381,347 research outputs found
All-to-all connected networks by multi-frequency excitation of polaritons
We analyze theoretically a network of all-to-all coupled polariton modes,
realized by a trapped polariton condensate excited by a comb of different
frequencies. In the low-density regime the system dynamically finds a state
with maximal gain defined by the average intensities (weights) of the
excitation beams, analogous to active mode locking in lasers, and thus solves a
maximum eigenvalue problem set by the matrix of weights. The method opens the
possibility to tailor a superposition of populated bosonic modes in the trapped
condensate by appropriate choice of drive
Refutation of C. W. Misner's claims in his article "Yilmaz Cancels Newton''
It is shown that an article by C. W. Misner contains serious errors. In
particular, the claim that the Yilmaz theory of gravitation cancels the
Newtonian gravitational interaction is based on a false premise. With the
correct premise the conclusion of the article regarding the absence of
gravitational interactions applies to general relativity and not to the Yilmaz
theory.Comment: 12 pages, LaTeX, submitted to Il Nuovo Ciment
Nonperturbative solution of the Nonconfining Schwinger Model with a generalized regularization
Nonconfining Schwinger Model [AR] is studied with a one parameter class of
kinetic energy like regularization. It may be thought of as a generalization
over the regularization considered in [AR]. Phasespace structure has been
determined in this new situation. The mass of the gauge boson acquires a
generalized expression with the bare coupling constant and the parameters
involved in the regularization. Deconfinement scenario has become transparent
at the quark-antiquark potential level.Comment: 13 pages latex fil
Supersymmetric features of the Maxwell fish-eye lens
We provide a supersymmetric analysis of the Maxwell fisheye (MF) wave problem
at zero energy. Working in the so-called sector, we obtain the
corresponding superpartner (fermionic) MF effective potential within Witten's
one-dimensional (radial) supersymmetric procedure.Comment: 5 pages in Latex, one figure not included has been published as Fig.
2 in Phys. Lett. A 208 (1995) 33-3
Wavelength- and material-dependent absorption in GaAs and AlGaAs microcavities
The quality factors of modes in nearly identical GaAs and
Al_{0.18}Ga_{0.82}As microdisks are tracked over three wavelength ranges
centered at 980 nm, 1460 nm, and 1600 nm, with quality factors measured as high
as 6.62x10^5 in the 1600-nm band. After accounting for surface scattering, the
remaining loss is due to sub-bandgap absorption in the bulk and on the
surfaces. We observe the absorption is, on average, 80 percent greater in
AlGaAs than in GaAs and in both materials is 540 percent higher at 980 nm than
at 1600nm.Comment: 4 pages, 2 figures, 1 table, minor changes to disucssion of Qrad and
Urbach tai
Continuous THz emission from dipolaritons
We propose a scheme of continuous tunable THz emission based on dipolaritons
--- mixtures of strongly interacting cavity photons and direct excitons, where
the latter are coupled to indirect excitons via tunnelling. We investigate the
property of multistability under continuous wave (CW) pumping, and the
stability of the solutions. We establish the conditions of parametric
instability, giving rise to oscillations in density between the direct exciton
and indirect modes under CW pumping. In this way we achieve continuous and
tunable emission in the THz range in a compact single-crystal device. We show
that the emission frequency can be tuned in a certain range by varying an
applied electric field and pumping conditions. Finally, we demonstrate the
dynamic switching between different phases in our system, allowing rapid
control of THz radiation.Comment: Main article 6 pages and 5 figures, two appendices 8 pages and 2
figure
Polarization phenomena in the reaction NN to NNpi near threshold
First calculations for spin-dependent observables of the reactions , and near threshold are presented,
employing the J\"ulich model for pion production. The influence of resonant
(via the excitation of the ) and non-resonant p-wave pion
production mechanisms on these observables is examined. For the reactions and nice agreement of our predictions with the
presently available data on spin correlation coefficents is observed whereas
for the description of the data is less satisfying.Comment: 10 pages, 4 figure
Simulation of a particle-laden turbulent channel flow using an improved stochastic Lagrangian model
The purpose of this paper is to examine the Lagrangian stochastic modeling of
the fluid velocity seen by inertial particles in a nonhomogeneous turbulent
flow. A new Langevin-type model, compatible with the transport equation of the
drift velocity in the limits of low and high particle inertia, is derived. It
is also shown that some previously proposed stochastic models are not
compatible with this transport equation in the limit of high particle inertia.
The drift and diffusion parameters of these stochastic differential equations
are then estimated using direct numerical simulation (DNS) data. It is observed
that, contrary to the conventional modeling, they are highly space dependent
and anisotropic. To investigate the performance of the present stochastic
model, a comparison is made with DNS data as well as with two different
stochastic models. A good prediction of the first and second order statistical
moments of the particle and fluid seen velocities is obtained with the three
models considered. Even for some components of the triple particle velocity
correlations, an acceptable accordance is noticed. The performance of the three
different models mainly diverges for the particle concentration and the drift
velocity. The proposed model is seen to be the only one which succeeds in
predicting the good evolution of these latter statistical quantities for the
range of particle inertia studied
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