73 research outputs found
Improving the flexibility of ship propeller additively manufactured from HDPE/long carbon fibre composite by pre-preg-coating
Classical double-layer atoms: artificial molecules
The groundstate configuration and the eigenmodes of two parallel
two-dimensional classical atoms are obtained as function of the inter-atomic
distance (d). The classical particles are confined by identical harmonic wells
and repel each other through a Coulomb potential. As function of d we find
several structural transitions which are of first or second order. For first
(second) order transitions the first (second) derivative of the energy with
respect to d is discontinuous, the radial position of the particles changes
discontinuously (continuously) and the frequency of the eigenmodes exhibit a
jump (one mode becomes soft, i.e. its frequency becomes zero).Comment: 4 pages, RevTex, 5 ps figures, to appear in Phys.Rev.Let
The Sasol Engineering and Leadership Academy
Contrary to the way it is often portrayed, the average organization or
company is far from being a cold, calculating machine. It is actually a
highly emotive place where interaction with people is a fundamental part
of its ability to perform satisfactorily.
The company, through its employers, expects employees, including new
graduates, to have the ability to cope adequately with this emotive
environment. The graduate is frequently unable to meet this expectation
because he/she has not been developed to do so. Technical knowledge is
his only asset. This deficiency manifests itself in leadership shortcomings,
both intrapersonal and interpersonal. Further analysis reveals a deficiency
in three elements of leadership – self-awareness, oral communication, and
an ability to work cooperatively in teams.
To address these three elements of leadership, Sasol Coal, a subsidiary
of the big petrochemical company in South Africa, sponsored a leadership
programme at the University of Pretoria for their final-year bursary
students in the faculty of Engineering. This programme, the Sasol
Engineering and Leadership Academy (SELA), consisted of a number of
interventions designed to address the three areas of self-awareness, oral
communication, and cooperative behaviour in teams. These interventions
varied from an intrapersonal nature to interpersonal aspects. Psychometric
assessments were followed by experiential modules dealing with the three
constructs.
SELA was evaluated at the end of the year. The results showed a
positive shift in the main constructs of self-awareness, communications,
and cooperation. This was measured quantitatively and qualitatively.
Conclusions were drawn and recommendations for improving the
programme were proposed.http://www.saimm.co.za/journal-papersam201
Phase equilibria and glass transition in colloidal systems with short-ranged attractive interactions. Application to protein crystallization
We have studied a model of a complex fluid consisting of particles
interacting through a hard core and a short range attractive potential of both
Yukawa and square-well form. Using a hybrid method, including a self-consistent
and quite accurate approximation for the liquid integral equation in the case
of the Yukawa fluid, perturbation theory to evaluate the crystal free energies,
and mode-coupling theory of the glass transition, we determine both the
equilibrium phase diagram of the system and the lines of equilibrium between
the supercooled fluid and the glass phases. For these potentials, we study the
phase diagrams for different values of the potential range, the ratio of the
range of the interaction to the diameter of the repulsive core being the main
control parameter. Our arguments are relevant to a variety of systems, from
dense colloidal systems with depletion forces, through particle gels,
nano-particle aggregation, and globular protein crystallization.Comment: 20 pages, 10 figure
The effect of seed traits on geographic variation in body size and sexual size dimorphism of the seed-feeding beetle Acanthoscelides macrophthalmus
Explaining large-scale patterns of variation in body size has been considered a central question in ecology and evolutionary biology because several life-history traits are directly linked to body size. For ectothermic organisms, little is known about what processes influence geographic variation in body size. Changes in body size and sexual size dimorphism (SSD) have been associated with environmental variables, particularly for Bruchinae insects, which feed exclusively on seeds during the larval stage. However, the effect of important seed traits on body size variation has rarely been investigated, and whether SSD varies substantially among populations within bruchine species is poorly known. Using the seed-feeding beetle Acanthoscelides macrophthalmus infesting its host plant Leucaena leucocephala, we investigated whether specific seed traits (hardness, size, water content, carbon/nitrogen ratio, and phenolic content) were determinant in generating geographic variation in body size and SSD of A. macrophthalmus. We also examined the relationships between body size and SSD with latitude and altitude. The body size of both sexes combined was not related to latitude, altitude, and any of the physical and chemical seed traits. However, the female body size tended to vary more in size than the males, generating significant variation in SSD in relation to latitude and altitude. The females were the larger sex at higher latitudes and at lower altitudes, precisely where seed water content was greater. Therefore, our results suggest that water content was the most important seed trait, most severely affecting the females, promoting geographic variation in SSD of A. macrophthalmus.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fed Univ Sao Paulo Unifesp, Lab Ecol Populac LEPOP, Dept Biol Sci, BR-09941510 Sao Paulo, BrazilDepartment of Biological Sciences, Laboratório de Ecologia Populacional (LEPOP), Universidade Federal de São Paulo (UNIFESP), Diadema, São Paulo, 09941‐510 BrazilFAPESP: 12/11612-4Web of Scienc
Genetic parameters for growth, reproductive and maternal traits in a multibreed meat sheep population
The genetic parameters for growth, reproductive and maternal traits in a multibreed meat sheep population were estimated by applying the Average Information Restricted Maximum Likelihood method to an animal model. Data from a flock supported by the Programa de Melhoramento Genético de Caprinos e Ovinos de Corte (GENECOC) were used. The traits studied included birth weight (BW), weaning weight (WW), slaughter weight (SW), yearling weight (YW), weight gain from birth to weaning (GBW), weight gain from weaning to slaughter (GWS), weight gain from weaning to yearling (GWY), age at first lambing (AFL), lambing interval (LI), gestation length (GL), lambing date (LD - number of days between the start of breeding season and lambing), litter weight at birth (LWB) and litter weight at weaning (LWW). The direct heritabilities were 0.35, 0.81, 0.65, 0.49, 0.20, 0.15 and 0.39 for BW, WW, SW, YW, GBW, GWS and GWY, respectively, and 0.04, 0.06, 0.10, 0.05, 0.15 and 0.11 for AFL, LI, GL, LD, LWB and LWW, respectively. Positive genetic correlations were observed among body weights. In contrast, there was a negative genetic correlation between GBW and GWS (-0.49) and GBW and GWY (-0.56). Positive genetic correlations were observed between AFL and LI, LI and GL, and LWB and LWW. These results indicate a strong maternal influence in this herd and the presence of sufficient genetic variation to allow mass selection for growth traits. Additive effects were of little importance for reproductive traits, and other strategies are necessary to improve the performance of these animals
An investigation into the design of a jacket or template oil producing platform to be situated on the Agulhas bank
Thesis (M.Ing.) -- University of Stellenbosch, 1986.Full text to be digitised and attached to bibliographic record
Contributions to the marine use of non-crimp reinforcement by means of strength tests
It has been found that the use of non-crimp reinforcements achieve acceptable levels of engineering parameters such as strength and stiffness when compared with other glass reinforced structures. Therefore, it is concluded that non-crimp reinforcements are suitable materials for boatbuilding since they offer the advantage of production of lighter structures with less work. Tensile and flexural tests were conducted on orthophitalic polyester resin with hand - laid E glass stitched multilayer angle laminae with ten different thicknesses and with five different directions (0degrees, 30degrees, 45degrees, 60degrees, 90degrees). The assessment of the material was made in light of those experiments, and results are presented together with comparison of other reinforcement fibers (mat and woven roving). It is believed that the presented results are of direct use for designers
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