周期演化区域上的Logistic捕获模型的动力学分析

为了理解栖息地区域的周期性变化对物种生存的影响,本文研究了周期演化区域上一类具捕获项的Logistic反应扩散模型.我们首先在区域的增长为各向同性这一前提下,将模型转换为固定区域上的反应扩散问题,再利用相关的特征值问题和上下解方法得出模型解的渐近性态.根据所得结论,我们进一步就区域演化对物种的影响给出了生物学解释.     

种群增长的分数阶反应扩散方程解的长时间性态

讨论了种群增长的分数阶反应扩散方程解的长时间行为.在初始状态满足不同条件时证明了其解的渐近稳定性或不存在性.     

具小扩散率种群的生长和灭绝行为

本文研究一类由反应扩散系统的初边问题描述的具常投放率的捕食食饵种群的生长模型,应用上、下解理论分析其解的长时间性态和具小扩散率种群的灭绝行为,给出参数环境．     

具有连续时滞和扩散的非自治Holling捕食系统的持续生存

本文给出了在具有连续时滞和11类功能性反应及扩散的非自治捕食系统中,种群持续生存,周期解存在及全局渐近稳定的充分条件.     

一类具时滞的禽流感模型

针对具扩散和时滞的SI-SIR传染病模型,用特征分析和Lyapunov泛函方法研究了相应的具齐次Neumann边界条件反应扩散方程组解的渐近性质.最后给出数值模拟来说明如果染病鸟类的接触率和染病人类的接触率小,那么全系统的无病平衡点是全局渐近稳定的;但当染病鸟类的接触率大或者和染病人类的接触率大时,变异的禽流感将在人类中扩散.     

反应扩散系统的渐近性态

考虑Lotka-Volterra反应扩散系统,给出了条件,保证其解的渐近性态与对应的常微系统相同。     

一类含时滞的Logistic反应扩散方程的波前解

研究一类含时滞的Logistic滞反应扩散方程的波前解．通过构造合适的上下解,证明了当时滞充分小时,方程存在波前解．用线性化方法,给出了存在波前解的时滞τ取值范围的一个估计．     

具常投放率的反应扩散系统的渐近性质

本文研究一类具常投放率的人口动力学中反应扩散系统的Neumann初边值问题,应用比较函数讨论其解的渐近性态,给出稳态解的存在条件．     

一类带一般功能反应的病原体捕食者-食饵模型中避难所的影响

本文讨论一类SIP型捕食者-食饵-病原体扩散模型,其中捕食者带有一般的功能反应函数.我们主要研究该模型中避难所与扩散的作用.首先通过线性化方法和Lypunov方法分别讨论非负常数平衡解的局部和全局渐近稳定性,然后给出交错扩散导致Turing不稳定的一个充分条件,最后,作为一个应用,我们研究一类带HollingⅡ型功能反应项的捕食者-食饵模型.     

具有分布时滞的一类反应扩散方程的波前解的存在性（英文）

本文考虑了一类广义分布时滞下的反应扩散方程的行波解的存在性问题。运用几何奇异摄动理论和线性链方法,我们研究了反应扩散方程若在没有时滞情形下具有行波解,则只要平均时滞充分小,所给的广义时滞核下这个行波解可以保持存在.     

A system for studying the effect of nutrient solution temperature on plant growth

Summary A simple system is described for growing plants in flowing nutrient solutions at different temperatures.     

In vitro propagation of Alangium salviifolium (L. f.) Wangerin: an important tropical medicinal tree

Plant Cell, Tissue and Organ Culture (PCTOC) - Nanotechnology is a rapidly growing field of science and technology, which deals with development of new solutions by understanding and controlling...     

Acid-induced wall loosening is confined to the accelerating region of the root growing zone

The aims of this study were to quantify developmental differences in acid growth along the root axis and to determine whether these differences were due to alterations in cell turgor or cell wall properties. The apoplast pH of maize roots growing in hydroponics was altered from pH 7.0 to pH 3.4 using 2 mol m^-3 citrate-phosphate buffer or unbuffered solutions. Whole root elongation rate rapidly increased and measurement of the local growth profile indicated that this increase in growth occurred in young cells in the accelerating zone (apical 0-4 mm) while more proximal growing cells were unaffected. Unbuffered solutions of identical pH produced qualitatively similar results. Single cell turgor pressures were unchanged between pH treatments both longitudinally and radially in the root tip. This suggests that the rapid acid-induced changes in growth rate were due to an increase in cell wall loosening. Single cell osmotic pressure and water potential were not significantly different between pH treatments. Acid pH caused net solute import at the root tip to increase 3- to 4-fold, which, coupled with the maintenance of turgor and osmotic pressure, indicated that solute import was not limiting expansion. Thus, acidic solutions cause an increase in growth in accelerating but not decelerating regions. It has been shown for the first time that acid growth in intact, growing roots is not due to differences in turgor, assigning these changes to cell wall properties. Possible cell wall biochemical alterations are discussed.     

Time resolved structure analysis of growing beta-amyloid fibers

Formation of beta-amyloid plaques is a crucial feature of Alzheimer's disease. In the present work time resolved static light scattering was applied to investigate the size and shape of growing beta-amyloid aggregates preceding plaque formation. The beta-amyloid protein with 40 amino acid residues was used. Salt free buffer solutions and solutions with 0.15M NaCl at 37 degrees C served as the aggregation medium. The focus lay on the first 2h following initiation of the aggregation process which corresponds to the protofibril phase. Addition of the NaCl accelerated the aggregation process considerably. Scattering data from aggregation in saline solutions indicated formation of long fibers which suggest interpretation of data with the worm-like chain model. Two important results were revealed: (i) At the end of the time resolved recordings, the worm-like chain model provided a fully adequate picture for the growing aggregates. Chain stiffness is characterised in terms of the persistence length, which is close to 50 nm. The linear mass density of the growing fibers approached a value of two monomers per nm corresponding to single stranded fibers, which is in accordance with presently existing models for the aggregation of beta-amyloid. The fibers finally reached contour lengths of several thousand nanometers. (ii) The plateau values for the persistence length and linear mass density observed in the final regime are gradually approached from higher values. This observation is inconsistent with simple worm-like chains. Rather does it indicate existence of another species during the initial phase of the aggregation, in addition to monomers and fibers. Aside from further insight into fundamental aspects of beta-amyloid aggregation, time resolved static light scattering provides an appropriate tool for assay tests with drugs designed to interfere with the aggregation process.     

Traveling wave solutions of a nonlinear reaction–advection equation

 We establish the existence of traveling wave solutions for a nonlinear partial differential equation that models a logistically growing population whose movement is governed by an advective process. Conditions are presented for which traveling wave solutions exist and for which they are stable to small semi-finite domain perturbations. The wave is of mathematical interest because its behavior is determined by a singular differential equation and those with small speed of propagation steepen into a shock-like solutions. Finally, we indicate that the smoothing presence of diffusion allows wave persistence when an advective slow moving wave may collapse. Received: 24 November 1997 / Revised version: 13 July 1998     

The Mechanism of Staining Explained on A Chemical Basis. I. The Reaction Between Dyes,Proteins and Nucleic Acid

Basic dyes cause an increase in hydrogen-ion concentration when added to a solution containing nucleic acid, the both solutions were originally at the same pH. Acid dyes have no effect on nucleic acid solutions. Basic dyes show the same behavior when treated with solutions of typical proteins. Acid dyes when treated with proteins show an analogous effect but in the opposite direction. The only adequate explanation found is that there is a definite reaction between the dye ions and the oppositely charged ions of protein or nucleic acid. The bearing of these results on the theory of staining is discussed. The growing recognition of the dominance of chemical forces in colloidal adsorption behavior is indicated, and certain of the experimental bases for this recognition are pointed out and discussed.     

The Mechanism of Staining Explained on A Chemical Basis. I. The Reaction Between Dyes, Proteins and Nucleic Acid

Basic dyes cause an increase in hydrogen-ion concentration when added to a solution containing nucleic acid, the both solutions were originally at the same pH. Acid dyes have no effect on nucleic acid solutions. Basic dyes show the same behavior when treated with solutions of typical proteins. Acid dyes when treated with proteins show an analogous effect but in the opposite direction. The only adequate explanation found is that there is a definite reaction between the dye ions and the oppositely charged ions of protein or nucleic acid. The bearing of these results on the theory of staining is discussed. The growing recognition of the dominance of chemical forces in colloidal adsorption behavior is indicated, and certain of the experimental bases for this recognition are pointed out and discussed.     

The effects of variable nitrogen and phosphorous concentrations on Eriophorum vaginatum tillers grown in nutrient solutions

Eriophorum vaginatum tillers were collected at Eagle Creek, Alaska and cultivated in aerated solutions under controlled environmental conditions. The nutrient solutions contained traces, 1.05 and 21 mg l⁻¹ N (nitrate) and traces, 0.15 and 3.10 mg l⁻¹ P (phosphate), pH was maintained at 5.5. The high N, 21 mg l⁻¹, and P, 3.18 mg l⁻¹, nutrient solution produced significant biomass increases. Functional leaf areas were significantly enhanced by high N and P doses in the solutions. Root surface areas varied considerably between treatments; however, significant differences were not found. The mean root surface area of a tiller reached 126 cm² (range 35–290 cm²), whereas the functional leaf area was 6.8 cm² (range 3.3–20.3 cm²). Tillers growing in the highest N + P solutions produced twice the number of daughter tillers as tillers growing in solutions with trace amounts of N and P.     

Cell size and mutual cell adhesion. II. Evidence for a relation between cell size, long-range electrostatic repulsion and intercellular adhesiveness during density-regulated growth in suspension.

The strength of the long-range electrostatic repulsion forces on HeLa cells is measured by agglutinative titration using low molecular weight polylysine (M.W. 11,000). Repulsion forces, found to be present on the smaller HeLa cells from density-inhibited suspension cultures, are weakened by incubation of the cells in hypotonic NaCl solutions. Repulsion forces, found to be absent on the larger cells from fast growing cultures, can be induced on these cells by incubation in hypertonic NaCl solutions. Both effects of anisotonicity are reversible, and disappear on restoration of the medium to normal tonicity. Induction of repulsion forces on fast growing cells is prevented by previous treatment of the cells with neuraminidase. Neuraminidase also abolishes repulsion on density-inhibited cells. It is proposed that alterations of the cell size, produced by anisotonicity or occurring during growth in isotonic suspension medium, affect mutual cell adhesiveness by modifying the strength of the repulsion forces generated by cell surface sialic acids.     

Kinetics of biopolymerization on nucleic acid templates

The kinetics of biopolymerization on nucleic acid templates is discussed. The model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation. Each growth center [growing chain end plus enzyme(s)] moves one template site at a time, but blocks L adjacent sites. Solutions are found for the probability n_j(t) that a template has a growing center that occupies the sites j — L + 1,…, j at time t. Two special sets of solutions are considered, the uniform-density solutions, for which n_j(t) = n, and the more general steady-state solutions, for which dn_j(t)/dt = 0. In the uniform-density case, there is an upper bound to the range of rates of polymerization that can occur. Corresponding to this maximum rate, there is one uniform solution. For a polymerization rate less than this maximum, there are two uniform solutions that give the same rate. In the steady-state case, only L = 1 is discussed. For a steady-state polymerization rate less than the maximum uniform-density rate, the steady-state solutions consist of either one or two regions of nearly uniform density, with the density value(s) assumed in the uniform region(s) being either or both of the uniform-density solutions corresponding to that polymerization rate. For a steady-state polymerization rate equal to or slightly larger than the maximum uniform-density rate, the steady-state solutions are nearly uniform to the single uniform-density solution for the maximum rate. The boundary conditions (rate of initiation and rate, of release of completed chains from the template) govern the choice among the possible solutions, i.e., determine the region(s) of uniformity and the value(s) assumed in the uniform region(s).