1,460 research outputs found
Comparison of Low-Thrust Control Laws for Application in Planetocentric Space
Recent interest at NASA for the application of solar electric propulsion for the transfer of significant payloads in cislunar space has led to the development of high-fidelity simulations of such missions. With such transfers involving transfer times on the order of months, simulation time can be significant. In the past, the examination of such missions typically began with the use of lower-fidelity trajectory optimization tools such as SEPSPOT to develop and tune guidance laws which delivered optimal or near- optimal trajectories, where optimal is generally defined as minimizing propellant expenditure or time of flight. The transfer of these solutions to a high-fidelity simulation is typically an iterative process whereby the initial solution may nearly, but not precisely, meet mission objectives. Further tuning of the guidance algorithm is typically necessary when accounting for high-fidelity perturbations such as those due to more detailed gravity models, secondary-body effects, solar radiation pressure, etc. While trajectory optimization is a useful method for determining optimal performance metrics, algorithms which deliver nearly optimal performance with minimal tuning are an attractive alternative
Polaronic optical absorption in electron-doped and hole-doped cuprates
Polaronic features similar to those previously observed in the photoinduced
spectra of cuprates have been detected in the reflectivity spectra of
chemically doped parent compounds of high-critical-temperature superconductors,
both -type and -type. In NdCuO these features, whose
intensities depend both on doping and temperature, include local vibrational
modes in the far infrared and a broad band centered at 1000 cm.
The latter band is produced by the overtones of two (or three) local modes and
is well described in terms of a small-polaron model, with a binding energy of
about 500 cm. Most of the above infrared features are shown to survive
in the metallic phase of NdCeCu0, BiSrCuO, and
YBaCuO, where they appear as extra-Drude peaks. The occurrence
of polarons is attributed to local modes strongly coupled to carriers, as shown
by a comparison with tunneling results.Comment: File latex, 31 p., submitted to Physical Review B. Figures may be
faxed upon reques
A Precision Calculation of the Next-to-Leading Order Energy-Energy Correlation Function
The O(alpha_s^2) contribution to the Energy-Energy Correlation function (EEC)
of e+e- -> hadrons is calculated to high precision and the results are shown to
be larger than previously reported. The consistency with the leading logarithm
approximation and the accurate cancellation of infrared singularities exhibited
by the new calculation suggest that it is reliable. We offer evidence that the
source of the disagreement with previous results lies in the regulation of
double singularities.Comment: 6 pages, uuencoded LaTeX and one eps figure appended Complete paper
as PostScript file (125 kB) available at:
http://www.phys.washington.edu/~clay/eecpaper1/paper.htm
Polaron Formation in the Three-Band Peierls-Hubbard Model for Cuprate Superconductors
Exact diagonalization calculations show a continuous transition from
delocalized to small polaron behavior as a function of intersite
electron-lattice coupling. A transition, found previously at Hartree-Fock level
[Yonemitsu et al., Phys. Rev. Lett. {\bf 69}, 965 (1992)], between a magnetic
and a non magnetic state does not subsist when fluctuations are included. Local
phonon modes become softer close to the polaron and by comparison with optical
measurements of doped cuprates we conclude that they are close to the
transition region between polaronic and non-polaronic behavior. The barrier to
adiabatically move a hole vanishes in that region suggesting large mobilities.Comment: 7 pages + 3 poscript figures, Revtex 3.0, MSC-199
Nonminimal Supersymmetric Standard Model with Baryon and Lepton Number Violation
We carry out a comprehensive analysis of the nonminimal supersymmetric
standard model (NMSSM) with baryon and lepton number violation. We catalogue
the baryon and lepton number violating dimension four and five operators of the
model. We then study the renormalization group evolution and infrared stable
fixed points of the Yukawa couplings and the soft supersymmetry breaking
trilinear couplings of this model with baryon and lepton number (and R-parity)
violation involving the heaviest generations. We show analytically that in the
Yukawa sector of the NMSSM there is only one infrared stable fixed point. This
corresponds to a non-trivial fixed point for the top-, bottom-quark Yukawa
couplings and the violating coupling , and a trivial one
for all other couplings. All other possible fixed points are either unphysical
or unstable in the infrared region. We also carry out an analysis of the
renormalization group equations for the soft supersymmetry breaking trilinear
couplings, and determine the corresponding fixed points for these couplings. We
then study the quasi-fixed point behaviour, both of the third generation Yukawa
couplings and the baryon number violating coupling, and those of the soft
supersymmetry breaking trilinear couplings. From the analysis of the fixed
point behaviour, we obtain upper and lower bounds on the baryon number
violating coupling , as well as on the soft supersymmetry
breaking trilinear couplings. Our analysis shows that the infrared fixed point
behavior of NMSSM with baryon and lepton number violation is similar to that of
MSSM.Comment: 35 pages, Revtex, 6 eps fig
Overview of the Nordic Seas CARINA data and salinity measurements
Water column data of carbon and carbon relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruises in the Arctic, Atlantic, and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic). The data have been subject to rigorous quality control (QC) in order to ensure highest possible quality and consistency. The data for most of the parameters included were examined in order to quantify systematic biases in the reported values, i.e. secondary quality control. Significant biases have been corrected for in the data products, i.e. the three merged files with measured, calculated and interpolated values for each of the three CARINA regions; the Arctic Mediterranean Seas (AMS), the Atlantic (ATL) and the Southern Ocean (SO). With the adjustments the CARINA database is consistent both internally as well as with GLODAP (Key et al., 2004) and is suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation. The Arctic Mediterranean Seas include the Arctic Ocean and the Nordic Seas, and the quality control was carried out separately in these two areas. This contribution provides an overview of the CARINA data from the Nordic Seas and summarises the findings of the QC of the salinity data. One cruise had salinity data that were of questionable quality, and these have been removed from the data product. An evaluation of the consistency of the quality controlled salinity data suggests that they are consistent to at least ±0.005
Involution and Constrained Dynamics I: The Dirac Approach
We study the theory of systems with constraints from the point of view of the
formal theory of partial differential equations. For finite-dimensional systems
we show that the Dirac algorithm completes the equations of motion to an
involutive system. We discuss the implications of this identification for field
theories and argue that the involution analysis is more general and flexible
than the Dirac approach. We also derive intrinsic expressions for the number of
degrees of freedom.Comment: 28 pages, latex, no figure
Radiative Corrections to Neutralino and Chargino Masses in the Minimal Supersymmetric Model
We determine the neutralino and chargino masses in the MSSM at one-loop. We
perform a Feynman diagram calculation in the on-shell renormalization scheme,
including quark/squark and lepton/slepton loops. We find generically the
corrections are of order 6%. For a 20 GeV neutralino the corrections can be
larger than 20%. The corrections change the region of
parameter space which is ruled out by LEP data. We demonstrate that, e.g., for
a given and the lower limit on the parameter can shift
by 20 GeV.Comment: 11 pages, JHU-TIPAC-930030, PURD-TH-93-13, uses epsf.sty, 6 uuencoded
postscript figures, added one sentence and a referenc
Screening by symmetry of long-range hydrodynamic interactions of polymers confined in sheets
Hydrodynamic forces may significantly affect the motion of polymers. In
sheet-like cavities, such as the cell's cytoplasm and microfluidic channels,
the hydrodynamic forces are long-range. It is therefore expected that that
hydrodynamic interactions will dominate the motion of polymers in sheets and
will be manifested by Zimm-like scaling. Quite the opposite, we note here that
although the hydrodynamic forces are long-range their overall effect on the
motion of polymers vanishes due to the symmetry of the two-dimensional flow. As
a result, the predicted scaling of experimental observables such as the
diffusion coefficient or the rotational diffusion time is Rouse-like, in accord
with recent experiments. The effective screening validates the use of the
non-interacting blobs picture for polymers confined in a sheet.Comment: http://www.weizmann.ac.il/complex/tlusty/papers/Macromolecules2006.pdf
http://pubs.acs.org/doi/abs/10.1021/ma060251
Dependent coordinates in path integral measure factorization
The transformation of the path integral measure under the reduction procedure
in the dynamical systems with a symmetry is considered. The investigation is
carried out in the case of the Wiener--type path integrals that are used for
description of the diffusion on a smooth compact Riemannian manifold with the
given free isometric action of the compact semisimple unimodular Lie group. The
transformation of the path integral, which factorizes the path integral
measure, is based on the application of the optimal nonlinear filtering
equation from the stochastic theory. The integral relation between the kernels
of the original and reduced semigroup are obtained.Comment: LaTeX2e, 28 page
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