Repetitive Impulses Research Articles

Wavelet decomposition of vibrations for detection of bearing-localized defects

This paper presents a new scheme for bearing-localized defect detection based on wavelet transform. Wavelet transform provides a variable resolution time-frequency distribution from which periodic structural ringing due to repetitive force impulses, generated upon the passing of each rolling element over the defect, are detected. In this paper, important properties of wavelet transform and its comparison with short-time Fourier transform are discussed. Then, a basic wavelet considered optimal for bearing-localized defect detection is constructed. Finally, the new scheme is described and its effectiveness is evaluated using actual vibration signals measured from bearings with defects at different locations and operating under different conditions.

Neuromuscular transmission studies in the healthy dog: EMG and muscle force measurement after repetitive nerve stimulation.

In 10 healthy anaesthetized female dogs the ulnar and the mandibular nerve were stimulated supramaximally by repetitive electric impulses according to a fixed programme. To evaluate the neuromuscular transmission system the course of the evoked compound muscle action potential and the near-isometric force of forelimb and masticatory muscles were studied respectively. The presented results are comparable to values obtained from small hand muscles of conscious, healthy human subjects. The simultaneous measurement of both the electrical and the force response may improve the diagnostic accuracy of the examination in presumed neuromuscular transmission failure in the dog, as it does in humans.

Autocatalytic membrane conductance and memory

A basic characteristic of biological memory is that it has a graded duration, which, even for so-called short-term memory, can vary from minutes to days (i.e. over about three orders of magnitude), depending on the training protocol, which one can think of as determining the "strength" of the memory. Furthermore, the molecular analysis of simple learning in invertebrates has revealed many examples where "learning" is produced by a decrease in an appropriate membrane conductance. This paper provides a quantitative analysis of a simple kinetic scheme whereby a conductance decrease can be produced by repetitive nerve impulses, with a duration that varies with stimulus frequency. The simplest model considered is based on the actual kinetics of the naturally-occurring ionophore Monazomycin. This model yields durations ranging only over a factor of about 10, for reasonable parameter values. However, a simple modification of the model yields memory durations ranging over three or more orders of magnitude. We also show that Monazomycin-like kinetics can appear as the result of a combination of simple uni- and bi-molecular reactions, thus making more plausible the possibility that the effects described here may operate in actual biological systems.

Entladungscharakteristika der durch transkranielle Kortexreizung aktivierten motorischen Einheiten in den Handmuskeln des Menschen

Using concentric needle electrode recording from hand muscles (abductor digiti minimi, first dorsal interosseus, or abductor pollicis brevis muscle) the latencies of single motor unit potentials in response to threshold magnetic brain stimuli were studied under different conditions. It has been shown that the motor units activated by threshold brain stimuli had the lowest threshold for voluntary activation (see Fig. 1: A = vol. activated, B = brain stim.). Onset latencies of 23 motor unit potentials from different sites in the relaxed muscles of four healthy subjects ranged from 22.4 to 32.4 ms (average: 26.4 ms; SD: 2.80 ms) but proved to be relatively stable when stimulating and recording conditions were kept constant (variation < 0.5 ms, see poststimulus time histogram in Fig. 2). With concurrent contraction of an ipsilateral neighbouring or of the contralateral homologuous muscle the motor unit potentials from the relaxed target muscle jumped to an earlier latency by 1.2 to 1.7 ms (C in Fig. 3 and B-2 in Fig. 4). On one occasion another motor unit of higher threshold was alternatively activated by this procedure (B-3 in Fig. 4). Since the same procedures are known to enhance the compound muscle action potentials as recorded from the relaxed muscle with surface electrodes, the shorter latencies of single motor units are considered to be caused by a facilitatory influence on the motoneurones. A possible explanation for these latency shifts would be that the motor units discharge later in response to the brain stimulus induced repetitive corticospinal impulses when there is no facilitation, whereas during facilitation the firing level is reached earlier. When using threshold electrical brain stimuli, the same motor unit with the same latency as with magnetic stimulation was activated (B in Fig. 6) and it also jumped to an earlier latency by the mentioned facilitatory measures (C in Fig. 6). A similar latency shift was sometimes observed when it was possible to increase the stimulus intensity without recruiting additional motor units within the pick up area of the needle electrodes, so that the original motor unit potential remained identifiable (B in Fig. 5; stimulus still more enhanced in C of Fig. 5). When increasing the stimulus intensity, the number of active cortico-spinal neurones impinging on a motoneurone is likely to be increased. This enhances the spatial summation of excitatory postsynaptic potentials in a motoneurone and may also result in an earlier firing of the motoneurone in response to the stimulus induced descending activity, since then less temporal summation is needed. Repetitive high frequency cortico-spinal trains in response to single brain stimuli must be assumed from animal experiments and epidural spinal cord recordings in humans. The interval between the descending impulses was found to be in the order of 1.4 (1.0-1.8) ms and therefore is similar to the latency shift we observed in motor unit potentials.

Buspirone attenuates synaptic activation of hippocampal pyramidal cells

The actions of 5-hydroxytryptamine (5-HT) and buspirone, an anxiolytic agent that displays high and selective affinity for 5-HT1A receptor sites, on synaptic activation of hippocampal CA1 pyramidal cells were studied in vitro. Whereas 5-HT application leads to a rapid hyperpolarization and decreased input resistance in pyramidal cells, buspirone has no measurable effects on membrane potential and input resistance. However, unlike 5-HT, buspirone application leads to a gradual and reversible reduction in excitatory postsynaptic potentials (EPSPs) elicited by stimulation of afferents in the stratum radiatum. Concurrent with this attenuation of the EPSP, buspirone decreases the excitability of afferent fibers in the stratum radiatum as evidenced by conduction slowing, increased refractory period, and decreased ability to generate repetitive impulses. 5-HT has no measurable effect on the afferent fibers. The attenuation of the EPSPs and the decrease in afferent fiber excitability appear to be independent of 5-HT receptors as 5-HT neither shares nor antagonizes the effects of buspirone. Thus, both 5-HT and buspirone can contribute to reduced spike activity in pyramidal cells, but they do so via different mechanisms: 5-HT hyperpolarizes pyramidal cells whereas buspirone attenuates their synaptic activation, possibly via action on the presynaptic fibers in the stratum radiatum.

Positive Corona and Atmospheric Negative Ion Density under Repetitive Impulse Conditions

The variations in the negative ion density in the atmosphere around an electrode gap in which positive corona is produced during repetitive voltage impulses is discussed. A set of equations is solved numerically for the time variation of negative ion density; the influence of positive and negative, small and large ions is included, together with the natural rate of production of ions in the atmosphere. The results show that in repetitive testing the background density of negative ions is always lower than the natural density, and that it is higher in humid air than in dry air.

Perceptual space for repetitive impulses and environmental noises

Perceptual space for repetitive impulses and environmental noises

Cable for High Pulse Power Applications

Recent development and application of a novel electromagnetic technique, to reposition the coolant tube spacers (garter springs) in the fuel channels of CANDU nuclear reactors, has created the need for a pulse power cable that has very low ac resistance at a frequency range of 700 to 1500 Hz. The technique involved discharging a 200 kJ capacitor bank into an electromagnetic coil, inserted inside the fuel channel, via a transmission line at least 11 m long. The electrical resistance of the transmission line, made of commercially available cables, was found to cause excessive damping of the discharge current waveform which was required to have an exponentially decaying sinusoidal shape. This paper describes the design, development and performance of a new compact cable that has been successfully used to carry repetitive current impulses generated by capacitor banks operating in the oscillatory mode at high current levels. Various dimensional and operational constraints, assembly of the cable terminations by an electromagnetic method and mechanical behaviour of the cable are also discussed.

Emergency department use of transcutaneous pacing for cardiac arrests.

Transcutaneous cardiac pacing is a rapid technique for pacing the heart using skin electrodes to pass repetitive electrical impulses through the thorax. This paper reports the results of transcutaneous pacing in a series of 52 emergency department patients. Patients were selected for pacing if they were unconscious and in asystole (30 patients) or unconscious with a pulseless or hemodynamically ineffective bradycardia (22 patients). In all cases, transcutaneous pacing was attempted after initial resuscitative drug therapy failed. Of the 26 patients with successful ECG capture, 14 were initially in asystole, 11 were initially in a pulseless bradycardia, and one had a hemodynamically ineffective bradycardia. Of the eight patients developing a pulse, four developed a measurable BP. The four patients who developed a measurable BP were young (ages 22 to 39 yr) and only one had an underlying cardiac etiology for his cardiac arrest. No patient survived to be discharged from the hospital. Twenty-five of the 52 patients also had a transvenous pacemaker inserted, with successful electrical capture in five of the patients. Only one of the transvenously paced asystolic patients subsequently developed a BP. There were no patients successfully paced transvenously who were not successfully paced transcutaneously.

An endplate potential due to potassium released by the motor nerve impulse.

A small endplate potential can be recorded in frog muscle fibres, after all acetylcholine-mediated transmission has been eliminated by pre- or postsynaptic blocking agents (botulinum toxin, calcium lack, manganese, curare, alpha-bungarotoxin). It is usually necessary to hyperpolarize the muscle membrane to detect this 'non-cholinergic' endplate potential. Below--100 mV little or no response is seen; a maximum is reached at about--140 mV, when the amplitude can be as large as 100 microV (endplate current up to about 1 nA). Other characteristic features are: the response shows no quantal fluctuations; its amplitude is not facilitated by repetitive impulses; its size and time course are not noticeably affected by prostigmine, curare or alpha-bungarotoxin; the half-time of decline of the endplate current is approximately 1.7 ms at 20 degrees C, and is lengthened by lowering the temperature with a Q10 of about 1.3; the response is abolished by barium. When iontophoretic pulses of potassium are applied to the endplate, local depolarization is recorded whose amplitude varies with membrane potential similarly to that of the nerve-evoked response. These observations strongly indicate that this 'non-cholinergic', 'non-quantal' endplate potential arises from a rapid synaptic transfer of potassium ions, released by the active nerve terminal into the synaptic cleft and entering the muscle fibre through 'anomalous rectifier' channels in the endplate membrane.

Phase locking of biological clocks.

Radial isochron clocks (RICs) and their response to external signals and coupling with other RICs are studied. RICs are derived as phase approximations to self-sustained oscillators. Their response to single impulses (phase resetting) and to repetitive impulses is determined. This response may be harmonic or chaotic. Finally, the effect of coupling between clocks is studied. Simple coupling is shown to exhibit rhythm splitting like that observed in fish and small mammals. New phase locking results for general weakly coupled RIC systems are also derived.

Facilitatory effects of 4-aminopyridine on strontium-mediated evoked and delayed transmitter release from motor nerve terminals.

The effect of 4-aminopyridine (4-AP) on Sr-mediated evoked and delayed transmitter release at the frog neuromuscular junction was examined using conventional electrophysiological techniques. 4-AP (5-50 microM) increased transmitter release evoked in response to conducted nerve impulses or to electrotonic depolarization of tetrodotoxin (TTX)-treated motor nerve terminals. Spontaneous quantal transmitter release was not affected by the drug as judged by the lack of effect on miniature end-plate potentials (MEPPs) frequency. However, 4-AP (10-20 microM) markedly enhanced the frequency of MEPPs appearing during conducted low rate repetitive nerve impulses or single electrotonic depolarization of TTX-blocked nerve terminals. The results suggest that 4-AP increases the influx of Sr2+ into nerve terminals in a way that modifies its sequestration and removal by the subcellular elements of the terminal.

Effects of calcium and strontium in the process of acetylcholine release from motor nerve endings

1. The effects of Ca and Sr ions on synchronous acetyleholine (ACh) secretion (the impulsive, physiologically functional form of secretion which produces an end-plate potential in response to a single nerve impulse) and on asynchronous ACh secretion (the delayed, residual increase in miniature end-plate potential frequency evoked by repetitive nerve impulses or by accumulation of intracellular divalent cations) were studied at frog neuromuscular junctions.2. In a comparison of their extracellular effects, Ca was far more effective than Sr in supporting synchronous ACh secretion but less effective than Sr in mediating asynchronous release evoked by repetitive nerve impulses.3. In studies of their intracellular effects, Sr and Ca were delivered to the nerve terminal cytoplasm using liposomes as a vehicle. Ca-containing liposomes, although producing effects on asynchronous ACh secretion that were indistinguishable from those of equimolar Sr-containing liposomes, were more effective than Sr-containing liposomes in increasing synchronous release.4. Extracellular Ca behaved as a potent competitve inhibitor of asynchronous, neurally evoked release mediated by Sr. In contrast, intracellular Ca (i.e. liposomal Ca), whilst increasing synchronous ACh release, failed to antagonize evoked asynchronous release.5. The results demonstrate that synchronous and asynchronous secretion have different sensitivities to alterations in intracellular divalent cation concentrations. It is suggested that selectivity for Ca over Sr may occur at intraterminal sites responsible for synchronous ACh secretion but not at sites responsible for asynchronous ACh release. Furthermore, Ca appears to bind with high affinity as an antagonist at the external surface of the nerve ending. These results are discussed in conjunction with current theories of depolarization-secretion coupling.

Experiments on the perceived noisiness of repetitive impulses.

Experiments on the perceived noisiness of repetitive impulses.

Dendritic impulse initiation in an epithelial sensory neuron

The effect of transepithelial voltage on the generation of nervous impulses in an epithelial mechanoreceptor cell has been studied in the tibial hair sensilla of the cricketAcheta. Other studies have demonstrated sensilla to be a part of a ‘tight’ epithelium. A natural transepithelial voltage (TEV) of about 20 mV exists across the epithelium studied (outside positive). 1. In the mechanically unstimulated state, both increase and decrease of TEV elicits repetitive nerve impulses. Their time course is diphasic in transepithelial recordings. During positive polarization the temporal order of impulse phases is the same as for mechanically induced impulses, whereas it is inverted during negative polarization. Following application of Tretrodotoxin (TTX) at the apical side, the regularly subsequent (negative) impulse phase is abolished and negative polarization becomes ineffective in generating impulses. 2. Adequate mechanical stimulation decreases increment sensitivity of impulse generation for most transepithelial voltages (impulse frequency incrementΔF/ΔTEV). Following application of TTX, mechanically induced impulse frequency is lowered by decreased or negative TEV; the increment sensitivity-ΔF/-ΔTEV of this influence of TEV is increased by increasing the mechanical stimulus strength. In contrast, little change ofΔF/ΔTEV is caused by TTX in the domain of increased positive TEV with respect to the effect of mechanical stimuli. 3. Mechanical sensitivity of afferent spike frequency in this receptor is increased by an increase of TEV only for small mechanical stimuli; negative TEV diminishes mechanical sensitivity in general. This dependence of sensitivity on TEV cannot be generalized for comparable sensilla. 4. We conclude: A transepithelial current traverses the sensory cell via its apical dendritic membrane (the membrane of the ciliary outer segment mainly) and it leaves the cell at the basal side of the epithelium via the membrane of the basal dendritic region (ciliary inner segment). The current enters the cell via a conductance which is increased by adequate mechanical stimuli and via a conductance which is considerably high in the mechanically unstimulated state. In order to explain the complex effects of combined mechanical and electrical stimulation, we suggest that some apical conductance is controlled by the membrane voltage as a rectifying K+-conductance is. Both apical and basal membrane areas of the dendrite are able to initiate impulses repetitively; the regular site of impulse initiation is in the basal area.

Irreverisble differential block of A- and C-fibres following local nerve heating in the cat.

1. Local heating of a nerve was used to block conduction in the myelinated or A-fibres while preserving normal function in most of the non-myelinated or C-fibres. Compound action potentials of A- and C-fibres, and impulses in single C-fibres were recorded to measure the block. 2. Most experiments were done on the posterior tibial nerve of the cat's hind limb. Conducted heat was applied in successive periods of about 2 min each to 15 mm of the exposed nerve. 3. The range of temperatures used was between 45 and 52 degrees C. Below 46 degrees C no conduction block was obtained. With increasing temperature the cumulative time of heating required to produce a block in at least 99% of A-fibres decreased from around 110 min at 46.5 degrees C to 10 min at 51 degrees C. 4. In the posterior tibial nerve the C-fibre compound action potential was reduced to 0.66 of control (mean of twenty-two experiments) when the A-fibre action potential was less than 1% of control. The corresponding value of this selectivity coefficient was 0.20 in seven superficial peroneal and sural nerves. 5. Once a conduction block of A-fibres was reached the remaining C-fibres showed normal functioning, including conduction of repetitive impulses at up to 30 Hz evoked by electrical nerve and adequate skin stimulation. C-fibre conduction persisted for at least 33 h, but not longer than 3 days. 6. This pure C-fibre nerve might be useful for studying central nervous system effects of C-fibres.

The action of allethrin on the peripheral nervous system of the frog

AbstractA study was made of the neurotoxic effects of the pyrethroid insecticide allethrin on the peripheral nervous system of the frog by means of electrophysiological techniques. The principal action of allethrin is to induce repetitive activity, not only in sensory nerve fibres and in sense organs, but also in the distal part of the motor fibres, leading to pronounced repetition in the motor end‐plate. Measured by the number of repetitive nerve impulses allethrin shows a marked negative temperature coefficient of activity in the lateral‐line sense organ and in the motor nerve terminal.

AN ESTIMATE OF THE EQUILIBRIUM DISSOCIATION CONSTANT FOR CALCIUM AS AN ANTAGONIST OF EVOKED ACETYLCHOLINE RELEASE: IMPLICATIONS FOR EXCITATION‐SECRETION COUPLING

The equilibrium dissociation constant (K(d)) for Ca(2+) as an antagonist of evoked acetylcholine (ACh) release was determined in the hope of distinguishing whether divalent cations control excitation-secretion coupling selectively (by binding with high affinity to an external membrane site) or non-selectively (by screening fixed negative charges on the external surface of the nerve terminal). ACh release was detected electrophysiologically by means of conventional intracellular recording techniques at frog motor endplates. Ba(2+) was used as the agonist to support the asynchronous release of ACh by repetitive motor nerve impulses. Despite its dispersed nature, release mediated by Ba(2+) occurs through the same conductance pathway as synchronous release mediated by Ca(2+). Ca(2+) was found to be a potent antagonist of Ba(2+)-dependent release with a K(d)=0.12+/-0.02 mM (mean+/-s.e. mean, n=5). This value is 30-50 times lower than the K(d) for Mg(2+) as an antagonist of the same release process. It is suggested that antagonism of release by Ca(2+) is likely to be exerted at the same external site that binds other divalent cation antagonists, a site that appears essential for the agonist behaviour of Ca(2+). The high affinity (low K(d)) of Ca(2+) as an antagonist of ACh release suggests that a selective, binding model appears to be the most appropriate single description of the action of divalent cations at the external surface of the motor nerve ending.

Analogue Control of Impulse Generators

An application of high voltage testing in undergraduate teaching is described in which a 400-kV impulse generator is operated from a solid state electronic control system. The impulse generator applied repetitive impulses to a spark gap with a consistency of ±0.2% and recorded the result.

Modulation of synaptic transmitter release by repetitive postsynaptic action potentials.

The effect of repetitive action potentials in the postsynaptic axon on the release of synaptic transmitter from the presynaptic terminal was investigated at the squid giant synapse. Repetitive antidromic stimulation of the postsynaptic axon resulted in a reduction in the excitatory postsynaptic potential (EPSP). The reduction in transmitter release was accompanied by a decrease in the presynaptic spike after-hyperpolarization (AH). Increasing the concentration of extracellular potassium ions also reduced the EPSP and decreased the amplitude of the presynaptic spike AH. The reduction in transmitter release resulting from repetitive postsynaptic impulses is attributed to the accumulation of extracellular potassium ions. It is proposed that the accumulation of extracellular potassium ions resulting from repetitive postsynaptic activity may modulate synaptic transmission and function as an integrative mechanism in the nervous system.