arXiv subjects

R. Weber

Publications and source records attributed to R. Weber.

5 recordsLinked to original sources

arXiv2011

A New Combined European Permanent Network Station Coordinates Solution

The EUREF (International Association of Geodesy (IAG) Reference Frame Sub-Commission for Europe) network of continuously operating GPS stations (EPN) was primarily established for reference frame maintenance, and also plays an important role for geodynamical research in Europe. The main goal of this paper is to obtain an independent homogeneous time-series of the EPN station coordinates, which is also available in SINEX format. A new combined solution of the EPN station coordinates was computed. The combination was performed independently for every week, in three steps: 1. the stated constraints on the coordinates were removed from the individual solutions of the Analysis Centers; 2. the de-constrained solutions were aligned to ITRF2000; 3. the resulting solutions were combined using the Helmert block-ing technique. All the data from GPS week 900 to week 1302 (April 1997 - December 2004) were used. We investigated in detail the behavior of the transformation parameters aligning the new combined solution to ITRF2000. In general, the time-series of the transformation parameters show a good stability in time although small systematic effects can be seen, most likely caused by station instabilities. A comparison of the new combined solution to the official EUREF weekly combined solution is also presented.

physics.geo-ph↗

arXiv2007

Electron-electron correlation in graphite

The full three dimensional dispersion of the pi-bands, Fermi velocities and effective masses are measured with angle resolved photoemission spectroscopy and compared to first-principles calculations. The band structure by density-functional theory strongly underestimates the slope of the bands and the trigonal warping effect. Including electron-electron calculation on the level of the GW approximation, however, yields remarkable agreement in the vicinity of the Fermi level. This demonstrates the breakdown of the independent electron picture in semi-metallic graphite and points towards a pronounced role of electron correlation for the interpretation of transport experiments and double-resonant Raman scattering for a wide range of carbon based materials.

cond-mat.mtrl-sci↗

arXiv2007

Pseudogap and charge density waves in two dimensions

An interaction between electrons and lattice vibrations (phonons) results in two fundamental quantum phenomena in solids: in three dimensions it can turn a metal into a superconductor whereas in one dimension it can turn a metal into an insulator. In two dimensions (2D) both superconductivity and charge-density waves (CDW) are believed to be anomalous. In superconducting cuprates, critical transition temperatures are unusually high and the energy gap may stay unclosed even above these temperatures (pseudogap). In CDW-bearing dichalcogenides the resistivity below the transition can decrease with temperature even faster than in the normal phase and a basic prerequisite for the CDW, the favourable nesting conditions (when some sections of the Fermi surface appear shifted by the same vector), seems to be absent. Notwithstanding the existence of alternatives to conventional theories, both phenomena in 2D still remain the most fascinating puzzles in condensed matter physics. Using the latest developments in high-resolution angle-resolved photoemission spectroscopy (ARPES) here we show that the normal-state pseudogap also exists in one of the most studied 2D examples, dichalcogenide 2H-TaSe2, and the formation of CDW is driven by a conventional nesting instability, which is masked by the pseudogap. Our findings reconcile and explain a number of unusual, as previously believed, experimental responses as well as disprove many alternative theoretical approaches. The magnitude, character and anisotropy of the 2D-CDW pseudogap are intriguingly similar to those seen in superconducting cuprates.

cond-mat.supr-con↗

arXiv2007

Building CMS Pixel Barrel Detectur Modules

For the barrel part of the CMS pixel tracker about 800 silicon pixel detector modules are required. The modules are bump bonded, assembled and tested at the Paul Scherrer Institute. This article describes the experience acquired during the assembly of the first ~200 modules.

physics.ins-det↗

arXiv2004

Separated flow behind a backward-facing step. Part II. Experimental and numerical investigation of a turbulent flow

We present the results of an experimental and numerical investigation of a turbulent flow over a backward-facing step in a channel. Experimental data are visualized using a Particle Image Velocimetry (PIV) device. As a mathematical model we used quasi-hydrodynamic (QHD) equations. We have carried out numerical modeling of the flow for three configurations that were also studied experimentally. The computed flow proved to be non-stationary. The averaged flow in the separation zone is in a good agreement with the experimental data.

math-ph↗