Provenance postulate

Despite the potential problems with using LA-ICP-MS to generate bulk compositional data for ceramics, there are exceptions where LA-ICP-MS can be effectively employed. The main requirements for ceramic studies of this nature are that the provenance postulate must be fulfilled (28)—that differences between groups must be greater than the differences within groups. 

For the reeord, we should point out that the equations developed in this ehapter are extensions of the nonrelativistie, time-independent Schroedinger equation. The Pauli prineiple arises from a relativistie treatment of the problem, but we shall follow the eustom of most ehemists and aeeept it as a postulate, proven beeause it gives the right answers. 

However, a critical examination of the enormous amount of the experimental material that has piled up over more than 80 years leads to the conclusion that the three tautomeric forms postulated by Gada-mer have not been proven in one single case. The so-called evidence is based on chemical reactions, " which are noncompelling, or on physical constants that have been interpreted in a biased manner. For the simultaneous existence of both forms of the ring-chain proto-tropic system, i.e., the carbinolamine and the amino-aldehyde, evidence is available only for one single case. ... 

The McGill workers postulated that, in their process, methylene nitramine (CH2=N—N02) is formed as an intermediate, which then tri-merizes to RDX. However, the existence of methylene nitramine has never been proven. Werner Bachmann (Ref 2) of the University of Michigan, during WWII, conceived of a combination process in which the Hale nitrolysis of Hexamine would occur first, and the remaining methylene would be converted to RDX by the Ross-Schiessler route. Using three feed streams Ac20, Hexamine In acetic acid, and AN in nitric acid, the Bachmann process results in an 80% yield of RDX (two moles from one of Hexamine), including a small amount of HMX. 

The state of the knowledge is at the moment such that still in each particular case, the investigator should analyse and establish experimentally how important are, relative to each other, the effects 1) and 2) for the activity and the selectivity of a given multimetallic catalyst. It is an historical experience that when the explanation of the data is not immediately obvious, the authors offer as an "explanation" "an electronic (ligand) effect" (7). In this way it happened that the effect sub 1) has been most frequently proven to operate, while the effect sub 2) is the most frequently postulated... 

The postulated and sufficiently proven notion that asphaltenes are oxidation products of resins and that resins are oxidation products of oil (11) sort of makes the probability of finding oils whose actual resin concentration is less than their critical resin concentration small. In other... 

It has also been postulated using molecular modeling and proven experimentally using temperature-programmed techniques that promotion with boron inhibits detrimental carbon formation.71 Ab initio calculations indicate that boron... 

In order to think about the nature and consequences of cell wall polymer phenolic cross-linking, we need a working model of the mode of assembly and the final structure of the primary cell wall. Unfortunately, there is no universally acceptable model that proposed by Albersheim and co-workers (3) is not now widely accepted because the postulated interpolysaccharide glycosidic bonds have not been demonstrated (4) and the warp-weft model of Lamport (5) rests on the assumptions that extensin (i) forms a defined-porosity network (not proven) (ii) is orientated anti-clinally to the cell surface [some evidence against (6)] and (iii) is a major component of all primary cell walls (not true). 

When the above reaction was carried out using the S)- +)-melhy cyclohexyl mme derivative of 97, the yield was similar (69%), but the de dropped to 0%. This was rationalized by the assumption that -stacking between the arene moiety and the Zn atom is crucial for facial selectivity as was postulated earlier44b for analogous reactions. The de could be further increased by changing the methyl substituent on nitrogen to ethyl (equations 47 and 48). The stereochemistry of 100 was proven by X-ray analysis of its... 

The influence of S-oxidizing bacteria on speciation of S in sediments has not yet been proven. Losher (56) postulated that layers of S-oxidizing bacteria in lakes Cadagno, Zurich, and Geneva caused a layer rich in toluene-soluble... 

As logical as this diagnostic method is, one needs to recognized its lack of absolute applicability The observed magnitude of the kinetic isotopic effect is not great, and the aforementioned statement of independence of electron affinity from the increase in the molecular mass of the substrate is not obvious. This postulate should be proven in each case. Benzophenone, taken as an isotopic mixture of 12C=0 and 13C=0 gives a mixture of anion radicals with a decreased proportion of 13C=0 isotomer when reduced with potassium in HMPA (G.R. Stevenson, Reiter, Espe, Bartmess 1987). In effect, this means that for the heavier isotopomer of benzophenone, the electron affinity is smaller. 

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