Point Source Release Research Articles

Laser-Induced Fluorescence Measurements of a Turbulent Plume

The laser-induced fluorescence (LIF) measurement technique is discussed in the context of environmental fluid mechanics. The measurement equipment and procedures employed in our laboratory are described in detail. The technique is applied to an isokinetic chemical plume (neutrally buoyant) in a turbulent open channel flow. A nonuniform laser sweep rate is employed to take full advantage of the dynamic range of the digital camera over the entire spatially varying concentration field. Statistical measures of the concentration field, such as the average and variance, are presented and discussed. Comparisons are made with theoretical models and previous experimental observations. The plume width grows at a greater rate in the downstream direction than that predicted by the analytical model of a point source release into a uniform flow. Probability density function distributions do not resemble Gaussian distributions, which reflects the highly intermittent nature of the concentration time record. The current measurements suggest that LIF is a valuable technique for nonintrusively recording the scalar field evolution in turbulent flows.

Intercellular calcium signaling mediated by point-source burst release of ATP.

Calcium signaling, manifested as intercellular waves of rising cytosolic calcium, is, in many cell types, the result of calcium-induced secretion of ATP and activation of purinergic receptors. The mechanism by which ATP is released has hitherto not been established. Here, we show by real-time bioluminescence imaging that ATP efflux is not uniform across a field of cells but is restricted to brief, abrupt point-source bursts. The ATP bursts emanate from single cells and manifest the transient opening of nonselective membrane channels, which admits fluorescent indicators of < or = 1.5 kDa. These observations challenge the existence of regenerative ATP release, because ATP efflux is finite and restricted to a point source. Transient efflux of cytosolic nucleotides from a subset of cells may represent a conserved pathway for coordinating local activity of electrically nonexcitable cells, because identical patterns of ATP release were identified in human astrocytes, endothelial cells, and bronchial epithelial cells.

Chemical Plume Tracing

Given a measurable concentration of a dissolved substance at a point within a fluid flow, where is the source? As physicists and engineers we often look at this problem from a more traditional perspective given a point source release of a substance, we seek to describe the temporal and spatial evolution of the effluent plume. Animals, seeking to evade predators or to locate mates or sources of food, contend with this problem routinely every day, and they have evolved a keen ability to locate these sources. Thus whereas our traditional approach when studying point source releases in the field of fluid mechanics is to seek to understand the fate of the source material and hence to study the forward problem, animals, and hence the biologists who study them, traditionally approach the study of the point-source-in-a-fluid as an inverse problem. This Special Issue on chemical plume tracing presents the work of an interdisciplinary research team, assembled by the Defense Advanced Research Projects Agency (DARPA) and the Office of Naval Research (ONR) to develop the ability to track chemical plumes to their sources. The fundamental approach to this research has been biomimetic. Both ONR and DARPA currently support research programs that seek either to integrate biological sensors or materials directly into new technology, or to capitalize on our knowledge about biological systems and processes to design new technological approaches to meet the demanding capability requirements of many armed services applications. This “biocentric” approach spans many disciplines and length scales. Some workers seek to enhance the performance of Navy surface and underwater platforms by a careful hydrodynamic analysis of swimming animals (Triantafyllou and Triantafyllou, 1995; Gordon et al., 2000; Bandyopadhyay, 2002). Others attempt to harness the power of single molecular motors to provide new energy sources (Montemagno and

Use of point source models for the dispersion of releases of finite size

If the releases are of finite size, the point source model is widely accepted as an approximation to the concentration in the far field. However, substantial improvement upon the point source model can be achieved by shifting the origin of the point source release to a virtual origin, a point upwind of the origin of the finite size release. In this paper, rigorous solutions for the finite size release models are compared against the point source model to determine the optimum virtual origin shift so as to produce the most accurate approximation in the intermediate and far fields. Also, the effects of anisotropic diffusion are considered in order to model atmospheric diffusion more closely.

Dispersal of Trichogramma platneri Nagarkatti (Hym., Trichogrammatidae) from point‐source releases in an apple orchard in California

AbstractEgg parasitoids of the genus Trichogramma are commonly released in inundative biological control programmes for lepidopteran pests in a range of cropping systems. In this study we evaluated the dispersal of Trichogramma platneri from a central release point in an apple orchard in relation to time and the number of parasitoids released. Dispersal was monitored by parasitism of codling moth eggs from an insectary culture—used as sentinel eggs. Higher release rates of T. platneri resulted in greater parasitism of sentinel eggs during the first 3 days, increasing from about 18% for a release rate of 5 400 to about 36% for a release rate of 32 400. T. platneri parasitized a greater percentage of sentinel eggs on the north side of the tree. Parasitism of sentinel eggs declined by 50% during the second 3 day period following release from a point source release in comparison to the first 3 day period. Parasitism of sentinel eggs declined from a mean of 62% at the point–source to less than 10% 14 m away during the first 3 days after release.

Tracer transport in a stochastic continuum model of fractured media

A stochastic continuum model of a fractured medium conditioned on a specific set of field data is developed. Both the more conductive fractures and the less permeable matrix are generated within the framework of a single‐continuum stochastic model based on nonparametric indicator geostatistics. In the stochastic model the fracture zones are distinguished from the matrix by imposing a long‐range correlation structure for a small fraction (the highest approximately 11%) of the hydraulic conductivity in the preferred planes of fracture zones. Results of flow arid transport simulation in three dimensions (3D) are used to illustrate the large spatial variability of point measurements, but for spatially integrated quantities the variability is reduced and results become less sensitive to correlation structure. Therefore it is suggested that spatially integrated quantities may be a more appropriate choice for predicting flow and transport in a strongly heterogeneous medium in that they are more commensurate with the level of our ignorance of the site. The issue of spatial variability giving rise to uncertainty in the site characterization of a heterogeneous medium and the prediction of transport results is also addressed. Simulations are carried out for 3D transport from point tracer sources at hundreds of locations in the medium. The breakthrough curve from each point source release is characterized by two parameters: the mean transport velocity and the dispersion coefficient. The results are presented as a statistical distribution of the transport parameters, thus quantifying the uncertainty in predicting flow and transport based on a limited amount of site characterization data.

A shoreline fumigation model with wind shear

A fumigation model has been developed for a plume discharged from an elevated stack in a shoreline environment by introducing different wind directions above and within thermal internal boundary laye:r (TIBL) into a dispersion model. When a continuous point source release occurs above the TIBL pollutants will disperse in the marine stable flow, until the plume intersects the TIBL surface. The fumigation in ithe TIBL is interpreted as occurring from an area source on the imaginary surface of the TIBL. It is assumed that the wind direction varies with height above and below L( x) = Ax 2, the height of the TIBL at the distance x. The change of wind direction above and within the TIBL causes the pollutants to change their direction of transport and leads to development of a curved ground level concentration (glc) axis; a decreasing glc along the centreline of the fumigation and a widening pollutant distribution in the transverse direction. Predicted concentration distributions using the wind shear model are compared with observations from an SF 6 tracer experiment near Hangzhou Bay in May–June of 1987. The comparison and an evaluation of the model performance show that the new model is not only more theoretically acceptable than those based on empirical coefficients but also provides concentration distributions which agree well with. SF 6 tracer experiments.

95/02130 Instantaneous structure and statistical feature of unsteady flow in a channel obstructed by a square rod

A fumigation model has been developed for a plume discharged from an elevated stack in a shoreline environment by introducing different wind directions above and within thermal internal boundary laye:r (TIBL) into a dispersion model. When a continuous point source release occurs above the TIBL pollutants will disperse in the marine stable flow, until the plume intersects the TIBL surface. The fumigation in ithe TIBL is interpreted as occurring from an area source on the imaginary surface of the TIBL. It is assumed that the wind direction varies with height above and below L(x) = Ax2, the height of the TIBL at the distance x. The change of wind direction above and within the TIBL causes the pollutants to change their direction of transport and leads to development of a curved ground level concentration (glc) axis; a decreasing glc along the centreline of the fumigation and a widening pollutant distribution in the transverse direction. Predicted concentration distributions using the wind shear model are compared with observations from an SF6 tracer experiment near Hangzhou Bay in May–June of 1987. The comparison and an evaluation of the model performance show that the new model is not only more theoretically acceptable than those based on empirical coefficients but also provides concentration distributions which agree well with. SF6 tracer experiments.

95/02134 Kerogen diversity demonstrated by oxidation. I. Type I kerogens

A fumigation model has been developed for a plume discharged from an elevated stack in a shoreline environment by introducing different wind directions above and within thermal internal boundary laye:r (TIBL) into a dispersion model. When a continuous point source release occurs above the TIBL pollutants will disperse in the marine stable flow, until the plume intersects the TIBL surface. The fumigation in ithe TIBL is interpreted as occurring from an area source on the imaginary surface of the TIBL. It is assumed that the wind direction varies with height above and below L(x) = Ax2, the height of the TIBL at the distance x. The change of wind direction above and within the TIBL causes the pollutants to change their direction of transport and leads to development of a curved ground level concentration (glc) axis; a decreasing glc along the centreline of the fumigation and a widening pollutant distribution in the transverse direction. Predicted concentration distributions using the wind shear model are compared with observations from an SF6 tracer experiment near Hangzhou Bay in May–June of 1987. The comparison and an evaluation of the model performance show that the new model is not only more theoretically acceptable than those based on empirical coefficients but also provides concentration distributions which agree well with. SF6 tracer experiments.

Zones of exocytotic release on bovine adrenal medullary cells in culture.

Secretion of catecholamines from individual bovine adrenal medullary cells in culture was examined by amperometry with 1-micron radius carbon-fiber electrodes. Vesicular secretion is observed as a series of current spikes upon exposure to a secretagogue. The small size of the electrodes was exploited to map exocytotic release sites on the surface of bovine adrenal medullary cells. These studies reveal for the first time that release sites are spatially localized on endocrine cells in culture for a time scale of at least 15 min. Fluorescent monitoring by confocal microscopy of deposition of dopamine-beta-hydroxylase from the vesicular membrane into the plasma membrane during exocytosis confirms the existence of zones of exocytotic inactivity on the surface of the cell. Measurement of coincident spikes with two adjacent electrodes (2.5-microns radius) has allowed the spatial resolution for measurement of exocytosis to be defined as 2 microns from the projected circumference of the electrode on the surface of the cell. In this small domain, point-source release and diffusional broadening would result in narrow spikes (Schroeder, T. J., Jankowski, J. A., Kawagoe, K. T., Wightman, R. M., Lefrou, C., and Amatore, C. (1992) Anal. Chem. 64, 3077-3083), a feature not seen in the data. Thus, for adrenal medullary cells, release following vesicular fusion is not instantaneous, but is a prolonged event occurring over several milliseconds.

Interpretation of Measured Tracer Concentration Fluctuations Using a Sinusoidal Meandering Plume Model

Abstract Simultaneous instantaneous concentration and wind velocity fluctuations were measured 100 to 752 m downwind of a point source release of SF6 tracer during two field studies conducted amid rolling wheat fields and at a flat desert site in eastern Washington. Data from stable, neutron, and unstable conditions are interpreted using a meandering plume model where the meander is defined to be sinusoidal and the instantaneous plume profile is Gaussian. A sensitivity analysis of the model shows that the characteristic concentration time scale is a direct function of the meander time scale and the receptor position relative to the meander centerline. For narrow instantaneous plumes relative to the meander amplitude, the predicted mean crosswind profiles of concentration, intermittency factor, concentration fluctuation intensity, and peak-to-mean ratios exhibit bimodal distributions. Conditional (nonzero) concentration fluctuation intensifies calculated from the model are scattered about 1.0;, the scatter...

3.2 GROUND SYSTEMS FOR RELEASING TRICHOGRAMMA MINUTUM RILEY IN PLANTATION FORESTS

AbstractTwo systems for releasing the egg parasitoid, Trichogramma minutum Riley, from ground level in forest stands are described: (1) a gridded point-source release using parasitized host eggs attached to cards, and (2) a hand-held leafblower distributing parasitized eggs in bulk. Neither technique affected the emergence of the parasitoids released. Parasitoids emerging from eggs released in bulk had a similar sex ratio, longevity, and fecundity to those not released. Both methods of ground release achieved uniform parasitoid distribution and resulted in levels of parasitism similar to those achieved with aerial releases. Parasitism was greater in the mid- to upper canopy of trees than in the lower canopy. The difficulties associated with each technique and its comparative usefulness in experimental and operational programs are discussed.

The effect of diffusion on tracer puffs simulated by a regional scale Eulerian model

On a spatial scale of up to 1,100 km and a temporal scale of up to 36 hours, we used Eulerian models to simulate the transport and diffusion of a passive tracer released from a point source near the surface. An Eulerian tracer model was driven by meteorological analysis of 6‐hour rawinsonde data supplemented by the simulations of an Eulerian mesoscale meteorological model. The tracer model simulations were compared with 6‐hour integrated samples collected at 86 surface stations during the Cross‐Appalachian Tracer Experiment (CAPTEX) for six different releases. We examined the effect of the parameterizations of vertical and horizontal sub‐grid scale turbulent transport and the finite difference advection scheme on the simulations of concentration and the trajectories of the center of mass of the tracer at the surface. We found that the simulated trajectory error was sensitive to the vertical eddy diffusivity but insensitive to the advection scheme and hence insensitive to (horizontal) numerical diffusion. Using 70‐km horizontal resolution, only the most sophisticated advection scheme tested here (Prather, 1986) simulated a tracer puff with a horizontal area that was not too large during the first 36 hours after a point source release. The other schemes tested (Russell and Lerner, 1981; a simplified version of Smolarkiewicz, 1983) had enough numerical diffusion that the simulated horizontal tracer puffs were larger than the observed puffs. There were considerable differences in the capability of the tracer models to simulate individual releases, particularly for quantitative comparisons of simulated and observed concentrations.

Seasonal and diurnal variability in normalized concentrations of atmospherically dispersed pollutants

Abstract We have predicted yearly, growing season, and growing season daylight normalized air concentrations ( C Q ) of an inert gas tracer for a point source release near Oak Ridge, Tennessee, using local meteorological data collected for the years 1967–1969. Pasquill-Gifford atmospheric stability categories were determined using the vertical temperature gradient method, and concentrations were determined assuming Gaussian plume transport of a nondepositing contaminant. A seasonal variability in the wind rose was found, and an accompanying variability in the geographical distribution of C Q was identified. Values of C Q typically changed by a factor of two between yearly and growing season daylight hours and for receptor points located up to km distance from the source. These results suggest that yearly average computations may in certain cases be inappropriate for determining compliance with air quality standards during the growing season or where a seasonal activity pattern exists.

Spatial diffusion of small particles in an exponential atmosphere

Calculations have been made of the spatial diffusion of small particles, released initially in the form of a point source, in an exponential atmosphere, and the results are presented in the form of relative density curves and absolute density contours. It is noted that the decrease along the horizontal direction of the relative density occurs most rapidly for the heavy particles, regardless of the altitude. The absolute density of a heavy particle may exceed that for a light one, but only in a narrower region near the position of maximum density, indicating the small dispersal of the heavy particles. The calculations are limited to the case of a point source release, but they may be extended in a direct manner to include an arbitrary initial distribution.