Band 31, Heft 7

A rigorous non-existence proof for runaway solutions in the finite-size model of the electron is given. Since a consistent point limit, such as the Lorentz-Dirac equation claims to be, should not exhibit features which are completely missing in the more general theory of finite extension, it is proposed that the point-like approximation of the finite-size theory be the integrodifferential formulation of the Lorentz-Dirac theory. This point of view is supported by a new discussion of the hyperbolic motion in the latter theory.

The classification of states in the fermion-fermion Bethe-Salpeter equation is discussed. They are related to the states in the fermion-antifermion case discussed before. This enables us to obtain restrictions on the interaction in quark models. Some models used in the literature are thereby found to lead to unphysical predictions.

Nuclear magnetic and dielectric relaxation formulas are given for a model of limited diffusion of defects. The limitation is introduced by the assumption of fixed reflecting barriers on both sides of the defect. The diffusion process is assumed to be one-dimensional and continuous. The effect of the finite length of the defects is included in the presented treatment.

A single picosecond pulse from a mode-locked dye laser was used for time resolved microphotography of the gasdynamic phenomena occurring in a lasertarget interaction experiment. A time resolution of 5 ps and a spatial resolution of better than 10 μm were experimentally obtained. Results are presented for the case of laser irradiation of a thin foil, shock wave propagation in a transparent target, expansion of the hot plasma and blast wave formation in a background gas.

The intensity and polarization state of the NaD 2 -fluorescence (3 2 P 3/2 →3 2 S 1/2 , λ 5890 Å) from a cell containing pure Na vapor, selectively excited by a flash lamp pumped dye laser was investigated. Measurements were performed both for excitation with π-and σ-light of spectral density ranging between 10 -23 and 10 -17 Ws 2 cm -3 and with Na number densities between 2.8 X10 9 and 4.0 X 10 10 cm -3 . The results are interpreted in terms of population of the 2 P 3/2 state and of hyperfine and Zeeman pumping of the 2 S 1/2 substates. The values for the degree of linear polarization measured at the smallest excitation densities and Na pressures agree well with theoretical values.

Liquid alloys of the Bi-Sn system have been studied to determine thermodynamic properties. Ion currents have been measured by a double-focusing mass spectrometer. The thermodynamic values were calculated by application of the monomer-dimer ratio technique and the integration technique. Special attention was paid to the correction of fragmentation effects. Activities of both components versus composition in the temperature range from 1023K to 1323K and values of Gibbs energies and heats of mixing are reported as results. At 1200K the species Bi 2 , Bi 3 , Bi 4 , BiSn, and Bi 2 Sn were observed in the gaseous phase above the Bi 50 Sn 50 alloy. The discussion shows a tendency to segregation of the liquid Bi-Sn alloys.

The axial population distributions in an expanding helium-neon mixture plasma flow have been calculated for three cases of the concentration of neon ions. The results show that the electron temperature distributions are strongly dependent on the concentration of the neon ions and that the populations of the upper levels of the helium atom depend on the electron temperature near downstream and on the flow expansion far downstream.

An approximate analytical method that is valid for the entire propagation regime of a blast wave is established for point explosions. The method is based on an application of the shock ex-pansion method to boundary conditions. The numerical calculations were carried out for spherical flows with constant adiabatic exponent. The results show that the value of the shock decay coefficient gives good agreement with the numerically exact solution by Goldstine and von Neumann. The profiles of the pressure, density, and particle velocity behind the shock were obtained. The solutions show the possible profiles as compared to other existing analyses.

The stress and temperature dependence of the activation volume is often explained by a similar dependence of the measured stress sensitivity. This explanation cannot be reconciled with the nonconservative motion of jogs, with dislocation climb, nor with the intersection mechanism. It is in contradiction with the results obtained in direct dislocation velocity measurements as well. It is now shown that when the backward movement of the dislocations is taken into consideration an explanation, consistent with the rate theory and with the dislocation mobility observations, can be developed. The analysis shows that with constant activation volume the stress sensitivity is stress and temperature dependent, in agreement with the corresponding measurements and mechanisms.

The general reaction X+Y→P+Q, catalyzed by a metal M via M+X⇄MX and MX+Y→M+P+Q (or, in another subcase, MX+Y⇄MXY→M+P+Q) renders a chemical oscillator, if in an open system X and Y are supplied from appropriate sources by influxes j 1 and j 2 , respectively, if X shows substrate inhibition by subtracting active catalyst by forming an inert complex MX 2 , and if at least X is limited by an additional first order side reaction. Introduction of dimensionless variables and parameters and assumption of a partial steady state for the catalyst compounds, the sum of wbich is constant, leads to 5 (or 6) parameters, 3 of which can be easily adjusted in a wide range. It is shown that for any given values of the 2 (or 3) fixed parameters the adjustable ones can in principle be chosen in such a way that the conditions for oscillation are met. This type of oscillator is thus a parametrically universal one. By appropriate choice of the adjustable parameters the yield of products can be conducted in bursts instead of a continuous flow. Another possibility is an excitable system that fires only on triggering. Proposals toward chemical realization are discussed especially with respect to transition metal complexes.

Laser-induced fluorescence has been used to investigate the reorientation of the molecular angular momentum due to inelastic collisions with atoms. We report on experiments for the Li 2 ( 1 IIu)-rare gas system, where the degree of polarisation of the emitted fluorescence has been measured. Within the framework of a classical theory mean angles for reorientation have been derived. Their dependence on the collision partner and the initial and final angular momentum is discussed.

The influence of ethylhalogenes on the polarization of the phosphorescence of naphthalene was studied by means of the photoselection technique. It is shown that with increasing concentration and with increasing nuclear charge of the heavy atom the phosphorescence of naphthalene becomes increasingly depolarized. The influence of the external heavy atom on the T x- and T z- substate is stronger than on the Ty-substate. From the concentration dependence of the depolarizatign conclusions concerning the mechanism of the external spin-orbit-coupling are drawn. The dirept spin-orbit-coupling mechanism is ruled out. In the model discussed the variation of the external heavy atom effect with the intermolecular distance is related to overlap integrals.

A new sample preparation method for eliminating the hydrogen impermeable oxide surface layers of base metals like V, Nb and Ta is described. Applying UHV-techniques the metal foils are heated inductively and subsequently coated with a thin metallic Pd-film. By this method the metals are cleaned, at the same time annealed, and protected successfully against the formation of new passive layers, as is shown by x-rays, SIMS, and AES investigations.

After suitable preparation (improvement) of samples H (D) -diffusion coefficients of V-, Nb-, and Ta-foils can be measured reliably at low H (D) -concentrations in the temperature range 0 to 100 °C by means of an electrochemical time-lag method. A modified strain model indicates that the tetrahedral sites in bcc lattices have to be taken as the stable positions for the dissolved hydrogen. The elementary jump in the diffusion process from one tetrahedral site to the next passes directly through a tetrahedral plane. This model describes qualitatively the experimental results concerning the sequence of the activation energies for hydrogen diffusion in the three Vb-metals [E(Ta)>E(Nb)>E(V)].

From the Tait equation an equation of state containing five adjustable parameters was developed which fits experimental density data of molten potassium chloride to 1320 K and 6 kbar with a standard deviation of 0.04%. The thermal expansion coefficient, isothermal compressibility, internal pressure, and molar heat capacities at constant pressure and constant volume were calculated as functions of pressure and temperature from the equation of state and were compared with computer simulation results. A method for an estimate of high-pressure PVT data for molten salts is suggested which yields results superior to the best computed data presently available.

The electric conductivity of the homogeneous liquid Bi-Hgl 2 system was measured in the temperature range 260-540 °C for several Bi mole fractions ranging from 0.00 to 0.38. The specific conductivity-composition isotherms are indicative of the occurrence of electronic conductivity also before reaching a bismuth concentration sufficient for a complete conversion of HgI 2 into Hg 2 I 2 · As the temperature rises the share of electronic conductivity in the total conductivity abruptly increases. Comparing the properties of this system with those of the BiI 3 -Bi system the conclusion is drawn that electronic conductivity in liquids is due to free metal atoms.

Electronic overlap population is explored as a reactivity measure for several bond cleavage and bond formation processes. The reactions considered include: I. decarboxylation of carboxylic acids and of their anions; II. carbon-hydrogen bond cleavage in γ-radiolysis of glutaric, methyl-malonic and 3-hexendioic acids; and, III. hydrogen atom addition to butadiene and to sorbic acid.

The mesomorphic behavior of N-(4-n-alkylbenzylidene)-4′-n-alkylanilines is investigated and nematic as well as smectic-B phases are found at comparatively low temperatures. Long aliphatic substituents on the aldehyde side of the molecule favor the smectic-B phase. Observations on smectic-B textures, transition enthalpies and density measurements are reported. The simple method used to determine transition temperatures despite impure samples can also be applied to other compounds, e. g. yielding 21.6 - 47.5 °C for the nematic range of MBBA.

The existence of a linear relationship the form Y=a x 1 +b x 2 +c between the charge density - calculated by semiempirical SCF -LCAO -MO-methods - and the 13 C -chemical shifts of mesoionic compounds has been shown. An influence of substituents in pyridinium betaines on the chemical shift is not observable.

The specific conductivities and densities of molten LiCl, LiBr and Lil have been investigated as a function of temperature. A comparison between the data in literature and the present data has been made and the reliability of the different data is discussed.

A two-dimensional Poiseuille flow in a radial direction allows to study simultaneously a whole range of flow rates. Three different deformation modes of the director field have been observed, the 'bow' mode, the 'screw' mode, and the 'peak' mode. Above a critical flow rate the bow mode transforms into the screw mode. Right and left screw mode can be produced side by side. The peak mode reached by temporary high flow rates is metastable at low flow rates. Quantitative results are reported and discussed. By reversing the flow direction in the screw mode region the left screw mode is transformed into the right screw mode and vice versa. By reversing the flow direction in the peak mode region special tube-like deformation structures are obtained. Each open tube has a point disclination at either end. Both are of opposite strength ± 1.

The scattering of a polarized photon by a polarized free electron is completely calculated in covariant form using Clifford's alternating vector algebra. The result is compared with several special results of the existing literature.

The starting-point of this paper are generalized Nernst Planck equations, which are deduced microscopically. Using a perturbation approach a result of this equation is given for a constant external field and a membran, which has a low concentration of fixed charges. The used conditions give a zeroth approximation which describes the homogeneous electrolyte. The first approximation shows the influence of the fixed charges, the friction between ions and membran and the influence of the correlations. The flows and the concentrations are then calculated for a system with equal concentrations on both sides of the membran.

In Part I 1 of this series we presented the notion of the material hypermomentum current and motivated its introduction into general relativity. In Part II 2 we showed that a general, linearly connected manifold with symmetric metric (L 4 , g) is the appropriate geometrical framework for such an introduction. The present paper completes the picture by giving dynamical definitions for energy-momentum and hypermomentum for a minimally coupled material Lagrangian. We derive and discuss the field equations of a new metricaffine gravitational theory which embodies these notions.

The enthalpy ΔH of general displacement reactions AB + CD AD + CB is derived with the aid of the ionic approximation to chemical bonding. This enthalpy compares favourably well with Pauling's corresponding equation ΔH= - 46 (x B - x D ) (x A - x C )-These ex-pressions are used as a basis to discuss various aspects of chemical reactivity: reversals in reactivity, ambident reactivity, the Hammett relation, the McDaniel-Yingst equation, the Drago E -C equation, the resolution of acid strength, the proton affinities of negative and neutral species and the hard and soft acid-base (HSAB) rule. Qualitatively, and in some cases even quantitatively, reasonable results are obtained, demonstrating the great flexibility of an electronegativity-based theory of chemical reactivity.

The microwave spectra of acetyl cyanide, CH 3 COCN, in the ground and in the two lowest excited states have been investigated. The rotational constants and the quadrupole coupling constants have been evaluated for all these states. The internal rotation parameters have been refined with respect to previous works. Evidence for a rotation-torsion -vibration interaction has been found in the spectra of the excited states.

Force constants and normal coordinates of MnS 2 , FeS 2 , RuS 2 , RuSe 2 , RuTe 2 , OsS 2 and PtP 2 are calculated based on the five ir active vibrations of the pyrite lattice. By setting up a valence force field consisting of short and long range M -X, X 2 -X 2 and M -M stretching constants it has proved possible to obtain good agreement between experimental and calculated frequencies with expection of FeS 2 and RuS 2 . The force constants corresponding to the shortest metal chalcogen distances (MnS 2 : 0.30, RuSe 2 : 0.88, RuTe 2 : 0.62, OsS 2 : 1.32, PtP 2 : 1.22 mdyn/Å) are mainly responsible for the ir frequencies. For RuSe 2 and RuTe 2 , the forces between adjacent X 2 groups are not negligible. Whereas the force constants of OsS 2 and PtP 2 are of comparable strength, the forces in MnS 2 are significantly weaker than those in the other compounds. The normal coordinates of MnS 2 , OsS 2 and PtP 2 , and RuSe 2 and RuTe 2 show significant differences according to both the contribution of the 6 symmetry coordinates to the 5 ir active vibrations and the assignment of the spectra.

A new model for the oriented adsorption of benzene molecules on graphitized carbon black at low temperatures is proposed which explains NMR relaxation data.

14 C in the Atmosphere from 1952 to 1971 According to Measurements of Wine Ethanol Previous measurements of 14 C in German wines (vintages 1952 — 1967) have been extended up to 1971 and are supple-mented by a series of samples from the southern hemisphere.

Since the first electron spectroscopic (ESCA) studies dealing with substituents effects upon core ionization energies (I.E.) of organic compounds 1 , little has been published on the subject. This was probably because the reported data did not always seem very meaningful. The absolute I.E. values obtainable in the solid phase are not very certain and also, the "shake-up" phenomena and the consequent broadening of the bands, which affect the I.E. values 2 , were not always taken into account. None the less we think that ESCA is a valuable tool for the study of substituent effects, and in particular of the transmission of electronic effects in aromatic systems. Previous work in this area has been published 2,3 , and more specifically an example of steric inhibition of resonance observed by means of ESCA I.E.'s and shake up data was recently reported 4 . Here we would like to report a further case in which the transmission of electronic effects through an aromatic ring is observed using ESCA.

The preparation starts from material in wire-form. One end of the wire is degassed under ultrahigh-vacuum conditions by a very simple electron-gun and finally melted to form a small smooth sphere. The tunneling barrier is formed by thermal oxidation of the investigated superconductor with oxygen under reduced pressure. The handling of the whole sample (masking and contacting procedures included) is very simple and allows to use this method for systematic tunneling-studies of the transition metal superconductors.