On a model in radiation hydrodynamics

We consider a simplified model arising in radiation hydrodynamics based on the Navier–Stokes–Fourier system describing the macroscopic fluid motion, and a transport equation modeling the propagation of radiative intensity. We establish global-in-time existence for the associated initial–boundary value problem in the framework of weak solutions.     

On a property of the set of radiation patterns

Consider the exterior boundary value problem (▽² + K²) u = 0, in Ω, k >0. $\text{u¦}{}_{\mathrm{\Gamma }}\text{= h}$, where Γ is a smooth closed connected surface in $\text{R}$³, $\text{u ~}\text{exp}\text{(ik ¦x¦)¦x¦}{}^{\mathrm{?1}}\text{∝(k, n)}\text{as}\text{¦X¦→ ∞, n = x¦x¦}{}^{\mathrm{?1}}$, ∝ is called the radiation pattern. We prove that when h runs through any dense set in L²(Γ) the corresponding radiation pattern ∝(k,n) runs through a dense set in L²(S²) for any k >0, where S² is the unit sphere in $\text{R}$³.     

Tunneling radiation of a Gibbons-Maeda dilaton black hole

We use the Parikh-Wilczek method to treat Hawking radiation as a tunneling process across the event horizon and calculate the emission rate of a Gibbons-Maeda dilaton black hole. We show that if self-gravitation is taken into account, then the radiation deviates from the purely thermal spectrum, and the corrected spectrum is consistent with an underlying unitary theory. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 1, pp. 172–175, April, 2007.     

Quantum statistical theory of radiation friction of a relativistic electron

We comprehensively investigate the effect of quantum space-time nonlocality that accounts for retardation of the electron interaction with both the electron’s own radiation field and the fluctuation field of the electromagnetic vacuum. We rigorously show that the quantum nonlocality effect eliminates the self-acceleration and the causality violation paradoxes that are inherent in the classical theory of radiation friction. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 158, No. 3, pp. 478–496, March, 2009.     

Emission of Cherenkov radiation as a mechanism for Hamiltonian friction

We study the motion of a heavy tracer particle weakly coupled to a dense, weakly interacting Bose gas exhibiting Bose–Einstein condensation. In the so-called mean-field limit, the dynamics of this system approaches one determined by nonlinear Hamiltonian evolution equations. We prove that if the initial speed of the tracer particle is above the speed of sound in the Bose gas, and for a suitable class of initial states of the Bose gas, the particle decelerates due to emission of Cherenkov radiation of sound waves, and its motion approaches a uniform motion at the speed of sound, as time t tends to ∞.     

Normal-mode radiation in the critical section of a variable-width waveguide

The problem of wave propagation in a slowly tapered waveguide is investigated. It is shown that in the case of a straight boundary between two media the field in the transition region is described in terms of Airy functions.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 165, pp. 166–176, 1987.     

Acoustic radiation from a phased line source at a fluid-solid boundary

Author to whom all correspondence should be addressed (email: Richard.Tew@Nottingham.ac.uk) The coupled wave dynamics of a compressible fluid and an elasticsolid are studied when the motion is forced by a non uniformline source lying in their common interface. The nonuniformityarises as a result of a distribution in phase along the forcingsite, and this is taken as being representative of the effectsof the scattering of an acoustic plane wave which is obliquelyincident upon a shallow, surface-breaking inhomogeneity in thesolid. An appropriate boundary-value problem is posed and solvedexactly using an integral transform. This solution is then decomposedinto its constituent asymptotic wave contributions, and thestructure of each of these contributions is examined in thefar field for all values of the phasing parameter.     

The electromagnetic field of a dipole radiation source in a slowly moving conducting medium

We solve the problem of determining the electromagnetic field created by a dipole radiation source in a conducting, homogeneous, isotropic, slowly moving medium. The investigations are carried out depending on the orientation of the dipole source and the velocity vector of the medium.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 28, 1988, pp. 31–35.     

Pointwise structure of a radiation hydrodynamic model in one-dimension

In this paper, we study the nonlinear stability and the pointwise structure around a constant equilibrium for a radiation hydrodynamic model in 1-dimension, in which the behavior of the fluid is described by a full Euler equation with certain radiation effect. It is well-known that the classical solutions of the Euler equation in 1-D may blow up in finite time for general initial data. The global existence of the solution in this paper means that the radiation effect stabilizes the system and prevents the formation of singularity when the initial data is small. To study the precise effect of the radiation in this model, we also treat the pointwise estimates of the solution for the original nonlinear problem by combining the Green's function for the linearized radiation hydrodynamic equations with the Duhamel's principle. The result in this paper shows that the pointwise structure of this model is similar to that of full Navier-Stokes equations in 1-D.     

An iterative method for solving a non-stationary radiation diffusion system

The purpose of this paper is to give a systematic treatment for a non-stationary radiation diffusion problem which involves a coupled system of integro-differential equations and some initial and boundary conditions. Using an iterative scheme we obtain a recursion formula for the calculation of approximate solutions as well as their error estimates. It is shown that the sequence of approximations converges to a unique classical solution which also leads to an existence-uniqueness theorem. In addition, we show that the solution is positive and depends continuously on the external source and the initial-boundary data. The latter property together with the existence-uniqueness theorem insure that the system is well-posed in the sense of Hadamard.

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Zusammenfassung Mit dieser Arbeit wird bezweckt, eine systematische Behandlung eines nichtstationären Strahlungsdiffusionsproblems zu geben, das mathematisch beschrieben werden kann durch ein gekoppeltes System von Integrodifferentialgleichungen mit Anfangs- und Randbedingungen. Wir stellen eine Rekursionsformel für die Berechnung von Näherungslösungen und zugehörigen Fehlerabschätzungen auf und zeigen, dass die Folge dieser Näherungslösungen gegen die eindeutige klassische Lösung konvergiert. Dabei ergibt sich auch ein Existenz- und Eindeutigkeitssatz, Ferner zeigen wir, dass die Lösung stetig von der externen Quelle und den Anfangs- und Randbedingungen abhängt. Zusammen mit dem Existenz- und Eindeutigkeitssatz garantiert uns dies, dass das System im Sinne von Hadamard wohldefiniert ist.

     

Calculation of the radiation intensity of a concentrated system of atoms

Using formulas for the decay probability of an inverted, concentrated atomic system, an exact equation is obtained for radiation intensity. In the asymptotic region of existence of a superradiant pulse, the given equation differs from the standard one obtained on the basis of a quasiclassical approximation.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 169, pp. 166–168, 1988.     

Temperature field of a layer of a fibrous composite material under conditions of external thermal radiation

On the basis of an expression for the scattering phase function of an individual fiber, relations modeling radiative properties of fibrous composites are obtained. We calculate the temperature state of a layer of such a material under condition of external thermal radiation. Dependences of temperature distributions on the volume fraction of fibers in the composite, their reflectance, and size are investigated. Translated from Matematychni Metody ta Fizyko-Mekhanichni Polya, Vol. 51, No. 1, pp. 185–193, January–March, 2008.     

Analysis of the radiation properties of a planar antenna on a photonic crystal substrate

This paper is concerned with the rigorous investigation of the radiation properties of a planar patch antenna on a photonic crystal substrate. Under the assumptions that the driving frequency of the antenna lies within the band gap of the photonic crystal substrate and that the crystal satisfies a symmetry condition, we prove that the power radiated into the substrate decays exponentially. To do this, we reduce the radiation problem to the study of the well‐posedness of a weakly singular integral equation on the patch antenna, and to the study of the asymptotic behaviour of the corresponding Green's function. We also provide a mathematical justification of the use of a photonic crystal substrate as a perfect mirror at any incidence angle. Copyright © 2001 John Wiley & Sons, Ltd.     

Heisenberg operators of a Dirac particle interacting with the quantum radiation field

We consider a quantum system of a Dirac particle interacting with the quantum radiation field, where the Dirac particle is in a 4×4-Hermitian matrix-valued potential V. Under the assumption that the total Hamiltonian HV is essentially self-adjoint (we denote its closure by ), we investigate properties of the Heisenberg operator (j=1,2,3) of the j-th position operator of the Dirac particle at time t∈R and its strong derivative dxj(t)/dt (the j-th velocity operator), where xj is the multiplication operator by the j-th coordinate variable xj (the j-th position operator at time t=0). We prove that D(xj), the domain of the position operator xj, is invariant under the action of the unitary operator for all t∈R and establish a mathematically rigorous formula for xj(t). Moreover, we derive asymptotic expansions of Heisenberg operators in the coupling constant q∈R (the electric charge of the Dirac particle).     

QED2+1 radiation effects in a strong magnetic field

We develop the eigenfunction method for the Dirac operator in a background magnetic field in the (2+1)-dimensional quantum electrodynamics (QED₂₊₁). In the eigenfunction repressentation, we find the exact solutions and the Green's functions of the Dirac equation in a strong constant homogeneous magnetic field in 2+1 dimensions. In the one-loop QED₂₊₁ approximation, we derive the effective Lagrangian, the density of vacuum fermions induced by the field, and the electron mass operator in a homogeneous background magnetic field. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 121, No. 3, pp. 412–423, December, 1999.     

Unsteady energy transfer in a layer of gray gas by thermal radiation

Zusammenfassung Das Aufheizen oder Abkühlen einer ruhenden Schicht eines strahlenden Gases wird analysiert. Streuung der Strahlung wird dabei vernachlässigt, und der Wärmetransport durch Leitung und Konvektion wird als vernachlässigbar klein im Vergleich zum Strahlungsaustausch betrachtet. Ein Schema wird entwickelt für die numerische Lösung der nichtlinearen Integral-Differentialgleichung der Energie. Von einer beliebig angenommenen Anfangsverteilung der Temperatur ausgehend werden Temperaturen und Strahlungs-Wärmestromdichten als Funktion der Zeit ermittelt. Weiterhin werden für konstante und sich ändernde Stoffgrössen die Einflüsse der optischen Dicke, der Anfangstemperaturverteilung und der einfallenden Strahlung auf die Temperaturverteilung und den Wärmetransport dargestellt.     

Analysis of the energetic radiation intensity of a linear antenna array radiating nonsinusoidal signals

We present the energetic radiation intensity (ERI) as the quadratic form of the family of integral operators on a finite interval. The kernel of each operator is the autocorrelation function of the signal, which is radiated in the given direction. Spectral representation of the operators gives a fast-converging series representation of the ERI. For the signals, whose Fourier transforms are rational functions of the frequency, spectral analysis of the operators is reduced to finite-dimensional linear systems. Moreover, for such signals we express the ERI as the linear combination of the monochromatic directivity diagrams, evaluated in the complex poles of the signal’s Fourier transform. For the isotropic array elements and the most important amplitude distributions the ERI is obtained explicitly. We consider in detail a signal given by a truncated decaying exponent. Bibliography: 32 titles. Dedicated to Vasilii Mikhailovich Babich with high respect and gratitude __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 332, 2006, pp. 239–267.     

Decay rates of solutions to a P1-approximation model arising from radiation hydrodynamics

This paper is concerned with the global existence and large time behavior of solutions to Cauchy problem for a P1-approximation radiation hydrodynamics model. The global-in-time existence result is established in the small perturbation framework around a stable radiative equilibrium states in Sobolev space $H^4({\mathbb{R}}^3)$. Moreover, when the initial perturbation is also bounded in $L^1({\mathbb{R}}^3)$, the $L^2$-decay rates of the solution and its derivatives are achieved accordingly. The proofs are based on the Littlewood–Paley decomposition techniques and elaborate energy estimates in different frequency regimes.     

Isoperimetric inequalities involving heat flow—The case of a one-sided linear radiation condition

We obtain an isoperimetric lower bound for the rate of heat flow across a strip-like region when the temperature is constant on one boundary component and satisfies a linear radiation condition on the other. By comparison to the author's related result in [2], this isoperimetric bound applies to more general regions under less general boundary conditions.

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Zusammenfassung Wir erhalten eine isoperimetrische untere Schranke für den Wärmefluß durch ein streifenartiges Gebiet in dem Fall, wo die Temperatur auf einer Randkomponente konstant ist und einer linearen Radiationsbedingung auf der anderen genügt. Im Vergleich mit dem verwandten Resultat in [2] bezieht sich diese isoperimetrische Schranke unter spezielleren Randbedingungen auf allgemeinere Gebiete.