22,814 research outputs found
New attractor mechanism for spherically symmetric extremal black holes
We introduce a new attractor mechanism to find the entropy for spherically
symmetric extremal black holes. The key ingredient is to find a two-dimensional
(2D) dilaton gravity with the dilaton potential . The condition of an
attractor is given by and
and for a constant dilaton ,
these are also used to find the location of the degenerate horizon of
an extremal black hole. As a nontrivial example, we consider an extremal
regular black hole obtained from the coupled system of Einstein gravity and
nonlinear electrodynamics. The desired Bekenstein-Hawking entropy is
successfully recovered from the generalized entropy formula combined with the
2D dilaton gravity, while the entropy function approach does not work for
obtaining this entropy.Comment: 20 pages, 4 figures, Accepted for publication in Physical Review D.
This version includes revisions suggested by the refere
Fluctuation of Conductance Peak Spacings in Large Semiconductor Quantum Dots
Fluctuation of Coulomb blockade peak spacings in large two-dimensional
semiconductor quantum dots are studied within a model based on the
electrostatics of several electron islands among which there are random
inductive and capacitive couplings. Each island can accommodate electrons on
quantum orbitals whose energies depend also on an external magnetic field. In
contrast with a single island quantum dot, where the spacing distribution is
close to Gaussian, here the distribution has a peak at small spacing value. The
fluctuations are mainly due to charging effects. The model can explain the
occasional occurrence of couples or even triples of closely spaced Coulomb
blockade peaks, as well as the qualitative behavior of peak positions with the
applied magnetic field.Comment: 13 pages, 4 figures, accepted for publication in PR
A Deep Relevance Matching Model for Ad-hoc Retrieval
In recent years, deep neural networks have led to exciting breakthroughs in
speech recognition, computer vision, and natural language processing (NLP)
tasks. However, there have been few positive results of deep models on ad-hoc
retrieval tasks. This is partially due to the fact that many important
characteristics of the ad-hoc retrieval task have not been well addressed in
deep models yet. Typically, the ad-hoc retrieval task is formalized as a
matching problem between two pieces of text in existing work using deep models,
and treated equivalent to many NLP tasks such as paraphrase identification,
question answering and automatic conversation. However, we argue that the
ad-hoc retrieval task is mainly about relevance matching while most NLP
matching tasks concern semantic matching, and there are some fundamental
differences between these two matching tasks. Successful relevance matching
requires proper handling of the exact matching signals, query term importance,
and diverse matching requirements. In this paper, we propose a novel deep
relevance matching model (DRMM) for ad-hoc retrieval. Specifically, our model
employs a joint deep architecture at the query term level for relevance
matching. By using matching histogram mapping, a feed forward matching network,
and a term gating network, we can effectively deal with the three relevance
matching factors mentioned above. Experimental results on two representative
benchmark collections show that our model can significantly outperform some
well-known retrieval models as well as state-of-the-art deep matching models.Comment: CIKM 2016, long pape
Thermodynamic duality between RN black hole and 2D dilaton gravity
All thermodynamic quantities of the Reissner-Nordstr\"om (RN) black hole can
be obtained from the dilaton and its potential of two dimensional (2D) dilaton
gravity. The dual relations of four thermodynamic laws are also established.
Furthermore, the near-horizon thermodynamics of the extremal RN black hole is
completely described by the Jackiw-Teitelboim theory which is obtained by
perturbing around the AdS-horizon.Comment: 10 pages, 3 figures, version accepted by MPL
The Progenitor of the New COMPTEL/ROSAT Supernova Remnant in Vela
We show that (1) the newly discovered supernova remnant (SNR), GRO
J0852--4642/RX J0852.0--4622, was created by a core-collapse supernova of a
massive star, and (2) the same supernova event which produced the Ti
detected by COMPTEL from this source is probably also responsible for a large
fraction of the observed Al emission in the Vela region detected by the
same instrument. The first conclusion is based on the fact that the remnant is
currently expanding too slowly given its young age for it to be caused by a
Type Ia supernova. If the current SNR shell expansion speed is greater than
3000 km/s, a Type II supernova with a moderate kinetic energy
exploding at about 150 pc away is favored. If the SNR expansion speed is lower
than 2000 km s, as derived naively from the X-ray data, a much more
energetic supernova is required to have occurred at pc away in a
dense environment at the edge of the Gum nebula. This progenitor has a
preferred ejecta mass of and therefore, it is probably a Type
Ib or Type Ic supernova. However, the required high ambient density of in this scenario is difficult to reconcile with the regional CO
data. A combination of our estimates of the age/energetics of the new SNR and
the almost perfect positional coincidence of the new SNR with the centroid of
the COMPTEL Al emission feature of the Vela region strongly favors a
causal connection. If confirmed, this will be the first case where both
Ti and Al are detected from the same young SNR and together they
can be used to select preferred theoretical core-collapse supernova models.Comment: Revised, 10 pages, 2 figures, to appear in ApJ Lett Vol.514 on April
1, 199
Effects of Solution, Soil and Sand Cultures on Nodulation and Growth of Phasey Bean
Plants of phasey bean (Macroptilium lathyroides cv. Murray) were grown in nitrogen-free
nutrient solution, sod, or sand culture in a naturally-Nt glasshouse. Nodulation, dry matter accumulation in plant parts, and seed yields were assessed. Partitioning of symbiotic nitrogen into various
plant parts during vegetative and reproductive growth stages was also determined. In all culture
media, nodule number and size increased with plant age but the rate of increase was generally greater
in solution than in the other cultures. In sand culture, the dry weight per nodule and per plant, and
plant growth were significantly suppressed. Although tap root elongation was consistently better in
solution than soil or sand culture, leaf development and dry matter accumulation in roots and stems
were enhanced by solution culture only during flowering and fruiting stage. Seed yields were significantly
increased by solution culture, an effect apparently associated with increased symbiotic nitrogen
fixation. During vegetative growth, nitrogen accumulated largely in the leaves and stems but pods
were major sinks of nitrogen during the reproductive growth stage. The benefits and applications of
solution culture in the study of nodule development and collection of root samples for acetylene reduction
assays are discussed
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