157 research outputs found
Simulating multiple merger pathways to the central kinematics of early-type galaxies
Two-dimensional integral field surveys such as ATLAS^3D are producing rich
observational data sets yielding insights into galaxy formation. These new
kinematic observations have highlighted the need to understand the evolutionary
mechanisms leading to a spectrum of fast-rotators and slow-rotators in
early-type galaxies. We address the formation of slow and fast rotators through
a series of controlled, comprehensive hydrodynamical simulations sampling
idealized galaxy merger scenarios constructed from model spiral galaxies.
Idealized and controlled simulations of this sort complement the more
'realistic' cosmological simulations by isolating and analyzing the effects of
specific parameters, as we do in this paper. We recreate minor and major binary
mergers, binary merger trees with multiple progenitors, and multiple sequential
mergers. Within each of these categories of formation history, we correlate
progenitor gas fraction, mass ratio, orbital pericenter, orbital ellipticity,
and spin with remnant kinematic properties. We create kinematic profiles of
these 95 simulations comparable to ATLAS^3D data. By constructing remnant
profiles of the projected specific angular momentum (lambda_R = /
, triaxiality, and measuring the incidences of kinematic
twists and kinematically decoupled cores, we distinguish between varying
formation scenarios. We find that binary mergers nearly always form fast
rotators. Slow rotators can be formed from zero initial angular momentum
configurations and gas-poor mergers, but are not as round as the ATLAS^3D
galaxies. Remnants of binary merger trees are triaxial slow rotators.
Sequential mergers form round slow rotators that most resemble the ATLAS^3D
rotators.Comment: MNRAS, in press, 12 pages, 15 figure
Expression of PEG11 and PEG11AS transcripts in normal and callipyge sheep
BACKGROUND: The callipyge mutation is located within an imprinted gene cluster on ovine chromosome 18. The callipyge trait exhibits polar overdominant inheritance due to the fact that only heterozygotes inheriting a mutant paternal allele (paternal heterozygotes) have a phenotype of muscle hypertrophy, reduced fat and a more compact skeleton. The mutation is a single A to G transition in an intergenic region that results in the increased expression of several genes within the imprinted cluster without changing their parent-of-origin allele-specific expression. RESULTS: There was a significant effect of genotype (p < 0.0001) on the transcript abundance of DLK1, PEG11, and MEG8 in the muscles of lambs with the callipyge allele. DLK1 and PEG11 transcript levels were elevated in the hypertrophied muscles of paternal heterozygous animals relative to animals of the other three genotypes. The PEG11 locus produces a single 6.5 kb transcript and two smaller antisense strand transcripts, referred to as PEG11AS, in skeletal muscle. PEG11AS transcripts were detectable over a 5.5 kb region beginning 1.2 kb upstream of the PEG11 start codon and spanning the entire open reading frame. Analysis of PEG11 expression by quantitative PCR shows a 200-fold induction in the hypertrophied muscles of paternal heterozygous animals and a 13-fold induction in homozygous callipyge animals. PEG11 transcripts were 14-fold more abundant than PEG11AS transcripts in the gluteus medius of paternal heterozygous animals. PEG11AS transcripts were expressed at higher levels than PEG11 transcripts in the gluteus medius of animals of the other three genotypes. CONCLUSIONS: The effect of the callipyge mutation has been to alter the expression of DLK1, GTL2, PEG11 and MEG8 in the hypertrophied skeletal muscles. Transcript abundance of DLK1 and PEG11 was highest in paternal heterozygous animals and exhibited polar overdominant gene expression patterns; therefore, both genes are candidates for causing skeletal muscle hypertrophy. There was unique relationship of PEG11 and PEG11AS transcript abundance in the paternal heterozygous animals that suggests a RNA interference mechanism may have a role in PEG11 gene regulation and polar overdominance in callipyge sheep
Total synthesis of the post-translationally modified polyazole peptide antibiotic plantazolicin A
The power of rhodium carbene methodology in chemistry is demonstrated by the synthesis of a structurally complex polyazole antibiotic. Plantazolicin A, a novel soil bacterium metabolite, comprises a linear array of 10 five-membered rings in two pentacyclic regions that derive from ribosomal peptide synthesis followed by extensive post-translational modification. The compound possesses potent antimicrobial activity, and is selectively active against the anthrax causing organism. A conceptually different synthesis of plantazolicin A is reported in which the key steps are the use of rhodium(II)-catalyzed reactions of diazocarbonyl compounds to generate up to six of the seven oxazole rings of the antibiotic. NMR Spectroscopic studies and molecular modeling, reveal a likely dynamic hairpin conformation with a hinge region around the two isoleucine residues.The compound has modest activity against methicillin-resistant Staphylococcus aureus (MRSA)
Star Formation and Clumps in Cosmological Galaxy Simulations with Radiation Pressure Feedback
Cosmological simulations of galaxies have typically produced too many stars
at early times. We study the global and morphological effects of radiation
pressure (RP) in eight pairs of high-resolution cosmological galaxy formation
simulations. We find that the additional feedback suppresses star formation
globally by a factor of ~2. Despite this reduction, the simulations still
overproduce stars by a factor of ~2 with respect to the predictions provided by
abundance matching methods for halos more massive than 5E11 Msun/h (Behroozi,
Wechsler & Conroy 2013).
We also study the morphological impact of radiation pressure on our
simulations. In simulations with RP the average number of low mass clumps falls
dramatically. Only clumps with stellar masses Mclump/Mdisk <= 5% are impacted
by the inclusion of RP, and RP and no-RP clump counts above this range are
comparable. The inclusion of RP depresses the contrast ratios of clumps by
factors of a few for clump masses less than 5% of the disk masses. For more
massive clumps, the differences between and RP and no-RP simulations diminish.
We note however, that the simulations analyzed have disk stellar masses below
about 2E10 Msun/h.
By creating mock Hubble Space Telescope observations we find that the number
of clumps is slightly reduced in simulations with RP. However, since massive
clumps survive the inclusion of RP and are found in our mock observations, we
do not find a disagreement between simulations of our clumpy galaxies and
observations of clumpy galaxies. We demonstrate that clumps found in any single
gas, stellar, or mock observation image are not necessarily clumps found in
another map, and that there are few clumps common to multiple maps.Comment: 13 pages, 6 figures, submitted to MNRA
On the structure and dynamics of stratified wakes generated by submerged propagating objects
The article of record as published may be found at http://dx.doi.org/10.1080/1755876X.2017.1307801The structure and intensity of the intermediate wake generated by a submerged propagating body in a stratified fluid was studied using a combination of (i) numerical simulations, (ii) field measurements, and (iii) laboratory experiments. The numerical component offered guidance for the field work performed in Monterey Bay (CA, USA) in the summer of 2015. The field work focused on subsurface thermal signatures of a submerged propagating object. Vertical temperature profiles suggested that long-term changes in thermal stratification can occur after the passage of a towed body. Horizontal temperature variability, measured by an autonomous underwater vehicle facilitated the identification of the wake using perturbation temperature variance as the key diagnostic variable. Analogous thermal signatures of stratified wakes were found in ocean observations and in modelling results. The influence of the tow ship on the wake was shown to be minimal. Laboratory experiments focused on the surface expression of stratified wakes were used to complement numerical simulations and field measurements. All three components of this project indicate that detection of the wake of a submerged object based on its thermal signatures is a viable and effective approach.Naval Research ProgramConsortium for Robotics and Unmanned Systems Education and Research (CRUSER)Office of Naval ResearchNPS-N16-N155-ANPS-FY17-N262-AN0001315WX0064
Dark-Matter Decays and Self-Gravitating Halos
We consider models in which a dark-matter particle decays to a slightly less
massive daughter particle and a noninteracting massless particle. The decay
gives the daughter particle a small velocity kick. Self-gravitating dark-matter
halos that have a virial velocity smaller than this velocity kick may be
disrupted by these particle decays, while those with larger virial velocities
will be heated. We use numerical simulations to follow the detailed evolution
of the total mass and density profile of self-gravitating systems composed of
particles that undergo such velocity kicks as a function of the kick speed
(relative to the virial velocity) and the decay time (relative to the dynamical
time). We show how these decays will affect the halo mass-concentration
relation and mass function. Using measurements of the halo mass-concentration
relation and galaxy-cluster mass function to constrain the
lifetime--kick-velocity parameter space for decaying dark matter, we find
roughly that the observations rule out the combination of kick velocities
greater than 100 km/s and decay times less than a few times the age of the
Universe.Comment: 17 pages, 10 figures, replaced with published versio
An Open Source Mesh Generation Platform for Biophysical Modeling Using Realistic Cellular Geometries
Advances in imaging methods such as electron microscopy, tomography and other
modalities are enabling high-resolution reconstructions of cellular and
organelle geometries. Such advances pave the way for using these geometries for
biophysical and mathematical modeling once these data can be represented as a
geometric mesh, which, when carefully conditioned, enables the discretization
and solution of partial differential equations. In this study, we outline the
steps for a na\"ive user to approach GAMer 2, a mesh generation code written in
C++ designed to convert structural datasets to realistic geometric meshes,
while preserving the underlying shapes. We present two example cases, 1) mesh
generation at the subcellular scale as informed by electron tomography, and 2)
meshing a protein with structure from x-ray crystallography. We further
demonstrate that the meshes generated by GAMer are suitable for use with
numerical methods. Together, this collection of libraries and tools simplifies
the process of constructing realistic geometric meshes from structural biology
data.Comment: 6 pages and 4 figures. Supplemental Movie available upon reques
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