MAXWELL3, 3-D FEM Electromagnetism
1 - Description of program or function: MAXWELL3 is a linear, time domain, finite element code designed for simulation of electromagnetic fields interacting with three-dimensional objects. The simulation region is discretized into 6-sided, 8-nodded elements which need not form a logically regular grid. Scatterers may be perfectly conducting or dielectric. Restart capability and a Muer-type radiating boundary are included. MAXWELL3 can be run in a two-dimensional mode or on infinitesimally thin geometries. The output of time histories on surfaces, or shells, in addition to volumes, is allowed. Two post-processors are included - HIST2XY, which splits the MAXWELL3 history file into simple xy data files, and FFTABS, which performs fast Fourier transformations on the xy data. 2 - Method of solution: The numerical method requires that the model be discretized with a mesh generator. MAXWELL3 then uses the mesh and computes the time domain electric and magnetic fields by integrating Maxwell's divergence-free curl equations over time. The output from MAXWELL3 can then be used with a post-processor to get the desired information in a graphical form. The explicit time integration is done with a leap-frog technique that alternates evaluating the electric and magnetic fields at half time steps. This allows for centered time differencing accurate in second order. The algorithm is naturally robust and requires no parameters. 3 - Restrictions on the complexity of the problem: MAXWELL3 has no mesh generation capabilities. Anisotropic, nonlinear, and magnetic materials cannot be modeled. Material interfaces only account for dielectric changes and neglect any surface charges that would be present at the surface of a partially conducting material. The radiation boundary algorithm is only accurate for normally incident fields and becomes less accurate as the angle of incidence increases. Thus, only models using scattered fields should use the radiation boundary. This limits MAXWELL3's
ESTABLISHMENT OF 3D FEM MODEL OF MULTI-PASS SPINNING
ZHAN Mei; ZHOU Qiang; YANG He; ZHANG Jinhui
2007-01-01
In order to improve the computational accuracy and efficiency, it is necessary to establish a reasonable 3D FEM model for multi-pass spinning including not only spinning process but also springback and annealing processes. A numerical model for multi-pass spinning is established using the combination of explicit and implicit FEM, with the advantages of them in accuracy and efficiency. The procedures for model establishment are introduced in detail, and the model is validated. The application of the 3D FEM model to a two-pass spinning shows the following: The field variables such as the stress, strahl and wall thickness during the whole spinning process can be obtained, not only during spinning process but also during springback and annealing processes, and the trends of their distributions and variations are in good agreement with a practical multi-spinning process. Thus the 3D FEM model for multi-pass spinning may be a helpful tool for determination and optimization of process Parameters of multi-pass spinning process.
3D FEM Simulation of Rolling Load Working on Piercer Plug in Mannesmann Piercing Process
Yoshida, Motohisa
2010-06-01
This paper presents 3D FEM simulation of piercer plug in Mannesmann piercing process. Target is establishment of a virtual piercing experiment tool to assistant piercer plug development. FEM simulation analysis has been applied to Mannesmann piercing process previously. Aspect of those studies is how to simulate material flow in piercing process, especially focused on how to describe ductile fracture which is known as Mannesmann effect. Thus far, simulation of rolling tools has not been focused. Present piercer plugs, made of special alloys, are damaged severely and quickly in case of piercing higher Cr contented alloys in seamless steel tube production process. Therefore, development of FEM simulation on rolling tools has been demanded in production side. 3D FEM analysis of piercer plug is performed with ALE (Arbitrary Lagrangian—Eulerian) method by using ABAQUS/Explicit 6.9. Simulations are thermo-mechanical, elasto-plastic coupled, and dynamic calculation. Piercer plug and the billet are modeled by solid elements to analyze various factors on stress, strain and temperature. Ductile fracture is not considered in the simulations. Simulation results are correlated sufficiently to experimental results on damage of piercer plugs. Verifying absolute value of simulated factors is hard since there are few empirical methods to measure them. As a conclusion, studied simulations are sufficient as a virtual piercing experiment tool to develop higher performance piercer plugs.
This paper presents an investigation of the welding sequence effect on induced angular distortion using FEM and experiments. The specimen of a combined joint geometry was modeled and simulated using Multipass Welding Advisor (MWA) in SYSWELD 2010 based on the thermal-elastic-plastic approach with low manganese carbon steel S3355J2G3 as specimen material and Goldak's double ellipsoid as heat source model. To validate the simulation results, a series of experiments was conducted with two different welding sequences using automated welding process, low carbon steel as parent metal, digital GMAW power source with premixed shielding gas and both-sided clamping technique. Based on the results, it was established that the thermo-elastic-plastic 3D FEM analysis shows good agreement with experimental results and the welding sequence “from outside to inside” induced less angular distortion compared to “from inside to outside”. -- Highlights: • 3D FEM was used to analyze the welding distortion on two different sequences. • Simulation results were validated with experiments using automated welding system. • Simulation results and experiments showed acceptable accuracy. • Welding sequence “outside–inside” showed less distortion than “inside–outside”
A 2D-3D FEM approach of fuel rod thermomechanical behaviour during a RIA
For better understanding of the fuel rod behaviour during a RIA and to extrapolate the CABRI tests results to PWR conditions, a pellet and its corresponding cladding part have been modelled by means of a 2D axisymmetric meshing, with EDF's finite element code ASTER. The pellet rim region, which is modelled with a 3D meshing, is represented in the global 2D-model with an equivalent homogenized material. The stress distribution is calculated by applying a thermal radial profile computed with the CEA/IPSN SCANAIR code. Then, the local stresses are determined in the rim region, in the neighbourhood of a gas bubble. This 2D-3D FEM approach has been applied successively to REP Na1 rod, at the time and location of the first failure, and to the postulated RCCA ejection accident in a PWR. (R.P.)
Evaluation of Bogie Frame Safety of Shanghai Metro Line 1 by 3D FEM Analysis
Xiongyao, Xie; Guolong, Jin; Rulu, Wang
2010-05-01
The vehicle bogies of Shanghai metro line 1 began to crack just in the third year after the trains operated. More than 50 cracks occurred in the succeeding six year during the train operation. This paper evaluated the safety of the motorized bogies. First, the loading conditions imposed on the vehicle structure were calculated based on the measured data in service of the train, and compared with the original design load. Then, this paper calculated simulated the stress of the vehicle bogie by 3D FEM, and presented the distribution of every stress concentration point in Goodman fatigue diagram. The computational locations of the strength less than the safety are agreed with where cracks have happened. Finally, this paper calculated the fatigue life of the motor bracket of the bogie through S-N curve based on revised Miner theory. In conclusion, this paper think that the bogie cracks of Shanghai metro line 1 are contributed by the overburden fatigue load, and ignoring the lateral vibration load in the design of the vehicle bogie is the important cause that bogie cracks occurred far earlier than in the designed time.
Frequency domain nonlinear optics
Legare, Francois
2016-05-01
The universal dilemma of gain narrowing occurring in fs amplifiers prevents ultra-high power lasers from delivering few-cycle pulses. This problem is overcome by a new amplification concept: Frequency domain Optical Parametric Amplification - FOPA. It enables simultaneous up-scaling of peak power and amplified spectral bandwidth and can be performed at any wavelength range of conventional amplification schemes, however, with the capability to amplify single cycles of light. The key idea for amplification of octave-spanning spectra without loss of spectral bandwidth is to amplify the broad spectrum ``slice by slice'' in the frequency domain, i.e. in the Fourier plane of a 4f-setup. The striking advantages of this scheme, are its capability to amplify (more than) one octave of bandwidth without shorting the corresponding pulse duration. This is because ultrabroadband phase matching is not defined by the properties of the nonlinear crystal employed but the number of crystals employed. In the same manner, to increase the output energy one simply has to increase the spectral extension in the Fourier plane and to add one more crystal. Thus, increasing pulse energy and shortening its duration accompany each other. A proof of principle experiment was carried out at ALLS on the sub-two cycle IR beam line and yielded record breaking performance in the field of few-cycle IR lasers. 100 μJ two-cycle pulses from a hollow core fibre compression setup were amplified to 1.43mJ without distorting spatial or temporal properties. Pulse duration at the input of FOPA and after FOPA remains the same. Recently, we have started upgrading this system to be pumped by 250 mJ to reach 40 mJ two-cycle IR few-cycle pulses and latest results will be presented at the conference. Furthermore, the extension of the concept of FOPA to other nonlinear optical processes will be discussed. Frequency domain nonlinear optics.
Oshikane, Y.; Murai, K.; Nakano, M.
2014-09-01
3D-electromagnetic (EM) analysis of surface plasmon polaritons (SPPs) excited by a single-mode (SM) propagation of visible lightwave in an optical fiber has been studied with a 3D-FEM package based on a finite element method. End of the fiber is formed to be a circular cone by wet etching process, and is FIBed to make a circular truncated conical shape with a flat circular surface a few micrometers in diameter. The flat end is covered with three layers of asymmetric metalinsulator- metal structure, thin metallic layer (M1), thick insulator layer (I), and thick metallic layer (M2), respectively. The outermost M2 layer has FIBed nanoholes to convert light waves at the extremity of the fiber into SPPs efficiently, and a bright tiny point light source will be generated on the surface of the M2 layer. In this study, the 3D-FEM models consists of both the MIM structure and the shrinking optical fiber tip coated with a metallic thin film has been designed and analyzed numerically. By applying perfect electric conductor and perfect magnetic conductor to planes containing the axis of rotation, the FEM model has a quarter of the circular truncated conical shape. The FEM analysis is formed in two steps. At the first step, a FEM mode analysis is performed to obtain a solution corresponding to the SM propagation in the fiber. The second level of action is the FEM analysis of EM field in the whole of model to find a stationary solution with the solution of mode analysis. Characteristic of wavelength-dependent excitation, propagation, and focusing of the SPPs will be presented with several experimental results of trial products of the fiber tip.
Katagi, T.; Hashimoto, M.; Hashizume, M.; Choosakul, N.; Takemoto, S.; Fukuda, Y.; Fujimori, K.; Satomura, M.; Wu, P.; Otsuka, Y.; Takiguchi, H.; Saito, S.; Maruyama, T.; Kato, T.
2007-12-01
We have studied postseismic displacement following the Sumatra-Andaman earthquake of December 26, 2004 in Thailand and other Southeast Asian countries using continuous GPS observation. We will report the results of our GPS analysis from the beginning of 2001 to the end of October 2007. We have also constructed 3D-FEM to evaluate the effect of viscoelastic relaxation following the earthquake. We will also report this result. We used continuous GPS data from 6 sites operated by Chulalongkorn Univ. and Kyoto Univ. or JAMSTEC, 2 sites by Shizuoka Univ. and JAMSTEC, 3 sites by NICT in Thailand and Myanmar, 1 site by STE-Lab, Nagoya Univ., and IGS sites which are located in countries surrounding the Indian Ocean include Japan, China and Australia. Bernese 5.0 was used for the processing of 30 sec. sampling data to obtain static solutions. From our analysis, no significant motions were detected at each site until the day of the earthquake. Although postseismic displacements still have been detected at CHMI and SIS2 in northern Thailand, far from the epicenter, they seem to be decelerated. On the other hand, at SAMP and PHKT, close to the epicenter, where postseismic displacements also became smaller, but still may take a time to stop. An about 29 cm SW-ward motion was detected at PHKT from just after the Sumatra-Andaman earthquake to June 2007, which is larger than its coseismic displacement, about 26 cm. We have constructed 3D-FEM model to estimate how much viscoelastic relaxation affects postseismic displacements after the earthquake. We adopted a Maxwell viscoelastic body as well as Katagi et al. (2006), and modeled around the Andaman-Sea area using isoparametric hexahedral elements with 8 nodes (Zienkiewicz and Cheng, 1967). The Andaman-Sea is well known as a back arc basins, and its ocean floor is still spreading. Therefore, the mantle viscosity under the Sunda-plate may be smaller because of upwelling warm mantle. We are going to investigate and report the
Comparison of the domain and frequency domain state feedbacks
In this paper, we present explicitly the equivalence of the time domain and frequency domain state feedbacks, as well as the dynamic state feedback and a modified frequency domain state feedback, from the closed-loop transfer function point of view. The difference of the two approaches is also shown
Zhang, Dongping
2009-10-26
Lateral forced cooling can significantly increase the temporary overload capacity of a cable system, but the design of such systems requires a time-dependent 3D analysis of the nonlinear thermal behavior as the cooling water along the cable is heated up, resulting in position-dependent and time-dependent heat uptake. For this, a new calculation method was developed on the basis of an available 3D FEM software. The new method enables 3D simulation of force-cooled cables in consideration of the potential partial dryout of soil and of thermal stabilizations. The new method was first applied to a 110 kV wind power transmission cable for different configurations and grid conditions. It was found that with lateral forced cooling, the 110 kV will have a temporal 50 percent overload capacity. Further, the thermal characteristics and limiting capacity of a force-cooled 380 kV cable system were investigated. According to the results so far, laterally cooled cable systems open up new operating options, with advantages in terms of availability, economic efficiency, and flexibility. (orig.) [German] Eine laterale Zwangskuehlung kann die temporaere Ueberlastbarkeit einer Kabelanlage signifikant erhoehen. Der Entwurf solcher zwangsgekuehlter Kabelanlagen erfordert jedoch eine zeitabhaengige, dreidimensionale Analyse des nichtlinearen thermischen Verhaltens, da sich das Kuehlwasser entlang der Trasse erwaermt und sich so eine orts- und zeitabhaengige Waermeaufnahme ergibt. Zu diesem Zweck wurde auf der Basis eines vorhandenen zweidimensionalen FEM-Programms ein neues Berechnungsverfahren entwickelt, das die dreidimensionale Simulation zwangsgekuehlter Kabelanlagen unter Beruecksichtigung einer moeglicherweise auftretenden partiellen Bodenaustrocknung und von thermischen Stabilisierungen erlaubt. Mit Hilfe dieses Berechnungsverfahrens wurde zuerst eine 110-kV-Kabelanlage zur Windenergieuebertragung bei unterschiedlichen Anordnungen und unterschiedlichen Netzsituationen untersucht
Time- vs. frequency-domain femtosecond surface sum frequency generation
Roke, S.; Kleyn, A. W.; Bonn, M.
2003-01-01
We present an experimental and theoretical investigation into time- vs. frequency-domain ferntosecond sum frequency spectroscopy at the metal-liquid interface. Although frequency and time-domain measurements are theoretically equivalent it is demonstrated here experimentally that the two approaches
Frequency domain image filtering using cuda
In this paper, we investigate the implementation of image filtering in frequency domain using NVIDIA's CUDA (Compute Unified Device Architecture). In contrast to signal and image filtering in spatial domain which uses convolution operations and hence is more compute-intensive for filters having larger spatial extent, the frequency domain filtering uses FFT (Fast Fourier Transform) which is much faster and significantly reduces the computational complexity of the filtering. We implement the frequency domain filtering on CPU and GPU respectively and analyze the speed-up obtained from the CUDA's parallel processing paradigm. In order to demonstrate the efficiency of frequency domain filtering on CUDA, we implement three frequency domain filters, i.e., Butter worth, low-pass and Gaussian for processing different sizes of images on CPU and GPU respectively and perform the GPU vs. CPU benchmarks. The results presented in this paper show that the frequency domain filtering with CUDA achieves significant speed-up over the CPU processing in frequency domain with the same level of (output) image quality on both the processing architectures. (author)
Frequency Domain Image Filtering Using CUDA
Muhammad Awais Rajput
2014-10-01
Full Text Available In this paper, we investigate the implementation of image filtering in frequency domain using NVIDIA?s CUDA (Compute Unified Device Architecture. In contrast to signal and image filtering in spatial domain which uses convolution operations and hence is more compute-intensive for filters having larger spatial extent, the frequency domain filtering uses FFT (Fast Fourier Transform which is much faster and significantly reduces the computational complexity of the filtering. We implement the frequency domain filtering on CPU and GPU respectively and analyze the speed-up obtained from the CUDA?s parallel processing paradigm. In order to demonstrate the efficiency of frequency domain filtering on CUDA, we implement three frequency domain filters, i.e., Butterworth, low-pass and Gaussian for processing different sizes of images on CPU and GPU respectively and perform the GPU vs. CPU benchmarks. The results presented in this paper show that the frequency domain filtering with CUDA achieves significant speed-up over the CPU processing in frequency domain with the same level of (output image quality on both the processing architectures
System Identification A Frequency Domain Approach
Pintelon, Rik
2012-01-01
System identification is a general term used to describe mathematical tools and algorithms that build dynamical models from measured data. Used for prediction, control, physical interpretation, and the designing of any electrical systems, they are vital in the fields of electrical, mechanical, civil, and chemical engineering. Focusing mainly on frequency domain techniques, System Identification: A Frequency Domain Approach, Second Edition also studies in detail the similarities and differences with the classical time domain approach. It high??lights many of the important steps in the identi
Domain Decomposition Solvers for Frequency-Domain Finite Element Equations
Copeland, Dylan
2010-10-05
The paper is devoted to fast iterative solvers for frequency-domain finite element equations approximating linear and nonlinear parabolic initial boundary value problems with time-harmonic excitations. Switching from the time domain to the frequency domain allows us to replace the expensive time-integration procedure by the solution of a simple linear elliptic system for the amplitudes belonging to the sine- and to the cosine-excitation or a large nonlinear elliptic system for the Fourier coefficients in the linear and nonlinear case, respectively. The fast solution of the corresponding linear and nonlinear system of finite element equations is crucial for the competitiveness of this method. © 2011 Springer-Verlag Berlin Heidelberg.
Detector nonlinearity in frequency-domain fluorometry.
Wirth, M J; Burbage, J D; Zulli, S L
1993-02-20
Frequency-domain fluorometry relies on the measurement of the phase and amplitudes of the Fourier components of the time-dependent fluorescence signal. Experimental results that show that a conventional photomultiplier is subject to intensity-dependent phase shifts are presented. The measurements indicate that this is a problem well below the maximum linear current of the photomultiplier response. These results have important implications in frequency-domain fluorescence anisotropy experiments, in which the parallel and the perpendicular components of the emission intensity are inherently different from one another: a phase shift can be introduced by the photomultiplier. PMID:20802776
Load Estimation by Frequency Domain Decomposition
Pedersen, Ivar Chr. Bjerg; Hansen, Søren Mosegaard; Brincker, Rune;
2007-01-01
When performing operational modal analysis the dynamic loading is unknown, however, once the modal properties of the structure have been estimated, the transfer matrix can be obtained, and the loading can be estimated by inverse filtering. In this paper loads in frequency domain are estimated by...... analysis of simulated responses of a 4 DOF system, for which the exact modal parameters are known. This estimation approach entails modal identification of the natural eigenfrequencies, mode shapes and damping ratios by the frequency domain decomposition technique. Scaled mode shapes are determined by use...
Frequency-Domain Robust Control Toolbox
Karimi, Alireza
2013-01-01
A new frequency-domain robust control toolbox is introduced and compared with some features of the robust control toolbox of Matlab. A summary of the theoretical background for H-infinity controller design using the spectral models is given. The main advantage of this toolbox is that almost all types of model uncertainties like unmodelled dynamics, multimodel uncertainty, spectral uncertainty and parametric uncertainty can be taken into account without conservatism. As a result, the uncertain...
Robust Image Watermarking in Frequency Domain
G. Dayalin Leena
2013-04-01
Full Text Available The spreading out of internet these days has raised the worth of digital media all over the planet. Digital watermarking has been a boon to digital media world as it endows various benefits like authentication, copy control and rights management of digital media. Digital images a category under digital media can be watermarked either in time domain or in frequency domain. The goal is to produce an efficient, secure and invisible watermarked image using digital watermarking thereby improving the quality and increasing the robustness of watermarked image. Here, digital image is watermarked using wavelet transforms which is an efficient multi-resolution frequency domain techniques. The low frequencies of wavelet decomposition of the carrier image which is a color image is watermarked with a color logo shuffled using a chaotic map technique. Embedding process is highly secured as chaotic map technique shuffles the watermark in order to confuse any unauthorized person who tries to modify or remove the corresponding watermark. The Peak Signal to Noise Ratio (PSNR of watermarked image has proved that the original image and the watermarked image are visually indistinguishable by human observers. Robustness is checked well by extracting the original watermark perfectly without any degradation in the original image.
Frequency domain analysis of knock images
High speed imaging-based knock analysis has mainly focused on time domain information, e.g. the spark triggered flame speed, the time when end gas auto-ignition occurs and the end gas flame speed after auto-ignition. This study presents a frequency domain analysis on the knock images recorded using a high speed camera with direct photography in a rapid compression machine (RCM). To clearly visualize the pressure wave oscillation in the combustion chamber, the images were high-pass-filtered to extract the luminosity oscillation. The luminosity spectrum was then obtained by applying fast Fourier transform (FFT) to three basic colour components (red, green and blue) of the high-pass-filtered images. Compared to the pressure spectrum, the luminosity spectra better identify the resonant modes of pressure wave oscillation. More importantly, the resonant mode shapes can be clearly visualized by reconstructing the images based on the amplitudes of luminosity spectra at the corresponding resonant frequencies, which agree well with the analytical solutions for mode shapes of gas vibration in a cylindrical cavity. (paper)
Communicating oscillatory networks: frequency domain analysis
Ihekwaba Adaoha EC
2011-12-01
Full Text Available Abstract Background Constructing predictive dynamic models of interacting signalling networks remains one of the great challenges facing systems biology. While detailed dynamical data exists about individual pathways, the task of combining such data without further lengthy experimentation is highly nontrivial. The communicating links between pathways, implicitly assumed to be unimportant and thus excluded, are precisely what become important in the larger system and must be reinstated. To maintain the delicate phase relationships between signals, signalling networks demand accurate dynamical parameters, but parameters optimised in isolation and under varying conditions are unlikely to remain optimal when combined. The computational burden of estimating parameters increases exponentially with increasing system size, so it is crucial to find precise and efficient ways of measuring the behaviour of systems, in order to re-use existing work. Results Motivated by the above, we present a new frequency domain-based systematic analysis technique that attempts to address the challenge of network assembly by defining a rigorous means to quantify the behaviour of stochastic systems. As our focus we construct a novel coupled oscillatory model of p53, NF-kB and the mammalian cell cycle, based on recent experimentally verified mathematical models. Informed by online databases of protein networks and interactions, we distilled their key elements into simplified models containing the most significant parts. Having coupled these systems, we constructed stochastic models for use in our frequency domain analysis. We used our new technique to investigate the crosstalk between the components of our model and measure the efficacy of certain network-based heuristic measures. Conclusions We find that the interactions between the networks we study are highly complex and not intuitive: (i points of maximum perturbation do not necessarily correspond to points of maximum
代燕; 张超; 赵华强
2011-01-01
目的 应用三维有限元方法,对不同固定方式的下颌角骨折进行生物力学分析,为临床选择下颌角骨折固定方式提供理论依据.方法 应用螺旋CT扫描及相关软件,建立下颌角骨折内固定系统三维有限元模型,并利用MSC.Marc软件对模型进行应力分析.结果 张力带固定时应力集中分布于钛板中部,而双列小型板固定时最大应力位于上缘钛板中部.张力带固定时骨折断端的最大相对位移大于双列小型板固定.在健侧后牙咬(牙合)和前牙咬(牙合)情况下,张力带固定的安全咬(牙合)力范围分别在102.7 N和40.3 N以下.结论 下颌角骨折时,双列小型板固定的稳定性优于张力带固定.选取适当的咬(牙合)方式,张力带固定也可以达到下颌骨骨折固定的安全范围.%Objective To observe the stress distribution of mandibular angle fracture under different rigid internal fixation (RIF) methods by developing a three-dimensional finite-element method (3-D FEM). Methods CT scan technology and related software were used to develop a 3 -D FEM of mandibular angle fracture under different RIF. On this basis, the mandibular stress distributions were analyzed by MSC.Marc software. Results The von Mises stress mainly concentrated on the middle of the titanium plate in tension band fixation, while in two mini-plate fixation, it concentrated on the middle of the superior titanium plate. In the tension band fixation, the max-values of displacement was more than that in the two mini-plate fixation. When the biting force dropped to 102.7 N (LMOL) and 40.3 N (ICP), the furthest fracture mobility got into margin of safety under the tension band fixation. Conclusion The two mini-plate fixation was more stable than the tension band fixation. Choosing the suitable occlusion, tension band fixation could also provide sufficient stability for the mandibular angle fracture.
On frequency and time domain models of traveling wave tubes
Théveny, Stéphane; Elskens, Yves
2016-01-01
We discuss the envelope modulation assumption of frequency-domain models of traveling wave tubes (TWTs) and test its consistency with the Maxwell equations. We compare the predictions of usual frequency-domain models with those of a new time domain model of the TWT.
Linear dispersion codes in space-frequency domain for SCFDE
Marchetti, Nicola; Cianca, Ernestina; Prasad, Ramjee
2007-01-01
This paper presents a general framework for applying the Linear Dispersion Codes (LDC) in the space and frequency domains to Single Carrier - Frequency Domain Equalization (SCFDE) systems. Space-Frequency (SF)LDC are more suitable than Space-Time (ST)-LDC in high mobility environment. However, th...
Transformation Algorithm of Dielectric Response in Time-Frequency Domain
Ji Liu
2014-01-01
Full Text Available A transformation algorithm of dielectric response from time domain to frequency domain is presented. In order to shorten measuring time of low or ultralow frequency dielectric response characteristics, the transformation algorithm is used in this paper to transform the time domain relaxation current to frequency domain current for calculating the low frequency dielectric dissipation factor. In addition, it is shown from comparing the calculation results with actual test data that there is a coincidence for both results over a wide range of low frequencies. Meanwhile, the time domain test data of depolarization currents in dry and moist pressboards are converted into frequency domain results on the basis of the transformation. The frequency domain curves of complex capacitance and dielectric dissipation factor at the low frequency range are obtained. Test results of polarization and depolarization current (PDC in pressboards are also given at the different voltage and polarization time. It is demonstrated from the experimental results that polarization and depolarization current are affected significantly by moisture contents of the test pressboards, and the transformation algorithm is effective in ultralow frequency of 10−3 Hz. Data analysis and interpretation of the test results conclude that analysis of time-frequency domain dielectric response can be used for assessing insulation system in power transformer.
Estimated Frequency Domain Model Uncertainties used in Robust Controller Design
Tøffner-Clausen, S.; Andersen, Palle; Stoustrup, Jakob;
1994-01-01
This paper deals with the combination of system identification and robust controller design. Recent results on estimation of frequency domain model uncertainty are......This paper deals with the combination of system identification and robust controller design. Recent results on estimation of frequency domain model uncertainty are...
Frequency Domain Electroretinography in Retinitis Pigmentosa versus Normal Eyes
Homa Hassan-Karimi
2012-01-01
Full Text Available Purpose: To compare electroretinogram (ERG characteristics in patients with retinitis pigmentosa (RP and normal subjects using frequency domain analysis. Methods: Five basic ERG recordings were performed in normal subjects and patients with a clinical diagnosis of RP according to the ISCEV (International Society of Clinical Electrophysiology of Vision protocol. Frequency domain analysis was performed by MATLAB software. Different frequency domain parameters were compared between the study groups. Results: Peak frequency (Fmod of flicker and oscillatory responses in RP patients showed significant (P<0.0001 high pass response as compared to normal controls. Peak frequency (Fmod of the other responses was not significantly different between the two groups. Conclusion: In addition to conventional ERG using time domain methods, frequency domain analysis may be useful for diagnosis of RP. Oscillatory and flicker responses may be analyzed in frequency domain. Fast Fourier transform may reveal two distinct high pass responses (shift to higher frequencies in Fmod. Time and frequency domain analyses may be performed simultaneously with many modern ERG machines and may therefore be recommended in RP patients.
Two-photon experiments in the frequency domain
Mbodji, I.; Olislager, L.; Woodhead, E.; Galmes, B.; Cussey, J.; Furfaro, L.; Emplit, P.; Massar, S.; Phan Huy, K.; Merolla, J.-M.
2012-06-01
We report on the study of two-photon interference in the frequency domain. Bell and Hong-Ou-Mandel experiments are investigated. These experiments involve the manipulation of photons in the frequency domain, using off-the-shelf telecommunication components such as electro-optic phase modulators and narrow-band frequency filters. In the first experiment, photon pairs entangled in frequency are created and separated. Each photon is then directed through an independent electro-optic phase modulator. Variation of the radio-frequency parameters of the modulation gives rise to a well-controlled Bessel-shape two-photon interference pattern in the frequency domain. This is efficiently measured with narrow-band frequency filters and superconducting single photon detectors. Experimental measurements exhibit high visibilities (over 99 percent both for net and raw visibilities) and allow the (theoretically proven) optimal violation of a Bell inequality for our setup (by more than 18 standard deviations). The second experiment is a Hong-Ou-Mandel experiment in the frequency domain. We show that a grating (spatial domain) or a phase modulator (temporal domain) can be seen as a frequency beam splitter. A broadband spectrum of photon pairs is divided into two interleaved frequency combs, each one used as an independent input to this acting beam splitter. A theoretical calculation shows clear photon anti-bunching behavior.
On Frequency Domain Models for TDOA Estimation
Jensen, Jesper Rindom; Nielsen, Jesper Kjær; Christensen, Mads Græsbøll;
2015-01-01
much more general method. In this connection, we establish the conditions under which the cross-correlation method is a statistically efficient estimator. One of the conditions is that the source signal is periodic with a known fundamental frequency of 2π/N radians per sample, where N is the number of...
Frequency-domain method for separating signal and noise
王正明; 段晓君
2000-01-01
A new method for separation of signal and noise (SSN) is put forward. Frequency is redefined according to the features of signal and its derivative in the sampling time interval, thus double orthogonal basis (DOB) is constructed so that a signal can be precisely signified with a linear combination of low-frequency DOB. Under joint consideration in time domain (TD) and frequency domain (FD), a method on SSN with high accuracy is derived and a matched algorithm is designed and analyzed. This method is applicable to SSN in multiple frequency bands, and convenient in applying signal characteristics in TD and FD synthetically with higher accuracy.
Frequency-domain method for separating signal and noise
无
2000-01-01
A new method for separation of signal and noise (SSN) is put forward. Frequency is redefined according to the features of signal and its derivative in the sampl ing time interval, thus double orthogonal basis (DOB) is constructed so that a signal can be precisely signified with a linear combination of low-frequency DOB . Under joint consideration in time domain (TD) and frequency domain (FD), a method on SSN with high accuracy is derived and a matched algorithm is designed and analyzed. This method is applicable to SSN in multiple frequency bands, and convenient in applying signal characteristics in TD and FD synthetically with highe raccuracy.
Incoherent Optical Frequency Domain Reflectometry for Distributed Thermal Sensing
Karamehmedovic, Emir; Jeppesen, Palle; Peucheret, Christophe; Bjarklev, Anders Overgaard
2006-01-01
This thesis reports the main results from an investigation of a fibre-optic distributed temperature sensor based on spontaneous Raman scattering. The technique used for spatial resolving is the incoherent optical frequency domain reflectometry, where a pump laser is sine modulated with a stepwise increasing frequency, after which the inverse Fourier transform is applied to the signal from the backscattered light. This technique is compared with the more conventional optical time domain reflec...
Robust time and frequency domain estimation methods in adaptive control
Lamaire, Richard Orville
1987-01-01
A robust identification method was developed for use in an adaptive control system. The type of estimator is called the robust estimator, since it is robust to the effects of both unmodeled dynamics and an unmeasurable disturbance. The development of the robust estimator was motivated by a need to provide guarantees in the identification part of an adaptive controller. To enable the design of a robust control system, a nominal model as well as a frequency-domain bounding function on the modeling uncertainty associated with this nominal model must be provided. Two estimation methods are presented for finding parameter estimates, and, hence, a nominal model. One of these methods is based on the well developed field of time-domain parameter estimation. In a second method of finding parameter estimates, a type of weighted least-squares fitting to a frequency-domain estimated model is used. The frequency-domain estimator is shown to perform better, in general, than the time-domain parameter estimator. In addition, a methodology for finding a frequency-domain bounding function on the disturbance is used to compute a frequency-domain bounding function on the additive modeling error due to the effects of the disturbance and the use of finite-length data. The performance of the robust estimator in both open-loop and closed-loop situations is examined through the use of simulations.
Optimal System Realization in Frequency Domain
Juang, Jer-Nan; Maghami, Peiman G.
1999-01-01
Several approaches are presented to identify an experimental system model directly from frequency response data. The formulation begins with a matrix-fraction description as the model structure. Frequency weighting such as exponential weighting is introduced to solve a weighted least-squares problem to obtain the coefficient matrices for the matrix-fraction description. A multi-variable state-space model can then be formed using the coefficient matrices of the matrix-fraction description. An approach is introduced to fine-tune the model using non-linear programming methods to minimize the desired cost function. The method deals with the model in the real Schur or modal form and reassigns a subset of system poles using a nonlinear optimizer. At every optimization step, the input and output influence matrices are refined through least-squares procedures. The proposed approaches are used to identify an analytical model for a NASA testbed from experimental data.
Estimation of luminescence lifetime in frequency domain
Zhang Fu-Jun; Xu Zheng; Zhao Su-Ling; Lou Zhi-Dong; Yang Sheng-Yi; Xu Xu-Rong
2006-01-01
Absorption is the origin of luminescence. But it must be noticed that the lifetime of luminescence might reversely influence the rate of absorption. In this paper, it is reported that the luminescence intensity of copper and manganese changes with the driving frequency at constant voltage. The variation of luminescent intensity depends only on the lifetime of luminescence but not on the type of quenching or other factors. Generally the rate of absorption is dominantly determined by the material property and the lifetime of luminescence centres, the absorption of shorter lifetime centre will be larger than that of the longer lifetime centre at the same excited condition.
Methodology of time-domain and frequency-domain calibration and equivalence for EMP sensor
In order to measure the waveform and amplitude of EMP accurately, the sensors need to be calibrated under the standard fields in the TEM or GTEM cell. A set of calibration system is discussed. A highly accurate method of calibrating such sensors is applicable to techniques in both the frequency domain and in the time domain. The complete frequency-domain transfer function or the time-domain impulse response function of sensor system can be obtained, thus allowing deconvolution processes to be used to remove perturbations from the measurement waveform by the instrumentation and TEM cell. (authors)
On the Compensation of Delay in the Discrete Frequency Domain
Gareth Parker
2004-10-01
Full Text Available The ability of a DFT filterbank frequency domain filter to effect time domain delay is examined. This is achieved by comparing the quality of equalisation using a DFT filterbank frequency domain filter with that possible using an FIR implementation. The actual performance of each filter architecture depends on the particular signal and transmission channel, so an exact general analysis is not practical. However, as a benchmark, we derive expressions for the performance for the particular case of an allpass channel response with a delay that is a linear function of frequency. It is shown that a DFT filterbank frequency domain filter requires considerably more degrees of freedom than an FIR filter to effect such a pure delay function. However, it is asserted that for the more general problem that additionally involves frequency response magnitude modifications, the frequency domain filter and FIR filters require a more similar number of degrees of freedom. This assertion is supported by simulation results for a physical example channel.
Vector optical fields broken in the spatial frequency domain
Gao, Xu-Zhen; Pan, Yue; Li, Si-Min; Wang, Dan; Li, Yongnan; Tu, Chenghou; Wang, Hui-Tian
2016-03-01
We theoretically and experimentally explore the redistribution of polarization states and orbital angular momentum (OAM) in the output plane, induced by the symmetry breaking in the spatial frequency domain. When the vector fields are obstructed by sector-shaped filters in the spatial frequency domain, the local polarization states in the output plane undergo an abrupt transition from linear to circular polarization. The results reveal the polarization-dependent splitting and the appearance of a series of opposite OAMs in the output plane. We also find the self-healing effect of the vector fields broken in the spatial frequency domain and further explore its potential application. If the vector optical fields are used for information transferring or for imaging, even if the optical field carrying the information or image is partially blocked, the complete information or image can still be obtained, implying that which may increase the robustness of the information transferring and the imaging.
Finite-Difference Frequency-Domain Method in Nanophotonics
Ivinskaya, Aliaksandra
often indispensable. This thesis presents the development of rigorous finite-difference method, a very general tool to solve Maxwell’s equations in arbitrary geometries in three dimensions, with an emphasis on the frequency-domain formulation. Enhanced performance of the perfectly matched layers is...... obtained through free space squeezing technique, and nonuniform orthogonal grids are built to greatly improve the accuracy of simulations of highly heterogeneous nanostructures. Examples of the use of the finite-difference frequency-domain method in this thesis range from simulating localized modes in a...
Frequency domain optical tomography using a Monte Carlo perturbation method
Yamamoto, Toshihiro; Sakamoto, Hiroki
2016-04-01
A frequency domain Monte Carlo method is applied to near-infrared optical tomography, where an intensity-modulated light source with a given modulation frequency is used to reconstruct optical properties. The frequency domain reconstruction technique allows for better separation between the scattering and absorption properties of inclusions, even for ill-posed inverse problems, due to cross-talk between the scattering and absorption reconstructions. The frequency domain Monte Carlo calculation for light transport in an absorbing and scattering medium has thus far been analyzed mostly for the reconstruction of optical properties in simple layered tissues. This study applies a Monte Carlo calculation algorithm, which can handle complex-valued particle weights for solving a frequency domain transport equation, to optical tomography in two-dimensional heterogeneous tissues. The Jacobian matrix that is needed to reconstruct the optical properties is obtained by a first-order "differential operator" technique, which involves less variance than the conventional "correlated sampling" technique. The numerical examples in this paper indicate that the newly proposed Monte Carlo method provides reconstructed results for the scattering and absorption coefficients that compare favorably with the results obtained from conventional deterministic or Monte Carlo methods.
Fast Cycle Frequency Domain Feature Detection for Cognitive Radio Systems
Da, Shan; Xiaoying, Gan; Hsiao-Hwa, Chen; Liang, Qian
2009-01-01
In cognitive radio systems, one of the main requirements is to detect the presence of the primary users' transmission, especially in weak signal cases. Cyclostationary detection is always used to solve weak signal detection, however, the computational complexity prevents it from wide usage. In this paper, a fast cycle frequency domain feature detection algorithm has been proposed, in which only feature frequency with significant cyclic signature is considered for a certain modulation mode. Si...
Frequency Domain Storage Ring Method for Electric Dipole Moment Measurement
Talman, Richard
2015-01-01
Precise measurement of the electric dipole moments (EDM) of fundamental charged particles would provide a significant probe of physics beyond the standard model. Any measurably large EDM would imply violation of both time reversal and parity conservation, with implications for the matter/anti-matter imbalance of the universe, not currently understood within the standard model. A frequency domain (i.e. difference of frequencies) method is proposed for measuring the EDM of electrons or protons ...
Broadband Beamspace DOA Estimation: Frequency-Domain and Time-Domain Processing Approaches
Yan Shefeng
2007-01-01
Full Text Available Frequency-domain and time-domain processing approaches to direction-of-arrival (DOA estimation for multiple broadband far field signals using beamspace preprocessing structures are proposed. The technique is based on constant mainlobe response beamforming. A set of frequency-domain and time-domain beamformers with constant (frequency independent mainlobe response and controlled sidelobes is designed to cover the spatial sector of interest using optimal array pattern synthesis technique and optimal FIR filters design technique. These techniques lead the resulting beampatterns higher mainlobe approximation accuracy and yet lower sidelobes. For the scenario of strong out-of-sector interfering sources, our approaches can form nulls or notches in the direction of them and yet guarantee that the mainlobe response of the beamformers is constant over the design band. Numerical results show that the proposed time-domain processing DOA estimator has comparable performance with the proposed frequency-domain processing method, and that both of them are able to resolve correlated source signals and provide better resolution at lower signal-to-noise ratio (SNR and lower root-mean-square error (RMSE of the DOA estimate compared with the existing method. Our beamspace DOA estimators maintain good DOA estimation and spatial resolution capability in the scenario of strong out-of-sector interfering sources.
Automated Frequency Domain Decomposition for Operational Modal Analysis
Brincker, Rune; Andersen, Palle; Jacobsen, Niels-Jørgen
2007-01-01
The Frequency Domain Decomposition (FDD) technique is known as one of the most user friendly and powerful techniques for operational modal analysis of structures. However, the classical implementation of the technique requires some user interaction. The present paper describes an algorithm for...
Incoherent Optical Frequency Domain Reflectometry for Distributed Thermal Sensing
Karamehmedovic, Emir
2006-01-01
This thesis reports the main results from an investigation of a fibre-optic distributed temperature sensor based on spontaneous Raman scattering. The technique used for spatial resolving is the incoherent optical frequency domain reflectometry, where a pump laser is sine modulated with a stepwise...
Charge domain filter operating up to 20 MHz clock frequency
Gal, R.A.J.; Wallinga, H.
1983-01-01
An analog sampled data low pass third order Butterworth filter has been realised in a buried channel CCD technology. This Charge Domain Filter, composed of transversal and recursive CCD filter sections, has been tested at clock frequencies up to 20 MHz.
A Frequency-domain test for long range dependence
Gromykov, G; Ould Haye, M; Philippe, Anne
2016-01-01
A new frequency-domain test statistic is introduced to test for short memory versus long memory. We provide its asymptotic distribution under the null hypothesis and show that it is consistent under any long memory alternative. Some simulation studies show that this test is more robust than various standard tests in terms of empirical size when the normality of observed process is lost.
Modal Identification from Ambient Responses Using Frequency Domain Decomposition
Brincker, Rune; Zhang, Lingmi; Andersen, Palle
2000-01-01
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical...
Modal Identification from Ambient Responses using Frequency Domain Decomposition
Brincker, Rune; Zhang, L.; Andersen, P.
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, ie. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical...
Frequency-domain thermal modelling of power semiconductor devices
Ma, Ke; Blaabjerg, Frede; Andresen, Markus;
2015-01-01
to correctly predict the device temperatures, especially when considering the thermal grease and heat sink attached to the power semiconductor devices. In this paper, the frequency-domain approach is applied to the modelling of thermal dynamics for power devices. The limits of the existing RC lump...
A Frequency Domain Design Method For Sampled-Data Compensators
Niemann, Hans Henrik; Jannerup, Ole Erik
1990-01-01
A new approach to the design of a sampled-data compensator in the frequency domain is investigated. The starting point is a continuous-time compensator for the continuous-time system which satisfy specific design criteria. The new design method will graphically show how the discrete...
High frequency resolution terahertz time-domain spectroscopy
Sangala, Bagvanth Reddy
2013-12-01
A new method for the high frequency resolution terahertz time-domain spectroscopy is developed based on the characteristic matrix method. This method is useful for studying planar samples or stack of planar samples. The terahertz radiation was generated by optical rectification in a ZnTe crystal and detected by another ZnTe crystal via electro-optic sampling method. In this new characteristic matrix based method, the spectra of the sample and reference waveforms will be modeled by using characteristic matrices. We applied this new method to measure the optical constants of air. The terahertz transmission through the layered systems air-Teflon-air-Quartz-air and Nitrogen gas-Teflon-Nitrogen gas-Quartz-Nitrogen gas was modeled by the characteristic matrix method. A transmission coefficient is derived from these models which was optimized to fit the experimental transmission coefficient to extract the optical constants of air. The optimization of an error function involving the experimental complex transmission coefficient and the theoretical transmission coefficient was performed using patternsearch algorithm of MATLAB. Since this method takes account of the echo waveforms due to reflections in the layered samples, this method allows analysis of longer time-domain waveforms giving rise to very high frequency resolution in the frequency-domain. We have presented the high frequency resolution terahertz time-domain spectroscopy of air and compared the results with the literature values. We have also fitted the complex susceptibility of air to the Lorentzian and Gaussian functions to extract the linewidths.
SPA- STATISTICAL PACKAGE FOR TIME AND FREQUENCY DOMAIN ANALYSIS
Brownlow, J. D.
1994-01-01
The need for statistical analysis often arises when data is in the form of a time series. This type of data is usually a collection of numerical observations made at specified time intervals. Two kinds of analysis may be performed on the data. First, the time series may be treated as a set of independent observations using a time domain analysis to derive the usual statistical properties including the mean, variance, and distribution form. Secondly, the order and time intervals of the observations may be used in a frequency domain analysis to examine the time series for periodicities. In almost all practical applications, the collected data is actually a mixture of the desired signal and a noise signal which is collected over a finite time period with a finite precision. Therefore, any statistical calculations and analyses are actually estimates. The Spectrum Analysis (SPA) program was developed to perform a wide range of statistical estimation functions. SPA can provide the data analyst with a rigorous tool for performing time and frequency domain studies. In a time domain statistical analysis the SPA program will compute the mean variance, standard deviation, mean square, and root mean square. It also lists the data maximum, data minimum, and the number of observations included in the sample. In addition, a histogram of the time domain data is generated, a normal curve is fit to the histogram, and a goodness-of-fit test is performed. These time domain calculations may be performed on both raw and filtered data. For a frequency domain statistical analysis the SPA program computes the power spectrum, cross spectrum, coherence, phase angle, amplitude ratio, and transfer function. The estimates of the frequency domain parameters may be smoothed with the use of Hann-Tukey, Hamming, Barlett, or moving average windows. Various digital filters are available to isolate data frequency components. Frequency components with periods longer than the data collection interval
Hybrid time/frequency domain modeling of nonlinear components
Wiechowski, Wojciech Tomasz; Lykkegaard, Jan; Bak, Claus Leth;
2007-01-01
This paper presents a novel, three-phase hybrid time/frequency methodology for modelling of nonlinear components. The algorithm has been implemented in the DIgSILENT PowerFactory software using the DIgSILENT Programming Language (DPL), as a part of the work described in [1]. Modified HVDC benchmark...... model is used as a basis for its implementation. First, the linear network part is replaced with an ideal voltage source and a time domain (EMT) simulation is performed. During the initial oscillations, harmonic content of the converter currents is calculated at every period by a fast Fourier transform...... and the periodic steady state is identified. Obtained harmonic currents are assigned to current sources and used in the frequency domain calculation in the linear network. The obtained three-phase bus voltage is then inverse Fourier transformed and assigned to the voltage source and the time domain simulation...
Time-domain control of ultrahigh-frequency nanomechanical systems.
Liu, N; Giesen, F; Belov, M; Losby, J; Moroz, J; Fraser, A E; McKinnon, G; Clement, T J; Sauer, V; Hiebert, W K; Freeman, M R
2008-12-01
Nanoelectromechanical systems could have applications in fields as diverse as ultrasensitive mass detection and mechanical computation, and can also be used to explore fundamental phenomena such as quantized heat conductance and quantum-limited displacement. Most nanomechanical studies to date have been performed in the frequency domain. However, applications in computation and information storage will require transient excitation and high-speed time-domain operation of nanomechanical systems. Here we show a time-resolved optical approach to the transduction of ultrahigh-frequency nanoelectromechanical systems, and demonstrate that coherent control of nanomechanical oscillation is possible through appropriate pulse programming. A series of cantilevers with resonant frequencies ranging from less than 10 MHz to over 1 GHz are characterized using the same pulse parameters. PMID:19057589
Thermal Loss of High-Q Antennas in Time Domain vs. Frequency Domain Solver
Bahramzy, Pevand; Pedersen, Gert Frølund
High-Q structures pose great challenges to their loss simulations in Time Domain Solvers (TDS). Therefore, in this work the thermal loss of high-Q antennas is calculated both in TDS and Frequency Domain Solver (FDS), which are then compared with each other and with the actual measurements. The...... thermal loss calculation in FDS is shown to be more accurate for high-Q antennas....
Feng, Xiaobing [Univ. of Tennessee, Knoxville, TN (United States)
1996-12-31
A non-overlapping domain decomposition iterative method is proposed and analyzed for mixed finite element methods for a sequence of noncoercive elliptic systems with radiation boundary conditions. These differential systems describe the motion of a nearly elastic solid in the frequency domain. The convergence of the iterative procedure is demonstrated and the rate of convergence is derived for the case when the domain is decomposed into subdomains in which each subdomain consists of an individual element associated with the mixed finite elements. The hybridization of mixed finite element methods plays a important role in the construction of the discrete procedure.
Frequency-domain waveform inversion using the phase derivative
Choi, Yun Seok
2013-09-26
Phase wrapping in the frequency domain or cycle skipping in the time domain is the major cause of the local minima problem in the waveform inversion when the starting model is far from the true model. Since the phase derivative does not suffer from the wrapping effect, its inversion has the potential of providing a robust and reliable inversion result. We propose a new waveform inversion algorithm using the phase derivative in the frequency domain along with the exponential damping term to attenuate reflections. We estimate the phase derivative, or what we refer to as the instantaneous traveltime, by taking the derivative of the Fourier-transformed wavefield with respect to the angular frequency, dividing it by the wavefield itself and taking the imaginary part. The objective function is constructed using the phase derivative and the gradient of the objective function is computed using the back-propagation algorithm. Numerical examples show that our inversion algorithm with a strong damping generates a tomographic result even for a high ‘single’ frequency, which can be a good initial model for full waveform inversion and migration.
Statistical multiresolution analysis in amplitude-frequency domain
SUN Hong; GUAN Bao; Henri Maitre
2004-01-01
A concept of statistical multiresolution analysis in amplitude-frequency domain is proposed, which is to employ the wavelet transform on the statistical character of a signal in amplitude domain. In terms of the theorem of generalized ergodicity, an algorithm to estimate the transform coefficients based on the amplitude statistical multiresolution analysis (AMA) is presented. The principle of applying the AMA to Synthetic Aperture Radar (SAR) image processing is described, and the good experimental results imply that the AMA is an efficient tool for processing of speckled signals modeled by the multiplicative noise.
High-speed frequency-domain terahertz coherence tomography.
Yahng, Ji Sang; Park, Choon-Su; Don Lee, Hwi; Kim, Chang-Seok; Yee, Dae-Su
2016-01-25
High-speed frequency-domain terahertz (THz) coherence tomography is demonstrated using frequency sweeping of continuous-wave THz radiation and beam steering. For axial scanning, THz frequency sweeping with a kHz sweep rate and a THz sweep range is executed using THz photomixing with an optical beat source consisting of a wavelength-swept laser and a distributed feedback laser diode. During the frequency sweep, frequency-domain THz interferograms are measured using coherent homodyne detection employing signal averaging for noise reduction and used as axial-scan data via fast Fourier transform. Axial-scan data are acquired while scanning a transverse range of 100 × 100 mm2 by use of a THz beam scanner with moving neither sample nor THz transmitter/receiver unit. It takes 100 s to acquire axial-scan data for 100 × 100 points with 5 averaged traces at a sweep rate of 1 kHz. THz tomographic images of a glass fiber reinforced polymer sample with artificial internal defects are presented, acquired using the tomography system. PMID:26832489
Single SQUID frequency-domain multiplexer for large bolometer arrays
We describe the development of a frequency-domain superconducting quantum interference device (SQUID) multiplexer which monitors a row of low-temperature sensors simultaneously with a single SQUID. Each sensor is ac biased with a unique frequency and all the sensor currents are added in a superconducting summing loop. A single SQUID measures the current in the summing loop, and the individual signals are lock-in detected after the room temperature SQUID electronics. The current in the summing loop is nulled by feedback to eliminate direct crosstalk. We have built an eight-channel prototype and demonstrated channel separation and signal recovery
Buried object location based on frequency-domain UWB measurements
In this paper, a wideband ground penetrating radar (GPR) system and a proposed frequency-domain data analysis technique are presented for the detection of shallow buried objects such as anti-personnel landmines. The GPR system uses one transmitting antenna and an array of six monopole receiving antenna elements and operates from 1 GHz to 20 GHz. This system is able to acquire, save and analyse data in the frequency domain. A common source or wide-angle reflection and refraction technique has been used for acquiring and processing the data. This technique is effective for the rejection of ground surface clutter. By applying the C-scan scheme, metallic and plastic mine-like targets buried in dry soil will be located
Speaker Identification using Frequency Dsitribution in the Transform Domain
Dr. H B Kekre
2012-02-01
Full Text Available In this paper, we propose Speaker Identification using the frequency distribution of various transforms like DFT (Discrete Fourier Transform, DCT (Discrete Cosine Transform, DST (Discrete Sine Transform, Hartley, Walsh, Haar and Kekre transforms. The speech signal spoken by a particular speaker is converted into frequency domain by applying the different transform techniques. The distribution in the transform domain is utilized to extract the feature vectors in the training and the matching phases. The results obtained by using all the seven transform techniques have been analyzed and compared. It can be seen that DFT, DCT, DST and Hartley transform give comparatively similar results (Above 96%. The results obtained by using Haar and Kekre transform are very poor. The best results are obtained by using DFT (97.19% for a feature vector of size 40.
Research on the frequency domain ∑△-DPCA
Shen Mingwei; Zhu Daiyin; Zhu Zhaoda
2008-01-01
The frequency domain ∑△-DPCA processing (F-∑△-DPCA) is investigated in detail, and an im-proved scheme for the F-]EA-DPCA is proposed, which can significantly reduce the computational burden. In practice, because of the sum and difference beam pattern designed independently and other system errors, the clutter suppression of the time domain ∑△-DPCA processing (T-∑△-DPCA) is significantly degraded. However,the F-∑△-DPCA adaptively calculates the optimum gain ratio for motion compensation within each Doppler cell,which is robust to system errors. Theoretical analysis and simulation results are presented to validate that the F-∑△-DPCA can achieve superior performance of clutter cancellation than the time domain processing, and its performance can be significantly increased if more pulses are used for the Doppler filtering. The improved approach is efficient, and feasible for real-time application.
Frequency-domain modelling of floating wind turbines
Lupton, Richard
2015-01-01
The development of new types of offshore wind turbine on floating platforms requires the development of new approaches to modelling the combined platform-turbine system. In this thesis a linearised frequency-domain approach is developed which gives fast but approximate results: linearised models of the structural dynamics, hydrodynamics, aerodynamics and control system dynamics are brought together to find the overall response of the floating wind turbine to harmonic wind...
Frequency domain stability criteria for fractional-order control systems
无
2006-01-01
This paper concerns about the frequency domain stability criteria for fractional-order control systems. On the base of characteristics of the fractional-order equations solutions, we consider the Nyquist stability criterion in a wider sense and obtain a more common means to analyze the stability of fractional-order systems conveniently. Finally, this paper illustrates the generalized stability criteria with an example to show the effect of the parameters variation on the fractional-order control systems.
Kumar, Anand T. N.
2013-01-01
It is demonstrated that high spatial frequency filtering of time domain fluorescence signals can allow efficient detection of intrinsic fluorescence lifetimes from turbid media and the rejection of diffuse excitation leakage. The basis of this approach is the separation of diffuse fluorescence signals into diffuse and fluorescent components with distinct spatiotemporal behavior.
Spatial frequency domain spectroscopy of two layer media
Yudovsky, Dmitry; Durkin, Anthony J.
2011-10-01
Monitoring of tissue blood volume and oxygen saturation using biomedical optics techniques has the potential to inform the assessment of tissue health, healing, and dysfunction. These quantities are typically estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in superficial tissue such as the skin can be confounded by the strong absorption of melanin in the epidermis. Furthermore, epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. This study describes a technique for decoupling the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. An artificial neural network was used to map input optical properties to spatial frequency domain diffuse reflectance of two layer media. Then, iterative fitting was used to determine the optical properties from simulated spatial frequency domain diffuse reflectance. Additionally, an artificial neural network was trained to directly map spatial frequency domain reflectance to sets of optical properties of a two layer medium, thus bypassing the need for iteration. In both cases, the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis were determined independently. The accuracy and efficiency of the iterative fitting approach was compared with the direct neural network inversion.
Frequency-domain waveform inversion using the unwrapped phase
Choi, Yun Seok
2011-01-01
Phase wrapping in the frequency-domain (or cycle skipping in the time-domain) is the major cause of the local minima problem in the waveform inversion. The unwrapped phase has the potential to provide us with a robust and reliable waveform inversion, with reduced local minima. We propose a waveform inversion algorithm using the unwrapped phase objective function in the frequency-domain. The unwrapped phase, or what we call the instantaneous traveltime, is given by the imaginary part of dividing the derivative of the wavefield with respect to the angular frequency by the wavefield itself. As a result, the objective function is given a traveltime-like function, which allows us to smooth it and reduce its nonlinearity. The gradient of the objective function is computed using the back-propagation algorithm based on the adjoint-state technique. We apply both our waveform inversion algorithm using the unwrapped phase and the conventional waveform inversion and show that our inversion algorithm gives better convergence to the true model than the conventional waveform inversion. © 2011 Society of Exploration Geophysicists.
Numerical methods for time-domain and frequency-domain analysis: applications in engineering
Tamas, R. D.
2015-11-01
Numerical methods are widely used for modeling different physical phenomena in engineering, especially when an analytic approach is not possible. Time-domain or frequency- domain type variations are generally investigated, depending on the nature of the process under consideration. Some methods originate from mechanics, although most of their applications belong to other fields, such as electromagnetism. Conversely, other methods were firstly developed for electromagnetism, but their field of application was extended to other fields. This paper presents some results that we have obtained by using a general purpose method for solving linear equations, i.e., the method of moments (MoM), and a time-domain method derived for electromagnetism, i.e., the Transmission Line Matrix method (TLM).
A review of time-domain and frequency-domain component mode synthesis method
Craig, R. R., Jr.
1985-01-01
Hurty (1965) has conducted a dynamic analysis of structural systems using component modes. The component mode synthesis (CMS) procedure considered by him represents a form of substructure coupling analysis which is often utilized in structural dynamics. Time-domain CMS methods employing real modes are discussed, taking into account real component modes, normal modes, redundant constraint modes, rigid-body modes, attachment modes, inertia-relief modes, statically-complete interface mode sets, dynamic component mode supersets, component modal models, the coupling of components, and the classification of methods. Attention is also given to the experimental determination of component mode synthesis parameters, time-domain CMS methods for damped systems, and frequency-domain CMS methods for damped systems.
A frequency domain approach to handling qualities design
Wolovich, W. A.
1978-01-01
A method for designing linear multivariable feedback control systems based on desired closed loop transfer matrix information is introduced. The technique which was employed to achieve the final design was based on a theoretical result, known as the structure theorem. The structure theorem was a frequency domain relationship which simplified the expression for the transfer matrix (matrix of transfer functions) of a linear time-invariant multivariable system. The effect of linear state variable feedback on the closed loop transfer matrix of the system was also clarified.
Frequency domain quantum optimal control under multiple constraints
Shu, Chuan-Cun; Ho, Tak-San; Xing, Xi; Rabitz, Herschel
2016-03-01
Optimal control of quantum systems with complex constrained external fields is one of the longstanding theoretical and numerical challenges at the frontier of quantum control research. Here, we present a theoretical method that can be utilized to optimize the control fields subject to multiple constraints while guaranteeing monotonic convergence towards desired physical objectives. This optimization method is formulated in the frequency domain in line with the current ultrafast pulse shaping technique, providing the possibility for performing quantum optimal control simulations and experiments in a unified fashion. For illustrations, this method is successfully employed to perform multiple constraint spectral-phase-only optimization for maximizing resonant multiphoton transitions with desired pulses.
Frequency Domain LED Compensation for Nonlinearity Mitigation in DMT Systems
Peng, Linning; Haese, Sylvain; Hélard, Maryline
2013-01-01
In this letter, a novel linear frequency-domain compensation (FDC) of the resonant cavity light emitting diode (RC-LED) for discrete multi-tone (DMT) modulation has been used for the first time in the nonlinearity mitigation of step-index polymer optical fiber (SI-POF) communication systems. The proposed FDC method can be easily implemented in any multi-carrier communication system. Compared to the classical DMT scheme, FDC DMT benefits from higher power efficiency in terms of clipping for pe...
Causality between regional stock markets: A frequency domain approach
Gradojević Nikola
2013-01-01
Full Text Available Using a data set from five regional stock exchanges (Serbia, Croatia, Slovenia, Hungary and Germany, this paper presents a frequency domain analysis of a causal relationship between the returns on the CROBEX, SBITOP, CETOP and DAX indices, and the return on the major Serbian stock exchange index, BELEX 15. We find evidence of a somewhat dominant effect of the CROBEX and CETOP stock indices on the BELEX 15 stock index across a range of frequencies. The results also indicate that the BELEX 15 index and the SBITOP index interact in a bi-directional causal fashion. Finally, the DAX index movements consistently drive the BELEX 15 index returns for cycle lengths between 3 and 11 days without any feedback effect.
Frequency domain identification for robust large space structure control design
Yam, Y.; Bayard, D. S.; Scheid, R. E.
1991-01-01
A methodology is demonstrated for frequency domain identification of large space structures which systematically transforms experimental raw data into a form required for synthesizing H(infinity) controllers using modern robust control design software (e.g., Matlab Toolboxes). A unique feature of this approach is that the additive uncertainty is characterized to a specified statistic confidence rather than with hard bounds. In this study, the difference in robust performance is minimal between the two levels of confidence. In general cases, the present methodology provides a tool for performance/confidence level tradeoff studies. For simplicity, the additive uncertainty on a frequency grid is considered and the interpolation error in between grid points is neglected.
Frequency Domain Storage Ring Method for Electric Dipole Moment Measurement
Talman, Richard
2015-01-01
Precise measurement of the electric dipole moments (EDM) of fundamental charged particles would provide a significant probe of physics beyond the standard model. Any measurably large EDM would imply violation of both time reversal and parity conservation, with implications for the matter/anti-matter imbalance of the universe, not currently understood within the standard model. A frequency domain (i.e. difference of frequencies) method is proposed for measuring the EDM of electrons or protons or, with modifications, deuterons. Anticipated precision (i.e. reproducibility) is $10^{-30}\\,$e-cm for the proton EDM, with comparable accuracy (i.e. including systematic error). This would be almost six orders of magnitude smaller than the present upper limit, and will provide a stringent test of the standard model. Resonant polarimetry, made practical by the large polarized beam charge, is the key (most novel, least proven) element of the method. Along with the phase-locked, rolling polarization "Koop spin wheel," reso...
Frequency-Wavenumber Domain Filtering for Improved Damage Visualization
This paper presents a technique for the analysis of full wavefield data in the wavenumber/frequency domain as an effective tool for damage detection, visualization and characterization. Full wavefield data contain a wealth of information regarding the space and time variation of propagating waves in damaged structural components. Such information can be used to evaluate the response spectrum in the frequency/wavenumber domain, which effectively separates incident waves from reflections caused by discontinuities encountered along the wave paths. This allows removing the injected wave from the overall response through simple filtering strategies, thus highlighting the presence of reflections associated to damage. The concept is first illustrated on analytical and numerically simulated data, and then tested on experimental results. In the experiments, full wavefield measurements are conveniently obtained using a Scanning Laser Doppler Vibrometer, which allows the detection of displacements and/or velocities over a user-defined grid, and it is able to provide the required spatial and time information in a timely manner. Tests performed on a simple aluminum plate with artificially seeded slits simulating longitudinal cracks, and on a disbonded tongue and groove joint show the effectiveness of the technique and its potential for application to the inspection of a variety of structural components
Frequency-wavenumber domain phase inversion along reflection wavepaths
Yu, Han
2014-12-01
A background velocity model containing the correct low-wavenumber information is desired for both the quality of the migration image and the success of waveform inversion. To achieve this goal, the velocity is updated along the reflection wavepaths, rather than along both the reflection ellipses and transmission wavepaths as in conventional FWI. This method allows for reconstructing the low-wavenumber part of the background velocity model, even in the absence of long offsets and low-frequency component of the data. Moreover, in gradient-based iterative updates, instead of forming the data error conventionally, we propose to exploit the phase mismatch between the observed and the calculated data. The phase mismatch emphasizes a kinematic error and varies quasi-linearly with respect to the velocity error. The phase mismatch is computed (1) in the frequency-wavenumber (f-k) domain replacing the magnitudes of the calculated common shot gather by those of the observed one, and (2) in the temporal-spatial domain to form the difference between the transformed calculated common-shot gather and the observed one. The background velocity model inverted according to the proposed methods can serve as an improved initial velocity model for conventional waveform inversion. Tests with synthetic and field data show both the benefits and limitations of this method.
Propagation of Optical Pulses and Pulsed Beams in the Frequency Domain
林强; 王立刚
2001-01-01
The diffraction integral formulae in the temporal and spatial-temporal frequency domains are derived by using a Fourier transform and tensor analysis method. Based on these formulae, the abcd law in the temporal frequency domain and the tensor ABCD law in the four-dimensional spatial-temporal frequency domain are derived. An application example of the derived formulae is provided.
Pan Jin; Wang De-yu
2006-01-01
In this paper, adaptive genetic algorithm (AGA) is applied to topology optimization of truss structure with frequency domain excitations. The optimization constraints include fundamental frequency, displacement responses under force excitations and acceleration responses under foundation acceleration excitations. The roulette wheel selection operator, adaptive crossover and mutation operators are used as genetic operators. Some heuristic strategies are put forward to direct the deletion of the extra bars and nodes on truss structures. Three examples demonstrate that the proposed method can yield the optimum structure form and the lightest weight of the given ground structure while satisfying dynamic response constraints.
Synchronous machine parameter identification in frequency and time domain
Hasni M.
2007-01-01
Full Text Available This paper presents the results of a frequency and time-domain identification procedure to estimate the linear parameters of a salient-pole synchronous machine at standstill. The objective of this study is to use several input signals to identify the model structure and parameters of a salient-pole synchronous machine from standstill test data. The procedure consists to define, to conduct the standstill tests and also to identify the model structure. The signals used for identification are the different excitation voltages at standstill and the flowing current in different windings. We estimate the parameters of operational impedances, or in other words the reactance and the time constants. The tests were carried out on synchronous machine of 1.5 kVA 380V 1500 rpm.
Spike sorting in the frequency domain with overlap detection
Rinberg, D; Davidowitz, H; Tishby, N; Rinberg, Dima; Bialek, William; Davidowitz, Hanan; Tishby, Naftali
2003-01-01
This paper deals with the problem of extracting the activity of individual neurons from multi-electrode recordings. Important aspects of this work are: 1) the sorting is done in two stages - a statistical model of the spikes from different cells is built and only then are occurrences of these spikes in the data detected by scanning through the original data, 2) the spike sorting is done in the frequency domain, 3) strict statistical tests are applied to determine if and how a spike should be classiffed, 4) the statistical model for detecting overlaping spike events is proposed, 5) slow dynamics of spike shapes are tracked during long experiments. Results from the application of these techniques to data collected from the escape response system of the American cockroach, Periplaneta americana, are presented.
Spectrally balanced detection for optical frequency domain imaging.
Chen, Yueli; de Bruin, Daniel M; Kerbage, Charles; de Boer, Johannes F
2007-12-10
In optical frequency domain imaging (OFDI) or swept-source optical coherence tomography, balanced detection is required to suppress relative intensity noise (RIN). A regular implementation of balanced detection by combining reference and sample arm signal in a 50/50 coupler and detecting the differential output with a balanced receiver is however, not perfect. Since the splitting ratio of the 50/50 coupler is wavelength dependent, RIN is not optimally canceled at the edges of the wavelength sweep. The splitting ratio has a nearly linear shift of 0.4% per nanometer. This brings as much as +/-12% deviation at the margins of wavelength-swept range centered at 1060nm. We demonstrate a RIN suppression of 33dB by spectrally corrected balanced detection, 11dB more that regular balanced detection. PMID:19550929
Noise characteristics of heterodyne/homodyne frequency-domain measurements
Kang, Dongyel; Kupinski, Matthew A.
2012-01-01
We theoretically develop and experimentally validate the noise characteristics of heterodyne and/or homodyne measurements that are widely used in frequency-domain diffusive imaging. The mean and covariance of the modulated heterodyne output are derived by adapting the random amplification of a temporal point process. A multinomial selection rule is applied to the result of the temporal noise analysis to additionally model the spatial distribution of intensified photons measured by a charge-coupled device (CCD), which shows that the photon detection efficiency of CCD pixels plays an important role in the noise property of detected photons. The approach of using a multinomial probability law is validated from experimental results. Also, experimentally measured characteristics of means and variances of homodyne outputs are in agreement with the developed theory. The developed noise model can be applied to all photon amplification processes.
Iterative procedures for wave propagation in the frequency domain
Kim, Seongjai [Rice Univ., Houston, TX (United States); Symes, W.W.
1996-12-31
A parallelizable two-grid iterative algorithm incorporating a domain decomposition (DD) method is considered for solving the Helmholtz problem. Since a numerical method requires choosing at least 6 to 8 grid points per wavelength, the coarse-grid problem itself is not an easy task for high frequency applications. We solve the coarse-grid problem using a nonoverlapping DD method. To accelerate the convergence of the iteration, an artificial damping technique and relaxation parameters are introduced. Automatic strategies for finding efficient parameters are discussed. Numerical results are presented to show the effectiveness of the method. It is numerically verified that the rate of convergence of the algorithm depends on the wave number sub-linearly and does not deteriorate as the mesh size decreases.
Face identification with frequency domain matched filtering in mobile environments
Lee, Dong-Su; Woo, Yong-Hyun; Yeom, Seokwon; Kim, Shin-Hwan
2012-06-01
Face identification at a distance is very challenging since captured images are often degraded by blur and noise. Furthermore, the computational resources and memory are often limited in the mobile environments. Thus, it is very challenging to develop a real-time face identification system on the mobile device. This paper discusses face identification based on frequency domain matched filtering in the mobile environments. Face identification is performed by the linear or phase-only matched filter and sequential verification stages. The candidate window regions are decided by the major peaks of the linear or phase-only matched filtering outputs. The sequential stages comprise a skin-color test and an edge mask filtering test, which verify color and shape information of the candidate regions in order to remove false alarms. All algorithms are built on the mobile device using Android platform. The preliminary results show that face identification of East Asian people can be performed successfully in the mobile environments.
An Improved Frequency Domain Technique for Determining Soil Water Content
SUN Yu-Rui; MA Dao-Kun; LIN Jian-Hui; P. SCHULZE LAMMERS; L. DAMEROW
2005-01-01
For many years a soil water content sensor with low cost, reliability and sufficient accuracy has been desirable. Thus,an improved measurement method based on the frequency domain (FD) principle for determining soil water content was considered. Unlike other measurement principles, a new measurable index, η, which was independent of the output impedance and the amplitude of the oscillator while relying on the electrical impedance of a multi-pin probe, was proposed. Moreover, a model for processing the impedance of the multi-pin soil probe was developed, and several important electrical parameters for establishing their operating ranges applicable to this probe were evaluated. In order to confirm the theoretical analysis, an experiment was conducted with a 4-pin probe. Using the developed model, the relationship between the proposed indexηand soil volumetric water content was shown to be linear (R2 = 0.9921). Thus, as the measurable index, ηseemed satisfactory.
A Frequency Domain Steganography using Z Transform (FDSZT)
Mandal, J K
2012-01-01
Image steganography is art of hiding information onto the cover image. In this proposal a transformed domain based gray scale image authentication/data hiding technique using Z transform (ZT) termed as FDSZT, has been proposed. ZTransform is applied on 2x2 masks of the source image in row major order to transform original sub image (cover image) block to its corresponding frequency domain. One bit of the hidden image is embedded in each mask of the source image onto the fourth LSB of transformed coefficient based on median value of the mask. A delicate handle has also been performed as post embedding operation for proper decoding. Stego sub image is obtained through a reverse transform as final step of embedding in a mask. During the process of embedding, dimension of the hidden image followed by the content of the message/hidden image are embedded. Reverse process is followed during decoding. High PSNR obtained for various images conform the quality of invisible watermark of FDSZT.
Broadband MC DS-CDMA Using Space-Time and Frequency-Domain Spreading
Yang, L-L.; Hanzo, L.
2002-01-01
In this contribution multicarrier direct-sequence codedivision multiple-access (MC DS-CDMA) using space-time spreading (STS) assisted transmit diversity and frequency-domain (F-domain) spreading is investigated in the context of broadband communications over frequency-selective Rayleigh fading channels. We consider the attainable capacity extension of broadband MC DS-CDMA with the advent of using Time-Frequency-domain (TF-domain) spreading. The BER performance of STS assisted broadband MC DS-...
An Analog Filter Approach to Frequency Domain Fluorescence Spectroscopy.
Trainham, R; O'Neill, M; McKenna, I J
2015-11-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modelled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as SPICE can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modelling of the entire system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. The techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response. The simplification of the analysis mathematics, and the ability to model the entire detection chain, make it possible to develop more compact instruments for remote sensing applications. PMID:26429345
On time-domain and frequency-domain MMSE-based TEQ design for DMT transmission
Vanbleu, K; Moonen, M; Ysebaert, G; 10.1109/TSP.2005.851161
2005-01-01
We reconsider the minimum mean square error (MMSE) time-domain equalizer (TEQ), bitrate maximizing TEQ (BM-TEQ), and per-tone equalizer design (PTEQ) for discrete multitone (DMT) transmission and cast them in a common least-squares (LS) based framework. The MMSE- TEQ design criterion can be formulated as a constrained linear least-squares (CLLS) criterion that minimizes a time-domain (TD) error energy. From this CLLS-based TD-MMSE-TEQ criterion, we derive two new least-squares (LS) based frequency-domain (FD) MMSE-TEQ design criteria: a CLLS-based FD-MMSE-TEQ criterion and a so-called separable nonlinear LS (SNLLS) based FD-MMSE-TEQ design. Finally, the original BM-TEQ design is shown to be equivalent to a so-called iteratively-reweighted (IR) version of the SNLLS-based FD-MMSE-TEQ design. This LS-based framework then results in the following contributions. The new, IR-SNLLS-based BM-TEQ design criterion gives rise to an elegant, iterative, fast converging, Gauss-Newton-based design algorithm that exploits th...
Sreenivas, Kidambi; Whitfield, David L.
1995-01-01
Two linearized solvers (time and frequency domain) based on a high resolution numerical scheme are presented. The basic approach is to linearize the flux vector by expressing it as a sum of a mean and a perturbation. This allows the governing equations to be maintained in conservation law form. A key difference between the time and frequency domain computations is that the frequency domain computations require only one grid block irrespective of the interblade phase angle for which the flow is being computed. As a result of this and due to the fact that the governing equations for this case are steady, frequency domain computations are substantially faster than the corresponding time domain computations. The linearized equations are used to compute flows in turbomachinery blade rows (cascades) arising due to blade vibrations. Numerical solutions are compared to linear theory (where available) and to numerical solutions of the nonlinear Euler equations.
Sukanya Ray
2012-05-01
Full Text Available In recent years there has been a massive growth in textual information in textual information especially in the internet. People now tend to read more e-books than hard copies of the books. While searching for some topic especially some new topic in the internet it will be easier if someone knows the pre-requisites and post- requisites of that topic. It will be easier for someone searching a new topic. Often the topics are found without any proper title and it becomes difficult later on to find which document was for which topic. A text categorization method can provide solution to this problem. In this paper domain based ontology is created so that users can relate to different topics of a domain and an automated text categorization technique is proposed that will categorize the uncategorized documents. The proposed idea is based on Term Frequency – Inverse Document Frequency (tf -idf method and a dependency graph is also provided in the domain based ontology so that the users can visualize the relations among the terms.
Kiyono, Ken; Tsujimoto, Yutaka
2016-07-01
We develop a general framework to study the time and frequency domain characteristics of detrending-operation-based scaling analysis methods, such as detrended fluctuation analysis (DFA) and detrending moving average (DMA) analysis. In this framework, using either the time or frequency domain approach, the frequency responses of detrending operations are calculated analytically. Although the frequency domain approach based on conventional linear analysis techniques is only applicable to linear detrending operations, the time domain approach presented here is applicable to both linear and nonlinear detrending operations. Furthermore, using the relationship between the time and frequency domain representations of the frequency responses, the frequency domain characteristics of nonlinear detrending operations can be obtained. Based on the calculated frequency responses, it is possible to establish a direct connection between the root-mean-square deviation of the detrending-operation-based scaling analysis and the power spectrum for linear stochastic processes. Here, by applying our methods to DFA and DMA, including higher-order cases, exact frequency responses are calculated. In addition, we analytically investigate the cutoff frequencies of DFA and DMA detrending operations and show that these frequencies are not optimally adjusted to coincide with the corresponding time scale.
Non-stationary frequency domain system identification using time-frequency representations
Guo, Yanlin; Kareem, Ahsan
2016-05-01
System properties of buildings and bridges may vary with time due to temperature changes, aging or extreme loadings. To identify these time-varying system properties, this study proposes a new output-only non-stationary system identification (SI) framework based on instantaneous or marginal spectra derived from the time-frequency representation, e.g., short time Fourier or wavelet transform. Spectra derived from these time-frequency representations are very popular in tracking time-varying frequencies; however, they have seldom been used to identify the time-varying damping ratio because a short window needed to capture the time-varying information amplifies the bandwidth significantly, which may lead to considerably overestimating the damping ratio. To overcome this shortcoming, this study modifies the theoretical frequency response function (FRF) to explicitly account for the windowing effect, and therefore enables SI directly using instantaneous or marginal spectra derived from the wavelet or short time Fourier transform. The response spectrum estimated using the short time window and the modified FRF are both influenced by the same time window, thus the instantaneous or time-localized marginal spectrum of response can be fitted to the modified FRF to identify frequency and damping ratio at each time instant. This spectral-based SI framework can reliably identify damping in time-varying systems under non-stationary excitations. The efficacy of the proposed framework is demonstrated by both numerical and full-scale examples, and also compared to the time-domain SI method, stochastic subspace identification (SSI), since the time-domain SI approaches and their extensions are popular in identifying time-varying systems utilizing recursive algorithms or moving windows.
Zhou, Hong; Melloni, Lucia; Poeppel, David; Ding, Nai
2016-01-01
Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid. PMID:27375465
Frequency domain methods applied to forecasting electricity markets
The changes taking place in electricity markets during the last two decades have produced an increased interest in the problem of forecasting, either load demand or prices. Many forecasting methodologies are available in the literature nowadays with mixed conclusions about which method is most convenient. This paper focuses on the modeling of electricity market time series sampled hourly in order to produce short-term (1 to 24 h ahead) forecasts. The main features of the system are that (1) models are of an Unobserved Component class that allow for signal extraction of trend, diurnal, weekly and irregular components; (2) its application is automatic, in the sense that there is no need for human intervention via any sort of identification stage; (3) the models are estimated in the frequency domain; and (4) the robustness of the method makes possible its direct use on both load demand and price time series. The approach is thoroughly tested on the PJM interconnection market and the results improve on classical ARIMA models. (author)
Multiscale Point Correspondence Using Feature Distribution and Frequency Domain Alignment
Zeng-Shun Zhao
2012-01-01
Full Text Available In this paper, a hybrid scheme is proposed to find the reliable point-correspondences between two images, which combines the distribution of invariant spatial feature description and frequency domain alignment based on two-stage coarse to fine refinement strategy. Firstly, the source and the target images are both down-sampled by the image pyramid algorithm in a hierarchical multi-scale way. The Fourier-Mellin transform is applied to obtain the transformation parameters at the coarse level between the image pairs; then, the parameters can serve as the initial coarse guess, to guide the following feature matching step at the original scale, where the correspondences are restricted in a search window determined by the deformation between the reference image and the current image; Finally, a novel matching strategy is developed to reject the false matches by validating geometrical relationships between candidate matching points. By doing so, the alignment parameters are refined, which is more accurate and more flexible than a robust fitting technique. This in return can provide a more accurate result for feature correspondence. Experiments on real and synthetic image-pairs show that our approach provides satisfactory feature matching performance.
Application of frequency domain analysis to transient response of nuclear containment structures
A combination of frequency domain and time domain analyses is proposed to obtain the dynamic responses of nuclear power plant containment structures. A soil-structure model of a boiling water reactor containment subjected to an assumed safety relief valve blowdown load is used as illustration. Linear time-invariant systems are analysed using input forcing functions with varying frequency contents. Time domain analysis is performed using a synthesized input forcing function. The system characteristic function is generated in the frequency domain through Fourier transforms of the response time history and the synthesized input time history. The frequency response due to any other forcing function is obtained in frequency domain by using the system characteristic function, and the response time history is obtained by inverse Fourier transforms of the frequency response. The results obtained by the proposed method are in close agreement with the conventional time domain dynamic finite element analysis. (Auth.)
Madsen, Kristoffer Hougaard; Hansen, Lars Kai; Mørup, Morten
2009-01-01
We propose the Time Frequency Gradient Method (TFGM) which forms a framework for optimization of models that are constrained in the time domain while having efficient representations in the frequency domain. Since the constraints in the time domain in general are not transparent in a frequency......-negative Matrix Factorization, Convolutive Sparse Coding as well as Smooth and Sparse Matrix Factorization. Matlab implementation of the proposed algorithms are available for download at www.erpwavelab.org....
Polyphase decompositions and shift-invariant discrete wavelet transforms in the frequency domain
Wink, Alle Meije; Roerdink, Jos B.T.M.
2010-01-01
Given a signal and its Fourier transform, we derive formulas for its polyphase decomposition in the frequency domain and for the reconstruction from the polyphase representation back to the Fourier representation. We present two frequency-domain implementations of the shift-invariant periodic discrete wavelet transform (SI-DWT) and its inverse: one that is based on frequency-domain polyphase decomposition and a more efficient 'direct' implementation, based on a reorganisation of the a trous a...
Performance of Downlink Frequency Domain Packet Scheduling for the UTRAN Long Term Evolution
Pokhariyal, Akhilesh; Kolding, Troels E.; Mogensen, Preben
2006-01-01
In this paper we investigate the potential of downlink frequency-domain packet scheduling (FDPS) for the 3GPP UTRAN long term evolution. Utilizing frequency-domain channel quality reports, the scheduler flexibly multiplexes users on different portions of the system bandwidth. Compared to frequen...
Inamori, Mamiko; Takayama, Shuzo; Sanada, Yukitoshi
Direct conversion receivers in orthogonal frequency division multiplexing (OFDM) systems suffer from direct current (DC) offset, frequency offset, and IQ imbalance. We have proposed an IQ imbalance estimation scheme in the presence of DC offset and frequency offset, which uses preamble signals in the time domain. In this scheme, the DC offset is eliminated by a differential filter. However, the accuracy of IQ imbalance estimation is deteriorated when the frequency offset is small. To overcome this problem, a new IQ imbalance estimation scheme in the frequency domain with the differential filter has been proposed in this paper. The IQ imbalance is estimated with pilot subcarriers. Numerical results obtained through computer simulation show that estimation accuracy and bit error rate (BER) performance can be improved even if the frequency offset is small.
Multiple Binary Images Watermarking in Spatial and Frequency Domains
K.Ganesan
2012-12-01
Full Text Available Editing, reproduction and distribution of the digital multimedia are becoming extremely easier and faster with the existence of the internet and the availability of pervasive and powerful multimedia tools. Digital watermarking has emerged as a possible method to tackle these issues. This paper proposes a scheme using which more data can be inserted into an image in different domains using different techniques. This increases the embedding capacity. Using the proposed scheme 24 binary images can be embedded in the DCT domain and 12 binary images can be embedded in the spatial domain using LSB substitution technique in a single RGB image. The proposed scheme also provides an extra level of security to the watermark image by scrambling the image before embedding it into the host image. Experimental results show that the proposed watermarking method results in almost invisible difference between the watermarked image and the original image and is also robust against various image processing attacks.
Multiple Binary Images Watermarking in Spatial and Frequency Domains
K.Ganesan
2011-02-01
Full Text Available Editing, reproduction and distribution of the digital multimedia are becoming extremely easier and fasterwith the existence of the internet and the availability of pervasive and powerful multimedia tools. Digitalwatermarking has emerged as a possible method to tackle these issues. This paper proposes a schemeusing which more data can be inserted into an image in different domains using different techniques. Thisincreases the embedding capacity. Using the proposed scheme 24 binary images can be embedded in theDCT domain and 12 binary images can be embedded in the spatial domain using LSB substitutiontechnique in a single RGB image. The proposed scheme also provides an extra level of security to thewatermark image by scrambling the image before embedding it into the host image. Experimental resultsshow that the proposed watermarking method results in almost invisible difference between thewatermarked image and the original image and is also robust against various image processing attacks.
Frequency Domain Fatigue Assessment of Vehicle Component under Random Load Spectrum
This research is focused on the application of frequency domain based fatigue life predict methods on vehicle component. The basic theory of these approaches is based on the frequency-based signals, the probability density function (PDF) of signals and Miner cumulative damage criterion. A typical suspension virtual prototype model is established to derive dynamic loading arisen from random road exciting. Several kinds of fatigue life predicting approaches in frequency domain are applied and compared. The influence factors for these methods, such as PSD average methods, frequency ranges and frequency intervals are also discussed. Appropriate results can be obtained at last.
Calculating thin-bed thickness in frequency domain
Jianyang, Y. (Shanghai Offshore Geological Survey Bureau, Ministry of Geology and Minerals, No. 340 Shenjia lu Alley, Pudong District, Shanghai City (CN))
1991-01-01
Thin-bed thickness can be quantitatively calculated by using amplitude information when the seismic waves were recorded in simple surface seismic-geological condition and stable shot-receiving condition. However, Seismic waves are rarely recorded on such ideal conditions. In this paper a method for calculating thin-bed thickness with the use of frequency information is proposed as a result of thin-bed model research. This method uses amplitude spectrum values of low frequency contents in seismic frequency spectrum to determine bed thickness error is minutely analyzed which may be caused by thin interbedding and different wavelets. This method is proved feasible.
Wideband Radar Echo Frequency-domain Simulation and Analysis for High Speed Moving Targets
Ning Chao
2014-04-01
Full Text Available A frequency-domain method is proposed for wideband radar echo simulation of high-speed moving targets. Based on the physical process of electromagnetic waves observing a moving target, a frequency-domain echo model of wideband radar is constructed, and the block diagram of the radar echo simulation in frequency-domain is presented. Then, the impacts of radial velocity and slant range on the matching filtering of LFM radar are analyzed, and some quantitative conclusions on the shift and expansion of the radar profiles are obtained. Simulation results illustrate the correctness and efficiency of the proposed method.
Frequency-Domain Identification of XV-15 Tilt-Rotor Aircraft Dynamics in Hovering Flight
Tischler, Mark B.; Leung, Joseph G. M.; Dugan, Daniel C.
1985-01-01
Frequency-domain methods are used to identify the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight tests. Piloting and data analysis techniques are presented to determine frequency response plots and equivalent transfer function models. The open-loop pitch and roll dynamics for the hover flight condition exhibit unstable low-frequency oscillations, whereas the dynamics in the remaining degrees of freedom are lightly damped and generally decoupled. Comparisons of XV-15 flight-test and simulator data are more favorable for high-frequency inputs (omega greater than 1.0 rad/sec) than low-frequency inputs. Time-domain comparisons of the extracted transfer functions with step response flight data are very favorable, even for large amplitude motions. The results presented in this paper demonstrate the utility of the frequency-domain techniques for dynamics identification and simulator fidelity studies.
Frequency-domain generelaized singular peruturbation method for relative error model order reduction
Hamid Reza SHAKER
2009-01-01
A new mixed method for relative error model order reduction is proposed.In the proposed method the frequency domain balanced stochastic truncation method is improved by applying the generalized singular perturbation method to the frequency domain balanced system in the reduction procedure.The frequency domain balanced stochastic truncation method,which was proposed in [15] and [17] by the author,is based on two recently developed methods,namely frequency domain balanced truncation within a desired frequency bound and inner-outer factorization techniques.The proposed method in this paper is a carry over of the frequency-domain balanced stochastic truncation and is of interest for practical model order reduction because in this context it shows to keep the accuracy of the approximation as high as possible without sacrificing the computational efficiency and important system properties.It is shown that some important properties of the frequency domain stochastic balanced reduction technique are extended to the proposed reduction method by using the concept and properties of the reciprocal systems.Numerical results show the accuracy,simplicity and flexibility enhancement of the method.
Hays, J. R.
1969-01-01
Lumped parametric system models are simplified and computationally advantageous in the frequency domain of linear systems. Nonlinear least squares computer program finds the least square best estimate for any number of parameters in an arbitrarily complicated model.
A MATLAB GUI for learning controller design in the frequency domain
Mitchell, Richard
2014-01-01
A MATLAB GUI is presented which is used to help students learn to design controllers in the frequency domain. It complements the author’s two previous GUIs for plotting and identification of systems in the frequency domain. It also incorporates the concept used in the “electronic calculator that makes students think” to assist learning. Positive student feedback affirms that the GUI has helped their understanding.
BER Performance of Frequency Domain Differential Demodulation OFDM in Flat Fading Channel
SONG Lijun; TANG Youxi; LI Shaoqian; HUANG Shunji
2003-01-01
A closed form expression for the bit error rate (BER) performance of frequency domain differential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fading channel is derived. The performance is evaluated by computer simulation and compared with the time domain differential demodulation(TDDD). The results indicate that the performance of FDDD is better than that of TDDD, and the lower band of BER in the former is lower than that of the latter.
Frequency domain volume rendering by the wavelet X-ray transform
Westenberg, Michel A.; Roerdink, Jos B. T. M.
2000-01-01
We describe a wavelet-based X-ray rendering method in the frequency domain with a smaller time complexity than wavelet splatting. Standard Fourier volume rendering is summarized and interpolation and accuracy issues are briefly discussed. We review the implementation of the fast wavelet transform in the frequency domain. The wavelet X-ray transform is derived, and the corresponding Fourier-wavelet volume rendering algorithm (FWVR) is introduced. FWVR uses Haar or B-spline wavelets and linear ...
Book, W. J.; Majett, M.
1982-01-01
The potential benefits of the ability to control more flexible mechanical arms are discussed. A justification is made in terms of speed of movement. A new controller design procedure is then developed to provide this capability. It uses both a frequency domain representation and a state variable representation of the arm model. The frequency domain model is used to update the modal state variable model to insure decoupled states. The technique is applied to a simple example with encouraging results.
Zeguang YI; Pan, Nan; Liu, Feng
2015-01-01
Aiming at fault diagnosis problems caused by complex machinery parts, serious background noises and the application limitations of traditional blind signal processing algorithm to the mechanical acoustic signal processing, a failure acoustic diagnosis based on reference signal frequency domain semi-blind extraction is proposed. Key technologies are introduced: Based on frequency-domain blind deconvolution algorithm, the artificial fish swarm algorithm which is good for global optimization is ...
Meta-model-based Design Method for Frequency-domain Performance Reliability Improvement
Son, Young Kap [Andong National University, Andong (Korea, Republic of)
2015-01-15
This paper proposes a design method for improving the frequency-domain performance reliability of dynamic systems with uncertain and degrading components. Discrete frequencies are used in this method as surrogates for the frequency band of interest, and the conformance of the frequency responses to the specification at these frequencies is utilized to model the frequency-domain performance reliability. A meta-model for the frequency responses, an extreme-value event, and the set-theory are integrated to improve the computational efficiency of the reliability estimation. In addition, a sample-based approach is presented to evaluate and optimize the estimated performance reliability. A case study of a vibration absorber system showed that the proposed design method has engineering applications.
Direction of arrival estimation using array model in time-frequency domain
LIU Yun; LI Zhishun
2004-01-01
Time-frequency analysis is combined with array processing to develop a direction of arrival (DOA) estimation method. The array data model is constructed in time-frequency domain by cross time-frequency distribution between the output of a reference sensor and those of two symmetric sub-arrays. Accordingly a subspace method is presented based on the average of two sub-arrays' time-frequency data vector model instead of the conventional array model, to estimate DOAs of multiple signals. Because the array data is processed both in spatial domain and 2-D time-frequency domain, the proposed method has an ability to select the signal of interesting, and is suitable for non-stationary signal. Additionally, the method is robust to noise and holds an advantage of low computational load. Simulations are conducted to verify the efficiency of the method and comparision is made with other methods.
Asymptotically Exact Localized Expansions for Signals in Time-Frequency Domain
Muzhikyan, Aramazd H
2011-01-01
Based on a unique waveform with strong exponential localization property, an exact mathematical method for solving problems in signal analysis in time-frequency domain is presented. An analogue of the Gabor frame exposes the non-commutative geometry of the time-frequency plane. Signals are visualized using graphical representation constructed.
Simulation of power fluctuation of wind farms based on frequency domain
Lin, Jin; Sun, Yuanzhang; Li, Guojie;
2011-01-01
With the capacity of installed wind power generators steadily increasing in China, power fluctuation from wind farms will significantly affect the security and reliability of the power system. Traditional modeling of power fluctuation is based on the time domain or statistics methodology which......, however, is incapable of completely explaining the physical mechanism of randomness of power fluctuation. To remedy such a situation, fluctuation modeling based on the frequency domain is proposed. The frequency domain characteristics of stochastic fluctuation on large wind farms are studied using the...... power spectral density of wind speed, the frequency domain model of a wind power generator and the information on weather and geography of the wind farms. The correctness and effectiveness of the model are verified by comparing the measurement data with simulation results of a certain wind farm. © 2011...
Soil-structure interaction analysis of NPP containments: substructure and frequency domain methods
Substructure and frequency domain methods for soil-structure interaction are addressed in this paper. After a brief description of mathematical models for the soil and of excitation, the equations for dynamic soil-structure interaction are developed for a rigid surface foundation and for an embedded foundation. The equations for the frequency domain analysis of MDOF systems are provided. An example of soil-structure interaction analysis with frequency-dependent soil properties is given and examples of identification of foundation impedance functions and soil properties are presented. (orig.)
Soil-structure interaction analysis of NPP containments: substructure and frequency domain methods
Venancio-Filho, F.; Almeida, M.C.F.; Ferreira, W.G. [Universidade Federal, Rio de Janeiro, RJ (Brazil); De Barros, F.C.P. [IME/CNEN, Pc. General Tiburcio, 80, 22290-270 Rio de Janeiro (Brazil)
1997-10-01
Substructure and frequency domain methods for soil-structure interaction are addressed in this paper. After a brief description of mathematical models for the soil and of excitation, the equations for dynamic soil-structure interaction are developed for a rigid surface foundation and for an embedded foundation. The equations for the frequency domain analysis of MDOF systems are provided. An example of soil-structure interaction analysis with frequency-dependent soil properties is given and examples of identification of foundation impedance functions and soil properties are presented. (orig.) 17 refs.
Klein, V.
1980-01-01
A frequency domain maximum likelihood method is developed for the estimation of airplane stability and control parameters from measured data. The model of an airplane is represented by a discrete-type steady state Kalman filter with time variables replaced by their Fourier series expansions. The likelihood function of innovations is formulated, and by its maximization with respect to unknown parameters the estimation algorithm is obtained. This algorithm is then simplified to the output error estimation method with the data in the form of transformed time histories, frequency response curves, or spectral and cross-spectral densities. The development is followed by a discussion on the equivalence of the cost function in the time and frequency domains, and on advantages and disadvantages of the frequency domain approach. The algorithm developed is applied in four examples to the estimation of longitudinal parameters of a general aviation airplane using computer generated and measured data in turbulent and still air. The cost functions in the time and frequency domains are shown to be equivalent; therefore, both approaches are complementary and not contradictory. Despite some computational advantages of parameter estimation in the frequency domain, this approach is limited to linear equations of motion with constant coefficients.
S.Ali Ghafari Oskoei; Ghyslaine McClure
2008-01-01
At present,high.speed computing capabilities and advanced nonlinear dynamic finite element procedures enable detailed dynamic analysis of cable structures.Although deterministic approaches require considerable analysis time and effort in relation to modeling,running,and data processing,they seem to be the only alternative to obtain high accuracy.Detailed dynamic analysis of cable roof networks is sophisticated and requires advanced modeling expertise.This paper presents a comparison between detailed nonlinear dynamic analysis and a simplified frequency domain approach to estimate the maximum probable response of weakly nonlinear cable roofs.The approach can be considered as alternative to detailed time-domain analysis in the preliminary design phase,or can be used to validate results obtained from more elaborated numerical models.The proposed method is illustrated with two examples of cable net roofs that were also analysed in the time domain.
Comparison of Frequency-Domain Array Methods for Studying Earthquake Rupture Process
Sheng, Y.; Yin, J.; Yao, H.
2014-12-01
Seismic array methods, in both time- and frequency- domains, have been widely used to study the rupture process and energy radiation of earthquakes. With better spatial resolution, the high-resolution frequency-domain methods, such as Multiple Signal Classification (MUSIC) (Schimdt, 1986; Meng et al., 2011) and the recently developed Compressive Sensing (CS) technique (Yao et al., 2011, 2013), are revealing new features of earthquake rupture processes. We have performed various tests on the methods of MUSIC, CS, minimum-variance distortionless response (MVDR) Beamforming and conventional Beamforming in order to better understand the advantages and features of these methods for studying earthquake rupture processes. We use the ricker wavelet to synthesize seismograms and use these frequency-domain techniques to relocate the synthetic sources we set, for instance, two sources separated in space but, their waveforms completely overlapping in the time domain. We also test the effects of the sliding window scheme on the recovery of a series of input sources, in particular, some artifacts that are caused by the sliding window scheme. Based on our tests, we find that CS, which is developed from the theory of sparsity inversion, has relatively high spatial resolution than the other frequency-domain methods and has better performance at lower frequencies. In high-frequency bands, MUSIC, as well as MVDR Beamforming, is more stable, especially in the multi-source situation. Meanwhile, CS tends to produce more artifacts when data have poor signal-to-noise ratio. Although these techniques can distinctly improve the spatial resolution, they still produce some artifacts along with the sliding of the time window. Furthermore, we propose a new method, which combines both the time-domain and frequency-domain techniques, to suppress these artifacts and obtain more reliable earthquake rupture images. Finally, we apply this new technique to study the 2013 Okhotsk deep mega earthquake
Time domain acoustic contrast control implementation of sound zones for low-frequency input signals
Schellekens, Daan H. M.; Møller, Martin Bo; Olsen, Martin
2016-01-01
-of-the-art time domain broadband acoustic contrast control (BACC) methods are designed for anechoic environments. These methods are not able to realize a flat frequency response in a limited frequency range within a reverberant environment. Sound field control in a limited frequency range is a requirement to...... accommodate the effective working range of the loudspeakers. In this paper, a new BACC method is proposed which results in an implementation realizing a flat frequency response in the target zone. This method is applied in a bandlimited low-frequency scenario where the loudspeaker layout surrounds two...
Online Identification of a Mechanical System in the Frequency Domain with Short-Time DFT
Niko Nevaranta
2015-07-01
Full Text Available A proper system identification method is of great importance in the process of acquiring an analytical model that adequately represents the characteristics of the monitored system. While the use of different time-domain online identification techniques has been widely recognized as a powerful approach for system diagnostics, the frequency domain identification techniques have primarily been considered for offline commissioning purposes. This paper addresses issues in the online frequency domain identification of a flexible two-mass mechanical system with varying dynamics, and a particular attention is paid to detect the changes in the system dynamics. An online identification method is presented that is based on a recursive Kalman filter configured to perform like a discrete Fourier transform (DFT at a selected set of frequencies. The experimental online identification results are compared with the corresponding values obtained from the offline-identified frequency responses. The results show an acceptable agreement and demonstrate the feasibility of the proposed identification method.
McKelvey, Tomas
1995-01-01
This paper deals with the analysis of a frequency domain identication algorithm The algorithm identies statespace models given samples of the frequency response given at equidistant frequencies A rst order per turbation analysis is performed revealing an explicit expression of resulting transfer function perturbation Stochastic analysis show that the estimate is asymptotically in data normal distributed and an explicit expression of the resulting variance is given Monte Carlo simulations illu...
Digital Frequency Domain Multiplexer for mm-Wavelength Telescopes
Dobbs, Matt; Spieler, Helmuth
2007-01-01
An FPGA based digital signal processing (DSP) system for biasing and reading out multiplexed bolometric detectors for mm-wavelength telescopes is presented. This readout system is being deployed for balloon-borne and ground based cosmology experiments with the primary goal of measuring the signature of inflation with the Cosmic Microwave Background Radiation. The system consists of analog superconducting electronics running at 250mK and 4K, coupled to digital room temperature backend electronics described here. The digital electronics perform the real time functionality with DSP algorithms implemented in firmware. A soft embedded processor provides all of the slow housekeeping control and communications. Each board in the system synthesizes multi-frequency combs of 8 to 32 carriers in the MHz band to bias the detectors. After the carriers have been modulated with the sky-signal by the detectors, the same boards digitize the comb directly. The carriers are mixed down to base-band and low pass filtered. The sig...
Fatigue of wind turbines in the frequency domain
Bishop, N.W.M. [Univ. College London (United Kingdom)
1996-09-01
Fatigue damage is traditionally determined from time signals of loading, usually in the form of stress or strain. However, there are three design scenarios when a spectral form of loading is more appropriate. In this case the loading is defined in terms of its magnitude at different frequencies in the form of a Power Spectral Density (PSD) plot. First, the measurement engineer recording responses from in-service components or structures may be interested in PSD`s because they are a efficient way of defining a random stress or strain time history. Secondly, the test engineer assessing the reliability of prototypes may be interested in spectral tools because such an approach allows the structural condition of the component to be monitored by continuous inspection of the system transfer function. However, the most important benefit of working with PSD`s is relevant to the structural analysis or designer because of the more sophisticated analysis options with which they can be use. For all three of these design scenarios the fatigue designer is presented with a PSD of stress or strain with which to perform his fatigue calculation. There is therefore a requirement for a reliable, accurate and robust spectral fatigue design tool. Such a tool allows the designer to estimate the rainflow range content and hence content and hence fatigue damage from the PSD. (EG)
Frequency-domain deviational Monte Carlo method for linear oscillatory gas flows
Ladiges, Daniel R.; Sader, John E.
2015-10-01
Oscillatory non-continuum low Mach number gas flows are often generated by nanomechanical devices in ambient conditions. These flows can be simulated using a range of particle based Monte Carlo techniques, which in their original form operate exclusively in the time-domain. Recently, a frequency-domain weight-based Monte Carlo method was proposed [D. R. Ladiges and J. E. Sader, "Frequency-domain Monte Carlo method for linear oscillatory gas flows," J. Comput. Phys. 284, 351-366 (2015)] that exhibits superior statistical convergence when simulating oscillatory flows. This previous method used the Bhatnagar-Gross-Krook (BGK) kinetic model and contains a "virtual-time" variable to maintain the inherent time-marching nature of existing Monte Carlo algorithms. Here, we propose an alternative frequency-domain deviational Monte Carlo method that facilitates the use of a wider range of molecular models and more efficient collision/relaxation operators. We demonstrate this method with oscillatory Couette flow and the flow generated by an oscillating sphere, utilizing both the BGK kinetic model and hard sphere particles. We also discuss how oscillatory motion of arbitrary time-dependence can be simulated using computationally efficient parallelization. As in the weight-based method, this deviational frequency-domain Monte Carlo method is shown to offer improved computational speed compared to the equivalent time-domain technique.
Wang, W.; Wen, L.
2013-12-01
Back projection is a method to back project the seismic energy recorded in a seismic array back to the earthquake source region and determine the rupture process of a large earthquake. The method takes advantage of the coherence of seismic energy in a seismic array and is quick in determining some important properties of earthquake source. The method can be performed in both time and frequency domains. In time domain, the most conventional procedure is beam forming with some measures of suppressing the noise, such as the Nth root stacking, etc. In the frequency domain, the multiple signal classification method (MUSIC) estimates the direction of arrivals of multiple waves propagating through an array using the subspace method. The advantage of this method is the ability to study rupture properties at various frequencies and to resolve simultaneous arrivals making it suitable for detecting biliteral rupture of an earthquake source. We present a comparison of back projection results on some large earthquakes between the methods in time domain and frequency domain. The time-domain procedure produces an image that is smeared and exhibits some artifacts, although some enhancing stacking methods can at some extent alleviate the problem. On the other hand, the MUSIC method resolves clear multiple arrivals and provides higher resolution of rupture imaging.
GMAW process stability evaluation through acoustic emission by time and frequency domain analysis
E. Huanca Cayo
2009-06-01
Full Text Available Purpose: In the present work was made the comparative analysis in time domain and frequency domain to the acoustical pressure generate by the electric arc to determinate which of the two analysis methods is better to evaluates the stability in GMAW process.Design/methodology/approach: Welds had been made with the parameters adjusted to get the highest stability. In these conditions, were simulated instabilities that had been generated by the grease presence in the weld trajectory. In both experimental groups was acquired the acoustical pressure signal produced by electric arc to made analysis based in time domain and frequency domain.Findings: After this comparative study we conclude that the acoustical evaluation of the stability on the GMAW process presents more clarity for the analysis based in the time domain that the frequency domain.Research limitations/implications: In the gotten results, the time domain analysis method could represent adequately the stability and the instability of the process. The stability characterizes for the continuity and minim variation of the statistical parameters, but in the presence of instabilities, these parameters present chaotic changes. In the frequency domain method the variations are imperceptible for steady and unstable regions, but it presents little definite variations in the amplitude of determined bands of frequencies.Originality/value: The stability evaluation in welding is crucial because it is responsible in the weld quality. The non contact methods as the acoustical method have a potentiality extraordinary to monitoring and detect instabilities in welding. The acoustical sensing has the capacity to make an on-line monitoring of the weld process.
Fractional Fourier transform for partially coherent beam in spatial-frequency domain
Cai Yang-Jian; Lin Qiang
2004-01-01
By using Fourier transform and the tensor analysis method, the fractional Fourier transform (FRT) in the spatialfrequency domain for partially coherent beams is derived. Based on the FRT in the spatial-frequency domain, an analytical transform formula is derived for a partially coherent twisted anisotropic Gaussian-Schell model (GSM) beam passing through the FRT system. The connections between the FRT formula and the generalized diffraction integral formulae for partially coherent beams through an aligned optical system and a misaligned optical system in the spatialfrequency domain are discussed, separately. By using the derived formula, the intensity distribution of partially coherent twisted anisotropic GSM beams in the FRT plane are studied in detail. The formula derived provide a convenient tool for analysing and calculating the FRTs of the partially coherent beams in spatial-frequency domain.
Analysis of wave packet motion in frequency and time domain: oxazine 1.
Braun, Markus; Sobotta, Constanze; Dürr, Regina; Pulvermacher, Horst; Malkmus, Stephan
2006-08-17
Wave packet motion in the laser dye oxazine 1 in methanol is investigated by spectrally resolved transient absorption spectroscopy. The spectral range of 600-690 nm was accessible by amplified broadband probe pulses covering the overlap region of ground-state bleach and stimulated emission signal. The influence of vibrational wave packets on the optical signal is analyzed in the frequency domain and the time domain. For the analysis in the frequency domain an algorithm is presented that accounts for interference effects of neighbored vibrational modes. By this method amplitude, phase and decay time of vibrational modes are retrieved as a function of probe wavelength and distortions due to neighbored modes are reduced. The analysis of the data in the time domain yields complementary information on the intensity, central wavelength, and spectral width of the optical bleach spectrum due to wave packet motion. PMID:16898679
A hybrid analysis method for linear dynamic soil-structure interaction in time and frequency domain
丁海平; 廖振鹏
2001-01-01
A hybrid analysis method in time and frequency domains for linear soil-structure interaction is presented. First, the time domain solution of the system with Rayleigh damping excited by a short time impulse is obtained by the decoupling numerical simulation technique of near-field wave motion. Then, the corresponding frequency domain solution can be got by Fourier transform. According to the relationship between damping value and dynamic re-sponse of a system, the solution of the system with complex damping can be got by Taylor expansion. The hybrid method makes the best of decoupling and explicit algorithm in time domain, and increases the calculation efficien-cy for linear soil-structure interaction analysis.
Frequency-Domain Adaptive Algorithm for Network Echo Cancellation in VoIP
Doroslovăcki Milŏs
2008-01-01
Full Text Available We propose a new low complexity, low delay, and fast converging frequency-domain adaptive algorithm for network echo cancellation in VoIP exploiting MMax and sparse partial (SP tap-selection criteria in the frequency domain. We incorporate these tap-selection techniques into the multidelay filtering (MDF algorithm in order to mitigate the delay inherent in frequency-domain algorithms. We illustrate two such approaches and discuss their tradeoff between convergence performance and computational complexity. Simulation results show an improvement in convergence rate for the proposed algorithm over MDF and significantly reduced complexity. The proposed algorithm achieves a convergence performance close to that of the recently proposed, but substantially more complex improved proportionate MDF (IPMDF algorithm.
Frequency Domain Criteria for Absolute Stability A Delay-integral-quadratic Constraints Approach
Altshuller, Dmitry
2013-01-01
Frequency Domain Criteria for Absolute Stability focuses on recently-developed methods of delay-integral-quadratic constraints to provide criteria for absolute stability of nonlinear control systems. The known or assumed properties of the system are the basis from which stability criteria are developed. Through these methods, many classical results are naturally extended, particularly to time-periodic but also to nonstationary systems. Mathematical prerequisites including Lebesgue-Stieltjes measures and integration are first explained in an informal style with technically more difficult proofs presented in separate sections that can be omitted without loss of continuity. The results are presented in the frequency domain – the form in which they naturally tend to arise. In some cases, the frequency-domain criteria can be converted into computationally tractable linear matrix inequalities but in others, especially those with a certain geometric interpretation, inferences concerning stability can be made direc...
Four-channel magnetic resonance imaging receiver using frequency domain multiplexing
He, Wang; Qin, Xu; Jiejing, Ren; Gengying, Li
2007-01-01
An alternative technique that uses frequency domain multiplexing to acquire phased array magnetic resonance images is discussed in detail. The proposed method has advantages over traditional independent receiver chains in that it utilizes an analog-to-digital converter and a single-chip multicarrier receiver with high performance to reduce the size and cost of the phased array receiver system. A practical four-channel digital receiver using frequency domain multiplexing was implemented and verified on a home-built 0.3T magnetic resonance imaging system. The experimental results confirmed that the cross talk between each channel was below -60dB, the phase fluctuations were about 1°, and there was no obvious signal-to-noise ratio degradation. It is demonstrated that the frequency domain multiplexing is a valuable and economical technique, particularly for array coil systems where the multichannel receiver is indispensable and dynamic range is not a critical problem.
Practical iterative learning control with frequency domain design and sampled data implementation
Wang, Danwei; Zhang, Bin
2014-01-01
This book is on the iterative learning control (ILC) with focus on the design and implementation. We approach the ILC design based on the frequency domain analysis and address the ILC implementation based on the sampled data methods. This is the first book of ILC from frequency domain and sampled data methodologies. The frequency domain design methods offer ILC users insights to the convergence performance which is of practical benefits. This book presents a comprehensive framework with various methodologies to ensure the learnable bandwidth in the ILC system to be set with a balance between learning performance and learning stability. The sampled data implementation ensures effective execution of ILC in practical dynamic systems. The presented sampled data ILC methods also ensure the balance of performance and stability of learning process. Furthermore, the presented theories and methodologies are tested with an ILC controlled robotic system. The experimental results show that the machines can work in much h...
Frequency-Domain Adaptive Algorithm for Network Echo Cancellation in VoIP
Patrick A. Naylor
2008-05-01
Full Text Available We propose a new low complexity, low delay, and fast converging frequency-domain adaptive algorithm for network echo cancellation in VoIP exploiting MMax and sparse partial (SP tap-selection criteria in the frequency domain. We incorporate these tap-selection techniques into the multidelay filtering (MDF algorithm in order to mitigate the delay inherent in frequency-domain algorithms. We illustrate two such approaches and discuss their tradeoff between convergence performance and computational complexity. Simulation results show an improvement in convergence rate for the proposed algorithm over MDF and significantly reduced complexity. The proposed algorithm achieves a convergence performance close to that of the recently proposed, but substantially more complex improved proportionate MDF (IPMDF algorithm.
Characterization of ZnSe(Te) scintillators by frequency domain luminescence lifetime measurements
Mickevicius, J. [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio 9-III, LT-10222 Vilnius (Lithuania)], E-mail: juras.mickevicius@ff.vu.lt; Tamulaitis, G; Vitta, P.; Zukauskas, A. [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio 9-III, LT-10222 Vilnius (Lithuania); Starzhinskiy, N.; Ryzhikov, V. [STC for Radiation Instruments, ST Complex ' Institute for Single Crystals' of the National Academy of Sciences of Ukraine, 60 Lenin Ave., 61001 Kharkov (Ukraine)
2009-10-21
Dynamics of photoluminescence (PL) decay in Te-doped ZnSe scintillator crystal is studied using frequency domain luminescence lifetime measurement technique, which enables simultaneous characterization of components in multicomponent PL decay in a wide time window ranging from millisecond to nanosecond domain. Evolution of decay times and relative contributions of the decay components corresponding to different PL decay mechanisms was revealed as a function of temperature.
Frequency-domain ultrasonic NDE of three-layered media : the inverse problem
Kinra, V.; Zhu, C
1994-01-01
This paper presents a frequency-domain ultrasonic technique for a simultaneous determination of the thickness (h) and wavespeed (c) of the individual layers comprising a multilayered medium using the entire complex spectrum. Each of the layers may be "thin" ; by thin we mean that the successive reflections of an ultrasonic pulse from the two faces of a layer are non-separable in the time domain. Plane longitudinal waves which are normally incident upon the medium are considered. A systematic ...
Time-domain representation of frequency dependent inertial forces on offshore structures
Krenk, Steen
2013-01-01
located above the peak frequency of the wave spectrum, and the frequency dependence of the inertial force coefficient can then result in a substantial reduction of the resonant part of the response. It is of interest to represent this effect in the time domain for response analysis including finite height...... waves and drag forces. The inertia coefficient has been determined within linear wave theory in terms of the wave-number by MacCamy and Fuchs. For diameters less than about half the water depth this solution can be transformed to frequency form by use of the deep-water dispersion relation. The frequency...
Simulation of power fluctuation of wind farms based on frequency domain
Lin, Jin; Sun, Yuanzhang; Li, Guojie;
2011-01-01
-frequency transformation related to the power spectrum density (PSD), which is more special and complicated than normal transformations. Meanwhile, the computational complexity also increases significantly, more computation resources are needed. These problems negatively affect the engineering application of the model. To...... Grid Electric Power Research Institute Press.......The wind power fluctuation model built up in the frequency domain is mathematically equivalent with that in the time domain, and has a clearer physical meaning therefore describes the fluctuation more accurately. However, the simulation of this model is required to deal with the time...
Gastric Emptying Assessment in Frequency and Time Domain Using Bio-impedance: Preliminary Results
Huerta-Franco, R.; Vargas-Luna, M.; Hernández, E.; Córdova, T.; Sosa, M.; Gutiérrez, G.; Reyes, P.; Mendiola, C.
2006-09-01
The impedance assessment to measure gastric emptying and in general gastric activity has been reported since 1985. The physiological interpretation of these measurements, is still under research. This technique usually uses a single frequency, and the conductivity parameter. The frequency domain and the Fourier analysis of the time domain behavior of the gastric impedance in different gastric conditions (fasting state, and after food administration) has not been explored in detail. This work presents some insights of the potentiality of these alternative methodologies to measure gastric activity.
Kwon, Jun Bum; Wang, Xiongfei; Blaabjerg, Frede;
2016-01-01
For the efficiency and simplicity of electric systems, the dc power electronic systems are widely used in a variety of applications such as electric vehicles, ships, aircraft and also in homes. In these systems, there could be a number of dynamic interactions and frequency coupling between network...... and loads and other converters. Hence, time-domain simulations are usually required to consider such a complex system behavior. However, simulations in the time-domain may increase the calculation time and the utilization of computer memory. Furthermore, frequency coupling driven by multiple...... converters with different switching frequency or harmonics from ac-dc converters makes that harmonics and frequency coupling are both problems of ac system and challenges of dc system. This paper presents a modeling and simulation method for a large dc power electronic system by using Harmonic State Space...
Investigation of Frequency-Domain Link Adaptation for a 5-MHz OFDMA/HSDPA system
Pokhariyal, Akhilesh; Kolding, Troels E.; Frederiksen, Frank;
2005-01-01
In this paper, we investigate frequency domain link adaptation (FDLA), e.g. utilizing the frequency selectivity of the channel in an OFDMA system. To make the study specific and based on realistic parameters, we re-use the specifications from a recent 3GPP 5-MHz OFDMA study item. The link...... adaptation and the frequency domain link adaptation are developed in a way compliant with the basic HSDPA specifications. With FDLA we show up to 75% cell throughput gain over the OFDMA reference system at the cost of increased uplink channel quality signaling overhead for frequency selective channels. We...... find that optimum waterfilling power distribution only provides a marginal gain over a simpler on/off equal power distribution algorithm per sub-carrier pool when signaling imperfections are taken into account....
Small, Matthew David
2001-01-01
A new method to predict the transport of non-uniform total pressure distributions through an axial flow compressor is presented. The method relies on frequency-domain transformations of total pressure distortion patterns, and the use of digital filter techniques to capture the effect of a blade row on the total pressure distortion. Compressor characteristics, described by a frequency response function, are obtained from experimental data and are related to fundamental blade row flow phenomena...
A Frequency Domain Test for Propriety of Complex-Valued Vector Time Series
Chandna, Swati; Walden, Andrew T.
2016-01-01
This paper proposes a frequency domain approach to test the hypothesis that a complex-valued vector time series is proper, i.e., for testing whether the vector time series is uncorrelated with its complex conjugate. If the hypothesis is rejected, frequency bands causing the rejection will be identified and might usefully be related to known properties of the physical processes. The test needs the associated spectral matrix which can be estimated by multitaper methods using, say, $K$ tapers. S...
Elastic wave attenuation and velocity of Berea sandstone measured in the frequency domain
Shankland, T.J. (Institut de Physique du Globe, Paris (France)); Johnson, P.A.; Hopson, T.M. (Los Alamos National Lab., NM (United States))
1993-03-05
Using measurements in the frequency domain the authors have measured quality factor Q and travel times of direct and side-reflected elastic waves in a 1.8 m long sample of Berea sandstone. The frequency domain travel rime (FDTT) method produces the continuous-wave (cw) response of a propagating wave by stepwise sweeping frequency of a driving source and detecting amplitude and phase of the received signal in reference to the source. Each separate travel path yields a characteristic repetition cycle in frequency space as its wave vector-distance product is stepped; an inverse fast Fourier transform (IFFT) reveals the corresponding travel time at the group velocity. Because arrival times of direct and reflected elastic waves appear as spikes along the time axis, travel times can be obtained precisely, and different arrivals can be clearly separated. Q can be determined from the amplitude vs. frequency response of each peak as obtained from a moving window IFFT of the frequency-domain signal. In this sample at ambient conditions compressional velocity V[sub P] is 2380 m/s and Q[sub P] is 55. 15 refs., 4 figs.
Elastic wave attenuation and velocity of Berea sandstone measured in the frequency domain
Shankland, T. J.; Johnson, P. A.; Hopson, T. M.
1993-03-01
Using measurements in the frequency domain we have measured quality factor Q and travel times of direct and side-reflected elastic waves in a 1.8 m long sample of Berea sandstone. The frequency domain travel time (FDTT) method produces the continuous-wave (CW) response of a propagating wave by stepwise sweeping frequency of a driving source and detecting amplitude and phase of the received signal in reference to the source. Each separate travel path yields a characteristic repetition cycle in frequency space as its wave vector-distance product is stepped; an inverse fast Fourier transform (IFFT) reveals the corresponding travel time at the group velocity. Because arrival times of direct and reflected elastic waves appear as spikes along the time axis, travel times can be obtained precisely, and different arrivals can be clearly separated. Q can be determined from the amplitude vs frequency response of each peak as obtained from a moving window IFFT of the frequency-domain signal. In this sample at ambient conditions compressional velocity Vp is 2380 m/s and Qp is 55.
Trautmann Steffen
2004-01-01
Full Text Available We propose a zero-forcing frequency domain block equalizer for discrete multitone (DMT systems with a guard interval of insufficient length. In addition to the insufficient guard interval in the time domain, the equalizer takes advantage of frequency domain redundancy in the form of subcarriers that do not transmit any data. After deriving sufficient conditions for zero-forcing equalization, that is, complete removal of intersymbol and intercarrier interference, we calculate the noise enhancement of the equalizer by evaluating the signal-to-noise ratio (SNR for each subcarrier. The SNRs are used by an adaptive loading algorithm. It decides how many bits are assigned to each subcarrier in order to achieve a maximum data rate at a fixed error probability. We show that redundancy in the time domain can be traded off for redundancy in the frequency domain resulting in a transceiver with a lower system latency time. The derived equalizer matrix is sparse, thus resulting in a low computational complexity.
Frequency domain volume rendering by the wavelet X-ray transform
Westenberg, Michel A.; Roerdink, Jos B.T.M.
2000-01-01
We describe a wavelet-based X-ray rendering method in the frequency domain with a smaller time complexity than wavelet splatting. Standard Fourier volume rendering is summarized and interpolation and accuracy issues are briefly discussed. We review the implementation of the fast wavelet transform in
Postural Analysis in Time and Frequency Domains in Patients with Ehlers-Danlos Syndrome
Galli, Manuela; Rigoldi, Chiara; Celletti, Claudia; Mainardi, Luca; Tenore, Nunzio; Albertini, Giorgio; Camerota, Filippo
2011-01-01
The goal of this work is to analyze postural control in Ehlers-Danlos syndrome (EDS) participants in time and frequency domain. This study considered a pathological group composed by 22 EDS participants performing a postural test consisting in maintaining standing position over a force platform for 30 s in two conditions: open eyes (OE) and closed…
Modal Identification of Output-only Systems Using Frequency Domain Decomposition
Brincker, Rune; Zhang, L.M.; Andersen, Palle
2001-01-01
In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classica...
Simulation of power fluctuation of wind farms based on frequency domain
Lin, Jin; Sun, Yuanzhang; Li, Guojie; Cheng, Lin; Li, Xiong; Sørensen, Poul Ejnar
2011-01-01
power spectral density of wind speed, the frequency domain model of a wind power generator and the information on weather and geography of the wind farms. The correctness and effectiveness of the model are verified by comparing the measurement data with simulation results of a certain wind farm. © 2011...
Frequency-Domain Green's Functions for Radar Waves in Heterogeneous 2.5D Media
Green’s functions for radar waves propagating in heterogeneous media may be calculated in the frequency domain using a hybrid of two numerical methods. The model is defined in the Cartesian coordinate system, and its electromagnetic properties may vary in the x and z directions, ...
Totally Coded Algorithm for Switched-Current Network Analysis in Frequency Domain
XU Jing-bo
2007-01-01
Based on mirror-blocks, a totally coded algorithm (TCA) for switched-current (SI) network analysis in frequency domain is presented. The algorithm is simple, available, and suitable for any switched-current networks.A basis of analysis and design for switched-current networks via this algorithm is provided.
Frequency and time domain analysis of an external cavity laser with strong filtered optical feedback
Detoma, Enrico; Tromborg, Bjarne; Montrosset, Ivo
The stability properties of an external cavity laser with strong grating-filtered optical feedback to an anti-reflection coated facet are studied with a general frequency domain model. The model takes into account non-linear effects like four wave mixing and gain compression. A small...
Doclo, Simon; Spriet, Ann; Wouters, Jan; Moonen, Marc
2007-01-01
Frequency-Domain Criterion for the Speech Distortion Weighted Multichannel Wiener Filter for Robust Noise Reduction correspondence: Corresponding author. Tel.: +32 16 32 1899; fax: +32 16 32 1970. (Doclo, Simon) (Doclo, Simon) Katholieke Universiteit Leuven, Dept. of Electrical Engineering (ESAT - SCD) - Kasteelpark Arenberg 10 bus 2446--> , 3001 Heverlee (Leuven)--> - BELGIUM (Doclo, Simon) B...
Simultaneous storage of medical images in the spatial and frequency domain: A comparative study
Acharya U Rajendra
2004-06-01
Full Text Available Abstract Background Digital watermarking is a technique of hiding specific identification data for copyright authentication. This technique is adapted here for interleaving patient information with medical images, to reduce storage and transmission overheads. Methods The patient information is encrypted before interleaving with images to ensure greater security. The bio-signals are compressed and subsequently interleaved with the image. This interleaving is carried out in the spatial domain and Frequency domain. The performance of interleaving in the spatial, Discrete Fourier Transform (DFT, Discrete Cosine Transform (DCT and Discrete Wavelet Transform (DWT coefficients is studied. Differential pulse code modulation (DPCM is employed for data compression as well as encryption and results are tabulated for a specific example. Results It can be seen from results, the process does not affect the picture quality. This is attributed to the fact that the change in LSB of a pixel changes its brightness by 1 part in 256. Spatial and DFT domain interleaving gave very less %NRMSE as compared to DCT and DWT domain. Conclusion The Results show that spatial domain the interleaving, the %NRMSE was less than 0.25% for 8-bit encoded pixel intensity. Among the frequency domain interleaving methods, DFT was found to be very efficient.
Florez, H M; Martinelli, M
2016-01-01
Correlation spectroscopy has been proposed as a spectroscopic technique for measuring the coherence between the ground states in electromagnetically induced transparency (EIT). While in time domain the steep dispersion in EIT condition accounts for the robustness of the correlation linewidth against power broadening, such physical insight was not directly established in the frequency domain. We propose a perturbative approach to describe the correlation spectroscopy of two noisy lasers coupled to a $\\Lambda$-transition in cold atoms, leading to EIT. Such approach leads to an analytical expression that maps the intensity correlation directly in terms of the absorption and dispersion of the light fields. Low and high perturbative regimes are investigated and demonstrate that, for coherent light sources, the first oder term in perturbation expansion represents a sufficient description for the correlation. Sidebands resonances are also observed, showing the richness of the frequency domain approach.
Quantitative modulated imaging of turbid media in the high spatial frequency domain
Lin, Weihao; Cao, Zili; Zeng, Bixin; Xu, M.
2016-03-01
The Spatial-frequency dependence of turbid media reflectance encodes both optical properties and depth information. The high spatial frequency domain imaging (HSFDI) can, in particular, extract key characteristics of the phase function of the scattering medium which carries the ultimate structural information of the medium. We first outline the principle of HSFDI and then present here a compact optical configuration integrating the modulated illumination and imaging systems, facilitating quantitative wide-field optical properties mapping at high spatial frequencies. The performance of HSFDI is assessed on both tissue phantoms and in vivo.
Frequency domain modeling and dynamic characteristics evaluation of existing wind turbine systems
Chiang, Chih-Hung; Yu, Chih-Peng
2016-04-01
It is quite well accepted that frequency domain procedures are suitable for the design and dynamic analysis of wind turbine structures, especially for floating offshore wind turbines, since random wind loads and wave induced motions are most likely simulated in the frequency domain. This paper presents specific applications of an effective frequency domain scheme to the linear analysis of wind turbine structures in which a 1-D spectral element was developed based on the axially-loaded member. The solution schemes are summarized for the spectral analyses of the tower, the blades, and the combined system with selected frequency-dependent coupling effect from foundation-structure interactions. Numerical examples demonstrate that the modal frequencies obtained using spectral-element models are in good agreement with those found in the literature. A 5-element mono-pile model results in less than 0.3% deviation from an existing 160-element model. It is preliminarily concluded that the proposed scheme is relatively efficient in performing quick verification for test data obtained from the on-site vibration measurement using the microwave interferometer.
The PolyMAX Frequency-Domain Method: A New Standard for Modal Parameter Estimation?
Bart Peeters
2004-01-01
Full Text Available Recently, a new non-iterative frequency-domain parameter estimation method was proposed. It is based on a (weighted least-squares approach and uses multiple-input-multiple-output frequency response functions as primary data. This so-called “PolyMAX” or polyreference least-squares complex frequency-domain method can be implemented in a very similar way as the industry standard polyreference (time-domain least-squares complex exponential method: in a first step a stabilisation diagram is constructed containing frequency, damping and participation information. Next, the mode shapes are found in a second least-squares step, based on the user selection of stable poles. One of the specific advantages of the technique lies in the very stable identification of the system poles and participation factors as a function of the specified system order, leading to easy-to-interpret stabilisation diagrams. This implies a potential for automating the method and to apply it to “difficult” estimation cases such as high-order and/or highly damped systems with large modal overlap. Some real-life automotive and aerospace case studies are discussed. PolyMAX is compared with classical methods concerning stability, accuracy of the estimated modal parameters and quality of the frequency response function synthesis.
Dynamics of spintronic materials: Exploration in the time and frequency domain
Zabel, Hartmut, E-mail: hartmut.zabel@rub.de [Ruhr-Universität Bochum, 44780 Bochum, Germany and Graduate School of Excellence, Materials Science in Mainz, 55128 Mainz (Germany)
2014-12-14
X-ray and neutron reflectivity are mature experimental techniques for the exploration of film thicknesses and interface roughnesses on the nanoscale. Combining with photon and neutron polarization, these methods can be carried forward to the analysis of magnetic thin films and magnetic domain structures. New opportunities open up when these methods are used either in the time or in the frequency domain. Then dynamical processes can be studied such as domain oscillations, domain propagation, precession of spins, and damping effects. Two methods are discussed which have been developed recently: polarized neutron reflectivity from magnetic films in an alternating magnetic field and time resolved resonant magnetic x-ray reflectivity of the free precessional dynamics in films and multilayers.
Dynamics of spintronic materials: Exploration in the time and frequency domain
X-ray and neutron reflectivity are mature experimental techniques for the exploration of film thicknesses and interface roughnesses on the nanoscale. Combining with photon and neutron polarization, these methods can be carried forward to the analysis of magnetic thin films and magnetic domain structures. New opportunities open up when these methods are used either in the time or in the frequency domain. Then dynamical processes can be studied such as domain oscillations, domain propagation, precession of spins, and damping effects. Two methods are discussed which have been developed recently: polarized neutron reflectivity from magnetic films in an alternating magnetic field and time resolved resonant magnetic x-ray reflectivity of the free precessional dynamics in films and multilayers
Simulation of power fluctuation of wind farms based on frequency domain
Lin, Jin; Sun, Yuanzhang; Li, Guojie; Cheng, Lin; Li, Xiong; Sørensen, Poul Ejnar
2011-01-01
-frequency transformation related to the power spectrum density (PSD), which is more special and complicated than normal transformations. Meanwhile, the computational complexity also increases significantly, more computation resources are needed. These problems negatively affect the engineering application of the model. To......The wind power fluctuation model built up in the frequency domain is mathematically equivalent with that in the time domain, and has a clearer physical meaning therefore describes the fluctuation more accurately. However, the simulation of this model is required to deal with the time...... overcome these disadvantages, the physical meaning of PSD based on fundamental concepts is presented, so that the specialties of this model compared with conventional ones can be understood. Then the time-frequency transformation algorithm is derived, which is fast to be implemented in digital computers...
Zarei, Ali Asghar; Foroutan, Seyyed Abbas; Foroutan, Seyyed Mohsen; Erfanian Omidvar, Abbas
2011-01-01
Pyridostigmine bromide (PB) is a reversible cholinesterase inhibitor. The aim of this study was to determine the effect of orally administration of single dose sustained-released tablet of pyridostigmine bromide (PBSR) on the frequency domain indices of heart rate variability (HRV). Thirty-two healthy young men were participated in this study. They were divided into 2 groups; the pyridostigmine group (n = 22) and the placebo group (n = 10). Electrocardiogram (ECG) was recorded at 10, 30, 60, 90, 120, 150, 180, 210, 240, 300 and 420 min after PBSR administration. At each time, simultaneously, a blood sample was prepared and PB plasma concentration was measured by high-performance liquid chromatography (HPLC) method. Statistical analysis showed that in different indices of HRV, there is a significant increase in low frequency (LF) band at 300 min, but no difference in high frequency band (HF). It also showed significant decreases in normalized high frequency band (Hfnu), normalized low frequency band (Lfnu) and LF/HF ratio at 120, 240 and 300 min after PBSR administration. Maximum plasma concentration of PB was 150 min after the administration. In conclusion, administration of a single dose PBSR can enhance the frequency domains indices of HRV and improvesympathovagal balance. PMID:24250427
Adaptive grid artifact reduction in the frequency domain with spatial properties for x-ray images
Kim, Dong Sik; Lee, Sanggyun
2012-03-01
By applying band-rejection filters (BRFs) in the frequency domain, we can efficiently reduce the grid artifacts, which are caused by using the antiscatter grid in obtaining x-ray digital images. However, if the frequency component of the grid artifact is relatively close to that of the object, then simply applying a BRF may seriously distort the object and cause the ringing artifacts. Since the ringing artifacts are quite dependent on the shape of the object to be recovered in the spatial domain, the spatial property of the x-ray image should be considered in applying BRFs. In this paper, we propose an adaptive filtering scheme, which can cooperate such different properties in the spatial domain. In the spatial domain, we compare several approaches, such as the mangnitude, edge, and frequency-modulation (FM) model-based algorithms, to detect the ringing artifact or the grid artifact component. In order to perform a robust detection whether the ringing artifact is strong or not, we employ the FM model for the extracted signal, which corresponds to a specific grid artifact. A detection of the position for the ringing artifact is then conducted based on the slope detection algorithm, which is commonly used as an FM discriminator in the communication area. However, the detected position of the ringing artifact is not accurate. Hence, in order to obtain an accurate detection result, we combine the edge-based approach with the FM model approach. Numerical result for real x-ray images shows that applying BRFs in the frequency domain in conjunction with the spatial property of the ringing artifact can successfully remove the grid artifact, distorting the object less.
Baumeister, K. J.; Kreider, K. L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in ducts. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Baumeister, Kenneth J.; Kreider, Kevin L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Frequency-domain correction of sensor dynamic error for step response
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.
Linearized Aeroelastic Computations in the Frequency Domain Based on Computational Fluid Dynamics
Amsallem, David; Choi, Youngsoo; Farhat, Charbel
2015-01-01
An iterative, CFD-based approach for aeroelastic computations in the frequency domain is presented. The method relies on a linearized formulation of the aeroelastic problem and a fixed-point iteration approach and enables the computation of the eigenproperties of each of the wet aeroelastic eigenmodes. Numerical experiments on the aeroelastic analysis and design optimization of two wing configurations illustrate the capability of the method for the fast and accurate aeroelastic analysis of aircraft configurations and its advantage over classical time-domain approaches.
Al-Fahoum, Amjed S; Al-Fraihat, Ausilah A
2014-01-01
Technically, a feature represents a distinguishing property, a recognizable measurement, and a functional component obtained from a section of a pattern. Extracted features are meant to minimize the loss of important information embedded in the signal. In addition, they also simplify the amount of resources needed to describe a huge set of data accurately. This is necessary to minimize the complexity of implementation, to reduce the cost of information processing, and to cancel the potential need to compress the information. More recently, a variety of methods have been widely used to extract the features from EEG signals, among these methods are time frequency distributions (TFD), fast fourier transform (FFT), eigenvector methods (EM), wavelet transform (WT), and auto regressive method (ARM), and so on. In general, the analysis of EEG signal has been the subject of several studies, because of its ability to yield an objective mode of recording brain stimulation which is widely used in brain-computer interface researches with application in medical diagnosis and rehabilitation engineering. The purposes of this paper, therefore, shall be discussing some conventional methods of EEG feature extraction methods, comparing their performances for specific task, and finally, recommending the most suitable method for feature extraction based on performance. PMID:24967316
Pokhariyal, Akhilesh; Pedersen, Klaus I.; Monghal, Guillaume Damien; Kovacs, Istvan Z.; Rosa, Claudio; Kolding, Troels E.; Mogensen, Preben
2007-01-01
In this paper we evaluate the performance of downlink channel dependent scheduling in both time and frequency domains. The investigation is based on 3GPP UTRAN long term evolution parameters. A scheduler framework is developed encompassing frequency domain packet scheduling, HARQ management and ...
Clinical skin imaging using color spatial frequency domain imaging (Conference Presentation)
Yang, Bin; Lesicko, John; Moy, Austin J.; Reichenberg, Jason; Tunnell, James W.
2016-02-01
Skin diseases are typically associated with underlying biochemical and structural changes compared with normal tissues, which alter the optical properties of the skin lesions, such as tissue absorption and scattering. Although widely used in dermatology clinics, conventional dermatoscopes don't have the ability to selectively image tissue absorption and scattering, which may limit its diagnostic power. Here we report a novel clinical skin imaging technique called color spatial frequency domain imaging (cSFDI) which enhances contrast by rendering color spatial frequency domain (SFD) image at high spatial frequency. Moreover, by tuning spatial frequency, we can obtain both absorption weighted and scattering weighted images. We developed a handheld imaging system specifically for clinical skin imaging. The flexible configuration of the system allows for better access to skin lesions in hard-to-reach regions. A total of 48 lesions from 31 patients were imaged under 470nm, 530nm and 655nm illumination at a spatial frequency of 0.6mm^(-1). The SFD reflectance images at 470nm, 530nm and 655nm were assigned to blue (B), green (G) and red (R) channels to render a color SFD image. Our results indicated that color SFD images at f=0.6mm-1 revealed properties that were not seen in standard color images. Structural features were enhanced and absorption features were reduced, which helped to identify the sources of the contrast. This imaging technique provides additional insights into skin lesions and may better assist clinical diagnosis.
Reducing Dataset Size in Frequency Domain for Brain Computer Interface Motor Imagery Classification
Ch.Aparna
2010-12-01
Full Text Available Brain computer interface is an emerging area of research where the BCI system is able to detect and interpret the mental activity into computer interpretable signals opening a wide area of applications where activities can be completed without using muscular movement. In Brain Computer Interface research, for classification of EEG signals the raw signals captured has to undergo some preprocessing, to obtain the right attributes for classification. In this paper, we present a system which allows for classification of mental tasks based on a statistical data obtained in frequency domain using Discrete cosine transform and extracting useful frequencies from the same with application of decision tree algorithms for classification.
Chládek, J; Brázdil, M; Halámek, J; Plešinger, F; Jurák, P
2013-01-01
We present an off-line analysis procedure for exploring brain activity recorded from intra-cerebral electroencephalographic data (SEEG). The objective is to determine the statistical differences between different types of stimulations in the time-frequency domain. The procedure is based on computing relative signal power change and subsequent statistical analysis. An example of characteristic statistically significant event-related de/synchronization (ERD/ERS) detected across different frequency bands following different oddball stimuli is presented. The method is used for off-line functional classification of different brain areas. PMID:24109865
Evaluating the coherence and time-domain profile of quantum cascade laser frequency combs.
Burghoff, David; Yang, Yang; Hayton, Darren J; Gao, Jian-Rong; Reno, John L; Hu, Qing
2015-01-26
Recently, much attention has been focused on the generation of optical frequency combs from quantum cascade lasers. We discuss how fast detectors can be used to demonstrate the mutual coherence of such combs, and present an inequality that can be used to quantitatively evaluate their performance. We discuss several technical issues related to shifted wave interference Fourier Transform spectroscopy (SWIFTS), and show how such measurements can be used to elucidate the time-domain properties of such combs, showing that they can possess signatures of both frequency-modulation and amplitude-modulation. PMID:25835878
Estimating C-CAPM and the equity premium over the frequency domain
Ekaterini Panopoulou; Sarantis Kalyvitis
2013-01-01
In this paper we estimate the single-factor Consumption Capital Asset Pricing Model (C-CAPM) over the frequency domain. We modify the standard two-step methodology (Fama and French, 1992) to account for the spectral properties of consumption risk and we find that its lower frequencies explain up to 98% of the cross-sectional variation of expected returns and that the equity premium puzzle is eliminated. These results are robust to the definitions of the variables, the sample span and the set ...
Distributed vibration sensing with time-resolved optical frequency-domain reflectometry.
Zhou, Da-Peng; Qin, Zengguang; Li, Wenhai; Chen, Liang; Bao, Xiaoyi
2012-06-01
The distributed vibration or dynamic strain information can be obtained using time-resolved optical frequency-domain reflectometry. Time-domain information is resolved by measuring Rayleigh backscatter spectrum in different wavelength ranges which fall in successive time sequence due to the linear wavelength sweep of the tunable laser source with a constant sweeping rate. The local Rayleigh backscatter spectrum shift of the vibrated state with respect to that of the non-vibrated state in time sequence can be used to determine dynamic strain information at a specific position along the fiber length. Standard single-mode fibers can be used as sensing head, while the measurable frequency range of 0-32 Hz with the spatial resolution of 10 cm can be achieved up to the total length of 17 m. PMID:22714342
A comparison of frequency domain design and l1-optimal control
Jayasuriya, Suhada; Sobhani, Massoud; Zentgraf, Peter
1991-01-01
A frequency-domain design methodology is applied to a DC motor-speed control system and the results are compared to those obtained using l1-optimal control theory (Pearson and Bamieh, 1990). Both methods synthesize controllers that maximize the allowable size of an unknown-but-bounded disturbance while satisfying prespecified constraints on the control, the control rate, and the outputs. The frequency-domain design technique in general results in much lower-order compensators than those required by the l1-optimal method for a given size of disturbance. Also, the design trade-offs regarding the bandwidth of the system, the size of the disturbance input, and the structural complexity of the controller transfer function become quite transparent.
Power System Harmonic Detection Using Frequency-Domain Interpolation Wavelet Transform
DU Tian-jun; CHEN Guang-ju
2005-01-01
Aiming at harmonic detection, fast Fourier transform can only detect integer harmonics precisely, short time Fourier transform can detect non-integer harmonics with low resolution, and some former wavelet based methods have no aliasing-reduction scheme which result in low measurement precision and poor robustness. A frequency-domain interpolation algorithm to detect harmonics is proposed by choosing Shannon wavelet. Shannon wavelet is an orthogonal wavelet possessing best ideal frequency domain localization ability, it can restrict wavelet aliasing but bring about Gibbs oscillation phenomenon simultaneously. An interpolation algorithm is developed to overcome this problem. Simulation reveals that the proposed method can effectively cancel aliasing, spectral leakage and Gibbs phenomenon, so it provides an effective means for power system harmonic analysis.
Surrogate model reduction for linear dynamic systems based on a frequency domain modal analysis
Kim, T.
2015-10-01
A novel model reduction methodology for linear dynamic systems with parameter variations is presented based on a frequency domain formulation and use of the proper orthogonal decomposition. For an efficient treatment of parameter variations, the system matrices are divided into a nominal and an incremental part. It is shown that the perturbed part is modally equivalent to a new system where the incremental matrices are isolated into the forcing term. To account for the continuous changes in the parameters, the single-composite-input is invoked with a finite number of predetermined incremental matrices. The frequency-domain Karhunen-Loeve procedure is used to calculate a rich set of basis modes accounting for the variations. For demonstration, the new procedure is applied to a finite element model of the Goland wing undergoing oscillations and shown to produce extremely accurate reduced-order surrogate model for a wide range of parameter variations.
Frequency-space domain acoustic wave simulation with the BiCGstab (ℓ) iterative method
Du, Zengli; Liu, Jianjun; Liu, Wenge; Li, Chunhong
2016-02-01
The vast computational cost and memory requirements of LU decomposition are major obstacles to 3D seismic modelling in the frequency-space domain. BiCGstab (ℓ) is an effective bi-conjugate gradient method to solve the giant sparse linear equations, but the convergence rate is extremely low when the threshold value is set small enough. The BiCGstab (ℓ) iterative method was introduced into 3D numerical simulation to overcome these problems in this paper. Numerical examples have shown that the precision of the BiCGstab (ℓ) iterative method meets the demand of seismic modelling and the result is equivalent to that of LU decomposition. The computational cost and memory resource demands of the BiCGstab (ℓ) iterative method are superior to that of LU decomposition. It is an effective method of 3D seismic modelling in the frequency-space domain.
Tanay, Sashwat; Gopakumar, Achamveedu
2016-01-01
Inspiraling compact binaries with non-negligible orbital eccentricities are plausible gravitational wave (GW) sources for the upcoming network of GW observatories. In this paper, we present two prescriptions to compute post-Newtonian (PN) accurate inspiral templates for such binaries. First, we adapt and extend the post-circular scheme of Yunes {\\it et al.} [Phys. Rev. D 80, 084001 (2009)] to obtain a Fourier-domain inspiral approximant that incorporates the effects of PN-accurate orbital eccentricity evolution. This results in a fully analytic frequency-domain inspiral waveform with Newtonian amplitude and 2PN order Fourier phase while incorporating eccentricity effects up to sixth order at each PN order. The importance of incorporating eccentricity evolution contributions to the Fourier phase in a PN consistent manner is also demonstrated. Second, we present an accurate and efficient prescription to incorporate orbital eccentricity into the quasi-circular time-domain {\\texttt{TaylorT4}} approximant at 2PN o...
Jacobsen, Niels-Jørgen; Andersen, Palle; Brincker, Rune
2006-01-01
The presence of harmonic components in the measured responses is unavoidable in many applications of Operational Modal Analysis. This is especially true when measuring on mechanical structures containing rotating or reciprocating parts. This paper describes a new method based on the popular...... Enhanced Frequency Domain Decomposition technique for eliminating the influence of these harmonic components in the modal parameter extraction process. For various experiments, the quality of the method is assessed and compared to the results obtained using broadband stochastic excitation forces. Good...
Stabilization of Inverted Cart-Pendulum System Using Controller: A Frequency-Domain Approach
Dinesh Chandra; Sunil Kumar Mishra
2013-01-01
This paper focuses on the angular stabilization of inverted cart-pendulum system using controller. The tuning of controller is formulated as a nonlinear optimization problem, in which the objective function is composed of five design conditions in frequency domain. Particle swarm optimization technique has been used for optimizing parameters. Also a PID controller has been designed based on same specifications, and a comparative study has been carried out. All the responses have been calculat...
NEW FREQUENCY DOMAIN POST-FILTERS FOR NOISE CANCELLATION USING TWO CLOSELY SPACED MICROPHONES
Djendi, Mohamed; Gilloire, A.; Pascal, Scalart
2009-01-01
International audience This paper addresses the problem of speech enhancement in a moving car through a blind source separation (BSS) scheme involving two closely spaced microphones. We propose two frequency domain methods to reduce the distortion caused by the forward BSS structure, which is most important when microphones are closely spaced. Both methods aim at estimating post-filters to compensate for the distortion by equalization. The first method is based on an open-loop estimation. ...
Lu, Yujie; Zhu, Banghe; Shen, Haiou; Rasmussen, John C.; WANG, GE; Sevick-Muraca, Eva M.
2010-01-01
Fluorescence molecular imaging/tomography may play an important future role in preclinical research and clinical diagnostics. Time- and frequency-domain fluorescence imaging can acquire more measurement information than the continuous wave (CW) counterpart, improving the image quality of fluorescence molecular tomography. Although diffusion approximation (DA) theory has been extensively applied in optical molecular imaging, high-order photon migration models need to be further investigated to...
Benoit Boulet; Vahid Raissi Dehkordi
2009-01-01
This paper deals with the robust performance problem of a linear time-invariant control system in the presence of robust controller uncertainty. Assuming that plant uncertainty is modeled as an additive perturbation, a geometrical approach is followed in order to find a necessary and sufficient condition for robust performance in the form of a bound on the magnitude of controller uncertainty. This frequency domain bound is derived by converting the problem into an optimization problem, whose ...
Soil-structure-interaction analysis in frequency domain using fixed base eigenvalues
Dynamic soil-structure-interaction analyses are usually performed in the frequency domain. Solutions for large buildings require much computer time because of the many degrees of freedom that are needed to represent the dynamic behaviour of the structure. The method presented takes advantage of the fact, that for seismic loading the behaviour of the structure can be represented by only a few natural modes. Thus the number of the equations of motion that have to be solved are drastically reduced. (author)
A frequency domain bootstrap for ratio statistics in time series analysis
Dahlhaus, R.; Janas, D.
1996-01-01
The asymptotic properties of the bootstrap in the frequency domain based on Studentized periodogram ordinates are studied. It is proved that this bootstrap approximation is valid for ratio statistics such as autocorrelations. By using Edgeworth expansions it is shown that the bootstrap approximation even outperforms the normal approximation. The results carry over to Whittle estimates. In a simulation study the behavior of the bootstrap is studied for empirical correlations and Whittle estima...
bouoiyour, jamal; Selmi, Refk; Tiwari, Aviral
2014-01-01
The present study addresses one of the most problematic phenomena: Bitcoin price. We explore the Granger causality for two relationships (Bitcoin price and transactions; Bitcoin price and investors’ attractiveness) from a frequency domain perspective using Breitung and Candelon’s (2006) approach. Intuitively, this research gauges empirically the causal links between these variables unconditionally on the one hand and conditionally to the Chinese stock market and the processing power of Bitcoi...
JAMAL BOUOIYOUR; REFK SELMI; AVIRAL KUMAR TIWARI
2015-01-01
The present study addresses one of the most problematic phenomena: Bitcoin price. We explore the Granger causality for two relationships (Bitcoin price and trade transactions; Bitcoin price and investors' attractiveness) from a frequency domain perspective-based on unconditional and conditional data analysis. Accurately, this research empirically assesses the causal links between these variables unconditionally on the one hand and conditioning upon relevant control variables (recorded in lite...
High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing
MacLachlan, Robert A.; Riviere, Cameron N.
2009-01-01
Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large ...
Effective post-processing for single-channel frequency-domain speech enhancement
Li, Weifeng
2007-01-01
Conventional frequency-domain speech enhancement filters improve signal-to-noise ratio (SNR), but also produce speech distortions. This paper describes a novel post-processing algorithm devised for the improvement of the quality of the speech processed by a conventional filter. In the proposed algorithm, the speech distortion is first compensated by adding the original noisy speech, and then the noise is reduced by a post-filter. Experimental results on speech quality show the effectiveness o...
Improvement of Reading Performance of Frequency-Domain Chipless RFID Transponders
Havlicek, J.; Svanda, M.; J. Machac; M. Polivka
2016-01-01
This review paper presents the summary of our investigations in several topics of frequency-domain chipless RFID transponders. The performance comparison of various types of scatterers used in the literature and recently proposed by the authors is presented. The issue of proper location of adjacent resonant elements in the scatterer array to reduce the mutual coupling and consequently ensure the robust RCS response for reliable reading of coded information is addressed. A major improvement in...
Time and Frequency-Domain Cross-Verification of SLS 6DOF Trajectory Simulations
VanZwieten, Tannen; Johnson, Matthew D.; McCullough, John P.; Gilligan, Eric T.
2014-01-01
The SLS GNC team and its partners have developed several time- and frequency-based simulations for development and analysis of the proposed SLS launch vehicle. The simulations differ in fidelity and some have unique functionality that allows them to perform specific analyses. Some examples of the purposes of the various models are: trajectory simulation, multi-body separation, Monte Carlo, hardware in the loop, loads, and frequency domain stability analyses. While no two simulations are identical, many of the models are essentially six degree-of-freedom (6DOF) representations of the SLS plant dynamics, hardware implementation, and flight software. Thus at a high level all of those models should be in agreement. Comparison of outputs from several SLS trajectory and stability analysis tools are ongoing as part of the program's current verification effort. The purpose of these comparisons is to highlight modeling and analysis differences, verify simulation data sources, identify inconsistencies and minor errors, and ultimately to verify output data as being a good representation of the vehicle and subsystem dynamics. This paper will show selected verification work in both the time and frequency domain from the current design analysis cycle of the SLS for several of the design and analysis simulations. In the time domain, the tools that will be compared are MAVERIC, CLVTOPS, SAVANT, STARS, ARTEMIS, and POST 2. For the frequency domain analysis, the tools to be compared are FRACTAL, SAVANT, and STARS. The paper will include discussion of these tools including their capabilities, configurations, and the uses to which they are put in the SLS program. Determination of the criteria by which the simulations are compared (matching criteria) requires thoughtful consideration, and there are several pitfalls that may occur that can severely punish a simulation if not considered carefully. The paper will discuss these considerations and will present a framework for responding to
Effects of laser frequency drift in phase-sensitive optical time-domain reflectometry fiber sensors
Zhirnov, Andrey; Stepanov, Konstantin; Nesterov, Evgeny; Karasik, Valery; Svelto, Cesare; Pnev, Alexey
2016-01-01
The present work studies the influence of laser frequency drifts on operating of phase-sensitive optical time-domain reflectometry ($\\Phi$-OTDR) fiber sensors. A mathematical model and numerical simulations are employed to highlight the influence of frequency drifts of light sources on two characteristic scales: large-time (minutes) and short-time (milliseconds) frequency drifts. Numerical simulation results are compared with predictions given by the fluctuation ratio coefficient (FRC), and they are in a qualitative agreement. In addition to qualitative criteria for light sources given by the FRC, quantitive requirements for optimal light sources for $\\Phi$-OTDR sensors are obtained. Numerical simulation results are verified by comparison with experimental data for three significantly different types of light source.
A Ray-Tracing Technique to Characterize GPS Multipath in the Frequency Domain
Naveen S. Gowdayyanadoddi
2015-01-01
Full Text Available Multipath propagation is one of the major sources of error in GPS measurements. In this research, a ray-tracing technique is proposed to study the frequency domain characteristics of multipath propagation. The Doppler frequency difference, also known as multipath phase rate and fading frequency, between direct (line-of-sight, LOS and reflected (non-line-of-sight, NLOS signals is studied as a function of satellite elevation and azimuth, as well as distance between the reflector and the static receiver. The accuracy of the method is verified with measured Doppler differences from real data collected in a downtown environment. The use of ray-tracing derived predicted Doppler differences in a receiver, as a means of alleviating the multipath induced errors in the measurement, is presented and discussed.
Photon acceleration versus frequency-domain interferometry for laser wakefield diagnostics
Dias, J.M.; Oliveira e Silva, L.; Mendonca, J.T. [GoLP/Centro de Fisica de Plasmas, Inst. Superior Tecnico, Lisbon (Portugal)
1998-03-01
A detailed comparison between the photon acceleration diagnostic technique and the frequency-domain interferometric technique for laser wakefield diagnostics, by using ray-tracing equations is presented here. The dispersion effects on the probe beam and the implications of an arbitrary phase velocity of the plasma wave are discussed for both diagnostic techniques. In the presence of large amplitude plasma wave and long interaction distances significant frequency shifts can be observed. The importance of this effect on the determination of the phase and frequency shifts measurements given by each of the two diagnostic techniques, is also analyzed. The accuracy of both diagnostic techniques is discussed and some of their technical problems are reviewed. (author)
Spectral evolution of two-dimensional kinetic plasma turbulence in the wavenumber-frequency domain
Comişel, H. [Institut für Theoretische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, D-38016 Braunschweig (Germany); Institute for Space Sciences, Atomiştilor 409, P.O. Box MG-23, Bucharest-Măgurele RO-077125 (Romania); Verscharen, D. [Space Science Center, University of New Hampshire, 8 College Rd., Durham, New Hampshire 03824 (United States); Narita, Y. [Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz (Austria); Motschmann, U. [Institut für Theoretische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, D-38016 Braunschweig (Germany); Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, Rutherfordstr. 2, D-12489 Berlin (Germany)
2013-09-15
We present a method for studying the evolution of plasma turbulence by tracking dispersion relations in the energy spectrum in the wavenumber-frequency domain. We apply hybrid plasma simulations in a simplified two-dimensional geometry to demonstrate our method and its applicability to plasma turbulence in the ion kinetic regime. We identify four dispersion relations: ion-Bernstein waves, oblique whistler waves, oblique Alfvén/ion-cyclotron waves, and a zero-frequency mode. The energy partition and frequency broadening are evaluated for these modes. The method allows us to determine the evolution of decaying plasma turbulence in our restricted geometry and shows that it cascades along the dispersion relations during the early phase with an increasing broadening around the dispersion relations.
Kodama, Kazuto; An, Zhisheng; Chang, Hong; Qiang, Xiaoke
2015-04-01
Measurement of low-field magnetic susceptibility over a wide band of frequencies spanning four orders of magnitude is a useful method for the assessment of the grain size distribution of ultrafine magnetic particles smaller than the SP/SSD boundary. This method has been applied to a loess/paleosol sequence at Luochuan in the Chinese Loess Plateau. The studied succession consists of sequences from the latest paleosol unit to the upper part of the loess unit, spanning the last glacial-interglacial cycle. Reconstructed grain size distributions (GSDs) consist of volume fractions on the order of 10-24 m3, and the mean GSDs are modal but with distinctive skewness among the loess, the weakly developed paleosol (weak paleosol), and the mature paleosol. This indicates that the mean volume of SP particles in this sequence tends to increase during the transition from the loess to the paleosol. An index, defined as the difference between χ130 at the lowest (130 Hz) and χ500k at the highest (500 kHz) frequencies normalized to χ130, is judged to be a more suitable index than previous frequency dependence parameters for the concentration of SP particles. This index has a strong correlation with χ130, showing a continuous 'growth curve' with the rate of increase being highest for the loess, moderate for the weak paleosol, and saturated for the paleosol. The characteristic curve suggests that smaller SP particles are preferentially formed in the earlier stage of pedogenesis rather than the later phase when even larger particles are formed in the mature paleosol. These results demonstrate that the broad-band-frequency susceptibility measurement will be useful for the quantitative assessment of magnetic nanoparticles in soils and sediments. Additionally, we point out that the measurement in the frequency domain generally requires time and may not be most suitable to routine measurements. We thus propose an alternative manner, the measurement in the time domain that can be
Phase Analysis for Frequency Standards in the Microwave and Optical Domains
Kazda, M; Huntemann, N; Lipphardt, B; Weyers, S
2015-01-01
Coherent manipulation of atomic states is a key concept in high-precision spectroscopy and used in atomic fountain clocks and a number of optical frequency standards. Operation of these standards can involve a number of cyclic switching processes, which may induce cycle synchronous phase excursions of the interrogation signal and thus lead to shifts in the output of the frequency standard. We have built a FPGA-based phase analyzer to investigate these effects and conducted measurements on two frequency standards. For the caesium fountain PTB-CSF2 we were able to exclude phase variations of the microwave source at the level of a few $\\mu$rad, corresponding to relative frequency shifts of less than 10$^{-16}$. In the optical domain, we investigated phase variations in PTB's Yb$^+$ optical frequency standard and made detailed measurements of AOM chirps and their scaling with duty cycle and driving power. We ascertained that cycle-synchronous as well as long-term phase excursion do not cause frequency shifts larg...
Analysis on the time and frequency domains of the acceleration in front crawl stroke.
Gil, Joaquín Madera; Moreno, Luis-Millán González; Mahiques, Juan Benavent; Muñoz, Víctor Tella
2012-05-01
The swimming involves accelerations and decelerations in the swimmer's body. Thus, the main objective of this study is to make a temporal and frequency analysis of the acceleration in front crawl swimming, regarding the gender and the performance. The sample was composed by 31 male swimmers (15 of high-level and 16 of low-level) and 20 female swimmers (11 of high-level and 9 of low-level). The acceleration was registered from the third complete cycle during eight seconds in a 25 meters maximum velocity test. A position transducer (200Hz) was used to collect the data, and it was synchronized to an aquatic camera (25Hz). The acceleration in the temporal (root mean square, minimum and maximum of the acceleration) and frequency (power peak, power peak frequency and spectral area) domains was calculated with Fourier analysis, as well as the velocity and the spectrums distribution in function to present one or more main peaks (type 1 and type 2). A one-way ANOVA was used to establish differences between gender and performance. Results show differences between genders in all the temporal domain variables (p<0.05) and only the Spectral Area (SA) in the frequency domain (p<0.05). Between gender and performance, only the Root Mean Square (RMS) showed differences in the performance of the male swimmers (p<0.05) and in the higher level swimmers, the Maximum (Max) and the Power Peak (PP) of the acceleration showed differences between both genders (p<0.05). These results confirms the importance of knowing the RMS to determine the efficiency of the swimmers regarding gender and performance level. PMID:23487001
Dynamic analysis of offshore structures with non-zero initial conditions in the frequency domain
Liu, Fushun; Lu, Hongchao; Li, Huajun
2016-03-01
The state of non-zero conditions is typically treated as fact when considering the dynamic analysis of offshore structures. This article extends a newly proposed method [1] to manage the non-zero initial conditions of offshore structures in the frequency domain, including new studies on original environmental loads reconstruction, response comparisons with the commercial software ANSYS, and a demonstration using an experimental cantilever beam. The original environmental loads, such as waves, currents, and winds, that act on a structure are decomposed into multiple complex exponential components are represented by a series of poles and corresponding residues. Counter to the traditional frequency-domain method, the non-zero initial conditions of offshore structures could be solved in the frequency domain. Compared with reference [1], an improvement reported in this article is that practical issues, including the choice of model order and central-processing-unit (CPU) time consumption, are further studied when applying this new method to offshore structures. To investigate the feasibility of the representation of initial environmental loads by their poles and corresponding residues, a measured random wave force collected from a column experiment at the Lab of Ocean University of China is used, decomposed, reconstructed and then compared with the original wave force; then, a numerical offshore platform is used to study the performance of the proposed method in detail. The numerical results of this study indicate that (1) a short duration of environmental loads are required to obtain their constitutive poles and residues, which implies good computational efficiency; and (2) the proposed method has a similar computational efficiency to traditional methods due to the use of the inverse Fourier transform technique. To better understand the performance, of time consumption and accuracy of the proposed method, the commercial software ANSYS is used to determine responses
Shanhai Jin
2012-01-01
Full Text Available This paper presents the results of quantitative performance evaluation of an authors’ new parabolic sliding mode filter, which is for removing noise from signals in robotics and mechatronics applications, based on the frequency and time domain characteristics. Based on the evaluation results, the paper presents selection guidelines of two parameters of the filter. The evaluation results show that, in the frequency domain, the noise removing capability of the filter is almost the same as that of the second-order Butterworth low-pass filter (2-LPF, but its phase lag is smaller (maximum 150 degree than that of 2-LPF (maximum 180 degree. Moreover, the filter produces smaller phase lag than a conventional parabolic sliding mode filter with appropriate selection of the parameters. In the time domain, the filter produces smaller overshoot than 2-LPF and the conventional one, while maintaining short transient time, by using an appropriately selected parameter. The presented parameter selection guidelines state that the values of the parameters should be chosen according to some estimated characteristics of the input and some desired characteristics of the output. The effectiveness of the filter and the presented guidelines is validated through numerical examples and their application to a closed-loop, force control of a robot manipulator.
Not extinct yet: innovations in frequency domain HEM triggered by sea ice studies
Pfaffhuber, Andreas A.; Hendricks, Stefan
2015-10-01
The last 15 years have brought major innovations in helicopter towed time domain electromagnetics (EM), while few further developments have been made within the classic frequency domain segment. Operational use of frequency domain EM for sea ice thickness mapping acted as a driving force to develop new concepts such as the system under our consideration. Since its introduction we have implemented new concepts aiming at noise reduction and drift elimination. We decreased signal noise base levels by one to two orders of magnitude with changes to the signal transmission concept. Further, we increased the receiver coil dynamic range creating an EM setup without the need for primary field bucking. Finally, we implemented control signals inside the receiver coils to potentially eliminate system drift. Ground tests demonstrate the desired noise reduction and demonstrate drift control, leading to essentially drift free data. Airborne field data confirm these results, yet also show that the procedures can still be improved. The remaining quest is whether these specialised system improvements could also be implemented in exploration helicopter EM (HEM) systems to increase accuracy and efficiency.
Feasible Frequency-domain Compensation Scheme for IQ Imbalances in OFDM Receivers
Feng, Shu; Xiajie, Shi; Weixin, Sheng; Renhong, Xie
2011-01-01
A pilot pattern across two OFDM symbols with special structure is devised for channel estimation in OFDM systems with IQ imbalance at receiver. Based on this pilot pattern, a high-efficiency time-domain (TD) least square (LS) channel estimator is proposed to significantly suppress channel noise by a factor N/(L+1) in comparison with the frequency-domain LS one in [1] where N and L+1 are the total number of subcarriers and the length of cyclic prefix, respectively. Following this, a low-complexity frequency-domain (FD) Gaussian elimination (GE) equalizer is proposed to eliminate IQ distortion by using only 2N complex multiplications per OFDM symbol. From simulation, the proposed scheme TD-LS/FD-GE using only two pilot OFDM symbols achieves the same bit error rate (BER) performance under ideal channel knowledge and no IQ imbalances at low and medium signal-to-noise ratio (SNR) regions whereas these compensation schemes including FD-LS/Post-FFT LS, FD-LS/Pre-FFT Corr, and SPP/Pre-FFT Corr in [1] require about tw...
Time-domain electromagnetic energy in a frequency-dispersive left-handed medium
From Maxwell's equations and the Poynting theorem, the time-domain electric and magnetic energy densities are generally defined in the frequency-dispersive media based on the conservation of energy. As a consequence, a general definition of electric and magnetic energy is proposed. Comparing with existing formulations of electric and magnetic energy in frequency-dispersive media, the new definition is more reasonable and is valid in any case. Using the new definition and staring from the equation of motion, we have shown rigorously that the total energy density and the individual electric and magnetic energy densities are always positive in a realistic artificial left-handed medium (LHM) [R. A. Shelby, D. R. Smith, and S. Schultz, Science 292, 77 (2001)], which obeys actually the Lorentz medium model, although such a LHM has negative permittivity and negative permeability simultaneously in a certain frequency range. We have also shown that the conservation of energy is not violated in LHM. The earlier conclusions can be easily extended to the Drude medium model and the cold plasma medium model. Through an exact analysis of a one-dimensional transient current source radiating in LHM, numerical results are given to demonstrate that the work done by source, the power flowing outwards a surface, and the electric and magnetic energy stored in a volume are all positive in the time domain
Hanus, Robert; Zych, Marcin; Petryka, Leszek; Jaszczur, Marek; Hanus, Paweł
2016-03-01
Knowledge of the structure of a flow is really significant for the proper conduct a number of industrial processes. In this case a description of a two-phase flow regimes is possible by use of the time-series analysis e.g. in frequency domain. In this article the classical spectral analysis based on Fourier Transform (FT) and Short-Time Fourier Transform (STFT) were applied for analysis of signals obtained for water-air flow using gamma ray absorption. The presented method was illustrated by use data collected in experiments carried out on the laboratory hydraulic installation with a horizontal pipe of 4.5 m length and inner diameter of 30 mm equipped with two 241Am radioactive sources and scintillation probes with NaI(Tl) crystals. Stochastic signals obtained from detectors for plug, bubble, and transitional plug - bubble flows were considered in this work. The recorded raw signals were analyzed and several features in the frequency domain were extracted using autospectral density function (ADF), cross-spectral density function (CSDF), and the STFT spectrogram. In result of a detail analysis it was found that the most promising to recognize of the flow structure are: maximum value of the CSDF magnitude, sum of the CSDF magnitudes in the selected frequency range, and the maximum value of the sum of selected amplitudes of STFT spectrogram.
Lin Wang
2010-01-01
Full Text Available Frequency-domain blind source separation (BSS performs poorly in high reverberation because the independence assumption collapses at each frequency bins when the number of bins increases. To improve the separation result, this paper proposes a method which combines two techniques by using beamforming as a preprocessor of blind source separation. With the sound source locations supposed to be known, the mixed signals are dereverberated and enhanced by beamforming; then the beamformed signals are further separated by blind source separation. To implement the proposed method, a superdirective fixed beamformer is designed for beamforming, and an interfrequency dependence-based permutation alignment scheme is presented for frequency-domain blind source separation. With beamforming shortening mixing filters and reducing noise before blind source separation, the combined method works better in reverberation. The performance of the proposed method is investigated by separating up to 4 sources in different environments with reverberation time from 100 ms to 700 ms. Simulation results verify the outperformance of the proposed method over using beamforming or blind source separation alone. Analysis demonstrates that the proposed method is computationally efficient and appropriate for real-time processing.
Comparison of geometrical and diffraction imaging in the space and frequency domains.
Mahajan, Virendra N; Díaz, José A
2016-04-20
The geometrical and diffraction point-spread functions of an optical imaging system have been reviewed and compared in the past [Proc. SPIE3729, 434 (1999)PSISDG0277-786X10.1117/12.346821]. In this paper, we review and compare corresponding optical transfer functions. While the truth lies with the diffraction optical-transfer functions (OTF), it is considered easier and quicker to calculate the geometrical OTF, especially for large aberrations. We describe the theory of the two OTFs and explore the range of spatial frequencies and the magnitude of the primary aberrations over which the geometrical OTF may provide a reasonable approximation of the diffraction OTF. Moreover, balancing of spherical aberration with defocus for optimum diffraction OTF is studied as a function of both the aberration value as well as the spatial frequency. How to gauge the progress of an optical design in the frequency domain based on the geometrical OTF is outlined as the ray spot size is used in the space domain. PMID:27140094
Time domain and frequency analysis of RTS noise in deep submicron SiGe HBTs
Our work is focused on the identification of defects responsible for the current fluctuations at the origin of low-frequency noise or random telegraphic signals in industrial 0.35 μm BiCMOS technologies. Gummel plots are modelled in order to identify generation-recombination or trap-assisted tunnelling process in the base current. We show that devices having excess base current present random discrete fluctuations on the base current. The analysis of the RTS noise parameters (amplitude, high and low state time durations) as a function of temperature and bias voltage allow us to characterize the traps involved. The conventional technique consists of a statistical treatment of the RTS time domain data. The single trap capture cross-sections and activation energy are deduced with an Arrhenius plot. In order to improve the RTS analysis, we have developed an FFT-based method. The technique allows us to calculate the noise spectrum and to measure the cut-off frequency of a single trap even at very low frequencies (from 0.1 Hz). Finally, it is shown that the frequency analysis of the random telegraphic signals is a well-suited tool for the study of single defects in very small devices. Furthermore, it is complementary with conventional LFN measurements and extended to the very-low-frequency range
This two part study introduces new developments in frequency domain optical tomography to take into account the collimated source direction in the computation of both the forward and the adjoint models. The solution method is based on the least square finite element method associated to the discrete ordinates method where no empirical stabilization is needed. In this first part of the study, the solution method of the forward model is highlighted with an easy handling of complex boundary condition through a penalization method. Gradient computation from an adjoint method is developed rigorously in a continuous manner through a lagrangian formalism for the deduction of the adjoint equation and the gradient of the objective function. The proposed formulation can be easily generalized to stationary and time domain optical tomography by keeping the same expressions.
Chillara, Vamshi Krishna; Ren, Baiyang; Lissenden, Cliff J
2016-04-01
This article describes the use of the frequency domain finite element (FDFE) technique for guided wave mode selection in inhomogeneous waveguides. Problems with Rayleigh-Lamb and Shear-Horizontal mode excitation in isotropic homogeneous plates are first studied to demonstrate the application of the approach. Then, two specific cases of inhomogeneous waveguides are studied using FDFE. Finally, an example of guided wave mode selection for inspecting disbonds in composites is presented. Identification of sensitive and insensitive modes for defect inspection is demonstrated. As the discretization parameters affect the accuracy of the results obtained from FDFE, effect of spatial discretization and the length of the domain used for the spatial fast Fourier transform are studied. Some recommendations with regard to the choice of the above parameters are provided. PMID:26746160
Multiobjective Optimization for Electronic Circuit Design in Time and Frequency Domains
J. Dobes
2013-04-01
Full Text Available The multiobjective optimization provides an extraordinary opportunity for the finest design of electronic circuits because it allows to mathematically balance contradictory requirements together with possible constraints. In this paper, an original and substantial improvement of an existing method for the multiobjective optimization known as GAM (Goal Attainment Method is suggested. In our proposal, the GAM algorithm itself is combined with a procedure that automatically provides a set of parameters -- weights, coordinates of the reference point -- for which the method generates noninferior solutions uniformly spread over an appropriately selected part of the Pareto front. Moreover, the resulting set of obtained solutions is then presented in a suitable graphic form so that the solution representing the most satisfactory tradeoff can be easily chosen by the designer. Our system generates various types of plots that conveniently characterize results of up to four-dimensional problems. Technically, the procedures of the multiobjective optimization were created as a software add-on to the CIA (Circuit Interactive Analyzer program. This way enabled us to utilize many powerful features of this program, including the sensitivity analyses in time and frequency domains. As a result, the system is also able to perform the multiobjective optimization in the time domain and even highly nonlinear circuits can be significantly improved by our program. As a demonstration of this feature, a multiobjective optimization of a C-class power amplifier in the time domain is thoroughly described in the paper. Further, a four-dimensional optimization of a video amplifier is demonstrated with an original graphic representation of the Pareto front, and also some comparison with the weighting method is done. As an example of improving noise properties, a multiobjective optimization of a low-noise amplifier is performed, and the results in the frequency domain are shown
Frequency-domain analysis of intrinsic neuronal properties using high-resistant electrodes
Christian Rössert
2009-08-01
Full Text Available Intrinsic cellular properties of neurons in culture or slices are usually studied by the whole cell clamp method using low-resistant patch pipettes. These electrodes allow detailed analyses with standard electrophysiological methods such as current- or voltage-clamp. However, in these preparations large parts of the network and dendritic structures may be removed, thus preventing an adequate study of synaptic signal processing. Therefore, intact in vivo preparations or isolated in vitro whole brains have been used in which intracellular recordings are usually made with sharp, high-resistant electrodes to optimize the impalement of neurons. The general non-linear resistance properties of these electrodes, however, severely limit accurate quantitative studies of membrane dynamics especially needed for precise modelling. Therefore, we have developed a frequency-domain analysis of membrane properties that uses a Piece-wise Non-linear Electrode Compensation (PNEC method. The technique was tested in second-order vestibular neurons and abducens motoneurons of isolated frog whole brain preparations using sharp potassium chloride- or potassium acetate-filled electrodes. All recordings were performed without online electrode compensation. The properties of each electrode were determined separately after the neuronal recordings and were used in the frequency-domain analysis of the combined measurement of electrode and cell. This allowed detailed analysis of membrane properties in the frequency-domain with high-resistant electrodes and provided quantitative data that can be further used to model channel kinetics. Thus, sharp electrodes can be used for the characterization of intrinsic properties and synaptic inputs of neurons in intact brains.
Moghimirad, Elahe; Mahloojifar, Ali; Mohammadzadeh Asl, Babak
2016-05-01
A new frequency-domain implementation of a synthetic aperture focusing technique is presented in the paper. The concept is based on synthetic aperture radar (SAR) and sonar that is a developed version of the convolution model in the frequency domain. Compared with conventional line-by-line imaging, synthetic aperture imaging has a better resolution and contrast at the cost of more computational load. To overcome this problem, point-by-point reconstruction methods have been replaced by block-processing algorithms in radar and sonar; however, these techniques are relatively unknown in medical imaging. In this paper, we extended one of these methods called wavenumber to medical ultrasound imaging using a simple model of synthetic aperture focus. The model, derived here for monostatic mode, can be generalized to multistatic as well. The method consists of 4 steps: a 2D fast Fourier transform of the data, frequency shift of the data to baseband, interpolation to convert polar coordinates to rectangular ones, and returning the data to the spatial-domain using a 2D inverse Fourier transform. We have also used chirp pulse excitation followed by matched filtering and spotlighting algorithm to compensate the effect of differences in parameters between radar and medical imaging. Computational complexities of the two methods, wavenumber and delay-and-sum (DAS), have been calculated. Field II simulated point data have been used to evaluate the results in terms of resolution and contrast. Evaluations with simulated data show that for typical phantoms, reconstruction by the wavenumber algorithm is almost 20 times faster than classical DAS while retaining the resolution. PMID:25900969
Vibrational frequencies of anti-diabetic drug studied by terahertz time-domain spectroscopy
Du, S. Q.; Li, H.; Xie, L.; Chen, L.; Peng, Y.; Zhu, Y. M.; Li, H.; Dong, P.; Wang, J. T.
2012-04-01
By using terahertz time-domain spectroscopy, the absorption spectra of seven anti-diabetic pills have been investigated. For gliquidone, glipizide, gliclazide, and glimepiride, an obvious resonance peak is found at 1.37 THz. Furthermore, to overcome the limit of density functional theory that can analyze the normal mode frequencies of the ground state of organic material, we also present a method that relies on pharmacophore recognition, from which we can obtain the resonance peak at 1.37 THz can be attributed to the vibration of sulfonylurea group. The results indicate that the veracity of density functional theory can be increased by combining pharmacophore recognition.
24 mm depth range discretely swept optical frequency domain imaging in dentistry
Kakuma, Hideo; Choi, DongHak; Furukawa, Hiroyuki; Hiro-Oka, Hideaki; Ohbayashi, Kohji
2009-02-01
A large depth range is needed if optical coherence tomography (OCT) is to be used to observe multiple teeth simultaneously. A discretely swept optical frequency domain imaging system with a 24-mm depth range was made by using a superstructure-grating distributed Bragg reflector (SSG-DBR) laser as the light source and setting the frequencystep interval to be 3.13 GHz (λ ~ 0.026 nm). The swept wavelength range was 40 nm centered at 1580 nm, the resolution was 29 μm, and the A-scan rate was 1.3 kHz. Application of the OCT system to a dental phantom was demonstrated.
Vahid Raissi Dehkordi
2009-01-01
Full Text Available This paper deals with the robust performance problem of a linear time-invariant control system in the presence of robust controller uncertainty. Assuming that plant uncertainty is modeled as an additive perturbation, a geometrical approach is followed in order to find a necessary and sufficient condition for robust performance in the form of a bound on the magnitude of controller uncertainty. This frequency domain bound is derived by converting the problem into an optimization problem, whose solution is shown to be more time-efficient than a conventional structured singular value calculation. The bound on controller uncertainty can be used in controller order reduction and implementation problems.
Time and frequency domains dc conductivity analysis in thin dielectric films at high temperature
Electrical conductivity of a thin dielectric film has been analysed at high temperature in both time and frequency domains (TD/FD). Two disturbing ionic space-charge phenomena have been highlighted in two different temperature ranges and a correlation of their electrical signature between TD and FD is carried out. These two phenomena were related to the thermal activation of ions coming from two different trap levels (shallow and deep traps). We validate here also the fact that the FD method is a powerful way to estimate the dc conductivity in dielectric solids at high temperature thanks to a better discrimination of ionic contributions and injection phenomena.
Modeling of Nanophotonic Resonators with the Finite-Difference Frequency-Domain Method
Ivinskaya, Aliaksandra; Lavrinenko, Andrei; Shyroki, Dzmitry
2011-01-01
Finite-difference frequency-domain method with perfectly matched layers and free-space squeezing is applied to model open photonic resonators of arbitrary morphology in three dimensions. Treating each spatial dimension independently, nonuniform mesh of continuously varying density can be built...... easily to better resolve mode features. We explore the convergence of the eigenmode wavelength $lambda $ and quality factor $Q$ of an open dielectric sphere and of a very-high- $Q$ photonic crystal cavity calculated with different mesh density distributions. On a grid having, for example, 10 nodes per...
Transformation optics: a time- and frequency-domain analysis of electron-energy loss spectroscopy
Kraft, Matthias; Pendry, J B
2016-01-01
Electron energy loss spectroscopy (EELS) and Cathodoluminescence (CL) play a pivotal role in many of the cutting edge experiments in plasmonics. EELS and CL experiments are usually supported by numerical simulations, which, whilst accurate, may not provide as much physical insight as analytical calculations do. Fully analytical solutions to EELS and CL systems in plasmonics are rare and difficult to obtain. This paper aims to narrow this gap by introducing a new method based on Transformation optics that allows to calculate the quasi-static frequency and time-domain response of plasmonic particles under electron beam excitation.
Xu, Tianhua; Popov, Sergei; Forzati, Marco; Martensson, Jonas; Mussolin, Marco; Li, Jie; Wang, Ke; Zhang, Yimo; Friberg, Ari T
2016-01-01
The frequency domain equalizers (FDEs) employing two types of overlap-add zero-padding (OLA-ZP) methods are applied to compensate the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system. Simulation results demonstrate that the OLA-ZP methods can achieve the same acceptable performance as the overlap-save method. The required minimum overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier transform length to minimize the computational complexity is also analyzed.
A Novel Ship Wake Detection Method of SAR Images Based on Frequency Domain
Liu Hao; Zhu Minhui
2003-01-01
Moving ships produce a set of waves of "V' pattern on the ocean. These waves can often be seen by Synthetic Aperture Radar (SAR). The detection of these wakes can provide important information for surveillance of shipping, such as ship traveling direction and speed. A novel approach to the detection of ship wakes in SAR images based on frequency domain is provided in this letter. Compared with traditional Radon-based approaches, computation is reduced by 20%-40% without losing nearly any of detection performance. The testing results using real data and simulation of synthetic SAR images test the algorithm's feasibility and robustness.
2008-01-01
Optical frequency domain phase conjugation(FDPC) is based on phase conjuga-tion of spectrum of an input signal.It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal.The use of FDPC to con-trol polarization signal distortion in birefringent optical fiber systems is proposed.Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically.It is shown that the distortion of polariza-tion signals can be controlled effectively by FDPC.The impairments due to disper-sion and nonlinear effects can be suppressed simultaneously.
BU Yang; WANG XiangZhao
2008-01-01
Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to con-trol polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polariza-tion signals can be controlled effectively by FDPC. The impairments due to disper-sion and nonlinear effects can be suppressed simultaneously.
Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments.
Benuzzi-Mounaix, A; Koenig, M; Boudenne, J M; Hall, T A; Batani, D; Scianitti, F; Masini, A; Di Santo, D
1999-09-01
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target approximately 5 x 10(13) W/cm(2) to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps. PMID:11970183
Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments
Benuzzi-Mounaix, A.; Koenig, M.; Boudenne, J. M.; Hall, T. A.; Batani, D.; Scianitti, F.; Masini, A.; di Santo, D.
1999-09-01
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target ~5×1013 W/cm2 to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps.
Takahashi, Ryosuke; Okajima, Takaharu
2016-08-01
We investigated how stress relaxation mapping is quantified compared with the force modulation mapping of confluent epithelial cells using atomic force microscopy (AFM). Using a multi-frequency AFM technique, we estimated the power-law rheological behaviors of cells simultaneously in time and frequency domains. When the power-law exponent α was low ( 0.1), α in the time domain was underestimated relative to that in the frequency domain, and the difference increased with α, whereas the cell modulus was overestimated in the time domain. These results indicate that power-law rheological parameters estimated by stress relaxation are sensitive to lag time during initial indentation, which is inevitable in time-domain AFM experiments.
RL Campbell; SA Hambric
2004-02-05
Frequency domain substructure synthesis is a modeling technique that enables the prediction of a combined response of individual structures using experimentally measured or numerically predicted frequency response functions (FRFs). The traditional synthesis algorithm [1,2] operates on component impedances and thus generally requires several matrix inversions. An improved algorithm, developed by Jetmundsen et al. [3], requires a single matrix inversion with a completely arbitrary interface definition that can easily incorporate connection impedances. The main limitations of the method are the large data requirements and sensitivity to data truncation. The utility of this technique is demonstrated through a comparison of synthesized and measured admittances of an edge-stiffened plate with attached equipment. The plate mobilities are obtained from a numerical analysis because of the ability to accurately model this structure using a finite element representation. The attachments are characterized experimentally because of their complexity. The sections describe the synthesis technique and show numerical and experimental results for the plate and equipment.
A Frequency Domain Approach to Registration of Aliased Images with Application to Super-resolution
Vandewalle Patrick
2006-01-01
Full Text Available Super-resolution algorithms reconstruct a high-resolution image from a set of low-resolution images of a scene. Precise alignment of the input images is an essential part of such algorithms. If the low-resolution images are undersampled and have aliasing artifacts, the performance of standard registration algorithms decreases. We propose a frequency domain technique to precisely register a set of aliased images, based on their low-frequency, aliasing-free part. A high-resolution image is then reconstructed using cubic interpolation. Our algorithm is compared to other algorithms in simulations and practical experiments using real aliased images. Both show very good visual results and prove the attractivity of our approach in the case of aliased input images. A possible application is to digital cameras where a set of rapidly acquired images can be used to recover a higher-resolution final image.
Highlights: → Passive battery-ultracapacitor hybrids are examined. → Frequency domain analysis is employed. → The ultracapacitor branch operates as a low-pass filter for the battery. → The battery supplies the average load demand. → Design requirements are discussed. - Abstract: A Fourier-based analysis of passive battery-ultracapacitor hybrid sources is introduced in the manuscript. The approach is first introduced for a general load, and then is followed by a study for a case of periodic pulsed current load. It is shown that the ultracapacitor branch is perceived by the battery as a low-pass filter, which absorbs the majority of the high frequency harmonic current and letting the battery to supply the average load demand in addition to the small part of dynamic current. Design requirements influence on the ultracapacitor capacitance and internal resistance choice are quantitatively discussed. The theory is enforced by simulation and experimental results, showing an excellent agreement.
Kuperman, Alon, E-mail: alonku@ariel.ac.il [Hybrid Energy Sources Center, Dept. of Electrical Engineering and Electronics, Ariel University Center, Kiryat Hamada, Ariel 40700 (Israel); Aharon, Ilan; Kara, Avi; Malki, Shalev [Hybrid Energy Sources Center, Dept. of Electrical Engineering and Electronics, Ariel University Center, Kiryat Hamada, Ariel 40700 (Israel)
2011-11-15
Highlights: {yields} Passive battery-ultracapacitor hybrids are examined. {yields} Frequency domain analysis is employed. {yields} The ultracapacitor branch operates as a low-pass filter for the battery. {yields} The battery supplies the average load demand. {yields} Design requirements are discussed. - Abstract: A Fourier-based analysis of passive battery-ultracapacitor hybrid sources is introduced in the manuscript. The approach is first introduced for a general load, and then is followed by a study for a case of periodic pulsed current load. It is shown that the ultracapacitor branch is perceived by the battery as a low-pass filter, which absorbs the majority of the high frequency harmonic current and letting the battery to supply the average load demand in addition to the small part of dynamic current. Design requirements influence on the ultracapacitor capacitance and internal resistance choice are quantitatively discussed. The theory is enforced by simulation and experimental results, showing an excellent agreement.
Elimination of amplitude-phase crosstalk in frequency domain near-infrared spectroscopy
Morgan, S. P.; Yong, K. Y.
2001-04-01
Changes in phase that occur with changes in amplitude impose severe limitations on the accuracy of frequency domain near-infrared spectrometers. Phase is related to the photon pathlength in tissue and phase errors introduced by the instrument can be interpreted as changes in tissue oxygenation. The instrument described in this article employs a reference radio frequency modulated laser diode to eliminate the effects of amplitude-phase crosstalk and requires no feedback. Light from the reference laser diode does not pass through the medium under investigation but passes directly onto the detector. The reference and medium signals follow a common path through the detector and so the same phase error is imposed on both. Summing the reference and medium phase eliminates the crosstalk and enables the resultant to be attributed only to the photon pathlength within the medium. It is also demonstrated that elimination of amplitude-phase crosstalk is a natural consequence of a phased array configuration.
Frequency Domain MMSE one-tap Equalizer for FBMC-OQAM System
Nisha Varghese
2005-07-01
Full Text Available The need for higher data rate in the modern communication world leads to the development of multicarrier modulation. OFDM, the most popular MCM technique, has some disadvantages like inefficiency due to the insertion of cyclic prefix, spectral leakage among the subchannels due to the poor stopband attenuation of prototype filter etc. Due to these drawbacks of OFDM, a Filter Bank based Multi Carrier system with Offset Quadrature Amplitude Modulation has been proposed. The analysis and synthesis filter banks in FBMC- OQAM system is designed using exponential modulation of a single prototype filter which is designed using frequency sampling method of filter design. In the presence of fading channels, Frequency Domain MMSE one-tap equalizer is designed. Simulation results for Vehicular A and Pedestrian B channels show that the proposed equalizer gives better results for BER performance for the system.
Merchant, Gabrielle R.; Siegel, Jonathan H.; Neely, Stephen T.; Rosowski, John J.; Nakajima, Hideko H.
2015-12-01
Wideband immittance and reflectance have not been well described at frequencies above 6-8 kHz, and past analyses of these measurements have focused on the responses to stimulus frequencies below 3-4 kHz, while ignoring high-frequency or time-domain information. This work uses a novel approach to measure reflectance that utilizes high-frequency signals and analyzes reflectance in both the frequency and the time domains. Experiments were performed with fresh normal human temporal bones before and after simulating various middle-ear pathologies. In addition to experimental data, novel model analyses were used to obtain fitted parameter values of middle-ear elements that vary systematically due to simulations and thus may have diagnostic implications. Our results show that high-frequency measurements improve temporal resolution of reflectance measurements, and this data combined with novel modeling techniques provides separation of three major conductive pathologies.
Tromberg, Bruce J.; Berger, Andrew J.; Cerussi, Albert E.; Bevilacqua, Frederic; Jakubowski, Dorota
2008-09-23
A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain and steady-state reflectance methods. Most of the wavelength coverage is provided by a white-light steady-state measurement, whereas the frequency-domain data are acquired at a few selected wavelengths. Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest. The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values.
Frequency domain ultrasound waveform tomography: breast imaging using a ring transducer
Application of the frequency domain acoustic wave equation on data acquired from ultrasound tomography scans is shown to yield high resolution sound speed images on the order of the wavelength of the highest reconstructed frequency. Using a signal bandwidth of 0.4–1 MHz and an average sound speed of 1500 m s−1, the resolution is approximately 1.5 mm. The quantitative sound speed values and morphology provided by these images have the potential to inform diagnosis and classification of breast disease. In this study, we present the formalism, practical application, and in vivo results of waveform tomography applied to breast data gathered by two different ultrasound tomography scanners that utilize ring transducers. The formalism includes a review of frequency domain modeling of the wave equation using finite difference operators as well as a review of the gradient descent method for the iterative reconstruction scheme. It is shown that the practical application of waveform tomography requires an accurate starting model, careful data processing, and a method to gradually incorporate higher frequency information into the sound speed reconstruction. Following these steps resulted in high resolution quantitative sound speed images of the breast. These images show marked improvement relative to commonly used ray tomography reconstruction methods. The robustness of the method is demonstrated by obtaining similar results from two different ultrasound tomography devices. We also compare our method to MRI to demonstrate concordant findings. The clinical data used in this work was obtained from a HIPAA compliant clinical study (IRB 040912M1F). (paper)
Zhou, Haigen; Lin, Jun; Liu, Changsheng; Kang, Lili; Li, Gang; Zeng, Xinsen
2016-03-01
Multi-source and multi-frequency emission method can make full use of the valuable and short flight time in frequency domain semi-airborne electromagnetic (FSAEM) exploration, which has potential to investigate the deep earth structure in complex terrain region. Because several sources are adjacent in multi-source emission method, the interaction of different sources should be considered carefully. An equivalent circuit model of dual-source is established in this paper to assess the interaction between two individual sources, where the parameters are given with the typical values based on the practical instrument system and its application. By simulating the output current of two sources in different cases, the influence from the adjacent source is observed clearly. The current waveforms show that the mutual resistance causes the fluctuation and drift in another source and that the mutual inductance causes transient peaks. A field test with dual-source was conducted to certify the existence of interaction between adjacent sources. The simulation of output current also shows that current errors at low frequency are mainly caused by the mutual resistance while those at high frequency are mainly due to the mutual inductance. Increasing the distance between neighboring sources is a proposed measure to reduce the emission signal errors with designed ones. The feasible distance is discussed in the end. This study gives a useful guidance to lay multi sources to meet the requirement of measurement accuracy in FSAEM survey.
Frequency-Domain Assessment of Integration Schemes for Earthquake Engineering Problems
Juana Arias-Trujillo
2015-01-01
Full Text Available Although numerical integration is a technique commonly employed in many time-dependent problems, usually its accuracy relied on a time interval small enough. However, taking into account that time integration formulae can be considered to be recursive digital filters, in this research a criterion based on transfer functions has been employed to characterize a wide range of integration algorithms from a frequency approach, both in amplitude and in phase. By adopting Nyquist’s criterion to avoid the aliasing phenomena, a total of seven integration schemes have been reviewed in terms of accuracy and distortion effects on the frequency content of the signal. Some of these schemes are very well-known polynomial approximations with different degrees of interpolation, but others have been especially defined for solving earthquake engineering problems or have been extracted from the digital signal processing methodology. Finally, five examples have been developed to validate this frequency approach and to investigate its influence on practical dynamic problems. This research, focused on earthquake and structural engineering, reveals that numerical integration formulae are clearly frequency-dependent, a conclusion that obviously has a relevant interest in all dynamic engineering problems, even when they are formulated and solved in the time-domain.
DeLong, K.L.; Quinn, T.M.; Mitchum, G.T.; Poore, R.Z.
2009-01-01
Do the chronological methods used in the construction of paleoclimate records influence the results of the frequency analysis applied to them? We explore this phenomenon using the Dongge Cave speleothem record (U-series chronology with variable time steps, ??t) and the El Malpais tree-ring index (cross-dating of ring-width series). Interpolation of the Dongge Cave record to a constant ??t resulted in the suppression of periodicities (<20 years) altering the red noise model used for significance testing. Frequency analysis of temporal subsets of the El Malpais tree-ring index revealed that concentrations of variance varied with the number of ring-width series. Frequency analyses of these records identified significant periodicities, some common to both (???25 and ???69 years). Cross-wavelet analysis, which examines periodicities in the time domain, revealed that coherency between these records occurs intermittently. We found the chronology methods can influence the ability of frequency analysis to detect periodicities and tests for coherency. Copyright 2009 by the American Geophysical Union.
Steuner, Annika; Siemon, Bernhard; Auken, Esben
2010-01-01
Two different airborne electromagnetic methods were applied in the same area: the frequency-domain helicopter-borne electromagnetic (HEM)system operated by the Federal Institute for Geosciences and Natural Resources, Germany, and the time-domain SkyTEM system of theHydroGeophysics Group at the Un...