7,455 research outputs found
Energy Conversion Alternatives Study (ECAS), Westinghouse phase 1. Volume 5: Combined gas-steam turbine cycles
The energy conversion efficiency of gas-steam turbine cycles was investigated for selected combined cycle power plants. Results indicate that it is possible for combined cycle gas-steam turbine power plants to have efficiencies several point higher than conventional steam plants. Induction of low pressure steam into the steam turbine is shown to improve the plant efficiency. Post firing of the boiler of a high temperature combined cycle plant is found to increase net power but to worsen efficiency. A gas turbine pressure ratio of 12 to 1 was found to be close to optimum at all gas turbine inlet temperatures that were studied. The coal using combined cycle plant with an integrated low-Btu gasifier was calculated to have a plant efficiency of 43.6%, a capitalization of $497/kW, and a cost of electricity of 6.75 mills/MJ (24.3 mills/kwh). This combined cycle plant should be considered for base load power generation
Zenithal bistable device: comparison of modeling and experiment
A comparative modeling and experimental study of the zenithal bistable liquid crystal device is presented. A dynamic Landau de Gennes theory of nematic liquid crystals is solved numerically to model the electric field induced latching of the device and the results are compared with experimental measurements and theoretical approximations. The study gives a clear insight into the latching mechanism dynamics and enables the dependence of the device latching on both material parameters and surface shape to be determined. Analytical approximation highlights a route to optimize material selection in terms of latching voltages and the numerical model, which includes an accurate surface representation, recovers the complex surface shape effects. Predictions of device performance are presented as a function of both surface anchoring strength and surface shape and grating pitch. A measurement of the homeotropic anchoring energy has been undertaken by comparing the voltage response as a function of cell gap; we find the homeotropic anchoring energies can be varied in the range 0.5 to 4 (10-44 J m-2)
Determination of the forward slope in and elastic scattering up to LHC energy
In the analysis of experimental data on (or ) elastic
differential cross section it is customary to define an average forward slope
in the form , where is the momentum transfer. Taking as
working example the results of experiments at Tevatron and SPS, we will show
with the help of the impact picture approach, that this simplifying assumption
hides interesting information on the complex non-flip scattering amplitude, and
that the slope is not a constant. We investigate the variation of this
slope parameter, including a model-independent way to extract this information
from an accurate measurement of the elastic differential cross section. An
extension of our results to the LHC energy domain is presented in view of
future experiments.Comment: 12 pages, 6 figures, to appear in EPJ
High Energy Hadron-Nucleus Cross Sections and Their Extrapolation to Cosmic Ray Energies
Old models of the scattering of composite systems based on the Glauber model
of multiple diffraction are applied to hadron-nucleus scattering. We obtain an
excellent fit with only two free parameters to the highest energy
hadron-nucleus data available. Because of the quality of the fit and the
simplicity of the model it is argued that it should continue to be reliable up
to the highest cosmic ray energies. Logarithmic extrapolations of proton-proton
and proton-antiproton data are used to calculate the proton-air cross sections
at very high energy. Finally, it is observed that if the exponential behavior
of the proton-antiproton diffraction peak continues into the few TeV energy
range it will violate partial wave unitarity. We propose a simple modification
that will guarantee unitarity throughout the cosmic ray energy region.Comment: 8 pages, 9 postscript figures. This manuscript replaces a partial
manuscript incorrectly submitte
Trends and Regional Variation in Hip, Knee and Shoulder Replacement
Analyzes patterns in underuse or overuse of joint replacements among Medicare beneficiaries by geographic regions and race/ethnicity. Explores underlying factors and highlights the need for physician and patient education and shared decision making
A new catalog of photometric redshifts in the Hubble Deep Field
Using the newly available infrared images of the Hubble Deep Field in the J,
H, and K bands and an optimal photometric method, we have refined a technique
to estimate the redshifts of 1067 galaxies. A detailed comparison of our
results with the spectroscopic redshifts in those cases where the latter are
available shows that this technique gives very good results for bright enough
objects (AB(8140) < 26.0). From a study of the distribution of residuals
(Dz(rms)/(1+z) ~ 0.1 at all redshifts) we conclude that the observed errors are
mainly due to cosmic variance. This very important result allows for the
assessment of errors in quantities to be directly or indirectly measured from
the catalog. We present some of the statistical properties of the ensemble of
galaxies in the catalog, and finish by presenting a list of bright
high-redshift (z ~ 5) candidates extracted from our catalog, together with
recent spectroscopic redshift determinations confirming that two of them are at
z=5.34 and z=5.60.Comment: 28 pages, 12PS+4JPEG figures, aaspp style. Accepted for publication
in The Astrophysical Journal. The catalog, together with a clickable map of
the HDF, Tables 4 and 5 (HTML, LaTeX or ASCII format), and the figures, are
available at http://bat.phys.unsw.edu.au/~fsoto/hdfcat.htm
Eikonal profile functions and amplitudes for and scattering
The eikonal profile function obtained from the Model of the Stochastic
Vacuum is parametrized in a form suitable for comparison with experiment. The
amplitude and the extended profile function (including imaginary and real
parts) are determined directly from the complete pp and p elastic
scattering data at high energies. Full and accurate representation of the data
is presented, with smooth energy dependence of all parameters. The changes
needed in the original profile function required for description of scattering
beyond the forward direction are described.Comment: Latex, 28 pages and 16 figure
Global optical potential for nucleus-nucleus systems from 50 MeV/u to 400 MeV/u
We present a new global optical potential (GOP) for nucleus-nucleus systems,
including neutron-rich and proton-rich isotopes, in the energy range of MeV/u. The GOP is derived from the microscopic folding model with the
complex -matrix interaction CEG07 and the global density presented by S{\~
a}o Paulo group. The folding model well accounts for realistic complex optical
potentials of nucleus-nucleus systems and reproduces the existing elastic
scattering data for stable heavy-ion projectiles at incident energies above 50
MeV/u. We then calculate the folding-model potentials (FMPs) for projectiles of
even-even isotopes, C, O, Ne, Mg,
Si, S, Ar, and Ca, scattered by stable
target nuclei of C, O, Si, Ca Ni, Zr,
Sn, and Pb at the incident energy of 50, 60, 70, 80, 100, 120,
140, 160, 180, 200, 250, 300, 350, and 400 MeV/u. The calculated FMP is
represented, with a sufficient accuracy, by a linear combination of 10-range
Gaussian functions. The expansion coefficients depend on the incident energy,
the projectile and target mass numbers and the projectile atomic number, while
the range parameters are taken to depend only on the projectile and target mass
numbers. The adequate mass region of the present GOP by the global density is
inspected in comparison with FMP by realistic density. The full set of the
range parameters and the coefficients for all the projectile-target
combinations at each incident energy are provided on a permanent open-access
website together with a Fortran program for calculating the microscopic-basis
GOP (MGOP) for a desired projectile nucleus by the spline interpolation over
the incident energy and the target mass number.Comment: 25 pages, 13 figure
Spatial Scaling in Model Plant Communities
We present an analytically tractable variant of the voter model that provides
a quantitatively accurate description of beta-diversity (two-point correlation
function) in two tropical forests. The model exhibits novel scaling behavior
that leads to links between ecological measures such as relative species
abundance and the species area relationship.Comment: 10 pages, 3 figure
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