Filament, plume

Froude number W1 /( bQ is nearly the same for the near and far field plumes, 1.60 0.1. The entrainment coefficients are much larger, which probably includes pressure effects near the base for the axisymmetric fires and tornado-flame filament effects for the line fire, which are actually three dimensional. It should be realized that the data corresponding to these correlations contain results for finite fires D > 0, not idealized sources. The correlations in Tables 10.1 and 10.2 are one set of formulas others exist with equal validity. 

Our neurophysiological studies have focused on three important properties of the sex-pheromonal signal its quality (chemical composition of the blend), quantity (concentrations of components), and intermit-tency [owing to the fact that the pheromone in the plume downwind from the source exists in filaments and blobs of odor-bearing air interspersed with clean air (47, 48)]. Each of these properties of the pheromonal message is important, as the male moth gives his characteristic behavioral responses only when the necessary and sufficient pheromone components A and B are present in the blend (44), when the concentrations and blend proportions of the components fall within acceptable ranges (49), and when the pheromone blend stimulates his antennae intermittently (39, 50). In our studies, we examine how each of these important aspects of the odor stimulus affects the activity of neurons at various levels in the olfactory pathway. 

A third important characteristic of a female moth s sex-pheromone plume is its nonuniformity. Simulation of odor plumes using ionized air has shown clearly that a plume is not a simple concentration gradient but instead is distinctly filamentous and discontinuous (47,48). Furthermore,... 

Internal structure of the tube worm Riftia pachyptila. (a) Oxygen, sulfide, and carbon dioxide are absorbed through the plume filaments and transported In the blood to the cells of the trophosome. (b) The chemicals are absorbed into these cells, which contain dense colonies of sulfur bacteria, where they are converted to organic compounds and (c) passed back into the circulatory system to act as an energy source for the worms. Source-. From Childress, J. J., et al. (1987). Scientific American, 256, 114-121. 

Farrell, J. A., J. Murlis, X. Long, W. Li, and R. T. Card6. Filament-based atmospheric dispersion model to achieve short time scale structure of odor plumes. Environ. Fluid Mech. 2, 143-169 (2002). 

The sample data presented in this chapter were collected for fairly simple flow conditions. The flow was a unidirectional open-channel flow without large-scale flow meander, and the release condition was isokinetic in the direction of the bulk flow. Thus, chemical filaments were advected by the bulk flow in the stream-wise direction, while turbulent mixing acted to expand the plume size and dilute the chemical concentration. Changes in the flow and release conditions lead to significant variation in the plume characteristics and structure. 

In the pheromone orientation system it has been shown how important time aspects are. Several species will not be attracted to a pheromone source unless the stimulus arrives in a pulsed fashion, mimicking the filamentous structure of a natural odor plume. Correlates to this requisite have been found among AL neurons, where both fast neurons, able to code fast fluctuations in concentration, and slow neurons, seemingly only coding qualitative aspects of the plume, are present. 

Because mechanical diffusion arises from velocity perturbations at scale d, this mechanism contributes little to mixing at scales smaller than d. A patch dispersing only under the action of mechanical dispersion will appear filamentous and choppy at scales of O(d). With the onset of vortex shedding (Re > 100), turbulence of scale d and smaller is introduced, and produces small-scale mixing that smooths the concentration over scales less than d (Dybbs and Edwards, 1984 [161] Nepf et al. [460]). For processes that depend non-linearly on concentration, there will be a large difference between a smooth (Re > 100) versus a spikey (Rerf < 100) concentration profile. In addition, animals that follow odor plumes to locate prey or mates may need different search strategies for smooth and spikey plumes (Finelli, [181]). 

If human olfaction can discern the filamentous character of scent plumes in air, then a headspace analysis, no matter how complete, might not suffice to reconstruct the fragrance. The distribution of molecules would play a role, as would the rate with which they are replenished after they have been depleted by sniffing. If, on the other hand, olfaction (independent of other sensory inputs) cannot differentiate a heterogeneous stimulus from one that has been well mixed with air, then a complete chemical analysis could serve to archive odors. 

Because event plumes represent the sudden injection of exploitable reducing chemical substrates, as well as inhibitory constituents, they are likely to induce successional changes in the microbial community structure and activity within plume waters over time (Cowen etal., 1998). For example, in studies following the 1998 Axial Volcano eruption, abundant putative bacterial sulphur filaments were observed in August 1998 (Feely etal., 1999), though they were not initially found in plumes in February 1998 (Cowen etal., 1999). 

Using both sensory systems, the male moth flies slowly upwind in the direction of the source when it finds a pheromone plume, performing a number of turns in a quite regular structure when the plume filaments are lost. 

A principle factor governing plume structure is the interaction between scales of individual odor filaments and scales of turbulent energy. It is essential to appreciate that turbulent flows contain eddies of a variety of sizes. Individual odor filaments are small, often because they are emitted from a small orifice or diffuse passively... 

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