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The flocculation behavior of clay minerals in aquatic environments is an important process in estuarine and riverine dynamics, where strong gradients in salinity can locally occur. Various contradicting observations have been reported in the literature on the impact of salt concentration on the settling process of cohesive sediments. To address this issue in a systematic manner, we investigate the settling behavior of clay minerals as a function of the salt concentration of the ambient water. Specifically, we focus on montmorillonite as a prototype clay mineral with a high cation exchange capacity (CEC). To this end, we study suspensions of Wyoming bentonite (Volclay SPV) as a very important constituent for many constructional and industrial purposes. We perform an experimental campaign to study the settling behavior of moderately turbid montmorillonite concentrations in monovalent salt solutions with different salinities (sodium chloride) to represent different environments ranging from deionized to ocean water, respectively. The subsequent settling process was monitored by taking pictures by a camera in regular time intervals over a total observation time up to 48 h. In addition, a modified hydrometer analysis is conducted to determine the grain size distribution (in terms of an equivalent diameter) of the flocculated clay suspension in salt water. Despite the rather high cation exchange capacity of the investigated clay (CEC=88.1), our results show that the settling speed drastically increases within a range of 0.6–1.0 PSU and stays approximately constant for higher salinities. This critical salt concentration is defined here as the critical coagulation concentration (CCC) and lies well below the salinity of natural open water bodies. The hydrometer analysis revealed that 60% of the agglomerates exceed the equivalent grain size of 20 μm. Finally, the findings of this study are supplemented with experiments studying the effect of Extracellular Polymeric Substances (EPS) on the flocculation behavior of bentonite in salt water. Our results demonstrate that salinity is the original trigger for flocculation, whereas EPS allows for even larger floc size but it does not play a significant role for the settling processes of bentonite in estuarine environments.

This study is about understanding how public policy is made. This is done through the lens of the political economy of gambling in the State of Victoria, Australia. The study critically evaluates a body of information relating to the introduction of poker machines in licensed clubs and hotels throughout Victoria between 1991 and 2002. Poker machines were introduced in Victoria in 1991. By 2002 gamblers were losing over $2.33 billion annually on poker machines. The gambling industry and the State Government of Victoria receive significant dividends from the poker machine largesse. Poker machine taxes contribute over ten per cent of state budget income. Making money from poker machines was vigorously pursued by government and industry. As losses from gamblers reached new heights year upon year, civil society and apolitical interests pondered how to confront the rise in problem gambling by influencing changes to gambling policy. A number of key government policy decisions were made between 1991 and 2002. This research seeks to understand how those decisions came into being. The social and political sciences provide the theoretical framework with which to assess the impact of elites and stakeholders on decisions. Drawing on publicly available data, including ABS statistics, available club data, and media reports, the study seeks to understand public policy making and the range of theorising that this has generated. The publicly available evidence on poker machines is examined so as to identity processes and gaps in policy theory in relation to policy making. This study demonstrates policy making operates simultaneously on two levels. One is the illusion of policy making promoted by dominant elites; the other is the reality of how meaningful public policy is made. Both realms involve engagement in conversations, interactions and decision making. This study draws attention to a third layer of engagement that is generally hidden from formal public view, scrutiny or accountability. The challenge for stakeholders who participate in the policy process is to know which environment they are engaging in at any given time, what objectives are likely to dominate debate and as a consequence, how those deemed as less powerful stakeholders could influence the formation of dominant stakeholder policy objectives. The research findings contribute to developing recommendations for strengthening theoretical approaches to understanding how public policy is made.

The shape and size of sedimentary bedforms play a key role in the reconstruction of sedimentary processes in modern and ancient environments. Recent laboratory experiments have shown that bedforms in mixed sand–clay develop at a slower rate and often have smaller heights and lengths than equivalent bedforms in pure sand. This is generally attributed to cohesive forces that can be of physical origin, caused by electrostatic forces of attraction between clay minerals, and of biological origin, caused by ‘sticky’ extracellular polymeric substances (EPS) produced by micro-organisms, such as microalgae (microphytobenthos) and bacteria. In the present paper, we demonstrate, for the first time, that these laboratory experiments are a suitable analogue for current ripples formed by tidal currents on a natural mixed sand–mud–EPS intertidal flat in a macrotidal estuary. Moreover, both the field data and the laboratory data demonstrate that the widely used definitions of ‘clean sand’ (

Landing an unmanned aerial vehicle (UAV) on a ground marker is an open problem despite the effort of the research community. Previous attempts mostly focused on the analysis of hand-crafted geometric features and the use of external sensors in order to allow the vehicle to approach the land-pad. In this article, we propose a method based on deep reinforcement learning that only requires low-resolution images taken from a down-looking camera in order to identify the position of the marker and land the UAV on it. The proposed approach is based on a hierarchy of Deep Q-Networks (DQNs) used as high-level control policy for the navigation toward the marker. We implemented different technical solutions, such as the combination of vanilla and double DQNs, and a partitioned buffer replay. Using domain randomization we trained the vehicle on uniform textures and we tested it on a large variety of simulated and real-world environments. The overall performance is comparable with a state-of-the-art algorithm and human pilots., Comment: The actual copy of the manuscript is a revised version resubmitted to IROS

Sediment gravity flows (SGFs) are the primary process by which sediment and organic carbon are transported from the continental margin to the deep ocean. Forty percent of the total marine organic carbon pool is represented by cohesive extracellular polymeric substances (EPS) produced by marine benthic and pelagic micro-organisms. EPS research to date has focussed on coastal environments, where EPS contribute to seabed stability by forming a cohesive matrix of bonds between sediment particles. The effects of this cohesive material on SGFs in the deep ocean have not been investigated, despite many decades of outcrop, subsurface, modern real-time observational, numerical, and experimental research. Here we present laboratory data that offer the first insights into the potential of biological cohesion for modulating muddy, physically cohesive, SGF dynamics. These data indicate that turbulence-modulated, high-density turbidity currents, mudflows and slides, are more susceptible to changes in flow properties than fully turbulent, low-density turbidity currents at concentrations of EPS encountered in the deep ocean. Even relatively low concentrations of EPS markedly decrease the head velocity and run-out distance of these high-density SGFs. These outcomes greatly improve our understanding of the natural distribution of SGF deposits, which form the world’s largest hydrocarbon reservoirs.

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Este libro cumple las expectativas de los alumnos de matemáticas en relación a los exámenes de secundaria (AQA) para obtener el General Certificate of Secondary Education (GCSE). Los temas del libro son: los números (tipos de números, fracciones, decimales, porcentajes, ratio y proporción), estadísticas (reuniendo y representando datos, probabilidad), álgebra (secuencias y símbolos, ecuaciones y fórmulas, coordenadas y gráficos), geometría y medida (ángulos, perímetro, área y volumen, medidas, el teorema de Pitágoras). SC Biblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín, 5 - 3 planta; 28014 Madrid; Tel. +34917748000; biblioteca@mecd.es GBR

Este libro cumple las expectativas de los alumnos de matemáticas en relación a los exámenes de secundaria (AQA) para obtener el General Certificate of Secondary Education (GCSE). Los temas del libro son: números (fracciones, decimales, porcentajes, ratio y proporción), estadísticas (reuniendo y representando datos, medidas estadísticas, probabilidad), álgebra (secuencias y símbolos, ecuaciones y fórmulas, coordenadas y gráficos, funciones al cuadrado), geometría y medidas (área y volumen, ángulos y polígonos, transformaciones y vectores, el teorema de Pitágoras, trigonometría). sc Biblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín, 5 - 3 planta; 28014 Madrid; Tel. +34917748000; biblioteca@mecd.es GBR

Many coastal and estuarine environments are dominated by mixtures of non-cohesive sand and cohesive mud. The migration rate of bedforms, such as ripples and dunes, in these environments is important in determining bed material transport rates to inform and assess numerical models of sediment transport and geomorphology. However, these models tend to ignore parameters describing the physical and biological cohesion (resulting from clay and extracellular polymeric substances, EPS) in natural mixed sediment, largely because of a scarcity of relevant laboratory and field data. To address this gap in knowledge, data were collected on intertidal flats over a spring-neap cycle to determine the bed material transport rates of bedforms in biologically-active mixed sand-mud. Bed cohesive composition changed from below 2 volume % up to 5.4 volume % cohesive clay, as the tide progressed from spring towards neap. The amount of EPS in the bed sediment was found to vary linearly with the clay content. Using multiple linear regression, the transport rate was found to depend on the Shields stress parameter and the bed cohesive clay content. The transport rates decreased with increasing cohesive clay and EPS content, when these contents were below 2.8 vol% and 0.05 weight%, respectively. Above these limits, bedform migration and bed material transport was not detectable by the instruments in the study area. These limits are consistent with recently conducted sand-clay and sand-EPS laboratory experiments on bedform development. This work has important implications for the circumstances under which existing sand-only bedform migration transport formulae may be applied in a mixed sand-clay environment, particularly as 2.8 vol% cohesive clay is well within the commonly adopted definition of ‘clean sand’.