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1.
On the mathematical theory of rumor spread 总被引:1,自引:0,他引:1
The applicability of the theory of random nets to the theory of rumor spread is shown. In particular the “weak connectivity”
of the net appears as the saturation fraction of “knowers” in a thoroughly mixed population through which a message diffuses
where each knower tells the message to a finite average number of individuals. Further it is shown how the time course equation
of rumor spread, where time is measured by the number of “removes” from the starters, can be translated into an ordinary continuous
time course equation if the distribution of the telling intervals is known. 相似文献
2.
Anatol Rapoport 《Bulletin of mathematical biology》1952,14(1):35-44
The spread of excitation in a “random net” is investigated. It is shown that if the thresholds of individual neurons in the
net are equal to unity, a positive steady state of excitation will be reached equal to γ, which previously had been computed
as the weak connectivity of the net. If, however, the individual thresholds are greater than unity, either no positive steady
state exists, or two such states depending on the magnitude of the axone density. In the latter case the smaller of the two
steady states is unstable and hence resembles an “ignition point” of the net. If the initial stimulation (assumed instantaneous)
exceeds the “ignition point,” the excitation of the net eventually assumes the greater steady state.
Possible connections between this model and the phenomenon of the “preset” response are discussed. 相似文献
3.
A “probabilistic” rather than a “deterministic” approach to the theory of neural nets is developed. Neural nets are characterized
by certain parameters which give the probability distributions of different kinds of synaptic connections throughout the net.
Given a “state” of the net (i.e., the distribution of firing neurons) at a given moment, an equation for the state at the
next moment of quantized time is deduced. Certain very special cases involving constant distributions are solved. A necessary
condition for a steady state is deduced in terms of an integral equation, in general non-linear. 相似文献
4.
An equation is derived from the spread of a “state” by contact through a thoroughly mixed population, in which the probability
of transmission depends both on the over-all duration of the process and on the time an individual has been in the “state.”
Cases in which this probability is a function of only one or the other of the two “times” are worked out. It is shown that
in the case of dependence on “private time” alone the asymptotic value of the fraction of the population effected is the same
as that derived by the random net approach. 相似文献
5.
Two control units, the switching and the two factor discriminating net are described. They are derived as a consequence of
the enzymic oscillatory behavior induced by substrate “perturbation”.
A complex network encompassing long sequences of metabolic reactions is constructed and the organization of cellular metabolic
activities in well defined “regimes” and “states” inferred. 相似文献
6.
A common method for measuring uptake by intact roots in situ is the depletion method, wherein intact fine roots are separated from soil and placed in nutrient solution. The difference
between initial and final amounts of nutrient in solution is attributed to root uptake. Variations on this method include
applying pretreatment solutions, training roots to grow into bags or trays, and varying concentrations of nutrient solution.
We tested whether variations in methods affected measured net uptake rates of NH
4
+
, NO
3
−
, and PO
4
3−
. Intact roots of 60 year-old sugar maple (Acer saccharum Marsh.), red pine (Pinus resinosa Ait.), and Norway spruce (Picea abies (L.) Karst.) were given one of four treatments prior to measuring net uptake. “Trained” roots were grown in a sand-soil mixture.
“Recovered” roots were excavated and allowed to recover in nutrient solution for two or four days (“two-day recovery” and
“four-day recovery”, respectively). “No recovery” roots were excavated and used immediately in experiments. We exposed roots
to three concentrations of nutrient solutions to observe the effects of initial nutrient solution concentration. Initial nutrient
solution concentration was an important source of variation in measured uptake rates, and N uptake was stimulated by low antecedent
concentrations. We found no significant differences in net uptake rates between pretreatments for any of the species studied,
indicating that our pretreatments were not effective in improving measurement of uptake. Such pretreatments may not be necessary
for measuring net uptake and may not hinder the comparison of rates measured using variations of the depletion method. 相似文献
7.
Anatol Rapoport 《Bulletin of mathematical biology》1957,19(4):257-277
The probabilistic theory of random and biased nets is further developed by the “tracing” method treated previously. A number
of biases expected to be operating in nets, particularly in sociograms, is described. Distribution of closed chain lengths
is derived for random nets and for nets with a simple “reflexive” bias. The “island model” bias is treated for the case of
two islands and a single axon tracing, resulting in a pair of linear difference equations with two indices. The reflexive
bias is extended to multiple-axon tracing by an approximate method resulting in a modification of the random net recursion
formula. Results previously obtained are compared with empirical findings and attempts are made to account for observed discrepancies. 相似文献
8.
The relational structure of RNA, DNA, and protein bears an interesting similarity to the determination problem in category
theory. In this paper, we present this deep-structure similarity and use it as a springboard for discussing some abstract
properties of coding in various systems. These abstract properties, in turn, may shed light on the evolution of the DNA world
from a semiotic perspective. According to the perspective adopted in this paper, living systems are not information processing
systems but “meaning-making” systems. Therefore, what flows in the genetic system is not “information” but “value.” We define
meaning, meaning-making, and value and then use these terms to explain the abstract dynamics of coding, which can illuminate many forms of sign-mediated activities
in biosystems. 相似文献
9.
Ryne A. Palombit 《International journal of primatology》1992,13(2):143-182
Vocal communication in wild long-tailed macaques (Macaca fascicularis) is described in terms of (1) a preliminary vocal repertoire
and the situations in which calls occur in the natural habitat of this species and (2) quantitative measurement of the natural
occurrence of calls in the field. Although a number of calls are relatively discrete (e.g., a male loud call), gradation is
pronounced for both wide-spectrum (“harsh”) and narrow-spectrum (“clear”) vocal signals. Thirteen general types of harsh calls
are identified provisionally as elements of the vocal repertoire. The exact number of discrete clear calls contributing to
the vocal repertoire could not be ascertained precisely, but these calls were classified operationally into six broadly acoustically
different classes in order to measure natural vocal behavior. Vocalizations tended to occur in temporal “clusters” during
sample, periods. Narrow-band clear or “coo” calls were more frequently performed by macaques than wide-band harsh calls. The
possible functional implications of the correlated occurrence of multiple vocal signals are discussed. 相似文献
10.
Ernesto Trucco 《Bulletin of mathematical biology》1952,14(4):365-374
As shown by A. Rapoport (1952), when a very brief stimulation or “instantaneous input” is applied to a random net, the subsequent
events are determined by the parameters of the net as follows: If the axon densitya is sufficiently large and the fraction γ of the neurons initially stimulated exceeds a certain value γ1 (theover-all threshold of the net for instantaneous stimulation), excitation will spread through the net until a steady state is reached
in which a fraction γ2 ⩾ γ1 of the neurons is firing (“ignition phenomenon”). If γ < γ1 the activity in the net dies out. However, if the axon density is too small, the activity will ultimately die out, no matter
how large the fraction of initially stimulated neurons. Thus there exists a limiting valueA of the axon density below which the net cannot “ignite”. ThisA is a function ofh, theindividual threshold of the neurons constituting the net (we assume hereh≥2, since forh=1 the situation is essentially different). Geometrically γ1 and γ2 are determined as the two intersection points of a straight line with a sigmoid curve. Whena<A the two curves do not intersect and fora=A they are tangent.
In this paper the “tangency case” is investigated and the general features of the functionA(h) are determined. It is shown thatA increases monotonically withh (as one would expect). For all values ofh>1 we haveA(h)>h, but the fractionA(h)/h and the derivativedA(h)/dh approach unity ash increases. An analytical expression of the functionA(h) valid for very large values ofh is derived. 相似文献
11.
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
12.
Spread of information through a population with socio-structural bias: I. Assumption of transitivity 总被引:3,自引:0,他引:3
Anatol Rapoport 《Bulletin of mathematical biology》1953,15(4):523-533
A previously derived iteration formula for a random net was applied to some data on the spread of information through a population.
It was found that if the axon density (the only free parameter in the formula) is determined by the first pair of experimental
values, the predicted spread is much more rapid than the observed one. If the successive values of the “apparent axon density”
are calculated from the successive experimental values, it is noticed that this quantity at first suffers a sharp drop from
an initial high value to its lowest value and then gradually “recovers”.
An attempt is made to account for this behavior of the apparent axon density in terms of the “assumption of transitivity”,
based on a certain socio-structural bias, namely, that the likely contacts of two individuals who themselves have been in
contact are expected to be strongly overlapping. The assumption of transitivity leads to a drop in the apparent axon density
from an arbitrary initial value to the vicinity of unity (if the actual axon density is not too small). However, the “recovery”
is not accounted for, and thus the predicted spread turns out to beslower than the observed. 相似文献
13.
The home range of resident animals is considered as “familiar area” including a “foraging area.” It has been revealed that
the activity of an average animal unit in the “foraging area” could be approximated by normal distribution. Estimation of
activity distribution in the “familiar area” (beyond the “foraging area”) was impeded by means of marking since it might be
difficult to record distant movements, and the method does not provide an essential body of data. In the case of the common
shrew Sorex araneus, the “familiar area” was estimated using pitfall as animals evade them in the known areal. The “foraging area” radius of
the average shrew was taken to be 30 m (95% of the animal unit activity), the radius of “familiar area” was within the range
of 180–240 m. The “foraging area” was expected to provide the animal with vital resources, and the “familiar area” reflects
its need for exploratory activity. 相似文献
14.
C. C. Walker 《Bulletin of mathematical biology》1984,46(5-6):845-857
Experiments on random binary, ternary, etc. (P=2, 3,…, 10) switching nets are reported. Behavioral cycle lengths are examined as functions of output variety,P, input connectance,K, and net size,N. Overall, output variety appears an influential, well-behaved net property. Strong, but well-behaved interactions appear
among net variables. In high connectance nets, median cycle length grows approx. asP
N/2. Other factors constant, one-connected nets show the shortest cycles, and connectance effects appear to converge asymptotically
aroundN. Data for cycle length as a function of net size suggest a concavity not compatible with the Kauffman “square root law” (Kauffman,
1969). Evidence of a positive relationship between cycle length and run-in length is found in two-input nets; weaker evidence
is obtained that in higher connectance nets this relationship becomes negative in sign. The “modular complexity” ofP>2 nets is examined briefly. 相似文献
15.
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
16.
Jacob Towber 《Bulletin of mathematical biology》1962,24(3):335-343
By “neural net” will be meant “neural net without circles.” Every neural net effects a transformation from inputs (i.e., firing
patterns of the input neurons) to outputs (firing patterns of the output neurons). Two neural nets will be calledequivalent if they effect the same transformation from inputs to outputs.
A canonical form is found for neural nets with respect to equivalence; i.e., a class of neural nets is defined, no two of
which are equivalent, and which contains a neural net equivalent to any given neural net.
This research was supported by the U.S. Air Force under Contract AF 49(638)-414 monitored by the Air Force Office of Scientific
Research. 相似文献
17.
Hilary O. Box 《Primates; journal of primatology》1977,18(2):395-400
Four male and four female marmoset monkeys were observed to make a total of 5,600 “right”, “left”, or “both” hand responses
over seven categories of spontaneous behaviour. Significant and consistent hand preferences were shown for the majority of
monkeys in two of the categories of behaviour, but not in the other five. The paper considers some of the methodological difficulties
involved in recording “handedness” in a species such as the common marmoset. 相似文献
18.
Mackay AL 《Journal of biosciences》2003,28(5):539-546
Conclusion We must conclude that the sub-title of Bernal’s “The Social Function of Science” — “What science does: what science could
do” is still the relevant challenge and indicates Bernal’s chief contribution, besides the foundation of molecular biology
to our civilization. It is manifest that resources spent on armaments are a monstrous pathological symptom of our social structure.
The ancient problem of “what is property” and what may be “owned” and by whom or by what organs of society is awakening. 相似文献
19.
The objective of this article is to study the effect of 5-aminolevulinic acid (ALA) and enhanced chlorophyll content, antioxidative
enzymes and photosynthesis rate by foliar application of ALA. We evaluated three concentrations (control-distilled water,
T1-50 mg l−1, T2-150 mg l−1, T3-250 mg l−1) of ALA and seven cultivars, “Sanchidaye” (Sa-1), “Lichuandasuomian” (Li-1), “Aijiaohuang” (Ai-1), “Qingyou” No. 4 (Qi-1),
“Aikang” No. 5 (Ak-1), “Hanxiao” (Ha-1) and “Shulv” (Sl-1). “Ak-1” showed strongest response of POD (peroxidase) enzyme activity
(0.4 U g−1 min−1) in 250 mg l−1 ALA solution. The highest CAT (catalase) activity (0.8 U g−1 min−1) after administration of 250 mg l−1 ALA was observed in “Li-1”. Meanwhile, highest (1.42 mg l−1) total chlorophyll content was also observed in “Ak-1”, when leaves were treated in 50 mg l−1 ALA, “Li-1” and “Ai-1” showed strongest response of specific activity of superoxide dismutase (SOD) in 50 mg l−1 and 50 mg l−1 ALA. Two hundred and fifty milligram per milliliter of ALA-treatment significantly improved the net photosynthetic rate. 相似文献
20.
Source-sink landscape theory and its ecological significance 总被引:2,自引:0,他引:2
Exploring the relationships between landscape pattern and ecological processes is the key topic of landscape ecology, for
which, a large number of indices as well as landscape pattern analysis model were developed. However, one problem faced by
landscape ecologists is that it is hard to link the landscape indices with a specific ecological process. Linking landscape
pattern and ecological processes has become a challenge for landscape ecologists. “Source” and “sink” are common concepts
used in air pollution research, by which the movement direction and pattern of different pollutants in air can be clearly
identified. In fact, for any ecological process, the research can be considered as a balance between the source and the sink
in space. Thus, the concepts of “source” and “sink” could be implemented to the research of landscape pattern and ecological
processes. In this paper, a theory of sourcesink landscape was proposed, which include: (1) In the research of landscape pattern
and ecological process, all landscape types can be divided into two groups, “source” landscape and “sink” landscape. “Source”
landscape contributes positively to the ecological process, while “sink” landscape is unhelpful to the ecological process.
(2) Both landscapes are recognized with regard to the specific ecological process. “Source” landscape in a target ecological
process may change into a “sink” landscape as in another ecological process. Therefore, the ecological process should be determined
before “source” or “sink” landscape were defined. (3) The key point to distinguish “source” landscape from “sink” landscape
is to quantify the effect of landscape on ecological process. The positive effect is made by “source” landscape, and the negative
effect by “sink” landscape. (4) For the same ecological process, the contribution of “source” landscapes may vary, and it
is the same to the “sink” landscapes. It is required to determine the weight of each landscape type on ecological processes.
(5) The sourcesink principle can be applied to non-point source pollution control, biologic diversity protection, urban heat
island effect mitigation, etc. However, the landscape evaluation models need to be calibrated respectively, because different
ecological processes correspond with different source-sink landscapes and evaluation models for the different study areas.
This theory is helpful to further study landscape pattern and ecological process, and offers a basis for new landscape index
design.
__________
Translated from Acta Ecologica Sinica, 2006, 26(5): 1444–1449 [译自: 生态学报] 相似文献