A new allotropic superhard and superdense structure of sp3‐bonded boron nitride (hP3‐BN) is proposed. Geometric, electronic, elastic, and optical properties of the structure are investigated by ...density functional theory‐generalized gradient approximation (DFT‐GGA) calculations. It is shown that the structure is an insulator with a band gap of 5.06 eV; its density is 5.03% higher than that of cubic boron nitride (c‐BN) and its bulk modulus is 2.25% higher than that of c‐BN. The calculated hP3‐BN refractive index in the range 200–800 nm is significantly higher than the indexes of diamond and all known carbon allotropes, except for the analogous carbon h‐P3 structure, and it has a large optical dispersion. In the range above 800 nm the refractive index changes from 2.60 to 2.35.
The results of mechanoluminescence (ML) and acoustic emission (AE) studies of the response of the ceramic materials ZnS and ZnSe to impact damage to the surface are presented. The experiment ...simulates the process of dust erosion of optical components made from these materials and installed on high-speed mobile carriers. A comparison of a time series of light and sound emissions showed that ML manifests two peaks approximately 50 – 200 and 150 – 200 μsec after impact, while AE occurs in a single peak near 200 μsec. This result is explained by plastic deformation of the material at the first stage of fracture and subsequent formation of microcracks.
We consider the problem of asymmetric strain and stress distribution in silica fiber under threepoint bending. The parameters of nonlinear elasticity of silica glass under tension and compression are ...estimated using available data from the literature. It has been found that consideration of the nonlinear elasticity of silica glass leads to a slight increase in the calculated values of strength compared to the data obtained from estimates based on the linear theory of elasticity.
Time series of acoustic emission pulses are recorded when the surface of MgAl
2
O
4
ceramics is damaged by the introduction of a Vickers pyramid. Based on the data of the frequency analysis of the ...emitted sound, the ratio of the size of intra- and intergranular microcracks is estimated depending on the load on the indenter. The statistical analysis shows that the energy distribution in acoustic pulses is always random, typical of the uncorrelated development of a fracture.
Results of laboratory and industrial testing of the effect of cold treatment on the structure, hardness and size stability of parts such as spools and sleeves entering the hydraulic drive of an ...ESh-20.90S dragline (bucket volume 20 m
3
, boom length 90 m) for mining applications under the conditions of the Far North are presented.
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New glasses in the TeO
2
–Na
6
P
6
O
18
system have been prepared, their thermal behavior has been studied by differential scanning calorimetry in the range 25–580°C, and their heat capacity has ...been determined as a function of temperature in the range 25–400°C. We have evaluated characteristics of the devitrification process and glassy state, obtained analytical representations of the glass transition temperature and the thermodynamic characteristics of the glasses as functions of their composition at 80°C, and carried out a comparative analysis of the results together with those for previously studied TeO
2
-based binary systems. Optical transmission of the glasses has been measured in the UV, visible, and IR spectral regions. We have demonstrated the possibility of doping the glasses with rare-earth oxides and studied luminescence properties of the glass with the composition 0.89TeO
2
–0.08Na
6
P
6
O
18
–0.03Nd
2
O
3
.
The linear parameters and number of Langerhans islets were evaluated in rats with alloxaninduced diabetes mellitus after transplantation of fetal pancreatic tissue to the anterior chamber of the eye. ...The islets significantly increased in size by week 3 after surgery and a trend to an increase in their number was observed.
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