731 research outputs found
Electroproduction of the d* dibaryon
The unpolarized cross section for the electroproduction of the isoscalar
di-delta dibaryon is calculated for deuteron target using a
simple picture of elastic electron-baryon scattering from the and the components of the deuteron. The calculated
differential cross section at the electron lab energy of 1 GeV has the value of
about 0.24 (0.05) nb/sr at the lab angle of 10 (30) for the
Bonn B potential when the dibaryon mass is taken to be 2.1 GeV. The cross
section decreases rapidly with increasing dibaryon mass. A large calculated
width of 40 MeV for combined with a small
experimental upper bound of 0.08 MeV for the decay width appears to have
excluded any low-mass model containing a significant admixture of the
configuration.Comment: 11 journal-style pages, 8 figure
The relative resistance of children to sepsis mortality: from pathways to drug candidates
Attempts to develop drugs that address sepsis based on leads developed in animal models have failed. We sought to identify leads based on human data by exploiting a natural experiment: the relative resistance of children to mortality from severe infections and sepsis. Using public datasets, we identified key differences in pathway activity (Pathprint) in blood transcriptome profiles of septic adults and children. To find drugs that could promote beneficial (child) pathways or inhibit harmful (adult) ones, we built an in silico pathway drug network (PDN) using expression correlation between drug, disease, and pathway gene signatures across 58,475 microarrays. Specific pathway clusters from children or adults were assessed for correlation with drug-based signatures. Validation by literature curation and by direct testing in an endotoxemia model of murine sepsis of the most correlated drug candidates demonstrated that the Pathprint-PDN methodology is more effective at generating positive drug leads than gene-level methods (e.g., CMap). Pathway-centric Pathprint-PDN is a powerful new way to identify drug candidates for intervention against sepsis and provides direct insight into pathways that may determine survival
Detection of Anti-Fungal Sapwood Extractives in Non-Durable Scots Pine (Pinus sylvestris), Rubberwood (Hevea brasiliensis) and Jelutong (Dyera costulata)
A general laboratory bioassay method of Woodward and Pearce (1985) was adopted to detect
anti-fungal activity of sapwood or heartwood extractives of 5 Malaysian hardwoods [dark red
meranti heartwood (Shorea spp.), red balau heartwood (Shorea spp.), kulim heartwood
(Scorodocarpus borneensis), jelutong sapwood (Dyera costulata) and rubberwood sapwood
(Hevea brasiliensis), including the temperate Pinus sylvestris (Scots pine sapwood). The
heartwoods of these species and Scots pine sapwood are known to be highly resistant to decay by
soft-rotting Ascomycetes and anamorphic fungi (about 1-7% wood mass loss), while the
sapwoods of rubberwood and jelutong had much reduced soft rot resistance (respectively 35,
32% wood mass loss) but obviously prone to sapstain and mold attack, including that of Scots
pine. Crude methanol extracts of woodmeal samples of each wood species were loaded on to
thin-layer chromatography plates at between 0.003 and 0.1 g fresh mass equivalent of woodmeal
per spot so as to optimize resolution of separated compounds, and developed with
chloroform:methanol solvent (ratio 19:1). The dried plates were sprayed with fresh fungal spores
of Cladosporium cucumerinum and incubated at >90% RH for 5 days in the dark. Presence of
anti-fungal compounds was revealed by white regions along the solvent transect for each extract
of each species where inhibited spore germination and mycelial growth of C. cucumerinum
occurred. Comparisons of anti-fungal activity of extracts between species and between sapwood
and heartwood were made. Results revealed that several zones of inhibitory activity, indicated by
their Rf-values, were clearly visible on chromatographic separations of methanol extracts of
these 5 wood species. The inhibitory zones for 2 heartwood extracts (except kulim) did not move
from the origin which was also resistant to infection. However inhibition zones were also
detected for the sapwoods of rubberwood, jelutong and Scots pine against C. cucumerinum
despite the known sapstain and decay susceptibility of these wood substrates. The presence of
hitherto unidentified anti-fungal compounds in the sapwoods of these species may elicit limited
potency or narrow spectrum protection from fungal infection and onset of stain or decay
Macrostate Data Clustering
We develop an effective nonhierarchical data clustering method using an
analogy to the dynamic coarse graining of a stochastic system. Analyzing the
eigensystem of an interitem transition matrix identifies fuzzy clusters
corresponding to the metastable macroscopic states (macrostates) of a diffusive
system. A "minimum uncertainty criterion" determines the linear transformation
from eigenvectors to cluster-defining window functions. Eigenspectrum gap and
cluster certainty conditions identify the proper number of clusters. The
physically motivated fuzzy representation and associated uncertainty analysis
distinguishes macrostate clustering from spectral partitioning methods.
Macrostate data clustering solves a variety of test cases that challenge other
methods.Comment: keywords: cluster analysis, clustering, pattern recognition, spectral
graph theory, dynamic eigenvectors, machine learning, macrostates,
classificatio
Elastic Scattering by Deterministic and Random Fractals: Self-Affinity of the Diffraction Spectrum
The diffraction spectrum of coherent waves scattered from fractal supports is
calculated exactly. The fractals considered are of the class generated
iteratively by successive dilations and translations, and include
generalizations of the Cantor set and Sierpinski carpet as special cases. Also
randomized versions of these fractals are treated. The general result is that
the diffraction intensities obey a strict recursion relation, and become
self-affine in the limit of large iteration number, with a self-affinity
exponent related directly to the fractal dimension of the scattering object.
Applications include neutron scattering, x-rays, optical diffraction, magnetic
resonance imaging, electron diffraction, and He scattering, which all display
the same universal scaling.Comment: 20 pages, 11 figures. Phys. Rev. E, in press. More info available at
http://www.fh.huji.ac.il/~dani
An explicit formula for the coefficients in Laplace's method
Laplace's method is one of the fundamental techniques in the asymptotic
approximation of integrals. The coefficients appearing in the resulting
asymptotic expansion, arise as the coefficients of a convergent or asymptotic
series of a function defined in an implicit form. Due to the tedious
computation of these coefficients, most standard textbooks on asymptotic
approximations of integrals do not give explicit formulas for them.
Nevertheless, we can find some more or less explicit representations for the
coefficients in the literature: Perron's formula gives them in terms of
derivatives of an explicit function; Campbell, Fr\"oman and Walles simplified
Perron's method by computing these derivatives using an explicit recurrence
relation. The most recent contribution is due to Wojdylo, who rediscovered the
Campbell, Fr\"oman and Walles formula and rewrote it in terms of partial
ordinary Bell polynomials. In this paper, we provide an alternative
representation for the coefficients, which contains ordinary potential
polynomials. The proof is based on Perron's formula and a theorem of Comtet.
The asymptotic expansions of the gamma function and the incomplete gamma
function are given as illustrations.Comment: 14 pages, to appear in Constructive Approximatio
Vertical Confinement and Evolution of Reentrant Insulating Transition in the Fractional Quantum Hall Regime
We have observed an anomalous shift of the high field reentrant insulating
phases in a two-dimensional electron system (2DES) tightly confined within a
narrow GaAs/AlGaAs quantum well. Instead of the well-known transitions into the
high field insulating states centered around , the 2DES confined
within an 80\AA-wide quantum well exhibits the transition at .
Comparably large quantum lifetime of the 2DES in narrow well discounts the
effect of disorder and points to confinement as the primary driving force
behind the evolution of the reentrant transition.Comment: 5 pages, 4 figure
Glassy Phase Transition and Stability in Black Holes
Black hole thermodynamics, confined to the semi-classical regime, cannot
address the thermodynamic stability of a black hole in flat space. Here we show
that inclusion of correction beyond the semi-classical approximation makes a
black hole thermodynamically stable. This stability is reached through a phase
transition. By using Ehrenfest's scheme we further prove that this is a glassy
phase transition with a Prigogine-Defay ratio close to 3. This value is well
placed within the desired bound (2 to 5) for a glassy phase transition. Thus
our analysis indicates a very close connection between the phase transition
phenomena of a black hole and glass forming systems. Finally, we discuss the
robustness of our results by considering different normalisations for the
correction term.Comment: v3, minor changes over v2, references added, LaTeX-2e, 18 pages, 3 ps
figures, to appear in Eour. Phys. Jour.
Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates
We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor,
using high precision torsional oscillator and DC calorimetry techniques. Our
investigation focused on the onset of superfluidity at low temperatures as the
4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel
system were used to determine the superfluid density of films with transition
temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor
system probed the excitation spectrum of both non-superfluid and superfluid
films for temperatures down to 10 mK. Both sets of measurements suggest that
the critical coverage for the onset of superfluidity corresponds to a mobility
edge in the chemical potential, so that the onset transition is the bosonic
analog of a superconductor-insulator transition. The superfluid density
measurements, however, are not in agreement with the scaling theory of an onset
transition from a gapless, Bose glass phase to a superfluid. The heat capacity
measurements show that the non-superfluid phase is better characterized as an
insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript
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