On centralizer algebras for spin representations

We give a presentation of the centralizer algebras for tensor products of spinor representations of quantum groups via generators and relations. In the even-dimensional case, this can be described in terms of non-standard q-deformations of orthogonal Lie algebras; in the odd-dimensional case only a certain subalgebra will appear. In the classical case q = 1 the relations boil down to Lie algebra relations

Quality predictors of abdominal fetal electrocardiography recording in antenatal ambulatory and bedside settings

Background: Fetal electrocardiography using an abdominal monitor (Monica AN24™) could increase the diagnostic use of fetal heart rate (fHR) variability measurements. However, signal quality may depend on factors such as maternal physical activity, posture, and bedside versus ambulatory setting. Methods: Sixty-three healthy women wore the monitor at home and 42 women during a hospital stay. All women underwent a posture experiment, and all home and 13 hospital participants wore the monitor during daytime and nighttime. The success rate (SR) of fHR detection was analyzed in relation to maternal physical activity, posture, daytime versus nighttime, and other maternal and fetal predictors. Results: Ambulatorily, the SR was 86.8% for nighttime and 40.2% for daytime. The low daytime SR was largely due to effects of maternal physical activity and posture. The in-hospital SR was lower during nighttime (71.1%) and similar during daytime (43.3%). SR was related to gestational age, but not affected by pre-pregnancy and current body mass index or fetal growth restriction. Conclusions: The success of beat-to-beat fHR detection strongly depends on the home/hospital setting and predictors such as time of recording, activity levels, and maternal posture. Its clinical utility may be limited in periods of unsupervised recording with physical activity or posture shifts

Effects of Monovalent and Divalent Cations on Ca2+ Fluxes Across Chromaffin Secretory Membrane Vesicles

Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na +, Li +, or choline +. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na +, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na + -dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na +-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na + -dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 μM and a Vmax= 14.5 nmol min−1 mg protein−1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations

The QCD string and the generalised wave equation

The equation for QCD string proposed earlier is reviewed. This equation appears when we examine the gonihedric string model and the corresponding transfer matrix. Arguing that string equation should have a generalized Dirac form we found the corresponding infinite-dimensional gamma matrices as a symmetric solution of the Majorana commutation relations. The generalized gamma matrices are anticommuting and guarantee unitarity of the theory at all orders of $v/c$. In the second quantized form the equation does not have unwanted ghost states in Fock space. In the absence of Casimir mass terms the spectrum reminds hydrogen exitations. On every mass level $r=2,4,..$ there are different charged particles with spin running from $j=1/2$ up to $j_{max}=r-1/2$, and the degeneracy is equal to $d_{r}=2r-1 = 2j_{max}$. This is in contrast with the exponential degeneracy in superstring theory.Comment: 11 pages LaTeX, uses lamuphys.sty and bibnorm.sty,; Based on talks given at the 6th Hellenic School and Workshop on Elementary Particle Physics, Corfu, Greece, September 19-26, 1998 and at the International Workshop "ISMP", Tbilisi, Georgia, September 12-18, 199

Defects Studies of ZnO Single Crystals Prepared by Various Techniques

The aim of the present work was a comparison of defects in ZnO crystals grown by various techniques available nowadays, namely hydrothermal growth, pressurized melt, Bridgman method growth and vapor phase growth. Positron annihilation spectroscopy was employed as a principal tool for characterization of defects in ZnO crystals grown by above mentioned various techniques. ZnO crystals can be divided into two groups: (i) hydrothermal grown crystals, which exhibit positron lifetime of 179-182 ps and (ii) ZnO crystals grown by the other techniques (pressurized melt, Bridgman method, vapor phase growth) which are characterized by the lower lifetimes falling in the range of 160-173 ps. Comparison of experimental data with ab initio theoretical calculations revealed that HT grown ZnO crystals contains Zn vacancies associated with hydrogen atom in a bond-centered site. On the other hand, ZnO crystals prepared by other techniques contain most probably stacking faults created by stresses induced by temperature gradients in the melt

Asymmetrically cut crystals as optical elements for highly collimated x‐ray beams

Asymmetrically cut perfect crystals, in both the Laue and Bragg geometries, are examined as single crystal monochromators for x‐ray beams that are collimated to a small fraction of the Darwin width, as is typical in experiments with coherent x rays. Both the Laue and asymmetric Bragg geometries are plagued by an inherent chromatic aberration that increases the beam divergence much beyond that of the symmetric Bragg geometry. Measurements from a recent experiment at the ESRF are presented to compare Si(220) (symmetric Bragg), diamond(111) (asymmetric Laue), and diamond(111) (symmetric Bragg inclined) geometries. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70952/2/RSINAK-66-2-1506-1.pd

Characterization of microstructural defects in melt grown ZnO single crystals

Various nominally undoped, hydrothermally or melt grown (MG) ZnO single crystals have been investigated by standard positron lifetime measurements. Furthermore, optical transmission measurements and structural characterizations have been performed; the content of hydrogen in the bound state was determined by nuclear reaction analysis. A positron lifetime of 165-167 ps, measured for a brownish MG ZnO sample containing (0.30 0.03) at.- of bound hydrogen, matches perfectly the value found for colorless MG ZnO crystals. The edge shift, observed in the blue light domain of the optical absorption for the former sample with respect to the latter samples, is estimated to be 0.70 eV, and found equal to a value reported previously. The possible role of zinc interstitials is considered and discussed. Microstructure analysis by X-ray diffraction and transmission electron microscopy revealed the presence of stacking faults in MG crystals in a high concentration, which suggests these defects to be responsible for the observed positron lifetime. © 2011 American Institute of Physics.published_or_final_versio

Phase Diagram of the Heisenberg Spin Ladder with Ring Exchange

We investigate the phase diagram of a generalized spin-1/2 quantum antiferromagnet on a ladder with rung, leg, diagonal, and ring-exchange interactions. We consider the exactly soluble models associated with the problem, obtain the exact ground states which exist for certain parameter regimes, and apply a variety of perturbative techniques in the regime of strong ring-exchange coupling. By combining these approaches with considerations related to the discrete Z_4 symmetry of the model, we present the complete phase diagram.Comment: 17 pages, 10 figure

Event horizons and apparent horizons in spherically symmetric geometries

Spherical configurations that are very massive must be surrounded by apparent horizons. These in turn, when placed outside a collapsing body, must propagate outward with a velocity equal to the velocity of radially outgoing photons. That proves, within the framework of (1+3) formalism and without resorting to the Birkhoff theorem, that apparent horizons coincide with event horizons.Comment: 5 pages, plainte

The unexpectedly short Holocene Humid Period in Northern Arabia

The early to middle Holocene Humid Period led to a greening of today's arid Saharo-Arabian desert belt. While this phase is well defined in North Africa and the Southern Arabian Peninsula, robust evidence from Northern Arabia is lacking. Here we fill this gap with unprecedented annually to sub-decadally resolved proxy data from Tayma, the only known varved lake sediments in Northern Arabia. Based on stable isotopes, micro-facies analyses and varve and radiocarbon dating, we distinguish five phases of lake development and show that the wet phase in Northern Arabia from 8800-7900 years BP is considerably shorter than the commonly defined Holocene Humid Period (similar to 11,000-5500 years BP). Moreover, we find a two century-long peak humidity at times when a centennial-scale dry anomaly around 8200 years BP interrupted the Holocene Humid Period in adjacent regions. The short humid phase possibly favoured Neolithic migrations into Northern Arabia representing a strong human response to environmental changes