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1.
Gerald Rosen 《Bulletin of mathematical biology》1980,42(1):95-106
For precise boundary conditions of biological relevance, it is proved that the steadily propagating plane-wave solution to
the Fisher equation requires the unique (eigenvalue) velocity of advance 2(Df)1/2, whereD is the diffusivity of the mutant species andf is the frequency of selection in favor of the mutant. This rigorous result shows that a so-called “wrong equation”, i.e.
one which differs from Fisher's by a term that is seemingly inconsequential for certain initial conditions, cannot be employed
readily to obtain approximate solutions to Fisher's, for the two equations will often have qualitatively different manifolds
of exact solutions. It is noted that the Fisher equation itself may be inappropriate in certain biological contexts owing
to the manifest instability of the lowerconcentration uniform equilibrium state (UES). Depicting the persistence of a mutantdeficient
spatial pocket, an exact steady-state solution to the Fisher equation is presented. As an alternative and perhaps more faithful
model equation for the propagation of certain species properties through a homogeneous population, we consider a reaction-diffusion
equation that features a cubic-polynomial rate expression in the species concentration, with two stable UES and one intermediate
unstable UES. This equation admits a remarkably simple exact analytical solution to the steadily propagating plane-wave eigenvalue
problem. In the latter solution, the sign of the eigenvelocity is such that the wave propagates to yield the “preferred” stable
UES (namely, the one further removed from the unstable intermediate UES) at all spatial points ast→∞. The cubic-polynomial equation also admits an exact steady-state solution for a mutant-deficient or mutant-isolated spatial
pocket. Finally, the perpetuating growth of a mutant population from an arbitrary localized initial distribution, a mathematical
problem analogous to that for ignition in laminar flame theory, is studied by applying differential inequality analysis, and
rigorous sufficient conditions for extinction are derived here. 相似文献
2.
N. Rashevsky 《Bulletin of mathematical biology》1966,28(2):283-308
To the extent that all biological phenomena are perceivable only through their physical manifestations, it may be justified
to assume that all biological phenomena will be eventually represented in terms of physics; perhaps not of present day physics,
but of some “extended” form of it. However, even if this should be correct, it must be kept in mind that representing individual
biological phenomena in terms of physics is not the same as deducing from known physical laws the necessity of biological
phenomena. Drawing an analogy from pure mathematics, it is possible that while every biological phenomenon may be represented
in terms of physics, yet biological statements represent a class of “undecidable” statements within the framework of physics.
Such a conjecture is reinforced by the history of physics itself and illustrated on several examples. The 19th century physicists
tried in vain todeduce electromagnetic phenomena from mechanical ones. A similar situation may exist in regard to biological and social sciences.
Quite generally, the possibility of representing a class B phenomena in terms of class A phenomena does not imply that the
phenomena of class B can be deduced from those of class A.
The consequences of the above on the relation between physics, biology, and sociology are studied. A tentative postulational
formulation of basic biological principles are given and some consequences are discussed. It is pointed out that not only
can the study of biological phenomena throw light on some physical phenomena, but that the study of social phenomena may be
of value for the understanding of the structures and functions of living organisms. The possibility of a sort of “socionics”
is indicated. 相似文献
3.
This article proposes an abstract mathematical frame for describing some features of cognitive and biological time. We focus
here on the so called “extended present” as a result of protentional and retentional activities (memory and anticipation).
Memory, as retention, is treated in some physical theories (relaxation phenomena, which will inspire our approach), while
protention (or anticipation) seems outside the scope of physics. We then suggest a simple functional representation of biological
protention. This allows us to introduce the abstract notion of “biological inertia”. 相似文献
4.
Kevin J. Painter 《Bulletin of mathematical biology》2009,71(5):1117-1147
Chemotaxis, the guided migration of cells in response to chemical gradients, is vital to a wide variety of biological processes,
including patterning of the slime mold Dictyostelium, embryonic morphogenesis, wound healing, and tumor invasion. Continuous models of chemotaxis have been developed to describe
many such systems, yet few have considered the movements within a heterogeneous tissue composed of multiple subpopulations.
In this paper, a partial differential equation (PDE) model is developed to describe a tissue formed from two distinct chemotactic
populations. For a “crowded” (negligible extracellular space) tissue, it is demonstrated that the model reduces to a simpler
one-species system while for an “uncrowded” tissue, it captures both movement of the entire tissue (via cells attaching to/migrating
within an extracellular substrate) and the within-tissue rearrangements of the separate cellular subpopulations. The model
is applied to explore the sorting of a heterogeneous tissue, where it is shown that differential-chemotaxis not only generates
classical sorting patterns previously seen via differential-adhesion, but also demonstrates new classes of behavior. These
new phenomena include temporal dynamics consisting of a traveling wave composed of spatially sorted subpopulations reminiscent
of Dictyostelium slugs. 相似文献
5.
Individual-based models describe the growth dynamics of a population by performing numerical simulations of the life histories
of its individuals. The life of an individual is determined by the basic processes of development, reproduction and mortality.
In this paper the model equations for the development process are stochastic difference equations with discrete time and describe
the time evolution of the status of an individual, in terms of a physiological age. We address the formulation of development
models, when “regression” effects (defined as negative development) on the status of an individual are forbidden; this is
a natural assumption when the physiological age is defined in terms of an abstract non-decreasing indicator measuring the
maturity or the percentage of development. Different stochastic models of the development process are presented, and their
behaviours are analyzed by varying the stochasticity level, which takes into account the degree of intraspecific variability.
Moreover, remarks on the choice of the time step are reported. 相似文献
6.
I. Opatowski 《Bulletin of mathematical biology》1946,8(3):101-119
The calculation of the size of the “sensitive volume” or “control center” in biological effects of radiations is discussed
from the viewpoint of the probabilistic theory of these phenomena based on the concept of random “effective events”. On the
bases of that theory, the resistivity of a microorganism to radiation is defined as its “mean life” under a radiation of one
roentgen per minute. This mean is calculated for processes with and without recovery. The case of variable sensitivity, as
it occurs for instance during mitosis, is discussed in detail. Methods are given to calculate this variability from survival
curves or similar experimental data. The theory is applied to experiments of A. Zuppinger on irradiation ofAscaris eggs with X-rays. 相似文献
7.
Bruce A. Luxon 《Bulletin of mathematical biology》1987,49(4):395-402
Compartmental models of biological or physical systems are often described by a system of “stiff” differential equations.
In this paper an algorithm for solving a system with linear coefficients is presented that employs numerical inversion of
the Laplace transform of the model equations. The inversion algorithms and Gear's backward differentiation method are compared
for two stiff test problems and a differential system governing a 27-compartment model of bile acid transport and metabolism.
The inversion algorithm is reliable, requires modest computation time on a desktop computer and provides better accuracy than
Gear's method, especially for the extremely stiff example. 相似文献
8.
Populations of the Chalcolithic Levant as defined by archaeological excavations has in many cases reinforced the traditional
scheme that a number of “races” are present. This scheme is usually based not only on differential cultural traditions as
identified by archeologists, but also on the available skeletal evidence as discussed by physical anthropologists. Recently
this view has been challenged and it has been suggested that the metrical and anatomical range of variability as identified
within Chalcolithic populations can be subsumed into a single population or “racial” range. This paper examines both the available
biological and archaeological evidence from the Chalcolithic Levant and concludes that there is no strong archaeological or
biological evidence to support a multiple “racial” origin for the Chalcolithic of the Levant. 相似文献
9.
John L. Stephenson 《Bulletin of mathematical biology》1960,22(2):113-138
If in a multiflux system theith flux is given by the integral equation,
, the corresponding equation in the Laplace transforms is Γ
i
= Σ
j
W
ij
Γ
j
+M
i
-the entire system having the matrix formulaion, [I−W]Γ=M. The general solution of this equation and its physical interpretation are discussed. Explicit solutions are given for the
general mammillary and catenary systems and for some capillary exchange problems. The theory is applied to the integrated
from of the fundamental continuity equation to give equations for total quantity of material in the various “compartments.”
If the compartments are uniformly mixed, the integral equation treatment is shown to be mathematically equivalent to the usual
differential equation formulation. 相似文献
10.
N. Rashevsky 《Bulletin of mathematical biology》1945,7(3):151-160
The fundamental equations for the interaction between neurons used in mathematical biophysics seem at first incompatible with
the actual neurophysiological findings on the synaptic transmission. It is shown, however, that those equations may be readily
interpreted in terms of accepted neurophysiological views. What has been termed “synapse” in mathematical biophysics must
be regarded as a complicated network of internuncial neurons. It is shown that, under rather conditions, the number of those
interneurons willstatistically vary with time according to the differential equation postulated for the excitatory and inhibitory factors. The latter are
thus interpreted as the number of excitatory and inhibitory interneurons. 相似文献
11.
John Z. Hearon 《Bulletin of mathematical biology》1951,13(1):23-26
An alternative method is suggested for integrating a certain differential equation associated with a conditioning process,
where the stimulus is presented in the form of a “square wave,” i.e., is of constant intensity during an interval of time
followed by no stimulus during the next interval, etc.
A solution is also given where the stimulus is a rectified sine wave. 相似文献
12.
Anatol Rapoport 《Bulletin of mathematical biology》1947,9(3):109-122
Motivations of two individuals governed by a satisfaction function are assumed to determine their respective “efforts”, which
result in the production of “output”, i.e., objects of satisfaction. In previous papers the sharing of output was prescribed
in advance. In the present article, however, the sharing formula itself is determined to a certain extent by the satisfaction
function. The rate of remuneration per unit of output for each individual is taken to be proportional to the derivative of
the satisfaction of the other individual with respect to the effort of the first. The formulation of this condition leads
to a partial differential equation whose solutions determine the sharing formula. Sharing determined in this way is referred
to as sharing according to the Condition of Mutual Need (C.M.N.). Satisfaction resulting from five different situations are
the computed and compared: (1) an individual producing and consuming alone; (2) two individuals sharing equally and neither
taking the “initiative” to determine the optimum output; (3) sharing determined by C.M.N. with optimum output determined as
in (2); (4) equal sharing but with one individual taking “initiative” in determining optimal output; and (5) sharing determined
by C.M.N. and optiml output by the “initiative” of one individual. further considerations concern conditions imposed on the
arbitrary function occurring in the solution of the above-mentioned partial differential equation. 相似文献
13.
Walter R. Stahl 《Bulletin of mathematical biology》1961,23(4):355-376
Dimensional analysis is discussed from the viewpoint of its basic group properties and shown to be an algebraic Abelian group
that is useful for analysis of physical measurements. The application of the method to various types of equations and the
formulation of previously unclassified dimensions are discussed. Functional dimensional analysis is applied to the problems
of cell size and biomass proliferation; future applications are also noted. A number of dimensionless terms have been formulated
for cellular physiochemical phenomena. They apparently represent the first systematic study of biological dimensionless numbers
recorded in the literature. A dimensionless proliferation law is suggested. A brief analysis of the physical dimensionality
associated with information measures is carried out. Entropy and “information” are shown to be completely different in their
dimensional meaning; other informational measures of possible interest in biology are proposed. The dimensional coding and
computor analysis of biomathematical equations is suggested. 相似文献
14.
Masaru Iizuka 《Journal of mathematical biology》1987,25(6):643-652
We consider a sequence of discrete parameter stochastic processes defined by solutions to stochastic difference equations. A condition is given that this sequence converges weakly to a continuous parameter process defined by solutions to a stochastic ordinary differential equation. Applying this result, two limit theorems related to population biology are proved. Random parameters in stochastic difference equations are autocorrelated stationary Gaussian processes in the first case. They are jump-type Markov processes in the second case. We discuss a problem of continuous time approximations for discrete time models in random environments. 相似文献
15.
Thomas Wennekers 《Cognitive neurodynamics》2008,2(2):137-146
The most prominent functional property of cortical neurons in sensory areas are their tuned receptive fields which provide
specific responses of the neurons to external stimuli. Tuned neural firing indeed reflects the most basic and best worked
out level of cognitive representations. Tuning properties can be dynamic on a short time-scale of fractions of a second. Such
dynamic effects have been modeled by localised solutions (also called “bumps” or “peaks”) in dynamic neural fields. In the
present work we develop an approximation method to reduce the dynamics of localised activation peaks in systems of n coupled nonlinear d-dimensional neural fields with transmission delays to a small set of delay differential equations for the peak amplitudes
and widths only. The method considerably simplifies the analysis of peaked solutions as demonstrated for a two-dimensional
example model of neural feature selectivity in the brain. The reduced equations describe the effective interaction between
pools of local neurons of several (n) classes that participate in shaping the dynamic receptive field responses. To lowest order they resemble neural mass models
as they often form the base of EEG-models. Thereby they provide a link between functional small-scale receptive field models
and more coarse-grained EEG-models. More specifically, they connect the dynamics in feature-selective cortical microcircuits
to the more abstract local elements used in coarse-grained models. However, beside amplitudes the reduced equations also reflect
the sharpness of tuning of the activity in a d-dimensional feature space in response to localised stimuli. 相似文献
16.
N. Rashevsky 《Bulletin of mathematical biology》1969,31(2):417-427
In a preceding paper (Rashevsky, 1969. “Outline of a Unified Approach to Physics, Biology and Sociology.”Bulletin of Mathematical Biophysics,31, 159–198) certain isomorphisms between biological and social systems on the one hand and physical systems on the other were
studied. The notion or relational forces, of which ordinary physical forces are a particular case, was introduced. In the
present paper an attempt is made to establish analogies between stable equilibria in physical systems, equilibria due to physical
forces, and stable equilibria in biological and social systems which are due to purely relational forces. The notion of relational
forces causing multiple equilibria similar to multiple equilibria in some physical systems is studied, and it is outlined
how this notion may possibly help the understanding of such phenomena as polymorphism, metamorphosis and the existence of
rudimentary organs or rudimentary functions. 相似文献
17.
The probable existence of oscillating chemical reactions has been attracting some interest in recent years for their possible
role in explaining certain biological phenomena. Perhaps the simplest model of oscillating reactions is that of Lotka (1910),
which consists of a chain of autocatalytic reactions. Two “reactor systems” in which such a chain of reactions could take
place are considered in this work and are called homogeneous and compartmental models, respectively. The differential equations
governing the temporal behavior of the reacting species are solved on an analog computer, and the conditions under which sustained
oscillations occur are obtained and discussed. Comparisons of the solution obtained in the two models are discussed. 相似文献
18.
N. Rashevsky 《Bulletin of mathematical biology》1967,29(3):643-648
In continuation of previous studies (Bull. Math. Biophysics,28, 283–308; 655–661, 1966;29, 139–152, 1967) it is shown that the difference between the “metric” aspects of physics and the “relational” aspects of biological
and social sciences disappear by accepting the broader definition of “relation”, such as that given in mathematics and logic.
A conceptual superstructure then becomes possible from which all three branches of knowledge may be derived, though none of
them can be derived from the others. 相似文献
19.
I. Opatowski 《Bulletin of mathematical biology》1945,7(4):161-180
A mathematical theory applicable to the biological effects of radiations as chain processes is developed. The theory may be
interpreted substantially as a “hit theory” involving the concepts of “sensitive volume” or “target area”. The variability
of the sensitivity of the organism to the radiation and its capacity of recovery between single hits is taken into account.
It is shown that in a continuous irradiation of a biological aggregate in which the effect of each single hit cannot be observed,
recovery and variation of sensitivity are formally equivalent to each other so that a discrimination between these two phenomena
is possible only by discontinuous irradiation or by using different radiation intensities. Methods for the calculation of
the “number of hits” and for the determination of the kinetics of the processes from “survival curves” or similar experimental
data are given. The relation between the recovery and the Bunsen-Roscoe law is discussed. The case in which the injury of
the organism is dependent on the destruction of more than one “sensitive volume” is also considered. 相似文献
20.
The analytical conditions by which a Volterra's general system describingn interacting species can be put in the “conservative” form have been examined. The cases forn=2, 3, 4 have been analyzed in detail and a general condition for any value ofn is deduced. The analytical and biological constraints following by this approach are compared to the conclusions drawn by
Leigh on the ground of purely biological considerations. 相似文献