15,188 research outputs found
Searching for an anomalous coupling via single top quark production at a collider
We investigate the potential of a high-energy collider to
detect an anomalous coupling from observation of the reaction
, , where or . We find that with
-tagging and suitable kinematic cuts this process should be observable if
the anomalous coupling is no less than about 0.05/TeV, where
is the scale of new physics associated with the anomalous
interaction. This improves upon the bound possible from observation of top
decays at the Tevatron.Comment: 13 pages, RevTeX, 1 PS figur
Description of Atmospheric Conditions at the Pierre Auger Observatory Using Meteorological Measurements and Models
Atmospheric conditions at the site of a cosmic ray observatory must be known
well for reconstructing observed extensive air showers, especially when
measured using the fluorescence technique. For the Pierre Auger Observatory, a
sophisticated network of atmospheric monitoring devices has been conceived.
Part of this monitoring was a weather balloon program to measure atmospheric
state variables above the Observatory. To use the data in reconstructions of
air showers, monthly models have been constructed. Scheduled balloon launches
were abandoned and replaced with launches triggered by high-energetic air
showers as part of a rapid monitoring system. Currently, the balloon launch
program is halted and atmospheric data from numerical weather prediction models
are used. A description of the balloon measurements, the monthly models as well
as the data from the numerical weather prediction are presented
Electromagnetic Production of Quarkonium in decay
The decay , where is a
quarkonium state, has a very clean final state, which should
make it easy to detect. The branching ratio of this mode is greater than
for , , and , indicating that these processes may
be detectable at LEP.Comment: Latex, 6 pages, 2 figure in postscript format (uuencoded), (or
available upon request), NUHEP-TH-93-1
Equivalence between two-dimensional alternating/random Ising model and the ground state of one-dimensional alternating/random XY chain
It is derived that the two-dimensional Ising model with alternating/random
interactions and with periodic/free boundary conditions is equivalent to the
ground state of the one-dimensional alternating/random XY model with the
corresponding periodic/free boundary conditions. This provides an exact
equivalence between a random rectangular Ising model, in which the
Griffiths-McCoy phase appears, and a random XY chain.Comment: 10 page
Variation of turbulent burning rate of methane, methanol, and iso-octane air mixtures with equivalence ratio at elevated pressure
Turbulent burning velocities for premixed methane, methanol, and iso-octane/air mixtures have been experimentally determined for an rms turbulent velocity of 2 m/s and pressure of 0.5 MPa for a wide range of equivalence ratios. Turbulent burning velocity data were derived using high-speed schlieren photography and transient pressure recording; measurements were processed to yield a turbulent mass rate burning velocity, utr. The consistency between the values derived using the two techniques, for all fuels for both fuel-lean and fuel-rich mixtures, was good. Laminar burning measurements were made at the same pressure, temperature, and equivalence ratios as the turbulent cases and laminar burning velocities and Markstein numbers were determined. The equivalence ratio (φ) for peak turbulent burning velocity proved not always coincident with that for laminar burning velocity for the same fuel; for isooctane, the turbulent burning velocity unexpectedly remained high over the range φ = 1 to 2. The ratio of turbulent to laminar burning velocity proved remarkably high for very rich iso-octane/air and lean methane/air mixtures
Self-organized critical neural networks
A mechanism for self-organization of the degree of connectivity in model
neural networks is studied. Network connectivity is regulated locally on the
basis of an order parameter of the global dynamics which is estimated from an
observable at the single synapse level. This principle is studied in a
two-dimensional neural network with randomly wired asymmetric weights. In this
class of networks, network connectivity is closely related to a phase
transition between ordered and disordered dynamics. A slow topology change is
imposed on the network through a local rewiring rule motivated by
activity-dependent synaptic development: Neighbor neurons whose activity is
correlated, on average develop a new connection while uncorrelated neighbors
tend to disconnect. As a result, robust self-organization of the network
towards the order disorder transition occurs. Convergence is independent of
initial conditions, robust against thermal noise, and does not require fine
tuning of parameters.Comment: 5 pages RevTeX, 7 figures PostScrip
Percolation and Conduction in Restricted Geometries
The finite-size scaling behaviour for percolation and conduction is studied
in two-dimensional triangular-shaped random resistor networks at the
percolation threshold. The numerical simulations are performed using an
efficient star-triangle algorithm. The percolation exponents, linked to the
critical behaviour at corners, are in good agreement with the conformal
results. The conductivity exponent, t', is found to be independent of the shape
of the system. Its value is very close to recent estimates for the surface and
bulk conductivity exponents.Comment: 10 pages, 7 figures, TeX, IOP macros include
Development of Onchocerca volvulus in humanized NSG mice and detection of parasite biomarkers in urine and serum.
BACKGROUND: The study of Onchocerca volvulus has been limited by its host range, with only humans and non-human primates shown to be susceptible to the full life cycle infection. Small animal models that support the development of adult parasites have not been identified.
METHODOLOGY/PRINCIPAL FINDINGS: We hypothesized that highly immunodeficient NSG mice would support the survival and maturation of O. volvulus and alteration of the host microenvironment through the addition of various human cells and tissues would further enhance the level of parasite maturation. NSG mice were humanized with: (1) umbilical cord derived CD34+ stem cells, (2) fetal derived liver, thymus and CD34+ stem cells or (3) primary human skeletal muscle cells. NSG and humanized NSG mice were infected with 100 O. volvulus infective larvae (L3) for 4 to 12 weeks. When necropsies of infected animals were performed, it was observed that parasites survived and developed throughout the infection time course. In each of the different humanized mouse models, worms matured from L3 to advanced fourth stage larvae, with both male and female organ development. In addition, worms increased in length by up to 4-fold. Serum and urine, collected from humanized mice for identification of potential biomarkers of infection, allowed for the identification of 10 O. volvulus-derived proteins found specifically in either the urine or the serum of the humanized O. volvulus-infected NSG mice.
CONCLUSIONS/SIGNIFICANCE: The newly identified mouse models for onchocerciasis will enable the development of O. volvulus specific biomarkers, screening for new therapeutic approaches and potentially studying the human immune response to infection with O. volvulus
Low-Temperature Orientation Dependence of Step Stiffness on {111} Surfaces
For hexagonal nets, descriptive of {111} fcc surfaces, we derive from
combinatoric arguments a simple, low-temperature formula for the orientation
dependence of the surface step line tension and stiffness, as well as the
leading correction, based on the Ising model with nearest-neighbor (NN)
interactions. Our formula agrees well with experimental data for both Ag and
Cu{111} surfaces, indicating that NN-interactions alone can account for the
data in these cases (in contrast to results for Cu{001}). Experimentally
significant corollaries of the low-temperature derivation show that the step
line tension cannot be extracted from the stiffness and that with plausible
assumptions the low-temperature stiffness should have 6-fold symmetry, in
contrast to the 3-fold symmetry of the crystal shape. We examine Zia's exact
implicit solution in detail, using numerical methods for general orientations
and deriving many analytic results including explicit solutions in the two
high-symmetry directions. From these exact results we rederive our simple
result and explore subtle behavior near close-packed directions. To account for
the 3-fold symmetry in a lattice gas model, we invoke a novel
orientation-dependent trio interaction and examine its consequences.Comment: 11 pages, 8 figure
The Generalized Jacobi Equation
The Jacobi equation in pseudo-Riemannian geometry determines the linearized
geodesic flow. The linearization ignores the relative velocity of the
geodesics. The generalized Jacobi equation takes the relative velocity into
account; that is, when the geodesics are neighboring but their relative
velocity is arbitrary the corresponding geodesic deviation equation is the
generalized Jacobi equation. The Hamiltonian structure of this nonlinear
equation is analyzed in this paper. The tidal accelerations for test particles
in the field of a plane gravitational wave and the exterior field of a rotating
mass are investigated. In the latter case, the existence of an attractor of
uniform relative radial motion with speed is pointed
out. The astrophysical implications of this result for the terminal speed of a
relativistic jet is briefly explored.Comment: LaTeX file, 4 PS figures, 28 pages, revised version, accepted for
publication in Classical and Quantum Gravit
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