940 research outputs found

    A Pinned Polymer Model of Posture Control

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    A phenomenological model of human posture control is posited. The dynamics are modelled as an elastically pinned polymer under the influence of noise. The model accurately reproduces the two-point correlation functions of experimental posture data and makes predictions for the response function of the postural control system. The physiological and clinical significance of the model is discussed.Comment: uuencoded post script file, 17 pages with 3 figure

    Mesenteric Thrombosis Complicating Influenza B Infection

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    To the Editor: A 44-year-old healthy, active man presented to an outside hospital complaining of a 1-day history of fever up to 39ïżœC, muscle aches, sinus pressure, nausea, vomiting, and diarrhea in April 2015. Review of systems was negative for abdominal pain, hematochezia, or melena. A chest radiograph was negative for infiltration, consolidation, edema, or other pathology. Lipase level was 37 U/L (within normal limits). A nasopharyngeal swab antigen test was positive for influenza B, and the patient was discharged on oseltamivir. Three days later, intermittent fevers persisted with chills, nausea, vomiting, and severe abdominal pain. Anorexia developed, and the patient described “something twisting and pulling at [his] insides.” An abdominal computed tomography scan showed extensive superior mesenteric vein thrombosis, which extended into the main portal vein and proximal splenic vein. He was transferred to our facility for transhepatic thrombolysis, which was complicated by intrahepatic hematoma requiring subselective hepatic artery embolization. He recovered completely and was discharged with rivaroxaban. Hematology evaluation was negative for predisposing hypercoagulable conditions including factor II mutation, factor V Leiden, and lupus anticoagulant. Of note, his past medical, surgical, and family history were unrevealing for malignancy, coagulopathy, cirrhosis, pancreatitis, or other prothrombotic states

    Exact steady state solution of the Boltzmann equation: A driven 1-D inelastic Maxwell gas

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    The exact nonequilibrium steady state solution of the nonlinear Boltzmann equation for a driven inelastic Maxwell model was obtained by Ben-Naim and Krapivsky [Phys. Rev. E 61, R5 (2000)] in the form of an infinite product for the Fourier transform of the distribution function f(c)f(c). In this paper we have inverted the Fourier transform to express f(c)f(c) in the form of an infinite series of exponentially decaying terms. The dominant high energy tail is exponential, f(c)≃A0exp⁥(−a∣c∣)f(c)\simeq A_0\exp(-a|c|), where a≡2/1−α2a\equiv 2/\sqrt{1-\alpha^2} and the amplitude A0A_0 is given in terms of a converging sum. This is explicitly shown in the totally inelastic limit (α→0\alpha\to 0) and in the quasi-elastic limit (α→1\alpha\to 1). In the latter case, the distribution is dominated by a Maxwellian for a very wide range of velocities, but a crossover from a Maxwellian to an exponential high energy tail exists for velocities ∣c−c0âˆŁâˆŒ1/q|c-c_0|\sim 1/\sqrt{q} around a crossover velocity c0≃ln⁥q−1/qc_0\simeq \ln q^{-1}/\sqrt{q}, where q≡(1−α)/2â‰Ș1q\equiv (1-\alpha)/2\ll 1. In this crossover region the distribution function is extremely small, ln⁥f(c0)≃q−1ln⁥q\ln f(c_0)\simeq q^{-1}\ln q.Comment: 11 pages, 4 figures; a table and a few references added; to be published in PR

    Setting the stage for individualized therapy in hemophilia: what role can pharmacokinetics play?

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    Replacement therapy with clotting factor concentrates (CFC) is the mainstay of treatment in hemophilia. Its widespread application has led to a dramatic decrease in morbidity and mortality in patients, with concomitant improvement of quality of life. However, dosing is challenging and costs are high. This review discusses benefits and limitations of pharmacokinetic (PK)-guided dosing of replacement therapy as an alternative for current dosing regimens. Dosing of CFC is now primarily based on body weight and based on its in vivo recovery (IVR). Benefits of PK-guided dosing include individualization of treatment with better targeting, more flexible blood sampling, increased insight into association of coagulation factor levels and bleeding, and potential overall lowering of overall costs. Limitations include a slight burden for the patient, and availability of closely collaborating, experienced clinical pharmacologists

    Monte-Carlo Event Generators at NLO

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    A method to construct Monte-Carlo event generators at arbitrarily non-leading order is explained for the case of a non-gauge theory. A precise and correct treatment of parton kinematics is provided. Modifications of the conventional formalism are required: parton showering is not exactly the same as DGLAP evolution, and the external line prescription for the hard scattering differs from the LSZ prescription. The prospects for extending the results to QCD are discussed.Comment: 57 pages, 16 eps figures, revtex

    Correcting the Colour-Dipole Cascade Model with Fixed Order Matrix Elements

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    An algorithm is presented in which the Colour-Dipole Cascade Model as implemented in the Ariadne program is corrected to match the fixed order tree-level matrix elements for e+e- -> n jets. The result is a full parton level generator for e+e- annihilation where the generated states are correct on tree-level to fixed order in alpha_S and to all orders with modified leading logarithmic (MLLA) accuracy. In this paper, matrix elements are used up to second order in alpha_S, but the scheme is applicable also for higher orders. An improvement to also include exact virtual corrections to fixed order is suggested and the possibility to extend the scheme to hadronic collisions is discussed

    Factorization constraints for soft anomalous dimensions in QCD scattering amplitudes

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    We study the factorization of soft and collinear singularities in dimensionally-regularized fixed-angle scattering amplitudes in massless gauge theories. Our factorization is based on replacing the hard massless partons by light-like Wilson lines, and defining gauge-invariant jet and soft functions in dimensional regularization. In this scheme the factorized amplitude admits a powerful symmetry: it is invariant under rescaling of individual Wilson-line velocities. This symmetry is broken by cusp singularities in both the soft and the eikonal jet functions. We show that the cancellation of these cusp anomalies in any multi-leg amplitude imposes all-order constraints on the kinematic dependence of the corresponding soft anomalous dimension, relating it to the cusp anomalous dimension. For amplitudes with two or three hard partons the solution is unique: the constraints fully determine the kinematic dependence of the soft function. For amplitudes with four or more hard partons we present a minimal solution where the soft anomalous dimension is a sum over colour dipoles, multiplied by the cusp anomalous dimension. In this case additional contributions to the soft anomalous dimension at three loops or beyond are not excluded, but they are constrained to be functions of conformal cross ratios of kinematic variables.Comment: v1: 35 pages, v2: minor changes - some clarifying remarks and references added. Journal version (to appear in JHEP

    Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)

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    We present a next-to-leading order QCD calculation for single-inclusive high-p_T jet production in longitudinally polarized pp collisions within the ``small-cone'' approximation. The fully analytical expressions obtained for the underlying partonic hard-scattering cross sections greatly facilitate the analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet} for this process in terms of the unknown polarization of gluons in the nucleon. We simultaneously rederive the corresponding QCD corrections to unpolarized scattering and confirm the results existing in the literature. We also numerically compare to results obtained with Monte-Carlo methods and assess the range of validity of the ``small-cone'' approximation for the kinematics relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure

    Single photon emitters based on Ni/Si related defects in single crystalline diamond

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    We present investigations on single Ni/Si related color centers produced via ion implantation into single crystalline type IIa CVD diamond. Testing different ion dose combinations we show that there is an upper limit for both the Ni and the Si dose 10^12/cm^2 and 10^10/cm^2 resp.) due to creation of excess fluorescent background. We demonstrate creation of Ni/Si related centers showing emission in the spectral range between 767nm and 775nm and narrow line-widths of 2nm FWHM at room temperature. Measurements of the intensity auto-correlation functions prove single-photon emission. The investigated color centers can be coarsely divided into two groups: Drawing from photon statistics and the degree of polarization in excitation and emission we find that some color centers behave as two-level, single-dipole systems whereas other centers exhibit three levels and contributions from two orthogonal dipoles. In addition, some color centers feature stable and bright emission with saturation count rates up to 78kcounts/s whereas others show fluctuating count rates and three-level blinking.Comment: 7 pages, submitted to Applied Physics B, revised versio
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