课程文献中心 更多>>

关键词： 3D-DIC   crack tip field   curved circumferential crack   differential geometry   non-planar surface  

摘要： This paper describes a novel differential geometry method that is used in combination with 3D digital image correlation (3D-DIC) for crack tip field characterization on non-planar (curved) surfaces. The proposed approach allows any of the two-dimensional crack tip field models currently available in the literature to be extended to the analysis of a 3D developable surface with zero Gaussian curvature. The method was validated by analyzing the crack tip displacement fields on hollow thin-walled cylindrical specimens, manufactured from either 304L or 2024-T3 alloy that contained a central circumferential crack. The proposed approach was checked via a comparison between experimentally measured displacement fields (3D-DIC) and those reconstructed from a modified 2D crack tip model (utilizing either 2, 3, or 4 terms of the William's expansion series) and implementing a 3D geometrical correction. Further validation was provided by comparing model-derived stress intensity factors with values provided by empirical correlations.

关键词： Calculus of tensors.   Geometry   Differential.  

ISBN: (数字)9781119795698 ISBN: (纸本)9781119795629

摘要： INTRODUCTION TO DIFFERENTIAL GEOMETRY WITH TENSOR APPLICATIONS This is the only volume of its kind to explain, in precise and easy-to-understand language, the fundamentals of tensors and their applications in differential geometry and analytical mechanics with examples for practical applications and questions for use in a course setting.

关键词： Alphaproteobacteria   partitioning system   plasmid evolution   plasmid segregation   repABC  

摘要： The repABC replication/partitioning loci are widespread in extrachromosomal replicons of Alphaproteobacteria. They are evolutionarily diverse, subject to multi-layer self-regulation, and are responsible for the maintenance of different types of replicons, such as plasmids (e.g., Agrobacterium pTi and pRi tumorigenic and rhizogenic plasmids), megaplasmids (e.g., Sinorhizobium pSymA and pSymB) and essential chromids (e.g., secondary chromosomes of Agrobacterium, Brucella and Rhodobacter). Partitioning systems ensure the stable inheritance of bacterial low-copy-number replicons, such as chromosomes, chromids, and megaplasmids. These loci consist of two genes encoding partition proteins A and B, and at least one parS centromere-like sequence. In chromids and megaplasmids, partitioning systems are often located in the vicinity of replication systems. An extreme example of this co-localization are alphaproteobacterial repABC replicons, where the partition (repAB) and replication (repC) genes form a single operon, with parS sequences usually positioned in close proximity to these genes. In this study, we characterized a more complex repABC system found in Paracoccus aminophilus (Rhodobacterales) megaplasmid pAMI4 (438 kb). Besides the repABC operon with a single parS site, this replicon has a 2-kb non-coding locus positioned 11.5 kb downstream of repC, which contains three additional parS repeats (3parS). We demonstrated that 3parS is bound by partition protein B in vitro and is essential for proper pAMI4 partitioning in vivo. In search of similar loci, we conducted a comparative analysis of parS distribution in other repABC replicons. This revealed different patterns of parS localization in Rhodobacterales and Rhizobiales. However, in both these taxonomic orders, parS sites are almost always located inside or close to the repABC operon. No other 3parS-like loci were found in the closest relatives of pAMI4. Another evolutionarily-independent example of such a locus was ide

摘要： Background and Objectives This prospective study sought to determine the association of modifiable/nonmodifiable components included in the Cardiovascular Risk Factors, Aging, and Incidence of Dementia (CAIDE) risk score with hippocampal volume (HV) loss and episodic memory (EM) decline in cognitively normal (CN) older adults classified as brain beta-amyloid (A beta) negative (A beta-) or positive (A beta+). Methods Australian Imaging, Biomarkers and Lifestyle study participants (age 58-91 years) who completed >= 2 neuropsychological assessments and a brain A beta PET scan (n = 592) were included in this study. We computed the CAIDE risk score (age, sex, APOE epsilon 4 status, education, hypertension, body mass index [BMI], hypercholesterolemia, physical inactivity) and a modifiable CAIDE risk score (CAIDE-MR;education, hypertension, BMI, hypercholesterolemia, physical inactivity) for each participant. A beta+ was classified using Centiloid >25. Linear mixed models assessed interactions between each CAIDE score, A beta group, and time on HV loss and EM decline. Age, sex, and APOE epsilon 4 were included as separate predictors in CAIDE-MR models to assess differential associations. Exploratory analyses examined relationships between individual modifiable risk factors and outcomes in A beta- cognitively normal (CN) adults. Results We observed a significant A beta group x CAIDE x time interaction on HV loss (beta [SE] = -0.04 [0.01];p < 0.000) but not EM decline (beta [SE] = -2.33 [9.96];p = 0.98). Decomposition revealed a significant CAIDE x time interaction in A beta+ participants only. When modifiable/nonmodifiable CAIDE components were considered separately, we observed a significant A beta group x CAIDE-MR x time interaction on EM decline only (beta [SE] = 3.03 [1.18];p = 0.01). A significant CAIDE-MR score x time interaction was observed in A beta- participants only. Significant interactions between APOE epsilon 4 and age x time on HV loss and EM decline were obs

关键词： Integral representation formulae   Polyharmonic operator   Differential inequalities  

摘要： We obtain integral representation formulae for functions u is an element of L-loc(1) (R-N) which satisfy P(-Delta)u = mu in the sense of distributions in R-N, where mu is a positive Radon measure on R-N and P(z) = z(m)(z(sigma) + a(sigma-1)z(sigma-1) + . . . + a(1)z+ a(0)) is a nonconstant real polynomial whose roots belong to the interval (-infinity, 0], m, sigma >= 0, N > 2m. Further, we apply these results to a number of nonhomogeneous higher order differential inequalities. (C) 2022 The Author(s). Published by Elsevier Inc.