Relation to point-groups

Diffraction symmetry in relation to point-group symmetry. So far, in our consideration of the intensities of X-ray reflections in the process of discovering the general arrangement in a crystal, we hare dealt only with reflections of zero intensity, and we have seen that when certain types of reflections have zero intensity the presence... 

Effect of screw axes and glide planes on X-ray diffraction patterns 251 Diffraction symmetry in relation to point-group symmetry 258... 

Symmetry Coordinates, a Simple Example and some Generalizations Related to Point Group Symmetry... 

A further difference between the X q and E q is in their relation to point group symmetry, to which we will return later. 

Molecules that are not superimposable on their mirror images are termed dissymmetric. This term is used rather than asymmetric, since the latter means, literally, have no symmetry that is, it is applicable only to a molecule belonging to point group Cx. All asymmetric molecules are dissymmetric, but the converse is not true. Dissymmetric molecules can and often do possess some symmetry. It is possible to give a very simple, compact rule expressing the relation between molecular symmetry and dissymmetric character ... 

The box-whisker plot is a tool for representing the distribution parameters of variables. This tool can be used to provide a visual idea in the sense of F- and /-test. Group means may be compared in relation to the group variances. A box-whisker plot may also be formed from robust statistical parameters the median as the centre line of the box, percentiles as the edges of the box, and minimum and maximum as horizontal lines outside the box. Outliers are points outside the structure. An example of measurements of trichloroethene in river water is given in Fig. 5-10. The five groups refer to... 

Diamond-like Phases and Carbon-based Films. Raman spectra were used to characterise ion-irradiated diamond samples.296 Raman data could be used to identify features related to point defects in diamond.297 There is Raman evidence for the formation of polycrystalline diamond from graphite at high pressures and temperatures.298 Surface C-H groups on diamond nanocrystals were characterised by IR (vC-H) and ab initio calculations, e.g. the vC-H band on a C(111)1 x 1 site is at 2834 cm-1.299... 

Table X-2. Isomorphisms and Direct Products Relating Certain Point Groups to e and SD ...

The types of vibrations (species) of molecules with related symmetry can be correlated and these correlations used to assign vibrations. For example, ethane and its various derivatives have somewhat similar symmetry elements. Ethane belongs to point group while CH3CCI3 has symmetry. The D d groups have... 

A point group is related to the corresponding point group by the inclusion of a plane. 

One further breaks down the secondary electron contributions into three groups SEI, SEII and SEIII. SEIs result from the interaction of the incident beam with the sample at the point of entry. SEIIs are produced by BSE s on exiting the sample. SEIIIs are produced by BSEs which have exited the surface of the sample and further interact with components on the interior of the SEM usually not related to the sample. SEIIs and SEIIIs come from regions far outside that defined by the incident probe and can cause serious degradation of the resolution of the image. 

Hollomon s ethos, combined with his ferocious energy and determination, and his sustained determination to recruit only the best researchers to join his group, over the next 15 years led to a sequence of remarkable innovations related to materials, including man-made diamond, high-quality thermal insulation, a vacuum circuit-breaker, products based on etched particle tracks in irradiated solids, polycarbonate plastic and, particularly, the Lucalox alumina envelope for a metal-vapour lamp. (Of course many managers besides Hollomon were involved.) A brilliant, detailed account of these innovations and the arrangements that made them possible was later written by Guy Suits and his successor as director, Arthur Bueche (Suits and Bueche 1967). Some of these specific episodes will feature later in this book, but it helps to reinforce the points made here about Hollomon s coneeption of broad research on materials if I point out that the invention of translucent alumina tubes for lamps was... 

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