99,024 research outputs found
Structure propagation for zero-shot learning
The key of zero-shot learning (ZSL) is how to find the information transfer
model for bridging the gap between images and semantic information (texts or
attributes). Existing ZSL methods usually construct the compatibility function
between images and class labels with the consideration of the relevance on the
semantic classes (the manifold structure of semantic classes). However, the
relationship of image classes (the manifold structure of image classes) is also
very important for the compatibility model construction. It is difficult to
capture the relationship among image classes due to unseen classes, so that the
manifold structure of image classes often is ignored in ZSL. To complement each
other between the manifold structure of image classes and that of semantic
classes information, we propose structure propagation (SP) for improving the
performance of ZSL for classification. SP can jointly consider the manifold
structure of image classes and that of semantic classes for approximating to
the intrinsic structure of object classes. Moreover, the SP can describe the
constrain condition between the compatibility function and these manifold
structures for balancing the influence of the structure propagation iteration.
The SP solution provides not only unseen class labels but also the relationship
of two manifold structures that encode the positive transfer in structure
propagation. Experimental results demonstrate that SP can attain the promising
results on the AwA, CUB, Dogs and SUN databases
Crumpling wires in two dimensions
An energy-minimal simulation is proposed to study the patterns and mechanical
properties of elastically crumpled wires in two dimensions. We varied the
bending rigidity and stretching modulus to measure the energy allocation,
size-mass exponent, and the stiffness exponent. The mass exponent is shown to
be universal at value . We also found that the stiffness exponent
is universal, but varies with the plasticity parameters and
. These numerical findings agree excellently with the experimental
results
A sharp stability criterion for the Vlasov-Maxwell system
We consider the linear stability problem for a 3D cylindrically symmetric
equilibrium of the relativistic Vlasov-Maxwell system that describes a
collisionless plasma. For an equilibrium whose distribution function decreases
monotonically with the particle energy, we obtained a linear stability
criterion in our previous paper. Here we prove that this criterion is sharp;
that is, there would otherwise be an exponentially growing solution to the
linearized system. Therefore for the class of symmetric Vlasov-Maxwell
equilibria, we establish an energy principle for linear stability. We also
treat the considerably simpler periodic 1.5D case. The new formulation
introduced here is applicable as well to the nonrelativistic case, to other
symmetries, and to general equilibria
Systematic {\em ab initio} study of the phase diagram of epitaxially strained SrTiO
We use density-functional theory with the local-density approximation to
study the structural and ferroelectric properties of SrTiO under misfit
strains. Both the antiferrodistortive (AFD) and ferroelectric (FE)
instabilities are considered. The rotation of the oxygen octahedra and the
movement of the atoms are fully relaxed within the constraint of a fixed
in-plane lattice constant. We find a rich misfit strain-induced phase
transition sequence and is obtained only when the AFD distortion is taken into
account. We also find that compressive misfit strains induce ferroelectricity
in the tetragonal low temperature phase only whilst tensile strains induce
ferroelectricity in the orthorhombic phases only. The calculated FE
polarization for both the tetragonal and orthorhombic phases increases
monotonically with the magnitude of the strains. The AFD rotation angle of the
oxygen octahedra in the tetragonal phase increases dramatically as the misfit
strain goes from the tensile to compressive strain region whilst it decreases
slightly in the orthorhombic (FO4) phase. This reveals why the polarization in
the epitaxially strained SrTiO would be larger when the tensile strain is
applied, since the AFD distortion is found to reduce the FE instability and
even to completely suppress it in the small strain region. Finally, our
analysis of the average polar distortion and the charge density distribution
suggests that both the Ti-O and Sr-O layers contribute significantly to the FE
polarization
Optimization of double drive pulse pumping in Ne-like Ge x-ray lasers
Pumping of the Ne-like Ge x-ray laser with two 100 ps duration pulses (a prepulse and main pulse) is investigated using a fluid and atomic physics code coupled to a 3D ray tracing postprocessor code. The modeling predicts the optimum ratio of the irradiance of the two pulses for the maximum x-ray laser output resulting from the balance between the relative lower electron density gradients and wider gain region which is produced with a larger prepulse and the higher peak gain coefficients produced with a small prepulse. With a longer pulse interval between prepulse and main pulse, a relatively lower optimum pulse ratio is found. The threshold irradiance of the main driving pulse with a prepulse required to make an order of magnitude enhancement of laser output compared to irradiation without a prepulse is also found at 3-4x10(13) W/cm(2) for Ne-like Ge. (C) 1998 American Institute of Physics
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