Effects of Surface Morphology on the Wear and Corrosion Resistance of Post-Treated Nitrided and Nitrocarburized 42CrMo4 Steel

The surface of alloyed carbon steel was subjected to thermochemical modification by nitrocarburizing and nitriding with or without postoxidation in order to improve its mechanical properties, corrosion, and wear resistance. Treated samples were characterized by testing their basic properties (compound layer thickness, nitriding, nitrocarburizing depth, and surface hardness) according to standards. Detailed estimation of the modified metal surface was performed by additional testing: X-ray diffraction, microstructure, surface roughness and topography, and wear and corrosion resistance. The surface layer obtained after nitrocarburizing treatment consists mainly of ε-Fe_2-3(N,C) and γ’-Fe₄(N,C); similarly, the nitrided surface is formed by ε-Fe_2-3N and γ’-Fe₄N iron nitrides. The surface layer after postoxidation contains additionally Fe₃O₄. The results obtained show that nitrocarburization, nitridation, and postoxidation result in better mechanical, wear, and corrosion resistance of 42CrMo4 steel, and postoxidized sample properties are influenced by surface morphology.     

Botanical pesticide production,trade and regulatory mechanisms in sub-Saharan Africa: making a case for plant-based pesticidal products

Pesticides are the major technology used in the management of field and postharvest losses due to pests. There is growing demand for effective alternatives that present low health risks and conserve ecosystems and biological diversity. Pesticidal plants are increasingly used as alternatives where synthetic products are unaffordable, have limited availability or are ineffective. Plant materials, however, are often used inefficiently and their effective use requires optimisation. In Africa wide-scale uptake of pesticidal plants remains limited despite the success of pyrethrum in some countries and other pesticidal plant products in China and India. This is mainly due to lack of data on efficacy and safety, inconsistent efficacy of plant products, the prohibitive cost of registration, and an inadequately developed conventional pesticides sector. Globally, the demand for botanicals is poised to grow due to an increasing shift in consumer demand for safe food, increasing organic farming, lobbying by environmentalists and the increasing pressure from new regulations on internationally traded foods in Europe. These demands can only be met by formalising production, marketing and use of pesticidal plants. This has to be supported by friendly registration procedures, sustainable forest management, propagation and cultivation of pesticidal plants. This paper presents a critical review of the enabling environment required for wide-scale adoption and commercialisation of botanical pesticides in sub-Saharan Africa. We conclude that regulations and protocols for production, marketing and trade need to be reviewed to facilitate the development of the botanicals sector in Africa.     

Elaboration and mechanical characterization of multi-phase alumina-based ultra-fine composites

Al₂O₃-10 vol.% YAG and Al₂O₃-10 vol.% ZrO₂ bi-phase composites as well as Al₂O₃-5 vol.% YAG-5 vol.% ZrO₂ tri-phase composite were developed by controlled surface modification of an alumina powder with inorganic precursors of the second phases. Green bodies were produced by dry pressing and slip casting and then sintered at 1500 °C. In particular, slip casting led to fully dense, defect-free, and highly homogenous samples, made of a fine dispersion of the second phases into the micronic alumina matrix, as observed by SEM. The mechanical characterization proved the predominant role of the final density on the Vickers hardness, while the elastic modulus was affected by the volume fraction of the constituent phases, in fairly good agreement with the rule of mixture prediction. The fracture toughness values of the bi- and tri-phase materials were similar, and their crack paths revealed the importance of the thermal residual stresses at the matrix-reinforcement interfaces, promoting inter-granular propagations.     

Links between energy access and food security in sub Saharan Africa: an exploratory review

Three quarters of the population in Sub Saharan Africa lacks access to modern energy, and relies instead on biomass fuels for cooking and heating. The environment and health implications of the use of biomass fuel has been widely documented in the literature, and has raised the topic of energy access in various policy and development arenas. Still, the impact of energy access on food security at the household level has not been explored in detail; consequently the two sectoral policies remain unaligned. Our aims for this review were to document how lack of access to energy can impact on food security through influence on dietary choices and cooking practices; and how reallocation of household resources from food to energy procurement causes a switch to biomass energy forms of lower grade. We searched the literature for published peer-reviewed articles available through major online publication databases, initially identifying 132 articles but finally reviewing a set of 19 that met our criteria. While most studies suggested that fuelwood scarcity can affect food security through three hypothesised pathways, very few of them provided empirical data to support this argument. Overall, the review found coping measures for woodfuel scarcity to be highly contextual and influenced by geography, household economy and labour availability. Due to the limited number of studies with detailed data, it was not possible to perform a comparative analysis that could support or refute a hypothesis that lack of access to energy can impact on food security. More rigorous studies on this topic are needed which could provide evidence for policy action.     

A futuristic least-cost optimisation model of CO2 transportation and storage in the UK/UK Continental Shelf

The owners of 8 power plants in the UK have announced interest in capturing and sequestering CO₂. Using various criteria from the literature twenty fields in the UK Continental Shelf were selected as possible sinks for the captured CO₂. Using a linear programming model, the study determined the least-cost transportation network under various constraints on the volumes of CO₂ captured from the sources and the injection rates at the sinks. Four scenarios were developed to gauge the sensitivity of the results to these and to the availability of fields for EOR and Permanent Storage. Depending on the scenario, the optimal transportation CAPEX was found to range between £3.5 and £5.2 billion in real terms. With higher minimum injection rates at the fields, accelerating CO₂–EOR investments was found to reduce unit transportation CAPEX compared to waiting for their cessation of production dates. On the other hand a combination of the later availability of the CO₂–EOR fields plus a lower minimum injection rate yielded the minimum transportation network CAPEX. The modelling also unveiled the problem of CO₂ supply overflows in the longer term. The modelling approach has wide applicability beyond the UK.     

Monte Carlo simulation of microstructure evolution in biphasic-systems

Over the past few decades, a variety of models have been proposed in order to investigate the grain growth kinetics and the development of crystallographic textures in polycrystalline materials. In particular, a full understanding of the microstructure evolution is a key issue for ceramic systems, since their mechanical or thermal behaviour is intimately related to their microstructure. Moreover, the development of appropriate simulative tools is crucial to reproduce, control and finally optimize the solid-state sintering process of ceramics. Monte Carlo simulations are particularly attractive because of their ability to reproduce the statistical behaviour of atoms and grain boundaries with time. However, Monte Carlo simulations applied to two-phase materials, such as many ceramic systems, result complex because both grain growth and diffusion processes should be taken into account. Here the Monte Carlo Potts model, which is widely used to investigate the crystallization kinetics for monophasic systems, is modified and extended to biphasic ones. The proposed model maps the microstructure onto a discrete lattice. Each lattice element contains a number representing its phase and its crystallographic orientation. The grain formation and growth are simulated by appropriate switching and reorientation attempts involving the lattice elements. The effect of temperature is also discussed.     

MATHEMATICAL MODELLING OF A ROTARY SWIRL CYCLONE SCRUBBER

A Rotary Swirl Cyclone Scrubber (RSCS) is a device designed to remove SO₂ and ash from the combustion products of an entrained-flow gasifier. It uses a combination of highly swirling flow and water sprays to produce high heat and mass transfer rates. In order to develop a better understanding of the operation of this device, modelling has been performed using an extended version of CFX-F3D. Simulations have been performed to examine the flowfield in the device and to determine SO₂ and ash capture efficiencies. The simulations show that the water jets used to remove the SO₂ from the gas completely change the direction or swirl in the device, resulting in a highly turbulent flow. The experimental SO₂ capture efficiency and the outlet temperature are well reproduced using a water droplet size of 60 μm, with this value being determined via fitting to a particular experiment. Predictions of ash particle capture are found to be in good agreement with the experimental data.     

Selecting nonlinear time series models using information criteria

Abstract.  This article considers the problem of selecting among competing nonlinear time series models by using complexity-penalized likelihood criteria. An extensive simulation study is undertaken to assess the small-sample performance of several popular criteria in selecting among nonlinear autoregressive models belonging to some families that have been popular with practitioners.     

Spoligotyping followed by double-repetitive-element PCR as rapid alternative to IS6110 fingerprinting for epidemiological studies of tuberculosis

A total of 129 clinical isolates of Mycobacterium tuberculosis representing 91 patients were typed by a combination of direct-repeat (DR)-based spoligotyping and an inter-IS6110-PGRS (polymorphic GC-rich region)-PCR, also designated double-repetitive-element PCR (DRE-PCR). During the first phase of this investigation, 72 clinical strains representing 52 patients were initially typed by IS6110-restriction fragment length polymorphism (RFLP) and DR-RFLP, followed by spoligotyping and DRE-PCR. In the second phase of this investigation, the discriminating ability of spoligotyping plus DRE-PCR was studied for 57 isolates from 39 patients who were suspected to be epidemiologically linked, and the typing results were later confirmed by IS6110-RFLP and DR-RFLP analyses. The molecular clustering of the isolates remained identical irrespective of the methods used. These results show that the association of two PCR-based fingerprinting techniques for molecular epidemiology of tuberculosis has a discriminating ability similar to the IS6110-RFLP reference method.