Use of bacterial ureolysis for improved gelation of silica sol in rock grouting

Low pH silica-based grouts suitable for penetrating fine aperture fractures are increasingly being developed for use in engineering applications. Silica sol has an initial low viscosity and mixing with an accelerator destabilises the suspension producing a gel. The influence of sodium, calcium and ammonium chloride accelerators on gel time, rate of gelation and shear strength of the resulting gel were investigated in this study. For the first time the potential use of bacterial ureolysis as an accelerator for the destabilisation of silica sol was also explored. This study demonstrates that bacterial ureolysis can be used to control the gelation of silica sol. The rate of ureolysis increases with increasing bacterial density, resulting in faster gel times and higher rates of gelation. In addition, for grouts with similar gel times, using bacterial ureolysis to induce destabilisation results in a higher rate of gelation, a higher final shear strength and a more uniform gel than direct addition of the corresponding chemical accelerator. These results suggest that bacterial ureolysis could potentially be used in rock grouting to achieve long gel times and hence greater penetration, while also maintaining sufficiently rapid gelation to minimise issues related to fingering and erosion of the fresh grout

Variation in Ringed Seal Density and Abundance in Western Hudson Bay Estimated from Aerial Surveys, 1995 to 2013

We conducted systematic aerial surveys of ringed seals along strip transects in western Hudson Bay (WHB), Canada, in late May to early June of 1995–97, 1999, 2000, 2007–10, and 2013. The density of ringed seals hauled out on ice over the entire study area ranged from 1.22 seals/km2 in 1995, to 0.20 seals/km2 in 2013. Density estimates varied significantly over the study period and, with the exception of 2013, appeared to follow a cyclical pattern. Although density estimates also appear to follow a downward trend over time, results of multiple linear regression, weighted by survey effort, indicated no significant trend in ringed seal density as a function of year, survey date, or proportion of open water. In addition, no significant correlation was observed among any of the environmental variables and density estimates. As the proportion of seals hauled out at the time of the survey is unknown, the density estimates of WHB ringed seals presented in this study should be considered indices that might be useful to explore trends in abundance. Although our results do not indicate that a significant decline has occurred, the low density estimate in 2013 may indicate that population changes unrelated to a natural cycle are taking place. We were unable to test for direct effects of changes in food supply or predation, but polar bears, Arctic foxes, and Inuit communities in the Hudson Bay region all would be negatively affected should ringed seal populations undergo significant declines. Further monitoring and directed research are necessary to understand what mechanism may be responsible for the observed changes in ringed seal density.Nous avons fait les levés aériens systématiques de phoques annelés sur de longs transects en bandes dans l’ouest de la baie d’Hudson (OBH), au Canada, de la fin de mai au début de juin des années 1995 à 1997, 1999, 2000, 2007 à 2010 et 2013. Pendant toute la durée de l’étude, la densité de phoques annelés hissés sur la glace a varié de 1,22 phoque/km2 en 1995 à 0,20 phoque/km2 en 2013. Les estimations de densité ont varié considérablement au cours de la période visée par l’étude et, à l’exception de 2013, elles semblaient suivre un profil cyclique. Bien que les estimations de densité semblent également suivre une tendance à la baisse au fil du temps, les résultats de la régression linéaire multiple, pondérée par les levés, n’ont indiqué aucune tendance importante sur le plan de la densité de phoques annelés en fonction de l’année, de la date des levés ou de la proportion d’eaux libres. Par ailleurs, aucune corrélation importante n’a été observée pour n’importe quelle variable environnementale et n’importe quelle estimation de densité. Puisque la proportion de phoques hissés au moment des levés est inconnue, les estimations de densité de phoques annelés dans l’OBH présentées dans cette étude devraient être considérées comme des indices susceptibles d’aider à explorer les tendances en matière d’abondance. Bien que nos résultats ne laissent pas entrevoir la présence d’un déclin important, la faible estimation de densité enregistrée en 2013 pourrait indiquer qu’il se produit des changements de population et que ceux-ci ne sont pas attribuables à un cycle naturel. Nous n’avons pu examiner les effets directs des changements en matière d’approvisionnement alimentaire ou de prédation, mais les ours polaires, les renards arctiques et les communautés inuites de la région de la baie d’Hudson subiraient tous des effets négatifs si les populations de phoques annelés diminuaient considérablement. Il y a lieu de faire de la surveillance et des recherches dirigées pour comprendre à quel mécanisme les changements observés sur le plan de la densité de phoques annelés pourrait être attribuable

An analytical model for the control of silica grout penetration in natural groundwater systems

Over the last three decades, colloidal silica has been investigated and more recently adopted as a low viscosity grouting technology (e.g. for grouting rock fractures within geological disposal facilities nuclear waste). The potential of colloidal silica as a favourable grouting material exists due to: its initial low viscosity; its low hydraulic conductivity after gelling (of the order of 10-7 cm/s); the very low injection pressures required; its controllable set/gel times (from minutes to several days); the fact it is environmentally inert; its small particle size (less than hundreds of nanometres) and its cost-effectiveness. Despite the documented success of colloidal silica based grouts for hydraulic barrier formation, research has not translated into widespread industrial use. A key factor in this limited commercial uptake is the lack of a predictive model for grout gelling which controls grout penetration: whilst data are available to underpin design of a grouting campaign in laboratory conditions, little research has been done to underpin applications in natural environments. Here we develop and validate an analytical model of colloidal silica gelling in groundwaters with varying pH and background electrolyte concentrations. This paper presents an analytical model that accounts for changes in pH, electrolyte concentration, cation valency and molar mass, silica particle size and silica concentration giving predictive capability without the need for site-specific calibration. The model is validated against experimental observations for gel times of 32 minutes to 766 minutes, the model accurately predicts the log(gel time) with an average error of 4% which corresponds to an R2 value of 0.96 The model is then applied to a hypothetical case study to demonstrate its use in grout design, based on published in-situ groundwater data from the Olkiluoto area of Finland. The model successfully predicts the required accelerator concentration to achieve a grout gel time of approximately 50 minutes, taking into account the cations already present within the synthetic groundwater

Extending DerSimonian and Laird's methodology to perform network meta-analyses with random inconsistency effects.

Network meta-analysis is becoming more popular as a way to compare multiple treatments simultaneously. Here, we develop a new estimation method for fitting models for network meta-analysis with random inconsistency effects. This method is an extension of the procedure originally proposed by DerSimonian and Laird. Our methodology allows for inconsistency within the network. The proposed procedure is semi-parametric, non-iterative, fast and highly accessible to applied researchers. The methodology is found to perform satisfactorily in a simulation study provided that the sample size is large enough and the extent of the inconsistency is not very severe. We apply our approach to two real examples.DJ, RT and IRW are employed by the UK Medical Research Council (code U105260558). JB is supported by the UK MRC grant numbers G0902100 and MR/K014811/1.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/sim.675

Photochemical Generation of a Tryptophan Radical within the Subunit Interface of Ribonucleotide Reductase

United States. National Institutes of Health (GM029595

A Microsoft-Excel-based tool for running and critically appraising network meta-analyses--an overview and application of NetMetaXL.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.BACKGROUND: The use of network meta-analysis has increased dramatically in recent years. WinBUGS, a freely available Bayesian software package, has been the most widely used software package to conduct network meta-analyses. However, the learning curve for WinBUGS can be daunting, especially for new users. Furthermore, critical appraisal of network meta-analyses conducted in WinBUGS can be challenging given its limited data manipulation capabilities and the fact that generation of graphical output from network meta-analyses often relies on different software packages than the analyses themselves. METHODS: We developed a freely available Microsoft-Excel-based tool called NetMetaXL, programmed in Visual Basic for Applications, which provides an interface for conducting a Bayesian network meta-analysis using WinBUGS from within Microsoft Excel. . This tool allows the user to easily prepare and enter data, set model assumptions, and run the network meta-analysis, with results being automatically displayed in an Excel spreadsheet. It also contains macros that use NetMetaXL's interface to generate evidence network diagrams, forest plots, league tables of pairwise comparisons, probability plots (rankograms), and inconsistency plots within Microsoft Excel. All figures generated are publication quality, thereby increasing the efficiency of knowledge transfer and manuscript preparation. RESULTS: We demonstrate the application of NetMetaXL using data from a network meta-analysis published previously which compares combined resynchronization and implantable defibrillator therapy in left ventricular dysfunction. We replicate results from the previous publication while demonstrating result summaries generated by the software. CONCLUSIONS: Use of the freely available NetMetaXL successfully demonstrated its ability to make running network meta-analyses more accessible to novice WinBUGS users by allowing analyses to be conducted entirely within Microsoft Excel. NetMetaXL also allows for more efficient and transparent critical appraisal of network meta-analyses, enhanced standardization of reporting, and integration with health economic evaluations which are frequently Excel-based.CC is a recipient of a Vanier Canada Graduate Scholarship from the Canadian Institutes of Health Research (funding reference number—CGV 121171) and is a trainee on the Canadian Institutes of Health Research Drug Safety and Effectiveness Network team grant (funding reference number—116573). BH is funded by a New Investigator award from the Canadian Institutes of Health Research and the Drug Safety and Effectiveness Network. This research was partly supported by funding from CADTH as part of a project to develop Excel-based tools to support the conduct of health technology assessments. This research was also supported by Cornerstone Research Group

Roost Selection by Synanthropic Bats in Rural Kenya: Implications for Human-wildlife Conflict and Zoonotic Pathogen Spillover

Many wildlife species are synanthropic and use structures built by humans, creating a high-risk interface for human–wildlife conflict and zoonotic pathogen spillover. However, studies that investigate features of urbanizing areas that attract or repel wildlife are currently lacking. We surveyed 85 buildings used by bats and 172 neighbouring buildings unused by bats (controls) in southeastern Kenya during 2021 and 2022 and evaluated the role of microclimate and structural attributes in building selection. We identified eight bat species using buildings, with over 25% of building roosts used concurrently by multiple species. Bats selected taller cement-walled buildings with higher water vapour pressure and lower presence of permanent human occupants. However, roost selection criteria differed across the most common bat species: molossids selected structures like those identified by our main dataset whereas Cardioderma cor selected buildings with lower presence of permanent human occupants. Our results show that roost selection of synanthropic bat species is based on specific buildings attributes. Further, selection criteria that facilitate bat use of buildings are not homogeneous across species. These results provide information on the general mechanisms of bat–human contact in rural settings, as well as specific information on roost selection for synanthropic bats in urbanizing Africa

The incidence and make up of ability grouped sets in the UK primary school

The adoption of setting in the primary school (pupils ability grouped across classes for particular subjects) emerged during the 1990s as a means to raise standards. Recent research based on 8875 children in the Millennium Cohort Study showed that 25.8% of children in Year 2 were set for literacy and mathematics and a further 11.2% of children were set for mathematics or literacy alone. Logistic regression analysis showed that the best predictors of being in the top set for literacy or mathematics were whether the child was born in the Autumn or Winter and cognitive ability scores. Boys were significantly more likely than girls to be in the bottom literacy set. Family circumstances held less importance for setting placement compared with the child’s own characteristics, although they were more important in relation to bottom set placement. Children in bottom sets were significantly more likely to be part of a long-term single parent household, have experienced poverty, and not to have a mother with qualifications at NVQ3 or higher levels. The findings are discussed in relation to earlier research and the implications for schools are set out

Microseismic monitoring illuminates phases of slope failure in soft soils

The role of microseismic monitoring in rock slope stability has been long established: large microseismic events associated with rock failure can be detected by seismometers, even at distances of a few kilometres from the source. This is a favourable characteristic for the monitoring of mountainous areas prone to failure. We show that microseismic monitoring, using short-period arrays and a sufficiently high sampling rate, can also record weak precursory signals, that could represent early phases of a larger scale slope failure in soft soils. We validate this hypothesis with field observations. We find that, even in high attenuation material such as clays, it is possible to record and detect in the frequency domain, soil failures at source-to-receiver distances up to 10 m for crack formation/propagation to more than 43 m for small (less than 2.5 m3) events. Our results show for the first time, an extended frequency range (10 Hz to 380 Hz) where small soil failures can be detected at short monitoring distances, even at sites with high background noise levels. This is the first published study focusing on ground-truthed only, slope failure induced seismic signals in soft soils at field scale and within the seismic frequency range (1–500 Hz). We suggest that microseismic monitoring could complement existing monitoring techniques to characterize the response and structural integrity of earth structures, such as embankments, where the monitoring distances are a few 10s of metres, with the potential to detect any material deterioration at the very early stages. This study does not focus on automatic classification of slope failure signals, however, our observations and methodology could form the basis for the future development of such an approach