23,783 research outputs found
Groundwater Resources in the Saline Valley Conservancy District, Saline and Gallatin Counties, Illinois
published or submitted for publicationis peer reviewedOpe
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
Using National Measures of Patients' Perceptions of Health Care to Design and Debrief Clinical Simulations
This article describes an innovative approach to using national measures of patients' perspectives of quality health care. Nurses from a regional simulation consortium designed and executed a simulation using the Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) survey to prepare nurses to improve care and, in turn, enhance patients' perceptions of care. The consortium is currently revising the reporting mechanism to collect data about specific learning objectives based on national quality indicator benchmarks, specifically HCAHPS. This revision reflects the changing needs of health care to include quality metrics in simulation
Payroll employment data: measuring the effects of annual benchmark revisions
During the recovery from the 2001 recession, the business press and economic analysts used payroll employment data released monthly by the U.S. Bureau of Labor Statistics (BLS) as evidence of protracted weakness in the labor market. But using these monthly releases for this type of analysis can be premature and potentially misleading. The initial BLS releases can differ substantially from payroll employment data that are revised to incorporate information from less timely but more complete sources. ; This article highlights the historical revisions to the aggregate nonfarm payroll employment series. Examining both monthly survey-based revisions and the more extensive annual benchmark revisions, the authors focus specifically on how the sequence of data revisions modifies payroll employment estimates from their initial release. The graphs in the article display the magnitude and direction of each revision from the initial estimate for a particular month to its currently published value, demonstrating that the largest portion of enduring change for the estimates occurs in the benchmark revisions. ; The authors then investigate empirically whether these revisions contain information that can be exploited to anticipate future revisions. The analysis shows that previous benchmark data revisions are useful for explaining the variation in subsequent payroll employment benchmark data. Such information, the authors note, could prove useful for further research aimed at modeling better real-time estimates of employment conditions.Employment (Economic theory)
Production and processing of Cu-Cr-Nb alloys
A new Cu-based alloy possessing high strength, high conductivity, and good stability at elevated temperatures was recently produced. This paper details the melting of the master alloys, production of rapidly solidified ribbon, and processing of the ribbon to sheet by hot pressing and hot rolling
Astrophysical Probes of the Constancy of the Velocity of Light
We discuss possible tests of the constancy of the velocity of light using
distant astrophysical sources such as gamma-ray bursters (GRBs), Active
Galactic Nuclei (AGNs) and pulsars. This speculative quest may be motivated by
some models of quantum fluctuations in the space-time background, and we
discuss explicitly how an energy-dependent variation in photon velocity \delta
c/ c \sim - E / M arises in one particular quantum-gravitational model. We then
discuss how data on GRBs may be used to set limits on variations in the
velocity of light, which we illustrate using BATSE and OSSE observations of the
GRBs that have recently been identified optically and for which precise
redshifts are available. We show how a regression analysis can be performed to
look for an energy-dependent effect that should correlate with redshift. The
present data yield a limit M \gsim 10^{15} GeV for the quantum gravity scale.
We discuss the prospects for improving this analysis using future data, and how
one might hope to distinguish any positive signal from astrophysical effects
associated with the sources.Comment: 37 pages LaTeX, 9 eps figures included, uses aasms4.st
M Theory from World-Sheet Defects in Liouville String
We have argued previously that black holes may be represented in a D-brane
approach by monopole and vortex defects in a sine-Gordon field theory model of
Liouville dynamics on the world sheet. Supersymmetrizing this sine-Gordon
system, we find critical behaviour in 11 dimensions, due to defect condensation
that is the world-sheet analogue of D-brane condensation around an extra
space-time dimension in M theory. This supersymmetric description of Liouville
dynamics has a natural embedding within a 12-dimensional framework suggestive
of F theory.Comment: 17 pages LATEX, 1 epsf figure include
Dynamical Formation of Horizons in Recoiling D Branes
A toy calculation of string/D-particle interactions within a world-sheet
approach indicates that quantum recoil effects - reflecting the gravitational
back-reaction on space-time foam due to the propagation of energetic particles
- induces the appearance of a microscopic event horizon, or `bubble', inside
which stable matter can exist. The scattering event causes this horizon to
expand, but we expect quantum effects to cause it to contract again, in a
`bounce' solution. Within such `bubbles', massless matter propagates with an
effective velocity that is less than the velocity of light in vacuo, which may
lead to observable violations of Lorentz symmetry that may be tested
experimentally. The conformal invariance conditions in the interior geometry of
the bubbles select preferentially three for the number of the spatial
dimensions, corresponding to a consistent formulation of the interaction of D3
branes with recoiling D particles, which are allowed to fluctuate independently
only on the D3-brane hypersurface.Comment: 25 pages LaTeX, 4 eps figures include
Telerobotics: A simulation facility for university research
An experimental telerobotics (TR) simulation suitable for studying human operator (H.O.) performance is described. Simple manipulator pick-and-place and tracking tasks allowed quantitative comparison of a number of calligraphic display viewing conditions. A number of control modes could be compared in this TR simulation, including displacement, rate and acceleratory control using position and force joysticks. A homeomorphic controller turned out to be no better than joysticks; the adaptive properties of the H.O. can apparently permit quite good control over a variety of controller configurations and control modes. Training by optimal control example seemed helpful in preliminary experiments. An introduced communication delay was found to produce decrease in performance. In considerable part, this difficulty could be compensated for by preview control information. That neurological control of normal human movement contains a data period of 0.2 second may relate to this robustness of H.O. control to delay. The Ames-Berkeley enhanced perspective display was utilized in conjunction with an experimental helmet mounted display system (HMD) that provided stereoscopic enhanced views
Supersymmetric Dark Matter and the Reheating Temperature of the Universe
Since the thermal history of the Universe is unknown before the epoch of
primordial nucleosynthesis, the largest temperature of the radiation dominated
phase (the reheating temperature) might have been as low as 1 MeV. We perform a
quantitative study of supersymmetric dark matter relic abundance in
cosmological scenarios with low reheating temperature. We show that, for values
of the reheating temperature smaller than about 30 GeV, the domains of the
supergravity parameter space which are compatible with the hypothesis that dark
matter is composed by neutralinos are largely enhanced. We also find a lower
bound on the reheating temperature: if the latter is smaller than about 1 GeV
neutralinos cannot be efficiently produced in the early Universe and then they
are not able to explain the present amount of dark matter.Comment: 21 pages, 5 figures, typeset with ReVTeX4. The paper may also be
found at http://www.to.infn.it/~fornengo/papers/reheating.ps.g
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