Artículos de revistas: "Time-domain analysis. Frequency selective surfaces"

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Skinner, Neal G. y Dale M. Byrne. "Finite-difference time-domain analysis of frequency-selective surfaces in the mid-infrared". Applied Optics 45, n.º 9 (20 de marzo de 2006): 1943. http://dx.doi.org/10.1364/ao.45.001943.

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Qing, Anyong. "VECTOR SPECTRAL-DOMAIN METHOD FOR THE ANALYSIS OF FREQUENCY SELECTIVE SURFACES". Progress In Electromagnetics Research 65 (2006): 201–32. http://dx.doi.org/10.2528/pier06091401.

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Wang, D. X., E. K. N. Yung y R. S. Chen. "Spectral domain analysis of frequency-selective surfaces on biaxially anisotropic substrate". IET Microwaves, Antennas & Propagation 1, n.º 2 (2007): 335. http://dx.doi.org/10.1049/iet-map:20060003.

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4

Xue, Wei, Chen Liu, Nan Zhu y Xiao Xiang He. "Electromagnetic Analysis of Frequency Selective Surfaces Using the SSED Method". Applied Mechanics and Materials 130-134 (octubre de 2011): 1365–69. http://dx.doi.org/10.4028/www.scientific.net/amm.130-134.1365.

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The Simplified sub-entire domain (SSED) basis function method has been introduced and modified to analyze some planar and curved Frequency selective surfaces (FSSs) with finite size. The number of unknowns and memory consumption of the methods are discussed in detail. The reflection coefficients and transmission coefficients are given, which agree well with the reference results.

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Yahaghi, A., A. Fallahi, H. Abiri, M. Shahabadi, C. Hafner y R. Vahldieck. "Analysis of Frequency Selective Surfaces on Periodic Substrates Using Entire Domain Basis Functions". IEEE Transactions on Antennas and Propagation 58, n.º 3 (marzo de 2010): 876–86. http://dx.doi.org/10.1109/tap.2009.2039327.

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6

Rogier, Hendrik, Daniël De Zutter y Frank Olyslager. "Rigorous analysis of frequency selective surfaces of finite extent using a hybrid finite difference time domain-boundary integral equation technique". Radio Science 35, n.º 2 (marzo de 2000): 483–94. http://dx.doi.org/10.1029/1999rs001911.

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7

Yu, Yan Xin, Chun Yang Wang, Yan Jun Sun y Wen Ting Jiang. "Study on Analysis and Simulation of Novel Frequency Selective Surfaces". Advanced Materials Research 1049-1050 (octubre de 2014): 790–93. http://dx.doi.org/10.4028/www.scientific.net/amr.1049-1050.790.

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Frequency selective surface (FSS) is a two-dimensional periodic structure. It exhibits total reflection and transmission in the neighborhood of the element resonances. As it performs as a filter, FSS is widely used in the fields of microwave and optics. In this paper, the finite element method is used to analysis frequency selective surface and study on the feasibility of Ansoft HFSS software for frequency selective surface simulation. Hexagonal element of frequency selective surface is as an example to explore the simulation method and the process of Ansoft HFSS. Through the comparison of the simulation curves and the measured curves of hexagonal element frequency selective surface film by photoetching technology, the simulation method of Ansoft HFSS software for frequency selective surface is correct. At the same time, this paper further verified the reliability of the simulation through the example of the ring and the cross unit structure.

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8

Mai, Wending, Benjamin Zerbe y Douglas Werner. "Discontinuous Galerkin Time Domain Method with Dispersive Modified Debye Model and its Application to the Analysis of Optical Frequency Selective Surfaces". Applied Computational Electromagnetics Society 36, n.º 1 (27 de febrero de 2021): 27–34. http://dx.doi.org/10.47037/2020.aces.j.360104.

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We develop a discontinuous Galerkin time domain (DGTD) algorithm with an experimentally validated modified Debye model (MDM) to take metal dispersion into consideration. The MDM equation is coupled with Maxwell’s equations and solved together through the auxiliary differential equation (ADE) method. A Runge-Kutta time-stepping scheme is proposed to update the semi-discrete transformed Maxwell’s equations and ADEs with high order accuracy. Then we employ the proposed algorithm to analyze an infinite doubly periodic frequency selective surface (FSS) operating in the optical regime that exhibits transmission enhancement due to the surface plasmatic effect. The accuracy and the efficiency enhancements are validated through a comparison with commercial simulation software. This work represents the first integration of MDM with DGTD, which enables the DGTD algorithm to efficiently analyze metallic structures in the optical regime.

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9

Wang, Quan-Quan, Hong-Bo Zhu, Ru-Shan Chen y Yun-Qin Hu. "Analysis of finite frequency selective surfaces backed by dielectric substrate using sub-entire-domain basis function method". COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 34, n.º 4 (6 de julio de 2015): 1144–55. http://dx.doi.org/10.1108/compel-08-2014-0205.

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Purpose – Analysis of the frequency selective surface (FSS) is of great significance. In the method of moments, when the electric size of the FSS increases, huge in-core memory and CPU time are required. The purpose of this paper is to efficiently analyze the finite FSS backed by dielectric substrate utilizing sub-entire-domain (SED) basis function method. Design/methodology/approach – Different types of SED basis functions are generated according to the locations of the cells in the entire structure, and a reduced system is constructed and solved. The couplings of all cells of the FSS are taken into account by using Green’s function and Galerkin’s test procedure. The spatial Green’s function is obtained with the discrete complex image method. The reflection and transmission coefficients of the FSS are calculated using the far field of the FSS and the metallic plate with the same size. Findings – Moderate problems of the finite FSS backed by dielectric substrate are solved with the SED basis function method. The original problem can be simplified to two smaller problems. It enables a significant reduction to the matrix size and storage, and efficient analysis of FSS can be performed. The band-stop type of FSS can be composed of periodic conductive patch cells on the dielectric substrate, and shows total reflection property at the resonant frequency. Originality/value – The SED basis function method is mostly used to analyze periodic PEC structures in free space. The layered medium Green’s function is successfully employed and several dielectric substrate backed finite FSSs are discussed in this paper. The calculation of reflection and transmission coefficients, which are more effective rather than far field scattering of the FSS, are described.

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Don, Nataliya, Maurizio Bozzi, Anatoly Kirilenko y Luca Perregrini. "Analysis of inductive frequency selective surfaces by the method of moments with entire-domain basis functions". Microwave and Optical Technology Letters 49, n.º 12 (2007): 2929–32. http://dx.doi.org/10.1002/mop.22923.

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Zheglov, L. F. y A. B. Fominykh. "The Choice of Evaluation Vibration Car Security". Mechanical Engineering and Computer Science, n.º 12 (11 de febrero de 2019): 1–14. http://dx.doi.org/10.24108/1218.0001441.

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In the presented material of the article the debatable question - a question of a choice of the field of mathematical modeling of system of vibration isolation of the car is considered. It is known that such a problem can be solved in the frequency and time domain. Since the primary vibration isolation system of the car has non-linear elements, the question arises: how does the solution of the linearized dynamic system in the frequency domain correspond to the data of calculations of the accepted indicators in the time domain? The problem is solved with a random kinematic perturbation from the road surface. Therefore, when working in the time domain, it is necessary to pre-select the method of statistical linearization from the known in practice design of automatic control systems.Four methods of statistical linearization, using which calculations were carried out in the frequency domain, are considered. For a similar dynamic system with its initial and statistically linearized nonlinear elements, calculations were carried out in the time domain. It is shown that the first method of statistical linearization is the most adaptive, according to the amplitude-frequency characteristics of the system. Such calculations were carried out for two surfaces corresponding to the cobblestone and dirt road at different speeds of the car.The analysis of the calculated amplitude-frequency characteristics was carried out for the "resonant" speed of motion, at which the greatest manifestation of the system nonlinearity takes place. When driving in this mode, the system significantly increases the probability of losing contact with the tire support surface. This violates the safety of the vehicle and the system is out of the vibration safety analysis area. Especially this phenomenon is observed when driving on a dirt road at a "resonant" speed. The final results of the calculations are separate-frequency and integral parameters. The latter do not give priority in the selection of the area of calculation, provided the safety of the vehicle.Thus, it can be concluded that the adequacy of the calculations in the frequency and time domain under really specified conditions of the vehicle on the corresponding road surface. However, testing of the problem to be solved, for example, by the eigenfrequency vector of a conservative system, is advisable to be carried out in the frequency domain.

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Boix, R. R., M. J. Freire y F. Medina. "New Method for the Efficient Summation of Double Infinite Series Arising From the Spectral Domain Analysis of Frequency Selective Surfaces". IEEE Transactions on Antennas and Propagation 52, n.º 4 (abril de 2004): 1080–94. http://dx.doi.org/10.1109/tap.2004.825671.

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O'Regan, C., R. A. Kenny, H. Cronin, C. Finucane y P. M. Kearney. "Antidepressants strongly influence the relationship between depression and heart rate variability: findings from The Irish Longitudinal Study on Ageing (TILDA)". Psychological Medicine 45, n.º 3 (30 de julio de 2014): 623–36. http://dx.doi.org/10.1017/s0033291714001767.

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BackgroundHeart rate variability (HRV) is known to be reduced in depression; however, is unclear whether this is a consequence of the disorder or due to antidepressant medication.MethodsWe analysed data on 4750 participants from the first wave of The Irish Longitudinal Study on Ageing (TILDA). Time [standard deviation of normal to normal intervals (SDNN ms2)] and frequency domain [low frequency (LF) and high frequency (HF)] measures of HRV were derived from 3-lead surface electrocardiogram records obtained during 10 min of supine rest. Depression was assessed using the Center for Epidemiologic Studies – Depression scale.ResultsParticipants on antidepressants [with (n = 80) or without depression (n = 185)] differed significantly from controls (not depressed and not taking antidepressants n = 4107) on all measures of HRV. Depressed participants not taking antidepressants (n = 317) did not differ from controls on any measures of HRV. In linear regression analysis adjusted for relevant factors all antidepressants were associated with lower measures HRV. Participants on selective serotonin reuptake inhibitors (SSRIs) had higher measures of HRV relative to participants on tricyclic antidepressants or serotonin–norepinephrine reuptake inhibitors respectively.ConclusionsOur results suggest that reductions in HRV observed among depressed older adults are driven by the effects of antidepressant medications. SSRIs have less impact on HRV than other antidepressants but they are still associated with lower measures of HRV. Study limitations include the use of a self-report measure of depression and floor effects of age on HRV could have limited our ability to detect an association between HRV and depression.

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Viruega, Hélène, Inès Gaillard, Laura Briatte y Manuel Gaviria. "Inter-Day Reliability and Changes of Surface Electromyography on Two Postural Muscles Throughout 12 Weeks of Hippotherapy on Patients with Cerebral Palsy: A Pilot Study". Brain Sciences 10, n.º 5 (6 de mayo de 2020): 281. http://dx.doi.org/10.3390/brainsci10050281.

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Cerebral palsy (CP) is an umbrella term covering a group of permanent developmental disorders of movement and posture characterized by highly variable clinical features. The aim of this study was to assess the short-term and mid-term effects of neurorehabilitation via hippotherapy on the contractile properties of two key postural muscles during functional sitting in such patients. Thirty-minute hippotherapy sessions were conducted biweekly for 12 weeks in 18 patients (18.1 ± 5.7 years old). Surface electromyography (EMG) was implemented bilaterally in rectus abdominis and adductor magnus. We quantitatively analyzed the amplitude of EMG signals in the time domain and its spectral characteristics in the frequency domain. EMGs were recorded at the beginning and end of each session on day one and at week six and week twelve. Statistical analysis revealed a substantial inter-day reliability of the EMG signals for both muscles, validating the methodological approach. To a lesser extent, while beyond the scope of the current study, quantitative changes suggested a more selective recruitment/contractile properties’ shift of the examined muscles. Exploring postural control during functional activities would contribute to understanding the relationship between structural impairment, activity performance and patient capabilities, allowing the design of neurorehabilitation programs aimed at improving postural and functional skills according to each individual’s needs. The present study provides basic quantitative data supporting the body of scientific evidence making hippotherapy an approach of choice for CP neurorehabilitation.

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Wu, G., V. Hansen, E. Kreysa y H. P. Gemünd. "Optimierung von FSS-Bandpassfiltern mit Hilfe der Schwarmintelligenz (Particle Swarm Optimization)". Advances in Radio Science 4 (4 de septiembre de 2006): 65–71. http://dx.doi.org/10.5194/ars-4-65-2006.

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Abstract. In diesem Beitrag wird ein neues Verfahren zur Optimierung von Bandpassfiltern aus mehrlagigen frequenzselektiven Schirmen (FSS), die in ein Dielektrikum eingebettet sind, vorgestellt. Das Ziel ist es, die Parameter der gesamten Struktur so zu optimieren, dass ihre Transmissionseigenschaften hohe Filteranforderungen erfüllen. Als Optimierungsverfahren wird die Particle Swarm Optimization (PSO) eingesetzt. PSO ist eine neue stochastische Optimierungsmethode, die in verschieden Gebieten, besonders aber bei der Optimierung nicht linearer Probleme mit mehreren Zielfunktionen erfolgreich eingesetzt wird. In dieser Arbeit wird die PSO in die Spektralbereichsanalyse zur Berechnung komplexer FSS-Strukturen integriert. Die numerische Berechnung basiert auf einer Integralgleichungsformulierung mit Hilfe der spektralen Greenschen Funktion für geschichtete Strukturen. This paper presents a novel procedure for the optimization of band-pass filters consisting of frequency selective surfaces (FSS) embedded in a dielectric. The aim is to optimize the parameters of the complete structure so that the transmission characteristics of the filters fulfill the demanding requirements. The Particle Swarm Optimization (PSO) is used as the optimization procedure. PSO is a new stochastic optimization method that is successfully applied in different areas for the optimization of non-linear problems with several object-functions. In this work, PSO is integrated into the spectral domain analysis for the calculation of the complex FSS structures. The numerical computation is based on the formulation of an integral equation with the help of the spectral Green's function for layered media.

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Zhang, Xiao Yu, Zhong Xin Zheng, Xin Xing Li, Ren Bing Tan, Zhi Peng Zhang, Yu Zhou, Jian Dong Sun, Bao Shun Zhang y Hua Qin. "Terahertz Filter Based on Frequency Selective Surfaces". Advanced Materials Research 571 (septiembre de 2012): 362–66. http://dx.doi.org/10.4028/www.scientific.net/amr.571.362.

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Terahertz filters based on the frequency selective surfaces (FSS) structure have been modeled and fabricated on the sapphire substrate. The terahertz (THz) transmission properties are investigated using a THz time-domain spectroscopy (THz-TDS) system. The designed two FSS-based THz filters exhibit the THz electromagnetic wave transmission and reflection characteristics, respectively, showing about 70% change of THz transmission at the frequency of 1.3 THz. It is suggested that the THz filtering effect results from the resonance behavior between THz plane-wave and resonant elements of designed metallic FSS structures. The agreement between experiments and simulations indicate that the designed THz filter show a great potential application for high-speed THz modulator.

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Karkkainen, M. K. y P. M. T. Ikonen. "Finite-difference time-domain modeling of frequency selective surfaces using impedance sheet conditions". IEEE Transactions on Antennas and Propagation 53, n.º 9 (septiembre de 2005): 2928–37. http://dx.doi.org/10.1109/tap.2005.851826.

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Immadi, Govardhani, M. Venkata Narayana, A. Navya, C. Anudeep Varma, A. Abhishek Reddy, A. Manisai Deepika y K. Kavya. "Analysis of substrateintegrated frequency selective surface antenna for IoT applications". Indonesian Journal of Electrical Engineering and Computer Science 18, n.º 2 (1 de mayo de 2020): 875. http://dx.doi.org/10.11591/ijeecs.v18.i2.pp875-881.

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<p>Antennas are long used for communication of data since a century and their usage has been diversified over the past two decades and the antennas also entered the domain of medical fields. A rectangular microstrip patch antenna has been designed on a substrate integrated waveguide with frequency selective surface which is in the shape of a square. The design of this antenna with SIW are done by using CST on a low cost FR4 substrate where є<sub>r</sub> =4.4, h=1.58 mm and tan δ=0.0035. The SIW structure merit is utilized on the traditional FSS is simulated and verified by using CST.</p>

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Zhuang, Wei, Riu S. Chen, Dazhi Z. Ding y Daoxiang X. Wang. "An efficient analysis of frequency selective surface in spectral domain with RWG basis functions". Microwave and Optical Technology Letters 51, n.º 11 (noviembre de 2009): 2567–70. http://dx.doi.org/10.1002/mop.24674.

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Ghosh, Santi Kumar. "Deconvolving the ghost effect of the water surface in marine seismics". GEOPHYSICS 65, n.º 6 (noviembre de 2000): 1831–36. http://dx.doi.org/10.1190/1.1444866.

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The ghost filters arising from the effect of the water surface on both source and receiver sides have a common time domain representation that consists of a unit impulse followed by its ghost, which is a delayed, negative unit impulse. The origin of the difficulties of deghosting lies in the zeroes in the spectrum of the ghost filter, which render incorrect any deghosting through least‐squares inverse filtering in the time domain. Another shortcoming of the time domain approach is that the digital description of the ghost filter is inexact when a sampling instant does not coincide with the instant of the onset of the ghost impulse. A frequency domain approach, on the other hand, is straightforward and accurate because it can avoid the zeroes of the filter either by explicitly choosing a recording band that excludes the zeroes or by recording at two depths. These two depths should be selected according to the criterion that their highest common measure is small enough to prevent zeroes at a common frequency of the two recordings. As the source‐side and the receiver‐side ghost filters have the same form, the criterion derived for the selection of the depths of the receivers would also hold for the selection of the depths of two sources whose aggregate signature is desired to have no zeroes in the spectrum, within the operative band. An important ramification of the analysis consists of the disproof of a prevalent conjecture that the zeroes in the spectrum of a wavelet make its autocorrelation matrix singular; actually, the zeroes cause an inexact and unacceptable least‐squares inverse, although the matrix itself is well conditioned.

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Ng, Jason, Sri Sundaram, Alan H. Kadish y Jeffrey J. Goldberger. "Autonomic effects on the spectral analysis of heart rate variability after exercise". American Journal of Physiology-Heart and Circulatory Physiology 297, n.º 4 (octubre de 2009): H1421—H1428. http://dx.doi.org/10.1152/ajpheart.00217.2009.

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Although frequency-domain analysis of heart rate variability (HRV) has been performed in the setting of exercise and recovery from exercise, the relationship of specific frequency components to sympathetic and parasympathetic inputs has not been validated in this setting. The aim of this study is to evaluate the relationship of frequency components of HRV to sympathetic and parasympathetic modulation in the setting of recovery after exercise using selective autonomic blockade. Normal subjects ( n = 27, 17 men, 53 ± 7 yr old) underwent bicycle stress testing on four separate days. On day 1, a baseline study without autonomic blockade was performed. On days 2 through 4, either β-adrenergic, parasympathetic, or double blockade was administered during exercise and completed 3 min before recovery. Continuous ECG was recorded for 5 min starting from the end of exercise. Time- and frequency-domain measures of HRV were computed for each of the five 1-min segments of RR intervals. Parasympathetic blockade significantly decreased all the HRV measures compared with baseline ( P < 0.02 for all). Root mean square of successive differences of RR intervals (rMSSD) was increased by β-adrenergic blockade ( P < 0.0002). All the HRV measures except rMSSD showed increases with time after the first minute of recovery. The low frequency-to-high frequency ratio did not respond to autonomic blockade or to recovery time, consistent with the expected changes in sympathovagal influence. Root mean square (detrended SD) and rMSSD were highly correlated with the square root of the total power ( r = 0.96) and high-frequency power ( r = 0.95), respectively. Although there are marked reductions in the frequency-domain measures in recovery versus rest, the fluctuations in the low- and high-frequency bands respond to autonomic blockade in the expected fashion. Time-domain measures of HRV were highly correlated with frequency-domain measures and therefore provide a computationally more efficient assessment of autonomic influences during recovery from exercise that is less susceptible to anomalies of frequency-domain analysis.

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Polley, Spencer D., Watcharee Chokejindachai y David J. Conway. "Allele Frequency-Based Analyses Robustly Map Sequence Sites Under Balancing Selection in a Malaria Vaccine Candidate Antigen". Genetics 165, n.º 2 (1 de octubre de 2003): 555–61. http://dx.doi.org/10.1093/genetics/165.2.555.

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Abstract The Plasmodium falciparum apical membrane antigen 1 (AMA1) is a leading candidate for a malaria vaccine. Here, within-population analyses of alleles from 50 Thai P. falciparum isolates yield significant evidence for balancing selection on polymorphisms within the disulfide-bonded domains I and III of the surface accessible ectodomain of AMA1, a result very similar to that seen previously in a Nigerian population. Studying the frequency of nucleotide polymorphisms in both populations shows that the between-population component of variance (FST) is significantly lower in domains I and III compared to the intervening domain II and compared to 11 unlinked microsatellite loci. A nucleotide site-by-site analysis shows that sites with exceptionally high or low FST values cluster significantly into serial runs, with four runs of low values in domain I and one in domain III. These runs may map the sequences that are consistently under the strongest balancing selection from naturally acquired immune responses.

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Koenig, T., D. Studer, D. Hubl, L. Melie y W. K. Strik. "Brain connectivity at different time-scales measured with EEG". Philosophical Transactions of the Royal Society B: Biological Sciences 360, n.º 1457 (29 de mayo de 2005): 1015–24. http://dx.doi.org/10.1098/rstb.2005.1649.

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We present an overview of different methods for decomposing a multichannel spontaneous electroencephalogram (EEG) into sets of temporal patterns and topographic distributions. All of the methods presented here consider the scalp electric field as the basic analysis entity in space. In time, the resolution of the methods is between milliseconds (time-domain analysis), subseconds (time- and frequency-domain analysis) and seconds (frequency-domain analysis). For any of these methods, we show that large parts of the data can be explained by a small number of topographic distributions. Physically, this implies that the brain regions that generated one of those topographies must have been active with a common phase. If several brain regions are producing EEG signals at the same time and frequency, they have a strong tendency to do this in a synchronized mode. This view is illustrated by several examples (including combined EEG and functional magnetic resonance imaging (fMRI)) and a selective review of the literature. The findings are discussed in terms of short-lasting binding between different brain regions through synchronized oscillations, which could constitute a mechanism to form transient, functional neurocognitive networks.

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Hajian, Gelareh, Ali Etemad y Evelyn Morin. "Automated Channel Selection in High-Density sEMG for Improved Force Estimation". Sensors 20, n.º 17 (27 de agosto de 2020): 4858. http://dx.doi.org/10.3390/s20174858.

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Accurate and real-time estimation of force from surface electromyogram (EMG) signals enables a variety of applications. We developed and validated new approaches for selecting subsets of high-density (HD) EMG channels for improved and lower-dimensionality force estimation. First, a large dataset was recorded from a number of participants performing isometric contractions in different postures, while simultaneously recording HD-EMG channels and ground-truth force. The EMG signals were acquired from three linear surface electrode arrays, each with eight monopolar channels, and were placed on the long head and short head of the biceps brachii and brachioradialis. After data collection and pre-processing, fast orthogonal search (FOS) was employed for force estimation. To select a subset of channels, principal component analysis (PCA) in the frequency domain and a novel index called the power-correlation ratio (PCR), which maximizes the spectral power while minimizing similarity to other channels, were used. These approaches were compared to channel selection using time-domain PCA. We selected one, two, and three channels per muscle from the original seven differential channels to reduce the redundancy and correlation in the dataset. In the best case, we achieved an approximate improvement of 30% for force estimation while reducing the dimensionality by 57% for a subset of three channels.

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Chen, Dongju, Jihong Han, Xianxian Cui y Jinwei Fan. "Identification and evaluation for the dynamic signals caused by pressure fluctuation of aerostatic slider". Industrial Lubrication and Tribology 70, n.º 6 (13 de agosto de 2018): 927–34. http://dx.doi.org/10.1108/ilt-11-2016-0271.

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Purpose To identify the dynamic feature of the aerostatic slider caused by gas film, an evaluation system by a piezoelectric acceleration sensor is presented in time and frequency domain. Design/methodology/approach The dynamic pressure fluctuation is evaluated by the wavelet transform, cross correlation analysis and power spectral density (PSD). Wavelet transform is used to process the measured result of the aerostatic slider and the signal is decomposed into high-frequency and low-frequency signal. Correlation analysis method is used to evaluate the impact of the initial gas gap on the fluctuation in time domain. Findings According to the PSD analysis of the processed signal in the frequency domain, the natural frequency of the aerostatic slider is identified from the measured signal in frequency domain; this method provides a basis for the identification of guideway errors. Research limitations/implications The method can also be applied to the error identification of other components of the machine tool. Originality/value Wavelet transform is used to process the measured result of the aerostatic slider by acceleration sensor, and the signal is decomposed into high-frequency and low-frequency signal. Correlation analysis method is used to evaluate the impact of the initial gas gap on the fluctuation in time domain. According to the PSD analysis of the processed signal in the frequency domain, the natural frequency of the aerostatic slider is identified from the measured signal in frequency domain; this method provides a basis for the identification of slider errors.

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Zhao, Shan, Nai Qian Zhang y Dong Li. "Method of Moments (MoM) for the Analysis of Dielectric Double Periodic Structures". Applied Mechanics and Materials 241-244 (diciembre de 2012): 1531–34. http://dx.doi.org/10.4028/www.scientific.net/amm.241-244.1531.

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The space-domain volume integral equation (VIE) method is presented for the analysis of three-dimension (3-D) scattering from dielectric frequency selective structures (DFSS) involved homogeneous and inhomogeneous lossy material. The method solves directly for the electric field in order to easily enable periodic boundary conditions in the spatial domain. The computation of the spatial domain periodic Green’s function (PGF) is accelerated by the modified Ewald transformation. Optimized interpolation procedures for the PGFs can be applied, resulting in a considerable reduction of matrix-filling time without any significant effect on the accuracy.

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Wang, Yi, Hai Feng Cheng, Jun Wang y Yong Jiang Zhou. "Infrared Emissivity of Capacitive Frequency-Selective Surfaces and its Application in Radar and IR Compatible Stealth Sandwich Structures". Advanced Materials Research 382 (noviembre de 2011): 65–69. http://dx.doi.org/10.4028/www.scientific.net/amr.382.65.

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Infrared emissivity of capacitive frequency-selective surfaces is affected by many factors, such as metal area, emissivity of medium part, surface roughness, metal oxidation, and surface cleanness, etc. In this paper, the influence of metal area and emissivity of medium part on the emissivity of CFSSs were depicted in detail. Furthermore, a kind of radar and IR compatible stealth sandwich structures, radar absorbing properties of which were calculated by the finite-difference time-domain (FDTD) method, were designed and prepared. We conclude that emissivity of CFSSs will be below 0.3 while metal area is above 80% and radar reflectivity of fabricated sandwich structure will be below -10dB in 8-18GHz.

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DAROWICKI, K. y W. FELISIAK. "APPLICATION OF COHEN'S CLASS TIME-FREQUENCY DISTRIBUTIONS IN THE BELOUSOV–ZHABOTINSKY REACTION ANALYSIS". International Journal of Bifurcation and Chaos 14, n.º 10 (octubre de 2004): 3679–88. http://dx.doi.org/10.1142/s0218127404011569.

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The systematic study of application of Cohen's class time-frequency representations in the analysis of periodic BZ oscillations generated in batch reactor has been presented. Several distributions belonging to Cohen's class have been applied in the analysis of selected signal being the register of bromide selective electrode. Among them were Wigner–Ville, Choi–Williams and cone-shaped distributions. The application of mentioned methods allow instantaneous power spectra to be obtained and simultaneously give the possibility of observing evolution of frequency composition of investigated oscillations. The systematic filtering of signal, using so-called kernel functions, allows to eliminate undesirable cross terms and finally leads to the selection of a suitable method for chemical oscillations decomposition. The results presented in the form of three-dimensional pictures, illustrate the decrease in frequency of oscillations of exponential character. On the basis of the obtained results the cone-shaped distribution for kernel function parameter α=1 has been selected as the best method for Belousov–Zhabotinsky oscillations analysis in joint time-frequency domain.

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Buyong, M. R., J. Yunas, A. A. Hamzah, B. Yeop Majlis, F. Larki y N. Abd Aziz. "Design, fabrication and characterization of dielectrophoretic microelectrode array for particle capture". Microelectronics International 32, n.º 2 (5 de mayo de 2015): 96–102. http://dx.doi.org/10.1108/mi-10-2014-0041.

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Purpose – The purpose of this study is to design and characterize the dielectrophoretic (DEP) microelectrodes with various array structure arrangements in order to produce optimum non-uniform electric field for particle capture. The DEP-electrodes with 2D electrode structure was fabricated and characterized to see the effect of electrode structure configuration on the capture capability of the cells suspending in the solution. Design/methodology/approach – The presented microelectrode array structures are made of planar conductive metal structure having same size and geometry. Dielectrophoretic force (FDEP) generated in the fluidic medium is initially simulated using COMSOL Multi-physics performed on two microelectrodes poles, which is then continued on three-pole microelectrodes. The proposed design is fabricated using standard MEMS fabrication process. Furthermore, the effect of different sinusoidal signals of 5, 10 and 15 volt peak to peak voltage (Vpp) at fixed frequency of 1.5 MHz on capturing efficiency of microelectrodes were also investigated using graphite metalloids particles as the suspended particles in the medium. The graphite particles that are captured at the microelectrode edges are characterized over a given time period. Findings – Based on analysis, the capturing efficiency of microelectrodes at the microelectrode edges is increased as voltage input increases, confirming its dependency to the FDEP strength and direction of non-uniform electric field. This dependency to field consequently increases the surface area of the accumulated graphite. It is also showed that the minimum ratio of the surface accumulated area of captured graphite is 1, 2.75 and 9 μm2 for 5, 10 and 15 Vpp, respectively. The simulation result also indicates a significant improvement on the performance of microelectrodes by implementing third pole in the design. The third pole effect the particles in the medium by creating stronger non-uniform electric field as well as more selective force toward the microelectrodes’ edges. Originality/value – The microelectrode array arrangement is found as a reliable method to increase the strength and selectivity of non-uniform electric field distribution that affect FDEP. The presented findings are verified through experimental test and simulation results.

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30

Gao, Tao, Feng Huang, Yanqing Chen, Weilin Zhu, Xuewei Ju y Xiangfeng Wang. "Resonant Coupling Effects in a Double-Layer THz Bandpass Filter". Applied Sciences 10, n.º 15 (22 de julio de 2020): 5030. http://dx.doi.org/10.3390/app10155030.

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Cascading similar frequency selective surfaces (FSSs) improves the roll-off rate and frequency selectivity of THz bandpass filters. However, resonant coupling between FSS layers causes anomalous transmission peaks. In this work, we have employed an equivalent circuit model to analyze a double-layer FSS structure with periodic cross apertures at different interlayer spacing. We found that the anomalous peaks can be attributed to the resonant coupling between the upper and lower layer FSSs, and their periodic appearance with changing interlayer spacing is related to the half-wavelength repeatability of the circuit. We have fabricated a double-layer FSS sample using femtosecond laser micromachining and measured it using time-domain THz spectroscopy. The results using the equivalent circuit model agree with the Finite-Difference Time-Domain (FDTD) and experimental results.

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31

Ferraro, Antonio, Dimitrios C. Zografopoulos, Roberto Caputo y Romeo Beccherelli. "Terahertz polarizing component on cyclo-olefin polymer". Photonics Letters of Poland 9, n.º 1 (31 de marzo de 2017): 2. http://dx.doi.org/10.4302/plp.v9i1.699.

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Wire-grid polarizers constitute a traditional component for the control of polarization in free-space devices that operate in a broad part of the electromagnetic spectrum. Here, we present an aluminium-based THz wire grid polarizer, fabricated on a sub-wavelength thin flexible and conformal foil of Zeonor polymer having a thickness of 40um. The fabricated device,characterized by means of THz time-domain spectroscopy, exhibitsa high extinction ratio between 30 and 45dB in the 0.3-2.1THz range. The insertion losses oscillate between 0 and 1.1dB andthey stemalmost exclusively from moderate Fabry-Perót reflections and it is engineered forvanishing at 2THz for operation with quantum cascade lasers. Full Text: PDF ReferencesI. F. Akyildiz, J. M. Jornet, C. Han, "Terahertz band: Next frontier for wireless communications", Phys. Commun. 12, 16 (2014). CrossRef M.C. Kemp, P.F. Taday, B.E. Cole, J.A. Cluff, A.J. Fitzgerald, W.R. Tribe, "Security applications of terahertz technology", Proc. SPIE 5070, 44 (2003). CrossRef M. Schirmer, M. Fujio, M. Minami, J. Miura, T. Araki, T. Yasui, "Biomedical applications of a real-time terahertz color scanner", Biomed. Opt. Express 1, 354 (2010). CrossRef R.P. Cogdill, R.N. Forcht, Y. Shen, P.F. Taday, J.R. Creekmore, C.A. Anderson, J.K. Drennen, "Comparison of Terahertz Pulse Imaging and Near-Infrared Spectroscopy for Rapid, Non-Destructive Analysis of Tablet Coating Thickness and Uniformity", J. Pharm. Innov. 2, 29 (2007). CrossRef Y.-C. Shen, "Terahertz pulsed spectroscopy and imaging for pharmaceutical applications: A review", Int. J. Pharm. 417, 48(2011). CrossRef A.G. Davies, A.D. Burnett, W. Fan, E.H. Linfield, J.E. Cunningham, "Terahertz spectroscopy of explosives and drugs", Mater. Today 11, 18 (2008). CrossRef J.F. Federici, B. Schulkin, F. Huang, D. Gary, R. Barat, F. Oliveira, D. Zimdars, "THz imaging and sensing for security applications?explosives, weapons and drugs", Semicond. Sci. Technol. 20, S266 (2005). CrossRef D. Saeedkia, Handbook of Terahertz Technology for Imaging, Sensing and Communications (Elsevier, 2013).N. Born, M. Reuter, M. Koch, M. Scheller, "High-Q terahertz bandpass filters based on coherently interfering metasurface reflections", Opt. Lett. 38, 908 (2013). CrossRef A. Ferraro, D.C. Zografopoulos, R. Caputo, R. Beccherelli, "Periodical Elements as Low-Cost Building Blocks for Tunable Terahertz Filters", IEEE Photonics Technol. Lett. 28, 2459 (2016). CrossRef A. Ferraro, D.C. Zografopoulos, R. Caputo, R. Beccherelli, "Broad- and Narrow-Line Terahertz Filtering in Frequency-Selective Surfaces Patterned on Thin Low-Loss Polymer Substrates", IEEE J. Sel. Top. Quantum Electron. 23 (2017). CrossRef B. S.-Y. Ung, B. Weng, R. Shepherd, D. Abbott, C. Fumeaux, "Inkjet printed conductive polymer-based beam-splitters for terahertz applications", Opt. Mater. Express 3, 1242 (2013). CrossRef J.-S. Li, D. Xu, J. Yao, "Compact terahertz wave polarizing beam splitter", Appl. Opt. 49, 4494 (2010). CrossRef K. Altmann, M. Reuter, K. Garbat, M. Koch, R. Dabrowski, I. Dierking, "Polymer stabilized liquid crystal phase shifter for terahertz waves", Opt. Express 21, 12395 (2013). CrossRef D.C. Zografopoulos, R. Beccherelli, "Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching", Sci. Rep. 5, 13137 (2015). CrossRef G. Isić, B. Vasić, D. C. Zografopoulos, R. Beccherelli, R. Gajić, "Electrically Tunable Critically Coupled Terahertz Metamaterial Absorber Based on Nematic Liquid Crystals", Phys. Rev. Appl. 3, 064007 (2015). CrossRef K. Iwaszczuk, A.C. Strikwerda, K. Fan, X. Zhang, R.D. Averitt, P.U. Jepsen, "Flexible metamaterial absorbers for stealth applications at terahertz frequencies", Opt. Express 20, 635 (2012). CrossRef F. Yan, C. Yu, H. Park, E.P.J. Parrott, E. Pickwell-MacPherson, "Advances in Polarizer Technology for Terahertz Frequency Applications", J. Infrared Millim. Terahertz Waves 34, 489 (2013). CrossRef http://www.tydexoptics.com DirectLink K. Imakita, T. Kamada, M. Fujii, K. Aoki, M. Mizuhata, S. Hayashi, "Terahertz wire grid polarizer fabricated by imprinting porous silicon", Opt. Lett. 38, 5067 (2013). CrossRef A. Isozaki, et al., "Double-layer wire grid polarizer for improving extinction ratio", Solid-State Sens. Actuators Microsyst. Transducers Eurosensors XXVII 2013 Transducers Eurosensors XXVII 17th Int. Conf. On, IEEE, pp. 530?533 (2013). DirectLink A. Ferraro, D. C. Zografopoulos, M. Missori, M. Peccianti, R. Caputo, R. Beccherelli, "Flexible terahertz wire grid polarizer with high extinction ratio and low loss", Opt. Lett. 41, 2009(2016). CrossRef M.S. Vitiello, G. Scalari, B. Williams, P.D. Natale, "Quantum cascade lasers: 20 years of challenges", Opt. Express 23, 5167(2015). CrossRef A. Podzorov, G. Gallot, "Low-loss polymers for terahertz applications", Appl. Opt. 47, 3254(2008). CrossRef

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32

Delgado, Carlos, Eliseo García y Felipe Cátedra. "Fast Hybrid Computational Technique for the Analysis of Radome Structures Using Dual Domain Decomposition". Electronics 10, n.º 18 (8 de septiembre de 2021): 2196. http://dx.doi.org/10.3390/electronics10182196.

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This work details a technique tailored to the analysis of complex radome structures based on the non-overlapping separation of two different domains: antenna and radome. Both domains are analyzed isolated using the method of moments with the multilevel fast multipole algorithm (MoM-MLFMA) for the antenna domain and a modified characteristic basis function method with the multilevel fast multipole algorithm approach for the radome domain. An iterative procedure is then applied to compute the effect of each domain over the complementary domain. This approach usually converges into a few iterations, yielding very good results and significant efficiency improvements with respect to other efficient approaches such as a full-wave MoM-MLFMA analysis of the full problem. A realistic test case is included, considering a radome with an embedded frequency selective structure on one of its interfaces. The results show a very good agreement considering only three iterations between domains, requiring only one-third of the CPU-time needed by the conventional approach.

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33

García Plaza, E., P. Núñez López y E. Beamud González. "Multi-Sensor Data Fusion for Real-Time Surface Quality Control in Automated Machining Systems". Sensors 18, n.º 12 (11 de diciembre de 2018): 4381. http://dx.doi.org/10.3390/s18124381.

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Multi-sensor data fusion systems entail the optimization of a wide range of parameters related to the selection of sensors, signal feature extraction methods, and predictive modeling techniques. The monitoring of automated machining systems enables the intelligent supervision of the production process by detecting malfunctions, and providing real-time information for continuous process optimization, and production line decision-making. Monitoring technologies are essential for the reduction of production times and costs, and an improvement in product quality, discarding the need for post-process quality controls. In this paper, a multi-sensor data fusion system for the real-time surface quality control based on cutting force, vibration, and acoustic emission signals was assessed. A total of four signal processing methods were analyzed: time direct analysis (TDA), power spectral density (PSD), singular spectrum analysis (SSA), and wavelet packet transform (WPT). Owing to the nonlinear and stochastic nature of the process, two predictive modeling techniques, multiple regression and artificial neural networks, were evaluated to correlate signal parametric characterization with surface quality. The results showed a high correlation of surface finish with cutting force and vibration signals. The signal processing methods based on signal decomposition in a combined time and frequency domain (SSA and WPT) exhibited better signal feature extraction, detecting excitation frequency ranges correlated to surface finish. The artificial neural network model obtained the highest predictive power, with better behavior for the whole data range. The proposed on-line multi-sensor data fusion provided significant improvements for in-process quality control, with excellent predictive power, reliability, and response times.

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34

Nicovich, Philip R., Erin L. Macartney, Renee M. Whan y Angela J. Crean. "Measuring Sperm Movement within the Female Reproductive Tract using Fourier Analysis". Microscopy and Microanalysis 21, n.º 1 (febrero de 2015): 256–63. http://dx.doi.org/10.1017/s1431927614014627.

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AbstractThe adaptive significance of variation in sperm phenotype is still largely unknown, in part due to the difficulties of observing and measuring sperm movement in its natural, selective environment (i.e., within the female reproductive tract). Computer-assisted sperm analysis systems allow objective and accurate measurement of sperm velocity, but rely on being able to track individual sperm, and are therefore unable to measure sperm movement in species where sperm move in trains or bundles. Here we describe a newly developed computational method for measuring sperm movement using Fourier analysis to estimate sperm tail beat frequency. High-speed time-lapse videos of sperm movement within the female tract of the neriid flyTelostylinus angusticolliswere recorded, and a map of beat frequencies generated by converting the periodic signal of an intensity versus time trace at each pixel to the frequency domain using the Fourier transform. We were able to detect small decreases in sperm tail beat frequency over time, indicating the method is sensitive enough to identify consistent differences in sperm movement. Fourier analysis can be applied to a wide range of species and contexts, and should therefore facilitate novel exploration of the causes and consequences of variation in sperm movement.

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35

Oblitas, Jimy y Jorge Ruiz. "Multivariate Analysis for the Classification of Chocolate According to its Percentage of Cocoa by Using Terahertz Time-Domain Spectroscopy (THz-TDS)". Proceedings 70, n.º 1 (12 de noviembre de 2020): 109. http://dx.doi.org/10.3390/foods_2020-08029.

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Terahertz time-domain spectroscopy is a useful technique for determining some physical characteristics of materials, and is based on selective frequency absorption of a broad-spectrum electromagnetic pulse. In order to investigate the potential of this technology to classify cocoa percentages in chocolates, the terahertz spectra (0.5–10 THz) of five chocolate samples (50%, 60%, 70%, 80% and 90% of cocoa) were examined. The acquired data matrices were analyzed with the MATLAB 2019b application, from which the dielectric function was obtained along with the absorbance curves, and were classified by using 24 mathematical classification models, achieving differentiations of around 93% obtained by the Gaussian SVM algorithm model with a kernel scale of 0.35 and a one-against-one multiclass method. It was concluded that the combined processing and classification of images obtained from the terahertz time-domain spectroscopy and the use of machine learning algorithms can be used to successfully classify chocolates with different percentages of cocoa.

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36

Zeng, Ming, Zhan Xie Wu, Qing Hao Meng, Jing Hai Li y Shu Gen Ma. "Recurrence Characteristics Analysis of Near-Surface Wind Speed Signal with Different Sampling Frequencies". Applied Mechanics and Materials 599-601 (agosto de 2014): 1605–9. http://dx.doi.org/10.4028/www.scientific.net/amm.599-601.1605.

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The wind is the main factor to influence the propagation of gas in the atmosphere. Therefore, the wind signal obtained by anemometer will provide us valuable clues for searching gas leakage sources. In this paper, the Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) are applied to analyze the influence of recurrence characteristics of the wind speed time series under the condition of the same place, the same time period and with the sampling frequency of 1hz, 2hz, 4.2hz, 5hz, 8.3hz, 12.5hz and 16.7hz respectively. Research results show that when the sampling frequency is higher than 5hz, the trends of recurrence nature of different groups are basically unchanged. However, when the sampling frequency is set below 5hz, the original trend of recurrence nature is destroyed, because the recurrence characteristic curves obtained using different sampling frequencies appear cross or overlapping phenomena. The above results indicate that the anemometer will not be able to fully capture the detailed information in wind field when its sampling frequency is lower than 5hz. The recurrence characteristics analysis of the wind speed signals provides an important basis for the optimal selection of anemometer.

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37

Xie, Wentao, Qian Zhang y Jin Zhang. "Acoustic-based Upper Facial Action Recognition for Smart Eyewear". Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies 5, n.º 2 (23 de junio de 2021): 1–28. http://dx.doi.org/10.1145/3448105.

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Smart eyewear (e.g., AR glasses) is considered to be the next big breakthrough for wearable devices. The interaction of state-of-the-art smart eyewear mostly relies on the touchpad which is obtrusive and not user-friendly. In this work, we propose a novel acoustic-based upper facial action (UFA) recognition system that serves as a hands-free interaction mechanism for smart eyewear. The proposed system is a glass-mounted acoustic sensing system with several pairs of commercial speakers and microphones to sense UFAs. There are two main challenges in designing the system. The first challenge is that the system is in a severe multipath environment and the received signal could have large attenuation due to the frequency-selective fading which will degrade the system's performance. To overcome this challenge, we design an Orthogonal Frequency Division Multiplexing (OFDM)-based channel state information (CSI) estimation scheme that is able to measure the phase changes caused by a facial action while mitigating the frequency-selective fading. The second challenge is that because the skin deformation caused by a facial action is tiny, the received signal has very small variations. Thus, it is hard to derive useful information directly from the received signal. To resolve this challenge, we apply a time-frequency analysis to derive the time-frequency domain signal from the CSI. We show that the derived time-frequency domain signal contains distinct patterns for different UFAs. Furthermore, we design a Convolutional Neural Network (CNN) to extract high-level features from the time-frequency patterns and classify the features into six UFAs, namely, cheek-raiser, brow-raiser, brow-lower, wink, blink and neutral. We evaluate the performance of our system through experiments on data collected from 26 subjects. The experimental result shows that our system can recognize the six UFAs with an average F1-score of 0.92.

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38

Sanliturk, K. Y., M. Imregun y D. J. Ewins. "Harmonic Balance Vibration Analysis of Turbine Blades With Friction Dampers". Journal of Vibration and Acoustics 119, n.º 1 (1 de enero de 1997): 96–103. http://dx.doi.org/10.1115/1.2889693.

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Although considerable effort has been devoted to the formulation of predictive models of friction damper behavior in turbomachinery applications, especially for turbine blades, the problem is far from being solved due to the complex nonlinear behavior of the contact surfaces. This paper primarily focuses on analytical and numerical aspects of the problem and addresses the problem in the frequency domain while exploring the viability of equivalent time-domain alternatives. The distinct features of this work are: (i) the modelling of nonlinear friction damper behavior as an equivalent amplitude-dependent complex stiffness via a first-order harmonic balance method (HBM), (ii) the use of sine sweep excitation in time-marching analysis, (iii) the application of the methodology to numerical test cases, including an idealised 3D turbine blade model with several friction dampers, (iv) the verification of the numerical findings using experimental data, and (v) a detailed assessment of the suitability of HBM for the analysis of structures with friction dampers.

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39

Butryło, Bogusław. "Analysis of the electromagnetic response of complex dispersive material with the single-step wideband finite element method". Archives of Electrical Engineering 62, n.º 1 (1 de marzo de 2013): 111–22. http://dx.doi.org/10.2478/aee-2013-0008.

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Abstract The paper describes the formulation and implementation of the broadband finite element time domain algorithm. The presented formalism is valid to analysis of electromagnetic phenomena in linear, frequency selective materials. The complex profile of permittivity of materials is approximated using a set of the Lorentz resonance models. The solution of the integro-differential second order equation is obtained using a singlestep integration scheme and a recursive convolution algorithm. The discussed formulation enables to adopt the structure of the narrowband part as well as the phase of calculation of the convolution equations for the subsequent components. The properties of the algorithm are validated using a finite difference broadband algorithm.

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40

Wu, K. y J. H. Ginsberg. "Mid-Frequency Range Acoustic Radiation From Slender Elastic Bodies Using the Surface Variational Principle". Journal of Vibration and Acoustics 120, n.º 2 (1 de abril de 1998): 392–400. http://dx.doi.org/10.1115/1.2893843.

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The surface variational principle (SVP) yields analytical-type results for radiation and scattering from submerged bodies whose shape does not suit classical techniques for analyzing the Helmholtz equation. The approach employs Ritz series expansions for surface pressure and velocity in the frequency domain. The relation between the series coefficients is obtained by extremizing the SVP functional. The present work extends the earlier developments to the case of an axisymmetric elastic shell that is subjected to an arbitrary excitation. The surface pressure and normal velocity are represented as a sequence of surface waves that are the trace of the waves in the surrounding fluid medium. SVP is used to determine the wavenumber spectrum of pressure amplitudes generated by a specific wave having unit velocity amplitude. The structural displacement field is also represented by Ritz expansions, and equations governing the generalized coordinates associated with these series are obtained by invoking Hamilton’s principle. Difficulties in satisfying the continuity conditions at the apexes are circumvented by selecting basis functions that map spherical shell eigenmodes onto the surface of the shell. The structural dynamic equations are coupled to the SVP equations by matching the normal velocity in the fluid to the time derivative of the normal displacement, as well as using the series expansion for surface pressure to form the acoustic contribution to the generalized forces. Results for a spherical shell subjected to a transverse point force at the equator, which is a nonaxisymmetric representation of the excitation, are compared with analytic results. Predictions for a long hemi-capped cylindrical shell in the mid-frequency range are compared to those obtained from SARA-2D (Allik, 1991), which is a finite/infinite element program. In addition to providing validation of the SVP implementation, the cylinder example is used to illustrate the convergence and error measures provided by an SVP analysis.

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41

Serdyukov, Aleksander S., Aleksander V. Yablokov, Anton A. Duchkov, Anton A. Azarov y Valery D. Baranov. "Slant f-k transform of multichannel seismic surface wave data". GEOPHYSICS 84, n.º 1 (1 de enero de 2019): A19—A24. http://dx.doi.org/10.1190/geo2018-0430.1.

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We have addressed the problem of estimating surface-wave phase velocities through the spectral processing of seismic data. This is the key step of the well-known near-surface seismic exploration method, called multichannel analysis of surface waves. To increase the accuracy and ensure the unambiguity of the selection of dispersion curves, we have developed a new version of the frequency-wavenumber ([Formula: see text]-[Formula: see text]) transform based on the S-transform. We obtain the frequency-time representation of seismic data. We analyze the obtained S-transform frequency-time representation in a slant-stacking manner but use a spatial Fourier transform instead of amplitude stacking. Finally, we build the [Formula: see text]-[Formula: see text] image by analyzing the spatial spectra for different steering values of the surface-wave group velocities. The time localization of the surface-wave packet at each frequency increases the signal-to-noise ratio because of an exclusion of noise in other time steps (which does not fall in the effective width of the corresponding wavelet). The new [Formula: see text]-[Formula: see text] transform, i.e., the slant [Formula: see text]-[Formula: see text] (SFK) transform, renders a better spectral analysis than the conventional [Formula: see text]-[Formula: see text] transform and yields more accurate phase-velocity estimation, which is critical for the surface-wave analysis. The advantages of the SFK transform have been confirmed by synthetic- and field-data processing.

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42

Uddin, Ghulam Moeen, Sajawal Gul Niazi, Syed Muhammad Arafat, Muhammad Sajid Kamran, Muhammad Farooq, Nasir Hayat, Sher Afghan Malik et al. "Neural networks assisted computational aero-acoustic analysis of an isolated tire". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 234, n.º 10-11 (4 de mayo de 2020): 2561–77. http://dx.doi.org/10.1177/0954407020915104.

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The computational aero-acoustic study of an isolated passenger car tire is carried out to understand the effect of dimensions of longitudinal tire grooves and operational parameters (velocity and temperature) on tire noise. The computational fluid dynamics and acoustic models are used to obtain aero-acoustic tire noise at near-field and far-field receivers around the tire and artificial neural networks-based regression are used to study the highly non-linear and interactive causal relationships in the system. Unsteady Reynolds-Averaged Navier-Stokes based realizable k-epsilon model is used to solve the flow field in the computational domain. The Ffowcs Williams and Hawkings model is used to obtain aero-acoustic tire noise at far-field positions. Spectral analysis is used to convert the output time domain to frequency domain and to obtain A-weighted sound pressure level. Artificial neural network–based response surface regression is conducted to understand casual relationships between A-weighted sound pressure level and control variables (Groove depth, Groove width, Temperature and velocity). Maximum A-weighted sound pressure level is observed in the wake region of the tire model. The interaction study indicates that ∼10% reduction in the aero-acoustic emissions is possible by selecting appropriate combinations of groove width and groove depth. The interaction of velocity with width is found to be most significant with respect to A-weighted sound pressure level at all receivers surrounding the tire. The interaction of operational parameters, that is, velocity and temperature are found to be significant with respect to A-weighted sound pressure level at wake and front receivers. Therefore, the regional speed limits and seasonal temperatures need to be considered while designing the tire to achieve minimum aero-acoustic emissions.

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43

Ramezanzadeh, B., S. Y. Arman, M. Mehdipour y B. P. Markhali. "Analysis of electrochemical noise (ECN) data in time and frequency domain for comparison corrosion inhibition of some azole compounds on Cu in 1.0M H2SO4 solution". Applied Surface Science 289 (enero de 2014): 129–40. http://dx.doi.org/10.1016/j.apsusc.2013.10.119.

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44

Soulsby, David. "Band-selective excitation NMR spectroscopy and quantitative time-domain analysis using Complete Reduction to Amplitude-Frequency Table (CRAFT) to determine distribution coefficients during drug development". Magnetic Resonance in Chemistry 57, n.º 11 (6 de junio de 2019): 953–60. http://dx.doi.org/10.1002/mrc.4888.

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45

Li, Yufeng y Aric Kumaran Menon. "A Theoretical Analysis of Breakaway Friction Measurement". Journal of Tribology 116, n.º 2 (1 de abril de 1994): 280–86. http://dx.doi.org/10.1115/1.2927210.

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The transient response of an I-beam friction measurement system to a constant disk acceleration is theoretically analyzed. The friction measurement system is modeled as a single-degree-of-freedom system. It is found that the true breakaway friction is different from the measured breakaway friction, and that the true breakaway time is also different from the measured breakaway time. The system measurement error is evaluated as a function of the acceleration, the effective mass, the spring stiffness, as well as the static and kinetic coefficients of friction. A closed-form dimensionless solution is derived for the system measurement error. If the dynamic effect of the measurement system can be neglected by selecting an appropriate effective mass and acceleration, the maximum possible discretization error can be estimated as a dimensionless function of the discretization frequency, the breakaway friction, the spring stiffness, and the acceleration.

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46

Nhan, TRAN Huu. "Vibration Analysis of a Bus’s Air Spring Suspension Subjected to Random Road Profile". Science & Technology Development Journal - Engineering and Technology 3, SI2 (15 de abril de 2021): first. http://dx.doi.org/10.32508/stdjet.v3isi2.576.

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Vehicle dynamics model in type of 1/4 is used for vibration analysis under the effect of random road profile with different grades. The mathematical model to describe the used random road profile is able to change the type of investigated road grades by selecting the corresponding power spectral density parameter of the road grade according to the ISO 8608 standard. Random road profile is ivestigated in the range of frequency domain from 0 to 50 (Hz). The air spring stiffness and the damping coefficience are determined on the basis of reference to the practical vehicle. The variation of relative displacement amplitude of the suspension in the range of investigation domain is small, the air spring stiffness used in the calculation is constant. The obtained results corresponding to different grades of road surface roughness including displacement and acceleration parameters. Relative displacement is a parameter that aims to verify the ability to ensure safe working of the suspension, namely rattle spacing. Acceleration is used to evaluate the vehicle's comfort. Calculation results are analyzed as the basis for evaluating the influence of the air spring stiffness and road surface conditions on the comfort of the vehicle, as the basis for changing the air spring stiffness in accordance with adjusting the pressure of it according to the type of road profile quality.

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47

Xie, Zedong, Xihong Chen, Xiaopeng Liu y Yu Zhao. "MMSE-NP-RISIC-Based Channel Equalization for MIMO-SC-FDE Troposcatter Communication Systems". Mathematical Problems in Engineering 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/5158406.

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The impact of intersymbol interference (ISI) on single-carrier frequency-domain equalization with multiple input multiple output (MIMO-SC-FDE) troposcatter communication systems is severe. Most of the channel equalization methods fail to solve it completely. In this paper, given the disadvantages of the noise-predictive (NP) MMSE-based and the residual intersymbol interference cancellation (RISIC) equalization in the single input single output (SISO) system, we focus on the combination of both equalization schemes mentioned above. After extending both of them into MIMO system for the first time, we introduce a novel MMSE-NP-RISIC equalization method for MIMO-SC-FDE troposcatter communication systems. Analysis and simulation results validate the performance of the proposed method in time-varying frequency-selective troposcatter channel at an acceptable computational complexity cost.

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48

Iqbal, Tanveer, S. S. Camargo, Saima Yasin, Ujala Farooq y Ahmad Shakeel. "Nano-Indentation Response of Ultrahigh Molecular Weight Polyethylene (UHMWPE): A Detailed Analysis". Polymers 12, n.º 4 (2 de abril de 2020): 795. http://dx.doi.org/10.3390/polym12040795.

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Nano-indentation, a depth sensing technique, is a useful and exciting tool to investigate the surface mechanical properties of a wide range of materials, particularly polymers. Knowledge of the influence of experimental conditions employed during nano-indentation on the resultant nano-mechanical response is very important for the successful design of engineering components with appropriate surface properties. In this work, nano-indentation experiments were carried out by selecting various values of frequency, amplitude, contact depth, strain rate, holding time, and peak load. The results showed a significant effect of amplitude, frequency, and strain rate on the hardness and modulus of the considered polymer, ultrahigh molecular weight polyethylene (UHMWPE). Load-displacement curves showed a shift towards the lower indentation depths along with an increase in peak load by increasing the indentation amplitude or strain rate. The results also revealed the strong dependence of hardness and modulus on the holding time. The experimental data of creep depth as a function of holding time was successfully fitted with a logarithmic creep model (R2 ≥ 0.98). In order to remove the creeping effect and the nose problem, recommended holding times were proposed for the investigated polymer as a function of different applied loads.

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49

Chen, Xiaoxiao y Ramakrishna Mukkamala. "Selective quantification of the cardiac sympathetic and parasympathetic nervous systems by multisignal analysis of cardiorespiratory variability". American Journal of Physiology-Heart and Circulatory Physiology 294, n.º 1 (enero de 2008): H362—H371. http://dx.doi.org/10.1152/ajpheart.01061.2007.

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Heart rate (HR) power spectral indexes are limited as measures of the cardiac autonomic nervous systems (CANS) in that they neither offer an effective marker of the β-sympathetic nervous system (SNS) due to its overlap with the parasympathetic nervous system (PNS) in the low-frequency (LF) band nor afford specific measures of the CANS due to input contributions to HR [e.g., arterial blood pressure (ABP) and instantaneous lung volume (ILV)]. We derived new PNS and SNS indexes by multisignal analysis of cardiorespiratory variability. The basic idea was to identify the autonomically mediated transfer functions relating fluctuations in ILV to HR (ILV→HR) and fluctuations in ABP to HR (ABP→HR) so as to eliminate the input contributions to HR and then separate each estimated transfer function in the time domain into PNS and SNS indexes using physiological knowledge. We evaluated these indexes with respect to selective pharmacological autonomic nervous blockade in 14 humans. Our results showed that the PNS index derived from the ABP→HR transfer function was correctly decreased after vagal and double (vagal + β-sympathetic) blockade ( P < 0.01) and did not change after β-sympathetic blockade, whereas the SNS index derived from the same transfer function was correctly reduced after β-sympathetic blockade in the standing posture and double blockade ( P < 0.05) and remained the same after vagal blockade. However, this SNS index did not significantly decrease after β-sympathetic blockade in the supine posture. Overall, these predictions were better than those provided by the traditional high-frequency (HF) power, LF-to-HF ratio, and normalized LF power of HR variability.

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OSIANDER, ROBERT, MICHAEL J. FITCH, MEGAN LEAHY-HOPPA, YAMAC DIKMELIK y JAMES B. SPICER. "SIGNATURE AND SIGNAL GENERATION ASPECTS OF EXPLOSIVE DETECTION USING TERAHERTZ TIME-DOMAIN SPECTROSCOPY". International Journal of High Speed Electronics and Systems 18, n.º 02 (junio de 2008): 295–306. http://dx.doi.org/10.1142/s0129156408005357.

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In the last few years, a number of researchers including our collaboration have assembled databases of terahertz (THz) time-domain spectroscopy (TDS) absorption spectra from bulk explosives. While this was a necessary and important step in demonstrating the feasibility of THz TDS for explosives detection, the goal of our research is to demonstrate selectivity of THz spectra from the clutter of background spectra coming from the substrate such as soil or sand. We have investigated THz TDS reflection spectra from sand with different grain sizes as well as from metallic powders in order to distinguish between the signals reflected from the rough surfaces compared to distributed reflections at finite depths in the granular material. With marker materials such as tartaric acid, which have absorption features in the 1-2 THz range, we have investigated the reflection spectra of granular substrates with marker chemicals, and compared this to reflection and transmission spectra of solid materials prepared in polyethylene sample pellets. In principle, the same experiments can then be performed using TNT, RDX, HMX and PETN, which all have characteristic features in the 0.5-8 THz frequency range. Absolute molecular absorption coefficients can be measured as well, and we include here preliminary values for RDX. A full analysis will be reported elsewhere.

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