Fast-switching effect using viscous chiral-nematic materials

We report on chiral-nematic mixtures containing viscous chiral dopants, composed of rigid rod-like chiral molecules, in order to solve the problem of backflow in the middle layers of the liquid crystal cells. During the study, the viscoelastic properties of the liquid crystal compositions have been optimised, as well as the helical twisting power of the chiral compounds, the anchoring energy and the pre-tilt angle of alignment materials, the ratio between the cell gap and the helical pitch (d/P₀). After optimisation, we prepared test cells with low operating voltage – from 1.5 till 5.0 V, fast response time (τ_on + τ_off) – less than 1 ms, wide operating temperature range from ?40°C till +100°C, and good thermal stability. It should be noted that the response time of the new electro-optical mode does not strongly depend on the cell gap, which is in contrast to other known operating modes. We have achieved rather linear than quadratic dependence of the response time when changing the thickness of the cell.     

Inversion in an extended three-level medium produced by adiabatic population transfer

Features of the adiabatic population transfer are studied with the spatial evolution of interacting pulses propagating in an optically dense medium of three-level Λ-atoms taken into account. A self-consistent analytical solution describing the spatial-temporal dynamics of interacting short pulses under the conditions of adiabatic population transfer is constructed in the adiabatic approximation with consideration for the first nonadiabatic correction. Practically complete inversion on a forbidden transition determined by coherent (adiabatic) population transfer is shown to take place over a length of the medium, which may exceed the absorption length of a weak probing pulse in the absence of control radiation on the adjacent transition by several orders of magnitude.     

Regiochemistry of the addition of mercury salts to bornylene

The dependence of the regiochemistry of the mercuration of bornylene on the nature of the mercurating reagent and on the solvent has been found. The structures of the intermediate and transition state in these reactions have been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 501–505, March, 1994.     

Diamond anvil microcell

Abstract

A microminiature cryogenic diamond anvil cell (DAC) of overall dimensions ø10x24 mm made of nonmagnetic steel is described. A new principle allows to align anvils as perfectly as in traditional DACs. The microcell has been tested to 110 GPa.     

Mechanism of Formation of Tetrahydrofuran in the Catalytic Hydrogenation of Dialkyl Succinates

The kinetics of formation of tetrahydrofuran from dibutyl succinate were studied. The mechanism of catalytic hydrogenation of dialkyl succinates was found to involve consecutive formation of ?-butyrolactone, butane-1,4-diol, and tetrahydrofuran. Parameters of kinetic equations that properly describe the system of concurrent and consecutive reactions were determined.     

Recombinant formate dehydrogenase from <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>: Preparation,crystal growth in microgravity,and preliminary X-ray diffraction study

Crystals of high-purity recombinant NAD⁺-dependent formate dehydrogenase from the higher plant Arabidopsis thaliana (AraFDH) were grown in microgravity in the Modul’-1 protein crystallization apparatus on the International Space Station. The space-grown crystals have larger sizes than those grown on Earth. X-ray diffraction data suitable for determining the three-dimensional structure were collected from the space-grown crystals to a resolution of 1.22 Å using an X-ray synchrotron source. The crystals belong to sp. gr. P4₃2₁2; the unit-cell parameters are a = b = 107.865 Å, c = 71.180 Å, α = β = γ = 90°.     

Anomalous kinetic energy of a system of dust particles in a gas discharge plasma

The system of equations of motion of dust particles in a near-electrode layer of a gas discharge has been formulated taking into account fluctuations of the charge of a dust particle and the features of the nearelectrode layer of the discharge. The molecular dynamics simulation of the system of dust particles has been carried out. Performing a theoretical analysis of the simulation results, a mechanism of increasing the average kinetic energy of dust particles in the gas discharge plasma has been proposed. According to this mechanism, the heating of the vertical oscillations of dust particles is initiated by induced oscillations generated by fluctuations of the charge of dust particles, and the energy transfer from vertical to horizontal oscillations can be based on the parametric resonance phenomenon. The combination of the parametric and induced resonances makes it possible to explain an anomalously high kinetic energy of dust particles. The estimate of the frequency, amplitude, and kinetic energy of dust particles are close to the respective experimental values.     

About an acting field and a ponderomotive force in dielectrics

The assumption implicitly used in the standard derivation of expression for an acting electric field in dielectrics is revealed. It is demonstrated that if it is accepted for the starting point, the derivation can be simplified. Problems that are not considered in courses of the theory of electricity and electrodynamics are discussed. Namely, a relationship between the ponderomotive force and the acting field is discussed together with reasons by which the ponderomotive force differs from the electric force acting on a polarized charge. The simplest nonpolar gaseous and liquid dielectrics are considered.