566 research outputs found

    Triggering synchronized oscillations through arbitrarily weak diversity in close-to-threshold excitable media

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    It is shown that arbitrarily weak (frozen) heterogeneity can induce global synchronized oscillations in excitable media close to threshold. The work is carried out on networks of coupled van der Pol-FitzHugh-Nagumo oscillators. The result is shown to be robust against the presence of internal dynamical noise.Comment: 4 pages (RevTeX 3 style), 5 EPS figures, submitted to Phys. Rev. E (16 aug 2001

    Afforestation Effects on Soil Carbon Storage in the United States: A Synthesis

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    Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152514/1/saj2sssaj20120236.pd

    Emergent global oscillations in heterogeneous excitable media: The example of pancreatic beta cells

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    Using the standard van der Pol-FitzHugh-Nagumo excitable medium model I demonstrate a novel generic mechanism, diversity, that provokes the emergence of global oscillations from individually quiescent elements in heterogeneous excitable media. This mechanism may be operating in the mammalian pancreas, where excitable beta cells, quiescent when isolated, are found to oscillate when coupled despite the absence of a pacemaker region.Comment: See home page http://lec.ugr.es/~julya

    Hole concentration and phonon renormalization in Ca-doped YBa_2Cu_3O_y (6.76 < y < 7.00)

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    In order to access the overdoped regime of the YBa_2Cu_3O_y phase diagram, 2% Ca is substituted for Y in YBa_2Cu_3O_y (y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Delta \omega) and linewidth (\Delta 2\gamma) of the 340 cm^{-1} B_{1g} phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration (p), and not simply the oxygen content. The changes in \Delta \omega with p imply that the superconducting gap (\Delta_{max}) decreases monotonically with increasing hole concentration in the overdoped regime, and \Delta \omega falls to zero in the underdoped regime. The linewidth renormalization \Delta 2\gamma is negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.Comment: 18 pages; 5 figures; submitted to Phys. Rev. B Oct. 24, 2002 (BX8292

    Magnetic Field Effects on the Far-Infrared Absorption in Mn_12-acetate

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    We report the far-infrared spectra of the molecular nanomagnet Mn_12-acetate (Mn_12) as a function of temperature (5-300 K) and magnetic field (0-17 T). The large number of observed vibrational modes is related to the low symmetry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular dynamics simulations and model compound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involving intramolecular vibrations of the Mn_12 molecule centered at 284, 306 and 409 cm-1 show changes with applied magnetic field. The structure near 284 cm1^{-1} displays the largest deviation with field and is mainly intensity related. A comparison between the temperature dependent absorption difference spectra, the gradual low-temperature cluster framework distortion as assessed by neutron diffraction data, and field dependent absorption difference spectra suggests that this mode may involve Mn motion in the crown.Comment: 5 pages, 4 figures, PRB accepte

    National Register Testing At Sites 41BP585, 41BP594, And 41BP595 Three Oaks Mine, Bastrop County, Texas

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    Between October 2012 and July 2013, Atkins conducted National Register of Historic Places (NRHP) eligibility testing at historic sites 41BP585 and 41BP594 and prehistoric site 41BP595, located within the Three Oaks Mine in Bastrop County, Texas, which is owned and operated by Luminant. Impacts to all three sites are anticipated as a result of planned mine development. This work was conducted under the direction of Principal Investigator David L. Sherman. This report of investigations was written at Atkins and is being finalized by Blanton & Associates, with David L. Sherman remaining as the Principal Investigator. This work demonstrated that significant archeological deposits that may contribute to the overall NRHP eligibility statuses of the two historic sites are absent at both sites. Standing architecture at 41BP594, however, has previously been determined to be eligible for listing on the NRHP (Martin 2001). Archival research conducted as part of the current investigation into the histories of the historic sites remains inconclusive with respect to the identity of their 1870s and earlier occupants. Testing at prehistoric site 41BP595 indicated it resulted from multiple occupational episodes during the period from the late Paleoindian to the Late Prehistoric. Shovel testing and mechanical trenching revealed the presence of an expansive buried anthrogenic A soil horizon, or midden, replete with preserved subsistence remains. Mechanical trenching also exposed a variety of burned rock cooking facilities partially surrounding the midden area. Radiocarbon assays of burned nut shells recovered from feature contexts, along with the assemblage of diagnostic lithic artifacts, suggest the site was most intensively occupied from the Late Archaic to the early Late Prehistoric. A suite of special studies was conducted on burned rock samples recovered from four of the better-preserved burned rock features. These studies, which include residue, starch, and phytolith analysis, suggest that the burned rock features were used in part to process tubers/roots and grass seeds for subsistence. Macrobotanical analysis of flotation samples recovered from feature contexts identified spent fuel remains including oak and hickory wood and subsistence remains including oak, hickory, black walnut, and acorn burned nut shells. A small amount of burned bulb, possibly representing wild onion, was also recovered through flotation. These findings suggest that significant archeological deposits important to understanding the Late Archaic to early Late Prehistoric period have been preserved at 41BP595

    An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics

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    For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types

    Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

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    We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters
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