Self-oscillating Process Research Articles

Self-oscillations in a weakly ionized energy absorbed substance

A new mathematical model for the description of self-oscillation processes in a weakly ionized low-temperature plasma is suggested.

Optical self-oscillatory medium based on a Fabry–Perot interferometer

An experimental demonstration is reported of the feasibility of using an MIS–liquid crystal cell inside a Fabry–Perot interferometer as a self-oscillatory medium for the transmission of excitations in the form of traveling pulses. It is shown that the processes in such an active medium are similar to self-oscillatory processes in the Belousov–Zhabotinskii reaction.

Self-oscillations of the mirrorlike sodium vapor driven by counterpropagating light beams.

The threshold characteristics of the static and periodic instability of the single feedback mirror device are investigated for a homogeneously broadened two-level medium as a function of the input intensity, the detuning, the buffer-gas pressure, the atomic concentration, and the round-trip time d, and compared with experimental results. For a large range of parameters that agrees with the experiment, the self-oscillation process is shown to be mainly induced by the longitudinal grating, which ensures a large instability domain, and controlled by the buffer-gas pressure, which must be low enough in order that the threshold period of the oscillation is constant on a doughnutlike transverse profile and nearly equal to 2d. This oscillation, called the 2d oscillation, is neither a result of pure phase-conjugate-mirror operation of the atomic medium nor a result of a Rabi sideband gain process. It is shown to take place through a mixture of phase-conjugate-mirror and ordinary mirror operations, which are both allowed by the specific optical arrangement of the device.

Circadian rhythms of calcitonin gene expression in the rat.

The daily changes in rat thyroid calcitonin and its specific mRNA concentrations, and the relationship between their dynamics and the plasma levels of calcitonin, calcium and phosphate over a 24-h period were investigated. The circulating calcitonin concentration rose during the daily dark period when plasma calcium and phosphate levels were minimal, indicating that plasma calcitonin rhythm cannot be generated directly by a linear effect of calcium on hormone secretion. Moreover, we established that the expression of the calcitonin gene also exhibited periodic dynamics observable at the pretranslational level: the gland content of hybridizable specific calcitonin RNA displayed daily rhythms; specific RNA levels peaked during the light period and were minimal during the first part of the dark period. Significant changes in thyroid calcitonin concentrations also occurred over a 24-h period. Statistical analyses which distinguished between variations over the 24-h period and residual variations were performed to test the relationships between the various parameters. The daily rhythms of hybridizable RNA, thyroid calcitonin and plasma minerals appeared to be in phase, while the plasma calcitonin concentration displayed variations out of phase with these rhythms. The implication of the correlations observed on the residual variations is discussed in comparison with the temporal relationship between the daily variations. The results fit the hypothesis that hormone production and secretion are self-oscillating processes. Plasma concentrations of calcium and phosphate might play a role in the synchronization of the calcitonin metabolism periodicity.

Thermal grating-mediated wave mixing and beam amplification in nematic liquid crystal thin films

A model is presented of thermal grating-mediated wave mixing and amplification. The model includes a strong pump beam, a weak probe beam, and a first-order diffracted beam. The coupled Maxwell's wave equations and the thermal diffusion equation are solved using a self-consistent formalism. The influence of various input beam parameters (the pump to probe beam intensity ratio, beam intensities, crossing angle, wavelength) and sample parameters (the thermal nonlinear coefficient, thermal conductivity, sample thickness) on the wave mixing effects is considered. Some recently observed infrared beam amplification effects have been qualitatively described by the theory of the optimum configuration for signal (probe) beam amplification with nematic liquid crystals. The results are important for optical phase conjugation and self-oscillation processes involving infrared lasers, and demonstrate the particular usefulness of liquid crystals for these applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Leao's spreading depression: Synaptic regulation of a diffuse self-oscillating process in the central nervous system

The evidence reviewed in the paper shows that the spreading depression (SD) belongs to the mass of closely packed neurons which can support qualitatively new phenomena occurring at a more primitive level of cellular interaction. The latter becomes prepotent under extreme conditions, overloading the local energy supply and homeostatic mechanisms. The two levels of neural integration, the highly heterogeneous specifically connected synaptic level and the statistically uniform diffusively organized nonsynaptic level, are always present in all forms of brain activity and mutually influence each other. While phenomena mediated by nonsynaptic interaction overrule the synaptic ones under resting conditions, excessive synaptic excitation may either switch the affected brain region from synaptic to nonsynaptic interaction (spike-triggered SD) or assert the synaptic interaction over the nonsynaptic one (functional blockade of SD). Nonsynaptic interaction is an inherent property of brain, an obligatory consequence of the trade-off between maximal packing density and independent function of individual elements of the system which sets definite limits to the maximum activation of synaptic processes, contributes to slow synchronization of neural populations and plays an important role in various instances of brain pathology. The phenomena generated at this level belong to the family of autowaves, share their typical properties and can be described by similar formal rules.

Free convection in geophysical processes

A highly significant geophysical process, free convection, is examined. Thermal convection often controls the dynamical behavior in several of the earth's envelopes: the atmosphere, ocean, and mantle. Section 2 sets forth the thermohydrodynamic equations that describe convection in a compressible or incompressible fluid, thermochemical convection, and convection in the presence of thermal diffusion. Section 3 reviews the mechanisms for the origin of the global atmospheric and oceanic circulation. Interlatitudinal convection and jet streams are discussed, as well as monsoon circulation and the mean meridional circulation of ocean waters due to the temperature and salinity gradients. Also described are the hypotheses for convective motion in the mantle and the thermal-wave (moving flame) mechanism for inducing global circulation (the atmospheres of Venus and Mars provide illustrations). Eddy formation by convection in a centrifugal force field is considered. Section 4 deals with medium- and small-scale convective processes, including hurricane systems with phase transitions, cellular cloud structure, and convection penetrating into the ocean, with its stepped vertical temperature and salinity microstructure. Self-oscillatory processes involving convection in fresh-water basins are discussed, including effects due to the anomalous (p,T) relation for water.

Plasma self-oscillations in semiconductors within submillimetre frequency range

In strong electric fields, when the impact ionization becomes intensive and the electron drift velocity may decrease with the growing field, self-oscillating processes arise in semiconductors at very high frequencies up to the submillimetre range. These processes are due to negative dynamic differential conductivity of plasma within the corresponding frequency region. The highest frequency branch results from the excitation of plasma oscillations.

Self-Oscillations of Heterogeneous Catalytic Reaction Rates

Abstract The dynamics of a chemical system is thc main characteristic of the system. An attracrivc problem of the dynamics pertains to selfoscillation processes. These processes are promising for a study of regularities tnttetant in the Lmemctioa of a reaction medium wttfi a catalytic surface under norrsteady-state conditions operating for a longer time.

Self-oscillations in an underexpanded jet flowing into a barrier

The distribution of the phases and amplitudes of the static pressure fluctuations with self-oscillations of an underexpanded jet flowing into a barrier is obtained experimentally in the present paper. The distribution of the Mach number in the compressed layer and in the subsonic flow in front of the barrier is shown. The results of the measurements of the characteristics of the self-oscillation process are discussed.

Protein synthesis rhythm

Variations of protein content and of the rate of amino acid incorporation into protein were studied for several cells types as a function of time. It was found that both characteristics displayed a definite periodicity. The evidence available suggests that this periodicity reflects the existence of a rhythm of protein synthesis. The period of this rhythm, varying between 20 min and 2–4 hr for different cell types, suggests that we are dealing with a new class of biological rhythms with a period about 1 hr; for these rhythms the term circahoralian is proposed. This class of rhythms appears to include periodic changes of cell permeability, size of the precursor pool, electric properties (for certain cell types) and the activity of several enzymes. All these rhythms represent endogenous self-oscillating processes, frequently showing no requirement for external initiation. The regulation of protein synthesis rhythm appears to occur predominantly at the cytoplasmic level and to involve interactions of circahoralian rhythms at the membranes and at the ribosomes. Rhythms are found both in non-differentiated and in maximally differentiated cells. The period may be different in different specialized cells of a given organ. The existence of functional adaptations of protein synthesis rhythm is found and some evidence for cellular “memory” in this process is obtained. Non-identity of oscillation periods for different cell types in a given tissue and different degree of synchrony might represent a basis for the temporal regulation of tissue functions.

Low-frequency self-oscillatory processes in propellant combustion

Low-frequency self-oscillatory processes in propellant combustion

On the asymptotic behavior of solutions of certain nonlinear problems of hydrodynamics: PMM vol. 35, n≗6, pp. 978–985, 1971

Periodic solutions of heat conduction equations with boundary conditions of the relay kind are found for a finite interval, and the behavior of such solutions at unlimited time increase is analyzed. Periodic solutions of heat conduction equations with nonlinear boundary conditions were considered in [1–4, 10], while in [5, 6] periodic solutions of nonhomogeneous heat conduction equations with their right-hand sides nonlinear with respect to the unknown functions are presented, and the asymptotic behavior of related initial problems is analyzed. Solutions of this kind define self-oscillating processes occurring in various branches of hydrodynamics (theory of filtration and diffusion [3–6]).

A Method of Analysis in the Theory of Sinusoidal Self-Oscillations

The article is devoted to the theory of weak resonance action on self-oscillating systems. The theory is based on the method of secondary-simplification of "shortened" equations for amplitudes and phases of the self-oscillating process. A series of new results is obtained. These results are taken as a basis for the creation of new radiotechnical devices.