WiMAX - Worldwide Interoperability for Microwave Access

WiMAX is a wireless digital communications system, also known as IEEE 802.16, that is intended for wireless "metropolitan area networks". 

WiMAX can provide broadband wireless access (BWA) up to 30 miles (50 km) for fixed stations, and 3 - 10 miles (5 - 15 km) for mobile stations. In contrast, the WiFi/802.11 wireless local area network standard is limited in most cases to only 100 - 300 feet (30 - 100m).

With WiMAX, WiFi-like data rates are easily supported, but the issue of interference is lessened. WiMAX operates on both licensed and non-licensed frequencies, providing a regulated environment and viable economic model for wireless carriers.

WiMAX can be used for wireless networking in much the same way as the more common WiFi protocol. 


WiMAX is a second-generation protocol that allows for more efficient bandwidth use, interference avoidance, and is intended to allow higher data rates over longer distances.

Solar Cells

Solar Cells

Solar cells (as the name implies) are designed to convert (at least a portion of) available light into electrical energy. They do this without the use of either chemical reactions or moving parts.

History
The development of the solar cell stems from the work of the French physicist Antoine-César Becquerel in 1839. Becquerel discovered the photovoltaic effect while experimenting with a solid electrode in an electrolyte solution; he observed that voltage developed when light fell upon the electrode. About 50 years later,

Charles Fritts constructed the first true solar cells using junctions formed by coating the semiconductor selenium with an ultrathin, nearly transparent layer of gold.

Fritts's devices were very inefficient, transforming less than 1 percent of the absorbed light into electrical energy.

By 1927 another metalÐsemiconductor-junction solar cell, in this case made of copper and the semiconductor copper oxide, had been demonstrated

.

By the 1930s both the selenium cell and the copper oxide cell were being employed in light-sensitive devices, such as photometers, for use in photography.

These early solar cells, however, still had energy-conversion efficiencies of less than 1 percent. This impasse was finally overcome with the development of the silicon solar cell by Russell Ohl in 1941. In 1954, three other American researchers, G.L. Pearson, Daryl Chapin, and Calvin Fuller, demonstrated a silicon solar cell capable of a 6-percent energy-conversion efficiency when used in direct sunlight. By the late 1980s silicon cells, as well as those made of gallium arsenide, with efficiencies of more than 20 percent had been fabricated. In 1989 a concentrator solar cell, a type of device in which sunlight is concentrated onto the cell surface by means of lenses, achieved an efficiency of 37 percent due to the increased intensity of the collected energy. In general, solar cells of widely varying efficiencies and cost are now available.

Structure

Modern solar cells are based on semiconductor physics -- they are basically just P-N junction photodiodes with a very large light-sensitive area.

The photovoltaic effect, which causes the cell to convert light directly into electrical energy, occurs in the three energy-conversion layers.

Diagram courtesy U.S. Department of Energy

The first of these three layers necessary for energy conversion in a solar cell is the top junction layer (made of N-type semiconductor ). The next layer in the structure is the core of the device; this is the absorber layer (the P-N junction). The last of the energy-conversion layers is the back junction layer (made of P-type semiconductor).

As may be seen in the above diagram, there are two additional layers that must be present in a solar cell. These are the electrical contact layers. There must obviously be two such layers to allow electric current to flow out of and into the cell. The electrical contact layer on the face of the cell where light enters is generally present in some grid pattern and is composed of a good conductor such as a metal. The grid pattern does not cover the entire face of the cell since grid materials, though good electrical conductors, are generally not transparent to light. Hence, the grid pattern must be widely spaced to allow light to enter the solar cell but not to the extent that the electrical contact layer will have difficulty collecting the current produced by the cell. The back electrical contact layer has no such diametrically opposed restrictions. It need simply function as an electrical contact and thus covers the entire back surface of the cell structure. Because the back layer must be a very good electrical conductor, it is always made of metal.

Operation

Solar cells are characterized by a maximum Open Circuit Voltage (Voc) at zero output current and a Short Circuit Current (Isc) at zero output voltage. Since power can be computed via this equation:

P = I * V

Then with one term at zero these conditions (V = Voc / I = 0, V = 0 / I = Isc ) also represent zero power. As you might then expect, a combination of less than maximum current and voltage can be found that maximizes the power produced (called, not surprisingly, the "maximum power point"). Many BEAM designs (and, in particular, solar engines) attempt to stay at (or near) this point. The tricky part is building a design that can find the maximum power point regardless of lighting conditions.

Source--http://encyclobeamia.solarbotics.net/articles/solar_cell.html

Solar Cooker

:: Solar Cooker

Domestic Solar Cooker

What is Solar Cooker ? A solar cooker looks like a simple square aluminium suitcase, with five main components with an outer box measuring 500 x 500 x 165 mm with three containers.

Benefits of using the solar cooker

• In an age where domestic fuel costs are rising each year, the solar cooker is a real boon.
• Reasonably priced, easy-to-use and completely trouble-free, the solar cooker is an ideal supplement to the conventional cooking appliances.
• Can be used 300 days a year.
• No fuel required for cooking.
• All items can be cooked except the fried and chapatis.
• Cooking is safe and clean.
• Solar cooking is entirely non-polluting and has no ill effects on health.
• Food cooked in solar cooker tastes better, is more nutritious and healthy.
• No need to keep close watch during cooking as the process is slow.
• Cooking time is around 1.30 to 2.30 hours.
• Food remains hot as long as the glass assembly is not opened.
• Three LPG cylinders can be saved annually as a result of solar cooking.
• Pay-back period is around three years.
• Life is around 10-15 years.
• O & M cost is almost negligible.

Did you know?

• The first box type solar cooker was built by Horace de Saussure, a Swiss naturalist, in 1767! He is said to have cooked fruits in it.
• That box type solar cookers can be fabricated using just cardboard and aluminum foil? Check out this website for the design http://www.i4at.org/surv/solarbox.htm
• In the 1950’s UN and other funding agencies commissioned studies to design solar cookers. The conclusion was encouraging – that solar cooker can cook food thoroughly and nutritiously and was easy to make and use.
• Based on the above study, UN sponsored programmes to introduce them in communities where there was a felt need, but this did not meet with much success.
• A World Conference on Solar Cooking was held in Stockton, California, in 1992. (http://solarcooking.org/stockton.htm )

THE INDIAN SCENE: Some of the policy initiatives taken by the Indian Government to promote the use of solar energy in general are:

• 1981 - Recognising the importance of renewable energy sources as the best alternative to conventional fuels, the Government of India set up a Commission for Additional Sources of Energy (CASE) in the Department of Science and Technology
• 1982 - A full-fledged, independent department, the Department of Non-conventional Energy Sources, is set up.
• 1992 - This ‘department’ is made into a ‘Ministry’, called the Ministry of Non-conventional Energy Sources (MNES).
• Gave subsidy for box type solar cookers from 1984 to 1994.

MNES is the nodal agency of the Government of India for all matters relating to non-conventional/renewable energy.

For more information click on www.mnes.nic.in

As the MNES felt that the use of solar energy for cooking and water heating was on the increase, the subsidy on solar water heaters and solar cookers were withdrawn in 1993-94. It is interesting to note that the Government continues to subsidize cooking gas, at a heavy cost to the exchequer, but is doing little about solar cookers. With over 40manufacturers of different types ofsolar cookers in the India, the combined capacity is to the tune of 75, 000 cookers pre annum. The manufacturers are mostly in the north - Delhi, Gujarat, Himachal Pradesh, Madhya Pradesh, Maharashtra, Punjab, Uttar Pradesh and West Bengal. The cookers have to adhere to the norms recommended by the MNES and the end product needs to be approved by the Bureau of Indian Standards. We understand that an estimated ‘potential’ demand for solar cookers in India is nearly 10 million!

MNES has also opened Aditya Solar Shops across the country,

which serves as convenient consumer points for sales, service and repair of renewable energy devices.

Box Cookers	Panel Cookers	Parabolic Cookers
When a glass covered chamber coated black inside and insulated all around is exposed to sunlight the temperature inside exceeds 100 degree Celsius, which is sufficient to cook food. More heat can be achieved by having an exterior reflector. The solar box cooker incorporates these features.	Roger Bernard in France came up with this design, where various flat panels concentrate the sun's rays on to a pot inside a plastic bag or under a glass bowl. The advantage of this design is that they can be built in an hour or so, from next to nothing. In Kenya, these are being manufactured for the Kakuma Refugee Camp project for US$2 each.	These are usually concave disks that focus the light onto the bottom of a pot. The advantage is that foods cook about as fast as on a conventional stove. Seen above is one model and there are many others possible.
Slow, even cooking of large quantities of food is possible Takes more than 3 hours to cook	Relatively quicker, but can cook only smaller quantities	Food can be cooked in half an hour. The disadvantage is that they are complicated to make, they must be focused often to follow the sun, and they can cause burns and eye injury if not used correctly.
With a single-reflector box cooker, once the food is cooked, it just stays warm and doesn't scorch.You can put in a few pots with different foods and then come back later in the day and each pot will cook to perfection and stay hot until you take it out.	Some people have reported the need to stir food every once in a while when using this kind of cooker, to ensure that the food heats evenly.	Cooking with a parabolic cooker is very similar to cooking on one burner of a conventional stove. Since the concentrated sunlight shines directly on the bottom of a pot, the pot heats up and cooks very quickly. The food will burn though. So you have to stir it and watch it carefully.
Box cookers with one back reflector don't need to be turned unless you are cooking beans, which take up to 5 hours.	Panel cookers need to be turned more often than box cookers, since they have side reflectors that can shade the pot.	Parabolic cookers are the most difficult to keep in focus. These need to be turned every 10 to 30 minutes, depending on the focal length.

Courtesy--www.mnes.nic.in

Wavelength

-

Wavelength is the distance between identical points in the adjacent cycles of a waveform signal propogated in space or along a wire, as shown in the illustration. In wirelesssystems, this length is usually specified in meters,centimeters, or millimeters.

Inthe case of infrared, visible light, ultraviolet, and gammaradiation, the wavelength ismore often specified in nanometers (units of 10^-9meter) or Angstrom units(units of 10^-10 meter).

Wavelength is inversely related to frequency. The higher the frequency of the signal, the shorter the wavelength. Iff is the frequency of the signal as measured in megahertz, and w isthe wavelength as measuredin meters, then

w = 300/f

and conversely

f = 300/w

Wavelength is sometimes represented by the Greek letter lambda.

Source---

hEALTH dOSE (BCG)

BCG - the current vaccine for tuberculosis

Bacille Calmette Guerin (BCG) is the current vaccine for tuberculosis. It was first used in 1921. BCG is the only vaccine available today for protection against tuberculosis.

It is most effective in protecting children from the disease.

History of the vaccine

Bacille Calmette Guerin (BCG) containes a live attenuated (weakened) strain of Mycobacterium bovis. It was originally isolated from a cow with tuberculosis by Calmette and Guren who worked in Paris at the Institute Pasteur. This strain was carefully subcultured every three weeks for many years. After about thirteen years the strain was seen to be less virulent for animals such as cows and guinea pigs. During these thirteen years many undefined genetic changes occurred to change the original stain of M. bovis. This altered organism was called BCG. In addition to the loss of virulence, other changes to BCG were noted. These included a pronounced change in the appearance of colonies grown in the laboratory. Colonies of M. bovis have a rough granular appearance whereas colonies of BCG are moist and smooth.

Today there are several strains of “BCG”.

BCG was first used as a vaccine to protect humans against tuberculosis in 1921.

At first, cultures of BCG were maintained in Paris. Later, it was subcultured and distributed to several laboratories throughout the world where the vaccine strain called BCG continued to be maintained by continuous subculture. After many years it became clear that the various strains maintained ain different laboratories were no longer identical to each other. Indeed, it was likely that all the various strains maintained by continuous subculture continued to undergo undefined genetic changes. Indeed, the "original" strain of BCG maintained at in Paris had continued to change during the subcultures needed to maintain the viability of the culture. To limit these continuing changes the procedures needed to maintain the strain were modified. Today, the organism is maintained in several laboratories using a "seed lot" production technique to limit further genetic variation using freeze-dried (also called lyphilized) cells so that each batch starts with the same cells.

Safety

After extensive tests in animals, BCG was first used as a vaccine in 1921. It was given orally to infants. Since this time the vaccine has been widely used. Today, it is estimated that more than 1 billion people have received BCG.

BCG is widely used and the safety of this vaccine has not been a serious issue until recently. There is a concern that use of the vaccine in persons who are immune compromised may result is an infection caused by the BCG itself. Also, even among immune competent persons, local reactions, including ulceration at the site of vaccination may result in shedding of live organisms which could infect others who may be immune compromised.

The early use of BCG was marked by a tragic accident. In Lubeck more than 25% of the approximately 250 infants who received a batch of the vaccine developed tuberculosis. It was later recognized that this batch was accidentally contaminated with a virulent strain of M. tuberculosis.

BCG production and substrains

The BCG vaccines that are currently in use are produced at several (seven?) sites throughout the world. These vaccines are not identical. To what extent they differ in efficacy and safety in humans is not clear at present. Some differences in molecular and genetic characteristics are known. What is not known is if the "BCG" from one manufacturer is "better" than one produced at another site. Each BCG is now know by the location where it is produced. For example, we have BCG (Paris), BCG (Copenhagen), BCG (Tice) and BCG (Montreal) among others.

Elasticity

An important property of many structural materials is their ability to regain their original shape after a load is removed. These materials are called elastic.

Steel, glass and rubber are elastic; putty or modeling clay are not elastic. Each of these materials is elastic to varying degrees; steel and glass are both more elastic than rubber. The degree of elasticity, or "stiffness" of a material is called its Modulus of Elasticity (E). Given the modulus of elasticity, possible deformations can be calculated for any material and loading.

All materials are assumed to be elastic except when indicated otherwise in this course.

Robert Hooke (1635 - 1703), a great English scientist, experimented with springs, clocks and watches. During his investigation of the spring he discovered that in elastic materials, stress and strain are proportional. He first presented this in a lecture in 1678 and it is known today simply as Hooke's Law.

Hooke's Law applies as long as the material stress does not pass a certain point known as its proportional limit. This is the point at which the physical properties of the material actually change. Any time an elastic material is loaded between zero and the proportional limit, the stress and strain are directly proportional and if the load is released the material will regain its initial dimensions. If the stress is doubled the strain is doubled; if the stress is tripled the deformation is three times as great, etc.

The English physician and physicist Thomas Young (1773 - 1829) noted that if stress is proportional to strain, then for any given material, stress divided by strain would be a constant. This constant is known today as Young's Modulus or the Modulus of Elasticity.

The Modulus of Elasticity is represented by E = Stress / Strain.

This relationship is found as the slope of the curve of the stress-strain curve from initial loading to the proportional limit. A higher value of the modulus indicates a more brittle material (i.e. glass, ceramics). A very low value represents a ductile material (i.e. rubber).

Modulus of Elasticity

The values of the modulus of elasticity for structural materials have been determined by tests and are readily available in references such as the AISC manual. Some of the more common values are:

* Steel: E=29,000 KSI (sometimes rounded to 30,000 KSI)
* Aluminum: E=10,000 KSI
* Wood: E=1,000 - 2,000 KSI (usual range)
* Concrete E=2,500 - 5,000 KSI (usual range)

It is often necessary to be able to determine the deformation of a structural member once the loads and physical properties of the structural member are known. This is simply derived and is developed from the stress/strain relationships that have already been established.

dOSE -- pHYSICS

1. Piezomagnetism is a phenomenon observed in some antiferromagnetic crystals. It is characterised by a linear coupling between the system's magnetic polarisation and mechanical strain. In a piezomagnetic, one may induce a spontaneous magnetic moment by applying physical stress, or a physical deformation by applying a magnetic field.
2. In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboringspins (on different sublattices) pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism.
3. An electron is a subatomic particle that carries a negative electric charge. It has no known components or substructure, and therefore is believed to be anelementary particle. An electron has a mass that is approximately 1/1836 that of the proton.
4. In physics, subatomic particles are the particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles.Particle physics and nuclear physics study these particles and how they interact.
5. In physics, a nucleon is a collective name for two baryons: the neutron and the proton.
6. Baryons are the family of composite particles made of three quarks, as opposed to the mesons which are the family of composite particles made of one quark and one antiquark. Both baryons and mesons are part of the larger particle family comprising all particles made of quarks—the hadrons. The term baryon is derived from the Greek βαρύς (barys), meaning "heavy", because at the time of their naming it was believed that baryons were characterized by having greater masses than other particles.
7. A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particlescalled hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.
8. In particle physics, a hadron is a particle made of quarks held together by the strong force (similar to how molecules are held together by theelectromagnetic force). Hadrons are either mesons (made of one quark and one antiquark) or baryons (made of three quarks). Other combinations, such as tetraquarks (an "exotic" meson) and pentaquarks (an"exotic" baryon), may be possible but no evidence conclusively suggests their existence as of 2009. The best known mesons are pions and kaons, while the best known baryons are protons and neutrons.
9. In particle physics, a pion (short for pi meson; denoted π) is any of three subatomic particles: π⁰, π⁺ and π⁻. Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force.
10. In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness. In the quark model they are understood to contain a single strange quark (or antiquark).

11. In particle physics, strangeness S is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic reactions, which occur in a short period of time. The strangeness of a particle is defined as:

    

    where n_s represents the number of strange quarks (s) and n_s represents the number of strange antiquarks (s).

Charge density

The linear, surface, or volume charge density is the amount of electric charge in a line, surface, or volume. It is measured in coulombs per metre (C/m), square metre (C/m²), or cubic metre (C/m³), respectively. Since there are positive as well as negative charges, the charge density can take on negative values. Like any density it can depend on position. It should not be confused with the charge carrier density. As related to chemistry, it can refer to the charge distribution over the volume of a particle, molecule, or atom. Therefore, a lithium cation will carry a higher charge density than a sodium cation due to its smaller ionic radius.

Homogeneous charge density

For the special case of a homogeneous charge density, that is one that is independent of position, equal to ρ_q,0 the equation simplifies to:

The proof of this is simple. Start with the definition of the charge of any volume:

Then, by definition of homogeneity, is a constant that we will denote ρ_q,0 to differentiate between the constant and non-constant forms, and thus by the properties of an integral can be pulled outside of the integral resulting in:

so,

The equivalent proofs for linear charge density and surface charge density follow the same arguments as above.

Discrete charges

If the charge in a region consists of N discrete point-like charge carriers like electrons the charge density can be expressed via the Dirac delta function, for example, the volume charge density is:

;

where is the test position， is the charge of the ith charge carrier, whose position is .

If all charge carriers have the same charge q (for electrons q = − e) the charge density can be expressed through the charge carrier density : Again, the equivalent equations for the linear and surface charge densities follow directly from the above relations.

[]Quantum charge densitY

In quantum mechanics, charge density is related to wavefunction by the equation

when the wavefunction is normalized as

sOURCE--http://en.wikipedia.org/wiki/Charge_density

Compact Disk or CD

A compact disk (cd) is a popular form of digital storage media used for computer files, pictures, and music. The plastic platter is read and written to by a laser in a CD drive. It comes in several varieties including CD-ROM, CD-R, and CD-RW.

James Russell invented the compact disk in 1965. James Russell was granted a total of 22 patents for various elements of his compact disk system. However, the compact disk did not become popular until it was mass manufactured by Philips in 1980.

Calorific value of fuels

Calorific value of fuels
Heat energy is measured in units of joules or calories (1calorie = 4.18 joules). The heat generated by fuels when they burn in joules or calories measures quality of fuels. All fuels do not burn efficiently. Thus there are fuels that produce more heat than the others are. This can be distinguished in terms of number of joules or calories that they generate on burning.

The amount of energy generated when 1 unit mass of fuel is burnt completely is known as the calorific value of the fuel. The word calorific is used, not “joulific” because of the use of the word calorific has been in use for a very long time. When 1 gram of charcoal is burnt, it produces 33 kilo joules. Thus the calorific value of charcoal is 33kJ/g. Sometimes instead of calorific value, another term kilowatt per kilogram (KWh/kg) is used.

hydrogens calorific value is 150

India to host 4th Environment Friendly Vehicles Conference 2009

India will host the 4th Environmentally Friendly Vehicle (EFV) Conference in New Delhi from November 23-24th this year. This is for the first time that such a prestigious and international event on automobile sector is being organized in a developing country. The EFV conference aims at promotion of environmental friendly vehicles to ensure sustainable road transport. Reduction of greenhouse gases, improvement of air quality, reduction in traffic noise, protection of resources and prevention of the release of harmful substances are the main objectives of the Conference. It will also pave the way in achieving the ambitious targets on human health at a cost effective and sustainable manner. The Conference offers a platform for senior government officials, industry leaders, academicians and key decision makers, to discuss environment friendly mode of public transport and development. As a part of WP-29 initiative, Environmentally Friendly Vehicle (EFV) Conferences are being organized biennially. The first such Conference was held in Tokyo, Japan in 2003, second in Birmingham, UK in 2005 and the third conference in Dresden, Germany in 2007. The 2009 Delhi Conference will deal with issues such as – • Mobility and Environment - Role of EFVs • Future of EFVs & electric vehicles, • Gaseous Fuels Technology, Alternative fuels and Drives – Technology of Future • Regulatory and Legislative Framework for EFVs. The Conference is being jointly hosted by Ministry of Heavy Industries and Public Enterprises and other stakeholders viz. Ministry of Shipping, Road Transport and Highways, Ministry of Environment and Forest, Ministry of New and Renewable Energy, Ministry of Urban Development, Ministry of Petroleum and Natural Gas as well as Industry association i.e. Society of Indian Automobile Manufacturers (SIAM) and Auto Components Manufacturers Association (ACMA).