The local phase transitions of the solvent in the neighborhood of a solvophobic polymer at high pressures

We investigate local phase transitions of the solvent in the neighborhood of a solvophobic polymer chain which is induced by a change of the polymer-solvent repulsion and the solvent pressure in the bulk solution. We describe the polymer in solution by the Edwards model, where the conditional partition function of the polymer chain at a fixed radius of gyration is described by a mean-field theory. The contributions of the polymer-solvent and the solvent-solvent interactions to the total free energy are described within the mean-field approximation. We obtain the total free energy of the solution as a function of the radius of gyration and the average solvent number density within the gyration volume. The resulting system of coupled equations is solved varying the polymer-solvent repulsion strength at high solvent pressure in the bulk. We show that the coil-globule (globule-coil) transition occurs accompanied by a local solvent evaporation (condensation) within the gyration volum

Nature of the metal-nonmetal transition in metal-ammonia solutions. I. Solvated electrons at low metal concentrations

Using a theory of polarizable fluids, we extend a variational treatment of an excess electron to the many-electron case corresponding to finite metal concentrations in metal-ammonia solutions (MAS). We evaluate dielectric, optical, and thermodynamical properties of MAS at low metal concentrations. Our semi-analytical calculations based on a mean-spherical approximation correlate well with the experimental data on the concentration and the temperature dependencies of the dielectric constant and the optical absorption spectrum. The properties are found to be mainly determined by the induced dipolar interactions between localized solvated electrons, which result in the two main effects: the dispersion attractions between the electrons and a sharp increase in the static dielectric constant of the solution. The first effect provides a classical phase separation for the light alkali metal solutes (Li, Na, K) below a critical temperature. The second effect leads to a dielectric instability, i.e., polarization catastrophe, which is the onset of metallization. The locus of the calculated critical concentrations is in a good agreement with the experimental phase diagram of Na-NH3 solutions. The proposed mechanism of the metal-nonmetal transition is quite general and may occur in systems involving self-trapped quantum quasiparticles.Comment: 13 figures, 42 page

Structural and transport properties of GaAs/delta<Mn>/GaAs/InxGa1-xAs/GaAs quantum wells

We report results of investigations of structural and transport properties of GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn layer, separated from the QW by a 3 nm thick spacer. The structure has hole mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher than in known ferromagnetic two-dimensional structures. The analysis of the electro-physical properties of these systems is based on detailed study of their structure by means of high-resolution X-ray diffractometry and glancing-incidence reflection, which allow us to restore the depth profiles of structural characteristics of the QWs and thin Mn containing layers. These investigations show absence of Mn atoms inside the QWs. The quality of the structures was also characterized by photoluminescence spectra from the QWs. Transport properties reveal features inherent to ferromagnetic systems: a specific maximum in the temperature dependence of the resistance and the anomalous Hall effect (AHE) observed in samples with both "metallic" and activated types of conductivity up to ~100 K. AHE is most pronounced in the temperature range where the resistance maximum is observed, and decreases with decreasing temperature. The results are discussed in terms of interaction of 2D-holes and magnetic Mn ions in presence of large-scale potential fluctuations related to random distribution of Mn atoms. The AHE values are compared with calculations taking into account its "intrinsic" mechanism in ferromagnetic systems.Comment: 15 pages, 9 figure

Curing of epoxy resin DER-331by Hexakis (4-acetamidophenoxy) cyclotriphosphazene and properties of the prepared composition

The method of optical wedge revealed that the optimum temperature for compatibility of hexakis(4-acetamidophenoxy)cyclotriphosphazene (ACP) and DER-331 epoxy resin is in the range of 220–260◦C. The interdiffusion time of components at these temperatures is about 30 min. The TGA and differential scanning calorimetry (DSC) methods revealed the curing temperature of 280◦C for thiscomposition. IRspectroscopyconfirmedthatthereactionbetweentheresinandACPiscompleted within 10 mi

(1 R,3 S)-3-(1 H -Benzo[ d ]imidazol-2-yl)-1,2,2-tri­methyl­cyclo­pentane-1-carb­oxy­lic acid as a new anti-diabetic active pharmaceutical ingredient

The chiral title compound, C 16 H 20 N 2 O 2, which can be used for producing active pharmaceutical ingredients for treatment of type 2 pancreatic diabetes and other pathologies dependent on insulin resistance, was prepared from (1R,3S)-camphoric acid and o-phenyl­enedi­amin

Specular reflection intensity modulated by grazing-incidence diffraction in a wide angular range

Grazing-incidence X-ray diffraction (GID) is a well known technique for the characterization of crystal surfaces. A theoretical study has been performed of the sensitivity of GID to the structure of a crystal surface and distorted nanometre-thin surface layers. To simulate GID from crystals that have a complex subsurface structure, a matrix formalism of the dynamical diffraction theory has been applied. It has been found that the azimuthal rocking curves of a crystal that has a distorted subsurface, measured over a wide angular range, show asymmetric thickness oscillations with two distinguishable sets of frequencies: one corresponding to the diffraction in the single-crystal subsurface layer and the second corresponding to the diffraction in the single-crystal substrate. Therefore, azimuthal rocking curves allow characterization of the subsurface structure of a single crystal. Furthermore, thickness oscillations induced by evanescent diffraction modulate the specular reflection intensity, showing high-intensity modulations. This will potentially allow implementation of subsurface crystal characterization using, for instance, a laboratory-scale X-ray diffractometer.</p

Crystal structure of the non-steroidal anti-inflammatory drug (NSAID) tolmetin sodium

The asymmetric unit of the title compound, sodium 2-[1-methyl-5-(4-methylbenzoyl)- 1H-pyrrol-2-yl]acetate dihydrate, Na⁺C₁₅H₁₄NO₃⁻2H₂O, contains two sodium cations, two organic anions (A and B) and two water molecules. The coordination geometry around the sodium cations corresponds to a distorted octahedro

Pecularities of Hall effect in GaAs/{\delta}<Mn>/GaAs/In\timesGa1-\timesAs/GaAs (\times {\approx} 0.2) heterostructures with high Mn content

Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content, are studied. In these structures DL is separated from QW by GaAs spacer with the thickness ds = 2-5 nm. All structures possess a dielectric character of conductivity and demonstrate a maximum in the resistance temperature dependence Rxx(T) at the temperature {\approx} 46K which is usually associated with the Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is found that the Hall effect concentration of holes pH in QW does not decrease below TC as one ordinary expects in similar systems. On the contrary, the dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer thickness, then increases at low temperatures more strongly than ds is smaller and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are interpreted in the terms of magnetic proximity effect of DL on QW, leading to induce spin polarization of the holes in QW. Strong structural and magnetic disorder in DL and QW, leading to the phase segregation in them is taken into consideration. The high pH value is explained as a result of compensation of the positive sign normal Hall effect component by the negative sign anomalous Hall effect component.Comment: 19 pages, 6 figure

THE ANALYSIS OF PHYSICAL AND MECHANICAL CHARACTERISTICS OF FACING COMPOSITE MATERIALS CERAMAGE («SHOFU») AND ULTRAGLASS («VLADMIVA»)

According to the Ministry of Industry and Trade, the degree of dependence of the medical industry and practical medicine on imports is 81%. Critical dependence causes a shortage of inexpensive consumables, medicines and medical devices, and as a consequence of the increase in the cost of medical services, which is estimated as a threat to national security. In various regions of the Russian Federation in the general structure of dental care for patients in all age groups, dental arch defects range from 40 to 75%. Non-removable prosthetics for socially unprotected segments of the population are carried out mainly by bridges with lining the metal frame with hot-curing plastic, short-lived due to low strength characteristics, significant abrasion, and hygroscopicity. To a large extent, the service life of fixed prostheses is determined by the combination of the physicomechanical properties of the facing material, such as flexural strength, modulus of elasticity, and hardness. Flexural strength characterizes the ability of a material to resist unaxial occlusal loading, the modulus of elasticity determines the stiffness of a material and its ability to withstand applied loads without significant deformations, and the hardness characterizes the wear resistance of a material and its ability to withstand abrasion by antagonists. This paper presents the results of a study of the physicomechanical properties of facing composite materials: Ceramage (Shofu, Japan) and Ultra Glass (VladMiVa, Russia). The revealed differences in flexural strength, modulus of elasticity and Vickers microhardness of the material “UltraGlass” allow us to recommend it for widespread clinical use. Expanding the range of domestic materials for orthopedic dentistry by developing a coating composite material UltraGlass helps to improve the quality of dental care to the population with social benefits

Wavelet treatment of the intra-chain correlation functions of homopolymers in dilute solutions

Discrete wavelets are applied to parametrization of the intra-chain two-point correlation functions of homopolymers in dilute solutions obtained from Monte Carlo simulation. Several orthogonal and biorthogonal basis sets have been investigated for use in the truncated wavelet approximation. Quality of the approximation has been assessed by calculation of the scaling exponents obtained from des Cloizeaux ansatz for the correlation functions of homopolymers with different connectivities in a good solvent. The resulting exponents are in a better agreement with those from the recent renormalisation group calculations as compared to the data without the wavelet denoising. We also discuss how the wavelet treatment improves the quality of data for correlation functions from simulations of homopolymers at varied solvent conditions and of heteropolymers.Comment: RevTeX, 19 pages, 7 PS figures. Accepted for publication in PR