23,495 research outputs found
Development of an Operational Northern Aquatic Ecosystem Model: Completion Report
OWRR Contract No. 14-31-0001-5217 Grant No. C-6169The work upon which this completion report is based was supported
by funds provided by the U. S. Department of the Interior, Office of
Water Research and Technology as authorized under the Water Resources
Research Act of 1964, Public Law 88-379, as amended
Prospects for a mHz-linewidth laser
We propose a new light source based on having alkaline-earth atoms in an
optical lattice collectively emit photons on an ultra-narrow clock transition
into the mode of a high Q-resonator. The resultant optical radiation has an
extremely narrow linewidth in the mHz range, even smaller than that of the
clock transition itself due to collective effects. A power level of order
is possible, sufficient for phase-locking a slave optical local
oscillator. Realizing this light source has the potential to improve the
stability of the best clocks by two orders of magnitude.Comment: minor revisions + shortening; factor 2 algebra mistake correcte
Baryon Resonance Analysis from MAID
The unitary isobar model MAID2007 has been used to analyze the recent data of
pion electroproduction. The model contains all four-star resonances in the
region below W=2 GeV and both single-Q^2 and Q^2 dependent transition form
factors could be obtained for the Delta, Roper, D13(1520), S11(1535),
S31(1620), S11(1650), D15(1675), F15(1680) and P13(1720). From the complete
world data base, including also pi- data on the neutron, also Q^2 dependent
neutron form factors are obtained. For all transition form factors we also give
convenient numerical parameterizations that can be used in other reactions.
Furthermore, we show how the transition form factors can be used to obtain
empirical transverse charge densities and our first results are given for the
Roper, the S11 and D13 resonances.Comment: 8 pages, 11 figures, 4 tables, Proc. of NSTAR2009, Beijin
Rate dependent shear bands in a shear transformation zone model of amorphous solids
We use Shear Transformation Zone (STZ) theory to develop a deformation map
for amorphous solids as a function of the imposed shear rate and initial
material preparation. The STZ formulation incorporates recent simulation
results [Haxton and Liu, PRL 99 195701 (2007)] showing that the steady state
effective temperature is rate dependent. The resulting model predicts a wide
range of deformation behavior as a function of the initial conditions,
including homogeneous deformation, broad shear bands, extremely thin shear
bands, and the onset of material failure. In particular, the STZ model predicts
homogeneous deformation for shorter quench times and lower strain rates, and
inhomogeneous deformation for longer quench times and higher strain rates. The
location of the transition between homogeneous and inhomogeneous flow on the
deformation map is determined in part by the steady state effective
temperature, which is likely material dependent. This model also suggests that
material failure occurs due to a runaway feedback between shear heating and the
local disorder, and provides an explanation for the thickness of shear bands
near the onset of material failure. We find that this model, which resolves
dynamics within a sheared material interface, predicts that the stress weakens
with strain much more rapidly than a similar model which uses a single state
variable to specify internal dynamics on the interface.Comment: 10 pages, 13 figures, corrected typos, added section on rate
strengthening vs. rate weakening material
Incompatibility of modulated checkerboard patterns with the neutron scattering resonance peak in cuprate superconductors
Checkerboard patterns have been proposed in order to explain STM experiments
on the cuprates BSCCO and Na-CCOC. However the presence of these patterns has
not been confirmed by a bulk probe such as neutron scattering. In particular,
simple checkerboard patterns are inconsistent with neutron scattering data, in
that they have low energy incommsensurate (IC) spin peaks rotated 45 degrees
from the direction of the charge IC peaks. However, it is unclear whether other
checkerboard patterns can solve the problem. In this paper, we have studied
more complicated checkerboard patterns ("modulated checkerboards") by using
spin wave theory and analyzed noncollinear checkerboards as well. We find that
the high energy response of the modulated checkerboards is inconsistent with
neutron scattering results, since they fail to exhibit a resonance peak at
(pi,pi), which has recently been shown to be a universal feature of cuprate
superconductors. We further argue that the newly proposed noncollinear
checkerboard also lacks a resonance peak. We thus conclude that to date no
checkerboard pattern has been proposed which satisfies both the low energy
constraints and the high energy constraints imposed by the current body of
experimental data in cuprate superconductors.Comment: 5 pages, 5 figures, Fig.2 update
Stick-Slip Motion and Phase Transition in a Block-Spring System
We study numerically stick slip motions in a model of blocks and springs
being pulled slowly. The sliding friction is assumed to change dynamically with
a state variable. The transition from steady sliding to stick-slip is
subcritical in a single block and spring system. However, we find that the
transition is continuous in a long chain of blocks and springs. The size
distribution of stick-slip motions exhibits a power law at the critical point.Comment: 8 figure
DAILY KNEE JOINT LAXITY IN FEMALES ACROSS A MENSTRUAL CYCLE AND MALES ACROSS A CALENDAR MONTH
Increased athletic participation of females has resulted in a high occurrence of anterior cruciate ligament (ACL) injuries. Excessive knee joint laxity during hormonal peaks of endogenous sex hormones during the follicular, ovulatory, and luteal phases of the menstrual cycle has been associated with ACL injury risk. The purpose of this study was to determine the effect of gender and menstrual phase on knee joint laxity over the full course of a normal menstrual cycle in females and across a calendar month in males. A repeated measures ANOVA revealed no interaction effect between gender and phase, no main effect for gender, but a statistically significant main effect for phase. Since male participants demonstrated a similar inclination between phases, the significance of this trend should be interpreted as a possible random occurrence
Investigations of lubricant rheology as applied to elastohydrodynamic lubrication
The pressure viscometer was modified to permit the measurement of viscosity at elevated pressures and shear stresses up to 5 x 10 to the 6th power N/sq m (720 psi). This shear stress is within a factor of three of the shear stress occurring in a sliding ehd point contact such as occurs in the ehd simulator. Viscosity data were taken on five lubricant samples, and it was found that viscous heating effects on the viscosity were predominant and not non-Newtonian behavior at the high shear stresses. The development of the infrared temperature measuring technique for the ehd simulator was completed, and temperature data for a set of operating conditions and one lubricant are reported. The numerical analysis of the behavior of nonlinear lubricants in the lubrication of rollers is reported
Approach to Perturbative Results in the N-Delta Transition
We show that constraints from perturbative QCD calculations play a role in
the nucleon to Delta(1232) electromagnetic transition even at moderate momentum
transfer scales. The pQCD constraints, tied to real photoproduction data and
unseparated resonance response functions, lead to explicit forms for the
helicity amplitudes wherein the E2/M1 ratio remains small at moderately large
momentum transfer.Comment: 4 pages, 2 figures, ReVTe
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