Science & Technology

Advantages of using LEDs > LEDs produce more light per watt than do incandescent bulbs; this is useful in battery powered or energy saving devices.> LEDs can emit light of an intended color without the use of color filters that traditional lighting methods require. This is more efficient and can lower initial costs.> The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.> When used in applications where dimming is required, LEDs do not change their color tint as the current passing through them is lowered, unlike incandescent lamps, which turn yellow.> LEDs are ideal for use in applications that are subject to frequent on- off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that require a long time before restarting.> LEDs, being solid state components, are difficult to damage with external shock. Fluorescent and incandescent bulbs are easily broken if subjected to external shock.> LEDs can have a relatively long useful life. Reports estimates 60,000 hours of useful life, though time to complete failure longer.2 Fluorescent tubes typically are rated at about 30,000 hours, HID and MH are rated anywhere between 10,000 and 24,000 hours and incandescent light bulbs at 1,000–2,000 hours.> LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent or HID bulbs.3 This provides extra safety for any area illuminated by LEDs. Even if the LEDs dim over time, they never fail completely like HID sources before needing to be replaced. LEDs need to be replaced only after they reach 30% lumen depreciation (17-20 years for quality LEDs).> LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds; Philips Lumileds technical datasheet DS23 for the Luxeon Star states “less than 100ns.” LEDs used in communications devices can have even faster response times.> LEDs can be very small and are easily populated onto printed circuit boards.> LEDs do not contain mercury, unlike compact fluorescent lamps.Disadvantages of using LEDs > On an initial capital cost basis, LEDs are currently more expensive, measured in price per lumen, than more conventional lighting technologies. The additional expense partially stems from the relatively low lumen output, combined with the cost of the drive circuitry and power supplies needed. However, when considering the total cost of ownership (including energy and maintenance costs), LEDs far surpass other sources. In December 2007, scientists at Glasgow University claimed to have found a way to make Light Emitting Diodes brighter and use less power than energy efficient light bulbs currently on the market by imprinting holes into billions of LEDs in a new and cost effective method using a process known as nanoimprint lithography.4 Around the same time, in Montreal Canada, Lumec inc. developed an LED light engine that consumes 20% to 30% less energy than HPS (high pressure sodium) and 40% to 50% less than MH (metal halide) while delivering comparable photometric performance, if not better, than HID lights.> LED performance largely depends on the ambient temperature of the operating environment. Driving the LED hard in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, outdoor, medical, and military applications where the device must operate over a large range of temperatures, and is required to have a low failure rate. The most heat resistant LEDs available commercially, such as those used by Lumec inc. In their light engine, the LifeLEDTMcan function at optimal efficiency from -40°C to +50°C(-40°F to 122°F)    

Organic water pollutants include   • Detergents • Disinfection by-products found in chemically disinfected drinking water, such as chloroform • Food processing waste, which can include oxygen-demanding substances, fats and grease • Insecticides and herbicides, a huge range of organohalides and other chemical compounds • Petroleum hydrocarbons, including fuels (gasoline, diesel fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel combustionbyproducts, from stormwater runoff • Tree and bush debris from logging operations • Volatile organic compounds (VOCs), such as industrial solvents, from improper storage. • Chlorinated solvents, which are dense non-aqueous phase liquids may fall to the bottom of reservoirs, since they don’t mix well with water and are denser. • Polychlorinated biphenyl (PCBs) • Trichloroethylene • Perchlorate • Various chemical compounds found in personal hygiene and cosmetic products • Drug pollution involving pharmaceutical drugs and their metabolites Inorganic water pollutants include: • Acidity caused by industrial discharges (especially sulfur dioxide from power plants) • Ammonia from food processing waste • Chemical waste as industrial by-products • Fertilizers containing nutrients–nitrates and phosphates—which are found in stormwater runoff from agriculture, as well as commercial and residential use • Heavy metals from motor vehicles (via urban stormwater runoff) and acid mine drainage Silt (sediment) in runoff from construction sites, logging, slash and burn practices or land clearing sites. Macroscopic pollution—large visible items polluting the water—may be termed “floatables” in an urban stormwater context, or marine debris when found on the open seas, and can include such items as: • Trash or garbage (e.g. paper, plastic, or food waste) discarded by people on the ground, along with accidental or intentional dumping of rubbish, that are washed by rainfall into storm drains and eventually discharged into surface waters • Nurdles, small ubiquitous waterborne plastic pellets • Shipwrecks, large derelict ships.    

  Multi-drug-resistant tuberculosis (MDR-TB) is defined as tuberculosis that is resistant to at least isoniazid (INH) and rifampicin(RMP), the two most powerful first-line treatment anti-TB drugs. Isolates that are multiply resistant to any other combination of anti-TB drugs but not to INH and RMP are not classed as MDR-TB.MDR-TB develops in otherwise treatable TB when the course of antibiotics is interrupted and the levels of drug in the body are insufficient to kill 100% of bacteria. This can happen for a number of reasons: Patients may feel better and halt their antibiotic course, drug supplies may run out or become scarce, patients may forget to take their medication from time to time or patients do not receive effective therapy. Most tuberculosis therapy consists of short-course chemotherapy which is only curing a small percentage of patients with multi-drug resistant tuberculosis. Delays in second line drugs make multi-drug resistant tuberculosis more difficult to treat. MDR-TB is spread from person to person as readily as drug-sensitive TB and in the same manner.. Even with the patent off second line antituberculosis medication the price is still high and therefore a big problem for patients living in poor countries to be treated. With patients not treated, the spread of Tuberculosis would be problematic in poor countries. In order to fully cure infectious diseases, such as Tuberculosis, we need a plan to ensure equal access to health care.    

ENDOSULFAN Endosulfan is an off-patent organochlorine insecticide and acaricide that is being phased out globally. The two isomers, endo and exo, are known popularly as I and II. Endosulfan sulfate is a product of oxidation containing one extra O atom attached to the S atom. Endosulfan became a highly controversial agrichemical due to its acute toxicity, potential for bioaccumulation, and role as anendocrine disruptor. Because of its threats to human health and the environment, a global ban on the manufacture and use of endosulfan was negotiated under the Stockholm Convention in April 2011. The ban will take effect in mid-2012, with certain uses exempted for five additional years. More than 80 countries, including the European Union, Australia, New Zealand, several West African nations, the United States. Brazil, and Canada had already banned it or announced phase-outs by the time the Stockholm Convention ban was agreed upon. It is still used extensively in India, China, and few other countries. It is produced byMakhteshim Agan and several manufacturers in India and China.    

  Blu-ray Disc (BD) is a digital optical disc data storage format designed to supersede the DVD format, in that it is capable of storing high- definition video resolution (1080p). The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Conventional (pre-BD-XL) Blu-ray Discs contain 25 GB per layer, with dual layer discs (50 GB) being the industry standard for feature-length video discs. Triple layer discs (100 GB) and quadruple layers (128 GB) are available for BD-XL re-writer drives. The name Blu-ray Disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs. The major application of Blu-ray Discs is as a medium for video material such as feature films and physical distribution of video games for the PlayStation 3, PlayStation 4 and Xbox One. Besides the hardware specifications, Blu-ray Disc is associated with a set of multimedia formats. These formats allow for the option of video and audio to be stored with greater definition than on DVD.    

  Nuclear Hazards and Safety Issues   Recently there has been much apprehension about the dangers inherent in nuclear plants—fears of radiation hazard, waste disposal, disastrous accidents. While some of the hazards are real, nuclear scientists point out that many of them are not based on scientific facts and unbiased observation. Radiation Hazard: There is no doubt that radiation causes damage to living cells—but this depends on the intensity of radiation and the time of exposure. When an atom of a complex organic cell is exposed to radiation, ionization takes place and molecules disintegrate, adversely affecting the biological system, sometimes even destroying the cell.While high doses are fatal, low doses may have cumulative effect and cause cancers, especially of the skin, and leukemia. It may affect lymphatic tissues, the nervous system, and the reproductive organs. However, die adverse effects take place after considerably high and constant doses of radiation.The release of radioactivity into air and water from reactors does take place, but it is kept well within the limits prescribed by the AERB. The earth is being constantly bombarded by cosmic ray nuclear particles (65 per cent of natural radiation experienced by a human being is due to this).Background radiation from terrestrial and extra-terrestrial sources is much higher than radiation from nuclear plants. In the circumstances, the radiation exposures from nuclear plants is of a negligible quantity. The fear of radiation arises because most people are unwilling to believe in any “safe level” for radiation exposure.Hazard from Nuclear Waste:Another aspect of nuclear hazard is waste management. The general technique of dealing with radioactive wastes is to concentrate and contain as much radioactivity as possible, and discharge to the environment only effluent of as low a concentration level as is possible.At inland sites like Narora and Rawatbhatta, low level liquid wastes are discharged into the environment at a minimum level. At coastal sites such as Tarapur and Chennai significant dilution in the sea is possible. For solid wastes, different types of containments are used and located at sites selected on the basis of geological and geohydrological evaluation.The fissioning of U-235 produces many radioactive isotopes, such as strontium 90, caesium 137, and barium 140. These wastes remain radioactive and dangerous for about 600 years because of the strontium and caesium isotopes. If these get into food or water supplies, they can be taken into people’s bodies where they can cause harm.The body is unable to distinguish between radioactive strontium and calcium, for instance. The plutonium and other artificially created elements in the wastes remain radioactive for thousands of years. Even in small amounts, plutonium can cause cancer or genetic (reproductive) damage in humans.Larger amounts can cause radiation sickness and death. Safe disposal of these wastes is one of the problems involved in nuclear power production. The wastes are carefully managed by incorporating them in inert solid matrices and placing them in canisters which are kept under cooling till the radioactivity comes to desired level. Finally, the canisters are stored in suitable geological media. However, the problem is not entirely resolved. Effects of a Nuclear Explosion: The effects that a nuclear explosion has on people, buildings, and the environment can vary greatly, depending on a number of factors. These factors include weather, terrain, the point of explosion in relation to the earth’s surface, and the weapon’s yield.The weapon’s explosion would produce four basic effects: (i) Blast Wave: The explosion begins with the formation of a fireball, which consists of a cloud of dust and of extremely hot gases under very high pressure. A fraction of a second after the explosion, the gases begin to expand and form a blast wave, also called a shock wave.The blast wave and wind probably would kill the majority of people within 5 kilometers of ground zero and some of the people between 5 and 10 kilometers from ground zero. Many other people within 10 kilometers of groupd zero would be injured. (ii) Thermal radiation: This consists of ultraviolet, visible, and infra¬red radiation given off by the fireball. The ultraviolet radiation is rapidly absorbed by particles in the air, and so it does little harm. However, the visible and infrared radiation can cause eye injuries as well as skin burns called flash burns.Between 20 and 30 per cent of the deaths of Hiroshima and Nagasaki resulted from flash burns. Thermal radiation also can ignite such highly flammable materials as newspapers and dry leaves. The burning of these materials can lead to large fires. (iii) Initial nuclear radiation: This is given off within the first minute after the explosion. It consists of neutrons and gamma rays. The neutrons and some of the gamma rays are emitted from the fireball almost instantaneously. The rest of the gamma rays are given off by a huge mushroom-shaped cloud of radioactive material that is formed by the explosion. Nuclear radiation can cause the swelling and destruction of human cells and prevent normal cell replacement.Large doses of radiation can cause death. The amount of harm a person would suffer from initial nuclear radiation depends in part on the person’s location in relation to ground zero. Initial radiation decreases rapidly in strength as it moves away from ground zero. (iv) Residual Nuclear Radiation: This comes later than one minute after the explosion. Residual radiation created by fission consists of gamma rays and beta particles. Residual radiation produced by fusion is made up primarily of neutrons. It strikes particles of rock, soil, water, and other materials that make up the mushroom-shaped cloud. As a result, these particles become radioactive. When the particles fall back to earth, they are known as fallout. The closer an explosion occurs to the earth’s surface, the more fallout it produces.Early fallout consists of heavier particles that reach the ground during the first 24 hours after the explosion. These particles fall mostly downwind from ground zero. Early fallout is highly radioactive and will kill or severely damage living things.Delayed fallout reaches the ground from 24 hours to a number of years

Radioactive Dating   Radiocarbon dating is a process used to determine the age of an ancient object by measuring its radiocarbon content. This technique was devel¬oped in the late 1940s by Willard F. Libby, an American chemist.Radiocarbon atoms, like all radioactive substance, decay at an exact and uniform rate. Half of the radiocarbon disappears after about 5,700 years. Therefore, radiocarbon has a half-life of that period of time.After about 11,400 years, a fourth of the original amount of radiocarbon remains. After another 5,700 years, only an eighth remains, and so on.The radiocarbon in the tissues of a living organism decays extremely slowly, but it is continuously renewed as long as the organism lives. After the organism dies, it no longer takes in air or food, and so it no longer absorbs radiocarbon. The radiocarbon already in the tissues continues to decrease at a constant rate. This steady decay at a known rate—a half- life of about 5,700 years—enables scientists to determine an object’s age.After scientists measure an object’s radiocarbon content, they compare it with the radiocarbon in tree-rings whose ages are known. This technique enables them to compensate for small variations of radiocarbon content in the atmosphere at different times in the past. By doing so, scientists can convert an object’s radiocarbon age to a more precise date.Radioisotopes with very long half-lives are used for dating rock specimens such as Uranium-238. Uranium-235 which becomes lead 207; thorium 232, which becomes lead 208; rubidium 87, which changes into strontium 87; and potassium 40, which changes into argon 40 are radio¬isotope which can be used to calculate the age of rocks.    

Radioisotopes   Different forms of radiation originate in the nuclei of radioactive atoms. There are three kinds of radioactive radiation: alpha particles, which were first identified by Becquerel; beta rays, identified by Ernest Rutherford; and gamma rays, identified by Marie and Pierre Curie. Emission of alpha or beta rays causes transmutation, but gamma radiation does not result in transformation.One element can be changed into another artificially. Ail artificial radioisotope is produced by making stable isotopes radioactive—i.e., unstable, their nuclei breaking apart to release small particles and energy (radioactivity). Every element with atomic number greater than that of lead (82) is radioactive.Artificial radioisotopes may be produced by bombarding atoms with particles and rays emitted by radioactive elements in a nuclear reactor. They can also be produced by smashing atoms in particle accelerators such as the cyclotron. The fact that radioactive materials can be detected by their radiation makes them useful in many fields.Radioactive isotopes are effectively used as tracers for diagnostic purposes in medicine. Arsenic-74 is used to detect tumours. Sodium-24 is used to detect blood clots in the circulatory system. Iodine-131 (1-131) is used to determine the activity of the thyroid gland. Cobalt-60 is used in the treatment of cancer; also in use are iridium-192, and caesium-137.The production of radioisotopes in India began in 1956 with the commissioning of the research reactor Apsara at Trombay. The radioiso¬tope production capability was augmented in 1963 when the 40MWt Cirus became operational at Trombay. In 1985 with Dhruva being made operational by BARC, India came to the fore as a major producer of wide spectrum of radioisotopes.The research reactors at Trombay produce a variety of radioisotopes for various uses. Power reactors are also equipped to produce cobalt-60 radioisotope.The variable energy cyclotron at VECC is also used for manufacture of radioisotopes, which are processed for medical applications. Radiation and radioisotope based products and services offered by DAE through BARC and BRIT include radio sources and industrial radiography equip¬ment; radiotracer technologies in leak detection, silt movement, and applications in hydrology; radiation processing, radiation polymerisation, soil-salinity and others.BRIT has been entrusted with the responsibility for processing a variety of radioisotopes and their derived products and supply of industrial radiography equipment and gamma irradiation equipment for applications of this technology.BARC’s Radiation Medicine Centre (RMC) at Mumbai, a premier centre in the country in the field of radio diagnosis and radiotherapy, is a regional referral centre of the World Health Organisation (WHO) for South-East-Asia.The activities of the centre cover the fields of nuclear medicine and allied services, clinical diagnosis and treatment, in-house development of radiopharmaceuticals, RIA technology for thyroid hor¬mones and tubercular antigen and antibodies, etc.Radioisotopes for medical applications are also manufactured by using the variable energy cyclotron at Kolkata. The regional radiation medicine centre (RRMC) meets the radio diagnostic and radiotherapy requirements of the eastern region of the country. CAT at Indore has developed lasers for medical applications.In India, radiation has been in use for decades for sterilisation of medical products. A commercial radiation sterilisation plant (ISOMED) at Trombay provides sterilisation services to the medical industry. A large radiopharmaceuticals laboratory named ISOPHARM has been set up at Vashi, Mumbai.Plants similar to Isomed have been working at Bengaluru, New Delhi and Jodhpur. For use in blood banks and hospitals, BRIT has developed a blood irradiator equipment which is an important import substitute. Uses of Radioisotopes: In Industry Gamma rays can be used to examine metallic castings or welds in oil pipelines for weak points. The rays pass through the metal and darken a photographic film at places opposite the weak spots. Manufacturers may place a radio-isotope that emits beta particles above a sheet of material.A beta-particle detector on the other side measures the strength of the radiations coming through. If the sheet thickness increases, fewer particles reach the detector. The detector can control rollers and keep the sheet at desired thicknesses. Gamma radiation may be used in pest control, especially ingrain stores. Irradiated food has a longer shelf life.In Research Scientists use radio-isotopes as tracers, to determine how chemicals act in the bodies of plants and animals. All isotopes of an element are chemically the same, so the radio-isotope can be used in the same way as the ordinary isotopes.For example, to trace the course of phosphorus in a plant, a botanist may mix radioactive phosphorus with the ordinary phosphorus. To learn when the phosphorus reaches a leaf, he may place a Geiger counter, which detects radioactivity, on the leaf. To find where the phosphorus lodges in the leaf, he may place the leaf on a photographic plate. In the developed plate, called an autoradiograph, darkened regions show the position of the radio-isotope. In Medicine: The use of radio-isotopes is part of a speciality called nuclear medicine. The chief use of radio-isotopes is to study the function of various body organs. To accomplish this, a doctor administers a radio¬isotope attached to a carrier substance. The carrier substance accumulates in the organ that the doctor wants to study.For example, if the doctor wishes to study a patient’s kidney function, a radio-isotope will be attached to a carrier substance that accumulates in the kidneys. As the radio-isotope breaks down, it emits gamma rays. Some of the rays are picked up by a device called a scanner. The doctor “reads” the image on the scanner to determine if the kidneys are working properly.Radioisotopes are also used to treat cancer. Radiation in large doses destroys living tissues, especially cells undergoing division. Because cancer cells divide more frequently than do normal cells, radiation kills more cancerous cells than normal ones. A doctor may take advantage of this fact by administering a radio-isotope that accumulates in a cancerous organ.For example, a radio-isotope of iodine, 1-131 may be used to treat cancer of the thyroid gland, because this gland accumulates iodine. As the radioactive iodine transforms, it gives off radiation that kills the cancerous cells. Cobalt-60 is also used in treatment of cancer. Arsenic- 74 is employed to detect tumours. Blood clots in the

Nuclear Weapons   Nuclear weapons may be of the fission type (atomic weapons) or the fusion type (thermonuclear or hydrogen weapons).Fission weapons get their destructive power from the splittings of atomic nuclei. Only three kinds of atoms are known to be suitable for fissioning in such weapons. These atoms are of the uranium (U) isotopes U-235 and U-238 and of the plutonium (Pu) isotope, Pu-239. An accelerating uncontrolled chain reaction occurs when, for example, two pieces of U-235 come together and exceed the critical mass.Thermonuclear weapons get their power from the fusion atomic nuclei under intense heat. The nuclei fused in thermonuclear weapons are of the hydrogen isotopes, deuterium and tritium. Fusion reactions require temperatures equal to, or greater than, those found in the sun’s core.The only practical way to achieve such temperature si by means of a fission explosion. Thus, thermonuclear explosions are triggered by an implosion-type fission device. (In the implosion method, a subcritical mass is made supercritical by compressing it into a smaller volume.)The first nuclear weapons were two fission bombs used by the United States during World War II (1939-1945). In the war, one was dropped on each of Japanese cities of Hiroshima and Nagasaki.Nuclear explosive devices can have a wide variety of yields. Some older bombs had yields of about 20 megatons, or 1,540 Hiroshima bombs. A megaton is the amount of energy released by 907,000 metric tons of TNT. Today, because of the higher accuracy of missiles, most nuclear devices have yields of less than 1 megaton.    

Nuclear Fusion   Nuclear fusion occurs when two lightweight nuclei fuse (combine) and form a nucleus of a heavier element. The products of the fusion weigh less than the combined weights of the original nuclei. The lost matter has therefore been changed into energy. Fusion reactions that produce large amounts of energy can be created only by means of extremely intense heat. Such reactions are called thermo-nuclear reactions. Thermonuclear reactions produce the energy of both the sun and the hydrogen bomb. A thermo-nuclear reaction can occur only in plasma, a special form of matter which has free electrons and free nuclei. Normally, nuclei repel one another.But if a plasma containing lightweight atomic nuclei is heated many millions of degrees, the nuclei begin moving so fast that they break through one another’s electrical barriers and fuse. Problems of Controlling Fusion: Scientists have not yet succeeded in harnessing the energy of fusion to produce power. In their fusion experiments, scientists generally work with plasmas that are made from one or two isotopes of hydrogen. Deuterium is considered an ideal thermo-nuclear fuel because it can be obtained from ordinary water. A given weight of deuterium can supply about four times as much energy as the same weight of uranium.To produce a controlled thermo-nuclear reaction, a plasma of deuterium or tritium or of both isotopes must be heated many millions of degrees. Bui scientists have yet to develop a container than can hold superhot plasma.Most experimental fusion reactors are designed to contain superhot plasma in “magnetic bottles” twisted into various coil-like shapes. The walls of the bottles are made of copper or some other metal. The walls are surrounded by a magnet.An electric current is passed through the magnet and creates a magnetic field on the inside of the walls. The magnetism pushes the plasma away from the walls and toward the centre of each coil. This technique is called magnetic confinement All the fusion devices thus far developed; however, use much more energy than they create.The most successful fusion reactor, called a tokamak, was originally designed by Russian scientists. Tokamak means strong current in Russian. Like other experimental fusion reactors, a tokamak uses a magnetic field to push plasma away from its containing walls. It also passes a strong current through the plasma. The current acts with the magnetic field to help confine the plasma. India has developed a tokamak Aditya, for research purposes at the Institute of Plasma Research, Ahmedabad. Another experimental method to achieve fusion uses beams of laser to compress and heat tiny pellets of frozen deuterium and tritium. This process creates miniature thermo-nuclear explosions that release energy before the pellets reach the containing walls. But all experiments with this method have not yet produced usable amounts of energy.