Experimental investigation of static and cyclic behaviour of scaled railway ballast and the effect of stress reversal

The aim of the research was to improve the fundamental understanding of mechanical behaviour of ballast and study the effect of tamping on ballast. The experiments were carried out on scaled railway ballast to eliminate the difficulties associated with testing large particle granular materials. Consideration was given to the gradation, mineralogy and shape during scaling. Particle characterisation work was carried out on scaled and full size ballast using imaging techniques to examine the validity of the use of scaled ballast. Detailed analysis of results is used to quantitatively measure the changes in shape with particle size. The results show measurable differences in particle shape between different particle size intervals. As the differences are small in magnitude, they do not invalidate the use of scaled ballast.Monotonic, cyclic experiments were carried out as part of a laboratory testing programme. Scaled ballast shows generally similar stress strain behaviour to larger granular materials. The friction angle of 40o to 50o for the confining pressure range of 15 kPa to 200 kPa falls within the range of friction angle obtained for full size ballast in the literature. The effect of changing confining pressure during train loading was examined. The results show that the settlement increases and the stiffness reduces when the confining pressure cycles. The effect of principal stress reversal during tamping was examined by an extension stage after the cyclic loading. It is shown that massive settlement occurs after the extension stage during initial cycles and settlement returns back to the pre-extension stage soon under loading. The results evidence the disruption of ballast structure and loss of stiffness due to tamping. Specimens were resin stabilised within the triaxial cell after specific stress paths had been followed. The changes in structure during a specific stress path can be studied by CT examination

cAMP-Signalling Regulates Gametocyte-Infected Erythrocyte Deformability Required for Malaria Parasite Transmission.

Blocking Plasmodium falciparum transmission to mosquitoes has been designated a strategic objective in the global agenda of malaria elimination. Transmission is ensured by gametocyte-infected erythrocytes (GIE) that sequester in the bone marrow and at maturation are released into peripheral blood from where they are taken up during a mosquito blood meal. Release into the blood circulation is accompanied by an increase in GIE deformability that allows them to pass through the spleen. Here, we used a microsphere matrix to mimic splenic filtration and investigated the role of cAMP-signalling in regulating GIE deformability. We demonstrated that mature GIE deformability is dependent on reduced cAMP-signalling and on increased phosphodiesterase expression in stage V gametocytes, and that parasite cAMP-dependent kinase activity contributes to the stiffness of immature gametocytes. Importantly, pharmacological agents that raise cAMP levels in transmissible stage V gametocytes render them less deformable and hence less likely to circulate through the spleen. Therefore, phosphodiesterase inhibitors that raise cAMP levels in P. falciparum infected erythrocytes, such as sildenafil, represent new candidate drugs to block transmission of malaria parasites

Predicting long term performance of offshore wind turbines using cyclic simple shear apparatus

Offshore wind turbine (OWT) foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, 1P (rotor frequency) and 2P/3P (blade passing frequency) loads. Under cyclic/dynamic loading, most soils change their characteristics. Cyclic behaviour (in terms of change of shear modulus change and accumulation of strain) of a typical silica sand (RedHill 110) was investigated by a series of cyclic simple shear tests. The effects of application of 50,000 cycles of shear loading having different shear strain amplitude, cyclic stress ratio (ratio of shear to vertical stress), and vertical stress were investigated. Test results were reported in terms of change in shear modulus against the number of loading cycles. The results correlated quite well with the observations from scaled model tests of different types of offshore wind turbine foundations and limited field observations. Specifically, the test results showed that; (a) Vertical and permanent strain (accumulated strain) is proportional to shear strain amplitude but inversely proportional to the vertical stress and relative density; (b) Shear modulus increases rapidly in the initial cycles of loading and then the rate of increase diminishes and the shear modulus remains below an asymptote. Discussion is carried out on the use of these results for long term performance prediction of OWT foundations

Modelling the effects of trafficking and tamping on scaled railway ballast in triaxial tests

Most of the world’s railways are on ballasted track, which is generally used in preference to slab track because of its lower initial cost and the relative ease with which track geometry can be adjusted. However, the accumulation of track movements as a result of trafficking leads to a gradual deterioration in track line and level, hence the need for periodic corrective maintenance. This is usually by tamping; a process in which the track is lifted and vibrating tines are inserted into the ballast and moved horizontally to raise the ballast surface back to the required level. The period before further maintenance is required decreases with each tamp. This paper investigates one of the reasons for the deterioration in ballast robustness following tamping, with reference to triaxial tests on scaled ballast in which vertical loading cycles and the stress reversal caused below the railseat by tamping were simulated. It is shown that the stress reversal disrupts and loosens the vertical load bearing ballast structure developed during trafficking to support vertical train loads. On re-loading after tamping, the track settles significantly and, as a result of the loss of vertical load-bearing structure, with further load cycles rapidly returns to its reduced height. The implication is that maintenance by tamping is, on its own, disruptive to the structure and resilience of the ballast to vertical cyclic loading, and should be carried out as rarely as possible

Cyclic seasonal effects on infrastructure earthworks

Slope failures may cause substantial loss of life and damage to infrastructure. In UK much of the rail network was constructed over 150 years ago, and the earth structures were not built to modern standards. As these structures get older, they have become a potential threat to the safety of transport operations. Climate conditions directly influence the behaviour and failure of slopes. The presence of trees increases the depth and extent of desiccation and cracking and may increase the permeability to greater depths, leading to greater changes in seasonal pore water pressures. Seasonal pore water pressure changes lead to corresponding cyclic changes in effective stress. The fatigue of the clay brought about by seasonal effective stress cycles is a possibility though not well established. Climate change is expected to bring extreme weather patterns to the UK in which wetter winters and drier summers will prevail, potentially giving larger cycles of stress. Field investigations of cracks and other macro pores are carried out as part of the current study. To establish appropriate values for the change in near surface permeability of infrastructure cut slopes caused by opening and closing of cracks, field permeability experiments on a cut slope in Newbury were carried out during different seasons of the year. Appropriate near surface permeability was established based on this. A mathematical and numerical study of the influence of a single crack on permeability is presented. To investigate the influence of cycles of effective stress associated with pore pressure changes brought about by seasonal variations in climate on the development of accumulated strain and on the strength of stiff over consolidated clay materials, a series of cyclic triaxial experiments were carried out on soil samples from railway embankments. The results from cyclic triaxial tests on undisturbed and reconstituted Gault and Lias Clay embankment fill materials are presented and analysed. The near surface vertical permeability of the cut slope in Newbury (10-8 m/s — 10-6 m/s) is found to be at least two orders of magnitude higher than that of intact London clay (10-10 m/s) and the end of summer vertical permeability (~10-6 m/s) two orders of magnitude higher than that of end of winter (~10-8 m/s). Near surface vertical permeability varies between summer and winter possibly mainly due to cracks opening and closing. The undrained shear strength of the reconstituted Lias Clay is consistent between 42.5 kPa to 47.5 kPa. Critical friction angle of reconstituted Lias Clay varies between 24° and 27°. For Lias Clay triaxial samples, permanent axial strains are accumulated with cycles of pore water pressure. The rate of accumulated strain decreases with the number of cycles when the effective stress ratio is below that corresponding to critical state line. The stress conditions under which the sample failed (ϕ’mob = 340) when pore pressure is cycled is with in the range of strength obtained for monotonic tests on the undisturbed fill material (which was between 28° and 37°)

MEMORY SUBSYSTEM CONSISTING OF AN ON-BOARD CROSSBAR, LEVEL-2 CACHE, AND MEMORY CONTROLLERS FOR A HIGHLY INTEGRATED DESIGN THAT EXPLOITS THE THREAD-LEVEL PARALLELISM INHERENT TO SERVER APPLICATIONS, WHILE TARGETING LOW LEVELS OF POWER CONSUMPTION.

Over the past two decades, microprocessor designers have focused on improving the performance of a single thread in a desktop processing environment by increasing frequencies and exploiting instruction level parallelism (ILP) using techniques such as multiple instruction issue, out-of-order issue, and aggressive branch prediction. The emphasis on single-thread performance has shown diminishing returns because of the limitations in terms of latency to main memory and the inherently low ILP of applications. This has led to an explosion in microprocessor design complexity and made power dissipation a major concern