear reaction in which two or more light atomic nuclei are combined into a heavier atomic nucleus. Since a small part of the mass is converted into energy in the course of nuclear fusion, the mass of resulting heavier atomic nucleus is slightly less the original total mass of the lighter atomic nuclei. Therefore, nuclear fusion can produce a huge amount of energy by virtue of the mass - energy equivalence (E=mc2) proposed by the famous physicist, Albert Einstein. Hydrogen bomb, which releases a huge amount of energy from nuclear fusion during detonation, is a good example of converting mass into energy.  
What is the mode of nuclear reaction in the sun's energy production?  
The American physicist, Hans Bethe (born in Germany), based on his research results, pointed out that the most important nuclear reaction in a bright star is a "carbon - nitrogen cycle". However, the nuclear reactions in comparatively dimmer stars such as our sun, are mainly the "proton-proton (hydrogen nucleus - hydrogen nucleus) chain reaction". Because of Hans Bette's contributions in the nuclear reaction theory and particularly the discovery of stellar energy generation, he received the Nobel Prize for Physics in 1967.
Why nuclear fusion does not occur readily?  
Since atomic nuclei consist of positively charged protons, they repel each other by virtue of electrostatic force. Under high temperature condition, particles possess sufficient kinetic energy to overcome the electrostatic repulsion and approach each other. The subsequent collisions among atomic nuclei provide the opportunities of nuclear fusion to occur. However, particles can recoil and separate without undergoing nuclear fusion after collision (called elastic collision). In fact, many collisions among atomic nuclei are elastic in nature without any resultant nuclear fusion.  George Gamow proposed that for any given temperature, there is a narrow range of energies known as the "Gamow window" where nuclear fusion is most likely to occur.
What are the conditions favourable for the occurrence of nuclear fusion?  
Besides a suitably high temperature, the number or chance of mutual collisions among atomic nuclei will increase when the gaseous density is high. Since only a small portion of the collisions can result in nuclear fusion, both high temperature and high density are necessary conditions for nuclear fusion to occur.
1Fig. 1: The forces counteracting each other in the sun's interior
Is the entire sun undergoing nuclear fusion? 
The sun is a huge volume of gas and its total mass is very great. As a result of gravitational force, the pressure will be greater when it is closer to the center of the sun. Therefore, the solar core is a highly compressed region in which nuclear fusion can occur under the high-density, high-temperature conditions.  On the other hand, both the density and the temperature are much lower in the sun's outer layer where occurrence of nuclear fusion is unfavourable. Hence, nuclear fusion mainly occurs and persists deep inside the sun near its center - the solar core region (Fig. 1).  In other words, nuclear fusion does not occur in the entire sun.
Why can the sun produce an enormous amount of energy in the form of light and heat? 
The sun contains massive hydrogen that serves as a lasting supply of fuel for the generation of large amount of energy through persistent nuclear fusion in the solar core region.
The sun acts as if it is a self-regulating nuclear power reactor.  The force of gravity, gas pressure and radiation pressure of the sun interact to maintain a state of dynamic equilibrium (Fig. 1). For example, when the nuclear reaction slows down, less energy is produced and the temperature decreases. The sun's great volume of gas will shrink, resulting in an increase of density and temperature in the solar core region, which in turn speeds up the reaction of nuclear fusion. On the other hand, if the nuclear reaction becomes faster, more energy is produced. The sun's great volume of gas will expand, resulting in a decrease of density and temperature in the solar core region. The reaction of nuclear fusion will eventually slow down.
To summarize, the sun's nuclear fusion reaction occurs in an orderly manner.  In the process, hydrogen is consumed, energy is produced, and there is a steady release of light and heat.



  XO___XO DW DW INFORM Moonlight controls lunar-phase-dependency and regular oscillation   of clock gene expressions in a lunar-synchronized spawner fish, Goldlined spinefoot


Goldlined spinefoot, Siganus guttatus, inhabits tropical and subtropical waters and synchronizes its spawning around the first quarter moon likely using an hourglass-like lunar timer. In previous studies, we have found that clock genes (Cryptochrome3 and Period1) could play the role of state variable in the diencephalon when determining the lunar phase for spawning. Here, we identified three Cry, two Per, two Clock, and two Bmal genes in S. guttatus and investigated their expression patterns in the diencephalon and pituitary gland. We further evaluated the effect on their expression patterns by daily interruptions of moonlight stimuli for 1 lunar cycle beginning at the new moon. It significantly modified the expression patterns in many of the examined clock(-related) genes including Cry3 in the diencephalon and/or pituitary gland. Acute interruptions of moonlight around the waxing gibbous moon upregulated nocturnal expressions of Cry1b and Cry2 in the diencephalon and pituitary gland, respectively, but did not affect expression levels of the other clock genes. These results highlighted the importance of repetitive moonlight illumination for stable or lunar-phase-specific daily expression of clock genes in the next lunar cycle that may be important for the lunar-phase-synchronized spawning on the next first quarter moon.

Introduction

Most organisms exhibit biological rhythms by synchronizing their behavioral and physiological activities with cyclic changes in the environment. Among these rhythms of diverged period lengths, circadian rhythms are widely observed.
The molecular mechanism of the circadian clock has been well studied in contrast to those of clocks with longer (infradian rhythms) and shorter (ultradian rhythms) period lengths. The circadian clock is known to be composed of clock genes and their products1. In animals, positive transcriptional components CLOCK and BMAL and negative components CRYPTOCHROME (CRY) and PERIOD (PER) constitute the core negative feedback loop and drive the circadian oscillatory expression of clock genes in cooperation with sub molecular loops2. Multiple gene duplication events occurred in lower vertebrates such as fish species resulted in multiple paralogs of the clock(-related) genes3, although their functional divergence is less characterized.
In temperate zones, reproductive events of birds, fish, and insects often synchronize with seasonal changes in the environment to increase the chance of mating and decrease predation risk4. These seasonal breeding animals use daylengths as the principal environmental cue to decide suitable timing for reproduction5,6. In vertebrates, the daylength measurement (photoperiodicity) is mostly served by a circadian phase-specific photoresponse that integrates photic and circadian signals in the diencephalon7,8,9. Besides this gating mechanism of photoinduction, some animals are equipped with an internal clock called a ‘circannual clock’ that oscillates with a period of approximately one year10,11,12.
Lunar-synchronized spawning has been reported in hermatypic corals, marine insects, and tropical marine fishes13,14,15. Zantke et al.15 have reported that the marine worm Platynereis dumerilii has an endogenous circalunar clock that controls the timing of reproduction and is possibly entrained by nocturnal light. Although the molecular mechanism of circalunar clock driving is still unknown in any species, the circalunar clock of P. dumerilii has been suggested to be independent of the circadian clock and to affect both the circadian behavior and the transcriptions of core clock genes15. On the other hand, in the Goldlined spinefoot, lunar-phase specific synchronized spawning, which occurrs at night around the first quarter moon, seemed to be strongly related to a cyclic change in moonlight illumination with a period of 29.5 days (Fig. 1); their spawning was disrupted by interrupted moonlight that occured 1 month before the expected spawning day, while the fish spawned under conditions in which they were deprived of moonlight from 2 weeks before the expected spawning day16. Based on these results, lunar-synchronized spawning of the spinefoot may be explainable by a mechanism controlled through an hourglass-like lunar timer, which can measure a period of less than 1 month, instead of a self-sustainable circalunar clock as seen in P. dumerilii.
Figure 1
Figure 1
Sampling schedule and nocturnal light conditions during repetitive moonlight interruption for 2 lunar cycles. The Goldlined spinefoots were reared from May 18 to July 8 in 2015 in either the moonlight-exposed group (ME) (n = 80) or the moonlight-interrupted group (MI) (n = 64). Open diamonds indicate time points of the sample collection. Lunar phases (NM; new moon; FQM: first quarter moon; FM: full moon; LQM: last quarter moon) are indicated by schematic moon images.
Although the involvement of clock-related genes in the molecular mechanisms underlying lunar-related rhythmicity are far less understood, lunar phase-dependent changes in Cryptochrome (Cry) expression were observed in the Goldlined spinefoot17 and a lunar-synchronized spawning coral, Acropora millepora18. In Fukushiro et al.17, we reported lunar phase-dependent changes in Cry1b (termed as Cry1 in ref.17) and Cry3 mRNA expression in the diencephalon of the Goldlined spinefoot with an increase observed around the new moon and a decrease around the full moon. In Toda et al.19, we investigated whether the 2-week interruption in moonlight from the new moon to full moon around the spawning phase (the first quarter moon) changed the expression pattern of Cry3. The interruption resulted in little to no effect on the lunar phase-dependent expression of Cry3, indicating that Cry3 does not just acutely respond to daily moonlight illumination but that it follows the lunar phase for at least 2 weeks. This study together with our previous results arise a question that Cry3 and/or other circadian genes of the Goldlined spinefoot may act as signaling molecule(s) in the putative hourglass-like lunar timer which potentially contributes to spawning-lunar-phase recognition. Alternatively, it was possible that Cry3 might constitute an unidentified lunar clock that sustainably oscillates more than two lunar phases without moonlight stimuli.
The present study aims to evaluate the above question and better elucidate the molecular mechanism underlying lunar phase-recognition of the Goldlined spinefoot. We investigated the daily and monthly patterns of Cry, Per, Clock, and Bmal expression in both the diencephalon and its downstream pituitary gland. Their expression patterns were compared with those after a 4 week moonlight interruption period. The repetitive moonlight stimuli plays a significant role in both stabilizing daily expression of circadian clock genes and triggering lunar-phase-synchronized expression of Cry3.

Results

Identification of Cry and Per paralogs in the Goldlined spinefoot

First, we conducted massive transcriptome sequencing in the brain of the Goldlined spinefoot to identify core clock gene paralogs unexamined in our previous study. Phylogenetic analyses followed by Blast search (Fig. S1A–D) revealed three unreported Cry paralogs (Cry1a [FX985477], Cry2a [FX985476], Cry6 [FX985478]), two Per paralogs (Per2a [FX985479], Per3 [FX985480]), two Clock paralogs (Clock1a [FX985868], Clock1b [LC367223]), two Bmal paralogs (Bmal1 [FX985869], Bmal2 [LC367224]), in addition to the known paralogs Cry1b (AB643455), Cry3 (AB643456), Per1 (DQ198087), and Per2b (EF208027, formerly termed Per2 in ref.20.

Sampling and analysis of clock gene mRNA expression by qPCR

To investigate whether the core clock genes show lunar phase-dependent variation and whether those changes might continue in the absence of moonlight cues, rearing tanks were either repeatedly covered with a black sheet during nighttime to interrupt the moonlight (moonlight-interrupted; MI) or were exposed to natural moonlight conditions (moonlight-exposed; ME) for 2 lunar cycles (Fig. 1). We collected the diencephalon and pituitary gland at 4 representative lunar phases in the 2nd lunar cycle (Fig. 1, open diamonds) to analyze the daily expression patterns of clock genes by qPCR using specific primers (Table 1). The daily expression profiles in the diencephalon (Cry, Fig. 2; Per; Fig. 3; Clock, Fig. 4A–L; Bmal, Fig. 4M–X; statistics for all examined genes, Table S1) and the pituitary gland (Cry, Fig. S2; Per; Fig. S3; Clock, Fig. S4A–L; Bmal, Fig. S4M–X; statistics for all examined genes, Table S2) were further analyzed by the Cosinor method (Fig. 5; Tables S3 and S4).
Table 1 Primers used in quantitative RT-PCR analysis.

Figure 2
Figure 2
The daily expression profiles of Cry genes in the diencephalon of the Goldlined spinefoot after interrupted moonlight for 1 lunar cycle. The diencephalons of the fish (n = 5) were collected at ZT0, ZT6, ZT12, ZT18 on the day of the new moon (NM), first quarter moon (FQM), full moon (FM), and last quarter moon (LQM) phase (Fig. 1). The bar at the bottom of each graph represents the sunlight conditions. (Panels on the left: A,B,G,H,M,N,S and T) The daily expression profiles of genes at four lunar phases in moonlight-exposed (ME: panels A, G, M and S) and moonlight-interrupted (MI: panels B,H,N and T) groups. The different letters (a, b) in panels (A,M,N,S and T) indicate statistical differences among lunar phases (two-way factorial ANOVA followed by Tukey’s HSD test, p < 0.05). (Panels on the right: C–F, I–L, O–R, and U–X) The daily profiles shown on the left are replotted to compare the daily profiles of ME and MI groups at each lunar phase. Lunar phase is indicated by a schematic moon image. s.i. and asterisks indicate significant interactions and significant differences, respectively, between ME and MI analyzed using two-way factorial ANOVA followed by Tukey’s HSD test (p < 0.05). The statistical difference between ME and MI at each time point is indicated by a dagger (Student’s t-test or Mann–Whitney U test, p < 0.05). Curves indicate significant rhythmicities detected by Cosinor analysis, while lines indicate no significant rhythmicity.
Figure 3
Figure 3
The daily expression profiles of Per genes in the diencephalon of the Goldlined spinefoot after interrupted moonlight for 1 lunar cycle. The diencephalons of the fish (n = 5) were collected at time points shown in Fig. 1. The bar at the bottom of each graph represents the sunlight conditions. (Panels on the left: A,B,G,H,M,N,S and T) The daily expression profiles of the genes at four lunar phases in moonlight-exposed (ME: panels A,G,M and S) and moonlight-interrupted (MI: panels B,H,N and T) groups. s.i. in panel N indicates a significant interaction. Different letters in panel B indicate statistical differences among lunar phase (two-way factorial ANOVA followed by Tukey’s HSD test, p < 0.05). (Panels on the right: C–F, I–L, O–R, and UX) The daily profiles shown on the left are replotted to compare the daily profiles of ME and MI groups at each lunar phase. s.i. and asterisks indicate significant interactions and significant differences, respectively, between ME and MI groups analyzed using two-way factorial ANOVA followed by Tukey’s HSD test (p < 0.05). Statistical differences between ME and MI at each time point are indicated by daggers (Student’s t-test or Mann–Whitney U test, p < 0.05). Curves indicate significant rhythmicities detected with Cosinor analysis, while lines indicate no significant rhythmicity.

Figure 4
Figure 4
The daily expression profiles of Clock and Bmal genes in the diencephalon of the Goldlined spinefoot after interrupted moonlight for 1 lunar cycle. The diencephalons of the fish (n = 5) were collected at time points shown in Fig. 1. The bar at the bottom of each graph represents the sunlight conditions. (Panels on the left: A,B,G,H,M,N,S and T) The daily expression profiles of the genes at four lunar phases in moonlight-exposed (ME: panels A,G,M and S) and moonlight-interrupted (MI: panels B,H,N and T) groups. s.i. in panel (H) indicates a significant interaction. Different letters in panels (N and S) indicate statistical differences among lunar phase (two-way factorial ANOVA followed by Tukey’s HSD test, p < 0.05). (Panels on the right: C–F, I–L, O–R and U–X) The daily profiles shown on the left are replotted to compare the daily profiles of ME and MI groups at each lunar phase. s.i. and asterisks indicate significant interactions and significant differences, respectively, between ME and MI groups analyzed using two-way factorial ANOVA followed by Tukey’s HSD test (p < 0.05). Statistical differences between ME and MI at each time point are indicated by daggers (Student’s t-test or Mann–Whitney U test, p < 0.05). Curves indicate significant rhythmicities detected with Cosinor analysis, while lines indicate no significant rhythmicity.
Figure 5
Figure 5
Peak phases of the clock gene expression in the Goldlined spinefoot. The acrophases of the clock gene expressions for ME and MI groups at each lunar phase (Figs 24, S2S4; Tables S3, S4) estimated by Cosinor analysis are plotted. Open diamonds and filled squares show ME and MI, respectively. Error bars represent ± SEM. Schematic moon images represent lunar phase (new moon, NM; first quarter moon, FQM; full moon, FM; last quarter moon, LQM).

Daily and monthly profiles of clock gene expression under moonlight-exposed (ME) conditions

In the diencephalon, Cry3 expression levels showed no significant daily fluctuation at most lunar phases but showed phase-dependency (Figs S2, 5D); the average daily level of Cry3 was significantly higher at the new moon than at the other lunar phases (Fig. S2). Every examined gene except for Cry3 showed daily variation, mostly with peaks at a fixed time of day regardless of moon phase (Fig. 5A–C,I–L,Q–T; Table S1); Cry1a, Cry1b, and all Per genes had peaks in the morning, while Cry2, Clock1a, Clock1b, Bmal1, and Bmal2 had peaks in the evening. The results of Cry1b, Cry3, and Per1 mRNA expression in ME fish were consistent with our previous observations17,19,21.
Importantly, in fish maintained under natural conditions, not only Cry3 but also Cry1a, Cry2, and Bmal2 showed lunar phase (LP)-dependent expression (p = 4.48e-06 for Cry3, p = 0.00317 for Cry1a, p = 0.00171 for Cry2, p = 0.00015 for Bmal2, LP effect in ME fish; Figs 2A,M and S4; Table S1). Expression levels of Cry1a and Cry2 were higher at FM and LQM, respectively (Fig. 2A,M), than levels at other moon phases, while those of Bmal2 were lowest at FM (Fig. S4).
In the pituitary gland, the daily profiles of clock gene expression were similar to those of the diencephalon (Figs 5, S2S4), albeit with some differences. Cosinor analyses detected significant daily variations in every examined gene except for Per2a (Fig. 5N, Table S4). Cry1a showed significant interaction between Zeitgeber time and lunar phase (p = 0.02855, Table S2), but the profiles were similar (Fig. S2A). All of the other genes showed no lunar phase-dependent change under ME condition.

Daily and monthly profiles of clock gene expression under moonlight-interrupted (MI) conditions

In the diencephalon of fish reared under MI conditions, most of the examined genes exhibited robust daily variation, Cry3 and Per2a being the two exceptions. Per2a lost its rhythmicity after the FQM in MI fish (Fig. 5J). Another observation worth of noting was that the peak time of Cry1b was advanced according to the lunar phase progression (Fig. 5B). This may be relevant to the moonlight-interruption-dependent upregulation of Cry1b expression at ZT18 in FM (Fig. 2K) and LQM (Fig. 2L), implying a possible moonlight-dependent suppression.
Similarly, mRNA expression at ZT18 is upregulated by moonlight-interruption in FQM to LQM in the case of Per1 and Per3 (Fig. 3D–F,V–X), causing phase advances of peak time (Fig. 5I,L) as observed in Cry1b (Fig. 5B). Cry1a expression levels were significantly lower in MI fish than ME fish during the full moon phase (Fig. 2E), suggesting that nocturnal moonlight may upregulate the expression level of Cry1a during the daytime.
Cry1b, Cry2, Cry3, Per1, Per2a, Per2b, and Clock1a showed moonlight-interruption-dependent changes in the daily expression profile even in the absence of moonlight at NM (Figs 2I,O,U, 3C,I,O and 4C). This indicates that daily rhythms of many clock(-related) genes are affected by moonlight in the preceding cycle (Fig. 1, May 18-Jun 10). MI fish had significantly lower Cry3 expression levels at NM, FQM, and LQM (Fig. 2U,V,X, Fig. 6) and higher Clock1a expression levels at all four lunar phases (Fig. 4C–F).
Figure 6
Figure 6
Effects of repetitive moonlight interruption on the lunar phase-dependency of Cry3 gene expression in the diencephalon of the Goldlined spinefoot. The lunar phase-dependent changes in Cry3 expression in moonlight-exposed (+) and moonlight-interrupted (−) groups. The relative expression levels of Cry3 in ME and MI (Fig. 2M,N) groups were respectively averaged at each lunar phase. Because significant interactions between nocturnal light conditions (ME and MI) and lunar phase (NM, FQM, FM, and LQM) were detected with two-way factorial ANOVA (p < 0.05), the statistical differences between ME (n = 20) and MI (n = 16) groups at each lunar phase were analyzed using the Student’s t-test as indicated by daggers (p < 0.05).

Some genes (Per1 (Fig. 3B) Per2b (Fig. 3N), Clock1b (Fig. 4H), and Bmal1 (Fig. 4N)) showed moon phase-dependency in the expression levels under MI condition but not under ME condition, suggesting that repetitive moonlight-interruption for 1 lunar cycle may affect on the regular daily oscillation of circadian clock in the diencephalon of Goldlined spinefoots.
In the pituitary gland, Cry2, Per2a, and Per2b showed lunar-phase-dependent changes (Figs S2N, S3H and S3N), but the interruption of moonlight seemed to have little effect on clock gene peak expressions. Cry1a, Per2a, and Per2b levels were significantly higher in MI fish than ME fish (Figs S2C–F, S3I–L,O–R), suggesting that moonlight may have inhibitory effects on their expression. In contrast to the diencephalon, no lunar phase-dependent change in Cry3 expression was observed in the pituitary gland under ME or MI conditions (Fig. S2S,T).

Acute effects of moonlight illumination around waxing gibbous moon on clock gene mRNA expressions

As mentioned above, daily changes in clock gene expressions were observed in the diencephalon and pituitary gland, some of which may be modulated by moonlight. In particular, the nocturnal mRNA expression (ZT18) of Cry1b (Figs 2K,L, S2K), Per1 (Figs 3D–F, S3E), and Per3 (Figs 3W,X, S3W) were likely increased by moonlight interruption in both the diencephalon and pituitary gland. These modulations were observed during the FM and LQM but not the NM or FQM when the intensity of moonlight illumination were much lower than the FM.
To clarify whether such moonlight interruption-dependent elevation was an acute response to the absence of moonlight or a slow response to the repetitive interruptions of moonlight illumination, the effect of short term moonlight deprivation (1 or 2 nights) on the clock gene expression was evaluated around the waxing gibbous moon, when the intensity of moonlight illumination dramatically increases (Figs 7 and S5). Interestingly, expression levels of Cry1b (Fig. 7C) and Cry2 (Fig. 7H) were significantly higher in moonlight-interrupted fish than in natural moonlight-exposed or artificial moonlight-exposed fish. Per expressions in the diencephalon (Fig. S5A–D) showed a similar trend, albeit only on Day 1. On the other hand, neither Cry3, Clock nor Bmal genes in the diencephalon (Figs 7E, S5I–L) nor any of the examined genes in the pituitary gland (Fig. S5E–H,M–P) showed such moonlight interruption-dependent elevation.
Figure 7
Figure 7
Acute effects of interrupted moonlight on Cry gene expressions in the diencephalon and the pituitary gland. (A) Sampling schedule and nocturnal light conditions during the moonlight interruption experiment around the waxing gibbous moon. Before the onset of the experiment, the Goldlined spinefoot fish were divided into three groups: moonlight exposed (ME, n = 12), moonlight interrupted (MI, n = 11), and artificial moonlight exposed (AM, n = 12) groups. The fish in each group were reared for 2 days around the waxing gibbous moon in June 2016 (full moon was June 20). The fish were randomly taken from each group at ZT0 on Day1 and 2 as indicated by arrows, and the diencephalons and pituitary glands were collected (each n = 5 except for MI on Day2 [n = 4]). (BI) The relative expression levels of Cry1a (B,F), Cry1b (C,G), Cry2 (D,H), and Cry3 (E,I) in the diencephalon (BE) and pituitary gland (FI) under three different nocturnal conditions. Presence or absence of natural moonlight and artificial moonlight is indicated by + or − along the x-axis. Asterisks indicate significant differences among nocturnal light conditions (two-way factorial ANOVA followed by Tukey’s HSD test, p < 0.05).

Discussion

Our previous studies implied that Cry3 acts as a possible state variable internally expressing lunar-phase in an hourglass-like timer mechanism or a self-oscillating lunar clock underlying the lunar phase-specific spawning of the Goldlined spinefoot17,19. In the present study, we aimed to answer this question through comparative measurements of the daily expression profiles of Cry, Per, Clock, and Bmal genes at the four principle lunar phases in fish maintained under natural conditions or in the absence of moonlight illumination for over 1 lunar cycle.
The lunar phase dependency of Cry3 expression was markedly changed after repetitive deprivation of moonlight for over 1 month (Fig. 6), which contrasts with the 2-week interruption from the NM to FQM that had no such effect19. Cry3 is less likely to be a circalunar clock element, in which case it would exhibit lunar phase-dependent oscillatory expression even in the absence of external cues. The present results suggest that the lunar phase-dependent change in Cry3 expression could be regulated by moonlight signals from the previous lunar cycle, possibly preceding spawning. Thus, Cry3 could constitute an hourglass-like timer with a period of one lunar cycle, although its association with lunar-response is yet unclear.
According to the phylogenetic analysis of vertebrate CRY, CRY3 of both zebrafish and the Goldlined spinefoot were classified into the vertebrate CRY2 cluster (Fig. S1A) which is suggested to operate in the circadian clock. Ishikawa et al.22 has reported that the inhibition of CLOCK:BMAL1-mediated transcriptional activity by zebrafish CRY3 (zCRY3) was weaker than that of zCRY1a and zCRY2b, both of which are classified into the vertebrate CRY1 cluster. This, together with the present observation, led us to speculate that CRY3 may retain a non-circadian function in addition to the established circadian function. In particular, SgCRY3 may play a role as a modifier of circadian clock inhibiting the circadian core elements according to the moon phase in the Goldlined spinefoot.
Previous study performed by Takemura et al.16 suggested that lunar-synchronized spawning of the Goldlined spinefoot requires moonlight signals from the previous lunar cycle before spawning. The synthesis and secretion of a maturation-inducing steroid hormone, 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) is constitutively activated from the new moon to the first quarter moon during reproductive season23. Thus, moonlight signals are considered to play a key role in triggering sexual maturation for spawning in the next lunar cycle, and hence an hourglass-like timer may be reset by moonlight signals to contribute to the recognition of the timing of spawning within one lunar cycle. The expression manner of Cry3 that changed upon the interruption of moonlight illuminations in the last cycle (Fig. 6) seems to fit well with these physiological findings where we speculate that Cry3 is involved in the hourglass-like lunar timer.
The comparative investigations of clock gene expressions in the presence (ME) and absence (MI) of moonlight stimuli unexpectedly highlighted important observations. Many clock genes showed lunar phase-dependent daily profiles under MI condition, while rather stable profiles were shown under ME condition (Figs 2N,T, 3B,N, 4H, S2N, S3H,N). We believe that these differences are not artifacts of covering the tanks with sheets, because the difference between ME and MI is whether the fish were repeatedly covered by clear or black sheets, respectively. Although the involvement of clock genes in the lunar timer nor circalunar clock is yet to be elucidated, these results suggest significant association between the clock gene expression and moonlight which periodically changes both in intensity and duration (timing of moonrise and moonset) in accordance with the moon phase (Fig. 1). The moonlight stimuli may be necessary for stable daily expression of clock genes over the lunar cycle in the Goldlined spinefoot.
The light responsiveness of clock gene expression was additionally examined by investigation of the acute effect of moonlight interruption on clock gene expression around the waxing gibbous moon (Fig. 7). Cry1b and Cry2 were likely induced by interrupted moonlight (Fig. 7C,H), and the possible light-dependent repression was mimicked by illumination from artificial moonlight in a diencephalon-specific manner. It is interesting to assume that the moonlight-dependent downregulation of Cry1b and Cry2 may contribute to the upregulation of Cry1a (Fig. 2E) at the FM and Cry3 at the following NM (Figs 2U, 6) in the diencephalon. Further studies including promoter analyses of these clock genes and genome-wide transcriptome analyses would assist in elucidation of the complex molecular networks underlying the lunar-phase dependent change in Cry3 expression.
Because the luminosity of moonlight (less than 1 lux) is a lot lower than that of sunlight, moonlight cues are probably detected by a highly light-sensitive organ such as the eyes and/or the pineal gland in the Goldlined spinefoot. Melatonin is synthesized mainly in these organs, the production of which is typically accelerated at night24. It is widely known that melatonin production is inhibited by external light signals in vertebrates, including fish25,26. In the Goldlined spinefoot, this nocturnal elevation of melatonin production in the eyes and the pineal gland was reported to be suppressed by moonlight16. This result implies that lunar phase information can be encoded into lunar changes in the daily plasma melatonin levels that in turn can be detected by Cry expressing cells that express melatonin receptors in the diencephalon and pituitary gland. In this regard, the expression of a melatonin receptor gene, MT1, was found in the mediobasal region of the diencephalon of the European seabass27. This likely overlaps with the location where we previously reported immunopositive reactions to anti-CRY3 antibody in the Goldlined spinefoot19. In addition, it is interesting to note that the CRY3 immunopositive cells in the Goldlined spinefoot diencephalon resemble CSF-contacting neurons called “deep brain photoreceptors”. In the pigeon and toad, the deep brain photoreceptors are shown to express opsin proteins that may detect external sunlight directly and operate as a sensor for detecting seasonal change in photoperiod28,29,30. In the case of the Goldlined spinefoot, a similar mechanism may exist in CRY3-expressing cells of the diencephalon that are directly sensitive to sunlight for the photoentrainment of clock genes. Such a mechanism could discriminate and integrate signals of sunlight and moonlight in the cell, which could help to determine the timing of spawning.
The present study along with our previous studies provide an insight that Cry3 of the Goldlined spinefoot could be an internal signal for recognizing external lunar phase. Cry3 might be involved in forming a putative hourglass-type lunar timer that regulates spawning associated with the lunar cycle in the Goldlined spinefoot. However, we cannot rule out the possibility that the moonlight-dependent changes in clock gene expression in the diencephalon might be due to systemic changes such as oocyte development or sexual maturation that is initiated by FM light. Also, it is still possible that the Goldlined spinefoot might have a self-sustainable circalunar clock that is rather independent of circadian clock as shown in P. dumerilii.
The next step is to examine the impact of moonlight on nocturnal levels of melatonin and clock gene expression in the diencephalon as well as to analyze the moonlight-dependent transcription regulation on the promoter of clock genes such as Cry1a and Cry3. Physiological and molecular biological approaches would also be desired such as the diencephalon-specific induction and knockdown of Cry3 and ex vivo culturing of the diencephalon to test responses to melatonin and light.

Materials and Methods

Experimental animals

Juvenile Goldlined spinefoots were originally collected from the Teima river (26°33′25.8′N 128°04′12.3′E) and the Manna river (26°40′41.4′N 127°53′15.9′E), which are located in the northern part of Okinawa island, Japan. They were reared under a natural photoperiod in concrete tanks (10 metric tons capacity) with running seawater at Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, and were fed daily with commercial pellets (EP1, Marubeni Nisshin, Tokyo, Japan). Fish aged 3–5 years, with a body mass ranging from 162–792 g, were used in the present study. All experiments were conducted in accordance with the guidelines of WASEDA University. All protocols were approved by the Committee for the Management of Biological Experiment at WASEDA University, and experimental animal care was conducted under permission from the Committee for Animal Experimentation at the School of Science and Engineering at Waseda University (permission # WD15–060; WD16-056). Animal experiments were conducted under permission from Sesoko Station Tropical Biosphere Research Center at the University of the Ryukyus (permission # 20150518-0708; 20160531-0619). The fish were anesthetized deeply with 2-phenoxyethanol (Kanto Chemical, Tokyo, Japan) and euthanized by decapitation.

Massive sequencing of transcriptome in the brain of the Goldlined spinefoot

Total RNA was extracted from the telencephalon, diencephalon, and optic tectum of 3–5 year old Goldlined spinefoots reared under natural conditions. Total RNA was collected at ZT0, ZT6, ZT12, and ZT18 (n = 1 each) and pooled. Samples were sent to Eurofin Genomics (Tokyo, Japan) for cDNA library construction and transcriptome sequencing using Illumina Hiseq. 2500 (read length 2 × 125 bp). After trimming the bases from the 5′end and 3′end of each read with low quality (Q <25) adapter sequences using Trimmomatic (ver. 0.3.6, ref.31), trimmed reads shorter than 90 bases and of low averaged quality (Q <25) were removed by PRINSEQ lite (ver. 0.20.4, ref.32). The cleaned raw reads were then assembled with Trinity software (ver. 2.3.2, ref.33) using default parameters. To search Cry and Per paralogs of the Goldlined spinefoot against the assembled sequences, the tBlastn program34 was utilized (E-value < 0.01) on zebrafish CRY and PER protein sequences as queries.

Repetitive interruptions in moonlight illumination for 2 lunar cycles

Moonlight irradiation was interrupted for 2 lunar cycles (from the new moon on May 18, 2015 to the last quarter moon on July 8, 2015) at Sesoko Station (Fig. 1). The goldlined spinefoots (n = 144) were divided into two groups (the moonlight-interrupted group, MI, and moonlight-exposed group, ME) and reared in outdoor tanks (1 metric ton capacity) equipped with running seawater and an aeration system. The tank holding the MI group was covered with a black plastic sheet during the night hours (19:20-5:40) to prevent moonlight penetration. The tank holding the ME group was covered with a clear plastic sheet that allowed moonlight to filter in at night. After rearing the fish under these conditions for 1 lunar cycle, samples were taken from the diencephalon and pituitary gland of MI (n = 4) and ME (n = 5) fish at ZT0 (6:00), ZT6 (12:00), ZT12 (18:00), and ZT18 (24:00) on the day of the new moon (June 16), first quarter moon (June 24), full moon (July 2), and last quarter moon (July 8). Collected samples were immersed in RNAlater (Thermo Fisher Scientific, MA, USA) at 4 °C for at least 24 hours, and then stored at −80 °C until total RNA extraction. Samplings at ZT0, ZT6, and ZT12 were conducted under fluorescent lighting (Toshiba, FHF32EX-N-H 32 W, approximately 800 lux) and sampling at ZT18 was done under dim red LED lighting (2.5 W red LED; OPTILED, Optiled Lighting International Ltd., Kwun Tong, Hong Kong, λpeak = 627 nm).

Two-night interruptions of moonlight illumination

Fish aged three to five years old (n = 35) were divided into three groups (Moonlight exposed group, ME, n = 12; Moonlight interrupted group, MI, n = 11; and the Artificial moonlight-irradiated group, AM, n = 12) and kept in outdoor 200 L polyethylene tanks with running seawater and aeration under natural conditions before the onset of the experiment (May 31, 2016). After acclimation in the tanks for 17 days, the MI and AM groups were covered with a black plastic sheet to prevent moonlight illumination at night (ZT12-18) for 2 days beginning from the day of the waxing gibbous moon (moon age = 12)(Fig. 7A). AM fish were exposed to illumination from hand-made LED lights designed to mimic moon light (1 lux on the water surface; Fig. S6) while the tank was covered with a black sheet at night. The ME tank was covered with a clear plastic sheet to allow moonlight to shine into the tank as a control. Fish (n = 4–5) from each group were taken from the tanks randomly on Day1 at ZT0 (n = 5), and on Day2 at ZT0 (n = 5 except for MI [n = 4]), and the diencephalon and pituitary gland of each fish were collected. The samples were stored as mentioned above until total RNA extraction. Throughout the experimental period (the time of sunrise was 05:40 JST and that of sunset was 19:24 JST), the weather was conducive to having enough moonlight at night.

Quantitative RT-PCR

Total RNA was extracted from the collected samples using Trizol (Thermo Scientific) according to the manufacturer’s instructions. The quantity of total RNA was assayed spectrophotometrically at 260 and 280 nm. ReverTra Ace qPCR Master Mix with gDNA Remover (TOYOBO) was used to digest genomic DNA contaminating the total RNA and to synthesize cDNA from 1 μg of total RNA according to the manufacturer’s instructions. Quantitative RT-PCR analyses were performed using StepOnePlus (Applied Biosystems) along with a Fast SYBR Green Master Mix (Applied Biosystems). The primers for quantitative RT-PCR are shown in Table 1. The PCR products were subjected to 3% agarose gel electrophoresis and analyzed using a Typhoon 9410 scanner (GE healthcare). The relative mRNA expression levels of target genes were calculated using the ΔΔCt method, and the reference gene was virtually defined as the average of the threshold cycles (Ct) for SgPGK (AB643458), SgEF1α (AB643459) and Sgβ-actin (AB643460) as described in ref.19.

Statistics

In moonlight interruption experiments conducted in 2015 (Figs 24 and S2S4), a three-way interaction involving the effect of lunar phase (NM, FQM, FM, LQM), Zeitgeber time (ZT: 0, 6, 12, 18), and nocturnal light condition (NLC; exposed, interrupted) was analyzed using three-way ANOVA. Because there was no significant interaction detected in three-way ANOVA analysis, a simple interaction between LP and ZT in each NLC and between NLC and ZT in each LP was analyzed using two-way factorial ANOVA (Tables S1 and S2). When a significant simple interaction was detected, a simple-simple main effect was analyzed using the Student’s t-test or Mann–Whitney U test according to results of the F test to compare the expression levels at each time point. The rhythmicity and acrophase of the daily expression profiles were analyzed using the Cosinor method on CircWave ver. 1.4 [ref.35] at a fixed period of 24 h. The acute effects of nocturnal light treatment (Fig. 7) were evaluated by two-way factorial ANOVA. Values of p < 0.05 were considered statistically significance for all analyses. Error bars represent ± SD (Figs 24, S2S4).


    

              Elemental Digital Circuits 

Analog vs. Digital: What’s the Difference?

Air temperature, sound loudness,light intensity—in nature, all of these quantities vary smoothly and continuously over a range. Such quantities is called "analog" value.
Today’s computers, in contrast, work with discrete quantities. These discrete quantities are called "digital" values. Where an analog measurement is a smooth curve that " looks like" the measured property, digital measurements are a series of discontinuous levels.
Here’s another way to put it: analog values are real numbers, whereas digital values are integers. Real numbers can represent any point on a number line, whereas integer are limited to express those special points evenly spaced on the line.
An analog circuit works with analog signals—where values change continuously. A digital circuit works with digital signals, where all values are discrete.
Figure 1 : Analog vs. Digital
Figure 1 : Analog vs. Digital
To input nature’s analog information into digital circuits, it is first necessary to digitize the information: that is, to convert the analog signal into a digital signal. An analog/digital (A/D) converter samples the analog signal (reads the value at a set time interval), and converts each reading into a corresponding binary number (a base 2 value, expressed in 0’s and 1’s).
Since the converter is changing an analog signal that can take any fractional value into a digital signal that can take discrete values only, some information will be lost. Each analog reading must be rounded up or down to the nearest digital value. And since the converter reads the analog signal at a specific interval only, it loses the analog information that exists between these intervals.
As a result, digital values are only an approximation of the analog signal and always contain conversion error. This error can be reduced, however, by shortening the interval between measurements, and by using more precise (that is, longer bit-length) digital values.
But what’s the point of converting a smooth analog signal into a jumpy and imprecise series of numbers? There are at least two advantages: digital signals are much more resistant to noise; and, because modern computers work with digital values only.
Today’s powerful microcontrollers are capable of rapidly processing large volumes of digital information. These microcontrollers use digital circuits that take full advantage of the fact that, unlike analog signals, digital signals do not lose information during transmission and playback.

Binary Numbers

Digital signals typically express values using binary (also called " base 2" ) numbering, where each number is written using only 0’s and 1’s. Specifically, the rightmost digit of the number represents 20, the next digit to the left represents 21, then 22, etc. A four-digit binary number, therefore, can represent 16 values, from 0 to 15, as you can see in the Table 1. Values higher than 15 can be represented by adding additional digits, as necessary.
One advantage of treating digital signals as binaries is that it is easy to design logic circuits with binary output: the circuits are either ON or OFF, corresponding to the 1’s and 0’s of numeric binary numbers. The ON and OFF states are physically implemented as two voltage states: high (" H" ) and low (" L" ). In a typical CMOS IC with a 5-volt power source, " L" denotes a voltage from 0 up to 1.35 V, while " H" denotes a voltage from 3.15 V on up. Because 0 and 1 correspond to these relatively wide voltage ranges, the circuit produces the correct output even when there is moderate noise on the line.
Decimal Binary
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
10 1010
11 1011
12 1100
13 1101
14 1110
15 1111
Table 1: Binary Representation of Decimal Values

Digital Circuits = Logic Circuits

A digital circuit, also called a logic circuit, carries out a logical operation. Three elemental circuits—AND, OR, and NOT—can be combined to build any desired logical operation.
Logic circuits are expressed using logical expressions and circuit symbols. (Here we use MIL symbols, although JIS symbols or other symbologies may be used instead.) A truth table indicates what the circuit’s output will be for all combination of inputs.

The AND Circuit, A Series Circuit

An AND circuit, also called a logical product circuit, take two inputs, and outputs a 1 if both inputs are 1, and a 0 otherwise.
Logical Expression of AND
Written using the " ・" operator. Example: Y = A・B

AND Circuit Notation
The AND Circuit, A Series Circuit
Truth Table
A B Y
0 0 0
0 1 0
1 0 0
1 1 1
Let’s look at how an AND circuit works. Figure 2 shows an AND circuit comprising two switches (SW A and SW B) and a LED indicator. Note that:
  • SW A is On if input A is 1; SW A is Off if input A is 0.
  • SW B is On if input B is 1; SW B is Off if input B is 0.
  • LED Y is On (lit) if output Y is 1; LED Y is Off (dark) if output Y is 0
Figure 2: An AND Circuit
Figure 2: An AND Circuit
This AND circuit works as follows.
  • If SW A and SW B are both On, then LED Y is On (lit).
  • If one switch is On but the other is Off, then LED Y is Off (dark).
  • If both switches are Off, then LED Y is Off (dark).
Basic logic circuits are also called gates. Note that you can control the value of the output by leaving one switch closed while controlling the other switch. Figure 2 illustrates the AND circuit’s gate operation.
  • If either SW A or SW B is fixed at Off, the LED will remain dark; that is, the output will also be fixed at Off (the gate is closed).
  • If either SW A or SW B is fixed at On, then the gate will output the value of the unfixed SW (the gate is open).

The OR Circuit, A Parallel Circuit

An OR circuit, also called a " logical sum circuit," outputs a 1 if either or both inputs are 1, and outputs a 0 if both inputs are 0. Example: Y = A+B.
Logical Expression of OR
Written using the " +" operator. Example: Y = A+B

OR Circuit Notation
The OR Circuit, A Parallel Circuit
Truth Table
A B Y
0 0 0
0 1 1
1 0 1
1 1 1
Figure 3 shows an OR circuit: a parallel circuit with two switches and one LED indicator.
  • Since this a parallel circuit, the output will be On (LED Y will light up) if only SW A, only SW B, or both SW A and SW B are On.
The gate operation of the OR circuit is the reverse of the AND circuit’s operation.
  • If either SW A or SW B is fixed at On, the LED will light; that is, the output will also be fixed at On (the gate is closed).
  • If either SW A or SW B is fixed at Off, the gate will output the value of the unfixed SW (the gate is open)
Figure 3: An OR Circuit
Figure 3: An OR Circuit

The NOT Circuit, An Inverter Circuit

A NOT circuit (also called an " inverter circuit," ) takes only one input, and outputs the inverse of the input. If the input is 1, the output is 0. If the input is 0, the output is 1.
Logical Expression of NOT
Written using the " ¯" operator. Example: Y =
NOT Circuit Notation
The NOT Circuit, An Inverter Circuit
Truth Table
A Y
0 1
1 0

Amorphous selenium (a-Se) has been proved to have excellent detective quantum efficiency, which suggests that a-Se would provide good image quality that is equivalent to or better than conventional film. We implemented a simulation model using Monte Carlo method to acquire the characteristics of detection material itself, not of whole detection system, to compare with conventional film or screen, and obtained PSF, LSF and MTF of photon absorption in alpha -Se relative to X-ray energy, thickness, and so on. First, we translated XCOM front Fortran into C++ language, which was needed to generate cross sections and attenuation coefficients to obtain path length and interaction type of photons. Using Monte Carlo simulation codes in Visual C++ incorporated with this program, total cross sections, attenuation coefficients, partial cross sections for incoherent and coherent scatterings, photoelectric absorption and pair production were obtained for photons with energy between 1keV and 100GeV. The Monte Carlo simulation codes developed in this study allowed the users to select a random number generator among four suggested ones in Numerical Recipes in C. Based on three interaction types occurring for photons in energy range of diagnostic X-ray (1-100keV), we estimated the position of interaction and the direction of scattered photons in alpha -Se. Via Fourier transformation of PSF and LSF, we obtained MTF. Density and thickness of a-Se detector was 4.26g/cm3 and 300 mu m, respectively, and number of induced photons was 100,000. The percentage of absorbed photons in induced direction was 99.8% for 5keV and 86.4% in 30keV photons. Probability of interaction became higher for lower energy photon and in thicker a-Se.

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