Evidence scarce

The 3 -heterocychcs ia the mid-distiUate range are primarily the thiacyclanes, ben2othiophenes, and diben2othiophenes. There are lesser amounts of dialkyl—, diaryl—, and aryl—alkyl sulfides (29). Alkylthiophenes are scarce or absent, but some evidence exists for ben2thiacyclanes (Fig. 6). As for the naphtha fractions, these sulfur species account for a minimal fraction of the total sulfur ia the cmde. 

Metal-reducing bacteria, such as those that convert ferric to ferrous ion, have been suggested as an accelerant for steel corrosion in oxygenated waters, lb date, evidence of these bacteria influencing corrosion in industrial systems is scarce. 

Because sugars are involved in most of the mechanisms established for the synthesis of these heterocycles, the development of carbohydrate chemistry has been most helpful in these researches—especially for the preparation of specifically labeled molecules. Conversely, the contribution of these efforts to carbohydrate chemistry and biochemistry has shown the involvement in biosynthesis of 1 -deoxy-D-f/rreo-pentulose—scarcely before recognized and considered a rare sugar—and of fully functionalized pentuloses of still unknown configuration (or their phosphates). Finally, evidence has been found in prokaryotes for a most extraordinary transformation of 5-amino-l-(P-D-ribofuranosyl)imidazole 5 -phos-phate into a pyrimidine. Surely, this transformation should be explained in terms... 

Recent exact measurements (196) can be interpreted by eq. (18) as well as by several other simple functions the reaction chosen was, however, not quite appropriate because of the low degree of correlation. The direct evidence for the second postulate is very scarce (9, 59, 217-219) and seems to be even negative (176, 197) we believe, however, that the main reason is the experimental inaccuracy. 

It follows that for a special value of one parameter, the observed value of y is independent of the second parameter. This happens at Ii= a2/ai2 or I2 = -ai/ai2 any of these values determines y= a -aia2/ai2, the so called isoparametrical point. The argument can evidently be extended to more than two independently variable parameters. Experimental evidence is scarce. In the field of extrathermodynamic relationships, i.e., when j and 2 are kinds of a constants, eq. (84) was derived by Miller (237) and the isoparametrical point was called the isokinetic point (170). Most of the available examples originate from this area (9), but it is difficult to attribute to the isoparametrical point a definite value and even to obtain a significant proof that a is different from zero (9, 170). It can happen—probably still more frequently than with the isokinetic temperature—that it is merely a product of extrapolation without any immediate physical meaning. 

Tea flavonoids, or tea extracts, have been linked to benefits in reducing the risk of certain cancers and cardiovascular diseases in experimental animals. However, epidemiological studies have produced inconsistent evidence in the relationship between tea drinking and cancer (Blot et a/., 1997 Goldbohm etal, 1996 Hertog eta/., 1997 Yang eta/., 1996). Therefore, further research is needed before definitive conclusions on the impact of tea consumption upon the cancer risk in humans can be reached. The metabolites of catechins and flavonols after consumption of tea infusions have scarcely been investigated, and thus more research is needed as to the role of those compounds in the reported health benefits of tea consumption. 

Tin concentrations in water, air, soils, sediments, and other nonbiological materials are documented, but information is scarce except for aquatic systems (Maguire 1991 Table 8.6). In aquatic systems, several trends were evident. First, tin and organotin compounds tend to concentrate in... 

Data are scarce on the toxicity of PCP to mammalian wildlife, but studies with livestock and small laboratory animals show that the chemical is rapidly excreted. However, there is great variability between species in their ability to depurate PCP, as well as in their overall sensitivity. Acute oral LD50 values in laboratory animals were 27 to 300 mg/kg BW. Tissue residues were elevated at dietary levels as low as 0.05 mg/kg feed and at air levels >0.1 mg/m3. Histopathology, reproductive impairment, and retarded growth were evident at doses of 0.2 to 1.25 mg/kg BW, and when the diets fed contained >30 mg PCP/kg. 

This behaviour means that residual co-catalyst, usually assumed to be water, is very scarce and is consumed during the reaction, which stops when the supply of co-catalyst is exhausted it implies a termination reaction. Evidently, the need for a co-catalyst other than one of the main components of the reaction mixture is satisfactorily proved by such an experiment. 

Such high EM s (> 1010 M) are scarcely to be expected for the formation of three-, or especially four-membered rings, because of the angle strain associated with the small ring of the product, and they are not found in any system where the open-chain form has significant conformational flexibility. An effective molarity of 1010 M or more may therefore be taken as prima facie evidence for strain in the ground state which is relieved in the cyclic product. 

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