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1.
Chains of coupled oscillators of simple “rotator” type have been used to model the central pattern generator (CPG) for locomotion
in lamprey, among numerous applications in biology and elsewhere. In this paper, motivated by experiments on lamprey CPG with
brainstem attached, we investigate a simple oscillator model with internal structure which captures both excitable and bursting
dynamics. This model, and that for the coupling functions, is inspired by the Hodgkin–Huxley equations and two-variable simplifications
thereof. We analyse pairs of coupled oscillators with both excitatory and inhibitory coupling. We also study traveling wave
patterns arising from chains of oscillators, including simulations of “body shapes” generated by a double chain of oscillators
providing input to a kinematic musculature model of lamprey..
Received: 25 November 1996 / Revised version: 9 December 1997 相似文献
2.
We consider a partially coupled diffusive population model in which the state variables represent the densities of the immature
and mature population of a single species. The equation for the mature population can be considered on its own, and is a delay
differential equation with a delay-dependent coefficient. For the case when the immatures are immobile, we prove that travelling
wavefront solutions exist connecting the zero solution of the equation for the matures with the delay-dependent positive equilibrium
state. As a perturbation of this case we then consider the case of low immature diffusivity showing that the travelling front
solutions continue to persist. Our findings are contrasted with recent studies of the delayed Fisher equation. Travelling
fronts of the latter are known to lose monotonicity for sufficiently large delays. In contrast, travelling fronts of our equation
appear to remain monotone for all values of the delay.
Received: 1 November 2001 / Revised version: 10 May 2002 / Published online: 23 August 2002
Mathematics Subject Classification (2000): 35K57, 92D25
Key words or phrases: Age-structure – Time-delay – Travelling Fronts – Reaction-diffusion 相似文献
3.
We describe a new algorithm for the detection of dynamical interdependence in bivariate time-series data sets. By using geometrical
and dynamical arguments, we produce a method that can detect dynamical interdependence in weakly coupled systems where previous
techniques have failed. We illustrate this by comparison of our algorithm with another commonly used technique when applied
to a system of coupled Hénon maps. In addition, an improvement of ∼20% in the detection rate is observed when the technique
is applied to human scalp EEG data, as compared with existing techniques. Such an improvement may assist an understanding
of the role of large-scale nonlinear processes in normal brain function.
Received: 28 December 2001 / Accepted in revised form: 2 October 2002
Correspondence to: J.R. Terry (e-mail: J.R.Terry@lboro.ac.uk)
Acknowledgements. JRT acknowledges the support of the Royal Society and the London Mathematical Society for jointly funding a trip to the School
of Physics at the University of Sydney and The Brain Dynamics Centre at Westmead Hospital, Sydney. The authors thank Professor
Peter Robinson for useful conversations and the provision of local facilities within the School of Physics during the visit
of JRT. The support of the EPSRC via Grant GR/N00340 is also acknowledged. MJB is a recipient of a University Postgraduate
Award from the University of Sydney. 相似文献
4.
A traveling wave in a two-dimensional spinal cord model constitutes a stable pattern generator for quadruped gaits. In the
context of the somatotopic organization of the spinal cord, this pattern generator is sufficient to generate stable locomotive
limb trajectories. The elastic properties of muscles alone, providing linear negative feedback, are sufficient to stabilize
stance and locomotion in the presence of perturbative forces. We further show that such a pattern generator is capable of
organizing sensory processing in the spinal cord. A single-layer perceptron was trained to associate the sensory feedback
from the limb (coding force, length, and change of length for each muscle) with the two-dimensional activity profile of the
traveling wave. This resulted in a well-defined spatial organization of the connections within the spinal network along a
rostrocaudal axis. The spinal network driven by peripheral afferents alone supported autonomous locomotion in the positive
feedback mode, whereas in the negative feedback mode stance was stabilized in response to perturbations. Systematic variation
of a parameter representing the effect of gamma-motor neurons on muscle spindle activity in our model led to a corresponding
shift of limb position during stance and locomotion, resulting in a systematic displacement alteration of foot positions.
Received: 30 July 2001 / Accepted in revised form: 17 April 2002
Correspondence to: A. Kaske (e-mails: alexander.kaske@mtc.ki.se, alexander.kaske@vglab.com) 相似文献
5.
A theory of hippocampal memory based on theta phase precession 总被引:10,自引:0,他引:10
Yamaguchi Y 《Biological cybernetics》2003,89(1):1-9
The neural dynamics of the hippocampal network for memory encoding of novel temporal sequences is proposed based on the theta
rhythm modulated firing of place cells called theta phase precession. It is hypothesized that theta phase precession is generated
at the entorhinal cortex by phase locking between local field theta oscillation and neural oscillators and that the hippocampal
closed network with feedforward and backward projections employ theta phase precession to create selectivity in the associative
connections needed for temporal sequence storage. Our analyses and computer experiments reveal that the phase precession generated
by phase locking instantaneously endows stable phase relations among neural activities in the successively changing neural
population. It is concluded that theta phase precession provides biologically plausible dynamics for the memory encoding of
novel temporal sequences as episodic events.
Received: 18 December 2002 / Accepted: 18 March 2003 /
Published online: 20 May 2003
Correspondence to: Y. Yamaguchi (e-mail: yokoy@brain.riken.go.jp, Fax: +81-48-4676938)
Acknowledgements. The author would like to express acknowledgement to Drs. McNaughton and Skaggs for their discussion and comment and to Dr.
Amari for his continuous encouragement. Further thanks are given to Mr. Haga and Dr. Wu for their discussion and cooperation. 相似文献
6.
Lindström T 《Journal of mathematical biology》2002,45(5):396-418
In this paper we derive and analyze a discrete version of Rosenzweig's (Am. Nat. 1973) food-chain model. We provide substantial
analytical and numerical evidence for the general dynamical patterns of food chains predicted by De Feo and Rinaldi (Am. Nat.
1997) remaining largely unaffected by this discretization. Our theoretical analysis gives rise to a classification of the
parameter space into various regions describing distinct governing dynamical behaviors. Predator abundance has a local optimum
at the edge of chaos.
Received: 13 August 1999 / Revised version: 12 March 2002 / Published online: 17 October 2002
Mathematics Subject Classification (1991): 92D40
Keywords or phrases: Discrete food-chain – Discrete Hopf (Neimark-Sacker) bifurcation – Pulsewise birth processes – Mean yield maximization –
Nicholson-Bailey model 相似文献
7.
In biological systems, the task of computing a gait trajectory is shared between the biomechanical and nervous systems. We
take the perspective that both of these seemingly different computations are examples of physical computation. Here we describe
the progress that has been made toward building a minimal biped system that illustrates this idea. We embed a significant
portion of the computation in physical devices, such as capacitors and transistors, to underline the potential power of emphasizing
the understanding of physical computation. We describe results in the exploitation of physical computation by (1) using a
passive knee to assist in dynamics computation, (2) using an oscillator to drive a monoped mechanism based on the passive
knee, (3) using sensory entrainment to coordinate the mechanics with the neural oscillator, (4) coupling two such systems
together mechanically at the hip and computationally via the resulting two oscillators to create a biped mechanism, and (5)
demonstrating the resulting gait generation in the biped mechanism.
Received: 31 October 2001 / Accepted in revised form: 17 September 2002
Correspondence to: M.A. Lewis 相似文献
8.
Andreasen V 《Journal of mathematical biology》2003,46(6):504-536
The persistence of Influenza A in the human population relies on continual changes in the viral surface antigens allowing
the virus to reinfect the same hosts every few years. The epidemiology of such a drifting virus is modeled by a discrete season-to-season
map. During the epidemic season only one strain is present and its transmission dynamics follows a standard epidemic model.
After the season, cross-immunity to next year's virus is determined from the proportion of hosts that were infected during
the season. A partial analysis of this map shows the existence of oscillations where epidemics occur at regular or irregular
intervals.
Received: 16 February 2001 / Revised version: 11 June 2002 /
Published online: 28 February 2003
Key words or phrases: Infectious disease – Influenza drift – Cross-immunity – Seasonal epidemics – Iterated map 相似文献
9.
A neural network architecture based on the neural anatomy and function of retinal neurons in tiger salamander and mudpuppy
retinae is proposed to study basic aspects of early visual information processing. The model predictions for the main response
characteristics of retinal neurons are found to be in agreement with neurophysiological data, including the antagonistic role
of horizontal cells in the outer plexiform layer. The examination of possible γ-aminobutyric acid (GABA) action from horizontal
cells suggests that GABAA alone, GABAB alone, or their weighted combination can generate the response characteristics observed in bipolar cells.
Received: 25 June 2002 / Accepted: 28 January 2003 /
Published online: 20 May 2003
Acknowledgements. The authors would like to thank an anonymous reviewer for valuable comments.
Correspondence to: S. X. Yang (e-mail: syang@uoguelph.ca) 相似文献
10.
We start from a stochastic SIS model for the spread of epidemics among a population partitioned into M sites, each containing
N individuals; epidemic spread occurs through within-site (`local') contacts and global contacts. We analyse the limit behaviour
of the system as M and N increase to ∞. Two limit procedures are considered, according to the order in which M and N go to ∞; independently of the order, the limiting distribution of infected individuals across sites is a probability measure,
whose evolution in time is governed by the weak form of a PDE. Existence and uniqueness of the solutions to this problem is
shown. Finally, it is shown that the infected distribution converges, as time goes to infinity, to a Dirac measure at the
value x
*
, the equilibrium of a single-patch SIS model with contact rate equal to the sum of local and global contacts.
Received: 18 July 2001 / Revised version: 16 March 2002 / Published online: 26 September 2002
Mathematics Subject Classification (2000): 92D30, 60F99
Key words or phrases: SIS epidemic – Metapopulation – Markov population processes – Weak convergence of measures 相似文献
11.
We establish the existence of traveling front solutions and small amplitude traveling wave train solutions for a reaction-diffusion
system based on a predator-prey model with Holling type-II functional response. The traveling front solutions are equivalent
to heteroclinic orbits in R
4
and the small amplitude traveling wave train solutions are equivalent to small amplitude periodic orbits in R
4
. The methods used to prove the results are the shooting argument and the Hopf bifurcation theorem.
Received: 25 May 2001 / Revised version: 5 August 2002 / Published online: 19 November 2002
RID="*"
ID="*" Research was supported by the National Natural Science Foundations (NNSF) of China.
RID="*"
ID="*" Research was partially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada. On leave
from the Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada.
Mathematics Subject Classification (2000): 34C35, 35K57
Key words or phrases: Traveling wave solution – Wazewski set – Shooting argument – Hopf bifurcation
Acknowledgements. We would like to thank the two referees for their careful reading and helpful comments. 相似文献
12.
The urine concentrating mechanism of mammals and birds depends on a counterflow configuration of thousands of nearly parallel
tubules in the medulla of the kidney. Along the course of a renal tubule, cell type may change abruptly, resulting in abrupt
changes in the physical characteristics and transmural transport properties of the tubule. A mathematical model that faithfully
represents these abrupt changes will have jump discontinuities in model parameters. Without proper treatment, such discontinuities
may cause unrealistic transmural fluxes and introduce suboptimal spatial convergence in the numerical solution to the model
equations. In this study, we show how to treat discontinuous parameters in the context of a previously developed numerical
method that is based on the semi-Lagrangian semi-implicit method and Newton's method. The numerical solutions have physically
plausible fluxes at the discontinuities and the solutions converge at second order, as is appropriate for the method.
Received: 13 November 2001 / Revised version: 28 June 2002 / Published online: 26 September 2002
This work was supported in part by the National Institutes of Health (National Institute of Diabetes and Digestive and Kidney
Diseases, grant DK-42091.)
Mathematics Subject Classification (2000): 65-04, 65M12, 65M25, 92-04, 92C35, 35-04, 35L45
Keywords or phrases: Mathematical models – Differential equations – Mathematical biology – Kidney – Renal medulla – Semi-Lagrangian semi-implicit 相似文献
13.
A Scleroderma species collected on sandy soil under trees of Lithocarpus edulis in Saitama Prefecture, central Japan, is identified as Scleroderma laeve, a new record for Japan. Macroscopic and microscopic features are given.
Received: May 24, 2002 / Accepted: September 9, 2002
Acknowledgments We thank Ms. Ryoko Onuma, who offered some useful literature on Scleroderma. We are also grateful to Dr. Toshimitsu Fukiharu (Natural History Museum and Institute, Chiba) for his help with preserving
the specimens. For collecting specimens, we are grateful to Ms. Ayano Kimura, Mr. Tomoya Matsuyama, and Mr. Takahiro Uchida.
Correspondence to:T. Kasuya 相似文献
14.
Early development and quorum sensing in bacterial biofilms 总被引:3,自引:0,他引:3
Ward JP King JR Koerber AJ Croft JM Sockett RE Williams P 《Journal of mathematical biology》2003,47(1):23-55
We develop mathematical models to examine the formation, growth and quorum sensing activity of bacterial biofilms. The growth
aspects of the model are based on the assumption of a continuum of bacterial cells whose growth generates movement, within
the developing biofilm, described by a velocity field. A model proposed in Ward et al. (2001) to describe quorum sensing, a process by which bacteria monitor their own population density by the use of quorum
sensing molecules (QSMs), is coupled with the growth model. The resulting system of nonlinear partial differential equations
is solved numerically, revealing results which are qualitatively consistent with experimental ones. Analytical solutions derived
by assuming uniform initial conditions demonstrate that, for large time, a biofilm grows algebraically with time; criteria
for linear growth of the biofilm biomass, consistent with experimental data, are established. The analysis reveals, for a
biologically realistic limit, the existence of a bifurcation between non-active and active quorum sensing in the biofilm.
The model also predicts that travelling waves of quorum sensing behaviour can occur within a certain time frame; while the
travelling wave analysis reveals a range of possible travelling wave speeds, numerical solutions suggest that the minimum
wave speed, determined by linearisation, is realised for a wide class of initial conditions.
Received: 10 February 2002 / Revised version: 29 October 2002 /
Published online: 19 March 2003
Key words or phrases: Bacterial biofilm – Quorum sensing – Mathematical modelling – Numerical solution – Asymptotic analysis – Travelling wave
analysis 相似文献
15.
Seven species of the genus Lophiostoma were the subject of this study. Among these, Lophiostoma mucosum is described and illustrated as a new species. All other species, L. macrostomum, L. semiliberum, L. arundinis, L. caulium, L. caudatum, and L. winteri, are reported for the first time in Japan. A key to the species of Lophiostoma in Japan is given.
Received: August 5, 2002 / Accepted: November 28, 2002
Acknowledgments We are grateful to Dr. Hideki Takahashi (curator of SAPA) for the loan of fungal material.
Correspondence to:Y. Harada 相似文献
16.
A kinematical model for excitable wave propagation is analyzed to describe the dynamics of a typical neurological symptom
of migraine. The kinematical model equation is solved analytically for a linear dependency between front curvature and velocity.
The resulting wave starts from an initial excitation and moves in the medium that represents the primary visual cortex. Due
to very weak excitability the wave propagates only across a confined area and eventually disappears. This cortical excitation
pattern is projected onto a visual hemifield by reverse retinotopic mapping. Weak excitability explains the confined appearance
of aura symptoms in time and sensory space. The affected area in the visual field matches in growth and form the one reported
by migraine sufferers. The results can be extended from visual to tactile and to other sensory symptoms. If the spatiotemporal
pattern from our model can be matched in future investigations with those from introspectives, it would allow one to draw
conclusions on topographic mapping of sensory input in human cortex.
Received: 25 April 2002 / Accepted: 20 February 2003 /
Published online: 20 May 2003
RID="*"
ID="*" Present address: M. A. Dahlem Leibniz-Institut für Neurobiologie, Brenneckestr. 6, 39118 Magdeburg, Germany
Acknowledgements. We would like to thank V. Zykov for useful discussions on wave Propagation, and one of us (MAD) would like to thank Ed Chronicle
for useful discussions on functional excitability. This project was supported by a scholarship Landesstipendium Sachsen-Anhalt
to MAD.
Correspondence to: M. A. Dahlem (e-mail: dahlem@ifn-magdeburg.de) 相似文献
17.
Rolando Brawer Facundo D. Batista Oscar R. Burrone Daniel O. Sordelli M. C. Cerquetti 《Archives of microbiology》1998,169(6):530-533
A temperature-sensitive mutant of Salmonella typhimurium was isolated earlier after transposon mutagenesis with Tn10d Tet. The mutant D220 grows well at 28 °C but has a lower growth rate and forms filaments at 37 °C. Transposon-flanking fragments
of mutant D220 DNA were cloned and sequenced. The transposon was inserted in the dam gene between positions 803 and 804 (assigned allele number: dam-231 : : Tn10d Tet) and resulted in a predicted ten-amino-acid-shorter Dam protein. The insertion created a stop codon that led to a truncated
Dam protein with a temperature-sensitive phenotype. The insertion dam-231 : : Tn10d Tet resulted in a dam“leaky” phenotype since methylated and unmethylated adenines in GATC sequences were present. In addition, the dam-231 : : Tn10d Tet insertion rendered dam mutants temperature-sensitive for growth depending upon the genetic background of the S. typhimurium strain. The wild-type dam gene of S. typhimurium exhibited 82% identity with the Escherichia coli dam gene. 相似文献
18.
Dynamical models of two coupled biological oscillators interpret the detuning term as an arithmetic difference between the
uncoupled frequencies, Δω= (ω1−ω2). This Δω interpretation of detuning was addressed in four experiments in which human subjects oscillated pendulums in their
right and left hands in 1 : 1 frequency locking in antiphase (Experiments 1–3) or inphase (Experiment 4). Differences between
the uncoupled frequencies were manipulated through differences in the equivalent simple pendulum lengths, and the effects
of this manipulation on the detuning of relative phase from π or 0 and the standard deviation of relative phase SDφ were measured.
In Experiment 1, the same values of ω
i
were satisfied by several different physical configurations. The experiment confirmed that the detuning term is related strictly
to the uncoupled frequencies rather than to other physical characteristics of the oscillators. Experiments 2, 3 and 4 showed,
however, that the particular dependency of fixed point drift and SDφ on Δω depends on the particulars of ω1 and ω2. With variations in Δω brought about by different ω1 and ω2 that always formed a constant ratio, fixed point drift related inversely to Δω, and SDφ varied with Δω in ways that depended
on the magnitude of the constant ratio. These outcomes do not conform to expectations from models of coordination dynamics
that interpret detuning as (ω1−ω2).
Received: 18 October 1993/Accepted in revised form: 2 December 1994 相似文献
19.
Ezrachi EA 《Biological cybernetics》2003,88(1):33-45
I present a comprehensive biologically oriented computational model to account for the escape response of the cockroach on
the ground. This model is an expansion of previous work that accounted only for discriminating left from right wind directions
[Ezrachi et al. (1999) Biol Cybern 81: 89–99]. The model is composed of computational elements describing the biological processes
taking place in the various neurons and includes input which emulates empirical data. With this model it is possible to obtain
escape behavior that resembles natural behavior. The model is used to address an ongoing debate as to whether the cockroach's
turn direction is determined by computations carried out by the entire neuronal population (PC) or rather by a “winner-take-all”
(WTA) mechanism. I suggest that the computation mechanism that underlies the cockroach escape response is composed of both
PC and WTA principles. Based on the properties of the suggested new mechanism I denote it a “Darwinian population code.”
Received: 26 March 2002 / Accepted in revised form: 24 June 2002
Acknowledgements. I thank H. Parnas for her advice and assistance, J. M. Camhi for helpful comments, and D. Lipson for developing the simulation
tools.
Correspondence to: E. A. Ezrachi (e-mail: erez@piano.ls.huji.ac.il, Tel.: +972-2-6585818, Fax: +972-2-6585569) 相似文献
20.
Summary. The 14-residue peptaibol antibiotic trichovirin I 4A of the structure Ac-Aib-L-Asn-L-Leu-Aib-L-Pro-L-Ala-L-Val-Aib-L-Pro-Aib-L-Leu-Aib-L-Pro-L-Leuol
(Aib = α-aminoisobutyric acid, Leuol = leucinol) was synthesized by stepwise conventional solution phase synthesis using the Z/OtBu(OMe) strategy and HOBt/EDC as coupling reagents. Intermediates were fully characterized and the identity of the synthetic
peptide with the component 4A of the natural, microheterogeneous peptide mixture was proven by electrospray mass spectrometry,
HPLC, and bioassay.
Received March 25, 2002 Accepted June 14, 2002 Published online December 18, 2002
RID="*"
ID="*" Dedicated to Prof. Dr. Günther Jung. Tübingen University, on the occasion of his 65th anniversary.
Authors' address: Prof. Dr. Hans Brückner, Interdisciplinary Research Center, Institute of Nutritional Science, Department of Food Sciences,
Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26, D-35392 Giessen, Germany, Fax: +49-641-99-39149, E-mail: hans.brueckner@ernaehrung.uni-giessen.de
Abbreviations: Amino acids are abbreviated according to three-letter-nomenclature; Aib, α-aminoisobutyric acid (2-methylalanine); Iva (isovaline, 2-ethylalanine); Leuol, L-leucinol [(S)-2-amino-4-methyl-1-pentanol]; AAA, amino acid analysis; EI-MS, electron impact mass spectrometry; ESI-MS, electrospray ionization
mass spectrometry; HPLC, high performance liquid chromatography; Z, benzyloxycarbonyl; Fmoc, 9-fluorenylmethyoxycarbonyl;
OtBu, tertiary butoxy (tert-butylester); OMe, methoxy (methyl ester); OBzl, benzyloxy (benzyl ester); TDM, N,N,N′,N′-tetramethyl-4,4′-diamino-diphenylmethane
(Arnold's base); for other abbreviations see Experimental. 相似文献