Phytoplankton patchiness: the role of lateral stirring and mixing

The diesel oxidation catalyst (DOC) has been part of diesel exhaust systems since regulations were introduced to limit the amount of harmful emissions released to the environment from diesel engines. The DOC primary functions are oxidation of CO, unburned hydrocarbons, and NO, while active hydrocarbon oxidation can also be used to generate exotherms required for downstream components. This review will describe work that has attempted to understand the reactions, both desired and undesired, that occur over the catalyst. First, the history, configuration, and components of the DOC will be discussed, followed by in-depth coverage of the fundamental reactions that occur over a DOC, including reaction mechanisms, reaction inhibition, and other reactivity effects. Finally, DOC deactivation mechanisms and their effects on the DOC are described. While there is a lot of research literature regarding Pt- and Pd-based catalysts for many different reaction schemes, this review tries to highlight work most relevant to...

Diesel Oxidation Catalysts

In the past decade, theoretical ecologists have empha- sized that local interactions between predators and prey may invoke emergent spatial patterning at larger spatial scales. However, empir- ical evidence for the occurrence of emergent spatial patterning is scarce, which questions the relevance of the proposed mechanisms to ecological theory. We report on regular spatial patterns in young mussel beds on soft sediments in the Wadden Sea. We propose that scale-dependent feedback, resulting from short-range facilitation by mutual protection from waves and currents and long-range com- petition for algae, induces spatial self-organization, thereby providing a possible explanation for the observed patterning. The emergent self-organization affects the functioning of mussel bed ecosystems by enhancing productivity and resilience against disturbance. More- over, self-organization allows mussels to persist at algal concentra- tions that would not permit survival of mussels in a homogeneous bed. Our results emphasize the importance of self-organization in affecting the emergent properties of natural systems at larger spatial scales.

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Scale-dependent feedback and regular spatial patterns in young mussel beds

The biological and physical processes contributing to planktonic thin layer dynamics were examined in a multidisciplinary study conducted in East Sound, Washington, USA between June 10 and June 25, 1998. The temporal and spatial scales characteristic of thin layers were determined using a nested sampling strategy utilizing 4 major types of platforms: (1) an array of 3 moored acoustical instrument packages and 2 moored optical instrument packages that recorded distributions and inten- sities of thin layers; (2) additional stationary instrumentation deployed outside the array comprised of meteorological stations, wave-tide gauges, and thermistor chains; (3) a research vessel anchored 150 m outside the western edge of the array; (4) 2 mobile vessels performing basin-wide surveys to define the spatial extent of thin layers and the physical hydrography of the Sound. We observed numerous occur- rences of thin layers that contained locally enhanced concentrations of material; many of the layers per- sisted for intervals of several hours to a few days. More than one persistent thin layer may be present at any one time, and these spatially distinct thin layers often contain distinct plankton assemblages. The results suggest that the species or populations comprising each distinct thin layer have responded to different sets of biological and/or physical processes. The existence and persistence of planktonic thin layers generates extensive biological heterogeneity in the water column and may be important in maintaining species diversity and overall community structure.

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Characteristics, distribution and persistence of thin layers over a 48 hour period

Chemical and biological activity in open flows: A dynamical system approach

Convective instability induced by differential transport in the tubular packed-bed reactor

On transverse patterns in packed-bed catalytic reactors

The diffusive instability is considered as one important mechanism that accounts for the patchiness of ecosystems, e.g. the phytoplankton/zooplankton system. We show here that spatial differentiation of the plankton communities may occur alternatively through the differential flow instability. A differential flow (advection) between phyto-and zooplankton species arises naturally in the shear flow of a marine current due to the diurnal, differential vertical migration of the counteracting plankton species. Model calculations using an extension of Scheffer's plankton model and literature values of the kinetic parameters predict a travelling wave pattern of biological activity on the spatial scale from a few kilometers to ca 100 km, depending on the parameter values, in agreement with the scales of observed structures. Most importantly we find that the productivity (the spatial average of biomass and production rate) of both predator and prey subpopulations may be enhanced in the patterned state by factors of the order of 2 and 20. The mechanism is discussed by which the productivity of both counteracting species may change (i.e. be enhanced) through the differential flow.

Vladimir Z. Yakhnin

Papers

Convective instability induced by differential transport in the tubular packed-bed reactor

On transverse patterns in packed-bed catalytic reactors

Patchiness and enhancement of productivity in plankton ecosystems due to the differential advection of predator and prey

Moving hot spots and resonance in adiabatic packed-bed reactors

Dynamic responses of packed bed reactors