44,687 research outputs found
Profiles of thermal line emission from advection dominated accretion flows
Recently, Narayan & Raymond (1999) proposed that the thermal emission lines
from the hot plasma in advection dominated accretion flows (ADAFs) are
potentially observable with the next generation of X-ray observatories, with
which the physical properties of some X-ray sources can be probed. In ADAFs,
the temperature of the ion is so high that the thermal broadening of the line
is important. We calculate the profiles of thermal line emission from ADAFs, in
which both the thermal and Doppler broadening have been considered. It is found
that the double-peaked profiles are present for high inclination angles between
the axis of disk and the line of sight. The double-peaked profiles are smeared
in low inclination cases, and completely disappear while the inclination angle
is less than , where the thermal and turbulent broadening dominated
on the line profiles. We also note that the thermal line profile is affected by
the location of the transition radius of ADAF. The self-similar
height-integrated disk structure and the emissivity with power-law dependence
of radius are adopted in our calculations. The results obtained in this work
can be used as a diagnosis on the future X-ray observations of the thermal
lines. Some important physical quantities of ADAFs could be inferred from
future thermal line observations.Comment: 7 page
When Both Transmitting and Receiving Energies Matter: An Application of Network Coding in Wireless Body Area Networks
A network coding scheme for practical implementations of wireless body area
networks is presented, with the objective of providing reliability under
low-energy constraints. We propose a simple network layer protocol for star
networks, adapting redundancy based on both transmission and reception energies
for data and control packets, as well as channel conditions. Our numerical
results show that even for small networks, the amount of energy reduction
achievable can range from 29% to 87%, as the receiving energy per control
packet increases from equal to much larger than the transmitting energy per
data packet. The achievable gains increase as a) more nodes are added to the
network, and/or b) the channels seen by different sensor nodes become more
asymmetric.Comment: 10 pages, 7 figures, submitted to the NC-Pro Workshop at IFIP
Networking Conference 2011, and to appear in the conference proceedings,
published by Springer-Verlag, in the Lecture Notes in Computer Science (LNCS)
serie
Inflation from Tsunami-waves
We investigate inflation driven by the evolution of highly excited quantum
states within the framework of out of equilibrium field dynamics. These states
are characterized by a non-perturbatively large number of quanta in a band of
momenta but with vanishing expectation value of the scalar field.They represent
the situation in which initially a non-perturbatively large energy density is
localized in a band of high energy quantum modes and are coined tsunami-waves.
The self-consistent evolution of this quantum state and the scale factor is
studied analytically and numerically. It is shown that the time evolution of
these quantum states lead to two consecutive stages of inflation under
conditions that are the quantum analogue of slow-roll. The evolution of the
scale factor during the first stage has new features that are characteristic of
the quantum state. During this initial stage the quantum fluctuations in the
highly excited band build up an effective homogeneous condensate with a non-
perturbatively large amplitude as a consequence of the large number of quanta.
The second stage of inflation is similar to the usual classical chaotic
scenario but driven by this effective condensate.The excited quantum modes are
already superhorizon in the first stage and do not affect the power spectrum of
scalar perturbations. Thus, this tsunami quantum state provides a field
theoretical justification for chaotic scenarios driven by a classical
homogeneous scalar field of large amplitude.Comment: LaTex, 36 pages, 7 .ps figures. Improved version to appear in Nucl.
Phys.
Non-Markovian disentanglement dynamics of two-qubit system
We investigated the disentanglement dynamics of two-qubit system in
Non-Markovian approach. We showed that only the couple strength with the
environment near to or less than fine-structure constant 1/137, entanglement
appear exponential decay for a certain class of two-qubit entangled state.
While the coupling between qubit and the environment is much larger, system
always appears the sudden-death of entanglement even in the vacuum environment.Comment: 17 pages, 3 figure
Tripartite Graph Clustering for Dynamic Sentiment Analysis on Social Media
The growing popularity of social media (e.g, Twitter) allows users to easily
share information with each other and influence others by expressing their own
sentiments on various subjects. In this work, we propose an unsupervised
\emph{tri-clustering} framework, which analyzes both user-level and tweet-level
sentiments through co-clustering of a tripartite graph. A compelling feature of
the proposed framework is that the quality of sentiment clustering of tweets,
users, and features can be mutually improved by joint clustering. We further
investigate the evolution of user-level sentiments and latent feature vectors
in an online framework and devise an efficient online algorithm to sequentially
update the clustering of tweets, users and features with newly arrived data.
The online framework not only provides better quality of both dynamic
user-level and tweet-level sentiment analysis, but also improves the
computational and storage efficiency. We verified the effectiveness and
efficiency of the proposed approaches on the November 2012 California ballot
Twitter data.Comment: A short version is in Proceeding of the 2014 ACM SIGMOD International
Conference on Management of dat
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