Microwave-induced resistance oscillations and zero-resistance states in 2D electron systems with two occupied subbands

We report on theoretical studies of recently discovered microwave-induced resistance oscillations and zero resistance states in Hall bars with two occupied subbands. In the same results, resistance presents a peculiar shape which appears to have a built-in interference effect not observed before. We apply the microwave-driven electron orbit model, which implies a radiation-driven oscillation of the two-dimensional electron system. Thus, we calculate different intra and inter-subband electron scattering rates and times that are revealing as different microwave-driven oscillations frequencies for the two electronic subbands. Through scattering, these subband-dependent oscillation motions interfere giving rise to a striking resistance profile. We also study the dependence of irradiated magnetoresistance with power and temperature. Calculated results are in good agreement with experiments.Comment: 7 pages, 6 figure

A heuristic quantum theory of the integer quantum Hall effect

Contrary to common belief, the current emitted by a contact embedded in a two-dimensional electron gas (2DEG) is quantized in the presence of electric and magnetic fields. This observation suggests a simple, clearly defined model for the quantum current through a Hall device that does not invoke disorder or interactions as the cause of the integer quantum Hall effect (QHE), but is based on a proper quantization of the classical electron drift motion. The theory yields a quantitative description of the breakdown of the QHE at high current densities that is in agreement with experimental data. Furthermore, several of its key points are in line with recent findings of experiments that address the dependency of the QHE on the 2DEG bias voltage, results that are not easily explained within the framework of conventional QHE models.Comment: 20 pages, 6 figure

Magnetoresistance of a semiconducting magnetic wire with domain wall

We investigate theoretically the influence of the spin-orbit interaction of Rashba type on the magnetoresistance of a semiconducting ferromagnetic nanostructure with a laterally constrained domain wall. The domain wall is assumed sharp (on the scale of the Fermi wave length of the charge carriers). It is shown that the magnetoresistance in such a case can be considerably large, which is in a qualitative agreement with recent experimental observations. It is also shown that spin-orbit interaction may result in an increase of the magnetoresistance. The role of localization corrections is also briefly discussed.Comment: 5 pages, 2 figure

Tunneling of a Quantized Vortex: Roles of Pinning and Dissipation

We have performed a theoretical study of the effects of pinning potential and dissipation on vortex tunneling in superconductors. Analytical results are obtained in various limits relevant to experiment. In general we have found that pinning and dissipation tend to suppress the effect of the vortex velocity dependent part of the Magnus force on vortex tunneling.Comment: Latex, 12 page

Possibilities of transcranial direct current stimulation (tDCS) use in elite sport

Transcranial direct current stimulation has proven to be the method that can modulate neural activity in various cases. As this method has been shown to be effective in improving muscular strength, reaction time and accuracy, motor learning, it seems to be promising in elite sports.This paper provides an overview of studies on tDCS and its impact on central nervous system functioning, with an emphasis on potential sports utility. This review demonstrates that the basic mechanism of the effect of tDCS on nervous system functioning is its ability to modulate the excitability of neurons.tDCS is able to influence various components of electrocortical potentials, the amplitude of the motor evoked potential, as well as the mechanisms of long-term potentiation and, as a consequence, the cellular mechanisms of motor learning and neuroplasticity in general. The beneficial effect of tDCS on attention selectivity and signal detection has been noted. It is also shown that tDCS can accelerate learning and enhance performance in a range of complex cognitive tasks.In addition, a number of studies showing that tDCS can increase the efficiency of performing arithmetic and problem solving tasks are considered.In the context of sports, the influence of tDCS over motor areas on motor learning and on the accuracy of voluntary movements seems to be important. Its ability to influence speed and strength indicators, namely, the maximum isometric force of various muscle groups and explosive strength, as well as endurance indicators seems promising, too. The review also shows that tDCS is reasonably safe and that serious adverse effects are extremely rare; the most common adverse effect is local skin irritation due to poor electrode placement

Revisiting the need for optimization of psychological interventions in the medical service system for elite athletes

Objective: revelation of disadaptation among Russian elite athletesof necessity to optimize psychological interventions among biomedical support system for elite athletes. All participants were athletes of several Russian national teams, among them cyclic sports, game sports, complex coordination sports, and combat sports. Materials and methods: data obtained from 1176 elite athletes during extended medical examinations (EME) within the period from 2015 to 2018 were studied. Results: research reveals the relationship between psychical adaptation and athletes’ gender, age, level of experience, and sport-related specifics. Conclusions: athletes of various Russian national teams (from juniors to elite) suffer from notable disadaptation. Thereupon the necessity of changes to the existing system of psychophysiological interventions within national teams (namely: development of preventive treatment programs and correction of disadaptation programs) verify its importance

Attitudes towards vaccination against COVID-19 among athletes of Russian national teams in comparison with non-athletes aged 18 to 40

The purpose of this work was to study the attitude of the Russian population to vaccination against COVID-19. Vaccination attitudes in young adults were studied both in the general population and among those who are professionally involved in sports, since attitudes towards health and the initial level of physical resources are important for forming attitudes towards vaccination. A total of 2579 people aged 18 to 40 were examined. Of these, 2233 are from the general population, 346 are high performance athletes.Methods. This was a cohort cross-sectional study. A specially designed questionnaire was used, located on Internet resources 2 months after the start of mass vaccination in Russia.Results. In the group of elite athletes, there are significantly more people who consider vaccination unnecessary or treat it indifferently, and a smaller proportion of those who consider it useful or doubt its effectiveness as compared to the general population of the same age. Low adherence to vaccination may be associated with fear of potential complications. Among elite athletes, there are significantly more people who are seriously afraid of complications from vaccination — 143 (41.3 %), compared to the first group of respondents — 745 (33.4 %) (p < 0.01, φ = 2.839). Probably, these concerns are related to the crucial importance of health and physical condition for professional athletes.Conclusions. It is advisable to develop recommendations for vaccination against COVID-19 for elite athletes, which will describe in detail the benefits of vaccination for athletes, possible side effects, their frequency and impact on the training process

Psychophysiological and psychological features of elite young volleyball players

Objective: to analyze the psychological and psychophysiological features of effective volleyball play. Materials and methods: the study involved 19 female athlets with average age of 17±1 years. The study was conducted during the pre-competition period. Personality traits, sport motivation, coping strategies, emotional burnout, skills of mental training and visualization, were assessed by adapted Russian-language versions of questionnaires «Freiburg multi-factor personal questionnaire (FPI)», «Sport motivation scale (SMS)», «The Sport Imagery Questionnaire (SIQ)», «Strategic Approach to Coping Scale (SACS)», «Maslach burnout inventory». The levels of chronic and acute stress were assessed by «Acute and chronic stress scale». Attentional set-shifting, concentration of attention were examined by the Munsterberg test and the «Entangled lines» test. The speed and stability of sensorimotor functioning were assessed by Simple Reaction Time test and Choice Reaction Time test. Stress load was simulated by the game-biofeedback approach to examine the effectiveness of self-regulation. The obtained data were compared with the assessment of athletes’ gaming efficiency. Results: Revealed significant connection between game effectiveness and the reduced level of stress: high speed, reaction stability, internal motivation, decreased neuroticity, depressiveness, aggressiveness, emotional lability, developed skills of self-regulation, visualization and ideomotor training are discussed. Conclusions: Revealed psychological and psychophysiological features might be considered as components of the young female volleyball players’ model psychophysiological state