The Experts below are selected from a list of 146859 Experts worldwide ranked by ideXlab platform
Eliot Quataert - One of the best experts on this subject based on the ideXlab platform.
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The Long-Term Evolution of Double White Dwarf Mergers
The Astrophysical Journal, 2012Co-Authors: Ken J. Shen, Lars Bildsten, Daniel Kasen, Eliot QuataertAbstract:In this paper, we present a model for the Long-Term Evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 1e-4 to 1 yr, Long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of Evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon-burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 1e3-1e4 yr compresses the base of the envelope, again yielding off-center burning. As a result, the Long-Term Evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inwards over ~1e4 yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WD merger rate of a few per 1000 yr, tens of these ~1e38 erg/s sources should exist in a Milky Way-type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal Evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.
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the Long Term Evolution of double white dwarf mergers
The Astrophysical Journal, 2012Co-Authors: Ken J. Shen, Lars Bildsten, Daniel Kasen, Eliot QuataertAbstract:In this paper, we present a model for the Long-Term Evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 10{sup -4}-1 yr, Long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of Evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 10{sup 3}-10{sup 4} yr compresses the base of the envelope, again yielding off-center burning. As a result, the Long-Term Evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inward over {approx}10{sup 4} yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star, rather than a Type Ia supernova. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WDmore » merger rate of a few per 1000 yr, a few dozen of these {approx}10{sup 38} erg s{sup -1} sources should exist in a Milky Way type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, substantial remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal Evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.« less
Ken J. Shen - One of the best experts on this subject based on the ideXlab platform.
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The Long-Term Evolution of Double White Dwarf Mergers
The Astrophysical Journal, 2012Co-Authors: Ken J. Shen, Lars Bildsten, Daniel Kasen, Eliot QuataertAbstract:In this paper, we present a model for the Long-Term Evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 1e-4 to 1 yr, Long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of Evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon-burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 1e3-1e4 yr compresses the base of the envelope, again yielding off-center burning. As a result, the Long-Term Evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inwards over ~1e4 yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WD merger rate of a few per 1000 yr, tens of these ~1e38 erg/s sources should exist in a Milky Way-type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal Evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.
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the Long Term Evolution of double white dwarf mergers
The Astrophysical Journal, 2012Co-Authors: Ken J. Shen, Lars Bildsten, Daniel Kasen, Eliot QuataertAbstract:In this paper, we present a model for the Long-Term Evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 10{sup -4}-1 yr, Long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of Evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 10{sup 3}-10{sup 4} yr compresses the base of the envelope, again yielding off-center burning. As a result, the Long-Term Evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inward over {approx}10{sup 4} yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star, rather than a Type Ia supernova. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WDmore » merger rate of a few per 1000 yr, a few dozen of these {approx}10{sup 38} erg s{sup -1} sources should exist in a Milky Way type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, substantial remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal Evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.« less
Daniel Kasen - One of the best experts on this subject based on the ideXlab platform.
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The Long-Term Evolution of Double White Dwarf Mergers
The Astrophysical Journal, 2012Co-Authors: Ken J. Shen, Lars Bildsten, Daniel Kasen, Eliot QuataertAbstract:In this paper, we present a model for the Long-Term Evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 1e-4 to 1 yr, Long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of Evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon-burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 1e3-1e4 yr compresses the base of the envelope, again yielding off-center burning. As a result, the Long-Term Evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inwards over ~1e4 yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WD merger rate of a few per 1000 yr, tens of these ~1e38 erg/s sources should exist in a Milky Way-type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal Evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.
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the Long Term Evolution of double white dwarf mergers
The Astrophysical Journal, 2012Co-Authors: Ken J. Shen, Lars Bildsten, Daniel Kasen, Eliot QuataertAbstract:In this paper, we present a model for the Long-Term Evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid-body rotation on a viscous timescale of 10{sup -4}-1 yr, Long before significant cooling can occur. Due to heating during the dynamical and viscous phases, the less massive WD is transformed into a hot, slowly rotating, and radially extended envelope supported by thermal pressure. Following the viscous phase of Evolution, the maximum temperature near the envelope base may already be high enough to begin off-center convective carbon burning. If not, Kelvin-Helmholtz contraction of the inner region of the envelope on a thermal timescale of 10{sup 3}-10{sup 4} yr compresses the base of the envelope, again yielding off-center burning. As a result, the Long-Term Evolution of the merger remnant is similar to that seen in previous calculations: the burning shell diffuses inward over {approx}10{sup 4} yr, eventually yielding a high-mass O/Ne WD or a collapse to a neutron star, rather than a Type Ia supernova. During the cooling and shell-burning phases, the merger remnant radiates near the Eddington limit. Given the double WDmore » merger rate of a few per 1000 yr, a few dozen of these {approx}10{sup 38} erg s{sup -1} sources should exist in a Milky Way type galaxy. While the end result is similar to that of previous studies, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, substantial remaining uncertainties related to the convective structure near the photosphere and mass loss during the thermal Evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the eventual fate of double WD mergers, including those for which one or both of the components is a He WD.« less
Markus Rupp - One of the best experts on this subject based on the ideXlab platform.
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EUSIPCO - Simulating the Long Term Evolution physical layer
2009Co-Authors: Christian Mehlführer, Martin Wrulich, Josep Colom Ikuno, Dagmar Bosanska, Markus RuppAbstract:Research and development of signal processing algorithms for UMTS Long Term Evolution (LTE) requires a realistic, flexible, and standard-compliant simulation environment. To facilitate comparisons with work of other research groups such a simulation environment should ideally be publicly available. In this paper, we present a MATLAB-based downlink physical-layer simulator for LTE. We identify different research applications that are covered by our simulator. Depending on the research focus, the simulator offers to carry out single-downlink, single-cell multi-user, and multi-cell multi-user simulations. By utilizing the Parallel Computing Toolbox of MATLAB, the simulator can efficiently be executed on multi-core processors to significantly reduce the simulation time.
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Simulating the Long Term Evolution physical layer
2009 17th European Signal Processing Conference, 2009Co-Authors: Christian Mehlführer, Martin Wrulich, Josep Colom Ikuno, Dagmar Bosanska, Markus RuppAbstract:Research and development of signal processing algorithms for UMTS Long Term Evolution (LTE) requires a realistic, flexible, and standard-compliant simulation environment. To facilitate comparisons with work of other research groups such a simulation environment should ideally be publicly available. In this paper, we present a MATLAB-based downlink physical-layer simulator for LTE. We identify different research applications that are covered by our simulator. Depending on the research focus, the simulator offers to carry out single-downlink, single-cell multi-user, and multi-cell multi-user simulations. By utilizing the Parallel Computing Toolbox of MATLAB, the simulator can efficiently be executed on multi-core processors to significantly reduce the simulation time.
Jungfu Cheng - One of the best experts on this subject based on the ideXlab platform.
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arq concept for the umts Long Term Evolution
Vehicular Technology Conference, 2006Co-Authors: Mikael Meyer, Henning Wiemann, Mats Sagfors, Johan Torsner, Jungfu ChengAbstract:Work is ongoing in 3GPP to significantly extend the performance of UMTS in the work item Long Term Evolution (LTE). LTE contains a new system architecture with fewer infrastructure nodes and it has been decided to Terminate the ARQ functionality in the evolved node B. This paper describes the requirements that exists for an LTE ARQ concept and outlines a solution that fulfills these requirements in the new LTE architecture. The solution builds on two layered ARQ feedback mechanisms that provide sufficient reliability with a low resource cost for the feedback The paper contains thorough stepwise argumentation how we arrived at the proposed ARQ concept.
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VTC Fall - ARQ Concept for the UMTS Long-Term Evolution
IEEE Vehicular Technology Conference, 2006Co-Authors: Mikael Meyer, Henning Wiemann, Mats Sagfors, Johan Torsner, Jungfu ChengAbstract:Work is ongoing in 3GPP to significantly extend the performance of UMTS in the work item Long Term Evolution (LTE). LTE contains a new system architecture with fewer infrastructure nodes and it has been decided to Terminate the ARQ functionality in the evolved node B. This paper describes the requirements that exists for an LTE ARQ concept and outlines a solution that fulfills these requirements in the new LTE architecture. The solution builds on two layered ARQ feedback mechanisms that provide sufficient reliability with a low resource cost for the feedback The paper contains thorough stepwise argumentation how we arrived at the proposed ARQ concept.
