Investigation of the role of Mg and Ca in the structure and durability of aluminoborosilicate glass

The structure and dissolution behaviour of Na 2 O·CaO·(15–x)Al 2 O 3 ·xB 2 O 3 ·SiO 2 and Na 2 O·MgO·(15–x)Al 2 O 3 ·xB 2 O 3 ·SiO 2 glasses, relevant to compositions of UK nuclear waste glass, have been investigated using nuclear magnetic resonance (NMR) spectroscopy and static dissolution experiments using the PCT protocol. Structural data from 11 B, 27 Al and 29 Si NMR analyses show that increasing the [B 2 O 3 ]/([Al 2 O 3 ] + [B 2 O 3 ]) ratio of the alkali-alkaline-earth aluminoborosilicate glasses led to an overall decrease in the proportion of non-silicate tetrahedral species ( IV Al + IV B) and a decrease in Si–O–X bonds (X[dbnd]B, Al). The Mg-containing glasses exhibited lower IV B fractions than their Ca-containing counterparts, which is thought to be due to the presence of IV Mg tetrahedra in the network. The measured corrosion rates were similar for both Ca and Mg-containing glasses although unexpectedly some Ca-containing glasses exhibited higher corrosion losses than the Mg-containing ones for time periods up to 112 d. However, there was evidence of a greater tendency to rate resumption in the Mg containing than the Ca containing ones. Alteration products were found to contain Ca, Si and Al with the Ca containing glasses and Ca, Mg, Si and Al with the Mg containing glasses; Na was not detected in the alteration products although its presence cannot be ruled out based on the data obtained

Gaseous carbonation of cementitious backfill for geological disposal of radioactive waste: Nirex Reference Vault Backfill

The ability of Nirex Reference Vault Backfill (NRVB), a cement backfill material, to capture carbon dioxide from Intermediate Level Radioactive waste packages after repository backfilling, has been assessed. Large-scale trials assessed the physical and chemical reaction of carbon dioxide with the hardened backfill grout. A carbonation front, radial in nature, was observed extending into the grout and three distinct regions were identified in the hardened grouts. A carbonated region, a carbonation front, and a partially carbonated zone were discerned. Potassium, and to a lesser extent sodium, were concentrated in the carbonated region just behind of the main reaction front. The area just ahead of the carbonation front was enriched in both sulphur and aluminium, while sulphur was found to be depleted from the carbonated material behind the main reaction front. Within the main carbonated region, virtually all of the hydrated cement phases were found to be carbonated, and carbonation extended throughout the grout, even within material indicated by phenolphthalein solution to be uncarbonated. Importantly, carbonation was observed to impact both the mineral assemblage and porosity of the cement backfill; it is therefore important to understand these characteristics in terms of the long term evolution of NRVB and its groundwater buffering safety function within the geological disposal facility near-field

Identifying lineage effects when controlling for population structure improves power in bacterial association studies

Bacteria pose unique challenges for genome-wide association studies because of strong structuring into distinct strains and substantial linkage disequilibrium across the genome1,2. Although methods developed for human studies can correct for strain structure3,4, this risks considerable loss-of-power because genetic differences between strains often contribute substantial phenotypic variability5. Here, we propose a new method that captures lineage-level associations even when locus-specific associations cannot be fine-mapped. We demonstrate its ability to detect genes and genetic variants underlying resistance to 17 antimicrobials in 3,144 isolates from four taxonomically diverse clonal and recombining bacteria: Mycobacterium tuberculosis, Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae. Strong selection, recombination and penetrance confer high power to recover known antimicrobial resistance mechanisms and reveal a candidate association between the outer membrane porin nmpC and cefazolin resistance in E. coli. Hence, our method pinpoints locus-specific effects where possible and boosts power by detecting lineage-level differences when fine-mapping is intractable

Seed Regeneration Potential of Canopy Gaps at Early Formation Stage in Temperate Secondary Forests, Northeast China

Promoting the seed regeneration potential of secondary forests undergoing gap disturbances is an important approach for achieving forest restoration and sustainable management. Seedling recruitment from seed banks strongly determines the seed regeneration potential, but the process is poorly understood in the gaps of secondary forests. The objectives of the present study were to evaluate the effects of gap size, seed availability, and environmental conditions on the seed regeneration potential in temperate secondary forests. It was found that gap formation could favor the invasion of more varieties of species in seed banks, but it also could speed up the turnover rate of seed banks leading to lower seed densities. Seeds of the dominant species, Fraxinus rhynchophylla, were transient in soil and there was a minor and discontinuous contribution of the seed bank to its seedling emergence. For Quercus mongolica, emerging seedling number was positively correlated with seed density in gaps (R = 0.32, P<0.01), especially in medium and small gaps (<500 m2). Furthermore, under canopies, there was a positive correlation between seedling number and seed density of Acer mono (R = 0.43, P<0.01). Gap formation could promote seedling emergence of two gap-dependent species (i.e., Q. mongolica and A. mono), but the contribution of seed banks to seedlings was below 10% after gap creation. Soil moisture and temperature were the restrictive factors controlling the seedling emergence from seeds in gaps and under canopies, respectively. Thus, the regeneration potential from seed banks is limited after gap formation