Density-matrix spectra for integrable models

The spectra which occur in numerical density-matrix renormalization group (DMRG) calculations for quantum chains can be obtained analytically for integrable models via corner transfer matrices. This is shown in detail for the transverse Ising chain and the uniaxial XXZ Heisenberg model and explains in particular their exponential character in these cases.Comment: 14 pages, 7 figures, to appear in Ann. Physi

On Measuring Gravitomagnetism via Spaceborne Clocks: A Gravitomagnetic Clock Effect

DOI:10.1002/(SICI)1521-3889(199902)8:2<135The difference in the proper azimuthal periods of revolution of two standard clocks in direct and retrograde orbits about a central rotating mass is proportional to J/Mc^2, where J and M are, respectively, the proper angular momentum and mass of the source. In connection with this gravitomagnetic clock effect, we explore the possibility of using spaceborne standard clocks for detecting the gravitomagnetic field of the Earth. It is shown that this approach to the measurement of the gravitomagnetic field is, in a certain sense, theoretically equivalent to the Gravity Probe-B concept.This work has been supported in part by the Alexander von Humboldt Foundation

Time-resolved impulse response of the magnetoplasmon resonance in a two-dimensional electron gas

We have used optically excited ultrashort electrical pulses to measure the magnetoplasmon resonance of a two-dimensional electron gas formed in an AlGaAs/GaAs heterostructure at frequencies up to 200 gigahertz. This is accomplished by incorporating the sample into a guided wave probe operating in a pumped (^{3}He) system. We are able to detect the resonance by launching a stimulus pulse in the guide, and monitoring the system response in a time resolved pump-probe arrangement. Data obtained from measurements yield resonant frequencies that agree with the magnetoplasmon dispersion relation.Comment: 4 pages, 4 figure

Anisotropic dielectric function in polar nano-regions of relaxor ferroelectrics

The paper suggests to treat the infrared reflectivity spectra of single crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally frozen polarization makes the dielectric function strongly anisotropic in the phonon frequency range and the random orientation of the polarization at nano-scopic scale requires to take into account the inhomogeneous depolarization field. Employing a simple effective medium approximation (Bruggeman symmetrical formula) to dielectric function describing the polar optic modes as damped harmonic oscillators turns out to be sufficient for reproducing all principal features of room temperature reflectivity of PMN. One of the reflectivity bands is identified as a geometrical resonance entirely related to the nanoscale polarization inhomogeneity. The approach provides a general guide for systematic determination of the polar mode frequencies split by the inhomogeneous polarization at nanometer scale.Comment: 5 pages, 2 figure

Silicon nanoparticles and interstellar extinction

To examine a recently proposed hypothesis that silicon nanoparticles are the source of extended red emission (ERE) in the interstellar medium, we performed a detailed modeling of the mean Galactic extinction in the presence of silicon nanoparticles. For this goal we used the appropriate optical constants of nanosized Si, essentially different from those of bulk Si due to quantum confinement. It was found that a dust mixture of silicon nanoparticles, bare graphite grains, silicate core-organic refractory mantle grains and three-layer silicate-water ice-organic refractory grains works well in explaining the extinction and, in addition, results in the acceptable fractions of UV/visible photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions barely agree with the fraction of UV/visible photons needed to excite the observed ERE, we conclude that the intrinsic photon conversion efficiency of the photoluminescence by silicon nanoparticles must be near 100%, if they are the source of the ERE.Comment: Latex2e, uses emulateapj.sty (included), multicol.sty, epsf.sty, 6 pages, 3 figures (8 Postscript files), accepted for publication in ApJ Letters, complete Postscript file is also available at http://physics.technion.ac.il/~zubko/eb.html#SNP

Patterns of labour solidarity towards precarious workers and the unemployed in critical times in Greece, Poland and the UK

The purpose of this article is to examine whether and by what means traditional unions and other labour-oriented organisations engage in solidarity activities in favour of precarious workers and the unemployed. Our findings derive from qualitative data analysed from 10 in-depth interviews per country conducted as part of a large collaborative project with participants sampled from trade unions and other labour-oriented solidarity organisations based in three European national contexts: Greece, Poland, and the UK. Our aim here is to discern common features and differences in the strategies and answers given, within the three national contexts. To this end, we examine the actors engaged in labour solidarity; the value frames upon which these actions draw; the beneficiaries of their solidarity actions; the type of activities adopted mainly in favour of precarious workers and the unemployed; and their engagement in transnational labour solidarity activities

Using competence modeling to create knowledge engineering team

The present paper is about applying competence modeling for a knowledge engineer in the case of the company WBSA Sistemas Inteligentes S.A. The process was based on Lucia and Lepsinger model, by which competences are characterized through the identification of situations and behaviors considered relevant to the engineer performance. As one of the different techniques suggested by the model for collecting data, a number of individual interviews were undertaken and at the end it was defined and validated a set of eleven competence regarded as necessary for a satisfactory performance of a knowledge engineerApplications in Artificial Intelligence - Knowledge EngineeringRed de Universidades con Carreras en Informática (RedUNCI

Direct comparison of steroid and non-steroid eluting small surface pacing leads: Randomized, multicenter clinical trial

BACKGROUND: The aim of the study was to evaluate the effi cacy and safety of small surface steroid-eluting atrial and ventricular pacing leads in comparison to non-steroid leads using remote monitoring system (Biotronik Home Monitoring(R)). METHODS: In this randomized multicenter prospective trial, SIELLO T steroid-eluting ventricular leads (n = 42) were compared to BPPU T non-steroid leads (n = 46) and SIELLO JT steroid-eluting atrial leads (n = 24) to BPPU JT non-steroid leads (n = 27) (Biotronik, Berlin, Germany) in pacemaker devices with remote monitoring capabilities. Lead parameters were evaluated during implantation, at 1-week and 1, 3, 6-month outpatient follow-up. Remote monitoring data were collected weekly. RESULTS: Atrial and ventricular steroid-eluting leads had stable sensing and impedance as compared to non-steroid leads at implantation and during follow-up. Patients with non-steroid atrial leads had signifi cantly higher threshold compared to steroid leads at 1-week and at 1, 3, 6-month follow-up with a peak at 1-month (1-month 1.4 +/- 0.6 vs. 0.7 +/- 0.3 V at 0.4 ms, p < 0.001; 6-month 0.3 +/- 0.5 vs. 0.2 +/- 0.3 V at 0.4 ms, p = 0.002). Patients with non-steroid ventricular leads had signifi cantly higher threshold compared to steroid leads at 1, 3, 6-month (6-month 1.0 +/- 0.3 vs. 0.6 +/- 0.2 V at 0.4 ms, p < 0.001). Remote monitoring confi rmed consistent results. During the study, 3 patients died of non-lead-related death. Lead repositioning was necessary in 2 atrial, 2 ventricular steroid leads and in 1 ventricular non-steroid lead. CONCLUSIONS: Atrial and ventricular pacemaker leads with steroid showed signifi cantly lower pacing threshold compared to non-steroid leads, confi rmed by remote monitoring