11,094 research outputs found
Theory of emission from an active photonic lattice
The emission from a radiating source embedded in a photonic lattice is
calculated. The analysis considers the photonic lattice and free space as a
combined system. Furthermore, the radiating source and electromagnetic field
are quantized. Results show the deviation of the photonic lattice spectrum from
the blackbody distribution, with intracavity emission suppressed at certain
frequencies and enhanced at others. In the presence of rapid population
relaxation, where the photonic lattice and blackbody populations are described
by the same equilibrium distribution, it is found that the enhancement does not
result in output intensity exceeding that of the blackbody at the same
frequency. However, for slow population relaxation, the photonic lattice
population has a greater tendency to deviate from thermal equilibrium,
resulting in output intensities exceeding those of the blackbody, even for
identically pumped structures.Comment: 19 pages, 11 figure
Thermal Empirical Equations for Post-Flashover Compartment Fires
10th International Symposium on Fire Safety Science, College Park, MD, 19-24 June 2011Many useful correlation equations derived for estimating the heat release rate are believed to be adequate in fire engineering application. However, heat release rates in deriving those equations were mainly based on estimating mass loss rate of fuel. Flashover in a compartment fire had been studied experimentally on gasoline pool fires with results on heat release rate reported earlier. Transient heat release rates were measured by oxygen consumption calorimetry. The gas temperature curves at different locations in the room were measured instantaneously. Correlation equations on heat release rates with gas temperature reported in the literature will be reviewed and justified with the experimental results. It was observed that heat release rate estimated were lower than the experimental measurement.Department of Building Services EngineeringRefereed conference pape
Spinor Fields and Symmetries of the Spacetime
In the background of a stationary black hole, the "conserved current" of a
particular spinor field always approaches the null Killing vector on the
horizon. What's more, when the black hole is asymptotically flat and when the
coordinate system is asymptotically static, then the same current also
approaches the time Killing vector at the spatial infinity. We test these
results against various black hole solutions and no exception is found. The
spinor field only needs to satisfy a very general and simple constraint.Comment: 19 page
Averaging approximation to singularly perturbed nonlinear stochastic wave equations
An averaging method is applied to derive effective approximation to the
following singularly perturbed nonlinear stochastic damped wave equation \nu
u_{tt}+u_t=\D u+f(u)+\nu^\alpha\dot{W} on an open bounded domain
\,, \,. Here is a small parameter
characterising the singular perturbation, and \,, \,, parametrises the strength of the noise. Some scaling transformations
and the martingale representation theorem yield the following effective
approximation for small , u_t=\D u+f(u)+\nu^\alpha\dot{W} to an error of
\ord{\nu^\alpha}\,.Comment: 16 pages. Submitte
Electron tunneling time measured by photoluminescence excitation correlation spectroscopy
The tunneling time for electrons to escape from the lowest quasibound state in the quantum wells of GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures with barriers between 16 and 62 Ă
has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Ă
(â12 ps) to 34 Ă
(â800 ps) depends exponentially on barrier thickness, in good agreement with calculations of electron tunneling time derived from the energy width of the resonance. Electron and heavy hole carrier densities are observed to decay at the same rate, indicating a coupling between the two decay processes
Giant Modal Gain, Amplified Surface Plasmon Polariton Propagation, and Slowing Down of Energy Velocity in a Metal-Semiconductor-Metal Structure
We investigated surface plasmon polariton (SPP) propagation in a
metal-semiconductor-metal structure where semiconductor is highly excited to
have optical gain. We show that near the SPP resonance, the imaginary part of
the propagation wavevector changes from positive to hugely negative,
corresponding to an amplified SPP propagation. The SPP experiences a giant gain
that is 1000 times of material gain in the excited semiconductor. We show that
such a giant gain is related to the slowing down of average energy propagation
in the structur
Dynamics of two laterally coupled semiconductor lasers: strong- and weak-coupling theory.
Copyright Š 2008 The American Physical SocietyThe stability and nonlinear dynamics of two semiconductor lasers coupled side to side via evanescent waves are investigated by using three different models. In the composite-cavity model, the coupling between the lasers is accurately taken into account by calculating electric field profiles (composite-cavity modes) of the whole coupled-laser system. A bifurcation analysis of the composite-cavity model uncovers how different types of dynamics, including stationary phase-locking, periodic, quasiperiodic, and chaotic intensity oscillations, are organized. In the individual-laser model, the coupling between individual lasers is introduced phenomenologically with ad hoc coupling terms. Comparison with the composite-cavity model reveals drastic differences in the dynamics. To identify the causes of these differences, we derive a coupled-laser model with coupling terms which are consistent with the solution of the wave equation and the relevant boundary conditions. This coupled-laser model reproduces the dynamics of the composite-cavity model under weak-coupling conditions
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