Образцы с пористостью 2–3 и 13%, состоящие из мелкозернистого кварца, диспергированного в серебряной матрице, были подвергнуты ударному сжатию до 28, 33 и 37 ГПа в плоских ампулах сохранения. В образцах с пористостью 2–3% после очистки от серебра наряду с аморфизованным кварцем рентгенографически обнаруживалась кристаллическая фаза высокого давления диоксида кремния, отличная от стишовита и предположительно имеющая моноклинную решетку.

Samples with porosities of 2–3 and 13

Using a laser velocity interferometer, wave profiles were recorded in porous (porosity 30%) nickel aluminide samples. Data on shock compressibility were obtained. An abnormally high compaction was found, manifested in the intersection of Hugoniots of solid and porous samples at a pressure of 28 GPa, which indicates a phase transition. Keywords: shock waves, Hugoniot, phase transitions, laser Doppler interferometers, intermetallides.

This study reports the results of experimental research on the dynamic yield strength and spall strength of polycrystalline NiAl under shock-wave loading. Wave profiles obtained by laser interferometry are presented. The free surface velocity profiles of NiAl demonstrate shock wave splitting with the formation of a two-wave configuration of elastic and plastic waves, and a spall pulse caused by tensile fracture of the material. The dynamic yield strength and the spall strength are determined as functions of the shock compression amplitude and strain rate in the unloading part of the pulse. The influence of the shock wave amplitude on the stress relaxation behind the elastic precursor front is described.

Using a laser velocity interferometer, wave profiles were recorded in porous (porosity 30%) nickel aluminide samples. Data on shock compressibility were obtained. An abnormally high compaction was found, manifested in the intersection of Hugoniots of solid and porous samples at a pressure of 24 GPa, which indicates a phase transition.

The electrosurface properties have been experimentally studied for different monodisperse fractions of hydrosol particles of detonation nanodiamond (DND) obtained by air annealing of particle agglomerates, their deagglomeration by sonication in demineralized water, and subsequent centrifugation of resulting hydrosols. The acid-base potentiometric titration and laser Doppler electrophoresis have been employed to obtain the pH dependences of the surface charge density and electrophoretic mobility of the nanoparticles in hydrosols containing 0.001 M KCl within a pH range of 3.5–10.5. A decrease in the average size of DND nanoparticles leads to an increase in the absolute values of the density of their negative surface charge. The high surface potential values calculated for these DND samples are independent of the nanoparticle size. The absolute values of the electrokinetic charge density, which are an order of magnitude lower than those of the surface charge, increase significantly with a decrease in the particle size.

We present experimental data on Hugoniot and release isentropes of nickel aluminide obtained for shock pressures up to 83 GPa and make comparison with previously published calculation data. We estimate a Hugoniot elastic limit of samples, construct the EOS of nickel aluminide and investigate the Hugoniot position relative to the melting curve.

Sound velocity variation behind a shock wave front is measured in pressed samples of micro- and nanodispersed mixtures of nickel and aluminum powders at pressures of 10, 30, and 60 GPa in order to verify the possibility of a reaction with the formation of nickel aluminide in a submicrosecond time range. It is shown that, in a pressure range of up to 60 GPa, the sound velocity in the samples from a nanodispersed mixture is higher than in the samples from a mi-crodispersed mixture. Moreover, upon reaching 60 GPa, the sound velocities in both mixtures with account for errors are practically equalized, which is related to melting of the samples. Based on the data obtained, it is concluded that there is no noticeable progress of the Ni + Al reaction during less than 1 μs.

Shock compressibility of porous samples prepared from mixtures of micro- and nanosized nickel and aluminum powders is experimentally studied in the pressure range up to 60 GPa. Shock wave profiles in the samples are recorded, and Hugoniots are determined. The equation of state of the samples is derived within the framework of the Zel’dovich model. The shape of the shock wave profiles does not reveal any specific features that can be associated with a possible reaction between the components. The Hugoniots of the samples of two types of powder mixtures coincide within the experimental error despite significantly different sizes of powder particles, which implies that either there are no noticeable chemical transformations or, vice versa, they are completed within the shock loading time. The predicted Hugoniot with the reaction between the components being ignored passes in an immediate vicinity of the experimental data, which testifies to the absence of the reaction.

Detailed results of an x-ray diffraction analysis of equimolar mixtures of nickel and aluminum with different particle sizes before and after shock loading in flat recovery ampoules are reported.

Determining threshold values of key economic security indices describing an economic situation in any country is an important stage in the assessment of the country’s economic stability. A research was undertaken to determine how this problem can be effectively solved with such Data Mining algorithm as decision trees. According to the results of the research the effectiveness of the method was proved, but only with sufficient amount of data available. However, such data collection has a number of significant problems. These problems can be attributed to the following factors: the data for the analysis are presented with varying frequency, there is no possibility to use data over longer time intervals, the lack of a common list of indicators of economic security, which are used in different countries. The purpose of this paper is to analyze the existing problems of the data collection and to submit proposals of solving them. Keywords: Economic security, Issues of data collection, Data Mining, thresholds.

Determining threshold values of key economic security indices describing an economic situation in any country is an important stage in the assessment of the country's economic stability. Threshold values must be periodically reevaluated due to their continuous deterioration as far as the global economic environment is undergoing changes. The authors offer a rough estimate method for achieving this goal.

Based on the results of studying the coagulation kinetics of monodisperse sol of SiO2 in NaCl solutions at various pH values, it is shown that the coagulation rate, flowing in the far potential minimum while maintaining a high repulsion barrier between the particles, depends on the formation and decomposition times of the aggregates. The boundary values of the depth and power of the far potential minimum-at the excess of which sol coagulates-are determined.

Conditions for the preparation of Fe3O4@SiO2 core-shell nanoparticles aggregatively stable in aqueous solutions were determined.

The influence of the concentration of potassium and barium chlorides on the aggregation stability of a hydrosol of monodisperse negatively charged detonation nanodiamond with particle sizes of 4−5 nm obtained by annealing of its agglomerates in air has been studied by turbidimetry. The experimental results have been discussed within the classical and generalized Derjaguin−Landau−Verwey−Overbeek theories. The analysis of the pair interaction potentials calculated for ultradispersed particles of detonation nanodiamond has led to the conclusion that the coagulation occurs by the barrier mechanism in the primary potential minimum. It has been assumed that the structural component of the interparticle interaction energy contributes to the total balance of the surface forces.

Nafion- and Aquivion-based composite solid polyelectrolytes containing deagglomerated detonation nanodiamonds were studied by the impedance spectroscopy method. It was found that introduction of these dopants leads to a substantial increase in proton conductivity of hybrid membranes with low relative humidity.