Monday, October 11, 2010


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The second law of thermodynamics is a big hit with the beret-wearing college crowd because of its implicit existential crunch. The tendency of a closed systems to become increasingly disordered if no energy is added or removed is a popular, if not depressing, "things fall apart" sort-of-law that would seem to confirm the adolescent experience.

Now a joint team of Ukrainian and American scientists has demanded more work and less poetry from the second law of thermodynamics, proposing a novel "pyroelectric" method to power tiny devices using waste heat.

Using tiny structures called ferroelectric nanowires, they can rapidly generate an electrical current in response to any change in the ambient temperature, harvesting otherwise wasted energy from thermal fluctuations. Their report appears in the Journal of Applied Physics, which is published by the American Institute of Physics.

Explains lead researcher Anna Morozovska of the National Academy of Sciences of Ukraine, "The second law of thermodynamics rules modern life: Through all kinds of industry, humans consistently produce an enormous amount of waste heat. However, the laws of thermodynamics do not exclude rescuing some of this energy by harvesting the thermal fluctuations to produce electricity."

Pyroelectrictricity can play key role in consumer electronics, says Morozovska, and recovering this heat in the form of pyroelectric energy may bring about a new era of "tiny energy." Pyroelectric nanogenerators could be extremely useful for powering specific tasks in biological applications, medicine and nanotechnology, particularly in space because they perform well in low temperatures.

In an investigation of the pyroelectric properties of ferroelectric nanowires, the team analyzed how the pyroelectric coefficient corresponds to the radius of the wire and its coupling. They found that the smaller the wire radius, the more the pyroelectric coefficient diverges until a critical radius at which the response changes to paraelectric (above the Curie temperature). This so-called "size effect" could be used to tune the phase transition temperatures in ferroelectric nanostructures, thus enabling a system with a large, tunable, pyroelectric response.

In theory, the use of rectifying contacts could enable the polarized ferroelectric nanowire to generate a giant, pyroelectric, direct current and voltage in response to temperature fluctuations that could be harvested and detected using a bolometric detector. Such a nanoscale device would not contain any moving parts and could be suitable for long-term operation in ambient applications such as in-vitro biological systems and outer space. The researchers calculate that these little nanogenerators would have very high efficiency at low temperatures, decreasing at warmer temperatures.

American Institute of Physics


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The rules that govern the world of the very small, quantum mechanics, are known for being bizarre. One of the strangest tenets is something called quantum entanglement, in which two or more objects (such as particles of light, called photons) become inextricably linked, so that measuring certain properties of one object reveals information about the other(s), even if they are separated by thousands of miles. Einstein found the consequences of entanglement so unpalatable he famously dubbed it "spooky action at a distance."

Now a team led by Yale researchers has harnessed this counterintuitive aspect of quantum mechanics and achieved the entanglement of three solid-state qubits, or quantum bits, for the first time. Their accomplishment, described in the Sept. 30 issue of the journal Nature, is a first step towards quantum error correction, a crucial aspect of future quantum computing.

"Entanglement between three objects has been demonstrated before with photons and charged particles," said Steven Girvin, the Eugene Higgins Professor of Physics & Applied Physics at Yale and an author of the paper. "But this is the first three-qubit, solid-state device that looks and feels like a conventional microprocessor."

The new result builds on the team's development last year of the world's first rudimentary solid-state quantum processor, which they demonstrated was capable of executing simple algorithms using two qubits.

The team, led by Robert Schoelkopf, the William A. Norton Professor of Applied Physics & Physics at Yale, used artificial "atoms"—actually made up of a billion aluminum atoms that behave as a single entity—as their qubits. These "atoms" can occupy two different energy states, akin to the "1" and "0" or "on" and "off" states of regular bits used in conventional computers. The strange laws of quantum mechanics, however, allow for qubits to be placed in a "superposition" of these two states at the same time, resulting in far greater information storage and processing power.

In this new study, the team was able to achieve an entangled state by placing the three qubits in a superposition of two possibilities—all three were either in the 0 state or the 1 state. They were able to attain this entangled state 88 percent of the time.

With the particular entangled state the team achieved, they also demonstrated for the first time the encoding of quantum information from a single qubit into three qubits using a so-called repetition code. "This is the first step towards quantum error correction, which, as in a classical computer, uses the extra qubits to allow the computer to operate correctly even in the presence of occasional errors," Girvin said.

Such errors might include a cosmic ray hitting one of the qubits and switching it from a 0 to a 1 state, or vice versa. By replicating the qubits, the computer can confirm whether all three are in the same state (as expected) by checking each one against the others.

"Error correction is one of the holy grails in quantum computing today," Schoelkopf said. "It takes at least three qubits to be able to start doing it, so this is an exciting step."

Yale University


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The key to the stability of any building is its foundation, but it is difficult to test some building sites in advance – such as those on the moon. New research from North Carolina State University is helping resolve the problem by using computer models that can utilize a small sample of soil to answer fundamental questions about how soil at a building site will interact with foundations.

“If you are going to build a large structure, you have to run a lot of tests on the building site to learn how the soil will behave in relation to the building’s foundation,” says Dr. Matt Evans, assistant professor of civil, construction and environmental engineering at NC State and co-author of a paper describing the research. “How stable is it? How much might the foundation settle over time? Traditionally, that testing process involves a great deal of equipment, time and money.”

But in some situations, that equipment, time and money is not available. For example, it would be tough to transport the relevant equipment to the surface of the moon.

“We initiated this project, with funding from the North Carolina Space Grant, to answer questions that are essential to the construction of buildings on the moon,” Evans says. “It’s cost-prohibitive to do traditional testing on lunar sites, so we developed a technique for applying computer models that can use a tiny sample to tell us about the potential interface between moon soil and anything we might build.”

And the model may also have applications closer to home. The model could potentially be used to assess soil conditions for remote building sites where traditional testing is impractical or unduly expensive. For example, it could be useful for military applications or for siting remote research facilities.

The paper, “Analysis of Pile Behavior in Granular Soils Using DEM,” focuses on how the model can be used when incorporating Earth-specific variables – such as gravity. However, those variables can be modified to account for conditions on the moon, or even on Mars.

North Carolina State University




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