Electron‐Ion Relaxation,Phase Transitions,and Surface Nano‐Structuring Produced by Ultrashort Laser Pulses in Metals

Fundamental physical phenomena in metals irradiated by ultrashort laser pulses with absorbed fluences higher than few tens of mJ/cm² are investigated. For those fluences, laser‐produced electron distribution function relaxes to equilibrium Fermi distribution with electron temperature T_e within a short time of 10‐100 fs. Because the electron subsystem has T_e highly exceeding much the ion subsystem temperature T_i the well‐known twotemperature hydrodynamic model (2T‐HD) is used to evaluate heat propagation associated with hot conductive electron diffusion and electron‐ion energy exchange. The model coefficients of electron heat conductivity κ (?, T_e, T_i) and electron‐ion coupling parameter α (?, T_e) together with 2T equation of state E (?, T_e, T_i) and P (?, T_e, T_i) are calculated. Modeling with 2T‐HD code shows transition of electron heat wave from supersonic to subsonic regime of prop‐agation. At the moment of transition the heat wave emits a compression wave moving into the bulk of met al. Nonlinear evolution of the compression wave after its separation from the subsonic heat wave till spallation of rear‐side layer of a film is traced in both 2T‐HD modeling and molecular dynamics (MD) simulation. For fluences above some threshold the nucleation of voids in frontal surface layer is initiated by strong tensile wave following the compression wave. If the absorbed fluence is ～30 % above the ablation threshold than void nucleation develops quickly to heavily foam the molten met al. Long‐term evolution of the metal foam including foam breaking and freezing is simulated. It is shown that surface nano‐structures observed in experiments are produced by very fast cooling of surface molten layer followed by recrystallization of supercooled liquid in disintegrating foam having complex geometry. Characteristic lengths of such surface nanostructures, including frozen pikes and bubbles, are of the order of thickness of molten layer formed right after laser irradiation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of heterocyclic azoxy compounds from C-nitroheterocyclic compounds and metal derivatives oftert-butylamine

The reaction of 3-nitropyrazole and 3(5)-nitro-1,2,4-triazole with t-BuNHMgBr gives the corresponding asymmetrical diazene oxides. Furthermore, 3(5)-(1,1-dimethylethyl)azoxy-1,2,4-triazole was also synthesized by the reaction of 1-trimethylsilyl-3(5)-nitro-1,2,4-triazole with t-BuNHLi.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1653–1654, July, 1992.     

Powerful pulsed electrophysical transformers from the Institute of High-Current Electronics,Siberian Branch of the Russian Academy of Sciences

Problems in the creation and exploitation of powerful pulsed electrophysical transformers, developed at the Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences, are discussed. The power of the largest installations is 2.5·10¹² W (pulsed). The small size, the outside location of the main components requiring maintenance, and the absence of large volumes of transformer oil make the pulsed transformers competitive with pulsed voltage generators. Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 58–66, December, 1995.     

LiB3O5 crystal structure at 20, 227 and 377 °C

Crystal structure of LiB₃O₅ (a framework of [B₃O₅]⁻ rings and Li atoms located in interspaces) was refined at high temperatures using single-crystal X-ray diffraction, MoKα-radiation, anharmonic approximation, orthorhombic; Pna2₁; Z=4; 20 °C (a=8.444, b=7.378, c=5.146 Å, 1411 F(hkl), R=0.022); 227 °C (a=8.616, b=7.433, c=5.063 Å, 1336 F(hkl), R=0.026), 377 °C (a=8.746, b=7.480, c=5.013 Å, 1193 F(hkl), R=0.035). A high mobility of Li atoms and their highly asymmetric vibrations are revealed. Ellipsoid of Li thermal vibrations is oviform. Li is shifted on heating to 0.26 Å mainly along a-axis causing high thermal expansion in this direction; Li temperature factors are multiplied by 4 on heating. Rigid boron-oxygen groups in LiB₃O₅ remain practically stable on heating similar to α-Na₂B₈O₁₃ and α-CsB₅O₈. At the same time these groups rotate relative to each other like hinges leading to extremely anisotropic thermal expansion (α_a=101, α_b=31, α_c=−71, α_v=60×10⁻⁶ °C⁻¹, 20-530 °C, HTXRPD data).     

A single structural type in the series of oxyorthosilicates of the rare earth elements

Summary We have carried out a roentgenostructural analysis of monocrystals and polycrystals of the oxyorthosilicates of rare earth elements of the third group. of rare earth elements of the third group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 925–926, May, 1965 Original article submitted August 22, 1964     

Chimera states in ensembles of bistable elements with regular and chaotic dynamics

We consider ensembles of bistable elements with nonlocal interaction. It is shown that the bistability of units in the case of nonlocal interaction leads to the formation of chimera structures of a special type, which we have called double-well chimeras. Their distinctive feature consists in the formation of incoherence clusters with an irregular distribution of elements between two attractive sets existing in an individual element (two “potential wells”). Ensembles of different bistable units are considered, namely ensembles of cubic maps, FitzHugh–Nagumo oscillators in the regime of two stable equilibrium points and Chua’s circuits. The spatiotemporal behavior of the ensembles is studied in the cases of regular and chaotic dynamics in time, and different types of chimera structures are revealed.     

X-ray diffraction study of ion thermal vibrations in R2CuO4 (R=Pr and Gd) crystals

An X-ray diffraction study is reported of the symmetry in the spatial distribution of thermal vibrations of Cu₂₊, Gd³⁺, and Pr³⁺ ions in Gd₂CuO₄ crystals. An analysis of the pattern of the angular thermal-vibration amplitude distribution obtained experimentally at different temperatures allows a conclusion about the character of the local Jahn-Teller effect for the Cu²⁺ ions, structural phase transitions, and the orbital ground state of the Cu²⁺ ions.     

Effect of low molecular additives on the electrospinning of nonwoven materials from a polyamide-6 melt

The effect of low molecular additives on the structure and properties of polyamide-6-based nonwoven materials obtained via electrospinning from a melt is studied. The introduction of up to 10% salts of higher fatty acids into the polymer melt leads to a decrease in its viscosity and to an increase in its electrical conductivity, thereby making it possible to produce nonwoven materials with an average fiber diameter of <1.5 µm. With the use of DSC, IR spectroscopy, and X-ray diffraction, it is shown that, in nonwoven materials based on polyamide-6, the metastable γ form of crystals prevails, while, in the native polymer, the stable a form predominates. The resulting materials demonstrate high filtration characteristics, and their surface properties are close to superhydrophobic.