Band 44, Heft 11

The validity of macroscopic models in the limit of large mean-free path is examined by solving a one-dimensional model equation, where the term v Vf 1 is retained in the kinetic equation. A standard thirteen-moments approximation yields accurate results in all collisionality regimes if the fluid velocity is sufficiently small. In contrast, the Chapman-Enskog scheme is only accurate in the collision-dominated regime

It is shown that a small anisotropy of the magnetic diffusivity tensor admits stationary axisymmetric solutions of the kinetic dynamo problem. For the case of a large aspect ratio the solutions can be expressed explicitly in terms of elementary functions

We study the cooperative spatio-temporal behavior of semiconductor breakdown via both probabilistic and dynamical characterization methods (fractal dimensions, entropies, Lyapunov exponents, and the corresponding scaling functions). Agreement between the results obtained from the different numerical concepts (e.g., verification of the Kaplan-Yorke conjecture and the Newhouse- Ruelle-Takens theorem) gives a self-consistent picture of the physical situation investigated. As a consequence, the affirmed chaotic hierarchy of generalized horseshoe-type strange attractors may be ascribed to weak nonlinear coupling between competing localized oscillation centers intrinsic to the present semiconductor system

A recently advanced theory of quantum electrodynamics which is not second quantized, but rather based on self-fields is adopted to a relativistic calculation of (g-2). In analogy to classical electrodynamics, radiative corrections are seen as arising from the back reaction of the self-field upon the source. Vacuum field fluctuations, assumed to be the physical cause of radiative correction in standard QED. are absent in the present self-field approach, which recently has been applied to calculate spontaneous emission, Lamb shift, vacuum polarization, and to a non-relativistic calculation of (g-2), all in free space as well as in cavities. We conclude that the self-field of the electron can be consistently considered to be the physical origin of all radiative processes, as an alternative picture to hypothetical vacuum fluctuations

The polarized optical absorption and emission (spectra, decay times) of single-crystal [lr(CO) 2 mnt] TBA at temperatures 2 K≦T≤295 K and homogeneous magnetic fields O≦H≦6T are reported. The highly resolved spectra show 0-0 transitions with vibrational satellites and phonon side bands. Applied magnetic fields yield no effect on the emission. The lowest excited electronic states can be assigned to the spin-orbit components A′ 1 B′ 1 and B′ 1 of the charge transfer triplet 3 A 2 (symmetry C 2v )

The rotational Zeeman effect has been observed in methanimine which was produced from ethylenediamine by flash pyrolysis. The observed vibronic ground state expectation values of the molecular g-values, the magnetic susceptibility anisotropies and the molecular electric quadrupole moments are: g aa = -1.27099(22), g bb = -0.18975(7), g cc = -0.03440(8), 2ξ aa -ξ bb -ξ cc = 12.49(19) · 10 -6 ergG -2 mol -1 , 2ξ bb -ξ cc -ξ aa = 5.22(11) · 10 -6 ergG -2 mol -1 Q aa = 0.43(17) · 10 -26 esu cm 2 , Q bb = 1.08(10) · 10 -26 esu cm 2 , and Q cc = -1.51 (26) . 10 -26 esu cm 2 . With the TZVP ab initio value for the out-off plane electronic second moment as additional input, reliable values can be given also for the individual components of the magnetic susceptibility tensor and for the bulk susceptibility: ξ = (ξ aa + ξ bb + ξ cc )/3=-13.13(88) · 10 -6 erg G -2 mol -1 . From low-J a-and b-type zero field transitions the spin-rotation coupling constants and the 14 N nuclear quadrupole coupling constants could be redetermined with improved accuracy. These data are compared with our new theoretical results.

Microwave Fourier transform spectra have been measured for hydrazoic acid as its normal isotopomer, H 14 N 3 , and two substituted isotopomers, H 15 N 14 N 14 N and H 14 N 14 N 15 N. The 14 N quadrupole hyperfine structure has been resolved in all cases, and the quadrupole coupling constants of all 14 N atoms have been determined. They are compared with those from ab initio predictions. Rotational constants A have been evaluated accurately for the first time for the two 15 N species, and have been used to confirm a previously published structure

The high field molecular Zeeman effect of low-J rotational transitions has been observed in methyl nitrate. The spectrum is complicated by the presence of the small 14 N nuclear quadrupole coupling. Methyl top internal rotating splitting is negligible in the transitions studied here. From line shape analyses the individual satellite frequencies in the Zeeman-hfs-multiplets could be determined with experimental uncertainties typically smaller than ±2 kHz. The molecular Zeeman parameters and the 14 N nitrogen coupling constants were fitted simultaneously to the observed splittings. The molecular g-values are g aa = -0.1168(5), g bb = -0.0449(3), and g cc = -0.0235(4). The molecular magnetic susceptibility anisotropies in units of 10 -6 erg gauss -2 mol -1 are 2ξ aa -ξ bb -ξ cc = +1.24(54) and 2ξ bb - ξ cc - ξ aa = +13.14(53). The 14 N nuclear quadrupole coupling constants are χaa - + 0.308(17) MHz, χ bb - χ cc -0.262(31) MHz. The molecular electric quadrupole moments calculated from the observed rotational constants and Zeeman parameters in units of 10 -26 esu cm 2 are Q aa = +3.4(6), Q bb = -4.6(6), and Q cc = +1.2(10). Knowledge of the molecular structure and the molecular g-values also gives the diagonal elements in the paramagnetic susceptibility tensor and the ansiotropies in the second moments of the electronic charge distribution. The results in units of 10 -6 era gauss -2 mole -1 are ξ p aa = + 118.14(10), ξ p bb = +279.73(14), and ξ p cc = + 357.40(26), and ⟨a 2 ⟩ - ⟨b 2 ⟩ = + 37.14(14) Å 2 , ⟨b 2 ⟩ - ⟨c 2 ⟩ = +20.46(22) Å 2 , and ⟨c 2 ⟩ -⟨a 2 ⟩ = -57.60(21) Å 2

A semilattice defined by Ohkami et al. on the set of the Kukulé structures of a benzenoid hydrocarbon is examined and some of its properties are pointed out

Dielectric, DSC and preliminary X-ray diffraction studies on [(C 2 H 5 ) 4 N] 3 Sb 2 Br 9 (TEABA) and [(C 2 H 5 ) 4 N] 3 Bi 2 Br 9 (TEABB) are reported. The compounds are isomorphous, space group P6 3 22. The static electric permittivity measurements on single crystals in the temperature range 220 - 290 K revealed that both compounds show two distinct dielectric anomalies; TEABA at T c1 = 258 K and T c2 = 252 K, while TEABB at T c1 = 265 K and T c2 = 248 K. The DSC studies show only one anomaly of first order at T c1 =258 K for TEABA, and T c1 =266 K for TEABB. These transitions are presumably related to a freezing of the reorientational motion of the tetraethylammonium cations

We investigate the dynamics of a reaction-diffusion-convection enzyme system as a function of relevant parameters and observe reproducible types of periodic and aperiodic oscillations. These oscillations arise within a narrow diffusion layer only. Some implications for more complex reaction networks are considered

For crystals of pyridinium dichloroiodate (I), (pyH)ICl 2 , the temperature dependences of the 1 H NMR spin-lattice relaxation time T 1 and the 1 H second moment M 2 were determined. M 2 was found to be small ( ~ 1 G 2 ) above room temperature, indicating that the cations perform rapid reorientational motion about their pseudohexad axis perpendicular to the cationic plane. 1 H T 1 at its minimum was unusually long, indicating this motion occurring in the low symmetry local environments. Phase transitions between stable solid phases were revealed at 282 and 373 K by the 1 H NMR measurements and differential thermal analysis. The highest-temperature phase was easily supercooled and transformed reversibly into another metastable phase and back on cooling and warming at almost the same temperature of 138 K. The kinetics of the phase transition from the supercooled to the stable phase at room temperature was analyzed using an Avrami type relation. The growth time of the stable phase was estimated to be about 14 h at room temperature

Fluorescence and phosphorescence properties of dibenzo [2,3:10,11] perylo [1,12-bcd] furan (1), dibenzo [2,3:10,11] perylo [1,12-bcd] thiophene (2), and dibenzo [2,3:10,11 ] perylo [1,12-bcd] selenophene (3) have been studied. Fluorescence quantum yields as well as phosphorescence lifetimes correlate linearly with where c k are the Hückel AO coefficients in the HOMO of the parent carbocyclic system dibenzo [b, n] perylene (4) on carbon centres k to which the hetero-atom is bound, and ζ is the spin-orbit coupling constant of the heavy-atom present. The half-value concentration of fluorescence quenching (quencher: methyl iodide) of 1 - 3 increases with increasing strength of the internal heavy-atom effect present

The rate of the reaction between naphthalene and atomic oxygen in the electronic ground state was determined in a discharge flow system with mass spectrometric detection for temperatures between 362 and 773 K. All measurements were performed in an excess of O atoms over hydrocarbon. The second order rate constant was determined to be Kinetic data are compared with data about the reactions of other aromatic substances and atomic oxygen in the ground state. Some possible reaction channels are discussed

The temperature dependences of the 1 H spin-lattice relaxation time T 1 , the linewidth parameter T 2 *. and the second moment M 2 of 1 H NMR absorption were measured for solid (CH 3 NH 3 )PbX 3 (X: CI. Br). In the room-temperature cubic phases of both salts, and also in the high-temperature tetragonal phase of (CH 3 NH 3 )PbBr 3 , the cations undergo rapid overall rotation or reorientation. In the lowest-temperature phase of both salts the orientation of the cations is fixed but rapid C 3 reorientation of the CH 3 and NH + 3 groups of the cations about their C - N bond axes takes place. From the M 2 measurements, a precessional motion of the cations in the intermediate-temperature phase of both complexes is suggested. Above room temperature, 1 H T 1 of both salts can be explained by assuming spin-rotational relaxation operative due to the rapid rotation of the cations. An anomalous behavior of 1 H T 1 , attributable to cross relaxation between 1 H and 81 Br nuclei, was detected for (CH 3 NH 3 ) PbBr 3 when T 1 was measured at 42 MHz

Liquid crystalline norcholesteryl anisic esters were prepared in which the methylgroups 19, 21, 27, and 18 are removed successively from the cholestene skeleton. The influence of the axial methylgroups on the phase transition temperatures and the choleric helical structure has been investigated. On heating the 18.19.21.27-tetranorcholesteryl ester, at 155 °C an inversion of the helical screw sense from left to right was observed

Molecular dynamics (MD) simulation has been performed on molten (Li, Na, K)Cl of nearly the eutectic composition at 773 K, 873 K and 973 K. The employed pair potential parameters are based on the Tosi-Fumi ones except the softness parameter, which is somewhat modified. The self-exchange velocities (SEV’s) of Li + , Na + and K + with reference to CP have been calculated. The sequence of the internal mobilities of these cations is well reproduced by the corresponding SEV’s, v; that is V Li < V k < V Na at 773 K, V Li < V Na ≅ V K at 873 K and V Li < V Na < V K at 973 K

The Schrödinger equation has been solved by \/N expan­ sion for a two nucleon system which interacts by an attrac­ tive Yukawa potential. For the ground and first excited states, energy eigenvalues have been obtained.