SCIENCE & TECHNOLOGY

Holographic solar power
S. S. Verma

Finding out the means for making the efficient use of solar energy, whether for cooking/heating or generating electricity, has always been on the priority of the scientists and engineers. Solar photovoltaic cells have been developed but using them has limitations. 

What shrank the dogs
Steve Connor

The genetic trick that has allowed small dogs to shrink in size from their wolf-like ancestors has been discovered by scientists in a pioneering investigation of canine DNA.

Prof Yash Pal

Prof Yash Pal

THIS UNIVERSE
PROF YASH PAL

If two stars with green and red colours merge together, what will be the colour of the resulting star?

Stars are not just pots of paint. The rules of combining basic colours to get new ones have no meaning here. For example, you cannot say that combining blue and yellow would automatically give you green. It would be useful, perhaps to spend a few sentences on the relation between properties of a star and its surface colour. The spectrum of the light emitted by the surface of a star depends on its temperature.

 


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Holographic solar power
S. S. Verma

Holographic Solar concentrator
Holographic Solar concentrator

Figure 1 (a): With mirror
 Figure 1 (a): With mirror 

Finding out the means for making the efficient use of solar energy, whether for cooking/heating or generating electricity, has always been on the priority of the scientists and engineers. Solar photovoltaic cells have been developed but using them has limitations. The main limitation of solar power right now is cost because the crystalline silicon used to make most solar photovoltaic cells is very expensive. The high demand for solar cells in developed countries has already outstripped the supply, which has led to a silicon shortage and a shortage of manufacturing in the photovoltaic world.

One approach to overcoming this cost factor is to concentrate light from the sun using mirrors or lenses (Figure 1 a & b), thereby reducing the total area of silicon needed to produce a given amount of electricity. Other disadvantage is the requirement of a solar concentrator, which uses lenses, called Fresnel lenses, which take a large area of sunlight and direct it towards a specific spot by bending the rays of light and focusing them. The traditional light concentrators (Figure 2) with solar tracking system (as Earth is always on move with respect to sun) to catch the solar light are bulky and unattractive — less than ideal for use on house rooftops.

Figure 1 (b): With lens
Figure 1 (b): With lens

Holography is the science of producing holograms, an advanced form of photography, that allows an image to be recorded in three dimensions. Hologram is a laser-created pattern that diffracts light. Once the film is processed, if illuminated once again with the reference beam, diffraction from the fringe pattern on the film reconstructs the original object beam in both intensity and phase.

To date, little attention has been given to optics technologies in solar module R&D. Holographic technology can impact solar module output and application. It is believed that holographic technologies might be next promising frontier for increasing energy efficiency from solar photovoltaic modules.

Although the idea of holographic solar concentrators has been around since the early 1980s, no one has developed them commercially yet. Now Prism Solar Technologies of Stone Ridge, NY (USA) has developed a proof-of-concept solar module that uses holograms to concentrate light. They are going to manufacture a new solar module that incorporates its patented holographic planar concentrator (HPC) technology.

In their ability to concentrate light, holograms are not as powerful as conventional concentrators. They can multiply the amount of light falling on the cells only by as much as a factor of 10, whereas lens-based systems can increase light by a factor of 100, and some even up to 1,000. But traditional concentrators are complicated and they also heat up the solar cells, and so require a cooling system. As a result, although they redirect light with more intensity than the hologram device, they’re unwieldy and not as practical for residential uses.

Holograms have advantages that make up for their relatively weak concentration power. They can select certain frequencies and focus them on solar cells that work best at those frequencies, converting the maximum possible light into electricity. The holographic module technology is “cell-neutral” and can spectrally select the desired portion of sunlight allowing for “cooler” solar cell operation while maintaining an increased power output by concentrating specific solar wavelengths unto the cells. In this way, we can efficiently use only that part of the sunlight that really matters.

The new technology replaces unsightly concentrators with sleek flat panels laminated with holograms. Also, different holograms in a concentrator module can be designed to focus light from different angles — so they don’t need moving parts to track the sun.

The panels, says company’s president and CEO, are a “more elegant solution” to traditional concentrators, and can be installed on rooftops — or even incorporated into windows and glass doors.

The system needs 25 to 85 percent less silicon than a crystalline silicon panel of comparable wattage because the photovoltaic material need not cover the entire surface of a solar panel. Instead, the PV material is arranged in several rows. A layer of holograms directs light into a layer of glass where it continues to reflect off the inside surface of the glass until it finds its way to one of the strips of PV silicon.
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What shrank the dogs
Steve Connor

The genetic trick that has allowed small dogs to shrink in size from their wolf-like ancestors has been discovered by scientists in a pioneering investigation of canine DNA.

A major study of more than 3,200 dogs from 143 different breeds has located the part of the canine genome that is responsible for producing diminutive stature in breeds such as the bichon frise, chihuahua and pekinese.

The part of the canine genome responsible for small size is not a gene but a “regulatory sequence” that controls a separate gene responsible for a key growth factor.

Scientists found that all small dogs they examined possessed the same kind of regulatory sequence. They believe the findings can explain the huge variations in dog size - the largest of any mammal.

“The identification and characterisation of a key genetic variant that accounts for differences in dog size is particularly exciting because the underlying gene is present in all dogs and other diverse species, including humans,” said Eric Green, of the US National Human Genome Research Institute.

The findings will also lead to a better understanding of many human conditions that are affected by the same insulin-like growth factor gene, said Elaine Ostrander, head of cancer genetics at the genome research institute.

“Nearly all of what we learn from studying body structure, behaviour and disease susceptibility in dogs helps us to understand some aspect of human health and biology,” said Dr Ostrander.

“By learning how genes control body size in dogs, we are apt to learn something about how skeletal body size is genetically programmed in humans.

“We also will increase our data set of genes likely to play a role in diseases such as cancer, in which regulation of cell growth has been lost,” she said.

Dogs evolved from wolves between 12,000 and 15,000 years ago when they were domesticated by humans for hunting and guarding. At some point soon after, the genetic variant for small size evolved and spread rapidly. Although the scientists have not yet been able to pinpoint the precise changes to the DNA that account for the size of small dogs, they believe it resides within a variation in the segment of DNA that lies next to the gene for insulin-like growth factor.

By arrangement with The Independent, London.
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THIS UNIVERSE
PROF YASH PAL

If two stars with green and red colours merge together, what will be the colour of the resulting star?

Stars are not just pots of paint. The rules of combining basic colours to get new ones have no meaning here. For example, you cannot say that combining blue and yellow would automatically give you green. It would be useful, perhaps to spend a few sentences on the relation between properties of a star and its surface colour. The spectrum of the light emitted by the surface of a star depends on its temperature. This is no different from the case when we have other surfaces, such as pots and pans or chunks of any other material.

We have to remember that in the case of stars the energy generation is at their centres where nuclear fusion takes place. There the temperatures would be much higher. For our sun the core temperature is about 15 million degrees Centigrade while at its surface it is only abut 6ooo degrees. The heat produced at the centre is transported to the surface through various processes involving convection and radiation.

Any way, the colour of the surface of a star is a basic measure of its surface temperature. Bluish stars are hotter than red stars and yellow stars lie in between. The rate of production of energy in a star depends on its mass.

A star that is more massive necessarily has a higher temperature at the core, capable of producing the higher pressure required for withstanding the gravitational compression of its higher mass. In fact very heavy stars burn more furiously and exhaust their fuel faster. They are bright but also live shorter lives.

So coming to the question you have asked, if merging means that the two stars become ONE, of a mass higher than that of either of them, it seems to me that the massive star now created would run hotter and the colour on the surface would move towards blue. This is not what would happen when you combine green and red in a paint box. Not even so if you combine green and yellow.

So my answer to your question is that a merger of the two stars, one red and the other green, would produce one that will appear bluish!
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