Numerical simulation of hydrogen–air detonation for damage assessment in realistic accident scenarios

An accidental hydrogen release within an equipment enclosure may result in the presence of detonable mixture in a confined environment. From a safety standpoint, it is then useful to assess the potential for damage. In that context, numerical simulation of the sequence of events subsequent to detonative ignition provides a useful tool, although with obvious limitations. This article describes the procedure, summarizes two case studies, and reviews the limitations. First, a hydrogen dispersion pattern is obtained from numerical simulation of dispersion, using a commercial package designed primarily for incompressible flow. This dispersion cloud is then used as the initial condition in an inviscid, compressible, reactive flow simulation. To force detonative ignition, a sufficiently large amount of energy is deposited in a small region that corresponds to the ignition location. Chemistry is modeled using a single step Arrhenius model. Because the wave thickness is small compared with the computational domain, a fine mesh is needed, limiting the practicality of the process to two-dimensional geometries. This is the most significant limitation; it is conservative. The two cases described in the paper include an electrolyzer, in which a small release occurs, leading potentially to some damage to the enclosure, and a reformer, in which the consequences are potentially more serious.     

Meta‐analytic tests of relationships between organizational justice and citizenship behavior: testing agent‐system and shared‐variance models

Research on the unique effects of different types of perceived fairness on citizenship behavior that benefits individuals (organizational citizenship behavior (OCB‐I) and organizations (OCB‐O) has produced mixed results. We assert that how OCB‐O and OCB‐I are conceptualized affects the patterns of results, and we hypothesize that, when OCB is conceptualized appropriately, an agent‐system model is supported (interactional and procedural justice are the strongest unique predictors of OCB‐I and OCB‐O, respectively). We also hypothesize that shared variance among the justice types explains additional variance in OCB. Analyses of semi‐ partial correlations conducted on meta‐analytic coefficients supported our hypotheses. Theoretical and practical implications are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

聚偏氟乙烯中空纤维疏水膜及其初步应用

使用聚偏氟乙烯中空纤维疏水膜,比较了三种膜蒸馏过程用于质量分数为3．5％的氯化钠溶液的脱盐效果。实验结果表明：真空膜蒸馏的通量最大,达到21．8kg／（m^2·h）,其次为直接接触式膜蒸馏,气扫式膜蒸馏的通量最小;三种膜蒸馏过程的脱盐率均在99．99％以上;膜蒸馏通量随膜内径增加略有增加,与膜壁厚呈反比。真空膜蒸馏法可用于反渗透浓水的进一步处理,当反渗透浓水浓缩4倍时,原水电导率从5980μS／cm增加到22800μS／cm,膜蒸馏产水电导率保持在1．8～1．9μS／cm以内,脱盐率大于99．99％。     

Effects of bed materials on the performance of an anaerobic sequencing batch biofilm reactor treating domestic sewage

The objective of this study was to determine the best performance of an anaerobic sequencing batch biofilm reactor (AnSBBR) based on the use of four different bed materials as support for biomass immobilization. The bed materials utilized were polyurethane foam (PU), vegetal carbon (VC), synthetic pumice (SP), and recycled low-density polyethylene (PE). The AnSBBR, with a total volume of 7.2L, was operated in 8-h batch cycles over 10 months, and fed with domestic sewage with an average influent chemical oxygen demand (COD) of 358+/-110mg/L. The average effluent COD values were 121+/-31, 208+/-54, 233+/-52, and 227+/-51mg/L, for PU, VC, SP, and PE, respectively. A modified first-order kinetic model was adjusted to temporal profiles of COD during a batch cycle, and the apparent kinetic constants were 0.52+/-0.05, 0.37+/-0.05, 0.80+/-0.04, and 0.30+/-0.02h(-1) for PU, VC, SP, and PE, respectively. Specific substrate utilization rates of 1.08, 0.11, and 0.86mg COD/mgVS day were obtained for PU, VC, and PE, respectively. Although SP yielded the highest kinetic coefficient, PU was considered the best support, since SP presented loss of chemical constituents during the reactor's operational phase. In addition, findings on the microbial community were associated with the reactor's performance data. Although PE did not show a satisfactory performance, an interesting microbial diversity was found on its surface. Based on the morphology and denaturing gradient gel electrophoresis (DGGE) results, PE showed the best capacity for promoting the attachment of methanogenic organisms, and is therefore a material that merits further analysis. PU was considered the most suitable material showing the best performance in terms of efficiency of solids and COD removal.     

An environmental perspective of the post-tsunami scenario along the coast of Tamil Nadu, India: role of sand dunes and forests

An endeavor to feel the pulse of a coast devastated by a powerful oceanographic event is made. Results of field investigations along Tamil Nadu seaside revealed that the tsunami of December 2004 demolished dwellings within strips ranging from 6 to 132m (average width, 41m) from the dune, and flooded up to 862m (average, 247m) from the shore. The event damaged sand dunes, ripped dune vegetation, created new water bodies and shattered high value assets. Comparatively, casuarina forests performed remarkably. Uprooting of trees was exclusively restricted to a frontal strip ranging from 5 to 25m (average width, 14m) nearest to the shore where the maximum wave run-up was 6.5m above sea level. Sand dunes in general, and casuarina forests in particular, posses an innate capacity to dissipate powerful waves. This inference is supported by (a) negligible over wash along belts characterized by high dune complexes, (b) intact villages shielded by dense forests as well as sand dunes, and (c) maximum destruction of open beach front influenced by intense human activity. In this context, the coastal regulation zone (CRZ) Notification of 1991 offers sufficient scientific validity to be endorsed. However, post-tsunami ecosystem management initiatives lack a scientific basis. Therefore, a coastal hazards policy, that considers adaptation, dune restoration and forested buffer zones, is a sustainable long-term option for Indian coasts.     

重金属检测方法研究综述

重金属超标会造成环境污染,同时重金属在生物体内的积累效应会对人类的健康造成潜在地威胁.主要从应用新型的科技成果到结合生物技术对重金属的检测方法做一综述,以期为建立灵敏度更高、更准确、更快速的检测方法提供参考.     

Maternal transfer of brominated flame retardants in zebrafish (Danio rerio)

In many species reproduction and embryonic development have been shown to be sensitive to environmental contaminants. Understanding embryonic exposure to environmental contaminants is thus highly important. In this study concentrations of brominated flame retardants (BFRs) were measured in zebrafish eggs after parental exposure for 42 days via the diet. Zebrafish were exposed to two doses of eleven structurally-diverse BFRs. Eight BFRs were detected in the female zebrafish and maternal transfer to eggs was evident for all eight compounds. The highest concentrations in eggs were observed for hexabromocyclododecane (HBCD) and 2,4,4'-tribromodiphenyl ether (BDE 28), followed by 2,2',3,4,4',5',6-heptabromodiphenyl ether (BDE 183) and tetrabromobisphenol A 2,3-dibromopropyl ether (TBBPA DBPE). Five potential BFR metabolites were tentatively identified in female fish and maternal transfer was observed also for these compounds. The lipid adjusted concentrations in eggs were significantly higher than the concentrations in female fish for several of the BFRs. Further, the results showed a generally higher transfer in the lower exposure level and also indicated a dependency on the physico-chemical properties of the compounds.     

Spatial trends of polyfluorinated compounds in guillemot (Uria aalge) eggs from North-Western Europe

Polyfluorinated alkyl compounds (PFCs) are a group of chemicals of growing concern that have been detected in biological and abiotic samples worldwide. This study reports the concentrations of a suite of PFCs: perfluorooctyl sulfonate (PFOS), perfluorooctyl sulfonamide (PFOSA) and perfluorinated carboxylic acids (PFCAs) in guillemot (Uria aalge) eggs, collected in North-Western Europe, from Iceland, the Faroe Islands, Sweden and two locations in Norway. The highest concentrations of PFOS were found in samples from Sweden (mean 400 ng g(-1) wet weight (w.w.)), which were almost five times higher than concentrations found in Norwegian samples (mean 85 ng g(-1)w.w. from both sample sites). The concentrations found in Icelandic and Faroe samples were lowest (mean 16 and 15 ng g(-1)w.w., respectively). Only Swedish samples differed significantly from the other locations. In general, PFCAs show a different spatial trend than PFOS. Perfluorooctanoic acid (PFOA) was not detected in any sample and perfluorononanoic acid (PFNA) was only detected in samples from Sweden. The most abundant PFCA was perfluoroundecanoic acid (PFUA) with highest concentrations in samples from Sweden (mean 82 ng g(-1)w.w.), samples from the Faroe Islands had the second highest concentration (mean 57 ng g(-1)w.w.) and samples from Iceland and Norway had concentrations ranging between 18 and 30 ng g(-1)w.w. The original hypothesis was based on the idea that PFC concentrations are the highest close to more densely populated and industrialized areas and lower levels in remote areas. However, the geographic pattern is more complicated than predicted and varies among different PFCs.     

The effect of nitroaromatics' composition on their toxicity in vivo: novel, efficient non-additive 1D QSAR analysis

Novel 1D QSAR approach that allows analysis of non-additive effects of molecular fragments on toxicity has been proposed. Twenty-eight nitroaromatic compounds including some well-known explosives have been chosen for this study. The 50% lethal dose concentration for rats (LD50) was used as the estimation of toxicity in vivo to develop 1D QSAR models on the framework of Simplex representation of molecular structure. The results of 1D QSAR analysis show that even the information about the composition of molecules provides the main trends of toxicity changes. The necessity of consideration of substituents' mutual impacts for the development of adequate QSAR models of nitroaromatics' toxicity was demonstrated. Statistic characteristics for all the developed partial least squares QSAR models, except the additive ones are quite satisfactory (R2=0.81-0.92; Q2=0.64-0.83; R2 test=0.84-0.87). A successful performance of such models is due to their non-additivity i.e. possibility of taking into account the mutual influence of substituents in benzene ring which plays the governing role for toxicity change and could be mediated through the different C-H fragments of the ring. The correspondence between observed and predicted by these models toxicity values is good. This allowing combine advantages of such approaches and develop adequate consensus model that can be used as a toxicity virtual screening tool.     

Influence of gas flow-induced shear stress on the operation of the Anammox process in a SBR

The start up and performance of the Anammox process were tested in sequencing batch reactors with two different configurations: a bubble column (SBR-B) and a gas-lift reactor (SBR-G). Different off-gas upflow velocities were tested (3.53-12.3 cm min(-1)) in order to expose the biomass to different shear conditions and to study their effects on both efficiency and physical properties of the Anammox granular biomass. For the SBR-B the minimum gas upflow velocity needed to achieve biomass suspension inside the reactor was 12.3 cm min(-1). Such velocity made impossible the stable operation of the process. The fluidization of biomass for the SBR-G was reached at a gas upflow velocity of 3.52 cm min(-1). This system maintained an efficiency of nitrite removal around 98% at values up to 5.29 cm min(-1) but when the gas upflow velocity was increased from 5.29 to 9.70 cm min(-1) a significant decrease of the specific Anammox activity of the biomass from 0.35 to 0.05 g Ng(-1) VSS d(-1) was measured. The system lost 85% of its nitrogen removal efficiency which was not restored in spite of returning the gas upflow velocity to its initial value.