1,025 research outputs found
Asymptotic behavior of positive solutions to a degenerate elliptic equation in the upper half space with a nonlinear boundary condition
We consider positive solutions of the problem \begin{equation}
\left\{\begin{array}{l}-\mbox{div}(x_{n}^{a}\nabla u)=0\qquad
\mbox{in}\;\;\mathbb{R}_+^n,\\ \frac{\partial u}{\partial \nu^a}=u^{q} \qquad
\mbox{on}\;\;\partial \mathbb{R}_+^n,\\ \end{array} \right. \end{equation}
where , and .
We obtain some qualitative properties of positive axially symmetric solutions
in
for the case under the condition
. In particular, we establish the asymptotic expansion
of positive axially symmetric solutions.Comment: 28 page
Further study on periodic solutions of elliptic equations with a fractional Laplacian
We obtain some existence theorems for periodic solutions to several linear
equations involving fractional Laplacian. We also prove that the lower bound of
all periods for semilinear elliptic equations involving fractional Laplacian is
not larger than some exact positive constant. Hamiltonian identity, Modica-type
inequalities and an estimate of the energy for periodic solutions are also
established
Properties of the extremal solution for a fourth-order elliptic problem
Let denote the largest possible value of such that
\{{array}{lllllll} \Delta^{2}u=\frac{\lambda}{(1-u)^{p}} & \{in}\ \ B,
0 has a solution, where is the unit ball in centered
at the origin, and is the exterior unit normal vector. We show that
for this problem possesses a unique weak solution
, called the extremal solution. We prove that is singular when
for large enough and on the unit ball, where and
.
Our results actually complete part of the open problem which \cite{D} lefComment: 18 pages 2figure
Photoinduced phase transitions in narrow-gap Mott insulators: the case of VO
We study the nonequilibrium dynamics of photoexcited electrons in the
narrow-gap Mott insulator VO. The initial stages of relaxation are treated
using a quantum Boltzmann equation methodology, which reveals a rapid (
femtosecond time scale) relaxation to a pseudothermal state characterized by a
few parameters that vary slowly in time. The long-time limit is then studied by
a Hartree-Fock methodology, which reveals the possibility of nonequilibrium
excitation to a new metastable metal phase that is qualitatively
consistent with a recent experiment. The general physical picture of
photoexcitation driving a correlated electron system to a new state that is not
accessible in equilibrium may be applicable in similar materials.Comment: 11 pages, 9 figure
LSICC: A Large Scale Informal Chinese Corpus
Deep learning based natural language processing model is proven powerful, but
need large-scale dataset. Due to the significant gap between the real-world
tasks and existing Chinese corpus, in this paper, we introduce a large-scale
corpus of informal Chinese. This corpus contains around 37 million book reviews
and 50 thousand netizen's comments to the news. We explore the informal words
frequencies of the corpus and show the difference between our corpus and the
existing ones. The corpus can be further used to train deep learning based
natural language processing tasks such as Chinese word segmentation, sentiment
analysis
Two-phase flow regime prediction using LSTM based deep recurrent neural network
Long short-term memory (LSTM) and recurrent neural network (RNN) has achieved
great successes on time-series prediction. In this paper, a methodology of
using LSTM-based deep-RNN for two-phase flow regime prediction is proposed,
motivated by previous research on constructing deep RNN. The method is featured
with fast response and accuracy. The built RNN networks are trained and tested
with time-series void fraction data collected using impedance void meter. The
result shows that the prediction accuracy depends on the depth of network and
the number of layer cells. However, deeper and larger network consumes more
time in predicting
Strain Control of Electronic Phase in Rare Earth Nickelates
We use density functional plus methods to study the effects of a tensile
or compressive substrate strain on the charge-ordered insulating phase of
LuNiO. The numerical results are analyzed in terms of a Landau energy
function, with octahedral rotational distortions of the perovskite structure
included as a perturbation. Approximately 4% tensile or compressive strain
leads to a first-order transition from an insulating structure with large
amplitude breathing mode distortions of the NiO octahedra to a metallic
state in which breathing mode distortions are absent but Jahn-Teller
distortions in which two Ni-O bonds become long and the other four become short
are present. Compressive strain produces uniform Jahn-Teller order with the
long axis aligned perpendicular to the substrate plane while tensile strain
produces a staggered Jahn-Teller order in which the long bond lies in the plane
and alternates between two nearly orthogonal in-plane directions forming a
checkerboard pattern. In the absence of the breathing mode distortions and
octahedral rotations, the tensile strain-induced transition to the staggered
Jahn-Teller state would be of second order.Comment: 10 pages, 5 figure
Entanglement entropy and computational complexity of the Anderson impurity model out of equilibrium I: quench dynamics
We study the growth of entanglement entropy in density matrix renormalization
group calculations of the real-time quench dynamics of the Anderson impurity
model. We find that with appropriate choice of basis, the entropy growth is
logarithmic in both the interacting and noninteracting single-impurity models.
The logarithmic entropy growth is understood from a noninteracting chain model
as a critical behavior separating regimes of linear growth and saturation of
entropy, corresponding respectively to an overlapping and gapped energy spectra
of the set of bath states. We find that with an appropriate choices of basis
(energy-ordered bath orbitals), logarithmic entropy growth is the generic
behavior of quenched impurity models. A noninteracting calculation of a
double-impurity Anderson model supports the conclusion in the multi-impurity
case. The logarithmic growth of entanglement entropy enables studies of quench
dynamics to very long times.Comment: 8 pages, 9 figure
Tensor Methods for Additive Index Models under Discordance and Heterogeneity
Motivated by the sampling problems and heterogeneity issues common in high-
dimensional big datasets, we consider a class of discordant additive index
models. We propose method of moments based procedures for estimating the
indices of such discordant additive index models in both low and
high-dimensional settings. Our estimators are based on factorizing certain
moment tensors and are also applicable in the overcomplete setting, where the
number of indices is more than the dimensionality of the datasets. Furthermore,
we provide rates of convergence of our estimator in both high and
low-dimensional setting. Establishing such results requires deriving tensor
operator norm concentration inequalities that might be of independent interest.
Finally, we provide simulation results supporting our theory. Our contributions
extend the applicability of tensor methods for novel models in addition to
making progress on understanding theoretical properties of such tensor methods
On Stein's Identity and Near-Optimal Estimation in High-dimensional Index Models
We consider estimating the parametric components of semi-parametric multiple
index models in a high-dimensional and non-Gaussian setting. Such models form a
rich class of non-linear models with applications to signal processing, machine
learning and statistics. Our estimators leverage the score function based first
and second-order Stein's identities and do not require the covariates to
satisfy Gaussian or elliptical symmetry assumptions common in the literature.
Moreover, to handle score functions and responses that are heavy-tailed, our
estimators are constructed via carefully thresholding their empirical
counterparts. We show that our estimator achieves near-optimal statistical rate
of convergence in several settings. We supplement our theoretical results via
simulation experiments that confirm the theory
- β¦