Modeling of the localy-functional properties of the material damaged by fields of defects

It is shown that for Mindlin media with fields of defects there is an alternative interpretation allowing to describe the material affected by defects as equivalent functionally-gradient material with varying properties for coordinates, modeled in the classical theory of elasticity. We establish clear relationships for determining the properties of functionally graded materials by the solutions, taking into account the availability of fields of defects. It is shown that, in general, the properties of equivalent functionally-gradient material depend on the coordinates, as well as on the loading and boundary conditions.     

Decoration of Carbon Nanotubes with MnO2 Nanoparticles Under Potassium Permanganate Treatment

Russian Physics Journal -     

Fast evaluation of Helmholtz potential on graphics processing units (GPUs)

This paper presents a parallel algorithm implemented on graphics processing units (GPUs) for rapidly evaluating spatial convolutions between the Helmholtz potential and a large-scale source distribution. The algorithm implements a non-uniform grid interpolation method (NGIM), which uses amplitude and phase compensation and spatial interpolation from a sparse grid to compute the field outside a source domain. NGIM reduces the computational time cost of the direct field evaluation at N observers due to N co-located sources from O(N²) to O(N) in the static and low-frequency regimes, to O(N log N) in the high-frequency regime, and between these costs in the mixed-frequency regime. Memory requirements scale as O(N) in all frequency regimes. Several important differences between CPU and GPU implementations of the NGIM are required to result in optimal performance on respective platforms. In particular, in the CPU implementations all operations, where possible, are pre-computed and stored in memory in a preprocessing stage. This reduces the computational time but significantly increases the memory consumption. In the GPU implementations, where handling memory often is a critical bottle neck, several special memory handling techniques are used to accelerate the computations. A significant latency of the GPU global memory access is hidden by implementing coalesced reading, which requires arranging many array elements in contiguous parts of memory. Contrary to the CPU version, most of the steps in the GPU implementations are executed on-fly and only necessary arrays are kept in memory. This results in significantly reduced memory consumption, increased problem size N that can be handled, and reduced computational time on GPUs. The obtained GPU–CPU speed-up ratios are from 150 to 400 depending on the required accuracy and problem size. The presented method and its CPU and GPU implementations can find important applications in various fields of physics and engineering.     

Changes in the structural parameters and molecular dynamics of polyhydroxybutyrate-chitosan mixed compositions under external influences

Differential scanning calorimetry (DSC), EPR probe analysis, large-angle X-ray diffraction (XRD), and UV spectroscopy are used to study the molecular dynamics and structure of hydroxybutyrate (PHB) copolymer, chitosan, and mixed compositions thereof upon thermal treatment in an aquatic medium. It is shown that, in mixed compositions, starting from 30% PHB, the correlation time increases by an order of magnitude, indicative of a sharp slowdown of the molecular mobility of the probe, and, concurrently, the degree of crystallinity decreases abruptly, as evidenced by DSC and XRD analyses. The diffusion coefficient of rifampicin in mixed compositions also decreases with increasing PHB content. A short-term (1 h) thermal treatment (at 70°C) in water results in an increase in the molecular mobility of the probe in the system. Crystallinity changes in complex ways.     

Macrokinetics of carbonaceous feedstock pyrolysis in a tubular reactor of variable cross section

A macrokinetic model of carbonaceous feedstock pyrolysis in a tubular reactor of variable cross section was constructed. It was shown that, to intensify the pyrolysis in such a tubular reactor, its diameter should vary depending on the viscosity of the reaction products.     

Plasma oscillations in fullerene molecules within the random phase approximation

A method is presented for calculating the density of plasma excitation modes in fullerene molecules, which makes it possible to describe more accurately the specific features of the spectra as compared to the models proposed previously. The method is based on the inclusion of the total contribution of π and σ electrons to the spectra of collective oscillations in the molecules. This allows one to consider fullerene molecules with an arbitrary symmetry and arbitrary substituents. A comparative analysis of the experimental curves obtained for resonance electron capture and the results of numerical simulations for C₆₀, C₇₀, and C₇₆ molecules has demonstrated that not only the main maxima but also the ranges of the formation of negative ions coincide.     

Evaluation of the humidity state of glued wooden constructions during monitoring

The work presents the research method for determining the humidity of wood in glued structures during their exploitation. The conductometric method serves a basis for the above-mentioned technique, but instead of regular sensors of humidity meter, we suggest the use of special sensors with electrodes of different lengths. It has been shown that the developed method has a number of advantages compared to the gravimetric method for determining wood humidity and can be used to monitor wooden structures during their exploitation with minimal time and labor inputs.