Spallative ablation of dielectrics by X-ray laser

A short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron–ion equilibrium and increases pressure in a heated layer. The case where the pulse duration τ _L is shorter than acoustic relaxation time t _s is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless of wavelength. While the physics of electron–ion relaxation strongly depends on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse.     

Structure and some thermodynamic characteristics of the polymorphs of rubidium silicate Rb6Si10O23

The crystal structure of Rb₆Si₁₀O₂₃ at 296 and 773 K is determined using single-crystal X-ray diffraction. At room temperature the crystals are orthorhombic (space group Cm2m, a = 16.280(5) Å, b = 9.380(5) Å, c = 8.060(5) Å, Z = 2). At 698 K, a first-order phase transition occurs to a hexagonal phase (space group $P\bar 6$ , a = 9.475(5) Å, c = 8.200(5) Å, Z = 1). The silicon-oxygen tetrahedral frameworks of both polymorphs have the same topology: 12-membered channels running along axis c are connected through six-membered windows. The enthalpies of polymorphic transition and melting are determined to be 3.9 ± 0.3 and 160 ± 16 kJ/mol, respectively.     

Electrochemical properties and morphology of composite fibers based on silicon and carbon obtained by electroforming

Pyrolized Si/C composite fibers and films were studied in the processes of lithium intercalation-extraction during the operation of rechargeable lithium-ion batteries and supercapacitors. It was found that their electrochemical characteristics differ from those of pure silicon and pure carbon. Analysis of these parameters under charge-discharge conditions allowed us to determine the optimum composition of precursors: FM-1 and TEOS mixtures used as silicon-containing components. The optimum modes and temperatures of fiber pyrolysis were found to have a Si/C ratio of 3/2 in the pyrolyzed fibers and an oxygen content not much greater than 20 at %. The prospects for applying fibers in the form of film electrodes (the best stability in cycling) and adhesives with developed structural networks are shown.     

Digital Recording Video System for Control of Laser Radiation Parameters

Russian Physics Journal - The method for control of the parameters of laser radiation based on its recording in the diffuse reflecting screen plane and subsequent digital processing of the recorded...     

Powerful pulsed source of seismic oscillations

A source of seismic oscillations for surface and borehole seismic prospecting is described. The source was developed at the Institute of High-Current Electronics Siberian Branch, Russian Academy of Sciences. The results of preliminary field tests are reported, and the prospects for further improvement are discussed. Deceased Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 100–104, December, 1997.     

Synthesis and crystal structure of strontium borate Sr<Subscript>4</Subscript>B<Subscript>14</Subscript>O<Subscript>25</Subscript>

The new compound Sr₄B₁₄O₂₅ (4SrO · 7B₂O₃) corresponding to an oxide ratio of 4: 7 has been identified and synthesized in the SrO-B₂O₃ system. The crystal structure of the compound has been determined (space group Cmc2₁, a = 7.734(5) Å, b = 16.332(5) Å, c = 14.556(5) Å, Z = 4, 702 F(hkl), R = 0.078). The borate anions form a three-dimensional framework consisting of borate groups of two types: three-ring structures (2□, Δ) and BO₃ triangles. Layers formed by 14-membered rings composed of boron-oxygen tetrahedra and triangles packed within the layer according to the herringbone pattern can be distinguished in the framework. The strontium atoms are located on the mirror symmetry planes between these layers. The compound is metastable and decomposes, on long-term storage, into strontium di- and metaborate.     

Action of ozone on polysulfone-based microfibrous filters

The action of ozone in high (1.3 vol %) concentrations on polysulfone microfibers was studied by iodometric titration, IR spectroscopy, and electron microscopy.     

Structure of selenium and tellurium clusters in cavities of NaX zeolite

The structure of NaX zeolite crystals with the Se and Te atoms incorporated into the structure from their vapors has been studied. It is shown that selenium atoms form clusters in the shape of six-and four-membered rings located in the cuboctahedral cavities of the structure framework. Single Se₂ molecules are located in large cavities, whereas Te atoms form four-membered rings located in cuboctahedra. Large cavities are occupied by two alternating configurations of Te atoms forming either a chain consisting of 16 links or an eight-membered ring.