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  • richardmitnick 12:38 pm on March 11, 2020 Permalink | Reply
    Tags: "Two-dimensional metals open pathways to new science", A special type of graphene dubbed epitaxial graphene., , CHet-confinement heteroepitaxy., , Opening a wide range of new applications in biomolecular sensing; quantum phenomena; catalysis; and nonlinear optics., Penn State University   

    From Pennsylvania State University: “Two-dimensional metals open pathways to new science” 

    Penn State Bloc

    From Pennsylvania State University

    March 09, 2020
    Walt Mills

    1
    A single atomic layer of metal is capped by a layer of graphene, allowing for new layered materials with unique properties. Image: Yihuang Xiong/Penn State.

    An atomically thin materials platform developed by Penn State researchers in conjunction with Lawrence Berkeley National Lab and Oak Ridge National Lab will open a wide range of new applications in biomolecular sensing, quantum phenomena, catalysis and nonlinear optics.

    “We have leveraged our understanding of a special type of graphene, dubbed epitaxial graphene, to stabilize unique forms of atomically thin metals,” said Natalie Briggs, a doctoral candidate and co-lead author on a paper in the journal Nature Materials. “Interestingly, these atomically thin metals stabilize in structures that are completely different from their bulk versions, and thus have very interesting properties compared to what is expected in bulk metals.”

    Traditionally, when metals are exposed to air they rapidly begin to oxidize — rust. In as short as one second, metal surfaces can form a rust layer that would destroy the metallic properties. In the case of a 2D metal, this would be the entire layer. If you were to combine a metal with other 2D materials via traditional synthesis processes, the chemical reactions during synthesis would ruin the properties of both the metal and layered material. To avoid these reactions, the team exploited a method that automatically caps the 2D metal with a single layer of graphene while creating the 2D metal.

    The researchers start with silicon carbide that they heat to a high temperature. The silicon leaves the surface, and the remaining carbon reconstructs into epitaxial graphene. Importantly, the graphene/silicon carbide interface is only partially stable and is readily passivated by nearly any element, if the element has access to this interface.

    The team provides this access by poking holes in the graphene with an oxygen plasma, and then they evaporate pure metal powders onto the surface at high temperatures. The metal atoms migrate through the holes in the graphene to the graphene/silicon carbide interface, creating a sandwich structure of silicon carbide, metal and graphene. The process to create the 2D metals is called confinement heteroepitaxy, or CHet.

    “We call it CHet because of the confined nature of the metal, and the fact that it is epitaxial — the atoms all line up — to the silicon carbide, an important aspect to the unique properties we see in these systems,” noted Joshua Robinson, senior author and associate professor of materials science and engineering, Penn State.

    “In this paper, the focus is on the fundamental properties of the metals that are going to enable a new set of research topics,” said Robinson. “It shows that we are able to develop novel 2D materials systems that are applicable in a variety of hot topics such as quantum, where graphene is a key link that allows us to think about combining very different materials that normally could not be combined to form the basis for superconducting or photonic qubits.”

    Next steps in their studies will involve proving out the superconducting, sensing, optical and catalytical properties of these layered materials. Beyond creating unique 2D metals, the team is continuing to explore new 2D semiconducting materials with CHet that would be of interest to the electronics industry in future electronics beyond silicon.

    Additional authors from Penn State include former doctoral student in the Robinson group and co-lead author Brian Bersch, doctoral student Yuanxi Wang, and professors Cui-Zu Chang, Jun Zhu, Adri van Duin and Vincent Crespi.

    The Northrop Grumman Corp. primarily funded this work with additional funding from the Semiconductor Research Corporation, the National Science Foundation and the Alfred P. Sloan Research Fellowship.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    About Penn State

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 9:57 pm on January 27, 2020 Permalink | Reply
    Tags: "Method detects defects in 2D materials for future electronics sensors", , Dark field imaging-a technique in which extraneous light is filtered out so that defects shine through., , Penn State University,   

    From Pennsylvania State University: “Method detects defects in 2D materials for future electronics, sensors” 

    Penn State Bloc

    From Pennsylvania State University

    January 27, 2020
    Walt Mills

    1
    A laser beam (yellow) reflects off a 2D material (orange) highlighting a grain boundary defect in the atomic lattice. Image: MRI/Penn State

    To further shrink electronic devices and to lower energy consumption, the semiconductor industry is interested in using 2D materials, but manufacturers need a quick and accurate method for detecting defects in these materials to determine if the material is suitable for device manufacture. Now a team of researchers has developed a technique to quickly and sensitively characterize defects in 2D materials.

    Two-dimensional materials are atomically thin, the most well-known being graphene, a single-atom-thick layer of carbon atoms.

    “People have struggled to make these 2D materials without defects,” said Mauricio Terrones, Verne M. Willaman Professor of Physics, Penn State. “That’s the ultimate goal. We want to have a 2D material on a four-inch wafer with at least an acceptable number of defects, but you want to evaluate it in a quick way.”

    The researchers’ — who represent Penn State, Northeastern University, Rice University and Universidade Federal de Minas Gerais in Brazil – solution is to use laser light combined with second harmonic generation, a phenomenon in which the frequency of the light shone on the material reflects at double the original frequency. They add dark field imaging, a technique in which extraneous light is filtered out so that defects shine through. According to the researchers, this is the first instance in which dark field imaging was used, and it provides three times the brightness of the standard bright field imaging method, making it possible to see types of defects previously invisible.

    “The localization and identification of defects with the commonly used bright field second harmonic generation is limited because of interference effects between different grains of 2D materials,” said Leandro Mallard, a senior author on a recent paper in Nano Letters and a professor at Universidade Federal de Minas Gerais. “In this work we have shown that by the use of dark field SHG we remove the interference effects and reveal the grain boundaries and edges of semiconducting 2D materials. Such a novel technique has good spatial resolution and can image large area samples that could be used to monitor the quality of the material produced in industrial scales.”

    Vincent H. Crespi, Distinguished Professor of Physics, Materials Science and Engineering, and Chemistry, Penn State, added, “Crystals are made of atoms, and so the defects within crystals — where atoms are misplaced — are also of atomic size.

    “Usually, powerful, expensive and slow experimental probes that do microscopy using beams of electrons are needed to discern such fine details in a material,” said Crespi. “Here, we use a fast and accessible optical method that pulls out just the signal that originates from the defect itself to rapidly and reliably find out how 2D materials are stitched together out of grains oriented in different ways.”

    Another coauthor compared the technique to finding a particular zero on a page full of zeroes.

    “In the dark field, all the zeroes are made invisible so that only the defective zero stands out,” said Yuanxi Wang, assistant research professor at Penn State’s Materials Research Institute.

    The semiconductor industry wants to have the ability to check for defects on the production line, but 2D materials will likely be used in sensors before they are used in electronics, according to Terrones. Because 2D materials are flexible and can be incorporated into very small spaces, they are good candidates for multiple sensors in a smartwatch or smartphone and the myriad of other places where small, flexible sensors are required.

    “The next step would be an improvement of the experimental setup to map zero dimension defects — atomic vacancies for instance — and also extend it to other 2D materials that host different electronic and structural properties,” said lead author Bruno Carvalho, a former visiting scholar in Terrones’ group,

    Other co-authors on the Nano Letters paper, are Kuzanori Fujisawa, Tianyi Zhang, Ethan Kahn, Ismail Bilgin, Pulickel Ajayan, Ana de Paula, Marcos Pimenta and Swastik Kar.

    The National Science Foundation, The Air Force Office of Scientific Research and various Brazilian funding agencies funded this work.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    About Penn State

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 7:48 am on August 19, 2019 Permalink | Reply
    Tags: "How many Earth-like planets are around sun-like stars?", , , , , , , Penn State University   

    From Pennsylvania State University: “How many Earth-like planets are around sun-like stars?” 

    Penn State Bloc

    From Pennsylvania State University

    14 August 2019
    Sam Sholtis

    Media Contacts
    Eric B. Ford
    Professor of Astronomy and Astrophysics
    ebf11@psu.edu
    814- 863-5558

    Sam Sholtis
    Science Writer
    samsholtis@psu.edu
    (814) 865-1390

    1
    Artist’s impression of NASA’s Kepler space telescope, which discovered thousands of new planets. New research, using Kepler data, provides the most accurate estimate to date of how often we should expect to find Earth-like planets near sun-like stars. Credit: NASA/Ames Research Center/W. Stenzel/D. Rutter

    A new study provides the most accurate estimate of the frequency that planets that are similar to Earth in size and in distance from their host star occur around stars similar to our Sun. Knowing the rate that these potentially habitable planets occur will be important for designing future astronomical missions to characterize nearby rocky planets around sun-like stars that could support life. A paper describing the model appears August 14, 2019 in The Astronomical Journal.

    Thousands of planets have been discovered by NASA’s Kepler space telescope.

    NASA/Kepler Telescope, and K2 March 7, 2009 until November 15, 2018

    Kepler, which was launched in 2009 and retired by NASA in 2018 when it exhausted its fuel supply, observed hundreds of thousands of stars and identified planets outside of our solar system—exoplanets—by documenting transit events.*

    [On July 14, 2012, one of the spacecraft’s four reaction wheels used for pointing the spacecraft stopped turning, and completing the mission would only be possible if all other reaction wheels remained reliable. Then, on May 11, 2013, a second reaction wheel failed, disabling the collection of science data and threatening the continuation of the mission. This was the origin of the K2 misson.]

    Planet transit. NASA/Ames

    Transits events occur when a planet’s orbit passes between its star and the telescope, blocking some of the star’s light so that it appears to dim. By measuring the amount of dimming and the duration between transits and using information about the star’s properties astronomers characterize the size of the planet and the distance between the planet and its host star.

    “Kepler discovered planets with a wide variety of sizes, compositions and orbits,” said Eric B. Ford, professor of astronomy and astrophysics at Penn State and one of the leaders of the research team. “We want to use those discoveries to improve our understanding of planet formation and to plan future missions to search for planets that might be habitable. However, simply counting exoplanets of a given size or orbital distance is misleading, since it’s much harder to find small planets far from their star than to find large planets close to their star.”

    To overcome that hurdle, the researchers designed a new method to infer the occurrence rate of planets across a wide range of sizes and orbital distances. The new model simulates ‘universes’ of stars and planets and then ‘observes’ these simulated universes to determine how many of the planets would have been discovered by Kepler in each `universe.’

    “We used the final catalog of planets identified by Kepler and improved star properties from the European Space Agency’s Gaia spacecraft to build our simulations,” said Danley Hsu, a graduate student at Penn State and the first author of the paper.

    ESA/GAIA satellite

    “By comparing the results to the planets cataloged by Kepler, we characterized the rate of planets per star and how that depends on planet size and orbital distance. Our novel approach allowed the team to account for several effects that have not been included in previous studies.”

    The results of this study are particularly relevant for planning future space missions to characterize potentially Earth-like planets. While the Kepler mission discovered thousands of small planets, most are so far away that it is difficult for astronomers to learn details about their composition and atmospheres.

    “Scientists are particularly interested in searching for biomarkers—molecules indicative of life—in the atmospheres of roughly Earth-size planets that orbit in the ‘habitable-zone’ of Sun-like stars,” said Ford. “The habitable zone is a range of orbital distances at which the planets could support liquid water on their surfaces. Searching for evidence of life on Earth-size planets in the habitable zone of sun-like stars will require a large new space mission.”

    How large that mission needs to be will depend on the abundance of Earth-size planets. NASA and the National Academies of Science are currently exploring mission concepts that differ substantially in size and their capabilities. If Earth-size planets are rare, then the nearest Earth-like planets are farther away and a large, ambitious mission will be required to search for evidence of life on potentially Earth-like planets. On the other hand, if Earth-size planets are common, then there will be Earth-size exoplanets orbiting stars that are close to the sun and a relatively small observatory may be able to study their atmospheres.

    “While most of the stars that Kepler observed are typically thousands of light years away from the Sun, Kepler observed a large enough sample of stars that we can perform a rigorous statistical analysis to estimate of the rate of Earth-size planets in the habitable zone of nearby sun-like stars.” said Hsu.

    Based on their simulations, the researchers estimate that planets very close to Earth in size, from three-quarters to one-and-a-half times the size of earth, with orbital periods ranging from 237 to 500 days, occur around approximately one in six stars. Importantly, their model quantifies the uncertainty in that estimate. They recommend that future planet-finding missions plan for a true rate that ranges from as low about one planet for every 33 stars to as high as nearly one planet for every two stars.

    “Knowing how often we should expect to find planets of a given size and orbital period is extremely helpful for optimize surveys for exoplanets and the design of upcoming space missions to maximize their chance of success,” said Ford. “Penn State is a leader in bringing state-of-the-art statistical and computational methods to the analysis of astronomical observations to address these sorts of questions. Our Institute for CyberScience (ICS) and Center for Astrostatistics (CASt) provide infrastructure and support that makes these types of projects possible.”

    The Center for Exoplanets and Habitable Worlds at Penn State includes faculty and students who are involved in the full spectrum of extrasolar planet research. A Penn State team built the Habitable Zone Planet Finder, an instrument to search for low-mass planets around cool stars, which recently began science operations at the Hobby-Eberly Telescope, of which Penn State is a founding partner.

    U Texas Austin McDonald Observatory Hobby-Eberly Telescope, Altitude 2,026 m (6,647 ft)

    A second Penn State-built spectrograph is in being tested before it begins a complementary survey to discover and measure the masses of low-mass planets around sun-like stars. This study makes predictions for what such planet surveys will find and will help provide context for interpreting their results.

    In addition to Ford and Hsu, the research team includes Darin Ragozzine and Keir Ashby at Brigham Young University. The research was supported by NASA; the U.S. National Science Foundation (NSF); and the Eberly College of Science, the Department of Astronomy and Astrophysics, the Center for Exoplanets and Habitable Worlds, and the Center for Astrostatistics at Penn State. Advanced computing resources and services were provided by the Penn State Institute for CyberScience, including the NSF funded CyberLAMP cluster.

    • Kepler has been replaced by the TESS spacecraft.

    NASA/MIT TESS replaced Kepler in search for exoplanets

    TESS is designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the Kepler mission.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 9:48 am on March 30, 2019 Permalink | Reply
    Tags: , , , Penn State University, ,   

    From Pennsylvania State University: “Extremely accurate measurements of atom states for quantum computing” 

    Penn State Bloc

    From Pennsylvania State University

    25 March 2019

    David Weiss
    dsweiss@phys.psu.edu
    (814) 863-3076

    Sam Sholtis
    samsholtis@psu.edu
    814-865-1390

    1
    New method allows extremely accurate measurement of the quantum state of atomic qubits—the basic unit of information in quantum computers. Atoms are initially sorted to fill two 5×5 planes (dashed yellow grid marks their initial locations). After the first images are taken, microwaves are used to put the atoms into equal superpositions of two spin states. A shift to the left or right in the final images corresponds to detection in one spin state or the other. Associated square patterns denote atom locations (cyan: initial position, orange and blue: shifted positions). Credit: Weiss Laboratory, Penn State

    A new method allows the quantum state of atomic “qubits”—the basic unit of information in quantum computers—to be measured with twenty times less error than was previously possible, without losing any atoms. Accurately measuring qubit states, which are analogous to the one or zero states of bits in traditional computing, is a vital step in the development of quantum computers. A paper describing the method by researchers at Penn State appears March 25, 2019 in the journal Nature Physics.

    “We are working to develop a quantum computer that uses a three-dimensional array of laser-cooled and trapped cesium atoms as qubits,” said David Weiss, professor of physics at Penn State and the leader of the research team. “Because of how quantum mechanics works, the atomic qubits can exist in a ‘superposition’ of two states, which means they can be, in a sense, in both states simultaneously. To read out the result of a quantum computation, it is necessary to perform a measurement on each atom. Each measurement finds each atom in only one of its two possible states. The relative probability of the two results depends on the superposition state before the measurement.”

    To measure qubit states, the team first uses lasers to cool and trap about 160 atoms in a three-dimensional lattice with X, Y, and Z axes. Initially, the lasers trap all of the atoms identically, regardless of their quantum state. The researchers then rotate the polarization of one of the laser beams that creates the X lattice, which spatially shifts atoms in one qubit state to the left and atoms in the other qubit state to the right. If an atom starts in a superposition of the two qubit states, it ends up in a superposition of having moved to the left and having moved to the right. They then switch to an X lattice with a smaller lattice spacing, which tightly traps the atoms in their new superposition of shifted positions. When light is then scattered from each atom to observe where it is, each atom is either found shifted left or shifted right, with a probability that depends on its initial state. The measurement of each atom’s position is equivalent to a measurement of each atom’s initial qubit state.

    “Mapping internal states onto spatial locations goes a long way towards making this an ideal measurement,” said Weiss. “Another advantage of our approach is that the measurements do not cause the loss of any of the atoms we are measuring, which is a limiting factor in many previous methods.”

    The team determined the accuracy of their new method by loading their lattices with atoms in either one or the other qubit states and performing the measurement. They were able to accurately measure atom states with a fidelity of 0.9994, meaning that there were only six errors in 10,000 measurements, a twenty-fold improvement on previous methods. Additionally, the error rate was not impacted by the number of qubits that the team measured in each experiment and because there was no loss of atoms, the atoms could be reused in a quantum computer to perform the next calculation.

    “Our method is similar to the Stern-Gerlach experiment from 1922—an experiment that is integral to the history of quantum physics,” said Weiss. “In the experiment, a beam of silver atoms was passed through a magnetic field gradient with their north poles aligned perpendicular to the gradient. When Stern and Gerlach saw half the atoms deflect up and half down, it confirmed the idea of quantum superposition, one of the defining aspects of quantum mechanics. In our experiment, we also map the internal quantum states of atoms onto positions, but we can do it on an atom by atom basis. Of course, we do not need to test this aspect of quantum mechanics, we can just use it.”

    In addition to Weiss, the research team at Penn State includes Tsung-Yao Wu, Aishwarya Kumar, and Felipe Giraldo. The research was supported by the U.S. National Science Foundation.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 1:37 pm on January 29, 2019 Permalink | Reply
    Tags: , , , , In this work we see a dimming of the X-rays from the neutron star and a prominent line from neutral iron in the X-ray spectrum—two signatures supporting the clumpy nature of stellar winds, , , Penn State University, Stellar winds are the fast-flowing material—composed of protons electrons and metal atoms—ejected from stars, The neutron star observed is part of a high-mass X-ray binary system-the compact incredibly dense neutron star paired with a massive ‘normal’ supergiant star, This material enriches the star’s surroundings with metals kinetic energy and ionizing radiation   

    From Pennsylvania State University: “Stellar winds, the source material for the universe, are clumpy” 

    Penn State Bloc

    From Pennsylvania State University

    24 January 2019

    Pragati Pradhan
    pup69@psu.edu
    (814) 865-6834

    Sam Sholtis (PIO)
    samsholtis@psu.edu
    (814) 865-1390

    1
    Illustration of a high-mass X-ray binary system made up of a compact, incredibly dense neutron star paired with a massive normal supergiant star. New data from NASAs Chandra X-ray Observatory shows that the neutron star in the high-mass X-ray binary, OAO 1657-415, passed through a dense patch of stellar wind from its companion star, demonstrating the clumpy nature of stellar winds. Credit: NASA/CXC/M.Weiss

    NASA/Chandra X-ray Telescope

    Data recorded by NASA’s Chandra X-ray Observatory of a neutron star as it passed through a dense patch of stellar wind emanating from its massive companion star provide valuable insight about the structure and composition of stellar winds and about the environment of the neutron star itself. A paper describing the research, led by Penn State astronomers, appears January 15, 2019, in the journal, Monthly Notices of the Royal Astronomical Society.

    “Stellar winds are the fast-flowing material—composed of protons, electrons, and metal atoms—ejected from stars,” said Pragati Pradhan, a postdoctoral researcher in astronomy and astrophysics at Penn State and the lead author of the paper. “This material enriches the star’s surroundings with metals, kinetic energy, and ionizing radiation. It is the source material for star formation. Until the last decade, it was thought that stellar winds were homogenous, but these Chandra data provide direct evidence that stellar winds are populated with dense clumps.”

    The neutron star observed is part of a high-mass X-ray binary system—the compact, incredibly dense neutron star paired with a massive ‘normal’ supergiant star. Neutron stars in binary systems produce X-rays when material from the companion star falls toward the neutron star and is accelerated to high velocities. As a result of this acceleration, X-rays are produced that can inturn interact with the materials of the stellar wind to produce secondary X-rays of signature energies at various distances from the neutron star. Neutral—uncharged—iron atoms, for example, produce fluorescence X-rays with energies of 6.4 kilo-electron volts (keV), roughly 3000 times the energy of visible light. Astronomers use spectrometers, like the instrument on Chandra, to capture these X-rays and separate them based on their energy to learn about the compositions of stars.

    “Neutral iron atoms are a more common component of stars so we usually see a large peak at 6.4 keV in the data from our spectrometers when looking at X-rays from most neutron stars in a high-mass X-ray binary system,” said Pradhan. “When we looked at X-ray data from the high-mass X-ray binary system known as OAO 1657-415 we saw that this peak at 6.4 keV had an unusual feature. The peak had a broad extension down to 6.3 keV. This extension is referred to as a ‘Compton shoulder’ and indicates that the X-rays from neutral iron are being back scattered by dense matter surrounding the star. This is only the second high-mass X-ray binary system where such a feature has been detected.”

    The researchers also used the Chandra’s state-of-the-art engineering to identify a lower limit on the distance from the neutron star that the X-rays from neutral iron are formed. Their spectral analysis showed that neutral iron is ionized at least 2.5 light-seconds, a distance of approximately 750 million meters or nearly 500,000 miles, from the neutron star to produce X-rays.

    “In this work, we see a dimming of the X-rays from the neutron star and a prominent line from neutral iron in the X-ray spectrum—two signatures supporting the clumpy nature of stellar winds,” said Pradhan. “Furthermore, the detection of Compton shoulder has also allowed us to map the environment around this neutron star. We expect to be able to improve our understanding of these phenomenon with the upcoming launch of spacecrafts like Lynx and Athena, which will have improved X-ray spectral resolution.”

    For Pradhan’s post-doctoral work at Penn State under the supervision of Professor of Astronomy and Astrophysics David Burrows, Associate Research Professor of Astronomy and Astrophysics Jamie Kennea, and Research Professor of Astronomy and Astrophysics Abe Falcone, she is majorly involved in writing algorithms for on-board detection of X-rays from transient astronomical events such as those seen from these high-mass X-ray binary systems for instruments that will be on the Athena spacecraft.

    Pradhan and her team also have a follow-up campaign looking at the same high-mass X-ray binary with another NASA satellite—NuSTAR, which will cover a broader spectrum of X-rays from this source ranging in energies from ~ 3 to 70 keV—in May 2019.

    NASA NuSTAR X-ray telescope

    “We are excited about the upcoming NuSTAR observation too,” said Pradhan. “Such observations in hard X-rays will add another dimension to our understanding of the physics of this system and we will have an opportunity to estimate the magnetic field of the neutron star in OAO 1657-415, which is likely a million times stronger than strongest magnetic field on Earth.”

    In additions to Pradhan, the research team for this paper includes Gayathri Raman and Pradhan’s Ph.D. supervisor Biswajit Paul at the Raman Research Institute in Bangalore, India.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 1:47 pm on January 22, 2019 Permalink | Reply
    Tags: , , , , How hot are atoms in the shock wave of an exploding star?, Penn State University,   

    From Pennsylvania State University: “How hot are atoms in the shock wave of an exploding star?” 

    Penn State Bloc

    From Pennsylvania State University

    21 January 2019

    CONTACTS:
    David Burrows
    dxb15@psu.edu
    (814) 863-2466

    Gail McCormick (PIO)
    gailmccormick@psu.edu
    (814) 863-0901

    1
    An international team of researchers combined observations of nearby supernova SN1987A, made with NASA’s Chandra X-Ray Observatory, with simulations to measure the temperature atoms in the shock wave that occurs from the explosive death of a star. This image superimposes synthetic X-ray emission data onto a density map with from the simulation of SN1987A. Credit: Marco Miceli, Dipartimento di Fisica e Chimica, Università di Palermo, and INAF-Osservatorio Astronomico di Palermo, Palermo, Italy.

    NASA/Chandra X-ray Telescope

    A new method to measure the temperature of atoms during the explosive death of a star will help scientists understand the shock wave that occurs as a result of this supernova explosion. An international team of researchers, including a Penn State scientist, combined observations of a nearby supernova remnant—the structure remaining after a star’s explosion—with simulations in order to measure the temperature of slow-moving gas atoms surrounding the star as they are heated by the material propelled outward by the blast.

    The research team analyzed long-term observations of the nearby supernova remnant SN1987A using NASA’s Chandra X-ray Observatory and created a model describing the supernova. The team confirmed that the temperature of even the heaviest atoms—which had not yet been investigated—is related to their atomic weight, answering a long-standing question about shock waves and providing important information about their physical processes. A paper describing the results appears January 21, 2019, in the journal Nature Astronomy.

    “Supernova explosions and their remnants provide cosmic laboratories that enable us to explore physics in extreme conditions that cannot be duplicated on Earth,” said David Burrows, professor of astronomy and astrophysics at Penn State and an author of the paper. “Modern astronomical telescopes and instrumentation, both ground-based and space-based, have allowed us to perform detailed studies of supernova remnants in our galaxy and nearby galaxies. We have performed regular observations of supernova remnant SN1987A using NASA’s Chandra X-ray Observatory, the best X-ray telescope in the world, since shortly after Chandra was launched in 1999, and used simulations to answer longstanding questions about shock waves.”

    The explosive death of a massive star like SN1987A propels material outwards at speeds of up to one tenth the speed of light, pushing shock waves into the surrounding interstellar gas. Researchers are particularly interested in the shock front, the abrupt transition between the supersonic explosion and the relatively slow-moving gas surrounding the star. The shock front heats this cool slow-moving gas to millions of degrees—temperatures high enough for the gas to emit X-rays detectable from Earth.

    “The transition is similar to one observed in a kitchen sink when a high-speed stream of water hits the sink basin, flowing smoothly outward until it abruptly jumps in height and becomes turbulent,” said Burrows. “Shock fronts have been studied extensively in the Earth’s atmosphere, where they occur over an extremely narrow region. But in space, shock transitions are gradual and may not affect atoms of all elements the same way.”

    3
    The supernova shock front, the abrupt transition between the supersonic explosion and the gas surrounding the exploding star, is similar to transition in a “hydraulic jump,” where a high-speed stream of water hitting a surface flows smoothly outwards and then abruptly jumps in height and becomes turbulent. Credit: James Kilfiger, Wikimedia Commons.

    The research team, led by Marco Miceli and Salvatore Orlando of the University of Palermo, Italy, measured the temperatures of different elements behind the shock front, which will improve understanding of the physics of the shock process. These temperatures are expected to be proportional to the elements’ atomic weight, but the temperatures are difficult to measure accurately. Previous studies have led to conflicting results regarding this relationship, and have failed to include heavy elements with high atomic weights. The research team turned to supernova SN1987A to help address this dilemma.

    Supernova SN1987A, which is located in a nearby galaxy called the Large Magellanic Cloud, was the first supernova visible to the naked eye since Kepler’s Supernova in 1604. It is also the first to be studied in detail with modern astronomical instruments. The light from its explosion first reached earth on February 23, 1987, and since then it has been observed at all wavelengths of light, from radio waves to X-rays and gamma waves. The research team used these observations to build a model describing the supernova.

    SN1987a fromNASA/ESA Hubble Space Telescope in Jan. 2017 using its Wide Field Camera 3 (WFC3).

    Models of SN1987A have typically focused on single observations, but in this study, the researchers used three-dimensional numerical simulations to incorporate the evolution of the supernova, from its onset to the current age. A comparison of the X-ray observations and the model allowed the researchers to accurately measure atomic temperatures of different elements with a wide range of atomic weights, and to confirm the relationship that predicts the temperature reached by each type of atom in the interstellar gas.

    “We can now accurately measure the temperatures of elements as heavy as silicon and iron, and have shown that they indeed do follow the relationship that the temperature of each element is proportional to the atomic weight of that element,” said Burrows. “This result settles an important issue in the understanding of astrophysical shock waves and improves our understanding of the shock process.”

    It is also the first to be studied in detail with modern astronomical instruments. The light from its explosion first reached earth on February 23, 1987, and since then it has been observed at all wavelengths of light, from radio waves to X-rays and gamma waves. The research team used these observations to build a model describing the supernova.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 4:21 pm on December 5, 2018 Permalink | Reply
    Tags: , Penn State University   

    From Pennsylvania State University: “LIGO supercomputer upgrade will speed up groundbreaking astrophysics research” 

    Penn State Bloc

    From Pennsylvania State University

    1
    Gravitational wave astronomy is used to detect events such as binary star mergers, like the one depicted here. Image: Bangalore Sathyaprakash

    December 04, 2018

    In 2016, an international team of scientists found definitive evidence — tiny ripples in space known as gravitational waves — to support one of the last remaining untested predictions of Einstein’s theory of general relativity. The team used the Laser Interferometer Gravitational-Wave Observatory (LIGO), which has since made several gravitational wave discoveries. Each discovery was possible in part because of a global network of supercomputer clusters, one of which is housed at Penn State. Researchers use this network, known as the LIGO Data Grid, to analyze the gravitational wave data.

    Penn State recently invested in an upgrade to its portion of the data grid that will roughly quadruple the cluster’s capacity for conducting cutting-edge astronomy and astrophysics research. The new cluster, 192 servers working in tandem, is administered by the Institute for CyberScience (ICS). Bangalore Sathyaprakash, professor of astronomy and astrophysics and Elsbach Professor of Physics; and Chad Hanna, associate professor of physics and astronomy and astrophysics, and ICS co-hired faculty member, are the primary researchers who will be using the new system with their research team and collaborators.

    Speeding up faculty and student research

    “At Penn State we’re involved in all aspects of gravitational wave astronomy, which we use to learn about the universe,” said Sathyaprakash. “Until the discovery of gravitational waves, the only way we could observe the universe was using light, radio waves or gamma rays, which all belong to the electromagnetic spectrum. Gravitational waves allow us to create a complementary picture of the universe and reveal processes and phenomena that might not otherwise be revealed through electromagnetic observation.”

    The new cluster will vastly increase the speed at which researchers can complete analysis, according to Chad Hanna. He and colleagues recently finished the first study that used data housed on Penn State’s LIGO cluster. The team designed an experiment to quantify the number of binary black holes in the universe that have less mass than the Sun, which may have implications for the amount of dark matter in the universe.

    “Our first study that solely used the Penn State LIGO cluster took 12 weeks,” said Hanna. “If we were to complete that same investigation on the upgraded cluster today, it would only take three weeks.”

    The upgrade boosts the cluster from 1,152 compute cores to 4,608 cores, which will allow more researchers to use the system simultaneously. For reference, this is roughly equivalent to more than 1,000 desktop computers working in unison.

    “I’m most excited about the extra machines,” said Ryan Magee, graduate student in physics. “It allows for multiple analyses to run at once without much bottlenecking.”

    Magee plans to use the cluster to search for sub-solar mass compact objects in the universe, he said, because “they are not produced by stellar mechanisms, so it would be a hint of new physics.”

    Researchers at all levels will be using the new resource, including undergraduate students like Phoebe McClincy, a sophomore studying astronomy and astrophysics, and a Millennium Scholar. McClincy was first exposed to gravitational wave research as a high school student attending a Penn State summer camp led by Hanna.

    “During that summer camp I was actually afforded the opportunity to visit the cluster, and I remember thinking it was really cool and fascinating to see the other side of the computer,” said McClincy, now a member of Hanna’s research team. “I’ve always thought tech like this is amazing, so I can’t wait to see what can be done now that it will be even more advanced.”

    Building capacity for future LIGO discoveries

    The first iteration of LIGO’s observatories collected data from 2002 to 2010 but did not detect any gravitational waves. Upgrading the observatories to their current state, known as Advanced LIGO, greatly increased their detection capabilities, and, as a result, the system has detected six gravitational wave events since 2016.

    Sathyaprakash said there are plans to continue enhancing the detection capabilities of gravitational wave observatories, which will pose both opportunities and challenges for researchers.

    “When advanced LIGO reaches its design sensitivity, we will observe binary black hole collisions as far as tens of billions of light years and binary neutron star mergers billions of light years away. With the construction in the 2030s of new detectors that are 10 times more sensitive than the current ones, we will be able to observe the entire universe in gravitational waves for black holes and most of the universe for neutron stars,” he said.

    Coming with that will be challenges in collecting, storing and analyzing huge amounts of data. It has taken between one and three months to analyze each gravitational wave detected to date.

    “With advanced LIGO we expect to observe one event every day or every other day, this will offer a huge computational challenge, and so every bit helps,” he said. “With this new LIGO cluster, what we’ve done is to secure enough resources to be completely independent in doing our analyses. ICS and Penn State are enabling this challenging science. Without this new cluster, we would be very severely hampered from doing the science that we want to do.”


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 2:25 pm on October 12, 2018 Permalink | Reply
    Tags: , , , , , Penn State University, , This neutron star named RX J0806.4-4123   

    From Pennsylvania State University: “The surprising environment of an enigmatic neutron star” 

    Penn State Bloc

    From Pennsylvania State University

    September 17, 2018
    Bettina Posselt
    bup13@psu.edu
    Work Phone:
    (814) 863-9341

    Sam Sholtis
    sjs144@psu.edu
    Work Phone:
    814-865-1390

    1
    Infrared image of a neutron star (source on right in box) with an extended infrared emission obtained from observations with the Hubble Space Telescope. The blue circle indicates the pulsar’s X-ray position (obtained with the Chandra X-ray Space Telescope), the cross marks the position of the pulsar in the UV-Optical (measured with the Hubble Space Telescope). Credit: Bettina Posselt, Penn State

    NASA/ESA Hubble Telescope

    NASA/Chandra X-ray Telescope

    An unusual infrared emission detected by the Hubble Space Telescope from a nearby neutron star could indicate that the pulsar has features never before seen. The observation, by a team of researchers at Penn State, Sabanci University in Turkey, and the University of Arizona, could help astronomers better understand the evolution of neutron stars — the incredibly dense remnants of massive stars after a supernova. A paper describing the research and two possible explanations for the unusual finding appears Sept. 17 in The Astrophysical Journal.

    “This particular neutron star belongs to a group of seven nearby X-ray pulsars — nicknamed ‘the Magnificent Seven’ — that are hotter than they ought to be considering their ages and available energy reservoir provided by the loss of rotation energy,” said Bettina Posselt, associate research professor of astronomy and astrophysics at Penn State and the lead author of the paper. “We observed an extended area of infrared emissions around this neutron star — named RX J0806.4-4123 — the total size of which translates into about 200 astronomical units, or 2.5 times the orbit of Pluto around the Sun, at the assumed distance of the pulsar.”

    This is the first neutron star in which an extended emission has been seen only in the infrared. The researchers suggest two possibilities that could explain the extended infrared emission seen by the Hubble Space Telescope. The first is that there is a disk of material — possibly mostly dust — surrounding the pulsar.

    “One theory is that there could be what is known as a ‘fallback disk’ of material that coalesced around the neutron star after the supernova,” said Posselt. “Such a disk would be composed of matter from the progenitor massive star. Its subsequent interaction with the neutron star could have heated the pulsar and slowed its rotation. If confirmed as a supernova fallback disk, this result could change our general understanding of neutron star evolution.”

    2
    Animated llustrated GIF showing a neutron star with a circum-pulsar disk. If seen at the proper angle the scattered emission from the inner part of the disk could produce the extended infrared emission observed by astronomers around the neutron star RX J0806.4-4123.
    IMAGE: Nahks Tr’Ehnl, Penn State

    The second possible explanation for the extended infrared emission from this neutron star is a “pulsar wind nebula.”

    “A pulsar wind nebula would require that the neutron star exhibits a pulsar wind,” said Posselt. “A pulsar wind can be produced when particles are accelerated in the electric field that is produced by the fast rotation of a neutron star with a strong magnetic field. As the neutron star travels through the interstellar medium at greater than the speed of sound, a shock can form where the interstellar medium and the pulsar wind interact. The shocked particles would then radiate synchrotron emission, causing the extended infrared emission that we see. Typically, pulsar wind nebulae are seen in X-rays and an infrared-only pulsar wind nebula would be very unusual and exciting.”

    3
    Illustrated GIF showing a neutron star with a pulsar wind nebula produced by the interaction of the pulsar wind and the oncoming interstellar medium. A pulsar wind nebula could explain the extended infrared emission observed by astronomers around the neutron star RX J0806.4-4123. Such an infrared-only pulsar wind nebula is unusual because it implies a rather low energy of the accelerated particles.
    IMAGE: Nahks Tr’Ehnl, Penn State

    Although neutron stars are generally studied in radio and high-energy emissions, such as X-rays, this study demonstrates that new and interesting information about neutron stars can also be gained by studying them in the infrared. Using the new NASA James Webb Space Telescope, due to launch in 2021, astronomers will be able to further explore this newly opened discovery space in the infrared to better understand neutron star evolution.

    In addition to Posselt, the research team included George Pavlov and Kevin Luhman at Penn State; Ünal Ertan and Sirin Çaliskan at Sabanci University in Instanbul, Turkey; and Christina C. Williams at the University of Arizona. The research was supported by NASA, The Scientific and Technological Research Council of Turkey, the U.S. National Science Foundation, Penn State, the Penn State Eberly College of Science, and the Pennsylvania Space Grant Consortium.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 4:07 pm on January 3, 2018 Permalink | Reply
    Tags: Four-dimensional physics in two dimensions, Penn State University, , Waveguide array   

    From Penn State: “Four-dimensional physics in two dimensions” 

    Penn State Bloc

    Pennsylvania State University

    03 January 2018

    Mikael Rechtsman
    mcrworld@gmail.com

    Barbara K. Kennedy (PIO)
    barbarakennedy@psu.edu,
    814-863-4682

    For the first time, physicists have built a two-dimensional experimental system that allows them to study the physical properties of materials that were theorized to exist only in four-dimensional space. An international team of researchers from Penn State, ETH Zurich in Switzerland, the University of Pittsburgh, and the Holon Institute of Technology in Israel have demonstrated that the behavior of particles of light can be made to match predictions about the four-dimensional version of the “quantum Hall effect” — a phenomenon that has been at the root of three Nobel Prizes in physics — in a two-dimensional array of “waveguides.”

    A paper describing the research appears January 4, 2018 in the journal Nature along with a paper from a separate group from Germany that shows that a similar mechanism can be used to make a gas of ultracold atoms exhibit four-dimensional quantum Hall physics as well.

    1
    Illustration of light passing through a two-dimensional waveguide array. Each waveguide is essentially a tube, which behaves like a wire for light, inscribed through high-quality glass using a powerful laser. Many of these waveguides are inscribed closely spaced through a single piece of glass to form the array. Light that flows through the device behaves precisely according to the predictions of the four-dimensional quantum Hall effect. CREDIT: Rechtsman laboratory, Penn State University

    “When it was theorized that the quantum Hall effect could be observed in four-dimensional space,” said Mikael Rechtsman, assistant professor of physics and an author of the paper, “it was considered to be of purely theoretical interest because the real world consists of only three spatial dimensions; it was more or less a curiosity. But, we have now shown that four-dimensional quantum Hall physics can be emulated using photons — particles of light — flowing through an intricately structured piece of glass — a waveguide array.”

    When electric charge is sandwiched between two surfaces, the charge behaves effectively like a two-dimensional material. When that material is cooled down to near absolute-zero temperature and subjected to a strong magnetic field, the amount that it can conduct becomes “quantized” — fixed to a fundamental constant of nature and cannot change. “Quantization is striking because even if the material is ‘messy’ — that is, it has a lot of defects — this ‘Hall conductance’ remains exceedingly stable,” said Rechtsman. “This robustness of electron flow — the quantum Hall effect — is universal and can be observed in many different materials under very different conditions.”

    This quantization of conductance, first described in two-dimensions, cannot be observed in an ordinary three-dimensional material, but in 2000, it was shown theoretically that a similar quantization could be observed in four spatial dimensions. To model this four-dimensional space, the researchers built waveguide arrays. Each waveguide is essentially a tube, which behaves like a wire for light. This “tube” is inscribed through high-quality glass using a powerful laser.

    Many of these waveguides are inscribed closely spaced through a single piece of glass to form the array. The researchers used a recently-developed technique to encode “synthetic dimensions” into the positions of the waveguides. In other words, the complex patterns of the waveguide positions act as a manifestation of the higher-dimensional coordinates. By encoding two extra synthetic dimensions into the complex geometric structure of the waveguides, the researchers were able to model the two-dimensional system as having a total of four spatial dimensions. The researchers then measured how light flowed through the device and found that it behaved precisely according to the predictions of the four-dimensional quantum Hall effect.

    “Our observations, taken together with the observations using ultracold atoms, provide the first demonstration of higher-dimensional quantum Hall physics,” said Rechtsman. “But how can understanding and probing higher-dimensional physics have some relevance to science and technology in our three-dimensional world? There are a number of examples where this is the case. For example, ‘quasicrystals’ — metallic alloys that are crystalline but have no repeating units and are used to coat some non-stick pans — have been shown to have ‘hidden dimensions:’ their structures can be understood as projections from higher-dimensional space into the real, three-dimensional world. Furthermore, it is possible that higher-dimensional physics could be used as a design principle for novel photonic devices.”

    In addition to Rechtsman, the research team includes Jonathan Guglielmon at Penn State; Oded Zilberberg at ETH Zurich; Sheng Huang, Mohan Wang, and Kevin Chen at the University of Pittsburgh; and Yaacov E. Kraus at the Holon Institute of Technology. The research was supported by the U.S. National Science Foundation, the Charles E. Kaufman Foundation, the Alfred P. Sloan Foundation, and the Swiss National Science Foundation.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 2:17 pm on December 31, 2017 Permalink | Reply
    Tags: , , HiCRep method to accurately assess the reproducibility of data from Hi-C experiments, New insights into how the genome works inside of a cell, New statistical method for evaluating reproducibility in studies of genome organization" 2017, Penn State University, Quite often correlation is treated as a proxy of reproducibility in many scientific disciplines but they actually are not the same thing, , With the massive amount of data that is being produced in whole-genome studies it is vital to ensure the quality of the data   

    From Pennsylvania State University: “New statistical method for evaluating reproducibility in studies of genome organization” 2017 

    Penn State Bloc

    Pennsylvania State University

    03 October 2017
    Qunhua Li:
    qunhua.li@psu.edu
    (814) 863-7395

    Barbara K. Kennedy:
    bkk2@psu.edu
    (814) 863-4682

    Sam Sholtis

    A new, statistical method to evaluate the reproducibility of data from Hi-C — a cutting-edge tool for studying how the genome works in three dimensions inside of a cell — will help ensure that the data in these “big data” studies is reliable.

    1
    Schematic representation of the HiCRep method. HiCRep uses two steps to accurately assess the reproducibility of data from Hi-C experiments. Step 1: Data from Hi-C experiments (represented in triangle graphs) is first smoothed in order to allow researchers to see trends in the data more clearly. Step 2: The data is stratified based on distance to account for the overabundance of nearby interactions in Hi-C data. Credit: Li Laboratory, Penn State University

    “Hi-C captures the physical interactions among different regions of the genome,” said Qunhua Li, assistant professor of statistics at Penn State and lead author of the paper. “These interactions play a role in determining what makes a muscle cell a muscle cell instead of a nerve or cancer cell. However, standard measures to assess data reproducibility often cannot tell if two samples come from the same cell type or from completely unrelated cell types. This makes it difficult to judge if the data is reproducible. We have developed a novel method to accurately evaluate the reproducibility of Hi-C data, which will allow researchers to more confidently interpret the biology from the data.”

    The new method, called HiCRep, developed by a team of researchers at Penn State and the University of Washington, is the first to account for a unique feature of Hi-C data — interactions between regions of the genome that are close together are far more likely to happen by chance and therefore create spurious, or false, similarity between unrelated samples. A paper describing the new method appears in the journal Genome Research.

    “With the massive amount of data that is being produced in whole-genome studies, it is vital to ensure the quality of the data,” said Li. “With high-throughput technologies like Hi-C, we are in a position to gain new insight into how the genome works inside of a cell, but only if the data is reliable and reproducible.”

    Inside the nucleus of a cell there is a massive amount of genetic material in the form of chromosomes — extremely long molecules made of DNA and proteins. The chromosomes, which contain genes and the regulatory DNA sequences that control when and where the genes are used, are organized and packaged into a structure called chromatin. The cell’s fate, whether it becomes a muscle or nerve cell, for example, depends, at least in part, on which parts of the chromatin structure is accessible for genes to be expressed, which parts are closed, and how these regions interact. HiC identifies these interactions by locking the interacting regions of the genome together, isolating them, and then sequencing them to find out where they came from in the genome.

    2
    The HiCRep method is able to accurately reconstruct the biological relationship between different cell types, where other methods fail. Credit: Li Laboratory, Penn State University

    “It’s kind of like a giant bowl of spaghetti in which every place the noodles touch could be a biologically important interaction,” said Li. “Hi-C finds all of these interactions, but the vast majority of them occur between regions of the genome that are very close to each other on the chromosomes and do not have specific biological functions. A consequence of this is that the strength of signals heavily depends on the distance between the interaction regions. This makes it extremely difficult for commonly-used reproducibility measures, such as correlation coefficients, to differentiate Hi-C data because this pattern can look very similar even between very different cell types. Our new method takes this feature of Hi-C into account and allows us to reliably distinguish different cell types.”

    “This reteaches us a basic statistical lesson that is often overlooked in the field,” said Li. “Quite often, correlation is treated as a proxy of reproducibility in many scientific disciplines, but they actually are not the same thing. Correlation is about how strongly two objects are related. Two irrelevant objects can have high correlation by being related to a common factor. This is the case here. Distance is the hidden common factor in the Hi-C data that drives the correlation, making the correlation fail to reflect the information of interest. Ironically, while this phenomenon, known as the confounding effect in statistical terms, is discussed in every elementary statistics course, it is still quite striking to see how often it is overlooked in practice, even among well-trained scientists.“

    The researchers designed HiCRep to systematically account for this distance-dependent feature of Hi-C data. In order to accomplish this, the researchers first smooth the data to allow them to see trends in the data more clearly. They then developed a new measure of similarity that is able to more easily distinguish data from different cell types by stratifying the interactions based on the distance between the two regions. “This is like studying the effect of drug treatment for a population with very different ages. Stratifying by age helps us focus on the drug effect. For our case, stratifying by distance helps us focus on the true relationship between samples.”

    To test their method, the research team evaluated Hi-C data from several different cell types using HiCRep and two traditional methods. Where the traditional methods were tripped up by spurious correlations based on the excess of nearby interactions, HiCRep was able to reliably differentiate the cell types. Additionally, HiCRep could quantify the amount of difference between cell types and accurately reconstruct which cells were more closely related to one another.

    In addition to Li, the research team includes Tao Yang, Feipeng Zhang, Fan Song, Ross C. Hardison, and Feng Yue at Penn State; and Galip Gürkan Yardımcı and William Stafford Noble at the University of Washington. The research was supported by the U.S. National Institutes of Health, a Computation, Bioinformatics, and Statistics (CBIOS) training grant at Penn State, and the Huck Institutes of the Life Sciences at Penn State.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Penn State Campus

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
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