Influence of bottom topography on integral constraints in zonal flows with parameterized potential vorticity fluxes

An integral constraint for eddy fluxes of potential vorticity (PV), corresponding to global momentum conservation, is applied to two-layer zonal quasi-geostrophic channel flow. This constraint must be satisfied for any type of parameterization of eddy PV fluxes. Bottom topography strongly influence the integral constraint compared to a flat bottom channel. An analytical solution for the mean flow solution has been found by using asymptotic expansion in a small parameter which is the ratio of the Rossby radius to the meridional extent of the channel. Applying the integral constraint to this solution, one can find restrictions for eddy PV transfer coefficients which relate the eddy fluxes of PV to the mean flow. These restrictions strongly deviate from restrictions for the channel with flat bottom topography

Electron scattering in quantum wells subjected to an in-plane magnetic field

It is shown that the electron scattering by static defects, acoustic or optical phonons in quantum wells subjected to an in-plane magnetic field is asymmetric. The probability of scattering contains terms which are proportional to both the electron wave vector and the magnetic field components. The terms under study are caused by the lack of an inversion center in quantum wells due to structure or bulk inversion asymmetry although they are of pure diamagnetic origin. Such a magnetic field induced asymmetry of scattering can be responsible for a number of phenomena. In particular, the asymmetry of inelastic electron-phonon interaction leads to an electric current flow if only the electron gas is driven out of thermal equilibrium with the crystal lattice.Comment: 5 pages, 1 figur

Characteristics of the microscopic hair structure of domestic mammals from Equidae family

Hair is an indispensable component of the animal body. Having structural features of the structure, it allows you likely to identify the type and age of animals, conditions of keeping animals, feeding and even sex. Paleontologist's findings  prove, the hairline stores the undisputed information on its “owner” for thousands of years. According to the results of the conducted research it is established, that the hair coat of the studied animal species – Equinus asinus and Equus caballus – has significant differences in the structure of the brain substance and superficial drawing of the cuticle. Microscopic examination of discolored samples of animal hair well-recognizes the structure of the brain substance, which makes it possible to differentiate the species of animal. The brain substance in the donkey mane hair occupies most of the hair, is represented by densely grouped cells, sometimes interrupted, whereas in the horse mane hair, it has the appearance of grouped rounded cells with small intervals between sections of 6–10 cells. The brain substance of the donkey covering hair is represented by cells of different size and shape, which disappear from the middle of the hair to the peripheral end. This tendency is also typical for the brain substance of the horse covering hair, but unlike donkey hair – cells of the same size, begin with a continuous cord at a distance of 1–1.5 mm from the root of the hair, towards the peripheral end of the hair the gaps between them increase to the complete disappearance of cells. Ultramicroscopic examination of the cuticle superficial drawing of hair samples allowed to establish the peculiarities of two species of the same animal genus. The donkey and horse mane hair had almost the same thickness, the number of scales (waves) per 100 μm of hair length and the size of the scales (wavelength), however, the overall drawing was significantly different. Superficial drawing of hair cuticle from horse mane represented by irregular waves with sharp pointed edges of scales, instead, the donkey has fringed edges of scales. The horse's covering hair was thicker than the donkey's hair and had differences in the location and shape of the scales. Superficial drawing of covering hair cuticle of donkey represented by a regular wave of scales with clear and even edges, while the scales on the surface of the covering hair of the horse have indistinct torn edges and collected in intermittent (irregular) waves

Magneto-Gyrotropic Photogalvanic Effects in Semiconductor Quantum Wells

We show that free-carrier (Drude) absorption of both polarized and unpolarized terahertz radiation in quantum well (QW) structures causes an electric photocurrent in the presence of an in-plane magnetic field. Experimental and theoretical analysis evidences that the observed photocurrents are spin-dependent and related to the gyrotropy of the QWs. Microscopic models for the photogalvanic effects in QWs based on asymmetry of photoexcitation and relaxation processes are proposed. In most of the investigated structures the observed magneto-induced photocurrents are caused by spin-dependent relaxation of non-equilibrium carriers

Direct current driven by ac electric field in quantum wells

It is shown that the excitation of charge carriers by ac electric field with zero average driving leads to a direct electric current in quantum well structures. The current emerges for both linear and circular polarization of the ac electric field and depends on the field polarization and frequency. We present a micoscopic model and an analytical theory of such a nonlinear electron transport in quantum wells with structure inversion asymmetry. In such systems, dc current is induced by ac electric field which has both the in-plane and out-of-plane components. The ac field polarized in the interface plane gives rise to a direct current if the quantum well is subjected to an in-plane static magnetic field.Comment: 6 pages, 3 figure

Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces

We describe the fine structure of Dirac states in HgTe/CdHgTe quantum wells of critical and close-to-critical thickness and demonstrate the formation of an anticrossing gap between the tips of the Dirac cones driven by interface inversion asymmetry. By combining symmetry analysis, atomistic calculations, and k-p theory with interface terms, we obtain a quantitative description of the energy spectrum and extract the interface mixing coefficient. The zero-magnetic-field splitting of Dirac cones can be experimentally revealed in studying magnetotransport phenomena, cyclotron resonance, Raman scattering, or THz radiation absorption.Comment: 6 pages, 5 figure

On dispersive energy transport and relaxation in the hopping regime

A new method for investigating relaxation phenomena for charge carriers hopping between localized tail states has been developed. It allows us to consider both charge and energy {\it dispersive} transport. The method is based on the idea of quasi-elasticity: the typical energy loss during a hop is much less than all other characteristic energies. We have investigated two models with different density of states energy dependencies with our method. In general, we have found that the motion of a packet in energy space is affected by two competing tendencies. First, there is a packet broadening, i.e. the dispersive energy transport. Second, there is a narrowing of the packet, if the density of states is depleting with decreasing energy. It is the interplay of these two tendencies that determines the overall evolution. If the density of states is constant, only broadening exists. In this case a packet in energy space evolves into Gaussian one, moving with constant drift velocity and mean square deviation increasing linearly in time. If the density of states depletes exponentially with decreasing energy, the motion of the packet tremendously slows down with time. For large times the mean square deviation of the packet becomes constant, so that the motion of the packet is ``soliton-like''.Comment: 26 pages, RevTeX, 10 EPS figures, submitted to Phys. Rev.