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Burn to kill: Wood ash a silent killer in Africa
No full textAside the emissions, burning of wood in traditional cookstoves (TCs) also generates substantial amount of ash containing hazardous pollutants such as polycyclic aromatic hydrocarbons (PAHs) and toxic metals. But, their concentrations in the ash, particularly in Africa where over 70% of the population utilize TCs, remain unknown. Here, we determined concentrations of sixteen PAHs and eleven heavy metals in ashes from twelve different African TCs, comprising six three-stone fires (TSFs) and six built-in-place cookstoves (BIPCs), burning common African wood species under real world situation. For each TC, ash samples were collected for six consecutive days (Monday–Saturday), and a total of seventy-two daily samples were collected from January–June 2019. Ash yields were measured gravimetrically, and concentrations of the pollutants were determined following standard analytical protocols. The results were used alongside secondary data (annual fuelwood consumption, African fuelwood densities, population proportion using fuelwood and surface human population density) to estimate annual tonnage, exposure potential and risk to health in Africa, using Monte Carlo simulation technique. The ash yields from all TCs studied exceeded 1% on dry weight basis, indicating that ash is a major waste by-product of wood combustion in TCs. TSFs produced more ash (5.7 ± 0.7%) than BIPCs (3.4 ± 1.0%). Concentrations of As, Cd, Hg and Pb in ashes were significantly higher (α = 0.05) for TSFs than BIPCs. In contrast, concentrations of PAHs were higher in ashes from BIPCs than TSFs. Assuming ash consumption rates range from 250 to 500 mg/day for young children weighing 10 to 30 kg, the upper dose (μg/kg-day) of Pb (0.2–3.9) or Σ16PAHs (0.02–0.34), for instance, surpasses the 0.3 μg/kg-day of Pb or PAH recognized as causing adverse effects in children, indicating a concern. The top five countries with the highest annual tonnage or exposure potential to toxic pollutants are Nigeria>Ethiopia>DR-Congo>Tanzania>Uganda, or Rwanda>Burundi>Uganda>Nigeria>Guinea-Bissau, respectively
The impact of Natural Flood Management on the performance of surface drainage systems: A case study in the Calder Valley
No full textThe evaluation of Natural Flood Management (NFM) has traditionally focused on the ability of interventions to mitigate downstream fluvial flooding by attenuating catchment response. However, the justification for the implementation of NFM projects at a local level is often supported by other benefits provided by such interventions (e.g. improvements to water quality or biodiversity). This study investigates the potential for a further, largely unrecognised, benefit. It is suggested that, by moderating water levels in downstream watercourses, upstream interventions could also help sustain free discharge from drainage outfalls, thereby improving the performance of urban surface drainage systems. A coupled modelling methodology is applied to the upper Calder Valley and the surface drainage in an area of the downstream town of Todmorden. The rural response and subsequent NFM interventions are characterised using hydrological (Dynamic TOPMODEL) and hydraulic (HEC-RAS) models. Several downstream surface drainage systems are then incorporated using an Infoworks ICM model to examine their response to changes in outfall inundation. The results suggest that catchment-scale tree planting and in-channel woody debris create modest benefits for downstream surface drainage systems. Under frequent storm events (e.g. a 1 in 10 year storm), the inundation of low-lying outfalls is completely removed. As storm severity increases (and surface flooding becomes an issue), impact from upstream NFM attenuation on outfall inundation durations diminishes significantly. However, the slight delay in rural response allows more water to escape surface systems, increasing the effective capacity of networks and reducing surface flooding. For instance, outfall inundation during an estimated 20 year event is delayed by 0.5 h, which results in up to 25% reduction in surface flood volumes. While the benefits are limited in extent, this modelling indicates that NFM can help improve downstream surface drainage performance
Integrated Wireless-Optical Backhaul and Fronthaul Provision through Multicore Fiber
No full text© 2013 IEEE. In this paper we propose multicore fiber (MCF) as the medium to transport the different signals associated with various wireless applications (ranging from access to fronthauling and backhauling) from the baseband unit (BBU) to the cell-site. Using 1 km of a 7-core MCF, we simultaneously transmit fronthaul and backhaul signals from the BBU to the cell site, where they are converted to carrier frequencies in the mm-wave and sub-THz band, respectively. The backhaul is evaluated with a 12.5 GBd 16-quadrature amplitude modulation (QAM) signal, whereas the fronthaul is evaluated with a 7 Gbit/s on-off keying (OOK) signal carrying 14 LTE-compatible channels. The fronthaul signal is generated with a novel compression technique that achieves an efficiency 3-times higher than the one obtained with the common public radio interface (CPRI) protocol. Optical heterodyining is implemented at the cell site for optical-to-RF conversion. The local oscillator (LO) signal required for optical heterodyning is transmitted in a dedicated core, reducing the system complexity and enabling its straight-forward reuse for uplink (UL) transmission. The experimental demonstration includes the simultaneous full-duplex transmission of both the fronthaul and backhaul signals, using 6 cores of the MCF at the same time and achieving a gross data rate of 57 Gbit/s
Ignition probability and lean ignition behaviour of a swirled premixed bluff body stabilised annular combustor
No full textAn experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (φ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition" is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH∗ chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors
Green but not altruistic warm-glow predicts conservation behavior
No full textEnvironmental policies frequently assume that people only act to help the environment if such behavior is in their self-interest. A growing amount of literature, however, shows that people also derive positive emotional benefits or “warm-glow from acting green. Yet, it remains unclear to what extent this motivation is derived from classical accounts of altruistic concern. In the current study, we leveraged a prospective design of a unique sample (N1= 341, N2 = 251) of customers who subscribe to a local sustainable food store. We measured altruistic and green warm-glow at T1 and predicted to what extent such prospective warm-glow predicted a range of self-reported conservation behaviors four weeks later (T2). Results suggest that the anticipated warm-glow from helping other people did not significantly predict green intentions nor green behavior despite being highly correlated with green warm-glow. In fact, only green warm-glow significantly predicted conservation behavior over time. These findings are important because they elucidate a basic differential motivation between helping other people versus protecting the planet. This differentiation is critical to the design of effective conservation interventions
Inertial interaction in pile-groups: A study of the influence of coupling via an iterative wave-scattering approach
No full textThe increasing urban population is leading to the exploitation of building sites close to sources of ground-borne vibration, such as railways and busy roads. Piled foundations can provide a significant vibration transmission path into a building, which can then cause disturbance to occupants and sensitive equipment. There is a strong need to develop numerical models that can capture the essential dynamics of a piled foundation, over the frequency range associated with ground-borne vibration, to help practising engineers decide on appropriate countermeasures. In this paper, a piled foundation is modelled as a pile-group embedded in a homogeneous half-space. Previous research has explored the dynamics of pile-groups to inertial loading at relatively low frequencies, over the seismic range. Here, an iterative approach is developed using a source-receiver boundary-element model to account for the wave-scattering effect that becomes more significant at higher frequencies. Predictions of the dynamic interaction factors, which describe the pile-soil-pile interaction, show very good agreement with a standard boundary-element model for a range of geometric and material parameters. The results show that using uncoupled source-receiver models can account effectively for the interaction between piles without resorting to fully coupled models, even at frequencies well above those of previously published results
Performing Qualitative Mask Fit Testing without a Commercial Kit: Fit Testing Which can be Performed at Home and at Work.
No full textINTRODUCTION: Qualitative fit testing is a popular method of ensuring the fit of sealing face masks such as N95 and FFP3 masks. Increased demand due to the COVID-19 pandemic has led to shortages in testing equipment and has forced many institutions to abandon fit testing. Three key materials are required for qualitative fit testing: the test solution, nebulizer, and testing hood. Accessible alternatives to the testing solution have been studied. This exploratory qualitative study evaluates alternatives to the nebulizer and hoods for performing qualitative fit testing. METHODS: Four devices were trialed to replace the test kit nebulizer. Two enclosures were tested for their ability to replace the test hood. Three researchers evaluated promising replacements under multiple mask fit conditions to assess functionality and accuracy. RESULTS: The aroma diffuser and smaller enclosures allowed participants to perform qualitative fit tests quickly and with high accuracy. DISCUSSION & CONCLUSION: Aroma diffusers show significant promise in their ability to allow individuals to quickly, easily, and inexpensively perform qualitative fit testing. Our findings indicate that aroma diffusers and homemade testing hoods may allow for qualitative fit testing when conventional apparatus is unavailable. Additional research is needed to evaluate the safety and reliability of these devices
Now you see me (CME): Concept-based model extraction
No full textDeep Neural Networks (DNNs) have achieved remarkable performance on a range of tasks. A key step to further empowering DNN-based approaches is improving their explainability. In this work we present CME: a concept-based model extraction framework, used for analysing DNN models via concept-based extracted models. Using two case studies (dSprites, and Caltech UCSD Birds), we demonstrate how CME can be used to (i) analyse the concept information learned by a DNN model (ii) analyse how a DNN uses this concept information when predicting output labels (iii) identify key concept information that can further improve DNN predictive performance (for one of the case studies, we showed how model accuracy can be improved by over 14%, using only 30% of the available concepts)
Modelling analysis of periodically arranged high-temperature superconducting tapes
No full textThe practical operation of a high-temperature superconducting (HTS) tape to form a HTS device is strongly related to the HTS tape electromagnetic environment in the device. With regard to the HTS tapes commonly stacked for practical applications, it is necessary to study the electromagnetic interaction of the proximity HTS tapes to design and optimize the HTS tapes and devices. This paper presents a numerical model of periodically arranged HTS tapes using the finite element method (FEM). The numerical method has been developed to build the equivalent periodical arrangement of infinite HTS tapes and applied to simulate two basic arrangements, horizontal and vertical periodical arrangements. The magnetic field and current distributions of HTS tapes by periodical arrangements have been investigated. The effects on critical current with different arrangements have been illustrated. It is found that the Y-stack can reduce the current carrying capacity while the X-array can increase that in comparison to a single tape. The differences between the FEM results and analytical models have been analysed and also compared with the Norris model. The two mathematical models derived for AC loss prediction have shown higher accuracy than the existing analytical models. This study presents an effective method to optimize the electromagnetic design by considering favorable structure or environment for the stacked HTS tapes and estimate the AC loss, shows the phenomenon of central tapes in an HTS array, which could be further used in performance analysis of superconducting devices, e.g. HTS transformers
Amplifier considerations in ROADM-free space-switched nonlinear optical links
No full textPower fluctuations accumulate in ROADM-free space-switched networks. Thousands of randomized nonlinear transmissions demonstrate that capacity with an inventory of {5,10,15,20} dB gain amplifiers is within 10 % of optimal and triple that with {10,20} dB amplifiers over 1,000 km