316 research outputs found
Distorted-wave born approximation calculations for turbulence scattering in an upward-refracting atmosphere
Weiner and Keast observed that in an upward-refracting atmosphere, the relative sound pressure level versus range follows a characteristic 'step' function. The observed step function has recently been predicted qualitatively and quantitatively by including the effects of small-scale turbulence in a parabolic equation (PE) calculation. (Gilbert et al., J. Acoust. Soc. Am. 87, 2428-2437 (1990)). The PE results to single-scattering calculations based on the distorted-wave Born approximation (DWBA) are compared. The purpose is to obtain a better understanding of the physical mechanisms that produce the step-function. The PE calculations and DWBA calculations are compared to each other and to the data of Weiner and Keast for upwind propagation (strong upward refraction) and crosswind propagation (weak upward refraction) at frequencies of 424 Hz and 848 Hz. The DWBA calculations, which include only single scattering from turbulence, agree with the PE calculations and with the data in all cases except for upwind propagation at 848 Hz. Consequently, it appears that in all cases except one, the observed step function can be understood in terms of single scattering from an upward-refracted 'skywave' into the refractive shadow zone. For upwind propagation at 848 Hz, the DWBA calculation gives levels in the shadow zone that are much below both the PE and the data
A Riemannian Primal-dual Algorithm Based on Proximal Operator and its Application in Metric Learning
In this paper, we consider optimizing a smooth, convex, lower semicontinuous
function in Riemannian space with constraints. To solve the problem, we first
convert it to a dual problem and then propose a general primal-dual algorithm
to optimize the primal and dual variables iteratively. In each optimization
iteration, we employ a proximal operator to search optimal solution in the
primal space. We prove convergence of the proposed algorithm and show its
non-asymptotic convergence rate. By utilizing the proposed primal-dual
optimization technique, we propose a novel metric learning algorithm which
learns an optimal feature transformation matrix in the Riemannian space of
positive definite matrices. Preliminary experimental results on an optimal fund
selection problem in fund of funds (FOF) management for quantitative investment
showed its efficacy.Comment: 8 pages, 2 figures, published as a conference paper in 2019
International Joint Conference on Neural Networks (IJCNN
A Graph Regularized Point Process Model For Event Propagation Sequence
Point process is the dominant paradigm for modeling event sequences occurring
at irregular intervals. In this paper we aim at modeling latent dynamics of
event propagation in graph, where the event sequence propagates in a directed
weighted graph whose nodes represent event marks (e.g., event types). Most
existing works have only considered encoding sequential event history into
event representation and ignored the information from the latent graph
structure. Besides they also suffer from poor model explainability, i.e.,
failing to uncover causal influence across a wide variety of nodes. To address
these problems, we propose a Graph Regularized Point Process (GRPP) that can be
decomposed into: 1) a graph propagation model that characterizes the event
interactions across nodes with neighbors and inductively learns node
representations; 2) a temporal attentive intensity model, whose excitation and
time decay factors of past events on the current event are constructed via the
contextualization of the node embedding. Moreover, by applying a graph
regularization method, GRPP provides model interpretability by uncovering
influence strengths between nodes. Numerical experiments on various datasets
show that GRPP outperforms existing models on both the propagation time and
node prediction by notable margins.Comment: IJCNN 202
Online Mixed Discrete and Continuous Optimization: Algorithms, Regret Analysis and Applications
We study an online mixed discrete and continuous optimization problem where a
decision maker interacts with an unknown environment for a number of
rounds. At each round, the decision maker needs to first jointly choose a
discrete and a continuous actions and then receives a reward associated with
the chosen actions. The goal for the decision maker is to maximize the
accumulative reward after rounds. We propose algorithms to solve the online
mixed discrete and continuous optimization problem and prove that the
algorithms yield sublinear regret in . We show that a wide range of
applications in practice fit into the framework of the online mixed discrete
and continuous optimization problem, and apply the proposed algorithms to solve
these applications with regret guarantees. We validate our theoretical results
with numerical experiments
Similarity Principle and its Acoustical Verification
This study finds a similarity principle the waves emanated from the same source are similar to each other as long as two wave receivers are close enough to each other the closer to each other the wave receivers are the more similar to each other the received waves are We define the similarity mathematically and verify the similarity principle by acoustical experiment
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