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61.
A functional differential equation which is nonlinear and involves forward and backward deviating arguments is solved numerically. The equation models conduction in a myelinated nerve axon in which the myelin completely insulates the membrane, so that the potential change jumps from node to node. The equation is of first order with boundary values given at t=±. The problem is approximated via a difference scheme which solves the problem on a finite interval by utilizing an asymptotic representation at the endpoints, cubic interpolation and iterative techniques to approximate the delays, and a continuation method to start the procedure. The procedure is tested on a class of problems which are solvable analytically to access the scheme's accuracy and stability, then applied to the problem that models propagation in a myelinated axon. The solution's dependence on various model parameters of physical interest is studied. This is the first numerical study of myelinated nerve conduction in which the advance and delay terms are treated explicitly.Supported in part by NSF Grant MCS8301724 and by a Biomedical Research Support Grant 2SO7RR0706618 from NIH 相似文献
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In rats, infections with 100-2000 Trichinella spiralis muscle larvae lead to a prompt immunity that is expressed in parasite expulsion within 14 days. Rats infected with more than 2000 larvae display impaired immunity with rejection delayed by 50% (7 days) or more. Suppression is selective for expulsive immunity as the antifecundity response of rats is directly proportional to dose and is expressed sooner in heavily infected subjects. Suppression of intestinal expulsive immunity was suggested by the fact that, with low doses (2000 larvae or less), worm rejection was inhibited by cortisone, whereas cortisone inhibited antifecundity but had no discernable effect on worm rejection in high-dose infections. Evidence for local immune deviation as opposed to systemic immunosuppression was obtained in experiments using parabiotic rats. When one partner was infected with 6000 worms and the other with 200, the rat infected with 200 parasites showed earlier rejection than was seen in single controls infected with 200 worms. The prolonged survival of high-dose adults was not accompanied by a change in the site of worm residence in the gut. Immunological parameters such as serum antibody levels, the number of activated cells or specific anti-T. spiralis lymphocytes in thoracic duct lymph were all increased in a dose-dependent manner. These experiments therefore demonstrate a novel autoprotective mechanism by which adult T. spiralis selectively reduce the expression of expulsive immunity in the gut. 相似文献
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Influence of sewage treatment and urbanization on selection of multiple resistance in fecal coliform populations. 总被引:7,自引:4,他引:3 下载免费PDF全文
The fecal coliform populations found in the raw sewages and final sewage effluents of mechanical treatment plants, a long-term retention lagoon, shorter-term retention lagoons, a remote northern Canada river, and a heavily urbanized prairie river were examined for antibiotic resistance and the possession of R factors. It was determined that there was a decrease in the percentage of multiresistant fecal coliform populations in the mechanical sewage treatment plants and shorter-term retention lagoons; however, there was an increase in populations from the long-term retention lagoon. The percentage of the populations possessing transmissible R factors was constant in the mechanical treatment and shorter-term retention facilities; however, the ability to transmit was lost in 50% of the infective population of the long-term retention facility. A striking contrast was found between the populations of the remote northern Slave River and those of the urbanized Red River. Of the fecal coliforms in the Slave River, 7.1% were multiresistant, and only 0.79% possessed transmissible R factors. The Red River fecal coliform populations were 52.9% multiresistant, and 18.77% of the total population possessed transmissible R factors. The influence of urbanization and the type of sewage treatment have been shown to affect the selection and survival of multiresistant fecal coliforms and R+ fecal coliforms. Determination of other factors influencing the development and the survival of these populations is needed for rational wastewater management and water quality consideration. 相似文献
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Partial NH2- and COOH-terminal sequence and cyanogen bromide peptide analysis of Escherichia coli sn-glycerol-3-phosphate acyltransferase 总被引:2,自引:0,他引:2
P R Green T C Vanaman P Modrich R M Bell 《The Journal of biological chemistry》1983,258(18):10862-10866
The sn-glycerol-3-phosphate acyltransferase from Escherichia coli, an integral membrane protein whose activity is dependent on phospholipids, was purified to near homogeneity (Green, P. R., Merrill, A. H., Jr., and Bell, R. M., (1981) J. Biol. Chem. 256, 11151-11159). Determination of a partial NH2-terminal sequence and the COOH terminus permitted alignment of the polypeptide on the sequenced sn-glycerol-3-phosphate acyltransferase structural gene (Lightner, V. A., Bell, R. M., and Modrich, P. (1983) J. Biol. Chem. 258, 10856-10861). Processing of the sn-glycerol-3-phosphate acyltransferase is apparently limited to the removal of the NH2-terminal formylmethionine. Thirteen of 27 possible cyanogen bromide peptides predicted from the DNA sequence were purified, characterized, and assigned to their location in the primary structure. Three peptides located at positions throughout the sequence were partially sequenced by automated Edman degradation. The partial sequence analysis of the homogeneous sn-glycerol-3-phosphate acyltransferase is fully in accord with the primary structure inferred from the DNA sequence. 相似文献
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Toxicity to Chicks of Aspergillus and Penicillium Species Isolated from Moldy Pecans 总被引:3,自引:3,他引:0 下载免费PDF全文
Isolates of Aspergillus chevalieri, A. flavus, A. ochraceus, A. repens, and Penicillium funiculosum and complexes of P. citrinum-P. implicatum isolated from moldy pecan meats were toxic to chicks. 相似文献
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Development Genes and Evolution - UnfertilizedCiona eggs were centrifuged, stratifying their mitochondria and some other cytoplasmic components. Each centrifuged egg had a mitochondria-free,... 相似文献