50,842 research outputs found
Dark matter cores all the way down
We use high resolution simulations of isolated dwarf galaxies to study the
physics of dark matter cusp-core transformations at the edge of galaxy
formation: M200 = 10^7 - 10^9 Msun. We work at a resolution (~4 pc minimum cell
size; ~250 Msun per particle) at which the impact from individual supernovae
explosions can be resolved, becoming insensitive to even large changes in our
numerical 'sub-grid' parameters. We find that our dwarf galaxies give a
remarkable match to the stellar light profile; star formation history;
metallicity distribution function; and star/gas kinematics of isolated dwarf
irregular galaxies. Our key result is that dark matter cores of size comparable
to the stellar half mass radius (r_1/2) always form if star formation proceeds
for long enough. Cores fully form in less than 4 Gyrs for the M200 = 10^8 Msun
and 14 Gyrs for the 10^9 Msun dwarf. We provide a convenient two parameter
'coreNFW' fitting function that captures this dark matter core growth as a
function of star formation time and the projected stellar half mass radius.
Our results have several implications: (i) we make a strong prediction that
if LCDM is correct, then 'pristine' dark matter cusps will be found either in
systems that have truncated star formation and/or at radii r > r_1/2; (ii)
complete core formation lowers the projected velocity dispersion at r_1/2 by a
factor ~2, which is sufficient to fully explain the 'too big to fail problem';
and (iii) cored dwarfs will be much more susceptible to tides, leading to a
dramatic scouring of the subhalo mass function inside galaxies and groups.Comment: 20 pages; 9 figures; final version to appear in MNRAS including typos
corrected in proo
Statistical comparison of ensemble implementations of Grover's search algorithm to classical sequential searches
We compare pseudopure state ensemble implementations, quantified by their
initial polarization and ensemble size, of Grover's search algorithm to
probabilistic classical sequential search algorithms in terms of their success
and failure probabilities. We propose a criterion for quantifying the resources
used by the ensemble implementation via the aggregate number of oracle
invocations across the entire ensemble and use this as a basis for comparison
with classical search algorithms. We determine bounds for a critical
polarization such that the ensemble algorithm succeeds with a greater
probability than the probabilistic classical sequential search. Our results
indicate that the critical polarization scales as N^(-1/4) where N is the
database size and that for typical room temperature solution state NMR, the
polarization is such that the ensemble implementation of Grover's algorithm
would be advantageous for N > 10^2
From urban to national heat island: The effect of anthropogenic heat output on climate change in high population industrial countries
The project presented here sought to determine whether changes in anthropogenic thermal emission can have a measurable effect on temperature at the national level, taking Japan and Great Britain as type examples. Using energy consumption as a proxy for thermal emission, strong correlations (mean r2 = 0.90 and 0.89, respectively) are found between national equivalent heat output (HO) and temperature above background levels Δt averaged over 5‐ to 8‐yr periods between 1965 and 2013, as opposed to weaker correlations for CMIP5 model temperatures above background levels Δmt (mean r2 = 0.52 and 0.10). It is clear that the fluctuations in Δt are better explained by energy consumption than by present climate models, and that energy consumption can contribute to climate change at the national level on these timescales
Momentum Flow Correlations from Event Shapes: Factorized Soft Gluons and Soft-Collinear Effective Theory
The distributions of two-jet event shapes contain information on
hadronization in QCD. Near the two-jet limit, these distributions can be
described by convolutions of nonperturbative event shape functions with the
same distributions calculated in resummed perturbation theory. The shape
functions, in turn, are determined by correlations of momentum flow operators
with each other and with light-like Wilson lines, which describe the coupling
of soft, wide-angle radiation to jets. We observe that leading power
corrections to the mean values of event shapes are determined by the
correlation of a single momentum flow operator with the relevant Wilson lines.
This generalizes arguments for the universality of leading power corrections
based on the low-scale behavior of the running coupling or resummation. We also
show how a study of the angularity event shapes can provide information on
correlations involving multiple momentum flow operators, giving a window to the
system of QCD dynamics that underlies the variety of event shape functions. In
deriving these results, we review, develop and compare factorization techniques
in conventional perturbative QCD and soft-collinear effective theory (SCET). We
give special emphasis to the elimination of double counting of momentum regions
in these two formalisms.Comment: 25 pages revtex
Estimations for the Single Diffractive production of the Higgs boson at the Tevatron and the LHC
The single diffractive production of the standard model Higgs boson is
computed using the diffractive factorization formalism, taking into account a
parametrization for the Pomeron structure function provided by the H1
Collaboration. We compute the cross sections at next-to-leading order accuracy
for the gluon fusion process, which includes QCD and electroweak corrections.
The gap survival probability () is also introduced to account for
the rescattering corrections due to spectator particles present in the
interaction, and to this end we compare two different models for the survival
factor. The diffractive ratios are predicted for proton-proton collisions at
the Tevatron and the LHC for the Higgs boson mass of = 120 GeV.
Therefore, our results provide updated estimations for the diffractive ratios
of the single diffractive production of the Higgs boson in the Tevatron and LHC
kinematical regimes.Comment: 20 pages, 6 figures, 3 table
Evaluation of protected areas in Côte d’Ivoire and Ghana, West Africa, using a remote sensing-based approach
This study assesses the representation of defined ecoregions, slope profiles, and species richness of threatened mammals in the International Union for Conservation of Nature (IUCN)-listed protected areas in Ghana and Côte d’Ivoire. It also evaluates the exposure of protected area categories to the cumulative degree of human modification and their vulnerability to future agricultural expansion. Spatial gap and statistical analyses were performed using quantitative data from publicly available online global databases. Analyses indicated key conservation priorities for both countries: (1) to increase the protection of the Guinean forest–savanna mosaic, West Sudanian savanna, and Eastern Guinean forests, especially of the Eastern Guinean forests’ ecoregion associated with the Guinean forests of the West Africa biodiversity hotspot; (2) to increase the protected area coverage of flat lands and low slopes; and (3) to enhance the size and connectivity of existing protected areas, including restoring degraded habitats. The study emphasizes that improving the ability of tropical protected areas to conserve nature and mitigate anthropogenic threats should be a global conservation priority. Improving the data quality and detail within the World Database on Protected Areas and ground-truthing them are recommended urgently to support accurate and informative assessments
Variants within the MMP3 gene are associated with achilles tendinopathy: possible interaction with the COL5A1 gene
Objectives: Sequence variation within the COL5A1 and TNC genes are known to associate with Achilles tendinopathy. The primary aim of this case-control genetic association study was to investigate whether variants within the matrix metalloproteinase 3 (MMP3) gene also contributed to both Achilles tendinopathy and Achilles tendon rupture in a Caucasian population. A secondary aim was to establish whether variants within the MMP3 gene interacted with the COL5A1 rs12722 variant to raise risk of these pathologies.
Methods: 114 subjects with symptoms of Achilles tendon pathology and 98 healthy controls were genotyped for MMP3 variants rs679620, rs591058 and rs650108.
Results: As single markers, significant associations were found between the GG genotype of rs679620 (OR = 2.5, 95% CI 1.2 to 4.90, p = 0.010), the CC genotype of rs591058 (OR = 2.3, 95% CI 1.1 to 4.50, p = 0.023) and the AA genotype of rs650108 (OR = 4.9, 95% CI 1.0 to 24.1, p = 0.043) and risk of Achilles tendinopathy. The ATG haplotype (rs679620, rs591058, and rs650108) was under-represented in the tendinopathy group when compared to the control group (41% vs 53%, p = 0.038). Finally, the G allele of rs679620 and the T allele of COL5A1 rs12722 significantly interacted to raise risk of AT (p = 0.006). No associations were found between any of the MMP3 markers and Achilles tendon rupture.
Conclusion: Variants within the MMP3 gene are associated with Achilles tendinopathy. Furthermore, the MMP3 gene variant rs679620 and the COL5A1 marker rs12722 interact to modify the risk of tendinopathy. These data further support a genetic contribution to a common sports related injur
Squeezed: Why Rising Exposure to Health Care Costs Threatens the Health and Financial Well-Being of American Families
Examines U.S. healthcare costs compared with other industrialized countries, individual health insurance coverage, individual market regulations, and the impact of high deductible plans on the health of individuals with chronic disease
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