Random walks in disordered systems and their investigations by means of magnetic resonance and relaxation of polarized beta-active nuclei

The experimental investigations of the polarization transport in the disordered spin system⁸Li −⁶Li in LiF crystal are considered. This process is initiated by one originally polarized beta-active⁸Li nucleus produced in a nuclear reaction. The autocorrelation function Foo(t) for the ran dom-walks-in-disordered-system problem has been measured over the range Foo(t)≥0.1 Foo(0) by analysing the β-emission anisotropy. The influence of the resonance process at double larmor frequency and of the thermal translational motion of⁸Li and⁶Li spins is studied. Results are in a good agre ement with the theory.     

Dynamic and Isothermal Thermogravimetric Degradation of Poly(vinyl Chloride)/Chlorinated Poly(ethylene) Blends

The thermal degradation of poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends of different compositions was investigated by means of dynamic and isothermal thermogravimetric analysis in flowing atmosphere of nitrogen. Kinetic parameters (the apparent activation energy E, and pre-exponential factor Z) were calculated after Flynn-Wall-Ozawa method for the first stage of dynamic degradation of PVC/CPE blends, and after Flynn method for the isothermal degradation. In both cases, there is the compensation dependence between the values E and logZ. The values of compensation ratios as well as the characteristics of TG and DTG curves, confirm the stabilizing effect of CPE on PVC dehydrochlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low temperature nuclear orientation of239Np in gadolinium host

The angular distribution of γ-radiation from the decay of²³⁹Np oriented at low temperatures in gadolinium host was investigated. The orientation parameters B2 and B4 were determined. The attenuation factors for two long-living states in²³⁹Pu at 391.5 keV and 285.4 keV were calculated. From the anisotropies measured the multipole mixing ratios for 11 gamma-transitions in²³⁹Pu were deduced. The results obtained support the assignment of spins of the levels at 492.2 keV and 391.6 keV as 3/2⁻ and 7/2⁻, respectively.     

Resonant States in High-Temperature Superconductors with Impurities

A microscopic theory of resonant states for the Zn-doped CuO₂ plane in the superconducting phase is formulated in the effective t–J model. In the model derived from the original p–d model, Zn impurities are considered as vacancies for the d states at Cu sites. In the superconducting phase, in addition to the local static perturbation induced by the vacancy, a dynamical perturbation appears that results in a frequency-dependent perturbation matrix. Using the T-matrix formalism for the Green's functions in terms of the Hubbard operators, we calculate the local density of electronic states with d, p, and s symmetries.     

Solution of porous medium type systems by linear approximation schemes

Summary The convergence of semi-discrete and discrete linear approximation schemes is analysed for nonlinear degenerate parabolic systems of porous medium type. The enthalpy formulation and variational technique are used. The semi-discretization used reduces the original parabolic P.D.E. to linear elliptic P.D.E. The algebraic correction arising from nonlinearities is treated by Newton-like iterations in finite steps. Some numerical experiments are discussed and compared with the analytical solutions.Supported by the Alexander von Humboldt-Foundation in 1989, and by SFB 123, University Heidelberg     

Laser Microbeams and Optical Tweezers in Ageing Research

We show how a technique developed within the framework of physics and physical chemistry—in a true interdisciplinary approach—can answer questions in life sciences that are not solvable by using other techniques. Herein, we focus on blood‐pressure regulation and DNA repair in ageing studies. Laser microbeams and optical tweezers are now established tools in many fields of science, particularly in the life sciences. A short glimpse is given on the wide field of non‐age‐research applications in life sciences. Then, optical tweezers are used to show that exerting a vertical pressure on cells representing the inner lining of blood vessels results in bursts of NO liberation concomitant with large changes in cell morphology. Repeated treatment of such human umbilical vein endothelial cells (HUVEC) results in stiffening, a hallmark of manifest high blood pressure, a disease primarily of the elderly. As a second application in ageing research, a laser microbeam is used to induce, with high spatial and temporal resolution, DNA damages in the nuclei of U2OS human osteosarcoma cells. A pairwise study of the recruitment kinetics of different DNA repair proteins reveals that DNA repair starts with non‐homologous end joining (NHEJ), a repair pathway, and may only after several minutes switch to the error‐free homologous recombination repair (HRR) pathway. Since DNA damages—when incorrectly repaired—accumulate with time, laser microbeams are becoming well‐used tools in ageing research.     

Self-similar properties of collisions between light nuclei

A new way of representing data on the fragmentation of nuclei is suggested. The self-similar behavior of these processes, that is dictated by their kinematics, is demonstrated. The convenience of working in accelerated nuclei is emphasized, particularly for the determination of the binding energy of a wide class of nuclear fragments.