1,805 research outputs found
A variational algorithm for the detection of line segments
In this paper we propose an algorithm for the detection of edges in images
that is based on topological asymptotic analysis. Motivated from the
Mumford--Shah functional, we consider a variational functional that penalizes
oscillations outside some approximate edge set, which we represent as the union
of a finite number of thin strips, the width of which is an order of magnitude
smaller than their length. In order to find a near optimal placement of these
strips, we compute an asymptotic expansion of the functional with respect to
the strip size. This expansion is then employed for defining a (topological)
gradient descent like minimization method. As opposed to a recently proposed
method by some of the authors, which uses coverings with balls, the usage of
strips includes some directional information into the method, which can be used
for obtaining finer edges and can also result in a reduction of computation
times
A Finite Element Procedure for Three-dimensional Analyses of Thermopiezoelectric Structures in Static Applications
The development and application ofsmart structures and smart composite materials require eflicient numerical tools to evaluate the thermopiezoelectric behavior and stress state. In this paper, finite element techniques are suggested for three-dimensional coupled thermo-electromechanical static analyses. The actual thermopiezoelectric responses subjected to thermal loadings can be determined by adopting a procedure TPESAP. The detailed implementation is presented with emphasis on the integration with software ABAQUS. Several verification example problems are discussed, including the benchmark problem ofafive-layer hybrid plate
A Reconstruction Algorithm for Photoacoustic Imaging based on the Nonuniform FFT
Fourier reconstruction algorithms significantly outperform conventional
back-projection algorithms in terms of computation time. In photoacoustic
imaging, these methods require interpolation in the Fourier space domain, which
creates artifacts in reconstructed images. We propose a novel reconstruction
algorithm that applies the one-dimensional nonuniform fast Fourier transform to
photoacoustic imaging. It is shown theoretically and numerically that our
algorithm avoids artifacts while preserving the computational effectiveness of
Fourier reconstruction.Comment: 22 pages, 8 figure
Use of cystatin C to inform metformin eligibility among adult veterans with diabetes.
AimsRecommendations for metformin use are dependent on eGFR category: eGFR >45 ml/min/1.73 m2 - "first-line agent"; eGFR 30-44 - "use with caution"; eGFR<30 - "do not use". Misclassification of metformin eligibility by creatinine-based MDRD GFR estimates (eGFRcr) may contribute to its misuse. We investigated the impact of cystatin c estimates of GFR (eGFRcys) on metformin eligibility.MethodsIn a consecutive cohort of 550 Veterans with diabetes, metformin use and eligibility were assessed by eGFR category, using eGFRcr and eGFRcys. Discrepancy in eligibility was defined as cases where eGFRcr and eGFRcys categories (<30, 30-44, 45-60, and >60 ml/min/1.73 m2) differed with an absolute difference in eGFR of >5 ml/min/1.73 m2. We modeled predictors of metformin use and eGFR category discrepancy with multivariable relative risk regression and multinomial logistic regression.ResultsSubjects were 95% male, median age 68, and racially diverse (45% White, 22% Black, 11% Asian, 22% unknown). Metformin use decreased with severity of eGFRcr category, from 63% in eGFRcr >60 to 3% in eGFRcr <30. eGFRcys reclassified 20% of Veterans into different eGFR categories. Factors associated with a more severe eGFRcys category compared to eGFRcr were older age (aOR = 2.21 per decade, 1.44-1.82), higher BMI (aOR = 1.04 per kg/m2, 1.01-1.08) and albuminuria >30 mg/g (aOR = 1.81, 1.20-2.73).ConclusionsMetformin use is low among Veterans with CKD. eGFRcys may serve as a confirmatory estimate of kidney function to allow safe use of metformin among patients with CKD, particularly among older individuals and those with albuminuria
Nonparametric instrumental regression with non-convex constraints
This paper considers the nonparametric regression model with an additive
error that is dependent on the explanatory variables. As is common in empirical
studies in epidemiology and economics, it also supposes that valid instrumental
variables are observed. A classical example in microeconomics considers the
consumer demand function as a function of the price of goods and the income,
both variables often considered as endogenous. In this framework, the economic
theory also imposes shape restrictions on the demand function, like
integrability conditions. Motivated by this illustration in microeconomics, we
study an estimator of a nonparametric constrained regression function using
instrumental variables by means of Tikhonov regularization. We derive rates of
convergence for the regularized model both in a deterministic and stochastic
setting under the assumption that the true regression function satisfies a
projected source condition including, because of the non-convexity of the
imposed constraints, an additional smallness condition
A Dynamic Programming Solution to Bounded Dejittering Problems
We propose a dynamic programming solution to image dejittering problems with
bounded displacements and obtain efficient algorithms for the removal of line
jitter, line pixel jitter, and pixel jitter.Comment: The final publication is available at link.springer.co
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