Ion Current Fluctuations Research Articles

Noise Characteristics of Turbulent Diffusion Flames with Coherent Structure

Abstract In order to elucidate the interrelationship between flame structure and noise characteristics and to obtain those properties which are easily measurable and understandable, and are strongly correlated with the acoustic pressure perturbation, three kinds of flames with different structure are first formed in a plane shear layer by varying the flow and turbulence conditions: a flame within which organized eddies are clearly observed, a flame which has a rather complicated appearance and a higher eddy-formation frequency than the first due to the increased mean convection velocity, and a flame without any organized eddy, which is stabilized under the same flow conditions as the first flame, but has increased turbulence levels. Simultaneous measurements and FFT-analyses of the fluctuations of sound pressure, ion current, temperature, and CH-emission are made on these three flames. The results are shown concerning not only clear properties of the correlations between flame structure and sound intensit...

Local Reaction Zone Configuration of High Intensity Turbulent Premixed Flames

Abstract The present study has been performed to explore the local reaction zone configuration of high intensity turbulent premixed flames in detail by using a micro-electrostatic probe of two identical sensors. The local reaction zone configuration is shown to be determined by analyzing the ion current fluctuations. The radii of the local reaction zone curvatures are examined and expressed in frequency distribution. The radii of curvatures of the local reaction zone convex toward unburned mixture are distributed in a wider range than those convex toward burned gas. The mean radius of the local reaction zone curvatures decreases as the turbulent intensity increases, while the smallest and the most probable radii of curvatures scarcely change with the turbulent intensity. Both the most probable and the mean radii of curvatures measured in the present study are larger than the micro scale of turbulence. It is presumed that even in intense turbulence, whose Kolmogoroff scale is smaller than a laminar flame t...

On Current Fluctuations in Near‐Earth Space Plasma with Lower‐Hybrid‐Drift Turbulence

AbstractElectron and ion current fluctuations caused by lower‐hybrid‐drift turbulence are estimated within nonlinear theory for the plasma of the ionospheric F‐layer, as well as for the plasma mantle and the plasma sheet boundary layer of the tail of the earth's magnetosphere. They are found to be of the order of 10−14 — 10−11 A/m2 and 10−13 — 10−9 A/m2, respectively.

Characterization of an ECR Microwave Plasma Etching System

ABSTRACTAn ECR microwave plasma etching system and an alternating bias voltage source with variable frequencies ( 10kHz to 10 MHz ) have been built for the study of the effects of the substrate bias on the submicron feature etching. A quadrupole mass spectrometer was used for the end-point monitoring and the plasma chemistry analysis. A Langmuir probe was used to characterize the etching plasma. The system can generate plasmas with densities ranging from 1×1015m−3 to 5×1016m−3 corresponding to gas pressures from 1×10−4 torr to 6×10−3torr at a fairly low microwave power. This condition results in a stable electron temperature. The magnetic field profile can be adjusted to obtain a constant plasma density of 2.8×1016m−3 and an electron temperature in kTe of 4 eV to 5 eV. The plasma beam is of 75mm in diameter with the ion current intensity fluctuation of about ±5% at the etching position for the gas pressures ranging from 4×10−4 torr to 3×10−3 torr at an absorbed power of 70Watts. The plasma density, the electron temperature, the breakdown power, and the sustaining power have been studied as functions of gas pressure in order to optimize the etching performance.

A fundamental study of electrostatic probe measurements to explore the microstructure of turbulent premixed flames. 1st Report. Effects of the curvature and path of the local flame front on ion current fluctuations.

In order to examine the structure of a high-intensity turbulent premixed flame to a further extent, an attempt has been made to examine the dependence of the characteristics of ion current on the flame configuration, i.e., the local flame curvature. When the curvature is smaller than the critical value, the maximum value of the ion current decreases and the half value period of the ion current increases as the flame curvature decreases. Even though the local flame curvature is constant, the ion current fluctuation changes its shape significantly as the flame path across the probe changes.

Local reaction zone thickness of a high intensity turbulent premixed flame

The present study has been performed to explore the detailed aspects of the reaction zone of a high intensity turbulent premixed flame, classified as a distributed reaction zone flame based on the Klimov-Williams criterion. A co-axial burner, and a micro-electrostatic probe were used to examine the local reaction intensity profiles across the flame. The measured ion current records imply that unburned mixtures and burned gases exist separately in the flame zone and local reaction zones of thicknesses much thinner than the flame zone can be defined. Assuming that the half value period of an ion curent fluctuation is a measure of the local reaction zone thickness in the direction passing the probe, the probability density function of it was examined to explore the aspects of local reaction zones in the flame zone. In order to interpret the probability density function distrubution of half value period, the ion current fluctuations to be recorded were predicted on the basis of the knowledge of ion current characteristics at premixed flame measurements. Considering the fluctuations of the inclined angle and velocity of the local reaction zones passing the probe, the probability density functions of the half value period were predicted for various thicknesses of the local reaction zones. Comparing the predicted probability density functions with the experimentally obtained ones, it was concluded that even in the extremely intense turbulence which satisfies the distributed reaction zone condition based on the Klimov-Williams criterion, the local reaction zone thickness is close to that of the laminar flame. This implies necessity to discuss the structure of the distributed reaction or to establish a novel criterion for existence of the distributed reaction zone not based on the characteristics of unbruned mixture turbulence.

Selective electrochemical biosensors from state-switching of bilayer and monolayer lipid membranes by lectin-polysaccharide complexes

Interaction of the lectin concanavalin A with the polysaccharide glycogen can provide rapid spontaneous transients of the surface potential at bilayer and monolayer lipid membranes. The selective binding process can cause large, rapid potassium ion current fluctuations across bilayer membranes in a manner that is periodic and reproducible. The frequency of these transient ion current signals was shown to be related to sub-nanomolar concentrations of the reactive agents in aqueous solution. The physical mechanism responsible for ion current modulation was investigated by fluorescence methods using lipid vesicles, by the thermal dependence of the potassium ion current across planar bilayers and by pressure-area and dipolar potential measurements of lipid monolayers at an air-water interface. The mechanism is primarily associated with physical perturbations of lipid membranes by lectin-polysaccharide aggregates, resulting in the formation of localised domains of variable electrostatic potential and conductivity.

Effects of ambient gases on ion emission stability of liquid-metal ion sources

Effects of ambient gases on ion emission stability of Au–Si–Be and Pd–Ni–Si–Be–B liquid‐metal (LM) ion sources have been studied. Water vapor and oxygen gas have significant effects on ion emission stability. These effects are thought to be due to oxidation of the liquid‐metal surface, especially the Be atoms. A higher operating temperature enhances these effects, while it reduces the effects for Ga‐ion sources. Vapor pressures of resultant oxides are discussed to explain these results. We have obtained positionally stable ion beams (fluctuation <0.08 μm) with a constant ion current (fluctuation <0.02%) and a constant beam diameter (fluctuation<0.03 μm at beam diameter of 0.2 μm) by operating the sources under a vacuum pressure of 2×10−7 Torr in a 100 kV FIBI (focused‐ion‐beam implanter).

Spontaneous lipid bilayer transmembrane electrical oscillations induced by concanavalin A — polysaccharide interaction

Potassium ion currents through bilayer lipid membranes were modified by the membrane-surface reaction of concanavalin A and the polysaccharides dextran and glycogen. Aggregative reaction with glycogen occasionally induced spontaneous periodic ion current fluctuations with cycle times of minutes and durations of over one hour. Different electrochemical characteristics were observed between large planar lipid membranes and filter paper supported membranes, providing an indication that the aqueous unstirred surface layer participates in the control of the surface aggregative event. Lipid chemical composition was implicated in the development of spontaneous oscillations.

Fractionation Effect in Surface Diffusion of Potassium Isotopes on Tungsten

The isotope effect has been measured for surface diffusion of potassium isotopes on polycrystalline tungsten using ion thermoemission noise method. It has been noted that the isotopic ratio 41K/39K obtained by measurement of noise component is different from isotopic ratio for DC component. This shift was interpreted as isotope fractionation effect in surface diffusion of adsorbed potassium. It was found that the spectral density function of the ion current fluctuation can be approximate by the Lorentzian function S = S0/1 + (ωτ)2.

Fluctuations of a negative ion current in turbulent He-II

The power spectral density of the fluctuations of an ion current through a region of vortex-line turbulence in He-II shows a high frequency asymptotic behavior of f −4 over four orders of magnitude. This frequency dependence is consistent with a generalized description of the motion of ions trapped on vortex-lines.

液体ガリウムイオン源と走査型イオンマイクロビーム

Emission characteristics, such as ion current vs. voltage relationships, ion emission angle, ion current fluctuation, temperature effect, and mass analysis, are measured for a hydrodynamic (EHD) liquid-gallium ion source. A scanning ion microprobe system using a liquid-gallium ion source and a voltage asymmetric three-electrode lens is developed. It produces 2-20 keV Ga+ beams of 0.1-5 μm diameter with 20 pA-8nA current. This ion optical system is well suited for variable-energy microprobe applications.

Ion-current fluctuations recorded with a cylindrical electrostatic probe passing premixed flames

The ion-current fluctuation recorded with a cylindrical, electrostatic probe traversing a premixed flame has been studied. The experiments were performed by moving the probe across a rectangular or circular-nozzle burner flame. Effects of the ion-denesity distribution on the ion-current fluctuation were estimated by analyzing the phenomena near the probe on the basis of the continuum probe theory, and the deviation of the ion current was shown to increase with the ion-density gradient. By comparing the maximum ion currents to the probe traversing the flame in different directions, the deviation was found to decrease with increasing probe velocity. It was estimated to be less than 15% if the probe was used in the range of probe velocities higher than 3 m/sec. An analysis was made for inferring the ion-current fluctuations to be recorded with the probe being passed through flames of known configuration. The results showed that the ion-current fluctuation of an inclined or curved flame could be inferred fairly well on the basis of the fluctuation derived from a plane flame parallel to the probe axis.

Absolute cosmic ray ionization measurements in a 900‐liter chamber

We report a new measurement for the cosmic ray sea level ionization, 2.15 ± 0.05 in ion pairs/s cm³, in agreement with the previous determination by Shamos and Liboff (1966) (2.18 ± 0.05 ion pairs/s cm³) and the calculation by O'Brien (1970) for solar minimum (2.22 ion pairs/s cm³). In contrast with the 1966 measurement (which used CCl2F2), the present work was done in an air‐filled 906‐l aluminum chamber, with a wall thickness of ∼0.3 g/cm². Measurements were conducted over Lake St. Clair and Lake Huron during 1973 and 1974. Corrections for alpha and beta wall contamination were made in two independent ways, by an analysis of the ion current fluctuations and by operating the chamber in the low‐background Morton Salt Company Mine, located 600 m below ground in Painesville, Ohio.

Ionic channels in excitable membranes. Current problems and biophysical approaches

Ionic channels are gated aqueous pores whose conformational changes are driven by the electric field in the membrane. Gating may be studied by three electrical methods: ionic current transients, ionic current fluctuations, and "gating current," and probably occurs through a series of conformational changes in the channel leading to an all-or-nothing opening of the pore. When the potential is held constant, the gating steps come to equilibrium rather than reaching an energy-dissipating, cyclic steady state. The kinetic models now in use eventually need to be changed to correct disagreements with several recent studies. Diffusion of ions through open channels is very fast but involves many interactions of ions, pore, and solvent that lead to ionic selectivity, saturation, block, and flux coupling. Our description of the ionic fluxes can be improved by abandoning continuum models in favor of more structured ones. Problems to be solved include determining how many ions occupy a channel at once and what to be solved include determining how many ions occupy a channel at once and what kind of energy barriers they must cross in traversing the membrane. Ultimately we will need to know the chemical structure of the whole system to understand how it functions.

Electrostatic Probe Measurements in Propagating Flames : Part 1, The Relation between Flame Front Configuration and Ion Current

An experimental study has been made for ascertaining the relation between the combustion phenomena of a propagating flame and the ion current from the flame to an electrostatic probe or ionization gap. A schlieren system was simultaneously used together with the electrostatic probe to study a flame propagating through a stoichiometric propane-air mixture in a closed combustion tube in the initial pressure range from 100 to 600 mm Hg. It was found that the flame front might be disturbed by the turbulence of the unburned gas flow. The measured distance between the locations of schlieren front and maximum ion current lay in the range from 2 to 6 mm. When the flame front was disturbed, the ion current fluctuations were observed. These ion current of the flame front and were inferred to be closely to the flame front configuration.