Material properties and operating configurations of membrane reactors for propane dehydrogenation

A modeling‐based approach is presented to understand physically realistic and technologically interesting material properties and operating configurations of packed‐bed membrane reactors (PBMRs) for propane dehydrogenation (PDH). PBMRs composed of microporous or mesoporous membranes combined with a PDH catalyst are considered. The influence of reaction and membrane transport parameters, as well as operating parameters such as sweep flow and catalyst placement, are investigated to determine desired “operating windows” for isothermal and nonisothermal operation. Higher Damköhler (Da) and lower Péclet (Pe) numbers are generally helpful, but are much more beneficial with highly H₂‐selective membranes rather than higher‐flux, lower‐selectivity membranes. H₂‐selective membranes show a plateau region of conversion that can be overcome by a large sweep flow or countercurrent operation. The latter shows a complex trade‐off between kinetics and permeation, and is effective only in a limited window. H₂‐selective PBMRs will greatly benefit from the fabrication of thin (～1 µm or less) membranes. © 2014 American Institute of Chemical Engineers AIChE J, 61: 922–935, 2015     

Bridging the Gap between Quantitative and Qualitative Accelerated Life Tests

Test planners have long sought the ability to incorporate the results of highly accelerated life testing (HALT) into an early estimate of system reliability. While case studies attest to the effectiveness of HALT in producing reliable products, the capability to translate the test's limited failure data into a meaningful measure of reliability improvement remains elusive. Further, a review of quality and reliability literature indicates that confusion exists over what defines a HALT and how HALT differs from quantitative accelerated life testing methods. Despite many authors making a clear distinction between qualitative and quantitative accelerated life tests, an explanation as to why this delineation exists cannot be found. In this paper, we consider an exemplary HALT composed of a single stressor to show that the HALT philosophy precludes the estimation of a system's hazard rate function parameters because of the test's fix implementation strategy. Four common accelerated failure data analysis methods are highlighted to show their limitations with respect to estimating reliability from HALT data. Finally, a modified accelerated reliability growth test is proposed as a way forward for future research in HALT scenarios to characterize the risk of attaining a reliability requirement and improve parameter estimation. Copyright © 2014 John Wiley & Sons, Ltd.     

Measuring the severity of transboundary freshwater conflict: structural vs. behavioural indices in Africa

In the global crisis over access to clean, adequate freshwater, Africa is a special case. Not only are many African states under severe water stress, but the continent is one of the most hydrologically interconnected regions on the planet. With 113 rivers, lakes and aquifers that cross an international border, over 60% of Africa’s territory falls into a transboundary watershed. Africa’s hydrology is interdependent, and mass poverty and political volatility heighten the risk of conflict over freshwater resources. This paper compares two approaches to understanding the severity of transboundary freshwater conflict; one based in behavior and the other based on structural factors unique to each water resource and its users. The goal is to identify Africa’s water hot spots, or those areas where violence over water resources is most likely. The broader aim is to better understand how the way we measure severity affects our understanding of freshwater conflict, and how policy-makers might best approach water politics in Africa.     

Challenges to successful seismic retrofit implementation: a socio-behavioural perspective

Seismic retrofit implementation has been a major challenge in many earthquake-prone cities. This paper examines why building owners are reluctant to adopt measures to reduce earthquake losses despite advancement in seismic design methods and the enactment of intervening legislative frameworks. A case study approach revealed the socio-behavioural barriers affecting seismic retrofit implementation. Significant barriers identified included the perception of earthquake risks, a lack of trust in seismic strengthening techniques and a lack of support for pro-social mitigation behaviours from public authorities. The findings suggest that a reappraisal of the policy implementation approach used by government agencies is required, and that greater attention should be given to seismic designs recommended by professionals and approved by regulatory authorities in order to earn building owners' trust regarding the efficacy of earthquake risk-reduction measures.

La mise aux normes parasismiques des constructions existantes est un défi majeur dans de nombreuses villes sujettes aux tremblements de terre. Le présent article examine pourquoi les propriétaires d'immeubles sont peu disposés à adopter des mesures permettant de réduire les sinistres dus aux tremblements de terre en dépit des progrès réalisés dans les méthodes de conception parasismique et malgré la promulgation de cadres législatifs d'intervention. Une approche par étude de cas a mis en évidence les barrières sociocomportementales affectant la mise en ?uvre des normes parasismiques dans les immeubles existants. Ont été identifiés parmi ces obstacles importants la perception des risques de tremblements de terre, un manque de confiance dans les techniques de renforcement parasismique et un manque de soutien de la part des autorités publiques en faveur de comportements pro-sociaux permettant d'adoucir ces politiques. Les résultats obtenus suggèrent qu'il est nécessaire d'opérer une réévaluation de l'approche utilisée par les organismes publics pour mettre en ?uvre ces politiques, et qu'il devrait être porté une plus grande attention aux conceptions parasismiques recommandées par les professionnels et homologuées par les organismes de réglementation de façon à gagner la confiance des propriétaires d'immeubles, s'agissant de l'efficacité des mesures de réduction des risques liés aux tremblements de terre.

Mots clés: propriétaires d'immeubles, prise de décision, immeubles sujets aux tremblements de terre, politique publique, perception des risques, mise aux normes parasismiques, comportement des parties prenantes     

Conversion of Canola Meal into a High-Protein Feed Additive via Solid-State Fungal Incubation Process

The study goal was to determine the optimal fungal culture to reduce glucosinolates (GLS), fiber, and residual sugars while increasing the protein content and nutritional value of canola meal. Solid‐state incubation conditions were used to enhance filamentous growth of the fungi. Flask trials were performed using 50 % moisture content hexane‐extracted (HE) or cold‐pressed (CP) canola meal with incubation for 168 h at 30 °C. Incubation on HE canola meal Trichoderma reesei (NRRL‐3653) achieved the greatest increase in protein content (23 %), while having the lowest residual levels of sugar (8 % w/w) and GLS (0.4 μM/g). Incubation on CP canola meal Trichoderma reesei (NRRL‐3653), A. pullulans (NRRL‐58522), and A. pullulans (NRRL‐Y‐2311‐1) resulted in the greatest improvement in protein content (22.9, 16.9 and 15.4 %, respectively), while reducing total GLS content from 60.6 to 1.0, 3.2 and 10.7 μM/g, respectively. HE and CP canola meal GLS levels were reduced to 65.5 and 50.7 % by thermal treatments while solid‐state microbial conversion further reduced GLS up to 99 and 98 %, respectively. Fiber levels increased due to the concentration effect of removing oligosaccharides and GLS.     

A Functionally Graded Carbide in the Ta–C System

Hard materials used in such abrasive wear applications as cutting tools and wear inserts in drilling tools require high hardness to resist wear, high fracture toughness to withstand mechanical and thermal shock, and high chemical and thermal stability. Such a combination of properties is difficult to achieve in single‐phase materials. Functional grading is an approach that overcomes this limitation by designing and processing a graded microstructure that provides high hardness and chemical resistance at the surface with a tough interior or bulk. While functional grading is a widely used practice in the cemented carbides industry, it has not been demonstrated with “pure” carbides. This article reports the feasibility of designing and processing a graded carbide in the Ta–C binary system. It is shown that a simple carburization treatment of the high‐toughness carbide, ζ‐Ta₄C_3?x, can lead to the formation of the hard carbide phase, γ‐TaC_y, on the surface. The thickness, microstructure (grain size), and composition (C/Ta atomic ratio, y) of the γ‐TaC_y layer can be optimized to obtain both high hardness and high strength for the graded material.     

The Role of Matrix Metalloproteinase Polymorphisms in Ischemic Stroke

Stroke remains the fifth leading cause of mortality in the United States with an annual rate of over 128,000 deaths per year. Differences in incidence, pathogenesis, and clinical outcome have long been noted when comparing ischemic stroke among different ethnicities. The observation that racial disparities exist in clinical outcomes after stroke has resulted in genetic studies focusing on specific polymorphisms. Some studies have focused on matrix metalloproteinases (MMPs). MMPs are a ubiquitous group of proteins with extensive roles that include extracellular matrix remodeling and blood-brain barrier disruption. MMPs play an important role in ischemic stroke pathophysiology and clinical outcome. This review will evaluate the evidence for associations between polymorphisms in MMP-1, 2, 3, 9, and 12 with ischemic stroke incidence, pathophysiology, and clinical outcome. The role of polymorphisms in MMP genes may influence the presentation of ischemic stroke and be influenced by racial and ethnic background. However, contradictory evidence for the role of MMP polymorphisms does exist in the literature, and further studies will be necessary to consolidate our understanding of these multi-faceted proteins.