3,202 research outputs found
Nonlinear cross Gramians and gradient systems
We study the notion of cross Gramians for non-linear gradient systems, using the characterization in terms of prolongation and gradient extension associated to the system. The cross Gramian is given for the variational system associated to the original nonlinear gradient system. We obtain linearization results that precisely correspond to the notion of a cross Gramian for symmetric linear systems. Furthermore, first steps towards relations with the singular value functions of the nonlinear Hankel operator are studied and yield promising results.
Transductive Learning with String Kernels for Cross-Domain Text Classification
For many text classification tasks, there is a major problem posed by the
lack of labeled data in a target domain. Although classifiers for a target
domain can be trained on labeled text data from a related source domain, the
accuracy of such classifiers is usually lower in the cross-domain setting.
Recently, string kernels have obtained state-of-the-art results in various text
classification tasks such as native language identification or automatic essay
scoring. Moreover, classifiers based on string kernels have been found to be
robust to the distribution gap between different domains. In this paper, we
formally describe an algorithm composed of two simple yet effective
transductive learning approaches to further improve the results of string
kernels in cross-domain settings. By adapting string kernels to the test set
without using the ground-truth test labels, we report significantly better
accuracy rates in cross-domain English polarity classification.Comment: Accepted at ICONIP 2018. arXiv admin note: substantial text overlap
with arXiv:1808.0840
Effect of carbon nanotube doping on critical current density of MgB2 superconductor
The effect of doping MgB2 with carbon nanotubes on transition temperature,
lattice parameters, critical current density and flux pinning was studied for
MgB2-xCx with x = 0, 0.05, 0.1, 0.2 and 0.3. The carbon substitution for B was
found to enhance Jc in magnetic fields but depress Tc. The depression of Tc,
which is caused by the carbon substitution for B, increases with increasing
doping level, sintering temperature and duration. By controlling the extent of
the substitution and addition of carbon nanotubes we can achieve the optimal
improvement on critical current density and flux pinning in magnetic fields
while maintaining the minimum reduction in Tc. Under these conditions, Jc was
enhanced by two orders of magnitude at 8T and 5K and 7T and 10K. Jc was more
than 10,000A/cm2 at 20K and 4T and 5K and 8.5T, respectively
Weighted Low-Regularity Solutions of the KP-I Initial Value Problem
In this paper we establish local well-posedness of the KP-I problem, with
initial data small in the intersection of the natural energy space with the
space of functions which are square integrable when multiplied by the weight y.
The result is proved by the contraction mapping principle. A similar (but
slightly weaker) result was the main Theorem in the paper " Low regularity
solutions for the Kadomstev-Petviashvili I equation " by Colliander, Kenig and
Staffilani (GAFA 13 (2003),737-794 and math.AP/0204244). Ionescu found a
counterexample (included in the present paper) to the main estimate used in the
GAFA paper, which renders incorrect the proof there. The present paper thus
provides a correct proof of a strengthened version of the main result in the
GAFA paper
A Model of Heat Conduction
We define a deterministic ``scattering'' model for heat conduction which is
continuous in space, and which has a Boltzmann type flavor, obtained by a
closure based on memory loss between collisions. We prove that this model has,
for stochastic driving forces at the boundary, close to Maxwellians, a unique
non-equilibrium steady state
On the particle paths and the stagnation points in small-amplitude deep-water waves
In order to obtain quite precise information about the shape of the particle
paths below small-amplitude gravity waves travelling on irrotational deep
water, analytic solutions of the nonlinear differential equation system
describing the particle motion are provided. All these solutions are not closed
curves. Some particle trajectories are peakon-like, others can be expressed
with the aid of the Jacobi elliptic functions or with the aid of the
hyperelliptic functions. Remarks on the stagnation points of the
small-amplitude irrotational deep-water waves are also made.Comment: to appear in J. Math. Fluid Mech. arXiv admin note: text overlap with
arXiv:1106.382
Variational derivation of two-component Camassa-Holm shallow water system
By a variational approach in the Lagrangian formalism, we derive the
nonlinear integrable two-component Camassa-Holm system (1). We show that the
two-component Camassa-Holm system (1) with the plus sign arises as an
approximation to the Euler equations of hydrodynamics for propagation of
irrotational shallow water waves over a flat bed. The Lagrangian used in the
variational derivation is not a metric.Comment: to appear in Appl. Ana
Smooth cutoff formulation of hierarchical reference theory for a scalar phi4 field theory
The phi4 scalar field theory in three dimensions, prototype for the study of
phase transitions, is investigated by means of the hierarchical reference
theory (HRT) in its smooth cutoff formulation. The critical behavior is
described by scaling laws and critical exponents which compare favorably with
the known values of the Ising universality class. The inverse susceptibility
vanishes identically inside the coexistence curve, providing a first principle
implementation of the Maxwell construction, and shows the expected
discontinuity across the phase boundary, at variance with the usual sharp
cutoff implementation of HRT. The correct description of first and second order
phase transitions within a microscopic, nonperturbative approach is thus
achieved in the smooth cutoff HRT.Comment: 8 pages, 4 figure
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