Showing papers on "Impulse (physics) published in 1997"

Generalised Impulse Response Analysis in Linear Multivariate Models

Abstract: Building on Koop, Pesaran and Potter (1996), the authors propose the `generalised' impulse response analysis for unrestricted vector autoregressive (VAR) and cointegrated VAR models. Unlike the traditional impulse response analysis, this approach does not require orthogonalisation of shocks and is invariant to the ordering of the variables in the VAR. In particular, it is shown that in general both generalised and orthogonalised impulse responses are equivalent only when the effects of the shock for the first equation in the VAR is examined. An empirical illustration is also provided showing that the two impulse responses could differ substantially.

Role of wavefront curvature in propagation of cardiac impulse

Abstract: It is traditionally assumed that impulse propagation in cardiac muscle is determined by the combination of two factors: (1) the active properties of cardiac cell membranes and (2) the passive electrical characteristics of the network formed by cardiac cells. However, advances made recently in the theory of generic excitable media suggest that an additional factor—the geometry of excitation wavefronts—may play an important role. In particular, impulse propagation strongly depends on the wavefront curvature on a small spatial scale. In the heart, excitation wavefronts have pronounced curvatures in several situations including waves initiated by small electrodes, waves emerging from narrow tissue structures, and waves propagating around the sharp edges of anatomical obstacles or around a zone of functional conduction block during spiral wave rotation. In this short review we consider the theoretical background relating impulse propagation to wavefront curvature and we estimate the role of wavefront curvature in electrical stimulation, formation of conduction block, and the dynamic behavior of spiral waves.

Impulse excitation apparatus to measure resonant frequencies, elastic moduli, and internal friction at room and high temperature

Abstract: This paper presents a new apparatus to measure elastic properties and internal friction of materials. The apparatus excites the test specimen by a light mechanical impact (impulse excitation) and performs a software-based analysis of the resulting vibration. The resonant frequencies fr of the test object are determined and, in the case of isotropic and regular shaped specimens, the elastic moduli are calculated. The internal friction value (Q−1) is determined for each fr as Q−1=k/(πfr) with k the exponential decay parameter of the vibration component of frequency fr. A furnace was designed and equipped with automated impulse excitation and vibration detection devices, thus allowing computer-controlled measurements at temperatures up to 1750 °C. The precision of the measured fr depends on the size and stiffness of the specimen, and varies from the order of 10−3 (that is ±1 Hz at 1 kHz) in soft, high damping materials or light specimens, to values as precise as 10−5 (that is ±0.1 Hz at 10 kHz) in larger or ...

Method and apparatus for shaping force signals for a force feedback device

Abstract: A method and apparatus for shaping force signals for a force feedback device. A source wave is provided and is defined by a set of control parameters and modified by a set of impulse parameters. Using a host or local processor, the force signal is formed from the source wave, the control parameters and the impulse parameters, where the force signal includes an impulse signal followed by a continuous steady-state signal to generate a feel sensation to the user.

Transient power quality problems analyzed using wavelets

Abstract: In the literature, wavelet techniques have been proposed for the identification of power system transient signals (e.g., lightning impulse, and capacitor switching transients). In this paper, the wavelet technique is proposed for the analysis of the propagation of transients in power systems. The advantages and disadvantages of the method are discussed and the way in which these analysis methods complement previously reported identification methods is described. An example based on the discretized solution of a differential equation is given.

Application of fractional derivatives to the analysis of damped vibrations of viscoelastic single mass systems

Abstract: Free damped vibrations of an oscillator, whose viscoelastic properties are described in terms of the fractional calculus Kelvin-Voight model, Maxwell model, and standard linear solid model are determined. The problem is solved by the Laplace transform method. When passing from image to pre-image one is led to find the roots of an algebraic equation with fractional exponents. The method for solving such equations is proposed which allows one to investigate the roots behaviour in a wide range of single-mass system parameters. A comparison between the results obtained on the basis of the three models has been carried out. It has been shown that for all models the characteristic equations do not possess real roots, but have one pair of complex conjugates, i.e. the test single-mass systems subjected to the impulse excitation do not pass into an aperiodic regime in none of magnitudes of the relaxation and creep times. Main characteristics of vibratory motions of the single-mass system as functions of the relaxation time or creep time, which are equivalent to the temperature dependencies, are constructed and analyzed for all three models.

Frequency Dependent and Transient Characteristics of Substation Grounding Systems

Abstract: In spite of the existence of a number of analytical models aimed for transient analysis of large grounding systems, more detailed analysis of the influence of different parameters on the transient performance of large ground grids subjected to lightning current impulse is not available. This paper presents analysis of the influence of soil conductivity, location of feed point, grid size, depth, conductor separation, ground rods, and shape of the lightning current impulse, on the transient performance of ground grids with sizes ranging from 10/spl times/10 m/sup 2/ to 120/spl times/120 m/sup 2/ and with 4 to 124 meshes. Maximal transient ground potential rise and frequency dependent impedance are analyzed in time and frequency domain, respectively. Computations are made with computer model based on the electromagnetic field theory approach, taking accurately into account frequency dependent characteristics of large ground grids. Instead of usual simple approximations of the lightning current impulse, recorded channel base currents from triggered lightning are used for the time domain analysis.

Discrete-time linear and nonlinear aerodynamic impulse responses for efficient cfd analyses

Abstract: This dissertation discusses the mathematical existence and the numerical identification of linear and nonlinear aerodynamic impulse response functions. Differences between continuous-time and discrete-time system theories, which permit the identification and efficient use of these functions, will be detailed. Important input/output definitions and the concept of linear and nonlinear systems with memory will also be discussed. It will be shown that indicial (step or steady) responses (such as Wagner's function), forced harmonic responses (such as Theodorsen's function or those from doublet lattice theory), and responses to random inputs (such as gusts) can all be obtained from an aerodynamic impulse response function. This will establish the aerodynamic discrete-time impulse response function as the most fundamental and computationally efficient aerodynamic function that can be extracted from any given discrete-time, aerodynamic system. The results presented in this dissertation help to unify the understanding of classical two-dimensional continuous-time theories with modern three-dimensional, discrete-time theories. Nonlinear aerodynamic impulse responses are identified using the Volterra theory of nonlinear systems. The theory is described and a discrete-time kernel identification technique is presented. The kernel identification technique is applied to a simple nonlinear circuit for illustrative purposes. The method is then applied to the nonlinear viscous Burger's equation as an example of an application to a simple CFD model. Finally, the method is applied to a three-dimensional aeroelastic model using the CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code and then to a two-dimensional model using the CFL3D Navier-Stokes code. Comparisons of accuracy and computational cost savings are presented. Because of its mathematical generality, an important attribute of this methodology is that it is applicable to a wide range of nonlinear, discrete-time systems.

The mechanical waveform of the basilar membrane. I. Frequency modulations ("glides") in impulse responses and cross-correlation functions

Abstract: The purpose of this investigation is to present evidence from experimental as well as model results on temporal variations of the frequency of oscillation in the basilar membrane’s impulse response. Stimuli were either clicks leading to a direct estimate of the impulse response, or bands of pseudo-random noise (one or two octaves wide) which lead to an indirect estimate of the impulse response via a cross-correlation procedure. The noise bands were centered at the best frequency of the BM location under observation. Responses were obtained from the basal turn of the guinea-pig cochlea, from a location with a best frequency (for the weakest stimuli) between 17.0 and 18.5 kHz. Data acquisition was done with a sample frequency of 208 kHz. Input–output cross-correlation functions were found to share with impulse responses the property that the initial oscillations have a noticeably lower frequency than the later ones. During the impulse response the frequency of oscillation increases gradually. This increase occurs and continues to beyond the time that the oscillations reach the largest amplitude. This frequency variation is called a “glide.” Using the “analytic signal” method the frequency of oscillation is found to increase continually throughout the duration of the main lobe of oscillation, even at the lowest tested stimulus intensities (about 20 dB SPL). At high stimulus intensity both the direct and indirect impulse response change their appearance drastically but the glide retains its basic form. In the case of the direct impulse response estimate the glide can be attributed to temporal variation of the degree of nonlinearity. For the indirect impulse response this is not true, because with a constant level noise stimulus there is no regular temporal variation of nonlinearity. In this case the glide should be interpreted as an intrinsic property of the cochlear system. From our and others’ data the glide was found to exist over a topographic frequency range of best frequencies of at least from 1.76 to 18 kHz. Two examples of present-day models of the cochlea are discussed of which one is found to demonstrate the glide phenomenon in its response, and the other one does not.

Imaging radar suitable for material penetration

Abstract: A ground penetrating impulse radar system provides three-dimensional images of targets. A moving array of transmitting and receiving antennas provides narrow beamwidths and high gain by real and synthetic aperture beam processing. Narrow pulsewidth impulse signals are utilized to obtain high resolution. Round trip time is calculated for each three-dimensional pixel in a search volume, and is used to process three dimensional imagery. Analog to digital conversion can be utilized, so all signal processing is accomplished digitally. The radar system is applicable to detecting small objects near the surface by using very narrow pulses, and also can be applied to detect large, deep objects by wider pulses.

Impulse line blockage detector systems and methods

Abstract: A differential pressure sensor is attached to a process via a high and a low pressure impulse line. An absolute pressure sensor is also attached to each impulse line. To determine if an impulse line is blocked, a noise signal is acquired from the corresponding absolute pressure sensor. A variance of the noise signal is determined and compared to a threshold. If the variance is less than the threshold, an impulse line blockage is indicated.

Joint angle and delay estimation using shift-invariance properties

Abstract: Assuming a multipath propagation scenario, we derive a closed-form subspace-based method for the simultaneous estimation of arrival angles and path delays from measured channel impulse responses, using knowledge of the transmitted pulse shape function and assuming a uniform linear array and uniform sampling. The algorithm uses a two-dimensional (2-D) ESPRIT-like shift-invariance technique to separate and estimate the phase shifts due to delay and direction-of-incidence, with automatic pairing of the two parameter sets. A straightforward extension to the multiuser case allows to connect rays to users as well.

Multi-load cell force sensing apparatus

Abstract: A multi-load cell force sensing apparatus which includes a controller (50) for determining the location and magnitude of an applied force. Impulse forces may be distinguished from static forces, thereby enabling a user to start preprogrammed functions by touching the scale pan (202) in specified locations (206).

Money in a Real Business Cycle Model

Abstract: This paper constructs a real business cycle model in which real money balances yield utility. We calibrate the model to fit the first moments of US data and simulate a set of impulse response functions that are generated by the model for GDP, the rate of interest, money growth and real balances. These theoretical impulse responses are compared with actual impulse responses from US data. The model does a reasonably good job of capturing the dynamic interactions of money and real variables in US data. It differs from most existing approaches by choosing a parameterization of utility for which the model admits the existence of indeterminate equilibria. It is argued that this fact is critical in explaining the monetary propagation mechanism.

A structured channel estimator for maximum-likelihood sequence detection

Abstract: This letter describes a channel estimator using known prior information about the transmit and receive filters. It is shown that the composite channel lies in the subspace of the transmit and receive filter impulse responses. A structured linear channel model is then developed that is linearly parametrized by an unknown vector. To illustrate the potential usefulness of such an approach, the estimated structured channel is used in a multisensor and oversampled maximum-likelihood sequence estimation (MLSE) receiver.

Time-based method and device for determining the dielectric constant of a fluid

Abstract: A device utilizes micropower, impulse radar and time domain reflectometry to determine the dielectric constant of a fluid. An electrically conductive probe preferably in the form of a transmission line, is inserted at least partially into the fluid. The device includes a signal generator that generates an impulse signal that is propagated along the probe. The time that it takes for the signal to reach the end of the probe is determined. The time of travel of the signal along the probe is then used to determine the dielectric constant of the fluid.

A predictive model of the positive discharge in long air gaps under pure and oscillating impulse shapes

Abstract: This paper presents a general model allowing the prediction of the behaviour of given gap submitted to a given voltage. The only input data are the electrode geometry, the applied voltage waveform and the atmospheric pressure and temperature. The model also allows for various conditions for arrest or instability of the discharge. By assuming the discharge channel to be a long conductor and using a typical single LCR conductor line (L, C and R being respectively the line inductance, capacitance and resistance), we derive a predictive model for a positive discharge in long air gaps. This allows one to describe the evolution of the entire discharge, with the parameters L, C and R varying with time according to the channel characteristics and discharge geometry. The model allows us to determine the time histories of the current both during the leader and during the return stroke, the charge, the potential gradient in the leader channel, the power and energy injected into the gap and the channel's thermal radius. It also permits the simulation of an image converter working in streak or frame mode and the leader propagation velocities. Furthermore, it allows the trajectory of the discharge, which is obtained from a probability distribution, to be plotted in real time. Good agreement between computed and experimental results was obtained for various test configurations.

Identification of linear and nonlinear aerodynamic impulse responses using digital filter techniques

Abstract: This paper discusses the mathematical existence and the numerically-correct identification of linear and nonlinear aerodynamic impulse response functions. Differences between continuous-time and discrete-time system theories, which permit the identification and efficient use of these functions, will be detailed. Important input/output definitions and the concept of linear and nonlinear systems with memory will also be discussed. It will be shown that indicial (step or steady) responses (such as Wagner's function), forced harmonic responses (such as Theodorsen's function or those from doublet lattice theory), and responses to random inputs (such as gusts) can all be obtained from an aerodynamic impulse response function. This paper establishes the aerodynamic impulse response function as the most fundamental, and, therefore, the most computationally efficient, aerodynamic function that can be extracted from any given discrete-time, aerodynamic system. The results presented in this paper help to unify the understanding of classical two-dimensional continuous-time theories with modern three-dimensional, discrete-time theories. First, the method is applied to the nonlinear viscous Burger's equation as an example. Next the method is applied to a three-dimensional aeroelastic model using the CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code and then to a two-dimensional model using the CFL3D Navier-Stokes code. Comparisons of accuracy and computational cost savings are presented. Because of its mathematical generality, an important attribute of this methodology is that it is applicable to a wide range of nonlinear, discrete-time problems.

The influence of surface charge upon flash-over of particle-contaminated insulators in under impulse-voltage conditions

Abstract: This paper presents an experimental investigation of the effect of surface charge upon the impulse flash-over of metallic-particle-contaminated insulators, which were clamped between two parallel planar electrodes, in at 1.0 bar. The results show that the accumulated surface charge greatly affects the impulse flash-over strength of insulators. The influence of the surface charge is closely dependent upon its polarity and density, as well as upon the electrode configuration. For a PTFE cylindrical insulator with a metallic particle in contact with the anode, a 25% reduction in the 50% impulse flash-over voltage occurs when negative charge of peak density about is present. However, with positive charge, the impulse flash-over voltage is not decreased, but increased instead, the enhancement in impulse strength being 21% at . When metal inserts are used to shield the electrode triple junction, charge accumulation on the insulator surface will be predominantly determined by the field normal to the surface. In this case, the accumulated surface charge appears to have little influence upon the impulse flash-over voltage.

One-dimensional model for nonlinear stress control in cable terminations

Abstract: A one-dimensional model for field control in cable terminations is analyzed mathematically both for linear and nonlinear field grading materials. Far an applied ac voltage, the concept of the penetration length allows for a useful characterization of the voltage profile, even for materials where both the conductivity and the permittivity are field dependent. For lightning impulse events an analytical solution for purely resistive field control is presented, allowing for an arbitrarily strong nonlinearity of the conductivity. The model results yield a useful input for more detailed finite element calculations. The results show that conclusions for nonlinear field control based on linear calculations in general are misleading.

Method and apparatus for digital compensation of radio distortion over a wide range of temperatures

Abstract: Radio distortion in a radio signal is compensated for in a digital modem in a wireless communication system over a wide range of temperatures. Actual frequency responses of components in the wireless communication system contributing to distortion at various temperatures are determined. Inverses of the actual frequency responses are multiplied with a desired frequency response of the wireless communication system to produce compensation frequency responses for various temperatures. An appropriate compensation frequency response for an operating temperature is applied to the radio signal to compensate for radio distortion. Alternately, actual impulse responses of components in the wireless communication system contributing to distortion at the various temperatures are determined. The actual impulse responses are convolved with a reference signal to produce actual output signals. The desired impulse response is convolved with the same reference signal to produce a desired output signal. The actual output signals are subtracted from the desired output signal to produce error signals, and adaptive algorithms are applied to the error signals to produce adaptive compensation impulse responses. When an appropriate adaptive compensation impulse response for the operating temperature converges to an optimal solution, it is applied to the radio signal to compensate for radio distortion.