13,742 research outputs found
Aging in China
This article reports on a description of aging in China, in general, and Shanghai, in particular, with contrasts to the aging taking place in Hong Kong. Focused upon are the consequences of population aging on informal and formal support systems in the present and for the future. The efforts in the two cities of Shanghai and Hong Kong reflect differences in systems but are both influenced by traditional practices of a Chinese society
Pinned modes in lossy lattices with local gain and nonlinearity
We introduce a discrete linear lossy system with an embedded "hot spot" (HS),
i.e., a site carrying linear gain and complex cubic nonlinearity. The system
can be used to model an array of optical or plasmonic waveguides, where
selective excitation of particular cores is possible. Localized modes pinned to
the HS are constructed in an implicit analytical form, and their stability is
investigated numerically. Stability regions for the modes are obtained in the
parameter space of the linear gain and cubic gain/loss. An essential result is
that the interaction of the unsaturated cubic gain and self-defocusing
nonlinearity can produce stable modes, although they may be destabilized by
finite amplitude perturbations. On the other hand, the interplay of the cubic
loss and self-defocusing gives rise to a bistability.Comment: Phys. Rev. E (in press
Anomalous kinetics of attractive reactions
We investigate the kinetics of reaction with the local attractive
interaction between opposite species in one spatial dimension. The attractive
interaction leads to isotropic diffusions inside segregated single species
domains, and accelerates the reactions of opposite species at the domain
boundaries. At equal initial densities of and , we analytically and
numerically show that the density of particles (), the size of domains
(), the distance between the closest neighbor of same species
(), and the distance between adjacent opposite species ()
scale in time as , , and respectively. These dynamical exponents form a new
universality class distinguished from the class of uniformly driven systems of
hard-core particles.Comment: 4 pages, 4 figure
Pinned modes in two-dimensional lossy lattices with local gain and nonlinearity
We introduce a system with one or two amplified nonlinear sites ("hot spots",
HSs) embedded into a two-dimensional linear lossy lattice. The system describes
an array of evanescently coupled optical or plasmonic waveguides, with gain
applied at selected HS cores. The subject of the analysis is discrete solitons
pinned to the HSs. The shape of the localized modes is found in
quasi-analytical and numerical forms, using a truncated lattice for the
analytical consideration. Stability eigenvalues are computed numerically, and
the results are supplemented by direct numerical simulations. In the case of
self-focusing nonlinearity, the modes pinned to a single HS are stable or
unstable when the nonlinearity includes the cubic loss or gain, respectively.
If the nonlinearity is self-defocusing, the unsaturated cubic gain acting at
the HS supports stable modes in a small parametric area, while weak cubic loss
gives rise to a bistability of the discrete solitons. Symmetric and
antisymmetric modes pinned to a symmetric set of two HSs are considered too.Comment: Philosophical Transactions of the Royal Society A, in press (a
special issue on "Localized structures in dissipative media"
Excitation Induced Dephasing in Semiconductor Quantum Dots
A quantum kinetic theory is used to compute excitation induced dephasing in
semiconductor quantum dots due to the Coulomb interaction with a continuum of
states, such as a quantum well or a wetting layer. It is shown that a frequency
dependent broadening together with nonlinear resonance shifts are needed for a
microscopic explanation of the excitation induced dephasing in such a system,
and that excitation induced dephasing for a quantum-dot excitonic resonance is
different from quantum-well and bulk excitons.Comment: 6 pages, 4 figures. Extensively revised text, two figures change
Spinor Fields and Symmetries of the Spacetime
In the background of a stationary black hole, the "conserved current" of a
particular spinor field always approaches the null Killing vector on the
horizon. What's more, when the black hole is asymptotically flat and when the
coordinate system is asymptotically static, then the same current also
approaches the time Killing vector at the spatial infinity. We test these
results against various black hole solutions and no exception is found. The
spinor field only needs to satisfy a very general and simple constraint.Comment: 19 page
Modeling sequential annotations for sequence labeling with crowds
Crowd sequential annotations can be an efficient and cost-effective way to
build large datasets for sequence labeling. Different from tagging independent
instances, for crowd sequential annotations the quality of label sequence
relies on the expertise level of annotators in capturing internal dependencies
for each token in the sequence. In this paper, we propose Modeling sequential
annotation for sequence labeling with crowds (SA-SLC). First, a conditional
probabilistic model is developed to jointly model sequential data and
annotators' expertise, in which categorical distribution is introduced to
estimate the reliability of each annotator in capturing local and non-local
label dependency for sequential annotation. To accelerate the marginalization
of the proposed model, a valid label sequence inference (VLSE) method is
proposed to derive the valid ground-truth label sequences from crowd sequential
annotations. VLSE derives possible ground-truth labels from the token-wise
level and further prunes sub-paths in the forward inference for label sequence
decoding. VLSE reduces the number of candidate label sequences and improves the
quality of possible ground-truth label sequences. The experimental results on
several sequence labeling tasks of Natural Language Processing show the
effectiveness of the proposed model
Duration modeling with semi-Markov Conditional Random Fields for keyphrase extraction
Existing methods for keyphrase extraction need preprocessing to generate
candidate phrase or post-processing to transform keyword into keyphrase. In
this paper, we propose a novel approach called duration modeling with
semi-Markov Conditional Random Fields (DM-SMCRFs) for keyphrase extraction.
First of all, based on the property of semi-Markov chain, DM-SMCRFs can encode
segment-level features and sequentially classify the phrase in the sentence as
keyphrase or non-keyphrase. Second, by assuming the independence between state
transition and state duration, DM-SMCRFs model the distribution of duration
(length) of keyphrases to further explore state duration information, which can
help identify the size of keyphrase. Based on the convexity of parametric
duration feature derived from duration distribution, a constrained Viterbi
algorithm is derived to improve the performance of decoding in DM-SMCRFs. We
thoroughly evaluate the performance of DM-SMCRFs on the datasets from various
domains. The experimental results demonstrate the effectiveness of proposed
model
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