23,042 research outputs found
Application of direct-inverse techniques to airfoil analysis and design
The direct-inverse technique was developed into a numerical method, called TRANDES, that is suitable for the analysis and design of subsonic and transonic airfoils and for the evaluation of design concepts. A general description of the method is given and its application to a design analysis type of problem is demonstrated. A usage of the method for the low speed high lift case is discussed
Effective Widths and Effective Number of Phonons of Multiphonon Giant Resonances
We discuss the origin of the difference between the harmonic value of the
width of the multiphonon giant resonances and the smaller observed value.
Analytical expressions are derived for both the effective width and the average
cross-section. The contribution of the Brink-Axel mechanism in resolving the
discrepancy is pointed out.Comment: 9 pages, 4 figure
Optimal vaccination in a stochastic epidemic model of two non-interacting populations
Developing robust, quantitative methods to optimize resource allocations in
response to epidemics has the potential to save lives and minimize health care
costs. In this paper, we develop and apply a computationally efficient
algorithm that enables us to calculate the complete probability distribution
for the final epidemic size in a stochastic Susceptible-Infected-Recovered
(SIR) model. Based on these results, we determine the optimal allocations of a
limited quantity of vaccine between two non-interacting populations. We compare
the stochastic solution to results obtained for the traditional, deterministic
SIR model. For intermediate quantities of vaccine, the deterministic model is a
poor estimate of the optimal strategy for the more realistic, stochastic case.Comment: 21 pages, 7 figure
Effect of mesoscopic inhomogeneities on local tunnelling density of states
We carry out a theoretical analysis of the momentum dependence of the
Fourier-transformed local density of states (LDOS) in the superconducting
cuprates within a model considering the interference of quasiparticles
scattering on quenched impurities. The impurities introduce an external
scattering potential, which is either nearly local in space or it can acquire a
substantial momentum dependence due to a possible strong momentum dependence of
the electronic screening near a charge modulation instability. The key new
effect that we introduce is an additional mesoscopic disorder aiming to
reproduce the inhomogeneities experimentally observed in scanning tunnelling
microscopy. The crucial effect of this mesoscopic disorder is to give rise to
point-like spectroscopic features, to be contrasted with the curve-like shape
of the spectra previously calculated within the interfering-quasiparticle
schemes. It is also found that stripe-like charge modulations play a relevant
role to correctly reproduce all the spectral features of the experiments.Comment: 11 pages and 5 figure
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
Tracer Dispersion in a Self-Organized Critical System
We have studied experimentally transport properties in a slowly driven
granular system which recently was shown to display self-organized criticality
[Frette {\em et al., Nature} {\bf 379}, 49 (1996)]. Tracer particles were added
to a pile and their transit times measured. The distribution of transit times
is a constant with a crossover to a decaying power law. The average transport
velocity decreases with system size. This is due to an increase in the active
zone depth with system size. The relaxation processes generate coherently
moving regions of grains mixed with convection. This picture is supported by
considering transport in a cellular automaton modeling the experiment.Comment: 4 pages, RevTex, 1 Encapsulated PostScript and 4 PostScript available
upon request, Submitted to Phys. Rev. Let
New approach to He charge distribution
We present a study of the He charge distribution based on realistic
nucleonic wave functions and incorporation of the nucleon's quark substructure.
The central depression of the proton point density seen in modern four-body
calculations is too small by itself to lead to a correct description of the
charge distribution. We utilize six-quark structures calculated in the
Chromodielectric Model for N-N interactions, and we find a swelling of the
proton charge distribution as the internucleon distance decreases. These charge
distributions are combined with the He wave function using the Independent
Pair Approximation and two-body distributions generated from Green's Function
Monte Carlo calculations. We obtain a reasonably good fit to the experimental
charge distribution without including meson exchange currents.Comment: 9 pages, LaTeX, 4 figures (Figures 1 and 2 doesn't exist as
postscript files : they are only available on request
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