Upward flux sampling

Of the three kinds of problem, this is the easiest theoretically but its main practical use is as a stepping stone in the solution of the other two problems. The solution in discrete form is given directly by Ecp (17). Sample results are shown in Figure 2, which shows the concentration profiles calculated from Eq. (17) (with D-,j specified using Ecps. (24) to (27)) for three assumed source profiles. A sharp, strongly peaked elevated source profile produces a peak in the concentration profile and hence a countergradient flux in the layer just below the peak where the flux is upward but dc/dz is positive, because of the strongly localized near-fleld contribution to the concentration held. By contrast, a more uniform source profile, in-... 

The rates in which the nutrient is fixed by phytoplankton and transferred upward in the food web to zooplankton can largely determine the productivity of fish in the marine system. Traditionally, studies of nutrient flux rates have been conducted using incubation experiments with artificial C or N isotope tracer and the transfer of activity over time into the various size classes of phytoplankton and zooplankton examined. The difficulty with such types of research is that they involve significant perturbations to the system of interest. For example, samples are first separated from the ecosystem before incubation. Bottle incubations will, at best, miss sporadic bloom events and provide rate estimates that are only valid for discrete depths and time. Recently, naturally produced and have been used to investigate directly the uptake rates... 

The macroporosity, created by the trace fossil Ophiomorpha, is principally well connected and of centimeter scale. These macropores occur in broadly continuous stratiform zones that create preferential flow layers within the hydrogeologic units of the Biscayne. This arrangement of porosity is important because in coastal areas. It could produce a preferential pathway for salt water intrusion. NMR imaging Results reveal a substantial flux of fresh water into the matrix porosity with a simultaneous loss of D20. Specifically, rates upward of 0.001 mL/h/g of sample in static conditions were measuread. " ... 

Fig. 13 Heat flux thermograms obtained under different pressures from 50 to 200 MPa during isobaric T scans at 0.833 mK s on heating downward exothermic peaks) and cooling upward endothermic peaks) for a Hg-pressurized MDPE sample. The base lines are shifted for the sake of clarity to show the effect of pressure on melting/crystallization temperatures...

For the propagation of light inside the sample, only two flux channels are assumed upward and downward. The letters I and J represent radiation in the downward and the upward directions, respectively. The downward flux through a layer of thickness dr is decreased by absorption and scattering processes and increased by scattering process from the reflected light. As a result the flux equations can be written ... 

Two different conventions exist for the display of the heat flow curve one shows en-dotherms in the downward direction, the other upward. The operator has a choice with most software packages. Traditionally, with heat flux systems (Section 1.7.2) endotherms are shown as going down, since endothermic transitions result in a negative temperature differential, whilst with power compensation systems (Section 1.7.1) they are shown as going up since with this principle endothermic transitions result in an increase in power supplied to the sample. In this chapter data are shown with endotherms up. 

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