24,800 research outputs found
The bird: A pressure-confined explosion in the interstellar medium
The non-thermal radio continuum source G5.3-1.0, mapped at 20 cm with the Very Large Array (VLA) by Becker and Helfand, has an unusual bird-like shape. In order to determine possible interaction of this source with adjacent cold gas, we have mapped this region in the J=1-0 line of CO using the AT and T Bell Laboratories 7m antenna and the FCRAO 14m antenna. The map shown contains 1859 spectra sampled on a 1.5 arcminute grid; each spectrum has an rms noise of 0.2 K in 1 MHz channels. There are several molecular clouds at different velocities along the line of sight. The outer regions of a previously unknown Giant Molecular Cloud (GMC) at l=4.7 deg., b=-0.85 deg., v=200 km s(-1) appears to be interacting with G5.3-10: the molecular cloud has a bird-shaped hole at the position of the continuum source, except that the brightest continuum point (the bird's head) appears to be embedded in the cloud. The velocity of this GMC indicates it is within 2 kpc of the galactic center. The morphology suggests that a supernova or other explosive event occurred near the outside of the GMC, in a region where (n) is approximately 300 cm(-3), and expanded into a region of lower density and pressure. The pressures, densities, and velocity gradients of molecular clouds near the galactic center are on average higher than those of clouds near the Sun. We therefore expect that Type II supernovae near the galactic center would be distorted by their interactions with their parent molecular clouds
An Introduction to Slice-Based Cohesion and Coupling Metrics
This report provides an overview of slice-based software metrics. It brings together information about the development of the metrics from Weiser’s original idea that program slices may be used in the measurement of program complexity, with alternative slice-based measures proposed by other researchers. In particular, it details two aspects of slice-based metric calculation not covered elsewhere in the literature: output variables and worked examples of the calculations. First, output variables are explained, their use explored and standard reference terms and usage proposed. Calculating slice-based metrics requires a clear understanding of ‘output variables’ because they form the basis for extracting the program slices on which the calculations depend. This report includes a survey of the variation in the definition of output variables used by different research groups and suggests standard terms of reference for these variables. Our study identifies four elements which are combined in the definition of output variables. These are the function return value, modified global variables, modified reference parameters and variables printed or otherwise output by the module. Second, slice-based metric calculations are explained with the aid of worked examples, to assist newcomers to the field. Step-by-step calculations of slice-based cohesion and coupling metrics based on the vertices output by the static analysis tool CodeSurfer (R) are presented and compared with line-based calculations
Soluble CD40 ligand can replace the normal T cell-derived CD40 ligand signal to B cells in T cell-dependent activation
We have constructed a soluble chimeric fusion protein between the mouse CD8 alpha chain and the mouse CD40 T cell ligand. This protein binds to both human and mouse B cells. By itself it induced a modest degree of B cell proliferation, but together with anti-immunoglobulin (anti-Ig) antibody it greatly stimulated B cell proliferation, as determined by both [3H]thymidine uptake and increase in cell numbers. These data are evidence that the CD40 ligand on T cells provides a signal that drives B cell proliferation. This signal is synergistic with that delivered by anti-Ig antibody
Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates
We propose a new approach to understand the origin of the pseudogap in the
cuprates, in terms of bosonic entropy. The near-simultaneous softening of a
large number of different -bosons yields an extended range of short-range
order, wherein the growth of magnetic correlations with decreasing temperature
is anomalously slow. These entropic effects cause the spectral weight
associated with the Van Hove singularity (VHS) to shift rapidly and nearly
linearly toward half filling at higher , consistent with a picture of the
VHS driving the pseudogap transition at a temperature . As a
byproduct, we develop an order-parameter classification scheme that predicts
supertransitions between families of order parameters. As one example, we find
that by tuning the hopping parameters, it is possible to drive the cuprates
across a {\it transition between Mott and Slater physics}, where a
spin-frustrated state emerges at the crossover.Comment: 24 pgs, 15 figs + Supp. Material [6pgs, 3 figs]. Major revision of
arXiv:1505.0477
Morphology-dependent trends of galaxy age with environment in Abell 901/902 seen with COMBO-17
We investigate correlations between galaxy age and environment in the Abell
901/2 supercluster for separate morphologies. Using COMBO-17 data, we define a
sample of 530 galaxies, complete at on an area of (Mpc/). We explore several age indicators including an
extinction-corrected residual from the colour-magnitude relation (CMR). As a
result, we find a clear trend of age with density for galaxies of all
morphologies that include a spheroidal component, in the sense that galaxies in
denser environments are older. This trend is not seen among Scd/Irr galaxies
since they all have young ages. However, the trend among the other types is
stronger for fainter galaxies. While we also see an expected age-morphology
relation, we find no evidence for a morphology-density relation at fixed age.Comment: Accepted for publication in MNRAS (Letters
Statistical Geometry in Quantum Mechanics
A statistical model M is a family of probability distributions, characterised
by a set of continuous parameters known as the parameter space. This possesses
natural geometrical properties induced by the embedding of the family of
probability distributions into the Hilbert space H. By consideration of the
square-root density function we can regard M as a submanifold of the unit
sphere in H. Therefore, H embodies the `state space' of the probability
distributions, and the geometry of M can be described in terms of the embedding
of in H. The geometry in question is characterised by a natural Riemannian
metric (the Fisher-Rao metric), thus allowing us to formulate the principles of
classical statistical inference in a natural geometric setting. In particular,
we focus attention on the variance lower bounds for statistical estimation, and
establish generalisations of the classical Cramer-Rao and Bhattacharyya
inequalities. The statistical model M is then specialised to the case of a
submanifold of the state space of a quantum mechanical system. This is pursued
by introducing a compatible complex structure on the underlying real Hilbert
space, which allows the operations of ordinary quantum mechanics to be
reinterpreted in the language of real Hilbert space geometry. The application
of generalised variance bounds in the case of quantum statistical estimation
leads to a set of higher order corrections to the Heisenberg uncertainty
relations for canonically conjugate observables.Comment: 32 pages, LaTex file, Extended version to include quantum measurement
theor
Effectiveness of slow motion video compared to real time video in improving the accuracy and consistency of subjective gait analysis in dogs
Objective measures of canine gait quality via force plates, pressure mats or kinematic analysis are considered superior to subjective gait assessment (SGA). Despite research demonstrating that SGA does not accurately detect subtle lameness, it remains the most commonly performed diagnostic test for detecting lameness in dogs. This is largely because the financial, temporal and spatial requirements for existing objective gait analysis equipment makes this technology impractical for
use in general practice. The utility of slow motion video as a potential tool to augment SGA is currently untested. To evaluate a more accessible way to overcome the limitations of SGA, a slow motion video study was undertaken. Three experienced veterinarians reviewed video footage of 30 dogs, 15 with a diagnosis of primary limb lameness based on history and physical examination, and 15 with no indication of limb lameness based on history and physical examination. Four different videos were made for each dog, demonstrating each dog walking and trotting in real time, and then again walking and trotting in 50% slow motion. For each video, the veterinary raters assessed both the degree of lameness, and which limb(s) they felt represented the source of the lameness. Spearman’s rho, Cramer’s V, and t-tests were performed to determine if slow motion video increased either the accuracy or consistency of raters’ SGA relative to real time video. Raters demonstrated no significant increase in consistency or accuracy in their SGA of slow motion video relative to real time video. Based on these findings, slow motion video does not increase the consistency or accuracy of SGA values. Further research is required to determine if slow motion video will benefit SGA in other ways
Metric approach to quantum constraints
A new framework for deriving equations of motion for constrained quantum
systems is introduced, and a procedure for its implementation is outlined. In
special cases the framework reduces to a quantum analogue of the Dirac theory
of constrains in classical mechanics. Explicit examples involving spin-1/2
particles are worked out in detail: in one example our approach coincides with
a quantum version of the Dirac formalism, while the other example illustrates
how a situation that cannot be treated by Dirac's approach can nevertheless be
dealt with in the present scheme.Comment: 13 pages, 1 figur
Interferometric Observations of V838 Monocerotis
We have used long-baseline near-IR interferometry to resolve the peculiar
eruptive variable V838 Mon and to provide the first direct measurement of its
angular size. Assuming a uniform disk model for the emission we derive an
apparent angular diameter at the time of observations (November-December 2004)
of milli-arcseconds. For a nominal distance of kpc,
this implies a linear radius of . However, the data are
somewhat better fit by elliptical disk or binary component models, and we
suggest that the emission may be strongly affected by ejecta from the outburst.Comment: 12 pages, 1 two-part encapsulated postscript figure. Accepted by
ApJL. Added a table of observation
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