St Petersburg Polytechnic University Journal-Physics and Mathematics最新文献

In the present work, the optical identification of a group of radio sources located in the Aquarius and Cetus constellations in a field with the size of 1.2 square degrees has been carried out. Ten radio sources under investigation were identified with stars and one object was identified with a diffuse image (ESO-538-10). It should be stressed that eight radio objects were found to have a non-thermal radio spectrum. This fact is likely to indicate the presence of the significant magnetic field in the atmosphere of the sources. Precise radio and optical coordinates of the identified objects were suggested. Significant radio refraction in the interstellar medium in the tested space direction was revealed.

The obtained results of direct numerical simulation of the free mercury convection in a rotating cylindrical container heated from below are presented. Setting the Prandtl number equal to 0.025 and the height-to-diameter ratio equal to 1.0, effects of container rotation and heat transfer in horizontal solid walls have been studied. The effective Rayleigh number was close to 10⁶. The Navier–Stokes equations, written with the Boussinesq approximation, were solved using the fractional-step method. The instant and time-averaged flow fields, the pulsation spectra and the integral heat transfer data were analyzed. The in-house code SINF/Flag-S results were compared with the available experimental data, and with the data obtained using the commercial software ANSYS Fluent 15.0.

The problem on an antiplane semi-infinite crack approaching an elastic wedge-shaped inclusion is considered. The problem has been solved exactly using the Mellin integral transformation and the Wiener–Hopf method. The asymptotic behavior of the stress intensity factor K_III in the crack tip was studied for short distances from the crack to the inclusion vicinity. Depending on the composition parameters, the crack was shown to be stable (K_III → 0) or unstable (K_III → ∞). Provided that the interface has a corner point, the crack growth can be unstable (unlike the smooth interface) for some parameter values even though the crack approaches, from a soft material, a relatively harder inclusion. Alternatively, the possibility of K_III → 0 exists provided the crack approaching a soft inclusion from a hard material.

The aim of the study is to reveal the special features of radio control link model in LR-WPAN under operating conditions of interference of the reflected and the line-of-sight component and to evaluate the radio link's range of positive light source control. The results of development and practical implementation of controlled spectrally tunable light emitting diode (LED) light sources with ISM- and ZigBee (IEEE 802.15.04)-based radio frequency transceivers are presented. A software application developed in LabVIEW simulation of a radio control link for light sources and used for evaluating the radio control link's range of various combinations of polarization of transmitting and receiving antennas has been discussed. It was established and experimentally verified that the received energy was able to be computed using the two-ray model: a line-of-sight ray and the reflected one. This approach is simpler as compared to cellular networks in which multiple reflections from various objects result in multi-path propagation without line-of-sight component.

The paper describes a nondestructive noncontact method for investigating the sea-bottom structure using hydroacoustic and laser radiation. A practical implementation of this method is also presented. The research complex incorporates a state-of-the-art low-frequency hydroacoustic radiating system and a system of coastal laser strainmeters arranged in the specially selected sea waters and coastal grounds. The hydroacoustic radiators are used to generate a seismic signal. Seismic superficial waves are recorded by the coastal laser strainmeters. Optical parts of the strainmeters are constructed as the unequal-path Michelson interferometer where the frequency-stable helium-neon lasers serve as emission sources. A preliminary model of the sea-bottom testing ground has been developed by application of geologic-geophysical procedures. The model-based analysis of the timing data of the recorded seismic waves was carried out. The prospectivity of the used method was proved.

The experimental studies of elasto-plastic deformation of tubular steel samples under proportional and non-proportional (monotonic and cyclic) loadings, including partial and intermediate loadings, have been conducted with the aim of improving the accuracy of the description of the complex passive loading processes. The plastic strain accumulation was observed in the course of tests carried out under passive loading. However, this effect turned out not to be described by the plastic flow theory. This result required the development of an alternative material model. The comparisons of experimental results with the predictions of the structural (rheological) elasto-plastic model and the multisurface theory of plasticity with one active surface were made. Modifications of the constitutive equations were proposed in order to improve the accuracy of the material response prediction.

The paper puts forward a modification of the no-boundary Hartle–Hawking wave function in which, in the general case, the Euclidean functional integral can be described by an inhomogeneous universe. The regularization of this integral is achieved in arbitrary canonical calibration by abandoning integration over the lapse and shift functions. This makes it possible to ‘correct’ the sign of the Euclidean action corresponding to the scale factor of geometry. An additional time parameter associated with the canonical calibration condition then emerges. An additional condition for the stationary state of the wave function's phase after returning to the Lorentzian signature, serving as the quantum equivalent of the classical principle of the least action, was used to find this time parameter. We have substantiated the interpretation of the modified wave function as the amplitude of the universe's birth from ‘nothing’ with the additional parameter as the time of this process. A homogeneous model of the universe with a conformally invariant scalar field has been considered. In this case, two variants of the no-boundary wave function which are solutions of the Wheeler–DeWitt equation have been found.

The paper is dedicated to techniques for reduction of background radiation in the room for conducting proton eye radiotherapy. The necessity of this reduction stems from the health risk of low-dose effect on the personnel and patients. We have touched the aspects of background reduction both at the cost of secondary particles, produced in beam-forming systems, and the dose reduction for the patient's healthy tissue (when carrying out beam therapy) owing to correct assessment of the biological effects of protons with energies up to 60 MeV. The obtained calculation results prove that an increase in the proton beam diameter provides the possibility of reducing the background radiation by more than a factor of three in the room and of correspondingly decreasing the body's radiation exposure. It is necessary to take correct account of RBE to reduce the radiation exposure of adjacent organs.

Spectrographic electron and ion optical structures markedly raise the possibilities of modern energy and mass analysis. Electric and magnetic fields which potentials are expressed by functions homogeneous in Euler's sense are the effective instrumentation that is used for creating new spectrographic analytical devices with the determined working characteristics. This paper puts forward and discusses some methods for building 3D harmonic and homogeneous in Euler's sense structures representable as the polynomials of finite degree with respect to one of variables. These strictly mathematical approaches provide a possibility of expanding significantly a class of quasi-polynomial potentials and of enriching modern analytical instrumentation by new spectrographic electrical and magnetic configurations.

The chemical composition and morphological properties of сlinoptilolite-bearing materials modified by MnО₂ have been studied using modern physical methods. Scanning electron microscopy, X-ray spectral microanalysis and optical reflection microscopy were applied. It was experimentally shown that MnО₂-modified samples with high and low Si/Al ratios differed in such parameters as the layer thickness, the surface concentration, the degree of particle-surface dealumination, and also in morphological peculiarities of the MnО₂-phase. This phase in the samples with high Si/Al ratios exhibited the structure formed by nanorods of 10–20 nm in diameter and 500–700 nm in length. These nanorods are intermeshed in the net which is cross-linked with the surface of clinoptilolite particles. The MnО₂-modification of the samples was established to result in improving their mechanical and chemical strength as compared with the initial forms.