1,079 research outputs found
Simulating Star Formation and Feedback in Galactic Disk Models
We use a high-resolution grid-based hydrodynamics method to simulate the
multi-phase interstellar medium in a Milky Way-size quiescent disk galaxy. The
models are global and three-dimensional, and include a treatment of star
formation and feedback. We examine the formation of gravitational instabilities
and show that a form of the Toomre instability criterion can successfully
predict where star formation will occur. Two common prescriptions for star
formation are investigated. The first is based on cosmological simulations and
has a relatively low threshold for star formation, but also enforces a
comparatively low efficiency. The second only permits star formation above a
number density of 1000 cm^-3 but adopts a high efficiency. We show that both
methods can reproduce the observed slope of the relationship between star
formation and gas surface density (although at too high a rate for our adopted
parameters). A run which includes feedback from type II supernovae is
successful at driving gas out of the plane, most of which falls back onto the
disk. This feedback also substantially reduces the star formation rate.
Finally, we examine the density and pressure distribution of the ISM, and show
that there is a rough pressure equilibrium in the disk, but with a wide range
of pressures at a given location (and even wider for the case including
feedbackComment: 14 pages, 12 figures, accepted to Astrophysical Journa
Moving Past Assumptions: Recognizing Parents as Allies in Promoting the Sexual Literacies of Adolescents through a University-Community Collaboration
This article recounts how a university-community collaborative challenged prevailing assumptions about parents as barriers to the provision of gender and sexuality information to their children, allowing for the recognition of parents as critical stakeholders and partners in sexual literacy work with youth. We provide evidence that parents’ support for inclusive sexuality education uniquely situates them to educate and advocate for young people around these issues, and in so doing we hope to disrupt the rhetoric that casts parents in the United States as solely gatekeepers when it comes to young people’s access to information about the broad spectrum of human sexuality
Contrast Mechanisms for the Detection of Ferroelectric Domains with Scanning Force Microscopy
We present a full analysis of the contrast mechanisms for the detection of
ferroelectric domains on all faces of bulk single crystals using scanning force
microscopy exemplified on hexagonally poled lithium niobate. The domain
contrast can be attributed to three different mechanisms: i) the thickness
change of the sample due to an out-of-plane piezoelectric response (standard
piezoresponse force microscopy), ii) the lateral displacement of the sample
surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample
interaction at the domain boundaries caused by surface charges on the
crystallographic y- and z-faces. A careful analysis of the movement of the
cantilever with respect to its orientation relative to the crystallographic
axes of the sample allows a clear attribution of the observed domain contrast
to the driving forces respectively.Comment: 8 pages, 8 figure
Hepatozoon canis in three imported dogs: a new tickborne disease reaching the United Kingdom
An increasing number of non-endemic vectorborne pathogens have been described in dogs imported to the UK in the past two decades. Recently, an outbreak of canine babesiosis in south-east England has raised veterinary awareness with regard to the impact of such diseases on the UK canine population. Canine hepatozoonosis, caused by Hepatozoon canis and transmitted by the ingestion of Rhipicephalus sanguineus ticks, is widespread in the Mediterranean basin. Herein we describe the first three molecularly confirmed clinical cases of canine hepatozoonosis in dogs imported into the UK. Veterinarians in the UK should be aware of H canis as a potential infection in imported dogs, especially in the face of the expanding distribution of R sanguineus ticks in Europe
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NMR-based metabolomics associated with chronic kidney disease in humans and animals: a one health perspective
First-principles study of the polar O-terminated ZnO surface in thermodynamic equilibrium with oxygen and hydrogen
Using density-functional theory in combination with a thermodynamic formalism
we calculate the relative stability of various structural models of the polar
O-terminated (000-1)-O surface of ZnO. Model surfaces with different
concentrations of oxygen vacancies and hydrogen adatoms are considered.
Assuming that the surfaces are in thermodynamic equilibrium with an O2 and H2
gas phase we determine a phase diagram of the lowest-energy surface structures.
For a wide range of temperatures and pressures we find that hydrogen will be
adsorbed at the surface, preferentially with a coverage of 1/2 monolayer. At
high temperatures and low pressures the hydrogen can be removed and a structure
with 1/4 of the surface oxygen atoms missing becomes the most stable one. The
clean, defect-free surface can only exist in an oxygen-rich environment with a
very low hydrogen partial pressure. However, since we find that the
dissociative adsorption of molecular hydrogen and water (if also the
Zn-terminated surface is present) is energetically very preferable, it is very
unlikely that a clean, defect-free (000-1)-O surface can be observed in
experiment.Comment: 10 pages, 4 postscript figures. Uses REVTEX and epsf macro
An investigation of polymorphisms in innate and adaptive immune response genes in canine leishmaniosis
The outcome of infection with Leishmania infantum in dogs is variable, which is thought to be due to the nature of the immune response mounted by the host. As a consequence, the clinical signs and severity of canine leishmaniosis vary between individual dogs. Host immunogenetic factors might play an important role in determining the outcome of infection. The aim of this study was to examine polymorphisms in innate and adaptive immune response genes, to determine whether any of these were associated with susceptibility or resistance to L. infantum infection. Genomic DNA was obtained from two groups: pet dogs in endemic regions of Europe and a group of Beagles exposed to sand fly infection as part of a vaccine study. Genotyping was performed using a SNP (single nucleotide polymorphism) array for selected immune response genes. The first part of the study compared 62 clinical cases with 101 clinically unaffected dogs that were seronegative for Leishmania antibodies. One SNP in the CIITA gene demonstrated a significantly higher minor allele frequency in the case group, compared with the control group at the individual SNP level after permutation, but was not significant after correction for multiple testing. The second part of the study examined 48 Beagle dogs exposed to L. infantum over two transmission seasons. Twenty-seven dogs with a resistant phenotype (no evidence of clinical disease, seronegative at the end of the study period, negative on lymph node culture and only transiently PCR positive in bone marrow) were compared with 21 dogs demonstrating a susceptible phenotype (clinical disease, seropositive, positive lymph node culture and consistently PCR positive in bone marrow). Three SNPs in TLR3, two SNPs in PTPN22 and one SNP in TLR4 and IL1A were associated with the susceptible phenotype in the Beagle group at the individual SNP level after permutation analysis, but were not significant after correction for multiple testing. Further validation of these SNPs is required in a larger cohort of dogs, ideally with extreme phenotypes to confirm an association with the outcome of L. infantum infection
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