Volume 45, Issue 5

The fully developed decaying turbulence of 3-d resistive, viscous, incompressible magnetohydrodynamics is investigated using Elsasser variables and Hopf equation for probability distributions. The method is an extension of a previous work for Navier Stokes equations done by Foias et al. based on a suggestion by Hopf. It uses essentially self-similar properties of the statistics, which "almost" determine the turbulence spectrum up to a mild assumption on an unknown function. This spectrum is the well known Kolmogorov spectrum

For equilibria stable with respect to ideal ballooning modes it is shown by means of a simple argument that, owing to plasma compressibility, resistive ballooning modes with small growth rates can only exist if they are extended along a field line. In particular, a small region of bad curvature along a field line is not sufficient for the existence of unstable modes

A previous derivation of formulae for calculating the growth rate of resistive ballooning modes which are described by a simple model equation is extended here to a large class of general tokamak and stellarator equilibria

Based on the results of a foregoing paper (Z. Naturforsch. 44 a, 519 - 523 (1989)) the density-dependence of the discrete energy states and the continuum level is calculated with better accuracy. A static approximation to the line shifts is derived and discussed

Analytical expressions of absorption and fluorescence spectra of some coumarins in ethyl alcohol at room temperature are given. Satisfactory agreement of measured and calculated spectra is obtained. It was possible to obtain the pure electronic transition energies immediately after excitation (from absorption spectra) and after the thermal and orientational equilibrium is reached (from fluorescence). An optical transition carries a dye-solvent system to a state in which the mutual interaction energy is larger than in the initial state

The structure of molten NdClj at 800 CC has been investigated by X-ray scattering and the correlation method. The nearest neighbor distance and coordination number of Nd-Cl are 2.77 Ä and 5.5 A, respectively. The Nd-Nd and CI-CI distances are 5.08 and 4.04 Ä, respectively. The average nearest neighbor distance and coordination number decrease markedly on melting, and the resulting short range structure of the melt is approximately octahedral

Amorphous and quasicrystalline samples of Al 84 Mn 16 and Al 84 V 16 were produced by sputtering and melt-spinning, respectively. From X-ray and neutron-diffraction-results the total structure factors were evaluated. For amorphous as well as for quasicrystalline Al 84 V 16 the partial S Al-Al - and S Al-V -structure factors were obtained, which yield the corresponding partial pair correlation functions, the atomic distances, and the partial coordination numbers. Also some information concerning the partial Bhatia-Thornton correlation functions could be obtained. Both the amorphous and the quasicrystalline Al-V-alloys show a linear expansion by a factor of 1.03 compared to the corresponding Al-Mn-alloy. The two amorphous alloys can be designed as isomorphous, whereas the quasicrystalline ones show pronounced deviations in the distance between unequal atoms. The shortest atomic distance in amorphous Al 84 V 16 is 2.69 A, being,formed by Al-V-pairs with a coordination number 2. The nearest Al-Al-distance amounts to 2.84 A with a coordination number 8. The partial density-concentration correlation function clearly deviates from the hard sphere model. With the quasicrystalline specimens, the isomorphous substitution of Mn- and V-atoms is not perfect. The Al-V-correlation is split up, and this is not observed for the Al-Mn-correlation. Comparison of the amorphous and the corresponding quasicrystalline alloy shows some similarities

Electromagnetic fields in a periodically inhomogeneous chiral medium are examined. The constitutive properties of the chiral medium vary along the z axis, and reduced fields with prescribed x-variations are used. Coupled first-order differential equations are derived to describe the reduced fields. Two special cases -(i) piecewise constant inhomogeneity, and (ii) constant impedance inhomogeneity, - are discussed in detail, and solution procedures are provided

It is demonstrated that the cycle graphs corresponding to the carbon atom skeletons of cycloalkanes and annulenes are the only graphs having the same Z-counting and independence polynomials.

The reactions of CH 2 (ã 1 A 1 ) with the inert gases He, Ar, N 2 , with H 2 and with the hydrocarbon reactants CH 4 , C 2 H 6 , C 2 H 4 and C 6 H 6 have been investigated at 210, 295 and 475 K. CH 2 (ã 1 A 1 ) was generated by pulsed laser photolysis in a quasistatic thermostated gas cell and detected by pulsed laser induced fluorescence. Concentration profiles of CH 2 (ã 1 A 1 ) were recorded under first order reaction conditions by varying the time delay between the photolysis and the probe laser pulses. The second order rate constants determined at room temperature are in good agreement with those of earlier work. No differences between the removal rates of ortho-and para-methylene nuclear spin states by the inert gases were observed. The experimental rate constants were fitted to an expression k = A -(77295 K) n . The results are given in the form {A ± AΔA} {n ± Δn) with A in units of 10 13 cm 3 /mol • s:

The luminescence of BaCl 2 -Ga single crystals at temperatures down to liquid helium under excitation with different energies is studied. The emission consists of several bands, the intensities of which depend on the temperature and the exciting energy. The excitation spectra of the different emission bands measured at 4 K, 78 K and 293 K are also reported. The results indicate the coexistence of centres of different structure and composition. The Jahn- Teller effect might also take place

The quadrupole splitting patterns for 23 Na and 27 Al in NaAlCl 4 can very satisfactorily be reproduced by the distortions of their first coordination spheres, as shown by application of the superposition model. The same exponent of 7 for the dependence on bond lengths was used as previously found for NMR data of 9 Be, 23 Na, 25 Mg, 27 Al and 29 Si with oxygen as ligand. The intrinsic splitting parameters are in the same range, perhaps a little larger than for oxygen as ligand. Small deviations between observed and calculated splitting patterns just outside the limits of error of the crystal structure data may be due to influences of the lattice, especially in the case of 27 Al, for which the distortions are fairly small

A hierarchy of «-Tori is demonstrated numerically in volume-preserving (n + l)-dimensional invertible maps.

The luminescence of synthetic ZnS: V crystals is studied at low temperatures (T % 4 K). The emission spectra comprise (i) a structured band centred around v = 5600 cm -1 , assigned to 3 T 2 (F) ->• 3 A 2 (F) transitions of substitutional V 3+ (3d 2 ) ions in a tetrahedral field, and (ii) a band around 4800 cm -1 assigned to 4 T 2 (F) -> 4 T 1 (F) transitions of V 2+ (3d 3 ) ions. In the range of the narrow no-phonon lines detected with both these emission bands, a temperature rise from 2 to 5 K entails a thermalisation in the population of the spin-orbit multiplets forming the initial states of the corresponding transitions. A third emission band near 3800 cm -1 grows after annealing the crystals in Zn vapour. It is tentatively attributed to 5 E(D) -> 5 T 2 (D) transitions of V + (3d 4 ). A model of one-electron states represents donor-type as well as acceptor-type changes of the vanadium oxidation states, commencing from V 2+ , the state with neutral effective charge. The model is substantially founded on the measured excitation spectra of the V 3+ and V 2+ emission bands, supplemented by transmission spectra. Besides the corresponding broad charge transfer bands, the spectra display a number of structures which are associated with excited states of the ions. These energy levels are approximated in a computation following the strong-field Tanabe-Sugano scheme but in addition allowing for different radial extensions of e- and t 2 -type wave functions. The method used also includes the possibility of fitting the free-ion levels. Various sets of numerical values are eventually obtained for the crystal-field splitting and the Racah parameters. Some of the levels involved are found to be subject to Jahn-Teller interaction.

A practical version of a homodyne method for measuring the complex permittivity of high loss liquids at 3 and 9 GHz is described. The systematic errors are discussed in detail, because the homodyne method seems to be suitable as a simple standard method for precise measurements. The results of measurements on water in the temperature range 6 °C-45 °C are presented. The determination of all five parameters of the Debye function is possible. Finally, accuracy limiting factors for the determination of the relaxation parameters are discussed in detail

The role of electrostatic and packing contributions to the structure of water and aqueous electrolyte solutions has been investigated by the comparison of results of Molecular Dynamics simulations with those of analytical calculations for the corresponding Lennard-Jones systems. It is demonstrated that the electrostatic interactions play a dominant role in determining the characteristic data of the various radial distribution functions in the solutions, although their relative importance decreases with increasing pressure, temperature, and ionic concentration. It is proposed that for the analytical treatment of hydrogen bonded liquids the total potential should be subdivided into three regions - short range repulsion, potential minimum, long range electrostatic interactions - and a different theoretical approach should be employed for each region

Photoelectrochemical cells (PECs), composed of different epitaxial n-Si photoanodes coated with evaporated metal film of Ni, Pt, Ni/Pt and immersed in solution with redox couple Br 2 /Br - or Fe(NC) 3 6 Fe(CN) 4 6 - were investigated. The open circuit photovoltage and short circuit curent density of these PECs under optimum conditions by illuminating with a bromine-tungsten lamp (65 mW/cm 2 ), are 0.494 V and 45.8 mA/cm 2 , respectively. By using a p/n + junction for the epitaxial silicon and the Schottky barrier effect formed at the silicon-metal interface, a much higher conversion efficiency of optical to electrical energy up to 12.3% could be achieved

We report the analysis of the rotational spectrum of dimethylether measured between 60 and 400 GHz. Rotational and quartic centrifugal distortion constants are given. Internal rotation splittings are analysed with the I AM method. The value of is compared to the values obtained for similar molecules

Two-dimensional (2 D) correlation techniques in microwave Fourier transform spectroscopy have been extended to study triple resonance phenomena. Dipole-forbidden double- and triple-quantum transitions have been observed with a five-pulse sequence. The introduction of a phase cycle acting as a triple-quantum filter has simplified the recorded spectra. Experimental results on trifluoromethylacetylene are given as an example

We report the design and performance of an improved version of a microwave Fourier transform spectrometer in the frequency region between 26 and 40 GHz for the investigation of rotational spectra. The performance is illustrated by rotational transitions of allene-d4 and isotopomers of carbonyl sulfide in natural abundance. The high sensitivity of the spectrometer allows the measurement of very weak lines in only a few minutes

The ground stafe microwave spectrum of isopropyl iodide has been investigated by microwave Fourier transform (MWFT) spectroscopy. 212 hyperfine components of 39 mainly a-type transitions have been assigned from the measured spectra in the frequency range between 4 and 30 GHz. With a MWFT double resonance modulation (MWFTDR) spectrometer a weak c-type transition and a "forbidden" ΔJ = 2 line could be observed. The spectra were analysed using a diagonalization procedure of the complete Hamiltonian matrix and a simultaneous least squares fit of the rotational, quartic centrifugal distortion and the iodine quadrupole and spin rotation coupling constants directly to the measured frequencies. A set of 14 constants could be obtained with high accuracy. The rotational constant A and some of the centrifugal distortion constants could be improved using some large higher order quadrupole perturbations and the results of the MWFTDR measurements for the analysis.

Design and performance of a microwave Fourier transform spectrometer in the frequency region around 8 GHz are reported. Operation and experimental set-up are simplified compared to previous designs.

The luminescence of hexabenzo [be,ef,hi,kl,no,qr] coronene (I) has been studied in a perhydrocoronene matrix at temperatures from 77 to 353 K. I exhibits phosphorescence and prompt and E-type delayed fluorescence. The phosphorescence transition is symmetry-forbidden. The luminescence behaviour of I is closely related to that of coronene (II)

MINDO-forces calculations are performed, with complete optimization of geometries, on α-Xcyclopropylcations, where X is CF 3 , CF 2 H, and CFH 2 . It was found that the fluorine atom interacts with the localized empty Pπ-type orbital on α-carbon atom and forms a bridge with an angle 57.1 degree. Calculations also are performed on CF 3 -cyclopropyl anion and CF 2 H-cyclopropenyl cation. The fluorine atom in CF 3 and CF 2 H shows no such interaction with the a-carbon atom because there is no localized empty Prc-type orbital

17 O nuclear quadrupole resonance spectra have been measured in an 17 O enriched polycristalline sample of DL-proline with the help of 1 H - 17 O nuclear quadrupole double resonance technique. The results show the presence of eight chemically inequivalent oxygen sites corresponding to four inequivalent proline molecules in the unit cell. The oxygen sites may be grouped into two sets of four sites. One set with the short proton-oxygen distances belongs to the C - O • • • H groups whereas the other with the long proton-oxygen distances to the C = O groups

The generalized Galilei covariant Maxwell equations and their EM field transformations are applied to the vacuum electrodynamics of a charged particle moving with an arbitrary velocity v in an inertial frame with EM carrier (ether) of velocity w. In accordance with the Galilean relativity principle, all velocities have absolute meaning (relative to the ether frame with isotropic light propagation), and the relative velocity of two bodies is defined by the linear relation uG = v 1 - v 2 . It is shown that the electric equipotential surfaces of a charged particle are compressed in the direction parallel to its relative velocity v - w (mechanism for physical length contraction of bodies). The magnetic field H(r, t) excited in the ether by a charge e moving uniformly with velocity v is related to its electric field E(r, t) by the equation H=ε 0 (v - w)xE/[ 1 +w • (t>- w)/c 2 0 ], which shows that (i) a magnetic field is excited only if the charge moves relative to the ether, and (ii) the magnetic field is weak if v - w is not comparable to the velocity of light c0 . It is remarkable that a charged particle can excite EM shock waves in the ether if |i> - w\ > c0. This condition is realizable for anti-parallel charge and ether velocities if |v-w| > c 0 - | w|, i.e., even if |v| is subluminal. The possibility of this Cerenkov effect in the ether is discussed for terrestrial and galactic situations

By means of the generalized Galilei covariant EM field equations, the EM potentials and EM fields of a charged particle moving with an arbitrary nonuniform velocity v(t) in an inertial frame with substratum flow w are calculated. It is shown that the dynamic EM fields are excitations of the EM ether caused by the motion v(t) - w of the charge relative to the wave carrier with velocity w. Qualitatively and quantitatively significant EM inductions and convective deformations of EM fields by the ether flow w exist in inertial frames with ether velocities w~c0 comparable to the velocity of light. For many terrestrial applications, the ordinary Maxwell equations agree in good approximation with the Galilei covariant EM field equations since w/c 0 ~ 10 -3 on the earth

It is suggested that the evidence for the putative phenomenon of cold fusion is valid, but that the effect is not dominated by a DD reaction.

If the amount of heat reported by Fleischmann and Pons to occur in their electrochemical "fusion" experiment is assumed to be produced entirely by the "clean" nuclear reaction 6 Li + 2 D → 2 d He (22.4 MeV), then the concentration of 6Li in the reaction fluid should during a period of 120 hours go down by a measurable amount, namely between 3.4 and 0.25 percent dependent on whether the natural isotopic mixture of (less likely) pure 6 Li was used in the experiment

The dynamical nature of the cold fusion problem is considered. A general model of two slow charged particles interacting in a metal crystal is developed. It is shown that there exists a resonance state of this system. The value of the positive real resonance energy depends on the properties of the metal crystal. An estimate of the probability of cold nuclear fusion in condensed matter is given