Anisotropic Artifact

It is important to check is the effect of a rather large population of vacant atomic orbitals at the electron correlation level specific for alkaline-earth atoms or it has a general character. In Table VII we present the results of net valence population calculations for noble-gas atoms performed by the Natural Bond Orbital Analysis at the MP4 level. We found non-negligible valence orbital population, especially for the d-orbitals. The results obtained for three different basis sets are quite close. Thus, the population of vacant orbitals in noble-gas atoms is not an artifact of the calculations. From this follows that elements traditionally assumed as closed-shell (noble gases) or closed-subshell (alkaline earths) atoms can to some extent manifest an anisotropic p-or d-symmetry behavior. It would be very interesting to obtain experimental evidence confirming this theoretical prediction. 

In an effort to further validate the proposal that the Iq, and forms were the primary constituents of native celluloses, VanderHart and Atalla undertook another extensive study to exclude the possibility that experimental artifacts contributed to the key spectral features assigned to the two forms. A number of possible sources of distinctive spectral features were explored. The first was the question whether the surface layers associated with crystalline domains within particular morphological features in the native celluloses could give rise to features other than those of the core crystalline domains. The second was whether variations in the anisotropic... 

It is knownis that small metallic particle effects arising from random depolarization factors in highly anisotropic metallic grains in ceramic samples can lead to artifacts in the infrared reflection (and absorption) spectrum. Since the samples used in the photoinduced absorption experiments are insulating micron sized crystallites embedded in an insulating medium, such small particle effects will not affect either the infrared spectrum or the photoinduced IR absorption spectrum where the measured AT/T is of order i0-3. 

It is interesting to note that haversian bones, whether human or bovine, have both their compressive and shear anisotropy factors considerably lower than the respective values for plexiform bone. Thus, not only is plexiform bone both stiffer and more rigid than haversian bone, it is also more anisotropic. These two scalar anisotropy quantities also provide a means of assessing whether there is the possibility either of systematic errors in the measurements or artifacts in the modeling of the elastic properties of hard tissues. This is determined when the values of Ac (%) and/or As (%) are much greater than the close range of lower values obtained by calculations on a variety of different ultrasonic measurements (Table 47.5). A possible example of this is the value of As (%) = 7.88 calculated from the mechanical testing data of Knets [1978], Table 47.2. 

From our daily life it is well known that chiral objects like spiral staircases or flowers look different from different directions. Therefore, it seems evident that chiral molecules and chiral suprastructural phases are anisotropic, too. Until now, chiroptical methods have been only very sparsely applied to chiral anisotropic systems because of serious experimental problems. At first one has to draw attention to artifacts induced by the always existent linear dichroism and birefringence of anisotropic systems (elliptical dichroism and birefringence). Secondly, objects without symmetry do not allow to measure directly chiral and achiral anisotropies without additional requirements. That is, new techniques and unequivocal definitions are needed to decompose the results of measurements with chiral anisotropic phases into chiral and achiral components. A minimum of symmetry is needed to adapt suitable situations where the CD and ORD as chirality measurements of anisotropic systems can be observed directly. 

This is a very powerful technique for imaging particles in their native state. However, unfortunately, it is not suitable for big particles and artifacts can also be observed. In contrast, 2D NOESY NMR may provide indirect evidence of a phase-separated nature within a particle based on whether different domains are in close contact or not. However, using this technique, it is not possible to distinguish which kind of anisotropic particles have been prepared. Overall, a combination of the above techniques is required as well as the development of new methods to provide convincing evidence for the formation and characterization of anisotropic particles. 

In most cases the CPL component is a very httle fraction of the emitted light (typically below 1%). The exclusion of any source of error or artifact in CPL experiments is therefore of the highest importance. The most dangerous interference, because it is difficult to spot out, is the presence of linearly polarized light in the sample emission [24]. This can happen if the excited states are anisotropically distributed as a consequence, for example, of a non isotropic distribution of the molecules in the ground state, or of the photoselection effect operated by the incident radiation. 

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