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  • richardmitnick 9:10 am on April 27, 2017 Permalink | Reply
    Tags: , , APS, , , , , , SCOAP3   

    From CERN: “CERN and the American Physical Society sign an open access agreement for SCOAP3” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    Geneva, 27 April 2017. The European Organization for Nuclear Research (CERN) and the American Physical Society (APS) signed an agreement today for SCOAP3 – the Sponsoring Consortium for Open Access Publishing in Particle Physics. Under this agreement, high-energy physics articles published in three leading journals of the APS will be open access as from January 2018.

    1

    All authors worldwide will be able to publish their high-energy physics articles in Physical Review C, Physical Review D and Physical Review Letters at no direct cost. This will allow free and unrestricted exchange of scientific information within the global scientific community and beyond, for the advancement of science.

    “Open access reflects values and goals that have been enshrined in CERN’s Convention for more than sixty years, such as the widest dissemination of scientific results. We are very pleased that the APS is joining SCOAP3 and we look forward to welcoming more partners for the long-term success of this initiative”, said Fabiola Gianotti, CERN’s Director General.

    APS CEO Kate Kirby commented that, “APS has long supported the principles of open access to the benefit of the scientific enterprise. As a non-profit society publisher and the largest international publisher of high-energy physics content, APS has chosen to participate in the SCOAP3 initiative in support of this community.”

    With this new agreement between CERN and the APS, SCOAP3 will cover about 90 percent of the journal literature in the field of high-energy physics.

    Convened and managed by CERN, SCOAP3 is the largest scale global open access initiative ever built. It involves a global consortium of 3,000 libraries and research institutes from 44 countries, with the additional support of eight research funding agencies. Since its launch in 2014, it has made 15 000 articles by about 20 000 scientists from 100 countries accessible to anyone.
    The initiative is possible through funds made available from the redirection of former subscription monies. Publishers reduce subscription prices for journals participating in the initiative, and those savings are pooled by SCOAP3 partners to pay for the open access costs, for the wider benefit of the community.

    Received via email.

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    THE FOUR MAJOR PROJECT COLLABORATIONS

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  • richardmitnick 5:31 am on July 7, 2016 Permalink | Reply
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    From APS: “NASA and ESA May Team Up to Measure Gravitational Waves” 

    AmericanPhysicalSociety

    American Physical Society

    7.6.16
    Katherine Kornei

    After parting ways five years ago, the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) may yet collaborate on an orbiting observatory to detect gravitational waves. Public and professional support for this observatory, which would launch in 2034, has been buoyed by two major milestones that occurred this year: the first direct, ground-based detection of gravitational waves,,,

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced LIGO, installations in Washington State and Lousiana, USA

    ,,,and the successful demonstration by an ESA spacecraft of technologies necessary to detect gravitational waves in space.

    ESA/LISA Pathfinder
    ESA/LISA Pathfinder

    In 1975 the concept of a ground-based gravitational wave detector “was literally sketched on a napkin at a NASA review panel meeting,” says Ira Thorpe, an astrophysicist at NASA’s Goddard Space Flight Center. It was at this meeting that Rainer Weiss, then an associate professor of physics teaching a course on general relativity at the Massachusetts Institute of Technology, met Kip Thorne, a physicist at Caltech. The two men talked late into the evening about ideas for a gravitational wave detector.

    What emerged from those initial conversations and many others paved the way for the Laser Interferometer Gravitational-Wave Observatory (LIGO), a National Science Foundation-funded facility managed by MIT and Caltech that started searching for gravitational waves in 2002. In February 2016 LIGO announced the momentous first direct detection of gravitational waves, which were produced by the merger of two black holes in a distant galaxy; a second such detection followed in June.

    LIGO’s exquisite sensitivity to gravitational waves means that its detectors record many spurious signals from vibrations caused by, for example, traffic and ocean waves. “Ground-based detectors have a hard lower limit on the frequencies they can detect at about 1 hertz because of seismic noise, which limits them to seeing very massive objects moving very fast,” says Charles Dunn, Project Technologist at NASA’s Jet Propulsion Laboratory. Furthermore, LIGO’s ability to detect gravitational waves is limited by the relatively short lengths of its arms, because constructing extremely straight, long tubes on Earth’s curved surface is both difficult and expensive.

    The next literal jump in technology will be to take gravitational-wave detectors to space; an orbiting gravitational-wave observatory would overcome both the limitations of vibrations and the difficulty of achieving long laser pathlengths. “In space, we can get down to the 0.1 millihertz frequency range, which should allow observation of many more sources, including things that can be seen with more conventional telescopes,” notes NASA’s Dunn.

    In the 2000s, NASA and ESA collaborated on developing a Laser Interferometer Space Antenna (LISA), a triangular interferometer with arms several million kilometers on a side that would be launched into orbit around the Sun.

    ESA/eLISA
    ESA/eLISA

    However, NASA withdrew from the collaboration in 2011 due to budget cuts, and ESA continued to develop the technologies necessary for LISA. “ESA took a gamble,” says Paul McNamara, an astrophysicist at ESA and the deputy project scientist for LISA. “They wanted the science, and they spent a large chunk of money to demonstrate that it was possible.” In 2013, ESA announced a science theme of “The Gravitational Universe” for the third large-class mission (L3) component of its Cosmic Vision 2015 – 2025 program, which solidified LISA’s position in ESA’s long-term planning.

    Before NASA withdrew from the collaboration, the two agencies had decided to develop a small spacecraft to test the technologies necessary for a successful LISA mission. In December 2015, ESA launched that spacecraft, called LISA Pathfinder [see above], to the L1 Lagrange point 1.5 million kilometers from Earth. One of the primary science goals of LISA Pathfinder was to demonstrate that two paperweight-sized cubes of gold and platinum onboard the spacecraft could be shielded from all forces save for gravity.

    1
    A cube of platinum-gold alloy was the centerpiece of the LISA Pathfinder test. Photo: ESA

    “LISA Pathfinder shows that we can put a test mass in perfect free fall, which is what we’d need to do a full-scale gravitational-wave detector,” says NASA’s Thorpe, the U.S. lead for data analysis on the LISA Pathfinder mission.

    An orbiting gravitational-wave observatory such as LISA would be complementary to ground-based facilities like LIGO. “The same sources that LIGO sees in their last couple of orbits before inspiral, LISA could see months to years before they merge,” explains Thorpe. “LISA would see some of these sources first and could basically be an early warning system for LIGO and also, more importantly, for telescopes [that measure electromagnetic radiation]. That would be transformational science.”

    NASA is once again entertaining the idea of officially partnering with ESA on LISA. The U.S. agency has assembled an “L3 Study Team” to see how NASA might participate in LISA. Scientists and NASA leadership also have their eye on the 2020 Decadal Survey in Astronomy and Astrophysics, which will be conducted by the National Research Council to survey the priorities of the astronomy and astrophysics community. Most major missions require endorsement from the Decadal Survey before they can go forward, and previous Decadal Surveys have endorsed a LISA-like mission. “This science is so compelling, and we’re making great strides with the technology,” remarks Thorpe. “I’d be surprised if the U.S. community didn’t want to be involved.”

    See the full article here .

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    American Physical Society
    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

     
  • richardmitnick 7:09 am on June 7, 2016 Permalink | Reply
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    From APS Physics: “LISA Pathfinder Paves the Way for Space-Based Gravitational Wave Observatory” 

    AmericanPhysicalSociety

    American Physical Society

    June 7, 2016

    ESA/LISA Pathfinder
    ESA/LISA Pathfinder

    A key component of a future gravitational wave observatory passed a series of tests with flying colors. The Laser Interferometer Space Antenna (LISA) Pathfinder mission is a European Space Agency (ESA) project that proves in principle that an orbiting formation of spacecraft will be able to function as a space-based gravitational wave observatory. A paper detailing the first results from the LISA Pathfinder mission appears in Physical Review Letters along with an accompanying Viewpoint commentary in Physics.

    At the heart of the experiment is a two-kilogram cube of a high-purity gold and platinum alloy, called a test mass. The cube is nestled inside the shell-like LISA Pathfinder spacecraft, and has been in orbit since February 2016. The researchers found the test mass could be sufficiently stable and isolated from outside forces to fly in space and detect a whole new range of violent events that create gravitational waves.

    The LISA Pathfinder spacecraft is equipped with electrodes adjacent to each side of the test mass cube to detect the relative position and orientation of the test mass with respect to the spacecraft. An array of tiny thrusters on the outside of the spacecraft compensates for forces that could affect the test mass orbit, chiefly including the pressure from the solar photon flux.

    The mission is a crucial test of systems that will be incorporated in three spacecraft that will comprise the Laser Interferometer Space Antenna (LISA) gravitational wave observatory scheduled to launch in 2034.

    ESA/eLISA
    ESA/eLISA

    The LISA observatory will follow a heliocentric orbit trailing fifty million kilometers behind the Earth. Each LISA spacecraft will contain two test masses like the one currently in the LISA Pathfinder spacecraft. The LISA Pathfinder mission’s success is a crucial step in developing the LISA observatory.

    In the LISA observatory mission planned for 2034, laser interferometers will measure the distances between test masses housed in spacecraft flying in a triangular configuration roughly a million kilometers on a side. The LISA Pathfinder spacecraft contains a second test mass to form a minuscule equivalent of one leg of the triangular LISA formation. The second Pathfinder mass is electrostatically manipulated to maintain its position relative to the free falling test mass. The masses are separated by only about a third of a meter, which is far too short for the detection of gravitational waves, but is vital for testing the systems that will eventually make up the LISA observatory.

    Researchers report that the system reduces acceleration noise between the test masses to less than 0.54 x 10-15 g/(Hz)^½ over a frequency range of 0.7 mHz to 20 mHz. The noise in this range is five times lower than the LISA Pathfinder design threshold, and within a factor of 1.25 of the LISA observatory requirements. Above 60 mHz, acceleration noise is two orders of magnitude better than design requirements. According to the researchers, the measured performance of the Pathfinder mission systems would allow gravitational wave observations close to the original plan for the LISA Observatory.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    American Physical Society
    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

     
  • richardmitnick 8:53 pm on June 2, 2016 Permalink | Reply
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    From APS: “Advancing Beyond Advanced LIGO” 

    AmericanPhysicalSociety

    American Physical Society

    APS April Meeting 2016
    Gabriel Popkin

    1
    Contour lines show likelihood of where in the sky the black-hole merger GW159014 took place. Photo: LIGO

    Members of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration took a victory lap of sorts at the APS April Meeting 2016 in Salt Lake City, Utah.

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

    MIT Caltech  Advanced Ligo Hanford, WA, USA installation
    Caltech/MIT Advanced Ligo Hanford, WA, USA installation

    Talk after talk began with slides showing the now-famous signal from GW150914, the formal name for the September 14, 2015 detection of gravitational waves from two black holes that merged 1.3 billion years ago.

    “For the first time when I present this talk, I can start with a discovery, not just upper limits,” said Alessandra Corsi, an astrophysicist at Texas Tech University.

    But speakers quickly pivoted to new astrophysics emerging from GW150914 and LVT151012, a second candidate event that appeared in LIGO data but did not reach the critical “5-sigma” statistical threshold needed to claim a true detection. Researchers also shared new ideas for peering deeper into the universe and increasing the frequency spectrum that gravitational-wave detectors can probe.

    For astrophysics, GW150914 heralded a series of firsts — not just the first detection of a gravitational wave, but also the the first proof that black holes form merging pairs (only inspiraling neutron stars had been previously seen), and the first evidence of black holes more than 25 times the mass of the sun.

    Cornell SXS team. Two merging black holes simulation
    Cornell SXS team. Two merging black holes simulation

    The large sizes of the merging black holes also revealed that their source stars were low in heavy elements, and that their spins were substantially lower than the maximum possible value allowed under general relativity.

    The finding has also allowed scientists for the first time to test aspects of general relativity in the “strong-field regime” — the highly warped regions of spacetime near extremely dense objects. Astrophysicists have used GW150914 to place more stringent limits on a number of general relativity’s parameters, including the speed of gravitational waves and parameters related to the waves’ phase evolution, but so far Einstein’s theory continues to pass every test. “Don’t believe the New York Times — we did not prove that general relativity is correct,” said MIT physicist Salvatore Vitale. “We just found it’s consistent with our data.”

    Though it resolved some mysteries, the gravitational wave detection also opened up new ones. “The question that’s on everyone’s mind” now that one black hole pair has been found is how many are out there, said Chad Hanna, an astrophysicist at Pennsylvania State University. Based on one detection and one candidate event, LIGO scientists have shrunk the theoretically predicted range of between 0.1 and 1,000 black hole mergers per cubic gigaparsec of space per year (one gigaparsec equals 3.26 billion light-years) to a somewhat narrower 2 to 400. While that’s still a lot of wiggle room, Hanna said “0.1 is really off the table.”

    And more detections may soon constrain the rate further. LIGO’s first observing run lasted from September, 2015 to mid-January, 2016 (project leaders decided after the September 14 find to extend the original end date by about a month), but so far the collaboration has published results only from data taken through early October. Collaboration members were tightlipped about whether additional detections popped up in the more recently acquired data, promising an update within a month or two.

    Gamma-ray Intrigue

    Those new results could also help resolve another mystery. Using the time delay between when the gravitational wave arrived at the twin Hanford, Washington and Livingston, Louisiana detectors, LIGO scientists narrowed the location of the black hole pair to a banana-shaped region that represents around 1.5% of the sky, equivalent to the angular size of around 2,500 full moons. Scientists with NASA’s Fermi Gamma-ray Space Telescope then found in their data a candidate event from a region of sky that overlaps part of LIGO’s region, occurring only 0.4 seconds after the LIGO signal began.

    NASA/Fermi Telescope
    NASA/Fermi Telescope

    Though the gamma-ray signal has a 2 in 1,000 chance of being spurious — making it far less than a 5-sigma event — Fermi scientists published it in February on the arXiv.

    The possible coincidence of a gamma ray signal with GW150914 is intriguing, because leading theories do not predict that black hole mergers would produce electromagnetic radiation. Within days of the Fermi team’s announcement, theorists had posted a pile of papers on the arXiv proposing explanations for the gamma rays.

    But scientists are remaining cautious, because of the imprecise sky localizations of the two events, and because data from the European Space Agency’s (ESA’s) Integral satellite, which also looks for gamma rays, showed no hints of a detection.

    ESA/Integral
    ESA/Integral

    Right now scientists have “a big blob from LIGO, and a big blob from Fermi,” Texas Tech’s Corsi said. “I’m personally going to get convinced when I see more [gravitational wave and gamma-ray] associations.”

    Fermi team members are also remaining circumspect until LIGO releases more results. “We would not have reported this event just by itself, unless there was a gravitational-wave detection,” explained Adam Goldstein of the Marshall Space Flight Center in Huntsville, Alabama. But, he added, the data are public, and “the most appropriate people to do this particular, difficult, detailed analysis is the instrument team, so there was particular pressure on us.”

    Gaining a Better View

    Even before they finish analyzing their latest round of data, gravitational-wave scientists are looking toward the future. LIGO is in the midst of a long-planned series of upgrades known collectively as Advanced LIGO; improvements include increasing the laser power in the detector arms, “squeezing” the laser light to reduce quantum uncertainty, and developing new mirror coatings to reduce thermal noise. The detectors will eventually capture gravitational waves from more than 25 times as much space as they did in the first observing run, which was already a more than 25-fold increase over their original sensitivity. By 2018, collaboration members expect dozens of detections per year.

    And more detectors will soon join the network. The Virgo facility in Cascina, Italy is slated to come online late this year, though problems with the glass fibers that hold the detector’s mirrors have caused delays.

    VIRGO Gravitational Wave interferometer
    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    An underground, cryogenically cooled detector in Japan called KAGRA will become the world’s most sensitive starting around 2018.

    KAGRA
    KAGRA, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    And on March 31, officials from the U.S. National Science Foundation and India’s Department of Atomic Energy and Department of Science and Technology signed a memorandum of understanding to build a LIGO clone in India. The synchronous operation of detectors around the world will greatly improve how precisely scientists can resolve the origins of gravitational waves.

    Meanwhile, mindful of the time required to get a facility funded and built, researchers are already planning a “third generation” of detectors that could potentially scan almost the entire visible universe. The European Commission is studying the possibility of an experiment with 10-kilometer arms, proposed under the name “Einstein Telescope.”

    ASPERA Einstein Telescope
    ASPERA Einstein Telescope

    Syracuse University’s Stefan Ballmer noted that new facilities could deliver more bang for the buck by including two detectors with different orientations at one site, which would help scientists resolve gravitational waves’ polarizations — something LIGO alone was not able to do for GW150914.

    U.S. researchers also need to be thinking beyond LIGO, said Caltech astrophysicist Sheila Dwyer. She is part of a team preparing a proposal for a future facility, provisionally called “Cosmic Explorer,” which would have 40-kilometer arms. “We have a clear path for the next five to seven years with Advanced LIGO. But people were figuring that out 10, 15 years ago,” she said. “You have to think pretty far ahead.”

    Going into Space

    Amid the celebrations, astrophysicist Neil Cornish of Montana State University reminded his colleagues that there are some things LIGO and its earthbound partners will never do. Specifically, ground-based detectors cannot sense gravitational waves of frequencies below a few hertz, because they become swamped by seismic disturbances and the gravitational influence of objects moving on Earth.

    To escape this noisy environment, scientists have for 20 years developed plans for the Laser Interferometer Space Antenna (LISA), which would orbit the sun behind Earth, and send laser beams among three spacecrafts at a distance of a million kilometers or more from each other.

    ESA/LISA Pathfinder
    ESA/LISA Pathfinder

    ESA/LISA
    Proposed ESA/eLISA

    Such a detector could potentially capture thousands of signals per year from orbiting black hole and neutron star pairs, well before the final moments when ground-based detectors pick them up. “They’re really complementary,” Cornish said. “GW150914 would have been seen 5 to 10 years before in the LISA detector.”

    The ESA-led project has had more than its share of hiccups, however, with NASA initially committing and then in 2011 withdrawing as a partner. Currently a modified experiment called “evolved LISA,” or eLISA, is slated to fly in the mid-2030s, though Cornish thinks the LIGO detection could inspire NASA to get back in the game — or push China, which has expressed interest in a mission, to partner with ESA or launch its own satellites. Either could shorten the wait for a functioning space-based observatory.

    ESA’s LISA Pathfinder mission, which launched late last year and has already demonstrated that mirrors inside the spacecraft can be kept stable enough, could also provide a rationale for moving faster, says Cornish.

    Scientists are also pursuing a third gravitational wave search method that utilizes radio telescopes to search for small changes in the timing of rapidly rotating “millisecond pulsars” in our galaxy. Such changes are predicted to be produced by very low-frequency gravitational waves emitted from supermassive black hole pairs that result from mergers of distant galaxies. Project leaders predict a detection by early next decade.

    [A possible mission for the Event Horizon Telescope?

    Event Horizon Telescope map
    Event Horizon Telescope map

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL]

    One point of complete agreement among meeting attendees is that it’s a great time to be a gravitational-wave physicist. “I’m excited about all of [the proposed gravitational-wave detectors],” said Gabriela González, a physicist at Louisiana State University and LIGO spokesperson. Though the ultimate funding levels for new experiments remain to be seen, she said LIGO’s long-sought detection can only be a boost for the whole field. “We are more optimistic about the future now.”

    See the full article here .

    Please help promote STEM in your local schools.

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    American Physical Society
    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

     
  • richardmitnick 2:25 pm on February 12, 2015 Permalink | Reply
    Tags: , APS, ,   

    From APS: “Viewpoint: Making Waves with DNA” 

    AmericanPhysicalSociety

    American Physical Society

    February 9, 2015
    Irving R. Epstein

    Strands of DNA can be used to generate waves of chemical reactions with programmable shape and velocity.

    1
    Figure 1 Schematic view of the system studied by Zadorin et al. A single-stranded DNA (A) binds to one of the two complementary ends of the DNA template T. The resulting A:T complex uses the polymerase enzyme (pol) to generate another molecule of A on the template. A second enzyme (nick) facilitates the splitting of the two A molecules and their detachment from T. The net result is an “autocatalytic” reaction in which A catalyzes its own production: A+T+monomers→2A+T. By varying the concentration of DNA strands and enzymes, the authors were able to generate waves of chemical reactions with controllable shape and velocity.

    Research in chemistry can be roughly divided into two categories: analysis—the measurement of existing objects and phenomena—and synthesis—the construction of those objects and phenomena from simpler pieces. Typically, synthesis lags behind analysis: one first determines the formula of a molecule (and often its structure) before attempting to make it. However, as chemistry advances, investigators are increasingly attempting to synthesize first, designing chemical systems that realize desired phenomena. A team led by André Estevez-Torres at CNRS in France and co-workers has demonstrated an experimental toolkit that could be used for the rational engineering of nonlinear chemical effects in solution. Using DNA strands moving in a narrow channel and reacting under the action of enzymes, the authors are able to create chemical waves whose shapes and velocity can be finely controlled. Their setup could be programmed to yield a broad spectrum of other nonlinear phenomena in systems governed by a combination of chemical reactivity and molecular diffusion (“reaction-diffusion” systems).

    Nonlinear chemical dynamics characterizes many natural and industrial processes and is a quintessential feature of living organisms: most of their chemistry occurs far from equilibrium, has a nonlinear dependence on parameters like molecular concentrations, and may exhibit temporal oscillations (many biological functions are, for instance, synchronized to a 24-hour cycle). Researchers have applied a number of algorithms to design systems featuring such nonlinear behavior, engineering chemical oscillators (reactions in which the concentration of one or more components exhibits periodic changes), propagating reaction fronts or “Turing patterns” —spatial patterns of concentrations that, as Alan Turing proposed, might be related to biological morphogenesis (e.g., the formation of leopard spots or zebra stripes).

    But design algorithms are severely limited by the realities imposed by nature. One may write down a set of equations that generates a desired phenomenon, e.g., spatiotemporal chaos, for a set of reaction rates and diffusion coefficients. There is, however, no guarantee that an actual collection of molecules can be found that realizes the theorized behavior. For example, over the past several decades, researchers have successfully engineered, through systematic studies, new chemical oscillators with desired parameters for a variety of applications. These efforts have resulted in the discovery of several oscillators, but none of these oscillators “by design” has attained the importance of the Belousov-Zhabotinsky (BZ) reactions, a family of oscillating reactions (discovered serendipitously) that remains the most versatile and reliable chemical oscillator for most applications.

    Most efforts to design reaction-diffusion phenomena have utilized small inorganic molecules, largely because these substances are cheap, easy to work with, and produce visible color changes when they undergo reduction and oxidation (redox) reactions. Unfortunately, these reaction mixtures are typically not biocompatible, and they cannot be used in applications that place them in contact with components of living systems like proteins. The BZ reaction, for example, only works at acidity levels lethal to most biological cells.

    A solution may be offered by oligonucleotides (short single strands of DNA or RNA), which have been utilized as versatile building blocks for oscillators, computational elements, and structures with arbitrary shapes. In their new work, Estevez-Torres et al. have focused on dynamical aspects: They demonstrated that DNA strands can be used to realize an experimental model for reaction-diffusion systems whose spatiotemporal dynamics is fully controllable by programming three key elements of the system: the reaction rates, the diffusion coefficients, and the topology of the chemical reaction network (i.e., which reactions are linked to each other in ways that generate positive or negative feedback).

    Figure 1 shows a schematic of the authors’ setup: a linear channel in which they are able to generate traveling waves of chemical concentrations whose velocity can be precisely controlled. A single strand of DNA (A) can attach to either half of a complementary strand (T) to form a complex (A:T). In the presence of an enzyme (pol), the A:T complex serves as a template for growth of an additional A strand from monomeric precursors in the solution. A second “nicking” enzyme (nick) causes the two A molecules to detach from the T strand. The net result is an “autocatalytic” reaction in which A acts as a catalyst of its own production: A+T+monomers→2A+T

    It is known that autocatalytic reactions can generate chemical waves that travel with a characteristic velocity (ν) depending on the effective rate constant (k) for the reaction and the diffusion coefficient (D) of the autocatalyst (A in this case): ν=(kD)1/2. This idea has been exploited to generate a family of propagating acidity fronts in inorganic reactions, where the hydrogen ion (H+) was the autocatalyst. It was not possible, however, to control the velocity of those fronts, because the reaction rate depends on diffusion and the diffusion coefficient of H+ in water is fixed. Here, the authors are instead able to tune the effective rate constant k by varying the concentration of either the template or the enzyme. They can also control D, the effective diffusion rate of A (which depends on the diffusion rate of A relative to the A:T complex). By binding a heavy but chemically inert group C to T, they can reduce its diffusion rate and that of the complex without affecting its affinity to A. In other words, by choosing the concentrations of T, C, and pol, they can act on the two independent “control knobs” of the diffusion coefficient and the reaction rate constant. In this way, they can generate reaction waves with velocities that vary by as much as 3 orders of magnitude.

    What is exciting about this approach is that it is not limited to the generation of chemical waves. The scheme could be extended to generate any desired reaction-diffusion phenomenon for which one can write a set of elementary reactions. Turing patterns, for example, could be produced, as suggested by a previous study, by picking a slightly different reaction network, including an activator (like A in this case) but also an inhibitor that diffuses 1 order of magnitude faster than A. The “toolbox” employed by Estevez-Torres’ team, in which the activator species (A) can be slowed down by the massive inert group (C), already contains all elements needed to achieve the necessary range for diffusion coefficients.

    Approaches like the one explored by the authors, building on eons of evolution in the ability to control nucleic acids, suggest a bright future for this research line. The fact that DNA-based reactions are inherently biocompatible makes them attractive for potential applications, in particular if the system can be coupled to mechanical forces, as has been done for the BZ reaction. For example, one could envision inserting an anticancer drug into a DNA shell designed to undergo a mechanical deformation and release the drug when it encounters a molecule with a characteristic shape on the tumor surface.

    This research is published in Physical Review Letters.

    See the full article here.

    For those who are interested, the original article has a complete list of references and a numeric key for those references.

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

     
  • richardmitnick 12:53 pm on February 10, 2015 Permalink | Reply
    Tags: APS, Cold Atom Interferometer,   

    From APS: “Focus: A Better Quantum Gyroscope” 

    AmericanPhysicalSociety
    American Physical Society

    February 9, 2015
    Adam Mann

    An improved cold atom gyroscope could lead to portable, ultraprecise devices for navigation and tests of fundamental physics.

    1
    Rotation detection. In a cold atom gyroscope, atoms acting as waves travel along two paths (yellow) and are hit by laser pulses (red). In the new design, there are multiple laser pulses at each of the three interaction points, rather than a single pulse at each point. The extra pulses manipulate the atomic states and keep atoms on different paths in the same state for most of their trip, which reduces noise. The wave interference detected at the right in this design can determine the Earth’s rotation rate to an accuracy of 1%. NASA/P. Berg/Leibniz Univ. of Hannover

    An improved design for a rotation-measuring device based on cold atom clouds has twice the sensitivity of similar instruments and could, with further refinements, be among the best in the world, say its creators. The device is an atom interferometer, an instrument that makes use of the wave nature of atoms, and a team used it to measure the Earth’s rotation with an accuracy of about 1%. They say that because atom interferometers can be made small and portable, future versions could be used in extremely sensitive and stable gyroscopes for navigation onboard airplanes and ships. They could also make precise measurements of gravity and test the fundamentals of relativity theory.

    Researchers have used atom interferometers for precision measurements of gravity and rotation. Improvements in the technology could be useful for measuring continental drift rates and seismic shifts as well as providing an external check and backup to navigational technology such as GPS. The most accurate measurements of the Earth’s rotation come from large machines, but cold atom interferometers promise highly precise yet portable devices.

    The classical interferometer uses light waves. For example, in a Mach-Zehnder interferometer, a half-silvered mirror (“beam splitter”) splits a pulse of light in two and sends the beams in different directions. The pulses then hit other mirrors that direct them back toward one another, and they recombine at a second beam splitter, where the output light is detected. The two beams trace out a diamond shape, with each pulse following two sides. If one of the beams traveled slightly farther than the other, the waves in the two beams will be slightly out of phase when they meet, and they will partially cancel. The sensitivity of an interferometer depends on the wavelength, so researchers dramatically improve precision by using atoms, whose quantum nature produces much shorter wavelengths.

    In one version of an atom interferometer, a cloud of cold atoms is launched horizontally and is hit with a series of three laser pulses as it traverses the region being probed. The laser pulses play the roles of the mirrors and the two beam splitters of an optical interferometer. The first pulse puts the atoms into a quantum combination of two conditions—(1) deflecting to the left in the ground state and (2) deflecting to the right in an excited state. The second pulse deflects the two clouds back toward each other and swaps their quantum states, and the third combines the clouds in preparation for measurement of the number of atoms in the excited state. In an atom interferometer, the wave is an oscillating probability for atoms to be in this excited state, rather than an oscillating electric field, as in an optical interferometer. Because the Earth rotates, one of the clouds will travel slightly farther than the other, which will cause a partial cancellation of the probability waves and will affect the number of atoms measured at the end.

    One major source of error for previous atom interferometers was that the two clouds travel a relatively long distance while in different quantum states (ground and excited states). Outside forces, particularly magnetic fields, can affect the two clouds differently, introducing uncertainty (noise) into the measurement. A team led by Ernst Rasel of the Leibniz University of Hannover, Germany, was able to reduce this noise by arranging for both clouds to be in the ground state for most of the experiment, so that the two clouds were affected by outside forces in the same way. The team used multiple laser pulses at each of the three interaction points and generated only brief transitions between the two states.

    Based on their measurement of the Earth’s rotation rate to an accuracy of 1%, the team says their technique is twice as sensitive as state-of-the-art, cold-atom gyroscopes. They believe they can increase their sensitivity by at least ten times, equaling the best gyroscopes currently operating, but using an area of just 40mm2, compared with the 16m2 needed for the most sensitive gyroscopes. Hannover team member Peter Berg says the same technique could also improve experiments where a vertically oriented interferometer tests the equivalence of gravitational and inertial forces, a central principle of relativity. Holger Müller, of the University of California, Berkeley, says that by reducing one of the leading causes of error in atom interferometers, this type of work can help bring the technology out of the lab and into more general use.

    This research is published in Physical Review Letters.

    See the full article here.

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    STEM Icon

    American Physical Society
    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries.

     
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