General Waveform Research Articles

Cardiovascular functions in two macruran decapod crustaceans (Procambarus clarkii and Homarus americanus) during periods of inactivity, tail flexion and cardiorespiratory pauses

Arterial hemolymph flow was measured in restrained crayfish (Procambarus clarkii) and lobsters (Homarus americanus). Implanted pulsed Doppler flow transducers were used to measure arterial flows in the anterior aorta, posterior aorta, sternal artery, lateral artery, ventral thoracic artery and ventral abdominal artery, allowing determination of flow simultaneously in several arteries over a period of 4 days. Calculated Doppler hemolymph flow showed a strong correlation (P<0.05) with 'pumped' hemolymph flow as determined by in situ calibration. Arterial flow patterns remained constant during quiet conditions. In crayfish, cardiac output was 7.5&plusmn;1.1 ml min-1 (252 ml kg-1 min-1), of which the anterior aorta received 1.3&plusmn;0.15 ml min-1 (20.1&plusmn;4.0 %), the posterior aorta received 0.8&plusmn;0.1 ml min-1 (12.3&plusmn;2.7 %) and the sternal artery received 5.2&plusmn;1.4 ml min-1 (67.5&plusmn;37.0 %). Mean heart frequency at rest was 125.6&plusmn;5.2 beats min-1 and stroke volume was 0.06&plusmn;0.01 ml beat-1 (1.98 ml kg-1 beat-1). In lobsters, cardiac output was 60.8&plusmn;4.4 ml min-1 (93.6&plusmn;6.8 ml kg-1 min-1), with the anterior aorta receiving 7.8&plusmn;0.8 ml min-1 (12.8&plusmn;2.7 %), the lateral arteries receiving 0.6&plusmn;0.2 ml min-1 (1.0&plusmn;0.5 %), the posterior aorta receiving 12.6&plusmn;1.0 ml min-1 (20.7&plusmn;3.3 %) and the sternal artery receiving 38.9&plusmn;4.1 ml min-1 (64.0&plusmn;13.4 %). Flows in the branches of the sternal artery were 0.3&plusmn;0.05 ml min-1 (0.5&plusmn;2 %) in the ventral abdominal artery and 4.0&plusmn;0.1 ml min-1 (6.5&plusmn;0.3 %) in the ventral thoracic artery. Lobster heart rate was 82.5&plusmn;2.9 beats min-1 and stroke volume was 0.7&plusmn;0.05 ml beat-1. Periods of constant hemolymph flow were interrupted by tail flexions (abdominal flexion) and, in lobsters, periods of cardiac/respiratory pause. Tail movement increased flow (peak height and minimum flow values) in both crayfish and lobsters, although the general wave form of hemolymph flow and pressure did not change. In lobsters, periodic respiratory pauses were observed during which all arteries received hemolymph, despite the low heart rate.

Convergence of Waveform Relaxation Methods for Differential-Algebraic Systems

This paper gives sufficient conditions for existence and uniqueness of solutions and for the convergence of Picard iterations and more general waveform relaxation methods for differential-algebraic systems of neutral type. The results are obtained by the contraction mapping principle on Banach spaces with weighted norms and by the use of the Perron--Frobenius theory of nonnegative and nonreducible matrices. It is demonstrated that waveform relaxation methods are convergent faster than the classical Picard iterations.

Effect of voids on the propagation of waves in an elastic layer

The present paper investigates the propagation of waves in an elastic layer containing voids. Numerical calculations and discussions indicate that the velocity of the propagation of waves decreases due to the presence of voids in the material medium of the layer and the voids cause dispersion of the general waveform.

Analysis of the middle latency evoked potentials to angular acceleration impulses in man

The middle latency vestibular evoked potential (ML-VsEP) recorded with scalp electrodes in man in response to impulses of angular acceleration is dominated by a forehead positive peak at about 15 ms and a negative peak at about 20 ms; the peak amplitude of this component is about 30 μV. This is followed by slower, smaller amplitude activity. The latency of this initial peak is similar to the latency of the vestibulo-ocular reflex (VOR) in monkeys. The present study was undertaken to elucidate the possible relation between the ML-VsEPs and VOR. This included recordings from forehead-mastoid electrodes (sites used to record VsEP) and other scalp electrodes and the recording of potentials due to eye movement: the electro-oculogram. Direct recording of eye movements was also conducted using an infra-red reflection device in those experiments in which the head was not moved. The recordings were conducted in man during vestibular stimulation eliciting VsEPs, during voluntary eye movements and during caloric and optokinetic stimulation. These experiments indicated that the 15–20 ms component of the ML-VsEP was not due to movements of the eye (corneoretinal dipole). The large amplitude 15–20 ms component of the ML-VsEP was similar in general magnitude, waveform, polarity, duration and rise time to the highly synchronous pre-saccadic spike (neural and/or myogenic) which precedes nystagnys and voluntary saccades. It therefore probably represents vestibular-initiated electrical activity in motor units of the extra-ocular muscles which then produce anti-compensatory saccades.

Current ripple bounds of interleaved power converters

We extend the main claims for more general waveforms. Specifically, we show that for any power converter module, if its input/output current ripple waveform is of full-sinusoidal-type or half-sinusoidal-type with peak-to-peak amplitude A(/spl Delta/I/sub 0/), then the amplitude of the input/output current ripple of N (/spl ges/1) parallelly interleaved such modules (with equal phase shift 2/spl pi//N) is always less than or equal to A(/spl Delta/I/sub 0/).

Acceptance and generation of general wave by a natural observation filter

AbstractDuring the past few years, there has been a series of papers published on the theory of the natural observation method. As one of the important applications of this theory, the problems of acceptance and generation of a general waveform are discussed here. The case of polynomial waveforms and its corresponding theory was published previously. A great extension of that theory which covers general waveforms is presented here and its full picture is clarified.

Programmable shaping of ultrabroad-bandwidth pulses from a Ti:sapphire laser

We have used a commercially available liquid-crystal spatial light modulator within a reflective optics pulse-shaping apparatus to shape ultrashort pulses with temporal resolution approaching 10 fs. Using the spatial light modulator as a phase modulator, we produce a variety of complex ultrafast waveforms, including odd pulses, high repetition rate (&gt;23 THz) pulse trains, and asymmetric pulse trains. We also show that it is possible to compensate for large amounts of high-order phase dispersion (in excess of 60π) by appropriate cubic- and quartic-phase modulations of the pulse. Finally, we examine the limitations of shaping ultrabroad-bandwidth pulses. We find that, for specific classes of waveforms, Fourier-transform pulse-shaping techniques can be used for pulses with 5-fs durations, which exceed the current state of the art in ultrashort pulse generation. However, synthesis of general waveforms with 5-fs resolution will require compensating for nonlinear spatial dispersion of frequency in the masking plane.

Modeling of one-dimensional weakly nonlinear waves that propagate in media with arbitrary dissipation and dispersion mechanisms.

In his paper [J. Acoust. Soc. Am. 77, 2050 (1985)] Blackstock presented a generalized Burgers equation for the propagation of one-dimensional weakly nonlinear waves in various media. His results, and the approach he employed there, however, are limited to harmonic waves. In this paper, we present a general approach to model nonlinear waves of more general wave forms that propagate in media with arbitrary absorption and dispersion relations. The resulting equation is again called the generalized Burgers equation (to follow the terminology of the literature). It is found that steady shock solutions for various media can be described by the corresponding simplified version of the equation. An efficient numerical method by means of spectral analysis is developed for solving the generalized Burgers equation. Typical results exemplified by the case of a sinusoidal wave source are also reported in this paper.

Effect of hearing loss in electrocochleographic investigation of endolymphatic hydrops using tone-pip and click stimuli

Extratympanic electrocochleography (ECochG) was performed on 37 patients referred to the Evoked Potential Clinic with suspected Ménière's disease. The patients were classified according to their hearing impairment and audiometric configuration. Click and tone-pip stimuli with tone frequencies of 1 and 4 kHz were presented at a rate of 10 per second. Amplitude, latency and general waveform characteristics of the summation potential (SP) and action potential (AP) were analysed for each averaged response with respect to the level and configuration of the hearing loss. The highest incidence of abnormal percentage SP was in patients with average hearing loss in the range of 40-64 dB HL using the click stimulus. In low tone hearing loss, hydrops was identified from an enhanced SP in significantly more patients using the click and 4 kHz tone-pip than the 1 kHz stimulus. Measurement of the width of the 1 kHz tone-pip response waveform was abnormal in some patients even though the click and 4 kHz responses were normal. The optimum stimulus for identification of hydrops from an enhanced SP is dependent on the level and configuration of the hearing loss.

The hit array: a synthesis tool for multiple access frequency hop signals

The hit array formalism was developed for the analysis of general frequency hop waveforms, in the context of coherent active radar and sonar echolocation systems, or multiple access spread spectrum communications. This formalism is shown to be useful for synthesis as well. Necessary and sufficient conditions are derived for a given hit array to be realizable, i.e., to correspond to a valid frequency hopping pattern. A general backtracking-type algorithm is presented to reconstruct the pattern(s) associated with this hit array. This makes it possible to synthesize a set of frequency hop waveforms directly from any given (realizable) hit array, and thus, because of the correspondence between hit array and ambiguity function, from any physically meaningful ambiguity function. In particular, for limited a priori range and Doppler shifts, this is the first efficient algorithm for direct synthesis from ideal ambiguity function specifications. Several reconstruction examples are shown for illustration purposes. >

The hit array: an analysis formalism for multiple access frequency hop coding

A formalism is presented for the analysis of general frequency hop waveforms, such as those suitable for use in coherent active radar and sonar echolocation systems as well as multiple-access spread-spectrum communications. This formalism is based on the concept of coincidence, or 'hit', between two frequency hopping patterns. The collection of all possible hits, together with their locations, is recorded in time-frequency space, which produces the high array associated with the two patterns considered. If the code length is sufficiently small with respect to the time-bandwidth product chosen, the hit array can be viewed as a digital representation of the corresponding ambiguity function. Salient properties of the hit array formalism are derived, including simple relationships between hit arrays resulting from basic symmetry-preserving transformations. These properties make it possible to predict the performance of a given set of frequency hop waveforms directly from the associated set of frequency hopping patterns. >

Processing of acoustic waveforms

A sinusoidal model for acoustic waveforms is applied to develop a new analysis/synthesis technique which characterizes a waveform by the amplitudes, frequencies, and phases of component sine waves. These parameters are estimated from a short-time Fourier transform. Rapid changes in the highly-resolved spectral components are tracked using the concept of "birth" and "death" of the underlying sine waves. The component values are interpolated from one frame to the next to yield a representation that is applied to a sine wave generator. The resulting synthetic waveform preserves the general waveform shape and is perceptually indistinguishable from the original. Furthermore, in the presence of noise the perceptual characteristics of the waveform as well as the noise are maintained. The method and devices disclosed herein are particularly useful in speech coding, time-scale modification, frequency scale modification and pitch modification.

Transient studies of screw and edge dislocation generation at crack edges

Exact transient analyses of the generation of screw and edge dislocations at the edges of stationary cracks subjected to the diffraction of, respectively, plane SH- and SV-waves, and their subsequent arrest are performed. The solutions are examined in light of a dislocation emission criterion which is based, simultaneously, on standard dislocation force concepts and quasi-static emission studies. This examination allows expressions for the times of emission and arrest, the distances traveled by the dislocations, and the dynamic stress intensity factors to be derived in terms of parameters such as dislocation speed and yield stress. These expressions exhibit distinctive dynamic effects and reveal several features of the generation process: In particular, the times and distances are, while on a micromechanical scale, not necessarily insignificant, and imply that purely brittle fracture may not easily occur. Then, edge dislocation emission would appear to occur at a preferred speed, while screw dislocation emission apparently prefers to take place quasi-statically. Examination of a general incident waveform class shows that a continuous wave could cause dislocation generation to occur before a step-stress wave can. Moreover, the emission process depends upon a weighted time history of the incident wave stress, not its instantaneous value. This, in turn, implies that dislocation emission does not necessarily shield the crack edge by lowering the dynamic stress intensity factor. Finally, unless the dislocations are allowed to decelerate to zero speed upon arrest, a repetitious process of start-stop motion can in principle take place.

Source coding of speech and video signals

Some digital source coding techniques for speech and video are reviewed. Predictive coding of speech, multipulse and code-excited coders and frequency-domain coders are discussed and compared for the coding of speech signals, and intraframe and still image coding and interframe coding are examined for the coding of image and video signals. The emphasis is on those algorithms that offer high compression while maintaining the perceptual quality of the source signals are discussed. Some algorithms that are general waveform coding algorithms and do not strictly depend on the input source are included. >

A new approach to the definition of electric power, under conditions of distorted voltages and currents

A generalized time-domain definition of electric power, using autocorrelation and cross-correlation techniques, is proposed for measurement, characterization and compensation of fictitious power in any network, under conditions of nonsinusoidal and in general aperiodic voltage and current waveforms. This leads to the proposal of a new equivalent network parameter, disseptance, which describes the nonlinear properties of the load. The problems associated with the existing definitions of electric power are pointed out by means of a descriptive summary of the different power definitions and their associated limitations. A new philosophy for compensation of fictitious power in distorted supplies, is based on this definition of power and network parameters.

General waveform shape analyser

The paper describes a general waveform shape analyser (Wavenet), and a system that uses the representation that it forms for a particular waveform application (Synnet). Wavenet incorporates ideas from models of low-level vision, including Gestalt grouping and the search for symmetry and structure. The novel design includes a lattice network of nodes combined with an attributed grammar, which hunts for perceptually salient structures in overlapping sections of the waveform. The parallel multiscale representation formed by Wavenet is used by the second system, Synnet, to find instances of clinically significant EEG shapes. Synnet chooses the best of the wavenet primitives, using relaxation, and combines them syntactically into higher-level shapes, assigning confidence values calculated from their attributes. Wavenet and Synnet were able to find EEG spikes and waves, of various sizes and with superimposed noise, in a variety of EEG data.

Speech analysis/Synthesis based on a sinusoidal representation

A sinusoidal model for the speech waveform is used to develop a new analysis/synthesis technique that is characterized by the amplitudes, frequencies, and phases of the component sine waves. These parameters are estimated from the short-time Fourier transform using a simple peak-picking algorithm. Rapid changes in the highly resolved spectral components are tracked using the concept of birth and death of the underlying sine waves. For a given frequency track a cubic function is used to unwrap and interpolate the phase such that the phase track is maximally smooth. This phase function is applied to a sine-wave generator, which is amplitude modulated and added to the other sine waves to give the final speech output. The resulting synthetic waveform preserves the general waveform shape and is essentially perceptually indistinguishable from the original speech. Furthermore, in the presence of noise the perceptual characteristics of the speech as well as the noise are maintained. In addition, it was found that the representation was sufficiently general that high-quality reproduction was obtained for a larger class of inputs including: two overlapping, superposed speech waveforms; music waveforms; speech in musical backgrounds; and certain marine biologic sounds. Finally, the analysis/synthesis system forms the basis for new approaches to the problems of speech transformations including time-scale and pitch-scale modification, and midrate speech coding [8], [9].

EFFECT OF HALOTHANE ON SPINAL SOMATOSENSORY EVOKED POTENTIALS IN SHEEP

The effects of increasing concentrations of halothane on the morphology of spinal somatosensory evoked potentials (SEP) were studied in seven anaesthetized sheep. Anaesthesia was induced with thiopentone and maintained with nitrous oxide in oxygen. Ventilation was controlled throughout. Arterial pressure, temperature and end-tidal carbon dioxide tension were monitored. A lumbar laminectomy was performed, the sciatic nerve exposed and a baseline spinal SEP was recorded from the surface of the lumbar spinal cord. Halothane was introduced in incremental steps of 1% up to 3% and further SEP were recorded. These recordings revealed that the spinal SEP peak latencies and general waveform configuration were stable under halothane anaesthesia. Baseline SEP amplitude was similar to that obtained with 1% halothane; however, at concentrations of 2% halothane or greater, there was a significant (P less than 0.005) attenuation of all components of the spinal SEP. These findings have important anaesthetic implications for patients undergoing spinal cord monitoring using SEP, although interspecies differences may occur.

Group velocity in general waveforms

Group velocity in general waveforms

Generation and measurement of ultrashort current pulses with Josephson devices

Experimental demonstration of an ultrashort-pulse generator and a novel sampling technique to measure its pulse shape is reported. The pulse generator, which uses Josephson interferometers, is designed to be dc powered and self-resetting. Its pulses are measured to be 26 ps in duration at a simulated maximum frequency of 2.5 GHz. The sampling technique is useful for measuring general fast waveforms with unprecented sensitivity and resolution extendable to subpicosecond time scale.