2,005 research outputs found
Structural and magnetic dynamics of a laser induced phase transition in FeRh
We use time-resolved x-ray diffraction and magnetic optical Kerr effect to
study the laser induced antiferromagnetic to ferromagnetic phase transition in
FeRh. The structural response is given by the nucleation of independent
ferromagnetic domains (\tau_1 ~ 30ps). This is significantly faster than the
magnetic response (\tau_2 ~ 60ps) given by the subsequent domain realignment.
X-ray diffraction shows that the two phases co-exist on short time-scales and
that the phase transition is limited by the speed of sound. A nucleation model
describing both the structural and magnetic dynamics is presented.Comment: 5 pages, 3 figures - changed to reflect version accepted for PR
FUSE observations of HD 5980: The wind structure of the eruptor
HD 5980 is a unique system containing one massive star (star A) that is
apparently entering the luminous blue variable phase, and an eclipsing
companion (star B) that may have already evolved beyond this phase to become a
Wolf-Rayet star. In this paper we present the results from FUSE observations
obtained in 1999, 2000, and 2002 and one far-UV observation obtained by
ORFEUS/BEFS in 1993 shortly before the first eruption of HD 5980. The eight
phase-resolved spectra obtained by FUSE in 2002 are analyzed in the context of
a wind-eclipse model. This analysis shows that the wind of the eruptor obeyed a
very fast velocity law in 2002, which is consistent with the line-driving
mechanism. Large amplitude line-profile variations on the orbital period are
shown to be due to the eclipse of star B by the wind of star A, although the
eclipse due to gas flowing in the direction of star B is absent. This can only
be explained if the wind of star A is not spherically symmetric, or if the
eclipsed line radiation is "filled-in" by emission originating from somewhere
else in the system, e.g., in the wind-wind collision region. Except for a
slightly lower wind speed, the ORFEUS/BEFS spectrum is very similar to the
spectrum obtained by FUSE at the same orbital phase: there is no indication of
the impending eruption. However, the trend for decreasing wind velocity
suggests the occurrence of the "bi-stability" mechanism, which in turn implies
that the restructuring of the circumbinary environment caused by the transition
from "fast, rarefied wind" to "slow, dense wind" was observed as the eruptive
event. The underlying mechanism responsible for the long-term decrease in wind
velocity that precipitated this change remains an open issue.Comment: 19 pages, 13 figure
Haplotype assignment of longitudinal viral deep sequencing data using covariation of variant frequencies.
Longitudinal deep sequencing of viruses can provide detailed information about intra-host evolutionary dynamics including how viruses interact with and transmit between hosts. Many analyses require haplotype reconstruction, identifying which variants are co-located on the same genomic element. Most current methods to perform this reconstruction are based on a high density of variants and cannot perform this reconstruction for slowly evolving viruses. We present a new approach, HaROLD (HAplotype Reconstruction Of Longitudinal Deep sequencing data), which performs this reconstruction based on identifying co-varying variant frequencies using a probabilistic framework. We illustrate HaROLD on both RNA and DNA viruses with synthetic Illumina paired read data created from mixed human cytomegalovirus (HCMV) and norovirus genomes, and clinical datasets of HCMV and norovirus samples, demonstrating high accuracy, especially when longitudinal samples are available
Self-similar magnetoresistance of Fibonacci ultrathin magnetic films
We study numerically the magnetic properties (magnetization and
magnetoresistance) of ultra-thin magnetic films (Fe/Cr) grown following the
Fibonacci sequence. We use a phenomenological model which includes Zeeman,
cubic anisotropy, bilinear and biquadratic exchange energies. Our physical
parameters are based on experimental data recently reported, which contain
biquadratic exchange coupling with magnitude comparable to the bilinear
exchange coupling. When biquadratic exchange coupling is sufficiently large a
striking self-similar pattern emerges.Comment: 5 pages, 5 EPS figures, REVTeX, accepted for publication in Phys.
Rev.
Phase Diagram of Multilayer Magnetic Structures
Multilayer "ferromagnet-layered antiferromagnet" (Fe/Cr) structures
frustrated due to the roughness of layer interfaces are studied by numerical
modeling methods. The "thickness-roughness" phase diagrams for the case of thin
ferromagnetic film on the surface of bulk antiferromagnet and for two
ferromagnetic layers separated by an antiferromagnetic interlayer are obtained
and the order parameter distributions for all phases are found. The phase
transitions nature in such systems is considered. The range of applicability
for the "magnetic proximity model" proposed by Slonczewski is evaluated.Comment: 8 pages, 8 figure
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