Band 55, Heft 6-7

Light-pulses that are reflected recurrently to one another by two kinematically equivalent dynamically identical inertial systems moving collinearly and irrotationally with uniform relative velocity generate sequences of contiguous time-intervals in both. By means of clocks stationed in the two systems, each time-interval is both measurable locally and calculable non-locally in accord with basic requirements of special relativity theory. Their ratio yields the velocity dependent dilation-of-time relation of Einstein, but an equivalent spatially dependent version of it is obtained as well, because the time-intervals involved are actually determined by the distances that exist between the systems when the reflections occur. As a result, the Einstein relation involves no time-rates of clocks that are actually affected kinematically by the systems containing them.

The proton NMR second moment and spin-lattice relaxation time of polycrystalline [C(NH 2 ) 3 ] 3 Bi 2 Br 9 were studied in a wide-temperature range. Dynamical inequivalence of two crystallographically different guanidinium cations has been revealed . The C3 reorientation of the two types of cations was found to be hindered by different potential barriers (25.1 kJ/mol and 34.7 kJ/mol). At higher temperatures an overall reorientation of the cations was revealed. The existence and order-disorder character of the phase transitions at 333, 350, 415, and 425 K have been confirmed.

54a, The anionic species (Al n X 3n + 1 ) − with X = CI or Br and n ≥ 1 have been recognized for a number of years to form in acidic liquid mixtures of aluminium chloride or bromide with the corresponding halides of alkali or organic cations, in relative proportions which vary with the composition of the mixture. In this work we evaluate the structure and the energetics of such polymeric series in a comparative study of Al and Ga compounds. To this end we first extend an earlier study of the ionic interactions in the Al 2 Cl 6 molecule [Z. Akdeniz and M. P. Tosi, Z. Naturforsch. 180 (1999)] to determine microscopic ionic models for Ga 2 Cl 6 , Al 2 Br 6 , and Ga 2 Br 6 . The models are then used (i) to evaluate the polymeric clusters for n ≤ 4 in the two trivalent-metal chlorides, and (ii) to explore the potential-energy hypersurface of alkali counterions in the case n = 2. We present tests of the results against available data and an evaluation of the convergence of the energy of the polymeric series towards a value of about 0.5 eV per monomer.

Nickel-Silica nanocomposites with a nickel content equal to 10, 15, 20 wt% have been prepared by a sol-gel method starting from ethanolic solutions of tetraethoxysilane and nickel nitrate hexahydrate. After selation the samples were reduced in H-> flow at selected temperature (450 °C < T < 600 °C). The morphological, structural and magnetic properties were investigated by transmission electron microscopy (TEM), wide and small angle X-ray scattering (WAXS, SAXS), magnetic susceptibility in zero field cooled and field cooled mode (ZFC and FC), and magnetic hysteresis loop. Nanometric nickel particles are observed in all the investigated samples. TEM, WAXS and SAXS techniques indicate that the average nickel particle size grows slightly but almost regularly with the nickel concentration. TEM results moreover indicate that also the width of the particle size distribution, which can be simulated by log-normal functions, follows this trend. All the sample treated in hydrogen show superparamagnetic behaviour. The magnetisation falls to reach saturation up to highest measuring field of 70 kOe even at 3 K, while the observed coercivity Hc is much higher than the theoretical bulk one. Some uncertainty in the complete interpretation of the sequence of magnetic measurements is attributed to a progressive oxidation of the samples when these are air exposed.

In this paper, some Virasoro integrable models are obtained by means of the realizations of the generalized centerless Virasoro-type symmetry algebra, [σj(̅ƒ 1 ), σ(̅ƒ 2 )] = σ(̅ƒ 2̅ ƒ 1 - ̅ƒ 1 ƒ 2 ) - It is interesting that some of them may be not only Virasoro integrable but also Painleve integrable.

The AC conductivity in the frequency range 5.0 Hz -10.0 kHz, the magnetic susceptibility in a field of 14.7 and 17.8·10 4 A/m, and differential thermal analysis at 78 K up to room temperature for bis-(ethanolammonium)Co 2 X 6 ,,X = CI and Br are reported. The bromide dimer undergoes an order-disorder transition at 302 K and a displacive type ferroelectric transition at T ~ 220 K. The chloride dimer shows two transitions, the first being in a displacive ferroelectric one at T ~ 210 K showing critical slowing down. The second phase transition, occuring at 282 K, is found to be inactive in the electric measurements.

The self-diffusion coefficients D of the isomers of liquid N-isopropyl-N-methylacetamide (IPMAA) and acetylacetone (AC AC) are studied as functions of temperature. For AC AC also pressure dependent studies were undertaken. In IPMAA the eis and trans conformers have almost identical D. In liquid ACAC, D Kclo is always smaller than D enol , this difference being 15% around 300 K.

A method to calculate the lattice energies of organic molecular crystals is described. It is based on the semiempirical quantum chemical MINDO/3 approximation but might also be used within the framework of any other quantum chemical method. The lattice energy is approximated by the sum of dispersion-, induction-, exchange repulsion-, and electrostatic energy. Different, however, from other schemes employed in this field, like for example the atom-atom-potential method, the variables in the expression for the lattice energy have not been fitted to reproduce experimental values and, therefore, the single contributions retain their original physical meaning. Moreover, the method offers the advantage that it may be directly applied to all compounds that can be treated within the framework of the underlying quantum chemical method. Thus, time consuming readjustment of the entire parameter set upon extension of the group of target molecules by another class of compounds becomes obsolete. As an example, the lattice energies of the three polymorphs of glycine are calculated.

Effects of pressure on the thermal Z/E isomerization of4-(dimethylamino)-4'-nitroazobezene were studied in a silicon oil at various temperatures. The results were compared with the ones previously obtained in glycerol triacetate (GTA) and 2-methylpentane-2,4-diol (MPD).Even in the polymer, pressure effects expected from the transition state theory were obtained at low pressures (P < 200 MPa).However, as in GTA and MPD, the transition state theory became invalid at higher pressures. For the polymeric liquid, the macroscopic shear viscosity obviously does not suffice for a quantitative description of the microscopic frictions between the reactant and the solvent molecules.

Molecular orbital calculations at the HF/6-3 lG(d) level were carried out for polyboric acids and poly-borate anions up to a pentamer to estimate their 11 B -to- 10 B isotopic reduced partition function ratios (RPFRs) and examine the additivity of logarithms of RPFRs. Approximate RPFR-values calculated by the use of the additivity agreed with exact RPFR-values within a margin of 1% error. This error was equivalent to a 5% error on ln(RPFR). The equilibrium constants of mono boron isotope exhange reac-tions between three-coordinate boron and four-coordinate boron ranged from 1.0203 to 1.0360 at 25 °C, indicating the importance of exact evaluation of RPFRs of polymers.

Dielectric loss spectra between 1 MHz and 36 GHz have been measured at 20°C for solutions of hexadecyl trimethylammonium bromide and chloride, tetrahexylammonium bromide and tetrabutylam-monium bromide in chloroform and 1-octanol (three solutes per solvent) at moderate and high concen-trations. The discussion is aimed at identifying relaxation processes involving ions. Describing the relax -ational part of the spectra (after subtraction of the conductivity contribution) by a sum of spectral com-ponents, the lowest frequency component can be attributed to the solute in all cases. Its concentration dependence is indicative of two ionic relaxation processes differing in physical nature. The solvent is partly involved in those processes; moreover a structure breaking effect is likely to occur in case of the alcoholic solvent. The results are also discussed in comparison with a molten alkylammonium salt and with solutions of this and of inorganic salts.

The paper presents results of shear viscosity measurements performed on nematogenic 4-(trans-4'-n-alkylcyclohexyl)isothiocyanatobenzenes (C n H 2 n + 1-CyHx-Ph-N=C=S, /nCHBT) in the isotropic (n = 0 ÷ 12) and nematic (« = 4 ÷ 12) phases. The viscosity measured in the nematic phase is, due to the flow alignment phenomenon, close to the Migsowicz T? 2 viscosity coefficient. An odd-even effect in the n dependence of the viscosity-activation energy is observed both in the nematic and isotropic phases of nCHBT.

To begin with, relaxation equations will be generally examined within the framework of the thermo-dynamics of irreversible processes. The relaxation in the glass transition region specifically proves to be a non-linear process which resembles an accelerated or retarded autocatalytic reaction. Therefore it is physically not very useful to split the relaxation in the glass transition region into a sum of linear re-laxation mechanisms. The linear response theory and the concept of normal modes lose their validity.

The temperature difference ΔT = T* -T (where T* is the local temperature and T the ambient tem-perature) is studied as a function of the excitation wavenumber v̂̃ cxc in the longwave region of the absorption band of 4-amino-4'-nitrostilbene (ANS) and 4-dimethylamino-4'-nitrostilbene (DNS) as well as rhodamine S, rhodamine 6G and Na-fluorescein in poly(vinyl alcohol) (PVA) films heated up to 403 K. Local temperatures T* are determined by a universal Kennard-Stepanov relation. A linear dependence of ΔTon v̂̃ cxc has been found for all investigated luminescent compounds. For dyes, due to the big spectral overlaps between the absorption and fluorescence bands, it was possible to excite also in the anti-Stokes region. In this case for ΔT = 0, i.e. when T* = T, one has v̂̃ cxc . = V ()-() . In view of the slow geometrical relaxation of excitation energy excess in PVA polymers, the relaxation time τ R for thermal equilibration between the luminescent molecule and the vicinal polymer exceeds distinctly the mean fluorescence lifetime τ F .

On the basis of the perimeter model for 4N-electron [n]annulenes, algebraic expressions for the B values of perturbed four-membered rings (n = 4) with four ;r electrons (N = 1) have been derived. The results are used to interpret the MCD spectrum of l,3-di-fm-butyl-2,4-diethyI-1,3,2,4-diazadiboretidine.