Influence of shear reinforcement corrosion on the performance of under-reinforced concrete beams

The in-service performance of reinforced concrete beams can be severely affected through cor-rosion of the steel reinforcement when it becomes subjected to harsh corrosive environments containing chlo-rides and carbon dioxide. In such instances, corrosion is likely to occur in the steel reinforcement, with the expansive nature of the corrosion products likely to induce cracking and spalling of the concrete. A loss of structural integrity (stiffness) will occur and this can severely influence the serviceability of the member. The purpose of this paper is to investigate the relationship between degree of corrosion and loss of stiffness in corrosion damaged under-reinforced concrete beams. Beams (100mm x 150mm cross section) were subjected to accelerated corrosion in the laboratory and subsequently tested in flexure to failure. The paper reports on the results of these tests and relates the degree of corrosion in the main steel to the percentage loss in stiffness in the concrete beams

One step multiderivative methods for first order ordinary differential equations

A family of one-step multiderivative methods based on Padé approximants to the exponential function is developed. The methods are extrapolated and analysed for use in PECE mode. Error constants and stability intervals are calculated and the combinations compared with well known linear multi-step combinations and combinations using high accuracy Newton-Cotes quadrature formulas as correctors. w926020

The diagnosis of malaria infection using a solid-phase radioimmunoassay for the detection of malaria antigens: Application to the detection of Plasmodium berghei infection in mice

A method has been devised to show that malaria parasites can be detected serologically in infected blood with a high degree of sensitivity. Using a murine malaria model, parasites were demonstrated in a solid-phase radio-immunoassay which measured antibody-binding inhibition. Lysed red blood cells (r.b.c.) were incubated with labelled specific antibody and were then reacted in antigen-coated tubes. The degree of inhibition of antibody binding in the tubes correlated with the level of parasitaemia in the test blood. Using homologous antisera the test detected infection at a level of 1 parasite/million r.b.c. The specificity of the method was shown by comparison of antibody-binding inhibition in normal and infected r.b.c. and in r.b.c. from non-infected mice with induced reticulocytosis. The sensitivity was shown in vitro in tests of serially diluted blood of high parasitaemia and in vivo for the detection of early infection. The presence of antibody in the test blood did not significantly affect the sensitivity of parasite detectio

Host immune response and pathological expression in malaria: possible implications for malaria vaccines

Recent progress in parasite immunobiology has led to the identification of several plasmodial antigens representing the target of the protective antibody response of the infected host. As a consequence, some of these antigens have been envisaged as potential malaria vaccines in man. However, in spite of these achievements, the fine mechanisms which lead to the development of a state of partial protective immunity or to the triggering of immunopathology during malaria infection are not yet fully understood. Thus, it may be appropriate to evaluate the relative importance of individual host immune responsiveness to parasite epitopes involved in the induction of immunity, or of some immunologically mediated adverse reactions such as glomerulonephritis, anaemia, thrombocytopenia, and cerebral syndrom

Influence of steel reinforcement corrosion on the stiffness of simply supported concrete beams

The in-service performance of reinforced concrete beams can be severely affected through cor-rosion of the steel reinforcement when it becomes subjected to harsh corrosive environments containing chlo-rides and carbon dioxide. In such instances, corrosion is likely to occur in the steel reinforcement, with the expansive nature of the corrosion products likely to induce cracking and spalling of the concrete. A loss of structural integrity (stiffness) will occur and this can severely influence the serviceability of the member. The purpose of this paper is to investigate the relationship between degree of corrosion and loss of stiffness in corrosion damaged under-reinforced concrete beams. Beams (100mm x 150mm cross section) were subjected to accelerated corrosion in the laboratory and subsequently tested in flexure to failure. The paper reports on the results of these tests and relates the degree of corrosion in the main steel to the percentage loss in stiffness in the concrete beams

Sub-gap conductance in ferromagnetic-superconducting mesoscopic structures

We study the sub-gap conductance of a ferromagnetic mesoscopic region attached to a ferromagnetic and a superconducting electrode by means of tunnel junctions. In the absence of the exchange field, the ratio $r= \gamma / \epsilon_T$ of the two tunnel junction resistances determines the behaviour of the sub-gap conductance which possesses a zero-bias peak for $r\gg 1$ and for $r\ll 1$ a peak at finite voltage. We show that the inclusion of the exchange field leads to a peak splitting for $r\ll 1$, while it shifts the zero-bias anomaly to finite voltages for $r\gg 1$.Comment: 5 pages revte

Self consistent theory of unipolar charge-carrier injection in metal/insulator/metal systems

A consistent device model to describe current-voltage characteristics of metal/insulator/metal systems is developed. In this model the insulator and the metal electrodes are described within the same theoretical framework by using density of states distributions. This approach leads to differential equations for the electric field which have to be solved in a self consistent manner by considering the continuity of the electric displacement and the electrochemical potential in the complete system. The model is capable of describing the current-voltage characteristics of the metal/insulator/metal system in forward and reverse bias for arbitrary values of the metal/ insulator injection barriers. In the case of high injection barriers, approximations are provided offering a tool for comparison with experiments. Numerical calculations are performed exemplary using a simplified model of an organic semiconductor.Comment: 21 pages, 8 figure

Changing times in England: the influence on geography teachers’ professional practice

School geography in England has been characterised as a pendulum swinging between policies that emphasise curriculum and pedagogy alternately. In this paper, I illustrate the influence of these shifts on geography teacher's professional practice, by drawing on three “moments” from my experience as a student, teacher and teacher educator. Barnett's description of teacher professionalism as a continuous project of “being” illuminates how geography teachers can adapt to competing influences. It reflects teacher professionalism as an unfinished project, which is responsive, but not beholden, to shifting trends, and is informed by how teachers frame and enact policies. I argue that recognising these contextual factors is key to supporting geography teachers in “being” geography education professionals. As education becomes increasingly competitive on a global scale, individual governments are looking internationally for “solutions” to improve educational rankings. In this climate, the future of geography education will rest on how teachers react locally to international trends. Geography teacher educators can support this process by continuing to inform the field through meaningful geography education research, in particular in making the contextual factors of their research explicit. This can be supported through continued successful international collaboration in geography education research

Space Station Freedom automation and robotics: An assessment of the potential for increased productivity

This report presents the results of a study performed in support of the Space Station Freedom Advanced Development Program, under the sponsorship of the Space Station Engineering (Code MT), Office of Space Flight. The study consisted of the collection, compilation, and analysis of lessons learned, crew time requirements, and other factors influencing the application of advanced automation and robotics, with emphasis on potential improvements in productivity. The lessons learned data collected were based primarily on Skylab, Spacelab, and other Space Shuttle experiences, consisting principally of interviews with current and former crew members and other NASA personnel with relevant experience. The objectives of this report are to present a summary of this data and its analysis, and to present conclusions regarding promising areas for the application of advanced automation and robotics technology to the Space Station Freedom and the potential benefits in terms of increased productivity. In this study, primary emphasis was placed on advanced automation technology because of its fairly extensive utilization within private industry including the aerospace sector. In contrast, other than the Remote Manipulator System (RMS), there has been relatively limited experience with advanced robotics technology applicable to the Space Station. This report should be used as a guide and is not intended to be used as a substitute for official Astronaut Office crew positions on specific issues

Effective range function below threshold

We demonstrate that the kernel of the Lippmann-Schwinger equation, associated with interactions consisting of a sum of the Coulomb plus a short range nuclear potential, below threshold becomes degenerate. Taking advantage of this fact, we present a simple method of calculating the effective range function for negative energies. This may be useful in practice since the effective range expansion extrapolated to threshold allows to extract low-energy scattering parameters: the Coulomb-modified scattering length and the effective range.Comment: 14 pages, 1 figur