7,858 research outputs found
Isometric embedding via strongly symmetric positive systems
We give a new proof for the local existence of a smooth isometric embedding
of a smooth -dimensional Riemannian manifold with nonzero Riemannian
curvature tensor into -dimensional Euclidean space. Our proof avoids the
sophisticated arguments via microlocal analysis used in earlier proofs.
In Part 1, we introduce a new type of system of partial differential
equations, which is not one of the standard types (elliptic, hyperbolic,
parabolic) but satisfies a property called strong symmetric positivity. Such a
PDE system is a generalization of and has properties similar to a system of
ordinary differential equations with a regular singular point. A local
existence theorem is then established by using a novel local-to-global-to-local
approach. In Part 2, we apply this theorem to prove the local existence result
for isometric embeddings.Comment: 39 page
Long Fading Mid-Infrared Emission in Transient Coronal Line Emitters: Dust Echo of Tidal Disruption Flare
The sporadic accretion following the tidal disruption of a star by a
super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the
galactic nucleus. The gas and dust surrounding the black hole responses to such
a flare with an echo in emission lines and infrared emission. In this paper, we
report the detection of long fading mid-IR emission lasting up to 14 years
after the flare in four TDE candidates with transient coronal lines using the
WISE public data release. We estimate that the reprocessed mid-IR luminosities
are in the range between and erg~s
and dust temperature in the range of 570-800K when WISE first detected these
sources three to five years after the flare. Both luminosity and dust
temperature decreases with time. We interpret the mid-IR emission as the
infrared echo of the tidal disruption flare. We estimate the UV luminosity at
the peak flare to be 1 to 30 times erg s and for warm dust
masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results
suggest that the mid-infrared echo is a general signature of TDE in the
gas-rich environment
A Qiang Perspective on Promoting the Rehabilitation of Children Affected by the Earthquake
The Qiang ethnic minority had a population of around 300,000 at the time of the earthquake. The Qiang mostly inhabit the poorest and most socially disadvantaged remote rural mountainous areas of the Wen Chuan and Mao Wen Qiang Autonomous Counties of Sichuan. The Qiang have a continuous cultural history dating from the Diqiang groups of the Xia Dynasty (16th to 11th century BC). They have their own language and animistic belief system, and have developed their own traditional ways of dealing with disasters. The Qiang’s myth of “Bubita” (God) and the legend of “Mutazhu and Douanzhu” (a heroic story) are key messages in understanding disasters; the village “Duyaomao” (poisonous cat, meaning witch) is important for explaining children’s illness and health. The rites conducted by the Shibi (cultural leader) are the core activity in advocating collective action for responding to disaster. To reach out quickly to children who have been affected by their traumatic experiences, many volunteers have given their assistance, including doctors, psychologists, counselling staff and social workers. In particular, a large-scale program of psychiatric counselling/therapies administered by the government is being carried out. However, employing psychological counselling and psychiatric therapies from the western individualistic perspective has led to a dilemma for public health based on medical/psychological agendas. Widespread evidence has also shown that there is a very limited effect from outside community visitors, whose one-off, inconsistent, non-indigenous messages do not carry over into the children’s everyday lives. The need for an indigenous approach is stressed
Design and fabrication of robust broadband extreme ultraviolet multilayers
The random layer thickness variations can induce a great deformation of the
experimental reflection of broadband extreme ultraviolet multilayer. In order
to reduce this influence of random layer thickness fluctuations, the
multiobjective genetic algorithm has been improved and used in the robust
design of multilayer with a broad angular bandpass. The robust multilayer with
a lower sensitivity to random thickness errors have been obtained and the
corresponding multilayer mirrors were fabricated. The experimental results of
robust Mo/Si multilayer with a wide angular band were presented and analyzed,
and the advantage of robust multilayer design was demonstrated
Drug-Loaded Chitosan Film Prepared via Facile Solution Casting and Air-Drying of Plain Water-Based Chitosan Solution for Ocular Drug Delivery
Chitosan is a nature-based polymer with low toxicity, excellent biocompatibility and biodegradability. However, the intractable solubility of chitosan in water and most conventional solvents hampers its biomedical applications. Following the dissolution method for dissolving chitosan in plain water developed by us, chitosan was dissolved in ionic liquid followed by overnight freezing at −20 °C and subsequent solvent exchange with plain water at room temperature. In this study, we fabricated a drug-carrying chitosan film via solution casting and air-drying by using the plain water-based chitosan solution. Specifically, brimonidine tartrate (BT), an antiglaucoma drug, was dissolved in the plain-water based solution and used to prepare BT-loaded chitosan film, i.e., chitosan-BT film. The resulting film is transparent, structurally stable, and mucoadhesive. Micro-sized antiglaucoma BT drug crystals form and are well dispersed in the chitosan film. The chitosan-BT film enables BT to have a high corneal permeability with fast drug release kinetics for potential ocular drug delivery
Attention Optimization for Abstractive Document Summarization
Attention plays a key role in the improvement of sequence-to-sequence-based
document summarization models. To obtain a powerful attention helping with
reproducing the most salient information and avoiding repetitions, we augment
the vanilla attention model from both local and global aspects. We propose an
attention refinement unit paired with local variance loss to impose supervision
on the attention model at each decoding step, and a global variance loss to
optimize the attention distributions of all decoding steps from the global
perspective. The performances on the CNN/Daily Mail dataset verify the
effectiveness of our methods
- …