Communication: drift velocity of Brownian particle in a periodically tapered tube induced by a time-periodic force with zero mean: dependence on the force period

We study the drift of a Brownian particle in a periodically tapered tube, induced by a longitudinal time-periodic force of amplitude ∣F∣ that alternates in sign every half-period. The focus is on the velocity dependence on the force period, which is usually considered not tractable analytically. For large ∣F∣ we derive an analytical solution that gives the velocity as a function of the amplitude and the period of the force as well as the geometric parameters of the tube. The solution shows how the velocity decreases from its maximum value to zero as the force period decreases from infinity (adiabatic regime) to zero. Our analytical results are in excellent agreement with those obtained from 3D Brownian dynamics simulations.     

Peculiarities of the synthesis and thermolysis of heterometallic coordination compounds used as precursors for nickelates of rare-earth elements

The influence of the solvent on the composition of solid products is investigated using the example of the interaction of rare-earth element (REE) nitrates, Ln(NO₃)₃, with square-planar complexes of nickel and Schiff bases, Ni(SB). The composition of solid products is determined by X-ray fluorescence analysis and elemental analysis. It is shown that from the labile Ln(NO₃)₃-Ni(SB) systems, individual heterometallic compounds can be obtained, moreover, if in systems there are complexes with more dentate Ni(mosalen) ligands, only binuclear heterocomplexes can be produced. In case of Ni(salen) ligand, the formation of trinuclear complexes is achieved by selecting the optimal solvent. Among the considered compounds, binuclear complexes are of special interest due to the possibility of their use as precursors of REE nickelates.     

Erratum to: Effect of Shock-wave Dusting and Ways to Suppress It

Journal of Experimental and Theoretical Physics - An Erratum to this paper has been published: https://doi.org/10.1134/S106377612230001X     

Comparative analysis of the structure of two thermotropic LC copolyesters

A comparative study of the structures of two thermotropic liquid crystal copolyesters (LCP) was carried out. The first copolymer, LCP-1, comprises three different monomer units of equal length, whereas the second copolymer, LCP-2, contains two monomer units which differ significantly in length. Both copolymers exhibit random structure. It was established that despite the irregular structure both copolymers have the ability to crystallize. Moreover, during crystallization of LCP-1 microphase separation into two phases occurs. Each phase has an orthorhombic crystal structure but with slightly different parameters of the unit cell. The reason for this difference is probably associated with configuration isomerism because of possible head-to-head or head-to-tail additions during synthesis of the copolyester. Upon annealing, the maximum degrees of crystallinity are 35% and 25% for LCP-1 and LCP-2, respectively. The noncrystalline fraction of the material, whose content exceeds appreciably the content of the crystalline phase, shows a LC smectic structure. However, the fundamental difference between the two copolymers is that, in the case of LCP-1, the periodic layer structure is observed, whereas for LCP-2 the layer structure is aperiodic. The above phenomena are universal, and this makes it possible to predict the structure and character of temperature behavior of any representative of the class of fully aromatic rigid-chain copolyesters only from the chemical formula of the copolymer.     

Synthesis, crystal structure and magnetic properties of the Sr2Al0.78Mn1.22O5.2 anion-deficient layered perovskite

A new layered perovskite Sr₂Al_0.78Mn_1.22O_5.2 has been synthesized by solid state reaction in a sealed evacuated silica tube. The crystal structure has been determined using electron diffraction, high-resolution electron microscopy, and high-angle annular dark field imaging and refined from X-ray powder diffraction data (space group P4/mmm, a=3.89023(5) Å, c=7.8034(1) Å, R_I=0.023, R_P=0.015). The structure is characterized by an alternation of MnO₂ and (Al_0.78Mn_0.22)O_1.2 layers. Oxygen atoms and vacancies, as well as the Al and Mn atoms in the (Al_0.78Mn_0.22)O_1.2 layers are disordered. The local atomic arrangement in these layers is suggested to consist of short fragments of brownmillerite-type tetrahedral chains of corner-sharing AlO₄ tetrahedra interrupted by MnO₆ octahedra, at which the chain fragments rotate over 90°. This results in an averaged tetragonal symmetry. This is confirmed by the valence state of Mn measured by EELS. The relationship between the Sr₂Al_0.78Mn_1.22O_5.2 tetragonal perovskite and the parent Sr₂Al_1.07Mn_0.93O₅ brownmillerite is discussed. Magnetic susceptibility measurements indicate spin glass behavior of Sr₂Al_0.78Mn_1.22O_5.2. The lack of long-range magnetic ordering contrasts with Mn-containing brownmillerites and is likely caused by the frustration of interlayer interactions due to presence of the Mn atoms in the (Al_0.78Mn_0.22)O_1.2 layers.     

Electronic mechanism for refractive-index changes in intensively pumped Yb:YAG laser crystals

Refractive-index changes accompanying changes in population of electronic levels of Yb3+ ions in a Yb:YAG laser disk under intense diode and laser pumping have been studied by use of both a highly sensitive polarization interferometer and transient grating testing at 633 nm. The electronic change of the index that is due to excitation of the Yb3+ ions (which have different polarizability of ground state 2F7/2 and excited level 2F5/2) is strongly predominant over the thermal component. The polarizability differences are deltap (1.9 +/- 0.8) x 10(-26) and (1.95 +/- 0.25) x 10(-26) cm3 as measured at 633 nm in interferometric and transient grating experiments, respectively.     

Epitaxial Growth of Cadmium Selenide Films on Silicon with a Silicon Carbide Buffer Layer

An epitaxial cubic 350-nm-thick cadmium selenide has been grown on silicon for the first time by the method of evaporation and condensation in a quasi-closed volume. It is revealed that, in this method, the optimum substrate temperature is 590°C, the evaporator temperature is 660°C, and the growth time is 2 s. To avoid silicon etching by selenium with formation of amorphous SiSe₂, a high-quality ~100-nm-thick buffer silicon carbide layer has been synthesized on the silicon surface by substituting atoms. The powder diffraction pattern and the Raman spectrum unambiguously correspond to cubic cadmium selenide crystal. The ellipsometric, Raman, and electron diffraction analyses demonstrate high structural perfection of the cadmium selenide layer and the absence of a polycrystalline phase.     

Nonlinear comb spectroscopy

A numerical solution for the polarization of two-level atoms that interact with a polyharmonic field was obtained. An analytical solution for the particular case of a symmetrical position of carrier frequency relative to transition frequency is possible. The results showed that nonlinear effects occur in a polarization spectrum at the small amplitudes of comb components and small frequency distances between them. Consequently, it is necessary to take into account nonlinear effects in comb spectroscopy.     

Raman study of ethylene-propylene copolymers and polyethylene-polypropylene reactor blends

The Raman spectra of the ethylene-propylene copolymers (EPC) synthesized using new metallocene catalytic systems and the polypropylene/polyethylene/diblockcopolymer of propylene and ethylene (PP/PE/DBC) blends obtained using the sequential polymerization are studied. The copolymer and reactor blend spectra are analyzed using the Raman spectra of a series of liquid n-alkanes. Significant monotonic changes are observed in the spectra of EPC and the PP/PE/DBC blends when the ethylene content increases. Substantial differences between the series of samples of blends and copolymers are revealed. In contrast to the EPC spectra, the spectra of the PP/PE/DBC reactor blends are represented as an exact superposition of the homopolymer spectra with the weight coefficients proportional to the contents of the blend components. A monotonic blue shift of the line that corresponds to the symmetric stretching mode of the CH₂ groups is observed in the EPC Raman spectra when the ethylene content increases. It is demonstrated that, for this line, the peak position only depends on the relative content of comonomers and does not depend on the contents of the PP and PE crystalline phases. The intensity ratio of two fundamental vibrations of PE and PP with frequencies of 1295 and 1330 cm^?1 can be used to determine the relative contents of the PE molecules in the trans-conformation and PP macromolecules in the helical conformation in the PP/PE blends. It is demonstrated that variations in the Raman spectra of n-alkanes, EPC, and PP/PE/DBC reactor blends related to variations in the relative contents of various chemical groups are reliably traced in the spectra of all of the materials under study.