摘要:

We consider macroscopic systems driven away from thermodynamic equilibrium by an imposed gradient in temperature, velocity, or concentration. For a sufficiently small imposed gradient, a system will assume (asymptotically) the symmetry of the boundary conditions. However, when the imposed gradient exceeds a critical value, a system will spontaneously break the symmetry of the boundary conditions and form a spatial pattern. In two dimensions the pattern could be traveling waves (e.g., spirals) or an array of squares, stripes, or hexagons. With larger imposed gradients, the patterns can become more complex and even disordered in both space and time. We discuss the general principles of pattern formation in systems driven away from equilibrium and illustrate the principles with examples from experiments. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59956

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

When the dynamics of a spatially distributed excitable or oscillatory medium is complex, synchronization defect lines may exist which lead to a variety of pattern formation processes. If a medium with period-nlocal dynamics supports spiral waves, such synchronization defect lines are necessary to reconcile the fact thatnrotations of a spiral wave are needed to restore the entire concentration field to its initial value. We show how such synchronization defect lines may be classified and how they can lead to line-defect turbulent states through non-equilibrium phase transitions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59938

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

For Rayleigh-Be´nard convection of a fluid with Prandtl number&sgr;≈1,we report experimental results of the competition between two stable attractors—Ideal Straight Rolls (ISR) and Spiral Defect Chaos (SDC). For convection cells containing regions of both ISR and SDC, we show that the SDC region invades the ISR region with a time-independent front speedv(&egr;),where &egr; is the reduced Rayleigh number(R−Rc)/Rc.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59948

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Formation dynamics of transient spiral and target patterns are studied for vertically oscillated thin granular layer systems. When the dimensionless acceleration amplitude is changed from 2.5 of a flat pattern state to 3.0 of a steady stripe pattern state by linearly ramping the oscillation amplitude in time at a constant oscillation frequency, two different routes to the stripe pattern are observed depending on the ramping rate. For small ramping rate, spiral or target patterns are formed as an intermediate state before the stripe pattern. For large ramping rate, however, stripe patterns are formed without the transient spiral or target pattern. Furthermore, we study the short time dynamics of spiral and target patterns. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59949

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Spiral waves are observed in many different spatially extended systems with oscillatory, excitable or bistable nature. The interaction of spiral waves with extrinsic perturbation is an important, but not fully resolved, issue. We study the effect of parametric modulations on a simple spiral shaped domain wall that forms in a model system described by a Ginzburg-Landau equation. The local dynamics of the unperturbed system is basically bistable, and the patterns that arise in the system consist of two stable domains separated by bloch domain walls. Periodic modulations on two parameters of the equation cause the tip of a spiral meander forming a complex quasi-periodic trajectory. No evidence of frequency-locking is observed. A simple argument for the unusual shape of tip trajectories is presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59950

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We have conducted numerical precise simulations using an event-driven method to investigate the pattern formations in two-dimensional, shallow, granular materials on a vertically vibrating plate. A detailed analysis of the profiles of the vertical and the horizontal velocities inside a granular system during the formation of subharmonic waves has been done for the first time. Kinetic information inside the granular system over time explains the diffusion mechanism of the energy input from the bottom plate through continuous collisions and the mechanism of subharmonic wave formation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59951

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We study the effects of delayed coupling on spatio-temporal dynamics in a locally coupled chain of identical Ginzburg-Landau oscillators. Using the biorthogonal decomposition method, we construct the phase diagrams in the parameter space of coupling and nonlinearity for various time delays. We find that the time delay reduces the dynamic complexity of chaotic states in most regions of the parameter space beyond the Benjamin-Feir (BF) instability limit. We find, however, that in regions of spatio-temporal intermittency, the time delay leads to the recurrence of states with high dynamic complexity from pattern competition. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59952

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The biopolymers and membranes constitute the basic ingredients of the biological systems in cellular level. Due to complexity and low dimensionality in their primary structures, they manifest variety and flexibility, which is the basis of conformational transitions relevant to biological functions. Also, the novel noise-induced phenomena such as stochastic resonance and ratchet give rise to new possibilities for biological cooperativity and sensitivity to environments. In this vein, this paper reviews our recent theoretical studies of conformational transition and dynamics occurring in the polymer/membrane systems, along with the basic methodology of soft matter and stochastic process theory. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59953

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The number of protein structures is far less than the number of sequences. By imposing simple generic features of proteins (low energy and compaction) on all possible sequences we show that the structure space is sparse compared to the sequence space. Even though the sequence space grows exponentially withN(the number of amino acid residues) we conjecture that the number of low energy compact structures only scales aslnN. This implies that many sequences must map onto countable number of basins in the structure space. The number of sequences for which a given fold emerges as a native structure is further reduced by the dual requirements of stability and kinetic accessibility. The factor that determines the dual requirement is related to the sequence dependent temperatures,T&thgr;(collapse transition temperature) andTF(folding transition temperature). Sequences, for which&sgr;=(T&thgr;−TF)/T&thgr;is small, typically fold fast by generically collapsing to the native-like structures and then rapidly assembling to the native state. Such sequences satisfy the dual requirements over a wide temperature range. We also suggest that the functional requirement may further reduce the number of sequences that are biologically competent. The scheme developed here for thinning of the sequence space that leads to foldable structures arises naturally using simple physical characteristics of proteins. The reduction in sequence space leading to the emergence of foldable structures is demonstrated using lattice models of proteins. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59954

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The motion of single biological cells is a fascinating phenomena which has puzzled scientists for many decades. The current physical concepts of cell motility are reviewed and the recent progress of our understanding concerning the role of polymerization processes are summarized. In particular, the cooperativity between actin polymerization and steric membrane-filament interactions is discussed. Possible mechanisms of rectified motions are suggested. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59931

出版商:AIP    

年代:1900

数据来源: AIP