Mathematical model and numerical simulation of faceted crystal growth

A new mathematical macroscopic model is proposed to describe the nonstationary process of faceted crystal growth by the methods of directional crystallization with a slow change in external thermal conditions and low pulling rate of a cell through the growth system. The facet-growth rate is determined by the Stefan condition, integral over the face. Two boundary conditions are set for temperature: the continuity condition and the relation between the heat-flux jump and the supercooling at the facet points. The supercooling is determined by solving the entire heat problem. A facet is selected as a planar part of the phase boundary. The kinetic coefficient at the facet may depend on the supercooling. The energy conservation law is valid within the model developed. Examples of calculations of some model problems are presented.     

Near-Wall Aggregation of Amyloidogenic Aβ 1-40 Peptide: Direct Observation by the FRET

The formation of amyloid fibrils is one of the variants of the self-organization of polypeptide chains. For the amyloid aggregation, the solution must be oversaturated with proteins. The interface of the liquid (solution) and solid (vessel walls) phases can trigger the adsorption of protein molecules, and the resulting oversaturation can initiate conformational transitions in them. In any laboratory experiment, we cannot exclude the presence of surfaces such as the walls of vessels, cuvettes, etc. However, in many works devoted to the study of amyloid formation, this feature is not considered. In our work, we investigated the behavior of the Aβ 1-40 peptide at the water–glass, water–quartz, and water–plastic interface. We carried out a series of simple experiments and showed that the Aβ 1-40 peptide is actively adsorbed on these surfaces, which leads to a significant interaction and aggregation of peptides. This means that the interface can be the place where the first amyloid nucleus appears. We suggest that this effect may also be one of the reasons for the difficulty of reproducing kinetic data when studying the aggregation of the amyloid of the Aβ 1-40 peptide and other amyloidogenic proteins     

Echo spectroscopy of two-level systems in a Y2SiO5: Pr3+ crystal

The results of an experimental investigation of low-temperature optical spectra and phase relaxation of electronic excitations of Pr³⁺ impurity ions in a Y₂SiO₅ crystal are reported. It is established that at low temperatures spectral lines are broadened by a mechanism that is uncharacteristic for crystals and is due to the interaction of impurity ions with two-level systems. The constants characterizing the interaction of Pr³⁺ impurity ions with phonons and two-level systems are found. Zh. éksp. Teor. Fiz. 115, 704–715 (February 1999)     

Nondiffusion atomic ordering in the low-temperature deposition of copper

A new mechanism of atomic ordering in the low-temperature homoepitaxial deposition of copper onto a close-packed (111) plane has been discovered by means of molecular-dynamics simulation. This nondiffusion mechanism is caused by the collective motion of clusters along the dislocation lines of partial Shockley dislocations. We predict the existence of dislocation-induced coalescence, which is an increase in the mean size of face-centered cubic (fcc) clusters owing to a decrease in the number of hexagonal close-packed (hcp) clusters due to the motion of surface dislocations.     

Static trajectories of the development of two staggered parallel cracks

The problem of the development of two staggered parallel cracks in a finite plate subjected to uniaxial static tension at infinity is examined on the basis of the method of singular integral equations. The trajectories are calculated by the step-by-step method using the criterion of maximum circumferential stresses. In this case, a segment of the trajectory is approximated by a third-degree polynomial in each step. The results of numeric calculations are presented.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 20, pp. 44–50, 1989.     

Phase composition diagnostics of surfaces,thin films,and interfaces by Auger electron spectroscopy

The methods of phase composition diagnostics of materials by Auger spectra, developed in IMT RAS over a number of years, are presented. Examples of their use are generally in the determination of phase depth profiles. However, the considered methods can be also used for the composition diagnostics of small size objects (nanostructures) under conditions of significant noisiness of the Auger spectra and when the studied objects probably leave an analyzed region.     

Dynamics of paramagnets at zero temperature

A macroscopic theory of low-frequency excitations in nearly unstable exchange spin systems with the singlet ground state is developed. Examples of dynamics near the pressure-and magnetic-field-instability points are considered. The development of the theory for the case of the instability of the system with respect to the appearance of magnetization is complicated.