April 25, 2007, 9:31 PM CT

Why Nanowires Make Great Photodetectors

The geometry of semiconducting nanowires makes them uniquely suited for light detection, as per a new UC San Diego study that highlights the possibility of nanowire light detectors with single-photon sensitivity.

Nanowires are crystalline fibers about one thousandth the width of a human hair, and their inherent properties are expected to enable new photodetector architectures for sensing, imaging, memory storage, intrachip optical communications and other nanoscale applications, as per a new study in an upcoming issue of the journal Nano Letters. The UCSD engineers illustrate why the large surface areas, small volumes and short lengths of nanowires make them extremely sensitive photodetectors - much more sensitive than larger photodetectors made from the same materials.

"These results are encouraging and suggest a bright future for nanowire photodetectors, including single-photon detectors, built from nanowire structures," said Deli Wang, an electrical and computer engineering (ECE) professor from the UCSD Jacobs School of Engineering and corresponding author on the Nano Letters paper.

For a nanowire to serve as a photodetector, photons of light with sufficient energy must hit the nanowire in such a way that electrons are split from their positively charged holes. Electrons must remain free from their holes long enough to zip along the nanowire and generate electric current under an applied electric field - a sure sign that light has been detected......... Posted by: Kevin      Read more         Source

April 25, 2007, 9:18 PM CT

Closer To The Goal Of High-yield Fusion Reactor

An electrical circuit that should carry enough power to produce the long-sought goal of controlled high-yield nuclear fusion and, equally important, do it every 10 seconds, has undergone extensive preliminary experiments and computer simulations at Sandia National Laboratories' Z machine facility.

Z, when it fires, is already the largest producer of X-rays on Earth and has been used to produce fusion neutrons. But rapid bursts are necessary for future generating plants to produce electrical power from sea water. This had not been thought achievable till now.

Sandia is a National Nuclear Security Administration laboratory.

How does it work?

An automobile engine that fired one cylinder and then waited hours before firing again wouldn't take a car very far.

Similarly, a machine to provide humanity unlimited electrical energy from cheap, abundant seawater can't fire once and quit for the day. It must deliver energy to fuse pellets of hydrogen every 10 seconds and keep that pace up for millions of shots between maintenance - a kind of an internal combustion engine for nuclear fusion. That's so, at least, for the fusion method at Sandia National Laboratories' Z machine and elsewhere known as inertial confinement.

But, unable to produce fusion except episodically, the method has been overshadowed by the technique called magnetic confinement - a method that uses a magnetic field to enclose a continuous fusion reaction from which to draw power......... Posted by: Kevin      Read more         Source

April 25, 2007, 9:15 PM CT

computer modeling system for organ allocation

The International Society for Heart and Lung Transplantation (ISHLT) announces evaluation of a new mathematical modeling system for lung allocation in the United States and the ethical issues surrounding organ allocation facing patients awaiting transplants. Both will be discussed at its 27th Annual Meeting and Scientific Sessions, today in Satellite Symposium 9, Continued Evaluation of Heart and Lung Allocation Using Evidence Based Research.

Worldwide, patients in need of transplant are placed on a waiting list for donor lungs, using a wide variety of systems. In the United States, patients are currently assessed for organ allocation based on a new mathematical modeling system, in which patient information is entered into a computer database and donors are then matched with recipients based on specific characteristics. Two of the most important criteria are the chance of survival without the transplant and the projected condition of the patient post transplant. The computer program then generates a list of patients that are ranked according to preset organ allocation policies. Once selected, there are a number of tests that must be performed in order to evaluate whether the recipient may in fact receive the organ. Taking into consideration the novelty of the system, an international representation of ISHLT membership will convene to evaluate this new modeling system to determine its effectiveness and Leah Edwards, Ph.D., United Network for Organ Sharing, will present How is the Lung Allocation Score Working in the US? during the Symposium......... Posted by: Sean      Read more         Source

April 24, 2007, 11:11 PM CT

Study Could Help Stroke Victims

A University of Leicester study could help to provide a new lease of life for patients who have suffered a stroke.

The research published in the American Journal of Hypertension confirms the safety of a drug, Lisinopril, that lowers their blood pressure-without reducing the blood flow to the brain.

Now a larger Leicester trial is under way to investigate the drugs benefits for victims of strokes.

Dr David Eveson, of the Department of Cardiovascular Sciences at the University of Leicester, said: "High blood pressure is common immediately after a stroke. Stroke patients with high blood pressure tend to have a worse outcome than those with normal blood pressure and therefore it may be helpful to lower blood pressure immediately after stroke.

"However, trials to date have shown variable results, probably because treatment was either started too late or the wrong drug was used.

"The ACE inhibitor class of blood pressure lowering drugs, of which Lisinopril is a member, have been shown in studies to lower blood pressure but preserve the blood flow to the brain which may be all important after stroke. This study compared the use of blood pressure lowering with Lisinopril versus placebo treatment within a few hours of acute stroke in patients presenting to University Hospitals Leicester. The results showed that blood pressure was effectively lowered in the treated group and this did not result in any adverse outcome in comparison with placebo......... Posted by: Sean      Read more         Source

April 24, 2007, 10:35 PM CT

Avalanche Behavior Of Superfluid Helium

By utilizing ideas developed in disparate fields, from earthquake dynamics to random-field magnets, scientists at the University of Illinois have constructed a model that describes the avalanche-like, phase-slip cascades in the superflow of helium.

Just as superconductors have no electrical resistance, superfluids have no viscosity, and can flow freely. Like superconductors, which can be used to measure extremely tiny magnetic fields, superfluids could create a new class of ultra-sensitive rotation sensors for use in precision guidance systems and other applications.

But, before new sensors can be built, researchers and engineers must first acquire a better understanding of the odd quirks of superfluids arising in these devices.

In the April 23 issue of Physical Review Letters, U. of I. physicist Paul Goldbart, graduate student David Pekker and postdoctoral research associate Roman Barankov describe a model they developed to explain some of those quirks, which were found in recent experiments conducted by scientists at the University of California at Berkeley.

In the Berkeley experiments, physicist Richard Packard and his students Yuki Sato and Emile Hoskinson explored the behavior of superfluid helium when forced to flow from one reservoir to another through an array of several thousand nano-apertures. Their intent was to amplify the feeble whistling sound of phase-slips linked to superfluid helium passing through a single nano-aperture by collecting the sound produced by all of the apertures acting in concert......... Posted by: Sarah      Read more         Source

April 24, 2007, 10:33 PM CT

Satellites offer sunny outlook

Far beyond signaling the days weather, clouds play a key role in regulating and understanding climate. A team of researchers recently completed a project to confirm what NASA satellites are telling us about how changes in clouds can affect climate in the coldest regions on Earth.

Clouds and their traits their temperature, depth, size and shape of their droplets play a significant role in how much of the sun's radiation reaches Earth's surface and what amount of heat energy Earth reflects back into the atmosphere. In 2006, NASA simultaneously launched a pair of satellites, CloudSat and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), which together use state-of-the-art instruments as they orbit the globe to reveal detailed information about clouds and their effect on climate.

Scientists predict that certain changes in cloud properties can accelerate climate change. "The polar regions are very sensitive indicators of climate change," said Deborah Vane, project manager and deputy principal investigator for the CloudSat mission at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's been well reported now that the polar ice caps are undergoing net melting. There's a complicated interaction between clouds and climate in polar regions that can contribute to temperature changes, and, in turn, speed the rate at which ice melts"......... Posted by: Tyler      Read more         Source

April 24, 2007, 10:21 PM CT

New Family of Pseudo-Metallic Chemicals

The periodic table of elements, all 111 of them, just got a little competition. A new discovery by a University of Missouri-Columbia research team, published in Angewandte Chemie, the journal of the German Society of Chemists, allows researchers to manipulate a molecule discovered 50 years ago in such as way as to give the molecule metal-like properties, creating a new, "pseudo" element. The pseudo-metal properties can be adjusted for a wide range of uses and might change the way researchers think about attacking disease or even building electronics.

Five decades ago, Fred Hawthorne, professor of radiology and director of the International Institute for Nano and Molecular Medicine at MU, discovered an extremely stable molecule consisting of 12 boron atoms and 12 hydrogen atoms. Known as "boron cages," these molecules were difficult to change or manipulate, and sat dormant in Hawthorne's laboratory for a number of years.

Recently, Hawthorne's scientific team found a way to modify these cages, resulting in a large, new family of nano-sized compounds. In their study, which was published this month, Hawthorne, and Mark Lee, assistant professor at the institute and first author of the study, observed that attaching different compounds to the cages gave them the properties of a number of different metals......... Posted by: Sarah      Read more         Source

April 23, 2007, 10:43 PM CT

Prehistoric mystery organism verified as giant fungus

Researchers at the University of Chicago and the National Museum of Natural History in Washington, D.C., have produced new evidence to finally resolve the mysterious identity of what they regard as one of the weirdest organisms that ever lived.

Their chemical analysis indicates that the organism was a fungus, the researchers report in the recent issue of the journal of Geology, published by the Geological Society of America. Called Prototaxites (pronounced pro-toe-tax-eye-tees), the organism went extinct approximately 350 million years ago.

Prototaxites has generated controversy for more than a century. Originally classified as a conifer, researchers later argued that it was instead a lichen, various types of algae or a fungus. Whatever it was, it stood in tree-like trunks more than 20 feet tall, making it the largest-known organism on land in its day.

"No matter what argument you put forth, people say, well, thats crazy. That doesnt make any sense," said C. Kevin Boyce, an Assistant Professor in Geophysical Sciences at Chicago. "A 20-foot-tall fungus doesnt make any sense. Neither does a 20-foot-tall algae make any sense, but heres the fossil".

The Geology paper adds a new line of evidence indicating that the organism is a fungus. The fungus classification first emerged in 1919, with Francis Hueber of the National Museum of Natural History in Washington, D.C., reviving the idea in 2001. His detailed studies of internal structure have provided the strongest anatomical evidence that Prototaxites is not a plant, but a fungus......... Posted by: William      Read more         Source

April 23, 2007, 10:34 PM CT

Are higher doses of cholesterol drugs worth the extra money?

When it comes to cholesterol-lowering drugs, more is better. At least, thats what heart doctors and heart patients have been hearing in recent years. And as a result, more patients are taking higher doses of drugs called statins leading to lower heart and stroke risk, but higher prescription drug costs and more frequent side effects.

Now, a new study looks at whether those higher doses, and higher costs, are really going to pay off for some patients. For those with a recent heart attack or what doctors call acute coronary syndrome, the answer is yes, the researchers say.

But the picture is less clear for those patients with known heart blockages who have stable symptoms. For them, the usual dose of their statin may provide adequate heart-protecting benefit, and the higher cost of high-dose statins may provide only marginal benefit at much greater cost, especially if they use generic statins.

The study, from a team at the University of Michigan Cardiovascular Center and the VA Ann Arbor Healthcare System, is published online in the journal Circulation, and will be in the May 8 print issue of the journal. Its based on a sophisticated computer analysis of data from thousands of patients.

The team finds that patients with a recent history of acute coronary syndrome (ACS) either a heart attack or hospital stay for chest pain get so much benefit from higher doses of statins (over four additional quality-adjusted months of life) that the extra cost of the increased dose is worthwhile, even if the difference is a few dollars a day......... Posted by: Sean      Read more         Source

April 23, 2007, 10:24 PM CT

Managing Forests in Hurricane Impact Zones

Forest Service scientists have developed an adaptive strategy to help natural resource managers in the southeastern United States both prepare for and respond to disturbance from major hurricanes. In an article reported in the journal Forest Ecology and Management, John Stanturf, Scott Goodrick, and Ken Outcalt from the Forest Service Southern Research Station (SRS) unit in Athens, GA, report the results of a case study based on the effects of hurricanes Katrina and Rita.

The past 10 hurricane seasons have been the most active on record, with climatologists predicting that heightened activity could continue for another 10 to 40 years. In early April, Colorado State University meteorologists predicted a very active 2007 hurricane season for the Atlantic coast, with 17 named storms, including 5 major Hurricanes. The analysis included a 74 percent probability of a major hurricane hitting the U.S. coast before the season ends on November 30.

"Coastal areas in the southern United States are adapted to disturbance from both fire and high wind," says Stanturf, project leader of the SRS disturbance ecology unit based in Athens, GA. "But those adaptations only go so far in the face of a major hurricane. Forest owners and natural resource managers need strategies to deal with hurricane damage to coastal forests"......... Posted by: Tyler      Read more         Source