Allowance For Dissipation Research Articles

The Surface polaritons with negative group velocity at the vacuum-resonant dielectric interface

Surface polaritons most clearly manifest their properties when the processes of energy dissipation are neglected. In this case, they are collective excitations that propagate exclusively along the interface, and the energy flux of surface polaritons deep into the medium becomes zero. A more realistic model of a surface polariton assumes that dissipation processes are always present. In this case, the surface polariton partially penetrates deep into the medium due to the appearance of the real part of the propagation constant in this direction. It should be emphasized that in the region of existence of a surface polariton, the dielectric constant of the medium has strong frequency dependence; therefore, by virtue of the Kramers-Kronig relations, the dielectric constant must have an imaginary part, which is precisely responsible for the dissipation processes. In this paper we show that when surface polaritons are considered at the vacuum-resonance insulator boundary and strict allowance for dissipation, frequency regions arise in which surface polaritons have a negative group velocity and the dielectric acquires the properties of a metamaterial.

Slow-Wave System of Double Shifted Impedance Comb

Using the partial domain method, surface integral equations are obtained for slow-wave systems of double shifted combs taking dissipation on all metal surfaces into account. The case of aliquot comb periods is considered. The quadratic functionals are proposed as dispersion equations. A method to solve complex dispersion equations in the form of functionals for complex constants of propagation is proposed by means of their joint iterations with integral equations. The results of calculating the dispersion with allowance for dissipation in several structures considered are presented.

Замедляющая система двойная сдвинутая импедансная гребенка"

AbstractUsing the partial domain method, surface integral equations are obtained for slow-wave systems of double shifted combs taking dissipation on all metal surfaces into account. The case of aliquot comb periods is considered. The quadratic functionals are proposed as dispersion equations. A method to solve complex dispersion equations in the form of functionals for complex constants of propagation is proposed by means of their joint iterations with integral equations. The results of calculating the dispersion with allowance for dissipation in several structures considered are presented.

The Influence of Dissipation on the Dispersion Characteristics of Surface Spin Waves

Dissipation of surface spin waves propagating in arbitrary directions in a magnetized ferromagnetic film is studied. It is shown that the allowance for dissipation restricts the domain of possible wave vectors to a finite region and leads to the appearance above this region of the continuation of a dispersion surface in the form of an inverted cap with a negative slope and a large damping of the waves. It is noted that the solution gives an infinite number of almost coincident dispersion surfaces with a sharp increase in the damping coefficient with each next surface, so that the waves become practically nonpropagating. The analysis of the dispersion surfaces shows that the lower part has a positive slope and describes forward waves, the damping of which is proportional to a small dissipation constant but, in the upper part of the surface, the damping coefficient sharply increases. It is found that the directions of the group velocities of the waves substantially change in comparison with a dissipationless medium and some frequency and angular restrictions on the propagation of surface waves also become different.

Magnetization Dynamics in Two-Dimensional Arrays of Square Microelements

The collective magnetization motion in an array of magnetostatically interacting ferromagnetic square elements is studied theoretically and experimentally. Dispersion laws are obtained for collective modes for some particular cases of the distribution of the topological charges π T of magnetic vortices in particles. Resonance curves are plotted with allowance for dissipation for various values of π T . An experimental investigation of the ferromagnetic resonance in a two-dimensional array of particles qualitatively supports the calculation results.

Amplification and generation of surface plasmon polaritons in a semiconductor film – dielectric structure

The peculiarities of propagation and amplification of surface waves of plasmon polariton type in a planar semiconductor film – dielectric structure are considered for the THz frequency region, with allowance for dissipation in a semiconductor. Two spectral regions are found, where the group velocity of surface plasmon polaritons is negative. It is shown that in these regions the structure can be considered as an amplifying waveguide with distributed feedback and a high gain with respect to the reflected and transmitted signals. The possibility of generation of electromagnetic radiation in such structures is established.

Stabilizing effect of a harmonized field on the magnetic resonance position

An effect wherein the magnetic resonance position is stabilized by a magnetic-field modulation periodic in time is investigated in a two-level system in the density-matrix formalism. An exact solution for the density matrix at resonance is found. It is shown that at resonance the spin-flip transition probability is independent of the shape of the field, i.e., the fundamental resonance is stabilized against a matched variation of the longitudinal and transverse magnetic fields. A differential equation for the transition probability is obtained. The dependence of the time-averaged spin-flip probability an normalized Larmor frequency is investigated numerically for different model parameters with allowance for dissipation and decoherence. It is shown that the resonance linewidths increase substantially with increasing dissipation and decoherence. The position of the fundamental resonance is independent of the field deformation and the dissipation; only the width of the resonance varies. The odd parametric (multiphoton) resonance transitions are investigated. The static magnetization induced by a harmonized field is examined. This study may find application for analysis of interference experiments, refinement of the design of magnetic spectrometers, and manipulation of qubits.

Quantum Nonlinear Oscillator with Two Degrees of Freedom in a Laser Field

The semiclassical dynamics of a quantum nonlinear oscillator with two degrees of freedom and anharmonicity of the fourth order in a periodic laser field is studied both analytically and numerically. In the absence of external excitation and dissipation, the equations of motion for the mean values of the coordinate and momentum operators of both degrees of freedom reduce to the equation of a one‐dimensional nonlinear pendulum. The general solution of this equation is written in terms of the Jacobian elliptic functions. As can be expected, the energy of the free oscillator is redistributed periodically between degrees of freedom. The periodic excitation of the nonlinear oscillator may substantially change its motion pattern. Using as an example an oscillator with two coupled vibrational degrees of freedom, it is numerically shown that the amount of laser photons absorbed depending on the parameter values and initial conditions may vary with time in a rather complex manner, including chaotic oscillations. A nonlinear oscillator is capable of manifesting bistable behavior with allowance for dissipation. The analytical condition for the origination of bistability is found. Examples of the bistable dependence of the number of quanta in the oscillator vibrational mode on the level of laser excitation are presented.

Critical layer formation in a stratified medium with mean shear flows

The problem of the excitation of internal waves with a given wave number k and frequency ω in a stratified medium with shear flows is considered. The internal wave field of the form v(z)exp(−iωt+ikx) established as t→∞ in a medium without dissipation has a singular point at the level z=z0 (critical level), at which the flow velocity U(z) coincides with the phase velocity ω/k. Dissipative effects (viscosity and heat conduction) smooth out this singularity. An exact solution of the model equation describing as t→∞ and z→z0 the field excited by oscillating sources activated at t=0 is constructed with allowance for dissipation. This makes it possible to describe the limiting steady-state field, determine the critical layer as the neighborhood of the critical level in which dissipation effects are important, and to estimate its width and the rate of convergence to the limiting steady-state regime. The asymptotic behavior of the fields is examined for Ri≫1, where Ri is the Richardson number. It is shown that when the well-known Miles stability condition Ri>1/4 is satisfied there are no natural oscillations with a critical level.

Stability of non isothermal flow of a film of viscous liquid on an inclined plane

A study is made of the stability of nonisothermal flow of a film of viscous liquid down an inclined plane under the influence of gravity with allowance for dissipation of energy in the flow. It is assumed that the liquid is incompressible, and that its physical properties do not depend on the temperature. On the free surface of the film, allowance is made for evaporation and condensation effects. The treatment is in the long-wavelength approximation of the method proposed by Yih Chia-shun [1]. The expression obtained for the critical Reynolds number at which the flow becomes unstable indicates that viscous dissipation plays a destabilizing part in a nonisothermal flow.

Equilibrium and stability in a high-current discharge in a dense plasma under conditions of radiative conduction

Equilibrium and stability are examined for a high-current self-compressed discharge:in a dense, optically opaque plasma of finite conductivity, with allowance for dissipation via radiative heat transfer. If the thermal conductivity is high, the plasma temperature is virtually constant throughout the cross-section of the discharge, whereas the density and pressure fall off fairly rapidly away from the axis. The spectrum for small oscillations shows that such an equilibrium discharge is unstable with respect to short-wave hydrodynamic oscillations (bending and necking) if the plasma conductivity is low. Instability can develop only for long-wave perturbations in a cylindrical discharge, and also for a nonequilibrium discharge when the rise time is iess than the equilibration time. A planar equilibrium discharge is stable, while a cylindrical equilibrium discharge in a dense low-temperature plasma is more stable than one in a high-temperature plasma.