4,960 research outputs found
On Finite Time Singularity and Global Regularity of an Axisymmetric Model for the 3D Euler Equations
We investigate the large time behavior of an axisymmetric model for the 3D
Euler equations. In \cite{HL09}, Hou and Lei proposed a 3D model for the
axisymmetric incompressible Euler and Navier-Stokes equations with swirl. This
model shares many properties of the 3D incompressible Euler and Navier-Stokes
equations. The main difference between the 3D model of Hou and Lei and the
reformulated 3D Euler and Navier-Stokes equations is that the convection term
is neglected in the 3D model. In \cite{HSW09}, the authors proved that the 3D
inviscid model can develop a finite time singularity starting from smooth
initial data on a rectangular domain. A global well-posedness result was also
proved for a class of smooth initial data under some smallness condition. The
analysis in \cite{HSW09} does not apply to the case when the domain is
axisymmetric and unbounded in the radial direction. In this paper, we prove
that the 3D inviscid model with an appropriate Neumann-Robin boundary condition
will develop a finite time singularity starting from smooth initial data in an
axisymmetric domain. Moreover, we prove that the 3D inviscid model has globally
smooth solutions for a class of large smooth initial data with some appropriate
boundary condition.Comment: Please read the published versio
Composite Correlation Quantization for Efficient Multimodal Retrieval
Efficient similarity retrieval from large-scale multimodal database is
pervasive in modern search engines and social networks. To support queries
across content modalities, the system should enable cross-modal correlation and
computation-efficient indexing. While hashing methods have shown great
potential in achieving this goal, current attempts generally fail to learn
isomorphic hash codes in a seamless scheme, that is, they embed multiple
modalities in a continuous isomorphic space and separately threshold embeddings
into binary codes, which incurs substantial loss of retrieval accuracy. In this
paper, we approach seamless multimodal hashing by proposing a novel Composite
Correlation Quantization (CCQ) model. Specifically, CCQ jointly finds
correlation-maximal mappings that transform different modalities into
isomorphic latent space, and learns composite quantizers that convert the
isomorphic latent features into compact binary codes. An optimization framework
is devised to preserve both intra-modal similarity and inter-modal correlation
through minimizing both reconstruction and quantization errors, which can be
trained from both paired and partially paired data in linear time. A
comprehensive set of experiments clearly show the superior effectiveness and
efficiency of CCQ against the state of the art hashing methods for both
unimodal and cross-modal retrieval
Pseudo-magnetoexcitons in strained graphene bilayers without external magnetic fields
The structural and electronic properties of graphene leads its charge
carriers to behave like relativistic particles, which is described by a
Dirac-like Hamiltonian. Since graphene is a monolayer of carbon atoms, the
strain due to elastic deformations will give rise to so-called `pseudomagnetic
fields (PMF)' in graphene sheet, and that has been realized experimentally in
strained graphene sample. Here we propose a realistic strained graphene bilayer
(SGB) device to detect the pseudo-magnetoexcitons (PME) in the absence of
external magnetic field. The carriers in each graphene layer suffer different
strong PMFs due to strain engineering, which give rise to Landau quantization.
The pseudo-Landau levels (PLLs) of electron-hole pair under inhomogeneous PMFs
in SGB are analytically obtained in the absence of Coulomb interactions. Based
on the general analytical optical absorption selection rule for PME, we show
that the optical absorption spectrums can interpret the corresponding formation
of Dirac-type PME. We also predict that in the presence of inhomogeneous PMFs,
the superfluidity-normal phase transition temperature of PME is greater than
that under homogeneous PMFs.}Comment: 16 pages, 6 figure
Tidal capture of an asteroid by a magnetar: FRB-like bursts, glitch and anti-glitch
Recently, remarkable anti-glitch and glitch accompanied by bright radio
bursts of the Galactic magnetar SGR J1935+2154 were discovered. These two
infrequent temporal coincidences between the glitch/anti-glitch and the fast
radio burst (FRB)-like bursts reveal their physical connection of them. Here we
propose that the anti-glitch/glitch and FRB-like bursts can be well understood
by an asteroid tidally captured by a magnetar. In this model, an asteroid is
tidally captured and disrupted by a magnetar. Then, the disrupted asteroid will
transfer the angular momentum to the magnetar producing a sudden change in the
magnetar rotational frequency at the magnetosphere radius. If the orbital
angular momentum of the asteroid is parallel (or anti-parallel) to that of the
spinning magnetar, a glitch (or anti-glitch) will occur. Subsequently, the
bound asteroid materials fall back to the pericenter and eventually are
accreted to the surface of the magnetar. Massive fragments of the asteroid
cross magnetic field lines and produce bright radio bursts through coherent
curvature radiation. Our model can explain the sudden magnetar spin changes and
FRB-like bursts in a unified way.Comment: 6 pages, 1 figure, published by MNRAS
https://doi.org/10.1093/mnras/stad158
The Hierarchical Structure of the Face Network Revealed by Its Functional Connectivity Pattern
A major principle of human brain organization is “integrating” some regions into networks while “segregating” other sets of regions into separate networks. However, little is known about the cognitive function of the integration and segregation of brain networks. Here, we examined the well-studied brain network for face processing, and asked whether the integration and segregation of the face network (FN) are related to face recognition performance. To do so, we used a voxel-based global brain connectivity method based on resting-state fMRI to characterize the within-network connectivity (WNC) and the between-network connectivity (BNC) of the FN. We found that 95.4% of voxels in the FN had a significantly stronger WNC than BNC, suggesting that the FN is a relatively encapsulated network. Importantly, individuals with a stronger WNC (i.e., integration) in the right fusiform face area were better at recognizing faces, whereas individuals with a weaker BNC (i.e., segregation) in the right occipital face area performed better in the face recognition tasks. In short, our study not only demonstrates the behavioral relevance of integration and segregation of the FN but also provides evidence supporting functional division of labor between the occipital face area and fusiform face area in the hierarchically organized FN
Impact of IVIG vs. SCIG on IgG trough level and infection incidence in primary immunodeficiency diseases: A systematic review and meta-analysis of clinical studies.
Background: Monthly intravenous immunoglobulin (IVIG) and weekly subcutaneous immunoglobulin (SCIG) have been regarded as therapeutically equivalent treatments for primary immunodeficiency diseases (PIDD). Immunoglobulin G (IgG) trough level is used as a monitoring measure for infection prevention.
Objective: A systematic review and meta-analysis were performed to elucidate the relationship between IgG dosing, trough IgG levels with overall infection incidence in patients with PIDD receiving IVIG and SCIG therapy.
Methods: Medline, EMBASE, Cochrane, Central, and Scopus were searched for studies published from Jan 2010-June 2018, fulfilling the inclusion criteria. DerSimonian and Laird random-effects method were used to pool the difference of IgG trough levels. Random-effect meta-regression was used to evaluate infection incidence per 100 mg/dl IgG trough increase though IVIG and SCIG.
Results: Out of 24 observational studies included, 11 compared IgG trough levels among SCIG and IVIG (mean difference: 73.4 mg/dl, 95% CI: 31.67-119.19 mg/dl, I2 = 45%, p = 0.05), favoring weekly SCIG. For every 100 mg/dl increase in the trough, a linear trend of decreased incidence rates of infection was identified in SCIG patients (p = 0.03), but no similar trend was identified in trough levels vs. infection rates for patients receiving IVIG (p = 0.67).
Conclusion: In our study, weekly SCIG attained a higher trough level in comparison to monthly IVIG. Higher SCIG troughs were associated with lower infection rates, while IVIG troughs demonstrated no relationship
X-ray Observation and Analysis of The Composite Supernova Remnant G327.1-1.1
Based on the data from the observation of the SNR G327.1-1.1 by ASCA and
ROSAT, we find that G327.1-1.1 is a composite remnant with both a nonthermal
emission component and a diffuse thermal emission component. The nonthermal
component is well fitted by a power-law model with photon index about 2.2. This
component is attributed to the emission from the synchrotron nebula powered by
an undiscovered central pulsar. The thermal component has a temperature of
about 0.4 keV. We attribute it to the emission from the shock-heat swept-up
ISM. Its age, explosion energy and density of ambient medium are derived from
the observed thermal component. Some charactistics about the synchrotron nebula
are also derived. We search for the pulsed signal, but has not found it. The
soft X-ray(0.4 - 2 keV) and hard X-ray(2 - 10 keV) images are different, but
they both elongate in the SE-NW direction. And this X-ray SE-NW elongation is
in positional coincidence with the radio ridge in MOST 843MHz radio map. We
present a possibility that the X-ray nonthermal emission mainly come from the
trail produced by a quickly moving undiscoverd pulsar, and the long radio ridge
is formed when the pulsar is moving out of the boundary of the plerionic
structure.Comment: 20 pages, 4 Postscript figures, aasms4.sty and psfig.sty, to be
published in Astrophysical Journal, January 20, 1999, Vol. 51
Genome-scale analysis and comparison of gene expression profiles in developing and germinated pollen in Oryza sativa
<p>Abstract</p> <p>Background</p> <p>Pollen development from the microspore involves a series of coordinated cellular events, and the resulting mature pollen has a specialized function to quickly germinate, produce a polar-growth pollen tube derived from the vegetative cell, and deliver two sperm cells into the embryo sac for double fertilization. The gene expression profiles of developing and germinated pollen have been characterised by use of the eudicot model plant <it>Arabidopsis</it>. Rice, one of the most important cereal crops, has been used as an excellent monocot model. A comprehensive analysis of transcriptome profiles of developing and germinated pollen in rice is important to understand the conserved and diverse mechanism underlying pollen development and germination in eudicots and monocots.</p> <p>Results</p> <p>We used Affymetrix GeneChip<sup>® </sup>Rice Genome Array to comprehensively analyzed the dynamic changes in the transcriptomes of rice pollen at five sequential developmental stages from microspores to germinated pollen. Among the 51,279 transcripts on the array, we found 25,062 pollen-preferential transcripts, among which 2,203 were development stage-enriched. The diversity of transcripts decreased greatly from microspores to mature and germinated pollen, whereas the number of stage-enriched transcripts displayed a "U-type" change, with the lowest at the bicellular pollen stage; and a transition of overrepresented stage-enriched transcript groups associated with different functional categories, which indicates a shift in gene expression program at the bicellular pollen stage. About 54% of the now-annotated rice F-box protein genes were expressed preferentially in pollen. The transcriptome profile of germinated pollen was significantly and positively correlated with that of mature pollen. Analysis of expression profiles and coexpressed features of the pollen-preferential transcripts related to cell cycle, transcription, the ubiquitin/26S proteasome system, phytohormone signalling, the kinase system and defense/stress response revealed five expression patterns, which are compatible with changes in major cellular events during pollen development and germination. A comparison of pollen transcriptomes between rice and <it>Arabidopsis </it>revealed that 56.6% of the rice pollen preferential genes had homologs in <it>Arabidopsis </it>genome, but 63.4% of these homologs were expressed, with a small proportion being expressed preferentially, in <it>Arabidopsis </it>pollen. Rice and <it>Arabidopsis </it>pollen had non-conservative transcription factors each.</p> <p>Conclusions</p> <p>Our results demonstrated that rice pollen expressed a set of reduced but specific transcripts in comparison with vegetative tissues, and the number of stage-enriched transcripts displayed a "U-type" change during pollen development, with the lowest at the bicellular pollen stage. These features are conserved in rice and <it>Arabidopsis</it>. The shift in gene expression program at the bicellular pollen stage may be important to the transition from earlier cell division to later pollen maturity. Pollen at maturity pre-synthesized transcripts needed for germination and early pollen tube growth. The transcription regulation associated with pollen development would have divergence between the two species. Our results also provide novel insights into the molecular program and key components of the regulatory network regulating pollen development and germination.</p
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