2,151 research outputs found
Simulation of three supersonic transport configurations with the Boeing 367-80 in-flight dynamic simulation airplane
In-flight dynamic simulator used to evaluate problems of low-speed approach and landing of supersonic transpor
Operation speed of polariton condensate switches gated by excitons
We present a time-resolved photoluminescence (PL) study in real- and
momentum-space of a polariton condensate switch in a quasi-1D semiconductor
microcavity. The polariton flow across the ridge is gated by excitons inducing
a barrier potential due to repulsive interactions. A study of the device
operation dependence on the power of the pulsed gate beam obtains a
satisfactory compromise for the ON/OFF-signal ratio and -switching time of the
order of 0.3 and ps, respectively. The opposite transition is
governed by the long-lived gate excitons, consequently the OFF/ON-switching
time is ps, limiting the overall operation speed of the device
to GHz. The experimental results are compared to numerical
simulations based on a generalized Gross-Pitaevskii equation, taking into
account incoherent pumping, decay and energy relaxation within the condensate.Comment: 11 pages, 11 figure
Spin Selective Filtering of Polariton Condensate Flow
Spin-selective spatial filtering of propagating polariton condensates, using
a controllable spin-dependent gating barrier, in a one-dimensional
semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam
provides the source of propagating polaritons while a second circularly
polarized weak beam imprints a spin dependent potential barrier, which gates
the polariton flow and generates polariton spin currents. A complete spin-based
control over the blocked and transmitted polaritons is obtained by varying the
gate polarization.Comment: 5 pages, 4 figure
Energy relaxation of exciton-polariton condensates in quasi-1D microcavities
We present a time-resolved study of energy relaxation and trapping dynamics
of polariton condensates in a semiconductor microcavity ridge. The combination
of two non-resonant, pulsed laser sources in a GaAs ridge-shaped microcavity
gives rise to profuse quantum phenomena where the repulsive potentials created
by the lasers allow the modulation and control of the polariton flow. We
analyze in detail the dependence of the dynamics on the power of both lasers
and determine the optimum conditions for realizing an all-optical polariton
condensate transistor switch. The experimental results are interpreted in the
light of simulations based on a generalized Gross-Pitaevskii equation,
including incoherent pumping, decay and energy relaxation within the
condensate.Comment: 15 pages, 20 figure
Dynamics of a polariton condensate transistor switch
We present a time-resolved study of the logical operation of a polariton
condensate transistor switch. Creating a polariton condensate (source) in a
GaAs ridge-shaped microcavity with a non-resonant pulsed laser beam, the
polariton propagation towards a collector, at the ridge edge, is controlled by
a second weak pulse (gate), located between the source and the collector. The
experimental results are interpreted in the light of simulations based on the
generalized Gross-Pitaevskii equation, including incoherent pumping, decay and
energy relaxation within the condensate.Comment: 4 pages, 2 figure
Optical control of spin textures in quasi-one-dimensional polariton condensates
We investigate, through polarization-resolved spectroscopy, the spin
transport by propagating polariton condensates in a quasi one-dimensional
microcavity ridge along macroscopic distances. Under circularly polarized,
continuous-wave, non-resonant excitation, a sinusoidal precession of the spin
in real space is observed, whose phase depends on the emission energy. The
experiments are compared with simulations of the spinor-polariton condensate
dynamics based on a generalized Gross-Pitaevskii equation, modified to account
for incoherent pumping, decay and energy relaxation within the condensate.Comment: 10 pages, 9 figure
Observational properties of massive black hole binary progenitors
The first directly detected gravitational waves (GW 150914) were emitted by
two coalescing black holes (BHs) with masses of ~36Msun and ~29Msun. Several
scenarios have been proposed to put this detection into an astrophysical
context. The evolution of an isolated massive binary system is among commonly
considered models. Various groups have performed detailed binary-evolution
calculations that lead to BH merger events. However, the question remains open
as to whether binary systems with the predicted properties really exist. The
aim of this paper is to help observers to close this gap by providing spectral
characteristics of massive binary BH progenitors during a phase where at least
one of the companions is still non-degenerate. Stellar evolution models predict
fundamental stellar parameters. Using these as input for our stellar atmosphere
code (PoWR), we compute a set of models for selected evolutionary stages of
massive merging BH progenitors at different metallicities. The synthetic
spectra obtained from our atmosphere calculations reveal that progenitors of
massive BH merger events start their lives as O2-3V stars that evolve to
early-type blue supergiants before they undergo core-collapse during the
Wolf-Rayet phase. When the primary has collapsed, the remaining system will
appear as a wind-fed high-mass X-ray binary. We provide feedback parameters,
broad band magnitudes, and spectral templates that should help to identify such
binaries in the future. Comparisons of empirically determined mass-loss rates
with those assumed by evolution calculations reveal significant differences.
The consideration of the empirical mass-loss rates in evolution calculations
will possibly entail a shift of the maximum in the predicted binary-BH merger
rate to higher metallicities, that is, more candidates should be expected in
our cosmic neighborhood than previously assumed.Comment: 64 pages, 30 figures, accepted for publication in Astronomy &
Astrophysics, v2: typos correcte
Absence of the Rashba effect in undoped asymmetric quantum wells
To an electron moving in free space an electric field appears as a magnetic
field which interacts with and can reorient the electron spin. In semiconductor
quantum wells this spin-orbit interaction seems to offer the possibility of
gate-voltage control in spintronic devices but, as the electrons are subject to
both ion-core and macroscopic structural potentials, this over-simple picture
has lead to intense debate. For example, an externally applied field acting on
the envelope of the electron wavefunction determined by the macroscopic
potential, underestimates the experimentally observed spin-orbit field by many
orders of magnitude while the Ehrenfest theorem suggests that it should
actually be zero. Here we challenge, both experimentally and theoretically, the
widely held belief that any inversion asymmetry of the macroscopic potential,
not only electric field, will produce a significant spin-orbit field for
electrons. This conclusion has far-reaching consequences for the design of
spintronic devices while illuminating important fundamental physics.Comment: 7 pages, 5 fig
VFTS 243 as predicted by the BPASS fiducial models
The recent discovery of an unambiguous quiescent BH and main sequence O star
companion in VFTS 243 opens the door to new constraints on theoretical stellar
evolution and population models looking to reproduce the progenitors of black
hole - black hole binaries. Here we show that the Binary Population and
Spectral Synthesis fiducial models (BPASSv2.2.1) natively predict VFTS 243-like
systems: We find that VFTS 243 likely originated from a binary system in a
\about 15 day orbit with primary mass ranging from 40 to 50 \msol\, and
secondary star with initial mass 24--25\msol. %BPASS systems with initial
parameters similar to the ones inferred in the discovery paper result in a
final system with an O star 10\msol more massive than indicated by the
observations. Additionally we find that the death of the primary star must have
resulted in a low energy explosion ergs. With a uniform prior we
find that the kick velocity of the new-born black hole was \kms (90
percent credible interval). The very low eccentricity reported for VFTS~243 and
the subsequent conclusion by the authors that the SN kick must have been very
small is in line with the peak in the posterior distribution between 0 and 5
\kms. Finally, the reduced Hobbs kick distribution commonly used in black hole
population synthesis is strongly disfavoured, whereas the Bray kick with the
most recent parameter calibration predicts 2 3.5 \kms, which is very
consistent with the posterior velocity distributions obtained for our matching
VFTS 243-like models using a uniform kick prior.Comment: 3 figures, 1 table, submitted to MNRA
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