Tentative Conclusions

The responses of cultured cells to ascorbate are variable and still poorly understood. Cell growth may be enhanced or inhibited and finally prevented for toxicity reasons, and certainly the various events are triggered by different mechanisms. 

Growth enhancement in some tumor cell lines is observed at ascorbate concentrations of 0.2-0.3 mM. The underlying mechanisms are unknown yet concomitant oxidative events, alkalinization of the cytoplasm due to activation of the transmembrane redox system, redox activation of growth factor receptors, and interference with protein kinase/phosphatase systems may be offered as hypotheses to be further investigated. Why growth of other cell lines such as melanoma cells and some leukemia cells is inhibited at approximately the same concentration of ascorbate remains obscure. 

The toxicity of ascorbate starting at the physiological range with some cultured cells and regularly observed above 1 mM ascorbate in the medium is certainly due to the by-products of autoxidation, particularly to oxygen-centered radicals. 

Alcain, F. J., Buron, M. I., Rodriguez-Aguilera, J. C., Villalba, J. M., and Navas, P., 1990, Ascorbate free radical stimulates the growth of a human promyelocytic leukemia cell line. Cancer Res. 50 5887-5891. 

Anderson, H. C., 1974, The mechanisms of cartilage growth and replacement in endochondral ossification, in Craniofacial Growth in Man, (R. E. Moyer and W. M. Krogmann, eds.), pp. 15-25, Pergamon Press Oxford, England. 

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At this stage of my enquiry 1 can draw only a few tentative conclusions from the case-histories presented above. I shall return at the end of the book to the issue of how disciplines evolve and when, to adopt biological parlance, a new discipline becomes self-fertile. 

The halo-2-nitronaphthalenes (Table XIII) enable one to draw tentative conclusions about intranitclear and internitclear activation in the isoquinolines for which data are not available. These compounds are numbered so as to show their relation to their isoquinoline analogs. The relative rates are summarized in the following tabulation along with the ratio of the rates of piperidino-debromination to that of the appropriate bromonaphthalene (res. = resonance activation, ind. = inductive activation). 

The detection of microgram quantities of pyrethrins, cinerins, keto alcohols, and chrysanthemum acids by paper chromatography and by application of these techniques to a study of possible metabolites enabled certain tentative conclusions that imply hydrolysis in insects of a large portion of the radioactive pyrethrins and synergists to corresponding keto alcohols and chrysanthemum acids. 

A very tentative conclusion from the relatively small sample of cities studied shows that people living In as many as half the cities In the world may be exposed to CO concentrations In excess of the WHO short-term guideline. 

Althou sufficient data to provide thorough tests of mechanism are lacking, it is possible to make some tentative conclusions. Sets 15-67, 15-69, and 15-71 give highly significant correlations with eq. (30). These sets include both monosubstituted and disubstituted dienophiles. Obviously, then, both mono-substituted and disubstituted dienophiles lie on the same correlation line and have the same values of a and 3. It therefore seems likely that these sets undergo a concerted mechanism. 

The mechanisms that we propose to explain the H3 data has led us to revisit and to reexamine earlier data on the recombination of other ions (see Section V). The goal was to see to what extent the experimental observations in afterglow plasmas support the assumption that only binary as opposed to third-body assisted recombination is important. While this is most likely true in many cases, the evidence is not as firm as one might think. Often, the original authors stated their conclusions rather cautiously, but over the years tentative conclusions have often assumed a status that is not justified by the original data. We will point out some gaps in our knowledge which should be closed by more detailed studies. 

We have drawn the following tentative conclusions as a working hypothesis for future studies, (i) PGD2 and PGE2 are endogenous sleep and wake substances,... 

Many of the early reports of spin-trapping experiments were focused on mechanistic investigations, and some of these feature in the early reviews (see p. 4). Unfortunately, it is in this application that inferences drawn may be most suspect. For example, the inability of the method to differentiate between radical trapping on the one hand, and a combination of nucleophile trapping with one-electron oxidation on the other, is a serious shortcoming. An early example of this was the tentative conclusion that acetoxyl radicals were spin-trapped by PBN competitively with their decarboxylation in reactions of lead tetraacetate. In view of the rapidity of the decarboxylation reaction, trapping of acetate ion and subsequent oxidation seems a likely alternative. 

In complexes of crown ethers [303] to [305] (types IV and V) both large groups are located in the larger of the two non-equivalent chiral cavities (Kyba et al., 1978). This was concluded from H nmr spectra of the diastereomeric complexes of [303] with a-phenylethylammonium salts. In the spectra the position of the methyl protons in both diastereomeric complexes is the same, in contrast to the methyl protons in complexes of [284] or [285] with the same salt. In the latter the upheld shift of the methyl protons in the more stable SS-(R) enantiomeric complex differs from that in the less stable SS-(S) enantiomer. Taking into account the available data summarized above, the tentative conclusion seems to be that the simple steric model (see structure... 

An effort to match the subjects with respect to age, education, AFQT intelligence scores and marital status proved unsuccessful. Only three of thirty men who were suitable matches agreed to spend a week undergoing examination (understandable, since they would receive only minimal compensation). Ultimately, the best McFarling could do was to draw tentative conclusions by comparing the frequency of post-LSD problems with corresponding national averages. 

The number of well-established intramolecular genered base-catalysed reactions is quite small, but from the available examples a tentative conclusion is possible that such a mechanism is not greatly... 

Root Mean Square Error of Calibration (RMSEC) Plot (Model Diagnostic) The RMSEC as a function of the number of variables included in the model is shown in Figure 5-77. It decreases as variables are added to the model and the largest decrease is observed between a one- and two-variable model. The reported error in the reference caustic concentration is approximately 0.033 vrt.% (la). The tentative conclusion is that four variables are appropriate because the RMSEC is less than the reference concentration error after five variables are included in the model. 

For the example data, the RMSEC is calculated for models containing 1 -22 variables (adding the variables in the order listed in Table 5.9). The RMSEC versus the number of variables included in the model is plotted in Figure 5.66 for component A. nte fit improves as variables are added to the model (RMSEC decreases). However, knowing these results reflect model fit, there is a concern about overfitting (i.e., fitting noise from the calibration data). It is known that the error in the concentration values is 0.010 (la). The RMSEC drops below this level after the fifth variable is included, and therefore the tentative conclusion is that a four-variable model is appropriate. 

Autonomic changes were quite prominent In DMHP-treated animals— hypothermia, mydriasis, hypersallvatlon, bradycardia, and reduced respiratory rate. Several experimental manipulations were undertaken to determine the mechanism of these autonomic changes. The tentative conclusion was that the drug was acting centrally to reduce sympathetic tone. 

Considering these different limiting forms of the recombination term an Important tentative conclusion emerges the concentration dependence of the reciprocal relaxation time is a direct measure of the main ionic recombination process and yields therefore information on the ionic species present in solution. A linear dependence on total ion-pair concentration would therefore indicate unilateral triple ion formation or, if both kinds of triple ions are present as indicated by conductance, a sufficient difference in their stability. At this point it should be noted that the usual method of Fuoss and Draus... 

It should be emphasized that the interpretation of the present results depended on the assumption that the substances were present in solution in one form only ( the di-anion of eosin and the monoprotonated form of proflavine) and that no association or dissociation occurred in the excited states. A full investigation should have included the dependence of the absorption and luminescence spectra on pH, concentration, and solvent. With this reservation in mind, the following tentative conclusions have been drawn from the present results ... 

Finally, an important if tentative conclusion emerges concerning the symmetry of distribution functions, which could be relevant to the general theory of polarization and to current ideas about liquid structure. Theoretical analysis in terms of radially symmetric models does not necessarily tell us about the structure of a system, because the short-range forces, by their very nature, have a directional character which is not lost in any averaging process. Is it this averaged directional force which is responsible for structure in liquids and solutions ... 

The tentative conclusions described above regarding the form of and f (x) dx for self-avoiding walks were substantially strengthened by a relation formulated by Fisher.21 Strong numerical evidence had been adduced by Domb, Gillis, and Wilmers19 to indicate that the distributions... 

Although the NBS standards were collected from several sources, some tentative conclusions can be reached concerning the combustion process. Using selected elements for comparison which are of a refractory nature and would be expected to be conserved in the ash following the combustion process, it becomes apparent that other elements such as selenium and antimony are not being conserved, but rather are lost from the ash. Refractory elements selected for illustration are Eu, Hf, Sc, Ta, Tb, and La, although most other elements display the same conservative behavior. Table VI shows the concentrations of these elements in both... 

The qualitative, overall effect of small N is a stress in the deformed network which is larger than the corresponding Gaussian stress. This effect is, however, very small in normally crosslinked rubbers, whereas these rubbers exhibit large deviations from Gaussian behaviour. The tentative conclusion must therefore be that the deviations from Gaussian behaviour at moderate extensions cannot be caused by short chains only. 

The initial experiences with polyisocyanides, especially solubilities and some Debye-Scherrer X-ray data (3), and an consideration of the most probable molecular structure (4), led to an early tentative conclusion that poly(a-phenyl-ethyl isocyanide) and poly(conformational model of a tightly wound helix with an overall shape of a cylindrical rod of about 15 A diameter (3). 

While discussing vibrations we may ask whether 60 cycle electromagnetic field fluctuations caused by electrical power transmission can affect the human body Considerable effort has been expended in addressing this question. The tentative conclusion is that such effects, if they exist, are extremely difficult to detect. However, the possibility has not been disproven.965... 

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