Roth cluster

The defect structure of Fei O with the NaCl-type structure had been estimated to be a random distribution of iron vacancies. In 1960, Roth confirmed, by powder X-ray diffraction, that the defect structure of wiistite quenched from high temperatures consists of iron vacancies (Vp ) and interstitial iron (Fcj) (there are about half as many FCj as Vpe). This was a remarkable discovery in the sense that it showed that different types of crystal defects with comparable concentrations are able to exist simultaneously in a substance, Roth also proposed a structure model, named a Roth cluster, shown in Fig. 1.84. Later this model (defect complex = vacancy -F interstitial) was verified by X-ray diffraction on a single crystal and also by in-situ neutron diffraction experiments. Moreover, it has been shown that the defect complex arranges regularly and results in a kind of super-structure, the model structure of which (called a Koch-Cohen model) is shown in Fig. 1.85 together with the basic structures (a) and (b). 

Fig. 1.84 Defect complexes of wustite proposed by Roth (Roth cluster). ...

Fig. 1.85 Defect complexes of wustite. (a) Basic structure (Roth cluster) (b) edge-sharing tetrahedra (6 2 complex) (c) cornersharing tetrahedra (Koch-Cohen complex).

R. A. Provencal, J. B. Paul, K. Roth, C. Chapo, R. N. Casaes, R. J. Saykally, G. S. Tschumper, and H. F. Schaefer III, Infrared cavity ringdown spectroscopy of methanol clusters Single donor hydrogen bonding. J. Chem. Phys. 110, 4258 4267 (1999). 

M. Fichtner, O. Fuhr, O. Kircher, J. Rothe, Small Ti clusters for catalysis of hydrogen exchange in NaAlH4 , Nanotechnology 14 (2003) 778-785. 

In a non-stoichiometric oxide of the type Mi jO (where M is a metal), the association of the vacancy and the positive hole, or M + ion, can form the simplest cluster complex for Fei , 0. X-ray and neutron diffraction measurements (Roth 1960) suggested that some Fe + ions are in tetrahedral sites (flgure 1.11(a)). An... 

Excess adiposity, particularly the abdominal obesity associated with increased waist circumference, is associated with insulin resistance, hypertension, and proinflammatory states. The prevalence of this complex of comorbidities associated with obesity, now referred to as the metabolic syndrome, is reaching epidemic proportions in the United States (Grundy et al., 2004 Roth et al., 2002). Indeed, increased abdominal adiposity is one of a cluster of factors that are used in the diagnosis of metabolic syndrome. Abdominal tissue in the trunk occurs in several compartments, including subcutaneous and intraperitoneal or visceral fat. Visceral fat in particular appears to contribute to perturbed fuel metabolism by at least two mechanisms. First, hormones and free fatty acids released from visceral fat are released into the portal circulation and impact directly on metabolism of the liver. Second, the visceral adipose depot produces a different spectrum of adipocytokines than that produced by subcutaneous fat (Kershaw and Flier, 2004). 

Let us now construct a representation of the electronic structure of SiOj. There have been many early studies of Si02, principally aimed at interpreting various experimental spectra these have been reviewed recently by Ruffa (1968, 1970). More recently, studios based upon calculations for large clusters of atoms have been made by Reilly (1970), Bennett and Roth (1971a,b), Gilbert ct al. (1973), and Yip and Fowler (1974). Most recently, a full, self-consistent pseudopotential calculation on quartz was made by trhelikowsky and Schliitcr (1977). Here, we shall... 

Roth, F. P Hughes, J. D., Estep, P. W., and Church, G. M. (1998) Finding DNA regulatory motifs within unaligned non-coding sequences clustered by whole-genome mRNA quantitation. Nat. Biotechnol. 16, 939-945. 

H. Bock, R. Dammel and B. Roth, Molecular state fingerprints and semiempirical hypersurface calculations, in Inorganic Rings and Clusters (Ed. A. H. Cowley), ACS Symp. Ser., 232, 139 (1983). 

R. S. Narcisi and W. Roth, The formation of cluster ions in laboratory sources and the ionosphere, Adv. Electr. Electron Phys. 29, 79 (1970). 

Roth, S.V. et al. (2011). In situ observation of cluster formation during nanoparticle solution casting on a colloidal film, J. Phys. Condens. Matter Vol. 23 (2011), 254208... 

Fio. 3. Genetic map of histidine mutations in Salmonella. The genes specifying the histidine enzymes, hisA through hisi, are in a cluster near 6 o clock on the map. HisR, U, W, S, O, and T are regulatory genes (see Section IV). HisP is involved with histidine trans port. This map is adapted from Fink and Roth [42]. 

Another approach to the deposition of nanometre-sized particles on a surface has been described by Roth el a/. who thermally evaporated gold onto polystyrene in a vacuum chamber to form a thin film. Since the polymer-metal interaction is much weaker than the metal-metal interaction, the gold atoms form clusters in a self-assembly process. The gradient in cluster density was induced by using a blocking mask to shadow parts of the substrate. 

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