Noise-induced effects in an active medium with periodic boundary conditions

A model of an active medium with periodic boundary conditions in which the elementary cell is represented by a FitzHugh-Nagumo oscillator has been studied. Depending on the system parameters, the elementary cell can occur in either auto-oscillatory or excitable state. In both cases, an autonomous medium in the absence of noise performs sustained oscillations and exhibits the phenomenon of multistability. A method for diagnostics of the character of medium with the aid of external noise is proposed, specific features in behavior of the system near the point of transition from the excitable to auto-oscillatory state are considered, and the phenomena of coherent resonance and noise-induced switching are described.     

Noise-induced transitions in a system of coagulating particles

Rigorously solvable models of the system of coagulating particles in a stochastic medium are proposed. It is demonstrated that such systems are featuring additional noise-induced stationary states. The results are considered from the standpoint of using this phenomenon for evaluating the effective parameters of the medium.     

Unbalanced versus balanced operation in an optical coherence tomography system

The choice of a balanced optical coherence tomography (OCT) configuration versus an unbalanced OCT configuration with optimized reference-arm attenuation is discussed. The choice depends on the receiver noise, the fiber-end reflection R, and the power to the object. When OCT is used to investigate biological tissue an equivalent R? can be evaluated as the compound reflected light from tissue. In this case an additional parameter has to be considered: the confocal optical sectioning interval of the OCT system.     

Chaotization of oscillations in a nonatonomous rigidly excitable system with time delay

An external harmonic drive signal is used for stimulating chaos in a system with time delay, in which the parameters admit only rigid excitation of oscillations and a single impact produces only regular motions. The results of numerical simulations are presented and the mechanism of chaos induction is considered.     

Non-sinusoidal power theory in a power system having transmission lines with frequency-dependent resistances

Recently power systems suffer from harmonic pollution, and the resistances of transmission lines are frequency-dependent due to eddy currents and the skin effect. This frequency dependency should be taken into account, so that apparent power and the power factor accurately reflect transmission loss under non-sinusoidal conditions. A generalised power theory that is applicable to a power system whose transmission/distribution lines have frequency-dependent resistances, and where a unity power factor is given as the minimum loss condition is proposed     

Crystal growth as an excitable medium

Crystal growth has been widely studied for many years, and, since the pioneering work of Burton, Cabrera and Frank, spirals and target patterns on the crystal surface have been understood as forms of tangential crystal growth mediated by defects and by two-dimensional nucleation. Similar spirals and target patterns are ubiquitous in physical systems describable as excitable media. Here, we demonstrate that this is not merely a superficial resemblance, that the physics of crystal growth can be set within the framework of an excitable medium, and that appreciating this correspondence may prove useful to both fields. Apart from solid crystals, we discuss how our model applies to the biomaterial nacre, formed by layer growth of a biological liquid crystal.     

Transients in an autostochastic oscillator with delayed feedback

A numerical analysis of the turn-on transients in an autostochastic oscillator with delayed feedback is reported. Dependence of the transients on the intensity of chaotic initial conditions is studied. It is demonstrated that the chaotic oscillations may switch from one basin of attraction to another.     

Bridge-to-computer data acquisition system with feedback nulling

A system is presented with which a computer can be used to provide electronic feedback nulling of a Wheatstone bridge measurement system used for data acquisition. This system provides compensation for drifts away from null resulting from the measurement setup or amplifier drifts with time or temperature. An example of the system in the case of a strain gauge bridge used with a cantilever beam is described     

Single-cavity, multiline laser system with large coherence length

We present a new approach of generating the several wavelengths required for color holography with coherence lengths in the range of several meters. Our proposed laser system consists of an argon-ion laser, which is equipped with broadband optics. Its main lasing lines include 457, 488, and 514 nm. Sufficient coherence length is achieved by means of an intracavity etalon. We report single-frequency operation at several competing wavelengths and the successful recording of multicolor holograms with the described laser system.     

Interaction of noise with excitable dynamics

In this paper, the interaction of noise with excitable dynamics of a three-electrode electrochemical cell is examined. Different scenarios involving both external and internal noise sources are considered. In the case of external noise, aperiodic stochastic resonance and regulation of the noise-induced spiking behaviour are investigated. In the case of internal noise, the interaction of intrinsic electrochemical noise with autonomous nonlinear dynamics is studied. The amplitude of this internal noise, determined by the concentration of chloride ions, is monotonically increased and the provoked dynamics are analysed. Our results indicate that internal noise, similar to its external counterpart, is able to induce regularity in the system response.     

A resonant bridge with frequency-dependent negative resistance

Investigations were conducted on the properties of 24 circuits for which the impedance in the ideal case is equal to s² E, where s is the complex frequency and E is a constant. For harmonic excitation each circuit forms a negative resistance-ω²E and is hence called a frequency-dependent negative resistance (FDNR). From these 24 circuits, four that are stable were selected; measurements were made on these, and their equivalent circuit diagrams were determined. A resonant bridge was constructed with one branch containing an FDNR. Using this bridge it is possible to measure inductances with dissipation factors, tan δ, as high as 10⁴     

Parallel optical coherence tomography system

We present the design and procedures for implementing a parallel optical coherence tomography (POCT) imaging system that can be adapted to an endoscopic format. The POCT system consists of a single mode fiber (SMF) array with multiple reduced diameter (15 microm) SMFs in the sample arm with 15 microm center spacing between fibers. The size of the array determines the size of the transverse imaging field. Electronic scanning eliminates the need for mechanically scanning in the lateral direction. Experimental image data obtained with this system show the capability for parallel axial scan acquisition with lateral resolution comparable to mechanically scanned optical coherence tomography systems.     

随机临界频点识别与声反馈智能处理系统

室内扩音中,由于拾音器的布点位置不同,其声场环境更加复杂,具体表现在声反馈条件下,多点声反馈产生。其特点是相互交叉反射波,在不同拾音点形成声波的复杂、时变、多向、随机及非线性。这破坏了扩声系统的稳定和应有的增益,对于该难题,提出用随机阻带识别技术来处理和替代过去的子带识别处理方法。以全通滤波器为主通道,运用随机阻带识别技术,在对随机临界频点识别的同时,自动生成反向抑制波（阻带）。在保证原扩声系统增益前提下,解决因声反馈带来的啸叫频点的不稳定性,确保室内扩声系统的稳定性。实验在扩音系统中加入以随机阻带识别技术的声反馈智能处理系统,得出两者之间扩声增益的对照,从而证实该声反馈智能处理系统不仅功效显著,而且又快又好地解决了远距离拾音布点容易降低扩声增益的难题。     

Digital refraction distortion correction with an astigmatic coherence sensor

We demonstrate the sensing and correction of an isoplanatic refractive distortion (not lens aberrations), using the complete measurement of the partially coherent field in an aperture that the previously described astigmatic coherence sensor provides. Isoplanatic distortions, and in general distortions that do not cause energy loss, maintain the orthogonality of the coherent modes. We use the fact that a common distortion will occur to all coherent modes to separate the distortion from the source behind it, rather than requiring a reference source at a different wavelength. Digital deconvolution was performed on the full four-dimensional partially coherent field for simultaneously computing the distortion and the source intensity distribution.     

Noise-induced binary synchronization in nonlinear systems

The phenomenon of noise-induced binary synchronization has been discovered in two independent dynamical systems generating aperiodic binary signals under the action of a common noise source. The presence of a synchronous regime was confirmed by the calculation of Lyapunov exponents for the two systems. The mechanism of development of the noise-induced binary synchronization regime has been found. A relation of the observed regime to binary generalized synchronization is established.