Why does paper become translucent when smeared with oil or fat?

Why does paper become translucent when smeared with oil or fat?

When light is incident upon a medium or surface, three processes occur, viz., (1) transmission, (2) absorption, and (3) reflection.

`Transmission' is the process by which the incident light leaves a medium or surface from a side other than the incident side, usually, the opposite side. `Absorption' is the process by which incident light is converted into another form of energy, usually, heat. `Reflection' is the process where a fraction of the light incident on a medium or surface is returned to the surface which contains the incident light. `Transparency' is that property of a medium or surface by which it transmits light rays.`Translucency' is that property of a medium by which it transmits light rays, so diffused, that objects cannot be seen distinctly. That is to say, it is only partially transparent.

Based on the measurement of angles (`goniometric'), materials can be classified under three heads, viz., (1) exclusively reflecting — Eg., mirror, lacquer and enamel coatings, oil and paint films, (2) weakly transmitting, but strongly, reflecting — e.g. Sun glasses, highly turbid glass, paper, and (3) strongly transmitting but weakly reflecting — e.g. Plastic film, window glass. Now, consider a sheet of (ordinary) paper. It is weakly transmitting and strongly reflecting the incident light. Hence, it is somewhat transparent. Suppose, one side of the sheet is smeared with oil. Thus, we are superimposing an exclusively reflecting material, (Zero transparency) over a weakly transmitting but, strongly reflecting material, paper. This results in the further reduction of the transmission in the paper. The paper, therefore, becomes translucent.

Source : The Hindu

What is meant by embryonic stem cells?

What is meant by embryonic stem cells?

The only way to cure the diabetes disease is by pancreas re-plantation. However, due to the shortage of organ donations and other factors there remains a greatly insufficient supply of organs.But this can be overcome by obtaining organs generated in the lab by culturing certain cells of our body, called stem cells. The stem cells are capable of self-renewal and have the ability to divide and differentiate through a variety of stages to produce the mature tissues.

There are two types of stem cells in our body 1. somatic stem cells, 2. embryonic stem cells. The somatic stem cells are cells taken from mature tissues. The stem cells of bone marrow are an example. The bone marrow stem cells are pluripotent and give rise to progenitor cells, which differentiate to produce lymphocytes and multi potent precursors called myeloid progenitors, from which myeloid series are derived. The embryonic stem cells are cells taken from blastocyte, which is an embryo removed from the womb or brought from the fertility clinic.

The embryonic stem cells are more flexible the somatic stem cells. They can proliferate far more than stem cells from adults, producing far more descendant cells. This is important because many millions of cells are needed to repair organs. In addition the embryonic stem cells can differentiate into all the tissues of the body while a given type of adult stem cells seems to differentiate into only a small set of tissue types destined to them.

The derivatives of embryonic stem cells can be optimised to produce differentiated growth. For example, by adding and removing certain proteins these cells are directed to develop in the lab into new heart, bone, pancreas or other cells.

Source : The Hindu

What is freshness in fruits and vegetables? How does refrigeration play a role in maintaining the freshness? If so, is not the shrinkage due to dehydration, a measure of loss of freshness?

What is freshness in fruits and vegetables? How does refrigeration play a role in maintaining the freshness? If so, is not the shrinkage due to dehydration, a measure of loss of freshness?

Many fresh vegetables and fruits retain their top quality only for a few days if they are not properly preserved. All green vegetables and fruits of high water content are best when fresh. If allowed to stand for a long period after gathering, they become wilted through loss of moisture by transpiration. The transpiration loss of water is one of the main processes that affect the commercial and physiological deterioration of fruits and vegetables after harvest. The moisture loss adversely affects the appearance, texture, flavour and weight of the products. Most notable effect of moisture loss is the softening of the tissues caused by the loss of turgidity. Storing them in the refrigerator can prevent this water loss. But the optimum storage temperature differs for vegetables and fruits.

Tropical vegetables and a variety of greens are in general susceptible to chilling injury. Therefore they must be stored at a temperature between 8 and 12 {+0}C. At this temperature the rate of metabolism of these vegetables is still considerably high, which reduces both the quality and storage life. So refrigerated storage of these vegetables should be well supplemented with Modified Atmospheric Packaging (MAP). Simple cost effective device is the use of perforated poly-packages that can maintain the desired oxygen and carbon dioxide levels within the packages.

Low temperature close to 0{+0}C with a preferred relative humidity of about 85% furnishes satisfactory conditions for commercial storage of fruits. Fruits stored in the home refrigerators tend to lose moisture. To prevent this the fruits must be kept in ventilated covered containers, enabling the circulation of air around sides, tops and bottoms of the fruits.

Source : The Hindu

Some people think in English, others in other languages. How do deaf people, who have never heard words in any language, think?

Some people think in English, others in other languages. How do deaf people, who have never heard words in any language, think?

Answer 1 :

For pre-lingually deaf people who are neither exposed to nor allowed to communicate in a sign language, this is a very serious concern. It seems that the development of language allows humans not only to discuss, but also to conceptualise abstract ideas.

Many deaf children in the past were assumed to have an intellectual disability, but the problem evaporated once they were given access to language via signing. For those deaf people who do learn sign, sign languages seem to function just as any aural language does, the only difference being the channel used for communication.

Those who learn to sign as a first language will think in it as well, even if they go on learn other languages, as is the case in hearing children of deaf parents. This is not such a strange idea — very few hearing people would claim to actually hear voices when they are thinking.

However, the signers develop slightly faster, probably because speech requires complex motor movements while sign languages use very precise hand signals.

Contrary to popular belief, sign language is not merely a visual from of English, as English is spoken.

It is actually a language in its own right, and in the U.S, American Sign Language (Ameslan) is much closer to spoken French than it is to English, thanks to its separate development.

Answer 2: 

Recent research has produced reliable evidence of thought in babies, who obviously cannot think in words.

Much adult thought, particularly abstract theoretical speculation, is language-based, and some is conditioned by the constraints of the language we know, but the idea that it is always so (known as the Sapir-whorf hypothesis) is now thoroughly discredited.

Non-linguistic thought is more frequent than one might expect. However, any attempts to reflect on it inevitably involve language, the normal form of abstract thought.

Because both this reflective process and the non-verbal thinking which is its object occur in the mind, it is easy to merge one with the other and ignore the wordlessness of much thinking.

Hence the Sapir-Wharf, hypothesis, and the consequent prejudice that dumb animals lack consciousness.

Non-verbal thought consists of the logically integrated structuring of proprioception — awareness of the body's posture and of the response to external and internal stimuli by its sense organs — and the recollection and projection of visual images, emotions and sense data.

Worldless thought is clearly the norm for animals, much of whose behaviour cannot be explained without assuming they are capable of elaborate thought processes such as anticipation, correlation and deduction. Even a humble squid has enough cognitive ability not to eat itself.

Source : The Hindu

Why are some medicinal and acid solution bottles brown in colour?

Why are some medicinal and acid solution bottles brown in colour?

Bottles (containers) made of ordinary, clear, colourless glass and of plastics (organic glasses) are normally used to hold chemicals (medicinal solutions and reagents) in labs and hospitals. The main reasons for using such containers are chemical inertness, transparency, ease of handling and cleaning, and economical. But in certain cases, the containers will have to be coloured — brown, yellowish-green and black. This is to prevent the action of (Sun) light on the contained chemical which otherwise would be deleterious. Eg. Silver chloride when exposed to sunlight, if a trace of moisture were present, assumes a violet tint and finally turns black (decomposition into its elements). Hydrogen peroxide decomposes when exposed to the rays of light from a mercury lamp.

Certain chemical effects are produced by electromagnetic radiation (visible, ultra violet and the near infra red) of wavelengths within the range, say, 7000 to 1000 Angstrom.

Light may be regarded as waves characterised by their wavelengths (or by their frequency). The Sun is a source of visible light as well as ultra violet light. The addition of such radiant or light energy to a system produces electronically excited molecules that are capable of undergoing chemical reactions.When (Sun) light falls on any body, part of it is reflected, part may be transmitted and part may be absorbed. It is only the absorbed light that is effective in bringing about the above type of chemical action — `Grotthus-Draper' Law.

However, the converse of the law is not true. All absorbed light does not bring about chemical action. For, in such cases, the energy so absorbed, is converted mainly into thermal energy. It, therefore, follows that, wherever the above law is relevant, if the container itself absorbs the incident radiation considerably, the contained chemical will remain unaffected.

This is the principle of the `optical filters'. Therefore, by using coloured glasses — optical filters — , the spectral radiant energy can be altered, modulated and controlled precisely. Thus, the action of light on the contained chemical can be prevented. The colouring agents are selective. Thus, ferrous oxide imparts a yellowish green colour — strong infrared absorption; manganese dioxide imparts brown and violet red colour — ultraviolet absorption; iron, copper, chromium, manganese oxides give a black glass — light absorption.

Source : The Hindu

Sunflowers rotate to keep the flower facing the Sun during the day. Do they face sunset all night and then flip around when dawn comes up behind them?

Sunflowers rotate to keep the flower facing the Sun during the day. Do they face sunset all night and then flip around when dawn comes up behind them?

When the sunflower plant, Helianthus annuus, is in the bud stage, the head and the leaves do indeed track the path of the Sun. The genus name Helianthus is from the Greek helios "sun" and anthos "flower."

Interestingly, however, and contrary to popular belief, once the massive topmost flower opens into the radiance of yellow petals, it slows and then stops moving, ending up permanently facing east.

This fixed orientation is thought to be an adaptive feature. Sunflower pollen gets damaged at temperatures greater than 30{+o}C, so by facing east all the time, the flower reduces the net radiation falling on its face at noon, keeping itself cool and promoting fertilisation and seed development.

It also increases the temperature of the flower head in the chilly early morning, attracting warmth-loving insect pollinators.

The heliotropic movements of the leaves and sunflower bud are the result of bending during rapid growth.

This is caused by build-up of the plant growth hormone auxin on the side of the stem opposite the Sun. The direction of the head lags behind the Sun's position by about 12 degrees, or a time of 48 minutes.

Source : The Hindu

How does cyanide cause rapid death?

How does cyanide cause rapid death?

Poisons act in a variety of ways, but the most deadly of them is by inhibiting enzymes. They may do this by tying up an enzyme in the form of a stable complex, by denaturing it, or by blocking its formation from its apoenzyme and cofactor.

Cyanide acts almost instantly and only a small amount is needed for a lethal dose. The average fatal dose is only 50 or 60 milligram. Cyanide is used as gaseous hydrogen cyanide (H-C=N) and as solid salts, which contain the cyanide ions (H=N). The gas is used for extermination of insects and rodents in ships, warehouses, and railway cars and on certain fruit trees.

Cyanide has more affinity with iron atoms. So it gets tied immediately with the iron atom, which forms haeme part of the Haemoglobin. This makes the iron atom unavailable to carry oxygen atom to the tissues through haemoglobin. So oxygen deficiency at the tissue level occurs. This is called Hypoxia.

Since the poisonous substance causes it, it is also called histotoxic hypoxia. In histotoxic hypoxia the brain is affected first. It results in loss of consciousness in 10-20 seconds and death in 4-5 minutes.

Cyanide blocks the oxidation of glucose inside a cell by forming a stable complex with the oxidation enzymes. Certain enzymes of our body cells, like cytochrome oxidases, contain iron and copper atoms. They normally act by providing electrons for the reduction of oxygen in the cell. Cyanide ties up those mobile electrons, rendering them unavailable for the reduction process.

Thus, cyanide brings an abrupt end to cellular respiration. When this process, which is holding the life of an individual is stopped abruptly, it causes death in a matter of minutes, since all the cells in the body die immediately.

Administration of antidote for cyanide poison is not possible, since the fatal end comes immediately within minutes to a person who has consumed the poison. But if the quantity consumed is below the lethal dose sodium nitrate and sodium thiosulphate may be used to treat cyanide poisoning.

Source : The Hindu

Why do most natural antibiotics come from soil fungi and bacteria? Why do they produce them?

Why do most natural antibiotics come from soil fungi and bacteria? Why do they produce them?

Answer 1 : 

A simple, though possibly simplistic, explanation is that these organisms use antibiotics to protect their food supply. Soil bacteria and fungi live by digesting and recycling dead plant material such as leaves and seed cases.

Obviously it is impossible for the bacteria to carry away their prized food supply and therefore it is argued that they lace surrounding food with compounds that are toxic to those of other species. While there is some lab-based experimental evidence to support this hypothesis, it has been difficult to prove this theory in the wild. Antibiotics that work just fine in the lab may be absorbed or diluted by different soils and clays to the point of being rendered useless, while organisms that are typically found in the soil may have robust resistance to antibiotics. A second explanation is that antibiotic production is rooted in the plant material that is the food source.

This material is typically carbon-rich and nitrogen-poor. Rather like a human who is given a 2-kilogram portion of chips with every meal he orders, the soil organism has the problem of achieving a balanced diet.

Most common antibiotics are carbon-rich polymers made by enzymes that strongly resemble those that normally make saturated fats.

The building blocks of these polymers are often exactly the same as those used to make saturated fats.

So perhaps we are seeing a form of clever bacterial bulimia: faced with a situation in which the bacteria literally swim in a soup of fat-producing carbon compounds, the bacteria turn these compounds not into fatty lipids but into their structurally close relations, the antibiotics.

These are then excreted and, should they prove to have a useful, coincidental effect, the bacteria thrive.

Answer 2: 

Most antibiotics stem from research programmes that were inspired by the discovery of penicillin. It was simpler to screen for antibiotics made by microbes than for antibiotics made by other organisms.It was easier to produce chemically complex antibiotics by batch culture of the microbe than it was to attempt a synthesis of a molecule made by a plant or animal. So for purely practical reasons microbes were the best route for discovering new antibiotics.

Actually, antibiotics are not that easy to find in microbes. One study screened 400,000 microbial cultures over a 10-year-period and yielded three useful compounds. It can be argued that the ability to produce and retain a rich chemical diversity enhances the chances of an organism producing the very rare compound that gives it enhanced fitness.

This means that individual chemicals with potent antibiotic properties will be made by many organisms but may be only some of these chemicals will give the maker increased fitness because of that antibiotic property.

Source : The Hindu

What are T-rays?

What are T-rays?

Terahertz rays are electromagnetic pulses which has a frequency in the Terahertz range. Hence called as T-rays. One Terahertz (THz) has a frequency of 10{+1}{+2} (one thousand billion hertz), a frequency range which places T-rays between microwaves and infrared radiation in the electromagnetic family.

There are two main methods of producing T-rays, _ the Free Electron Laser and down conversion of pulses from visible lasers. Although worldwide study of T-rays is in its infancy, it has the potential for many applications not only to complement X-rays but also in certain circumstances, replace them.For ex, T-rays can detect different substances with great sensitivity (in ways X-rays, MRI and Infrared Lasers cannot), an ability that has strong significance for medical, agricultural, food and wine industries. They also are not cancerous, unlike X-rays. Plastics are transparent to T-rays, which gives many security applications. They are non-ionising, which means they do not cause cell damage like X-rays or even UV light.

Source : The Hindu

Why do most natural antibiotics come from soil fungi and bacteria? Why do they produce them?

Why do most natural antibiotics come from soil fungi and bacteria? Why do they produce them?

Answer 1 : 

A simple, though possibly simplistic, explanation is that these organisms use antibiotics to protect their food supply. Soil bacteria and fungi live by digesting and recycling dead plant material such as leaves and seed cases.

Obviously it is impossible for the bacteria to carry away their prized food supply and therefore it is argued that they lace surrounding food with compounds that are toxic to those of other species. While there is some lab-based experimental evidence to support this hypothesis, it has been difficult to prove this theory in the wild. Antibiotics that work just fine in the lab may be absorbed or diluted by different soils and clays to the point of being rendered useless, while organisms that are typically found in the soil may have robust resistance to antibiotics. A second explanation is that antibiotic production is rooted in the plant material that is the food source.

This material is typically carbon-rich and nitrogen-poor. Rather like a human who is given a 2-kilogram portion of chips with every meal he orders, the soil organism has the problem of achieving a balanced diet.

Most common antibiotics are carbon-rich polymers made by enzymes that strongly resemble those that normally make saturated fats.

The building blocks of these polymers are often exactly the same as those used to make saturated fats.

So perhaps we are seeing a form of clever bacterial bulimia: faced with a situation in which the bacteria literally swim in a soup of fat-producing carbon compounds, the bacteria turn these compounds not into fatty lipids but into their structurally close relations, the antibiotics.

These are then excreted and, should they prove to have a useful, coincidental effect, the bacteria thrive.

Answer 2: 

Most antibiotics stem from research programmes that were inspired by the discovery of penicillin. It was simpler to screen for antibiotics made by microbes than for antibiotics made by other organisms.It was easier to produce chemically complex antibiotics by batch culture of the microbe than it was to attempt a synthesis of a molecule made by a plant or animal. So for purely practical reasons microbes were the best route for discovering new antibiotics.

Actually, antibiotics are not that easy to find in microbes. One study screened 400,000 microbial cultures over a 10-year-period and yielded three useful compounds. It can be argued that the ability to produce and retain a rich chemical diversity enhances the chances of an organism producing the very rare compound that gives it enhanced fitness.

This means that individual chemicals with potent antibiotic properties will be made by many organisms but may be only some of these chemicals will give the maker increased fitness because of that antibiotic property.

Source : The Hindu

Why are stones placed in and around railway tracks?

Why are stones placed in and around railway tracks?

 The stones placed in and around railway tracks are technically called `ballast'. The railway track, named `Permanent Way' in rail lingo, is a multi-entity structure which comprises the pair of rail lines running parallel, the spaced sleepers, the ballast and the formation.The force exerted by the wheels of the train is transmitted successively in a proportionally diminishing extent down the rails, the sleepers and the ballast to the formation, a well prepared and consolidated road bed.

The ballast consists of broken stones of specific dimensions. The stability of the track depends on the depth of the ballast which imparts a cushioning effect to the track. The standard depth of ballast for trunk route is 25 cms ,for the Broad Gauge and 20 cms, for the Metre Gauge.Besides distributing the pressure on the track, as stated earlier, the ballast provides a foundation for the sleepers holding them in position albeit the shear produced on the rails by the moving train and protects the formation by diverting rain water to the cess, the exposed top portion of the formation.

Railway maintains periodical screening and packing of ballast. Currently, high-tech Ballast Regulating Machines are employed for the purpose supplanting the human agency.The depth of ballast under the ties has been increased in recent years to accommodate increasingly heavy trains. On some lines this layer is now laid 60.9 cm or even 76.2 cm. thick.

Source : The Hindu

How does electric current cause death?

How does electric current cause death?

Electrocution depends on the amount of current that flows through or over the body. It may be determined by the formula I = E/R (Ohm's Law), where I is current and is expressed in amperes, E is voltage and is expressed in volts, and R is resistance and is expressed in ohms.  The flow of the current through the body is greater, if the voltage is high or if the resistance is low.

High voltages (higher tensions) may cause the person to be thrown, while lower tensions, around 240 volts, cause muscle contraction due to which the person holds on to the source of the current. This is also dangerous, because severity is directly proportional to the duration of current flow.

If the body is well insulated it does not conduct the current and no harm results. Dry skin offer high resistance but the resistance is diminished when the skin is moist or covered with sweat. Blood has a low resistance and as such within the body, electricity tends to be conducted along blood vessels.

The intense heat, which may results from flash over produces burns. High voltage burns may be very severe with charring of the body. If the area of contact is relatively large e.g. when a hot wire is grasped with a wet hand or when a person is electrocuted in a bathtub, death may occur without any visible skin burning.

Electrocution also depends on the path of the current in our body. Death is more likely to occur if the brain stem or heart is in the direct path of the current. Circuits from any of the limbs to the head involve the brain stem and upper cervical cord.Arm-to-arm circuit may also involve the upper cervical cord. In these cases, death probably occurs from paralysis of the medullary (respiratory) centers. Arm-to-arm or left arm to either leg circuits, involve the heart and death occurs either from ventricular fibrillation or cardiac arrest without fibrillation.

Source : The Hindu

How is electricity produced from nuclear materials?

How is electricity produced from nuclear materials?

Uranium has three major isotopes, U233, U235 and U238, out of which the last two are naturally occurring. U233 and U235 are fissionable materials, i.e., they can be split by bombarding with neutrons. U233 can be produced from Thorium, which is a non-fissile material and is known as fast breeding. Plutonium 239 can be produced from U238, but Plutonium is not a naturally occurring element and is fissile.Fission is a nuclear reaction, which splits the Uranium atom into two or more small atoms on bombardment with a neutron. The combined mass of the split atoms is slightly less than that of the Uranium atom and the loss of this small mass is known as mass defect. According to Einstein's famous theory of relativity formula, E = mc{+2} where E = Energy, m = mass, and c = velocity of light, this mass to energy conversion takes place.

The released thermal energy is absorbed by the coolant of the reactor and in a heat exchanger the coolant gives its heat to water and steam is produced. The steam drives a turbine, which is coupled to a generator. This is how electricity is produced. On bombardment by a neutron, an uranium atom releases three neutrons out of which two are absorbed by a moderator in the reactor and only one is allowed to continue the reaction. The moderator can be a control rod and the coolant itself sometimes serves as the moderator. This type of arrangement is known as controlled chain reaction. Many types of reactors are in use today.

Source : The Hindu

Why is eu-de-cologne applied to the forehead of a person suffering from high fever?

Why is eu-de-cologne applied to the forehead of a person suffering from high fever?

We have temperature signals in the peripheral areas of our body. These areas are found especially in the skin and certain deep body tissues. These centres contribute very significantly to body temperature regulation. They do this by altering the set point of the hypothalamic temperature control centres. Set point is the particular temperature at which sweating begins. The average normal temperature i.e., the hypothalamic temperature of our body is considered to be between 36.7 to 37 degrees centigrade (98 degrees Fahrenheit to 98.6 degrees Fahrenheit). It is also called as core temperature. Here the skin temperature will be 33 degrees centigrade.

When the skin temperature rises above this, due to warm weather and other reasons, immediately sweating begins. So when the skin temperature is very high sweating begins at a lower hypothalamic temperature i.e., is at the core temperature itself.

On the other hand during high fever both the skin temperature and the hypothalamic temperature begin to rise. The skin temperature will be above 33 degrees centigrade and the hypothalamic temperature will be above 37 degrees centigrade. Since the core temperature is above normal sweating will not occur and so there will not be loss of body head. But when the skin temperature is reduced to 29 degrees centigrade we can induce sweating even at much high hypothalamic temperature. This can be done artificially by spreading wet cloth dipped in ice cold water over the body, especially in the forehead or applying eu-de-cologne, which is a cooling agent.

Source : The Hindu

What is chemotherapy? What are the advantages and disadvantages of this treatment?

What is chemotherapy? What are the advantages and disadvantages of this treatment?

The word `chemotherapy' means `drug treatment'. Chemotherapy is the use of anti-cancer (cytotoxic) drugs to destroy cancer cells (including leukaemias and lymphomas). It may be used alone to treat some types of cancer. Sometimes it can be used together with other types of treatment such as surgery, radiotherapy, immunotherapy, or a combination of both.

Cells in the body constantly grow and divide to replace old and damaged cells. Normally, cells divide and reproduce in an orderly manner. In cancer, cells keep dividing randomly, without proper control, forming a lump (which is called a tumour). In leukaemia, too many white blood cells are produced.

Many chemotherapy drugs act against cancer cells by interacting with the DNA or RNA, or the genetic makeup, of the cancer cell.

Unfortunately, chemotherapy drugs can also affect some of the normal cells in the body. However, damage to the normal is usually temporary and most side effects will disappear once the treatment is over.

Common side effects of chemotherapy may include: nausea and vomiting, hair loss, anaemia, reduced ability of blood to clot, mouth sores and increased likelihood of developing infections.

Four of the chemotherapy drug types that act directly to impair the DNA in cancer cells are the DNA-damaging agents; antitumour antibiotics; antimetabolites; and DNA-repair enzyme inhibitors.

Chemotherapy drugs are often given in combination with each other, and can be given in different ways. The four most common methods are: intravenous, oral, intramuscular, and intrathecal. The method is based on the actual disease diagnosed and the agent's effectiveness.

Source : The Hindu

What are antioxidants?

What are antioxidants?

Antioxidants are compounds that inhibit chemical reactions with oxygen. The term `antioxidant' refers to the activity possessed by numerous vitamins, minerals and other phytochemicals to serve as protection against the damaging effects of highly reactive molecules known as free radicals.

Free radicals are molecules that have lost an electron and try to replace it by reacting with other molecules. They can cause damage to our cells, impairing our immune system and leading to various diseases.

There are three known free radicals: the Superoxide, the Hydroxyl, and the Peroxide. They may be formed by exposure to radiation and toxic chemicals, over-exposure to the sun's rays, or through the action of various metabolic processes, such as the use of stored fat molecules for energy.

Free radical or oxidative damage can be likened to the rusting of metal. Antioxidant nutrients themselves don't become free radicals by donating an electron because they are stable in either form.

They act as scavengers, helping to prevent cell and tissue damage that could lead to cellular damage and disease.

Naturally occurring antioxidants include retinoids (vitamin A), ascorbic acid (vitamin C-found in citrus and other fruits and vegetables) and vitamin E or other related tocopherols found in many animals and plants; beta carotene, found in deep orange and dark green vegetables, are effective antioxidants.

These may play a significant role in the prevention of cancer, heart disease, immune-deficiency diseases, and ageing. Synthetic antioxidants include butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate and ethoxyquin.

Natural and synthetic antioxidants are added to food to prevent undesirable deterioration. Antioxidants, which are typically considered under the general category of preservative, are used to prevent the reaction of certain food constituents (primarily fat and oil or foods of animal origin, such as egg) with oxygen.

This protective effect is necessary to prevent a food or diet from spoiling, becoming rancid or discoloured. Foods preserved with antioxidants include vegetable oils, bread, and cheese. Antioxidants are also frequently applied to the packaging materials of cereals and nuts.

Source : The Hindu

What is the physics involved in achieving the maximum range when throwing the javelin?

What is the physics involved in achieving the maximum range when throwing the javelin?

The physics involved in achieving the maximum range and the forces acting on the javelin are no different from those found when throwing any other projectile. Air resistance and gravity are the primary forces working against the javelin in flight. The air resistance is very small, because a javelin is designed to be aerodynamic.

Gravity is working to pull the javelin back towards the ground. Although this does not affect the javelin's horizontal motion directly, the javelin is more likely to land sooner if it is launched at an angle that is very close to the ground, or conversely, an angle that is too close to vertical.

The optimum release angle for any thrown object is 45 degrees, or exactly halfway from the horizontal to the vertical. The relatively simple geometry used to prove this statement can be found in any fundamental text dealing with kinematics. The javelin rotates about its long axis as it travels through the air, a feature that helps to keep it stable in flight — just like the rifling in the barrel of a gun that causes the bullet to spin.

Source : The Hindu

How does intake of common salt cause heart disease?

How does intake of common salt cause heart disease?

Intake of common salt is primarily related to the development of hypertension 9HT, which is a major risk factor for the development of heart attack called Coronary Heart Disease(CHD).

For many diseases, the disease agent is still unidentified, e.g., CHD, cancer, peptic ulcer, mental illness, etc.

In these conditions, the cause of the disease is generally discussed in terms of risk factors. Risk factors are often suggestive, but absolute proof of cause and effect between a risk factor and disease is usually lacking.

The effect of risk factors is multiplicative rather than additive; thus, people with combination of risk factors (e.g., smoking, HT, diabetes etc.,) have the greater risk of developing CHD.

It is important to distinguish between relative risk (the proportional increase in risk) and the absolute risk (the actual chance of an event).

Thus, a person of 35 with high cholesterol level who smokes 40 cigarettes a day is relatively much more likely to die from CHD within the next decade than a non-smoking woman of same age with a normal cholesterol level.

But the absolute likelihood of his dying during this time is still small (high relative risk, low absolute risk).

Even though a number of environmental factors have been implicated in the development of HT, salt intake has received the greatest attention.

Even this factor illustrates the heterogeneous nature of the hypertensive population, in that the BP in only 60 per cent of hypertensives is responsible to the level of sodium intake.

The cause of this special sensitivity to salt varies. In about half the patients, there is some primary pathology which accounts for the salt sensitivity.

In the remainder, the pathophysiology is still uncertain but postulated contributing factors include chloride intake, calcium intake, a generalised cellular membrane defect, insulin resistance and `non modulation' to rennin ( a hormone secreted by kidneys).

Most studies assessing the role of salt in HT have assumed that it is the sodium ion that is important. However, some investigators have suggested that the chloride ion may be equally important.

This is based on the observation that feeding chloride free sodium salts to salt-sensitive hypertensive animals fails to increase arterial pressure. A low calcium intake has also been associated with an increase in blood pressure in epidemiological studies.

Since there is no easy test to distinguish salt responsive from salt resistant humans, the current emphasis on decreasing sodium intake in all humans makes some sense.

However, the degree to which HT can be ameliorated or prevented (HT is a non-curable disease) will obviously vary with the salt sensitivity of the individual.

Previously patients were instructed to curtail sodium intake drastically. But now investigators have suggested that this is not necessary. They base their conclusion on studies, which have documented that, mild sodium restriction significantly potentiates the efficacy of nearly all antihypertensive drugs.

Thus, by making it possible to control blood pressure with lower doses of drugs, sodium restriction leads to a reduction in side effects. In addition, it is quite proved that the level of sodium intake does influence the blood pressure.

Source : The Hindu

What Is The Difference Between The Working Systems Of Fax And Telegram?

What Is The Difference Between The Working Systems Of Fax And Telegram?

Though the essential purpose of both the fax and telegram, is the transmission of some information from one place to another, the profile, and the technical arrangements in these two equipment are much different.

Fax: This is the abbreviation for `facsimile auto transmission'. The equipment consists mainly of electronic circuits for scanning a matter, written, typed or printed on a paper. This scanning is done by a device called `magic eye'. Along with the scanning process, the information gathered by the magic eye is converted into electric pulses. This much is the transmission portion. The machine on the receiving portion has been designed to convert electrical pulses into corresponding letters/ figures.

To transmit the contents of a document, machines have to be used both at the transmitting and receiving ends. They have to be connected by a telephone line. For sending the contents, the document is placed in the space provided in the fax machine. The telephone number of the distant end fax is dialled from the sending side, as if for a telephone call. If the machine at the distant end is normal, a specific tone is heard, which means that the fax there is ready to receive the contents. We can then press the `start key'. The operation of this key triggers the mechanism for scanning and converting into pulses, and sending these pulses along the telephone line to the other end.

At the receiver side, there is arrangement to get a print of the matter received through the telephone line. In the earlier type of fax machines, the paper used for getting the print was thermal paper. The property of the thermal paper is that, the chemical coating provided on it gets melted and leaves black spots in portions which are subjected to low heat as a result of passage of electric pulses, so as to form the shapes of the letters/ figures/ digits etc.

In the latest type of machines, however, the usage of plain paper is becoming more popular, where inking arrangements have to be provided separately.

The word `telegram has' its origin from the words `tele and gram'. `Tele' — means distance and the `gram' stands for `write'. Naturally, therefore the combination of these two indicates `write at a distance'. The method employed to write at a distance has undergone many changes ever since it was invented during the latter half of the 19th century. To begin with, a single mechanical wire was drawn in between two places. By using a battery, a key and a sounder, at both the ends, it was possible to create a mechanical sound at the other end by the simple stroke of the key at one end. The sounds were produced by the skilful operation of the key, making dots and dashes (._) distinguishable by the time interval between two sounds. Different combinations of these dots & dashes were earmarked for alphabets, digits and other characters required for the transmission of a message, data etc. A system, namely Morse Code has been internationally accepted and continues to be in use still, adopting this dot and dash combination.

However, in tune with the various technological advancements, easier, faster and more reliable methods have since been introduced, say, teleprinter/ telex, etc.

The wireless telegraphy also has been widely used. In these systems, instead of dots and dashes, electric pulses are formed by a relay mechanism, which is controlled by the operation of a key board of letters. The pulses so generated, are converted into voice frequencies and transmitted along carrier wave channels. At the receiving end we are able to get a print of the message.

Published in 'The Hindu' on July 04, 2002.

Does Solar Exlipse Occur During Every New Moon Day? If So, Can It Be Seen From Some Part Of The Earth?

Does Solar Exlipse Occur During Every New Moon Day? If So, Can It Be Seen From Some Part Of The Earth?

The moon revolves around the earth in a plane slightly inclined (5 degrees) to the earth's orbit. Eclipses occur when sun, moon, and earth are aligned in a straight line.

When the moon is in between the earth and the sun we get to see the dark side of the moon called the new moon.

However due to the inclination of the moon's plane with respect to the earth, the moon does not block the sun's light every time it passes between the earth and sun. When the new moon occurs close to the sun, the sun's light is partially obscured resulting in a partial solar eclipse. On rare occasions, the moon directly moves between the sun and the earth blocking the sun's light from reaching the earth thus producing a total solar eclipse. On such occasions the sun, moon and the earth are in the same plane (and in a straight line).

Similarly, when the moon is on the opposite side of the earth from the sun we get to see a full moon.

At certain times the moon passes directly through the centre of the earth's shadow called the umbra. This results in the earth completely blocking the moon from the sun. The net result of this alignment is the total eclipse of the moon otherwise known as the total lunar eclipse. When the moon just grazes the earth's shadow passing within the penumbra we see the moon eclipsed only slightly.

This is partial lunar eclipse. Since the moon is not directly aligned with the earth and sun, the earth's shadow rarely falls on the moon. The inclination of the moon's plane with respect to the earth's orbit thus does not result in a total solar and total lunar eclipse every 28 days.

Published in The Hindu on June 27, 2002.

What Is Meant By Test Tube Babies?

What Is Meant By Test Tube Babies?

The technique of in-vitro fertilisation (IVF) and in-vitro development followed by the embryo-transfer in the uterus of the normal female to start the development and finally leading to normal birth is called test tube baby creation.

Methodology involves the following steps:

• Removal of unfertilised ovum from reproductive tract of a female.
• Ovum is kept under asceptic conditions.
• Fusion of sperm and ovum in a culture medium, outside the female body to form the zygote.
• ygote is stimulated to develop in vitro upto 32-celled stage.
• Developing embryo is implanted on the endometrium of the uterus at 32-celled stage. So the pregnancy in the woman starts and further the development of the child continues in the womb till it is born.

The IVF technology is a boon to childless couples. First attempt to produce a test tube baby was made by an Italian scientist Dr. Petrucci (1959 A.D.)

But this human embryo survived for only 29 days. The first test tube baby was born to Lesley and Gilbert Brown on July 26, 1978 in Oldham, England. Mrs. Brown had obstructed fallopian tubes. Dr. Patrick Steptoe and Dr. Robert Edwards, both from England, experimented on Mrs. Brown successfully.

The world's first test tube baby (a baby girl) was named as Louise Joy Brown. India's first test tube baby was born in Calcutta on October 3rd, 1978. Her name is Durga.

Published in The Hindu on June 27, 2002.

What Purpose Do The Two Outer Panes Of A Passenger Aircraft Cabin Window Serve And What Are They Made Of?

What Purpose Do The Two Outer Panes Of A Passenger Aircraft Cabin Window Serve And What Are They Made Of?

 

Airline windows typically comprise three or more layers of glass (or acrylic) to provide insulation from the very cold atmosphere at altitude.

The tiny silvery cylinder is really the edge of a small hole drilled in the middle layer to allow the pressure to equalise between the layers while minimising convection.

The condensation around the hold is due to the inner airspace cooling. Ice often forms here.

The position of the hole is chosen to maintain the best clear viewing area when condensation forms, to minimise the likelihood of a crack forming between the hole and the edge of the window, and to avoid excessive condensation pooling over the hole, which could freeze and block it.

Published in The Hindu on June 20, 2002.

Why Do Men Have More Body Hair Than Women Do?

Why Do Men Have More Body Hair Than Women Do?

Testosterone, the male sex hormone (androgenic hormone) is responsible for the distinguishing characteristics of the masculine body and the female sex hormone namely estrogen is responsible likewise for the feminine body.

In a foetus the sex organ develops from the newly organised genital ridge. If the foetus is a male the male chromosome causes the genital ridge to secrete testosterone, which decides the development of foetal testes and if the foetus is a female the female chromosome causes this ridge to secrete estrogen, which decides the development of female gonads (ovaries).

In male foetal testes the testosterones begin to elaborate at about the seventh week of embryonic life, during which the development of male body characteristics, including the formation of a penis and scrotum rather than the formation of clitoris and a vagina occurs.

The testosterone production increases rapidly under the stimulus of anterior pituitary gonadotropic hormones at the onset of puberty and lasts throughout most of the remainder of life, but dwindling rapidly beyond the age of 50 and gradually becoming 20 to 50 per cent of the peak value by the age of 80.

The re-initiation of testosterone secretion after puberty causes the increase in size of the male genital organ eightfold before the age of 20 years. In addition it also causes the `secondary sexual characteristics' of the male beginning at puberty and ending at maturity. One among the secondary sexual characteristics is the distribution of body hairs.

Beard appears, hairline on scalp (on the top of the head) recedes anterolaterally, pubic hair grows with male pattern (triangle with apex up), hair appears in axillas. .

Although body hair is increased by androgens, scalp hair is decreased. So there is possibility of development of baldness in man who has large quantity of androgenic hormones.

The testosterone secretion rate is 4-9 mg/ day in normal adult males resulting in the plasma testosterone level as 300-1000 nanogram/ decilitre (ng/dl), which is only 30-70 ng/dl in adult woman.

This is the only reason for the presence of more body hair in men than in women.

Published in The Hindu on June 20, 2002.

How Does A Lie Detector Work?

How Does A Lie Detector Work?

When a person takes a lie-detector test, four to six sensors are attached to the person. It is a machine in which the multiple signals from the sensors are recorded on a single strip of moving paper (or graph).

The sensors usually record the person's breathing rate, pulse, blood pressure and perspiration. Sometimes it may also record arm and leg movement.

When the test starts, the questioner asks three or four simple questions to establish the norms for the person's signals. Then the real questions being tested by the lie detector are asked. Throughout questioning, all the person's signals are recorded on the moving paper.

Both during and after the test, the examiner can look at the graphs and can see whether the vital signs show change on any of the questions. In general, a significant change (such as a faster heart rate, higher blood pressure, increased perspiration indicates that the person is lying."

Published in The Hindu on June 13, 2002.

What Is The Difference Between Bacteria And Virus?

What Is The Difference Between Bacteria And Virus?

Both bacteria and viruses fall under the group `micro-organisms' meaning `living creatures which cannot be seen by naked eyes.' The other groups of micro-organisms include fungi, algae and protozoa. Bacteria are of the size 10{+-}{+3} mm in diameter where as viruses are still smaller, 10{+-}{+4} _ 10{+-}{+5} mm in diameter. Bacteria are unicellular organisms in the sense that their entire body is made up of a single cell.

But unlike other living organisms viruses are acellular creatures, i.e., they don't have a proper cellular organisation. They appear like nonliving particles composed of nucleic acids (the genetic material), proteins and in some cases lipid layers. Viruses lack the ability to synthesize proteins and other cellular materials on their own because of their simple structural organization.

The viral particles usually remain inactive and need living systems for their growth and multiplication.

Bacteria can be cultured in laboratories artificially using synthetic chemical preparations called `medium.' But none of the viruses can be grown in artificial media and instead can be grown either in living cells or in living animals or plants. Because of this requirement of living systems, viruses almost always cause diseases in hosts.

A few examples of viral diseases are AIDS — caused by the virus HIV, polio — caused by poliomyelitis virus, rabies — caused by rabies virus, etc. Interestingly, viruses which cause diseases in animals won't cause diseases in plants and vice versa.

The above examples are diseases of human beings. Mosaic diseases are common plant diseases caused by viruses. Though bacteria don't require living systems they too cause diseases in animals and plants.

Typhoid, cholera, and diphtheria are examples of bacterial diseases caused in human beings.

Bacteria like most of the other living organisms have DNA as the genetic material while viruses can have either DNA or RNA as their genetic material.

Published in The Hindu on June 13, 2002.

Why Does Cutting Our Nails Not Hurt?

Why Does Cutting Our Nails Not Hurt?

The nails, present on the dorsal surfaces of the distal parts of fingers and toes are flattened, elastic structures. The proximal part of the nail, which overlapped by the nail fold (fold of skin) is called nail root. The part that is not covered by the nail fold is called body of the nail.

Beneath the nail lies the nail bed. The nail bed has two parts, the part under the root, which is called germinal matrix (concerned with the growth of the nail) and the part below the body of the nail is called sterile matrix.

The nail is analogous to the stratum cornium of thick skin, which is the outer most structure of the epidermis. It consists of flattened dead squames, which are the remnants of cells, which are filled with keratin. After gliding over the nail bed, the extreme distal end of the nail projects out.

When this projected portion is cut we cannot feel pain, since we are cutting a dead mass of hard squames. But when we cut the nail part, which is over the nail bed we feel the pain since the dermis in this region is supplied with rich nerve endings.

Published in The Hindu on June 06, 2002.

How Do Icebergs Form?

How Do Icebergs Form?

Icebergs are blocks of fresh-water ice that break off from glaciers and float out to sea. Glaciers are formed in polar regions where snowfall lasts for centuries, or even millennia, without entirely melting, and is eventually compressed into ice.

In the North Atlantic, most icebergs originate from the tidewater glaciers of Western Greenland. Compressed snow becomes firm, a granular snow, transformed eventually by pressure into a dense ice. The weight of the icecap builds, causing the ice to flow as much as 60 feet a day through openings in the coastal mountains.

Rising and falling tides cause slabs of ice to break off and form moving `rivers of ice.'

Published in The Hindu on June 06, 2002.

How Is Artificial Rain Produced?

How Is Artificial Rain Produced?

Answer 1:

The need to develop and improve rain-making techniques in terms of design, operation, monitoring and evaluation by giving them a more scientific character is today's need.

This includes using computers to study cloud formations and help the rain-making operations achieve the goals of the project. The role of weather modification, or rain-making, is an important component in water resource management.

The process involved in artificial rain-making involves three easy-to-understand stages. The first stage is agitation. That is using chemicals to stimulate the air mass upwind of the target area to rise and form rain clouds.

The chemicals used during this stage are calcium chloride calcium carbide, calcium oxide, a compound of salt and urea, or a compound of urea and ammonium nitrate. These compounds are capable of absorbing water vapour from the air mass, thus stimulating the condensation process.

The second stage is called building-up stage. Here the cloud mass is built up using chemicals such as kitchen salt, the T.1 formula, urea, ammonium nitrate, dry ice, and occasionally also calcium chloride to increase nuclei which also increase the density of the clouds. In the third stage of bombardment chemicals such as super-cool agents: silver iodide and dry ice are used to reach the most unbalanced status which builds up large beads of water (Nuclei) and makes them fall down as raindrops.

In planning every stage a high degree of expertise and experience is required, in selecting the types and amounts of chemicals to be used, while taking into consideration weather conditions, topographical conditions, wind direction and velocity as well as the location or delimitation of the area for chemical seeding. Several other ideas are also involved in rain making. Rockets containing rain-making chemicals can be fired into the clouds either from the ground or from aircraft.

A jet of rain-making chemicals is shot from a highly pressurised cannister directly into the cloud base, so as to coerce clouds which normally hang above mountain tops to cluster up and rain on the mountain or their slopes.

Rain-making chemicals are added to super-cooled clouds, i.e., those at altitudes above 18,000 metres, to stimulate the formation of ice crystals in the cloud or cloud cluster.

Answer 2:

Artificial rain is produced by spraying clouds with substances like Silver Iodide (costly) or cheaper ones like solid carbon dioxide (dry ice) or even finely powdered Sodium Chloride. The process is called seeding.

Often there are clouds, but no rain. This is because of a phenomenon called supercooling. The temperature of the cloud might be close to zero and there might even be crystals of ice in it.

The water vapour in the cloud does not condense to liquid water. The super cooling gets disturbed by spraying the cloud with the chemicals mentioned above, using a small aeroplane for the purpose.

The `super' phenomena (cooling, heating, saturation etc.) are perverse in a sense. Very pure water when heated in a clean vessel, often does not start boiling when expected. Crystals of the photographer's hypo (Sodium thiosulphate) easily dissolve in a little water when heated. But on cooling, crystals do not separate out.

If the vessel is shaken vigorously, or if a small crystal of hypo is freshly added, then crystallization starts immediately.

Making artificial rain is a similar way of intervening in the super cooling phenomenon.

Published in The Hindu on May 30, 2002.