共查询到20条相似文献,搜索用时 31 毫秒
1.
I. D. Kolesin 《Biophysics》2014,59(3):511-513
Pre-epidemic circulation of a multivariate agent is simulated. An assumption on the possibility of forming a new variant as a combination of properties of circulating variants is examined. 相似文献
2.
A model for insulin secretion with a storage and a labile compartment, as well as a provisionary factor, is combined with
a signal model in which the signal can be the difference between an excitation and an inhibition, or the difference in concentrations
inside and outside some cell components. The model, using a single set of values for the parameters, accounts in a semiquantitative
manner for all of the regularly appearing features of the insulin secretion from thein vitro perfused pancreas to a wide range of patterns of glucose and tolbutamide stimulation. Among the features which can be accounted
for are: early and late secretion of insulin as a function of glucose in terms of a single parameter; the apparent depletion
and recovery during a pulsed pattern of stimulation by tolbutamide; the hypersecretion following a short period of rest during
a prolonged stimulation by glucose; the negative spike which occurs when the concentration of glucose, which has been maintained
for a period of time, is suddenly reduced to a lower level; and the appropriate responses to slow and fast ramp functions
of glucose concentration. 相似文献
3.
Henry B. F. Dixon 《The Biochemical journal》1973,131(1):149-154
A simple case is considered in which the rate of a two-step reaction depends on pH because the intermediate formed in the first step has to gain (or lose) a proton before it can react in the second step, and in which the rate-determining step therefore changes with pH. The curves of reaction rate against pH are shown to be symmetrical, and the sharpest peak possible has a width at half its height of 1.53pH units, i.e. of 2log(3+2 radical2). Any particular curve for this situation proves to be identical with a curve that could be generated for the pH-dependence of a single-step reaction in which the rate is proportional to the concentration of a particular ionic form of a reactant. Curves for the latter situation, however, can have forms impossible for the former case in which the rate-determining step changes, but only if the protonations that activate and deactivate the reactant are co-operative. The peak can then become even sharper, and its width at half its height can fall to 1.14pH units, i.e. to 2log(2+ radical3). 相似文献
4.
A syntactic representation of units of genetic information--a syntax of units of genetic information 总被引:1,自引:0,他引:1
J Collado-Vides 《Journal of theoretical biology》1991,148(3):401-429
5.
Simulations of action of DNA topoisomerases to investigate boundaries and shapes of spaces of knots
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The configuration space available to randomly cyclized polymers is divided into subspaces accessible to individual knot types. A phantom chain utilized in numerical simulations of polymers can explore all subspaces, whereas a real closed chain forming a figure-of-eight knot, for example, is confined to a subspace corresponding to this knot type only. One can conceptually compare the assembly of configuration spaces of various knot types to a complex foam where individual cells delimit the configuration space available to a given knot type. Neighboring cells in the foam harbor knots that can be converted into each other by just one intersegmental passage. Such a segment-segment passage occurring at the level of knotted configurations corresponds to a passage through the interface between neighboring cells in the foamy knot space. Using a DNA topoisomerase-inspired simulation approach we characterize here the effective interface area between neighboring knot spaces as well as the surface-to-volume ratio of individual knot spaces. These results provide a reference system required for better understanding mechanisms of action of various DNA topoisomerases. 相似文献
6.
7.
Faraji M Okhovvat SM 《Communications in agricultural and applied biological sciences》2005,70(3):305-309
Twenty isolates of Fusarium oxysporum and F. solani were isolated from the infected roots of bean in different farms of east Azarbaijan and Tehran Provinces and their pathogenicity determined. Most isolates of the fungi were identified as F. oxysporun. They caused root rot, yellowing and wilting of bean in the field. In this test, the roots of 6 cultivars of bean seedlings soaked in suspension of the 7 isolates of the fungi (a1, Gogan, a2, Bilverdi, a3, Savojbolagh-Hashtgerd, a4, field of Agr. Coll. a5, Khomein, a6, Ramjin of F. oxysporum and a7 of F. solani of Varamin, Iran) for 5 minute (106 spores/ml.) then transplanted into the sterilized soil in 4 pots (as replication). For control (a8) the roots soaked in distilled water. The results showed that percentage average of necrotic roots and crowns of isolates al, a2, a3, a5, a6, a7 was %20.31 in group a, a4 was %43.52 in group b and a8 was %2.77 in group c after 3 weeks. The isolate a4 (from the field of Agricultural College, Karaj) was more infectious than the other because it caused wilting, yellowing the leaves and decreased the growth very soon, followed by a5 with %25.32 rate was more pathogenic. Bean cultivar Goli-Red was more tolerant with %10.02 than the others of 16.29 (Naz Red) to 25.15 percent of necrotic the roots & stems. 相似文献
8.
H. S. Lew 《Biophysical journal》1969,9(2):235-245
A general form of the statistical equation of motion of the blood is derived by averaging the motion of individual elements of the blood over a small volume in space. This equation can be transformed into an explicit form to find the constitutive equations of the blood provided the detailed motion of the plasma in some neighborhood of a suspended particle is known. As a demonstration of such transformation, the general form of the statistical equation of motion is applied to the suspension of sphere with a very low concentration to find the effective viscosity. 相似文献
9.
N. S. Willetts 《Journal of bacteriology》1972,112(2):773-778
The location of the origin of transfer on the map of Flac has been determined by two different techniques. The first showed that no transfer cistrons were transferred early by a transposition Hfr strain with a known point of chromosomal integration into Flac, and the second used a series of transfer-deficient Hfr deletion strains to map a locus required in cis for chromosome transfer by an incoming Flac factor. Both techniques gave results consistent with a location for the origin of transfer between traJ and the phi(R) (11) locus. 相似文献
10.
A study was made of the kinetics of thermoinactivation of lysyl-tRNA-synthetase isolated from rat liver at early times of radiation damage development after the effect of a minimum absolutely lethal X-radiation dose (0.21 C/kg). The thermostability of a dimer form of the enzyme was shown to be higher than that of a monomer. It was established that substrates had a stabilizing effect on the enzyme during thermoinactivation. On the basis of the data obtained from the studies in the kinetic properties of the enzyme and the thermoinactivation a conclusion is made that lysyl-tRNA-synthetase is stabilized during subunit aggregation. The thermostability of the enzyme was decreased by irradiation. 相似文献
11.
James K. Petell Yoram Bujanover Jeannine Gocayne Sergio Amarri Darrell Doyle 《Experimental cell research》1987,173(2):473-485
Several recent studies have demonstrated the ability of techniques based on immunoadsorption to selectively isolate specialized subregions of membranes, termed domains, which are derived from a larger more complex parent membrane like the plasma membrane. The immunoadsorbent is directed against a specific antigen that resides exclusively or predominantly in the membrane domain to be isolated. Thus, a monospecific antibody to the domain-specific antigen is required. In the present study we developed a method employing a modified immunoblotting strategy which could utilize polyspecific antibodies to isolate membrane vesicles derived from a specific membrane domain of the hepatocyte plasma membrane. We also used specific cell surface labeling of the hepatocyte plasma membrane by lactoperoxidase-catalyzed iodination at 4 degrees C and preparation of different sized vesicles by sonication to facilitate isolation of the specific domain. For this study, polyspecific antisera were raised in goats against a membrane fraction, denoted N2u, which is enriched in bile canalicular proteins. This antiserum recognizes, among other antigens, a 110,000 Mr polypeptide previously shown to be localized in the bile canaliculus (J. Cook et al. (1983) J. Cell. Biol. 97, 1823-1833). A monospecific antiserum was raised in rabbits against the rat hepatocyte asialoglycoprotein receptor, a sinusoidal domain-specific set of glycoproteins whose major form has a Mr of 43,000. These antisera were each coupled indirectly to different pieces of nitrocellulose by the immunoblotting protocol and were used to isolate membrane vesicles from a crude extract of liver plasma membrane prepared by sonication. The ratio of iodinated asialoglycoprotein receptor to the 110,000 Mr polypeptide in vesicles isolated by the affinity nitrocellulose immunoadsorbent method indicate a 10- to 15-fold enrichment of sinusoidal-derived vesicles relative to bile canalicular-derived membrane vesicles. These results show that the affinity nitrocellulose immunoadsorbent method can be used to isolate domain-specific vesicles. Further, the affinity immunoadsorbent method described here for the isolation of domains of the plasma membrane is an integrative one allowing isolation of vesicles present in relatively small concentration in crude cell extracts and it requires minimal ultracentrifugation time. 相似文献
12.
Effects of the Timing of Flashes of Light during the Course of Cellular Rotation on Phototactic Orientation of Individual Cells of Cryptomonas
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The swimming movement of Cryptomonas sp. cells generates a helical path, as a result of rotations with an average period of 500 milliseconds. When a flash of light at 570 nanometers for 20 microseconds was applied unidirectionally at intervals of 500 milliseconds, only a fixed side of each rotating cell was repeatedly exposed to the flashes of light. The relationship between the irradiated side of a cell and the phototactic orientation of the cell, rotating with a period of 475 to 525 milliseconds, was determined by infrared videomicrography. Only when the ventral sides of the cells were exposed to the flashes of light did their courses shift predominantly toward the light source. This result suggests that light is efficiently detected by the ventral side of these organisms. 相似文献
13.
Thermostability of Proteases and Lipases from a Number of Species of Psychrotrophic Bacteria of Dairy Origin 总被引:6,自引:2,他引:4
Proteases and lipases from a number of different species of psychrotrophic bacteria isolated from dairy products are resistant to heat treatments of 77°C for a holding time of 17 s and 140°C for a holding time of 5s. A further treatment combining the 77°C for 17 s heating process with a heat treatment involving a temperature of 55°C for 1 h was also examined. The proteases and, to a lesser extent, the lipases were also resistant to the treatments in combination. The resistance of proteases and lipases to inactivation by a treatment of 55°C for 1 h varied between and within species. Therefore, this treatment may not have a widespread practical application. 相似文献
14.
《Journal of Russian & East European Psychology》2013,51(6):69-87
The psychosemantic approach has developed a number of methodological techniques for studying the distinctive features of artistic perception. These include a multidimensional evaluation by the semantic differential method of a visual relation to a work of art [3,5,7,9, and others]; a procedure for determining the cognitive complexity of perception by Kelly's method of personality constructs [5]; construction of a character similarity matrix on the basis of subjective scaling [12]; and a method of "multiple identification" that evaluates the probability of adopting some particular role position [6]. This line of inquiry has yielded considerable substantive material characterizing the categorical features of visual assessments of a work of art. 相似文献
15.
Taking into account Caianiello's work of 1961 a model of a neuron quite similar to his is proposed and studied. For this model, where a temporal summation and a period of refractoriness are assumed, a mathematical approach and a simulation on computer were realized. Particular types of nets were used, namely: nets with topological structures, and fully random nets. The difference between the two types is that the first type has a two-dimensional square structure and depends on the rules of the formation of connection between the neurons, while the second type is realized by means of the probability distribution function governing the formation of the structure of the net.These types of neural nets are analysed by means of a method which permits to obtain various parameters which characterize their behaviour in time and space in terms of the trajectory of the system. Many experiments are also reported; the statistical analyses, made on them, show the great importance and influence of refractoriness on the behaviour of neural networks.In the last part of the work an interesting case is reported, in which the reaction of the net to a disturbance shows that a kind of adaptation takes place, although the structure of the net stays unchanged.On leave of absence from the Lithuanian Academy of Sciences, Vilnius, Lithuanian S.S.R. 相似文献
16.
The significance of variability of biological properties of lipopolysaccharides (LPS) is discussed in the paper within the pathogenesis of infectious process. On the basis of an analysis of published data and of results of independent research of two microorganisms (Yersinia pestis and Francisella tularensis) a conclusion is made on that a biologically inert LPS form (with a weak cytokine-inducing ability, apirogenicity and non-toxicity etc.) is typical of highly pathogenic bacteria. It is suggested that the above phenomenon is biologically expedient. Presumably, the inert LPS transforms to the active form inside a sensitive host and, according to an infection stage, each of them being functionally significant. It is the inert status of LPS that enables the pathogens, at the initial stages, to surmount freely the humoral and cell barriers of host. As the infection progressively aggravates and the proliferation of bacteria modifies itself due to LPS micro- and macroorganisms, its chemical structure and biopolymer conformation change. Both modification mechanisms enhance the LPS toxic potential. In case of a sensitive host, such variations transform the biologically inert LPS into a toxically active form with its function of endotoxin being realized. There is no LPS modification in a host insensitive to such infection, which entails either recovery or prolonged persistence of the pathogen inside the microorganism. 相似文献
17.
E A Thompson 《American journal of human genetics》1976,28(5):442-452
The problem considered is that of estimating the age or rate of increase of a variant on the basis of the present number of replicates observed in a population. In place of previous diffusion equation analyses of age probability distributions, the likelihood for the age is studied on the basis of a discrete branching process model. It is shown that variations inherent in the process of gene evolution in natural populations make it impossible to provide a reliable point estimate of the age of a specified variant, although the likelihood analysis provides a confidence interval which may place useful bounds on the period in which a variant originated. The observed distribution of numbers of several variants may also provide useful information. The problems of estimation are discussed with reference to rare variants arising in American Indian populations. 相似文献
18.
In the course of psychophysiological experiments with a tachistiscopic presentation of geometrical figures as transformations
from a square into a triangle, the subjects worked out a distance scale for optical mouse movement depending on the degree
of similarity between the presented figure and a square. This curve appears as a gradual decrease in the distance during the
figure’s transformation from a square into a triangle. Significant variation in the shape of the curve was revealed upon exclusion
of one of the images of the alphabet. The results are discussed in the context of the lateral inhibition phenomena and compared
with the data of the theory of identification. 相似文献
19.
Four types of hydrosol filters, two reusable (diatomaceous cylinder and fritted-glass funnel) and two disposable (asbestos pad and membrane filter) were challenged with a heavy bacterial suspension to assess their ability to produce sterile filtrates. Two of the four diatomaceous earth filters, the four fritted-glass funnels, and all of the asbestos pads tested generally gave sterile filtrates. However, only one type of filter, one of the membranes in its manufacturer's own holder, consistently gave sterile filtrates. The two other types of membranes usually gave sterile filtrates if tested in one manufacturer's holder, but all types invariably gave contaminated filtrates when tested in another manufacturer's holder. Contaminated filtrates were generally attributed to a poor reusable filter or to a faulty holder used with a disposable filter. If a high degree of certainty is required for sterile heat-labile filtrate, it is suggested that the liquid be passed through two or more filters in a previously tested and proven system. 相似文献
20.
蓝尾石龙子(Eumeces elegans)附睾以2.5%戊二醛和1%锇酸双重固定,按常规制作超薄切片,用H-600透射电镜研究观察精子的超微结构。精子由头部和尾组成,头部由顶体复合体和核组成,尾由颈段、中段、主段和末段组成。头部的顶体囊前部扁平,分为皮质和髓质,顶体下锥由类结晶状的顶体下物质组成,穿孔器顶端尖,、穿孔器基板塞子状,细胞核延长,核内小管缺,核伸展部前端具一电子透明区,核肩圆,核陷窝锥形。颈段具片层结构,近端中心粒和远端中心粒的长轴呈直角,9束外周致密纤维与远端中心粒相应的9束三联微管相联,向后与轴丝相应的9束双联微管相联,中央纤维与2个中央单微管相联。中段短,含有线状嵴的柱状线粒体,由连续的规则小卵状或小梯形致密体组成线粒体间的环状结构,纤维鞘伸入中段,终环紧贴于细胞膜的内表面。线粒体与环状结构的模式为:rs1/mi1,rs2/mi2,rs3/mi3,rs4/mi4,横切面上每圈线粒体数目为10个。主段前面部分具薄的细胞质颗粒区。纤维3和8至主段前端消失。轴丝复合体呈“9 2”型。蓝尾石龙子精子超微结构与已描述的石龙子科种类比较发现,与蜓蜥群和胎生群的石龙子相似;但没有发现石龙子科精子的独征。 相似文献