Journal articles: 'High frequency averaging'

1

Giannoulis, Johannes, Alexander Mielke, and Christof Sparber. "High-frequency averaging in semi-classical Hartree-type equations." Asymptotic Analysis 70, no. 1-2 (2010): 87–100. http://dx.doi.org/10.3233/asy-2010-1007.

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Dolganov, M. V. "High-frequency sampling error of averaging digital phase meters." Measurement Techniques 30, no. 4 (April 1987): 379–82. http://dx.doi.org/10.1007/bf00864771.

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Mouzaoui, Lounès. "High-frequency averaging in the semi-classical singular Hartree equation." Asymptotic Analysis 84, no. 3-4 (2013): 229–45. http://dx.doi.org/10.3233/asy-131175.

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Tahmasian, Sevak, David W. Allen, and Craig A. Woolsey. "On averaging and input optimization of high-frequency mechanical control systems." Journal of Vibration and Control 24, no. 5 (July 6, 2016): 937–55. http://dx.doi.org/10.1177/1077546316655706.

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This paper presents the optimization of input amplitudes for mechanical control-affine systems with high-frequency, high-amplitude inputs. The problem consists of determining the input waveform shapes and the relative phases between inputs to minimize the input amplitudes while accomplishing some control objective. The effects of the input waveforms and relative phases on the dynamics are investigated using averaging. It is shown that of all zero-mean, periodic functions, square waves require the smallest amplitudes to accomplish a control objective. Using the averaging theorem the problem of input optimization is transformed into a constrained optimization problem. The constraints are algebraic nonlinear equalities in terms of the amplitudes of the inputs and their relative phases. The constrained optimization problem may be solved using analytical or numerical methods. A second approach uses finite Fourier series to solve the input optimization problem. This second approach confirms the earlier results concerning minimum amplitude inputs and is then applied to the problem of minimizing control energy.

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Pandey, Vishakha, and V. K. Giri. "Removal of High Frequency Noise from the ECG Signal Using Averaging Filters." i-manager's Journal on Digital Signal Processing 3, no. 3 (September 15, 2015): 7–14. http://dx.doi.org/10.26634/jdp.3.3.3590.

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Wang, Chengyang, and Yoshihiko Nishiyama. "Volatility forecast of stock indices by model averaging using high-frequency data." International Review of Economics & Finance 40 (November 2015): 324–37. http://dx.doi.org/10.1016/j.iref.2015.02.014.

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Levenshtam, V. B. "The averaging method in the convection problem with high-frequency oblique vibrations." Siberian Mathematical Journal 37, no. 5 (September 1996): 970–82. http://dx.doi.org/10.1007/bf02110727.

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Lecomte, Christophe. "A frequency averaging framework for the solution of complex dynamic systems." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2166 (June 8, 2014): 20130743. http://dx.doi.org/10.1098/rspa.2013.0743.

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A frequency averaging framework is proposed for the solution of complex linear dynamic systems. It is remarkable that, while the mid-frequency region is usually very challenging, a smooth transition from low- through mid- and high-frequency ranges is possible and all ranges can now be considered in a single framework. An interpretation of the frequency averaging in the time domain is presented and it is explained that the average may be evaluated very efficiently in terms of system solutions.

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Antonakakis, T., and R. V. Craster. "High-frequency asymptotics for microstructured thin elastic plates and platonics." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, no. 2141 (February 8, 2012): 1408–27. http://dx.doi.org/10.1098/rspa.2011.0652.

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We consider microstructured thin elastic plates that have an underlying periodic structure, and develop an asymptotic continuum model that captures the essential microstructural behaviour entirely in a macroscale setting. The asymptotics are based upon a two-scale approach and are valid even at high frequencies when the wavelength and microscale length are of the same order. The general theory is illustrated via one- and two-dimensional model problems that have zero-frequency stop bands that preclude conventional averaging and homogenization theories. Localized defect modes created by material variations are also modelled using the theory and compared with numerical simulations.

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Levenshtam, V. B. "Justification of the averaging method for the convection problem with high-frequency vibrations." Siberian Mathematical Journal 34, no. 2 (1992): 280–96. http://dx.doi.org/10.1007/bf00970954.

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STAFFORD, PETER J., JOANNE COOPER, and CLIFFORD J. GARRATT. "Improved Recovery of High Frequency P Wave Energy by Selective P Wave Averaging." Pacing and Clinical Electrophysiology 19, no. 8 (August 1996): 1225–29. http://dx.doi.org/10.1111/j.1540-8159.1996.tb04193.x.

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Levenshtam, V. B. "Some questions of averaging theory for parabolic equations with large high-frequency summands." Doklady Mathematics 74, no. 3 (December 2006): 827–30. http://dx.doi.org/10.1134/s1064562406060111.

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Liu, Zhi, Xiaochao Xia, and Guoliang Zhou. "Pre-averaging estimate of high dimensional integrated covariance matrix with noisy and asynchronous high-frequency data." Random Matrices: Theory and Applications 07, no. 03 (June 19, 2018): 1850005. http://dx.doi.org/10.1142/s2010326318500053.

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With rapid development of the global market, the number of financial securities has significantly grown, which greatly challenges the measuring of financial quantities. Among others, the estimation of covariance matrix which plays an important role in risk management becomes no longer accurate. In this paper, we consider the estimation of integrated covariance matrix of semi-martingales under framework of high dimension by using high frequency data. We assume that the multivariate asset prices are observed asynchronously and all the observed prices are contaminated by microstructure noise. We employ the pre-averaging method to remove the microstructure noise and the generalized synchronization method to deal with the non-synchronicity. Moreover, to avoid the inconsistency in the high-dimensional covariance matrix estimation, we propose a regularized estimate. The consistency under matrix [Formula: see text]-norm is established. Compared to existing results, our estimator improves the accuracy of the estimation. Finally, we assess the theoretical results via some simulation studies.

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Yan, Fuyong, De-Hua Han, Tongcheng Han, and Xue-Lian Chen. "Comparison of seismic anisotropy of sedimentary strata at low- and high-frequency limits." GEOPHYSICS 85, no. 1 (November 22, 2019): MR1—MR10. http://dx.doi.org/10.1190/geo2018-0677.1.

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The layer-induced seismic anisotropy of sedimentary strata is frequency-dependent. At the low-frequency limit, the effective anisotropic properties of the layered media can be estimated by the Backus averaging model. At the high-frequency limit, the apparent anisotropic properties of the layered media can be estimated by ray theory. First, we build a database of laboratory ultrasonic measurement on sedimentary rocks from the literature. The database includes ultrasonic velocity measurements on sandstones and carbonate rocks, and velocity-anisotropy measurements on shales. Then, we simulate the sedimentary strata by randomly selecting a certain number of rock samples and using their laboratory measurement results to parameterize each layer. For each realization of the sedimentary strata, we estimate the effective and apparent seismic anisotropy parameters using the Backus average and ray theory, respectively. We find that, relative to Backus averaging, ray theory usually underestimates the Thomsen parameters [Formula: see text] and [Formula: see text], and overestimates [Formula: see text]. For an effective layered medium consisting of isotropic sedimentary rocks, the differences are significant. These differences decrease when shales with intrinsic seismic anisotropy are included. For the same sedimentary strata, the seismic wave should perceive stronger seismic anisotropy than the ultrasonic wave.

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Guo, Xinxing, Yanfeng Qiu, Bo Liu, Weicheng Kong, Tao Liu, Ruifang Dong, and Shougang Zhang. "A High-Precision Transfer of Time and RF Frequency via the Fiber-Optic Link Based on Secure Encryption." Applied Sciences 12, no. 13 (June 30, 2022): 6643. http://dx.doi.org/10.3390/app12136643.

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This paper presents a high-precision transfer system of time and RF frequency via the fiber optic link based on secure encryption. On the basis of the two-way time transfer of optical fiber, a security strategy composed of an SM2 encryption algorithm is introduced, which can resist the security risk of time information being tampered with. The experimental results show that the developed picosecond-precision fiber-optic time transfer equipment can ensure high stability while realizing the encryption function. Time synchronization stability in terms of time deviation (TDEV) of 1 PPS can reach around 10.7 ps at 1 s and 7.1 ps at 10 s averaging time. The stability of the 10 MHz frequency can reach around 4.7 × 10−12 at 1 s and 1.1 × 10−12 at 10 s averaging time. There is no significant difference in time transfer accuracy, compared with unencrypted conditions. Furthermore, this paper realizes a ring time transfer network via a 150 km fiber-optic link with three nodes using three devices. The TDEV of 1PPS can reach around 20.8 ps at 1s averaging time. This paper provides a reference to establish a high-precision, safe, and stable time synchronization fiber network in the future.

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Suttner, Raik, and Sergey Dashkovskiy. "Robustness and averaging properties of a large-amplitude, high-frequency extremum seeking control scheme." Automatica 136 (February 2022): 110020. http://dx.doi.org/10.1016/j.automatica.2021.110020.

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Oon, F. E., and Rainer Dumke. "Compact single-seed, module-based laser system on a transportable high-precision atomic gravimeter." AVS Quantum Science 4, no. 4 (December 2022): 044401. http://dx.doi.org/10.1116/5.0119151.

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A single-seed, module-based compact laser system is demonstrated on a transportable [Formula: see text]-based high-precision atomic gravimeter. All the required laser frequencies for the atom interferometry are provided by free-space acousto-optic modulators (AOMs) and resonant electro-optic phase modulators (EOMs). The optical phase-locked loop between the two optical paths derived from the same laser provides an easy frequency manipulation between two laser frequencies separated by the hyperfine frequency of 6.835 GHz using an AOM and an EOM, respectively. Our scheme avoids parasite Raman transitions present in the direct EOM modulation scheme (modulating directly at the frequency of the hyperfine splitting), which have detrimental effects on the accuracy of the gravity measurements. The optical phase-locked loop also provides a convenient way for vibration compensation through the Raman lasers' phase offset. Furthermore, the modular design approach allows plug-and-play nature on each individual optic module and also increases the mechanical stability of the optical systems. We demonstrate high-precision gravity measurements with 17.8 [Formula: see text] stability over 250 s averaging time and 2.5 [Formula: see text] stability over 2 h averaging time.

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Unger, Stephan. "The Volume-Price Relationship at the High-Frequency Scale: Evidence From DCC-GARCH." Journal of Prediction Markets 12, no. 3 (February 13, 2019): 23–39. http://dx.doi.org/10.5750/jpm.v12i3.1592.

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This article investigates the time-varying high-frequency price-volume relationship from two perspectives. At the high-frequency time scale, we show that the time varying conditional correlation between price and volume changes exhibits distinct excitational spike regimes that provide a rich set of patterns unexplored before. Impulse response analysis based on a high-frequency Vector-autoregressive specification show that volume has greater impact on price than vice versa. Our results therefore suggests that volume can be seen as a proxy for information flows. Due to market micro-structure contamination, we show that smoothing and pre-averaging is necessary to uncover the high-frequency relationship between price and volume.

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Stovas, Alexey, and Børge Arntsen. "Vertical propagation of low-frequency waves in finely layered media." GEOPHYSICS 71, no. 3 (May 2006): T87—T94. http://dx.doi.org/10.1190/1.2197488.

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Multiple scattering in finely layered sediments is important for interpreting stratigraphic data, matching well-log data with seismic data, and seismic modeling. Two methods have been used to treat this problem in seismic applications: the O’Doherty-Anstey approximation and Backus averaging. The O’Doherty-Anstey approximation describes the stratigraphic-filtering effects, while Backus averaging defines the elastic properties for an effective medium from the stack of the layers. It is very important to know when the layered medium can be considered as an effective medium. In this paper, we only investigate vertical propagation. Therefore, no anisotropy effect is taken into consideration. Using the matrix-propagator method, we derive equations for transmission and reflection responses from the stack of horizontal layers. From the transmission response, we compute the phase velocity and compare the zero-frequency limit with the effective-medium velocity from Backus averaging. We also investigate how the transition from time-average medium to effective medium depends on contrast; i.e., strength of the reflection-coefficient series. Using numerical examples, we show that a transition zone exists between the effective medium (low-frequency limit) and the time-average medium (high-frequency limit), and that the width of this zone depends on the strength of the reflection-coefficient series.

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Aliev, Yu M., B. M. Jovanović, and A. A. Frolov. "Generation of quasi-stationary magnetic fields by external electromagnetic radiation in a cold magneto-active plasma." Journal of Plasma Physics 49, no. 1 (February 1993): 51–54. http://dx.doi.org/10.1017/s0022377800016809.

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Starting from the hydrodynamic equations for a cold electron fluid, we develop a theory of the ponderomotive effect of the interaction of high-frequency electromagnetic radiation with a magneto-active plasma. Using the method of averaging on high-frequency oscillations, we obtain expressions for the low- frequency nonlinear currents. We also obtain an equation describing the space–time evolution of a quasi-stationary magnetic field in the plasma.

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THOMSEN, JON JUEL. "SLOW HIGH-FREQUENCY EFFECTS IN MECHANICS: PROBLEMS, SOLUTIONS, POTENTIALS." International Journal of Bifurcation and Chaos 15, no. 09 (September 2005): 2799–818. http://dx.doi.org/10.1142/s0218127405013721.

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Strong high-frequency excitation (HFE) may change the "slow" (i.e. effective or average) properties of mechanical systems, e.g. their stiffness, natural frequencies, equilibriums, equilibrium stability, and bifurcation paths. This tutorial describes three general HFE effects: Stiffening — an apparent change in the stiffness associated with an equilibrium; Biasing — a tendency for a system to move towards a particular state which does not exist or is unstable without HFE; and Smoothening — a tendency for discontinuities to be apparently smeared out by HFE. The effects and a method for analyzing them are introduced, first in terms of simple physical examples, and then in generalized form for mathematical models covering broad classes of discrete and continuous mechanical systems. Several application examples are summarized. Three mathematical tools for analyzing HFE effects are described and compared: The Method of Direct Separation of Motions, the Method of Averaging, and the Method of Multiple Scales. The tutorial concludes with a suggestion that more vibration experts, researchers and students should be aware of HFE effects, for the benefit of general vibration troubleshooting, and also for furthering the creation of innovative technical devices and processes utilizing HFE effects.

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Berdnikov, A. S., A. N. Verenchikov, and A. G. Kuzmin. "On the Correct Averaging of the Equations of Ion Motion in High-Frequency Electric Fields." Journal of Analytical Chemistry 74, no. 14 (December 2019): 1378–89. http://dx.doi.org/10.1134/s106193481914003x.

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Wang, X. H., and C. S. Poon. "Spectral vs. compartmental averaging of VA/Q distributions: confidence limits." Journal of Applied Physiology 70, no. 3 (March 1, 1991): 1290–99. http://dx.doi.org/10.1152/jappl.1991.70.3.1290.

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We have investigated the method of statistical averaging as a nonparametric approach to obtain a representative ventilation-perfusion (VA/Q) distribution that exemplifies the family of compatible solutions for multiple inert gas elimination data. The variability of the compatible solutions was examined by determining the standard deviation of the statistical average. For six inert gases, it can be predicted that a distribution with up to seven contiguous nonzero VA/Q compartments can be uniquely recovered, whereas the compatible family becomes more diverse, the broader the distribution. For a given compatible family consisting of multimodal distributions with various phase relationships, the average distribution was found to display an uncharacteristically unimodal shape as a result of modal smoothing. To avoid this possible artifact, an alternative approach was adopted in which statistical averaging was performed in the frequency domain. For both deterministic and empirical data, the energy spectra of all feasible VA/Q distributions displayed a well-defined low-frequency band that was invariant within the compatible family and with a bandwidth that approximated the predicted sampling cutoff frequency. The nonuniqueness of the result was ascribable to a variable high-frequency band that was due to an aliasing effect. For a wide range of clinical data, the representative distributions resulting from compartmental and spectral averaging were indistinguishable from each other and had little variability both in the VA/Q and frequency domains. For these cases, therefore, the resolving power of the recovery algorithm was not critical. Finally, an efficient method of finding the average distribution was proposed.

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Mahmud, Md Rasel, Ahmed F. Abdou, and Hemanshu Pota. "Stability Analysis of Grid-Connected Photovoltaic Systems with Dynamic Phasor Model." Electronics 8, no. 7 (July 2, 2019): 747. http://dx.doi.org/10.3390/electronics8070747.

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The typical layout of power systems is experiencing significant change, due to the high penetration of renewable energy sources (RESs). The ongoing evaluation of power systems is expecting more detailed and accurate mathematical modeling approaches for RESs which are dominated by power electronics. Although modeling techniques based on state–space averaging (SSA) have traditionally been used to mathematically represent the dynamics of power systems, the performance of such a model-based system degrades under high switching frequency. The multi-frequency averaging (MFA)-based higher-index dynamic phasor modeling tool is proposed in this paper, which is entirely new and can provide better estimations of dynamics. Dynamic stability analysis is presented in this paper for the MFA-based higher-index dynamical model of single-stage single-phase (SSSP) grid-connected photovoltaic (PV) systems under different switching frequencies.

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Wang, Enlong, Guochao Wang, Xiao Yu, Kang Ying, Mingyue Yang, Xu Zhang, Xuan Li, Shuhua Yan, Jun Yang, and Lingxiao Zhu. "Agile offset frequency locking for single-frequency fiber lasers." Review of Scientific Instruments 93, no. 8 (August 1, 2022): 083002. http://dx.doi.org/10.1063/5.0089303.

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Single frequency fiber lasers (SFFLs) have seen increasing applications in state-of-the-art quantum technologies, which usually require precise and stable offset frequency locking (OFL). However, limited by the piezoelectric transducer bandwidth in SFFLs and the loop bandwidth of the OFL, the large-gap jumping between two locked offset frequencies will take an undesirable amount of time. In order to diminish that consuming time, we developed an agile offset frequency locking system based on a hybrid loop of a feed-forward path and a feedback path. In accordance with the experimental demonstration, we characterized the performances of the offset frequency locking system, as frequency-locking stability with an Allan deviation of 3.2 × 10−14 at 1 s averaging time and jumping agility with a duration of 0.6 ms at 1.3 GHz frequency gap, which is a factor of 60 faster than that without the feed-forward path. This mechanism can find direct applications in existing quantum metrology experiments with SFFLs where high-speed frequency jumping or sweeping is needed.

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Shim, Jeong-Min, Young-Bo Kim, and Chang-Ki Kang. "Artifact Reduction in Compressed Sensing Averaging Techniques for High-Resolution Magnetic Resonance Images." Applied Sciences 11, no. 21 (October 20, 2021): 9802. http://dx.doi.org/10.3390/app11219802.

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This study aims to introduce a new compressed sensing averaging (CSA) technique for the reduction of blurring and/or ringing artifacts, depending on the k-space sampling ratio. A full k-space dataset and three randomly undersampled datasets were obtained for CSA images in a brain phantom and a healthy subject. An additional simulation was performed to assess the effect of the undersampling ratio on the images and the signal-to-noise ratios (SNRs). The image sharpness, spatial resolution, and contrast between tissues were analyzed and compared with other CSA techniques. Compared to CSA with multiple acquisition (CSAM) at 25%, 35%, and 45% undersampling, the reduction rates of the k-space lines of CSA with keyhole (CSAK) were 10%, 15%, and 22%, respectively, and the acquisition time was reduced by 16%, 23%, and 32%, respectively. In the simulation performed with a full sampling k-space dataset, the SNR decreased to 10.41, 9.80, and 8.86 in the white matter and 9.69, 9.35, and 8.46 in the gray matter, respectively. In addition, the ringing artifacts became substantially more predominant as the number of sampling lines decreased. The 50% modulation transfer functions were 0.38, 0.43, and 0.54 line pairs per millimeter for CSAM, CSAK with high-frequency sharing (CSAKS), and CSAK with high-frequency copying (CSAKC), respectively. In this study, we demonstrated that the smaller the sampling line, the more severe the ringing artifact, and that the CSAKC technique proposed to overcome the artifacts that occur when using CSA techniques did not generate artifacts, while it increased spatiotemporal resolution.

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Boudjellaba, H., and T. Sari. "Oscillations in a Prey-Predator-Superpredator System." Journal of Biological Systems 06, no. 01 (March 1998): 17–33. http://dx.doi.org/10.1142/s0218339098000066.

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The behaviour of a food chain with three populations of the type prey-predator-superpredator is studied in the case where the growth rates of the three populations are highly diversified. The analysis shows that the system can have high-frequency oscillations, due to the interaction between prey and predator, which arise during a low-frequency cycle, due to the interaction between predator and superpredator. Using an averaging method, the dynamics of the superpredator is determined, during the high-frequency oscillations of the prey and predator.

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Tushev, O. N., and D. S. Chernov. "Pendulum Quasi-Static Drift Effect at Suspension Point Excitation by High-Frequency Polyharmonic Multiple Frequency Vibration." Herald of the Bauman Moscow State Technical University. Series Natural Sciences, no. 5 (98) (October 2021): 4–16. http://dx.doi.org/10.18698/1812-3368-2021-5-4-16.

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The paper dwells upon the dynamic behavior of a 2d pendulum under polyharmonic vibration. The study shows that the angles between the vertical coordinate axis and the directions of the individual harmonic components effects are generally different. Relying on the well-known approach, we solved the problem in two approximations. The movement of the pendulum contains two components: the "low-frequency" component and the "high-frequency" one. As the frequencies are not multiple, the movement is essentially an aperiodic process. Hence, when deriving the basic relations, it is impossible to use an effective method of averaging the solution within a period of fast oscillations. Dividing the solution by the frequencies of oscillations, we obtained an equation describing the slow motion and an approximate formula based on it for determining the pendulum quasi-static displacement, i.e., the "drift effect". The result is generalized by taking energy dissipation into account. Findings of research show that near the quasi-static position of the pendulum, loss of stability is possible as a result of parametric resonance at the combination frequencies of the external action. The paper gives an example in which an approximate solution is compared with an exact numerical simulation and shows the results of this comparison

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Grebenikov, E. A. "Concerning New Perturbation Methods in Solar System Dynamics." International Astronomical Union Colloquium 165 (1997): 399–404. http://dx.doi.org/10.1017/s0252921100046868.

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In this paper a new method of construction of the perturbation motion theory of celestial bodies, based on the averaging principle in view of frequency resonances, is stated. The first approximation of the asymptotic theory is the exact solution of the dynamics averaging equations, in which are included “secular” and “long-periodic” terms. The high-degree approximations are the exact solution of a known Krylov-Bogoliubov generalized equation. It is shown that these iterations are expressed in the analytical form by multiple Fourier series.

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Tan, C. Y., W. K. Ngui, M. S. Leong, and M. H. Lim. "Blade fault diagnosis using empirical mode decomposition based feature extraction method." MATEC Web of Conferences 255 (2019): 06009. http://dx.doi.org/10.1051/matecconf/201925506009.

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Blade fault diagnosis had become more significant and impactful for rotating machinery operators in the industry. Many works had been carried out using different signal processing techniques and artificial intelligence approaches for blade fault diagnosis. Frequency and wavelet based features are usually used as the input to the artificial neural network for blade fault diagnosis. However, the application of others time-frequency based feature extraction technique and artificial intelligence approach for blade fault diagnosis is still lacking. In this study, a novel blade fault diagnosis method based on ensemble empirical mode decomposition and extreme learning machine was developed. Bandpass filtering was applied to the raw vibration signals and integrated with the high pass filter to obtain the velocity signal. Synchronous time averaging was then applied to the velocity signals. Three ensemble empirical mode decomposition based feature extraction methods were proposed: direct statistical parameters extraction, intrinsic mode functions averaging statistical parameters extraction and features averaging statistical parameters extraction. The effectiveness of different feature vector sets for blade fault diagnosis was examined. Feature vector set of intrinsic mode functions averaging statistical parameters extraction was found to be more effective for blade fault diagnosis. With the novel proposed method, blade fault diagnosis could be more accurate and precise.

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Hill, Frank, Douglas Gough, Juri Toomre, and Deborah A. Haber. "Solar equatorial rotation rate inferred from inversion of frequency splitting of high-degree modes." Symposium - International Astronomical Union 123 (1988): 45–48. http://dx.doi.org/10.1017/s0074180900157705.

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The equatorial rotation rate has been inferred as a function of depth through the outer 16 Mm of the Sun from observations of high-degree five-minute oscillations. An optimal averaging inversion procedure due to Backus & Gilbert (1970) has been applied to frequency splittings measured from power spectra obtained using Doppler data spanning three and five consecutive days. The resulting rotation curves have proven to be much more stable than the curves obtained from data sets of single days. The results imply that the solar rotation rate increases with depth by 0.023 μHz reaching a maximum at about 2 Mm below the surface, then decreases by 0.037 μHz down to 16 Mm.

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Yu, Haoyang, Qian Zhou, Xinghui Li, Xiaohao Wang, Xilin Wang, and Kai Ni. "Improving Resolution of Dual-Comb Gas Detection Using Periodic Spectrum Alignment Method." Sensors 21, no. 3 (January 29, 2021): 903. http://dx.doi.org/10.3390/s21030903.

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Dual-comb spectroscopy has been an infusive spectroscopic tool for gas detection due to its high resolution, high sensitivity, and fast acquisition speed over a broad spectral range without any mechanical scanning components. However, the complexity and cost of high-performance dual-comb spectroscopy are still high for field-deployed applications. To solve this problem, we propose a simple frequency domain post-processing method by extracting the accurate position of a specific absorption line frame by frame. After aligning real-time spectra and averaging for one second, the absorbance spectrum of H13C14N gas in the near-infrared is obtained over 1.1 THz spectral range. By using this method, the standard deviation of residual error is only ~0.002, showing great agreement with the conventional correction method. In addition, the spectral resolution is improved from 13.4 GHz to 4.3 GHz compared to direct spectrum averaging. Our method does not require a specially designed common-mode suppression comb, rigorous frequency control system, or complicated computational algorithm, providing a cost-effective scheme for field-deployed Doppler-limited spectroscopy applications.

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Chua, Chew Lian, Sandy Suardi, and Sarantis Tsiaplias. "Predicting short-term interest rates using Bayesian model averaging: Evidence from weekly and high frequency data." International Journal of Forecasting 29, no. 3 (July 2013): 442–55. http://dx.doi.org/10.1016/j.ijforecast.2012.10.003.

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Plujko, V. A., O. M. Gorbachenko, K. M. Solodovnyk, and V. M. Petrenko. "Reconstruction of high-energy part of the gamma-ray spectrum in thermal neutron capture by 113Cd." Nuclear Physics and Atomic Energy 22, no. 3 (September 25, 2021): 221–29. http://dx.doi.org/10.15407/jnpae2021.03.221.

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The average gamma-ray spectrum of 114Cd after thermal neutron capture in 113Cd was evaluated in units of mb/MeV. Two approaches are considered for estimation of the average gamma-ray spectrum with normalization of the experimental data: mean spectra for all gamma-energies were found by averaging frequency polygon for experimental data histogram, and mean spectra were estimated as the combination of theoretical values at low gamma-ray energies and averaging experimental data in high-energy range. The experimental spectra were evaluated from the gamma-intensities presented by Mheemeed et al. [A. Mheemeed et al. Nucl. Phys. A 412 (1984) 113] and Belgya et al. [T. Belgya et al. EPJ Web of Conf. 146 (2017) 05009]. They were normalized to the average theoretical spectrum which was calculated using EMPIRE and TALYS codes. The procedure of normalization of the high-energy part of the spectrum was described. Estimated gamma-spectra for 113Cd(n, {xγ}) reaction induced by thermal neutrons were presented.

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BAL, GUILLAUME, GEORGE PAPANICOLAOU, and LEONID RYZHIK. "SELF-AVERAGING IN TIME REVERSAL FOR THE PARABOLIC WAVE EQUATION." Stochastics and Dynamics 02, no. 04 (December 2002): 507–31. http://dx.doi.org/10.1142/s0219493702000522.

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We analyze the self-averaging properties of time-reversed solutions of the paraxial wave equation with random coefficients, which we take to be Markovian in the direction of propagation. This allows us to construct an approximate martingale for the phase space Wigner transform of two wave fields. Using a prioriL2-bounds available in the time-reversal setting, we prove that the Wigner transform in the high frequency limit converges in probability to its deterministic limit, which is the solution of a transport equation.

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Varon, Daniel J., Dylan Jervis, Jason McKeever, Ian Spence, David Gains, and Daniel J. Jacob. "High-frequency monitoring of anomalous methane point sources with multispectral Sentinel-2 satellite observations." Atmospheric Measurement Techniques 14, no. 4 (April 12, 2021): 2771–85. http://dx.doi.org/10.5194/amt-14-2771-2021.

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Abstract. We demonstrate the capability of the Sentinel-2 MultiSpectral Instrument (MSI) to detect and quantify anomalously large methane point sources with fine pixel resolution (20 m) and rapid revisit rates (2–5 d). We present three methane column retrieval methods that use shortwave infrared (SWIR) measurements from MSI spectral bands 11 (∼ 1560–1660 nm) and 12 (∼ 2090–2290 nm) to detect atmospheric methane plumes. The most successful is the multi-band–multi-pass (MBMP) method, which uses a combination of the two bands and a non-plume reference observation to retrieve methane columns. The MBMP method can quantify point sources down to about 3 t h−1 with a precision of ∼ 30 %–90 % (1σ) over favorable (quasi-homogeneous) surfaces. We applied our methods to perform high-frequency monitoring of strong methane point source plumes from a well-pad device in the Hassi Messaoud oil field of Algeria (October 2019 to August 2020, observed every 2.5 d) and from a compressor station in the Korpezhe oil and gas field of Turkmenistan (August 2015 to November 2020, observed every 5 d). The Algerian source was detected in 93 % of cloud-free scenes, with source rates ranging from 2.6 to 51.9 t h−1 (averaging 9.3 t h−1) until it was shut down by a flare lit in August 2020. The Turkmen source was detected in 40 % of cloud-free scenes, with variable intermittency and a 9-month shutdown period in March–December 2019 before it resumed; source rates ranged from 3.5 to 92.9 t h−1 (averaging 20.5 t h−1). Our source-rate retrievals for the Korpezhe point source are in close agreement with GHGSat-D satellite observations for February 2018 to January 2019, but provide much higher observation density. Our methods can be readily applied to other satellite instruments with coarse SWIR spectral bands, such as Landsat-7 and Landsat-8. High-frequency satellite-based detection of anomalous methane point sources as demonstrated here could enable prompt corrective action to help reduce global methane emissions.

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Elzenheimer, Eric, Helmut Laufs, Tilmann Sander-Thömmes, and Gerhard Schmidt. "Magnetoneurograhy of an Electrically Stimulated Arm Nerve." Current Directions in Biomedical Engineering 4, no. 1 (September 1, 2018): 363–66. http://dx.doi.org/10.1515/cdbme-2018-0087.

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AbstractFor further development and optimization of novel uncooled magnetoelectric (ME) sensors, a better understanding of spectral power distribution and signal strength of nerve signals is of high interest. For obtaining information on these signal properties, Superconducting Quantum Interference Device (SQUID) measurements were performed at the Physikalisch-Technische Bundesanstalt (PTB) in Berlin. Signal amplitudes were subject-dependent and ranged from 17 fT to 60 fT in a frequency range from 100 Hz to 1 kHz. The required SQUID averaging time was in the range of minutes, while for current ME sensors significantly longer averaging times are expected to be necessary.

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Huan, R. H., W. Q. Zhu, F. Ma, and Z. H. Liu. "The Effect of High-Frequency Parametric Excitation on a Stochastically Driven Pantograph-Catenary System." Shock and Vibration 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/792673.

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In high-speed electric trains, a pantograph is mounted on the roof of the train to collect power through contact with an overhead catenary wire. The effect of fast harmonic and parametric excitation on a stochastically driven pantograph-catenary system is studied in this paper. A single-degree-of-freedom model of the pantograph-catenary system is adopted, wherein the stiffness of the nonlinear spring has a time-varying component characterized by both low and high frequencies. Using perturbation and harmonic averaging, a Fokker-Planck-Kolmogorov equation governing the stationary response of the pantograph-catenary system is set up. Based on the transition probability density of the stationary response, it is found that even small high-frequency parametric excitation has an appreciable effect on the system response. Among other things, it shifts the resonant frequency and often changes the response characteristics markedly.

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39

Hsu, K., and R. Burridge. "Effects of averaging and sampling on the statistics of reflection coefficients." GEOPHYSICS 56, no. 1 (January 1991): 50–58. http://dx.doi.org/10.1190/1.1442957.

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The reflection coefficients derived from sonic and density logs are frequently used in seismic exploration. Even though they measure the in‐situ formation slowness and density, sonic and density tools do not measure the exact, continuous formation properties but locally averaged properties sampled at discrete depth points. Furthermore, the logs are frequently reinterpolated to form a Goupillaud medium for many applications such as synthetic seismogram computation. Both the logging tools and the Goupillaud interpolation introduce averaging and sampling effects into the reflection coefficients and significantly alter the autocorrelation of the reflection coefficient sequence. Analytical formulas are derived to show how the autocorrelation is altered and to calculate how the autocorrelation depends on the averaging and sampling intervals. Essentially, these effects impose sincsquared envelopes on the power spectrum of the reflection coefficient sequence and alias high‐frequency components to low‐frequency components in the spectral domain. These findings are verified using synthetic and real examples.

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Mitraszewski, P., P. Penczek, and W. Grochulski. "Application of Combined Median- Averaging Filters to Scintigraphic Image Processing." Nuklearmedizin 24, no. 04 (1985): 164–68. http://dx.doi.org/10.1055/s-0038-1624297.

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SummaryStatistical and deterministic properties of median filters are briefly discussed and their inherent advantages as a prospective tool in scintigraphic data processing are pointed out. The ability of median filters of suppressing impulse noise while the edge-like features of an image are preserved, is demonstrated on phantom data. The residual high-frequency noise remaining after median filtering can be subsequently reduced by standard smoothing procedures. A simple algorithm, made up of the superposition of a median and an averaging filter, is presented and shown to be a promising candidate in the quest for fast and easy-to-implement processing routine.

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Minullin, R. G., E. I. Lukin, F. T. Shaikhutdinov, and R. G. Khalilov. "An averaging method for identification of location probing signals in the high-frequency channel of transmission lines." Russian Electrical Engineering 83, no. 1 (January 2012): 30–34. http://dx.doi.org/10.3103/s1068371212010099.

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Qi Yang, N. Kaneda, Xiang Liu, and W. Shieh. "Demonstration of Frequency-Domain Averaging Based Channel Estimation for 40-Gb/s CO-OFDM With High PMD." IEEE Photonics Technology Letters 21, no. 20 (October 2009): 1544–46. http://dx.doi.org/10.1109/lpt.2009.2029554.

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Dahl, Nicolai J., Ahmed M. Ammar, Arnold Knott, and Michael A. E. Andersen. "An Improved Linear Model for High-Frequency Class-DE Resonant Converter Using the Generalized Averaging Modeling Technique." IEEE Journal of Emerging and Selected Topics in Power Electronics 8, no. 3 (September 2020): 2156–66. http://dx.doi.org/10.1109/jestpe.2019.2945182.

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Zhang, Shuang, Hao Qiao, Di Ai, Min Zhou, and Xinye Xu. "Frequency stabilization of multiple wavelength lasers based on a broadband spectrum." Laser Physics Letters 19, no. 9 (July 27, 2022): 095701. http://dx.doi.org/10.1088/1612-202x/ac8283.

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Abstract We report on frequency stabilization of multiple wavelength lasers operating at 1389 and 1695 nm simultaneously on a broadband spectrum. These lasers are implemented in ytterbium optical lattice clock experiments, which need to have a narrow enough linewidth and maintain high long-term frequency stability. A 1560 nm femtosecond mode-locked laser with a narrow mode spacing of 250 MHz is used as a master laser, which is referenced to a local ultrastable optical cavity with the instability better than 1 × 10−15 at 1 s averaging time. Through the combination of erbium-doped fiber amplifier and high nonlinear fiber, the spectral width of the maser laser is broadened from 10 nm to more than 300 nm. The range of the broadened spectrum can cover 1389 and 1695 nm. Meanwhile, the spectral intensity at the corresponding wavelength can ensure that the signal-to-noise ratio of the beat signals between the two lasers and the broadened spectrum is about 30 dB at a resolution bandwidth (RBW) of 100 kHz. After phase locking the 1389 and 1695 nm lasers on the broadband spectrum, the residual linewidths are obtained to be about 0.8 Hz at 1 Hz RBW, and the stabilities are 3.5 × 10−16 and 4.7 × 10−16 at 1 s averaging time respectively, improving about six orders of magnitude. Our result can be conducive to obtaining the stabilized laser sources for the atomic optical clock, and will be of great significance for simplifying and miniaturizing the optical clock system.

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Love, J. J., V. C. Tsai, and J. L. Gannon. "Averaging and sampling for magnetic-observatory hourly data." Annales Geophysicae 28, no. 11 (November 12, 2010): 2079–96. http://dx.doi.org/10.5194/angeo-28-2079-2010.

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Abstract. A time and frequency-domain analysis is made of the effects of averaging and sampling methods used for constructing magnetic-observatory hourly data values. Using 1-min data as a proxy for continuous, geomagnetic variation, we construct synthetic hourly values of two standard types: instantaneous "spot" measurements and simple 1-h "boxcar" averages. We compare these average-sample types with others: 2-h average, Gaussian, and "brick-wall" low-frequency-pass. Hourly spot measurements provide a statistically unbiased representation of the amplitude range of geomagnetic-field variation, but as a representation of continuous field variation over time, they are significantly affected by aliasing, especially at high latitudes. The 1-h, 2-h, and Gaussian average-samples are affected by a combination of amplitude distortion and aliasing. Brick-wall values are not affected by either amplitude distortion or aliasing, but constructing them is, in an operational setting, relatively more difficult than it is for other average-sample types. It is noteworthy that 1-h average-samples, the present standard for observatory hourly data, have properties similar to Gaussian average-samples that have been optimized for a minimum residual sum of amplitude distortion and aliasing. For 1-h average-samples from medium and low-latitude observatories, the average of the combination of amplitude distortion and aliasing is less than the 5.0 nT accuracy standard established by Intermagnet for modern 1-min data. For medium and low-latitude observatories, average differences between monthly means constructed from 1-min data and monthly means constructed from any of the hourly average-sample types considered here are less than the 1.0 nT resolution of standard databases. We recommend that observatories and World Data Centers continue the standard practice of reporting simple 1-h-average hourly values.

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Ide, Hideto, and Masafumi Uchida. "Analysis of Somatosensory Evoked Potentials by Tactile Board Stimuli Skin." Journal of Robotics and Mechatronics 8, no. 4 (August 20, 1996): 378–82. http://dx.doi.org/10.20965/jrm.1996.p0378.

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Up to now, the analysis of the event-related potential has been carried out by the averaging method or the frequency analysis method. However, the averaging method is defective in that high-frequency off-phased components tend to cancel each other out and so detailed information may easily be lost. On the other hand, in the frequency analysis, time-axis information may easily be lost. In addition, in the past analysis of data, the amount of fluctuation represented by the 1/f power spectrum has been treated in its entirety as noise. Novertheless, nonlinear phenomena as represented by chaos of fractals indicate the possibility of quantification in numerical analysis. In this paper, the fractal analysis of event-related potential is carried out, and its results are used to examine fluctuational conditions in intellectual activity. In addition, peaks equivalent to N100 or P300 did not show up clearly. This is considered to be because fractal analysis is more suited to the detection of variations in the inducement amount rather than that of peaks.

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Zhou, Chun. "Control Lorenz System with Vibration Estimation with Averaging Method." Applied Mechanics and Materials 43 (December 2010): 36–39. http://dx.doi.org/10.4028/www.scientific.net/amm.43.36.

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The vibrational control theory stems from the well-known of stabilization of the upper unstable equilibrium position of the inverted pendulum having suspension point vibration along the vertical line with amplitude as small as desired and a frequency reason high. Chaotic phenomena have been found in many nonlinear systems including continuous time and discrete time. The chaotic systems are characterized by their extreme sensitivity to initial conditions, nonperiodic and boundary. The trajectories start even from close initial states will diverge from each other at an exponential rate as time goes. The vibrational control method was applied to Lorenz system. The effect of the control can be estimated with the APAZ method. It was showed that vibrational control brought the controlled Lorenz system to stable equilibrium with appropriate parameters. Numerical simulation demonstrated validity of the proposed method.

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Costa e Silva, Mercia Betania, and Alexey Stovas. "Correspondence between the low- and high-frequency limits for anisotropic parameters in a layered medium." GEOPHYSICS 74, no. 2 (March 2009): WA25—WA33. http://dx.doi.org/10.1190/1.3075143.

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Wave propagation in a layered medium when the wavelength is much greater than each layer thickness (low frequency) produces a response equivalent to that of wave propagation in an equivalent single-layer medium. This equivalent medium is transversely isotropic with symmetry about a vertical axis (VTI), and the elastic parameters are computed with the Backus averaging technique. Conversely, when the wavelength is comparable to each layer thickness (high frequency), the directional dependence of the phase velocity in the transmission response also can be simulated by replacing the layered medium with a single homogeneous medium with properties derived from a time average. It then can be treated approximately as a VTI medium. To compute the medium parameters, a method based on fitting the traveltime parameters is used. We investigated the relationship between Thomsen’s anisotropic parameters [Formula: see text] and [Formula: see text] computed for the equivalent medium in the low-frequency limit and for the homogenized medium in the high-frequency limit. In our experiments, we used a medium in which layers of only two isotropic materials alternate repeatedly. For the high-frequency limit, we obtained solutions for PP- and SS-wave propagation.

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A, Parivazhagan, and Dr Brintha Therese.A. "Face Recognition Using Location Averaging and Intensity’s Position Estimation Techniques for Human Authentication." International Journal of Engineering & Technology 7, no. 4.10 (October 2, 2018): 24. http://dx.doi.org/10.14419/ijet.v7i4.10.20697.

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Face recognition is an effective tool in the biometric human recognition system. In this competitive world, several techniques and systems are emerging to satisfy the needs of the face recognition system’s performance. To obtain the high-performance ratio novel techniques are combined and created a new face recognition system. Spatial domain techniques like Gray averaging technique, Location averaging technique and Intensity’s position estimation technique are united with frequency domain technique like Discrete Cosine Transform. Intensity’s position estimation is a novel feature extraction and classification technique proposed in this work. Three standard face databases are tested using this system. Accuracy and runtime are major parameters used to validate the obtained results. The maximum accuracy rate of about 86% is obtained.

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Weyssow, B., and R. Balescu. "Hamiltonian theory of the generalized oscillation-centre transformation." Journal of Plasma Physics 39, no. 1 (February 1988): 81–102. http://dx.doi.org/10.1017/s0022377800012873.

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The theory of the slow reaction of a charged particle in the combined presence of a strong quasi-static magnetic field and a high-frequency electromagnetic field (generalized oscillation-centre motion) is constructed by using a Hamiltonian formalism with non-canonical variables and pseudo-canonical transformations. The theory combines the features studied in our previous works for the case in which only one of the previously mentioned fields is present. The new averaging transformation is based on the fact that the Larmor frequency of the quasi-static field is of the same order as the external frequency of the high-frequency field. Our theory is manifestly gauge-invariant and involves only physical quantities (particle velocity and electromagnetic fields). Explicit expressions for the drift velocity of the oscillation centre and for the ponderomotive force are derived.

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Journal articles on the topic 'High frequency averaging'

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