Experimental optimization of microbially induced calcite precipitation (Micp) for contact erosion control in earth dams

Microbial Induced Calcite Precipitation (MICP) is a bio-mediated soil improvement technique which is low-cost, low-maintenance and non-disruptive to wild life and aesthetics. It holds the potential for simultaneously retaining the hydraulic conductivity, increasing the shear resistance and preferentially cementing the interface between coarse and fine particles. Previous studies have shown that, unlike other biocementation works—such as liquefaction control and railroad embankment stabilisation—the shear strength increase necessary on interfaces vulnerable to contact erosion in earth dams is very low, requiring different optimal MICP treatment formulations to be explored. The study presented herein focuses on MICP treatment across the boundary between a fine sand and a coarse sand in the context of one-dimensional flow column experiments. Treatment optimisation is evaluated by varying important parameters including formulations of chemical amendments, and the particle size distribution of the fine grained fraction. Subsequently, a procedure is developed for measuring the calcite bond shear strength using an Erosion Function Apparatus (EFA), whereby an undisturbed MICP treated specimen is slowly protruded into a flume and eroded by surface-parallel flow. Measurements of the surface movement of the eroding sample are made with a laser reflecting on the soil surface in the flume. The progress of erosion can hence be monitored as the flow velocity is increased. Results open up new interesting perspectives on the treatment scheme needed for MICP implementation for contact erosion control in dams

Prevalence of Symptomatic and Asymptomatic Peripheral Arterial Disease and the Value of the Ankle-brachial Index to Stratify Cardiovascular Risk

AbstractObjectivesTo determine the prevalence of ankle-brachial index (ABI)<0.9 and symptomatic peripheral arterial disease (PAD), association with cardiovascular risk factors (CVRF), and impact of adding ABI measurement to coronary heart disease (CHD) risk screening.DesignPopulation-based cross-sectional survey of 6262 participants aged 35–79 in Girona, Spain.MethodsStandardized measurements (CVRF, ABI, 10-year CHD risk) and history of intermittent claudication (IC), CHD, and stroke were recorded. ABI<0.9 was considered equivalent to moderate-to-high CHD risk (≥10%).ResultsABI<0.9 prevalence was 4.5%. Only 0.62% presented low ABI and IC. Age, current smoker, cardiovascular disease, and uncontrolled hypertension independently associated with ABI<0.9 in both sexes; IC was also associated in men and diabetes in women. Among participants 35–74 free of cardiovascular disease, 6.1% showed moderate-to-high 10-year CHD risk; adding ABI measurement yielded 8.7%. Conversely, the risk function identified 16.8% of these participants as having 10-year CHD risk>10%. In participants 75–79 free of cardiovascular disease, the prevalence of ABI<0.9 (i.e., CHD risk≥10%) was 11.9%.ConclusionsABI<0.9 is relatively frequent in those 35–79, particularly over 74. However, IC and CHD risk≥10% indicators are often missing. Adding ABI measurement to CHD-risk screening better identifies moderate-to-high cardiovascular risk patients

A Cross-Site Analysis of Neotropical Bird Hunting Profiles

© The Author(s) 2017. Subsistence hunting of neotropical birds is common and widespread in the tropical forests of Latin America. Although its sustainability under different scenarios is subject to debate, hunting has already contributed to the decline and local extirpation of several taxa and is considered to be a significant threat to a range of large-bodied species. Gaining a better understanding of the variability of hunting patterns, as well as the factors that can potentially be used to predict them, is important if we are to develop conservation strategies that target the species most likely to be experiencing declines. In this article, we examine the avian hunting profiles of 65 communities in the neotropics. We describe their variability and look at the relationship between a hunting profile and (a) its geographical location, (b) the community’s age, (c) the community’s population size, and (d) the year in which the survey was carried out. We find that there is a significant but weak relationship between a community’s geographic location and the composition of its bird hunting profile, and that prey profiles can be considerably different even among close neighbors. We found no relationship between a community’s age or size and the mean biomass of bird prey hunted. Our results challenge the assumption that older and larger settlements have a predictable impact upon avian prey communities and suggest that cultural preferences or the starting availability of prey species can change rapidly over short distances

Online collaboration and cooperation : the recurring importance of evidence, rationale and viability

This paper investigates collaboration in teaching and learning and draws out implications for the promotion of collaboration within online environments. It is divided into four sections. First the case for collaboration, including specifically cooperative approaches, is explored. This case revolves around the impact of collaboration on the quality of learning and on learning outcomes. Collaboration is seen as constrained by context but, if structured and rewarded, it will bring important motivational and cognitive benefits. Next, the case for online collaboration is examined. This is based on longstanding arguments about the benefits of working together albeit in an environment which offers greater reach; a mix of media; and archives of interaction. The third section of the paper compares perspectives on online collaboration with a longer tradition of research into collaboration in general; it critiques the idea that online mediation offers a paradigm change in teaching and learning. The fourth section of the paper considers future directions for promoting online collaboration

Experimental optimization of microbially induced calcite precipitation (Micp) for contact erosion control in earth dams

Microbial Induced Calcite Precipitation (MICP) is a bio-mediated soil improvement technique which is low-cost, low-maintenance and non-disruptive to wild life and aesthetics. It holds the potential for simultaneously retaining the hydraulic conductivity, increasing the shear resistance and preferentially cementing the interface between coarse and fine particles. Previous studies have shown that, unlike other biocementation works—such as liquefaction control and railroad embankment stabilisation—the shear strength increase necessary on interfaces vulnerable to contact erosion in earth dams is very low, requiring different optimal MICP treatment formulations to be explored. The study presented herein focuses on MICP treatment across the boundary between a fine sand and a coarse sand in the context of one-dimensional flow column experiments. Treatment optimisation is evaluated by varying important parameters including formulations of chemical amendments, and the particle size distribution of the fine grained fraction. Subsequently, a procedure is developed for measuring the calcite bond shear strength using an Erosion Function Apparatus (EFA), whereby an undisturbed MICP treated specimen is slowly protruded into a flume and eroded by surface-parallel flow. Measurements of the surface movement of the eroding sample are made with a laser reflecting on the soil surface in the flume. The progress of erosion can hence be monitored as the flow velocity is increased. Results open up new interesting perspectives on the treatment scheme needed for MICP implementation for contact erosion control in dams

Characterisation of CaCO<inf>3</inf> phases during strain-specific ureolytic precipitation

Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, however, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. We have studied microbial induced calcium carbonate (CaCO3) precipitation (MICP) in three ureolytic bacterial strains from the Sporosarcina family, including S. newyorkensis, a newly isolated microbe from the deep sea. We find that the interplay between structural water and strain-specific amino acid groups is fundamental to the stabilisation of vaterite and that, under the same conditions, different isolates yield distinctly different polymorphs. The latter is found to be associated with different urease activities and, consequently, precipitation kinetics, which change depending on pressure-temperature conditions. Further, CaCO3 polymorph selection also depends on the coupled effect of chemical treatment and initial bacterial concentrations. Our findings provide new insights into strain-specific CaCO3 polymorphic selection and stabilisation, and open up promising avenues for designing bio-reinforced geo-materials that capitalise on the different particle bond mechanical properties offered by different polymorphs

Characterisation of CaCO 3 phases during strain-specific ureolytic precipitation

Abstract: Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, however, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. We have studied microbial induced calcium carbonate (CaCO3) precipitation (MICP) in three ureolytic bacterial strains from the Sporosarcina family, including S. newyorkensis, a newly isolated microbe from the deep sea. We find that the interplay between structural water and strain-specific amino acid groups is fundamental to the stabilisation of vaterite and that, under the same conditions, different isolates yield distinctly different polymorphs. The latter is found to be associated with different urease activities and, consequently, precipitation kinetics, which change depending on pressure-temperature conditions. Further, CaCO3 polymorph selection also depends on the coupled effect of chemical treatment and initial bacterial concentrations. Our findings provide new insights into strain-specific CaCO3 polymorphic selection and stabilisation, and open up promising avenues for designing bio-reinforced geo-materials that capitalise on the different particle bond mechanical properties offered by different polymorphs