23,223 research outputs found
The entanglement dynamics of interacting qubits embedded in a spin environment with Dzyaloshinsky-Moriya term
We investigate the entanglement dynamics of two interacting qubits in a spin
environment, which is described by an XY model with Dzyaloshinsky-Moriya (DM)
interaction. The competing effects of environmental noise and interqubit
coupling on entanglement generation for various system parameters are studied.
We find that the entanglement generation is suppressed remarkably in
weak-coupling region at quantum critical point (QCP). However, the suppression
of the entanglement generation at QCP can be compensated both by increasing the
DM interaction and by decreasing the anisotropy of the spin chain. Beyond the
weak-coupling region, there exist resonance peaks of concurrence when the
system-bath coupling equals to external magnetic field. We attribute the
presence of resonance peaks to the flat band of the self-Hamiltonian. These
peaks are highly sensitive to anisotropy parameter and DM interaction.Comment: 8 pages, 9 figure
Evolution of black-hole intermediate-mass X-ray binaries: the influence of a circumbinary disc
Justham, Rappaport & Podsiadlowski (2006) recently suggested that black-hole
low-mass X-ray binaries (BHLMXBs) with short orbital periods may have evolved
from black-hole intermediate-mass X-ray binaries (BHIMXBs). In their model the
secondaries in BHIMXBs are assumed to possess anomalously high magnetic fields,
so that magnetic braking can lead to substantial loss of angular momentum. In
this paper we propose an alternative mechanism for orbital angular momentum
loss in BHIMXBs. We assume that a small fraction of the transferred
mass from the donor star form a circumbinary disc surrounding the binary
system. The tidal torques exerted by the disc can effectively drain orbital
angular momentum from the binary. We have numerically calculated the
evolutionary sequences of BHIMXBs, to examine the influence of the circumbinary
disc on the binary evolution. Our results indicate when \delta\la 0.01-0.1
(depending on the initial orbital periods), the circumbinary disc can cause
secular orbital shrinking, leading to the formation of compact
BHLMXBs, otherwise the orbits always expand during the evolution. This
scenario also suggests the possible existence of luminous, persistent BHLMXBs,
but it suffers the same problem as in Justham, Rappaport & Podsiadlowski (2006)
that, the predicted effective temperatures of the donor stars are significantly
higher than those of the observed donor stars in BHLMXBs.Comment: 7 pages, 5 figures, accepted for publication in MNRA
Automatic Prediction Of Small Group Performance In Information Sharing Tasks
In this paper, we describe a novel approach, based on Markov jump processes,
to model small group conversational dynamics and to predict small group
performance. More precisely, we estimate conversational events such as turn
taking, backchannels, turn-transitions at the micro-level (1 minute windows)
and then we bridge the micro-level behavior and the macro-level performance. We
tested our approach with a cooperative task, the Information Sharing task, and
we verified the relevance of micro- level interaction dynamics in determining a
good group performance (e.g. higher speaking turns rate and more balanced
participation among group members).Comment: Presented at Collective Intelligence conference, 2012
(arXiv:1204.2991
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