Comments on “A New Model of Two Directional Jc Distributions for Bi 2Sr2CaCu2O 8 Materials”

The authors comments on the claim of Takahashi et al. that the distribution model, utilizing the mixture of Gaussian distributions, for the local critical current density of superconducting materials they proposed is a new idea. The authors points out the the method have been known since 1886.     

Optical properties of doped bismuth telluride crystals in the region of plasma effects

The optical properties of bismuth telluride crystals doped with donor-and acceptor-type impurities are studied. The fact that energy corresponding to the resonance frequency of plasma oscillations of free charge carriers (plasmons) approaches the band-gap energy is detected in the infrared spectral region, where the main elementary excitations in the electronic system of these materials are observed. The mentioned approach of energies varies the intensity of electron-plasmon interaction, which affects the recombination processes in the materials widely used for the fabrication of thermoelectric energy converters.     

Studies on adsorption equilibrium of xylenes in AEL framework using biased GCMC and energy minimization

The adsorption of xylene isomers in AlPO₄-11 (AEL network) was investigated using biased grand canonical Monte Carlo (GCMC) simulations. Preferential o-xylene adsorption was predicted by the simulations, in agreement with previously reported experimental data. In AlPO₄-11 the selective adsorption behavior comes from the smaller length of the o-xylene molecule along the crystallographic c-axis compared to p-xylene. This is in contrast to AlPO₄-5 and AlPO₄-8, where the ortho-selectivity is caused by the characteristic face-to-face positioning of o-xylene. Energy minimization studies were also performed in a flexible AlPO₄-11 lattice to study the structural changes upon xylene adsorption. The energy minimization study showed that the AlPO₄-11 crystal distorts upon p- and o-xylene adsorption. The distortion mechanism is related to the strong interaction between xylene methyl groups and the sieve oxygen atoms in the O3 position in the wide region of the pore.     

X-ray topography studies of dislocations in single crystal CVD diamond

X-ray topography has been used to study single crystal diamond samples homoepitaxially grown by microwave plasma-assisted chemical vapour deposition (CVD) on high pressure high temperature (HPHT) and CVD synthetic diamond substrates. Clusters of dislocations in the CVD diamond layers emanated from points at or near the interface with the substrate. The Burgers vectors of observed dislocations have been determined from sets of {111} projection topographs. Dislocations have line directions close to the [001] growth direction and are either edge or 45° mixed dislocations. Where groups of dislocations originated at isolated points they tended to be of the edge variety. Where the substrate surface was deliberately damaged before growth, two sets of dislocations were observed to have propagated from each line of damage and there was a tendency for dislocations to be of the 45° mixed variety with a component of their Burgers vector parallel to the polishing direction. It is demonstrated that X-ray topography can be used to deduce the growth history of CVD synthetic diamond samples produced in multiple growth stages.     

Drying Kinetics of a Porous Spherical Particle and the Inversion Temperature

A model is presented for drying of a single porous particle with superheated steam and humid air. Experimental data for spherical porous ceramic particle reported in the literature were used for the validation of the model. An inversion temperature at which the evaporation rates within superheated steam and humid air are equal was predicted. The effect of thermophysical properties of the particle (permeability 10^-14 - 10^-17 m², diameter 3 × 10^-3 - 10 × 10^-3 m) and operating variables (gas mass flux 0.26 - 0.78 kg m^-2 s^-1, drying agent temperature 120-200°C) is tested. The inversion temperature is shown to be affected by the thermophysical properties of the porous particle and of the drying agent.     

Effect of process parameters on impact strength of Al-7% Si alloy castings produced by VAEPC process

The castings produced by the evaporative pattern casting (EPC) process have blow holes. The blow holes in EPC castings are because of the non-escape of the gas produced as a result of burning of polystyrene pattern in the sand mold. To overcome the problem of blow holes, the EPC process is combined with the vacuum (V)- process. The vacuum applied to EPC mold draws the decomposed gases and improves the casting quality produced by the EPC process. The developed hybrid process has been termed as the vacuum assisted evaporative pattern casting (VAEPC) process. The objective of this paper to investigates the effect of process parameters, i.e, degree of vacuum, pouring temperature, grainfineness number, amplitude of vibration and time of vibration on the impact strength of Al-7% Si alloy castings in VAEPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired impact strength. The central composite rotatable design has been used to conduct the experiments. The results indicate that the impact strength decreases with increases in the grainfineness number and pouring temperature. Whereas, it has an inverse relationship with amplitude of vibration, time of vibration and degree of vacuum. The best value of impact strength (2.34 N/mm²) has been obtained at 400 mm Hg degree of vacuum imposed, 650°C as pouring temperature, 60 as sand grainfineness number, 460 μm as amplitude of vibration, and 70 s as time of vibration.     

Thomson scattering diagnostic systems in the ITER divertor

A diagnostic array has been developed for studying the operating modes of the divertor in the ITER tokamak-reactor using the Thomson scattering technique. The aim of this study is to measure the spatial profiles of the electron temperature and density. The structure of the diagnostic setup was selected on the basis of a classical diagnostic geometry and the high-resolution LIDAR system, which provide access to different regions of the divertor plasma. A severe radiation environment, limited access to the plasma in the ITER divertor, and a high-dust environment (the divertor plate erosion material) in the divertor volume pose many problems for performing diagnostics under unique conditions having no analogs in the tokamaks that are now in operation. Different methods for protecting optical surfaces from plasma-enriched deposition are proposed and analyzed. The efficiency of these methods has been demonstrated in bench tests. The concept of laser and detector systems and diffraction polychromators capable of operating at different electron temperatures with a lower limit of 1 eV, has been justified and approved.     

An efficient electron-beam-pumped semiconductor laser for the green spectral range based on II–VI multilayer nanostructures

Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ～0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ～8.5% are attained for the electron-beam energy of 23 keV.     

Structural and Superconducting Property Variations with Nominal Mg Non‐Stoichiometry in MgxB2 and Its Enhancement of Upper Critical Field

By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in Mg_xB₂ are found. The non‐stoichiometry produces enhanced in‐field critical current densities (J_c's) and upper critical field / irreversibility field (H_c2/H_irr(T)) values. Upper critical fields of ～ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ～ 17 T (4.2 K) for near‐stoichiometric samples.     

Total classes of composition systems of discrete signals in isomorphous Galois fields

It is proposed a rule of total classes of composition systems of discrete frequency signals (CDF-signals) construction in extended Galois fields. It is carried out modeling and research a correlation properties of CDF-signals, and determined their practical attraction.