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C. Kayhan - One of the best experts on this subject based on the ideXlab platform.
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fundamental properties of kepler and corot targets iii tuning scaling relations using the first Adiabatic Exponent
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Mutlu Yildiz, Celik Z Orhan, C. KayhanAbstract:So called scaling relations have the potential to reveal the mass and radius of solar-like oscillating stars, based on oscillation frequencies. In derivation of these relations, it is assumed that the first Adiabatic Exponent at the surface (Gamma_1s) of such stars is constant. However, by constructing interior models for the mass range 0.8-1.6 Msun, we show that Gamma_1s is not constant at stellar surfaces for the effective temperature range with which we deal. Furthermore, the well-known relation between large separation and mean density also depends on Gamma_1s. Such knowledge is the basis for our aim of modifying scaling relations. There are significant differences between masses and radii found from modified and conventional scaling relations. However, comparison of predictions of these relations with the non-asteroseismic observations of Procyon A reveals that new scaling relations are effective in determining the mass and radius of stars. In the present study, solar-like oscillation frequencies of 89 target stars (mostly Kepler and CoRoT) were analysed. As well as two new reference frequencies (nu_min1 and nu_min2) found in the spacing of solar-like oscillation frequencies of stellar interior models, we also take into account nu_min0. In addition to the frequency of maximum amplitude, these frequencies have very strong diagnostic potential for determination of fundamental properties. The present study involves the application of derived relations from the models to the solar-like oscillating stars, and computes their effective temperatures using purely asteroseismic methods. There are in general very close agreements between effective temperatures from asteroseismic and non-asteroseismic (spectral and photometric) methods. For the Sun and Procyon A, for example, the agreement is almost total.
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Fundamental properties of Kepler and CoRoT targets – III. Tuning scaling relations using the first Adiabatic Exponent
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Mutlu Yildiz, Z. Çelik Orhan, C. KayhanAbstract:So called scaling relations have the potential to reveal the mass and radius of solar-like oscillating stars, based on oscillation frequencies. In derivation of these relations, it is assumed that the first Adiabatic Exponent at the surface (Gamma_1s) of such stars is constant. However, by constructing interior models for the mass range 0.8-1.6 Msun, we show that Gamma_1s is not constant at stellar surfaces for the effective temperature range with which we deal. Furthermore, the well-known relation between large separation and mean density also depends on Gamma_1s. Such knowledge is the basis for our aim of modifying scaling relations. There are significant differences between masses and radii found from modified and conventional scaling relations. However, comparison of predictions of these relations with the non-asteroseismic observations of Procyon A reveals that new scaling relations are effective in determining the mass and radius of stars. In the present study, solar-like oscillation frequencies of 89 target stars (mostly Kepler and CoRoT) were analysed. As well as two new reference frequencies (nu_min1 and nu_min2) found in the spacing of solar-like oscillation frequencies of stellar interior models, we also take into account nu_min0. In addition to the frequency of maximum amplitude, these frequencies have very strong diagnostic potential for determination of fundamental properties. The present study involves the application of derived relations from the models to the solar-like oscillating stars, and computes their effective temperatures using purely asteroseismic methods. There are in general very close agreements between effective temperatures from asteroseismic and non-asteroseismic (spectral and photometric) methods. For the Sun and Procyon A, for example, the agreement is almost total.
Mutlu Yildiz - One of the best experts on this subject based on the ideXlab platform.
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fundamental properties of kepler and corot targets iii tuning scaling relations using the first Adiabatic Exponent
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Mutlu Yildiz, Celik Z Orhan, C. KayhanAbstract:So called scaling relations have the potential to reveal the mass and radius of solar-like oscillating stars, based on oscillation frequencies. In derivation of these relations, it is assumed that the first Adiabatic Exponent at the surface (Gamma_1s) of such stars is constant. However, by constructing interior models for the mass range 0.8-1.6 Msun, we show that Gamma_1s is not constant at stellar surfaces for the effective temperature range with which we deal. Furthermore, the well-known relation between large separation and mean density also depends on Gamma_1s. Such knowledge is the basis for our aim of modifying scaling relations. There are significant differences between masses and radii found from modified and conventional scaling relations. However, comparison of predictions of these relations with the non-asteroseismic observations of Procyon A reveals that new scaling relations are effective in determining the mass and radius of stars. In the present study, solar-like oscillation frequencies of 89 target stars (mostly Kepler and CoRoT) were analysed. As well as two new reference frequencies (nu_min1 and nu_min2) found in the spacing of solar-like oscillation frequencies of stellar interior models, we also take into account nu_min0. In addition to the frequency of maximum amplitude, these frequencies have very strong diagnostic potential for determination of fundamental properties. The present study involves the application of derived relations from the models to the solar-like oscillating stars, and computes their effective temperatures using purely asteroseismic methods. There are in general very close agreements between effective temperatures from asteroseismic and non-asteroseismic (spectral and photometric) methods. For the Sun and Procyon A, for example, the agreement is almost total.
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Fundamental properties of Kepler and CoRoT targets – III. Tuning scaling relations using the first Adiabatic Exponent
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Mutlu Yildiz, Z. Çelik Orhan, C. KayhanAbstract:So called scaling relations have the potential to reveal the mass and radius of solar-like oscillating stars, based on oscillation frequencies. In derivation of these relations, it is assumed that the first Adiabatic Exponent at the surface (Gamma_1s) of such stars is constant. However, by constructing interior models for the mass range 0.8-1.6 Msun, we show that Gamma_1s is not constant at stellar surfaces for the effective temperature range with which we deal. Furthermore, the well-known relation between large separation and mean density also depends on Gamma_1s. Such knowledge is the basis for our aim of modifying scaling relations. There are significant differences between masses and radii found from modified and conventional scaling relations. However, comparison of predictions of these relations with the non-asteroseismic observations of Procyon A reveals that new scaling relations are effective in determining the mass and radius of stars. In the present study, solar-like oscillation frequencies of 89 target stars (mostly Kepler and CoRoT) were analysed. As well as two new reference frequencies (nu_min1 and nu_min2) found in the spacing of solar-like oscillation frequencies of stellar interior models, we also take into account nu_min0. In addition to the frequency of maximum amplitude, these frequencies have very strong diagnostic potential for determination of fundamental properties. The present study involves the application of derived relations from the models to the solar-like oscillating stars, and computes their effective temperatures using purely asteroseismic methods. There are in general very close agreements between effective temperatures from asteroseismic and non-asteroseismic (spectral and photometric) methods. For the Sun and Procyon A, for example, the agreement is almost total.
Juhi Jang - One of the best experts on this subject based on the ideXlab platform.
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Expanding large global solutions of the equations of compressible fluid mechanics
Inventiones mathematicae, 2018Co-Authors: Mahir Hadžić, Juhi JangAbstract:Without any symmetry assumptions on the initial data we construct global-in-time unique solutions to the vacuum free boundary three-dimensional isentropic compressible Euler equations when the Adiabatic Exponent $$\gamma $$ γ lies in the interval $$(1,\frac{5}{3}]$$ ( 1 , 5 3 ] . Our initial data lie sufficiently close to the expanding compactly supported affine motions recently constructed by Sideris and they satisfy the physical vacuum boundary condition.
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Instability theory of the Navier–Stokes–Poisson equations
Analysis & PDE, 2013Co-Authors: Juhi Jang, Ian TiceAbstract:The stability question of the Lane‐Emden stationary gaseous star configurations is an interesting problem arising in astrophysics. We establish both linear and nonlinear dynamical instability results for the Lane‐Emden solutions in the framework of the Navier‐Stokes‐Poisson system with Adiabatic Exponent 6 5 < < 4 3 .
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Instability theory of the Navier-Stokes-Poisson equations
arXiv: Analysis of PDEs, 2011Co-Authors: Juhi Jang, Ian TiceAbstract:The stability question of the Lane-Emden stationary gaseous star configurations is an interesting problem arising in astrophysics. We establish both linear and nonlinear dynamical instability results for the Lane-Emden solutions in the framework of the Navier-Stokes-Poisson system with Adiabatic Exponent $6/5 < \gamma < 4/3$.
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Nonlinear Instability in Gravitational Euler–Poisson Systems for $$\gamma=\frac{6}{5}$$
Archive for Rational Mechanics and Analysis, 2008Co-Authors: Juhi JangAbstract:The dynamics of gaseous stars can be described by the Euler–Poisson system. Inspired by Rein’s stability result for $$\gamma > \frac{4}{3}$$ , we prove the nonlinear instability of steady states for the Adiabatic Exponent $$\gamma=\frac{6}{5}$$ under spherically symmetric and isentropic motion.
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Nonlinear Instability in Gravitational Euler–Poisson Systems for $$\gamma=\frac{6}{5}$$
Archive for Rational Mechanics and Analysis, 2008Co-Authors: Juhi JangAbstract:The dynamics of gaseous stars can be described by the Euler–Poisson system. Inspired by Rein’s stability result for \(\gamma > \frac{4}{3}\), we prove the nonlinear instability of steady states for the Adiabatic Exponent \(\gamma=\frac{6}{5}\) under spherically symmetric and isentropic motion.
Dehua Wang - One of the best experts on this subject based on the ideXlab platform.
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global weak solution and large time behavior for the compressible flow of liquid crystals
Archive for Rational Mechanics and Analysis, 2012Co-Authors: Dehua Wang, Cheng YuAbstract:The three-dimensional equations for the compressible flow of liquid crystals are considered. An initial-boundary value problem is studied in a bounded domain with large data. The existence and large-time behavior of a global weak solution are established through a three-level approximation, energy estimates, and weak convergence for the Adiabatic Exponent $${\gamma > \frac{3}{2}}$$ .
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global existence and large time behavior of solutions to the three dimensional equations of compressible magnetohydrodynamic flows
Archive for Rational Mechanics and Analysis, 2010Co-Authors: Xianpeng Hu, Dehua WangAbstract:The three-dimensional equations of compressible magnetohydrodynamic isentropic flows are considered. An initial-boundary value problem is studied in a bounded domain with large data. The existence and large-time behavior of global weak solutions are established through a three-level approximation, energy estimates, and weak convergence for the Adiabatic Exponent \({\gamma > \frac 32}\) and constant viscosity coefficients.
Huihui Zeng - One of the best experts on this subject based on the ideXlab platform.
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nonlinear asymptotic stability of the lane emden solutions for the viscous gaseous star problem with degenerate density dependent viscosities
Communications in Mathematical Physics, 2016Co-Authors: Tao Luo, Zhouping Xin, Huihui ZengAbstract:The nonlinear asymptotic stability of Lane-Emden solutions is proved in this paper for spherically symmetric motions of viscous gaseous stars with the density dependent shear and bulk viscosities which vanish at the vacuum, when the Adiabatic Exponent \({\gamma}\) lies in the stability regime \({(4/3, 2)}\), by establishing the global-in-time regularity uniformly up to the vacuum boundary for the vacuum free boundary problem of the compressible Navier-Stokes-Poisson systems with spherical symmetry, which ensures the global existence of strong solutions capturing the precise physical behavior that the sound speed is \({C^{{1}/{2}}}\)-Holder continuous across the vacuum boundary, the large time asymptotic uniform convergence of the evolving vacuum boundary, density and velocity to those of Lane-Emden solutions with detailed convergence rates, and the detailed large time behavior of solutions near the vacuum boundary. Those uniform convergence are of fundamental importance in the study of vacuum free boundary problems which are missing in the previous results for global weak solutions. Moreover, the results obtained in this paper apply to much broader cases of viscosities than those in Fang and Zhang (Arch Ration Mech Anal 191:195–243, 2009) for the theory of weak solutions when the Adiabatic Exponent \({\gamma}\) lies in the most physically relevant range. Finally, this paper extends the previous local-in-time theory for strong solutions to a global-in-time one.