Dynamics of spatial coherence and momentum distribution of polaritons in a semiconductor microcavity under conditions of Bose-Einstein condensation

The study was supported by the Russian Foundation for Basic Research (project nos. 12-02-33091, 13-02-12197, and 14-02-01073) and the Presidium of the Russian Academy of Sciences. The work of V.V.B. was supported in part by a scholarship of the President of the Russian Federation.The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses are investigated. It is shown that the establishment of the condensate coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the spatial distribution of coherence. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wavefunction, which equilibrates on a much longer time scale.Publisher PDFPeer reviewe

Технические железнодорожные училища и ремесленные железнодорожные курсы

 News from the archivesThe article in Rail Business [Zheleznodorozhnoe Delo] published 110 years ago, in 1911, analysed in detail the organisation, in modern terms, of professional training and high vocational education of railway employees. Besides, it contains the opinion on curriculum, range of taught disciplines, qualifications, competences, and skills.  Пресс-архивПубликация в журнале «Железнодорожное дело» за 1911 год, то есть 110 лет назад, самым подробным образом анализировала организацию подготовки технических специалистов для железных дорог, как мы сказали бы сейчас, на базе профессионального обучения и среднего  профессионального образования. Более того, приводятся взгляды на содержание обучения, набор востребованныхдисциплин, квалификации, компетенции и навыки.

Dissipative phase transition in systems with two-photon drive and nonlinear dissipation near the critical point

We study dissipative phase transition near the critical point for a system with two-photon driving and nonlinear dissipation. The proposed mean-field theory, which explicitly takes into account quantum fluctuations, allowed us to describe properly the evolution dynamics of the system and to demonstrate the new effects in the steady-state. We show that the presence of quantum fluctuations leads to a power-law dependence of the anomalous average at the phase transition point, with which the critical exponent is associated. Also, we investigate the effect of the quantum fluctuations on the critical point renormalization and demonstrate the existence of a two-photon pump threshold. It is noteworthy that the obtained results are in a good agreement with the numerical simulations.Comment: 7 pages, 4 figure

Усталостная прочность и частотная стабильность титанового сплава

We conducted a study on fatigue in flat samples of the VT3-1 titanium alloy using “soft” cyclic beam bending tests. For this purpose, we developed an innovative electromagnetic test bench. The test bench's electromechanical system induces mechanical vibrations at a frequency that matches the eigenfrequency of the sample, ensuring that the cyclic load frequency remains constant. The electromagnetic force bends the sample while the elastic force unbends it, producing a quasi-sinusoidal cyclic load. Through our investigation, we determined the impact of this cyclic loading on both cyclic strength and durability. Our findings indicate that the VT3-1 titanium alloy possesses high resistance to fatigue and an endurance limit. Furthermore, we observed a low variability of the experimental fatigue resistance in relation to the approximating fatigue curve, suggesting the alloy has high structural stability. This finding indicates that the VT3-1 titanium alloy possesses high structural stability. To assess eigenfrequency stability, we subjected the alloy samples to cyclic tests, interrupting them at a reference number of 50 million cycles to evaluate changes in eigenfrequencies and stability under loads close to the fatigue limit. The results showed that the titanium alloy has a high level of eigenfrequency stability. Interruptions in cyclic tests resulted in jump-like increases in eigenfrequencies, which was not observed in continuous tests. Nevertheless, the total eigenfrequency deviations from the initial value at the end of the tests were similar in both casesИсследованы образцы титанового сплава ВТ3-1 на усталость при нагружении по «мягкой» схеме консольного изгиба плоских образцов. Для таких исследований была разработана оригинальная электромагнитная установка. В ней реализована работа на основе электромеханической системы, в которой возбуждение механических колебаний осуществляется исходя из собственной частоты колебания испытуемого образца, т.е. реализуется режим, когда частота возбуждающей силы (частота циклического нагружения) всегда равна частоте собственных колебаний образца. Изгиб образца производится электромагнитной силой, а разгиб происходит под действием сил упругости материала, тем самым обеспечивается циклическое нагружение, близкое к синусоидальному. Изучено влияние реализуемого в данной установке вида циклического нагружения на циклическую прочность и долговечность. Установлено, что исследуемый титановый сплав имеет высокие характеристики показателей сопротивления усталости и предела выносливости. В ходе проведенных исследований отмечен небольшой разброс экспериментальных значений сопротивления усталости образцов относительно аппроксимирующей линии кривой усталости, что свидетельствует о высокой стабильности структурно-чувствительных свойств титанового сплава ВТ3-1. Также исследованы образцы этого сплава на частотную стабильность. За контрольное число наработки было принято 50 млн циклов нагружения, при которых проводилась сравнительная оценка изменения частотных характеристик. Представлены частотные характеристики и выявлена динамика частотной стабильности испытаний образцов при нагрузках, близких к пределу усталости. Установлено, что исследуемый титановый сплав имеет высокие значения частотной стабильности. При этом перерывы в циклических испытаниях приводят к скачкообразному приросту частоты, а при непрерывных испытаниях такого не наблюдалось, однако общее отклонение частоты от первоначальной к концу испытаний примерно одинаковое

Partially coherent conical refraction promises new counter-intuitive phenomena

In this paper, we extend the paraxial conical refraction model to the case of the partially coherent light using the unified optical coherence theory. We demonstrate the decomposition of conical refraction correlation functions into well-known conical refraction coherent modes for a Gaussian Schell-model source. Assuming randomness of the electrical field phase of the input beam, we reformulated and significantly simplified the rigorous conical refraction theory. This approach allows us to consider the propagation of light through a conical refraction crystal in exactly the same way as in the classical case of coherent radiation. Having this in hand, we derive analytically the conical refraction intensity both in the focal plane and in the far field, which allows us to explain and rigorously justify earlier experimental findings and predict new phenomena. The last include the counterintuitive effect of narrowing of the conical refraction ring width, disappearance of the dark Poggendorff’s ring in the Lloyd’s plane, and shift of Raman spots for the low-coherent conical refraction light. We also demonstrate a universal power-law dependence of conical refraction cones coherence degree on the input correlation length and diffraction-free propagation of the low-coherent conical refraction light in the far field

Effect of ethylmethylhydroxypyridine succinate on the functional activity of the transporter P-glycoprotein in the blood-brain barrier of rats under normal conditions and under hypoxic hypoxia

Relevance. Ethylmethylhydroxypyridine succinate (EMHPS) is a reference domestic drug with pronounced antioxidant and antihypoxic activity. P-Glycoprotein (Pgp) is an ATP-dependent transport protein localized in tissue barriers and protecting cells and organs from the effects of xenobiotics. Being expressed in the blood-brain barrier (BBB), Pgp limits the penetration of drugs and toxic substances into the brain tissue. Aim – to evaluate the effect of EMHPS on the functional activity of Pgp in the BBB of rats in normal conditions and in acute hypoxic hypobaric hypoxia in the experiment. Methods. The studies were carried out on male Wistar rats weighing 200–250 g, which were divided into 4 groups: group 1 (control, n = 30) – intact rats; Group 2 (control of hypoxia, n = 30) – rats, which were simulated hypoxia and before that they were once injected with water for injection; Group 3 (n = 30) – intact animals, which were injected intravenously with EMHPS at a dose of 50 mg / kg body weight; Group 4 (n = 30) – rats, which were injected intravenously with EMHPS at a dose of 50 mg/kg body weight before modeling hypoxia. 30 minutes after injection, animals of groups 2 and 4 were simulated acute hypoxic hypoxia for 30 minutes by ascending to an altitude of 8000 m with an ascent and descent speed of 50 m/s. 3 h after descent animals of groups 2 and 4 and 30 min after intravenous injection in animals of groups 1 and 3, the functional activity of Pgp in the BBB was assessed by the penetration of fexofenadine, a marker substrate of Pgp, into the brain tissue. For this, fexofenadine was injected into the tail vein of rats at a dose of 10 mg/kg of body weight. After 5, 10, 15, 30, 45, 60 minutes after administration, they were euthanized, at least 4 ml of blood was taken from the abdominal aorta into heparinized tubes and the cortex of the frontal lobes of the brain. The concentration of fexofenadine in biosamples was analyzed by HPLC-UV according to original methods. Results. In the course of the study, it was shown that a single intravenous injection of EMHPS at a dose of 50 mg/kg of body weight causes an increase in the content of fexofenadine in the cerebral cortex of rats, which indicates a decrease in the activity of the Pgp transporter protein. Simulation of acute hypoxic hypoxia was also accompanied by an increase in the permeability of the transport protein substrate into the brain tissue. At the same time, the prophylactic administration of EMHPS before hypoxic exposure did not significantly affect the BBB permeability, which remained significantly higher than the control and did not differ from the permeability during isolated hypoxic exposure. Conclusions: EMHPS with a single intravenous injection at a dose of 50 mg/kg body weight reduces the activity of Pgp in the BBB in normal conditions and does not significantly affect the penetration of the transporter substrate – fexofenadine into the brain tissue in acute hypoxic hypoxi

Development and validation of the method for the quantitative determination of methotrexate in a transport medium by HPLC-MS/MS

Relevance. BCRP is an efflux transporter protein that plays an important role in the pharmacokinetics of a wide range of drugs. The BCRP activity in vitro experiments is assessed by the transport of transporter protein substrates (methotrexate, etc.) across the bilipid membrane of cells overexpressingBCRP, for example, Caco-2 cells. The aim is to develop and validate a method for the quantitative determination of the BCRP substrate, methotrexate, in the transport medium of Caco-2 cells by HPLC-MS/MS. Methods. The work was performed on an Ultimate 3000 HPLC chromatograph (ThermoFisher, USA) with a TSQ Fortis tandem mass-selective detector (ThermoFisher, USA). The conditions of chromatographic analysis were as follows: column UCT Selectra C18 4.6 mm * 100 mm 5um, 100A, Selectra C18 Guard Cartridges SLC-18GDC46-5UM, separation temperature 35 °С, flow rate 0.3 ml/min, injected sample volume - 2 μl, analysis time - 10 min. Used a gradient elution: the ratio of the solution of 0.1 % formic acid and acetonitrile was at 0 min 75 and 25 %; 0.4 min 60 and 40 %; 6 minutes 20 and 80 %; 8 minutes 75 and 25 %. Under these conditions, the retention time of methotrexate is 3.11 minutes. Detection conditions: methotrexate - positive ionization mode, 455.15 m / z → 308.125 m / z, collision energy 22.99 V, source fragmentation 5, CID gas pressure 2 mTorr. The extraction of methotrexate from the transport medium (Hanks solution with 25 mM Hepes and 1% dimethyl sulfoxide) after incubation with Caco-2 cells for 3 h was carried out with a mixture of methanol + water in a ratio of 1: 1. Results. The developed method was validated according to the following parameters: selectivity, linearity, accuracy, precision, limit of quantitative determination, sample transfer, sample stability. The confirmed analytical range of the method was 60 -10,000 nmol / L in the transport medium. Conclusions: a method for the quantitative determination of methotrexate in the transport medium of Caco-2 cells by HPLC-MS / MS was developed and validated

Mn-Doped BaTiO3Ceramics: Thermal and electrical properties for multicaloric applications

Multiferroic materialsare widely used in microelectronics because they are sensitive to elastic, magnetic, and electric fields and there is an intrinsic coupling between them. In particular, transition metal-doped BaTiO3 is consideredas a viable multiferroic because of the simultaneous presence of ferroelectricity and magnetism.In this work, we study the electrical and thermal properties of Mn-doped BaTiO3 ceramics that can be used for multicaloric applications. We found that Mn doping leads to the broadening and shifting of the phase transition accompanied with simultaneous decrease of latent heat and entropy. Mn doping causes a decrease in the bulk resistivity while contact resistance remains intact. Doped ceramics can withstand high electric fields(up to 40 kV/cm) and exhibit linear I-V characteristics followed by the Schottkylimited current in contrast to earlier observations. As such, these ceramics are promising for multicaloric applications. © 2019 by the authors.Russian Science Foundation, RSF: № 18-19-00512Funding: This work was supported by the Russian Science Foundation (grant № 18-19-00512)

Development and validation of methods for quantitative determination of α-solanine, α-chaconine, solanidine in extracts from potato tuber peels BY High-performance liquid chromatography–tandem mass spectrometry

Promising metabolites of potato tuberosum (Solanum tuberosum L., f. Solanaceae) are α-solanine, α-chaconine and their aglycone solanidine.The aim of the work was to develop and validate methods for a quantitative analysis of α-solanine, α-chaconine and solanidine in dry extracts from the potato tuber peels by a high-performance liquid chromatography with a tandem  mass-selective detection (HPLC/MS/MS).Materials and methods. The analysis was performed in a gradient mode on an Ultimate 3000 chromatograph (ThermoFisher, USA) with a TSQ Fortis tandem mass-selective detector and a 4.6 mm×100 mm, 5 μm, 100 Å UCT Selectra C18 column. An electrospray in a positive ionization mode was used in this work. The following mass transitions were used for the quantitative analysis: α-solanine, 868.4→398.3 m/z; α-chaconine, 853.4→706.3 m/z; solanidine, 398.3→98.1 m/z. The following mass transitions were used for the internal standard fexofenadine: 502.3→171 m/z and 502.3→466.2 m/z. The analysis time was 10 min. The developed chromatography conditions were validated for a suitability. The validation was performed according to the following parameters: specificity, analytical range, linearity, correctness, precision and a lower limit of quantification. Results. The validation procedure showed that the methodology was selective, sufficiently sensitive for α-solanine, α-chaconine and solanidine (lower limits of the quantification were 50, 10 and 2 ng/mL, respectively), the linear in the concentration range of 50–5000, 10–5000 and 2–100 ng/mL, respectively; it was satisfactorily correct (RSD did not  exceed 7% for each of the substances) and sufficiently sensitive (RSD for α-solanine did not exceed 5%, for α-chaconine and solanidine – not more than 10%).Conclusion. A technique for a quantitative determination of α-solanine, α-chaconine and solanidine in dry extracts obtained from potato tuber peels by HPLC/MS/MS has been developed and validated. This technique can be used in the routine practice of the glycoalkaloids quantitative determination when analyzing their content in food products and combination medicines

Zero-bias photodetection in 2d materials via geometric design of contacts

Structural or crystal asymmetry are necessary conditions for emergence of zero-bias photocurrent in light detectors. Structural asymmetry has been typically achieved via $p-n$ doping being a technologically complex process. Here, we propose an alternative approach to achieve zero-bias photocurrent in 2d material flakes exploiting the geometrical non-equivalence of source and drain contacts. As a prototypical example, we equip a square-shaped flake of PdSe$_2$ with mutually orthogonal metal leads. Upon uniform illumination with linearly-polarized light, the device demonstrates non-zero photocurrent which flips its sign upon 90$^\circ$ polarization rotation. The origin of zero-bias photocurrent lies in polarization-dependent lightning-rod effect. It enhances the electromagnetic field at one contact from the orthogonal pair, and selectively activates the internal photoeffect at the respective metal-PdSe$_2$ Schottky junction. The proposed technology of contact engineering can be extended to arbitrary 2d materials and detection of both polarized and natural light