24,153 research outputs found
On a model mechanism for the spatial patterning of teeth primordia in the Alligator
We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator,Alligator mississippiensis. Detailed embryological studies by Westergaard & Ferguson (1986, 1987, 1990) show that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a reaction-diffusion mechanism, which crucially includes domain growth. The model can reproduce the spatial pattern development of the first seven teeth primordia in the lower half jaw ofA. mississippiensis. The results for the precise spatio-temporal sequence compare well with detailed developmental experiments
Vaccinia virus immune evasion: mechanisms, virulence and immunogenicity
Virus infection of mammalian cells is sensed by pattern recognition receptors and leads to an innate immune response that restricts virus replication and induces adaptive immunity. In response, viruses have evolved many countermeasures that enable them to replicate and be transmitted to new hosts, despite the host innate immune response. Poxviruses, such as vaccinia virus (VACV), have large DNA genomes and encode many proteins that are dedicated to host immune evasion. Some of these proteins are secreted from the infected cell, where they bind and neutralize complement factors, interferons, cytokines and chemokines. Other VACV proteins function inside cells to inhibit apoptosis or signalling pathways that lead to the production of interferons and pro-inflammatory cytokines and chemokines. In this review, these VACV immunomodulatory proteins are described and the potential to create more immunogenic VACV strains by manipulation of the gene encoding these proteins is discussed
Grain Physics and Rosseland Mean Opacities
Tables of mean opacities are often used to compute the transfer of radiation
in a variety of astrophysical simulations from stellar evolution models to
proto-planetary disks. Often tables, such as Ferguson et al. (2005), are
computed with a predetermined set of physical assumptions that may or may not
be valid for a specific application. This paper explores the effects of several
assumptions of grain physics on the Rosseland mean opacity in an oxygen rich
environment. We find that changing the distribution of grain sizes, either the
power-law exponent or the shape of the distribution, has a marginal effect on
the total mean opacity. We also explore the difference in the mean opacity
between solid homogenous grains and grains that are porous or conglomorations
of several species. Changing the amount of grain opacity included in the mean
by assuming a grain-to-gas ratio significantly affects the mean opacity, but in
a predictable way.Comment: 19 pages, 6 figures, accepted for publication in Ap
Uncertainty as a Key Influence in the Decision To Admit Patients with Transient Ischemic Attack
Background
Patients with transient ischemic attacks (TIA) are at high risk of subsequent vascular events. Hospitalization improves quality of care, yet admission rates for TIA patients vary considerably.
Objectives
We sought to identify factors associated with the decision to admit patents with TIA.
Design
We conducted a secondary analysis of a prior studyâs data including semi-structured interviews, administrative data, and chart review.
Participants
We interviewed multidisciplinary clinical staff involved with TIA care. Administrative data included information for TIA patients in emergency departments or inpatient settings at VA medical centers (VAMCs) for fiscal years (FY) 2011 and 2014. Chart reviews were conducted on a subset of patients from 12 VAMCs in FY 2011.
Approach
For the qualitative data, we focused on intervieweesâ responses to the prompt: âTell me what influences you in the decision to or not to admit TIA patients.â We used administrative data to identify admission rates and chart review data to identify ABCD2 scores (a tool to classify stroke risk after TIA).
Key Results
Providersâ decisions to admit TIA patients were related to uncertainty in several domains: lack of a facility TIA-specific policy, inconsistent use of ABCD2 score, and concerns about facilitiesâ ability to complete a timely workup. There was a disconnect between staff perceptions about TIA admission and facility admission rates. According to chart review data, staff at facilities with higher admission rates in FY 2011 reported consistent reliance on ABCD2 scores and related guidelines in admission decision-making.
Conclusions
Many factors contributed to decisions regarding admitting a patient with TIA; however, cliniciansâ uncertainty appeared to be a key driver. Further quality improvement interventions for TIA care should focus on facility adoption of TIA protocols to address uncertainty in TIA admission decision-making and to standardize timely evaluation of TIA patients and delivery of secondary prevention strategies
The Andromeda Stream
The existence of a stream of tidally stripped stars from the Sagittarius
Dwarf galaxy demonstrates that the Milky Way is still in the process of
accreting mass. More recently, an extensive stream of stars has been uncovered
in the halo of the Andromeda galaxy (M31), revealing that it too is
cannibalizing a small companion. This paper reports the recent observations of
this stream, determining it spatial and kinematic properties, and tracing its
three-dimensional structure, as well as describing future observations and what
we may learn about the Andromeda galaxy from this giant tidal stream.Comment: 3 Pages. Refereed contribution to the 5th Galacto Chemodynamics
conference held in Swinburne, July 2003. Accepted for publication in PAS
On the primordial scenario for abundance variations within globular clusters. The isochrone test
Self-enrichment processes occurring in the early stages of a globular cluster
lifetime are generally invoked to explain the observed CNONaMgAl abundance
anticorrelations within individual Galactic globulars.We have tested, with
fully consistent stellar evolution calculations, if theoretical isochrones for
stars born with the observed abundance anticorrelations satisfy the
observational evidence that objects with different degrees of these anomalies
lie on essentially identical sequences in the Color-Magnitude-Diagram (CMD). To
this purpose, we have computed for the first time low-mass stellar models and
isochrones with an initial metal mixture that includes the extreme values of
the observed abundance anticorrelations, and varying initial He mass fractions.
Comparisons with 'normal' alpha-enhanced isochrones and suitable Monte Carlo
simulations that include photometric errors show that a significant broadening
of the CMD sequences occurs only if the helium enhancement is extremely large
(in this study, when Y=0.35) in the stars showing anomalous abundances. Stellar
luminosity functions up to the Red Giant Branch tip are also very weakly
affected, apart from - depending on the He content of the polluting material -
the Red Giant Branch bump region. We also study the distribution of stars along
the Zero Age Horizontal Branch, and derive general constraints on the relative
location of objects with and without abundance anomalies along the observed
horizontal branches of globular clusters.Comment: Accepted for publication in Ap
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