Empowering a society of future users of information technology: a longitudinal study of an application in early education

This paper presents a six-year study of the use of computers in a Greek primary school, based on the premise that, in contrast to current technocentric views regarding the use of information technology in the Greek educational system, computers can be used as tools for self-enhancement. The aim of the school project was to infuse a child-centred pedagogy, through the learning of Logo programming, into the whole of the school's society, i.e. all children and all teachers. Within this context, we have identified and explored how children may learn programming through a process of forming ‘naive’ or locally applicable theorems concerning key programming ideas such as the use of primitives, structuring a problem by means of writing procedures, and constructing and working with generalised notional objects by means of defining procedures with variable inputs. We discuss the emerging interrelated educational and technological aspects concerning this kind of learning, and then set these against the challenge to exploit the developing technology further in order to design expressive media of increasing flexibility and power, and to focus on specific learning domains.     

A Framework for Providing User Level Quality of Service Guarantees in Multi-Class Rate Adaptive Systems

The problem of channel sharing by rate adaptive streams belonging to various classes is considered. Rate adaptation provides the opportunity for accepting more connections by adapting the bandwidth of connections that are already in the system. However, bandwidth adaptation must be employed in a careful manner in order to ensure that (a) bandwidth is allocated to various classes in a fair manner (system perspective) and (b) bandwidth adaptation does not affect adversely the perceived user quality of the connection (user quality). The system perspective aspect has been studied earlier. This paper focuses on the equally important user perspective. It is proposed to quantify user Quality of Service (QoS) through measures capturing short and long-term bandwidth fluctuations that can be implemented with the mechanisms of traffic regulators, widely used in networking for the purpose of controlling the traffic entering or exiting a network node. Furthermore, it is indicated how to integrate the user perspective metrics with the optimal algorithms for system performance metrics developed earlier by the authors. Simulation results illustrate the effectiveness of the proposed framework.

Rheological characterization of okra pectins

Polysaccharides from okra pods (Abelmoschus esculentus) were extracted using a sequential extraction protocol and compared with a simple extraction at pH 6. Rheological properties of three okra extracts were then investigated by means of molecular weight determination, dilute solution rheology, steady shear and oscillatory rheological measurements. The extraction protocols resulted in extracts of relatively high purity and multimodal molecular weight distribution. Furthermore, molecular parameters of the isolated biopolymers such as intrinsic viscosity, Huggins constant, critical concentration and coil overlap parameter were calculated from dilute solution viscometry. Investigation of the generalized flow behaviour using a modified Cross equation and Cox–Merz plots showed evidence that as concentration increases specific interactions start taking place among the polymeric chains that modify the rheological behaviour of the extracts. The change in the rheological behaviour could not only be explained by differences in the molecular weight of the samples but also should be attributed to the fine structure of the chains that are obtained under the different extraction protocols. Present investigation shows that further optimization of such protocols may result in polysaccharide fractions with specific rheological properties.     

Lateral bearing capacity of rigid piles near clay slopes

Analytical equations were derived to determine the undrained lateral bearing capacity of rigid piles in cohesive soil. Piles in level ground and piles placed at a distance from the crest of a slope were examined, taking account of the effect of the adhesion at the pile–soil interface. The derived analytical solutions were used to develop charts relating the lateral pile capacity to the pile length/diameter ratio, the pile–soil adhesion, the distance of the point of load application from the ground to the pile diameter ratio, the inclination of the slope and the distance of the pile from the crest of the slope to the pile diameter ratio. They were also used to derive a reduction factor which, when multiplied by the lateral bearing capacity for level ground, gives the bearing capacity of the same pile near a slope. In addition, a critical non-dimensional distance between the pile and the crest of the slope, at which the bearing capacity approaches that for a level ground, was determined. The bearing capacity charts obtained for level ground were compared to the classic Broms' charts and to others derived using several different lateral earth pressure distributions along the pile. Comparisons were also made between the results of the proposed method for piles near slopes and those obtained from charts based on upper bound calculations. Finally, the proposed new method was validated through a comparison with the results of a large number of pile load tests, in which a remarkable agreement was observed between the analytical results and the measurements.     

Moving punch on a highly orthotropic elastic layer

Summary An analytical solution was given to the problem of a long rigid punch moving rapidly on a strip of a highly orthotropic material. This elastic layer rests in turn on a rigid frictionless foundation. Obviously, the problem presents a lot of interest from the view-point both of geophysical and mechanical sciences. The solution was effected by means of integral transforms and the Wiener-Hopf technique. Asymptotic results were obtained valid near the edge of the moving punch.With 3 Figures     

THE COUPLED THERMOELASTICITY PROBLEM OF THE TRANSIENT MOTION OF A LINE HEAT/MECHANICAL SOURCE OVER A HALF-SPACE

Abstract

A procedure is developed for obtaining fundamental thermoelastic two-dimensional solutions for thermal and/or mechanical loadings moving unsteadily over the surface of a half-space. These solutions are within the bounds of the transient coupled thermoelastodynamic theory of M. A. Biot. The concentrated line loadings (sources) are suddenly applied on the surface of the half-space and then move in a fixed direction with nonuniform speed. The problem is of basic interest in contact mechanics and tribology, and it is especially related to the well-known heat checking problem (thermo-mechanical cracking in an unflawed half-space material from high-speed asperity excitations). Here, an exact and general formulation is considered and explicit results are given for some special cases. These results are obtained by generating asymptotic expressions from one- and two-sided Laplace transforms and then performing the inversions in an exact manner.     

Proximal locking screw repositioning in reconstruction femoral nails

Chard (Beta vulgaris L. var. cicla) is one of the plants used as hypoglycaemic agent by diabetics in Turkey and it has been reported to reduce blood glucose. The purpose of this study was to investigate the effect of feeding chard on diabetes induced impairments in rat skins. Uncontrolled induced diabetes caused significant increases in nonenzymatic glycosylation of skin proteins, lipid peroxidation and blood glucose. Administration of chard extract inhibited these effects except the increase in lipid peroxidation. SDS-polyacrylamide gel electrophoresis revealed no significant differences in any protein bands between any of the groups. The data indicate that the use of chard may be effective in preventing or at least retarding the development of some diabetic complications.     

QoS provisioning and tracking fluid policies in input queueingswitches

The concept of tracking fluid policies by packetized policies is extended to input queueing switches. It is considered that the speedup of the switch is one. One of the interesting applications of the tracking policy in TDMA satellite switches is elaborated. For the special case of 2×2 switches, it is shown that a tracking nonanticipative policy always exists. It is found that, in general, nonanticipative policies do not exist for switches with more than two input and output ports. For the general case of N×N switches, a heuristic tracking policy is provided. The heuristic algorithm is based on two notions: port tracking and critical links. These notions can be employed in the derivation of other heuristic tracking policies as well. Simulation results show the usefulness of the heuristic algorithm and the two basic concepts it relies on     

Determination of SIF in a cracked plane orthotropic strip by the Wiener-Hopf technique

The stress intensity factor for a long cracked strip was determined within the context of the linear orthotropic clasticity. The body had the form of an infinite strip containing a semi-infinite crack at the middle distance of the strip faces. Fourier transforms in combination with the Wiener-Hopf technique were employed to evaluate asymptotically the cleavage stress and its intensity at the crack tip.

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Résumé On détermine le facteur d'intensité d'entaille relatif à une longue bande fissurée, dans un contexte d'élasticité linéaire et orthotrope. On considère un corps ayant la forme d'une bande infinie et comportant une fissure semi-infinie à mi-distance des faces de la bande. On recourt à une transformée de Fourier en combinaison avec la technique de Wiener-Hopf pour évaluer par voie asymptotique la tension de clivage et son intensité à l'extrémité de la fissure.