Surface polaritons in a dielectric at a boundary with a metal in a static electric field

The existence of surface polaritons in a dielectric at a boundary with an ideal metal or superconductor in a static electric field is predicted. The frequency regions in which polaritons exist are substantially different for opposite orientations of the electric field, so that a change in the direction of the field signifies “switching on” or “switching off” of surface polaritons with a fixed frequency. Pis'ma Zh. éksp. Teor. Fiz. 68, No. 12, 876–880 (25 December 1998)     

Dust particles in a thermophoretic trap in a plasma

The feasibility of confining dust particles in a plasma by thermophoretic forces was demonstrated. An extended dust structure in a positive glow discharge column was experimentally obtained at liquid nitrogen temperature. The dust structure was confined in an electrostatic-thermal trap, in which vertical stability was provided by the summed action of longitudinal electrostatic field and thermophoretic forces. Traps of this kind can be analyzed in terms of the general principles developed for confining particles in traps with the use of electric and magnetic multipole fields. We were able to change the shape and volume of the structure and even separate it into parts by varying temperature fields.     

Chaotic mixing in a steady flow in a microchannel

We report experiments on mixing of a passively advected fluorescent dye in a low Reynolds number flow in a microscopic channel. The channel is a chain of repeating segments with a custom designed profile that generates a steady three-dimensional flow with stretching and folding, and chaotic mixing. A few statistical characteristics of mixing in the flow are studied and are all found to agree with theoretical and experimental results for the flows in the Batchelor regime of mixing that are chaotic in time. The proposed microchannel provides fast and efficient mixing and is simple to fabricate.     

Impurity diffusion in a gas flow in a channel

The impurity concentration N in a gas flow in a channel is approximately calculated. In a number of cases, the wall losses of impurities in the channel can be taken into account by introducing an effective lifetime τ that describes the diffusion drift of the impurity from the flow toward the walls.     

Thermodynamics of a Charged Particle in a Noncommutative Plane in a Background Magnetic Field

Landau system in noncommutative space has been considered. To take into account the issue of gauge invariance in noncommutative space, we incorporate the Seiberg-Witten map in our analysis. Generalised Bopp-shift transformation is then used to map the noncommutative system to its commutative equivalent system. In particular we have computed the partition function of the system and from this we obtained the susceptibility of the Landau system and found that the result gets modified by the spatial noncommutative parameter θ. We also investigate the de Hass–van Alphen effect in noncommutative space and observe that the oscillation of the magnetization and the susceptibility gets noncommutative corrections. Interestingly, the susceptibility in the noncommutative scenario is non-zero in the range of the magnetic field greater than the threshold value which is in contrast to its commutative counterpart. The results obtained are valid upto all orders in the noncommutative parameter θ.     

Avalanches in a nonlinear oscillator chain in a periodic potential

We consider the dynamics of a chain of coupled units evolving in a periodic substrate potential. The chain is initially in a flat state and situated in a potential well. A bias force, acting as a weak driving mechanism, is applied at a single unit of the chain. We study the instigation of directed transport in two types of system: (i) a microcanonical situation associated with deterministic and conservative dynamics and (ii) the Langevin dynamics when the system is in contact with a heat bath. Interestingly, for the deterministic and conservative dynamics the directed transport is drastically enhanced compared with its Langevin counterpart. In particular, in the deterministic and conservative regime a self-organised redistribution of energy triggers huge-sized avalanches yielding ultimately accelerated transport of the chain. In contrast, in the thermally-assisted process between avalanches the chain settles always into a pinned metastable state impeding continual accelerated chain motion.     

Mean force on a small sphere in a sound field in a viscous fluid

A mean force exerted on a small rigid sphere by a sound wave in a viscous fluid is calculated. The force is expressed as a sum of drag force coming from the external steady flow existing in the absence of the sphere and contributions that are cross products of velocity and velocity derivatives of the incident field. Because of the drag force and an acoustic streaming generated near the sphere, the mean force does not coincide with the acoustic radiation pressure, i.e., the mean momentum flux carried by the sound field through any surface enclosing the sphere. If the sphere radius R is considerably smaller than the viscous wave penetration depth delta, the drag force can give the leading-order contribution (in powers of delta/R) to the mean force and the latter can then be directed against the radiation pressure. In another limit, delta< or =R, the drag force and acoustic streaming play a minor role, and the mean force reduces to the radiation pressure, which can be expressed through source strengths of the scattered sound field. The effect of viscosity can then be significant only if the incident wave is locally plane traveling.     

Relaxation of a dislocation in a nanocrystallite

Experimental studies of dislocations in nanoparticles are just beginning. The corresponding theoretical models are still lacking. In this context, the author analyzes relaxation of a dislocation in a nanoparticle. Mechanistically, this process is considered to occur primarily via dislocation drift induced by the stress-related image forces. Elementary dislocation displacements include the formation of a kink at one of the sides of the dislocation line, its diffusion along this line, and annihilation at the opposite side. For this mechanism, the dependence of the time of dislocation disappearance on the nanoparticle size has been identified.     

Dipolar excitons in a potential trap in a magnetic field

The conditions for observing the Zeeman spin splitting compensation in an exciton Bose gas have been investigated. The magnetoluminescence of spatially indirect, dipolar excitons in a 25-nm-wide GaAs/AlGaAs quantum well upon their accumulation in a lateral electrostatic trap has been studied in the Faraday geometry. The critical magnetic field B _cr below which the spin (paramagnetic) splitting of the luminescence line for a heavy-hole exciton at the trap center is almost completely compensated due to the exchange interaction in a dense Bose gas has been found to increase linearly with exciton concentration in qualitative agreement with the theory. Using a potential trap is fundamentally important. Incomplete compensation is observed in a homogeneous photoexcitation spot for dipolar excitons: the splitting is considerably smaller than that for a spatially direct exciton but differs noticeably from zero. The spin splitting compensation effect is observed only under neutral charge balance conditions—there is no Zeeman splitting suppression in a charged quantum well.     

Dynamics of a nonmagnetic drop suspended in a magnetic fluid in a rotating magnetic field

The behavior of a nonmagnetic drop suspended in a magnetic fluid and subjected to the action of a rotating magnetic field is studied experimentally. The configurations of the drop in the form of prolate and oblate ellipsoids of revolution in the rotating field are investigated, and disintegration of the drop in the rotating field and the development of comb instability of its surface under certain conditions are observed.     

Plasmons at a hole in a screen

The field distribution and the spectrum of plasma eigenmodes are determined for a circular hole in a screen having the form of a hyperboloid of revolution. The spectrum of plasmons is obtained for a planar screen with a circular hole. The symmetric mode with m=1 can be excited in the field of a dipole oriented along the screen plane, whereas the antisymmetric mode with m=0 can be excited by a dipole perpendicular to the screen plane.     

Application of a reflector with a nonuniform field in a mass-reflectron

The conditions under which the nonuniform compensating field of the reflector of the mass-reflectron can be generated with an acceptable accuracy at the symmetry axis of the reflector and extrapolated to the radial neighborhood of the axial line are determined. The plots that illustrate the distribution of the calculated nonuniform field of the reflector, the possibilities for implementation, and errors of focusing with respect to time of flight in the radial neighborhood are presented. Analytical expressions for the calculation of the time of flight of ions in the reflector in which the field distribution is described using a power series and analytical expressions for the calculation of the field distribution in the reflector in which the time of flight is determined using a power series are derived. A method for the analytical calculation of the compensating nonuniform field of the reflector based on the given dependence of the time of flight in the absence of such a field is proposed using a solution to the Abel integral equation. The solution to this equation yields analytical expressions for the calculation of the compensating field of the reflector in mass-reflectrons that contain the zero-field drift space and regions of acceleration (deceleration) of ions with a uniform field.     

Three Wave Interactions in a Beam-Plasma-System in a Cylindrical Waveguide

Interaction of three waves in a beam-plasma system in a circular cylindrical waveguide is studied. The dispersion relation and the axial growth rate have been obtained.     

Antiferromagnets in a field and ferromagnets in a random field

A new mean field approach for antiferromagnets in a field is shown to be equivalent to a mean field treatment of ferromagnets in a random field. Phase diagrams of the two systems are analogous.     

Mass transfer in a two-phase flow in a curvilinear channel

In this paper, the results of an experimental investigation of the distribution of local coefficients of mass transfer on a pipe wall for a flow of a two-phase gas-liquid mixture with a turn of 90° are presented. The mass transfer coefficients were measured by using an electrodiffusion method. It has been shown that the distribution of local mass transfer coefficients on the inner surface of a curvilinear channel is nonuniform both in length and along the perimeter and depends on the content of gas in the two-phase flow.     

Cherenkov radiation of a Josephson vortex moving in a sandwich embedded in a dielectric medium

A motion of a Josephson vortex in a long sandwich embedded in a dielectric medium is described. If the velocity of the vortex is greater than the velocity of light in the dielectric, terahertz-band Cherenkov radiation is generated and emitted from the lateral surface of the sandwich. The radiation loss power is determined. In the case when radiation loss is compensated for by the energy gain due to transport current, a relation between the current and the velocity of the vortex is obtained.     

Study of a soliton in a medium

The solution of the sine-Gordon equation for a medium is studied in a simplified “quasi-linear” approximation. Several aspects of this approximation are explored and compared with other approximate solutions for the sine-Gordon soliton.     

Photo-magnetic phenomenon in a semi-conductor in a non-homogeneous magnetic field

The emf which is produced on illuminating a homogeneous semiconductor located in a non-homogeneous magnetic field is calculated. It is shown that this emf is composed of two parts — bulk and boundary. Further, there are given the results of experiments carried out on indium antimonide by means of which the conclusions of the theory were verified.     

Decay of a Linear Pendulum in a Free-Molecular Gas and in a Special Lorentz Gas

A circular disk without thickness is placed in a gas, and an external force, obeying Hooke’s law, is acting perpendicularly on the disk. If the disk is displaced perpendicularly from its equilibrium position and released, then it starts an oscillatory or non-oscillatory unsteady motion, which decays as time goes on because of the drag exerted by the gas molecules. This unsteady motion, i.e., the decay of this linear pendulum, is investigated numerically, under the diffuse reflection condition on the surface of the disk, with special interest in the manner of its decay, for two kinds of gases: one is a collisionless gas (or Knudsen gas) and the other is a special Lorentz gas interacting with a background. It is shown that the decay of the displacement of the disk is slow and is in proportion to an inverse power of time for the collisionless gas. The result complements the existing mathematical study of a similar problem (Caprino et al. in Math. Models Methods Appl. Sci. 17:1369–1403, 2007) in the case of non-oscillatory decay. It is also shown that the manner of the decay changes significantly for the special Lorentz gas.