8,942 research outputs found
On the minimum jet power of TEV BL Lac objects in the p- model
We study the requirement on the jet power in the conventional p-
models (photopion production and Bethe-Heitler pair production) for TeV BL Lac
objects. We select a sample of TeV BL Lac objects whose SEDs are difficult to
be explained by the one-zone leptonic model. Based on the relation between the
p- interaction efficiency and the opacity of absorption,
we find that the detection of TeV emission poses upper limits on the p-
interaction efficiencies in these sources and hence minimum jet powers can be
derived accordingly. We find that the obtained minimum jet powers exceed the
Eddington luminosity of the supermassive black holes. Implications for the
accretion mode of the supermassive black hole in these BL Lac objects and the
origin of their TeV emissions are discussed.Comment: 11 pages, 4 figures, 2 tables, accepted for publication in Ap
Quasi-SLCA based Keyword Query Processing over Probabilistic XML Data
The probabilistic threshold query is one of the most common queries in
uncertain databases, where a result satisfying the query must be also with
probability meeting the threshold requirement. In this paper, we investigate
probabilistic threshold keyword queries (PrTKQ) over XML data, which is not
studied before. We first introduce the notion of quasi-SLCA and use it to
represent results for a PrTKQ with the consideration of possible world
semantics. Then we design a probabilistic inverted (PI) index that can be used
to quickly return the qualified answers and filter out the unqualified ones
based on our proposed lower/upper bounds. After that, we propose two efficient
and comparable algorithms: Baseline Algorithm and PI index-based Algorithm. To
accelerate the performance of algorithms, we also utilize probability density
function. An empirical study using real and synthetic data sets has verified
the effectiveness and the efficiency of our approaches
Efficient Truss Maintenance in Evolving Networks
Truss was proposed to study social network data represented by graphs. A
k-truss of a graph is a cohesive subgraph, in which each edge is contained in
at least k-2 triangles within the subgraph. While truss has been demonstrated
as superior to model the close relationship in social networks and efficient
algorithms for finding trusses have been extensively studied, very little
attention has been paid to truss maintenance. However, most social networks are
evolving networks. It may be infeasible to recompute trusses from scratch from
time to time in order to find the up-to-date -trusses in the evolving
networks. In this paper, we discuss how to maintain trusses in a graph with
dynamic updates. We first discuss a set of properties on maintaining trusses,
then propose algorithms on maintaining trusses on edge deletions and
insertions, finally, we discuss truss index maintenance. We test the proposed
techniques on real datasets. The experiment results show the promise of our
work
Pentaquark states with the configuration in a simple model
We discuss the mass splittings for the -wave triply heavy pentaquark
states with the configuration which is a mirror
structure of . The latter configuration is related with the nature
of observed by the LHCb Collaboration. The considered pentaquark
masses are roughly estimated with a simple method. One finds that such states
are probably not narrow even if they do exist. This leaves room for molecule
interpretation for a state around the low-lying threshold of a doubly heavy
baryon and a heavy-light meson, e.g. , if it were observed. As a by
product, we conjecture that upper limits for the masses of the conventional
triply heavy baryons can be determined by the masses of the conventional doubly
heavy baryons.Comment: 19 pages, 1 figure, 10 tables; Version accepted by Eur. Phys. J.
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