High-resolution calorimetric study of the phase transitions of tridecylcyanobiphenyl and tetradecylcyanobiphenyl liquid crystals

A thermal study of the liquid crystals tridecylcyanobiphenyl and tetradecylcyanobiphenyl has been performed by means of adiabatic scanning calorimetry. Both compounds exhibit only the smectic-A mesophase between the normal liquid and the crystalline phase and their phase transitions are strongly first order. A summary of the enthalpies and transition temperatures for all the smectic homologues of the cyanobiphenyl family is given, based on high-resolution measurements of the present work and previous studies.     

Upper bounds for discrete moments of the derivatives of the riemann zeta-function on the critical line*

Assuming the Riemann hypothesis, we establish upper bounds for discrete moments of the Riemann zeta-function and its derivatives on the critical line. Moreover, we express continuous moments of the Riemann zeta-function and its derivatives in terms of these discrete moments. This allows us to give conditional upper bounds for $ {\int_0^T {\left| {{\zeta^{(l)}}\left( {{{1} \left/ {2} \right.} + {\text{i}}t} \right)} \right|}^{2k}}{\text{d}}t $ , where l and k are nonnegative integers.     

Photoionisation loading of large Sr<Superscript>+</Superscript> ion clouds with ultrafast pulses

This paper reports on the use of ultrafast pulses for photoionisation loading of singly-ionised strontium ions in a linear Paul trap. We take advantage of an autoionising resonance of Sr neutral atoms to form Sr⁺ by two-photon absorption of femtosecond pulses at a wavelength of 431 nm. We compare this technique to electron-bombardment ionisation and observe several advantages of photoionisation. It actually allows for the loading of a pure Sr⁺ ion cloud in a low radio-frequency voltage amplitude regime. In these conditions, up to 4×10⁴ laser-cooled Sr⁺ ions were trapped.     

The Extrapolation Method in the Electron Probe Microanalysis

From the energy dependance of the k-ratio measured for the SbL_α and BiL_α-lines in the alloy system Bi_1–xSb_x the k-ratio at the critical energy E_c is determined by extrapolation. The stopping power correction is discussed for the system investigated here on the basis of the known composition of the specimens. The mean ionization potentials J for Sb and Bi are estimated from the experiments.     

Kinetic investigations on the basis of isothermal DSC measurements of hydrogenation and dehydrogenation of magnesium hydride

Results of kinetic investigations on the basis of isothermal DSC measurements by means of defined pressure changes are presented and interpreted for the Mg/MgH₂ system. From an evaluation of the experimentally obtained DSC-signals, the dependence of reaction rate on hydrogen pressure p₀, temperature and sample morphology could be described. Under certain conditions, it is possible to visualise individual rate-determining steps and, thus, to arrive at conclusions on the reaction mechanism.     

Synthesis of 2-(Perfluoroalkylether)- and -(Perfluoroaryl) Benzothiazoles(su1)

Benzothiazoles containing 2-perfluoroalkylether as well as perfluoroaryl substituents have been synthesized by two methods: (1) direct acylation of 2-aminobenzenethiol with perfluoroacyl halides, and (2) the reduction of N, Nt?-diacy1-2, 2t?-diaminodiphenyldisulfides followed by dehydrative cyclization. The intermediates formed in the direct acylation procedure are the N-acylaminobenzenethiols rather than the S-acyl derivatives.     

Hyperfine structure investigation on the (3d 4)3 G 4,5 levels of47Ti

Using two-step laser spectroscopy with the sideband technique the hyperfine structure (hfs) splittings of the levels (3d ⁴)³ G _4,5 in⁴⁷Ti have been measured. These are the first hfs measurements of the levels belonging to the 3d ^N+2 configuration of the system (3d+4s) ^N+2. The experimental results indicate a strong increase of the core polarization effect due to excitation of both 4s-electrons to the open 3d-shell.