A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat. Layers of materials with distinct electrochemical properties are sandwiched together to form a single galvanic cell. At the heart lies a membrane that can only be crossed by charged molecules. Gas-permeable electrodes coated with a catalyst adhere to this membrane, adding a layer on either side. The electrodes are in turn connected to a device that can utilize electricity. Hydrogen gas flows into channels on one face of the cell and migrates through that electrode, while the same occurs with oxygen gas along the opposite electrode. Spurred by a catalyst, favorable chemistry causes the hydrogen to oxidize into hydrogen protons and give up its electrons to the neighboring electrode, which thereby becomes the anode. This buildup of negative charge then follows the path of least resistance via the external circuit to the other electrode. It is this flow of electrons through a circuit that creates electricity.
Most important problem involved in the practical use of hydrogen car is hydrogen storage materials. If it uses a fuel cell that generates electricity through reaction between hydrogen and oxygen, it does not matter. However, if method is that hydrogen is sprayed to internal-combustion engine, it does matter. Now hydrogen storage tank with highest possibility is method using metal hydride. Metal hydride is that reversible reaction between metal and hydrogen make new form of compound. Now Hydrogen storing technology using Hydrogen storage compound metal comes to practical use step in the side of technical, however, hydrogen storing capacity per weight is no match for demand of user, so this technology is not widely used yet. Therefore, that problem should be solved.
Standard-definition television
Standard-Definition Television is a kind of television system that provides lower resolution than HDTV and higher resolution than analog TV does.
The word 'SDTV' is generally used at the digital television broadcasting system that has a similar or litle bit higher state of resolution to the 'analog television system'. Digital broadcasting system uses digital signals when they receive sound and movie. It is compared to analog TV that uses analog signals.
According to an ATSC standard, SDTV broadcasts in three ways.
First, at ratio of length and width 16:9 and resolution 704x480.
Second, at ratio 4:3 and resolution 704x480
Lastly, at ratio 4:3 and resolution 640x480.
The first one has best quality, second one is next, and the last one is the worst.
The screen's frame can be 24, 30, 60 per second. These are similar level with DVD.
As mentioned at the 'Definition' tab, it has a better resolution than analog TV system, and has lower resolution than HDTV.
Because it is a kind of digital broadcasting system, it can broadcast not only analog TV programs but also HDTV program (Of course there exists a difference in resolution).
SDTV has a similar state of resolution compared to analog TV. But SDTV is more vivid than
analog TV because it has less noise. And it has better sound. The point that SDTV uses a digital broadcasting system makes SDTV have many accompaning functions. For example, multitasking, electronic program guide, and so on. This functions are
impossible at analog TV. Compared to HDTV, it has lower resolution. But in fact, HDTV programs are not spread widely yet, and the cheaper price of SDTV makes consumers to use SDTV.
Generally, there are three types of TV. They are analog TV, SDTV and HDTV.Price : AnalogTV < SDTV < HDTVQuality : AnalogTV ≒ SDTV < HDTVAnalogTV only can be compatible with analog signals, but both SDTV and HDTV can be compatible with not only analog but also digital signals.
Thermocouple
A thermocouple, TC for short, is a device that converts heat directly into electricity. A thermocouple can also work in reverse - using an electric current to transform into heat as well as cold.
Imagine that two wires made of different types of metal are connected at one end. If the junction of the two wires is heated, electricity will flow through the wire.
Electrons, when heated, will begin to cross the junction on their own. Because of the different properties of the different metals, the electrons will lose potential energy and gain kinetic energy, just like a ball rolling over a hill to a lower area. Although the voltage created by a thermocouple is very small (in the millivolt range), many thermocouples can be hooked together to make a larger voltage. This is called a thermopile.
Thermocouples can also generate heat from electricity, and even cold from electricity, acting as a refrigerator. If two different wires are connected at both ends, and some voltage source makes current flow through the loop, one junction will get hot and the other junction will become cold. The electrons at the hot junction are gaining kinetic energy as they cross the junction. This is why they make the metal hot. The electrons at the cold junction are losing kinetic energy as they cross the junction. This is why they make the junction cold.
It is difficult to measure the precise voltage that a thermocouple is producing when heat is applied to its junction. This is because any voltmeter wires that are connected to the thermocouple will probably be made of a different material than the wires of a thermocouple. This means that the connection between the voltmeter and the thermocouple is itself another thermocouple. Engineers designing microchips face the problem that virtually every electrical connection on a microchip is a thermocouple whether they want it to be or not.
Gas heaters with pilot flames are one of the most famous examples for the use of thermocouples. Thermocouples are stacked to make a thermopile, which can generate enough voltage from the heat of the pilot flame to keep the gas valve open which in turn supplies the gas for the pilot flame. If the gas runs out, the flame extinguishes and the voltage across the thermopile decreases, which causes the electric gas valve to close. Many space probes get their electric power from a thermocouple in a radioisotope thermoelectric generator.
Thermocouples are also used in other ways. For instance, they monitor temperatures in air conditioning and refrigerators, and of CPUs in computers, which could be destroyed by overheating.
There are hundreds of thermocouples, but only eight of them are standardized internationally.Type E (chromel–constantan), type J (iron–constantan), type N (nicrosil–nisil), type T (copper–constantan) and type K (chromel–alumel) are base metals.Types B, R, and S thermocouples use platinum or a platinum–rhodium.
Control engineering
Control engineering is the engineering field that focuses on mathematical modeling of dynamical systems, and uses control theory to create controllers that cause the systems to behave in some desired manner. Modern control engineering is closely related to electrical, electronic, and computer engineering. As engineering continues to develop, control engineering is often wanted.
In most cases, control engineers make use of feedback when designing control systems. For example, in an automobile with sail control, the machine's speed is continuously checked and fed back to the system, which then adjusts the motor's spin power on the fly. Recently, control systems are also used in nanotechnology. In chemical engineering, control engineering is known as process control. Many advancements in science, finance, and even human action, can be attributed to control engineering.