Thursday, August 6,
1998
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War of the
satellites Intelligent
electronic books A
galaxy engine found Science notebook Mice
offer new uses for cloning Science Quiz |
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War of the satellites THIS year saw the launching of satellites which will eventually become part of a global mobile personal communications by satellite (GMPCS) system. For some years, a number of consortia have been planning to use satellites and the technology of wireless communication to build these networks. Some of the firms are only looking at providing service to designated regions, while others have global coverage in mind. Naturally, their plans have long-term implication on the current structure of the telecommunication business and technical standards, but also emerging are questions concerning national sovereignty and economic department. As direct-to-home (DTH) services such as television have developed using satellite, the last few years have seen the development of interest in using satellite technology to offer global mobile narrow band services including relatively low-speed data on a global or regional basis. These systems do not use traditional geostationary orbits (GEOs) but are planning to use low earth orbits (LOEs), medium earth orbits (MEOs) and highly inclined elliptical orbits (HEOs). Since Arthur C. Clarke first wrote about using a web of satellites to help pass signals across the globe, his words were followed in 1963 by the first communication satellite, Early Bird. Today there are over 320 geostationary satellites strung across the equator at an altitude of 22000 miles. The problem that direct contract with these satellites using small hand-held terminals is unrealistic. Existing systems, such as Inmarsat-M need equipment that fits in a briefcase, something that would be unmarketable in today’s world of slim-line cellular handsets. To give people handsets that permit the reception and transmission of phone calls anywhere on earth, the use of lower altitude satellites is needed. With GEO satellite, three or four stationed above the earth are enough to give global coverage but the most simple downside of GEO technology is that the users need more powerful transmitters to reach them, and there is time delay that most consumers today would not tolerate. LEO spacecraft are visible in the service area for only tens of minutes at a time, several times a day - depending on exactly how high or at what angle the satellites are placed, but usually around 700 km and up. For the network to operate, a constellation of satellites is needed ensuring that at least one satellite is visible 100% of the time from anywhere on the surface. The main advantage of a CEO system is that, while it needs far more than 3 or 4 satellites in orbit, it gives better transmission quality and a greater, more manageable subscriber capacity. Most of the satellite systems on the planning board plan to offer paging, voice and low-to medium data transmission rates. Of course, their voice service will have to be comparable to current cellular technology, and users will expect a personal number for worldwide connection and one bill sent to the same place. Iridium plans to be the first in service by December, 1998. It originally planned to launch 77 satellites (there being 77 electrons in the systems namesake — the element Iridium). As the system developed, however the number was reduced to 66. The consortium is led by Motorola, and the first five satellites were launched last year. Against Iridium stands Global Star, ICO and Odyssey. Global Star, a 48 — satellite system founded by Loral Qualcomm satellite services, uses LEO satellites as radio base stations. They work like base stations of terrestrial cellular networks but, because they are moving at high speed and connections must be transferred relatively frequently to adjacent satellites. Also, because the system has smaller radio cells, it can get more callers on a more limited frequency. While at first sight the various LEO systems appear similar, they do differ. Global Star plans to use code division multiple access (CDMA) technology, While Iridium uses time division multiple access (TDMA). There are also differences in how the signals are passed on. Iridium plans to route the systems around its own satellites, Global Star has no direct connection between its satellites and plans to use ground stations. The other two systems — Odyssey planned by TRW Inc. and Teleglobe and ICO, an off shoot of Inmarsat with 60 governments as partners, will use slightly higher MEO satellites. Then there are technical challenges. Since LEO satellites are moving quickly over the earth’s surface, the cells and their size must move also, using what are known as phased array antenna systems. The satellites control the call cells of the users to terrestrial downlink/uplink sites and to other satellites. The satellites generally need spare cell capacity, so that if one satellite fails, there is a back-up. They must also be able to switch off the cells while passing over countries which might not wish their people to have access to the system. To add to the complexity, while these systems carry individually and two-way communications, they can carry data a little faster than 2400 bps. For Bill Gates of Microsoft and Craig McCaw, founder of world’s biggest cellular company which is now owned by AT&T, this wasn’t good enough. Founding Teledesic, they plan to put up 840 satellite with all cell sizes of only 53 km giving their network broadband capacity for transmitting Internet signals. Most of these consortia are engineering handsets which should have a standby mode of 24 hours and talk time of one hour, with power consumption no more than that of a GSM handset (350 mw). Most of the firms are already accepting the fact that the handsets will have to be dual-mode capable of using a local cellular service provider as well as being able to switch over to satellite. Assuming these projects do get off the ground, all the companies admit they are having to design new technology to achieve their plans. The drawback is that no one is really sure if the myriad of signals bouncing so close to each other will allow any of the systems to work without interference. Apart from the technical difficulties in achieving these features, the companies also face challenges in the political and legal arena. Estimates put fixed-line telephony providing service to about 15% of the world. Most of the remaining 85% live in developing nations, and it is becoming clearer that wireless technologies are the only way forward to deliver efficient telecommunications services globally. These satellite systems are regarded as one solution. But, as with everything, it is not that simple. The use of global satellite networks GSNs will be costly. The companies already in the running are talking about $1 to $3 per call, and handsets costing anywhere from $700 to $3000. It will also be politically sensitive — authorities in many developing countries have voiced fears that the systems will be used to “bypass” their domestic networks, depriving them of revenues. If governments don’t allow such operations within their borders, satellite operators will have to be able to switch off connections as the satellites fly over objecting countries. According to Pyramid Research, if things go well and developing countries can afford to board the bandwagon, satellite mobile phone users will hit 35 million by 2007 with service revenues hitting $25 billion a year. If things don’t go according to plan, it will have been an expensive experiment. The author is Member
(VLSI) with Semiconductor Complex, Chandigarh. |
Intelligent electronic books BOOKS had always been considered to be records of knowledge, mostly on paper. It was implicit that this record had to be un-reactive, static and time-invariant; the precious life-blood of a master-spirit (Milton), or a message from human souls we never saw (Kingsley). One could preserve books as precious records but none ever thought of talking to them, as books were not known to talk back. All that, however, has changed — thanks to the birth of electronic books. Electronic books have become possible due to the application of micro-computer technology to advanced data storage media. This has made books reactive (or interactive), dynamic in space and time-variant. One can interact with the stored information, hear it, see it in motion and get a live response at if from a companion. One can adjust the stored data, update it or play with it in any other manner. Pages of an electronic (or e-) book need not exist, until they are needed. These are created in real-time from a corpus of knowledge carried to the reader by various means, called multi-media. The American Academic Encyclopaedia and the Oxford Textbook of Medicine, available on Compact Discs (CD) are two examples of e-books. The compact (or optical or laser) discs came in use in 1983 and can store vast data in their read-only memories (ROM). Now Digital Audio Tape (DAT) is available, with a cassette of just two inches, that can store the equivalent of 600,000 printed pages of standard size. A typical e-book can have two million pages of A4 text and more than 20,000 PCX files. Electronic pages have unlimited potential for embedding intelligence and introducing reader text, static or mobile pictures, sounds, special effects like simulations and participative conversations based on tactile and sonic dialogue. A typical e-book may have several thousands of TV quality images, hours of C-level sounds and animations including cartoons. Multi-media and AI
books Telemedia e-books Hyper-media
e-books An example is the dynamic visualisation of human systems (eg. working of the heart and the circulatory system) or the numerous complex processes in nature. One such e-book “Family Doctor” answers on the MPBAN format 2000 common questions on diseases, injuries and infections with dynamic illustrations and guides the readers on drugs usually prescribed. Imaginary e-books In the words of Bill Gates
(CEO, Microsoft) “Incremental improvements in
computer and screen technology will ultimately give a
universal e-book...that can show high resolution text
videos...with voice commands to search for
information”. In spite of these mind-boggling
advances, it must be admitted that paper-based books,
magazines and newspapers are today cheaper and easier to
read. Only drastic reductions in the costs of PC’s,
CD-ROMS, DAT’s and other electronic inputs can make
the interactive e-books popular. Till then lovers of
e-books can enjoy the information in explosion special
libraries equipped with hyper-media or tele-media
gadgets. In any case, the world of books promises to
change soon, beyond recognition. |
A galaxy engine found THE International Ultraviolet Explorer, a pathbreaking astronomical probe launched in early 1978, has led the European astronomers to come to a definite conclusion on the mass of gas that swirls towards oblivion around a giant black hole in the heart of a stormy galaxy. For long, astrophysicists believed that the gravity marshals doomed matter into a flat disk shaped like a music record with the hole at the centre. However, thanks to the painstaking analysis of data provided by IUE it has been revealed that in the galaxy 3C 390.3 and at ultraviolet wavelengths, the gassy mass is indeed rotating around the block hole and is one fifth of a light year wide. Significantly, Willem Wamsteker and Norbert Schartel of European space Agency’s Astrophysics Division working with Ting-gui-Wang of Hefei, China, and Roberto Vio of Padua, Itlay, used the travel time of light to achieve this result in a galaxy more than a billion light years away. When its black hole swallows a morsel larger than the usual 3C 390.3 flares up and radiant energy travels outside from the centre, causing the falling matter to glow more intensely. The study based on IUE data pins down the mass of the black hole 3C 390.3 to be of about 200 million suns. By Einstein’s theory of gravity the horizon of the black hole, where infalling matter disappears, is 600 million kilometres from the centre. That is little less than the distance from the Sun to Jupiter. “This is only one of many new results to be expected as we sift through the monumental set of data from IUE”, Wamsteker comments. “The World’s astronomers can look back at our 18 years of observation with fresh ideas, novel questions and improved techniques.” Since quasars were discovered more than 30 years ago, as compact sources of unimaginable luminosity, most astrophysicists have come to believe that only a black hole, operating in the nucleus of a galaxy and swallowing stars and gas can explain the phenomenon. The same mechanism is required for other galaxies with bright centres and for galaxies that shoot out jets of atomic particles like water cannons. Sometimes the jets are seen in visible light. Often the product of the jets is a radio galaxy like 3C 390.3 with large of radio emission on either side of the galaxy. This black hole itself with the mass of millions of billions of suns, is a small region where gravity is too strong for light or anything else to escape. Central black holes in many galaxies may be inert and truly black because they have eaten all the stars and gas within the range. In active galaxies, energy pours from captured matter forming new accretion disk around the black hole. As it spirals in unlike water going down a plughole, the matter becomes incandescent in visible light, then in ultraviolet rays and ultimately into X-rays and gamma rays. The accretion disk also acts as an electric motor propelling outwards, at right angles to disk, the jets of particles that emit radiowaves. The central engine tests astrophysical theory and observational techniques to their limits. Astronomers have established in many galaxies the presence of a very massive object. High speeds of motion of nearby stars are the usual clue, and radio astronomers linking their telescopes intercontinentally have found even faster motions of gas molecules. Intense gravity is also indicated by reduction in X-ray frequencies detected by the Japanese ASCA satellite. But a typical accretion disk should be less than a light year wide so the central engine is far too small to be seen by any telescope. Lying more than a billion light years beyond the Draco constellation in the north polar sky, 3 C3 390.3 first attracted astronomers’ attention as a radio galaxy. It acquired its name and number in the revised third Cambridge radio survey. By a well known astronomical illusion, jets from the galaxy appear to travel faster than light. IUE began observing 3C 390.3 by ultraviolet light during the satellite’s first year of operations, on Nov. 21, 1978. On the same day US space probe Einstein registered X-rays coming from the galaxy. Subsequently IUE and various X-ray satellite revisited the galaxy at irregular intervals. During the 1980s, astronomers noticed that 3C 390.3 was highly variable in its output of visible, ultraviolet and X-rays. The present breakthrough comes with the identification of rays from opposite sides of the accretion disk of 3C 390.3. The disk is seen almost edge-on from the earth-perhaps at a slant of 18 degrees. There at the disk, gas falling at high speed towards the hole is also heading in the earth’s direction. The ultraviolet rays it emits are squeezed and shortened in wavelength by the Doppler effect. On the other hand, gas
falling towards the black hole from the near side of the
accretion disk is receding from the earth at high speed,
causing a Doppler redshift that stretches and lengthens
the wavelengths of its emissions. These also have less
distance to travel to reach the earth. By the shifts in
wavelength, analysed by spectroscopy, astronomers
distinguish the nearer and farther sources. |
Science
notebook THE solar system consists of a central star, that is the sun, surrounded by a disk containing the planets. All theories concerning the origin of the solar system are agreed that the planetary disk and the central star formed at the same time. Disks of gas and dust have been seen around newly forming sun-like stars and it is believed that planets would be forming in these disks. However the general assumption that planetary disks are invariably associated with young stars has now been shown to be wrong. As often happens in astronomy one example or counter-example is enough to convince the astronomers of a trend. In this case, the counter-example is provided by an astronomical object called the Red Rectangle discovered in 1975. This is a nebula, that is an object containing a large amount of gas. The nebula comprises a central star which once was like the sun, but has by now ejected layers of mass on its way to becoming a non-descript white dwarf. The ejected layers surrounded the star. The central star in fact is not alone ; it has a companion star which has captured the mass ejected by the central star and whipped it into a disk surrounding both the stars.It is this disk that has been subjected to close scrutiny. Recent infrared observations have revealed that this disk abounds in oxygen-rich material including silicates and carbon dioxide. The dust grains in the disk are very similar to those seen in disks around new born stars. Radio observations reveal that these dust grains have started aggregating into larger clumps. These clumps are the building blocks of planetesimals (which in turn combine to form planets). The observations however are unable to say whether there are larger bodies in the disk. It is surmised that the disk would not last long enough to form Jupiter-sized planets, but small rocky planets may indeed form. Would it be possible to see such small planets around dead, or more correctly retired, stars? It is unlikely. What makes the present object detectable is the nubulosity, that is the presence of gas. Once the nebulosity clears, the system would not be emitting any radiation which could provide clues about the physical objects and processes. What the astronomers can indeed look forward to is searching for similar objects at different stages of evolution, so that we may reconstruct the whole process step by step. Black sheep The physicist was more cautious in his conclusions : “I would say that some sheep here are black.” The mathematician was
aghast. How could his friends be so rash : “All you
can say is that there exists at least one sheep in the
immediate neighbourhood and at least one side of which is
black.” |
Mice offer new uses for cloning HAWAIIAN scientists have followed Dolly the cloned sheep with replica mice. And in a world first, they cloned more mice from the first clones. Their work means that researchers can use clones to study what happens in cancer, Aids, diabetes, multiple sclerosis and ageing. It could also lead to surer ways of ``copying'' the best farm animals. The Hawaiian team is to collaborate with PPL Therapeutics at Roslin near Edinburgh - the company which uses genetically engineered sheep to make vital human proteins - it was announced last night. The research, published recently in Nature, opens the way for much faster research experiments because mice breed quicker than sheep. Ryuzo Yanagimachi of the University of Hawaii and colleagues created 50 identical mice. They took the DNA from the cell of a female adult and injected it into a egg from which the DNA had been removed. They popped the artificially fertilised egg into a surrogate mother and produced the first clone. They went on to make second and third generations of cloned mice, some of which have been mated and have raised normal offspring. The achievement puts a stop to speculation about Dolly, the sheep that shook the world. Humans have been cloning plants for generations and animals for almost a decade. Dolly was the first creature cloned from an adult: a ``carbon copy'' generated from one cell from the mammary gland of a six-year-old ewe at the Roslin Institute. This, until March 1997, was believed impossible. Embryo cells can be divided to make twins. But embryo cells soon differentiate into skin, bone, blood, nerve tissue and so on: after that, the argument went, the clock could not be turned back. But it was turned back: the Roslin researchers persuaded a six-year-old adult cell to ``reset'' its clock and become the nucleus of an identical infant. The announcement caused a worldwide storm, and raised the spectre of cloned humans. But late last year, researchers speculated that the Roslin team might have been misled: that Dolly's parent had been pregnant at the time and that, against huge odds, the researchers had used a foetal cell which had made its way into the sheep's udder. But the two Hawaiian
reports show that cloning from adult cells can be done. (The
Guardian) |
Science Quiz 1. Name
the three Indian scientists who were recently denied visa
by the USA and Britain. ANSWERS:1.
Dr R. Chidambaram, Chairman, Atomic Energy Commission, Dr
Placid Rodriguez and Dr Baldev Raj, both Directors at
Indira Gandhi Centre for Atomic Research, Kalpakkam
(Tamil Nadu) 2. Partial Test Ban Treaty;
Non-Proliferation Treaty; Comprehensive Test Ban Treaty
3. Param 10000; Centre for Development of Advanced
Computing, Pune 4. A, D, E and G 5. Pig 6. Gujarat 7.
Copper and zinc 8. Sunflower 9. A metallic coil called
element 10. Polonium; it was named after Marie
Curie’s homeland, Poland. |
| H |
Built-for-speed
truck The Pickster’s sculpted flanks, 21-inch wheels, and massive airfoil spoiler in the tail make it a show car, not an off-roader or heavy-load carrier. Amazing drilling
feats About a decade ago, HDD technology was not available in the market for eco-friendly trenchless construction. But today there are a host of American manufacturers offering this technology for eco-conscious market. The models range from machinery attachments to large, self-contained and compact machines that can routinely install 4-, 6- or 8-inch diameter conduits 1000 feet below the ground level, reports a recent issue of World Water Journal. The new technology is less disruptive and more cost-effective for remediation work. Take the example of Tennessee-based Marion Environmental Incorporated who recently installed a horizontal remediation well to clean ground water, contaminated due to the leakage of fuel from underground storage tanks. The bore path began on one side of a grocery store, went under a fuel pump area and surfaced on the opposite side of the store having an average depth of 15 feet. The bore was filled with high density polyethylene pipes for extracting the sludge. Another firm from Minnesota — Outdoor Design has installed a sewer line to correct an ageing septic system using directional drilling technology. The 300-feet bore has a 57 feet difference in elevation from the entrance hole to the exit hole and it takes only two and half hours to cover the distance. Priestly tradition
confirmed Divid Goldstein and colleagues at Oxford University in England tested descendants of both tribes to see if their chromosomes, which are inherited from their fathers, were distinguishable from those of the general Jewish population. They found many different types of Y chromosomes among the descendants of the tribe of Levi and among most Jews, but there was much less diversity among the men who considered themselves to be Cohanim. “This is the signal of fairly strict adherence to a father-son inheritance of priestly status,” Goldstein said. “In other words, there has not been arbitrary adoption of priestly status because if there were the Y chromosome of the priest would look like those of the general Jewish population,” he added. The scientists, who reported their findings in Nature, also said the oral tradition of priestly status among the Cohanim is fairly old because of the type of variations they saw in the Chromosomes. They calculate that the latest common ancestor of the Y chromosomes of present-day Cohanim was in existence sometime between the Exodus and the destruction of the first temple in 586 BC. Goldstein also noted that the characteristic Cohanim Y chromosome is rarely observed outside the Jewish community. “It raises the possibility that this chromosome type could be used to test whether particular populations have a relationship with the ancestral Jewish population,” he added. Gateway to the 3-D
world The latest gizmo from Belgian researchers not only helps bio-scientists to investigate organisms in their natural environment but also allows physical science researchers to study microscopic objects with utmost precision. The new device called “desk-top X-ray microtomograph”, designed by the scientist from the University of Antwerp is a relatively inexpensive instrument for 3-D microscopy, reports a recent issue of the journal Asia/Pacific Microscopy and Analysis. The state-of-the-art technology is based on the principle of making radiographs of an object in 3-D plane to show the internal structure of the object in a detailed manner, which is impossible by the conventional methods. There are several
applications of this new device ranging from determining
defects in electronic components to the reconstruction of
3-D structures of living organisms without any specimen
preparation. |
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