Sample profile, variation

ID ESRI experiments provided the concentration profiles of the nitroxides for the various aging methods and 2D spectral-spatial ESRI experiments described the spatial variation of the ESR spectra with sample depth, in terms of the variation of the fast/slow ratio with sample depth. In both ABS and HPEC samples, the variation of percentage fast with sample depth was translated... 

Figure 5.14 shows the depth-profile variation of hardness (Hv) and fracture toughness (KiC) of the hybrid sample. Fracture toughness is evidently higher near the surface due to the abundant presence of both AT and mullite. As the depth increases, the abundance of both phases and thus the fracture toughness decreases. Hardness is lower near the surface due to the abundant presence of much softer AT, but increases with depth towards the alumina region. It should be noted that since measurements were made on a polished cross-sectioned sample, the indentation data could not be collected at distances less than 0.5 mm from the surface. Hence, hardness and fracture toughness values on the surface were measured separately. 

There are significant relationships between the values of both shell carbonate and organic tissues with immersion time. There are a large number of explanations for variations in the carbonate skeletons of organisms in nature, however few of the available explanations would produce the small, systematic change of c. l%e observed over the 3.5 m of sample profile. Only kinetic effects, metaholic effects, varying pH or the local influx of C-depleted waters are likely to have been able to significantly influence shell isotope composition over the spatial scale sampled. An influx of C-depleted meteoric water derived from adjacent terrestrial areas should lead to covariance between and 8 0 in the shell carbonate. This is not observed and hence can be discounted as the mechanism behind the observed relationship. 

This technique also allows for the resolution of spectrally similar components and severely overlapping components in a multicomponent mixture. In addition, multidimensional fluorescence measurements provide significant spectral information for distinguishing between closely related samples. The variations in the excitation and emission profiles add to a full understanding of the minimum number of fluorescing components in the sample matrix. 

Variation of the sample profile along its travel convective and diffusive phenomena... 

An interesting development of the PHB technique leads to four-dimensional data storage. By variation of an electric field appHed to the sample the spectral profile of the absorption holes can specifically be altered. This adds two more dimensions to the geometrically two-dimensional matrix frequency of laser light and electrical field strength (174). 

Electroosmotic flow in a capillary also makes it possible to analyze both cations and anions in the same sample. The only requirement is that the electroosmotic flow downstream is of a greater magnitude than electrophoresis of the oppositely charged ions upstream. Electro osmosis is the preferred method of generating flow in the capillary, because the variation in the flow profile occurs within a fraction of Kr from the wall (49). When electro osmosis is used for sample injection, differing amounts of analyte can be found between the sample in the capillary and the uninjected sample, because of different electrophoretic mobilities of analytes (50). Two other methods of generating flow are with gravity or with a pump. 

AES analysis is done in one of four modes of analysis. The simplest, most direct, and most often used mode of operation of an Auger spectrometer is the point analysis mode, in which the primary electron beam is positioned on the area of interest on the sample and an Auger survey spectrum is taken. The next most often used mode of analysis is the depth profiling mode. The additional feature in this mode is that an ion beam is directed onto the same area that is being Auger analyzed. The ion beam sputters material off the surface so that the analysis measures the variation, in depth, of the composition of the new surfaces, which are being continu-... 

In the process of SNMS analysis, sputtered atoms are ionized while passii through the ionizer and are accelerated into the mass spectrometer for mass analysis. The ion currents of the analyzed ions are measured and recorded as a function of mass while stepping the mass spectrometer through the desired mass or element sequence. If the purpose of the analysis is to develop a depth profile to characterize the surface and subsurface regions of the sample, the selected sequence is repeated a number of times to record the variation in ion current of a selected elemental isotope as the sample surfiice is sputtered away. 

Neutron reflectivity measures the variation in concentration normal to the surface of the specimen. This concentration at any depth is averaged over the coherence length of the neutrons (on the order of 1 pm) parallel to the sur ce. Consequendy, no information can be obtained on concentration variadons parallel to the sample surface when measuring reflectivity under specular conditions. More imponantly, however, this mandates that the specimens be as smooth as possible to avoid smearing the concentration profiles. 

The value of spruce-oil chemistry in sorting out problems of hybridization and introgression—major factors in Picea taxonomy—was succinctly summarized by von Rudloff who defined three situations (1) Terpene variation is limited such that it is not possible to use these characters in studies of introgression this is the case in eastern North America where the ranges of black spruce and red spruce overlap. (2) Sufficient variation in terpene profiles exists for the compounds to be useful markers in systematic studies as seen in white spruce. Brewer s spruce, and Sitka spruce. (3) Tree-to-tree variation in terpene content is so variable that use in che-mosystematic studies is precluded, or at least requires very large sample sizes for statistical reliability, as seen with Engelmann s spruce. 

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