12,928 research outputs found
Pade-Improved Estimate of Perturbative Contributions to Inclusive Semileptonic Decays
Pade-approximant methods are used to estimate the three-loop perturbative
contributions to the inclusive semileptonic decay rate. These
improved estimates of the decay rate reduce the theoretical uncertainty in the
extraction of the CKM matrix element from the measured inclusive
semileptonic branching ratio.Comment: 3 pages, latex, write-up of talk presented at DPF 200
Invariants of Artinian Gorenstein Algebras and Isolated Hypersurface Singularities
We survey our recently proposed method for constructing biholomorphic
invariants of quasihomogeneous isolated hypersurface singularities and, more
generally, invariants of graded Artinian Gorenstein algebras. The method
utilizes certain polynomials associated to such algebras, called
nil-polynomials, and we compare them with two other classes of polynomials that
have also been used to produce invariants.Comment: 13 page
The Star Formation Law in Nearby Galaxies on Sub-Kpc Scales
(Abridged) We present a comprehensive analysis of the relationship between
star formation rate surface density (SFR SD) and gas surface density (gas SD)
at sub-kpc resolution in a sample of 18 nearby galaxies. We use high resolution
HI data from THINGS, CO data from HERACLES and BIMA SONG, 24 micron data from
the Spitzer Space Telescope, and UV data from GALEX. We target 7 spiral
galaxies and 11 late-type/dwarf galaxies and investigate how the star formation
law differs between the H2-dominated centers of spiral galaxies, their
HI-dominated outskirts and the HI-rich late-type/dwarf galaxies.
We find that a Schmidt-type power law with index N=1.0+-0.2 relates the SFR
SD and the H2 SD across our sample of spiral galaxies, i.e., that H2 forms
stars at a constant efficiency in spirals. The average molecular gas depletion
time is ~2*10^9 yrs. We interpret the linear relation and constant depletion
time as evidence that stars are forming in GMCs with approximately uniform
properties and that the H2 SD may be more a measure of the filling fraction of
giant molecular clouds than changing conditions in the molecular gas.
The relationship between total gas SD and SFR SD varies dramatically among
and within spiral galaxies. Most galaxies show little or no correlation between
the HI SD and the SFR SD. As a result, the star formation efficiency (SFE = SFR
SD / gas SD) varies strongly across our sample and within individual galaxies.
We show that in spirals the SFE is a clear function of radius, while the dwarf
galaxies in our sample display SFEs similar to those found in the outer optical
disks of the spirals. Another general feature of our sample is a sharp
saturation of the HI SD at ~9 M_sol/pc^2 in both the spiral and dwarf galaxies.Comment: Accepted for publication in the AJ special THINGS issue. For a
high-resolution version visit: http://www.mpia.de/THINGS/Publications.htm
Liquid-vapor interface of a polydisperse fluid
We report a Grand Canonical Monte Carlo simulation study of the liquid-vapor
interface of a model fluid exhibiting polydispersity in terms of the particle
size . The bulk density distribution, , of the system
is controlled by the imposed chemical potential distribution . We
choose the latter such that assumes a Schulz form with
associated degree of polydispersity . By introducing a smooth
attractive wall, a planar liquid-vapor interface is formed for bulk state
points within the region of liquid-vapor coexistence. Owing to fractionation,
the pure liquid phase is enriched in large particles, with respect to the
coexisting vapor. We investigate how the spatial non-uniformity of the density
near the liquid-vapor interface affects the evolution of the local distribution
of particle sizes between the limiting pure phase forms. We find (as previously
predicted by density functional theory, Bellier-Castella {\em et al}, Phys.
Rev. {\bf E65}, 021503 (2002)) a segregation of smaller particles to the
interface. The magnitude of this effect is quantified for various via
measurements of the relative adsorption. Additionally, we consider the utility
of various estimators for the interfacial width and highlight the difficulties
of isolating the intrinsic contribution of polydispersity to this width.Comment: 9 pages, 10 Fig
Renormalization-Scale Invariance, Minimal Sensitivity, and the Inclusive Hadronic Decays of a 115 GeV Higgs Particle
Known perturbative expressions for the decay rates of 115 GeV Higgs particle
into either two gluons or a pair are shown to exhibit
renormalization-scale-()-dependence that is largely removed via
renormalization-group/Pade-approximant estimates of these rates' next order
contributions. The extrema in characterizing both rates, as determined
from fully-known orders of perturbation theory, are very nearly equal to
corresponding -insensitive rates obtained via estimation of their next
order contributions, consistent with "minimal-sensitivity" expectations.Comment: 12 pages, 3 figures, LaTe
A study on the discrimination of human skeletons using X-ray fluorescence and chemometric tools in chemical anthropology
Forensic anthropological investigations are often restricted in their outcomes by the resources allocated to them, especially in terms of positively identifying the victims exhumed from commingled mass graves. Commingled mass graves can be defined as those graves that contain a number of disarticulated human remains from different individuals that have been mixed by either natural processes or human interventions. The research developed aimed to apply the technique of non-destructive XRF analysis to test whether there is substantial differentiation within the trace elemental composition and their ratios of individuals to separate them using chemometric analysis. The results of the different atomic spectroscopic analyses combined with the use of multivariate analysis on a set of 5 skeletons produced a series of plots using Principal Component Analysis that helped to separate them with a high percentage of accuracy when two, three or four skeletons needed to be separated. Also, two new elemental ratios, Zn/Fe related to metabolic activities and K/Fe related to blood flow into the bone, have been defined for their use in forensic anthropology for the first time to aid in the separation. © 2013 Elsevier Ireland Ltd
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