1,768 research outputs found
Aharonov-Bohm effect for excitons in a semiconductor quantum ring dressed by circularly polarized light
We show theoretically that the strong coupling of circularly polarized
photons to an exciton in ring-like semiconductor nanostructures results in
physical nonequivalence of clockwise and counterclockwise exciton rotations in
the ring. As a consequence, the stationary energy splitting of exciton states
corresponding to these mutually opposite rotations appears. This excitonic
Aharonov-Bohm effect depends on the intensity and frequency of the circularly
polarized field and can be detected in state-of-the-art optical experiments.Comment: Published versio
The Survival Rate of Ejected Terrestrial Planets with Moons
During planet formation, a gas giant will interact with smaller protoplanets
that stray within its sphere of gravitational influence. We investigate the
outcome of interactions between gas giants and terrestrial-sized protoplanets
with lunar-sized companions. An interaction between a giant planet and a
protoplanet binary may have one of several consequences, including the delivery
of volatiles to the inner system, the capture of retrograde moons by the giant
planet, and the ejection of one or both of the protoplanets. We show that an
interesting fraction of terrestrial-sized planets with lunar sized companions
will likely be ejected into interstellar space with the companion bound to the
planet. The companion provides an additional source of heating for the planet
from tidal dissipation of orbital and spin angular momentum. This heat flux
typically is larger than the current radiogenic heating of the Earth for up to
the first few hundred million years of evolution. In combination with an
atmosphere of sufficient thickness and composition, the heating can provide the
conditions necesary for liquid water to persist on the surface of the
terrestrial mass planet, making it a potential site for life. We also determine
the possibility for directly detecting such systems through all-sky infrared
surveys or microlensing surveys. Microlensing surveys in particular will
directly measure the frequency of this phenomenon.Comment: 4 pages, 2 figures, Accepted to ApJ
Switching waves in multi-level incoherently driven polariton condensates
We show theoretically that an open-dissipative polariton condensate confined
within a trapping potential and driven by an incoherent pumping scheme gives
rise to bistability between odd and even modes of the potential. Switching from
one state to the other can be controlled via incoherent pulsing which becomes
an important step towards construction of low-powered opto-electronic devices.
The origin of the effect comes from modulational instability between odd and
even states of the trapping potential governed by the nonlinear
polariton-polariton interactions
Parity solitons in nonresonantly driven-dissipative condensate channels
We study analytically and numerically the condensation of a
driven-dissipative exciton-polariton system using symmetric nonresonant pumping
geometries. We show that the lowest condensation threshold solution carries a
definite parity as a consequence of the symmetric excitation profile. At higher
pump intensities competition between the two parities can result in critical
quenching of one and saturation of the other. Using long pump channels, we show
that the competition of the condensate parities gives rise to a different type
of topologically stable defect propagating indefinitely along the condensate.
The defects display repulsive interactions and are characterized by a sustained
wavepacket carrying a pair of opposite parity domain walls in the condensate
channel
Vortices in spinor cold exciton condensates with spin-orbit interaction
We study theoretically the ground states of topological defects in a spinor
four-component condensate of cold indirect excitons. We analyze possible ground
state solutions for different configurations of vortices and half-vortices. We
show that if only Rashba or Dreselhaus spin-orbit interaction (SOI) for
electrons is present the stable states of topological defects can represent a
cylindrically symmetric half-vortex or half vortex-antivortex pairs, or a
non-trivial pattern with warped vortices. In the presence of both of Rashba and
Dresselhaus SOI the ground state of a condensate represents a stripe phase and
vortex type solutions become unstable
Information processing with topologically protected vortex memories in exciton-polariton condensates
We show that in a non-equilibrium system of an exciton-polariton condensate,
where polaritons are generated from incoherent pumping, a ring-shaped pump
allows for stationary vortex memory elements of topological charge or
. Using simple potential guides we can choose whether to copy the same
charge or invert it onto another spatially separate ring pump. Such
manipulation of binary information opens the possibility of a new type
processing using vortices as topologically protected memory components
Cool Customers in the Stellar Graveyard IV: Spitzer Search for Mid-IR excesses Around Five DAs
Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require
external accretion of material to explain the presence of weak metal line
absorption in their photospheres. The source of this material is currently
unknown, but could come from the interstellar medium, unseen companions, or
relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate
mid-infrared photometry of these white dwarfs provide additional information to
solve the mystery of this accretion and to look for evidence of planetary
systems that have survived post main sequence evolution. We present {\em
Spitzer} IRAC photometry accurate to 3% for four DAZs and one DA with
circumstellar absorption lines in the UV. We search for excesses due to unseen
companions or circumstellar dust disks. We use {\em Hubble Space Telescope}
NICMOS imaging of these white dwarfs to gauge the level of background
contamination to our targets as well as rule out common proper motion
companions to WD 1620-391. All of our targets show no excesses due to
companions 20 M, ruling out all but very low mass companions to these
white dwarfs at all separations. No excesses due to circumstellar disks are
observed, and we place limits on what types of disks may still be present.Comment: 18 pages, 8 figures, Accepted to A
Effects of halothane and isoflurane anaesthesia on microcirculatory blood flow in musculocutaneous flaps
Hypoperfusion and necrosis in musculocutaneous flaps used for reconstruction of tissue defects is still a significant clinical problem. Although the causes of hypoperfusion are frequently surgical in nature, little is known about the effects of anaesthetic management on blood flow in flaps or the outcome of flap surgery. We compared in minipigs the effects of halothane and isoflurane anaesthesia in equipotent doses on microcirculatory blood flow (MBF) in the skin and muscle part of musculocutaneous flaps and also in intact (control) skin and muscle. Measurements were made during stable normovolaemic conditions and during mild to moderate hypovolaemia (withdrawal of 5%, 10% and 15% of total blood volume). Multi-channel laser Doppler flowmetry (LDF) was used to measure MBF and electromagnetic flowmetry (EMF) for total flap blood flow. During normovolaemic conditions there was no significant difference between the two groups in central haemodynamic or respiratory data. After 15% blood loss, however, there was a significant decrease in mean arterial pressure and cardiac output in the halothane group while there was no significant change in the isoflurane group (P < 0.05). MBF in control skin, control muscle and flap muscle remained approximately 10−15% higher in the isoflurane than in the halothane group throughout the study. In the isoflurane group, MBF in flap skin was unchanged during normovolaemia and there was less than 10% decrease during hypovolaemia. In the halothane group hypovolaemia caused a significant decrease in MBF in flap skin: 27% decrease after 5% blood loss, 45% decrease after 10% blood loss and 49% decrease after 15% blood loss compared with 5%, 20% and 21%, respectively, in intact skin. We conclude that during normovolaemic conditions MBF was well maintained in musculocutaneous flaps in minipigs both with halothane and isoflurane anaesthesia; however, during mild to moderate hypovolemia MBF decreased markedly in flap skin with halothane anaesthesia while it remained unchanged with isofluran
Geology of Tindfjallajökull volcano, Iceland
The geology of Tindfjallajökull volcano, southern Iceland, is presented as a 1:50,000 scale map. Field mapping was carried out with a focus on indicators of past environments. A broad stratocone of interbedded fragmental rocks and lavas was constructed during Tindfjallajökull’s early development. This stratocone has been dissected by glacial erosion and overlain by a variety of mafic to silicic volcanic landforms. Eruption of silicic magma, which probably occurred subglacially, constructed a thick pile of breccia and lava lobes in the summit area. Mafic to intermediate flank eruptions continued through to the end of the last glacial period, producing lavas, hyaloclastite-dominated units and tuyas that preserve evidence of volcano-ice interactions. The Thórsmörk Ignimbrite, a regionally important chronostratigraphic marker, is present on the SE flank of the volcano. The geological mapping of Tindfjallajökull gives insights into the evolution of stratovolcanoes in glaciated regions and the influence of ice in their development
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