Volume 44, Issue 12

The linear correlation factor of spatially coupled nonlinear self-generated oscillations in the post-breakdown regime of p-Gc at 4.2 K is investigated. The observed results can be consistently explained in terms of a two-cell model of energy relaxation oscillations, which yields resonance transitions between correlated and anticorrelated oscillations. These are due to node-focus transitions of the fixed point of the passive cell which is slaved by the active cell.

It is shown that a substratum interpretation reveals a close relationship between the Sagnac- and the Aharonov-Bohm-effect. The characteristic peculiarity of the Aharonov-Bohm-effect, to produce a phase shift of the electron wave function even in the absence of any electromagnetic force fields, can be duplicated by a thought experiment for light waves in the gravitational field of a massive rotating cylinder, which demonstrates that the somewhat similar Sagnac-effect is not caused by centrifugal and Corioli’s forces, as it is sometimes claimed. In the substratum interpretation, both the Sagnac and Aharonov-Bohm effect find their explanation in a rotational motion of the substratum. If the substratum flow is irrotational, having the form of a potential vortex, these effects persist even though there are no force fields present.

Magnetic field inhomogeneities cause blurring and distortion of images gained by nuclear magnetic resonance. In order to adjust the magnetic coils finely, a precise and rapid method for measuring the magnetic field is needed. We describe a gradient echo technique of the FLASH version for mapping static magnetic fields.

The spinning motion of aspherical satellites whose center of mass moves in a given elliptic polar orbit around an oblate central body is investigated using analytical and numerical methods. In the case of a magnetic satellite, dipole-dipole interaction with the central body is included. For small eccentricity, oblateness and magnetic interaction, the Melnikov method is used to study chaotic and perodic motions. The parameter dependence of the width of the chaotic layer and of the periodic resonances is discussed. For some selected parameter values the theoretical predictions are checked by numerical methods.

The effect of substituents R (R=N(CH 3 ) 2 , OCH 3 , CH 3 , H, Cl, Br, CN) on the polarity of trans-styryl-methyl-sulfones in the first excited singlet state is investigated. Linear relations are found between the dipole moment in the excited state, μ e , and the Hammett constant, σ p + , and also between μ e and the dipole moment in the ground state, μ g . On increasing the electron-donor power of R, μ e grows faster than μ g .

Electrical resistivity measurements were carried out on polycrystalline YBa 2 Cu 3 O 7-x at temperatures 300 < T < 1023 K and oxygen partial pressures 5 ·10 -7 ≤ po 2 ≤ 1 atm. The samples, equilibrated in the range from 5 ·10 -4 to 1 atm, show metallic behaviour, the one equilibrated at po 2 = 2 ·10 -5 shows a transition between metallic and semiconducting behaviour at 920 K, and that equilibrated at po 2 = 5 ·10 -7 shows semiconducting behaviour: for the latter the relevant resistivity is due to the oxygen-ion migration. The isotherms log σ vs. log po 2 (in the temperature range from 723 to 1023 K) show slopes of about 1/6 at 723 K (orthorhombic phase) and about 1/2 at 1023 K (tetragonal phase). These results are discussed in terms of appropriate defect models.

A new evaluation of DSC-curves of binary mixtures is given. By analyzing the phase diagrams of methyltrichlorosilane and dimethyldichlorosilane with some lutidines the existence of the incongruently melting addition compounds MeSiCl 3 · (2.3-Lutidine)-,, MeSiCl 3 · 2.3-Lutidine, (MeSiCl 3 ) 2 · 3.4-Lutidine, Me,SiCl 2 · (2.3-Lutidine) 2 , Me 2 SiCl 2 · (2.5-Lutidine),, Me 2 SiCl 2 · 2.5-Lutidine, Me 2 SiCl 2 · (2.6-Lutidine) 2 , Me 2 SiCl 2 · 2.6-Lutidine, Me 2 SiCl 2 · (3.4-Lutidine) 2 , Me,SiCl 2 · 3.4-Lutidine, (Me 2 SiCl 2 ) 2 · 3.4-Lutidine, Me 2 SiCl 2 · (3.5-Lutidine) 2 , Me 2 SiCl 2 · 3.5-Lutidine, and the congruently melting compound MeSiCl 3 ·(3.4-Lutidine) 2 was proven.

Deuteron magnetic resonance (DMR) spectroscopic was performed on a single crystal of CD 3 NH 3 HgCl 3 . The electric field gradient tensors of the independent CD 3 NH 3 + - groups were determined by quadrupole perturbed NMR. NMR-NQR-rotation patterns were recorded in the ferro- (T = 295 K) and paraelectric (F = 342 K) phases. In the ferroelectric phase a precessional motion of the CD 3 NH 3 + -group was detected. The angle % (T) between the axis of the molcculc and the precession-axis increases with temperature. In the paraelectric phase the precession of methylammonium is superimposed by an anisotropic 90° -flipping motion. The flipping planes are parallel to the polar axis.

For volume selective nuclear magnetic resonance spectroscopy with protons a modified version of the double spin echo method has been implemented on a 1.5 T whole body imager. The high performance of the localization sequence has been verified with phantoms and tissue. A spectral resolution of about 2 · 10 -8 was obtained. The volume elements are well shaped and positioned, the minimal size was 2.2 cm 3 . Spectra of porcine leg muscle tissue with different echo times are presented.

The microwave spectrum of HNC 17 O is reported for the first time. The measurements were made with both Stark modulated and microwave Fourier transform spectrometers. The 17 O and 14 N quadrupole hyperfine structure has been resolved and rotational, centrifugal distortion and 17 O and 14 N quadrupole coupling constants have been evaluated. The 17 O coupling constants are compared with those from an ab initio prediction.

The 11 B quadrupole hyperfine structure in the rotational spectra of three isotopic species of hydroxydifluoroborane, BF 2 OH, BF 2 OD, and BF 2 18 OH has been investigated and the quadrupole coupling constants of these species have been determined. Using the variation of the 11 B quadrupole coupling constants with isotopic substitution, it has been possible to evaluate the complete quadrupole coupling tensor, including the off-diagonal element % ab , for each isotopic species.

The rotational spectra of pyridine-N-oxide and x-picoline-N-oxide ( = 2-methvlpyridine-N-oxide) have been observed by means of pulsed microwave spectroscopy. For both molecules, the 14 N quadrupole coupling constants have been obtained. For α-picoline-N-oxide. in addition the parameters of the internal rotation motion and the centrifugal distortion constants have been determined.

We present structural investigations using the energy dispersive X-ray diffraction (EDXD)- method on amorphous Fe-Tb- and Fe-Co-Tb-alloys over an extended concentration range. Atomicdistances. partial coordination numbers, and chemical short range order parameters are reported. The short range order is characterized by a compound forming tendency. In an amorphous Fe-Co- Tb-alloy, doping with hydrogen affects the short range order and gives rise to an in-plane magnetization direction.

Self diffusion coefficients of CF 3 Br and CF 3 Cl are given for the temperature range 140 - 430 K at pressures up to 200 MPa. The are analysed by the interacting sphere model.

The ion dip spectrum of the fluorobenzene-Argon van der Waals complex has been measured and the complex shift in the ground state is determined. The observed dips then could be assigned by comparison with the ion dip spectra and hotband spectra of the fluorobenzene molecule.

We present a new laser tandem mass spectrometry technique in a reflectron time of flight (TOF) instrument. A first pulsed laser performs the multiphoton ionization and the primary photodissociation. A newly designed ion source permits a high mass resolution in the space focus of the 12 cm long first linear TOF, where then the secondary excitation can take place. For high resolution applications the pure secondary or pure metastable mass spectrum of a preselected precursor ion can be recorded using a new reflectron scanning technique. It is also possible to obtain the whole secondary mass spectrum with one cycle using a new postacceleration method. Several techniques for ejection of interfering ions are shown. The features of our techniques are demonstrated at various primary fragments of benzene.

To elucidate the phase transition of pyridinium tetrachloroiodate(III) at T c = 217 K, the temperature dependences of the chlorine NQR frequencies and corresponding NQR spin-lattice and spin-spin relaxation times (T 1Q and T 2Q ) have been measured in the range 77-370 K. Above ca. 370 K and between 206 and 223 K no chlorine NQR frequency could be observed, the chlorine relaxation times becoming extremely short (ca. 100 μs). Except for near T c , the T 1Q values below ca. 310 K can be explained by fluctuations of the electric field gradient at the chlorine nuclei due to in-plane reorientations of the cations about their pseudohexad axis. The increase of T 1q -1 in the vicinity of T c suggests a critical slowing down of the orientational fluctuations of the cations and a distortion of the complex anions. The decrease of T 1Q above 310 K is considered to be mainly due to the in-plane reorientation of the complex anions. An activation energy of 64 kJ mol -1 is evaluated for that motion.

The temperature dependence of the ionic conductivity in the PPG-rich part of the ternary system poly(propylene glycol)-poly(methyl methacrylate)-LiCF 3 SO 3 has been investigated. The highest conductivity values, 3 x 10 -5 (ohm cm) -1 at 31 °C and 4 × 10 -4 (ohm cm) -1 at 77 C, were obtained for samples which had the properties of a pressure sensitive adhesive. The temperature dependence of the ionic conductivity could be well described by the Vogel-Tammann-Fulcher equation.

The relativistic Dirac equation with a scalar potential and the fourth component of a vector potential of the Woods-Saxon shape is solved numerically for potential parameters obtained by a last squares fitting procedure of the ground state binding energies of the Λ in a number of hypernuclei and its binding energies in the ground and excited states (as well as the relevant spacings) for various hypcrnuclei are determined. The results are in very good agreement with the preliminary experimental ones given by Chrien on the basis of the (π + , K + ) reaction on nuclei.