The dynamics of near-bed seston flux and suspension-feeding benthos

Benthic suspension feeders depend on the fluid medium for their supply of edible particles. The horizontal flux of organic seston is a function of the interaction of particles of varying densities with the near-bed velocity field. Analytical and numerical models of this process predict that the shape of the flux profile varies with flow rate, bottom roughness and particle settling velocity. Bulk horizontal particle flux may either decrease or increase with height above the bed. Flume experiments with natural sediments from Eastern Passage, Nova Scotia confirmed the trends predicted by the model. In a complex suspension, denser, inorganic particles have flux maxima closer to the bed than lighter, organic seston, so suspension feeders must reach several centimeters above bed level to maximize the organic composition of their ration. The feeding ecology and diet of a passive suspension feeder, the polychaete, Spio setosa, were examined in light of the modelled seston dynamics and suggested that S. setosa is adapted to feed at 4 to 5 centimeters above the bed and specializes on suspended macrophyte detritus and flocculated organic-mineral aggregates. The influx of this organic seston at Eastern Passage is periodic and coincident with the local seiche period, showing that the hydrodynamic control of seston transport is an important factor in benthic trophic interactions

Towards the design of new and improved drilling fluid additives using molecular dynamics simulations

During exploration for oil and gas, a technical drilling fluid is used to lubricate the drill bit, maintain hydrostatic pressure, transmit sensor readings, remove rock cuttings and inhibit swelling of unstable clay based reactive shale formations. Increasing environmental awareness and resulting legislation has led to the search for new, improved biodegradable drilling fluid components. In the case of additives for clay swelling inhibition, an understanding of how existing effective additives interact with clays must be gained to allow the design of improved molecules. Owing to the disordered nature and nanoscopic dimension of the interlayer pores of clay minerals, computer simulations have become an increasingly useful tool for studying clay-swelling inhibitor interactions. In this work we briefly review the history of the development of technical drilling fluids, the environmental impact of drilling fluids and the use of computer simulations to study the interactions between clay minerals and swelling inhibitors. We report on results from some recent large-scale molecular dynamics simulation studies on low molecular weight water-soluble macromolecular inhibitor molecules. The structure and interactions of poly(propylene oxide)-diamine, poly(ethylene glycol) and poly(ethylene oxide)-diacrylate inhibitor molecules with montmorillonite clay are studied.<br>Durante a exploração de óleo e gás um fluido de perfuração é usado para lubrificar 'bit' da perfuradora, manter a pressão hidrostática, transmitir sensores de leitura, remover resíduos da rocha e inibir o inchamento da argila instável baseada nas formações dos folhelhos. O aumento das preocupações ambientais bem como a legislação resultante levou à procura de novos fluidos de perfuração com componentes biodegradáveis. No caso dos aditivos para inibir o inchamento das argilas o entendimento das interações entre os aditivos e as argilas tem que ser adquirido para permitir o projeto de moléculas commelhores propriedades. Devido à natureza desordenada da dimensão nanoscópica dos nano poros dos minerais argilosos, simulações computacionais têm se tornado uma ferramenta poderosa para estudar as interações entre o inchamento da argila e o inibidor. Neste trabalho revisamos brevemente o histórico do desenvolvimento de fluidos técnicos de perfuração, o impacto ambiental dos fluidos de perfuração e o uso de simulações computacionais para estudar as interações entre os fluidos de perfuração e os inibidores do inchamento. Nós reportamos resultados para alguns estudos baseados em simulações de dinâmica molecular em larga escala em uma solução aquosa de baixo peso molecular com solutos compostos por macromoléculas inibidoras. A estrutura e as interações entre inibidores compostos por polipropileno óxido, polietileno óxido e moléculas e a argila montmorilonita são estudadas