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691.
692.
Pigment distribution presages hydranth regeneration in the marine hydroidTubularia. We suggest that such a distribution could result from a reaction-diffusion system. A model system based on a practical reaction
scheme is studied and spatial structures found which closely resemble this pigment distribution. Finite-amplitude spatial
structures in reaction-diffusion systems are considered. Whereas in one spatial dimension the final structures are normally
very similar to the transient patterns which emerge from a linear analysis, it is shown that in more than one dimension this
is not necessarily the case. The reasons for this are discussed. 相似文献
693.
694.
Alpha and beta adrenergic blocking drugs were administered, either singly or in combination, prior to a 3hr adrenaline infusion (2 microgram kg body wt-1 min-1)), Animals were premediated with either phenoxybenzamine (1 mg kg body wt-1 min-1). Phenoxybenzamine did not affect circulating adrenaline levels, but propranolol, either alone or in combination with phenoxybenzamine, resulted in a significant reduction in plasma adrenaline levels when compared with the control unblocked situation of adrenaline infusion without premedication. The results provide a possible explanation for the protective effect of combined adrenergic blockade in shock situations. 相似文献
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696.
Isolation and Characterization of Suppressors of Two Escherichia Coli Dnag Mutations, Dnag2903 and Parb 下载免费PDF全文
The dnaG gene of Escherichia coli encodes the primase protein, which synthesizes a short pRNA that is essential for the initiation of both leading and lagging strand DNA synthesis. Two temperature-sensitive mutations in the 3'' end of the dnaG gene, dnaG2903 and parB, cause a defect in chromosome partitioning at the nonpermissive temperature 42°. We have characterized 24 cold-sensitive suppressor mutations of these two dnaG alleles. By genetic mapping and complementation, five different classes of suppressors have been assigned: sdgC, sdgD, sdgE, sdgG and sdgH. The genes responsible for suppression in four of the five classes have been determined. Four of the sdgC suppressor alleles are complemented by the dnaE gene, which encodes the enzymatic subunit of DNA polymerase III. The sdgE class are mutations in era, an essential GTPase of unknown function. The sdgG suppressor is likely a mutation in one of three genes: ubiC, ubiA or yjbI. The sdgH class affects rpsF, which encodes the ribosomal protein S6. Possible mechanisms of suppression by these different classes are discussed. 相似文献
697.
N.F. Britton 《Journal of theoretical biology》1982,97(4):691-698
A new differential equation model for the growth of trees, involving structure/storage partitioning, is set up. The model, which is relatively simple, is shown to exhibit suppression and dominance effects. It also suggests a possible mechanism for the bimodal distributions of tree size which are observed in even-aged monoculture stands. 相似文献
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699.
Claudia Carrillo Kirill Cherednichenko Nicholas Britton Michael Mogie 《Bulletin of mathematical biology》2009,71(7):1612-1625
The role of long-range dispersal in the coexistence of sexual and asexual relatives in a population of hermaphrodite flowering
plants is investigated. In these populations, growth and reproduction often occur during a sedentary stage that is then followed
by dispersal of propagules. These two stages are clearly distinguishable and show strong seasonality. A modeling approach
that accurately describes this kind of dynamics of mixed populations is a system of two nonlinear integro-difference equations.
It is shown that this kind of model can accommodate coexistence of the two different reproductive types. 相似文献
700.