The nonlinear effects in 2DEG conductivity investigation by an acoustic method

The parameters of two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure were determined by an acoustical (contactless) method in the delocalized electrons region ($B\le$2.5T). Nonlinear effects in Surface Acoustic Wave (SAW) absorption by 2DEG are determined by the electron heating in the electric field of SAW, which may be described in terms of electron temperature $T_e$. The energy relaxation time $\tau_{\epsilon}$ is determined by the scattering at piezoelectric potential of acoustic phonons with strong screening. At different SAW frequencies the heating depends on the relationship between $\omega\tau_{\epsilon}$ and 1 and is determined either by the instantaneously changing wave field ($\omega\tau_{\epsilon}$$<1$), or by the average wave power ($\omega\tau_{\epsilon}$$>1$).Comment: RevTeX, 5 pages, 3 PS-figures, submitted to Physica Status Sol.(Technical corrections in PS-figs

Electron localization in sound absorption oscillations in the quantum Hall effect regime

The absorption coefficient for surface acoustic waves in a piezoelectric insulator in contact with a GaAs/AlGaAs heterostructure (with two-dimensional electron mobility $\mu= 1.3\times 10^5 cm^2/V\cdot s)$ at T=4.2K) via a small gap has been investigated experimentally as a function of the frequency of the wave, the width of the vacuum gap, the magnetic field, and the temperature. The magnetic field and frequency dependencies of the high-frequency conductivity (in the region 30-210 MHz) are calculated and analyzed. The experimental results can be explained if it assumed that there exists a fluctuation potential in which current carrier localization occurs. The absorption of the surface acoustic waves in an interaction with two-dimensional electrons localized in the energy "tails" of Landau levels is discussed.Comment: RevTeX 6 pages+6 EPS pic

Magnetic-field-dependent zero-bias diffusive anomaly in Pb oxide-n-InAs structures: Coexistence of two- and three-dimensional states

The results of experimental and theoretical studies of zero-bias anomaly (ZBA) in the Pb-oxide-n-InAs tunnel structures in magnetic field up to 6T are presented. A specific feature of the structures is a coexistence of the 2D and 3D states at the Fermi energy near the semiconductor surface. The dependence of the measured ZBA amplitude on the strength and orientation of the applied magnetic field is in agreement with the proposed theoretical model. According to this model, electrons tunnel into 2D states, and move diffusively in the 2D layer, whereas the main contribution to the screening comes from 3D electrons.Comment: 8 double-column pages, REVTeX, 9 eps figures embedded with epsf, published versio

Interaction effects and phase relaxation in disordered systems

This paper is intended to demonstrate that there is no need to revise the existing theory of the transport properties of disordered conductors in the so-called weak localization regime. In particular, we demonstrate explicitly that recent attempts to justify theoretically that the dephasing rate (extracted from the magnetoresistance) remains finite at zero temperature are based on the profoundly incorrect calculation. This demonstration is based on a straightforward evaluation of the effect of the electron-electron interaction on the weak localization correction to the conductivity of disordered metals. Using well-controlled perturbation theory with the inverse conductance $g$ as the small parameter, we show that this effect consists of two contributions. First contribution comes from the processes with energy transfer smaller than the temperature. This contribution is responsible for setting the energy scale for the magnetoresistance. The second contribution originates from the virtual processes with energy transfer larger than the temperature. It is shown that the latter processes have nothing to do with the dephasing, but rather manifest the second order (in $1/g$) correction to the conductance. This correction is calculated for the first time. The paper also contains a brief review of the existing experiments on the dephasing of electrons in disordered conductors and an extended qualitative discussion of the quantum corrections to the conductivity and to the density of electronic states in the weak localization regime.Comment: 34 pages, 13 .eps figure

The Role of Native Language and the Fundamental Design of the Auditory System in Detecting Rhythm Changes

Accepted December 13, 2018Purpose: We investigated whether rhythm discrimination is mainly driven by the native language of the listener or by the fundamental design of the human auditory system and universal cognitive mechanisms shared by all people irrespective of rhythmic patterns in their native language. Method: In multiple experiments, we asked participants to listen to 2 continuous acoustic sequences and to determine whether their rhythms were the same or different (AX discrimination). Participants were native speakers of 4 languages with different rhythmic properties (Spanish, French, English, and German) to understand whether the predominant rhythmic patterns of a native language affect sensitivity, bias, and reaction time in detecting rhythmic changes in linguistic (Experiment 2) and in nonlinguistic (Experiments 1 and 2) acoustic sequences. We examined sensitivity and bias measures, as well as reaction times. We also computed Bayes factors in order to assess the effect of native language. Results: All listeners performed better (i.e., responded faster and manifested higher sensitivity and accuracy) when detecting the presence or absence of a rhythm change when the 1st stimulus in an AX test pair exhibited regular rhythm (i.e., a syllable-timed rhythmic pattern) than when the 1st stimulus exhibited irregular rhythm (i.e., stress-timed rhythmic pattern). This result pattern was observed both on linguistic and nonlinguistic stimuli and was not modulated by the native language of the participant. Conclusion: We conclude that rhythm change detection is a fundamental function of a processing system that relies on general auditory mechanisms and is not modulated by linguistic experience.The authors acknowledge support from Spanish Ministry of Economy and Competitiveness Grant PSI2017-82563-P (awarded to A. G. S.), the “Severo Ochoa” Programme for Centres/Units of Excellence in R&D Grant SEV-2015-490 (BCBL), and the Basque Foundation for Science Grant IKERBASQUE (awarded to A. G. S. and M. O.). D. M. G. was supported by Grant PIA/Basal FB0003 from the Chilean Research Council. L. P. was supported by the Spanish Ministry of Economy and Competitiveness via Juan de la Cierva fellowship

Analysis of health passports students of the second course

The article analyzes the biochemical (in blood, glucose, cholesterol) and clinical (heart rate, blood pressure) indicators of the body of medical students on the basis of 70 passports of health. Self-assessment of physical activity, eating behavior carried out by anonymous questioning 120 respondents. All studies were conducted with the voluntary consent of the respondents. Students prefer baking, "snacking". The deviation of body mass index above the standard value was found in 14%, among them in 43% - primary obesity (6% of the total number of patients). The method of paired correlations revealed a high correlation between the level of cholesterol and the systolic component of blood pressure.В статье проведен анализ биохимических (глюкоза, холестерин крови) и клинических (частота сердечных сокращений, артериальное давление) показателей организма студентов-медиков на основе 70 сведений паспортов здоровья. Самооценки физической активности, пищевого поведения осуществлены путем анонимного анкетирования 120 респондентов. Все исследования проведены при добровольном согласии анкетированных. Студенты предпочитают выпечку, «перекусы». Отклонение индекса массы тела выше стандартной величины обнаружено у 14%, среди них у 43% — первичное ожирение (6% об общего числа обследованных). Метод парных корреляций выявил высокую связь между уровнем холестерина и систолической составляющей артериального давления

Thyroid cancer risk in Belarus among children and adolescents exposed to radioiodine after the Chornobyl accident

BACKGROUND: Previous studies showed an increased risk of thyroid cancer among children and adolescents exposed to radioactive iodines released after the Chornobyl (Chernobyl) accident, but the effects of screening, iodine deficiency, age at exposure and other factors on the dose-response are poorly understood. METHODS: We screened 11 970 individuals in Belarus aged 18 years or younger at the time of the accident who had estimated (131)I thyroid doses based on individual thyroid activity measurements and dosimetric data from questionnaires. The excess odds ratio per gray (EOR/Gy) was modelled using linear and linear-exponential functions. RESULTS: For thyroid doses \u3c5 \u3eGy, the dose-response was linear (n=85; EOR/Gy=2.15, 95% confidence interval: 0.81-5.47), but at higher doses the excess risk fell. The EOR/Gy was significantly increased among those with prior or screening-detected diffuse goiter, and larger for men than women, and for persons exposed before age 5 than those exposed between 5 and 18 years, although not statistically significant. A somewhat higher EOR/Gy was estimated for validated pre-screening cases. CONCLUSION: 10-15 years after the Chornobyl accident, thyroid cancer risk was significantly increased among individuals exposed to fallout as children or adolescents, but the risk appeared to be lower than in other Chornobyl studies and studies of childhood external irradiation

Прогностическое значение наличия в крови циркулирующей опухолевой ДНК как маркера минимального резидуального заболевания при колоректальном раке I–III стадии

Introduction. Studies on non-metastatic colorectal cancer have demonstrated the prognostic role of circulating tumor (ctDNA) after surgery, and the ability to identify patients with the greatest risk of progression. This makes it possible in the future to personalize neoadjuvant and adjuvant treatment.The study objective – to evaluate the correlation of the ctDNA status before and after surgery with a clinical outcome in patients with stage I–III colorectal cancer.Materials and methods. The study included data from patients with morphologically verified colorectal cancer with stage I–III who were treated at the N. N. Blokhin National Oncology Research Center in the period from 2016 to 2021. Blood samples were collected before and after surgical treatment (on the 7–10th day after surgery). The minimum permissible concentration at which ctDNA in a plasma sample was considered positive was 0.4 copies of mutant DNA in 1 mcL of plasma. The main criterion of effectiveness was disease-free survival (DFS). The presence of cDNA before and after surgery was a negative prognostic factor for progression in stage I–III of CRC. Patients with positive cDNA after surgery had worse DFS results despite adjuvant chemotherapy. Patients with stage II CRC with negative ctDNA, regardless of adjuvant CT after surgery, did not have disease progression in 100 % of cases.Results. The study included 146 patients with stage I–III colorectal cancer. Progression was detected in 34 patients. The median follow-up time was 22 months (0–66 months). Data on progression were known in 119 patients. Positive cDNA data were detected before surgery in 55 of 120 patients (45 %), after surgery in 46 of 119 (38.6 %). In the group with positive cDNA before surgery, the median DFS was 35 months (95 % confidence interval (CI) 24,0–45.9), in the group with negative cDNA before surgery, the median DFS was not achieved (hazard ratio (HR) 4.6; 95 % CI 2.0–10.4), 1‑year DFS in the cDNA positive group was 62 % versus 100 % in the cDNA negative group (p &lt;0.001). In the group with positive cDNA after surgery, the median DFS was 20 months (95 % CI 8,1–31,9), in the group with negative cDNA was not achieved (HR 27,7; 95 % CI 6,6–116,6; p &lt;0,001). Patients with positive cDNA after surgery had worse DFS scores despite adjuvant chemotherapy. Patients with stage II CRC without ctDNA after surgery in 100 % did not have disease progression regardless of adjuvant CT.Conclusion. The presence of cDNA before and after surgery was a negative prognostic factor of progression after surgical treatment at stage I–III. The high negative prognostic value of cDNA makes it possible to select patients with stage II who do not need adjuvant chemotherapy.Введение. Исследования, посвященные неметастатическому колоректальному раку, продемонстрировали прогностическое значение анализа циркулирующей опухолевой ДНК (цоДНК) после операции, что в перспективе позволит персонализировать как неоадъювантное, так и адъювантное лечение.Цель исследования – изучить прогностическое значение статуса цоДНК до и после операции у пациентов с колоректальным раком I–III стадии.Материалы и методы. В исследование были включены данные пациентов с морфологически верифицированным колоректальным раком I–III стадии, проходивших лечение в Национальном медицинском исследовательском центре онкологии им. Н. Н. Блохина в период с 2016 по 2021 г. Забор образцов крови осуществлялся до и после хирургического лечения (на 7–10‑е сутки после операции). Минимально допустимая концентрация, при которой цоДНК в образце плазмы считали позитивной, – 0,4 копий мутантного ДНК в 1 мкл плазмы. Основным критерием эффективности являлась выживаемость без признаков болезни (ВБПБ).Результаты. В исследование были включены 146 пациентов с колоректальным раком I–III стадии. Прогрессирование выявлено у 34 больных. Медиана времени наблюдения составила 22 мес (1–66 мес). Данные о прогрессировании заболевания получены для 119 пациентов. Положительный цоДНК-статус до операции выявлен у 55 (45 %) из 120 больных, после хирургического вмешательства – у 46 (38,6 %) из 119. В группе цоДНК+ медиана ВБПБ до операции составила 35 мес (95 % доверительный интервал (ДИ) 24,0–45,9), в группе цоДНК она не была достигнута (отношение рисков (ОР) 4,6; 95 % ДИ 2,0–10,4). Однолетняя ВБПБ в группах положительного и отрицательного статуса цоДНК оказалась равна 62 и 100 % соответственно (p &lt;0,001). При цоДНК+ медиана ВБПБ после операции составила 20 мес (95 % ДИ 8,1–31,9), при цоДНК– она не была достигнута (ОР 27,7; 95 % ДИ 6,6–116,6; p &lt;0,001). Пациенты с положительным статусом цоДНК после операции имели худшие показатели ВБПБ, несмотря на проведение адъювантной химиотерапии. При колоректальном раке II стадии и отрицательном цоДНК-статусе после операции в 100 % случаев прогрессирования заболевания не наблюдалось (независимо от проведения адъювантной химиотерапии).Заключение. Наличие цоДНК до и после операции является негативным прогностическим фактором прогрессирования заболевания при колоректальном раке I–III стадии. Высокое негативное прогностическое значение цоДНК позволяет выбирать пациентов с заболеванием II стадии, не нуждающихся в проведении адъювантной химиотерапии