2,136 research outputs found
Superlinear Increase of Photocurrent due to Stimulated Scattering into a Polariton Condensate
We show that when a monopolar current is passed through an n-i-n structure,
superlinear photocurrent response occurs when there is a polariton condensate.
This is in sharp contrast to the previously observed behavior for a standard
semiconductor laser. Theoretical modeling shows that this is due to a
stimulated exciton-exciton scattering process in which one exciton relaxes into
the condensate, while another one dissociates into an electron-hole pair.Comment: 17 pages with 10 figure
Soliton content in the standard optical OFDM signal
The nonlinear Schrödinger equation (NLSE) is often used as a master path-average model for fiber-optic transmission lines. In general, the NLSE describes the co-existence of dispersive waves and soliton pulses. The propagation of a signal in such a nonlinear channel is conceptually different from linear systems. We demonstrate here that the conventional orthogonal frequency-division multiplexing (OFDM) input optical signal at powers typical for modern communication systems might have soliton components statistically created by the random process corresponding to the information content. Applying the Zakharov–Shabat spectral problem to a single OFDM symbol with multiple subcarriers, we quantify the effect of the statistical soliton occurrence in such an information-bearing optical signal. Moreover, we observe that at signal powers optimal for transmission, an OFDM symbol incorporates multiple solitons with high probability. The considered optical communication example is relevant to a more general physical problem of the generation of coherent structures from noise
An adjustable law of motion for relativistic spherical shells
A classical and a relativistic law of motion for an advancing shell are
deduced applying the thin layer approximation. A new parameter connected with
the quantity of absorbed matter in the expansion is introduced; this allows of
matching theory and observation.Comment: 15 pages, 10 figures and article in press; Central European Journal
of Physics 201
Dynamics of fluctuations in an optical analog of the Laval nozzle
Using the analogy between the description of coherent light propagation in a
medium with Kerr nonlinearity by means of nonlinear Schr\"odinger equation and
that of a dissipationless liquid we propose an optical analogue of the Laval
nozzle. The optical Laval nozzle will allow one to form a transonic flow in
which one can observe and study a very unusual dynamics of classical and
quantum fluctuations including analogue of the Hawking radiation of real black
holes. Theoretical analysis of this dynamics is supported by numerical
calculations and estimates for a possible experimental setup are presented.Comment: 7 pages, 4 figure
Kinematic Self-Similarity
Self-similarity in general relativity is briefly reviewed and the differences
between self-similarity of the first kind and generalized self-similarity are
discussed. The covariant notion of a kinematic self-similarity in the context
of relativistic fluid mechanics is defined. Various mathematical and physical
properties of spacetimes admitting a kinematic self-similarity are discussed.
The governing equations for perfect fluid cosmological models are introduced
and a set of integrability conditions for the existence of a proper kinematic
self-similarity in these models is derived. Exact solutions of the irrotational
perfect fluid Einstein field equations admitting a kinematic self-similarity
are then sought in a number of special cases, and it is found that; (1) in the
geodesic case the 3-spaces orthogonal to the fluid velocity vector are
necessarily Ricci-flat and (ii) in the further specialisation to dust the
differential equation governing the expansion can be completely integrated and
the asymptotic properties of these solutions can be determined, (iii) the
solutions in the case of zero-expansion consist of a class of shear-free and
static models and a class of stiff perfect fluid (and non-static) models, and
(iv) solutions in which the kinematic self-similar vector is parallel to the
fluid velocity vector are necessarily Friedmann-Robertson-Walker (FRW) models.Comment: 29 pages, AmsTe
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