Influence Of AC Electric Field Research Articles

Formation criterion and mechanism of electrical pitting on the lubricated surface under AC electric field

The formation mechanism of electrical pitting on the lubricated surface of steel pair was investigated, and the threshold condition to avoid the occurrence of electrical pitting was also established by using a static electrical pitting tester with high precision under the influence of AC electric field. Experimental results show that when the electrical pitting occurs, the interface voltage, interface impedance, and interface power increases slowly with increasing film thickness at a certain supply current. However, the interface voltage and interface power increases with increasing supply current, and the interface impedance decreases with increasing supply current at a certain film thickness. Furthermore, the pitting area versus the interface power relationship is a cubic function, where the pitting area increases with increasing interface power. It is also found that the supply current is the parameter that influences the pitting area the most. Moreover, three electrical pitting regimes are found under the influences of shaft voltage and oil film thickness, namely, pitting, transition, and no-pitting regimes. The boundary between the transition and no-pitting regimes is called the first threshold voltage, and another boundary between the transition and pitting regimes is called the second threshold voltage. However, the supply current insignificantly influences these two threshold voltages. Correlation formula of threshold voltage and oil film thickness is also derived as the formation criterion of electrical pitting for a wide range of oil film thickness.

ELECTRO-OPTICAL PHENOMENA DUE TO INFLUENCE OF LIGHT BEAMS ON MATERIAL PARAMETERS OF LIQUID CRYSTALS

Modulation of material parameters of liquid crystals (LC) due to absorption of light beams allows to control the reorientation of the LC under the influence of ac electric fields. Particularly, it makes possible recording of photorefractive-like orientation gratings. Such gratings are phase shifted with respect to the pattern of interfering light beams. The material and external parameters determine the magnitude of the shift. These photorefractive-like phase shifted gratings are stationary, and no diffusion processes are involved in their build-up.

Influence of Polarization Rate and Dielectric Loss on ER Effects

A simplified model is considered to describe the resistive transport and diffusion of charge carriers within or around an ER active particle under influence of AC electric field and temperature. The effective polarization strength, dielectric constant and dielectric loss of the particle are derived from this model. Considered the effects of shear field, the criteria for ER activity are presented as ωτ >10-4, 1<d/λ<102 and ωτ d/λ<1 for ω<103s-1. The criteria determine the lower and upper limits of the polarization rate and dielectric loss of ER particles. The criteria are testified by the following experimental results. First, the measured lower limit of diatomite particle conductivity is 7.3×10-8S/m. Second, the shear stresses at the shear rates from 9.9 to 100 s -1 at 1kV/mm field start to rise with temperature from 25°C. Third, with decreasing shear rate or/and increasing electric field strength, the peaks of shear stress shift down the lower temperatures.

Active Transport in Biological Membranes and Stochastic Resonances

The role of intrinsic fluctuations of the membrane electric potential (barrier height) in the active transport of ions through cell membranes is examined. Experimental data [D.-S. Liu et al., J. Biol. Chem. 265, 7260 (1990)] on active transport of ${\mathrm{Na}}^{+}$ in human erythrocytes under the influence of ac electric fields can be interpreted as the evidence of stochastic resonance between the external field and the fluctuations of the membrane potential. The calculations show that in the considered system one can expect also the appearance of aperiodic stochastic resonance.

Electric field induced domain structure in ferroelectric liquid crystal DOBAMBC

Abstract The influence of an ac electric field on the helical pitch in ferroelectric liquid crystal DOBAMBC has been investigated in a broad range of frequency. The role of the permanent polarization and dielectric anisotropy in the helix unwinding process were studied. The formation of a periodic domain structure under influence of ac electric field was observed. The period of this structure decreases with increasing ac electric field frequency. The possible mechanisms leading to the observed periodic domain structure and its behavior in ac electric field are discussed. The experimental results are compared with predictions of the Dmitrienko-Belyakov and Martinot-Lagarde models.

Electric-field-dependent thermal fluctuations of giant vesicles

The influence of ac electric field on the shape and thermal fluctuations of giant vesicles is theoretically investigated. The experiments show that at high frequencies (dielectric regime) vesicles deform into oblate ellipsoids with the symmetry axis parallel to the applied electric field, while at low frequencies (conductive regime) they deform into prolate ones. Depending on the medium conductivity, the transition frequency between both regimes may be as low as a few kilohertz.