A technique has been developed for the interpretation of composition-depth profiles from angleresolved X-ray data using a Monte Carlo electron scattering simulation. This is a nondestructive depth profiling procedure. Software has been developed that uses a Monte Carlo scattering simulation to generate the signal intensity from a multilayer sample for any combination of primary beam angle of incidence and take-off angle to the X-ray detector. An interactive C++ application uses this simulation to interpret measured angle-resolved depth profiles. The method has been tested using a custom-made Ag/Al “staircase” sample containing two layers each of Ag and Al. Using the technique, it is possible to quantify the composition-depth profile for the two- and three-layer “steps” of the sample. Qualitative information may be gained about the four-layer area of the sample.

Atherosclerotic lesions are heterogeneous in terms of their cellular and lipid composition. While heterogeneity can be the result of stochastic noise, an alternate hypothesis is that the differences observed among individual lesions arise from deterministic chaos. Five New Zealand white rabbits were fed a diet containing 0.15% cholesterol for 6 months. Segments of the aorta were fixed in formalin, stained en bloc with Nile red (NR) and filipin (F), and en face fluorescence microscopy was used to map the distribution of lipids in fatty streaks (FS). The smallest lesions detected stained only with filipin. Larger lesions stained with both Nile red and filipin and two distinct regions of Nile red staining, NR-orange (rich in polar lipids) and NR-yellow (rich in neutral lipids) were observed. Digital overlays revealed a “nested” arrangement of F, NR-orange, and NR-yellow. The lesions also showed marked heterogeneity in their lipid composition. Thus, although initially similar, as FS increased in size, their composition became divergent, suggesting that the ultimate composition of a FS was highly sensitive to its initial composition. Sensitivity to initial condition is one of the hallmarks of deterministic systems. To determine if FS were self-similar, another hallmark of deterministic chaos, the borders of the different regions defined by NR and F staining were subjected to fractal analysis. For each lesion, the borders of the F, NR-orange, and NR-yellow regions were found to be fractal. Return maps were constructed for the differently stained regions. Analysis of the entire 104-lesion data set showed that although the data could be described by a four-parameter logistic model, the population was not chaotic. However, return maps drawn for the maxima of the NR-orange stained regions demonstrated chaos. Taken together, the data suggest that deterministic chaos plays a role in the evolution of atheromatous disease but, in common with most biologic systems, as the lesions progress, chaotic behavior is dampened.

The production and characterization of NBS K-411 glass microspheres in the 2–40 μm range for certification as NIST Standard Reference Material® 2066 (SRM®) are described. Quantitative analysis and heterogeneity testing of the microspheres were done with an electron probe microanalyzer-X-ray energy dispersive spectrometry (EPMA-EDS) automated particle analysis procedure. Results for the trimmed and normalized data produced mean compositions for the elements Mg, Si, Ca, Fe, and O (calculated from stoichiometry) that are in good agreement with the certified values for the K-411 bulk glass (NBS SRM 470 Glasses for Mineral Analysis), but with uncertainties about twice as large as those for the bulk material. Differences from the bulk are attributable to microsphere geometry as well as mass and size effects.

Despite the great potential of fluorescence microscopy, its application to date has largely been in the study of biological specimens. It will be shown that conventional fluorescence microscopy provides an invaluable tool with which to study the photophysics of polymer-supported luminescence-based oxygen sensors. The design of the imaging system, the measurement methods, and the data analysis used in the investigation of sensor systems are described. Fluorescence microscopic images of sensor films in which microheterogeneous regions exhibiting enhanced luminescence intensity and poorer oxygen quenching relative to the bulk response are shown. This is the first direct evidence that sensor molecules in various domains of the polymer support can exhibit different oxygen quenching properties. It will be shown that μ- and nano-crystallization of the sensor molecule are the probable source of both the observed heterogeneous microscopic responses and the microscopic and macroscopic nonlinear Stern-Volmer plots. The implications of these results in the rational design of luminescence-based oxygen sensors are discussed.