Flocculation settling characteristics of mud: sand mixtures

When natural muds become mixed with sandy sediments in estuaries, it has a direct effect on the flocculation process and resultant sediment transport regime. Much research has been completed on the erosion and consolidation of mud/sand mixtures, but very little is known quantitatively about how mixed sediments interact whilst in suspension, particularly in terms of flocculation. This paper presents the settling velocity findings from a recent laboratory study which examined the flocculation dynamics for three different mud/sand mixtures at different concentrations (0.2–5 g.l^?1) and turbulent shear stresses (0.06–0.9 Pa) in a mini-annular flume. The low intrusive video-based Laboratory Spectral Flocculation Characteristics instrument was used to determine floc/aggregate properties (e.g., size, settling velocity, density and mass) for each population. Settling data was assessed in terms of macrofloc (>160 μm) and microfloc (<160 μm) settling parameters: Ws_macro and Ws_micro, respectively. For pure muds, the macroflocs are regarded as the most dominant contributors to the total depositional flux. The parameterised settling data indicates that by adding more sand to a mud/sand mixture, the fall velocity of the macrofloc fraction slows and the settling velocity of microflocs quickens. Generally, a mainly sandy suspension comprising 25% mud and 75% sand (25M:75S), will produce resultant Ws_macro which are slower than Ws_micro. The quickest Ws_micro appears to consistently occur at a higher level of turbulent shear stress (τ?～?0.6 Pa) than both the macrofloc and microfloc fractions from suspensions of pure natural muds. Flocculation within a more cohesively dominant muddy-sand suspension (i.e., 75M:25S) produced macroflocs which fell at similar speeds (±10%) to pure mud suspensions at both low (200 mg l^?1) and intermediate (1 g?l^?1) concentrations at all shear stress increments. Also, low sand content suspensions produced Ws_macro values that were faster than the Ws_micro rates. In summary, the experimental results of the macrofloc and microfloc settling velocities have demonstrated that flocculation is an extremely important factor with regards to the depositional behaviour of mud/sand mixtures, and these factors must be considered when modelling mixed sediment transport in the estuarine or marine environment.     

Materializing complementary and alternative medicine: aromatherapy, chiropractic, and Chinese herbal medicine in the UK

The paper explores the materiality of complementary and alternative medicine (CAM), with particular reference to aromatherapy, Chinese herbal medicine, and chiropractic, as presented in the journals of UK-based practitioner associations. The paper begins by arguing for a poststructuralist approach to materiality. It then considers how certain materials play a signature (or emblematic) role in the definition and practice of various CAM modalities. Focusing primarily on the examples of essential oils and herbal remedies, we consider how such materials are valued for their agency and expressiveness within the therapeutic encounter. However, these signature materials also possess the ability to produce unwanted effects which regulators, practitioners, and manufacturers seek to control. Consequently, the materialization of CAM is fraught with tension. In addition to these signature materials, the paper also considers the wider assemblage of materials (especially treatment couches) that supplement the taking place of CAM. Although these supplementary materials are often treated in a functional, instrumental, and taken-for-granted manner, these materials are also shown to be duplicitous. The paper concludes by arguing that the continuing professionalization and regulation of the UK CAM sector is radically changing the situated consistency of its signature and supplementary materials.     

Short life-span of the ore-forming system at the Porgera gold deposit, Papua New Guinea: laser 40Ar/39Ar dates for roscoelite, biotite, and hornblende

The Porgera gold deposit, Papua New Guinea, is associated with sodic-alkalic, hypabyssal intrusions of alkali basaltic to mugearitic composition. The intrusions were emplaced into Cretaceous mudstones and siltstones in the latest Miocene, and both igneous and sedimentary rocks are mineralized. Three types of veins occur: (1) magnetite-sulfide - Au-carbonate veins; (2) base-metal sulfide - Au-carbonate veins; and, economically most important, (3) quartz-roscoelite-Au veins and breccias. Magmatic hornblende and biotite, hydrothermal biotite from alteration selvages associated with the magnetite-sulfide - Au veins, and roscoelite were dated using the laser ⁴⁰Ar/³⁹Ar step-heating technique. Magmatic biotite yielded a date of 5.99ǂ.11 Ma (2C error; MSWD=3.7), and two samples of magmatic hornblende provided dates of 6.35ǂ.23 Ma (MSWD=1.0) and 6.3ǂ.7 Ma (MSWD=2.6). Hydrothermal biotite provided a date of 5.98ǂ.13 Ma (MSWD=2.7), and analyses of two roscoelite samples yielded dates of 5.92ǂ.09 Ma (MSWD=2.0) and 5.92ǂ.17 Ma (MSWD=2.0). The date of the magmatic biotite is interpreted to represent the age of the intrusions more accurately than the hornblende dates because small amounts of excess ⁴⁰Ar were present in the hornblende samples. The date for hydrothermal biotite is interpreted to be the age of the alteration associated with the magnetite-sulfide - Au veins (the paragenetically earliest veins), and thus reflects the age of the onset of the mineralizing activity at Porgera. Based on the two dates for roscoelite, the age of the main ore deposition event is interpreted to be 5.92ǂ.08 Ma. The apparent ages for the intrusive and the mineralizing events are thus identical within error, and suggest that the magmatic and ore-forming system at Porgera was short-lived.     

The use of the possibility theory to investigate the epistemic uncertainties within scenario-based earthquake risk assessments

This paper presents a methodology to represent and propagate epistemic uncertainties within a scenario-based earthquake risk model. Unlike randomness, epistemic uncertainty stems from incomplete, vague or imprecise information. This source of uncertainties still requires the development of adequate tools in seismic risk analysis. We propose to use the possibility theory to represent three types of epistemic uncertainties, namely imprecision, model uncertainty and vagueness due to qualitative information. For illustration, an earthquake risk assessment for the city of Lourdes (Southern France) using this approach is presented. Once adequately represented, uncertainties are propagated and they result in a family of probabilistic damage curves. The latter is synthesized, using the concept of fuzzy random variables, by means of indicators bounding the true probability to exceed a given damage grade. The gap between the pair of probabilistic indicators reflects the imprecise character of uncertainty related to the model, thus picturing the extent of what is ignored and can be used in risk management.     

Comparing the behaviour of spherical beads and natural grains in bedload mixtures

It is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. © 2020 John Wiley & Sons, Ltd.     

Buried glacier ice in southern Iceland and its wider significance

Geo-electrical resistivity surveys have been carried out at recently deglaciated sites in front of three glaciers in southern Iceland: Skeiðarájökull, Hrútárjökull, and Virkisjökull. The results show the presence of old glacier ice beneath debris mantles of various thickness. We conclude that buried glacier ice has survived for at least 50 years at Virkisjökull and Hrútárjökull, and probably for over 200 years at Skeiðarájökull. Additional data from a further site have identified a discontinuous ice core within 18th-century jökulhlaup deposits. Photographic and lichenometric evidence show that the overlying debris has been relatively stable, and hence melting of the ice at all four sites is proceeding slowly due to the heat-shielding properties of the overburden. The geomorphic implications are pertinent when considering the potential longevity of buried ice. The possible implications for dating techniques, such as lichenometry, radiocarbon dating and cosmogenic surface-exposure dating are also important, as long-term readjustments of surface forms may lead to dating inaccuracy. Finally, it is recognised that landscape development in areas of stagnant ice topography may post-date initial deglaciation by a considerable degree.     

Seeing ghosts: parsing China’s “ghost city” controversy

Controversy has arisen in recent years over the creation of so-called “ghost cities” across China. The ghost city term tends to describe large-scale urban areas, sometimes planned as new towns, featuring an abundance of new built space and appearing to also have extremely low tenancy. This article examines key questions related to the ghost city phenomenon, such as: what is a ghost city? Are ghost cities driven by a tendency toward over-supply in housing? How are local-level political incentives aligned to foster the production of ghost cities? Are ghost cities temporary anomalies or structural features of China’s urban-led economic growth model? We discuss recent scholarly research into ghost cities and present original findings to show how an excess of urban space may plague certain Chinese cities.     

Environmental Justice in Hamburg,Germany

This environmental justice study investigates whether disempowered segments of the population in Hamburg, Germany, namely, foreigners and the poor, reside disproportionately in neighborhoods that contain, have higher concentrations of, and are in closer proximity to facilities releasing toxic chemicals into the environment. Methods include choropleth mapping; comparisons of means, correlation, and ordinary least squares (OLS); and spatial econometric regression. The results provide evidence that toxic release facilities are disproportionately located within, and closer to, neighborhoods with comparatively higher proportions of foreigners and the poor as compared to those with higher proportions of German citizens and the non-poor. We speculate that the causes of this pattern of environmental inequity are similar to the causes scholars have proposed for comparable patterns observed in many U.S. cities, where marginalized immigrant or minority groups subject to discrimination in housing and employment have sought low-wage labor in industrial areas, whereas wealthier German citizens have settled in environmentally safer parts of the city.     

Crustal structure of the Newfoundland rifted continental margin from constrained 3-D gravity inversion

The rifting history of the Atlantic continental margin of Newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2-D seismic surveys. While informative, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin. A 3-D gravity inversion of the free air data over the Newfoundland margin allows us to generate a 3-D density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage. Results of the gravity inversion show good correspondence with Moho depths from seismic results. A shallowing of the Moho to 12 km depth is resolved on the shelf at the northern edge of the Grand Banks, in a region poorly sampled by other methods. Comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends. Such insights must act as constraints for future palaeoreconstructions of North Atlantic rifting.