4,227 research outputs found
Non-Markovian stochastic Liouville equation and anomalous relaxation kinetics
The kinetics of phase and population relaxation in quantum systems induced by
noise with anomalously slowly decaying correlation function P (t) ~ (wt)^{-
alpha}, where 0 < alpha < 1 is analyzed within continuous time random walk
approach. The relaxation kinetics is shown to be anomalously slow. Moreover for
alpha < 1 in the limit of short characteristic time of fluctuations w^{-1} the
kinetics is independent of w. As alpha \to 1 the relaxation regime changes from
the static limit to fluctuation narrowing. Simple analytical expressions are
obtained describing the specific features of the kinetics.Comment: 7 pages, 2 figure
Fractional Operators, Dirichlet Averages, and Splines
Fractional differential and integral operators, Dirichlet averages, and
splines of complex order are three seemingly distinct mathematical subject
areas addressing different questions and employing different methodologies. It
is the purpose of this paper to show that there are deep and interesting
relationships between these three areas. First a brief introduction to
fractional differential and integral operators defined on Lizorkin spaces is
presented and some of their main properties exhibited. This particular approach
has the advantage that several definitions of fractional derivatives and
integrals coincide. We then introduce Dirichlet averages and extend their
definition to an infinite-dimensional setting that is needed to exhibit the
relationships to splines of complex order. Finally, we focus on splines of
complex order and, in particular, on cardinal B-splines of complex order. The
fundamental connections to fractional derivatives and integrals as well as
Dirichlet averages are presented
A Search for H2CO 6cm Emission toward Young Stellar Objects III: VLA Observations
We report the results of our third survey for formaldehyde (H2CO) 6cm maser
emission in the Galaxy. Using the Very Large Array, we detected two new H2CO
maser sources (G23.01-0.41 and G25.83-0.18), thus increasing the sample of
known H2CO maser regions in the Galaxy to seven. We review the characteristics
of the G23.01-0.41 and G25.83-0.18 star forming regions. The H2CO masers in
G23.01-0.41 and G25.83-0.18 share several properties with the other known H2CO
masers, in particular, emission from rich maser environments and close
proximity to very young massive stellar objects.Comment: Accepted for publication in the Astrophysical Journal Supplement
Serie
The Supercooling of a Nematic Liquid Crystal
We investigate the supercooling of a nematic liquid crystal using fluctuating
non-linear hydrodynamic equations. The Martin-Siggia-Rose formalism is used to
calculate renormalized transport coefficients to one-loop order. Similar
theories for isotropic liquids have shown substantial increases of the
viscosities as the liquid is supercooled or compressed due to feedback from the
density fluctuations which are freezing. We find similar results here for the
longitudinal and various shear viscosities of the nematic. However, the two
viscosities associated with the nematic director motion do not grow in any
dramatic way; i.e.\ there is no apparent freezing of the director modes within
this hydrodynamic formalism. Instead a glassy state of the nematic may arise
from a ``random anisotropy" coupling of the director to the frozen density.Comment: Late
Thermal transport of the XXZ chain in a magnetic field
We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic
fields where magnetothermal effects arise. Due to the integrability of this
model, all transport coefficients diverge, signaled by finite Drude weights.
Using exact diagonalization and mean-field theory, we analyze the temperature
and field dependence of the thermal Drude weight for various exchange
anisotropies under the condition of zero magnetization-current flow. First, we
find a strong magnetic field dependence of the Drude weight, including a
suppression of its magnitude with increasing field strength and a non-monotonic
field-dependence of the peak position. Second, for small exchange anisotropies
and magnetic fields in the massless as well as in the fully polarized regime
the mean-field approach is in excellent agreement with the exact
diagonalization data. Third, at the field-induced quantum critical line between
the para- and ferromagnetic region we propose a universal low-temperature
behavior of the thermal Drude weight.Comment: 9 pages REVTeX4 including 5 figures, revised version, refs. added,
typos correcte
QTL Analysis of Mineral Content in Perennial Ryegrass (\u3cem\u3eLolium Perenne\u3c/em\u3e L.)
Variation in mineral content of grasses can be strongly influenced by genetic factors. Grass tetany (hypomagnesemia) of cattle and sheep is due to disturbances in serum magnesium levels. In Southern Australia, resultant levels of mortality in cattle vary between 0.5-1.5% of total stock numbers. Serum magnesium variation may be due to feed deficits, or dietary imbalances that interfere with magnesium metabolism. High levels of potassium appear to exert negative effects on the levels of magnesium in the blood. Italian ryegrass genotypes with high levels of magnesium can alleviate the incidence of grass tetany. The genetic control of mineral content, including magnesium, in perennial ryegrass has been investigated using molecular marker-based analysis
Comparison of homoeolocus organisation in paired BAC clones from white clover (Trifolium repens L.) and microcolinearity with model legume species
<p>Abstract</p> <p>Background</p> <p>White clover (<it>Trifolium repens </it>L.) is an outbreeding allotetraploid species and an important forage legume in temperate grassland agriculture. Comparison of sub-genome architecture and study of nucleotide sequence diversity within allopolyploids provides insight into evolutionary divergence mechanisms, and is also necessary for the development of whole-genome sequencing strategies. This study aimed to evaluate the degree of divergence between the O and P' sub-genomes of white clover through sequencing of BAC clones containing paired homoeoloci. The microsyntenic relationships between the genomes of white clover and the model legumes <it>Lotus japonicus </it>and <it>Medicago truncatula </it>as well as <it>Arabidopsis thaliana </it>were also characterised.</p> <p>Results</p> <p>A total of four paired homoeologous BACs were selected and sequenced to generate 173 kb of overlapping sequence between the O and P' sub-genomes. Equivalent gene content was generally observed, apart from small-scale deletions, in contrast to conservation of intergenic sequences, which varied between the four selected regions. Measurement of the number of synonymous substitutions between homoeologous genes led to estimation of a 4.2 million year divergence time between the two sub-genomes. Microsynteny was observed between the genomes of white clover and <it>L. japonicus </it>for all four targeted regions, but corresponding <it>M. truncatula </it>genomic regions were only identified for two BAC pairs.</p> <p>Conclusions</p> <p>This study describes the first analysis of sub-genome structural conservation across selected genomic regions in white clover. Although the high levels of sequence conservation between the O and P' sub-genomes would complicate efforts for whole genome sequence assembly, the conserved microsynteny with model legume genomes, especially that of <it>L. japonicus</it>, will be highly valuable for the future of white clover genomics and molecular breeding.</p
HST and Spitzer imaging of red and blue galaxies at z~2.5: A correlation between size and star formation activity from compact quiescent galaxies to extended star forming galaxies
We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies
at 2<z<3.5 in the FIRES MS1054 field with red and blue rest-frame optical
colors. About half of the galaxies are very compact (effective radii r_e < 1
kpc) at rest-frame optical wavelengths, the others are extended (1< r_e < 10
kpc). For reference, 1 kpc corresponds to 0.12 arcsec at z=2.5 in the adopted
cosmology. We separate actively star forming galaxies from quiescent galaxies
by modeling their rest-frame UV-NIR SEDs. The star forming galaxies span the
full range of sizes, while the quiescent galaxies all have r_e<2kpc. In the
redshift range where MIPS 24 micron imaging is a sensitive probe of re-radiated
dust emission (z<2.5), the 24 micron fluxes confirm that the light of the small
quiescent galaxies is dominated by old stars, rather than dust-enshrouded star
formation or AGN activity. The inferred surface mass densities and velocity
dispersions for the quiescent galaxies are very high compared to those in local
galaxies. The galaxies follow a Kormendy relation (between surface brightness
and size) with approximately the same slope as locally, but shifted to brighter
surface brightnesses, consistent with a mean stellar formation redshift of
z_f~5. This paper demonstrates a direct relation between star formation
activity and size at z~2.5, and the existence of a significant population of
massive, extremely dense, old stellar systems without readily identifiable
counterparts in the local universe.Comment: Accepted for publication in Ap
Finite Size Effects in Vortex Localization
The equilibrium properties of flux lines pinned by columnar disorder are
studied, using the analogy with the time evolution of a diffusing scalar
density in a randomly amplifying medium. Near H_{c1}, the physical features of
the vortices in the localized phase are shown to be determined by the density
of states near the band edge. As a result, H_{c1} is inversely proportional to
the logarithm of the sample size, and the screening length of the perpendicular
magnetic field decreases with temperature. For large tilt the extended ground
state turns out to wander in the plane perpendicular to the defects with
exponents corresponding to a directed polymer in a random medium, and the
energy difference between two competing metastable states in this case is
extensive. The divergence of the effective potential associated with strong
pinning centers as the tilt approaches its critical value is discussed as well.Comment: 10 pages, 2 figure
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