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| SCIENCE & TECHNOLOGY |
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Invisibility cloak Intelligent video scanning Scientists “listen” to plants
THIS UNIVERSE |
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Scientists say they are a step closer to developing materials that could render people and objects invisible. Researchers have demonstrated for the first time they were able to cloak three-dimensional objects using artificially engineered materials that redirect light around the objects.
Previously, they only have been able to cloak very thin two-dimensional objects. The findings, by scientists at the University of California, Berkeley, led by Xiang Zhang, moves scientists a step closer to hiding people and objects from visible light, which could have broad applications, including military ones. People can see objects because they scatter the light that strikes them, reflecting some of it back to the eye. Cloaking uses materials, known as metamaterials, to deflect radar, light or other waves around an object, like water flowing around a smooth rock in a stream. Metamaterials are mixtures of metal and circuit board materials such as ceramic, Teflon or fiber composite. They are designed to bend visible light in a way that ordinary materials don’t. Scientists are trying to use them to bend light around objects so they don’t create reflections or shadows. It differs from stealth technology, which does not make an aircraft invisible but reduces the cross-section available to radar, making it hard to track. The research was funded in part by the U.S. Army Research Office and the National Science Foundation’s
Nano-Scale Science and Engineering Center. — AP |
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Intelligent video scanning One of the more common sequences one comes across in Hollywood thrillers is a security guard seated in front of a bank of monitors which are relaying scenes from the CCTV cameras they are attached to and suddenly noticing the presence of an intruder in one of the monitors. He reaches for the intercom and alerts the security on the suspect floor to go check. Now, in reality , such intruder detection is possible if the security man has to supervise perhaps a dozen monitors. But what happens if there are a few hundred cameras to be monitored, as is the case nowadays in big malls, rail stations, airports , large commercial establishments and the like ? Either the numbers of security persons manning the monitors will have to be increased, which leads to increased costs , not to mention the chance of confusion in the monitoring room with a large crowd of video supervisors present ; or , if only one supervisor is in place, the chances are that he will miss seeing the intruder in the frame of one camera as he is concentrating on another. Then, there is the problem of video boredom. It has been recognised that if a person keeps staring at a scene on one monitor for over 5 minutes, during which nothing unusual happens, he tends to lose focus and gazes at the scene without actually mentally acknowledging what is going on in the frame. And, in all probability, he will miss noticing the intruder, even if the monitor shows it. To overcome such problems and make large-scale video surveillance worth its while modern security technology has come up with an IT based solution called Video Analytics. What this does is enable the CCTV system to automatically detect such unusual events as illegal parking, baggage left unattended, sudden crowd movements, suspicious human activity etc. and alert the security supervisor. This approach of giving intelligence to the CCTV camera is done by utilising such techniques as Pattern Matching, Profiling, Behavioural Analysis etc. and using an Inference Engine to detect unusual events in the camera frame. Basically what is done is to give the camera some reference patterns and then ask it to match the pattern under observation against these references. The matching is in real time and, based on certain rules that are provided about any mismatch, the camera can automatically raise an alarm to the human supervisor . Such software is regularly deployed in visual inspection systems for culling flawed pieces in a microprocessor manufacturing line. The rules could be anything, like “Look out for an extra person in the frame” or “Check for unattended bag left in the scene” or “Pick up any bright spark or flame in the picture” and the like. Many of these rules are based on human psychology. For example, a mall always has crowds moving in random fashion. However, if there is an unusual event, this pattern of movement will suddenly change. A child falling from an escalator will see a sudden rush of people to the bottom of that escalator. A man suddenly fainting will generate a bunch of people surrounding the person. A man waving a gun will see a sudden dispersal of persons from him. A spark and flames will show a rush of people away from the spot. It is the detection of these unsual patterns that a CCTV camera can be programmed to detect, using video analytics software. Or take the scene in a parking garage. The owner of a car will approach it casually and directly and unlock the door. A car thief, on the other hand, will furtively approach several cars one after another in order to make out which one has been left unlocked or the window left open. The surveillance camera in the garage can be programmed to make out this different type of movement and alert the guard and even automatically lock the exit barrier.
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Scientists in Israel have discovered a new way to test for water pollution by “listening” to what the plants growing in water have to say. By shining a laser beam on the tiny pieces of algae floating in the water, the researchers said they hear sound waves that tell them the type and amount of contamination in the water. “It is a red light, telling us that something is beginning to go wrong with the quality of water,” said Zvy Dubinsky, an aquatic biologist at Israel’s Bar Ilan University. “Algae is the first thing to be affected by a change in water quality.” Although most of the earth is covered in water, 44 percent of the world’s population live in areas with high water stress, and the number is likely to increase because of factors such as global warming and rising population. As water sources deteriorate worldwide, the testing of algae could be used to monitor water quality faster, more cheaply and more accurately than techniques now in use, Dubinsky said. The secret, he said, is to measure the rate of photosynthesis in the algae, meaning the plant’s ability to transform light into energy. During photosynthesis, plants also release oxygen into the
air. — Reuters
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THIS UNIVERSE
We have a stone and a plastic ball of same mass. We drop both of them simultaneously. But the ball bounces up and the stone does not. Why? Let us examine what happens to the energy and momentum of the two balls when they hit the ground. First the stone ball: It is possible that the stone ball will break the ground, scatter some dust around, perhaps itself be chipped or broken. Therefore its energy will be used up in all these things. Depending on the height from which it falls, quite some energy would be used up in heating the ground and the fragments produced. The nature of these happenings might vary depending on the structure of the ball and the ground surface and the height from which the ball is dropped. Most of the energy and momentum would
be dissipated.
Now consider the other ball:
If it is like a tennis ball or something like a football the destruction of the ball and the ground would be much less. Little energy would be lost. If the ground is hard the ball would be compressed at the time of impact and its decompression would make it bounce up. Yes, even the earth would move a bit but because of its infinitely greater mass this would be minuscule, even though after the collision the momentum of the earth and the ball would be equal and opposite. There might be a little loss in heat and sound, but not much. What I have said for the two balls mentioned above would also apply to a stiff plastic ball.
Why does the earth spin?
The earth was probably born through condensation of a large cloud of gas and dust that was spinning slowly. You might justifiably ask: “Why was cloud spinning?” The answer to that is that the probability of zero spin is zero. A small spin in any direction is amplified during condensation in order to conserve angular momentum. If you have seen a movie of an ice skater you would recall that when a slowly rotating skater pulls in her arms she begins to rotate very fast. Readers wanting to ask Prof Yash Pal a question can e-mail him at palyash.pal@gmail.com |
