Journal articles on the topic 'Time-Varying Impulse Responses'
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Piwowar, Anna, and Janusz Walczak. "Models of n-th order linear time – varying systems." Archives of Electrical Engineering 64, no. 2 (June 1, 2015): 315–31. http://dx.doi.org/10.1515/aee-2015-0025.
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Abstract Effective algorithms of constructing models of generalized parametric sections of the n-th order consisting of cascade and parallel elementary LTV section connections are presented in this paper. Moreover, the methods of impulse responses determination have been shown
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Cho, Jung-Keun, and Youn-Sik Park. "Vibration reduction in flexible systems using a time-varying impulse sequence." Robotica 13, no. 3 (May 1995): 305–13. http://dx.doi.org/10.1017/s0263574700017835.
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SummaryAn input shaping technique using a time-varying impulse sequence is presented to reduce the motion-induced vibration of flexible systems in a feedforward way.The decoupled modal responses for a general linear time-varying system are firstly approximated. Upon this approximation, the time-varying impulse sequences to suppress the vibrational modes are found. The reference inputs to the systems are shaped by convolving with the time-varying impulse sequence to suppress the multimode vibrations. This technique can be also applied to suppress the vibration of nonlinear time-varying systems.The performance of this method is demonstrated with two practical examples: a moving overhead crane and a two-link robot manipulator. Consequently, this study provides an input shaping technique applicable to the vibration suppression of broader classes of flexible systems.
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Rideout, Brendan P., Eva-Marie Nosal, and Anders Host-Madsen. "Blind channel estimation of time-varying underwater acoustic waveguide impulse responses." Journal of the Acoustical Society of America 140, no. 4 (October 2016): 3360. http://dx.doi.org/10.1121/1.4970720.
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Zheng, Min, and Fan Shen. "Modal Identification Based on Hilbert Transform for Time-Varying System." Applied Mechanics and Materials 226-228 (November 2012): 303–7. http://dx.doi.org/10.4028/www.scientific.net/amm.226-228.303.
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Modal identification methods based on the Hilbert Transform are applied to identify modal parameters of time-varying system using impulse response time histories. First, the response data are decomposed into modal responses through the empirical mode decomposition (EMD). Then, the Hilbert transform is applied to each modal response to obtain the instantaneous frequencies. The applications of the proposed methods are illustrated using a 3 degree-of-freedom (DOF) systems with time-varying dynamic characteristics. Numerical simulation results demonstrate that the proposed system identification methods yield good results.
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Ma, Xiuying, Yongjing Wang, Haiyan Song, and Han Liu. "Time-varying mechanisms between foreign direct investment and tourism development under the new normal in China." Tourism Economics 26, no. 2 (August 27, 2019): 324–43. http://dx.doi.org/10.1177/1354816619870948.
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This study is aimed at investigating what has happened to the dynamic linkages between foreign direct investment (FDI) and tourism development in China since the emergence of the so-called new normal economy. A time-varying parameter vector autoregressive (TVP-VAR) model is used for the first time to analyze the equi-spaced and time-point impulse responses between FDI, foreign exchange earnings from international tourism (FEE), and gross domestic product using annual data taken from 1983 to 2017. The results for the equi-spaced impulse response show that a difference in intensity for the interaction effect between FDI and FEE will change with different intervals. In addition, impulse response diagrams for FDI and FEE based on changes in economic development at three significant points in time reveal that the effect FDI in the new normal period has had the greatest impact on FEE in 2012, followed in decreasing impact by 2003 and then 1997.
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Shaheen. "Impact of Fiscal Policy on Consumption and Labor Supply under a Time-Varying Structural VAR Model." Economies 7, no. 2 (June 17, 2019): 57. http://dx.doi.org/10.3390/economies7020057.
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This paper investigates the impact of fiscal policy on private consumption and labor supply in the UK economy using time-varying parameter vector autoregression (TVP-VAR) with stochastic volatility for the period Q2 1987 to Q2 2017. It considers fiscal variables such as government expenditure and net tax revenue and evaluates their impact on private consumption and average hours worked per week. Three sample periods were selected and two approaches were used to identify impulse responses, first taking the average of stochastic volatility over the sample period, and then allowing for sign restrictions based on contemporaneous relationships among the selected variables. The study found a negative wealth effect of public spending on private consumption and a positive effect on hours worked, as people tend to work more hours to maintain the same standard of living. Similarly, a tax shock generates negative effects on consumption but the impact on worked hours remains unclear over a three-year time horizon. These findings are almost consistent across sample periods and alternative specifications of impulse responses. This is one of only a few studies to determine the linkages between fiscal policy and the labor market using a macroeconomic framework.
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Müller, Kaspar, and Franz Zotter. "Auralization based on multi-perspective ambisonic room impulse responses." Acta Acustica 4, no. 6 (2020): 25. http://dx.doi.org/10.1051/aacus/2020024.
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Most often, virtual acoustic rendering employs real-time updated room acoustic simulations to accomplish auralization for a variable listener perspective. As an alternative, we propose and test a technique to interpolate room impulse responses, specifically Ambisonic room impulse responses (ARIRs) available at a grid of spatially distributed receiver perspectives, measured or simulated in a desired acoustic environment. In particular, we extrapolate a triplet of neighboring ARIRs to the variable listener perspective, preceding their linear interpolation. The extrapolation is achieved by decomposing each ARIR into localized sound events and re-assigning their direction, time, and level to what could be observed at the listener perspective, with as much temporal, directional, and perspective context as possible. We propose to undertake this decomposition in two levels: Peaks in the early ARIRs are decomposed into jointly localized sound events, based on time differences of arrival observed in either an ARIR triplet, or all ARIRs observing the direct sound. Sound events that could not be jointly localized are treated as residuals whose less precise localization utilizes direction-of-arrival detection and the estimated time of arrival. For the interpolated rendering, suitable parameter settings are found by evaluating the proposed method in a listening experiment, using both measured and simulated ARIR data sets, under static and time-varying conditions.
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Olama, Mohammed M., Seddik M. Djouadi, Yanyan Li, and Aly Fathy. "Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels." International Journal of Antennas and Propagation 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/467670.
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Stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean-square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and nonresolvable multipath received signals are considered and represented as small-scaled Nakagami fading. The proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method’s viability and the results are presented.
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Keating, John W., and Victor J. Valcarcel. "THE TIME-VARYING EFFECTS OF PERMANENT AND TRANSITORY SHOCKS TO REAL OUTPUT." Macroeconomic Dynamics 19, no. 3 (October 31, 2014): 477–507. http://dx.doi.org/10.1017/s1365100514000595.
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A time-varying-parameter VAR for real output growth and inflation is estimated with annual U.S. series dating back to 1870. Volatility for both variables rises quickly with World War I and its aftermath, stays high until the end of World War II, and drops rapidly until the 1960s. This Postwar Moderation yields the largest decline in volatilities, surpassing the Great Moderation. Conditional on temporary shocks, inflation and output growth are positively correlated. Our model implies that aggregate demand played a key role in inflation volatility fluctuations. Conversely, the two variables are negatively correlated conditional on permanent shocks. Our model suggests that aggregate supply played an important role in output volatility fluctuations. Most impulse responses support an aggregate supply interpretation for permanent shocks. However, before World War I, a permanent increase in output raised the price level at longer horizons, and these responses are frequently statistically significant. This evidence supports the hypothesis that aggregate demand had a long-run positive effect on output during the pre–World War I period.
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Holm, Sverre, Thomas Holm, and Ørjan Grøttem Martinsen. "Simple circuit equivalents for the constant phase element." PLOS ONE 16, no. 3 (March 26, 2021): e0248786. http://dx.doi.org/10.1371/journal.pone.0248786.
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The constant phase element (CPE) is a capacitive element with a frequency-independent negative phase between current and voltage which interpolates between a capacitor and a resistor. It is used extensively to model the complexity of the physics in e.g. the bioimpedance and electrochemistry fields. There is also a similar element with a positive phase angle, and both the capacitive and inductive CPEs are members of the family of fractional circuit elements or fractance. The physical meaning of the CPE is only partially understood and many consider it an idealized circuit element. The goal here is to provide alternative equivalent circuits, which may give rise to better interpretations of the fractance. Both the capacitive and the inductive CPEs can be interpreted in the time-domain, where the impulse and step responses are temporal power laws. Here we show that the current impulse responses of the capacitive CPE is the same as that of a simple time-varying series RL-circuit where the inductor’s value increases linearly with time. Similarly, the voltage response of the inductive CPE corresponds to that of a simple parallel RC circuit where the capacitor’s value increases linearly with time. We use the Micro-Cap circuit simulation program, which can handle time-varying circuits, for independent verification. The simulation corresponds exactly to the expected response from the proposed equivalents within 0.1% error. The realization with time-varying components correlates with known time-varying properties in applications, and may lead to a better understanding of the link between CPE and applications.
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Glantz, Raymon M., and John P. Schroeter. "Encoder Adaptation Modulates the Visual Responses of Crayfish Interneurons." Journal of Neurophysiology 92, no. 1 (July 2004): 327–40. http://dx.doi.org/10.1152/jn.00035.2004.
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The responses of sustaining and dimming fibers were characterized by the time varying firing rates elicited by extrinsic current and flashes of light. These data were simulated by an adaptive integrate-and-fire model. A postimpulse shunt conductance simulated spike-frequency adaptation. The correlation between observed and model current-elicited impulse rates was 0.94–0.98. However, except for a difference in input resistance (both measured and simulated), the voltage to impulse encoders of the two cell groups was similar and exhibited comparable degrees of spike-frequency adaptation (40 to 45%). The encoder model derived from current-elicited responses (with fixed parameters) was used to simulate visual responses elicited by light flashes. These simulations included a synaptic current derived from the time course of the postsynaptic potential (PSP). The sustaining fiber visual response consisted of a large excitatory PSP and high-frequency transient burst that adapted (by ∼80%) to a low-frequency plateau discharge. The simulations indicated that spike-frequency adaptation had no effect on the transient discharge but reduced the plateau firing rate by ∼60%. Encoder adaptation enhances the sustaining fiber response to the time derivative of the stimulus. In dimming fibers, the light flash elicits an inhibitory PSP that interrupts the “dark discharge” and an off response following the end of the flash. The simulations indicated that spike-frequency adaptation reduces the firing rate of both the dark discharge and the off response. Thus the model suggests that different effects of encoder adaptation on the two cell types arise from the same encoder mechanisms, but different actions are determined by differences in impulse rate and the time course of the discharge.
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Lundberg, Karl-Ola. "An Alternative Method for Measurement of Airborne Sound Insulation." Building Acoustics 8, no. 1 (March 2001): 57–74. http://dx.doi.org/10.1260/1351010011501731.
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A method for determination of the transmission coefficient from Complex Modulation Transfer Functions CMTF:s based on measured impulse-responses is shown. In the method a separate measurement of the equivalent sound absorption area is not needed in contrast to in the standardised measurement. By averaging over a number of estimates of the impulse-response the influence of background noise can be reduced substantially, implying that low-power sources can be used. A model for the power balance in the receiving room with time-varying power is considered. In the model the quotient of the receiving room intensity and the source room intensity has one pole, which is proportional to the equivalent sound absorption area in the receiving room, and a gain, proportional to the transmission coefficient. In the physical system the power can be time-varied by letting the system excitation signal consist of random noise modulated with a deterministic time-varying function. However, since the ensemble average of the squared response is proportional to the squared impulse-response convolved with the squared modulating function, random excitation is avoided and replaced by impulse-response measurements. The quotient of intensities in the model is in the physical system a quotient of CMTF:s. Experiments are carried out in an airborne sound insulation laboratory. For comparison, standardised measurements are also carried out. It is found that the presented method gives as result comparatively small transmission coefficients, though the relative differences are small. By refining the power balance model by introducing an energy propagation time delay, and selecting an appropriate delay, the differences were diminished.
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Glantz, R. M. "Motion detection and adaptation in crayfish photoreceptors. A spatiotemporal analysis of linear movement sensitivity." Journal of General Physiology 97, no. 4 (April 1, 1991): 777–97. http://dx.doi.org/10.1085/jgp.97.4.777.
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Impulse and sine wave responses of crayfish photoreceptors were examined to establish the limits and the parameters of linear behavior. These receptors exhibit simple low pass behavior which is well described by the transfer function of a linear resistor-capacitor cascade of three to five stages, each with the same time constant (tau). Additionally, variations in mean light intensity modify tau twofold and the contrast sensitivity by fourfold. The angular sensitivity profile is Gaussian and the acceptance angle (phi) increases 3.2-fold with dark adaptation. The responses to moving stripes of positive and negative contrast were measured over a 100-fold velocity range. The amplitude, phase, and waveform of these responses were predicted from the convolution of the receptor's impulse response and angular sensitivity profile. A theoretical calculation based on the convolution of a linear impulse response and a Gaussian sensitivity profile indicates that the sensitivity to variations in stimulus velocity is determined by the ratio phi/tau. These two parameters are sufficient to predict the velocity of the half-maximal response over a wide range of ambient illumination levels. Because phi and tau vary in parallel during light adaptation, it is inferred that many arthropods can maintain approximately constant velocity sensitivity during large shifts in mean illumination and receptor time constant. The results are discussed relative to other arthropod and vertebrate receptors and the strategies that have evolved for movement detection in varying ambient illumination.
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Montasser, Ghassen El, Rangan Gupta, Jooste Charl, and Stephen M. Miller. "The Time-series Linkages between US Fiscal Policy and Asset Prices." Public Finance Review 48, no. 3 (April 9, 2020): 303–39. http://dx.doi.org/10.1177/1091142120916032.
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This article studies the interplay of fiscal policy and asset price returns of the United States in a time-varying parameter vector autoregressive (VAR) model. Using annual data from 1890 to 2013, we study the effects of dynamic shocks to both fiscal policy on asset returns and asset returns on fiscal policy. Distinguishing between low-volatility (bull market) and high-volatility (bear market) regimes together with a time-varying parameter VAR model enables us to isolate the different sizes and signs of responses to shocks during different time periods. The results indicate that increases in the primary surplus-to-gross-domestic-product ratio decrease house returns over the entire sample and at each impulse horizon. Unlike the house return responses, stock returns only decrease in the first year after the fiscal shock but then increase for the following eight years. Furthermore, the findings show that asset return movements affect fiscal policy, whereby fiscal policy responds more to equity returns than to house returns. The response of fiscal policy to asset returns proves relatively stable and constant over time while controlling for various asset return regimes. Asset returns respond uniformly to fiscal policy shocks since the 1900s.
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Lai, Heather, and Brian Hamilton. "Computer Modeling of Barrel-Vaulted Sanctuary Exhibiting Flutter Echo with Comparison to Measurements." Acoustics 2, no. 1 (February 17, 2020): 87–109. http://dx.doi.org/10.3390/acoustics2010007.
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Computer modeling in acoustics allows for the prediction of acoustical defects and the evaluation of potential remediations. In this article, computer modeling is applied to the case of a barrel-vaulted sanctuary whose architectural design and construction led to severe flutter echoes along the main aisle, which was later mitigated through acoustical remediations. State-of-the-art geometrical acoustics and wave-based simulations are carried out to analyze the acoustics of this space, with a particular focus on the flutter echoes along the main aisle, before and after remediations. Multi-resolution wavelet and spectrogram analyses are carried out to isolate and characterize flutter echoes within measurements and computer-simulated room impulse responses. Comparisons of simulated responses to measurements are also made in terms of decay times and curves. Simulated room impulse responses from both geometrical acoustics and wave-based methods show evidence of flutter echoes matching measurements, to varying degrees. Time-frequency analyses isolating flutter echoes demonstrate better matches to measurements from wave-based simulated responses, at the cost of longer simulation times than geometrical acoustics simulations. This case study highlights the importance of computer modeling of acoustics in early design phases of architectural planning of worship spaces.
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Zhao, Haipeng, and Joseph Bentsman. "Biorthogonal Wavelet Based Identification of Fast Linear Time-Varying Systems—Part I: System Representations12." Journal of Dynamic Systems, Measurement, and Control 123, no. 4 (December 27, 2000): 585–92. http://dx.doi.org/10.1115/1.1409549.
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An analytical framework is developed that permits the input-output representations of discrete-time linear time-varying (LTV) systems in terms of biorthogonal bases on compact time intervals. Using these representations, the companion paper, Part II develops computational procedures for rapid identification of fast nonsmooth LTV systems based on short data records. One of the representations proposed is also used in H. Zhao and J. Bentsman, “Block Diagram Reduction of the Interconnected Linear Time-Varying Systems in the Time Frequency Domain,” accepted for publication by Multidimensional Systems and Signal Processing to form system interconnections, or wavelet networks, and develop subsystem connectibility conditions and reduction rules. Under the assumption that the inputs and the outputs of the plants considered in the present work belong to lp spaces, where p=2 or p=∞, their impulse responses are shown to belong to Banach spaces. Further on, by demonstrating that the set of all bounded-input bounded-output (BIBO) stable discrete-time LTV systems is a Banach space, the system representation problem is shown to be reducible to the linear approximation problem in the Banach space setting, with the approximation errors converging to zero as the number of terms in the representation increases. Three types of LTV system representation, based on the input-side, the output-side, and the input-output transformations, are developed and the suitability of each representation for matching a particular type of the LTV system behavior is indicated.
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Rahman, Md Jahidur, and Jiaxin Yang. "Multiple-Observation-Based Robust Channel and Doppler Estimation in High Mobility Applications." International Journal of Vehicular Technology 2013 (May 13, 2013): 1–8. http://dx.doi.org/10.1155/2013/472154.
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Channel estimation is a challenging task, especially in high mobility applications due to the rapid variation of the propagation environment. This paper presents a new technique that exploits past channel impulse responses (CIRs) in order to trace and compensate Doppler frequency in mobile applications, enabling robust estimation of time-varying channel. Based on the fact that channel taps at different time instants can be fitted with a sinusoidal wave, a joint estimator is proposed to estimate the channel parameters. Therefore, the efficiency of the channel estimation can be improved and stringent delay requirements for the communication systems can also be satisfied. Simulation results show that system performance in terms of bit error rate (BER) is significantly improved with the proposed algorithm.
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Balcilar, Mehmet, Rangan Gupta, and Charl Jooste. "The dynamic response of the rand real exchange rate to fundamental shocks." Journal of Economic Studies 43, no. 1 (January 11, 2016): 108–21. http://dx.doi.org/10.1108/jes-08-2014-0148.
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Purpose – The authors analyse the relationship between the South African real exchange rate and economic fundamentals – demand, supply and nominal shocks. The paper aims to discuss these issues. Design/methodology/approach – The authors use a time-varying parameter VAR to study the coherence, conditional volatility and impulse responses of the exchange rate over specific periods and policy regimes. The model is identified using sign-restrictions that allow for some neutrality of impulse responses over contemporaneous and long horizons. Findings – The results suggest that the importance of fundamental shocks on the exchange rate is time dependent. Hence there is a loss in information when using standard linear models that average out effects over time. The response of the exchange rate to demand and supply shocks have weakened over the 1994-2010 period. Research limitations/implications – The period following financial crisis has strengthened the relationship between supply and demand shocks to the exchange rate, but has weakened the relationship between interest rate shocks and the exchange rate response. Practical implications – This paper provides deeper insight as to how the exchange rate responds to fundamental shocks. This should help monetary policy understand the consequences of interest rate decisions on the exchange rate and the indirect effect of inflation on the exchange rate. Originality/value – This application is new to the South African literature. The authors propose that the use of interest rates is limited in affecting the value of the rand exchange rate over particular periods. Isolating fundamental shocks to exchange rates over time helps policy makers make clearer and more informed decisions.
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Valadkhani, Abbas, and Russell Smyth. "Self-exciting effects of house prices on unit prices in Australian capital cities." Urban Studies 54, no. 10 (May 4, 2016): 2376–94. http://dx.doi.org/10.1177/0042098016643476.
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This paper examines the long- and short-run relationship between Australian house and unit prices across all capital cities over the period December 1995 to June 2015. We find that house and unit prices are cointegrated and, based on the results of Granger causality and generalised impulse responses, that house prices significantly influence unit prices across all cities. However, bi-directional causality (responses) exists only for major capital cities with the exception of Brisbane. We also, for the first time, apply self-excited threshold models to explore the complex interplay between house and unit prices in Australia. We find that when the market for units is self-excited, or bullish, the positive effects of house prices on unit prices are noticeably larger than otherwise. There is a varying degree of herd mentality in the Australian property market with Sydney and Darwin being the most and least ‘excitable’ capital cities, respectively.
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Lee, Doheon, and Densil Cabrera. "Effect of listening level and background noise on the subjective decay rate of room impulse responses: Using time-varying loudness to model reverberance." Applied Acoustics 71, no. 9 (September 2010): 801–11. http://dx.doi.org/10.1016/j.apacoust.2010.04.005.
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Kram, Sebastian, Maximilian Stahlke, Tobias Feigl, Jochen Seitz, and Jörn Thielecke. "UWB Channel Impulse Responses for Positioning in Complex Environments: A Detailed Feature Analysis." Sensors 19, no. 24 (December 16, 2019): 5547. http://dx.doi.org/10.3390/s19245547.
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Radio signal-based positioning in environments with complex propagation paths is a challenging task for classical positioning methods. For example, in a typical industrial environment, objects such as machines and workpieces cause reflections, diffractions, and absorptions, which are not taken into account by classical lateration methods and may lead to erroneous positions. Only a few data-driven methods developed in recent years can deal with these irregularities in the propagation paths or use them as additional information for positioning. These methods exploit the channel impulse responses (CIR) that are detected by ultra-wideband radio systems for positioning. These CIRs embed the signal properties of the underlying propagation paths that represent the environment. This article describes a feature-based localization approach that exploits machine-learning to derive characteristic information of the CIR signal for positioning. The approach is complete without highly time-synchronized receiver or arrival times. Various features were investigated based on signal propagation models for complex environments. These features were then assessed qualitatively based on their spatial relationship to objects and their contribution to a more accurate position estimation. Three datasets collected in environments of varying degrees of complexity were analyzed. The evaluation of the experiments showed that a clear relationship between the features and the environment indicates that features in complex propagation environments improve positional accuracy. A quantitative assessment of the features was made based on a hierarchical classification of stratified regions within the environment. Classification accuracies of over 90% could be achieved for region sizes of about 0.1 m 2 . An application-driven evaluation was made to distinguish between different screwing processes on a car door based on CIR measures. While in a static environment, even with a single infrastructure tag, nearly error-free classification could be achieved, the accuracy of changes in the environment decreases rapidly. To adapt to changes in the environment, the models were retrained with a small amount of CIR data. This increased performance considerably. The proposed approach results in highly accurate classification, even with a reduced infrastructure of one or two tags, and is easily adaptable to new environments. In addition, the approach does not require calibration or synchronization of the positioning system or the installation of a reference system.
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Yang, Xite, Jidi Cao, Zihan Liu, and Yongzeng Lai. "Environmental policy uncertainty and green innovation: A TVP-VAR-SV model approach." Quantitative Finance and Economics 6, no. 4 (2022): 604–21. http://dx.doi.org/10.3934/qfe.2022026.
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<abstract><p>This paper aims to measure the impacts of environmental policy uncertainty on green innovation and explore the transmission channel that is less understood in past scientific works. In this paper, we use a newspaper-based sentiment mining approach to establish an index of environmental policy uncertainty in China and implement web crawlers and text analysis techniques to construct a network public opinion index of the Chinese financial market. Then, we explore the relationships between environmental policy uncertainty, network public opinion, and green innovation through the time-varying parameter structural vector autoregressive with stochastic volatility (TVP-VAR-SV) model. The transmission channels of environmental policy uncertainty to green innovation are depicted by selecting different timing of policy release. Our empirical study results show that the fluctuations of environmental policy uncertainty, network public opinion, and green innovation have time-varying characteristics. Furthermore, the findings reveal interactions among the three variables: 1) The environmental policy uncertainty can influence green innovation through network public opinion. 2) The environmental policy uncertainty has both inhibited and promoted effects on network public opinion and green innovation. 3) There are differences in the direction and the degree of impulse responses among the above three variables in the context of uncertainty shocks. Besides, managerial relevance and policy implications are also provided for decision-makers facing sustainable development challenges.</p></abstract>
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Abbasi, Mustafa Z., Preston S. Wilson, and Ofodike A. Ezekoye. "Ray tracing and finite element modeling of sound propagation in a compartment fire." Journal of the Acoustical Society of America 151, no. 5 (May 2022): 3177–88. http://dx.doi.org/10.1121/10.0009800.
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A compartment fire (a fire in a room or building) creates temperature gradients and inhomogeneous time-varying temperature, density, and flow fields. This work compared experimental measurements of the room acoustic impulse/frequency response in a room with a fire to numerically modeled responses. The fire is modeled using a Fire Dynamics Simulator (FDS). Acoustic modeling was performed using the temperature field computed by FDS. Room acoustics were modeled using two-dimensional ray and finite element modeling. A three-dimensional model was used to simulate an open flame. COMSOLTM Multiphysics was used for finite element acoustic modeling and BELLHOPTM for ray trace acoustics modeling. The results show that the fire causes wave-fronts to arrive earlier (due to the higher sound speed) and with more variation in the delay times (due to the sound speed perturbations). The resonance frequencies of low-frequency modes were shifted upwards. Model results are compared with data and show good agreement in observed trends.
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Yang, Wenqi, Chenzi Yang, Bing Yang, and Guoqiang Feng. "Time-Varying Research on Investors’ Trading Psychology Rational and Irrational Market Sentiment Based on the Perspective of 5G Networks and Information Economics." Wireless Communications and Mobile Computing 2022 (February 25, 2022): 1–11. http://dx.doi.org/10.1155/2022/3594213.
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Amid the ongoing rapid digitalization, consistent advancements in technologies such as 5G have become crucial. The demand for 5G technologies is expected to surge owing to the continued hybrid work culture, and 5G stock will emerge from the stocks of older tech and telecom companies. However, the COVID-19 epidemic continues to spread globally, causing a major impact on China’s macroeconomy and the stock market. It has a significant impact on the trading behavior of investors in 5G stock. Based on the framework of information economics and 5G Networks, we use the TVP-VAR model to empirically analyze the time-varying effects of rational and irrational market sentiment on investor herd behavior and overconfidence. The results show that rational market sentiment can always suppress herding behavior and overconfidence, while irrational market sentiment intensifies investors’ herd behavior most of the time, suppressing overconfidence in the short term and turning it into a positive effect in the medium term, and its long-term effects have almost disappeared. Compared with rational market sentiment, irrational market sentiment has a more direct and significant impact on herd behavior. The absolute values of the impulse responses of both market sentiments to the impact of overconfidence are relatively close. In addition, both market sentiments have typical characteristics of vulnerability to investor psychology. After the epidemic spread, both market sentiments accelerate the generation of overconfidence, while the positive impact on herd behavior gradually decreases. Our research shows that in the environment of information asymmetry, although investors will restrain their irrational conformity psychology, they still have not demonstrated their reasonable investment capabilities. Our conclusions will provide some references for government regulatory agencies and market investors under the background of the epidemic.
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Pepperberg, David R., David G. Birch, and Donald C. Hood. "Photoresponses of human rods in vivo derived from paired-flash electroretinograms." Visual Neuroscience 14, no. 1 (January 1997): 73–82. http://dx.doi.org/10.1017/s0952523800008774.
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AbstractIn the human eye, domination of the electroretinogram (ERG) by the b−wave and other postreceptor components ordinarily obscures all but the first few milliseconds of the rod photoreceptor response to a stimulating flash. However, recovery of the rod response after a bright test flash can be analyzed using a paired-flash paradigm in which the test flash, presented at time zero, is followed at time t by a bright probe flash that rapidly saturates the rods (Birch et al., 1995). In ERG experiments on normal subjects, the hypothesis that a similar method can be used to obtain the full time course of the rod response to test flashes of subsaturating intensity was tested. Rod-only responses to probe flashes presented at varying times t after the test flash were used to derive a family of amplitudes A(t) that represented the putative rod response to the test flash. These rod-only responses to the probe flash were obtained by computational subtraction of the cone-mediated component of each probe flash response. With relatively weak test flashes (11–15 scot-td-s), the time course of the rod response to the test flash derived in this manner was consistent with a four-stage impulse response function of time-to-peak ≃170 ms. A(170), the amplitude of the derived response at 170 ms, increased with test flash intensity (Itest) to a maximum value Amo and exhibited a dependence on Itest given approximately by the relation, A(170)/Amo = 1 - exp(-kItest), where k = 0.092 (scot-td-s)−1. In steady background light, the falling (i.e. recovery) phase of the derived response began earlier, and the sensitivity parameter k was reduced several-fold from its dark-adapted value. As the sensitivity, kinetics, and light-adaptation properties of the derived response correspond closely with those of photocurrent flash responses previously obtained from isolated rods in vitro, it was concluded that the response derived here from the human ERG approximates the course of the massed in vivo rod response to a test flash.
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Lacquaniti, F., N. A. Borghese, and M. Carrozzo. "Transient reversal of the stretch reflex in human arm muscles." Journal of Neurophysiology 66, no. 3 (September 1, 1991): 939–54. http://dx.doi.org/10.1152/jn.1991.66.3.939.
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1. Load perturbation responses can violate the law of reciprocal innervation between antagonist muscles under particular conditions. Thus flexor and extensor muscles of wrist and elbow joints are reflexly coactivated by the impact of a ball on the hand during a catching task. The aim of this study was to determine whether reflex coactivation can be preset within the central nervous system (CNS) or whether it is entirely due to the peripheral stimulus. To this end, we studied the behavior of stretch reflex responses of arm muscles evoked by torque motor perturbations applied before and during the catching task. 2. Subjects were instructed to catch a ball dropped from 1.6 m. A torque motor delivered perturbations to the elbow joint, resulting in angular motion at both elbow and wrist joints because of their dynamic mechanical coupling. Two series of experiments were performed that differed in the perturbation waveform. In the first series, a single torque pulse could be randomly applied at different times during the task. The corresponding responses were recovered by subtracting the average of the unperturbed trials from the averages of perturbed trials. In the second series of experiments, a train of pseudorandom pulses was applied continuously during each trial. The time-varying impulse responses were computed at 20-ms intervals by cross-correlation methods. 3. The pattern of the short-latency electromyographic responses evoked by either single pulses or pseudorandom perturbations obeyed the law of reciprocal innervation of antagonist muscles under basal conditions. However, the pattern of the responses evoked by the same perturbations around the time of ball impact on the hand consisted of a substantial coactivation of both stretched and shortening muscles. Reflex coactivation resulted from response patterns that differed at different joints. At the elbow, reflex coactivation resulted from a transient reversal of the direction of the short-latency responses of flexor muscles, with little changes of the responses of extensor muscles. At the wrist, instead, reflex coactivation resulted from simultaneous changes in the response waveform of both flexor and extensor muscles. 4. The peripheral conditions associated with the applied perturbations were constant before the time of ball impact. Thus, because the changes of the stretch reflex responses began before that time, they must have been generated within the CNS. It is here hypothesized that the reversal of the reflex responses is centrally gated by switching from the pathways of reciprocal inhibition to those of coactivation of antagonist alpha-motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)
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Singh, Amanjot, and Manjit Singh. "Intertemporal risk-return relationship in BRIC equity markets after the US financial crisis." International Journal of Law and Management 59, no. 4 (July 10, 2017): 547–70. http://dx.doi.org/10.1108/ijlma-12-2015-0065.
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PurposeThis paper aims to attempt to capture the intertemporal/time-varying risk–return relationship in the Brazil, Russia, India and China (BRIC) equity markets after the global financial crisis (2007-2009), i.e. during a relative calm period. There has been a significant increase in advanced economies’ equity allocations to the emerging markets ever since the financial crisis. So, the present study is an attempt to account for the said relationship, thereby justifying investments made by the international investors. MethodologyThe study uses non-linear models comprising asymmetric component generalised autoregressive conditional heteroskedastic model in mean (CGARCH-M) (1,1) model, generalised impulse response functions under vector autoregressive framework and Markov regime switching in mean and standard deviation model. The span of data ranges from 1 July 2009 to 31 December 2014. FindingsThe ACGARCH-M (1,1) model reports a positive and significant risk-return relationship in the Russian and Chinese equity markets only. There is leverage and volatility feedback effect in the Russian market because falling returns further increase conditional variance making the investors to expect a risk premium in the expected returns. The impulse responses indicate that for all of the BRIC markets, the ex-ante returns respond positively to a shock in the long-term risk component, whereas the response is negative to a shock in the short-term risk component. Finally, the Markov regime switching model confirms the existence of two regimes in all of the BRIC markets, namely, Bull and Bear regimes. Both the regimes exhibit negative relationship between risk and return. Practical implicationsIt is an imperative task to comprehend the relationship shared between risk and returns for an investor. The investors in the emerging economies should understand the risk-return dynamics well ahead of time so that the returns justify the investments made under riskier environment. Originality/valueThe present study contributes to the literature in three senses. First, the data relate to a period especially after the global financial crisis (2007-2009). Second, the study has used a relatively newer version of GARCH based model [ACGARCH-M (1,1) model], generalised impulse response functions and Markov regime switching model to account for the relationship between risk and return. Finally, the study provides an insightful understanding of the risk–return relationship in the most promising emerging markets group “BRIC nations”, making the study first of its kind in all the perspectives.
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Abas, Zafar, Dong Ho Yang, Heung Soo Kim, Moon Kyu Kwak, and Jaehwan Kim. "Characterization of Electro-Active Paper Vibration Sensor by Impact Testing and Random Excitation." International Journal of Applied Mechanics 07, no. 04 (August 2015): 1550065. http://dx.doi.org/10.1142/s1758825115500659.
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We characterized a vibration sensor made of piezoelectric paper by measuring the frequency response function of an aluminum cantilever that was subjected to impulse loading and random excitation. The dynamic characteristics of the device were measured by recording the transient response of the smart cantilever beam with a pair of electro-active paper (EAPap) and polyvinylidene fluoride (PVDF) sensors located at a 5 mm distance from the clamped end as well as from a second pair of piezoelectric sensors located at a distance of 140 mm. The responses were measured by impacting the cantilever at its tip and at its mid-point. A fast Fourier transform was applied on the time domain data to measure the resonant frequencies of the vibrating structure. Both the EAPap and the PVDF sensors were observed to be very sensitive to varying levels of dynamic strain. The EAPap sensor showed a low strain sensitivity that was found to be desirable due to the inherent piezoelectricity and eco-friendly behavior of the material. The results revealed that the dynamic sensing ability of the EAPap at a low frequency range was quite comparable to that of PVDF when monitoring structural vibrations. The frequency response function was also measured via random excitation, piezoelectricity of the EAPap sensor shows potential for sensing vibrations with a dynamic response.
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Akhtman, J., and L. Hanzo. "Channel Impulse Response Tap Prediction for Time-Varying Wireless Channels." IEEE Transactions on Vehicular Technology 56, no. 5 (September 2007): 2767–69. http://dx.doi.org/10.1109/tvt.2007.900395.
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Kwon, Bo-Kyu. "An Exponentially Weighted Finite Impulse Response Filter for Discrete-time Linear Time-varying Systems." Journal of Institute of Control, Robotics and Systems 26, no. 8 (August 31, 2020): 669–74. http://dx.doi.org/10.5302/j.icros.2020.20.0088.
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Weathers, J. B., and Rogelio Luck. "Time-Varying Uncertainty in Shock and Vibration Applications Using the Impulse Response." Shock and Vibration 19, no. 3 (2012): 433–46. http://dx.doi.org/10.1155/2012/139309.
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Design of mechanical systems often necessitates the use of dynamic simulations to calculate the displacements (and their derivatives) of the bodies in a system as a function of time in response to dynamic inputs. These types of simulations are especially prevalent in the shock and vibration community where simulations associated with models having complex inputs are routine. If the forcing functions as well as the parameters used in these simulations are subject to uncertainties, then these uncertainties will propagate through the models resulting in uncertainties in the outputs of interest. The uncertainty analysis procedure for these kinds of time-varying problems can be challenging, and in many instances, explicit data reduction equations (DRE's), i.e., analytical formulas, are not available because the outputs of interest are obtained from complex simulation software, e.g. FEA programs. Moreover, uncertainty propagation in systems modeled using nonlinear differential equations can prove to be difficult to analyze. However, if (1) the uncertainties propagate through the models in a linear manner, obeying the principle of superposition, then the complexity of the problem can be significantly simplified. If in addition, (2) the uncertainty in the model parameters do not change during the simulation and the manner in which the outputs of interest respond to small perturbations in the external input forces is not dependent on when the perturbations are applied, then the number of calculations required can be greatly reduced. Conditions (1) and (2) characterize a Linear Time Invariant (LTI) uncertainty model. This paper seeks to explain one possible approach to obtain the uncertainty results based on these assumptions.
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Coulson, A. J., and R. Kakarala. "Excess delay estimation from time-varying mobile radio channel impulse response measurements." IEEE Communications Letters 3, no. 8 (August 1999): 239–41. http://dx.doi.org/10.1109/4234.781007.
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van de Kerkhof, L. M., and W. J. W. Kitzen. "Tracking of a time-varying acoustic impulse response by an adaptive filter." IEEE Transactions on Signal Processing 40, no. 6 (June 1992): 1285–94. http://dx.doi.org/10.1109/78.139235.
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Ward, Rabab K., and Bahaa E. A. Saleh. "Restoration of images distorted by systems of random time-varying impulse response." Journal of the Optical Society of America A 3, no. 6 (June 1, 1986): 800. http://dx.doi.org/10.1364/josaa.3.000800.
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Al-Samman, A. M., M. H. Azmi, T. A. Rahman, I. Khan, M. N. Hindia, and A. Fattouh. "Window-Based Channel Impulse Response Prediction for Time-Varying Ultra-Wideband Channels." PLOS ONE 11, no. 12 (December 19, 2016): e0164944. http://dx.doi.org/10.1371/journal.pone.0164944.
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Adeosun, Opeoluwa Adeniyi, Philip Akanni Olomola, Adebayo Adedokun, and Olumide Steven Ayodele. "Public investment and inclusive growth in Africa." International Journal of Social Economics 47, no. 12 (October 29, 2020): 1669–91. http://dx.doi.org/10.1108/ijse-05-2020-0333.
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PurposeThe increasing debate on the viability of broad-based productive employment in stimulating the participatory tendencies of growth makes it instructive to inquire how the African “Big Five” have fared in their quests to ensure growth inclusiveness through public investment-led fiscal policy.Design/methodology/approachTime varying structures and nonlinearities in the government investment series are captured through the non-linear autoregressive distributed lag, asymmetric impulse responses and variance decomposition estimation techniques.FindingsStudy findings show that positive investment shocks stimulate growth inclusiveness by enabling access to opportunities through job creation and productive employment for the populace; this result is evident for Morocco and Algeria. However, there is a non-negligible evidence that shocks due to decline in the government investment manifest in insufficient capital stocks and limited investment opportunities, impede access to opportunities by the populace, hinder labour employability and make growth less inclusive. Furthermore, all short-run findings corroborate long-run results regarding the reaction of inclusive growth to positive investment shocks with the exclusion of South Africa; which, unlike its long-run finding, shows that shocks due to increases in investment can foster growth inclusiveness. Also, in respect to short-run negative investment shocks, Nigeria is the only country that does not align its long-run findings.Practical implicationsThat public investment shocks make or mar inclusive growth effectiveness shows the need for appropriate fiscal policy consolidation and automatic stabilization guidelines to ensure buffers against shocks and to enhance government investment generation efficiency for a sustainable inclusive growth process that is more participatory in Africa.Originality/valueThis study is the first to accommodate possibilities of shocks in the inclusivity of growth analysis for the five biggest African economies which jointly account for over half of the recorded growth in the continent. As such, there is quantitative evidence that government investment is a potent determinant of growth inclusiveness and it is susceptible to structural changes and time variation of shocks.
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Kwon, Bo-Kyu. "A Time-varying Optimal Finite Impulse Response Filter Based Estimation of Short-time Fourier Coefficients." Journal of Institute of Control, Robotics and Systems 24, no. 1 (January 31, 2018): 6–11. http://dx.doi.org/10.5302/j.icros.2018.17.0201.
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Toledo de la Garza, Karel, Jorge Torres Gomez, Rodrigo C. de Lamare, and Maria Julia Fernandez-Getino Garcia. "A Variational Approach for Designing Infinite Impulse Response Filters With Time-Varying Parameters." IEEE Transactions on Circuits and Systems I: Regular Papers 65, no. 4 (April 2018): 1303–13. http://dx.doi.org/10.1109/tcsi.2017.2746747.
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Kocoń, Sławomir, and Jacek Piskorowski. "Time-Varying IIR Notch Filter with Reduced Transient Response Based on the Bézier Curve Pole Radius Variability." Applied Sciences 9, no. 7 (March 29, 2019): 1309. http://dx.doi.org/10.3390/app9071309.
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In this paper a concept of the second order digital infinite impulse response narrow band-reject filter with reduced transient response is proposed. In order to suppress the transient response of the considered infinite impulse response (IIR) notch filter its pole radius is temporarily varied in time using the Bézier parametric curve. Computer simulations verifying the effectiveness of the proposed pole-radius-varying notch filter are presented and compared to the performance of the traditional time-invariant filter using ECG signals distorted by unwanted powerline interference.
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Eaton, Perry A., and Gerald W. Hohmann. "An evaluation of electromagnetic methods in the presence of geologic noise." GEOPHYSICS 52, no. 8 (August 1987): 1106–26. http://dx.doi.org/10.1190/1.1442376.
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An important element of electromagnetic (EM) prospecting is survey design; numerical modeling algorithms may be used to calculate signal‐to‐geologic‐noise (S/N) ratios to compare different survey configurations and measured responses quantitatively. Our models consist of a prismatic three‐dimensional (3-D) target in a conductive half‐space which may contain an overburden conductor; the models are energized by a time‐varying current transmitted in a loop of wire. The signal is the scattered or anomalous response of the target, while the geologic noise is either the response of the half‐space or the anomalous response of the overburden conductor. For typical loop sizes in exploration, the coincident‐loop configuration has a relatively high S/N ratio and thus a relatively high capability to resolve the target in the case of half‐space noise. Measurements made with the horizontal‐loop, moving‐coil configuration can be just as effective if the coil separation is one and one‐half to two times the depth of burial of the target and the transmitting and receiving coils are on opposite sides of the target. For coil positions on one side of the target, the S/N ratio decreases with increasing separation. The advantage in resolving power provided by the coincident loop’s superior S/N ratio diminishes as the size of the loop increases. For the case of noise due to the overburden conductor, the horizontal‐loop configuration with a large coil separation is optimal. If the depth of the target is unknown, the fixed‐loop, roving‐receiver configuration is useful for detecting the target but poor in resolving its depth because its S/N ratio is the least sensitive to the depth. With the fixed‐loop configuration, galvanic effects enhance the detectability of the target in a conductive half‐space, but inhibit detection if an overburden conductor is present. Regarding the S/N ratio, there does not appear to be any advantage in measuring the step response of a 3-D target in a conductive environment versus measuring the impulse response. The shapes of their respective S/N anomalies are essentially the same and the maximum impulse S/N ratio is 10 to 30 percent larger than the maximum step S/N ratio, though it occurs later in time by a factor of about 1.7. Although transient S/N ratios for a 3-D target in a conductive host reach a maximum value and then decrease with increasing time, harmonic S/N ratios do not necessarily reach a maximum value at an intermediate frequency. For all three survey configurations and both types of noise, target depths, and half‐space conductivities studied here, maximum transient S/N ratios are larger than harmonic S/N ratios. Peak step S/N ratios are 30 to 50 percent larger than corresponding in‐phase ratios in the case of half‐space noise, and several times larger in the case of the overburden conductor. A phase rotation of the target’s response due to the conductive host appears to amplify the quadrature S/N ratio relative to the in‐phase S/N ratio. However, in‐phase S/N ratios are always much larger than quadrature S/N ratios over the range of host resistivities used in this study.
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Kwon, Bo-Kyu. "Harmonic Estimation of Power Signal Based on Time-varying Optimal Finite Impulse Response Filter." Journal of Korean Institute of Information Technology 16, no. 11 (November 30, 2018): 97–103. http://dx.doi.org/10.14801/jkiit.2018.16.11.97.
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Wang, Yuanyuan, and Peter J. Fish. "Simulating nonstationary in-phase and quadrature Doppler signals using a time-varying impulse response filter." Ultrasound in Medicine & Biology 22, no. 4 (January 1996): 529–31. http://dx.doi.org/10.1016/0301-5629(96)88019-7.
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Tomislav Barić, Zijad Haznadar, and Sead Berberović. "PARAMETERS AFFECTING THE TRANSIENT RESPONSE OF VERTICAL PIPE ELECTRODES TO IMPULSE EXCITATION." Journal of Energy - Energija 57, no. 2 (October 11, 2022): 226–45. http://dx.doi.org/10.37798/2008572323.
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In this article, an application of the transmission line theory is presented for analyzing various parameters that affect the transient response of ground electrodes. In order to simplify the presentation and the interpretation of the results obtained, a vertical buried pipe electrode was chosen as the ground electrode. The ground electrode is connected to a grounding conductor, the upper part of which is connected to an ideal current source. The impact of the overhead geometry of the grounding conductor upon the transient response of the ground electrode is analyzed by varying the length of the grounding conductor. The ideal current source generates a normalized wave shape current impulse, a so-called double exponential impulse. The effect of the time to peak of the impulse (steepness of the rising edge of the peak current) on the transient response of the ground electrode is analyzed by varying the current wave shape parameters. The impact of soil parameters on the transient response of the ground electrode is also analyzed. The soil is modeled as a single-layer homogeneous isotropic semispace. The soil-air boundary is represented by a plane. The results obtained are presented graphically and discussed.
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Wu, Yutao, Shuai Liu, Yueyang Li, and Zhonghua Wang. "Fault estimation of linear discrete time-varying systems with multiplicative noise based on finite impulse response filter." Transactions of the Institute of Measurement and Control 42, no. 3 (October 6, 2019): 461–71. http://dx.doi.org/10.1177/0142331219874229.
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This paper aims to construct a finite impulse response (FIR) based fault estimator for a class of linear discrete time-varying systems (LDTV) with multiplicative noise. Drawing support of intensive stochastic analyses and matrix manipulations, a novel performance index is proposed such that the fault estimation error is minimized in stochastic sense. A necessary and sufficient condition is established to guarantee the existence of the FIR-based fault estimator with satisfied estimation accuracy. The optimal gain of the desired fault estimator is calculated in an analytical way by minimizing the aforementioned performance index. Several examples are presented to demonstrate the effectiveness and superiority of the proposed methods.
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Grechka, Vladimir, and Ilya Tsvankin. "3-D moveout velocity analysis and parameter estimation for orthorhombic media." GEOPHYSICS 64, no. 3 (May 1999): 820–37. http://dx.doi.org/10.1190/1.1444593.
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Orthorhombic symmetry describes several azimuthally anisotropic models typical for fractured formations, such as those containing two orthogonal crack systems or parallel vertical cracks in a VTI (transversely isotropic with a vertical symmetry axis) background. Here, we present a methodology for inverting multiazimuth P-wave reflection traveltimes for the parameters of vertically inhomogeneous orthorhombic media. Our approach is based on the general analytic representation of normal‐moveout (NMO) velocity as an ellipse in the horizontal plane. A minimum of three differently oriented common‐midpoint (CMP) lines (or a “wideazimuth” 3-D survey) is needed to reconstruct the ellipse and thus obtain NMO velocity in any azimuthal direction. Then, the orientation and the semiaxes of the NMO ellipse, which are dependent on both anisotropy and heterogeneity, can be inverted for the medium parameters. Our analytic and numerical study shows that for the model of a homogeneous orthorhombic layer above a dipping reflector, the exact P-wave NMO velocity is determined by the symmetry‐plane orientation and five parameters: the NMO velocities from a horizontal reflector measured in the symmetry planes [[Formula: see text]] and three anisotropic coefficients η(1,2,3) introduced by analogy with the Alkhalifah‐Tsvankin parameter η for VTI media. The importance of the medium parameterization in terms of the η coefficients goes well beyond the NMO-velocity function. By generating migration impulse responses, we demonstrate that the parameters [Formula: see text] and η(1,2,3) are sufficient to perform all time processing steps (normal‐moveout and dip‐moveout corrections, prestack and poststack time migration) in orthorhombic models. The velocities [Formula: see text] and the orientation of the vertical symmetry planes can be found using the azimuthally dependent NMO velocity from a horizontal reflector. Then the NMO ellipse of at least one dipping event is additionally needed to obtain the coefficients η(1,2,3) that control the dip dependence of normal moveout. We discuss the stability of the inversion procedure and specify the constraints on the dip and azimuth of the reflector; for instance, for all three η coefficients to be resolved individually, the dip plane of the reflector should not coincide with either of the symmetry planes. To carry out parameter estimation in vertically inhomogeneous orthorhombic media, we apply the generalized Dix equation of Grechka, Tsvankin and Cohen, which operates with the matrices responsible for interval NMO ellipses rather than with the NMO velocities themselves. Our algorithm is designed to find the interval values of [Formula: see text] and η(1,2,3) using moveout from horizontal and dipping reflectors measured at different vertical times (i.e., only surface P-wave data are needed). Application to a synthetic multiazimuth P-wave data set over a layered orthorhombic medium with depth‐varying orientation of the symmetry planes verifies the accuracy of the inversion method.
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Kwon, Bokyu, and Sang-il Kim. "Recursive Optimal Finite Impulse Response Filter and Its Application to Adaptive Estimation." Applied Sciences 12, no. 5 (March 7, 2022): 2757. http://dx.doi.org/10.3390/app12052757.
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In this paper, the recursive form of an optimal finite impulse response filter is proposed for discrete time-varying state-space models. The recursive form of the finite impulse response filter is derived by employing finite horizon Kalman filtering with optimally estimated initial conditions. The horizon initial state and its error covariance on the horizon are optimally estimated by using recent finite measurements, in the sense of maximum likelihood estimation, then initiating the finite horizon Kalman filter. The optimality and unbiasedness of the proposed filter are proved by comparison with the conventional optimal finite impulse response filter in batch form. Moreover, an adaptive FIR filter is also proposed by applying the adaptive estimation scheme to the proposed recursive optimal FIR filter as its application. To evaluate the performance of the proposed algorithms, a computer simulation is performed to compare the conventional Kalman filter and adaptive Kalman filters for the gas turbine aircraft engine model.
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Khalili, Seyyed Mohammad Reza, K. Malekzadeh, and A. Davar. "Dynamic Response of Functionally Graded Circular Cylindrical Shells." Advanced Materials Research 47-50 (June 2008): 608–11. http://dx.doi.org/10.4028/www.scientific.net/amr.47-50.608.
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In this paper the response of circular cylindrical shell made of Functionally Graded Material (FGM) subjected to lateral impulse load was investigated. The effective material properties are assumed to vary continuously along the thickness direction according to a volume fraction power law distribution. First order shear deformation theory (FSDT) and Love's first approximation theory were utilized in the equilibrium equations. The boundary condition was considered to be simply supported. Displacement components are product of functions of position and time. Equilibrium equations for free and forced vibrations were solved using the Galerkin method. The impulse load in the form of time varying uniform pressure was applied onto a small rectangular area of the shell surface. The function of time for displacement components is obtained using the results of free vibration and convolution integral. Finally time response of displacement components is derived using mode superposition method. The influence of material composition (power law exponent), geometrical parameters (length to radius and radius to thickness ratios) and load parameters (position and size of the area of the applied load and peak pressure value for different pulse type) on the dynamic response was investigated.
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Rapanová, Nina, and Ján Kortiš. "Numerical Simulation of Pavement Response to Dynamic Load." Transport and Telecommunication Journal 14, no. 3 (September 1, 2013): 230–36. http://dx.doi.org/10.2478/ttj-2013-0020.
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Road structures are loaded by heavy vehicles and also they have an influence of temperature changes, which cause a difficult stress and strain distribution over layers of the pavement and the subgrade. Knowing this, distribution of stress and strain can help to better understand the behaviour of the pavement during the service time. For this purpose, the mechanical characteristics like elastic modulus, Poisson ratio, or damping ratio have to be known. The special device is used for determination of these mechanical characteristics, which loads the surface of the pavement by a force impulse. The deflections are measured in the surroundings of point of load impulse. The signal can be evaluated by use of 2D or 3D calculation model of pavement construction. In this case was used the axially-symmetric 2D model. This reduced the time consumption of individual tasks solution. The article considers also the influence of boundary conditions on deflections of models with varying width. The following text describes findings acquired from numerical simulation of pavement response to dynamic load.
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Orłowski, Przemysław. "Linear parameter varying, finite impulse response filter design with application to reducing rise-time for rapid signal changes." IFAC Proceedings Volumes 42, no. 19 (2009): 115–19. http://dx.doi.org/10.3182/20090921-3-tr-3005.00022.
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He, Rong, and Hong Zhou. "Time-Domain Substructure Transient Vibration Transfer Path Analysis Based on Time-Varying Frequency Response Functions under Operational Excitations." Shock and Vibration 2019 (March 28, 2019): 1–16. http://dx.doi.org/10.1155/2019/2030326.
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The time-domain substructure inverse matrix method has become a popular method to detect and diagnose problems regarding vehicle noise, vibration, and harshness, especially for those impulse excitations caused by roads. However, owning to its reliance on frequency response functions (FRFs), the approach is effective only for time-invariable linear or weak nonlinear systems. This limitation prevents this method from being applied to a typical vehicle suspension substructure, which shows different nonlinear characteristics under different wheel transient loads. In this study, operational excitation was considered as a key factor and applied to calculate dynamic time-varying FRFs to perform accurate time-domain transient vibration transfer path analysis (TPA). The core idea of this novel method is to divide whole coupled substructural relationships into two parts: one involved time-invariable components; normal FRFs could be obtained through tests directly. The other involved numerical computations of the time-domain operational loads matrix and FRFs matrix in static conditions. This method focused on determining dynamic FRFs affected by operational loads, especially the severe transient ones; these loads are difficult to be considered in other classical TPA approaches, such as operational path analysis with exogenous inputs (OPAX) and operational transfer path analysis (OTPA). Experimental results showed that this new approach could overcome the limitations of the traditional time-domain substructure TPA in terms of its strict requirements within time-invariable systems. This is because in the new method, time-varying FRFs were calculated and used, which could make the FRFs at the system level directly adapt to time-varying systems from time to time. In summary, the modified method extends TPA objects studied in time-invariable systems to time-varying systems and, thus, makes a methodology and application innovation compared to traditional the time-domain substructure TPA.