|SCIENCE TRIBUNE||Thursday, June 12, 2003, Chandigarh, India|
Safe radiation use
UNDERSTANDING THE UNIVERSE
Factors behind erratic summer monsoon
THE vagaries of Southwest monsoon are well known which are capable of destabilising our Indian economy. The erratic nature of monsoon raises the same questions every year in the months of May-June-Will the monsoon burst on time? If so, will the rainfall be normal? Will the rain be delayed and if so, how long? Will the rain be widespread or limited to certain pockets? Such questions always haunt the weathermen, farmers and policy makers alike.
Sir Gilbert Walker was the first scientist who introduced a technique to predict the Indian monsoon. In 1924, he made important discovery of "Walker Circulation" and "Southern Oscillations". Both these phenomenon are associated with monsoon rainfall. He introduced the concept of correlation coefficient to seasonal forecasting.
It is well known that monsoon circulation is a thermally driven low pressure are arising due to the thermal contrast between the vast Asian continent and the Indian Ocean to its south during the summer season. Heating due to elevated land mass such as the Tibetan plateau and Himalayan ranges and the latent heat released due to large-scale convection in Southeast Asia also contributes towards the differential heating. Greater the temperature contrast, better it is for monsoon rainfall. The temperatures are, therefore, considered to be directly linked with the monsoon rainfall.
Then the question arises that how the long-range forecast of summer monsoon rainfall is done. For this a model using 16 weather related parameters had been in use since 1988 by the India Meteorological Department. But from year 2003, a power regression model using only eight weather related parameters has been operationalised. This new model has enabled the India Meteorological Department to advance the date of issue of Long Range Forecast from May 25 to April 16. Some of these parameters are global and others are regional in nature. The important parameters which are physically linked with monsoon rainfall are temperature, pressure, wind pattern and snow cover over the Himalayas.
Of all the weather parameters, "El-Nino" is one of the important teleconnections of monsoon which is global in nature. It has the capability to distort the global wind pattern and has far-reaching effects on world trade. Many experts have expressed their view that the weak monsoon of 1982, 1987 and 2002 may be attributed to the famous "El-Nino effect". The name "El-Nino" comes from the Spanish speaking people who live along the Pacific coast of Peru. Each year in late December, a southward moving current warms the water. The Peruvians started calling the warm current "El-Nino" ó boychild, for the infant Jesus ó because it comes around Christmas.
"El-Nino" refers to all the conditions associated with warmer than normal water in the tropical Pacific from the International Date Line to South America. On the contrary when the water in this area is colder than normal, it is called "La Nina" ó little girl. "La Nina" has also global effects, but not as striking as "El-Nino".
Comparison of monsoon rainfall data over 100 years has shown clear evidence of the association between weak monsoon, large negative Southern Oscillation index and El-Nino events and also strong monsoon, large positive Southern Oscillation Index and La-Nina events. The success of "El-Nino" predictions generated great interest among the scientists to use the ocean conditions in predicting the weather in coming months or even a year in the future.
Closer to home in a study compiled by the authors over 100-year monsoon rainfall variability at Ludhiana (Figure) indicates that maximum monsoon rainfall of 1242 mm occurred in 1988 and the lowest monsoon rainfall of 164 mm occurred in 1987 against a normal of 558 mm. The monsoon months of June, July, August and September experience a normal rainfall of 57, 210, 178 and 113 mm, respectively.
The activities of monsoon over India are influenced by the position of seasonal low-pressure area, position of the monsoon trough and the frequency and movement of monsoon depression towards Northwest India. Out of these features, "monsoon depression" is the main driving force for the monsoon to move into many parts of India.
The past record of monsoon indicates that North-west India receives widespread heavy to very heavy rainfall whenever there is an interaction between western disturbance and the monsoon depression. Such type of interaction between these two systems was experienced during the month of September in 1988, 1997 and even 1998 when very heavy rainfall was recorded in many areas of north-west India.
The monsoon drought of 2002 is still very fresh in our memory. This year the India Meteorological Department has predicted overall Indian monsoon to be 96% of normal.
Indian agriculture is dependent on the timely receipt of the rains. Therefore, correct forecast of the season will go a long way in helping the farmers to prepare a contingent plan to undertake suitable cropping pattern. Similarly it will enable the planners to formulate correct and effective food policies for the next season.
Safe radiation use
DURING the early eighties, while visiting Washington, I stayed with my friend for a day. We exchanged notes on our other friends. While taking dinner, we heard a hooting sound, so loud that I nearly fell down from the chair.
"Oh no! It is the smoke alarm," my friend said. "Now the fire brigade crew will come over", "I have to convince them that it is a false alarm". I felt more embarrassed later, when I realised that my friendís wife fried some "papad" for us. The smoke detector cannot distinguish between smoke and coconut oil fumes! In residences in many states in USA, strategically placed smoke detectors are mandatory.
Smoke detectors have a small radioactive source (Americium-241), the alpha particles from which ionise the air and allow a current between two electrodes. Smoke entering the detector interrupts the current setting off the alarm. The timely wake-up call from this relatively inexpensive device helps to save enormous amounts of money.
Many uses of ionising radiation are unique. A few of them are indispensable. Radioisotope techniques assure the quality of industrial products. During oil well logging, radioisotopes help to identify hydrocarbon layers several kilometres underground. Radioisotope techniques are irreplaceable in hydrology.
The radiation equipment used in industry includes gamma irradiators, gamma chambers, industrial gamma radiography exposure devices, electron accelerators and ionising radiation gauging devices. Other products are radioluminous timepieces, gaseous tritium light devices, ionisation chamber smoke detectors, fluorescent light starters, anti-static devices and incandescent gas mantles containing thorium. Of the nearly 40,000 radiation workers in the country, over 5000 are in the industrial applications of radiation.
Sterilisation of medical products by gamma rays is cheaper and more effective than steam heat sterilisation. Many Powders and biological preparations containing bone, nerve and skin and ointments and solutions are heat-sensitive. These can be sterilised by gamma irradiation. Other medical products which could be gamma sterilised include surgical instruments, heart valves, bandages, cotton wool, plastic and rubber sheets.
More than 1150 gamma radiography exposure devices are used in India. This is a unique non-destructive testing procedure similar to medical x-ray examination. Workers who handle radiography sources carelessly may receive high radiation doses. Obviously, industrial gamma radiography is the most stringently controlled application of radiation all over the world.
Various industries in India use over 7500 nucleonic gauges. These are designed with adequate level of built-in-safety, as they have to withstand adverse conditions such as high humidity, corrosive atmosphere and even ingress of water. These are ideal to detect levels of materials in containers. Nucleonic gauges contain a radiation source and a detector. The intensity of radiation passing through a material depends on the type of material and its thickness. This principle may be used to control the thickness of paper or thin metal sheets and to study chemical processes on line.
No regulatory controls are necessary to protect public from radiation exposure from consumer products such as gas mantles containing thorium-232 and radioluminous compounds, as they satisfy the specifications prescribed by the competent authority at the manufacturing stage.
Seventyfive manufacturing units in the country handle about 200 metric tonnes of thorium annually to make about 200 million gas mantles.
The Atomic Energy Regulatory Board
(AERB) enforces radiation safety requirements in institutions using
radiation sources. The board issues type approval certificates for
radiation sources, approves Radiological Safety Officers and issues No
Objection Certificates (NOC) to import radiation sources.
Type-approved equipment satisfies the built-in- safety features.
NEW PRODUCTS & DISCOVERIES
As it scurries along the ceiling, a gecko has the sticking power to support not just its own body weight, but about 400 times as much. Besides that sticking power, the natural adhesive on this animalís feet is clean and reusable, and it works on all surfaces, wet or dry.
Scientists at the University of Manchester in England and the Institute for Microelectronics Technology in Russia have emulated the animalís adhesive mechanism by creating "gecko tape." It comes closer to the lizardís sticking power than any other gecko-styled adhesive so far.
The 1-square-centimetre prototype patch can bear about 3 kilograms, almost one-third the weight that the same area of gecko sole can support.
In the July Nature Materials, Andre Geim of the University of Manchester and his colleagues claim that the tape is scalable to human dimensions: Wearing a "gecko glove," a person could dangle from the ceiling. In theory, the tape could hold tissues together after surgery or support stunt doubles climbing around movie sets.
The gecko tape is modeled on the gecko sole, an intricate fingernail-size surface covered with a half-million microscopic, hair-like structures known as setae. Each setaís tip branches into even finer hairs that nestle so closely with every surface the gecko touches that intermolecular attractions called van der Waals bonds and capillary forces kick in. These bond the geckoís foot to the surface
Geim and his team made their synthetic gecko adhesive by fabricating a tidy array of microscale hairs out of polyimide, a flexible and wear-resistant plastic. When mounted on a flexible base, the arrangement and density of the hairs maximise the number of hairs contacting a surface.
Researchers at Indiaís Central Salt and Marine Chemicals Research Institute at Bhavnagar in Gujarat have produced salt from a vegetable plant.
"This is the first time salt has been produced from a vegetable source and we have filed an international patent," Pushpito Ghosh, director of CSMCRI, an institute under the Council of Scientific and Industrial Research told PTI. The salt currently used for cooking worldwide is derived from seawater.
Named "saloni", it contains several important nutrients not normally found in sea salt and is therefore promising as a health salt, Ghosh said. Samples have been sent to some companies overseas to assess its commercial potential and "the preliminary feedback is encouraging," he said.
Most plants are intolerant to salt but some
plants grow under high saline conditions. CSMCRI scientists, surveying the
Gujarat coast, found one such salt-loving species "Salicornia
brachaita," a leafless shrub that accumulates salt within its tissue.
Subsequently they developed a proprietary process for extraction of salt from
the plant. PTI
UNDERSTANDING THE UNIVERSE
We have solid, liquid, gas and plasma states of matter. In which of these can we include fire?
Consider this. We take a solid and start heating. This increases the vibration of the molecules of the solid. At some point their vibration energy overcomes the bonds of the lattice and the solid turns into a liquid. Molecules in the liquid are not completely free; they are still subject to intermolecular forces. We go on heating to the point where the thermal energy of the molecules allows them to escape the shackle of their neighbours. Then we have a gas. If we go on heating this gas we may come to a point where the energy of collision of the molecules is high enough to break up the atoms. In other words electrons can be knocked out of the atoms. This is a state where the overall charge of the gas is still zero but the gas is made up of positive and negative particles. Such a gas becomes a highly conducting medium.
It would be all right to call this state as a plasma state. In this state electricity is easily conducted. Movement of charged particles produces magnetic fields. Coupling between currents and magnetic fields is central. If the plasma is propelled in a certain direction the entangled magnetic fields travel along with it. This is the phenomenon that is encountered when streams of solar plasma travel out during solar activity. When this plasma, along with its frozen magnetic fields hits the magnetosphere of the earth we experience problems in radio communication and magnetic storms.
A familiar example of plasma is encountered in the fluorescent tubes that all of us use in our homes. The current in the tube is sustained by plasma. The interactions produce high frequency radiation, mostly in ultraviolet, which when falling over the fluorescent material of the walls of the tube produces visible light.
At this point you might think that I am dodging you question "in what state of matter can we include fire". Fire is not a thing but a happening. It is a happening in which high temperature does produce ionised particles that emit light during recombination. In that sense there is plasma in fire. But its flame and dance are due to turbulent convection in which air rushes in from outside, helps sustain the combustion in which energy is produced, rising gases include plasma and neutral gases. Fire would look rather different in a gravity-free atmosphere. In short, fire does contain some plasma along with other gases, besides the happening of a reaction in which energy is produced.
Why do pictures of big objects like mountains, rivers, buildings etc. on our small TV screens appear as big as in real life?
To understand this all you have to
remember is this. Ultimately the image you sense is that created on
the tiny retina of your eye. The size you sense is in relation to
other objects in the frame. What you see of a mountain five kilometers
away is captured by the camera and transferred to a TV screen in front
of you. The image on your retina is about the same size as that you
would get while seeing the mountain directly.