Showing papers on "Impulse (physics) published in 2007"

System and method for person or object position location utilizing impulse radio

Abstract: A System and Method for Person or Object Position Location Utilizing Impulse Radio, comprising a plurality of reference impulse radios; an object or person to be tracked having a mobile impulse radio associated therewith; an architecture with an associated positioning algorithm associated with said plurality of impulse radio reference radios and said mobile impulse radio; and display means for displaying the position of the person or object whose position is to be determined.

Gap Junction Channels and Cardiac Impulse Propagation

Abstract: The role of gap junction channels on cardiac impulse propagation is complex. This review focuses on the differential expression of connexins in the heart and the biophysical properties of gap junction channels under normal and disease conditions. Structural determinants of impulse propagation have been gained from biochemical and immunocytochemical studies performed on tissue extracts and intact cardiac tissue. These have defined the distinctive connexin coexpression patterns and relative levels in different cardiac tissues. Functional determinants of impulse propagation have emerged from electrophysiological experiments carried out on cell pairs. The static properties (channel number and conductance) limit the current flow between adjacent cardiomyocytes and thus set the basic conduction velocity. The dynamic properties (voltage-sensitive gating and kinetics of channels) are responsible for a modulation of the conduction velocity during propagated action potentials. The effect is moderate and depends on the type of Cx and channel. For homomeric-homotypic channels, the influence is small to medium; for homomeric-heterotypic channels, it is medium to strong. Since no data are currently available on heteromeric channels, their influence on impulse propagation is speculative. The modulation by gap junction channels is most prominent in tissues at the boundaries between cardiac tissues such as sinoatrial node-atrial muscle, atrioventricular node-His bundle, His bundle-bundle branch and Purkinje fibers-ventricular muscle. The data predict facilitation of orthodromic propagation.

Wideband Impulse Modulation and Receiver Algorithms for Multiuser Power Line Communications

Abstract: We consider a bit-interleaved coded wideband impulse-modulated system for power line communications. Impulse modulation is combined with direct-sequence code-division multiple access (DS-CDMA) to obtain a form of orthogonal modulation and to multiplex the users. We focus on the receiver signal processing algorithms and derive a maximum likelihood frequency-domain detector that takes into account the presence of impulse noise as well as the intercode interference (ICI) and the multiple-access interference (MAI) that are generated by the frequency-selective power line channel. To reduce complexity, we propose several simplified frequency-domain receiver algorithms with different complexity and performance. We address the problem of the practical estimation of the channel frequency response as well as the estimation of the correlation of the ICI-MAI-plus-noise that is needed in the detection metric. To improve the estimators performance, a simple hard feedback from the channel decoder is also used. Simulation results show that the scheme provides robust performance as a result of spreading the symbol energy both in frequency (through the wideband pulse) and in time (through the spreading code and the bit-interleaved convolutional code).

Plasma Actuator Force Measurements

Abstract: In previous work at the U.S. Air Force Academy, the phenomenology and behavior of the aerodynamic plasma actuator, a dielectric barrier discharge plasma, was investigated. To provide insight into the phenomenology associated with the transfer of momentum to air by a plasma actuator, the velocity distributions upstream and downstream of a plasma actuator with an induced boundary layer were measured using freestream velocities of approximately 4.6 and 6.8 m/s for a range of frequencies (5-20 kHz) and voltages (5-10-kV amplitude). The body forces on the air were calculated using a control volume momentum balance. In a second experiment, time-averaged results were also obtained by measuring the reaction force using a pendulum. A third experiment uses an accelerometer to gain insight into the time-dependent forces or, more specifically, the direction of the forces. The results show that the body force acts within the first 4 mm above the surface of the actuator (within the boundary layer). For a constant peak-to-peak voltage, the body force is proportional to frequency, producing a constant impulse per cycle, and the energy dissipation per cycle and efficiency are independent of frequency. The time-dependent measurements support the theory that the body force of the actuator consists of one large push followed by one small pull during each cycle.

Piezoelectric transducer actuated leading edge de-icing with simultaneous shear and impulse forces

Abstract: Piezoelectric actuations for simultaneous generation of shear and impulse forces for effective and energy efficient de-icing applications are proposed. Aircraft leading edge structures are considered for analysis and lab experiments. Piezoelectric actuators are affixed on the inner surface of the leading edge at the locations where highest amount of ice accretion on the outer surface has occurred. Simultaneous shear and impulse force generation is achieved with actuators consisting of two sets of electrodes, one arranged in parallel to the poling direction, and the other perpendicular to it, to generate shear forces and normal forces, respectively. Finite element models of the leading edge structure with ice accretion layer are formulated. Simulations of the de-icing process are performed and the actuator locations, electric charge applied, and impulse duration are optimized to achieve effective ice removal

Fluid-structure interaction effects in the dynamic response of free-standing plates to uniform shock loading

Abstract: The problem of uniform shocks interacting with free-standing plates is studied analytically and numerically for arbitrary shock intensity and plate mass. The analysis is of interest in the design and interpretation of fluid-structure interaction (FSI) experiments in shock tubes. In contrast to previous work corresponding to the case of incident blast profiles of exponential distribution, all asymptotic limits obtained here are exact. The contributions include the extension of Taylor's FSI analysis for acoustic waves, the exact analysis of the asymptotic limits of very heavy and very light plates for arbitrary shock intensity, and a general formula for the transmitted impulse in the intermediate plate mass range. One of the implications is that the impulse transmitted to the plate can be expressed univocally in terms of a single nondimensional compressible FSI parameter.

Landslide generated impulse waves: prediction of near field characteristics

Abstract: Large water waves in oceans, bays, lakes, or reservoirs may be generatedby landslides,rock falls, shore instabilities, snow avalanches, glacier calvings, or meteorite impacts. These socalled impulse waves are particular relevant for the Alpine environment because of steep valley sides, possible large slide masses and impact velocities, and the considerable number of artificialreservoirs. An impulse wave occurred in Vaiont in North-Italy in 1963, overtopping a concrete damby more than 70 m and having destroyedthe village Longarone: about 2,000 people perished. Althoughthe total amount of fatalities due to such documentedcatastrophes probably exceeds 60,000 people, only limited field data are available.Humans may face such natural hazards mainly with passive methods such as evacuationor water level draw-down in artificial reservoirs.Methods for precise wave predictions are nowadays limited because the effects of the governing parameters in general model studies are sometimes controversial,the model data are often not generally applicable, characterised by a large scatter, or not based on systematic or independent parameter variations. Further, the model tests are often insufficiently documentedfor numerical simulations. The present study aims to complete the 2D impulse wave generation research initiated by Fritz (2002) and continuedby Zweifel (2004). The generation of subaerial landslide generated impulse waves was investigated in an undistorted hydraulic model based on the Froude similitude. Considerable scale effects due to fluid viscosity and surface tension were expected for still water depths smaller than 0.200 m. Four different granulär slide materials were accelerated with a pneumatic landslide generatorand produced impulse waves in a rectangular wave channel of 11 m length, 1 m height, and 0.5 m width. An independent Variation of the seven governing parameters was attempted including the still water depth, the slide thickness, the slide impact velocity, the bulk slide volume, the bulk slide density, the slide impact angle, and the grain diameter; the effects of the two latter were particularly investigated in the present study whereas the five former effects were tested in the two previous studies. All measure¬ ment componentswere recorded in the channel axis. Two laser distance sensors scanned the slide profiles prior to the impact, seven capacitance wave gages measured the wave profiles along the channel, and a Particle Image Velocimetry PIV system allowed to determine the velocity vector fields in the slide impact zone. The 211 conducted experiments resulted in highly nonlinearimpulse waves in the ränge from intermediate to shallow-waterwith sparse to considerable fluid mass transport, Empiri¬ cal formulas in the slide impact zone for the maximumwave amplitude including its period and location,the maximumwaveheight, the wavevolume, and in the wave propagation zone for the wave amplitude and wave height decay were presented as a function of the seven governing parameters. The impulse product parameter P was identifiedas the relevant term in all these formulas consisting of the dominantslide Froude number, the relative slide thick¬ ness, the relative slide mass, and the slide impact angle. The wave height was found to be in the average (5/4) times the wave amplitude resulting from both the wave maximum and the wave decay analysis. The wave celerity is therefore well described with the solitary wave

Simulation of Neutral Particle Flow During High Power Magnetron Impulse

Abstract: The behavior of neutral component of the plasma during high power impulse magnetron sputtering was studied. Movement of the neutral particles including sputtered metal (Ti) and Ar gas during an impulse (200 µs, 1 kA, 1 kV) has been simulated using direct simulation Monte Carlo method. When the discharge current reaches kA range, very strong gas rarefaction in the main plasma region occurs and the volume density of sputtered metal exceeds the gas density several times. This may contribute to the high ratio of metal ions to Ar ions observed in experiments. Rapid gas movement in the form of a shock wave toward the substrate results in a temporary increase in density and pressure of the substrate. This again influences both the deposition flux and the discharge behavior.

Reverberation-Time Prediction Method for Room Impulse Responses Simulated with the Image-Source Model

Abstract: The image-source method has become a ubiquitous tool in many fields of acoustics and signal processing. A technique was recently proposed to predict the energy decay (energy-time curve) in room impulse responses simulated using the image-source model. The present paper demonstrates how this technique can be efficiently used to determine the enclosure's absorption coefficients in order to achieve a desired reverberation level, even with a non-uniform distribution of the sound absorption in the room. As shown in this work, classical expressions for the prediction of an enclosure's reverberation time, such as Sabine and Eyring's formulae, do not provide accurate results when used in conjunction with the image method. The proposed approach hence ensures that the image-source model effectively generates impulse responses with a proper reverberation time, which is of particular importance, for instance, for the purpose of assessing the performance of audio signal processing algorithms operating in reverberant conditions.

Robust Three-impulse Sequence Input Shaper Design:

Abstract: This article presents an unsophisticated method for tuning the amplitudes and time locations of a three-impulse sequence input shaper. The method helps to solve the insufficient constraint equation...

On mini-halo encounters with stars

Abstract: We study, analytically and numerically, the energy input into dark matter mini-haloes by interactions with stars. We find that the fractional energy input in simulations of Plummer spheres agrees well with the impulse approximation for small and large impact parameters, with a rapid transition between these two regimes. Using the impulse approximation, the fractional energy input at large impact parameters is fairly independent of the mass and density profiles of the mini-halo; however, low-mass mini-haloes experience a greater fractional energy input in close encounters. We formulate a fitting function which encodes these results and use it to estimate the disruption time-scales of mini-haloes, taking into account the stellar velocity dispersion and mass distribution. For mini-haloes with mass formula on typical orbits which pass through the disc, we find that the estimated disruption time-scales are independent of mini-halo mass, and are of the order of the age of the Milky Way. For more massive mini-haloes, the estimated disruption time-scales increase rapidly with increasing mass.

Reflection of Alfvén waves in the corona and solar wind: An impulse function approach

Abstract: [1] We consider the reflection of Alfven waves in the corona and solar wind, using variables f and g which follow sunward and antisunward characteristics, respectively. We show that the basic equations for f and g have the same structure as the Klein-Gordon equation. Unlike previous studies which used a harmonic analysis, we emphasize the impulse response of the system. This is equivalent to finding the Green's function, but it may have direct application to situations where Alfven waves are launched impulsively. We provide an approximate analysis which can be used to understand most features that appear in detailed numerical solutions. The analysis reveals the origin of a previous result that f and g each has both sunward and antisunward propagating phase in a harmonic analysis, even though f (g) follows only the sunward (antisunward) characteristic. We numerically study the propagation of an antisunward moving impulse in the corona and solar wind. We find that the sunward moving “wake” tends to become more important at greater distances beyond the Alfven critical point, possibly providing a natural explanation of the observation that outward propagating waves become less dominant at greater distances from the Sun. There is an extended region behind the initial impulse in which magnetic energy dominates kinetic energy; it is not clear, however, whether our result can explain the observed dominance of magnetic energy throughout many decades of frequency in the observed power spectrum. We also find that the outgoing wake has a tendency to “ring,” with periods of the order of 15–30 min. The ringing is associated mainly with propagation through a structured Alfven speed profile rather that with the cutoff in the Klein-Gordon equation. These oscillation periods seem too short to explain why Alfven waves in the solar wind have most power at periods of hours, but other Alfven speed profiles could yield longer periods. We also investigate whether the same approach can be used for acoustic-gravity waves propagating along magnetic flux tubes in the solar atmosphere.

Global dynamic analysis of general Cohen–Grossberg neural networks with impulse

Abstract: In this paper, a class of general Cohen–Grossberg neural networks with impulse is studied. Based on the method of Lyapunov functional, sufficient conditions on global exponential stability are given. Furthermore, many corollaries are obtained. Our results improve some of the earlier findings, and are suitable for many applications.

Free Vibration of the High Temperature Superconducting Maglev Vehicle Model

Abstract: Free vibration of the high temperature superconducting (HTS) Maglev vehicle model has been investigated after an impulse force over the permanent magnet guideway. The impulse force was used to simulate the external disturbances on the HTS Maglev vehicle so as to study its vibration characteristics. In the experiments, the free vibration curves of time dependence of acceleration and frequency dependence of displacement were measured. It was found that the free vibration curves were some damped free vibration curves which seemed to decrease exponentially. Applying the impulse response curves to the dynamic equation of the HTS Maglev vehicle model, the stiffness and the damping coefficient were evaluated. The relationships between field cooling height (FCH) and the stiffness and damping coefficient were investigated. A 30 mm FCH has been proposed for the good dynamic stiffness and damping coefficient so that the unnecessary vibration of the HTS Maglev vehicle model can be eliminated automatically. The dynamic results are helpful to the further design of the HTS Maglev transport system for high-speed application.

Electrophoretic displays using gaseous fluids

Abstract: An electrophoretic display comprises a pair of facing substrates, at least one of which is transparent, a plurality of particles and a gas between the substrates, and means for applying an electric field to cause the particles to move and thus change the electro-optic state of the display. The electric field means is arranged to increase the impulse applied to the display with increasing time since a reference time, or with increasing number of images written on the display. In another embodiment, an alternating current pulse is applied to the display, and the duration and/or amplitude of the alternating current pulse is increased with increasing time since a reference time.

Stability of Takagi–Sugeno Fuzzy Delay Systems With Impulse

Abstract: The Takagi-Sugeno (T-S) model of fuzzy delay systems with impulse is first presented in this paper By means of classical analysis methods and Razumikhin technique, the criteria of uniform stability and uniform asymptotic stability for T-S fuzzy delay systems with impulse are obtained, respectively Three numerical examples are also discussed to illustrate the efficiency of the obtained results

Dynamic measurement of room impulse responses using a moving microphone.

Abstract: A technique for the recording of large sets of room impulse responses or head-related transfer functions is presented. The technique uses a microphone moving with constant speed. Given a setup (e.g., length of the room impulse response), a careful choice of the recording parameters (excitation signal, speed of movement) leads to the reconstruction of all impulse responses along the trajectory. In the case of a moving microphone along a circle, the maximal angular speed is given as a function of the length of the impulse response, its maximal temporal frequency, the speed of sound propagation, and the radius of the circle. As a result of the presented algorithm, head-related transfer functions sampled at 44.1kHz can be measured at all angular positions along the horizontal plane in less than 1s. The presented theory is compared with a real system implementation using a precision moving microphone holder. The practical setup is discussed together with its limitations.

Phase-error analysis of high-order finite difference time domain scheme and its influence on calculation results of impulse response in closed sound field

Abstract: To obtain accurate impulse responses in a sound field by numerical analysis, a high-order finite difference time domain (FDTD) method was formulated on the basis of a simple Taylor expansion. The accuracy of the FDTD scheme was evaluated by Von Neumann and Richtmyer dispersion analysis. It was found that the unavoidable phase error obtained from the conventional FDTD algorithm is reduced using the high-order scheme with 8 or more reference points. When using higher orders in the scheme used in this study, the time resolution should be small to reduce the phase error. To validate the FDTD scheme for calculating the impulse response in a closed sound field, the numerical result was compared with an analytical solution obtained by the separation of variables method. It was found that the phase error for a low-order FDTD appeared as fluctuations of the arriving pulses and that the fluctuations can be reduced using the high-order scheme with a small time resolution. The accuracy of the FDTD calculation for a large-scale sound field or a long-time calculation, which we should consider when making a sound field analysis of room acoustics or outdoor noise propagation, is strongly influenced by the phase error and therefore the error should be considered when performing such numerical analyses.

A Time Domain Formulation of the Uniform Geometrical Theory of Diffraction for Scattering From a Smooth Convex Surface

Abstract: A time-domain version of the uniform geometrical theory of diffraction (TD-UTD) is developed to describe, in closed form, the transient electromagnetic scattering from a smooth convex surface excited by a general time impulsive astigmatic ray field. This TD-UTD impulse response is obtained by employing an analytic time transform (ATT) for the inversion in time of an available and accurate corresponding frequency domain UTD (FD-UTD) solution. The ATT is employed because it overcomes the difficulties that occur when inverting FD-UTD fields associated with rays that traverse line or smooth caustics. Furthermore, the TD-UTD response to a general pulsed astigmatic wave excitation may be found by a convolution of the general excitation with the TD-UTD impulse response which can be performed in closed form. Some numerical examples illustrating the utility of this TD-UTD are presented.

Acoustic impact localization in plates: properties and stability to temperature variation

Abstract: Localizing an impact generated by a simple finger knock on plate-shaped solid objects is made possible in an acoustic time reversal experiment. It is shown that the technique works with a single accelerometer. To better understand the phenomenon and to know exactly the nature of the created waves, a two-dimensional (2-D) elastic simulation is used, showing that in a very good approximation the A0 Lamb mode is the only propagating one. However, it is shown that, within one wavelength distance from the edges, evanescent waves must be taken into account. As a first consequence, the ability to distinguish two neighboring impacts improves when the plate thickness decreases and the frequency increases. As a second consequence, it is expected theoretically that temperature variations lead to a stretching or a contraction of acoustic signatures. The experimental demonstration used a heterodyne interferometer to measure the impulse responses created by a knock on a plate during the cooling. A simple algorithm is shown to perfectly compensate for temperature impacts, which demonstrates the feasibility of the technique for outdoor time reversal interactive experiments

Impulse loading resulting from shallow buried explosives in water-saturated sand:

Abstract: A transient non-linear dynamics analysis of the detonation of a landmine buried to different depths in water-saturated sand is carried out in order to determine the resulting impulse loading The results obtained are compared with their experimental counterparts obtained using the vertical impulse measurement fixture (VIMF), a structural mechanical device that enables direct experimental determination of the blast-loading impulse The mechanical response of the structural steel used in the construction of the VIMF and the hydrodynamic response of the TNT high-energy high-pressure detonation products generated during detonation of a mine and of the air surrounding the VIMF are represented using the standard materials models available in the literature The mechanical response of the sand surrounding the mine, on the other hand, is represented using the present authors' recent modified compaction model [1], which incorporates the effects of degree of saturation and the rate of deformation, two important eff

Effect of Group Delay in RF BPF on Impulse Radio Systems

Abstract: This paper presents an analysis of the effects of RF filter characteristics on the system performance of an impulse radio. The impulse radio system transmits modulated pulses having very short time duration. Information can be extracted in the receiver side based on the cross-correlation between received and reference pulses. Accordingly, the pulse distortion due to in-band group delay variation can cause serious degradation in system performance. In general, RF band pass filters inevitably cause non-uniform group delays to the signal passing through the filter that are proportional to its skirt characteristic due to its resonance phenomenon. In this work, a small signal scattering parameter, S 21 , which is a frequency domain parameter, and its Fourier transform are utilized to characterize the output pulse waveform under the condition that the input and output ports are matched. The output pulse waveform of the filter is predicted based on the convolution integral between the input pulse and filter transfer function, and the analysis result is compared with previously reported experimental result. The resulting bit error rate performances in a bi-phase modulation and a pulse position modulation based impulse radio system are also calculated. Moreover, improvement of system performance by the pulse shaping method, a potential solution for pulse waveform distortion, is analyzed.

The full impulse response of two-dimensional jet/wake flows and implications for confinement

Abstract: In this theoretical study, a linear spatio-temporal analysis is performed on unconfined and confined inviscid jet/wake flows in order to determine whether they are absolutely or convectively unstable. The impulse response is evaluated in the entire outer fluid, rather than just at the point of impulse, over a wide range of density ratios. This confirms that the dominant saddle point can validly migrate into the plane of diverging eigenfunctions. This reveals that, at certain density ratios and shear numbers, the response can grow upstream in some directions with a cross-stream component, even though it decays directly upstream of, and at, the point of impulse. This type of flow is convectively unstable when unconfined, but becomes absolutely unstable when confined. Other effects of confinement are described in a previous paper. Together, these articles have important implications for the design of fuel injectors, which often employ confined shear flows at high Reynolds number and large density ratios to generate strong mixing in combustion chambers.