Category Applied Science & Technology

The cordless phone is an FM transmitter/receiver. The frequency range lies between 26.6 and 49.8 MHz A cordless phone essentially converts the audio signals from the telephone line into the FM waves and it is detected by the mobile handset, and vice versa. For security reasons the range is limited to about 100 metres and their power is about 500 milliwatts. Each cordless phone is assigned a particular channel (or frequency range) to avoid interference with nearby instruments. 

Cordless phone is based on wireless transmission and frequency modulation. The main components of a cordless phone are the base unit and the portable unit. While the base unit is kept at a fixed point, connected to power supply and the working telephone line, the portable unit can be carried to a certain distance, depending on the frequency range limitation. Normally in India, the permissible distance is about 100 metres.

 The base unit and the portable unit essentially consist of radio wave transmission and reception devices which enable a two way wireless communication between these units.

The radio waves are broadcast in the air through the antenna fitted to the units. Just like the signals emanating from the telephone are converted to radio frequency in the transmission side, the reverse happens in the receiver side, (i.e.) the radio frequency signals are converted into original signals, bell or speech.

 Since the handset does not have and connecting cord or wire, the name cordless phone.

    In normal telephone exchange systems, a pair of wires extends each telephone instrument to the telephone exchange.

Normally, copper conductors are used to give loop to indicate the exchange that the telephone hand set had been lifted for making a call or for receiving a call. In advanced countries, Optical Fibre is also used or for extending the loop.

When you make a call to your friend who is connected to another exchange, the digits are sent to the exchange to which you are connected, in the form of pulses (break and make of loop) or frequencies.

The originating exchange analyses these digits and establishes a path to the terminating exchange where your friend is connected. Over this path, signals (some of the digits dialed by you and other technical information) are sent in the form of bits or frequencies. 

The terminating exchange analyses and marks your friend’s line and if it is free, a ring is sent to him and ring back tone is sent to you. When the call is answered, metering takes place.

In the cell phone system, there is no permanent wire connection between the instrument and the mobile telephone exchange. The connection between the instrument and mobile exchange is established via an intermediate station called Base Station (BS) where a transmitting tower is erected. The connectivity between the mobile exchange and the BS may be wire and between BS and Cell Phone is a Radio Channel.

The connection between a mobile exchange and another mobile exchange or public telephone exchange is by wire.

 Cell phones are technically called Mobile Station (MS) and its telephone exchange is called Mobile Switching Centre (MSC). The radio channel for both-way voice and control channel for controlling are established between BS and MS whenever required only.                                

A town or an area is divided into smaller areas called Cells. At the centre of the cell, there exists the Base Station (BS). When the MS moves around inside the cell, the signals including voice will be strong. When you use a cell phone to talk to your friend with conventional phone, you will   be connected to the BS over a booth-way Radio channel. From BS to MSC over a copper cable or Optic Fibre cable, from MSC to another Exchange and further to your friend over a copper cable

            As you are moving and when you enter into another cell, old BS reports to MSC that you have left the cell and your signals are weak. Immediately, the MSC orders all other Base stations to search for a new comer (as far as other cells are concerned, you are a new comer).

 The BS which is very near to you reports to the MSC that it has found a new corner with strong signals. The MSC orders the old BS to hand off (you) to new BS. Handing off is done in less than 400 milliseconds. But you do not feel any disturbance in your conversation. You may cross many cells during your long conversation without knowing that so many hands off have taken place. Each cell phone is associated with a unique identity stored in Subscriber Identity Module (SIM). This identity is sent to MSC through Base Station when ‘Send’ button is pressed.

The MSC analyses this and validates as to whether cell phone is authorized to make a call. If yes, the call will be put through. When there is an incoming call to the MS, first it is received by the MSC. MSC analyses the received information that contains the MS number also. This number is paged in all cells. If the MS is kept powered on, a page response is received on the control channel from the MS. A voice channel is allotted by MSC. BS and MS are ordered to tune to that channel. Once tuned through connection information is returned to the caller who gets ring-back tone. Ringing is initiated in the MS. When the MS answers, conversation can start and metering starts in MSC.

         Earth rotates from west to east causing the Sun, the Moon, stars and other planets rise from east and set in the west. On the surface of the earth each point is moving eastward with respect to an astronaut in space.

            Thus if a rocket is launched at a small angle eastward vertically the speed of earth gets added to the rocket’s speed. This reduces the amount of fuel required. If the rocket is inclined along any other direction, the speed of the earth gets subtracted from the speed of rocket and will necessitate burning of more fuel.

            In addition, in case of any failure during launch the rocket will fall back to the earth. Hence if it is launched from the east coast, the rocket will fall into the sea only. If it is launched from the west coast, in case of failure, the rocket will fall on the land endangering human habitats. Thus choosing eastward inclination is scientific but choice of eastern coast concerns safety.

            A small amount of air is trapped and pressurized when the fixed end of the thumb and the free end of the middle finger are brought together. When this pressurized air is released suddenly during the clicking it produces a sound as in the case of a balloon burst.

Sound is caused by the cracking of knuckles when a bubble which has formed in the lubricating fluid (the synovial fluid) which surrounds the two bones of the knuckles bursts.

Normally there is a lubricating fluid which prevents the two bones which forms the knuckles from grating against each other. This fluid contains tiny bubbles which cannot be seen by the naked eye.

So when the knuckle bones remain close together the fluid is under pressure and the bubbles remain tiny.

But when one clenches his fist, the bones are pulled apart which causes the bubbles to join together to form one large bubble. Then when one works the fist, the pressure changes and makes the bubble to burst which then produces a loud cracking, noise. Doctors are not sure whether cracking them is harmful or not, though there is a belief that cracking ones knuckles could make them large and unsightly.

TFM is the abbreviated form of ‘Total Fat Matter’ in soap. According to the provisions of the Drugs and Cosmetic Rules, in all toilet soaps, the TFM content has to be mentioned in terms of percentage on the wrapper of the product apart from the other details required under the rules.

The standard fixed by the Bureau of Indian Standard (formerly I.S.I.), the ideal and safe percentage of TFM in any toiletry preparation should be between 60 and 80 per cent.

However, having been unsure of the standard, even many of the reputed soap manufacturers have omitted ‘toilet soap’ from their name and simply state ‘bathing bar’. Similarly shaving soaps are marketed as showing creams without mention of TFM content.  

Water boils at 100°C at sea level. The atmospheric pressure which acts on water is 14.7 psia (pounds per square inch –absolute).  This atmospheric pressure varies with the altitude. So the boiling point of water is influenced with respect to the atmospheric pressure. Perfect vacuum is ‘O’ psia.

Any pressure between 14.7 psia and o-psia is ‘negative pressure’ that is, partial vacuum.

Vacuum drying takes advantage of the decrease in the boiling point of water that occurs as the pressure is lowered. This type of drying keeps the products with very low moisture content. If salt water is subjected to this negative pressure, the water will boil by taking the heat from the ambient. In case of reducing atmospheric pressure, i.e. 14.7 psia to 0.15 psia, water will start boiling at  C itself.

Freeze drying, convection drying, microwave drying, dielectric drying, conduction drying, U-V radiation drying, etc, are some other drying methods applied in various industries such as textile, plywood manufacturing, paper products, production of dried milk, soaps, detergents, pharmaceuticals, serums, bacterial and viral cultures, vaccines, fruit juices, vegetables, coffee and tea extracts, sea foods, meats, cereals etc. 

Trains are generally equipped with vacuum brakes. In steam locomotives, ejectors help create the vacuum and in diesel and electric locomotives, air-compressors and vacuum exhausters are used.

Pipes passing through the underside of coaches are connected to vacuum cylinders (provided in the coach) which help maintain a vacuum throughout the length of the pipe. The pipes (of each coach) are then linked.

When the train is on the run, a vacuum of about 20-22 inches per square inch is maintained throughout the system (atmospheric pressure is 30 pounds per square inch).

 When the driver wants to stop the train, he gradually allows air to enter the vacuum pipe and activates the pistons of the vacuum cylinders which help to apply the brake.

For emergency application of brakes by passengers, coaches are provided with alarm chains connected to the vacuum system. When the chain is pulled, a small valve open up and allows air to enter the system slowly, gradual application of the brakes.

Direct admission valves are provided in each coach near the vacuum cylinder and they help in the uniform application of the brake throughout the train.

Anything that is formed without the act of fertilization is biologically called “vegetative”. The term “vegetative” is more appropriate to the plants but not for animals. But it has become customary to term the unfertilized eggs of hens as vegetarian eggs since they are formed without the fusion of sperm.

Country breed birds lay fertilized eggs. Such eggs are laid a week or more after the cock has mated the hens, but white leghorns which are suitable for egg production lay only unfertilized eggs as they are not allowed to mate with cocks. The leghorns are genetically improved birds which produce through successive generations under improved breeding methods.

Nutritionally there is no difference between a vegetarian egg and an ordinary egg, but in certain physiological characteristics they differ. Leghorn eggs cannot be incubated, but eggs of country breed can be incubated. Such hatching eggs deteriorate with storage and therefore should not be stored beyond seven days, while leghorn eggs can be stored for several days.

The eggs of poultry bred leghorn birds are larger in size, with more amount of albumin and always white in colour. The eggs of country bred birds are smaller in size and have less amount of albumin and the shell colour may vary from white to pale straw yellow colour. The natural feeding habit of these birds is the only reason for these characteristics.

Eggs are egg-shaped for several reasons. First, it enables them to fit more snugly together in the nest, with smaller air spaces between them. This reduces heat loss and allows best use of the nest space.

 Second, if the eggs roll, it will roll in a circular path around the pointed end. This will reduce the danger of the egg rolling out of the nest. Moreover le strongest shape would be a sphere, but spherical eggs will roll away, and this will be unfortunate, for birds that nest on cliffs.

Most eggs will roll in a curved path, coming to rest with the sharper end pointing uphill.

There is in fact a noticeable tendency for the eggs of cliff-nesting birds to deviate more from the spherical, and thus roll in a tighter arc.

Third, an egg shape is more comfortable for the bird while it is lying, rather than a sphere or a cylinder. Other shapes have structurally weak points and edges. Finally, another important reason is that hen’s eggs are the ideal shape for fitting into egg cups and egg holders on the fridge door. No other shape would do.

Food poisoning is caused either by ingestion of food contaminated with chemical or metallic poisons, bacteria or bacterial toxins or by eating poisonous foods such as certain species of mushrooms.

Molds and bacteria are responsible for microbial food poisoning. Molds grow on food (especially if they are moist). During their growing period they produce toxic substances called mycotoxins whose effect on man and animals cause mycotoxicosis. Mycotoxins remain the food long after the mold producing them has died and can therefore be present in foods that are not visibly moldy. Some mycotoxins are stable and survive the usual conditions of cooking and processing.

Food grains, especially bajra, rye and jowar get infected with a parasitic ergot fungus Claviceps purpurea. Ergotism, a toxicosis results from eating grains contaminated with this fungus. Alimentary toxic aleukia (ATA) is another mycotoxicosis caused due to eating moldy grains.

 Asperigillus flavis and A. parasiticus growth in food results in the production of aflatoxins. This mycotoxin has been much studied. There are 14 chemically related toxins and one of them aflatoxin-B is most frequently found in food and is the most potent carcinogen known. Liver cancer due to aflatoxin ranks high in India.

Over 50 genera of bacteria have been associated with food poisoning. Bacteria cause food poisoning in two ways; due to food infection or intoxication. The former is on account of the organism present in the food during consumption. Salmonella species, vibro, parahaemolyticus, Escherichia coli, yersinia enterocolitiea, clostridium perfringens and Campylobacter jejuni, belong to this category. The bacteria then grow in the host and cause a disease. For example, Salmonella in food causes an illness called Salmonellosis. Diarrohea, abdominal pain, vomiting and fever are caused by this type of poisoning.

The second type of poisoning is due to the toxins produced by bacteria in the food prior to consumption. Examples of this type are Clostridium botulinum, Staphylococcus aureus and Bacillus cereus. These produce toxins in the food which cause illness in susceptible hosts. For example the disease caused by the toxins of Clostridium botulinum is known as botulism. The toxicity will last for 6-8 months and disturb vision, speech and swallowing. Progressive weakness and respiratory failure set in.

              Poisoning of food due to contaminants arising from food processing is also common. For example when fumigant like ethylene oxide is used to sterilize food under conditions in which steam heat is impartial, it reacts with inorganic chlorides in food to form toxic compounds.

Food poisoning or intoxication usually refers to gastrointestinal diseases caused by the ingestion of food contaminated by pathogens and their toxins. The toxins are called enterotoxins because they disrupt the functioning of the internal mucosa, causing symptoms such as nausea, vomiting and diarrhoea. Mostly food poisoning is caused by bacteria and viruses.

            Cholera, an epidemic in various parts of the world is caused by Vibrio Cholerae, mainly through water and food contaminated by fecal material. Botulism is a form poisoning caused by Clostridium botulism. This common source of infection is canned food that has not been heated sufficiently to kill the contaminating C. botulinum spores.

Staphylococcal food poisoning is a major type of food intoxication caused by ingestion of improperly stored or cooked food (particularly processed meat, chicken salad, pastries, ice cream) in which Staphylococcus aureus grow.

Salmonellosis or salmonella food poisoning is caused by over 2,000 Salmonella serovars. The most frequent one in humans is S. Serovar typphimurium. Human acquire the bacteria from contaminated foods such as bee products, poultry, eggs and egg products.

Shigellosis or bacterial dysentery is caused by several species of Shigella. Normally it is transmitted by direct fecal-oral route although water and food are involved in some of bacterial dysentery. 

Paper is made of cellulose obtained from pulp of cotton lint, wood, straw and rag. Blotting paper is an unsized paper, since sizing agents are not employed in the manufacture of this paper. This is in order to retain the absorbent property, which is more in blotting paper. This absorbent property is due to the presence of more microscopic capillaries, which exhibit more capillary action resulting in the easy entry and spreading of any liquid, which come in to contact. Another property of blotting paper is that it is not hard, since it is manufactured without loading.

 The ordinary writing paper is a sized paper. So it is impregnated with sizing and coating materials. This prevents the incorporation of microscopic capillaries. These papers are permanence, resistant to ink penetration and better finish. Polyvinyl alcohol, carboxyl methyl cellulose, alginates and certain wax emulsions in combination with starch are also used as loading agents for the manufacture of these papers. Tissue papers are entirely different from ordinary writing papers and blotting papers.

Unlike these two papers they are very thin, glazed and sometimes slightly waxed. Even though tissue papers are thin, they are very strong. Since they are highly glazed they are transparent. These papers are specially made for the purpose of taking carbon copies and packing cakes and butter.

A blotting paper absorbs ink by capillary action which is a natural phenomenon exhibited by liquids in the attempts to reduce surface tension.

Any thin tube having a very fine ne bore (say, less than one mm) is called a capillary tube. When such a tube is immersed n a liquid rises inside the tube to a level higher than that outside it. (Only liquids which have an angle of contact less than 90 degrees will show a rise. Other liquids like mercury will show a dip.)

Blotting paper is made of cellulose obtained from the pulp of cotton linter, wood or straw. A purified pulp paste is directly pressed to form blotting paper sheets without any treatment. So as to incorporate microscopic capillaries. When such a paper is placed in ink, water or any aqueous solution, the solution immediately enter in to these capillaries and spreads all over the sheet.

Capillary action is also responsible for many common phenomenon seen in our everyday life. It helps plants in raising the sap from the roots to the top through the stem. It also makes kerosene or oil in wick tip where it is burnt. 

The problem lies in power to weight ratio of the bike. Bikes that use diesel as fuel are heavy in size. The power output from the diesel engine is high and more over noise and vibrations are at a high level, prohibiting them in common use.

Diesel cannot be used with 50, 100 and 150 cc engines, because of high power output. Diesel engine is a compression ignition engine where diesel injected into a cylinder of high pressure and temperature compressed air, under a very high pressure.

            Atomized diesel particles come through a tiny hole of fuel injection nozzle burn and release mechanical power output. Design and manufacturing of such minute mechanical parts, withstanding high temperature and pressure is not cost effective.

And usage of diesel demands heavier   construction   of all   structural parts to endure high   vibrations. The cost   is   also high.   If the engine   is   not   serviced properly and periodically the pollutants level emitted will be very high when compared to petrol engines. At present only Enfield India Manufactures motorbikes which use diesel as fuel.

Yes, Liquefied petroleum gas (LPG) can be used in petrol vehicles without any harm to the engine. On the contrary, many benefits to the engine are provided by the use of LPG. It is a clean burning gas without causing deposits to the combustion chamber. The octane rating of LPG is significantly higher than that of petrol. So it can bear higher compression ratio conducive to higher efficiency. But this can only be achieved in dedicated engines but not in converted engines as is the practice. The converted engine has to switch back to petrol when the supply of gas from the cylinder is exhausted!

Nevertheless, clean burning characteristics with lesser maintenance, absence of mal-distribution from cylinder to cylinder and cycle to cycle (unlike that encountered in petrol engines) will result in better performance both fuel economy-wise and emission-wise. There is no danger of benzene and other carcinogenic aromatics in the exhaust much less the much dreaded lead since it has naturally a high octane value.

 In the U.S, where there is intensive research on alternate fuel technology,  LPG or Propane, as it is called there, accounts for the largest number of vehicles working on this alternate fuel technology.

            There are two types of light duty vehicles: dedicated which operates exclusively on LPG and the dual fuel, which can operate on either LPG or petrol.

Bulk of LPG is propane with varying quantities of ethane and butane; such that it can he liquefied at ambient temperatures by pressurizing it to moderate range of 25 to 125 psi, depending on temperature. These pressures can be safely contained in simple thick-wall steel fuel tanks. This is in contrast to natural gas which must be pressurized to 3000 psi and stored in reinforced tanks, or chilled to minus 260 F and stored in double-wall cryogenic tanks.

Two crucial factors in the use of LPG must be borne in mind. First: Safety. Have sufficient safety measures been taken to prevent risk involved in case of an explosion of gas cylinder consequent to a possible disastrous collision? Look at the damages to innocent road user by careless installation of the conversion kit.

Has the government given a nod to this conversion taking into account whether or not the vehicle can be insured against the third party risk. A gas cylinder explosion can be as disastrous as a bomb blast! Next a moral obligation to society: Is there any chance that the LPG used is from the highly subsidized domestic sources. Let us learn from the experiences of adulterating petrol with the subsidized kerosene.

A scientific answer to this relevant question must also be in tune with the societal benefits of science to the community. Hence this is a warning note to the otherwise a commendable fuel from a purely scientific point of view.

Bond paper belongs to the class of paper called ‘writing’ paper. It is made of cotton rag pulp which gives it strength. It is also sized for opacity and toughness and the metallic sound. Bond paper is different in its non- absorbent qualities as it is well sized so as not to absorb water-based writing ink. It is also tough and strong due to rag content in the pulp.

The sizing may be animal or gelatin or tub sized as distinct from engine sizing used for printing paper. The word ‘bond’ owes its origin due to the fact that originally IOU’s or promissory notes (bonds) were widely using this rag content durable paper.

Smooth printing paper is used for photocopying to attract the toner powder. In the U.S, hardwood sulphite is beaten well and hydrated to produce bond paper. It produces crackle (sound) and results in a high mullen (tensile strength) bond paper which is water marked as ‘sunlit’, JK and ‘Executive’. They are used in making paper for insurance policies, stock certificates, bank notes and other important documents for longevity. There are machine dried and air dried bond papers. 

Not any more than eating enough of any other protein, according to dermatologists. If someone is severely protein-deficient, high-quality protein might make a difference, it is said. As an average person gets plenty of protein, it would take someone who was ‘malnourished or a food faddist, to see a real benefit.

 It’s the same case with calcium; it would help the nails if the person were totally deficient, but if one’s bones are falling apart the person would not care about their nails. To make a real difference in nail strength, it is said, they are to be treated as carefully as the skin is. If you moisturize your hands after you wash the dishes, for example, rub the product into the nails as well. Keep your nails out of harsh chemicals. Wear gloves to do housework.

People whose nails are really brittle might even wear latex gloves when washing hair. Nail polish and other drying nail care products are to be avoided. Polish covers nail abnormality but actually make it worse, according to them, but polish remover, even the kind without acetone, is incredibly drying to nails.

What if your nails split rather than break? There are two kinds of splitting, according to dermatologists. The longitudinal splitting is something that occurs with age. Ridges and valleys develop, and splitting occurs along fracture lines because the nails dry like the skin. Again, help for this problem lies in moisturizing. The nails are to be wet and covered with Vaseline or even alpha-hydroxyl acid, it is suggested. It is not a quick fix, but must be done until the nail grows out entirely which takes 6-8 months. The other kind of splitting, called onychoschisia, which occurs in layers at the tip of the nail, is something, dermatologists find most often ‘in chronic polishers or those who use fingernails as tools.’

Hairs are made of dead epithelial cells strengthened by a protein called keratin. Actually, epidermis (the upper layer of the skin) descend into the dermis (inner layer of skin) to form flask shaped structures. These structures hair follicles have a group of epithelial cells that form a bulb. Below this bulb is the dermal papilla or hair papilla which consists of connective tissue, supplied richly with blood vessels and connected by nerves. This region supplies nourishment to the root cells of the hair.

The epidermal cells of the hair root are very active and they divide rapidly. As new cells form, the old cells are pushed upwards in the form of hair.

Beyond the bulb region, the cells die and become horny with the addition of keratin. As the dead cells continue to add rapidly in the root, the shaft grows in length and pierces through the epidermal layer and projects out as hair. The hairs normally grow for about 18 cm in a year.

Thus the root is the only living part of the hair. Hence, when the hair above the skin is cut, we don’t feel any pain. But, if the hair is pulled out, because of the presence of the sensory nerves in the hair papilla, we feel the pain. A similar mechanism operates in the nail also. The root or matrix of the nail is made of soft epithelial cells and the growth takes place here as the cells are active and alive. As the cells grow the older cells are pushed out as the nail plate. Beyond the root region, the plate cells die and become horny again with keratin addition. Beyond the finger tip these horny cells project out as nails. From the root to the finger tip, the nail plate is connected to the underlying epithelial cells (nail bed), which are provided with blood vessels and nerves. When we pull this part out, we feel the pain, because the epithelial cells are also damaged. But beyond the finger tip, it is all dead cells and no pain is felt when cut. The nails grow to about 5 cm in a year.

Farm lands and fields are not smooth and hard like play grounds, and so the steering effort needed to be put in by a driver has to be more to drive a vehicle in them.

In case of tractors, the front wheels are meant for stability and steering only. They are small in size to aid in steering and to give a better view of the field to the driver. But the big rear wheels have specially designed tyres for an entirely different purpose – to give a better grip on the ground. Their larger surface areas in conjunction with a low air pressure (0.8 – 1.2 kg per square cm) ensure adequate contact area (and friction) between the tyre and the ground. This is necessary to increase the driving force in muddy fields.

If rear wheels are also small in diameter and width, their contact area with the soil surface will be small. This may, if the field is muddy, make the wheels penetrate and get bogged down in the mud, due to its own weight. If the wheels are large this cannot happen as a considerable amount of sand beneath the tyres has to be disturbed.

Lead in the form of tetra-ethyl lead (TEL) is added to petrol to suppress abnormal combustion called knocking.  High local pressure due to knocking results in excessive noise, power loss and eventual damage to petrol engines fitted to any motor vehicle – be it two, three, or four – wheeled vehicle. But the question posed apparently addresses two-stroke engines which are commonly used in two and three wheelers, accounting for nearly 60 percent of petrol consumption and discharging nearly 20 percent of raw petrol with lead directly into the atmosphere.

The unleaded petrol recommended for use in cars fitted with catalytic converters, can be safely used for any petrol vehicle. In fact, the use of unleaded petrol causes cleaner combustion without deposits on the chamber walls. These deposits caused by lead are known to hide raw petrol in their crevices and prevent them from combustion. These are discharged in the exhaust causing pollution besides higher fuel consumption. The engine also requires frequent decarbonising due to excessive deposits.

 In two stroke engines, the actual compression ratio is lower than the normal compression ratio, based on the ratio of cylinder volumes at the outer and inner dead centres, as the actual compression will not start until the piston covers the ports on the return stroke. So the probability of knocking in a two stroke engine with unleaded petrol is lesser than that in a four stroke engine of the same nominal compression ratio.

For leaded engines, the valves have to be coated with anti- corrosive materials and the piston rings need special treatment. Now comes the logical question: why not use unleaded petrol to all vehicles?

 Unfortunately, all our refineries are not geared up with modern refining methods like hydro-cracking or quality feed-stocks to produce lead-free anti-knock petrol (designated by high octane number) to meet the demands of all the petrol driven vehicles. The amount of lead depends on the fuel composition-paraffins with long chains needing most, the shorter and the branched chain hydrocarbons lesser and the aromatics the least or none, if the compression ratio is compatible.

In India, the limit fixed varies from 0.18 to 0.56 g/litre depending on the feed stocks available and the type of refining process infrastructure. Whatever unleaded petrol produced is only restricted to those cars plying in metropolitan cities which are mandatorily fitted with catalytic converters. Otherwise, leaded petrol will poison the catalysts. The problem of alternatives to leaded petrol is engaging the attention of the researchers for a long time. Natural gas or LPG is admirably suited as they are inherently knock-resistant because of their short chains.

Alcohols are also excellent knock -resistant fuels. Tertiary-butyl alcohol (TBA) and methyl tertiary-butyl ether (MTBE) have also been contemplated as additives.

 Lead poisoning is a serious health hazard. Many social organizations, worldwide, are making a study of this and are creating public awareness to this problem.

 The George foundation, a charitable and non-profit trust has pioneered a project ‘Lead Free’ in Bangalore and is collecting data in order to test and treat people severely affected by lead pollution. Hopefully, the project would be extended to other metropolitan cities. 

  There are 3 major reasons for a four-stroke engine of a two-wheeler being more eco-friendly than a two-stroke engine: In a two stroke engine, a part of the incoming air and fuel is short-circuited directly through the exhaust port of the cylinder and is carried away with the exhaust gases. This pollutes the atmosphere. But, the design of four-stroke engine is different there are valves (inlet and exhaust).

            Scavenging is effectively done in a four-stroke engine than in a two-stroke. (‘Scavenging’ is a process of removal of burnt gases from the engine cylinder.)

            If scavenging is not done properly, the residual burnt gas that inside the cylinder will be combusted again, this leads to smoky emission in two-stroke engines.

The lubrication system of a two-stroke engine is different from that of a four-stroke engine. In two-stroke engines, oil is mixed with the fuel (to provide lubrication for moving surfaces such as piston skirt and roller bearings). It is subsequently carried into the combustion chamber by the air stream, where it is partially burnt and partially pushed through the exhaust port, along with the exhaust gases. This results in smoky emission.

The suction, compression, expansion and exhaust strokes takes place in four strokes of the piston or two revolution of the crank shaft, in a four stroke engine

 In a two stroke engine compression and suction takes place in one stroke of piston and expansion and exhaust strokes also takes place in one stroke of piston. Hence in two strokes of piston all the four processes are completed which makes scavenging less efficient.

Scavenging is the process in which the products of combustion (i.e. burnt exhaust gases) are cleared from the cylinder and filling it with more or less completely with a fresh mixture of air and fuel. The incoming fresh mixture entering into the engine cylinder at certain velocity sweeps out the products of combustion from the cylinder.

 The fresh mixture entering acts as a scavenging or sweeping agent. But instead of acting as a sweeping agent, the fresh mixture also escapes through the exhaust port, as unburn hydrocarbons which are a pollutant.    

Most of the heavy vehicles are fitted with diesel engines, which generate more vibrations and noise than petrol engines.

When the engine is placed in the front it gives rise vibrations from the engine and the transmission line. It also causes discomfort to the passengers especially in case of long journeys.

If the engine is fitted at the rear it is comfortable to the passengers but problems such as remote operation of accelerator, gear shifting and inferior engine cooling arises. 

Rear engines reduce fatigue of the driver. He is also free from noise and vibration from the engine. Moreover, the weight on the front portion of the vehicle is reduced and so the torque needed to steer the vehicle would be less. Also, the hot air from the engine does not enter inside the cabin. However, the cost of manufacturing a rear engine vehicle is higher compared to front engine vehicle.

Fitting engines at the rear side has many advantages. First, the weight of the driving wheels (rear) is increased in slopes. This gives better traction through improved road adhesion.

 As the propeller shaft is absent, chassis height can be decreased. Further, the front portion of the vehicle is amenable to better designing and front axle construction can be simplified. But this type has certain disadvantages. They are difficult to service, have decreased cooling efficiency and are unstable at high speeds.

            In India, only front engine with front axle drive or rear axle drive is preferred as they give considerable ground clearance which is suitable for the road conditions.

The active ingredient in any mosquito repeller (whether it is mats, coils or solution) is d-trans allethrin or allethrin a.i (house hold insecticide). In the case of mats, apart from the main ingredient, the following are present – stabilizer (piperonyl butoxide), dye (blue), perfume, solvents (isopropyl myristate, butyl stearate) plus an inert ingredient like paper.

            Although mats and other repellants are not directly harmful to humans, symptoms of poisoning such as nervousness and anxiety may be experienced because of its active ingredients. Anyhow, on the basis of observations made from the use, experience and studies, no such symptoms have been acknowledged.

             If ingested, vomiting should be induced with care to prevent aspiration. If skin is contaminated, wash immediately with soap and water. If eyes are affected, wash them immediately with copious amounts of water. There is specific antidote for the chemical compound.

   When dry wood pieces and seeds of certain tree species are put in water, they absorb water and swell noticeably. This phenomenon of water absorption is called imbibitions.

            Imbibition is due to the presence of large number of hydrophilic colloids in both the living and dead cells of wooden materials. They include proteins and carbohydrates such as starch, cellulose and pectin. In the case of dry wood, there are more dead cells with lignified walls. As a result it readily absorbs and releases water depending on the environmental conditions.

            For example, during rains, relative humidity of atmospheric air is high. Hence, wooden doors absorb water molecules and swell. If the clearance between the door frame and door is insufficient to accommodate the swell, we experience difficulty in closing and opening it.

            Periodic painting helps to reduce moisture absorption and the difficulty.

     Physiologically, alimentary canal (gastrointestinal tract) is lined with mucous layer. Mucous contains mucin protein and water. Mucous is secreted by mucous glands present on the epithelium. Mucous, is present not only inside the alimentary canal, but also lines the respiratory and urinogenital tracts. This mucous lining primarily acts as a protective barrier and protects the underlying living cells from pathogens and from other physical and chemical hazards.

            When we drink very hot liquid this mucous lining protects the living cells beneath it from getting burnt. This happens mainly due to liquid water molecules in mucous. Water molecules have high enthalpy (E) and boiling point. This property of water molecules in mucous enables it to act as a heat absorbent and prevent the penetration of heat beneath it. Our skin is also involved in protection of underlying tissues and organs from external environmental hazards.

            Skin is composed of a superficial layer (the epidermis) and a deeper layer (the dermis). Dermis consists of many cell layers and most of the layers are made up of satiated, denucleated, keratinized dead cells. These layers act as physical barriers against the invasion of pathogens and harmful substances.

            But these stratified layers are not as effective as the mucous in the heat production mechanism. Because, these layers are dry in nature and contain no water molecules to absorb heat, and are permeable, when hot substances are poured on the skin, the dry horny layers manage to give little protection to the living cells from the heat.

    The liquid that leaves the body is almost unrelated, in chemical composition, to the liquid consumed. Any substance, solid or liquid, that goes down the esophagus, passes through the digestive tract and, if not absorbed, is incorporated into the faecal matter. Urine, in contrast, is created by the kidneys from metabolic waste produced in the tissues and transported through the bloodstream. Any coloured compound that one drinks either will or will not interact biochemically with the body’s system. If it does, this interaction (like any other chemical reaction it might undergo) will tend to alter or eliminate its colour. If it does not, the digestive system will usually decline to absorb it and will be excerted in the faeces which, you will have noticed, show considerable colour variation than the urine.

            Coloured substances in food and drink are usually organic compounds that the human body has an amazing ability to metabolize, turning them into colourless carbon dioxide, water and urea.

            The toughest stuff is often taken care of by the liver, which is a veritable waste incinerator. However, on the very infrequent occasion when the intake of coloured substances exceeds what the body can quickly metabolize, the colour is not necessarily removed as the liquid leaves the body. This is well known to anyone who has indulged in large quantities of borsch, or the Russian beetroot soup.

     While being made, the cereals are cooked into dry, crispy froths of syrupy, starchy stuff. In the process, and on cooling, they harden, and stresses induced during drying distort them. If you let them slowly absorb humidity from the air, they soften and the stresses relax gently, evenly and quietly. The cereals go leathery and sullen, and pass gently into milk and stomach.

            However, if you wet the fresh, crisp cereals their stresses are relieved suddenly and unevenly and thousands of minute shells suddenly find themselves with one side hard and stressed and the other side soft. They are bite.

            The processing of cereals for some breakfast foods creates bubbles in what is a brittle but weak material which swells when it absorbs water. As liquid touches one side of the bubble it swells and distorts so that the opposite side splits.

            The sound of this splitting is amplified by the air cavity in the same way as a stringed musical instrument vibration is amplified by its sound box.

Alcohol generally refers to drinks which contain varying amounts of absolute alcohol (chemically termed ethyl alcohol). Alcoholic beverages are usually made by fermentation of sugars and carbohydrates (from different sources). Yeast is used to convert these into ethyl alcohol and carbon dioxide. As a food substance, alcoholic drinks have a restricted food value in the form of sugar (as in sweet wine) and carbohydrates (in beer). About 190-240 grams of pure alcohol per day is equivalent to 1300-1600 calories which is enough to provide basic energy for the body for a day. Inspite of its high calorific value it is better known as ‘empty calories’ because it does not provide the essential nutrients to the body. In addition, alcohol impairs absorption and metabolism of essential nutrients from other foods. ‘Alcoholics’ usually suffer from such deficiencies. This can be reduced by the type and manner of alcoholic beverage consumption.

Red meat is red because the muscle fibres which make up the bulk of the meat contain a high content of myoglobin and mitochondria, which are coloured red. Myoglobin, a protein similar to haemoglobin in red blood cells, acts as a store for oxygen within the muscle fibres.

            Mitochondria are organelles within cells which use oxygen to manufacture the compound ATP which supplies the energy for muscle contraction.

            The muscle fibres of white meat, by contrast, have a low content of myoglobin and mitochondria. The difference in colour between the fleshes of various animals is determined by the relative proportions of these two basic muscle fibre types. The fibres in red muscle fatigue slowly, whereas the fibres in white muscle fatigue rapidly.

            An active, fast swimming fish such as a tuna has a high proportion of fatigue-resistant red muscle in its flesh, whereas a much less active fish such as the plaise has mostly white muscle.

The colour of meat is governed by the concentration of myoglobin in the muscle tissue which produces the brown colouring during cooking.

 Chickens and turkeys are always assumed to have white meat, but free-range meat from these species (especially from the legs) is brown. This is because birds reared in the open exercise and become fitter than poultry grown in cages. The fitter the bird, the greater the ease of muscular respiration, and hence increased myoglobin levels in the muscle tissue, making the meat browner. All beef is brown because cattle are allowed to run around in fields, but pork is whiter because pigs are lazy. 

High-strength ceramics such as silicon nitride, dual hardness steel and layers of heavy nylon fabric make a bullet-proof glass impervious to bullets. The hard ceramic stops the bullet abruptly, dissipates its energy as it destroys the first layers of the glass at the point of impact and entangles it in as coarse mesh.

A textile bullet-proof vest is fashioned of 16-24 layers of nylon cloth of heavy weave, the layers stitched together like a quiet. Such vests or full-torso protectors can be worn undetected under regular clothing. A vest of 16 layers will stop regular handgun and submachine-gun bullets, those of 24 layers will stop the move powerful magnum bullets from the same weapons. 

Shattering of panes can be explained using the well-known principle of resonance. We have seen window panes vibrate when heavy vehicles such as a lorry pass by.

Likewise the panes of houses near airports also vibrate when aircraft fly nearby. In these cases, the noise (a mixture of sound waves of varying frequencies) generated by the vehicle sets up vibrations in the atmospheric air surrounding it. These vibrations (sound waves) transfer the energy from the source (vehicle) to the surrounding and dissipate it. If the noise is not intense, the sound dies away with in a short distance.

If it is intense, the waves travel long distances. When these waves come across solid objects such as window panes, they transfer their energy to the object and force them to vibrate.

 If the frequency of the sound wave matches with the natural frequency (Any object will have a natural frequency of vibration which depends on the nature of the material) of the object, resonance sets in the object begins to absorb the incident energy and forced to vibrate with large amplitudes. In case of window panes, its edges are held (if not tightly) by the window frame which prevent the oscillation. This results in shattering. 

The bristles of a shaving brush are bunched together to ensure that there are a large number of thin columns of air in-between them. When the brush is moved to and fro, the soap solution seeps into the brush, due to surface tension, partially filling the air columns.

 While shaving, the soap solution stuck to the skin is dragged to form thin films. But when stretched beyond a certain length, limited by surface tension, the films break and in that process trap a little bit of air to form small bubbles. As there are hundreds of bristles involved in the bubble making process, we get lather within a short time.

 The same principle applies to tooth brush and the brushes used for washing.

Honey is a very dry product, mostly sugar. Any water that comes into contact with it will be drawn in by osmosis. As a result, most bacteria are dehydrated, killing them or rendering them weak and fragile.

 Bees also treat the honey with an enzyme that generates free radicals, in effect sterilizing the honey with hydrogen peroxide.

In ancient times, honey was sometimes used as a wound dressing, and some modern doctors still use sugar. Experts say the treatment probably works because sugar dries the bed of the wound to promote new tissue growth and dehydrates the bacteria that cause infection.

There are commercial wound pastes made of synthetic microscopic water-absorbing, bends that do the something. 

Honey is adulterated by way of adding jiggery syrup. To verify whether honey is pure, take a glass of water and pour one tablespoon of honey in it. Gently shake the glass (note not to stir). If the honey completely dissolves in water it is adulterated, On the other hand if it stays as a mass, it is pure honey. 

Generally a substance dissolved in a liquid lowers the freezing point or melting point of that liquid. When salt is added to ice at room temperature, some of the ice melts and cools the salt to zero degrees Celsius. The salt solution produced cannot remain in equilibrium with ice at zero degrees. It is possible only when the ice is at the freezing point of the solution (less than 0 degrees Celsius). So more ice in contact with the salt solutions melts taking the necessary latent heat of fusion from the salt solution, whose temperature is consequently lowered.

More salt thus dissolves, keeping the solution saturated and the process continues till the temperature of the solution reduced to -21 degrees Centigrade. Only at this point (eutectic point) ice is in equilibrium with saturated salt solution. When 23 per cent of salt is added to ice, the freezing point is lowered to -21 degrees.      

Solid ice exists at zero degrees Celsius and salt at room temperature which is bound to be higher. So, when the two mix, ice begins to melt. But the temperature still remains at zero. A little of the salt dissolves in the water thus formed. In this process, the fine, solid particles of salt breaks down to positive sodium ions and negative chloride ions (dissociation). This change requires energy which is absorbed from the solution which is cooled below zero degrees Celsius. As more and more salt dissolves, temperature goes down further till -21 degrees Celsius is reached. At this stage, the solution is saturated, that is, the maximum solubility of salt at that temperature has been attained. Ice, solution and salt co-exist at this point called eutectic point.

This principle is used in making freezing mixtures which provide sub-zero temperatures. If calcium chloride is employed instead of sodium chloride, temperatures as low as -55 degrees Celsius could be obtained.

 Another application of salt and ice is in de-icing of roads during winter. The smooth, slippery surface of ice is dangerous to fast moving vehicles. When salt is thrown on the ice, it dissolves and the solution though at a low temperature flows away leaving the roads free. Because of the presence of about 3 percent of salts (chiefly common salt) sea water freezes at -2 degrees Celsius instead of at zero.

Salt is used to melt ice on roads and sidewalks. On contact with ice, some of the salt dissolves.

The salt solution has a lower freezing point than pure ice and exists as a liquid at zero degrees Celsius. So even on a cold day, the ice can be melted drained using salt.

One can use sodium chloride (common salt) and calcium chloride for the above purpose. The depression of the freezing point depends on the number of particles in a given amount of solvent.

Electrolytes are compounds which produce ions in solution. NaCI exists as a sodium ion and a chloride ion in solution and calcium chloride as a calcium ion and two chloride ions. Among these the calcium salt is better clearing ice from sidewalks as it produces more particles (three ions – one calcium ion and two chloride ions) in the solution. But we cannot use them for cleaning ice in automobile radiators because of their corrosive nature. For that ethylene glycol is used as antifreeze even though it is not as efficient as the calcium salt. 

Obviously because of the string and the tail. How the string is tied to the sheet of paper (at certain angles) plays an important role in the successful flight of the kite. First, the sheet of paper is made stiff using thin sticks so that it does not bend due to the forces of the wind. Next, 3-4 small strings of equal length are attached. All this is to make the kite fly at an angle with the direction of the wind.

According to the laws of physics, any force acting on can be separated into two components – one horizontal and the other vertical. Generally the vertical component lifts the object (against gravity) and the horizontal component pushes the object (along the direction of the force). Here the force acting on the kite is due to the wind.

 In the case of pieces of paper, the wind force blows them away as they are not secured anywhere. But in the case of the kite, it is held by the string in on e direction (a restoring force) and the wind is exerting its force in the opposite direction.

 The net force on the kite is resolved into the horizontal and vertical components mentioned above. These force components depend on the angle of the kite’s axis to the wind direction. When the lifting force is sufficient enough, the kite begins to fly. 

 At times we pull the string or run into the wind. These are tricks to increase the lifting force and make the kite fly higher. Some kites tend to rotate along the axis of the string. To prevent this rotation, a long tail is attached.

 The flight of the kite may look simple going by the above explanation. But there is a lot more to it: For example, if we closely watch the flying kite we can see that it is very dynamic. It adjusts its position continuously depending on the movement of the air surrounding it. All this it does, may be because it wants to fly! 

            In most cases dirt adheres to the fibres of textile fabrics by 2 kinds of forces – first by sticking to a coating of grease or a dried coating of substances which swell up in water or other solvents (starch, Proteins and other glue like substances); second by direct adhesion because of the physico – chemical character of the fibres and the dirt. Dirt consists of fatty substances, proteins, and dust and soot particles. Such dirt is largely insoluble in water or is water repellent. Used shirt is soiled with greasy substances constituting about 0.25 percent of its weight; collar may contain as much as 1.2 percent of its weight of greasy dirt.

The dirt may be held by the fibres in various ways; mechanically (pigments are jammed between fibres), chemically (fruit oil or ink strains) by absorption (feebler chemical band, dissoluble by detergents) and by electric forces. As most of the dirt is firmly held by the fibres, pure water is not very effective. Chemical cleaning or dry cleaning uses liquids other than water for cleaning of fabrics. In this treatment adhering dirt of the first kind is removed by dissolving the grease or their sticky matter to which the dirt particles are clinging.

A wide range of solvents are employed: carbon tetrachloride, trichloroethylene, tetrachloro ethylene, naphtha (petroleum ether) and benzene. A modern dry cleaning plant comprises a number of specialized machines and appliances. The soiled garments are treated with the solvents in rotating drums.

Contaminated solvent is drained off and purified for re-use. Cleaned garments are dried, impregnated and reshaped. In some cases, however, it is necessary to use water as an additional solvent or swelling agent.

The second type of dirt is dislodged from the fabric by means of detergents added to water. After this wet treatment the fabric is usually treated in weak acid solutions (to revive colours). Rinsed, centrifuged and dried.

Impregnation treatment may be applied at an intermediate stage to stiffen the fabric and make it water- and dirt-repellent. Garments are finally pressed on special machines operated with steam and air. 

      Fabrics such as cotton and linen are treated with thermosetting resins such as urea formaldehyde and melamine formaldehyde to get a durable finish, writes Mr. Surya Kumar of Tuticorin.

A thermosetting resin is a plastic that Solidifies when heated under pressure. They improve the capacity of the fabrics to resist and recover from creases formed during wear. According to him, only when clothes are pressed by a heated iron, under slight pressure, the resins develop cross linked chains between them which give stiffness to the clothes. A cold iron will not be able to do that.

Dr. J. Venkat Rao, Head of the Department of Textile Technology, Anna University, Madras, says  that  this explanation holds good only for certain fabrics. There are a few other factors which are to be considered for ironing clothes, he says.

The first is moistening the cloth. The water makes fabrics such as wool or silk to swell whereas it imparts plasticity to polyester. This allows the fabric to set in any predetermined pattern when pressed with a hot iron box. Because of the heat the moisture evaporates and the cloth sets neatly (as it is made mouldable) as the creases are removed.

According to Dr. Rao, different kinds of clothes are capable of withstanding varying quantities of heat. Natural fabrics such as cotton and linen are not thermoplastic by nature and hence are capable of withstanding high temperature. Synthetic fabrics such as nylon and polyester are thermoplastic. They melt at even slightly high temperatures and hence too much heat should not be applied to these fabrics. Another factor that controls ironing is the pressure applied – heavier iron boxes can exe greater pressure. This explains why dhobi’s ironing is far better than the housewife’s.

A soft bed above a hard surface perhaps helps in distributing the pressure evenly on the cloth.

Left-handedness is due to asymmetry of the brain. It is not a disorder and is more common in males than in females. Actually, in the foetus, the left and right hemispheres of the brain are symmetrical.

Only after about six months of its birth, babies show a preference for either the right or left side of the body. This is due to functional asymmetry of two sides of the brain. It is said that the left hemisphere of the brain controls the right side of the rest of the body and vice versa.

As a result, it seems the left hemisphere is more active than the right, in a majority of the population. Though this theory is not accepted by neurologists in humans it has been proved in the case of dolphins.

Due to lack of symmetry in the brain, in 90 per cent of the population, the right leg, right arm and muscles on the right side are slightly larger and heavier than those on the left. It is almost the reverse in the rest of the population.

Left handedness is generally associated with special talents and also with certain disorders such as stuttering, dyslexia, depression and emotional withdrawal.                                                                                                                                                                          

Nearly 75 per cent of the population is strongly right- handed and about 90 per cent is predominantly right-handed. Among the rest, a great deal of variability exists. Some are strongly left-handed, and others, called ambidextrous, are left-handed for some activities and right-handed for others.

            Handedness is defined as a preference for the use of either the right hand or the left hand. Although most animals have a preferred paw or hand, only people have a species-typical preference for the right hand. Researchers suggest that differences in left and right-handers in patterns of brain organization may be associated with differences in skills, aptitudes, and perhaps even personalities. In the large majority of right-handers (98 or 99 per cent), speech is controlled by the left side of the brain.

The right hemisphere of the brain is usually specialized for recognizing and remembering faces and understanding spatial relationships.  In left-handers, the brain organization is unpredictable. In about 70 per cent of the left-handers speech is controlled by the left hemisphere of the brain, as is the case for right-handers, but in the remaining left-handers speech is controlled by the right hemisphere.  In some left-handers, both the hemispheres are capable of controlling, speech.

The hand an individual comes to prefer is determined, in part, genetically, but this does not mean, for example, that two right-handed parents cannot have a left-handed child, or the reverse.

The precise mechanisms by which genes affect handedness are still unknown. A physical injury may also be involved.

During the birth process, the region of the brain controlling the hand is sometimes damaged, so that a child who would have been right-handed without such damage becomes left-handed.

 Social pressures have had a considerable effect on handedness. Using the left hand to pass on or receive something from others is strongly discouraged even now in many countries including India.

Only in recent years has society become tolerant of differences among people to accept left-handedness as a benign trait.

 Many famous persons, including Leonardo da Vinci, Benjamin Franklin, and Lewis Carroll, were left-handed.

Clouds are made of water droplets and dust in the atmosphere at altitudes of 1 to 16 km. While travelling through air, due to friction, the water droplets get electrically charged.

 Lightning occurs due to sparking between oppositely charged clouds – a high voltage spark rushes towards the ground (at zero potential) through moisture-filled air.

If any around based structure is on the path of the spark, the top of that structure is excited to a high electrical potential while its bottom (in contact with the around) remains at zero voltage. This high potential difference sets a very high current in the structure causing sudden heat generation in the material and destruction. But in flying aero-planes, there is nothing like a ground point which remains always at zero voltage.

Hence even if hit a lightning, the plane’s entire surface acquires the same high potential and due to lack of potential difference there is no current and hence no destruction.

           The mechanism of seeing in the dark involves two types of cells – rods and cones, in the eye. These cells are present in the light – sensitive innermost layer of the eye called the retina. They lie in front of a pigmented tissue layer. Cones are present in the area of greatest visual activity – fovea contrails, which lies at the centre of small yellow pigment spot behind the pupil. Rods and cones are present around the fovea.

            Cones are active under intense illumination, whereas rods are active in dim light. In the dark rods are sensitized by a pigment called Rhodospin or the visual purple that is formed within the rods. Rhodospin is bleaches by light and is reformed by the rods in darkness. Hence a person who steps from sunlight into a dark room experiences a blinding feeling till the pigments begin to form. This process takes around 30 minutes to reach maximum sensitivity.

            On completion the eyes become sensitive to low levels of illumination and are said to be dark-adapted. Meanwhile the cones adapt themselves to fainter light in the ambience of low intensity illumination, which may take around five minutes.

            The best example is finding our way to our seats in a movie theatre after the show begins. Initially there is a blinding feeling when we do not see anything. But later the cones in the retina get adapted to the light from the film screen, when we are able to find the seats; this is followed by adaption of the rods which enables us to see everyone around us.

          Mummies are embalmed bodies that have been preserved for thousands of years. The dead have been mummified with the help of good drying agents applied all over the body.

            Drying agents and other materials were stuffed inside the body to maintain its shape after removing the internal organs. The word mummy is derived from the Persian word mummia meaning bitumen because the black resin used for embalming the dead looked like bitumen.

            Three techniques of mummification have been discovered by Greek historians. The methodology was the same in all the three cases and the differences lie in the process of extraction of internal organs. Mummies belonging to 1570-1070 BC are still found to be in good condition.

            Actually in the process of mummification embalmers removed all the internal organs except the heart and kidneys. The brain was removed through the nostril using a hook. They soaked them in natron (a mixture of salt, sodium bi-carbonate and sodium carbonate). It was then bandaged and kept in jars. The internal cavities were stuffed with lines bags of sawdust, natron bags, and resin coated material.

            The nostrils and eyes were stuffed with linen rolls. Cedar oil, natron and purgatives were then smeared on the body to close the pores. After this, the body was wrapped in long sheets of fine line. Toes, fingers and limbs were separately wrapped and then the torso was wrapped up in several layers.

            A mask revealing the external features, made of pliable linen treated with resin was fixed on the face. According to ancient texts a complete treatment could take about 70 days. Though resin has burnt the skin of the dead body in many cases the hairs were seen to be intact.

            Human skin is made of four layers – the topmost layer is stratum cornium, followed by epidermis and sub-cutaneous layers. When mehndhi is applied on the skin, the red pigments present in it are transported along with water through the small pores in the stratum cornium. These pigments get trapped between the stratum cornium and epidermis. As the hand dries, the water evaporates leaving the pigments which impart the colour.

            In the case of the nail, the pigments are trapped between the horny plate-like cells which are piled in lamellar layers. The pores in the skin are larger than those in the nail. This actually accounts for the rapid fading of the colour in the skin compared to that of the nail.

  Any object will be stable in its position if the line drawn perpendicular to the ground from the object’s centre of gravity falls within its base.

            While walking on a rope, as the base is very thin (as thin as the rope), to be stable the artist has to move his centre of gravity appropriately. This he does by holding a bamboo pole horizontally or using an umbrella or just by spreading his hands.

            When the artist feels that he is falling to his left, he moves the pole to his right (and the vice versa) and counters the forces disturbing his balance and makes the centre of gravity fall within his base.

            Now one may ask, how does one sense these forces and maintain balance? This is achieved only by practice.

            According to the theory of rhythm perception, the perception of rhythm involves the motor system just as much as the sensory system. It postulates that a ‘beat’ is actually perceived as a movement.

            The theory then suggests that because a beat is perceived as a movement, the activation of a stereotyped behaviour such as tapping your foot in time with the beat is a natural extension of the way motor and sensory systems often work together to produce a percept.

A pencil mark actually consists of graphite particles abraded from the pencil point by the paper. These particles, which have an angular, gritty look under the microscope, are for an HB lead pencil, typically between 2 and 10 micrometers in diameter. The particles lie slightly below the surface of the paper, interlocked between its fibres.

            A signal rub using a rubber sufficiently soft to reach between the fibres will pick up most of them. Inspection of the rubber shows the undamaged particles adhering to the surface.

            An effective erasing material is also abraded by the paper surface, producing the familiar small spindles of rubber or eraser material, which wrap up the graphite particles. At 200 x magnification, these look like roly-poly puddings studded with graphite raisins.

   Parboiling involves soaking paddy in water for a short time followed by heating once or twice in steam and drying before milling. Dehusking of parboiled rice is easy and the grain becomes tougher resulting in reduced losses during milling.

            The nutritive value of rice increases after parboiling, because the water dissolves the vitamins and minerals present in the hull and brancoat carries them into the endosperm. So the loss of vitamin B1, riboflavin and niacin due to milling and polishing is comparatively low in the parboiled rice than raw rice. Parboiled rice will not turn into glutinous mass when cooked. Baking of leavened dough of wheat helps to make bread. Baking is done in an oven preheated to 204 degrees C. During the first 10-12 minutes of baking there is an increase in dough volume. This is called oven spring. This is caused by an expansion of gases owing to the high temperature of the oven and due to increased enzyme activity in the centre of the dough. As baking continues, gluten a constituent of wheat dough expands without breaking and finally forms a rigid structure due to coagulation.

            This helps in the retention to the rapidly expanding gases. Excess gases, CO2, alcohol and water vapour help to gelatinize the starch and structure is established. This aerated and finely vesicated crumb is very helpful for easy mastication of bread.

            Using heat to bring about desirable changes in foods is called cooking. Cooking improves flavour and appearance and makes the food more palatable and digestible. Legumes and cereal grains contain trypsin inhibitors and other toxic substances which affect the digestibility and availability of sulphur containing amino acids.

            Cooking destroys these toxic proteins and favours easy digestion Starch molecules which are the main source of calories in many diets when in an aqueous or moist environment swell and rupture and this permits greater enzymatic digestion by enzymes like amylase. Cooking thus increases the digestibility of carbohydrates.

         We can’t fry food with water because its boiling point is lower than that of oil. Generally all food materials contain water in an occluded from or as water of hydration.

    We fry food essentially to remove this water. For this, the food needs to be heated beyond the boiling point of water (100 degrees C). If we use water as the frying medium, the water from the food cannot be removed as the medium itself gets vapourized.

                                                                                     However, oil can be heated to more than      without                                                                                        charring the food. Being nonvolatile at this                                                                                                        temperature, heat from the oil facilities frying. 

Fuel has to be heated to a minimum temperature, know as kindling temperature or ignition temperature for a successful and continuous burning.  We largely depend upon match sticks for creating fire. It contains combustible W (oxidisable) substance and an oxidizing (oxygen supplying) agent. We supply heat energy by rubbing the head against rough surface. Every fuel has to mix up with oxygen present in air to form a mixture of right composition for successful combustion.

The composition of the mixture can be between two limits namely lower and upper limits. Those limits are called limits of inflammability or explosive range. We should know that even when the temperature maintained is equal to kindling temperature, we cannot produce fire with fuel only or with oxygen only.

Kindling temperature depends upon the chemical nature and explosive range depends upon the volatile (vapour forming) nature of the fuel. Those two properties do not have any direct relation with size or shape of the fuel. But, of course, it seems that powdered fuel, say saw-dust in case of wood catches fire quickly rather than large log.

This difference in size or shape affects neither the kindling temperature nor the volatile nature of the fuel. The rapidity in catching fire is due to different reasons. In case of powdered fuel, small fuel particle is introduced into a large flame. That means supply of activation energy in the form of heat is very fast. In this case, availability of oxygen will also be a very high. Hence the quick ignition. But in case of logs, large mass is heated by relatively small flame. That means supply of activation energy in the form of heat is very slow.

Also, a large portion of the heat supplied to the log will be dissipated to other parts due to conduction. Chance for loss of heat energy to the surrounding cannot be also neglected. This will further slow down the process of attainment of ignition temperature.

Even when the whole log attains the ignition temperature, only the particles present on the surface can form explosive mixture combining the oxygen present, in air. Hence the delayed ignition. 

Ignition temperature is specific to a substance. It is temperature at which the substance starts burning. A piece of wood catches fire quickly attain the fire point quickly. But in case of a large log when you apply flame a point of edge, the temperature transfer takes of big log a long time. 

When a candle is lit, paraffin wax (a hydrocarbon) vaporuizes and mixes with air to form a combustible mixture, and burns. The air-fuel ratio changes as we move away from the wick. As a result, broadly, we have three different flame regions – blue, violet and yellow.

The region immediately close to the wick is fuel rich and there is insufficient oxygen. Hence the mix does not burn and the region is dark. Outside this region, the fuel-air ratio of the mixture is right enough to burn. The blue-violet colour is due to the presence of CH radicals formed during the combustion reactions. The outer yellow region is due to the radiation from fine hot soot (carbon) particles.

Milk fat as it occurs in milk has unusual characteristics. It is made up of fat globules which are 4-10 microns in diameter. These globules are covered by protective membranes made of bipolar compounds phospholipids, protein, diacylglycerides and monoacylglycerides and other surface active materials. They are collectively designated the milk fat globule membrane (MFGM).

It is likely that the violent mixing of milk, during churning, disrupts a sufficient portion of the milk fat globule membrane (MFGM) to render milk fat globules ‘sticky’.

            Further churning simply cause the ‘sticky’ fat globules to aggregrate, form bigger butter granules and rise rapidly. Excessive churning increase abrasion and leads to quicker separation.

    Lie detector, also known as polygraph, is generally used during interrogation by police.

The instrument works by recording our physiological functions such as blood pressure, heartbeat, respiration and perspiration. An anemograph tube is fastened around the subject’s chest and a blood-pressure-pulse cuff is strapped around the arm. Psycho-galvanic skin reflex (electro-dermal response) and flow of current between different parts of the body are also measured.

Sensitive electrodes are used to pick up the impulses which are recorded on a moving graph paper. The parameters are recorded when a suspect answers questions put to him by an operator. The data is then used as a basis for deciding whether the person is lying or not.

When a person lies, the graph deviates from the normal shape in one or core of the body functions. Such changes occur due to our emotional response to telling a lie.

While most of the questions asked are interrelated, some are included to improve the test’s accuracy. The questions are usually answered in ‘yes’ or ‘no’ mode only.

The modern polygraph was first constructed in 1921 by John A. Lagoon, a medical student at the University of California, along with a police officer. His instrument was capable of continuously recording blood pressure, pulse and respiration. As it recorded these conditions simultaneously it was called a polygraph. Though this has been in use since 124, it has not developed into a complete fool-proof system and is yet to be accepted judicially.

  A speech synthesizer converts computer based text (usually ASCII- American Standard Code of Information Interchange) into the spoken word. Text-to-speech technology transforms ordinary text into natural-sounding, highly intelligible speech. Speech synthesis is widely used by blind and other handicapped persons to make use of computer technology.

            Now, synthesized speech is also used in a wide range of commercial applications to tell us the phone numbers we request when we dial Information, to announce station stops, to vocalize instrument readings, and so on. The speech synthesizers used to give instrument readings and to make brief informational announcements vocalize pre-stored speech.

            A speech synthesizers converts ASCII text into speech in real time, by stringing together phonemes according to an algorithm that encodes rules for the relation of English spelling to English pronunciation. Such algorithms can be extremely sophisticated. It first parses sentences and words, then checks for any matches in a stored dictionary; if no match is found, it invokes rules for converting letters to phonemes, then applies prosodic rules for speaking in phrases and finally applies rules for converting phonemes to speech.

            It provides the highest level of speech quality and accuracy, producing clear, correct pronunciation of single characters, words even homograph pronunciations, phrases, and proper names.

            Wheat flour is kneaded with water to get a homogenous paste. This flour is made into a poori and fried in oil heated to more than  C. This temperature is higher than the boiling point of water ( C) and so the water (in liquid state) in the poori is converted into steam (in gaseous state) which occupies a greater volume. This results in the poori swelling up.

            One can see steam bubbles escaping from the oil before the poori is completely fried. Actually, only a small quantity of water converted into steam is trapped between the layers of poori. When the volume of the steam trapped exceeds a certain level, the poori bursts.

We have seen weathercocks fixed on tall towers to indicate the direction of the wind. A weathercock is essentially an arrow free to rotate on a horizontal plane about a vertical axis. It has two fins symmetrically placed on either side of the rod forming the arrow.

As the wind blows, the arrow turns and faces the direction of the wind. If the arrows does not face the wind, the pressure exerted by the wind on one fin will be lesser or greater than that on the other. Consequently the cock is forced to rotate up to a position in which the force acting on the fins are equal and opposite, is reached.

This argument can be extended to a flying flag. When the flag faces the wind, the wind blows from edge which is secured by the rope to the free edge. As it blows, the flag is subject to frictional drag. Friction is a reaction force and, in this case, it acts in a horizontal direction opposite to that of the wind force. Depending on wind turbulence (the changes in the wind speed and direction) the horizontal component of the frictional force on the flag moves from one side to the other. This causes fluttering.

 Flames heat a few layers of air nearby and make them less dense. Due to buoyancy this lot air moves vertically upwards creating a sort of low pressure near the flames. This causes the cool air from faraway layers to flow towards the flame form the sides and below. Oxygen present in the air keeps the fuel burning. The air near the flame gets heated very much and moves up faster. The dynamics of air flow near the flame is a complex process however mathematicians have modelled it and found that there is a greater (faster) outflow of hot air right above the flame with a smaller (slower) inflow from the sides and below. The hot air goes up and then mixes with the environment and cools down. This theory holds good only the candles or wick stoves and not for welders torch or the like where the fuel is forced in a particular direction.

            Corn is generic term to describe the fruit (grain) of cereal plants in particular. Popping corn and sweet corn are just two of the many varieties of maize grown commercially. Each variety has different properties and is grown for different reasons.

            The bulk of tissue within a grain of corn is called the endosperm. Endosperm is specialized storage tissue providing nutrients for the embryo when the seed germinates. It is also a source of carbohydrate for humans.

            In popcorn the outer part of the endosperm is hard but the centre is soft. When the corn is heated the water in the central part turns to steam causing the seed to burst (the pop that we hear) and turn inside out. Sweet corn contains more sucrose in the endosperm than other varieties, which is what makes it sweet.

            Maize, like all cereals, stores a carbohydrate food reserve in its seeds. Sugars enter the developing seed and are converted into starch. As the grain matures, excess water is removed leaving a hard, dry starch.

            In the maize varieties used for most purposes the sugar is all converted to dry starch: this type of corn is called flint corn. In sweet corn the process is not completed by the time the plant is harvested, leaving the grain moist and sweet.

            There are other forms of maize including flour corn where the starch remains soft- this was used by Native Americans because it is easy to grind and waxy corn which on milling produces flour with the texture of tapioca.

            Corn is classified into five principal commercial types according to the structure of the kernel: dent maize, flint maize, flour maize, popcorn and sweet corn.

            These crops were cultivated in the Americas before the arrival of Europeans, maize being the basic food plant of all pre-Colombian American civilizations. The grain of sweet corn contains a glossy, sweetish endosperm which is translucent when immature. A recessive gene on the fourth chromosome prevents the conversation of some of the sugar into starch. It is harvested when young and immature, when the kernels are plump but still soft and milky. As soon as the silk threads above the winter husk wither and turn brown, the cobs can be broken off, boiled and eaten as a vegetable. However, 20 minutes after picking, the sugar begins to converting to starch.

            Therefore, corn on the cob should be absolutely fresh if one wants it to be sweet. For the same reason canned or frozen sweet corn is processed as soon as possible after harvesting. The grains of popcorn are small with a high proportion of very hard endosperm and a little soft starch in the centre. On heating, the moisture in the centre expands as steam, causing the grain to pop and explode, the endosperm becoming averted as a palatable and fluffy mass. Other types of corn will crack but will not explode.

     The layer that forms on top beverages consists of fat. Such a layer is formed only on top of hot liquids because in the unheated milk the fat globules are surrounded by a thin film of protein, phospholipids and neutral fats.

When the milk is heated, this thin film breaks, making the fat globules free. These then coalesce on the surface which then come to contact with the air and forms a layer. Formation of this layer can be prevented by beating of string the heated milk continuously, as the process of homogenization increased the surface tension of the milk. But when the heated milk is allowed to cool and left undisturbed the layer formation occurs. In this condition the surface tension gets lowered and the freed fat globules rise to the surface because their specific gravity is less than that of the aqueous portion of the milk. Also black tea or coffee will not be able to form any such layer.

Bar codes are simple machine readable codes that the computer can reproduce directly into the bit streams of zeros and ones which is the machine language of computers. The information or data is encoded using the width of printed bars, width of space between bars, and relative positions of wide or narrow bars and spaces (that is, a unique thick and thin combination of black and white bars).

The equipment used to read the code is called the scanner, which converts the dark bars and white spaces into equivalent Os and Is which computers can understand.

 The information in the bar code can contain anything from country of origin, manufacturer’s name and product detail. In fact, the amount of information that can be stored in these labels is limited only by the choice of symbology.  Symbology is the term used to describe the rules specifying the way data is encoded into bars and white spaces.

To give an example, the UPC A version bar code, is shown with the codes 05 1111 2 8 8 17. UPC is the Universal Product Code, widely adopted in retail stores to indentify products. The first digit 0 can stand for the country code, the next five digits (5 1 1 1 1) for the manufacturer’s code and the next five digits (2 8 8 1 7) for the product, and the last digit is called the check digit used for checking the accuracy of the reading system.

The computer checks the code and matches it with information in its own database and does the identification. It simplifies billing and inventory of products. The billing person has only to scan the label of different items sold and the bill is printed almost instatantaneously, saving time for the customer and the clerk. The other important benefit is that the inventory is automatically updated, without the need for laboriously checking each and every item, at the end of the day.

If EDI (electronic data interchange) is integrated, the system automatically  prepares a buying order for items which are about to be sold out based on a predetermined stock set by the store manager, Bar codes have helped organizations increase efficiency, reduce operational costs,  and in turn increase profits. 

            Black boxes which usually hold the clues to a plane’s crash are built strong enough to survive bomb blasts, violent impacts and intense fires. They measure approximately 4 by 6 by 8 inches and weigh about 30 kg and are kept in a which can withstand 30 minutes of 1100 degrees C at 50,000 (Btu’s) British Thermal Units per square foot per hour.

            They are actually orange in colour and a very high quality heat resistant paint is used, so that they can be spotted easily even at dimly lit crash sites. They are always placed in the tail end of the flight.

            The black box records voice and flight data. The cockpit voice recorder continuously collects data and retains a record of the most recent 30 minutes, the conversation between the pilot and the Ground Control Room.

            The flight data recorder keeps a record of the most recent 25 hours of a plane’s operating data, including altitude, air speed, vertical acceleration and heading.

            Flight data are recorded either by magnetic tape or in solid-state memory. Modern data recorders can log more than 200 different parameters and transmit data either 64 times or 128 times a second. Thus when recovered from the airplane crash sites the black helps to reconstruct a clear picture of the crash.

     Air conditioning system is the system which keeps on control and maintains the particular condition (that is required temperature and humidity of air) in the closed space.

            It is technically defined as a system which controls temperature, humidity, purity and motion of air to produce desired effects upon the occupants of the space. In case of air cooler, which has the capability to cool the air inside the space does not maintain particular temperature and humidity of the air. In response to atmospheric seasons we can have winter, or summer air-conditioning system, but any air cooler will not do so.

            A so-called air cooler or desert cooler is basically a humidifier (Humidity is the moisture or water content of air). An “air-cooler” mixes water vapour with air by means of a rolling pad of moist cloths of fibre, and makes the air seem cool, but actually more humid (high moisture content).

            An Air conditioner/refrigerator, basically a dehumidifier, works as follows:

            A fluorocarbon refrigerant gas (such as “a Freon”) is compressed. On compression it is pressurized and heated. The extra heat is removed by air (from a fan) or by cooling water as in the case of large (Central A/c) units.                                                                            

            The high-pressure refrigerant is expanded. In contrast to heating on compression the refrigerant, on expansion by sudden reduction in pressure, becomes very cold due to Joule Thomson effect.

            By heat exchange with the very cold refrigerant (which has now become liquid) passing through tubes (that have fins for good heat exchange) the air paning ore, becomes cold and is circulated in the space (room etc) to be cooled. Because the air is cooled considerably, extra moisture content on humid days may be seen dripping from the air conditioner.

            For efficient operation the room in which an air conditioner is used will have to have its doors & windows closed. On the other hand, when direct cooler are in use, at least one window should be kept open as otherwise the humidity will become very uncomfortable.

            P.S.: When humidity in the atmosphere is more, curcating will be more as the sweat will not dry fast enough. In contrast, when humidity is very less as in very cold days when all the moisture in the air would have condensed leaving the atmospheric air “dry”, lips and body skin may be seen getting cracks.

            The water for frost formation comes from the articles placed in the refrigerator and the occasional air that gets into the gadget when it is opened and closed.

            Refrigeration is the process of lowering the temperature and maintaining it in a given space. In mechanical refrigeration, constant cooling is achieved by the circulation of a refrigerant in a closed system, in which it evapourates to a gas and then condenses back into a liquid in an evapourates to a gas and then condenses back into a liquid in a continuous cycle.

            The two main types of mechanical refrigeration systems used are the compression system (used in domestic units for large cold-storage applications and for most air conditioning) and the absorption system (now employed largely for heat-operated air-conditioning units).

            In the compression systems four elements – compressor, condenser, expansion valve, and evapourates are involved in the refrigeration cycle. In the evapourator the refrigerant is vapourized and heat is absorbed from the material contents or the space being cooled. The vapour is next drawn into a compressor and elevated to high pressure, which raises its temperature. The resulting superheated, high-pressure, gas is then condensed to liquid in an air-or-water-cooled condenser. From the condenser the liquid flows through an expansion valve, in which its pressure and temperature are reduced to the conditions that are maintained in the evapourator. The cycle thus continues. The amount of water vapour in the atmosphere is termed as humidity. Air at a given temperature can contain only a certain amount of water vapour. This amount increases as the temperature rises and decreases as temperature falls. In air containing a given amount of water vapour, the temperature at which dew (water that condenses on cool objects from the water vapour in warm air) begins to form is known as the dew point. If the dew point is below the freezing temperature of water, frost is formed.

            When the air surrounding the evapourator coil is cooled the moisture present in the air condenses and sticks on to the coil in the form of water droplets. These droplets are cooled in the subsequent cycle and results in frost.

            The moisture present in the items placed is absorbed by the air and carried to the evapourated coil. The condensation takes place as explained earlier.

   To understand refrigeration, pour a small quantity of petrol in your hand and expose it to the atmosphere. The petrol evaporates leaving a cooling sensation. This is because the petrol has taken the heat from the hand and transformed it into vapour. (This is known as latent heat of vaporization).

            The working substance in the refrigerator is called a refrigerant. It compressed to a high pressure and then pressure and then allowed to condense by rejecting its heat to the atmosphere surrounding it. The liquid is then allowed to expand at a low pressure. During this process it absorbs heat from the spaced inside the refrigerator and become a vapour. The above cycle is repeated in vapour-compression refrigerator which differs fundamentally from vapour absorption system.

            The major compounds in a refrigerant are halocarbon compounds (which includes halogens: chlorine, fluorine and bromine); hydrocarbons (such as methane, ethane and propane); inorganic compounds (such as ammonia, water and air) and unsaturated organic compounds (hydrocarbon with ethylene and propylene base).

            Refrigerant is the working fluid in a fridge. It should have a low boiling point so that it vaporizes at low temperatures and absorbs the heat from a substance. Some of the common refrigerants are ammonia, carbon-dioxide and Freon. Ammonia is often used as it is cheap and easily available. But it is toxic and explosive at high temperatures. Carbon-dioxide was one of the first refrigerants used but presently its use is limited. It is non-toxic and non explosive but causes suffocation when its concentration is high. Freon 12 has a boiling point of -30 degree Celsius. This refrigerant is fluorocarbon of methane and ethane series. It is a combination of halogens, chlorine and fluorine. It is the most commonly used refrigerant. Its chemical name is dichloro-difluoro-methane. It condenses at a moderate pressure under normal atmospheric temperature. This property makes it the most suitable refrigerant.

   Our retina can only respond to stimuli in one way: by sending a signal along optic nerve to the brain, which interprets this signal as light. Normally, the stimulus is light impinging on the retina, but other stimuli work too.

            One of the commonest is a mild trauma to the eyeball. If you close your eyes in a dark room and press gently on the front of your eye will see a faint flow in your peripheral vision.

            This can also happen when a blow to the head causes you to close your eyes hard for a moment. You sometimes see stars or flashes when you sneeze, which is again the result of eyeball compression as the eyelid is forced closed. The retina will also send a light signal response to the brain if it becomes torn or detached. This is a serious condition requiring treatment by an ophthalmologist. Another potential source of problem is the jelly-like vitreous humour that fills the rear two-thirds of the eye. It is attached to the retina at several points, and tugging on it can result in the sensation of light when, for example, you move your eyeball around rapidly under your lid.

            These attachments can fail as we age, which is normally not a problem unless the vitreous pulls some retina with it. This, incidentally, is the cause of floaters, the little bits of matter you can sometimes see floating about inside your eye. Light flashes can also be associated with migraine headache and central nervous system disorders, which can act on the vision centres of the brain to produce the sensation of light.

            This effect is the result of a marked increase in intra-ocular pressure (IOP) caused by the blow. This pressure is exerted on the eye by the vitreous humour – the fluid within the eye that gives it its shape.

            The increase in IOP triggers the rods and cones that make up the retina, sending an electrical signal via the optic nerve to the visual cortex at the back of the head. The visual cortex is where we perceive what we see, and hence we think we are seeing a star for a few second nicely matches the timescale of the temporary rise in IOP.