32,875 research outputs found
Real fluid properties of normal and parahydrogen
Computer program calculates the real fluid properties of normal or parahydrogen using a library of single function calls without initial estimates. Accurate transport and thermodynamic properties of molecular hydrogen are needed for advanced propulsion systems
Exact Nonperturbative Unitary Amplitudes for 1->N Transitions
I present an extension to arbitrary N of a previously proposed field
theoretic model, in which unitary amplitudes for processes were
obtained. The Born amplitude in this extension has the behavior
expected in a bosonic field theory. Unitarity
is violated when , or when Numerical
solutions of the coupled Schr\"odinger equations shows that for weak coupling
and a large range of N>\ncrit, the exact unitary amplitude is reasonably fit
by a factorized expression |A(1->N)| \sim (0.73 /N) \cdot \exp{(-0.025/\g2)}.
The very small size of the coefficient 1/\g2 , indicative of a very weak
exponential suppression, is not in accord with standard discussions based on
saddle point analysis, which give a coefficient The weak dependence
on could have experimental implications in theories where the exponential
suppression is weak (as in this model). Non-perturbative contributions to
few-point correlation functions in this theory would arise at order $K\ \simeq\
\left((0.05/\g2)+ 2\ ln{N}\right)/ \ ln{(1/\g2)}\g2.$Comment: 11 pages, 3 figures (not included
On the Nature and Location of the Microlenses
This paper uses the caustic crossing events in the microlens data sets to
explore the nature and location of the lenses. We conclude that the large
majority of lenses, whether they are luminous or dark, are likely to be
binaries. Further, we demonstrate that blending is an important feature of all
the data sets. An additional interpretation suggested by the data, that the
caustic crossing events along the directions to the Magellanic Clouds are due
to lenses located in the Clouds, implies that most of the LMC/SMC events to
date are due to lenses in the Magellanic Clouds. All of these conclusions can
be tested. If they are correct, a large fraction of lenses along the direction
to the LMC may be ordinary stellar binary systems, just as are the majority of
the lenses along the direction to the Bulge. Thus, a better understanding of
the larger-than-anticipated value derived for the Bulge optical depth may allow
us to better interpret the large value derived for the optical depth to the
LMC. Indeed, binarity and blending in the data sets may illuminate connections
among several other puzzles: the dearth of binary-source light curves, the
dearth of non-caustic-crossing perturbed binary-lens events, and the dearth of
obviously blended point-lens events.Comment: 15 pages, 2 figures. Submitted to the Astrophysical Journal Letters,
4 January 199
Evidence of Skyrmion excitations about in n-Modulation Doped Single Quantum Wells by Inter-band Optical Transmission
We observe a dramatic reduction in the degree of spin-polarization of a
two-dimensional electron gas in a magnetic field when the Fermi energy moves
off the mid-point of the spin-gap of the lowest Landau level, . This
rapid decay of spin alignment to an unpolarized state occurs over small changes
to both higher and lower magnetic field. The degree of electron spin
polarization as a function of is measured through the magneto-absorption
spectra which distinguish the occupancy of the two electron spin states. The
data provide experimental evidence for the presence of Skyrmion excitations
where exchange energy dominates Zeeman energy in the integer quantum Hall
regime at
Exciton mediated one phonon resonant Raman scattering from one-dimensional systems
We use the Kramers-Heisenberg approach to derive a general expression for the
resonant Raman scattering cross section from a one-dimensional (1D) system
explicitly accounting for excitonic effects. The result should prove useful for
analyzing the Raman resonance excitation profile lineshapes for a variety of 1D
systems including carbon nanotubes and semiconductor quantum wires. We apply
this formalism to a simple 1D model system to illustrate the similarities and
differences between the free electron and correlated electron-hole theories.Comment: 10 pages, 6 figure
Properties of Nucleon Resonances by means of a Genetic Algorithm
We present an optimization scheme that employs a Genetic Algorithm (GA) to
determine the properties of low-lying nucleon excitations within a realistic
photo-pion production model based upon an effective Lagrangian. We show that
with this modern optimization technique it is possible to reliably assess the
parameters of the resonances and the associated error bars as well as to
identify weaknesses in the models. To illustrate the problems the optimization
process may encounter, we provide results obtained for the nucleon resonances
(1230) and (1700). The former can be easily isolated and thus
has been studied in depth, while the latter is not as well known
experimentally.Comment: 12 pages, 10 figures, 3 tables. Minor correction
Using Astrometry to Deblend Microlensing Events
We discuss the prospect of deblending microlensing events by observing
astrometric shifts of the lensed stars. Since microlensing searches are
generally performed in very crowded fields, it is expected that stars will be
confusion limited rather than limited by photon statistics. By performing
simulations of events in crowded fields, we find that if we assume a dark lens
and that the lensed star obeys a power law luminosity function, , over half the simulated events show a measurable astrometric
shift. Our simulations included 20000 stars in a Nyquist
sampled CCD frame. For , we found that 58% of the events were
significantly blended , and of those, 73% had a
large astrometric shift . Likewise, for , we found
that 85% of the events were significantly blended, and that 85% of those had
large shifts. Moreover, the shift is weakly correlated to the degree of
blending, suggesting that it may be possible not only to detect the existence
of a blend, but also to deblend events statistically using shift information.Comment: 24 pages, 7 postscript Figure
Chirality dependence of the radial breathing phonon mode density in single wall carbon nanotubes
A mass and spring model is used to calculate the phonon mode dispersion for
single wall carbon nanotubes (SWNTs) of arbitrary chirality. The calculated
dispersions are used to determine the chirality dependence of the radial
breathing phonon mode (RBM) density. Van Hove singularities, usually discussed
in the context of the single particle electronic excitation spectrum, are found
in the RBM density of states with distinct qualitative differences for zig zag,
armchair and chiral SWNTs. The influence the phonon mode density has on the two
phonon resonant Raman scattering cross-section is discussed.Comment: 6 pages, 2 figures, submitted to Phys. Rev.
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