12,127 research outputs found
Installed performance of air-augmented nozzles based on analytical determination of internal ejector characteristics
Procedures for matching intake and ejector pumping characteristics of air-augmented nozzle
Excitation Induced Dephasing in Semiconductor Quantum Dots
A quantum kinetic theory is used to compute excitation induced dephasing in
semiconductor quantum dots due to the Coulomb interaction with a continuum of
states, such as a quantum well or a wetting layer. It is shown that a frequency
dependent broadening together with nonlinear resonance shifts are needed for a
microscopic explanation of the excitation induced dephasing in such a system,
and that excitation induced dephasing for a quantum-dot excitonic resonance is
different from quantum-well and bulk excitons.Comment: 6 pages, 4 figures. Extensively revised text, two figures change
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
Numerical calculation of transonic boattail flow
A viscid-inviscid interaction procedure for the calculation of subsonic and transonic flow over a boattail was developed. This method couples a finite-difference inviscid analysis with an integral boundary-layer technique. Results indicate that the effect of the boundary layer is as important as an accurate inviscid method for this type of flow. Theoretical results from the solution of the full transonic-potential equation, including boundary layer effects, agree well with the experimental pressure distribution for a boattail. Use of the small disturbance transonic potential equation yielded results that did not agree well with the experimental results even when boundary-layer effects were included in the calculations
Relaxation properties of the quantum kinetics of carrier-LO-phonon interaction in quantum wells and quantum dots
The time evolution of optically excited carriers in semiconductor quantum
wells and quantum dots is analyzed for their interaction with LO-phonons. Both
the full two-time Green's function formalism and the one-time approximation
provided by the generalized Kadanoff-Baym ansatz are considered, in order to
compare their description of relaxation processes. It is shown that the
two-time quantum kinetics leads to thermalization in all the examined cases,
which is not the case for the one-time approach in the intermediate-coupling
regime, even though it provides convergence to a steady state. The
thermalization criterion used is the Kubo-Martin-Schwinger condition.Comment: 7 pages, 8 figures, accepted for publication in Phys. Rev.
Exact States in Waveguides With Periodically Modulated Nonlinearity
We introduce a one-dimensional model based on the nonlinear
Schrodinger/Gross-Pitaevskii equation where the local nonlinearity is subject
to spatially periodic modulation in terms of the Jacobi dn function, with three
free parameters including the period, amplitude, and internal form-factor. An
exact periodic solution is found for each set of parameters and, which is more
important for physical realizations, we solve the inverse problem and predict
the period and amplitude of the modulation that yields a particular exact
spatially periodic state. Numerical stability analysis demonstrates that the
periodic states become modulationally unstable for large periods, and regain
stability in the limit of an infinite period, which corresponds to a bright
soliton pinned to a localized nonlinearity-modulation pattern. Exact
dark-bright soliton complex in a coupled system with a localized modulation
structure is also briefly considered . The system can be realized in planar
optical waveguides and cigar-shaped atomic Bose-Einstein condensates.Comment: EPL, in pres
Single-charge rotating black holes in four-dimensional gauged supergravity
We consider four-dimensional U(1)^4 gauged supergravity, and obtain
asymptotically AdS_4, non-extremal, charged, rotating black holes with one
non-zero U(1) charge. The thermodynamic quantities are computed. We obtain a
generalization that includes a NUT parameter. The general solution has a
discrete symmetry involving inversion of the rotation parameter, and has a
string frame metric that admits a rank-2 Killing-Stackel tensor.Comment: 9 page
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 Å has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Å (≈12 ps) to 34 Å(≈800 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
The influence of early surgical intervention in patients with Perthes Disease
Concurrent Free Papers 7 - Paediatric Orthopaedics / General Orthopaedics: no. 7.7INTRODUCTION: This retrospective review aimed to examine the influence of early surgical intervention in patients with Perthes disease. MATERIALS AND METHODS: Children with Perthes disease treated between 1995 and 2013 in our institution were reviewed. The age of onset, gender, severity of disease, and the treatment details were retrieved from patient records. Herring classification was used to classify the hips. Modified Elizabethtown staging was used to stage the disease at the time of intervention. The final outcomes of both operative and non-operative groups were assessed using Stulberg classification (S) at skeletal maturity. RESULTS: A total of 28 ...published_or_final_versio
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