275 research outputs found
The Application of Shape Gradient for the Incompressible Fluid in Shape Optimization
This paper is concerned with the numerical simulation for shape optimization of the Stokes flow around a solid body. The shape gradient for the shape optimization problem in a viscous incompressible flow is evaluated by the velocity method. The flow is governed by the steady-state Stokes equations coupled with a thermal model. The structure of continuous shape gradient of the cost functional is derived by employing the differentiability of a minimax formulation involving a Lagrange functional with the function space parametrization technique. A gradient-type algorithm is applied to the shape optimization problem. Numerical examples show that our theory is useful for practical purpose, and the proposed algorithm is feasible and effective
Shape Hessian for generalized Oseen flow by differentiability of a minimax: A Lagrangian approach
summary:The goal of this paper is to compute the shape Hessian for a generalized Oseen problem with nonhomogeneous Dirichlet boundary condition by the velocity method. The incompressibility will be treated by penalty approach. The structure of the shape gradient and shape Hessian with respect to the shape of the variable domain for a given cost functional are established by an application of the Lagrangian method with function space embedding technique
Testing for Treatment Effect in Covariate-Adaptive Randomized Clinical Trials with Generalized Linear Models and Omitted Covariates
Concerns have been expressed over the validity of statistical inference under
covariate-adaptive randomization despite the extensive use in clinical trials.
In the literature, the inferential properties under covariate-adaptive
randomization have been mainly studied for continuous responses; in particular,
it is well known that the usual two sample t-test for treatment effect is
typically conservative, in the sense that the actual test size is smaller than
the nominal level. This phenomenon of invalid tests has also been found for
generalized linear models without adjusting for the covariates and are
sometimes more worrisome due to inflated Type I error. The purpose of this
study is to examine the unadjusted test for treatment effect under generalized
linear models and covariate-adaptive randomization. For a large class of
covariate-adaptive randomization methods, we obtain the asymptotic distribution
of the test statistic under the null hypothesis and derive the conditions under
which the test is conservative, valid, or anti-conservative. Several commonly
used generalized linear models, such as logistic regression and Poisson
regression, are discussed in detail. An adjustment method is also proposed to
achieve a valid size based on the asymptotic results. Numerical studies confirm
the theoretical findings and demonstrate the effectiveness of the proposed
adjustment method
Efficient Match Pair Retrieval for Large-scale UAV Images via Graph Indexed Global Descriptor
SfM (Structure from Motion) has been extensively used for UAV (Unmanned
Aerial Vehicle) image orientation. Its efficiency is directly influenced by
feature matching. Although image retrieval has been extensively used for match
pair selection, high computational costs are consumed due to a large number of
local features and the large size of the used codebook. Thus, this paper
proposes an efficient match pair retrieval method and implements an integrated
workflow for parallel SfM reconstruction. First, an individual codebook is
trained online by considering the redundancy of UAV images and local features,
which avoids the ambiguity of training codebooks from other datasets. Second,
local features of each image are aggregated into a single high-dimension global
descriptor through the VLAD (Vector of Locally Aggregated Descriptors)
aggregation by using the trained codebook, which remarkably reduces the number
of features and the burden of nearest neighbor searching in image indexing.
Third, the global descriptors are indexed via the HNSW (Hierarchical Navigable
Small World) based graph structure for the nearest neighbor searching. Match
pairs are then retrieved by using an adaptive threshold selection strategy and
utilized to create a view graph for divide-and-conquer based parallel SfM
reconstruction. Finally, the performance of the proposed solution has been
verified using three large-scale UAV datasets. The test results demonstrate
that the proposed solution accelerates match pair retrieval with a speedup
ratio ranging from 36 to 108 and improves the efficiency of SfM reconstruction
with competitive accuracy in both relative and absolute orientation
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