A new semi-solid casting technique for fabricating SiC-reinforced Mg alloys matrix composites

The capability of the newly developed rheocasting (RC) technique in combination with the RheoMetal process for producing SiC particulate-reinforced AM50 and AZ91D matrix composites (Mg-based MMCs) was investigated. The quality of the MMCs was studied by analyzing the fraction of casting pores, number density of SiC clusters and the uniformity of SiC particles. Solid fraction, particle size and oxidation of SiC particles had strong impacts on the overall quality of the MMCs. The MMCs produced by 40% solid fraction and oxidized micron-sized SiC particles exhibited an excellent casting quality. A low-quality MMC was obtained when non-oxidized sub-micron sized SiC particles were employed. The results showed the formation of various types intermetallic particles and carbides such as MgO, Mg2Si, Al2MgC2, Mg2C3, Al4C3 as the interfacial reaction products of SiC/Mg alloy's melts. Mg hydride (alpha-MgH2) was also identified in inter-dendritic regions of the MMCs for the first time

Discussion on “Stable eutectoid transformation in nodular cast iron: modeling and validation”

The Minerals, Metals & Materials Society and ASM International 2017 Given that cast irons are multicomponent alloys, the decomposition of the high temperature austenite into ferrite and graphite happens within a finite temperature range and not at an invariant point, as often described schematically. Only a few models explicitly consider the existence of such an austenite–ferrite–graphite range: the contribution under discussion,[1]those that inspired it[2,3] and one previous study from the present author.[4]For kinetics reasons, this latter work explained that ferrite could not grow within the equilibrium three-phase field under continuous cooling; this is in contradiction with the other three reports. The aim of this discussion is first to recall the experimental evidence about ferrite formation during eutectoid transformation of cast iron and then to provide an explanation as to why ferrite starts forming upon cooling only when the temperature of the material is below the equilibrium three-phase field range, as observed experimentally

Comparative metagenomic, phylogenetic and physiological analyses of soil microbial communities across nitrogen gradients

Terrestrial ecosystems are receiving elevated inputs of nitrogen (N) from anthropogenic sources and understanding how these increases in N availability affect soil microbial communities is critical for predicting the associated effects on belowground ecosystems. We used a suite of approaches to analyze the structure and functional characteristics of soil microbial communities from replicated plots in two long-term N fertilization experiments located in contrasting systems. Pyrosequencing-based analyses of 16S rRNA genes revealed no significant effects of N fertilization on bacterial diversity, but significant effects on community composition at both sites; copiotrophic taxa (including members of the Proteobacteria and Bacteroidetes phyla) typically increased in relative abundance in the high N plots, with oligotrophic taxa (mainly Acidobacteria) exhibiting the opposite pattern. Consistent with the phylogenetic shifts under N fertilization, shotgun metagenomic sequencing revealed increases in the relative abundances of genes associated with DNA/RNA replication, electron transport and protein metabolism, increases that could be resolved even with the shallow shotgun metagenomic sequencing conducted here (average of 75 000 reads per sample). We also observed shifts in the catabolic capabilities of the communities across the N gradients that were significantly correlated with the phylogenetic and metagenomic responses, indicating possible linkages between the structure and functioning of soil microbial communities. Overall, our results suggest that N fertilization may, directly or indirectly, induce a shift in the predominant microbial life-history strategies, favoring a more active, copiotrophic microbial community, a pattern that parallels the often observed replacement of K-selected with r-selected plant species with elevated N

Characterizing Types of Human Mobility to Inform Differential and Targeted Malaria Elimination Strategies in Northeast Cambodia

Human population movements currently challenge malaria elimination in low transmission foci in the Greater Mekong Subregion. Using a mixed-methods design, combining ethnography (n?=?410 interviews), malariometric data (n?=?4996) and population surveys (n?=?824 indigenous populations; n?=?704 Khmer migrants) malaria vulnerability among different types of mobile populations was researched in the remote province of Ratanakiri, Cambodia. Different structural types of human mobility were identified, showing differential risk and vulnerability. Among local indigenous populations, access to malaria testing and treatment through the VMW-system and LLIN coverage was high but control strategies failed to account for forest farmers’ prolonged stays at forest farms/fields (61% during rainy season), increasing their exposure (p?=?0.002). The Khmer migrants, with low acquired immunity, active on plantations and mines, represented a fundamentally different group not reached by LLIN-distribution campaigns since they were largely unregistered (79%) and unaware of the local VMW-system (95%) due to poor social integration. Khmer migrants therefore require control strategies including active detection, registration and immediate access to malaria prevention and control tools from which they are currently excluded. In conclusion, different types of mobility require different malaria elimination strategies. Targeting mobility without an in-depth understanding of malaria risk in each group challenges further progress towards elimination

Shear band formation in shaped rheocast aluminium component at various plunger velocities

Significant progress has been made in recent years in understanding and modelling the rheology of semi-solid metals. These models show the effects of the microstructure in terms of size and morphology of globules on the material response. More recently it has been shown that semi-solid metals can behave as compacted granular materials such as sand. A particular signature of such deformation is that the deformation becomes concentrated into shear bands which are 10-20 grains wide. Such bands have also been observed in a range of cast products. Recently, it has been clearly shown that shear bands in high pressure die cast (HPDC) products are also the results of Reynolds dilatancy. Shear bands are also known to be a common feature in semi-solid metal products. The segregation banding in semi-solid metal (SSM) material and its dependence of plunger velocity were investigated. Shaped castings were made with the RHEOMETAL™ process with a range of different plunger velocities. The microstructural characteristics were investigated, with a particular emphasis on shear bands. It is shown that ingate velocities influence the location and characteristics of the shear bands. © 2010 The Nonferrous Metals Society of China

An analysis of medical students' residency and specialty choices

The contemporary geographic maldistribution of physicians and shortages in some specialty areas is a persistent problem facing United States federal and state wide health planners. This paper attempts to illustrate some of the formal and informal processes of the selection of specialties and recidency programs based on a survey of senior students of 37 selected American medical schools at the time of the National Residency Matching Program in 1982. Results of a factor analysis on influences on specialty choice produced two major clusters of medical students; those predominantly influenced in specialty choice by the faculty and other senior physicians (sponsorship), and those predominantly influenced by the social dimension of the physicians' role (social responsibility). These medical specialty choice orientations were also systematically related to either choice of specialty vs primary care medicine, to a life-style or status related choice of residency program, and to students' perceptions regarding a program's evaluation of a candidate. The results of the survey suggested that students who chose primary care were more apt to be influenced by sources outside of the medical school. These findings raise questions regarding the efficacy of medical school curriculum in motivating career choices in primary care. This is particularly important in view of the stated need to increase the proportion of medical school graduates choosing primary care careers.medical education postgraduate training specialty choice residency choice

Historical baselines and the future of shell calcification for a foundation species in a changing ocean

Seawater pH and the availability of carbonate ions are decreasing due to anthropogenic carbon dioxide emissions, posing challenges for calcifying marine species. Marine mussels are of particular concern given their role as foundation species worldwide. Here, we document shell growth and calcification patterns in Mytilus californianus, the California mussel, over millennial and decadal scales. By comparing shell thickness across the largest modern shells, the largest mussels collected in the 1960s–1970s and shells from two Native American midden sites (∼1000–2420 years BP), we found that modern shells are thinner overall, thinner per age category and thinner per unit length. Thus, the largest individuals of this species are calcifying less now than in the past. Comparisons of shell thickness in smaller individuals over the past 10–40 years, however, do not show significant shell thinning. Given our sampling strategy, these results are unlikely to simply reflect within-site variability or preservation effects. Review of environmental and biotic drivers known to affect shell calcification suggests declining ocean pH as a likely explanation for the observed shell thinning. Further future decreases in shell thickness could have significant negative impacts on M. californianus survival and, in turn, negatively impact the species-rich complex that occupies mussel beds