History of Tattoo

The word Tattoo has been derived from the Polynesian word 'tatao', which means tapping or marking something. This term was first coined by Captain James Cook in the year 1769, when he met the Tahitians during his voyage, who had decorated their bodies with tattoos. At that time, tattooing was a very painful procedure. The technique of tattooing has now undergone a major modification. Read on to know more about the origin & history of tattoo.
Initially this body art involved piercing into the body, which was done by dropping a sharp-pointed comb into lampblack and then inserting it into the skin. Despite the trouble involved, many people got their bodies tattooed, especially arms. The tradition of tattooing, which was originally practiced in Tahiti and other Polynesian islands spread its influence in Europe too. In those days, it was mainly worn by the sailors, drunkards and criminals.The archeological excavations have revealed that this tradition of tattooing has been an integral part of many ancient cultures. In the year 1992, in the Alp region that lies between the border of Austria and Italy, a properly preserved body of a man was found. According to the estimations of the archeological department, it is expected that this man died near about 5000 years ago. He had 58 tattoos all over his body. Most of the ancient Egyptian mummies had tattoos. The Greeks and Romans of the bygone times used tattoo for identifying the slaves and criminals.

nanomaterials

Nanomaterials are materials with morphological features smaller than a one tenth of a micrometre in at least one dimension. Despite the fact that there is no consensus upon the minimum or maximum size of nanomaterials, some authors restricting their size from 1 to ~30 nm, a logical definition would situate the nanoscale between microscale (0.1 micrometre) and atomic/molecular scale (about 0.2 nanometers).

Fundamental concepts

A unique aspect of nanotechnology is the vastly increased ratio of surface area to volume present in many nanoscale materials which opens new quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes dominant when the nanometer size range is reached. Additionally, a number of physical properties change when compared to macroscopic systems. Novel mechanical properties of nanomaterials is the subject of nanomechanics research. Their catalytic activity reveals novel properties in the interaction with biomaterials.
Nanotechnology can be thought of as extensions of traditional disciplines towards the explicit consideration of these properties. Additionally, traditional disciplines can be re-interpreted as specific applications of nanotechnology. This dynamic reciprocation of ideas and concepts contributes to the modern understanding of the field. Broadly speaking, nanotechnology is the synthesis and application of ideas from science and engineering towards the understanding and production of novel materials and devices. These products generally make copious use of physical properties associated with small scales.
Materials reduced to the nanoscale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); inert materials become catalysts (platinum); stable materials turn combustible (aluminum); solids turn into liquids at room temperature (gold); insulators become conductors (silicon). Materials such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these unique quantum and surface phenomena that matter exhibits at the nanoscale.
Nanosize powder particles (a few nanometres in diameter, also called nanoparticles) are potentially important in ceramics, powder metallurgy, the achievement of uniform nanoporosity and similar applications. The strong tendency of small particles to form clumps ("agglomerates") is a serious technological problem that impedes such applications. However, a few dispersants such as ammonium citrate (aqueous) and imidazoline or oleyl alcohol (nonaqueous) are promising additives for deagglomeration.

Size concerns

Another concern is that the volume of an object decreases as the third power of its linear dimensions, but the surface area only decreases as its second power. This somewhat subtle and unavoidable principle has huge ramifications. For example the power of a drill (or any other machine) is proportional to the volume, while the friction of the drill's bearings and gears is proportional to their surface area. For a normal-sized drill, the power of the device is enough to handily overcome any friction. However, scaling its length down by a factor of 1000, for example, decreases its power by 10003 (a factor of a billion) while reducing the friction by only 10002 (a factor of "only" a million). Proportionally it has 1000 times less power per unit friction than the original drill. If the original friction-to-power ratio was, say, 1%, that implies the smaller drill will have 10 times as much friction as power. The drill is useless.
This is why, while super-miniature electronic integrated circuits can be made to function, the same technology cannot be used to make functional mechanical devices in miniature: the friction overtakes the available power at such small scales. So while you may see microphotographs of delicately etched silicon gears, such devices are curiosities with limited real world applications, for example in moving mirrors and shutters. Surface tension increases in the same way, causing very small objects to tend to stick together. This could possibly make any kind of "micro factory" impractical: even if robotic arms and hands could be scaled down, anything they pick up will tend to be impossible to put down. The above being said, molecular evolution has resulted in working cilia, flagella, muscle fibers, and rotary motors in aqueous environments, all on the nanoscale. These machines, however, exploit the increase of the frictional forces found at the micro or nanoscale. Unlike an oar, paddle or propeller the mechanics of which are dominated by normal frictional forces (the frictional forces perpendicular to the surface) for propulsion, cilia, etc., develop motion resulting from the exaggerated drag or laminar forces (frictional forces parallel to the surface) present at micro and nano dimensions. To develop meaningful "machines" at the nanoscale, the relevant forces need to be considered. We are faced with the development and design of relevant machines rather than the simple reproductions of macroscopic ones.
All these scaling issues have to be kept in mind while evaluating any kind of nanotechnology

Materials used in nanotechnology

Materials referred to as "nanomaterials" generally fall into two categories: fullerenes, and inorganic nanoparticles. See also Nanomaterials in List of nanotechnology topics

Fullerenes

The fullerenes are a class of allotropes of carbon which conceptually are graphene sheets rolled into tubes or spheres. These include the carbon nanotubes which are of interest due to both their mechanical strength and their electrical properties.
For the past decade, the chemical and physical properties of fullerenes have been a hot topic in the field of research and development, and are likely to continue to be for a long time. In April 2003, fullerenes were under study for potential medicinal use: binding specific antibiotics to the structure to target resistant bacteria and even target certain cancer cells such as melanoma. The October 2005 issue of Chemistry and Biology contains an article describing the use of fullerenes as light-activated antimicrobial agents. In the field of nanotechnology, heat resistance and superconductivity are some of the more heavily studied properties.
A common method used to produce fullerenes is to send a large current between two nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc between the electrodes cools into sooty residue from which many fullerenes can be isolated.
There are many calculations that have been done using ab-initio Quantum Methods applied to fullerenes. By DFT and TDDFT methods one can obtain IR, Raman and UV spectra. Results of such calculations can be compared with experimental results.

Nanoparticles

Nanoparticles or nanocrystals made of metals, semiconductors, or oxides are of interest for their mechanical, electrical, magnetic, optical, chemical and other properties. Nanoparticles have been used as quantum dots and as chemical catalysts.
Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic or molecular structures. A bulk material should have constant physical properties regardless of its size, but at the nano-scale this is often not the case. Size-dependent properties are observed such as quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials.
Nanoparticles exhibit a number of special properties relative to bulk material. For example, the bending of bulk copper (wire, ribbon, etc.) occurs with movement of copper atoms/clusters at about the 50 nm scale. Copper nanoparticles smaller than 50 nm are considered super hard materials that do not exhibit the same malleability and ductility as bulk copper. The change in properties is not always desirable. Ferroelectric materials smaller than 10 nm can switch their magnetisation direction using room temperature thermal energy, thus making them useless for memory storage. Suspensions of nanoparticles are possible because the interaction of the particle surface with the solvent is strong enough to overcome differences in density, which usually result in a material either sinking or floating in a liquid. Nanoparticles often have unexpected visible properties because they are small enough to confine their electrons and produce quantum effects. For example gold nanoparticles appear deep red to black in solution.
Nanoparticles have a very high surface area to volume ratio. This provides a tremendous driving force for diffusion, especially at elevated temperatures. Sintering can take place at lower temperatures, over shorter time scales than for larger particles. This theoretically does not affect the density of the final product, though flow difficulties and the tendency of nanoparticles to agglomerate complicates matters. The surface effects of nanoparticles also reduces the incipient melting temperature.

Safety of Manufactured Nanomaterials

Nanomaterials behave differently than other similarly-sized particles. It is therefore necessary to develop specialized approaches to testing and monitoring their effects on human health and on the environment. The OECD Chemicals Committee has established the Working Party on Manufactured Nanomaterials to address this issue and to study the practices of OECD member countries in regards to nanomaterial safety

While nanomaterials and nanotechnologies are expected to yield numerous health and health care advances, such as more targeted methods of delivering drugs, new cancer therapies, and methods of early detection of diseases, they also may have unwanted effects.

Increased rate of absorption is the main concern associated with manufactured nanoparticles.
When materials are made into nanoparticles, their surface area to volume ratio increases. The greater specific surface area (surface area per unit weight) may lead to increased rate of absorption through the skin, lungs, or digestive tract and may cause unwanted effects to the lungs as well as other organs. However, the particles must be absorbed in sufficient quantities in order to pose health risks

NIKOLA TESLA'S WIRELESS TRANSMISSION

We are now only days away from our manuscript-delivery-deadline for the Damn Interesting book. Once that's behind us, we can return to our regularly scheduled writing. In the meantime, here's a re-run from 10 July 2007.
Wardenclyffe TowerIn 1905, a team of construction workers in the small village of Shoreham, New York labored to erect a truly extraordinary structure. Over a period of several years the men had managed to assemble the framework and wiring for the 187-foot-tall Wardenclyffe Tower, in spite of severe budget shortfalls and a few engineering snags. The project was overseen by its designer, the eccentric-yet-ingenious inventor Nikola Tesla (10 July 1856 - 7 January 1943). Atop his tower was perched a fifty-five ton dome of conductive metals, and beneath it stretched an iron root system that penetrated more than 300 feet into the Earth's crust. "In this system that I have invented, it is necessary for the machine to get a grip of the earth," he explained, "otherwise it cannot shake the earth. It has to have a grip… so that the whole of this globe can quiver."
Though it was far from completion, it was rumored to have been tested on several occasions, with spectacular, crowd-pleasing results. The ultimate purpose of this unique structure was to change the world forever.
Tesla's inventions had already changed the world on several occasions, most notably when he developed modern alternating current technology. He had also won fame for his victory over Thomas Edison in the well-publicized "battle of currents," where he proved that his alternating current was far more practical and safe than Edison-brand direct current. Soon his technology dominated the world's developing electrical infrastructure, and by 1900 he was widely regarded as America's greatest electrical engineer. This reputation was reinforced by his other major innovations, including the Tesla coil, the radio transmitter, and fluorescent lamps.
In 1891, Nikola Tesla gave a lecture for the members of the American Institute of Electrical Engineers in New York City, where he made a striking demonstration. In each hand he held a gas discharge tube, an early version of the modern fluorescent bulb. The tubes were not connected to any wires, but nonetheless they glowed brightly during his demonstration. Tesla explained to the awestruck attendees that the electricity was being transmitted through the air by the pair of metal sheets which sandwiched the stage. He went on to speculate how one might increase the scale of this effect to transmit wireless power and information over a broad area, perhaps even the entire Earth. As was often the case, Tesla's audience was engrossed but bewildered.
Back at his makeshift laboratory at Pike's Peak in Colorado Springs, the eccentric scientist continued to wring the secrets out of electromagnetism to further explore this possibility. He rigged his equipment with the intent to produce the first lightning-scale electrical discharges ever accomplished by mankind, a feat which would allow him to test many of his theories about the conductivity of the Earth and the sky. For this purpose he erected a 142-foot mast on his laboratory roof, with a copper sphere on the tip. The tower's substantial wiring was then routed through an exceptionally large high-voltage Tesla coil in the laboratory below. On the night of his experiment, following a one-second test charge which momentarily set the night alight with an eerie blue hum, Tesla ordered his assistant to fully electrify the tower.
Though his notes do not specifically say so, one can only surmise that Tesla stood at Pike's Peak and cackled diabolically as the night sky over Colorado was cracked by the man-made lightning machine. Colossal bolts of electricity arced hundreds of feet from the tower's top to lick the landscape. A curious blue corona soon enveloped the crackling equipment. Millions of volts charged the atmosphere for several moments, but the awesome display ended abruptly when the power suddenly failed. All of the windows throughout Colorado Springs went dark as the local power station's industrial-sized generator collapsed under the strain. But amidst such dramatic discharges, Tesla confirmed that the Earth itself could be used as an electrical conductor, and verified some of his suspicions regarding the conductivity of the ionosphere. In later tests, he recorded success in an attempt to illuminate light bulbs from afar, though the exact conditions of these experiments have been lost to obscurity. In any case, Tesla became convinced that his dream of world-wide wireless electricity was feasible.
In 1900, famed financier J.P. Morgan learned of Tesla's convictions after reading an article in Century Magazine, wherein the scientist described a global network of high-voltage towers which could one day control the weather, relay text and images wirelessly, and provide ubiquitous electricity via the atmosphere. Morgan, hoping to capitalize on the future of wireless telegraphy, immediately invested $150,000 to relocate Tesla's lab to Long Island to construct a pilot plant for this "World Wireless System." Construction of Wardenclyffe Tower and its dedicated power generating facility began the following year.
Tesla's lab at pike's peakIn December 1901, a scant few months after construction began, a competing scientist named Guglielmo Marconi executed the world's first trans-Atlantic wireless telegraph signal. Tesla's investors were deeply troubled by the development despite the fact that Marconi borrowed from seventeen Tesla patents to accomplish his feat. Though Marconi's plans were considerably less ambitious in scale, his apparatus was also considerably less expensive. Work at Wardenclyffe continued, but Tesla realized that this his competitor's success with simple wireless telegraphy had greatly diminished the likelihood of further investments in his own, much grander project.
In 1908, Tesla described his sensational aspirations in an article for Wireless Telegraphy and Telephony magazine:
"As soon as completed, it will be possible for a business man in New York to dictate instructions, and have them instantly appear in type at his office in London or elsewhere. He will be able to call up, from his desk, and talk to any telephone subscriber on the globe, without any change whatever in the existing equipment. An inexpensive instrument, not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or song, the speech of a political leader, the address of an eminent man of science, or the sermon of an eloquent clergyman, delivered in some other place, however distant. In the same manner any picture, character, drawing, or print can be transferred from one to another place. Millions of such instruments can be operated from but one plant of this kind. More important than all of this, however, will be the transmission of power, without wires, which will be shown on a scale large enough to carry conviction."
In essence, Tesla's global power grid was designed to "pump" the planet with electricity which would intermingle with the natural telluric currents that move throughout the Earth's crust and oceans. At the same time, towers like the one at Wardenclyffe would fling columns of raw energy skyward into the electricity-friendly ionosphere fifty miles up. To tap into this energy conduit, customers' homes would be equipped with a buried ground connection and a relatively small spherical antenna on the roof, thereby creating a low-resistance path to close the giant Earth-ionosphere circuit. Oceangoing ships could use a similar antenna to draw power from the network while at sea. In addition to electricity, these currents could carry information over great distances by bundling radio-frequency energy along with the power, much like the modern technology to send high-speed Internet data over power lines.
Nikola TeslaGiven his supporting experimental data and previous engineering accomplishments, there was little reason to doubt the veracity of Tesla's claims. But building the power station, the huge wooden tower, and the fifty-five ton conductive dome depleted the original investment money relatively quickly, leading to chronic funding shortages. The complications were further compounded by a stock market crash in 1901 which doubled the cost of building materials and sent investors scurrying for financial cover.
The Wardenclyffe team tested their tower a handful of times during construction, and the results were very encouraging; but the project soon devoured Tesla's personal savings, and it became increasingly clear that no new investments were forthcoming. In 1905, having exhausted all practical financial options, the construction efforts were abandoned. Regarding the project's demise, Tesla stated:
"It is not a dream, it is a simple feat of scientific electrical engineering, only expensive — blind, faint-hearted, doubting world! […] Humanity is not yet sufficiently advanced to be willingly led by the discoverer's keen searching sense. But who knows? Perhaps it is better in this present world of ours that a revolutionary idea or invention instead of being helped and patted, be hampered and ill-treated in its adolescence — by want of means, by selfish interest, pedantry, stupidity and ignorance; that it be attacked and stifled; that it pass through bitter trials and tribulations, through the strife of commercial existence. So do we get our light. So all that was great in the past was ridiculed, condemned, combatted, suppressed — only to emerge all the more powerfully, all the more triumphantly from the struggle."
If Tesla's plans had come to fruition, the pilot plant would have been merely the first of many. Such "magnifying transmitter" towers would have peppered the globe, saturating the planet with free electricity and wireless communication as early as the 1920s. Instead, the futuristic facility's potential went untapped for over a decade, until the tower was finally demolished for salvage in 1917.
The fall of Wardenclyffe thrust the brilliant inventor into a deep depression and financial distress, and in the years that followed his colleagues began to seriously doubt his mental well-being. His eccentricities became increasingly exaggerated, underscored by his tendency to bring home and care for the injured pigeons he encountered during his daily visits to the park. He also developed an unnatural fear of germs, washing his hands compulsively and refusing to eat any food which had not been disinfected through boiling. But his mind remained pregnant with groundbreaking ideas, as he demonstrated when he described radar technology in 1917, almost twenty years before it became a reality. Tesla in front of the spiral coil of his high-frequency transformer.In 1928, aged seventy-two years, he filed one of his last patents; it described an ingenious lightweight flying machine that was an early precursor to today's tilt-rotor Vertical Short Takeoff and Landing (VSTOL) planes such as the V-22 Osprey.
Nikola Tesla shuffled off this mortal coil in 1943, suffering a heart attack alone in his hotel room. Though he kept copious diaries of his experiments and ideas throughout his life, they were notoriously vague and lacking in technical details. He preferred to rely on his photographic memory for such nuances, therefore much of his knowledge went with him to the grave. Some modern investigations and calculations, however, do support Tesla's contention that wireless electricity is not only feasible, but it may have even been a superior alternative to the extensive and costly grid of power lines which crisscross our globe today.
Had Wardenclyffe been completed without interruption, Tesla may have once again managed to alter the course of history. Instant access to power, information, pirated phonograph cylinders, and lewd photos of bare-ankled floozies on the TeslaNet may have ushered in the Information Age almost a century ahead of schedule, making today's world a very different place indeed. Perhaps one day we will enjoy the future that Tesla envisioned, albeit a bit behind schedule.
Happy 151st birthday, Nikola.

Are the mobile phone Towers SAFE..???

Huge, bulky telecommunication towers on top of tall buildings is not an uncommon site in the major cities these days. But there is a possibility that these towers may not be safe for humans living near it in ways more than one..

THERE IS a widespread apprehension among people that some mobile operators have constructed the towers on top of structurally weak buildings in the city and any physical damage caused to the buildings by these towers may put the lives of the people living in and around such installations at grave risk.
There is also a serious concern that since we are living in Seismic Zone-V, these towers could cause devastating damage, in case an earthquake, if not designed properly. Therefore, it is necessary to monitor and appropriately regulate the erection of mobile phone towers on top of buildings.
Structural safety of the buildings has to be accorded top priority before giving permission for the construction of mobile towers. The agencies empowered to give building permissions should not allow erection of mobile towers on buildings, which have been constructed without valid permission. These measures will also put an end to the alleged unregulated erection of hoardings and other outdoor displays on top of the buildings in the city.
Mobile phone towers should also be subject to the enforcement of building laws along with the unauthorised buildings. A structural engineer should inspect and sign the site plan and drawings of the mobile phone towers, certifying that necessary safety measures have been taken and that the structure is safe and earthquake resistant.
There are, so far, no restrictions on the locations of towers. A city like Srinagar requires numerous towers, as telephone operators need large number of towers for better coverage and transmission. At the same time, number of towers needs to be kept at minimum in the interest of proper urban planning, public health and safety.
Base stations are usually tall structures servicing large areas (cells). In recent times, there has been a trend towards smaller antennas servicing smaller cells. The aerials are normally erected on tall buildings to cover the widest area possible. Operators need to replace old model towers with single pole towers. There are four telecom operators in the city: BSNL, Airtel, Aircel and Reliance. Three or more firms should share each tower, and no individual firm should be allowed to set up a separate tower for itself.
It is difficult to confine the construction of mobile towers to non-residential areas, as the distance between two towers is determined by factors such as transmission frequency, density of consumers and the desired sound quality, among others. However, telecommunication towers atop buildings in residential areas may need to be relocated, where they are considered to be a hazard. There are fears that the people living in and around such installations are susceptible to health hazards.
Electromagnetic radiations emitted from the towers are debated all over the world. However, there is no conclusive study stating that radiation emitted by mobile phones affects health adversely. Medical research material is available on health-related effects of electromagnetic radiation emitted from antennae on telecommunication towers, yet no conclusive evidence of hazards to human health has been established for possible exposure levels from the cellular towers.
Modified currents and voltage generate oscillation of the electrical and magnetic field, which propagates in space. The electric and magnetic components oscillate at right angels to each other, these waves are termed as Electro Magnetic Radiations (EMRs). Mobile phone towers emit electro magnetic rays with a frequency of 1900 MHz. With this high frequency, they can easily pass through our bodies and concrete walls. Our immune system can be harmfully affected when these EMR rays pass through our body. Mobile phone towers’ radioactivity can thus affect every living thing in one square kilometer range.
Density ranges of this radioactivity are 17,100 - 72,000 micro watt per square metre. Mobile towers, installed on top of buildings can penetrate radio activity among those who live in the same buildings. Electromagnetic field of these towers attract Radon gas from atmosphere. EMR can cause memory loss, headache, allergy and skin diseases mostly affecting those who live nearby. Sperm-count in men is known to reduce with daily use of cell phone.
The mobile phone operators however, argue that Radio Frequency (RF) emissions from antennas used for wireless transmissions such as cellular and Personal Communication Systems (PCS) signals are within safe limits. Therefore, there is no reason to believe that such towers could constitute a potential health hazard to nearby residents. They claim that the roof of the building absorbs large amounts of the RF energy.
Cell phones communicate with nearby base stations even when these are not being used for a call. This is necessary to tell the system where the user is, in case a call should come in. Thus, even while they are inactive, the phones are a source of RF energy exposure to the user. Hands-free kits reduce exposure to a user by removing the phone from the vicinity of the head. There is no identifiable health benefit in using the kits, but there is no detriment either and using them may increase a user’s peace of mind.
There is not much that you can do if there is already a phone tower on the roof of your own or a nearby building, except getting the building assessed by a structural engineer, for its safety and in case it is found that the building is not capable of taking the load and stresses of the telecommunication towers, these should be relocated immediately, to safe guard the lives of people. Before the installation of a mobile tower aerial on your roof top, make sure that the required safety measures have been taken.
Ensure that the building has had a proper structural survey done by a qualified structural engineer, to see if it is capable of taking the weight of the aerial. The calculations should include effect of earthquake and wind resistance on the aerial to make sure that it will be able to stand up to severe winds.
There remains a lack of consensus among the experts about whether and at what levels electric magnetic fields and electromagnetic radiation can affect humans. The reality is also that there is a high level of concern regarding possible effects. The best approach to adopt, therefore, is a precautionary one. Should health be put at potential risk by waiting for proof of harm beyond all reasonable doubts before preventative action is taken; or should the action be taken as a precaution before any conclusive evidence is found to prevent any potential harm?
It is possible that EMFs and EMR at the current levels are harmless, but it may not be the case.
The question is whether we wait for overwhelmingly convincing proof, by which time many people may have been harmed or whether we take precautionary preventative steps now. At the rate that demand for mobile phones is increasing, there will soon be more mobile phone towers standing than trees.
Without waiting for a single day, the municipal authorities need to immediately assess the safety of all buildings where mobile towers have been erected and ensure that in future no permission is given unless the building is certified to be structurally safe and is capable of taking the load of the tower and bear all effects of earthquake and severe winds. On our part, we should prefer landline phones over cell phones and wherever we use cell phones, we should use a proper head-set.

photoelectric cell

An electronic device having an electrical output that varies in response to incident radiation, especially to visible light. Also called electric eye.

A device incorporated in an electric circuit; in response to light that falls on the cell, the electrical output or the resistance varies; used in measuring devices and in control devices that depend on illumination level or the interruption of a light beam.

photoelectric cell
or photocell, device whose electrical characteristics (e.g., current, voltage, or resistance) vary when light is incident upon it. The most common type consists of two electrodes separated by a light-sensitive semiconductor material. A battery or other voltage source connected to the electrodes sets up a current even in the absence of light; when light strikes the semiconductor section of the photocell, the current in the circuit increases by an amount proportional to the intensity of the light. In the phototube, an older type of photocell, two electrodes are enclosed in a glass tube—an anode and a light-sensitive cathode, i.e., a metal that emits electrons in accordance with the photoelectric effect. Although the phototube itself is now obsolete, the principle survives in the photomultiplier tube, which can be used to detect and amplify faint amounts of light. In this tube, electrons ejected from a photosensitive cathode by light are attracted toward and strike a positive electrode, liberating showers of secondary electrons; these are drawn to a more positive electrode, producing yet more secondary electrons—and so on, through several stages, until a large pulse of current is produced. Besides its use in measuring light intensity, a photomultiplier can be built into a television camera tube, making it sensitive enough to pick up the visual image of a star too faint to be seen by the human eye. The photovoltaic type of photoelectric cell, when exposed to light, can generate and support an electric current without being attached to any external voltage source. Such a cell usually consists of a semiconductor crystal with two zones composed of dissimilar materials. When light shines on the crystal, a voltage is set up across the junction between the two zones. A phototransistor, which is a type of photovoltaic cell, can generate a small current that acts like the input current in a conventional transistor and controls a larger current in the output circuit. Photovoltaic cells are also used to make solar batteries (see solar cell). Since the current from a photocell can easily be used to operate switches or relays, it is often used in light-actuated counters, automatic door openers, and intrusion alarms. Photocells in such devices are popularly known as electric eyes.

other languages:

Dansk (Danish)n. - fotocelle
Nederlands (Dutch)foto-elektrische cel
Français (French) n. - cellule photo-électrique
Deutsch (German) n. - Photozelle
Ελληνική (Greek) n. - (τεχνολ.) φωτοηλεκτρικό κύτταρο
Italiano (Italian) cellula fotoelettrica
Português (Portuguese) n. - fotocélula (f)
Русский (Russian) фотоэлемент, электронный "глаз"
Español (Spanish) n. - célula fotoeléctrica
Svenska (Swedish) n. - fotocell
中文（简体） (Chinese (Simplified)) 光电池
中文（繁體） (Chinese (Traditional)) n. - 光電池
한국어 (Korean) n. - 광전지
日本語 (Japanese) n. - 光電セル, 光電池
العربيه (Arabic) ‏(الاسم) خليه ضوئيه أو كهروضوئيه‏
עברית (Hebrew) n. - ‮תא פוטואלקטרי, תא חשמל-אורי‬

How to increase your adsense revenue

In this lesson you will learn to boost your Adsense revenue. You must have heard about peoples achieving high payments per click with AdSense. For high total earnings, your website requires a lot of page views and a high click-through rate. So to boost your Adsense revenue you need high traffic on your web site along with high click-through rates. By using this tutorial you will learn how to increase web traffic and click-through rates. In short you can increase your Adsense income by increasing Impressions, Click-through and Effective CPM. Improving your web statistics in any, or preferably, all of these three key areas will increase your Adsense revenue.
Increasing Impressions (Increasing web traffic)

Basically the impressions are the number of times your web pages with Adsense ads have been viewed. So it is directly proportional to the number or visitors to your web site. So, you can increase Impressions by increasing traffic to your web site.

In short here are some of the best ways to increase targeted traffic to your web pages:
More web pages means more traffic. So, create more web pages, with relevant, laser focused content.
Increase the link popularity for your web site
List your website/s under relevant categories in more directories
Set up a directory of relevant sites on your website and accept relevant reciprocal links
Write articles relevant to your web site and submit in the article directories
Increasing Adsense click-throughEven if your web site is receiving a lot of traffic, you will be earn only if your visitors clicks on the Adsense Ads and visits the advertiser web site. Clickthroughs are nothing but it is percentage of viewers who click on your Adsense ads. You can increase click-through by increasing the relevance of Adsense ads on your site, and by tweaking the format and placement of your ads. You can try different placements and colors of the ads, but be careful that the ads mixes with the content of your web site style.Try to make the different pages with different kinds of content. And make sure that these content pages are very clearly focused. Then Google will be able to serve highly relevant AdWords to your visitors. And in this way your visitors will be more interested in the ads, which results in higher click through rates -- and more money for you! Increasing Adsense CPMYou can also increase your Adsense income by increasing Adsense CPM. The effective CPM is a measure of your average earnings, per thousand clicks. The CPM can be increased by selecting topics (keywords) that attract high bids from Adsense advertisers in your web pages. You can use overture bid tool http://uv.bidtool.overture.com/d/USm/search/tools/bidtool/ to find the bid amount for your key words. On the internet there are a number of keyword research tools available, both free and paid, that you can use to find the high paid key words.In short here is steps that you should follow to Increase your total Adsense revenue:
Develop your web site using high paying key words
Design layout of your web site and put the ads focusing on the maximum click-through
Promote your web site in search engines and get more traffic on your web site

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I also recomend you to use adbrite, you can make some bucks in here....!!!

The Life and Death of Stars

Where are Stars Born?

Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star.

Main Sequence Stars

Main sequence stars are stars, like our Sun, that fuse hydrogen atoms together to make helium atoms in their cores. For a given chemical composition and stellar age, a stars' luminosity, the total energy radiated by the star per unit time, depends only on its mass. Stars that are ten times more massive than the Sun are over a thousand times more luminous than the Sun. However, we should not be too embarrassed by the Sun's low luminosity: it is ten times brighter than a star half its mass. The more massive a main sequence star, the brighter and bluer it is. For example, Sirius, the dog star, located to the lower left of the constellation Orion, is more massive than the Sun, and is noticeably bluer. On the other hand, Proxima Centauri, our nearest neighbor, is less massive than the Sun, and is thus redder and less luminous.
Since stars have a limited supply of hydrogen in their cores, they have a limited lifetime as main sequence stars. This lifetime is proportional to f M / L, where f is the fraction of the total mass of the star, M, available for nuclear burning in the core and L is the average luminosity of the star during its main sequence lifetime. Because of the strong dependence of luminosity on mass, stellar lifetimes depend sensitively on mass. Thus, it is fortunate that our Sun is not more massive than it is since high mass stars rapidly exhaust their core hydrogen supply. Once a star exhausts its core hydrogen supply, the star becomes redder, larger, and more luminous: it becomes a red giant star. This relationship between mass and lifetime enables astronomers to put a lower limit on the age of the universe.

Death of an "Ordinary" Star

After a low mass star like the Sun exhausts the supply of hydrogen in its core, there is no longer any source of heat to support the core against gravity. Hydrogen burning continues in a shell around the core and the star evolves into a red giant. When the Sun becomes a red giant, its atmosphere will envelope the Earth and our planet will be consumed in a fiery death.
Meanwhile, the core of the star collapses under gravity's pull until it reaches a high enough density to start burning helium to carbon. The helium burning phase will last about 100 million years, until the helium is exhausted in the core and the star becomes a red supergiant. At this stage, the Sun will have an outer envelope extending out towards Jupiter. During this brief phase of its existence, which lasts only a few tens of thousands of years, the Sun will lose mass in a powerful wind. Eventually, the Sun will lose all of the mass in its envelope and leave behind a hot core of carbon embedded in a nebula of expelled gas. Radiation from this hot core will ionize the nebula, producing a striking "planetary nebula", much like the nebulae seen around the remnants of other stars. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star.

Death of a Massive Star

Massive stars burn brighter and perish more dramatically than most. When a star ten times more massive than Sun exhaust the helium in the core, the nuclear burning cycle continues. The carbon core contracts further and reaches high enough temperature to burn carbon to oxygen, neon, silicon, sulfur and finally to iron. Iron is the most stable form of nuclear matter and there is no energy to be gained by burning it to any heavier element. Without any source of heat to balance the gravity, the iron core collapses until it reaches nuclear densities. This high density core resists further collapse causing the infalling matter to "bounce" off the core. This sudden core bounce (which includes the release of energetic neutrinos from the core) produces a supernova explosion. For one brilliant month, a single star burns brighter than a whole galaxy of a billion stars. Supernova explosions inject carbon, oxygen, silicon and other heavy elements up to iron into interstellar space. They are also the site where most of the elements heavier than iron are produced. This heavy element enriched gas will be incorporated into future generations of stars and planets. Without supernova, the fiery death of massive stars, there would be no carbon, oxygen or other elements that make life possible.

The fate of the hot neutron core depends upon the mass of the progenitor star. If the progenitor mass is around ten times the mass of the Sun, the neutron star core will cool to form a neutron star. Neutron stars are potentially detectable as "pulsars", powerful beacons of radio emission. If the progenitor mass is larger, then the resultant core is so heavy that not even nuclear forces can resist the pull of gravity and the core collapses to form a black hole.
Learn more about the late stages of stellar evolution from the Chandra mission's web pages:
White Dwarfs
Neutron Stars
Black Holes
Supernovae