Mechanical analysis of hollow fiber membrane integrity in water reuse applications

In order to gain insight into membrane fiber failure (i.e., loss of integrity), properties of five hollow fiber membranes and four hollow fiber modules were evaluated. Specifically, membrane material, membrane symmetry, fiber modulus of elasticity, fiber diameter and thickness, module potting technique, module flow pattern (inside-out or outside-in), and coliform breakthrough were investigated. The approach combined evaluation of the above properties with mathematical modeling of structure-fluid interactions to comprehensively evaluate the properties most important for maintaining hollow fiber membrane integrity. Tensile strength testing revealed that the strongest fiber was an asymmetric polyacrylonitrile membrane fiber. The weakest fiber was a symmetric polyethylene membrane fiber. Pilot plant testing on the four membrane modules revealed that membrane symmetry may be a more important factor than potting technique for hollow fiber integrity. Results from the SEM and tensile testing were used as input to a finite element analysis model used to evaluate time-dependent structure-fluid interactions. It was found that additional stresses at the juncture of the potting material and the hollow fiber membranes exist. These stresses likely lead to the formation of fractures.     

Ventilation of a dead-end duct having a porous barrier

Analytic expressions for the flow and pressure in a dead-end duct which has loss of fluid through a porous wall are developed. The presence of an obstruction or auxiliary fan at the end of the duct is included. In either case there is a maximum permissible length of duct. As the duct length approaches this maximum, the main supply fan power and flow increase dramatically. There is no recirculation within the duct when there is an obstruction at the end of the duct. If an auxiliary fan is used, there is always recirculation. However the use of an auxiliary fan can yield major savings in total power requirements.     

Ozonation of Humic Substances: Effects on Molecular Weight Distributions of Organic Carbon and Trihalomethane Formation Potential

Four different sources of humic substances were studied to determine the effects of ozonation on molecular weight-distributions, based on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP). Solutions of two soil-derived fulvic acids and a one soil-derived humic acid, as well as dissolved organic matter (DOM) associated with a natural water source were studied. Both gel permeation chromatography (GPC) and ultrafiltration (UF) were employed to define apparent molecular weight (AMW). Applied ozone doses ranged from 2.0 to 2.5 mg O₃/mg DOC. Overall samples of untreated and ozonated waters, as well as individual molecular weight fractions, were characterized according to DOC, UV absorbance, and THMFP. Ozonation resulted in a significant disappearance of higher AMW material with a corresponding increase in lower AMW material. Although little overall reduction in DOC concentration was observed, significant overall reductions in UV absorbance and THMFP levels were observed.     

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass,part II: Structure

High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al + Na):Si substitutions in a simplified nuclear waste model glass (ISG, international simple glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and ²⁷Al, ²³Na, ²⁹Si, and ¹¹B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (eg, bond distance, coordination number, etc) and medium-range (eg, oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al + Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase in tri-bridging oxygen species, whereas (Al + Na):Si substitution creates nonbridging oxygen species. Charge compensator preferences were found for Si-[NBO] (Na⁺), ^[3]B-[NBO] (Na⁺), ^[4]B (mostly Ca²⁺), ^[4]Al (nearly equally split Na⁺ and Ca²⁺), and ^[6]Zr (mostly Ca²⁺). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-^[3]B and ^[3]B-O-^[3]B linkages. These results provide insights on the structural origins of property changes such as glass-transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models.     

Development of Habitat Suitability Criteria and In‐Stream Habitat Assessment for the Benthic Cyanobacteria Phormidium

Global demand for freshwater has led to unprecedented levels of water abstraction from riverine systems. This has resulted in large alterations in natural river flows. The deleterious impacts of reduced flows on fish and macroinvertebrate abundances have been thoroughly investigated; in contrast, there is a limited understanding of the potential for changes in the abundance of nuisance benthic algal/cyanobacterial blooms. In New Zealand, Phormidium sp. blooms are common in numerous rivers during summer low flows. In this study, an in‐stream habitat assessment is used to examine the relationship between Phormidium habitat availability and reducing flows. Over 650 observations of Phormidium mats, from seven sites (Hutt River, lower North Island, New Zealand), were used to construct habitat suitability curves for depth, velocity and substrate. Preference curves were fitted using both the ‘forage ratio’ and ‘quantile regression’ methods. Phormidium growth, observed at all seven sites, increased significantly from upstream (uppermost site, 5.2% mat cover) to downstream (63.5%). The habitat suitability curves revealed Phormidium had a large tolerance to velocity, depth and substrate type. Consequently, decreases in flow had only negligible effects on available Phormidium habitat. During periods of stable flow, Phormidium abundance positively correlated with increased nitrogen concentrations, potentially explaining the large variation in Phormidium cover from upstream to downstream. Quantile regression generated habitat suitability criteria were a more accurate predictor of available Phormidium habitat than the forage ratio criteria. Copyright © 2013 John Wiley & Sons, Ltd.     

Better Safe than Sorry: A Study of Investigating Individuals’ Protection of Privacy in the Use of Storage as a Cloud Computing Service

Since the use of network-based storage as a cloud computing service [Storage as a Service (StaaS)] becomes ubiquitous, users who store data in the cloud are exposed to risk and potentially severe consequences. Therefore, individuals should carefully consider security and privacy issues when using StaaS. Drawing upon the principle of self-preservation and the theory of protection motivation, this study develops a research model explaining the mechanisms leading to the development of a protection strategy for individuals’ safe use of StaaS and empirically tests the proposed model. The results show that the natural propensity to trust, an individual trait, influences an individual’s need for privacy. This, in turn, along with perception of privacy risk, significantly affects individuals’ perception of the need to protect themselves. Three coping appraisal factors, preventive measures, self-efficacy, and willingness to incur cost of prevention, together with the individual perceived need to protect self, directly and positively affect users’ need to develop a protection strategy in a cloud computing environment. Theoretical and practical implications are discussed.     

An empirical study of integration activities in distributions of open source software

Reuse of software components, either closed or open source, is considered to be one of the most important best practices in software engineering, since it reduces development cost and improves software quality. However, since reused components are (by definition) generic, they need to be customized and integrated into a specific system before they can be useful. Since this integration is system-specific, the integration effort is non-negligible and increases maintenance costs, especially if more than one component needs to be integrated. This paper performs an empirical study of multi-component integration in the context of three successful open source distributions (Debian, Ubuntu and FreeBSD). Such distributions integrate thousands of open source components with an operating system kernel to deliver a coherent software product to millions of users worldwide. We empirically identified seven major integration activities performed by the maintainers of these distributions, documented how these activities are being performed by the maintainers, then evaluated and refined the identified activities with input from six maintainers of the three studied distributions. The documented activities provide a common vocabulary for component integration in open source distributions and outline a roadmap for future research on software integration.