Friday, January 22, 2010

IN SEARCH OF SPEED

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You couldn't have asked for a better day for a competition. It's minus five degrees, the sun's shining and there's not a breath of wind. The snow's perfect and the biathlete's in top form. He's one of the best – he can win the race. Often there's only a few thousandths of a second between the victor and the vanquished, so the gliding ability of his skis is very important. And this depends on several factors, not least whether the wax mixture he's applied suits the particular type of snow.

Anyone looking for optimal ski performance must first understand the laws of friction. That is why wax and ski coating manufacturers are counting on the expertise of researchers at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg. The scientists have been studying the gliding ability of skis and know how to make ski athletes go like the wind. Prof. Dr. Matthias Scherge, Head of the new Microtrobilogy Center in Karlsruhe, says: »The snow, the ski coating and the wax that is applied all unite to form a single entity. We can't alter the snow, but we can adapt both the wax and the coating to suit particular snow conditions.« The researchers use a special technique to analyze the friction and gliding effects; they simulate the contact between a single snow crystal and the coating with the aid of a test rig, and then measure the coefficient of friction in relation to temperature. »It's the first 10 to 15 nanometers of the coating surface that determine the gliding effects,« explains Scherge. And they have another item of equipment in their armory as well: a ski tribometer. Here, a small section of ski travels in a circle over a snow-covered disc, allowing the researchers to test different combinations of waxes and coatings and ascertain the optimum combinations for specific conditions such as temperature. The ultimate test is then conducted in the ski hall, where biathletes perform glide tests on a hundred-meter test run with a defined gradient. Their times are measured with the aid of a leg-mounted transponder, which guarantees split-second accuracy; this enables the researchers to establish how many thousandths of a second can be shaved off their times by the right combination of ski coating and wax.

The researchers are working with Holmenkol and other partners to develop novel waxes and super fast coatings. Scherge says: “We've talked with athletes and also with the technicians who wax their skis prior to every competition. It's only with their knowledge and experience that we'll be able to create skis that glide perfectly.”

(Photo: (© Fraunhofer IWM)

Fraunhofer Institute

QUANTUM COMPUTER CALCULATES EXACT ENERGY OF MOLECULAR HYDROGEN

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In an important first for a promising new technology, scientists have used a quantum computer to calculate the precise energy of molecular hydrogen. This groundbreaking approach to molecular simulations could have profound implications not just for quantum chemistry, but also for a range of fields from cryptography to materials science.

"One of the most important problems for many theoretical chemists is how to execute exact simulations of chemical systems," says author Alán Aspuru-Guzik, assistant professor of chemistry and chemical biology at Harvard University. "This is the first time that a quantum computer has been built to provide these precise calculations."

The work, described this week in Nature Chemistry, comes from a partnership between Aspuru-Guzik's team of theoretical chemists at Harvard and a group of experimental physicists led by Andrew White at the University of Queensland in Brisbane, Australia. Aspuru-Guzik's team coordinated experimental design and performed key calculations, while his partners in Australia assembled the physical "computer" and ran the experiments.

"We were the software guys," says Aspuru-Guzik, "and they were the hardware guys."

While modern supercomputers can perform approximate simulations of simple molecular systems, increasing the size of the system results in an exponential increase in computation time. Quantum computing has been heralded for its potential to solve certain types of problems that are impossible for conventional computers to crack.

Rather than using binary bits labeled as "zero" and "one" to encode data, as in a conventional computer, quantum computing stores information in qubits, which can represent both "zero" and "one" simultaneously. When a quantum computer is put to work on a problem, it considers all possible answers by simultaneously arranging its qubits into every combination of "zeroes" and "ones."

Since one sequence of qubits can represent many different numbers, a quantum computer would make far fewer computations than a conventional one in solving some problems. After the computer's work is done, a measurement of its qubits provides the answer.

"Because classical computers don't scale efficiently, if you simulate anything larger than four or five atoms -- for example, a chemical reaction, or even a moderately complex molecule -- it becomes an intractable problem very quickly," says author James Whitfield, research assistant in chemistry and chemical biology at Harvard. "Approximate computations of such systems are usually the best chemists can do."

Aspuru-Guzik and his colleagues confronted this problem with a conceptually elegant idea.

"If it is computationally too complex to simulate a quantum system using a classical computer," he says, "why not simulate quantum systems with another quantum system?"

Such an approach could, in theory, result in highly precise calculations while using a fraction the resources of conventional computing.

While a number of other physical systems could serve as a computer framework, Aspuru-Guzik's colleagues in Australia used the information encoded in two entangled photons to conduct their hydrogen molecule simulations. Each calculated energy level was the result of 20 such quantum measurements, resulting in a highly precise measurement of each geometric state of molecular hydrogen.

"This approach to computation represents an entirely new way of providing exact solutions to a range of problems for which the conventional wisdom is that approximation is the only possibility," says Aspuru-Guzik.

Ultimately, the same quantum computer that could transform Internet cryptography could also calculate the lowest energy conformations of molecules as complex as cholesterol.

(Photo: Stephanie Mitchell)

Harvard University

CAN A DROP OF WATER CAUSE SUNBURN OR FIRE?

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To the gardening world it may have always been considered a fact, but science has never proved the widely held belief that watering your garden in the midday sun can lead to burnt plants. Now a study into sunlit water droplets, published in New Phytologist, provides an answer that not only reverberates across gardens and allotments, but may have implications for forest fires and human sunburn.

"The problem of light focusing by water droplets adhered to plants has never been thoroughly investigated, neither theoretically, nor experimentally", said lead researcher Dr Gabor Horvath, from Hungary's Eotvos University. "However, this is far from a trivial question. The prevailing opinion is that forest fires can be sparked by intense sunlight focused by water drops on dried-out vegetation."

The team conducted both computational and experimental studies to determine how the contact angle between the water droplet and a leaf affects the light environment on a leaf blade. The aim was to clarify the environmental conditions under which sunlit water drops can cause leaf burn.

These experiments found that water droplets on a smooth surface, such as maple or ginkgo leaves, cannot cause leaf burn. However in contrast the team found that floating fern leaves, which have small wax hairs, are susceptible to leaf burn. This is because the hairs can hold the water droplets in focus above the leaf's surface, acting as a magnifying glass. The latter not only partly confirms the widely held belief of gardeners, but also opens an analogous issue of sunburn on hairy human skin after bathing.

"In sunshine water drops residing on smooth hairless plant leaves are unlikely to damage the leaf tissue", summarised Horvath and co-authors. "However water drops held by plant hairs can indeed cause sunburn and the same phenomenon can occur when water droplets are held above human skin by body hair."

While the same process could theoretically lead to forest fires if water droplets are caught on dried-out vegetation, Horvath and colleagues added a note of caution:

"If the focal region of drops falls exactly on the dry plant surface intensely focused sunlight could theoretically start a fire," Horvath said. "However, the likelihood is reduced as the water drops should evaporate before this, so these claims should be treated with a grain of salt."

Wiley-Blackwell

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