Time Domain Transfer Function Research Articles

Two‐sided Krylov enhanced proper orthogonal decomposition methods for partial differential equations with variable coefficients

AbstractIn this paper, new fast computing methods for partial differential equations with variable coefficients are studied and analyzed. They are two kinds of two‐sided Krylov enhanced proper orthogonal decomposition (KPOD) methods. First, the spatial discrete scheme of an advection‐diffusion equation is obtained by Galerkin approximation. Then, an algorithm based on a two‐sided KPOD approach involving the block Arnoldi and block Lanczos processes for the obtained time‐varying equations is put forward. Moreover, another type of two‐sided KPOD algorithm based on Laguerre orthogonal polynomials in frequency domain is provided. For the two kinds of two‐sided KPOD methods, we present a theoretical analysis for the moment matching of the discrete time‐invariant transfer function in time domain and give the error bound caused by the reduced‐order projection between the Galerkin finite element solution and the approximate solution of the two‐sided KPOD method. Finally, the feasibility of four two‐sided KPOD algorithms is verified by several numerical results with different inputs and setting parameters.

The reciprocal relationship between cardiac baroreceptor sensitivity and cerebral autoregulation during simulated hemorrhage in humans.

A reciprocal relationship between the baroreflex and cerebral autoregulation (CA) has been demonstrated at rest and in response to acute hypotension. We hypothesized that the reciprocal relationship between cardiac baroreflex sensitivity (BRS) and CA would be maintained during sustained central hypovolemia induced by lower body negative pressure (LBNP), and that the strength of this relationship would be greater in subjects with higher tolerance to this stress. Healthy young adults (n=51; 23F/28M) completed a LBNP protocol to presyncope. Subjects were classified as high tolerant (HT; completion of -60mmHg LBNP stage, ≥20-min) or low tolerant (LT; did not complete -60mmHg LBNP stage, <20-min). R-R intervals (RRI), systolic arterial pressure (SAP), mean arterial pressure (MAP), and middle cerebral artery velocity (MCAv) were measured continuously. Cardiac BRS was calculated in the time domain (ΔHR/ΔSAP) and frequency domain (RRI-SAP low frequency (LF) transfer function gain), and CA was calculated in the time domain (ΔMCAv/ΔMAP) and frequency domain (MAP-mean MCAv LF transfer function gain). There was a moderate relationship between cardiac BRS and CA for the group of 51 subjects in both the time (R=-0.54, P<0.0001) and frequency (R=0.61, P<0.001) domains; there was a stronger relationship in the HT group (R=0.73) compared to the LT group (R=0.31) in the frequency domain (P=0.08), but no difference between groups in the time domain (HT: R=-0.73 vs. LT: R=-0.63; P=0.27). These findings suggest that an interaction between BRS and CA may be an important compensatory mechanism that contributes to tolerance to simulated hemorrhage in young healthy adults.

Characterization of the acoustic output of single marine-seismic airguns and clusters: The Svein Vaage dataset.

The acoustical output of marine-seismic airguns is determined from recordings of the sound pressure made on hydrophones suspended below a floating barge from which the airguns are also deployed. The signals from multiple types of airguns are considered and each type is operated over a range of deployment depths and chamber pressures. The acoustical output is characterized in terms of a "source waveform" with dimensions of the pressure-times-distance and in an infinite idealized medium, could be divided by the source-receiver distance to give the sound pressure at that receiver. In more realistic environments, the source waveform may be used to predict the pressure at any arbitrary receiver position simply by the application of a time-domain transfer function describing the propagation between the source and receiver. The sources are further characterized by metrics such as the peak source waveform and energy source level. These metrics are calculated in several frequency bands so that the resulting metrics can be used to characterize the acoustical output of the airguns in terms of their utility for seismic image-processing or possible effects on marine life. These characterizations provide reference data for the calibration of models that predict the airguns' acoustical output. They are validated via comparisons of the acoustic pressure measured on far-field hydrophones and predicted using the source waveforms. Comparisons are also made between empirically derived expressions relating the acoustic metrics to the chamber volume, chamber pressure, and deployment depth and similar expressions from the literature.

Design of optimum filters for signal processing with silicon drift detectors

In order to improve noise filtering for high‐resolution X‐ray spectroscopy using silicon drift detectors, optimum finite impulse response filters are calculated and tested experimentally. Common matched filter theory cannot be applied for this problem since the filters need to fulfill several requirements regarding their time domain transfer function, like, for example, the presence of a flat‐top, zero‐filter area. Therefore, the utilization of digital penalized least mean square method with silicon drift detectors is presented. Adaptations to the method are applied in order to suit the considered application targeting low dead‐time at high count rates using modern silicon drift detectors with fast charge amplifiers. The workflow for filter calculation is presented: Signal data are acquired using a spectroscopy setup in order to obtain pulse shape and noise information. Desired constraints regarding the time‐domain transfer function of the filters are written out, and limits for the precision of their fulfillment are derived. Optimization is carried out, and resulting filters are presented. In order to experimentally test the calculated filters, implementation in hardware is done. 55Fe spectra are acquired and evaluated. Noise reduction is rated by calculation of residual electronic noise in the recorded 55Fe spectra. Comparison to the noise reduction of trapezoid filters is done. Improvement up to (5.2 ± 0.3)% was found using the calculated optimum filter, proving the successful utilization of digital penalized least mean square method for signal processing with modern silicon drift detectors.

Research on improving measurement accuracy of acoustic transfer function of underwater vehicle

To address the problem that acoustic transfer functions with underwater platforms cannot be measured accurately, this paper presents a method based on phase compensation to improve the accuracy of acoustic transfer function measurements on underwater platforms. The time-domain impulse response signals with multiple cycles are first collected and intercepted, and then their phase differences are estimated using the least-squares method, and phase compensation is used to align the phases of all the signals, and then the impulse response signals are weighted and averaged over all the impulse response signals to cancel out the random noise. The water pool test proves that this method reduces the measurement random noise while obtaining a high-fidelity time domain transfer function, which effectively improves the signal-to-noise ratio of the measurement. The method adopts only one measurement signal, and without changing the measurement system, the random noise is cancelled out by the in-phase superposition of the multi-cycle impulse response signals to avoid the nonlinear distortion of the measurement results.

Latency prediction of earmuff using a lumped parameter model

Attenuation and latency are important performances of earmuff, where the former defines passive noise reduction capability, the latter is a key factor in the design of a feedforward active noise control earmuff. Previously an earmuff lumped parameter model was developed to predict earmuff attenuation. The aim of this work was to predict earmuff latency by using the lumped parameter model (LPM). The latency analytic solution was derived from the time domain transfer function between inside and outside of earmuff using earmuff LPM. Results demonstrated that the decreases of earmuff cushion stiffness, damping, and air stiffness or the increase of earmuff mass would achieve a longer passive latency. To examine the validity of the proposed method, an earmuff prototype was built, and experiments were conducted. The measured attenuation and latency were in agreement with the theoretical prediction.

Teaching Tool for a Control Systems Laboratory Using a Quadrotor as a Plant in MATLAB

This paper presents a MATLAB-based application to teach the guidance, navigation, and control concepts of a quadrotor to undergraduate students, using a graphical user interface (GUI) and 3-D animations. The Simulink quadrotor model is controlled by a proportional integral derivative controller and a linear quadratic regulator controller. The GUI layout's many components can be easily programmed to perform various experiments by considering the simulation of the quadrotor as a plant; it incorporates control systems (CS) fundamentals such as time domain response, transfer function and state-space form, pole-zero location, root locus, frequency domain response, steady-state error, position and disturbance response, controller design and tuning, unity, and the use of a Kalman filter as a feedback sensor. 3-D animations are used to display the quadrotor flying in any given condition selected by the user. For each simulation, users can view the output response in the form of 3-D animations, and can run time plots. The quadrotor educational tool (QET) helps students in the CS laboratory understand basic CS concepts. The QET was evaluated based on student feedback, grades, satisfaction, and interest in CS.

Error Analysis of Clay-Rock Water Content Estimation with Broadband High-Frequency Electromagnetic Sensors--Air Gap Effect.

Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling.

Design of Low Pass Microwave Filter using Impulse Invariant Transform

paper introduces a new approach to design low pass microwave filter using impulse invariant transform. In this approach, the analog specifications of desired low pass filter is transformed into the digital specification and then apply an optimization technique (DSP based) to get an approximate transfer function in digital domain. Further, the transfer function in continuous time domain is obtained by applying inverse impulse invariant technique. Now the lumped element circuit is obtained by using a classical network synthesis technique on the transfer function in analog domain. The theoretical result of low pass microwave filter is also verified on ADS Simulation tool. Keywordsinvariant transform, Low-pass filter, Microwave Filter, Quasi-Newton algorithm.

Linearization of Coupled Pointing and Tracking Dynamical Equations

Cooperative pointing and tracking is one important characteristic of deep space inter-satellite laser communication, so that the dynamic mathematical model is complicated nonlinearity and coupling. The contribution of this paper is to substitute the time-domain error transfer function of state equations and to linearize the state space for the sake of physical realization easily in terms of previous authors’ work. The method applied is state feedback and coordinate transformation in nonlinear field, the calculated result is demonstrated that differential equations modeled can be transferred into canonical controllable form and realized physically.

Time Domain Transfer Function of the Induction Motor

Small signal stability of electrical machines at frequency domain has been shown by toque coefficients and eigenvalue of motional impedance matrix in state space form. The relation of damping, synchronizing and total synchronizing torque coefficients with the eigenvalue or the roots of the characteristic equation of the perturbed machine shows that the instability occurs at 2 different modes. Static mode represented by real root at over load condition, and dynamic mode represented by complex root at the condition when the total synchronizing coefficient exhibits zero value within the negative range of the damping torque coefficient. However, small signal instability details at time domain are not given in the literatures. This paper discusses with figures the time domain signals of the induction motor perturbation variables under hunting condition, and presents the differences observed between inverse Laplace transform and Fourier transform in time domain response, based on the transform of the transfer function from the frequency domain, The figures demonstrate and confirm the machine small signal stability performance given in frequency domain.

Study of Channel Characteristics for Galvanic-Type Intra-Body Communication Based on a Transfer Function from a Quasi-Static Field Model

Intra-Body Communication (IBC), which modulates ionic currents over the human body as the communication medium, offers a low power and reliable signal transmission method for information exchange across the body. This paper first briefly reviews the quasi-static electromagnetic (EM) field modeling for a galvanic-type IBC human limb operating below 1 MHz and obtains the corresponding transfer function with correction factor using minimum mean square error (MMSE) technique. Then, the IBC channel characteristics are studied through the comparison between theoretical calculations via this transfer function and experimental measurements in both frequency domain and time domain. High pass characteristics are obtained in the channel gain analysis versus different transmission distances. In addition, harmonic distortions are analyzed in both baseband and passband transmissions for square input waves. The experimental results are consistent with the calculation results from the transfer function with correction factor. Furthermore, we also explore both theoretical and simulation results for the bit-error-rate (BER) performance of several common modulation schemes in the IBC system with a carrier frequency of 500 kHz. It is found that the theoretical results are in good agreement with the simulation results.

Basic Study on the Transform Method of Frequency-Dependent Functions into Time Domain: Relation to Duhamel’s Integral and Time-Domain-Transfer Function

The time-domain evaluation of the frequency-dependent dynamic stiffness was studied, and some transform methods were proposed. Although various kinds of stiffness have been well-transformed by these methods, some problems remain. In this paper, the following two problems are studied. First, the relationship between the proposed transform methods and Duhamel’s integral is studied to understand the meaning of the two series of impulse responses obtained by the methods. Next, the time-domain transfer function, obtained by the transform of frequency-domain transfer function, is shown to expand the applicability of the methods. Seismic response values are easily calculated in the time domain using the function without FFT. The efficiency of the function is confirmed with a practical example problem.

A BASIC STUDY ON THE TRANSFER METHOD OF FREQUENCY DEPENDENT FUNCTIONS INTO TIME DOMAIN

The author has studied and proposed transform methods of frequency dependent dynamic stiffness into time domain. Although various kinds of stiffness got to be transformed by the methods, some problems were still remained. In this paper, followings two problems were studied. First, the relation between the proposed transform methods and the Duhamel's integral was studied in order to understand the meaning of the 2 series of impulse responses obtained by the methods. Next, to expand the applicability of the methods, the time domain transfer function, obtained by the transform of frequency domain transfer function, was shown. The seismic response values are easily calculated in the time domain using the function without FFT. The efficiency of the function was confirmed by a practical example problem.

Thunder‐induced ground motions: 1. Observations

Acoustic pressure from thunder and its induced ground motions were investigated using a small array consisting of five three‐component short‐period surface seismometers, a three‐component borehole seismometer, and five infrasound microphones. We used the array to constrain wave parameters of the incident acoustic and seismic waves. The incident slowness differences between acoustic pressure and ground motions suggest that ground reverberations were first initiated somewhat away from the array. Using slowness inferred from ground motions is preferable to obtain the seismic source parameters. We propose a source equalization procedure for acoustic/seismic deconvolution to generate the time domain transfer function, a procedure similar to that of obtaining teleseismic earthquake receiver functions. The time domain transfer function removes the incident pressure time history from the seismogram. An additional vertical‐to‐radial ground motion transfer function was used to identify the Rayleigh wave propagation mode of induced seismic waves complementing that found using the particle motions and amplitude variations in the borehole. The initial motions obtained by the time domain transfer functions suggest a low Poisson's ratio for the near‐surface layer. The acoustic‐to‐seismic transfer functions show a consistent reverberation series at frequencies near 5 Hz. This gives an empirical measure of site resonance that depends on the ratio of the layer velocity to layer thickness for earthquake P and S waves. The time domain transfer function approach by transferring a spectral division into the time domain provides an alternative method for studying acoustic‐to‐seismic coupling.

Estimation of magnetotelluric transfer functions in the time domain over a wide frequency band

SUMMARY Determination of the transfer function is the main objective in magnetotelluric (MT) and geomagnetic data processing. In this paper we describe a new algorithm for finding a transfer function through determination of the impulse response in the time domain. The proposed method was developed for the long time-series with which we are usually dealing in short-period recording. It allows the determination of the transfer function for a broad range of frequencies, the only limitation being the duration of recording. In contrast to other methods for determination of the time-domain transfer function we selected an approximation of impulse response in which the number of unknowns to be determined is proportional to the frequency range of interest on a logarithmic scale. This is a natural way to deal with functions such as the MT impedance tensor or geomagnetic vector. Our approximation makes it easy to find the predicted electric field, which is very useful for assessing the quality of the recorded data.

Axial current reversal promotes synchronous correlation between dendritic membrane potentials during large-scale synaptic input

We report two results from a simulation study of spatial temporal interactions in a dendritic tree during large-scale synaptic input. The first is a feedback mechanism following individual synaptic inputs, which results in a reversal of the axial current 1– 2 ms after activation of an input. The second is a time domain transfer function analysis between the membrane potential fluctuations at different sites. During large-scale synaptic input, this has a symmetrical structure, indicative of a two-way flow of axial current in the dendritic tree. We interpret this as an indication of a synchronous correlation structure between membrane potential fluctuations during large-scale synaptic input, which may have implications for our understanding of synaptic integration.

Construction of a New Forced Nutation Theory of the Nonrigid Earth

We have obtained a transfer function satisfying the two necessary geophysical constraints, based on the formulation of Sasao, Okubo, & Saitō. We have also developed a realistic model of the free core nutation (FCN) by taking into account the recent discovery of FCN excitations. Using these, we construct a new theory of the forced nutation of the nonrigid Earth. First we adopt RDAN97 as the rigid-Earth nutation theory. Next, this is convolved numerically with the transfer function in the time domain. Then the free parameters of the transfer function are adjusted by fitting the convolved nutation theory to the latest VLBI observations of the nutation for the period 1979–2000, after subtracting the geodesic nutation and the FCN model. Through examination of the dependence of the residuals on the number of nutation terms, we truncate the series to only 194 terms. The resulting weighted rms of the residuals for the new nutation series is 0.280 mas, which is significantly smaller than 0.296 mas, that of the best empirical model, IERS 1996, which contains 381 terms. We estimate the oscillatory period of the FCN term to be -431.0(6) sidereal days and its Q-value to be 1.53(10) × 104. We estimate the correction to the celestial ephemeris pole offsets at J2000.0 to be -0042888(10) in longitude and -0005171(10) in obliquity. Further, the corrections to the precession constants are determined to be -029856(30) per century in longitude and -002408(16) per century in obliquity. As for the geophysical parameters, we estimate the dynamical ellipticity of the whole Earth to be 0.003273972(3). We also determine the Love number of the solid Earth to be 0.2788(11) with a phase lag of 713(23).

Astronomical time series analysis in South Africa

This review is essentially a bibliography. In the first part, work done locally on period-finding methods is discussed. Some of the topics referred to are: periodogram significance testing, identification of non-sinusoidal periodicities, and computational shortcuts useful for calculating periodograms of large data sets. A number of aspects of period-finding inγ ray astronomy are briefly mentioned: these include various test statistics for the presence of a periodicity, the influence of oversampling on significance levels, estimation of the pulse shape, and the specification of a flux limit in the case of a non-detection. The second part of the review deals with the analysis of stochastic astronomical time series. Topics dealt with are ARMA modelling, Kalman filtering, problems associated with O-C analyses, and continuous time ARMA modelling. Two aspects of bivariate astronomical time series are touched on, namely time domain transfer function modelling and the estimation of the lag between two irregularly observed series.

A data acquisition and analysis system for voltage versus luminous intensity transfer characteristic measurements in flat panel displays

In this study the time domain transfer function h(t) of luminescent display panels has been determined for the first time by the cross-correlation technique. The signature of the impulse response is immediately useful as a research tool and has potential application in the control of manufacturing process parameters. A prototype data acquisition and analysis system was designed and constructed. The system was interfaced to a Thorn EMI 9813 photomultiplier. The primary application of the system, in this case, was to measure the forward transfer characteristics of ZnS:Mn,Cu DCEL (DC electroluminescence) pixels. The system employs cross-correlation techniques based on a 1023, PRBS (pseudo random binary sequence) maximal length sequence with a bit rate of 50 kHz. The digitized luminous output is temporarily stored in static RAM. The data is subsequently transferred to a microcomputer where h(t) is derived by a cross-correlation algorithm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>