922017 research outputs found
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ENVIRONMENTAL SUSTAINABILITY PERFORMANCE OF A MEMBRANE-BASED TECHNOLOGY FOR LIVESTOCK WASTEWATER TREATMENT WITH NUTRIENT RECOVERY
No full textThe gas-permeable membrane (GPM) technology is one of the most novel techniques capable of minimizing ammonia (NH3) emissions associated to wastewaters, while recovering nitrogen as nutrient. This study conducted for the first time a life cycle assessment of this technology (treatment scenario), to compare the environmental trade-offs with the conventional manure management (conventional scenario), and determine which strategy performs better. The environmental impact results per m3 of manure, estimated using the ReCiPe method V 1.1, indicated that the treatment scenario reduces global warming (GW) by 14% and marine eutrophication (ME) by 32% with respect to the conventional scenario, whilst it increases particulate matter formation (PMF) and terrestrial acidification (TA) by 16% and 17%, respectively, due to some NH3 volatilization. Other impact categories considered were ozone formation (affecting human health (HOF) and ecosystems (EOF)), where the treatment scenario was able to reduce this impact by 48% and 50%, respectively. For freshwater eutrophication (FE), the net value was similar for both scenarios. A sensitivity analysis looking at optimum membrane design parameters (optimized treatment scenario) resulted in further reductions between 26% and 86% for GW, ME, PMF and TA with respect to the conventional scenario, although one potential drawback is the application of higher amount of phosphorous with the organic fertilizer, which resulted in higher FE impacts. Overall, the GPM system-based treatment is more environmentally sustainable compared to the conventional scenario thus making this an attractive option for environmental management systems, especially in areas with low water quality or high nutrient imbalance. Keywords: Life cycle assessment, manure treatment, ammonia reduction, nutrient imbalance, agricultural effluents.<br/
ESBMC-Solidity: An SMT-Based Model Checker for Solidity Smart Contracts
No full textSmart contracts written in Solidity are programs used in blockchain networks, such as Etherium, for performing transactions. However, as with any piece of software, they are prone to errors and may present vulnerabilities, which malicious attackers could then use. This paper proposes a solidity frontend for the efficient SMT-based context-bounded model checker (ESBMC), named ESBMC-Solidity, which provides a way of verifying such contracts with its framework. A benchmark suite with vulnerable smart contracts was also developed for evaluation and comparison with other verification tools. The experiments performed here showed that ESBMC-Solidity detected all vulnerabilities, was the fastest tool, and provided a counterexample for each benchmark. A demonstration is available at https://youtu.be/3UH8_1QAVN0
FuSeBMC v4: Smart Seed Generation for Hybrid Fuzzing
No full textFuSeBMC is a test generator for finding security vulnerabilities in C programs. In Test-Comp 2021, we described a previous version that incrementally injected labels to guide Bounded Model Checking (BMC) and Evolutionary Fuzzing engines to produce test cases for code coverage and bug finding. This paper introduces an improved version of FuSeBMC that utilizes both engines to produce smart seeds. First, the engines run with a short time limit on a lightly instrumented version of the program to produce the seeds. The BMC engine is particularly useful in producing seeds that can pass through complex mathematical guards. Then, FuSeBMC runs its engines with extended time limits using the smart seeds created in the previous round. FuSeBMC manages this process in two main ways. Firstly, it uses shared memory to record the labels covered by each test case. Secondly, it evaluates test cases, and those of high impact are turned into seeds for subsequent test fuzzing. In this year’s competition, we participate in the Cover-Error, Cover-Branches, and Overall categories. The Test-Comp 2022 results show that we significantly increased our code coverage score from last year, outperforming all tools in all categories.<br/
Non-thermal plasma catalytic ammonia synthesis over Ni catalyst supported on MgO/SBA-15
No full textNon-thermal plasma (NTP) enabled ammonia synthesis is recently considered a sustainable technique as compared to the Haber–Bosch (HB) process. Herein we demonstrate the NTP catalytic ammonia synthesis in an dielectric barrier discharge (DBD) plasma reactor using mesoporous silica (SBA-15) supported Ni catalysts under ambient condition. Specifically, two types of MgO modified SBA-15 were developed (as the catalyst support) by the in situ doping and incipient wetness impregnation (IWI) methods, respectively. Experimental results demonstrated that the addition of Mg in SBA-15 via the IWI method favored the ammonia synthesis rate under NTP conditions. The developed Ni-Mg0.02/SBA-15-IWI catalyst exhibited the highest ammonia synthesis rate and energy efficiency value of 4.4 mmol h−1 gcat−1 and 1.05 gNH3 kWh−1, outperformed the Ni/SBA-15 and Ni-Mg0.02/SBA-15-In situ catalyst (i.e. the doping of Mg via in situ method). HRTEM and EDS mapping analysis showed that the addition of Mg (on SBA-15) via the IWI method favored the dispersion of Ni on the catalyst surface and the Ni-support interaction, i.e., uniform distribution of Ni nanoparticles of 5.1 ± 1.1 nm in the Ni-Mg0.02/SBA-15-IWI catalyst, which enhanced the ammonia synthesis performance. Finally, the developed Ni-Mg0.02/SBA-15-IWI catalyst displayed a slight decrease of ammonia synthesis rate from ~4.42 to ~3.89 mmol h−1 gcat−1 over a 40 h on stream, which could be attriburated to the aggregation of Ni particles based on the post-reaction HRTEM analysis.<br/
Bounds for the chi-square approximation of the power divergence family of statistics
No full textIt is well-known that each statistic in the family of power divergence statistics, across n trials and r classifications with index parameter λ ∈ R (the Pearson, likelihood ratio and Freeman-Tukey statistics correspond to λ = 1, 0, −1/2, respectively) is asymptotically chi-square distributed as the sample size tends to infinity. In this paper, we obtain explicit bounds on this distributional approximation, measured using smooth test functions, that hold for a given finite sample n, and all index parameters (λ > −1) for which such finite sample bounds are meaningful. We obtain bounds that are of the optimal order n¯¹. The dependence of our bounds on the index parameter λ and the cell classification probabilities is also optimal, and the dependence on the number of cells is also respectable. Our bounds generalise, complement and improve on recent results from the literature
Structure restoration and coarsening of nanocrystalline cementite in cold drawn pearlitic wire induced by low temperature annealing
No full textInternal structure evolution of nano-scale cementite during annealing has exhibited a critical impact on mechanical performance for various heavily strained high-carbon steel materials. Through a combination of post-annealing and in-situ annealing transmission electron microscopy observations, structural evolution of heavily strained cementite during low-temperature annealing was investigated. During annealing, the morphology of cementite lamellae is stable when the temperature (Ta) is lower than 350 °C. Meanwhile, lattice structure restoration and coarsening of nanocrystalline cementite (θ- NC) occurred inside the lamellae. Starting from a nanocrystalline structure in the as-drawn state, the interiors of cementite lamellae were observed to transform into coarsened isometric shape θ-NC (140 °C < Ta < 210 °C) or elongated θ-NC (Ta < 350 °C). The coarsening activation energy of heavily strained cementite nanocrystalline in lamellae is estimated to be in a range of 37 ~ 50 kJ mol-1, while the coarsening behaviour is limited by the ferrite-cementite phase boundary
People in a Pandemic: Rethinking the role of ‘Community’ in Community Resilience Practices
No full textHow has the idea of community featured in attempts to build resilience to emergencies? The paper explores this question by presenting evidence from interviews with emergency responders across the world in the midst of the early and uncertain phases of the Covid-19 pandemic. Although reflecting different contexts, we discern two ways in which the notion of community featured in authorities’ narrations of their efforts to respond to the pandemic. Firstly, we demonstrate how community was deployed as a discursive mechanism that offered a particular framing of the vulnerabilities the pandemic instigated. Departing from accounts that reduce people’s identities to demographic categories, the deployment of community stressed that the pandemic’s effects should be understood by the different, yet coexistent, vulnerabilities it brought to the surface for people. Such renditions of vulnerability paved the way for styles of governance that prioritised adapting to the pandemic’s uncertain and indeterminate unfolding in the absence of prepared plans. Secondly, addressing a register of collective social life between individuals and the state, an emphasis on community engendered the decentralised arrangement of emergency governance with which resilience has become synonymous. Here, community proved pivotal in temporarily expanding resources to deal with an emergency whose effects threatened to exceed governments’ pre-existing capabilities. We substantiate this claim through examining how allusions to community worked to enrol non-state based efforts at response into a broader public security apparatus. Enveloped within the broader politics of emergency resilience, community shaped how the pandemic’s effects were understood whilst also ensuring adequate provisions for its governance
Selective laser melting of Er modified AlSi7Mg alloy: Effect of processing parameters on forming quality, microstructure and mechanical properties
No full textSelective Laser Melting (SLM) was used to fabricate Erbium-modified AlSi7Mg alloy. The work aims to investigate the effects of laser volumetric energy density and focus shift on surface quality, internal defects and microstructure during the SLM process. Based on the optimized process parameters, the effect of rare earth element Er to AlSi7Mg alloy on its microstructure and mechanical properties were studied. With a raise of volumetric energy density, the size of aluminum sub-cells increases, and the high energy density promotes the in-situ precipitation of supersaturated silicon elements in the form of dispersed silicon particles. It was thought that the laser focus shift could change the energy density and the molten pool size, which affected the internal defects and the size of sub-cells plus eutectic silicon particles. The alloy (A357 + 0.2Er wt.%) fabricated by SLM was operating with the optimized processing parameters, then a small amount of equiaxed grains were formed at the boundary of the molten pool, which would promote the refinement of columnar grains and improve the mechanical properties. Meanwhile, the yield strength was 297 MPa, the tensile strength was 441 MPa and the elongation was 8%
THE DEVELOPMENT OF A NEW METHOD TO COMPARE THE FATIGUE CRACK GROWTH RATES OF AUSTENITIC STAINLESS STEEL OPERATING IN A PWR PRIMARY COOLANT SUBJECTED TO PLANT REALISTIC TEMPERATURE LOADING
No full textFatigue Crack Growth Rates (FCGRs) of austenitic stainless steels can be significantly enhanced when tested in a high temperature water environment compared to those tested in air. Existing FCGR models are based on simple isothermal waveform loading. Recent work has highlighted that there may be a potential benefit into taking account of plant realistic loading waveforms in fatigue assessments as these may be less damaging than predict ions based on simple loading conditions. As a result, new methods to account for these plant realistic loads have been developed to reduce excess conservatism of existing methods for predicting FCGRs.To provide confidence in these methods, a previous UK thermomechanical fatigue testing program me has been conducted on Compact Tension (C(T)) specimens subjected to plant realistic loads, with the crack length and Crack Growth Rates CGRs being monitored in situ using the Direct Current Potential Drop (DCPD) technique. This paper utilizes three different methodologies to evaluate the CGR of samples that underwent corrosion fatigue in different conditions namely; DCPD, post mortem measurement of crack advance using Scanning Electron Microscopy (SEM) and the measurement of the spacing between striations to infer CGR.It was found that DCPD provided a good global average of FCGRs at the crack front but does not capture local changes associated with the local microstructureOverall, it was shown that post mortem examination for stage measurements can be reliably applied to infer CGR on samples that were not instrumented with DCP