Winning with English

“I can’t able to tell you.” This might just be one instance of a grammatically wrong sentence that often is a part of everyday conversations but it is just the tip of the iceberg as far as communication in business rooms is concerned.

According to the survey by employability measurement company Aspiring Minds, the English learning level among engineering graduates is very poor in India. The survey which analysed the English skills of over 55,000 aspiring engineers in 250 different engineering colleges, said “around 36 per cent of engineering graduates would be unable to read official reports and transcripts and derive information out of them, even when the information is explicitly stated.”

“The worse of it often comes out in mails — the most important medium of communication in corporate offices,” says R. Rajaram, HR head of an IT major. He explains, “They write incomplete sentences; their punctuation is non-existent and grammar very poor. This is why most companies have readymade templates with sentences, and employees just have to choose what they have to say.”

While Tamil Nadu has an excellent recruitment record with the State supplying the largest number of engineers, surveys on employability have cast the State in a poor light. A few months ago, Aspiring Minds also came out with a survey that said Tamil Nadu figured the lowest on the employability index. “This is mainly because they are not able to converse in English. Most of them are not confident of themselves,” the study concluded.

“Companies take communication very seriously and there are frequent training sessions for them. But all of that is focussed on their speaking skills. There is little done to improve their vocabulary or grammar,” says a senior HR Official.

Courtesy The Hindu
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Infants tell human from other sounds

Even nine-month-old infants can distinguish between speech and non-speech sounds in both humans and animals, a study says.

“Our results show that speech perception of infants is resilient and flexible. This means that our recognition of speech is more refined at an earlier age than we’d thought,” says Athena Vouloumanos, assistant professor of psychology at New York University, who led the study.

It is well-known that adults’ speech perception is fine-tuned and they can detect speech among a range of ambiguous sounds. But much less is known about the capability of infants to make similar assessments, the journal Developmental Psychology reports. In order to gauge the aptitude to perceive speech at any early age, the researchers examined the responses of infants, approximately nine months in age, to recorded human and parrot speech and non-speech sounds.

The results showed that infants listened longer to human speech compared to human non-speech sounds regardless of the visual stimulus, revealing their ability to recognise human speech independent of the context.

“Parrot speech is unlike human speech, so the results show infants have the ability to detect different types of speech, even if they need visual cues to assist in this process,” Vouloumanos said.

Courtesy The Hindu
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Higher you live, faster you age

The world’s most accurate atomic clock has clearly proved the nearly 100-year-old theory by Albert Einstein that time is a relative concept and the higher you live above sea level the faster you should age.

Einstein’s theory of relativity states that time and space are not as constant as everyday life would suggest. He suggested that the only true constant, the speed of light, meant that time can run faster or slower depending on how high you are, and how fast you are travelling.

Now researchers have demonstrated the true nature of Einstein’s theory for the first time with an incredibly accurate atomic clock that is able to keep time to within one second in about 3.7 billion years — roughly the same length of time that life has existed on Earth, The Independent reported.

James Chin-Wen Chou and his colleagues from the US National Institute of Standards and Technology in Boulder, Colorado, found that when they monitored two such clocks positioned just a foot apart in height above sea level, they found that time really does run more quickly the higher you are — just as Einstein predicted.

“These precise clocks reveal the effects of gravitational pull, so if we position one clock closer to a planet, you also increase the gravitational pull and time actually runs slower than for another, similar clock positioned higher up,” Chou said.

“No one has seen such effects before with clocks, which is why we wanted to see if these effects are there. We would say our results agree with Einstein’s theory — we weren’t expecting any discrepancies and we didn’t find any,” he explained.

The atomic clocks used in the study are based on the tiny vibrations of aluminium atoms trapped in an electric field.

These vibrations are in the same frequency range of ultraviolet light, detected by lasers, which effectively means that the atomic timepieces are optical clocks, accurate enough to measure billionths of a second and to keep time accurately over millions of years.

It means that the clocks were able to perceive the dilation of time with height above ground that was first predicted by Einstein.

For every foot above ground, for instance, the clocks showed that someone would age about 90 billionths of a second faster over a 79-year lifetime, Chou said.

The time dilation experiment, published in the journal Science, is vivid proof of how time is not what we think it is.

Besides, the scientists demonstrated that when the atomic clocks were altered in a way that mimics the effect of travelling through space, time began to slow down, as the theory of relativity says it should.

Courtesy The Hindu

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'Silly label, God particle'

Physicists hate the term, 'God particle' but they love the publicity. The Higgs boson 'discovery'.... attaches a real particle to an expectation that, buried inside force fields, was the key to why subatomic particles have mass. Behind all the hoopla and uncertainty, the news flew around the world that a basic building block of the universe has been uncovered, bringing quantum physics closer to its triumphant goal of explaining creation - hence the inflated and rather silly label of God particle. Yet, from another perspective, nothing like an explanation of the universe is emerging at all. Physics may be getting closer to the day, in fact, when the way it views the universe classically reaches a dead end....

The Missing Link

The preliminary discovery comes as a culmination of many years of both theoretical and experimental work, since 1964 when the British physicist Peter Higgs, along with six others hypothesised the existence of a field, filling all vacuum. They used symmetry breaking (which would allow particles to acquire their masses without violating other aspects of theory that were correct). This ubiquitous Higgs field would allow all particles in the universe to acquire mass through interactions with it, through a kind of dragging as they move in space. High energy proton collisions at the Large Hadron Collider should, in principle, reveal the elusive Higgs. The Higgs, unlike the photon, has a mass, expected to be in the approximate range of 125 (or more) times the mass of the proton.

The Higgs boson is the last missing link in the highly successful quantum theory of particles, called the Standard Model. It is also highly unstable, very elusive. To detect it, one has to observe many, many high energy collisions of protons and build up the statistics. In the LHC, particles are accelerated through a tunnel, brought together at speeds close to the speed of light, producing showers of particles, with high energies, capable of generating the Higgs particle. It exists for only a tiny fraction of a second before breaking up into many other particles, and can be detected only indirectly by identifying the results of its immediate decay and analysing them to show they were probably produced from a Higgs boson.

Even in its lowest energy state, the Higgs field filling all vacuum has non-zero values everywhere. In fact, ripples or waves in the quantum Higgs field, create for fleeting moments the Higgs particles.The Higgs boson is itself very massive, and it must interact with itself. It itself mediates interactions with the Higgs field, and is itself an excitation of the Higgs field.

The full properties of the Higgs (or whatever was observed by the teams) are not yet known. In fact, the signature of what they observed, may be multiple Higgs bosons with the properties required by the next theory that the Standard Model would extend into supersymmetry.

Cosmologists seem to agree that all luminous matter in the universe makes up only four per cent of whatever there is in the universe.... The rest of it may be in the form of dark matter and dark energy. So if the 'Higgs-like' particle near-discovery at CERN turns out to be a more exotic form, it could help us understand at least dark energy. These possible future developments could get us closer to what particle physicists call the Theory of Everything, but the theory cannot say anything about life, evolution and the phenomena of mind and awareness.

It is not even clear how gravity, the last of the four forces of nature, will fit into the Standard Model, developing into supersymmetry and perhaps superstring theory. But it would be a start.

Some scientists see that the materialist view of the universe doesn't hold water because quantum theory demolished the solid, reassuring physical universe almost a century ago. Once it was discovered that matter is made up of invisible clouds of energy, once photons were found to behave like particles in one mode and energy waves in another, once the Uncertainty Principle turned actual existence into virtual existence, the blows to materialism became decisive. Quantum pioneers noted definitively, that all other fundamental particles, have no fixed physical attributes. Instead, particles are pure potential existing in a quantum force field, and they collapse into being a particle you can see and measure only when observed by the scientist who is measuring them.

'Why are we here?' is a universal question, and to answer it, you must ask, 'Why are we conscious? Where did mind come from?' In the alternative explanation, the entire universe is imbued with consciousness. Just as there are force fields, invisible but all-pervasive, a consciousness field can exist to uphold the activity we call 'mind'.

Infinite Consciousness

The universe evolves, regulates itself, takes creative leaps, and exhibits exquisite mathematical rigour and beauty. The hallmarks of intelligence are there, waiting for the next paradigm shift. At the moment, the word 'intelligence' brings up the red herring of intelligent design, which no one except religious fundamentalists want to be associated with. 'Consciousness' gives us a less tainted word, and there is a growing community of theorists seriously thinking about a conscious universe.

If it exists, then you and I are embedded in the consciousness field. It is the source of our own consciousness, which means that we are not alone. As one physicist said, "The universe knew that we were coming." An infinite consciousness that spans all of creation sounds like a new definition of God; we are part of God's mind; that includes science.

Take Your Time, Discover

The whole argument leads to a wild conclusion by most people's standards: it is God who is discovering the God particle. Infinite consciousness has created individual consciousness to go out into creation and look around. As it does, individual consciousness - meaning you and I - has been given free will and choice. We don't have to see our link to the infinite consciousness field. We can take our time discovering who we are and where we come from. Soon it might seem quite natural to say that the conscious universe saw us coming.

Rudolph Tanzi teaches at Harvard Medical School; Prof M Kafatos, Chapman University.

Courtesy The Times of India
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Dumping iron in oceans ‘may cure climate change’

A ship dumping iron into the Southern Ocean has shown a technique that could be used as a “cure” for climate change.

The iron stimulates plankton growth, which “binds” carbon dioxide out of the atmosphere, getting rid of one of the gases which warms Earth’s atmosphere.

A trial, called Eifex, has been hailed a success, after a bloom of plankton sank 1,000 metres below the ocean, taking with it carbon dioxide.

At present, the technique could only be used to “mop up” around a tenth of global carbon emissions — but scientists continue to investigate.

"We were able to prove that over 50 per cent of the plankton bloom sank below 1000 metre depth indicating that their carbon content can be stored in the deep ocean and in the underlying seafloor sediments for time scales of well over a century,” the Daily Mail quoted Prof. Victor Smetacek from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association, as saying.

Previous experiments which aimed to “bind” carbon in this way failed. "Such controlled iron fertilization experiments in the ocean enable us to test hypotheses and quantify processes that cannot be studied in laboratory experiments. The results improve our understanding of processes in the ocean relevant to climate change,” Smetacek said.

The experiments attempts to recreate conditions during previous ice ages. The ocean iron fertilization (EIFEX) experiment has shown that a substantial proportion of carbon from the induced algal bloom sank to the deep sea floor. These results, which were thoroughly analyzed before being published now, provide a valuable contribution to our better understanding of the global carbon cycle.

An international team on board the research vessel Polarstern fertilized in spring 2004 (i.e. at the end of the summer season in the southern hemisphere) a part of the closed core of a stable marine eddy in the Southern Ocean with dissolved iron, which stimulated the growth of unicellular algae (phytoplankton). The team followed the development of the phytoplankton bloom for five weeks from its start to its decline phase.

The maximum biomass attained by the bloom was with a peak chlorophyll stock of 286 Milligram per square metre higher than that of blooms stimulated by the previous 12 iron fertilization experiments. According to Smetacek, this was all the more remarkable because the EIFEX bloom developed in a 100 metre deep mixed layer which is much deeper than hitherto believed to be the lower limit for bloom development.

The bloom was dominated by diatoms, a group of algae that require dissolved silicon to make their shells and are known to form large, slimy aggregates with high sinking rates at the end of their blooms.

These results contrast with those of the LOHAFEX experiment carried out in 2009 where diatom growth was limited by different nutrient conditions, especially the absence of dissolved silicon in the chosen eddy.

Instead, the plankton bloom consisted of other types of algae which, however, have no protective shell and were eaten more easily by zooplankton. The study has been published in the journal Nature.

 Courtesy The Hindu
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Where did Earth's water come from?

Researchers examining hydrogen isotope ratios in meteorites appear to have thrown a spanner in the works of the latest models of how elements such as hydrogen and nitrogen reached the early Earth. The finding throws up questions about where all the Earth's water came from and how life on Earth began.

One big question that remains unanswered about the evolution of the early Earth is how volatiles such as hydrogen, nitrogen and carbon arrived – their presence being crucial to the origins of water and life. The two main candidates for the sources of these elements are asteroids, found between the orbits of Mars and Jupiter, and comets, which come from the colder outer reaches of the Solar System. Current models suggest that at some point in the evolution of the Solar System, a jolt to the orbits of Saturn and Jupiter caused  comet-like material in the outer Solar System to be flung inwards into the present-day asteroid belt – eventually arriving at Earth and bringing the crucial volatiles.

Now, a new study led by Conel Alexander at the Carnegie Institution of Washington, US, has taken a significant step towards solving the conundrum.  Alexander’s team compared the hydrogen isotope ratios in chondritic meteorites, ancient fragments of asteroids, with those that have been measured in comets. In the outer Solar System, the birthplace of comets, the extreme cold results in frozen water having a higher proportion of deuterium than ice formed in the less cold regions. ‘We can measure the hydrogen isotope ratio of ice in comets remotely by infrared and submillimetre spectroscopy. We can measure the ratios in meteorites by analysing the hydrogen that is there – which is typically in the form of hydrated silicates, such as clays, that are the remnants of ancient water,’ explains Alexander. The team analysed the hydrogen isotope ratios in 86 meteorites, and showed that the proportion of deuterium to hydrogen was lower than in comets. ‘So, if we seem to have ruled out comets as a source of Earth’s volatiles, that leaves asteroids. We also analysed the nitrogen isotope ratios of the meteorites. We found that of the various types of chondrite the hydrogen and nitrogen isotopic compositions of one type, the CI chondrites, tallied most closely with what we see on Earth, suggesting that the parent bodies – asteroids – of these types of meteorite were the dominant source of the Earth’s volatiles.’

Other experts are intrigued and impressed by the work. Philip Bland of Curtin University in Australia says: ‘This is a really nice piece of work, a fascinating contribution to an old question – where did Earth’s water and organic material come from? The work is especially timely as it places compositional constraints on recent dynamical models of early Solar System evolution, contradicting a number of their predications.’

Jamie Gilmour of the University of Manchester in the UK comments: ‘It's interesting in itself that these asteroids have a distinct D/H [deuterium to hydrogen] ratio from the comets, since dynamical models have predicted that they share an origin. It seems that some meteorites arriving today are from asteroids similar to the precursor material that brought water in the early Solar System, so future  work may shed more light on this enigmatic early step in the formation of the Earth.’

Courtesy RSC Advancing the chemical sciences (Chemistry World)

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EXPERIMENTS ON PHOTOSYNTHESIS

Test tube and funnel experiment

The test tube funnel experiment demonstrates that oxygen is evolved during photosynthesis. A few branches of Hydrilla are kept in a beaker containing pond water in which a small amount of sodium bicarbonate is dissolved. The branches are covered with a glass funnel and a test tube full of water is kept inverted over the stem of the funnel as shown in the figure. Now the apparatus is kept in sunlight for 4 to 6 hours. The gas bubbles may be observed from the ends of hydrilla branches kept within the glass funnel. These gas bubbles are collected in the test tube by the downward displacement of water. The gas is tested for oxygen. When a burnt splinter is taken near the mouth of the tube, it glows brightly and proves that the gas is oxygen.The test tube and funnel experiment demonstrates that oxygen evolves during photosynthesis.

You tube link : http://youtu.be/4oNeULIg_Yo

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What is Holme’s signal ?

          Containers which have a perforated bottom and a hole at the top are filled with calcium phosphide and calcium carbide. These are thrown into the sea. Water enters the container through the bottom and reacts with calcium carbide and calcium phosphide to give acetylene and phosphine. Phosphine gets ignited spontaneously as it comes in contact with air and also ignites acetylene. Thus a bright red flame is produced which is accompanied by huge smoke due to the burning of phosphine. This serves as a signal to the approaching ships.

Youtube link :   http://www.youtube.com/watch?v=wdMEF6MbJB4&feature=plcp


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Bittersweet result for dark chocolate

UK scientists have clinically proven that consuming polyphenol-rich dark chocolate has health benefits for overweight and obese females, whilst showing adverse effects for polyphenol-deficient chocolate.

Evidence already shows that polyphenol-rich dark chocolate can benefit blood pressure and glucose levels in healthy people, thanks to dark chocolate's antioxidant properties. Fewer studies have examined the involvement of the endocrine system – glands that secrete hormones – in mediating the cardiometabolic health-effects of polyphenols, until now.

Suzana Almoosawi from Medical Research Council Human Nutrition Research, in Cambridge, and her colleagues, applied these findings to a group of healthy women with a range of body mass indexes (BMIs). Obesity is often linked to numerous chronic diseases, such as hypertension and type 2 diabetes, so the team were keen to study the metabolic effects observed for different concentrations of polyphenols in dark chocolate, across a range of BMIs.

BMI is a number calculated using a person’s weight and height, which provides an indication of body fat. In this study, the group consisted of normal (19–25kg/m²), overweight (>25kg/m²) and obese (>30kg/m²) women. The single-blind, randomised study involved the consumption of polyphenol-rich dark chocolate (500mg of polyphenols), or a polyphenol-deficient dark chocolate placebo, over a four week period. ‘The placebo matched the polyphenol-rich dark chocolate for taste, texture, colour and macronutrient composition, but contained no polyphenols,’ explains Almoosawi.

On examining the metabolic effects on each female, the team found that the polyphenol-deficient placebo had an adverse effect on insulin sensitivity, antioxidant status, glucose levels and blood pressure. ‘Of note is that beneficial effects on metabolic endpoints were most readily observed in subjects with a BMI over 25,’ says Francisco Villarreal, an expert in cardiac mechanics from the University of California-San Diego, US. ‘This suggests that polyphenol-rich dark chocolate is helping to counter the effects of a high BMI, and in this manner potentially reducing cardiometabolic risks,’ he adds.

‘We hope that the findings from this research will encourage the industry to consider making polyphenol-rich chocolate available on the market,’ says Almoosawi. ‘However, we are still faced by many challenges. We still don’t know the implications of consuming large amounts of polyphenols and whether there could be adverse effects associated with long-term consumption.The health benefits of consuming polyphenol-rich dark chocolate should still be carefully balanced against any long-term adverse effects.’

Courtesy RSC Advancing the chemical sciences (Chemistry World)
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"A bacterium that did not live on arsenic"

Life as we know it does not include a bacterium that is able to live off arsenic, according to two papers published online by the journal Science.

In December 2010, a sensational discovery of a unique bacterium isolated from the toxic waters of Mono Lake in California was announced in the same journal. The bacterial strain, GFAJ-1, was substituting “arsenic for phosphorus to sustain its growth,” declared Felisa Wolfe-Simon, then at the NASA Astrobiology Institute in the U.S., and 11 other scientists in their paper.

Life forms on Earth rely on six elements to build their molecules — oxygen, carbon, hydrogen, nitrogen, sulphur and phosphorus. There was, it seemed, at least one organism capable of substituting arsenic, which is usually toxic, when phosphorus was not available. The GFAJ-1 bacterium was able to use arsenic in this manner in its DNA and proteins, according to Dr. Wolfe-Simon and her colleagues.

The implications were enormous. “The definition of life has just expanded,” remarked a senior official of the U.S. space agency, NASA, in a press release.

But many in the scientific community were unimpressed, arguing that extraordinary claims should be matched by similar levels of proof. The evidence that had been put forward for arsenic being incorporated into the bacterium’s DNA was seen as questionable. In May last year, Science published eight technical comments that raised several issues with the paper.

Now, two teams of scientists have independently studied the bacterium using much more stringent procedures and tests. One of them was led by Rosemary Redfield of the University of British Columbia in Canada, whose forthright critique of the original paper on her blog garnered a great deal of attention . The other was a group of Swiss scientists at ETH Zurich.

The GFAJ-1 bacterium “does not break the long-held rules of life, contrary to how Wolfe-Simon had interpreted her group’s data,” said Science in an editorial statement that accompanied the publication of the two papers.

The new research clearly showed that the bacterium could not substitute arsenic for phosphorus to survive. Instead, the two papers revealed that the medium used to growth the organism in the original experiments contained enough phosphate contamination to support its growth.

This bacterium was likely to be adept at scavenging phosphate under harsh conditions, which would help to explain why it could grow even when arsenic was present within the cells, statement noted.

But, as the journal also pointed out, the bacterium’s extraordinary resistance and its arsenic tolerance mechanisms would be of interest for further study.

Courtesy The Hindu
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Girls suffer from maths anxiety more than boys

LONDON: Girls often fail to do just as well at math as boys because of heightened fear and apprehension over number problems, a new study has claimed. The study, published in the journal Behavioral and Brain Functions, found that a number of school-age children suffer from mathematics anxiety, but girls' maths performance is more likely to suffer than boys as a result.

Mathematics anxiety is a state of discomfort associated with performing mathematics tasks and is thought to affect a notable proportion of both children and adults, having a negative impact on their mathematics performance.

In the study, researchers from Cambridge University in the UK investigated 433 secondary school children whether mathematics anxiety has any effect on mathematics performance on boys and girls. The researchers controlled for test anxiety, a related construct, but which isn't typically controlled for in mathematics anxiety studies.

They found children with higher mathematics anxiety have a lower mathematics performance, and girls showed higher levels of mathematics anxiety than boys.

http://timesofindia.indiatimes.com/home/science/Girls-suffer-from-maths-anxiety-more-than-boys/articleshow/14791441.cms

Courtesy The Times of India

What next after a Higgs boson-like particle?

The ATLAS (A Toroidal LHC Apparatus) collaboration at CERN has announced the sighting of a Higgs boson-like particle in the energy window of 125.3 ± 0.6 GeV. The observation has been made with a statistical significance of 5 sigma. This means the chances of error in their measurements are 1 in 3.5 million, sufficient to claim a discovery and publish papers detailing the efforts in the hunt.

Rolf-Dieter Heuer, Director General of CERN since 2009, said at the special conference called by CERN in Geneva, “It was a global effort, it is a global effort. It is a global success.” He expressed great optimism and concluded the conference saying this was “only the beginning.”

Another collaboration, called CMS (Compact Muon Solenoid), announced the mass of the Higgs-like particle with a 4.9 sigma result. While insufficient to claim a discovery, it does indicate only a one-in-two-million chance of error.

Joe Incandela, CMS spokesman, added, “We’re reaching into the fabric of the universe at a level we’ve never done before.”

The LHC will continue to run its experiments so that results revealed on Wednesday can be revalidated before it shuts down at the end of the year for maintenance. Even so, by 2013, scientists, such as Dr. Rahul Sinha, a participant of the Belle Collaboration in Japan, are confident that a conclusive result will be out.

“The LHC has the highest beam energy in the world now. The experiment was designed to yield quick results. With its high luminosity, it quickly narrowed down the energy-ranges. I’m sure that by the end of the year, we will have a definite word on the Higgs boson’s properties,” he said.

However, even though the Standard Model, the framework of all fundamental particles and the dominating explanatory model in physics today, predicted the particle’s existence, slight deviations have been observed in terms of the particle’s predicted mass. Even more: zeroing in on the mass of the Higgs-like particle doesn’t mean the model is complete. While an answer to the question of mass formation took 50 years to be reached, physicists are yet to understand many phenomena. For instance, why aren’t the four fundamental forces of nature equally strong?

The weak, nuclear, electromagnetic, and gravitational forces were born in the first few moments succeeding the Big Bang 13.75 billion years ago. Of these, the weak force is, for some reason, almost 1 billion, trillion, trillion times stronger than the gravitational force! Called the hierarchy problem, it evades a Standard Model explanation.

In response, many theories were proposed. One theory, called supersymmetry (SUSY), proposed that all fermions, which are particles with half-integer spin, were paired with a corresponding boson, or particles with integer spin. Particle spin is the term quantum mechanics attributes to the particle’s rotation around an axis.

Technicolor was the second framework. It rejects the Higgs mechanism, a process through which the Higgs boson couples stronger with some particles and weaker with others, making them heavier and lighter, respectively.

Instead, it proposes a new form of interaction with initially-massless fermions. The short-lived particles required to certify this framework are accessible at the LHC. Now, with a Higgs-like particle having been spotted with a significant confidence level, the future of Technicolor seems uncertain. However, “significant constraints” have been imposed on the validity of these and such theories, labelled New Physics, according to Prof. M.V.N. Murthy of the Institute of Mathematical Sciences (IMS), whose current research focuses on high-energy physics

Courtesy The Hindu

Satellite communication

Space technology has witnessed a phenomenal growth, since the launch of man-made satellite Sputnik in 1957. One of the most significant applications of space technology has been in the field of communications. The people over world watch international events like Olympic games via satellite. A number of countries are using satellites for military communications, which include services to ships, air crafts and land mobile terminals. Several direct TV broadcasting satellite systems are also being used.

Satellite communication is basically a microwave link repeater. A satellite receives energy from an earth station, amplifies it and returns it to each at a frequency about 2 GHz away from the uplink frequency (earth to satellite) . This prevents interference between the uplink and the downlink (satellite to earth). Satellite so used is a geostationary satellite which appears to be stationary at a given spot above the equator. Actually, it moves with the same angular velocity as the earth i.e. it completes one revolution per 24 hours and hence appears to be stationed over one spot on the globe. Satellite orbiting the earth will be geostationary when it is about 36,000 km away from the earth. A satellite in space links many earth stations. The user is connected to the earth station through terrestrial network. This network may assume various configurations including a telephone switch or a dedicated link to the earth station. Signal generated by the user is processed and transmitted from the earth station to the satellite. The satellite receives the modulated RF carrier at the pre-determined uplink frequencies from all the earth stations in the network, amplifies these frequencies and then re-transmits them back to earth at downlink frequencies. The downlink frequencies are kept different from the uplink frequencies in order to avoid interference. The modulated carrier received at receiving earth station is processed to get back the original baseband signal. This signal is then sent to the user through a terrestrial network. As per WARC (World Administrative Radio Conference) 1979 allocation, commercial communication satellites use 500 MHz bandwidth near 6 GHz for uplink transmission and use 500 MHz bandwidth near 4 GHz for downlink transmission. In actual practice, uplink of 5.725 -- 7.075 GHz is used while downlink of 3.4 -- 4.8 GHz is used.

REF : http://www.youtube.com/watch?v=t9nDMl9xNmg