5,742 research outputs found
The dynamical distance and intrinsic structure of the globular cluster omega Centauri
We determine the dynamical distance D, inclination i, mass-to-light ratio M/L
and the intrinsic orbital structure of the globular cluster omega Cen, by
fitting axisymmetric dynamical models to the ground-based proper motions of van
Leeuwen et al. and line-of-sight velocities from four independent data-sets. We
correct the observed velocities for perspective rotation caused by the space
motion of the cluster, and show that the residual solid-body rotation component
in the proper motions can be taken out without any modelling other than
assuming axisymmetry. This also provides a tight constraint on D tan i.
Application of our axisymmetric implementation of Schwarzschild's orbit
superposition method to omega Cen reveals no dynamical evidence for a
significant radial dependence of M/L. The best-fit dynamical model has a
stellar V-band mass-to-light ratio M/L_V = 2.5 +/- 0.1 M_sun/L_sun and an
inclination i = 50 +/- 4 degrees, which corresponds to an average intrinsic
axial ratio of 0.78 +/- 0.03. The best-fit dynamical distance D = 4.8 +/- 0.3
kpc (distance modulus 13.75 +/- 0.13 mag) is significantly larger than obtained
by means of simple spherical or constant-anisotropy axisymmetric dynamical
models, and is consistent with the canonical value 5.0 +/- 0.2 kpc obtained by
photometric methods. The total mass of the cluster is (2.5 +/- 0.3) x 10^6
M_sun. The best-fit model is close to isotropic inside a radius of about 10
arcmin and becomes increasingly tangentially anisotropic in the outer region,
which displays significant mean rotation. This phase-space structure may well
be caused by the effects of the tidal field of the Milky Way. The cluster
contains a separate disk-like component in the radial range between 1 and 3
arcmin, contributing about 4% to the total mass.Comment: 37 pages (23 figures), accepted for publication in A&A, abstract
abridged, for PS and PDF file with full resolution figures, see
http://www.strw.leidenuniv.nl/~vdven/oc
Bdellovibrio and Like Organisms Are Predictors of Microbiome Diversity in Distinct Host Groups
Biodiversity is generally believed to be a main determinant of ecosystem functioning. This principle also applies to the microbiome and could consequently contribute to host health. According to ecological theory, communities are shaped by top predators whose direct and indirect interactions with community members cause stability and diversity. Bdellovibrio and like organisms (BALOs) are a neglected group of predatory bacteria that feed on Gram-negative bacteria and can thereby influence microbiome composition. We asked whether BALOs can predict biodiversity levels in microbiomes from distinct host groups and environments. We demonstrate that genetic signatures of BALOs are commonly found within the 16S rRNA reads from diverse host taxa. In many cases, their presence, abundance, and especially richness are positively correlated with overall microbiome diversity. Our findings suggest that BALOs can act as drivers of microbial alpha-diversity and should therefore be considered candidates for the restoration of microbiomes and the prevention of dysbiosis
Political brand image: an investigation into the operationalisation of the external orientation of David Cameron’s Conservative brand
This paper seeks to address the limited understanding of how to operationalise the external brand image of a political brand. More specifically, this research critically assesses the transfer potential of the six variables of brand image by Bosch, Venter, Han and Boshoff to deconstruct the UK Conservative Party brand from the perspective of young people aged 18–24 years during the 2010 UK General Election campaign. This research demonstrates the applicability of the six variables otherwise known as the ‘brand image framework’ to the political environment. However, the application of the brand image framework in its original conceptualisation proved problematic. Many of the brand image variables were clarified, rearticulated and simplified to address the political context. This refined conceptualisation provided an in-depth understanding of how to investigate the political brand image of David Cameron’s Conservative Party. This study addresses the paucity of research that operationalises external brand image and provides practitioners and academics within and beyond the context of political branding a mechanism to understand the external orientation of brands. This research may also be used by political and non-political brands as a basis to explore external brand image and compare its consistency with internal brand identity
Brief review on semileptonic B decays
We concisely review semileptonic B decays, focussing on recent progress on
both theoretical and experimental sides.Comment: 18 pages, 2 figures; version to be published in Mod. Phys. Lett.
Precision Flavour Physics with and
We show that a combined analysis of and
allows for new physics tests practically free of form factor uncertainties.
Residual theory errors are at the level of several percent. Our study
underlines the excellent motivation for measuring these modes at a Super
Flavour Factory.Comment: 26 pages, 2 figure
Spin and charge order in the vortex lattice of the cuprates: experiment and theory
I summarize recent results, obtained with E. Demler, K. Park, A. Polkovnikov,
M. Vojta, and Y. Zhang, on spin and charge correlations near a magnetic quantum
phase transition in the cuprates. STM experiments on slightly overdoped BSCCO
(J.E. Hoffman et al., Science 295, 466 (2002)) are consistent with the
nucleation of static charge order coexisting with dynamic spin correlations
around vortices, and neutron scattering experiments have measured the magnetic
field dependence of static spin order in the underdoped regime in LSCO (B. Lake
et al., Nature 415, 299 (2002)) and LaCuO_4+y (B. Khaykovich et al., Phys. Rev.
B 66, 014528 (2002)). Our predictions provide a semi-quantitative description
of these observations, with only a single parameter measuring distance from the
quantum critical point changing with doping level. These results suggest that a
common theory of competing spin, charge and superconducting orders provides a
unified description of all the cuprates.Comment: 18 pages, 7 figures; Proceedings of the Mexican Meeting on
Mathematical and Experimental Physics, Mexico City, September 2001, to be
published by Kluwer Academic/Plenum Press; (v2) added clarifications and
updated reference
Tree-level FCNC in the B system: from CP asymmetries to rare decays
Tree-level Flavor-Changing Neutral Currents (FCNC) are characteristic of
models with extra vector-like quarks. These new couplings can strongly modify
the B^0 CP asymmetries without conflicting with low--energy constraints. In the
light of a low CP asymmetry in B --> J/\psi K_{S}, we discuss the implications
of these contributions. We find that even these low values can be easily
accommodated in these models. Furthermore, we show that the new data from B
factories tend to favor an O(20) enhancement of the b --> d l \bar{l}
transition over the SM expectation.Comment: 5 pages, 4 figures. Accepted version in PRD. Updated analysis with
the new results from BaBar and BELLE. Figures enlarged, small typos
corrected. Conclusions essentially unchange
Present and Future Experiments with Stored Exotic Nuclei at Relativistic Energies
Recent progress is presented from experiments on masses and lifetimes of bare
and few-electron exotic nuclei at GSI.Comment: Proceedings of International Conference on "Frontiers in Nuclear
Structure, Astrophysics and Reactions", Kos, Greece, September 12-17, 200
Isospin Dependence in the Odd-Even Staggering of Nuclear Binding Energies
The FRS-ESR facility at GSI provides unique conditions for precision
measurements of large areas on the nuclear mass surface in a single experiment.
Values for masses of 604 neutron-deficient nuclides (30<=Z<=92) were obtained
with a typical uncertainty of 30 microunits. The masses of 114 nuclides were
determined for the first time. The odd-even staggering (OES) of nuclear masses
was systematically investigated for isotopic chains between the proton shell
closures at Z=50 and Z=82. The results were compared with predictions of modern
nuclear models. The comparison revealed that the measured trend of OES is not
reproduced by the theories fitted to masses only. The spectral pairing gaps
extracted from models adjusted to both masses, and density related observables
of nuclei agree better with the experimental data.Comment: Physics Review Letters 95 (2005) 042501
http://link.aps.org/abstract/PRL/v95/e04250
A Revised Model for the Formation of Disk Galaxies: Low Spin and Dark-Halo Expansion
We use observed rotation velocity-luminosity (VL) and size-luminosity (RL)
relations to single out a specific scenario for disk galaxy formation in the
LCDM cosmology. Our model involves four independent log-normal random
variables: dark-halo concentration c, disk spin lam_gal, disk mass fraction
m_gal, and stellar mass-to-light ratio M/L_I. A simultaneous match of the VL
and RL zero points with adiabatic contraction requires low-c halos, but this
model has V_2.2~1.8 V_vir (where V_2.2 and V_vir are the circular velocity at
2.2 disk scale lengths and the virial radius, respectively) which will be
unable to match the luminosity function (LF). Similarly models without
adiabatic contraction but standard c also predict high values of V_2.2/V_vir.
Models in which disk formation induces an expansion rather than the commonly
assumed contraction of the dark-matter halos have V_2.2~1.2 V_vir which allows
a simultaneous fit of the LF. This may result from non-spherical, clumpy gas
accretion, where dynamical friction transfers energy from the gas to the dark
matter. This model requires low lam_gal and m_gal values, contrary to naive
expectations. However, the low lam_gal is consistent with the notion that disk
galaxies predominantly survive in halos with a quiet merger history, while a
low m_gal is also indicated by galaxy-galaxy lensing. The smaller than expected
scatter in the RL relation, and the lack of correlation between the residuals
of the VL and RL relations, respectively, imply that the scatter in lam_gal and
in c need to be smaller than predicted for LCDM halos, again consistent with
the idea that disk galaxies preferentially reside in halos with a quiet merger
history.Comment: 28 pages, 16 figures, ApJ accepted, minor changes from unpublished
version, uses emulateapj.cls, high-resolution version available at
http://www.ucolick.org/~dutton/65200/hi-res-version/ms.dutton.v2_hr.p
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