Extinction vortex

Populations of endangered species often consist of small numbers that may be trapped in the so-called extinction vortex. This means that the combination of inbreeding, demographic stochasticity, and genetic drift leads to feedback loops that make small populations even smaller (Caughley 1994). According to Klok (2000), the minimum viable population size is species specific because the life history of a species can have a large impact on the outcome of the aforementioned stochastic events. Moreover, the MVP size will also depend on the quality of the habitat and, consequently, on the temporal and spatial distribution and availability of pollutants. 

Figure 7.2.5 provides a visualization of a localized extinction event in a turbulent jet flame, using a temporal sequence of OH planar LIF measurements. The OH-LIF measurements, combined with particle image velocimetry (PIV) reveal that a distinct vortex within the turbulent flow distorts and consequently breaks the OH front. These localized extinction events occur intermittently as the strength of the coupling between the turbulent flow and the flame chemistry fluctuates. The characteristics of the turbulent flame can be significantly altered as the frequency of these events increases. 

Temporal sequence of OH-LIF measurements captures a localized extinction event in a turbulent nonpremixed CH4/H2/N2 jet flame (Re 20,000) as a vortex perturbs the reaction zone. The time between frames is 125 ps. The velocity field from PIV measurements is superimposed on the second frame and has the mean vertical velocity of 9m/s subtracted. (From Hult, J. et al.. Paper No. 26-2, in 10th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, 2000. With permission.)... 

Procedure Measure absorbances of each of the three PNP Standard Solutions to calculate the molar extinction coefficient. Equilibrate the PNPG Solution in a 50° water bath for at least 15 min. For active samples, transfer 2.0 mL of the Sample Solution to a test tube. Loosely stopper, and place the tube in the water bath to equilibrate for 5 min. At zero time, add 2.0 mL of PNPG Solution, and mix at moderate speed on a vortex mixer. Return the mixture to the water bath. Exactly 10.0 min later, add 3.0 mL of the Sodium Carbonate Solution, mix on the vortex, and remove from the water bath. 

High latitude aerosol observations have been secured by the Stratospheric Aerosol Measurement (SAM II) satellite system these have shown that the aerosol extinction profiles measured within the northern polar vortex differ significantly above 18 km from those measured outside the vortex (Me Cormick et d., 1983). 

There is evidence that polar air masses, one and half years after the eruption, carry a good deal less aerosols indicating that meridional mixing is incomplete. In an analysis of the SAM II data satellite extinction data for the Northern hemisphere winter of 1982, supplemented by airborne lidar observations, McCormick et al. (1983) found the polar vortex to be an area of substantially low aerosol content where the El Chichon cloud does not seem to have penetrated and that either an aerosol sink or a supply of clean air exists in the polar winter vortex. 

Following [10] the flame response to a turbulent flow can be considered as the sum of its responses to the vortices composing the turbulence spectrum in a first approximation. The principle regimes of interaction were identified by [10] as a function of two main parameters the ratio of the maximum rotational speed of the vortices to laminar flame speed U0/si and of the vortex core diameter to laminar flame thickness d/si While most qualitative results were confirmed by experimental investigations [11,12], the simulations did not reproduce flame extinction observed in the experiments. Complex chemical kinetics phenomena are a possible explanation for flame extinction due to excessive strain as encountered during flame-vortex interaction. 

Light emission during the flame-vortex interaction for a poor CH4/Air flame was recently measured and a decrease of the luminous intensity, indicating possible local flame extinction, was noticed [13]. The current study permits a direct compar-... 

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