Rectangular Waveform Research Articles

Between-subject variability and within-subject reliability of the human eye-movement response to bilateral galvanic (DC) vestibular stimulation

Recent studies have shown that responses to surface galvanic vestibular stimulation (GVS) show substantial interindividual variation. Between-subject variability may be due to individual differences between subjects, or to the poor reliability of the test, or to differences in test details, or to host factors. The aim of the present study was to compare variability between and within subjects in binocular 3-D eye-movement responses to long-duration, maintained, large-amplitude, bilateral, bipolar, surface GVS. Subjects were seated and restrained, and in one condition fixated a small, centrally located visual target; in the other condition, testing was carried out in complete darkness. Surface GVS of 5 mA, with a rectangular waveform was delivered bilaterally for 5 min while eye movements were measured using computerised video-oculography (VTM). In the first experiment, ten subjects participated in both conditions in one session, and in the second experiment, two subjects participated in both conditions for a total of five repeated sessions. The stimulation was well tolerated by all subjects and produced a change in torsional position with the upper pole of both eyes rolling towards the anode and away from the cathode in all subjects in both conditions. Although little vertical nystagmus was evident in either condition, most subjects showed relatively strong horizontal nystagmus (slow phases towards the anode) in darkness. This study confirms previous observations that the torsional response to GVS is highly variable between subjects, whilst also showing for the first time that eye-movement responses to GVS show good within-subject repeatability. This study also demonstrates considerable between-subject variability in the relative ratios of response components (torsional and horizontal nystagmus, torsional position), whereas the relatively small within-subject variability can be characterised more by changes in the overall amplitude of the eye-movement response. Subjects show idiosyncratic oculomotor response patterns to GVS, varying slightly in absolute magnitude between sessions. Thus, GVS may be a more reliable stimulus than may have been anticipated from the literature.

PLANETARY GEAR PARAMETRIC INSTABILITY CAUSED BY MESH STIFFNESS VARIATION

Parametric instability is investigated for planetary gears where fluctuating stiffness results from the changing contact conditions at the multiple tooth meshes. The time-varying mesh stiffnesses of the sun–planet and ring–planet meshes are modelled as rectangular waveforms with different contact ratios and mesh phasing. The operating conditions leading to parametric instability are analytically identified. Using the well-defined properties of planetary gear vibration modes, the boundaries separating stable and unstable conditions are obtained as simple expressions in terms of mesh parameters. These expressions allow one to suppress particular instabilities by adjusting the contact ratios and mesh phasing. Tooth separation from parametric instability is numerically simulated to show the strong impact of this non-linearity on the response.

Long arc in free air: laboratory testing, modelling, simulation and model-parameters estimation

The results of an investigation into the long arc in free air is presented. The long arc in free air is initiated under laboratory conditions in the FGH-Mannheim high-power test laboratory (Germany). Based on the arc voltage and the arc current data records obtained in the laboratory, the main features of the arc are derived. In the second stage of the research, a new arc model is developed. The arc is modelled as a current dependent voltage source with the characteristic distorted rectangular waveform. Examples of computer simulations of the arc using new models are given. The main features of the simulated arc are also described. Features of the real and modelled arc are given in the time and the spectral domains. The interaction between the arc and the network is analysed. Through computer simulation, a typical example of an arcing fault on an overhead transmission line is given. Finally, the least squares error estimation method for arc model parameter estimation is presented. The unknown model parameters are successfully estimated from the computer-simulated and laboratory-obtained data.

Influence of alternating extremely low frequency ELF magnetic field on structure and function of pancreas in rats.

The aim of this study was to estimate the influence on ultrastructure and function of endocrine and excretoric part of pancreas in rats of extremely low frequency alternating magnetic fields with parameters used in therapy in humans. The animals from the two experimental groups were exposed to a rectangular magnetic field waveform at a frequency of 10 Hz and induction of 1.8-3.8 mT--(group P) or a sinusoidal magnetic field at a frequency of 40 Hz and induction of 1.3-2.7 mT--(group S), respectively. The control rats were subjected to sham exposure. The cycle of 1, 3, 6, 9, and 14 daily exposure sessions lasting 30 min was made in all groups. Some of rats after finishing the cycle of 14 exposures were left in the same conditions except for the magnetic field for 3 or 10 days. In both groups of rats exposed to magnetic field, a distinct tendency to decrease glucose concentration, compared to control group, was observed during the exposure cycle. Serum glucose became normal after the end of exposure sessions. The concentrations of insulin in both groups of rats exposed to magnetic field were significantly higher, compared to the controls, during the exposure cycle. After the end of exposure cycle the concentration of insulin in group S became normal. In contrast, in group P the concentration of insulin decreased significantly on the last day of exposure, with a subsequent increase in the following days. The activity of alpha-amylase and lipase in the serum of experimental and control rats was not affected. In both groups of exposed rats, reversible changes of ultrastructure of the pancreatic islets, including expansion of the Golgi apparatus, extension of rough endoplasmatic reticulum, mitochondrial swelling, expansion of beta-granules and increase in number of empty vesicles in beta cells, occurred during the exposure. In acinar cells of exposed animals, a slight extension of rough endoplasmatic reticulum and mitochondrial swelling as transitory changes were observed. The structural and functional changes in pancreas are probably adaptative ones.

Influence of spike current in different shaped waveforms on the hardness and grain size of nickel electroforms

This paper studies experimentally and theoretically the effects of a ramp-down spike-shaped waveform on the grain size and the hardness of nickel electroforms in pulse current electroforming. Experimental results show that the quality of the electroforms, in terms of hardness improvement, influenced by the types of waveform is in the order of: ramp-down and triangular, both with spike>rectangular with spike>ramp-down; and triangular, both with relaxation time>rectangular. Compared with the results for the conventional rectangular waveform, the experimental results show that the hardness value can be improved by about 46% when a ramp-down spike and a relaxation time are used in the case of triangular or ramp-down waveform. The finest grain size and the highest hardness value were obtained by using a ramp-down spike in either triangular or ramp-down waveform. These results are supported by theoretical predictions and study of the surface morphology of the electroforms using a scanning electron microscope.

Mesh Stiffness Variation Instabilities in Two-Stage Gear Systems

Mesh stiffness variation, the change in stiffness of meshing teeth as the number of teeth in contact changes, causes parametric instabilities and severe vibration in gear systems. The operating conditions leading to parametric instability are investigated for two-stage gear chains, including idler gear and countershaft configurations. Interactions between the stiffness variations at the two meshes are examined. Primary, secondary, and combination instabilities are studied. The effects of mesh stiffness parameters, including stiffness variation amplitudes, mesh frequencies, contact ratios, and mesh phasing, on these instabilities are analytically identified. For mesh stiffness variation with rectangular waveforms, simple design formulas are derived to control the instability regions by adjusting the contact ratios and mesh phasing. The analytical results are compared to numerical solutions.

A new approach to arc resistance calculation

An important macroscopic arc parameter, describing its complex nature is arc resistance. As known, the fault arc resistance can be calculated by the Warrington formula. The authors investigated the results of Warrington's tests. Warrington derived a relation for the arc voltage by using the measured arc voltage gradient and arc current as input data. By analyzing these measurements and by taking into account the conditions under which they are obtained (inaccurate measurement devices), it is unquestionable that the results are highly empirical and not accurate and general enough. Laboratory testing, provided in the high power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the base for the research results presented. In this paper a new approach to arc resistance calculation is given. Two independent approaches delivered the same equation. Both approaches are based on a suitable and a simple arc model assuming the rectangular wave form of the arc voltage, which is in phase with the arc current wave form. The new formula for arc resistance is compared with the Warrington formula. The influences of arc elongation are also investigated.

New dynamic model, laboratory testing and features of long arc in free air

In this paper the long arc in free air is investigated. First, arc is initiated under laboratory conditions in the high power test laboratory FGH-Mannheim (Germany). Based on the laboratory obtained data records, the main features of arc are derived. By this arc, voltage and current are processed. An important feature of arc, the variation of arc length, is analyzed. Based on the analysis of arc voltage and current wave forms, the new dynamic arc model, taking into account the arc length variation, is derived. Arc is modeled as a current dependent voltage source with the characteristic distorted rectangular waveform and arc length dependent amplitude. Arc is considered as a source of higher harmonics distorting by this other signals in the network. An example of arc computer simulation using the new model is given. The main features of simulated arc are presented, too. Features of both the real and the simulated arc are given in the time and the spectral domains.

Frequency dependence of output voltage generated from bundled compound magnetic wires

The output voltage generated from bundles of twisted Vicalloy wires was studied. When the magnetically soft layers of the wires were reversed by an applied external magnetic field, a pulse voltage, owing to a large Barkhausen jump, was induced in a search coil wound around the wires. The output did not depend on the exciting frequency of the applied field for the bundled wires with n (number of bundled wires) <5. The frequency dependence for n=10 was attributed to the demagnetizing field in the thicker shape of the bundle. The bundled wires of n=25 exhibited dispersed peaks in output waveform due to a self-biasing effect, which was advantageous for obtaining a rectangular output waveform.

Quadriceps Femoris Muscle Torques and Fatigue Generated by Neuromuscular Electrical Stimulation With Three Different Waveforms

Neuromuscular electrical stimulation is used by physical therapists to improve muscle performance. Optimal forms of stimulation settings are yet to be determined, as are possible sex-related differences in responsiveness to electrical stimulation. The objectives of the study were: (1) to compare the ability of 3 different waveforms to generate isometric contractions of the quadriceps femoris muscles of individuals without known impairments, (2) to compare muscle fatigue caused by repeated contractions induced by these same waveforms, and (3) to examine the effect of sex on muscle force production and fatigue induced by electrical stimulation. Fifteen women and 15 men (mean age=29.5 years, SD=5.4, range=22-38) participated in the study. A portable battery-operated stimulator was used to generate either a monophasic or biphasic rectangular waveform. A stimulator that was plugged into an electrical outlet was used to generate a 2,500-Hz alternating current. Phase duration, frequency, and on-off ratios were kept identical for both stimulators. Participants did not know the type of waveform being used. Torque was measured using a computerized dynamometer. A maximal voluntary isometric contraction (MVIC) of the right quadriceps femoris muscle set at 60 degrees of knee flexion was determined during the first session. In each of the 3 testing sessions, torque of contraction and fatigue elicited by one waveform were measured. Order of testing was randomized. Torque elicited by electrical stimulation was expressed as a percentage of average MVIC. A mixed-model analysis of variance was used to determine the effect of stimulation and sex on strength of contraction and fatigue. Bonferroni-corrected post hoc tests were used to further distinguish between the effects of the 3 stimulus waveforms. The results indicated that the monophasic and biphasic waveforms generated contractions with greater torque than the polyphasic waveform. These 2 waveforms also were less fatiguing. The torques from the maximally tolerated electrically elicited contractions were greater for the male subjects than for the female subjects. Muscle torque and fatigue of electrically induced contractions depend on the waveform used to stimulate the contraction, with monophasic and biphasic waveforms having an advantage over the polyphasic waveform. All tested waveforms elicited, on average, stronger contractions in male subjects than in female subjects when measured as a percentage of MVIC.

Modeling of electrocrystallization for pulse current electroforming of nickel

A mathematical model has been established for formulating the effect of different types of waveform on the three-dimensional electrocrystallization of nickel electroforms. The model describes how the different types of waveform influence the rate of three-dimensional nucleation, J, the rate of three-dimensional step growth via surface diffusion path, J SD, and the rate of three-dimensional step growth via direct transfer path, J DT, at the cathodic surface. Moreover, the dynamic electrocrystallization process including J, J SD and J DT was simulated. The highest maximum nucleation rate was obtained when a ramp-down waveform was employed. The highest step growth rate either via surface diffusion path or direct transfer path was obtained when conventional rectangular waveform was used. The best quality of electroforms, in terms of fine-grained structure, was found when a ramp-down waveform was employed. These results are in agreement with the findings of our previous studies.

Influence of spike current in different shaped waveforms on the surface finish of nickel electroforms

This paper studies the effects of ramp-down spike-shaped waveform on the surface finish of nickel electroforms in pulse current electroforming. Experimental results show that the quality of the electroforms, in terms of surface roughness improvement, influenced by the types of waveform is of the order of ramp-down and triangular both with spike>rectangular with spike>ramp-down and triangular both with relaxation time>rectangular. The results show that at the same cathodic peak current density, pulse period and a fixed electro-deposition time or electro-deposition thickness, the surface roughness can be reduced by as much as 2–3 times when a ramp-down spike was used in the cases of triangular, rectangular and ramp-down waveforms. The best surface finish was obtained when a ramp-down spike in a ramp-down waveform was used. These results are supported by the theoretical predictions and the study of the surface morphology of the electroforms by scanning electron microscopy.

Microwave pulse compression in a chain of ring-type resonators

Compression of a rectangular chirp-pulse waveform by a chain of nondissipative ring-type resonators is studied theoretically. A three-resonator chain is shown to be capable of compressing a microwave pulse by a factor of 8 with an almost 80% efficiency.

13.56MHz Current Source Inverter Based on Immittance Conversion Topology

This paper proposes a novel 13.56MHz current source high frequency inverter based on immittance conversion topology. One of the most distinctive characteristics of immittance conversion topology is that the voltage source is converted into the current source and vice versa. Some components contained in rectangular waveform are converted by utilizing immittance conversion element of distributed constant line type. When the operation frequency of the voltage source inverter is set to 4.52MHz, the voltage source with third harmonic frequency on the voltage source inverter, 13.56MHz component, is converted to the current source by the effect of immittance conversion element with the length λ/4. By utilizing these principles, 13.56MHz current source high frequency inverter is derived. The experimental results from a prototype system verify the theoretical procedure.

Oscillations in inspiratory synaptic inputs: role in controlling the repetitive firing behaviour of inspiratory motoneurons

The transformation of neuronal input into patterns of action potential output, a key element of signal processing in the brain, is determined by the interaction between synaptic and intrinsic membrane properties. Traditional use of rectangular, ramp-like or sinusoidal waveforms to stimulate neurons has focussed attention on the role of intrinsic membrane properties and their modulation in determining repetitive firing behaviour. However, such studies do not address the role that dynamic features of endogenous synaptic inputs play in controlling output. Oscillations are prominent features of synaptic currents/potentials in many networks including those that provide rhythmic excitatory drive to motoneurons involved in behaviours such as locomotion and respiration [1,2,3]. Phrenic motoneurons (PMNs), for example, receive inspiratory currents of brainstem origin that oscillate with peak power in the 20–120 Hz bandwidth. These oscillations are ubiquitous throughout the respiratory network, in vivo [2,4] and in vitro [3,5], and although well-characterized, their function, if any, is not known. Using rhythmically active brainstem spinal cord preparations from neonatal rat and recently developed stimulation techniques [6], we explored the physiological significance to motor control of such oscillations by activating PMNs with native inspiratory synaptic currents that oscillate in the 20–50 Hz bandwidth. Action potentials arose predominantly from peaks of the current oscillations and the timing of spikes within trains was reproducible within 2%. Activation of neurons with low-pass filtered currents produced spike trains with considerably more variability; filtering also reduced the number of action potentials by 35%. Finally, the excitatory neuromodulator, phenylephrine, which significantly increased instantaneous firing frequency responses to filtered inspiratory or square-wave stimuli, had no effect on frequency evoked by endogenous (unfiltered) synaptic waveforms. Results indicate that oscillations in synaptic inputs generated by central respiratory circuits maximise neuronal output, and play a dominant role in controlling the timing of action potentials during behaviourally relevant repetitive firing, even in the presence of neuromodulators.

Electrodiagnóstico y electroestimulación de músculos denervados

AbstractThe main parameters of electro-diagnostic stimulation are the following: strength–duration curve, cronaxia, quality valuation of muscular response, Fishgold test, accommodation quotient and the excitability faradic.The electrical stimulation of the denervated muscles has generated large scale controversies.The proposed protocol has as an objective the prevention of muscular fibrosis during the period of reinnervation of a denervated muscle.This consists in electrical stimulation of the denervated muscle (total or partial) with a rectangular monophasic waveform with a pulse duration of 30-300 miliseconds.The treatment consists of five impulses each day, with a separation of four seconds between them (0.2 Hz)

A study of hardness and grain size in pulse current electroforming of nickel using different shaped waveforms

This paper describes an experimental and theoretical study of the effects of different types of waveform on the grain size and the hardness of nickel electroforms in pulse current electroforming. The highest hardness value and the finest grain size were obtained using a ramp-down waveform with relaxation time. The experimental results show that compared with the conventional rectangular waveform and with relaxation time, the hardness value can be improved by about 28% when a ramp-down waveform, also with relaxation time, is used. These results are supported by theoretical predictions and the study of the surface morphology of the electroforms by scanning electron microscopy.

Modelling the effect of complex waveform on surface finishing in pulse current electroforming of nickel

A mathematical model has been established for formulating the effect of different types of waveform on surface finishing in pulse current electroforming of nickel. The model describes the change of the concentration profile of electroactive ions, micro-current distribution and the rate of protrusion growth at the cathodic surface. The theoretical predictions are compared with the experimental results: within the range of the study, a maximum discrepancy of 10% on surface roughness values between the two was found. This discrepancy could be due to the evolution of hydrogen gases at the cathodic surface during electrodeposition. The best surface finish was found by using a ramp-down waveform with relaxation time. Both theoretical predictions and experimental results show that the quality of the electroforms, in terms of surface roughness improvement, influenced by the types of waveform is of the order of ramp-down waveform>triangular waveform>ramp-up waveform>rectangular waveform, all with relaxation time. This is also supported by the study of the surface morphology of the electroforms by scanning electron microscopy.

Electroinjection of colloid particles and biopolymers into single unilamellar liposomes and cells for bioanalytical applications.

A combined electroporation and pressure-driven microinjection method for efficient loading of biopolymers and colloidal particles into single-cell-sized unilamellar liposomes was developed. Single liposomes were positioned between a approximately 2-microm tip diameter solute-filled glass micropipet, equipped with a Pt electrode, and a 5-microm-diameter carbon fiber electrode. A transient, 1-10 ms, rectangular waveform dc voltage pulse (10-40 V/cm) was applied between the electrodes, thus focusing the electric field over the liposome. Dielectric membrane breakdown induced by the applied voltage pulse caused the micropipet tip to enter the liposome and a small volume (typically 50-500 x 10(-15) L) of fluorescein, YOYO-intercalated T7-phage DNA, 100-nm-diameter unilamellar liposomes, or fluorescent latex spheres could be injected into the intraliposomal compartment. We also demonstrate initiation of a chemical intercalation reaction between T2-phage DNA and YOYO-1 by dual injection into a single giant unilamellar liposome. The method was also successfully applied for loading of single cultured cells.

Oscillation elimination in the Hopkinson bar apparatus and resultant complete dynamic stress–strain curves for rocks

This paper highlights an improved experimental approach for eliminating oscillation that exists in the dynamic stress–strain response of rocks and other brittle materials obtained from tests using a split Hopkinson pressure bar (SHPB). Both analytical and experimental results for a number of rock types are presented to verify the idea. Results from the investigation indicate that oscillation in the dynamic stress–strain response of these materials originates from the Pochhammer–Chree dispersion of the loading incident wave, and more evidently from the relatively low strength and elastic modulus of the samples compared with metallic materials. In order to control the oscillation effectively, it is proposed that a half-sine loading waveform should be used instead of the conventional rectangular loading waveform in SHPB tests. Experimental results obtained from both the conventional and the improved methods are presented, including dynamic complete stress–strain curves for granite, sandstone and limestone. The improved method eliminates oscillation in the tests, provides better stability of strain rate and more representative results than those obtained from the conventional rectangular loading waveform shape.