Optically induced resonant tunneling of electrons in nanostructures.

We developed the theory of elastic electron tunneling through a potential barrier driven by a strong high-frequency electromagnetic field. It is demonstrated that the driven barrier can be considered as a stationary two-barrier potential which contains the quasi-stationary electron states confined between these two barriers. When the energy of an incident electron coincides with the energy of the quasi-stationary state, the driven barrier becomes fully transparent for the electron (the resonant tunneling). The developed theory is applied to describe electron transport through a quantum point contact irradiated by an electromagnetic wave.

All-optical control of excitons in semiconductor quantum wells.

Applying the Floquet theory, we developed the method to control excitonic properties of semiconductor quantum wells (QWs) by a high-frequency electromagnetic field. It is demonstrated, particularly, that the field induces the blue shift of exciton emission from the QWs and narrows width of the corresponding spectral line. As a consequence, the field strongly modifies optical properties of the QWs and, therefore, can be used to tune characteristics of the optoelectronic devices based on them.

Optically induced hybrid Bose-Fermi system in quantum wells with different charge carriers.

It is demonstrated theoretically that the circularly polarized irradiation of two-dimensional conducting systems can produce composite bosons consisting of two electrons with different effective masses (different charge carriers), which are stable due to the Fermi sea of conduction electrons. As a result, an optically induced mixture of paired electrons and normal conduction electrons (the hybrid Bose-Fermi system) appears. Elementary excitations in such a hybrid system are analyzed, and possible manifestations of the light-induced electron pairing are discussed for semiconductor quantum wells.

Energy relaxation of quantum dot hot electrons in hybrid quantum dot-Bose-Einstein condensate system.

The theory of electron energy relaxation in a hybrid structure consisting of quantum dot interacting with a two dimensional exciton gas in Bose-Einstein condensate (BEC) regime is developed. A new type of the relaxation mechanism in the presence of BEC is introduced and theoretically analyzed. It is shown that, in the first order of electron-exciton interaction, two microscopic processes of energy relaxation appear. The first one is related to the emission of a single Bogoliubov excitation (bogolon) by an electron, whereas the second process is associated with the emission of two bogolons. It is shown that the second type processes dominate in the QD electron energy relaxation.

Proposal for Plasmon Spectroscopy of Fluctuations in Low-Dimensional Superconductors.

We propose to employ an optical spectroscopy technique to monitor the superconductivity and properties of superconductors in the fluctuating regime. This technique is operational close to the plasmon resonance frequency of the material, and it intimately connects with the superconducting fluctuations slightly above the critical temperature T_{c}. We find the Aslamazov-Larkin corrections to ac linear and dc nonlinear electric currents in a generic two-dimensional superconductor exposed to an external longitudinal electromagnetic field. First, we study the plasmon resonance of normal electrons near T_{c}, taking into account their interaction with superconducting fluctuations, and show that fluctuating Cooper pairs reveal a redshift of the plasmon dispersion and an additional mechanism of plasmon scattering, which surpasses both the electron-impurity and the Landau dampings. Second, we demonstrate the emergence of a drag effect of superconducting fluctuations by the external field resulting in considerable, experimentally measurable corrections to the electric current in the vicinity of the plasmon resonance.

Unconventional Bloch-Grüneisen Scattering in Hybrid Bose-Fermi Systems.

We report on the novel mechanism of electron scattering in hybrid Bose-Fermi systems consisting of a two-dimensional electron gas in the vicinity of an exciton condensate: We show that in certain ranges of temperatures, the bogolon-pair-mediated scattering proves to be dominating over the conventional acoustic phonon channel, over the single-bogolon scattering, and over the scattering on impurities. We develop a microscopic theory of this effect, focusing on GaAs and MoS_{2} materials, and we find the principal temperature dependence of resistivity, distinct from the conventional phonon-mediated processes. Further, we scrutinize parameters and suggest a way to design composite samples with predefined electron mobilities, and we propose a mechanism of electron pairing for superconductivity.

Valley Acoustoelectric Effect.

We report on the novel valley acoustoelectric effect, which can arise in a 2D material, like a transition metal dichalcogenide monolayer, residing on a piezoelectric substrate. The essence of this effect lies in the emergence of a drag electric current (and a spin current) due to a propagating surface acoustic wave. This current consists of three contributions, one independent of the valley index and proportional to the acoustic wave vector, the other arising due to the trigonal warping of the electron dispersion, and the third one is due to the Berry phase, which Bloch electrons acquire traveling along the crystal. As a result, there appear components of the current orthogonal to the acoustic wave vector. Further, we build an angular pattern, encompassing nontrivial topological properties of the acoustoelectric current, and suggest a way to run and measure the conventional diffusive, warping, and acoustoelectric valley Hall currents independently. We develop a theory, which opens a way to manipulate valley transport by acoustic methods, expanding the applicability of valleytronic effects on acoustoelectronic devices.

Photogalvanic effect in monolayer transition metal dichalcogenides under double illumination.

We study the photogalvanic effect caused by a simultaneous action of two light sources: circular-polarized interband and linearly-polarized intraband. It is found that, in such conditions, the steady photocurrent appears. The effect originates from the valley-selective pumping by the circular-polarized light, the trigonal symmetry of the valleys and the linear polarization of intraband electromagnetic field, that produces a polar in-plane asymmetry of the electron and hole distribution functions, leading to the photocurrent. The approach is based on the solution of the classical kinetic equation for carriers with accounting for the quantum interband excitation.

Paramagnetic resonance in spin-polarized disordered Bose-Einstein condensates.

We study the pseudo-spin density response of a disordered two-dimensional spin-polarized Bose gas to weak alternating magnetic field, assuming that one of the spin states of the doublet is macroscopically occupied and Bose-condensed while the occupation of the other state remains much smaller. We calculate spatial and temporal dispersions of spin susceptibility of the gas taking into account spin-flip processes due to the transverse-longitudinal splitting, considering microcavity exciton polaritons as a testbed. Further, we use the Bogoliubov theory of weakly-interacting gases and show that the time-dependent magnetic field power absorption exhibits double resonance structure corresponding to two particle spin states (contrast to paramagnetic resonance in regular spin-polarized electron gas). We analyze the widths of these resonances caused by scattering on the disorder and show that, in contrast with the ballistic regime, in the presence of impurities, the polariton scattering on them is twofold: scattering on the impurity potential directly and scattering on the spatially fluctuating condensate density caused by the disorder. As a result, the width of the resonance associated with the Bose-condensed spin state can be surprisingly narrow in comparison with the width of the resonance associated with the non-condensed state.

Ultrafast exciton-polariton scattering towards the Dirac points.

Using the Feynman-Dyson diagram technique, we study nonlinear polariton-polariton scattering in a two-dimensional micropillar-based optical superlattice with hexagonal symmetry. We demonstrate that both the emerging polariton chirality and the loop Feynman diagrams up to infinite order should be strictly accounted for in the evaluation of the self-energy of the system. Further, we explicitly show that in such a design the time of polariton scattering towards the Dirac points can be drastically decreased which can be used, for instance, in engineering novel classes of polariton lasers with substantially reduced thresholds.

Nonlinear effects in multi-photon polaritonics.

We consider theoretically nonlinear effects in a semiconductor quantum well embedded inside a photonic microcavity. Two-photon absorption by a 2p exciton state is considered and investigated; the matrix element of two-photon absorption is calculated. We compute the emission spectrum of the sample and demonstrate that under coherent pumping the nonlinearity of the two photon absorption process gives rise to bistability.

Self-induced acoustic transparency in semiconductor quantum films.

We develop a quantum theory of the nonlinear interaction between intense surface acoustic waves and electrons in a quantum well in the regime of moving quantum wires and dots. In the quantum nonlinear regime, the sound attenuation exhibits quantum oscillations and dramatically decreases with increasing quantization. In the case of dynamically created electron dots formed by two acoustic waves, the waves can propagate without any dissipation in the limit of high sound intensity and, hence, the electron quantum film acts as an acoustically quasitransparent material.

[Undiagnosed early secondary syphilis with horny palmar and plantar papules]. / Neraspoznannyi vtorichnyi svezhii sifilis s rogovymi ladonno-podoshvennymi papulami.

A 20-year-old female patient is described who contracted syphilis in a rape attempt. She consulted a dermatovenereologist twice but the disease was not diagnosed, for despite the fact that the patient had hard chancre fragments on the posterior adhesion of the vagina, polyscleradenitis, abundant roseolar eruption on the trunk skin, horny palmar and plantar papular efflorescence, erythematous syphilitic tonsillitis, she was not examined nor serological tests were carried out. The condition was diagnosed as callosity and acute respiratory viral disease, antihistaminic and antibiotic drugs were prescribed. The condition was diagnosed only in a month after the first visit to a doctor.

[Acute Lipschütz-Chapin vulvar ulcer]. / Ostraia iazva vul'vy Lipshiuttsa--Chapina.

A 17-year-old female patient is described, who had a sexual intercourse, the only in her life, a year before. Hectic temperature has developed in the presence of an exacerbation of chronic decompensated tonsillitis; the general status has essentially deteriorated. A sharply painful ulcer, up to 2 cm in diameter, was seen on the lower third of the involved labium majus; Lactobacilli casei were isolated from the discharge from this ulcer. After 2 weeks of antibiotic and immunocorrective therapy a delicate atrophic cicatrix has formed. The factors that helped diagnose the Lipschütz-Chapin acute vulvar ulcer were exacerbation of a chronic focal infection, anemia, leucocytosis, thrombocytopenia, dysproteinemia, and disordered cellular and humoral immunity.

[The mastery of the elements of professional activities in the process of the student performance of independent work in a department of skin and venereal diseases]. / Osvoenie élementov professional'noi deiatel'nosti v protsesse vypolneniia studentami samostoiatel'noi raboty na kafedre kozhnykh i venericheskikh boleznei.

The authors sum up the experience gained by the chair for skin and sexually transmitted diseases in training the students within the frames of a universal methodological system in accordance with their future specialization as therapists, pediatricians, dentists, or sanitary physicians. The purpose and motivation of training are defined, basic knowledge of the students are checked up, and the contents of students' self-training presented. Written control tests are described, intended to check up the knowledge and skills; these tests include questions in basic theory, treatment and diagnosis strategy, and prophylactic measures used in prevalent skin and sexually transmitted diseases. Such training organization promotes high-quality mastering the profession and adapts the students to physicians' daily routine.

[A case of chromomycosis in a nonendemic region]. / Sluchai khromomikoza v neéndemichnom regione.

A 43-year-old miner of the Donetsk coal fields is described, who developed in a month after a microinjury of the skin of the thoracic left side an intumescence and skin reddening. Later an agglomeration of nodules formed there with small ulcers regularly appearing, that did not heal for a long time. Histologic and bacteriologic analysis confirmed chromomycosis. The disease focus was resected. No recurrences were recorded in the following 8 months. This observation points to a wider prevalence of chromomycosis in a nonendemic area, the European part of the USSR, than it is reported in literature.

[The clinical picture and therapy of nodular mastocytosis]. / K klinike i terapii uzlovatogo mastotsitoza.

The authors review the literature data on and describe 6 cases of nodular mastocytosis presenting as multiple blending nodes. The patients (2 girls and 4 boys aged under 4) have developed a disseminated process with multiple nodes up to 3.0-3.5 cm in diameter colored brownish or yellowish, mostly with a smooth surface, localized on the hairy part of the head, trunk, and limbs. Some nodes blended to form larger foci of lesions, particularly on the back and in large skin folds. In 5 patients the diagnosis has been confirmed histologically. No visceral or systemic abnormalities have been revealed. Enlarged (pea-size) inguinal and cubital lymph nodes have been detected in one child. Zaditen therapy has been fairly effective.

[New aspects of the pathogenesis and treatment of Schulmann's eosinophilic fasciitis]. / Novye aspekty patogeneza i lecheniia éozinofil'nogo fastsiita Shul'mana.

A female patient, aged 64, was admitted to hospital with a tentative diagnosis of dermatomyositis or systemic scleroderma. Basing on the clinical symptoms and histologic findings in examination of a musculocutaneofascial biopsy specimen from the focus of involvement on the left thigh, Schulmann's eosinophilic fasciitis was diagnosed. The mechanism of the disease is polypathogenic, it includes newly detected disorders of the blood rheology, of the enzymic and electrolyte metabolism, of the immunologic homeostasis at the cellular (E0-RFC) and humoral (IgE) levels, of the peripheral skin analyzer function, of the orocaudal relationships, and of the microcirculation. Treatment with enzymic, vasoactive, and immunocorrective drugs combined with D-penicillamine and He-Ne laser therapy has yielded a good clinical effect without resorting to glucocorticoids; the time of the treatment was reduced to 28 days. A stable clinical remission for 1.5 years was achieved.

[Chronic benign familial pemphigus]. / Khronicheskaia dobrokachestvennaia semeinaia puzyrchatka.

A female patient aged 50 is described, in whom candidiasis of the large folds has been erroneously diagnosed for 10 years; the diagnosis has not been confirmed by bacteriologic analysis, the therapy has been ineffective, the recurrences developed every year. The patient has developed symmetrical erythematous infiltrative areas in the armpits, groin, and in the folds under mammary glands, with solitary bullae up to 0.5-1.0 cm in diameter, with transparent contents, with thin flaccid covers and fragments thereof, as well as small pigmented vegetation. Basing on the histologic findings (suprabasal vesicles above the basal layer, acantholysis in the epidermis, and negligible lymphocytic infiltrate in the derma), Gougerot-Hailey-Hailey's disease has been diagnosed. The familial nature of the disease could not be established. Therapy with diphenhydramine, methyluracil, dimocifon, aloe extract, and aniline dyes, administered for 20 days, has resulted in clinical cure.