1,914 research outputs found

    2008src0864

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    Holographic Screening Length in a Hot Plasma of Two Sphere

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    We study the screening length of a quark-antiquark pair moving in a hot plasma living in two sphere S2S^2 manifold using AdS/CFT correspondence where the background metric is four dimensional Schwarzschild-AdS black hole. The geodesic solution of the string ends at the boundary is given by a stationary motion in the equatorial plane as such the separation length LL of quark-antiquark pair is parallel to the angular velocity ω\omega. The screening length and the bound energy are computed numerically using Mathematica. We find that the plots are bounded from below by some functions related to the momentum transfer PcP_c of the drag force configuration. We compare the result by computing the screening length in the quark-antiquark reference frame where the gravity dual are "Boost-AdS" and Kerr-AdS black holes. Finding relations of the parameters of both black holes, we argue that the relation between mass parameters MSchM_{Sch} of the Schwarzschild-AdS black hole and MKerrM_{Kerr} of the Kerr-AdS black hole in high temperature is given by MKerr=MSch(1−a2l2)3/2M_{Kerr}=M_{Sch}(1-a^2l^2)^{3/2}, where aa is the angular momentum parameter.Comment: Major revision: title changed, adding authors, 13 pages, 8 figures, etc. Accepted for publication in European Physical Journal

    Local free-fall temperature of a RN-AdS black hole

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    We use the global embedding Minkowski space (GEMS) geometries of a (3+1)-dimensional curved Reissner-Nordstr\"om(RN)-AdS black hole spacetime into a (5+2)-dimensional flat spacetime to define a proper local temperature, which remains finite at the event horizon, for freely falling observers outside a static black hole. Our extended results include the known limiting cases of the RN, Schwarzschild--AdS, and Schwarzschild black holes.Comment: 18 pages, 11 figures, version to appear in Int. J. Mod. Phys.

    Gravity and Nonequilibrium Thermodynamics of Classical Matter

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    Renewed interest in deriving gravity (more precisely, the Einstein equations) from thermodynamics considerations [1, 2] is stirred up by a recent proposal that 'gravity is an entropic force' [3] (see also [4]). Even though I find the arguments justifying such a claim in this latest proposal rather ad hoc and simplistic compared to the original one I would unreservedly support the call to explore deeper the relation between gravity and thermodynamics, this having the same spirit as my long-held view that general relativity is the hydrodynamic limit [5, 6] of some underlying theories for the microscopic structure of spacetime - all these proposals, together with that of [7, 8], attest to the emergent nature of gravity [9]. In this first paper of two we set the modest goal of studying the nonequilibrium thermodynamics of classical matter only, bringing afore some interesting prior results, without invoking any quantum considerations such as Bekenstein-Hawking entropy, holography or Unruh effect. This is for the sake of understanding the nonequilibrium nature of classical gravity which is at the root of many salient features of black hole physics. One important property of gravitational systems, from self-gravitating gas to black holes, is their negative heat capacity, which is the source of many out-of-the ordinary dynamical and thermodynamic features such as the non-existence in isolated systems of thermodynamically stable configurations, which actually provides the condition for gravitational stability. A related property is that, being systems with long range interaction, they are nonextensive and relax extremely slowly towards equilibrium. Here we explore how much of the known features of black hole thermodynamics can be derived from this classical nonequilibrium perspective. A sequel paper will address gravity and nonequilibrium thermodynamics of quantum fields [10].Comment: 25 pages essay. Invited Talk at Mariofest, March 2010, Rosario, Argentina. Festschrift to appear as an issue of IJMP

    Residents\u27 Confidence Providing Primary Care With Behavioral Health Integration

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    BACKGROUND AND OBJECTIVES: Behavioral health integration (BHI) entails integrated behavioral health clinicians (IBHCs) providing care-generally for mental health and substance abuse disorders and behavioral comorbidity- within the operational functioning of primary care. Because limited data exist regarding BHI in residency, we studied its impact on resident education by examining whether increased behavioral health (BH) co-management improved residents\u27 perceived ability to treat BH conditions. METHODS: We included residents from internal and family medicine training programs using BHI in residents\u27 continuity clinics and assessed the level of co-management between primary care and IBHCs and the following domains: (1) confidence in managing BH conditions, (2) barriers to BH provision, (3) perception of autonomy when working with IBHCs, (4) satisfaction with the clinic, and (5) perceived educational value of BH learning modes. RESULTS: Altogether, 117 residents participated in our survey (73.1% response rate). Residents who had co-managed \u3e /= five patients alongside IBHCs reported significantly higher confidence than those who had co-managed andlt; five patients with BH conditions. The association remained significant after adjustment for residents\u27 level of training and specialty. In rating BH learning modes, residents rated most highly active collaboration with IBHCs and observation with feedback from clinic preceptors. CONCLUSIONS: BHI training within residency enhances perceived learning and confidence in providing BH care

    Single-Step Methylation of Chitosan Using Dimethyl Carbonate as a Green Methylating Agent

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    N,N,N-Trimethyl chitosan (TMC) is one chitosan derivative that, because of its improved solubility, has been studied for industrial and pharmaceutic applications. Conventional methods for the synthesis of TMC involve the use of highly toxic and harmful reagents, such as methyl iodide and dimethyl sulfate (DMS). Although the methylation of dimethylated chitosan to TMC by dimethyl carbonate (DMC, a green and benign methylating agent) was reported recently, it involved a formaldehyde-based procedure. In this paper we report the single-step synthesis of TMC from chitosan using DMC in an ionic liquid. The TMC synthesised was characterised by 1H NMR spectroscopy and a functionally meaningful degree of quaternisation of 9% was demonstrated after a 12-h reaction time

    Real-time Stereo Visual Servoing for Rose Pruning with Robotic Arm

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    The paper presents a working pipeline which integrates hardware and software in an automated robotic rose cutter. To the best of our knowledge, this is the first robot able to prune rose bushes in a natural environment. Unlike similar approaches like tree stem cutting, the proposed method does not require to scan the full plant, have multiple cameras around the bush, or assume that a stem does not move. It relies on a single stereo camera mounted on the end-effector of the robot and real-time visual servoing to navigate to the desired cutting location on the stem. The evaluation of the whole pipeline shows a good performance in a garden with unconstrained conditions, where finding and approaching a specific location on a stem is challenging due to occlusions caused by other stems and dynamic changes caused by the win

    Dimethylsulfide oxidation over the tropical South Atlantic: OH and other oxidants

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    The general course of events in the formation of a marine cloud begins with the emission of species which can eventually serve as nuclei around which water can condense to form a cloud droplet. In remote marine regions, cloud condensation nuclei (CCN) are primarily composed of sulfate, in either its acid or ammonium salt form. Most sulfate in these regions is the product of atmospheric oxidation of dimethyl sulfide (DMS), a reduced sulfur gas that is released by phytoplankton at the ocean surface. Therefore, in order to effectively quantify the links in the cloud-formation cycle, one must begin with a well-defined description of the atmospheric chemistry of DMS. The intent of this project has been to initiate development of a comprehensive model of the chemistry and dynamics responsible for the formation of clouds in the remote marine boundary layer. The primary tool in this work has been the Global/Regional Atmospheric Chemistry Event Simulator (GRACES), a global atmospheric chemistry model, which is under development within the Atmospheric Chemistry and Dynamics Branch of NASA-Ames Research Center. In this effort, GRACES was used to explore the first chemical link between DMS and sulfate by modeling the diurnal variation of DMS
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