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

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

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

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

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)

Heterotrophic Flagellates from Freshwater and Soil Habitats in Subtropical China (Wuhan Area, Hubei Province)

We studied the diversity of heterotrophic flagellates from the sandy sediments of the Yangtze River, sandy and silty sediments of Donghu Lake, soil, moss and litter from the Luojiashan and Moshan hills as well as litter from the floodplain near Donghu Lake in April 2010. Sixty-seven heterotrophic flagellate species were identified by means of phase and interference contrast light microscopy and transmission electron microscopy. The majority of the observed flagellates were bacterivorous. Local species richness of river sediment communities was significantly lower than that of lake sediments and terrestrial habitats. The communities from the terrestrial habitats were more heterogeneous than those from freshwater sediments. Common species for the aquatic habitats were Rhynchomonas nasuta, Paraphysomonas sp., Neobodo designis, N. curvifilis, Bodo saltans and Spumella spp. In the soils only Spumella spp. was found in the majority of samples. Most characteristic taxa for the lake sediments were Helkesimastix faecicola, Petalomonas minuta, P. pusilla, Diphylleia rotans, Amastigomonas caudata. Amoeboflagellates such as Cercomonas angustus, C. granulifera, Paracercomonas crassicauda were specific for the terrestrial habitats. There were no specific taxa in the river sediments. The majority of the heterotrophic flagellates identified in this survey have been noted in China earlier. They are common (and usually predominant) for other regions in both freshwater and soil habitats

Mitoxantrone Quantification by HPLC-MS/MS in Caco-2 Culture Media

Mitoxantrone is a marker substrate of breast cancer resistance protein (BCRP). BCRP is involved in a number of pharmacokinetic drug-drug interactions. The transporter’s possible saturability makes it advisable to use low concentrations of mitoxantrone for in vitro studies. Consequently, mitoxantrone quantification requires   a method with high sensitivity.The aim of the study was to develop and validate a procedure for mitoxantrone quantification in Caco-2 culture media by HPLC-MS/MS.Materials and methods.  The  authors  used  an  Ultimate  3000  HPLC  system  and a TSQ Fortis triple quadrupole mass spectrometer by Thermo Fisher Scientific and a Selectra C18 column (4.6×100 mm, 5 μm, 100 Å) by United Chemical Technologies. The elution ran in a gradient mode with a mobile phase of 1% formic acid solution and methanol. Experimental parameters were as follows: eluent flow rate, 0.3 mL/min; separation column temperature, 35 °C; injection volume, 5  μL; ana lysis time, 10 min; approximate mitoxantrone retention time, 5.51 min. The sample preparation involved protein precipitation from the culture medium with methanol, followed by centrifugation at 13,000 g for 10 min. The detection was performed using electrospray ionisation in the positive ion mode. Detection parameters were   as follows: electrospray voltage, 3700 V; sheath gas flow rate, 50 L/min; auxiliary    gas flow rate, 10 L/min; sweep gas flow rate, 1 L/min; ion-transfer tube temperature, 300 °C; and evaporator temperature, 350 °C. The detection was set at mass transitions of m/z 455 to 88.2 and m/z 455 to 358.1, with the collision energy for these transitions amounting to 25 V and 18 V, respectively. The source fragmentation was at 0, and the CID gas pressure was at 2 mTorr.Results. The analytical procedure showed selectivity, high sensitivity (limit of detection, 10 nmol/L; lower limit of quantification, 50 nmol/L), accuracy, precision, and linearity in the concentration range of 50–1000 nmol/L. The authors observed no carryover or matrix effects. A simulation of real-life storage conditions demonstrated high stability of mitoxantrone samples. Thus, the analytical procedure enables preclinical evaluation of medicinal product effects on the functional activity of BCRP, based on assessing the transcellular mitoxantrone transport in the presence of a test product.Conclusion. The authors developed and validated the analytical procedure for mitoxantrone quantification in Caco-2 culture media by HPLC-MS/MS

ИССЛЕДОВАНИЕ ПОВРЕЖДАЕМОСТИ ПОВЕРХНОСТИ ЧИСТЫХ МЕТАЛЛОВ С УЧЕТОМ ЧАСТОТЫ ЦИКЛИЧЕСКОГО НАГРУЖЕНИЯ

The research results of pure metal surface damaging have been obtained in the course of fatigue tests. Mathematical dependences of changing the fatigue resistance indicators on frequency of cyclic loading during bending deformation of rotating samples are deduced. Fatigue curve equations are given and changes in the microstructure at cyclic loading are shown.Изложены результаты исследования повреждаемости поверхности чистых металлов, полученные при усталостных испы- таниях. Выведены математические зависимости изменения показателя сопротивления усталости от частоты цикличес- кого нагружения при деформации изгиба вращающихся образцов. Приведены уравнения кривых усталости и показано изменение микроструктуры при циклических нагружениях