Axial Voltage Research Articles

Inversion of extracellular current and axial voltage profile inChara andNitella

Reducing the pH of the bathing solution from 8.2 to pH 6 can induce an inversion of the extracellular current pattern that develops at the surface of Chara corallina internodal cells. A similar result can be obtained on some cells by changing the medium to a pH value of 10. In noninverting Chara cells the currents were strongly reduced when the pH value of the medium was changed between 3 and 11. Simultaneous measurements of the Chara transmembrane potential in the acid and alkaline regions revealed that a light-induced electrical potential gradient of approximately 24 mV was present in the axial (or longitudinal) direction. Correlated to the external current pattern inversion was an inversion of this internal longitudinal voltage gradient. Reillumination of Nitella cells, after a period of darkness, often resulted in a complete inversion of the extracellular current pattern. These results are discussed in terms of spatial and temporal control of membrane transport processes, and in particular the control of current loops that pass through these cells.

Cortical axon branches of ventrolateral nucleus neurons in the cat thalamus

GABA-ergic thalamic reticular neurons function generically or singularly in a state-dependent manner: during quiet sleep they synchronously and rhythmically inhibit thalamocortical neurons (TCNs) via bursts, thereby eliciting the low-threshold Ca2+ potentials in TCNs that are crucial to oscillatory network behavior in the thalamo-reticulo-cortical system; during wakefulness they shape the flux of ascending sensory information by inhibiting TCNs with asynchronous and arrhythmic single-spikes. To investigate how the reticulo-thalamic synapses, which occur throughout TCN dendrites, are able to effect such disparate functions, we have: (1) used a 1416 compartment model of a 3D reconstructed TCN; (2) triggered dendritic miniature (TTX-independent) and unitary (single-afferent) conductance-based synaptic events, and (3) recorded axial currents and voltage transients in all 1416 compartments simultaneously. For synapses at all dendritic locations, more than 79% of the charge transfer reached the soma, where it dispersed into other dendritic trees to return to the extracellular space. In accord, dendritic synapses in 80% of the arbor induced voltage responses that were severely attenuated at the soma (>75% loss). Spatio-temporal aspects of distributed postsynaptic responses were examined as well. Except for synapses in the 13 most proximal compartments, the amplitude and phase of the voltage responses degraded rapidly within a focal region that did not extend beyond the host tree, and was limited most often to a subtree. The bulk response (outside the focal region) was highly synchronous and uniform. Interestingly, there were not 1403 different focal regions, but only 20, each clearly distinct from the rest and sharply delineated. Structural attributes of the arbor determined their boundaries. Boundaries were invariant when the analysis was repeated on rescaled versions (length, diameter) of the reconstructed arbor. Unitary events also induced focal/bulk structures for both burst and single-spike triggers — paradigms that correspond to single-afferent drives during quiet sleep and arousal, respectively. Such qualities differ dramatically from previously proposed motifs of dendritic clustering, each of which carried nonlinear sensitivities to parameter values. We propose that dendritic clustering underlies the role of reticulo-thalamic synapses in the early processing of ascending sensory information and that bulk responses contribute robustness to the induction and maintenance oscillations in the thalamo-reticulo-cortical network.

Radioactive 2-DG uptake into the monkey brain examined in saggital sections

GABA-ergic thalamic reticular neurons function generically or singularly in a state-dependent manner: during quiet sleep they synchronously and rhythmically inhibit thalamocortical neurons (TCNs) via bursts, thereby eliciting the low-threshold Ca2+ potentials in TCNs that are crucial to oscillatory network behavior in the thalamo-reticulo-cortical system; during wakefulness they shape the flux of ascending sensory information by inhibiting TCNs with asynchronous and arrhythmic single-spikes. To investigate how the reticulo-thalamic synapses, which occur throughout TCN dendrites, are able to effect such disparate functions, we have: (1) used a 1416 compartment model of a 3D reconstructed TCN; (2) triggered dendritic miniature (TTX-independent) and unitary (single-afferent) conductance-based synaptic events, and (3) recorded axial currents and voltage transients in all 1416 compartments simultaneously. For synapses at all dendritic locations, more than 79% of the charge transfer reached the soma, where it dispersed into other dendritic trees to return to the extracellular space. In accord, dendritic synapses in 80% of the arbor induced voltage responses that were severely attenuated at the soma (>75% loss). Spatio-temporal aspects of distributed postsynaptic responses were examined as well. Except for synapses in the 13 most proximal compartments, the amplitude and phase of the voltage responses degraded rapidly within a focal region that did not extend beyond the host tree, and was limited most often to a subtree. The bulk response (outside the focal region) was highly synchronous and uniform. Interestingly, there were not 1403 different focal regions, but only 20, each clearly distinct from the rest and sharply delineated. Structural attributes of the arbor determined their boundaries. Boundaries were invariant when the analysis was repeated on rescaled versions (length, diameter) of the reconstructed arbor. Unitary events also induced focal/bulk structures for both burst and single-spike triggers — paradigms that correspond to single-afferent drives during quiet sleep and arousal, respectively. Such qualities differ dramatically from previously proposed motifs of dendritic clustering, each of which carried nonlinear sensitivities to parameter values. We propose that dendritic clustering underlies the role of reticulo-thalamic synapses in the early processing of ascending sensory information and that bulk responses contribute robustness to the induction and maintenance oscillations in the thalamo-reticulo-cortical network.

Steady growth cone currents revealed by a novel circularly vibrating probe: a possible mechanism underlying neurite growth.

The rate and direction of neurite growth have been shown in a number of studies to be determined by the distribution of adhesive sites on the growth cone. Recent evidence showing that the application of extrinsic electric fields can redistribute membrane molecules and alter both the rate and direction of neurite growth have raised the question whether endogenous electric fields might be produced by steady currents in growth cones. To investigate this question, we have devised a novel circularly vibrating microprobe capable of measuring current densities in the range of 5 nA/cm2 (near the theorectical limit of sensitivity), with a spatial resolution of 2 micron. The design of this device and the development of a novel algorithm for computing current vectors on-line is described. Using this probe we have found that cultured goldfish retinal ganglion cell growth cones generate steady inward currents at their tips. The measured currents, in the range of 10-100 nA/cm2, appear to flow into the filopodia at their tips and back outward near the junctures of the filopodia and the growth cone. The currents appear to be produced only during active growth. Ion substitution experiments support the conclusion that the majority of this current is carried by Ca2+ ions, which we postulate flow through a population of activated voltage-sensitive Ca2+ channels located on the filopodial tips. Calculation of the transmembrane current density (4 X 10(-6) nA/cm2) leads to an estimate of channel density (10 channels/micron2) in close agreement with the measured density of Ca2+ channels in other systems. The assumption that calcium channel proteins are conveyed to nerve terminals by active transport, whereas sodium channel proteins are conveyed passively by a slower somatofugal diffusion process [Strichartz et al, 1984], would explain why developing neurons tend to display Ca2+-sensitive electrogenesis at their growing tips, and Na+-sensitive action potentials later in development. In order to gain some insight into the possible role of these steady growth currents, we estimated the membrane depolarization and axial voltage gradient they produce. It is likely that the currents produce sufficient membrane depolarization (approximately equal to 4 mV) to cause autogenous activation of ion channel permeabilities. Similarly, the axial voltage gradient (approximately equal to 4 mV/cm) would be expected to move intracytoplasmic vesicles by electrophoresis at a rate (20-40 microns/hr) very close to that at which the filopodia are observed to grow.(ABSTRACT TRUNCATED AT 400 WORDS)

Electro-optic harmonic conversion switch for large-aperture multipass laser systems

We have demonstrated electro-optically tuned second-harmonic generation using Type I KDP inside a plasma-electrode discharge cell. An axial voltage of +/-52 kV is required to switch a 1.064-microm beam by conversion to 0.53/microm, in agreement with theory. Electro-optically tuned harmonic generation may be combined with a recently developed transparent plasma electrode to produce a large-aperture switch for multipass laser systems.

Experimental Investigation of Axial Field Limitations in MHD Generators

Axial field breakdown in nonslagging wall, combustion-driven MHD generators was characterized by a rapid decline in axial voltage and a change in the mode of current transport from a relatively diffuse mode to a highly constricted and destructive mode. Cinephotographic records obtained for a simplified configuration demonstrated that breakdown could be initiated either in the plasma or in the interelectrode insulator. Breakdown resulted only when a threshold voltage was exceeded, with the voltage increasing with insulator gap size. For the electrode wall configuration studied, the threshold voltage for plasma-initiated breakdown was significantly higher than that for insulator-initiated breakdown. For the maximum voltages achieved in the full generator experiments, only insulator-initiated breakdowns were observed. No qualitative difference in anode and cathode wall breakdown behavior was observed. The threshold voltage for the generator configuration was lower than the value observed for the same insulator gap size in the simplified experiments; however, the qualitative features were similar.

The Cornell Electron Beam Ion Source

An electron beam ion source (EBIS) for the production of low energy, multiply charged ion beams to be used in atomic physics experiments has been designed and constructed. An external high perveance electron gun is used to launch the electron beam into a conventional solenoid. Novel features of the design include a distributed sputter ion pump to create the ultrahigh vacuum environment in the ionization region of the source and microprocessor control of the axial trap voltage supplies.

Bifurcated tokamak equilibria related to the shrinking and the disruption of the current

A class of neighbouring resistive equilibria for a cylindrical tokamak is constructed, characterized by the invariance of the helical flux χ and of the quantity K = ∫ dV. The equilibria of this class bifurcate for critical values of the distance of the current channel from the metallic wall, while a cold plasma remains in contact with the wall. The bifurcation only exists for q < m/n in the current channel and for a peaked current, the critical distance from the wall depending solely on the degree of peaking. Any helically deformed equilibrium with a sufficiently peaked and constricted current (so as to reach the bifurcation point) is unstable with respect to a dissipative purely radial compressible mode which conserves approximately K and χ. The building up of the mode implies a decrease of the current, accompanied by a negative axial voltage near the wall. The resistive mode evolves towards a non-linear phase in which the instability exhibits an explosive behaviour. This phase, however, can only be reached if the radial mode is triggered by a helical deformation with sufficiently large amplitude as can be provided by a non-linearly saturated tearing or kink mode.

Computer-assisted monocyte esterase assay by flow-cytophotometry.

A Wang model 2200 computer has been interfaced with the Bio/Physics Systems, Inc. model 6300 Cytograf and model 2100 Distribution Analyzer. Using a custom designed software program, in conjunction with an azo-dye technic for staining monocytes for nonspecific esterase activity, it has been possible to obtain rapid and reliable data concerning relative values for intracellular monocyte esterase activity. The method is based on measuring the axial light-loss voltage signal for each of one thousand stained monocytes. Individual stained monocytes were assigned to one of four groups (A, B, C, D), dependent upon the magnitude of the signal and were given different rating values (1, 2, 3, 4) according to their group designation. A "score" was derived for each blood sample by multiplying the percentage of cells (monocytes) in each group category by the appropriate factor and summing these values. The technic permits rapid objective assessment of intracellular nonspecific esterase activity in monocytes suspended in a mixed cell population. Both Gaussian and bi-modal patterns for monocyte esterase were observed. The latter suggests a dual monocyte population.

Improvement in the voltage grading (axial and radial) of the generator column of a Van de Graaf generator by the use of a resistor chain

It is well known that the use of a series of resistors, connected between the equipotential rings of a Van de Graaff generator, improves the axial voltage grading of the generator. The work reported in this paper shows how the resistor chain also improves the radial voltage gradient. The electrolytic field mapping technique was adopted in the present work.

Interaction between a high-current arc and the air flow in an air-blast circuit breaker

Results are reported of experiments performed on the arc and air flow in an air-blast circuit breaker having a 19 mm-diameter profiled orifice. The arcs were sustained between fixed electrodes by triangular current pulses (risetime 1.3 ms, total duration 5–25 ms, peak values 3–17.5 kA) and subjected to mass-flow rates in the range 0.244–0.675 kg/s generated by reservoir pressures of 4.46–14.11 bars absolute (50–190 lb/in2 g). The parameters measured were the overall arc voltage and current, the axial voltage distributions, the extent of the luminous-arc core and thermal region surrounding the arc, and the radial and axial pressure distributions through the orifice. The experimental results indicate the influence upon local and overall arc properties of the position, polarity and material of the upstream electrode. The detailed nature of these measurements has allowed a critical assessment to be made, for the first time, of integral boundary-layer analysis for high-current arcs under realistic circuit-breaker conditions.

Comments on 'Pinch effect in electrical explosion of metal cylinders'

Lipiec et al. (see ibid., vol.13, 537, 1971) are correct in surmising that their data do not represent a situation dominated by magnetic pinch forces, but they do not go far enough in interpreting their results. It is clear that their hollow cylinder is undergoing a vaporization expansion limited by exactly the same kind of wave as is encountered in exploding wire experiments. The main difference lies in the implosion geometry. Because of the boundary conditions the hollow cylinder vaporizes from its inner surface and the expanding vapor implodes. The conducting cross-section decreases as the vaporization wave traverses the annulus toward larger radii. The axial voltage follows the resistance rise. Because the singularity at the origin is excluded in this geometry the voltage peak will not be as sharp as in the case of cylindrical wires, nevertheless, when voltage in the axial direction reaches high enough values, a breakdown will occur in the expanding vapor close to its leading edge where densities are high enough so that conduction processes can begin.

Numerical calculations of the electric fields around the hoop structure of Van de Graaff accelerators

Electric field strengths have been evaluated at the surface of circular and oval hoops in the geometry of a Van de Graaff accelerator. The results are compared with the analytical results of Boag 1) and it is shown that the use of oval hoops is only effective for small axial voltage gradients.

Investigation of the glow phase in spark discharges

The axial voltage distribution of spark discharges in hydrogen, nitrogen and carbon dioxide is studied during the transient glow phase over a wide range of pressures. The results indicate that a glow mode develops in discharges which is initiated by the Townsend mechanism and is independent of external impedance. It is characterized by fixed values of cathode fall voltage and the ratio electric field to pressure in the positive column.

Distribution of temperature, voltage and electric field in the d.c. arc plasma of uranium matrix in air under atmospheric pressure

The “axial” temperature of the d.c. arc with uranium matrix between graphite electrodes was investigated using the “two lines” method with Zn, Cu and Fe. An axial gradient was found. Beginning at the anode the temperature rises towards the cathode, through an isothermal region in the centre of the arc core. Core dimensions, measured with the aid of a cine-camera and densitometric measurements of its negative, are given. A new method for measuring voltage and electric field in the arc plasma was developed. The method consists of passing a “ladder” of tungsten wires through the plasma and measuring the voltage oscilloscopically. The axial voltage gradient, axial and radial electric field and plasma width were measured directly. A comparison of this method with the usual “ V a + V c + E z . l” method was made. An empirical relation between the axial voltages and temperatures was developed.

On the Response of Interleaved Transformer Windings to Surge Voltages

The high series capacitance theory for the response of interleaved transformer windings to surge voltages is criticized from the point of view that an increased series capacitance as a result of interleaving is incompatible with the concept of a pure capacitive initial voltage distribution. A new theory is proposed according to which the distributed earth capacitances are charged up during an initial period by heavy currents flowing into the winding through surge impedances formed by the coils as a result of interleaving. Formulas are derived for the initial voltage distribution and for the maximum axial voltage gradient.

A new electron gun for picture display with low drive signals

The paper discribes an approach to the problem of picture tube guns for small signal service. A Pierce-type cathode delivers a collimated parallel beam of 1600 microamperes at 250 volts (microperveance: 0.4). This beam is injected into a cylindrical cavity of appreciable length (3/4-inch long, 1/4-inch diameter). It is focused upon a small aperture at the far end using a parabolic axis potential. This axial focusing field is approximated by three cylinder segments at two intermediate voltages. To modulate the beam by lateral deflection, the cavity is again bisected through an axial plane and signal voltage is set up between half cylinders. This modulation by two crossed-electrostatic fields ("CFM" modulation) has been successfully applied in transistorized television, using a seven-volt video signal on a beam of 900 microamperes.

A new electron gun for picture display with low-drive signals

The paper discribes an approach to the problem of picture tube guns for small signal service. A Pierce-type cathode delivers a collimated parallel beam of 1600 microamperes at 250 volts (microperveance: 0.4). This beam is injected into a cylindrical cavity of appreciable length (3/4-inch long, 1/4-inch diameter). It is focused upon a small aperture at the far end using a parabolic axis potential. This axial focusing field is approximated by three cylinder segments at two intermediate voltages. To modulate the beam by lateral deflection, the cavity is again bisected through an axial plane and signal voltage is set up between half cylinders. This modulation by two crossed-electrostatic fields (CFM modulation) has been successfully applied in transistorized television, using a seven-volt video signal on a beam of 900 microamperes.