Thursday, July 19, 1998
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Thursday, July 19, 1998 |
| Infrared imaging makes things
smarter From missile guidance to microwave cooking to medicine, infrared imaging has become a valuable tool for measuring temperature... New products & discoveries Magic
of astro-festivities |
Infrared imaging makes things smarter From missile guidance to microwave cooking to medicine, infrared imaging has become a valuable tool for measuring temperature by H.S. Jatana WHERE’S the heat coming from? The answer to this, and other often-asked, thermally related questions, now may be readily obtained with visual infrared (IR) imaging of temperature gradients. IR imaging can collect and store much more data quicker and over a greater temperature range than thermocouples or liquid crystals. And because it is a noncontact technique, it can do so without any risk of affecting the temperature of the object it is measuring. Research and development applications for this relatively new, nondestructive, thermal measurement technique are increasing at a rapid rate. Most recently, infrared themography earned its stripes in the shortlived Persian Gulf war. It was, in fact, largely responsible for the war’s brevity, as IR — equipped aircraft and tanks found their Iraqi targets with unerring accuracy. The efficiency of these missiles was due to data encoded on chips in the minicomputers which guided them. The data, consisting of thermal profiles or signatures of the targets, were gathered using infrared imaging. And after that, IR played a role in cleanup following the Gulf war, as well as in such places as Afghanistan. Researchers at Lawrence Livermore National Laboratory have perfected a way to use the technique to detect buried land mines from the safety of a helicopter. The patented Livermore technology is incorporated in a dual-band IR scanning system with real-time, 12 bit digital processing and display. It creates color-coded images based on surface temperature variations as small as 0.2C. Unlike other less sensitive methods, it is able to map true temperatures because it can remove the surface emissivity mask that hinders interpretation of the temperature of objects under a surface. The technique is able to identify surface temperature patterns resulting from small diffusivity changes of buried objects which heat and cool differently from their surroundings. Objects made of different materials and buried at different depths are identified by their unique spectral, spatial, thermal emissivity and diffusivity signatures. In general, the infrared energy radiated by all warn or hot objects is focussed by an infrarred lens onto an oscillating mirror, passed to a synchronised horizontal polygon, filtered and focussed onto a single multi-element detector. The detector element, which operates at 77K or less, produces an electronic output signal which varies in proportion to the radiation from the object. The signal is amplified within the scanner unit and produces a video signal which is fed to a monitor where it can be viewed in distinctive color shades. The evaluation of an IR imaging system often hinges on the quality of its camera, and is based on such factors as sensitivity, the temperature range it operates within, and how much temperature data it can capture. All of these affect the resolution of its image and the accuracy of its data. Also important are the speed and efficiency with which the camera can transfer its information to the recording unit for storage and analysis. The earliest IR equipment took over 10 min just to get an image, so long as the object didn’t move. Today’s more advanced systems can capture and record an image of a moving jet airplane in real time! For most temperature studies, it’s not particularly important to know within which part of the infrarred spectrum the camera operates. Although long-wave bandwidth (8 to 10 um) cameras enhance sensitivity for extremely low temperature measurements and have a greater range in surveillance applications, short wave cameras provide better image contrast. Also their detector materials are considerably more rugged, and therefore better suited for the rigorous measurement standards found in industrial and research environments. For defence — related applications requiring maximum spectral flexibility and s\ ystem response, such as rapidly moving objects or fast evolving temperature changes, a dual system combining a short and long bandwidth scanner is often configured. The output data is electronically coupled for display and analysis. Infrarred measurement systems for R&D use are not selected solely for the resolution and accuracy of the images that their cameras can achieve, but also for their ability to capture and transmit their data for immediate or later analysis as quickly as possible and with minimal loss in definition. To do this, most infrarred systems rely on a controller/recorder unit to digitize and store their camera’s signal. All operational modes including scanner mode and remote focus, range and level are also handled from the system controller. The versatility of IR systems is truly impressive. For example, researchers are studying the feasibility of using infrared scanners in a production environment to detect faults in printed circuit boards. The technique has already proven its ability to identify such faults as improperly fastened, misaligned, or defective components by analysing the temperature distribution across the board. All of these might go undetected in routine circuit testing. At Lockheed Aeronautical System, Marietta, IR is used to develop a practical and repeatable technique for verifying the quality of composite materials used in airframes for the US Dept. of Defence. The remarkable combination of strength and light weight of such composite materials as graphite/epoxy/fibreglass/urethane and carbon/carbon lamination as well as kevlar and Nomex honey combs, is giving them a greater role in aircraft designs, where both tremendous strength and light weight are essential. IR is also being used to observe the effect of different package designs and constructions on the heating rate and distribution of foods cooked in a microwave oven. And food manufacturers use IR to determine the moisture contents required to ensure that the various courses in a TV dinner heat-up and cook evenly. IR imaging technology also benefits medically oriented investigations. The US Army Research Institute is using infrared to assist in a variety of projects on the pathogenesis, treatment, and management of such major cold injuries as trenchfoot, frostbite and hypothermia. One of its earlier uses was to evaluate the effectiveness of a treatment for individuals suffering from Raynaud’s disease, a peripheral blood-flow problem resulting in extreme cold sensitivity in the hands and feet. A recent study was performed on Argentine troops injured during the Falkland Islands conflict. Unfortunately, because of the abysmal weather conditions, low temperatures, and immobility of the troops, the environment provided an ideal incubator for trenchfoot. As part of this study, the US Army researchers determined that after seven years, not only do the residual effects of trenchfoot still exist, and are exemplified by a decreased surface temperature of the affected extremity, but also that a significant percentage of the normal population may also be at risk for cold injury. Conclusion
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New products & discoveries Optical amplifier American researchers have developed a new amplifier to boost capacities of currently overloaded networks such as the Internet. The ultra-wideband, erbium-doped, silicafibre amplifier, developed by Lucent Technologies, provides a seven-fold increase in bandwidth over current commercial systems, reports Optics and Photonics News. According to team leader John Zyskind, the new amplifier builds on current erbium-doped amplifier technology, but takes advantage of a new two-state architecture that provides two spectral bands following parallel paths. The first band, known as the C-band, operates between 1525 and 1565 nanometres (nm), while the second, known as the L-band, operates between 1570 and 1610 nm. To combine transmitted signals and then separate them at the receiver, the device used broad-band fibre Bragg gratings. This device offers more capacity to network backbones as well as reliability because it is based on a proven technology, explains Zyskind. When this technology is used at a data rate of 2.5 gigabits per second (gbits/sec) per channel, it can transmit enough data for 5,000,000 telephone calls or 100,000 movies on a single fibre. At 10 gbits/sec per channel, this translates into 20,000,000 phone calls or 400,000 moves. By routing the signal channels according to the wavelengths, the networking capability can also be enhanced, says Zyskind. The new devices can be used with existing fibresystems. Additional receivers and transmitters would be required at central offices to accommodate additional channels made possible by the new amplifiers, the report says.  |
Robot’s next steps The successor to Honda’s P2 humanoid robot, the P3, is more coordinated. Standing at about 5 feet, it adds 3-D vision to move more independently, correcting its balance while changing direction. The P3 is dexterous enough to climb through a manhole cover and it is stronger than a human — so it could be of service in a nuclear power plant or medical facility. |
Free software on Internet The Department of Electronics (DoE) has launched softwares for Indian languages free on the Internet as part of a national initiative to promote information technology in Indian languages. Internet users can now freely download two specific softwares — ALP-Personal and Leap-lite word processors for major Indian languages — from the website of Centre for Development of Advanced Computing (C-DAC) based in Pune. The ALP-Personal is DOS-based, while Leap-lite operates on various versions of Windows operating system. The softwares can be downloaded using the "anonymous file transfer protocol (FTP)". These two softwares are among several others developed by C-DAC to popularise use of computers in Indian languages. |
Gallbladder surgery Keyhole surgery has made one more progress in the hands of Japanese surgeons who have performed gallbladder surgery using a tiny jet of water instead of a knife. The surgeons have dissected gallbladders for 72 patients with waterjets pumped along tubes inserted through the abdomen. No patient developed any complications such as injuries to the liver, hepatic artery and common bile duct. The waterjet dissector, developed by doctors of Kitasato University, is meant for laparoscopic surgery in which the surgery is done using miniature tools inserted through three or four tiny holes in the abodomen. |
Magic of astro-festivities by Rajesh Kochar THE gaiety and revelry of Holi neatly masks the fact that what we are celebrating is the ending of a year. When we exchange wishes for a happy new year on the first of January, we are talking of one particular calender that is the Gregorian calendar, named after Pope Gregory XIII who established it in 1582 by correcting the older, Julian calendar. Although the Gregorian calendar is now globally used for civil purposes, most Indian festivals are determined by another calendar, often called the Hindu calendar. It is, however, more appropriate to use a non-sectarian, scientifically descriptive term and call it the Siddhantic calendar, because this calendar, in vogue for the last 1500 years or so, is based on ancient astronomical texts called the Siddhantas. The Siddhantic calendar is one of considerable complexity, as any one trying to deep track of Hindu religious festivals would have noticed. (Recall the Hindu idiom Meen-Mekh Nikaalana, "quibbling about zodiacal signs, Meena and Mesha") The Gregorian calendar uses a tropical year, but delinks the month from the moon, so that its month can be of arbitrary duration ranging from 28 days to 31 days. The Hejira calendar (the religious calendar of the Muslims) does away with the tropical year altogether and uses the lunar month as the basic unit. This is why Muslim festivals rotate through the year. The complexity of the Siddhantic calendar arises from the fact that it insists on retaining both the sun and the moon as time-keepers, sun as the year-maker and moon as the month-maker. A lunar month or a lunation is the period from say one new moon (amavasya) to the next. It is about 29 days and a half in length. Obviously, a year of 365 days cannot contain an integral number of lunations. A Siddhantic year, therefore, consists of either 12 or 13 lunar months. There are a number of geographical variations in the Siddhantic calendars in use in India. The basic astronomical principles are as follows. The benchmark for the Siddhantic calendar is the Meshasamkranti, the ingress of the sun into the zodiacal sign of Mesha (Aries). This Samkranti is better known in Punjab as Baisakhi (13/14 April). In about AD 300, Baisakhi actually coincided with the spring equinox, although now, thanks to the phenomenon known as the precession of equinoxes, the spring equinox occurs about three weeds earlier (about March.22) The aim of the Siddhantic calendar is to begin the new moon just year near the spring equinox. It is,however, a theoretical calendar whose elements have been derived by calculation rather than observation. Fixated at AD 300, it even now takes Baisakhi to symbolise the spring equinox. The Siddantic new year begins on the new moon just preceding Baisakhi. The year beginning is marked by a nine-’day’ celebration, called the navaratri. (The "day" here is in fact a tithi, one thirteenth of a month). The last navaratri is Ramanavami. The reason why Ramanavami and Easter both come close together is that both are related to the spring equinox. (Easter is observed on the first Sunday after the full moon following the spring equinox day). Six months later, another navaratri celebration comes, this time associated with autumn equinox. after the navaratri comes Dasehra. The following amavasya is Divali. The full moon immediately after Divali is Guru Nanak’s birthday. The last full moon of the Siddhantic year is celebrated as Holi. Like Baisakhi, there is another major festival not connected with the moon. It is Lohri, formally called the Makara-samkranti, the ingress of the sun into the zodiacal sign of Capricorn. The reason why Christmas, Gregorian new year and Lohri fall so close together is that they all seek to commemorate the winter solstice (about 22 December). Notwithstanding the progress made in science in general and astronomy in particular, it is ironical that today laypersons know much less about the visible sky than their ancestors did. It will perhaps be worthwhile to remember that many of our rituals and festivals today are a relic of the times when curiosity about the cosmic environment went hand in hand with fear of the celestial gods and desire to appease them. |
Computerised tomography by Deepak Bagai COMPUTERISED tomography (CT) was discovered in 1972 by G.N. Hounsfield. The X-ray technique involves the exposure of a photographic film by placing the object between a photographic emulsion and an X-ray source. The limitation here is that once the photographic image has been taken no other information can be gained from it regarding the state of the object. The CT equipment penetrates the object/body with a thin, fan shaped X-ray beam while the scanner produces a cross-sectional view of the tissues inside. Traditional X-ray radiographs view the body from only one angle and are difficult to interpret when the shadows of bones, muscles and organs are super imposed on one another. Large molecules like calcium absorb X-rays as they penetrate through the body, partially masking whatever lies behind them. CT machines view the particular part of the body from many angles by revolving an X-ray tube around the patient. Sensitive detectors on the opposite side store what the scanner sees and finally the computer compares the different views to generate a single video image. Since the CT machines make use of X-rays only in the form of short pulses, the effect of X-rays on the patient is also kept within limits. The cross-section of the object to be imaged is divided into tiny blocks, (called voxels) and a matrix is formed. The matrix can be 80x80, 160x160, 320x320 etc. Increase in matrix size results in improved resolution of the image but this requires more time for image processing. The computer assigns each voxel a number proportional to the degree that the voxel has attenuated the X-ray beam passing through it. Once the voxel has been given a numerical value, it is called a pixel. Each voxel is analyzed by the X-ray beam coming from different positions resulting in numerous ‘positional equations’. The final picture is produced depending on the linear attenuation coefficients of various voxels obtained from the solution of positional equations. In spite of various beenfits of CTscan, there are times when the need for a different imaging method viz. MRI is strongly felt. The writer is Asstt. Professor, Department of Electronics, Punjab Engg. College, Chandigarh. |
| Tailpiece Teacher: Name a liquid that does not solidify. Pupil: Hot water. |
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