Range Of Bistability Research Articles

Fluctuation phenomena in a multibranch potential.

Fluctuation phenomena, to be anticipated in all systems for which the internal fluctuating variable is a multivalued function of the observable quantity, are reported. Analog electronic experiments on a model optically bistable Fabry-P\'erot cavity have shown that the observable may be described in terms of a Boltzmann distribution with a multibranch effective potential. The distribution was observed to possess up to four peaks (two twin peaks) within the range of bistability, and to become singular at outer boundaries corresponding to the branching points of the potential. The experimental results are compared with theory.

All-optical bistability in a type II GaAs/GaAlAs heterostructure

We have observed a bistability of low-temperature photoluminescence in a n-i-n type II GaAs/AlGaAs/AlAs quantum heterostructure. The integrated luminescence intensity ratio between the two states may reach 50. In as-grown samples, the bistability range lies between 40 and 250 W/cm2. These threshold values may be reduced on mesa-type samples, using an external load resistor. Spectral analysis and electrical measurements indicate that the two states correspond to hole accumulation in different layers of the structure. The transition occurs with the alignment of electronic Γ and X states due to optical pumping.

Soliton propagation and soliton collision in double-doped fibers with a non-Kerr-like nonlinear refractive-index change

A physical mechanism for a non-Kerr-like nonlinear refractive-index change in double-doped fibers is proposed, which shows for realistic material parameters a bistable (or two-valued) soliton regime with a large bistability range. The collision of two bistable solitons with a frequency difference in such materials is investigated. Solitons of the lower solution branch retain their shape after the collision. In contrast, two solitons of the upper solution branch with a low-frequency difference fuse to a single high-energy soliton after the collision. The possible applications of this effect for nonlinear photonic switching are discussed.

All-optical bistability due to charge transfer in a type II heterostructure

We report bistability of low temperature photoluminescence in a n-i-n type II GaAs/AlGaAs/AlAs heterostructure. The luminescence intensity ratio between the two states reaches 50, and no external bias is needed. The bistability range lies between 40 and 280 W/cm 2. The two states are thought to correspond to different charge accumulations in the structure. The redistribution of charges is due to competition between slow type II and fast type I recombination in the center of the structure.

Systematic design of chemical oscillators. 69. A general model for pH oscillators

A four-variable, five-reaction model is proposed for the family of pH oscillators. All major characteristics of these systems, both those observed in experiments and those found in mechanistic studies, are well represented by the model. The model can be further reduced to two smaller versions. In addition to the characteristic pH oscillation, a broad range of bistability is found in one of the reduced versions. The most important feature, which is common to the three versions, but distinct from other oscillatory models, is the role of the fast protonation-deprotonatiun equilibrium in generating oscillation. This step plays a role both in the autocatalysis and in the negative feedback. Nine pH oscillators are discussed and explained on the basis of these models.

Theory of intrinsic bistability in a resonant tunnelling diode

There is a high charge density in the well of a double barrier structure when it is at resonance. This alters the potential profile through the diode and may cause it to have two stable states for a given applied bias. The authors have studied this effect both analytically and numerically. The analytical work extends the earlier calculations of Sheard and Toombs (1988). Their main result is a condition that must be satisfied for bistability to occur: the potential due to the trapped charge must shift the centre of the resonance by more than its width. This requires the resonance to be strong, which can be achieved by designing the barriers to be asymmetric at zero bias, but symmetric when the bias is near that required for resonance. The build-up of charge and the range of bistability can be increased by making the exit barrier more opaque, but the current through the diode decreases. These results are supported by numerical calculations, in which the Poisson and Schrodinger equations are solved self-consistently. The analytical and numerical calculations agree quantitatively, but they are only able to explain the experiments qualitatively. This is because their numerical model has a severe flaw, which plagues all simple quantum-mechanical simulations: it omits scattering which is vital in treating the contacts, particularly the accumulation layer from which charge is injected into the barrier.

Influence on the Hysteresis Effect of Various Parameters in Supertwisted Nematic Liquid Crystals

Abstract The influence of materials and cell parameters on the hysteresis effect in a supertwisted nematic LCD composed of chiral nematic layers is theoretically investigated. The variation of tilt angle of the director in a midplane of the LC layer with an applied voltage change is numerically calculated. Transition voltage Vn1 , recovery voltage Vn2 and reduced hysteresis width H=(Vn1 - Vn2)/Vn1 are evaluated under the different combinations of such parameters as the elastic constant ratios k = k33/k11 and ξ = k33/k22 , dielectric anisotropy Δe, pretilt angles θo on the electrode surfaces, total twist angle φ and the thickness of the LC layer d. The lower limits of the cell thickness and the pretilt angle, as well as the total twist angle, below which the bistable range completely disappears, are found to exist. The influence of various parameters on those characters are investigated.

Influence of boundaries on dissipative structures in the Schl�gl model

The stationary spatial structures arising in the Schlogl model of first order nonequilibrium phase transitions are investigated for a one-dimensionals system of finite length. The solution manifold and the occurring bifurcations are analysed systematically by varying the type of boundary condition, the boundary valuev R ,the system lengthL and the control parameterg. It is shown by plotting appropriate state diagrams that the bistability range of the infinite system is shifted to larger values ofg for small fixedv R and to smaller values ofg for largev R ,and that the shift depends sensitively uponL.

Destruction of bimodality by multiplicative noise.

We analyze the effects which arise from frequency noise in dispersive optical bistability. Over almost all the bistable range of the deterministic theory, the stationary probability distribution is strictly one-peaked instead of showing the expected bimodal configuration.

Characteristics of mode intensity and bistability in multimode lasers with saturable absorber. II. Multimode operation

The characteristics of the mode intensity and conditions for occurrence of optical bistability in a ring laser with a saturable absorber are considered. It is shown that the condition for the occurrence of optical bistability is common to single-mode and multimode lasers with a saturable absorber. The range of optical bistability is transformed as a result of changes in the homogeneous broadening, in the difference between the two relaxation coefficients of the upper levels in amplifying and absorbing parts of a laser, and in the rates of pumping of these parts.

A wedge cell characterization method for the bistable cholesteric twist cell

The bistable cholesteric twist cell (BCTC) described here is a liquid-crystal device which can be in either of two stable laminar configurations while a particular holding voltage is applied. The major shortcoming of previous implementations of this device was the narrow thickness tolerance required for proper bistable operation. In order to ascertain the effect which material parameters might have on increasing this thickness tolerance an adequate method is needed for characterizing the behavior of the cell. In this paper we describe a wedge cell method for characterizing the behavior of a given BCTC system. The characterization can be conveniently done within a single cell. The data obtained include both the thickness to pitch range for pratical bistable operation and the switching properties. All of these features can be interpreted in terms of static free energy curves calculated for the system. We have also used this wedge cell method to determine the effect of the bend to splay elastic constant ratio on the thickness range of bistable operation in the BCTC. The range is observed to increase with increasing ratio of bend to splay elastic constant. A material has been identified with a bistable thickness range in excess of 10%.

A Numerical and Experimental Study of the Bistable-Unstable Transition in Pressurized Flexible Disk Files

The bistable operating region of flexible disk files is limited at decreasing air flow rates by a transition at which undesirable gaps appear in the otherwise uniformly spaced disks of the pack. These spontaneous gaps, as opposed to the externally controlled gaps of the bistable range, are a consequence of local air flow fields at the outer edge of the disks. Experiments with external shrouds of various clearance showed axial periodicity in the occurrence of the gaps and provided physical insight which led to quantitative numerical solution of the nonlinear fluid equations. Two scales of the flow, i.e., the flow between individual disks and a peripheral unstable Couette flow, are found to couple in such a manner as to delineate the transition.

Origin of the bistable voltage margin in the AC plasma display panel

Bistability in gas-discharge cells is discussed from a general viewpoint. The physical mechanisms controlling the extent of this bistable range are examined by performing numerical simulations of the discharge dynamics in ac plasma panel cells under various assumed conditions. For the particular case of the commonly used neon + 0.1-percent argon mixture, the results give realistic bistable operating margins only when all three of the following conditions are satisfied: 1)incorporation of the electric-field distortion due to space charge; 2) inclusion of the dependence of the secondary-emission coefficient, γ, on the reduced electric field, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{c}/p_{0}</tex> , at the cathode; and 3) assumption of an insignificant value of γ for argon ions in comparison to that for neon ions.