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71.
A note on estimation for gamma and stable processes 总被引:1,自引:0,他引:1
72.
I. W. Saunders 《Journal of mathematical biology》1981,11(3):311-318
When two or more epidemic agents are simultaneously present in a population, they may interact to increase or decrease each other's effectiveness. One form of interaction is competition where each agent confers immunity to the others. Such competition occurs, for example, between different strains of myxomatosis in rabbit populations. We consider some consequences of introducing competition into mathematical epidemic models. Both deterministic and stochastic simple epidemic models are examined. In either case the conclusions are similar: the faster spreading epidemic has a considerable advantage. 相似文献
73.
A probability model for the number of complete conceptions (that is, live births) taking into account foetal wastages, occurring
in a couple during a specified period of time (T0, T0+T) is developed assuming that the data was collected starting a long time after marriage. A method of estimating some of
the underlying parameters is given. The model is applied to data obtained in a Varanasi Survey in 1969–70. 相似文献
74.
V. N. Soyfer N. A. Kartel 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1978,53(1):9-15
Summary The influence of repair and replication on the frequency of spontaneous chromosome aberrations and of those induced by gamma-irradiation is reported.Using the technique of labelling DNA with radioactive 3H-thymidine and measuring the radioactivity of DNA isolated from embryos, the time of initiation and the duration of DNA synthesis in barley seeds was studied after the soaking of the seeds had begun. The average duration of each phase of the first DNA synthesis cycle in soaking barley seeds was found to be as follows: pre-DNA synthesis stage, 10–11 hrs; DNA synthesis stage, 8 hrs. After gamma-irradiation, the intensity of DNA synthesis decreased and the beginning of DNA synthesis was delayed.It was found that the inhibition of repair by caffeine led to an increase in the frequency of both spontaneous and induced chromosome aberrations. Caffeine enhanced several times the frequency of chromosome and chromatid aberrations at the time of the maximal activity of repair enzymes. During DNA replication, caffeine had a lower effect on the realization of premutational lesions.An inhibitor of DNA replication — hydroxyurea — had no influence on the frequency of spontaneous chromosome aberrations during the replication period, whereas after gamma-irradiation, hydroxyurea enhanced the frequency of aberrations mainly at the stage of DNA replication.The relatively small mutagenic action of both agents (caffeine and hydroxyurea) was observed during all stages of the cell cycle of germinating barley seeds. 相似文献
75.
D.B. Archer 《Enzyme and microbial technology》1983,5(3):162-170
The essential requirement for anaerobic digestion of industrial wastes is that the process should operate reliably at high performance. In the digestion of dilute, soluble wastes it is necessary to retain the active biomass within the digester at short liquid retention times for the process to be economically feasible and this is reflected in digester design. Performance of digesters can only be assessed by interpretation of measurable parameters such as pH2, Eh, pH, volatile fatty acid concentrations, temperature, gas production, biomass content and feed rate and composition. The effects of changes in these parameters on the microbiology of methanogenic digestion and the application of this knowledge in control of the process is discussed. 相似文献
76.
Stream pretreatment of wheat straw solubilized most of the xylan present. Xylose and other sugars were recovered by washing the substrate with water but only a minor part (34%) was monomeric. Treatment of this solutions with celulases and hemicellulases improved the yield of monomeric sugars to 69%, the main product being xylose. Some xylose was also obtained during enzymatic hydrolysis of the solid substrate although the pretreatment step contributed 64% (mean value) of total xylose formed. A reference model, No. 1, and two other models, Nos. 2 and 4, described in the first part of this article series (this issue) have been studied experimentally and results confirm the theoretical conclusions. An uninterrupted hydrolysis over a given time period leads to a lower degree of saccharification than when hydrolysate is withdrawn several times. Saccharification is also favored if the residue is removed at a late stage, i.e., at the end of the 24 h hydrolysis cycle. Extended recirculation of the enzymes during a 4 x 24-h experimental period gave the following average yields of saccharification on a 24-h basis: 65% (Reference), 73% (Model 2), and 79% (Model 4). It is concluded that enzyme recovery with model 4 is 70% or more, while the Reference and Model 2 attain a lower level of recovery. The design of an improved hydrolysis model is also discussed. 相似文献
77.
Christopher A. Zoladeski 《植被学杂志》1991,2(2):255-258
Vegetation zones in dune slacks on the Leba Bar on the Polish Baltic Sea coast are described. Plant colonization starts on moist sand in eastern ends of slacks, in the wake of receding mobile dunes. Communities on deflation ribs, dominated by psammophytic grasses, sedges and lichens, are structurally simple. Communities in troughs, dominated by species of fresh habitats, become structurally more complex in a western direction and they culminate with the Pinus silvestris forest. The main lines of vegetation variation correlate with groundwa-ter depth, micro topography, soil profile build-up and substrate acidification. 相似文献
78.
79.
Summary The establishment of actinorhizal root nodules involves penetration of host cell walls and intracellular colonization by the nitrogen-fixing endosymbiont,Frankia (Actinomycetales). In the early stages of the infection process inAlnus, unusual cell walls with undulate profiles were observed in root tip meristematic derivatives, and in early (preinfection) derivatives of the nodule lobe meristem, inFrankia-inoculated plants. The irregular cell walls attached obliquely to preexisting walls, but were not discontinuous. Serial sections revealed that the unusual walls divided two daughter cells. Microtubules in bundled arrays were abundant near the undulate walls, and radiated in several planes. In the root tips, the anomalous cell walls were observed within one day of inoculation withFrankia. 相似文献
80.
A spectrofluorimetric investigation of calf thymus DNA modified by BP diolepoxide and 1-pyrenyloxirane 总被引:1,自引:0,他引:1
N C Yang L K Ng S B Neoh D Leonov 《Biochemical and biophysical research communications》1978,82(3):929-934
7β,8α-Dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BP diolepoxide, ) and 1-pyrenyloxirane () bind chemically to calf thymus DNA. The fluorescence efficiency of pyrenyl groups in mutagen modified DNA varies appreciably with its conformation and decreases in the order: pyrenees, modified denatured DNA and modified native DNA. A particularly interesting observation is that the fluorescence efficiency of mutagen modified DNA intensifies substantially upon denaturation. Our results suggest that the pyrenyl groups in mutagen modified DNA are intercalated between the base pairs of DNA. Since both and are powerful frame-shifting mutagens for S. typhimurium TA-98, the intercalative covalent binding of these compounds to DNA may provide a molecular basis for their mutagenic activity. 相似文献