Discount Designer Watches: August 2013

Saturday, August 31, 2013

Solar energy: A richer harvest on the horizon

Aug. 31, 2013 — Semiconductor nanostructures are poised to play a big role in future solar-powered hydrogen generation systems, according to a new study by researchers at the A*STAR Institute of High Performance Computing1. Hui Pan and Yong-Wei Zhang report that model interfaces made from gallium nitride (GaN) and zinc oxide (ZnO) semiconductors have tunable magnetic and light-harvesting capabilities -- factors that can greatly improve the photocatalytic transformation of water into hydrogen fuel.

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Most photoelectrochemical cells use titanium dioxide electrodes to absorb light and split water molecules into hydrogen and oxygen gas. But because this mineral has a large bandgap -- a measure of energy needed to initiate photoreactions -- these devices respond only to a tiny fraction of the solar spectrum. A promising way to boost this efficiency is with 'superlattice' materials that stack two different semiconductors into alternate, nanometer-thin layers. The two-dimensional channels that emerge from superlattices resemble conductive nanowires for swift charge-carrier movement. Bandgaps in these hetero-nanostructures have a demonstrated dependence on semiconductor composition and layer thickness.

Pan and Zhang investigated superlattices based on stacked GaN and ZnO layers, two semiconductors with similar electronic and structural properties that are widely used in optoelectronic devices. Using density functional theory calculations, they optimized a periodic GaN-ZnO model superlattice (see image). These computations, which describe the charge and electron spin states of materials, showed that the two semiconductor layers formed crystalline nanowire arrangements with no magnetic characteristics.

The duo then systematically introduced small defects -- atomic substitutions that slightly disrupt semiconductor crystallinity -- into the GaN-ZnO superlattice. To Pan and Zhang's surprise, they observed significant magnetism at several types of defect interface. According to Pan, this extraordinary activity is due to 'polar discontinuities' that form when positively charged defects partially neutralize negative charges at Ga-O interface points. Unpaired electrons then accumulate around Zn-N connections and generate magnetic forces that can boost charge separation and mobility during the reaction known as photocatalysis.

The researchers also found that engineered polar discontinuities could significantly alter semiconductor bandgaps by generating intermediate energy levels. These zones act as 'stepping stones' that make it easier for photons, or light-transmitting particles, to excite electrons for water-splitting reactions. Pan notes that once these intriguing properties of GaN-ZnO nanostructures are verified through laboratory studies, the materials may find application in energy-harvesting solar cells. "If this design proves efficient in both theory and experiment, we would then look for commercial applications by collaborating with industry," he says.

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Magnetic materials: Forging ahead with a back-to-basics approach

Aug. 31, 2013 — Scientists have recently started to explore the possibility of using an intrinsic property of the electron known as spin for processing and storing information. Magnetic fields can influence the dynamics of electron spin, so harnessing this potential relies on precision engineering of crystalline storage materials. Chee Kwan Gan and co‐workers at the A*STAR Institute of High Performance Computing and the A*STAR Data Storage Institute in Singapore have used theoretical calculations to show how the magnetic characteristics of specific materials can be controlled at the atomic level.

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Their results could lead to novel magnetic recording devices.

One promising route to such spintronic devices is to design structures consisting of alternating layers of different magnetic atoms. The strength of the magnetic influence is stronger in the direction of the multilayer stack than it is parallel to the planes of the atoms. This so-called perpendicular magnetic anisotropy is useful for spintronic memory devices because it allows a greater storage density than a conventional electronic device.

The properties of these structures, however, are highly sensitive to the precise arrangement of the crystal. Just one misplaced layer of atoms -- a stacking fault -- can noticeably alter device performance (see image). Previous studies usually ignored these special defects, "but nature sometimes makes 'mistakes'," explains Gan. "It is important to understand these defects and subsequently use them to control the material's physical properties."

Gan and his team went back to basics to better understand how atom-level imperfections affect the properties of these multilayers. They used a powerful mathematical approach known as density functional theory. This approach uses only fundamental equations from quantum mechanics to model the behavior of electrons in these structures, without requiring any prior assumptions.

The researchers modeled a material consisting of alternating layers of cobalt and palladium atoms. Multilayers of these atoms have previously exhibited a large perpendicular magnetic anisotropy when the cobalt layers are less than 0.8 nanometers thick. Gan and co-workers then assessed how stacking faults and the ratio of cobalt to palladium atoms affected this anisotropy. Their results showed that a stacking fault could enhance the magnetic anisotropy in structures with a relatively thick cobalt layer. They also found that the anisotropy increased almost linearly with increasing cobalt content.

High magnetic anisotropy materials have potential for use in the next generation of ultrafast and high-capacity magnetic random-access memory, Gan explains. The improved understanding of these materials from this research will guide the way to realizing such devices.

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High dose statins prevents dementia, study suggests

Dr Lin said: "Statins are widely used in the older population to reduce the risk of cardiovascular disease. But recent reports of statin-associated cognitive impairment have led the US Food and Drug Administration (FDA) to list statin-induced cognitive changes, especially for the older population, in its safety communications."

He added: "Previous studies had considered statin therapy to exert a beneficial effect on dementia. But few large-scale studies have focused on the impact of statins on new-onset, non-vascular dementia in the geriatric population."

Accordingly, the current study examined whether statin use was associated with new diagnoses of dementia. The researchers used a random sample of 1 million patients covered by Taiwan's National Health Insurance. From this they identified 57,669 patients aged >65 years who had no history of dementia in 1997 and 1998. The analysis included pre-senile and senile dementia but excluded vascular dementia.

There were 5,516 new diagnoses of dementia during approximately 4.5 years of follow-up. The remaining 52,153 patients aged >65 formed the control group. Subjects were divided into tertiles according to their mean daily equivalent1 dosage and total (across the entire follow up period) equivalent dosage.

The adjusted hazard ratios (HRs) for dementia were significantly inversely associated with increased daily or total equivalent statin dosage. The HRs for the three tertiles of mean equivalent daily dosage (lowest to highest) were 0.622, 0.697 and 0.419 vs control (p<0.001 for trend). The HRs for the three tertiles of total equivalent dosage (lowest to highest) were 0.773, 0.632 and 0.332 vs control (p<0.001 for trend). The protective effect of statins remained in different age, gender and cardiovascular risk subgroups.

Dr Lin said: "The adjusted risks for dementia were significantly inversely associated with increased total or daily equivalent statin dosage. Patients who received the highest total equivalent doses of statins had a 3-fold decrease in the risk of developing dementia. Similar results were found with the daily equivalent statin dosage."

He added: "It was the potency of the statins rather than their solubility (lipophilic or hydrophilic) which was a major determinant in reducing dementia. High potency statins such as atorvastatin and rosuvastatin showed a significant inverse association with developing dementia in a dose-response manner. Higher doses of high potency statins gave the strongest protective effects against dementia."

Dr Lin continued: "The results were consistent when analysing daily doses of different kinds of statins. Almost all the statins (except lovastatin) decreased the risk for new onset dementia when taken at higher daily doses. A high mean daily dosage of lovastatin was positively associated with the development of dementia, possibly because lovastatin is a lipophilic statin while the anti-inflammatory cholesterol lowering effect of lovastatin is not comparable to that of atorvastatin and simvastatin."

Dr Lin concluded: "To the best of our knowledge, this was the first large-scale, nation-wide study which examined the effect of different statins on new onset dementia (except vascular dementia) in an elderly population. We found that high doses of statins, particularly high potency statins, prevent dementia."

Notes

1. Equivalent dosages are used when comparing the effects of different drugs. Each statin was assigned an appropriate equivalent dose according to the following formula: lovastatin 40mg = pravastatin 40mg = simvastatin 20mg = atorvastatin 10mg = fluvastatin 80mg = rosuvastatin 5mg.

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Friday, August 30, 2013

Membranes contain beautiful patterns, but their function is a mystery

Biological cells are surrounded by a membrane, and here some of the most important processes for sustaining life take place. There can also be something very beautiful happening in membranes, researchers from the University of Southern Denmark have discovered: Membranes can contain beautiful, mysterious patterns.

"We do not yet know what the possible biological function of this might be. There should be a reason for the patterns, we just have not discovered it yet," says associate professor Adam Cohen Simonsen, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark.

With his colleagues Jes Dreier, Jonathan Brewer, John Hjort Ipsen and Uffe Bernchou (now Odense University Hospital) from the research group MEMPHYS at Department of Physics, Chemistry and Pharmacy at the University of Southern Denmark, he has discovered that cell membranes can form spectacular patterns.

The patterns are formed by highly organized lipids (fats) which make up the membrane, and the patterns vary according to conditions such as temperature and the particular type of lipid molecules. The scientists have recently published their latest work identifying two different patterns: a spiral pattern and a uniform pattern.

"This is just the beginning. There may be more than the two patterns we have identified," says Adam Cohen Simonsen.

The patterns are so difficult to "see" that only few research groups in the world yet have the experimental facilities required to visualize the mysterious patterns. In the laboratory at the University of Southern Denmark in Odense the scientists have constructed a custom-designed light microscope, which takes advantage of polarized light to reveal the patterns, and the scientists have managed to produce detailed microscope images of them.

The phenomenon -- that membranes can form such so-called texture patterns -- was discovered at SDU five years ago. Now the researchers have discovered the possibility of more than one pattern and, using artificial membranes, they have identified the conditions under which two particular types of patterns are formed in the laboratory.

Artificial membranes have the advantage that they can easily be spread out on a flat surface and placed under a microscope, while a cell membrane taken from a biological organism is round and much more difficult to work with. Like the membranes of living cells the artificial laboratory membranes are composed of different molecules, in this case, a particular family of lipid molecules -- phospholipids. These are also found in the biological cell membranes.

"The precise type of lipid molecules, that the membrane consists of, appears to play a big role. Some lipid molecules produce spiral patterns and other lipid molecules produce the uniform pattern. The molecules we use are not all of the same length, and therefore different molecules create different membrane thicknesses. The thickness of the membrane can vary from say 5 nm to 6 nm, depending on the molecules used," Adam Cohen Simonsen explains.

When he speaks about the thickness of the membrane, the important quantity is in fact the change in thickness of an elevated area of the membrane, where the lipid molecules are more densely packed. Such a densely packed region of the membrane is called a membrane domain, and it is in such areas that the patterns exist.

"The first pattern we discovered was the spiral pattern. It can be compared to the pattern that is created when you rake long grass in patterns. Lipid molecules are in this picture, like the leaves of grass, organized in a distinctive direction. The next pattern observed was the uniform pattern. Here we saw how lipid molecules organized themselves in a much simpler way, with all molecules pointing in the same direction. Our results suggest that it is the change in membrane thickness across a domain that determines whether one or the other pattern is formed," says Adam Cohen Simonsen.

It takes a few minutes for a spiral pattern to form in the laboratory where the growth takes place under controlled conditions. The formation starts at a relatively high temperature, 55 degrees Celsius, where the lipid molecules are in a liquid state and slide effortlessly around between each other. When the temperature drops, the lipid molecules start condensing together, and at app. 34 degrees the pattern formation starts.

"When we studied the spiral pattern, we saw that a nucleus was formed at 34 degrees, and that the spiral domain grew from the nucleus. It took approximately five minutes for it to finish," says Adam Cohen Simonsen.

"We have now shown that the type of pattern depends on which kind of lipid molecules that is present in the cell membrane. But what the function is -- or what significance, these patterns may have for the biological functionality of living cells -- that is something we do not know yet. It is the next big question," Adam Cohen Simonsen concludes.

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Sea-level rise drives shoreline retreat in Hawaii

The authors of the work point out that knowing that SLR is a primary cause of shoreline change on a regional scale allows managers and other coastal zone decision-makers to target SLR impacts in their research programs and long-term planning. This study is confirmation that future SLR is a major concern for decision-makers charged with managing beaches.

"It is common knowledge among coastal scientists that sea level rise leads to shoreline recession," stated Dr. Brad Romine, coastal geologist with the University of Hawaii Sea Grant College Program. "Shorelines find an equilibrium position that is a balance between sediment availability and rising ocean levels. On an individual beach with adequate sediment availability, beach processes may not reflect the impact of SLR. With this research we confirm the importance of SLR as a primary driver of shoreline change on a regional to island-wide basis."

Globally-averaged sea-level rose at about 2 mm per year over the past century. Previous studies indicate that the rate of rise is now approximately 3 mm per year and may accelerate over coming decades. The results of the recent publication show that SLR is an important factor in historical shoreline change in Hawaii and will be increasingly important with projected SLR acceleration in this century. "Improved understanding of the influence of SLR on historical shoreline trends will aid in forecasting beach changes with increasing SLR," said Dr. Charles Fletcher, Associate Dean and Professor of Geology and Geophysics at the UHM SOEST.

"The research being conducted by SOEST provides us with an opportunity to anticipate SLR effects on coastal areas, including Hawaii's world famous beaches, coastal communities, and infrastructure. We hope this information will inform long range planning decisions and allow for the development of SLR adaptation plans," said Sam Lemmo, Administrator, Department of Land and natural Resources, Office of Conservation and Coastal Lands.

Results of island-wide historical trends indicate that Maui beaches are significantly more erosional than beaches on Oahu. On Maui, 78% of beaches eroded over the past century with an overall (island-wide) average shoreline change rate of 13 cm of erosion per year, while 52% of Oahu beaches eroded with an overall average shoreline change rate of 3 cm of erosion per year.

The variation in long-term relative SLR rates along the Hawaii archipelago is due, in large part, to variations in island subsidence with distance from actively growing Hawaii Island and/or variations in upper ocean water masses. The islands of Oahu and Maui, Hawaii, with significantly different rates of localized sea-level rise (SLR has been approximately 65% higher rate on Maui) over the past century, provided a natural laboratory to investigate possible relations between historical shoreline changes and SLR.

Island-wide and regional historical shoreline trends were calculated for the islands using shoreline positions measured from aerial photographs and survey charts. Shoreline positions were manually digitized using photogrammetric and geographic information system (GIS) software from aerial photo mosaics and topographic and hydrographic survey charts provided by the National Ocean Service (NOS). Shoreline movement through time was measured using GIS software. Historical shoreline data were optimized to reduce anthropogenic influences (e.g., constructing seawalls or sand mining) on shoreline change measurements. The researchers controlled for influences other than SLR to determine if SLR remains as the best explanation for observed changes. They also utilized a series of consistency checks to determine if results are significant and to eliminate other possible explanations.

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Sideline teleconcussion robot to be tested at football games

Mayo Clinic will be working with NAU to test the feasibility of using a telemedicine robot to assess athletes with suspected concussions during football games as part of a research study. With sophisticated robotic technology, use of a specialized remote controlled camera system allows patients to be "seen" by the neurology specialist, miles away, in real time. During the study, the robot equipped with a specialized camera system, remotely operated by a Mayo Clinic neurologist located in Phoenix who has the ability to assess a player for symptoms and signs of a concussion and to consult with sideline medical personnel.

The first time the robot will be used in a game is this Friday, Aug. 30 when NAU kicks off its season against the University of Arizona in Tucson at 7 p.m. (MST).

"Athletes at professional and collegiate levels have lobbied for access to neurologic expertise on the sideline. As we seek new and innovative ways to provide the highest level of concussion care and expertise, we hope that teleconcussion can meet this need and give athletes at all levels immediate access to concussion experts," said Bert Vargas, M.D., a neurologist at Mayo Clinic who is heading up the research.

This study would be the first to explore whether a remote neurological assessment is as accurate as a face-to-face evaluation in identifying concussion symptoms and making return to play decisions. Mayo Clinic physicians will not provide medical consultations during the study, they will only assess the feasibility of using the technology. If it appears feasible, this may open the door for countless schools, athletic teams, and organizations without access to specialized care to use similar portable technology for sideline assessments.

"As nearly 60 percent of U.S. high schools do not have access to an athletic trainer, youth athletes, who are more susceptible to concussion and its after-effects, have the fewest safeguards in place to identify possible concussion signs and symptoms at the time of injury, Dr. Vargas says. "Teleconcussion is one way to bridge this gap regardless of when or where they may be playing."

Others involved collegiate sports agree.

"At NAU, our primary goal is to provide an outstanding student-athlete experience culminating in graduation," says Dr. Lisa Campos, vice president for Intercollegiate Athletics at Northern Arizona University. "We charge our staff to research the most current and best practices to ensure the safety and care of our students. Partnering with the Mayo Clinic in its telemedicine study will further this research and potentially improve diagnosis for rural areas that may not have access to team doctors or neurologists. The study allows the NAU Sports Medicine Staff and team doctors to continue to make all diagnoses and return to play decisions for our students, while investigating the effectiveness and efficiencies of telemedicine. We are excited to have the teleconcussion robot on our sideline this fall."

"There were a number of examples last football season where college football players clearly demonstrating concussion-like symptoms were quickly thrown back in games or weren't even taken out of the game for an evaluation," said Ramogi Huma, executive director of the National College Players Association. "College football players are in desperate need for independent concussion experts on the sidelines, and this study could help make that safeguard a reality."

Mayo Clinic in Arizona first used telemedicine technology with the telestroke program in 2007, when statistics revealed that 40 percent of residents in Arizona did not live in an area where they were availed of stroke expertise. Mayo Clinic was the first medical center in Arizona to do pioneering clinical research to study telemedicine as a means of serving patients with stroke in non-urban settings, and today serves as the "hub" in a network of 12 "spoke" centers, all but one in Arizona. Since the telestroke program began nearly 3,000 emergency consultations for neurological emergencies like stroke between Mayo neurologists and physicians at the spoke centers have taken place.

In 2011, Mayo Clinic expanded its telemedicine evaluations to include concussion evaluations. Concussion experts at the Mayo Clinic Comprehensive Concussion Program in Arizona coined the term "teleconcussion" and described the concept as an effective means to assess concussed patients in a case study published in the December 2012 issue of Telemedicine and e-Health.

"Teleconcussion is an excellent new example of connected care in action, as athletes with suspected concussion, anywhere and anytime, can be effectively connected to Mayo Clinic concussion knowledge and expertise," says Bart Demaerschalk, M.D., co-author of study, Director of Mayo Clinic Teleneurology and Telestroke, and Chair of American Academy of Neurology Telemedicine Work Group.

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Researchers a step closer to finding cosmic ray origins

Cosmic rays can damage electronics on Earth, as well as human DNA, putting astronauts in space especially at risk.

The research, which draws on data collected by IceTop, the IceCube Observatory's surface array of detectors, is published online in Physical Review D, a leading journal in elementary particle physics.

University of Delaware physicist Bakhtiyar Ruzybayev is the study's corresponding author. UD scientists were the lead group for the construction of IceTop with support from the National Science Foundation and coordination by the project office at the University of Wisconsin, Madison.

The more scientists learn about the energy spectrum and chemical composition of cosmic rays, the closer humanity will come to uncovering where these energetic particles originate.

Cosmic rays are known to reach energies above 100 billion giga-electron volts (1011 GeV). The data reported in this latest paper cover the energy range from 1.6 times 106 GeV to 109 GeV.

Researchers are particularly interested in identifying cosmic rays in this interval because the transition from cosmic rays produced in the Milky Way Galaxy to "extragalactic" cosmic rays, produced outside our galaxy, is expected to occur in this energy range.

Exploding stars called supernovae are among the sources of cosmic rays here in the Milky Way, while distant objects such as collapsing massive stars and active galactic nuclei far from the Milky Way are believed to produce the highest energy particles in nature.

As Ruzybayev points out, the cosmic-ray energy spectrum does not follow a simple power law between the "knee" around 4 PeV (peta-electron volts) and the "ankle" around 4 EeV (exa-electron volts), as previously thought, but exhibits features like hardening around 20 PeV and steepening around 130 PeV.

"The spectrum steepens at the 'knee,' which is generally interpreted as the beginning of the end of the galactic population. Below the knee, cosmic rays are galactic in origin, while above that energy, particles from more distant regions in our universe become more and more likely," Ruzybayev explained. "These measurements provide new constraints that must be satisfied by any models that try to explain the acceleration and propagation of cosmic rays."

IceTop consists of 81 stations in its final configuration, covering an area of one square kilometer on the South Pole surface above the detectors of IceCube, which are buried over a mile deep in the ice. The analysis presented in this article was performed using data taken from June 2010 to May 2011, when the array consisted of only 73 stations.

The IceCube collaboration includes nearly 250 people from 39 research institutions in 11 countries, including the University of Delaware.

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LED Lighting Proved: Why LED efficiency drops at high current

2013/08/30

04sep13Rensselaer Researchers at the US Rensselaer Polytechnic have proven a link between LED efficiency drop at high current and carrier mobility. Better lighting LEDs could result.

“Efficiency droop, first reported in 1999, has been a key obstacle in the development of LED lighting for situations, like household lighting, that call for economical sources of versatile and bright light,” said the university.

Published in Applied Physics Letters, the work shows that at high current an electric field develops within the p-type region of the diode allowing electrons to escape the active region where they would otherwise re-combine with holes to emit photons – a mechanism previously proposed, but not proven, said Rensselaer.

“We measure excellent correlation between the onset of field build-up and the onset of droop. This is clear evidence that the mechanism is electron leakage, and we can describe it quantitatively,” said Rensselaer researcher David Meyaard. “For example, in one result reported in the paper, we show the onset of high injection and the onset of droop and you can see that they are very nicely correlated. And that was just not possible in the past because there was really no theoretical model that described how electron leakage really works.”

“If the holes and the electrons had similar properties, there is a symmetry; both would meet in the middle, where the quantum well is, and there they recombine,” said Professor Fred Schubert. “What we have instead is a material system where the electrons are much more mobile than the holes. And because they are very mobile, they diffuse more easily, they also react more easily to an electric field. Because of that asymmetry, or disparity, we have a propensity of the electrons to shoot over and to be extracted from the quantum well. And so they don’t meet the hole in the active region and so they don’t emit light.”

Based on the theoretical model, Meyaard and Schubert will look for LED structures that reduce the issue.

The paper is ‘Identifying the cause of the efficiency droop in GaInN light-emitting diodes by correlating the onset of high injection with the onset of the efficiency droop.’

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Hydrogen fuel from sunlight: Researchers make unique semiconductor/catalyst construct

"We've developed a method by which molecular hydrogen-producing catalysts can be interfaced with a semiconductor that absorbs visible light," says Gary Moore, a chemist with Berkeley Lab's Physical Biosciences Division and principal investigator for JCAP. "Our experimental results indicate that the catalyst and the light-absorber are interfaced structurally as well as functionally."

Moore is the corresponding author, along with Junko Yano and Ian Sharp, who also hold joint appointments with Berkeley Lab and JCAP, of a paper describing this research in the Journal of the American Chemical Society (JACS). The article is titled "Photofunctional Construct That Interfaces Molecular Cobalt-Based Catalysts for H₂ Production to a Visible-Light-Absorbing Semiconductor." Co-authors are Alexandra Krawicz, Jinhui Yang and Eitan Anzenberg.

Earth receives more energy in one hour's worth of sunlight than all of humanity uses in an entire year. Through the process of photosynthesis, green plants harness solar energy to split molecules of water into oxygen, hydrogen ions (protons) and free electrons. The oxygen is released as waste and the protons and electrons are used to convert carbon dioxide into the carbohydrate sugars that plants use for energy. Scientists aim to mimic the concept but improve upon the actual process.

JCAP, which has a northern branch in Berkeley and a southern branch on the campus of the California Institute of Technology (Caltech), was established in 2010 by DOE as an Energy Innovation Hub. Operated as a partnership between Caltech and Berkeley Lab, JCAP is the largest research program in the United States dedicated to developing an artificial solar-fuel technology. While artificial photosynthesis can be used to generate electricity, fuels can be a more effective means of storing and transporting energy. The goal is an artificial photosynthesis system that's at least 10 times more efficient than natural photosynthesis.

To this end, once photoanodes have used solar energy to split water molecules, JCAP scientists need high performance semiconductor photocathodes that can use solar energy to catalyze fuel production. In previous efforts to produce hydrogen fuel, catalysts have been immobilized on non-photoactive substrates. This approach requires the application of an external electrical potential to generate hydrogen. Moore and his colleagues have combined these steps into a single material.

"In coupling the absorption of visible light with the production of hydrogen in one material, we can generate a fuel simply by illuminating our photocathode," Moore says. "No external electrochemical forward biasing is required."

The new JCAP photocathode construct consists of the semiconductor gallium phosphide and a molecular cobalt-containing hydrogen production catalyst from the cobaloxime class of compounds. As an absorber of visible light, gallium phosphide can make use of a greater number of available solar photons than semiconductors that absorb ultraviolet light, which means it is capable of producing significantly higher photocurrents and rates of fuel production. However, gallium phosphide can be notoriously unstable during photoelectrochemical operations.

Moore and his colleagues found that coating the surface of gallium phosphide with a film of the polymer vinylpyridine alleviates the instability problem, and if the vinylpyridine is then chemically treated with the cobaloxime catalyst, hydrogen production is significantly boosted.

"The modular aspect of our method allows independent modification of the light-absorber, linking material and catalyst, which means it can be adapted for use with other catalysts tethered over structured photocathodes as new materials and discoveries emerge," Moore says. "This could allow us, for example, to replace the precious metal catalysts currently used in many solar-fuel generator prototypes with catalysts made from earth-abundant elements."

Despite its promising electronic properties, gallium phosphide features a mid-sized optical band gap which ultimately limits the total fraction of solar photons available for absorption. Moore and his colleagues are now investigating semiconductors that cover a broader range of the solar spectrum, and catalysts that operate faster at lower electrical potentials. They also plan to investigate molecular catalysts for carbon dioxide reduction.

"We look forward to adapting our method to incorporate materials with improved properties for converting sunlight to fuel," Moore says. "We believe our method provides researchers at JCAP and elsewhere with an important tool for developing integrated photocathode materials that can be used in future solar-fuel generators as well as other technologies capable of reducing net carbon dioxide emissions."

This research was funded by the DOE Office of Science.

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New understanding of formation of cilia: Cilia provide mobility to cells, and defects are implicated in many disease

Aug. 30, 2013 — Tiny hair-like structures (cilia) are found on the surface of most cells. Cilia are responsible for the locomotion of cells (e.g. sperm cells), they process external signals and coordinate the correct arrangement of the inner organs during the development of an organism. For proper assembly and function of cilia, they need to be supplied with the appropriate building blocks.

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Scientists at the Max Planck Institute of Biochemistry (MPIB) in Martinsried near Munich, Germany, now identified the mechanism of how Tubulin, the main building block of cilia, is transported within the cilium. "Defects in cilia cause numerous diseases that affect millions of people worldwide," says Sagar Bhogaraju, scientist at the MPI of Biochemistry.

The results now published in the journal Science could help to understand and potentially prevent these diseases.

Although cilia fulfill various tasks, they all have a similar structure: They are only five to ten micrometers (0.0005 to 0.001 centimeters) long and are located on the surface of eukaryotic cells. About 600 different ciliary proteins are synthesized inside the cell and then transported into the cilium. Disruption of this transport system, which scientists call intraflagellar transport (IFT), can lead to errors during the assembly of the cilia and thus cause diseases resulting in mental and physical symptoms. Mistakes in ciliary function can for example cause a "situs inversus," a condition where the left/right arrangement of the inner organs in the body is reversed.

Even though the importance of the intraflagellar transport (IFT) and the cilium to human health has been known for a long time, a structural and mechanistic understanding of IFT has been missing so far. Scientists from the research group "Intraflagellar Transport" headed by Esben Lorentzen now succeeded in identifying the transport mechanism of the key protein Tubulin. It is the most abundant protein in the cilium and forms its backbone. "We found that the two proteins IFT74 and IFT81 work together to form a tubulin-binding module," says Sagar Bhogaraju. When the researchers disturbed the binding of IFT74 and -81 to tubulin in human cells, it had severe impact on the formation of the cilia. "Our results provide the first glimpse into the assembly of the cilium at the molecular level," says the biochemist.

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