Showing papers on "Impulse (physics) published in 2009"

Simultaneous Confidence Regions for Impulse Responses

Abstract: Inference about an impulse response is a multiple testing problem with serially correlated coefficient estimates. This paper provides a method to construct simultaneous confidence regions for impulse responses and conditional bands to examine significance levels of individual impulse response coefficients given propagation trajectories. The paper also shows how to constrain a subset of impulse response paths to anchor structural identification and how to formally test the validity of such identifying constraints. Simulation and empirical evidence illustrate the new techniques. A broad summary of asymptotic analytic formulas is provided to make the methods easy to implement with commonly available statistical software.

Image quality, tissue heating, and frame rate trade-offs in acoustic radiation force impulse imaging

Abstract: The real-time application of acoustic radiation force impulse (ARFI) imaging requires both short acquisition times for a single ARFI image and repeated acquisition of these frames. Due to the high energy of pulses required to generate appreciable radiation force, however, repeated acquisitions could result in substantial transducer face and tissue heating. We describe and evaluate several novel beam sequencing schemes which, along with parallel-receive acquisition, are designed to reduce acquisition time and heating. These techniques reduce the total number of radiation force impulses needed to generate an image and minimize the time between successive impulses. We present qualitative and quantitative analyses of the trade-offs in image quality resulting from the acquisition schemes. Results indicate that these techniques yield a significant improvement in frame rate with only moderate decreases in image quality. Tissue and transducer face heating resulting from these schemes is assessed through finite element method modeling and thermocouple measurements. Results indicate that heating issues can be mitigated by employing ARFI acquisition sequences that utilize the highest track-to-excitation ratio possible.

Modeling CO2 laser ablation impulse of polymers in vapor and plasma regimes

Abstract: An improved model for CO2 laser ablation impulse in polyoxymethylene and similar polymers is presented that describes the transition effects from the onset of vaporization to the plasma regime in a continuous fashion. Several predictions are made for ablation behavior.

Impulse attack free double-random-phase encryption scheme with randomized lens-phase functions.

Abstract: Security of the conventional Fourier-based double-random-phase encryption (DRPE) technique is prone to impulse attacks, as the Fourier transform (FT) of a delta function results in a unity function. To negate such an attack, the phase factors of the lenses are modified by multiplying these with random-phase functions. Owing to this modification of the FT as a result of the randomized lens phase function, a modified FT (MFTLR) gives the random output for a delta function input. Employing MFTLR in the DRPE technique enhances the security features and makes the encryption system safer from the impulse attack. Numerical and experimental results are given for the validation of the proposed technique.

Fast Image Restoration Methods for Impulse and Gaussian Noises Removal

Abstract: In this paper, we study the restoration of blurred images corrupted by impulse noise or mixed impulse plus Gaussian noises. In the proposed method, we use the modified total variation minimization scheme to regularize the deblurred image and fill in suitable values for noisy image pixels where these are detected by median-type filters. An alternating minimization algorithm is employed to solve the proposed total variation minimization problem. Our experimental results show the proposed algorithm is very efficient and the quality of restored images by the proposed method is competitive with those restored by the existing variational image restoration methods.

Deformation and Failure Modes of I-Core Sandwich Structures Subjected to Underwater Impulsive Loads

Abstract: This article reports an experimental study carried out with the aim of quantifying performance and failure modes of sandwich structures when subjected to impulsive blast loading. In particular, performance enhancement with respect to solid panels of equal mass per unit area is assessed. Likewise, the optimal distribution of the mass per unit area in the design of sandwich structures is investigated by comparing the behavior of sandwich structures with various distributions of face sheets thickness. By employing a previously developed FSI experiment, the study confirmed that usage of sandwich structures is beneficial and that performance enhancements, in terms of maximum panel deflection, as high as 68% are possible. The study also confirms theoretical and computational analyses suggesting that use of soft cores maximizes the benefits. Another interesting aspect revealed by this work is that the level of enhancement is highly related to the applied normalized impulse. The same distribution of mass per unit area between face sheets resulted in different normalized maximum deflection. A better performance enhancement was achieved at lower impulses. Here again, failure modes and their sequence seem to be the directly related to this finding. The work here reported clearly reveals a number of important features in the study of lightweight structures and points out to the synergies between structure geometry, materials, manufacturing methods, and threat levels as manifested by the strength of the impulse. Further theoretical and computational studies accounting for experimentally observed failure modes and its interdependence with the fabrication methods is needed to achieve additional predictive capabilities.

Frictionless multiple impacts in multibody systems. II. Numerical algorithm and simulation results

Abstract: Part I of this paper develops a framework that is an extension of the Darboux-Keller shock dynamics towards frictionless multiple impacts between bodies composed of rateindependent materials. A numerical algorithm is proposed in this paper, in which the impulsive differential equation is discretized with respect to the primary impulse corresponding to the contact with the highest potential energy, and the integration step size is estimated at the momentum level. This algorithm respects the energetic constraints and avoids the stiff ordinary differential equation problem arising by directly using the compliant model. The well-known example of Newton's cradle, as well as Bernoulli's system, is used to illustrate the developments.

Object and movement detection

Abstract: Motions, positions or configurations off, for example a human hand can be recognised by transmitting a plurality of transmit signals in respective time frames; receiving a plurality of receive signals; determining a plurality of channel impulse responses using the transmit and receive signals; defining a matrix of impulse responses, with impulse responses for adjacent time frames adjacent each other; and analysing the matrix for patterns (22) corresponding to the motion position or configuration.

Axisymmetric Synthetic Jets: An Experimental and Theoretical Examination

Abstract: The flowfield of a round synthetic jet driven by a piezoelectric membrane issuing into a quiescent environment is studied in this paper. The self-similar behavior exhibited by both synthetic and continuous turbulent jets leads to the hypothesis that synthetic jetsmay bemodeled using similarity analysis, just as continuous turbulent jets aremodeled. Accordingly, synthetic jets are modeled using both the Schlichting solution to boundary-layer equations in cylindrical coordinates and the Landau–Squire solution to the Navier–Stokes equations in spherical coordinates, for which the virtual viscosity coefficient of a continuous turbulent jet is replaced with that measured for a synthetic jet. The virtual viscosity of the synthetic jet for bothmodels is obtained from the spreading rate and velocity decay rate of the jet. Hot-wire anemometry is used to characterize the flow downstream of the orifice. The flowfield is observed to consist of two regions, as distinguished by the centerline velocity decay: namely, a developing and adeveloped region. The developing region is characterized by a velocity increase followed by a plateau, for which the axial extent of this region scales with the stroke length L. The developed region is identified by the centerline velocity decaying as x , and it is within this region that the jet models are applicable. The velocity decay rate and spreading rate of synthetic jets are observed to increase with stroke ratio L=d, while being independent of the Reynolds number Re. This dependency on stroke ratio is attributed to the increase in impulse and energy of the emerging vortex rings as the stroke ratio increases and their subsequent enhanced interaction. The geometry of the actuator is additionally seen to impact the spreading and decay rates by means of influencing the initial conditions at the orifice. The experiments verify that byusing the adjusted value of the virtual viscosity, the theoreticalmodels of a continuous turbulent jetmay still be used to model a periodic synthetic jet. The virtual viscosity of the synthetic jets under test proves to be larger than that of equivalent turbulent continuous jet based on the same momentum flux. The enhanced viscosity is attributed to the additional momentum transfer and mixing brought about by the periodic introduction and breakdown of the vortex rings in synthetic jets.

System and Method for Multiple Signal Carrier Time Domain Channel Estimation

Abstract: The present invention provides a method of characterizing a frequency response of a transmission channel between a transceiver and a subscriber unit. The method includes once per predetermined interval of time, the transceiver transmitting a signal including multiple carriers, a plurality of the carriers including training symbols, a plurality of the carriers including information symbols. The subscriber unit generates frequency response estimates at the frequencies of the carriers including training symbols, each interval of time. The frequency response estimates are converted into a time domain response generating an impulse response once per interval of time. The impulse responses are filtered over a plurality of intervals of time. A channel profile is determined from the filtered impulse responses. The channel profile is converted to the frequency domain generating a channel interpolator. The characterized frequency response is generated from the channel interpolator and the frequency response estimates. The filtering can include averaging the impulse responses over a plurality of intervals of time, accumulating the impulse responses over a plurality of intervals of time, or weighted averaging of the impulse responses over a plurality of intervals of time. The weighted averaging can be dependent upon a phase error between the impulse responses, and/or an amplitude error between the impulse responses.

Periodic solution of a delayed ratio-dependent predator–prey model with monotonic functional response and impulse

Abstract: In this paper, a delayed ratio-dependent predator–prey model with monotonic functional response and impulse is investigated. By using the continuation theorem of coincidence degree theory, an easily verifiable sufficient condition for the existence of at least one positive periodic solution is established. In particular, our results generalize some known criteria.

Removing S‐wave noise in TTI reverse time migration

Abstract: Summary Anisotropy is intrinsically an elastic phenomenon. The widely-used acoustic anisotropic wave equation results in significant shear wave presence in both modeling data and reverse time migration images. In this abstract, we discuss two approaches to reduce the S-wave noise in migration. The first is based on an elastic anisotropic wave equation with non-zero S-wave velocity to attenuate S-wave noise. The second approach uses a supplementary routine to remove the S-waves after wavefield modeling in each time step. Impulse responses and a simple 2D TTI example show that both methods reduce S-wave energy significantly and lead to a cleaner image than those based on the conventional acoustic anisotropic wave equation.

Low power, high resolution timing generator for ultra-wide bandwidth communication systems

Abstract: A data communication method is provided, comprising: processing high-speed digital data for communication to produce processed data; generating short impulse wavelets; constructing a digitally modulated ultra wideband signal from the short impulse wavelets in response to bits of the processed data, wherein the digitally modulated ultra wideband signal comprises a series of the short impulse wavelets, and the value of each bit of the processed data is digitally modulated onto the shape of at least one of the short impulse wavelets of the series, to produce a series of digitally shape modulated impulse wavelets; and transmitting the digitally modulated ultra wideband signal, including the series of digitally shape modulated impulse wavelets, via an antenna.

Influence of the voltage waveform and hydrostatic pressure on morphology and final length of discharges propagating over solid-liquid interfaces

Abstract: This paper is aimed at the influence of the voltage waveform (lightning impulse, dc and ac) and hydrostatic pressure on the morphology and final length of creeping discharges propagating over solid/liquid insulating surfaces in a point-plane electrode arrangement. Different solid materials immersed in mineral oil are tested. It is shown that under ac and dc, the discharges do not present a radial shape as observed with the negative discharges under lightning impulse voltages. For a given solid sample, the final length Lf (i.e. the maximum extension) of discharges is longer with ac than with lightning impulse voltage and dc. The currents waveforms are similar to those observed in liquids. On the other hand, the length of discharge branches is reduced when the hydrostatic pressure is increased whatever the voltage waveforms and polarity. Lf increases quasi-linearly with the voltage and decreases when the hydrostatic pressure is increased. And for given voltage and pressure, the thinner the solid sample and/or the higher its dielectric constant, the longer the discharges are, indicating the important role of capacitive effects in the propagation mechanisms of discharges.

Solving frictionless rocking block problem with multiple impacts

Abstract: In this paper, we present a solution to the frictionless multiple impact problems that may arise in the rocking blocks. We use an approach based on the impulse–momentum methods, the energetic coefficient of restitution and the impulse correlation ratio. Subsequently, we present the results of an experimental study that is used to compare the results predicted by the proposed method with the experimental outcomes.

Removal of surface-wave noise in seismic data

Abstract: The invention is a method to predict surface-wave waveforms (306) and subtract them (307) from seismic data. Prediction is done by estimating a set of surface-consistent components (transfer functions in the frequency domain or impulse responses in time domain) that best represent changes in the waveforms for propagation along the surface from source to receiver (303). The prediction uses a mathematical expression, or model, of the earth's filtering effects, both amplitude and phase, as a function of frequency. The desired surface-consistent components are model parameters, and model optimization is used to solve for the surface-consistent components. The surface-consistent components may include filter transfer functions for each source location, each receiver location, and for propagation (302) through each region (301) of the surface that exhibits lateral variation.

Apparatus and method for generating filter characteristics

Abstract: An apparatus for generating filter characteristics for filters connectible to at least three loudspeakers at defined locations with respect to a sound reproduction zone comprises an impulse response reverser (10) for time-reversing impulse responses associated to the loudspeakers to obtain time-reversed impulse responses. The apparatus furthermore comprises an impulse response modifier (14) for modifying the impulse responses or the time-reversed impulse responses such that impulse response portions occurring before a maximum of a time-reversed impulse response are reduced in amplitude to obtain the filter characteristics for the filters.

Thrust Performance of Microwave Rocket Under Repetitive-Pulse Operation

Abstract: An experiment was conducted on a microwave rocket (repetitive-pulse millimeter-wave-beam-powered thruster) with repetitive pulses. A thruster model with a forced-breathing system was used. The forced-breathing system supplies fresh air from the thrust wall into the thruster. The pressure histories in the thruster weremeasured and the propagation velocity of the shock wave and the thrust impulse were deduced. Results show that although the propagation velocity was identical to the result for the single-pulse operation at the first pulse, the propagation velocity increased after the second pulse. Similarly, the impulse decreased after the second pulse. The dependence of the propagation velocity of the shock wave and the thrust performance on the partial-filling rate of the fresh air was comparedwith that of the thrust-generationmodel with a forced-breathing system. The experimental results showed good agreement with those obtained using the model.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

Abstract: To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six kinds of non-standard lightning impulse waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Then, the dielectric breakdown voltage iquest time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gaps and partly the coneshaped insulating spacers that represent insulation elements of GIS for six kinds of nonstandard lightning impulse waveforms. In this paper, the resultant breakdown voltages were evaluated in terms of the overvoltage duration, which led to their formulation in a unified way. On the basis of these insulation characteristics and their unified formulation, the paper investigated a method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. When the constructed algorithm was applied to five examples of representative two type waveforms in the lightning surge time region, they were converted into standard lightning impulse waveforms with crest values reduced by 20% to 34%, suggesting potentiality for reduction of lightning impulse insulation specifications of GIS.

Boussinesq Model for Weakly Nonlinear Fully Dispersive Water Waves

Abstract: In the present work a new Boussinesq dispersive wave propagation model is proposed. The model is based on a system of equations expressed in terms of the free-surface elevation and the depth-averaged horizontal velocities. The approach is developed for fully dispersive and weakly nonlinear irregular waves propagating over any constant water depth in two horizontal dimensions, but it can also be applied in mildly sloping beaches with considerable accuracy. The model in its two-dimensional formulation involves in total five terms in each momentum equation, including the classical shallow water terms and only one frequency dispersion term. The latter is expressed through convolution integrals, which are estimated using appropriate impulse functions. The formulation is fully explicit in space and thus no inversion is required for the numerical solution. The model is applied to simulate the propagation of regular and irregular waves using a simple explicit scheme of finite differences. Numerical integration of a convolution integral is also required. The results of the simulations are compared with experimental data, as well as with linear and nonlinear wave theory. The comparisons show that the method is capable of simulating weakly nonlinear dispersive wave propagation over finite constant or slowly diminishing water depth in a satisfactory way.

Impulse response measurement techniques and their applicability in the real world

Abstract: Measurement of impulse responses is a common task in audio signal processing. In this paper three common measurement techniques are reviewed: Maximum length sequences, exponentially swept sines and time delay spectrometry. The aim is to give the reader a brief tutorial of the methods with a special focus on deficiencies of the algorithms, aiding in the choice of the best algorithm for a task at hand. Additionally, for time delay spectrometry, a novel improvement is presented, lifting its restriction to relatively short impulse responses.

Hydrodynamic Damping Identification from an Impulse Response of a Vibrating Blade

Abstract: In the present study, the identification of hydrodynamic damping is investigated in the case of 2D blade placed in the test section of the EPFL High Speed Cavitation Tunnel. A non intrusive technique, based on a spark generated bubble, is used to generate a wide band mechanical excitation. An underwater electric discharge at the bottom of the test section creates a fast growing and collapsing bubble which generates strong shock waves in the test section. The response of the blade to this excitation impulse is monitored with the help of a digital Laser Doppler vibrometer. Assuming a Single Degree of Freedom (SDOF) system, the hydrodynamic damping is estimated in the time domain by fitting an exponentially damped function on the impulse response envelope. Tests are performed for flow velocities ranging from rest up to 15 m/s. A linear relationship is found between the hydrodynamic damping and the reduced flow velocity for the first bending mode, while surprisingly a constant damping factor is experienced for the first torsion mode.

A Computational Method for Stochastic Impulse Control Problems

Abstract: Stochastic control refers to the optimal control of systems subject to randomness. Impulse and singular controls are those that can instantaneously change the system state as opposed to the more common controls that change the rate of change of state. When the cost of control has a fixed component it is usually optimal to affect instantaneous changes that cause discontinuity in state evolution. Examples of impulse controls are abundant in several diverse areas that include finance, operations management and economics. Stochastic impulse control problems are usually solved by converting them to differential equation problems using dynamic programming arguments. In all but the simplest of cases, the resulting differential equations for impulse control problems cannot be solved analytically. They are relatively harder to solve since they have free boundaries, which are unknown boundaries that need to be determined as part of the solution. In this dissertation, we construct a transformation scheme that transforms the arising free boundary problem to a sequence of fixed-boundary problems that are easy to solve. We show that the arising sequence has monotonically improved solutions and that the sequence of solutions converge to the optimal solution. We also provide an e-optimality result that establishes a bound on the difference from the optimal value function for any terminated iteration. Applications in finance and operations management are illustrated.