The spall strength limit of matter at ultrahigh strain rates induced by laser shock waves

New results concerning the process of dynamic fracture of materials (spallation) by laser-induced shock waves are presented. The Nd-glass laser installations SIRIUS and KAMERTON were used for generation of shock waves with pressure up to 1 Mbar in plane Al alloy targets. The wavelengths of laser radiation were 1.06 and 0.53 μm, the target thickness was changed from 180 to 460 μm, and the laser radiation was focused in a spot with a 1-mm diameter on the surface of AMg6M aluminum alloy targets. Experimental results were compared to predictions of a numerical code which employed a real semiempirical wide-range equation of state. Strain rates in experiments were changed from 106 to 5 × 107 s−1. Two regimes of spallation were evidenced: the already known dynamic regime and a new quasi-stationary regime. An ultimate dynamic strength of 80 kbar was measured. Finally, experiments on targets with artificial spall layers were performed showing material hardening due to shock-wave compression

Genetic diversity of the Aporrectodea caliginosa complex in Russia

Earthworms of the Aporrectodea caliginosa species complex are abundant in many anthropogenic and natural habitats and often predominate in earthworm communities. In Russia, there are two subspecies of the complex, A. c. caliginosa and A. c. trapezoides; Aporrectodea longa was also recently mentioned as a putative member of the complex. In this study, we made an attempt to review available data on the species complex studied based on our collection from Russia, Belarus, and Kazakhstan. The subspecies A. c. caliginosa is represented in Russia by two genetic lineages, 2 and 3, the former being the prevalent (about 73 % of the total sample). Additionally, these lineages have different distributions: while lineage 2 was found in almost all locations studied, lineage 3 was detected only in a few samples from the periphery of the region studied. The genetic diversity of lineage 2 significantly exceeded that of lineage 3, and its estimated divergence time was almost three times as high. A subset of individuals with pigmentation characteristic of A. c. caliginosa contained cox1 haplotypes of A. c. trapezoides; analysis of nuclear gene sequences confirmed this diagnosis. Thus, pigmentation intensity in this subspecies was demonstrated to vary to a significant degree. In addition, we analyzed two A. longa individuals from West Siberia and the Urals; their cox1 sequences were identical to those from the lineage 1 of this species from the north of Western Europe. These are the first reports of A. c. trapezoides and A. longa from West Siberia. On the whole, both genetic diversity and abundance was shown to decrease in the following series: A. c. caliginosa lineage 2 – A. c. caliginosa lineage 3 – A. c. trapezoides and A. longa

Высокотеплопроводная карбидокремниевая керамика для крупногабаритной космической оптики

The paper describes the important aspects of the developed technology for manufacturing silicon-carbide substrates for optical mirrors intended for future use in space applications. It is shown that the material with the best combination of thermophysical and mechanical properties (Maksutov’s criterion) among the known analogs used for making astronomical mirrors is obtained. The characteristics of a mirror made of a lightweight mirror substrate with a diameter of 205 mm are described, compared with the parameters of most known mirrors made of silicon carbide for various space missions and as proto types. It is shown that the produced substrate is characterized by a rather low specific gravity – 16.5 kg/m2, which is comparable with the indicators of the best world analogues.Описаны важные аспекты разработанной технологии изготовления карбидокремниевых подложек для оптических зеркал, предназначенных для перспективного использования в космических приложениях. Показано, что получен материал с лучшим сочетанием теплофизических и механических свойств (критерий Максутова) среди известных аналогов, применяемых при создании астрономических зеркал. Описаны характеристики изготовленной из него облегченной подложки зеркала диаметром 205 мм, проведено сравнение с параметрами большинства известных зеркал, изготовленных из карбида кремния для различных космических миссий и в качестве опытных образцов. Показано, что изготовленная подложка характеризуется низкой удельной массой – 16,5 кг/м2, что сопоставимо с показателями лучших мировых аналогов