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Kinetic Equations for Stark Line Shapes 斯塔克线形的动力学方程
Pub Date : 2012-09-14 DOI: 10.1080/00411450.2012.671210
J. Rosato, H. Capes, Y. Marandet, A. Mekkaoui, R. Stamm
The Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) formalism is revisited in the framework of plasma spectroscopy. We address the issue of Stark line shape modeling by using kinetic transport equations. In the most simplified treatment of these equations, triple correlations between an emitter and the perturbing charged particles are neglected and a collisional description of Stark effect is obtained. Here we relax this assumption and retain triple correlations using a generalization of the Kirkwood truncature hypothesis to quantum operator. An application to hydrogen lines is done in the context of plasma diagnostic. It is shown that the neglect of triple correlations can lead to a significant overestimate of the line width.
Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY)形式主义在等离子体光谱学框架下被重新审视。我们通过使用动力学输运方程来解决斯塔克线形建模的问题。在这些方程的最简化处理中,忽略了发射器和扰动带电粒子之间的三重关联,得到了斯塔克效应的碰撞描述。在这里,我们放宽了这一假设,并使用柯克伍德截断假设对量子算子的推广来保持三重相关性。在等离子体诊断的背景下,对氢谱进行了应用。结果表明,忽略三重相关性会导致线宽的显著高估。
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引用次数: 3
Quantum Corrections on the Radiative Transfer Equation 辐射传递方程的量子修正
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671211
J. Rosato
The quantum phase space formalism proposed by Wigner is applied to radiation transport problems. It is shown that a generalization of the radiative transfer equation, which accounts for coherence effects, can be obtained within the second quantization formalism. A simplification in the case of stationary medium and slab geometry is considered and applied to low- and high-density plasmas. The obtained results indicate that spectra can be misinterpreted if the light's spatial coherence is neglected.
将Wigner提出的量子相空间形式理论应用于辐射输运问题。结果表明,考虑相干效应的辐射传递方程可以在第二量子化形式中得到推广。考虑了固定介质和平板几何形状的简化,并将其应用于低密度和高密度等离子体。结果表明,忽略光的空间相干性会导致光谱的误读。
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引用次数: 5
The Asymptotic Telegrapher’s Equation (P1) Approximation for Time-Dependent, Thermal Radiative Transfer 随时间变化的热辐射传递的渐近电报员方程(P1)近似
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671205
Shay I. Heizler
We develop the asymptotic P 1 approximation for the time-dependent thermal radiative transfer equation for a multidimensional general geometry. Careful derivation of the asymptotic P 1 equations, directly from the time-dependent Boltzmann equation, yields a particle velocity that is closer (v≈0.91c) to the exact value of c but is based on an asymptotic analysis rather than diffusion theory (infinite velocity) or conventional P 1 theory (which gives rise to the Telegrapher’s equation, ). While this approach does not match the exact value of c as does the P 1/3 method, the latter method is an ad hoc approach that has not been justified on theoretical grounds. This article provides the theoretical justification for the almost-correct value of c that yields improved results for the well-known (one-dimensional) Su-Olson benchmark for radiative transfer, for which we obtain a semi-analytic solution in the case of local thermodynamic equilibrium. We found that the asymptotic P 1 approximation yields a better solution than the diffusion, the classic P 1, and the P 1/3 approximations, yielding the correct steady-state behavior for the energy density and the (almost) correct particle velocity.
我们建立了多维一般几何的时变热辐射传递方程的渐近p1近似。直接从随时间变化的玻尔兹曼方程仔细推导渐近p1方程,得到的粒子速度(v≈0.91c)更接近c的精确值,但它是基于渐近分析而不是扩散理论(无限速度)或传统的p1理论(它产生了电报员方程)。虽然这种方法不像P 1/3方法那样匹配c的确切值,但后一种方法是一种特殊的方法,在理论基础上没有得到证明。本文提供了c几乎正确值的理论依据,该值对众所周知的(一维)Su-Olson辐射传递基准得到了改进的结果,我们得到了局部热力学平衡情况下的半解析解。我们发现渐近p1近似比扩散、经典p1和p1 /3近似产生更好的解,对于能量密度和(几乎)正确的粒子速度产生正确的稳态行为。
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引用次数: 12
A Consistent, Moment-Based, Multiscale Solution Approach for Thermal Radiative Transfer Problems 热辐射传递问题的一致、基于矩的多尺度求解方法
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671224
H. Park, D. Knoll, R. M. Rauenzahn, A. Wollaber, J. Densmore
We present an efficient numerical algorithm for solving the time-dependent grey thermal radiative transfer (TRT) equations. The algorithm utilizes the first two angular moments of the TRT equations (Quasi-diffusion (QD)) together with the material temperature equation to form a nonlinear low-order (LO) system. The LO system is solved via the Jacobian-free Newton-Krylov method. The combined high-order (HO) TRT and LO-QD system is used to bridge the diffusion and transport scales. In addition, a “consistency” term is introduced to make the truncation error in the LO system identical to the truncation error in the HO equation. The derivation of the consistency term is rather general; therefore, it can be extended to a variety of spatial and temporal discretizations.
提出了一种求解随时间变化的灰色热辐射传递方程的有效数值算法。该算法利用TRT方程的前两个角矩(准扩散(QD))与材料温度方程构成非线性低阶(LO)系统。采用无雅可比牛顿-克里洛夫方法求解了该系统。结合高阶TRT和LO-QD系统来桥接扩散和输运尺度。此外,引入了“一致性”项,使LO系统中的截断误差与HO方程中的截断误差相同。一致性项的推导是相当一般的;因此,它可以扩展到各种空间和时间离散化。
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引用次数: 41
SP 2—Asymptotic P 1 Equivalence SP 2 -渐近p1等价
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.672358
Shay I. Heizler, P. Ravetto
This article is devoted to analyzing the physical features of the time-dependent P 2 model in plane geometry and the simplified P 2 (SP 2) model for general geometry. The relationships that can be established with the P 1 model (which gives rise to the telegrapher’s equation) are discussed in detail. In particular, the propagation properties are considered, showing that the signal is characterized by propagation velocity that is times the correct particle velocity. This result is also obtained by direct observation of the equivalent three discrete ordinates equations (S 3) in a slab geometry. In addition, a consistent asymptotic approach is carried out on the SP 2 equations, as can be done in a P 1 formulation. We find that in the diffusion limit, the SP 2 approximation yields the same asymptotic behavior as the asymptotic P 1 approximation that is derived from the exact time-dependent Boltzmann equation. In the absorbing limit, the asymptotic behavior of the SP 2 equations tends to be the exact behavior of SP 2; i.e., with a propagation velocity that is times the particle velocity, which is lower than that for the asymptotic P 1 approximation that tends to the exact particle velocity. These observations are supported by numerical results for a simple problem in a one-dimensional transport problem. The asymptotic P 1 and P 2 approximations are much closer to the exact transport solution than the classic P 1 approximation.
本文分析了平面几何中随时间变化的p2模型和一般几何中简化的p2 (sp2)模型的物理特征。详细讨论了可以用p1模型(由此产生电报员方程)建立的关系。特别是,考虑了传播特性,表明信号的特征是传播速度乘以正确的粒子速度。这一结果也可以通过直接观察等效的三个离散坐标方程(S 3)在平板几何。此外,对SP 2方程进行了一致渐近逼近,可以在p1公式中完成。我们发现,在扩散极限下,SP 2近似与由精确时变玻尔兹曼方程导出的P 1近似产生相同的渐近行为。在吸收极限下,SP - 2方程的渐近行为趋向于SP - 2的精确行为;也就是说,传播速度乘以粒子速度,这比趋近于粒子速度的p1近似要低。这些观测结果得到了一维输运问题中一个简单问题的数值结果的支持。渐近的p1和p2近似比经典的p1近似更接近精确的输运解。
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引用次数: 6
Radiative Transport Reconsidered 重新考虑辐射输运
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671208
N. Corngold
We describe situations where coherent and incoherent effects take place in a disordered medium illuminated by a coherent source. We illustrate the transition from coherence to incoherence by considering the propagation of a scalar wave in a medium of point, isotropic scatterers. We note how a traditional transport equation evolves and that it is enriched by a boundary layer in which coherence decays and the intensity is of damped oscillatory nature.
我们描述了相干和非相干效应在由相干源照射的无序介质中发生的情况。我们通过考虑标量波在点、各向同性散射体介质中的传播来说明从相干到非相干的转变。我们注意到传统输运方程是如何演变的,并且它被一个边界层所丰富,在这个边界层中相干性衰减并且强度具有阻尼振荡性质。
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引用次数: 1
On Radiative Transfer in Dense Vegetation Canopies 稠密植被冠层的辐射转移研究
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671218
P. Picca, R. Furfaro, B. Ganapol
This article presents a review of the special features exhibited by the transport of photons in dense vegetation canopies. The conservation of photons for particles moving in canopy media yields a linear Boltzmann Equation similar to conventional participating media. However, because of the turbid medium approximation where the atomic leaves are modeled as a gas cloud of infinitesimal plates with specified orientation, the overall system is not rotationally invariant. The latter affects the mathematical nature of the canopy equation and requires special numerical treatment to generate accurate numerical solutions. Here, the most common solution techniques are reviewed with special emphasis on two highly accurate methodologies, namely the Singular Eigenfunction Expansion, which is the basis of the F N method for canopy transport and the Analytical Discrete Ordinate (ADO) method. It is shown that the conventional ADO method can be easily extended to canopy transport problems by taking advantage of special symmetries exhibited by the intercept function and the area scattering function employed to describe the canopy optical properties.
本文综述了密集植被冠层中光子输运所表现出的特殊特征。在树冠介质中运动的粒子的光子守恒产生一个类似于传统参与介质的线性玻尔兹曼方程。然而,由于在浑浊介质近似中,原子叶被建模为具有特定方向的无限小板组成的气体云,因此整个系统不是旋转不变的。后者影响冠层方程的数学性质,需要特殊的数值处理才能得到精确的数值解。本文回顾了最常见的求解技术,特别强调了两种高精度的方法,即奇异特征函数展开法和解析离散坐标法(ADO)。奇异特征函数展开法是求解冠层迁移的F - N方法的基础。结果表明,利用描述冠层光学性质的截距函数和面积散射函数所表现出的特殊对称性,传统的ADO方法可以很容易地扩展到冠层输运问题。
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引用次数: 4
Remarks on the Speed of Heat Waves 关于热浪速度的评论
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671220
M. Makai
We discuss heat conductance and diffusion, two remarkable transport processes characterized by instantaneous actions. We show that the assumption of local thermal equilibrium sets a limit to the speed of change in the distribution function of a statistical system . Using Onsager’s approximation, we show that the balance equations of the extensive parameters also have solutions with finite velocities involved. At the same time the infinite speed is obtainable when second order terms are neglected. We show how the presented technique is applied in heat transfer, diffusion, and plasma physics to determine the speeds of the physical processes.
我们讨论了热传导和扩散这两个以瞬时作用为特征的显著传递过程。我们证明了局部热平衡的假设为统计系统的分布函数的变化速度设定了一个极限。利用Onsager近似,我们证明了扩展参数的平衡方程也有涉及有限速度的解。同时,在忽略二阶项的情况下,可以得到无限速度。我们展示了该技术如何应用于传热、扩散和等离子体物理中,以确定物理过程的速度。
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引用次数: 0
Analytic Treatment of Source Photon Emission Times to Reduce Noise in Implicit Monte Carlo Calculations 隐式蒙特卡罗计算中源光子发射时间的解析处理以降低噪声
Pub Date : 2012-05-01 DOI: 10.1080/00411450.2012.671221
T. Trahan, N. Gentile
Statistical uncertainty is inherent to any Monte Carlo simulation of radiation transport problems. In space-angle-frequency independent radiative transfer calculations, the uncertainty in the solution is entirely due to random sampling of source photon emission times. We have developed a modification to the Implicit Monte Carlo algorithm that eliminates noise due to sampling of the emission time of source photons. In problems that are independent of space, angle, and energy, the new algorithm generates a smooth solution, while a standard implicit Monte Carlo solution is noisy. For space- and angle-dependent problems, the new algorithm exhibits reduced noise relative to standard implicit Monte Carlo in some cases, and comparable noise in all other cases. The improvements are limited to short time scales; over long time scales, noise due to random sampling of spatial and angular variables tends to dominate the noise reduction from the new algorithm.
统计不确定性是任何辐射输运问题的蒙特卡罗模拟所固有的。在与空间角频率无关的辐射传输计算中,解的不确定性完全是由于源光子发射时间的随机抽样。我们对隐式蒙特卡罗算法进行了改进,消除了由于对源光子发射时间采样而产生的噪声。在独立于空间、角度和能量的问题中,新算法生成平滑解,而标准隐式蒙特卡罗解是有噪声的。对于空间和角度相关的问题,新算法在某些情况下相对于标准隐式蒙特卡罗显示出更低的噪声,并且在所有其他情况下具有可比较的噪声。这些改进仅限于短时间尺度;在较长的时间尺度上,由于空间变量和角度变量的随机采样而产生的噪声往往会主导新算法的降噪。
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引用次数: 4
Calculation of entropy production in slightly rarefied gas flows by Sonine polynomial expansion 用Sonine多项式展开计算微稀薄气体流动的熵产
Pub Date : 2012-01-18 DOI: 10.1080/00411459708221778
Liu Guangjun
Abstract The expansion method in the kinetic theory of gases is often used for the calculation of entropy production in rarefied gas flows, usually in terms of Her-mite polynomials. In this paper, the method of Sonine polynomials expansion is used and the calculation of entropy production is carried out. First, the formal evaluation of the entropy production in rarefied gas flows is introduced. Then the calculation of the entropy production for arbitrary molecules with spherically symmetric intermolecular forces by Sonine polynomials expansion is presented and the formula for entropy production in the thirteen-moment approximation is obtained. It is shown that the entropy production can be expressed as a linear combination of square terms in the thirteen-moment approximation. This formula can be applied to slightly rarefied gas flows.
气体运动论中的展开法常用于计算稀薄气体流动中的熵产,通常采用hermite多项式。本文采用索宁多项式展开的方法,进行了熵产的计算。首先,介绍了稀薄气体流动中熵产的形式化评价。然后用Sonine多项式展开法计算了具有球对称分子间力的任意分子的熵产,得到了13矩近似下的熵产公式。结果表明,在十三矩近似中,熵的产生可以表示为平方项的线性组合。这个公式可以应用于稍微稀薄的气体流动。
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引用次数: 0
期刊
Transport Theory and Statistical Physics
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