5,678 research outputs found

    An experimental method for the in-situ observation of eutectic growth patterns in bulk samples of transparent alloys

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    We present an experimental method for the in-situ observation of directional-solidification fronts in bulk samples of transparent eutectic alloys. The growth front is observed obliquely in dark field through the liquid and a glass wall of the container with a long-distance microscope. We show that a focused image of the whole growth front can be obtained at a certain tilt angle of the microscope. At this tilt angle, eutectic fibers of about 3.5\mic in diameter can be clearly seen over the whole growth front in 400-\mic thick samples

    Langevin + Hydrodynamics Approach to Heavy Quark Propagation and Correlation in QGP

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    We develop a relativistic Langevin dynamics under the background of strongly interacting quark-gluon fluid described by the (3+1)-dimensional hydrodynamics. The drag force acting on charm and bottom quarks is parametrized according to the formula obtained from the anti-de-Sitter space/conformal field theory (AdS/CFT) correspondence. In this setup, we calculate the nuclear modification factor RAAR_{\rm{AA}} for the single-electrons from the charm and bottom quarks to extract the magnitude of the drag force from the PHENIX and STAR data. The RAAR_{\rm{AA}} for single-electrons with pT≥3p_{T}\geq 3 GeV indicates that the drag force is close to the AdS/CFT prediction. Effects of the drag force on the elliptic flow of single-electrons are also discussed. Moreover, we predict the electron-muon correlation which is closely related to the heavy-quark pair correlation in hot matter.Comment: 4 pages, 2 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

    A Simplified Approach to Analyzing Multi-regional Core-Periphery Models

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    This paper shows that the evolutionary process of spatial agglomeration in multi-regional core-periphery models can be explained analytically by a much simpler method than the continuous space approach of Krugman (1996). The proposed method overcomes the limitations of Turing's approach which has been applied to continuous space models. In particular, it allows us not only to examine whether or not agglomeration of mobile factors emerges from a uniform distribution, but also to trace the evolution of spatial agglomeration patterns (i.e., bifurcations from various polycentric patterns as well as from a uniform pattern) with decreases in transportation cost.agglomeration; core-periphery model; multi-regional; stability; bifurcation

    Spatial Period-Doubling Agglomeration of a Core-Periphery Model with a System of Cities

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    The orientation and progress of spatial agglomeration for Krugman's core--periphery model are investigated in this paper. Possible agglomeration patterns for a system of cities spread uniformly on a circle are set forth theoretically. For example, a possible and most likely course predicted for eight cities is a gradual and successive one---concentration into four cities and then into two cities en route to a single city. The existence of this course is ensured by numerical simulation for the model. Such gradual and successive agglomeration, which is called spatial-period doubling, presents a sharp contrast with the agglomeration of two cities, for which spontaneous concentration to a single city is observed in models of various kinds. It exercises caution about the adequacy of the two cities as a platform of the spatial agglomerations and demonstrates the need of the study on a system of cities

    A new relativistic hydrodynamics code for high-energy heavy-ion collisions

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    We construct a new Godunov type relativistic hydrodynamics code in Milne coordinates, using a Riemann solver based on the two-shock approximation which is stable under the existence of large shock waves. We check the correctness of the numerical algorithm by comparing numerical calculations and analytical solutions in various problems, such as shock tubes, expansion of matter into the vacuum, the Landau-Khalatnikov solution, and propagation of fluctuations around Bjorken flow and Gubser flow. We investigate the energy and momentum conservation property of our code in a test problem of longitudinal hydrodynamic expansion with an initial condition for high-energy heavy-ion collisions. We also discuss numerical viscosity in the test problems of expansion of matter into the vacuum and conservation properties. Furthermore, we discuss how the numerical stability is affected by the source terms of relativistic numerical hydrodynamics in Milne coordinates.Comment: 20 pages, 16 figure
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