Magnetotunnelling spectroscopy: an experimental tool for studying chaos in quantum transport

Resonant tunnelling spectroscopy is used to investigate the energy level spectrum of a wide potential well in the presence of a large magnetic field oriented at angles θ between 0° and 90° to the normal to the plane of the well. In the tilted field geometry, the current-voltage characteristics exhibit a large number of quasiperiodic resonant peaks even though the classical motion of electrons in the potential well is chaotic. The voltage range and spacing of the resonances both change dramatically with θ. We give a quantitative explanation for this behaviour by considering the classical period of unstable periodic orbits within the chaotic sea of the potential well.

Development of teaching resources for physical modelling community

Physical modelling of interesting geotechnical problems has helped clarify behaviours and failure mechanisms of many civil engineering systems. Interesting visual information from physical modelling can also be used in teaching to foster interest in geotechnical engineering and recruit young researchers to our field. With this intention, the Teaching Committee of TC2 developed a web-based teaching resources centre. In this paper, the development and organisation of the resource centre using Wordpress. Wordpress is an open-source content management system which allows user content to be edited and site administration to be controlled remotely via a built-in interface. Example data from a centrifuge test on shallow foundations which could be used for undergraduate or graduate level courses is presented and its use illustrated. A discussion on the development of wiki-style addition to the resource centre for commonly used physical model terms is also presented. © 2010 Taylor & Francis Group, London.

Attenuated Salmonella Typhimurium lacking the pathogenicity island-2 type 3 secretion system grow to high bacterial numbers inside phagocytes in mice.

Intracellular replication within specialized vacuoles and cell-to-cell spread in the tissue are essential for the virulence of Salmonella enterica. By observing infection dynamics at the single-cell level in vivo, we have discovered that the Salmonella pathogenicity island 2 (SPI-2) type 3 secretory system (T3SS) is dispensable for growth to high intracellular densities. This challenges the concept that intracellular replication absolutely requires proteins delivered by SPI-2 T3SS, which has been derived largely by inference from in vitro cell experiments and from unrefined measurement of net growth in mouse organs. Furthermore, we infer from our data that the SPI-2 T3SS mediates exit from infected cells, with consequent formation of new infection foci resulting in bacterial spread in the tissues. This suggests a new role for SPI-2 in vivo as a mediator of bacterial spread in the body. In addition, we demonstrate that very similar net growth rates of attenuated salmonellae in organs can be derived from very different underlying intracellular growth dynamics.

Shear transfer across a diagonal crack in reinforced concrete strengthened with externally bonded FRP fabric

Aging concrete infrastructure in developed economies and more recently constructed concrete infrastructure in the developing world are frequently found to be deficient in structural strength relative to current needs. This can be attributed to a variety of factors including deterioration, construction defects, accidental damage, changes in understanding and failure to design for future loading requirements. Strengthening existing concrete structures can be a cost and carbon effective alternative to replacement. A competitive option for the strengthening of concrete slab-on-beam structures that are deficient in shear capacity is the U-wrapping of the down-stand beam portion of the shear span with externally bonded FRP fabric. While guidance exists for the strengthening of reinforced concrete by U-wrapping, the interaction between internal steel reinforcement, concrete and external FRP in the presence of a dominant diagonal shear crack is not well understood. An approach adopted in previous work has been to explore this interaction through conventional push-off testing. In conventional push-off testing, unlike in a beam, the shear plane is parallel to the direction of loading and perpendicular to the principal fibre orientation. This paper presents a novel push-off test variation in which the shear plane is inclined at 45° to the direction of loading and the principal fibre orientation. A variety of reinforcement ratios, FRP thicknesses and FRP end conditions are modelled. The implications of inclined cracking on debonding of FRP are investigated. The suitability and relevance of inclined push-off tests for further work in this area is also assessed. © 2013, NetComposite Limited.