Carleton University

About: Carleton University is a education organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 15852 authors who have published 39650 publications receiving 1106610 citations.

Exploring the Link Between Giftedness and Self-Concept

Abstract: We explored three broad issues in the article. First, do gifted and nongifted children differ in their self-concepts? Second, what are the effects on the self-concept of labeling the child as gifted? Third, are there any effects on self-concept of placing a child in special programs for the gifted? The review begins with a discussion of theoretical and methodological issues associated with the self-concept and giftedness constructs. This is followed by a meta-analysis of studies bearing on the three issues. Two types of studies are reviewed: (a) cases where gifted and average students are compared in terms of the self-concept and (b) studies in which gifted children are exposed to differential programming and the effects on self-concept explored. The studies indicated generally higher academic self-concepts for gifted students, but otherwise the results of the investigations were highly variable. The article concludes with a discussion of research and practical implications.

Tansley Review No. 22 What becomes of the transpiration stream

Abstract: SUMMARY Changes of view on the course of the transpiration stream beyond the veins in leaves are followed from the imbibition theory of Sachs, through the (symplastic) endosmotic theory of Pfeffer (which prevailed almost unquestioned until the late 1930s), to Strugger's experiments with fluorescent dye tracers and the epifluorescence microscope. This latter work persuaded many to return to the apoplastic-(wall)-path viewpoint, which, despite early and late criticisms that were never rebutted, is still widely held. Tracer experiments of the same kind are still frequently published without consideration of the evidence that they do not reveal the paths of water movement. Experiments on rehydration kinetics of leaves have not produced unequivocal evidence for either path. The detailed destinies of the solutes that reach the leaf in the transpiration stream have received little attention. Consideration of physical principles governing flow and evaporation in a transpiring leaf emphasizes that: (1) Diffusion over interveinal distances at the rates in water will account for substantial solute movement in a few minutes, even in the absence of flow. (2) Diffusion can occur also against opposing now. (3) Volume fluxes in veins are determined by the diameter of the largest leaves examined contain high conductance supply veins which are tapped into by low-conductance distributing veins. (4) Edges and teeth of leaves will be places of especially rapid evaporation, and they often have high-conductance veins leading to them. (5) Solutes in the stream will tend to accumulate at leaf margins. On the basis of recent work, the view is maintained that the water of the stream enters the symplast through cell membranes very close to tracheary elements. Also, that this occurs locally over a small area of membrane. Many solutes in the stream are left outside in the apoplast. This produces regions of high solute concentration in the apoplast and an enrichment of solutes in the stream as it perfuses the leaf. Solutes that enter the symplast are not so easily tracked. Suggestions about where some of them may go can be gained from a fluorescent probe that identifies particular cells (scavenging cells) as having H+-ATPase porter systems to scrub selected solutes from the stream. Unpublished case-histories are presented which illustrate many aspects of these processes and principles. These are: (1) Maize leaf veins, where the symplastic water path starts at the parenchyma sheath; (2) Lupin veins, where the symplastic path starts at the bundle sheath and where solutes are concentrated in blind terminations; (3) The edges of maize leaves where flow is enhanced by a large vein (open to the apoplast), and solutes are deposited in the apoplast by evaporation; (4) Poplar leaf teeth, which receive strong flows, and where the epithem cells are scavenging cells; (5) Mimosa leaf marginal hairs, which have scavenging cells at their base; (6) Active hydathodes, whose epithem cells are scavenging cells; (7) Pine needle transfusion tissue, which is a site of both solute enrichment (in the tracheids), and scavenging (in the parenchyma); (8) Estimates are made of diffusion coefficients of a solute both along and at right angles to the major diffusive pathway in wheat leaves. The first is 1000 times the second, but is 1/100 of free diffusion in water. Five general themes of the behaviour and organization of the transpiration stream are induced from the facts reviewed. These are: (1) The stream is channelled into courses of graded intensities by the interplay of the physical forces with the anatomical features, each course with a distinct contribution to the processing of the stream. (2) Water enters the symplast at precise locations as close as possible to the tracheary elements. (3) As the stream moves through the leaf its solute concentration is enriched many-fold at predictable sites. (4) Solutes excluded from the symplast diffuse from these sources of high concentration in specially formed wall paths, in precise patterns, at rates which can be measured, and which are low compared with diffusion in water. (5) Other solutes permeate the symplast, often over the surfaces of groups of cells which are organized into recognized structural features.

An Investigation of Risk and Protective Factors in a Sample of Youthful Offenders

Abstract: The study explored a set of potential risk and protective factors in relation to criminal activity and adjustment with a group of delinquent youths. The results indicated, first, that risk variables reflecting family relationship and parenting problems were associated with heightened rates of re-offending and lower overall adjustment. Second, the presence of protective factors relating to positive peer relations, good school achievement, positive response to authority and effective use of leisure time was associated with more positive outcomes with controls for the risk variables. Third, there was no evidence of interaction between risk and protective factors; the latter operated similarly at low and high levels of risk. These results are discussed in terms of their theoretical and applied significance.

Persevering with Positivity and Purpose: An Examination of Purpose Commitment and Positive Affect as Predictors of Grit

Abstract: Grit, defined as a passion and perseverance for one’s goals, has been consistently demonstrated as an adaptive resource across multiple domains. Less explored, however, are the correlates of and sources from which grit is derived. The current studies examined two plausible candidates for promoting grit, positive affect and commitment to a purpose, using college student samples from Canada and the United States. Study 1 confirmed our predictions that grittier students tended to report greater positive affect and purpose commitment, and demonstrated that these variables appear to be unique and independent predictors of grit. Study 2 examined these claims using two-wave data collected across a semester, and found that while both purpose and positive affect were initially correlated with grit, only initial levels of purpose predicted grit at wave two. In other words, having a life direction may help more than positive affect when predicting who is likely to become grittier over a college semester. Implications of these findings are discussed.

Creep and drying shrinkage characteristics of concrete produced with coarse recycled concrete aggregate

Abstract: Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete.