Use of the photoacoustic spectroscopy in the investigation of the dilution process in surface-coated nanoparticles

In this study photoacoustic spectroscopy was used to investigate the effect of water dilution of a biocompatible magnetic fluid sample upon the nanoparticle surface-coating. The observed spectral features, in the 300–1000 nm wavelength region, are analyzed in terms of three distinct bands (L, S, and C). Band-L, in the spectral range of 650–900 nm, is related to the characteristic coating layer of the magnetic nanoparticle. Band-S, occurring around 470 nm, is related to the metal–polyoxy-hydroxy surface layer built up at the surface during the nanoparticle synthesis. Changes of band-L and band-S features upon water dilution of the stock magnetic fluid sample are discussed in terms of surface reorganization of the DMSA (dimercaptosuccinic acid) surface-coating agent with simultaneous surface release of hydroxyl-groups. The model picture of the surface reorganization is consistent with the picture of disruption of longer chain-like structures into shorter ones as a result of the sample dilution.     

Mathematical modeling of impurity distribution in the melt meniscus in the growth of profiled sapphire crystals

The distribution of impurities in the growth of profiled sapphire crystals is simulated. The distribution of impurities was calculated with the use of the diffusion equation with convective terms. The melt flow was found by solving the Navier-Stokes equation. The distributions of impurities over the melt meniscus are obtained at different crystallization rates. The maximum concentration supersaturation in the meniscus is studied as a function of its geometric parameters.     

Amplification of the Fluorescence Propagating in the Waveguide Regime in a Planar Layer of NLC

Crystallography Reports - The amplification of spontaneous fluorescence in a planar layer of nematic liquid crystal doped with DCM dye in the mode of waveguide light propagation has been studied....     

Investigation of the Pigments of the Ancient Portrait Terracotta Found in the Kerch Bay

Crystallography Reports - The results of studying an ancient terracotta sculpture found in the Kerch bay are presented. An attempt is made to reconstruct the initial terracotta color and determine...     

Manifestation of the Sapphire Crystal Structure in the Surface Nanopattern and Its Application in the Nitride Film Growth

The “quenching” technique was used to investigate the initial stage of the formation of a terracestep nanostructure on the R-cut surface of sapphire crystal upon high-temperature annealing in air. The morphological features of the formation of A- and R-sapphire planes are experimentally shown in dependence on the misorientation direction and qualitatively interpreted with allowance for the surface energy density for the main sapphire faces. The possibilities of forming AlN layers on the R-sapphire surface with a terrace-step nanostructure under thermochemical effect and high-temperature substrate annealing in a mixture of nitrogen and reducing gases are considered.     

Peculiarities of the diffraction contrast in plane-wave X-ray topographs of weakly deformed crystals in the bragg geometry

The regularities of the topographic contrast formation in weakly deformed nonabsorbing crystals in the Bragg geometry for the diffraction of a plane X-ray wave have been investigated by the method of Riemann functions. It is shown that in this case the extinction contrast has an interference character, alternates, and is proportional to the strain gradient rather than to the squared strain (like in the case of strong lattice distortions). The data of the analysis are compared with the results of a model numerical experiment. The possibility of implementing an X-ray-acoustic resonance in the Bragg geometry is shown.     

An investigation of the structural effects of Fe in the alkali-silicate glasses

The coordination states of Fe³⁺, B³⁺ and Al³⁺ ions in the alkali-silicate glasses have been determined. The structural effects of these cations coexisting in the glass, and the effects of the iron and boric oxide anomaly on glass density, are also analysed.     

Influences of ethanol on the thermodynamics and kinetics in the crystallization of xylitol

The metastable zone and crystal growth rates of xylitol in water were investigated under the influence of small volume fractions of ethanol. The utilization of low amounts of ethanol is necessary to help adding slightly soluble ingredients during the fabrication of xylitol products, e.g. in food industry. Therefore, the metastable zone and crystal growth rates were determined by means of an ultrasound measurement technique and batch crystallization experiments. It can clearly be seen that the addition of ethanol is lowering the solubility of xylitol in water. The higher the volume fraction of ethanol, the lower the solubility. The metastable zone width is increased whereas the smallest investigated ethanol content results in the widest metastable zone. The crystal growth of xylitol is inhibited by the addition of ethanol whereby the crystal growth rates are decreasing with increasing ethanol content.     

On the conformation of the five-membered D ring in steroids

The effects on the conformation of steroids owing to substituents at C (17) and other atoms of the five-membered (D) ring are studied and parametrized.     

Analytical description of the yield drop in the Alexander-Haasen model

The analytical solution of the equations of the Alexander-Haasen model, which describes the shape of the deformation-curve peak (the so-called yield drop), has been obtained for the case of a low initial dislocation density. It is shown that the self-development of the dislocation structure results in the specific kinetic transition with a dramatic decrease of the elastic-deformation rate and an increase of the plastic-flow rate. It is natural to interpret this phenomenon as an elastoplastic transition, and to consider the corresponding stress as the yield stress despite the fact that, being considered in the traditional way, its value does not coincide with either the upper or lower yield stress. The conditions of the existence of the yield drop are studied, and the quantitative criterion of the corresponding change in the deformation-curve shape is proposed.     

Crystallization of glasses in the germanium-tellurium-sulphur system

The glasses of the germanium-tellurium-sulphur ternary system were investigated in order to determine the formation and crystallization processes. Vitreous samples were prepared by quenching. The vitreous transition and crystallization temperatures, together with microhardnesses, were measured throughout the vitreous region. The latter was sub-divided into several zones, and the behaviour of the glasses in each of these zones was analyzed separately.     

Study of the initial transient in the one-dimensional analytical models of impurity segregation during melt crystallization in the presence of convection

The well-known one-dimensional Burton-Prim-Slichter and Ostrogorsky-Müller analytical models obtained for the stationary mass transfer regime describe in a simple form the dependence of the effective impurity segregation coefficient on the ratio of the crystal growth and convective flow rates. Solutions for the initial transient regime are found in both models. It is shown that the formulas obtained make it possible to determine both the crystal growth rate and the convective mixing intensity on the basis of the analysis of impurity segregation in crystal.     

Analysis of the kinetics of crystal growth and epitaxy in the framework of the multilayer model of mass crystallization

The method for calculating the kinetics of crystal growth and epitaxy based on the two-dimensional model of the mass crystallization in many atomic layers has been developed. The kinetics of crystal growth is analyzed with due regard for the initial (critical) size of two-dimensional nuclei, the dependence of the growth rate of two-dimensional nuclei on their size, and the non-steady-state frequency of the formation of two-dimensional nuclei. The effect of characteristic parameters of crystallization on the kinetics of formation of epitaxial films and structure is also studied.     

On the Method of Constructing the Radial Distribution Function in the Structure of Amorphous Materials on the Basis of Diffraction Data

Crystallography Reports - The method of constructing the radial distribution function, proposed by the authors previously, has been developed. The method includes calculation of the normalization...     

Three-dimensionality of space in the structure of the periodic table of chemical elements

The effect of the dimension of the 3D homogeneous and isotropic Euclidean space, and the electron spin on the self-organization of the electron systems of atoms of chemical elements is considered. It is shown that the finite dimension of space creates the possibility of periodicity in the structure of an electron cloud, while the value of the dimension determines the number of stable systems of electrons at different levels of the periodic table of chemical elements and some characteristics of the systems. The conditions for the stability of systems of electrons and the electron system of an atom as a whole are considered. On the basis of the results obtained, comparison with other hierarchical systems (nanostructures and biological structures) is performed.     

On the temperature Dependence of the orientational Order Parameter in the Nematic Phase of Cyanophenyl Behzoates

The orientational order parameters fot two liquid crystal materials, 4-cyanophenyl 4-butylbenzoate and 4-cyanophenyl 4-pentylbenzoate, have been derived by measuring the change in the refractive index as function of temperature. The order parameters are compared with MaierSaupe theory, and the sharpness of the transitions has been shown using the Haller's plot.     

Stimulation of the Electrohydrodynamic Instability in the Smectic a Phase

The electrooptical properties of 4-n-octyl-4′-cyano-biphenyl (8CB) in the smectic A phase were investigated. The electrohydrodynamic instability in the smectic A phase was observed, when a small quantity of any homologue (C₇, C₈, C₉) of 4-n-alkoxyben-zoic acid was adzed to this material. After the electrical field is turned off, the stable focal-conic texture is formed. A reverse focal-conic to homeotropic transition can be as well induced by means of an electric field.     

Ultrasound propagation in glasses in the metastable immiscibility region of the sodium borosilicate system

Measurements of ultrasound wave velocity and attenuation have been made between 1.3 K and 400 K in a series of both quenched and heat-treated Na₂OB₂O₃SiO₂ glasses. As in many other inorganic glasses, the ultrasound attenuation of both longitudinal and shear waves below room temperature is dominated by a broad and intense loss peak; the height and temperature of the peak maximum are frequency sensitive. The loss peak characteristics are consistent with a structural relaxation mechanism with a distribution of activation energies and this model is used to analyse the data. The features of the acoustic loss peak and also the absolute value and temperature coefficient of ultrasound velocity are strongly dependent on the total Na₂O network modifier content of the glasses. The ultrasound wave propagation is also affected by phase-separation inducing heat treatment: a steady rise in the height of the acoustic loss peak and an upward shift in the peak temperature takes place with increasing time of heat treatment at 550°C, a finding which suggests that structural rearrangements are still occurring in the individual glassy phases even after long periods of heat treatment. It is proposed that heat treatment causes migration of Na⁺ ions away from BOB bonds in the B₂O₃ rich phase.