Capillarity in pressure infiltration: improvements in characterization of high-temperature systems

In the pressure infiltration of metal matrix composites, molten metal is injected under external pressure into a porous preform of the reinforcing material. Equilibrium capillary parameters characterizing wetting for this process are summarized in plots of metal saturation versus applied pressure, also known as drainage curves. Such curves can be measured in our laboratory during a single experiment with an infiltration apparatus designed to track the rate of metal penetration into porous preforms under conditions characteristic of metal matrix composite processing (temperatures in excess of 1000°C and pressures in the order of 10MPa). For such measurements to be valid, infiltration of the preform with molten metal must be mechanically quasi-static, i.e., the metal must flow at a rate sufficiently low for the metal pressure to be essentially uniform across the preform at all times. We examine this requirement quantitatively, using a finite-difference model that simulates the unsaturated unidirectional ingress of molten metal into a ceramic particle preform of finite width. We furthermore present improvements in the experimental apparatus developed in our laboratory to measure the entire drainage curve in a single experiment. We compare numerical results with new experimental data for the copper/alumina system to show (i) that pressurization rates sufficiently low for quasi-static infiltration can be produced with this apparatus, and (ii) that taking the relative permeability equal to the saturation yields better agreement with experiment than does the expression originally proposed by Brooks and Core

New approach of fragment charge correlations in 129Xe+(nat)Sn central collisions

A previous analysis of the charge (Z) correlations in the $\Delta Z-$ plane for Xe+Sn central collisions at 32 MeV/u has shown an enhancement in the production of equally sized fragments (low $\Delta Z$) which was interpreted as an evidence for spinodal decomposition. However the signal is weak and rises the question of the estimation of the uncorrelated yield. After a critical analysis of its robustness, we propose in this paper a new technique to build the uncorrelated yield in the charge correlation function. The application of this method to Xe+Sn central collision data at 32, 39, 45 and 50 MeV/u does not show any particular enhancement of the correlation function in any $\Delta Z$ bin.Comment: 23 pages, 9 figures, revised version with an added figure and minor changes. To appear in Nuclear Physics

Clinical trials in children: Equity, quality and relevance

This thesis investigates the equity, quality and relevance of clinical trials in children to inform better evidence-based child healthcare and outcomes worldwide. A comprehensive review of the literature revealed that despite current initiatives to encourage more trials in children, there is still a paucity of safety and efficacy data of many medicines prescribed in this population. An analysis of trials registered in children showed that disease burden was moderately correlated to trials and this scarcity was particularly prevalent in low-and middle-income countries. We explored the contributory factors to this inequity by conducting a systematic review of stakeholders’ views of trials in children in low-and middle-income countries. In the study evaluating the completeness of protocols of trials in children submitted to ethics committees, we found that protocols are generally comprehensive, but many key domains in trial design and conduct are not reported. Key-informant trial stakeholders who were interviewed proposed strategies to improve trials such as addressing the unique needs of children, embedding trials as part of routine clinical care and streamlining regulatory approvals. Increasing international collaboration, establishing sustainable centralised trials infrastructure, and aligning research to child health priorities were proposed to encourage more high-quality trials that address global child healthcare needs

Late winter under ice pelagic microbial communities in the high Arctic Ocean and the impact of short-term exposure to elevated CO2 levels

Polar Oceans are natural CO2 sinks because of the enhanced solubility of CO2 in cold water. The Arctic Ocean is at additional risk of accelerated ocean acidification (OA) because of freshwater inputs from sea ice and rivers, which influence the carbonate system. Winter conditions in the Arctic are of interest because of both cold temperatures and limited CO2 venting to the atmosphere when sea ice is present. Earlier OA experiments on Arctic microbial communities conducted in the absence of ice cover, hinted at shifts in taxa dominance and diversity under lowered pH. The Catlin Arctic Survey provided an opportunity to conduct in situ, under-ice, OA experiments during late Arctic winter. Seawater was collected from under the sea ice off Ellef Ringnes Island, and communities were exposed to three CO2 levels for 6 days. Phylogenetic diversity was greater in the attached fraction compared to the free-living fraction in situ, in the controls and in the treatments. The dominant taxa in all cases were Gammaproteobacteria but acidification had little effect compared to the effects of containment. Phylogenetic net relatedness indices suggested that acidification may have decreased the diversity within some bacterial orders, but overall there was no clear trend. Within the experimental communities, alkalinity best explained the variance among samples and replicates, suggesting subtle changes in the carbonate system need to be considered in such experiments. We conclude that under ice communities have the capacity to respond either by selection or phenotypic plasticity to heightened CO2 levels over the short term

Squatina occulta, Hidden Angelshark

The Hidden Angelshark (Squatina occulta) is a medium-sized shark (to 160 cm total length) endemic to the Southwest Atlantic inhabiting waters from Rio de Janeiro, Brazil, to Buenos Aires Province, Argentina and likely further south to the northern Patagonia-Argentine region. It is mainly found on the continental shelf at depths of 10-150 m, but has been found at depths to 350 m. The species' low reproductive potential (litter size of 4-10 and a possible three-to-five-year female breeding cycle) together with its susceptibility to capture in both trawl and gillnet gear makes it highly susceptible to population depletion. Angel sharks are heavily fished in southern Brazil and significant reductions have been documented there. In the period from 1988 to 2002, on the continental shelf of southern Brazil, the abundance of Squatina species was reduced by approximately 85%, and benthic trawl fishing continued to intensively exploit this population in more recent years. In the same region, scientific fishing cruises conducted between 1986 to 2001 using bottom trawls revealed that the frequency of occurrence and CPUE (in kg/hour and number of individuals/hour) of this species was reduced by 80% confirming trends observed in commercial fisheries. In Argentina, trawl catches of Squatina underwent a reduction of 58% in the years 1992-1998, showing a continuing negative trend since then. These are the equivalent of a >99% reduction over three generation lengths (46.5 years), however there may be other areas within its range where fishing intensity is not as high. The catch and trade of this species has been banned in Brazil since 2004, but it is still targeted illegally and caught as bycatch and sold in markets. Given the species' relatively low productivity, the presence of intensive fisheries throughout the species' range, and the level of localized reductions reported, the Hidden Angelshark is inferred to have undergone a population reduction of over 80% over three generation lengths (46.5 years) across its range, and is therefore assessed as Critically Endangered A2bd.Fil: Awruch, C. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Barreto, R.. Instituto Chico Mendes de Conservacao Da Biodiversidade; BrasilFil: Charvet, P.. Universidade Federal do Paraná; BrasilFil: Chiaramonte, Gustavo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". Estación Hidrobiológica de Puerto Quequén (sede Quequén); ArgentinaFil: Cuevas, J. M.. Wildlife Conservation Society; Estados UnidosFil: Faria, V.. Universidade Federal Do Ceara; BrasilFil: Paesch, L.. Dirección Nacional de Recursos Acuáticos; UruguayFil: Rincon, G.. Universidade Federal Do Maranhao.; Brasi

Properties of projectile-fragments in the 40^{40}Ar + 27^{27}Al reaction at 44 A MeV. Comparison with a multisequential decay model

GANIL-EXPResults on projectile fragment–fragment coincidences in the forward direction and for the reaction 40Ar + 27Al at 44 A MeV are presented and compared with the predictions of two different entrance channel models, a two-body and a three-body mechanism both followed by a binary multisequential decay including fission. This analysis shows that many features of the projectile decay products are well accounted for by the binary multisequential decay model. However the results depend critically upon the initial masses and excitation energies of the primary projectile fragments. In this respect, the three-body approach underestimates the excitation energy imparted to the primary fragments whereas the two-body scenario overestimates it. The present data put strong constraints on the initial excitation energy imparted to the primary fragments which appears to be intermediate between the predictions of the two models

Transition from participant to spectator fragmentation in Au+Au reaction between 60 AMeV and 150 AMeV

Using the quantum molecular dynamics approach, we analyze the results of the recent INDRA Au+Au experiments at GSI in the energy range between 60 AMeV and 150 AMeV. It turns out that in this energy region the transition toward a participant-spectator scenario takes place. The large Au+Au system displays in the simulations as in the experiment simultaneously dynamical and statistical behavior which we analyze in detail: The composition of fragments close to midrapidity follows statistical laws and the system shows bi-modality, i.e. a sudden transition between different fragmentation pattern as a function of the centrality as expected for a phase transition. The fragment spectra at small and large rapidities, on the other hand, are determined by dynamics and the system as a whole does not come to equilibrium, an observation which is confirmed by FOPI experiments for the same system.Comment: published versio

Correlation functions and emission time sequence of light charged particles from projectile-like fragment source in E/A = 44 and 77 MeV 40Ar + 27Al collisions

Two-particle correlation functions, involving protons, deuterons, tritons, and alpha-particles, have been measured at very forward angles (0.7 deg < theta_lab < 7 deg), in order to study projectile-like fragment (PLF) emission in E/A = 44 and 77 MeV 40Ar + 27Al collisions. Peaks, originating from resonance decays, are larger at E/A = 44 than at 77 MeV. This reflects the larger relative importance of independently emitted light particles, as compared to two-particle decay from unstable fragments, at the higher beam energy. The time sequence of the light charged particles, emitted from the PLF, has been deduced from particle-velocity-gated correlation functions (discarding the contribution from resonance decays). Alpha-particles are found to have an average emission time shorter than protons but longer than tritons and deuterons.Comment: 18 pages, 5 figures, submitted to Nuclear Physics

Evidence of Z=120 compound nucleus formation from lifetime measurement in the 238^{238}U+Ni reaction at 6.62 MeV/nucleon

CAS NIMThe formation of compound nuclei with Z=120, followed by fission, has been evidenced in the 238U+Ni system at 6.62 MeV/nucleon by very long reaction times (t ~ 10-17s) measured by the blocking technique in single crystals