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  • richardmitnick 11:13 am on April 16, 2019 Permalink | Reply
    Tags: "Astronomers Have Found Potential Life-Supporting Conditions on The Nearest Exoplanet", , , , Carl Sagan Institute, Cornell University, , ,   

    From Carl Sagan Institute via Science Alert: “Astronomers Have Found Potential Life-Supporting Conditions on The Nearest Exoplanet” 

    From Carl Sagan Institute

    via

    ScienceAlert

    Science Alert

    16 APR 2019
    MATT WILLIAMS

    1
    Artist impression of an exoplanet from its moon. (IAU/L. Calçada)

    In August of 2016, astronomers from the European Southern Observatory (ESO) announced the discovery of an exoplanet in the neighboring system of Proxima Centauri. The news was greeted with considerable excitement, as this was the closest rocky planet to our Solar System that also orbited within its star’s habitable zone.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    Since then, multiple studies have been conducted to determine if this planet could actually support life.

    Unfortunately, most of the research so far has indicated that the likelihood of habitability are not good. Between Proxima Centauri’s variability and the planet being tidally-locked with its star, life would have a hard time surviving there.

    However, using lifeforms from early Earth as an example, a new study [MNRAS] conducted by researchers from the Carl Sagan Institute (CSI) has shows how life could have a fighting chance on Proxima b after all.

    2
    Artist’s impression of Proxima b’s surface, orbiting the red dwarf star. (ESO)

    The study, which recently appeared in the Monthly Notices of the Royal Astronomical Society [link is above], was conducted by Jack O’Malley-James and Lisa Kaltenegger – an research associate and the director of the Carl Sagan Institute at Cornell University.

    Together, they examined the levels of surface UV flux that planets orbiting M-type (red dwarf) stars would experience and compared that to conditions on primordial Earth.

    The potential habitability of red dwarf systems is something scientists have been debated for decades. On the one hand, they have a number of attributes that are encouraging, not the least of which is their commonality.

    Essentially, red dwarfs are the most common type of star in the Universe, accounting for 85 percent of the stars in the Milky Way alone.

    They also have the greatest longevity, with lifespans that can last into the trillions of years. Last, but not least, they appear to be the most likely stars to host systems of rocky planets.

    This is attested to by the sheer number of rocky planets discovered around neighboring red dwarf stars in recent years – such as Proxima b, Ross 128b, LHS 1140b, Gliese 667Cc, GJ 536, the seven rocky planets orbiting TRAPPIST-1.

    A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. NASA


    ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile


    ESO Belgian robotic Trappist-South National Telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    However, red dwarf stars also present a lot of impediments to habitability, not the least of which is their variable and unstable nature. As O’Malley-James explained to Universe Today via email:

    “The chief barrier to the habitability of these worlds is the activity of their host stars. Regular stellar flares can bathe these planets in high levels of biologically harmful radiation. Furthermore, over longer periods of time, the onslaught of X-ray radiation and charged particle fluxes from the host stars places the atmospheres of these planets at risk of being stripped away over time if a planet cannot replenish its atmosphere fast enough.”

    For generations, scientists have struggled with questions regarding the habitability of planets that orbit red dwarf stars.

    Unlike our Sun, these low-mass, ultra-cool dwarf stars are variable, unstable and prone to flare-ups. These flares release a lot of high-energy UV radiation, which is harmful to life as we know it and capable of stripping a planet’s atmospheres away.

    This places significant limitations on the ability of any planet orbiting a red dwarf star to give rise to life or remain habitable for long. However, as previous studies have shown, much of this depends on the density and composition of the planets’ atmospheres, not to mention whether or not the planet has a magnetic field.

    To determine if life could endure under these conditions, O’Malley-James and Kaltenegger considered what conditions were like on planet Earth roughly 4 billion years ago.

    At that time, Earth’s surface was hostile to life as we know it today. In addition to volcanic activity and a toxic atmosphere, the landscape was bombarded by UV radiation in a way that is similar to what planets that orbit M-type stars experience today.

    To address this, Kaltenegger and O’Malley-James modeled the surface UV environments of four nearby “potentially habitable” exoplanets – Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b – with various atmospheric compositions. These ranged from ones similar to present-day Earth to those with “eroded” or “anoxic” atmospheres – i.e. those that don’t block UV radiation well and don’t have a protective ozone layer.

    These models showed that as atmospheres become thinner and ozone levels decrease, more high-energy UV radiation is able to reach the ground. But when they compared the models to what was present on Earth, roughly 4 billion years ago, the results proved interesting. As O’Malley-James said:

    “The unsurprising result was that the levels of surface UV radiation were higher than we experience on Earth today. However, the interesting result was that the UV levels, even for the planets around the most active stars, were all lower than the Earth experienced in its youth. We know the young Earth supported life, so the case for life on planets in M star systems may not be quite so dire after all.”

    What this means, in essence, is that life could exist on neighboring planets like Proxima b right now despite being subjected to harsh levels of radiation. If you consider the age of Proxima Centauri – 4.853 billion years, which is roughly 200 million years older than our Sun – the case for potential habitability may become even more intriguing.

    The current scientific consensus is that the first lifeforms on Earth emerged a billion years after the planet formed (3.5 billion years ago). Assuming Proxima b formed from a protoplanetary debris disk shortly after Proxima Centauri was born, life would have had enough time to not only emerge, but get a significant foothold.

    While that life may consist solely of single-celled organisms, it is encouraging nonetheless. Aside from letting us know that there could very well be life beyond our Solar System, and on nearby planets, it provides scientists with constraints on what type of biosignatures may be discernible when studying them. As O’Malley-James concluded:

    “The results from this study builds the case for focusing on life on Earth a few billion years ago; a world of single-celled microbes – prokaryotes – that lived with high UV radiation levels. This ancient biosphere may have the best overlaps with conditions on habitable planets around active M stars, so could provide us with the best clues in our search for life in these star systems.”

    As always, the search for life in the cosmos begins with the study of Earth, since it is the only example we have of a habitable planet. It is therefore important to understand how (i.e. under what conditions) life was able to survive, thrive and respond to environmental changes throughout Earth’s geological history.

    For while we may know of only one planet that supports life, that life has been remarkably diverse and has changed drastically over time.

    Be sure to check out this video about these latest findings, courtesy of the CSI and Cornell University:

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Carl Sagan Institute (CSI) was founded to find life in the universe. Based on the pioneering work of Carl Sagan at Cornell, our interdisciplinary team is developing the forensic toolkit to find life in the universe, inside the Solar System and outside of it, on planets and moons orbiting other stars.

    Recent scientific results show that in our galaxy alone there are billions of planets orbiting other suns. After billions of years of evolution on our own Pale Blue Dot and thousands of years of questioning, we finally have the technology in hand to explore other worlds inside and outside of our solar system. The information generated by the search for signs of life on other worlds also helps us understand and safeguard our own planet — our Pale Blue Dot — better.

    CSI for the search of life in the universe: CSI explores factors that determine if a planet or moon can host life and how we could find it by bringing together experts from a wide range of disciplines, from sciences, engineering to media who work together with some of the planet’s most talented students at the undergraduate, graduate and postdoctoral level. CSI researchers use the latest data from space telescopes, probes to the solar system’s diverse worlds, field and satellite data on our home planet, laboratory studies of terrestrial organisms, and modeling of complex processes from the astronomical to the biological to explore these profound questions. And CSI researchers participate in the development of the next generation of space- and Earth-based facilities to probe ever deeper and farther.

    CSI also interprets these results for the widest possible audience, sharing the fascination of science with everyone who is interested in where humankind stands in the quest to understand our place in the cosmos.

    HISTORY

    The Carl Sagan Institute was founded in 2015 at Cornell University to find life in the universe and explore other worlds – how they form, evolve and if they could harbor life both inside and outside of our own Solar System. Directed by astronomer Lisa Kaltenegger, the Institute has built an entirely new research group, spanning 14 departments at Cornell and including more than 25 faculty who focus on a wide range of the search for life in the universe interdisciplinarily.

    The research group is embedded in a rich environment of established international interdisciplinary cooperation at Cornell. The Institute’s collaboration brings together researchers from fields as far apart as astrophysics, engineering, earth and atmospheric science, geology and biology to tackle questions as diverse as those about the astronomical context of the emergence of life on Earth, how to find it and what this discovery would mean for humankind.

     
  • richardmitnick 9:19 am on March 29, 2019 Permalink | Reply
    Tags: , Cornell University, ,   

    From Cornell Chronicle: “Merged satellite, ground data may forecast volcanic eruptions” 

    From Cornell Chronicle

    1
    Kevin Reath, a Cornell University postdoctorate associate and USGS Powell Center Fellow, studied 17 years of satellite data on volcanic activity in Latin America to propose a way to predict deadly eruptions before they occur. John Munson/Cornell University

    March 28, 2019
    Blaine Friedlander
    bpf2@cornell.edu

    On Nov. 13, 1985, the Nevado del Ruiz volcano in the Andes – about 80 miles west of Bogota, Colombia – erupted, sending a pyroclastic flow down its mountainside.

    The heat melted the snow at an elevation of more than 17,000 feet, and volcanic ash muddied the resulting water – called lahar – that rushed into the nearby town of Amero. More than 23,000 people died.

    1
    Guatemala’s cone-shaped, very active Fuego volcano spews an ash column. It last erupted in June 2018. Kevin Reath/Cornell University

    “This volcano killed over 70 percent of the town’s population. They were unprepared for the eruption,” said Kevin Reath, a Cornell postdoctoral researcher.

    Reath’s work aims to prevent that from happening again. He has merged 17 years of satellite data on volcanoes with ground-based detail to form a model for state-of-the-art volcanic eruption prediction.

    Reath’s paper, “Thermal, Deformation, and Degassing Remote Sensing Time Series (CE 2000–2017) at the 47 Most-Active Volcanoes in Latin America: Implications for Volcanic Systems,” was published in the Journal of Geophysical Research: Solid Earth (American Geophysical Union) in February.

    “Volcanoes are hazardous to local and global populations, but only a fraction of volcanoes are continuously monitored by ground‐based sensors,” Reath said.

    In South America, volcanoes lace the Ring of Fire around the Pacific Ocean. More than 60 percent of Holocene-era volcanoes in Latin America are unmonitored by ground-based sensors, and those with ground sensors still have gaps that satellites can fill, Reath said.

    “We are compiling remote sensing data that has been underutilized,” he said.

    The model aggregates three types of critical information: thermal data, such as volcanic hot spots and how they change over time; degassing data, which examines the presence of sulfur dioxide; and deformation data, accounting for inflation and deflation of magma reservoirs – pockets of lava inside the Earth.

    “These data types have never really been intercompared in such an extensive database,” said Reath, who hopes to extract a more-robust understanding of volcanic processes.

    But his work is not all volcanic eruptions. With over 17 years of satellite data, the scientists can find value in observing quiet among the volcanoes. “When we can see the volcano calm and then see the volcano when it is erupting, we can observe what’s happening leading to eruption. We can get a comprehensive picture of a volcanic behavior,” he said.

    “Volcanoes have personalities,” Reath said. “Sometimes they have multiple personalities. Volcanoes can behave differently from each other, and volcanic behavior – from the same volcano – can vary from eruption to eruption. It helps geologists to understand what to look for before an eruption. We’re looking for typical volcanic background behavior and pre-eruptive behavior.”

    Joining Reath on the paper are: Matthew Pritchard, Cornell professor, earth and atmospheric sciences; Francisco Delgado, Ph.D. ’18; Samantha Moruzzi ’20 and Allison Alcott ’18; and Scott Henderson, Ph.D. ’15, former Cornell postdoctoral researcher. This work was supported by NASA; the European Space Agency; and the Volcano Remote Sensing Working Group, John Wesley Powell Center for Analysis and Synthesis, U.S. Geological Survey.

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 1:08 pm on January 23, 2019 Permalink | Reply
    Tags: , , , Cornell University, , , , Saturn’s icy rings reveal another secret: they’re young   

    From Cornell Chronicle: “Saturn’s icy rings reveal another secret: they’re young” 

    Cornell Bloc

    From Cornell Chronicle

    January 23, 2019
    Blaine Friedlander

    1
    Cassini’s wide-angle camera captures the sunlit side of Saturn’s rings June 26, 2016, offering a good view of the B ring from about 940,000 miles away.
    NASA/JPL-Caltech/Space Science Institute

    Data from the last days of the NASA spacecraft Cassini show that Saturn’s beautiful, extensive rings are relatively young – perhaps created when dinosaurs roamed the Earth – because the ring’s mass is less than previously thought and its frozen components are surprisingly bright and free from dusty cosmic impurities, according to a study published Jan. 17 in Science.

    “Based on previous research, we suspected the rings were young, but not everyone was convinced,” said Phil Nicholson, Cornell professor of astronomy and a co-author of “Measurement and Implications of Saturn’s Gravity Field and Ring Mass”[Science above].

    Before Cassini’s demise when it crashed into Saturn in September 2017, the spacecraft passed repeatedly between the rings and the planet’s cloud tops to study Saturn’s gravity field and the rings’ mass.

    NASA/ESA/ASI Cassini-Huygens Spacecraft

    Cassini (and two Voyager spacecraft) had studied Saturn’s rings from afar, but no craft had yet ventured into the rings to obtain up-close data.

    NASA/Voyager 1

    NASA/Voyager 2

    Before its final planetary plunge, Cassini dove through the rings 22 times, using six passes to measure the gravity field by tracking the radio signal from the spacecraft. (The technique is similar to a police radar, but more precise; Cassini’s velocity was measured with an accuracy of better than 0.1 millimeter per second.)

    The scientists found that the rings – particularly the dense B-ring, one of the three main rings and the brightest visible in a telescope – had lower masses than many had expected, indicating a relatively young age. While Saturn is about 4.5 billion years old, the new Cassini data indicate that the rings probably formed between 10 million and 100 million years ago, according to the lead researchers from Sapienza University in Rome.

    Had the rings been contaminated and darkened by interplanetary debris over a longer period, they would appear much darker, according to NASA’s Jet Propulsion Laboratory.

    “The new mass measurement is firm, because Cassini was able to pass inside the rings. In our prior research, we used waves driven in the rings by Saturn’s moons to indirectly estimate their mass density at several locations, which we then extrapolated to estimate the total mass of the rings,” said Nicholson, who had conducted that earlier research at Cornell with Matt Hedman, now an assistant professor of astronomy at the University of Idaho. “Our final result was very close to the new measurement, but lower than most earlier estimates.”

    “From what we know based on Cassini’s spectral and radar measurements, the rings are also less contaminated than previously thought – probably less than 1 percent,” said Nicholson. “They are close to pure water ice.”

    In 2016, Zhimeng Zhang, Ph.D. ’16, led work examining the dust content of Saturn’s C ring. This research determined that the C ring, once thought to have formed in the primordial era, was less than 100 million years old. In 2017, she reported on similar measurements of the A and B rings, obtaining similarly young ages.

    “Think of an unused desk in an unused room. The more it sits there, the more it collects dust,” Zhang said when she published her work. “The C ring is the same way. While it is composed mostly of water ice, it collects silicate-containing dust from the far-off Kuiper Belt. … [I]n this case, the dust – in terms of the age of the solar system – has not been here a long time.”

    Among ring scientists, Nicholson and others had wagered what Cassini might find in terms of ring mass. The result was close to Nicholson’s prediction. He said: “This is quite gratifying from a scientific and personal point-of-view that we got close to the real number when Cassini finally measured it.”

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 1:23 pm on January 4, 2019 Permalink | Reply
    Tags: , Cornell University, Cornell-Brookhaven “Energy-Recovery Linac” Test Accelerator or CBETA, , , When it comes to particle accelerators magnets are one key to success   

    From Brookhaven National Lab: “Brookhaven Delivers Innovative Magnets for New Energy-Recovery Accelerator” 

    From Brookhaven National Lab

    January 2, 2019
    Karen McNulty Walsh
    kmcnulty@bnl.gov

    Test accelerator under construction at Cornell will reuse energy, running beams through multi-pass magnets that help keep size and costs down.

    1
    Members of the Brookhaven National Laboratory team with the completed magnet assemblies for the CBETA project.

    When it comes to particle accelerators, magnets are one key to success. Powerful magnetic fields keep particle beams “on track” as they’re ramped up to higher energy, crashed into collisions for physics experiments, or delivered to patients to zap tumors. Innovative magnets have the potential to improve all these applications.

    That’s one aim of the Cornell-Brookhaven “Energy-Recovery Linac” Test Accelerator, or CBETA, under construction at Cornell University and funded by the New York State Energy Research and Development Authority (NYSERDA). CBETA relies on a beamline made of cutting-edge magnets designed by physicists at the U.S. Department of Energy’s Brookhaven National Laboratory that can carry four beams at very different energies at the same time.

    Cornell BNL ERL test accelerator

    “Scientists and engineers in Brookhaven’s Collider-Accelerator Department (C-AD) just completed the production and assembly of 216 exceptional quality fixed-field, alternating gradient, permanent magnets for this project—an important milestone,” said C-AD Chair Thomas Roser, who oversees the Lab’s contributions to CBETA.

    The novel magnet design, developed by Brookhaven physicist Stephen Brooks and C-AD engineer George Mahler, has a fixed magnetic field that varies in strength at different points within each circular magnet’s aperture. “Instead of having to ramp up the magnetic field to accommodate beams of different energies, beams with different energies simply find their own ‘sweet spot’ within the aperture,” said Brooks. The result: Beams at four different energies can pass through a single beamline simultaneously.

    In CBETA, a chain of these magnets strung together like beads on a necklace will form what’s called a return loop that repeatedly delivers bunches of electrons to a linear accelerator (linac). Four trips through the superconducting radiofrequency cavities of the linac will ramp up the electrons’ energy, and another four will ramp them down so the energy stored in the beam can be recovered and reused for the next round of acceleration.

    “The bunches at different energies are all together in the return loop, with alternating magnetic fields keeping them oscillating along their individual paths, but then they merge and enter the linac sequentially,” explained C-AD chief mechanical engineer Joseph Tuozzolo. “As one bunch goes through and gets accelerated, another bunch gets decelerated and the energy recovered from the deceleration can accelerate the next bunch.”

    Even when the beams are used for experiments, the energy recovery is expected to be close to 99.9 percent, making this “superconducting energy recovery linac (ERL)” a potential game changer in terms of efficiency. New bunches of near-light-speed electrons are brought up to the maximum energy every microsecond, so fresh beams are always available for experiments.

    That’s one of the big advantages of using permanent magnets. Electromagnets, which require electricity to change the strength of the magnetic field, would never be able to ramp up fast enough, he explained. Using permanent fixed field magnets that require no electricity—like the magnets that stick to your refrigerator, only much stronger—avoids that problem and reduces the energy/cost required to run the accelerator.

    To prepare the magnets for CBETA, the Brookhaven team started with high-quality permanent magnet assemblies produced by KYMA, a magnet manufacturing company, based on the design developed by Brooks and Mahler. C-AD’s Tuozzolo organized and led the procurement effort with KYMA and the acquisition of the other components for the return loop.

    Engineers in Brookhaven’s Superconducting Magnet Division took precise measurements of each magnet’s field strength and used a magnetic field correction system developed and built by Brooks to fine-tune the fields to achieve the precision needed for CBETA. Mahler then led the assembly of the finished magnets onto girder plates that will hold them in perfect alignment in the finished accelerator, while C-AD engineer Robert Michnoff led the effort to build and test electronics for beam position monitors that will track particle paths through the beamline.

    “Brookhaven’s CBETA team reached the goals of this milestone nine days earlier than scheduled thanks to the work of extremely dedicated people performing multiple magnetic measurements and magnet surveys over many long work days,” Roser said.

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    BNL Campus

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

     
  • richardmitnick 8:50 am on July 20, 2018 Permalink | Reply
    Tags: , Cornell University, Electron microscopes, EMPAD-electron microscope pixel array detector,   

    From Cornell University via Science Alert: “A Genius Microscopy Method Just Set a Record in Imaging Individual Atoms” 

    Cornell Bloc

    From Cornell University

    via

    ScienceAlert

    Science Alert

    20 JUL 2018
    MIKE MCRAE

    1
    Two overlaid sheets of molybdenum disulfide (Cornell University)

    Electron microscopes have been capable of taking snapshots of individual atoms for nearly half a century. But we’ve never seen anything quite on this scale.

    A new method for catching and measuring the spray of electron beams is giving us a whole new resolution of the sub-ångström world, opening the way to studying molecular structures that would be impossible to see using existing methods.

    Last year, engineers at Cornell University in the US performed the equivalent of eye surgery on the traditional electron microscope, ditching the need for corrective lenses and improving the way the eye itself collects and measures light.

    Now we have evidence of exactly what that technology can achieve, measuring the bonds between atoms with unprecedented clarity.

    At a fundamental level, all microscopes work in a fairly similar way – an object is showered in waves of energy, which are collected and arranged in such a way that we can deduce its shape. Smaller waves mean smaller details.

    Electrons can have pretty small wave-like properties that depend on the energy they contain, making them perfect for seeing extra small objects. Instead of lenses, they’re focussed using electromagnetic fields.

    Aberrations in these fields can limit the size of objects we can see, much as deviations in lenses can blur images. Engineers usually fix these with the electron microscope equivalent of glasses, adding corrective devices to ‘fix’ the picture.

    This fix only goes so far, though. Multiple aberrations demand additional devices, which could theoretically pile up to the point that it’s an engineering nightmare.

    A device called an electron microscope pixel array detector (EMPAD) does away with the need for these ‘glasses’ by taking another approach. It’s a catcher’s mitt for electrons that bounce off the sample made up of a 128 x 128 array of electron-sensitive pixels.

    Rather than build an image based on the location of the electrons, it detects the angles of each electron’s reflection.

    Working backwards using a technique usually applied to X-ray microscopy called ptychography, it’s possible to build a four-dimensional map that tells not only where the electrons came from, but their momentum as well.

    The team put the combination of EMPAD and ptychography to the test by analysing the structure of two stacked sheets of molybdenum disulfide, each a single atom thick.

    By rotating one sheet a few degrees, they could compare distances in overlapping atoms, setting a record of resolving a distance of just 0.39 ångströms.

    “It’s essentially the world’s smallest ruler,” says physicist Sol Gruner.

    The lattice (pictured above) was so clear, they spotted a single missing sulphur atom.

    But apart from bragging rights, the technique has another massive advantage.

    Electron waves can be made smaller by pumping up their energy. More energy means shorter wavelengths. State-of-the-art microscopes can emit streams of electrons at 300 kiloelectronvolts that can resolve details just under 0.05 nanometres, or 0.5 ångströms.

    But more energy can also turn those electrons from a gentle sprinkle of particles into a machine gun burst, putting molecules at risk of disintegrating.

    Since this beam was a gentle 80 keV, the electrons weren’t energetic enough to break up the structure of the molybdenum disulfide sheets, as they might in a more traditional setup.

    Lower energy electron beams mean we can now study bonds in delicate molecules like never before, giving electron microscopy a more gentle touch while providing a whole new level of detail.

    This is some artwork we look forward to hanging on our wall.

    This research was published in Nature.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 3:31 pm on May 3, 2018 Permalink | Reply
    Tags: A New Data Science Center for Improving Decision-Making, Cornell University   

    From Cornell University: ” A New Data Science Center for Improving Decision-Making” 

    Cornell Bloc

    Cornell University

    1
    Beatrice Jin

    Undated
    No writer credit

    As data science becomes pervasive across many areas of society and is increasingly used to aid decision making in sensitive domains, we need to guarantee its fairness and understand its limitations. A large team of Cornell University researchers, led by Kilian Q. Weinberger, Computer Science, are establishing the Center of Data Science for Improved Decision-Making, which combines expertise from computer science, information science, mathematics, operations research, and statistics.

    The goal of the center is to pursue basic research that will contribute to the theoretical foundations of data science, with topics of broad applications that impact and benefit society. Five concrete research directions include privacy and fairness, learning on social graphs, learning to intervene, uncertainty quantification, and deep learning. The center will advance knowledge in these areas and broaden the range of disciplines and perspectives that can contribute to these challenging issues.

    Key inquiries include how to protect the privacy of individuals and their data, how to preserve fairness in decision making, how the structure of processes within social networks impacts the application of data science, and how to determine and quantify the uncertainty of machine learning’s predictions. Researchers will also probe deep learning algorithms—what they learn and why they generalize so well—and the foundation of experimental design and reasoning, underpinning algorithms that propose interventions, from policy to treatment recommendations. The deep integration of knowledge, techniques, and expertise from multiple fields will form new and expanded frameworks for addressing scientific and societal challenges and for finding new opportunities.

    Cornell Researchers

    2
    Kilian Q. Weinberger
    Computer Science, Computing and Information Science

    3
    Giles Hooker
    Statistical Science, Computing and Information Science/Biological Statistics and Computational Biology, College of Agriculture and Life Sciences

    4
    Jon Kleinberg
    Computer Science/Information Science, Computing and Information Science

    5
    David B. Shmoys
    Operations Research and Information Engineering, College of Engineering/Computer Science, Computing and Information Science

    7
    Steven H. Strogatz
    Mathematics, College of Arts and Sciences

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 9:39 am on March 26, 2018 Permalink | Reply
    Tags: , Cornell University, ,   

    From Cornell University: “Students work in the collaborative lab of Kin Fai Mak’ 

    Cornell Bloc

    Cornell University

    Students work in the collaborative lab of Kin Fai Mak

    1

    Their research is exploring new physical phenomena in atomically thin materials.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 3:53 pm on March 19, 2018 Permalink | Reply
    Tags: , , , Cornell University, Cornell-Brookhaven ERL Test Accelerator, Linacs, , , , Small Accelerator Promises Big Returns   

    From BNL: “Small Accelerator Promises Big Returns” 

    Brookhaven Lab

    March 16, 2018
    Georg Hoffstaetter and Rick Ryan of Cornell University
    For more information about Brookhaven Lab’s role in this work, contact:
    Karen McNulty Walsh
    kmcnulty@bnl.gov
    631-344-8350

    Under construction in the US, the CBETA multi-turn energy-recovery linac will pave the way for accelerators that combine the best of linear and circular machines.

    1
    The main linac cryomodule. No image credit.

    When deciding on the shape of a particle accelerator, physicists face a simple choice: a ring of some sort, or a straight line? This is about more than aesthetics, of course. It depends on which application the accelerator is to be used for: high-energy physics, advanced light sources, medical or numerous others.

    Linear accelerators (linacs) can have denser bunches than their circular counterparts, and are widely used for research. However, for both high-energy physics collider experiments and light sources, linacs can be exceedingly power-hungry because the beam is essentially discarded after each use. This forces linacs to operate at an extremely low current compared to ring accelerators, which in turn limits the data rate (or luminosity) delivered to an experiment. On the other hand, in a collider ring there is a limit to the focusing of the bunches at an interaction point as each bunch has to survive the potentially disruptive collision process on each of millions of turns. Bunches from a linac have to collide only once and can, therefore, be focused to aggressively collide at a higher luminosity.

    Linacs could outperform circular machines for light-source and collider applications, but only if they can be operated with higher currents by not discarding the energy of the spent beam. Energy-recovery linacs (ERLs) fill this need for a new accelerator type with both linac-quality bunches and the large currents more typical of circular accelerators. By recovering the energy of the spent beam through deceleration in superconducting radio-frequency (SRF) cavities, ERLs can recycle that energy to accelerate new bunches, combining the dense beam of a linear accelerator with the high current of a storage ring to achieve significant RF power savings.

    A new facility called CBETA (Cornell-Brookhaven ERL Test Accelerator) that combines some of the best traits of linear and circular accelerators has recently entered construction at Cornell University in the US. Set to become the world’s first multi-turn SRF ERL, with a footprint of about 25 × 15 m, CBETA is designed to accelerate an electron beam to an energy of 150 MeV. As an additional innovation, this four-turn ERL relies on only one return loop for its four beam energies, using a single so-called fixed-field alternating-gradient return loop that can accommodate a large range of different electron energies. To further save energy, this single return loop is constructed from permanent Halbach magnets (an arrangement of permanent magnets that augments the magnetic field on the beam side while cancelling the field on the outside).

    2
    CBETA floor plan. No image credit.

    Initially, CBETA is being built to test the SRF ERL and the single-return-loop concept of permanent magnets for a proposed future electron-ion collider (EIC). Thereafter, CBETA will provide beam for applications such as Compton-backscattered hard X-rays and dark-photon searches. This future ERL technology could be an immensely important tool for researchers who rely on the luminosity of colliders as well as for those that use synchrotron radiation at light sources. ERLs are envisioned for nuclear and elementary particle-physics colliders, as in the proposed eRHIC and LHeC projects, but are also proposed for basic-research coherent X-ray sources, medical applications and industry, for example in lithography sources for the production of yet-smaller computer chips.

    The first multi-turn SRF ERL

    The theoretical concept of ERLs was introduced long before a functional device could be realized. With the introduction of the CBETA accelerator, scientists are following up on a concept first introduced by physicist Maury Tigner at Cornell in 1965. Similarly, non-scaling fixed-field alternating-gradient optics for beams of largely varying energies were introduced decades ago and will be implemented in an operational accelerator for only the second time with CBETA, after a proof-of-principle test at the EMMA facility at Daresbury Laboratory in the UK, which was commissioned in 2010.

    The key behind the CBETA design is to recirculate the beam four times through the SRF cavities, allowing electrons to be accelerated to four very different energies. The beam with the highest energy (150 MeV) will be used for experiments, before being decelerated in the same cavities four times. During deceleration, energy is taken out of the electron beam and is transferred to electromagnetic fields in the cavities, where the recovered energy is then used to accelerate new particles. Reusing the same cavities multiple times significantly reduces the construction and operational costs, and also the overall size of the accelerator.

    The energy-saving potential of the CBETA technology cannot be understated, and is a large consideration for the project’s funding agency the New York State Energy Research and Development Authority. By incrementally increasing the energy of the beam through multiple passes in the accelerator section, CBETA can achieve a high-energy beam without a high initial energy at injection – characteristics more commonly found in storage rings. CBETA’s use of permanent magnets provides further energy savings. The precise energy savings from CBETA are difficult to estimate at this stage, but the machine is expected to require about a factor of 20 less RF power than a traditional linac. This saving factor would be even larger for future ERLs with higher beam energy.

    SRF linacs have been operated in ERL mode before, for example at Jefferson Lab’s infrared free-electron laser, where a single-pass energy recovery has reclaimed nearly all of the electron’s energy.

    3
    Jefferson Lab’s infrared free-electron laser vault

    CBETA will be the first SRF ERL with more than one turn and is unique in its use of a single return loop for all beams. Simultaneously transporting beam at four very different energies (from 42 to 150 MeV) requires a different bending field strength for each energy. While traditional beamlines are simply unable to keep beams with very different energies on the same “track”, the CBETA design relies on fixed-field alternating-gradient optics. To save energy, permanent Halbach magnets containing all four beam energies in a single 70 mm-wide beam pipe were designed and prototyped at Brookhaven National Laboratory (BNL). The special optics for a large energy range had already been proposed in the 1960s, but a modern rediscovery began in 1999 at the POP accelerator at KEK in Japan. This concept has various applications, including medicine, nuclear energy, and in nuclear and particle physics, culminating so far with the construction of CBETA. Important aspects of these optics will be investigated at CBETA, including the following: time-of-flight control, maintenance of performance in the presence of errors, adiabatic transition between curved and straight regions, the creation of insertions that maintain the large energy acceptance, the operation and control of multiple beams in one beam pipe, and harmonic correction of the fields in the permanent magnets.

    Harmonic field correction is achieved by an elegant invention first used in CBETA: in order to overcome the magnetisation errors present in the NdFeB blocks and to produce magnets with 10–3 field accuracy, 32 to 64 iron wires of various lengths are inserted around the magnet bore, with lengths chosen to minimise the lowest 18 multipole harmonics.

    A multi-turn test ERL was proposed by Cornell researchers following studies that started in 2005. Cornell was the natural site, given that many of the components needed for such an accelerator had been prototyped by the group there. A collaboration with BNL was formed in the summer of 2014; the test ERL was called CBETA and construction started in November 2016.

    CBETA has some quite elaborate accelerator elements. The most complex components already existed before the CBETA collaboration, constructed by Cornell’s ERL group at Wilson Lab: the DC electron source, the SRF injector cryomodule, the main ERL cryomodule, the high-power beam stop, and a diagnostic section to map out six-dimensional phase-space densities. They were designed, constructed and commissioned over a 10-year period and hold several world records in the accelerator community. These components have produced the world’s largest electron current from a photo-emitting source, the largest continuous current in an SRF linac and the largest normalized brightness of an electron bunch.

    Setting records

    Meanwhile, the DC photoemission electron gun has set a world record for the average current from a photoinjector, demonstrating operation at 350 kV with a continuous current of 75 mA with 1.3 GHz pulse structure. It operates with a KCsSb cathode, which has a typical quantum efficiency of 8% at a wavelength of 527 m and requires a large ceramic insulator and a separate high voltage, high current, power supply to be able to support the high voltage and current. The present version of the Cornell gun has a segmented insulator design with metal guard rings to protect the ceramic insulator from punch-through by field emission, which was the primary limiting factor in previous designs. This gun has been processed up to 425 kV under vacuum, typically operating at 400 kV.

    The SRF injector linac, or injector cryomodule (ICM), set new records in current and normalized brightness. It operates with a bunch train containing a series of five two-cell 1.3 GHz SRF cavities, each with twin 50 kW input couplers that receive microwaves from high-power klystrons, and the input power couplers are adjustable to allow impedance matching for a variety of different beam currents. The ICM is capable of a total energy gain of around 15 MeV, although CBETA injects beam at a more modest energy of 6 MeV. The high-current CW main linac cryomodule, meanwhile, has a maximum energy gain of 70 MeV and a beam current of up to 40 mA, and for CBETA will accelerate the beam by 36 MeV on each of the four beam passes.

    Several other essential components that have also been commissioned include a high-power beam stop and diagnostics tools for high-current and high-brightness beams, such as a beamline for measuring 6D phase-space densities, a fast wire scanner for beam profiles and beam-loss diagnostics. All these components are now being incorporated in CBETA. While the National Science Foundation provided the bulk funding for the development of all these components, the LCLS-II project contributed funding to investigate the utility of Cornell’s ERL technology, and the company ASML contributed funds to test the use of ERL components for an industrial EUV light source.

    Complementary development work has been ongoing at BNL, and last summer the BNL team successfully tested a fixed-field alternating-gradient beam transport line at the Accelerator Test Facility. It uses lightweight, 3D-printed frames to hold blocks of permanent magnets and uses the above-mentioned innovative method for fine-tuning the magnetic field to steer multiple beams at different energies through a single beam pipe. With this design, physicists can accelerate particles through multiple stages to higher and higher energies within a single ring of magnets, instead of requiring more than one ring to achieve these energies. The beams reached a top momentum that was more than 3.8 times that of the lowest transferred momentum, which is to be compared to the previous result in EMMA, where the highest momentum was less than twice that of the lowest one. The properties of the permanent Halbach magnets match or even surpass those of electromagnets, which require much more precise engineering and machining to create each individual piece of metal. The success of this proof-of-principle experiment reinforces the CBETA design choices.

    The initial mission for CBETA is to prototype components for BNL’s proposed version of an EIC called eRHIC, which would be built using the existing Relativistic Heavy Ion Collider infrastructure at BNL. JLAB also has a design for an EIC, which requires an ERL for its electron cooler and therefore also benefits from research at CBETA. Currently, the National Academy of Sciences is studying the scientific potential of an EIC. More than 25 scientists, engineers and technicians are collaborating on CBETA and they are currently running preliminary beam tests, with the expectation of completing CBETA installation by the summer of 2019. Then we will test and complete CBETA commissioning by the spring of 2020, and begin to explore the scientific applications of this new acceleration and energy-saving technique.

    See the full article here .

    Please help promote STEM in your local schools.

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    BNL Campus

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

     
  • richardmitnick 12:20 pm on December 20, 2017 Permalink | Reply
    Tags: Astronomers see clash of ‘titan’ galaxies … 13 billion years ago, , , , Cerro Chajnantor Atacama Telescope-prime, Cornell University, ,   

    From Cornell: “Astronomers see clash of ‘titan’ galaxies … 13 billion years ago” 

    Cornell Bloc

    Cornell University

    November 13, 2017 [Just made available to me from Cornell]
    Blaine Friedlander
    bpf2@cornell.edu

    1
    Dominik Riechers, left, and doctoral candidate Daisy Leung discovered two hyper-luminous galaxies, which help to reveal cosmic creation.
    Jason Koski/University Photography

    A pair of massive, hyper-luminous galaxies are merging in front of astronomer’s eyes for the first time and revealing secrets of cosmic creation.

    3

    “Discovering a hyper-luminous starburst galaxy is an extraordinary feat, but discovering two – this close to each other – is amazing,” said Dominik Riechers, assistant professor of astronomy and lead author on new research published Nov. 13 in The Astrophysical Journal. “It’s nearly 13 billion light-years away and in its frenzied star-forming action, we may be seeing the most extreme galaxy merger known.”

    Found in the Southern Hemisphere’s Dorado constellation – known as the swordfish – the ADFS-27 galactic pair is located about 12.7 billion light years away. Astronomers are seeing these galaxies in their infancy – at a few hundred million years old – and the light from the galaxies have taken nearly 13 billion years to reach our eyes.

    In the paper, “Rise of the Titans: A Dusty, Hyper-luminous ‘870 µM Riser’ Galaxy at Z~6, Riechers, doctoral candidate T.K. Daisy Leung and their colleagues captured coalescing galaxies – likely the most massive systems in the universe – by using the Atacama Large Millimeter/submillimeter Array (ALMA), a high-elevation radio telescope in Chile, to detect their merger into a single galaxy.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    The merger of the two galaxies has triggered violent, ongoing star formation and lead to the growth of a very massive galaxy in later cosmic epochs, Riechers said.

    Leung explained that this pair must have formed efficiently in early cosmic time, forming the foundation of massive galaxies and clusters astronomers see today. “These massive systems in the early universe are showing us snapshots of their early evolution,” she said.

    “Finding these galaxies – about 30,000 light-years apart – helps astronomers to understand how very extreme structures form, as they continue to birth stars and become even more massive,” said Riechers. “These galactic progenitors help us to understand massive galaxies of the present day, as we’ve tried to understand how these actually form. In other words, this discovery is helping astronomers to understand the timeline of the cosmos.”

    Riechers explained that his group first detected these systems with the European Space Agency’s Herschel Space Observatory. It appeared as a red dot.

    ESA/Herschel spacecraft

    “Galaxies usually look bluer or greener. This one popped out because of its color. It was literally really red, which means it’s a brighter object at longer wavelengths and it is farther away than most galaxies,” Riechers said.

    Earlier this year, this group of astronomers using the ALMA radio telescope examined the red dot and saw two galaxies that have about 50 times the amount of star-forming gas as the Milky Way.

    Riechers said an enormous amount of observed gas will be converted into new stars quickly as the two merging galaxies produce stars at a “breakneck pace,” about 1,000 times faster than in the current Milky Way.

    Leung said that the ALMA telescope has revolutionized our understanding of young galaxies with its unprecedented resolution. “We can now see distant galaxies in exquisite detail, as we were able to uncover the compact, starburst nature of this merger pair – known only as a dusty blob in the good old days.”

    In addition to Riechers and Leung, 13 scientists from 11 institutions served as co-authors on the paper. The Atacama Large Millimeter/submillimeter Array – close to Cornell’s forthcoming Cerro Chajnantor Atacama Telescope-prime, slated for completion in 2021 – is an international astronomy facility, in partnership between the European Southern Observatory, the National Science Foundation and the National Institutes of Natural Sciences of Japan, in cooperation with the Republic of Chile.

    2
    Cerro Chajnantor Atacama Telescope-prime (CCAT-p) Cornell 5,600 metres on Cerro Chajnantor, Chile’s Atacama desert

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 5:50 pm on December 11, 2017 Permalink | Reply
    Tags: , Cornell Collaboration Reports Unique Property of Bilayer Graphene, Cornell University, Cornell’s Laboratory of Atomic and Solid State Physics, Excitons – electrically neutral quasiparticles, Graphene is intrinsically a metal but by adjusting its bandgap you can tune it from a metal to a semiconductor, , Optical properties of single-atom-thick layers of graphene, Photocurrent spectroscopy   

    From Cornell: “Cornell Collaboration Reports Unique Property of Bilayer Graphene” 

    Cornell Bloc

    Cornell University

    KavliFoundation

    The Kavli Foundation

    November 16, 2017
    Tom Fleischman
    tjf85@cornell.edu

    Imagine walking through the Northwest wilderness, camera phone at the ready, hoping to catch at least a faint glimpse of Bigfoot, and instead returning home with an Ansel Adams-quality picture of the mythical beast as he lumbers past you.

    That’s kind of what a team led by physics professor Paul McEuen has done in research into the optical properties of single-atom-thick layers of graphene.

    Combining the technical strengths of two Kavli Institute at Cornell for Nanoscale Science (KIC) postdoctoral fellows, as well as measuring tools from the lab of electrical and computer engineering professor Farhan Rana, the group reports remarkably clear observations of excitons – electrically neutral quasiparticles – in bilayer graphene.

    And the excitons’ unique properties and behavior make this material of possible interest in the development of optoelectronic devices, including lasers.

    1
    Infrared light illuminates bilayer graphene and create an exciton – a pairing of electron and hole, locating mostly at the top and bottom layers, respectively, of carbon atoms. Provided.

    “We kind of knew we’d have a chance to see these excitons, but the outcome turned out to be even more interesting than we thought it would be,” said Long Ju, co-lead author of “Tunable Excitons in Bilayer Graphene,” to be published Nov. 17 in Science.

    Ju and fellow lead author Lei Wang are both Kavli postdocs and members of Cornell’s Laboratory of Atomic and Solid State Physics.

    An exciton is the bound state of an electron and a hole (the space left by an electron following excitation), and is “the most fundamental optical property of any semiconductor,” Ju said. Most materials have properties that make them either a metal or a semiconductor, but graphene can act as either by tuning its bandgap – basically, the measure of its ability to conduct electricity – by hitting it with an electric field.

    Graphene is intrinsically a metal, but by adjusting its bandgap, you can tune it from a metal to a semiconductor.

    “It’s kind of a universal material,” McEuen said. “People theoretically knew this, and there had been some experimental evidence that this worked in this system, but the optical spectrum was nothing like the data these guys showed.”

    For this experiment, Wang constructed bilayer graphene encapsulated in a hexagonal lattice of boron nitride. “The high quality of samples is one key element to observe the intrinsic properties in this experiment.” Wang said. This means that when the bilayer graphene was hit with an electric field, the resulting exciton was clear to see.

    When the sample was hit with electricity, an electron preferably occupied one of the two layers, and exhibited much greater “pseudospin” magnetism than electrons in typical semiconductors. The exciton inherits this very large electron “magnetic moment” (basically, sensitivity to magnetism) in the material.

    The excitonic resonances the group observed are tunable from the mid-infrared to the terahertz range, making bilayer graphene of potential interest in the development of new kinds of lasers and detectors.

    “Vibrations of molecules – which provide chemical information about what a material is – often occur at a frequency that corresponds in energy to this bandgap that you can tune through,” McEuen said.

    A key piece of this research was the availability on campus of the instruments used to clearly see what was happening at the nanoscale level. The group employed photocurrent spectroscopy, along with a magneto-optical cryostat, from the Rana lab.

    McEuen, the John A. Newman Professor of Physical Science, said this work is the product of a collaboration between several groups at Cornell, UC Berkeley, Columbia and the National Institute of Materials Science in Japan. Leading it are two of the top young scientists in their respective disciplines. Both developed their technical expertise as doctoral students – Ju at the University of California, Berkeley, and Wang at Columbia University.

    “Long is one of the best young people studying the optics of these 2-D materials such as graphene,” McEuen said, “and Lei is arguably the best maker of samples of his generation. This [Kavli] postdoctoral fellow program brought these people here so they can work together.”

    In addition to the Kavli Institute, this work was supported by the Cornell Center for Materials Research, which is funded by the National Science Foundation, and by grants from the Air Force Office of Scientific Research and the Office of Naval Research.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
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