Synthesis and structure of cluster compounds containing a novel cluster core {Re4STe3}

Three novel cluster compounds K₄[Re₄STe₃(CN)₁₂]·₄H₂O (I), [{Cu(en)₂}₂Re₄STe₃(CN)₁₂]·₅H₂O (II) and [{Cu(trien)}₂Re₄STe₃(CN)₁₂]·2H₂O (III) (en is ethylenediamine, trien is triethylenetetraamine) containing a new cluster core {Re₄STe₃} have been prepared and structurally characterized. According to single crystal X-ray diffraction data, compound I is ionic and represents the arrangement of ions K⁺ and [Re₄STe₃(CN)₁₂]^4?; compounds II and III are molecular and formed by two cationic moieties {Cu(en)₂}²⁺ and {Cu(trien)}²⁺, respectively, coordinated to one cluster anion. In the solid state, S atom positions in the tetrahedron Q₄ (Q = S, Te) are disordered for all three compounds: in I and III sulfur atoms are split over all four Q positions, while in II over two positions.     

Bispectral analysis of numerical simulations of wave processes in hypersonic shock layers

Results of numerical simulations of the evolution of disturbances in a hypersonic shock layer on a flat plate at high Mach numbers (M_∞ = 21) and moderate Reynolds numbers (Re _L = 1.44 · 10⁵) are analyzed by an adapted method of bispectral analysis. All basic types of nonlinear interactions are obtained. The calculated results are compared with experimental data.     

Modification of Graphene on a Copper Grid during Femtosecond Laser Irradiation: Electron Diffraction and Raman Spectroscopy Studies

The initial stage of a nanosecond discharge in gaps with a high electric field at a cathode is studied by laser methods (interferometric, shadow, schlieren methods). The studies are performed in air at atmospheric pressure. Prominence is given to studying the evolution (appearance and growth) of the plasma channels at an anode and to estimating their parameters.     

Analysis of Noise Generation by Turbulent Jets from Consideration of Their Near Acoustic Field

Acoustical Physics - The paper studies the generation of acoustic waves near the boundaries of swirling and nonswirling turbulent jets outside a jet flow. Nonstationary motion of the medium is...     

Hose instability of relativistically strong femtosecond laser pulses with few field oscillations in a plasma under the excitation of a plasma wake wave

A detailed theoretical analysis is carried out of the hose instability of relativistically strong laser pulses propagating in a plasma, whose duration is less than the period of a plasma wake wave. An analytic expression is obtained for the displacement of the mass center of a wave pulse, and the effect of this instability on the modification of the spectrum of laser radiation is analyzed for a wide range of initial parameters. It is shown that the development of instability is characterized by a power-law (rather than exponential) time dependence along the propagation path and does not deteriorate the self-compression of laser pulses.     

Development of a compact hardware/software package for noninvasive diagnostics of skin diseases in the THz frequency range

The key elements of a mobile hardware/software package for noninvasive diagnostics of skin diseases in the THz frequency range have been designed, produced, and approved in model experiments. These elements are a compact THz oscillator based on an all-fiber femtosecond laser system and a unit for recovering electrodynamic characteristics of layered objects from scattered THz radiation spectra. Generation of 250-fs optical pulses at a wavelength of 1.03 µm with energy of 0.3 µJ and a repetition frequency of 1MHz is demonstrated and the efficiency of optical-THz conversion is found to be 5×10^?6. The proposed algorithm is constructed based on an iterative procedure and can be used for dispersive and absorbing media. It has higher operating speed in comparison with the algorithms for solving inverse problems, which are based on functional minimization methods.     

Collapse and revival of electromagnetic cascades in focused intense laser pulses

We consider interaction of a high-energy electron beam with superstrong laser pulses. Nonlinear Compton scattering and electron–positron pair production by the emitted photons result in development of an electromagnetic “shower-type” cascade, which however collapses rather quickly due to energy losses by secondary particles. Nevertheless, the laser field accelerates the slowed down electrons and positrons, thus giving rise to development of electromagnetic cascade of another type (“avalanche-type”). This effect of cascade collapse and revival can be observed at the electron beam energy of the order of several GeV and laser pulses intensity ∼10²⁴ W/cm²$\sim {10}^{24}\text{W}/{\text{cm}}^2$. This means that it can be readily observed at the novel laser facilities which are either planned for the nearest future, or are already under construction. The proposed experimental setup provides the most realistic and promissory way to observe the “avalanche-type” cascades.     

Algebra of differential operators associated with Young diagrams

We establish a correspondence between Young diagrams and differential operators of infinitely many variables. These operators form a commutative associative algebra isomorphic to the algebra of the conjugated classes of finite permutations of the set of natural numbers. The Schur functions form a complete system of common eigenfunctions of these differential operators, and their eigenvalues are expressed through the characters of symmetric groups. The structure constants of the algebra are expressed through the Hurwitz numbers.     

Controlling boron diffusion during rapid thermal annealing with co-implantation by amphoteric impurity atoms

A model for simulating the rapid thermal annealing of silicon structures implanted with boron and carbon is developed. The model provides a fair approximation of the process of boron diffusion in silicon, allowing for such effects as the electric field, the impact of the implanted carbon, and the clustering of boron. The migration process of interstitials is described according to their drift in the field of internal elastic stress.     

Energy spectrum and correlation functions of clusters of carbon nanotubes with the (5, 5) chirality

The correlation functions and energy spectra of clusters of carbon nanotubes with the (5, 5) chirality that consist of 30, 50, 70, 90, and 190 atoms have been obtained in terms of the Hubbard model. It has been assumed that, taking into account the Hubbard correlations, carbon nanotubes with the (5, 5) chirality should be semiconductors with a band gap of ～1 eV. This contradicts the generally accepted concept, according to which carbon nanotubes with the (m, n) chirality should be metals if the difference in the chirality indices m ? n is multiple to three or equal to zero. The results obtained have been compared with experimental data on electrical conductivity and scanning tunneling microscopy of carbon nanotubes.