摘要:

Dynamics of the Bray‐Liebhafsky (BL) oscillatory reaction is analyzed in a Continuously‐fed well‐Stirred Thank Reactor (CSTR). Deterministic chaos is found under different conditions, when temperature and acidity are chosen as control parameters. Dynamic patterns observed in real experiments are also numerically simulated. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846452

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The formation of target patterns in oscillatory CO oxidation on Pt(110) is studied using laser‐induced, controlled creation of temperature heterogeneities. For the first time, inward traveling target waves are observed in this reaction‐diffusion system. The experimental results are compared to numerical studies of the complex Ginzburg‐Landau equation and the Krischer‐Eiswirth‐Ertl model, both extended by additional terms accounting for global gas‐phase coupling to obtain good agreement with the experimental observations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846453

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have experimentally identified a periodic‐adding transition in the shape of conversion oscillatory solutions observed during CO oxidation over Pd supported on a glass‐fiber disk‐shaped cloth catalyst in a continuous reactor. Typical thermograms exhibit a breathing motion in which a hot spot expands and contracts continuously and its temporal pattern matches the conversion oscillations.A mathematical model captures the main features of the experimentally observed patterns and characterizes the transition to complex oscillations as either period‐adding or period‐doubling. We have determined that a canard bifurcation of the fast subsystem with respect to the solid temperature (slow variable) is the source of the mixed‐mode oscillations in the full system. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846454

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Interaction of noise with nonlinear chemical dynamics is studied experimentally. In particular, noise invoked resonance phenomena are investigated. The existence of the standard Coherence Resonance (CR) and Periodic Stochastic Resonance (PSR) effects, manifested by signature unimodal curves, are verified in experiments. Moreover, the possibility of the coexistence of CR and PSR is entertained. This coexistence is subsequently confirmed by the bimodal shape of the generated resonance curve. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846455

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

It is known from extensive work with the diode resonator that the nonlinear properties of a PN junction can lead to period doubling, chaos, and other complicated behaviors in a driven circuit. There has been very little work on what happens when more than one PN junction is present. In this work, in addition to the usual period doubling and chaos, I observe low frequency oscillations caused by bistability in several different transistor amplifier circuits. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846456

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The series resonance circuit with a linear inductance and a ferroelectric capacitance has been used to realize a nonlinear dynamical system. As dielectric material in the capacitor we use triglycine sulfate, usually abbreviated TGS, which is one of the most thoroughly investigated ferroelectrics. Below the Curie temperatureTC= 49°CTGS has two possible states of polarization. The switching of domains under the influence of an external electric field higher than the coercive field from one state of polarization to the opposite one is a highly nonlinear process. If the series resonance circuit is driven by AC voltage of sufficiently high amplitude and suitably chosen frequencies different kinds of bifurcations up to chaotic behaviour can be observed. It is well known, that in the vicinity of a bifurcation the resonance circuit can act to amplify small periodic perturbations. In our system we have demonstrated this effect near a period doubling bifurcation by introducing the periodic perturbation as an amplitude modulation of the driving voltage.Now we present another kind of perturbation of the resonance circuit. Because TGS is a material with a very large pyroelectric effect we introduced the perturbation into the system by periodic infrared irradiation of the ferroelectric. The resulting periodic modulation of the temperature of the TGS‐crystal yields an electrical signal via the pyroelectric effect, which can be amplified near a period doubling bifurcation. Detailed investigations were performed to optimize this effect. The result may be considered as a new method of pyroelectric detection. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846457

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Chaotic oscillators are an intriguing source of waveforms for ultra wideband‐radar applications. The broadband and nonrepeating nature of chaos provides an ideal combination of high range resolution and no range ambiguity. In addition, synchronization via local coupling of array elements is an efficient alternative to the use of a master oscillator in a phased array. However, a difficulty in any wideband array is achieving a practical mechanism for beam steering. Conventional approaches using phase shifters are impractical for bandwidths exceeding just a few percent of the carrier frequency, and for larger bandwidths true time‐delay steering is required. Here, we explore the use of lag synchronization in a chaotic array to achieve steering. The natural frequency of each oscillator is adjusted using a variable capacitor to achieve a uniform lag across the array. To first order this tuning is equivalent to a standard method of inducing lag synchronization. The direction and extent of the steering is directly controlled by the orientation and magnitude of the induced lag. Using chaotic rf circuits, we experimentally show that lag synchronization can be achieved and controlled in arrays of rf devices. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846458

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In the present paper statistical properties of the Lorentz attractor are studied and general regularities of the temporal behavior of the autocorrelation function are determined. Using a symbolic dynamics the character of a random process of switchings between two symmetric areas of the attractor is investigated. It is shown that this process posseses the statistic of a telegraphic signal with a non Poisson distribution of impulses duration. It is demonstrated that the ACF of the Lorentz attractor decays with the linear law on small times. The theoretical and numerical results are compared with data of physical experimental data. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846459

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present theoretical and experimental investigations of the fundamental idea that coupling‐induced oscillations can enhance the sensitivity of an array of magnetic sensors. In particular, we consider arrays made up of fluxgate magnetometers inductively coupled through electronic circuits. The underlying dynamics of the coupled system is more complicated as it shows new spatio‐temporal features that are not observed in a single fluxgate. Among these new features, self‐induced oscillations in the form of a traveling wave pattern are of particular interest because they can lead to higher sensitivity levels at reduced costs. Details of the experiments, a new signal detection mechanism, and results from numerical bifurcation analyzes are described in this work. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846460

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Noise stabilization can occur in nonlinear dynamical systems driven by noise. The essential idea is that the noise‐free system is unstable, but with noise present the system exhibits bounded persistent fluctuations. An extreme example would be a dynamical system that has no bounded behavior without noise (e.g.almost all orbits eventually reach infinity), but which exhibits bounded persistent behavior for any finite level of noise. Such systems are qualitatively different in character from deterministic chaotic systems, yet they can mimic low‐dimensional chaos, implying that new time series methods must be developed to distinguish noise‐stabilized systems (where the attractor is ‘created’ by the noise) from a ‘noisy’ strange attractor (where the noise simply ‘fuzzes’ out the natural probability density of the noise‐free deterministic system). In this talk we will discuss a simple dynamical model, motivated by a problem encountered in plasma physics, that exhibits this behavior. After a brief summary of the theoretical background and motivation, we will describe what we believe to be the first experimental realization of this phenomenon: a nonlinear circuit that is noise stabilized. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846461

出版商:AIP    

年代:1904

数据来源: AIP