Effects of Sample Geometry

In CL measurements many factors that influence the intensity of the CL signal should be taken into account. The CL signal may depend on the geometry of the sample. Internal refraction and reflection at the air-solution interfaces are important factors in determining the measured CL intensity, and should be taken into account, for example, when a CL cocktail is placed over a sample. The effect of sample geometry can be evaluated using model systems, such as enzymes... 

In the degradation of polyurethanes, the dominant process changes markedly during the course of the reaction. The activation energy vs. extent of reaction plots provide useful information on the effects of sample geometry (Fig. la), the dominant processes (Fig. la vs, Fig. lb) and the extent to which processes are (Fig. la), or are not (Fig. 2a) separated. However, as the initial activation energy is not determined by the factor jump method, it provides little Information of value for use in extrapolating from test to service conditions. 

In Chapter 6, I discussed the effect of sample geometry on count rate. Once again, it would be useful to consider a practical example. Table 8.4 lists the peak areas measured when the same amount of Eu was counted as a point source and when distributed in water and in sand. The distributed sources were 13 mm in diameter and 20 mm high and measured on the cap of a 45 % p-type HPGe detector. As one would expect, there is an obvious overall loss of count rate due to the lower effective solid angle of the distributed sources and a more pronounced loss of count rate in the low energy peaks. 

Figure 18 shows frequency-domain intensity decays for the free-space emission (top) and the surface plasmon-coupled emission (bottom). Overall, the lifetimes of SPCE (bottom) and free-space do not differ significantly. This was an unexpected result which we do not fully understand. We carefully considered possible artifacts and the effects of sample geometry, but can only conclude that our experiments indicate that the component of SPCE that we observe occurs without a substantial change in lifetime. At present we do not understand the origin of this discrepancy. 

Effect of Sample Holder Geometry on Pressure-Time Curves of Lead Dioxide-Cupric Oxide-Silicon Starter Composition A New Test Fixture Design , NAVAMDEP RDTR142, Crane (1969) 9a) J.R, Gibson J.D. Weber, Hand-... 

Shultz-Lockyear, L.L., Colyer, C.L., Fan, Z.H., Roy, K.I., Harrison, D.J., Effects of injector geometry and sample matrix on injection and sample loading in integrated capillary electrophoresis devices. Electrophoresis 1999, 20(3), 529-538. 

Just before the end, transfer the sample to a Marinelli beaker for counting to observe the effect of improved geometry. Figure 2B.3 shows a schematic drawing of the Marinelli beaker with the design feature that allows it to fit over the Ge detector. The counting results with the same sample for the re-entrant beaker and the cylinder are compared. 

The same, but poorer effects are found for the samples B3 and G3. The wet samples B2 and G2 do not show significant differences because the influences of sample geometry are interfered by other irregularities of the measurement. 

No matter how much time has been spent on the sample preparation and how good the resulting specimen is, it always needs to be properly positioned on the goniometer. Consider, for example. Figure 3.26, which shows the effect of sample displacement in the Bragg-Brentano geometry. 

Figure 3.28. The effect of sample displacement, s, on the observed Bragg angles calculated from Eq. 3.4 assuming Bragg-Brentano geometry and goniometer radius R = 285 mm. 0 is the observed Bragg angle, 0 is the Bragg angle in the absence of sample displacement.

Since the results obtained are independent of sample geometry and scattering power, sample attenuation, multiple scattering and detector dead time effects can all be eliminated as a possible cause of the observed anomalies. 

Translucent suspensions are difficult to measure, and direct nnobserved interpretation of instrumental data can lead to confusion because of the way the incident light is dispersed in the sample. Most consistent results are obtained if the instrument aperture is large relative to the incident beam (Kent 1987 MacDougall 1987). The effects of optical geometry on colom and the Kubelka-Munk absorption K (mm ) and scatter S (nun ) coefficients for orange juice were studied by MacDougall (1983) who foimd Too, the luminous reflectance at calculated infinite thickness, increased by 50 per cent if the aperture diameter was increased from 2 cm to 5 cm while the incident beam was maintained at 1 cm. 

Figure 2.12. Effect of sample-holdeT geometry on theTG curve of CaC204 H20 in a dynamic C02 atmosphere ------, quartz dish -----. porcelain crucible (1).

When the thermal decomposition reaction was carried out in a dynamic atmosphere of nitrogen, both the loss of water and the loss of carbon dioxide were affected by the geometry of the container. Likewise, the decomposition of CaC204 was unaffected. The marked effect of the geometry of the sample holder provides evidence that a significant pressure of water vapor and carbon... 

Figure 2.16. Effect of sample packing and sample-holder geometry on the evolution of water from CaC204 H20 (44).

Oxide Supported Metallic Catalysts.- The local geometry about a metal atom provided by EXAFS may, in principle, provide a guide to the mean particle size, morphology, atomic distribution, cluster-support, and metal-adsorbate interactions. How much of this information is available in a particular case may also be a function of some of these same variables eg- particle size and structural order. But by a series of related experiments, the effects of sample history on catalyst structure may be identified. 

Figure 6.6 reveals the effect of the geometry of the sample on the form of the heat flow rate-time function. 

The reproducibility and reliability of results obtained from pyrolysis depend on many factors [530]. Sample sizes should be kept small to facilitate good heat transfer from the pyrolyser to the sample. An-dersson et al. [531] have discussed the effects of sample size on the reproducibility of pyrolysis results, and Wampler et al. [532] have considered the effects of sample size, sample geometry, contamination, and other variables. 

We have developed a fiber-optic probe configuration that overcomes the effects of sample self-absorption using a unique geometry (as illustrated in Figure 2b) where the collection volume includes the entire excited sample volume near the tip of the excitation fiber (5). Here, the collection efficiency is optimized for resonance Raman experiments where virtually all the signal... 

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