Electron Metal-Dielectric Phase Transitions in Semiconductors under Pressure

The effect of uniform pressure on the character of metal-dielectric transitions in compensated weakly- and highly doped semiconductors (WHDCS) is considered. The influence of hybridization of resonance quasilocalized impurity states with band continuum states on the transition is shown. Minimum metallic conductivities in p-CdSnAs₂ are determined for Mott and Anderson transitions. Special features of the metal-dielectric transformation in weakly-doped narrow- and high energy-gap semiconductors are discussed for the case of hydrogen-like impurities. Anderson localization in WHDCS is also considered. Phase diagrams are presented.     

Dielectric properties of liquid crystals of the cyano derivative compounds with different fragments in the molecular core

This paper reports on the results of investigations into the influence of variations in the chemical composition of the aromatic core of cyano-containing molecules of liquid crystals on their dielectric properties in the frequency range 1–2000 MHz. It is shown that the dispersion of the longitudinal permittivity is adequately described by the sum of two Debye processes with different weighting factors and relaxation times. The frequency dependence of the transverse permittivity is well approximated by the Debye process with a continuous distribution of relaxation times in a specified range. It is established that the replacement of one benzene ring in the biphenyl core of the 5CB liquid-crystal molecule by a cyclohexane (or bicyclooctane) fragment leads to a considerable decrease in both relaxation times for the longitudinal permittivity, a change in the low-frequency limit of the relaxation time range for the transverse permittivity, and the evolution of the frequency dependence of the dielectric anisotropy.     

Elasticity and inelasticity of biomorphic silicon carbide ceramics

The effect of the vibration strain amplitude on the Young modulus and ultrasonic absorption (internal friction) in biomorphic SiC ceramics is investigated in the temperature range 116–296 K. The biomorphic SiC ceramics is prepared through pyrolysis of eucalyptus with subsequent infiltration of silicon. It is demonstrated that the vibration loading of samples in air and under vacuum is accompanied by a number of unexpected effects. The behavior of the studied ceramics is governed by at least two mechanisms, which, to a large extent, are responsible for the elastic and inelastic properties of the material. One mechanism is associated with the adsorption-desorption of environmental molecules (hypothetically, owing to the presence of pores and residual carbon), and the other mechanism involves microplastic deformation due to the motion of dislocations or other (similar) structural units.     

Generation of a homogeneous plasma and wide ion beams in a penning system with a nonequipotential cathode

A study is made of the possibility of controlling the spatial distribution of the degree of ionization in a modified Penning cell with a cathode divided into several sections that are at different potentials. It is shown that an almost uniform plasma can be produced when applying an optimal potential of the control electrode. This enables the generation of wide ion beams in this system. An ion extraction efficiency of several tens of percent is achieved, which is substantially higher than in conventional ion sources.     

Associated φΛ0 production in the EXCHARM experiment

The features of the associated production of φ mesons with Λ⁰ hyperons in neutron-carbon interactions were investigated. The experiment was performed with the aid of the EXCHARM spectrometer at the Serpukhov accelerator in a neutron beam of energy in the interval 20–70 GeV. The differential cross section for inclusive associated φΛ⁰ production was measured.     

Cyclotron production and quality control of “high specific activity' radionuclides in “no-carrier-added” form for radioanalytical applications in the life sciences

Radionuclides of very high specific activity A _S(t) have great relevance for applications in the life sciences. Updated definitions of A _S are given. The real A _S(t) must be measured by analytical and radioanalytical techniques. No-carrier-added (NCA) radionuclides have A _S(NCA) sometimes close to the carrier-free (CF) value A _S(CF). The accurate knowledge of excitation functions of nuclear reactions vs. ion beam energy is mandatory to maximize A _S(NCA); the minimization of isotopic dilution factor IDF(t) has been achieved too. A range of accelerator production and radioanalytical QC methods for A _S(NCA) optimization and determination is presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Bone mineral density of lumbar spine and proximal femur in healthy males

The aim of this study was to investigate the relationship between BMD and age at lumbar spine and proximal femur in Turkish males. Two hundred ninety healthy males (aged 20-59 years) were investigated. BMD of the lumbar spine had its peak at ages 30-39, however, the peak for the proximal femur was between the ages of 20 and 29. There was a significant decrease in BMD at proximal femur after these peak values with increasing age. In conclusion, there was a significant correlation between age and the proximal femoral BMD in males and age has a strong predictive power on proximal femur BMD score. This revised version was published online in August 2006 with corrections to the Cover Date.