Low Current Pulses Research Articles

Investigation of trapped charge in oxides under Fowler-Nordheim stress using low bias conditions

This work describes the influence of low current pulses during high current stress on the trapping properties of thin silicon dioxide layers. The determination of the trapped oxide charge during Fowler-Nordheim stress from low current steps is discussed. It is shown that low bias steps are not a reliable indicator of the amount of trapped charge in the oxide due to trapping of additional charges during this measurement period.

The notion of response invariance in trade-off studies of self-stimulation

Trade-off profiles, displaying the co-variations of 2 electrical parameters required to maintain a constant magnitude of brain stimulation reward (BSR), have been used extensively in order to characterize the self-stimulation (SS) neurons. It has often been assumed that constancy in the magnitude of BSR can be achieved more accurately by holding SS at a constant proportion of the maximum rate, rather than at a constant rate. The validity of this assumption was tested in 2 experiments using rats. In Exp. 1, we first computed the function that relates SS barpressing rate to pulse frequency (RF function) for two different pulse intensities, separately. The peak SS rate was found to be lower in the low current than in the high current RF function. The rats were then placed in a 2-lever box and were allowed to select either a fixed frequency of the high current pulses or a variable frequency of the low current pulses. In Exp. 2, the RF function was first computed for 2 different lever weights, separately. The peak SS rate was found to be lower in the heavy-lever RF function than in the light-weight lever RF function. The rats were then allowed to select either a fixed pulse frequency delivered by the heavy lever or a variable pulse frequency delivered by the light-weight lever. Isopreference was noted in both experiments, for pulse frequencies which, in the single-lever box, elicited the same proportion of the maximum SS rate, not the same SS rate. The data thus validate the idea that a constant magnitude of BSR is translated into a constant proportion of the maximum SS rate, not a constant SS rate.

A new dual gate design for low current pulse operation in 16 Mb ion-implanted bubble memory devices

A design for a dual gate which has both pseudoswap and block-replicate functions for 16-Mb ion-implanted bubble memory devices has been proposed and shown by Sato et al. (1987) to reduce the operation current-pulse amplitude. The dual gate is composed of a pair of hair-pin conductor patterns in two layers and ion-implanted tracks for the major line and the minor loop corner. The current pulses are applied through the hair-pin conductor patterns to stretch, cut, or annihilate bubbles for the operation of the dual gate. The functions of the dual gate were realized with low current pulses of less than 150 mA using 0.8- mu m-diameter bubbles. It is therefore confirmed that the dual gate with low-current operation makes the 16-Mb ion-implanted bubble memory devices more practical. >

An instrument control and data acquisition system for time-of-flight measurements of low ion current pulses

A data system facilitates the study of ion—ion pair production in individual scans from a time-of-flight mass spectrometer at repetition rates of up to 1.5 kHz. Commercial modules, fitted into a computer automated measurement and control (CAMAC) crate, are controlled using a personal computer. The system controls the instrument and accumulates data from two detectors over a time range which is continuously variable from 0 to 1.6 ms. Eight stop events can be measured per mass scan, with a timing accuracy of 1 ns for each detector. The interval between detected particles is 5 ns. The system also provides independent time gates for each detector, thus permitting the measurement of ion—ion pair and ion—neutral pair (or higher order) production by programming the data system to record only the time frames of interest. A special operational mode allows the extraction of a conventional mass spectrum without undue bias in the mass intensities which could be caused by the limit of eight ions per scan.

Low frequency pulse excitation in zero field magnetic resonance

Zero field magnetic resonance experiments using semiselective excitation by low frequency pulses are analyzed. The prospects of phase cycling experiments in zero field are discussed and the differences between excitation by low frequency and direct current pulses are outlined. It is demonstrated that despite the selectivity of excitation all three transitions in a three-level system are observed. Deuterium quadrupolar resonance and computer simulations are employed to verify predictions.

Rate Responsive Pacing Using a Minute Ventilation Sensor

Minute ventilation, the product of respiratory rate and tidal volume, correlates directly with oxygen consumption, cardiac output, and heart rate. An implantable pacemaker has been developed which allows variation in pacing rate in response to measured changes in minute ventilation. This single chamber system measures transthoracic impedance between the tip electrode of a standard bipolar lead and the pulse generator case. Low amplitude current pulses (1 mA for 15 microseconds) are generated each 50 msec between the the ring electrode and the case. In the adaptive mode, the pulse generator calculates a rate response factor or slope after maximal exercise. This slope, which describes the relationship between pacing rate and minute ventilation together with the pacing rate limits are the only programmable rate responsive features. Minute ventilation rate responsive systems have been implanted in 12 patients (8 females, 4 males), of mean age 63 years. Indications were His bundle ablation (6), acquired complete heart block (4), and sick sinus syndrome (2). At post-implant exercise testing, pacing rate rose within the first minute. Peak rate and time to upper rate were dependent on workload. After exercise, pacing rate remained at peak for up to 2 minutes before a gradual fall to resting rate. Comparative studies of the minute ventilation and the activity sensor pacing systems in the same patients confirmed that the minute ventilation system more closely parallels normal sinus response to activity. The minute ventilation rate responsive pacing system is simple to programme, no special lead is required and the system is highly physiologic.

The retrieval of low current pulses from noise for attachment measurements in weakly attaching gases

Describes the use of a digital storage oscilloscope linked to a microprocessor via a GPIB digital interface for the improvement of the signal-to-random-noise ratio of low-level ( approximately 10-10 A) repetitive current waveforms obtained from drift tubes. The analysis of such signals allows attachment coefficient to be calculated for very weakly attaching gas mixtures.

Converging cerebellofugal inputs to the thalamus. I. Mapping of monosynaptic field potentials in the ventrolateral nucleus of the thalamus.

The extent of thalamic projections from punctate sites in the cerebellar nuclei was examined in 22 acutely prepared cats by mapping monosynaptic field potentials evoked in the ventrolateral (VL) nucleus by stimulation of the interpositus and dentate nuclei (IN and DN). The monosynaptic field potentials were evoked in the VL by low current stimulating pulses applied at high frequency to these cerebellar nuclei. Quantification of the projections was possible since the conditions of stimulation and recording were strictly controlled. The incoming volley recorded in the brachium conjunctivum caudally to the VL was also analysed. It was composed of two amplitude peaks with different latencies, corresponding to two groups of fibres conducting at 60-90 m/s and 20-25 m/s respectively. The negative field potentials in VL also showed two amplitude peaks and different latencies. The differences in latency between the first and second peaks in the presynaptic and postsynaptic field potentials are compatible with the possibility that both groups of afferent fibres may be monosynaptically connected to VL relay cells. The cerebello-thalamic projections were mapped and their density gradient was established. Two or three small thalamic strips of dense projections surrounded by a large zone of weaker projections were observed to emerge from each punctate cerebellar site. In the discussion of the functional significance of these findings, it is suggested that this organization might constitute a modulatable morphological support for a mechanism focalizing the cerebello-cortical inputs.

Locomotion-inducing sites in the vicinity of the pedunculopontine nucleus

The mesencephalic locomotor region (MLR) was identified physiologically by inducing controlled locomotion on a treadmill in the precollicular rat following application of low amplitude current pulses to areas of the pontomesencephalic tegmentum. The same brains were processed using either of two techniques known to label neurons of the pedunculopontine nucleus (PPN)-choline acetyltransferase (ChAT) immunocytochemistry or nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. Histologieal reconstruction of locomotion-inducing sites were localized within or adjacent to ChAT or NADPH-diaphorase labeled cell groups. Three dimensional reconstructions of the PPN were used to visualize the colocalization of low threshold locomotion-inducing stimulation sites within PPN neuronal aggregates. These findings lend further support to the suggestion that the PPN is part of the MLR. A theoretical framework is proposed to account for results derived from various lines of research on this area.

Wall conditioning in JT-60

The vacuum vessel of JT-60 has a volume of 160 m 3 and a vacuum side surface of 2750 m 2 containing the surfaces of the first wall and many types of ports. The first wall is made of 20 μm TiC coated molybdenum and Inconel 625, bolted to the inner surface of the vacuum vessel. The vacuum vessel is evacuated with four identical pumping systems with a total pumping speed of 29 m 3/s for hydrogen. The wall conditioning procedure consisted of two wipes with special cloths wetted by freon after hot water and freon jet cleaning, and three bakeouts were carried out before the first plasma production. An ultimate pressure of 7.4 × 10 −7 Pa and an outgassing rate of 6.8 × 10 −10 Pa m 3/s m 2 were obtained. Low current pulse discharge cleaning (TDC) was carried out for two weeks at a vacuum vessel temperature of 200°C. The TDC is performed typically with a plasma current of 30 kA, a pulse duration of 40 ms, a repetition period in the range from 0.3 s to 1.2 s, a hydrogen pressure of 5.0 × 10 −3 Pa, and a toroidal field of 0.45 T. The TDC conditioning for 50 h removed a quantity of water vapor corresponding to approximately 0.3 g. The main residual gases consisting of hydrocarbons, were monitored in addition to hydrogen and carbon monoxide.

Monolithic integration of InGaAsP/InP LED and transistor—a light-coupled bistable electro-optical device

A new bistable electro-optical integrated three-terminal InGaAsP/InP LED-transistor device is presented. Bistability is obtained by coupling part of the emitted LED light into the transistor base. The light output can be switched on and off by relatively low current pulses with 50 ns duration.

Control of Spasticity and Involuntary Movements – Cerebellar Stimulation

By stimulating the medial aspect of the superior surface of the cerebellum with relatively short, low current stimulating pulses, spasticity and some involuntary movements have been reduced. Voluntary movements, as a result, are able to come through better; however, if the child has little voluntary ability, he is at least more relaxed, thus allowing the parents to care for him more easily. The children and adults with cerebral palsy have not been transformed from their previous status, although CCS has allowed them to become more independent, more ambulatory, and more communicative.

Observation of Low Frequency Current Pulses in Si p-ν-n Diodes

Observation of Low Frequency Current Pulses in Si p-ν-n Diodes

Superconducting Thin-Film Detector of Nuclear Particles

Superconducting films of tin and indium on supporting substrates have functioned successfully as detectors of individual nuclear particles. The films are sufficiently thin and narrow that individual α-particle impacts initiate superconducting to normal transitions which spread, in the presence of a transport current, to span a full film cross section. The transitions are observed by means of the ir drop produced by a transport current. For low current densities self-terminating voltage pulses of a few nsec duration are observed. At higher current densities the boundaries of a normal region initiated by an α particle propagate by Joule heating to the ends of the film. The range of the 5.3-MeV α particles utilized for these experiments greatly exceeds the 0.1 μm thickness of the films and the resulting deposition of energy in the substrate affects the response of any film which is in direct contact with its substrate. The introduction of a thin thermally insulating layer of varnish between the film and its substrate, which in these experiments was either glass or crystalline quartz, increases the thermal decay constant to the extent that the film is thermally isolated from its substrate for a period comparable to that of pulse formation. The variation of count rate with film current has been studied and is shown to be consistent with the variation of critical current density along the length of the film. This model, coupled with classical heat diffusion within the film, accounts for the observed behavior of the thermally isolated films.

Bidirectional triode P-N-P-N switches

The theory of operation, construction, and electrical characteristics of a new family of silicon thyristors for use as bidirectional (ac) switches are discussed. With these p-n-p-n devices, load current flow in either direction can be controlled by the application of a low voltage, low current pulse between a gate trigger terminal and one of the load current terminals. Blocking current and voltage characteristics are similar to those of a silicon-controlled rectifier (SCR); but unlike SCR's they can switch load current of either polarity. Devices have been made which, in the blocking state, will support several hundred volts with very little current flow; yet, when in the conducting state, will carry many amperes with a voltage drop of approximately a volt. Static power switching with these devices in such applications as lamp dimming, temperature controls, small motor speed controls, etc., appears to be particularly important. For triggering, these new devices depend on the manipulation of lateral current paths. The potential differences created by the flow of current in these paths determine, in turn, the lateral distribution of injected charge carriers within the device during the triggering interval. This paper presents an analysis of lateral biasing effects and the parameters which control them.

Using an arc to extinguish an arc

Periodic igniting and extinguishing devices are described in which an arc is established by a trigger spark and after a selected interval is extinguished by the striking of a second arc that by-passes the current for a few msec, after which the second arc goes out automatically and the system recovers its original quiescent state. Three types of circuit are described and their operation illustrated by experimental oscillograms showing pulse lengths of 1 msec to 40 msec, amplitudes of up to 100 A and repetition rates up to 50sec. The systems can also be used to produce sharp reversal of current in the middle of a pulse or a high-peak pulse superposed on a low-current pulse.