The stumbling-block

The Cambrian explosion, on the other hand, had its roots precisely in the developing strategies of Cambrian embryos, and as long as the logic of development remains a mystery, we have no chance of understanding what happened. And we have also little chance of understanding the rest of metazoan evolution, because animals are, first of all, what their embryos make of them. 

While physics has built its fortunes on mathematics, biology is still an essentially empirical science, and mathematical models are mainly used for descriptive purposes, not as guiding principles. In this case, however, the problem is not that biologists are sceptical about mathematical models of epigenesis, but the fact that such models do not exist. As a matter of fact, one does exist, but nobody has taken any notice of it, which amounts to almost the same thing. 

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Until recently the stumbling block on the road to a more precise theory of hydrogen hyperfine splitting was the inability to calculate the polarizability... 

The stumbling block did not lie with obtaining pure PNP or converting the protein into crystals. Robert... 

All of the systems previously outlined will produce acceptable results when dealing with test specimens. The stumbling block is the inability of these systems to cope with the deformity of the evidence specimen. The evidence bullet, in most instances, will have suffered some deformity from the time it exited from a gun barrel until it finally comes to rest. It may be deformed in any number of ways, for example through contact with hard materials which may mutilate areas of the surface or perhaps it may suffer deformity through compression or expansion of the surface area of bullet which would make the bullet land and groove dimensions wider or narrower, compressing or expanding the pattern of striae that appear within them. As... 

The real problem, here, is that the development of the mind is characterised by a convergent increase of complexity both before and after birth, and the present compromise solution on language doesn t help us in the least to understand this fundamental process. The stumbling-block is that any dualistic scheme such as heredity-environment, or genotype-phenotype, is a priori incapable of solving the problem because any machine, or system, that works on the basis... 

In the fall of 1948, I was measuring the adsorption characteristics of numerous commercial adsorbents and of the natural zeolite, chabazite. Several uses for silica gel in air separation plants were identified. But the more we learned about chabazite, the more intrigued I became by its potential as a commercial adsorbent as well as its possible use in air purification and separation. I envisioned, as others had before me [1-5], major new separation processes based on a series of different pore size zeolites. The stumbling blocks were that (1) chabazite was the only known zeolite with seemingly practical adsorption... 

Environmental Exposure — the Stumbling Block of Hair Testing.17... 

ENVIRONMENTAL EXPOSURE — THE STUMBLING BLOCK OF HAIR TTSTING... 

It is the partitioning of the potential energy of interaction that is the stumbling block in partitioning a total energy. It is shown that the virial... 

Details of Centrifugal Separators and Use.—No continuously operating separator of the extractor type has been successful. The stumbling block to attaining this end has been the continuous removal of the solids formed but a choice of machine best suited to the work will often increase capacity. If there be not much liquid to be extracted the batch to be placed in the machine may be worked in a removable basket. 

The net results of reactions (8MI0) is the linking of two molecules of acetyl-CoA to give one of acetoacetyl-CoA. As the equilibrium of the reactions is favourable to synthesis, we have overcome the stumbling block provided by the -ketothiolase reaction of equation (6). Once again, reversal of equilibrium has been bought at the price of a molecule of ATP. The acetoacetyl-... 

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