Phase transitions and molecular properties of new divinyl and diepoxy compounds

The aim of this paper is to compare some physical properties of six new divinyl and diepoxy compounds. The compounds differ in the length of the rigid central segments. Optical observations and differential scanning calorimetry confirmed the existence of a mesophase in five compounds and enabled the determination of the phase transition temperatures. The wide angle X-ray scattering (WAXS) measurements of samples aligned in a magnetic field and the optical observations allowed the identification of the mesophase types. In four compounds a nematic mesophase was detected during both heating and cooling. In one case two higher ordered phases were observed during cooling. The analysis of WAXS images and the positions and shapes of the scattering intensity peaks suggests a smectic B-crystal E transition. Using the data obtained in WAXS measurements carried out in the nematic phase, the lengths of the molecules and the average nearest neighbour distances were estimated. The average intermolecular distances and the layer spacings were also estimated for the SmB and E phases. The lengths of the molecules were also calculated by means of theoretical ab initio methods. The results obtained are in very good agreement with the experimental data.     

Weakly non-linear waves in a tapered elastic tube filled with an inviscid fluid

In the present work, treating the artery as a tapered, thin walled, long and circularly conical prestressed elastic tube and using the longwave approximation, we have studied the propagation of weakly non-linear waves in such a fluid-filled elastic tube by employing the reductive perturbation method. By considering the blood as an incompressible inviscid fluid, the evolution equation is obtained as the Korteweg-de Vries equation with a variable coefficient. It is shown that this type of equation admits a solitary wave-type solution with variable wave speed. It is observed that, the wave speed decreases with distance for positive tapering while it increases for negative tapering. It is further observed that, the progressive wave profile for expanding tubes (a>0) becomes more steepened whereas for narrowing tubes (a<0) it becomes more flattened.     

First-Order geometrical response equations for state-averaged multiconfigurational self-consistent field (SA-MCSCF) wave functions

The first-order geometrical response equations for a state-averaged multiconfigurational self-consistent field (SA -MCSCF ) calculation are derived. This derivation is carried through from first principles to final working equations suited for computer implementation. The final equations are expressed such that the energies and wave functions must be known only for the internal SA -MCSCF states. In the derivation, the special but important case where two or more internal states have equal weighting factors is treated in a manner fully consistent with all other cases. Except for introducing extra equations that are straightforward to solve, the case where two or more internal states have equal weighting factors introduces no new complications.     

Production and microwave spectra of dithioformic acid,HCSSH

Hitherto unknown dithioformic acid, HCSSH, has been produced by pyrolysis (300°C) of methanetrithiol, HC(SH)₃, and identified by the microwave spectrum (18–40 GHz) of its most abundant species H¹²C³²S³²SH. Rotational transitions of this species in its ground state have been assigned to a trans and a cis rotamer. Both rotamers are planar, the trans conformer being the more stable by ca. 350 cm^?1 mole^?1. For each rotamer spectra of molecules in two vibrationally excited states have been assigned. Frequencies of transitions of importance for search for HCSSH in interstellar space are reported.     

Electrical properties and defect chemistry of TiO2 single crystal. I. Electrical conductivity

The present work reports the electrical properties of high-purity single-crystal TiO(2) from measurements of the electrical conductivity in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities in the range 10(-13) to 10(5) Pa. The effect of the oxygen activity on the electrical conductivity indicates that oxygen vacancies are the predominant defects in the studied ranges of temperature and oxygen activities. The electronic and ionic lattice charge compensations were revealed at low and high oxygen activities, respectively. The determined semiconducting quantities include: the activation energy of the electrical conductivity (E(sigma) = 125-205 kJ.mol(-1)), the activation energies of the electrical conductivity components associated with electrons (E(n) = 218 kJ.mol(-1)), electron holes (E(p) = 34 kJ.mol(-1)), and ions (E(i) = 227 kJ.mol(-1)), and the enthalpy of motion for electronic defects (DeltaH(m) = 4 kJ/mol). The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. The obtained data allow the determination of the n-p demarcation line in terms of temperature and oxygen activities. The band gap determined from the electronic component of the electrical conductivity is 3.1 eV.     

Electrical properties of niobium-doped titanium dioxide. 1. Defect disorder

The present work reports the electrical conductivity and thermoelectric power for Nb-doped TiO(2) at elevated temperatures (1073-1298 K) in the gas phase of controlled oxygen activity, 10(-14) Pa < p(O(2)) < 75 kPa. It is shown that in reduced conditions the Nb-doped TiO(2) exhibits metallic-type conductivity. This finding paves the way for the development of high-performance photoelectrodes with substantially reduced internal energy losses during charge transport. The present work also determined the equilibrium constant for the formation of oxygen vacancies and titanium vacancies for Nb-doped TiO(2).