Day: 12/22/2011

‘Plasmonic nanoantennas’ show promise in optical innovations.

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Researchers have shown how arrays of tiny “plasmonic nanoantennas” are able to precisely manipulate light in new ways that could make possible a range of optical innovations such as more powerful microscopes, telecommunications and computers.

The researchers at Purdue University used the nanoantennas to abruptly change a property of light called its phase. Light is transmitted as waves analogous to waves of water, which have high and low points. The phase defines these high and low points of light.

“By abruptly changing the phase we can dramatically modify how light propagates, and that opens up the possibility of many potential applications,” said Vladimir Shalaev, scientific director of nanophotonics at Purdue’s Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering.

Findings are described in a paper to be published online Thursday (Dec. 22) in the journal Science.

The new work at Purdue extends findings by researchers led by Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at the Harvard School of Engineering and Applied Sciences. In that work, described in an October Science paper, Harvard researchers modified Snell’s law, a long-held formula used to describe how light reflects and refracts, or bends, while passing from one material into another.

“What they pointed out was revolutionary,” Shalaev said.

Until now, Snell’s law has implied that when light passes from one material to another there are no abrupt phase changes along the interface between the materials. Harvard researchers, however, conducted experiments showing that the phase of light and the propagation direction can be changed dramatically by using new types of structures called metamaterials, which in this case were based on an array of antennas.

The Purdue researchers took the work a step further, creating arrays of nanoantennas and changing the phase and propagation direction of light over a broad range of near-infrared light. The paper was written by doctoral students Xingjie Ni and Naresh K. Emani, principal research scientist Alexander V. Kildishev, assistant professor Alexandra Boltasseva, and Shalaev.

The wavelength size manipulated by the antennas in the Purdue experiment ranges from 1 to 1.9 microns.

“The near infrared, specifically a wavelength of 1.5 microns, is essential for telecommunications,” Shalaev said. “Information is transmitted across optical fibers using this wavelength, which makes this innovation potentially practical for advances in telecommunications.”

The Harvard researchers predicted how to modify Snell’s law and demonstrated the principle at one wavelength.

“We have extended the Harvard team’s applications to the near infrared, which is important, and we also showed that it’s not a single frequency effect, it’s a very broadband effect,” Shalaev said. “Having a broadband effect potentially offers a range of technological applications.”

The innovation could bring technologies for steering and shaping laser beams for military and communications applications, nanocircuits for computers that use light to process information, and new types of powerful lenses for microscopes.

Critical to the advance is the ability to alter light so that it exhibits “anomalous” behavior: notably, it bends in ways not possible using conventional materials by radically altering its refraction, a process that occurs as electromagnetic waves, including light, bend when passing from one material into another.

Scientists measure this bending of radiation by its “index of refraction.” Refraction causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material. All natural materials, such as glass, air and water, have positive refractive indices.

However, the nanoantenna arrays can cause light to bend in a wide range of angles including negative angles of refraction.

“Importantly, such dramatic deviation from the conventional Snell’s law governing reflection and refraction occurs when light passes through structures that are actually much thinner than the width of the light’s wavelengths, which is not possible using natural materials,” Shalaev said. “Also, not only the bending effect, refraction, but also the reflection of light can be dramatically modified by the antenna arrays on the interface, as the experiments showed.”

The nanoantennas are V-shaped structures made of gold and formed on top of a silicon layer. They are an example of metamaterials, which typically include so-called plasmonic structures that conduct clouds of electrons called plasmons. The antennas themselves have a width of 40 nanometers, or billionths of a meter, and researchers have demonstrated they are able to transmit light through an ultrathin “plasmonic nanoantenna layer” about 50 times smaller than the wavelength of light it is transmitting.

“This ultrathin layer of plasmonic nanoantennas makes the phase of light change strongly and abruptly, causing light to change its propagation direction, as required by the momentum conservation for light passing through the interface between materials,” Shalaev said.

Source:Phycics

 

New device could bring optical information processing

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Researchers have created a new type of optical device small enough to fit millions on a computer chip that could lead to faster, more powerful information processing and supercomputers.

The “passive optical diode” is made from two tiny silicon rings measuring 10 microns in diameter, or about one-tenth the width of a human hair. Unlike other optical diodes, it does not require external assistance to transmit signals and can be readily integrated into computer chips.

The diode is capable of “nonreciprocal transmission,” meaning it transmits signals in only one direction, making it capable of information processing, said Minghao Qi (pronounced Chee), an associate professor of electrical and computer engineering at Purdue University.

“This one-way transmission is the most fundamental part of a logic circuit, so our diodes open the door to optical information processing,” said Qi, working with a team also led by Andrew Weiner, Purdue’s Scifres Family Distinguished Professor of Electrical and Computer Engineering.

The diodes are described in a paper to be published online Thursday (Dec. 22) in the journal Science. The paper was written by graduate students Li Fan, Jian Wang, Leo Varghese, Hao Shen and Ben Niu, research associate Yi Xuan, and Weiner and Qi.

Although fiberoptic cables are instrumental in transmitting large quantities of data across oceans and continents, information processing is slowed and the data are susceptible to cyberattack when optical signals must be translated into electronic signals for use in computers, and vice versa.

“This translation requires expensive equipment,” Wang said. “What you’d rather be able to do is plug the fiber directly into computers with no translation needed, and then you get a lot of bandwidth and security.”

Electronic diodes constitute critical junctions in transistors and help enable integrated circuits to switch on and off and to process information. The new optical diodes are compatible with industry manufacturing processes for complementary metal-oxide-semiconductors, or CMOS, used to produce computer chips, Fan said.

“These diodes are very compact, and they have other attributes that make them attractive as a potential component for future photonic information processing chips,” she said.

The new optical diodes could make for faster and more secure information processing by eliminating the need for this translation. The devices, which are nearly ready for commercialization, also could lead to faster, more powerful supercomputers by using them to connect numerous processors together.

“The major factor limiting supercomputers today is the speed and bandwidth of communication between the individual superchips in the system,” Varghese said. “Our optical diode may be a component in optical interconnect systems that could eliminate such a bottleneck.”

Infrared light from a laser at telecommunication wavelength goes through an optical fiber and is guided by a microstructure called a waveguide. It then passes sequentially through two silicon rings and undergoes “nonlinear interaction” while inside the tiny rings. Depending on which ring the light enters first, it will either pass in the forward direction or be dissipated in the backward direction, making for one-way transmission. The rings can be tuned by heating them using a “microheater,” which changes the wavelengths at which they transmit, making it possible to handle a broad frequency range.

Source:Physics

 

Rectal Cancer Incidence Rose After Radiation Therapy for Prostate Cancer.

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Excess 10-year risk was roughly one case per 100 men.

A U.S. study demonstrated an increased risk for rectal cancer following external-beam radiation therapy for prostate cancer . Now, Israeli researchers have analyzed data from their national cancer registry to address this issue.

Of nearly 30,000 men with prostate cancer diagnosed between 1982 and 2005, 2163 received radiation therapy (either external-beam or brachytherapy), and 26 of these men received subsequent diagnoses of rectal cancer. Compared with the age-adjusted incidence of rectal cancer in the entire Israeli male population, the incidence was significantly higher in the radiation-therapy group (standardized incidence ratio, 1.8). This increase would correspond roughly to one additional case per 100 men during 10 years of follow-up. In contrast, patients who underwent radical prostatectomy did not have excess risk for rectal cancer.

Comment: Radiation therapy for prostate cancer appears to raise risk for rectal cancer, although the absolute excess risk is fairly low. This potential complication should be factored into decisions about prostate cancer treatment.

Source: Journal Watch General Medicine

 

Midlife Blood Pressure Predicts Future Heart Risk

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High Blood Pressure in Middle Age Linked to Later Heart Attack, Stroke
taking blood pressure

Increases and decreases in blood pressure during middle age and even earlier in adulthood can significantly affect heart attack and stroke risk later in life, a new study shows.

The analysis of data from seven studies involving more than 61,000 people is one of the most comprehensive studies ever conducted examining how changes in blood pressure during middle age affect lifetime risk of heart disease and stroke.

Researchers confirmed that people with normal blood pressure at age 55 had a relatively low lifetime risk for heart disease or stroke — between 22% and 41%.

In contrast, those who had already developed high blood pressure by this age had a higher lifetime risk of between 42% and 69%.

The findings highlight the importance of maintaining normal blood pressure throughout middle age and even earlier, says researcher Norrina Allen, PhD, of Chicago’s Northwestern University Feinberg School of Medicine.

More than 74 million adults in the U.S. have high blood pressure, meaning that their systolic pressure (the top number) is 140 mmHg or higher and their diastolic pressure is 90 mmHg or above.

“People who maintained a low blood pressure of less than 120 over 80 had the lowest lifetime risk for [heart disease and stroke], and those who stayed above 140 over 90 had the highest,” Allen tells WebMD. “The longer people can delay the onset of hypertension, the better off they are.”

Middle-Age BP Predicts Heart, Stroke Risk

Using the data, the researchers were able to estimate lifetime risk for heart attack, stroke, and other heart-related events for white and African-American adults.

Starting with a first-time reading at an average age of 41, the researchers tracked blood pressure changes until age 55 and then continued to follow the study participants until the occurrence of a heart attack, stroke, or other medically similar event, or until death or age 95.

By their mid-50s, about one in four men and two in five women still had normal blood pressure, and about half of men and women had blood pressure that was above normal but not yet high enough to be considered high.

Women had greater increases in blood pressure during middle age than men did, and African-American men and African-American women had a higher lifetime risk for high blood pressure, heart attack, and stroke than white men and women.

Based on their analysis, the researchers predicted that:

  • More than two out of three (70%) men who developed high blood pressure in middle age will have a heart attack, stroke, or other such event by age 85.
  • Half of women who develop high blood pressure by their early 40s will develop heart disease or increase their stroke risk later in life.

source:Circulation

Maggot Therapy May Assist in Wound Healing.

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 Maggot Therapy Works Faster Than Conventional Therapy in First Week to Clean Wounds.

 

maggot

It sounds medieval, but it’s an accepted part of modern medicine: Maggots may assist in wound healing, French researchers report.

Maggots have been used to help treat wounds for thousands of years. Their use declined with the advent of antibiotics. Now, they seem to be making a comeback because of the alarming increase in antibiotic-resistant infections. Maggots may reduce the risk of wound infection because the larvae secrete substances that fight infection.

In the new study of 119 people with non-healing wounds, maggot therapy worked quicker than conventional surgical wound-cleaning during the first week only. There was no significant added benefit by day 15, though.

During the surgical procedure, the area is numbed and the unhealthy tissue in the wound is cut away.

Some maggot therapy practitioners place the maggots directly on the wound, where they remove dead tissue. In the new study, however, about 80 maggots were placed in a dressing over the wound twice a week for two weeks.

There was not much of a yuck factor. All participants were willing to try maggot therapy, says researcher Kristina Opletalová, a dermatologist at Caen University in France.

Donald S. Waldorf, MD, a dermatologist in Nanuet, N.Y., has never used maggot therapy, but he has seen them used. “They have been used on wounds since antiquity and especially in wartime,” he says in an email. “Their use seems to come in and out of favor. I can see using them when surgery would be medically difficult in very sick patients who cannot undergo anesthesia or when competent surgeons are not available. They clearly work to get rid of wound debris and may even clear out bacteria that grow on the debris.”

Maggots, Inc.

As the laboratory director and co-founder of Monarch Labs in Irvine, Calif., Ronald Sherman, MD, is the go-to guy for medical-grade maggots in the U.S. The FDA regulates the use of maggots, and they are only available via prescription here.

Sherman supplies 2,000 facilities in the U.S. with medical maggots. They are mainly used to treat diabetic ulcers and pressure ulcers, but can also have a role in treating post-surgery wounds that are slow to heal and may become infected. “These wounds are very, very serious and the doctor needs to make sure that [maggot therapy] is the right treatment,” he says.

Sherman reviewed the study for WebMD and says it “brings new data to the whole field.”

Maggots are not a last resort. “They are very effective, very inexpensive, and very safe relative to the alternatives,” Sherman tells WebMD. Surgery is the gold standard, but not all people are candidates.

Maggot therapy costs about $100, and some insurers will cover these costs.

source: webMD

Use of Sunless Tanners May Cut Exposure to UV Radiation

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People Who Use Self-Tanners May Cut Back on Sun Bathing, Tanning Beds

 

 Women who often use sunless tanners — those creams and sprays that fake a tan — may reduce their sunbathing time and tanning bed use, according to a new study.

“Using the sunless tanners can change tanning behaviors,” says researcher Suephy C. Chen, MD, associate professor of dermatology at Emory University School of Medicine. ”People who used the sunless tanners decreased the number of times they laid out or went to tanning booths.”

In the study, nearly 37% of people who used sunless tanning products and sunbathed reported they cut down their sunbathing time. And 38% who used sunless tanners and tanning beds cut back on the tanning bed sessions.

The study is published online in the Archives of Dermatology.

Sunless Tanners: Doctors Debate

“There is a controversy among dermatologists about whether to promote sunless tanning,” Chen says. “Some think it sends a message that tanning is OK.”

Others are more pragmatic, she says. They figure many people won’t give up trying to tan, so they should point them to safer options that don’t carry a risk of skin cancer.

Nearly 93% of the 415 women Chen polled said tanned skin is more attractive than pale. Nearly 80% said they feel better about themselves when tan.

Chen’s team set out to discover if using the sunless tanning products would reduce exposure to ultraviolet (UV)  radiation from  the sun and to tanning beds.

More than 2 million cases of non-melanoma skin cancer are diagnosed each year in the U.S. In 2010, more than 68,000 new cases of the more deadly skin cancer, melanoma, were found, according to the American Cancer Society.

Sunless Tanning Study Details

Chen’s team interviewed women aged 18 to 71 from the Emory University campus and the surrounding community. The average age was about 28. Most of the women had fair skin, classified as white or very white.

While 201 women used self tanners; 214 did not. Those who used the self-tanners had an average age of 27.

Those who used sunless tanning products were more likely also to tan in the sun and in tanning beds. However, Chen found, the more they used the sunless tanning, the more likely they were to reduce the use of sunbathing or tanning beds.

While the decline is welcome, Chen wishes it were a greater decline.

The researchers did not specify which types of sunless tanning products the women used. Some used do-it-yourself products at home and others got their spray tans at salons. “The overwhelming majority did it at home,” Chen says. They studied only women because they are the primary users of the sunless tanning products.

Sunless Tanning Study Is ‘Powerful’

“This is a very powerful study,” says Jeffrey S. Dover, MD, an associate clinical professor of dermatology at Yale University, and a Boston-area dermatologist. He reviewed the study for WebMD but was not involved in the research.

The findings are a welcome relief from all the negative skin cancer news, such as increases in skin cancers among younger people, says Dover, a spokesman for the American Academy of Dermatology.

The finding that most women in Chen’s study think they look better with a tan is an important message for dermatologists, Dover says. Instead of discouraging patients from tans altogether, he says, they can point to the good news. “The positive message here is sunless tanning is safe; tanning beds and going to the beach is not.”

One warning: Barbara Reed, MD, a Denver dermatologist and clinical professor of dermatology at the University of Colorado Hospital, Denver, says rashes have been reported by some using the products. The FDA cautions users not to inhale the sunless tanning creams and lotions.

In most sunless tanning products, the active ingredient is DHA (dihydroxyacetone). It reacts with the cells found in the outermost skin layer to darken the appearance of the skin temporarily.

source:webMD

Overweight Children May Be at Risk for Asthma

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Overweight children may be more likely to develop asthma by the time they go to school, but losing weight early on may counter that risk.

A new study shows children who were overweight at ages 1, 4, and 7 were up to twice as likely to have asthma by age 8 as normal-weight children.

But overweight children who reached a normal weight by age 7 were no more likely to have asthma by the time they turned 8 than other children, regardless of their previous weight.

Researchers say childhood asthma and obesity are both more common in the U.S. than they were a few decades ago. Although some studies have suggested that being overweight increases the risk of childhood asthma, few have looked at whether losing weight during childhood affects the risk of asthma.

“Our study indicates that high BMI [body mass index] during the first four years does not increase the risk of asthma at school age among children who have developed a normal weight by age 7 years,” write researcher Jessica Öhman Magnusson, MSc, of the Karolinska Institutet in Stockholm, Sweden, and colleagues in Pediatrics.

In the study, researchers looked at the relationship between BMI at ages 1, 1 1/2, 4, and 7 and asthma at age 8 in more than 2,000 Swedish children.

The results showed that children who had a high BMI at ages 1, 4, or 7 were more likely to be diagnosed with asthma by age 8 than normal-weight children.

Children who were overweight at age 7 also had signs of a higher risk for allergies.

But overweight children who reached a normal weight by age 7 were no more likely to have asthma by age 8 than other children.

Researchers say there may be several biological explanations for the link between being overweight and asthma.

One explanation may involve the hormone leptin, which is derived from fat and found in higher amounts in people who are overweight. Previous studies have suggested that leptin may cause exaggerated inflammatory responses by the immune system, a key feature of asthma.

source:webMD

New calculations suggest Jupiter’s core may be liquefying

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Jupiter, the largest planet in our solar system, may be causing its own core to liquefy, at least according to Hugh Wilson and colleague Burkhard Militzer of UC, Berkeley. They’ve come to this conclusion after making quantum mechanical calculations on the conditions that exist within the big planet. In a paper published on the preprint server arXiv, and submitted to Physical Review Letters, the two explain that because the gas giant has a relatively small core made of mostly iron, rock (partly magnesium oxide) and ice, and sits embedded in fluid hydrogen and helium all under great pressure from the planet’s gravity (which has created very high temperatures (16,000 K)), there is a likelihood that the core is liquefying due to the heat and pressure exerted on the magnesium oxide.

Calculating the possibility of the magnesium oxide liquefying had to be done to predict the outcome because recreating the environment that exists inside of Jupiter for experimentation purposes isn’t feasible. They have in essence shown that magnesium oxide, when exposed to such high temperatures and pressure, has high solubility, which of course means a high probability of dissolving into a liquid. In a previous study, the team also made calculations showing that the core ice would likely be dissolving as well.

The findings suggest that Jupiter’s core might not be as big as it once was, though it currently weights about as much as ten Earth’s (the whole planet weighs as much as 318 Earth’s). This implies that the core could eventually be reduced down to nothing at all. And if that’s the case, than those who study exoplanets, particularly the giant gas variety, will have to do some rethinking, because those others might not have a core at all, contrary to conventional wisdom.

Unfortunately, the calculations the two performed can’t give a rate of erosion, thus a timeline for how long it’s taken for the core to come to its current size can’t be made, nor can predictions be made on how long it might take for the core to disappear altogether; both of which would be useful in helping to predict the ages of other gas giants out beyond our solar system. Luckily, NASA has a space probe on the way to measure Jupiter’s gravitational field more accurately, though it won’t get there till 2016; that should give scientists plenty of time to consider the impact these new findings might have on their current models regarding giant gas planets.

Source: Physics.org

New particle at the Large Hadron Collider discovered by ATLAS experiment

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Researchers from the University of Birmingham and Lancaster University, analysing data taken by the ATLAS experiment, have been at the centre of what is believed to be the first clear observation of a new particle at the Large Hadron Collider. The research is published today on the online repository arXiv.

The particle, the cb(3P) [pronounced kye-bee three P], is a new way of combining a beauty quark and its antiquark so that they bind together. Like the more famous Higgs particle, the cb(3P) is a boson. However, whereas the Higgs is not made up of smaller particles, the cb(3P) combines two very heavy objects via the same ‘strong force’ which holds the atomic nucleus together.

Andy Chisholm, a PhD student from the University of Birmingham who worked on the analysis said: ‘Analysing the billions of particle collisions at the LHC is fascinating. There are potentially all kinds of interesting things buried in the data, and we were lucky to look in the right place at the right time.’

‘The cb(3P) is a particle that was predicted by many theorists, but was not observed at previous experiments, such as in my previous work on the D-Zero experiment in Chicago,’ continued Dr James Walder, a Lancaster research associate who worked on the analysis.

Dr Miriam Watson, a research fellow working in the Birmingham group observed: ‘The lighter partners of the cb(3P) were observed around 25 years ago. Our new measurements are a great way to test theoretical calculations of the forces that act on fundamental particles, and will move us a step closer to understanding how the universe is held together.’

Professor Roger Jones, Head of the Lancaster ATLAS group said: “While people are rightly interested in the Higgs boson, which we believe gives particles their mass and may have started to reveal itself, a lot of the mass of everyday objects comes from the strong interaction we are investigating using the cb.”

Source:Provided by University of Birmingham

 

Ultracold science finds new method to get even colder

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Researchers have developed a clever way to achieve the lowest temperatures ever recorded on Earth.Achieving such temperatures is necessary to study fundamental properties of matter and the strange effects caused by quantum mechanics.

The new method relies on “optical lattices” of atoms from which only the hottest atoms are selectively removed.

The approach, reported in Nature, may be well-suited to create memory for future quantum computers.

The limits of low temperature have been constantly pushed in recent years, and the current best lies somewhere in the nanoKelvin regime – that is, within just billionths of a degree of “absolute zero” at zero Kelvin or -273.15C.

That ultimate limit is set formally as the lowest possible entropy, or disorder, that is achievable.

Optical lattices are an ideal system in which to attain temperatures ever nearer that limit. The peaks and troughs of intensity in crossed beams of light form a kind of “egg-crate” structure in which atoms are inclined to remain in the troughs – a point of lowest energy.

As the atoms are added to each trough – or each point in the lattice – it becomes more difficult to add another, in a situation called a blockade.

But researchers from Harvard University have invented a modification to this effect called orbital exchange blockade.

It is a way to cool these assemblages of atoms that could be extended to the picoKelvin regime: within trillionths of a degree of the coldest possible temperature.

The team carefully adjusted the intensity of the crossed light beams. The trick was to do so in such a way that only the most energetic atoms in each lattice site absorbed energy from the light fields, becoming more energetic again.

By adjusting how frequently the light beam intensities were changed, the team was able to remove these “hottest” atoms from the system, leaving only the “coolest” ones behind.

The approach removed entropy, or in other words, reduced the overall temperature of the lattice.

In an accompanying article in Nature, optical lattice expert Gretchen Campbell from US measurement agency Nist points out that this ability to specifically address single lattice sites, and potentially to cool to never-before-achieved temperatures, may make the approach useful in quantum computers.

These devices, still in early developmental stages, would make use of the slippery nature of quantum states to perform computation at incredible speeds.

But like any computer, they would need memory, and optical lattices that keep delicate quantum information preserved in cold atoms could be a suitable solution.

source:Journal of  Particle Physics