333 research outputs found
Noise-induced switching between vortex states with different polarization in classical two-dimensional easy-plane magnets
In the 2-dimensional anisotropic Heisenberg model with XY-symmetry there are
non-planar vortices which exhibit a localized structure of the z-components of
the spins around the vortex center. We study how thermal noise induces a
transition of this structure from one polarization to the opposite one. We
describe the vortex core by a discrete Hamiltonian and consider a stationary
solution of the Fokker-Planck equation. We find a bimodal distribution function
and calculate the transition rate using Langer's instanton theory (1969). The
result is compared with Langevin dynamics simulations for the full many-spin
model.Comment: 15 pages, 4 figures, Phys. Rev. B., in pres
The Potential of Restarts for ProbSAT
This work analyses the potential of restarts for probSAT, a quite successful
algorithm for k-SAT, by estimating its runtime distributions on random 3-SAT
instances that are close to the phase transition. We estimate an optimal
restart time from empirical data, reaching a potential speedup factor of 1.39.
Calculating restart times from fitted probability distributions reduces this
factor to a maximum of 1.30. A spin-off result is that the Weibull distribution
approximates the runtime distribution for over 93% of the used instances well.
A machine learning pipeline is presented to compute a restart time for a
fixed-cutoff strategy to exploit this potential. The main components of the
pipeline are a random forest for determining the distribution type and a neural
network for the distribution's parameters. ProbSAT performs statistically
significantly better than Luby's restart strategy and the policy without
restarts when using the presented approach. The structure is particularly
advantageous on hard problems.Comment: Eurocast 201
Cloning, expression and functional characterization of the full-length murine ADAMTS13
Functional deficiency or absence of the human von Willebrand factor (VWF)-cleaving protease (VWF-cp), recently termed ADAMTS13, has been shown to cause acquired and congenital thrombotic thrombocytopenic purpura (TTP), respectively. As a first step towards developing a small animal model of TTP, we have cloned the complete (non-truncated) murine Adamts13 gene from BALB/c mice liver poly A + mRNA. Murine ADAMTS13 is a 1426-amino-acid protein with a high homology and similar structural organization to the human ortholog. Transient expression of the murine Adamts13 cDNA in HEK 293 cells yielded a protein with a molecular weight of approximately 180âkDa which degraded recombinant murine VWF (rVWF) in a dose-dependent manner. The cleavage products of murine rVWF had the expected size of 140 and 170âkDa. Murine ADAMTS13 was inhibited by EDTA and the plasma from a TTP patient.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73592/1/j.1538-7836.2005.01246.x.pd
Electron spin relaxation of the PO3 2- radical in ferroelectric betaine phosphite and in the proton glass betaine phosphate/betaine phosphite
Measurements of the electron spin-lattice relaxation time T1 and the phase memory time TM of the PO3 2- radical in γ-irradiated betaine phosphite and betaine phosphate/betaine phosphite are presented. The temperature dependence of T1 indicates the interaction of the electron spin with two groups of optical branches via Raman processes in both crystals. An additional relaxation path due to the interaction with two-level local tunneling states has been observed in the mixed crystal confirming glassy behaviour. The TM temperature dependence reflects thermally activated local motional effects of the PO3 group in both crystals. © 1994
Electron spin-lattice relaxation in Mn2+-doped ferroelectric TSCC
The spin-lattice relaxation of ferroelectric TSCC: Mn2+ has been investigated by means of the electron spin echo method in the range between 4.2 and 160 K. In the vicinity of the phase transition an anomalous increase of T1 has been detected deviating from the spin-lattice relaxation in the remaining temperature range. © 1978
Magnetic Vortex Core Reversal by Excitation of Spin Waves
Micron-sized magnetic platelets in the flux closed vortex state are
characterized by an in-plane curling magnetization and a nanometer-sized
perpendicularly magnetized vortex core. Having the simplest non-trivial
configuration, these objects are of general interest to micromagnetics and may
offer new routes for spintronics applications. Essential progress in the
understanding of nonlinear vortex dynamics was achieved when low-field core
toggling by excitation of the gyrotropic eigenmode at sub-GHz frequencies was
established. At frequencies more than an order of magnitude higher vortex state
structures possess spin wave eigenmodes arising from the magneto-static
interaction. Here we demonstrate experimentally that the unidirectional vortex
core reversal process also occurs when such azimuthal modes are excited. These
results are confirmed by micromagnetic simulations which clearly show the
selection rules for this novel reversal mechanism. Our analysis reveals that
for spin wave excitation the concept of a critical velocity as the switching
condition has to be modified.Comment: Minor corrections and polishing of previous versio
Evidence of the Jahn-Teller splitting of C60- in C60- tetraphenylphosphoniumchloride from an electron-spin-relaxation study
Pulsed EPR measurements of the transverse and longitudinal relaxation times of the C60 - anion radical in crystalline C60-tetraphenylphosphoniumchloride were done at temperatures from 4 to 40 K. Above 40 K to room temperature the longitudinal relaxation time was taken from the cw-EPR linewidth. The low-temperature data are explained in terms of local magnetic fluctuations, slow C60- motion, and localized two-level states related with the local disorder. The relaxation data at higher temperatures reveal experimental evidence for the Jahn-Teller distortion of the C60 - anion radical and allow to determine the Jahn-Teller splitting between the a2u electronic ground state and the excited e1u state of the unpaired electron. © 1995 The American Physical Society
Dynamics of ferroelectric nano cluster in BaTiO3 observed as a real time correlation between two soft X-ray laser pulses
We carry out a theoretical investigation to clarify the dynamic property of
photo-created nano-sized ferroelectric cluster observed in the paraelectric
BaTiO3 as a real time correlation of speckle pattern between two soft X-ray
laser pulses, at just above the paraelectric-ferroelectric phase transition
temperature. Based on a model with coupled soft X-ray photon and ferroelectric
phonon mode, we study the time dependence of scattering probability by using a
perturbative expansion approach. The cluster-associated phonon softening as
well as central peak effects are well reproduced in the phonon spectral
function via quantum Monte Carlo simulation. Besides, it is found that the time
dependence of speckle correlation is determined by the relaxation dynamics of
ferroelectric clusters. Near the transition point, cluster excitation is
stable, leading to a long relaxation time. While, at high temperature, cluster
structure is subject to the thermal fluctuation, ending up with a short
relaxation time.Comment: 9 pages, 3 figure
A Q-Band Pulsed ENDOR Spectrometer for the Study of Transition Metal Ion Complexes in Solids
We describe the design of a pulsed electron nuclear double resonance (ENDOR) spectrometer operating at Q-band frequencies (35 GHz) for studies of transition metal ion complexes in the temperature range between 4.2 and 297 K. Specific features of the spectrometer are a microwave IMPATT generator, a homebuilt cavity, and a commercial Bruker magnet. Standard Davies and Mims ENDOR sequences have been implemented. The performance of the spectrometer is demonstrated for a broad radio frequency range by 1H, 14N, 31P, 133Cs, and 207Pb pulsed ENDOR experiments of Cu 2+, Cr 5+, and V 4+ transition metal ion complexes in both single crystals and disordered materials
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