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Superconducting signature

For a while now, some scientists have thought that conditions necessary for superconductivity at higher temperatures exist. Now, a paper published in Science adds some fuel to their argument. It concerns the work of a group of U.S. and Japanese researchers – sponsored by a set of U.S. and Japanese government agencies – doing observations of low-temperature superconducting materials who say the spectroscopic signature of the materials seems to indicate that some superconductivity properties continue as the temperature increases.

“Our measurements give the most definitive spectroscopic evidence that the material we studied is a superconductor, even above the transition temperature, but one without the quantum phase coherence required for current to flow with no resistance,” said team leader Seamus Davis, a physicist at the Brookhaven National Lab and Cornell University, who led the research team. “The spectroscopic ‘fingerprint’ confirms that, at these higher temperatures, electrons are pairing up as they must in a superconductor, but for some reason they are not co-operating coherently to carry current.”

Recently there has been interest in the high-temperature possibilities of copper-oxide superconductors containing bismuth, strontium and calcium (BSCCO). Previously, Davis’ group was able to assemble a detailed spectroscopic signature containing all the quantum mechanical details of that superconducting state. Once this was established, they made spectroscopic observations of the cuprate material as it warmed above the 37 K transition temperature.

BNL scientists are now able to grow large BSCCO crystals. Credit: BNL

“We found that the characteristic signature passes unchanged from the superconducting state into the parent state - up to temperatures of at least 55 K, or 1.5 times the transition temperature,” Davis said. “We know of no explanation for why this fingerprint should remain other than that it represents the phase-incoherent superconducting state which has been proposed to exist based on other kinds of measurements.”

The group’s next step is to try to get a handle on why the cooperation between electron pairs breaks down. Their plan is to start tinkering with the doping of the copper-oxide planes in the layered material and measure the strength of quantum phase fluctuations.

Also, another group of BNL researchers has been on a similar mission, but studying how the magnetic properties of BSCCO change as temperatures are increased above normal superconducting ranges. One hurdle for this group has been creating BSCCO crystals large enough for observation, but as the accompanying picture shows, that the size problem has been solved.

“Many theorists believe that magnetism is important for high-temperature superconductivity, although they don’t agree on how it is important,” said Brookhaven physicist John Tranquada, who led the research team.

“The calculations based on the material’s electronic properties — which change dramatically as the material is cooled and transitions from its electrically resistive state to become a superconductor — predicted there would be a similar large change in magnetic characteristics below the transition temperature,” said Brookhaven physicist Guangyong Xu.

“But our direct measurements of the magnetic properties showed surprisingly little change. This implies that the model the theorists have been using to describe these magnetic properties is incomplete. It could be that the magnetism somehow drives the electronic structure, rather than the other way around — or that something underlying both magnetism and electronic structure influences both but in different ways,” Xu said.

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The Houston Chronicle reports that the insides of some bridges and other concrete structures in the state, and elsewhere in the region, are turning to gel, and the culprit is alkali-silica reaction. Depending on the amount of moisture that seeps into the concrete, the gel can grow and cause the concrete to expand, crack and eventually fail.

“In recent years concrete bridge structures in the U.S. have been experiencing an unusually high level of premature concrete deterioration,” noted a recent study by Houston engineering consultant firm Walter P. Moore.

The ASR reaction is caused when local aggregate reacts chemically to the alkali in the cement. In some cases, the concrete will crack long before reaching a structure’s expected service life of 70 to 90 years, experts say.

One solution began being tested in 2000 when the Texas Department of Transportation added a requirement that fly ash be added to the cement mix, thereby lowing the alkalinity of the concrete. But, that results in a concrete that takes longer to gain strength. This has lead to complaints because it slows the work schedule of contractors who must keep the poured concrete in support forms for longer periods, highway engineers say.

The ASR problem has been found in several thousand bridge support beams across the state, said TxDOT engineer Lisa Lukefahr, director of the rigid pavement and concrete materials branch.

Highway engineers have repaired damaged bridge beams, bridge supports and other structures affected by ASR by applying reinforced carbon fiber material to strengthen the concrete. In addition, a number of sealants and caulks are applied to concrete to keep out moisture that can increase the growth of ASR gel.

The ASR problem is not limited to highway bridges. University of Texas researchers cited 29 failures of the 150-foot tall high mast towers that illuminate freeways in nine states. Some of those failures were attributed to broken welds or stripped bolts, but several were caused by ASR weakening the concrete bases that anchor the light towers.

In the Houston area, state highway crews have installed supportive wraps around the bases of six light towers, said TxDOT engineer John Vogel. He said ASR has been detected in concrete structures in the Houston district, particularly those built before new concrete standards took effect in 2000.

“It’s the climate we have, and how it affects concrete,” causing the problem, said LaWanda Howse, a spokeswoman for the state’s Toll Road Authority. “All the roadways were built to specification, there wasn’t anything done wrong.”

ASR is a problem highway officials say is unusually severe in the South due to excessive heat and humidity that can cause moisture to seep into concrete.

Highway experts are continuing to look for a solution, and note that testing shows 80 percent of sands and 60 percent of aggregate rock from Texas quarries is reactive.

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A lithium niobate waveguide (bottom left) combines a pump laser and a near-infrared signal, "up-converting" the signal to a visible wavelength. Two prisms (right) separate the signal from the combined beam and send it to an avalanche photodiode detector (top left), which reads the up-converted signal. Credit: NIST

The good folks at the National Institute of Standards and Technology say they have a new method for measuring light in the near-infrared range that is highly sensitive (in the single photon range) and relatively inexpensive.

NIST researchers Lijun Ma, Oliver Slattery and Xiao Tang figured out a way to “up convert” photons at one frequency to a higher frequency using a tunable laser. This allows them to up convert infrared photons to the visible range which can then be matched with existing detectors such as avalanche photodiode detectors.

In a news release from NIST, Tang says they have achieved a sensitivity 1,000 times better than common commercial optical spectral instruments.

“Our key achievement here was to reduce the noise, but our success would not have been possible without the many years of work by others in this field,” says Tang. “We hope that our discovery will open doors for researchers studying diseases, pharmaceuticals, secure communications and even solving crimes. We are very excited to make this technology available to the larger scientific community.”

More information about this can be found in Optics Express.

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Photovoltaic tiles are installed alongside traditional clay tiles. (Credit: SRS Energy)

With this August heat we have solar on the mind! Here is another interesting advancement in solar cell technology, brought to us from Re-Nest.com.

SRS Energy claims to have the first building-integrated photovoltaic roofing product designed for curved roofing systems. The Solé Power Tile is an electricity-generating tile that can be installed alongside traditional clay tile roofing (but only those made by US Tile). The company claims they can generate up to 500 watts per 100 square-feet — comparable with that of traditional solar panel installations. According to the manufacturer, about 20-25 percent of an average roof would feature the solar tiles and the rest would use traditional, matching ceramic tiles.

The molded-plastic body is fused with a sheet of flexible solar chips that give it its distinctive blue color. And although its noncrystalline silicon cells gather less energy than conventional tilt-up panels with stiff crystalline cells, they react to a broader spectrum of light even on foggy, cloudy days.

The roofing system produces a natural air flow beneath the tiles to reduce cooling requirements of the home by 5-20 percent. (Credit: SRS Energy)

The roofing system produces a natural air flow beneath the tiles to reduce cooling requirements of the home by 5-20 percent.

What about the energy footprint of manufacturing process, itself, used to make these solar tiles? According to SRS, the tiles take less time than conventional solar panels to generate the same amount of energy required to produce them.

What does a system like this run? 1,000 square feet of solar tile would cost about $25,000-$30,000 installed, but you can knock 30% off that cost after government energy rebates, plus state and local government incentives may be available to cut the cost.

SRS Energy and US Tile are currently launching the Solé Power Tile system in select West Coast markets, and will begin a nationwide rollout of the product in spring of 2010.

Not everyone, however, is convinced that these tiles will live up to their billing. Some observers (see comments here) raise important questions about whether, for example, the curvature of the tiles will decrease the theoretical energy output of the tiles.

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Aldo Boccaccini is a professor in materials science at Imperial College, U.K. and a member of the London Center for Nanotechnology, a joint project between Imperial College and University College, U.K. In this video, he discusses some of his early work in developing vitrification techniques to render hazardous wastes, such as incinerator residues, inert. He delves into some of his work to develop bioglass materials for tissue engineering scaffolds. Finally, Boccaccini explains some of his pioneering work in the use of electrophoretic deposition for production of nanostructured materials and composites, including composites that contain carbon nanotubes. 13 minutes.

Earlier this year, Boccaccini was named the scientific international adviser to the Ministry of Science, Technology and Innovation of Argentina (his homeland).

For more information about vitrification of hazardous wastes, see this post about DC plasma techniques.

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