Substitutional Body-Centered Cubic Superstructures: Feasibility and Stability Analysis

A stability analysis of classical binary bcc superstructures with one or two long-range order parameters is performed. The feasibility criteria for ordered phases formulated for fcc superstructures are found to apply to bcc superstructures. The feasibility criteria assume that the ordering energy in the first coordination sphere is positive, and the energy range in interaction space where bcc superstructures are stable (stability range) is unlimited.     

Scroll wave dynamics in a model of the heterogeneous heart

Scroll waves are found in physical, chemical and biological systems and underlie many significant processes including life-threatening cardiac arrhythmias. The theory of scroll waves predicts scroll wave dynamics should be substantially affected by heterogeneity of cardiac tissue together with other factors including shape and anisotropy. In this study, we used our recently developed analytical model of the human ventricle to identify effects of shape, anisotropy, and regional heterogeneity of myocardium on scroll wave dynamics. We found that the main effects of apical-base heterogeneity were an increased scroll wave drift velocity and a shift towards the region of maximum action potential duration. We also found that transmural heterogeneity does not substantially affect scroll wave dynamics and only in extreme cases changes the attractor position.     

Spectral-luminescence properties of a norbornene-substituted tetraazachlorin and its metal complexes

The spectral-luminescence properties of a tetraazachlorin derivative with a norbornene fragment annelated to a reduced pyrrole ring and its complexes with zinc and palladium have been studied at 293 and 77 K. For the norbornene-substituted free base, differences in fluorescence from unsubstituted tetraazachlroin and its dibenzobarrelene-substituted analog are found. The fluorescence lifetime is observed to rise by ∼7 times for the free base and by ∼1.6 ties for the Zn complex on going from 293 to 77 K. An essential dependence of the photophysical parameters on the nature of the solvent is noted. The fluorescence polarization spectrum of the norbornene-substituted tetraazachlorin reveals in the Soret band region at least four electronic transitions. For the Pd complex, weak phosphorescence in the near IR region has been detected; the 0–0 band maximum is at 990 nm and the singlet–triplet interval amounts to 5800 cm^–1, which is larger by 400 cm^–1 than for Pd tetraazaporphine. The quantum yields of the photosensitized formation of singlet oxygen have been determined using a relative luminescence method.     

Synthesis of δ-Valerolactone Using Stable Hydrogen Peroxide Derivatives

Russian Journal of Organic Chemistry - The efficiencies of hydrogen peroxide derivatives in the Baeyer–Villiger oxidation of cyclopen­tanone to δ-valerolactone have been compared....     

Approach to Detecting Aberrations in Transcranial Ultrasound Imaging

The presence of cranial bones in the ultrasound propagation path seriously complicates the imaging of tissues and blood vessels of the brain since the bones distort the ultrasound field, introducing phase and amplitude aberrations. Such distortions are not always apparent since complete information about the studied object is fundamentally inaccessible. The article develops a new approach that uses the synthetic aperture method to detect wavefront aberrations. A quantitative parameter is proposed that characterizes the presence of aberrations by measuring the RMS width of the angular intensity distribution. Experimental results were obtained at a frequency of 2 MHz using phantom and in vivo transcranial data. It is shown that in the presence of aberrations, the value of the proposed parameter increases by 22–45% with respect to the theoretical value for the aberrationless case.

     

Gadolinium and Neodymium-Containing Liquid Organic Scintillators

Factors affecting the stability of gadolinium- and neodymium-loaded liquid organic scintillators intended for use in large-scale experimental facilities for neutrino physics and astrophysics are examined. The effect of composition (type and structural formula of gadolinium and neodymium compounds) on the optical properties of such scintillators is analyzed. It is shown that the oxidation of alkylbenzenes is one of the reasons for the degradation (decrease in transparency) of the scintillators. Gadolinium and neodymium compounds may be catalysts for the oxidation processes.     

Electron-conformational transformations in nanoscopic RyR channels governing both the heart’s contraction and beating

We show that a simple biophysically based electron-conformational model of RyR channel can explain and describe on equal footing the oscillatory regime of the heart’s cell release unit both in sinoatrial node (pacemaker) cells under normal physiological conditions and in ventricular myocytes under Ca²⁺ sarcoplasmic reticulum overload.     

Effect of preparation conditions on fractal structure and phase transformations in the synthesis of nanoscale M-type barium hexaferrite

The conditions of the synthesis of carbonate-hydroxide precursors (pH of FeOOH precipitation and heat treatment regimes) were studied in terms of their effect on the fractal structure and physical-chemical properties of precursors. Phase transformations which occur during the synthesis of nanosize M-type barium hexaferrite (BHF) were studied as well.The first structural level of precursors' aggregation for mass fractals, the correlation between fractal dimension and precursors' activity during the synthesis of BHF were determined.Synthesis parameters for the precursors with the optimal fractal structure were determined. These data permit an enhancement of the filtration coefficient of the precipitates by a factor of 4-5, obtaining substantial decrease in the temperature required for synthesis of a single-phase BHF, and monodispersed plate-like nanoparticles (60 nm diameter) with the shape anisotropy and good magnetic characteristics (saturation magnetization (M_s)=68,7 emu/g and coercitivity (H_c)=5440 Oe).     

MO?ZrO2 catalysts for nitrogen oxides reduction by hydrocarbons in oxygen excess. Preparation and properties

The physico-chemical and catalytic properties of MO–ZrO₂ systems (where M is Ca, Sr, Ba) have been studied as a function of the synthesis parameters. Finely powdered heterogeneous mixtures of solid solutions with cubic+monoclinic or tetragonal+monoclinic phase composition were found to be formed. These systems possess quite good high-temperature activity in the reaction of NOx selective reduction by propane under oxygen excess. For a given system, the rate constant depends linearly upon the M–O bond dissociation energy in the surface layer, the slope being positive for Ca and Sr and negative for Ba.