Band 55, Heft 3-4

Two different lengths of P-O bonds in the PO 4 units of phosphate glasses are found by neutron diffraction experiments of high resolution in real space. The two lengths are related to bonds of the phosphorus atom with the terminal and the bridging oxygen atoms. The mean lengths and widths of both P-0 distance peaks change as a function of the glass composition. In a large range, starting from vitreous P 2 O 5 s up to the pyrophosphate composition, the behavior of the bond lengths is compared with that in the related crystals and with that resulting from ab initio calculations. The bond lengths depend not only on the species of the participating oxygen atoms and on the number of links of the concerning PO 4 unit but also on the number of links of the neighboring PO 4 unit and on the species of the modifier cation

Liquid copper, bismuth, and eleven bismuth-copper alloys were investigated at temperatures above the liquidus with X-ray diffraction. The experimental procedure was adjusted to reduce the effects of evaporation. The Faber-Ziman total structure factors S(Q) feature a splitting of the first maximum and negative values for Q around 1 Å -1 in a large concentration range. The results are compared to previous neutron diffraction results by Zaiss and Steeb, to square-well potential model calculations by Gopala Rao and Satpathy and to a simple segregation model. The segregation model reproduces the features qualitatively. Partial structure factors are assessed by fitting both neutron and X-ray scattering results with reverse Monte-Carlo simulation

The structure of the condensed bromocadmate anions in [C(NH 2 ) 3 ]Cd 2 Br 5 (1) and [H 2 NNH 3 ] 3 CdBr 5 (2) were studied at room temperature by X-ray diffraction. (1) crystallizes with double-chains bridged by Br atoms (orthorhombic, Pmmn, Z= 2, a = 1394.0(5), b = 394.5(1), c = 1086.9(5) pm). This chain structure was not described previously. (1) shows three 81 Br NQR lines at temperatures between 77 and 323 K. Structural phase transitions take place at 283 K and at 535 K. (2) crystallizes with Br bridged zigzag-chains (monoclinic, P2 1 , Z=2,a = 943.1(1), b = 778.8(2), c = 942.0(2) pm, β = 102.10(2)°) and shows a first-order phase transition around 304 K with a large thermal hysteresis. Below the transition point five 81 Br NQR lines are observed at temperatures between 122 and 304 K, and above the transition point four 81 Br NQR lines at tem-peratures between 288 and 353 K. Two 81 Br NQR lines are observed in [H 2 NNH 3 ] 2 CdBr 4 -4H 2 0 (3) at temperatures between 77 and around 320 K with positive temperature coefficients

By means of the coupled amplitude-phase method we find analytical dark solitary wave solutions for the higher order nonlinear Schrödinger equation with cubic-quintic terms describing the effects of quintic nonlinearity on the ultra-short (femtosecond) optical soliton propagation in non-Kerr media. The dark solitary wave solution exists even for the coefficients of quintic terms much larger than those of cubic terms.

The usual (2+1)-dimensional Schwartz Kadomtsev-Petviashvili (KP) equation is extended to (n+1)-dimensions. The extension is Painleve integrable in the sense that it possesses the Painleve property. A (3+1)-dimensional special one is just found when we solve a real (3+1)-dimensional KP equation approximately.

The concept of the time dependent instantaneously occupied phase space volume is applied to multi-component systems. It allows for the investigation of entropy flows betweeen the components of the system and the evaluation of partial entropies assigned to the subsystems. We give numerical examples by means of molecular dynamics simulations of a 100-particle gas. Using a symplectic exactly reversible algorithm, a consistent and reliable evalutation of energy and entropy exchanges as well as the intake of work is achieved. The entropy flow which is related to an information flow is linked to an observational situation. This yields a further indication for the necessity of an intrinsic observer for a better understanding of the physical world. In addition, it indicates the Gödelian structure of cognition in a most serious way because only “first-principle” assumptions are made. Thereby, the paradoxical situation which is created by Jaynes’ concept of an “anthropomorphic entropy” can be resolved by putting the anthropomorphic contents of thermodynamics down to an ontological basis. This is a straightforward extension of Szilard’s and Brillouin’s information theoretical treatment of cognition

The reorientation of the tetrahedral complex anion ZnCl 4 2- and the self-diffusion of the cation in (CH 3 NH 3 ) 2 ZnCl 4 were studied by 1 H NMR spin-lattice relaxation time ( 1 H T 1 ) experiments. In the second highest-temperature phase, the temperature dependence of 1 H T 1 observed at 8.5 MHz could be explained by a magnetic dipolar-electric quadrupolar cross relaxation between 1 H and chlorine nuclei, and the activation energy of the anion motion was determined to be 105 kJ mol -1 . In the highest-temperature phase, the activation energy of the self-diffusion of the cation was determined to be 58 kJ mol -1 from the temperature and frequency dependence of 1 H T 1

By a decomposition theorem a higher order nonlinear spinorfield equation can be transformed into a set of first order nonlinear spinorfield equations, i. e. into an auxiliary field formulation which allows canonical quantization. The quantum dynamics of the auxiliary fields is expressed in algebraic Schrödinger representation and admits only unphysical state spaces with indefinite metric. Regularization of the classical theory is transferred into quantum field theory by a noninvertible map from the corresponding auxiliary field state space into an associated physical state space, the metric of which is positive definite. For the effective dynamics in the physical state space probability current conservation is proved, and for physical states which describe composite particle configurations the existence of the state space is demonstrated

Chemiluminescent reactions of metastable Mg*( 3 P J ) atoms with F 2 , Cl 2 , Br 2 , I 2 , IC1, IBr molecules were studied in a beam-gas experiment. For all homonuclear targets the MgX(A 2 Π -X 2 Σ + ) emission was observed, but for IC1 and IBr reactants the Mgl(A-X) emission was absent and only MgCl(A-X) or MgBr(A-X) spectra were found. In addition, for the I 2 , IBr, IC1, Br 2 reactions, broad pseudocontinua extend from above 400 nm into the infrared. These pseudocontinua are ten-tatively attributed to the Mgl, MgBr (B' 2 Σ + -X 2 Σ + ) transition. The total attenuation cross sections, chemiluminescence cross sections and quantum yields were measured. The quantum yields are all below 5%. The results are analyzed using information theory. The low yields for the Mg* + F 2 system are explained by a barrier in the entrance channel. For other reactions the low yields are most probably caused by predissociation of the MgX*(A 2 Π) products

The rotational spectrum of 13 C 18 O has been measured up to 1 THz. The lowest rotational transitions of 13 C 18 O (J =2←1 to J = 6 ← 5) have been measured by saturation-dip spectroscopy with an experimental accuracy of 2 kHz. These five low J rotational transitions cover the frequency range between 209 and 628 GHz. The narrow linewidths of about 20 kHz of the saturation dips allowed to resolve the two main hyperfine components. The splitting is caused by coupling of the 13 C nuclear spin with the rotation of the molecule. The appropriate coupling constant C 1 ( 13 C 18 O) is 33.90(81) kHz. In addition we have measured in the Doppler limited mode, the line positions of the rotational transitions J = 7 ← 6 , J = 8 ← 7 , and J = 9 ← 8 with accuracies of 5 kHz. We provide a set of improved constants together with frequency predictions up to 4.1 THz (J = 40 ← 39)

Based on the Kennard-Stepanov relation between the extinction coefficient and fluorescence inten-sity in their overlapping region, local temperatures T* are determined for several dyes and stilbene de-rivatives in PVA and PVC polymers. It is found that excitation energy excess for ṽ exc >ṽ 0-0 causes local heating in a rigid polymer, and the temperature difference ΔT= T*-T holds during the emission process. Such a behaviour results from slow geometrical relaxation in a polymer. Excitation energy excess is also evidenced by the fact that the intensity distribution in the emission band depends slightly on the excitation wavelength. This effect is stronger for higher energy excess

Using the experimental data on the dielectric anisotropy, density, polarizability, dipole moment, and order parameter in the nematic phase of seven typical liquid crystalline substances, the applicability of the Maier-Meier theory for the description of the dielectric properties of nematics is checked. Substanc-es with different polarity and different tendency to form associates in the nematic phase were studied. It is found that the Maier-Meier equations describe fairly well the dielectric permittivity components of nematics. The estimated values of the angle β formed by the dipole moment with the long molecular axis are compared with those obtained in other studies

The plasma screening effect on the photorecombination of free electrons, with ions in a weakly plas-ma is investigated. The recombination cross section is obtained by the principle of detailed balance with the photoionization cross section of the hydrogenic ion including the plasma screening effects on the bound and continuum states of the electron. It is found that the plasma screening effects on the recom-bination cross section are less than 11% when the Debye length (Λ) is greater than ten times of the Bohr radius (a z ) of the hydrogenic ion with nuclear charge Z

The effect of a horizontal magnetic field and a non-Newtonian stress tensor, as described by the Wal-ters B’ model, on the instability of two second order fluids of high kinematic viscosities and viscoelas-ticities is investigated. For the potentially stable configuration, it is found that the system is stable or unstable for a wavenumber range depending on the kinematic viscoelasticity. For the potentially un-stable configuration, it is found that the stability criterion is dependent on orientation and magnitude of the magnetic field which is found to stabilize a certain range of the unstable configuration related to the viscoelasticity values. The behaviour of growth rates with respect to Alfvén velocities are examined analytically, and it is found that the magnetic field has a dual role on the instability problem. For the exponentially varying stratifications, the system is found to be stable or unstable for the stable and un-stable stratifications under certain physical conditions, and the growth rates are found to increase or de-crease with increasing the stratification parameter values, according to some restrictions satisfied by the chosen wavenumbers range

Cu-L III in XANES data collected on Ba 0.98 CuO 1.98+δ samples with different oxygen content are reported. The near-edge structures are discussed together with previous conductivity measurements, and an estimate of the hole density evolution with oxygen doping is given. The reported results give evidence of the increase with δ of the localization of doping holes on oxygen atoms

The hydroxyl proton chemical shifts δ (H-O) of supercooled methanol (T min = 149 K) and water have been determined (T min = 183 K), and the pressure dependence of these shifts was measured up to 200 MPa. In both compounds the downfield shift of δ (H-O) continues down to the lowest temperatures reached. This result disagrees with the two state models for the hydrogen bond formation in both liquids. The isotherms δ(H 2 O) show for T< 273 K an upfield shift that becomes more pronounced with decreasing temperature. For δ ( H-O-CH 3 ), increasing p causes at all temperatures a downshift

An ab initio classical trajectory study of intramolecular vibrational dynamics in H + 3 molecule revealed a transition from regular quasiperiodic to stochastic motion at an energy slightly higher than the zero point vibrational energy