Edge of the plume

The pressure forces are derived in Figure 10.5(b), taking into account the pressure at the perimeter region 27rb d,v, where b is a mean between z and z + dz. Likewise, so is p x. The vertical component of the shear force also follows from similar arguments. However, at the edge of the plume we have a static fluid (approximately) or dw/dr = 0 for the actual profile. Since... 

We design our studies of plume-hthosphere interactions to (1) predict the distribution in space and time of hot, buoyant plume material beneath cratons of various shapes (2) determine the physical conditions favourable for the lateral distribution of plume material beneath cratonic keels, which may give rise to small-volume melts (e.g. kimberlites) (3) evaluate the longevity of cratonic keels beneath large and small cratons (4) predict the behaviour of viscous plume material at the edges of the plume in terms of thickness and temperature. As we show below, a significant thickness of plume material flows beneath a cratonic keel only where the plume rises beneath part of the craton, providing a viable mechanism for the emplacement of kimberlites. 

The dimensional equation (4) instead uses the width of the edge of the plume material x at time t... 

The case for the edge of the plume material where /i = 0 stays constant follows similarly. The thickness of the centre of the plume is... 

Summarizing, coohng of plume material and consequent increase in viscosity near the edge of the plume has little effect on the rest of the flow. This result implies that plume material maintains a relatively constant thickness beneath a craton, except very near its steep edges. 

In the discussion of the Bear Creek Uranium site in 6.2, we note that more than a dozen regulated metals and radionuclides have elevated concentrations in the acidic plume. The relative mobility of the radionuclides at the leading edge of the plume can be estimated by using the diffusive double layer model of Dzombak and Morel (1990). 

However, the predicted uranium concentration at the edge of the plume is far higher than the observation. Observational data indicate that the maximum uranium concentration outside of the plume is less than 92 pCi/L, while the model predicts it to be in excess of 1000 pCi/L. This discrepancy between observed and predicted uranium concentrations is an indication that the model parameters used to predict U partitioning may not accurately represent conditions at the site. Examination of Dzombak and Morel s (1990) work reveals that they have used a predicted surface complexation constant rather than retrieve a value from experiments. Newer experimental data show that uranium(VI) adsorption onto ferrihydrite can be fitted by a two-site model with a bidentate complex (Waite et al 1994). However, this type of modeling ability is not included with minteqa2. Another explanation could be that co-precipitation is ignored, but apparently is a major attenuation mechanism at a similar site (Opitz et al. 1983). 

A view of the plume from either above or the side is sketched in Figure 18.P.1, where yE and ze represent the coordinates of the visible edge of the plume, and ym and zm denote the maximum values of yE and zE with respect to downwind distance x. Let us consider the visible edge in the y direction, that is, the plume as observed from above. Integrating (A) over z from 0 to oo and evaluating y at yE gives... 

Xe(x) represents the mean concentration normalized by the source strength, evaluated at the value of y corresponding to the visible edge of the plume and integrated through the depth of the plume. 

A view of the plume from either above or the side is sketched in Figure 18.P.1, where y and ze represent the coordinates of the visible edge of the plume, and y ,... 

Figure 9.10 Distribution of naphthalene-degrading genotypes, as judged by the concentration of nahA gene sequence per gram of soil, in subsurface aquifer sediments. Bold arrows represent the distance the front edge of the plume has traveled. [Reprinted with permission from R. D. Stapleton, G. S. Sayler, J. M. Boggs, E. L. Libelo, T. Stauffer, and W. G. MacIntyre, Environ. Sci. Technol. 34, 1991 (2000). Copyright 2000, American Chemical Society.]...

In both fishes and insects, the amplitude of zig-zags seems to be related to the slope of the gradient across the edge of the plume. 

Another important aspect of the zig-zag behavior is the detection of the edge of the plume and the absence of stimuli. We know from peripheral nerve recordings that the response of olfactory nerves does not totally adapt after prolonged exposure. Thus, the animal is presumably able to sense the off-set of a stimulus and would be capable of detecting movement out of the stimulus. However, there are other explanations of the animal s ability to detect the edge of the plume. These may include re-stimulation after rinsing out by the subthreshold water and a re-stimulation by suprathreshold water found at the discontinuously mixed interface. Experiments on the fish s ability to detect decreasing concentrations will be required to determine the actual mechanism of the release of zig-zag behavior. 

No influence of the wavelength on the variety of decomposition products was observed. The leading edge of the plume of irradiated primary explosives consists mainly of metal atoms. The high temperature and the high concentration of species resulted in self-absorption and line-broadening due to radiation transfer. Later, other reaction products did show up. 

Selectivity in electrospray is also affected by flow rate. This can happen in several ways. Tang and Smith have shown that as the droplets undergo fission in the electrospray plume, the satellite droplets tend to concentrate on the outer edges of the plume cone. Since these droplets are enriched in the more surface active of the analytes present, the relative response ratios of analytes would be affected by the needle position relative to the aperture. 

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