Molecular dynamics in thin grafted and spin-coated polymer layers

Broadband Dielectric Spectroscopy is employed to study the molecular dynamics in thin layers of grafted and spin-coated polydimethylsiloxane (PDMS) and of the type-A polymer cis-1,4-polyisoprene (PI). Strong resemblance with low-molecular-weight systems is found but additionally the conformation of the chain and its extension becomes important. For PI a confinement-induced relaxation is found. It is observable if the layer thickness is comparable to the end-to-end vector of the chain and it depends strongly on the separation between interfaces. In contrast, the dynamic (and hence the calorimetric) glass transition is not affected by the geometrical confinement.Received: 1 January 2003, Published online: 8 October 2003PACS: 64.70.Pf Glass transitions - 83.10.Mj Molecular dynamics, Brownian dynamics - 68.60.-p Physical properties of thin films, nonelectronic     

Fourier's Law confirmed for a class of small quantum systems

Within the Lindblad formalism we consider an interacting spin chain coupled locally to heat baths. We investigate the dependence of the energy transport on the type of interaction in the system as well as on the overall interaction strength. For a large class of couplings we find a normal heat conduction and confirm Fourier's Law. In a fully quantum mechanical approach linear transport behavior appears to be generic even for small quantum systems.Received: 14 May 2003, Published online: 11 August 2003PACS: 05.60.Gg Quantum transport - 05.30.-d Quantum statistical mechanics - 05.70.Ln Nonequilibrium and irreversible thermodynamics     

Transvection free groups and invariants of polynomial tensor exterior algebras

Let :GGl(n, ) be a representation of a finite groupG over a field such that the ring of invariants is a polynomial algebra . It is known that in the nonmodular case (i.e., when the order of the group is not divisible by the characteristic of ), the invariants ofG acting on the tensor product of a polynomial and an exterior algebra are given by ,d denoting the exterior derivative. We show that in the modular case, the ring of invariants in is of this form if and only if is a polynomial algebra and all pseudoreflections in (G) are diagonalizable.     

Spin domains generate hierarchical ground state structure in J = +/-1 spin glasses

Unbiased samples of ground states were generated for the short-range Ising spin glass with J(ij) = +/-1, in three dimensions. Clustering the ground states revealed their hierarchical structure, which is explained by correlated spin domains, serving as cores for macroscopic zero energy "excitations."     

A QR Decomposition for Matrix Pencils

This paper describes an efficient and numerically stable modification of the QR decomposition for solving a parametric set of linear least squares problems with a parametric matrix A + B for several values of the parameter . The method is demonstrated on a typical application.     

Operation characteristics of the Au-II 690-nm laser transition in a segmented hollow-cathode discharge

Single-mode operation at the Au-II 690-nm transition was obtained in a segmented hollow-cathode discharge laser without the use of any additional frequency-selective device. The pressure of the helium buffer gas, which is responsible for the significant homogeneous broadening of the laser line, was varied between 10 and 20 mbar. The discharge was excited with rectangular current pulses (up to 3 A) six times exceeding the threshold value. The time dependence of the laser output during the 1-ms-long discharge pulses is explained on the basis of the temperature and pressure changes in the tube. The highest small-signal gain at optimal discharge conditions was 11%m⁻¹. Received: 1 July 1999 / Revised version: 4 November 1999 / Published online: 23 February 2000     

Erfassungsverm?gen von Analysenverfahren

Summary Frequently different concepts are designated by the terms limit of detection, limit of determination and limit of quantification in the chemical literature. The statistical models used for the definitions can be classified as to their primary purpose: to estimate concentrations or to test hypotheses. In addition a further classification with respect to the control of the local or the multiple type-I error can be carried out.For characterizing an analytical method, an analytical system or a series of analyses the application of a statistical test is appropiate. However, the attempt to control the probability of the multiple type-I error should not be made in this context in order to avoid an unreasonably high probability of the type-II error, which consists of overlooking the presence of some substance of interest.