摘要:

Chaotic intensity fluctuations of an intracavity frequency‐doubled Nd:YAG laser are experimentally stabilized using Multiple Delay Feedback Control (MDFC) based on delayed feedback signals with two different delay times. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846482

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We study the phenomenon of ghost resonance in a system of two bidirectionally coupled nonlinear oscillators. Ghost resonance was reported recently in an excitable system when perturbed by two periodic signals of different frequencies. Under these circumstances and with the help of noise, the system is able to resonate at a frequency not present in the external perturbations but related with them. In the current work, we give the first experimental evidence of ghost resonance in a coupled system which consists on two bidirectionally coupled semiconductor lasers. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846483

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Coherence Resonance is demonstrated in a semiconductor laser without external noise. The experimental evidence is reported in the Low Frequency Fluctuations of a chaotic diode laser with optical feedback. The phenomenon is also verified numerically using the Lang‐Kobayashi equations for a single solitary mode laser, without noise terms. Fast deterministic dynamics plays the role of an effective exciting noise, narrowing the resonance in the autonomous slow power drops cycles of the laser. This phenomena is the extension of deterministic Stochastic Resonance and Coherence Resonance as predicted and observed in recent years. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846484

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We evidence experimentally the convective and absolute instabilities in an optical system. In our system, the presence of noise and spatial non‐uniformities (as in most of the “real systems”) add additional complexities. First we derive analytical expressions of both thresholds for the ideal noiseless and spatially uniform situation. Then numerical simulations allow to determine signatures of those instabilities. The corresponding noise sustained and dynamical patterns are observed experimentally in a liquid crystal layer subjected to a laser beam with tilted feedback. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846485

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We report experimental results on the dynamics and synchronization of a 19‐broad‐area semiconductor laser array in an external cavity containing a lens array, projection optics, and a diffractive grating. All lasers are locked to single longitudinal mode. Significant improvement of the spatial profile of the entire laser array output beam has been observed. Laser coupling is investigated through the radio‐frequency (RF) spectrum and temporal correlation of coupled laser emitters. Such coupling is found to exert certain effects on the frequency locking of the laser array. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846486

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

An array of systems can get jammed: traffic jams, compaction of granular materials, the glass transition, colloidal gels, panic and stampedes of people, foams, &ellip; The question that arises is whether all these systems share their features in a more fundamental way, enabling us to think of a jammed system as a new state of matter. Jamming could then be amenable to be described as a phase transition. A particular experiment aimed at understanding this phenomenon is presented here. It consists of a silo filled with grains, with an orifice in the base. Grains begin to pour freely, and then — if the orifice is not much larger than several grain diameters — the flow stops because an arch is formed: it jams. By measuring the number of grains between successive jammings (an avalanche), a measurement of the jamming probability is obtained. From the features of the statistical distribution of avalanches, some interesting characteristics of this process can be grasped. In particular, the probability density function of avalanches shows a clear exponential tail, therefore the system is not critical. It can be rescaled with only one parameter, namely the mean avalanche size (or, alternatively, the jamming probability of a single grain). We pay particular attention to the study of some variables that could, in principle, influence the process in order to ascertain which are relevant to the phenomenon of jamming, and we show the existence of a critical radius for the orifice above which no jamming can occur. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846487

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We summarize the experimental observation of a large variety of self‐organized patterns in the electrical current density of the discharge space of planar gas‐discharge systems with high impedance electrodes. In the center of interest are static and dynamic well‐localized solitary patterns (dissipative solitons, DSs) and their interaction leading e.g. to scattering, the formation of “molecules”, generation, annihilation and the formation of patterns of higher complexity consisting of DSs. A simple 3‐component reaction‐diffusion system qualitatively takes account of most of the observed phenomena. In addition, we present a rigorous reduction of these equations to a set of ordinary differential equations near the transition point from a stationary to a travelling DS, giving a mathematical foundation of a description of DSs as particles. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846488

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We report on our successful real‐time measurement of the dynamic frequency‐shift of light by particles in Brownian motion through self‐mixing laser spectroscopy with extreme optical sensitivity. We show that the changes over time in the non‐stationary random walks of small particles suspended in water result in different averaged dynamics when the field of vision for particles seen by the laser beam (scale of the observation) is changed. At a small focal volume of the laser beam, in which the relevant diffusion broadening is observed, the averaged motion which can be represented by the motion of a “virtual” single particle, whose velocity possesses a Gaussian‐white property, constitutes stationary fluctuations, featuring random sequences of the Lorentz‐type spectrum and double‐peaked probability distribution function for displacements. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846489

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Complex systems made of nonlinear interacting cells are gaining ever and ever interest. An universal environment for the study these systems should provide to the user the possibility of defining the dynamics of the cells as well as the connections among them in a simple and flexible way. In this paper the main characteristics of E∧3, an universal emulator of complex systems, are discussed. This simulator is based on the paradigm of Cellular Nonlinear Network and makes use of parallel computing allowing to considerably extend the size of the simulated system. Each cell is conceived as anth‐order dynamical system. Moreover, numerical results obtained by emulating a complex system made of a large number (more than 500000) of interacting chaotic units arranged in a 3D lattice are presented. These simulations show an emerging result: organized forms and structure arise from the dynamic evolution of such systems. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846490

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Heart rate variability of rats is investigated using concepts from the nonlinear dynamical system theory. Among the important techniques offered, symbolic dynamics is very appealing by its power to investigate patterns which can be repeated in a time series. The present analysis was performed in six control rats and six chronic cardiac insufficient rats (myocardial infarction due to left descendent coronary artery ligation). Rats are left in clean atmosphere or exposed to atmosphere containing diluted engine emission pollutants. The evolution of the heart rate variability is then investigated with a three element symbolic dynamics which allows to distinguish extrasystoles from tachycardia or bradycardia using the symbol sequences. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846491

出版商:AIP    

年代:1904

数据来源: AIP