3D-FEM electrical-thermal-mechanical analysis and experiment of Si-based MEMS infrared emitters
Wang, Xiang; Wang, Na; Chen, Ran-Bin; San, Hai-Sheng; Chen, Xu-Yuan
2016-11-01
Designs, simulations, and fabrications of silicon-based MEMS infrared (IR) emitters for gas sensing application are presented. A 3D finite element method (3D-FEM) was used to analyze the coupled electrical-thermal-mechanical properties of a bridge hotplate structure (BHS) IR emitter and closed hotplate structure (CHS) IR emitter using Joule heating and thermal expansion models of COMSOL™. The IR absorptions of n- and p-silicon were calculated for the design of self-heating structure. The BHS and CHS IR emitters were fabricated synchronously using micro-electromechanical systems technology for a direct performance comparison. Both types of IR emitters were characterized by electrical and optical measurements. The experimental results show that BHS IR emitters have higher radiation density, lower power consumption, and faster frequency-response than CHS IR emitters due to the use of a thermal isolation structure and self-heating structure. Meanwhile, the simulated results agree well with the corresponding measured results, which indicate that the 3D-FEM-model is effective and can be used in the optimal design of electro-thermal devices.
ESTABLISHMENT OF 3D FEM MODEL OF MULTI-PASS SPINNING
Institute of Scientific and Technical Information of China (English)
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.
Anomalous Surface Deformation of Sapphire Clarified by 3D-FEM Simulation of the Nanoindentation
Nowak, Roman; Manninen, Timo; Li, Chunliang; Heiskanen, Kari; Hannula, Simo-Pekka; Lindroos, Veikko; Soga, Tetsuo; Yoshida, Fusahito
This work clarifies the origin of anomalous surface deformation reflected by peculiar surface patterns around indentation impressions on various crystallographic planes of sapphire. The three-dimensional finite element simulation (3D-FEM) of nanoindentation in Al2O3 crystal allowed the authors to localize the regions in which various kinds of twinning and slip are most prone to be activated. The work provides a novel approach to the “hardness anisotropy”, which was modeled so far using a modified uniaxial-stress approximation of this essentially 3D, non-isotropic contact problem. The calculated results enabled the authors to unravel the asymmetric surface deformation detected on prismatic planes by the high-resolution microscopy, which cannot be explained using simple crystallographic considerations.
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.
DEFF Research Database (Denmark)
Bottasso, C. L.; Campagnolo, F.; Croce, A.;
2014-01-01
model fully-populated cross sectional stiffness matrices. Next, a "fine"-level 3D FEM model is used for the refinement of the coarse-level solution. Improved results obtained at the level of the 3D model are utilized at the following coarse-level iteration through a heuristic modification of the design...... level. At first, a "coarse"-level constrained design optimization is performed by using a 1D spatial geometrically exact beam model for aero-servo-elastic multibody analysis and load calculation, integrated with a 2D FEM cross sectional model for stress/strain analysis, and the evaluation of the 1D...
Pragmatic circuits frequency domain
Eccles, William
2006-01-01
Pragmatic Circuits: Frequency Domain goes through the Laplace transform to get from the time domain to topics that include the s-plane, Bode diagrams, and the sinusoidal steady state. This second of three volumes ends with a-c power, which, although it is just a special case of the sinusoidal steady state, is an important topic with unique techniques and terminology. Pragmatic Circuits: Frequency Domain is focused on the frequency domain. In other words, time will no longer be the independent variable in our analysis. The two other volumes in the Pragmatic Circuits series include titles on DC
3D FEM numerical simulation and experimental study on symmetric thin-wall tube neck-spinning
Institute of Scientific and Technical Information of China (English)
KUANG Wei-hua; XIA Qin-xiang; RUAN Feng
2006-01-01
A 3D FEM model for symmetric thin-wall tube neck-spinning is established. The spinning process is simulated by means of ANSYS software, and the dynamic boundary and contact problems in simulation are solved. The transient stress distribution of contact area, the transient strain distribution of nodes in typical section and the strain distribution of the whole part at last are attained, and the place and the cause of crack are analyzed. Simulation results show how the strain distribution of typical section, the thickness of some typical nodes, the Z coordinate in typical section and the spinning force of three rollers change with the time. According to study the variation curve, the material flow law along radial, tangential and axial direction is attained and the whole spinning process is studied. The experiment data reflect how the spinning force is influenced by different process parameters, such as feed rate, roundness radius and pass reduction. The simulation and the experiment results supply criteria for optimum design and reasonable parameter selection.
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
Frequency-Domain Optical Mammogram
2002-10-01
the tumor. * Combination of the above two points into a composite false-color breast image containing structural information (from the second...Antonangeli, A. Savoia, T. Parasassi, and N. Rosato, " Plastique : a synchrotron radiation beamline for time resolved fluorescence in the frequency domain
三维有限元刚度矩阵的压缩存储算法%Compressed storage algorithm of 3D-FEM stiffness matrix
Institute of Scientific and Technical Information of China (English)
王忠雷; 赵国群; 马新武
2012-01-01
为提高有限元分析效率、减少存储空间消耗,对刚度矩阵的压缩存储算法进行了研究.研究了＂广义相邻节点对＂与刚度矩阵中非零子矩阵的关系,确定了刚度矩阵中非零子矩阵的分布规律;提出了一种新的刚度矩阵压缩存储方法—＂改进的CSR存储方法＂,给出了基于压缩存储的刚度矩阵的生成过程以及线性方程组迭代解法方法,并将提出的算法应用于三维体积成形有限元分析软件.有限元分析实例表明,该算法可以有效地减少存储空间,提高计算效率.%To improve the efficiency and reduce the storage space of finite element analysis,compression and storage algorithm of 3D-FEM stiffness matrix is studied.The relationship between ＂generalized adjacent double nodes＂ and the non-zero sub-matrix in stiffness matrix is researched for getting distribution of non-zero sub-matrix in stiffness matrix.A new algorithm of stiffness matrix of compressed storage-＂improved CSR storage method＂ is proposed.Based on the algorithm,the generation process of stiffness matrix is given and iterative solution of linear equations method is proposed to improve the efficiency of solving linear equations.The algorithm is applied to the three-dimensional bulk forming finite element analysis software and the numerical results show that the algorithm can effectively decrease the storage space and improve the computation efficiency.
Energy Technology Data Exchange (ETDEWEB)
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
Comparison of the domain and frequency domain state feedbacks
Energy Technology Data Exchange (ETDEWEB)
Zhang, S.Y.
1986-01-01
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.
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 FIR and IIR adaptive filters
Lynn, D. W.
1990-01-01
A discussion of the LMS adaptive filter relating to its convergence characteristics and the problems associated with disparate eigenvalues is presented. This is used to introduce the concept of proportional convergence. An approach is used to analyze the convergence characteristics of block frequency-domain adaptive filters. This leads to a development showing how the frequency-domain FIR adaptive filter is easily modified to provide proportional convergence. These ideas are extended to a block frequency-domain IIR adaptive filter and the idea of proportional convergence is applied. Experimental results illustrating proportional convergence in both FIR and IIR frequency-domain block adaptive filters is presented.
Frequency Domain Image Filtering Using CUDA
Directory of Open Access Journals (Sweden)
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.
Load Estimation by Frequency Domain Decomposition
DEFF Research Database (Denmark)
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...
Realization of Thermal Inertia in Frequency Domain
Directory of Open Access Journals (Sweden)
Boe-Shong Hong
2014-02-01
Full Text Available To realize the lagging behavior in heat conduction observed in these two decades, this paper firstly theoretically excludes the possibility that the underlying thermal inertia is a result of the time delay in heat diffusion. Instead, we verify in experiments the electro-thermal analogy, wherein the thermal inertial is parameterized by thermal inductance that formulates hyperbolic heat-conduction. The thermal hyperbolicity exhibits a special frequency response in Bode plot, wherein the amplitude ratios is kept flat after crossing some certain frequency, as opposed to Fourier heat-conduction. We apply this specialty to design an instrument that reliably identifies thermal inductances of some materials in frequency domain. The instrument is embedded with a DSP-based frequency synthesizer capable of modulating frequencies in utmost high-resolution. Thermal inertia implies a new possibility for energy storage in analogy to inductive energy storage in electricity or mechanics.
Frequency domain processing of on-chip biphoton frequency comb
Jaramillo-Villegas, Jose A; Odele, Ogaga D; Leaird, Daniel E; Ou, Zhe-Yu; Qi, Minghao; Weiner, Andrew M
2016-01-01
Quantum information processing (QIP) promises to improve the security of our communications as well as to solve some algorithms with exponential complexity in polynomial time. Biphotons have been demonstrated as one of the most promising platforms for real implementations of QIP systems. In particular, time-bin entangled photons have been used for implementations of quantum gates which require highly stable interferometers. On the other hand, frequency-bin entanglement has been proposed to avoid the use of interferometers and the complexity of their stabilization, which potentially makes the implementation of quantum gates highly scalable. Through Fourier transform pulse shaping and electro-optic modulation, there has been a wide range of experiments that show control of entangled photons in the frequency domain. In addition, biphoton frequency combs (BFC) have also been generated using bulk optics and frequency filtering of broadband continuous biphoton spectra. However, on-chip entangled photon pair generat...
Time delay measurement in the frequency domain
Energy Technology Data Exchange (ETDEWEB)
Durbin, Stephen M., E-mail: durbin@purdue.edu; Liu, Shih-Chieh [Purdue University, West Lafayette, IN 47907 (United States); Dufresne, Eric M.; Li, Yuelin; Wen, Haidan [Argonne National Laboratory, Argonne, IL 60439 (United States)
2015-08-06
A simple frequency domain technique for determining the time delay between laser pump and X-ray probe pulses achieves 1 ps resolution even for ∼100 ps synchrotron pulses, permitting improved pump–probe characterization of ultrafast processes. Pump–probe studies at synchrotrons using X-ray and laser pulses require accurate determination of the time delay between pulses. This becomes especially important when observing ultrafast responses with lifetimes approaching or even less than the X-ray pulse duration (∼100 ps). The standard approach of inspecting the time response of a detector sensitive to both types of pulses can have limitations due to dissimilar pulse profiles and other experimental factors. Here, a simple alternative is presented, where the frequency response of the detector is monitored versus time delay. Measurements readily demonstrate a time resolution of ∼1 ps. Improved precision is possible by simply extending the data acquisition time.
Communicating oscillatory networks: frequency domain analysis
Directory of Open Access Journals (Sweden)
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
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.
AU-FREDI - AUTONOMOUS FREQUENCY DOMAIN IDENTIFICATION
Yam, Y.
1994-01-01
The Autonomous Frequency Domain Identification program, AU-FREDI, is a system of methods, algorithms and software that was developed for the identification of structural dynamic parameters and system transfer function characterization for control of large space platforms and flexible spacecraft. It was validated in the CALTECH/Jet Propulsion Laboratory's Large Spacecraft Control Laboratory. Due to the unique characteristics of this laboratory environment, and the environment-specific nature of many of the software's routines, AU-FREDI should be considered to be a collection of routines which can be modified and reassembled to suit system identification and control experiments on large flexible structures. The AU-FREDI software was originally designed to command plant excitation and handle subsequent input/output data transfer, and to conduct system identification based on the I/O data. Key features of the AU-FREDI methodology are as follows: 1. AU-FREDI has on-line digital filter design to support on-orbit optimal input design and data composition. 2. Data composition of experimental data in overlapping frequency bands overcomes finite actuator power constraints. 3. Recursive least squares sine-dwell estimation accurately handles digitized sinusoids and low frequency modes. 4. The system also includes automated estimation of model order using a product moment matrix. 5. A sample-data transfer function parametrization supports digital control design. 6. Minimum variance estimation is assured with a curve fitting algorithm with iterative reweighting. 7. Robust root solvers accurately factorize high order polynomials to determine frequency and damping estimates. 8. Output error characterization of model additive uncertainty supports robustness analysis. The research objectives associated with AU-FREDI were particularly useful in focusing the identification methodology for realistic on-orbit testing conditions. Rather than estimating the entire structure, as is
Time-domain modeling of electromagnetic diffusion with a frequency-domain code
Mulder, W.A.; Wirianto, M.; Slob, E.C.
2007-01-01
We modeled time-domain EM measurements of induction currents for marine and land applications with a frequency-domain code. An analysis of the computational complexity of a number of numerical methods shows that frequency-domain modeling followed by a Fourier transform is an attractive choice if a s
Estimated Frequency Domain Model Uncertainties used in Robust Controller Design
DEFF Research Database (Denmark)
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
Directory of Open Access Journals (Sweden)
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.
Damping Estimation by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Ventura, C. E.; Andersen, P.
2001-01-01
frequencies can be accurately estimated without being limited by the frequency resolution of the discrete Fourier transform. It is explained how the spectral density matrix is decomposed into a set of single degree of freedom systems, and how the individual SDOF auto spectral density functions are transformed...
Frequency domain analysis of triggered lightning return stroke luminosity velocity
Carvalho, F. L.; Uman, M. A.; Jordan, D. M.; Moore, R. C.
2017-02-01
Fourier analysis is applied to time domain return stroke luminosity signals to calculate the phase and group velocities and the amplitude of the luminosity signals as a function of frequency measured between 4 m and 115 m during 12 triggered lightning strokes. We show that pairs of time domain luminosity signals measured at different heights can be interpreted as the input and the output of a system whose frequency domain transfer function can be determined from the measured time domain signals. From the frequency domain transfer function phase we find the phase and group velocities, and luminosity amplitude as a function of triggered lightning channel height and signal frequency ranging from 50 kHz to 300 kHz. We show that higher-frequency luminosity components propagate faster than the lower frequency components and that higher-frequency luminosity components attenuate more rapidly than lower frequency components. Finally, we calculate time domain return stroke velocities as a function of channel height using two time delay techniques: (1) measurement at the 20% amplitude level and (2) cross correlation.
Evaluation of Damping Using Frequency Domain Operational Modal Analysis Techniques
DEFF Research Database (Denmark)
Bajric, Anela; Georgakis, Christos T.; Brincker, Rune
2015-01-01
Operational Modal Analysis (OMA) techniques provide in most cases reasonably accurate estimates of structural frequencies and mode shapes. In contrast though, they are known to often produce uncertain structural damping estimates, which is mainly due to inherent random and/or bias errors...... domain techniques, the Frequency Domain Decomposition (FDD) and the Frequency Domain Polyreference (FDPR). The response of a two degree-of-freedom (2DOF) system is numerically established with specified modal parameters subjected to white noise loading. The system identification is evaluated with well...
Frequency-domain method for separating signal and noise
Institute of Scientific and Technical Information of China (English)
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
Institute of Scientific and Technical Information of China (English)
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.
Conversion of Dielectric Data from the Time Domain to the Frequency Domain
Directory of Open Access Journals (Sweden)
Vladimir Durman
2005-01-01
Full Text Available Polarisation and conduction processes in dielectric systems can be identified by the time domain or the frequency domain measurements. If the systems is a linear one, the results of the time domain measurements can be transformed into the frequency domain, and vice versa. Commonly, the time domain data of the absorption conductivity are transformed into the frequency domain data of the dielectric susceptibility. In practice, the relaxation are mainly evaluated by the frequency domain data. In the time domain, the absorption current measurement were prefered up to now. Recent methods are based on the recovery voltage measurements. In this paper a new method of the recovery data conversion from the time the frequency domain is proposed. The method is based on the analysis of the recovery voltage transient based on the Maxwell equation for the current density in a dielectric. Unlike the previous published solutions, the Laplace fransform was used to derive a formula suitable for practical purposes. the proposed procedure allows also calculating of the insulation resistance and separating the polarisation and conduction losses.
On Frequency Domain Models for TDOA Estimation
DEFF Research Database (Denmark)
Jensen, Jesper Rindom; Nielsen, Jesper Kjær; Christensen, Mads Græsbøll
2015-01-01
of data points, and a known number of harmonics. The more general method only relies on that the source signal is periodic and is, therefore, able to outperform the cross-correlation method in terms of estimation accuracy on both synthetic and real-world data. The simulation code is available online....... of a 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...
Estimation of luminescence lifetime in frequency domain
Institute of Scientific and Technical Information of China (English)
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.
High-speed optical frequency-domain imaging
Yun, S. H.; Tearney, G. J.; Boer; Iftimia, N. V.; Bouma, B. E.
2003-01-01
We demonstrate high-speed, high-sensitivity, high-resolution optical imaging based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. We derive and show experimentally that frequency-domain ranging provides a superior signal-to-noise ratio compared with conventional time-domain ranging as used in optical coherence tomography. A high sensitivity of −110 dB was obtained with a 6 mW source at an axial resolution of 13.5 µm and an A-line rate of 15.7 kHz, rep...
Error Analysis in Frequency Domain for Linear Multipass Algorithms
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Error analysis methods in frequency domain are developed in this paper for determining the characteristic root and transfer function errors when the linear multipass algorithms are used to solve linear differential equations.the relation between the local truncation error in time domain and the error in frequency domain is established, which is the basis for developing the error estimation methods. The error estimation methods for the digital simulation model constructed by using the Runge-Kutta algorithms and the linear multistep predictor-corrector algorithms are also given.
Time delay measurement in the frequency domain
Durbin, Stephen M.; Liu, Shih-Chieh; Dufresne, Eric M.; Li, Yuelin; Wen, Haidan
2015-01-01
Pump–probe studies at synchrotrons using X-ray and laser pulses require accurate determination of the time delay between pulses. This becomes especially important when observing ultrafast responses with lifetimes approaching or even less than the X-ray pulse duration (∼100 ps). The standard approach of inspecting the time response of a detector sensitive to both types of pulses can have limitations due to dissimilar pulse profiles and other experimental factors. Here, a simple alternative is presented, where the frequency response of the detector is monitored versus time delay. Measurements readily demonstrate a time resolution of ∼1 ps. Improved precision is possible by simply extending the data acquisition time. PMID:26289282
An Improved Traffic Matrix Decomposition Method with Frequency Domain Regularization
Wang, Zhe; Yin, Baolin
2012-01-01
In this letter, we propose a novel network traffic matrix decomposition method named as Stable Principal Component Pursuit with Frequency Domain Regularization (SPCP-FDR). SPCP-FDR improves the Stable Principal Component Pursuit (SPCP) method by using a new noise regularization function defined in frequency domain. Compared with SPCP, SPCP-FDR is more adaptive to empirical frequency properties of diverse traffic components. The Accelerated Proximal Gradient (APG) algorithm for SPCP-FDR is presented. Our experiment results demonstrate the rationality of this new method.
Design PID controllers for desired time-domain or frequency-domain response.
Zhang, Weidong; Xi, Yugeng; Yang, Genke; Xu, Xiaoming
2002-10-01
Practical requirements on the design of control systems, especially process control systems, are usually specified in terms of time-domain response, such as overshoot and rise time, or frequency-domain response, such as resonance peak and stability margin. Although numerous methods have been developed for the design of the proportional-integral-derivative (PID) controller, little work has been done in relation to the quantitative time-domain and frequency-domain responses. In this paper, we study the following problem: Given a nominal stable process with time delay, we design a suboptimal PID controller to achieve the required time-domain response or frequency-domain response for the nominal system or the uncertain system. An H(infinity) PID controller is developed based on optimal control theory and the parameters are derived analytically. Its properties are investigated and compared with that of two developed suboptimal controllers: an H2 PID controller and a Maclaurin PID controller. It is shown that all three controllers can provide the quantitative time-domain and frequency-domain responses.
Thermal Loss of High-Q Antennas in Time Domain vs. Frequency Domain Solver
DEFF Research Database (Denmark)
Bahramzy, Pevand; Pedersen, Gert Frølund
2014-01-01
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...
Directory of Open Access Journals (Sweden)
Tong Wu
2016-11-01
Full Text Available We present a spatial frequency domain multiplexing method for extending the imaging depth range of a spectral domain optical coherence tomography (SDOCT system without any expensive device. This method uses two galvo scanners with different pivot-offset distances in two independent reference arms for spatial frequency modulation and multiplexing. The spatial frequency contents corresponding to different depth regions of the sample can be shifted to different frequency bands. The spatial frequency domain multiplexing SDOCT system provides an approximately 1.9-fold increase in the effective ranging depth compared with that of a conventional full-range SDOCT system. The reconstructed images of phantom and biological tissue demonstrate the expected increase in ranging depth. The parameters choice criterion for this method is discussed.
Frequency-domain thermal modelling of power semiconductor devices
DEFF Research Database (Denmark)
Ma, Ke; Blaabjerg, Frede; Andresen, Markus
2015-01-01
The thermal behavior of power electronics devices has being a crucial design consideration because it is closely related to the reliability and also the cost of the converter system. Unfortunately, the widely used thermal models based on lumps of thermal resistance and capacitance have their limits...... 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......-based thermal networks are explained from a point of view of frequency domain. Based on the discovery, a more advanced thermal model developed in the frequency domain is proposed, which can be easily established by characterizing the slope variation from the bode diagram of the typically used Foster thermal...
Finite-Difference Frequency-Domain Method in Nanophotonics
DEFF Research Database (Denmark)
Ivinskaya, Aliaksandra
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...... is 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...
Frequency domain simultaneous algebraic reconstruction techniques: algorithm and convergence
Wang, Jiong; Zheng, Yibin
2005-03-01
We propose a simultaneous algebraic reconstruction technique (SART) in the frequency domain for linear imaging problems. This algorithm has the advantage of efficiently incorporating pixel correlations in an a priori image model. First it is shown that the generalized SART algorithm converges to the weighted minimum norm solution of a weighted least square problem. Then an implementation in the frequency domain is described. The performance of the new algorithm is demonstrated with fan beam computed tomography (CT) examples. Compared to the traditional SART and its major alternative ART, the new algorithm offers superior image quality and potential application to other modalities.
An operational modal analysis method in frequency and spatial domain
Wang, Tong; Zhang, Lingmi; Tamura, Yukio
2005-12-01
A frequency and spatial domain decomposition method (FSDD) for operational modal analysis (OMA) is presented in this paper, which is an extension of the complex mode indicator function (CMIF) method for experimental modal analysis (EMA). The theoretical background of the FSDD method is clarified. Singular value decomposition is adopted to separate the signal space from the noise space. Finally, an enhanced power spectrum density (PSD) is proposed to obtain more accurate modal parameters by curve fitting in the frequency domain. Moreover, a simulation case and an application case are used to validate this method.
An operational modal analysis method in frequency and spatial domain
Institute of Scientific and Technical Information of China (English)
Wang Tong; Zhang Lingmi; Tamura Yukio
2005-01-01
A frequency and spatial domain decomposition method (FSDD) for operational modal analysis (OMA) is presented in this paper, which is an extension of the complex mode indicator function (CMIF) method for experimental modal analysis (EMA). The theoretical background of the FSDD method is clarified. Singular value decomposition is adopted to separate the signal space from the noise space. Finally, an enhanced power spectrum density (PSD) is proposed to obtain more accurate modal parameters by curve fitting in the frequency domain. Moreover, a simulation case and an application case are used to validate this method.
A Visible Watermarking Scheme for Digital Images in Frequency Domain
Directory of Open Access Journals (Sweden)
D.R.Denslin Brabin
2012-11-01
Full Text Available A novel method is proposed for visible watermarking of digital image in frequency domain. The method is based on DCT modification of original image with respect to watermark image. The host image pixels are transformed into frequency coefficients as well as the watermark image pixels are also transformed into frequency coefficients using DCT. The compound mapping function is used to adjust the pixel values close to those of desired visible watermarks. Thus the watermarking is done in frequency domain using compound mapping function. One who has the watermark image and mapping function parameters only can remove the watermark. Thus it enhances the security. Experimental results demonstrate the effectiveness of the proposed approach.
A Frequency Domain Design Method For Sampled-Data Compensators
DEFF Research Database (Denmark)
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...
Higher order statistical frequency domain decomposition for operational modal analysis
Nita, G. M.; Mahgoub, M. A.; Sharyatpanahi, S. G.; Cretu, N. C.; El-Fouly, T. M.
2017-02-01
Experimental methods based on modal analysis under ambient vibrational excitation are often employed to detect structural damages of mechanical systems. Many of such frequency domain methods, such as Basic Frequency Domain (BFD), Frequency Domain Decomposition (FFD), or Enhanced Frequency Domain Decomposition (EFFD), use as first step a Fast Fourier Transform (FFT) estimate of the power spectral density (PSD) associated with the response of the system. In this study it is shown that higher order statistical estimators such as Spectral Kurtosis (SK) and Sample to Model Ratio (SMR) may be successfully employed not only to more reliably discriminate the response of the system against the ambient noise fluctuations, but also to better identify and separate contributions from closely spaced individual modes. It is shown that a SMR-based Maximum Likelihood curve fitting algorithm may improve the accuracy of the spectral shape and location of the individual modes and, when combined with the SK analysis, it provides efficient means to categorize such individual spectral components according to their temporal dynamics as coherent or incoherent system responses to unknown ambient excitations.
Automated Frequency Domain Decomposition for Operational Modal Analysis
DEFF Research Database (Denmark)
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 au...
Modal Identification from Ambient Responses Using Frequency Domain Decomposition
DEFF Research Database (Denmark)
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
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, L.; Andersen, P.
2000-01-01
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...
Broadband Beamspace DOA Estimation: Frequency-Domain and Time-Domain Processing Approaches
Directory of Open Access Journals (Sweden)
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.
Hybrid time/frequency domain modeling of nonlinear components
DEFF Research Database (Denmark)
Wiechowski, Wojciech Tomasz; Lykkegaard, Jan; Bak, Claus Leth;
2007-01-01
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......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...
Microcirculation monitoring with real time spatial frequency domain imaging
Chen, Xinlin; Cao, Zili; Lin, Weihao; Zhu, Danfeng; Zhu, Xiuwei; Zeng, Bixin; Xu, M.
2017-01-01
We present a spatial frequency domain imaging (SFDI) study of local hemodynamics in the forearm of healthy volunteers performing paced breathing. Real time Single Snapshot Multiple Frequency Demodulation - Spatial Frequency Domain Imaging (SSMD-SFDI) was used to map the optical properties of the subsurface of the forearm continuously. The oscillations of the concentrations of deoxy- and oxyhemoglobin at the subsurface of the forearm induced by paced breathing are found to be close to out-of-phase, attributed to the dominance of the blood flow modulation by paced breathing. The properties of local microcirculation including the blood transit times through capillaries and venules are extracted by fitting to Simplified Hemodynamics Model. Our preliminary results suggest that the real time SSMD-SFDI platform may serve as one effective imaging modality for microcirculation monitoring.
Time-domain and frequency-domain approaches to identification of bridge flutter derivatives
Institute of Scientific and Technical Information of China (English)
Zhengqing CHEN
2009-01-01
Flutter derivatives are essential for flutter analysis of long-span bridges, and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel. Making use of the forced vibration testing data of three sectional models,namely, a thin-plate model, a nearly streamlined model,and a bluff-body model, a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method. It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method, respectively, agree very well. Moreover, some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent. More precisely, the frequency-domain method usually results in smooth curves of the flutter derivatives.The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.
Energy Technology Data Exchange (ETDEWEB)
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.
Small signal frequency domain model of an HVDC converter
Energy Technology Data Exchange (ETDEWEB)
Osauskas, C.M.; Hume, D.J.; Wood, A.R. [UnIversity of Canterbury, Christchurch (New Zealand). Dept. of Electrical and Electronic Engineering
2001-11-01
A small-signal analytic frequency domain model of a 6-pulse HVDC converter is presented. The model consists of a set of explicit algebraic equations which relate the transfer of distortion from AC voltage, DC current and firing angle modulation, to AC current and DC voltage. The equations represent the linearisation of the transfers around a base operating point, and are derived from a piecewise linear description of the AC current and DC voltage waveforms. The model provides an understanding of the transfer of distortion by the converter and is in excellent agreement with time domain simulations. (author)
Statistical multiresolution analysis in amplitude-frequency domain
Institute of Scientific and Technical Information of China (English)
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.
Parameter Identification of Weakly Nonlinear Vibration System in Frequency Domain
Directory of Open Access Journals (Sweden)
Jiehua Peng
2004-01-01
Full Text Available A new method of identifying parameters of nonlinearly vibrating system in frequency domain is presented in this paper. The problems of parameter identification of the nonlinear dynamic system with nonlinear elastic force or nonlinear damping force are discussed. In the method, the mathematic model of parameter identification is frequency response function. Firstly, by means of perturbation method the frequency response function of weakly nonlinear vibration system is derived. Next, a parameter transformation is made and the frequency response function becomes a linear function of the new parameters. Then, based on this function and with the least square method, physical parameters of the system are identified. Finally, the applicability of the proposed technique is confirmed by numerical simulation.
Speaker Identification using Frequency Dsitribution in the Transform Domain
Directory of Open Access Journals (Sweden)
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.
Structural eigenfrequency optimization based on local sub-domain "frequencies"
DEFF Research Database (Denmark)
Pedersen, Pauli; Pedersen, Niels Leergaard
2013-01-01
The engineering approach of fully stressed design is a practical tool with a theoretical foundation. The analog approach to structural eigenfrequency optimization is presented here with its theoretical foundation. A numerical redesign procedure is proposed and illustrated with examples.......For the ideal case, an optimality criterion is fulfilled if the design have the same sub-domain ”frequency” (local Rayleigh quotient). Sensitivity analysis shows an important relation between squared system eigenfrequency and squared local sub-domain frequency for a given eigenmode. Higher order...... eigenfrequencies may also be controlled in this manner.The presented examples are based on 2D finite element models with the use of subspace iteration for analysis and a recursive design procedure based on the derived optimality condition. The design that maximize a frequency depend on the total amount...
The Peltier driven frequency domain approach in thermal analysis.
De Marchi, Andrea; Giaretto, Valter
2014-10-01
The merits of Frequency Domain analysis as a tool for thermal system characterization are discussed, and the complex thermal impedance approach is illustrated. Pure AC thermal flux generation with negligible DC component is possible with a Peltier device, differently from other existing methods in which a significant DC component is intrinsically attached to the generated AC flux. Such technique is named here Peltier Driven Frequency Domain (PDFD). As a necessary prerequisite, a novel one-dimensional analytical model for an asymmetrically loaded Peltier device is developed, which is general enough to be useful in most practical situations as a design tool for measurement systems and as a key for the interpretation of experimental results. Impedance analysis is possible with Peltier devices by the inbuilt Seebeck effect differential thermometer, and is used in the paper for an experimental validation of the analytical model. Suggestions are then given for possible applications of PDFD, including the determination of thermal properties of materials.
The Peltier driven frequency domain approach in thermal analysis
Marchi, Andrea De; Giaretto, Valter
2014-10-01
The merits of Frequency Domain analysis as a tool for thermal system characterization are discussed, and the complex thermal impedance approach is illustrated. Pure AC thermal flux generation with negligible DC component is possible with a Peltier device, differently from other existing methods in which a significant DC component is intrinsically attached to the generated AC flux. Such technique is named here Peltier Driven Frequency Domain (PDFD). As a necessary prerequisite, a novel one-dimensional analytical model for an asymmetrically loaded Peltier device is developed, which is general enough to be useful in most practical situations as a design tool for measurement systems and as a key for the interpretation of experimental results. Impedance analysis is possible with Peltier devices by the inbuilt Seebeck effect differential thermometer, and is used in the paper for an experimental validation of the analytical model. Suggestions are then given for possible applications of PDFD, including the determination of thermal properties of materials.
Incoherent Optical Frequency Domain Reflectometry for Distributed Thermal Sensing
DEFF Research Database (Denmark)
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...... 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 reflectometry, where a short pulse is sent through the fibre, and the location of the scattering section...... is determined by the time difference from the emission to the detection of light. A temperature sensor with a range of 2-4km comprising a step-index multi-mode fibre and a high-power 980nm pump laser existed prior to the start of the PhD study. In this study, a sensor range of approximately 10km, and a spatial...
Research on the frequency domain ∑△-DPCA
Institute of Scientific and Technical Information of China (English)
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 stability criteria for fractional-order control systems
Institute of Scientific and Technical Information of China (English)
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.
Frequency domain analysis of noise in autoregulated gene circuits
Simpson, Michael L.; Cox, Chris D.; Sayler, Gary S.
2003-01-01
We describe a frequency domain technique for the analysis of intrinsic noise within negatively autoregulated gene circuits. This approach is based on the transfer function around the feedback loop (loop transmission) and the equivalent noise bandwidth of the system. The loop transmission, T, is shown to be a determining factor of the dynamics and the noise behavior of autoregulated gene circuits, and this T-based technique provides a simple and flexible method for the analysis of noise arisin...
Reduced Order Internal Models in the Frequency Domain
Laakkonen, Petteri; Paunonen, Lassi
2016-01-01
The internal model principle states that all robustly regulating controllers must contain a suitably reduplicated internal model of the signal to be regulated. Using frequency domain methods, we show that the number of the copies may be reduced if the class of perturbations in the problem is restricted. We present a two step design procedure for a simple controller containing a reduced order internal model achieving robust regulation. The results are illustrated with an example of a five tank...
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.
3D FEM Simulations of a shape rolling process
Wisselink, H.H.; Huetink, J.; Dijk, van M.H.H.; Leeuwen, van A.J.
2001-01-01
A finite element model has been developed for the simulation of the shape rolling of stator vanes. These simulations should support the design of rolling tools for new vane types. For the time being only straight vanes (vanes with a constant cross-section over the length) are studied. In that case t
Quantitative analysis of a frequency-domain nonlinearity indicator.
Reichman, Brent O; Gee, Kent L; Neilsen, Tracianne B; Miller, Kyle G
2016-05-01
In this paper, quantitative understanding of a frequency-domain nonlinearity indicator is developed. The indicator is derived from an ensemble-averaged, frequency-domain version of the generalized Burgers equation, which can be rearranged in order to directly compare the effects of nonlinearity, absorption, and geometric spreading on the pressure spectrum level with frequency and distance. The nonlinear effect is calculated using pressure-squared-pressure quadspectrum. Further theoretical development has given an expression for the role of the normalized quadspectrum, referred to as Q/S by Morfey and Howell [AIAA J. 19, 986-992 (1981)], in the spatial rate of change of the pressure spectrum level. To explore this finding, an investigation of the change in level for initial sinusoids propagating as plane waves through inviscid and thermoviscous media has been conducted. The decibel change with distance, calculated through Q/S, captures the growth and decay of the harmonics and indicates that the most significant changes in level occur prior to sawtooth formation. At large distances, the inviscid case results in a spatial rate of change that is uniform across all harmonics. For thermoviscous media, large positive nonlinear gains are observed but offset by absorption, which leads to a greater overall negative spatial rate of change for higher harmonics.
Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media
Schmidt, Felix; Lünenschloss, Peter; Mai, Juliane; Wagner, Norman; Töpfer, Hannes; Bumberger, Jan
2016-04-01
The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections. Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric
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.
Baseband feedback for SAFARI-SPICA using Frequency Domain Multiplexing
Bounab, A.; de Korte, P.; Cros, A.; van der Kuur, J.; van Leeuwen, B. J.; Monna, B.; Mossel, R.; Nieuwenhuizen, A.; Ravera, L.
We report on the performance of the digital baseband feedback circuit developed to readout and process signals from arrays of transition edge sensors for SPICA-SAFARI in frequency domain multiplexing (FDM). The standard procedure to readout the SQUID current amplifiers is to use a feedback loop (flux-locked loop: FLL). However the achievable FFL bandwidth is limited by the cable transport delay t_d, which makes standard feedback inconvenient. A much better approach is to use baseband feedback. We have developed a model of the electronic readout chain for SPICA-SAFARI instrument by using an Anlog-digital co-simulation based on Simulink-System Generator environment.
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.
A frequency-domain derivation of shot-noise
Rice, Frank
2016-01-01
A formula for shot-noise is derived in the frequency-domain. The derivation is complete and reasonably rigorous while being appropriate for undergraduate students; it models a sequence of random pulses using Fourier sine and cosine series, and requires some basic statistical concepts. The text here may serve as a pedagogic introduction to the spectral analysis of random processes and may prove useful to introduce students to the logic behind stochastic problems. The concepts of noise power spectral density and equivalent noise bandwidth are introduced.
High-Performance Computational Electromagnetics in Frequency-Domain and Time-Domain
2015-03-04
aforementioned contributions, for a given 1In view of its applications to seismic wave propagation Dr. Amlani’s PhD thesis received two awards at Cal- tech, one...for wave scattering problems. PhD thesis, California Institute of Technol- ogy, 2014. Available at http://www.its.caltech.edu/~obruno/preprints...solutions for some of the most challenging scattering problems in science and engineering. Electromagnetic scattering . Frequency domain solvers. Integral
Qi, Feng; Tavakol, Vahid; Ocket, Ilja; Xu, Peng; Schreurs, Dominique; Wang, Jinkuan; Nauwelaers, Bart
2010-01-01
Active millimeter wave imaging systems have become a promising candidate for indoor security applications and industrial inspection. However, there is a lack of simulation tools at the system level. We introduce and evaluate two modeling approaches that are applied to active millimeter wave imaging systems. The first approach originates in Fourier optics and concerns the calculation in the spatial frequency domain. The second approach is based on wave propagation and corresponds to calculation in the spatial domain. We compare the two approaches in the case of both rough and smooth objects and point out that the spatial frequency domain calculation may suffer from a large error in amplitude of 50% in the case of rough objects. The comparison demonstrates that the concepts of point-spread function and f-number should be applied with careful consideration in coherent millimeter wave imaging systems. In the case of indoor applications, the near-field effect should be considered, and this is included in the spatial domain calculation.
Causality between regional stock markets: A frequency domain approach
Directory of Open Access Journals (Sweden)
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 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...
Damping identification in frequency domain using integral method
Guo, Zhiwei; Sheng, Meiping; Ma, Jiangang; Zhang, Wulin
2015-03-01
A new method for damping identification of linear system in frequency domain is presented, by using frequency response function (FRF) with integral method. The FRF curve is firstly transformed to other type of frequency-related curve by changing the representations of horizontal and vertical axes. For the newly constructed frequency-related curve, integral is conducted and the area forming from the new curve is used to determine the damping. Three different methods based on integral are proposed in this paper, which are called FDI-1, FDI-2 and FDI-3 method, respectively. For a single degree of freedom (Sdof) system, the formulated relation of each method between integrated area and loss factor is derived theoretically. The numeral simulation and experiment results show that, the proposed integral methods have high precision, strong noise resistance and are very stable in repeated measurements. Among the three integral methods, FDI-3 method is the most recommended because of its higher accuracy and simpler algorithm. The new methods are limited to linear system in which modes are well separated, and for closely spaced mode system, mode decomposition process should be conducted firstly.
Frequency-domain optical mammography: edge effect corrections.
Fantini, S; Franceschini, M A; Gaida, G; Gratton, E; Jess, H; Mantulin, W W; Moesta, K T; Schlag, P M; Kaschke, M
1996-01-01
We have investigated the problem of edge effects in laser-beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency-domain measurements by employing a two-step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge-corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency-domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two-step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images.
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.
Patellofemoral pain syndrome: electromyography in a frequency domain analysis
Catelli, D. S.; Kuriki, H. U.; Polito, L. F.; Azevedo, F. M.; Negrão Filho, R. F.; Alves, N.
2011-09-01
The Patellofemoral Pain Syndrome (PFPS), has a multifactorial etiology and affects approximately 7 to 15% of the population, mostly women, youth, adults and active persons. PFPS causes anterior or retropatelar pain that is exacerbated during functional motor gestures, such as up and down stairs or spending long periods of time sitting, squatting or kneeling. As the diagnostic evaluation of this syndrome is still indirect, different mechanisms and methodologies try to make a classification that distinguishes patients with PFPS in relation to asymptomatic. Thereby, the purpose of this investigation was to determine the characteristics of the electromyographic (EMG) signal in the frequency domain of the vastus medialis oblique (VMO) and vastus lateralis (VL) in patients with PFPS, during the ascent of stairs. 33 young women (22 control group and 11 PFPS group), were evaluated by EMG during ascent of stairs. The VMO mean power frequency (MPF) and the VL frequency 95% (F95) were lower in symptomatic individuals. This may be related to the difference in muscle recruitment strategy exerted by each muscle in the PFPS group compared to the control group.
Institute of Scientific and Technical Information of China (English)
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.
On the Analysis Methods for the Time Domain and Frequency Domain Response of a Buried Objects*
Poljak, Dragan; Šesnić, Silvestar; Cvetković, Mario
2014-05-01
There has been a continuous interest in the analysis of ground-penetrating radar systems and related applications in civil engineering [1]. Consequently, a deeper insight of scattering phenomena occurring in a lossy half-space, as well as the development of sophisticated numerical methods based on Finite Difference Time Domain (FDTD) method, Finite Element Method (FEM), Boundary Element Method (BEM), Method of Moments (MoM) and various hybrid methods, is required, e.g. [2], [3]. The present paper deals with certain techniques for time and frequency domain analysis, respectively, of buried conducting and dielectric objects. Time domain analysis is related to the assessment of a transient response of a horizontal straight thin wire buried in a lossy half-space using a rigorous antenna theory (AT) approach. The AT approach is based on the space-time integral equation of the Pocklington type (time domain electric field integral equation for thin wires). The influence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The obtained results for the transient current induced along the electrode due to the transmitted plane wave excitation are compared to the numerical results calculated via an approximate transmission line (TL) approach and the AT approach based on the space-frequency variant of the Pocklington integro-differential approach, respectively. It is worth noting that the space-frequency Pocklington equation is numerically solved via the Galerkin-Bubnov variant of the Indirect Boundary Element Method (GB-IBEM) and the corresponding transient response is obtained by the aid of inverse fast Fourier transform (IFFT). The results calculated by means of different approaches agree satisfactorily. Frequency domain analysis is related to the assessment of frequency domain response of dielectric sphere using the full wave model based on the set of coupled electric field integral
Frequency domain synthesis of trajectory learning controllers for robot manipulators
Directory of Open Access Journals (Sweden)
Tom Kavli
1993-07-01
Full Text Available Trajectory learning control is a method for generating near to optimal feedforward control for systems that are controlled along a reference trajectory in repeated cycles. Iterative refinements of a stored feedforward control sequence corresponding to one cycle of the control trajectory is computed based upon the recorded trajectory error from the previous cycle. Several learning operators have been proposed in earlier work, and convergence proofs are developed for certain classes of systems, but no satisfactory method for design and analysis of learning operators under the presence of uncertainties in the system model have been presented. This article presents frequency domain methods for analysing the convergence properties and performance of the learning controller when the amplitude and phase of the system transfer function is assumed to be within specified windows. Experimental results with an industrial robot manipulator confirm the theoretical results.
Broadband ultrasonic sensor array via optical frequency domain reflectometry
Gabai, Haniel; Steinberg, Idan; Eyal, Avishay
2015-03-01
We introduce a new approach for multiplexing fiber-based ultrasound sensors using Optical Frequency Domain Reflectometry (OFDR). In the present demonstration of the method, each sensor was a short section of Polyimide-coated single-mode fiber. One end of the sensing fiber was pigtailed to a mirror and the other end was connected, via a fiber optic delay line, to a 1X4 fiber coupler. The multiplexing was enabled by using a different delay to each sensor. Ultrasonic excitation was performed by a 1MHz transducer which transmitted 4μs tone-bursts above the sensor array. The ultrasound waves generated optical phase variations in the fibers which were detected using the OFDR method. The ultrasound field at the sensors was successfully reconstructed without any noticeable cross-talk.
An Improved Frequency Domain Technique for Determining Soil Water Content
Institute of Scientific and Technical Information of China (English)
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.
Iterative procedures for wave propagation in the frequency domain
Energy Technology Data Exchange (ETDEWEB)
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.
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.
Imaging scattering orientation with spatial frequency domain imaging.
Konecky, Soren D; Rice, Tyler; Durkin, Anthony J; Tromberg, Bruce J
2011-12-01
Optical imaging techniques based on multiple light scattering generally have poor sensitivity to the orientation and direction of microscopic light scattering structures. In order to address this limitation, we introduce a spatial frequency domain method for imaging contrast from oriented scattering structures by measuring the angular-dependence of structured light reflectance. The measurement is made by projecting sinusoidal patterns of light intensity on a sample, and measuring the degree to which the patterns are blurred as a function of the projection angle. We derive a spatial Fourier domain solution to an anisotropic diffusion model. This solution predicts the effects of bulk scattering orientation on the amplitude and phase of the projected patterns. We introduce a new contrast function based on a scattering orientation index (SOI) which is sensitive to the degree to which light scattering is directionally dependent. We validate the technique using tissue simulating phantoms, and ex vivo samples of muscle and brain. Our results show that SOI is independent of the overall amount of bulk light scattering and absorption, and that isotropic versus oriented scattering structures can be clearly distinguished. We determine the orientation of subsurface microscopic scattering structures located up to 600 μm beneath highly scattering (μ(') (s) = 1.5 mm(-1)) material.
A new image cipher in time and frequency domains
Abd El-Latif, Ahmed A.; Niu, Xiamu; Amin, Mohamed
2012-10-01
Recently, various encryption techniques based on chaos have been proposed. However, most existing chaotic encryption schemes still suffer from fundamental problems such as small key space, weak security function and slow performance speed. This paper introduces an efficient encryption scheme for still visual data that overcome these disadvantages. The proposed scheme is based on hybrid Linear Feedback Shift Register (LFSR) and chaotic systems in hybrid domains. The core idea is to scramble the pixel positions based on 2D chaotic systems in frequency domain. Then, the diffusion is done on the scrambled image based on cryptographic primitive operations and the incorporation of LFSR and chaotic systems as round keys. The hybrid compound of LFSR, chaotic system and cryptographic primitive operations strengthen the encryption performance and enlarge the key space required to resist the brute force attacks. Results of statistical and differential analysis show that the proposed algorithm has high security for secure digital images. Furthermore, it has key sensitivity together with a large key space and is very fast compared to other competitive algorithms.
MULTILOOP PI CONTROLLER FOR ACHIEVING SIMULTANEOUS TIME AND FREQUENCY DOMAIN SPECIFICATIONS
2015-01-01
Most of the controllers in control system are designed to satisfy either time domain or frequency domain specifications. This work presents the computation of a multiloop PI controller for achieving time and frequency domain specifications simultaneously. The desired time and frequency domain measures are to be specified initially to the design. To obtain the desired value of the performance measures the graphical relationship between the PI controller and the performance criteria is given. T...
Frequency domain analysis of noise in autoregulated gene circuits
Simpson, Michael L.; Cox, Chris D.; Sayler, Gary S.
2003-01-01
We describe a frequency domain technique for the analysis of intrinsic noise within negatively autoregulated gene circuits. This approach is based on the transfer function around the feedback loop (loop transmission) and the equivalent noise bandwidth of the system. The loop transmission, T, is shown to be a determining factor of the dynamics and the noise behavior of autoregulated gene circuits, and this T-based technique provides a simple and flexible method for the analysis of noise arising from any source within the gene circuit. We show that negative feedback not only reduces the variance of the noise in the protein concentration, but also shifts this noise to higher frequencies where it may have a negligible effect on the noise behavior of following gene circuits within a cascade. This predicted effect is demonstrated through the exact stochastic simulation of a two-gene cascade. The analysis elucidates important aspects of gene circuit structure that control functionality, and may provide some insights into selective pressures leading to this structure. The resulting analytical relationships have a simple form, making them especially useful as synthetic gene circuit design equations. With the exception of the linearization of Hill kinetics, this technique is general and may be applied to the analysis or design of networks of higher complexity. This utility is demonstrated through the exact stochastic simulation of an autoregulated two-gene cascade operating near instability. PMID:12671069
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...
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.
Directory of Open Access Journals (Sweden)
Hong eZhou
2016-06-01
Full Text Available 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.
In vivo spatial frequency domain spectroscopy of two layer media
Yudovsky, Dmitry; Nguyen, John Quan M.; Durkin, Anthony J.
2012-10-01
Monitoring of tissue blood volume and local oxygen saturation can inform the assessment of tissue health, healing, and dysfunction. These quantities can be estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in skin can be confounded by the strong absorption of melanin in the epidermis and epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. Therefore, a method is desired that decouples the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. A previously developed inverse method based on a neural network forward model was applied to simulated spatial frequency domain reflectance of skin for multiple wavelengths in the near infrared. It is demonstrated that the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis can be determined independently and with minimal coupling. Then, the same inverse method was applied to reflectance measurements from a tissue simulating phantom and in vivo human skin. Oxygen saturation and total hemoglobin concentrations were estimated from the volar forearms of weakly and strongly pigmented subjects using a standard homogeneous model and the present two layer model.
Multiscale Point Correspondence Using Feature Distribution and Frequency Domain Alignment
Directory of Open Access Journals (Sweden)
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.
A frequency domain based rigid motion artifact reduction algorithm
Luo, Hai; Huang, Xiaojie; Pan, Wenyu; Zhou, Heqin; Feng, Huanqing
2009-10-01
During a CT scan, patients' conscious or unconscious motions would result in motion artifacts which undermine the image quality and hamper doctors' accurate diagnosis and therapy. It is desirable to develop a precise motion estimation and artifact reduction method in order to produce high-resolution images. Rigid motion can be decomposed into two components: translational motion and rotational motion. Since considering the rotation and translation simultaneously is very difficult, most former studies on motion artifact reduction ignore rotation. The extended HLCC based method considering the rotation and translation simultaneously relies on a searching algorithm which leads to expensive computing cost. Therefore, a novel method which does not rely on searching is desirable. In this paper, we focus on parallel-beam CT. We first propose a frequency domain based method to estimate rotational motion, which is not affected by translational motion. It realizes the separation of rotation estimation and translation estimation. Then we combine this method with the HLCC based method to construct a new method for general rigid motion called separative estimation and collective correction method. Furthermore, we present numerical simulation results to show the accuracy and robustness of our approach.
Spacial and Frequency Domain Calculation of Terrain Roughness Metric Root-Mean-Square (RMS)
2014-11-01
TARDEC Technical Report No. 26042 November 2014 SPACIAL AND FREQUENCY DOMAIN CALCULATION OF TERRAIN ROUGHNESS METRIC ROOT-MEAN...DATE (DD-MM-YYYY) 11-15-2014 2. REPORT TYPE TECHNICAL 3. DATES COVERED (From - To) 2013-2014 SPACIAL AND FREQUENCY DOMAIN CALCULATION OF TERRAIN...roughness. Based on mathematics of the Fourier transform and duality, calculations are performed in the spacial and frequency domains to show equivalent
Institute of Scientific and Technical Information of China (English)
Ke Xiao; Shang-Bo Zhou; Wei-Wei Zhang
2008-01-01
For a general nonlinear fractional-orderdifferential equation, the numerical solution is a goodway to approximate the trajectory of such systems. Inthis paper, a novel algorithm for numerical solution offractional-order differential equations based on thedefinition of Grunwald-Letnikov is presented. Theresults of numerical solution by using the novel methodand the frequency-domain method are compared, and the limitations of frequency-domain method arediscussed.
Institute of Scientific and Technical Information of China (English)
Ke Xiao; Shang-Bo Zhou; Wei-Wei Zhang
2008-01-01
For a general nonlinear fractional-order differential equation, the numerical solution is a good way to approximate the trajectory of such systems. In this paper, a novel algorithm for numerical solution of fractional-order differential equations based on the definition of Grunwald-Letnikov is presented. The results of numerical solution by using the novel method and the frequency-domain method are compared, and the limitations of frequency-domain method arediscussed.
Comparison of pulse and SFCW GPR in time, frequency and wavelet domain
De Pue, Jan; Van De Vijver, Ellen; Cornelis, Wim; Van Meirvenne, Marc
2014-05-01
Ground penetrating radar (GPR) systems operating in the time- or frequency domain are two fundamentally different concepts, pursuing the same objective: non-invasive characterization of the subsurface. The aim of this study is to compare the performance of these two GPR systems in the time, frequency and wavelet domain. The time domain GPR investigated is the Utilityscan DF. This is a ground coupled GPR with a digital dual-frequency antenna (300 and 800 MHz). The Geoscope GS3F and VX1213 antenna array from 3DRadar is the frequency domain GPR used in this comparison. It is an air coupled stepped frequency continuous wave (SFCW) GPR with a frequency bandwidth from 200 MHz to 3000 MHz. Using data from several test sites of various soil types, the data is evaluated in the time domain, the frequency domain and the wavelet domain. Each of these domains contains specific information regarding the data quality. Presenting the data in the time domain, allows visualizing the subsurface reflections. This makes it visible how strong the data is affected by internal interference, ringing and other noise. To compensate for the attenuation of the signal in time, automatic gain control is applied. The maximum of this gain function indicates the time where the signal is attenuated completely and noise becomes more dominant, corresponding with the maximal penetration depth of the different GPR systems. In the frequency domain, the data allows to investigate which frequencies contain most valuable information and which ones are affected by noise. Finally, by performing a wavelet transformation the data is transformed to the time-frequency domain. Due to frequency dependent attenuation of electromagnetic signals in the soil, low frequencies will be more dominant in deeper layers, and high frequencies will not be present anymore. This is determining for the range resolution of the data throughout the traveltime of the signal. This work is a contribution to COST Action TU1208 "Civil
Fast Frequency-domain Waveforms for Spin-Precessing Binary Inspirals
Klein, Antoine; Yunes, Nicolás
2014-01-01
The detection and characterization of gravitational wave signals from compact binary coalescence events relies on accurate waveform templates in the frequency domain. The stationary phase approximation (SPA) can be used to compute closed-form frequency-domain waveforms for non-precessing, quasi-circular binary inspirals. However, until now, no fast frequency-domain waveforms have existed for generic, spin-precessing quasi-circular compact binary inspirals. Templates for these systems have had to be computed via a discrete Fourier transform of finely sampled time-domain waveforms, which is far more computationally expensive than those constructed directly in the frequency-domain, especially for those systems that are dominated by the inspiral part. There are two obstacles to deriving frequency-domain waveforms for precessing systems: (i) the spin-precession equations do not admit closed-form solutions for generic systems; (ii) the SPA fails catastrophically. Presently there is no general solution to the first ...
Characterization of static bifurcations for n-dimensional flows in the frequency domain
Institute of Scientific and Technical Information of China (English)
Li ZENG; Yi ZHAO
2006-01-01
In this paper n-dimensional flows (described by continuous-time system) with static bifurcations are considered with the aim of classification of different elementary bifurcations using the frequency domain formalism. Based on frequency domain approach, we prove some criterions for the saddle-node bifurcation, transcritical bifurcation and pitchfork bifurcation, and give an example to illustrate the efficiency of the result obtained.
Fatigue Damage Assessment by Considering Mean Value Effect in Frequency Domain
Institute of Scientific and Technical Information of China (English)
丁红岩; 朱奇; 张浦阳
2015-01-01
Fatigue damage assessment is carried out considering mean value effect by applying four criteria of failure. Three frequency domain methods, i.e., level crossing counting (LCC), range counting (RC) and a new proposed method, are applied. The core of frequency domain method is the construction of probability density function for the mean stress and stress range of the stress process. The applicability of these frequency domain methods are inspected by comparing with time domain method. Numerical simulations verify the applicability of LCC and the proposed method, while RC gives poor estimations.
Solving forward and inverse seismic problems by boundary-element method in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Xianxi, J.
1988-01-01
Solving the boundary value problem of wave equation by boundary element method in frequency domain involves these steps: 1. ID Fourier transform of time variable is made to convert the wave equation into Helmholtz equation; 2. this equation is then solved using boundary-element method in frequency domain; 3. the result is returned to time domain by making inverse Fourier transform. Compared with other formulas, the formula in this paper brings higher accuracy but less computation.
Fingerprint Ridge Frequency Estimation in the Fourier Domain
Directory of Open Access Journals (Sweden)
PATRICIU, V.-V.
2014-11-01
Full Text Available Ridge frequency is an important parameter in fingerprint image processing and feature extraction. However, ridge frequency estimation is a difficult task in noisy fingerprint images. A simple and accurate method for the computation of fingerprint ridge frequency using the Fourier spectrum is proposed. The results of the experiments conducted on a collection of fingerprints as well as a quantitative method for performance evaluation based on a Gabor filter-bank are presented. The proposed method is robust with respect to noise and reliable frequency images are obtained.
Energy Technology Data Exchange (ETDEWEB)
Duan Zhisheng [State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics and Engineering Science, Peking University, Beijing 100871 (China)], E-mail: duanzs@pku.edu.cn; Wang Jinzhi; Yang Ying; Huang Lin [State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics and Engineering Science, Peking University, Beijing 100871 (China)
2009-04-30
This paper surveys frequency-domain and time-domain methods for feedback nonlinear systems and their possible applications to chaos control, coupled systems and complex dynamical networks. The absolute stability of Lur'e systems with single equilibrium and global properties of a class of pendulum-like systems with multi-equilibria are discussed. Time-domain and frequency-domain criteria for the convergence of solutions are presented. Some latest results on analysis and control of nonlinear systems with multiple equilibria and applications to chaos control are reviewed. Finally, new chaotic oscillating phenomena are shown in a pendulum-like system and a new nonlinear system with an attraction/repulsion function.
Time and Frequency Domain Identification and Analysis of a Gas Turbine Engine
Boaghe, O.M.; S. A. Billings; L. M. Li; Fleming, P J; Liu, J
2000-01-01
The NARMAX (Nonlinear Auto Regressive Moving Average model with eXogenous inputs) approach has been used to analyse the dynamics of a gas turbine engine. The fuel flow-shaft speed relationship is analysed by identifying both time and frequency domain models of the system. The frequency domain analysis is studied by mapping the discrete-time NARMAX models into the Generalised Frequency Response Functions (GFRF's) to reveal the nonlinear coupling between the various input spectral components an...
Microwave Frequency Ferroelectric Domain Imaging of Deuterated Triglycine Sulfate Crystals
Steinhauer, David E.; Anlage, Steven M.
2001-03-01
We have used a near-field scanning microwave microscope(D. E. Steinhauer, C. P. Vlahacos, F. C. Wellstood, Steven M. Anlage, C. Canedy, R. Ramesh, A. Stanishevsky, and J. Melngailis, "Quantitative Imaging of Dielectric Permittivity and Tunability with a Near-Field Scanning Microwave Microscope," Rev. Sci. Instrum. 71), 2751-2758 (2000). to image domain structure and quantitatively measure dielectric permittivity and nonlinearity in ferroelectric crystals at 8.1 GHz with a spatial resolution of 1 μm. We imaged ferroelectric domains in periodically-poled LiNbO_3, BaTiO_3, and deuterated triglycine sulfate (DTGS) with a signal-to-noise ratio of 7. Measurement of the permittivity and nonlinearity of DTGS in the temperature range 300--400 K shows a peak at the Curie temperature, TC ≈ 340 K, as well as reasonable agreement with thermodynamic theory. In addition, the domain growth relaxation time shows a minimum near T_C. We observe coarsening of ferroelectric domains in DTGS after a temperature quench from 360 K to 330 K, and evaluate the structure factor.
Wideband Radar Echo Frequency-domain Simulation and Analysis for High Speed Moving Targets
Directory of Open Access Journals (Sweden)
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.
Spectral element method for elastic and acoustic waves in frequency domain
Shi, Linlin; Zhou, Yuanguo; Wang, Jia-Min; Zhuang, Mingwei; Liu, Na; Liu, Qing Huo
2016-12-01
Numerical techniques in time domain are widespread in seismic and acoustic modeling. In some applications, however, frequency-domain techniques can be advantageous over the time-domain approach when narrow band results are desired, especially if multiple sources can be handled more conveniently in the frequency domain. Moreover, the medium attenuation effects can be more accurately and conveniently modeled in the frequency domain. In this paper, we present a spectral-element method (SEM) in frequency domain to simulate elastic and acoustic waves in anisotropic, heterogeneous, and lossy media. The SEM is based upon the finite-element framework and has exponential convergence because of the use of GLL basis functions. The anisotropic perfectly matched layer is employed to truncate the boundary for unbounded problems. Compared with the conventional finite-element method, the number of unknowns in the SEM is significantly reduced, and higher order accuracy is obtained due to its spectral accuracy. To account for the acoustic-solid interaction, the domain decomposition method (DDM) based upon the discontinuous Galerkin spectral-element method is proposed. Numerical experiments show the proposed method can be an efficient alternative for accurate calculation of elastic and acoustic waves in frequency domain.
Mixed Discretization of the Time Domain MFIE at Low Frequencies
Ulku, Huseyin Arda
2017-01-10
Solution of the magnetic field integral equation (MFIE), which is obtained by the classical marching on-in-time (MOT) scheme, becomes inaccurate when the time step is large, i.e., under low-frequency excitation. It is shown here that the inaccuracy stems from the classical MOT scheme’s failure to predict the correct scaling of the current’s Helmholtz components for large time steps. A recently proposed mixed discretization strategy is used to alleviate the inaccuracy problem by restoring the correct scaling of the current’s Helmholtz components under low-frequency excitation.
Frequency-domain generelaized singular peruturbation method for relative error model order reduction
Institute of Scientific and Technical Information of China (English)
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.
The application of finite element method to forward and inverse seismic problems in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Shaoyou, J.; Xiangheng, J.; Shizhe, X.
1987-04-01
Unstable result is obtained when the boundary problem of wave equation is solved using finite element method in time domain. However, when the boundary problem of wave equation is solved by finite element method in frequency domain, not only the unstablity can be avoided but also computation is speeded up because of using FFT. The procedure for solving the boundary problem using finite element method in frequency domain is as follows: 1. the wave equation is transformed into Helmholtz equation by making one-dimensional Fourier transform with respect to time; 2. Helmholtz equation is solved using finite element method in frequency domain; 3. the obtained result is returned to time domain by making inverse Fourier transform. Both forward and inverse seismic problems can be solved by this method.
Investigation of Frequency-Domain Link Adaptation for a 5-MHz OFDMA/HSDPA system
DEFF Research Database (Denmark)
Pokhariyal, Akhilesh; Kolding, Troels E.; Frederiksen, Frank;
2005-01-01
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......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...
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.
The Capability of Time- And Frequency-domain Algorithms for Bistatic SAR Processing
Vu, Viet; Sjögren, Thomas; Pettersson, Mats
2013-01-01
The paper presents a study of the capability of time- And frequency-domain algorithms for bistatic SAR processing. Two typical algorithms, Bistatic Fast Backprojection (BiFBP) and Bistatic Range Doppler (BiRDA), which are both available for general bistatic geometry, are selected as the examples of time- And frequency-domain algorithms in this study. Their capability is evaluated based on some criteria such as processing time required by the algorithms to reconstruct SAR images from bistatic ...
BER Performance of Frequency Domain Differential Demodulation OFDM in Flat Fading Channel
Institute of Scientific and Technical Information of China (English)
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.
Direction of arrival estimation using array model in time-frequency domain
Institute of Scientific and Technical Information of China (English)
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.
Microball lens integrated fiber probe for optical frequency domain imaging
Institute of Scientific and Technical Information of China (English)
Jae-Ho Han; J.U.Kang
2011-01-01
An integrated microball lens fiber catheter probe is demonstrated, which has better lateral resolution and longer working distance than a corresponding bare fiber probe with diverging beam for Fourier domain optical coherence tomography (FDOCT). Simulation results are shown to gain the effect of the distance between the microball lens and the bare fiber to the focusing plane and beam width. The freedom of modifying the working distance and lateral resolution is shown. This is achieved by changing the gap distance between the single-mode fiber and the microball lens within the packaged surgical needle catheter without using an additional beam expander having a fixed length. The probe successfully acquired cross-sectional images of ocular tissues from an animal sample with the proposed miniaturized imaging probe.%@@ An integrated microball lens fiber catheter probe is demonstrated,which has better lateral resolution and longer working distance than a corresponding bare fiber probe with diverging beam for Fourier domain optical coherence tomography(FDOCT).Simulation results are shown to gain the effect of the distance between the microball lens and the bare fiber to the focusing plane and beam width.The freedom of modifying the working distance and lateral resolution is shown.This is achieved by changing the gap distance between the single-mode fiber and the microball lens within the packaged surgical needle catheter without using an additional beam expander having a fixed length.The probe successfully acquired crosssectional images of ocular tissues from an animal sample with the proposed miniaturized imaging probe.
Boukamp, Bernard A.; Otter, den Matthijs W.; Bouwmeester, Henny J.M.
2004-01-01
The conductivity relaxation (CR) method is often used for measuring the surface transfer rate, Ktr, and the bulk diffusion coefficient, $$\\tilde{D},$$ for oxygen transport in mixed conducting oxides (MIECs). The time domain analysis of the obtained CR response is rather complex and is based on lsquo
Xiao, Pei; Lin, Zihuai; Fagan, Anthony; Cowan, Colin; Vucetic, Branka; Wu, Yi
2011-12-01
In this paper, we propose a novel transceiver structure for orthogonal frequency division multiple access-based uplink multiuser multiple-input multiple-output systems. The numerical results show that the proposed frequency-domain equalization schemes significantly outperform conventional linear minimum mean square error-based equalizers in terms of bit error rate performance with moderate increase in computational complexity.
Statistics and frequency-domain moveout for multiple-taper receiver functions
Park, J.; Levin, V.
2016-10-01
The multiple-taper correlation (MTC) algorithm for the estimation of teleseismic receiver functions (RFs) has desirable statistical properties. This paper presents several adaptations to the MTC algorithm that exploit its frequency-domain uncertainty estimates to generate stable RFs that include moveout corrections for deeper interfaces. Narrow-band frequency averaging implicit in spectral cross-correlation restricts the MTC-based RF estimates to resolve Ps converted phases only at short delay times, appropriate to the upper 100 km of Earth's lithosphere. The Ps conversions from deeper interfaces can be reconstructed by the MTC algorithm in two ways. Event cross-correlation computes a cross-correlation of single-taper spectrum estimates for a cluster of events rather than for a set of eigenspectrum estimates of a single P coda. To extend the reach of the algorithm, pre-stack moveout corrections in the frequency domain preserves the formal uncertainties of the RF estimates, which are used to weight RF stacks. Moving-window migration retains the multiple-taper approach, but cross-correlates the P-polarized motion with time-delayed SH and SV motion to focus on a Ps phase of interest. The frequency-domain uncertainties of bin-averaged RFs do not translate directly into the time domain. A jackknife over data records in each bin stack offers uncertainty estimates in the time domain while preserving uncertainty weighting in the frequency-domain RF stack.
Frequency and time domain analysis of an external cavity laser with strong filtered optical feedback
DEFF Research Database (Denmark)
Detoma, Enrico; Tromborg, Bjarne; Montrosset, Ivo
-signal analysis in the frequency domain allows a calculation of the range of operation without mode hopping around the grating reflectivity peak. This region should be as large as possible for proper operation of the tunable laser source. The analysis shows this stabilizing effect of mode coupling and gain......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...... copression in the lasing mode. An integral equation for the electrical field is derived from the frequency domain model and used for time domain simulations of large-signal behavior....
MULTILOOP PI CONTROLLER FOR ACHIEVING SIMULTANEOUS TIME AND FREQUENCY DOMAIN SPECIFICATIONS
Directory of Open Access Journals (Sweden)
M. SENTHILKUMAR
2015-08-01
Full Text Available Most of the controllers in control system are designed to satisfy either time domain or frequency domain specifications. This work presents the computation of a multiloop PI controller for achieving time and frequency domain specifications simultaneously. The desired time and frequency domain measures are to be specified initially to the design. To obtain the desired value of the performance measures the graphical relationship between the PI controller and the performance criteria is given. Thus by using graphical method a set of PI controller parameters to meet the desired performance measures are obtained in an effective and simpler way. The coupled tank has become a classic design of control engineering for multivariable process. The proposed control strategy has been implemented in the same coupled tank process and validated through simulation studies.
Time and frequency domain models for multiaxial fatigue life estimation under random loading
Directory of Open Access Journals (Sweden)
Andrea Carpinteri
2015-07-01
Full Text Available Engineering structures and components are often subjected to random fatigue loading produced, for example, by wind turbulences, marine waves and vibrations. The methods available in the literature for fatigue assessment under random loading are formulated in time domain or, alternatively, in frequency domain. The former methods require the knowledge of the loading time history, and a large number of experimental tests/numerical simulations is needed to obtain statistically reliable results. The latter methods are generally more advantageous with respect to the time domain ones, allowing a rapid fatigue damage evaluation. In the present paper, a multiaxial criterion formulated in the frequency-domain is presented to estimate the fatigue lives of smooth metallic structures subjected to combined bending and torsion random loading. A comparison in terms of fatigue life prediction by employing a time domain methods, previously proposed by the authors, is also performed.
Frequency domain transfer function identification using the computer program SYSFIT
Energy Technology Data Exchange (ETDEWEB)
Trudnowski, D.J.
1992-12-01
Because the primary application of SYSFIT for BPA involves studying power system dynamics, this investigation was geared toward simulating the effects that might be encountered in studying electromechanical oscillations in power systems. Although the intended focus of this work is power system oscillations, the studies are sufficiently genetic that the results can be applied to many types of oscillatory systems with closely-spaced modes. In general, there are two possible ways of solving the optimization problem. One is to use a least-squares optimization function and to write the system in such a form that the problem becomes one of linear least-squares. The solution can then be obtained using a standard least-squares technique. The other method involves using a search method to obtain the optimal model. This method allows considerably more freedom in forming the optimization function and model, but it requires an initial guess of the system parameters. SYSFIT employs this second approach. Detailed investigations were conducted into three main areas: (1) fitting to exact frequency response data of a linear system; (2) fitting to the discrete Fourier transformation of noisy data; and (3) fitting to multi-path systems. The first area consisted of investigating the effects of alternative optimization cost function options; using different optimization search methods; incorrect model order, missing response data; closely-spaced poles; and closely-spaced pole-zero pairs. Within the second area, different noise colorations and levels were studied. In the third area, methods were investigated for improving fitting results by incorporating more than one system path. The following is a list of guidelines and properties developed from the study for fitting a transfer function to the frequency response of a system using optimization search methods.
Time-domain analysis of frequency dependent inertial wave forces on cylinders
DEFF Research Database (Denmark)
Krenk, Steen
2013-01-01
-number, and the relevant range of waves shorter than about six times the diameter typically corresponds to deep water waves. This permits a universal non-dimensional frequency representation, that is converted to rational form to provide the relevant filter equation. Simple time-domain simulations demonstrate...... a simple time-domain procedure for the inertial force, in which the frequency dependence is represented via a simple explicit time filter on the wave particle acceleration or velocity. The frequency dependence of the inertia coefficient is known analytically as a function of the wave...
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
DEFF Research Database (Denmark)
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...
Institute of Scientific and Technical Information of China (English)
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.
Channel estimation in space and frequency domain for MIMO-OFDM systems
Institute of Scientific and Technical Information of China (English)
PAN Pei-sheng; ZHENG Bao-yu
2009-01-01
Multiple-input multiple-output (MIMO) systems can be combined with orthogonal frequency division multiplexing (OFDM) systems to improve the capacity and quality of wireless communications. In this article, a channel estimation technique in both space and frequency domain for MIMO-OFDM systems is proposed. It is shown that the proposed scheme with space-frequency pilot tones achieve optimal minimum mean square error (MMSE) channel estimation. Simulation results indicate that the proposed method achieves good performance.
Modeling of earthquake ground motion in the frequency domain
Thrainsson, Hjortur
In recent years, the utilization of time histories of earthquake ground motion has grown considerably in the design and analysis of civil structures. It is very unlikely, however, that recordings of earthquake ground motion will be available for all sites and conditions of interest. Hence, there is a need for efficient methods for the simulation and spatial interpolation of earthquake ground motion. In addition to providing estimates of the ground motion at a site using data from adjacent recording stations, spatially interpolated ground motions can also be used in design and analysis of long-span structures, such as bridges and pipelines, where differential movement is important. The objective of this research is to develop a methodology for rapid generation of horizontal earthquake ground motion at any site for a given region, based on readily available source, path and site characteristics, or (sparse) recordings. The research includes two main topics: (i) the simulation of earthquake ground motion at a given site, and (ii) the spatial interpolation of earthquake ground motion. In topic (i), models are developed to simulate acceleration time histories using the inverse discrete Fourier transform. The Fourier phase differences, defined as the difference in phase angle between adjacent frequency components, are simulated conditional on the Fourier amplitude. Uniformly processed recordings from recent California earthquakes are used to validate the simulation models, as well as to develop prediction formulas for the model parameters. The models developed in this research provide rapid simulation of earthquake ground motion over a wide range of magnitudes and distances, but they are not intended to replace more robust geophysical models. In topic (ii), a model is developed in which Fourier amplitudes and Fourier phase angles are interpolated separately. A simple dispersion relationship is included in the phase angle interpolation. The accuracy of the interpolation
Panayappan, Kadappan
With the advent of sub-micron technologies and increasing awareness of Electromagnetic Interference and Compatibility (EMI/EMC) issues, designers are often interested in full- wave solutions of complete systems, taking to account a variety of environments in which the system operates. However, attempts to do this substantially increase the complexities involved in computing full-wave solutions, especially when the problems involve multi- scale geometries with very fine features. For such problems, even the well-established numerical methods, such as the time domain technique FDTD and the frequency domain methods FEM and MoM, are often challenged to the limits of their capabilities. In an attempt to address such challenges, three novel techniques have been introduced in this work, namely Dipole Moment (DM) Approach, Recursive Update in Frequency Domain (RUFD) and New Finite Difference Time Domain ( vFDTD). Furthermore, the efficacy of the above techniques has been illustrated, via several examples, and the results obtained by proposed techniques have been compared with other existing numerical methods for the purpose of validation. The DM method is a new physics-based approach for formulating MoM problems, which is based on the use of dipole moments (DMs), as opposed to the conventional Green's functions. The absence of the Green's functions, as well as those of the vector and scalar potentials, helps to eliminate two of the key sources of difficulties in the conventional MoM formulation, namely the singularity and low-frequency problems. Specifically, we show that there are no singularities that we need to be concerned with in the DM formulation; hence, this obviates the need for special techniques for integrating these singularities. Yet another salutary feature of the DM approach is its ability to handle thin and lossy structures, or whether they are metallic, dielectric-type, or even combinations thereof. We have found that the DM formulation can handle these
Acoustic Imaging Frequency Dynamics of Ferroelectric Domains by Atomic Force Microscopy
Institute of Scientific and Technical Information of China (English)
ZHAO Kun-Yu; Shunji Takekawa; Kenji Kitamura; ZENG Hua-Rong; SONG Hong-Zhang; HUI Sen-Xing; LI Guo-Rong; YIN Qing-Rui; Kiyoshi Shimamura; Chinna Venkadasamy Kannan; Encarnacion Antonia Garcia Villora
2008-01-01
We report the acoustic imaging frequency dynamics of ferroelectric domains by low-frequency acoustic probe microscopy based on the commercial atomic force microscopy. It is found that ferroelectric domain could be firstly visualized at lower frequency down to 0.h kHz by AFM-based acoustic microscopy. The frequency-dependent acoustic signal revealed a strong acoustic response in the frequency range from 7 kHz to lO kHz, and reached maximum at 8.1 kHz. The acoustic contrast mechanism can be ascribed to the different elastic response of ferroelectric microstructures to local elastic stress fields, which is induced by the acoustic wave transmitting in the sample when the piezoelectric transducer is vibrating and exciting acoustic wave under ac electric fields due to normal piezoelectric effects.
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.
Fractional Fourier transform for partially coherent beam in spatial-frequency domain
Institute of Scientific and Technical Information of China (English)
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.
A hybrid analysis method for linear dynamic soil-structure interaction in time and frequency domain
Institute of Scientific and Technical Information of China (English)
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.
USING CROSS-CORRELATION THEORY TO EXTRACT MODAL PARAMETERS IN FREQUENCY-DOMAIN
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Conventional modal parameter identifications are usually based on frequency response functions, which require measurements of both the input force and the resulting response. However, in many cases, only response data are available while the actual excitations (such as wind/wave load) are not measurable. Modal parameters estimation must base itself on response-only data. Over the past years, many time-domain modal parameter identification techniques from output-only are proposed. A poly-reference frequency-domain modal identification scheme on response-only is presented. It is based on coupling the cross-correlation theory with conventional frequency-domain modal parameter extraction. An experiment using an airplane model is performed to verify the proposed method.
Frequency-Domain Adaptive Algorithm for Network Echo Cancellation in VoIP
Directory of Open Access Journals (Sweden)
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.
Frequency-Domain Thermal Modelling and Characterization of Power Semiconductor Devices
DEFF Research Database (Denmark)
Ma, Ke; He, Ning; Liserre, Marco
2016-01-01
The thermal behavior of power electronics devices has being a crucial design consideration because it is closely related to the reliability and also the cost of the converter system. Unfortunately, the widely used thermal models based on lumps of thermal resistances and capacitances have...... their limits to correctly predict the device temperatures, especially when considering the thermal grease and heat sink attached to the power semiconductor devices. In this paper, frequency-domain approach is applied to the modelling of the thermal dynamics for power devices. The limits of the existing RC lump......-based thermal networks are explained from a point of view of frequency domain. Based on the discovery, a more advanced thermal model developed in the frequency domain is proposed, which can be easily established by characterizing the slope variation from the bode diagram of the typically used Foster thermal...
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...
A frequency domain design of PID controller for an AVR system
Institute of Scientific and Technical Information of China (English)
Md Nishat ANWAR; Somnath PAN
2014-01-01
We propose a new proportional-integral-derivative (PID) controller design method for an automatic voltage regula-tion (AVR) system based on approximate model matching in the frequency domain. The parameters of the PID controller are obtained by approximate frequency response matching between the closed-loop control system and a reference model with the desired specifications. Two low frequency points are required for matching the frequency response, and the design method yields linear algebraic equations, solution of which gives the controller parameters. The effectiveness of the proposed method is demonstrated through examples taken from the literature and comparison with some popular methods.
The capability of time- and frequency-domain algorithms for bistatic SAR processing
Vu, Viet T.; Sjögren, Thomas K.; Pettersson, Mats I.
2013-05-01
The paper presents a study of the capability of time- and frequency-domain algorithms for bistatic SAR processing. Two typical algorithms, Bistatic Fast Backprojection (BiFBP) and Bistatic Range Doppler (BiRDA), which are both available for general bistatic geometry, are selected as the examples of time- and frequency-domain algorithms in this study. Their capability is evaluated based on some criteria such as processing time required by the algorithms to reconstruct SAR images from bistatic SAR data and the quality assessments of those SAR images.
Nonlinear system identification NARMAX methods in the time, frequency, and spatio-temporal domains
Billings, Stephen A
2013-01-01
Nonlinear System Identification: NARMAX Methods in the Time, Frequency, and Spatio-Temporal Domains describes a comprehensive framework for the identification and analysis of nonlinear dynamic systems in the time, frequency, and spatio-temporal domains. This book is written with an emphasis on making the algorithms accessible so that they can be applied and used in practice. Includes coverage of: The NARMAX (nonlinear autoregressive moving average with exogenous inputs) modelThe orthogonal least squares algorithm that allows models to be built term by
Real-time frequency-domain fiber optic sensor for intra-arterial blood oxygen measurements
Alcala, J. R.; Scott, Ian L.; Parker, Jennifer W.; Atwater, Beauford W.; Yu, Clement; Fischer, Russell; Bellingrath, K.
1993-05-01
A real time frequency domain phosphorimeter capable of measuring precise and accurate excited state lifetimes for determining oxygen is described. This frequency domain instrument does not make use of cross correlation techniques traditionally used in frequency domain fluorometers. Instead, the electrical signal from the detector is filtered to contain only the first several harmonics. This filtered signal is then sampled and averaged over a few thousand cycles. The absolute phase and absolute modulation of each sampled harmonic of the excitation and of the luminescence is computed by employing fast Fourier transform algorithms. The phase delay and the modulation ratio is then calculated at each harmonic frequency. A least squares fit is performed in the frequency domain to obtain the lifetimes of discrete exponentials. Oxygen concentrations are computed from these lifetimes. Prototypes based on these techniques were built employing commercially available components. Results from measurements in saline solution and in the arterial blood of dogs show that oxygen concentrations can be determined reproducibly. The system drift is less than 1% in over 100 hours of continuous operation. The performance of fiber optic sensors was evaluated in dogs over a period of 10 hours. The sensors tracked changes in arterial oxygen tension over the course of the experiment without instabilities. The overall response of the system was about 90 seconds. The update time was 3 seconds.
DEFF Research Database (Denmark)
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...... 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 (HSS) modeling...... 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...
A frequency domain radar interferometric imaging (FII) technique based on high-resolution methods
Luce, H.; Yamamoto, M.; Fukao, S.; Helal, D.; Crochet, M.
2001-01-01
In the present work, we propose a frequency-domain interferometric imaging (FII) technique for a better knowledge of the vertical distribution of the atmospheric scatterers detected by MST radars. This is an extension of the dual frequency-domain interferometry (FDI) technique to multiple frequencies. Its objective is to reduce the ambiguity (resulting from the use of only two adjacent frequencies), inherent with the FDI technique. Different methods, commonly used in antenna array processing, are first described within the context of application to the FII technique. These methods are the Fourier-based imaging, the Capon's and the singular value decomposition method used with the MUSIC algorithm. Some preliminary simulations and tests performed on data collected with the middle and upper atmosphere (MU) radar (Shigaraki, Japan) are also presented. This work is a first step in the developments of the FII technique which seems to be very promising.
Geostrophic Turbulence in the Frequency-Wavenumber Domain: Eddy-Driven Low-Frequency Variability
2014-08-01
snapshot is multiplied by a two-dimensional Tukey window having a ratio of taper to constant sections equal to 0.2 in each horizontal direction. To enforce... taper to constant sections.3 Because the QG model is doubly periodic, and because c1 has a zero time mean at each grid point, we do not employ any spatial...frequencies, the Neither curve has an unphysically sharp jump due to substantial energy in the (nominally) zero frequency. In the remainder of this paper, we
Directory of Open Access Journals (Sweden)
Wu Yi
2011-01-01
Full Text Available Abstract In this paper, we propose a novel transceiver structure for orthogonal frequency division multiple access-based uplink multiuser multiple-input multiple-output systems. The numerical results show that the proposed frequency-domain equalization schemes significantly outperform conventional linear minimum mean square error-based equalizers in terms of bit error rate performance with moderate increase in computational complexity.
Directory of Open Access Journals (Sweden)
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 Packet Scheduling Under Fractional Load for the UTRAN LTE Downlink
DEFF Research Database (Denmark)
Pokhariyal, Akhilesh; Monghal, Guillaume Damien; Pedersen, Klaus I.
2007-01-01
In this paper we investigate performance of frequency domain packet scheduling (FDPS) under fractional load (FL), based on the UTRAN Long Term Evolution downlink. FL may be regarded as an inter-cell interference (ICI) mitigation technique, which can improve the user experienced SINR. We consider...
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…
Plastique: A synchrotron radiation beamline for time resolved fluorescence in the frequency domain
De Stasio, Gelsomina; Zema, N.; Antonangeli, F.; Savoia, A.; Parasassi, T.; Rosato, N.
1991-06-01
PLASTIQUE is the only synchrotron radiation beamline in the world that performs time resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and dynamics of molecules. We describe the beamline and some initial data.
Modal Identification of Output-Only Systems using Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, L.; Andersen, P.
2000-01-01
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 ...
Modeling of Nanophotonic Resonators with the Finite-Difference Frequency-Domain Method
DEFF Research Database (Denmark)
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 ea...
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
Joint AVO inversion in the time and frequency domain with Bayesian interference
Zong, Zhao-Yun; Yin, Xing-Yao; Li, Kun
2016-12-01
Amplitude variations with offset or incident angle (AVO/AVA) inversion are typically combined with statistical methods, such as Bayesian inference or deterministic inversion. We propose a joint elastic inversion method in the time and frequency domain based on Bayesian inversion theory to improve the resolution of the estimated P- and S-wave velocities and density. We initially construct the objective function using Bayesian inference by combining seismic data in the time and frequency domain. We use Cauchy and Gaussian probability distribution density functions to obtain the prior information for the model parameters and the likelihood function, respectively. We estimate the elastic parameters by solving the initial objective function with added model constraints to improve the inversion robustness. The results of the synthetic data suggest that the frequency spectra of the estimated parameters are wider than those obtained with conventional elastic inversion in the time domain. In addition, the proposed inversion approach offers stronger antinoising compared to the inversion approach in the frequency domain. Furthermore, results from synthetic examples with added Gaussian noise demonstrate the robustness of the proposed approach. From the real data, we infer that more model parameter details can be reproduced with the proposed joint elastic inversion.
Simultaneous storage of medical images in the spatial and frequency domain: A comparative study
Directory of Open Access Journals (Sweden)
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.
Florez, H. M.; González, C.; Martinelli, M.
2016-07-01
Correlation spectroscopy has been proposed as a spectroscopic technique for measuring the coherence between the ground states in electromagnetically induced transparency (EIT). While in the time domain the steep dispersion in the 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 Λ 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-order term in perturbation expansion represents a sufficient description for the correlation. Sideband resonances are also observed, showing the richness of the frequency domain approach.
Directory of Open Access Journals (Sweden)
M.I.Khalil
2017-02-01
Full Text Available Steganography is the discipline of invisible communication by hiding the exchanged secret information (message in another digital information media (image, video or audio. The existence of the message is kept indiscernible in sense that no one, other than the intended recipient, suspects the existence of the message. The majority of steganography techniques are implemented either in spatial domain or in frequency domain of the digital images while the embedded information can be in the form of plain or cipher message. Medical image steganography is classified as a distinctive case of image steganography in such a way that both the image and the embedded information have special requirements such as achieving utmost clarity reading of the medical images and the embedded messages. There is a contention between the amount of hidden information and the caused detectable distortion of image. The current paper studies the degradation of the medical image when undergoes the steganography process in the frequency domain.
Institute of Scientific and Technical Information of China (English)
何艳丽; 董石麟
2002-01-01
Large span spatial lattice structures have many natural frequencies in a narrow frequency range, the conventional frequency domain method is difficult to contain all significant contribution modes. Through numerical examples, it is found that some high order modes are likely to be overlooked because of their higher positions of modal order, in spite of their significance to wind response. According to the contributions of modes to strain energy of system, the paper presented an efficient method to compensate the errors owing to missing out some significant high order modes. The effectiveness of the proposed method is verified through a numerical analysis of the wind responses of a spherical dome.
Praveena, K.; Chen, Hsiao-Wen; Liu, Hsiang-Lin; Sadhana, K.; Murthy, S. R.
2016-12-01
Nowadays electronic industries prerequisites magnetic materials, i.e., iron rich materials and their magnetic alloys. However, with the advent of high frequency applications, the standard techniques of reducing eddy current losses, using iron cores, were no longer efficient or cost effective. Current market trends of the switched mode power supplies industries required even low energy losses in power conversion with maintenance of adequate initial permeability. From the above point of view, in the present study we aimed at the production of Manganese-Zinc ferrites prepared via solution combustion method using mixture of fuels and achieved low loss, high saturation magnetization, high permeability, and high magnetic domain relaxation frequency. The as-synthesized Zn2+ substituted MnFe2O4 were characterized by X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The fractions of Mn2+, Zn2+ and Fe2+ cations occupying tetrahedral sites along with Fe occupying octahedral sites within the unit cell of all ferrite samples were estimated by Raman scattering spectroscopy. The magnetic domain relaxation was investigated by inductance spectroscopy (IS) and the observed magnetic domain relaxation frequency (fr) was increased with the increase in grain size. The real and imaginary part of permeability (μ‧ and μ″) increased with frequency and showed a maximum above 100 MHz. This can be explained on the basis of spin rotation and domain wall motion. The saturation magnetization (Ms), remnant magnetization (Mr) and magneton number (μB) decreased gradually with increasing Zn2+ concentration. The decrease in the saturation magnetization was discussed with Yafet-Kittel (Y-K) model. The Zn2+ concentration increases the relative number of ferric ions on the A sites, reduces the A-B interactions. The frequency dependent total power losses decreased as the zinc concentration increased. At 1 MHz, the total power loss (Pt) changed from 358 mW/cm3 for x=0-165 mW/cm3
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?
Directory of Open Access Journals (Sweden)
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.
Frequency domain wave equation forward modeling using gaussian elimination with static pivoting
Jian-Yong, Song; Xiao-Dong, Zheng; Yan, Zhang; Ji-Xiang, Xu; Zhen, Qin; Xue-Juan, Song
2011-03-01
Frequency domain wave equation forward modeling is a problem of solving large scale linear sparse systems which is often subject to the limits of computational efficiency and memory storage. Conventional Gaussian elimination cannot resolve the parallel computation of huge data. Therefore, we use the Gaussian elimination with static pivoting (GESP) method for sparse matrix decomposition and multi-source finite-difference modeling. The GESP method does not only improve the computational efficiency but also benefit the distributed parallel computation of matrix decomposition within a single frequency point. We test the proposed method using the classic Marmousi model. Both the single-frequency wave field and time domain seismic section show that the proposed method improves the simulation accuracy and computational efficiency and saves and makes full use of memory. This method can lay the basis for waveform inversion.
Le, Thien-Phu; Argoul, Pierre
2016-12-01
This paper proposes a new modal identification method of ambient vibration responses. The application of the singular value decomposition to continuous wavelet transform of power spectral density matrix gives singular values and singular vectors in frequency-scale domain. Analytical development shows a direct relation between local maxima in frequency-scale representation of singular values and modal parameters. This relation is then carried on for the identification of modal parameters via a complete practical procedure. The main novelties of this work involve the new formulation in frequency-scale domain and the capacity for the identification of modal parameters without the step of ridges extraction in comparison with previous wavelet-based modal identification methods.
Frequency-Domain Maximum-Likelihood Estimation of High-Voltage Pulse Transformer Model Parameters
Aguglia, D
2014-01-01
This paper presents an offline frequency-domain nonlinear and stochastic identification method for equivalent model parameter estimation of high-voltage pulse transformers. Such kinds of transformers are widely used in the pulsed-power domain, and the difficulty in deriving pulsed-power converter optimal control strategies is directly linked to the accuracy of the equivalent circuit parameters. These components require models which take into account electric fields energies represented by stray capacitance in the equivalent circuit. These capacitive elements must be accurately identified, since they greatly influence the general converter performances. A nonlinear frequency-based identification method, based on maximum-likelihood estimation, is presented, and a sensitivity analysis of the best experimental test to be considered is carried out. The procedure takes into account magnetic saturation and skin effects occurring in the windings during the frequency tests. The presented method is validated by experim...
FILDIG: a program to filter brain electrical signals in the frequency domain.
Guevara, M A; Ramos, J; Hernández-González, M; Corsi-Cabrera, M
2005-11-01
A software program to filter brain electrical signals in the frequency domain has been developed and is presently reported. Many other filters are commercially available; however, most of them are linked to data acquisition and/or analysis programs rendering them costly. Depending on the experimental field, the full programs are not always needed. To overcome the need to obtain narrow bands in EEG research and other biological signals in an easy, fast and cheap way, we developed a computer program (FILDIG) that renders an almost ideal in-phase filter in the frequency domain and can be used in all types of personal microcomputers (PC and Mac's) and with few resources. The system uses an interactive graphic display and, with a minimum interface, it is capable of filtering multiple channels and simultaneously obtaining electrical signals (EEG, EMG, EOG, etc.) without noise or specific frequency bands.
Numerical Calculation of Beam Coupling Impedances in the Frequency Domain using FIT
Niedermayer, U
2012-01-01
The transverse impedance of kicker magnets is considered to be one of the main beam instability sources in the projected SIS-100 at FAIR and also in the SPS at CERN. The longitudinal impedance can contribute to the heat load, which is especially a concern in the cold sections of SIS-100 and LHC. In the high frequency range, commercially available time domain codes like CST Particle Studio serve to calculate the impedance but they are inapplicable at medium and low frequencies which become more important for larger size synchrotrons. We present the ongoing work of developing a Finite Integration Technique (FIT) solver in frequency domain which is based on the Parallel and Extensible Toolkit for Scientific computing (PETSc) framework in C++. Proper beam adapted boundary conditions are important to validate the concept. The code is applied to an inductive insert used to compensate the longitudinal space charge impedance in low energy machines. Another application focuses on the impedance contribution of a ferrit...
DEFF Research Database (Denmark)
Borg, Michael; Collu, M.
2015-01-01
The re-emerging interest in vertical axis wind turbines for floating offshore applications has led to a need to investigate the relatively complex dynamics of such floating offshore structures. Through the use of a coupled model of dynamics this article investigates the frequency-domain character......The re-emerging interest in vertical axis wind turbines for floating offshore applications has led to a need to investigate the relatively complex dynamics of such floating offshore structures. Through the use of a coupled model of dynamics this article investigates the frequency-domain...... characteristics of floating vertical axis wind turbine aerodynamic loads. The impact of platform induced motion on aerodynamic loads is discussed in detail, with results indicating an increase in aerodynamic loads of several orders of magnitude over the range of frequencies usually containing significant wave...
Ding, Zhenyang; Yao, X Steve; Liu, Tiegen; Du, Yang; Liu, Kun; Han, Qun; Meng, Zhuo; Chen, Hongxin
2012-12-17
We present a novel method to achieve a space-resolved long- range vibration detection system based on the correlation analysis of the optical frequency-domain reflectometry (OFDR) signals. By performing two separate measurements of the vibrated and non-vibrated states on a test fiber, the vibration frequency and position of a vibration event can be obtained by analyzing the cross-correlation between beat signals of the vibrated and non-vibrated states in a spatial domain, where the beat signals are generated from interferences between local Rayleigh backscattering signals of the test fiber and local light oscillator. Using the proposed technique, we constructed a standard single-mode fiber based vibration sensor that can have a dynamic range of 12 km and a measurable vibration frequency up to 2 kHz with a spatial resolution of 5 m. Moreover, preliminarily investigation results of two vibration events located at different positions along the test fiber are also reported.
Linear systems modeling of adaptive optics in the spatial-frequency domain.
Ellerbroek, Brent L
2005-02-01
Spatial-frequency domain techniques have traditionally been applied to obtain estimates for the independent effects of a variety of individual error sources in adaptive optics (AO). Overall system performance is sometimes estimated by introducing the approximation that these individual error terms are statistically independent, so that their magnitudes may be summed in quadrature. More accurate evaluation methods that account for the correlations between the individual error sources have required Monte Carlo simulations or large matrix calculations that can take much longer to compute, particularly as the order of the AO system increases beyond a few hundred degrees of freedom. We describe an approach to evaluating AO system performance in the spatial-frequency domain that is relatively computationally efficient but still accounts for many of the interactions between the fundamental error sources in AO. We exploit the fact that (in the limits of an infinite aperture and geometrical optics) all the basic wave-front propagation, sensing, and correction processes that describe the behavior of an AO system are spatial-filtering operations in the Fourier domain. Essentially all classical wave-front control algorithms and evaluation formulas are expressed in terms of these filters and may therefore be evaluated one spatial-frequency component at a time. Performance estimates for very-high-order AO systems may be obtained in 1 to 2 orders of magnitude less time than needed when detailed simulations or analytical models in the spatial domain are used, with a relative discrepancy of 5% to 10% for typical sample problems.
Estimation of tire-road friction coefficient based on frequency domain data fusion
Chen, Long; Luo, Yugong; Bian, Mingyuan; Qin, Zhaobo; Luo, Jian; Li, Keqiang
2017-02-01
Due to the noise of sensing equipment, the tire states, such as the sideslip angle and the slip ratio, cannot be accurately observed under the conditions with small acceleration, which results in the inapplicability of the time domain data based tire-road friction coefficient (TRFC) estimation method. In order to overcome this shortcoming, frequency domain data fusion is proposed to estimate the TRFC based on the natural frequencies of the steering system and the in-wheel motor driving system. Firstly, a relationship between TRFC and the steering system natural frequency is deduced by investigating its frequency response function (FRF). Then the lateral TRFC is determined by the steering natural frequency which is only identified using the information of the assist motor current and the steering speed of the column. With spectral comparison between the steering and driving systems, the data fusion is carried out to get a comprehensive TRFC result, using the different frequency information of the longitudinal and lateral value. Finally, simulations and experiments on different road surfaces validated the correctness of the steering system FRF and the effectiveness of the proposed approach.
Bilateral collicular interaction: modulation of auditory signal processing in frequency domain.
Cheng, L; Mei, H-X; Tang, J; Fu, Z-Y; Jen, P H-S; Chen, Q-C
2013-04-01
In the ascending auditory pathway, the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from a variety of lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and the auditory cortex. All these connections make the IC a major center for subcortical temporal and spectral integration of auditory information. In this study, we examine bilateral collicular interaction in the modulation of frequency-domain signal processing of mice using electrophysiological recording and focal electrical stimulation. Focal electrical stimulation of neurons in one IC produces widespread inhibition and focused facilitation of responses of neurons in the other IC. This bilateral collicular interaction decreases the response magnitude and lengthens the response latency of inhibited IC neurons but produces an opposite effect on the response of facilitated IC neurons. In the frequency domain, the focal electrical stimulation of one IC sharpens or expands the frequency tuning curves (FTCs) of neurons in the other IC to improve frequency sensitivity and the frequency response range. The focal electrical stimulation also produces a shift in the best frequency (BF) of modulated IC (ICMdu) neurons toward that of electrically stimulated IC (ICES) neurons. The degree of bilateral collicular interaction is dependent upon the difference in the BF between the ICES neurons and ICMdu neurons. These data suggest that bilateral collicular interaction is a part of dynamic acoustic signal processing that adjusts and improves signal processing as well as reorganizes collicular representation of signal parameters according to the acoustic experience.
Joglekar, D. M.; Mitra, Mira
2017-02-01
The nonlinear interaction of a dual frequency flexural wave with a breathing crack generates a peculiar frequency mixing phenomena, which is manifested in form of the side bands or peaks at combinations frequencies in frequency spectrum of the response. Although these peaks have been proven useful in ascertaining the presence of crack, they barely carry any information about the crack location. In this regards, the present article analyzes the time domain representation of the response obtained by employing a wavelet spectral finite element method. The study reveals that the combination tones generated at the crack location travel with dissimilar speeds along the waveguide, owing to its dispersive nature. The separation between the lobes corresponding to these combination tones therefore, depends on the distance that they have travelled. This observation is then used to formulate a method to predict the crack location with respect to the sensor. A brief parametric study shows marginal errors in predicting the crack location, which ascertains the validity of the method. This article also studies the frequency spectrum of the response. The peaks at combination tones are quantified in terms of a modulate parameter which depends on the severity of the crack. The inferences drawn from the time and the frequency domain study can be instrumental in designing a robust strategy for detecting location and severity of the crack.
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.
Simulation of power fluctuation of wind farms based on frequency domain
DEFF Research Database (Denmark)
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...... 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...
Frequency-domain imaging algorithm for ultrasonic testing by application of matrix phased arrays
Directory of Open Access Journals (Sweden)
Dolmatov Dmitry
2017-01-01
Full Text Available Constantly increasing demand for high-performance materials and systems in aerospace industry requires advanced methods of nondestructive testing. One of the most promising methods is ultrasonic imaging by using matrix phased arrays. This technique allows to create three-dimensional ultrasonic imaging with high lateral resolution. Further progress in matrix phased array ultrasonic testing is determined by the development of fast imaging algorithms. In this article imaging algorithm based on frequency domain calculations is proposed. This approach is computationally efficient in comparison with time domain algorithms. Performance of the proposed algorithm was tested via computer simulations for planar specimen with flat bottom holes.
Kumar, Sunil; Kamaraju, N; Karthikeyan, B; Tondusson, M; Freysz, E; Sood, A K
2010-07-01
Terahertz time domain spectroscopy has been used to study low frequency confined acoustic phonons of silver nanoparticles embedded in poly(vinyl alcohol) matrix in the spectral range of 0.1-2.5 THz. The real and imaginary parts of the dielectric function show two bands at 0.60 and 2.12 THz attributed to the spheroidal and toroidal modes of silver nanoparticles, thus demonstrating the usefulness of terahertz time domain spectroscopy as a complementary technique to Raman spectroscopy in characterizing the nanoparticles.
Rolling element bearing faults diagnosis based on kurtogram and frequency domain correlated kurtosis
Gu, Xiaohui; Yang, Shaopu; Liu, Yongqiang; Hao, Rujiang
2016-12-01
Envelope analysis is one of the most useful methods in localized fault diagnosis of rolling element bearings. However, there is a challenge in selecting the optimal resonance band. In this paper, a novel method based on kurtogram and frequency domain correlated kurtosis is proposed. To obtain the correct relationship between the node and frequency band in wavelet packet transform, a vital process named frequency ordering is conducted to solve the frequency folding problem due to down sampling. Correlated kurtosis of envelope spectrum instead of correlated kurtosis of envelope signal or kurtosis of envelope spectrum is utilized to generate the kurtogram, in which the maximum value can indicate the optimal band for envelope analysis. Several cases of experimental bearing fault signals are used to evaluate the immunity of the proposed method to strong noise interference. The improved performance has also been compared with two previous developed methods. The results demonstrate the effectiveness and robustness of the method in fault diagnosis of rolling element bearings.
Visco-acoustic transmission waveform inversion of velocity structure in space-frequency domain
Institute of Scientific and Technical Information of China (English)
Guihua Long; Xiaofan Li; Meigen Zhang; Tong Zhu
2009-01-01
According to the least square criterion of minimizing the misfit between modeled and observed data, this paper provides a preconditioned gradient method to invert the visco-acoustic velocity structure on the basis of using sparse matrix LU factorization technique to directly solve the visco-acoustic wave forward problem in space-frequency domain. Numerical results obtained in an inclusion model inversion and a layered homogeneous model inversion demonstrate that different scale media have their own frequency responses, and the strategy of using low-frequency inverted result as the starting model in the high-frequency inversion can greatly reduce the non-uniqueness of their solutions. It can also be observed in the experi-ments that the fast convergence of the algorithm can be achieved by using diagonal elements of Hessian matrix as the pre-conditioned operator, which fully incorporates the advantage of quadratic convergence of Gauss-Newton method.
Lu, Lidong; Sun, Xiaoyan; Bu, Xiande; Li, Binglin
2017-02-01
A scheme using timed random frequency hopping and signal logarithmic mean method is proposed and experimentally demonstrated in a coherent optical time domain reflectometry (OTDR) system to reduce the fading noise of the OTDR trace and simplify the signal processing procedure. The timed random frequency hopping is realized by randomly changing the driving current of the laser at certain time points. By this method, the fading noise of OTDR trace can be reduced to be 1/5 of that without using it. Also, a radio frequency power detector (RFPD), whose output voltage has linear relationship with the input logarithmic RF power, is used to extract the power of the RF signals from the balanced photodetector. Then, a data acquisition card directly captures and adds the digital voltage signals from the RFPD to reduce the fading noise and improve the measurement dynamic range. Compared with synchronous and asynchronous frequency hopping scheme, the proposed method is of high efficiency.
Energy Technology Data Exchange (ETDEWEB)
Li Guoyu; Li Yan [Institute of Information Engineering, Handan College, Handan, 056005 (China); Zhao Peng, E-mail: guoyu_li@yahoo.cn [School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China)
2011-02-01
In optical frequency domain reflectometry (OFDR) system, the spatial resolution is obtained by using the total frequency-sweep span of the tunable laser. However, in practice, the spatial resolution is severely limited by nonlinearity in the lightwave-frequency sweep of the tunable laser. A closed-loop PZT modulated DBR linear fiber laser is proposed to improve the spatial resolution of the OFDR system. Experimental results show that the spatial resolution of OFDR system has improved greatly. When the frequency sweep excursion is 66GHz and the fiber under test (FUT) is 7 m, the OFDR system has a spatial resolution of 1.5 m with open-loop PZT modulated laser. But the spatial resolution increases to 35 cm with closed-loop PZT modulated laser.
DEFF Research Database (Denmark)
Pittalà, Fabio; Hauske, Fabian N.; Ye, Yabin;
2011-01-01
CD and DGD monitoring from Frequency- Domain Zero-Forcing and MMSE filter functions adapted with the aid of short CAZAC training sequences is demonstrated.......CD and DGD monitoring from Frequency- Domain Zero-Forcing and MMSE filter functions adapted with the aid of short CAZAC training sequences is demonstrated....
Microwave signal processing in two-frequency domain for ROF systems implementation: training course
Morozov, Oleg G.; Morozov, Gennady A.
2014-04-01
This article is presented materials from two tutorials: "Optical two-frequency domain reflectometry1, 2" and "Microwave technologies in industry, living systems and telecommunications3". These materials were prepared for master training courses and listed in the "SPIE Optical Education Directory" for 2013/2014. The main its theme is microwave photonics. Microwave photonics has been defined as the study of photonic devices operating at microwave frequencies and their application to microwave and optical systems. Its initial rationale was to use the advantages of photonic technologies to provide functions in microwave systems that are very complex or even impossible to carry out directly in the radiofrequency domain. But microwave photonics is also succeeding in incorporating a variety of techniques used in microwave engineering to improve the performance of photonic communication networks and systems. Three parts of this chapter are devoted to applications and construction principles of systems forming microwave photonic filters, measuring instantaneous frequency of microwave heterodyne signals and characterizing stimulated Mandelstam- Brillouin scattering spectrum in ROF systems. The main emphasis is on the use of the two-frequency symmetric radiation, generated by the Il'in-Morozov's method4, in given systems. It is forming radiation for the synthesis of optical filters coefficients, it's application and processing determine the increase in the signal-to-noise ratio during heterodyne frequencies monitoring and characterization of nonlinear effects spectrum.
Reducing Dataset Size in Frequency Domain for Brain Computer Interface Motor Imagery Classification
Directory of Open Access Journals (Sweden)
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.
The research on recognition and extraction of river feature in IKNOS based on frequency domain
Wang, Ke; Feng, Xuezhi; Xiao, Pengfeng; Wu, Guoping
2009-10-01
Because the resolution of remotely sensed imagery becomes higher, new methods are introduced to process the high-resolution remotely sensed imagery. The algorithms introduced in this paper to recognize and extract the river features based on the frequency domain. This paper uses the Gabor filter in frequency domain to enhance the texture of river and remove the noise from remotely sensed imagery. And then according to the theory of phase congruency, this paper retrieves the PC of every point such that features such as edge of river, building and farmland in the remotely sensed imagery. Lastly, the skeletal methodology is introduced to determine the edge of river within the help of the trend of river.
Frequency domain stability analysis of nonlinear active disturbance rejection control system.
Li, Jie; Qi, Xiaohui; Xia, Yuanqing; Pu, Fan; Chang, Kai
2015-05-01
This paper applies three methods (i.e., root locus analysis, describing function method and extended circle criterion) to approach the frequency domain stability analysis of the fast tool servo system using nonlinear active disturbance rejection control (ADRC) algorithm. Root locus qualitative analysis shows that limit cycle is generated because the gain of the nonlinear function used in ADRC varies with its input. The parameters in the nonlinear function are adjustable to suppress limit cycle. In the process of root locus analysis, the nonlinear function is transformed based on the concept of equivalent gain. Then, frequency domain description of the nonlinear function via describing function is presented and limit cycle quantitative analysis including estimating prediction error is presented, which virtually and theoretically demonstrates that the describing function method cannot guarantee enough precision in this case. Furthermore, absolute stability analysis based on extended circle criterion is investigated as a complement.
Spatial and frequency domain interferometry using the MU radar - A tutorial and recent developments
Fukao, Shoichiro; Palmer, Robert D.
Fundamental notions of spatial and frequency-domain interferometry are reviewed, and a novel method is proposed for steering the antenna beam after the data are stored. Also presented is a comparison of techniques for wind-vector determination with emphasis given to a method based on the linear variation of the phase of the cross-spectra. Recent applications of spatial interferometry (SI) and frequency-domain interferometry (FDI) are listed including an implementation of FDI with MU radar. The vertical wind velocity estimated from the Doppler technique is shown to be a measure of the wind perpendicular to tilted refractivity surfaces. The bias generated by horizontal wind is found to have a significant effect on the Doppler estimate in SI. The use of MU radar in FDI can facilitate measurements of the positions of high reflectivity layers smaller than the resolution volume.
Frequency domain volume rendering by the wavelet X-ray transform.
Westenberg, M A; Roerdink, J 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 or cubic spline interpolation. Various combinations are tested and compared with wavelet splatting (WS). We use medical MR and CT scan data, as well as a 3-D analytical phantom to assess the accuracy, time complexity, and memory cost of both FWVR and WS. The differences between both methods are enumerated.
Performance of Spatial Division Multiplexing MIMO with Frequency Domain Packet Scheduling
DEFF Research Database (Denmark)
Wei, Na; Pokhariyal, Akhilesh; Sørensen, Troels Bundgaard;
2008-01-01
This paper addresses the performance of Spatial Division Multiplexing (SDM) Multiple-input Multiple-output (MIMO) techniques together with Frequency Domain Packet Scheduling (FDPS) in both theory and practice. We start with a theoretical analysis under some ideal assumptions to derive the perform......This paper addresses the performance of Spatial Division Multiplexing (SDM) Multiple-input Multiple-output (MIMO) techniques together with Frequency Domain Packet Scheduling (FDPS) in both theory and practice. We start with a theoretical analysis under some ideal assumptions to derive...... is to investigate the impact of realistic factors on performance. Results confirm that the combination of SDM and FDPS can increase the spectral efficiency significantly, particularly in a micro-cell scenario, and up to 30%-60% gain is observed over 1x2 with FDPS depending on the traffic models considered. Finally...
On the convergence and causality of a frequency domain method for dynamic structural analysis
Institute of Scientific and Technical Information of China (English)
Kuifu Chen; Senwen Zhang
2006-01-01
Venanico-Filho et al.developed an elegant matrix formulation for dynamic analysis by frequency domain (FD),but the convergence,causality and extended period need further refining.In the present Paper,it was argued that:(1) under reasonable assumptions (approximating the frequency response function by the discrete Fourier transform of the discretized unitary impulse response function),the matrix formulation by FD is equivalent to a circular convolution;(2) to avoid the wraparound Interference,the excitation vector and impulse response must be padded with enough zeros:(3) provided that the zero padding requirement satisfied,the convergence and accuracy of direct time domain analysis,which is equivalent to that by FD,are guaranteed by the numerical integration scheme;(4) the imaginary part of the computational response approaching zero is due to the continuity of the impulse response functions.
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...
Zhou, Si-Da; Heylen, Ward; Sas, Paul; Liu, Li
2014-05-01
This paper investigates the problem of modal parameter estimation of time-varying structures under unknown excitation. A time-frequency-domain maximum likelihood estimator of modal parameters for linear time-varying structures is presented by adapting the frequency-domain maximum likelihood estimator to the time-frequency domain. The proposed estimator is parametric, that is, the linear time-varying structures are represented by a time-dependent common-denominator model. To adapt the existing frequency-domain estimator for time-invariant structures to the time-frequency methods for time-varying cases, an orthogonal polynomial and z-domain mapping hybrid basis function is presented, which has the advantageous numerical condition and with which it is convenient to calculate the modal parameters. A series of numerical examples have evaluated and illustrated the performance of the proposed maximum likelihood estimator, and a group of laboratory experiments has further validated the proposed estimator.
Institute of Scientific and Technical Information of China (English)
蔡阳健; 林强
2002-01-01
The generalized Collins formula for partially coherent beams through axially non-symmetrical optical systems in the spatial-frequency domain is derived by means of the tensor method. Based on this formula, the tensor ABCD law in the spatial-frequency domain for partially coherent twisted anisotropic Gaussian-Schell model (GSM) beams is derived, which governs the transformation of the twisted anisotropic GSM beams in the spatialfrequency domain. An example of an application is provided.
A Novel Absorbing Boundary Condition for the Frequency-DependentFinite-Difference Time-Domain Method
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A new absorbing boundary condition (ABC) for frequency-dependent finite-difference time-domain algorithm for the arbitrary dispersive media is presented. The concepts of the digital systems are introduced to the (FD)2TD method. On the basis of digital filter designing and vector algebra, the absorbing boundary condition under arbitrary angle of incidence are derived. The transient electromagnetic problems in two-dimensions and three-dimensions are calculated and the validity of the ABC is verified.
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 ...
Design of UWB pulse radio transceiver using statistical correlation technique in frequency domain
Directory of Open Access Journals (Sweden)
M. Anis
2007-06-01
Full Text Available In this paper, we propose a new technique to extract low power UWB pulse radio signals, near to noise level, using statistical correlation technique in frequency domain. The receiver consists of many narrow bandpass filters which extract energy either from transmitted UWB signal, interfering channels or noise. Transmitted UWB data can be eliminated by statistical correlation of multiple bandpass filter outputs. Super-regenerative oscillators, tuned within UWB spectrum, are designed as bandpass filters. Summers and comparators perform statistical correlation.
Frequency-domain photoacoustic phased array probe for biomedical imaging applications.
Telenkov, Sergey; Alwi, Rudolf; Mandelis, Andreas; Worthington, Arthur
2011-12-01
We report the development of a frequency-domain biomedical photoacoustic imaging system that utilizes a continuous-wave laser source with a custom intensity modulation pattern, ultrasonic phased array for signal detection, and processing coupled with a beam-forming algorithm for reconstruction of photoacoustic correlation images. Sensitivity to optical contrast was demonstrated using tissue-mimicking phantoms and in-vivo tissue samples.
A frequency-spatial domain decomposition (FSDD) method for operational modal analysis
Zhang, Lingmi; Wang, Tong; Tamura, Yukio
2010-07-01
Following a brief review of the development of operational modal identification techniques, we describe a new method named frequency-spatial domain decomposition (FSDD), with theoretical background, formulation and algorithm. Three typical applications to civil engineering structures are presented to demonstrate the procedure and features of the method: a large-span stadium roof for finite-element model verification, a highway bridge for damage detection and a long-span cable-stayed bridge for structural health monitoring.
DEFF Research Database (Denmark)
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...
Suspension parameter estimation in the frequency domain using a matrix inversion approach
Thite, A. N.; Banvidi, S.; Ibicek, T.; Bennett, L.
2011-12-01
The dynamic lumped parameter models used to optimise the ride and handling of a vehicle require base values of the suspension parameters. These parameters are generally experimentally identified. The accuracy of identified parameters can depend on the measurement noise and the validity of the model used. The existing publications on suspension parameter identification are generally based on the time domain and use a limited degree of freedom. Further, the data used are either from a simulated 'experiment' or from a laboratory test on an idealised quarter or a half-car model. In this paper, a method is developed in the frequency domain which effectively accounts for the measurement noise. Additional dynamic constraining equations are incorporated and the proposed formulation results in a matrix inversion approach. The nonlinearities in damping are estimated, however, using a time-domain approach. Full-scale 4-post rig test data of a vehicle are used. The variations in the results are discussed using the modal resonant behaviour. Further, a method is implemented to show how the results can be improved when the matrix inverted is ill-conditioned. The case study shows a good agreement between the estimates based on the proposed frequency-domain approach and measurable physical parameters.
Directory of Open Access Journals (Sweden)
Pei-Chen Lin
2016-02-01
Full Text Available In the ICU, fluid therapy is conventional strategy for the patient in shock. However, only half of ICU patients have well-responses to fluid therapy, and fluid loading in non-responsive patient delays definitive therapy. Prediction of fluid responsiveness (FR has become intense topic in clinic. Most of conventional FR prediction method based on time domain analysis, and it is limited ability to indicate FR. This study proposed a method which predicts FR based on frequency domain analysis, named instantaneous pulse rate variability (iPRV. iPRV provides a new indication in very high frequency (VHF range (0.4-0.8Hz of spectrum for peripheral responses. Twenty six healthy subjects participated this study and photoplethysmography signal was recorded in supine baseline, during head-up tilt (HUT, and passive leg raising (PLR, which induces variation of venous return and helps for quantitative assessment of FR individually. The result showed the spectral power of VHF decreased during HUT (573.96±756.36 ms2 in baseline; 348.00±434.92 ms2 in HUT and increased during PLR (573.96±756.36 ms2 in baseline; 718.92±973.70 ms2 in PLR, which present the compensated regulation of venous return and FR. This study provides an effective indicator for assessing FR in frequency domain and has potential to be a reliable system in ICU.
Quantifying Stability Using Frequency Domain Data from Wireless Inertial Measurement Units
Directory of Open Access Journals (Sweden)
Stephen Slaughter
2012-08-01
Full Text Available The quantification of gait stability can provide valuable information when evaluating subjects for age related and neuromuscular disease changes. Using tri-axial inertial measurement units (IMU for acceleration and rotational data provide a non-linear profile for this type of movement. As subjects traverse various surfaces representing decreasing stability, the different phasing of gait data make comparisons difficult. By converting from time to frequency domain data, the phase effects can be ignored, allowing for significant correlations. In this study, 12 subjects provided gait information over various surfaces while wearing an IMU. Instabilities were determined by comparing frequency domain data over less stable surfaces to frequency domain data of neural network (NN models representing the normal gait for any given participant. Time dependent data from 2 axes of acceleration and 2 axes of rotation were converted using a discrete Fourier transform (FFT algorithm. The data over less stable surfaces were compared to the normal gait NN model by averaging the Pearson product moment correlation (r values. This provided a method to quantify the decreased stability. Data showed progressively decreasing correlation coefficient values as subjects encountered progressively less stable surface environments. This methodology has allowed for the quantification of instability in gait situations for application in real-time fall prevention situations.
Single trial time-frequency domain analysis of error processing in post-traumatic stress disorder.
Clemans, Zachary A; El-Baz, Ayman S; Hollifield, Michael; Sokhadze, Estate M
2012-09-13
Error processing studies in psychology and psychiatry are relatively common. Event-related potentials (ERPs) are often used as measures of error processing, two such response-locked ERPs being the error-related negativity (ERN) and the error-related positivity (Pe). The ERN and Pe occur following committed error in reaction time tasks as low frequency (4-8 Hz) electroencephalographic (EEG) oscillations registered at the midline fronto-central sites. We created an alternative method for analyzing error processing using time-frequency analysis in the form of a wavelet transform. A study was conducted in which subjects with PTSD and healthy control completed a forced-choice task. Single trial EEG data from errors in the task were processed using a continuous wavelet transform. Coefficients from the transform that corresponded to the theta range were averaged to isolate a theta waveform in the time-frequency domain. Measures called the time-frequency ERN and Pe were obtained from these waveforms for five different channels and then averaged to obtain a single time-frequency ERN and Pe for each error trial. A comparison of the amplitude and latency for the time-frequency ERN and Pe between the PTSD and control group was performed. A significant group effect was found on the amplitude of both measures. These results indicate that the developed single trial time-frequency error analysis method is suitable for examining error processing in PTSD and possibly other psychiatric disorders.
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
Time and Frequency-Domain Cross-Verification of SLS 6DOF Trajectory Simulations
Johnson, Matthew; McCullough, John
2017-01-01
The Space Launch System (SLS) Guidance, Navigation, and Control (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
Design of a multivariable RF control system using gain-shaping in the frequency domain
Ziomek, C. D.; Jachim, S. P.; Natter, E. F.
1991-05-01
Due to the time-varying nature of the radio-frequency (RF) accelerator, RF field amplitude and phase parameters must be precisely controlled in order to confine and accelerate the charged particle beam. Typically, a feedback control system regulates the RF field, rejects noise and disturbances, and maintains operational stability over changes in the electrical structure of the accelerator. This paper describes a multivariable control system that compensates the electrical structure of the accelerator by using gain-shaping in the frequency domain. The amplitude and phase quantities have been resolved into in-phase and quadrature (I and Q) variables. These orthogonal variables have simple mathematical relationships, and can be analyzed using linear transfer function matrices. The transfer matrix theory has been applied to the design of the multivariable control system that regulates the RF field in-phase and quadrature components. Frequency-domain controllers compensate these two signals to provide desired frequency response characteristics. A control predistorter performs an inverse coupling function, so that the I and Q components are effectively decoupled by the accelerator. Furthermore, computer interface circuitry allows the adaptive optimization of the mathematical transfer functions of the compensators.
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.
Photon acceleration versus frequency-domain interferometry for laser wakefield diagnostics
Energy Technology Data Exchange (ETDEWEB)
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)
Identification of the Swiss Z24 Highway Bridge by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, P.
2002-01-01
This paper presents the result of the modal identification of the Swiss highway bridge Z24. A series of 15 progressive damage tests were performed on the bridge before it was demolished in autumn 1998, and the ambient response of the bridge was recorded for each damage case. In this paper the modal...... properties are identified from the ambient responses by frequency domain decomposition. 6 modes were identified for all 15 damage cases. The identification was carried out for the full 3D data case i.e. including all measurements, a total of 291 channels, a reduced data case in 2D including 153 channels......, and finally, a 1D case including 20 channels. The modal properties for the different damage cases are compared with the modal properties of the undamaged bridge. Deviations for frequencies, damping ratios and MAC values are used as monitoring variables. From these results it can be concluded, that frequencies...
Spectral evolution of two-dimensional kinetic plasma turbulence in the wavenumber-frequency domain
Comişel, H; Narita, Y; Motschmann, U
2013-01-01
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 Alfv\\'en/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.
Resolution enhancement of robust Bayesian pre-stack inversion in the frequency domain
Yin, Xingyao; Li, Kun; Zong, Zhaoyun
2016-10-01
AVO/AVA (amplitude variation with an offset or angle) inversion is one of the most practical and useful approaches to estimating model parameters. So far, publications on AVO inversion in the Fourier domain have been quite limited in view of its poor stability and sensitivity to noise compared with time-domain inversion. For the resolution and stability of AVO inversion in the Fourier domain, a novel robust Bayesian pre-stack AVO inversion based on the mixed domain formulation of stationary convolution is proposed which could solve the instability and achieve superior resolution. The Fourier operator will be integrated into the objective equation and it avoids the Fourier inverse transform in our inversion process. Furthermore, the background constraints of model parameters are taken into consideration to improve the stability and reliability of inversion which could compensate for the low-frequency components of seismic signals. Besides, the different frequency components of seismic signals can realize decoupling automatically. This will help us to solve the inverse problem by means of multi-component successive iterations and the convergence precision of the inverse problem could be improved. So, superior resolution compared with the conventional time-domain pre-stack inversion could be achieved easily. Synthetic tests illustrate that the proposed method could achieve high-resolution results with a high degree of agreement with the theoretical model and verify the quality of anti-noise. Finally, applications on a field data case demonstrate that the proposed method could obtain stable inversion results of elastic parameters from pre-stack seismic data in conformity with the real logging data.
Phase Analysis for Frequency Standards in the Microwave and Optical Domains.
Kazda, Michael; Gerginov, Vladislav; Huntemann, Nils; Lipphardt, Burghard; Weyers, Stefan
2016-07-01
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 field-programmable gate array (FPGA)-based phase analyzer to investigate these effects and conducted measurements on two kinds of frequency standards. For the caesium fountains PTB-CSF1 and PTB-CSF2, we were able to exclude phase variations of the microwave source at the level of a few microradians, corresponding to relative frequency shifts of less than [Formula: see text]. In the optical domain, we investigated phase variations in PTB's Yb (+) optical frequency standard and made detailed measurements of acousto-optic modulator (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 larger than [Formula: see text].
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...
Eriksen, Vibeke R.; Hahn, Gitte H.; Greisen, Gorm
2015-03-01
The aim was to compare two conventional methods used to describe cerebral autoregulation (CA): frequency-domain analysis and time-domain analysis. We measured cerebral oxygenation (as a surrogate for cerebral blood flow) and mean arterial blood pressure (MAP) in 60 preterm infants. In the frequency domain, outcome variables were coherence and gain, whereas the cerebral oximetry index (COx) and the regression coefficient were the outcome variables in the time domain. Correlation between coherence and COx was poor. The disagreement between the two methods was due to the MAP and cerebral oxygenation signals being in counterphase in three cases. High gain and high coherence may arise spuriously when cerebral oxygenation decreases as MAP increases; hence, time-domain analysis appears to be a more robust-and simpler-method to describe CA.
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
Directory of Open Access Journals (Sweden)
Qiuming Cheng
2007-06-01
Full Text Available The patterns shown on two-dimensional images (fields used in geosciences reflect the end products of geo-processes that occurred on the surface and in the subsurface of the Earth. Anisotropy of these types of patterns can provide information useful for interpretation of geo-processes and identification of features in the mapped area. Quantification of the anisotropy property is therefore essential for image processing and interpretation. This paper introduces several techniques newly developed on the basis of multifractal modeling in space, Fourier frequency, and eigen domains, respectively. A singularity analysis method implemented in the space domain can be used to quantify the intensity and anisotropy of local singularities. The second method, called S-A, characterizes the generalized scale invariance property of a field in the Fourier frequency domain. The third method characterizes the field using a power-law model on the basis of eigenvalues and eigenvectors of the field. The applications of these methods are demonstrated with a case study of Environment Scan Electric Microscope (ESEM microimages for identification of sphalerite (ZnS ore minerals from the Jinding Pb/Zn/Ag mineral deposit in Shangjiang District, Yunnan Province, China.
Directory of Open Access Journals (Sweden)
Maria Romano
2016-01-01
Full Text Available Monitoring of foetal heart rate and its variability (FHRV covers an important role in assessing health of foetus. Many analysis methods have been used to get quantitative measures of FHRV. FHRV has been studied in time and in frequency domain and interesting clinical results have been obtained. Nevertheless, a standardized definition of FHRV and a precise methodology to be used for its evaluation are lacking. We carried out a literature overview about both frequency domain analysis (FDA and time domain analysis (TDA. Then, by using simulated FHR signals, we defined the methodology for FDA. Further, employing more than 400 real FHR signals, we analysed some of the most common indexes, Short Term Variability for TDA and power content of the spectrum bands and sympathovagal balance for FDA, and evaluated their ranges of values, which in many cases are a novelty. Finally, we verified the relationship between these indexes and two important parameters: week of gestation, indicator of foetal growth, and foetal state, classified as active or at rest. Our results indicate that, according to literature, it is necessary to standardize the procedure for FHRV evaluation and to consider week of gestation and foetal state before FHR analysis.
Automated frequency domain analysis of oxygen saturation as a screening tool for SAHS.
Morillo, Daniel Sánchez; Gross, Nicole; León, Antonio; Crespo, Luis F
2012-09-01
Sleep apnea-hypopnea syndrome (SAHS) is significantly underdiagnosed and new screening systems are needed. The analysis of oxygen desaturation has been proposed as a screening method. However, when oxygen saturation (SpO(2)) is used as a standalone single channel device, algorithms working in time domain achieve either a high sensitivity or a high specificity, but not usually both. This limitation arises from the dependence of time-domain analysis on absolute SpO(2) values and the lack of standardized thresholds defined as pathological. The aim of this study is to assess the degree of concordance between SAHS screening using offline frequency domain processing of SpO(2) signals and the apnea-hypopnea index (AHI), and the diagnostic performance of such a new method. SpO(2) signals from 115 subjects were analyzed. Data were divided in a training data set (37) and a test set (78). Power spectral density was calculated and related to the desaturation index scored by physicians. A frequency desaturation index (FDI) was then estimated and its accuracy compared to the classical desaturation index and to the apnea-hypopnea index. The findings point to a high diagnostic agreement: the best sensitivity and specificity values obtained were 83.33% and 80.44%, respectively. Moreover, the proposed method does not rely on absolute SpO(2) values and is highly robust to artifacts.
Frequency domain analysis of errors in cross-correlations of ambient seismic noise
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2016-12-01
We analyse random errors (variances) in cross-correlations of ambient seismic noise in the frequency domain, which differ from previous time domain methods. Extending previous theoretical results on ensemble averaged cross-spectrum, we estimate confidence interval of stacked cross-spectrum of finite amount of data at each frequency using non-overlapping windows with fixed length. The extended theory also connects amplitude and phase variances with the variance of each complex spectrum value. Analysis of synthetic stationary ambient noise is used to estimate the confidence interval of stacked cross-spectrum obtained with different length of noise data corresponding to different number of evenly spaced windows of the same duration. This method allows estimating Signal/Noise Ratio (SNR) of noise cross-correlation in the frequency domain, without specifying filter bandwidth or signal/noise windows that are needed for time domain SNR estimations. Based on synthetic ambient noise data, we also compare the probability distributions, causal part amplitude and SNR of stacked cross-spectrum function using one-bit normalization or pre-whitening with those obtained without these pre-processing steps. Natural continuous noise records contain both ambient noise and small earthquakes that are inseparable from the noise with the existing pre-processing steps. Using probability distributions of random cross-spectrum values based on the theoretical results provides an effective way to exclude such small earthquakes, and additional data segments (outliers) contaminated by signals of different statistics (e.g. rain, cultural noise), from continuous noise waveforms. This technique is applied to constrain values and uncertainties of amplitude and phase velocity of stacked noise cross-spectrum at different frequencies, using data from southern California at both regional scale (˜35 km) and dense linear array (˜20 m) across the plate-boundary faults. A block bootstrap resampling method
Hein, Annette; Larsen, Jakob Juul; Parsekian, Andrew D.
2017-02-01
Surface nuclear magnetic resonance (NMR) is a unique geophysical method due to its direct sensitivity to water. A key limitation to overcome is the difficulty of making surface NMR measurements in environments with anthropogenic electromagnetic noise, particularly constant frequency sources such as powerlines. Here we present a method of removing harmonic noise by utilizing frequency domain symmetry of surface NMR signals to reconstruct portions of the spectrum corrupted by frequency-domain noise peaks. This method supplements the existing NMR processing workflow and is applicable after despiking, coherent noise cancellation, and stacking. The symmetry based correction is simple, grounded in mathematical theory describing NMR signals, does not introduce errors into the data set, and requires no prior knowledge about the harmonics. Modelling and field examples show that symmetry based noise removal reduces the effects of harmonics. In one modelling example, symmetry based noise removal improved signal-to-noise ratio in the data by 10 per cent. This improvement had noticeable effects on inversion parameters including water content and the decay constant T2*. Within water content profiles, aquifer boundaries and water content are more accurate after harmonics are removed. Fewer spurious water content spikes appear within aquifers, which is especially useful for resolving multilayered structures. Within T2* profiles, estimates are more accurate after harmonics are removed, especially in the lower half of profiles.
Directory of Open Access Journals (Sweden)
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.
Directory of Open Access Journals (Sweden)
Hanus Robert
2016-01-01
Full Text Available 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.
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.
Institute of Scientific and Technical Information of China (English)
Tang Wei; Shi Zhongke; Chen Jie
2008-01-01
Recently, frequency-based least-squares (LS) estimators have found wide application in identifying aircraft flutter parameters. However, the frequency methods are often known to suffer from numerical difficulties when identifying a continuous-time model, espe-cially, of broader frequency or higher order. In this article, a numerically robust LS estimator based on vector orthogonal polynomial is proposed to solve the numerical problem of multivariable systems and applied to the flutter testing. The key idea of this method is to represent the frequency response function (FRF) matrix by a right matrix fraction description (RMFD) model, and expand the numerator and denominator polynomial matrices on a vector onhogonal basis. As a result, a perfect numerical condition (numerical condition equals 1) can be obtained for linear LS estimator. Finally, this method is verified by flutter test of a wing model in a wind tunnel and real flight flutter test of an aircraft. The results are compared to those with notably LMS PolyMAX, which is not troubled by the numerical problem as it is established in z domain (e.g. derived from a discrete-time model). The verification has evidenced that this method, apart from overcoming the numerical problem, yields the results comparable to those acquired with LMS PolyMAX, or even considerably better at some frequency bands.
Time domain acoustic contrast control implementation of sound zones for low-frequency input signals
DEFF Research Database (Denmark)
Schellekens, Daan H. M.; Møller, Martin Bo; Olsen, Martin
2016-01-01
Sound zones are two or more regions within a listening space where listeners are provided with personal audio. Acoustic contrast control (ACC) is a sound zoning method that maximizes the average squared sound pressure in one zone constrained to constant pressure in other zones. State-of-the-art t......Sound zones are two or more regions within a listening space where listeners are provided with personal audio. Acoustic contrast control (ACC) is a sound zoning method that maximizes the average squared sound pressure in one zone constrained to constant pressure in other zones. State......-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...
Thalmayr, Florian; Hashimoto, Ken-Ya; Omori, Tatsuya; Yamaguchi, Masatsune
2010-07-01
This paper demonstrates a novel frequency domain analysis (FDA) to evaluate the scattering behavior of a waveguide mode at arbitrary scattering geometries by a time harmonic simulation based on the finite element method (FEM). To this end, we add an injection-damping mechanism (IDM) to avoid interference at the acoustic input port. The IDM can be easily constructed by a numerical operation. Our approach offers improved time consumption and calculation power necessary over the established method in the time domain. After checking the validity of the proposed method, we discuss the importance of considering wave scattering phenomena in film bulk acoustic wave resonator (FBAR) devices by applying the proposed method to two simplified models of an FBAR device.
Frequency-domain algorithm for the Lorenz-gauge gravitational self-force
Akcay, Sarp; Barack, Leor
2013-01-01
State-of-the-art computations of the gravitational self-force (GSF) on massive particles in black hole spacetimes involve numerical evolution of the metric perturbation equations in the time-domain, which is computationally very costly. We present here a new strategy, based on a frequency-domain treatment of the perturbation equations, which offers considerable computational saving. The essential ingredients of our method are (i) a Fourier-harmonic decomposition of the Lorenz-gauge metric perturbation equations and a numerical solution of the resulting coupled set of ordinary equations with suitable boundary conditions; (ii) a generalized version of the method of extended homogeneous solutions [Phys. Rev. D {\\bf 78}, 084021 (2008)] used to circumvent the Gibbs phenomenon that would otherwise hamper the convergence of the Fourier mode-sum at the particle's location; and (iii) standard mode-sum regularization, which finally yields the physical GSF as a sum over regularized modal contributions. We present a work...
Multiobjective Optimization for Electronic Circuit Design in Time and Frequency Domains
Directory of Open Access Journals (Sweden)
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
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.
Frequency-domain analysis of intrinsic neuronal properties using high-resistant electrodes
Directory of Open Access Journals (Sweden)
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.
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.
SDCMA BLIND DETECTION IN FREQUENCY DOMAIN FOR MC DS-CDMA SYSTEMS
Institute of Scientific and Technical Information of China (English)
Ju Meiyan; Feng Guangzeng
2006-01-01
This paper proposes Steepest Decreasing Constant Modulus Algorithm (SDCMA) detection in frequency domain for MultiCarrier Direct Sequence-Code Division Multiple Access (MC DS-CDMA) systems.The proposed algorithm is used to equalize independent fadings of all subcarriers. At the same time we compare the SDCMA blind detection with subspace-based Minimum Mean-Squared Error (MMSE) detection. The simulation results show that the performance of SDCMA blind detection is superior to. that of subspace-based MMSE detection and the complexity of the former is much lower than that of the latter.
Nöther, Nils; Wosniok, Aleksander; Krebber, Katerina; Thiele, Elke
2008-03-01
We report on the development of a complete system for spatially resolved detection of critical soil displacement in river embankments. The system uses Brillouin frequency domain analysis (BOFDA) for distributed measurement of strain in silica optical fibers. Our development consists of the measurement unit, an adequate coating for the optical fibers and a technique to integrate the coated optical fibers into geotextiles as they are commonly used in dike construction. We present several laboratory and field tests that prove the capability of the system to detect areas of soil displacement as small as 2 meters. These are the first tests of truly distributed strain measurements on optical fibers embedded into geosynthetics.
Spatial and frequency domain effects of defects in 1D photonic crystal
Rudziński, A; Szczepański, P; 10.1007/s11082-007-9095-3
2009-01-01
The aim of this paper is to present the analysis of influence of defects in 1D photonic crystal (PC) on the density of states and simultaneously spontaneous emission, in both spatial and frequency domains. In our investigations we use an analytic model of 1D PC with defects. Our analysis reveals how presence of a defect causes a defect mode to appear. We show that a defect in 1D PC has local character, being negligible in regions of PC situated far from the defected elementary cell. We also analyze the effect of multiple defects, which lead to photonic band gap splitting.
Frequency domain optical tomography using a conjugate gradient method without line search
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyun Keol [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, P4-3240, Chicoutimi, Quebec, G7H 2B1 (Canada); Charette, Andre [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, P4-3240, Chicoutimi, Quebec, G7H 2B1 (Canada)]. E-mail: andre_charette@uqac.ca
2007-03-15
A conjugate gradient method without line search (CGMWLS) is presented. This method is used to retrieve the local maps of absorption and scattering coefficients inside the tissue-like test medium, with the synthetic data. The forward problem is solved with a discrete-ordinates finite-difference method based on the frequency domain formulation of radiative transfer equation. The inversion results demonstrate that the CGMWLS can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by reducing cross-talk between absorption and scattering coefficients.
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.
Optical frequency domain reflectometry: principles and applications in fiber optic sensing
Kreger, Stephen T.; Rahim, Nur Aida Abdul; Garg, Naman; Klute, Sandra M.; Metrey, Daniel R.; Beaty, Noah; Jeans, James W.; Gamber, Robert
2016-05-01
Optical Frequency Domain Reflectometry (OFDR) is the basis of an emerging high-definition distributed fiber optic sensing (HD-FOS) technique that provides an unprecedented combination of resolution and sensitivity. OFDR employs swept laser interferometry to produce strain or temperature vs. sensor length with fiber Bragg gratings (FBGs) or Rayleigh scatter as the source signal. We look at the influence of HD-FOS on design and test of new, lighter weight, stronger and more fuel efficient vehicles. Examples include defect detection, model verification and structural health monitoring of composites, and temperature distribution monitoring of battery packs and inverters in hybrid and electric powertrains.
Functional cerebral activation detected by frequency-domain near-infrared spectroscopy
Toronov, Vladislav Y.; Webb, Andrew G.; Choi, Jee H.; Wolf, Martin; Safonova, Larisa P.; Wolf, Ursula; Gratton, Enrico
2002-07-01
The aim of our study was to explore the possibility of detecting haemodynamic changes in the brain using frequency- domain near-IR spectroscopy by exploiting the phase of the intensity modulated optical signal. To obtain optical signals with eh highest possible signal-to-noise ratio, we performed simultaneous NIRS-fMRI measurements, with subsequent correlation of the time courses of both measurements. The cognitive paradigm used arithmetic calculations, with optical signals acquired with sensors placed on the forehead. In three subjects we demonstrated correlation between the haemodynamic signals obtained using NIRS and BOLD fMRI.
A Novel Ship Wake Detection Method of SAR Images Based on Frequency Domain
Institute of Scientific and Technical Information of China (English)
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.
Lin, Alexander J.; Konecky, Soren D.; Rice, Tyler B.; Green, Kim N.; Choi, Bernard; Durkin, Anthony J.; Tromberg, Bruce J.
2012-02-01
Early neurovascular coupling (NVC) changes in Alzheimer's disease can potentially provide imaging biomarkers to assist with diagnosis and treatment. Previous efforts to quantify NVC with intrinsic signal imaging have required assumptions of baseline optical pathlength to calculate changes in oxy- and deoxy-hemoglobin concentrations during evoked stimuli. In this work, we present an economical spatial frequency domain imaging (SFDI) platform utilizing a commercially available LED projector, camera, and off-the-shelf optical components suitable for imaging dynamic optical properties. The fast acquisition platform described in this work is validated on silicone phantoms and demonstrated in neuroimaging of a mouse model.
A perspective on single-channel frequency-domain speech enhancement
Benesty, Jacob
2010-01-01
This book focuses on a class of single-channel noise reduction methods that are performed in the frequency domain via the short-time Fourier transform (STFT). The simplicity and relative effectiveness of this class of approaches make them the dominant choice in practical systems. Even though many popular algorithms have been proposed through more than four decades of continuous research, there are a number of critical areas where our understanding and capabilities still remain quite rudimentary, especially with respect to the relationship between noise reduction and speech distortion. All exis
Institute of Scientific and Technical Information of China (English)
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.
Institute of Scientific and Technical Information of China (English)
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.
Frequency-domain Model Matching PID Controller Design for Aero-engine
Liu, Nan; Huang, Jinquan; Lu, Feng
2014-12-01
The nonlinear model of aero-engine was linearized at multiple operation points by using frequency response method. The validation results indicate high accuracy of static and dynamic characteristics of the linear models. The improved PID tuning method of frequency-domain model matching was proposed with the system stability condition considered. The proposed method was applied to the design of PID controller of the high pressure rotor speed control in the flight envelope, and the control effects were evaluated by the nonlinear model. Simulation results show that the system had quick dynamic response with zero overshoot and zero steadystate error. Furthermore, a PID-fuzzy switching control scheme for aero-engine was designed, and the fuzzy switching system stability was proved. Simulations were studied to validate the applicability of the multiple PIDs fuzzy switching controller for aero-engine with wide range dynamics.
An Adaptive Steganographic Method in Frequency Domain Based on Statistical Metrics of Image
Directory of Open Access Journals (Sweden)
Seyyed Amin Seyyedi
2015-05-01
Full Text Available Steganography is a branch of information hiding. A tradeoff between the hiding payload and quality of digital image steganographic schemes is major challenge of the steganographic methods. An adaptive steganographic method for embedding secret message into gray scale images is proposed. Before embedding the secret message, the cover image is transformed into frequency domain by integer wavelet. The middle frequency band of cover image is partitioned into 4×4 non overlapping blocks. The blocks by deviation and entropy metrics are classified into three categories: smooth, edge, and texture regions. Number of bits which can be embedded in a block is defined by block features. Moreover, RC4 encryption method is used to increase secrecy protection. Experimental results denote the feasibility of the proposed method. Statistical tests were conducted to collect related data to verify the security of method.
The frequency domain causality analysis between energy consumption and income in the United States
Directory of Open Access Journals (Sweden)
Aviral Kumar Tiwari
2014-03-01
Full Text Available We investigated Granger-causality in the frequency domain between primary energy consumption/electricity consumption and GDP for the US by employing approach of Lemmens et al. (2008 and covering the period of January, 1973 to December, 2008. We found that causal and reverse causal relations between primary energy consumption and GDP and electricity consumption and GDP vary across frequencies. Our unique contribution in the existing literature lies in decomposing the causality on the basis of time horizons and demonstrating bidirectional the short-run, the medium-run and the long-run causality between GDP and primary energy consumption/electricity consumption and thus providing evidence for the feedback hypothesis. These results have important implications for the US for planning of the short, the medium and the long run energy and economic growth related policies.
Frequency Domain MMSE one-tap Equalizer for FBMC-OQAM System
Directory of Open Access Journals (Sweden)
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.
DEFF Research Database (Denmark)
Pedersen, Pauli; Pedersen, Niels Leergaard
2014-01-01
result has many applications. It is therefore presented before specific use in optimization examples. The engineering approach of fully stressed design is a practical tool with a theoretical foundation. The analog approach to structural eigenfrequency optimization is presented here with its theoretical...... foundation. A numerical heuristic redesign procedure is proposed and illustrated with examples. For the ideal case, an optimality criterion is fulfilled if the design have the same sub-domain frequency (local Rayleigh quotient). Sensitivity analysis shows an important relation between squared system...... on the derived optimality condition. The design that maximize a frequency depend on the total amount of available material and on a necessary interpolation as illustrated by different design cases.In this note we have assumed a linear and conservative eigenvalue problem without multiple eigenvalues. The presence...
Single carrier frequency domain equalization and diversity combining for cooperative systems
Institute of Scientific and Technical Information of China (English)
Xiong Haitao; Xu Jing; Wang Ping
2009-01-01
A low-complexity single carrier frequency-domain equalizer (SC/FDE) and diversity combining method for cooperative systems with demodulate-and-forward relaying over frequency-selective channels is proposed. At the relay nodes, linear SC/FDE is adopted and normalized correlation coefficient is introduced to derive an equivalent source-to-relay-destination (S-R-D) channel that is highlighted in this study. At the destination, a joint SC/FDE and diversity combining receiver is proposed by utilizing the equivalent S-R-D channel. Simulation results demonstrate the superiority of the proposed SC/FDE scheme over the straightforward SC/FDE which ignores the decisions errors at the intermediate relay nodes.
Sauvé, Alexandre; Montier, Ludovic
2016-12-01
Context: Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for ν linearized versions of the bolometer electro thermal equilibrium. A custom description of signals in frequency is used to solve the problem with linear algebra. The model performances is validated using time domain simulations. Results: The provided expression is suitable for calibration and data processing. It can also be used to provide constraints for fitting optical transfer function using real data from steady state electronic response and optical response. The accurate description of electronic response can also be used to improve the ADC nonlinearity correction for quickly varying optical signals.
Use of Time- and Frequency-Domain Approaches for Damage Detection in Civil Engineering Structures
Directory of Open Access Journals (Sweden)
V. H. Nguyen
2014-01-01
Full Text Available The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The methodology is based on Principal Component Analysis of the Hankel matrix built from output-only measurements and of Frequency Response Functions. Damage detection is performed using the concept of subspace angles between a current (possibly damaged state and a reference (undamaged state. The first structure is the Champangshiehl Bridge located in Luxembourg. Several damage levels were intentionally created by cutting a growing number of prestressed tendons and vibration data were acquired by the University of Luxembourg for each damaged state. The second example consists in reinforced and prestressed concrete panels. Successive damages were introduced in the panels by loading heavy weights and by cutting steel wires. The illustrations show different consequences in damage identification by the considered techniques.
A Frequency Domain Approach to Registration of Aliased Images with Application to Super-resolution
Directory of Open Access Journals (Sweden)
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.
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
This letter deals with the frequency domain Blind Source Separation of Convolutive Mixtures(CMBSS).From the frequency representation of the"overlap and save",a Weighted General Discrete Fourier Transform (WGDFT) is derived to replace the traditional Discrete Fourier Transform (DFT).The mixing matrix on each frequency bin could be estimated more precisely from WGDFT coefficients than from DFT coefficients,which improves separation performance.Simulation results verify the validity of WGDFT for frequency domain blind source separation of convolutive mixtures.
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 Assessment of Integration Schemes for Earthquake Engineering Problems
Directory of Open Access Journals (Sweden)
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.
Mid Frequency Shock Response Determination by Using Energy Flow Method and Time Domain Correction
Directory of Open Access Journals (Sweden)
Sung-Hyun Woo
2013-01-01
Full Text Available Shock induced vibration can be more crucial in the mid frequency range where the dynamic couplings with structural parts and components play important roles. To estimate the behavior of structures in this frequency range where conventional analytical schemes, such as statistical energy analysis (SEA and finite element analysis (FEA methods may become inaccurate, many alternative methodologies have been tried up to date. This study presents an effective and practical method to accurately predict transient responses in the mid frequency range without having to resort to the large computational efforts. Specifically, the present study employs the more realistic frequency response functions (FRFs from the energy flow method (EFM which is a hybrid method combining the pseudo SEA equation (or SEA-Like equation and modal information obtained by the finite element analysis (FEA. Furthermore, to obtain the time responses synthesized with modal characteristics, a time domain correction is practiced with the input force signal and the reference FRF on a position of the response subsystem. A numerical simulation is performed for a simple five plate model to show its suitability and effectiveness over the standard analytical schemes.
Detail-preserving construction of neonatal brain atlases in space-frequency domain.
Zhang, Yuyao; Shi, Feng; Yap, Pew-Thian; Shen, Dinggang
2016-06-01
Brain atlases are commonly utilized in neuroimaging studies. However, most brain atlases are fuzzy and lack structural details, especially in the cortical regions. This is mainly caused by the image averaging process involved in atlas construction, which often smoothes out high-frequency contents that capture fine anatomical details. Brain atlas construction for neonatal images is even more challenging due to insufficient spatial resolution and low tissue contrast. In this paper, we propose a novel framework for detail-preserving construction of population-representative atlases. Our approach combines spatial and frequency information to better preserve image details. This is achieved by performing atlas construction in the space-frequency domain given by wavelet transform. In particular, sparse patch-based atlas construction is performed in all frequency subbands, and the results are combined to give a final atlas. For enhancing anatomical details, tissue probability maps are also used to guide atlas construction. Experimental results show that our approach can produce atlases with greater structural details than existing atlases. Hum Brain Mapp 37:2133-2150, 2016. © 2016 Wiley Periodicals, Inc.
Shifting of wrapped phase maps in the frequency domain using a rational number
Gdeisat, Munther A.; Burton, David R.; Lilley, Francis; Arevalillo-Herráez, Miguel; Abushakra, Ahmad; Qaddoura, Maen
2016-10-01
The number of phase wraps in an image can be either reduced, or completely eliminated, by transforming the image into the frequency domain using a Fourier transform, and then shifting the spectrum towards the origin. After this, the spectrum is transformed back to the spatial domain using the inverse Fourier transform and finally the phase is extracted using the arctangent function. However, it is a common concern that the spectrum can be shifted only by an integer number, meaning that the phase wrap reduction is often not optimal. In this paper we propose an algorithm than enables the spectrum to be frequency shifted by a rational number. The principle of the proposed method is confirmed both by using an initial computer simulation and is subsequently validated experimentally on real fringe patterns. The technique may offer in some cases the prospects of removing the necessity for a phase unwrapping process altogether and/or speeding up the phase unwrapping process. This may be beneficial in terms of potential increases in signal recovery robustness and also for use in time-critical applications.
A critical analysis of the Mises stress criterion used in frequency domain fatigue life prediction
Directory of Open Access Journals (Sweden)
Adam Niesłony
2016-10-01
Full Text Available Multiaxial fatigue failure criteria are formulated in time and frequency domain. The number of frequency domain criteria is rather small and the most popular one is the equivalent von Mises stress criterion. This criterion was elaborated by Preumont and Piefort on the basis of well-known von Mises stress concept, first proposed by Huber in 1907, and well accepted by the scientific community and engineers. It is important to know, that the criterion was developed to determine the yield stress and material effort under static load. Therefore the direct use of equivalent von Mises stress criterion for fatigue life prediction can lead to some incorrectness of theoretical and practical nature. In the present study four aspects were discussed: influence of the value of fatigue strength of tension and torsion, lack of parallelism of the SN curves, abnormal behaviour of the criterion under biaxial tensioncompression and influence of phase shift between particular stress state components. Information contained in this article will help to prevent improper use of this criterion and contributes to its better understanding
Directory of Open Access Journals (Sweden)
Zeguang YI
2015-08-01
Full Text Available 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 used to construct improved multi-scale morphological filters which is applicable to mechanical failure in order to weaken the background noises; combining the structural parameters of parts to build a reference signal, complex components blind separation is carried out on the signals after noise reduction paragraph by paragraph by reference signal unit semi-blind extraction algorithm; then the improved KL-distance of complex independent components is employed as distance measure to resolve the permutation, and finally the mechanical fault characteristic signals are extracted and separated. The actual acoustic diagnosis of rolling bearing fault in sound field environment results proves the effectiveness of this algorithm.
High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing.
Maclachlan, Robert A; Riviere, Cameron N
2009-06-01
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 angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm × 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-μm peak-to-peak resolution at 1-kHz sampling.
Frequency-Domain Tomography for Single-shot, Ultrafast Imaging of Evolving Laser-Plasma Accelerators
Li, Zhengyan; Zgadzaj, Rafal; Wang, Xiaoming; Downer, Michael
2011-10-01
Intense laser pulses propagating through plasma create plasma wakefields that often evolve significantly, e.g. by expanding and contracting. However, such dynamics are known in detail only through intensive simulations. Laboratory visualization of evolving plasma wakes in the ``bubble'' regime is important for optimizing and scaling laser-plasma accelerators. Recently snap-shots of quasi-static wakes were recorded using frequency-domain holography (FDH). To visualize the wake's evolution, we have generalized FDH to frequency-domain tomography (FDT), which uses multiple probes propagating at different angles with respect to the pump pulse. Each probe records a phase streak, imprinting a partial record of the evolution of pump-created structures. We then topographically reconstruct the full evolution from all phase streaks. To prove the concept, a prototype experiment visualizing nonlinear index evolution in glass is demonstrated. Four probes propagating at 0, 0.6, 2, 14 degrees to the index ``bubble'' are angularly and temporally multiplexed to a single spectrometer to achieve cost-effective FDT. From these four phase streaks, an FDT algorithm analogous to conventional CT yields a single-shot movie of the pump's self-focusing dynamics.
High-resolution wind profiling using combined spatial and frequency domain interferometry
Palmer, R. D.; Huang, X.; Fukao, S.; Yamamoto, M.; Nakamura, T.
1995-11-01
A novel approach to wind profiling is presented which is based on the hybrid use of spatial interferometry (SI) and frequency domain interferometry (FDI). Many algorithms exist that can be used to determine the wind field using SI. However, the imaging Doppler interferometry (IDI) technique is somewhat unique in that the wind field within the radar beam is angularly "imaged" using the Doppler sorting effect. The spatial locations of scatterers are determined by assuming a wind field across the beam and Fourier analyzing signals to sort Doppler velocities. Pulsed radar systems are limited in range resolution by the length of the transmitted pulse, and wind estimates are obtained for a discrete set of altitudes determined by sampling the continuous stream of signals. Frequency domain interferometry (FDI) can be used to determine the radial location of scattering layers within the resolution volume. Thus the combined use of FDI and IDI can provide the radial and angular location of particular scattering points. Using the Doppler sorting idea, a new wind profiling technique is presented which uses FDI to increase the altitude resolution of wind estimates obtained from IDI. Experimental data that illustrate the implementation of the algorithm are presented from the Middle and Upper (MU) Atmosphere radar.
Brain connectivity study of joint attention using frequency-domain optical imaging technique
Chaudhary, Ujwal; Zhu, Banghe; Godavarty, Anuradha
2010-02-01
Autism is a socio-communication brain development disorder. It is marked by degeneration in the ability to respond to joint attention skill task, from as early as 12 to 18 months of age. This trait is used to distinguish autistic from nonautistic populations. In this study, diffuse optical imaging is being used to study brain connectivity for the first time in response to joint attention experience in normal adults. The prefrontal region of the brain was non-invasively imaged using a frequency-domain based optical imager. The imaging studies were performed on 11 normal right-handed adults and optical measurements were acquired in response to joint-attention based video clips. While the intensity-based optical data provides information about the hemodynamic response of the underlying neural process, the time-dependent phase-based optical data has the potential to explicate the directional information on the activation of the brain. Thus brain connectivity studies are performed by computing covariance/correlations between spatial units using this frequency-domain based optical measurements. The preliminary results indicate that the extent of synchrony and directional variation in the pattern of activation varies in the left and right frontal cortex. The results have significant implication for research in neural pathways associated with autism that can be mapped using diffuse optical imaging tools in the future.
Frequency-domain elastic full waveform inversion using encoded simultaneous sources
Jeong, W.; Son, W.; Pyun, S.; Min, D.
2011-12-01
Currently, numerous studies have endeavored to develop robust full waveform inversion and migration algorithms. These processes require enormous computational costs, because of the number of sources in the survey. To avoid this problem, the phase encoding technique for prestack migration was proposed by Romero (2000) and Krebs et al. (2009) proposed the encoded simultaneous-source inversion technique in the time domain. On the other hand, Ben-Hadj-Ali et al. (2011) demonstrated the robustness of the frequency-domain full waveform inversion with simultaneous sources for noisy data changing the source assembling. Although several studies on simultaneous-source inversion tried to estimate P- wave velocity based on the acoustic wave equation, seismic migration and waveform inversion based on the elastic wave equations are required to obtain more reliable subsurface information. In this study, we propose a 2-D frequency-domain elastic full waveform inversion technique using phase encoding methods. In our algorithm, the random phase encoding method is employed to calculate the gradients of the elastic parameters, source signature estimation and the diagonal entries of approximate Hessian matrix. The crosstalk for the estimated source signature and the diagonal entries of approximate Hessian matrix are suppressed with iteration as for the gradients. Our 2-D frequency-domain elastic waveform inversion algorithm is composed using the back-propagation technique and the conjugate-gradient method. Source signature is estimated using the full Newton method. We compare the simultaneous-source inversion with the conventional waveform inversion for synthetic data sets of the Marmousi-2 model. The inverted results obtained by simultaneous sources are comparable to those obtained by individual sources, and source signature is successfully estimated in simultaneous source technique. Comparing the inverted results using the pseudo Hessian matrix with previous inversion results
Improved free-surface expression for frequency-domain elastic optimal mixed-grid modeling
Cao, Jian; Chen, Jing-Bo; Dai, Meng-Xue
2016-07-01
An accurate and efficient forward modeling is the foundation of full-waveform inversion (FWI). In elastic wave modeling, one of the key problems is how to deal with the free-surface boundary condition appropriately. For the representation of the free-surface boundary condition, conventional displacement-based approaches and staggered-grid approaches are often used in time-domain. In frequency-domain, considering the saving of storage and CPU time, we integrate the idea of physical parameter-modified staggered-grid approach in time-domain with an elastic optimal mixed-grid modeling scheme to design an improved parameter-modified free-surface expression. Accuracy analysis shows that an elastic optimal mixed-grid modeling scheme using the parameter-modified free-surface expression can provide more accurate solutions with only 4 grid points per smallest shear wavelength than conventional displacement-based approaches and is stable for most Poisson ratios. Besides, it also yields smaller condition number of the resulting impedance matrix than conventional displacement-based approaches in laterally varying complex media. These advantages reveal great potential of this free-surface expression in big-data practical application.
Ground penetrating radar data analyzed in frequency and time domain for engineering issues
Capozzoli, Luigi; Giampaolo, Valeria; Votta, Mario; Rizzo, Enzo
2014-05-01
Non-destructive testing (NDT) allows to analyze reinforced concrete and masonry structures, in order to identify gaps, defects, delaminations, and fracture. In the field of engineering, non-invasive diagnostic is used to test the processes of construction and maintenance of buildings and artifacts of the individual components, to reduce analysis time and costs of intervention (Proto et al., 2010). Ground penetrating radar (GPR) allows to evaluate with a good effectiveness the state of conservation of engineering construction (Mellet 1995)). But there are some uncertainties in GPR data due to the complexity of artificial objects. In this work we try to evaluate the capability of GPR for the characterization of building structures in the laboratory and in-situ. In particular the focus of this research consists in integrate spectral analysis to time domain data to enhance information obtained in a classical GPR processing approach. For this reason we have applied spectral analysis to localize and characterize the presence of extraneous bodies located in a test site rebuilt in laboratory to simulate a part of a typical concrete road. The test site is a segment of a road superimposed on two different layers of sand and gravel of varying thickness inside which were introduced steel rebar, PVC and aluminium pipes. This structure has also been cracked in a predetermined area and hidden internal fractures were investigated. The GPR has allowed to characterize the panel in a non-invasive mode and radargrams were acquired using two-dimensional and three-dimensional models from data obtained with the use of 400, 900, 1500 and 2000 Mhz antennas. We have also studied with 2 GHz antenna a beam of 'to years precast bridge characterized by a high state of decay. The last case study consisted in the characterization of a radiant floor analyzed with an integrated use of GPR and infrared thermography. In the frequency domain analysis has been possible to determine variations in the
Template-based CTA X-ray angio rigid registration of coronary arteries in frequency domain
Aksoy, Timur; Demirci, Stefanie; Degertekin, Muzaffer; Navab, Nassir; Unal, Gozde
2013-03-01
This study performs 3D to 2D rigid registration of segmented pre-operative CTA coronary arteries with a single segmented intra-operative X-ray Angio frame in both frequency and spatial domains for real-time Angiography interventions by C-arm fluoroscopy. Most of the work on rigid registration in literature required a close initial- ization of poses and/or positions because of the abundance of local minima and high complexity that searching algorithms face. This study avoids such setbacks by transforming the projections into translation-invariant Fourier domain for estimating the 3D pose. First, template DRRs as candidate poses of 3D vessels of segmented CTA are produced by rotating the camera (image intensifier) around the DICOM angle values with a wide range as in C-arm setup. We have compared the 3D poses of template DRRs with the real X-ray after equalizing the scales (due to disparities in focal length distances) in 3 domains, namely Fourier magnitude, Fourier phase and Fourier polar. The best pose candidate was chosen by one of the highest similarity measures returned by the methods in these domains. It has been noted in literature that these methods are robust against noise and occlusion which was also validated by our results. Translation of the volume was then recovered by distance-map based BFGS optimization well suited to convex structure of our objective function without local minima due to distance maps. Final results were evaluated in 2D projection space rather than with actual values in 3D due to lack of ground truth, ill-posedness of the problem which we intend to address in future.
Extended radar observations with the frequency radar domain interferometric imaging (FII) technique
Luce, H.; Yamamoto, M.; Fukao, S.; Crochet, M.
2001-07-01
In this paper, we present high-resolution observations obtained with the Middle and Upper Atmosphere (MU) radar (Shigaraki, Japan, /34.85°N, /136.10°E) using the frequency radar domain interferometric imaging (FII) technique. This technique has recently been introduced for improving the range resolution capabilities of the mesosphere-stratosphere-troposphere (MST) radars which are limited by their minimum pulse length. The Fourier-based imaging, the Capon method have been performed with 5 equally spaced frequencies between 46.25 and 46.75MHz and with an initial range resolution of 300m. These results have been compared firstly to results obtained using the frequency domain interferometry (FDI) technique with Δf=0.5MHz and, secondly, to results from a classical Doppler beam swinging (DBS) mode applied with a range resolution of 150m. Thin echoing structures could be tracked owing to the improved radar range resolution and some complex structures possibly related to Kelvin Helmholtz instabilities have been detected. Indeed, these structures appeared within the core of a wind shear and were associated with intense vertical wind fluctuations. Moreover, a well-defined thin echo layer was found in an altitude range located below the height of the wind shear. The radar observations have not been fully interpreted yet because the radar configuration was not adapted for this kind of study and because of the lack of complementary information provided by other techniques when the interesting echoing phenomena occurred. However, the results confirm the high potentialities of the FII technique for the study of atmospheric dynamics at small scales.
Sauvé, Alexandre; Montier, Ludovic
2016-10-01
uc(Context): Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for ν knowledge of detector response. However bolometers have highly nonlinear characteristics, coming from their electrical and thermal coupling making them very difficult to model. uc(Goal): We present a method to build the analytical transfer function in frequency domain which describe the voltage response of an Alternative Current (AC) biased bolometer to optical excitation, based on the standard bolometer model. This model is built using the setup of the Planck/HFI instrument and offers the major improvement of being based on a physical model rather than the currently in use had-hoc model based on Direct Current (DC) bolometer theory. uc(Method): The analytical transfer function expression will be presented in matrix form. For this purpose, we build linearized versions of the bolometer electro thermal equilibrium. A custom description of signals in frequency is used to solve the problem with linear algebra. The model performances is validated using time domain simulations. uc(Results): The provided expression is suitable for calibration and data processing. It can also be used to provide constraints for fitting optical transfer function using real data from steady state electronic response and optical response. The accurate description of electronic response can also be used to improve the ADC nonlinearity correction for quickly varying optical signals.
DEFF Research Database (Denmark)
Celestinos, Adrian; Nielsen, Sofus Birkedal
2008-01-01
Small- and medium-size rectangular rooms have a strong influence on the low-frequency performance of loudspeakers. A simulation program based on the finite-difference time-domain (FDTD) method is introduced to analyze the sound field produced by loudspeakers in rectangular rooms at low frequencies...
Ji, Yongzhen; Yuan, Sanyi; Wang, Shangxu; Deng, Li
2016-10-01
The prestack amplitude variation with angle (AVA) inversion method utilising angle information to obtain the elastic parameters estimation of subsurface rock is vital to reservoir characterisation. Under the assumption of blocky layered media, an AVA inversion algorithm combining prestack spectral reflectivity inversion with sparse Bayesian learning (SBL) is presented. Prior information of the model parameters is involved in the inversion through the hierarchical Gaussian distribution where each parameter has a unique variance instead of sharing a common one. The frequency-domain prestack SBL inversion method retrieves sparse P- and S-wave impedance reflectivities by sequentially adding, deleting or re-estimating hyper-parameters without pre-setting the number of non-zero P- and S-wave reflectivity spikes. The selection of frequency components can help get rid of noise outside the selected frequency band. The precondition of the parameters helps to balance the weight of different parameters and incorporate the relationship between those parameters into the inversion process, thus improves the inversion result. Synthetic and real data examples illustrate the effectiveness of the method.
Directory of Open Access Journals (Sweden)
S. Radhakrishnan
2016-08-01
Full Text Available The dielectric relaxation of benzyl alcohol substitutents (benzyl alcohol, m-methylbenzyl alcohol and m-nitrobenzyl alcohol with methyl methacrylate and butyl methacrylate in dilute solution of carbon tetrachloride is measured at 9.37 GHz using Frequency domain (X-band technique. Different dielectric parameters like dielectric constant (ε׳, dielectric loss factor (ε״ at Microwave frequency, static dielectric constant (ε0 and dielectric constant at infinite dilution (ε∞ at optical frequency have been determined. From the measured dielectric data, the relaxation time (t calculated using Higasi method and activation energies (∆Ft and ∆Fη have been determined. All the dielectric parameters that are vary with the substitutent change in benzyl alcohol andchain length of acrylic esters. Suggests that, the proton donating ability is varying with the substitution of benzyl alcohol and proton accepting ability is varying with the chain length of acrylic esters. The relaxation time and molar free energy activation of 1:1 molar ratio is greater than other higher molar ratios (i.e. 3:1, 2:1, 1:2, 1:3 confirm that the existence of most likely 1:1 complex formation between the studied systems and also complex formation formed between free hydroxyl group of substituted benzyl alcohols and carbonyl group of acrylic esters (MMA and EMA.
Siemon, Bernhard; Steuer, Annika; Ullmann, Angelika; Vasterling, Margarete; Voß, Wolfgang
Airborne geophysical methods have been used successfully in groundwater exploration over the last decades. Particularly airborne electromagnetics is appropriate for large-scale and efficient groundwater surveying. Due to the dependency of the electrical conductivity on both the clay content of the host material and the mineralisation of the water, airborne electromagnetics is suitable for providing information on groundwater resources, water quality, aquifer conditions and protection levels. Frequency-domain helicopter-borne electromagnetic systems are used to investigate near-surface groundwater occurrences in detail even in rough terrain and populated areas. In order to reveal the subsurface conductivity distribution, the quantities measured, the secondary magnetic fields, are generally inverted into resistivity-depth models. Due to the skin-effect the penetration depths of the electromagnetic fields depend on the system characteristics used: high-frequency data describe the shallower parts of the conducting subsurface and the low-frequency data the deeper parts. Typical maximum investigation depths range from some ten metres (highly conductive saltwater saturated sediments) to several hundred metres (resistive hard rocks). In urban areas there are a number of man-made sources affecting the electromagnetic measurements. These effects on the secondary field values are discussed on the basis of synthetic data as well as uncorrected and corrected field data. The case histories of different hydrogeological setups in Indonesia, The Netherlands and Germany demonstrate that airborne electromagnetics can be applied to groundwater exploration purposes even in urban areas.
Sharma, Vikas; Parey, Anand
2017-02-01
In the purview of fluctuating speeds, gear fault diagnosis is challenging due to dynamic behavior of forces. Various industrial applications employing gearbox which operate under fluctuating speed conditions. For diagnostics of a gearbox, various vibrations based signal processing techniques viz FFT, time synchronous averaging and time-frequency based wavelet transform, etc. are majorly employed. Most of the time, theories about data or computational complexity limits the use of these methods. In order to perform fault diagnosis of a gearbox for fluctuating speeds, frequency domain averaging (FDA) of intrinsic mode functions (IMFs) after their dynamic time warping (DTW) has been done in this paper. This will not only attenuate the effect of fluctuating speeds but will also extract the weak fault feature those masked in vibration signal. Experimentally signals were acquired from Drivetrain Diagnostic Simulator for different gear health conditions i.e., healthy pinion, pinion with tooth crack, chipped tooth and missing tooth and were analyzed for the different fluctuating profiles of speed. Kurtosis was calculated for warped IMFs before DTW and after DTW of the acquired vibration signals. Later on, the application of FDA highlights the fault frequencies present in the FFT of faulty gears. The result suggests that proposed approach is more effective towards the fault diagnosing with fluctuating speed.
Real-time frequency domain temperature and oxygen sensor with a single optical fiber.
Liao, S C; Xu, Z; Izatt, J A; Alcala, J R
1997-11-01
The combined excited-state phosphorescence life-times of an alexandrite crystal and platinum tetraphenylporphyrin Pt(TPP) in a single-fiber sensor are used to monitor temperature and oxygen concentration in the physiological range from 15-45 degrees C and 0-50% O2 with precision of 0.24 degree C and 0.15% O2 and accuracy of 0.28 degree C and 0.2% O2. A 500-micron cubic alexandrite crystal bound to the distal end of a 750-micron-diameter optical fiber core and the Pt(TPP) coated circumferentially with a length of 1 cm from the end of the same fiber are excited with pulsed super-bright blue LED light. This apparatus uses a 125-kHz sampler for data acquisition and frequency domain methods for signal processing. The instrument amplifies both the dc and ac components of the photomultiplier output and band limits the signal to 20 kHz. The fundamental frequency of the excitation is set to 488.3 Hz and the highest harmonic used is the 35th. This bandlimited signal is sampled and averaged over a few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. At least four log-spaced harmonic phases or modulations are averaged before decoding the two lifetimes of temperature and oxygen phosphorescent sensors. A component of zero lifetime is introduced to account for the excitation backscatter leakage through optical interference filters seen by the photodetector. Linear and second-order empirical polynomials are employed to compute the temperatures and oxygen concentrations from the inverse lifetimes. In the situation of constant oxygen concentration, the lifetime of Pt(TPP) changes with temperature but can be compensated using the measured temperature lifetime. The system drift is 0.24 degree C for the temperature measurement and 0.59% for the oxygen concentration measurement over 30 h of continuous operation
DEFF Research Database (Denmark)
Nelson, Paul C.; Ewert, Stephan; Carney, Laurel H.;
2007-01-01
-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms=0.25) and a range of AM frequencies (4-64 Hz). In a second experiment, masked sinusoidal......In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level...
Electrical performance analysis of HTS synchronous motor based on 3D FEM
Baik, S. K.; Kwon, Y. K.; Kim, H. M.; Lee, J. D.; Kim, Y. C.; Park, G. S.
2010-11-01
A 1-MW class superconducting motor with High-Temperature Superconducting (HTS) field coil is analyzed and tested. This machine is a prototype to make sure applicability aimed at generator and industrial motor applications such as blowers, pumps and compressors installed in large plants. This machine has the HTS field coil made of Bi-2223 HTS wire and the conventional copper armature (stator) coils cooled by water. The 1-MW class HTS motor is analyzed by 3D electromagnetic Finite Element Method (FEM) to get magnetic field distribution, self and mutual inductance, and so forth. Especially excitation voltage (Back EMF) is estimated by using the mutual inductance between armature and field coils and compared with experimental result. Open and short circuit tests were conducted in generator mode while a 1.1-MW rated induction machine was rotating the HTS machine. Electrical parameters such as mutual inductance and synchronous inductance are deduced from these tests and also compared with the analysis results from FEM.
Improvement of 3-D FEM Coupled Model on Strip Crown in Hot Rolling
Institute of Scientific and Technical Information of China (English)
2012-01-01
In order to simulate and analyze hot strip crown and flatness accurately and efficiently, the 3-D （three-di- mensional） coupled model involved in RPFEM （rigid-plastic finite element method） is improved based on the analyti- cal model of forecasting rolling force distribution. In the analytical model, variational method is employed to solve the lateral flow of metal and influential function method is employed to calculate roll deflection, the lateral distribution of rolling force can be obtained rapidly by iterative strategy. Then the 3-D coupled model uses the result as initial distri- bution of rolling force to calculate roll deflection and makes the initial on-load roll gap profile close to the final value, so as to reduce iterations and increase efficiency. Compared with previous algorithms, the improved model can reduce the iterations by about 50% and shorten the computing time by about 60% on the basis of the calculation accuracy.
3 D FEM analysis of welding residual stress and deformation of aero-engine blisk
Institute of Scientific and Technical Information of China (English)
杨建国; 周号; 雷靖; 方洪渊; 张学秋; 曲伸
2014-01-01
Aero-engine blisk welded by electron beam welding(EBW)method is a complicated structure.Fixtures were used to control the deformation ofblisk during its manufacturing process.Finite element method was utilized to study the evolution of the welding residual stress and deformation of this structure.In which an attenuation function was applied to the double ellipsoid heat source model based on the characteristic ofEBW,and the effects offixtures on the welding residual stresses and deforamtion were also reserached.The simulation results showed that the temperature contour ofweld cross section vertical to the weld centerline followed a “V”shape.Moreover,large welding residual stress and distortion were found in the interface between blisk and fixtures.The stress concentration was reduced sufficiently in starting and end part ofweldment as the fixtures were removed after welding process,while the removing operation had almost no effects on the welding residual stress in the middle section ofweld bead.
3D FEM simulations of the rolling of stator vanes, including tool deformation
Wisselink, H.H.; Huetink, J.
2002-01-01
Tool deformation is an important issue in the shape rolling of stator vanes as it directly influences the thickness of the rolled vane. This means that for the design of an accurate production process the deformation of the tools has to be accounted for. The shape rolling of symmetrical straight van
3D FEM Simulation of shape rolling using an ALE method
Wisselink, H.H.; Huetink, J.
2003-01-01
The shape rolling of stator vanes has been modelled in 3D using the finite element method. Till now only the rolling of straight vanes, which have a constant cross section, is studied. Therefore this rolling process can be considered as a stationary process. Such processes can be described as a flow
Application of ANSYS 3D FEM in Studies of Surface Deformation Caused by Pipe Jacking
Institute of Scientific and Technical Information of China (English)
LI Fabin; FANG Kun; LI Hechao
2007-01-01
By using site observation data and establishing 3D model using ANSYS software, this paper has discussed the strain change of stratum stress during process of jacking-in and the impact of machine head on ground surface under different frontal resistances. Analysis of the two cases shows that soil pressure reaches its maximum point when the soil is right above machine head, and soil stress will gradually decline when machine head passes over it. It also shows that impact brought by pipe-jacking construction on stress change of the surrounding soil is limited. The thesis suggest that road surface should be consolidated and soil condition be improved before construction to prevent loss and disaster caused by road surface deformation, jacking force can be increased so that jacking efficiency can be enhanced when ground stratum is well filled with soil, but the frontal resistance facing machine head should be equal to surrounding soil pressure in order to avoid rise of ground surface.
Stability Analysis of Embankments Founded on Clay : a comparison between LEM & 2D/3D FEM
2014-01-01
Rapid constructed embankments founded on soft deposits have a negative influence on the short term stability. Many engineering constructions such as road and railway embankments are often constructed on soft clay deposits. In stability analysis calculation of safety factor (SF), as the primary design criteria can be evaluated through different numerous methods such as limit equilibrium method (LEM) and finite element method (FEM). It is of particular interest to determine/estimate appropriate...
Analysis of rolls deflection of Sendzimir mill by 3D FEM
Institute of Scientific and Technical Information of China (English)
YU Hai-liang; LIU Xiang-hua; LEE Gyoo Taek
2007-01-01
The deflection of rolls of Sendzimir mill with double AS-U-Roll was simulated by finite element method(FEM). The influences of rolling pressure, strip width and rolls-assignment on rolls deflection were analyzed. The results show that the work roll deflection increases with the increase of rolling pressure and the reduction of work roll radius, but the rigid displacement of work roll slightly changes; the work roll end might appear negative displacement for the narrow strip width and high rolling pressure that might cause the contact of work rolls. The research results are significant for guiding production and theoretical analysis of the rolls system of Sendzimir mill.
[A 3D FEM model for calculation of electromagnetic fields in transmagnetic stimulation].
Seilwinder, J; Kammer, T; Andrä, W; Bellemann, M E
2002-01-01
We developed a realistic finite elements method (FEM) model of the brain for the calculation of electromagnetic fields in transcranial magnetic stimulation (TMS). A focal butterfly stimulation coil was X-rayed, parameterized, and modeled. The magnetic field components of the TMS coil were calculated and compared for validation to pointwise measurements of the magnetic fields with a Hall sensor. We found a mean deviation of 7.4% at an axial distance of 20 mm to the coil. A 3D brain model with the biological tissues of white and gray matter, bone, and cerebrospinal fluid was developed. At a current sweep of 1000 A in 120 microseconds, the maximum induced current density in gray matter was 177 mA/m2 and the strongest electric field gradient covered an area of 40 mm x 53 mm.
Nanoreinforced polymer composites: 3D FEM modeling with effective interface concept
DEFF Research Database (Denmark)
Wang, H.W.; Zhou, H.W.; Peng, R.D.;
2011-01-01
A computational study of the effect of structures of nanocomposites on their elastic properties is presented. The special program code for the automatic generation of 3D multiparticle unit cells with/without overlapping, effective interface layers around particles is developed for nanocomposite...
Schuller-Götzburg, P; Pleschberger, M; Rammerstorfer, F G; Krenkel, C
2009-12-01
Biomechanical investigation of the mandible is difficult due to the complex geometrical structure. A three-dimensional finite element model of the mandible and masticatory muscles was produced with approximately 23,000 hexahedral elements. On this model, mesial and distal portions of the jaw were resected and bridged with a buccal and/or caudally positioned bridging plate. The plate was fixed caudal or buccal to the mandible. The defect was left as it was or reconstructed with an exactly fitting transplant defined as bone. The jaw was loaded at a predefined point. The changes in stresses and deformations of bone, the transplant and the bridging plate were analysed. In the caudally positioned bridging plate, finite element analysis showed lesser stresses around the fixation screws of the bridging plate. During reconstruction of the lateral defect, the buccal (ramus)-caudal (corpus) position of the bridging plate showed fewer stresses and deformations than purely buccal positioning. The caudal position of the bridging plate has biomechanical advantages and facilitates fixation of the plate, and fixation of a bone graft on the jaw stumps. Histomorphological investigations, 12 weeks and 7 years after reconstruction, show partial osseous integration or transformation of autologous iliac crest transplants.
Planar Lithographed Superconducting LC Resonators for Frequency-Domain Multiplexed Readout Systems
Rotermund, K.; Barch, B.; Chapman, S.; Hattori, K.; Lee, A.; Palaio, N.; Shirley, I.; Suzuki, A.; Tran, C.
2016-07-01
Cosmic microwave background (CMB) polarization experiments are increasing the number of transition edge sensor (TES) bolometers to increase sensitivity. In order to maintain low thermal loading of the sub-Kelvin stage, the frequency-domain multiplexing (FDM) factor has to increase accordingly. FDM is achieved by placing TES bolometers in series with inductor-capacitor (LC) resonators, which select the readout frequency. The multiplexing factor can be raised with a large total readout bandwidth and small frequency spacing between channels. The inductance is kept constant to maintain a uniform readout bandwidth across detectors, while the maximum acceptable value is determined by bolometer stability. Current technology relies on commercially available ceramic chip capacitors. These have high scatter in their capacitance thereby requiring large frequency spacing. Furthermore, they have high equivalent series resistance (ESR) at higher frequencies and are time consuming and tedious to hand assemble via soldering. A solution lies in lithographed, planar spiral inductors (currently in use by some experiments) combined with interdigitated capacitors on a silicon (Si) substrate. To maintain reasonable device dimensions, we have reduced trace and gap widths of the LCs to 4 \\upmu m. We increased the inductance from 16 to 60 \\upmu H to achieve a higher packing density, a requirement for FDM systems with large multiplexing factors. Additionally, the Si substrate yields low ESR values across the entire frequency range and lithography makes mass production of LC pairs possible. We reduced mutual inductance between inductors by placing them in a checkerboard pattern with the capacitors, thereby increasing physical distances between adjacent inductors. We also reduce magnetic coupling of inductors with external sources by evaporating a superconducting ground plane onto the backside of the substrate. We report on the development of lithographed LCs in the 1-5 MHz range for use
Jing, Xingjian
2015-01-01
This book is a systematic summary of some new advances in the area of nonlinear analysis and design in the frequency domain, focusing on the application oriented theory and methods based on the GFRF concept, which is mainly done by the author in the past 8 years. The main results are formulated uniformly with a parametric characteristic approach, which provides a convenient and novel insight into nonlinear influence on system output response in terms of characteristic parameters and thus facilitate nonlinear analysis and design in the frequency domain. The book starts with a brief introduction to the background of nonlinear analysis in the frequency domain, followed by recursive algorithms for computation of GFRFs for different parametric models, and nonlinear output frequency properties. Thereafter the parametric characteristic analysis method is introduced, which leads to the new understanding and formulation of the GFRFs, and nonlinear characteristic output spectrum (nCOS) and the nCOS based analysis a...
Hydrograph structure informed calibration in the frequency domain with time localization
Kumarasamy, K.; Belmont, P.
2015-12-01
Complex models with large number of parameters are commonly used to estimate sediment yields and predict changes in sediment loads as a result of changes in management or conservation practice at large watershed (>2000 km2) scales. As sediment yield is a strongly non-linear function that responds to channel (peak or mean) velocity or flow depth, it is critical to accurately represent flows. The process of calibration in such models (e.g., SWAT) generally involves the adjustment of several parameters to obtain better estimates of goodness of fit metrics such as Nash Sutcliff Efficiency (NSE). However, such indicators only provide a global view of model performance, potentially obscuring accuracy of the timing or magnitude of specific flows of interest. We describe an approach for streamflow calibration that will greatly reduce the black-box nature of calibration, when response from a parameter adjustment is not clearly known. Fourier Transform or the Short Term Fourier Transform could be used to characterize model performance in the frequency domain as well, however, the ambiguity of a Fourier transform with regards to time localization renders its implementation in a model calibration setting rather useless. Brief and sudden changes (e.g. stream flow peaks) in signals carry the most interesting information from parameter adjustments, which are completely lost in the transform without time localization. Wavelet transform captures the frequency component in the signal without compromising time and is applied to contrast changes in signal response to parameter adjustments. Here we employ the mother wavelet called the Mexican hat wavelet and apply a Continuous Wavelet Transform to understand the signal in the frequency domain. Further, with the use of the cross-wavelet spectrum we examine the relationship between the two signals (prior or post parameter adjustment) in the time-scale plane (e.g., lower scales correspond to higher frequencies). The non-stationarity of
Copot, Cosmin; Zhong, Yu; Ionescu, Clara; Keyser, Robin
2013-06-01
In this paper, two methods to tune a fractional-order PI λ D μ controller for a mechatronic system are presented. The first method is based on a genetic algorithm to obtain the parameter values for the fractionalorder PI λ D μ controller by global optimization. The second method used to design the fractional-order PI λ D μ controller relies on an auto-tuning approach by meeting some specifications in the frequency domain. The real-time experiments are conducted using a Steward platform which consists of a table tilted by six servo-motors with a ball on the top of the table. The considered system is a 6 degrees of freedom (d.o.f.) motion platform. The feedback on the position of the ball is obtained from images acquired by a visual sensor mounted above the platform. The fractional-order controllers were implemented and the performances of the steward platform are analyzed.
Frequency and Time Domain Packet Scheduling Based on Channel Prediction with Imperfect CQI in LTE
Directory of Open Access Journals (Sweden)
Yongxin Wang
2013-08-01
Full Text Available Channel-dependent scheduling of transmission of data packets in a wireless system is based onmeasurement and feedback of the channel quality. To alleviate the performance degradation due tosimultaneous multiple imperfect channel quality information (CQI, a simple and efficient packetscheduling (PS algorithm is developed in downlink LTE system for real time traffic. A frequency domainchannel predictor based on Kalman filter is first developed to restore the true CQI from erroneous channelquality feedback. Then, a time domain grouping technique employing the joint of Proportional Fair (PFand Modified Largest Weighted Delay First (M-LWDF algorithms is used. It was proved this proposalachieves better performance in terms of system throughput and packet loss ratio by simulation results.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A new method of resolving overlapped peak, Fourier self-deconvolution (FSD) using approximation CN obtained from frequency domain wavelet transform of F(ω) yielded by Fourier transform of overlapped peak signals f(t) as the linear function, was presented in this paper.Compared with classical FSD, the new method exhibits excellent resolution for different overlapped peak signals such as HPLC signals, and have some characteristics such as an extensive applicability for any overlapped peak shape signals and a simple operation because of no selection procedure of the linear function. Its excellent resolution for those different overlapped peak signals is mainly because F(ω) obtained from Fourier transform of f(t) and CN obtained from wavelet transform of F(ω) have the similar linearity and peak width. The effect of those fake peaks can be eliminated by the algorithm proposed by authors. This method has good potential in the process of different overlapped peak signals.
Frequency-domain identification of aircraft structural modes from short-duration flight tests
Vayssettes, J.; Mercère, G.; Vacher, P.; De Callafon, R. A.
2014-07-01
This article presents identification algorithms dedicated to the modal analysis of civil aircraft structures during in-flight flutter tests. This particular operational framework implies several specifications for the identification procedure. To comply with these requirements, the identification problem is formulated in the frequency domain as an output-error problem. Iterative identification methods based on structured matrix fraction descriptions are used to solve this problem and to identify a continuous-time model. These iterative methods are specifically designed to deal with experiments where short-duration tests with multiple-input excitations are used. These algorithms are first discussed and then evaluated through a simulation example illustrative of the in-flight modal analysis of a civil aircraft. Based on these evaluation results, an efficient iterative algorithm is suggested and applied to real flight-test data measured on board a military aircraft.
Frequency domain analysis of lightning protection using four lightning protection rods
Directory of Open Access Journals (Sweden)
Javor Vesna
2008-01-01
Full Text Available In this paper the lightning discharge channel is modeled as a vertical monopole antenna excited by a pulse generator at its base. The lightning electromagnetic field of a nearby lightning discharge in the case of lightning protection using four vertical lightning protection rods was determined in the frequency domain. Unknown current distributions were determined by numerical solving of a system of integral equations of two potentials using the Point Matching Method and polynomial approximation of the current distributions. The influence of the real ground, treated as homogeneous loss half-space of known electrical parameters, expressed through a Sommerfeld integral kernel, was modeled using a new Two-image approximation which gives good results in both near and far fields.
An improved wave-vector frequency-domain method for nonlinear wave modeling.
Jing, Yun; Tao, Molei; Cannata, Jonathan
2014-03-01
In this paper, a recently developed wave-vector frequency-domain method for nonlinear wave modeling is improved and verified by numerical simulations and underwater experiments. Higher order numeric schemes are proposed that significantly increase the modeling accuracy, thereby allowing for a larger step size and shorter computation time. The improved algorithms replace the left-point Riemann sum in the original algorithm by the trapezoidal or Simpson's integration. Plane waves and a phased array were first studied to numerically validate the model. It is shown that the left-point Riemann sum, trapezoidal, and Simpson's integration have first-, second-, and third-order global accuracy, respectively. A highly focused therapeutic transducer was then used for experimental verifications. Short high-intensity pulses were generated. 2-D scans were conducted at a prefocal plane, which were later used as the input to the numerical model to predict the acoustic field at other planes. Good agreement is observed between simulations and experiments.
Adaptive eigenspace method for inverse scattering problems in the frequency domain
Grote, Marcus J.; Kray, Marie; Nahum, Uri
2017-02-01
A nonlinear optimization method is proposed for the solution of inverse scattering problems in the frequency domain, when the scattered field is governed by the Helmholtz equation. The time-harmonic inverse medium problem is formulated as a PDE-constrained optimization problem and solved by an inexact truncated Newton-type iteration. Instead of a grid-based discrete representation, the unknown wave speed is projected to a particular finite-dimensional basis of eigenfunctions, which is iteratively adapted during the optimization. Truncating the adaptive eigenspace (AE) basis at a (small and slowly increasing) finite number of eigenfunctions effectively introduces regularization into the inversion and thus avoids the need for standard Tikhonov-type regularization. Both analytical and numerical evidence underpins the accuracy of the AE representation. Numerical experiments demonstrate the efficiency and robustness to missing or noisy data of the resulting adaptive eigenspace inversion method.
Nelson, C. A.; Zhu, X.-Y.
2016-10-01
Optical excitations at semiconductor surfaces or interfaces are accompanied by transient interfacial electric fields due to charge redistribution or transfer. While such transient fields may be probed by time-resolved second harmonic generation (TR-SHG), it is difficult to determine the field direction, which is invaluable to unveiling the underlying physics. Here we apply a time-resolved frequency domain interferometric second harmonic (TR-FDISH) generation technique to determine the phase relationship between the SH field emitted from bulk GaAs(1 0 0) and the transient SH field from the space charge region. The interference between these two SH fields allow us to unambiguously determine the directions of transient electric fields. Since SH fields from a static bulk contribution and a changing electric field contribution are present at most semiconductor surfaces or interfaces under optical excitation, the TR-FDISH technique is of general significance to probing the dynamics of interfacial charge transfer/redistribution.
Dutta, Saibal; Chatterjee, Amitava; Munshi, Sugata
2010-12-01
The present work proposes the development of an automated medical diagnostic tool that can classify ECG beats. This is considered an important problem as accurate, timely detection of cardiac arrhythmia can help to provide proper medical attention to cure/reduce the ailment. The proposed scheme utilizes a cross-correlation based approach where the cross-spectral density information in frequency domain is used to extract suitable features. A least square support vector machine (LS-SVM) classifier is developed utilizing the features so that the ECG beats are classified into three categories: normal beats, PVC beats and other beats. This three-class classification scheme is developed utilizing a small training dataset and tested with an enormous testing dataset to show the generalization capability of the scheme. The scheme, when employed for 40 files in the MIT/BIH arrhythmia database, could produce high classification accuracy in the range 95.51-96.12% and could outperform several competing algorithms.
Oblique frequency domain interferometry measurements using the middle and upper atmosphere radar
Palmer, R. D.; Fukao, S.; Larsen, M. F.; Yamamoto, M.; Tsuda, T.; Kato, S.
1992-09-01
First results are presented from oblique frequency domain interferometry (FDI) measurements conducted using the middle and upper atmosphere radar in Japan in October 1990. Using the idea of Doppler sorting, an equation is derived which shows a parabolic variation of the oblique FDI cross-spectral phase as a function of Doppler velocity. However, because of the small range of Doppler velocities observed with the measured cross spectra, the phase has an approximate linear variation; that is, the cross spectra sample only a small portion of the parabolic structure and are therefore approximately linear and are shown to follow the model closely. Using the oblique FDI configuration, a comparison is drawn between simultaneous measurements of signal-to-noise ratio, coherence, three-dimensional wind, and profiles of FDI cross spectra. We find that the regions that exhibit a well-defined scattering layer correspond to those regions of high aspect sensitivity. An explanation is suggested based on the anisotropy of the turbulence.
Broadband absorption spectroscopy by combining frequency-domain and steady-state techniques
Berger, Andrew J.; Bevilacqua, Frederic; Jakubowski, Dorota B.; Cerussi, Albert E.; Butler, John A.; Hsiang, D.; Tromberg, Bruce J.
2001-06-01
A technique for measuring broadband near-infrared absorption spectra of turbid media is presented using a combination of frequency-domain (FD) and steady-state (SS) reflectance methods. Most of the wavelength coverage is provided by a white-light SS measurement, while the FD data are acquired at a few selected wavelengths. Coefficients of absorption ((mu) a) and reduced scattering ((mu) s') derived from the FD data are used to intensity-calibrate the SS measurements and to estimate (mu) s' at all wavelengths in the spectral window of interest. After these steps are performed, (mu) a can be determined by comparing the SS reflectance values to the predictions of diffusion theory, wavelength by wavelength. We present an application of this method to breast tumor characterization. A case study of a fibroadenoma is shown, where different absorption spectra were found between the normal and the tumor sides.
Granet, Gérard
2013-01-01
This paper focuses on scatterometry problems arising in lithography production of periodic gratings. Namely, the paper introduces a theoretical and numerical-modeling-oriented approach to scatterometry problems and discusses its capabilities. The approach allows for reliable detection of deviations in gratings\\' critical dimensions (CDs) during the manufacturing process. The core of the approach is the one-to-one correspondence between the electromagnetic (EM) characteristics and the geometric/material properties of gratings. The approach is based on highly accurate solutions of initial boundary-value problems describing EM waves\\' interaction on periodic gratings. The advantage of the approach is the ability to perform simultaneously and interactively both in frequency and time domains under conditions of possible resonant scattering of EM waves by infinite or finite gratings. This allows a detection of CDs for a wide range of gratings, and, thus is beneficial for the applied scatterometry. (C) 2013 Optical Society of America
Parallel full-waveform inversion in the frequency domain by the Gauss-Newton method
Zhang, Wensheng; Zhuang, Yuan
2016-06-01
In this paper, we investigate the full-waveform inversion in the frequency domain. We first test the inversion ability of three numerical optimization methods, i.e., the steepest-descent method, the Newton-CG method and the Gauss- Newton method, for a simple model. The results show that the Gauss-Newton method performs well and efficiently. Then numerical computations for a benchmark model named Marmousi model by the Gauss-Newton method are implemented. Parallel algorithm based on message passing interface (MPI) is applied as the inversion is a typical large-scale computational problem. Numerical computations show that the Gauss-Newton method has good ability to reconstruct the complex model.
Demonstrations of analog-to-digital conversion using a frequency domain stretched processor.
Reibel, Randy Ray; Harrington, Calvin; Dahl, Jason; Ostrander, Charles; Roos, Peter Aaron; Berg, Trenton; Mohan, R Krishna; Neifeld, Mark A; Babbitt, Wm R
2009-07-06
The first proof-of-concept demonstrations are presented for a broadband photonic-assisted analog-to-digital converter (ADC) based on spatial spectral holography (SSH). The SSH-ADC acts as a frequency-domain stretch processor converting high bandwidth input signals to low bandwidth output signals, allowing the system to take advantage of high performance, low bandwidth electronic ADCs. Demonstrations with 50 MHz effective bandwidth are shown to highlight basic performance with approximately 5 effective bits of vertical resolution. Signal capture with 1600 MHz effective bandwidth is also shown. Because some SSH materials span over 100 GHz and have large time apertures (approximately 10 micros), this technique holds promise as a candidate for the next generation of ADCs.
Ferri, A. A.; Dowell, E. H.
1985-01-01
The anticipated low damping level in large space structures (LSS) has been a major concern for the designers of these structures. Low damping degrades the free response and complicates the design of shape and attitude controllers for flexible spacecraft. Dry friction damping has been considered as a means of increasing the passive damping of LSS, by placing it in the joints and connecting junctures of structures. However, dry friction is highly nonlinear and, hence, analytical investigations are difficult to perform. Here, a multi-harmonic, frequency domain solution technique is developed and applied to a multi-DOF, dry friction damped system. It is seen that the multi-harmonic method is much more accurate than traditional, one harmonic solution methods. The method also compares well with time integration. Finally, comparisons are made with experimental results.
NOVEL COLOR FILTER ARRAY DEMOSAICING IN FREQUENCY DOMAIN WITH SPATIAL REFINEMENT
Directory of Open Access Journals (Sweden)
R. Niruban
2014-01-01
Full Text Available The main idea behind wavelet based demosaicing with spatial refinement is to reconstruct the full resolution color image from the mosaiced image. In this study, a new effective wavelet based demosaicing algorithm for interpolating the missing color components in Bayer’s Color Filter Array (CFA pattern is proposed. This interpolation technique uses the interchannel correlation among the high frequency subbands to determine the missing pixels in each color channel, followed by a refining step in spatial domain which uses non-iterative technique that enforces color difference rule with fewer computations. As a result, the proposed demosaicing method yields better performance than bilinear, edge based and subband based demosaicing methods.
Yngvesson, Sigfrid K.; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew; Khan, Ashraf
2012-03-01
In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This possibility of re-excision is undesirable in terms of reducing patient morbidity, emotional stress and healthcare. It has been shown that terahertz (THz) images of breast specimens can accurately differentiate between breast carcinoma, normal fibroglandular tissue, and adipose tissue. That study employed the Time-Domain Spectroscopy (TDS) technique. We are instead developing a new technique, Frequency-Domain Terahertz Imaging (FDTI). In this joint project between UMass/Amherst and UMass Medical School/Worcester (UMMS), we are investigating the feasibility of the FDTI technique for THz reflection imaging of breast cancer margins. Our system, which produces mechanically scanned images of size 2cm x 2cm, uses a THz gas laser. The system is calibrated with mixtures of water and ethanol and reflection coefficients as low as 1% have been measured. Images from phantoms and specimens cut from breast cancer lumpectomies at UMMS will be presented. Finally, there will be a discussion of a possible transition of this FDTI setup to a compact and inexpensive CMOS THz camera for use in the operating room.
Directory of Open Access Journals (Sweden)
Rie Saotome
2015-01-01
Full Text Available In order to explore marine natural resources using remote robotic sensor or to enable rapid information exchange between ROV (remotely operated vehicles, AUV (autonomous underwater vehicle, divers, and ships, ultrasonic underwater communication systems are used. However, if the communication system is applied to rich living creature marine environment such as shallow sea, it suffers from generated Impulsive Noise so-called Shrimp Noise, which is randomly generated in time domain and seriously degrades communication performance in underwater acoustic network. With the purpose of supporting high performance underwater communication, a robust digital communication method for Impulsive Noise environments is necessary. In this paper, we propose OFDM ultrasonic communication system with diversity receiver. The main feature of the receiver is a newly proposed Frequency Domain Diversity Combined Impulsive Noise Canceller. The OFDM receiver utilizes 20–28 KHz ultrasonic channel and subcarrier spacing of 46.875 Hz (MODE3 and 93.750 Hz (MODE2 OFDM modulations. In addition, the paper shows Impulsive Noise distribution data measured at a fishing port in Okinawa and at a barge in Shizuoka prefectures and then proposed diversity OFDM transceivers architecture and experimental results are described. By the proposed Impulsive Noise Canceller, frame bit error rate has been decreased by 20–30%.
Saotome, Rie; Hai, Tran Minh; Matsuda, Yasuto; Suzuki, Taisaku; Wada, Tomohisa
2015-01-01
In order to explore marine natural resources using remote robotic sensor or to enable rapid information exchange between ROV (remotely operated vehicles), AUV (autonomous underwater vehicle), divers, and ships, ultrasonic underwater communication systems are used. However, if the communication system is applied to rich living creature marine environment such as shallow sea, it suffers from generated Impulsive Noise so-called Shrimp Noise, which is randomly generated in time domain and seriously degrades communication performance in underwater acoustic network. With the purpose of supporting high performance underwater communication, a robust digital communication method for Impulsive Noise environments is necessary. In this paper, we propose OFDM ultrasonic communication system with diversity receiver. The main feature of the receiver is a newly proposed Frequency Domain Diversity Combined Impulsive Noise Canceller. The OFDM receiver utilizes 20–28 KHz ultrasonic channel and subcarrier spacing of 46.875 Hz (MODE3) and 93.750 Hz (MODE2) OFDM modulations. In addition, the paper shows Impulsive Noise distribution data measured at a fishing port in Okinawa and at a barge in Shizuoka prefectures and then proposed diversity OFDM transceivers architecture and experimental results are described. By the proposed Impulsive Noise Canceller, frame bit error rate has been decreased by 20–30%. PMID:26351656
Saotome, Rie; Hai, Tran Minh; Matsuda, Yasuto; Suzuki, Taisaku; Wada, Tomohisa
2015-01-01
In order to explore marine natural resources using remote robotic sensor or to enable rapid information exchange between ROV (remotely operated vehicles), AUV (autonomous underwater vehicle), divers, and ships, ultrasonic underwater communication systems are used. However, if the communication system is applied to rich living creature marine environment such as shallow sea, it suffers from generated Impulsive Noise so-called Shrimp Noise, which is randomly generated in time domain and seriously degrades communication performance in underwater acoustic network. With the purpose of supporting high performance underwater communication, a robust digital communication method for Impulsive Noise environments is necessary. In this paper, we propose OFDM ultrasonic communication system with diversity receiver. The main feature of the receiver is a newly proposed Frequency Domain Diversity Combined Impulsive Noise Canceller. The OFDM receiver utilizes 20-28 KHz ultrasonic channel and subcarrier spacing of 46.875 Hz (MODE3) and 93.750 Hz (MODE2) OFDM modulations. In addition, the paper shows Impulsive Noise distribution data measured at a fishing port in Okinawa and at a barge in Shizuoka prefectures and then proposed diversity OFDM transceivers architecture and experimental results are described. By the proposed Impulsive Noise Canceller, frame bit error rate has been decreased by 20-30%.
Efficient 2D and 3D multiparameters frequency-domain full waveform inversion (Invited)
Virieux, J.; Operto, S.; Ribodetti, A.; Ben Hadj Ali, H.; Brossier, R.; Etienne, V.; Gholami, Y.; Hu, G.; Jia, Y.; Pageot, D.; Prieux, V.
2010-12-01
With the tremendous increase of the computational power provided by large-scale distributed-memory platforms and the development of dense 3D multi-component wide-aperture/wide-azimuth surveys, full waveform inversion (FWI) introduced in geophysics by Albert Tarantola has become a re-emerging technique to build high-resolution velocity models of the subsurface. Because of the cost of the forward modeling and the high dimensionality of the model space, full waveform inversion is actually a local optimization problem, the aim of which is the minimization of the misfit between the recorded and modeled seismic wavefields. Among all possible minimization criteria, the L1 norm provides the most robust and easy-to-tune criterion. With such criterion, white noise in all seismograms with outliers does not prevent the convergence to the nearly same minimum as for noise-free data. The frequency formulation of the FWI allows coarse sampling of the frequencies data over few frequencies for the reconstruction of the medium when wide-aperture geometries are considered. A preconditioned quasi-Newton L-BFGS modified algorithm provides scaled gradients of the misfit function for each class of parameters. The gradient is computed by the adjoint-state method where the forward field is stored in the core memory of the computer while computing the backpropagation of residuals for cross-correlation at each point of the medium, thanks to the frequency-domain approach. We are using a sequential multiscale hierarchical inversion algorithm with two nested levels of data preconditioning with respect to frequency and first-arrival time. We are able to reconstruct both Vp and Vs velocity structures in various offshore and onshore environments various configurations of crustal investigation where both body waves (and surface) waves are progressively included in the inversion scheme. Solving the forward problem for 2D geometry could be efficiently performed in frequency by using a direct solver
The simulation of far-field wavelets using frequency-domain air-gun array near-field wavelets
Institute of Scientific and Technical Information of China (English)
Song Jian-Guo; Deng Yong; Tong Xin-Xin
2013-01-01
Air-gun arrays are used in marine-seismic exploration. Far-field wavelets in subsurface media represent the stacking of single air-gun ideal wavelets. We derived single air-gun ideal wavelets using near-field wavelets recorded from near-field geophones and then synthesized them into far-field wavelets. This is critical for processing wavelets in marine-seismic exploration. For this purpose, several algorithms are currently used to decompose and synthesize wavelets in the time domain. If the traveltime of single air-gun wavelets is not an integral multiple of the sampling interval, the complex and error-prone resampling of the seismic signals using the time-domain method is necessary. Based on the relation between the frequency-domain phase and the time-domain time delay, we propose a method that first transforms the real near-field wavelet to the frequency domain via Fourier transforms;then, it decomposes it and composes the wavelet spectrum in the frequency domain, and then back transforms it to the time domain. Thus, the resampling problem is avoided and single air-gun wavelets and far-field wavelets can be reliably derived. The effect of ghost reflections is also considered, while decomposing the wavelet and removing the ghost reflections. Modeling and real data processing were used to demonstrate the feasibility of the proposed method.
Tantum, Stacy L.; Colwell, Kenneth A.; Scott, Waymond R.; Torrione, Peter A.; Collins, Leslie M.; Morton, Kenneth D.
2013-06-01
Frequency-domain electromagnetic induction (EMI) sensors have been shown to provide target signatures which enable discrimination of landmines from harmless clutter. In particular, frequency-domain EMI sensors are well-suited for target characterization by inverting a physics-based signal model. In many model-based signal processing paradigms, the target signatures can be decomposed into a weighted sum of parameterized basis functions, where the basis functions are intrinsic to the target under consideration and the associated weights are a function of the target sensor orientation. When sensor array data is available, the spatial diversity of the measured signals may provide more information for estimating the basis function parameters. After model inversion, the basis function parameters can form the foundation of model-based classification of the target as landmine or clutter. In this work, sparse model inversion of spatial frequency-domain EMI sensor array data followed by target classification using a statistical model is investigated. Results for data measured with a prototype frequency-domain EMI sensor at a standardized test site are presented. Preliminary results indicate that extracting physics-based features from spatial frequency-domain EMI sensor array data followed by statistical classification provides an effective approach for classifying targets as landmine or clutter.
Li, Gang; Li, Yuguo
2017-01-01
We present a joint inversion method for the transmitter navigation and the seafloor resistivity for frequency domain marine controlled-source electromagnetic (CSEM) data. The inversion approach is based on the modified BFGS scheme, which has an advantage that one can update the Hessian matrix by using the BFGS scheme rather than computing the Hessian matrix itself during the inversion process. The partial derivatives of the electromagnetic field responses with respect to both the seafloor resistivity and the transmitter navigation parameters including the azimuth, dip and horizontal positions of the transmitter antenna are analytically calculated. We invert for both the navigation parameters of the towed dipole source (including antenna azimuth, dip, and horizontal positions) and seafloor resistivity by using the whole range of data instead of the near-field data (usually source-receiver offset navigation parameters can be independently resolved, and a better reconstruction can be obtained with multiple frequency data. The inversions of both the synthetical and field data sets indicate that our inversion method can simultaneously reconstruct seafloor resistivity structures and transmitter navigation parameters.
McClatchy, David M; Rizzo, Elizabeth J; Wells, Wendy A; Cheney, Philip P; Hwang, Jeeseong C; Paulsen, Keith D; Pogue, Brian W; Kanick, Stephen C
2016-06-20
Localized measurements of scattering in biological tissue provide sensitivity to microstructural morphology but have limited utility to wide-field applications, such as surgical guidance. This study introduces sub-diffusive spatial frequency domain imaging (sd-SFDI), which uses high spatial frequency illumination to achieve wide-field sampling of localized reflectances. Model-based inversion recovers macroscopic variations in the reduced scattering coefficient [Formula: see text] and the phase function backscatter parameter (γ). Measurements in optical phantoms show quantitative imaging of user-tuned phase-function-based contrast with accurate decoupling of parameters that define both the density and the size-scale distribution of scatterers. Measurements of fresh ex vivo breast tissue samples revealed, for the first time, unique clustering of sub-diffusive scattering properties for different tissue types. The results support that sd-SFDI provides maps of microscopic structural biomarkers that cannot be obtained with diffuse wide-field imaging and characterizes spatial variations not resolved by point-based optical sampling.
Lakowicz, Joseph R.; Gryczynski, Ignacy; Szmacinski, Henryk; Nowaczyk, Kazimierz; Johnson, Michael L.
1992-02-01
During the past seven years, there have been remarkable advances in the frequency-domain method for measurement of time-resolved emission or light scattering. In this presentation we describe the recent extension of the frequency range to 10 GHz using a specially designed microchannel plate PMT. Experimental data will be shown for measurement of picosecond rotational diffusion and for sub-picosecond resolution of time delays. The resolution of ps to ns timescale processes is not obtained at the expense of sensitivity or is it shown by measurements on the intrinsic tryptophan emission from hemoglobin. We also describe a time- resolved reflectance imaging experiment on a scattering medium containing an absorbing object. Time-resolved imaging of the back-scattered light is realized by means of a RF-phase- sensitive camera, synchronized to the laser pulses. By processing the stored images, a final image can be created, the contrast of which is based only on time differences of the back- scattered photons. This image reveals the presence and position of the absorber within the scattering medium. And finally, we describe a new methodology, fluorescence lifetime imaging (FLIM), in which the contrast depends on the fluorescence lifetime at each point in a two-dimensional image, and not the local concentration and/or intensity of the fluorophore. We used FLIM to create lifetime images of NADH when free in solution and when bound to malate dehydrogenase. FLIM has numerous potential applications in cell biology and imaging.
Zero-guard-interval coherent optical OFDM with overlapped frequency-domain CD and PMD equalization.
Chen, Chen; Zhuge, Qunbi; Plant, David V
2011-04-11
This paper presents a new channel estimation/equalization algorithm for coherent OFDM (CO-OFDM) digital receivers, which enables the elimination of the cyclic prefix (CP) for OFDM transmission. We term this new system as the zero-guard-interval (ZGI)-CO-OFDM. ZGI-CO-OFDM employs an overlapped frequency-domain equalizer (OFDE) to compensate both chromatic dispersion (CD) and polarization mode dispersion (PMD) before the OFDM demodulation. Despite the zero CP overhead, ZGI-CO-OFDM demonstrates a superior PMD tolerance than the previous reduced-GI (RGI)-CO-OFDM, which is verified under several different PMD conditions. Additionally, ZGI-CO-OFDM can improve the channel estimation accuracy under high PMD conditions by using a larger intra-symbol frequency-averaging (ISFA) length as compared to RGI-CO-OFDM. ZGI-CO-OFDM also enables the use of ever smaller fast Fourier transform (FFT) sizes (i.e. OFDM. We show that ZGI-CO-OFDM requires reasonably small additional computation effort (~13.6%) compared to RGI-CO-OFDM for 112-Gb/s transmission over a 1600-km dispersion-uncompensated optical link.
Gizon, Laurent; Barucq, Hélène; Duruflé, Marc; Hanson, Chris S.; Leguèbe, Michael; Birch, Aaron C.; Chabassier, Juliette; Fournier, Damien; Hohage, Thorsten; Papini, Emanuele
2017-03-01
Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims: Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods: We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results: We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions: The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.
Multimedia Traffic Queueing Analysis in High-Speed Networks: a Frequency Domain Approach
Hwang, Chia-Lin
Multimedia traffic in high speed networks possesses correlation and burstiness properties. Classical queueing theory has generally ignored such properties by making renewal assumption on message interarrival time. Developing a new traffic theory for integration of multimedia services on high speed networks becomes absolutely essential. In this dissertation, we explore a new concept of spectral characterization of wide-band input process in high speed networks. It provides us a much richer and heterogeneous input environment, while keeping the complexity of queueing analysis tractable. The correlation nature of multimedia traffic is well captured by the input spectral functions. The queue response to the power spectrum and higher order statistics has been studied. Our study shows that the input power spectrum is the most essential statistic for queueing analysis. Further, the input power in low-frequency band has dominant impact on queueing performance, whereas the high-frequency power to a large extent can be neglected. Understanding of queue response to input spectrum provides us a great deal of knowledge to develop advanced network traffic measure theory, and to introduce effective network resource allocation policies. The interrelationship between the traffic spectral statistics and link capacity allocation in high speed network has been investigated. Finally we developed a sophisticated computational tool, called SMAQ, that can integrate traffic measurement and queueing analysis for stochastic modeling. The SMAQ tool takes a unique frequency-domain approach to combine the techniques of signal processing and performance analysis. Essentially, signal processing techniques are used to obtain the steady -state and second-order statistics of a traffic stream. The focus here is on the construction of a special class of Markov chains that can statistically match with each given traffic stream (or superposition of different traffic streams). The analytical queueing
Medina, J. S.; Prosmiti, R.; Villarreal, P.; Delgado-Barrio, G.; Alemán, J. V.
2011-12-01
An approximation to the Fourier transform (FT) of the Kohlrausch function (stretched exponential) with shape parameter 0<β⩽1 is presented by using Havriliak-Negami-like functions. Mathematical expressions to fit their parameters α, γ, and τ, as functions of β (0<β⩽1 and 1<β<2) are given, which allows a quick identification in the frequency domain of the corresponding shape factor β. Reconstruction via fast Fourier transform of frequency approximants to time domain are shown as good substitutes in short times though biased in long ones (increasing discrepancies as β→1). The method is proposed as a template to commute time and frequency domains when analyzing complex data. Such a strategy facilitates intensive algorithmic search of parameters while adjusting the data of one or several Kohlrausch-Williams-Watts relaxations.
Time-variable frequency of events in domains of Tilia cambium
Directory of Open Access Journals (Sweden)
Wiesław Włoch
2014-02-01
Full Text Available In the cambium of linden, producing xylem with interlocked grain, domains active, as regards the occurrence of events, and inactive ones can be distinguished. The area of the cambium investigated was an assemblage of small domains among which at certain periods domains Z, and, at another period, domains S were active. The inclination of the grain was changing in the direction corresponding to the type of the active domains. Alternative occurrence of periods of activity of Z and S domains led to the formation of interlocked grain in the xylem, with a much longer wave than the height of a pair domains.
Directory of Open Access Journals (Sweden)
Gul Ar Navi Khan
2014-08-01
Full Text Available Background: Preeclampsia is a disorder characterized by development of hypertension to the extent of 140/90 mmHg or more with proteinuria after 20th weeks of pregnancy in a previously normotensive and non proteinuric woman. Physiologically blood pressure is controlled by Autonomic Nervous System (ANS so study of ANS during pregnancy plays a significant role to extract some vital information which may be helpful to deal with Pregnancy Induced Hypertension (PIH or preeclampsia. The autonomic nervous system and changes in ANS during different pathophysiological conditions could be evaluated with heart rate variability analysis test. The modification in the autonomic control occurs during pregnancy and its evaluation through Heart Rate Variability (HRV analysis is very informative technique now a day but studied little thus the main objective of our project is to compare the maternal HRV changes between normal pregnancy and pre-eclamptic pregnancy. Methods: 48 subjects (33 of normotensive pregnant women i.e., control group and 15 pre-eclamptic pregnant women i.e, study group of more than 20 weeks pregnancy were recruited from the outpatients, antenatal unit and wards of obstetrics and gynaecology department of JNMC, AMU, Aligarh. Physical examination was done and anthropometric measurement like height and weight were taken. BMI was calculated as per Quetlet's index. Urine test was conducted to every pregnant woman for urine albumin and we designated the pregnant women as pre-eclamptic women on the basis of definition. The subject was advised to take complete bed rest in supine position for 15 minutes in a cool and calm environment. The recording of short term HRV was done according to recommendation of the task force on HRV. The data was transferred from Medicaid machine to window based computer with HRV analysis software. Frequency domain analysis of HRV was taken for further statistical analysis. Results: There was no significant difference of
Double-grid finite-difference frequency-domain (DG-FDFD) method for scattering from chiral objects
Alkan, Erdogan; Elsherbeni, Atef
2013-01-01
This book presents the application of the overlapping grids approach to solve chiral material problems using the FDFD method. Due to the two grids being used in the technique, we will name this method as Double-Grid Finite Difference Frequency-Domain (DG-FDFD) method. As a result of this new approach the electric and magnetic field components are defined at every node in the computation space. Thus, there is no need to perform averaging during the calculations as in the aforementioned FDFD technique [16]. We formulate general 3D frequency-domain numerical methods based on double-grid
Frequency domain phase noise analysis of dual injection-locked optoelectronic oscillators.
Jahanbakht, Sajad
2016-10-01
Dual injection-locked optoelectronic oscillators (DIL-OEOs) have been introduced as a means to achieve very low-noise microwave oscillations while avoiding the large spurious peaks that occur in the phase noise of the conventional single-loop OEOs. In these systems, two OEOs are inter-injection locked to each other. The OEO with the longer optical fiber delay line is called the master OEO, and the other is called the slave OEO. Here, a frequency domain approach for simulating the phase noise spectrum of each of the OEOs in a DIL-OEO system and based on the conversion matrix approach is presented. The validity of the new approach is verified by comparing its results with previously published data in the literature. In the new approach, first, in each of the master or slave OEOs, the power spectral densities (PSDs) of two white and 1/f noise sources are optimized such that the resulting simulated phase noise of any of the master or slave OEOs in the free-running state matches the measured phase noise of that OEO. After that, the proposed approach is able to simulate the phase noise PSD of both OEOs at the injection-locked state. Because of the short run-time requirements, especially compared to previously proposed time domain approaches, the new approach is suitable for optimizing the power injection ratios (PIRs), and potentially other circuit parameters, in order to achieve good performance regarding the phase noise in each of the OEOs. Through various numerical simulations, the optimum PIRs for achieving good phase noise performance are presented and discussed; they are in agreement with the previously published results. This further verifies the applicability of the new approach. Moreover, some other interesting results regarding the spur levels are also presented.
Spatially-dense, multi-spectral, frequency-domain diffuse optical tomography of breast cancer
Ban, Han Yong
Diffuse optical tomography (DOT) employs near-infrared light to image the concentration of chromophores and cell organelles in tissue and thereby providing access to functional parameters that can differentiate cancerous from normal tissues. This thesis describes research at the bench and in the clinic that explores and identifies the potential of DOT breast cancer imaging. The bench and clinic instrumentation differ but share important features: they utilize a very large, spatially dense, set of source-detector pairs (10 7) for imaging in the parallel-plate geometry. The bench experiments explored three-dimensional (3D) image resolution and fidelity as a function of numerous parameters and also ascertained the effects of a chest wall phantom. The chest wall is always present but is typically ignored in breast DOT. My experiments clarified chest wall influences and developed schemes to mitigate these effects. Mostly, these schemes involved selective data exclusion, but their efficacy also depended on reconstruction approach. Reconstruction algorithms based on analytic (fast) Fourier inversion and linear algebraic techniques were explored. The clinical experiments centered around a DOT instrument that I designed, constructed, and have begun to test (in-vitro and in-vivo). This instrumentation offers many features new to the field. Specifically, the imager employs spatially-dense, multi-spectral, frequency-domain data; it possesses the world's largest optical source-detector density yet reported, facilitated by highly-parallel CCD-based frequency-domain imaging based on gain-modulation heterodyne detection. The instrument thus measures both phase and amplitude of the diffusive light waves. Other features include both frontal and sagittal breast imaging capabilities, ancillary cameras for measurement of breast boundary profiles, real-time data normalization, and mechanical improvements for patient comfort. The instrument design and construction is my most significant
Digital Frequency Domain Fluorometry and the Study of Hoechst 33258 Dye-Dna Interactions
Feddersen, Brett Andrew
Fluorescence is a powerful tool for the study of chemical and biological processes. The typical decay times of fluorescence are ideal to study events in the pico to nanosecond range. On these time scales, the motions of many biological processes can be studied. The use of frequency domain fluorometry to measure the lifetime of the excited state has been used for many years. However, the development of an acquisition system based on modern digital techniques, presented in this thesis, has opened the door to different types of experiments that previously were either too time consuming or could not be done. The use of digital techniques and the development of a method to modulate an image intensifier have made it possible to incorporate linear and matrix detectors in frequency domain fluorometry. The extension of time -resolved fluorescence measurements to linear arrays has made it possible to follow the time evolution of the emission spectra while the use of matrix detectors has permitted the measurement of the lifetime at every "pixel" of an image. The dye Hoechst 33258 has been used for many years in the study of DNA and DNA binding. However, the fluorescent properties of Hoechst 33258 are not well understood. The dye is highly quenched in aqueous solutions and becomes brightly fluorescent when bound to Acdot T rich sequences of DNA or placed in non-aqueous solutions. The fluorescence of Hoechst 33258 seems to arise from two different solvation states of the molecule. When Hoechst 33258 binds to calf thymus DNA or poly(d(A cdotT)), the molecule becomes highly fluorescent, yet the two states can still be distinguished. The two states are attributed to different binding modes of the dye. The loose binding allows access of water molecules which results in different emission properties. On the other hand, when Hoechst binds onto d(CGCGAATTCGCG) only one lifetime is observed. The single lifetime has been attributed to strong binding of the Hoechst molecule onto the AATT
Ruge, P.; Birk, C.
2007-07-01
This paper deals with the dynamic analysis of infinite beam models. The translational and the rotational dynamic stiffness of both Timoshenko and Euler-Bernoulli beams on Winkler foundation are derived and compared in the frequency-domain. The situation of vanishing elastic foundation is included as a special case. Here, special emphasis is placed on the asymptotic behaviour of the derived stiffness expressions for high frequencies, since this is of importance in case of transient excitations. It is shown that the dynamic stiffness of the infinite Timoshenko beam follows a linear function of iω, whereas rational powers of iω are involved in case of Euler-Bernoulli's model. The stiffness formulations can be transformed into the time-domain using the mixed-variables technique. This is based on a rational approximation of the low-frequency force-displacement relationship and a subsequent algebraic splitting process. At the same time, the high-frequency asymptotic dynamic stiffness is transformed into the time-domain in closed-form. It is shown that the Timoshenko beam is equivalent to a simple dashpot in the high-frequency limit, whereas Euler-Bernoulli's beam model leads to fractional derivatives of the unknown state variables in an equivalent time-domain description. This finding confirms the superiority of Timoshenko's model especially for high frequencies and transient excitations. Numerical examples illustrate the differences with respect to the two beam models and demonstrate the applicability of the proposed method for the time-domain transformation of force-displacement relationships.
Institute of Scientific and Technical Information of China (English)
Hongde Qin; Jing Shen; Xiaobo Chen
2011-01-01
The free-surface Green function method is widely used in solving the radiation or diffraction problems caused by a ship or ocean structure oscillating on the waves.In the context of inviscid potential flow,hydrodynamic problems such as multi-body interaction and tank side wall effect cannot be properly dealt with based on the traditional free-surface frequency domain Green function method,in which the water viscosity is omitted and the energy dissipation effect is absent.In this paper,an open-sea Green function with viscous dissipation was presented within the theory of visco-potential flow.Then the tank Green function with a partial reflection from the side walls in wave tanks was formulated as a formal sum of open-sea Green functions representing the infinite images between two parallel side walls of the source in the tank.The new far-field characteristics of the tank Green function is vitally important for improving the validity of side-wall effects evaluation,which can be used in supervising the tank model tests.
Pratesi, S; Donzelli, G
2000-01-01
Near infrared spectroscopy (NIRS) is a non invasive, portable, safe technique for monitoring cerebral oxygenation and haemodynamics. A new frequency-domain tissue oximeter based on a multi-distance measurement protocol is presented. The effects of apneic episodes on cerebral and peripheral arterial oxygen saturation (SatO2) in preterm newborns, as monitored by NIRS and by pulse oximetry, are reported. The study population consist of 5 preterms (26 to 30 weeks of gestational age), in the second week of postnatal age, affected by apnea of prematurity. NIRS and pulse oximetric measurements were made contemporarily for a 40-minutes period for each infant. All monitorized apneic events were associated with bradicardia, and resolved spontaneously or after tactile stimulation. As results: a) there was always cerebral deoxygenation in association with apneic events, b) the mean SatO2 as measured by NIRS was slightly lower than the pulse oximeter readings, c) cerebral SatO2 decreased faster and the absolute value of the cerebral SaO2 decrease was greater than that measured peripherally (mean value of 27 versus 13%), d) increases of cerebral deoxyhemoglobin and total hemoglobin and a decrease of oxyhemoglobin were also observed. These preliminary results show that peripheral oxygen saturation measurements as measured by pulse oximetry could not always reflect brain oxygenation.
Indian Academy of Sciences (India)
Kallol Khan; Badri Prasad Patel; Yogendra Nath
2010-12-01
The forced vibration analysis of bimodulus material laminated structures is a challenging problem due to non-smooth nonlinear nature of governing equations. The most commonly used direct time integration schemes show numerical instability and do not predict steady state response except for limited number of cases without considering in-plane inertia. This is due to the sudden change of restoring force from positive/negative half cycle to negative/positive half cycle exciting higher modes/harmonics at every instant of a cycle change leading to numerical instability in the time marching scheme. In the present work, Galerkin time domain approach is successfully used for the forced vibration analysis of bimodular cylindrical panels. The effect of bimodularity ratio on the frequency response of cylindrical panels for few typical geometrical and lamination parameters is studied for the ﬁrst time. It is found that the positive half cycle amplitude is greater than the negative half cycle amplitude for $E_{2t}/E_{2c} < 1$ and is smaller for $E_{2t}/E_{2c} > 1$. Further, the percentage difference of positive and negative half cycle amplitudes decreases with the increase in $E_{2t}/E_{2c}$. The stresses under dynamic loading are different for positive and negative half of a vibration cycle.
Gizon, Laurent; Duruflé, Marc; Hanson, Chris S; Leguèbe, Michael; Birch, Aaron C; Chabassier, Juliette; Fournier, Damien; Hohage, Thorsten; Papini, Emanuele
2016-01-01
Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equati...
Singh-Moon, Rajinder P.; Roblyer, Darren M.; Bigio, Irving J.; Joshi, Shailendra
2014-09-01
We present an application of spatial frequency-domain imaging (SFDI) to the wide-field imaging of drug delivery to brain tissue. Measurements were compared with values obtained by a previously validated variation of diffuse reflectance spectroscopy, the method of optical pharmacokinetics (OP). We demonstrate a cross-correlation between the two methods for absorption extraction and drug concentration determination in both experimental tissue phantoms and freshly extracted rodent brain tissue. These methods were first used to assess intra-arterial (IA) delivery of cationic liposomes to brain tissue in Sprague Dawley rats under transient cerebral hypoperfusion. Results were found to be in agreement with previously published experimental data and pharmacokinetic models of IA drug delivery. We then applied the same scheme to evaluate IA mitoxantrone delivery to glioma-bearing rats. Good correlation was seen between OP and SFDI determined concentrations taken from normal and tumor averaged sites. This study shows the feasibility of mapping drug/tracer distributions and encourages the use of SFDI for spatial imaging of tissues for drug/tracer-tagged carrier deposition and pharmacokinetic studies.
Bender, Amy N; de Haan, Tijmen; Dobbs, Matt A; Gilbert, Adam J; Montgomery, Joshua; Rowlands, Neil; Smecher, Graeme M; Smith, Ken; Wilson, Andrew
2014-01-01
Frequency domain multiplexing (fMux) is an established technique for the readout of transition-edge sensor (TES) bolometers in millimeter-wavelength astrophysical instrumentation. In fMux, the signals from multiple detectors are read out on a single pair of wires reducing the total cryogenic thermal loading as well as the cold component complexity and cost of a system. The current digital fMux system, in use by POLARBEAR, EBEX, and the South Pole Telescope, is limited to a multiplexing factor of 16 by the dynamic range of the Superconducting Quantum Interference Device pre-amplifier and the total system bandwidth. Increased multiplexing is key for the next generation of large format TES cameras, such as SPT-3G and POLARBEAR2, which plan to have on the of order 15,000 detectors. Here, we present the next generation fMux readout, focusing on the warm electronics. In this system, the multiplexing factor increases to 64 channels per module (2 wires) while maintaining low noise levels and detector stability. This ...
A HYBRID TECHNIQUE FOR FREQUENCY DOMAIN IDENTIFICATION OF SERVO SYSTEM WITH FRICTION FORCE
Directory of Open Access Journals (Sweden)
SHAIK.RAFI KIRAN,
2011-03-01
Full Text Available The system identification process in servo system with frictional force seems to be a complex task becauseof its non-linear nature. For such non-linear systems, a good choice is system identification in frequencydomain. However, most of the techniques are manual and are inappropriate for determination of systemparameters. This makes system identification ineffective for servo systems with frictional force. Toovercome this issue, a hybrid technique is proposed in this paper. The proposed technique exploits neuralnetwork and genetic algorithm to determine the system parameters of servo systems with friction. In theproposed technique, the target parameters are determined from the transfer function derived for thesystem. Subsequently, the system parameters are identified by a process formed by blending the neuralnetwork and genetic algorithm techniques. Prior to performing the identification procedure, backpropagation training is given to the neural network using a pre-examined dataset. Then with thecombined operation of neural network and genetic algorithm, the system parameters that are closer tothe target parameters for the servo system with frictional force are determined. The technique isimplemented and compared with the existing frequency domain identification technique. From thecomparative results, it is evident that the proposed technique outperforms the existing technique.
Energy Technology Data Exchange (ETDEWEB)
Viana, Rodrigo S.S.; Tardelli, Tiago C.; Yoriyaz, Helio, E-mail: hyoriyaz@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Jackowski, Marcel P., E-mail: mjack@ime.usp.b [University of Sao Paulo (USP), SP (Brazil). Dept. of Computer Science
2011-07-01
In recent years, a new technique for in vivo spectrographic imaging of stable isotopes was presented as Neutron Stimulated Emission Computed Tomography (NSECT). In this technique, a fast neutrons beam stimulates stable nuclei in a sample, which emit characteristic gamma radiation. The photon energy is unique and is used to identify the emitting nuclei. The emitted gamma energy spectra can be used for reconstruction of the target tissue image and for determination of the tissue elemental composition. Due to the stochastic nature of photon emission process by irradiated tissue, one of the most suitable algorithms for tomographic reconstruction is the Expectation-Maximization (E-M) algorithm, once on its formulation are considered simultaneously the probabilities of photons emission and detection. However, a disadvantage of this algorithm is the introduction of noise in the reconstructed image as the number of iterations increases. This increase can be caused either by features of the algorithm itself or by the low sampling rate of projections used for tomographic reconstruction. In this work, a linear filter in the frequency domain was used in order to improve the quality of the reconstructed images. (author)
Frequency domain reduced order models for gravitational waves from aligned-spin black-hole binaries
Pürrer, Michael
2014-01-01
Black-hole binary coalescences are one of the most promising sources for the first detection of gravitational waves. Fast and accurate theoretical models of the gravitational radiation emitted from these coalescences are highly important for the detection and extraction of physical parameters. Spinning effective-one-body (EOB) models for binaries with aligned spins have been shown to be highly faithful, but are slow to generate and thus have not yet been used for parameter estimation studies. I provide a frequency-domain singular value decomposition (SVD)-based surrogate reduced order model that is thousands to hundred thousands times faster for typical system masses and has a faithfulness mismatch of better than $\\sim 0.1\\%$ with the original SEOBNRv1 model for advanced LIGO detectors. This model enables parameter estimation studies up to signal-to-noise ratios (SNRs) of 20 and even up to SNR 50 for masses below $50 M_\\odot$. This article discusses various choices for approximations and interpolation over th...
Klose, C. D.; Kim, H. K.; Netz, U.; Blaschke, S.; Zwaka, P. A.; Mueller, G. A.; Beuthan, J.; Hielscher, A. H.
2009-02-01
Novel methods that can help in the diagnosis and monitoring of joint disease are essential for efficient use of novel arthritis therapies that are currently emerging. Building on previous studies that involved continuous wave imaging systems we present here first clinical data obtained with a new frequency-domain imaging system. Three-dimensional tomographic data sets of absorption and scattering coefficients were generated for 107 fingers. The data were analyzed using ANOVA, MANOVA, Discriminant Analysis DA, and a machine-learning algorithm that is based on self-organizing mapping (SOM) for clustering data in 2-dimensional parameter spaces. Overall we found that the SOM algorithm outperforms the more traditional analysis methods in terms of correctly classifying finger joints. Using SOM, healthy and affected joints can now be separated with a sensitivity of 0.97 and specificity of 0.91. Furthermore, preliminary results suggest that if a combination of multiple image properties is used, statistical significant differences can be found between RA-affected finger joints that show different clinical features (e.g. effusion, synovitis or erosion).
Haverkort, Maurits W.
2016-05-01
Depending on the material and edge under consideration, core level spectra manifest themselves as local excitons with multiplets, edge singularities, resonances, or the local projected density of states. Both extremes, i.e., local excitons and non-interacting delocalized excitations are theoretically well under control. Describing the intermediate regime, where local many body interactions and band-formation are equally important is a challenge. Here we discuss how Quanty, a versatile quantum many body script language, can be used to calculate a variety of different core level spectroscopy types on solids and molecules, both in the frequency as well as the time domain. The flexible nature of Quanty allows one to choose different approximations for different edges and materials. For example, using a newly developed method merging ideas from density renormalization group and quantum chemistry [1-3], Quanty can calculate excitons, resonances and band-excitations in x-ray absorption, photoemission, x-ray emission, fluorescence yield, non-resonant inelastic x-ray scattering, resonant inelastic x-ray scattering and many more spectroscopy types. Quanty can be obtained from: http://www.quanty.org.
Volterra series truncation and kernel estimation of nonlinear systems in the frequency domain
Zhang, B.; Billings, S. A.
2017-02-01
The Volterra series model is a direct generalisation of the linear convolution integral and is capable of displaying the intrinsic features of a nonlinear system in a simple and easy to apply way. Nonlinear system analysis using Volterra series is normally based on the analysis of its frequency-domain kernels and a truncated description. But the estimation of Volterra kernels and the truncation of Volterra series are coupled with each other. In this paper, a novel complex-valued orthogonal least squares algorithm is developed. The new algorithm provides a powerful tool to determine which terms should be included in the Volterra series expansion and to estimate the kernels and thus solves the two problems all together. The estimated results are compared with those determined using the analytical expressions of the kernels to validate the method. To further evaluate the effectiveness of the method, the physical parameters of the system are also extracted from the measured kernels. Simulation studies demonstrates that the new approach not only can truncate the Volterra series expansion and estimate the kernels of a weakly nonlinear system, but also can indicate the applicability of the Volterra series analysis in a severely nonlinear system case.
Fusion of infrared and visible images based on saliency scale-space in frequency domain
Chen, Yanfei; Sang, Nong; Dan, Zhiping
2015-12-01
A fusion algorithm of infrared and visible images based on saliency scale-space in the frequency domain was proposed. Focus of human attention is directed towards the salient targets which interpret the most important information in the image. For the given registered infrared and visible images, firstly, visual features are extracted to obtain the input hypercomplex matrix. Secondly, the Hypercomplex Fourier Transform (HFT) is used to obtain the salient regions of the infrared and visible images respectively, the convolution of the input hypercomplex matrix amplitude spectrum with a low-pass Gaussian kernel of an appropriate scale which is equivalent to an image saliency detector are done. The saliency maps are obtained by reconstructing the 2D signal using the original phase and the amplitude spectrum, filtered at a scale selected by minimizing saliency map entropy. Thirdly, the salient regions are fused with the adoptive weighting fusion rules, and the nonsalient regions are fused with the rule based on region energy (RE) and region sharpness (RS), then the fused image is obtained. Experimental results show that the presented algorithm can hold high spectrum information of the visual image, and effectively get the thermal targets information at different scales of the infrared image.
Osburn, Thomas; Evans, Charles; Hopper, Seth
2014-01-01
We present an algorithm for calculating the metric perturbations and gravitational self-force for extreme-mass-ratio inspirals (EMRIs) with eccentric orbits. The massive black hole is taken to be Schwarzschild and metric perturbations are computed in Lorenz gauge. The perturbation equations are solved as coupled systems of ordinary differential equations in the frequency domain. Accurate local behavior of the metric is attained through use of the method of extended homogeneous solutions and mode-sum regularization is used to find the self-force. We focus on calculating the self-force with sufficient accuracy to ensure its error contributions to the phase in a long term orbital evolution will be $\\delta\\Phi \\lesssim 10^{-2}$ radians. This requires the orbit-averaged force to have fractional errors $\\lesssim 10^{-8}$ and the oscillatory part of the self-force to have errors $\\lesssim 10^{-3}$ (a level frequently easily exceeded). Our code meets this error requirement in the oscillatory part, extending the reach...
Probing the disassembly of ultrafast laser heated gold using frequency domain interferometry.
Ao, Tommy; Ping, Yuan; Lee, Edward
2005-10-01
Ultrafast laser heating of a solid offers a unique approach to examine the behavior of non-equilibrium high energy density states. Initially, the electrons are optically excited while the ions in the lattice remain cold. This is followed by electron-electron and electron-phonon relaxation. Recently, experiments were performed in which ultrathin freestanding, gold foils were heated by a femtosecond pump laser to a strongly overdriven regime with energy densities reaching 20 MJ/kg. Interestingly, femtosecond laser reflectivity and transmission measurements on the heated sample revealed a quasi-steady-state behavior before the onset of hydrodynamic expansion. This led to the conjecture of the existence of a metastable, disordered state prior to the disassembly of the solid. To further examine the dynamics of ultrafast laser heated solids, frequency domain interferometry (FDI) was used to provide an independent observation. The highly sensitive change in the phase shift of the FDI probe clearly showed evidence of the quasi-steady-state behavior. The new experiment also yielded a detailed measurement of the time scale of such a quasi-steady-state phase that may help elucidate the process of electron-phonon coupling and disassembly in a strongly overdriven regime.
Empirical frequency domain model for fixed-pattern noise in infrared focal plane arrays
Pérez, Francisco; Pezoa, Jorge E.; Figueroa, Miguel; Torres, Sergio N.
2014-11-01
In this paper, a new empirical model for the spatial structure of the fixed-pattern noise (FPN) observed in infrared (IR) focal-plane arrays (FPA) is presented. The model was conceived after analyzing, in the spatial frequency domain, FPN calibration data from different IR cameras and technologies. The analysis showed that the spatial patterns of the FPN are retained in the phase spectrum, while the noise intensity is determined by the magnitude spectrum. Thus, unlike traditional representations, the proposed model abstracts the FPN structure using one matrix for its magnitude spectrum and another matrix for its phase spectrum. Three applications of the model are addressed here. First, an algorithm is provided for generating random samples of the FPN with the same spatial pattern of the actual FPN. Second, the model is used to assess the performance of non-uniformity correction (NUC) algorithms in the presence of spatially correlated and uncorrelated FPN. Third, the model is used to improve the NUC capability of a method that requires, as a reference, a proper FPN sample.
Frequency and Spatial Domains Adaptive-based Enhancement Technique for Thermal Infrared Images
Directory of Open Access Journals (Sweden)
Debasis Chaudhuri
2014-09-01
Full Text Available Low contrast and noisy image limits the amount of information conveyed to the user. With the proliferation of digital imagery and computer interface between man-and-machine, it is now viable to consider digital enhancement in the image before presenting it to the user, thus increasing the information throughput. With better contrast, target detection and discrimination can be improved. The paper presents a sequence of filtering operations in frequency and spatial domains to improve the quality of the thermal infrared (IR images. Basically, two filters – homomorphic filter followed by adaptive Gaussian filter are applied to improve the quality of the thermal IR images. We have systematically evaluated the algorithm on a variety of images and carefully compared it with the techniques presented in the literature. We performed an evaluation of three filter banks such as homomorphic, Gaussian 5×5 and the proposed method, and we have seen that the proposed method yields optimal PSNR for all the thermal images. The results demonstrate that the proposed algorithm is efficient for enhancement of thermal IR images.Defence Science Journal, Vol. 64, No. 5, September 2014, pp.451-457, DOI:http://dx.doi.org/10.14429/dsj.64.6873
Directory of Open Access Journals (Sweden)
Carlo Ruzzo
2016-10-01
Full Text Available System identification of offshore floating platforms is usually performed by testing small-scale models in wave tanks, where controlled conditions, such as still water for free decay tests, regular and irregular wave loading can be represented. However, this approach may result in constraints on model dimensions, testing time, and costs of the experimental activity. For such reasons, intermediate-scale field modelling of offshore floating structures may become an interesting as well as cost-effective alternative in a near future. Clearly, since the open sea is not a controlled environment, traditional system identification may become challenging and less precise. In this paper, a new approach based on Frequency Domain Decomposition (FDD method for Operational Modal Analysis is proposed and validated against numerical simulations in ANSYS AQWA v.16.0 on a simple spar-type structure. The results obtained match well with numerical predictions, showing that this new approach, opportunely coupled with more traditional wave tanks techniques, proves to be very promising to perform field-site identification of the model structures.
Murdock, Richard J; Putnam, Shawn A; Das, Soumen; Gupta, Ankur; Chase, Elyse D Z; Seal, Sudipta
2017-01-16
A clinically relevant magneto-optical technique (fd-FRS, frequency-domain Faraday rotation spectroscopy) for characterizing proteins using antibody-functionalized magnetic nanoparticles (MNPs) is demonstrated. This technique distinguishes between the Faraday rotation of the solvent, iron oxide core, and functionalization layers of polyethylene glycol polymers (spacer) and model antibody-antigen complexes (anti-BSA/BSA, bovine serum albumin). A detection sensitivity of ≈10 pg mL(-1) and broad detection range of 10 pg mL(-1) ≲ cBSA ≲ 100 µg mL(-1) are observed. Combining this technique with predictive analyte binding models quantifies (within an order of magnitude) the number of active binding sites on functionalized MNPs. Comparative enzyme-linked immunosorbent assay (ELISA) studies are conducted, reproducing the manufacturer advertised BSA ELISA detection limits from 1 ng mL(-1) ≲ cBSA ≲ 500 ng mL(-1) . In addition to the increased sensitivity, broader detection range, and similar specificity, fd-FRS can be conducted in less than ≈30 min, compared to ≈4 h with ELISA. Thus, fd-FRS is shown to be a sensitive optical technique with potential to become an efficient diagnostic in the chemical and biomolecular sciences.
Mosher, Mark
Within a wave energy converter's operational bandwidth, device operation tends to be optimal in converting mechanical energy into a more useful form at an incident wave period that is proximal to that of a power-producing mode of motion. Point absorbers, a particular classification of wave energy converters, tend to have a relative narrow optimal bandwidth. When not operating within the narrow optimal bandwidth, a point absorber's response and efficiency is attenuated. Given the wide range of sea-states that can be expected during a point absorber's operational life, these devices require a means to adjust, or control, their natural response to maximize the amount of energy absorbed in the large population of non-optimal conditions. In the field of wave energy research, there is considerable interest in the use of non-linear control techniques to this end. Non-linear control techniques introduce time-varying and state dependent control parameters into the point absorber motion equations, which usually motivates a computationally expensive numerical integration to determine the response of the device - important metrics such as gross converted power and relative travels of the device's pieces are extracted through post processing of the time series data. As an alternative, the work presented in this thesis was based on a closed form perturbation based approach for analysis of the response of a device with periodically-varying control parameters, subject to regular wave forcing, in the frequency domain. The proposed perturbation based method provides significant savings in computational time and enables the device's response to be represented in a closed form manner with a relatively small number of solution components - each component is comprised of a complex amplitude and oscillation frequency. This representation of the solution was found to be very concise and descriptive, and to lend itself to the calculation of gross absorbed power and travel constraint
DEFF Research Database (Denmark)
Rodrigues, J.; Brincker, Rune; Andersen, P.
2004-01-01
that length. The idea is applied in the analysis of ambient vibration data collected in a ¼ scale model of a 4-story building. The results show that a considerable improvement is achieved, in terms of noise reduction in the spectral density functions and corresponding quality of the frequency domain modal...
DEFF Research Database (Denmark)
Escolano-Carrasco, José; Jacobsen, Finn; López, J.J.
2008-01-01
The finite-difference time-domain (FDTD) method provides a simple and accurate way of solving initial boundary value problems. However, most acoustic problems involve frequency dependent boundary conditions, and it is not easy to include such boundary conditions in an FDTD model. Although solutions...
Tantum, Stacy L.; Colwell, Kenneth A.; Morton, Kenneth D., Jr.; Scott, Waymond R., Jr.; Collins, Leslie M.; Torrione, Peter A.
2012-06-01
Frequency-domain electromagnetic induction (EMI) sensors have been shown to provide target signatures which enable discrimination of landmines from harmless clutter. In particular, frequency-domain EMI sensors are well-suited for target characterization by inverting a physics-based signal model. In many model-based signal processing paradigms, the target signatures can be decomposed into a weighted sum of parameterized basis functions, where the basis functions are intrinsic to the target under consideration and the associated weights are a function of the target sensor orientation. When spatial data is available, the diversity of the measured signals may provide more information for estimating the basis function parameters. After model inversion, the basis function parameters can be used as features for classifying the target as landmine or clutter. In this work, feature extraction from spatial frequency-domain EMI sensor data is investigated. Results for data measured with a prototype frequency-domain EMI sensor at a standardized test site are presented. Preliminary results indicate that Structured relevance vector machine (sRVM) regression model inversion using spatial data provides stable, and sparse, sets of target features.
Kierkegaard, Axel; Boij, Susann; Efraimsson, Gunilla
2010-02-01
Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.
Renormalized scattering series for frequency-domain waveform modelling of strong velocity contrasts
Jakobsen, M.; Wu, R. S.
2016-08-01
An improved description of scattering and inverse scattering processes in reflection seismology may be obtained on the basis of a scattering series solution to the Helmoltz equation, which allows one to separately model primary and multiple reflections. However, the popular scattering series of Born is of limited seismic modelling value, since it is only guaranteed to converge if the global contrast is relatively small. For frequency-domain waveform modelling of realistic contrasts, some kind of renormalization may be required. The concept of renormalization is normally associated with quantum field theory, where it is absolutely essential for the treatment of infinities in connection with observable quantities. However, the renormalization program is also highly relevant for classical systems, especially when there are interaction effects that act across different length scales. In the scattering series of De Wolf, a renormalization of the Green's functions is achieved by a split of the scattering potential operator into fore- and backscattering parts; which leads to an effective reorganization and partially re-summation of the different terms in the Born series, so that their order better reflects the physics of reflection seismology. It has been demonstrated that the leading (single return) term in the De Wolf series (DWS) gives much more accurate results than the corresponding Born approximation, especially for models with high contrasts that lead to a large accumulation of phase changes in the forward direction. However, the higher order terms in the DWS that are associated with internal multiples have not been studied numerically before. In this paper, we report from a systematic numerical investigation of the convergence properties of the DWS which is based on two new operator representations of the DWS. The first operator representation is relatively similar to the original scattering potential formulation, but more global and explicit in nature. The second
Maetzler, Walter; Karam, Marie; Berger, Monika Fruhmann; Heger, Tanja; Maetzler, Corina; Ruediger, Heinz; Bronzova, Juliana; Lobo, Patricia Pita; Ferreira, Joaquim J; Ziemssen, Tjalf; Berg, Daniela
2015-03-01
The autonomic nervous system (ANS) is regularly affected in Parkinson's disease (PD). Information on autonomic dysfunction can be derived from e.g. altered heart rate variability (HRV) and sympathetic skin response (SSR). Such parameters can be quantified easily and measured repeatedly which might be helpful for evaluating disease progression and therapeutic outcome. In this 2-center study, HRV and SSR of 45 PD patients and 26 controls were recorded. HRV was measured during supine metronomic breathing and analyzed in time- and frequency-domains. SSR was evoked by repetitive auditory stimulation. Various ANS parameters were compared (1) between patients and healthy controls, (2) to clinical scales (Unified Parkinson's disease rating scale, Mini-Mental State Examination, Becks Depression Inventory), and (3) to disease duration. Root mean square of successive differences (RMSSD) and low frequency/high frequency (LF/HF) ratio differed significantly between PD and controls. Both, HRV and SSR parameters showed low or no association with clinical scores. Time-domain parameters tended to be affected already at early PD stages but did not consistently change with longer disease duration. In contrast, frequency-domain parameters were not altered in early PD phases but tended to be lower (LF, LF/HF ratio), respectively higher (HF) with increasing disease duration. This report confirms previous results of altered ANS parameters in PD. In addition, it suggests that (1) these ANS parameters are not relevantly associated with motor, behavioral, and cognitive changes in PD, (2) time-domain parameters are useful for the assessment of early PD, and (3) frequency-domain parameters are more closely associated with disease duration.
Directory of Open Access Journals (Sweden)
SARIKA TALE,
2011-04-01
Full Text Available Heart disease occurs eventually in majority of patients with diabetes mellitus and to be the outstanding factor in over all diabetes morbidity and mortality rates. Thus the timely detection of diabetic autonomic neuropathy and the use of effective means to improve autonomic nervous system function become of almost significance. In this work Electrocardiogram (ECG data of 20 Diabetes Mellitus (DM and 20 normal control volunteers were recorded and autonomic nervous system activities are quantified by means of frequency and time domainanalysis. Time domain measure ,Standard deviation of successive NN intervals (SDNN,NN intervals differing more than 50 msec.( NN50 count,Percentage value of NN50 count( pNN50 count, HRV triangular index, show a lower variation in the DM patient group compared to normal subjects and p value <0.01. The frequency domain measures indicate significant differences in very low frequency (VLF, low frequency (LF power and high frequency (HF power. Value generated from the ratio of low frequency to high frequency, (LF/HF ispretty high, with not much significance between both groups.
Institute of Scientific and Technical Information of China (English)
Z.J.YANG; A.J.DEEKS
2008-01-01
A frequency-domain approach based on the semi-analytical scaled boundary finite element method (SBFEM) was developed to calculate dynamic stress intensity factors (DSIFs) at bimaterial interface cracks subjected to transient loading. Be-cause the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction, and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions, the mixed-mode DSIFs were calculated directly by definition. The complex frequency-response functions of DSIFs were then used by the fast Fourier transform (FFT) and the inverse FFT to calculate time histories of DSIFs. A benchmark example was modelled. Good re-sults were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM.
Kimura, Tomoki; Taki, Hirofumi; Sakamoto, Takuya; Sato, Toru
2009-07-01
We employed frequency domain interferometry (FDI) for use as a medical acoustic imager to detect multiple targets with high range resolution. The phase of each frequency component of an echo varies with the frequency, and target intervals can be estimated from the phase variance. This processing technique is generally used in radar imaging. When the interference within a range gate is coherent, the cross correlation between the desired signal and the coherent interference signal is nonzero. The Capon method works under the guiding principle that output power minimization cancels the desired signal with a coherent interference signal. Therefore, we utilize frequency averaging to suppress the correlation of the coherent interference. The results of computational simulations using a pseudoecho signal show that the Capon method with adaptive frequency averaging (AFA) provides a higher range resolution than a conventional method. These techniques were experimentally investigated and we confirmed the effectiveness of the proposed method of processing by FDI.
Zhai, Ding; Lu, Anyang; Li, Jinghao; Zhang, Qingling
2016-10-01
This paper deals with the problem of the fault detection (FD) for continuous-time singular switched linear systems with multiple time-varying delay. In this paper, the actuator fault is considered. Besides, the systems faults and unknown disturbances are assumed in known frequency domains. Some finite frequency performance indices are initially introduced to design the switched FD filters which ensure that the filtering augmented systems under switching signal with average dwell time are exponentially admissible and guarantee the fault input sensitivity and disturbance robustness. By developing generalised Kalman-Yakubovic-Popov lemma and using Parseval's theorem and Fourier transform, finite frequency delay-dependent sufficient conditions for the existence of such a filter which can guarantee the finite-frequency H- and H∞ performance are derived and formulated in terms of linear matrix inequalities. Four examples are provided to illustrate the effectiveness of the proposed finite frequency method.
First Frequency-Domain Interferometry Observations of Large-Scale Vertical Motion in the Atmosphere.
Muschinski, Andreas; Chilson, Phillip B.; Kern, Stefan; Nielinger, Jost; Schmidt, Gerhard; Prenosil, Thomas
1999-05-01
The spatiotemporal distribution of the vertical velocity at synoptic and subsynoptic scales is key to the patterns of weather and climate on earth. On these scales, the vertical velocity is on the order of one to a few centimeters per second, typically about three orders of magnitude smaller than typical horizontal wind velocities. Because of the smallness of large-scale vertical velocities relative to typical horizontal velocities, a direct observation of the large-scale vertical air velocity is extremely difficult.In a case study on observational material obtained during a 68-h experiment using the SOUSY very high frequency (VHF) radar in the Harz Mountains in Germany, the authors present the first intercomparison between three different sources of physical information that can provide large-scale vertical wind velocities: (i) the Doppler shifts observed with a vertically pointing VHF radar; (ii) the rates of change of the altitudes of refractive-index discontinuities as identified with frequency-domain interferometry (FDI), which is still a relatively unexplored technique in meteorology; and (iii) the output of a regional numerical weather prediction model (NWPM), which has been set up to model the meteorological situation during the observational period.There are several phenomena that have been known to possibly cause significant biases in mean vertical velocities retrieved from the Doppler shifts measured with vertically pointing clear-air VHF radars: (i) stationary or nonstationary gravity waves with vertical-velocity amplitudes up to the order of 1 m s1; (ii) stationary or horizontally advected tilted refractive-index discontinuities that are aspect sensitive in the VHF regime; and (iii) a correlation between the radar-reflectivity fluctuations and the vertical-velocity fluctuations within a vertically propagating gravity wave.On the basis of an intercomparison between the vertical velocities retrieved from (i) `standard Doppler' VHF radar observations, (ii
Taki, Hirofumi; Taki, Kousuke; Yamakawa, Makoto; Shiina, Tsuyoshi; Kudo, Motoi; Sato, Toru
2014-01-01
We have proposed an ultrasound imaging method based on frequency domain interferometry (FDI) with an adaptive beamforming technique to depict real-time high-resolution images of human carotid artery. Our previous study has investigated the performance of the proposed imaging method under an ideal condition with a high signal-to-noise ratio (SNR). In the present study, we propose a technique that has the potential to improve accuracy in estimating echo intensity using the FDI imaging method. We investigated the performance of the proposed technique in a simulation study that two flat interfaces were located at depths of 15.0 and 15.2 mm and white noise was added. Because the -6 dB bandwidth of the signal used in this simulation study is 2.6 MHz, the conventional B-mode imaging method failed to depict the two interfaces. Both the conventional and proposed FDI imaging methods succeeded to depict the two interfaces when the SNR ranged from 15 to 30 dB. However, the average error of the estimated echo intensity at the interfaces using the conventional FDI imaging method ranged from 7.2 to 10.5 dB. In contrast, that using the FDI imaging method with the proposed technique ranged from 2.0 to 2.2 dB. The present study demonstrates the potential of the FDI imaging method in depicting robust and high-range-resolution ultrasound images of arterial wall, indicating the possibility to improve the diagnosis of atherosclerosis in early stages.
Frequency-domain L2-stability conditions for time-varying linear and nonlinear MIMO systems
Institute of Scientific and Technical Information of China (English)
Zhihong HUANG; Y. V. VENKATESH; Cheng XIANG; Tong Heng LEE
2014-01-01
The paper deals with the L2-stability analysis of multi-input-multi-output (MIMO) systems, governed by integral equations, with a matrix of periodic/aperiodic time-varying gains and a vector of monotone, non-monotone and quasi-monotone nonlin-earities. For nonlinear MIMO systems that are described by differential equations, most of the literature on stability is based on an application of quadratic forms as Lyapunov-function candidates. In contrast, a non-Lyapunov framework is employed here to derive new and more general L2-stability conditions in the frequency domain. These conditions have the following features:i) They are expressed in terms of the positive definiteness of the real part of matrices involving the transfer function of the linear time-invariant block and a matrix multiplier function that incorporates the minimax properties of the time-varying linear/nonlinear block. ii) For certain cases of the periodic time-varying gain, they contain, depending on the multiplier function chosen, no restrictions on the normalized rate of variation of the time-varying gain, but, for other periodic/aperiodic time-varying gains, they do. Overall, even when specialized to periodic-coefficient linear and nonlinear MIMO systems, the stability conditions are distinct from and less restrictive than recent results in the literature. No comparable results exist in the literature for aperiodic time-varying gains. Furthermore, some new stability results concerning the dwell-time problem and time-varying gain switching in linear and nonlinear MIMO systems with periodic/aperiodic matrix gains are also presented. Examples are given to illustrate a few of the stability theorems.
Decay-ratio calculation in the frequency domain with the LAPUR code using 1D-kinetics
Energy Technology Data Exchange (ETDEWEB)
Munoz-Cobo, J. L.; Escriva, A.; Garcia, C.; Berna, C. [Instituto de Ingenieria Energetica, Universitat Politecnica de Valencia, Camino de Vera s/n, Valencia 46022 (Spain); Melara, J. [IBERDROLA Ingenieria Y Construccion, C/ Jose Bardasano Baos 9, 28016 Madrid (Spain)
2012-07-01
This paper deals with the problem of computing the Decay Ratio in the frequency domain codes as the LAPUR code. First, it is explained how to calculate the feedback reactivity in the frequency domain using slab-geometry i.e. 1D kinetics, also we show how to perform the coupling of the 1D kinetics with the thermal-hydraulic part of the LAPUR code in order to obtain the reactivity feedback coefficients for the different channels. In addition, we show how to obtain the reactivity variation in the complex domain by solving the eigenvalue equation in the frequency domain and we compare this result with the reactivity variation obtained in first order perturbation theory using the 1D neutron fluxes of the base case. Because LAPUR works in the linear regime, it is assumed that in general the perturbations are small. There is also a section devoted to the reactivity weighting factors used to couple the reactivity contribution from the different channels to the reactivity of the entire reactor core in point kinetics and 1D kinetics. Finally we analyze the effects of the different approaches on the DR value. (authors)
GUM2DFT—a software tool for uncertainty evaluation of transient signals in the frequency domain
Eichstädt, S.; Wilkens, V.
2016-05-01
The Fourier transform and its counterpart for discrete time signals, the discrete Fourier transform (DFT), are common tools in measurement science and application. Although almost every scientific software package offers ready-to-use implementations of the DFT, the propagation of uncertainties in line with the guide to the expression of uncertainty in measurement (GUM) is typically neglected. This is of particular importance in dynamic metrology, when input estimation is carried out by deconvolution in the frequency domain. To this end, we present the new open-source software tool GUM2DFT, which utilizes closed formulas for the efficient propagation of uncertainties for the application of the DFT, inverse DFT and input estimation in the frequency domain. It handles different frequency domain representations, accounts for autocorrelation and takes advantage of the symmetry inherent in the DFT result for real-valued time domain signals. All tools are presented in terms of examples which form part of the software package. GUM2DFT will foster GUM-compliant evaluation of uncertainty in a DFT-based analysis and enable metrologists to include uncertainty evaluations in their routine work.
Akcay, Sarp
2010-01-01
Fast, reliable orbital evolutions of compact objects around massive black holes will be needed as input for gravitational wave search algorithms in the data stream generated by the planned Laser Interferometer Space Antenna (LISA). Currently, the state of the art is a time-domain code by [Phys. Rev. D{\\bf 81}, 084021, (2010)] that computes the gravitational self-force on a point-particle in an eccentric orbit around a Schwarzschild black hole. Currently, time-domain codes take up to a few days to compute just one point in parameter space. In a series of articles, we advocate the use of a frequency-domain approach to the problem of gravitational self-force (GSF) with the ultimate goal of orbital evolution in mind. Here, we compute the GSF for a particle in a circular orbit in Schwarzschild spacetime. We solve the linearized Einstein equations for the metric perturbation in Lorenz gauge. Our frequency-domain code reproduces the time-domain results for the GSF up to $\\sim 1000$ times faster for small orbital rad...
Frequency-domain photoacoustic imaging system%频率域光声成像系统的研究
Institute of Scientific and Technical Information of China (English)
杨虹; 黄远辉; 苗少峰; 宫睿; 邵晓鹏; 毕祥丽
2016-01-01
Frequency-domain photoacoustic imaging is a new imaging modality, which uses the output amplitude information periodically modulated by a continuous-wave laser as a light source to stimulate biological tissues and to produce photoacoustic signals processed at frequency-domain and used to image the tissues. Firstly, the principles, developments and research status of photoacoustic imaging and frequency-domain photoacoustic imaging were introduced, and then the specific test methods and basic reconstruction algorithms of the frequency-domain photoacoustic imaging filed were described. In order to make up for time domain photoacoustic imaging with high costs, great harmful, poor portability and so on shortcomings, two imaging modalities were proposed and two complete experimental system structure diagrams were exhibited, showing different features and developing directions of photoacoustic imaging with respect to the traditional domain-photoacoustic imaging. At last, the outlook of the frequency-domain photoacoustic imaging was made to provide some references and guidance for our research and development about photoacoustic imaging.%频率域光声成像是指使用连续波激光器输出激光光源,利用该调制后的激光信号辐射组织,在频率域对激励的光声信号进行处理并成像的方式.首先阐述光声成像和频率域光声成像的原理、发展以及研究现状,然后介绍频率域光声成像的具体实验方法和基本重建算法.为了弥补时域光声成像成本高、伤害性大、便携性差等缺点,提出了频率域光声成像的两种成像方式,给出了完整的实验系统结构图,展示其相对于传统时域光声成像不同的研究特点与方向.最后对频率域光声成像进行展望,为光声成像在国内的研究和发展提供一定的借鉴和引导.
Analysis of Time and Frequency Domain Pace Algorithms for OFDM with Virtual Subcarriers
DEFF Research Database (Denmark)
Rom, Christian; Manchón, Carles Navarro; Deneire, Luc
2007-01-01
This paper studies common linear frequency direction pilot-symbol aided channel estimation algorithms for orthogonal frequency division multiplexing in a UTRA long term evolution context. Three deterministic algorithms are analyzed: the maximum likelihood (ML) approach, the noise reduction algori...
Bramhavar, Suraj
The concept of optical excitation and detection of nanoscale mechanical motion has led to a variety of tools for non-destructive materials characterization and remote sensing. These techniques, commonly referred to as laser ultrasonics, offer the benefit of high-bandwidth, highly localized measurements, and also allow for the ability to investigate nanoscale devices. The impact of laser ultrasonic systems has been felt in industries ranging from semiconductor metrology to biological and chemical sensing. In this thesis, we develop a variety of techniques utilizing a frequency domain laser ultrasonic approach, where amplitude modulated continuous wave laser light is used instead of traditional pulsed laser sources, and we apply these systems in free-space, optical fiber based, and integrated on-chip configurations. In doing so, we demonstrate the ability to efficiently transduce various types of mechanical motion including surface and bulk acoustic waves, guided acoustic waves, and resonant motion from nanomechanical systems (NEMS). First, we develop a superheterodyne free-space ultrasonic inspection system in an effort to characterize surface acoustic wave dispersion in thin-film material systems. We utilize a similar system to study negative refraction and focusing behavior of guided elastic waves in a thin metal plate, providing a novel approach for the study of negative index physics. Furthermore, we develop a near-field optical technique using optical fibers to simultaneously transduce the motion of 70 NEMS resonators using a single channel. This multiplexed approach serves as a crucial step in moving NEMS technology out of the research laboratory. Finally, we go on to study opto-mechanical interactions between optical whispering gallery mode (WGM) resonators and integrated NEMS devices on the same chip, using the enhanced interactions to study optical forces acting on the nanoscale mechanical devices. This integrated system provides a very efficient mechanical
Frequency domain reflectometry NDE for aging cables in nuclear power plants
Glass, S. W.; Jones, A. M.; Fifield, L. S.; Hartman, T. S.
2017-02-01
Degradation of the cable jacket, electrical insulation, and other cable components of installed cables within nuclear power plants (NPPs) is known to occur as a function of age, temperature, radiation, and other environmental factors. Although system tests verify cable function under normal loads, demonstration of some cable's ability to perform under exceptional loads associated with design-basis events is essential to assuring plant integrity. The cable's ability to perform safely over the initial 40-year planned and licensed life has generally been demonstrated and there have been very few age-related cable failures. With greater than 1000 km of power, control, instrumentation, and other cables typically found in an NPP, replacing all the cables would be a severe cost burden. Justification for life extension to 60 and 80 years requires a cable aging management program that includes condition monitoring to justify cable performance under normal operation as well as accident conditions. A variety of tests are available to assess various aspects of electrical and mechanical cable performance, but none are suitable for all cable configurations nor does any single test confirm all features of interest. One particularly promising test that is beginning to be used more and more by utilities is frequency domain reflectometry (FDR). FDR is a nondestructive electrical inspection technique used to detect and localize faults in power and communication system conductors along the length of a cable from a single connection point. FDR detects discontinuities in the electrical impedance that arise due to cable splices or similar changes along the path of the conductor pair. In addition, FDR has the potential to provide sensitivity to insulation degradation by detecting small changes in impedance between the cable conductors being examined. The technique is also sensitive to cable bends, the particular lay of the cable in tray, proximity to other cable, and other factors that
DEFF Research Database (Denmark)
Nelson, Paul C.; Ewert, Stephan; Carney, Laurel H.;
In the audio-frequency domain, the envelope apparently plays an important role in detection of intensity increments and in comodulation masking release (CMR). The current study addressed the question whether the second-order envelope ("venelope") contributes similarly for comparable experiments...... were found to be the same in conditions with a continuous (modulated) carrier and with traditional gated stimuli for AM frequencies ranging from 4 –64 Hz. The second set of experiments compared the amount of CMR in a tone-in-noise detection task when slow, regular fluctuations were imposed...
DEFF Research Database (Denmark)
Holdyk, Andrzej; Holbøll, Joachim; Arana, Ivan;
2012-01-01
Transient voltages resulting from switching operations depend on an interaction between the breaker, the transformer, cables and a neighbourhood grid and imply a risk for the transformer and other components. In this paper the Frequency Domain Severity Factor (FDSF) is used to assess the severity...... implemented in ATP-EMTP using standard component models and further validated against measurements. The results show the range of overvoltages on the transformer terminals as well as the corresponding FSDF for all turbines under a number of varying parameters. The maximum FDSF of 1.235 and frequency of 445 k...
Nakamura, Satoshi; Goto, Hayato; Kujiraoka, Mamiko; Ichimura, Kouichi
2016-12-01
We propose a scheme for frequency-domain quantum computation (FDQC) in which the errors due to crosstalk are suppressed using extra physical systems coupled to a cavity. FDQC is a promising method to realize large-scale quantum computation, but crosstalk is a major problem. When physical systems employed as qubits satisfy specific resonance conditions, gate errors due to crosstalk increase. In our scheme, the errors are suppressed by controlling the resonance conditions using extra physical systems.
Indian Academy of Sciences (India)
Qian Lin; Xiaofeng Wu; Yun Chen
2015-12-01
This paper studies the global synchronization of non-autonomous, time-delay, chaotic power systems via linear state-error feedback control. The frequency domain criterion and the LMI criterion are proposed and applied to design the coupling matrix. Some algebraic criteria via a single-variable linear coupling are derived and formulated in simple algebraic inequalities. The effectiveness of the new criteria is illustrated with numerical examples.
Numerical Study on Global Motion of Truss Spar in Frequency and Time Domains for the Liwan 3-1 Area
Institute of Scientific and Technical Information of China (English)
LI Lu; LI Binbin; OU Jinping
2011-01-01
Using frequency and time domain analysis, the authors analyzed the hydrodynamics and motion behavior of a Truss Spar platform at a water depth of 1500 m in the Liwan 3-1 area of the South China Sea. Firstly, the seakeeping ability is acquired in the frequency domain by calculating the hull's hydrodynamics and comparing with a semi-submersible platform. The random wave analysis for 100-year, 10-year and 1-year return periods in Liwan 3-1 distinctly shows lower heave but larger surge and pitch responses of the Truss Spar than those of a semi-submersible. Secondly, 3-hour motions of the Truss Spar are predicted and compared in the time domain under 100-year return period conditions in Liwan 3-1 and the Gulf of Mexico. Thirdly, the hull/mooring line coupled and uncoupled models are compared. Finally, the responses of the Truss Spar under 10-year and 1-year return period conditions are assessed. The results reveal that the mooring line damping reflected by the coupled model distinctly decreases the low frequency motior The maximum heave response for 100-year return period waves is 1.23m and below 0. 1m for the case of 1-year return period.
Matsuki, Yoh; Eddy, Matthew T; Herzfeld, Judith
2009-04-08
A simple and effective method, SIFT (spectroscopy by integration of frequency and time domain information), is introduced for processing nonuniformly sampled multidimensional NMR data. Applying the computationally efficient Gerchberg-Papoulis (G-P) algorithm, used previously in picture processing and medical imaging, SIFT supplements data at nonuniform points in the time domain with the information carried by known "dark" points (i.e., empty regions) in the frequency domain. We demonstrate that this rapid integration not only removes the severe pseudonoise characteristic of the Fourier transforms of nonuniformly sampled data, but also provides a robust procedure for using frequency information to replace time measurements. The latter can be used to avoid unnecessary sampling in sampling-limited experiments, and the former can be used to take advantage of the ability of nonuniformly sampled data to minimize trade-offs between the signal-to-noise ratio and the resolution in sensitivity-limited experiments. Processing 2D and 3D data sets takes about 0.1 and 2 min, respectively, on a personal computer. With these several attractive features, SIFT offers a novel, model-independent, flexible, and user-friendly tool for efficient and accurate processing of multidimensional NMR data.
Matsuki, Yoh; Eddy, Matthew T.; Herzfeld, Judith
2009-01-01
A simple and effective method, SIFT (Spectroscopy by Integrating Frequency and Time domain information) is introduced for processing non-uniformly sampled multidimensional NMR data. Applying the computationally efficient Gerchberg-Papoulis (G-P) algorithm, used previously in picture processing and medical imaging, SIFT supplements data at non-uniform points in the time domain with the information carried by known “dark” points (i.e. empty regions) in the frequency domain. We demonstrate that this rapid integration not only removes the severe pseudo-noise characteristic of the Fourier transforms of non-uniformly sampled data, but also provides a robust procedure for using frequency information to replace time measurements. The latter can be used to avoid unnecessary sampling in sampling-limited experiments and the former can be used to take advantage of the ability of non-uniformly sampled data to minimize trade-offs between the signal-to-noise ratio and the resolution in sensitivity-limited experiments. Processing 2D and 3D datasets takes about 0.1 and 2 min, respectively, on a personal computer. With these several attractive features, SIFT offers a novel, model-independent, flexible, and user-friendly tool for efficient and accurate processing of multidimensional NMR data. PMID:19284727
Hui, Xiaonan; Ye, Taihang; Zheng, Shilie; Zhou, Jinhai; Chi, Hao; Jin, Xiaofeng; Zhang, Xianmin
2014-10-01
For a phase-sensitive optical time-domain reflectometer (ϕ-OTDR) distributed sensor system, space-frequency analysis can reduce the false alarm by analyzing the frequency distribution compared with the traditional difference value method. We propose a graphics processing unit (GPU)-based parallel computing method to perform multichannel fast Fourier transform (FFT) and realize the real-time space-frequency analysis. The experiment results show that the time taken by the multichannel FFT decreased considerably based on this GPU parallel computing. The method can be completed with a sensing fiber up to 16 km long and an entry-level GPU. Meanwhile, the GPU can reduce the computing load of the central processing unit from 70% down to less than 20%. We carried out an experiment on a two-point space-frequency analysis, and the results clearly and simultaneously show the vibration point locations and frequency components. The sensor system outputs the real-time space-frequency spectra continuously with a spatial resolution of 16.3 m and frequency resolution of 2.25 Hz.
Spectral Analysis and Sonification of Simulation Data Generated in a Frequency Domain Experiment
2002-09-01
multiples of the fundamental frequencies in the sound. Fundamental frequencies are similar to notes on the musical scale. Fundamental frequencies are...Perceptually, we consider the complexity of a sound as timbre . 45 For example, the timbre of a violin is different than the timbre of a flute, even...two sounds that have the same intensity and timbre for the human ear to distinguish the two sounds as different 50 percent of the time. Similarly
Spencer, E. A.
2014-12-01
We describe the development of a Time Domain Plasma Impedance Probe for the measurement of plasma properties in the ionosphere. It is being designed and developed to fly on cubesat platforms. The new instrument will be capable of making measurements of absolute electron density and electron neutral collision frequency at temporal and spatial resolutions not previously attained. A single measurement can be made in a time as short as 50 microseconds, which yields a spatial resolution of 0.35 meters for a satellite orbital velocity of 7 km/s. By averaging over 100 samples we expect an average spatial resolution of 35 meters. The method essentially consists of applying a small amplitude time limited voltage signal into a probe and measuring the resulting current response. The electron resonant frequencies of interest in the ionosphere are between are typically between 100 kHz and 20 MHz, which sets the required bandwidth. The new time domain method will present a significant improvement over the frequency domain method currently in use. The RF impedance probe has a distinct advantage over other methods used to measure plasma properties, in that it's measurements are not strongly affected by spacecraft charging effects that contaminate measurements made in the plasma environment. We will demonstrate the effectiveness of the instrument using data from sounding rocket missions, give details of the new instrument methodology, and suggest some possible areas of application of the method to measuring space plasmas. The difficulties associated with performing the measurements in a cubesat platform, and subsequently interpreting the measurements, will also be presented.
Silveira, Vladímir de Aquino; Souza, Givago da Silva; Gomes, Bruno Duarte; Rodrigues, Anderson Raiol; Silveira, Luiz Carlos de Lima
2014-01-01
We used psychometric functions to estimate the joint entropy for space discrimination and spatial frequency discrimination. Space discrimination was taken as discrimination of spatial extent. Seven subjects were tested. Gábor functions comprising unidimensionalsinusoidal gratings (0.4, 2, and 10 cpd) and bidimensionalGaussian envelopes (1°) were used as reference stimuli. The experiment comprised the comparison between reference and test stimulithat differed in grating's spatial frequency or envelope's standard deviation. We tested 21 different envelope's standard deviations around the reference standard deviation to study spatial extent discrimination and 19 different grating's spatial frequencies around the reference spatial frequency to study spatial frequency discrimination. Two series of psychometric functions were obtained for 2%, 5%, 10%, and 100% stimulus contrast. The psychometric function data points for spatial extent discrimination or spatial frequency discrimination were fitted with Gaussian functions using the least square method, and the spatial extent and spatial frequency entropies were estimated from the standard deviation of these Gaussian functions. Then, joint entropy was obtained by multiplying the square root of space extent entropy times the spatial frequency entropy. We compared our results to the theoretical minimum for unidimensional Gábor functions, 1/4π or 0.0796. At low and intermediate spatial frequencies and high contrasts, joint entropy reached levels below the theoretical minimum, suggesting non-linear interactions between two or more visual mechanisms. We concluded that non-linear interactions of visual pathways, such as the M and P pathways, could explain joint entropy values below the theoretical minimum at low and intermediate spatial frequencies and high contrasts. These non-linear interactions might be at work at intermediate and high contrasts at all spatial frequencies once there was a substantial decrease in joint
Yin, Gang; Zhang, Yingtang; Mi, Songlin; Fan, Hongbo; Li, Zhining
2016-11-01
To obtain accurate magnetic gradient tensor data, a fast and robust calculation method based on regularized method in frequency domain was proposed. Using the potential field theory, the transform formula in frequency domain was deduced in order to calculate the magnetic gradient tensor from the pre-existing total magnetic anomaly data. By analyzing the filter characteristics of the Vertical vector transform operator (VVTO) and Gradient tensor transform operator (GTTO), we proved that the conventional transform process was unstable which would zoom in the high-frequency part of the data in which measuring noise locate. Due to the existing unstable problem that led to a low signal-to-noise (SNR) for the calculated result, we introduced regularized method in this paper. By selecting the optimum regularization parameters of different transform phases using the C-norm approach, the high frequency noise was restrained and the SNR was improved effectively. Numerical analysis demonstrates that most value and characteristics of the calculated data by the proposed method compare favorably with reference magnetic gradient tensor data. In addition, calculated magnetic gradient tensor components form real aeromagnetic survey provided better resolution of the magnetic sources and original profile.
Catapano, Ilaria; Soldovieri, Francesco
2015-04-01
In the research field of art and archaeology, scientific observation and analysis are hugely demanded to gather as more information as possible on the materials and techniques used to create artworks as well as in previous restoration actions. In this frame, diagnostic tools exploiting electromagnetic waves deserve massive interest tanks to their ability to provide non-invasive and possibly contactless characterization of the investigated objects. Among the electromagnetic diagnostic technologies, those working at frequencies belonging to the 0.1-10 THz range are currently deserving an increased attention since THz waves are capable of penetrating into optically opaque materials (up to the preparation layers), without direct contact and by involving sufficiently low energy to be considered as perfectly non-invasive in practice [1,2]. Moreover, being THz non-ionizing radiations, a moderate exposure to them implies minor long term risks to the molecular stability of the historical artifact and humans. Finally, recent developments of THz technology have allowed the commercialization of compact, flexible and portable systems. One of them is the Fiber-Coupled Terahertz Time Domain System (FICO) developed by Z-Omega, acquired by the Institute of Electromagnetic Sensing of the Environment (IREA) in 2013. This system works in the range from 60GHz to 3THz with a waveform acquisition speed up to 500Hz, it is equipped with fiber optic coupled transmitting and receiving probes and, few months ago, has been potentiated by means of an automatic positioning system enabling to scan a 150mm x 150mm area. In the frame of the IREA research activities regarding cultural heritage, the FICO system is currently adopted to perform both spectroscopy and imaging, which are the two kind of analysis wherein THz technology can be profitably explored [3]. In particular, THz spectroscopy is used to distinguish different artists materials by exploiting their peculiar fingerprint in the absorption
Nadeau, Kyle P.; Durkin, Anthony J.; Tromberg, Bruce J.
2014-05-01
We have developed a method for extracting spatial frequency information content from biological tissue, which is used to calculate tissue optical properties and determine tissue structural orientation. This demodulation method employs a two-dimensional Hilbert transform using a spiral phase function in Fourier space. The approach presented here allows for the determination of tissue optical properties using a single frame of data for each modulation frequency, increasing imaging speed by two to threefold versus conventional, three-phase spatial frequency domain imaging (SFDI). This new single-phase Hilbert transform approach recovers optical property and scattering orientation index values within 1% and 10% of three-phase SFDI, respectively. These results suggest that, using the Hilbert demodulation technique, SFDI data acquisition speed can be increased significantly while preserving data quality, which will help us move forward toward the implementation of a real-time SFDI platform.
Choi, Yun Seok
2012-01-01
The instantaneous traveltime based inversion was developed to solve the phase wrapping problem, thus generating long-wavelength structures even for a high single-frequency. However, it required aggressive damping to insure proper convergence. A reason for that is the potential for unstable division in the calculation of the instantaneous traveltime for low damping factors. Thus, we propose an inversion algorithm using the amplitude of the derivative wavefield to avoid the unstable division process. Since the amplitude of the derivative wavefield contains the unwrapped-phase information, its inversion has the potential to provide robust inversion results. On the other hand, the damping term rapidly diminishes the amplitude of the derivative wavefield at far source-receiver offsets. As an alternative, we suggest using the logarithmic amplitude of the derivative wavefield. The gradient of this inversion algorithm is obtained by the back-propagation approach, based on the adjoint-state technique. Numerical examples show that the logarithmic-amplitude approach yields better convergent results than the instantaneous traveltime inversion, whereas the pure-amplitude approach does not show much convergence.
Frequency-domain electromagnetic sounding with combination wave in near-field zone
Institute of Scientific and Technical Information of China (English)
苏发; 何继善
1996-01-01
By analysing the propagation law of electromagnetic wave,the distribution pattern of the field and the theory of frequency electromagnetic sounding,the physical mechanisms that make the frequency electromagnetic sounding in near-field zone difficult are discussed.Based on the theory of near source field,a new method of dual-frequency electromagnetic sounding of combination wave in near-field zone is advanced.Meanwhile,the method of measurement of fields,the definition of apparent resistivity and the numerical algorithm are approached.
Spatial and frequency domain ring source models for the single muscle fiber action potential
DEFF Research Database (Denmark)
Henneberg, Kaj-åge; R., Plonsey
1994-01-01
In the paper, single-fibre models for the extracellular action potential are developed that will allow the potential to the evaluated at an arbitrary field point in the extracellular space. Fourier-domain models are restricted in that they evaluate potentials at equidistant points along a line...
Directory of Open Access Journals (Sweden)
Guo Shuixia
2010-06-01
Full Text Available Abstract Background Reverse-engineering approaches such as Bayesian network inference, ordinary differential equations (ODEs and information theory are widely applied to deriving causal relationships among different elements such as genes, proteins, metabolites, neurons, brain areas and so on, based upon multi-dimensional spatial and temporal data. There are several well-established reverse-engineering approaches to explore causal relationships in a dynamic network, such as ordinary differential equations (ODE, Bayesian networks, information theory and Granger Causality. Results Here we focused on Granger causality both in the time and frequency domain and in local and global networks, and applied our approach to experimental data (genes and proteins. For a small gene network, Granger causality outperformed all the other three approaches mentioned above. A global protein network of 812 proteins was reconstructed, using a novel approach. The obtained results fitted well with known experimental findings and predicted many experimentally testable results. In addition to interactions in the time domain, interactions in the frequency domain were also recovered. Conclusions The results on the proteomic data and gene data confirm that Granger causality is a simple and accurate approach to recover the network structure. Our approach is general and can be easily applied to other types of temporal data.
Lee, Intae; Jang, Gil-Jin
2012-12-01
A novel method is proposed to improve the performance of independent vector analysis (IVA) for blind signal separation of acoustic mixtures. IVA is a frequency-domain approach that successfully resolves the well-known permutation problem by applying a spherical dependency model to all pairs of frequency bins. The dependency model of IVA is equivalent to a single clique in an undirected graph; a clique in graph theory is defined as a subset of vertices in which any pair of vertices is connected by an undirected edge. Therefore, IVA imposes the same amount of statistical dependency on every pair of frequency bins, which may not match the characteristics of real-world signals. The proposed method allows variable amounts of statistical dependencies according to the correlation coefficients observed in real acoustic signals and, hence, enables more accurate modeling of statistical dependencies. A number of cliques constitutes the new dependency graph so that neighboring frequency bins are assigned to the same clique, while distant bins are assigned to different cliques. The permutation ambiguity is resolved by overlapped frequency bins between neighboring cliques. For speech signals, we observed especially strong correlations across neighboring frequency bins and a decrease in these correlations with an increase in the distance between bins. The clique sizes are either fixed, or determined by the reciprocal of the mel-frequency scale to impose a wider dependency on low-frequency components. Experimental results showed improved performances over conventional IVA. The signal-to-interference ratio improved from 15.5 to 18.8 dB on average for seven different source locations. When we varied the clique sizes according to the observed correlations, the stability of the proposed method increased with a large number of cliques.
Nicolaides, Lena; Garcia, Jose A.; Mandelis, Andreas; Abrams, Stephen H.
2001-04-01
Frequency-domain IR photothermal radiometry is introduced as a dynamic dental diagnostic tool and its main features are compared with modulated laser luminescence for quantifying sound and carious enamel or dentin. Dental caries found in the fissures or grooves of teeth is very difficult to diagnose or quantify with the present clinical techniques. Visual examination and dental radiographs do not detect the presence of decay until there has been significant carious destruction of the tooth. A high-spatial-resolution dynamic experimental imaging set-up, which can provide simultaneous measurements of laser-induced frequency-domain IR photothermal radiometric and luminescence signals form defects in teeth, was developed. Following optical absorption of laser photons, the new set-up can monitor simultaneously and independently the non-radiative conversion, and the radiative de-excitation in turbid media such as hard dental tissue. This work is intended to show the complementarity between modulated luminescence and photothermal frequency scans in detecting carious lesions in teeth. A sound extracted molar with a dentin-enamel interface was introduced to examine the depth profilometric abilities of the method. Occlusal surfaces of teeth with potential areas of demineralization or carious destruction in the fissures were examined and compared to the signals produced by the sound enamel establishing the depth profilometric abilities of the method. The significance to clinical dentistry lies in the potential of this technique to detect and monitor early carious lesions in the pits and fissures of teeth.
Wei, Ying-Chieh; Wei, Ying-Yu; Chang, Kai-Hsiung; Young, Ming-Shing
2012-04-01
The objective of this study is to design and develop a programmable electrocardiogram (ECG) generator with frequency domain characteristics of heart rate variability (HRV) which can be used to test the efficiency of ECG algorithms and to calibrate and maintain ECG equipment. We simplified and modified the three coupled ordinary differential equations in McSharry's model to a single differential equation to obtain the ECG signal. This system not only allows the signal amplitude, heart rate, QRS-complex slopes, and P- and T-wave position parameters to be adjusted, but can also be used to adjust the very low frequency, low frequency, and high frequency components of HRV frequency domain characteristics. The system can be tuned to function with HRV or not. When the HRV function is on, the average heart rate can be set to a value ranging from 20 to 122 beats per minute (BPM) with an adjustable variation of 1 BPM. When the HRV function is off, the heart rate can be set to a value ranging from 20 to 139 BPM with an adjustable variation of 1 BPM. The amplitude of the ECG signal can be set from 0.0 to 330 mV at a resolution of 0.005 mV. These parameters can be adjusted either via input through a keyboard or through a graphical user interface (GUI) control panel that was developed using LABVIEW. The GUI control panel depicts a preview of the ECG signal such that the user can adjust the parameters to establish a desired ECG morphology. A complete set of parameters can be stored in the flash memory of the system via a USB 2.0 interface. Our system can generate three different types of synthetic ECG signals for testing the efficiency of an ECG algorithm or calibrating and maintaining ECG equipment.
Wei, Ying-Chieh; Wei, Ying-Yu; Chang, Kai-Hsiung; Young, Ming-Shing
2012-04-01
The objective of this study is to design and develop a programmable electrocardiogram (ECG) generator with frequency domain characteristics of heart rate variability (HRV) which can be used to test the efficiency of ECG algorithms and to calibrate and maintain ECG equipment. We simplified and modified the three coupled ordinary differential equations in McSharry's model to a single differential equation to obtain the ECG signal. This system not only allows the signal amplitude, heart rate, QRS-complex slopes, and P- and T-wave position parameters to be adjusted, but can also be used to adjust the very low frequency, low frequency, and high frequency components of HRV frequency domain characteristics. The system can be tuned to function with HRV or not. When the HRV function is on, the average heart rate can be set to a value ranging from 20 to 122 beats per minute (BPM) with an adjustable variation of 1 BPM. When the HRV function is off, the heart rate can be set to a value ranging from 20 to 139 BPM with an adjustable variation of 1 BPM. The amplitude of the ECG signal can be set from 0.0 to 330 mV at a resolution of 0.005 mV. These parameters can be adjusted either via input through a keyboard or through a graphical user interface (GUI) control panel that was developed using LABVIEW. The GUI control panel depicts a preview of the ECG signal such that the user can adjust the parameters to establish a desired ECG morphology. A complete set of parameters can be stored in the flash memory of the system via a USB 2.0 interface. Our system can generate three different types of synthetic ECG signals for testing the efficiency of an ECG algorithm or calibrating and maintaining ECG equipment.
Institute of Scientific and Technical Information of China (English)
ZHANG Fan; YANG Jian-min; LI Run-pei; CHEN Gang
2008-01-01
For the floating structures in deepwater, the coupling effects of the mooring lines and risers on the motion responses of the structures become increasingly significant. Viscous damping, inertial mass, current loading and restoring, etc. from these slender structures should be carefully handled to accurately predict the motion responses and line tensions. For the spar platforms, coupling the mooring system and riser with the vessel motion typically results in a reduction in extreme motion responses. This article presents numerical simulations and model tests on a new cell-truss spar platform in the State Key Laboratory of Ocean Engineering in Shanghai Jiaotong University. Results from three calculation methods, including frequency-domain analysis, time-domain semi-coupled and fully-coupled analyses, were compared with the experimental data to find the applicability of different approaches. Proposals for the improvement of numerical calculations and experimental technique were tabled as well.
Nonlinear Cascades of Surface Oceanic Geostrophic Kinetic Energy in the Frequency Domain
2012-09-01
hour per response, including ,h# ttm * ,or raviewmg instructions, searching existing data sources gathering and maintaining the data needed, and...two-layer quasigeostrophic (QG) turbulence models and realistic ocean general circulation models , as well as from gridded satellite altimeter data. The...spectral flux flfk) in the wavenumber k domain. Computations of n(u>) in the realistic model also display an "inverse temporal cascade." In satellite
Directory of Open Access Journals (Sweden)
Ran Wang, David H. Fukuda, Jeffrey R. Stout, Edward H. Robinson, Amelia A. Miramonti, Maren S. Fragala, Jay R. Hoffman
2015-06-01
Full Text Available To evaluate the time course of EMG frequency changes during a three-minute maximal effort cycling test (3MT session and to examine which parameter between mean (MNF and median (MDF frequency is more suitable for evaluation of changes in neuromuscular function throughout a 3MT. Eighteen recreationally-active men volunteered to participate in this study. Maximum voluntary contraction (MVC was measured using a dynamometer to determine maximal EMG frequency of the vastus lateralis (VL of the kicking leg during isometric knee extension. A maximal oxygen consumption test (VO2peak on a cycle ergometer was performed to establish the appropriate load profile for the 3MT which was completed after a period of at least 48 hours. MNF, MDF and power output (PO values were measured at 10-second epochs throughout the duration of the 3MT. Repeated measures analysis of variance was used to compare the changes in EMG frequency, relative to maximal values from the MVC, and change in PO during the testing procedure. MNF, Root Mean Square (RMS, and PO significantly decreased during the 3MT, while MDF did not change significantly. Statistically, EMG frequency and PO decreased at first and remained constant in response to the 3MT, which may be reflective of differing patterns of muscle fiber type fatigue throughout the testing session. Due to decreased variability, changes in neuromuscular function during this protocol may be better evaluated using MNF than MDF.
A Robust Image Watermarking in the Joint Time-Frequency Domain
Directory of Open Access Journals (Sweden)
Çekiç Yalçın
2010-01-01
Full Text Available With the rapid development of computers and internet applications, copyright protection of multimedia data has become an important problem. Watermarking techniques are proposed as a solution to copyright protection of digital media files. In this paper, a new, robust, and high-capacity watermarking method that is based on spatiofrequency (SF representation is presented. We use the discrete evolutionary transform (DET calculated by the Gabor expansion to represent an image in the joint SF domain. The watermark is embedded onto selected coefficients in the joint SF domain. Hence, by combining the advantages of spatial and spectral domain watermarking methods, a robust, invisible, secure, and high-capacity watermarking method is presented. A correlation-based detector is also proposed to detect and extract any possible watermarks on an image. The proposed watermarking method was tested on some commonly used test images under different signal processing attacks like additive noise, Wiener and Median filtering, JPEG compression, rotation, and cropping. Simulation results show that our method is robust against all of the attacks.
Fantini, Sergio; Hueber, Dennis; Franceschini, Maria Angela; Gratton, Enrico; Rosenfeld, Warren; Stubblefield, Phillip G.; Maulik, Dev; Stankovic, Miljan R.
1999-06-01
We have used continuous-wave (CW) and frequency-domain spectroscopy to investigate the optical properties of the newborn piglet brain in vivo and non-invasively. Three anaesthetized, intubated, ventilated and instrumented newborn piglets were placed into a stereotaxic instrument for optimal experimental stability, reproducible probe-to-scalp optical contact and 3D adjustment of the optical probe. By measuring the absolute values of the brain absorption and reduced scattering coefficients at two wavelengths (758 and 830 nm), frequency-domain spectroscopy provided absolute readings (in contrast to the relative readings of CW spectroscopy) of cerebral haemoglobin concentration and saturation during experimentally induced perturbations in cerebral haemodynamics and oxygenation. Such perturbations included a modulation of the inspired oxygen concentration, transient brain asphyxia, carotid artery occlusion and terminal brain asphyxia. The baseline cerebral haemoglobin saturation and concentration, measured with frequency-domain spectroscopy, were about 60% and 42 µM respectively. The cerebral saturation values ranged from a minimum of 17% (during transient brain asphyxia) to a maximum of 80% (during recovery from transient brain asphyxia). To analyse the CW optical data, we have (a) derived a mathematical relationship between the cerebral optical properties and the differential pathlength factor and (b) introduced a method based on the spatial dependence of the detected intensity (dc slope method). The analysis of the cerebral optical signals associated with the arterial pulse and with respiration demonstrates that motion artefacts can significantly affect the intensity recorded from a single optode pair. Motion artefacts can be strongly reduced by combining data from multiple optodes to provide relative readings in the dc slope method. We also report significant biphasic changes (initial decrease and successive increase) in the reduced scattering coefficient measured
Parameterised controller synthesis for SISO-LTI uncertain plants using frequency domain information
Parastvand, Hossein; Khosrowjerdi, Mohammad-Javad
2016-01-01
This paper extends the results of a new model-free approach which has been applied to guarantee nominal stability and performance. In this paper, using a particular controller structure, the robust stability (RS) and robust performance (RP) criteria for single input single output linear time invariant (SISO-LTI) plants with multiplicative uncertainty are transformed to affine functions in terms of controller parameters. It is shown that solving the feasibility problem of these new criteria will lead to controllers that guarantee the RS and performance. There is no need for a plant mathematical model. The required data for controller synthesis are just the frequency responses corresponding to limited samples of the uncertain plant. Also, there is no need for exact data at each frequency for the whole set of frequency responses. The approach is also applicable for designing both low- and high-order controllers. The effectiveness of the proposed technique is illustrated by simulation results.
Institute of Scientific and Technical Information of China (English)
YU Shi-jian; Cheng Jiu-long; LIU Jia-qi
2007-01-01
This paper took the abnormal geological objects with high or low resistivity in the coal face as the background to establish the physical model. 2D forward numerical simulation for electromagnetic wave equation was implemented by the finite-difference scheme. According to the simulative results, the attenuation-absorption coefficient were calculated respectively based on field intensity and frequency shift parameter. Research result indicates, when coal-bed contains high electric resistivity geological abnormal object or low electric resistivity geological abnormal object, absorption attenuation function researched by frequency shift parameter of electromagnetic wave signal is more sensitive than by electromagnetic field intensity parameter.
Simulation of power fluctuation of wind farms based on frequency domain
DEFF Research Database (Denmark)
Lin, Jin; Sun, Yuanzhang; Li, Guojie;
2011-01-01
. To 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......-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...
Dovlo, Edem; Lashkari, Bahman; Choi, Sung soo Sean; Mandelis, Andreas
2015-03-01
This paper demonstrates the co-registration of ultrasound (US) and frequency domain photoacoustic radar (FD-PAR) images with significant image improvement from applying image normalization, filtering and amplification techniques. Achieving PA imaging functionality on a commercial Ultrasound instrument could accelerate clinical acceptance and use. Experimental results presented demonstrate live animal testing and show enhancements in signal-to-noise ratio (SNR), contrast and spatial resolution. The co-registered image produced from the US and phase PA images, provides more information than both images independently.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In this paper, a Turbo aided Cyclic Prefix (CP) reconstruction scheme, termed Turbo-CPR, is proposed for Single-Carrier systems with Frequency-Domain Equalization (SC-FDE) that employ insufficient CP in the transmitter. In Turbo-CPR, the decoder output is incorporated in the process of equalization, i.e. Turbo equalizer is employed. It is shown in the simulation results that Turbo-CPR not only recovers the performance loss due to insufficiency of CP, but also provides extra gains over the lower bound of performance for conventional CP reconstruction schemes.
Richmond, J. H.
1974-01-01
Piecewise-sinusoidal expansion functions and Galerkin's method are employed to formulate a solution for an arbitrary thin-wire configuration in a homogeneous conducting medium. The analysis is performed in the real or complex frequency domain. In antenna problems, the solution determines the current distribution, impedance, radiation efficiency, gain and far-field patterns. In scattering problems, the solution determines the absorption cross section, scattering cross section and the polarization scattering matrix. The electromagnetic theory is presented for thin wires and the forward-scattering theorem is developed for an arbitrary target in a homogeneous conducting medium.
Giovanneschi, F.; Gonzalez-Huici, M. A.; Uschkerat, U.
2013-06-01
In this work we present a comprehensive analysis of the scattered signals from buried landmine-like targets via accurate numerical modeling of Ground Penetrating Radar (GPR) responses considering various antenna-soil-target scenarios. Different characteristics in time and frequency domain are extracted and interpreted for each configuration. The acquired knowledge is useful to better understand the scattering mechanisms of subsurface objects and can be incorporated to target recognition procedures. A brief explanation of the results is also provided together with an overview of the most relevant temporal and spectral features encountered.
Jo, Ju-Yeon; Tanimura, Yoshitaka
2016-01-01
Frequency-domain two-dimensional Raman signals, which are equivalent to coherent two-dimensional Raman scattering (COTRAS) signals, for liquid water and carbon tetrachloride were calculated using an equilibrium-nonequilibrium hybrid MD simulation algorithm. We elucidate mechanisms governing the 2D signal pro?les involving anharmonic mode-mode coupling and the nonlinearities of the polarizability for the intermolecular and intramolecular vibrational modes. The predicted signal pro?les and intensities can be utilized to analyze recently developed single-beam 2D spectra, whose signals are generated from a coherently controlled pulse, allowing the single-beam measurement to be carried out more efficiently.
Petrantonakis, Panagiotis C; Hadjileontiadis, Leontios J
2010-01-01
Emotion discrimination from electroencephalogram (EEG) has gained attention the last decade as a user-friendly and effective approach to EEG-based emotion recognition (EEG-ER) systems. Nevertheless, challenging issues regarding the emotion elicitation procedure, especially its effectiveness, raise. In this work, a novel method, which not only evaluates the degree of emotion elicitation but localizes the emotion information in the time-frequency domain, as well, is proposed. The latter, incorporates multidimensional directed information at the time-frequency EEG representation, extracted using empirical mode decomposition, and introduces an asymmetry index for adaptive emotion-related EEG segment selection. Experimental results derived from 16 subjects visually stimulated with pictures from the valence/arousal space drawn from the International Affective Picture System database, justify the effectiveness of the proposed approach and its potential contribution to the enhancement of EEG-ER systems.
Farooq, Vasim; Serruys, Patrick W; Heo, Jung Ho; Gogas, Bill D; Okamura, Takayuki; Gomez-Lara, Josep; Brugaletta, Salvatore; Garcìa-Garcìa, Hector M; van Geuns, Robert Jan
2011-08-01
Coronary artery bifurcations are a common challenging lesion subset accounting for approximately 10% to 20% of all percutaneous coronary interventions. The provisional T-stenting approach is generally recommended as the first-line management of most lesions. Carina shift is suggested to be the predominant mechanism of side-branch pinching during provisional T-stenting and has been indirectly inferred from bench work and other intravascular imaging modalities. Offline 3-dimensional (3D) reconstructions of patients studied in the first-in-man trial of the high-frequency (160 frames/s) Terumo optical frequency domain imaging system were undertaken using volume-rendering software. Through a series of 3D reconstructions, several novel hypothesis-generating concepts are presented.
Institute of Scientific and Technical Information of China (English)
Lidong Lü; Yuejiang Song; Fan Zhu; Xuping Zhang
2012-01-01
The nonlinear effects that limit the performance of the multi-frequency probe (MFP) based coherent optical time domain reflectometry (C-OTDR) are investigated.Based on theoretical analysis and experimental results,compared with conventional C-OTDR,when the probe pulse has power gradient within the pulse width,self-phase modulation (SPM) and cross-phase modulation (XPM) are strengthened in the new COTDR scheme.The generation of four-wave mixing (FWM) is dependent on SPM and XPM,and with modulation frequency of phase modulator higher than 40 MHz,the stimulated Brillouin scattering (SBS) threshold can be enhanced by more than 5 dB,which benefits the maximum dynamic range of the MFP C-OTDR.
Directory of Open Access Journals (Sweden)
Lin Shao
2016-01-01
Full Text Available This paper aims at the frequency-domain packet scheduling (FDPS problem in orthogonal frequency division multiple access (OFDMA system. Under users’ data queue size constraints, a new swap-based FDPS algorithm is proposed to achieve further improvement in system throughput. In this algorithm, the swap of physical resource blocks (PRBs between different users is introduced to give a comprehensive view of the overall scheduling process. Moreover, the proposed algorithm optimizes the choosing method of swap candidates and always tries to select the user who can maximize the throughput improvement. Simulation results demonstrate that this new algorithm can improve the system throughput significantly as well as reduce the resource waste effectively.
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, P.; Cantieni, R.
2001-01-01
A series of 15 progressive damage tests were performed on a prestressed concrete highway bridge in Switzerland. The ambient response of the bridge was recorded for each damage case with a relatively large number of sensors. Changes in frequencies, damping ratios and MAC values were determined...
Sauvé, Alexandre
2016-01-01
Context: Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for {\
Directory of Open Access Journals (Sweden)
Tomi Roinila
2014-07-01
Full Text Available Silicon nanowire-based field-effect transistors (SiNW FETs have demonstrated the ability of ultrasensitive detection of a wide range of biological and chemical targets. The detection is based on the variation of the conductance of a nanowire channel, which is caused by the target substance. This is seen in the voltage–current behavior between the drain and source. Some current, known as leakage current, flows between the gate and drain, and affects the current between the drain and source. Studies have shown that leakage current is frequency dependent. Measurements of such frequency characteristics can provide valuable tools in validating the functionality of the used transistor. The measurements can also be an advantage in developing new detection technologies utilizing SiNW FETs. The frequency-domain responses can be measured by using a commercial sine-sweep-based network analyzer. However, because the analyzer takes a long time, it effectively prevents the development of most practical applications. Another problem with the method is that in order to produce sinusoids the signal generator has to cope with a large number of signal levels. This may become challenging in developing low-cost applications. This paper presents fast, cost-effective frequency-domain methods with which to obtain the responses within seconds. The inverse-repeat binary sequence (IRS is applied and the admittance spectroscopy between the drain and source is computed through Fourier methods. The methods is verified by experimental measurements from an n-type SiNW FET.
Directory of Open Access Journals (Sweden)
Natalie Baddour
2015-12-01
Full Text Available This paper considers the effect of an impedance mismatch between the absorber and its surroundings on the aborber reconstructions from the photoacoustic signal profile, in particular when a non-delta input pulse is used. A transfer function approach is taken, demonstrating in the case of impedance mismatch how the total response can be modeled using the sum of the mismatch-free response and its time-delayed, time-reversed replicas, which may or may not overlap. It is shown how this approach can be exploited to accommodate the effects of non-delta pulses and/or pulse-equivalent waveforms such as linear-frequency-modulated (LFM chirps, and impedance mismatches in any inversion algorithms, even in the presence of large reflection coefficients. As a consequence, for simple-absorber reconstruction algorithms that assume impulses or ‘short enough’ pulses, the compressive portion of the measured response may be used in reconstruction formulas that do not model the impedance mismatch, regardless of the size of the mismatch. For longer-duration input waveforms, it is demonstrated how existing reconstruction methods can be successfully adapted to include the effect of the impedance mismatch. Simulations are used to illustrate these ideas. The gained physical insight into how components of the generated pressure wave carry absorber information is then exploited for signal inversion and absorber reconstruction in the frequency domain when multi-frequency modulation chirps are used for photoacoustic radar pressure measurements. The foundational theoretical developments ultimately address impendance mismatch issues germane to the major photoacoustic frequency-domain imaging modality to-date, which is the photoacoustic radar.
Brown, Andrew M.; Schmauch, Preston
2012-01-01
Turbine blades in rocket and jet engine turbomachinery experience enormous harmonic loading conditions. These loads result from the integer number of upstream and downstream stator vanes as well as the other turbine stages. Assessing the blade structural integrity is a complex task requiring an initial characterization of whether resonance is possible and then performing a forced response analysis if that condition is met. The standard technique for forced response analysis in rocket engine turbines is to decompose a computational fluid dynamics (CFD).generated flow field into its harmonic components, and to then perform a frequency response analysis at the problematic natural frequencies using cyclically symmetric structural dynamic models. Recent CFD analysis and water-flow testing at NASA/MSFC, though, indicates that this technique may miss substantial harmonic and non ]harmonic excitation sources that become present in complex flows. This complex content can only be captured by a CFD flow field encompassing at least an entire revolution. A substantial development effort to create a series of software programs to enable application of the 360 degree forcing function in a frequency response analysis on cyclic symmetric models has been completed (to be described in a future paper), but the question still remains whether the frequency response analysis itself is capable of capturing the excitation content sufficiently. Two studies comparing frequency response analysis with transient response analysis, therefore, of bladed-disks undergoing this complex flow environment have been performed. The first is of a bladed disk with each blade modeled by simple beam elements and the disk modeled with plates (using the finite element code MSC/NASTRAN). The focus of this model is to be representative of response of realistic bladed disks, and so the dimensions are roughly equivalent to the new J2X rocket engine 1st stage fuel pump turbine. The simplicity of the model allows
Directory of Open Access Journals (Sweden)
Yongqian Li
2017-03-01
Full Text Available A useful method for eliminating the detrimental effect of laser frequency instability on Brillouin signals by employing the self-heterodyne detection of Rayleigh and Brillouin scattering is presented. From the analysis of Brillouin scattering spectra from fibers with different lengths measured by heterodyne detection, the maximum usable pulse width immune to laser frequency instability is obtained to be about 4 µs in a self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR system using a broad-band laser with low frequency stability. Applying the self-heterodyne detection of Rayleigh and Brillouin scattering in BOTDR system, we successfully demonstrate that the detrimental effect of laser frequency instability on Brillouin signals can be eliminated effectively. Employing the broad-band laser modulated by a 130-ns wide pulse driven electro-optic modulator, the observed maximum errors in temperatures measured by the local heterodyne and self-heterodyne detection BOTDR systems are 7.9 °C and 1.2 °C, respectively.
Directory of Open Access Journals (Sweden)
Zhu Yi-Sheng
2003-01-01
Full Text Available An adaptive hierarchical lapped orthogonal transform (HLOT exciser is proposed for tracking, localizing, and rejecting the nonstationary interference in direct sequence spread spectrum (DSSS communications. The method is based on HLOT. It utilizes a fast dynamic programming algorithm to search for the best basis, which matches the interference structure best, in a library of lapped orthogonal bases. The adaptive HLOT differs from conventional block transform and the more advanced modulated lapped transform (MLT in that the former produces arbitrary time-frequency tiling, which can be adapted to the signal structure, while the latter yields fixed tilings. The time-frequency tiling of the adaptive HLOT can be time varying, so it is also able to track the variations of the signal time-frequency structure. Simulation results show that the proposed exciser brings significant performance improvement in the presence of nonstationary time-localized interference with or without instantaneous frequency (IF information compared with the existing block transform domain excisers. Also, the proposed exciser is effective in suppressing narrowband interference and combined narrowband and time-localized impulsive interference.
Zhang, Jianbo; Ge, Hao; Li, Zhe; Ding, Zhanming
2015-01-01
This study develops a method to internally preheat lithium-ion batteries at low temperatures with sinusoidal alternating current (AC). A heat generation rate model in frequency domain is developed based on the equivalent electrical circuit. Using this model as the source term, a lumped energy conservation model is adopted to predict the temperature rise. These models are validated against the experimental results of preheating an 18650 cell at different thermal insulation conditions. The effects of current amplitude and frequency on the heating rate are illustrated with a series of simulated contours of heating time. These contours indicate that the heating rate increases with higher amplitude, lower frequency and better thermal insulation. The cell subjected to an alternating current with an amplitude of 7 A (2.25 C) and a frequency of 1 Hz, under a calibrated heat transfer coefficient of 15.9 W m-2 K-1, can be heated from -20 °C to 5 °C within 15 min and the temperature distribution remains essentially uniform. No capacity loss is found after repeated AC preheating tests, indicating this method incurs little damage to the battery health. These models are computationally-efficient and can be used in real time to control the preheating devices in electric vehicles.
Data-Aided Frequency-Domain 2×2 MIMO Equalizer for 112 Gbit/s PDM-QPSK Coherent Transmission Systems
DEFF Research Database (Denmark)
Pittalà, Fabio; Hauske, Fabian N.; Ye, Yabin;
2012-01-01
Benefits of a low-complexity adaptive 32-tap 2×2 MIMO frequency-domain filter update by data-aided channel estimation over a time-domain filter with DD-LMS are shown. Superior stability and convergence speed is demonstrated with identical impairment tolerance....
The Sine Wave Tuning method: Robust PID controller design in the frequency domain
Directory of Open Access Journals (Sweden)
Š. Bucz
2015-12-01
Full Text Available The paper presents a novel robust PID controller design method for nominal performance specified in terms of maximum overshoot and settling time. The PID controller design provides guaranteed gain margin GM. The parameter of the tuning rules is a suitably chosen point of the plant frequency response obtained by a sine-wave signal with excitation frequency ωn. Then, the designed controller moves this point into the phase crossover with the required gain margin GM. The couple (ωn;GM is specified with respect to closed-loop performance requirements in terms of ηmax (maximum overshoot and ts (settling time according to developed parabolic dependences. The new approach has been verified on a vast batch of benchmark examples; subsequently, the developed algorithm has been extended to robust PID controller design for plants with unstable zero and unstructured uncertainties.
Frequency-domain nonlinear optics in two-dimensionally patterned quasi-phase-matching media
Phillips, C R; Gallmann, L; Keller, U
2015-01-01
Advances in the amplification and manipulation of ultrashort laser pulses has led to revolutions in several areas. Examples include chirped pulse amplification for generating high peak-power lasers, power-scalable amplification techniques, pulse shaping via modulation of spatially-dispersed laser pulses, and efficient frequency-mixing in quasi-phase-matched nonlinear crystals to access new spectral regions. In this work, we introduce and demonstrate a new platform for nonlinear optics which has the potential to combine all of these separate functionalities (pulse amplification, frequency transfer, and pulse shaping) into a single monolithic device. Moreover, our approach simultaneously offers solutions to the performance-limiting issues in the conventionally-used techniques, and supports scaling in power and bandwidth of the laser source. The approach is based on two-dimensional patterning of quasi-phase-matching gratings combined with optical parametric interactions involving spatially dispersed laser pulses...
HIGH RESOLUTION IMAGE PROJECTION IN FREQUENCY DOMAIN FOR CONTINUOUS IMAGE SEQUENCE
Directory of Open Access Journals (Sweden)
M. Nagaraju Naik
2010-09-01
Full Text Available Unlike most other information technologies, which have enjoyed an exponential growth for the past several decades, display resolution has largely stagnated. Low display resolution has in turn limited the resolution of digital images. Scaling is a non-trivial process that involves a trade-off between efficiency, smoothness and sharpness. As the size of an image is increased, so the pixels, which comprise the image, become increasingly visible, making the image to appear soft. Super scalar representation of image sequence is limited due to image information present in low dimensional image sequence. To project a image frame sequence into high-resolution static or fractional scalingvalue, a scaling approach is developed based on energy spectral interpolation and frequency spectral interpolation techniques. To realize the frequency spectral resolution Cubic-B-Spline method is used.
Time-domain representation of frequency dependent inertial forces on offshore structures
DEFF Research Database (Denmark)
Krenk, Steen
2013-01-01
The inertial wave force on a vertical cylinder decreases with decreasing wave length, when the wave length is less than about six times the diameter of the diameter of the cylinder. In structures with a largediameter component like mono-towers the resonance frequency of the structure is typically...... section are uncoupled, and they are easily integrated with e.g. a central difference scheme for the state-space variables. © 2013 Taylor & Francis Group, London....
The analysis of frequency domain characteristics of emotional images in eye-tracking experiment
Fan, Boqiang; Ma, Huimin; Wang, Xiang
2015-07-01
Although recently eye-tracking method has been introduced into behavioral experiments based on dot-probe paradigm, some characteristics in eye-tracking data do not draw as much attention as traditional characteristics like reaction time. It is also necessary to associate eye-tracking data to characteristics of images shown in experiments. In this research, new variables, such as fixation length, times of fixation and times of eye movement, in eye-tracking data were extracted from a behavioral experiment based on dot probe paradigm. They were analyzed and compared to traditional reaction time. After the analysis of positive and negative scenery images, parameters such as hue frequency spectrum PAR (Peak to Average Ratio) were extracted and showed difference between negative and positive images. These parameters of emotional images could discriminate scenery images according to their emotions in an SVM classifier well. Besides, it was found that images' hue frequency spectrum PAR is obviously relevant to eye-tracking statistics. When the dot was on the negative side, negative images' hue frequency spectrum PAR and horizontal eye-jumps confirmed to hyperbolic distribution, while that of positive images was linear with horizontal eye-jumps. The result could help to explain the mechanism of human's attention and boost the study in computer vision.
Cao, Shancheng; Ouyang, Huajiang
2017-01-01
The structural characteristic deflection shapes (CDS’s) such as mode shapes and operational deflection shapes are highly sensitive to structural damage in beam- or plate-type structures. Nevertheless, they are vulnerable to measurement noise and could result in unacceptable identification errors. In order to increase the accuracy and noise robustness of damage identification based on CDS’s using vibration responses of random excitation, joint approximate diagonalization (JAD) technique and gapped smoothing method (GSM) are combined to form a sensitive and robust damage index (DI), which can simultaneously detect the existence of damage and localize its position. In addition, it is possible to apply this approach to damage identification of structures under ambient excitation. First, JAD method which is an essential technique of blind source separation is investigated to simultaneously diagonalize a set of power spectral density matrices corresponding to frequencies near a certain natural frequency to estimate a joint unitary diagonalizer. The columns of this joint diagonalizer contain dominant CDS’s. With the identified dominant CDS’s around different natural frequencies, GSM is used to extract damage features and a robust damage identification index is then proposed. Numerical and experimental examples of beams with cracks are used to verify the validity and noise robustness of JAD based CDS estimation and the proposed DI. Furthermore, damage identification using dominant CDS’s estimated by JAD method is demonstrated to be more accurate and noise robust than by the commonly used singular value decomposition method.
Directory of Open Access Journals (Sweden)
Xiaodong Chen
2013-01-01
Full Text Available In this paper, the calibration factor of the superconducting gravimeter 057 (SG057 at the Lhasa station is accurately determined for the first time with a frequency-domain approach and the data recorded by the LaCoste Romberg Earth Tides No. 20 (LCR-ET20 gravimeter which is installed nearby SG057. The advantage of the frequency-domain approach is that it eliminates the influence of different gravimeter drifts on the determination of the calibration factor. The determined calibration factor of SG057 is (-77.7358 ± 0.0409 × 10-8 m s-2 V-1, and the relative accuracy is about 0.5‰. The newly determined calibration factor has been calculated with the Wuhan international tidal gravity reference values (ITGRVs based on the data recorded by LCR-ET20 at the Wuhan station before it was installed at the Lhasa station. A high-precision synthesized gravity tide is achieved at the Lhasa station with accurate tidal parameters and theoretical tidal parameters for the long tidal waves from the Dehant-Defraigne-Wahr (DDW earth tide model. The synthesized gravity tide can be used for tidal gravity corrections of future gravity measurements in the Tibetan area. The linear gravimeter drift of SG057 is estimated by gravity records without the effects of land uplift, atmosphere and polar motion yielding a rate of 6.8 × 10-8 m s-2 yr-1.
Li, Y.; Han, B.; Métivier, L.; Brossier, R.
2016-09-01
We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions.
Jeon, R. J.; Mandelis, A.; Sanchez, V.; Abrams, S. H.
2005-06-01
Non-intrusive, non-contacting frequency-domain photothermal radiometry (FD-PTR or PTR) and frequency-domain luminescence (FD-LUM or LUM) have been used with 659- nm and 830-nm laser sources to detect artificial and natural sub-surface defects in human teeth. Fifty-two human teeth were examined with simultaneous measurements of PTR and LUM and compared to conventional diagnostic methods including continuous (dc) luminescence (DIAGNOdent), visual inspection and radiographs by calculating sensitivities and specificities. With the combined criteria of four PTR and LUM signals (two amplitudes and two phases), it was found that the sensitivity of this method was much higher than any of the other methods used in this study, whereas the specificity was comparable to that of dc luminescence diagnostics. Therefore, PTR and LUM, used together as a combined technique, have the potential to be a reliable tool to diagnose early pit and fissure caries and could provide detailed information about deep lesions with its depth profilometric character. Also, from experiments with natural or artificial defects, some depth profilometric characteristics were confirmed.
Hallacoglu, Bertan; Matulewicz, Richard S.; Paltiel, Harriet J.; Padua, Horacio; Gargollo, Patricio; Cannon, Glenn; Alomari, Ahmad; Sassaroli, Angelo; Fantini, Sergio
2009-09-01
We present a quantitative near-IR spectroscopy study of the absolute values of oxygen saturation of hemoglobin before and after surgically induced testicular torsion in adult rabbits. Unilateral testicular torsions (0, 540, or 720 deg) on experimental testes and contralateral sham surgery on control testes are performed in four adult rabbits. A specially designed optical probe for measurements at multiple source-detector distances and a commercial frequency-domain tissue spectrometer are used to measure absolute values of testicular hemoglobin saturation. Our results show: (1) a consistent baseline absolute tissue hemoglobin saturation value of 78+/-5%, (2) a comparable tissue hemoglobin saturation of 77+/-6% after sham surgery, and (3) a significantly lower tissue hemoglobin saturation of 36+/-2% after 540- and 720-deg testicular torsion surgery. Our findings demonstrate the feasibility of performing frequency-domain, multidistance near-IR spectroscopy for absolute testicular oximetry in the assessment of testicular torsion. We conclude that near-IR spectroscopy has potential to serve as a clinical diagnostic and monitoring tool for the assessment of absolute testicular hemoglobin desaturation caused by torsion, with the possibility of serving as a complement to conventional color and spectral Doppler ultrasonography.
Mata, Luz Angelica Caudillo; Schwarzbach, Christoph
2016-01-01
In order to reduce the computational cost of the simulation of electromagnetic responses in geophysical settings that involve highly heterogeneous media, we develop a multiscale finite volume method with oversampling for the quasi-static Maxwell's equations in the frequency domain. We assume a coarse mesh nested within a fine mesh that accurately discretizes the problem. For each coarse cell, we independently solve a local version of the original Maxwell's system subject to linear boundary conditions on an extended domain, which includes the coarse cell and a neighborhood of fine cells around it. The local Maxwell's system is solved using the fine mesh contained in the extended domain and the mimetic finite volume method. Next, these local solutions (basis functions) together with a weak-continuity condition are used to construct a coarse-mesh version of the global problem. The basis functions can be used to obtain the fine-mesh details from the solution of the coarse-mesh problem. Our approach leads to a sig...
Mikóczi, Balázs; Vasúth, Mátyás
2015-01-01
The inspiral and merger of supermassive black hole binary systems with high orbital eccentricity are among the promising sources of the advanced gravitational wave observatories. In this paper we derive analytic ready-to-use first post-Newtonian eccentric waveform in Fourier domain with the use of Hansen coefficients. Introducing generic perturbations of celestial mechanics we have generalized the Hansen expansion to the first post-Newtonian order which are then used to express the waveforms. Taking into account the high eccentricity of the orbit leads to the appearance of secular terms in the waveform which are eliminated with the introduction of a phase shift. The waveforms have a systematic structure and as our main result these are expressed in a tabular form.
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, P.; Zhang, L.
2002-01-01
As a part of a research project co-founded by the European Community, a series of 15 damage tests were performed on a prestressed concrete highway bridge in Switzerland. The ambient response of the bridge was recorded for each damage case. A dense array of instruments allowed the identification...... is to show the application of the FDD-method as an efficient way to perform health monitoring of civil engineering structures. The modal properties, frequencies, damping ratios and mode shapes for the different damage cases were compared with those for the undamaged bridge....
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, Palle; Zhang, Lingmi
2007-01-01
As a part of a research project co-founded by the European Community, a series of 15 damage tests were performed on a prestressed concrete highway bridge in Switzerland. The ambient response of the bridge was recorded for each damage case. A dense array of instruments allowed the identification...... is to show the application of the FDD method as an efficient way to perform health monitoring of civil engineering structures. The modal properties, frequencies, damping ratios and mode shapes for the different damage cases were compared with those for the undamaged bridge....
Jeon, Raymond J.; Mandelis, Andreas; Sanchez, Victor; Abrams, Stephen H.
2004-07-01
Non-intrusive, non-contacting frequency-domain photothermal radiometry (FD-PTR or PTR) and frequency-domain luminescence (FD-LUM or LUM) have been used with 659-nm and 830-nm laser sources to detect artificial and natural sub-surface defects in human teeth. Fifty-two human teeth were examined with simultaneous measurements of PTR and LUM with the 659-nm laser and compared to conventional diagnostic methods including continuous (dc) luminescence (DIAGNOdent), visual inspection and radiographs. To compare each method, sensitivities and specificities were calculated by using histological observations as the gold standard. With the combined criteria of four PTR and LUM signals (two amplitudes and two phases), it was found that the sensitivity of this method was much higher than any of the other methods used in this study, whereas the specificity was comparable to that of dc luminescence diagnostics. Therefore, PTR and LUM, as a combined technique, has the potential to be a reliable tool to diagnose early pit and fissure caries and could provide detailed information about deep lesions with its depth profilometric character. Also, from the experiments with the teeth having natural or aritficial defect, some depth profilometric characteristics were confirmed. The major findings are (i) PTR is sensitive to very deep (>5 mm) defects at low modulation frequencies (5 Hz). Both PTR and LUM amplitudes exhibit a peak at tooth thicknesses ca. 1.4 - 2.7 mm. Furthermore the LUM amplitude exhibits a small trough at ca. 2.5~3.5 mm; (ii) PTR is sensitive to various defects such as a deep carious lesion, a demineralized area, and a crack while LUM exhibits low sensitivity and spatial resolution.
Jiang, Puqing; Huang, Bin; Koh, Yee Kan
2016-07-01
Accurate measurements of the cross-plane thermal conductivity Λcross of a high-thermal-conductivity thin film on a low-thermal-conductivity (Λs) substrate (e.g., Λcross/Λs > 20) are challenging, due to the low thermal resistance of the thin film compared with that of the substrate. In principle, Λcross could be measured by time-domain thermoreflectance (TDTR), using a high modulation frequency fh and a large laser spot size. However, with one TDTR measurement at fh, the uncertainty of the TDTR measurement is usually high due to low sensitivity of TDTR signals to Λcross and high sensitivity to the thickness hAl of Al transducer deposited on the sample for TDTR measurements. We observe that in most TDTR measurements, the sensitivity to hAl only depends weakly on the modulation frequency f. Thus, we performed an additional TDTR measurement at a low modulation frequency f0, such that the sensitivity to hAl is comparable but the sensitivity to Λcross is near zero. We then analyze the ratio of the TDTR signals at fh to that at f0, and thus significantly improve the accuracy of our Λcross measurements. As a demonstration of the dual-frequency approach, we measured the cross-plane thermal conductivity of a 400-nm-thick nickel-iron alloy film and a 3-μm-thick Cu film, both with an accuracy of ∼10%. The dual-frequency TDTR approach is useful for future studies of thin films.
Frequency-domain analysis of computer-controlled optical surfacing processes
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Mid-high spatial frequency errors are often induced on optical surfaces polished by computer-controlled optical surfacing (CCOS) processes. In order to efficiently remove these errors, which would degrade the performances of optical systems, the ability of a CCOS process to correct the errors have been investigated based on the convolution integral model in view of the availability of material removal. To quantify the ability, some conceptions, such as figure correcting ability and material removal availability (MRA), have been proposed. The research result reveals that the MRA of the CCOS process to correct a single spatial frequency error is determined by its tool removal function (TRF), and it equals the normalized amplitude spectrum of the Fourier transform of its TRF. Finally, three sine surfaces were etched using ion beam figuring (IBF), which is a typical CCOS process. The experimental results have verified the theoretical analysis. The employed method and the conclusions of this work provide a useful mathematical basis to analyze and optimize CCOS processes.
Frequency domain and wavelet analysis of the laser-induced plasma shock waves
Energy Technology Data Exchange (ETDEWEB)
Burger, Miloš, E-mail: milosb@ff.bg.ac.rs; Nikolić, Zoran
2015-08-01
In addition to optical emission, another trace of interest that laser-induced plasma provides is a form of acoustic feedback. The acoustic emission (AE) signals were obtained using both microphone and piezo transducers. This kind of optoacoustic signals have some distinct features resembling the short, burst-like sounds, that may differ significantly depending mainly on the sample exposed and irradiance applied. Experiments were performed on atmospheric pressure by irradiating various metallic samples. The recorded waveforms were examined and numerically processed. Single-shot acoustical spectra have shown significant potential of providing valuable supplementary information regarding plasma propagation dynamics. Moreover, the general approach suggests the possibility of making the whole measurement system cost-effective and portable. - Highlights: • We report acoustical waveform, and acoustical spectroscopy measurements and analysis in a laser-induced plasma of a different metals in air. • Both piezo and microphone transducer were used. • The acoustical spectra of the emission were obtained when the sample (and plasma) were enclosed in experimental chamber. • The acquired acoustical spectra are time-integrated and the frequency peaks were sharp and relatively isolated. • Finally, both time and frequency resolved wavelet spectrogram present a novel method of observing laser-induced plasma behavior.
Energy Technology Data Exchange (ETDEWEB)
Gholipour, Ali, E-mail: ali.gholipour@childrens.harvard.edu; Afacan, Onur; Scherrer, Benoit; Prabhu, Sanjay P.; Warfield, Simon K. [Department of Radiology, Boston Children’s Hospital, Boston, Massachusetts 02115 and Harvard Medical School, Boston, Massachusetts 02115 (United States); Aganj, Iman [Radiology Department, Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, Massachusetts 02129 and Harvard Medical School, Boston, Massachusetts 02115 (United States); Sahin, Mustafa [Department of Neurology, Boston Children’s Hospital, Boston, Massachusetts 02115 and Harvard Medical School, Boston, Massachusetts 02115 (United States)
2015-12-15
Purpose: To compare and evaluate the use of super-resolution reconstruction (SRR), in frequency, image, and wavelet domains, to reduce through-plane partial voluming effects in magnetic resonance imaging. Methods: The reconstruction of an isotropic high-resolution image from multiple thick-slice scans has been investigated through techniques in frequency, image, and wavelet domains. Experiments were carried out with thick-slice T2-weighted fast spin echo sequence on the Academic College of Radiology MRI phantom, where the reconstructed images were compared to a reference high-resolution scan using peak signal-to-noise ratio (PSNR), structural similarity image metric (SSIM), mutual information (MI), and the mean absolute error (MAE) of image intensity profiles. The application of super-resolution reconstruction was then examined in retrospective processing of clinical neuroimages of ten pediatric patients with tuberous sclerosis complex (TSC) to reduce through-plane partial voluming for improved 3D delineation and visualization of thin radial bands of white matter abnormalities. Results: Quantitative evaluation results show improvements in all evaluation metrics through super-resolution reconstruction in the frequency, image, and wavelet domains, with the highest values obtained from SRR in the image domain. The metric values for image-domain SRR versus the original axial, coronal, and sagittal images were PSNR = 32.26 vs 32.22, 32.16, 30.65; SSIM = 0.931 vs 0.922, 0.924, 0.918; MI = 0.871 vs 0.842, 0.844, 0.831; and MAE = 5.38 vs 7.34, 7.06, 6.19. All similarity metrics showed high correlations with expert ranking of image resolution with MI showing the highest correlation at 0.943. Qualitative assessment of the neuroimages of ten TSC patients through in-plane and out-of-plane visualization of structures showed the extent of partial voluming effect in a real clinical scenario and its reduction using SRR. Blinded expert evaluation of image resolution in
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyun Keol [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, Chicoutimi, Que., G7H 2B1 (Canada); Charette, Andre [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, Chicoutimi, Que., G7H 2B1 (Canada)]. E-mail: andre_charette@uqac.ca
2007-03-15
The Sensitivity Function-based Conjugate Gradient Method (SFCGM) is described. This method is used to solve the inverse problems of function estimation, such as the local maps of absorption and scattering coefficients, as applied to optical tomography for biomedical imaging. A highly scattering, absorbing, non-reflecting, non-emitting medium is considered here and simultaneous reconstructions of absorption and scattering coefficients inside the test medium are achieved with the proposed optimization technique, by using the exit intensity measured at boundary surfaces. The forward problem is solved with a discrete-ordinates finite-difference method on the framework of the frequency-domain full equation of radiative transfer. The modulation frequency is set to 600 MHz and the frequency data, obtained with the source modulation, is used as the input data. The inversion results demonstrate that the SFCGM can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by significantly reducing a cross-talk between inter-parameters. It is also observed that the closer-to-detector objects are better retrieved.
Dowdy, Josh; Anderson, Derek T.; Luke, Robert H.; Ball, John E.; Keller, James M.; Havens, Timothy C.
2016-05-01
Explosive hazards in current and former conflict zones are a threat to both military and civilian personnel. As a result, much effort has been dedicated to identifying automated algorithms and systems to detect these threats. However, robust detection is complicated due to factors like the varied composition and anatomy of such hazards. In order to solve this challenge, a number of platforms (vehicle-based, handheld, etc.) and sensors (infrared, ground penetrating radar, acoustics, etc.) are being explored. In this article, we investigate the detection of side attack explosive ballistics via a vehicle-mounted acoustic sensor. In particular, we explore three acoustic features, one in the time domain and two on synthetic aperture acoustic (SAA) beamformed imagery. The idea is to exploit the varying acoustic frequency profile of a target due to its unique geometry and material composition with respect to different viewing angles. The first two features build their angle specific frequency information using a highly constrained subset of the signal data and the last feature builds its frequency profile using all available signal data for a given region of interest (centered on the candidate target location). Performance is assessed in the context of receiver operating characteristic (ROC) curves on cross-validation experiments for data collected at a U.S. Army test site on different days with multiple target types and clutter. Our preliminary results are encouraging and indicate that the top performing feature is the unrolled two dimensional discrete Fourier transform (DFT) of SAA beamformed imagery.
Pürrer, Michael
2016-03-01
I provide a frequency domain reduced order model (ROM) for the aligned-spin effective-one-body model "SEOBNRv2" for data analysis with second- and third-generation ground-based gravitational wave (GW) detectors. SEOBNRv2 models the dominant mode of the GWs emitted by the coalescence of black hole binaries. The large physical parameter space (dimensionless spins -1 ≤χi≤0.99 and symmetric mass ratios 0.01 ≤η ≤0.25 ) requires sophisticated reduced order modeling techniques, including patching in the parameter space and in frequency. I find that the time window over which the inspiral-plunge and the merger-ringdown waveform in SEOBNRv2 are connected has a discontinuous dependence on the parameters when the spin parameter χ =0.8 or the symmetric mass ratio η ˜0.083 . This discontinuity increases resolution requirements for the ROM. The ROM can be used for compact binary systems with total masses of 2 M⊙ or higher for the Advanced LIGO design sensitivity and a 10 Hz lower cutoff frequency. The ROM has a worst mismatch against SEOBNRv2 of ˜1 %, but in general mismatches are better than ˜0.1 %. The ROM is crucial for key data analysis applications for compact binaries, such as GW searches and parameter estimation carried out within the LIGO Scientific Collaboration.
Frequency domain analysis of power system transients using Welch and Yule-Walker AR methods
Energy Technology Data Exchange (ETDEWEB)
Alkan, Ahmet [Department of Computer Engineering, Yasar University, 35500 Izmir (Turkey); Yilmaz, Ahmet S. [Department of Electrical and Electronics Engineering, Kahramanmaras Suetcue Imam University, 46050-9 Kahramanmaras (Turkey)
2007-07-15
In this study, power quality (PQ) signals are analyzed by using Welch (non-parametric) and autoregressive (parametric) spectral estimation methods. The parameters of the autoregressive (AR) model were estimated by using the Yule-Walker method. PQ spectra were then used to compare the applied spectral estimation methods in terms of their frequency resolution and the effects in determination of spectral components. The variations in the shape of the obtained power spectra were examined in order to detect power system transients. Performance of the proposed methods was evaluated by means of power spectral densities (PSDs). Graphical results comparing the performance of the AR method with that of the Welch technique are given. The results demonstrate superior performance of the AR method over the Welch method. (author)
Spatial damping identification in the frequency domain-A theoretical and experimental comparison
Brumat, Matija; Slavič, Janko; Boltežar, Miha
2016-08-01
This paper deals with spatial damping identification methods. In contrast to the commonly used damping methods (modal, proportional) the spatial damping information improves structural models with a known location of the damping sources. The Lee-Kim, Chen-Ju-Tsuei, Fritzen IV and local equation of motion methods were theoretically and experimentally compared. Experimentally, the spatial damping identification was tested against: modal and spatial incompleteness, differences in viscous and hysteretic damping models, the performance of identification methods and the effect of damping treatments. It was found that for a structure with a known equation of motion (beam, plate) the local equation of motion method is more efficient and gives a more precise location of the damping. Full frequency response function (FRF) matrix methods can also identify the spatial damping, but are more demanding because the numerical and measurement effort increases with n2, where n is the number of measurement points and, consequently, the size of the FRF matrix.
A Modified Frequency Domain Imaging Method for One-stationary Bistatic SAR
Directory of Open Access Journals (Sweden)
Jin Ri-chu
2014-04-01
Full Text Available Bistatic Synthetic Aperture Radar (BiSAR in one-stationary mode has many advantages over the traditional monostatic SAR. Its echo, however, shows serious space variance in both range and azimuth directions due to its complex imaging geometry, making it hard to be processed by the frequency methods used in the monostatic SAR. To solve that problem, a method based on blocks and interpolation has been proposed by Wang Yu et al.. With this method, points can be well focused except for those located on the edge of each block. In this paper, a modified method is put forward, which adopts new block-dividing strategy and new mapping relationship in the interpolation. With the proposed method, points on the edge can also be well focused, making the quality of the final image greatly improved.
Institute of Scientific and Technical Information of China (English)
Kang Xiaoning; Suonan Jiale
2007-01-01
This paper presents a novel algorithm of fault location for transmission line. Solving the network spectrum equations for different frequencies the fault can be located accurately by this algorithm with one terminal data of voltage and current, and the identified parameters, such as fault distance, fault resistance, and opposite terminal system resistance and inductance. The algorithm eliminates the influence of the opposite system impedance on the fault location accuracy, which causes the main error in traditional fault location methods using one terminal data. A method of calculating spectrum from sampled data is also proposed. EMTP simulations show the validity and higher accuracy of the fault location algorithm compared to the existing ones based on one terminal data.
A Two-Dimensional Fem Code for Impedance Calculation in High Frequency Domain
Energy Technology Data Exchange (ETDEWEB)
Wang, Lanfa; /SLAC; Lee, Lie-Quan; /SLAC; Stupakov, Gennady; /SLAC
2010-08-25
A new method, using the parabolic equation (PE), for the calculation of both high-frequency impedances of small-angle taper (or collimator) is developed in [1]. One of the most important advantages of the PE approach is that it eliminates the spatial scale of the small wavelength from the problem. As a result, only coarser spatial meshes are needed in calculating the numerical solution of the PE. We developed a new code based on Finite Element Method (FEM) which can handle arbitrary profile of a transition and speed up the calculation by orders of magnitude. As a first step, we completed and benchmarked a two-dimensional code. It can be upgraded to three-dimensional geometry.
Acworth, R. Ian; Halloran, Landon J. S.; Rau, Gabriel C.; Cuthbert, Mark O.; Bernardi, Tony L.
2016-11-01
The groundwater hydraulic head response to the worldwide and ubiquitous atmospheric tide at 2 cycles per day (cpd) is a direct function of confined aquifer compressible storage. The ratio of the responses of hydraulic head to the atmospheric pressure change is a measure of aquifer barometric efficiency, from which formation compressibility and aquifer specific storage can be determined in situ rather than resorting to laboratory or aquifer pumping tests. The Earth tide also impacts the hydraulic head response at the same frequency, and a method is developed here to quantify and remove this interference. As a result, the barometric efficiency can be routinely calculated from 6-hourly hydraulic head, atmospheric pressure, and modeled Earth tide records where available for a minimum of 15 days duration. This new approach will be of critical importance in assessing worldwide problems of land subsidence or groundwater resource evaluation that both occur due to groundwater abstraction.
Directory of Open Access Journals (Sweden)
Konold Timm
2011-07-01
Full Text Available Abstract Background Heart rate variability (HRV analysis is a method to assess the function of the autonomic nervous system. Brainstem nuclei that influence HRV are affected by vacuolar changes and accumulation of disease-associated prion protein (PrPd in bovine spongiform encephalopathy (BSE resulting in clinical signs suggestive of an increased parasympathetic tone. It was hypothesised that BSE in cattle causes changes in the autonomic nervous system; this was tested by comparing HRV indices derived from 1048 electrocardiograms, which were recorded from 51 naturally or experimentally infected cattle with BSE confirmed by postmortem tests, 321 clinical suspect cases or cattle inoculated with potentially infectious tissue without disease confirmation and 78 BSE-free control cattle. Findings Statistically significant differences were found for low or high frequency power, their normalised values and ratio when the last recording prior to cull or repeated recordings were compared but only between male and female cattle of the three groups and not between groups of the same gender, even though BSE cases of each gender appeared to be more nervous during the recording. The same findings were made for heart rate, deviation from the mean RR interval and vasovagal tonus index when repeated recordings were compared. BSE cases with severe vacuolar changes in the parasympathetic nucleus of the vagus nerve had a significantly lower low:high frequency power ratio but not a lower heart rate than BSE cases with mild vacuolation, whereas severity of vacuolar changes in the solitary tract nucleus or intensity of PrPd accumulation in both nuclei did not appear to have any affect on either index. Abnormalities in the electrocardiogram were detected in 3% of the recordings irrespective of the BSE status; sinus arrhythmia was present in 93% of the remaining recordings. Conclusions HRV analysis was not useful to distinguish BSE-positive from BSE-negative cattle
Directory of Open Access Journals (Sweden)
Hunt Anthony C
2002-03-01
Full Text Available Abstract Background T wave alternans (TA is a repolarisation phenomenon manifesting as a microvolt beat to beat change in the amplitude of the T wave and ST segment. TA has been shown to be a predictor of arrhythmic risk in unselected myocardial infarction populations. TA has not been used to differentiate risk within the ischaemic cardiomyopathy population. Methods The subjects investigated comprised, Group 1: 7 stable patients with remote (>20 months extensive myocardial scarring and no arrhythmic events (NYHA 3 and 4. Group2: 9 post infarction patients with malignant arrhythmia and implantable defibrillator. During breath holding, 20 continuous QRST complexes from each patients X, Y and Z leads were digitally recorded. Time domain, resultant absolute difference vectors (ATA, were calculated for alternate resultant T wave sequences. Group differences between the magnitude and temporal distribution of mean ATAs and their spectral and cross-spectral analysis were compared. Results Group 1 v Group 2 mean ATAs were 10.7 (7.17 v 11.7 (8.48 respectively, not significant. Each group had a homogenous temporal distribution of ATAs. Both group's largest mean ATA frequency components were between 0 to 25 Hz, the largest ATA component being at the DC frequency. Cross spectral analysis showed no significant differences in group ATA frequency content. Conclusion The frequency content and microvolt magnitude of T wave alternans was not significantly different in these two groups. The specificity of T wave alternans for differentiating arrhythmic risk in post infarction scarring and heart failure needs investigation.
Du, Congwu; Andersen, Carol; Chance, Britton
1998-01-01
An approach of using phase modulation spectroscopy (PMS) system has been proposed which has single frequency, dual- wavelength with phase-only output for oximetry to minimize the influences of room light in the clinical environment. The availability of this method has been verified by laboratory experiments both in vitro and in vivo. In this study, a 200 Mhz PMS system has been used for measuring on piglet brain in vivo, to detect blood volume and saturation change during normoxia to hypoxia periods, and to monitor the brain depolarization in the hypoxic stress. Our experimental results show that the brain saturation estimated by PMS is approximately 84% and lies between arterial and venous blood values of 97% and 80% in normoxia, and tends to move close to the venous side in hypoxia. In addition, the excessive hypoxic stress triggers the brain to be bio-energetic deficits and finally introduced the neural depolarization, which can be effectively detected by recording the increment of tissue scattering.
H2 consensus control of time-delayed multi-agent systems: A frequency-domain method.
Ye, Fei; Zhang, Weidong; Ou, Linlin
2017-01-01
An analytical H2 controller design approach of homogeneous multi-agent systems with time delays is presented to improve consensus performance. Firstly, a closed-loop multi-input multi-output framework in frequency domain is introduced, and a consensus tracking condition is given. Secondly, the decomposition method is utilized to simplify the analysis of internal stability and H2 performance index of the whole system to a set of independent optimization problems. Finally, the H2 optimal controller can be computed from all the stabilizing controllers. The contributions of the new approach are that the design procedure is conducted analytically for arbitrary delayed multi-agent systems, and a simple quantitative tuning way is developed to trade off the nominal performance and robustness. The simulation examples show the effectiveness of the proposed control strategy.
Waldbusser, George G.; Salisbury, Joseph E.
2014-01-01
Multiple natural and anthropogenic processes alter the carbonate chemistry of the coastal zone in ways that either exacerbate or mitigate ocean acidification effects. Freshwater inputs and multiple acid-base reactions change carbonate chemistry conditions, sometimes synergistically. The shallow nature of these systems results in strong benthic-pelagic coupling, and marine invertebrates at different life history stages rely on both benthic and pelagic habitats. Carbonate chemistry in coastal systems can be highly variable, responding to processes with temporal modes ranging from seconds to centuries. Identifying scales of variability relevant to levels of biological organization requires a fuller characterization of both the frequency and magnitude domains of processes contributing to or reducing acidification in pelagic and benthic habitats. We review the processes that contribute to coastal acidification with attention to timescales of variability and habitats relevant to marine bivalves.
Directory of Open Access Journals (Sweden)
Si-Da Zhou
2015-01-01
Full Text Available Real-time estimation of modal parameters of time-varying structures can conduct an obvious contribution to some specific applications in structural dynamic area, such as health monitoring, damage detection, and vibration control; the recursive algorithm of modal parameter estimation supplies one of fundamentals for acquiring modal parameters in real-time. This paper presents a vector multistage recursive method of modal parameter estimation for time-varying structures in hybrid time and frequency domain, including stages of recursive estimation of time-dependent power spectra, frozen-time modal parameter estimation, recursive modal validation, and continuous-time estimation of modal parameters. An experimental example validates the proposed method finally.
Wada, Daichi; Igawa, Hirotaka; Murayama, Hideaki; Kasai, Tokio
2014-03-24
A signal processing method based on group delay calculations is introduced for distributed measurements of long-length fiber Bragg gratings (FBGs) based on optical frequency domain reflectometry (OFDR). Bragg wavelength shifts in interfered signals of OFDR are regarded as group delay. By calculating group delay, the distribution of Bragg wavelength shifts is obtained with high computational efficiency. We introduce weighted averaging process for noise reduction. This method required only 3.5% of signal processing time which was necessary for conventional equivalent signal processing based on short-time Fourier transform. The method also showed high sensitivity to experimental signals where non-uniform strain distributions existed in a long-length FBG.
Yüksel, Kivilcim; Pala, Deniz
2016-06-01
This work presents a novel approach in interrogating Polarization Dependent Loss (PDL) of cascaded identical FBGs using Optical Frequency Domain Reflectometer (OFDR). The fundamentals of both polarisation properties of uniform FBGs and polarisation-sensitive OFDR are explained and the benefits of this novel approach in measuring transversal load are discussed. The numerical programs computing the spectral evolution of PDL of the FBGs in the array as a function of grating parameters (grating length and birefringence) are presented. Our simulation results show an excellent agreement with the previously reported simulation (and experimental) results in the literature obtained on a single FBG by using classical state-of-the-art measurement techniques. As an envisaged application, the proposed system shows the feasibility of measuring the residual stresses during manufacturing process of composite materials which is not straightforward by amplitude spectrum measurements and/or considering only the axial strains.
Yahav, Gilad; Fixler, Dror; Gershanov, Sivan; Goldenberg-Cohen, Nitza
2016-03-01
Brain tumors are the second leading cause of cancer-related deaths in children, after leukemia. Patients with cancer in the central nervous system have a very low recovery rate. Today known imaging and cytology techniques are not always sensitive enough for an early detection of both tumor and its metastatic spread, moreover the detection is generally limited, reviewer dependent and takes a relatively long time. Medulloblastoma (MB) is the most common malignant brain tumor in children. The aim of our talk is to present the frequency domain fluorescence lifetime imaging microscopy system as a possible method for an early detection of MB and its metastatic spread in the cerebrospinal fluids within the pediatric population.
Kim, J.; Mandelis, A.; Matvienko, A.; Abrams, S.; Amaechi, B. T.
2012-11-01
The ability of frequency-domain photothermal radiometry (PTR) and modulated luminescence (LUM) to detect secondary caries is presented. Signal behavior upon sequential demineralization and remineralization of a spot (diameter ~1 mm) on a vertical wall of sectioned tooth samples was investigated experimentally. From these studies, it was found that PTR-LUM signals change, showing a certain pattern upon progressive demineralization and remineralization. PTR amplitudes slightly decreased upon progressive demineralization and slightly increased upon subsequent remineralization. The PTR phase increased during both demineralization and remineralization. LUM amplitudes exhibit a decreasing trend at excitation/probe distances larger than 200 μm away from the edge for both demineralization and remineralization; however, at locations close to the edge (up to ~200 μm), LUM signals slightly decrease upon demineralization and slightly increase during subsequent remineralization.
Waldbusser, George G; Salisbury, Joseph E
2014-01-01
Multiple natural and anthropogenic processes alter the carbonate chemistry of the coastal zone in ways that either exacerbate or mitigate ocean acidification effects. Freshwater inputs and multiple acid-base reactions change carbonate chemistry conditions, sometimes synergistically. The shallow nature of these systems results in strong benthic-pelagic coupling, and marine invertebrates at different life history stages rely on both benthic and pelagic habitats. Carbonate chemistry in coastal systems can be highly variable, responding to processes with temporal modes ranging from seconds to centuries. Identifying scales of variability relevant to levels of biological organization requires a fuller characterization of both the frequency and magnitude domains of processes contributing to or reducing acidification in pelagic and benthic habitats. We review the processes that contribute to coastal acidification with attention to timescales of variability and habitats relevant to marine bivalves.
3D linear inversion of magnetic susceptibility data acquired by frequency domain EMI
Thiesson, J.; Tabbagh, A.; Simon, F.-X.; Dabas, M.
2017-01-01
Low induction number EMI instruments are able to simultaneously measure a soil's apparent magnetic susceptibility and electrical conductivity. This family of dual measurement instruments is highly useful for the analysis of soils and archeological sites. However, the electromagnetic properties of soils are found to vary over considerably different ranges: whereas their electrical conductivity varies from ≤ 0.1 to ≥ 100 mS/m, their relative magnetic permeability remains within a very small range, between 1.0001 and 1.01 SI. Consequently, although apparent conductivity measurements need to be inverted using non-linear processes, the variations of the apparent magnetic susceptibility can be approximated through the use of linear processes, as in the case of the magnetic prospection technique. Our proposed 3D inversion algorithm starts from apparent susceptibility data sets, acquired using different instruments over a given area. A reference vertical profile is defined by considering the mode of the vertical distributions of both the electrical resistivity and of the magnetic susceptibility. At each point of the mapped area, the reference vertical profile response is subtracted to obtain the apparent susceptibility variation dataset. A 2D horizontal Fourier transform is applied to these variation datasets and to the dipole (impulse) response of each instrument, a (vertical) 1D inversion is performed at each point in the spectral domain, and finally the resulting dataset is inverse transformed to restore the apparent 3D susceptibility variations. It has been shown that when applied to synthetic results, this method is able to correct the apparent deformations of a buried object resulting from the geometry of the instrument, and to restore reliable quantitative susceptibility contrasts. It also allows the thin layer solution, similar to that used in magnetic prospection, to be implemented. When applied to field data it initially delivers a level of contrast
Khan, Sebastian; Husa, Sascha; Hannam, Mark; Ohme, Frank; Pürrer, Michael; Forteza, Xisco Jiménez; Bohé, Alejandro
2016-02-01
We present a new frequency-domain phenomenological model of the gravitational-wave signal from the inspiral, merger and ringdown of nonprecessing (aligned-spin) black-hole binaries. The model is calibrated to 19 hybrid effective-one-body-numerical-relativity waveforms up to mass ratios of 1 ∶18 and black-hole spins of |a /m |˜0.85 (0.98 for equal-mass systems). The inspiral part of the model consists of an extension of frequency-domain post-Newtonian expressions, using higher-order terms fit to the hybrids. The merger ringdown is based on a phenomenological ansatz that has been significantly improved over previous models. The model exhibits mismatches of typically less than 1% against all 19 calibration hybrids and an additional 29 verification hybrids, which provide strong evidence that, over the calibration region, the model is sufficiently accurate for all relevant gravitational-wave astronomy applications with the Advanced LIGO and Virgo detectors. Beyond the calibration region the model produces physically reasonable results, although we recommend caution in assuming that any merger-ringdown waveform model is accurate outside its calibration region. As an example, we note that an alternative nonprecessing model, SEOBNRv2 (calibrated up to spins of only 0.5 for unequal-mass systems), exhibits mismatch errors of up to 10% for high spins outside its calibration region. We conclude that waveform models would benefit most from a larger number of numerical-relativity simulations of high-aligned-spin unequal-mass binaries.
Foote, David; Lin, Yingda; Hill, Wendell T., III
2015-05-01
In a recent set of coherent control experiments, an anomalous sinusoidal variation of the ionization yield was observed in Xe when ionized by a pairs of phase-locked, many-cycle 800 nm pulses. Compared with the signal of a single transform limited pulse, both enhancement and suppression was possible, which depended on the temporal separation and relative phase of the pulses. In the time domain, the control can be viewed as a temporal Young's double slit experiment - two coherent electron wavepackets interfering. In the frequency domain, the photoelectron spectrum is given by the modulus squared of the Fourier transform of the field, which is a few-cycle squared sinusodial function. In analogy to a few-cycle pulse where the carrier phase dictates the ejection direction of rescattered electrons, enhancement (suppression) occurs when the effective carrier waveform is cos[w-w0]2 (sin[w-w0]2). The contrast decreased with increasing pulse separation and decreasing multiphoton order. Detailed results and a model simulation will be presented.
The elusive half-pole in the frequency domain transfer function of Peltier thermoelectric devices.
De Marchi, Andrea; Giaretto, Valter
2011-03-01
A half-pole can be expected in the transfer function of a Peltier device because proportionality between the diffusion length and the square root of the diffusion time is intrinsic in the diffusion equation. The resulting -1∕2 bilogarithmic slope (10 dB∕dec) is, however, easily masked by the thermal time constant of the load, which makes it elusive. The goal of this work is to identify the arrangements which can reveal and make usable the half-pole, because the latter can be instrumental in a servo control to increase the open-loop gain without risking instability. The diffusion equation was solved in a sine wave regime for a one-dimensional model of a Peltier device. The Laplace transform method was used, and the periodic solution was obtained using Cauchy's theorem and the method of residues. The -1∕2 slope of the half-pole appeared observable in a frequency range which can be several decades wide, depending on details of device configuration and considered position within. Amplitude and phase of temperature and heat flux in various spots are discussed with emphasis on the physical meaning, and a comparison is provided with solutions yielded by the lumped model, which cannot show the half-pole. An experimental check of the theoretical approach and analysis was made taking into account the deviations from one-dimensionality occurring in a real Peltier device. Given a constant amplitude sine wave injected current, the quadrature component of the Seebeck voltage across the whole series of junctions was identified as the most easily measurable quantity related to the thermal response of the device. Experimental results for the latter turned out in good agreement with analytical solutions.
The elusive half-pole in the frequency domain transfer function of Peltier thermoelectric devices
De Marchi, Andrea; Giaretto, Valter
2011-03-01
A half-pole can be expected in the transfer function of a Peltier device because proportionality between the diffusion length and the square root of the diffusion time is intrinsic in the diffusion equation. The resulting -1/2 bilogarithmic slope (10 dB/dec) is, however, easily masked by the thermal time constant of the load, which makes it elusive. The goal of this work is to identify the arrangements which can reveal and make usable the half-pole, because the latter can be instrumental in a servo control to increase the open-loop gain without risking instability. The diffusion equation was solved in a sine wave regime for a one-dimensional model of a Peltier device. The Laplace transform method was used, and the periodic solution was obtained using Cauchy's theorem and the method of residues. The -1/2 slope of the half-pole appeared observable in a frequency range which can be several decades wide, depending on details of device configuration and considered position within. Amplitude and phase of temperature and heat flux in various spots are discussed with emphasis on the physical meaning, and a comparison is provided with solutions yielded by the lumped model, which cannot show the half-pole. An experimental check of the theoretical approach and analysis was made taking into account the deviations from one-dimensionality occurring in a real Peltier device. Given a constant amplitude sine wave injected current, the quadrature component of the Seebeck voltage across the whole series of junctions was identified as the most easily measurable quantity related to the thermal response of the device. Experimental results for the latter turned out in good agreement with analytical solutions.
Development of frequency domain multiplexing for the X-ray Integral Field Unit (X-IFU) on the Athena
Akamatsu, Hiroki; van der Kuur, Jan; de Vries, Cor P; Ravensberg, Kevin; Adams, Joseph S; Bandler, Simon R; Bruijn, Marcel P; Chervenak, James A; Kilbourne, Caroline A; Kiviranta, Mikko; Linden, A J van den; Jackson, Brian D; Smith, Stephen J
2016-01-01
We are developing the frequency domain multiplexing (FDM) read-out of transition-edge sensor (TES) microcalorimeters for the X-ray Integral Field Unit (X-IFU) instrument on board of the future European X-Ray observatory Athena. The X-IFU instrument consists of an array of $\\sim$3840 TESs with a high quantum efficiency ($>$90 \\%) and spectral resolution $\\Delta E$=2.5 eV $@$ 7 keV ($E/\\Delta E\\sim$2800). FDM is currently the baseline readout system for the X-IFU instrument. Using high quality factor LC filters and room temperature electronics developed at SRON and low-noise two stage SQUID amplifiers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. An integrated noise equivalent power resolution of about 2.0 eV at 1.7 MHz has been demonstrated with a pixel from a new TES array from NASA/Goddard (GSFC-A2). We have achieved X-ray energy resolutions $\\sim$2.5 eV at AC bias frequency at 1.7 MHz in the single pixel read-out. We have...
Directory of Open Access Journals (Sweden)
Madhukumar A. S.
2004-01-01
Full Text Available Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.
Luce, H.; Kubo, K.; Fukao, S.
2001-09-01
Studies of atmospheric structures and dynamics at small scales require high resolution observations in space and time. Stratosphere-troposphere radars offer high potentialities for such studies, in particular, with the dual-frequency domain interferometry (FDI) technique used for tracking thin atmospheric layers. In the present paper, attention is drawn to the performances of this technique, discussed in light of comparisons between data sets collected in different radar configurations with the middle and upper atmosphere (MU) radar (Shigaraki, Japan, 34.85°N, 136.10°E). Measurements in FDI mode with two range resolutions (300 and 600 m) and two frequency differences (0.50 and 0.25 MHz) have been conducted, interleaved with measurements in Doppler-beam-swinging mode performed at a range resolution of 150 m. From the data comparisons it is found that the thickness of the echoing layers in FDI mode strongly depends on the initial range resolution used. Thus, even if the FDI mode is believed to give a better description of the stable layers, the FDI-deduced thickness with an initial range resolution of 300 m may not be consistent with the true thickness of the atmospheric layers. It could then be misleading to use FDI observations in order to estimate the thickness of atmospheric layers. However, it is also shown that under some circumstances, FDI can provide reliable information on the characteristics of the atmospheric structures which cannot be available with "non-FDI" techniques.
Luce, H.; Crochet, M.; Hanuise, C.; Yamamoto, M.; Fukao, S.
1999-09-01
The frequency domain interferometry (FDI) technique has been developed for probing thin layered structures of the atmosphere. The position and thickness of a single layer embedded within the scattering volume can be deduced from the complex normalized cross correlation (coherence) of received signals at two closely spaced frequencies. Applied in the vertical pointing direction, this technique identified layered structures ("FDI layers") of 50-200 m in thickness in the lower atmosphere. These structures are 1 order of magnitude thicker than observed temperature sheets (about 10-m thick) which are very likely responsible for the main part of the VHF radar echoes in vertical direction. In this paper, although the ambiguity of the dual FDI technique is well known, we emphasize that the FDI layers do not necessarily correspond to a single atmospheric layer; they can also be interpreted as a more complex structure of very thin atmospheric layers. A simple model, introduced as an example, shows that the FDI layer thickness can also approximately be interpreted as the vertical separation of two very thin atmospheric layers. This result can explain by itself the differences between the estimated thicknesses by balloon and FDI radar techniques. Finally, we stress that comparisons with high-resolution in situ measurements are urgently needed for interpreting the FDI layers.
Chave, Alan D.; Everett, Mark E.; Mattsson, Johan; Boon, James; Midgley, Jonathan
2017-02-01
fully reverse the direction of energy flux in the reservoir layer toward rather than away from the source, resulting in a stronger and slower response. The Fréchet derivatives are dominated by preferential sensitivity to the reservoir layer conductivity for all water depths except at high frequencies, but also display a shift with offset from the galvanic to the inductive mode in the underburden and overburden due to the interplay of guided energy flow and the air interaction. This means that the sensitivity to the horizontal conductivity is almost as strong as to the vertical component in the shallow parts of the subsurface, and in fact is stronger than the vertical sensitivity deeper down. However, the sensitivity to horizontal conductivity is still weak compared to the vertical component within thin resistive regions. The horizontal sensitivity is gradually decreased when the water becomes deep. These observations in part explain the success of shallow towed CSEM using only measurements of the in-line component of the electric field.
Chave, Alan D.; Everett, Mark E.; Mattsson, Johan; Boon, James; Midgley, Jonathan
2016-11-01
partially or fully reverse the direction of energy flux in the reservoir layer toward rather than away from the source, resulting in a stronger and slower response. The Fréchet derivatives are dominated by preferential sensitivity to the reservoir layer conductivity for all water depths except at high frequencies, but also display a shift with offset from the galvanic to the inductive mode in the underburden and overburden due to the interplay of guided energy flow and the air interaction. This means that the sensitivity to the horizontal conductivity is almost as strong as to the vertical component in the shallow parts of the subsurface, and in fact stronger than the vertical sensitivity deeper down. However, the sensitivity to horizontal conductivity is still weak compared to the vertical component within thin resistive regions. The horizontal sensitivity is gradually decreased when the water becomes deep. These observations in part explain the success of shallow towed CSEM using only measurements of the in-line component of the electric field.
Chilson, Phillip B.; Muschinski, Andreas; Schmidt, Gerhard
1997-05-01
In this paper we report the first high-resolution observations of upper tropospheric Kelvin-Helmholtz billows using VHF frequency domain interferometry (FDI). The measurements were made using the sounding system VHF radar located in the German Harz Mountains operating at the frequencies of 53.25 and 53.75 MHz. Through an application of the FDI technique it has been possible to track the altitude of thin scattering layers with an accuracy of a few tens of meters and a temporal resolution of 13 s. Taking advantage of the FDI technique, we found several examples of Kelvin-Helmholtz instability (KHI) in regions coinciding with large values of wind shear. One particularly good example is presented in detail. The KHI occurred just below the axis of the jet at an altitude of 9.1 km. It produced oscillations in the vertical velocity field in the altitude range of 8-10 km. The oscillations had a local period of 90 s and persisted over a time interval of 10 min. On the basis of the magnitude of the horizontal wind at the time and height of the KHI, the billow train had a horizontal extent of about 27 km, while the horizontal length of the individual billow amounted to about 4.0 km. The 90-s oscillations were also observed in the radar signal power, the FDI-derived layer height, and the coherence between the received radar signals for the two frequencies. Using the FDI data, we were able to identify the individual billows located within the train and observe their maximum crest-to-trough amplitudes to be between 220 and 230 m. This was less than the conventional radar resolution of 300 m used during the experiment.
Wang, L.; Cheaito, R.; Braun, J. L.; Giri, A.; Hopkins, P. E.
2016-09-01
The thermoreflectance-based techniques time- and frequency-domain thermoreflectance (TDTR and FDTR, respectively) have emerged as robust platforms to measure the thermophysical properties of a wide array of systems on varying length scales. Routine in the implementation of these techniques is the application of a thin metal film on the surface of the sample of interest to serve as an opto-thermal transducer ensuring the measured modulated reflectivity is dominated by the change in thermoreflectance of the sample. Here, we outline a method to directly measure the thermal conductivities of bulk materials without using a metal transducer layer using a standard TDTR/FDTR experiment. A major key in this approach is the use of a thermal model with z-dependent heat source when the optical penetration depth is comparable to the beam sizes and measuring the FDTR response at a long delay time to minimize non-thermoreflectivity contributions to the modulated reflectance signals (such as free carrier excitations). Using this approach, we demonstrate the ability to measure the thermal conductivity on three semiconductors, intrinsic Si (100), GaAs (100), and InSb (100), the results of which are validated with FDTR measurements on the same wafers with aluminum transducers. We outline the major sources of uncertainty in this approach, including frequency dependent heating and precise knowledge of the pump and probe spot sizes. As a result, we discuss appropriate pump-frequency ranges in which to implement this TDTR/FDTR approach and present a procedure to measure the effective spot sizes by fitting the FDTR data of an 80 nm Al/SiO2 sample at a time delay in which the spot size sensitivity dominates an FDTR measurement over the substrate thermal properties. Our method provides a more convenient way to directly measure the thermal conductivities of semiconductors.
Directory of Open Access Journals (Sweden)
Omi Shizue
2010-11-01
Full Text Available Abstract Background Proteins may evolve through the recruitment and modification of discrete domains, and in many cases, protein action can be dissected at the domain level. PDZ domains are found in many important structural and signaling complexes, and are generally thought to interact with their protein partners through a C-terminal consensus sequence. We undertook a comprehensive search for protein partners of all individual PDZ domains in C. elegans to characterize their function and mode of interaction. Results Coupling high-throughput yeast two-hybrid screens with extensive validation by co-affinity purification, we defined a domain-orientated interactome map. This integrates PDZ domain proteins in numerous cell-signaling pathways and shows that PDZ domain proteins are implicated in an unexpectedly wide range of cellular processes. Importantly, we uncovered a high frequency of non-canonical interactions, not involving the C-terminus of the protein partner, which were directly confirmed in most cases. We completed our study with the generation of a yeast array representing the entire set of PDZ domains from C. elegans and provide a proof-of-principle for its application to the discovery of PDZ domain targets for any protein or peptide of interest. Conclusions We provide an extensive domain-centered dataset, together with a clone resource, that will help future functional study of PDZ domains. Through this unbiased approach, we revealed frequent non-canonical interactions between PDZ domains and their protein partners that will require a re-evaluation of this domain's molecular function. [The protein interactions from this publication have been submitted to the IMEx (http://www.imexconsortium.org consortium through IntAct (PMID: 19850723 and assigned the identifier IM-14654
Good, Jacob T.; Holland, Daniel B.; Finneran, Ian A.; Carroll, P. Brandon; Kelley, Matthew J.; Blake, Geoffrey A.
2015-10-01
We present the design and capabilities of a high-resolution, decade-spanning ASynchronous OPtical Sampling (ASOPS)-based TeraHertz Time-Domain Spectroscopy (THz-TDS) instrument. Our system employs dual mode-locked femtosecond Ti:Sapphire oscillators with repetition rates offset locked at 100 Hz via a Phase-Locked Loop (PLL) operating at the 60th harmonic of the ˜80 MHz oscillator repetition rates. The respective time delays of the individual laser pulses are scanned across a 12.5 ns window in a laboratory scan time of 10 ms, supporting a time delay resolution as fine as 15.6 fs. The repetition rate of the pump oscillator is synchronized to a Rb frequency standard via a PLL operating at the 12th harmonic of the oscillator repetition rate, achieving milliHertz (mHz) stability. We characterize the timing jitter of the system using an air-spaced etalon, an optical cross correlator, and the phase noise spectrum of the PLL. Spectroscopic applications of ASOPS-THz-TDS are demonstrated by measuring water vapor absorption lines from 0.55 to 3.35 THz and acetonitrile absorption lines from 0.13 to 1.39 THz in a short pathlength gas cell. With 70 min of data acquisition, a 50 dB signal-to-noise ratio is achieved. The achieved root-mean-square deviation is 14.6 MHz, with a mean deviation of 11.6 MHz, for the measured water line center frequencies as compared to the JPL molecular spectroscopy database. Further, with the same instrument and data acquisition hardware, we use the ability to control the repetition rate of the pump oscillator to enable THz frequency comb spectroscopy (THz-FCS). Here, a frequency comb with a tooth width of 5 MHz is generated and used to fully resolve the pure rotational spectrum of acetonitrile with Doppler-limited precision. The oscillator repetition rate stability achieved by our PLL lock circuits enables sub-MHz tooth width generation, if desired. This instrument provides unprecedented decade-spanning, tunable resolution, from 80 MHz down to sub
Energy Technology Data Exchange (ETDEWEB)
Leiste, H., E-mail: harald.leiste@imf.fzk.d [Forschungszentrum Karlsruhe, Institut fuer Materialforschung 1, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen (Germany); Seemann, K.; Ziebert, C. [Forschungszentrum Karlsruhe, Institut fuer Materialforschung 1, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen (Germany)
2010-05-15
For the application in high-frequency micromagnetic devices, the permeability and resonance frequency of ferromagnetic components is of high interest. It is dominantly influenced by different factors, the external field and direction and the domain distribution, shape and orientation. By the use of micromagnetic simulation, the domain pattern in films was determined and the effective permeability was calculated. The results of the calculations were compared with the domain shape of patterned microstructures of thin FeCoTaN-films, which were deposited onto oxidised silicon substrates by reactive r.f.-magnetron sputtering by employing 6-in Fe{sub 37}Co{sub 46}Ta{sub 17} targets. To achieve a high-frequency suitability, the films have to be annealed in a static magnetic field of 50 mT between 400 and 500 deg. C, which are typical temperatures used in CMOS processes, to induce an in-plane uniaxial anisotropy needed for the high-frequency performance. Magnetic softness was obtained by producing amorphous or nanocrystalline films, and additionally, by aspiring low magnetocrystalline anisotropies for, e.g., certain Fe/Co fractions. The unpatterned films with a lateral dimension of 5x5 mm{sup 2} were measured in a strip line permeameter in a frequency range up to 5 GHz and exhibited ferromagnetic resonance frequencies between 2 and 2.5 GHz within a low-loss permeability spectrum (low width of imaginary part of permeability). For possible integrations in passive microelectronic components the films were patterned to a few tenths of micrometers by near ultra-violet lithography and plasma beam etching, and then consequently annealed to obtain the static and dynamic magnetic properties. To influence the amount of closure domains, designs were conceived to influence the domain formation by creating additional internal boundaries. As a result, the ferromagnetic resonance frequency and the effective permeability are strongly driven by internal and external boundaries.
Vajuvalli, Nithin N.; Chikkemenahally, Dharmendra Kumar K.; Nayak, Krupa N.; Bhosale, Manoj G.; Geethanath, Sairam
2016-12-01
Dynamic contrast enhancement magnetic resonance imaging (DCE-MRI) is a well-established method for non-invasive detection and therapeutic monitoring of pathologies through administration of intravenous contrast agent. Quantification of pharmacokinetic (PK) maps can be achieved through application of compartmental models relevant to the pathophysiology of the tissue under interrogation. The determination of PK parameters involves fitting of time-concentration data to these models. In this work, the Tofts model in frequency domain (TM-FD) is applied to a weakly vascularized tissue such as the breast. It is derived as a convolution-free model from the conventional Tofts model in the time domain (TM-TD). This reduces the dimensionality of the curve-fitting problem from two to one. The approaches of TM-FD and TM-TD were applied to two kinds of in silico phantoms and six in vivo breast DCE data sets with and without the addition of noise. The results showed that computational time taken to estimate PK maps using TM-FD was 16-25% less than with TM-TD. Normalized root mean square error (NRMSE) calculation and Pearson correlation analyses were performed to validate robustness and accuracy of the TM-FD and TM-TD approaches. These compared with ground truth values in the case of phantom studies for four different temporal resolutions. Results showed that NRMSE values for TM-FD were significantly lower than those of TM-TD as validated by a paired t-test along with reduced computational time. This approach therefore enables online evaluation of PK maps by radiologists in a clinical setting, aiding in the evaluation of 3D and/or increased coverage of the tissue of interest.
Amir, F.; Farrington, N.; Mitchell, C.; Missous, M.
2010-10-01
Simulated RF time-domain characteristics for advanced Gunn diodes with hot electron injection and sub-micron transit region lengths for use at frequencies over 100GHz are reported. The physical models used have been developed in SILVACO and are compared to measured results. The devices measured were originally fabricated to investigate the feasibility of GaAs Gunn diode oscillators capable of operating at D-band frequencies and ultimately intended for use in high power (multi-mW) Terahertz sources (~0.6THz) when used in conjunction with novel Schottky diode frequency multiplier technology. The device models created using SILVACO are described and the DC and time-domain results presented. The simulations were used to determine the shortest transit region length capable of producing sustained oscillation. The operation of resonant disk second harmonic Gunn diode oscillators is also discussed and accurate electromagnetic models created using Ansoft High Frequency Structure Simulator presented. Novel methods for combining small-signal frequency-domain electromagnetic simulations with time-domain device simulations in order to account for the significant interactions between the diode and oscillator circuit are described.
Development of frequency domain multiplexing for the X-ray Integral Field unit (X-IFU) on the Athena
Akamatsu, Hiroki; Gottardi, Luciano; van der Kuur, Jan; de Vries, Cor P.; Ravensberg, Kevin; Adams, Joseph S.; Bandler, Simon R.; Bruijn, Marcel P.; Chervenak, James A.; Kilbourne, Caroline A.; Kiviranta, Mikko; van der Linden, A. J.; Jackson, Brian D.; Smith, Stephen J.
2016-07-01
We are developing the frequency domain multiplexing (FDM) read-out of transition-edge sensor (TES) microcalorimeters for the X-ray Integral Field Unit (X-IFU) instrument on board of the future European X-Ray observatory Athena. The X-IFU instrument consists of an array of 3840 TESs with a high quantum efficiency (>90 %) and spectral resolution ΔE=2.5 eV @ 7 keV (E/ ΔE 2800). FDM is currently the baseline readout system for the X-IFU instrument. Using high quality factor LC filters and room temperature electronics developed at SRON and low-noise two stage SQUID amplifiers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. An integrated noise equivalent power resolution of about 2.0 eV at 1.7 MHz has been demonstrated with a pixel from a new TES array from NASA/Goddard (GSFC-A2). We have achieved X-ray energy resolutions 2.5 eV at AC bias frequency at 1.7 MHz in the single pixel read-out. We have also demonstrated for the first time an X-ray energy resolution around 3.0 eV in a 6 pixel FDM read-out with TES array (GSFC-A1). In this paper we report on the single pixel performance of these microcalorimeters under MHz AC bias, and further results of the performance of these pixels under FDM.
Banerjee, Pradipta K.; Datta, Asit K.
2013-02-01
The paper proposes an improved strategy for face recognition using correlation filter under varying lighting conditions and occlusion where spatial domain preprocessing is carried out by two convolution kernels. The first convolution kernel is a contour kernel for emphasizing high frequency components of face image and the other kernel is a smoothing kernel used for minimization of noise those may arise due to preprocessing. The convolution kernels are obtained by training a generalized regression neural network using enhanced face features. Face features are enhanced by conventional principal component analysis. The proposed method reduces the false acceptance rate and false rejection rate in comparison to other standard correlation filtering techniques. Moreover, the processing is fast when compared to the existing illumination normalization techniques. A scheme of hardware implementation of all optical correlation technique is also suggested based on single spatial light modulator in a beam folding architecture. Two benchmark databases YaleB and PIE are used for performance verification of the proposed scheme and the improved results are obtained for both illumination variations and occlusions in test face images.
Huan, Huiting; Mandelis, Andreas; Lashkari, Bahman; Liu, Lixian
2017-04-01
The evaluation of the stress-strain state of metallic materials is an important problem in the field of non-destructive testing (NDT). Prolonged cyclic loading or overloading will lead to permanent changes of material strength in an inconspicuous manner that poses threat to the safety of structures, components and products. This research focuses on gauging the mechanical strength of metallic alloys through the application of frequency-domain laser ultrasound (FDLU) based on a continuous-wave diode laser source. The goal is to develop industrial NDT procedures for fatigue monitoring in metallic substrates and coatings so that the technique can be used for mechanical strength assessment. A small-scale, non-commercial rig was fabricated to hold the sample and conduct tensile FDLU testing in parallel with an adhesive strain gauge affixed on the tested sample for independent measurement of the applied stress. Harmonic modulation and lock-in detection were used to investigate the LU signal sensitivity to the stress-strain state of ordinary aluminum alloy samples. A 1 MHz focused piezoelectric transducer was used to detect the LU signal. During the tensile procedure, both amplitude and phase signals exhibited good repeatability and sensitivity to the increasing stress-strain within the elastic regime. Signals beyond the elastic limit also revealed significant change patterns.
Directory of Open Access Journals (Sweden)
Salim Bahçeci
2010-01-01
Full Text Available In impulse radio ultra-wideband (IR-UWB systems where the channel lengths are on the order of a few hundred taps, conventional use of frequency-domain (FD processing for channel estimation and equalization may not be feasible because the need to add a cyclic prefix (CP to each block causes a significant reduction in the spectral efficiency. On the other hand, using no or short CP causes the interblock interference (IBI and thus degradation in the receiver performance. Therefore, in order to utilize FD receiver processing UWB systems without a significant loss in the spectral efficiency and the performance, IBI cancellation mechanisms are needed in both the channel estimation and equalization operations. For this reason, in this paper, we consider the joint FD channel estimation and equalization for IR-UWB systems with short cyclic prefix (CP and propose a novel iterative receiver employing soft IBI estimation and cancellation within both its FD channel estimator and FD equalizer components. We show by simulation results that the proposed FD receiver attains performances close to that of the full CP case in both line-of-sight (LOS and non-line-of-sight (NLOS UWB channels after only a few iterations.
Yao, Yong-Sheng; Zheng, Jian-Long; Chen, Zeng-Shun; Zhang, Jun-Hui; Li, Yong
2016-06-10
This paper presents a systematic pioneering study on the use of agricultural-purpose frequency domain reflectometry (FDR) sensors to monitor temperature and moisture of a subgrade in highway extension and reconstruction engineering. The principle of agricultural-purpose FDR sensors and the process for embedding this kind of sensors for subgrade engineering purposes are introduced. Based on field measured weather data, a numerical analysis model for temperature and moisture content in the subgrade's soil is built. Comparisons of the temperature and moisture data obtained from numerical simulation and FDR-based measurements are conducted. The results show that: (1) the embedding method and process, data acquisition, and remote transmission presented are reasonable; (2) the temperature and moisture changes are coordinated with the atmospheric environment and they are also in close agreement with numerical calculations; (3) the change laws of both are consistent at positions where the subgrade is compacted uniformly. These results suggest that the data measured by the agricultural-purpose FDR sensors are reliable. The findings of this paper enable a new and effective real-time monitoring method for a subgrade's temperature and moisture changes, and thus broaden the application of agricultural-purpose FDR sensors.
Saager, Rolf B; Balu, Mihaela; Crosignani, Viera; Sharif, Ata; Durkin, Anthony J; Kelly, Kristen M; Tromberg, Bruce J
2015-06-01
The combined use of nonlinear optical microscopy and broadband reflectance techniques to assess melanin concentration and distribution thickness in vivo over the full range of Fitzpatrick skin types is presented. Twelve patients were measured using multiphoton microscopy (MPM) and spatial frequency domain spectroscopy (SFDS) on both dorsal forearm and volar arm, which are generally sun-exposed and non-sun-exposed areas, respectively. Both MPM and SFDS measured melanin volume fractions between (skin type I non-sun-exposed) and 20% (skin type VI sun exposed). MPM measured epidermal (anatomical) thickness values ~30-65 μm, while SFDS measured melanin distribution thickness based on diffuse optical path length. There was a strong correlation between melanin concentration and melanin distribution (epidermal) thickness measurements obtained using the two techniques. While SFDS does not have the ability to match the spatial resolution of MPM, this study demonstrates that melanin content as quantified using SFDS is linearly correlated with epidermal melanin as measured using MPM (R² = 0.8895). SFDS melanin distribution thickness is correlated to MPM values (R² = 0.8131). These techniques can be used individually and/or in combination to advance our understanding and guide therapies for pigmentation-related conditions as well as light-based treatments across a full range of skin types.
Directory of Open Access Journals (Sweden)
Yong-Sheng Yao
2016-06-01
Full Text Available This paper presents a systematic pioneering study on the use of agricultural-purpose frequency domain reflectometry (FDR sensors to monitor temperature and moisture of a subgrade in highway extension and reconstruction engineering. The principle of agricultural-purpose FDR sensors and the process for embedding this kind of sensors for subgrade engineering purposes are introduced. Based on field measured weather data, a numerical analysis model for temperature and moisture content in the subgrade’s soil is built. Comparisons of the temperature and moisture data obtained from numerical simulation and FDR-based measurements are conducted. The results show that: (1 the embedding method and process, data acquisition, and remote transmission presented are reasonable; (2 the temperature and moisture changes are coordinated with the atmospheric environment and they are also in close agreement with numerical calculations; (3 the change laws of both are consistent at positions where the subgrade is compacted uniformly. These results suggest that the data measured by the agricultural-purpose FDR sensors are reliable. The findings of this paper enable a new and effective real-time monitoring method for a subgrade’s temperature and moisture changes, and thus broaden the application of agricultural-purpose FDR sensors.
Taki, Hirofumi; Sakamoto, Takuya; Taki, Kousuke; Yamakawa, Makoto; Shiina, Tsuyoshi; Kudo, Motoi; Sato, Toru
2013-01-01
We have proposed a high-range-resolution ultrasound imaging method for human carotid artery using an adaptive beamforming technique based on frequency domain interferometry (FDI). The method assumes that the received signal consists of multiple echoes of targets and noise, where the waveform of each echo is similar to that of the reference signal. In this study, we examine the dependence of the echo waveform on the target depth, and investigate the proper measurement-range for the FDI imaging method using a reference signal. Furthermore, we propose a ROI-division process, where each sub-ROI has a proper measurement-range for the application of the FDI imaging method. Simulation and experimental results show the efficiency of the ROI-division process in improving the image quality of human carotid artery acquired using the FDI imaging method. We believe that the modified FDI imaging method with the ROI-division process has the potential to facilitate significant progress in the detection of vessel stenosis and in the assessment of cardiovascular disease risk.
Gao, Hong; Cao, Xiuhan; Li, Jinyi; Du, Zhenhui
2016-10-01
Multi-pass cells (MPCs) are commonly used to improve the sensitivity for trace gas detection using spectroscopy technologies. The determination of Effective Optical Path Length (EOPL) of a MPC is very important and challenging in applications which aim at absolute measurements. It is well-known that the temperature changing will exercise some influence on the MPCs' spatial structure, however, measurements of the influence haven't been reported which might due to the limitation of measuring method. In this paper, we used a direct high-precision measuring method with Optical Frequency Domain Reflectometer (OFDR) to evaluate the thermal stability of a multi-pass cell. To simulate the environment with a large range of temperature changing, this paper gave a series of experiments by setting the temperature control unit in system from 25 to 175 degree Celsius, and the MPC's EOPL was measured simultaneously for the investigation of temperature response. The results showed that the effective optical path length increase monotonically along with the variation of the temperature, and the rising rate is 0.5 mm/ºC with the total length of about 3 meters which should be pay attention to when the ultra-high accuracy results are demanded. To stabilize the EOPL of the system, if it is possible, the environment temperature of gas cell can be controlled with a constant temperature. In practical applications, the real-time monitoring of EOPL with a direct measuring method may be necessary.
Angelo, Joseph P.; Bigio, Irving J.; Gioux, Sylvain
2016-03-01
Imaging technologies working in the spatial frequency domain are becoming increasingly popular for generating wide-field optical property maps, enabling further analysis of tissue parameters such as absorption or scattering. While acquisition methods have witnessed a very rapid growth and are now performing in real-time, processing methods are yet slow preventing information to be acquired and displayed in real-time. In this work, we present solutions for rapid inverse problem solving for optical properties by use of advanced look-up tables. In particular, we present methods and results from a dense, linearized look-up table and an analytical representation that currently run 100 times faster than the standard method and within 10% in both absorption and scattering. With the resulting computation time in the tens of milliseconds range, the proposed techniques enable video-rate feedback of real-time techniques such as snapshot of optical properties (SSOP) imaging, making full video-rate guidance in the clinic possible.
Qiao, Yao-Bin; Qi, Hong; Zhao, Fang-Zhou; Ruan, Li-Ming
2016-12-01
Reconstructing the distribution of optical parameters in the participating medium based on the frequency-domain radiative transfer equation (FD-RTE) to probe the internal structure of the medium is investigated in the present work. The forward model of FD-RTE is solved via the finite volume method (FVM). The regularization term formatted by the generalized Gaussian Markov random field model is used in the objective function to overcome the ill-posed nature of the inverse problem. The multi-start conjugate gradient (MCG) method is employed to search the minimum of the objective function and increase the efficiency of convergence. A modified adjoint differentiation technique using the collimated radiative intensity is developed to calculate the gradient of the objective function with respect to the optical parameters. All simulation results show that the proposed reconstruction algorithm based on FD-RTE can obtain the accurate distributions of absorption and scattering coefficients. The reconstructed images of the scattering coefficient have less errors than those of the absorption coefficient, which indicates the former are more suitable to probing the inner structure. Project supported by the National Natural Science Foundation of China (Grant No. 51476043), the Major National Scientific Instruments and Equipment Development Special Foundation of China (Grant No. 51327803), and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51121004).
Velasco Soares, D.; Baesso Mauro, L.; Medina Neto, A.; Bicanic, D.D.; Koehorst, R.B.M.; Hooft, van der J.J.J.; Bento, A.C.
2011-01-01
The frequency-domain open photoacoustic cell (OPC) approach was used to determine room temperature thermal diffusivity of skins (pericarps) from the raw tomatoes (Lycopersicon esculetum Mill.) characterized by the three different stages of ripeness (from immature-green to a mature-red). Periodically
Bahler, D. D.
1978-01-01
Procedures are presented for obtaining valid frequency-domain transfer functions of regulated reactor energy-storage dc-to-dc converters. These procedures are for measuring loop gain, closed loop gain, output impedance, and audio susceptibility. The applications of these measurements are discussed.
Energy Technology Data Exchange (ETDEWEB)
Sheshyekani, K. [Dept. of Electrical and Computer Engineering, Shahid Beheshti University, Tehran, 1983963113 (Iran, Islamic Republic of); Sadeghi, S.H.H.; Moini, R. [Electromagnetics Research Laboratory of Amirkabir University of Technology, 424 Hafez Ave., Tehran 15914 (Iran, Islamic Republic of); Rachidi, F. [Swiss Federal Institute of Technology, Lausanne 1015 (Switzerland)
2011-02-15
A frequency-domain method is proposed for the transient analysis of grounding systems with ionized soil. The method involves two stages. First, the grounding system is transformed into a nonlinear equivalent circuit, in which the frequency-domain circuit parameters of the grounding electrodes are extracted by the method of moment (MoM) and the nonlinear part of the equivalent circuit represents the soil ionization. Soil ionization is represented by a nonlinear load whose characteristics can be specified based on either experimental data or theoretical models, without any limitations in the order of nonlinearity. In the second stage the nonlinear equivalent circuit is treated using the arithmetic operator method (AOM). The AOM uses a linear matrix transformation of spectra to perform basic arithmetic operations in the frequency-domain. The main feature of the proposed method is its efficiency in dealing with the nonlinear behavior of soil ionization in the frequency-domain solution of grounding systems by the MoM. It also enables one to consider the actual nonlinear behavior of soil ionization specified by experimental data or appropriate theoretical models. (author)