Numerical modelling of two-phase piezocomposites with interface mechanical anisotropic effects

This work was supported by the Russian Science Foundation (grant № 15-19-10008-P)

Atmospheric retrievals with petitRADTRANS

petitRADTRANS (pRT) is a fast radiative transfer code used for computing emission and transmission spectra of exoplanet atmospheres, combining a FORTRAN back end with a Python based user interface. It is widely used in the exoplanet community with 161 references in the literature to date, and has been benchmarked against numerous similar tools. The spectra calculated with pRT can be used as a forward model for fitting spectroscopic data using Monte Carlo techniques, commonly referred to as an atmospheric retrieval. The new retrieval module combines fast forward modelling with nested sampling codes, allowing for atmospheric retrievals on a large range of different types of exoplanet data. Thus it is now possible to use pRT to easily and quickly infer the atmospheric properties of exoplanets in both transmission and thermal emission.Comment: 5 pages, 1 figure, submitted to the Journal of Open Source Softwar

Atomistic molecular dynamics simulations of tubulin heterodimers explain the motion of a microtubule

Microtubules are essential parts of the cytoskeleton that are built by polymerization of tubulin heterodimers into a hollow tube. Regardless that their structures and functions have been comprehensively investigated in a modern soft matter, it is unclear how properties of tubulin heterodimer influence and promote the self-assembly. A detailed knowledge of such structural mechanisms would be helpful in drug design against neurodegenerative diseases, cancer, diabetes etc. In this work atomistic molecular dynamics simulations were used to investigate the fundamental dynamics of tubulin heterodimers in a sheet and a short microtubule utilizing well-equilibrated structures. The breathing motions of the tubulin heterodimers during assembly show that the movement at the lateral interface between heterodimers (wobbling) dominates in the lattice. The simulations of the protofilament curvature agrees well with recently published experimental data, showing curved protofilaments at polymerization of the microtubule plus end. The tubulin heterodimers exposed at the microtubule minus end were less curved and displayed altered interactions at the site of sheet closure around the outmost heterodimers, which may slow heterodimer binding and polymerization, providing a potential explanation for the limited dynamics observed at the minus end

Comparative analysis of spherical focusing transducers from dense and porous piezoceramic materials

The second author is grateful for the support of the Ministry of Education and Science of the Russian Federation, project 9.1001.2017/4.6

Finite element modelling of contact interaction between wheel and rail with three-layered thin coating

The stress-strain of thin multilayered coatings covered the surface of the rail is studied near the region of side contact in turning motion. The stress-strain state is studied for various geometric and mechanical coating parameters’ values. A theoretical and a finite element models are developed. Stress-strain state analysis has been made based on models developed and recommendations were given for an optimal coating parameters’ selection

The behaviours of Mg and Ca in some types of ultramaphic alkaline melts in the presence of H 2 O at high temperature and pressure (the experimental data)

The sample has been investigated, which was composed of olivine-melilite rock from the south-western part of the Kugda intrusion, situated in the eastern margin of the Maimecha-Kotuiskay alkaline- ultramaphic province (northern part of Siberia platform). The experiments were carried out using a high-pressure apparatus of the "piston-cylinder" type. The pressure was 5-15 kb and the temperature -800-1250 0 C. The water content in the system was 3 and 9 wt. All experiments were carried out in hermetically sealed Pt or Au ampoules. The samples were chemically analyzed using a scanning electron microscope (SEM). Besides, the chemical composition of the experimental phases was determined by means of more than 40 electron microprobe in 20 experimental samples. For phase identification the X-ray method was used too. The structural peculiarities of rocks and mineral compositions were studied by optical methods in polished and thin sections prior and after the experiment. It was shown that at pressures above 7.5-8 kb the olivine-melilite melt is separated into two melts: pyroxenite and melilite. Most part of Mg in this system was concentrated in a high temperature phase of diopside type. The remaining melt was depleted of Mg and enriched by Ca. The mineralization vapour practically did not contain Mg. The main components of the mineralization vapour were Ca, Na, Si and Fe

The banding in serpentinites and its influence on character of talc-magnesite and magnesite mineralization (natural and experimental data)

The geological setting of some banded talc-magnesite ores and magnesites was studied in the field (Urals, Russia; Finland, East Iran). Talc-magnesite and magnesite ores occur in ultramafic rocks. Experimental methods were used in order to determine the influence of physico-mechanical parameters on the formation of banded structures in talc-magnesite rocks and magnesites. Experiments were carried out with axial compression up to 10 kbar and confining pressure 2, 4, 6 and 8 kbars at room temperature. The samples were chemically analyzed using a Philips Analytical PW 2400 authomatic XRF Spectrometer and a scanning electron microscope (SEM). Some analyses were made with a "Camebax SX-50" electron microprobe, using an accelerating voltage of 20 kilovolts for all elements with a sample current of 20 nanoamps. X-ray method for phase identification was used. Structure peculiarities of rocks prior to the experiment and after were studied by optical methods in polished sections and thin sections. It was shown, that banding in talc-magnesite stone and magnesites are inherited from banded serpentinites and can affect on distribution and composition rock-forming minerals

Finite element modeling of effective properties of nanoporous thermoelastic composites with surface effects

This investigation concerns to the determination of the material properties of nanoscale thermoelastic composites of an arbitrary anisotropy class with stochastically distributed porosity. In order to take into account nanoscale level at the borders between material and pores, the GurtinMurdoch model of surface stresses and the highly conduct- ing model are used. Finite element package ANSYS was used to simulate representative volume and to calculate the effective material properties. This approach is based on the theory of effective moduli of composite mechanics, modeling of representative volumes and the finite element method. Here, the contact boundaries between material and pores were covered by the surface membrane elastic and thermal shell elements in order to take the surface effects into account

Fundamental Solutions in Plane Problem for Anisotropic Elastic Medium Under Moving Oscillating Source

In present article we consider the problems of concentrated point force which is moving with constant velocity and oscillating with cyclic frequency in unbounded homogeneous anisotropic elastic two-dimensional medium. The properties of plane waves and their phase, slowness and ray or group velocity curves for 2D problem in moving coordinate system are described. By using the Fourier integral transform techniques and established the properties of the plane waves, the explicit representation of the elastodynamic Green's tensor is obtained for all types of source motion as a sum of the integrals over the finite interval. The dynamic components of the Green's tensor are extracted. The stationary phase method is applied to derive an asymptotic approximation of the far wave field. The simple formulae for Poynting energy flux vectors for moving and fixed observers are presented too. It is noted that in the far zones the cylindrical waves are separated under kinematics and energy. It is shown that the motion bring some differences in the far field properties. They are modification of the wave propagation zones and their number, fast and slow waves appearance under trans- and superseismic motion and so on.Comment: 19 pages, Proceeding of the Conference "Advanced Problems in Mechanics", Russia, St.Petersburg (Repino), June 22-July 2, 200

Neural posterior estimation for exoplanetary atmospheric retrieval

Retrieving the physical parameters from spectroscopic observations of exoplanets is key to understanding their atmospheric properties. Exoplanetary atmospheric retrievals are usually based on approximate Bayesian inference and rely on sampling-based approaches to compute parameter posterior distributions. Accurate or repeated retrievals, however, can result in very long computation times due to the sequential nature of sampling-based algorithms. We aim to amortize exoplanetary atmospheric retrieval using neural posterior estimation (NPE), a simulation-based inference algorithm based on variational inference and normalizing flows. In this way, we aim (i) to strongly reduce inference time, (ii) to scale inference to complex simulation models with many nuisance parameters or intractable likelihood functions, and (iii) to enable the statistical validation of the inference results. We evaluate NPE on a radiative transfer model for exoplanet spectra petitRADTRANS, including the effects of scattering and clouds. We train a neural autoregressive flow to quickly estimate posteriors and compare against retrievals computed with MultiNest. NPE produces accurate posterior approximations while reducing inference time down to a few seconds. We demonstrate the computational faithfulness of our posterior approximations using inference diagnostics including posterior predictive checks and coverage, taking advantage of the quasi-instantaneous inference time of NPE. Our analysis confirms the reliability of the approximate posteriors produced by NPE. The accuracy and reliability of the inference results produced by NPE establishes it as a promising approach for atmospheric retrievals. Amortization of the posterior inference makes repeated inference on several observations computationally inexpensive since it does not require on-the-fly simulations, making the retrieval efficient, scalable, and testable.Comment: The paper has been submitted to AandA after a final revisio