Radial Strains of Double-layer Cylinders in Hydraulic Props of Powered Supports

At present a lot of efforts are made to use double-layer power cylinders in hydraulic props of powered supports. To study the response of these cylinders to loads a special finite-element model has been developed and used for investigations into tension effect and double-layer cylinder thickness – radial strain relation under pressure of hydraulic liquid 50 MPa. It has been revealed that double-layer cylinders are distinguished by much lower radial strains in the zone of cup-like sealing elements as if compared with one-layer cylinders, as well as equivalent stresses are lower, and safety factor is higher. The data of the study can be recommended to calculate appropriate geometrical parameters of hydraulic props with respect to lower radial strains of a hydraulic cylinder, which improve its leak-tightness and functioning of cup-like sealing elements. The obtained results can be useful for design and construction of powered supports

Survey on software tools that implement deep learning algorithms on intel/x86 and IBM/Power8/Power9 platforms

Neural networks are becoming more and more popular in scientific field and in the industry. It is mostly because new solutions using neural networks show state-of-the-art results in the domains previously occupied by traditional methods, eg. computer vision, speech recognition etc. But to get these results neural networks become progressively more complex, thus needing a lot more training. The training of neural networks today can take weeks. This problems can be solved by parallelization of the neural networks training and using modern clusters and supercomputers, which can significantly reduce the learning time. Today, a faster training for data scientist is essential, because it allows to get the results faster to make the next decision. In this paper we provide an overview of distributed learning provided by the popular modern deep learning frameworks, both in terms of provided functionality and performance. We consider multiple hardware choices: training on multiple GPUs and multiple computing nodes. © The Authors 2019.Council on grants of the President of the Russian Federation: MK-2330.2019.9You can use a special version of Caffe, NVCaffe, which is supported by NVidia. This version was created specifically for the use of several GPUs. User instructions can be found in [35].For NVidia, MXNet is supported by Nvidia Cloud. MXNet also has support for CUDA and CuDNN.The results described in this paper were obtained with the financial support of the grant from the Russian Federation President Fund (MK-2330.2019.9)

Multifrequency dial sensing of the atmospheric gaseous constituents using the first and second harmonics of a tunable CO2 laser radiation

The results of field measurements of concentration of some gaseous components of the atmosphere along the paths, in Sofia, Bulgaria, using a gas analyzer based on the use of a CO2 laser radiation frequency-doubled with ZnGeP2 monocrystals are presented. The gas analyzer is a traditional long path absorption meter. Radiation from the tunable CO2 laser of low pressure and from an additional He-Ne laser is directed to a colliminating hundredfold Gregori telescope with a 300 mm diameter of the principal mirror. The dimensions of the mirrors of a retroreflector 500 x 500 mm and a receiving telescope allow one to totally intercept the beam passed through the atmospheric layer under study and back

Effect of pulse flows of charged particles on the structure and mechanical properties of metals

We investigate the effect of pulse flows of hydrogen, helium, and hydrogen-helium plasma of a specific power of 20-30 GW/m² on the surface structure and mechanical properties of vanadium, niobium, and Kh16N15M3B and Kh18N10T austenitic stainless steelsyesBelgorod State Universit

ПАРАЛЛЕЛИЗМ В СЛОЖНЫХ ПРОГРАММНЫХ КОМПЛЕКСАХ (ПОЧЕМУ СЛОЖНО СОЗДАВАТЬ ЭФФЕКТИВНЫЕ ПРИКЛАДНЫЕ ПАКЕТЫ)

In the article, types of parallelism used in architectures of modern computer systems are considered, and the ways of their  manifestation in programs are described. Six paradigms of parallel  programming are analyzed, and the relationship of paradigms to  generations of highperformance computing systems is shown.  Different methods of description and representation of parallelism  based on various kinds of program models are considered. The  reasons that determine challenges of developing efficient software  packages for parallel computing systems are discussed. The connection between the  material under discussion and the actively developed Internet  encyclopedia of properties and features of AlgoWiki parallel algorithms is noted.В работе рассмотрены виды параллелизма, применяемые в архитектурах современных  компьютерных систем, и описаны способы их проявления в программах. Проанализированы  шесть парадигм параллельного программирования, и показана связь парадигм с поколениями высокопроизводительных вычислительных систем. Рассмотрены методы описания  и представления параллелизма с помощью разного рода моделей программ. Обсуждаются  причины, определяющие сложности разработки эффективного программного обеспечения для  параллельных вычислительных систем. Отмечается связь обсуждаемого материала с активно  развиваемой Интернет-энциклопедией свойств и особенностей параллельных алгоритмов AlgoWiki

Limited Thermal Conductance of Metal-Carbon Interfaces

The thermal conductance for a series of metal-graphite interfaces has been experimentally measured with time-domain thermoreflectance (TDTR). For metals with Debye temperatures up to ∼400 K, a linear relationship exists with the thermal conductance values. For metals with Debye temperatures in excess of ∼400 K, the measured metal-graphite thermal conductance values remain constant near 60 MW m−2 K−1. Titanium showed slightly higher conductance than aluminum, despite the closeness of atomic mass and Debye temperature for the two metals. Surface analysis was used to identify the presence of titaniumcarbide at the interface in contrast to the aluminum and gold-carbon interfaces (with no detectablecarbide phases). It was also observed that air-cleaved graphite surfaces in contact with metals yielded slightly higher thermal conductance than graphite surfaces cleaved in vacuo. Examination of samples with scanning electron microscopy revealed that the lack of absorbed molecules on the graphite surfaceresulted in differences in transducer film morphology, thereby altering the interface conductance.Classical molecular dynamic simulations of metal-carbon nanotube thermal conductance values were calculated and compared to the TDTR results. The upper limit of metal-graphite thermal conductance is attributed to the decreased coupling at higher frequencies of the lighter metals studied, and to the decreased heat capacity for higher vibrational frequency modes

Optical pump–terahertz probe study of HR GaAs:Cr and SI GaAs:El2 structures with long charge carrier lifetimes

The time dynamics of nonequilibrium charge carrier relaxation processes in SI GaAs:EL2 (semi-insulating gallium arsenide compensated with EL2 centers) and HR GaAs:Cr (high-resistive gallium arsenide compensated with chromium) were studied by the optical pump–terahertz probe technique. Charge carrier lifetimes and contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of surface and volume Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that, in most cases for HR GaAs:Cr and SI GaAs:EL2, Auger recombination mechanisms make the largest contribution to the recombination rate of nonequilibrium charge carriers at injection levels above ~(0.5–3)·1018 cm−3, typical of pump–probe experiments. At a lower photogenerated charge carrier concentration, the SRH recombination prevails. The derived charge carrier lifetimes, due to the SRH recombination, are approximately 1.5 and 25 ns in HR GaAs:Cr and SI GaAs:EL2, respectively. These values are closer to but still lower than the values determined by photoluminescence decay or charge collection efficiency measurements at low injection levels. The obtained results indicate the importance of a proper experimental data analysis when applying terahertz time-resolved spectroscopy to the determination of charge carrier lifetimes in semiconductor crystals intended for the fabrication of devices working at lower injection levels than those at measurements by the optical pump–terahertz probe technique. It was found that the charge carrier lifetime in HR GaAs:Cr is lower than that in SI GaAs:EL2 at injection levels > 1016 cm−3.В ст. ошибочно: Irina A. Kolesnikov