The Experts below are selected from a list of 29742 Experts worldwide ranked by ideXlab platform
Jinfeng Liao - One of the best experts on this subject based on the ideXlab platform.
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gluon transport equation with effective mass and dynamical onset of bose einstein condensation
Nuclear Physics, 2016Co-Authors: Jeanpaul Blaizot, Yin Jiang, Jinfeng LiaoAbstract:Abstract We study the transport equation describing a dense system of gluons, in the small scattering Angle Approximation, taking into account medium-generated effective masses of the gluons. We focus on the case of overpopulated systems that are driven to Bose–Einstein condensation on their way to thermalization. The presence of a mass modifies the dispersion relation of the gluon, as compared to the massless case, but it is shown that this does not change qualitatively the scaling behavior in the vicinity of the onset.
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Gluon Transport Equations with Condensate in the Small Angle Approximation
2015Co-Authors: Jeanpaul Blaizot, Jinfeng LiaoAbstract:We derive the set of kinetic equations that control the evolution of gluons in the presence of a condensate. We show that the dominant singularities remain logarithmic when the scattering involves particles in the condensate. This allows us to define a consistent small Angle Approximation.
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gluon transport equation in the small Angle Approximation and the onset of bose einstein condensation
Nuclear Physics, 2013Co-Authors: Jeanpaul Blaizot, Jinfeng Liao, Larry MclerranAbstract:Abstract In this paper, we study the evolution of a dense system of gluons, such as those produced in the early stages of ultra-relativistic heavy ion collisions. We describe the approach to thermal equilibrium using the small Angle Approximation for gluon scattering in a Boltzmann equation that includes the effects of Bose statistics. In the present study we ignore the effect of the longitudinal expansion, i.e., we restrict ourselves to spatially uniform systems, with spherically symmetric momentum distributions. Furthermore we take into account only elastic scattering, i.e., we neglect inelastic, number changing, processes. We solve the transport equation for various initial conditions that correspond to small or large initial gluon phase-space densities. For a small initial phase-space density, the system evolves towards thermal equilibrium, as expected. For a large enough initial phase-space density the equilibrium state contains a Bose condensate. We present numerical evidence that such over-populated systems reach the onset of Bose–Einstein condensation in a finite time. The approach to condensation is characterized by a scaling behavior that we briefly analyze.
Jeanpaul Blaizot - One of the best experts on this subject based on the ideXlab platform.
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Angular mode expansion of the Boltzmann equation in the small-Angle Approximation
Nucl.Phys.A, 2019Co-Authors: Jeanpaul Blaizot, Naoto TanjiAbstract:We use an expansion in angular mode functions in order to solve the Boltzmann equation for a gluon plasma undergoing longitudinal expansion. By comparing with the exact solution obtained numerically by other means we show that the expansion in mode functions converges rapidly for all cases of practical interest, and represents a substantial gain in numerical effort as compared to more standard methods. We contrast the cases of a non expanding plasma and of longitudinally expanding plasmas, and follow in both cases the evolutions towards thermalization. In the latter case, we observe that, although the spherical mode function appears to be well reproduced after some time by a local equilibrium distribution function depending on slowly varying temperature and chemical potential, thereby suggesting thermalization of the system, the longitudinal and transverse pressures take more time to equilibrate. This is because the expansion hinders the relaxation of the first angular mode function. This feature was also observed in a simpler context where the Boltzmann equation is solved in terms of special moments within the relaxation time Approximation, and attributed there to the particular coupling between the first two moments of the distribution function. The present analysis confirms this observation in a more realistic setting.
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gluon transport equation with effective mass and dynamical onset of bose einstein condensation
Nuclear Physics, 2016Co-Authors: Jeanpaul Blaizot, Yin Jiang, Jinfeng LiaoAbstract:Abstract We study the transport equation describing a dense system of gluons, in the small scattering Angle Approximation, taking into account medium-generated effective masses of the gluons. We focus on the case of overpopulated systems that are driven to Bose–Einstein condensation on their way to thermalization. The presence of a mass modifies the dispersion relation of the gluon, as compared to the massless case, but it is shown that this does not change qualitatively the scaling behavior in the vicinity of the onset.
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Gluon Transport Equations with Condensate in the Small Angle Approximation
2015Co-Authors: Jeanpaul Blaizot, Jinfeng LiaoAbstract:We derive the set of kinetic equations that control the evolution of gluons in the presence of a condensate. We show that the dominant singularities remain logarithmic when the scattering involves particles in the condensate. This allows us to define a consistent small Angle Approximation.
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gluon transport equation in the small Angle Approximation and the onset of bose einstein condensation
Nuclear Physics, 2013Co-Authors: Jeanpaul Blaizot, Jinfeng Liao, Larry MclerranAbstract:Abstract In this paper, we study the evolution of a dense system of gluons, such as those produced in the early stages of ultra-relativistic heavy ion collisions. We describe the approach to thermal equilibrium using the small Angle Approximation for gluon scattering in a Boltzmann equation that includes the effects of Bose statistics. In the present study we ignore the effect of the longitudinal expansion, i.e., we restrict ourselves to spatially uniform systems, with spherically symmetric momentum distributions. Furthermore we take into account only elastic scattering, i.e., we neglect inelastic, number changing, processes. We solve the transport equation for various initial conditions that correspond to small or large initial gluon phase-space densities. For a small initial phase-space density, the system evolves towards thermal equilibrium, as expected. For a large enough initial phase-space density the equilibrium state contains a Bose condensate. We present numerical evidence that such over-populated systems reach the onset of Bose–Einstein condensation in a finite time. The approach to condensation is characterized by a scaling behavior that we briefly analyze.
David J Smith - One of the best experts on this subject based on the ideXlab platform.
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model based image analysis of a tethered brownian fibre for shear stress sensing
Journal of the Royal Society Interface, 2017Co-Authors: Meurig Thomas Gallagher, Cara Victoria Neal, Kenton P Arkill, David J SmithAbstract:The measurement of fluid dynamic shear stress acting on a biologically relevant surface is a challenging problem, particularly in the complex environment of, for example, the vasculature. While an experimental method for the direct detection of wall shear stress via the imaging of a synthetic biology nanorod has recently been developed, the data interpretation so far has been limited to phenomenological random walk modelling, small-Angle Approximation, and image analysis techniques which do not take into account the production of an image from a three-dimensional subject. In this report, we develop a mathematical and statistical framework to estimate shear stress from rapid imaging sequences based firstly on stochastic modelling of the dynamics of a tethered Brownian fibre in shear flow, and secondly on a novel model-based image analysis, which reconstructs fibre positions by solving the inverse problem of image formation. This framework is tested on experimental data, providing the first mechanistically rational analysis of the novel assay. What follows further develops the established theory for an untethered particle in a semi-dilute suspension, which is of relevance to, for example, the study of Brownian nanowires without flow, and presents new ideas in the field of multi-disciplinary image analysis.
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model based image analysis of a tethered brownian fibre for shear stress sensing
arXiv: Quantitative Methods, 2017Co-Authors: Meurig Thomas Gallagher, Cara Victoria Neal, Kenton P Arkill, David J SmithAbstract:The measurement of shear stress acting on a biologically relevant surface is a challenging problem, particularly in the complex environment of, for example, the vasculature. While an experimental method for the direct detection of wall shear stress via the imaging of a synthetic biology nanorod has recently been developed, the data interpretation so far has been limited to phenomenological random walk modelling, small Angle Approximation, and image analysis techniques which do not take into account the production of an image from a 3D subject. In this report we develop a mathematical and statistical framework to estimate shear stress from rapid imaging sequences based firstly on stochastic modelling of the dynamics of a tethered Brownian fibre in shear flow, and secondly on novel model-based image analysis, which reconstructs phage positions by solving the inverse problem of image formation. This framework is tested on experimental data, providing the first mechanistically rational analysis of the novel assay. What follows further develops the established theory for an untethered particle in a semi-dilute suspension, which is of relevance to, for example, the study of Brownian nanowires without flow, and presents new ideas in the field of multidisciplinary image analysis.
Kenton P Arkill - One of the best experts on this subject based on the ideXlab platform.
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model based image analysis of a tethered brownian fibre for shear stress sensing
Journal of the Royal Society Interface, 2017Co-Authors: Meurig Thomas Gallagher, Cara Victoria Neal, Kenton P Arkill, David J SmithAbstract:The measurement of fluid dynamic shear stress acting on a biologically relevant surface is a challenging problem, particularly in the complex environment of, for example, the vasculature. While an experimental method for the direct detection of wall shear stress via the imaging of a synthetic biology nanorod has recently been developed, the data interpretation so far has been limited to phenomenological random walk modelling, small-Angle Approximation, and image analysis techniques which do not take into account the production of an image from a three-dimensional subject. In this report, we develop a mathematical and statistical framework to estimate shear stress from rapid imaging sequences based firstly on stochastic modelling of the dynamics of a tethered Brownian fibre in shear flow, and secondly on a novel model-based image analysis, which reconstructs fibre positions by solving the inverse problem of image formation. This framework is tested on experimental data, providing the first mechanistically rational analysis of the novel assay. What follows further develops the established theory for an untethered particle in a semi-dilute suspension, which is of relevance to, for example, the study of Brownian nanowires without flow, and presents new ideas in the field of multi-disciplinary image analysis.
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model based image analysis of a tethered brownian fibre for shear stress sensing
arXiv: Quantitative Methods, 2017Co-Authors: Meurig Thomas Gallagher, Cara Victoria Neal, Kenton P Arkill, David J SmithAbstract:The measurement of shear stress acting on a biologically relevant surface is a challenging problem, particularly in the complex environment of, for example, the vasculature. While an experimental method for the direct detection of wall shear stress via the imaging of a synthetic biology nanorod has recently been developed, the data interpretation so far has been limited to phenomenological random walk modelling, small Angle Approximation, and image analysis techniques which do not take into account the production of an image from a 3D subject. In this report we develop a mathematical and statistical framework to estimate shear stress from rapid imaging sequences based firstly on stochastic modelling of the dynamics of a tethered Brownian fibre in shear flow, and secondly on novel model-based image analysis, which reconstructs phage positions by solving the inverse problem of image formation. This framework is tested on experimental data, providing the first mechanistically rational analysis of the novel assay. What follows further develops the established theory for an untethered particle in a semi-dilute suspension, which is of relevance to, for example, the study of Brownian nanowires without flow, and presents new ideas in the field of multidisciplinary image analysis.
Alice K Harding - One of the best experts on this subject based on the ideXlab platform.
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high altitude particle acceleration and radiation in pulsar slot gaps
arXiv: Astrophysics, 2004Co-Authors: Alex G Muslimov, Alice K HardingAbstract:We explore the pulsar slot gap electrodynamics up to very high altitudes, where for most relatively rapidly rotating pulsars both the standard small-Angle Approximation and the assumption that the magnetic field lines are ideal stream lines break down. We address the importance of the electrodynamic conditions at the slot gap boundaries and the occurrence of a steady-state drift of charged particles across the slot gap field lines at very high altitudes. These boundary conditions and the deviation of particle trajectories from stream lines determine the asymptotic behavior of the scalar potential at all radii from the polar cap to near the light cylinder. As a result, we demonstrate that the steady-state accelerating electric field must approach a small and constant value at high altitude above the polar cap. This parallel electric field is capable of maintaining electrons moving with high Lorentz factors (a few times 10^7) and emitting curvature gamma-ray photons up to nearly the light cylinder. By numerical simulations, we show that primary electrons accelerating from the polar cap surface to high altitude in the slot gap along the outer edge of the open field region will form caustic emission patterns on the trailing dipole field lines. Acceleration and emission in such an extended slot gap may form the physical basis of a model that can successfully reproduce some pulsar high-energy light curves.
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high altitude particle acceleration and radiation in pulsar slot gaps
The Astrophysical Journal, 2004Co-Authors: Alex G Muslimov, Alice K HardingAbstract:We explore the pulsar slot gap (SG) electrodynamics up to very high altitudes, where for most relatively rapidly rotating pulsars both the standard small-Angle Approximation and the assumption that the magnetic field lines are ideal streamlines break down. We address the importance of the electrodynamic conditions at the SG boundaries and the occurrence of a steady state drift of charged particles across the SG field lines at very high altitudes. These boundary conditions and the deviation of particle trajectories from streamlines determine the asymptotic behavior of the scalar potential at all radii from the polar cap (PC) to near the light cylinder. As a result, we demonstrate that the steady state accelerating electric field, E∥, must approach a small and constant value at high altitude above the PC. This E∥ is capable of maintaining electrons moving with high Lorentz factors (~few × 107) and emitting curvature γ-ray photons up to nearly the light cylinder. By numerical simulations, we show that primary electrons accelerating from the PC surface to high altitude in the SG along the outer edge of the open field region will form caustic emission patterns on the trailing dipole field lines. Acceleration and emission in such an extended SG may form the physical basis of a model that can successfully reproduce some pulsar high-energy light curves.