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Articles de revues sur le sujet « RADIATIVE TRANSPORT THEORY »

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Auteur : Grafiati
Publié le 10 mars 2023

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1

Pomraning, G. C. « Multimode flux-limited diffusion theory ». Laser and Particle Beams 10, no 2 (juin 1992) : 239–51. http://dx.doi.org/10.1017/s0263034600004389.

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We present a diffusion approximation describing the flow of thermal radiation that preserves several important features of the underlying equation of radiative transfer. Specifically, this diffusion description: (1) is flux limited; (2) reduces to the correct transport weak gradient limit; (3) allows correct and simultaneous exponential growth and Decay for a certain class of problems; (4) gives correct transport results for certain contiguous half-space problems; and (5) allows the radiative flux and the gradient of the radiation energy density to point in independent directions. This treatment extends and generalizes earlier flux-limited diffusion approximations that are widely used in radiation–hydrodynamics calculations.
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2

Berberan‐Santos, M. N., E. J. Nunes Pereira et J. M. G. Martinho. « Stochastic theory of molecular radiative transport ». Journal of Chemical Physics 103, no 8 (22 août 1995) : 3022–28. http://dx.doi.org/10.1063/1.470491.

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3

Kim, Arnold D., et Miguel Moscoso. « Radiative transport theory for optical molecular imaging ». Inverse Problems 22, no 1 (9 décembre 2005) : 23–42. http://dx.doi.org/10.1088/0266-5611/22/1/002.

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4

Sandoval, Christopher, et Arnold D. Kim. « Deriving Kubelka–Munk theory from radiative transport ». Journal of the Optical Society of America A 31, no 3 (21 février 2014) : 628. http://dx.doi.org/10.1364/josaa.31.000628.

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5

Zahn, J. P. « Theory of Transport Processes ». International Astronomical Union Colloquium 121 (1990) : 425–36. http://dx.doi.org/10.1017/s0252921100068111.

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AbstractThis review focuses on the transport of matter and angular momentum in the radiative zones of stellar interiors. The two main causes of such transport are the convective overshooting in the vicinity of convection zones, and the slow motions (meridional circulation and turbulence) due to the rotation of the star. In addition, momentum can be transfered through waves (generated by the motions above) and through magnetic stresses. The characteristics of those processes are examined, with special emphasis on turbulent diffusion.
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6

Berberan-Santos, Mário N., Eduardo J. Nunes Pereira et José M. G. Martinho. « Stochastic theory of combined radiative and nonradiative transport ». Journal of Chemical Physics 107, no 24 (22 décembre 1997) : 10480–84. http://dx.doi.org/10.1063/1.474211.

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7

Song, Bai, Anthony Fiorino, Edgar Meyhofer et Pramod Reddy. « Near-field radiative thermal transport : From theory to experiment ». AIP Advances 5, no 5 (mai 2015) : 053503. http://dx.doi.org/10.1063/1.4919048.

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8

Kim, Arnold D., et John C. Schotland. « Self-consistent scattering theory for the radiative transport equation ». Journal of the Optical Society of America A 23, no 3 (1 mars 2006) : 596. http://dx.doi.org/10.1364/josaa.23.000596.

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9

Şahin, Derya, et Boaz Ilan. « Radiative transport theory for light propagation in luminescent media ». Journal of the Optical Society of America A 30, no 5 (8 avril 2013) : 813. http://dx.doi.org/10.1364/josaa.30.000813.

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10

Cox, Tyler, Kyle C. Armour, Gerard H. Roe, Aaron Donohoe et Dargan M. W. Frierson. « Radiative and Dynamic Controls on Atmospheric Heat Transport over Different Planetary Rotation Rates ». Journal of Climate 34, no 9 (mai 2021) : 3543–54. http://dx.doi.org/10.1175/jcli-d-20-0533.1.

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AbstractAtmospheric heat transport is an important piece of our climate system, yet we lack a complete theory for its magnitude or changes. Atmospheric dynamics and radiation play different roles in controlling the total atmospheric heat transport (AHT) and its partitioning into components associated with eddies and mean meridional circulations. This work focuses on two specific controls: a radiative one, namely atmospheric radiative temperature tendencies, and a dynamic one, the planetary rotation rate. We use an idealized gray radiation model to employ a novel framework to lock the radiative temperature tendency and total AHT to climatological values, even while the rotation rate is varied. This setup allows for a systematic study of the effects of radiative tendency and rotation rate on AHT. We find that rotation rate controls the latitudinal extent of the Hadley cell and the heat transport efficiency of eddies. Both the rotation rate and radiative tendency influence the strength of the Hadley cell and the strength of equator–pole energy differences that are important for AHT by eddies. These two controls do not always operate independently and can reinforce or dampen each other. In addition, we examine how individual AHT components, which vary with latitude, sum to a total AHT that varies smoothly with latitude. At slow rotation rates the mean meridional circulation is most important in ensuring total AHT varies smoothly with latitude, while eddies are most important at rotation rates similar to, and faster than, those of Earth.
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11

Prasher, Ravi. « Phonon Transport in Anisotropic Scattering Particulate Media ». Journal of Heat Transfer 125, no 6 (19 novembre 2003) : 1156–62. http://dx.doi.org/10.1115/1.1622718.

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Equation of phonon radiative transport (EPRT) is rewritten to include anisotropic scattering by a particulate media by including an acoustic phase function and an inscattering term which makes EPRT exactly same as equation of radiative transport (ERT). This formulation of EPRT is called generalized EPRT (GEPRT). It is shown that GEPRT reduces to EPRT for isotropic scattering and is totally consistent with phonon transport theory, showing that transport cross section is different from the scattering cross section. GEPRT leads to same formulation for transport cross section as given by phonon transport theory. However GEPRT shows that transport cross section formulations as described by phonon transport theory are only valid for acoustically thick medium. Transport cross section is different for the acoustically thin medium leading to the conclusion that mean free path (m.f.p) is size dependant. Finally calculations are performed for two types of scatterers for acoustic waves without mode conversion: (1) acoustically hard Rayleigh sphere; and (2) large sphere in the geometrical scattering regime. Results show that the scattering from these particles is highly anisotropic. It is also shown that for geometrical scattering case isotropic scattering leads to the conclusion of total internal reflection at the particle/medium interface.
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12

McMahon, Kara G., James F. Lynch, Ying‐Tsong Lin et William L. Siegmann. « Energy propagation in nonlinear internal wave ducts from radiative transport theory. » Journal of the Acoustical Society of America 128, no 4 (octobre 2010) : 2335. http://dx.doi.org/10.1121/1.3508257.

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13

Adzerikhc, K. S., et N. V. Podluzhnyak. « New methods in the theory of radiative transport. II. Anisotropic scattering ». Journal of Engineering Physics 49, no 5 (novembre 1985) : 1320–23. http://dx.doi.org/10.1007/bf00871247.

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14

Istomin, Vladimir A., Elena V. Kustova et Kirill A. Prutko. « Heat and radiative fluxes in strongly nonequilibrium flows behind shock waves ». Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy 9, no 4 (2022) : 705–19. http://dx.doi.org/10.21638/spbu01.2022.412.

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State-to-state and two-temperature theoretical models for high-temperature strongly nonequilibrium reacting and radiating air flows are developed in the framework of the generalized Chapman - Enskog method. In the theoretical approach, the sets of governing equations for coupled fluid dynamics, chemical kinetics, internal energy transitions and radiation are derived; the algorithms for the calculation of state-resolved transport coefficients are developed and implemented. The proposed models are applied for 1-D simulations of shock waves in air under high-temperature conditions observed in flight experiments. Nonequilibrium mixture composition, temperatures and pressure profiles are obtained and compared for various models of chemical reaction rate coefficients. Flow variables strongly depend on both the kinetic-theory approach and chemical reaction model; species molar fractions and temperature show significantly different behaviour for the state-to-state and two-temperature simulations. Transport properties and radiative fluxes are calculated as functions of the distance from the shock front. It is found that diffusion provides a major contribution to the total energy flux whereas the role of heat conduction is weak due to the compensation effects. It is shown that under considered conditions, two-temperature models are not applicable for correct predictions of radiative heating.
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15

Hauck, Cory, et Vincent Heningburg. « Filtered Discrete Ordinates Equations for Radiative Transport ». Journal of Scientific Computing 80, no 1 (3 mai 2019) : 614–48. http://dx.doi.org/10.1007/s10915-019-00950-1.

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16

Dombrovsky, L. A. « Quartz-Fiber Thermal Insulation : Infrared Radiative Properties and Calculation of Radiative-Conductive Heat Transfer ». Journal of Heat Transfer 118, no 2 (1 mai 1996) : 408–14. http://dx.doi.org/10.1115/1.2825859.

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Calculations of absorption, transport scattering, and radiation diffusion coefficients for a highly porous material of quartz fibers are performed by use of rigorous scattering theory for arbitrarily oriented cylinders. New results concerning resonance absorption in the semitransparency region and intensive “scattering by absorption” at refractive index n ≈ 1 in the opacity region are obtained. Numerical results for the radiation diffusion coefficient from a theoretical model without taking into account both dependent scattering and interference effects are in a good agreement with the experimental data for isotropic fibrous material of density 144 kg/m3. Calculations allow us to give practical proposals to simplify the determination of optical properties of poly disperse material with randomly oriented fibers. Some results on the radiative–conductive heat transfer in the material considered are presented. The radiation transfer is described in the P1 approximation. A two-band spectral model with bands corresponding to semitransparency and opacity regions is proposed. Applicability of a modified radiative conduction approximation both to transient and to steady-state calculations is discussed.
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17

Prasher, Ravi S. « Mie Scattering Theory for Phonon Transport in Particulate Media ». Journal of Heat Transfer 126, no 5 (1 octobre 2004) : 793–804. http://dx.doi.org/10.1115/1.1795243.

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Scattering theory for the scattering of phonons by particulate scatterers is developed in this paper. Recently the author introduced the generalized equation of phonon radiative transport (GEPRT) in particulate media, which included a phase function to account for the anisotropic scattering of phonons by particulate scatterer. Solution of the GEPRT showed that scattering cross section is different from the thermal transport cross-section. In this paper formulations for the scattering and transport cross section for horizontally shear (SH) wave phonon or transverse wave phonon without mode conversion is developed. The development of the theory of scattering and the transport cross section is exactly analogous to the Mie scattering theory for photon transport in particulate media. Results show that transport cross section is very different from the scattering cross section. The theory of phonon scattering developed in this paper will be useful for the predictive modeling of thermal conductivity of practical systems, such as nanocomposites, nano-micro-particle-laden systems, etc.
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18

McMahon, Kara G., James F. Lynch, Ying‐Tsong Lin, Ning Xiang et William L. Siegmann. « Nonlinear internal wave parameter influences on energy propagation using radiative transport theory. » Journal of the Acoustical Society of America 129, no 4 (avril 2011) : 2458. http://dx.doi.org/10.1121/1.3588080.

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19

Bal, G., et M. Moscoso. « Polarization effects of seismic waves on the basis of radiative transport theory ». Geophysical Journal International 142, no 2 (1 août 2000) : 571–85. http://dx.doi.org/10.1046/j.1365-246x.2000.00182.x.

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20

Cazé, A., et John C. Schotland. « Diagrammatic and asymptotic approaches to the origins of radiative transport theory : tutorial ». Journal of the Optical Society of America A 32, no 8 (13 juillet 2015) : 1475. http://dx.doi.org/10.1364/josaa.32.001475.

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21

Argyros, Ioannis K. « On the number of solutions of some integral equations arising in radiative transfer ». International Journal of Mathematics and Mathematical Sciences 12, no 2 (1989) : 297–304. http://dx.doi.org/10.1155/s0161171289000347.

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22

Majumdar, A. « Microscale Heat Conduction in Dielectric Thin Films ». Journal of Heat Transfer 115, no 1 (1 février 1993) : 7–16. http://dx.doi.org/10.1115/1.2910673.

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Heat conduction in dielectric thin films is a critical issue in the design of electronic devices and packages. Depending on the material properties, there exists a range of film thickness where the Fourier law, used for macroscale heat conduction, cannot be applied. This paper shows that in this microscale regime, heat transport by lattice vibrations or phonons can be analyzed as a radiative transfer problem. Based on Boltzmann transport theory, an equation of phonon radiative transfer (EPRT) is developed. In the acoustically thick limit, ξL ≫ 1, or the macroscale regime, where the film thickness is much larger than the phonon-scattering mean free path, the EPRT reduces to the Fourier law. In the acoustically thin limit, ξL ≪ 1, the EPRT yields the blackbody radiation law q = σ (T14 − T24) at temperatures below the Debye temperature, where q is the heat flux and T1 and T2 are temperatures at the film boundaries. For transient heat conduction, the EPRT suggests that a heat pulse is transported as a wave, which becomes attenuated in the film due to phonon scattering. It is also shown that the hyperbolic heat equation can be derived from the EPRT only in the acoustically thick limit. The EPRT is then used to study heat transport in diamond thin films in wide range of acoustical thicknesses spanning the thin and the thick regimes. The heat flux follows the relation q = 4σT3ΔT/(3ξL/4 + 1) as derived in the modified diffusion approximation for photon radiative transfer. The thermal conductivity, as currently predicted by kinetic theory, causes the Fourier law to overpredict the heat flux by 33 percent when ξL ≪ 1, by 133 percent when ξL = 1, and by about 10 percent when ξL increases to 10. To use the Fourier law in both ballistic and diffusive transport regimes, a simple expression for an effective thermal conductivity is developed.
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23

Smit, P. B., T. T. Janssen et T. H. C. Herbers. « Stochastic Modeling of Coherent Wave Fields over Variable Depth ». Journal of Physical Oceanography 45, no 4 (avril 2015) : 1139–54. http://dx.doi.org/10.1175/jpo-d-14-0219.1.

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AbstractRefractive focusing of swell waves can result in fast-scale variations in the wave statistics because of wave interference, which cannot be resolved by stochastic wave models based on the radiative transport equation. Quasi-coherent statistical theory does account for such statistical interferences and the associated wave inhomogeneities, but the theory has thus far been presented in a form that appears incompatible with models based on the radiative transfer equation (RTE). Moreover, the quasi-coherent theory has never been tested against field data, and it is not clear how the coherent information inherent to such models can be used for better understanding coastal wave and circulation dynamics. This study therefore revisits the derivation of quasi-coherent theory to formulate it into a radiative transport equation with a forcing term that accounts for the inhomogeneous part of the wave field. This paper shows how the model can be nested within (or otherwise used in conjunction with) quasi-homogeneous wave models based on the RTE. Through comparison to laboratory data, numerical simulations of a deterministic model, and field observations of waves propagating over a nearshore canyon head, the predictive capability of the model is validated. The authors discuss the interference patterns predicted by the model through evaluation of a complex cross-correlation function and highlight the differences with quasi-homogeneous predictions. These results show that quasi-coherent theory can extend models based on the RTE to resolve coherent interference patterns and standing wave features in coastal areas, which are believed to be important in nearshore circulation and sediment transport.
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24

Post, H. A. « Radiative transport at the 184.9-nm Hg resonance line. I. Experiment and theory ». Physical Review A 33, no 3 (1 mars 1986) : 2003–16. http://dx.doi.org/10.1103/physreva.33.2003.

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25

Shiang, J. J., et Anil R. Duggal. « Application of radiative transport theory to light extraction from organic light emitting diodes ». Journal of Applied Physics 95, no 5 (mars 2004) : 2880–88. http://dx.doi.org/10.1063/1.1644037.

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26

Tidriri, Moulay D. « An alternative model to boundary layers correctors in transport theory and radiative transfer ». Comptes Rendus de l'Académie des Sciences - Series I - Mathematics 333, no 3 (août 2001) : 195–200. http://dx.doi.org/10.1016/s0764-4442(01)02018-3.

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27

Prat, V., et S. Mathis. « Anisotropic turbulent transport with horizontal shear in stellar radiative zones ». Astronomy & ; Astrophysics 649 (mai 2021) : A62. http://dx.doi.org/10.1051/0004-6361/202039281.

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Context. Turbulent transport in stellar radiative zones is a key ingredient of stellar evolution theory, but the anisotropy of the transport due to the stable stratification and the rotation of these regions is poorly understood. The assumption of shellular rotation, which is a cornerstone of the so-called rotational mixing, relies on an efficient horizontal transport. However, this transport is included in many stellar evolution codes through phenomenological models that have never been tested. Aims. We investigate the impact of horizontal shear on the anisotropy of turbulent transport. Methods. We used a relaxation approximation (also known as τ approximation) to describe the anisotropising effect of stratification, rotation, and shear on a background turbulent flow by computing velocity correlations. Results. We obtain new theoretical scalings for velocity correlations that include the effect of horizontal shear. These scalings show an enhancement of turbulent motions, which would lead to a more efficient transport of chemicals and angular momentum, in better agreement with helio- and asteroseismic observations of rotation in the whole Hertzsprung-Russell diagram. Moreover, we propose a new choice for the non-linear time used in the relaxation approximation, which characterises the source of the turbulence. Conclusions. For the first time, we describe the effect of stratification, rotation, and vertical and horizontal shear on the anisotropy of turbulent transport in stellar radiative zones. The new prescriptions need to be implemented in stellar evolution calculations. To do so, it may be necessary to implement non-diffusive transport.
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28

Smit, P. B., et T. T. Janssen. « The Evolution of Nonlinear Wave Statistics through a Variable Medium ». Journal of Physical Oceanography 46, no 2 (février 2016) : 621–34. http://dx.doi.org/10.1175/jpo-d-15-0146.1.

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AbstractIn coastal areas and on beaches, nonlinear effects in ocean waves are dominated by so-called triad interactions. These effects can result in large energy transfers across the wave spectrum and result in non-Gaussian wave statistics, which is important for coastal wave propagation and wave-induced transport processes. To model these effects in a stochastic wave model based on the radiative transfer equation (RTE) requires a transport equation for three-wave correlators (the bispectrum) that is compatible with quasi-homogeneous theory. Based on methods developed in optics and quantum mechanics, the authors present a general approach to derive a transport equation for higher-order correlators. The principal result of this work is a coupled set of equations consisting of the radiative transfer equation with a nonlinear forcing term and a new, generalized transport equation for bispectrum. This study discusses the implications and characteristics of the resulting equations and shows that the model contains various shallow- and deep-water asymptotes for nonlinear wave propagation as special cases.
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29

Cattaneo, F. « Challenges to the theory of solar convection ». Proceedings of the International Astronomical Union 2, S239 (août 2006) : 35. http://dx.doi.org/10.1017/s1743921307000075.

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AbstractTurbulent convection carries most of the solar luminosity from the stable radiative interior to the visible surface over a substantial fraction of the solar radius. The turbulent motions are highly nonlinear displaying activity on several spatial and temporal scales. The effects of these motions are to redistribute angular momentum, mix light elements, excite gravity waves and power magnetic activity. In this talk, I shall review some of the recent efforts, mostly based on numerical simulations, to model turbulent convection spanning multiple scale heights. I will discuss what we have learnt about the nature of convective transport, and what the relevant timescales are on which convection operates.
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Prat, V., F. Lignières et G. Lesur. « New prescriptions of turbulent transport from local numerical simulations ». Proceedings of the International Astronomical Union 9, S307 (juin 2014) : 70–75. http://dx.doi.org/10.1017/s1743921314006292.

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AbstractMassive stars often experience fast rotation, which is known to induce turbulent mixing with a strong impact on the evolution of these stars. Local direct numerical simulations of turbulent transport in stellar radiative zones are a promising way to constrain phenomenological transport models currently used in many stellar evolution codes. We present here the results of such simulations of stably-stratified sheared turbulence taking notably into account the effects of thermal diffusion and chemical stratification. We also discuss the impact of theses results on stellar evolution theory.
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31

Garrett, C. Kristopher, et Cory D. Hauck. « On the eigenstructure of spherical harmonic equations for radiative transport ». Computers & ; Mathematics with Applications 72, no 2 (juillet 2016) : 264–70. http://dx.doi.org/10.1016/j.camwa.2015.05.030.

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32

Mehmood, Obaid Ullah, et Constantin Fetecau. « A Note on Radiative Heat Transfer to Peristaltic Flow of Sisko Fluid ». Applied Bionics and Biomechanics 2015 (2015) : 1–9. http://dx.doi.org/10.1155/2015/283892.

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This paper looks at the effects of radiative heat transfer on the peristaltic transport of a Sisko fluid in an asymmetric channel with nonuniform wall temperatures. Adopting the lubrication theory, highly nonlinear coupled governing equations involving power law index as an exponent have been linearized and perturbation solutions are obtained about the Sisko fluid parameter. Analytical solutions for the stream function, axial pressure gradient, axial velocity, skin friction, and Nusselt number are derived for three different cases (i.e., shear thinning fluid, viscous fluid, and shear thickening fluid). The effects of Grashof number, radiation parameter, and other configuration parameters on pumping, trapping, temperature, Nusselt number, and skin friction have been examined in detail. A good agreement has been found for the case of viscous fluid with existing results.
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Olbrant, Edgar, et Martin Frank. « Generalized Fokker–Planck Theory for Electron and Photon Transport in Biological Tissues : Application to Radiotherapy ». Computational and Mathematical Methods in Medicine 11, no 4 (2010) : 313–39. http://dx.doi.org/10.1080/1748670x.2010.491828.

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In this paper, we study a deterministic method for particle transport in biological tissues. The method is specifically developed for dose calculations in cancer therapy and for radiological imaging. Generalized Fokker–Planck (GFP) theory [Leakeas and Larsen, Nucl. Sci. Eng. 137 (2001), pp. 236–250] has been developed to improve the Fokker-Planck (FP) equation in cases where scattering is forward-peaked and where there is a sufficient amount of large-angle scattering. We compare grid-based numerical solutions to FP and GFP in realistic medical applications. First, electron dose calculations in heterogeneous parts of the human body are performed. Therefore, accurate electron scattering cross sections are included and their incorporation into our model is extensively described. Second, we solve GFP approximations of the radiative transport equation to investigate reflectance and transmittance of light in biological tissues. All results are compared with either Monte Carlo or discrete-ordinates transport solutions.
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34

Yan, Kai, Yiman Zhang, Yiyi Tong, Yelu Zeng, Jiabin Pu, Si Gao, Linyuan Li et al. « Modeling the radiation regime of a discontinuous canopy based on the stochastic radiative transport theory : Modification, evaluation and validation ». Remote Sensing of Environment 267 (décembre 2021) : 112728. http://dx.doi.org/10.1016/j.rse.2021.112728.

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35

Begley, S. M., et M. Q. Brewster. « Radiative Properties of MoO3 and Al Nanopowders From Light-Scattering Measurements ». Journal of Heat Transfer 129, no 5 (28 juin 2006) : 624–33. http://dx.doi.org/10.1115/1.2712476.

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The combustion behavior of nanometer-scale energetic materials is much different than micron size or larger materials. Burning rates up to 950 m∕s have been reported for a thermite composition of nanosized aluminum and molybdenum trioxide. The energy transport mechanisms in the reactive wave are still uncertain. The relative contribution of radiation has not yet been quantified. To do so analytically requires dependent scattering theory, which has not yet been fully developed. Radiative properties for nanoaluminum and nanomolybdenum-trioxide were obtained experimentally by comparing light scattering measurements on a one-dimensional slab of powder with multiple-scattering simulations using Monte Carlo and discrete ordinate methods. The equivalent isotropic-scattering extinction coefficient for close-packed molybdenum trioxide (MoO3) nanopowder was found to be 5900±450cm−1; the equivalent isotropic-scattering albedo was 0.97±0.035. Aluminum (Al), which proved to be more difficult to work with, had an albedo of 0.35 and 0.38 from two tests. The radiative conductivity based on the MoO3 results is two orders of magnitude less than the diffusive thermal conductivity, indicating that radiation is not a dominant heat transfer mode for the reactive wave propagation of nanothermites under optically thick conditions.
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36

Liemert, André, Simeon Geiger et Alwin Kienle. « Solutions for single-scattered radiance in the semi-infinite medium based on radiative transport theory ». Journal of the Optical Society of America A 38, no 3 (19 février 2021) : 405. http://dx.doi.org/10.1364/josaa.409898.

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ENDO, Shigeki, Hiroyuki FUJII, Kazumichi KOBAYASHI et Masao WATANABE. « Numerical Investigation of Photon Transport in the Human Neck Based on the Radiative Transfer Theory ». Proceedings of the Thermal Engineering Conference 2019 (2019) : 0123. http://dx.doi.org/10.1299/jsmeted.2019.0123.

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38

HERTY, MICHAEL, et ALBERT N. SANDJO. « ON OPTIMAL TREATMENT PLANNING IN RADIOTHERAPY GOVERNED BY TRANSPORT EQUATIONS ». Mathematical Models and Methods in Applied Sciences 21, no 02 (février 2011) : 345–59. http://dx.doi.org/10.1142/s0218202511005076.

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This paper is devoted to the study of optimal control problems arising in radiotherapy planning problems. The distribution of the radiative intensity in the patient's body is described by a Boltzmann-integro differential equation with position, angular and energy-dependent scattering and absorption coefficients and an energy loss term. The presented discussion is the last in the series of Refs. 13 and 14 discussing radiotherapy problems using the Boltzmann transport equation. We show the existence, uniqueness and regularity of an optimal control using evolution group theory. We extend existing results in order to treat the important case of energy-dependent scattering coefficients.
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39

Keković, G., D. Raković et David Davidović. « Relevance of Polaron/Soliton-Like Transport Mechanisms in Cascade Resonant Isomeric Transitions of Q1D-Molecular Chains ». Materials Science Forum 555 (septembre 2007) : 119–24. http://dx.doi.org/10.4028/www.scientific.net/msf.555.119.

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Our recently proposed quantum approach to biomolecular isomeric-conformational changes and recognition processes, additionally supported by biomolecular resonant recognition model and by quantum-chemical theory of biomolecular non-radiative resonant transitions, is hereby extended to cascade resonant transitions via close intermediate participating isomeric states - which might be related to polaron/soliton-like energy and charge transport mechanisms in Q1Dmolecular chains, whose relevance is explored in this paper.
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Tan, Brent, S. Peng Oh et Max Gronke. « Radiative mixing layers : insights from turbulent combustion ». Monthly Notices of the Royal Astronomical Society 502, no 3 (11 janvier 2021) : 3179–99. http://dx.doi.org/10.1093/mnras/stab053.

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ABSTRACT Radiative mixing layers arise wherever multiphase gas, shear, and radiative cooling are present. Simulations show that in steady state, thermal advection from the hot phase balances radiative cooling. However, many features are puzzling. For instance, hot gas entrainment appears to be numerically converged despite the scale-free, fractal structure of such fronts being unresolved. Additionally, the hot gas heat flux has a characteristic velocity vin ≈ cs, cold(tcool/tsc, cold)−1/4 whose strength and scaling are not intuitive. We revisit these issues in 1D and 3D hydrodynamic simulations. We find that over-cooling only happens if numerical diffusion dominates thermal transport; convergence is still possible even when the Field length is unresolved. A deeper physical understanding of radiative fronts can be obtained by exploiting parallels between mixing layers and turbulent combustion, which has well-developed theory and abundant experimental data. A key parameter is the Damköhler number Da = τturb/tcool, the ratio of the outer eddy turnover time to the cooling time. Once Da > 1, the front fragments into a multiphase medium. Just as for scalar mixing, the eddy turnover time sets the mixing rate, independent of small scale diffusion. For this reason, thermal conduction often has limited impact. We show that vin and the effective emissivity can be understood in detail by adapting combustion theory scalings. Mean density and temperature profiles can also be reproduced remarkably well by mixing length theory. These results have implications for the structure and survival of cold gas in many settings, and resolution requirements for large scale galaxy simulations.
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Pomraning, G. C. « Radiative transfer in Rayleigh–Taylor unstable ICF pellets ». Laser and Particle Beams 8, no 4 (décembre 1990) : 741–51. http://dx.doi.org/10.1017/s0263034600009137.

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A formulation of radiative transfer is discussed describing energy flow in a turbulent mixture in the vicinity of a Rayleigh–Taylor unstable interface, as might be extant in an ICF pellet. Included in this discussion are (1) the method of smoothing and the Liouville master equation approaches in the case of Markovian statistics as the description of the fluid mixing, (2) the use of asymptotics to derive various limiting descriptions of the Markov model, (3) the use of the theory of alternating renewal processes to obtain an integral equation formulation for non-Markovian statistics, and (4) the reduction of this non-Markovian integral formulation to integro-differential equations of the generic transport form, with statistical effects represented by pseudoscattering terms.
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42

Kitiashvili, Irina N. « Radiative hydrodynamic simulations of turbulent convection and pulsations of Kepler target stars ». Proceedings of the International Astronomical Union 9, S301 (août 2013) : 193–96. http://dx.doi.org/10.1017/s1743921313014312.

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AbstractThe problem of interaction of stellar pulsations with turbulence and radiation in stellar convective envelopes is central to our understanding of excitation mechanisms, oscillation amplitudes and frequency shifts. Realistic (“ab initio”) numerical simulations provide unique insights into the complex physics of pulsation-turbulence-radiation interactions, as well as into the energy transport and dynamics of convection zones, beyond the standard evolutionary theory. 3D radiative hydrodynamics simulations have been performed for several Kepler target stars, from M- to A-class along the main sequence, using a new ‘StellarBox’ code, which takes into account all essential physics and includes subgrid scale turbulence modeling. The results reveal dramatic changes in the convection and pulsation properties among stars of different mass. For relatively massive stars with thin convective envelopes, the simulations allow us to investigate the dynamics the whole envelope convection zone including the overshoot region, and also look at the excitation of internal gravity waves. Physical properties of the turbulent convection and pulsations, and the oscillation spectrum for two of these targets are presented and discussed in this paper. In one of these stars, with mass 1.47 M⊙, we simulate the whole convective zone and investigate the overshoot region at the boundary with the radiative zone.
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Spence, E. W., et D. A. Kaminski. « Thermal Evaluation of a Dry Nonrotating Thin Section Contact Bearing ». Journal of Manufacturing Science and Engineering 118, no 4 (1 novembre 1996) : 610–14. http://dx.doi.org/10.1115/1.2831074.

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The thermal resistance of an angular contact ball bearing as a function of the radial and axial load is investigated numerically. An elastic stress analysis, based on Hertzian contact theory, provides circumferentially-varying contact areas for input to the thermal model. A finite difference model of the combined conductive, convective and radiative transport from the inner to outer race is used to calculate the overall thermal resistance of the bearing.
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Yu, Sungduk, et Michael S. Pritchard. « A Strong Role for the AMOC in Partitioning Global Energy Transport and Shifting ITCZ Position in Response to Latitudinally Discrete Solar Forcing in CESM1.2 ». Journal of Climate 32, no 8 (1 avril 2019) : 2207–26. http://dx.doi.org/10.1175/jcli-d-18-0360.1.

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Abstract Ocean circulation responses to interhemispheric radiative imbalance can damp north–south migrations of the intertropical convergence zone (ITCZ) by reducing the burden on atmospheric energy transport. The role of the Atlantic meridional overturning circulation (AMOC) in such dynamics has not received much attention. Here, we present coupled climate modeling results that suggest AMOC responses are of first-order importance to muting ITCZ shift magnitudes as a pair of hemispherically asymmetric solar forcing bands is moved from equatorial to polar latitudes. The cross-equatorial energy transport response to the same amount of interhemispheric forcing becomes systematically more ocean-centric when higher latitudes are perturbed in association with strengthening AMOC responses. In contrast, the responses of the Pacific subtropical cell are not monotonic and cannot predict this variance in the ITCZ’s equilibrium position. Overall, these results highlight the importance of the meridional distribution of interhemispheric radiative imbalance and the rich buffering of internal feedbacks that occurs in dynamic versus thermodynamic (slab) ocean modeling experiments. Mostly, the results imply that the problem of developing a theory of ITCZ migration is entangled with that of understanding the AMOC’s response to hemispherically asymmetric radiative forcing—a difficult topic deserving of focused analysis across more climate models.
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Mathews, Abhilash. « Impacts of first- and second-order optimization in deep learning of turbulent fluctuations from gas puff imaging ». Journal of Physics : Conference Series 2397, no 1 (1 décembre 2022) : 012001. http://dx.doi.org/10.1088/1742-6596/2397/1/012001.

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Abstract Following the results of [1], which demonstrates a novel method to translate 2-dimensional measurements of HeI line radiation on turbulent scale into local plasma fluctuations via an integrated deep learning framework, this manuscript investigates the results when applying two separate techniques for optimization: Adam and L-BFGS. Fundamentally, the two approaches apply the same set of constraints and loss functions that combine neutral transport physics and collisional radiative theory for the 33D − 23P (587.6 nm line) transition in atomic helium whilst training the networks. The impact of these first- and second-order optimization techniques are investigated to examine their influence on numerical convergence and stability when seeking to analyze turbulent dynamics via gas puff imaging in experimental plasmas.
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Walder, Rolf, et Doris Folini. « 3D-hydrodynamics of colliding winds in massive binaries ». Symposium - International Astronomical Union 212 (2003) : 139–47. http://dx.doi.org/10.1017/s0074180900211741.

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The pinwheel nebulae observed in some WC-binaries essentially mirror a transport phenomenon. We show the importance of the central wind collision zone in setting the ‘initial conditions’ for this transport. In order to understand some of the newly observed features, we postulate that standard theory of colliding flows must be extended by considering radiative breaking, heat-conduction, and the clumped character of the winds. We suggest that clumped winds can be modeled by highly compressible turbulence and outline some consequences for the physics of the wind collision zone. With regard to dust production we argue that the system center is the only location where dust nucleation can happen.
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Karnauskas, Kristopher B., Gregory C. Johnson et Raghu Murtugudde. « An Equatorial Ocean Bottleneck in Global Climate Models ». Journal of Climate 25, no 1 (1 janvier 2012) : 343–49. http://dx.doi.org/10.1175/jcli-d-11-00059.1.

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Abstract The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.
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Masada, Youhei. « Large solar-type magnetic reconnection model for magnetar giant flare ». Proceedings of the International Astronomical Union 4, S259 (novembre 2008) : 123–24. http://dx.doi.org/10.1017/s1743921309030282.

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AbstractWe construct a magnetic reconnection model for magnetar giant flare in the framework of solar flare/coronal mass ejection theory. As is the case with the solar flare, the explosive magnetic reconnection plays a crucial role in the energetics of the magnetar flare. A key physics controlling the energy transport in the system, on the other hand, is the radiative process unlike that in the solar flare. After the release of the magnetic energy via the magnetic reconnection, the radiative heat flux drives the baryonic evaporation. Our model can predict that the baryonic matter evaporated in the preflare stage would be the origin of the radio emitting ejecta observed in association with the giant flare on 2004 December 27 from SGR1806-20.
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Kahnert, M. « Modelling the optical and radiative properties of freshly emitted light absorbing carbon within an atmospheric chemical transport model ». Atmospheric Chemistry and Physics Discussions 9, no 6 (26 novembre 2009) : 25443–86. http://dx.doi.org/10.5194/acpd-9-25443-2009.

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Abstract. Light absorbing carbon (LAC) aerosols have a complex, fractal-like aggregate structure. Their optical and radiative properties are notoriously difficult to model, and approximate methods may introduce large errors both in the interpretation of aerosol remote sensing observations, and in quantifying the direct radiative forcing effect of LAC. In this paper a method based on rigorous electromagnetic theory is employed for computing the optical properties of freshly emitted, externally mixed LAC aggregates. The computations are performed at wavelengths of 440 nm and 870 nm, and they cover the entire size range relevant for modelling these kinds of aerosols. The method for solving the electromagnetic scattering and absorption problem for aggregates proves to be sufficiently stable and fast to make accurate multiple-band computations of LAC optical properties feasible. The results from the electromagnetic computations are processed such that they can readily be integrated into a chemical transport model (CTM), which is a prerequisite for constructing robust observation operators for chemical data assimilation of aerosol optical observations. A case study is performed, in which results obtained with the coupled optics/CTM model are employed as input to detailed radiative transfer computations at a polluted European location. It is found that the still popular homogeneous sphere approximation significantly underestimates the radiative forcing at top of atmosphere as compared to the results obtained with the aggregate model. Notably, the LAC forcing effect predicted with the aggregate model is less than that one obtains by assuming a prescribed mass absorption coefficient for LAC.
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Bhatti, M. M., C. M. Khalique, Tasveer A. Bég, O. Anwar Bég et Ali Kadir. « Numerical study of slip and radiative effects on magnetic Fe3O4-water-based nanofluid flow from a nonlinear stretching sheet in porous media with Soret and Dufour diffusion ». Modern Physics Letters B 34, no 02 (9 décembre 2019) : 2050026. http://dx.doi.org/10.1142/s0217984920500268.

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Increasingly sophisticated techniques are being developed for the manufacture of functional nanomaterials. A growing interest is also developing in magnetic nanofluid coatings which contain magnetite nanoparticles suspended in a base fluid and are responsive to external magnetic fields. These nanomaterials are “smart” and their synthesis features high-temperature environments in which radiative heat transfer is present. Diffusion processes in the extruded nanomaterial sheet also feature Soret and Dufour (cross) diffusion effects. Filtration media are also utilized to control the heat, mass and momentum characteristics of extruded nanomaterials and porous media impedance effects arise. Magnetite nanofluids have also been shown to exhibit hydrodynamic wall slip which can arise due to non-adherence of the nanofluid to the boundary. Motivated by the multi-physical nature of magnetic nanomaterial manufacturing transport phenomena, in this paper, we develop a mathematical model to analyze the collective influence of hydrodynamic slip, radiative heat flux and cross-diffusion effects on transport phenomena in ferric oxide ([Formula: see text]-water) magnetic nanofluid flow from a nonlinear stretching porous sheet in porous media. Hydrodynamic slip is included. Porous media drag is simulated with the Darcy model. Viscous magnetohydrodynamic theory is used to simulate Lorentzian magnetic drag effects. The Rosseland diffusion flux model is employed for thermal radiative effects. A set of appropriate similarity transformation variables are deployed to convert the original partial differential boundary value problem into an ordinary differential boundary value problem. The numerical solution of the coupled, multi-degree, nonlinear problem is achieved with an efficient shooting technique in MATLAB symbolic software. The physical influences of Hartmann (magnetic) number, Prandtl number, Richardson number, Soret (thermo-diffusive) number, permeability parameter, concentration buoyancy ratio, radiation parameter, Dufour (diffuso-thermal) parameter, momentum slip parameter and Schmidt number on transport characteristics (e.g. velocity, nanoparticle concentration and temperature profiles) are investigated, visualized and presented graphically. Flow deceleration is induced with increasing Hartmann number and wall slip, whereas flow acceleration is generated with greater Richardson number and buoyancy ratio parameter. Temperatures are elevated with increasing Dufour number and radiative parameter. Concentration magnitudes are enhanced with Soret number, whereas they are depleted with greater Schmidt number. Validation of the MATLAB computations with special cases of the general model is included. Further validation with generalized differential quadrature (GDQ) is also included.
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