Current Pulse Amplitude Research Articles

Temperature Influence on Properties of Microdischarges

The effect of temperature on the visual and electrical characteristics of the microdischarges generated inside porous alumina ceramics is presented. The temperature was found affecting discharge onset voltage, current pulse amplitudes, and other discharge properties. The increase in temperature caused the onset voltage to decrease and the current pulse amplitudes to increase. The uniformity of the discharge distribution was also improved by the temperature increase.

Computer Modeling of Capillary Pinching Discharge for the Purpose of XUV Radiation Source Design

Fast capillary discharge in nitrogen is studied as a source of incoherent monochromatic radiation in “water window” wavelength range. Namely, the generation of spectral line with the wavelength of 2.88 nm, corresponding to the quantum transition 1s2p → 1s2 of heliumlike nitrogen ions, is studied. Radial-time dependences of selected plasma quantities and of specified line emitted intensity, corresponding to our experimental setup with a 3.2-mm capillary diameter, discharge current pulse amplitude of 13.5 kA, and a 72-ns quarter period, are presented for various initial pressures of nitrogen. The evaluated peak value of the line intensity has been found at about 50 Pa and has been proved by the laboratory experiment.

A 1-MJ capacitive energy storage

A capacitive energy storage is intended for generating high-power current pulses. The setup consists of two capacitive energy storage modules, a control console, and a cable collector for connecting a load to the setup. Each module is a capacitive energy storage with a 0.5-MJ stored energy and 18-kV voltage, which is based on eight capacitor cells with reverse switch-on dynistors as switches. The module volume is 1.3 m3. The semiconductor switches in the capacitor cells are activated by light pulses, which are transmitted from the control console through fiber-optic cables. The unit is designed for operating in the programmable discharge mode, at which the semiconductor switches in the capacitor cells are switched on nonsimultaneously but in accordance with a specified program. When the discharge of all the cells is switched on simultaneously and the load is short-circuited, the maximal amplitude of the output current pulse is 800 kA. The rise time of the discharge current pulse of the cell is 150 μs.

Short, powerful, and agile current drivers for magnetic resonance

AbstractA system for the generation of short, powerful, and agile pulses of current drive is described. The system is made of several submodules, most of them “home‐made” and is capable of producing current pulses ranging from 9 A for 150 ns pulses to 94 A for 1400 ns pulse duration, when connected to a nominal 0.6 Ω/2.75 μH coil. The amplitude of successive current pulses can be updated in the ∼μs time scale. Such capabilities are very useful in the field of electron spin resonance microimaging and for the measurements of diffusion by electron spin resonance. A variant of the system can also be used for the nuclear magnetic resonance imaging of samples located in grossly inhomogeneous magnetic field or for solid‐state nuclear magnetic resonance imaging. Details of the system electronic design as well as some representative experimental results are provided. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 39B: 119–127, 2011

LEDs based on InAsSbP/InAsSb heterostructures (λ = 4.7 μm) for carbon monoxide detection

Light-emitting diodes (LEDs) operating in the 4.4–4.8-μm wavelength range have been developed for detecting the presence of carbon monoxide (CO) in air. The proposed LEDs are based on InAsSbP/InAsSb heterostructures with InAs0.85Sb0.15 active region, which were grown by metalorganic vapor-phase epitaxy. The electrolumuinescent properties of LEDs have been studied. The output power of LED operating in a pulsed mode reaches 50 μW at a current pulse amplitude of 2 A, and that in a quasi-continuous wave mode is 1 μW at a current of 200 mA. The absorption of LED radiation in a gaseous medium containing 10% CO has been studied. The proposed LEDs can be used to simultaneously detect both CO2 (absorbing at λ = 4.3 μm) and CO (λ = 4.67 μm).

Number of motor units in human abductor hallucis

Motor unit number was estimated for the human abductor hallucis (AH) muscle in 11 subjects by counting the number of increments in surface electromyographic responses to progressive increases in current-pulse amplitude applied to the muscle-nerve. The average motor unit count for AH (43) was substantially smaller than that estimated for other human muscles. Consequently, motor unit activity should be readily recordable up to high forces in AH, making it well suited for studies of recruitment and rate coding.

A 0.5-MJ 18-kV Module of Capacitive Energy Storage

A module of the capacitive energy storage is designed for experiments with high-current electrical discharges in dense media. The module is remotely controlled and consists essentially of eight capacitor cells with semiconductor switches built around reverse-switching dynistors (RSDs). It includes a charger with a high-frequency inverter, a protective contactor with normally closed high-voltage contacts, cell RSD switch controls, and control and diagnostic equipment provided with a programmable logic controller. The semiconductor switches in the capacitor cells are triggered by light pulses transmitted from a remote-control panel over eight fiber-optic cables. Information exchange between the module control and diagnostic system and the remote terminal is realized likewise over two fiber-optic cables. The storage is designed to operate in a programmable discharge mode in which the semiconductor switches in the capacitor cells are activated by a preset time-sequence program. The maximum current pulse amplitude of 400 kA at the module output is reached under synchronous discharge of all eight cells in the short-circuit mode. In these conditions, the pulse rise time is 150 μs. The volume of the capacitor module is 1.3 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Fabrication of Glass Nanopore Electrodes for Single-molecule Detection of β-Cyclodextrin

Nanopores are increasingly utilized as tools for single-molecule detection. We have developed a new and simple way for preparing nanopore electrodes by polishing the fused glass capillaries with sandpapers. The prepared nanopore electrodes can realize single β-cyclodextrin molecule detection with high signal-to-noise ratio, which were mechanically strong and easy to handle. Two clearly distinguishable current pulse amplitudes corresponding to the two orientations between β-cyclodextrin and pores were for the first time discovered. Pulse amplitude was closely related to size of the pore; in our case, 2–5 pA current pulse can be gained with (10 ± 5) nm electrode. The analysis of duration and amplitude of current pulse showed that the electroosmosis flow dictated by the values and direction of applied potential difference has significant effects on detections. When the direction of electroosmosis was opposite to the concentration gradient, the electrode can always produce excellent signals by adjusting potential difference from 100 mV to 600 mV. Moreover, we also observed that the amplitude of average current pulse increased first and then reached a maximum at the potential of around 300 mV, and it decreased again.

Effects of biphasic current pulse frequency, amplitude, duration, and interphase gap on eye movement responses to prosthetic electrical stimulation of the vestibular nerve.

An implantable prosthesis that stimulates vestibular nerve branches to restore sensation of head rotation and vision-stabilizing reflexes could benefit individuals disabled by bilateral loss of vestibular (inner ear balance) function. We developed a prosthesis that partly restores normal function in animals by delivering pulse frequency modulated (PFM) biphasic current pulses via electrodes implanted in semicircular canals. Because the optimal stimulus encoding strategy is not yet known, we investigated effects of varying biphasic current pulse frequency, amplitude, duration, and interphase gap on vestibulo-ocular reflex (VOR) eye movements in chinchillas. Increasing pulse frequency increased response amplitude while maintaining a relatively constant axis of rotation. Increasing pulse amplitude (range 0- 325 μA) also increased response amplitude but spuriously shifted eye movement axis, probably due to current spread beyond the target nerve. Shorter pulse durations (range 28- 340 μs) required less charge to elicit a given response amplitude and caused less axis shift than longer durations. Varying interphase gap (range 25- 175 μs) had no significant effect. While specific values reported herein depend on microanatomy and electrode location in each case, we conclude that PFM with short duration biphasic pulses should form the foundation for further optimization of stimulus encoding strategies for vestibular prostheses intended to restore sensation of head rotation.

Linear Control of Neuronal Spike Timing Using Phase Response Curves

We propose a simple, robust, and linear method to control the spike timing of a periodically firing neuron. The control scheme uses the neuron’s phase response curve to identify an area of optimal sensitivity for the chosen stimulation parameters. The spike advance as a function of current pulse amplitude is characterized at the optimal phase, and a linear least-squares regression is fit to the data. The inverted regression is used as the control function for this method. The efficacy of this method is demonstrated through numerical simulations of a Hodgkin–Huxley style neuron model as well as in real neurons from rat hippocampal slice preparations. The study shows a proof of concept for the application of a linear control scheme to control neuron spike timing in vitro. This study was done on an individual cell level, but translation to a tissue or network level is possible. Control schemes of this type could be implemented in a closed loop implantable device to treat neuromotor disorders involving pathologically neuronal activity such as epilepsy or Parkinson’s disease.

Influence of high-field electron injection regimes on modification of dielectric films of MOS devices

The influence of high-field electron injection regimes on modification of metal-oxide-semiconductor (MOS) transistors with multilayered gate dielectric SiO2-PSG containing electron traps is studied. It is shown that the preferable regime for injection modification of MOS transistors is the regime of electron injection from the silicon substrate for which the maximum shift of the threshold voltage is higher and the gate dielectric breakdown probability is much lower as compared to injection from an aluminum electrode. The amplitude of current pulses used for charge injection into the gate dielectric should be chosen from the geometric size of the transistor and particular electrophysical characteristics of the dielectric film and should be in the range 10−7–10−4A/cm2. It is shown that, for obtaining MOS devices with high thermal field stability after modification of the charge state by electron injection, it is necessary to anneal devices at temperatures of about 200°C.

10.1007/s11455-008-2001-y

The possibility of the electrodynamic acceleration of small conducting particles in a pulsed magnetic field generated by induction coils is theoretically justified. It is shown that, at a current pulse amplitude on a kiloampere level and a pulse duration of several dozen microseconds, a metal particle of submillimeter size can be directionally accelerated up to a velocity ranging from units to tens of centimeters per second.

LEDs based on InAs/InAsSb heterostructures for CO2 spectroscopy (λ = 4.3 μm)

Light-emitting diodes (LEDs) operating in a 4.1–4.3 μm wavelength range have been created on the basis of InAs/InAsSb heterostructures grown by metalorganic vapor-phase epitaxy. The output radiation power of LEDs is increased using flip-chip design. Investigation of the electrolumuinescent properties of LEDs with smooth and profiled output edge surface showed that the latter LEDs possess a greater efficiency, which is related to an increase in the radiation yield due to multiply repeated reflection from the curved surface. The output power of LED operating in a quasi-continuous wave mode was 30 μW at a current of 200 mA and that in a pulse mode was 0.6 mW at a current pulse amplitude of 2 A.

Formation of the continuous visible emission spectrum of pulsed discharge in cesium vapor

The formation of a continuous emission spectrum of pulsed discharge in high-pressure cesium vapor (P ≤ 1 bar) has been experimentally studied under conditions of increased power deposited in discharge. Experimental data well agree with the results of theoretical calculations. Physical mechanisms underlying the observed phenomenon are discussed. It is shown that, as the pumping current pulse amplitude is increased from 15 to 80 A, a discrete line spectrum transforms into the continuous spectrum. This is accompanied by an increase in the light yield (from 15 to 85 lm/W) and color-rendering index (from 86 to 98).

Optical characteristics and parameters of a gas discharge plasma based on a mixture of mercury dibromide vapor and helium

We present the results of studies of the optical characteristics and parameters of a gas discharge plasma produced by a barrier discharge at atmospheric pressure, based on a mixture of mercury dibromide vapor and helium (the working medium of a small (emitting area 8 cm2) exciplex gas discharge emitter). An average emission power of 70 mW (λmax = 502 nm) was achieved for pump pulse repetition frequency 6 kHz, voltage pulse amplitude 2.3 kV, and current pulse amplitude 8 A of duration ~100 nsec. We established the plasma parameters: the electron energy distribution functions, the transport characteristics, the discharge power losses per unit pressure going toward electron processes, the electron concentration and temperature, and also the rate constants for processes of elastic and inelastic scattering of electrons by the components of the working mixture as a function of the parameter E/N, where E is the electric field strength and N is the total concentration of mercury dibromide molecules and helium atoms.

Effect of Arc Current Ultrasonic-Frequency Pulsation on Plasma Cut Quality

The present work proposes a novel plasma cutting system using the ultrasonic frequency pulsed arc, and then experimentally investigates the effect of pulse process parameters on cut quality in the frequencies of 20-60 kHz. It is shown that kerf widths, bevel angle, straightness and dross attached level decrease obviously with the appropriate increases in the frequency and amplitude of pulse current. Furthermore, cutting heat affected zone narrows and cut hardness drops clearly in the pulsed cutting. This current pulsation can thus improve plasma cut quality remarkably, and finally leads to a narrower, flatter and more perpendicular cut of better remachinability. Experimental results simultaneously demonstrate that the effectiveness of the ultrasonic-frequency pulsed cutting process developed at the low current of arc.

Radiofrequency current source (RFCS) drive and decoupling technique for parallel transmit arrays using a high-power metal oxide semiconductor field-effect transistor (MOSFET)

A radiofrequency current source (RFCS) design using a high-power metal oxide semiconductor field effect transistor (MOSFET) that enables independent current control for parallel transmit applications is presented. The design of an RFCS integrated with a series tuned transmitting loop and its associated control circuitry is described. The current source is operated in a gated class AB push-pull configuration for linear operation at high efficiency. The pulsed RF current amplitude driven into the low impedance transmitting loop was found to be relatively insensitive to the various loaded loop impedances ranging from 0.4 to 10.3 ohms, confirming current mode operation. The suppression of current induced by a neighboring loop was quantified as a function of center-to-center loop distance, and was measured to be 17 dB for nonoverlapping, adjacent loops. Deterministic manipulation of the B(1) field pattern was demonstrated by the independent control of RF phase and amplitude in a head-sized two-channel volume transmit array. It was found that a high-voltage rated RF power MOSFET with a minimum load resistance, exhibits current source behavior, which aids in transmit array design.

Spiral-wave turbulence and its control in the presence of inhomogeneities in four mathematical models of cardiac tissue.

Regular electrical activation waves in cardiac tissue lead to the rhythmic contraction and expansion of the heart that ensures blood supply to the whole body. Irregularities in the propagation of these activation waves can result in cardiac arrhythmias, like ventricular tachycardia (VT) and ventricular fibrillation (VF), which are major causes of death in the industrialised world. Indeed there is growing consensus that spiral or scroll waves of electrical activation in cardiac tissue are associated with VT, whereas, when these waves break to yield spiral- or scroll-wave turbulence, VT develops into life-threatening VF: in the absence of medical intervention, this makes the heart incapable of pumping blood and a patient dies in roughly two-and-a-half minutes after the initiation of VF. Thus studies of spiral- and scroll-wave dynamics in cardiac tissue pose important challenges for in vivo and in vitro experimental studies and for in silico numerical studies of mathematical models for cardiac tissue. A major goal here is to develop low-amplitude defibrillation schemes for the elimination of VT and VF, especially in the presence of inhomogeneities that occur commonly in cardiac tissue. We present a detailed and systematic study of spiral- and scroll-wave turbulence and spatiotemporal chaos in four mathematical models for cardiac tissue, namely, the Panfilov, Luo-Rudy phase 1 (LRI), reduced Priebe-Beuckelmann (RPB) models, and the model of ten Tusscher, Noble, Noble, and Panfilov (TNNP). In particular, we use extensive numerical simulations to elucidate the interaction of spiral and scroll waves in these models with conduction and ionic inhomogeneities; we also examine the suppression of spiral- and scroll-wave turbulence by low-amplitude control pulses. Our central qualitative result is that, in all these models, the dynamics of such spiral waves depends very sensitively on such inhomogeneities. We also study two types of control schemes that have been suggested for the control of spiral turbulence, via low amplitude current pulses, in such mathematical models for cardiac tissue; our investigations here are designed to examine the efficacy of such control schemes in the presence of inhomogeneities. We find that a local pulsing scheme does not suppress spiral turbulence in the presence of inhomogeneities; but a scheme that uses control pulses on a spatially extended mesh is more successful in the elimination of spiral turbulence. We discuss the theoretical and experimental implications of our study that have a direct bearing on defibrillation, the control of life-threatening cardiac arrhythmias such as ventricular fibrillation.

Studying a spark discharge in the ground during reproduction of a negative lightning-current pulse using magnetic cumulation generators

Using an energy source based on a single BMΓ-160 generator, a current pulse with an amplitude of 50 kA and a rise time of 2 μs has been formed in a grounding rod electrode with a length of 1 m in the ground with a resistivity of 160 Ω m. The maximum length of spark channels on the ground surface from the point of current injection is 3–4 m. An energy source based on two BMΓ-160 generators connected in series allows an increase in the current pulse amplitude to 90 kA, the rise-time duration being the same, 2 μs. In this experiment, the maximum length of spark channels on the ground surface from the point of current injection exceeds 8 m.

Metabolic Prosthesis for Oxygenation of Ischemic Tissue

This communication discloses new ideas and preliminary results on the development of a metabolic prosthesis for local oxygenation of ischemic tissue under physiologically neutral conditions. We report for the first time selective electrolysis of physiological saline by repetitively pulsed, charge-limited electrolysis for the production of oxygen and suppression of free chlorine. Using 800-microA amplitude current pulses and < 200 micros pulse duration, we demonstrate prompt oxygen production and delayed chlorine production at the surface of a fused 0.85-mm diameter spherical platinum electrode. The data, interpreted in terms of the ionic structure of the electric double layer, suggest a strategy for in situ production of metabolic oxygen via a new class of "smart" prosthetic implants for ischemic disease such as diabetic retinopathy. We also present data indicating that collateral pH drift, if any, can be held constant using a feedback-controlled three-electrode electrolysis system that chooses an anode and cathode pair based on pH data provided by a local sensor.