On Killing vectors in initial value problems for asymptotically flat space-times

The existence of symmetries in asymptotically flat space-times are studied from the point of view of initial value problems. General necessary and sufficient (implicit) conditions are given for the existence of Killing vector fields in the asymptotic characteristic and in the hyperboloidal initial value problem (both of them are formulated on the conformally compactified space-time manifold)

Polariton Local States in Periodic Bragg Multiple Quantum Well Structures

We analytically study optical properties of several types of defects in Bragg multiple quantum well structures. We show that a single defect leads to two local polariton modes in the photonic band gap. These modes lead to peculiarities in reflection and transmission spectra. Detailed recommendations for experimental observation of the studied effects are given.Comment: 3 pages, 1 figure, RevTex, Submitted to Opt. Let

Ultrafast Spin Dynamics in Nickel

The spin dynamics in Ni is studied by an exact diagonalization method on the ultrafast time scale. It is shown that the femtosecond relaxation of the magneto-optical response results from exchange interaction and spin-orbit coupling. Each of the two mechanisms affects the relaxation process differently. We find that the intrinsic spin dynamics occurs during about 10 fs while extrinsic effects such as laser-pulse duration and spectral width can slow down the observed dynamics considerably. Thus, our theory indicates that there is still room to accelerate the spin dynamics in experiments.Comment: 4 pages, Latex, 4 postscript figure

Electronic Theory for the Nonlinear Magneto-Optical Response of Transition-Metals at Surfaces and Interfaces: Dependence of the Kerr-Rotation on Polarization and on the Magnetic Easy Axis

We extend our previous study of the polarization dependence of the nonlinear optical response to the case of magnetic surfaces and buried magnetic interfaces. We calculate for the longitudinal and polar configuration the nonlinear magneto-optical Kerr rotation angle. In particular, we show which tensor elements of the susceptibilities are involved in the enhancement of the Kerr rotation in nonlinear optics for different configurations and we demonstrate by a detailed analysis how the direction of the magnetization and thus the easy axis at surfaces and buried interfaces can be determined from the polarization dependence of the nonlinear magneto-optical response, since the nonlinear Kerr rotation is sensitive to the electromagnetic field components instead of merely the intensities. We also prove from the microscopic treatment of spin-orbit coupling that there is an intrinsic phase difference of 90$^{\circ }$ between tensor elements which are even or odd under magnetization reversal in contrast to linear magneto-optics. Finally, we compare our results with several experiments on Co/Cu films and on Co/Au and Fe/Cr multilayers. We conclude that the nonlinear magneto-optical Kerr-effect determines uniquely the magnetic structure and in particular the magnetic easy axis in films and at multilayer interfaces.Comment: 23 pages Revtex, preprintstyle, 2 uuencoded figure

Feynman integral in regularized non-relativistic quantum electrodynamics

We express the unitary time evolution in non-relativistic regularized quantum electrodynamics at zero and positive temperature by a Feynman integral defined in terms of a complex Brownian motion. An average over the quantum electromagnetic field determines the form of the quantum mechanics in an environment of a quantum black body radiation. In this non-perturbative formulation of quantum electrodynamics we prove the existence of the classical limit $\hbar \rightarrow 0$.We estimate an error to some approximations commonly applied in quantum radiation theory.Comment: 30 pages, LaTex fil

Electron spin relaxation in bulk GaAs for doping densities close to the metal-to-insulator transition

We have measured the electron spin relaxation rate and the integrated spin noise power in n-doped GaAs for temperatures between 4 K and 80 K and for doping concentrations ranging from 2.7 x 10^{-15} cm^{-3} to 8.8 x 10^{-16} cm^{-3} using spin noise spectroscopy. The temperature dependent measurements show a clear transition from localized to free electrons for the lower doped samples and confirm mainly free electrons at all temperatures for the highest doped sample. While the sample at the metal-insulator-transition shows the longest spin relaxation time at low temperatures, a clear crossing of the spin relaxation rates is observed at 70 K and the highest doped sample reveals the longest spin relaxation time above 70 K.Comment: 6 pages, 4 figure

Impurity-induced polaritons in a one-dimensional chain

A detailed analytical study of an impurity induced polariton band arising inside a spectral gap between lower and upper polariton branches is presented. Using the microcanonical method, we calculate the density of states and localization length of the impurity polaritons. Analytical results are compared with numerical simulations and excellent agreement is found.Comment: 10 pages, 3 figures, RevTe

Serum albumin is an early predictor of complications after liver surgery.

The morbidity associated with liver surgery remained substantially high despite considerable surgical and anesthetic improvements. The unmet need of accurate biomarkers to predict postoperative complications is widely accepted. This pilot study aimed to assess serum albumin as a surrogate marker of surgical stress and to test its potential predictive role for postoperative complications. This retrospective pilot study included 106 patients who underwent liver surgery between 2010 and 2014. Serum albumin levels were measured pre- and post-operatively. Maximal albumin decrease (AlbΔmin) was correlated with complications. Serum albumin rapidly dropped after surgery. AlbΔmin was significantly increased in patients with complications (14.5±6.0g/L vs. 10.3±7.2, p=0.009). On multivariate analysis, ASA III/IV (p=0.016) and AlbΔmin (p=0.037) were the only predictors of overall complications. Early postoperative drop of serum albumin reflects the intensity of the surgical stress and may predict complications after liver surgery. Serum albumin is a biomarker displaying precious features and deserving further prospective investigations

Conversion of hole states by acoustic solitons

The hole states in the valence band of a large class of semiconductors are degenerate in the projections of angular momentum. Here we show that the switching of a hole between the states can efficiently be realized by acoustic solitons. The microscopic mechanism of such a state conversion is related to the valence band splitting by local elastic strain. The conversion is studied here for heavy holes localized at shallow and deep acceptors in silicon quantum wells.Comment: 4 pages, 2 figure