19,473 research outputs found
Bose-stimulated scattering off a cold atom trap
The angle and temperature dependence of the photon scattering rate for
Bose-stimulated atom recoil transitions between occupied states is compared to
diffraction and incoherent Rayleigh scattering near the Bose-Einstein
transition for an optically thin trap in the limit of large particle number, N.
Each of these processes has a range of angles and temperatures for which it
dominates over the others by a divergent factor as N->oo.Comment: 18 pages (REVTeX), no figure
A qubit strongly-coupled to a resonant cavity: asymmetry of the spontaneous emission spectrum beyond the rotating wave approximation
We investigate the spontaneous emission spectrum of a qubit in a lossy
resonant cavity. We use neither the rotating-wave approximation nor the Markov
approximation. The qubit-cavity coupling strength is varied from weak, to
strong, even to lower bound of the ultra-strong. For the weak-coupling case,
the spontaneous emission spectrum of the qubit is a single peak, with its
location depending on the spectral density of the qubit environment. Increasing
the qubit-cavity coupling increases the asymmetry (the positions about the
qubit energy spacing and heights of the two peaks) of the two spontaneous
emission peaks (which are related to the vacuum Rabi splitting) more.
Explicitly, for a qubit in a low-frequency intrinsic bath, the height asymmetry
of the splitting peaks becomes larger, when the qubit-cavity coupling strength
is increased. However, for a qubit in an Ohmic bath, the height asymmetry of
the spectral peaks is inverted from the same case of the low-frequency bath,
when the qubit is strongly coupled to the cavity. Increasing the qubit-cavity
coupling to the lower bound of the ultra-strong regime, the height asymmetry of
the left and right peak heights are inverted, which is consistent with the same
case of low-frequency bath, only relatively weak. Therefore, our results
explicitly show how the height asymmetry in the spontaneous emission spectrum
peaks depends not only on the qubit-cavity coupling, but also on the type of
intrinsic noise experienced by the qubit.Comment: 10pages, 5 figure
Heat conductivity in the presence of a quantized degree of freedom
We propose a model with a quantized degree of freedom to study the heat
transport in quasi-one dimensional system. Our simulations reveal three
distinct temperature regimes. In particular, the intermediate regime is
characterized by heat conductivity with a temperature exponent much
greater than 1/2 that was generally found in systems with point-like particles.
A dynamical investigation indicates the occurrence of non-equipartition
behavior in this regime. Moreover, the corresponding Poincar\'e section also
shows remarkably characteristic patterns, completely different from the cases
of point-like particles.Comment: 7 pages, 4 figure
On C*-algebras related to constrained representations of a free group
We consider representations of the free group on two generators such
that the norm of the sum of the generators and their inverses is bounded by
. These -constrained representations determine a C*-algebra
for each . We prove that these C*-algebras form a
continuous bundle of C*-algebras over and calculate their K-groups.Comment: 9 page
Active Thrusting and Folding Along the Northern Tien Shan and Late Cenozoic Rotation of the Tarim Relative to Dzungaria and Kazakhstan
We have studied geometries and rates of late Cenozoic thrust faulting and folding along the northern piedmont of the Tien Shan mountain belt, West of Urumqi, where the M= 8.3 Manas earthquake occurred on December 23, 1906. The northern range of the Tien Shan, rising above 5000 m, overthrusts a flexural foredeep, filled with up to 11,000 m of sediment, of the Dzungarian basement. Our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front, within a 200-km-long zone of Neogene-Quaternary anticlines. Fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range. In all the valleys, the scarps offset vertically the highest terrace surface by the same amount (10.2±0.7 m). Inferring an early Holocene age (10±2 kyr) for this terrace, which is continuous with the largest recent fans of the piedmont, yields a rate of vertical throw of 1.0±0.3mm/yr on the main active thrust at the surface. A quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5.5±2.5 m^2/kyr. A rather fresh surface scarp, 0.8±0.15 m high, that is unlikely to result from shallow earthquakes with 6 < M < 7 in the last 230 years, is visible at the extremities of the main fold zone. We associate this scarp with the 1906 Manas earthquake and infer that a structure comprising a deep basement ramp under the range, gently dipping flats in the foreland, and shallow ramps responsible for the formation of the active, fault propagation anticlines could have been activated by that earthquake. If so, the return period of a 1906 type event would be 850 ±380 years. The small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth (≈2/3) is taken up by incremental folding near the surface. Comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising Quaternary ranges such as the San Gabriel mountains in California or the Mont Blanc-Aar massifs in the Alps. We estimate the finite Cenozoic shortening of the folded Dzungarian sediments to be of the order of 30 km and the Cenozoic shortening rate to have been 3 ± 1.5 mm/yr. Assuming comparable shortening along the Tarim piedmont and minor additional active thrusting within the mountain belt, we infer the rate of shortening across the Tien Shan to be at least 6 ± 3 mm/yr at the longitude of Manas (≈85.5°E). A total shortening of 125±30 km is estimated from crustal thickening, assuming local Airy isostatic equilibrium. Under the same assumption, serial N-S sections imply that Cenozoic shortening across the belt increases westwards to 203±50 km at the longitude of Kashgar (≈ 76 °E), as reflected by the westward increase of the width of the belt. This strain gradient implies a clockwise rotation of Tarim relative to Dzungaria and Kazakhstan of 7±2.5° around a pole located near the eastern extremity of the Tien Shan, west of Hami (≈96°E, 43.5°N), comparable to that revealed by paleomagnetism between Tarim and Dzungaria (8.6° ± 8.7°). A 6 mm/yr rate of shortening at the longitude of Manas would imply a rate of rotation of 0.45°/m.y. and would be consistent with a shortening rate of 12 mm/yr north of Kashgar. Taking such values to be representative of Late Cenozoic rates would place the onset of reactivation of the Tien Shan by the India-Asia collision in the early to middle Miocene (16 +22/−9 m.y.), in accord with the existence of particularly thick late Neogene and Quaternary deposits. Such reactivation would thus have started much later than the collision, roughly at the time of the great mid-Miocene changes in tectonic regimes, denudation and sedimentation rates observed in southeast Asia, the Himalayas and the Bay of Bengal, and of the correlative rapid change in seawater Sr isotopic ratio (20 to 15 Ma). Like these other changes, the rise of the Tien Shan might be a distant consequence of the end of Indochina's escape
Magnification of spin Hall effect in bilayer electron gas
Spin transport properties of a coupled bilayer electron gas with Rashba
spin-orbit coupling are studied. The definition of the spin currents in each
layer as well as the corresponding continuity-like equations in the bilayer
system are given. The curves of the spin Hall conductivities obtained in each
layer exhibit sharp cusps around a particular value of the tunnelling strength
and the conductivities undergo sign changes across this point. Our
investigation on the impurity effect manifests that an arbitrarily small
concentration of nonmagnetic impurities does not suppress the spin Hall
conductivity to zero in the bilayer system. Based on these features, an
experimental scheme is suggested to detect a magnification of the spin Hall
effect.Comment: Revtex 10 pages, 4 figures; largely extended versio
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