364 research outputs found
A comprehensive approach to establish the impact of worksites air emissions
Worksite activities are time-limited events associated with continuous releases of airborne pollutants, such as carbon monoxide, particulate matter, and NOx, and they impact potentially vast areas. The side-effects on the environment can be severe, and they are subject of literature studies, with the final aim of proposing solutions that may improve the management of air emissions. No general assessment method or approach is yet available to estimate their effects on the environment and workers’ health. In this work, a general procedure that can be potentially applied to every type of worksite is proposed (i.e., construction sites, upgrading of chemical plants, road sites, etc..). The approach involves a detailed assessment of emissions and their expected pollutant concentrations. A dedicated mathematical model has been defined to assess pollutant emissions over time, consistent with all the different phases of foreseen activities. Emissions are defined on base of the GANTT descriptions of the activities and air pollutant dispersion is simulated with a dedicated model. Finally, the obtained results are evaluated against air quality thresholds as defined by laws and conditioning the human health risks for workers and citizens potentially exposed to pollutants
Response of electrically coupled spiking neurons: a cellular automaton approach
Experimental data suggest that some classes of spiking neurons in the first
layers of sensory systems are electrically coupled via gap junctions or
ephaptic interactions. When the electrical coupling is removed, the response
function (firing rate {\it vs.} stimulus intensity) of the uncoupled neurons
typically shows a decrease in dynamic range and sensitivity. In order to assess
the effect of electrical coupling in the sensory periphery, we calculate the
response to a Poisson stimulus of a chain of excitable neurons modeled by
-state Greenberg-Hastings cellular automata in two approximation levels. The
single-site mean field approximation is shown to give poor results, failing to
predict the absorbing state of the lattice, while the results for the pair
approximation are in good agreement with computer simulations in the whole
stimulus range. In particular, the dynamic range is substantially enlarged due
to the propagation of excitable waves, which suggests a functional role for
lateral electrical coupling. For probabilistic spike propagation the Hill
exponent of the response function is , while for deterministic spike
propagation we obtain , which is close to the experimental values
of the psychophysical Stevens exponents for odor and light intensities. Our
calculations are in qualitative agreement with experimental response functions
of ganglion cells in the mammalian retina.Comment: 11 pages, 8 figures, to appear in the Phys. Rev.
Physics of Psychophysics: Stevens and Weber-Fechner laws are transfer functions of excitable media
Sensory arrays made of coupled excitable elements can improve both their
input sensitivity and dynamic range due to collective non-linear wave
properties. This mechanism is studied in a neural network of electrically
coupled (e.g. via gap junctions) elements subject to a Poisson signal process.
The network response interpolates between a Weber-Fechner logarithmic law and a
Stevens power law depending on the relative refractory period of the cell.
Therefore, these non-linear transformations of the input level could be
performed in the sensory periphery simply due to a basic property: the transfer
function of excitable media.Comment: 4 pages, 5 figure
Safe optimization of 2-octanol oxidation and vinyl acetate emulsion polymerization
In this work the possibility to develop reliable optimization procedures, particularly suitable for full plant
exothermic semibatch processes operated in the isoperibolic temperature control mode, has been
investigated. It has been found that a general optimization procedure could be developed by using a
particular curve, called topological curve, resulting from the numerical solution of the ordinary
differential equation system describing the process dynamics. Such a curve exhibits a series of
inversion points that represent, physically, transitions between different system thermal behaviour
regions.
The optimization procedure based on the analysis of the topological curve uses the QFS inversion as a
boundary beyond which the optimum operating conditions can be searched accounting for reacting
mixture thermal stability and desired productivity constraints.
Experimental temperature vs. time data spring from laboratory studies of two different potentially
runaway systems (the nitric acid oxidation of 2-octanol to 2-octanone and the free radical emulsion
homopolymerization of vinyl acetate) have been modelled to demonstrate that the topological criterion
for the QFS detection is independent of all the thermodynamic and process variables control equations
used to describe the system. Such a result suggests that this approach could be safely used to
optimize even processes operated at the full plant scale
Emulsion polymerization of butyl acrylate: safe optimization using topological criteria
Fast and strongly exothermic emulsion polymerization processes are particularly difficult to be optimized from both safety and productivity point of view because of the occurrence of a number of side undesired reactions (e.g. propagation of tertiary radicals, chain transfer to monomer, backbiting, termination by disproportion etc.) and the triggering of boiling phenomena with consequent stable foams
formation under atmospheric pressure. Therefore, it would be useful to develop a suitable combined theoretical and experimental procedure able to detect both the optimum process dosing time and initial reactor temperature. In this work, it is discussed how an extended version of the topological criterion theory, originally developed for isoperibolic semibatch reactors, can be used to safely optimize indirectly cooled isothermal semibatch reactor. Moreover, such a methodology is applied to a case-study
represented by the synthesis of polybutyl acrylate through the radical emulsion polymerization of butyl acrylate
Criteri topologici per l'ottimizzazione sicura di reazioni potenzialmente fuggitive
In this work, optimization procedures, particurarly suitable for potentially runaway reactions carried out in indirectly cooled semibatch reactors operated in isoperibolic temperature control mode, have been developed. Such optimization procedures based on a particular criterion, referred to as "topological", in order tio select a set of operating conditions which is able of ensuring both process thermochemical stability and high productivity and selectivity with respect the desired product. This topological approach has been validated both experimentally and theoretically by studing kinetic schemes characterized by different complexity degrees. As an example, the relevant case study of the free radical emulsion polymerization of vinyl acetate has been analyzed and reported
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