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1.
B. L. Jones 《Bulletin of mathematical biology》1979,41(1):119-127
Some models for selection in enzyme coupled, selfreproducing, macromolecular systems are considered. The enzyme coupling provides
a mechanism for the buildup of systems with large information content. The concept of “selective value” and criteria for selection
is discussed. 相似文献
2.
Alber M Glimm T Hentschel HG Kazmierczak B Zhang YT Zhu J Newman SA 《Bulletin of mathematical biology》2008,70(2):460-483
A recently proposed mathematical model of a “core” set of cellular and molecular interactions present in the developing vertebrate
limb was shown to exhibit pattern-forming instabilities and limb skeleton-like patterns under certain restrictive conditions,
suggesting that it may authentically represent the underlying embryonic process (Hentschel et al., Proc. R. Soc. B 271, 1713–1722, 2004). The model, an eight-equation system of partial differential equations, incorporates the behavior of mesenchymal cells as
“reactors,” both participating in the generation of morphogen patterns and changing their state and position in response to
them. The full system, which has smooth solutions that exist globally in time, is nonetheless highly complex and difficult
to handle analytically or numerically. According to a recent classification of developmental mechanisms (Salazar-Ciudad et
al., Development 130, 2027–2037, 2003), the limb model of Hentschel et al. is “morphodynamic,” since differentiation of new cell types occurs simultaneously with
cell rearrangement. This contrasts with “morphostatic” mechanisms, in which cell identity becomes established independently
of cell rearrangement. Under the hypothesis that development of some vertebrate limbs employs the core mechanism in a morphostatic
fashion, we derive in an analytically rigorous fashion a pair of equations representing the spatiotemporal evolution of the
morphogen fields under the assumption that cell differentiation relaxes faster than the evolution of the overall cell density
(i.e., the morphostatic limit of the full system). This simple reaction–diffusion system is unique in having been derived
analytically from a substantially more complex system involving multiple morphogens, extracellular matrix deposition, haptotaxis,
and cell translocation. We identify regions in the parameter space of the reduced system where Turing-type pattern formation
is possible, which we refer to as its “Turing space.” Obtained values of the parameters are used in numerical simulations
of the reduced system, using a new Galerkin finite element method, in tissue domains with nonstandard geometry. The reduced
system exhibits patterns of spots and stripes like those seen in developing limbs, indicating its potential utility in hybrid
continuum-discrete stochastic modeling of limb development. Lastly, we discuss the possible role in limb evolution of selection
for increasingly morphostatic developmental mechanisms. 相似文献
3.
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
4.
The effects (and interaction) of two solution concentrations of Mg (50, 500, μM) and two of K (250, 4250 μM) on the growth of micropropagated plants of “F. 12/1” and “Colt” were investigated using a flowing solution culture system.
Magnesium inflow and growth of “Colt” and “F. 12/1” were inhibited to a similar extent by an increased concentration of K
in the nutrient solution. However, the consequences of this inhibition were different. Reduced inflow of Mg in “F. 12/1” caused
Mg deficiency symptoms at high and low concentrations of K, whereas this only occurred with a combination of high K concentration
and low Mg concentration in “Colt”. The distribution of dry matter within the plant was significant in determining susceptibility
to Mg deficiency. Since “F. 12/1” has a smaller root:shoot ratio than Colt it is unable to sustain the same concentration
of Mg in leaves as “Colt” irrespective of external K concentration. The molar ratio of K:Mg in soil solutions should remain
<8.5:1 in order to ensure maximum growth of “F. 12/1” and “Colt”.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
Anatol Rapoport 《Bulletin of mathematical biology》1961,23(4):321-335
As a “base line” of memorization performance, the behavior of a “perfect learner” is considered. He is characterized by a
perfect memory and by the ability to choose the best search procedure in problems where the correct response from a given
repertoire is to be found to each of several stimuli under the condition of “right” and “wroing” promptings by the experimenter.
Expected learning curves are derived for the case of disjoint response repertoires associated with the stimuli under cyclic
and random presentation of the stimuli and for the case of a single response repertoire (a one-to-one matching problem) under
cyclic presentation. 相似文献
6.
Kenji Konishi Tsutomu Tamura Ryoko Zenitani Takeharu Bando Hidehiro Kato Lars Walløe 《Polar Biology》2008,31(12):1509-1520
The annual trend in energy storage in the Antarctic minke whale was examined using catch data from all 18 survey years in
the Japanese Whale Research Program (JARPA). Regression analyses clearly showed that blubber thickness, girth and fat weight
have been decreasing for nearly 2 decades. The decrease per year is estimated at approximately 0.02 cm for mid-lateral blubber
thickness and 17 kg for fat weight, corresponding to 9% for both measurements over the 18-year period. Furthermore, “date”,
“extent of diatom adhesion”, “sex”, “body length”, “fetus length”, “latitude”, “age” and “longitude” were all identified as
partially independent predictors of blubber thickness. The direct interpretation of this substantial decline in energy storage
in terms of food availability is difficult, since no long-term krill abundance series is available. However, an increase in
the abundance of krill feeders other than minke whales and a resulting decrease in the krill population must be considered
as a likely explanation. 相似文献
7.
This article is a review of scientific publications, in which issues of pathogenetics of multifactorial diseases (MFDs) are
considered from the viewpoint of evolution and ontogeny. Concepts explaining significance of evolutionary processes in the
formation of genetic architecture of human chronic diseases (“thrifty” genomes and phenotypes, “drifty genes,” decanalization)
are analyzed. The roles of natural selection and genetic drift in the formation of hereditary diversity of genes for susceptibility
to MFDs are considered. The modern concept of “disease ontogeny” (somatic mosaicism, loss of heterozygosity, paradominant
inheritance, epigenetic variability) is discussed. It is demonstrated that the evolutionary and ontogenetic approaches to
analysis of genimuc and other “-omic” data are essential for understanding the biology of diseases. 相似文献
8.
A. M. Semenov 《Microbial ecology》1991,22(1):239-247
Three groups of physiological processes in microorganisms are considered the physiological basis of oligotrophy: the greater
substrate affinity of the oligotrophs' transport systems, efficient or “economical” metabolism, and existence of a “master
reaction” or “rate-determining steps” controlling the rate of metabolism. Heterotrophic microorganisms are divided into three
unequal groups according to “reaction norma.” Two groups representing the extremes are small groups with the “narrow” reaction
norma, regarding the concentrations and structure of the assimilated organic compounds and variability limits of the physiological
characteristics mentioned above. The third, intermediate group includes the majority of microorganisms with the “wide” reaction
norma. 相似文献
9.
This is a model for the time-variation of helium concentrations in lung wash-out curves. The helium (or other inert gas) is
in a spirometer, which is connected by a common dead space to two separate dead spaces, each of which leads into a chamber.
The chambers expand and contract, thus taking in some helium at each “breath.” Equations for the changes in helium concentration
in each part of the system are set up; in this way difference equations are derived for the amount of helium in the spirometer
after each breath, in and out, and complete solutions when the initial concentration is zero in all parts of the system except
the spirometer. A simple solution when the chambers do not essentially differ (“equal ventilation”) is compared with the general
case. The concept of “unequal lung ventilation” is discussed critically in relation to the model; some physiological interpretations
are also mentioned. Numerical examples are given to show the effect of changes in various constants, in particular tidal volumes,
end volumes, and the common dead space. 相似文献
10.
I. N. Konareva 《Neurophysiology》2006,38(3):201-208
Modifications of different EEG rhythms induced by a single neurofeedback session (by the EEG characteristics) directed toward
an increase in the ratio of the spectral powers (SPs) of the α vs θ oscillations were compared with the psychological characteristics of the tested subjects (the group included 30 persons).
A generally accepted neurofeedback technique was used; the intensity of acoustic white noise served as the feedback signal.
EEG potentials were recorded from the C3 and C4 leads. Psychological testing was carried out using Eysenck’s (EPQ), Rusalov’s
(OST), and (16 PF) questionnaires. The directions of changes in the SPs of EEG frequency components were found to significantly
correlate with some individuality-related peculiarities of the tested subjects. The SP of the δ rhythm correlated with the
EPQ scale “neuroticism,” OST scale “social plasticity,” and 16 PF factors H (“parmia”), I (“premsia”), and Q3 (“self-control of behavior”). The SP of the θ component demonstrated correlations with the OST scales “ergisity,” “plasticity,”
and “social temp” and with 16 PF factors M (“autia”), Q4 (“frustration”), and Q1 (“exvia”). The SP of the α rhythm correlated with 16 PF factors Q3 (“self-control of behavior”), G (“strength of superEgo”), O (“hypothymia”), L (“protension”), and N (“shrewdness”). The SP
of the β rhythm correlated with the OST scale “emotionality,” while that of the γ rhythm showed correlations with the 16 PF
indices L (“protension”) and M (“autia”). Changes in the ratio of the α vs θ SPs correlated with the EPQ scale “neuroticism.” Thus, our data confirm the statement that a high individual variability
of the results of a single (first in the series) neurofeedback session is to a great extent related to peculiarities of the
individual psychological pattern of the subject.
Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 239–247, May–June, 2006. 相似文献
11.
Jorge C. S. André Daniela R. Lopes 《The International Journal of Life Cycle Assessment》2012,17(3):350-361
Purpose
The purpose of this paper is to enhance the mathematical and physical understanding of practitioners of uncertainty analysis of life cycle inventory (LCI), on the application of possibility theory. The main questions dealt with are (1) clear definition of the terms—“necessity–possibility,” “probability,” “belief–plausibility,” and of their mutual relationships; (2) what justifies the substitution of classical probability for possibility; (3) mutual comparison of, and transformations in both senses between probability and possibility uncertainty measures; (4) how to construct meaningful input possibility measures from available probabilistic/statistic information; and (5) comparative analysis of the solutions of the problem of data uncertainty propagation in LCI, afforded, respectively, by probabilistic Monte Carlo simulation and possibilistic fuzzy interval arithmetic. 相似文献12.
A permeant ion is known to create in the channel pore a local electrical field, the intensity of which exceeds the intensity
of an electrical field produced by the membrane potential. In our study, we consider a sodium channel model, in which the
effects of a permeant ion, an inactivating particle, and pharmacological agents on mobile charged groups of the channel are
semi-phenomenologically taken into account by using motion equations for a generalized structural variable. Stationary solutions
for the equation correspond to “open,” “closed,” and “inactivated” channel states. Because of this, the channel free energy
profile, as a function of the structural variable, has three local minima. The three energy values of these states depend
both on the electrical field applied externally and on the near-membrane concentrations of permeant ions and acting pharmacological
agents. Sodium channel activation and inactivation kinetics are considered resulting from relative changes of the free energy
typical of the above three states of the channel. The results we obtained in the course of channel activation and inactivation
modeling and their voltage dependence are qualitatively consistent with the commonly known experimental data. The proposed
model allows one to qualitatively predict the dependence of the sodium channel kinetic characteristics on the concentrations
of permeant ions and pharmacological agents. 相似文献
13.
Approximately 1 500 angiosperm species, in previous papers, have been sampled for the assessment of the amino acids (a. a.)
in their nectar. We reaffirm that the findings provide statistically significant data linking differences in the concentration
with pollinator type. Flowers that are pollinated by animals that have alternative sources of protein-building a. a.’s show
lower a. a. concentration than those that are not. There is a tendency for woody plant nectar a. a.’s to be less concentrated
than those of herbaceous plants, but there can be “phylogenetic constraints” which may reduce the correlations of a. a. concentration
with pollinator type and with life form. The individual a. a.’s form complements which are qualitatively extremely constant
within species. Proline is a normal constituent of many nectars and does not necessarily indicate contamination of the nectar
by pollen. Criticism of our findings byGottsberger & al. (1984) is answered by reference to our previous publications and those of other workers, and to the presentation of
data from California native species, not published previously. All previous postulates are borne out by these new data with
the exception of positive correlations of a. a. concentration with “primitive” and “advanced” floral characteristics taken
one at a time, which appear to be inconsistent and are affected strongly by the nature of the family in which they occur.
Summary data are provided for families and genera which indicate that high or low a. a. concentration can typify certain families
and genera of both relatively “primitive” and relatively “advanced” nature. Needs for future research on an ecosystem basis
are quoted. 相似文献
14.
N. Rashevsky 《Bulletin of mathematical biology》1969,31(4):789-795
The author's theory of the adoption of certain types of behavior patterns (Rashevsky, N., 1957, “Contributions to the Theory
Initiative Behavior”.Bull. Maths. Biophysics,19, 91–119; 1968,Looking at History through Mathematics, Cambridge, Massachusetts: M.I.T. Press) consisting of elementary behaviors for each of which there is an opposite one and
the two are mutually exclusive, is applied to describe the changes in the general type of behavior of a society. The elementary
acts of which the whole problem consists may be either overt activities or beliefs or opinions. The general behavior patternsadopted by the society are considered as the “proper” or “just” ones. Any deviation from it in either one or more of the component
elementary behaviors is considered as “unjust” and is subject to some punitive action. The total number of possible mutually
exclusive behavior patterns is very large but finite. Within this very large range of possible patterns, we find that this
notion of justice is relative, because changes from any behavior pattern to any other may occur. It is further shown that
the amount of punishment for the deviation from the accepted pattern in order to be effective as well as efficient must be
applied in different ways to different individuals even for the same transgression. 相似文献
15.
K. Vit 《Bulletin of mathematical biology》1978,40(3):359-368
The two-element muscle model considered consists of a contractile element defined by a hyperbolic force-velocity relation
connected in series with an “exponential spring”. Differential equations for the isometrically developed force during a tetanic
contraction and the corresponding contractile element shortening velocity are derived and their stability is investigated.
Analytical solutions to both equations are obtained. Two numerical examples are given, the second chosen to illustrate pressure-induced
hypertrophy of a cardiac muscle. 相似文献
16.
Studies on drawing circles with both hands in the horizontal plane have shown that this task is easy to perform across a
wide range of movement frequencies under the symmetrical mode of coordination, whereas under the asymmetrical mode (both limbs
moving clockwise or counterclockwise) increases in movement frequency have a disruptive effect on trajectory control and hand
coordination. To account for these interference effects, we propose a simplified computer model for bimanual circle drawing
based on the assumptions that (1) circular trajectories are generated from two orthogonal oscillations coupled with a phase
delay, (2) the trajectories are organized on two levels, “intention” and “motor execution”, and (3) the motor systems controlling
each hand are prone to neural cross-talk. The neural cross-talk consists in dispatching some fraction of any force command
sent to one limb as a mirror image to the other limb. Assuming predominating coupling influences from the dominant to the
nondominant limb, the simulations successfully reproduced the main characteristics of performance during asymmetrical bimanual
circle drawing with increasing movement frequencies, including disruption of the circular form drawn with the nondominant
hand, increasing dephasing of the hand movements, increasing variability of the phase difference, and occasional reversals
of the movement direction in the nondominant limb. The implications of these results for current theories of bimanual coordination
are discussed.
Received: 23 June 1998 / Accepted in revised form: 20 April 1999 相似文献
17.
Edward D. Weinberger 《Bulletin of mathematical biology》1991,53(4):623-638
A generalization of the “constant overall organization” constraint of Eigen's quasispecies and hypercycle models, called herein
“global population regulation”, is shown to lead to mathematically tractable spatial generalizations of these two models.
The spatially uniform steady state of Eigen's quasispecies model is shown to be stable and globally attracting for all possible
values of the mutation and replication rates. In contrast, the spatially and temporally uniform solutions to the hypercycle
with fewer than five members, the only ones insensitive to stochastic perturbations, are shown to be unstable, and a lower
bound to the spatial inhomogeneities is obtained. The prospect that the spatially localized hypercycle might be immune to
various instabilities cited in the literature is then briefly considered. Although spatial localization makes possible a much
richer dynamical repertoire than previously considered, it is also more difficult to understand how Darwinian selection of
hypercycles could result in a unique genetic code. 相似文献
18.
19.
Anatol Rapoport 《Bulletin of mathematical biology》1955,17(1):15-33
Some principles of information theory are utilized in the design of neural nets of the McCulloch-Pitts type. In particular,
problems are considered where signals from several neurons must pass through a single one, thus resulting in a “bottleneck”
in the flow of information, an abstract model of the corresponding bottleneck from the retina to the optic nerve. The first
part of the paper deals with a construction of a McCulloch-Pitts net in which the redundancy in the messages originating in
two neurons is utilized so that the messages can be sent over a single neuron with little loss of information. In the second
part, messages from a set of neurons are “pumped” into two channel neurons. The optimum connection scheme is computed for
this case, i.e, one resulting in a minimum loss of information. Possible biological implications of this approach are indicated. 相似文献
20.
“Fairmount 1 thorny” (“FM1 thorny”) (a Rosa multiflora Thunb ex. J. Murr.) and a thornless sport of “FM1 thorny” (“Fairmount 1” (“FM1”)) were established in vitro to investigate
chimeral segregation under various levels of BA and to obtain a pure thornless rose. While the chimeral thornless sport was
expected to segregate in vitro and yield both thorny and thornless plantlets, “FM1 thorny” was to yield only thorny plants.
“FM1” segregated in vitro into its constituent genotypes and yielded thorny and thornless plantlets, suggesting that “FM1”
is chimeral. “FM1 thorny” produced only thorny plants in vitro. These results indicate that the “FM1 thorny” clone was not chimeral (pure thorny) and that the thornless regenerates of “FM1”
did not develop via somaclonal variation. There was a significant linear relationship between increasing BA concentration
and the percentage of thorny plants. Among a population of 690 tissue culture derived plants from all the BA experiments,
6 plants were classified as pure thornless plants 1 year later. 相似文献