Call number: LD2668 .T4 1960 A44

LD2668 .T4 1962 P34

LD2668 .T4 1962 T44

Call number: LD2668 .T4 1965 J79 / Master of Science

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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Background: Studies have shown that children and adolescents who are relatively older than their younger peers have advantages in sports, partly because they are more biologically mature, a relative age effect (RAE). However the occurrence of RAE in physical performance is still somewhat unclear and more knowledge is needed. Aim: The aim of this study was to investigate if there were any RAEs on anthropometric measures and physical performance in adolescents who are 13 years old and active in sports. Methods: 128 subjects (78 boys, 50 girls) from Malmö idrottsakademi, a school with a sports profile, were included in this study. Measurements of height and weight were taken and the physical performance was tested for grip strength, sprint and countermovement jump (CMJ). To analyse RAEs the subjects were divided into three groups (teriles) according to their month of birth. Subjects born in Tertile 1 (Jan-Apr) and Tertile 3 (Sep-Dec) were compared together as well as within and between the sexes with independent t-tests. Results: RAEs were present in height (p=0.01), weight (p=0.01), and grip strength (0.03) where higher values were found in the relatively older subjects. Additionally, if weight was accounted for, RAE was present in CMJ where the relatively younger subjects performed better (p=0.03). Further, when sexes was analysed separately the older boys were taller (p=0.01), heavier (p=0.02), and stronger (p=0.05) compared with the younger boys. The older girls were heavier (p=0.01) compared with the younger girls whereas the younger girls got a higher CMJ weight ratio (p=0.05). Conclusion: RAEs were found on anthropometric measures, but were less clear in physical performance. This indicates that although relatively older adolescents are taller and heavier, they are not always in advantage over their younger peers regarding physical performance.

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This research is concerned with the effects of temperature and frequency on the fatigue crack propagation behaviour. The fatigue behaviour at elevated temperature has been reviewed with emphasis on the mechanisms of propagation proposed to explain the effects of temperature and frequency. The crack propagation characteristics of a single crystal superalloy have been investigated at various temperatures and frequencies. Determination of the fatigue crack propagation rates was combined with the measurement of crack tip plastic zone sizes and observation of the deformation behaviour. At elevated temperature, the fatigue crack propagation rates were determined to be dependent on the frequency of loading. At low and high crack growth rates increased crack propagation rates were associated with higher cycling frequencies. At intermediate crack growth rates, the highest propagation rates were associated with the lowest frequency. Selected area channelling pattern techniques were used to determine the plastic zone sizes and revealed that at high frequencies (>10Hz) the plastic zone sizes at elevated and ambient temperature are similar. With decreasing frequency at elevated temperature creep may lead to increased plastic zone sizes but may also affect the crack tip geometry thereby restricting further effects. At room temperature crack propagation is observed to occur by shear of the γ' precipitate on <110> {111} resulting in {111} crystallographic facets on the fracture surface. At elevated temperature (>6000 C) however, the crack growth mechanism changes and propagation takes place on {100}. Observations of the dislocation structure indicate that deformation is concentrated within the γ matrix. It is proposed that the observed crack propagation in the γ matrix on {100} arises by the constraints imposed by the surrounding γ' precipitate. A model is presented for the frequency dependence of the intermediate crack growth rate in terms of the observed strain gradients within the plastic zone and the achievement of a critical local fracture strain.