Measurement of flux

The atom flux sputtered from a solid surface under energetic ion bombardment provides a representative sampling of the solid. Sputtered neutral mass spectrometry has been developed as method to quantitatively measure the composition of this atom flux and thus the composition of the sputtered material. The measurement of ionized sputtered neutrals has been a significant improvement over the use of sputtered ions as a measure of flux composition (the process called SIMS), since sputtered ion yields are seriously affected by matrix composition. Neutral panicles are ionized by a separate process after sputter atomization, and SNMS quantitation is thus independent of the matrix. Also, since the sputtering and ionization processes are separate, an ionization process can be selected that provides relatively uniform yields for essentially all elements. 

It should be noted that when we compare the brightness of a LGS to a NGS, the result depends on the spectral bandwidth, because the LGS is a line source, whereas the NGS is a continuum one. The magnitude scale is a logarithmic measure of flux per spectral interval (see Ch. 15). This means that a (flat) continuum source has a fixed magnitude, no matter how wide the filter is. In contrast, the magnitude of a line source is smaller for narrower bandpasses. It is therefore advisable to use the equivalent magnitude only for qualitative arguments. The photon flux should be used in careful system analyses. 

Measurement of flux rates of ionic copper from metallic copper (ATSDR 1990)... 

Numerous and disparate copper criteria are proposed for protecting the health of agricultural crops, aquatic life, terrestrial invertebrates, poultry, laboratory white rats, and humans (Table 3.8) however, no copper criteria are now available for protection of avian and mammalian wildlife, and this needs to be rectified. Several of the proposed criteria do not adequately protect sensitive species of plants and animals and need to be reexamined. Other research areas that merit additional effort include biomarkers of early copper stress copper interactions with interrelated trace elements in cases of deficiency and excess copper status effects on disease resistance, cancer, mutagenicity, and birth defects mechanisms of copper tolerance or acclimatization and chemical speciation of copper, including measurement of flux rates of ionic copper from metallic copper. 

M. K. Hellerstein, In vivo measurement of fluxes through metabolic pathways The missing link in functional genomics and pharmaceutical research. Annu. Rev. Nutr. 23, 379 402 (2003). 

Caco-2 monolayer, a model for human intestinal permeability, is commonly used in drug discovery to screen discovery compounds.34,35 The method involves measurement of flux of... 

The basic measurement of flux creep is magnetization versus time (relaxation) in a constant field at fixed temperature (73). The... 

Micrometeorological Flux Measurements. It is important to quantify the flux of the nitrogen species to or from the atmosphere due to surface emission or deposition. Measurements of fluxes of NO and N20 have been made by enclosure techniques, but the enclosures placed on a surface must be suspected of disturbing the flux that they are designed to measure. Fluxes... 

Brindle, K.M. (1988b). 3IP NMR magnetization transfer measurements of flux between inorganic phosphate and ATP in yeast cells genetically modified to over-produce phosphoglycerate kinase. Biochemistry 27,6187-61%. 

Volcanoes are an important source of trace metals to the atmosphere—for some species (e.g., arsenic, cadmium, copper, lead, and selenium) they may be the principal natural source (e.g., Nriagu, 1998). Measurements of fluxes are complicated because of rapid condensation of the vapor phases carrying the... 

In practical terms, such a comprehensive analysis is hardly possible. However, as shown in the examples given below, the comparison of label flux to a small number of metabolites or even to different substructure components of a given metabolite can provide more detailed information than the measurement of flux from a single source node to a single sink metabolite. 

The usefulness of Eq, (8) under varied experimental conditions has been examined the measurement of flux compared with the classical procedure of direct contact has shown that membrane pore diameters of about 2.4 nm do no affect the interfacial transfer mechanism that occurs in microemulsion systems. 

The ultimate desirable outcome in any chemical reaction dynamic experiment is the measurement of flux-velocity contour maps for quantum-state-selected products from photofragmentation, or inelastic and reactive collisions processes for which the initial state is also well defined. From such contour maps, complete information on the chemical process can be deduced in favourable cases. 

Measurement of flux spectrum/flux variations (such as beam ports and thermal columns). 

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