Oscillation of electric potential

II. SPONTANEOUS OSCILLATION OF ELECTRICAL POTENTIAL ACROSS A LIQUID MEMBRANE... 

SPONTANEOUS OSCILLATION OF ELECTRICAL POTENTIAL AND INTERFACE TENSION IN AN OIL-WATER-SURFACTANT SYSTEM... 

The electrical potential across a LB film of dioleoyl-lecithin deposited onto a fine-pore membrane, imposed between equimolar aqueous solutions of NaCl and KC1, was reported to exhibit rhythmic and sustained pulsing or oscillations of electrical potential between the two solutions. These oscillations were attributed to the change of permeability of Na+ and K+ ions across the membrane, which originated from the phase transition of lecithin. 

The examples mentioned so far point to considerable flexibility of the auxin transport system. This view is also supported by the observation of oscillations of electric potential moving down Avena coleoptiles after illumination or after the supply of auxin (Newman 1959, 1963), by the report of fluctuations of lAA movement in segments of oat coleoptiles after blue light illumination (Thornton and Thimann 1967), and in individual plant parts, by the demonstration of even more pronounced oscillations of the export rate of radiocarbon from auxin-depleted segments of oat and corn coleoptiles, supplied with labeled lAA (Hertel and Flory 1968). It is further supported by previously mentioned (see Sect. 3.3.3.4) experiments of Shen-Miller (1973a), where rhythmic fluctuations of the lAA transport intensity in intact coleoptiles of oat and corn were observed, moreover the rhythmicity was out of phase between the upper and lower halves of geostimulated coleoptiles (Shen-Miller 1973b, p 169). 

FIGURE 3.7. The time course of electric potential. Time 0 indicates the onset of the first oscillation, (b) The simultaneous measurement of the time course of interfacial tension. The value at the onset of each oscillation fluctuated due to the macroscopic wave-linked interfacial movements and the subsequent fluctuation of the scattered light. A few tens of seconds after the onset of oscillation, we could measure the interfacial tension correctly again. 

Thus, equality of tangential components of the field, consisting of oscillations of electric and magnetic types on the borehole surface (r = a), results in the following system of boundary conditions for potentials A and A ... 

From a mathematical point of view eq. 10.27 present the field through a sum of oscillations of electric and magnetic types, in spite of the fact that in a uniform medium only one type of oscillation is present. However, it is obvious that between potentials Aq and there is a relation ... 

The pioneering experiments in this area are due to Teorell [6]. In this setup, aqueous solutions of electrolytes of different concentrations were kept in the two compartments (NaCl, KCl, LiCl) separated by the membrane, and a current of fixed magnitude was passed. Synchronous oscillations in electric potentials, resistance and pressure differences were observed. Teorell observed that (i) there exists a threshold value of current density below which one obtains highly damped or moderately damped oscillations, (ii) in the undamped case the oscillations go on for hours and start to die away when current becomes too low or Ag/AgCl electrodes gets exhausted, (iii) oscillations are... 

Instability at the liquid-liquid interface can also give rise to exotic phenomena. We will discuss in the following sections the generation of electric potential oscillations due to such instabilities at the interface (i) between nitrobenzene containing picric acid and... 

CAT+ would vary periodically in both the phases along with the ratio r= [CAT ]org/[CAT+]aq, which would be responsible for electric potential oscillations. The formation of reverse micelles in the non-aqueous phase would be responsible for the decrease in concentration of [CAT ] ,g in the non-aqueous phase. On the other hand, it would be compensated by the transfer from the aqueous phase. But this would require more H in the aqueous phase to interact with CTAB to generate CTA. The required amount of H+ would be produced by transfer of HP from the non-aqueous phase and the cycle would be repeated over and over again, giving rise to oscillations in electric potential and PH. Using relevant kinetic equations [27] and linear stability analyses, mathematical formalism has been developed. 

Outer vessel contains liquid of lower density while the inner vessel contains liquid of higher density. The system is intrinsically unstable and is naturally maintained far away from equilibrium. Up and down flow of liquid occurs through the capillary, which is reflected by the oscillatory movement of the fluid in the inner vessel. When the electrodes in the two chambers are connected to a voltage-measuring device, oscillations in electric potentials are also observed for the cases when aqueous solutions of electrolyte-water system or aqueous solution of polar non-electrolytes are used in the system. This type of hydrodynamic instability is different from Benard instability or Taylor instability [29]. 

Mathematical formalism has been developed using semi-empirical considerations [36, 37]. Computer simulation smdies show that resulting equation predicts oscillations. Attempt has been made to provide justification on the bases of Navier-Stokes equation but it is open to question. Dimensional analysis has recently been employed for investigating the phenomena [31]. Flow dynamics and stability in a density oscillator have been examined by Steinbock and co-workers [38], They have related it to Rayleigh-Taylor instability of two different dense viscous liquids. A theoretical description has been presented which is based on a one-fluid model and a steady state approximation for a two-dimensional flow using Navier-Stokes equation. However, the treatment is quite complex and cannot explain the generation of electric potential oscillations. 

Figure 11.11. Variation of amplitude of electric potential oscillation using aqueous solution of same concentration (1.0 m) of the substances belonging to different taste categories with the logrithm of their relative state indices.

Spontaneous oscillations are a widespread phenomenon in nature. They have been studied for a large number of experiments, including electrochemical systems such as the oxidation of metals and organic materials [Miller and Chen (2006)]. Electrochemical systems exhibiting instabilities often behave like activator-inhibitor systems. In these systems the electrode potential is an essential variable and takes on the role of either activator or the inhibitor. If certain conditions are met, an activator-inhibitor system generates oscillations [Krischer (2001)]. In this section we present experimental data of electric potential self-oscillations on the electrode of IPMC which results in the oscillating actuation of the material. Furthermore, we also present a physical model to predict these oscillations. 

To assess the effect of drugs on a neuromuscular synapse, either the endplate potentials or the intensity of muscular contractions in response to rhythmic electric stimulation of the nerve are registered In the first case, the evoked gradual responses of the neuromuscular junctions are recorded by means of thin electrodes. Changes in the magnitude of these responses are criteria of the efficiency of the drugs with respect to naptic transmission. In the second case, the facilitation or inhibition of synaptic transmission is reflected by either an increase or a decrease in the intensity of muscular contractions. For convenience, the latter are usually transformed into corresponding oscillations of electric current. 

Owing to the effects of mechanical anharmonicity - to which we shall refer in future simply as anharmonicity since we encounter electrical anharmonicity much less frequently -the vibrational wave functions are also modified compared wifh fhose of a harmonic oscillator. Figure 6.6 shows some wave functions and probabilify densify functions (iA A ) for an anharmonic oscillator. The asymmefry in and (iA A ) 5 compared wifh fhe harmonic oscillator wave functions in Figure f.i3, increases fheir magnitude on the shallow side of the potential curve compared with the steep side. 

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