Can new information on suspended sediment floc characteristics improve understanding of cohesive sediment behaviour?

Within aquatic environments cohesive fine-grained sediments and mixed sediments are transported as loosely bound aggregates, or flocs, with low density, high porosity and irregular, fragile structures. Their transport behaviour, particularly settling velocity, is largely controlled by their physical characteristics including floc size, shape, porosity and density. Current measurement techniques, such as optical microscopy, floc cameras and electron microscopy, either measure these characteristics as 2-dimensional simplifications of 3-dimensional structures or estimate parameters using assumptions of e.g., spherical shape or fractal mathematics. Yet the accuracy of these techniques is questionable given their reliance on 2D imagery which cannot be used to accurately reconstruct the 3D geometries of irregularly shaped structures. Here, we present new data on the novel 3D quantification of these characteristics using 3D micro-computed tomography (3D micro-CT). Comparing these results against 2D measurements for the same floc samples enables the validity of traditional 2D imaging methods as a means of describing floc geometries to be tested.The 2D and 3D geometries of flocs with different organic matter (OM) concentrations were investigated. Three 'synthetic' floc populations were generated consisting of bentonite clay with concentrations of OM (xanthan gum) at 0.1%, 2% and 5%. In addition, a 'natural' floc population was generated from natural estuarine sediment containing intrinsic OM. To measure 2D floc geometries, flocs were settled in a floc camera system, equipped with a modified settling column to facilitate floc capture. Captured flocs were subsequently stabilised in agarose gel and transferred for 3D analysis via micro-CT. 3D quantification of floc size, shape, porosity and density at resolution c. 10 microns indicates that floc shapes are highly irregular and non-fractal with up to 5 orders of aggregation. Comparison between 2D and 3D physical characteristics (variables quantifying size, shape and density) indicate floc properties estimated from 2D representations are highly misleading and are skewed in a systematic way that appears to related to the orientation of the floc particles when imaged in the water column

Investigation of the dynamics of 3-D flocs with complex morphology via Stokesian dynamics simulations

Understanding the transport behaviors of suspended particulate matter (SPM) is crucial for analyzing the impact and the flux of sediment in natural aquatic environment. SPM usually exists in form of flocs which are fragile and loosely bound aggregates characterized by highly irregular 3D shape, low effective densities and high porosity [1]. Previous studies of the physical characteristics of flocs are often based on simplified 2-D geometries of complex 3-D shapes. With the availability of 3-D sampling data of flocs, we employ Stokesian dynamics simulations to investigate the vertical or horizontal transport behaviors of flocs, e.g. settling under gravity or movement under shear flows. The correlations between the floc shapes, the transport behaviors and the floc internal stresses imposed by surrounding fluid are investigated. 3-D voxel-based datasets of the flocs are generated by conducting non-destructive 3-D X-ray computed tomography imaging on the stabilized floc samples, following the preparation protocol described in Wheatland et al. [2]. Based on the resulting voxel-based images of the flocs, the structure of each individual floc is modelled as an assembly of identical solid spheres and the velocity of the assembly is solved via Stokesian dynamics [3,4]. An automated process of predicting the dynamics of a floc in liquid environment from its voxel image is established. The entire modelling approach can serve as a powerful tool for analyzing the parameters determining the flocs transport behaviors and possibly provide inputs for modelling sediment bed growth rate at macro scales. Acknowledgements: The funding support from NERC project NE/N011678/1 has been acknowledged. References: [1] Droppo (2001) Hydrol. Process. 15:1551-1564; [2] Wheatland et al. (2017) Environ. Sci. Technol. 51:8917-8925; [3] Bossis et al. (1991) J. Chem. Phys. 94:5064-5070; [4] Swan et al. (2011) Phys. Fluids 23:071901. [5] Brady et al. (1988) Annu. Rev. Fluid Mech. 20.1:111-157

The cross-sectional associations of chronic conditions and disability with self-reported physical activity among adults in England

Objective: Using cross-sectional data from the 2018 Health Survey for England, this study describes the types of impairment reported by people with chronic conditions and the association of chronic conditions and impairments with physical activity(PA).   Methods: Participants self-reported the presence of seven chronic health conditions (diabetes; stroke/ischemic heart disease; hypertension; chronic obstructive pulmonary disease (COPD); asthma; arthritis/rheumatism/fibrositis; back problems), 11 types of impairment (vision, hearing, mobility, dexterity; learning; memory; mental health; stamina; social or behavioural; other; none); and their PA using the International Physical Activity Questionnaire. Multivariable Poisson regression was used to estimate the association of a)impairment type, b)number of impairments, and c)impairment type and chronic condition (mutually adjusted) with PA.   Results: In total, 2243 adults (55% female, 44% age > 55 yrs) reported having a chronic condition. PA volume (MET minutes per week: median (IQR)) was highest in participants with asthma (2093 (693–4479)), and lowest in those with COPD (454 (0–2079)). There was a negative association between number of impairments and levels of PA. After adjustment for age, sex, ethnicity and education, and mutually adjusting for all other conditions and impairments, diabetes (Incident rate ratio (95% confidence interval): 0.83 (0.73–0.94)), COPD (0.76 (0.59–0.99)), a mobility impairment (0.63 (0.56–0.72)), a dexterity impairment (0.86 (0.75–0.98)), or a memory impairment (0.84 (0.72–0.99)) was negatively associated with PA.   Conclusion: Future PA research requires consideration of the number and types of impairments that individuals experience, as well as assessing chronic conditions. This will improve understanding of the barriers to PA participation and inform interventions

An evolving model of best practice in a community physical activity programme: A case study of "Active Herts"

Background: Community-based physical activity programs typically evolve to respond to local conditions and feedback from stakeholders. Process evaluations are essential for capturing how programs are implemented, yet often fail to capture delivery evolution over time, meaning missed opportunities for capturing lessons learned. Methods: This research paper reports on a staged approach to a process evaluation undertaken within a community-based UK 12-month physical activity program that aimed to capture change and adaptation to program implementation. Twenty-five one-to-one interviews and 12 focus groups took place over the 3 years of program delivery. Participants included program participants, management, and service deliverers. Results: Program adaptations that were captured through the ongoing process evaluation included changes to the design of promotional material, program delivery content, ongoing training in behavior change, and the addition of regular participant community events. The authors address how these strands evolved over program delivery, and how the process evaluation was able to capture them. Conclusion: The pragmatic evaluation approach enabled changes in response to the local context, as well as improvements in the program to be captured in a timely manner, allowing the delivery to be responsive and the evaluation flexible

New Moon Explorer Mission Concept

New Moon Explorer (NME) is a smallsat reconnaissance mission concept to explore Earths New Moon, the recently discovered Earth orbital companion asteroid 469219 Kamooalewa (formerly 2016HO3), using solar sail propulsion. NME would determine Kamooalewas spin rate, pole position, shape, structure, mass, density, chemical composition, temperature, thermal inertia, regolith characteristics, and spectral type using onboard instrumentation. If flown, NME would demonstrate multiple enabling technologies, including solar sail propulsion, large-area thin film power generation, and small spacecraft technology tailored for interplanetary space missions. Leveraging the solar sail technology and mission expertise developed by NASA for the Near Earth Asteroid (NEA) Scout mission, affordably learning more about our newest near neighbor is now a possibility. The mission is not yet planned for flight

A scoping review of disability assessment in prospective and cross-sectional studies that included device-based measurement of physical activity

Background: Evidence on the prevalence, determinants, and health outcomes of physical activity in disabled people is limited. It is possible that the limited availability of high-quality scientific evidence is due to the extent and nature of disability assessment in physical activity research. This scoping review explores how disability has been measured in epidemiological studies that included accelerometer-based measurement of physical activity. Methods: Data sources: MEDLINE (Ovid), Embase, PsychINFO, Health Management Information Consortium, Web of Science, SPORTDiscus, and CINAHL. Eligibility criteria: Prospective and cross-sectional studies that included an accelerometer measurement of physical activity. Survey instruments used in these studies were obtained, and questions relating to the International Classification of Functioning, Disability and Health domains of (1) health conditions, (2) body functions and structures, and (3) activities and participation, were extracted for analysis. Results: Eighty-four studies met the inclusion criteria, from which complete information on the 3 domains was obtained for 68. Seventy-five percent of studies (n = 51) captured whether a person had at least one health condition, 63% (n = 43) had questions related to body functions and structures, and 75% (n = 51) included questions related to activities and participation. Conclusion: While most studies asked something about one of the 3 domains, there was substantial diversity in the focus and style of questions. This diversity indicates a lack of consensus on how these concepts should be assessed, with implications for the comparability of evidence across studies and subsequent understanding of the relationships between disability, physical activity, and health

Functional behaviour of flocs explained by observed 3D structure and porosity

Clay-rich flocculated suspended sediments are an important constituent of estuarine and coastal systems globally. They are responsible for the host, movement and deposition of a variety of pollutants, contaminants and sediment itself. Accurate modelling of the movement of these sediments is crucial for a number of industries including fisheries, aquaculture, shipping and waste management. This requires an accurate and reliable measurements of the physical properties of flocs and their behaviour. Porosity is a key element in floc structures, and this research provides updated 3D quantified porosity and pore space morphological data in relation to influences on floc settling behaviour. We report the questionable relationship between floc size and settling velocity, and explore alternative influences such as floc composition, porosity and pore morphology. These outcomes suggest that a shift in focus from floc size to a combination of factors is necessitated to understand the complex movement behaviour of flocculated suspended sediments