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

Ballistic and quasiballistic tunnel transit time oscillators for the terahertz range: Linear admittance

We have considered interactions between ballistic (or quasiballistic) electrons accelerated by a dc electric field in an undoped transit space (T space) and a small ultrahigh frequency ac electric field and have calculated the linear admittance of the T space. Electrons in the T space have a conventional, nonparabolic dispersion relation. After consideration of the simplest specific case when the current is limited by the space charge of the emitted electrons, we turned to an actual case when the current is limited by a heterostructural tunnel barrier (B barrier) separating the heavily doped cathode contact and the T space. We assumed that the B barrier is much thinner than the T space and both dc and ac voltages drop mainly across the T space. The emission tunnel current through the B barrier is determined by the electric field E(0)E(0) in the T space at the boundary B barrier/T space. The more substantial is, the tunnel current limitation the higher the electric field E(0)E(0) becomes. We have shown that for a space-charge limited current the change from parabolic dispersion to the nonparabolic branch induces narrowing and closing of the frequency windows of transit-time negative conductance starting with the lowest-frequency windows. These narrowing and closing frequency windows become effective only for very high voltages U across the T space: U≫mVS2/2e,U≫mVS2/2e, where m is the effective mass for the parabolic branch and VSVS is the saturated velocity for the nonparabolic branch. For moderate voltages U, the effects of nonparabolicity are not very substantial. The tunnel current limitation decreases the space-charge effects in the T space and diminishes the role of the detailed electron dispersion relation. As a result, restoration of the frequency windows of transit-time negative conductance and an increase in the value of this negative conductance occur. The implementation of the considered tunnel injection transit time oscillator diode promises to lead to efficient and powerful sources of terahertz range radiation. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70564/2/JAPIAU-93-9-5435-1.pd

Quantum real-space transfer in a heterostructure overgrown on the cleaved edge of a superlattice

A dispersion relation for an electron in a two-layer (and also multilayer) quantum well (QW) is formed as a result of a certain combination of initial dispersion relations for each of the forming layers. Such a combination can be used to engineer new dispersion relations with desirable properties. The same relates to a two-dimensional electron gas (2DEG) induced in a multilayer medium. In this study, we consider first such a 2DEG in a specific two-layer structure where a superlattice (SL) plays the role of the second half-infinite layer, and electrons with large wave numbers along the SL vector spread from the first ordinary QW layer to this SL. As a result of such a quantum (dynamic) real-space transfer, electrons become heavier, and the dispersion relation achieves an additional negative effective mass (NEM) section. Such NEM dispersion relations were studied for several different material systems, including the two most interesting three-material systems: (1) an isomorphic Al0.15Ga0.85As//GaAs/Al0.5Ga0.5AsAl0.15Ga0.85As//GaAs/Al0.5Ga0.5As structure and (2) a strained In0.53Ga0.47As//InxGa1−xAs/InyAl1−yIn0.53Ga0.47As//InxGa1−xAs/InyAl1−y As structure (x>0.53,(x>0.53, y<0.52)y<0.52) with a strain-balanced InxGa1−xAs/InyAl1−yAsInxGa1−xAs/InyAl1−yAs SL. Most of the results were verified using a simplified 1D model, but some of them were verified by more complicated 2D-model calculations. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70061/2/JAPIAU-93-1-330-1.pd

Aspects of psychosomatic disorders in highly qualified athletes

Objective: to observe general abundance of various psychosomatic disorders among highly qualified athletes. Materials and methods: the study involved 3 094 athletes of Russian national teams with age range from 18 to 77 years. Analysis of data collected during the extend medical examinations (EME) of the national Russian team athletes in 2014-2016 years was conducted. Results: research shows high frequency of psychosomatic disorders among athletes of Russian national teams - 28,1%. The most common conditions among diseases with psychosomatic mechanisms in athletes of Russian national teams were disorders of the musculoskeletal system, the gastrointestinal tract, and the nervous system. Gender and age specific differences were shown. Conclusions: both psychological and psycho-physiological factors play significant role in the formation of psychosomatic disorders in athletes. Apparently, in view of the importance of social status (success) and, consequently, the tendency to negate problems, we expect late medical resource utilization in this group of the population (only in the case of a long and severe somatic disorder)

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

EPR study of polycrystalline superconductors with YBa2Cu3O7 structure

Electron paramagnetic resonance (EPR) of Gd3+, Eu2+, and copper ions has been investigated in the high-Tc superconductor with YBa2Cu3O7-α structure. It has been established that the system is heterogeneous at 0.15≤δ≤0.5 and consists of metallic and dielectric regions. The former arises due to oxygen enrichment while the later due to oxygen deficiency. The integral of exchange interaction between Gd3+ localized moments and conduction electrons Jsf=0.016 eV has been determined from the normal state temperature dependence of Gd3+ EPR linewidth for metallic regions. Tc depression by gadolinium-localized moments for GdBa2Cu3O7-α was estimated to be ΔTc{reversed tilde equals}-2K. Anomalies in linewidth temperature dependence upon transition from the normal to the superconducting state have given information about the value and temperature behavior of the superconductor's energy gap. The model, which gives the opportunity to understand some peculiarities of the EPR signal for YBa2Cu3O7-α samples, is proposed in terms of several bottlenecked spinsubsystems: spin-liquid in CuO planes and Cu2+-O- and Cu2+-O2- fragments in CuO chains. © 1989 Plenum Publishing Corporation

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

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

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 &lt; 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