Modelling the combined effect of surface roughness and topography on bacterial attachment

Bacterial attachment is a complex process affected by flow conditions,imparted stresses,and the sur-face properties and structure of both the supporting material and the cell.Experiments on the initial attachment of cells of the bacterium Streptococcus gordonii (S.gordonii),an important early coloniser of dental plaque,to samples of stainless steel (SS) have been reported in this work.The primary aim motivating this study was to establish what affect,if any,the surface roughness and topology of sam-ples of SS would have on the initial attachment of cells of the bacterium S.gordonii.This material and bacterium were chosen by virtue of their relevance to dental implants and dental implant infections.Prior to bacterial attachment,surfaces become conditioned by the interfacing environment (salivary pellicle from the oral cavity for instance).For this reason,cell attachment to samples of SS pre-coated with saliva was also studied.By implementing the Extended Derjaguin Landau Verwey and Overbeek(XDLVO) theory coupled with convection-diffusion-reaction equations and the surface roughness infor-mation,a computational model was developed to help better understand the physics of cell adhesion.Surface roughness was modelled by reconstructing the surface topography using statistical parame-ters derived from atomic force microscopy (AFM) measurements.Using this computational model,the effects of roughness and surface patterns on bacterial attachment were examined quantitatively in both static and flowing fluid environments.The results have shown that rougher surfaces (within the sub-microscale) generally increase bacterial attachment in static fluid conditions which quantitatively agrees with experimental measurements.Under flow conditions,computational fluid dynamics (CFD) simula-tions predicted reduced convection-diffusion inside the channel which would act to decrease bacterial attachment.When combined with surface roughness effects,the computational model also predicted that the surface topographies discussed within this work produced a slight decrease in overall bacterial attachment.This would suggest that the attachment-preventing effects of surface patterns dominate over the adhesion-favourable sub-microscale surface roughness;hence,producing a net reduction in adhered cells.This qualitatively agreed with experimental observations reported here and quantitatively matched experimental observations for low flow rates within measurement error.     

Nitrogen gas supersaturation in the recent sediments of lake erie and two polluted harbors

Nitrogen gas distributions in sediment pore water were determined for cores collected in Lake Erie and two nearby harbors. Concentrations of N₂ gas ranged from 11.9 to 37.0 ml l⁻¹ and from 8.9 to 58.3 ml l⁻¹ for open lake and polluted harbor sediments, respectively. Maximum concentrations in the harbor sediments were as high as 3.5 times N₂ saturation calculated for the overlying water. Indirect diffusive flux estimates for nitrogen gas ranged from 20 to 32% of the particulate nitrogen sedimentation rate in Lake Erie. At one location, the amount of nitrogen gas lost by diffusion was calculated to be greater than the nitrogen deposited to the sediments. Nitrogen gas production and diffusive loss from surficial sediments probably represents a major pathway for nitrogen removal from Lake Erie.     

Assessment of strain bursting in deep tunnelling by using the finite-discrete element method

Rockbursting in deep tunnelling is a complex phenomenon posing significant challenges both at the design and construction stages of an underground excavation within hard rock masses and under high in situ stresses. While local experience, field monitoring, and informed data-rich analysis are some of the tools commonly used to manage the hazards and the associated risks, advanced numerical techniques based on discontinuum modelling have also shown potential in assisting in the assessment of rockbursting. In this study, the hybrid finite-discrete element method (FDEM) is employed to investigate the failure and fracturing processes, and the mechanisms of energy storage and rapid release resulting in bursting, as well as to assess its utility as part of the design process of underground excavations. Following the calibration of the numerical model to simulate a deep excavation in a hard, massive rock mass, discrete fracture network (DFN) geometries are integrated into the model in order to examine the impact of rock structure on rockbursting under high in situ stresses. The obtained analysis results not only highlight the importance of explicitly simulating pre-existing joints within the model, as they affect the mobilised failure mechanisms and the intensity of strain bursting phenomena, but also show how the employed joint network geometry, the field stress conditions, and their interaction influence the extent and depth of the excavation induced damage. Furthermore, a rigorous analysis of the mass and velocity of the ejected rock blocks and comparison of the obtained data with well-established semi-empirical approaches demonstrate the potential of the method to provide realistic estimates of the kinetic energy released during bursting for determining the energy support demand.     

Modeling metal bioaccumulation in a deposit-feeding polychaete from labile sediment fractions and from pore water

Estuarine sediments are often highly enriched in particle-reactive metal contaminants and because aquatic animals have often been shown to acquire metals predominantly from their diet, benthic animals feeding on deposited or resuspended sediments may also accumulate metals through this uptake pathway. Laboratory experiments were performed in which the surface deposit-feeding polychaete, Nereis succinea, was exposed to As(+ 5), Cd, and Cr(+ 3) in pore water or in estuarine sediments with and without enrichment with algal debris. These experiments generated metal uptake parameters (assimilation efficiency of ingested metal [AE], uptake rate constant of dissolved metal, efflux rate constants following dietary or aqueous metal exposures) used in a kinetic model of metal bioaccumulation. The model showed that > 97% of the body burden of these metals is accumulated through ingested sediment. The kinetic model was further modified to consider the geochemical fractionation of the metals in the sediments because metals bound to some fractions were shown to be unavailable to these polychaetes. The modified model substituted the AE term for each metal by the percentage of metal extracted in neutral and weak acid exchangeable fractions (termed “carbonex” fraction) multiplied by the slope of the regression between the metal AE and its fractionation in carbonex. The modified model generated predictions of As, Cd, and Cr body burdens in polychaetes at three different estuarine sites that matched independent field observations at these sites (r² = 0.84 for sediments without organic enrichment, r² = 0.87 with organic enrichment). Model predictions that relied on total metal concentrations showed weaker relationships (r² = 0.11-0.50). This study adds to the evidence for the dominance of dietary uptake of metals in aquatic animals and identifies a key sedimentary fraction of metals that can account for bioavailability of sediment-bound metals.     

Fire Performance Assessment of a Fiber Reinforced Polymer Wall Panel Used in a Single Family Dwelling

This paper describes a fire performance assessment of a sandwich panel selected as the primary material in a high-performance house developed for the 2013 China Solar Decathlon competition. The sandwich panel has fiber reinforced polymer skins and a foam plastic core. Evaluation of fire performance showed that the selected panel would not comply with U.S. building code requirements for a single-family dwelling without additional protection. However, the use of an intumescent fire protective coating, coupled with the installation of a residential fire sprinkler system, is shown to be effective in meeting the intent of the fire and life safety requirements of the International Residential Code. Fire testing shows that the application of an intumescent fire protective coating to the panels significantly decreases the heat release rate, the smoke production characteristics, and the extent of flame spread on the panels.     

Housing and Economic Development in Indian Country: Challenge and Opportunity

Global Warming: Climate Change: The IPCC Scientific Assessment J. T. Houghton, G. J. Jenkins, and J. J. Ephraums, editors. Cambridge University Press, Cambridge, UK, 1990. 305 pp. $34.95 (paperback).

Global Warming: Leaving Eden to Protect and Manage the Earth E. G. Nisbet. Cambridge University Press, Cambridge, UK, 1991. 358 pp. $14.95 (paperback).

Global Warming: Global Environmental Issues: A Climatological Approach David D. Kemp. Routledge, Chapman and Hall, London, 1990. 220 pp. $15.95 (paperback).

Global Warming: Global Climate Change and Life on Earth Richard L. Wyman, editor. Rout-ledge, Chapman and Hall, London, 1991. 282 pp. $24.95 (paperback).

Global Warming: Global Climate Change and California Joseph B. Knox and Ann Foley Scheuring, editors. University of California Press, Berkeley, 1992. 184 pp. $12.95 (paperback).

The Environment: Race and the Incidence of Environmental Hazards: A Time for Discourse Bunyan Bryant and Paul Mohai, editors. Westview Press, San Francisco, 1992. 251 pp. $32.00 (paperback).

The Environment: Sustaining the Earth John Young. Harvard University Press, Cambridge, MA, 1990. 202 pp. $10.95 (paperback).

The Environment: Rural Environmental Planning for Sustainable Communities Frederick O. Sargent, Paul Lusk, Jose A. Rivera, and Maria Varela. Island Press, Washington, DC, 1991. 254 pp. $24.95 (paperback).

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Planning and Its Subfields: Put up or Give Way: States, Economic Competitiveness, and Poverty John Sidor. Council of State Community Development Agencies, Washington, DC, 1991.243 pp. $20.00 (paperback).

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Briefly Noted: Reclaiming the Past Landmarks of Women's History Page Putnam Miller, editor. Indiana University Press, Bloomington, 1992. 232 pp. $35.00.

Briefly Noted: Renewing Cities Ross J. Gittell. Princeton University Press, Princeton, NJ, 1992. 232 pp., $39.50.

Briefly Noted: Regions Reconsidered: Economic Networks, Innovation, and Local Development in Industrialized Countries Edward Bergman, Gunther Maier, and Franz Todtling, editors. Mansell, London, 1991. 312 pp. $80.00.

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Briefly Noted: The Changing Image of the City: Planning for Downtown Omaha, 1945-1973 Janet R. Daly-Bednarek. University of Nebraska Press, Lincoln, 1992. 292 pp. $37.50.