The tensile fatigue behaviour of a silica nanoparticle-modified glass fibre reinforced epoxy composite

Abstract An anhydride-cured thermosetting epoxy polymer was modified by incorporating 10 wt.% of welldispersed 20 nm diameter silica nanoparticles. The stress-controlled tensile fatigue behaviour at a stress ratio of R = 0.1 was investigated for bulk specimens of the neat and the silica-modified epoxy. The addition of the silica nanoparticles increased the fatigue life by about three to four times. The neat and the nanoparticle-modified epoxy resins were used to fabricate glass fibre reinforced plastic (GFRP) composite laminates by resin infusion under flexible tooling (RIFT). Tensile fatigue tests were performed on these composites, during which the matrix cracking and stiffness degradation was monitored. The fatigue life of the GFRP composite was increased by about three to four times due to the silica nanoparticles. Suppressed matrix cracking and a reduced crack propagation rate in the nanoparticle-modified matrix were observed to contribute towards the enhanced fatigue life of the composite containing the silica nanoparticles

The tensile fatigue behavior of a glass-fiber reinforced plastic composite using a hybrid-toughened epoxy matrix

ABSTRACT A thermosetting epoxy-polymer was modified by incorporating 9 wt.% of carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber microparticles and 10 wt.% of silica nanoparticles. The tensile fatigue behaviour at a stress ratio, R = 0.1 for both the neat (i.e. unmodified) epoxy-polymer and the hybridepoxy polymer was first investigated. The fatigue life of the hybrid-epoxy * Corresponding author: Tel. +91-80-2508 6310 ; Fax: +91-80-2508 6301 E-mail address: [email protected] (CM Manjunatha) 2 polymer was about six to ten times higher than that the neat-epoxy polymer. Secondly, the neat and the hybrid-epoxy resins were infused into a quasiisotropic lay-up, E-glass fiber fabric via a 'Resin Infusion under Flexible Tooling' (RIFT) set-up to fabricate glass-fiber reinforced-plastic (GFRP) composite panels. The tensile fatigue tests at a stress ratio, R = 0.1 were performed on both of these GFRP composites during which the matrix cracking and stiffness degradation were routinely monitored. The fatigue life of the GFRP composite increased by about six to ten times due to employing the hybrid-epoxy matrix, compared to the neat-epoxy matrix. Suppressed matrix cracking and a reduced crack propagation rate were observed in the hybrid-epoxy matrix, which resulted from the various toughening micromechanisms induced by the presence of both the rubber microparticles and silica nanoparticles. These factors were considered to contribute towards the enhanced fatigue life which was observed for the GFRP composite employing the hybrid-epoxy matrix

Graduates from a reformed undergraduate medical curriculum based on Tomorrow's Doctors evaluate the effectiveness of their curriculum 6 years after graduation through interviews

<p>Abstract</p> <p>Background</p> <p>In 1996 Liverpool reformed its medical curriculum from a traditional lecture based course to a curriculum based on the recommendations in Tomorrow's Doctors. A project has been underway since 2000 to evaluate this change. This paper focuses on the views of graduates from that reformed curriculum 6 years after they had graduated.</p> <p>Methods</p> <p>Between 2007 and 2009 45 interviews took place with doctors from the first two cohorts to graduate from the reformed curriculum.</p> <p>Results</p> <p>The interviewees felt like they had been clinically well prepared to work as doctors and in particular had graduated with good clinical and communication skills and had a good knowledge of what the role of doctor entailed. They also felt they had good self directed learning and research skills. They did feel their basic science knowledge level was weaker than traditional graduates and perceived they had to work harder to pass postgraduate exams. Whilst many had enjoyed the curriculum and in particular the clinical skills resource centre and the clinical exposure of the final year including the "shadowing" and A & E attachment they would have liked more "structure" alongside the PBL when learning the basic sciences.</p> <p>Conclusion</p> <p>According to the graduates themselves many of the aims of curriculum reform have been met by the reformed curriculum and they were well prepared clinically to work as doctors. However, further reforms may be needed to give confidence to science knowledge acquisition.</p

Biolistic inoculation of cassava (Manihot esculenta Crantz) with South African cassava mosaic virus

Cassava mosaic disease (CMD) is undoubtedly the most widespread disease in cassava (Manihot esculenta Crantz) in sub-Saharan Africa. While African cassava mosaic virus-Kenya (ACMV-KE), African cassava mosaic virus-Uganda (ACMV UG), African cassava mosaic virus-India (ACMV-IC), East African cassava mosaic virus-Cameroon (EACMV-CM) and a recombinant East African cassava mosaic virus-India/Cameroon (EACMV-CM/IC) can be transmitted easily and repeatedly to Nicotiana benthamiana plants, difficulty in mechanical transmission and multiplication of EACMV-UG and South African cassava mosaic virus (SACMV) in N. benthamiana appears to place them biologically in a different group. In vitro grown 3-week-old cassava plants were biolistically inoculated with SACMV DNA A and B dimers and infectivity measured using a system based on visual assessment. We report for the first time successful infection, induced by SACMV DNA A and B dimer, of cassava cultivar TMS60444 using biolistic inoculation. Typical mosaic symptoms started to show at 14 days post-inoculation (dpi) in infected cassava plants, and SACMV replication was confirmed using PCR. Potential applications of biolistic infection of SACMV are also discussed.Keywords: Cassava, biolistic, inoculation, SACM

Climate–groundwater dynamics inferred from GRACE and the role of hydraulic memory

Groundwater is the largest store of freshwater on Earth after the cryosphere and provides a substantial proportion of the water used for domestic, irrigation and industrial purposes. Knowledge of this essential resource remains incomplete, in part, because of observational challenges of scale and accessibility. Here we examine a 14-year period (2002–2016) of Gravity Recovery and Climate Experiment (GRACE) observations to investigate climate–groundwater dynamics of 14 tropical and sub-tropical aquifers selected from WHYMAP's (Worldwide Hydrogeological Mapping and Assessment Programme) 37 large aquifer systems of the world. GRACE-derived changes in groundwater storage resolved using GRACE Jet Propulsion Laboratory (JPL) mascons and the Community Land Model's land surface model are related to precipitation time series and regional-scale hydrogeology. We show that aquifers in dryland environments exhibit long-term hydraulic memory through a strong correlation between groundwater storage changes and annual precipitation anomalies integrated over the time series; aquifers in humid environments show short-term memory through strong correlation with monthly precipitation. This classification is consistent with estimates of groundwater response times calculated from the hydrogeological properties of each system, with long (short) hydraulic memory associated with slow (rapid) response times. The results suggest that groundwater systems in dryland environments may be less sensitive to seasonal climate variability but vulnerable to long-term trends from which they will be slow to recover. In contrast, aquifers in humid regions may be more sensitive to climate disturbances such as drought related to the El Niño–Southern Oscillation but may also be relatively quick to recover. Exceptions to this general pattern are traced to human interventions through groundwater abstraction. Hydraulic memory is an important factor in the management of groundwater resources, particularly under climate change

White matter integrity as a predictor of response to treatment in first episode psychosis

The integrity of brain white matter connections is central to a patient's ability to respond to pharmacological interventions. This study tested this hypothesis using a specific measure of white matter integrity, and examining its relationship to treatment response using a prospective design in patients within their first episode of psychosis. Diffusion tensor imaging data were acquired in 63 patients with first episode psychosis and 52 healthy control subjects (baseline). Response was assessed after 12 weeks and patients were classified as responders or non-responders according to treatment outcome. At this second time-point, they also underwent a second diffusion tensor imaging scan. Tract-based spatial statistics were used to assess fractional anisotropy as a marker of white matter integrity. At baseline, non-responders showed lower fractional anisotropy than both responders and healthy control subjects (P < 0.05; family-wise error-corrected), mainly in the uncinate, cingulum and corpus callosum, whereas responders were indistinguishable from healthy control subjects. After 12 weeks, there was an increase in fractional anisotropy in both responders and non-responders, positively correlated with antipsychotic exposure. This represents one of the largest, controlled investigations of white matter integrity and response to antipsychotic treatment early in psychosis. These data, together with earlier findings on cortical grey matter, suggest that grey and white matter integrity at the start of treatment is an important moderator of response to antipsychotics. These findings can inform patient stratification to anticipate care needs, and raise the possibility that antipsychotics may restore white matter integrity as part of the therapeutic response

The group structure of non-Abelian NS-NS transformations

We study the transformations of the worldvolume fields of a system of multiple coinciding D-branes under gauge transformations of the supergravity Kalb-Ramond field. We find that the pure gauge part of these NS-NS transformations can be written as a U(N) symmetry of the underlying Yang-Mills group, but that in general the full NS-NS variations get mixed up non-trivially with the U(N). We compute the commutation relations and the Jacobi identities of the bigger group formed by the NS-NS and U(N) transformations.Comment: Latex, 11 pages. v2: Typos corrected; version to appear in JHEP