20,800 research outputs found
Thermal entanglement in a two-qubit Heisenberg XXZ spin chain under an inhomogeneous magnetic field
The thermal entanglement in a two-qubit Heisenberg \emph{XXZ} spin chain is
investigated under an inhomogeneous magnetic field \emph{b}. We show that the
ground-state entanglement is independent of the interaction of
\emph{z}-component . The thermal entanglement at the fixed temperature
can be enhanced when increases. We strictly show that for any
temperature \emph{T} and the entanglement is symmetric with respect to
zero inhomogeneous magnetic field, and the critical inhomogeneous magnetic
field is independent of . The critical magnetic field
increases with the increasing but the maximum entanglement value that the
system can arrive becomes smaller.Comment: 5 EPS figure
Why does the apparent mass of a coronal mass ejection increase?
Mass is one of the most fundamental parameters characterizing the dynamics of
a coronal mass ejection (CME). It has been found that CME apparent mass
measured from the brightness enhancement in coronagraph images shows an
increasing trend during its evolution in the corona. However, the physics
behind it is not clear. Does the apparent mass gain come from the mass outflow
from the dimming regions in the low corona, or from the pileup of the solar
wind plasma around the CME when it propagates outwards from the Sun? We
analyzed the mass evolution of six CME events. Their mass can increase by a
factor of 1.6 to 3.2 from 4 to 15 Rs in the field of view (FOV) of the
coronagraph on board the Solar Terrestrial Relations Observatory (STEREO). Over
the distance about 7 to 15 Rs, where the coronagraph occulting effect can be
negligible, the mass can increase by a factor of 1.3 to 1.7. We adopted the
`snow-plough' model to calculate the mass contribution of the piled-up solar
wind in the height range from about 7 to 15 Rs. For 2/3 of the events, the
solar wind pileup is not sufficient to explain the measured mass increase. In
the height range from about 7 to 15 Rs, the ratio of the modeled to the
measured mass increase is roughly larger than 0.55. Although the ratios are
believed to be overestimated, the result gives evidence that the solar wind
pileup probably makes a non-negligible contribution to the mass increase. It is
not clear yet whether the solar wind pileup is a major contributor to the final
mass derived from coronagraph observations. However, our study suggests that
the solar wind pileup plays increasingly important role in the mass increase as
a CME moves further away from the Sun.Comment: 27 pages, 2 tables, 9 figures, accepted by Ap
How perceived personalities of earlier contributors influence the content generation on online knowledge-sharing platforms?
Recent years have witnessed the prevalence of online knowledge-sharing platforms, in which user management and content creation are the central issues to the governance. Interactions take place through users’ linguistics, which helps shape users’ perceived personalities in the eyes of others. To understand the impact of perceived personality on online discussions, a novel method that combines natural language processing method and unsupervised learning is developed to extract contributors’ perceived personalities based on the contents they generated on the platform, which is further validated by a lab experiment. An empirical analysis is then carried out to unpack the role of different personality dimensions on online discussions. Our results reveal that the first contributor’s perceived conscientiousness and openness exhibit a significant but contrary role on content generation. Our method and empirical analysis can provide insights into the governance of online knowledge-sharing platforms
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