51,102 research outputs found
Robust and Irreversible Development in Cell Society as a General Consequence of Intra-Inter Dynamics
A dynamical systems scenario for developmental cell biology is proposed,
based on numerical studies of a system with interacting units with internal
dynamics and reproduction. Diversification, formation of discrete and recursive
types, and rules for differentiation are found as a natural consequence of such
a system. "Stem cells" that either proliferate or differentiate to different
types stochastically are found to appear when intra-cellular dynamics are
chaotic. Robustness of the developmental process against microscopic and
macroscopic perturbations is shown to be a natural consequence of such
intra-inter dynamics, while irreversibility in developmental process is
discussed in terms of the gain of stability, loss of diversity and chaotic
instability.Comment: 17 pages with 3 ps figures. submitted to Physica A as a proceeding
paperfor Paladin Memorial Con
Coupled Maps with Growth and Death: An Approach to Cell Differentiation
An extension of coupled maps is given which allows for the growth of the
number of elements, and is inspired by the cell differentiation problem. The
growth of elements is made possible first by clustering the phases, and then by
differentiating roles. The former leads to the time sharing of resources, while
the latter leads to the separation of roles for the growth. The mechanism of
the differentiation of elements is studied. An extension to a model with
several internal phase variables is given, which shows differentiation of
internal states. The relevance of interacting dynamics with internal states
(``intra-inter" dynamics) to biological problems is discussed with an emphasis
on heterogeneity by clustering, macroscopic robustness by partial
synchronization and recursivity with the selection of initial conditions and
digitalization.Comment: LatexText,figures are not included. submitted to PhysicaD
(1995,revised 1996 May
Relevance of Dynamic Clustering to Biological Networks
Network of nonlinear dynamical elements often show clustering of
synchronization by chaotic instability. Relevance of the clustering to
ecological, immune, neural, and cellular networks is discussed, with the
emphasis of partially ordered states with chaotic itinerancy. First, clustering
with bit structures in a hypercubic lattice is studied. Spontaneous formation
and destruction of relevant bits are found, which give self-organizing, and
chaotic genetic algorithms. When spontaneous changes of effective couplings are
introduced, chaotic itinerancy of clusterings is widely seen through a feedback
mechanism, which supports dynamic stability allowing for complexity and
diversity, known as homeochaos. Second, synaptic dynamics of couplings is
studied in relation with neural dynamics. The clustering structure is formed
with a balance between external inputs and internal dynamics. Last, an
extension allowing for the growth of the number of elements is given, in
connection with cell differentiation. Effective time sharing system of
resources is formed in partially ordered states.Comment: submitted to Physica D, no figures include
Diversity, Stability, Recursivity, and Rule Generation in Biological System: Intra-inter Dynamics Approach
Basic problems for the construction of a scenario for the Life are discussed.
To study the problems in terms of dynamical systems theory, a scheme of
intra-inter dynamics is presented. It consists of internal dynamics of a unit,
interaction among the units, and the dynamics to change the dynamics itself,
for example by replication (and death) of units according to their internal
states. Applying the dynamics to cell differentiation, isologous
diversification theory is proposed. According to it, orbital instability leads
to diversified cell behaviors first. At the next stage, several cell types are
formed, first triggered by clustering of oscillations, and then as attracting
states of internal dynamics stabilized by the cell-to-cell interaction. At the
third stage, the differentiation is determined as a recursive state by cell
division. At the last stage, hierarchical differentiation proceeds, with the
emergence of stochastic rule for the differentiation to sub-groups, where
regulation of the probability for the differentiation provides the diversity
and stability of cell society. Relevance of the theory to cell biology is
discussed.Comment: 19 pages, Int.J. Mod. Phes. B (in press
Coupled map gas: structure formation and dynamics of interacting motile elements with internal dynamics
A model of interacting motile chaotic elements is proposed. The chaotic
elements are distributed in space and interact with each other through
interactions depending on their positions and their internal states. As the
value of a governing parameter is changed, the model exhibits successive phase
changes with novel pattern dynamics, including spatial clustering, fusion and
fission of clusters and intermittent diffusion of elements. We explain the
manner in which the interplay between internal dynamics and interaction leads
to this behavior by employing certain quantities characterizing diffusion,
correlation, and the information cascade of synchronization. Keywords:
collective motion, coupled map system, interacting motile elementsComment: 27 pages, 12 figures; submitted to Physica
Bifurcations in Globally Coupled Chaotic Maps
We propose a new method to investigate collective behavior in a network of
globally coupled chaotic elements generated by a tent map. In the limit of
large system size, the dynamics is described with the nonlinear
Frobenius-Perron equation. This equation can be transformed into a simple form
by making use of the piecewise linear nature of the individual map. Our method
is applied successfully to the analyses of stability of collective stationary
states and their bifurcations.Comment: 12 pages, revtex, 10 figure
Competition between isoscalar and isovector pairing correlations in N=Z nuclei
We study the isoscalar (T=0) and isovector (T=1) pairing correlations in N=Z
nuclei. They are estimated from the double difference of binding energies for
odd-odd N=Z nuclei and the odd-even mass difference for the neighboring
odd-mass nuclei, respectively. The empirical and BCS calculations based on a
T=0 and T=1 pairing model reproduce well the almost degeneracy of the lowest
T=0 and T=1 states over a wide range of even-even and odd-odd N=Z nuclei. It is
shown that this degeneracy is attributed to competition between the isoscalar
and isovector pairing correlations in N=Z nuclei. The calculations give an
interesting prediction that the odd-odd N=Z nucleus 82Nb has possibly the
ground state with T=0.Comment: 5 pages, 4 figures, to be published in Phys. Rev. C (R
Shell gaps and pn pairing interaction in N = Z nuclei
We analyze the observed shell gaps in N=Z nuclei determined from the binding
energy differences. It is found that the shell gaps can be described by the
combined contributions from the single-particle level spacing, the like-nucleon
pairing, and the proton-neutron pairing interaction. This conclusion is
consistent with that of Chasman in Phys. Rev. Lett. 99 (2007) 082501. For the
double-closed shell N=Z nuclei, the single-particle level spacings calculated
with Woods-Saxon potential are very close to those obtained by subtracting the
nn pairing interaction from the observed shell gap. For the sub-closed or
non-closed shell N=Z nuclei, the pn pairing interaction is shown to be
important for the observed shell gaps.Comment: 9 pages, 5 figure
Macroscopic chaos in globally coupled maps
We study the coherent dynamics of globally coupled maps showing macroscopic
chaos. With this term we indicate the hydrodynamical-like irregular behaviour
of some global observables, with typical times much longer than the times
related to the evolution of the single (or microscopic) elements of the system.
The usual Lyapunov exponent is not able to capture the essential features of
this macroscopic phenomenon. Using the recently introduced notion of finite
size Lyapunov exponent, we characterize, in a consistent way, these macroscopic
behaviours. Basically, at small values of the perturbation we recover the usual
(microscopic) Lyapunov exponent, while at larger values a sort of macroscopic
Lyapunov exponent emerges, which can be much smaller than the former. A
quantitative characterization of the chaotic motion at hydrodynamical level is
then possible, even in the absence of the explicit equations for the time
evolution of the macroscopic observables.Comment: 24 pages revtex, 9 figures included. Improved version also with 1
figure and some references adde
New group of stable icosahedral quasicrystals: structural properties and formation conditions
Structural studies on the icosahedral quasicrystals in Zn-Mg-Sc, Cu-Ga-Mg-Sc,
and Zn-Mg-Ti alloys as well as their corresponding 1/1 cubic approximants, have
revealed that these quasicrystals belong to a new structural group similar to
Cd-based quasicrystals. This group is characterized by a triple-shell
icosahedral cluster different from both Mackay- and Bergman-types. The presence
of the atomic cluster has been deduced from the structure model of the
approximant crystal, Zn17Sc3, in which the clusters are embedded in a periodic
network of so-called "glue atoms". Density measurement suggested the presence
of at least 2.7 Zn atoms in the first shell of the cluster in this approximant.
The substitutional relationship in these three quasicrystals indicates the
important role of Hume-Rothery rule for the formation of this type of
quasicrystal. The occurrence of a P-type icosahedral quasicrystal in Zn-Mg-Yb
alloy is also reported.Comment: 11 pages, 1 table, 6 figure
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