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

The PI Launchpad: Expanding the base of potential Principal Investigators across space sciences

The PI Launchpad attempts to provide an entry level explanation of the process of space mission development for new Principal Investigators (PIs). In particular, PI launchpad has a focus on building teams, making partnerships, and science concept maturity for a space mission concept, not necessarily technical or engineering practices. Here we briefly summarize the goals of the PI Launchpad workshops and present some results from the workshops held in 2019 and 2021. The workshop attempts to describe the current process of space mission development (i.e. space-based telescopes and instrument platforms, planetary missions of all types, etc.), covering a wide range of topics that a new PI may need to successfully develop a team and write a proposal. It is not designed to replace real experience but to provide an easily accessible resource for potential PIs who seek to learn more about what it takes to submit a space mission proposal, and what the first steps to take can be. The PI Launchpad was created in response to the high barrier to entry for early career or any scientist who is unfamiliar with mission design. These barriers have been outlined in several recent papers and reports, and are called out in recent space science Decadal reports.Comment: 7 Pages, 2 Figure, Accepted to Frontier

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

Changes in N-Transforming Archaea and Bacteria in Soil during the Establishment of Bioenergy Crops

Widespread adaptation of biomass production for bioenergy may influence important biogeochemical functions in the landscape, which are mainly carried out by soil microbes. Here we explore the impact of four potential bioenergy feedstock crops (maize, switchgrass, Miscanthus X giganteus, and mixed tallgrass prairie) on nitrogen cycling microorganisms in the soil by monitoring the changes in the quantity (real-time PCR) and diversity (barcoded pyrosequencing) of key functional genes (nifH, bacterial/archaeal amoA and nosZ) and 16S rRNA genes over two years after bioenergy crop establishment. The quantities of these N-cycling genes were relatively stable in all four crops, except maize (the only fertilized crop), in which the population size of AOB doubled in less than 3 months. The nitrification rate was significantly correlated with the quantity of ammonia-oxidizing archaea (AOA) not bacteria (AOB), indicating that archaea were the major ammonia oxidizers. Deep sequencing revealed high diversity of nifH, archaeal amoA, bacterial amoA, nosZ and 16S rRNA genes, with 229, 309, 330, 331 and 8989 OTUs observed, respectively. Rarefaction analysis revealed the diversity of archaeal amoA in maize markedly decreased in the second year. Ordination analysis of T-RFLP and pyrosequencing results showed that the N-transforming microbial community structures in the soil under these crops gradually differentiated. Thus far, our two-year study has shown that specific N-transforming microbial communities develop in the soil in response to planting different bioenergy crops, and each functional group responded in a different way. Our results also suggest that cultivation of maize with N-fertilization increases the abundance of AOB and denitrifiers, reduces the diversity of AOA, and results in significant changes in the structure of denitrification community

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

Responses of bacterial and archaeal ammonia oxidizers to soil organic and fertilizer amendments under long-term management

Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) co-exist in soil, but their relative distribution may vary depending on the environmental conditions. Effects of changes in soil organic matter and nutrient content on the AOB and AOA are poorly understood. Our aim was to compare effects of long-term soil organic matter depletion and amendments with labile (straw) and more recalcitrant (peat) organic matter, with and without easily plant-available nitrogen, on the activities, abundances and community structures of AOB and AOA. Soil was sampled from a long-term field site in Sweden that was established in 1956. The potential ammonia oxidation rates, the AOB and AOA amoA gene abundances and the community structures of both groups based on T-RFLP of amoA genes were determined. Straw amendment during 50 years had not altered any of the measured soil parameters, while the addition of peat resulted in a significant increase of soil organic carbon as well as a decrease in pH. Nitrogen fertilization alone resulted in a small decrease in soil pH, organic carbon and total nitrogen, but an increase in primary production. Type and amount of organic matter had an impact on the AOB and AOA community structures and the AOA abundance. Our findings confirmed that AOA are abundant in soil, but showed that under certain conditions the AOB dominate, suggesting niche differentiation between the two groups at the field site. The large differences in potential rates between treatments correlated to the AOA community size, indicating that they were functionally more important in the nitrification process than the AOB. The AOA abundance was positively related to addition of labile organic carbon, which supports the idea that AOA could have alternative growth strategies using organic carbon. The AOB community size varied little in contrast to that of the AOA. This indicates that the bacterial ammonia oxidizers as a group have a greater ecophysiological diversity and potentially cover a broader range of habitats