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  • richardmitnick 4:41 pm on September 20, 2014 Permalink | Reply
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    From Princeton: “‘Solid’ light could compute previously unsolvable problems” 

    Princeton University
    Princeton University

    Sep 08, 2014
    John Sullivan

    Researchers at Princeton University have begun crystallizing light as part of an effort to answer fundamental questions about the physics of matter.

    The researchers are not shining light through crystal – they are transforming light into crystal. As part of an effort to develop exotic materials such as room-temperature superconductors, the researchers have locked together photons, the basic element of light, so that they become fixed in place.

    “It’s something that we have never seen before,” said Andrew Houck, an associate professor of electrical engineering and one of the researchers. “This is a new behavior for light.”

    The results raise intriguing possibilities for a variety of future materials. But the researchers also intend to use the method to address questions about the fundamental study of matter, a field called condensed matter physics.

    “We are interested in exploring – and ultimately controlling and directing – the flow of energy at the atomic level,” said Hakan Türeci, an assistant professor of electrical engineering and a member of the research team. “The goal is to better understand current materials and processes and to evaluate materials that we cannot yet create.”

    The team’s findings, reported online on Sept. 8 in the journal Physical Review X, are part of an effort to answer fundamental questions about atomic behavior by creating a device that can simulate the behavior of subatomic particles. Such a tool could be an invaluable method for answering questions about atoms and molecules that are not answerable even with today’s most advanced computers.

    light

    In part, that is because current computers operate under the rules of classical mechanics, which is a system that describes the everyday world containing things like bowling balls and planets. But the world of atoms and photons obeys the rules of quantum mechanics, which include a number of strange and very counterintuitive features. One of these odd properties is called “entanglement” in which multiple particles become linked and can affect each other over long distances.

    The difference between the quantum and classical rules limits a standard computer’s ability to efficiently study quantum systems. Because the computer operates under classical rules, it simply cannot grapple with many of the features of the quantum world. Scientists have long believed that a computer based on the rules of quantum mechanics could allow them to crack problems that are currently unsolvable. Such a computer could answer the questions about materials that the Princeton team is pursuing, but building a general-purpose quantum computer has proven to be incredibly difficult and requires further research.

    Another approach, which the Princeton team is taking, is to build a system that directly simulates the desired quantum behavior. Although each machine is limited to a single task, it would allow researchers to answer important questions without having to solve some of the more difficult problems involved in creating a general-purpose quantum computer. In a way, it is like answering questions about airplane design by studying a model airplane in a wind tunnel – solving problems with a physical simulation rather than a digital computer.

    In addition to answering questions about currently existing material, the device also could allow physicists to explore fundamental questions about the behavior of matter by mimicking materials that only exist in physicists’ imaginations.

    To build their machine, the researchers created a structure made of superconducting materials that contains 100 billion atoms engineered to act as a single “artificial atom.” They placed the artificial atom close to a superconducting wire containing photons.

    By the rules of quantum mechanics, the photons on the wire inherit some of the properties of the artificial atom – in a sense linking them. Normally photons do not interact with each other, but in this system the researchers are able to create new behavior in which the photons begin to interact in some ways like particles.

    “We have used this blending together of the photons and the atom to artificially devise strong interactions among the photons,” said Darius Sadri, a postdoctoral researcher and one of the authors. “These interactions then lead to completely new collective behavior for light – akin to the phases of matter, like liquids and crystals, studied in condensed matter physics.”

    Türeci said that scientists have explored the nature of light for centuries; discovering that sometimes light behaves like a wave and other times like a particle. In the lab at Princeton, the researchers have engineered a new behavior.

    “Here we set up a situation where light effectively behaves like a particle in the sense that two photons can interact very strongly,” Türeci said. “In one mode of operation, light sloshes back and forth like a liquid; in the other, it freezes.”

    The current device is relatively small, with only two sites where an artificial atom is paired with a superconducting wire. But the researchers say that by expanding the device and the number of interactions, they can increase their ability to simulate more complex systems – growing from the simulation of a single molecule to that of an entire material. In the future, the team plans to build devices with hundreds of sites with which they hope to observe exotic phases of light such as superfluids and insulators.

    “There is a lot of new physics that can be done even with these small systems,” said James Raftery, a graduate student in electrical engineering and one of the authors. “But as we scale up, we will be able to tackle some really interesting questions.”

    Besides Houck, Türeci, Sadri and Raftery, the research team included Sebastian Schmidt, a senior researcher at the Institute for Theoretical Physics at ETH Zurich, Switzerland. Support for the project was provided by: the Eric and Wendy Schmidt Transformative Technology Fund; the National Science Foundation; the David and Lucile Packard Foundation; the U.S. Army Research Office; and the Swiss National Science Foundation.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 3:39 pm on September 17, 2014 Permalink | Reply
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    From Princeton: “Neutrino experiment that reaches for the sun has Princeton roots” 

    Princeton University
    Princeton University

    September 17, 2014
    Catherine Zandonella, Office of the Dean for Research

    The detection announced Aug. 28 of an elusive subatomic particle forged in the sun’s core was a crowning achievement in the 25-year international effort to design and build one of the most sensitive neutrino detectors in the world, a feat that directly involved Princeton University scientists and engineers. With ongoing improvements in its sensitivity, the Borexino neutrino detector located a mile beneath a mountaintop at Italy’s Gran Sasso National Laboratory has the potential to reveal more about how the sun and other stars produce energy.

    Gran Sasso
    LABORATORI NAZIONALI del GRAN SASSO

    Sometimes called “ghost particles,” neutrinos are extremely difficult to detect because they slip through ordinary matter without leaving a trace. The four-story high Borexino detector is one of a handful worldwide that are capable of detecting the weakest of the neutrinos, including the proton-proton solar neutrino that is emitted during the first of several fusion reactions that generate 99 percent of the sun’s energy. The discovery of the proton-proton neutrino was reported in the journal Nature.

    “The detection of this type of solar neutrino confirms an important piece of the theory about how the sun makes energy, and if you understand the sun then you understand stars in general,” said Professor of Physics Frank Calaprice, who has led Princeton’s part of the Borexino collaboration.

    image
    The Borexino collaboration, which announced the detection of an elusive solar neutrino in August, involved several scientific contributions from Princeton over its 25-year history. The detector consists of two massive transparent nylon balloons filled with a petroleum-based liquid called “scintillator,” which emits a flash of light when it detects a neutrino. These flashes are picked up by an array of sensors embedded in a stainless steel sphere that surrounds the balloons. (Image courtesy of the Borexino collaboration)

    Although proton-proton neutrinos have been detected indirectly, Borexino is the first to measure the particles directly as well as to count the rate at which neutrinos are produced. Knowing how many neutrinos are produced tells scientists how much solar energy is being generated at the core of the sun.

    It takes tens of thousands of years for the energy made in the sun’s center to migrate to its surface. Neutrinos, on the other hand, travel at near the speed of light, reaching Earth in about eight minutes. So neutrinos essentially reveal what the sun’s surface will be like thousands of years in the future. The Borexino result revealed that the sun’s energy as measured by proton-proton neutrinos agreed with the energy measured at the sun’s surface within about 10 percent, indicating that the sun’s energy output has remained stable over the last 100,000 years or so.

    In addition to providing a way of forecasting the sun’s energy production for the next 100,000 years, the detection of these fleeting solar particles offers a way to probe the composition of the sun’s core, Calaprice said: “In principle you can tell what is happening in the center of the sun by measuring these neutrinos.”

    The standard model of the sun suggests that it is a mixed ball of hydrogen and helium with trace amounts of oxygen, carbon, nitrogen and other elements. Studies of the sun’s seismic activity have challenged that finding, however, suggesting that the core of the sun contains greater amounts of carbon, nitrogen and oxygen, while the fringes contain more hydrogen and helium.

    A type of neutrino that has not been detected before but is predicted to exist — the carbon-nitrogen neutrino — could put the controversy to rest. These neutrinos form during the process that makes the other 1 percent of the sun’s energy. Although the carbon-nitrogen process contributes little to the total energy produced in slowly evolving stars such as our sun, it is common in massive, rapidly evolving stars in the universe.

    Borexino is close to having the sort of sensitivity needed to detect carbon-nitrogen neutrinos, Calaprice said. “If we measure carbon-nitrogen neutrinos, we may be able to learn something about the amount of carbon and other elements in the core of the sun,” he said. “This could help researchers explore whether the formation of the planets affected the composition of the outer zone of the sun.”

    Balloons in Jadwin Gym

    Princeton faculty members and students have been involved in the design and construction of Borexino since its inception in the early 1990s, Calaprice said. The project is funded by Italy’s National Institute for Nuclear Physics and the U.S. National Science Foundation, as well as by science agencies from Germany, Russia, Poland, Hungary and several other countries.

    The detector, which was switched on in 2007, consists of two giant, transparent nylon balloons, one nested inside the other, that are filled with a petroleum-based liquid called “scintillator,” which emits a flash of light when a neutrino is detected. That flash of light is picked up by roughly 2,000 sensors spaced evenly around the interior of a stainless steel sphere that surrounds the balloons.

    The idea for using balloons to contain the liquid came from Calaprice’s long-time colleague, Robert Parsells, an engineer at the Princeton Plasma Physics Laboratory. “It was one of those crazy ideas that sometimes work,” Calaprice said.

    pppl

    Engineers and students at Princeton designed and built the balloons under the guidance of Calaprice and Professor of Physics Cristiano Galbiati. The team included then-graduate students Laura Cadonati, now an associate professor of physics at the University of Massachusetts-Amherst, and Andrea Pocar, now an assistant professor at the University of Massachusetts-Amherst. With Princeton engineer Allan Nelson and others, the researchers assembled the balloons — which were 28-feet and 38-feet in diameter — by gluing together strips of nylon in a dust-free “cleanroom” in the physics building. They then inflated prototypes of the balloons for testing in Princeton’s Jadwin Gym before transporting them to Italy.

    While members of the collaboration from Italy and other nations worked on the network of sensors and the electronics to process the results, the Princeton team made sure that the entire detector was free from background contaminants that could obscure the results. “Within the collaboration, the Princeton group historically has tackled some of the most challenging aspects of the experiment,” said Pocar, who now works on Borexino data analysis at Amherst and served as the corresponding author on behalf of the collaboration for the finding reported in Nature.
    Balloon construction in clean room

    team
    In the early 2000s, Princeton graduate students and engineers built large transparent nylon balloons to contain the scintillator. The team glued strips of nylon together in a special cleanroom constructed in the physics building to be as free as possible of radioactivity and dust. From left to right: Andrea Pocar, then a graduate student and now an assistant professor at the University of Massachusetts-Amherst; the late John Bahcall, a physicist at the Institute of Advance Study, who was instrumental in studying solar neutrinos and advocating for the Borexino project; and Princeton technicians Charles Sule, Allan Nelson, Elizabeth Harding (in background) and Brian Kennedy. (Image courtesy of Frank Calaprice, Department of Physics)
    Leave no trace of radioactivity

    Solar neutrinos stream from the sun to Earth at a rate of 420 billion per second per square-inch but are invisible and harmless. Their signals are nearly impossible to distinguish from the signals coming from the decay of common radioactive elements such as radon. The extremely clean and radioactive-free environment achieved at the Borexino detector has enabled the elimination of false detections, yielding the sensitivity needed for the detection of the proton-proton neutrino, which was not part of the project’s original goals, Calaprice said: “No one really thought that we could succeed with this experiment — it was too hard to get the backgrounds down as low as were needed.”

    To reduce false readings from radioactive particles — which are common in rocks and water in Italy and New Jersey — Calaprice turned to Princeton’s Jay Benziger, professor of chemical and biological engineering, an expert in the industrial-scale refining of petroleum. “We realized we needed surfaces that dust cannot stick to, so we borrowed techniques from the pharmaceutical industry, and we used purification methods borrowed from the petroleum industry, all to get the background down,” Benziger said. The resulting purification system was built and tested at Princeton before being shipped to Gran Sasso.

    In the past three years, a team of undergraduates successfully improved the purification process. Puzzled by the difficulty of removing a certain radioactive element called polonium-210, Brooke Russell, a Class of 2011 physics student who stayed on as a staff researcher, discovered a publication showing that the polonium can be converted by bacteria to another compound that allows it to resist being removed by the techniques the group was using. The team, which included William Taylor, Class of 2014, and Christian Aurup, a summer research associate and undergraduate at the University of Delaware, made adjustments to the procedure that dramatically reduced the level of the contamination. The techniques developed at Princeton to prevent false detections at Borexino have been employed in the DarkSide dark matter detector also located at Gran Sasso, as well as other neutrino and dark matter detectors around the world.

    “The thesis experience and also the two years after graduation were really pivotal for me,” Russell said. “Before doing my thesis, I had not been exposed to experimental physics. I enjoyed it so thoroughly that I decided to pursue it as a career,” said Russell, who is now in her second year of graduate studies at Yale University.

    With this latest purification step, Calaprice said, he hopes that Borexino can detect the last known solar neutrino, the carbon-nitrogen neutrino. The detector also will begin searching for the so-called “sterile neutrino” that some physicists think exists. If it is found, this type of neutrino could explain discrepancies in the so-called Standard Model of particle physics.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The international team that reported the proton-proton neutrino in the August 28 issue of Nature included the following Princeton researchers: Borexino general engineers Augusto Goretti and Andrea Ianni; Alvaro Chavarria, who earned his doctorate in physics in 2012; Pablo Mosteiro, who earned his doctorate in physics in 2014; Richard Saldanha, who earned his doctorate in physics in 2012; R. Bruce Vogelaar, a former assistant professor now at Virginia Polytechnic Institute and State University; and Alex Wright, former postdoctoral researcher and now assistant professor at Queen’s University.

    The article, “Neutrinos from the primary proton–proton fusion process in the Sun,” was published Aug. 28 in Nature.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 8:42 pm on September 10, 2014 Permalink | Reply
    Tags: , , , , , Princeton University   

    From Princeton: “PPPL scientists take key step toward solving a major astrophysical mystery” 

    Princeton University
    Princeton University

    September 10, 2014
    John Greenwald, Princeton Plasma Physics Laboratory Communications

    PPPL Large

    PPPL

    Magnetic reconnection in the Earth and sun’s atmospheres can trigger geomagnetic storms that disrupt cell phone service, damage satellites and blackout power grids. Understanding how reconnection transforms magnetic energy into explosive particle energy has been a major unsolved problem in plasma astrophysics.

    Scientists at the Princeton Plasma Physics Laboratory (PPPL) and Princeton University have taken a key step toward a solution, as described in a paper published this week in the journal Nature Communications. In research conducted on the Magnetic Reconnection Experiment (MRX) at PPPL, the scientists not only identified how the mysterious transformation takes place, but measured experimentally the amount of magnetic energy that turns into particle energy. This work was supported by the U.S. Department of Energy’s Office of Science.

    Magnetic field lines represent the direction, and indicate the shape, of magnetic fields. In magnetic reconnection, the magnetic field lines in plasma snap apart and violently reconnect. The MRX, built in 1995, allows researchers to study the process in a controlled laboratory environment.
    Reconnecting field lines

    lines
    This fast-camera image shows plasma during magnetic reconnection, with magnetic field lines rendered in white based on measurements made during the experiment. The converging horizontal lines represent the field lines prior to reconnection. The outgoing vertical lines represent the field lines after reconnection. (Image by Jongsoo Yoo, Princeton Plasma Physics Laboratory)

    The new research shows that reconnection converts about 50 percent of the magnetic energy, with one-third of the conversion heating the electrons and two-thirds accelerating the ions — or atomic nuclei — in the plasma. In large bodies like the sun, such converted energy can equal the power of millions of tons of TNT.

    “This is a major milestone for our research,” said Masaaki Yamada, a research physicist, the principal investigator for the MRX and first author of the Nature Communications paper. “We can now see the entire picture of how much of the energy goes to the electrons and how much to the ions in a proto-typical reconnection layer.”

    The findings also suggested the process by which the energy conversion occurs. Reconnection first propels and energizes the electrons, according to the researchers, and this creates an electrically charged field that “becomes the primary energy source for the ions,” said Jongsoo Yoo, an associate research physicist at PPPL and co-author of the paper.

    The other contributors to the paper were Hantao Ji, professor of astrophysical sciences at Princeton; Russell Kulsrud, professor of astrophysical sciences, emeritus, at Princeton; and doctoral candidates in astrophysical sciences Jonathan Jara-Almonte and Clayton Myers.

    If confirmed by data from space explorations, the PPPL results could help resolve decades-long questions and create practical benefits. These could include a better understanding of geomagnetic storms that could lead to advanced warning of the disturbances and an improved ability to cope with them. Researchers could shut down sensitive instruments on communications satellites, for example, to protect the instruments from harm.

    Next year NASA plans to launch a four-satellite mission to study reconnection in the magnetosphere — the magnetic field that surrounds the Earth. The PPPL team plans to collaborate with the venture, called the Magnetospheric Multiscale (MMS) Mission, by providing MRX data to it. The MMS probes could help to confirm the laboratory’s findings.

    four
    All four MMS spacecraft are stacked and ready for transport to the vibration chamber for environmental tests. Although they will be disassembled again later this month, this image is a sneak preview of what will be the final flight configuration of the MMS fleet.

    PPPL, on Princeton University’s Forrestal Campus in Plainsboro, New Jersey, is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Fusion takes place when atomic nuclei fuse and release a burst of energy. This compares with the fission reactions in today’s nuclear power plants, which operate by splitting atoms apart.

    Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 2:39 pm on September 2, 2014 Permalink | Reply
    Tags: , Autism, , Princeton University   

    From Princeton: “Early cerebellum injury hinders neural development, possible root of autism, theory suggests” 

    Princeton University
    Princeton University

    September 2, 2014
    Morgan Kelly, Office of Communications

    A brain region largely known for coordinating motor control has a largely overlooked role in childhood development that could reveal information crucial to understanding the onset of autism, according to Princeton University researchers.

    The cerebellum — an area located in the lower rear of the brain — is known to process external and internal information such as sensory cues that influence the development of other brain regions, the researchers report in the journal Neuron. Based on a review of existing research, the researchers offer a new theory that an injury to the cerebellum during early life potentially disrupts this process and leads to what they call “developmental diaschisis,” which is when a loss of function in one part of the brain leads to problems in another region.

    cere
    Drawing of the human brain, showing cerebellum and pons

    The researchers specifically apply their theory to autism, though they note that it could help understand other childhood neurological conditions. Conditions within the autism spectrum present “longstanding puzzles” related to cognitive and behavioral disruptions that their ideas could help resolve, they wrote. Under their theory, cerebellar injury causes disruptions in how other areas of the brain develop an ability to interpret external stimuli and organize internal processes, explained first author Sam Wang, an associate professor of molecular biology and the Princeton Neuroscience Institute (PNI).

    wang
    Princeton University researchers offer a new theory that an early-life injury to the cerebellum disrupts the brain’s processing of external and internal information and leads to “developmental diaschisis,” wherein a loss of function in one brain region leads to problems in another. Applied to autism, cerebellar injury could hinder how other areas of the brain interpret external stimuli and organize internal processes. Based on a review of existing research, the researchers found that a cerebellar injury at birth can make a person 36 times more likely to score highly on autism screening tests, and is the largest un-inherited risk (above).

    “It is well known that the cerebellum is an information processor. Our neocortex [the largest part of the brain, responsible for much higher processing] does not receive information unfiltered. There are critical steps that have to happen between when external information is detected by our brain and when it reaches the neural cortex,” said Wang, who worked with doctoral student Alexander Kloth and postdoctoral research associate Aleksandra Badura, both in PNI.

    “At some point, you learn that smiling is nice because Mom smiles at you. We have all these associations we make in early life because we don’t arrive knowing that a smile is nice,” Wang said. “In autism, something in that process goes wrong and one thing could be that sensory information is not processed correctly in the cerebellum.”

    Mustafa Sahin, a neurologist at Boston’s Children Hospital and associate professor of neurology at Harvard Medical School, said that Wang and his co-authors build upon known links between cerebellar damage and autism to suggest that the cerebellum is essential to healthy neural development. Numerous studies — including from his own lab — support their theory, said Sahin, who is familiar with the work but was not involved in it.

    “The association between cerebellar deficits and autism has been around for a while,” Sahin said. “What Sam Wang and colleagues do in this perspective article is to synthesize these two themes and hypothesize that in a critical period of development, cerebellar dysfunction may disrupt the maturation of distant neocortical circuits, leading to cognitive and behavioral symptoms including autism.”

    Traditionally, the cerebellum has been studied in relation to motor movement and coordination in adults. Recent studies, however, strongly suggest that it also influences childhood cognition, Wang said. Several studies also have found a correlation between cerebellar injury and the development of a disorder in the autism spectrum, the researchers report. For instance, the researchers cite a 2007 paper in the journal Pediatrics that found that individuals who experienced cerebellum damage at birth were 40 times more likely to score highly on autism screening tests. They also reference studies in 2004 and 2005 that found that the cerebellum is the most frequently disrupted brain region in people with autism.

    “What we realized from looking at the literature is that these two problems — autism and cerebellar injury — might be related to each other” via the cerebellum’s influence on wider neural development, Wang said. “We hope to get people and scientists thinking differently about the cerebellum or about autism so that the whole field can move forward.”

    The researchers conclude by suggesting methods for testing their theory. First, by inactivating brain-cell electrical activity, it should be possible to pinpoint the developmental stage in which injury to one part of the brain affects the maturation of another. A second, more advanced method is to reconstruct the neural connections between the cerebellum and other brain regions; the federal BRAIN Initiative announced in 2013 aims to map the activity of all the brain’s neurons. Finally, mouse brains can be used to disable and restore brain-region function to observe the “upstream” effect in other areas.

    The paper, The cerebellum, sensitive periods, and autism,” was published Aug. 6 in Neuron. The work was supported by grants from the National Institutes of Health (grant nos. R01 NS045193 and F31 MH098651), the Nancy Lurie Marks Family Foundation, and the Sutherland Cook Fund.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 11:46 am on August 19, 2014 Permalink | Reply
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    From Princeton: “Bubbling down: Discovery suggests surprising uses for common bubbles” 

    Princeton University
    Princeton University

    August 19, 2014
    John Sullivan, Office of Engineering Communications

    Anyone who has ever had a glass of fizzy soda knows that bubbles can throw tiny particles into the air. But in a finding with wide industrial applications, Princeton researchers have demonstrated that the bursting bubbles push some particles down into the liquid as well.

    “It is well known that bursting bubbles produce aerosol droplets, so we were surprised, and fascinated, to discover that when we covered the water with oil, the same process injected tiny oil droplets into the water,” said Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering at Princeton and the lead researcher for the project.

    The conclusions provide new insight into the mixture of non-soluble liquids — a process at the center of many fields from drug manufacturing to oil spill cleanups.

    two
    Princeton researchers have discovered that bursting bubbles can push tiny droplets of a surface material down into a base liquid as well as sending them into the air above. The finding has important implications for science and industries that are concerned with mixing liquid solutions. From right, Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering, and graduate student Jie Feng observe bubbles in a tank. (Photos by Frank Wojciechowski for the Office of Engineering Communications)

    In an article published on July 13 in the scholarly journal Nature Physics, the researchers describe how they reached their conclusions after examining bubbles in containers holding water covered by a layer of oil. Using several experimental approaches, they presented a detailed physical description of how the bubbles burst and how that affected the oil and water mix.

    “If you look at this system, which has a thin layer of oil over water, the bursting bubbles were dispersing the oil phase in the form of nano-droplets into the water,” said Jie Feng, a graduate student in Stone’s lab and the lead author of the paper. “Essentially, it is an unrealized form of mass transport related to bubble bursting.”

    In one observation, the researchers noted that the water in one container changed from clear to translucent after bubbles ran through the mixture for some time. The change in appearance “suggested that small objects had been dispersed in the lower water phase,” the researchers wrote.

    dev
    The researchers send bubbles through a tank containing a thin surface of oil above a water bath to make their observations.

    To get a better understanding of how this was happening, they used a high-speed camera to break down the steps involved in a bubble’s final pop. They found that a bubble’s collapse caused a pressure wave just below the bubble; this wave pushed a small amount of liquid out and down, away from the collapsing void.

    The researchers also found that the addition of a surfactant, which decreases surface tension, was critical to the formation of the nano-droplets. In fact, they concluded that without a proper amount of surfactant, the droplets would not form.

    The nano-droplets are so small they are impossible to see with the naked eye, so the researchers performed further experiments to test their analysis. In one, they spread an extremely thin layer of latex particles over the water and were able to observe the particles moving into the water. They also added a layer of material that is sensitive to ultraviolet light and then used the light to solidify the droplets for observation in the water mixture.

    Bubbles’ ability to mix liquids offers insights into a number of important systems. During oil spills, for example, it is important to understand how the oil moves from the surface of the water into deeper layers. This has generally been attributed to wave action, but the researchers’ findings indicate that even in a flat calm the oil can gradually filter down into the water because of tiny bubbles.

    “Bubbles are used to make foams and are part of common gas-liquid processes used in chemical processing,” Stone said. “But bubbles also occur in lakes, rivers and oceans because of wave breaking and rain. As a consequence, bubbles can impact many systems.”

    The researchers said that bubbling also might play a role in a critical system in which organic matter circulates through the ocean. A thin film of material, called the sea surface microlayer, rests at the very top of ocean water. The microlayer contains lipids, proteins and hydrocarbon pollutants.

    “Our work suggests that the sea surface microlayer may not only be transported into the atmosphere within aerosol droplets produced by bursting bubbles, but it might also be dispersed into the bulk of the oceans, thus redistributing organic matter into the ecosystem,” they wrote.

    Feng also said that applying this approach could play an important role in many industrial mixing systems. For one, this manner of bubbling to produce nanoemulsions uses much less energy than traditional mixers, so it is cheaper and more efficient. It also does not require extremely low surface tensions, which some types of industrial processes require. And it provides a good method to mix typically insoluble liquids, such as oil and water.

    “This system offers an energy-efficient route to produce nanoparticles, with the potential to increase in scale, for applications in a variety of fields such as drug delivery, food production and materials science,” he said.

    Besides Stone and Feng, the project researchers included Matthieu Roche and Daniele Vigolo (now research associates in Paris and Zurich, respectively) who worked as postdoctoral researchers in Princeton’s Department of Mechanical and Aerospace Engineering; Luben Arnaudov and Simeon Stoyanov, of Unilever Research and Development; and Theodor Gurkov and Gichka Tsutsumanova, of Sofia University, Bulgaria.

    Support for the research was provided in part by grant from the Consortium for the Molecular Engineering of Dispersant Systems funded by the BP/Gulf of Mexico Research Initiative, and the European Union’s Beyond Everest project.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 12:48 pm on June 18, 2014 Permalink | Reply
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    From Princeton: “Familiar yet strange: Water’s ‘split personality’ revealed by computer model” 

    Princeton University
    Princeton University

    June 18, 2014
    Catherine Zandonella, Office of the Dean for Research

    Seemingly ordinary, water has quite puzzling behavior. Why, for example, does ice float when most liquids crystallize into dense solids that sink?

    Using a computer model to explore water as it freezes, a team at Princeton University has found that water’s weird behaviors may arise from a sort of split personality: at very cold temperatures and above a certain pressure, water may spontaneously split into two liquid forms.

    The team’s findings were reported in the journal Nature.

    “Our results suggest that at low enough temperatures water can coexist as two different liquid phases of different densities,” said Pablo Debenedetti, the Class of 1950 Professor in Engineering and Applied Science and Princeton’s dean for research, and a professor of chemical and biological engineering.

    The two forms coexist a bit like oil and vinegar in salad dressing, except that the water separates from itself rather than from a different liquid. “Some of the molecules want to go into one phase and some of them want to go into the other phase,” said Jeremy Palmer, a postdoctoral researcher in the Debenedetti lab.

    The finding that water has this dual nature, if it can be replicated in experiments, could lead to better understanding of how water behaves at the cold temperatures found in high-altitude clouds where liquid water can exist below the freezing point in a “supercooled” state before forming hail or snow, Debenedetti said. Understanding how water behaves in clouds could improve the predictive ability of current weather and climate models, he said.

    chart
    Pressure–temperature phase diagram, including an illustration of the liquid–liquid transition line proposed for several polyamorphous materials. This liquid–liquid phase transition would be a first order, discontinuous transition between low and high density liquids (labelled 1 and 2). This is analogous to polymorphism of crystalline materials, where different stable crystalline states (solid 1, 2 in diagram) of the same substance can exist (e.g. diamond and graphite are two polymorphs of carbon). Like the ordinary liquid–gas transition, the liquid–liquid transition is expected to end in a critical point. At temperatures beyond these critical points there is a continuous range of fluid states, i.e. the distinction between liquids and gasses is lost. If crystallisation is avoided the liquid–liquid transition can be extended into the metastable supercooled liquid regime.

    The new finding serves as evidence for the “liquid-liquid transition” hypothesis, first suggested in 1992 by Eugene Stanley and co-workers at Boston University and the subject of recent debate. The hypothesis states that the existence of two forms of water could explain many of water’s odd properties — not just floating ice but also water’s high capacity to absorb heat and the fact that water becomes more compressible as it gets colder.

    deb
    Princeton University researchers conducted computer simulations to explore what happens to water as it is cooled to temperatures below freezing and found that the supercooled liquid separated into two liquids with different densities. The finding agrees with a two-decade-old hypothesis to explain water’s peculiar behaviors, such as becoming more compressible and less dense as it is cooled. The X axis above indicates the range of crystallinity (Q6) from liquid water (less than 0.1) to ice (greater than 0.5) plotted against density (ρ) on the Y axis. The figure is a two-dimensional projection of water’s calculated “free energy surface,” a measure of the relative stability of different phases, with orange indicating high free energy and blue indicating low free energy. The two large circles in the orange region reveal a high-density liquid at 1.15 g/cm3 and low-density liquid at 0.90 g/cm3. The blue area represents cubic ice, which in this model forms at a density of about 0.88 g/cm3. (Image courtesy of Jeremy Palmer)

    At cold temperatures, the molecules in most liquids slow to a sedate pace, eventually settling into a dense and orderly solid that sinks if placed in liquid. Ice, however, floats in water due to the unusual behavior of its molecules, which as they get colder begin to push away from each other. The result is regions of lower density — that is, regions with fewer molecules crammed into a given volume — amid other regions of higher density. As the temperature falls further, the low-density regions win out, becoming so prevalent that they take over the mixture and freeze into a solid that is less dense than the original liquid.

    The work by the Princeton team suggests that these low-density and high-density regions are remnants of the two liquid phases that can coexist in a fragile, or “metastable” state, at very low temperatures and high pressures. “The existence of these two forms could provide a unifying theory for how water behaves at temperatures ranging from those we experience in everyday life all the way to the supercooled regime,” Palmer said.

    Since the proposal of the liquid-liquid transition hypothesis, researchers have argued over whether it really describes how water behaves. Experiments would settle the debate, but capturing the short-lived, two-liquid state at such cold temperatures and under pressure has proved challenging to accomplish in the lab.

    Instead, the Princeton researchers used supercomputers to simulate the behavior of water molecules — the two hydrogens and the oxygen that make up “H2O” — as the temperature dipped below the freezing point.

    The team used computer code to represent several hundred water molecules confined to a box, surrounded by an infinite number of similar boxes. As they lowered the temperature in this virtual world, the computer tracked how the molecules behaved.

    The team found that under certain conditions — about minus 45 degrees Celsius and about 2,400-times normal atmospheric pressure — the virtual water molecules separated into two liquids that differed in density.

    The pattern of molecules in each liquid also was different, Palmer said. Although most other liquids are a jumbled mix of molecules, water has a fair amount of order to it. The molecules link to their neighbors via hydrogen bonds, which form between the oxygen of one molecule and a hydrogen of another. These molecules can link — and later unlink — in a constantly changing network. On average, each H2O links to four other molecules in what is known as a tetrahedral arrangement.

    The researchers found that the molecules in the low-density liquid also contained tetrahedral order, but that the high-density liquid was different. “In the high-density liquid, a fifth neighbor molecule was trying to squeeze into the pattern,” Palmer said.

    image
    Normal ice (left) contains water molecules linked into ring-like structures via hydrogen bonds (dashed blue lines) between the oxygen atoms (red beads) and hydrogen atoms (white beads) of neighboring molecules, with six water molecules per ring. Each water molecule in ice also has four neighbors that form a tetrahedron (right), with a center molecule linked via hydrogen bonds to four neighboring molecules. The green lines indicate the edges of the tetrahedron. Water molecules in liquid water form distorted tetrahedrons and ring structures that can contain more or less than six molecules per ring. (Image courtesy of Jeremy Palmer)

    The researchers also looked at another facet of the two liquids: the tendency of the water molecules to form rings via hydrogen bonds. Ice consists of six water molecules per ring. Calculations by Fausto Martelli, a postdoctoral research associate advised by Roberto Car, the Ralph W. *31 Dornte Professor in Chemistry, found that in this computer model the average number of molecules per ring decreased from about seven in the high-density liquid to just above six in the low-density liquid, but then climbed slightly before declining again to six molecules per ring as ice, suggesting that there is more to be discovered about how water molecules behave during supercooling.

    A better understanding of water’s behavior at supercooled temperatures could lead to improvements in modeling the effect of high-altitude clouds on climate, Debenedetti said. Because water droplets reflect and scatter the sunlight coming into the atmosphere, clouds play a role in whether the sun’s energy is reflected away from the planet or is able to enter the atmosphere and contribute to warming. Additionally, because water goes through a supercooled phase before forming hail or snow, such research may aid strategies for preventing ice from forming on airplane wings.

    “The research is a tour de force of computational physics and provides a splendid academic look at a very difficult problem and a scholarly controversy,” said C. Austen Angell, professor of chemistry and biochemistry at Arizona State University, who was not involved in the research. “Using a particular computer model, the Debenedetti group has provided strong support for one of the theories that can explain the outstanding properties of real water in the supercooled region.”

    In their computer simulations, the team used an updated version of a model noted for its ability to capture many of water’s unusual behaviors first developed in 1974 by Frank Stillinger, then at Bell Laboratories in Murray Hill, N.J., and now a senior chemist at Princeton; and Aneesur Rahman, then at the U.S. Argonne National Laboratory. The same model was used to develop the liquid-liquid transition hypothesis.

    Collectively, the work took several million computer hours, which would take several human lifetimes using a typical desktop computer, Palmer said. In addition to the initial simulations, the team verified the results using six calculation methods. The computations were performed at Princeton’s High-Performance Computing Research Center’s Terascale Infrastructure for Groundbreaking Research in Science and Engineering (TIGRESS).

    The team included Yang Liu, who earned her doctorate at Princeton in 2012, and Athanassios Panagiotopoulos, the Susan Dod Brown Professor of Chemical and Biological Engineering.

    Support for the research was provided by the National Science Foundation (CHE 1213343) and the U.S. Department of Energy (DE-SC0002128 and DE-SC0008626).

    The article, Metastable liquid-liquid transition in a molecular model of water, by Jeremy C. Palmer, Fausto Martelli, Yang Liu, Roberto Car, Athanassios Z. Panagiotopoulos and Pablo G. Debenedetti, appeared in the journal Nature.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 5:22 pm on June 9, 2014 Permalink | Reply
    Tags: , , Plasma studies, , Princeton University   

    From PPPL: “PPPL receives $4.3 million to increase understanding of the role that plasma plays in synthesizing nanoparticles” 


    PPPL

    This post is dedicated to JHM, who brings me lots of people at the sciencesprings Facebook Fan Page. I really appreciate what she does for this blog.

    June 9, 2014
    John Greenwald

    The U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) has received some $4.3 million of DOE Office of Science funding, over three years, to develop an increased understanding of the role of plasma in the synthesis of nanoparticles. Such particles, which are measured in billionths of a meter, are prized for their use in everything from golf clubs and swimwear to microchips, paints and pharmaceutical products. They also have potentially wide-ranging applications in the development of new energy technologies.

    “Plasma is widely used as a tool for producing nanoparticles, but there is no deep understanding of the role that plasma plays in this process,” said physicist Yevgeny Raitses, the principal investigator for the project. “Our goal is to develop an understanding that can lead to improved synthesis of these particles.”

    yr
    Physicist Yevgeny Raitses, the principal investigator for research into the role of plasma in synthesizing nano particles, in PPPL’s nanotechnology laboratory. (Photo by Elle Starkman/PPPL Office of Communications)

    The new funds will expand research in a nanotechnology laboratory that PPPL launched in 2012 with PPPL Laboratory Directed Research and Development (LDRD) funds. The facility studies the complex interactions that occur when hot, electrically charged plasma gas is used as a synthesizing agent to produce material such as carbon nanontubes — items that are tens of thousands of times thinner than a human hair, yet stronger than steel on an ounce-per-ounce basis. These interactions must be precisely controlled to ensure the quality and purity of such material.

    Many collaborators worked on the funding proposal for the new research. Key contributors included physicists Igor Kaganovich and Brent Stratton, who led the plasma theory and diagnostic sections of the proposal, respectively, and will continue to lead these project areas. Also essential were physicists Edward Startsev and Benoit LeBlanc, who worked on the theory and diagnostic parts of the proposal, respectively, and physicist Andrei Khodak, who contributed computer modeling.

    Key collaboration also came from Predrag Krstic, a professor in the Institute for Advanced Computational Science at Stony Brook University, and Mikhail Shneider a senior research scientist in the Mechanical and Aerospace Department at Princeton University. Krstic is an expert on the atomistic computer modeling of materials; Shneider has invented new laser diagnostics for plasma applications.

    Major contributors also include Bruce Koel, a Princeton professor of chemical and biological engineering, who will help characterize nanomaterials that come from the PPPL laboratory; Roberto Car, a Princeton professor of chemistry who will contribute to the atomistic modeling; Michael Keidar, a George Washington University professor of engineering and an expert on plasma nanotechnology; and Mohan Sankaran, an associate professor of chemical engineering at Case Western Reserve University and an expert on the plasma-based synthesis of nanoparticles.

    Philip Efthimion, head of the Plasma Science and Technology Department at PPPL, provided guidance and support for the funding proposal. Olga Tishinin, a PPPL budget analyst and P&C Officer, also provided key support. “She did an excellent job in helping this multi-institutional team in planning a budget request and doing all paper work related to the proposal,” Raitses said.

    In discussing the new research, PPPL Director Stewart Prager noted that, “The synthesis of nanoparticles is a challenging and exciting field with wide-ranging applications. This project combines our expertise in plasma science with the material science capabilities of Princeton University and other institutions.”

    The expanded research “fits right into our core competency,” said Adam Cohen, PPPL deputy director for operations, who teamed with Prager to champion the initial development of the nanolaboratory, which was assembled with guidance from engineer Charles Gentile, and the new funding. “We’ve gained knowledge of plasma from our fusion research,” Cohen said, “and this enables us to grow into a whole new research opportunity.”

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.


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  • richardmitnick 6:30 am on May 22, 2014 Permalink | Reply
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    From Princeton: “A Faster Track to the Tools that Track Disease” 

    Princeton University
    Princeton University

    May 21, 2014
    Tien Nguyen

    Radioactivity is usually associated with nuclear fallout or comic-book spider bites, but in very small amounts it can be a useful tool for diagnosing diseases.

    Small molecules containing a radioactive isotope of fluorine called 18F radiotracers are used to detect and track certain diseases in patients. Once injected into the body, these molecules accumulate in specific targets, such as tumors, and can be visualized by their radioactive tag on a positron emission tomography (PET) scan. The 18F tags quickly decay so no radioactivity remains after about a day.
    pet
    Image of a typical positron emission tomography (PET) facility

    ad
    Associate Professor Abigail Doyle

    But there are only a few methods available for making 18F radiotracers. And existing methods tend to require harsh conditions that scramble the placement of a radiotracer’s more delicate chemical bonds. Now, researchers at Princeton University report a route to 18F radiotracers that avoids that problem.

    “It’s the first method to do enantioselective carbon-18F bond formation,” said principal investigator Abigail Doyle, a Princeton associate professor of chemistry.

    Up to this point, radiotracers have mostly been evaluated as mixtures of enantiomers. Enantiomers are molecules that are completely identical in composition but the arrangement of atoms at the chiral center are mirror images, like how a person’s left and right hands are similar, but oppositely oriented. A chiral center is an atom, usually carbon, which is connected to four different groups.

    “We know in biology, small molecule interactions with enzymes often depend on the 3D properties of the molecule. Being able to prepare the enantiomers of a given chiral tracer, in order to optimize which tracer has the best binding and imaging properties could be really useful,” Doyle said.

    Doyle’s research team developed a cobalt fluoride catalyst—[18F](salen)CoF—to install the radioactive fluoride through the ring-opening reaction of epoxides. Their method demonstrated excellent enantioselectivity for eleven substrates, five of which are known pre-clinical PET tracers.

    tracer
    Strategy for the direct radio synthesis of PET tracers

    With this new method, researchers can now test single enantiomers of existing or new PET radiotracers and evaluate if these compounds offer any advantage over the enantiomeric mixtures. Ultimately the goal is to use this chemistry to identify a completely novel PET radiotracer for imaging.

    Currently there are only four FDA-approved 18F radiotracers. One of the major limitations to discovering PET tracers is the fact that the only commercially available source of 18F is nucleophilic fluoride.

    Existing 18F sources are strongly basic, and during the process of making the 18F radiotracer, can cause the elimination of alcohol and amine groups and rearrange the groups around a chiral center in a process called racemization. Under Doyle’s less basic reaction conditions, even alcohols and secondary amines are tolerated and no racemization is observed.

    “Forming carbon-fluorine bonds by nucleophilic fluoride is challenging. One typically needs to use high temperatures or else the reactions are too slow to permit radioisotope incorporation,” Doyle said. “Whereas most reactions require temperatures greater than 100 degrees Celsius, our reaction can be run at 50 degrees Celsius,” she said.

    Graduate students in the Doyle lab, Thomas Graham and Frederick Lambert, commuted to the University of Pennsylvania, where they conducted the radiolabeling experiments in the laboratory of collaborator Hank Kung, an emeritus professor of radiology.

    tg
    Tom Graham, lead author and recent doctoral graduate from the Doyle lab

    “At UPenn, we worked behind lead bricks and used a very small amount of radioactivity, about how much you would give a human patient,” said Graham, lead author on the article.

    Small amounts of radioactivity were sufficient to develop the reaction initially but to perform imaging studies, larger amounts of radioactivity are necessary. “When you go to higher activity, that’s when you do automated chemistry in a hot cell, which is basically a block of lead so you get no exposure,” Doyle said.

    To be useful in an industrial setting, the chemistry needs to be translated from the lab to an automated hot cell. The researchers were given access to an automated hot cell nearby at Merck’s West Point, Pennsylvania site.

    “The whole process of radiolabeling takes about 30 to 45 minutes when it’s automated,” says Graham. The set-up includes a robotic arm that delivers solutions to designated vials, an HPLC and a rotary evaporator, which are instruments for the analysis and purification of the radiotracers.

    “The catalyst is very robust and the fact that we can translate the reaction directly to the hot cell bodes very well for non-experts to be able to run these sorts of reactions,” Doyle said.

    “We demonstrated that the radioactivity is high enough that we could actually use it for imaging. That’s an exciting next step,” Doyle said.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    The home of the Princeton Plasma Physics lab one of seventeen D.O.E. labs supported by the DOE Office of Science.

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  • richardmitnick 4:59 pm on May 16, 2014 Permalink | Reply
    Tags: , , Princeton University   

    From Princeton: “Fast and curious: Electrons hurtle into the interior of a new class of quantum materials” 

    Princeton University
    Princeton University

    May 16, 2014
    Catherine Zandonella, Office of the Dean for Research

    As smartphones get smarter and computers compute faster, researchers actively search for ways to speed up the processing of information. Now, scientists at Princeton University have made a step forward in developing a new class of materials that could be used in future technologies.

    They have discovered a new quantum effect that enables electrons — the negative-charge-carrying particles that make today’s electronic devices possible — to dash through the interior of these materials with very little resistance.

    The discovery is the latest chapter in the story of a curious material known as a “topological insulator,” in which electrons whiz along the surface without penetrating the interior. The newest research indicates that these electrons also can flow through the interior of some of these materials.

    “With this discovery, instead of facing the challenge of how to use only the electrons on the surface of a material, now you can just cut the material open and you have light-like electrons flowing in three dimensions inside the materials,” said M. Zahid Hasan, a professor of physics at Princeton, who led the discovery.

    The finding was conducted by a team of scientists from the United States, Taiwan, Singapore, Germany and Sweden and published in two papers in the journal Nature Communications. The first paper, published May 7, demonstrates that fast electrons can flow in the interior of crystals made from cadmium and arsenic, or cadmium arsenide. The second paper, published May 12, explores fast electrons in a material made from the elements bismuth and selenium.

    In most materials, including copper and other metals that conduct electricity, electrons navigate an obstacle course of microscopic outcroppings, ledges and other imperfections that obstruct the tiny particles and send them scattering in the wrong directions. This causes resistance and the conversion of electrical current into heat, which is why electronic appliances become warm during use.

    two

    Scientists at Princeton University have shown that negatively charged particles known as electrons can flow extremely rapidly due to quantum behaviors in a type of material known as a topological Dirac semi-metal. Previous work by the same group indicated that these electrons can flow on the surface of certain materials, but the new research indicates that they can also flow through the bulk of the material, in this case cadmium arsenide. Using a technique called angle-resolved photoemission spectroscopy (left), the researchers measured the energy and momentum of electrons as they were ejected from the cadmium arsenide. The resulting data revealed each electron as two cones oriented opposite each other that converge at a point, a telltale sign of the quantum behavior that allows electrons to act like light, which has no mass. A 3-D reconstruction (right) shows that the cone-shaped electrons are able to move in all directions in the material. The top-right panel reveals that these electrons are linked, allowing them to move even when deformed by bending or stretching, an attribute that gives them their topological nature. (Image courtesy of M. Zahid Hasan and Suyang Xu)

    In topological insulators and the new class of materials the Princeton researchers studied, the unique properties of the atoms combine to create quantum effects that coax electrons into acting similar to a light wave instead of like individual particles. These waves can weave around and dodge — and even move through — barriers that would typically stop most electrons. These properties were theoretically proposed by Charles Kane and a team at the University of Pennsylvania from 2005 to 2007 and first observed experimentally in solid materials by the Hasan group in 2007 and 2008.

    In 2011, the Hasan group detected this fast electron-flow in the interior of a material made from combining several elements — bismuth, thallium, sulfur and selenium. The results were published in the journal Science.

    In the new study in cadmium arsenide, the electrons have an average velocity that is 10,000 times more than that of the previous bismuth-based materials identified by the group. “This is a big deal,” Hasan said. “It means the electrons can flow quite easily in the material and many more exotic quantum effects can now be studied. That just wasn’t possible in the past.”

    The most promising application for these materials may be for a proposed “topological quantum computer” based on novel electronics that would use a property of electrons known as “spin” to do calculations and transmit information.

    The quantum behavior in this new class of materials has led them to be called “topological Dirac semi-metals” in reference to English quantum physicist and 1933 Nobel Prize winner Paul Dirac, who noted that electrons could behave like light. Semi-metals that are “topological” are ones that retain their spatial electronic properties — and their speedy electrons — even when deformed by certain types of stretching and twisting.

    pd
    Paul Dirac

    The speeds achieved by these electrons have led to comparisons to another novel electronic material, graphene. The new class of materials has the potential to be superior to graphene in some aspects, Hasan said, because graphene is a single layer of atoms in which electrons can flow only in two dimensions. Cadmium arsenide permits electrons to flow in three dimensions.

    The new study redefines what it means to be a topological material, according to Su-Yang Xu, a graduate student in Hasan’s lab and co-first author of the May 7 paper with postdoctoral research associate Madhab Neupane at Princeton and Raman Sankar of National Taiwan University.

    “The term topological insulator is now quite famous, and the yet term ‘insulator’ means that there are no electrons flowing in the bulk of the material,” Xu said. “Our study shows that electrons are flowing in the bulk of the material, so clearly cadmium arsenide is not an insulator, but it is still topological in nature, so this is a totally new type of quantum matter,” he said.

    The team made the discovery using a technique called angle-resolved photoemission spectroscopy. The researchers shined a very powerful X-ray beam — using a particle accelerator at the Advanced Light Source at Lawrence Berkeley National Laboratory — onto the surface of the material then monitored the electrons as they were knocked out of the interior.

    “When the electron comes out, we measure its energy and velocity, and what we found is that electrons coming out of the cadmium arsenide had measurements that were similar to what is seen in particles that are massless,” Neupane said.

    In the second paper in Nature Communications, Neupane and co-authors presented a model for controlling the spin direction of the electron particles in a different material, bismuth selenide.

    “The Princeton group showed in exquisite details that electrons in certain solids obey the three- dimensional massless Dirac equation,” said Patrick Lee, a professor of physics at the Massachusetts Institute of Technology who was not involved in the work. “While predicted by theoretical calculations, this behavior has never been seen before in real materials until this past year. This work adds greatly to the ongoing excitement of how topology can impact electronic states in real materials.”

    The first study, “Observation of a three-dimensional topological Dirac semimetal phase in high-mobility Cd3As2″ appeared in the journal Nature Communications on May 7, 2014. The co-first-authors were Madhab Neupane and Su-Yang Xu of Princeton University and Raman Sankar of National Taiwan University. Additional researchers at Princeton who contributed to the work were graduate students Nasser Alidoust and Ilya Belopolski, and postdoctoral research associates Guang Bian and Chang Liu. The team also included Tay-Rong Chang of National Tsing Hua University in Taiwan; Horng-Tay Jeng of National Tsing Hua University and Academia Sinica in Taiwan; Hsin Lin of National University of Singapore; Arun Bansil of Northeastern University; and Fangcheng Chou of National Taiwan University.

    The second study, “Observation of a quantum-tunnelling-modulated spin texture in ultrathin topological insulator Bi2Se3 films,” appeared in the journal Nature Communications on May 12, 2014. The first author was Madhab Neupane. Co-authors at Princeton were Su-Yang Xu, Nasser Alidoust, Ilya Belopolski, Chang Liu and Guang Bian. Also on the team were Anthony Richardella, Duming Zhang and Nitin Samarth of Pennsylvania State University; Jaime Sánchez-Barriga, Dmitry Marchenko, Oliver Rader and Andrei Varykhalov of Helmholtz Centre Berlin for Materials and Energy; Mats Leandersson and Thiagarajan Balasubramanian of MAX-lab, Sweden; Tay-Rong Chang of National Tsing Hua University in Taiwan; Horng-Tay Jeng of National Tsing Hua University and Academia Sinica in Taiwan; Hsin Lin of the National University of Singapore; and Susmita Basak and Arun Bansil of Northeastern University.

    Primary funding for both studies was provided by the U.S. Department of Energy’s Office of Basic Energy Sciences.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 4:02 am on May 15, 2014 Permalink | Reply
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    From Princeton: “Q&A: Lucianne Walkowicz, Astronomer on Board” 

    Princeton University

    Princeton University

    May 14, 2014
    Dorian Rolston ’10

    She rides the C train to bring astrophysics to New York City commuters

    lucy

    Lucianne Walkowicz calls herself an alien hunter. To search for life on other planets, she studies how the magnetic activity of low-mass stars impacts the habitability of the planets around them. Unlike the 1970s, when NASA launched Voyager 1 — a space probe carrying a phonograph record with information about Earth in case it was found by an intelligent life form — today planetary habitability is a burgeoning field.

    Walkowicz, an associate research scholar in the astrophysics department, is a postdoctoral associate on NASA’s Kepler team, which has discovered Earth-size planets orbiting other stars. She seeks to bring astrophysics to a wider audience through Science Train, an initiative in which experts chat with New York City subway riders about the final frontier and spur wider public discussion of science. PAW spoke with Walkowicz about her research and her outreach campaign.

    When you say “alien-hunting”…

    It’s not very X-Files, in the sense that I’m not going to Roswell or anything like that. It definitely is a different concept of finding aliens than exists in science fiction and pop culture. But that’s still fundamentally what’s motivating a lot of us, and it certainly is something that motivates me.

    My research is very much about the kinds of questions that people who aren’t scientists wonder about. Is there life beyond Earth? Where would we look for it? How would we recognize it? We’re at an interesting time where we can actually begin to answer these kinds of questions.

    Why are low-mass stars important to the study of extraterrestrial life?

    It was once assumed that stellar flares (which are massive energy ejections) from low-mass stars would sterilize planets around them and make it impossible for life to exist there. It turns out that may not be the case. My collaborators and I studied how stellar flares affect planets like Earth, and found that the planet’s atmosphere actually shields it from most of that harmful radiation. Those planets are still good places to search for life.

    With some colleagues, you first approached New York City subway riders to chat about space last summer. Why does the public need astronomers in transit?

    Most of our public science education targets people who are already interested. The idea behind Science Train was to take it somewhere that you don’t encounter it. You can encounter a poem on the train. You can go for a walk in the park and encounter a piece of sculpture. But there are very few opportunities for people to have an unplanned encounter with science.

    Science Train gives people an opportunity to talk to an actual scientist. What’s appealing about going into science if you have this idea that scientists are mad, crazy people in lab coats, working by themselves? With Science Train, anyone can go out and talk about science.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

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