6,888 research outputs found
Magnetic anisotropies and magnetization reversal of the CoCrFeAl Heusler compound
Magnetic anisotropies and magnetization reversal properties of the epitaxial
Heusler compound CoCrFeAl (CCFA) deposited on Fe and Cr
buffer layers are studied. Both samples exhibit a growth-induced fourfold
anisotropy, and magnetization reversal occurs through the formation of stripy
domains or 90 degree domains. During rotational magnetometric scans the sample
deposited on Cr exhibits about 2 degree sharp peaks in the angular dependence
of the coercive field, which are oriented along the hard axis directions. These
peaks are a consequence of the specific domain structure appearing in this
particular measurement geometry. A corresponding feature in the sample
deposited on Fe is not observed.Comment: 11 pages, 7 figure
Ray-tracing in pseudo-complex General Relativity
Motivated by possible observations of the black hole candidate in the center
of our galaxy and the galaxy M87, ray-tracing methods are applied to both
standard General Relativity (GR) and a recently proposed extension, the
pseudo-complex General Relativity (pc-GR). The correction terms due to the
investigated pc-GR model lead to slower orbital motions close to massive
objects. Also the concept of an innermost stable circular orbit (ISCO) is
modified for the pc-GR model, allowing particles to get closer to the central
object for most values of the spin parameter than in GR. Thus, the
accretion disk, surrounding a massive object, is brighter in pc-GR than in GR.
Iron K emission line profiles are also calculated as those are good
observables for regions of strong gravity. Differences between the two theories
are pointed out.Comment: revised versio
Polymer chain stiffness versus excluded volume: A Monte Carlo study of the crossover towards the wormlike chain model
When the local intrinsic stiffness of a polymer chain varies over a wide
range, one can observe both a crossover from rigid-rod-like behavior to
(almost) Gaussian random coils and a further crossover towards self-avoiding
walks in good solvents. Using the pruned-enriched Rosenbluth method (PERM) to
study self-avoiding walks of up to steps and variable flexibility,
the applicability of the Kratky-Porod model is tested. Evidence for
non-exponential decay of the bond-orientational correlations for large distances along the chain contour is presented, irrespective
of chain stiffness. For bottle-brush polymers on the other hand, where
experimentally stiffness is varied via the length of side-chains, it is shown
that these cylindrical brushes (with flexible backbones) are not described by
the Kratky-Porod wormlike chain model, since their persistence length is
(roughly) proportional to their cross-sectional radius, for all conditions of
practical interest.Comment: 6 pages, 5 figures, to be published in Europhys. Lett. (2010
Training Strategies for Deep Learning Gravitational-Wave Searches
Compact binary systems emit gravitational radiation which is potentially detectable by current Earth bound detectors. Extracting these signals from the instruments' background noise is a complex problem and the computational cost of most current searches depends on the complexity of the source model. Deep learning may be capable of finding signals where current algorithms hit computational limits. Here we restrict our analysis to signals from non-spinning binary black holes and systematically test different strategies by which training data is presented to the networks. To assess the impact of the training strategies, we re-analyze the first published networks and directly compare them to an equivalent matched-filter search. We find that the deep learning algorithms can generalize low signal-to-noise ratio (SNR) signals to high SNR ones but not vice versa. As such, it is not beneficial to provide high SNR signals during training, and fastest convergence is achieved when low SNR samples are provided early on. During testing we found that the networks are sometimes unable to recover any signals when a false alarm probability is required. We resolve this restriction by applying a modification we call unbounded Softmax replacement (USR) after training. With this alteration we find that the machine learning search retains of the sensitivity of the matched-filter search down to a false-alarm rate of 1 per month
Disentanglement of the electronic and lattice parts of the order parameter in a 1D Charge Density Wave system probed by femtosecond spectroscopy
We report on the high resolution studies of the temperature (T) dependence of
the q=0 phonon spectrum in the quasi one-dimensional charge density wave (CDW)
compound K0.3MoO3 utilizing time-resolved optical spectroscopy. Numerous modes
that appear below Tc show pronounced T-dependences of their amplitudes,
frequencies and dampings. Utilizing the time-dependent Ginzburg-Landau theory
we show that these modes result from linear coupling of the electronic part of
the order parameter to the 2kF phonons, while the (electronic) CDW amplitude
mode is overdamped.Comment: 4 pages, 3 figures + supplementary material, accepted for publication
in Phys. Rev. Let
Tailoring laser pulses with spectral and fluence constraints using optimal control theory
Within the framework of optimal control theory we develop a simple iterative
scheme to determine optimal laser pulses with spectral and fluence constraints.
The algorithm is applied to a one-dimensional asymmetric double well where the
control target is to transfer a particle from the ground state, located in the
left well, to the first excited state, located in the right well. Extremely
high occupations of the first excited state are obtained for a variety of
spectral and/or energetic constraints. Even for the extreme case where no
resonance frequency is allowed in the pulse the algorithm achieves an
occupation of almost 100%
Fidelity amplitude of the scattering matrix in microwave cavities
The concept of fidelity decay is discussed from the point of view of the
scattering matrix, and the scattering fidelity is introduced as the parametric
cross-correlation of a given S-matrix element, taken in the time domain,
normalized by the corresponding autocorrelation function. We show that for
chaotic systems, this quantity represents the usual fidelity amplitude, if
appropriate ensemble and/or energy averages are taken. We present a microwave
experiment where the scattering fidelity is measured for an ensemble of chaotic
systems. The results are in excellent agreement with random matrix theory for
the standard fidelity amplitude. The only parameter, namely the perturbation
strength could be determined independently from level dynamics of the system,
thus providing a parameter free agreement between theory and experiment
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