Spooling and Sleek latency

SPOOLING

Spooling is a process in which data is temporarily held to be used and executed by a device, program or the system. Data is sent to and stored in memory or other volatile storage until the program or computer requests it for execution.

"Spool" is technically an acronym for simultaneous peripheral operations online.

Spooling works like a typical request queue or spool where data, instructions and processes from multiple sources are accumulated for execution later on. Generally, the spool is maintained on the computer’s physical memory, buffers or the I/O device-specific interrupts. The spool is processed in ascending order, working on the basis of a FIFO (first in, first out) algorithm.

The most common implementation of spooling can be found in typical input/output devices such as the keyboard, mouse and printer. For example, in printer spooling, the documents/files that are sent to the printer are first stored in the memory or printer spooler. Once the printer is ready, it fetches the data from that spool and prints it.



SLEEK LATENCY

The red circle is a track, you'll have many tracks. A sector is shown in purple. You should also note that the disk will be rotating and there's a head which reads from the rotating disk.

Let us label the tracks from 0 (innermost, inside red circle) to 3 (outermost circular strip). Similarly the purple sector as 0 and going clockwise we name the others till 7. For our convenience we can refer (x,y) as the track sector (aqua blue) whose track is x and sector is y.

Seek time: Say you're reading some data from the (0,4). You receive instructions to read from track (2,5). The time it takes for you to move from track 0 to track 2 is seek time.

Latency: Once you reach track 2, you realize the head is above the 1st sector you'll have to wait till the disk rotates to the 5th sector so that you can start reading from (2,5). The time you wait for the sector to be accessible by your head here is known as latency.

Edison Effect

In early 1880, Thomas Edison and his team were hard at work trying to find a light bulb filament that worked well. He had already settled on a carbonized (burned) bamboo filament, but even this solution was not perfect. After glowing for a few hours, carbon from the filament would be deposited on the inside walls of the bulb, turning it black. This would not do. Edison tried to understand what was happening. His assistant noticed that the carbon seemed to be coming from the end of the filament that was attached to the power supply, and seemed to be flying through the vacuum onto the walls of the bulb. Edison determined that not only was carbon flying through the vacuum, but that it carried a charge. That is, electricity was flowing not only through the filament but also through the evacuated bulb. In order to measure this flow, he made a special bulb with a third electrode, to which he could attach an instrument to measure the current. He reasoned that if the current would flow between the two ends of the filament, it would also flow to this third electrode.

While he was proven to be right about the flow, Edison could not explain it, and the third electrode did not prevent blackening of the bulb, so he moved on to other experiments. But he did patent the new device, because he believed that it might have some commercial applications, such as measuring electric current. Although he did not realize it, Edison had discovered the basis of the electron tube (also called a vacuum tube). Many years later, modified light bulbs would be used not to make light, but to control a flow of electrons through a vacuum. The electron tube would become the basis of modern electronics. Years later, when he was elderly, the discovery of what became known as the “Edison Effect” was remembered, but because Edison had no idea what it was or how it worked, he is rarely given credit for this contribution to the development of electronics.

Vacuum Tube

The simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode (the filament itself acts as the cathode in some diodes), and a plate (anode). Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the cathode travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids. Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display.

The earliest vacuum tubes evolved from incandescent light bulbs, containing a filament sealed in an evacuated glass envelope. When hot, the filament releases electrons into the vacuum, a process called thermionic emission, originally known as the "Edison Effect". A second electrode, the anode or plate, will attract those electrons if it is at a more positive voltage. The result is a net flow of electrons from the filament to plate. However, electrons cannot flow in the reverse direction because the plate is not heated and does not emit electrons. The filament (cathode) has a dual function: it emits electrons when heated; and, together with the plate, it creates an electric field due to the potential difference between them. Such a tube with only two electrodes is termed a diode, and is used for rectification. Since current can only pass in one direction, such a diode (or rectifier) will convert alternating current (AC) to pulsating DC. Diodes can therefore be used in a DC power supply, as a demodulator of amplitude modulated (AM) radio signals and for similar functions.

          

                                                                                                                                                                                                   triode

           diode                   

Early tubes used the filament as the cathode, this is called a "directly heated" tube. Most modern tubes are "indirectly heated" by a "heater" element inside a metal tube that is the cathode. The heater is electrically isolated from the surrounding cathode and simply serves to heat the cathode sufficiently for thermionic emission of electrons. The electrical isolation allows all the tubes' heaters to be supplied from a common circuit (which can be AC without inducing hum) while allowing the cathodes in different tubes to operate at different voltages. H. J. Round invented the indirectly heated tube around 1913.

The filaments require constant and often considerable power, even when amplifying signals at the microwatt level. Power is also dissipated when the electrons from the cathode slam into the anode (plate) and heat it; this can occur even in an idle amplifier due to quiescent currents necessary to ensure linearity and low distortion. In a power amplifier, this heating can be considerable and can destroy the tube if driven beyond its safe limits. Since the tube contains a vacuum, the anodes in most small and medium power tubes are cooled by radiation through the glass envelope. In some special high-power applications, the anode forms part of the vacuum envelope to conduct heat to an external heat sink, usually cooled by a blower, or water-jacket.

Bolometer

A bolometer consists of an absorptive element, such as a thin layer of metal, connected to a thermal reservoir (a body of constant temperature) through a thermal link. The result is that any radiation impinging on the absorptive element raises its temperature above that of the reservoir — the greater the absorbed power, the higher the temperature. The intrinsic thermal time constant, which sets the speed of the detector, is equal to the ratio of the heat capacity of the absorptive element to the thermal conductance between the absorptive element and the reservoir.  The temperature change can be measured directly with an attached resistive thermometer , or the resistance of the absorptive element itself can be used as a thermometer. Metal bolometers usually work without cooling. They are produced from thin foils or metal films. Today, most bolometers use semiconductor or superconductor absorptive elements rather than metals. These devices can be operated at cryogenic temperatures, enabling significantly greater sensitivity.

Bolometers are directly sensitive to the energy left inside the absorber. For this reason they can be used not only for ionizing particles and photons, but also for non-ionizing particles, any sort of radiation, and even to search for unknown forms of mass or energy (like dark matter ); this lack of discrimination can also be a shortcoming. The most sensitive bolometers are very slow to reset (i.e., return to thermal equilibrium with the environment). On the other hand, compared to more conventional particle detectors, they are extremely efficient in energy resolution and in sensitivity. They are also known as thermal detectors.

Ballistic Galvanometer

Ballistic galvanometer

A ballistic galvanometer is a type of sensitive galvanometer, commonly a mirror galvanometer . Unlike a current-measuring galvanometer, the moving part has a large moment of inertia , thus giving it a long oscillation period. It is really an integrator measuring the quantity of charge discharged through it. It can be either of the moving coil or moving magnet type.

Grassot Fluxmeter

An interesting form of ballistic galvanometer is the Grassot fluxmeter. In order to operate correctly, the discharge time through the regular ballistic galvanometer must be shorter than the period of oscillation. For some applications, especially those involving inductors, this condition cannot be met. The Grassot fluxmeter solves this. Its construction is similar to that of a ballistic galvanometer, but its coil is suspended without any restoring forces in the suspension thread or in the current leads. The core (bobbin) of the coil is of a non-conductive material. When an electric charge is connected to the instrument, the coil starts moving in the magnetic field of the galvanometer's magnet, generating an opposing e.m.f. and coming to a stop regardless of the time of the current flow. The change in the coil position is proportional only to the quantity of charge. The coil is returned to the zero position by the reversing of the current or manually.

Flux Meter

Principle of Fluxmeters

As magnetic flux cuts through the search coil, it induces a voltage in the search coil. As per Faradays law of induction, this voltage is the differential of the magnetic flux that passed through the search coil. By feeding this voltage into an integrating fluxmeter, the integration process removes the differential (of the search coil) resulting in the fluxmeter displaying the total magnetic flux. Fluxmeters require a dynamic component for the measurement, as it is necessary for magnetic flux to cut the search coil to produce a voltage.

By calibrating the fluxmeter with the area and number turns of the search coil it is possible to display values of flux density on a fluxmeter (Tesla, gauss) as well as magnetic flux (Webers, Vs or Maxwell turns)

Order Of Instruments

Zero Order Instruments

A zero order linear instrument has an output which is proportional to the input at all times in accordance with the equation

y(t) = Kx(t)

where K is a constant called the static gain of the instrument. The static gain is a measure of the sensitivity of the instrument.

An example of a zero order linear instrument is a wire strain gauge in which the change in the electrical resistance of the wire is proportional to the strain in the wire.

All instruments behave as zero order instruments when they give a static output in response to a static input.

First Order Instruments

A first order linear instrument has an output which is given by a non-homogeneous first order linear differential equation

tau .dy(t)/dt + y(t) = K.x(t)

where tau is a constant, called the time constant of the instrument.

In these instruments there is a time delay in their response to changes of input. The time constant tau is a measure of the time delay.

Thermometers for measuring temperature are first-order instruments. The time constant of a measurement of temperature is determined by the thermal capacity of the thermometer and the thermal contact between the thermometer and the body whose temperature is being measured.

A cup anemometer for measuring wind speed is also a first order instrument. The time constant depends on the anemometer's moment of inertia.

Second Order Instruments

A second order linear instrument has an output which is given by a non-homogeneous second order linear differential equation

d 2y(t)/dt 2 + 2. rho .omega.dy(t)/dt +omega 2.y(t) = K. omega2.x(t)

where rho is a constant, called the damping factor of the instrument, and omega is a constant called the natural frequency of the instrument.

Under a static input a second order linear instrument tends to oscillate about its position of equilibrium. The natural frequency of the instrument is the frequency of these oscillations.

Friction in the instrument opposes these oscillations with a strength proportional to the rate of change of the output. The damping factor is a measure of this opposition to the oscillations.

An example of a second order linear instrument is a galvanometer which measures an electrical current by the torque on a coil carrying the current in a magnetic field. The rotation of the coil is opposed by a spring. The strength of the spring and the moment of inertia of the coil determine the natural frequency of the instrument. The damping of the oscillations is by mechanical friction and electrical eddy currents.

Excitation

An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation .

Except for permanent magnet generators, a generator produces output voltage proportional to the magnetic field, which is proportional to the excitation current; if there is no excitation current there is zero voltage. A small amount of (electric) power may control a large amount of power. This principle is very useful for voltage control: if the system voltage is low, excitation can be increased; if the system voltage is high, excitation can be decreased. A synchronous condenser operates on the same principle, but there is no "prime mover" power input; however, the "flywheel effect" means that it can send or receive power over short periods of time.

Self excitation

Modern generators with field coils are self-excited , where some of the power output from the rotor is used to power the field coils. The rotor iron retains a magnetism when the generator is turned off. The generator is started with no load connected; the initial weak field creates a weak voltage in the stator coils, which in turn increases the field current, until the machine "builds up" to full voltage.

Starting

Self-excited generators must be started without any external load attached. An external load will continuously drain off the buildup voltage and prevent the generator from reaching its proper operating voltage.

Field flashing

If the machine does not have enough residual magnetism to build up to full voltage, usually a provision is made to inject current into the rotor from another source. This may be a battery , a house unit providing direct current , or rectified current from a source of alternating current power. Since this initial current is required for a very short time, it is called "field flashing". Even small portable generator sets may occasionally need field flashing to restart.

The critical field resistance is the maximum field circuit resistance for a given speed with which the shunt generator would excite. The shunt generator will build up voltage only if field circuit resistance is less than critical field resistance. It is a tangent to the open circuit characteristics of the generator at a given speed.

Slip Ring

A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires rotation while transmitting power or signals. It can improve mechanical performance, simplify system operation and eliminate damage-prone wires dangling from movable joints.

Also called rotary electrical interfaces, rotating electrical connectors , collectors , swivels , or electrical rotary joints , these rings are commonly found in slip ring motors, electrical generators for alternating current (AC) systems and alternators and in packaging machinery, cable reels, and wind turbines . They can be used on any rotating object to transfer power, control circuits, or analog or digital signals including data such as those found on aerodrome beacons, rotating tanks , power shovels , radio telescopes or heliostats .

A slip ring is a method of making an electrical connection through a rotating assembly. Formally, it is an electric transmission device that allows energy flow between two electrical rotating parts, such as in a motor.

Thermal Anemometers

Thermal anemometers use a very fine wire (on the order of several micrometers) or element heated up to some temperature above the ambient. Air flowing past over has a cooling effect. As the electrical resistance of most metals is dependent upon the temperature of the metal (tungsten is a popular choice for hot wires), a relationship can be obtained between the resistance of the wire and the flow velocity.

Several ways of implementing this exist, and hot-wire devices can be further classified as CCA (Constant-Current Anemometer), CVA (Constant-Voltage Anemometer) and CTA (Constant-Temperature Anemometer). The voltage output from these anemometers is thus the result of some sort of circuit within the device trying to maintain the specific variable (current, voltage or temperature) constant. Additionally, PWM (Pulse Width Modulation) anemometers are also used, wherein the velocity is inferred by the time length of a repeating pulse of current that brings the wire up to a specified resistance and then stops until a threshold "floor" is reached, at which time the pulse is sent again.

Hot-wire anemometers, while extremely delicate, have extremely high frequency-response and fine spatial resolution compared to other measurement methods, and as such are almost universally employed for the detailed study of turbulent flows, or any flow in which rapid velocity fluctuations are of interest. Thermal anemometers are available with additional functions such as temperature measurement, data logging ability.

Residual Magnetism

Unlike the separately excited generator, there is no current in the field circuit when the armature is motionless. Since a small amount of residual magnetism is present in the field poles, a weak residual voltage is induced in the armature as soon as the armature is rotated. This residual voltage produces a weak current in the field circuit. If this current is in the proper direction, an increase in magnetic strength occurs with a corresponding increase in voltage output. The increased voltage output, in turn, increases the field current and the field flux which, again, increase the voltage output. As a result of this action, the output voltage builds up until the increasing field current saturates the field poles. Once the poles are saturated, the voltage remains at a constant level, unless the speed of the armature rotation is changed.

If the direction of armature rotation is reversed, the brush polarity also is reversed. The residual voltage now produces a field current which weakens the residual magnetism and the generator voltage fails to build up. Therefore, a self-excited machine develops its operating voltage for one direction of armature rotation only. The generator load switch may be closed when the desired voltage is reached.

GAUSSMETER

A gaussmeter is also called as a magnetometer. A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument.

A direct current flowing in an inductor creates a strong magnetic field around a hydrogen-rich fluid, causing the protons to align themselves with that field. The current is then interrupted, and as protons are realigned with Earth's magnetic field they precess at a specific frequency. This produces a weak alternating magnetic field that is picked up by a (sometimes separate) inductor. The relationship between the frequency of the induced current and the strength of Earth's magnetic field is called the proton gyromagnetic ratio, and is equal to 0.042576 hertz per nanotesla (Hz/nT).

Inductive Pickup Coils

Inductive pickup coils measure the magnetization by detecting the current induced in a coil due to the changing magnetic moment of the sample. The sample’s magnetization can be changed by applying a small ac magnetic field (or a rapidly changing dc field), as occurs in capacitor-driven pulsed magnets. These measurements require differentiating between the magnetic field produced by the sample and that from the external applied field. Often a special arrangement of cancellation coils is used. For example, half of the pickup coil is wound in one direction, and the other half in the other direction, and the sample is placed in only one half. The external uniform magnetic field will be detected by both halves of the coil and since they are counterwound the external magnetic field produces no net signal.

In 1833, Carl Friedrich Gauss , head of the Geomagnetic Observatory in Göttingen, published a paper on measurement of the Earth's magnetic field.  It described a new instrument that consisted of a permanent bar magnet suspended horizontally from a gold fibre. The difference in the oscillations when the bar was magnetised and when it was demagnetised allowed Gauss to calculate an absolute value for the strength of the Earth's magnetic field.

Communication Channels

The medium by which information is transmitted is known as a communication channel. Some of the common communication channels are fiber optic cable, coaxial cable, satellite and microwave. The transfer of data takes place in the form of analog signals and the transfer of data is measured in the form of bandwidth, the higher the bandwidth the more the data that will be transferred.

Kinds of Communication Channel:

Communication channels are divided in two categories, namely guided media and unguided media.

Guided Media

In this category the communication device is attached to each other directly with cables. The data signals are restricted to a cabling platform and thus they are also known as bounded media. Generally the guided media is called LAN. Some kinds of guided media are coaxial cable, twisted pair wire and fiber optic cable.

1) Twisted Pair Cable - It is the most common used communication media and used in LAN (local area network) for transfer of data between various computers. They are also used in landline telephones to transfer data signals and voice. They are made from a pair of copper wire. They are covered with insulating materials like plastic. The transmission of data takes place at a speed of 9600 bits/second within a distance of 100 meters.

2) Coaxial Cable - They are also known as coaxes and carries signals with high frequency range. They are made from a single copper wire. They are also used in telephone lines. The bandwidth is 80 times more than twisted pair cable. They are also used in LAN.

3) Fiber Optic Cable - They use light to transfer data. The data is transferred at a very high speed of billions bit/second. They are highly used by cable operators, telephone, and broadband internet companies. They are made from glass and is as thin as the human hair. They are coated with plastic also known as jacket.

Unguided Media

In this form the data is transferred in the form of waves. This means that they do not travel along a specific path. It is also known as unbounded media. Data can be transferred all over the globe. Kinds of unguided media are microwave, cellular radio, radio broadcast and satellite.

1) Microwaves- In this kind the data is transferred via air. The waves travel in a straight line. The data is received and transferred via microwave stations. The speed at which data is transferred is 150 Mbps. They are widely used by telephone and cable companies.

2) Satellite- The signals are received from earth stations. Devices like GPS and PDAs also receive signals from these earth based stations. These satellites are located at a distance of 22300 miles above the earth. The process of transferring and receiving data takes place within few seconds. The data is transferred at a speed of 1 Gbps. They are used for purposes like weather forecast, military communication, radio transmission, satellite TV , data transmission, etc.

3) Cellular Radio- they are used for communication via mobile. High frequency radio waves are used for the transmission of data. You can receive and make calls and also access the internet .

4) Radio Broadcasting- Data is transferred and received via radio signals in the air. The transmission takes place for a long distance across cities or countries. The data is received and transferred via a transmitter. The speed at which data travels is 54 Mbps.

Conductive Polymers

Conductive polymers  are organic polymers that conduct electricity.Such compounds may have metallic conductivity or can be semiconductors . The biggest advantage of conductive polymers is their processability, mainly by dispersion.

A dispersion is a phenomenon  in which particles are dispersed in a continuous phase of a different state.

Conductive polymers are generally not thermoplastics , i.e. , they are not thermoformable. But, like insulating polymers, they are organic materials. They can offer high electrical conductivity but do not show similar mechanical properties to other commercially available polymers. The electrical properties can be fine-tuned using the methods of organic synthesis  and by advanced dispersion techniques.

Thermoplastics:

The polymer chains associate through intermolecular forces , which weaken rapidly with increased temperature, yielding a viscous liquid. Thus, thermoplastics may be reshaped by heating and are typically used to produce parts by various polymer processing techniques.

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions .

Each step of a synthesis involves a chemical reaction, and reagents and conditions for each of these reactions must be designed to give an adequate yield of pure product.

The conductivity of such polymers is the result of several processes. For example, in traditional polymers such as polyethylenes, the valence electrons are bound in sp3 hybridized covalent bonds . Such "sigma-bonding electrons" have low mobility and do not contribute to the electrical conductivity of the material. However, in conjugated materials, the situation is completely different. Conducting polymers have backbones of contiguous sp 2 hybridized carbon centers. One valence electron on each center resides in a p z orbital, which is orthogonal to the other three sigma-bonds. All the pz orbitals combine with each other to a molecule wide delocalized set of orbitals. The electrons in these delocalized orbitals have high mobility when the material is "doped" by oxidation, which removes some of these delocalized electrons. Thus, the conjugated p-orbitals form a one-dimensional electronic band , and the electrons within this band become mobile when it is partially emptied.

Electrophoretic

In the simplest implementation of an electrophoretic display, titanium dioxide (titania) particles approximately one micrometer in diameter are dispersed in a hydrocarbon oil. A dark-colored dye is also added to the oil, along with surfactants and charging agents that cause the particles to take on an electric charge. This mixture is placed between two parallel, conductive plates separated by a gap of 10 to 100 micrometres . When a voltage is applied across the two plates, the particles migrate electrophoretically  to the plate that bears the opposite charge from that on the particles. When the particles are located at the front (viewing) side of the display, it appears white, because light is scattered back to the viewer by the high-index titania particles. When the particles are located at the rear side of the display, it appears dark, because the incident light is absorbed by the colored dye. If the rear electrode is divided into a number of small picture elements (pixels), then an image can be formed by applying the appropriate voltage to each region of the display to create a pattern of reflecting and absorbing regions.

Electrophoretic displays are considered prime examples of the electronic paper category, because of their paper-like appearance and low power consumption.

Smart Glass

Recent advancements in modified porous nano-crystalline films have enabled the creation of electrochromic display or smart glass. This can be of various types.

Single Substrate Display Structure:

The single substrate display structure consists of several stacked porous layers printed on top of each other on a substrate modified with a transparent conductor.Each printed layer has a specific set of functions. A working electrode consists of a positive porous semiconductor (say Titanium Dioxide, TiO2) with adsorbed chromogens (different chromogens for different colors). These chromogens change color by reduction or oxidation. A passivator is used as the negative of the image to improve electrical performance. The insulator layer serves the purpose of increasing the contrast ratio and separating the working electrode electrically from the counter electrode. The counter electrode provides a high capacitance to counterbalances the charge inserted/extracted on the electrode (and maintain overall device charge neutrality). Carbon is an example of charge reservoir film. A conducting carbon layer is typically used as the conductive back contact for the counter electrode. In the last printing step, the porous monolith structure is overprinted with a liquid or polymer-gel electrolyte, dried, and then may be incorporated into various encapsulation or enclosures, depending on the application requirements. Displays are very thin, typically 30 micrometer, or about 1/3 of a human hair. The device can be switched on by applying an electrical potential to the transparent conducting substrate relative to the conductive carbon layer. This causes a reduction of viologen molecules (coloration) to occur inside the working electrode. By reversing the applied potential or providing a discharge path, the device bleaches. A unique feature of the electrochromic monolith is the relatively low voltage (around 1 Volt) needed to color or bleach the viologens.

Viologens are toxic bi pyridinium derivatives of 4,4'-bipyridyl . [1] The name is because this class of compounds is easily reduced to the radical mono cation, which is colored intensely blue.

Suspended Particle Devices (SPDs):

In suspended particle devices (SPDs), a thin film laminate of rod-like nano-scale particles is suspended in a liquid and placed between two pieces of glass or plastic, or attached to one layer. When no voltage is applied, the suspended particles are randomly organized, thus blocking and absorbing light. When voltage is applied, the suspended particles align and let light pass. Varying the voltage of the film varies the orientation of the suspended particles, thereby regulating the tint of the glazing and the amount of light transmitted.

SPDs can be manually or automatically "tuned" to precisely control the amount of light, glare and heat passing through, reducing the need for air conditioning during the summer months and heating during winter. Smart glass can be controlled through a variety of mediums, such as automatic photosensors and motion detectors, smartphone applications, integration with intelligent building and vehicle systems, knobs or light switches.

Smart glass light-control technology increases users' control over their environment, provides for better user comfort and well-being and improves energy efficiency. The technology provides over 99% UV blockage and state switching in 1 to 3 seconds. In cars, the range of light transmission for the technology is 50-60 times darker than a typical sunroof to twice as clear as an ordinary sunroof. Published data by Mercedes-Benz shows that SPD technology can reduce cabin temperatures inside a vehicle by 18 °F (10 °C). Other advantages include reduction of carbon emissions and the elimination of a need for expensive window dressings.

Electrowetting

Electro-wetting display (EWD) is based on controlling the shape of a confined water/oil interface by an applied voltage. With no voltage applied, the (colored) oil forms a flat film between the water and a hydrophobic (water-repellent) insulating coating of an electrode, resulting in a colored pixel.

When a voltage is applied between the electrode and the water, the interfacial tension between the water and the coating changes. As a result, the stacked state is no longer stable, causing the water to move the oil aside.

This makes a partly transparent pixel, or, if a reflective white surface is under the switchable element, a white pixel. Because of the small pixel size, the user only experiences the average reflection, which provides a high-brightness, high-contrast switchable element.

Displays based on electro-wetting provide several attractive features. The switching between white and colored reflection is fast enough to display video content.

Charging Currents in Transmission Lines

Any two conductors separated by an insulating medium constitutes a condenser or capacitor.In case of overhead transmission lines, two conductors form the two plates of the capacitor and the air between the conductors behaves as dielectric medium. Thus an overhead transmission line can be assumed to have capacitance between the conductors throughout the length of the line. The capacitance is uniformly distributed over the length of the line and may be considered as uniform series of condensers connected between the conductors.

When an alternating voltage is applied across the transmission line it draws the leading current even when supplying no load. This leading current will be in quadrature with the applied voltage and is termed as charging current. It must be noted that charging current is due to the capacitive effect between the conductors of the line and does not depend on the load. The strength of the charging currents depends on the voltage of transmission, the capacitance of the line and frequency of the ac supply.

If the capacitance of the overhead line is high, the line draws more charging currents which cancels out the lagging component of the load current (normally load is inductive in nature). Hence the resultant current flowing in the line is reduced. The reduction in the resultant current flowing through the transmission line for given load current results in:

• Reduction of the line losses and so increase of transmission efficiency.

• Reduction in the voltage drop in the system or improvement of the voltage regulation.

• Increased load capacity and improved power factor

Significance of Charging currents:

Capacitance effect (responsible for charging currents) of the short transmission lines are negligible. However they are significant in medium and long distance transmission lines.

In long distance transmission lines, during light loaded conditions receiving end voltage will be higher than sending end voltage. This is because of the charging currents and capacitive effect of the line.

Synchroscopes

Synchroscopes are electrodynamic instruments, which rely on the interaction of magnetic fields to rotate a pointer. In most types,there is no restoring spring torque for the magnetically produced torques to overcome therefore  pointer system is free to rotate continually. Synchroscopes have a damping vane to smooth out vibration of the moving system.

A polarized-vane synchroscope has a field winding with a phase-shifting network arranged to produce a rotating magnetic field. The field windings are connected to the incoming machine. A single phase polarizing winding is connected to the running system. It is mounted perpendicular to the field winding and produces a magnetic flux that passes through the moving vanes. The moving vanes turn a shaft that carries a pointer moving over a scale. If the frequency of the source connected to the polarizing winding is different from the source connected to the field winding, the pointer rotates continually at a speed proportional to the difference in system frequencies.

The scale is marked to show the direction of rotation corresponding to the incoming machine running faster than the running system. When the frequencies match, the moving vanes will rotate to a position corresponding to the phase difference between the two sources. The incoming machine can then be adjusted in speed  and than phase sequence is checked.

EM Wave Propogation

There are two main types of waves. Mechanical wave and Electromagnetic wave.
Mechanical waves propagate through a medium, and the substance of this medium is deformed. The deformation reverses itself owing to restoring forces resulting from its deformation. For example, sound waves propagate via air molecules colliding with their neighbors. When air molecules collide, they also bounce away from each other (a restoring force). This keeps the molecules from continuing to travel in the direction of the wave.

The second main type of wave, electromagnetic waves, do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles, and can therefore travel through a vacuum. These types of waves vary in wavelength, and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. An electromagnetic wave (i.e., a light wave) is produced by accelerating electric charge. As the wave moves through the vacuum of empty space, it travels at a speed of c (3 x 108 m/s). This value is the speed of light in a vacuum. When the wave impinges upon a particle of matter, the energy is absorbed and sets electrons within the atoms into vibrational motion. If the frequency of the electromagnetic wave does not match the resonant frequency of vibration of the electron, then the energy is reemitted in the form of an electromagnetic wave. This new electromagnetic wave has the same frequency as the original wave and it too will travel at a speed of c through the empty space between atoms. The newly emitted light wave continues to move through the interatomic space until it impinges upon a neighboring particle. The energy is absorbed by this new particle and sets the electrons of its atoms into vibration motion. And once more, if there is no match between the frequency of the electromagnetic wave and the resonant frequency of the electron, the energy is reemitted in the form of a new electromagnetic wave. 

The cycle of absorption and reemission continues as the energy is transported from particle to particle through the bulk of a medium. Every photon (bundle of electromagnetic energy) travels between the interatomic void at a speed of c; yet time delay involved in the process of being absorbed and reemitted by the atoms of the material lowers the net speed of transport from one end of the medium to the other. Subsequently, the net speed of an electromagnetic wave in any medium is somewhat less than its speed in a vacuum - c (3 x 10^8 m/s).
How much the wave will delay will depend upon the optical density of material.
The optical density of a medium is not the same as its physical density. The physical density of a material refers to the mass/volume ratio. The optical density of a material relates to the tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance. The more optically dense that a material is, the slower that a wave will move through the material.