Polymorphism cluster analysis

Chatfield C and A J CoHns 1980. Introduction to Multivariate Analysis. London, Chapman Hall. Desiraju G R 1997. Crystal Gazing Structure Prediction and Polymorphism. Sdence 278 404-405. Everitt B.S. 1993 Cluster Analysis. Chichester, John Wiley Sons. 

The bottleneck in utilizing Raman shifted rapidly from data acquisition to data interpretation. Visual differentiation works well when polymorph spectra are dramatically different or when reference samples are available for comparison, but is poorly suited for automation, for spectrally similar polymorphs, or when the form was previously unknown [231]. Spectral match techniques, such as are used in spectral libraries, help with automation, but can have trouble when the reference library is too small. Easily automated clustering techniques, such as hierarchical cluster analysis (HCA) or PCA, group similar spectra and provide information on the degree of similarity within each group [223,230]. The techniques operate best on large data sets. As an alternative, researchers at Pfizer tested several different analysis of variance (ANOVA) techniques, along with descriptive statistics, to identify different polymorphs from measurements of Raman... 

Janne PA, Li C, Zhao X et al. High-resolution single-nucleotide polymorphism array and clustering analysis of loss of heterozygosity in human lung cancer cell lines. Oncogene 2004 23 2716-2726. 

Cellular automata modeling, 17 Charge distributions, 2, 5, 14 Charge transfer, 18 Cheminformatics, 1, 7, 18 Chemometrics, 1 Clustering methods, 18 Computational chemistry literature, 2, 17 Conformational analysis, 2, 9 Coupled cluster theory, 14 Crystal polymorphs, 12... 

For many problems in solid-state science, one can usefully employ either localized cluster approaches or delocalized band-structure approaches. Comparison of results between the two different approaches is sometimes straightforward, for example, in comparing equilibrium bond distances from cluster calculations on SiCOH) or band calculations on polymorphs of SiOj (although analysis of the reasons for discrepancies may be very difficult). Comparison of energy spectra obtained by the different approaches can, however, be difficult. 

Wang, L., Romana, L. K., and Reeves, P. R. (1992). Molecular analysis of a Salmonella enterica group El rfb gene cluster O antigen and the genetic basis of the major polymorphism. Genetics 130, 429 3. 

Some new insights into the nature of organic crystal polymorphism have been gleaned from a recent systematic analysis [79] of data for polymorphic structures retrieved from the Cambridge Structural Database. A total of 345 crystal structures were reduced to 163 clusters (a cluster referring to a group of two or more polymorphs of the same compound). These clusters comprised 147... 

Silver fulminate (SF) is a white crystalline material with heat of formatiOTi 179 kJ mol [15]. It crystallizes in the form of small rosettes or star-shaped clusters. Two polymorphic forms have been reported—orthorhombic and trigonal. The crystal shape depends on reaction conditions (temperature, concentration) during sUver fulminate preparation [94]. Recrystallization from ammonia leads to needles and multiple growths of leaf-like habits [92]. Long (4—5 mm) needle-shaped crystals were prepared by Singh and investigated by X-ray analysis. It was found that the crystal is orthorhombic [95]. The crystal structure of SF was later investigated in detail by Britton and Dunitz [96, 97] and their results were confirmed by Barrick et al. [98]. Ammonium acetate solution ( 20 %) is recommended as the solvent for... 

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