977 research outputs found
Role of "Intrinsic Charm" in Semi-Leptonic B-Meson Decays
We discuss the role of so-called "intrinsic-charm" operators in semi-leptonic
B-meson decays, which appear first at order 1/m_b^3 in the heavy quark
expansion. We show by explicit calculation that -- at scales mu <= m_c -- the
contributions from "intrinsic-charm" effects can be absorbed into
short-distance coefficient functions multiplying, for instance, the Darwin
term. Then, the only remnant of "intrinsic charm" are logarithms of the form
ln(m_c^2/m_b^2), which can be resummed by using renormalization-group
techniques. As long as the dynamics at the charm-quark scale is perturbative,
alpha_s(m_c) << 1, this implies that no additional non-perturbative matrix
elements aside from the Darwin and the spin-orbit term have to be introduced at
order 1/m_b^3. Hence, no sources for additional hadronic uncertainties have to
be taken into account. Similar arguments may be made for higher orders in the
1/m_b expansion.Comment: 14 pages, 1 figure, uses slashed.sty, slight modifications to match
published versio
A qualitative assessment of the probability of human exposure to Trichinella spp. in Switzerland
Trichinellosis is a zoonotic disease caused by Trichinella spp. Pork is a potential source of infection for humans. A qualitative assessment was conducted to assess the probability of human exposure to Trichinella spp. in Switzerland via the consumption of pork. For the assessment, both the wildlife cycle and the domestic cycle were taken into account. The probability of occurrence of Trichinella infections in domestic pigs was assessed negligible under controlled housing systems due to biosecurity measures. Free-range pigs were assessed to have a very low probability of being infected. Pork from free-range pigs that were not tested for Trichinella spp. was estimated to carry a very low probability for human exposure to Trichmella spp
Human C-peptide Dose Dependently Prevents Early Neuropathy in the BB/Wor-rat
In order to explore the neuroprotective and crossspecies
activities of.C-peptide on type 1 diabetic
neuropathy, spontaneously diabetic BB/W-rats were
given increasing doses of human recombinant Cpeptide
(hrC-peptide). Diabetic rats received 10, 100,
500, or 1000 μg of hrC-peptide/kg body weight/
day from onset of diabetes. After 2 months of hrC-peptide
administration, 100 μg and greater doses
completely prevented the nerve conduction defect,
which was associated with a significant but incomplete
prevention of neural Na+/K+-ATPase activity
in diabetic rats with 500 μg or greater C-peptide replacement.
Increasing doses of hrC-peptide showed
increasing prevention of early structural abnormalities
such as paranodal swelling and axonal degeneration
and an increasing frequency of regenerating
sural nerve fibers. We conclude that hrC-peptide exerts
a dose dependent protection on type 1 diabetic
neuropathy in rats and that this effect is probably
mediated by the partially conserved sequence of the
active C-terminal pentapeptid
The Two Roads to "Intrinsic Charm" in B Decays
We describe two complementary ways to show the presence of higher order
effects in the 1/m_Q expansion for inclusive B decays that have been dubbed
"Intrinsic Charm". Apart from the lessons they can teach us about QCD's
nonperturbative dynamics their consideration is relevant for precise
extractions of |V_{cb}|: for they complement the estimate of the potential
impact of 1/m_Q^4 contributions. We draw semiquantitative conclusions for the
expected scale of Weak Annihilation in semileptonic B decays, both for its
valence and non-valence components.Comment: 17 pages, 3 figure
Development of Readout Interconnections for the Si-W Calorimeter of SiD
The SiD collaboration is developing a Si-W sampling electromagnetic
calorimeter, with anticipated application for the International Linear
Collider. Assembling the modules for such a detector will involve special
bonding technologies for the interconnections, especially for attaching a
silicon detector wafer to a flex cable readout bus. We review the interconnect
technologies involved, including oxidation removal processes, pad surface
preparation, solder ball selection and placement, and bond quality assurance.
Our results show that solder ball bonding is a promising technique for the Si-W
ECAL, and unresolved issues are being addressed.Comment: 8 pages + title, 6 figure
Local Anisotropy of Fluids using Minkowski Tensors
Statistics of the free volume available to individual particles have
previously been studied for simple and complex fluids, granular matter,
amorphous solids, and structural glasses. Minkowski tensors provide a set of
shape measures that are based on strong mathematical theorems and easily
computed for polygonal and polyhedral bodies such as free volume cells (Voronoi
cells). They characterize the local structure beyond the two-point correlation
function and are suitable to define indices of
local anisotropy. Here, we analyze the statistics of Minkowski tensors for
configurations of simple liquid models, including the ideal gas (Poisson point
process), the hard disks and hard spheres ensemble, and the Lennard-Jones
fluid. We show that Minkowski tensors provide a robust characterization of
local anisotropy, which ranges from for vapor
phases to for ordered solids. We find that for fluids,
local anisotropy decreases monotonously with increasing free volume and
randomness of particle positions. Furthermore, the local anisotropy indices
are sensitive to structural transitions in these simple
fluids, as has been previously shown in granular systems for the transition
from loose to jammed bead packs
Minkowski Tensors of Anisotropic Spatial Structure
This article describes the theoretical foundation of and explicit algorithms
for a novel approach to morphology and anisotropy analysis of complex spatial
structure using tensor-valued Minkowski functionals, the so-called Minkowski
tensors. Minkowski tensors are generalisations of the well-known scalar
Minkowski functionals and are explicitly sensitive to anisotropic aspects of
morphology, relevant for example for elastic moduli or permeability of
microstructured materials. Here we derive explicit linear-time algorithms to
compute these tensorial measures for three-dimensional shapes. These apply to
representations of any object that can be represented by a triangulation of its
bounding surface; their application is illustrated for the polyhedral Voronoi
cellular complexes of jammed sphere configurations, and for triangulations of a
biopolymer fibre network obtained by confocal microscopy. The article further
bridges the substantial notational and conceptual gap between the different but
equivalent approaches to scalar or tensorial Minkowski functionals in
mathematics and in physics, hence making the mathematical measure theoretic
method more readily accessible for future application in the physical sciences
Observation of single collisionally cooled trapped ions in a buffer gas
Individual Ba ions are trapped in a gas-filled linear ion trap and observed
with a high signal-to-noise ratio by resonance fluorescence. Single-ion storage
times of ~5 min (~1 min) are achieved using He (Ar) as a buffer gas at
pressures in the range 8e-5 - 4e-3 torr. Trap dynamics in buffer gases are
experimentally studied in the simple case of single ions. In particular, the
cooling effects of light gases such as He and Ar and the destabilizing
properties of heavier gases such as Xe are studied. A simple model is offered
to explain the observed phenomenology.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. A. Minor
text and figure change
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