Sequence Of Impulses Research Articles

Autoregressive modeling of transfer functions in frequency domain to determine complex travel times

We present a method to determine the complex travel times of impulses in the time domain on the basis of an autoregressive (AR) modeling of superimposed sinusoids in a finite complex series in the frequency domain. We assume that the complex frequency series consists of signals represented by a complex AR equation with additional noise. The AR model in the frequency domain corresponds to a complex Lorentzian in the time domain. In a similar way to the Sompi or extended Prony method, the complex travel times are given by solutions of a characteristic equation of complex AR coefficients, which are obtained as the eigenvector corresponding to a minimum eigenvalue in an eigenvalue problem of non-Toeplitz autocovariance matrix of the complex series. Our method is tested for synthetic frequency series of transfer functions, which show that (1) the complex travel times of closely adjacent pulses in the time domain are clearly resolved, and that (2) the frequency dependence of the complex travel times for physical and structural dispersions is precisely determined by the analysis within a narrow frequency window. These results demonstrate the usefulness of our method with high resolvability and accuracy in the analysis of impulse sequences.

Repeated sequences of interspike intervals in baroresponsive respiratory related neuronal assemblies of the cat brain stem.

Many neurons exhibit spontaneous activity in the absence of any specific experimental perturbation. Patterns of distributed synchrony embedded in such activity have been detected in the brain stem, suggesting that it represents more than "baseline" firing rates subject only to being regulated up or down. This work tested the hypothesis that nonrandom sequences of impulses recur in baroresponsive respiratory-related brain stem neurons that are elements of correlational neuronal assemblies. In 15 Dial-urethan anesthetized vagotomized adult cats, neuronal impulses were monitored with microelectrode arrays in the ventral respiratory group, nucleus tractus solitarius, and medullary raphe nuclei. Efferent phrenic nerve activity was recorded. Spike trains were analyzed with cycle-triggered histograms and tested for respiratory-modulated firing rates. Baroreceptors were stimulated by unilateral pressure changes in the carotid sinus or occlusion of the descending aorta; changes in firing rates were assessed with peristimulus time and cumulative sum histograms. Cross-correlation analysis was used to test for nonrandom temporal relationships between spike trains. Favored patterns of interspike interval sequences were detected in 31 of 58 single spike trains; 18 of the neurons with significant sequences also had short-time scale correlations with other simultaneously recorded cells. The number of distributed patterns exceeded that expected under the null hypothesis in 12 of 14 data sets composed of 4-11 simultaneously recorded spike trains. The data support the hypothesis that baroresponsive brain stem neurons operate in transiently configured coordinated assemblies and suggest that single neuron patterns may be fragments of distributed impulse sequences. The results further encourage the search for coding functions of spike patterns in the respiratory network.

Coulomb propagator in the WKB approximation

Employing the WKB approximation, we derive an analytical expression for the two-body Coulomb propagator in terms of the asymptotic momentum pas, coordinates r and r' and the difference of time τ. The momentum pas is a solution of the stationary phase equation. The problem of solving it is reduced to seeking the roots of some one-dimensional equation. The WKB Coulomb propagator is applied to calculate the continuum state of an atomic electron, subject to a sequence of δ-function impulses. The derived continuum state includes the effects of electron rescatterings into the continuum that may play an important role in various processes of atomic fragmentation.

On preshaped reference inputs to reduce swing of suspended objects transported with robot manipulators

One of the application areas of robot manipulators is pick-and-place operations where some objects may not be grasped by robot manipulators due to the task constraints. Such objects, for example those simply suspended, need to be carried by a hook or a similar device attached to the manipulator endpoint. This paper presents the results and implications of a study into preshaped reference inputs to reduce the swing of suspended objects at the end of a desired trajectory. Two reference input preshaping methods are considered; (i) superimposing a ramp function onto another function, and (ii) convolving a sequence of impulses with a desired reference input to generate a shaped input. A hydraulically actuated robot manipulator carrying a compound pendulum was employed as an experimental system to test the methods. Simulation and experimental results are presented to demonstrate the feasibility of both methods. It is concluded that while superimposing a ramp function onto another function such as a cycloid does not increase the transportation time while reducing the swing, whereas the latter, convolving a sequence of impulses with a cycloid, increases the transportation time. In addition to this, the robustness of the first method to the uncertainties in the natural frequency of the suspended object is better than that of the second method. The simulation and experimental results prove that by properly preshaping the reference input of a robot manipulator, a swing-free stop is obtainable. The proposed approaches are simple and easy to implement.

Design and Sensitivity Analysis of Input Shaping Filter in the Z-domain

Input shaping method is to convolute input shaper, which is sequence of impulses, with reference input command not to excite the natural frequency of system. To reduce residual vibration for the ch ange of frequency, the number of impulses should be increased. Until now, amplitudes and time interval of those has been searched from the derivative of residual vibration. However, if time interval of impulses is fixed as the half of vibration period of system, input shaper H(z) in z-domain becomes (I-pz-1)n/K in which increasing n is the mean that robustness for change of parameter is improved. Also, design of many types of input shapers in z-domain is very easy because sensitivity curve is displayed with H(z)zn100. In the z-domain, EI(Extra-Insensitive) input shaper could be designed without solving nonlinear simultaneous equations as design in continuous time domain. In addition to, the design possibility of input shaper for a damped system was shown.

Closed-Loop Input Shaping for Flexible Structures Using Time-Delay Control1

Input shaping techniques reduce the residual vibration in flexible structures by convolving the command input with a sequence of impulses. The exact cancellation of the residual structural vibration via input shaping is dependent on the amplitudes and instances of impulse application. A majority of the current input shaping schemes are inherently open-loop where impulse application at inaccurate instances can lead to system performance degradation. In this paper, we develop a closed-loop control design framework for input shaped systems. This framework is based on the realization that the dynamics of input shaped systems give rise to time delays in the input. Thus, we exploit the feedback control theory of time delay systems for the closed-loop control of input shaped flexible structures. A Riccati equation-based and a linear matrix inequality-based frameworks are developed for the stabilization of systems with uncertain, multiple input delays. Next, the aforementioned framework is applied to two input shaped flexible structure systems. This framework guarantees closed-loop system stability and performance when the impulse train is applied at inaccurate instances. Two illustrative numerical examples demonstrate the efficacy of the proposed closed-loop input shaping controller. [S0022-0434(00)00103-9]

Behavioural and acoustic observations of sperm whales in Scapa Flow, Orkney Islands

Six juvenile sperm whales were observed visually and acoustically in the confined waters of Scapa Flow, Orkney Islands during March 1993. General visual behaviours observed included slow travelling, head-outs, logging and side fluking but there were no observations of tail fluking within the confines of Scapa Flow. Recordings of the whales' vocalizations through hydrophones revealed a remarkably wide repertoire including clicks, rapid clicks, gunshots, chirrups, creaks, short trumpets, pips, squeals and clangs. Selected examples of these sounds were digitized and analysed as spectrograms. Clicks, rapid clicks, gunshots and clangs all showed a characteristic impulsive broadband signature. Chirrups, short trumpets and creaks were composed of rapid sequences of broadband impulses, although creaks were invariably faint and were difficult to illustrate well. Chirrups, short trumpets and clangs showed strong spectral peaks and pips were particularly unusual sounds with impulsive narrowband signatures composed of harmonically spaced peaks. Squeals exhibited prolonged, narrowband swept frequency signatures often with slight oscillation. All types of vocalization with the exception of clangs were heard from sperm whales during pure observation, minimum disturbance encounters in the field. Two attempts were made to remove the whales from Scapa Flow, the first being an enticement operation to lure the whales to open water with the use of underwater playback of sounds of socializing female sperm whales and the second a shepherding operation to drive the whales with a flotilla of vessels. The enticement operation was unsuccessful but the shepherding operation was successful, although the whales showed considerable reluctance to navigate a narrow channel to the open sea. During the shepherding operation there was a distinct change in the nature of the whales' vocalizations, with clangs predominating over other forms.

Guidance Preconditioning by an Impulse Sequence for Robust Residual Vibration Suppression

In order to suppress residual vibrations, a general method is presented for preconditioning any guidance function prior to its application to a dynamic system, by convolving it with a sequence of impulses. The approach includes first the development of the necessary design specifications for the impulse sequence, so that the robustness properties cover the widest possible variation of the system natural frequencies. Three solution methods are proposed then, with special emphasis in the achievement of the minimum possible duration time of the impulse sequence. Numerical experiments verify the effectiveness of the robustness, not only with respect to variations of the natural frequency, but also with respect to variations of a range of other linear and non‐linear variables.

Comparison of Filtering Methods for Reducing Residual Vibration

This paper compares command filtering techniques for reducing the residual vibration of computer-controlled machines. Input shaping is a relatively new technique that generates vibration-reducing commands by convolving a sequence of impulses with any desired command. The convolution product is then used as the command signal. The simple version of input shaping considered in this paper is a form of finite impulse response (FIR) notch filtering designed to suppress vibration in mechanical systems. Given the great variety of FIR and infinite impulse response (IIR) filters, it is of interest to compare input shaping to conventional filtering. Several types of input shapers are presented and shown to be more effective at reducing residual vibration than any of the conventional filters considered in this paper.

Multi-input shaping design for vibration reduction

The performance of many flexible systems can be improved by employing command shaping techniques to reduce machine vibration. The input shaping technique, in particular, has proven to be highly effective for a wide class of systems. While most real systems are multi-input systems, however, the method has primarily only been developed for single-input systems. This paper presents an approach for designing multi-input shapers using an s-plane pole placement technique. Slightly more information about the system model is taken into account than has been traditionally done with input shaping designs. The input shaping sequences for all system inputs are solved for simultaneously, and the resulting designs lead to shorter impulse sequences than solving for input shaping sequences for each input independently of each other.

558 The influence of linear frequency and intensity modulation of sound impulse sequence on evaluation of simulated movement

558 The influence of linear frequency and intensity modulation of sound impulse sequence on evaluation of simulated movement

Experimental Results of Impulsive Synchronization Between Two Chua's Circuits

Impulsive synchronization of chaotic dynamic systems has some important applications to chaotic secure communication and chaotic spread-spectrum communication systems. In this paper we present some experimental results on impulsive synchronization between two Chua's circuits. In our experiments, only one synchronizing impulse sequence is transmitted. The robustness of impulsive synchronization with respect to variations in the frequency and the width of impulses is studied. Experimental results show that robust impulsive synchronization can be achieved under noisy conditions and a 2% parameter mismatch between the driving system and the driven system. We also found that an amplified impulse sequence with a gain greater than unity can make the impulsive synchronization more robust. Moreover, we found that impulsive synchronization can be achieved with very narrow impulses.

Lie-algebraic approach to the calculation of quasi-energies

For two- and three-level systems analytical expression for the quasi-energies are obtained in the case when the external nonstationary field is a periodical sequence of rectangular impulses.

Treatment possibilities with a high-energy pulsed light source (PhotoDerm VL)

By varying the light spectrum, impulse length, impulse sequences and fluences, the PhotoDerm VL allows a large choice of individual treatment parameters. Superficial as well as deeper localized vascular malformations (essential telangiectases, port-wine stains, Poikiloderma of Civatte, hemangiomatous malformations) and cosmetically bothering hypertrichosis can be treated successfully with this high intensity polychromatic pulsed light source.

Evaluation of a reiterant force impulse task: A constructive replication

In the current study, characteristics of labial force–impulse tasks were investigated under three speaking conditions using a minipressure transducer. In the task, neurologically normal adults were first asked to read aloud two sentences of different lengths (ten repetitions each) containing bilabial voiced and unvoiced consonants, and were then required to repeat the series of utterances using mimed speech. Mimed speech was produced with subjects holding their breath; subsequently, the experimenter cued subjects to use a normal airflow and the mimed utterances were repeated. Subjects were then trained to produced sequences of labial force impulses modeled on the real-speech utterances by substituting /ba/ or /pa/ for each syllable. The reiterant condition was also recorded as mimed. The goal of the analyses were to (a) compare the timing of the real-speech sequences to the timing of mimed and reiterant versions, and (b) compare the force magnitudes associated with labial stress produced during real speech to mimed and reiterant repetitions. Results will be discussed in terms of the relationship between orofacial, nonspeech motor performance and speech production performance. [Work supported by NIH Award No. T32 DC00042 and R01 DC00319.]

A recovery model for coincidence neurons

A new model for firings of coincidence neurons in the MSO is presented. The model is similar to one by Colburn et al. [Hearing Res. 49, 335–346 (1990)]: Both are point processes, both have inputs which are impulse-train representations of the firing events of primarylike neurons, both operate on a low-pass filtered sum of those inputs, and both output a sequence of impulses at the event times of the coincidence neuron’s firings. In this model, their threshold-crossing neuron model is replaced by a recovery model similar to that modeling the input firings. The coincidence neuron’s drive function is a nonlinearly distorted version of the filtered sum of inputs; for simplicity, its recovery function is the same as that of the input neurons. The model’s firing rates, vector strengths, period histograms, and interval histograms are compared to data from dog and cat and with similar responses of the Colburn et al. model.

Convolved and simultaneous two-mode input shapers

Input shaping is a method of reducing residual vibrations in computer controlled machines. Vibration is eliminated by convolving a sequence of impulses with a desired system command to produce a shaped input that is then used to drive the system. Techniques for designing the impulse sequence for two-mode systems are presented. Properties of the various techniques are compared as a function of the mode ratio. Simulations of a two-mode system demonstrate key results.

Vibration Reduction Using Multi-Hump Input Shapers

Input shaping is a method for reducing residual vibrations in computer-controlled machines. Vibration is eliminated by convolving an input shaper, which is a sequence of impulses, with a desired system command to produce a shaped input. The shaped input then becomes the command to the system. Requiring the vibration reduction to be robust to modeling errors and system nonlinearities is critical to the success of the shaping process on any real system, Input shapers can be made very insensitive to parameter uncertainty; however, increasing robustness usually increases system delays. A design process is presented that generates input shapers with insensitivity-to-time-delay ratios that are much larger than traditionally designed input shapers. The advantages of the new shapers are demonstrated with computer simulations and their performance is verified with experimental results from the MIT Middeck Active Control Experiment, which was performed on board the Space Shuttle Endeavor.

Time-Optimal Negative Input Shapers

Input shaping reduces residual vibration in computer controlled machines by convolving a sequence of impulses with a desired system command. The resulting shaped input is then used to drive the system. The impulse sequence has traditionally contained only positively valued impulses. However, when the impulses are allowed to have negative amplitudes, the rise time can be improved. Unfortunately, excitation of unmodeled high modes and overcurrenting of the actuators may accompany the improved rise time. Solutions to the problem of high-mode excitation and overcurrenting are presented. Furthermore, a simple look-up method is presented that facilitates the design of negative input shapers. The performance of negative shapers is evaluated experimentally on two systems; one driven by a piezo actuator and the other equipped with DC motors.

Self-Organized Short-Term Memories

We report short-term memory formation in a nonlinear dynamical system with many degrees of freedom. The system ``remembers'' a sequence of impulses for a transient period, but it coarsens and eventually ``forgets'' nearly all of them. The memory duration increases as the number of degrees of freedom in the system increases. We demonstrate the existence of these transient memories in a laboratory experiment.