Hard loss of stability in Painlev\'e-2 equation

A special asymptotic solution of the Painlev\'e-2 equation with small parameter is studied. This solution has a critical point $t_*$ corresponding to a bifurcation phenomenon. When $t<t_*$ the constructed solution varies slowly and when $t>t_*$ the solution oscillates very fast. We investigate the transitional layer in detail and obtain a smooth asymptotic solution, using a sequence of scaling and matching procedures

Voronoi-Delaunay analysis of normal modes in a simple model glass

We combine a conventional harmonic analysis of vibrations in a one-atomic model glass of soft spheres with a Voronoi-Delaunay geometrical analysis of the structure. ``Structure potentials'' (tetragonality, sphericity or perfectness) are introduced to describe the shape of the local atomic configurations (Delaunay simplices) as function of the atomic coordinates. Apart from the highest and lowest frequencies the amplitude weighted ``structure potential'' varies only little with frequency. The movement of atoms in soft modes causes transitions between different ``perfect'' realizations of local structure. As for the potential energy a dynamic matrix can be defined for the ``structure potential''. Its expectation value with respect to the vibrational modes increases nearly linearly with frequency and shows a clear indication of the boson peak. The structure eigenvectors of this dynamical matrix are strongly correlated to the vibrational ones. Four subgroups of modes can be distinguished

Prediction of inter-particle adhesion force from surface energy and surface roughness

Fine powder flow is a topic of great interest to industry, in particular for the pharmaceutical industry; a major concern being their poor flow behavior due to high cohesion. In this study, cohesion reduction, produced via surface modification, at the particle scale as well as bulk scale is addressed. The adhesion force model of Derjaguin-Muller-Toporov (DMT) was utilized to quantify the inter-particle adhesion force of both pure and surface modified fine aluminum powders (∼8 μm in size). Inverse Gas Chromatography was utilized for the determination of surface energy of the samples, and Atomic Force Microscopy was utilized to evaluate surface roughness of the powders. Surface modification of the original aluminum powders was done for the purpose of reduction in cohesiveness and improvement in flowability, employing either silane surface treatment or dry mechanical coating of nano-particles on the surface of original powders. For selected samples, the AFM was utilized for direct evaluation of the particle pull-off force. The results indicated that surface modification reduced the surface energy and altered the surface nano-roughness, resulting in drastic reduction of the inter-particle adhesion force. The particle bond number values were computed based on either the inter-particle adhesion force from the DMT model or the inter-particle pull-off force obtained from direct AFM measurements. Surface modification resulted in two to three fold reductions in the Bond number. In order to examine the influence of the particle scale property such as the Bond number on the bulk-scale flow characterization, Angle of Repose measurements were done and showed good qualitative agreements with the Bond number and acid/base surface characteristics of the powders. The results indicate a promising method that may be used to predict flow behavior of original (cohesive) and surface modified (previously cohesive) powders utilizing very small samples

Anharmonicity, vibrational instability and Boson peak in glasses

We show that a {\em vibrational instability} of the spectrum of weakly interacting quasi-local harmonic modes creates the maximum in the inelastic scattering intensity in glasses, the Boson peak. The instability, limited by anharmonicity, causes a complete reconstruction of the vibrational density of states (DOS) below some frequency $\omega_c$, proportional to the strength of interaction. The DOS of the new {\em harmonic modes} is independent of the actual value of the anharmonicity. It is a universal function of frequency depending on a single parameter -- the Boson peak frequency, $\omega_b$ which is a function of interaction strength. The excess of the DOS over the Debye value is $\propto\omega^4$ at low frequencies and linear in $\omega$ in the interval $\omega_b \ll \omega \ll \omega_c$. Our results are in an excellent agreement with recent experimental studies.Comment: LaTeX, 8 pages, 6 figure

Опыт дистанционного температурно-влажностного зондирования атмосферы в период дрейфа НЭС «Академик Трешников»

For the first time experience was gained with the operation of Russian equipment for water content and temperature remote sensing of the lower atmosphere in the Arctic. The comparison the results of measurements by radiometric systems with data of radiosoundings in wide range of meteorological conditions had been executed. It is shown that mean difference between integral atmospheric water content, measured by water vapor radiometer WVR, and calculated from radiosoundings data does not exceed 6 % with standard deviation 0.54 kg/m2 and significant correlation coefficient 0,92. Analysis the data of meteorological temperature profiler MTR-5 allows to conclude that in general its adequately reproduce air temperature profiles in the atmospheric lower 1000 m layer. Some deviations take place only in cases of large temperature gradients. Preliminary analysis of WVR data showed that monthly mean value of integral atmospheric water content in area under study in April 2019 year practically coincides with calculated from radiosoundings, performed in 1983—1988 years at the polar station Barentsburg, nearest to the drift region, 3.61 and 3.62 kg/m2 respectively. Same time hourly mean values of integral atmospheric water content during drift varied from 2 to 10 kg/m2, with extreme values recorded between April 15 and April 20, probably due to intensive transport of air masses of the Atlantic origin. Based on MTR-5 data it was concluded that despite differences in sounding technology, the place and time of observations, the statistics of inversions registered during drift correspond well to statistics of inversions, recorded on the Arctic coastal stations and over sea ice cover of the Weddell Sea in winter.Приведено описание работы комплекса аппаратуры влажностно-температурного дистанционного зондирования нижнего слоя атмосферы (радиометр РВП и метеорологический профилемер МТР-5РЕ) в условиях Арктики. Выполнено сравнение результатов измерений радиометрических систем с данными аэрологического зондирования в широком спектре метеорологических условий. Получены оценки интегрального влагосодержания атмосферы и характеристик инверсий в нижнем 1000-метровом слое атмосферы в период дрейфа НЭС «Академик Трёшников» в северной части Баренцева моря