7,221 research outputs found
Unconventional strong pinning in the low temperature phase of U_.9725Th_.0275Be_13
We investigated low field vortex dynamics in a single crystal of
U_.9725Th_.0275Be_13. We found a sharp transition in the vortex creep rate at
the lower transition temperature T_c2, coincident with the second jump in the
specific heat. In the high-temperature phase, rather strong creep rates are
observed. In the low temperature phase, the rates drop to undetectabely low
levels. This behaviour indicates that a very strong pinning mechanism is
present in the low temperature phase of U_.9725Th_.0275Be_13, which could be
explained by the existence of domain walls, separating discreetly degenerate
states of a superconductor, that can sustain fractional vortices and thus act
as very strong pinning centers.Comment: 2 pages, 2 figures, accepted in PhysicaB, LT2
The effect of emulsion stabilizers on the rate of solution of silver halide grains
The effects of the emulsion stabilizers, 4-hydroxy- 6-methyl-l ,33a,7-tetraazaindene and l-phenyl-2-tetrazoline- 5-thione on the rate of solution-physical development of a monodisperse AgBr emulsion containing Carey-Lea silver sol were measured at a series of concentrations. A study of the effects of the silver halide solvent, sulfite has been stud ied along with a low-solvent surface developer. It was found that the tetraazaindene definitely had an effect on the rate of solution-physical development, while the l-phenyl-2- tetrazoline- 5-thione did not have a significant effect
Significant Strain Variation in the Mutation Spectra of Inbred Laboratory Mice.
Mutation provides the ultimate source of all new alleles in populations, including variants that cause disease and fuel adaptation. Recent whole genome sequencing studies have uncovered variation in the mutation rate among individuals and differences in the relative frequency of specific nucleotide changes (the mutation spectrum) between populations. Although parental age is a major driver of differences in overall mutation rate among individuals, the causes of variation in the mutation spectrum remain less well understood. Here, I use high-quality whole genome sequences from 29 inbred laboratory mouse strains to explore the root causes of strain variation in the mutation spectrum. My analysis leverages the unique, mosaic patterns of genetic relatedness among inbred mouse strains to identify strain private variants residing on haplotypes shared between multiple strains due to their recent descent from a common ancestor. I show that these strain-private alleles are strongly enriched for recent de novo mutations and lack signals of widespread purifying selection, suggesting their faithful recapitulation of the spontaneous mutation landscape in single strains. The spectrum of strain-private variants varies significantly among inbred mouse strains reared under standardized laboratory conditions. This variation is not solely explained by strain differences in age at reproduction, raising the possibility that segregating genetic differences affect the constellation of new mutations that arise in a given strain. Collectively, these findings imply the action of remarkably precise nucleotide-specific genetic mechanisms for tuning the de novo mutation landscape in mammals and underscore the genetic complexity of mutation rate control
Alien Registration- Dumont, Marie L. (Auburn, Androscoggin County)
https://digitalmaine.com/alien_docs/31233/thumbnail.jp
Variability of the H-beta line profiles as an indicator of orbiting bright spots in accretion disks of quasars: a case study of 3C 390.3
Here we show that in the case when double peaked emission lines originate
from outer parts of accretion disk, their variability could be caused by
perturbations in the disk emissivity. In order to test this hypothesis, we
introduced a model of disk perturbing region in the form of a single bright
spot (or flare) by a modification of the power law disk emissivity in
appropriate way. The disk emission was then analyzed using numerical
simulations based on ray-tracing method in Kerr metric and the corresponding
simulated line profiles were obtained. We applied this model to the observed
H-beta line profiles of 3C 390.3 (observed in the period 1995-1999), and
estimated the parameters of both, accretion disk and perturbing region. Our
results show that two large amplitude outbursts of the H-beta line observed in
3C 390.3 could be explained by successive occurrences of two bright spots on
approaching side of the disk. These bright spots are either moving, originating
in the inner regions of the disk and spiralling outwards by crossing small
distances during the period of several years, or stationary. In both cases,
their widths increase with time, indicating that they most likely decay.Comment: 14 pages, 5 figures, 1 table. Accepted for publication in Ap
The origin of emission and absorption features in Ton S180 Chandra observations
We present new interpretation of Ton S180 spectrum obtained by {\it Chandra}
Spectrometer (Low Energy Transmission Grating). Several narrow absorption lines
and a few emission disk lines have been successfully fitted to the data. We
have not found any significant edges accompanying line emission. We propose the
interpretation of narrow lines consistent with the paper recently written by
Krolik (2002), where warm absorber is strongly inhomogeneous. Such situation is
possible in so called multi-phase medium, where regions with different
ionization states, densities and temperatures may coexist in thermal
equilibrium under constant pressure. We illustrate this scenario with
theoretical spectra of radiation transfered through a stratified cloud with
constant pressure (instead of constant density) computed by code {\sc titan} in
plane parallel approximation. Detected spectral features are faint and their
presence do not alter the broad band continuum. We model the broad band
continuum of Ton S180 assuming an irradiated accretion disk with a dissipative
warm skin. The set of parameters appropriate for the data cannot be determined
uniquely but models with low values of the black hole mass have too hot and
radially extended warm skin to explain the formation of soft X-ray disk lines
seen in the data.Comment: accepted to Ap
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