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Vladimir Z. Yakhnin

Bio: Vladimir Z. Yakhnin is an academic researcher from University of Toronto. The author has contributed to research in topics: Packed bed & Exothermic reaction. The author has an hindex of 13, co-authored 21 publications receiving 299 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors show that convective instability in a non-isothermal packed-bed tubular reactor can be caused by the interplay of the differential transport of heat and matter and of the activator-inhibitor kinetics inherent in nonisothermal, exothermic reactions, where heat plays the role of autocatalytic species or activator, and matter represents the inhibitor.

40 citations

Journal ArticleDOI
01 Feb 1997-Oikos
TL;DR: It is shown here that spatial differentiation of the plankton communities may occur alternatively through the differential flow instability, and that the productivity of both predator and prey subpopulations may be enhanced in the patterned state by factors of the order of 2 and 20.
Abstract: 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.

22 citations

Journal ArticleDOI
TL;DR: In this paper, a modified Peclet number based on the length of the reaction zone is proposed as a criterion for the importance of disturbance amplification in packed-bed catalytic reactors.

21 citations


Cited by
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Journal ArticleDOI
TL;DR: The role played by lateral advection and mixing in marine phytoplankton patchy distribution has been discussed in this paper, with a focus on the role of the physical circulation in this regime.

347 citations

Journal ArticleDOI
27 Oct 2011
TL;DR: 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 as discussed by the authors, while active hydrocarbon oxidation can also be used to generate exotherms required for downstream components.
Abstract: 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...

326 citations

Journal ArticleDOI
TL;DR: It is proposed that scale‐dependent feedback, resulting from short‐range facilitation by mutual protection from waves and currents and long‐range competition for algae, induces spatial self‐organization, thereby providing a possible explanation for the observed patterning in young mussel beds in the Wadden Sea.
Abstract: 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.

259 citations

Journal ArticleDOI
TL;DR: In this article, a multidisciplinary study was conducted in East Sound, Washington, USA between June 10 and June 25, 1998, using a nested sampling strategy utilizing four 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
Abstract: 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.

214 citations

Journal ArticleDOI
TL;DR: In this paper, the authors review recent progress in this field, which became possible due to the application of methods taken from dynamical system theory, and place special emphasis on the derivation of effective rate equations which contain singular terms expressing the fact that the reaction takes place on a moving fractal catalyst, on the unstable foliation of the reaction free advection dynamics.

210 citations