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The effect of weld residual stresses and their re-distribution with crack growth during fatigue under constant amplitude loading
In this work the evolution of the residual stresses in a MIG-welded 2024-T3 aluminium alloy M(T) specimen during in situ fatigue crack growth at constant load amplitude has been measured with neutron diffraction. The plastic relaxation and plasticity-induced residual stresses associated with the fatigue loading were found to be small compared with the stresses arising due to elastic re-distribution of the initial residual stress field. The elastic re-distribution was modelled with a finite element simulation and a good correlation between the experimentally-determined and the modelled stresses was found. A significant mean stress effect on the fatigue crack growth rate was seen and this was also accurately predicted using the measured initial residual stresses
Using Synthetic Aperture Radar to Define Spring Breakup on the Kuparuk River, Northern Alaska
Spring runoff measurements of Arctic watersheds are challenging given the remote location and the often dangerous field conditions. This study combines remote sensing techniques and field measurements to evaluate the applicability of synthetic aperture radar (SAR) to defining spring breakup of the braided lower Kuparuk River, North Slope, Alaska. A statistical analysis was carried out on a time series (2001â10) of SAR images acquired from the European Remote-Sensing Satellite (ERS-2) and the Canadian RADARSAT satellite, as well as on measured runoff. On the basis of field information, the SAR images were separated into pre-breakup, breakup, and post-breakup periods. Three variables were analyzed for their suitability to bracket the river breakup period: image brightness, variance in brightness over the river length, and a sum of rank order change analysis. Variance in brightness was found to be the most reliable indicator. A combined use of that variance and sum of rank order change appeared promising when enough images were available. The temporal resolution of imagery served as the major limitation in constraining the timing of the hydrologic event. Challenges associated with spring runoff monitoring and the sensitive nature of SAR likely resulted in an earlier detection of surficial changes by the remote sensing technique compared to the field runoff observations. Given a sufficient temporal resolution, SAR imagery has the potential to improve the spatiotemporal monitoring of Arctic watersheds for river breakup investigations.La mesure de lâĂ©coulement printanier des bassins hydrographiques de lâArctique nâest pas facile Ă rĂ©aliser en raison de lâĂ©loignement ainsi quâen raison des conditions souvent dangereuses qui ont cours sur le terrain. Cette Ă©tude fait appel Ă des techniques de tĂ©lĂ©dĂ©tection de mĂȘme quâaux mesures prises sur le terrain pour Ă©valuer lâapplicabilitĂ© du radar Ă synthĂšse dâouverture SAR pour dĂ©finir la dĂ©bĂącle printaniĂšre de la basse riviĂšre Kuparuk anastomosĂ©e sur la North Slope de lâAlaska. Lâanalyse statistique dâune sĂ©rie temporelle (2001-2010) dâimages SAR acquises Ă partir du satellite europĂ©en de tĂ©lĂ©dĂ©tection (ERS-2) et du satellite canadien RADARSAT ainsi que des Ă©coulements mesurĂ©s a Ă©tĂ© effectuĂ©e dans le cadre de cette Ă©tude. DâaprĂšs les renseignements recueillis sur le terrain, les images SAR ont Ă©tĂ© divisĂ©es en fonction de la pĂ©riode prĂ©cĂ©dant la dĂ©bĂącle, de la pĂ©riode de la dĂ©bĂącle mĂȘme et de la pĂ©riode suivant la dĂ©bĂącle. Trois variables ont Ă©tĂ© analysĂ©es afin de dĂ©terminer si elles permettaient dâisoler la pĂ©riode de la dĂ©bĂącle de la riviĂšre, soit la luminance de lâimage, la variance de la luminance en fonction de la longueur de la riviĂšre et la somme de lâanalyse des changements de classement suivant le rang. La variance de la luminance sâest avĂ©rĂ©e lâindicateur le plus fiable. Lâutilisation conjointe de cette variance et de la somme des changements de classement suivant le rang sâavĂ©raient prometteuse lorsque le nombre dâimages Ă©tait suffisant. La rĂ©solution temporelle de lâimagerie a constituĂ© la plus grande limitation pour contraindre la temporisation de lâĂ©vĂ©nement hydrologique. Les dĂ©fis liĂ©s Ă la surveillance de lâĂ©coulement printanier et la nature sensible du SAR ont vraisemblablement donnĂ© lieu Ă la dĂ©tection prĂ©coce des changements superficiels au moyen de la technique de tĂ©lĂ©dĂ©tection comparativement aux observations mĂȘmes de lâĂ©coulement printanier. Moyennant une rĂ©solution temporelle suffisante, lâimagerie SAR pourrait permettre dâamĂ©liorer la surveillance spatiotemporelle des bassins hydrographiques de lâArctique en vue de lâĂ©tude des dĂ©bĂącles printaniers
The Static Failure of Adhesively Bonded Metal Laminate Structures: A Cohesive Zone Approach
Data on distribution, ecology, biomass, recruitment, growth, mortality and productivity of the West African bloody cockle Anadara senilis were collected at the Banc d'Aguuin, Mauritania, in early 1985 and 1986. Ash-free dry weight appeared to be correlated best with shell height. A. senilis was abundant on the tidal flats of landlocked coastal bays, but nearly absent on the tidal flats bordering the open sea. The average biomass for the entire area of tidal flats was estimated at 5.5 g·mâ2 ash-free dry weight. The A. senilis population appeared to consist mainly of 10 to 20-year-old individuals, showing a very slow growth and a production: biomass ratio of about 0.02 yâ1. Recruitment appeared negligible and mortality was estimated to be about 10% per year. Oystercatchers (Haematopus ostralegus), the gastropod Cymbium cymbium and unknown fish species were responsible for a large share of this. The distinction of annual growth marks permitted the assessment of year-class strength, which appeared to be correlated with the average discharge of the river Senegal. This may be explained by assuming that year-class strength and river discharge both are correlated with rainfall at the Banc d'Arguin.
Affect in mathematics education
There are two different uses for the word âaffectâ in behavioral sciences. Often it is used as an overarching umbrella concept that covers attitudes, beliefs, motivation, emotions, and all other noncognitive aspects of human mind. In this article, however, the word affect is used in a more narrow sense, referring to emotional states and traits. A more technical definition of emotions, states, and traits will follow later.Peer reviewe
Teacher Questioning in Problem Solving in Community College Algebra Classrooms
In this chapter, we focus on the ways two community college instructors worked with students to demonstrate the solution of contextualized algebra problems in their college algebra lessons. We use two classroom episodes to illustrate how they sought to elicit students' mathematical ideas of algebraic topics, attending primarily to teachers' questioning approaches. We found that the instructors mostly asked questions of lower cognitive demand and used a variety of approaches to elicit the mathematical ideas of the problems, such as using examples relevant to the students and dividing the problems into smaller tasks, that together help identify a solution. We conclude by offering considerations for instruction at community colleges and potential areas for professional development
Mathematical talent in Braille code pattern finding and invention
The recognition of patterns and creativity are two characteristics associated with mathematical
talent. In this study, we analyzed these characteristics in a group of 37 mathematically talented
students. The students were asked to find the pattern the Braille code had been built upon and
reinvent it with the aim of making its mathematical language become more functional.
Initially, the students were unable to identify the formation pattern of Braille, but after
experiencing the difficulties that blind people face when reading it, they recognized the
generating element and the regularity. The results were in contrast with those of a control
group, and it is noted that the students with mathematical talent were more effective in using
visualization to identify the regularity of the pattern and their invention proposals were more
sophisticated and used less conventional mathematical content.This research is part of the R+D+I project EDU2015-
69,731-R (Spanish Government/MinEco and ERDF)
Genetic risk and a primary role for cell-mediated immune mechanisms in multiple sclerosis.
Multiple sclerosis is a common disease of the central nervous system in which the interplay between inflammatory and neurodegenerative processes typically results in intermittent neurological disturbance followed by progressive accumulation of disability. Epidemiological studies have shown that genetic factors are primarily responsible for the substantially increased frequency of the disease seen in the relatives of affected individuals, and systematic attempts to identify linkage in multiplex families have confirmed that variation within the major histocompatibility complex (MHC) exerts the greatest individual effect on risk. Modestly powered genome-wide association studies (GWAS) have enabled more than 20 additional risk loci to be identified and have shown that multiple variants exerting modest individual effects have a key role in disease susceptibility. Most of the genetic architecture underlying susceptibility to the disease remains to be defined and is anticipated to require the analysis of sample sizes that are beyond the numbers currently available to individual research groups. In a collaborative GWAS involving 9,772 cases of European descent collected by 23 research groups working in 15 different countries, we have replicated almost all of the previously suggested associations and identified at least a further 29 novel susceptibility loci. Within the MHC we have refined the identity of the HLA-DRB1 risk alleles and confirmed that variation in the HLA-A gene underlies the independent protective effect attributable to the class I region. Immunologically relevant genes are significantly overrepresented among those mapping close to the identified loci and particularly implicate T-helper-cell differentiation in the pathogenesis of multiple sclerosis
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