Artificial recharge of ground water
by G.S. Gill
THE concept of augmenting groundwater reservoirs by various artificial techniques is gaining acceptance in most of the developing countries. Only 32 per cent of the total supply of fresh water on the earth occurs underground, flowing through spaces between sedimentary grains and cracks in rocks.

Developing solar cells for space
by Suneel Deambi
SPACE technology is the moving force behind modern day marvels of telecommunication, remote sensing, weather forecasts. The satellites used for the purpose require a very high degree of technological sophistication in design, fabrication fueling and the ultimate launch. In this kind of stringency, how often have you pondered about the role of solar energy?

Electronic pen to disinfect water
A new battery-powered pen that electrochemically generates mixed oxidants to disinfect drinking water has been developed by US researchers.

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Artificial recharge of ground water
by G.S. Gill

THE concept of augmenting groundwater reservoirs by various artificial techniques is gaining acceptance in most of the developing countries. Only 32 per cent of the total supply of fresh water on the earth occurs underground, flowing through spaces between sedimentary grains and cracks in rocks. Such sites are called “aquifers”. The indiscriminate use of this fresh water has resulted in the depletion of groundwater reservoirs at a fast rate. India has suffered serious droughts. The artificial recharge of the depleted aquifers remains the only solution.

The basic requirement for artificial recharge of groundwater is the availability of source water, which in this part of the globe is provided by monsoon surplus runoff. This surface runoff in the urban areas can be trapped from the metalled streets, roads and rooftops.

Before starting a project, detailed study of the geological and hydrogeological features of the area is essential. Some of the important parameters to be considered in such cases are geological boundaries, hydraulic boundaries, inflow and outflow of water, storage capacity of aquifers, porosity, hydraulic conductivity, transmissivity, lithology, depth of aquifer and tectonic boundaries. The acquifers capable of absorbing large quantities of water and retaining it for long times, are best suitable for artificial recharge. Thus the recharge capabilities of underlying hydrogeological formations must be assessed before taking up any project on recharging. The projects undertaken and accomplished hurriedly to show off results often lead to environmental hazards.

After such preliminary surveys, the availability of source water is assessed. Surplus monsoon run-off is the easily exploitable source, which otherwise goes unutilised. The assessment is based on the rainfall data. The rainwater can be harvested for recharging from street flows, road crossings and rooftops.

The following tools come in handy:

1. Abandoned dug wells
2. Abandoned or running hand pump.
3. Recharge pit for shallow aquifers
4. Recharge trench for shallow aquifers
5. Recharge well
6. Recharge shaft

Developing solar cells for space
by Suneel Deambi

SPACE technology is the moving force behind modern day marvels of telecommunication, remote sensing, weather forecasts. The satellites used for the purpose require a very high degree of technological sophistication in design, fabrication fueling and the ultimate launch. In this kind of stringency, how often have you pondered about the role of solar energy?

The power needed for satellite roving in the outer space are generated through the Solar Photovoltaic (SPV) cells, which convert light energy of the solar radiation into useful electricity.

SPV cell technology is being currently used globally for meeting a variety of end-use terrestrial applications like the lighting, water pumping and battery charging etc. But you may wonder that these types of solar cells are not suitable for space applications. Incidentally, the discovery of the PV effect originally culminated in the use of solar cells for space applications only way back in 1957. It was much later during the fuel crisis of early seventies, when serious efforts to develop terrestrial cells began to take a concrete shape.

Beyond doubt, SPV cells for satellites represent one of the most difficult areas of material technology from several important considerations. First, the solar cells have to operate under extreme conditions, in which the performance life are also not known. Further, it is rather impossible to undertake the repair of defective units, and that too at quite a high cost. The solar arrays mounted on the body of the satellite also need special material difficulties due to their large size and exposed working surfaces. In addition, the cyclic temperature variations of hundreds of degrees, high velocity micro-particles and powerful radiation combine to take their toll on the space-borne systems.

The most important thing is that the space-borne cells should have a very high efficiency and be much smaller in size to economise cost. Today, semiconducting materials like the Silicon, Gallium Arsenide (GaAs) and Gallium Antimonide etc. are being used to fabricate the solar cells. Performance wise the GaAs cells are preferred, owing to their very high tolerance to extreme temperatures and radiation, when compared to the rival silicon. The radiation essentially consists of high-energy particles like Electrons, Protons, Gamma Rays and X-rays etc. Out of this, protons cause more severe damage than electrons.

However, silicon cells are definitely much cheaper than GaAs cells, which makes their use more widespread. More recently, the tandem cells based on a combination GaAs and GaSb are being actively examined for space applications. Such cells have the design capability to absorb both long and short wavelength radiations of the solar spectrum to optimise power output from within the same array.

Solar cells convert the light energy incident on their surface into useful electricity through photovoltaic effect. More the efficiency of a solar cell, higher is the power output available from the solar panel and the array. The new generation silicon solar cells available today have a light-to-electric conversion efficiency ranging between 14 and 17 per cent. As sensitivity to radiation damage increases with efficiency, the satellites for high radiation areas such as polar orbits are generally designed with less efficient cells.

Researchers experimenting with different material forms of cells find that GaAs cells do not lose much efficiency at high temperatures.

This is probably because of a rapid annealing effect on such cells. Moreover, these cells do not undergo a quick degradation due to radiation and thus have a fairly high long-term stability in an outdoor environment. However, the predominant use of GaAs cells has so far been made on military missions. Despite a cost saving measure to use the Germanium as a cell substrate, the cells made of GaAs are still very expensive, when compared to silicon. (PTI)

Electronic pen to disinfect water

A new battery-powered pen that electrochemically generates mixed oxidants to disinfect drinking water has been developed by US researchers.

Developed at University of North Carolina at Chapell Hill the pen in tests could make water virtually free of many bacteria and viruses that include highly chlorine resistant Cryptosporidium, parvum, a major source of water contamination, within ten minutes.

Users put a small amount of water in the pen. The salt pellets dissolve in the water, which comes in contact with battery powered electrodes, says a release from the university.

The findings on the pen were presented at a meeting of the American Society for Microbiology in Los Angeles last month.

After that a mixture of oxidants are generated from the salt solution that inactivates C. parvum eggs, bacteria, viruses to produce safe drinking water in minutes. Within 30 seconds of flicking a switch, electrolysis takes place generating chlorine and other oxidants from the saltwater.

The solution contents are then added to water bottles or containers to deliver enough oxidants for disinfection within ten minutes. The process gives better results than what plain chlorine gives, the researchers say. Several designs of the pen are available.

Powered by the sun

Auto manufacturers are being driven by a sudden sense of urgency. The realisation that oil supplies are short-lived has been the final signal to make their search for a petrol substitute go into hyper drive.

Ever since the seventies researchers have been toying with concepts like wind and solar energy; even electricity and alcohol have been tried out as replacements.

Of these, solar energy seems to be the only alternative that holds the promise of really becoming a commercially viable solution. Many leading autogiants are already testing prototypes of solar cars.

Seen in the picture is the top view of Honda’s solar powered car. It can attain speeds of up to 90 kmph and as long as there is sunlight there is fuel. However, the powerful solar cells can store some as well and ensure that there is some for the rainy day as well!

New printing technique

An Australian invention will help revolutionise printing — an industry that goes back more than 600 years. Developed at Commonwealth Scientific and Industrial Research Organisation (CSIRO), the new offset printers reduce ink, paper wastage and printing costs.

Offset printing is the main technology used in newspapers, publications and package printing.

“One of the ways of achieving consistent print quality is to control the thickness of the dampening solution on the printing plates,” says Andrew Greatbatch, business development manager at CSIRO’s telecommunications and industrial physics division.

Too much ink and the print may darken and blur the point whereas too much dampening solution may fade the print. Getting the right balance of ink and dampening solution is critical to fine colour control.

Printers currently rely on the look of the finished product to adjust the ink/water balance. OPTI will help them to adjust it objectively. There are sensors that measures the colour density on the printing plate, and OPTI solves the other half of the equation too — water thickness measurement and control.

Improved human vision

Taking cue from a method originally developed by astronomers to obtain better images of the universe, a US researcher has come up with a technology that enhances people’s vision beyond what is normally perceived as perfect vision.

David Williams from University of Rochester has developed the technology using “adaptive optics” which was originally developed by astronomers to sharpen images from telescopes by correcting aberrations in the atmosphere.

The system detects visual distortions so subtle that physicians did not even known they existed. Today a visit to the eye doctor focuses mainly on two types of aberration — astigmatism and defocus. Most prescriptions are intended to correct these two defects. The new system can measure up to 65 different aberrations.

Detailed information of the eye is helpful to ophthalmologists monitoring patients with diseases like age-related molecular degeneration or diabetic retinopathy.

The scientists direct a harmless, highly focused spot of light into the eye of a research subject and measure the light that is reflected outward. The light provides a glimpse of the topography of the eye in exquisite detail.

The light is broken up into 217 laser beams that are sent into a sophisticated device known as a wavefront sensor. The sensor analyses deviations in each beam’s path, revealing tiny imperfections or aberrations that exist in the person’s cornea and lens.

These precise measurements are sent to a sensitive “deformable mirror — one that can bend and customise its shape according to the measurements of a person’s eye. Such flexible mirrors form the heart of traditional adaptive-optics system used in astronomy.

Circuit mimics brain wiring

Scientists have developed an electronic circuit that mimics the wiring of the human brain in some ways — an achievement that could revolutionise computer science and improve understanding of how nature’s most powerful processor works, reports Associated Press.

The circuit, built on a silicon chip the size of a fingernail, is far from the thinking machines of science fiction. For one thing, it cannot learn the way the brain can.

But researchers say it could result in better speech and object recognition by computers.

“This is a demonstration of what is possible when circuits compute in biological ways,” said Rahul Sarpeshkar, a computer science professor at the Massachusetts Institute of Technology who worked on the project. “We are still far away from building a brain.”

The findings, published in Nature are the culmination of more than two decades of work using transistors and silicon to mimic the natural circuitry in the brain’s cortex.