4,150 research outputs found
Dark influences III. Structural characterization of minor mergers of dwarf galaxies with dark satellites
In the current concordance cosmology small halos are expected to be
completely dark and can significantly perturb low-mass galaxies during minor
merger interactions. These interactions may well contribute to the diversity of
the dwarf galaxy population. Dwarf galaxies in the field are often observed to
have peculiarities in their structure, morphology, and kinematics, as well as
strong bursts of star formation without apparent cause. We aim to characterize
the signatures of minor mergers of dwarf galaxies with dark satellites to aid
their observational identification. We explore and quantify a variety of
structural, morphological, and kinematic indicators of merging dwarf galaxies
and their remnants using a suite of hydrodynamical simulations. The most
sensitive indicators of mergers with dark satellites are large asymmetries in
the gaseous and stellar distributions, enhanced central surface brightness and
starbursts, and velocity offsets and misalignments between the cold gas and
stellar components. In general, merging systems span a wide range of values of
the most commonly used indicators, while isolated objects tend to have more
confined values. Interestingly, we find in our simulations that a significantly
off-centered burst of star formation can pinpoint the location of the dark
satellite. Observational systems with such characteristics are perhaps the most
promising for unveiling the presence of the hitherto, missing satellites.Comment: 9 pages, 7 figures. Accepted in A&
Synthesis and structural characterization of 2Dioxane.2H2O.CuCl2: metal-organic compound with Heisenberg antiferromagnetic S=1/2 chains
A novel organometallic compound 2Dioxane.CuCl2.2H2O has been synthesized and
structurally characterized by X-ray crystallography. Magnetic susceptibility
and zero-field inelastic neutron scattering have also been used to study its
magnetic properties. It turns out that this material is a weakly coupled
one-dimensional S=1/2 Heisenberg antiferromagnetic chain system with chain
direction along the crystallographic c axis and the nearest-neighbor
intra-chain exchange constant J=0.85(4) meV. The next-nearest-neighbor
inter-chain exchange constant J' is also estimated to be 0.05 meV. The observed
magnetic excitation spectrum from inelastic neutron scattering is in excellent
agreement with numerical calculations based on the Muller ansatz.Comment: 4 pages; 5 figure
Chorionic gonadotrophin regulates CXCR4 expression in human endometrium via E-series prostanoid receptor 2 signalling to PI3K-ERK1/2:Implications for fetal-maternal crosstalk for embryo implantation
Magnetic excitations in weakly coupled spin dimers and chains material Cu2Fe2Ge4O13
Magnetic excitations in a weakly coupled spin dimers and chains compound
Cu2Fe2Ge4O13 are measured by inelastic neutron scattering. Both structure
factors and dispersion of low energy excitations up to 10 meV energy transfer
are well described by a semiclassical spin wave theory involving interacting
Fe () chains. Additional dispersionless excitations are
observed at higher energies, at meV, and associated with
singlet-triplet transitions within Cu-dimers. Both types of excitations
can be understood by treating weak interactions between the Cu and
Fe subsystems at the level of the Mean Field/ Random Phase
Approximation. However, this simple model fails to account for the measured
temperature dependence of the 24 meV mode.Comment: 9 pages, 11 figure
Genomic variations associated with attenuation in Mycobacterium avium subsp paratuberculosis vaccine strains
BACKGROUND: Mycobacterium avium subspecies paratuberculosis (MAP) whole cell vaccines have been widely used tools in the control of Johne's disease in animals despite being unable to provide complete protection. Current vaccine strains derive from stocks created many decades ago; however their genotypes, underlying mechanisms and relative degree of their attenuation are largely unknown.
RESULTS: Using mouse virulence studies we confirm that MAP vaccine strains 316 F, II and 2e have diverse but clearly attenuated survival and persistence characteristics compared with wild type strains. Using a pan genomic microarray we characterise the genomic variations in a panel of vaccine strains sourced from stocks spanning over 40 years of maintenance. We describe multiple genomic variations specific for individual vaccine stocks in both deletion (26-32 Kbp) and tandem duplicated (11-40 Kbp) large variable genomic islands and insertion sequence copy numbers. We show individual differences suitable for diagnostic differentiation between vaccine and wild type genotypes and provide evidence for functionality of some of the deleted MAP-specific genes and their possible relation to attenuation.
CONCLUSIONS: This study shows how culture environments have influenced MAP genome diversity resulting in large tandem genomic duplications, deletions and transposable element activity. In combination with classical selective systematic subculture this has led to fixation of specific MAP genomic alterations in some vaccine strain lineages which link the resulting attenuated phenotypes with deficiencies in high reactive oxygen species handling
Coupling Between An Optical Phonon and the Kondo Effect
We explore the ultra-fast optical response of Yb_{14}MnSb_{11}, providing
further evidence that this Zintl compound is the first ferromagnetic,
under-screened Kondo lattice. These experiments also provide the first
demonstration of coupling between an optical phonon mode and the Kondo effect.Comment: 4 Pages, 3 Figures, submitted to Phys. Rev. Let
The Possible Role of Resource Requirements and Academic Career-Choice Risk on Gender Differences in Publication Rate and Impact
Many studies demonstrate that there is still a significant gender bias,
especially at higher career levels, in many areas including science,
technology, engineering, and mathematics (STEM). We investigated
field-dependent, gender-specific effects of the selective pressures individuals
experience as they pursue a career in academia within seven STEM disciplines.
We built a unique database that comprises 437,787 publications authored by
4,292 faculty members at top United States research universities. Our analyses
reveal that gender differences in publication rate and impact are
discipline-specific. Our results also support two hypotheses. First, the
widely-reported lower publication rates of female faculty are correlated with
the amount of research resources typically needed in the discipline considered,
and thus may be explained by the lower level of institutional support
historically received by females. Second, in disciplines where pursuing an
academic position incurs greater career risk, female faculty tend to have a
greater fraction of higher impact publications than males. Our findings have
significant, field-specific, policy implications for achieving diversity at the
faculty level within the STEM disciplines.Comment: 9 figures and 3 table
Low-lying optical phonon modes in the filled skutterudite CeRu4Sb12
The phonon dynamics of filled skutterudite CeRu4Sb12 have been studied at
room temperature by inelastic neutron scattering. Optical phonons associated
with a large vibration of Ce atoms are observed at a relatively low energy of E
= 6 meV, and show anticrossing behavior with acoustic phonons. We propose that
the origin of the low lattice thermal conductivity in filled skutterudites can
be attributed to intensive Umklapp scattering originating from low-lying
optical phonons. By an analysis based on a Born-von Karman force model, the
longitudinal force constants of the nearest Ce-Sb and Ce-Ru pairs are estimated
to be 0.025 mdyn/A, while that of the nearest Ru-Sb pair is estimated to be 1.4
mdyn/A, indicating that the Ce atoms are bound very weakly to the surrounding
rigid RuSb6-octahedron cages.Comment: 4pages, 5 figures, J. Phys. Soc. Jpn. (2006) in pres
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