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91.
一类含间隙分布时滞的种群增长模型的稳定性 总被引:4,自引:0,他引:4
本文首先利用间隙分布时滞函数来建立更为符合实际的种群增长模型,然后运用两种不同的方法,对其平衡位置的局部稳定性进行了全面的讨论,得出了局部渐近稳定的充分必要条件,在参数平面上划分出了稳定和不稳地的区域。 相似文献
92.
Olga N. Danilevskaya Dmitri A. Petrov Maria N. Pavlova Akihiko Koga Elena V. Kurenova Daniel L. Hartl 《Chromosoma》1992,102(1):32-40
He-T sequences are a complex repetitive family of DNA sequences in Drosophila that are associated with telomeric regions, pericentromeric heterochromatin, and the Y chromosome. A component of the He-T family containing open reading frames (ORFs) is described. These ORF-containing elements within the He-T family are designated T-elements, since hybridization in situ with the polytene salivary gland chromosomes results in detectable signal exclusively at the chromosome tips. One T-element that has been sequenced includes ORFs of 1,428 and 1,614 bp. The ORFs are overlapping but one nucleotide out of frame with respect to each other. The longer ORF contains cysteine-histidine motifs strongly resembling nucleic acid binding domains of gag-like proteins, and the overall organization of the T-element ORFs is reminiscent of LINE elements. The T-elements are transcribed and appear to be conserved in Drosophila species related to D. melanogaster. The results suggest that T-elements may play a role in the structure and/or function of telomeres.by W. Hennig 相似文献
93.
A disseminated infection with Penicillium marneffei, a rare human pathogen that may infect both healthy and immunocompromised patients, was diagnosed by fine needle aspiration cytology in a patient infected with the human immunodeficiency virus. The presence of yeast-form organisms with an eccentric or central dot and occasional septate and elongated forms highly suggested the diagnosis, which was confirmed on culture. Establishment of the diagnosis is important because this infection is potentially curable. 相似文献
94.
M Gajewski H Laskowska-Bozek S Ma?liński J Ryzewski 《Journal of physiology and pharmacology》1991,42(4):407-415
Isolated, cultured rat neonatal cardiac myocytes were placed in medium supplemented with mitochondrial respiratory inhibitor potassium cyanide which caused a rapid adenosine triphosphate (ATP) depletion. These myocytes with the impaired energy metabolism ("hypoxia-like state") were exposed to unstimulated human neutrophils. Effect of human neutrophils on the myocytes in the "hypoxia-like state" was quantified as a total change in the amount of ATP in cardiac cells. After 5 hours of incubation of neutrophils with the myocytes in the "hypoxia-like state" an additional decrease (of 50 per cent) in ATP content was observed. Since catalase (which destroys hydrogen peroxide) prevented the further decline in ATP level in the myocytes with impaired energy metabolism, it seem that hydrogen peroxide and possibly their products are responsible for this effect. These results suggest that unstimulated human neutrophils after activation by the contact with injured cardiac cells caused further decrease of ATP level in target cells. 相似文献
95.
A new method is proposed for the microtitration of CBPP vaccines by performing eight parallel endpoint two-fold dilutions. When performed on a 96-well plate, it gives a titre with a precision of +/- 0.2 log10. By comparison, the established method, performed in tubes, gives a precision of only +/- 0.6 log10. The adaptation to microtitre plates allows much more economical culture of larger numbers of samples. Statistical analysis permits determination of vial-to-vial homogeneity of a batch and calculation of a titre with a precision of +/- 0.09 log10. The new method may be applied for the titration of mycoplasmas. 相似文献
96.
Dr. Laura Curatolo Christine Chaponnier Maria Benedetta Donati Luciano Morasca Giulio Gabbiani 《Cell and tissue research》1982,223(3):665-673
Summary It is known that human and animal fibroblasts are able to induce the retraction of a fibrin clot. In the present study the correlation between (i) fibrinclot retractile (FCR) activity, (ii) the number of actin stress-lines in mouse fibroblasts during growth in culture, and (iii) the sensitivity of actin stress-lines to a powerful actin-depolymerizing factor (ADF), present in plasma and serum of humans and laboratory animals was investigated. Fibroblasts at early passages (2–4) were tested for these parameters at various intervals after seeding (24, 96, and 168 h). The number of actin stress-lines was progressively higher, while the sensitivity to ADF action was progressively lower in cells cultured from 24 to 168 h; the FCR capacity was significantly decreased at 168 h. These data suggest that cells containing weakly polymerized and/or stabilized actin are more active than those containing highly polymerized and/or stabilized actin in triggering fibroblast contraction. 相似文献
97.
Age-dependent population diffusion with external constraint 总被引:3,自引:0,他引:3
We present a simple model for age dependent population diffusion when the dynamics is submitted to external constraints. Existence, uniqueness and dependence on the parameters of the solution are discussed.This work has been done within the framework of the cultural agreement between the Universities of Bordeaux and Rome 相似文献
98.
99.
Replication of bacteriophage lambda DNA. Examination of variants containing double origins and observation of a bias in directionality 总被引:1,自引:0,他引:1
Maria Schnös Katherine J. Denniston Frederick R. Blattner Ross B. Inman 《Journal of molecular biology》1982,159(3):441-455
Bacteriophage λ variants have been constructed that possess two λ ori sites. Replicative intermediates resulting from infection with these phages have been investigated. We find that initiation of replication from the ori site on an EcoRI fragment (containing all the DNA sequences from within the red gene to the middle of gene O) cloned in the inverted orientation is predominantly bidirectional but occurs at a decreased frequency. Double initiations were observed at low frequency. However, a second cloned ori fragment (carrying two large deletions and a small insertion) cloned in the normal orientation demonstrated insignificant levels of replication from the cloned site unless the normal ori had already initiated.A bias in directionality of λ replication has been observed. Molecules that replicate unidirectionally propagate to the right more often than to the left. If the cloned ori-containing EcoRI fragment is inserted with reversed polarity, then the bias is towards the left. Bidirectional λ replicative intermediates also appear to show a similar bias but this is superimposed on a large, apparently random, effect that results in asymmetric growing-point propagation. 相似文献
100.
The effective synthesis of 4,4,14α-trimethyl-19 (10 → 9β) abeo-steroids (iv), (v), and (Vl) with two- and five-carbon side chains from lanosterol is described. Their structures were proved on the basis of spectral data. The title compounds are the first synthetic synthons for the preparation of 4,4,14α-trimethyl-steroids with an unnatural configuration. 相似文献