26,942 research outputs found
Comment on Zwally and others (2015)-mass gains of the Antarctic ice sheet exceed losses
In their article ‘Mass gains of the Antarctic ice sheet exceed losses’ Zwally and others (2015) choose Vostok Subglacial Lake as an exemplary region to demonstrate their inference of surface height change rates from a portion of the ICESat mission’s laser altimetry data (2003–08). In their appendix, they discuss some of the remarkable differences between their results and those reported by Richter and others (2008, 2013, 2014). However, the selective consideration of our works and the misleading or incorrect interpretation of our results call for clarificationFil: Richter, Andreas Jorg. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Technische Universitaet Dresden; AlemaniaFil: Horwath, M.. Technische Universitaet Dresden; AlemaniaFil: Dietrich, R.. Technische Universitaet Dresden; Alemani
Semiclassical Theory of Chaotic Quantum Transport
We present a refined semiclassical approach to the Landauer conductance and
Kubo conductivity of clean chaotic mesoscopic systems. We demonstrate for
systems with uniformly hyperbolic dynamics that including off-diagonal
contributions to double sums over classical paths gives a weak-localization
correction in quantitative agreement with results from random matrix theory. We
further discuss the magnetic field dependence. This semiclassical treatment
accounts for current conservation.Comment: 4 pages, 1 figur
Periodic Pattern in the Residual-Velocity Field of OB Associations
An analysis of the residual-velocity field of OB associations within 3 kpc of
the Sun has revealed periodic variations in the radial residual velocities
along the Galactic radius vector with a typical scale length of
lambda=2.0(+/-0.2) kpc and a mean amplitude of fR=7(+/-1) km/s. The fact that
the radial residual velocities of almost all OB-associations in rich
stellar-gas complexes are directed toward the Galactic center suggests that the
solar neighborhood under consideration is within the corotation radius. The
azimuthal-velocity field exhibits a distinct periodic pattern in the region
0<l<180 degrees, where the mean azimuthal-velocity amplitude is ft=6(+/-2)
km/s. There is no periodic pattern of the azimuthal-velocity field in the
region 180<l<360 degrees. The locations of the Cygnus arm, as well as the
Perseus arm, inferred from an analysis of the radial- and azimuthal-velocity
fields coincide. The periodic patterns of the residual-velocity fields of
Cepheids and OB associations share many common features.Comment: 21 page
Lieb-Mattis ferrimagnetism in diluted magnetic semiconductors
We show the possibility of long-range ferrimagnetic ordering with a
saturation magnetisation of the order of 1 Bohr magneton per spin for
arbitrarily low concentration of magnetic impurities in semiconductors,
provided that the impurities form a superstructure satisfying the conditions of
the Lieb-Mattis theorem. Explicit examples of such superstructures are given
for the wurtzite lattice, and the temperature of ferrimagnetic transition is
estimated from a high-temperature expansion. Exact diagonalization studies show
that small fragments of the structure exhibit enhanced magnetic response and
isotropic superparamagnetism at low temperatures. A quantum transition in a
high magnetic field is considered and similar superstructures in cubic
semiconductors are discussed as well.Comment: 6 pages,4 figure
Implementierung eines Algorithmus für den LHCb Level-1 vertex-trigger
Current high-energy experiments for precision measurement of CP violation on the basis of B mesons from hadronic reactions make great demands on the trigger system. Only a very small fraction of all produced events qualifies for such analysis. In this thesis an algorithm for the Level-1 vertex trigger of the future LHCb detector at CERN is developed and implemented with the GAUDI framework. It recognizes and reconstructs secondary vertices with a significant distance from the primary interaction point. The existence of these is interpreted as an indication of the presence of interesting B decays in the event. The processing time is measured in great detail and the reconstruction results are qualitatively analyzed
Low-temperature properties of the Hubbard model on highly frustrated one-dimensional lattices
We consider the repulsive Hubbard model on three highly frustrated
one-dimensional lattices -- sawtooth chain and two kagom\'{e} chains -- with
completely dispersionless (flat) lowest single-electron bands. We construct the
complete manifold of {\em exact many-electron} ground states at low electron
fillings and calculate the degeneracy of these states. As a result, we obtain
closed-form expressions for low-temperature thermodynamic quantities around a
particular value of the chemical potential . We discuss specific
features of thermodynamic quantities of these ground-state ensembles such as
residual entropy, an extra low-temperature peak in the specific heat, and the
existence of ferromagnetism and paramagnetism. We confirm our analytical
results by comparison with exact diagonalization data for finite systems.Comment: 20 pages, 12 figures, 2 table
On the mechanism of action of the cytostatic drug anguidine and of the immunosuppressive agent ovalicin, two sesquiterpenes from fungi
Flat-Band Ferromagnetism as a Pauli-Correlated Percolation Problem
We investigate the location and nature of the para-ferro transition of
interacting electrons in dispersionless bands using the example of the Hubbard
model on the Tasaki lattice. This case can be analyzed as a geometric
site-percolation problem where different configurations appear with nontrivial
weights. We provide a complete exact solution for the 1D case and develop a
numerical algorithm for the 2D case. In two dimensions the paramagnetic phase
persists beyond the uncorrelated percolation point, and the grand-canonical
transition is via a first-order jump to an unsaturated ferromagnetic phase.Comment: 6 pages, 5 figure
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