Hysteresis in the temperature dependence of the intensity of light scattering by boron oxide melt in the 300–450°C temperature range

It has been found that the temperature dependence of the intensity of the polarized V _v and depolarized H _v components of light scattering by a boron oxide melt in the range of 300–450°C is characterized by the existence of hysteresis: the specific feature of the change in the polarized V _v component is the formation of a minimum, while the specific feature in the behavior of the depolarized H _v component is associated with the appearance of a maximum in the sample heating mode; the cooling mode is accompanied by a monotonic change in the intensity of the light-scattering components. It has been found also that in the process of a low-temperature stabilization of the melt at 300°C, the polarized V _v component after reaching its minimum values increases up to the initial level, while the depolarized H _v component after passing its maximum decreases to the values smaller than the initial one. The characteristic time of the change in the intensity of the V _v component at 300°C is determined; its value was found to be ~100 min. It has been shown that an insignificant change in the melt synthesis conditions affects the detected features of the intensity change in the range of 300–450°C.     

Photoreflectance Spectroscopy Study of LT-GaAs Layers Grown on Si and GaAs Substrates

The mechanical strains and densities of surface charge states in GaAs layers grown by low-temperature (LT) molecular-beam epitaxy on Si(100) and GaAs(100) substrates are investigated by photoreflectance spectroscopy. Lines corresponding to the fundamental transition (E _g ) and the transition between the conduction band and spin-orbit-split valence subband (E _g + Δ _SO ) in GaAs are observed in the photoreflectance spectra of Si/LT-GaAs structures at 1.37 and 1.82 eV, respectively. They are shifted to lower and higher energies, respectively, relative to the corresponding lines in GaAs/LT-GaAs structures. Comparing the spectra of the Si/LT-GaAs and GaAs/LT-GaAs structures, it is possible to estimate mechanical strains in LT-GaAs layers grown on Si (by analyzing the spectral-line shifts) and the density of charge-carrier states at the GaAs/Si heterointerface (by analyzing the period of Franz–Keldysh oscillations).     

Deterministic safety study of advanced molten salt nuclear systems for prospective nuclear power

The inter-comparative analysis of the deterministic safety potential of innovative molten salt systems with critical and sub-critical cores is presented for both fast and thermal neutron spectra. The analysis includes two aspects: the choice of an initial level of sub-criticality and the study of multiple unprotected transients which have been simulated on the basis of one-point kinetics and two-point thermo-hydraulic schemes considering realistic feedback effects. Our preliminary results show that even small levels of sub-criticality (2–3 dollars) of cores can improve their safety characteristics significantly.     

Specific Features of Light Scattering in Oxide Glasses in the Glass Transition Range

The change in the intensity of light scattering after temperature jumps in the glass transition range is investigated for phosphate and silicate glasses. It is demonstrated that the time dependence of the intensity exhibits a universal character, which manifest itself in the peak whose height and location depend on the thermal prehistory of the glass. The influence of the thermal prehistory on the height and the lifetime of the intensity peak is elucidated and the experimental conditions that correspond to the maximum scattering intensity and the longest duration of the transient process are determined for phosphate glass. It is revealed that the maximum height of the intensity peak nonmonotonically depends on the annealing temperature. An analysis of the results obtained shows that the mechanism of relaxation process of the low-temperature stabilization undergoes a crossover in the vicinity of the glass transition temperature. It is established that the observed variation in the intensity is characterized by the size effect. This makes it possible to assume that the intensity peak can be associated with the temperature gradient across the sample after the temperature jump.     

Pneumatic gauge empirical-mechanistic modelling

Back-pressure gauge steady-state empirical-mechanistic modelling has been introduced. This technique contains gauge theoretic modelling and for model performance enhancement entertains empirical-mechanistic steady-flow models of gauge flow restrictors which are formulated as the mathematical products of available theoretical and polynomial empirical approximating functions. Flow restrictor discharge coefficient variations were considered as the polynomial empirical functions of the same variables as the theoretical functions. Motivated iteration procedure was employed for minimization of model errors. The comparison of modelling results and reference experimental data has revealed that the empirical-mechanistic modelling permits to attend minimized discrepancy from empirical evidence.     

On the Applicability of the Influence Function Obtained from Single-Pile Calculations for the Calculation of Pile Groups

Soil Mechanics and Foundation Engineering - The results of FEM calculations of the settlement of individual piles and pile groups are presented. A relation is shown between the additional...     

Surface Domain Structures and Mesoscopic Phase Transition in Relaxor Ferroelectrics

Relaxor ferroelectrics are a prototypical example of ferroic systems in which interplay between atomic disorder and order parameters gives rise to emergence of unusual properties, including non‐exponential relaxations, memory effects, polarization rotations, and broad spectrum of bias‐ and temperature‐induced phase transitions. Despite more than 40 years of extensive research following the original discovery of ferroelectric relaxors by the Smolensky group, the most basic aspect of these materials – the existence and nature of order parameter – has not been understood thoroughly. Using extensive imaging and spectroscopic studies by variable‐temperature and time resolved piezoresponse force microscopy, we find that the observed mesoscopic behavior is consistent with the presence of two effective order parameters describing dynamic and static parts of polarization, respectively. The static component gives rise to rich spatially ordered systems on the ～100 nm length scales, and are only weakly responsive to electric field. The surface of relaxors undergoes a mesoscopic symmetry breaking leading to the freezing of polarization fluctuations and shift of corresponding transition temperature.