Vergleichende Untersuchung der Nahordnung in unverzweigten Alkanen und im Poly?thylen

Ohne Zusammenfassung     

Spectroelectrochemical determination of the redox equivalent of magnesium porphine in the course of its electrooxidation

The spectroelectrochemical method has been applied for studying the electropolymerization of magnesium porphine with the aim to determine the number of electrons consumed per monomer molecule, which allows one to find out the number of bonds between the units in the resulting polymer. Based on the results, a conclusion has been made about the structure of macrochains of the basic representative of a new family of electroactive materials, magnesium porphine     

Asymmetry of the shape of surroundings as a mechanism for generating directed motion

A mechanism for generating a directed motion of a Brownian particle in an asymmetric channel under the action of a varying force field is considered. The setup implementing such a mechanism resembles typical Brownian motors using asymmetry of the energy potential (ratchet effect). It is shown that under certain conditions, the asymmetry of the shape may ensure the maximal level of rectification for a large intensity of the external field drawing the system from equilibrium. The main question formulated here is the dependence of the rectifying ability of such a mechanism on the external action parameters and, above all, on the form of the time dependence. The results obtained here for a sine signal and an aperiodic train of pulses are compared with the previous results obtained by the authors for bipolar rectangular pulses. General estimates obtained for pulses of an arbitrary shape determine its influence on the velocity of directed motion. Analysis of the proposed mechanism is based of the combination of analytic calculations for a strong external field with simulation by the method of Brownian dynamics for arbitrary parameters.     

Directed transport of a Brownian particle in a periodically tapered tube

The problem of the motion of a Brownian particle in a periodically tapered tube induced by a time-periodic longitudinal force with zero mean is considered. Under the action of this force, the particle is shown to drift in a direction opposite to the constant load force applied to it. Analytical solutions for the drift velocity, the stopping force (the load causing the effect to disappear), and the efficiency of converting the energy introduced by perturbations into directed motion have been obtained at a large amplitude of the driving force, when the effect being discussed is maximal. In the range of its applicability extending from zero to asymptotically large force switching frequencies (proportional to the amplitude of the driving force), these solutions are in good agreement with the results of Brownian dynamics simulations.     

Ejection of Particles from the Free Surface of Shock-Loaded Lead into Vacuum and Gas Medium

The presence and behavior of a gas–metal interfacial layer at the free surface of shock-wave driven flying vehicles in gases of various compositions and densities has not been sufficiently studied so far. We present new comparative data on “dusting” from the free surface of lead into vacuum and gas as dependent on the surface roughness, pressure amplitude at the shock-wave front, and phase state of the material. Methods of estimating the mass flux of ejected particles in the presence of a gas medium at the free metal surface are proposed.     

Asymptotics of the front motion in the reaction-diffusion-advection problem

A singularly perturbed initial boundary value problem is considered for a parabolic equation that is known in application as the reaction-diffusion-advection equation. An asymptotic expansion of solutions with a moving front is constructed. This asymptotics is proved by the method of differential inequalities, which is based on well-known comparison theorems and develops the ideas of formal asymptotics for constructing upper and lower solutions in singularly perturbed problems with internal and boundary layers.     

Dusty plasma structures in He-Kr DC glow discharge

Ion drift in gas mixtures has certain properties that can be used to generate ion flows with desired characteristics. For example, when the field is strong, ion heating is significant, and there is a large difference in atomic weight between ions and atoms, the ion velocity distribution can be highly anisotropic. Ion distribution anisotropy, in turn, can cause a substantial change in properties of dust structures in plasmas. Experiments on dusty plasma structures in glow discharge in mixtures of light and heavy gases (helium and krypton) are performed, and results of numerical simulations of ion and electron drift in the mixture are presented.     

Influence of the temperature modulation of an incident flux on the properties of films of cadmium selenotellurides synthesized under sharply nonequilibrium conditions

Results of structural and electrical investigations of the films of cadmium selenotellurides synthesized by evaporation and condensation in vacuum under sharply nonequilibrium conditions are presented. The modulating effect of a nonuniform thermal field on the vapor phase flux has been revealed. The possibility of controlling the stoichiometry of the film composition with the use of a thermal field applied on the path of the thermal phase from the evaporator to the substrate has been demonstrated. Curves of condensation and temperature dependences of the conductivity, Hall coefficient, and Hall mobility are presented.     

New scandium rhodium boride Sc<Subscript>4</Subscript>Rh<Subscript>17</Subscript>B<Subscript>12</Subscript> with a framework structure: synthesis,crystal structure,and properties

The new scandium rhodium boride Sc₄Rh₁₇B₁₂ was synthesized by arc-melting of the elements followed by annealing in inert atmosphere. The crystal structure of Sc₄Rh₁₇B₁₂ was solved using single crystal X-ray diffraction data. The structure can be described as a three-dimensional frame-work formed by trigonal prisms [BRh₆] and [BRh₅Sc] with isolated boron atoms inside the prisms and trigonal prisms [BRh₅B] representing the coordination polyhedra of paired boron atoms. The temperature dependences of the magnetic susceptibility and specific resistance of Sc₄Rh₁₇B₁₂ revealed that the compound is a Pauli paramagnet and shows metal-like specific resistance.     

Target-aimed synthesis of anion-deficient perovskites

The brownmillerite-type A 2B 2O 5 structure is considered as a parent one, giving rise to different derivatives: layered double perovskites, A-site and anion-vacancy-ordered perovskites, and the perovskite-like compounds with crystallographic shear planes. The structural relationships and synthesis pathways for these classes of materials are discussed with particular attention to the ordering at the A or B sublattices, anion vacancy ordering, and their mutual interaction.