SCIENCE TRIBUNE Thursday, December 20, 2001, Chandigarh, India
 

Water-proofing building roofs
G. S. Dhillon
I
T is a basic human desire to have a sound roof over his head. But if the provided roof starts leaking, it causes him great concern and he wants to take steps for water-proofing the roof without delay. Though the task of water-proofing a roof may seem to be simple, but in reality it is one of the most complex problems. This is on account of diverse methodologies of construction and materials used in construction and also the varying degree of care and supervision exercised during its construction. On account of several factors, some cracks in the roof may have been formed which may also need attention.

  • Crack sealants
  • Product available

Copper oxides as super conductors
S. P. Gupta
I
NJECTING electrons into the surface layers of materials has now been applied to the most mysterious superconductor: the copper oxides. The discovery of superconductivity in copper oxide materials in 1986 led to an explosion of research into these compounds. They became known as high temperature superconductors because they have negligible resistance to electric current at temperatures up to 160 K, much higher than other materials known at the time. They continue to excite interest because many of their properties cannot be explained by the quantum theory of solids developed over the past 70 years. To many researchers it seems that something fundamentally new is afoot.

CT-scan risk to children
K. S. Parthasarathy
O
N November 2, 2001, the Center for Devices and Radiological Health of the US Food and Drug Administration (FDA) gave recommendations to reduce radiation risk from computed Tomography for paediatric and small adult patients. The February issue of American Journal of Roentgenology had an editorial titled “Taking Care of Children”. This was also in the context of using CT-scan Units for examining children. Till now the Journal published in 2001 eight important articles on CT scan doses.

NEW PRODUCTS & DISCOVERIES
Lamp that emits natural daylight
S
INCE natural daylight is not always available, the next best thing is a lamp that can bring its healthy benefits indoors. Verilux, an American company, has created the Happy Eyes Floor Lamp that simulates the balanced spectrum of daylight. You will see with more comfort and ease as this lamp provides sharp visibility for close tasks. Its 27-watt compact fluorescent bulb is the equivalent to a 150-Watt ordinary light bulb.

  • Computers to identify faces
  • Market’s mood in colour

SCIENCE QUIZ
J. P. Garg tests your IQ

1. Two young scientists, Dr Daizy R. Batish from Panjab University, Chandigarh, and Dr. Naveen Arora from the Centre for Biochemical Technology, Delhi, have been jointly selected recently for a national award for their significant contribution in the areas of environmental and biological sciences respectively. This prize will be presented to them early next year at Kurukshetra University. What is the name of the prize?

   
 
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Water-proofing building roofs
G. S. Dhillon

IT is a basic human desire to have a sound roof over his head. But if the provided roof starts leaking, it causes him great concern and he wants to take steps for water-proofing the roof without delay.

Though the task of water-proofing a roof may seem to be simple, but in reality it is one of the most complex problems. This is on account of diverse methodologies of construction and materials used in construction and also the varying degree of care and supervision exercised during its construction. On account of several factors, some cracks in the roof may have been formed which may also need attention. In addition, there may be expansion joints provided and some construction joints existing which may have to be suitably bridged over by the water-proofing material or other measures used.

The traditional or conventional modes used since the time the construction of buildings started are still in use and may have performed the task very well particularly if the case of small residential houses. These methods comprise of lime-terracing or the ‘mud-phuska’ combined with the burnt clay-tile cover. The latter mode is very common in this region whereas the former is popular in the eastern region of the country on account of the climatic factors in that region.

Polymer-modified bitumen in its current form was developed in Italy in early 1970s but came to be adopted in the USA around 1975. Two modifiers namely APP (Atactic Polypropylene) and SBS (Styrene Butadiene Styrene), which not only resulted in softening point temperature but also their response to temperature variations.

App’s crystaline structure gives it a definite melting point of 1490C, with rapid transformation from solid to liquid state. In contrast SBS modified bitumen gradually melts in the range of 1000C to 1200C temperature range. Its behaviour is characteristic of a rubber with cross-linked molecular material.

SBS modified membranes offer greater versatility in approach than APP modified material. APP modified membranes with high polymer content require torching for melting the material. But with their much lower polymer content SBS modified bitumen can be mopped at application temperature around 1000C.

Reinforcement in most of the polymer bitumen membranes available is in the form of fibreglass combined with non-woven polyester mat or high molecular high density polyethylene (HMHDPE). The reinforcement serves the purpose of providing an increased tensile strength and puncture resistance and also enhanced fire protection. It acquires the capability to bridge small gaps or cracks in the substrata and enhanced elongation capability. The provided glass-fibres result in better dimensional stability, fatigue resistance.

Top covers need be provided for the modified bitumen felts so as to increase their resistance to wear and tear particularly if the roof is to be used as a terrace. The provision of the top cover helps in setting a proper slope for drainage of rain water. Choice of top cover can be made from the list of materials such as patent stone bricks, burnt clay bricks or polymer modified concrete, and mineral granules, metalic foil and applied protective coating, depending upon the availability of the raw material and the cost in a particular location.

Crack sealants

The new sealants available are based on polymers and elastomers and they are more resilient and capable of accommodating stresses and strains developed in the different types of joints in varying conditions and provide a durable solution.

These sealants are based on butyls, neoprenes, PVC, plastisols, acrylics, poly-carbonates, poly-sulphates, polyurethanes etc. Selection of a proper type of a sealant for a particular application should be made after careful considering the perspective and movement capability and the joint size.

Movement capability of a sealant constitutes the most important criterion for selection of sealant. The other properties need to be kept in mind are its consistency, vertical sagging, self-levelling, tensile modulus, elongation, resiliency, adhesion and cohesion.

SBS modified bitumen compounds impart excellent flexibility at low temperatures and pass the pliability test even at minus 250C to minus 300C. Their elastic recovery is also very high, so the products provided with SBS modifiers are considered suitable for cold climates. The resistance of such products to UV radiations is also high, so considered durable for subtropical climates. In comparison the conventional Tar Felts become brittle and glass-like at cold temperatures.

Product available

Choksey Chemicals of Mumbai has introduced a polymer modified bituminous membrane which has a central core reinforcement and is coated or impregnated on both sides with polymer modified bitumen and fillers.

The modified bitumen membranes or felts described above are best suited for flat roofs. But curved roofs, arches, folded plate roofs, shells and domes another product, Beck Bond WPC 30 is best suited. This system comprise of aqueous epoxy primer, followed by a middle course of acrylic elastomer and the top coat of aliphatic coloured PU coating.

For exposed conditions the top coat of Beck Bond PU Excoat 25 is recommended for better UV resistance. This system provides a lasting water-proofing. The primer can be applied to slightly damp surfaces. The acrylic coat has got high elongation capability of 500 per cent, and so can bridge cracks and has got self-sealing effect against heavy rains. The system is available in attractive colours and glossy or matt finish.

In concluding it may be stated that if before laying the Modified Bitumen Felt for the purpose of water-proofing of the roof, the cracks are properly sealed, then we can expect a durable, water-proof roof over our head.
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Copper oxides as super conductors
S. P. Gupta

INJECTING electrons into the surface layers of materials has now been applied to the most mysterious superconductor: the copper oxides. The discovery of superconductivity in copper oxide materials in 1986 led to an explosion of research into these compounds. They became known as high temperature superconductors because they have negligible resistance to electric current at temperatures up to 160 K, much higher than other materials known at the time. They continue to excite interest because many of their properties cannot be explained by the quantum theory of solids developed over the past 70 years. To many researchers it seems that something fundamentally new is afoot.

The superconducting properties of these materials are known to be sensitive to the density of mobile electrons in the CuO2. Small changes in electron density can transform these materials from an insulating into a superconducting state. In the past, the electron density has been modified by adding impurities, a process known as “doping”. However, the impurities inevitably introduce disorder, which can changes the properties of the superconductor in a way that has nothing to do with changes in their electron density. Schon have developed a system in which an undoped copper oxide material can be made superconducting by injecting charges from a metal contact into the material. This technique makes it possible, for the first time, to investigate how the properties of a given copper oxide superconductor vary with electron density, without the complicating influence of disorder. Their charge transport is blocked because the energy cost of moving an electron from one atom to a second, where it experiences repulsion from existing electrons, is too large. Insulators of this type, including the copper oxide material studies by Schon and colleagues, are known as Mott insulators.

Superconductivity in copper oxides occurs when the number of electrons per copper atom differs slightly from the integer value that gives rise to a Mott insulator. It can be fractionally larger if it has been doped with atoms that add electrons to the CuO2 planes (electron doped) or smaller if it is doped with atoms that remove electrons from the CuO2 planes (hole doped). The superconducting state in “underdoped” copper oxides (those with relatively low levels of doping) has proved particularly difficult to understand. For example, angle resolved photoemission experiments have shown that characteristic excitation energies in underdoped copper oxides do not drop to zero at the superconducting transition temperature, as they do in conventional superconductors. Moreover, experiments using neutrons and scanning tunneling microscopes have established that charges in a doped Mott insulator have a tendency a cluster, separating themselves from the antiferromagnetic background into which they have been introduced and sometimes forming charged “stripes”. These stripes have been studied both experimentally and theoretically, but the role they play in the superconducting state remains unclear.

So, at the flick of a switch, schon can convert an insulating copper oxide compound into a superconductor. They find maximum superconducting — transition temperatures of 89 K for the hole-doped copper oxide and 34 K for the electrondeped one. These transition temperatures are not particularly high, but they demonstrate that the CuO2 layers are similar to those generated by chemical doping. However, because the mobile electrons exist in a single two-dimensional layer, it will be difficult to use many of the experimental techniques to study bulk samples of copper oxide superconductors, such as angle-resolved photoemission and neutron scattering. Conversely, the geometry of these samples may be better suited to other techniques. Tunneling experiments should work easily, for example, and we should look for further inspiration from studies of two-dimensional semiconductors, where the ability to tune exploited for nearly 40 years. The challenge will be to design experiments that exploit the geometry of these tunable-single-layer superconductors, opening the way to disorder free observations probing the nature of superconductivity in the copper oxides.
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CT-scan risk to children
K. S. Parthasarathy

ON November 2, 2001, the Center for Devices and Radiological Health of the US Food and Drug Administration (FDA) gave recommendations to reduce radiation risk from computed Tomography for paediatric and small adult patients. The February issue of American Journal of Roentgenology had an editorial titled “Taking Care of Children”. This was also in the context of using CT-scan Units for examining children. Till now the Journal published in 2001 eight important articles on CT scan doses.

In view of its safety significance the Atomic Energy Regulatory Board intends to bring the FDA notification to the notice of CT scan users. Till 1997, AERB had collected addresses of 337 CT Units in India. As on May 31, 2001, Kerala alone has 75 Units. These are expensive pieces of equipment. So they are used fully at all institutions.

In many countries, though CT examination may account for only a small percentage of the national total of all X-ray examinations, the collective doses due to these procedures are highly significant. According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), CT accounted for only 2% of X-ray examinations in UK but the collective dose from these was about 40%. The data from eight other countries showed similar pattern.

CT scan examinations are immensely useful in diagnosing diseases and trauma and in the guidance of interventional and therapeutic procedures. But these benefits are not without risks. The individual risk from X-rays associated with a CT scan is quite small compared to the benefits of diagnosis, but it is important to keep the radiation doses during medical X-ray procedures as low as reasonably achievable.

Avoiding unnecessary medical X-ray exposure is particularly important when the patient is a child as they are at relatively greater risks than adults are. Children have more rapidly dividing cells than others. They have longer life expectancy. According to the US National Research Council’s committee on Biological Effects of Ionising Radiation, children less than 10 years of age are several times more radiation sensitive than middle aged adults. When a CT scan is performed on a child or small adult with the same technique factors that are used for a typically sized adult the small patient receives significantly larger dose than the adult. The exposure is not done knowingly or intentionally. Radiologists or technicians may simply be unaware of the potential dangers from higher doses.

In conventional X-ray procedures, if a patient is overexposed the medical personnel may recognise it as an overexposed film producing a darker image. Such evidence will not be obvious, if a patient is overexposed in a CT scan procedure because the quality of the image may not be compromised. The public health notification from FDA recommends that the CT scanner parameters should be adjusted appropriately for patient size.

The radiation dose can be reduced significantly without compromising clinical efficiency. The radiologist must evaluate whether the CT operating conditions of his equipment are optimally balanced between image quality and radiation dose. Reducing the tube current can reduce patient dose. The X-ray specialist must prepare and use a chart or table of current settings based on patient weight or diameter and anatomical region of interest. Medical physicists and scanner manufacturers can help in developing this chart. Increasing the table increment (axial scanning) or pitch (helical scanning) can reduce the radiation dose.

According to the FDA report, often CT scans are done before, during and after injection of contrast material. If it is medically appropriate, eliminating pre-contrast images may reduce multiple exposures. The FDA report pointed out that in some cases, conventional radiography and other techniques such as sonography or magnetic resonance imaging (MRI) could be just as effective as CT. Eliminating inappropriate referrals or using procedures with less or no ionising radiation is equally important.

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NEW PRODUCTS & DISCOVERIES
Lamp that emits natural daylight

SINCE natural daylight is not always available, the next best thing is a lamp that can bring its healthy benefits indoors. Verilux, an American company, has created the Happy Eyes Floor Lamp that simulates the balanced spectrum of daylight.

You will see with more comfort and ease as this lamp provides sharp visibility for close tasks. Its 27-watt compact fluorescent bulb is the equivalent to a 150-Watt ordinary light bulb.

This makes it perfect for activities such as reading, writing, sewing and needlepoint. For artists, the lamp can bring a source of natural light into a studio, and show the true colors of a work. This lamp has a flexible gooseneck design for maximum efficiency and two levels of light, with an “instant on” switch that is flicker-free. The high fidelity electronics, ergonomically correct design, and bulb that lasts five times longer than an ordinary bulb makes this an unusual product. It retails for about $ 130.

Computers to identify faces

Researchers are developing a procedure which enables computers to identify faces and their expressions, thereby holding a potential to develop into an application involving man-machine interaction.

The procedure being developed by the scientists at the Fraunhofer Institute for Integrated Circuits IIS works on the principal of “edge evaluation fields”.

“Each image can be represented using the evaluated edges. The direction and intensity of the edges denote the borders of the object and its distinguishing features, for example, how the shape of the face or parts of a face — eyes, nose, mouth — stand out against the background. At these edges, the intensity of the individual pixels changes,” explains Dr Christian Kublbeck of the IIS. The procedure benefits from the employment of gray level image-evaluation which means the system is considerably less reliant on lighting conditions. Colour calibration obviates the need for brightness adjustments. PTI

Market’s mood in colour

Scientists are working on a technique which promises to yield information for designers of consumer products in the global markets by measuring the mood of the marketplace from colour.

Researchers claim that if beauty is in the eyes of the beholder, it should be possible to measure it since the human eye is a physical mechanism which responds to objectively measurable stimuli.

Different colours create different subjective reactions in the viewer and they have demonstrated how the emotional “value” of a particular shade can be assessed.

Work done by Dr Jim Nobbs and Dr Alison Gilchrist of the Department of Colour Chemistry at the University of Leeds, northern England, makes possible the prediction of the average response that a given colour will evoke in a country, a report in British Commercial News said.

An individual’s emotional response to colour depends on a range of variables that include experience, education and culture. Accordingly, colours can be perceived as, for example, warm or cool, soft or hard, dynamic or passive, vivid or sombre. PTI

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SCIENCE QUIZ
J. P. Garg tests your IQ

1. Two young scientists, Dr Daizy R. Batish from Panjab University, Chandigarh, and Dr. Naveen Arora from the Centre for Biochemical Technology, Delhi, have been jointly selected recently for a national award for their significant contribution in the areas of environmental and biological sciences respectively. This prize will be presented to them early next year at Kurukshetra University. What is the name of the prize?

2. A set of three trees called “Triveni” in Indian culture are known for their medicinal and environmental values. What are these three types of trees?

3. We know atoms contain three types of particles. Which of these particles can be further subdivided? Which not?

4. Having main ingredient olein, this oil is rich in mono-unsaturated fatty acids, compound cycloarthanol, antioxidants polyphenols, vitamins E and K, etc. It is used for cooking in soaps, medicines, perfumes and cosmetics, and as a massage oil. Which is this oil that is useful for heart patients, lowers blood pressure, protects against ageing and cancer, strengthens brain and nervous system, and helps in some other ailments?

5. Name the bird that can fly throughout the day without flapping its wings even once.

6. A new catalyst, called POM, will soon make paper industry eco-friendly. In the conventional method, bleaching of the pulp (used to make white paper) is done with either chlorine or chlorine dioxide, which releases toxic chemicals in the environment. Use of POM for this purpose releases chemicals which are non-toxic. Can you think of the full name of POM?

7. Aspirin has been used to reduce headaches, fever, certain types of cataracts, arthritis, etc. Now it has been found that it also helps people with diabetes, obesity and blood pressure. From the bark of which tree was aspirin obtained earlier? What is modern aspirin chemically? Who synthesised it about 100 years ago?

8. Patients with skin problems are sometimes advised to sit in sun rays in the morning. Which type of radiations coming from the sun produce vitamins in the skin?

9. The image of an object is found to be virtual, erect and diminished. Near which optical device is the object placed?

10. INMARSAT is an international organisation which provides worldwide communication and other services via satellites to ships and offshore platforms. What is the full name of this organisation?

Answers

1. Rajiv Goyal prize for Young Scientists 2. Bohar (banyan), peepal and neem trees 3. Protons and neutrons can be subdivided into quarks; electrons cannot be divided further. 4. Olive oil 5. Albatross 6. Polyoxometalate 7. Willow tree; acetylsalicyclic acid’ German chemist Flix Hoffman 8. Ultraviolet radiations 9. Convex mirror 10. International Maritime Satellite Organisation..

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