星空体育频道: 2013-06-16

2013年6月20日星期四

Dark discovery could double solar cell efficiency

LONDON – The efficiency of solar cells could be doubled by the discovery of a quantum "shadow state" that allows two – rather than one – high-energy electrons to be produced by optoelectronic energy conversion. The latest research on the mechanisms of solar energy conversion was led by chemistry Professor Xiaoyang Zhu at The University of Texas at Austin and was published in Science magazine.

Zhu and his team have discovered that it's possible to double the number of electrons harvested from one photon of sunlight using pentacene, an organic plastic semiconductor material.

"Plastic semiconductor solar cell production has great advantages, one of which is low cost," said Zhu, in a statement. "Combined with the vast capabilities for molecular design and synthesis, our discovery opens the door to an exciting new approach for solar energy conversion, leading to much higher efficiencies."

The maximum theoretical efficiency of the silicon solar cell in use today is approximately 31 percent. This is because much of the photonic energy hitting the cell is not that at wavelengths that can be turned into usable electricity. That energy is instead lost as heat. Capturing the thermally excited hot electronic energy could potentially increase the efficiency of solar-to-electric power conversion to as high as 66 percent, according to the research team.

Zhu and his team previously demonstrated that those hot electrons could be captured using semiconductor nanocrystals. They published that research in Science in 2010, but Zhu says the actual implementation of a viable technology based on that research is very challenging. The primary one being that it requires focused sunlight rather than ambient light that typically hits a solar panel.

Zhu and his team have found an alternative. They discovered that in the semiconductor pentacene a photon produces a dark quantum "shadow state" from which two electrons can then be efficiently captured to generate more energy.

The absorption of a photon creates an excited electron-hole pair, called an exciton. The exciton is coupled quantum mechanically to a dark "shadow-state" called a multi-exciton. It so happens that the multi-exciton can be an efficient source of two electrons via transfer to an electron acceptor material such as fullerene, the ball-shaped 60-atom allotrope of carbon, which was used in the study. Exploiting this could raise pentacene solar cell efficiency to 44 percent without the need for a focused solar beam, according to the researchers.

The research team was led by Wai-lun Chan, a postdoctoral fellow in Zhu's group, with the help of postdoctoral fellows Manuel Ligges, Askat Jailaubekov, Loren Kaake and Luis Miaja-Avila.

Related links and articles:

Dark state announcement

News articles:

Heliatek achieves 9.8 percent organic solar cell efficiency

Solar firm claims efficiency record

Sharp claims world's highest solar cell conversion efficiency of 35.8 percent

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Environmentally friendly battery made from wood

Liangbing Hu, Teng Li and colleagues point out that today's batteries often use stiff, non-flexible substrates, which are too rigid to release the stress that occurs as ions flow through the battery. They knew that wood fibers from trees are supple and naturally designed to hold mineral-rich water, similar to the electrolyte in batteries. They decided to explore use of wood as the base of an experimental sodium-ion battery. Using sodium rather than lithium would make the device environmentally friendly.

Lead author Hongli Zhu and other team members describe lab experiments in which the device performed successfully though 400 charge-discharge cycles, putting it among the longest-lasting of all sodium-ion nanobatteries. Batteries using the new technology would be best suited for large-scale energy storage applications, such as wind farms or solar energy installations, the report indicates.

The authors acknowledge support from the National Science Foundation and the University of Maryland NanoCenter.

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Researchers discover immunity mechanism: Platelets patrolling the bloodstream

June 19, 2013 — Scientists at the University of Calgary's Faculty of Medicine have discovered a mechanism that is used to protect the body from harmful bacteria. Platelets, a component of blood typically associated with clotting, were discovered to actively search for specific bacteria, and upon detection, seal it off from the rest of the body.

The findings, which were published in Nature Immunology this week, provide the science community with a greater understanding of immunity.

"The science community has known that platelets do participate in immunity, but now it's been demonstrated that they have a way of actively searching for bacteria," says Craig Jenne, PhD, one of the authors of the study and a member of the university's Snyder Institute for Chronic Diseases.

The vast majority of bacteria in the blood stream is trapped by the liver in a network of specialized cells known as Kupffer cells. Once trapped, a series of immune processes take place to eradicate the bacteria; however, this can take several hours, lending time to harmful bacteria to multiply and release toxins into the neighboring cells, subsequently causing infection and cell damage and death.

"Upon entering the blood stream, bacteria can start to divide within several minutes," he says. "So if you're waiting for the immune system to deal with it, the bacteria could become an infection before it gets there."

Through imaging of the liver in animal models, scientists discovered that platelets are constantly interacting with the Kupffer cells by 'touching' them to search for captured bacteria. If nothing is detected, or if the bacteria isn't deemed particularly harmful, the platelets will move on; however, if harmful bacteria is detected, the platelets will bind to it, sealing it off from the body until the immune system can rid the bacteria altogether. This happens within seconds of cell capture and thus reduces the likelihood of infection.

"If this instantaneous response didn't exist, it could be a matter of life and death," he says.

Interestingly, it was observed that while this touch-and-go mechanism is happening continuously, platelets only appear to create this barrier around particularly harmful bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). MRSA can lead to serious and potential fatal conditions such as sepsis, and is spread through skin to skin contact.

"We now have a completely different angle of how the immune system deals with specific types of bacteria," says study author Paul Kubes, PhD, who is also director of the Snyder Institute for Chronic Diseases. "Going forth we can begin to look at how we can help our own defenses deal with these types of bacteria."

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The rhythm of the Arctic summer: Diverse activity patterns of birds during the Arctic breeding season

Biological rhythms are essential for the regulation of many life processes. During the annual cycle, seasonal rhythms regulate the timing of reproductive activities. In our latitudes this a relatively easy task, as the marked annual changes in a day-night cycle (the photoperiod) entrains the seasonal clock. At the equator, where there is almost no change in day length over the year the animals have to rely on cues other than the photoperiod to time reproduction. However, in order to adjust its circadian clock an organism needs a certain light-dark cycle as a Zeitgeber. In the absence of a suitable Zeitgeber animals run free, which means they develop their own rhythm that can substantially deviate from a 24 hours day. Free-running cycles have been observed in animals and humans. Polar regions constitute extreme environments in this respect, as there is, around the summer and winter solstices, either constant light or constant darkness. Therefore, animals living in these harsh environments may have to depend on other cues in order to adjust their internal clock. These cues are relatively hard to determine.

An attempt to identify such cues has been made by a team of researchers from the Max Planck Institute for Ornithology in Seewiesen and Radolfzell. They investigated four bird species living in Alaska; three shorebird species, the semipalmated sandpiper, the pectoral sandpiper, the red phalarope, and one songbird species, the Lapland longspur. Remarkably, all four species have different mating systems. While the semipalmated sandpiper is strictly monogamous, the Lapland longspur, in addition to its monogamous lifestyle, shows occasional polygyny, where one male mates with several females. Polygyny is the rule in the mating system of the pectoral sandpiper, while the red phalarope is polyandrous, i.e. one female simultaneously mates with several males. Moreover, in the latter species the sex roles are reversed. The study site was a mere two square kilometre tundra area near Barrow in Northern Alaska. The researchers equipped in total 142 birds with radiotelemetry transmitters and determined their daily activity patterns using so-called actograms.

When analysing the activity data the researchers detected a whole array of biological rhythms. The Lapland longspur exhibited a robust 24 hour activity cycle throughout the breeding season and showed a regular but short resting period from about midnight to 4:00 am. However, in the shorebirds, depending on sex and breeding stage, there was either a robust 24 hour rhythm, or continuous activity and "free-running" circadian rhythms. But why are there such different activity patterns within the same habitat? A closer look at the "lifestyles" of the investigated species provides an explanation. Although all these species are migratory and are entrained to a regular light-dark regime in their wintering and stopover sites, during the short breeding season of the Arctic summer, they have to cope with extreme environmental conditions. Food availability could be a major factor in entraining the 24 hour cycle found in the Lapland longspur and in the care-giving sexes of the two polygamous species during incubation. This reflects a higher nest attendance at night as there are marked daily fluctuations in ground temperature with "nights" being very cold.

Further, no insects are available at night and continuous incubation is necessary to prevent the eggs from cooling off. On the other hand, male pectoral sandpipers are almost continuously active. This intense wakefulness pays off as, in an earlier study, it has been shown that the most active males sired the most offspring. In the monogamous semipalmated sandpiper with biparental care, there is evidence of social synchronisation as both breeding partners exhibited the same "free running" activity pattern during the incubation period. Our comparative study revealed that the avian circadian system can be entrained by environmental as well as social factors within a short period in the Arctic summer, which suggests a remarkable plasticity, says Bart Kempenaers, head of the research team.

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2013年6月16日星期日

Incontinence takes mental toll on younger women

June 14, 2013 — Research from the University of Adelaide shows middle-aged women are more likely to suffer depression from a common medical problem that they find too embarrassing to talk about: urinary incontinence.

However, help is available for women if they seek medical advice, researchers say.

In a study of the experiences of women with urinary incontinence, researcher Jodie Avery found that middle-aged women with incontinence (aged 43-65) were more likely to be depressed than older women (aged 65-89).

Speaking in the lead up to World Continence Week (24-30 June), Ms Avery says the younger women's self esteem is often hit hard by urinary incontinence, while older women tend to be more resilient and accepting of their condition.

"Women with both incontinence and depression scored lower in all areas of quality of life because of the impact of incontinence on their physical wellbeing," says Ms Avery, a PhD student and Senior Research Associate with the University's School of Population Health and School of Medicine.

"Key issues for younger women affected by incontinence are family, sexual relationships and sport and leisure activities.

"The most common difficulties women express about their incontinence are things like: 'I can't play netball', 'I can't go to the gym', 'I can't go for walks', or 'I can't go dancing', and these are real issues for women who are still in the prime of their lives."

Urinary incontinence affects approximately 35% of the female population. The main cause in women is pregnancy, with the number of children they have increasing their chances of becoming incontinent.

"Our studies show that 20% of the incontinent population has depression, and this is something that we need both sufferers and GPs to better understand," Ms Avery says.

"Sufferers of incontinence are often reluctant to get help, but attitudes are slowly changing. It is very important for them to seek advice about their condition. In some cases, urinary incontinence can be curable with an operation, and this is quite literally a life-changing operation for many women.

"GPs need to be aware that if their patient is suffering from incontinence, this condition is often linked with depression which needs to be treated to increase their quality of life.

"Ultimately, we hope that our research helps to raise awareness in the community about both the mental and physical issues associated with incontinence. We know it's embarrassing, but if you discuss it with your GP, your life really can change."

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Doubling of deaths among sick moms-to-be amid poor evidence on drug safety in pregnancy

June 12, 2013 — The lack of hard data on the safety and effectiveness of a wide range of drugs in pregnancy has hindered the treatment of pregnant women, contributing to a doubling of deaths amongst mums-to-be with an underlying health problem over the past 20 years, argues an editorial in the Drug and Therapeutics Bulletin (DTB).

It's time to include pregnant women in drug trials so that they can get the medical treatment they need, says DTB.

In the absence of reliable information on the pros and cons of treatment during pregnancy, and haunted by the spectre of thalidomide, doctors are reluctant to prescribe, while pregnant women are wary of taking drugs that might harm their developing baby, contends the editorial.

Yet an estimated one in 10 mums-to-be has a long term condition that requires medication, while around four out of 10 develop new health problems during their pregnancy.

And it's going to get worse, prompted by the increasing trend for older age at childbirth and the expanding girth of the nation, both of which are pushing up the numbers of women requiring drug treatment during their pregnancy, warns the editorial.

Some 4% of women who gave birth in England and Wales in 2011 were aged 40 and over -- compared with just 1% a decade earlier -- while almost one in five women of childbearing age were obese in 2008.

But the unwillingness to prescribe and be treated can be fatal, warns DTB. The number of "indirect" deaths among new mums in the UK -- where pregnancy worsens a new or pre-existing medical or mental health problem -- has almost doubled over the past 20 years, and now exceeds deaths directly caused by pregnancy by 50%, it says.

It's rare for a drug company or research team to include pregnant women in drug trials, says DTB. All too often they are put off by the complex ethical issues involved.

Yet equally, it could be argued that it is unethical not to include them in drug trials, especially as side effects can take many years to emerge, it says, citing sodium valproate, the anti-epileptic drug, as a case in point.

["This] was hailed as a wonder anticonvulsant in the 1960s, linked with neural tube defects in the 1980s, and associated with adverse neurodevelopmental effects in the offspring with third trimester exposure in the 2000s," it notes.

It's time to emulate the way in which children's medicines are now being investigated properly, says DTB, which calls on industry and regulators to include women in drug trials.

"With increasing awareness that the intrauterine environment is important for the long term development of children, it is ever more important that those involved in drug development and trials look for ways to safely involved pregnant women rather than automatically exclude them," contends the editorial.

"Pregnancy is a natural state that has been ignored by the pharmaceutical industry for too long," it concludes.

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Obstructive sleep apnea raises risk of sudden cardiac death

June 12, 2013 — People who have obstructive sleep apnea -- when a person stops breathing for periods during sleep -- have a greater risk of sudden cardiac death, according to a study published online today in the Journal of the American College of Cardiology. An estimated 12 million American adults have obstructive sleep apnea, and many of them are undiagnosed, according to the National Heart, Lung and Blood Institute (NHLBI).

In the study, funded by the NHLBI, 10,701 people who participated in sleep studies were followed for an average of 5.3 years for incidence of sudden cardiac death. In that time, 142 patients died of sudden cardiac death. The most common predictors were an age of 60 or older, 20 or more apnea episodes per hour of sleep, and an oxygen saturation below 78 percent during sleep.

"What we found that is new with this study is that if you have sleep apnea, your risk of sudden death increases almost twofold, particularly if you stopped breathing more than 20 times per hour of sleep and if you had severe falls in oxygen saturation during sleep," says senior author Virend Somers, M.D., Ph.D., a Mayo Clinic cardiologist.

When a person is breathing properly, the oxygen saturation level -- when air flows through the lungs -- during sleep is 100 percent, Dr. Somers says. This study showed that if a person is not breathing properly and the oxygen saturation level falls to as low as 78 percent, the risk of sudden cardiac death significantly increases, he says.

Lead author Apoor Gami, M.D., says Mayo Clinic's previous research showed that people with sleep apnea have a much higher risk of sudden cardiac death between midnight and 6 a.m., when people are typically asleep, while people without sleep apnea die more often from sudden cardiac death between 6 a.m. and noon.

"So we knew that sleep apnea changed the time of sudden cardiac death, but we didn't know if it changed the overall risk," Dr. Gami says. "This new study shows that sleep apnea does indeed increase the overall risk of sudden cardiac death independently of other important risk factors.

"The prevalence of obstructive sleep apnea in Western populations is high, and because of the relationship between weight and sleep apnea, the current obesity epidemic is going to further increase the scope of this problem," noted Dr. Gami, formerly at Mayo Clinic and now a cardiologist at Midwest Heart Specialists-Advocate Medical Group in Elmhurst, Ill.

Research has shown that sleep apnea is potentially an important cause of cardiovascular conditions, such as high blood pressure, atrial fibrillation, heart attacks and strokes, Dr. Somers says. Sleep apnea is treatable. In addition to weight loss, physicians also can recommend sleep posture changes and devices, such as a machine that delivers air pressure through a mask placed over the nose while a person sleeps, he says.

The study was supported by grants HL65176 and NIH 1 UL1 RR024150 from the National Institutes of Health (NIH).

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Volunteering reduces risk of hypertension in older adults

New research from Carnegie Mellon University shows that older adults who volunteer for at least 200 hours per year decrease their risk of hypertension, or high blood pressure, by 40 percent. The study, published by the American Psychological Association's Psychology and Aging journal, suggests that volunteer work may be an effective non-pharmaceutical option to help prevent the condition. Hypertension affects an estimated 65 million Americans and is a major contributor to cardiovascular disease, the leading cause of death in the U.S.

"Everyday, we are learning more about how negative lifestyle factors like poor diet and lack of exercise increase hypertension risk," said Rodlescia S. Sneed, a Ph.D. candidate in psychology in CMU's Dietrich College of Humanities and Social Sciences and lead author of the study. "Here, we wanted to determine if a positive lifestyle factor like volunteer work could actually reduce disease risk. And, the results give older adults an example of something that they can actively do to remain healthy and age successfully."

For the study, Sneed and Carnegie Mellon's Sheldon Cohen studied 1,164 adults between the ages of 51 and 91 from across the U.S. The participants were interviewed twice, in 2006 and 2010, and all had normal blood pressure levels at the first interview. Volunteerism, various social and psychological factors, and blood pressure were measured each time.

The results showed that those who reported at least 200 hours of volunteer work during the initial interview were 40 percent less likely to develop hypertension than those who did not volunteer when evaluated four years later. The specific type of volunteer activity was not a factor -- only the amount of time spent volunteering led to increased protection from hypertension.

"As people get older, social transitions like retirement, bereavement and the departure of children from the home often leave older adults with fewer natural opportunities for social interaction," Sneed said. "Participating in volunteer activities may provide older adults with social connections that they might not have otherwise. There is strong evidence that having good social connections promotes healthy aging and reduces risk for a number of negative health outcomes."

The National Institutes of Health's National Institute on Aging and National Center for Complementary and Alternative Medicine supported this research.

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'Tailing' spiny lobster larvae to protect them

The study, which appears in the June 2013 issue of the journal PLOS ONE, synthesizes empirical data from laboratory studies, mail surveys and published works to parameterize an individual-based model of lobster larval connectivity, the Connectivity Modeling System (CMS), developed by Paris. Results were then verified using two independent studies, separated by over 500 km, giving validation to the model's performance -- something never before achieved for spiny lobster or other pelagic larvae over such large scales.

"Spiny lobster have extraordinary larvae with a prolonged planktonic existence that can last from five months to nearly a year, which confer them with high dispersal potential and complex pelagic pathways. Despite such challenges in documenting their pathways in the open ocean, just like hurricane models that help to reduce the 'cone of uncertainty', in this case we are improving settlement predictions by simulating large numbers of spawning events and tracking virtual larvae undergoing deep vertical migrations," says Paris.

The prevailing Caribbean current may not be the best path for successful long distance transportation for larvae. Contrary to the established belief, the team's results suggest that powerful currents entrain and push larvae out of the system, acting like a "Highway to Hell." The larvae that ultimately settle in the simulation spend little time within these strong currents. By moving to deeper depths as they age, spiny lobster larvae seem to increase their odds of settlement.

Butler adds, "Despite some expected degree of ocean mixing in the region, we found relatively high levels of larvae settling back to their place of origin. This was surprising for larvae that spend up to 12 months traveling in the plankton. But even more surprising was that these simple larval behaviors added to the model also enhanced population connectivity by preventing larvae from being flushed out of the system."

Based on the dynamics of long distance larval exchange uncovered using this computational model, the team proposes potential strategies that may be used to better manage the Caribbean spiny lobster population, and increase the sustainability of this economically important fishery.

"We blended ideas from international trade, terrestrial conservation, and carbon emission protocols to suggest 'larval lobster credits' as a viable cooperative management strategy. Predicted larval flow around in the region is dependent on several source regions, which are optimally located for wide ranging dispersal. If the nations receiving the influx of larvae and harvesting the adult lobsters were to invest and help protect these source regions, we believe that the future of the fishery will be more secure and may even improve, which would benefit the entire region ecologically and economically," explains Kough.

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Helmet crash tests: Don't hit the road without one

Crashing without a helmet exposes the head to accelerations and forces -- or loads -- up to 9.5 times greater than with a helmet and so greatly increases the risk of head, skull and brain injury, according to a detailed biomechanical study published in the journal Traffic Injury Prevention.

"Our findings confirm that bicycle helmets certified to AS/NZS 2063 do indeed work as intended and are effective in reducing linear and angular head accelerations, as well as impact force," says the lead author of the study, Dr Andrew McIntosh.

"These results directly counter unsupported claims to the contrary by some anti-helmet cycling campaigners."

Dr McIntosh is an adjunct Associate Professor at UNSW's Transport and Road Safety Research Group and the Monash Injury Research Institute at Monash University.

The study used crash-test dummies and an oblique-impact test rig to measure the loads placed on the human head in a variety of impacts that simulated the likely real-world results of falling from a bicycle at various speeds and heights.

The researchers dropped a dummy head and neck from selected heights onto a moving impact surface to replicate real-world oblique impacts, and measured angular and linear acceleration, impact force and other parameters. The dummies were dropped up to 1.5 m and at a horizontal speed of up to 25 km/h.

"When you look at injury risk, an unprotected head is likely to suffer concussion even dropping only half a metre while you are stationary," says Dr McIntosh. "As the height of the drop and the horizontal speed increase, so does the risk of skull and brain injury."

"We found that a helmeted head, however, is protected against serious injury until the most severe impacts in our study: even with a drop of 1.5 m and a speed of 25 km/h the helmet has an important protective effect."

"The study also reinforced the need to adjust the helmet restraint system correctly to gain the most benefit. It also points to areas where helmets can be improved further by introducing oblique impact tests into consumer rating programs and/or standards."

"An important component of the anti-bicycle helmet rhetoric is that helmets increase the risk of brain injury by increasing the angular acceleration of the head in an impact relative to no helmet. Our tests found that unsupported claim is wrong. In fact, there is a substantial effect of helmets in reducing head loads, including angular acceleration."

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Brain-imaging technique can help diagnose movement disorders

Utilizing the diffusion tensor imaging technique, as it is known, could allow clinicians to assess people earlier, leading to improved treatment interventions and therapies for patients.

The three-year study looked at 72 patients, each with a clinically defined movement disorder diagnosis. Using a technique called diffusion tensor imaging, the researchers successfully separated the patients into disorder groups with a high degree of accuracy.

The study is being published in the journal Movement Disorders.

"The purpose of this study is to identify markers in the brain that differentiate movement disorders which have clinical symptoms that overlap, making [the disorders] difficult to distinguish," said David Vaillancourt, associate professor in the department of applied physiology and kinesiology and the study's principal investigator.

"No other imaging, cerebrospinal fluid or blood marker has been this successful at differentiating these disorders," he said. "The results are very promising."

Movement disorders such as Parkinson's disease, essential tremor, multiple system atrophy and progressive supranuclear palsy exhibit similar symptoms in the early stages, which can make it challenging to assign a specific diagnosis. Often, the original diagnosis changes as the disease progresses, Vaillancourt said.

Diffusion tensor imaging, known as DTI, is a non-invasive method that examines the diffusion of water molecules within the brain and can identify key areas that have been affected as a result of damage to gray matter and white matter in the brain. Vaillancourt and his team measured areas of the basal ganglia and cerebellum in individuals, and used a statistical approach to predict group classification. By asking different questions within the data and comparing different groups to one another, they were able to show distinct separation among disorders.

"Our goal was to use these measures to accurately predict the original disease classification," Vaillancourt said. "The idea being that if a new patient came in with an unknown diagnosis, you might be able to apply this algorithm to that individual.

He compared the process to a cholesterol test.

"If you have high cholesterol, it raises your chances of developing heart disease in the future," he said. "There are tests like those that give a probability or likelihood scenario of a particular disease group. We're going a step further and trying to utilize information to predict the classification of specific tremor and Parkinsonian diseases."

Vaillancourt and his team are part of the National Institute of Neurological Disorders and Stroke Parkinson's Disease Biomarkers Program, an effort that was launched in 2012 and awarded nine grants to scientists across the U.S., totaling more than $5 million in the first year. The program gives researchers access to a much broader community of individuals and patients as part of a biomarker initiative for Parkinson's disease.

Vaillancourt's team is engaged in a longitudinal study at UF that will assess between 150 and 180 people over the next few years. His team will be using DTI as well as other MRI-based techniques to classify subjects and track their progression, he said.

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