35,122 research outputs found
Measurement and Simulation of Coaxial to Microstrip Transitions' Radiation Properties and Substrate Influence
A radiation and electro-magnetic (EM) field analysis of coaxial-to-microstrip transitions is presented. Radiation is quantified by simulation and measurement of a crosstalk between two Omni-Spectra's transitions using microstrip 'open' calibration standards at different positions. Simulation results are compared to the measured data and good agreement is reported on two different substrates. The evaluation method which is used to analyze quality of the transition and its radiation properties was already developed and verified on a grounded coplanar waveguide (CPWG) transmission line. Results can be used to estimate uncertainty budget of the calibrated measurement with respect to the measured radiation. Results on different substrates show interesting behaviour and can prove useful when choosing suitable substrate for specific test-fixture
Combined GABA-immunocytochemistry and TMB-HRP histochemistry of pretectal nuclei projecting to the inferior olive rats, cats and monkeys
Comment on "Secure direct communication with a quantum one-time pad"
In the paper [Phys. Rev. A \textbf{69}, 052319 (2004)], a quantum direct
communication protocol is proposed which is claimed to be unconditionally
secure even for the case of a noisy channel. We show that this is not the case
by giving an undetectable attack scheme
Sliced Wasserstein Distance for Learning Gaussian Mixture Models
Gaussian mixture models (GMM) are powerful parametric tools with many
applications in machine learning and computer vision. Expectation maximization
(EM) is the most popular algorithm for estimating the GMM parameters. However,
EM guarantees only convergence to a stationary point of the log-likelihood
function, which could be arbitrarily worse than the optimal solution. Inspired
by the relationship between the negative log-likelihood function and the
Kullback-Leibler (KL) divergence, we propose an alternative formulation for
estimating the GMM parameters using the sliced Wasserstein distance, which
gives rise to a new algorithm. Specifically, we propose minimizing the
sliced-Wasserstein distance between the mixture model and the data distribution
with respect to the GMM parameters. In contrast to the KL-divergence, the
energy landscape for the sliced-Wasserstein distance is more well-behaved and
therefore more suitable for a stochastic gradient descent scheme to obtain the
optimal GMM parameters. We show that our formulation results in parameter
estimates that are more robust to random initializations and demonstrate that
it can estimate high-dimensional data distributions more faithfully than the EM
algorithm
kmos: A lattice kinetic Monte Carlo framework
Kinetic Monte Carlo (kMC) simulations have emerged as a key tool for
microkinetic modeling in heterogeneous catalysis and other materials
applications. Systems, where site-specificity of all elementary reactions
allows a mapping onto a lattice of discrete active sites, can be addressed
within the particularly efficient lattice kMC approach. To this end we describe
the versatile kmos software package, which offers a most user-friendly
implementation, execution, and evaluation of lattice kMC models of arbitrary
complexity in one- to three-dimensional lattice systems, involving multiple
active sites in periodic or aperiodic arrangements, as well as site-resolved
pairwise and higher-order lateral interactions. Conceptually, kmos achieves a
maximum runtime performance which is essentially independent of lattice size by
generating code for the efficiency-determining local update of available events
that is optimized for a defined kMC model. For this model definition and the
control of all runtime and evaluation aspects kmos offers a high-level
application programming interface. Usage proceeds interactively, via scripts,
or a graphical user interface, which visualizes the model geometry, the lattice
occupations and rates of selected elementary reactions, while allowing
on-the-fly changes of simulation parameters. We demonstrate the performance and
scaling of kmos with the application to kMC models for surface catalytic
processes, where for given operation conditions (temperature and partial
pressures of all reactants) central simulation outcomes are catalytic activity
and selectivities, surface composition, and mechanistic insight into the
occurrence of individual elementary processes in the reaction network.Comment: 21 pages, 12 figure
The state space of short-range Ising spin glasses: the density of states
The state space of finite square and cubic Ising spin glass models is
analysed in terms of the global and the local density of states. Systems with
uniform and gaussian probability distribution of interactions are compared.
Different measures for the local state density are presented and discussed. In
particular the question whether the local density of states grows exponentially
or not is considered. The direct comparison of global and local densities leads
to consequences for the structure of the state space.Comment: 18 pages (including 6 figures); submitted to Z.f.Physik
Quantum Lubrication: Suppression of Friction in a First Principle Four Stroke Heat Engine
A quantum model of a heat engine resembling the Otto cycle is employed to
explore strategies to suppress frictional losses. These losses are caused by
the inability of the engine's working medium to follow adiabatically the change
in the Hamiltonian during the expansion and compression stages. By adding
external noise to the engine, frictional losses can be suppressed.Comment: references added some minor change
Reweighting towards the chiral limit
We propose to perform fully dynamical simulations at small quark masses by
reweighting in the quark mass. This approach avoids some of the technical
difficulties associated with direct simulations at very small quark masses. We
calculate the weight factors stochastically, using determinant breakup and low
mode projection to reduce the statistical fluctuations. We find that the weight
factors fluctuate only moderately on nHYP smeared dynamical Wilson-clover
ensembles, and we could successfully reweight 16^4, (1.85fm)^4 volume
configurations from m_q = 20MeV to m_q = 5MeV quark masses, reaching the
epsilon-regime. We illustrate the strength of the method by calculating the low
energy constant F from the epsilon-regime pseudo-scalar correlator.Comment: 17 pages, 8 figure
Visibility of Cold Atomic Gases in Optical Lattices for Finite Temperatures
In nearly all experiments with ultracold atoms time-of-flight pictures are
the only data available. In this paper we present an analytical strong-coupling
calculation for those time-of-flight pictures of bosons in an optical lattice
in the Mott phase. This allows us to determine the visibility, which quantifies
the contrast of peaks in the time-of-flight pictures, and we suggest how to use
it as a thermometer.Comment: Author Information under
http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir
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