Volume 29, Issue 9

We discuss the Baron-Jauch definition of entropy and show that it is the unique answer to an entropy which has the properties of extensivity, positivity and continuity in a weak sense. As an application we also show how one easily can derive the canonical distribution from this definition of entropy using information theoretical arguments.

Waldmann's work on forces on small particles suspended in a nonhomogeneous monatomic gas is extended to a polyatomic gas of rotating molecules. Under the assumption that the coefficient of diffuse reflection is equal to 1, the force the gas exerts on a particle is calculated from an expansion of the distribution function. In general, this force consists of three contributions which are determined by the flow velocity, the translational heat flux, and the pressure tensor in the gas. The latter force vanishes for spheroidal particles, leaving only the frictional and the thermal force. These two forces are given for prolate and oblate spheroids. In particular, the dependence of the thermal force on the orientation of the particle's axis relative to the temperature gradient is discussed, and a comparison with the hydrodynamic and free molecular results is made.

The thermomagnetic force for small spheroidal particles is given in the Waldmann limit. In this limit the force is proportional to the surface area of the particle, and depends on the gas pressure p and on the magnetic field strength H only via H/p. For the gases HD, CH 4 , CO and N2 the ratio of the thermomagnetic and thermal forces is calculated from Senftleben-Beenakker effect data. It is pointed out that the sign and magnitude of the thermomagnetic force in the Waldmann limit give information on the relative sign of two non-diagonal collision cross sections. The dependence of the force on the orientations of the magnetic field and of the axis of the particle relative to the temperature gradient is discussed.

The problem of the natural spectral line width ⊿ω oi individual waves of a coupled many wave system in non-thermal equilibrium is discussed within the Fokker Planck approach to fluctuation phenomena. Edwards' method in turbulence theory is reinterpreted to relate ⊿ω via a modified energy balance equation to the spectrum of the mean wave intensities. This equation is solved for a model of the non-resonant feedback laser. ⊿ω is found to consist of two contributions: The first one is associated with the usual internal noise of a "free" Gaussian wave due to spontaneous emissions. Its contribution to the line width is twice that of a single mode laser far above threshold as found earlier by Brunner and Paul. The second and new contribution stems from the wave-wave coupling. It is similar to half the effective intensity fluctuation line width of the single mode laser and thus dominates above threshold.

A careful investigation of different corrections to binding energies of electrons in almost critical fields is performed. We investigate quantitatively the influence of the nuclear charge parameters, nuclear mass, degree of ionization on the value of the critical charge of the nucleus. Rather qualitative arguments are given to establish the contribution of the quantumelectrodynamic corrections, which are found to be small. Some phenomenological modifications of QED are quantitatively investigated and found to be of negligible influence on the value of the critical field. For heavy ion collisions with Z 1 +Z 2 >Z cr the critical separations between ions are given as results of precise solutions of the relativistic two coulomb center problem. Corrections due to electron-electron interaction are considered. We find (with present theoretical accuracy) Z cr =173±2, in the heavy ion collisions R cr (U-U) = 34.7±2 fm and R cr (U-Cf)=47.7±2 fm. We shortly consider the possibility of spontaneous muon production in muonic supercritical fields.

Mass spectrometric measurements of positive ions emerging from Ar-plasmas at 0.1-0.6 Torr are described. The adaption of the mass spectrometer requires besides the extraction probe an ion optical system, which causes the focussing and bunching of the ion current on the entrance of the time-of-flight mass spectrometer. Systematic measurements of the velocity distributions of the different ion species reveal: 1. The Bohm-criterion is confirmed. In front of the wall the ions are heated in the quasineutral zone and are accelerated in the space charge zone, which here is in the order of magnitude of the ion mean free path. 2. Heating and accelerating increase with growing ion current to the extraction probe. 3. A further increase of the probe current causes collisions in the space charge zone which gives rise to a drop of the transmission of the optical system. 4. The measurement of the current of one ion species as a function of the probe current is a simple experimental proof for collisions of the ions in the space charge zone.

Measurements of the coherent scattering amplitudes of various mixtures of heavy and light water are reported. By means of mirror reflection technique the coherent scattering amplitudes of the D 2 O and H 2 O molecule are determined to be 19.148±0.004 F and -1.679±0.004 F, respectively. Use of a H =-3.740±0.003 F, obtained by the same technique, yields a D =6.674±0.006 F as the bound scattering amplitude of the deuterium nucleus. This value disagrees with the widely accepted 6.21±0.04 F, reported by Bartolini et al. in 1968.

Emittance diagrams of electron guns were measured by means of a shadow method and compared with computed diagrams given in the literature. The calculated ray characteristics and particularly the paraxial ray data could be confirmed, but not the data for the spherical aberration constant. The experimental diagrams can be described by a fifth order parametric expansion of rayinclination and ray coordinate as a function of the ray inclination at the cathode. This expansion is compatible with an electron gun model consisting of two subsequent electrostatic lenses having third order aberrations only. A short survey on this article is given in 11 .

It is often observed that the isothermal degassing of the systems KCl/Ar, CsBr/Xe, and CsJ/Xe cannot be described by Fick's law. According to the diffusion model of Hurst and Gaus one can interpretate such deviations by assuming a reaction of first order between rare gas atoms and lattice defects. This model explains qualitatively several experimentally observed phenomena very well. A quantitative interpretation of the obtained results, however, leads to contradictions.

Fano type surface polaritons in biaxial crystal plates are discussed. The dispersion relation for Fano modes is derived and has been evaluated for an a-quartz slab with regard to real and virtual extraordinary surface modes.

In the present paper, the nucleation of gold on thin carbon layers is investigated. By means of an image analysing computer it was possible to evaluate many electron micrographs with regard to nucleation rate, growth of crystallites, induction time and fractional part of the surface covered by crystallites. The comparison of the experimental results with nucleation theories shows that the explanation is possible by use of a simple atomic model.

Diffusion processes were investigated by means of quantitative electron probe microanalysis in the system Ti-Zr. The annealing temperatures ranged from 650 °C up to 1050 °C. The law d~t ½ is valid for the growing process of the total diffusion zone at all temperatures under observation. Grain boundary diffusion can be excluded. The coefficient of interdiffusion was determined. It ranges from 10 -10 up to 10 -8 cm 2 sec -1 and shows a slight rise with increasing Ti-concentration. The Arrhenius plot of the coefficient of interdiffusion shows two regions with an Arrhenius law valid for each region. The frequency factors and activation energies of the two regions approach with rising Ti-concentration. At 800 °C the Kirkendall effect could be observed. It yields the intrinsic diffusion coefficients. The intrinsic coefficient of Zr is larger than that of Ti.

Contrary to brittle material, the equilibrium grainsize for ductile powders is often approached as an oscillatory function of time. The following paper investigates this behaviour by means of a geometrical analysis of the powder particles, using wet-milled aluminium powder as an example. For the description of the milling kinetics we have used Hüttig's milling functions which are obtained from a sieve analysis, the measuring of the specific area of a powder monolayer, and the determination of the space-filling.

The electric conductivity and the initial thermoelectric power are determined for the solid solutions (Ag, Na)X (X = Cl, Br) over the whole composition range. Data drawn from both kinds of measurements allow to approximately estimate the contributions of cation vacancies and interstitial Ag* to the transport process. Two composition regions are distinguished: 0≦N NaX ≦0.6 and 0.7<N NaX <1 where interstitial Ag + and cation vacancies, respectively, are prevailing.

The microwave spectrum of CH 3 SS CD 3 was investigated in the range of 5 -40 GHz. Rotational spectra in different states of the S-S-torsion were assigned. The methyl torsion fine structure of these spectra was measured and compared with calculations based on a Hamiltonian formulated for a model with two internal degrees of freedom, the methyl and S-S-torsion.

The microwave spectra of CD 3 CH 2 CN, 13 CH 3 CH 2 CN, CH 3 13 CH 2 CN and CH 3 CH 2 C 15 N have been measured. In addition the spectrum of CH 3 CH 2 13 CN has been remeasured with greater accuracy. From these spectra and those previously reported - CH 3 CH 2 CN, CH 3 CD 2 CN, CH 2 DCH 2 CN (sym) and CH 2 DCH 2 CN (asym) - a complete r s -structure has been calculated by the equations of Kraitchman and Chutjian. r 0 -structure calculations were performed with different assumptions due to the symmetry of the molecule. A comparison between r 0 - and r s -structure was made and showed good agreement especially for the atoms of the frame. The quadrupole coupling constants of the above mentioned isotopes of ethyl cyanide were obtained from the hyperfine structure of the spectra with the exception of CH 3 CH 2 C 15 N, which has no nucleus with quadrupole moment. The quadrupole coupling tensor in its principal axis system was determined from the constants of CD 3 CH 2 CN and CH 3 CD 2 CN using the angle e between their principal axes of inertia in the a-b-plane. From Stark effect measurements the dipole moment of CH 3 CH 2 CN was reevaluated. To determine the direction of the dipole moment Stark effect measurements for CD 3 CH 2 CN and CH 3 CD 2 CN were carried out.

Inversion walls are generated by rotating the direction of a magnetic field by 180° with respect to the director in the homeotropically aligned nematic layer. A numerical procedure based on the Leslie-Ericksen theory allows for the calculation of the dynamic behaviour of the inversion walls. Experimental results obtained with MBBA by electric conductivity measurements show satisfying agreement with theory.

A series of complexes crystallizing in a columnar structure were prepared. They have the stoichiometry Ir(CO) 2 ClL and Ir(CO) 2 L-L, where L = monodendate neutral organic base and L-L = mononegative bidendate organic ligand. UV-VIS-spectra and conductivity measurements at variable temperatures show that with increasing size of the ligand system, the intermolecular metal interactions strongly diminish. Therefore these systems are inconvenient as possible exciton superconductors.

The electronic transitions in 5H-dibenzo (a,d)-cycloheptene (1), 5H-dibenz(b,f)azepine (2), dibenz( b,f)oxepine (3), 5-dibenzo(a,d)cyclohepten-5-one (4), dibenzo(b,f)thiepine (5) and dibenzo (b,f) selenepine (6) have been calculated by the SCF LCAO MO CI method for model conformations and compared with experimental uv absorption spectra. The spectral characteristics and conformations of the title compounds and their relationship to cis-stilbene and o-substituted cis-stilbenes are discussed.

A new molecular spectrum has been observed in the 3820 - 3920 Å region by submitting nitrogen molecules to the impact of hydrogen ions in the 5-30 KeV energy range. The most intense band may be attributed to the (0-0) transition of a new system 4 ∑u + →X 2 ∑ g + of N 2 + . The following molecular constants have been determined: T e =3,16 eV, r e =1,077 Å, 3 ε =0,7 cm -1 for the quartet state.

The mean life times of the excited state of the n→π* transitions of the nitroso group have been computed from observed spectra of cupferron in different solvents. The results are discussed in the light of various possible perturbations of the electronic states.

A special transmission device has been adapted on a scanning electron microscope, in which the image is formed by secondary electrons generated by the transmitted ones in an underlying foil of metal. It is shown how this stage allows diffraction patterns and dislocations to be imaged in a conventional microscope (30 kV voltage, hairpin tungsten filament).

Vapour pressures and vapour compositions of the liquid system water+acetic acid have been measured at 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, and 75 °C in the whole range of compositions. The molar excess Gibbs function is derived from the measurements. At 50 °C, where experimental values of the molar excess enthalpy (molar heat of mixing) are available, the molar excess entropy is also given.