3,143 research outputs found
Diamagnetic Response of Normal-metal -- Superconductor Double Layers
The magnetic response of a proximity-coupled superconductor-normal metal
sandwich is studied within the framework of the quasiclassical theory. The
magnetization is evaluated for finite values of the applied magnetic field
(linear and nonlinear response) at arbitrary temperatures and is used to fit
recent experimental low-temperature data. The hysteretic behavior predicted
from a Ginzburg-Landau approach and observed in experiments is obtained within
the quasiclassical theory and shown to exist also outside the Ginzburg-Landau
region.Comment: RevTex, 11 pages, 9 PostScript figures include
Properties of the energy landscape of network models for covalent glasses
We investigate the energy landscape of two dimensional network models for
covalent glasses by means of the lid algorithm. For three different particle
densities and for a range of network sizes, we exhaustively analyse many
configuration space regions enclosing deep-lying energy minima. We extract the
local densities of states and of minima, and the number of states and minima
accessible below a certain energy barrier, the 'lid'. These quantities show on
average a close to exponential growth as a function of their respective
arguments. We calculate the configurational entropy for these pockets of states
and find that the excess specific heat exhibits a peak at a critical
temperature associated with the exponential growth in the local density of
states, a feature of the specific heat also observed in real glasses at the
glass transition.Comment: RevTeX, 19 pages, 7 figure
Anomalous density of states of a Luttinger liquid in contact with a superconductor
We study the frequency and space dependence of the local tunneling density of
states of a Luttinger liquid (LL) which is connected to a superconductor. This
coupling {\em strongly} modifies the single-particle properties of the LL. It
significantly enhances the density of states near the Fermi level, whereas this
quantity vanishes as a power law for an isolated LL. The enhancement is due to
the interplay between electron-electron interactions and multiple
back-scattering processes of low-energy electrons at the interface between the
LL and the superconductor. This anomalous behavior extends over large distances
from the interface and may be detected by coupling normal probes to the system.Comment: 8 pages Revtex, two postscript figure
Single-qubit lasing and cooling at the Rabi frequency
For a superconducting qubit driven to perform Rabi oscillations and coupled
to a slow electromagnetic or nano-mechanical oscillator we describe previously
unexplored quantum optics effects. When the Rabi frequency is tuned to
resonance with the oscillator the latter can be driven far from equilibrium.
Blue detuned driving leads to a population inversion in the qubit and a
bi-stability with lasing behavior of the oscillator; for red detuning the qubit
cools the oscillator. This behavior persists at the symmetry point where the
qubit-oscillator coupling is quadratic and decoherence effects are minimized.
There the system realizes a "single-atom-two-photon laser".Comment: Replaced with final published version, fig. 2 compresse
Was sagen die Studierenden zur E-Learning- Strategie der Hochschule?
E-Learning an der Hochschule bedarf einer Strategie. Dies scheint unumstritten und heutzutage eine Notwendigkeit. Zunehmend stellt sich aber die Frage, wie dies die Studierenden sehen. In dieser Arbeit stellen wir kurz den Prozess der Strategieentwicklung einer Universität dar und bringen diesen mit einer parallel dazu durchgeführten Studierendenumfrage in Zusammenhang. Die Auswertung zeigt, dass Studierende vermehrt Online-Inhalte einfordern und dass E-Learning für sie ein klares Qualitätsmerkmal in der Hochschullehre ist.
27.04.2015 | Martin Ebner, Martin Schön & Walther Nagler (Graz
Xenogeneic, extracorporeal liver perfusion in primates improves the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio)
In fulminant hepatic failure (FHF), the development of hepatic encephalopathy is associated with grossly abnormal concentrations of plasma amino acids (PAA). Normalization of the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio) correlates with clinical improvement. This study evaluated changes in PAA metabolism during 4 h of isolated, normothermic extracorporeal liver perfusion using a newly designed system containing human blood and a rhesus monkey liver. Bile and urea production were within the physiological range. Release of the transaminases AST, ALT and LDH were minimal. The ratio of branched (valine, leucine, isoleucine) to aromatic (tyrosine, phenylalanine) amino acids increased significantly. These results indicate that a xenogeneic extracorporeal liver perfusion system is capable of significantly increasing Fischer's ratio and may play a role in treating and bridging patients in FHF in the future
Full Counting Statistics for a Single-Electron Transistor, Non-equilibrium Effects at Intermediate Conductance
We evaluate the current distribution for a single-electron transistor with
intermediate strength tunnel conductance. Using the Schwinger-Keldysh approach
and the drone (Majorana) fermion representation we account for the
renormalization of system parameters. Nonequilibrium effects induce a lifetime
broadening of the charge-state levels, which suppress large current
fluctuations.Comment: 4 pages, 1 figur
Low- and high-frequency noise from coherent two-level systems
Recent experiments indicate a connection between the low- and high-frequency
noise affecting superconducting quantum systems. We explore the possibilities
that both noises can be produced by one ensemble of microscopic modes, made up,
e.g., by sufficiently coherent two-level systems (TLS). This implies a relation
between the noise power in different frequency domains, which depends on the
distribution of the parameters of the TLSs. We show that a distribution,
natural for tunneling TLSs, with a log-uniform distribution in the tunnel
splitting and linear distribution in the bias, accounts for experimental
observations.Comment: minor corrections, references adde
A new physarum learner for network structure learning from biomedical data
A novel structure learning algorithm for Bayesian Networks based on a Physarum Learner is presented. The
length of the connections within an initially fully connected Physarum-Maze is taken as the inverse Pearson
correlation coefficient between the connected nodes. The Physarum Learner then estimates the shortest indirect
paths between each pair of nodes. In each iteration, a score of the surviving edges is incremented.
Finally, the highest scored connections are combined to form a Bayesian Network. The novel Physarum
Learner method is evaluated with different configurations and compared to the LAGD Hill Climber showing
comparable performance with respect to quality of training results and increased time efficiency for large data
sets
- …