Frequency-Domain Methods for Characterization of Pulsed Power Diagnostics
White, A D; Anderson, R A; Ferriera, T J; Goerz, D A
2009-07-27
This paper discusses methods of frequency-domain characterization of pulsed power sensors using vector network analyzer and spectrum analyzer techniques that offer significant simplification over time-domain methods, while mitigating or minimizing the effect of the difficulties present in time domain characterization. These methods are applicable to characterization of a wide variety of sensors.
Robust time and frequency domain estimation methods in adaptive control
NASA Technical Reports Server (NTRS)
Lamaire, Richard Orville
1987-01-01
A robust identification method was developed for use in an adaptive control system. The type of estimator is called the robust estimator, since it is robust to the effects of both unmodeled dynamics and an unmeasurable disturbance. The development of the robust estimator was motivated by a need to provide guarantees in the identification part of an adaptive controller. To enable the design of a robust control system, a nominal model as well as a frequency-domain bounding function on the modeling uncertainty associated with this nominal model must be provided. Two estimation methods are presented for finding parameter estimates, and, hence, a nominal model. One of these methods is based on the well developed field of time-domain parameter estimation. In a second method of finding parameter estimates, a type of weighted least-squares fitting to a frequency-domain estimated model is used. The frequency-domain estimator is shown to perform better, in general, than the time-domain parameter estimator. In addition, a methodology for finding a frequency-domain bounding function on the disturbance is used to compute a frequency-domain bounding function on the additive modeling error due to the effects of the disturbance and the use of finite-length data. The performance of the robust estimator in both open-loop and closed-loop situations is examined through the use of simulations.
A simple method for converting frequency domain aerodynamics to the time domain
NASA Technical Reports Server (NTRS)
Dowell, E. H.
1980-01-01
A simple, direct procedure was developed for converting frequency domain aerodynamics into indicial aerodynamics. The data required for aerodynamic forces in the frequency domain may be obtained from any available (linear) theory. The method retains flexibility for the analyst and is based upon the particular character of the frequency domain results. An evaluation of the method was made for incompressible, subsonic, and transonic two dimensional flows.
Frequency-domain multiscale quantum mechanics/electromagnetics simulation method
Meng, Lingyi; Yin, Zhenyu; Yam, ChiYung E-mail: ghc@everest.hku.hk; Koo, SiuKong; Chen, GuanHua E-mail: ghc@everest.hku.hk; Chen, Quan; Wong, Ngai
2013-12-28
A frequency-domain quantum mechanics and electromagnetics (QM/EM) method is developed. Compared with the time-domain QM/EM method [Meng et al., J. Chem. Theory Comput. 8, 1190–1199 (2012)], the newly developed frequency-domain QM/EM method could effectively capture the dynamic properties of electronic devices over a broader range of operating frequencies. The system is divided into QM and EM regions and solved in a self-consistent manner via updating the boundary conditions at the QM and EM interface. The calculated potential distributions and current densities at the interface are taken as the boundary conditions for the QM and EM calculations, respectively, which facilitate the information exchange between the QM and EM calculations and ensure that the potential, charge, and current distributions are continuous across the QM/EM interface. Via Fourier transformation, the dynamic admittance calculated from the time-domain and frequency-domain QM/EM methods is compared for a carbon nanotube based molecular device.
Frequency domain optical tomography using a Monte Carlo perturbation method
NASA Astrophysics Data System (ADS)
Yamamoto, Toshihiro; Sakamoto, Hiroki
2016-04-01
A frequency domain Monte Carlo method is applied to near-infrared optical tomography, where an intensity-modulated light source with a given modulation frequency is used to reconstruct optical properties. The frequency domain reconstruction technique allows for better separation between the scattering and absorption properties of inclusions, even for ill-posed inverse problems, due to cross-talk between the scattering and absorption reconstructions. The frequency domain Monte Carlo calculation for light transport in an absorbing and scattering medium has thus far been analyzed mostly for the reconstruction of optical properties in simple layered tissues. This study applies a Monte Carlo calculation algorithm, which can handle complex-valued particle weights for solving a frequency domain transport equation, to optical tomography in two-dimensional heterogeneous tissues. The Jacobian matrix that is needed to reconstruct the optical properties is obtained by a first-order "differential operator" technique, which involves less variance than the conventional "correlated sampling" technique. The numerical examples in this paper indicate that the newly proposed Monte Carlo method provides reconstructed results for the scattering and absorption coefficients that compare favorably with the results obtained from conventional deterministic or Monte Carlo methods.
Damping identification in frequency domain using integral method
NASA Astrophysics Data System (ADS)
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.
Refined method of frequency domain interferometry for the MST radar
NASA Astrophysics Data System (ADS)
Pan, C. J.; Liu, C. H.; Roettger, J.
1993-08-01
The frequency domain interferometry (FDI) technique consists of transmitting a series of pulses with alternative carrier frequencies f1 and f2. From the resulting data, two different time series V1(t) and V2(t) can be formed corresponding to the carrier frequencies f1 and f2, respectively. Processing V1(t) and V2(t) in the frequency domain, the normalized cross-spectrum S(sub 12)(f) can be obtained by the equation S(sub 12)(f) = (*V1(f) V2(f)*) / (*V1(f)(exp 2)* *V2(f)(exp 2)*)(exp 1/2), where V1(f) and V2(f) represent the Fourier transforms of V1(t) and V2(t), respectively, and * * indicates the ensemble mean of periodograms necessary to estimate the auto and cross spectrum. Then, the amplitude and phase of S(sub 12)(f), the coherence function, are both functions of the doppler frequency f. As the beamwidth of the Chung-Li VHF radar is about 7.4 deg, the beam broadening effect is significant. According to the simple model pointed out by Woodman and Chu, the doppler frequency is related to angle of arrival given by theta = (f - fm)lambda/2U, where U is the mean wind speed, theta is the angle of arrival, lambda is the wavelength, and fm is the mean doppler frequency. Combining these two ideas, the coherence function S(sub 12)(f) is a function of doppler frequency f and each f corresponds to an angle of arrival. Therefore, the layer's thickness and positions can be estimated from different angles of arrival. This is the so called refined FDI method. An experiment has been carried out to implement this idea. Two frequencies f1 = 52 MHz and f2 = 52.5 MHz were employed at Chung-Li VHF radar to carry out the FDI observations with a 300 meter range resolution. By using the refined FDI method, it is shown that more information is obtained than the traditional FDI method to look inside the fine structure of the layer.
Feng, Xiaobing
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.
Comparison of frequency-domain and time-domain rotorcraft vibration control methods
NASA Technical Reports Server (NTRS)
Gupta, N. K.
1984-01-01
Active control of rotor-induced vibration in rotorcraft has received significant attention recently. Two classes of techniques have been proposed. The more developed approach works with harmonic analysis of measured time histories and is called the frequency-domain approach. The more recent approach computes the control input directly using the measured time history data and is called the time-domain approach. The report summarizes the results of a theoretical investigation to compare the two approaches. Five specific areas were addressed: (1) techniques to derive models needed for control design (system identification methods), (2) robustness with respect to errors, (3) transient response, (4) susceptibility to noise, and (5) implementation difficulties. The system identification methods are more difficult for the time-domain models. The time-domain approach is more robust (e.g., has higher gain and phase margins) than the frequency-domain approach. It might thus be possible to avoid doing real-time system identification in the time-domain approach by storing models at a number of flight conditions. The most significant error source is the variation in open-loop vibrations caused by pilot inputs, maneuvers or gusts. The implementation requirements are similar except that the time-domain approach can be much simpler to implement if real-time system identification were not necessary.
On the Analysis Methods for the Time Domain and Frequency Domain Response of a Buried Objects*
NASA Astrophysics Data System (ADS)
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
Smallwood, D.O.; Paez, T.L.
1991-01-01
A procedure for generating vectors of time domain signals which are partially coherent in a prescribed manner is described. The procedure starts with the spectral density matrix, (G{sub xx}(f)), that relates pairs of elements of the vector random process (x(t), {minus}{infinity} < t < {infinity}). The spectral density matrix is decomposed into the form (G{sub xx}(f)) = (U(f)) (S(f)) (U(f)){prime} where (U(f)) is a matrix of complex frequency response functions, and (S(f)) is a diagonal matrix of real functions which can vary with frequency. The factors of the spectral density matrix, (U(f)) and (S(f)), are then used to generate a frame of random data in the frequency domain. The data is transformed into the time domain using an inverse FFT to generate a frame of data in the time domain. Successive frames of data are then windowed, overlapped, and added to form a vector of normal stationary sampled time histories, (x(t)), of arbitrary length. 11 refs., 4 figs., 1 tab.
Overview of multi-input frequency domain modal testing methods with an emphasis on sine testing
NASA Technical Reports Server (NTRS)
Rost, Robert W.; Brown, David L.
1988-01-01
An overview of the current state of the art multiple-input, multiple-output modal testing technology is discussed. A very brief review of the current time domain methods is given. A detailed review of frequency and spatial domain methods is presented with an emphasis on sine testing.
A method for efficient fractional sample delay generation for real-time frequency-domain beamformers
Breeding, J.E.; Karnowski, T.P.
1995-07-01
This paper presents an efficient method for fractional delay filter generation for frequency-domain beamformers. A common misunderstanding regarding frequency-domain beamforming is that any fractional time shift can be achieved using the delay property of the discrete Fourier transform (DFT). Blind application of the DFT delay property introduces circular convolution errors that may adversely affect the beam`s time series. The method presented avoids these errors while enabling real-time processing.
NASA Astrophysics Data System (ADS)
Wang, W.; Wen, L.
2013-12-01
Back projection is a method to back project the seismic energy recorded in a seismic array back to the earthquake source region and determine the rupture process of a large earthquake. The method takes advantage of the coherence of seismic energy in a seismic array and is quick in determining some important properties of earthquake source. The method can be performed in both time and frequency domains. In time domain, the most conventional procedure is beam forming with some measures of suppressing the noise, such as the Nth root stacking, etc. In the frequency domain, the multiple signal classification method (MUSIC) estimates the direction of arrivals of multiple waves propagating through an array using the subspace method. The advantage of this method is the ability to study rupture properties at various frequencies and to resolve simultaneous arrivals making it suitable for detecting biliteral rupture of an earthquake source. We present a comparison of back projection results on some large earthquakes between the methods in time domain and frequency domain. The time-domain procedure produces an image that is smeared and exhibits some artifacts, although some enhancing stacking methods can at some extent alleviate the problem. On the other hand, the MUSIC method resolves clear multiple arrivals and provides higher resolution of rupture imaging.
Determining XV-15 aeroelastic modes from flight data with frequency-domain methods
NASA Technical Reports Server (NTRS)
Acree, C. W., Jr.; Tischler, Mark B.
1993-01-01
The XV-15 tilt-rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier transformed). All spectral data were computed using chirp z-transforms. Modal frequencies and damping were determined by fitting curves to frequency-response magnitude and phase data. The results given in this report are for the XV-15 with its original metal rotor blades. Also, frequency and damping values are compared with theoretical predictions made using two different programs, CAMRAD and ASAP. The frequency-domain data-analysis method proved to be very reliable and adequate for tracking aeroelastic modes during flight-envelope expansion. This approach required less flight-test time and yielded mode estimations that were more repeatable, compared with the exponential-decay method previously used.
NASA Astrophysics Data System (ADS)
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
Comparison of Frequency-Domain Array Methods for Studying Earthquake Rupture Process
NASA Astrophysics Data System (ADS)
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
Identification of XV-15 aeroelastic modes using frequency-domain methods
NASA Technical Reports Server (NTRS)
Acree, Cecil W., Jr.; Tischler, Mark B.
1989-01-01
The XV-15 Tilt-Rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier transformed) with cross spectral and transfer function methods. Modal frequencies and damping were determined by performing curve fits to transfer function magnitude and phase data and to cross spectral magnitude data. Results are given for the XV-15 with its original metal rotor blades. Frequency and damping values are also compared with earlier predictions.
A frequency domain radar interferometric imaging (FII) technique based on high-resolution methods
NASA Astrophysics Data System (ADS)
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.
A frequency-spatial domain decomposition (FSDD) method for operational modal analysis
NASA Astrophysics Data System (ADS)
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.
Wave-Propagation Modeling and Inversion Using Frequency-Domain Integral Equation Methods
NASA Astrophysics Data System (ADS)
Strickland, Christopher E.
Full waveform inverse methods describe the full physics of wave propagation and can potentially overcome the limitations of ray theoretic methods. This work explores the use of integral equation based methods for simulation and inversion and illustrates their potential for computationally demanding problems. A frequency-domain integral equation approach to simulate wave-propagation in heterogeneous media and solve the inverse wave-scattering problem will be presented for elastic, acoustic, and electromagnetic systems. The method will be illustrated for georadar (ground- or ice-penetrating radar) applications and compared to results obtained using ray theoretic methods. In order to tackle the non-linearity of the problem, the inversion incorporates a broad range of frequencies to stabilize the solution. As with most non-linear inversion methods, a starting model that reasonably approximates the true model is critical to convergence of the algorithm. To improve the starting model, a variable reference inversion technique is developed that allows the background reference medium to vary for each source-receiver data pair and is less restrictive than using a single reference medium for the entire dataset. The reference medium can be assumed homogeneous (although different for each data point) to provide a computationally efficient, single-step, frequency-domain inversion approach that incorporates finite frequency effects not captured by ray based methods. The inversion can then be iterated on to further refine the solution.
Testing for Granger Causality in the Frequency Domain: A Phase Resampling Method.
Liu, Siwei; Molenaar, Peter
2016-01-01
This article introduces phase resampling, an existing but rarely used surrogate data method for making statistical inferences of Granger causality in frequency domain time series analysis. Granger causality testing is essential for establishing causal relations among variables in multivariate dynamic processes. However, testing for Granger causality in the frequency domain is challenging due to the nonlinear relation between frequency domain measures (e.g., partial directed coherence, generalized partial directed coherence) and time domain data. Through a simulation study, we demonstrate that phase resampling is a general and robust method for making statistical inferences even with short time series. With Gaussian data, phase resampling yields satisfactory type I and type II error rates in all but one condition we examine: when a small effect size is combined with an insufficient number of data points. Violations of normality lead to slightly higher error rates but are mostly within acceptable ranges. We illustrate the utility of phase resampling with two empirical examples involving multivariate electroencephalography (EEG) and skin conductance data.
Frequency-domain Monte Carlo method for linear oscillatory gas flows
NASA Astrophysics Data System (ADS)
Ladiges, Daniel R.; Sader, John E.
2015-03-01
Gas flows generated by resonating nanoscale devices inherently occur in the non-continuum, low Mach number regime. Numerical simulations of such flows using the standard direct simulation Monte Carlo (DSMC) method are hindered by high statistical noise, which has motivated the development of several alternate Monte Carlo methods for low Mach number flows. Here, we present a frequency-domain low Mach number Monte Carlo method based on the Boltzmann-BGK equation, for the simulation of oscillatory gas flows. This circumvents the need for temporal simulations, as is currently required, and provides direct access to both amplitude and phase information using a pseudo-steady algorithm. The proposed method is validated for oscillatory Couette flow and the flow generated by an oscillating sphere. Good agreement is found with an existing time-domain method and accurate numerical solutions of the Boltzmann-BGK equation. Analysis of these simulations using a rigorous statistical approach shows that the frequency-domain method provides a significant improvement in computational speed.
NASA Astrophysics Data System (ADS)
Xu, T.; Jacobsen, G.; Popov, S.; Forzati, M.; Mårtensson, J.; Mussolin, M.; Li, J.; Wang, K.; Zhang, Y.; Friberg, A. T.
2011-06-01
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 overlapsave 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.
Parallel full-waveform inversion in the frequency domain by the Gauss-Newton method
NASA Astrophysics Data System (ADS)
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.
Fast frequency domain method to detect skew in a document image
NASA Astrophysics Data System (ADS)
Mehta, Sunita; Walia, Ekta; Dutta, Maitreyee
2015-12-01
In this paper, a new fast frequency domain method based on Discrete Wavelet Transform and Fast Fourier Transform has been implemented for the determination of the skew angle in a document image. Firstly, image size reduction is done by using two-dimensional Discrete Wavelet Transform and then skew angle is computed using Fast Fourier Transform. Skew angle error is almost negligible. The proposed method is experimented using a large number of documents having skew between -90° and +90° and results are compared with Moments with Discrete Wavelet Transform method and other commonly used existing methods. It has been determined that this method works more efficiently than the existing methods. Also, it works with typed, picture documents having different fonts and resolutions. It overcomes the drawback of the recently proposed method of Moments with Discrete Wavelet Transform that does not work with picture documents.
Frequency-domain bridging multiscale method for wave propagation simulations in damaged structures
NASA Astrophysics Data System (ADS)
Casadei, F.; Ruzzene, M.
2010-03-01
Efficient numerical models are essential for the simulation of the interaction of propagating waves with localized defects. Classical finite elements may be computationally time consuming, especially when detailed discretizations are needed around damage regions. A multi-scale approach is here propose to bridge a fine-scale mesh defined on a limited region around the defect and a coarse-scale discretization of the entire domain. This "bridging" method is formulated in the frequency domain in order to further reduce the computational cost and provide a general framework valid for different types of structures. Numerical results presented for propagating elastic waves in 1D and 2D damaged waveguides illustrate the proposed technique and its advantages.
3D micro profile measurement with the method of spatial frequency domain analysis
NASA Astrophysics Data System (ADS)
Xu, Yongxiang
2015-10-01
3D micro profiles are often needed for measurement in many fields, e.g., binary optics, electronic industry, mechanical manufacturing, aeronautic and space industry, etc. In the case where height difference between two neighboring points of a test profile is equal to or greater than λ / 4, microscopic interferometry based on laser source will no longer be applicable because of the uncertainty in phase unwrapping. As white light possesses the characteristic of interference length approximate to zero, applying it for micro profilometry can avoid the trouble and can yield accurate results. Using self-developed Mirau-type scanning interference microscope, a step-like sample was tested twice, with 128 scanning interferograms recorded for each test. To process each set of the interferograms, the method of spatial frequency domain analysis was adopted. That is, for each point, by use of Furrier transform, white-light interference intensities were decomposed in spatial frequency domain, thus obtaining phase values corresponding to different wavenumbers; by using least square fitting on phases and wave numbers, a group-velocity OPD was gained for the very point; and finally in terms of the relation between relative height and the group-velocity OPD, the profile of the test sample was obtained. Two tests yielded same profile result for the sample, and step heights obtained were 50.88 nm and 50.94 nm, respectively. Meantime, the sample was also measured with a Zygo Newview 7200 topography instrument, with same profile result obtained and step height differing by 0.9 nm. In addition, data processing results indicate that chromatic dispersion equal to and higher than 2nd order is negligible when applying spatial frequency domain analysis method.
A frequency-domain thermoreflectance method for the characterization of thermal properties.
Schmidt, Aaron J; Cheaito, Ramez; Chiesa, Matteo
2009-09-01
A frequency-domain thermoreflectance method for measuring the thermal properties of homogenous materials and submicron thin films is described. The method can simultaneously determine the thermal conductivity and heat capacity of a sample, provided the thermal diffusivity is greater, similar3x10(-6) m(2)/s, and can also simultaneously measure in-plane and cross-plane thermal conductivities, as well the thermal boundary conductance between material layers. Two implementations are discussed, one based on an ultrafast pulsed laser system and one based on continuous-wave lasers. The theory of the method and an analysis of its sensitivity to various thermal properties are given, along with results from measurements of several standard materials over a wide range of thermal diffusivities. We obtain specific heats and thermal conductivities in good agreement with literature values, and also obtain the in-plane and cross-plane thermal conductivities for crystalline quartz.
NASA Astrophysics Data System (ADS)
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.
Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation
Jing, Yun; Tao, Molei; Clement, Greg T.
2011-01-01
A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green’s function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed. PMID:21302985
Frequency domain nonlinear optics
NASA Astrophysics Data System (ADS)
Legare, Francois
2016-05-01
The universal dilemma of gain narrowing occurring in fs amplifiers prevents ultra-high power lasers from delivering few-cycle pulses. This problem is overcome by a new amplification concept: Frequency domain Optical Parametric Amplification - FOPA. It enables simultaneous up-scaling of peak power and amplified spectral bandwidth and can be performed at any wavelength range of conventional amplification schemes, however, with the capability to amplify single cycles of light. The key idea for amplification of octave-spanning spectra without loss of spectral bandwidth is to amplify the broad spectrum ``slice by slice'' in the frequency domain, i.e. in the Fourier plane of a 4f-setup. The striking advantages of this scheme, are its capability to amplify (more than) one octave of bandwidth without shorting the corresponding pulse duration. This is because ultrabroadband phase matching is not defined by the properties of the nonlinear crystal employed but the number of crystals employed. In the same manner, to increase the output energy one simply has to increase the spectral extension in the Fourier plane and to add one more crystal. Thus, increasing pulse energy and shortening its duration accompany each other. A proof of principle experiment was carried out at ALLS on the sub-two cycle IR beam line and yielded record breaking performance in the field of few-cycle IR lasers. 100 μJ two-cycle pulses from a hollow core fibre compression setup were amplified to 1.43mJ without distorting spatial or temporal properties. Pulse duration at the input of FOPA and after FOPA remains the same. Recently, we have started upgrading this system to be pumped by 250 mJ to reach 40 mJ two-cycle IR few-cycle pulses and latest results will be presented at the conference. Furthermore, the extension of the concept of FOPA to other nonlinear optical processes will be discussed. Frequency domain nonlinear optics.
NASA Astrophysics Data System (ADS)
Holmberg, Andreas; Kierkegaard, Axel; Weng, Chenyang
2015-06-01
In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The proposed method is validated and analyzed in 2D only, although the formulation is fully presented in 3D. The result is applied in a study of the linear interaction between the acoustic and the hydrodynamic field in a 2D T-junction, subject to grazing flow at Mach 0.1. Part of the acoustic energy at the upstream edge of the junction is shed as harmonically oscillating disturbances, which are conveyed across the shear layer over the junction, where they interact with the acoustic field. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynold's stress, due to the acoustic field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-ε turbulence model. The spatially varying turbulent eddy viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented. Discrepancies remaining are likely due to inaccuracies in the selected turbulence model, which is known to produce large errors e.g. for flows with significant rotation, which the grazing flow across the T-junction certainly is. A natural next step is therefore to test the proposed methodology together with more sophisticated turbulence models.
Substructure coupling in the frequency domain
NASA Technical Reports Server (NTRS)
1985-01-01
Frequency domain analysis was found to be a suitable method for determining the transient response of systems subjected to a wide variety of loads. However, since a large number of calculations are performed within the discrete frequency loop, the method loses it computational efficiency if the loads must be represented by a large number of discrete frequencies. It was also discovered that substructure coupling in the frequency domain work particularly well for analyzing structural system with a small number of interface and loaded degrees of freedom. It was discovered that substructure coupling in the frequency domain can lead to an efficient method of obtaining natural frequencies of undamped structures. It was also found that the damped natural frequencies of a system may be determined using frequency domain techniques.
NASA Technical Reports Server (NTRS)
Yagle, A. E.
1981-01-01
Frequency domain methods are used to study the angles of arrival and departure for multivariable root loci. Explicit equations are obtained. For a special class of poles and zeros, some simpler equations that are generalizations of the single input/single output equations are presented.
A Fast Method of Transforming Relaxation Functions Into the Frequency Domain
Mopsik, Frederick I.
1999-01-01
The limits to the error due to truncation of the numeric integration of the one-sided Laplace transform of a relaxation function in the time domain into its equivalent frequency domain are established. Separate results are given for large and small ω. These results show that, for a given ω, only a restricted range of time samples is needed to perform the computation to a given accuracy. These results are then combined with a known error estimate for integration by cubic splines to give a good estimate for the number of points needed to perform the computation to a given accuracy. For a given data window between t1 and t2, the computation time is shown to be proportional to ln(t1/t2).
Frequency-domain elastic full-waveform multiscale inversion method based on dual-level parallelism
NASA Astrophysics Data System (ADS)
Li, Yuan-Yuan; Li, Zhen-Chun; Zhang, Kai; Zhang, Xuan
2015-12-01
The complexity of an elastic wavefield increases the nonlinearity of inversion. To some extent, multiscale inversion decreases the nonlinearity of inversion and prevents it from falling into local extremes. A multiscale strategy based on the simultaneous use of frequency groups and layer stripping method based on damped wave field improves the stability of inversion. A dual-level parallel algorithm is then used to decrease the computational cost and improve practicability. The seismic wave modeling of a single frequency and inversion in a frequency group are computed in parallel by multiple nodes based on multifrontal massively parallel sparse direct solver and MPI. Numerical tests using an overthrust model show that the proposed inversion algorithm can effectively improve the stability and accuracy of inversion by selecting the appropriate inversion frequency and damping factor in lowfrequency seismic data.
Method for measuring settling phenomena by means of frequency domain instrumentation
NASA Astrophysics Data System (ADS)
D'Apuzzo, M.; D'Arco, M.; Liccardo, A.; Vadursi, M.
2016-05-01
The paper deals with the analysis of settling phenomena that characterize the step response of digital to analog converters, amplifiers, and several other devices. Settling is described by means of a minimal second order model that is suitable to account for the distortion terms recognized in the signal spectrum. An alternative method for dynamic performance assessment of systems characterized by poor settling performance is then proposed. Thanks to the use of high bandwidth spectrum analyzers, the proposed method overtakes the limits characterizing the measurement approaches based on the use of time-domain instruments in the presence of modern ultra-wideband systems.
Method for measuring settling phenomena by means of frequency domain instrumentation.
D'Apuzzo, M; D'Arco, M; Liccardo, A; Vadursi, M
2016-05-01
The paper deals with the analysis of settling phenomena that characterize the step response of digital to analog converters, amplifiers, and several other devices. Settling is described by means of a minimal second order model that is suitable to account for the distortion terms recognized in the signal spectrum. An alternative method for dynamic performance assessment of systems characterized by poor settling performance is then proposed. Thanks to the use of high bandwidth spectrum analyzers, the proposed method overtakes the limits characterizing the measurement approaches based on the use of time-domain instruments in the presence of modern ultra-wideband systems. PMID:27250466
Vinegar, H.J.; Waxman, M.H.
1982-11-16
An apparatus is disclosed for borehole measurements of the induced polarization of earth formations. The apparatus consists of an induced polarization logger capable of measuring both in-phase and quadrature conductivities in the frequency domain. A method is described which uses these measurements to determine cation exchange capacity per unit pore volume, Qv, brine conductivity, Cw, and oil and water saturations, So and Sw, in shaly sands.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Kimura, Akira
In inverter-converter driving systems for AC electric cars, the DC input voltage of an inverter contains a ripple component with a frequency that is twice as high as the line voltage frequency, because of a single-phase converter. The ripple component of the inverter input voltage causes pulsations on torques and currents of driving motors. To decrease the pulsations, a beat-less control method, which modifies a slip frequency depending on the ripple component, is applied to the inverter control. In the present paper, the beat-less control method was analyzed in the frequency domain. In the first step of the analysis, transfer functions, which revealed the relationship among the ripple component of the inverter input voltage, the slip frequency, the motor torque pulsation and the current pulsation, were derived with a synchronous rotating model of induction motors. An analysis model of the beat-less control method was then constructed using the transfer functions. The optimal setting of the control method was obtained according to the analysis model. The transfer functions and the analysis model were verified through simulations.
Liu, Xiuyun; Czosnyka, Marek; Donnelly, Joseph; Budohoski, Karol P; Varsos, Georgios V; Nasr, Nathalie; Brady, Ken M; Reinhard, Matthias; Hutchinson, Peter J; Smielewski, Peter
2015-01-01
The impulse response (IR)-based autoregulation index (ARI) allows for continuous monitoring of cerebral autoregulation using spontaneous fluctuations of arterial blood pressure (ABP) and cerebral flow velocity (FV). We compared three methods of autoregulation assessment in 288 traumatic brain injury (TBI) patients managed in the Neurocritical Care Unit: (1) IR-based ARI; (2) transfer function (TF) phase, gain, and coherence; and (3) mean flow index (Mx). Autoregulation index was calculated using the TF estimation (Welch method) and classified according to the original Tiecks' model. Mx was calculated as a correlation coefficient between 10-second averages of ABP and FV using a moving 300-second data window. Transfer function phase, gain, and coherence were extracted in the very low frequency (VLF, 0 to 0.05 Hz) and low frequency (LF, 0.05 to 0.15 Hz) bandwidths. We studied the relationship between these parameters and also compared them with patients' Glasgow outcome score. The calculations were performed using both cerebral perfusion pressure (CPP; suffix ‘c') as input and ABP (suffix ‘a'). The result showed a significant relationship between ARI and Mx when using either ABP (r=−0.38, P<0.001) or CPP (r=−0.404, P<0.001) as input. Transfer function phase and coherence_a were significantly correlated with ARI_a and ARI_c (P<0.05). Only ARI_a, ARI_c, Mx_a, Mx_c, and phase_c were significantly correlated with patients' outcome, with Mx_c showing the strongest association. PMID:25407266
Shang, Jianyu; Deng, Zhihong; Fu, Mengyin; Wang, Shunting
2016-01-01
Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment. PMID:27322266
Shang, Jianyu; Deng, Zhihong; Fu, Mengyin; Wang, Shunting
2016-01-01
Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment. PMID:27322266
Yu, Xiao; Verho, Jarmo; Li, Tie; Kallio, Pasi; Vilkko, Matti; Gao, Anran; Wang, Yuelin
2014-01-01
Summary 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. PMID:25161832
Van Munster, E B; Gadella, T W J
2004-01-01
In conventional wide-field frequency-domain fluorescence lifetime imaging microscopy (FLIM), excitation light is intensity-modulated at megahertz frequencies. Emitted fluorescence is recorded by a CCD camera through an image intensifier, which is modulated at the same frequency. From images recorded at various phase differences between excitation and intensifier gain modulation, the phase and modulation depth of the emitted light is obtained. The fluorescence lifetime is determined from the delay and the decrease in modulation depth of the emission relative to the excitation. A minimum of three images is required, but in this case measurements become susceptible to aliasing caused by the presence of higher harmonics. Taking more images to avoid this is not always possible owing to phototoxicity or movement. A method is introduced, phiFLIM, requiring only three recordings that is not susceptible to aliasing. The phase difference between the excitation and the intensifier is scanned over the entire 360 degrees range following a predefined phase profile, during which the image produced by the intensifier is integrated onto the CCD camera, yielding a single image. Three different images are produced following this procedure, each with a different phase profile. Measurements were performed with a conventional wide-field frequency-domain FLIM system based on an acousto-optic modulator for modulation of the excitation and a microchannel-plate image intensifier coupled to a CCD camera for the detection. By analysis of the harmonic content of measured signals it was found that the third harmonic was effectively the highest present. Using the conventional method with three recordings, phase errors due to aliasing of up to +/- 29 degrees and modulation depth errors of up to 30% were found. Errors in lifetimes of YFP-transfected HeLa cells were as high as 100%. With phiFLIM, using the same specimen and settings, systematic errors due to aliasing did not occur.
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.
NASA Astrophysics Data System (ADS)
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.
Frequency domain optical parametric amplification
NASA Astrophysics Data System (ADS)
Schmidt, Bruno E.; Thiré, Nicolas; Boivin, Maxime; Laramée, Antoine; Poitras, François; Lebrun, Guy; Ozaki, Tsuneyuki; Ibrahim, Heide; Légaré, François
2014-05-01
Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43 mJ two-cycle pulses at 1.8 μm wavelength.
Frequency domain optical parametric amplification
Schmidt, Bruno E.; Thiré, Nicolas; Boivin, Maxime; Laramée, Antoine; Poitras, François; Lebrun, Guy; Ozaki, Tsuneyuki; Ibrahim, Heide; Légaré, François
2014-01-01
Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43 mJ two-cycle pulses at 1.8 μm wavelength. PMID:24805968
a Frequency Domain Based NUMERIC-ANALYTICAL Method for Non-Linear Dynamical Systems
NASA Astrophysics Data System (ADS)
Narayanan, S.; Sekar, P.
1998-04-01
In this paper a multiharmonic balancing technique is used to develop certain algorithms to determine periodic orbits of non-liner dynamical systems with external, parametric and self excitations. Essentially, in this method the non-linear differential equations are transformed into a set of non-linear algebraic equations in terms of the Fourier coefficients of the periodic solutions which are solved by using the Newton-Raphson technique. The method is developed such that both fast Fourier transform and discrete Fourier transform algorithms can be used. It is capable of treating all types of non-linearities and higher dimensional systems. The stability of periodic orbits is investigated by obtaining the monodromy matrix. A path following algorithm based on the predictor-corrector method is also presented to enable the bifurcation analysis. The prediction is done with a cubic extrapolation technique with an arc length incrementation while the correction is done with the use of the least square minimisation technique. The under determined system of equations is solved by singular value decomposition. The suitability of the method is demonstrated by obtaining the bifurcational behaviour of rolling contact vibrations modelled by Hertz contact law.
Comparison of the domain and frequency domain state feedbacks
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.
NASA Astrophysics Data System (ADS)
Fishkin, Joshua B.; So, Peter T. C.; Cerussi, Albert E.; Gratton, Enrico; Fantini, Sergio; Franceschini, Maria Angela
1995-03-01
We have measured the optical absorption and scattering coefficient spectra of a multiple-scattering medium (i.e., a biological tissue-simulating phantom comprising a lipid colloid) containing methemoglobin by using frequency-domain techniques. The methemoglobin absorption spectrum determined in the multiple-scattering medium is in excellent agreement with a corrected methemoglobin absorption spectrum obtained from a steady-state spectrophotometer measurement of the optical density of a minimally scattering medium. The determination of the corrected methemoglobin absorption spectrum takes into account the scattering from impurities in the methemoglobin solution containing no lipid colloid. Frequency-domain techniques allow for the separation of the absorbing from the scattering properties of multiple-scattering media, and these techniques thus provide an absolute
Frequency domain photoacoustic and fluorescence microscopy.
Langer, Gregor; Buchegger, Bianca; Jacak, Jaroslaw; Klar, Thomas A; Berer, Thomas
2016-07-01
We report on simultaneous frequency domain optical-resolution photoacoustic and fluorescence microscopy with sub-µm lateral resolution. With the help of a blood smear, we show that photoacoustic and fluorescence images provide complementary information. Furthermore, we compare theoretically predicted signal-to-noise ratios of sinusoidal modulation in frequency domain with pulsed excitation in time domain. PMID:27446698
Frequency domain photoacoustic and fluorescence microscopy.
Langer, Gregor; Buchegger, Bianca; Jacak, Jaroslaw; Klar, Thomas A; Berer, Thomas
2016-07-01
We report on simultaneous frequency domain optical-resolution photoacoustic and fluorescence microscopy with sub-µm lateral resolution. With the help of a blood smear, we show that photoacoustic and fluorescence images provide complementary information. Furthermore, we compare theoretically predicted signal-to-noise ratios of sinusoidal modulation in frequency domain with pulsed excitation in time domain.
Frequency domain photoacoustic and fluorescence microscopy
Langer, Gregor; Buchegger, Bianca; Jacak, Jaroslaw; Klar, Thomas A.; Berer, Thomas
2016-01-01
We report on simultaneous frequency domain optical-resolution photoacoustic and fluorescence microscopy with sub-µm lateral resolution. With the help of a blood smear, we show that photoacoustic and fluorescence images provide complementary information. Furthermore, we compare theoretically predicted signal-to-noise ratios of sinusoidal modulation in frequency domain with pulsed excitation in time domain. PMID:27446698
Frequency domain FIR and IIR adaptive filters
NASA Technical Reports Server (NTRS)
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.
Gyüre, B.; Márkus, B. G.; Bernáth, B.; Simon, F.; Murányi, F.
2015-09-15
We present a novel method to determine the resonant frequency and quality factor of microwave resonators which is faster, more stable, and conceptually simpler than the yet existing techniques. The microwave resonator is pumped with the microwave radiation at a frequency away from its resonance. It then emits an exponentially decaying radiation at its eigen-frequency when the excitation is rapidly switched off. The emitted microwave signal is down-converted with a microwave mixer, digitized, and its Fourier transformation (FT) directly yields the resonance curve in a single shot. Being a FT based method, this technique possesses the Fellgett (multiplex) and Connes (accuracy) advantages and it conceptually mimics that of pulsed nuclear magnetic resonance. We also establish a novel benchmark to compare accuracy of the different approaches of microwave resonator measurements. This shows that the present method has similar accuracy to the existing ones, which are based on sweeping or modulating the frequency of the microwave radiation.
Gyüre, B; Márkus, B G; Bernáth, B; Murányi, F; Simon, F
2015-09-01
We present a novel method to determine the resonant frequency and quality factor of microwave resonators which is faster, more stable, and conceptually simpler than the yet existing techniques. The microwave resonator is pumped with the microwave radiation at a frequency away from its resonance. It then emits an exponentially decaying radiation at its eigen-frequency when the excitation is rapidly switched off. The emitted microwave signal is down-converted with a microwave mixer, digitized, and its Fourier transformation (FT) directly yields the resonance curve in a single shot. Being a FT based method, this technique possesses the Fellgett (multiplex) and Connes (accuracy) advantages and it conceptually mimics that of pulsed nuclear magnetic resonance. We also establish a novel benchmark to compare accuracy of the different approaches of microwave resonator measurements. This shows that the present method has similar accuracy to the existing ones, which are based on sweeping or modulating the frequency of the microwave radiation. PMID:26429462
Tromberg, B.J.; Tsay, T.T.; Berns, M.W.; Svaasand, L.O.; Haskell, R.C.
1995-06-13
Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid. 14 figs.
Tromberg, Bruce J.; Tsay, Tsong T.; Berns, Michael W.; Svaasand, Lara O.; Haskell, Richard C.
1995-01-01
Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid.
Frequency Domain Sampling Using Biomedical Imaging Physics
NASA Astrophysics Data System (ADS)
Seo, Gun Ha; Chung, Minji; Kyung, Richard
2015-04-01
In magnetic resonance image analysis using physical and computational method, the process of transformation from frequency domain to image domain requires significant amount time because Inverse Fourier Transformation (IFT) takes every frequency points to determine the final output image. This paper shows the mechanisms and physics of image formation using the selectivity of proper k-space by removing different amounts of high or low frequencies to create the most optimal magnetic resonance image of a human tibial bone. Originally, square unit step function, N/2-N/10:N/2 + N/10 = 1, was used during the Fourier Transformations. And Gaussian filter, y = exp(-t2/40n) , where t = h-L/2, h = [0,M], L =2*7*N/40, the size of frequency matrix (M, N) = (365,557) was tested. Also circle equations as a filter, r = sqrt((x-M/2)2 + (y-N/2)2) , were tested in creating the images of the human tibial bone to find an efficient filter. The best efficiency occurred when the exponent n in the proposed Gaussian filter equation is in between 3 and 8, and therefore, a new algorithm is needed to find the exact number since the number is not only an integer.
Frequency domain optoacoustic tomography using amplitude and phase
Mohajerani, Pouyan; Kellnberger, Stephan; Ntziachristos, Vasilis
2014-01-01
We introduce optoacoustic tomographic imaging using intensity modulated light sources and collecting amplitude and phase information in the frequency domain. Imaging is performed at multiple modulation frequencies. The forward modeling uses the Green's function solution to the pressure wave equation in frequency domain and the resulting inverse problem is solved using regularized least squares minimization. We study the effect of the number of frequencies and of the bandwidth employed on the image quality achieved. The possibility of employing an all-frequency domain optoacoustic imaging for experimental measurements is studied as a function of noise. We conclude that frequency domain optoacoustic tomography may evolve to a practical experimental method using light intensity modulated sources, with advantages over time-domain optoacoustics. PMID:25431755
Frequency Domain Calculations Of Acoustic Propagation
NASA Technical Reports Server (NTRS)
Lockard, David P.
2004-01-01
Two complex geometry problems are solved using the linearized Euler equations. The impedance mismatch method1 is used to impose the solid surfaces without the need to use a body-fitted grid. The problem is solved in the frequency domain to avoid long run times. Although the harmonic assumption eliminates all time dependence, a pseudo-time term is added to allow conventional iterative methods to be employed. A Jameson type, Runge-Kutta scheme is used to advance the solution in pseudo time. The spatial operator is based on a seven-point, sixth-order finite difference. Constant coefficient, sixth-derivative artificial dissipation is used throughout the domain. A buffer zone technique employing a complex frequency to damp all waves near the boundaries is used to minimize reflections. The results show that the method is capable of capturing the salient features of the scattering, but an excessive number of grid points are required to resolve the phenomena in the vicinity of the solid bodies because the wavelength of the acoustics is relatively short compared with the size of the bodies. Smoothly transitioning into the immersed boundary condition alleviates the difficulties, but a fine mesh is still required.
In vivo mouse imaging using frequency domain optoacoustic tomography
NASA Astrophysics Data System (ADS)
Kellnberger, Stephan; Deliolanis, Nikolaos C.; Queirós, Daniel; Sergiadis, George; Ntziachristos, Vasilis
2013-06-01
Frequency domain optoacoustics relates to stimulation of optoacoustic signals using intensity modulated continuous wave light instead of pulsed laser light employed in time domain optoacoustic imaging. We present a method to generate frequency domain tomographic images of optical absorbers and cross sectional in-vivo mouse images, showing the changes of optical absorption before and after injection of indocyanine green (ICG). OCIS codes: 170.6960, 170.3880, 170.5220
Asymptotic Waveform Evaluation (AWE) Technique for Frequency Domain Electromagnetic Analysis
NASA Technical Reports Server (NTRS)
Cockrell, C. R.; Beck, F. B.
1996-01-01
The Asymptotic Waveform Evaluation (AWE) technique is applied to a generalized frequency domain electromagnetic problem. Most of the frequency domain techniques in computational electromagnetics result in a matrix equation, which is solved at a single frequency. In the AWE technique, the Taylor series expansion around that frequency is applied to the matrix equation. The coefficients of the Taylor's series are obtained in terms of the frequency derivatives of the matrices evaluated at the expansion frequency. The coefficients hence obtained will be used to predict the frequency response of the system over a frequency range. The detailed derivation of the coefficients (called 'moments') is given along with an illustration for electric field integral equation (or Method of Moments) technique. The radar cross section (RCS) frequency response of a square plate is presented using the AWE technique and is compared with the exact solution at various frequencies.
Frequency-domain analysis of absolute gravimeters
NASA Astrophysics Data System (ADS)
Svitlov, S.
2012-12-01
An absolute gravimeter is analysed as a linear time-invariant system in the frequency domain. Frequency responses of absolute gravimeters are derived analytically based on the propagation of the complex exponential signal through their linear measurement functions. Depending on the model of motion and the number of time-distance coordinates, an absolute gravimeter is considered as a second-order (three-level scheme) or third-order (multiple-level scheme) low-pass filter. It is shown that the behaviour of an atom absolute gravimeter in the frequency domain corresponds to that of the three-level corner-cube absolute gravimeter. Theoretical results are applied for evaluation of random and systematic measurement errors and optimization of an experiment. The developed theory agrees with known results of an absolute gravimeter analysis in the time and frequency domains and can be used for measurement uncertainty analyses, building of vibration-isolation systems and synthesis of digital filtering algorithms.
Ahn, Tae-Jung; Jung, Yongmin; Oh, Kyunghwan; Kim, Dug Young
2005-12-12
We propose a new chromatic dispersion measurement method for the higher-order modes of an optical fiber using optical frequency modulated continuous-wave (FMCW) interferometry. An optical fiber which supports few excited modes was prepared for our experiments. Three different guiding modes of the fiber were identified by using far-field spatial beam profile measurements and confirmed with numerical mode analysis. By using the principle of a conventional FMWC interferometry with a tunable external cavity laser, we have demonstrated that the chromatic dispersion of a few-mode optical fiber can be obtained directly and quantitatively as well as qualitatively. We have also compared our measurement results with those of conventional modulation phase-shift method. PMID:19503215
Autonomous Frequency-Domain Indentification
NASA Technical Reports Server (NTRS)
Mettler, Edward; Yam, Yeung; Bayard, David S.; Hadaegh, Fred Y.; Milman, Mark H.; Scheid, Robert E.
1992-01-01
Test and data-processing system determines plant models and uncertainties. Integrated system of methods, digital signal-processing, and algorithms identifies parametric model of large, flexible structures. Experiments in development of system conducted on laboratory model intended to represent large space antenna or flexible spacecraft. Also applicable to many terrestrial systems, robust control of dynamic plants and processes, robust control of systems about which knowledge uncertain or incomplete, decentralized control, and knowledge-based control systems.
NASA Astrophysics Data System (ADS)
Noh, Kyubo; Oh, Seokmin; Seol, Soon Jee; Lee, Ki Ha; Byun, Joongmoo
2016-03-01
We present a series of processes for understanding and analysing controlled-source electromagnetic (CSEM) responses for a conductive and permeable earth. To realize the CSEM response, a new 3-D CSEM forward modelling algorithm based on an edge finite element method for both electrically conductive and magnetically permeable heterogeneities is developed. The algorithm shows highly accurate results in validation tests against a semi-analytic solution for stratified earth and an integral form of the scattered field. We describe the vector behaviour of an anomalous magnetic field originating from a conductive and permeable anomaly when the loop sources are deployed over a conductive half-space. The CSEM response of the conductive and permeable anomaly is classified into three effects originating from: conductivity perturbations, permeability perturbations and the coupling of these two effects. The separated individual results and the corresponding integral equation form of the anomalous field help to better understand the physical behaviour. We confirm the characteristic features of the CSEM response from the conductive and permeable anomaly, for example, (1) the general dominance of the induction effect in the out-of-phase response accompanied by a non-negligible magnetization effect from the magnetic anomaly in a conductive half-space and (2) the dominance of near frequency-independent magnetization effects in the in-phase response at relatively low frequencies and change in ruling part of the in-phase response into the induction effect as the frequency increases. We also demonstrate the effect of coupling mode and show that its maximum contribution is limited to a few per cent level of other two modes, induction and magnetization mode, even when the heterogeneity of our model is strong. In our synthetic survey, using examples of land-based profiling surveys of low induction number and intermediate regime, we find that the effect of magnetization can be used as an
Fast Fourier backprojection for frequency-domain optoacoustic tomography.
Mohajerani, Pouyan; Kellnberger, Stephan; Ntziachristos, Vasilis
2014-09-15
We present a time-efficient backprojection image reconstruction approach applied to frequency-domain (FD) optoacoustic tomography based on tissue illumination at multiple, discrete frequencies. The presented method estimates the Fourier transform of a spatial, circular profile of the underlying image using the amplitude and phase data. These data are collected over multiple frequencies using an acoustic transducer positioned at several locations around the sample. Fourier-transform values for absent frequencies are estimated using interpolation based on low-pass filtering in the image domain. Reconstruction results are presented for synthetic measurements using numerical phantoms, and the results are compared with FD model-based reconstructions.
Potravkin, N N; Perezhogin, I A; Makarov, V A
2012-11-01
We propose an alternative method of integration of Maxwell equations. This method is the generalization of a finite-difference time-domain method with an auxiliary differential equation for the case of a linear optical medium with a frequency dispersion and an arbitrary source of spatial dispersion. We apply this method to the problem of the propagation of short plane-wave linearly polarized light pulses in such a medium. It is shown that some features of their propagation are completely different from those that are generally recognized for the linear optical activity phenomenon. For example, in some cases an initially linearly polarized light pulse becomes elliptically polarized during the propagation. This effect is more prominent in the front part of the pulse. PMID:23214905
NASA Technical Reports Server (NTRS)
Parker, Jr., Allen R (Inventor); Chan, Hon Man (Inventor); Piazza, Anthony (Nino) (Inventor); Richards, William Lance (Inventor)
2014-01-01
A method and system for multiplexing a network of parallel fiber Bragg grating (FBG) sensor-fibers to a single acquisition channel of a closed Michelson interferometer system via a fiber splitter by distinguishing each branch of fiber sensors in the spatial domain. On each branch of the splitter, the fibers have a specific pre-determined length, effectively separating each branch of fiber sensors spatially. In the spatial domain the fiber branches are seen as part of one acquisition channel on the interrogation system. However, the FBG-reference arm beat frequency information for each fiber is retained. Since the beat frequency is generated between the reference arm, the effective fiber length of each successive branch includes the entire length of the preceding branch. The multiple branches are seen as one fiber having three segments where the segments can be resolved. This greatly simplifies optical, electronic and computational complexity, and is especially suited for use in multiplexed or branched OFS networks for SHM of large and/or distributed structures which need a lot of measurement points.
Frequency versus time domain immunity testing of Smart Grid components
NASA Astrophysics Data System (ADS)
Gronwald, F.
2014-11-01
Smart Grid components often are subject to considerable conducted current disturbances in the frequency range 2-150 kHz and, as a consequence, it is necessary to provide reliable immunity test methods. The relevant basic standard IEC 61000-4-19 that is currently under discussion focusses on frequency domain test methods. It is remarked in this contribution that in the context of frequency domain testing the chosen frequency spacing is related to the resonance response of the system under test which, in turn, is characterized in terms of resonance frequencies and quality factors. These notions apply well to physical system but it is pointed out by the example of an actual smart meter immunity test that smart grid components may exhibit susceptibilities that do not necessarily follow a resonance pattern and, additionally, can be narrowband. As a consequence it is suggested to supplement the present frequency domain test methods by time domain tests which utilize damped sinusoidal excitations with corresponding spectra that properly cover the frequency range 2-150 kHz, as exemplified by the military standard MIL-STD-461.
Zhang, Hai-Feng; Ding, Guo-Wen; Lin, Yi-Bing; Chen, Yu-Qing
2015-05-15
In this paper, the properties of acceptor mode in two-dimensional plasma photonic crystals (2D PPCs) composed of the homogeneous and isotropic dielectric cylinders inserted into nonmagnetized plasma background with square lattices under transverse-magnetic wave are theoretically investigated by a modified finite-difference frequency-domain (FDFD) method with supercell technique, whose symmetry of every supercell is broken by removing a central rod. A new FDFD method is developed to calculate the band structures of such PPCs. The novel FDFD method adopts a general function to describe the distribution of dielectric in the present PPCs, which can easily transform the complicated nonlinear eigenvalue equation to the simple linear equation. The details of convergence and effectiveness of proposed FDFD method are analyzed using a numerical example. The simulated results demonstrate that the enough accuracy of the proposed FDFD method can be observed compared to the plane wave expansion method, and the good convergence can also be obtained if the number of meshed grids is large enough. As a comparison, two different configurations of photonic crystals (PCs) but with similar defect are theoretically investigated. Compared to the conventional dielectric-air PCs, not only the acceptor mode has a higher frequency but also an additional photonic bandgap (PBG) can be found in the low frequency region. The calculated results also show that PBGs of proposed PPCs can be enlarged as the point defect is introduced. The influences of the parameters for present PPCs on the properties of acceptor mode are also discussed in detail. Numerical simulations reveal that the acceptor mode in the present PPCs can be easily tuned by changing those parameters. Those results can hold promise for designing the tunable applications in the signal process or time delay devices based on the present PPCs.
NASA Astrophysics Data System (ADS)
Liu, Yun; Wang, Zhao; Li, Jiansu; Gao, Jianmin; Huang, Junhui
2016-11-01
The digital holography (DH) off-axis geometry in microscope configuration introduces the tilt phase aberration in construction, resulting in the reconstructed image distortion. The two typical methods of the tilt aberration compensation, digital reference wavefront method and spectrum centering method, all require the hologram spectrum's centering judgment of side band as a precondition. However, it is difficult to judge the center location of side band by the spectral amplitude maximum due to the presence of the quadratic phase aberration, thus producing the residual tilt phase aberration. Therefore, the method for location of the center of side band based on the unwrapped phase in spatial frequency domain is proposed in the pre-magnification configuration. The Fourier spectrum of the hologram is a complex function and its unwrapped phase distribution always appears the extremum corresponding to the carrier frequency. The correct hologram spectrum's center location of side band can be obtained by judging its unwrapped phase maximum, which makes assure of the tilt aberration compensation in the pre-magnification configuration. The feasibility of the proposed approach is demonstrated by applying it to the phase imaging of the micro-hole array, phase grating and phase steps.
High frequency resolution terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Sangala, Bagvanth Reddy
2013-12-01
A new method for the high frequency resolution terahertz time-domain spectroscopy is developed based on the characteristic matrix method. This method is useful for studying planar samples or stack of planar samples. The terahertz radiation was generated by optical rectification in a ZnTe crystal and detected by another ZnTe crystal via electro-optic sampling method. In this new characteristic matrix based method, the spectra of the sample and reference waveforms will be modeled by using characteristic matrices. We applied this new method to measure the optical constants of air. The terahertz transmission through the layered systems air-Teflon-air-Quartz-air and Nitrogen gas-Teflon-Nitrogen gas-Quartz-Nitrogen gas was modeled by the characteristic matrix method. A transmission coefficient is derived from these models which was optimized to fit the experimental transmission coefficient to extract the optical constants of air. The optimization of an error function involving the experimental complex transmission coefficient and the theoretical transmission coefficient was performed using patternsearch algorithm of MATLAB. Since this method takes account of the echo waveforms due to reflections in the layered samples, this method allows analysis of longer time-domain waveforms giving rise to very high frequency resolution in the frequency-domain. We have presented the high frequency resolution terahertz time-domain spectroscopy of air and compared the results with the literature values. We have also fitted the complex susceptibility of air to the Lorentzian and Gaussian functions to extract the linewidths.
NASA Astrophysics Data System (ADS)
Linville, L. M.; Pankow, K. L.; Kilb, D. L.; Velasco, A. A.; Hayward, C.
2013-12-01
Because of the abundance of data from the Earthscope U.S. Transportable Array (TA), data paucity and station sampling bias in the US are no longer significant obstacles to understanding some of the physical parameters driving dynamic triggering. Initial efforts to determine locations of dynamic triggering in the US following large earthquakes (M ≥ 8.0) during TA relied on a time domain detection algorithm which used an optimized short-term average to long-term average (STA/LTA) filter and resulted in an unmanageably large number of false positive detections. Specific site sensitivities and characteristic noise when coupled with changes in detection rates often resulted in misleading output. To navigate this problem, we develop a frequency domain detection algorithm that first pre-whitens each seismogram and then computes a broadband frequency stack of the data using a three hour time window beginning at the origin time of the mainshock. This method is successful because of the broadband nature of earthquake signals compared with the more band-limited high frequency picks that clutter results from time domain picking algorithms. Preferential band filtering of the frequency stack for individual events can further increase the accuracy and drive the detection threshold to below magnitude one, but at general cost to detection levels across large scale data sets. Of the 15 mainshocks studied, 12 show evidence of discrete spatial clusters of local earthquake activity occurring within the array during the mainshock coda. Most of this activity is in the Western US with notable sequences in Northwest Wyoming, Western Texas, Southern New Mexico and Western Montana. Repeat stations (associated with 2 or more mainshocks) are generally rare, but when occur do so exclusively in California and Nevada. Notably, two of the most prolific regions of seismicity following a single mainshock occur following the 2009 magnitude 8.1 Samoa (Sep 29, 2009, 17:48:10) event, in areas with few
NASA Astrophysics Data System (ADS)
Kato, Ryozo; Xu, Yibin; Goto, Masahiro
2011-10-01
In this paper, we describe the development of a new frequency-domain (FD) method using completely optical techniques for determining the interfacial thermal resistance between a metal film and its substrate. The 3ω method, which is a FD method based on the technique of photolithography to define a metal-film heater/thermometer pattern, has been most widely used so far. The 2ω method implemented a thermoreflectance technique for measuring ac temperature. In this study we additionally implement a laser technique for periodic heating. Our new method can provide the absolute value of interfacial thermal resistance between a film and its substrate, using the known thermophysical properties of the substrate material, even though the optical power of the pump laser and the optical properties of the metal film are unknown. To verify the method, we measure the thermal resistance of interfaces such as, Au-Al2O3, Bi-Al2O3, Au-SiO2 (thermally oxidized), and Bi-SiO2 (thermally oxidized). The results of the measurements show good agreement with the data obtained by the 2ω method and with the data theoretically predicted using the diffusion mismatch model (DMM).
Frequency-domain prediction of turbofan noise radiation
NASA Astrophysics Data System (ADS)
Özyörük, Y.; Alpman, E.; Ahuja, V.; Long, L. N.
2004-03-01
This paper describes a frequency-domain numerical method for predicting noise radiation from ducted fans, including acoustic treatment and non-uniform background flow effects. The method solves the Euler equations linearized about a mean flow in the frequency domain. A pseudo-time derivative term is added to the frequency-domain equations so that a time marching technique can be employed to drive the acoustic field to steady state explicitly. This approach makes distributed parallel computing more viable for equations of this type and will allow for future use of well-known convergence acceleration techniques, such as multigrid, to obtain the solutions efficiently. Simulations of the JT15D static test inlet are performed including the effects of liners, and the results are compared with experimental data. A generic engine geometry is used for demonstrating further the prediction capability of the code, calculating the attenuation effects of different liner impedances and liner installation locations on the radiated sound fields.
Kinefuchi, K.; Funaki, I.; Shimada, T.; Abe, T.
2012-10-15
Under certain conditions during rocket flights, ionized exhaust plumes from solid rocket motors may interfere with radio frequency transmissions. To understand the relevant physical processes involved in this phenomenon and establish a prediction process for in-flight attenuation levels, we attempted to measure microwave attenuation caused by rocket exhaust plumes in a sea-level static firing test for a full-scale solid propellant rocket motor. The microwave attenuation level was calculated by a coupling simulation of the inviscid-frozen-flow computational fluid dynamics of an exhaust plume and detailed analysis of microwave transmissions by applying a frequency-dependent finite-difference time-domain method with the Drude dispersion model. The calculated microwave attenuation level agreed well with the experimental results, except in the case of interference downstream the Mach disk in the exhaust plume. It was concluded that the coupling estimation method based on the physics of the frozen plasma flow with Drude dispersion would be suitable for actual flight conditions, although the mixing and afterburning in the plume should be considered depending on the flow condition.
Materials characterization using frequency domain photoacoustic microscopy
NASA Astrophysics Data System (ADS)
Balogun, Oluwaseyi Oladeinde
A frequency domain photoacoustic microscopy system is developed for the characterization of micro- and nanoscale materials. An amplified, intensity modulated continuous wave (CW) laser source is used to generate narrow-bandwidth acoustic waves through the thermoelastic effect. The displacement resulting from acoustic wave interaction with material boundaries is measured using a path-stabilized Michelson interferometer. The signal from the interferometer is coupled to a RF lock-in amplifier or vector network analyzer, allowing for the bandwidth of the detection system to be matched to that of the acoustic signals. Measurements are made over an extremely narrow bandwidth by modulating the excitation laser source on the sample surface over a long time interval and selecting a corresponding integration time for the detection system. An analysis of the signal-to-noise ratio (SNR) of this system indicates that it offers substantial improvements over existing systems that incorporate pulsed laser sources to generate broad bandwidth acoustic waves. Using a bandwidth of 1.0 Hz, for instance, experimental results show a minimum detectable displacement of 3.1 fm. Extracting quantitative material parameters from the complex acoustic spectrum can be difficult when multiple acoustic modes are excited, or in the presence of reflections from sample boundaries. Two techniques are used to process the measured signals. In the first technique, the modulation frequency of the excitation laser is scanned over the bandwidth of interest, and a transient sample response is constructed from the frequency domain data. Acoustic arrivals that are separated in the time domain are time gated for further analysis. In the second approach, the modulation frequency of the excitation laser is fixed, but the source to receiver distance is varied. The spatial frequencies of the acoustic modes are found by analyzing the spatial variation of the phase, allowing for the velocity of each mode generated at
Collins, Kimberlee C; Maznev, Alexei A; Cuffe, John; Nelson, Keith A; Chen, Gang
2014-12-01
Laser-based time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance (FDTR) techniques are widely used for investigating thermal transport at micro- and nano-scales. We demonstrate that data obtained in TDTR measurements can be represented in a frequency-domain form equivalent to FDTR, i.e., in the form of a surface temperature amplitude and phase response to time-harmonic heating. Such a representation is made possible by using a large TDTR delay time window covering the entire pulse repetition interval. We demonstrate the extraction of frequency-domain data up to 1 GHz from TDTR measurements on a sapphire sample coated with a thin layer of aluminum, and show that the frequency dependencies of both the amplitude and phase responses agree well with theory. The proposed method not only allows a direct comparison of TDTR and FDTR data, but also enables measurements at high frequencies currently not accessible to FDTR. The frequency-domain representation helps uncover aspects of the measurement physics which remain obscured in a traditional TDTR measurement, such as the importance of modeling the details of the heat transport in the metal transducer film for analyzing high frequency responses.
NASA Astrophysics Data System (ADS)
Collins, Kimberlee C.; Maznev, Alexei A.; Cuffe, John; Nelson, Keith A.; Chen, Gang
2014-12-01
Laser-based time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance (FDTR) techniques are widely used for investigating thermal transport at micro- and nano-scales. We demonstrate that data obtained in TDTR measurements can be represented in a frequency-domain form equivalent to FDTR, i.e., in the form of a surface temperature amplitude and phase response to time-harmonic heating. Such a representation is made possible by using a large TDTR delay time window covering the entire pulse repetition interval. We demonstrate the extraction of frequency-domain data up to 1 GHz from TDTR measurements on a sapphire sample coated with a thin layer of aluminum, and show that the frequency dependencies of both the amplitude and phase responses agree well with theory. The proposed method not only allows a direct comparison of TDTR and FDTR data, but also enables measurements at high frequencies currently not accessible to FDTR. The frequency-domain representation helps uncover aspects of the measurement physics which remain obscured in a traditional TDTR measurement, such as the importance of modeling the details of the heat transport in the metal transducer film for analyzing high frequency responses.
Frequency domain laser velocimeter signal processor
NASA Technical Reports Server (NTRS)
Meyers, James F.; Murphy, R. Jay
1991-01-01
A new scheme for processing signals from laser velocimeter systems is described. The technique utilizes the capabilities of advanced digital electronics to yield a signal processor capable of operating in the frequency domain maximizing the information obtainable from each signal burst. This allows a sophisticated approach to signal detection and processing, with a more accurate measurement of the chirp frequency resulting in an eight-fold increase in measurable signals over the present high-speed burst counter technology. Further, the required signal-to-noise ratio is reduced by a factor of 32, allowing measurements within boundary layers of wind tunnel models. Measurement accuracy is also increased up to a factor of five.
AU-FREDI - AUTONOMOUS FREQUENCY DOMAIN IDENTIFICATION
NASA Technical Reports Server (NTRS)
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
Frequency domain analysis of knock images
NASA Astrophysics Data System (ADS)
Qi, Yunliang; He, Xin; Wang, Zhi; Wang, Jianxin
2014-12-01
High speed imaging-based knock analysis has mainly focused on time domain information, e.g. the spark triggered flame speed, the time when end gas auto-ignition occurs and the end gas flame speed after auto-ignition. This study presents a frequency domain analysis on the knock images recorded using a high speed camera with direct photography in a rapid compression machine (RCM). To clearly visualize the pressure wave oscillation in the combustion chamber, the images were high-pass-filtered to extract the luminosity oscillation. The luminosity spectrum was then obtained by applying fast Fourier transform (FFT) to three basic colour components (red, green and blue) of the high-pass-filtered images. Compared to the pressure spectrum, the luminosity spectra better identify the resonant modes of pressure wave oscillation. More importantly, the resonant mode shapes can be clearly visualized by reconstructing the images based on the amplitudes of luminosity spectra at the corresponding resonant frequencies, which agree well with the analytical solutions for mode shapes of gas vibration in a cylindrical cavity.
A cost-efficient frequency-domain photoacoustic imaging system
NASA Astrophysics Data System (ADS)
LeBoulluec, Peter; Liu, Hanli; Yuan, Baohong
2013-09-01
Photoacoustic (PA) imaging techniques have recently attracted much attention and can be used for noninvasive imaging of biological tissues. Most PA imaging systems in research laboratories use the time domain method with expensive nanosecond pulsed lasers that are not affordable for most educational laboratories. Using an intensity modulated light source to excite PA signals is an alternative technique, known as the frequency domain method, with a much lower cost. In this paper, we describe a simple frequency domain PA system and demonstrate its imaging capability. The system provides opportunities not only to observe PA signals in tissue phantoms but also to acquire hands-on skills in PA signal detection. It also provides opportunities to explore the underlying mechanisms of the PA effect.
A cost-efficient frequency-domain photoacoustic imaging system
LeBoulluec, Peter; Liu, Hanli; Yuan, Baohong
2013-01-01
Photoacoustic (PA) imaging techniques have recently attracted much attention and can be used for noninvasive imaging of biological tissues. Most PA imaging systems in research laboratories use the time domain method with expensive nanosecond pulsed lasers that are not affordable for most educational laboratories. Using an intensity modulated light source to excite PA signals is an alternative technique, known as the frequency domain method, with a much lower cost. In this paper, we describe a simple frequency domain PA system and demonstrate its imaging capability. The system provides opportunities not only to observe PA signals in tissue phantoms, but also to acquire hands-on skills in PA signal detection. It also provides opportunities to explore the underlying mechanisms of the PA effect. PMID:24659823
Dehaes, Mathieu; Grant, P. Ellen; Sliva, Danielle D.; Roche-Labarbe, Nadège; Pienaar, Rudolph; Boas, David A.; Franceschini, Maria Angela; Selb, Juliette
2011-01-01
The near infrared spectroscopy (NIRS) frequency-domain multi-distance (FD-MD) method allows for the estimation of optical properties in biological tissue using the phase and intensity of radiofrequency modulated light at different source-detector separations. In this study, we evaluated the accuracy of this method to retrieve the absorption coefficient of the brain at different ages. Synthetic measurements were generated with Monte Carlo simulations in magnetic resonance imaging (MRI)-based heterogeneous head models for four ages: newborn, 6 and 12 month old infants, and adult. For each age, we determined the optimal set of source-detector separations and estimated the corresponding errors. Errors arise from different origins: methodological (FD-MD) and anatomical (curvature, head size and contamination by extra-cerebral tissues). We found that the brain optical absorption could be retrieved with an error between 8–24% in neonates and infants, while the error increased to 19–44% in adults over all source-detector distances. The dominant contribution to the error was found to be the head curvature in neonates and infants, and the extra-cerebral tissues in adults. PMID:21412461
NASA Astrophysics Data System (ADS)
Wu, Shun-Der; Glytsis, Elias N.
2002-10-01
The effects of finite number of periods (FNP) and finite incident beams on the diffraction efficiencies of holographic gratings are investigated by the finite-difference frequency-domain (FDFD) method. Gratings comprising 20, 15, 10, 5, and 3 periods illuminated by TE and TM incident light with various beam sizes are analyzed with the FDFD method and compared with the rigorous coupled-wave analysis (RCWA). Both unslanted and slanted gratings are treated in transmission as well as in reflection configurations. In general, the effect of the FNP is a decrease in the diffraction efficiency with a decrease in the number of periods of the grating. Similarly, a decrease in incident-beam width causes a decrease in the diffraction efficiency. Exceptions appear in off-Bragg incidence in which a smaller beam width could result in higher diffraction efficiency. For beam widths greater than 10 grating periods and for gratings with more than 20 periods in width, the diffraction efficiencies slowly converge to the values predicted by the RCWA (infinite incident beam and infinite-number-of-periods grating) for both TE and TM polarizations. Furthermore, the effects of FNP holographic gratings on their diffraction performance are found to be comparable to their counterparts of FNP surface-relief gratings. 2002 Optical Society of America
Thermal property microscopy with frequency domain thermoreflectance.
Yang, Jia; Maragliano, Carlo; Schmidt, Aaron J
2013-10-01
A thermal property microscopy technique based on frequency domain thermoreflectance (FDTR) is presented. In FDTR, a periodically modulated laser locally heats a sample while a second probe beam monitors the surface reflectivity, which is related to the thermal properties of the sample with an analytical model. Here, we extend FDTR into an imaging technique capable of producing micrometer-scale maps of several thermophysical properties simultaneously. Thermal phase images are recorded at multiple frequencies chosen for maximum sensitivity to thermal properties of interest according to a thermal model of the sample. The phase versus frequency curves are then fit point-by-point to obtain quantitative thermal property images of various combinations of thermal properties in multilayer samples, including the in-plane and cross-plane thermal conductivities, heat capacity, thermal interface conductance, and film thickness. An FDTR microscope based on two continuous-wave lasers is described, and a sensitivity analysis of the technique to different thermal properties is carried out. As a demonstration, we image ~3 nm of patterned titanium under 100 nm of gold on a silicon substrate, and simultaneously create maps of the thermal interface conductance and substrate thermal conductivity. Results confirm the potential of our technique for imaging and quantifying thermal properties of buried layers, indicating its utility for mapping thermal properties in integrated circuits.
Thermal property microscopy with frequency domain thermoreflectance
NASA Astrophysics Data System (ADS)
Yang, Jia; Maragliano, Carlo; Schmidt, Aaron J.
2013-10-01
A thermal property microscopy technique based on frequency domain thermoreflectance (FDTR) is presented. In FDTR, a periodically modulated laser locally heats a sample while a second probe beam monitors the surface reflectivity, which is related to the thermal properties of the sample with an analytical model. Here, we extend FDTR into an imaging technique capable of producing micrometer-scale maps of several thermophysical properties simultaneously. Thermal phase images are recorded at multiple frequencies chosen for maximum sensitivity to thermal properties of interest according to a thermal model of the sample. The phase versus frequency curves are then fit point-by-point to obtain quantitative thermal property images of various combinations of thermal properties in multilayer samples, including the in-plane and cross-plane thermal conductivities, heat capacity, thermal interface conductance, and film thickness. An FDTR microscope based on two continuous-wave lasers is described, and a sensitivity analysis of the technique to different thermal properties is carried out. As a demonstration, we image ˜3 nm of patterned titanium under 100 nm of gold on a silicon substrate, and simultaneously create maps of the thermal interface conductance and substrate thermal conductivity. Results confirm the potential of our technique for imaging and quantifying thermal properties of buried layers, indicating its utility for mapping thermal properties in integrated circuits.
Radiative Transport Based Frequency Domain Fluorescence Tomography
Joshi, Amit; Rasmussen, John C.; Sevick-Muraca, Eva M.; Wareing, Todd A.; McGhee, John
2011-01-01
We report the development of radiative transport model based fluorescence optical tomography from frequency domain boundary measurements. The coupled radiative transport model for describing NIR fluorescence propagation in tissue is solved by a novel software based on the established Attila™ particle transport simulation platform. The proposed scheme enables the prediction of fluorescence measurements with non-contact sources and detectors at minimal computational cost. An adjoint transport solution based fluorescence tomography algorithm is implemented on dual grids to efficiently assemble the measurement sensitivity Jacobian matrix. Finally, we demonstrate fluorescence tomography on a realistic computational mouse model to locate nM to μM fluorophore concentration distributions in simulated mouse organs. PMID:18364555
NASA Astrophysics Data System (ADS)
Dehaes, Mathieu; Grant, P. Ellen; Sliva, Danielle D.; Roche-Labarbe, Nadège; Pienaar, Rudolph; Boas, David A.; Franceschini, Maria Angela; Selb, Juliette
2011-03-01
NIRS is safe, non-invasive and offers the possibility to record local hemodynamic parameters at the bedside, avoiding the transportation of neonates and critically ill patients. In this work, we evaluate the accuracy of the frequency-domain multi-distance (FD-MD) method to retrieve brain optical properties from neonate to adult. Realistic measurements are simulated using a 3D Monte Carlo modeling of light propagation. Height different ages were investigated: a term newborn of 38 weeks gestational age, two infants of 6 and 12 months of age, a toddler of 2 year (yr.) old, two children of 5 and 10 years of age, a teenager of 14 yr. old, and an adult. Measurements are generated at multiple distances on the right parietal area of head models and fitted to a homogeneous FD-MD model to estimate the brain optical properties. In the newborn, infants, toddler and 5 yr. old child models, the error was dominated by the head curvature, while the superficial layer in the 10 yr. old child, teenager and adult heads. The influence of the CSF is also evaluated. In this case, absorption coefficients suffer from an additional error. In all cases, measurements at 5 mm provided worse estimation because of the diffusion approximation.
Autonomous Frequency-Domain System-Identification Program
NASA Technical Reports Server (NTRS)
Yam, Yeung; Mettler, Edward; Bayard, David S.; Hadaegh, Fred Y.; Milman, Mark H.; Scheid, Robert E.
1993-01-01
Autonomous Frequency Domain Identification (AU-FREDI) computer program implements system of methods, algorithms, and software developed for identification of parameters of mathematical models of dynamics of flexible structures and characterization, by use of system transfer functions, of such models, dynamics, and structures regarded as systems. Software considered collection of routines modified and reassembled to suit system-identification and control experiments on large flexible structures.
Optical wire guided lumpectomy: frequency domain measurements
NASA Astrophysics Data System (ADS)
Dayton, A. L.; Keränen, V. T.; Prahl, S. A.
2009-02-01
In practice, complete removal of the tumor during a lumpectomy is difficult; the published rates of positive margins range from 10% to 50%. A spherical lumpectomy specimen with tumor directly in the middle may improve the success rate. A light source placed within the tumor may accomplish this goal by creating a sphere surrounding the tumor that can serve as a guide for resection. In an optical phantom and a prophylactic mastectomy specimen, sinusoidally modulated light within the medium was collected by optical fiber(s) at fixed distance(s) from the source and used to measure the optical properties. These optical properties were then used to calculate the distance the light had traveled through the medium. The fiber was coupled to an 830nm diode laser that was modulated at 100, 200 and 300 MHz. A handheld optical probe collected the modulated light and a network analyzer measured the phase lag. This data was used to calculate the distance the light traveled from the emitting fiber tip to the probe. The optical properties were μa = 0.004mm-1 and μ1s = 0.38mm-1 in the phantom. The optical properties for the tissue were μa = 0.005mm-1 and μ1s = 0.20mm-1. The prediction of distance from the source was within 4mm of the actual distance at 30mm in the phantom and within 3mm of the actual distance at 25mm in the tissue. The feasibility of a frequency domain system that makes measurements of local optical properties and then extrapolates those optical properties to make measurements of distance with a separate probe was demonstrated.
Time domain and frequency domain design techniques for model reference adaptive control systems
NASA Technical Reports Server (NTRS)
Boland, J. S., III
1971-01-01
Some problems associated with the design of model-reference adaptive control systems are considered and solutions to these problems are advanced. The stability of the adapted system is a primary consideration in the development of both the time-domain and the frequency-domain design techniques. Consequentially, the use of Liapunov's direct method forms an integral part of the derivation of the design procedures. The application of sensitivity coefficients to the design of model-reference adaptive control systems is considered. An application of the design techniques is also presented.
Kiyono, Ken; Tsujimoto, Yutaka
2016-07-01
We develop a general framework to study the time and frequency domain characteristics of detrending-operation-based scaling analysis methods, such as detrended fluctuation analysis (DFA) and detrending moving average (DMA) analysis. In this framework, using either the time or frequency domain approach, the frequency responses of detrending operations are calculated analytically. Although the frequency domain approach based on conventional linear analysis techniques is only applicable to linear detrending operations, the time domain approach presented here is applicable to both linear and nonlinear detrending operations. Furthermore, using the relationship between the time and frequency domain representations of the frequency responses, the frequency domain characteristics of nonlinear detrending operations can be obtained. Based on the calculated frequency responses, it is possible to establish a direct connection between the root-mean-square deviation of the detrending-operation-based scaling analysis and the power spectrum for linear stochastic processes. Here, by applying our methods to DFA and DMA, including higher-order cases, exact frequency responses are calculated. In addition, we analytically investigate the cutoff frequencies of DFA and DMA detrending operations and show that these frequencies are not optimally adjusted to coincide with the corresponding time scale.
NASA Astrophysics Data System (ADS)
Yasui, Takashi; Hasegawa, Koji; Hirayama, Koichi
2016-07-01
The finite-difference time-domain (FD-TD) method using a staggered grid with the collocated grid points of velocities (SGCV) was formulated for elastic waves propagating in anisotropic solids and for a rectangular SGCV. Resonant frequency analysis of Lamé-mode resonators on a quartz plate was carried out to confirm the accuracy and validity of the proposed method. The resonant frequencies for the fundamental and higher-order Lamé-modes calculated by the proposed method agreed very well with their theoretical values.
NASA Technical Reports Server (NTRS)
Weissman, David E.; Staton, Leo D.
1991-01-01
A novel approach to the reduction of scattered, interfering signals that corrupt measurements of the signal backscattered from radar targets of interest is being developed. It is being explored with sphere measurements in an indoor microwave radar range. This method is based on the concept of Wiener filtering (which minimizes the difference between the signal plus noise and the desired signal in the time domain). In contrast to the traditional Wiener filter, in which the time domain error between two sequences are minimized, the approach reported uses the frequency domain phasor amplitudes of a swept frequency signal. It minimizes the difference (least-mean-square-magnitude) between the signal-plus-noise and the signal complex phasors, across the entire spectrum.
Analysis of frequency domain frame detection and synchronization in OQAM-OFDM systems
NASA Astrophysics Data System (ADS)
Thein, Christoph; Schellmann, Malte; Peissig, Jürgen
2014-12-01
For future communication systems, filter bank multicarrier schemes offer the flexibility to increase spectrum utilization in heterogeneous wireless environments by good separation of signals in the frequency domain. To fully exploit this property for frame detection and synchronization, the advantage of the filter bank should be taken at the receiver side. In this work, the concept of frequency domain processing for frame detection and synchronization is analyzed and a suitable preamble design as well as corresponding estimation algorithms is discussed. The theoretical performance of the detection and estimation schemes is derived and compared with simulation-based assessments. The results show that, even though the frequency domain algorithms are sensitive to carrier frequency offsets, satisfactory frame detection and synchronization can be achieved in the frequency domain. In comparison to time domain synchronization methods, the computational complexity increases; however, enhanced robustness in shared spectrum access scenarios is gained in case the described frequency domain approach is utilized.
Frequency and time domain modeling of high speed amplifier
NASA Astrophysics Data System (ADS)
Opalska, Katarzyna
2015-09-01
The paper presents the lumped model of high speed amplifier useful for frequency and time domain (also large signal) simulation. Model is constructed on the basis of two-domain device measurements, namely small signal frequency parameters and time response to the input step of varying amplitude. Rational approximation of frequency domain data leads to small signal model composed of RLC subcircuits and controlled sources. Next, the model is complimented with the nonlinearities identified from time-domain measurements, including those taken for large input signals. Final amplifier model implemented in SPICE simulator is shown to correctly render the behavior of the device over the wide variety of operating conditions.
Visual saliency: a biologically plausible contourlet-like frequency domain approach
Bian, Peng
2010-01-01
In this paper we propose a fast frequency domain saliency detection method that is also biologically plausible, referred to as frequency domain divisive normalization (FDN). We show that the initial feature extraction stage, common to all spatial domain approaches, can be simplified to a Fourier transform with a contourlet-like grouping of coefficients, and saliency detection can be achieved in frequency domain. Specifically, we show that divisive normalization, a model of cortical surround inhibition, can be conducted in frequency domain. Since Fourier coefficients are global in space, we extend to this model by conducting piecewise FDN (PFDN) using overlapping local patches to provide better biological plausibility. Not only do FDN and PFDN outperform current state-of-the-art methods in eye fixation prediction, they are also faster. Speed and simplicity are advantages of our frequency domain approach, and its biological plausibility is the main contribution of our paper. PMID:21886671
Frequency-domain approaches to quantitative brain SPECT
NASA Astrophysics Data System (ADS)
Cheng, Jui-Hsi
1997-12-01
Quantitative SPECT (Single Photon Emission Computed Tomography) has been limited mainly by (1) inadequate numbers of detected photons which are contaminated by Poisson noise in projections, (2) photon attenuation in the body, (3) inclusion of scattered photons in the projections, and (4) depth-dependent blurring due to the finite size of collimator holes. Various methods to compensate for the above effects via either spatial- domain approaches or frequency-domain approaches have been proposed. However, most of the proposed methods focus only on individual effects. A reconstruction method which can compensate for all of the effects simultaneously is necessary. We have developed an algorithm to compensate for all of the effects simultaneously using frequency-domain approaches. For noise suppression, a method to convert the signal-dependent Poisson noise into signal- independent Gaussian white noise was first applied. Then the Wiener filter with a designed butterfly window was used. For scatter-photon removal, a subtraction technique based on multiple energy-window acquisitions was employed. For collimation deblurring, a direct inverse filter was designed via stationary phase condition (depth-frequency relationship). For attenuation compensation, an exact analytical solution was derived by Fourier analysis. Our algorithm was executed on a HP/730 workstation. An improvement was shown in computing time, noise suppression, recognition of phantom features, and quantification of concentrations of regions of interest (ROI). In addition to simulation, we performed a series of experiments to verify our models and test our algorithm. These include (1) investigation of the characteristics of Poisson noise of SPECT, (2) comparison of the performance of dual-energy window and triple-energy window methods for scatter correction, (3) measurement of a depth- dependent PSF, (4) reconstruction of the attenuation map using scatter-window data, and (5) implementation of a simultaneous
Frequency Domain Optical Coherence Tomography Techniques in Eye Imaging
NASA Astrophysics Data System (ADS)
Wojtkowski, M.; Kowalczyk, A.; Targowski, P.; Gorczyñska, I.
2000-12-01
This contribution presents an application of frequency-domain optical tomography to ophthalmology. Essential theoretical foundations of time-domain and frequency-domain optical tomography are presented. Images of sections through the anterior chamber, the corneo-scleral angle and fundus of the eye are reconstructed from the spectral fringes. The morphological information gained by tomograms is important for diagnosing and planning of a treatment of glaucoma.
Real-Time Parameter Estimation in the Frequency Domain
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
1999-01-01
A method for real-time estimation of parameters in a linear dynamic state space model was developed and studied. The application is aircraft dynamic model parameter estimation from measured data in flight for indirect adaptive or reconfigurable control. Equation error in the frequency domain was used with a recursive Fourier transform for the real-time data analysis. Linear and nonlinear simulation examples and flight test data from the F-18 High Alpha Research Vehicle HARV) were used to demonstrate that the technique produces accurate model parameter estimates with appropriate error bounds. Parameter estimates converged in less than 1 cycle of the dominant dynamic mode natural frequencies, using control surface inputs measured in flight during ordinary piloted maneuvers. The real-time parameter estimation method has low computational requirements, and could be implemented aboard an aircraft in real time.
Pole-zero form fractional model identification in frequency domain
Mansouri, R.; Djamah, T.; Djennoune, S.; Bettayeb, M.
2009-03-05
This paper deals with system identification in the frequency domain using non integer order models given in the pole-zero form. The usual identification techniques cannot be used in this case because of the non integer orders of differentiation which makes the problem strongly nonlinear. A general identification method based on Levenberg-Marquardt algorithm is developed and allows to estimate the (2n+2m+1) parameters of the model. Its application to identify the ''skin effect'' of a squirrel cage induction machine modeling is then presented.
Frequency domain, waveform inversion of laboratory crosswell radar data
Ellefsen, Karl J.; Mazzella, Aldo T.; Horton, Robert J.; McKenna, Jason R.
2010-01-01
A new waveform inversion for crosswell radar is formulated in the frequency-domain for a 2.5D model. The inversion simulates radar waves using the vector Helmholtz equation for electromagnetic waves. The objective function is minimized using a backpropagation method suitable for a 2.5D model. The inversion is tested by processing crosswell radar data collected in a laboratory tank. The estimated model is consistent with the known electromagnetic properties of the tank. The formulation for the 2.5D model can be extended to inversions of acoustic and elastic data.
Frequency Domain Detection of Biomolecules using Silicon Nanowire Biosensors
Zheng, Gengfeng; Gao, Xuan P. A.; Lieber, Charles M.
2010-01-01
We demonstrate a new protein detection methodology based upon frequency domain electrical measurement using silicon nanowire field-effect transistor (SiNW FET) biosensors. The power spectral density of voltage from a current-biased SiNW FET shows 1/f-dependence in frequency domain for measurements of antibody functionalized SiNW devices in buffer solution or in the presence of protein not specific to the antibody receptor. In the presence of protein (antigen) recognized specifically by the antibody-functionalized SiNW FET, the frequency spectrum exhibits a Lorentzian shape with a characteristic frequency of several kHz. Frequency and conventional time domain measurements carried out with the same device as a function of antigen concentration show more than 10-fold increase in detection sensitivity in the frequency domain data. These concentration dependent results together with studies of antibody receptor density effect further address possible origins of the Lorentzian frequency spectrum. Our results show that frequency domain measurements can be used as a complementary approach to conventional time domain measurements for ultra-sensitive electrical detection of proteins and other biomolecules using nanoscale FETs. PMID:20698634
Iterative procedures for wave propagation in the frequency domain
Kim, Seongjai; 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.
Frequency domain fluorimetry using a mercury vapor lamp
NASA Astrophysics Data System (ADS)
Bohn, Matthew J.; Lundin, Michael A.; Marciniak, Michael A.
2009-04-01
Frequency Domain (FD) fluorimetry, capitalizes on the frequency response function of a fluorophore and offers independence from light scatter and excitation/emission intensity variations in order to extract the sample's fluorescent lifetime. Mercury vapor lamps, a common source of industrial facility lighting, emit radiation that overlaps the UV/blue absorption spectrum of many fluorophores and may be used as an efficient and portable excitation source. The AC power modulation of mercury vapor lamps modulates the lamp's intensity at 120 Hz (in the United States) and higher harmonics. The fluorescent lifetimes for 3 different materials (willemite, uranium doped glass and U3O8) are measured with conventional techniques and compared with the FD technique using the power harmonics from a mercury vapor lamp. The mercury lamp measurements agree to within 25% of the conventional methods.
Critical comparison between time- and frequency-domain relaxation functions
NASA Astrophysics Data System (ADS)
Snyder, Chad R.; Mopsik, Frederick I.
1999-07-01
Considerable work has been performed on providing a theoretical basis for the Kohlrausch-Williams-Watts (KWW) and Havriliak-Negami (HN) relaxation functions. Because of this, several papers have examined the ``interconnection'' of these two functions. In this paper, we demonstrate that, with achievable instrumental sensitivity, these two functions are distinguishable. We further address the issue of the ``universal'' limiting power laws and the ability to obtain the exponents associated with them. Finally, the stability and accuracy of our numerical Laplace transform is demonstrated by comparison between functions with known analytical time and frequency solutions. The stability of our algorithm indicates that the method of Alvarez and co-workers [F. Alvarez, A. Alegría, and J. Colmenero, Phys. Rev. B 44, 7306 (1991)] is an unnecessary approximation for converting between the time and frequency domain.
Remote Strain Sensing of CFRP Using Microwave Frequency Domain Reflectometry
NASA Technical Reports Server (NTRS)
Wilson, William C.; Moore, Jason P.; Juarez, Peter D.
2016-01-01
NASA's Advanced Composites Project is investigating technologies that increase automated remote inspection of aircraft composite structures. Therefore, microwave Frequency Domain Reflectometry (FDR) is being investigated as a method of enabling rapid remote measurement of strain occurring at the first ply of a composite fiber reinforced polymer (CFRP) structure using Radio Frequency (RF) Electro-Magnetic (EM) radiation. While microwave reflectometry has been used to detect disbonds in CFRP structures, its use in detecting strain has been limited. This work will present data demonstrating the measurement of the reactance changes due to loading conditions that are indicative of strain in a CFRP structure. In addition, the basic EM signature will be presented along with an analysis of temperature and humidity effects.
Time delay measurement in the frequency domain
Durbin, Stephen M.; Liu, Shih -Chieh; Dufresne, Eric M.; Li, Yuelin; Wen, Haidan
2015-08-06
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.
Time delay measurement in the frequency domain
Durbin, Stephen M.; Liu, Shih -Chieh; Dufresne, Eric M.; Li, Yuelin; Wen, Haidan
2015-08-06
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 bymore » simply extending the data acquisition time.« less
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
Real-Time Parameter Estimation in the Frequency Domain
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
2000-01-01
A method for real-time estimation of parameters in a linear dynamic state-space model was developed and studied. The application is aircraft dynamic model parameter estimation from measured data in flight. Equation error in the frequency domain was used with a recursive Fourier transform for the real-time data analysis. Linear and nonlinear simulation examples and flight test data from the F-18 High Alpha Research Vehicle were used to demonstrate that the technique produces accurate model parameter estimates with appropriate error bounds. Parameter estimates converged in less than one cycle of the dominant dynamic mode, using no a priori information, with control surface inputs measured in flight during ordinary piloted maneuvers. The real-time parameter estimation method has low computational requirements and could be implemented
Frequency domain compensation of a DYNGEN turbofan engine model
NASA Technical Reports Server (NTRS)
Schafer, R. M.; Gejji, R. R.; Hoppner, P. W.; Longenbaker, W. E.; Sain, M. K.
1977-01-01
Following Rosenbrock's ideas regarding the advantages of dominance in linear multivariable control systems, a new graphical technique is used for the design of compensators that achieve dominance. The technique is illustrated with an application to the problem of designing compensators for a linear turbofan-engine model. The resulting design is put into perspective by examining it in the light of two other multivariable frequency-domain methods. One, MacFarlane's method of characteristic loci, is used to realize a final design for stability and low interaction. The other is a direct technique based upon the algebraic expansion of the determinant of the return difference in terms of it's elements. Results from simulations carried out on the NASA DYNGEN software are included.
Ion mobility spectrometer using frequency-domain separation
Martin, S.J.; Butler, M.A.; Frye, G.C.; Schubert, W.K.
1998-08-04
An apparatus and method are provided for separating and analyzing chemical species in an ion mobility spectrometer using a frequency-domain technique wherein the ions generated from the chemical species are selectively transported through an ion flow channel having a moving electrical potential therein. The moving electrical potential allows the ions to be selected according to ion mobility, with certain of the ions being transported to an ion detector and other of the ions being effectively discriminated against. The apparatus and method have applications for sensitive chemical detection and analysis for monitoring of exhaust gases, hazardous waste sites, industrial processes, aerospace systems, non-proliferation, and treaty verification. The apparatus can be formed as a microelectromechanical device (i.e. a micromachine). 6 figs.
Ion mobility spectrometer using frequency-domain separation
Martin, Stephen J.; Butler, Michael A.; Frye, Gregory C.; Schubert, W. Kent
1998-01-01
An apparatus and method is provided for separating and analyzing chemical species in an ion mobility spectrometer using a frequency-domain technique wherein the ions generated from the chemical species are selectively transported through an ion flow channel having a moving electrical potential therein. The moving electrical potential allows the ions to be selected according to ion mobility, with certain of the ions being transported to an ion detector and other of the ions being effectively discriminated against. The apparatus and method have applications for sensitive chemical detection and analysis for monitoring of exhaust gases, hazardous waste sites, industrial processes, aerospace systems, non-proliferation, and treaty verification. The apparatus can be formed as a microelectromechanical device (i.e. a micromachine).
Frequency domain analysis of spreading-constriction thermal impedance
NASA Astrophysics Data System (ADS)
Casalegno, Francesco; De Marchi, Andrea; Giaretto, Valter
2013-02-01
Spreading-constriction effects are analyzed in the frequency domain. The existence of a half-pole altering the steady state solution at high frequencies is pointed out. Application to the case of thermoelectric devices allows direct comparison with experimental data because thermal quantities can be measured as electrical signals at the very spot where spreading takes place. Good agreement with theory is shown here for a thermoelectric device in which the particular constriction geometry enhances its effect, making easily observable the difference between frequency domain and the steady state approaches.
Frequency domain analysis of spreading-constriction thermal impedance.
Casalegno, Francesco; De Marchi, Andrea; Giaretto, Valter
2013-02-01
Spreading-constriction effects are analyzed in the frequency domain. The existence of a half-pole altering the steady state solution at high frequencies is pointed out. Application to the case of thermoelectric devices allows direct comparison with experimental data because thermal quantities can be measured as electrical signals at the very spot where spreading takes place. Good agreement with theory is shown here for a thermoelectric device in which the particular constriction geometry enhances its effect, making easily observable the difference between frequency domain and the steady state approaches.
AD Conversion Revisited in the Frequency Domain
NASA Astrophysics Data System (ADS)
Chikada, Y.
2010-12-01
The output of a quantizer is shown in the form of a sum of harmonics and inter-modulations, whose coefficient is also shown in an analytical form using Kummer confluent hypergeometric functions of the first kind. Methods to reduce quantization noise are also discussed.
Autonomous frequency domain identification: Theory and experiment
NASA Technical Reports Server (NTRS)
Yam, Yeung; Bayard, D. S.; Hadaegh, F. Y.; Mettler, E.; Milman, M. H.; Scheid, R. E.
1989-01-01
The analysis, design, and on-orbit tuning of robust controllers require more information about the plant than simply a nominal estimate of the plant transfer function. Information is also required concerning the uncertainty in the nominal estimate, or more generally, the identification of a model set within which the true plant is known to lie. The identification methodology that was developed and experimentally demonstrated makes use of a simple but useful characterization of the model uncertainty based on the output error. This is a characterization of the additive uncertainty in the plant model, which has found considerable use in many robust control analysis and synthesis techniques. The identification process is initiated by a stochastic input u which is applied to the plant p giving rise to the output. Spectral estimation (h = P sub uy/P sub uu) is used as an estimate of p and the model order is estimated using the produce moment matrix (PMM) method. A parametric model unit direction vector p is then determined by curve fitting the spectral estimate to a rational transfer function. The additive uncertainty delta sub m = p - unit direction vector p is then estimated by the cross spectral estimate delta = P sub ue/P sub uu where e = y - unit direction vectory y is the output error, and unit direction vector y = unit direction vector pu is the computed output of the parametric model subjected to the actual input u. The experimental results demonstrate the curve fitting algorithm produces the reduced-order plant model which minimizes the additive uncertainty. The nominal transfer function estimate unit direction vector p and the estimate delta of the additive uncertainty delta sub m are subsequently available to be used for optimization of robust controller performance and stability.
An analog filter approach to frequency domain fluorescence spectroscopy
Trainham, Clifford P.; O'Neill, Mary D.; McKenna, Ian J.
2015-10-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modeled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as Spicea can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modeling of the entiremore » system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. Furthermore, the techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response.« less
An Analog Filter Approach to Frequency Domain Fluorescence Spectroscopy.
Trainham, R; O'Neill, M; McKenna, I J
2015-11-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modelled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as SPICE can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modelling of the entire system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. The techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response. The simplification of the analysis mathematics, and the ability to model the entire detection chain, make it possible to develop more compact instruments for remote sensing applications. PMID:26429345
An analog filter approach to frequency domain fluorescence spectroscopy
Trainham, Clifford P.; O'Neill, Mary D.; McKenna, Ian J.
2015-10-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modeled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as Spicea can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modeling of the entire system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. Furthermore, the techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response.
NASA Astrophysics Data System (ADS)
Schamper, C.; Rejiba, F.; Tabbagh, A.; Spitz, S.
2011-03-01
We present a sensitivity study applied to water front monitoring of an onshore oil reservoir, using a remote controlled source electromagnetic method (CSEM) with electric dipoles and a borehole-to-surface configuration. We have developed an optimized and parallelized code based on the method of moments, in order to study the influence of several static or time-varying background uncertainties on the time-lapse CSEM signal (also called 4-D CSEM). Analysis of the relative and absolute variations in phase or quadrature of the time-lapse signal induced by the fluid substitution process, inside the reservoir, has shown that the vertical electric dipole allows the shape of the water front to be monitored, while remaining less sensitive (compared to a horizontal electric source dipole) to the total volume of substituted fluid. We have examined the influence of missed anomalies (1-D/3-D), with more or less conductive properties, near to the ground surface or the reservoir, and with or without time-varying properties. In most cases, the 4-D signal behaves like a reliable filter, canceling almost all response anomalies. However, it can also lead to strong, local perturbations of the time-lapse signal. We have also shown that in the presence of steel cased boreholes at the source location, or with outlying steel cased boreholes, the recording of exploitable data does not present insurmountable difficulties at low frequencies (˜1 Hz), and for a dense array of surface receivers. These positive results with CSEM monitoring suggest that minimal, coarse-time 3-D explorations should be used to ensure reliable interpretation of the monitored data.
Frequency Domain Tomography Of Evolving Laser-Plasma Accelerator Structures
Dong Peng; Reed, Stephen; Kalmykov, Serguei; Shvets, Gennady; Downer, Mike
2009-01-22
Frequency Domain Holography (FDH), a technique for visualizing quasistatic objects propagating near the speed of light, has produced 'snapshots' of laser wakefields, but they are averaged over structural variations that occur during propagation through the plasma medium. Here we explore via simulations a generalization of FDH--that we call Frequency Domain Tomography (FDT)--that can potentially record a time sequence of quasistatic snapshots, like the frames of a movie, of the wake structure as it propagates through the plasma. FDT utilizes a several probe-reference pulse pairs that propagate obliquely to the drive pulse and wakefield, along with tomographic reconstruction algorithms similar to those used in medical CAT scans.
Non-stationary frequency domain system identification using time-frequency representations
NASA Astrophysics Data System (ADS)
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.
Adaptive multidirectional frequency domain filter for noise removal in wrapped phase patterns.
Liu, Guixiong; Chen, Dongxue; Peng, Yanhua; Zeng, Qilin
2016-08-01
In order to avoid the detrimental effects of excessive noise in the phase fringe patterns of a laser digital interferometer over the accuracy of phase unwrapping and the successful detection of mechanical fatigue defects, an effective method of adaptive multidirectional frequency domain filtering is introduced based on the characteristics of the energy spectrum of localized wrapped phase patterns. Not only can this method automatically set the cutoff frequency, but it can also effectively filter out noise while preserving the image edge information. Compared with the sine and cosine transform filtering and the multidirectional frequency domain filtering, the experimental results demonstrate that the image filtered by our method has the fewest number of residues and is the closest to the noise-free image, compared to the two aforementioned methods, demonstrating the effectiveness of this adaptive multidirectional frequency domain filter. PMID:27505376
Design sensitivity analysis of mechanical systems in frequency domain
NASA Astrophysics Data System (ADS)
Nalecz, A. G.; Wicher, J.
1988-02-01
A procedure for determining the sensitivity functions of mechanical systems in the frequency domain by use of a vector-matrix approach is presented. Two examples, one for a ground vehicle passive front suspension, and the second for a vehicle active suspension, illustrate the practical applications of parametric sensitivity analysis for redesign and modification of mechanical systems. The sensitivity functions depend on the frequency of the system's oscillations. They can be easily related to the system's frequency characteristics which describe the dynamic properties of the system.
In vivo spatial frequency domain spectroscopy of two layer media
NASA Astrophysics Data System (ADS)
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.
Time-domain control of ultrahigh-frequency nanomechanical systems
NASA Astrophysics Data System (ADS)
Liu, N.; Giesen, F.; Belov, M.; Losby, J.; Moroz, J.; Fraser, A. E.; McKinnon, G.; Clement, T. J.; Sauer, V.; Hiebert, W. K.; Freeman, M. R.
2008-12-01
Nanoelectromechanical systems could have applications in fields as diverse as ultrasensitive mass detection and mechanical computation, and can also be used to explore fundamental phenomena such as quantized heat conductance and quantum-limited displacement. Most nanomechanical studies to date have been performed in the frequency domain. However, applications in computation and information storage will require transient excitation and high-speed time-domain operation of nanomechanical systems. Here we show a time-resolved optical approach to the transduction of ultrahigh-frequency nanoelectromechanical systems, and demonstrate that coherent control of nanomechanical oscillation is possible through appropriate pulse programming. A series of cantilevers with resonant frequencies ranging from less than 10 MHz to over 1 GHz are characterized using the same pulse parameters.
Time-domain mid-infrared frequency-comb spectrometer.
Keilmann, Fritz; Gohle, Christoph; Holzwarth, Ronald
2004-07-01
A novel type of Fourier-transform infrared spectrometer (FTIR) is demonstrated. It is based on two Ti:sapphire lasers emitting femtosecond pulse trains with slightly different repetition frequencies. Two mid-infrared beams-derived from those lasers by rectification in GaSe-are superimposed upon a detector to produce purely time-domain interferograms that encode the infrared spectrum. The advantages of this spectrometer compared with the common FTIR include ease of operation (no moving parts), speed of acquisition (100 micros demonstrated), and not-yet-shown collimated long-distance propagation, diffraction-limited microscopic probing, and electronically controllable chemometric factoring. Extending time-domain frequency-comb spectroscopy to lower (terahertz) or higher (visible, ultraviolet) frequencies should be feasible.
Optical Frequency Domain Visualization of Electron Beam Driven Plasma Wakefields
NASA Astrophysics Data System (ADS)
Zgadzaj, Rafal; Downer, Michael C.; Muggli, Patric; Yakimenko, Vitaly; Kusche, Karl; Fedurin, Michhail; Babzien, Marcus
2010-11-01
Bunch driven plasma wakefield accelerators (PWFA), such as the "plasma afterburner," are a promising emerging method for significantly increasing the energy output of conventional particle accelerators [1]. The study and optimization of this method would benefit from an experimental correlation of the drive bunch parameters and the accelerated particle parameters with the corresponding plasma wave structure. However, the plasma wave structure has not been observed directly so far. We will report ongoing development of a noninvasive optical Frequency Domain Interferometric (FDI) [2] and Holographic (FDH) [3] diagnostics of bunch driven plasma wakes. Both FDI and FDH have been previously demonstrated in the case of laser driven wakes. These techniques employ two laser pulses co-propagating with the drive particle bunch and the trailing plasma wave. One pulse propagates ahead of the drive bunch and serves as a reference, while the second is overlapped with the plasma wave and probes its structure. The multi-shot FDI and single-shot FDH diagnostics permit direct noninvasive observation of longitudinal and transverse structure of the plasma wakes. The experiment is being developed at the 70 MeV Linac in the Accelerator Test Facility at Brookhaven National Laboratory to visualize wakes generated by two [4] and multi-bunch [5] drive beams.
Characterization of microstrip discontinuities in the time and frequency domains
NASA Technical Reports Server (NTRS)
Feldman, U.; Mittra, R.
1985-01-01
A number of impedance transitions and interconnections to a microstrip were designed and investigated. The double-step discontinuity on a microstrip was studied in detail, and a procedure was developed to design these structures. Their response was determined by making measurements in both the frequency and time domains in a consistent and repeatable manner. The time-domain presentation of the data was the most useful feature of the measuring system. All undesirable signal components were filtered out through the use of gating functions. Theoretically computed results were verified experimentally.
High-resolution frequency domain second harmonic optical coherence tomography
NASA Astrophysics Data System (ADS)
Su, Jianping; Tomov, I. V.; Jiang, Yi; Chen, Zhongping
2007-02-01
We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain SH-OCT to 12μm. The acquisition time was shortened by more than two orders of magnitude compared to time domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on second harmonic has been used to obtain polarization resolved images.
Removing the depth-degeneracy in optical frequency domain imaging with frequency shifting
Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Bouma, B. E.
2009-01-01
A novel technique using an acousto-optic frequency shifter in optical frequency domain imaging (OFDI) is presented. The frequency shift eliminates the ambiguity between positive and negative differential delays, effectively doubling the interferometric ranging depth while avoiding image cross-talk. A signal processing algorithm is demonstrated to accommodate nonlinearity in the tuning slope of the wavelength-swept OFDI laser source. PMID:19484034
Domain adaptive boosting method and its applications
NASA Astrophysics Data System (ADS)
Geng, Jie; Miao, Zhenjiang
2015-03-01
Differences of data distributions widely exist among datasets, i.e., domains. For many pattern recognition, nature language processing, and content-based analysis systems, a decrease in performance caused by the domain differences between the training and testing datasets is still a notable problem. We propose a domain adaptation method called domain adaptive boosting (DAB). It is based on the AdaBoost approach with extensions to cover the domain differences between the source and target domains. Two main stages are contained in this approach: source-domain clustering and source-domain sample selection. By iteratively adding the selected training samples from the source domain, the discrimination model is able to achieve better domain adaptation performance based on a small validation set. The DAB algorithm is suitable for the domains with large scale samples and easy to extend for multisource adaptation. We implement this method on three computer vision systems: the skin detection model in single images, the video concept detection model, and the object classification model. In the experiments, we compare the performances of several commonly used methods and the proposed DAB. Under most situations, the DAB is superior.
Domain decomposition methods in aerodynamics
NASA Technical Reports Server (NTRS)
Venkatakrishnan, V.; Saltz, Joel
1990-01-01
Compressible Euler equations are solved for two-dimensional problems by a preconditioned conjugate gradient-like technique. An approximate Riemann solver is used to compute the numerical fluxes to second order accuracy in space. Two ways to achieve parallelism are tested, one which makes use of parallelism inherent in triangular solves and the other which employs domain decomposition techniques. The vectorization/parallelism in triangular solves is realized by the use of a recording technique called wavefront ordering. This process involves the interpretation of the triangular matrix as a directed graph and the analysis of the data dependencies. It is noted that the factorization can also be done in parallel with the wave front ordering. The performances of two ways of partitioning the domain, strips and slabs, are compared. Results on Cray YMP are reported for an inviscid transonic test case. The performances of linear algebra kernels are also reported.
NASA Astrophysics Data System (ADS)
Li, Zhengyan; Zgadzaj, Rafal; Wang, Xiaoming; Reed, Stephen; Dong, Peng; Downer, Michael C.
2010-11-01
We demonstrate a prototype Frequency Domain Streak Camera (FDSC) that can capture the picosecond time evolution of the plasma accelerator structure in a single shot. In our prototype Frequency-Domain Streak Camera, a probe pulse propagates obliquely to a sub-picosecond pump pulse that creates an evolving nonlinear index "bubble" in fused silica glass, supplementing a conventional Frequency Domain Holographic (FDH) probe-reference pair that co-propagates with the "bubble". Frequency Domain Tomography (FDT) generalizes Frequency-Domain Streak Camera by probing the "bubble" from multiple angles and reconstructing its morphology and evolution using algorithms similar to those used in medical CAT scans. Multiplexing methods (Temporal Multiplexing and Angular Multiplexing) improve data storage and processing capability, demonstrating a compact Frequency Domain Tomography system with a single spectrometer.
Polarization sensitive optical frequency domain imaging system for endobronchial imaging.
Li, Jianan; Feroldi, Fabio; de Lange, Joop; Daniels, Johannes M A; Grünberg, Katrien; de Boer, Johannes F
2015-02-01
A polarization sensitive endoscopic optical frequency domain imaging (PS-OFDI) system with a motorized distal scanning catheter is demonstrated. It employs a passive polarization delay unit to multiplex two orthogonal probing polarization states in depth, and a polarization diverse detection unit to detect interference signal in two orthogonal polarization channels. Per depth location four electro-magnetic field components are measured that can be represented in a complex 2x2 field matrix. A Jones matrix of the sample is derived and the sample birefringence is extracted by eigenvalue decomposition. The condition of balanced detection and the polarization mode dispersion are quantified. A complex field averaging method based on the alignment of randomly pointing field phasors is developed to reduce speckle noise. The variation of the polarization states incident on the tissue due to the circular scanning and catheter sheath birefringence is investigated. With this system we demonstrated imaging of ex vivo chicken muscle, in vivo pig lung and ex vivo human lung specimens. PMID:25836196
An implementation of synthetic aperture focusing technique in frequency domain.
Stepinski, Tadeusz
2007-07-01
A new implementation of a synthetic aperture focusing technique (SAFT) based on concepts used in synthetic aperture radar and sonar is presented in the paper. The algorithm, based on the convolution model of the imaging system developed in frequency domain, accounts for the beam pattern of the finite-sized transducer used in the synthetic aperture. The 2D fast Fourier transform (FFT) is used for the calculation of a 2D spectrum of the ultrasonic data. The spectrum is then interpolated to convert the polar coordinate system used for the acquisition of ultrasonic signals to the rectangular coordinates used for the presentation of imaging results. After compensating the transducer lobe amplitude profile using a Wiener filter, the transformed spectrum is subjected to the 2D inverse Fourier transform to get the time-domain image again. The algorithm is computationally attractive due to the use of 2D FFT. The performance of the proposed frequency-domain algorithm and the classical time-domain SAFT are compared in the paper using simulated and real ultrasonic data.
Spatial frequency domain spectroscopy of two layer media
Yudovsky, Dmitry; Durkin, Anthony J.
2011-01-01
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. PMID:22029367
Recovering Complex Conductivity from Frequency and Time Domain Geophysical Surveys
NASA Astrophysics Data System (ADS)
KANG, S.; Marchant, D.; Oldenburg, D.
2013-12-01
The electrical conductivity of earth materials can be frequency dependent. The bulk conductivity decreases with decreasing frequency because of the build-up of electric charges that occur under the application of an electric field. Effectively, the rock is electrically polarized. Finding the polarization response (often referred to as IP, Induced Polarization) can lead to economic benefits, as in the case of discovering sulphide minerals, but there is applicability in environmental problems, groundwater flow, and site characterization. We have the ability to model Maxwell's equations in 3D for complex conductivity in either the time or frequency domain. The challenge therefore is to invert the EM (electromagnetic) data to recover a four-dimensional conductivity (σ (ω, x, y, z)) using limited EM data generally acquired on, or above, the surface of the earth. At late times (or low frequencies) the static Maxwell's equation are valid and, if a background conductivity is known, then chargeability can be extracted. Unfortunately the static assumption is often violated and EM induction processes contaminate the sought signal. For example, signals in the time domain have three parts: a static on-time, an early-time inductive portion, and a late-time IP signal. Information about conductivity using the appropriate Maxwell's equations is available from each of these segments. The potential contamination of the IP from EM induction (often referred to as EM coupling) and the potential contamination of the EM signal from the IP data (IP coupling) can cause deleterious effects and must be addressed. The goal of this talk is to address such issues and outline a practical procedure for extracting IP information from existing time and frequency domain surveys.
Broad bandwidth frequency domain instrument for quantitative tissue optical spectroscopy
Pham, Tuan H.; Coquoz, Olivier; Fishkin, Joshua B.; Anderson, Eric; Tromberg, Bruce J.
2000-06-01
Near-infrared (NIR) optical properties of turbid media, e.g., tissue, can be accurately quantified noninvasively using methods based on diffuse reflectance or transmittance, such as frequency domain photon migration (FDPM). Factors which govern the accuracy and sensitivity of FDPM-measured optical properties include instrument performance, the light propagation model, and fitting algorithms used to calculate optical properties from measured data. In this article, we characterize instrument, model, and fitting uncertaintics of an FDPM system designed for clinical use and investigate how each of these factors affects the quantification of NIR absorption ({mu}{sub a}) and reduced scattering ({mu}{sub s}{sup '}) parameters in tissue phantoms. The instrument is based on a 500 MHz, multiwavelength platform that sweeps through 201 discrete frequencies in as little as 675 ms. Phase and amplitude of intensity modulated light launched into tissue, i.e., diffuse photon density waves (PDW), are measured with an accuracy of {+-}0.30 degree sign and {+-}3.5%, while phase and amplitude precision are {+-}0.025 degree sign and {+-}0.20%, respectively. At this level of instrument uncertainty, simultaneous fitting of frequency-dependent phase and amplitude nonlinear model functions derived from a photon diffusion approximation provides an accurate and robust strategy for determining optical properties from FDPM data, especially for media with high absorption. In an optical property range that is characteristic of most human tissues in the NIR (5x10{sup -3}<{mu}{sub a}<5x10{sup -2} mm{sup -1}, 0.5<{mu}{sub s}{sup '}<2 mm{sup -1}), we theoretically and experimentally demonstrate that the multifrequency, simultaneous-fit approach allows {mu}{sub a} and {mu}{sub s}{sup '} to be quantified with an accuracy of {+-}5% and {+-}3%, respectively. Although exceptionally high levels of precision can be obtained using this approach (<1% of the estimated absorption and scattering values), we show
Frequency domain stress intensity calibration of damped cracked panels
NASA Technical Reports Server (NTRS)
Doyle, James F.; Rizzi, Stephen A.
1993-01-01
This paper discusses two schemes for doing finite element K calibration in the frequency domain. The baseline scheme uses the definition of K as a limit toward the crack tip. The limiting process requires using a very fine mesh around the crack tip making the scheme computationally very expensive. It is shown that the behavior of K as a function of frequency is very similar to a modal response. Taking advantage of this, a more efficient scheme involves a modal analysis of the cracked sheet and scaling the response to that of the static stress intensity. In this way, only a static K calibration need be performed. All the examples shown are for a frequency range spanning multiple resonances and with two levels of damping.
Time and frequency-domain measurement of ground-state recovery times in red fluorescent proteins.
Manna, Premashis; Jimenez, Ralph
2015-04-16
The field of bioimaging and biosensors has been revolutionized by the discovery of fluorescent proteins (FPs) and their use in live cells. FPs are characterized with rich photodynamics due to the presence of nonfluorescent or dark states which are responsible for fluorescence intermittency or "blinking", which has been exploited in several localization-based super-resolution techniques that surpass the diffraction-limited resolution of conventional microscopy. Molecules that convert to these dark states recover to the ground states either spontaneously or upon absorption of another photon, depending on the particular FP and the structural transition that is involved. In this work, we demonstrate time- and frequency-domain methods for the measurement of the ground-state recovery (GSR) times of FPs both in live cells and in solutions. In the time-domain method, we excited the sample with millisecond pulses at varying dark times to obtain percent-recovery. In the frequency-domain method, dark-state hysteresis was employed to obtain the positive phase shift or "phase advance". We extracted the GSR time constants from our measurements using calculations and simulations based on a three-state model system. The GSR time constants of the red FPs studied in these experiments fall in the range from μs to msec time-scales. We find that the time- and frequency-domain techniques are complementary to each other. While accurate GSR times can be extracted from the time-domain technique, frequency-domain measurements are primarily sensitive to the rates of dark-state conversion (DSC) processes. A correlation between GSR times, DSC, and photobleaching rates for the red FPs mCherry, TagRFP-T, and Kriek were observed. These time- and frequency-domain methods can be used in high-throughput screening and sorting of FPs clones based on GSR time constant and photostability and will therefore be valuable for the development of new photoswitchable or photoactivatable FPs.
Frequency Domain Magnetic Measurements from Kilohertz to Gigahertz
NASA Astrophysics Data System (ADS)
Gregg, John F.
"......we applied much prolonged labor on investigating the magnetical forces; so wonderful indeed are they, compared with the forces in all other minerals, surpassing even the virtues of all bodies around us. Nor have we found this labor idle or unfruitful; since daily in our experimenting new unexpected properties came to light."William Gilbert, De Magnete, 1600Abstract. This review deals with practical aspects of making frequency-domain measurements of magnetic susceptibility and magnetic losses from 200 kHz up to 10 GHz. It sets out the types of measurement concerned, distinguishing resonant from nonresonant phenomena. The techniques available are categorized according to suitability for the different frequency regimes and types of investigation. Practical recipes are provided for undertaking such experiments across the entire frequency range. Marginal oscillator spectrometry is discussed which is applicable across the whole frequency range. Different instruments are presented, and particular emphasis is placed on designs which function on the Robinson principle. Analysis of oscillation condition and signal-to-noise performance is dealt with, also sample considerations such as filling factor. Practical circuits are presented and their merits and demerits evaluated. Layout and radio-frequency design considerations are dealt with. Ultrahigh/microwave frequency marginal oscillator spectrometry is given special treatment and several practical designs are given. The essentials of good microwave design are emphasized. A general discussion of resonant structures is included which treats multiple layer coil design, slow wave line structures, stripline and cavities. Unusual cavity designs such as the rhumbatron are treated. Use of striplines with microwave marginal spectrometry is described and compared with conventional network-analysis techniques. The use of parameter matrices for high-frequency analysis is alluded to. Some details of good construction practice are
A Frequency-Domain Substructure System Identification Algorithm
NASA Technical Reports Server (NTRS)
Blades, Eric L.; Craig, Roy R., Jr.
1996-01-01
A new frequency-domain system identification algorithm is presented for system identification of substructures, such as payloads to be flown aboard the Space Shuttle. In the vibration test, all interface degrees of freedom where the substructure is connected to the carrier structure are either subjected to active excitation or are supported by a test stand with the reaction forces measured. The measured frequency-response data is used to obtain a linear, viscous-damped model with all interface-degree of freedom entries included. This model can then be used to validate analytical substructure models. This procedure makes it possible to obtain not only the fixed-interface modal data associated with a Craig-Bampton substructure model, but also the data associated with constraint modes. With this proposed algorithm, multiple-boundary-condition tests are not required, and test-stand dynamics is accounted for without requiring a separate modal test or finite element modeling of the test stand. Numerical simulations are used in examining the algorithm's ability to estimate valid reduced-order structural models. The algorithm's performance when frequency-response data covering narrow and broad frequency bandwidths is used as input is explored. Its performance when noise is added to the frequency-response data and the use of different least squares solution techniques are also examined. The identified reduced-order models are also compared for accuracy with other test-analysis models and a formulation for a Craig-Bampton test-analysis model is also presented.
Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Sampathkumar, Ashwin
2015-05-01
In this paper, we describe a narrow-bandwidth generation and detection of photoacoustic (PA) signals in biological specimens using frequency-domain photoacoustics. An intensity-modulated laser was used for PA generation, and a homodyne Michelson interferometer coupled to a lock-in amplifier was used for optical PA detection. The amplitude and phase of the PA signal were measured at the modulation frequency as the frequency was swept over the bandwidth of interest. A synthesized pulse response was obtained using time-domain reconstruction and the absorber map was estimated using k-space reconstruction methods. Experimental results obtained from 500-μm graphite rods embedded in tissue-mimicking phantoms and slide-mounted tissue samples are presented along with their respective time-domain and time-reversal reconstruction maps.
Identification and verification of frequency-domain models for XV-15 tilt-rotor aircraft dynamics
NASA Technical Reports Server (NTRS)
Tischler, M. B.; Leung, J. G. M.; Dugan, D. C.
1984-01-01
Frequency-domain methods are used to extract the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight test data for the cruise condition (V = 170 knots). The frequency responses are numerically fitted with transfer-function forms to identify equivalent model characteristics. The associated handling quality parameters meet or exceed Level 2, Category A, requirements for fixed-wing military aircraft. Step response matching is used to verify the time-domain fidelity of the transfer-function models for the cruise and hover flight conditions. The transient responses of the model and aircraft are in close agreement in all cases, except for the normal acceleration response to elevator deflection in cruise. This discrepancy is probably due to the unmodeled rotor rpm dynamics. The utility of the frequency-domain approach for dynamics identification and analysis is clearly demonstrated.
Demultiplexing based on frequency-domain joint decision MMA for MDM system
NASA Astrophysics Data System (ADS)
Caili, Gong; Li, Li; Guijun, Hu
2016-06-01
In this paper, we propose a demultiplexing method based on frequency-domain joint decision multi-modulus algorithm (FD-JDMMA) for mode division multiplexing (MDM) system. The performance of FD-JDMMA is compared with frequency-domain multi-modulus algorithm (FD-MMA) and frequency-domain least mean square (FD-LMS) algorithm. The simulation results show that FD-JDMMA outperforms FD-MMA in terms of BER and convergence speed in the cases of mQAM (m=4, 16 and 64) formats. And it is also demonstrated that FD-JDMMA achieves better BER performance and converges faster than FD-LMS in the cases of 16QAM and 64QAM. Furthermore, FD-JDMMA maintains similar computational complexity as the both equalization algorithms.
A frequency-domain derivation of shot-noise
NASA Astrophysics Data System (ADS)
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.
Diagnosis of colon cancer using frequency domain fluorescence imaging technique
NASA Astrophysics Data System (ADS)
Dinish, U. S.; Gulati, P.; Murukeshan, V. M.; Seah, L. K.
2007-03-01
Early detection and treatment of colon cancer has been associated with better disease prognosis. Conventional and reported optical techniques have limitations in detecting early stages of colon cancer growth. In this paper, a homodyne signal processing assisted frequency domain (FD) fluorescence imaging methodology is proposed for the early diagnosis of colon cancer. Simulated phantom tissues representing the biopsy samples at different stages of colon cancer growth are prepared and used for the imaging study. Selective imaging of healthy and diseased sites simulated in the samples was achieved even for fluorescence emissions having close lifetimes and wavelength values. Possible extension of the methodology for in vivo investigations is also discussed.
Frequency domain multiplexing for large-scale bolometer arrays
Spieler, Helmuth
2002-05-31
The development of planar fabrication techniques for superconducting transition-edge sensors has brought large-scale arrays of 1000 pixels or more to the realm of practicality. This raises the problem of reading out a large number of sensors with a tractable number of connections. A possible solution is frequency-domain multiplexing. I summarize basic principles, present various circuit topologies, and discuss design trade-offs, noise performance, cross-talk and dynamic range. The design of a practical device and its readout system is described with a discussion of fabrication issues, practical limits and future prospects.
Transient stability assessment by pattern recognition in the frequency domain
Ostojic, D.R. ); Heydt, G.T. . School of Electrical Engineering)
1991-02-01
This paper presents pattern recognition methodology which utilizes spectral monitoring of electromechanical oscillations to assess the transient stability of interconnected power systems. The proposed frequency domain approach permits definitive recognition of unstable dynamic modes. This is used to design an adaptive linear classifier which, in the developmental implementation virtually eliminates both false dismissals, and false alarms. The result is an accurate and reliable decision-making system which performs transient stability monitoring and assessment in real-time. Production computer code has not yet been implemented, but it is expected that the cited performance in developmental tests will be duplicated.
Design of PI controllers for achieving time and frequency domain specifications simultaneously.
Hamamci, Serdar Ethem; Tan, Nusret
2006-10-01
This paper deals with the design of PI controllers which achieve the desired frequency and time domain specifications simultaneously. A systematic method, which is effective and simple to apply, is proposed. The required values of the frequency domain performance measures namely the gain and phase margins and the time domain performance measures such as settling time and overshoot are defined prior to the design. Then, to meet these desired performance values, a method which presents a graphical relation between the required performance values and the parameters of the PI controller is given. Thus, a set of PI controllers which attain desired performances can be found using the graphical relations. Illustrative examples are given to demonstrate the benefits of the method presented.
High-frequency Rayleigh-wave method
Xia, J.; Miller, R.D.; Xu, Y.; Luo, Y.; Chen, C.; Liu, J.; Ivanov, J.; Zeng, C.
2009-01-01
High-frequency (???2 Hz) Rayleigh-wave data acquired with a multichannel recording system have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave techniques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a non-invasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.
Frequency-domain single-shot optical frequency comb tomography using VIPA
NASA Astrophysics Data System (ADS)
Miyaoka, Takumi; Shioda, Tatsutoshi
2016-03-01
Novel two-dimensional single-shot imaging optical system based on Frequency-domain interferometry using a virtually imaged phased array is proposed. The VIPA simultaneously outputs incoherent optical frequency combs (OFCs) whose teeth interval are scanned as a function of its output angle. Teeth intervals of the OFCs only in a reference are spatially swept by using of a VIPA whose advantage compared to an optical resonator. Thus, the single-shot imaging system can be realized with the FSR scanned frequency-domain OFC interference monitored by CCD. This system enable high speed 2-dimensional tomographic image without mechanical moving part. And the axial measurement range is not limited by using multi-order interference that is generated by OFCs interferometry. We will present the operation principle with its confirmed results in terms of both simulation and experiment.
Distributed dynamic strain measurement using optical frequency-domain reflectometry.
Zhou, Da-Peng; Chen, Liang; Bao, Xiaoyi
2016-08-20
Distributed dynamic strain measurement based on optical frequency-domain reflectometry is proposed. The technique makes use of the wide scanning range of a tunable laser source in a short sweeping time, and subdivides the overall spectrum into narrower frequency windows. The advantage of subdividing the laser spectral range is to improve the measurement uncertainty induced by the laser wavelength difference between repeated scans. The noise-limited dynamic strain resolution is investigated experimentally, indicating that a minimum detectable strain is less than 200 nε for a spatial resolution of 20 cm. By measuring the subdivided spectral shifts in the time sequence along the sensing fiber, the dynamic strain can be properly quantified over a 30 m measurement range for a highest sampling rate of up to 50 Hz. PMID:27556996
Detecting structural information of scatterers using spatial frequency domain imaging.
Bodenschatz, Nico; Krauter, Philipp; Nothelfer, Steffen; Foschum, Florian; Bergmann, Florian; Liemert, André; Kienle, Alwin
2015-11-01
We demonstrate optical phantom experiments on the phase function parameter γ using spatial frequency domain imaging. The incorporation of two different types of scattering particles allows for control of the optical phantoms’ microscopic scattering properties. By laterally structuring areas with either TiO2 or Al2O3 scattering particles, we were able to obtain almost pure subdiffusive scattering contrast in a single optical phantom. Optical parameter mapping was then achieved using an analytical radiative transfer model revealing the microscopic structural contrast on a macroscopic field of view. As part of our study, we explain several correction and referencing techniques for high spatial frequency analysis and experimentally study the sampling depth of the subdiffusive parameter γ.
Frequency domain identification for robust large space structure control design
NASA Technical Reports Server (NTRS)
Yam, Y.; Bayard, D. S.; Scheid, R. E.
1991-01-01
A methodology is demonstrated for frequency domain identification of large space structures which systematically transforms experimental raw data into a form required for synthesizing H(infinity) controllers using modern robust control design software (e.g., Matlab Toolboxes). A unique feature of this approach is that the additive uncertainty is characterized to a specified statistic confidence rather than with hard bounds. In this study, the difference in robust performance is minimal between the two levels of confidence. In general cases, the present methodology provides a tool for performance/confidence level tradeoff studies. For simplicity, the additive uncertainty on a frequency grid is considered and the interpolation error in between grid points is neglected.
Detecting structural information of scatterers using spatial frequency domain imaging.
Bodenschatz, Nico; Krauter, Philipp; Nothelfer, Steffen; Foschum, Florian; Bergmann, Florian; Liemert, André; Kienle, Alwin
2015-11-01
We demonstrate optical phantom experiments on the phase function parameter γ using spatial frequency domain imaging. The incorporation of two different types of scattering particles allows for control of the optical phantoms’ microscopic scattering properties. By laterally structuring areas with either TiO2 or Al2O3 scattering particles, we were able to obtain almost pure subdiffusive scattering contrast in a single optical phantom. Optical parameter mapping was then achieved using an analytical radiative transfer model revealing the microscopic structural contrast on a macroscopic field of view. As part of our study, we explain several correction and referencing techniques for high spatial frequency analysis and experimentally study the sampling depth of the subdiffusive parameter γ. PMID:26590206
Frequency-Domain Green's Functions for Radar Waves in Heterogeneous 2.5D Media
Green’s functions for radar waves propagating in heterogeneous media may be calculated in the frequency domain using a hybrid of two numerical methods. The model is defined in the Cartesian coordinate system, and its electromagnetic properties may vary in the x and z directions, ...
Ultrasound breast imaging using frequency domain reverse time migration
NASA Astrophysics Data System (ADS)
Roy, O.; Zuberi, M. A. H.; Pratt, R. G.; Duric, N.
2016-04-01
Conventional ultrasonography reconstruction techniques, such as B-mode, are based on a simple wave propagation model derived from a high frequency approximation. Therefore, to minimize model mismatch, the central frequency of the input pulse is typically chosen between 3 and 15 megahertz. Despite the increase in theoretical resolution, operating at higher frequencies comes at the cost of lower signal-to-noise ratio. This ultimately degrades the image contrast and overall quality at higher imaging depths. To address this issue, we investigate a reflection imaging technique, known as reverse time migration, which uses a more accurate propagation model for reconstruction. We present preliminary simulation results as well as physical phantom image reconstructions obtained using data acquired with a breast imaging ultrasound tomography prototype. The original reconstructions are filtered to remove low-wavenumber artifacts that arise due to the inclusion of the direct arrivals. We demonstrate the advantage of using an accurate sound speed model in the reverse time migration process. We also explain how the increase in computational complexity can be mitigated using a frequency domain approach and a parallel computing platform.
Parametric Study of the Frequency-Domain Thermoreflectance Technique
C. Xing; C. Jensen; Z. Hua; H. Ban; D. H. Hurley; M. Khafizov; J. Rory Kennedy
2012-11-01
Without requiring regression for parameter determination, one-dimensional (1D) analytical models are used by many research groups to extract the thermal properties in frequency-domain thermoreflectance measurements. Experimentally, this approach involves heating the sample with a pump laser and probing the temperature response with spatially coincident probe laser. Micron order lateral resolution can be obtained by tightly focusing the pump and probe lasers. However, small laser beam spot sizes necessarily bring into question the assumptions associated with 1D analytical models. In this study, we analyzed the applicability of 1D analytical models by comparing to 2D analytical and fully numerical models. Specifically, we considered a generic nlayer two-dimensional (2D), axisymmetric analytical model including effects of volumetric heat absorption, contact resistance, and anisotropic properties. In addition, a finite element numerical model was employed to consider nonlinear effects caused by temperature dependent thermal conductivity. Nonlinearity is of germane importance to frequency domain approaches because the experimental geometry is such that the probe is always sensing the maximum temperature fluctuation. To quantify the applicability of the 1D model, parametric studies were performed considering the effects of: film thickness, heating laser size, probe laser size, substrate-to-film effusivity ratio, interfacial thermal resistance between layers, volumetric heating, substrate thermal conductivity, nonlinear boundary conditions, and anisotropic and temperature dependent thermal conductivity.
Frequency-Wavenumber Domain Filtering for Improved Damage Visualization
Ruzzene, M.
2007-03-21
This paper presents a technique for the analysis of full wavefield data in the wavenumber/frequency domain as an effective tool for damage detection, visualization and characterization. Full wavefield data contain a wealth of information regarding the space and time variation of propagating waves in damaged structural components. Such information can be used to evaluate the response spectrum in the frequency/wavenumber domain, which effectively separates incident waves from reflections caused by discontinuities encountered along the wave paths. This allows removing the injected wave from the overall response through simple filtering strategies, thus highlighting the presence of reflections associated to damage. The concept is first illustrated on analytical and numerically simulated data, and then tested on experimental results. In the experiments, full wavefield measurements are conveniently obtained using a Scanning Laser Doppler Vibrometer, which allows the detection of displacements and/or velocities over a user-defined grid, and it is able to provide the required spatial and time information in a timely manner. Tests performed on a simple aluminum plate with artificially seeded slits simulating longitudinal cracks, and on a disbonded tongue and groove joint show the effectiveness of the technique and its potential for application to the inspection of a variety of structural components.
Robust frequency-domain elastic Full Waveform Inversion: which norm?
NASA Astrophysics Data System (ADS)
Brossier, R.; Operto, S. O.; Virieux, J.
2009-12-01
Full waveform inversion (FWI) is becoming a powerful and efficient tool to derive high resolution models of subsurface visco-elastic parameters at different scales. In the frequency-domain (FD), 2D FWI is computationally affordable from both modeling and inversion viewpoints, because the inversion can be limited to few discrete frequencies when applied to wide-aperture acquisition geometries. However, FWI is an ill-posed data-fitting procedure that is sensitive to noise, inaccuracies of the starting model and definition of multi-parameter classes. The impact of the noise in FD FWI, when applied to decimated data sets, has been marginally illustrated in the past. We investigate here the sensitivities and performances of different minimization functionals, such as the least-square norm (L2), the least-absolute-values norm (L1), and some combinations of both (the Huber and the so-called Hybrid criteria), using realistic onshore and offshore synthetic case studies. The minimization functionals are implemented in a massively-parallel, 2D elastic FD FWI algorithm for imaging P- and S-wave velocities (VP and VS). Results show that the L1 norm provides the most reliable models, even when only few discrete frequencies are used in the inversion and when outliers pollute the data. The L2 norm can provide reliable results in the presence of uniform white noise if the data redundancy is increased by refining the frequency sampling interval in the inversion, at the expense of the computational efficiency. The Huber and the Hybrid criteria are shown to be sensitive to a threshold, which controls the transition between the L1 and L2 behaviors, and which requires tedious trial-and-error investigations for reliable estimation. The L1 norm provides a robust alternative to the L2 norm for the inversion of decimated data sets in the framework of efficient FD FWI. Synthetic onshore SEG/EAGE overthrust model experiment. Body and surface waves are jointly inverted. (a-b) true VP and VS
NASA Technical Reports Server (NTRS)
Wu, Andy
1995-01-01
Allan Deviation computations of linear frequency synthesizer systems have been reported previously using real-time simulations. Even though it takes less time compared with the actual measurement, it is still very time consuming to compute the Allan Deviation for long sample times with the desired confidence level. Also noises, such as flicker phase noise and flicker frequency noise, can not be simulated precisely. The use of frequency domain techniques can overcome these drawbacks. In this paper the system error model of a fictitious linear frequency synthesizer is developed and its performance using a Cesium (Cs) atomic frequency standard (AFS) as a reference is evaluated using frequency domain techniques. For a linear timing system, the power spectral density at the system output can be computed with known system transfer functions and known power spectral densities from the input noise sources. The resulting power spectral density can then be used to compute the Allan Variance at the system output. Sensitivities of the Allan Variance at the system output to each of its independent input noises are obtained, and they are valuable for design trade-off and trouble-shooting.
Multifrequency frequency-domain spectrometer for tissue analysis.
Spichtig, Sonja; Hornung, René; Brown, Derek W; Haensse, Daniel; Wolf, Martin
2009-02-01
In this paper we describe the modification and assessment of a standard multidistance frequency-domain near infrared spectroscopy (NIRS) instrument to perform multifrequency frequency-domain NIRS measurements. The first aim of these modifications was to develop an instrument that enables measurement of small volumes of tissue such as the cervix, which is too small to be measured using a multidistance approach. The second aim was to enhance the spectral resolution to be able to determine the absolute concentrations of oxy-, deoxy- and total hemoglobin, water, and lipids. The third aim was to determine the accuracy and error of measurement of this novel instrument in both in vitro and in vivo environments. The modifications include two frequency synthesizers with variable, freely adjustable frequency, broadband high-frequency amplifiers, the development of a novel avalanche photodiode (APD) detector and demodulation circuit, additional laser diodes with additional wavelengths, and a respective graphic user interface to analyze the measurements. To test the instrument and algorithm, phantoms with optical properties similar to those of biological tissue were measured and analyzed. The results show that the absorption coefficient can be determined with an error of <10%. The error of the scattering coefficient was <31%. Since the accuracy of the chromophore concentrations depends on the absorption coefficient and not on the scattering coefficient, the <10% error is the clinically relevant parameter. In addition, the new APD had similar accuracy as the standard photomultiplier tubes. To determine the accuracy of chromophore concentration measurements we employed liquid Intralipid(R) phantoms that contained 99% water, 1% lipid, and an increasing concentration of hemoglobin in steps of 0.010 mM. Water concentration was measured with an accuracy of 6.5% and hemoglobin concentration with an error of 0.0024 mM independent of the concentration. The measured lipid concentration
Patellofemoral pain syndrome: electromyography in a frequency domain analysis
NASA Astrophysics Data System (ADS)
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.
Development of a frequency-domain electromagnetic scattering measurement system
NASA Astrophysics Data System (ADS)
Oh, Kenneth K.
1993-12-01
This thesis describes the development of a system for measuring frequency-domain scattered fields in the Transient Electromagnetic Scattering Range at the Naval Postgraduate School. The new system employs a stepped-frequency CW waveform and utilizes an HP-8510B network analyzer as an RF front-end and a coherent receiver. A pair of AEL H1498 antennas was installed to cover a frequency range of 2 GHz to 18 GHz. An HP-82300C BASIC Language Processor was installed on a COMPAQ Deskpro-386 PC, and an HP-BASIC program was developed for remote control of the HP-8510B with data acquisition over the HPIB bus. A post-processing algorithm was created using MatLab for background subtraction, calibration, and deconvolution. A set of RCS measurements was made using various size spheres, and the postprocessing outputs were compared to computed values. Good agreement between these measurements and computed data indicates excellent accuracy of the measurement system and valid operations of the postprocessing algorithm.
NASA Astrophysics Data System (ADS)
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.
Simultaneous storage of medical images in the spatial and frequency domain: A comparative study
Nayak, Jagadish; Bhat, P Subbanna; Acharya U, Rajendra; UC, Niranjan
2004-01-01
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. PMID:15180899
Optical Frequency Domain Visualization of Electron Beam Driven Plasma Wakefields
NASA Astrophysics Data System (ADS)
Zgadzaj, Rafal; Downer, M. C.; Muggli, Patric; Yakimenko, Vitaly; Babzien, Marcus; Kusche, Karl; Fedurin, Mikhail
2010-11-01
Beam-driven plasma wakefield accelerators (PWFA), such as the ``plasma afterburner,'' are a promising approach for significantly increasing the particle energies of conventional accelerators. The study and optimization of PWFA would benefit from an experimental correlation between the parameters of the drive bunch, the accelerated bunch and the corresponding, accelerating plasma wave structure. However, the plasma wave structure has not yet been observed directly in PWFA. We will report our current work on noninvasive optical Frequency Domain Interferometric (FDI) and Holographic (FDH) visualization of beam-driven plasma waves. Both techniques employ two laser pulses (probe and reference) co-propagating with the particle drive-beam and its plasma wake. The reference pulse precedes the drive bunch, while the probe overlaps the plasma wave and maps its longitudinal and transverse structure. The experiment is being developed at the BNL/ATF Linac to visualize wakes generated by two and multi-bunch drive beams.
Frequency domain identification experiment on a large flexible structure
NASA Technical Reports Server (NTRS)
Bayard, D. S.; Hadaegh, F. Y.; Yam, Y.; Scheid, R. E.; Mettler, E.; Milman, M. H.
1989-01-01
Recent experiences in the field of flexible structure control in space have indicated a need for on-orbit system identification to support robust control redesign to avoid in-flight instabilities and maintain high spacecraft performance. The authors highlight an automated frequency domain system identification methodology recently developed to fill this need. The methodology supports (1) the estimation of system quantities useful for robust control analysis and design, (2) experiment design tailored to performing system identification in a typically constrained on-orbit environment, and (3) the automation of operations to reduce human-in-the-loop requirements. A basic overview of the methodology is presented first, followed by an experimental verification of the approach performed on the JPL/AFAL testbed facility.
Frequency-domain ultrasound waveform tomography breast attenuation imaging
NASA Astrophysics Data System (ADS)
Sandhu, Gursharan Yash Singh; Li, Cuiping; Roy, Olivier; West, Erik; Montgomery, Katelyn; Boone, Michael; Duric, Neb
2016-04-01
Ultrasound waveform tomography techniques have shown promising results for the visualization and characterization of breast disease. By using frequency-domain waveform tomography techniques and a gradient descent algorithm, we have previously reconstructed the sound speed distributions of breasts of varying densities with different types of breast disease including benign and malignant lesions. By allowing the sound speed to have an imaginary component, we can model the intrinsic attenuation of a medium. We can similarly recover the imaginary component of the velocity and thus the attenuation. In this paper, we will briefly review ultrasound waveform tomography techniques, discuss attenuation and its relations to the imaginary component of the sound speed, and provide both numerical and ex vivo examples of waveform tomography attenuation reconstructions.
EEG time and frequency domain analyses of primary insomnia.
Hamida, Sana Tmar-Ben; Penzel, Thomas; Ahmed, Beena
2015-08-01
In this work, we present a range of electroencephalographic (EEG) time and frequency domain features that can be used to characterize patients suffering with primary insomnia. When evaluated using 10 insomniacs and 10 healthy subjects, we found significant differences in the feature values between the two groups. Participants with primary insomnia were observed to have significantly elevated Hjorth's parameters particularly complexity, high zero crossing rates specifically during wake and sleep stage 1 and high gamma power in all sleep stages. Given the significant differences between the two groups, these features can be used to better understand the sleep dynamics of insomniacs and accurately discriminate insomniac EEG data from that of healthy subjects. PMID:26737710
Motion estimation in the frequency domain using fuzzy c-planes clustering.
Erdem, C E; Karabulut, G Z; Yanmaz, E; Anarim, E
2001-01-01
A recent work explicitly models the discontinuous motion estimation problem in the frequency domain where the motion parameters are estimated using a harmonic retrieval approach. The vertical and horizontal components of the motion are independently estimated from the locations of the peaks of respective periodogram analyses and they are paired to obtain the motion vectors using a procedure proposed. In this paper, we present a more efficient method that replaces the motion component pairing task and hence eliminates the problems of the pairing method described. The method described in this paper uses the fuzzy c-planes (FCP) clustering approach to fit planes to three-dimensional (3-D) frequency domain data obtained from the peaks of the periodograms. Experimental results are provided to demonstrate the effectiveness of the proposed method.
Frequency-domain fluorescence spectroscopy of human stratum corneum
NASA Astrophysics Data System (ADS)
Garrison, Michael D.; Potts, Russell O.; Abraham, William
1994-08-01
The intercellular lipid lamellae of mammalian stratum corneum (SC) constitute the major barrier to percutaneous penetration of drugs and other solute molecules. In order to understand the barrier property of skin on a molecular level, we have initiated fluorescence spectroscopic investigation of the membranous structures of the SC and related model systems using the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Incorporated into distearoylphosphatidylcholine and stratum corneum bilayers, DPH fluorescence reflected the change in lipid structure under thermal and chemical perturbations. Using a multiharmonic frequency approach, we measured the fluorescence lifetime and rotational correlation times for DPH in these systems. Our data indicated that a biexponential decay ((tau) 1 approximately equals 9 ns, (tau) 2 approximately equals 1.5 ns) described the intensity decay, while a hindered rotor model ((phi) approximately equals 5 ns, r(infinity ) approximately equals 0.3) described the anisotropy decay. These parameters reported the known thermotropic phase transition in porcine stratum corneum, and the influence of the penetration enhancer oleic acid in human epidermis. Thus, we have shown frequency- domain fluorescence spectroscopy to be a facile and powerful tool for monitoring the permeability of a solid tissue such as the SC.
A frequency-domain transient stability criterion for normal contingencies
Marceau, R.J.; Rizzi, J.C.; Mailhot, R.
1995-08-01
In a previous paper, a simple frequency-domain stability criterion was proposed for networks near the stability limit subjected to a 3-phase fault with no loss of line. The criterion can be summarized as follows: if a system is stable, the phase angle of the Fourier transform of a network`s transient voltage response exhibits a clockwise polar plot behavior at all buses (i.e. for increasing frequency); if the system is unstable, it exhibits a counterclockwise behavior in at least one location. Though these results are of interest, the criterion would be of greater practical use in mechanizing dynamic security analysis if it could be extended to the types of contingencies actually used in security analysis, namely normal contingencies. Normal contingencies are commonly defined as the loss of any element in a power system, either spontaneously or preceded by a fault, and such changes in topology impact post-contingency steady-state voltages in addition to their transient behavior. The present paper shows how such cases can be treated, thereby extending the applicable range of the criterion to normal contingencies.
Domain decomposition methods for mortar finite elements
Widlund, O.
1996-12-31
In the last few years, domain decomposition methods, previously developed and tested for standard finite element methods and elliptic problems, have been extended and modified to work for mortar and other nonconforming finite element methods. A survey will be given of work carried out jointly with Yves Achdou, Mario Casarin, Maksymilian Dryja and Yvon Maday. Results on the p- and h-p-version finite elements will also be discussed.
Efficient integration method for fictitious domain approaches
NASA Astrophysics Data System (ADS)
Duczek, Sascha; Gabbert, Ulrich
2015-10-01
In the current article, we present an efficient and accurate numerical method for the integration of the system matrices in fictitious domain approaches such as the finite cell method (FCM). In the framework of the FCM, the physical domain is embedded in a geometrically larger domain of simple shape which is discretized using a regular Cartesian grid of cells. Therefore, a spacetree-based adaptive quadrature technique is normally deployed to resolve the geometry of the structure. Depending on the complexity of the structure under investigation this method accounts for most of the computational effort. To reduce the computational costs for computing the system matrices an efficient quadrature scheme based on the divergence theorem (Gauß-Ostrogradsky theorem) is proposed. Using this theorem the dimension of the integral is reduced by one, i.e. instead of solving the integral for the whole domain only its contour needs to be considered. In the current paper, we present the general principles of the integration method and its implementation. The results to several two-dimensional benchmark problems highlight its properties. The efficiency of the proposed method is compared to conventional spacetree-based integration techniques.
NASA Astrophysics Data System (ADS)
Zhao, Liang; Ge, Jian-Hua
2012-12-01
Single-carrier (SC) transmission with frequency-domain equalization (FDE) is today recognized as an attractive alternative to orthogonal frequency-division multiplexing (OFDM) for communication application with the inter-symbol interference (ISI) caused by multi-path propagation, especially in shallow water channel. In this paper, we investigate an iterative receiver based on minimum mean square error (MMSE) decision feedback equalizer (DFE) with symbol rate and fractional rate samplings in the frequency domain (FD) and serially concatenated trellis coded modulation (SCTCM) decoder. Based on sound speed profiles (SSP) measured in the lake and finite-element ray tracking (Bellhop) method, the shallow water channel is constructed to evaluate the performance of the proposed iterative receiver. Performance results show that the proposed iterative receiver can significantly improve the performance and obtain better data transmission than FD linear and adaptive decision feedback equalizers, especially in adopting fractional rate sampling.
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.
Frequency-domain correction of sensor dynamic error for step response.
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly. PMID:23206091
NASA Technical Reports Server (NTRS)
Baumeister, K. J.; Kreider, K. L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in ducts. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
NASA Technical Reports Server (NTRS)
Baumeister, Kenneth J.; Kreider, Kevin L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Frequency-domain correction of sensor dynamic error for step response.
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.
Frequency-domain correction of sensor dynamic error for step response
NASA Astrophysics Data System (ADS)
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.
Time-domain representation of frequency-dependent foundation impedance functions
Safak, E.
2006-01-01
Foundation impedance functions provide a simple means to account for soil-structure interaction (SSI) when studying seismic response of structures. Impedance functions represent the dynamic stiffness of the soil media surrounding the foundation. The fact that impedance functions are frequency dependent makes it difficult to incorporate SSI in standard time-history analysis software. This paper introduces a simple method to convert frequency-dependent impedance functions into time-domain filters. The method is based on the least-squares approximation of impedance functions by ratios of two complex polynomials. Such ratios are equivalent, in the time-domain, to discrete-time recursive filters, which are simple finite-difference equations giving the relationship between foundation forces and displacements. These filters can easily be incorporated into standard time-history analysis programs. Three examples are presented to show the applications of the method.
NASA Technical Reports Server (NTRS)
Sreenivas, Kidambi; Whitfield, David L.
1995-01-01
Two linearized solvers (time and frequency domain) based on a high resolution numerical scheme are presented. The basic approach is to linearize the flux vector by expressing it as a sum of a mean and a perturbation. This allows the governing equations to be maintained in conservation law form. A key difference between the time and frequency domain computations is that the frequency domain computations require only one grid block irrespective of the interblade phase angle for which the flow is being computed. As a result of this and due to the fact that the governing equations for this case are steady, frequency domain computations are substantially faster than the corresponding time domain computations. The linearized equations are used to compute flows in turbomachinery blade rows (cascades) arising due to blade vibrations. Numerical solutions are compared to linear theory (where available) and to numerical solutions of the nonlinear Euler equations.
Frequency-dependent FDTD methods using Z transforms
NASA Technical Reports Server (NTRS)
Sullivan, Dennis M.
1992-01-01
While the frequency-dependent finite-difference time-domain, or (FD)2TD, method can correctly calculate EM propagation through media whose dielectric properties are frequency-dependent, more elaborate applications lead to greater (FD)2TD complexity. Z-transform theory is presently used to develop the mathematical bases of the (FD)2TD method, simultaneously obtaining a clearer formulation and allowing researchers to draw on the existing literature of systems analysis and signal-processing.
Aero-acoustics source separation with sparsity inducing priors in the frequency domain
NASA Astrophysics Data System (ADS)
Schwander, Olivier; Picheral, José; Gac, Nicolas; Mohammad-Djafari, Ali; Blacodon, Daniel
2015-01-01
The characterization of acoustic sources is of great interest in many industrial applications, in particular for the aeronautic or automotive industry for the development of new products. While localization of sources using observations from a wind tunnel is a well-known subject, the characterization and separation of the sources still needs to be explored. We present here a Bayesian approach for sources separation. Two prior modeling of the sources are considered: a sparsity inducing prior in the frequency domain and an autoregressive model in the time domain. The proposed methods are evaluated on synthetic data simulating noise sources emitting from an airfoil inside a wind tunnel.
Motion artifacts in optical coherence tomography with frequency-domain ranging
Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Bouma, B. E.
2009-01-01
We describe results of theoretical and experimental investigations of artifacts that can arise in spectral-domain optical coherence tomography (SD-OCT) and optical frequency domain imaging (OFDI) as a result of sample or probe beam motion. While SD-OCT and OFDI are based on similar spectral interferometric principles, the specifics of motion effects are quite different because of distinct signal acquisition methods. These results provide an understanding of motion artifacts such as signal fading, spatial distortion and blurring, and emphasize the need for fast image acquisition in biomedical applications. PMID:19483816
Frequency-domain seismic-wave modeling, migration, and full-waveform inversion
NASA Astrophysics Data System (ADS)
Xu, Kun
In the dissertation, I have proposed and developed new approaches for seismic modeling, migration, and full-waveform inversion in the frequency domain. For 3D scalar-wave simulations in the frequency-space domain, we develop a fourth-order compact finite-difference (FD) form with a high-order spatial accuracy (4-5 grid points per shortest wavelength), and optimal one-way wave-equation (OWWE) absorbing boundary conditions (ABCs) with only one outer layer; these strategies greatly reduce the total number of the model grid points, and thus the overall computational cost. For reverse-time migration (RTM) using the cross-correlation imaging condition in the time domain, extra disk storage or wavefield simulations are required to make the forward propagated source and backward-propagated receiver wavefields available at the same time. We propose a new method to implement RTM in the frequency domain. Using virtual sources for the backward propagation of the receiver wavefield, we can straightforwardly implement the excitation-time and cross-correlation imaging conditions at each frequency without any disk storage or I/O and with complete spatial coverage of the migrated images. As both time and frequency domains have their own advantages for the inversion, we implement a hybrid scheme to combine both advantages in elastic full-waveform inversion (FWI). We simulate the wavefields using a time-domain high-precision finite-element (FE) modeling parallelized over shots with the message passing interface (MPI), and implement the inversion in the frequency domain via Fourier transform. Thus, we can easily apply both frequency-selection and time-windowing techniques to reduce the nonlinearity in inversion. To decouple different parameters in elastic FWI, we propose a new multi-steplength gradient approach to assign individual weights separately for each parameter gradient, and search for an optimal steplength along the composite gradient direction. As variations in the results
Frequency Domain Analysis of Errors in Cross-Correlations of Ambient Seismic Noise
NASA Astrophysics Data System (ADS)
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2016-09-01
We analyze 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 preprocessing steps. Natural continuous noise records contain both ambient noise and small earthquakes that are inseparable from the noise with the existing preprocessing 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
Zhou, Hong; Melloni, Lucia; Poeppel, David; Ding, Nai
2016-01-01
Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid. PMID:27375465
Zhou, Hong; Melloni, Lucia; Poeppel, David; Ding, Nai
2016-01-01
Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid. PMID:27375465
NASA Astrophysics Data System (ADS)
Sasaki, Yutaka; Yi, Myeong-Jong; Choi, Jihyang; Son, Jeong-Sul
2015-01-01
We present frequency- and time-domain three-dimensional (3-D) inversion approaches that can be applied to transient electromagnetic (TEM) data from a grounded-wire source using a PC. In the direct time-domain approach, the forward solution and sensitivity were obtained in the frequency domain using a finite-difference technique, and the frequency response was then Fourier-transformed using a digital filter technique. In the frequency-domain approach, TEM data were Fourier-transformed using a smooth-spectrum inversion method, and the recovered frequency response was then inverted. The synthetic examples show that for the time derivative of magnetic field, frequency-domain inversion of TEM data performs almost as well as time-domain inversion, with a significant reduction in computational time. In our synthetic studies, we also compared the resolution capabilities of the ground and airborne TEM and controlled-source audio-frequency magnetotelluric (CSAMT) data resulting from a common grounded wire. An airborne TEM survey at 200-m elevation achieved a resolution for buried conductors almost comparable to that of the ground TEM method. It is also shown that the inversion of CSAMT data was able to detect a 3-D resistivity structure better than the TEM inversion, suggesting an advantage of electric-field measurements over magnetic-field-only measurements.
Spatial and frequency domain interferometry using the MU radar - A tutorial and recent developments
NASA Astrophysics Data System (ADS)
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.
Dynamic analysis of offshore structures with non-zero initial conditions in the frequency domain
NASA Astrophysics Data System (ADS)
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
Sun, Jianling; Li, Xiaoying; Guo, Jihong; Han, Fang; Zhang, Haicheng
2011-04-01
The application of ambulatory electrocardiography to identify obstructive sleep apnea syndrome (OSAS) patients was evaluated using time-domain and frequency-domain analyses of heart rate variability (HRV). For this, overnight sleep pattern was investigated in 95 individuals (48 OSAS(+) patients and 47 OSAS(-) controls) by polysomnography and 24-h ambulatory electrocardiography. Apnea scores were calculated using two different HRV analyses. Average age and body mass index, and percentages of men and of patients with history of hypertension and/or diabetes were higher in study group as compared with control group. PNN50(night), SDNNI(day-night) and SDNNI(day-night) in time-domain analysis were more sensitive than other indices. In frequency-domain analysis, mean night-time total power, night-time VLF power, night-time LF power, and the difference between these measures in day and night were significantly higher in study group. LF/HF ratio was also significantly higher in study group in day-time or night-time with a significant difference (P < 0.05) between day and night. At sleep apnea risk score >4, sensitivity, specificity, and positive predictive value were, respectively, 81.25, 46.81, and 64.21%. At sleep apnea risk scores >5, 6, or 7, the specificity increased, while the sensitivity and positive predictive value decreased. In conclusion, time-domain and frequency-domain HRV analyses are useful methods for OSAS screening, and the frequency-domain analysis is more sensitive.
Polarized spatial frequency domain imaging of heart valve fiber structure
NASA Astrophysics Data System (ADS)
Goth, Will; Yang, Bin; Lesicko, John; Allen, Alicia; Sacks, Michael S.; Tunnell, James W.
2016-03-01
Our group previously introduced Polarized Spatial Frequency Domain Imaging (PSFDI), a wide-field, reflectance imaging technique which we used to empirically map fiber direction in porcine pulmonary heart valve leaflets (PHVL) without optical clearing or physical sectioning of the sample. Presented is an extended analysis of our PSFDI results using an inverse Mueller matrix model of polarized light scattering that allows additional maps of fiber orientation distribution, along with instrumentation permitting increased imaging speed for dynamic PHVL fiber measurements. We imaged electrospun fiber phantoms with PSFDI, and then compared these measurements to SEM data collected for the same phantoms. PHVL was then imaged and compared to results of the same leaflets optically cleared and imaged with small angle light scattering (SALS). The static PHVL images showed distinct regional variance of fiber orientation distribution, matching our SALS results. We used our improved imaging speed to observe bovine tendon subjected to dynamic loading using a biaxial stretching device. Our dynamic imaging experiment showed trackable changes in the fiber microstructure of biological tissue under loading. Our new PSFDI analysis model and instrumentation allows characterization of fiber structure within heart valve tissues (as validated with SALS measurements), along with imaging of dynamic fiber remodeling. The experimental data will be used as inputs to our constitutive models of PHVL tissue to fully characterize these tissues' elastic behavior, and has immediate application in determining the mechanisms of structural and functional failure in PHVLs used as bio-prosthetic implants.
Frequency domain response of a parametrically excited riser under random wave forces
NASA Astrophysics Data System (ADS)
Lei, Song; Zhang, Wen-Shou; Lin, Jia-Hao; Yue, Qian-Jin; Kennedy, D.; Williams, F. W.
2014-01-01
Floating Production, Drilling, Storage and Offloading units represent a new technology with a promising future in the offshore oil industry. An important role is played by risers, which are installed between the subsea wellhead and the Tension Leg Deck located in the middle of the moon-pool in the hull. The inevitable heave motion of the floating hull causes a time-varying axial tension in the riser. This time dependent tension may have an undesirable influence on the lateral deflection response of the riser, with random wave forces in the frequency domain. To investigate this effect, a riser is modeled as a Bernoulli-Euler beam. The axial tension is expressed as a static part, along with a harmonic dynamic part. By linearizing the wave drag force, the riser's lateral deflection is obtained through a partial differential equation containing a time-dependent coefficient. Applying the Galerkin method, the equation is reduced to an ordinary differential equation that can be solved using the pseudo-excitation method in the frequency domain. Moreover, the Floquet-Liapunov theorem is used to estimate the stability of the vibration system in the space of parametric excitation. Finally, stability charts are obtained for some numerical examples, the correctness of the proposed method is verified by comparing with Monte-Carlo simulation and the influence of the parametric excitation on the frequency domain responses of the riser is discussed.
Optimal Frequency-Domain System Realization with Weighting
NASA Technical Reports Server (NTRS)
Juang, Jer-Nan; Maghami, Peiman G.
1999-01-01
Several approaches are presented to identify an experimental system model directly from frequency response data. The formulation uses a matrix-fraction description as the model structure. Frequency weighting such as exponential weighting is introduced to solve a weighted least-squares problem to obtain the coefficient matrices for the matrix-fraction description. A multi-variable state-space model can then be formed using the coefficient matrices of the matrix-fraction description. Three different approaches are introduced to fine-tune the model using nonlinear programming methods to minimize the desired cost function. The first method uses an eigenvalue assignment technique to reassign a subset of system poles to improve the identified model. The second method deals with the model in the real Schur or modal form, reassigns a subset of system poles, and adjusts the columns (rows) of the input (output) influence matrix using a nonlinear optimizer. The third method also optimizes a subset of poles, but the input and output influence matrices are refined at every optimization step through least-squares procedures.
Implementation of an LED-based clinical spatial frequency domain imaging system
NASA Astrophysics Data System (ADS)
Mazhar, Amaan; Sharif, Seyed A.; Saggese, Steve; Choi, Bernard; Cuccia, David J.; Durkin, Anthony J.
2012-03-01
Spatial Frequency Domain Imaging (SFDI) is a non-contact imaging method that uses multiple frequency spatial illumination to generate two dimensional maps of tissue optical properties (absorption and reduced scattering) and chromophore concentrations. We present phantom validation and pilot clinical data of a deployed light-emitting diode (LED) based system. The system employs four LED wavelengths (658 nm, 730 nm, 850 nm, 970 nm) to quantitatively assess tissue health by measurement of common tissue constituents. Phantom validation results and maps of oxyhemoglobin, deoxy-hemoglobin, water content, reduced scattering, and surface topography will be presented for pilot studies assessing burn severity and efficacy of port wine stain treatment.
Chládek, J; Brázdil, M; Halámek, J; Plešinger, F; Jurák, P
2013-01-01
We present an off-line analysis procedure for exploring brain activity recorded from intra-cerebral electroencephalographic data (SEEG). The objective is to determine the statistical differences between different types of stimulations in the time-frequency domain. The procedure is based on computing relative signal power change and subsequent statistical analysis. An example of characteristic statistically significant event-related de/synchronization (ERD/ERS) detected across different frequency bands following different oddball stimuli is presented. The method is used for off-line functional classification of different brain areas. PMID:24109865
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.
NASA Astrophysics Data System (ADS)
André, Frédéric; Lambot, Sébastien
2015-04-01
Accurate knowledge of the shallow soil properties is of prime importance in agricultural, hydrological and environmental engineering. During the last decade, numerous geophysical techniques, either invasive or resorting to proximal or remote sensing, have been developed and applied for quantitative characterization of soil properties. Amongst them, time domain reflectrometry (TDR) and frequency domain reflectometry (FDR) are recognized as standard techniques for the determination of soil dielectric permittivity and electrical conductivity, based on the reflected electromagnetic waves from a probe inserted into the soil. TDR data were first commonly analyzed in the time domain using methods considering only a part of the waveform information. Later, advancements have led to the possibility of analyzing the TDR signal through full-wave inverse modeling either in the time or the frequency domains. A major advantage of FDR compared to TDR is the possibility to increase the bandwidth, thereby increasing the information content of the data and providing more detailed characterization of the medium. Amongst the recent works in this field, Minet et al. (2010) developed a modeling procedure for processing FDR data based on an exact solution of Maxwell's equations for wave propagation in one-dimensional multilayered media. In this approach, the probe head is decoupled from the medium and is fully described by characteristic transfer functions. The authors successfully validated the method for homogeneous sand subject to a range of water contents. In the present study, we further validated the modelling approach using reference liquids with well-characterized frequency-dependent electrical properties. In addition, the FDR model was coupled with a dielectric mixing model to investigate the ability of retrieving water content, pore water electrical conductivity and sand porosity from inversion of FDR data acquired in sand subject to different water content levels. Finally, the
Water content evaluation in unsaturated soil using GPR signal analysis in the frequency domain
NASA Astrophysics Data System (ADS)
Benedetto, Andrea
2010-05-01
The evaluation of the water content of unsaturated soil is important for many applications, such as environmental engineering, agriculture and soil science. This study is applied to pavement engineering, but the proposed approach can be utilized in other applications as well. There are various techniques currently available which measure the soil moisture content and some of these techniques are non-intrusive. Herein, a new methodology is proposed that avoids several disadvantages of existing techniques. In this study, ground-coupled Ground Penetrating Radar (GPR) techniques are used to non-destructively monitor the volumetric water content. The signal is processed in the frequency domain; this method is based on Rayleigh scattering according to the Fresnel theory. The scattering produces a non-linear frequency modulation of the electromagnetic signal, where the modulation is a function of the water content. To test the proposed method, five different types of soil were wetted in laboratory under controlled conditions and the samples were analyzed using GPR. The GPR data were processed in the frequency domain, demonstrating a correlation between the shift of the frequency spectrum of the radar signal and the moisture content. The techniques also demonstrate the potential for detecting clay content in soils. This frequency domain approach gives an innovative method that can be applied for an accurate and non-invasive estimation of the water content of soils - particularly, in sub-asphalt aggregate layers - and assessing the bearing capacity and efficacy of the pavement drainage layers. The main benefit of this method is that no preventive calibration is needed.
Comparison of pulse and SFCW GPR in time, frequency and wavelet domain
NASA Astrophysics Data System (ADS)
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
Suspension parameter estimation in the frequency domain using a matrix inversion approach
NASA Astrophysics Data System (ADS)
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.
The research on recognition and extraction of river feature in IKNOS based on frequency domain
NASA Astrophysics Data System (ADS)
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.
New parallel SOR method by domain partitioning
Xie, D.; Adams, L.
1999-07-01
In this paper the authors propose and analyze a new parallel SOR method, the PSOR method, formulated by using domain partitioning and interprocessor data communication techniques. They prove that the PSOR method has the same asymptotic rate of convergence as the Red/Black (R/B) SOR method for the five-point stencil on both strip and block partitions, and as the four-color (R/B/G/O) SOR method for the nine-point stencil on strip partitions. They also demonstrate the parallel performance of the PSOR method on four different MIMD multiprocessors (a KSR1, an Intel Delta, a Paragon, and an IBM SP2). Finally, they compare the parallel performance of PSOR, R/B SOR, and R/B/G/O SOR. Numerical results on the Paragon indicate that PSOR is more efficient than R/B SOR and R/B/G/O SOR in both computation and interprocessor data communication.
Method of detecting system function by measuring frequency response
NASA Technical Reports Server (NTRS)
Morrison, John L. (Inventor); Morrison, William H. (Inventor); Christophersen, Jon P. (Inventor)
2012-01-01
Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.
Method of detecting system function by measuring frequency response
Morrison, John L.; Morrison, William H.; Christophersen, Jon P.
2012-04-03
Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.
Frequency domain analysis of the random loading of cracked panels
NASA Technical Reports Server (NTRS)
Doyle, James F.
1994-01-01
The primary effort concerned the development of analytical methods for the accurate prediction of the effect of random loading on a panel with a crack. Of particular concern was the influence of frequency on the stress intensity factor behavior. Many modern structures, such as those found in advanced aircraft, are lightweight and susceptible to critical vibrations, and consequently dynamic response plays a very important role in their analysis. The presence of flaws and cracks can have catastrophic consequences. The stress intensity factor, K, emerges as a very significant parameter that characterizes the crack behavior. In analyzing the dynamic response of panels that contain cracks, the finite element method is used, but because this type of problem is inherently computationally intensive, a number of ways of calculating K more efficiently are explored.
To Err is Normable: The Computation of Frequency-Domain Error Bounds from Time-Domain Data
NASA Technical Reports Server (NTRS)
Hartley, Tom T.; Veillette, Robert J.; DeAbreuGarcia, J. Alexis; Chicatelli, Amy; Hartmann, Richard
1998-01-01
This paper exploits the relationships among the time-domain and frequency-domain system norms to derive information useful for modeling and control design, given only the system step response data. A discussion of system and signal norms is included. The proposed procedures involve only simple numerical operations, such as the discrete approximation of derivatives and integrals, and the calculation of matrix singular values. The resulting frequency-domain and Hankel-operator norm approximations may be used to evaluate the accuracy of a given model, and to determine model corrections to decrease the modeling errors.
3D seismic data reconstruction based on complex-valued curvelet transform in frequency domain
NASA Astrophysics Data System (ADS)
Zhang, Hua; Chen, Xiaohong; Li, Hongxing
2015-02-01
Traditional seismic data sampling must follow the Nyquist Sampling Theorem. However, the field data acquisition may not meet the sampling criteria due to missing traces or limits in exploration cost, causing a prestack data reconstruction problem. Recently researchers have proposed many useful methods to regularize the seismic data. In this paper, a 3D seismic data reconstruction method based on the Projections Onto Convex Sets (POCS) algorithm and a complex-valued curvelet transform (CCT) has been introduced in the frequency domain. In order to improve reconstruction efficiency and reduce the computation time, the seismic data are transformed from the t-x-y domain to the f-x-y domain and the data reconstruction is processed for every frequency slice during the reconstruction process. The selection threshold parameter is important for reconstruction efficiency for each iteration, therefore an exponential square root decreased (ESRD) threshold is proposed. The experimental results show that the ESRD threshold can greatly reduce iterations and improve reconstruction efficiency compared to the other thresholds for the same reconstruction result. We also analyze the antinoise ability of the CCT-based POCS reconstruction method. The example studies on synthetic and real marine seismic data showed that our proposed method is more efficient and applicable.
Microwave signal processing in two-frequency domain for ROF systems implementation: training course
NASA Astrophysics Data System (ADS)
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.
Two-dimensional frequency-domain acoustic full-waveform inversion with rugged topography
NASA Astrophysics Data System (ADS)
Zhang, Qian-Jiang; Dai, Shi-Kun; Chen, Long-Wei; Li, Kun; Zhao, Dong-Dong; Huang, Xing-Xing
2015-09-01
We studied finite-element-method-based two-dimensional frequency-domain acoustic FWI under rugged topography conditions. The exponential attenuation boundary condition suitable for rugged topography is proposed to solve the cutoff boundary problem as well as to consider the requirement of using the same subdivision grid in joint multifrequency inversion. The proposed method introduces the attenuation factor, and by adjusting it, acoustic waves are sufficiently attenuated in the attenuation layer to minimize the cutoff boundary effect. Based on the law of exponential attenuation, expressions for computing the attenuation factor and the thickness of attenuation layers are derived for different frequencies. In multifrequency-domain FWI, the conjugate gradient method is used to solve equations in the Gauss-Newton algorithm and thus minimize the computation cost in calculating the Hessian matrix. In addition, the effect of initial model selection and frequency combination on FWI is analyzed. Examples using numerical simulations and FWI calculations are used to verify the efficiency of the proposed method.
Visualization of evolving laser-generated structures by frequency domain tomography
NASA Astrophysics Data System (ADS)
Chang, Yenyu; Li, Zhengyan; Wang, Xiaoming; Zgadzaj, Rafal; Downer, Michael
2011-10-01
We introduce frequency domain tomography (FDT) for single-shot visualization of time-evolving refractive index structures (e.g. laser wakefields, nonlinear index structures) moving at light-speed. Previous researchers demonstrated single-shot frequency domain holography (FDH), in which a probe-reference pulse pair co- propagates with the laser-generated structure, to obtain snapshot-like images. However, in FDH, information about the structure's evolution is averaged. To visualize an evolving structure, we use several frequency domain streak cameras (FDSCs), in each of which a probe-reference pulse pair propagates at an angle to the propagation direction of the laser-generated structure. The combination of several FDSCs constitutes the FDT system. We will present experimental results for a 4-probe FDT system that has imaged the whole-beam self-focusing of a pump pulse propagating through glass in a single laser shot. Combining temporal and angle multiplexing methods, we successfully processed data from four probe pulses in one spectrometer in a single-shot. The output of data processing is a multi-frame movie of the self- focusing pulse. Our results promise the possibility of visualizing evolving laser wakefield structures that underlie laser-plasma accelerators used for multi-GeV electron acceleration.
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.
A Method to Examine Content Domain Structures
ERIC Educational Resources Information Center
D'Agostino, Jerome; Karpinski, Aryn; Welsh, Megan
2011-01-01
After a test is developed, most content validation analyses shift from ascertaining domain definition to studying domain representation and relevance because the domain is assumed to be set once a test exists. We present an approach that allows for the examination of alternative domain structures based on extant test items. In our example based on…
Miyazaki, J; Kawasumi, K; Kobayashi, T
2014-09-01
We present a scheme for time-resolved pump-probe microscopy using intensity modulated laser diodes. The modulation frequencies of the pump and probe beams are varied up to 500 MHz with fixed frequency detuning typically set at 15 kHz. The frequency response of the pump-probe signal is detected using a lock-in amplifier referenced at the beat frequency. This frequency domain method is capable of characterizing the nanosecond to picosecond relaxation dynamics of sample species without the use of a high speed detector or a high frequency lock-in amplifier. Furthermore, as the pump-probe signal is based on the nonlinear interaction between the two laser beams and the sample, our scheme provides better spatial resolution than the conventional diffraction-limited optical microscopes. Time-resolved pump-probe imaging of fluorescence beads and aggregates of quantum dots demonstrates that this method is useful for the microscopic analysis of optoelectronic devices. The system is implemented using compact and low-cost laser diodes, and thus has a broad range of applications in the fields of photochemistry, optical physics, and biological imaging.
NASA Astrophysics Data System (ADS)
Zhang, Shengli; Tang, Jiong
2016-04-01
Gearbox is one of the most vulnerable subsystems in wind turbines. Its healthy status significantly affects the efficiency and function of the entire system. Vibration based fault diagnosis methods are prevalently applied nowadays. However, vibration signals are always contaminated by noise that comes from data acquisition errors, structure geometric errors, operation errors, etc. As a result, it is difficult to identify potential gear failures directly from vibration signals, especially for the early stage faults. This paper utilizes synchronous averaging technique in time-frequency domain to remove the non-synchronous noise and enhance the fault related time-frequency features. The enhanced time-frequency information is further employed in gear fault classification and identification through feature extraction algorithms including Kernel Principal Component Analysis (KPCA), Multilinear Principal Component Analysis (MPCA), and Locally Linear Embedding (LLE). Results show that the LLE approach is the most effective to classify and identify different gear faults.
Frequency-domain Model Matching PID Controller Design for Aero-engine
NASA Astrophysics Data System (ADS)
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.
High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing.
Oh, W Y; Yun, S H; Vakoc, B J; Shishkov, M; Desjardins, A E; Park, B H; de Boer, J F; Tearney, G J; Bouma, B E
2008-01-21
Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm.
Resolution enhancement of robust Bayesian pre-stack inversion in the frequency domain
NASA Astrophysics Data System (ADS)
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.
Three-dimensional phantoms for curvature correction in spatial frequency domain imaging
Nguyen, Thu T. A.; Le, Hanh N. D.; Vo, Minh; Wang, Zhaoyang; Luu, Long; Ramella-Roman, Jessica C.
2012-01-01
The sensitivity to surface profile of non-contact optical imaging, such as spatial frequency domain imaging, may lead to incorrect measurements of optical properties and consequently erroneous extrapolation of physiological parameters of interest. Previous correction methods have focused on calibration-based, model-based, and computation-based approached. We propose an experimental method to correct the effect of surface profile on spectral images. Three-dimensional (3D) phantoms were built with acrylonitrile butadiene styrene (ABS) plastic using an accurate 3D imaging and an emergent 3D printing technique. In this study, our method was utilized for the correction of optical properties (absorption coefficient μa and reduced scattering coefficient μs′) of objects obtained with a spatial frequency domain imaging system. The correction method was verified on three objects with simple to complex shapes. Incorrect optical properties due to surface with minimum 4 mm variation in height and 80 degree in slope were detected and improved, particularly for the absorption coefficients. The 3D phantom-based correction method is applicable for a wide range of purposes. The advantages and drawbacks of the 3D phantom-based correction methods are discussed in details. PMID:22741068
Quantum theory of optical coherence of nonstationary light in the space-frequency domain
Lahiri, Mayukh; Wolf, Emil
2010-10-15
Classical theories of coherence for statistically stationary, as well as, nonstationary optical fields are frequently discussed both in the space-time and in the space-frequency domains. However, the quantum treatment of coherence theory is generally carried out in the space-time domain. In this paper, we present a quantum-mechanical theory of first-order coherence for statistically nonstationary light in the space-frequency domain.
Characterization of an intraluminal differential frequency-domain photoacoustics system
NASA Astrophysics Data System (ADS)
Lashkari, Bahman; Son, Jungik; Liang, Simon; Castelino, Robin; Foster, F. Stuart; Courtney, Brian; Mandelis, Andreas
2016-03-01
Cardiovascular related diseases are ranked as the second highest cause of death in Canada. Among the most important cardiovascular diseases is atherosclerosis. Current methods of diagnosis of atherosclerosis consist of angiography, intravascular ultrasound (IVUS) and optical coherence tomography (OCT). None of these methods possesses adequate sensitivity, as the ideal technique should be capable of both depth profiling, as well as functional imaging. An alternative technique is photoacoustics (PA) which can perform deep imaging and spectroscopy. The presented study explores the application of wavelength-modulated differential photoacoustic radar (WM-DPAR) for characterizing arterial vessels. The wavelength-modulated differential photoacoustic technique was shown to be able to substantially increase the dynamic range and sensitivity of hemoglobin oxygenation level detection. In this work the differential PA technique was used with a very high frequency modulation range. To perform spectroscopic PA imaging, at least two wavelengths are required. The selected wavelengths for this work are 1210 nm and 980 nm. 1210 nm corresponds to the maximum optical absorption coefficient of cholesterol and cholesteryl esters which are the main constituents of plaques. Since water, elastin and collagen also have high absorption coefficients at 1210 nm, this wavelength alone cannot provide very high sensitivity and specificity. The additional wavelength, 980 nm corresponds to high absorption coefficient of those constituents of healthy artery tissue. The simultaneous application of the abovementioned wavelengths can provide higher sensitivity and improved specificity in detecting lipids in the arterial vessels.
NASA Astrophysics Data System (ADS)
Kodama, Kazuto; An, Zhisheng; Chang, Hong; Qiang, Xiaoke
2015-04-01
Measurement of low-field magnetic susceptibility over a wide band of frequencies spanning four orders of magnitude is a useful method for the assessment of the grain size distribution of ultrafine magnetic particles smaller than the SP/SSD boundary. This method has been applied to a loess/paleosol sequence at Luochuan in the Chinese Loess Plateau. The studied succession consists of sequences from the latest paleosol unit to the upper part of the loess unit, spanning the last glacial-interglacial cycle. Reconstructed grain size distributions (GSDs) consist of volume fractions on the order of 10-24 m3, and the mean GSDs are modal but with distinctive skewness among the loess, the weakly developed paleosol (weak paleosol), and the mature paleosol. This indicates that the mean volume of SP particles in this sequence tends to increase during the transition from the loess to the paleosol. An index, defined as the difference between χ130 at the lowest (130 Hz) and χ500k at the highest (500 kHz) frequencies normalized to χ130, is judged to be a more suitable index than previous frequency dependence parameters for the concentration of SP particles. This index has a strong correlation with χ130, showing a continuous 'growth curve' with the rate of increase being highest for the loess, moderate for the weak paleosol, and saturated for the paleosol. The characteristic curve suggests that smaller SP particles are preferentially formed in the earlier stage of pedogenesis rather than the later phase when even larger particles are formed in the mature paleosol. These results demonstrate that the broad-band-frequency susceptibility measurement will be useful for the quantitative assessment of magnetic nanoparticles in soils and sediments. Additionally, we point out that the measurement in the frequency domain generally requires time and may not be most suitable to routine measurements. We thus propose an alternative manner, the measurement in the time domain that can be
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.
New parallel SOR method by domain partitioning
Xie, Dexuan
1996-12-31
In this paper, we propose and analyze a new parallel SOR method, the PSOR method, formulated by using domain partitioning together with an interprocessor data-communication technique. For the 5-point approximation to the Poisson equation on a square, we show that the ordering of the PSOR based on the strip partition leads to a consistently ordered matrix, and hence the PSOR and the SOR using the row-wise ordering have the same convergence rate. However, in general, the ordering used in PSOR may not be {open_quote}consistently ordered{close_quotes}. So, there is a need to analyze the convergence of PSOR directly. In this paper, we present a PSOR theory, and show that the PSOR method can have the same asymptotic rate of convergence as the corresponding sequential SOR method for a wide class of linear systems in which the matrix is {open_quotes}consistently ordered{close_quotes}. Finally, we demonstrate the parallel performance of the PSOR method on four different message passing multiprocessors (a KSR1, the Intel Delta, an Intel Paragon and an IBM SP2), along with a comparison with the point Red-Black and four-color SOR methods.
Radio Frequency Power Load and Associated Method
NASA Technical Reports Server (NTRS)
Srinivasan, V. Karthik (Inventor); Freestone, Todd M. (Inventor); Sims, William Herbert, III (Inventor)
2014-01-01
A radio frequency power load and associated method. A radio frequency power load apparatus may include a container with an ionized fluid therein. The apparatus may include one conductor immersed in a fluid and another conductor electrically connected to the container. A radio frequency transmission system may include a radio frequency transmitter, a radio frequency amplifier connected to the transmitter and a radio frequency power load apparatus connected to the amplifier. The apparatus may include a fluid having an ion source therein, one conductor immersed in a fluid, and another conductor electrically connected to the container. A method of dissipating power generated by a radio frequency transmission system may include constructing a waveguide with ionized fluid in a container and connecting the waveguide to an amplifier of the transmission system.
Frequency Domain Ultrasound Waveform Tomography: Breast Imaging Using a Ring Transducer
Sandhu, G Y; Li, C; Roy, O; Schmidt, S; Duric, N
2016-01-01
Application of the frequency domain acoustic wave equation on data acquired from ultrasound tomography scans is shown to yield high resolution sound speed images on the order of the wavelength of the highest reconstructed frequency. Using a signal bandwidth of 0.4–1 MHz and an average sound speed of 1500 m/s, the resolution is approximately 1.5 mm. The quantitative sound speed values and morphology provided by these images have the potential to inform diagnosis and classification of breast disease. In this study, we present the formalism, practical application, and in vivo results of waveform tomography applied to breast data gathered by two different ultrasound tomography scanners that utilize ring transducers. The formalism includes a review of frequency domain modeling of the wave equation using finite difference operators as well as a review of the gradient descent method for the iterative reconstruction scheme. It is shown that the practical application of waveform tomography requires an accurate starting model, careful data processing, and a method to gradually incorporate higher frequency information into the sound speed reconstruction. Following these steps resulted in high resolution quantitative sound speed images of the breast. These images show marked improvement relative to commonly used ray tomography reconstruction methods. The robustness of the method is demonstrated by obtaining similar results from two different ultrasound tomography devices. We also compare our method to MRI to demonstrate concordant findings. The clinical data used in this work was obtained from a HIPAA compliant clinical study (IRB 040912M1F). PMID:26110909
NASA Astrophysics Data System (ADS)
Inamori, Mamiko; Takayama, Shuzo; Sanada, Yukitoshi
Direct conversion receivers in orthogonal frequency division multiplexing (OFDM) systems suffer from direct current (DC) offset, frequency offset, and IQ imbalance. We have proposed an IQ imbalance estimation scheme in the presence of DC offset and frequency offset, which uses preamble signals in the time domain. In this scheme, the DC offset is eliminated by a differential filter. However, the accuracy of IQ imbalance estimation is deteriorated when the frequency offset is small. To overcome this problem, a new IQ imbalance estimation scheme in the frequency domain with the differential filter has been proposed in this paper. The IQ imbalance is estimated with pilot subcarriers. Numerical results obtained through computer simulation show that estimation accuracy and bit error rate (BER) performance can be improved even if the frequency offset is small.
Multiple frequency method for operating electrochemical sensors
Martin, Louis P.
2012-05-15
A multiple frequency method for the operation of a sensor to measure a parameter of interest using calibration information including the steps of exciting the sensor at a first frequency providing a first sensor response, exciting the sensor at a second frequency providing a second sensor response, using the second sensor response at the second frequency and the calibration information to produce a calculated concentration of the interfering parameters, using the first sensor response at the first frequency, the calculated concentration of the interfering parameters, and the calibration information to measure the parameter of interest.
Frequency-Domain Analysis of Intrinsic Neuronal Properties using High-Resistant Electrodes.
Rössert, Christian; Straka, Hans; Glasauer, Stefan; Moore, Lee E
2009-01-01
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. PMID:20582288
NASA Astrophysics Data System (ADS)
Robinson, D. A.; Schaap, M. G.; Or, D.; Jones, S. B.
2005-02-01
Time domain reflectometry (TDR) is one of the most commonly used techniques for water content determination in the subsurface. The measurement results in a single bulk permittivity value that corresponds to a particular, but unknown, ``effective'' frequency (feff). Estimating feff using TDR is important, as it allows comparisons with other techniques, such as impedance or capacitance probes, or microwave remote sensing devices. Soils, especially those with high clay and organic matter content, show appreciable dielectric dispersion, i.e., the real permittivity changes as a function of frequency. Consequently, comparison of results obtained with different sensor types must account for measurement frequency in assessing sensor accuracy and performance. In this article we use a transmission line model to examine the impact of dielectric dispersion on the TDR signal, considering lossless materials (negligible electrical conductivity). Permittivity is inferred from the standard tangent line fitting procedure (KaTAN) and by a method of using the apex of the derivative of the TDR waveform (KaDER). The permittivity determined using the tangent line method is considered to correspond to a velocity associated with a maximum passable frequency; whereas we consider the permittivity determined from the derivative method to correspond with the frequency associated with the signal group velocity. The effective frequency was determined from the 10-90% risetime of the reflected signal. On the basis of this definition, feff was found to correspond with the permittivity determined from KaDER and not from KaTAN in dispersive dielectrics. The modeling is corroborated by measurements in bentonite, ethanol and 1-propanol/water mixtures, which demonstrate the same result. Interestingly, for most nonconductive TDR measurements, frequencies are expected to lie in a range from 0.7 to 1 GHz, while in dispersive media, feff is expected to fall below 0.6 GHz.
NASA Astrophysics Data System (ADS)
Robinson, D. A.; Schaap, M. G.; Or, D.; Jones, S. B.
2005-02-01
Time domain reflectometry (TDR) is one of the most commonly used techniques for water content determination in the subsurface. The measurement results in a single bulk permittivity value that corresponds to a particular, but unknown, "effective" frequency (feff). Estimating feff using TDR is important, as it allows comparisons with other techniques, such as impedance or capacitance probes, or microwave remote sensing devices. Soils, especially those with high clay and organic matter content, show appreciable dielectric dispersion, i.e., the real permittivity changes as a function of frequency. Consequently, comparison of results obtained with different sensor types must account for measurement frequency in assessing sensor accuracy and performance. In this article we use a transmission line model to examine the impact of dielectric dispersion on the TDR signal, considering lossless materials (negligible electrical conductivity). Permittivity is inferred from the standard tangent line fitting procedure (KaTAN) and by a method of using the apex of the derivative of the TDR waveform (KaDER). The permittivity determined using the tangent line method is considered to correspond to a velocity associated with a maximum passable frequency; whereas we consider the permittivity determined from the derivative method to correspond with the frequency associated with the signal group velocity. The effective frequency was determined from the 10-90% risetime of the reflected signal. On the basis of this definition, feff was found to correspond with the permittivity determined from KaDER and not from KaTAN in dispersive dielectrics. The modeling is corroborated by measurements in bentonite, ethanol and 1-propanol/water mixtures, which demonstrate the same result. Interestingly, for most nonconductive TDR measurements, frequencies are expected to lie in a range from 0.7 to 1 GHz, while in dispersive media, feff is expected to fall below 0.6 GHz.
Method of detecting system function by measuring frequency response
Morrison, John L.; Morrison, William H.
2008-07-01
Real time battery impedance spectrum is acquired using one time record, Compensated Synchronous Detection (CSD). This parallel method enables battery diagnostics. The excitation current to a test battery is a sum of equal amplitude sin waves of a few frequencies spread over range of interest. The time profile of this signal has duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known, synchronous detection processes the time record and each component, both magnitude and phase, is obtained. For compensation, the components, except the one of interest, are reassembled in the time domain. The resulting signal is subtracted from the original signal and the component of interest is synchronously detected. This process is repeated for each component.
Method of Detecting System Function by Measuring Frequency Response
NASA Technical Reports Server (NTRS)
Morrison, John L. (Inventor); Morrison, William H. (Inventor)
2008-01-01
Real time battery impedance spectrum is acquired using one time record, Compensated Synchronous Detection (CSD). This parallel method enables battery diagnostics. The excitation current to a test battery is a sum of equal amplitude sin waves of a few frequencies spread over range of interest. The time profile of this signal has duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known, synchronous detection processes the time record and each component, both magnitude and phase, is obtained. For compensation, the components, except the one of interest, are reassembled in the time domain. The resulting signal is subtracted from the original signal and the component of interest is synchronously detected. This process is repeated for each component.
Romano, Maria; Iuppariello, Luigi; Ponsiglione, Alfonso Maria; Improta, Giovanni; Bifulco, Paolo; Cesarelli, Mario
2016-01-01
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. PMID:27195018
Romano, Maria; Iuppariello, Luigi; Ponsiglione, Alfonso Maria; Improta, Giovanni; Bifulco, Paolo; Cesarelli, Mario
2016-01-01
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. PMID:27195018
Vibrational frequencies of anti-diabetic drug studied by terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Du, S. Q.; Li, H.; Xie, L.; Chen, L.; Peng, Y.; Zhu, Y. M.; Li, H.; Dong, P.; Wang, J. T.
2012-04-01
By using terahertz time-domain spectroscopy, the absorption spectra of seven anti-diabetic pills have been investigated. For gliquidone, glipizide, gliclazide, and glimepiride, an obvious resonance peak is found at 1.37 THz. Furthermore, to overcome the limit of density functional theory that can analyze the normal mode frequencies of the ground state of organic material, we also present a method that relies on pharmacophore recognition, from which we can obtain the resonance peak at 1.37 THz can be attributed to the vibration of sulfonylurea group. The results indicate that the veracity of density functional theory can be increased by combining pharmacophore recognition.
Transformation Optics: A Time- and Frequency-Domain Analysis of Electron-Energy Loss Spectroscopy.
Kraft, Matthias; Luo, Yu; Pendry, J B
2016-08-10
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-though 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 quasistatic frequency- and time-domain response of plasmonic particles under electron beam excitation. We study a nonconcentric annulus (and ellipse in the Supporting Information ) as an example.
Domain decomposition methods in computational fluid dynamics
NASA Technical Reports Server (NTRS)
Gropp, William D.; Keyes, David E.
1992-01-01
The divide-and-conquer paradigm of iterative domain decomposition, or substructuring, has become a practical tool in computational fluid dynamic applications because of its flexibility in accommodating adaptive refinement through locally uniform (or quasi-uniform) grids, its ability to exploit multiple discretizations of the operator equations, and the modular pathway it provides towards parallelism. These features are illustrated on the classic model problem of flow over a backstep using Newton's method as the nonlinear iteration. Multiple discretizations (second-order in the operator and first-order in the preconditioner) and locally uniform mesh refinement pay dividends separately, and they can be combined synergistically. Sample performance results are included from an Intel iPSC/860 hypercube implementation.
Domain decomposition methods in computational fluid dynamics
NASA Technical Reports Server (NTRS)
Gropp, William D.; Keyes, David E.
1991-01-01
The divide-and-conquer paradigm of iterative domain decomposition, or substructuring, has become a practical tool in computational fluid dynamic applications because of its flexibility in accommodating adaptive refinement through locally uniform (or quasi-uniform) grids, its ability to exploit multiple discretizations of the operator equations, and the modular pathway it provides towards parallelism. These features are illustrated on the classic model problem of flow over a backstep using Newton's method as the nonlinear iteration. Multiple discretizations (second-order in the operator and first-order in the preconditioner) and locally uniform mesh refinement pay dividends separately, and they can be combined synergistically. Sample performance results are included from an Intel iPSC/860 hypercube implementation.
Microwave Frequency Ferroelectric Domain Imaging of Deuterated Triglycine Sulfate Crystals
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
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.
Image blurring and deblurring using two biased photorefractive crystals in the frequency domain
NASA Astrophysics Data System (ADS)
Gan, Haiyong; Ma, Chong; Sun, Zhixu; Xu, Tao; Li, Jianwei; Xu, Nan; Wang, Jinjin; Song, Feng; Sheng, Chuanxiang; Sun, Ming; Li, Li
2014-11-01
In an imaging system based on a coherent source of moderate power density, images can be blurred when a biased photorefractive crystal is applied at the focal point of the imaging lens. In the frequency domain of the original images, the intensity patterns are diffracted through the photorefractive crystal with varied bias voltage. The high intensity region, which is usually the center or low frequency region of the intensity patterns, is more readily focused or defocused, resulting in blurred images in perception. Such blurred images could not be simply recovered by defocusing methods, which can only indistinguishably focus or defocus the whole intensity patterns. However, the blurred images may be deblurred to certain extent for recovery if a second photorefractive crystal with bias voltage is employed at the focal point of a tandem imaging system. The mechanism of deblurring is similar to that of blurring: the blurred images are transferred through the frequency domain again using an imaging lens, where the second biased photorefractive crystal diffracts the intensity patterns to revert the sensitive region where previously gets focused or defocused. In this work, theoretical analyses are presented in detail to explain the blurring-deblurring mechanism using two biased photorefractive crystals and compatible experimental results are obtained and illustrated. Considering the blurring and deblurring function subgroups of the experiment setup can be potentially developed into encryption and decryption units compatible with far field propagation, the technology presented herein may be promising to find applications in secure laser-based free-space communication systems.
Fu, Ying; Lam, Antony; Sato, Imari; Okabe, Takahiro; Sato, Yoichi
2016-05-01
Hyperspectral imaging is beneficial to many applications but most traditional methods do not consider fluorescent effects which are present in everyday items ranging from paper to even our food. Furthermore, everyday fluorescent items exhibit a mix of reflection and fluorescence so proper separation of these components is necessary for analyzing them. In recent years, effective imaging methods have been proposed but most require capturing the scene under multiple illuminants. In this paper, we demonstrate efficient separation and recovery of reflectance and fluorescence emission spectra through the use of two high frequency illuminations in the spectral domain. With the obtained fluorescence emission spectra from our high frequency illuminants, we then describe how to estimate the fluorescence absorption spectrum of a material given its emission spectrum. In addition, we provide an in depth analysis of our method and also show that filters can be used in conjunction with standard light sources to generate the required high frequency illuminants. We also test our method under ambient light and demonstrate an application of our method to synthetic relighting of real scenes. PMID:26336113
Frequency domain mediolateral balance assessment using a center of pressure tracking task.
Cofré Lizama, L Eduardo; Pijnappels, Mirjam; Reeves, N Peter; Verschueren, Sabine M P; van Dieën, Jaap H
2013-11-15
Since impaired mediolateral balance can increase fall risk, especially in the elderly, its quantification and training might be a powerful preventive tool. We propose a visual tracking task (VTT) with increasing frequencies (.3-2.0Hz) and with center of pressure as visual feedback as an assessment method. This mediolateral balance assessment (MELBA) consists of two tasks, tracking a predictable target signal to determine physical capacity and tracking an unpredictable target signal to determine sensorimotor integration limitations. Within and between sessions learning effects and reliability in balance performance descriptors in both tasks were studied in 20 young adults. Balance performance was expressed as the phase-shift (PS) and gain (G) between the target and CoP in the frequency domain and cut-off frequencies at which the performance dropped. Results showed significant differences between the MELBA tasks in PS and G indicating a lower delay and higher accuracy in tracking the predictable target. Significant within and between sessions learning effects for the same measures were found only for the unpredictable task. Reliability of the cut-off frequencies at which PS and G performance declined and the average values within cut-off frequencies was fair to good (ICC .46-.66) for the unpredictable task and fair to excellent for the predictable task (ICC .68-.87). In conclusion, MELBA can reliably quantify balance performance using a predictable VTT. Additionally, the unpredictable tasks can give insight into the visuomotor integration mechanisms controlling balance and highlights MELBA's potential as a training tool.
Radio frequency detection assembly and method for detecting radio frequencies
Cown, Steven H.; Derr, Kurt Warren
2010-03-16
A radio frequency detection assembly is described and which includes a radio frequency detector which detects a radio frequency emission produced by a radio frequency emitter from a given location which is remote relative to the radio frequency detector; a location assembly electrically coupled with the radio frequency detector and which is operable to estimate the location of the radio frequency emitter from the radio frequency emission which has been received; and a radio frequency transmitter electrically coupled with the radio frequency detector and the location assembly, and which transmits a radio frequency signal which reports the presence of the radio frequency emitter.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Zhou, Haigen; Lin, Jun; Liu, Changsheng; Kang, Lili; Li, Gang; Zeng, Xinsen
2016-03-01
Multi-source and multi-frequency emission method can make full use of the valuable and short flight time in frequency domain semi-airborne electromagnetic (FSAEM) exploration, which has potential to investigate the deep earth structure in complex terrain region. Because several sources are adjacent in multi-source emission method, the interaction of different sources should be considered carefully. An equivalent circuit model of dual-source is established in this paper to assess the interaction between two individual sources, where the parameters are given with the typical values based on the practical instrument system and its application. By simulating the output current of two sources in different cases, the influence from the adjacent source is observed clearly. The current waveforms show that the mutual resistance causes the fluctuation and drift in another source and that the mutual inductance causes transient peaks. A field test with dual-source was conducted to certify the existence of interaction between adjacent sources. The simulation of output current also shows that current errors at low frequency are mainly caused by the mutual resistance while those at high frequency are mainly due to the mutual inductance. Increasing the distance between neighboring sources is a proposed measure to reduce the emission signal errors with designed ones. The feasible distance is discussed in the end. This study gives a useful guidance to lay multi sources to meet the requirement of measurement accuracy in FSAEM survey.
Zhou, Haigen; Lin, Jun; Liu, Changsheng; Kang, Lili; Li, Gang; Zeng, Xinsen
2016-03-01
Multi-source and multi-frequency emission method can make full use of the valuable and short flight time in frequency domain semi-airborne electromagnetic (FSAEM) exploration, which has potential to investigate the deep earth structure in complex terrain region. Because several sources are adjacent in multi-source emission method, the interaction of different sources should be considered carefully. An equivalent circuit model of dual-source is established in this paper to assess the interaction between two individual sources, where the parameters are given with the typical values based on the practical instrument system and its application. By simulating the output current of two sources in different cases, the influence from the adjacent source is observed clearly. The current waveforms show that the mutual resistance causes the fluctuation and drift in another source and that the mutual inductance causes transient peaks. A field test with dual-source was conducted to certify the existence of interaction between adjacent sources. The simulation of output current also shows that current errors at low frequency are mainly caused by the mutual resistance while those at high frequency are mainly due to the mutual inductance. Increasing the distance between neighboring sources is a proposed measure to reduce the emission signal errors with designed ones. The feasible distance is discussed in the end. This study gives a useful guidance to lay multi sources to meet the requirement of measurement accuracy in FSAEM survey. PMID:27036795
DeLong, K.L.; Quinn, T.M.; Mitchum, G.T.; Poore, R.Z.
2009-01-01
Do the chronological methods used in the construction of paleoclimate records influence the results of the frequency analysis applied to them? We explore this phenomenon using the Dongge Cave speleothem record (U-series chronology with variable time steps, ??t) and the El Malpais tree-ring index (cross-dating of ring-width series). Interpolation of the Dongge Cave record to a constant ??t resulted in the suppression of periodicities (<20 years) altering the red noise model used for significance testing. Frequency analysis of temporal subsets of the El Malpais tree-ring index revealed that concentrations of variance varied with the number of ring-width series. Frequency analyses of these records identified significant periodicities, some common to both (???25 and ???69 years). Cross-wavelet analysis, which examines periodicities in the time domain, revealed that coherency between these records occurs intermittently. We found the chronology methods can influence the ability of frequency analysis to detect periodicities and tests for coherency. Copyright 2009 by the American Geophysical Union.
NASA Astrophysics Data System (ADS)
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.
Frequency-domain elastic full waveform inversion using encoded simultaneous sources
NASA Astrophysics Data System (ADS)
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
Feasibility of direct digital sampling for diffuse optical frequency domain spectroscopy in tissue
NASA Astrophysics Data System (ADS)
Roblyer, Darren; O'Sullivan, Thomas D.; Warren, Robert V.; Tromberg, Bruce J.
2013-04-01
Frequency domain optical spectroscopy in the diffusive regime is currently being investigated for biomedical applications including tumor detection, therapy monitoring, exercise metabolism and others. Analog homodyne or heterodyne detection of sinusoidally modulated signals has been the predominant method for measuring phase and amplitude of photon density waves that have traversed through tissue. Here we demonstrate the feasibility of utilizing direct digital sampling of modulated signals using a 3.6 gigasample/second 12 bit analog to digital converter. Digitally synthesized modulated signals between 50 MHz and 400 MHz were measured on tissue-simulating phantoms at six near-infrared wavelengths. An amplitude and phase precision of 1% and 0.6° were achieved during drift tests. Amplitude, phase, scattering and absorption values were compared with a well-characterized network analyzer-based diffuse optical device. Optical properties measured with both systems were within 3.6% for absorption and 2.8% for scattering over a range of biologically relevant values. Direct digital sampling represents a viable method for frequency domain diffuse optical spectroscopy and has the potential to reduce system complexity, size and cost.
NASA Technical Reports Server (NTRS)
Book, W. J.; Majett, M.
1982-01-01
The potential benefits of the ability to control more flexible mechanical arms are discussed. A justification is made in terms of speed of movement. A new controller design procedure is then developed to provide this capability. It uses both a frequency domain representation and a state variable representation of the arm model. The frequency domain model is used to update the modal state variable model to insure decoupled states. The technique is applied to a simple example with encouraging results.
Angle correction for small animal tumor imaging with spatial frequency domain imaging (SFDI).
Zhao, Yanyu; Tabassum, Syeda; Piracha, Shaheer; Nandhu, Mohan Sobhana; Viapiano, Mariano; Roblyer, Darren
2016-06-01
Spatial frequency domain imaging (SFDI) is a widefield imaging technique that allows for the quantitative extraction of tissue optical properties. SFDI is currently being explored for small animal tumor imaging, but severe imaging artifacts occur for highly curved surfaces (e.g. the tumor edge). We propose a modified Lambertian angle correction, adapted from the Minnaert correction method for satellite imagery, to account for tissue surface angles up to 75°. The method was tested in a hemisphere phantom study as well as a small animal tumor model. The proposed method reduced µa and µs` extraction errors by an average of 64% and 16% respectively compared to performing no angle correction, and provided more physiologically agreeable optical property and chromophore values on tumors. PMID:27375952
Yedvab, Y.; Reiss, I.; Bettan, M.; Harari, R.; Grober, A.; Ettedgui, H.; Caspi, E. N.
2006-07-01
A method for determining delayed neutrons source in the frequency domain based on measuring power oscillations in a non-critical reactor is presented. This method is unique in the sense that the delayed neutrons source is derived from the dynamic behavior of the reactor, which serves as the measurement system. An algorithm for analyzing power oscillation measurements was formulated, which avoids the need for a multi-parameter non-linear fit process used by other methods. Using this algorithm results of two sets of measurements performed in IRR-I and IRR-II (Israeli Research Reactors I and II) are presented. The agreement between measured values from both reactors and calculated values based on Keepin (and JENDL-3.3) group parameters is very good. (authors)
Angle correction for small animal tumor imaging with spatial frequency domain imaging (SFDI)
Zhao, Yanyu; Tabassum, Syeda; Piracha, Shaheer; Nandhu, Mohan Sobhana; Viapiano, Mariano; Roblyer, Darren
2016-01-01
Spatial frequency domain imaging (SFDI) is a widefield imaging technique that allows for the quantitative extraction of tissue optical properties. SFDI is currently being explored for small animal tumor imaging, but severe imaging artifacts occur for highly curved surfaces (e.g. the tumor edge). We propose a modified Lambertian angle correction, adapted from the Minnaert correction method for satellite imagery, to account for tissue surface angles up to 75°. The method was tested in a hemisphere phantom study as well as a small animal tumor model. The proposed method reduced µa and µs` extraction errors by an average of 64% and 16% respectively compared to performing no angle correction, and provided more physiologically agreeable optical property and chromophore values on tumors. PMID:27375952
A look at motion in the frequency domain
NASA Technical Reports Server (NTRS)
Watson, A. B.; Ahumada, A. J., Jr.
1983-01-01
A moving image can be specified by a contrast distribution, c(x,y,t), over the dimensions of space x,y, and time t. Alternatively, it can be specified by the distribution C(u,v,w) over spatial frequency u,v and temporal frequency w. The frequency representation of a moving image is shown to have a characteristic form. This permits two useful observations. The first is that the apparent smoothness of time-sampled moving images (apparent motion) can be explained by the filtering action of the human visual system. This leads to the following formula for the required update rate for time-sampled displays. W(c)=W(l)+ru(l) where w(c) is the required update rate in Hz, W(l) is the limit of human temporal resolution in Hz, r is the velocity of the moving image in degrees/sec, and u(l) is the limit of human spatial resolution in cycles/deg. The second observation is that it is possible to construct a linear sensor that responds to images moving in a particular direction. The sensor is derived and its properties are discussed.
NASA Astrophysics Data System (ADS)
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.
Automated removal of quasiperiodic noise using frequency domain statistics
NASA Astrophysics Data System (ADS)
Sur, Frédéric; Grédiac, Michel
2015-01-01
Digital images may be impaired by periodic or quasiperiodic noise, which manifests itself by spurious long-range repetitive patterns. Most of the time, quasiperiodic noise is well localized in the Fourier domain; thus it can be attenuated by smoothing out the image spectrum with a well-designed notch filter. While existing algorithms require hand-tuned filter design or parameter setting, this paper presents an automated approach based on the expected power spectrum of a natural image. The resulting algorithm enables not only the elimination of simple periodic noise whose influence on the image spectrum is limited to a few Fourier coefficients, but also of quasiperiodic structured noise with a much more complex contribution to the spectrum. Various examples illustrate the efficiency of the proposed algorithm. A comparison with morphological component analysis, a blind source separation algorithm, is also provided. A MATLAB implementation is available.
Sisini, Francesco; Zanca, Federica; Marshall, Nicholas W.; Taibi, Angelo; Cardarelli, Paolo; Bosmans, Hilde
2012-09-15
Purpose: Image quality indices based upon model observers are promising alternatives to laborious human readings of contrast-detail images. This is especially appealing in digital mammography as limiting values for contrast thresholds determine, according to some international protocols, the acceptability of these systems in the radiological practice. The objective of the present study was to compare the signal to noise ratios (SNR) obtained with two nonprewhitening matched filter model observer approaches, one in the spatial domain and the other in the frequency domain, and with both of them worked out for disks as present in the CDMAM phantom. Methods: The analysis was performed using images acquired with the Siemens Novation and Inspiration digital mammography systems. The spatial domain formulation uses a series of high dose CDMAM images as the signal and a routine exposure of two flood images to calculate the covariance matrix. The frequency domain approach uses the mathematical description of a disk and modulation transfer function (MTF) and noise power spectrum (NPS) calculated from images. Results: For both systems most of the SNR values calculated in the frequency domain were in very good agreement with the SNR values calculated in the spatial domain. Both the formulations in the frequency domain and in the spatial domain show a linear relationship between SNR and the diameter of the CDMAM discs. Conclusions: The results suggest that both formulations of the model observer lead to very similar figures of merit. This is a step forward in the adoption of figures of merit based on NPS and MTF for the acceptance testing of mammography systems.
A Unified Frequency Domain Model to Study the Effect of Demyelination on Axonal Conduction.
Chaubey, Saurabh; Goodwin, Shikha J
2016-01-01
Multiple sclerosis is a disease caused by demyelination of nerve fibers. In order to determine the loss of signal with the percentage of demyelination, we need to develop models that can simulate this effect. Existing time-based models does not provide a method to determine the influences of demyelination based on simulation results. Our goal is to develop a system identification approach to generate a transfer function in the frequency domain. The idea is to create a unified modeling approach for neural action potential propagation along the length of an axon containing number of Nodes of Ranvier (N). A system identification approach has been used to identify a transfer function of the classical Hodgkin-Huxley equations for membrane voltage potential. Using this approach, we model cable properties and signal propagation along the length of the axon with N node myelination. MATLAB/Simulink platform is used to analyze an N node-myelinated neuronal axon. The ability to transfer function in the frequency domain will help reduce effort and will give a much more realistic feel when compared to the classical time-based approach. Once a transfer function is identified, the conduction as a cascade of each linear time invariant system-based transfer function can be modeled. Using this approach, future studies can model the loss of myelin in various parts of nervous system. PMID:27103847
Shifting of wrapped phase maps in the frequency domain using a rational number
NASA Astrophysics Data System (ADS)
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 Unified Frequency Domain Model to Study the Effect of Demyelination on Axonal Conduction
Chaubey, Saurabh; Goodwin, Shikha J.
2016-01-01
Multiple sclerosis is a disease caused by demyelination of nerve fibers. In order to determine the loss of signal with the percentage of demyelination, we need to develop models that can simulate this effect. Existing time-based models does not provide a method to determine the influences of demyelination based on simulation results. Our goal is to develop a system identification approach to generate a transfer function in the frequency domain. The idea is to create a unified modeling approach for neural action potential propagation along the length of an axon containing number of Nodes of Ranvier (N). A system identification approach has been used to identify a transfer function of the classical Hodgkin–Huxley equations for membrane voltage potential. Using this approach, we model cable properties and signal propagation along the length of the axon with N node myelination. MATLAB/Simulink platform is used to analyze an N node-myelinated neuronal axon. The ability to transfer function in the frequency domain will help reduce effort and will give a much more realistic feel when compared to the classical time-based approach. Once a transfer function is identified, the conduction as a cascade of each linear time invariant system-based transfer function can be modeled. Using this approach, future studies can model the loss of myelin in various parts of nervous system. PMID:27103847
Template-based CTA X-ray angio rigid registration of coronary arteries in frequency domain
NASA Astrophysics Data System (ADS)
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.
Jeong, Hyok; Lam, Yiu Wai
2012-01-01
The finite difference time domain (FDTD) method is a numerical technique that is straight forward to implement for the simulation of acoustic propagation. For room acoustics applications, the implementation of efficient source excitation and frequency dependent boundary conditions on arbitrary geometry can be seen as two of the most significant problems. This paper deals with the source implementation problem. Among existing source implementation methods, the hard source implementation is the simplest and computationally most efficient. Unfortunately, it generates a large low-frequency modulation in the measured time response. This paper presents a detailed investigation into these side effects. Surprisingly, some of these side effects are found to exist even if a transparent source implementation is used. By combing a time limited approach with a class of more natural source pulse function, this paper develops a source implementation method in FDTD that is as simple and computationally as efficient as a hard source implementation and yet capable of producing results that are virtually the same as a true transparent source. It is believed that the source implementation method developed in this paper will provide an improvement to the practical usability of the FDTD method for room acoustic simulation. PMID:22280589
Method and apparatus for frequency spectrum analysis
NASA Technical Reports Server (NTRS)
Cole, Steven W. (Inventor)
1992-01-01
A method for frequency spectrum analysis of an unknown signal in real-time is discussed. The method is based upon integration of 1-bit samples of signal voltage amplitude corresponding to sine or cosine phases of a controlled center frequency clock which is changed after each integration interval to sweep the frequency range of interest in steps. Integration of samples during each interval is carried out over a number of cycles of the center frequency clock spanning a number of cycles of an input signal to be analyzed. The invention may be used to detect the frequency of at least two signals simultaneously. By using a reference signal of known frequency and voltage amplitude (added to the two signals for parallel processing in the same way, but in a different channel with a sampling at the known frequency and phases of the reference signal), the absolute voltage amplitude of the other two signals may be determined by squaring the sine and cosine integrals of each channel and summing the squares to obtain relative power measurements in all three channels and, from the known voltage amplitude of the reference signal, obtaining an absolute voltage measurement for the other two signals by multiplying the known voltage of the reference signal with the ratio of the relative power of each of the other two signals to the relative power of the reference signal.
NASA Astrophysics Data System (ADS)
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 < 1 Hz, and secondly the Analog To digital Converter (ADC) component had been insufficiently characterized on-ground. These two problems require an exquisite 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.
Botts, Jonathan; Savioja, Lauri
2015-04-01
For time-domain modeling based on the acoustic wave equation, spectral methods have recently demonstrated promise. This letter presents an extension of a spectral domain decomposition approach, previously used to solve the lossless linear wave equation, which accommodates frequency-dependent atmospheric attenuation and assignment of arbitrary dispersion relations. Frequency-dependence is straightforward to assign when time-stepping is done in the spectral domain, so combined losses from molecular relaxation, thermal conductivity, and viscosity can be approximated with little extra computation or storage. A mode update free from numerical dispersion is derived, and the model is confirmed with a numerical experiment.
Frequency-domain identification of aircraft structural modes from short-duration flight tests
NASA Astrophysics Data System (ADS)
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.
Athanasiou, L S; Bourantas, C V; Siogkas, P K; Sakellarios, A I; Exarchos, T P; Naka, K K; Papafaklis, M I; Michalis, L K; Prati, F; Fotiadis, D I
2012-01-01
The aim of this study is to describe a new method for three-dimensional (3D) reconstruction of coronary arteries using Frequency Domain Optical Coherence Tomography (FD-OCT) images. The rationale is to fuse the information about the curvature of the artery, derived from biplane angiographies, with the information regarding the lumen wall, which is produced from the FD-OCT examination. The method is based on a three step approach. In the first step the lumen borders in FD-OCT images are detected. In the second step a 3D curve is produced using the center line of the vessel from the two biplane projections. Finally in the third step the detected lumen borders are placed perpendicularly onto the path based on the centroid of each lumen border. The result is a 3D reconstructed artery produced by all the lumen borders of the FD-OCT pullback representing the 3D arterial geometry of the vessel.
Wavelet-transform-based time-frequency domain reflectometry for reduction of blind spot
NASA Astrophysics Data System (ADS)
Lee, Sin Ho; Park, Jin Bae; Choi, Yoon Ho
2012-06-01
In this paper, wavelet-transform-based time-frequency domain reflectometry (WTFDR) is proposed to reduce the blind spot in reflectometry. TFDR has a blind spot problem when the time delay between the reference signal and the reflected signal is short enough compared with the time duration of the reference signal. To solve the blind spot problem, the wavelet transform (WT) is used because the WT has linearity. Using the characteristics of the WT, the overlapped reference signal at the measured signal can be separated and the blind spot is reduced by obtaining the difference of the wavelet coefficients for the reference and reflected signals. In the proposed method, the complex wavelet is utilized as a mother wavelet because the reference signal in WTFDR has a complex form. Finally, the computer simulations and the real experiments are carried out to confirm the effectiveness and accuracy of the proposed method.
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-01-01
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10−3 m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination. PMID:27146550
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry.
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-05-05
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10(-3) m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination.
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry.
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-01-01
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10(-3) m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination. PMID:27146550
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry
NASA Astrophysics Data System (ADS)
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-05-01
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10‑3 m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination.
Statistics and frequency-domain moveout for multiple-taper receiver functions
NASA Astrophysics Data System (ADS)
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.
High-frequency programmable acoustic wave device realized through ferroelectric domain engineering
Ivry, Yachin E-mail: cd229@eng.cam.ac.uk; Wang, Nan; Durkan, Colm E-mail: cd229@eng.cam.ac.uk
2014-03-31
Surface acoustic wave devices are extensively used in contemporary wireless communication devices. We used atomic force microscopy to form periodic macroscopic ferroelectric domains in sol-gel deposited lead zirconate titanate, where each ferroelectric domain is composed of many crystallites, each of which contains many microscopic ferroelastic domains. We examined the electro-acoustic characteristics of the apparatus and found a resonator behavior similar to that of an equivalent surface or bulk acoustic wave device. We show that the operational frequency of the device can be tailored by altering the periodicity of the engineered domains and demonstrate high-frequency filter behavior (>8 GHz), allowing low-cost programmable high-frequency resonators.
Frequency domain interferometry using the 1290 MHz Soendre Stromfjord radar: First results
NASA Astrophysics Data System (ADS)
Palmer, Robert D.; Larsen, Miguel F.; Heinselman, C. J.; Mikkelsen, I. S.
1993-08-01
First results from the implementation of frequency domain interferometry (FDI) using an L-band frequency of 1290 MHz are presented. The experiment was conducted in September 1991 using the radar facility located in Soendre Stromford, Greenland. The spectra and the correlation functions obtained from the FDI data are compared to previous results at other frequencies. The data show the Soendre Stromford radar is providing reliable wind measurements in the lower atmosphere and that FDI can be implemented at L-band.
Digital Frequency Domain Multiplexer for mm-Wavelength Telescopes
Spieler, Helmuth G; Dobbs, Matt; Bissonnette, Eric; Spieler, Helmuth G.
2007-07-23
An FPGA based digital signal processing (DSP) system for biasing and reading out multiplexed bolometric detectors for mm-wavelength telescopes is presented. This readout system is being deployed for balloon-borne and ground based cosmology experiments with the primary goal of measuring the signature of inflation with the Cosmic Microwave Background Radiation. The system consists of analog superconducting electronics running at 250 mK and 4 K, coupled to digital room temperature backend electronics described here. The digital electronics perform the real time functionality with DSP algorithms implemented in firmware. A soft embedded processor provides all of the slow housekeeping control and communications. Each board in the system synthesizes multi-frequency combs of 8 to 32 carriers in the MHz band to bias the detectors. After the carriers have been modulated with the sky-signal by the detectors, the same boards digitize the comb directly. The carriers are mixed down to base-band and low pass filtered. The signal bandwidth of 0.050Hz-100 Hz places extreme requirements on stability and requires powerful filtering techniques to recover the sky-signal from the MHz carriers.
Measurement of tumor oxygenation using new frequency domain phosphorometers.
Wilson, David F; Vinogradov, Sergei A; Dugan, Benjamin W; Biruski, Dubravko; Waldron, Lee; Evans, Sydney A
2002-05-01
Oxygen dependent quenching of phosphorescence allows for non-invasive measurements of oxygen in tissue. We have designed and constructed a novel multi-frequency instrument for measurement of phosphorescence lifetimes and developed algorithms for determining the distribution of oxygen (oxygen histogram) in the microvasculature of tissue with good temporal resolution (Vinogradov et al., 2002, Compar. Biochem. A, these proceedings). This technology, in combination with a new water soluble near infra red phosphor (Oxyphor G2), was used to examine the oxygenation of subcutaneous Q7 tumors grown on the flank of Buffalo rats and their response to giving the rats oxygen or carbogen to breathe. Phosphorescence was measured using excitation at 635 nm and emission at >700 nm (the phosphorescence maximum is near 800 nm). The excitation and collection light guides were placed on the surface of the skin of the anesthetized animals separated by approximately 0.8 cm. A 6 x 6 or 7 x 7 grid (approx. 4 cm x 4 cm) was drawn on the flank and oxygen histograms were measured in each square, providing 'images' of the oxygen distribution in the tissue. This procedure determines the tissue oxygen distribution at each position in the grid. Regions of relative hypoxia (associated with the tumor) can be readily localized and the extent of hypoxia quantitatively evaluated.
Gimeno, B; Sorolla, E; Anza, S; Vicente, C; Gil, J; Pérez, A M; Boria, V E; Pérez-Soler, F J; Quesada, F; Alvarez, A; Raboso, D
2009-04-01
A technique for the accurate computation of the electromagnetic fields radiated by a charged particle moving within a parallel-plate waveguide is presented. Based on a transformation of the time-varying current density of the particle into a time-harmonic current density, this technique allows the evaluation of the radiated electromagnetic fields both in the frequency and time domains, as well as in the near- and far-field regions. For this purpose, several accelerated versions of the parallel-plate Green's function in the frequency domain have been considered. The theory has been successfully applied to the multipactor discharge occurring within a two metal-plates region. The proposed formulation has been tested with a particle-in-cell code based on the finite-difference time-domain method, obtaining good agreement.
Time-domain simulation of a guitar: model and method.
Derveaux, Grégoire; Chaigne, Antoine; Joly, Patrick; Bécache, Eliane
2003-12-01
This paper presents a three-dimensional time-domain numerical model of the vibration and acoustic radiation from a guitar. The model involves the transverse displacement of the string excited by a force pulse, the flexural motion of the soundboard, and the sound radiation. A specific spectral method is used for solving the Kirchhoff-Love's dynamic top plate model for a damped, heterogeneous orthotropic material. The air-plate interaction is solved with a fictitious domain method, and a conservative scheme is used for the time discretization. Frequency analysis is performed on the simulated sound pressure and plate velocity waveforms in order to evaluate quantitatively the transfer of energy through the various components of the coupled system: from the string to the soundboard and from the soundboard to the air. The effects of some structural changes in soundboard thickness and cavity volume on the produced sounds are presented and discussed. Simulations of the same guitar in three different cases are also performed: "in vacuo," in air with a perfectly rigid top plate, and in air with an elastic top plate. This allows comparisons between structural, acoustic, and structural-acoustic modes of the instrument. Finally, attention is paid to the evolution with time of the spatial pressure field. This shows, in particular, the complex evolution of the directivity pattern in the near field of the instrument, especially during the attack.
Grandchild of the frequency: Decomposition multigrid method
Dendy, J.E. Jr.; Tazartes, C.C.
1994-12-31
Previously the authors considered the frequency decomposition multigrid method and rejected it because it was not robust for problems with discontinuous coefficients. In this paper they show how to modify the method so as to obtain such robustness while retaining robustness for problems with anisotropic coefficients. They also discuss application of this method to a problem arising in global ocean modeling on the CM-5.
Automated frequency domain system identification of a large space structure
NASA Technical Reports Server (NTRS)
Yam, Y.; Bayard, D. S.; Hadaegh, F. Y.; Mettler, E.; Milman, M. H.
1989-01-01
This paper presents the development and experimental results of an automated on-orbit system identification method for large flexible spacecraft that yields estimated quantities to support on-line design and tuning of robust high performance control systems. The procedure consists of applying an input to the plant, obtaining an output, and then conducting nonparametric identification to yield the spectral estimate of the system transfer function. A parametric model is determined by curve fitting the spectral estimate to a rational transfer function. The identification method has been demonstrated experimentally on the Large Spacecraft Control Laboratory in JPL.
Extended radar observations with the frequency radar domain interferometric imaging (FII) technique
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
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.
Efficient 2D and 3D multiparameters frequency-domain full waveform inversion (Invited)
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Lee, Sin Ho; Park, Jin Bae; Choi, Yoon Ho
2013-09-01
In this paper, wavelet-transform-based time-frequency domain reflectometry (WTFDR) is proposed for load impedance measurement. In order to measure the load impedance, the energy of the measured signal in the time-frequency domain, the phase difference between the reference signal and the reflected signal, the characteristic impedance, and the attenuation factor of the measured cable must all be known. Since the complex wavelet transform is composed of real and imaginary parts, the phase difference is easily obtained using the ratio of the real coefficient to the imaginary coefficient. In addition, the wavelet energy denotes the sum of the square of the modulus of the wavelet transform and describes the energy of the measured signal in the time and frequency domains. To accurately determine the characteristic impedance and attenuation factors, the power cable should be estimated as a coaxial cable. Using WTFDR with the complex mother wavelet and the estimated power cable, the load impedance can be obtained simply and accurately. Finally, real experiments for the evaluation of various load impedances are carried out to confirm the effectiveness and accuracy of the proposed method compared to the conventional time-frequency domain reflectometry.
Parallel computation of a domain decomposition method
Chin, R.C.Y.; Hedstrom, G.W.; Scroggs, J.S.; Sorensen, D.C.
1987-01-01
The most easily tractable multiple scale problems are those in which there are only a small number of widely separated groups of scales and the motion on the fastest scales has little influence on the smooth part of the solution. An identifying feature of this class is the presence of regions in which the solution undergoes rapid variation. Such regions are called boundary or internal layers, depending on whether they are located near a boundary or in the interior of the domain. These are the problems which are most natural for multitasking because it makes sense to break up the domain according to the regions of different local behavior. This paper restricts its attention to this class of multiple scale problems.
Weng, Jidong; Tao, Tianjiong; Liu, Shenggang; Ma, Heli; Wang, Xiang; Liu, Cangli; Tan, Hua
2013-11-01
A new optical-fiber frequency domain interferometer (OFDI) device for accurate measurement of the absolute distance between two stationary objects, with centimeter measuring range and nanometer resolution, has been developed. Its working principle and on-line data processing method were elaborated. The new OFDI instrument was constructed all with currently available commercial communication products. It adopted the wide-spectrum amplified spontaneous emission light as the light source and optical-fiber tip as the test probe. Since this device consists of only fibers or fiber coupled components, it is very compact, convenient to operate, and easy to carry. By measuring the single-step length of a translation stage and the thickness of standard gauge blocks, its ability in implementing nanometer resolution and centimeter measuring range on-line measurements was validated.
Compensation of motion artifacts in catheter-based optical frequency domain imaging
Ha, J. Y.; Shishkov, M.; Colice, M.; Oh, W. Y.; Yoo, H.; Liu, L.; Tearney, G. J.; Bouma, B. E.
2010-01-01
A novel heterodyne Doppler interferometer method for compensating motion artifacts caused by cardiac motion in intracoronary optical frequency domain imaging (OFDI) is demonstrated. To track the relative motion of a catheter with regard to the vessel, a motion tracking system is incorporated with a standard OFDI system by using wavelength division multiplexing (WDM) techniques. Without affecting the imaging beam, dual WDM monochromatic beams are utilized for tracking the relative radial and longitudinal velocities of a catheter-based fiber probe. Our results demonstrate that tracking instantaneous velocity can be used to compensate for distortion in the images due to motion artifacts, thus leading to accurate reconstruction and volumetric measurements with catheter-based imaging. PMID:20589002
NASA Astrophysics Data System (ADS)
Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Shi, Yan
2016-06-01
In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effective way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.
Roudot, Philippe; Kervrann, Charles; Blouin, Cedric M; Waharte, Francois
2015-10-01
Fluorescence lifetime is usually defined as the average nanosecond-scale delay between excitation and emission of fluorescence. It has been established that lifetime measurements yield numerous indications on cellular processes such as interprotein and intraprotein mechanisms through fluorescent tagging and Förster resonance energy transfer. In this area, frequency-domain fluorescence lifetime imaging microscopy is particularly appropriate to probe a sample noninvasively and quantify these interactions in living cells. The aim is then to measure the fluorescence lifetime in the sample at each location in space from fluorescence variations observed in a temporal sequence of images obtained by phase modulation of the detection signal. This leads to a sensitivity of lifetime determination to other sources of fluorescence variations such as intracellular motion. In this paper, we propose a robust statistical method for lifetime estimation for both background and small moving structures with a focus on intracellular vesicle trafficking. PMID:26479936
SPECTRON, a neutron noise measurement system in frequency domain
Izarra, G. de; Jammes, C. Destouches, C.; Geslot, B.; Di Salvo, J.
2015-11-15
This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the β{sub eff} parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.
SPECTRON, a neutron noise measurement system in frequency domain.
de Izarra, G; Jammes, C; Geslot, B; Di Salvo, J; Destouches, C
2015-11-01
This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the β(eff) parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON. PMID:26628176
SPECTRON, a neutron noise measurement system in frequency domain
NASA Astrophysics Data System (ADS)
de Izarra, G.; Jammes, C.; Geslot, B.; Di Salvo, J.; Destouches, C.
2015-11-01
This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the βeff parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.
SPECTRON, a neutron noise measurement system in frequency domain.
de Izarra, G; Jammes, C; Geslot, B; Di Salvo, J; Destouches, C
2015-11-01
This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the β(eff) parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.
Frequency-Domain Intravascular Optical Coherence Tomography of the Femoropopliteal Artery
Karnabatidis, Dimitris Katsanos, Konstantinos; Paraskevopoulos, Ioannis; Diamantopoulos, Athanasios; Spiliopoulos, Stavros; Siablis, Dimitris
2011-12-15
Purpose: Optical coherence tomography (OCT) is a catheter-based imaging method that employs near-infrared light to produce high-resolution intravascular images. The authors report the safety and feasibility and illustrate common imaging findings of frequency-domain OCT (FD-OCT) imaging of the femoropopliteal artery in a series of 20 patients who underwent infrainguinal angioplasty. Methods: After crossing the lesion of interest, OCT was performed with a dextrose saline flush technique with simultaneous obstructive manual groin compression. An automatic pullback FD-OCT device was employed (each scan acquiring 54 mm of vessel lumen in 271 consecutive frames). OCT images were acquired before and after balloon dilatation and following provisional stenting if necessary and were evaluated for baseline characteristics of plaque or in-stent restenosis (ISR), vessel wall trauma after angioplasty, presence of thrombus, stent apposition, and tissue prolapse. Imaging follow-up was not included in this study's protocol. Results: Twenty-seven obstructive lesions (18 cases of de novo atherosclerosis and 9 of ISR) of the femoropopliteal artery were imaged and 148 acquisitions were analyzed in total. High-resolution intravascular OCT imaging with effective blood clearance was achieved in 93.9%. Failure was mainly attributed to preocclusive proximal lesions and/or collateral flow. Mixed features of lipid pool areas, calcium deposits, necrotic core, and fibrosis were identified in all of the imaged atherosclerotic lesions, whereas ISR was purely fibrotic. After balloon angioplasty, OCT identified extensive intimal tears in all cases and one case of severe dissection that biplane subtraction angiography failed to identify. Conclusions: Infrainguinal frequency-domain optical coherence tomography is safe and feasible and may provide intravascular high-resolution imaging of the femoropopliteal artery during infrainguinal angioplasty procedures.
NASA Astrophysics Data System (ADS)
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.
User`s guide for the frequency domain algorithms in the LIFE2 fatigue analysis code
Sutherland, H.J.; Linker, R.L.
1993-10-01
The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.
Frequency-domain localization of alpha rhythm in humans via a maximum entropy approach
NASA Astrophysics Data System (ADS)
Patel, Pankaj; Khosla, Deepak; Al-Dayeh, Louai; Singh, Manbir
1997-05-01
Generators of spontaneous human brain activity such as alpha rhythm may be easier and more accurate to localize in frequency-domain than in time-domain since these generators are characterized by a specific frequency range. We carried out a frequency-domain analysis of synchronous alpha sources by generating equivalent potential maps using the Fourier transform of each channel of electro-encephalographic (EEG) recordings. SInce the alpha rhythm recorded by EEG scalp measurements is probably produced by several independent generators, a distributed source imaging approach was considered more appropriate than a model based on a single equivalent current dipole. We used an imaging approach based on a Bayesian maximum entropy technique. Reconstructed sources were superposed on corresponding anatomy form magnetic resonance imaging. Results from human studies suggest that reconstructed sources responsible for alpha rhythm are mainly located in the occipital and parieto- occipital lobes.
Weighted least-squares algorithm for phase unwrapping based on confidence level in frequency domain
NASA Astrophysics Data System (ADS)
Wang, Shaohua; Yu, Jie; Yang, Cankun; Jiao, Shuai; Fan, Jun; Wan, Yanyan
2015-12-01
Phase unwrapping is a key step in InSAR (Synthetic Aperture Radar Interferometry) processing, and its result may directly affect the accuracy of DEM (Digital Elevation Model) and ground deformation. However, the decoherence phenomenon such as shadows and layover, in the area of severe land subsidence where the terrain is steep and the slope changes greatly, will cause error transmission in the differential wrapped phase information, leading to inaccurate unwrapping phase. In order to eliminate the effect of the noise and reduce the effect of less sampling which caused by topographical factors, a weighted least-squares method based on confidence level in frequency domain is used in this study. This method considered to express the terrain slope in the interferogram as the partial phase frequency in range and azimuth direction, then integrated them into the confidence level. The parameter was used as the constraints of the nonlinear least squares phase unwrapping algorithm, to smooth the un-requirements unwrapped phase gradient and improve the accuracy of phase unwrapping. Finally, comparing with interferometric data of the Beijing subsidence area obtained from TerraSAR verifies that the algorithm has higher accuracy and stability than the normal weighted least-square phase unwrapping algorithms, and could consider to terrain factors.
Analysis of stimulated Raman photoacoustics in frequency domain: A feasibility study
NASA Astrophysics Data System (ADS)
Li, Gaoming; Gao, Fei; Feng, Xiaohua; Zheng, Yuanjin
2016-08-01
The frequency domain analysis of stimulated Raman Photoacoustic (PA) induced by laser pulses with Gaussian and rectangular temporal profiles is presented. Utilizing the pulsed laser with nanosecond and microsecond pulse width with Gaussian temporal profile, the frequency component of the PA signals cannot be differentiated between the stimulated Raman PA and the linear optical absorption PA, which is limited by the response bandwidth of biological tissue. When the laser pulses with rectangular temporal profile are used, we deduced the PA expression and numerically derived its frequency spectrum. The frequency components of PA signal induced by the stimulated Raman phonons is more than that induced by optical absorption in some low frequency ranges, which is inside the bandwidth of tissue system. Therefore, stimulated Raman PA signal can be distinguished from the linear optical absorption PA signal in frequency domain. Numerical simulations were conducted in this paper to demonstrate the proposition and feasibility of stimulated Raman PA in frequency domain, which will be experimentally validated in future work.
A frequency-domain channel model and emulator for aeronautical communications
NASA Astrophysics Data System (ADS)
Yang, Xiaopeng; Liang, Jun; Yao, Kun; Shi, Haoshan
2005-11-01
In this paper, we propose a frequency domain simulation structure for aeronautical wideband frequency-selective channel, which features ground-air and air-air wireless links. With appropriate channel parameters, the emulator can model the parking, taxi and en-route scenarios. The wideband frequency-selective channel consists of some parallel sub-channels in frequency domain, which are assumed to be independent to each other and have Rayleigh-distributed envelopes. The sub-channel models and emulators are based on a simple structure and characterized by flat fading. Through such decomposition approach, a frequency domain frequency-selective channel model can be achieved, which is suitable for an implementation of orthogonal frequency-division multiplexing (OFDM) or multi-carrier code-division multi-access (MC-CDMA) channel emulator on computer. Some appropriate emulator parameters have been proposed through channel sounding data collected for different scenarios. Particularly, in order to emulate the time-varying fading model well, the parameter sets are generated from time to time before the simulation with the same statistics.
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%.
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
Gastric Emptying Assessment in Frequency and Time Domain Using Bio-impedance: Preliminary Results
NASA Astrophysics Data System (ADS)
Huerta-Franco, R.; Vargas-Luna, M.; Hernández, E.; Córdova, T.; Sosa, M.; Gutiérrez, G.; Reyes, P.; Mendiola, C.
2006-09-01
The impedance assessment to measure gastric emptying and in general gastric activity has been reported since 1985. The physiological interpretation of these measurements, is still under research. This technique usually uses a single frequency, and the conductivity parameter. The frequency domain and the Fourier analysis of the time domain behavior of the gastric impedance in different gastric conditions (fasting state, and after food administration) has not been explored in detail. This work presents some insights of the potentiality of these alternative methodologies to measure gastric activity.
Real-time frequency-domain fiber optic sensor for intra-arterial blood oxygen measurements
NASA Astrophysics Data System (ADS)
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.
Applying an FSK Based Transmission Scheme to Broadband Channels Using Frequency Domain Equalization
NASA Astrophysics Data System (ADS)
Georgi, Sebastian, Dr.; Peissig, Dr. Jürgen, Prof.
2012-05-01
Equalization of broadband signals can be efficiently realized in frequency domain. One prominent example is the orthogonal frequency division multiplexing (OFDM) transmission technique. With the introduction of a cyclic prefix and a modulation onto orthogonal subcarriers the equalization can be performed in frequency domain with one tap only. However the extremely high peak to average power ratio of OFDM modulated transmit signals and the demand of linearity inside the signal transmission chain results in a poor energy efficiency at the power amplifier. This paper claims, that as long as a cyclic prefix exists, any receive signal can be equalized in frequency domain. In this paper a transmission scheme with constant envelope is chosen for energy efficiency reasons. Therefore an FSK modulation and gaussian pulse shaping is used to create the transmit signal. Equalization at the receiver is done in frequency domain as known in OFDM. To simplify the equalization, a cyclic prefix is added to the transmit signal as well. This transmission scheme is introduced and evaluated in terms of spectral efficiency and bit error rate (BER) performance in this paper. The comparison is done with a typical OFDM system. In particular the characteristics of a nonlinear power amplifier are considered. It will be shown, that signals with constant envelope such as FSK modulated signals can also make use of an OFDM like equalization procedure with comparable BER performance and spectral requirements.
Frequency domain fluorescence lifetime microwell-plate platform for respirometry measurements
NASA Astrophysics Data System (ADS)
Chatni, M. R.; Yale, G.; Van Ryckeghem, A.; Porterfield, D. M.
2010-04-01
Traditionally micro-well plate based platforms used in biology utilize fluorescence intensity based methods to measure processes of biological relevance. However, fluorescence intensity measurements suffer from calibration drift due to a variety of factors. Photobleaching and self-quenching of the fluorescent dyes cause the intensity signal to drop over the lifetime of sensor immobilized inside the well. Variation in turbidity of the sample during the course of the measurement affects the measured fluorescence intensity. In comparison, fluorescence lifetime measurements are not significantly affected by these factors because fluorescence lifetime is a physico-chemical property of the fluorescent dye. Reliable and inexpensive frequency domain fluorescence lifetime instrumentation platforms are possible because the greater tolerance for optical alignment, and because they can be performed using inexpensive light sources such as LEDs. In this paper we report the development of a frequency domain fluorescence lifetime well-plate platform utilizing an oxygen sensitive transition-metal ligand complex fluorophore with a lifetime in the microsecond range. The fluorescence lifetime dye is incorporated in a polymer matrix and immobilized on the base of micro-well of a 60 well micro-well plate. Respiration measurements are performed in both aqueous and non-aqueous environment. Respirometry measurements were recorded from single Daphnia magna egg in hard water. Daphnia is an aquatic organism, important in environmental toxicology as a standard bioassay and early warning indicator for water quality monitoring. Also respirometry measurements were recorded from Tribolium castaneum eggs, which are common pests in the processed flour industry. These eggs were subjected to mitochondrial electron transport chain inhibitor such as potassium cyanide (KCN) and its effects on egg respiration were measured in real-time.
A Frequency Domain Approach for Controlling Fast-Scale Instabilities in Switching Power Converters
NASA Astrophysics Data System (ADS)
Rodriguez, E.; Alarcón, E.; Iu, H. H. C.; El Aroudi, A.
This paper deals with controllers of fast-scale instabilities in DC-DC switching power converters from a frequency domain standpoint with the aim of understanding their working principle and hence simplifying their design. Some approaches for controlling fast-scale instabilities and their limitations are revisited. Considering the frequency domain transfer function of already existing controllers, a simple and extended notch filter centered at half of the switching frequency is proposed to avoid these instabilities. However, a switching converter under this controller may still exhibit the undesired slow-scale instability. Accordingly, the paper explores an alternative approach based on amplifying the harmonic at the switching frequency. Numerical simulations show that the new proposed controller can concurrently improve both fast-scale and slow-scale stability margins. The results from the different controllers are contrasted in terms of stability boundaries, indicating that the last one presents a wider stability range.
NASA Astrophysics Data System (ADS)
Gao, Ping; Collins, Leslie M.; Carin, Lawrence
2000-08-01
Traditionally, field EMI sensors are operated in the time- domain. The time-domain (TD) EMI sensor usually is a pulsed system. It contains both a transmitting coil and a receiving coil. After transmitting an excitation pulse, which generates the primary field, the receiving coil records the secondary field in the late time. Since a TD EMI sensor measures only the late-time responses, the information contained in the early time response is lost thus limiting the types of objects that can be discriminated. Alternatively, EMI sensors can be operated in the frequency- domain (FD). In this case, the excitations are sinusoidal signals and the sensor measures the static response. The advantages and disadvantages of TD and FD EMI sensors are reviewed in this paper. For landmine and UXO detection, discrimination of targets of interest from clutter is required, since the cost of large false alarm rates is substantial amounts of money, labor and time. In order to discriminate targets from clutter, Bayesian optimal classifiers are derived. Traditional detectors for these applications only utilize the energy of the signal at the position under test or the output of a matched world scenario, the depth of the underground objects is uncertain. The optimal classifier that we utilize takes these uncertainties into account also. In this paper, we present classification performance for four metal objects using TD and FD EMI data. Experimental data were taken with the PSS- 12, a standard army issued metal detector, and the GEM-3, a prototype frequency-domain EMI sensor. Although the optimal classifier improves performance for both TD and FD data, FD classification rate are higher than those for TD systems. The theoretical basis for this result is explored.
Nonlinear dynamics of internet congestion control: A frequency-domain approach
NASA Astrophysics Data System (ADS)
Gentile, Franco S.; Moiola, Jorge L.; Paolini, Eduardo E.
2014-04-01
In this paper a fluid-flow model for TCP congestion avoidance combined with different AQM schemes is analyzed. The conditions for the appearance of Hopf bifurcations are stated analytically using frequency-domain techniques. The proposed methodology allows the characterization of the emerging periodic orbits, providing approximations of their amplitude and frequency. In addition, multiple oscillations and limit cycle bifurcations are found via numerical tools.
Flight testing and frequency domain analysis for rotorcraft handling qualities characteristics
NASA Technical Reports Server (NTRS)
Ham, Johnnie A.; Gardner, Charles K.; Tischler, Mark B.
1993-01-01
A demonstration of frequency domain flight testing techniques and analyses was performed on a U.S. Army OH-58D helicopter in support of the OH-58D Airworthiness and Flight Characteristics Evaluation and the Army's development and ongoing review of Aeronautical Design Standard 33C, Handling Qualities Requirements for Military Rotorcraft. Hover and forward flight (60 knots) tests were conducted in 1 flight hour by Army experimental test pilots. Further processing of the hover data generated a complete database of velocity, angular rate, and acceleration frequency responses to control inputs. A joint effort was then undertaken by the Airworthiness Qualification Test Directorate (AQTD) and the U.S. Army Aeroflightdynamics Directorate (AFDD) to derive handling qualities information from the frequency response database. A significant amount of information could be extracted from the frequency domain database using a variety of approaches. This report documents numerous results that have been obtained from the simple frequency domain tests; in many areas, these results provide more insight into the aircraft dynamics that affect handling qualities than to traditional flight tests. The handling qualities results include ADS-33C bandwidth and phase delay calculations, vibration spectral determinations, transfer function models to examine single axis results, and a six degree of freedom fully coupled state space model. The ability of this model to accurately predict aircraft responses was verified using data from pulse inputs. This report also documents the frequency-sweep flight test technique and data analysis used to support the tests.
Frequency-Domain Models for Nonlinear Microwave Devices Based on Large-Signal Measurements
Jargon, Jeffrey A.; DeGroot, Donald C.; Gupta, K. C.
2004-01-01
In this paper, we introduce nonlinear large-signal scattering ( S) parameters, a new type of frequency-domain mapping that relates incident and reflected signals. We present a general form of nonlinear large-signal S-parameters and show that they reduce to classic S-parameters in the absence of nonlinearities. Nonlinear large-signal impedance ( Z) and admittance ( D) parameters are also introduced, and equations relating the different representations are derived. We illustrate how nonlinear large-signal S-parameters can be used as a tool in the design process of a nonlinear circuit, specifically a single-diode 1 GHz frequency-doubler. For the case where a nonlinear model is not readily available, we developed a method of extracting nonlinear large-signal S-parameters obtained with artificial neural network models trained with multiple measurements made by a nonlinear vector network analyzer equipped with two sources. Finally, nonlinear large-signal S-parameters are compared to another form of nonlinear mapping, known as nonlinear scattering functions. The nonlinear large-signal S-parameters are shown to be more general. PMID:27366621
Signal generation and mixing electronics for frequency-domain lifetime and spectral fluorometry
NASA Technical Reports Server (NTRS)
Cruce, Tommy Clay (Inventor); Hallidy, William H. (Inventor); Chin, Robert C. (Inventor)
2007-01-01
The present invention additionally comprises a method and apparatus for generating and mixing signals for frequency-domain lifetime and spectral fluorometry. The present invention comprises a plurality of signal generators that generate a plurality of signals where the signal generators modulate the amplitude and/or the frequency of the signals. The present invention uses one of these signals to drive an excitation signal that the present invention then directs and transmits at a target mixture, which absorbs the energy from the excitation signal. The property of fluorescence causes the target mixture to emit an emitted signal that the present invention detects with a signal detector. The present invention uses a plurality of mixers to produce a processor reference signal and a data signal. The present invention then uses a processor to compare the processor reference signal with the data signal by analyzing the differences in the phase and the differences in the amplitude between the two signals. The processor then extracts the fluorescence lifetime and fluorescence spectrum of the emitted signal from the phase and amplitude information using a chemometric analysis.
Signal generation and mixing electronics for frequency-domain lifetime and spectral fluorometry
NASA Technical Reports Server (NTRS)
Cruce, Tommy C. (Inventor); Hallidy, William H. (Inventor); Chin, Robert C. (Inventor)
1999-01-01
The present invention additionally comprises a method and apparatus for generating and mixing signals for frequency-domain lifetime and spectral fluorometry. The present invention comprises a plurality of signal generators that generate a plurality of signals where the signal generators modulate the amplitude and/or the frequency of the signals. The present invention uses one of these signals to drive an excitation signal that the present invention then directs and transmits at a target mixture, which absorbs the energy from the excitation signal. The property of fluorescence causes the target mixture to emit an emitted signal that the present invention detects with a signal detector. The present invention uses a plurality of mixers to produce a processor reference signal and a data signal. The present invention then uses a processor to compare the processor reference signal with the data signal by analyzing the differences in the phase and the differences in the amplitude between the two signals. The processor then extracts the fluorescence lifetime and fluorescence spectrum of the emitted signal from the phase and amplitude information using a chemometric analysis.
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. PMID:25322248
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.
Hamilton-Jacobi method for curved domain walls and cosmologies
NASA Astrophysics Data System (ADS)
Skenderis, Kostas; Townsend, Paul K.
2006-12-01
We use Hamiltonian methods to study curved domain walls and cosmologies. This leads naturally to first-order equations for all domain walls and cosmologies foliated by slices of maximal symmetry. For Minkowski and AdS-sliced domain walls (flat and closed FLRW cosmologies) we recover a recent result concerning their (pseudo)supersymmetry. We show how domain-wall stability is consistent with the instability of AdS vacua that violate the Breitenlohner-Freedman bound. We also explore the relationship to Hamilton-Jacobi theory and compute the wave-function of a 3-dimensional closed universe evolving towards de Sitter spacetime.
NASA Astrophysics Data System (ADS)
Husa, Sascha; Khan, Sebastian; Hannam, Mark; Pürrer, Michael; Ohme, Frank; Forteza, Xisco Jiménez; Bohé, Alejandro
2016-02-01
In this paper we discuss the anatomy of frequency-domain gravitational-wave signals from nonprecessing black-hole coalescences with the goal of constructing accurate phenomenological waveform models. We first present new numerical-relativity simulations for mass ratios up to 18, including spins. From a comparison of different post-Newtonian approximants with numerical-relativity data we select the uncalibrated SEOBNRv2 model as the most appropriate for the purpose of constructing hybrid post-Newtonian/numerical-relativity waveforms, and we discuss how we prepare time-domain and frequency-domain hybrid data sets. We then use our data together with results in the literature to calibrate simple explicit expressions for the final spin and radiated energy. Equipped with our prediction for the final state we then develop a simple and accurate merger-ringdown model based on modified Lorentzians in the gravitational-wave amplitude and phase, and we discuss a simple method to represent the low frequency signal augmenting the TaylorF2 post-Newtonian approximant with terms corresponding to higher orders in the post-Newtonian expansion. We finally discuss different options for modelling the small intermediate frequency regime between inspiral and merger ringdown. A complete phenomenological model based on the present work is presented in a companion paper [S. Khan et al., following paper, Phys. Rev. D 93 044007 (2016)].
Postural Analysis in Time and Frequency Domains in Patients with Ehlers-Danlos Syndrome
ERIC Educational Resources Information Center
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…
Attenuation-corrected fluorescence extraction for image-guided surgery in spatial frequency domain
Yang, Bin; Sharma, Manu
2013-01-01
Abstract. A new approach to retrieve the attenuation-corrected fluorescence using spatial frequency-domain imaging is demonstrated. Both in vitro and ex vivo experiments showed the technique can compensate for the fluorescence attenuation from tissue absorption and scattering. This approach has potential in molecular image-guided surgery. PMID:23955392
Attenuation-corrected fluorescence extraction for image-guided surgery in spatial frequency domain.
Yang, Bin; Sharma, Manu; Tunnell, James W
2013-08-01
A new approach to retrieve the attenuation-corrected fluorescence using spatial frequency-domain imaging is demonstrated. Both in vitro and ex vivo experiments showed the technique can compensate for the fluorescence attenuation from tissue absorption and scattering. This approach has potential in molecular image-guided surgery. PMID:23955392
NASA Astrophysics Data System (ADS)
Kandaurova, Gerta S.
2002-10-01
Research into the phenomenon of dynamic self-organization and the excited ('anger') state of multidomain magnetic films with perpendicular anisotropy is reviewed. The phenomenon was dicsovered in 1988 when studying the domain structure of iron garnet films in low-frequency (0.1-10 kHz) ac magnetic fields.
Plastique: A synchrotron radiation beamline for time resolved fluorescence in the frequency domain
NASA Astrophysics Data System (ADS)
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.
A hybrid method for identification of structural domains.
Hua, Yongpan; Zhu, Min; Wang, Yuelong; Xie, Zhaoyang; Li, Menglong
2014-01-01
Structural domains in proteins are the basic units to form various proteins. In the protein's evolution and functioning, domains play important roles. But the definition of domain is not yet precisely given, and the update cycle of structural domain databases is long. The automatic algorithms identify domains slowly, while protein entities with great structural complexity are on the rise. Here, we present a method which recognizes the compact and modular segments of polypeptide chains to identify structural domains, and contrast some data sets to illuminate their effect. The method combines support vector machine (SVM) with K-means algorithm. It is faster and more stable than most current algorithms and performs better. It also indicates that when proteins are presented as some Alpha-carbon atoms in 3D space, it is feasible to identify structural domains by the spatially structural properties. We have developed a web-server, which would be helpful in identification of structural domains (http://vis.sculab.org/~huayongpan/cgi-bin/domainAssignment.cgi).
NASA Astrophysics Data System (ADS)
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.
NASA Technical Reports Server (NTRS)
Seidel, R. C.; Lehtinen, B.
1974-01-01
A technique is described for designing feedback control systems using frequency domain models, a quadratic cost function, and a parameter optimization computer program. FORTRAN listings for the computer program are included. The approach is applied to the design of shock position controllers for a supersonic inlet. Deterministic or random system disturbances, and the presence of random measurement noise are considered. The cost function minimization is formulated in the time domain, but the problem solution is obtained using a frequency domain system description. A scaled and constrained conjugate gradient algorithm is used for the minimization. The approach to a supersonic inlet included the calculations of the optimal proportional-plus integral (PI) and proportional-plus-integral-plus-derivative controllers. A single-loop PI controller was the most desirable of the designs considered.
Modeling XV-15 tilt-rotor aircraft dynamics by frequency and time-domain identification techniques
NASA Technical Reports Server (NTRS)
Tischler, Mark B.; Kaletka, Juergen
1986-01-01
Models of the open-loop hover dynamics of the XV-15 Tilt-Rotor Aircraft are extracted from flight data using two approaches: frequency-domain and time-domain identification. Both approaches are reviewed and the identification results are presented and compared in detail. The extracted models compare favorable, with the differences associated mostly with the inherent weighting of each technique. Step responses are used to show that the predictive capability of the models from both techniques is excellent. Based on the results of this study, the relative strengths and weaknesses of the frequency- and time-domain techniques are summarized, and a proposal for a coordinated parameter identification approach is presented.
Domain decomposition methods with applications to fluid dynamics
NASA Astrophysics Data System (ADS)
Kuznetsov, Yu. A.
In this presentation, a brief review of domain decomposition methods with emphasis on the applications to solving elliptic problems arising from the Navier-Stokes equations via operator splitting methods is given. The singularly perturbed convection-diffusion equation is chosen as a model problem. We consider both overlapping (multiplicative and additive Schwarz) and nonoverlapping (Neumann-Dirichlet and Neumann-Neumann) domain decomposition methods. Some convergence results for particular cases are presented.
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.
An Efficient Audio Watermarking Algorithm in Frequency Domain for Copyright Protection
NASA Astrophysics Data System (ADS)
Dhar, Pranab Kumar; Khan, Mohammad Ibrahim; Kim, Cheol-Hong; Kim, Jong-Myon
Digital Watermarking plays an important role for copyright protection of multimedia data. This paper proposes a new watermarking system in frequency domain for copyright protection of digital audio. In our proposed watermarking system, the original audio is segmented into non-overlapping frames. Watermarks are then embedded into the selected prominent peaks in the magnitude spectrum of each frame. Watermarks are extracted by performing the inverse operation of watermark embedding process. Simulation results indicate that the proposed watermarking system is highly robust against various kinds of attacks such as noise addition, cropping, re-sampling, re-quantization, MP3 compression, and low-pass filtering. Our proposed watermarking system outperforms Cox's method in terms of imperceptibility, while keeping comparable robustness with the Cox's method. Our proposed system achieves SNR (signal-to-noise ratio) values ranging from 20 dB to 28 dB, in contrast to Cox's method which achieves SNR values ranging from only 14 dB to 23 dB.
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 crosscorrelation 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.
NASA Astrophysics Data System (ADS)
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.
An implicit and adaptive nonlinear frequency domain approach for periodic viscous flows
NASA Astrophysics Data System (ADS)
Mosahebi, A.; Nadarajah, S.
2014-12-01
An implicit nonlinear Lower-Upper symmetric Gauss-Seidel (LU-SGS) solver has been extended to the adaptive Nonlinear Frequency Domain method (adaptive NLFD) for periodic viscous flows. The discretized equations are linearized in both spatial and temporal directions, yielding an innovative segregate approach, where the effects of the neighboring cells are transferred to the right-hand-side and are updated iteratively. This property of the solver is aligned with the adaptive NLFD concept, in which different cells have different number of modes; hence, should be treated individually. The segregate analysis of the modal equations prevents assembling and inversion of a large left-hand-side matrix, when high number of modes are involved. This is an important characteristic for a selected flow solver of the adaptive NLFD method, where a high modal content may be required in highly unsteady parts of the flow field. The implicit nonlinear LU-SGS solver has demonstrated to be both robust and computationally efficient as the number of modes is increased. The developed solver is thoroughly validated for the laminar vortex shedding behind a stationary cylinder, high angle of attack NACA0012 airfoil, and a plunging NACA0012 airfoil. An order of magnitude improvement in the computational time is observed through the developed implicit approach over the classical modified 5-stage Runge-Kutta method.
Frequency-domain Green's functions for radar waves in heterogeneous 2.5D media
Ellefsen, K.J.; Croize, D.; Mazzella, A.T.; McKenna, J.R.
2009-01-01
Green's functions for radar waves propagating in heterogeneous 2.5D media might be calculated in the frequency domain using a hybrid method. The model is defined in the Cartesian coordinate system, and its electromagnetic properties might vary in the x- and z-directions, but not in the y-direction. Wave propagation in the x- and z-directions is simulated with the finite-difference method, and wave propagation in the y-direction is simulated with an analytic function. The absorbing boundaries on the finite-difference grid are perfectly matched layers that have been modified to make them compatible with the hybrid method. The accuracy of these numerical Greens functions is assessed by comparing them with independently calculated Green's functions. For a homogeneous model, the magnitude errors range from -4.16% through 0.44%, and the phase errors range from -0.06% through 4.86%. For a layered model, the magnitude errors range from -2.60% through 2.06%, and the phase errors range from -0.49% through 2.73%. These numerical Green's functions might be used for forward modeling and full waveform inversion. ?? 2009 Society of Exploration Geophysicists. All rights reserved.
Apparatuses and methods for tuning center frequencies
Wojciechowski, Kenneth; Olsson, Roy H.
2016-02-23
Apparatuses and methods for tuning center frequencies are described herein. Examples of tuning described herein including tuning using feedback from the resonator. Variable gain feedback for tuning of acoustic wave resonators is provided in some examples. An example apparatus may include a resonator and a feedback loop. The resonator may be configured to receive a tuning signal and to provide a feedback signal. The feedback signal may be based on the tuning signal. The feedback loop may be configured to receive the feedback signal from the resonator. The feedback loop further may be configured to provide the tuning signal to actively tune a center frequency of the resonator. The tuning signal may be based on the feedback signal.
Flight-testing and frequency-domain analysis for rotorcraft handling qualities
NASA Technical Reports Server (NTRS)
Ham, Johnnie A.; Gardner, Charles K.; Tischler, Mark B.
1995-01-01
A demonstration of frequency-domain flight-testing techniques and analysis was performed on a U.S. Army OH-58D helicopter in support of the OH-58D Airworthiness and Flight Characteristics Evaluation and of the Army's development and ongoing review of Aeronautical Design Standard 33C, Handling Qualities Requirements for Military Rotorcraft. Hover and forward flight (60 kn) tests were conducted in 1 flight hour by Army experimental test pilots. Further processing of the hover data generated a complete database of velocity, angular-rate, and acceleration-frequency responses to control inputs. A joint effort was then undertaken by the Airworthiness Qualification Test Dirtectorate and the U.S. Army Aeroflightdynamics Directorate to derive handling-quality information from the frequency-domain database using a variety of approaches. This report documents numerous results that have been obtained from the simple frequency-domain tests; in many areas, these results provide more insight into the aircraft dynmamics that affect handling qualities than do traditional flight tests. The handling-quality results include ADS-33C bandwidth and phase-delay calculations, vibration spectral determinations, transfer-function models to examine single-axis results, and a six-degree-of-freedom fully coupled state-space model. The ability of this model to accurately predict responses was verified using data from pulse inputs. This report also documents the frequency-sweep flight-test technique and data analysis used to support the tests.
Frequency domain modeling and dynamic characteristics evaluation of existing wind turbine systems
NASA Astrophysics Data System (ADS)
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.
Tian, Yuan; Han, Yiping; Ai, Xia; Liu, Xiuxiang
2014-12-15
In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.
NASA Astrophysics Data System (ADS)
Tian, Yuan; Ai, Xia; Han, Yiping; Liu, Xiuxiang
2014-12-01
In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.
Zhou, Haiyang; Sun, Yurui; Tyree, Melvin T; Sheng, Wenyi; Cheng, Qiang; Xue, Xuzhang; Schumann, Henrik; Schulze Lammers, Peter
2015-04-01
One role of stems is that of water storage. The water content of stems increases and decreases as xylem water potential increases and decreases, respectively. Hence, a nondestructive method to measure stem water content (StWC) = (volume of water) : (volume of stem), could be useful in monitoring the drought stress status of plants. We introduce a frequency domain inner fringing capacitor-sensor for measuring StWC which operates at 100 MHz frequency. The capacitor-sensor consists of two wave guides (5-mm-wide braided metal) that snugly fit around the surface of a stem with a spacing of 4-5 mm between guides. Laboratory measurements on analog stems reveals that the DC signal output responds linearly to the relative dielectric constant of the analog stem, is most sensitive to water content between the waveguides to a depth of c. 3 mm from the stem surface, and calibrations based on the gravimetric water loss of excised stems of plants revealed a resolution in StWC of < ± 0.001 v/ v. The sensor performed very well on whole plants with a 100-fold increased resolution compared with previous frequency domain and time domain reflectometry methods and, hence, may be very useful for future research requiring nondestructive measurements of whole plants.
NASA Technical Reports Server (NTRS)
Scott, James R.; Atassi, Hafiz M.
1991-01-01
A numerical method is developed for solving periodic, three-dimensional, vortical flows around lifting airfoils in subsonic flow. The first-order method, that is presented, fully accounts for the distortion effects of the nonuniform mean flow on the convected upstream vortical disturbances. The unsteady velocity is split into a vortical component which is a known function of the upstream flow conditions and the Lagrangian coordinates of the mean flow, and an irrotational field whose potential satisfies a nonconstant-coefficient, inhomogeneous, convective wave equation. Using an elliptic coordinate transformation, the unsteady boundary value problem is solved in the frequency domain on grids which are determined as a function of the Mach number and reduced frequency. Extensive comparisons are made with known solutions to unsteady vortical flow problems, and it is seen that the agreement is generally very good for reduced frequencies ranging from 0 up to 4.
Nadeau, Kyle P.; Durkin, Anthony J.; Tromberg, Bruce J.
2014-01-01
Abstract. 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. PMID:24858131
Oganesyan, David L; Vardanyan, Aleksandr O; Oganesyan, G D
2013-06-30
Difference-frequency generation in a GaAs crystal with a periodic domain structure in the field of a few-cycle laser pulse is considered for the case of weakly pronounced material dispersion. The straight-line method is used to solve numerically the system of coupled nonlinear partial differential equations describing the evolution of the electric field of this laser pulse in GaAs crystals with periodic and chirped domain structures. It is shown that application of a GaAs crystal with a chirped domain structure makes it possible to control the frequency-modulation law for a broadband differencefrequency pulse. (nonlinear optical phenomena)
NASA Astrophysics Data System (ADS)
Zhang, Dong; Zhang, Xiaolei; Yuan, Jianzheng; Ke, Rui; Yang, Yan; Hu, Ying
2016-01-01
The Laplace-Fourier domain full waveform inversion can simultaneously restore both the long and intermediate short-wavelength information of velocity models because of its unique characteristics of complex frequencies. This approach solves the problem of conventional frequency-domain waveform inversion in which the inversion result is excessively dependent on the initial model due to the lack of low frequency information in seismic data. Nevertheless, the Laplace-Fourier domain waveform inversion requires substantial computational resources and long computation time because the inversion must be implemented on different combinations of multiple damping constants and multiple frequencies, namely, the complex frequencies, which are much more numerous than the Fourier frequencies. However, if the entire target model is computed on every complex frequency for the Laplace-Fourier domain inversion (as in the conventional frequency domain inversion), excessively redundant computation will occur. In the Laplace-Fourier domain waveform inversion, the maximum depth penetrated by the seismic wave decreases greatly due to the application of exponential damping to the seismic record, especially with use of a larger damping constant. Thus, the depth of the area effectively inverted on a complex frequency tends to be much less than the model depth. In this paper, we propose a method for quantitative estimation of the effective inversion depth in the Laplace-Fourier domain inversion based on the principle of seismic wave propagation and mathematical analysis. According to the estimated effective inversion depth, we can invert and update only the model area above the effective depth for every complex frequency without loss of accuracy in the final inversion result. Thus, redundant computation is eliminated, and the efficiency of the Laplace-Fourier domain waveform inversion can be improved. The proposed method was tested in numerical experiments. The experimental results show that
A multi-domain method for subsonic viscous flows
NASA Technical Reports Server (NTRS)
Chan, Daniel C.; Sindir, Munir M.
1992-01-01
We have developed a Schwarz type domain decomposition method for a pressure base, two- and three-dimensional Navier-Stokes solver. This technique allows one to partition a flow path, which can be characterized by complex geometry and/or complicated flow physics, into smaller sub-domains according to the local geometric simplicity or estimated flow scales. We can, then, sweep the sub-domains in some order and solve the Navier-Stokes equations using as boundary conditions, along the domain interfaces, the Dirichlet conditions which are taken from the most recent update of the solution in the adjacent neighboring domains. With this technique, one can minimize the adverse effects caused by grid skewness and the stiffness problem caused by disparate flow scales. Here, we report the results of a few fundamental flow cases to demonstrate that a judicious use of the multi-domain method can offer a significant convergence acceleration over the traditional one-domain method. This method can be extended to exploit the architecture of a parallel computer to further improve the speed.
NASA Astrophysics Data System (ADS)
Cheng, Yun; Tan, Jun; Liu, Liu; He, Jing; Tang, Jin; Chen, Lin; Zhang, Jun; Li, Qiang; Xiao, Minlei
2016-02-01
To improve the performance of channel estimation (CE), a method of joint frame synchronization and data-aided CE using less training overhead is proposed. A 100-Gb/s polarization-division multiplexing coherent transmission system with quaternary phase-shift keying based on the proposed method is demonstrated by simulation. The simulation results show that the proposed method could achieve accurate timing offset and CE in the presence of strong amplified spontaneous emission noise.
Estimation of Resolution of Shallow Layers by Frequency Domain Airborne Electromagnetic Measurements
NASA Astrophysics Data System (ADS)
Smith, B. D.; Minsley, B. J.; Kass, M. A.; Abraham, J. D.; Sams, J. I.; Veloski, G. A.; Esfahani, A.; Hodges, G.
2012-12-01
Helicopter frequency domain electromagnetic (HFDEM) that were conducted in two very different geoelectrical settings, permafrost and conductive alluvium, have been used to examine and quantify some aspects of the resolution of shallow layers (less than 5 meters). The surveys have used the Resolve system with six frequencies ranging from 400 Hz to 140 kHz. Though most discussion of the resolution of earth resistivity for airborne EM systems has concentrated on estimating the maximum depth of mapping or the resolution of deep layers, there are important applications for mapping shallow layers and it is useful to understand the capabilities and limitations of the HFDEM system in different environments. In permafrost terrains, mapping of the shallow active layer is important in understanding its distribution relative to surface processes such as thermal history, fires and carbon storage as well as in monitoring applications. Here the shallow active layer is a conductor relative to the very resistive permafrost. Mapping shallow layers in alluvial environments has been the focus of a study of subsurface drip irrigation in the Powder River of Wyoming. Here the focus of the HFDEM study has been in mapping the distribution of conductive clays and naturally occurring saline waters. Mapping of shallow layers in alluvial environments is important in agricultural applications to map recharge, soil salinity, and thickness of alluvium. Parameters for layered models (layer resistivity and thickness) have been estimated by inversion methods and the resolution of parameters has been evaluated using stochastic methods and an evaluation of linear estimates of resolution and uncertainty. Statistical estimates of resolution of parameters are compared with estimates from ground surveys.
NASA Astrophysics Data System (ADS)
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).
Frequency-Induced Bulk Magnetic Domain-Wall Freezing Visualized by Neutron Dark-Field Imaging
NASA Astrophysics Data System (ADS)
Betz, B.; Rauscher, P.; Harti, R. P.; Schäfer, R.; Van Swygenhoven, H.; Kaestner, A.; Hovind, J.; Lehmann, E.; Grünzweig, C.
2016-08-01
We use neutron dark-field imaging to visualize and interpret the response of bulk magnetic domain walls to static and dynamic magnetic excitations in (110)-Goss textured iron silicon high-permeability steel alloy. We investigate the domain-wall motion under the influence of an external alternating sinusoidal magnetic field. In particular, we perform scans combining varying levels of dcoffset (0 - 30 A /m ) , oscillation amplitude Aac (0 - 1500 A /m ) , and frequency fac ((0 - 200 Hz ) . By increasing amplitude Aac while maintaining constant values of dcoffset and fac , we record the transition from a frozen domain-wall structure to a mobile one. Vice versa, increasing fac while keeping Aac and dcoffset constant led to the reverse transition from a mobile domain-wall structure into a frozen one. We show that varying both Aac and fac shifts the position of the transition region. Furthermore, we demonstrate that higher frequencies require higher oscillation amplitudes to overcome the freezing phenomena. The fundamental determination and understanding of the frequency-induced freezing process in high-permeability steel alloys is of high interest to the further development of descriptive models for bulk macromagnetic phenomena. Likewise, the efficiency of transformers can be improved based on our results, since these alloys are used as transformer core material.
An adaptive selective frequency damping method
NASA Astrophysics Data System (ADS)
Jordi, Bastien; Cotter, Colin; Sherwin, Spencer
2015-03-01
The selective frequency damping (SFD) method is used to obtain unstable steady-state solutions of dynamical systems. The stability of this method is governed by two parameters that are the control coefficient and the filter width. Convergence is not guaranteed for arbitrary choice of these parameters. Even when the method does converge, the time necessary to reach a steady-state solution may be very long. We present an adaptive SFD method. We show that by modifying the control coefficient and the filter width all along the solver execution, we can reach an optimum convergence rate. This method is based on successive approximations of the dominant eigenvalue of the flow studied. We design a one-dimensional model to select SFD parameters that enable us to control the evolution of the least stable eigenvalue of the system. These parameters are then used for the application of the SFD method to the multi-dimensional flow problem. We apply this adaptive method to a set of classical test cases of computational fluid dynamics and show that the steady-state solutions obtained are similar to what can be found in the literature. Then we apply it to a specific vortex dominated flow (of interest for the automotive industry) whose stability had never been studied before. Seventh Framework Programme of the European Commission - ANADE project under Grant Contract PITN-GA-289428.
Performance analysis of image fusion methods in transform domain
NASA Astrophysics Data System (ADS)
Choi, Yoonsuk; Sharifahmadian, Ershad; Latifi, Shahram
2013-05-01
Image fusion involves merging two or more images in such a way as to retain the most desirable characteristics of each. There are various image fusion methods and they can be classified into three main categories: i) Spatial domain, ii) Transform domain, and iii) Statistical domain. We focus on the transform domain in this paper as spatial domain methods are primitive and statistical domain methods suffer from a significant increase of computational complexity. In the field of image fusion, performance analysis is important since the evaluation result gives valuable information which can be utilized in various applications, such as military, medical imaging, remote sensing, and so on. In this paper, we analyze and compare the performance of fusion methods based on four different transforms: i) wavelet transform, ii) curvelet transform, iii) contourlet transform and iv) nonsubsampled contourlet transform. Fusion framework and scheme are explained in detail, and two different sets of images are used in our experiments. Furthermore, various performance evaluation metrics are adopted to quantitatively analyze the fusion results. The comparison results show that the nonsubsampled contourlet transform method performs better than the other three methods. During the experiments, we also found out that the decomposition level of 3 showed the best fusion performance, and decomposition levels beyond level-3 did not significantly affect the fusion results.
Multipixel system for gigahertz frequency-domain optical imaging of finger joints
NASA Astrophysics Data System (ADS)
Netz, Uwe J.; Beuthan, Jürgen; Hielscher, Andreas H.
2008-03-01
Frequency-domain optical imaging systems have shown great promise for characterizing blood oxygenation, hemodynamics, and other physiological parameters in human and animal tissues. However, most of the frequency domain systems presented so far operate with source modulation frequencies below 150MHz. At these low frequencies, their ability to provide accurate data for small tissue geometries such as encountered in imaging of finger joints or rodents is limited. Here, we present a new system that can provide data up to 1GHz using an intensity modulated charged coupled device camera. After data processing, the images show the two-dimensional distribution of amplitude and phase of the light modulation on the finger surface. The system performance was investigated and test measurements on optical tissue phantoms were taken to investigate whether higher frequencies yield better signal-to-noise ratios (SNRs). It could be shown that local changes in optical tissue properties, as they appear in the initial stages of rheumatoid arthritis in a finger joint, are detectable by simple image evaluation, with the range of modulation frequency around 500MHz proving to yield the highest SNR.
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.
Flight test validation of a frequency-based system identification method on an F-15 aircraft
NASA Technical Reports Server (NTRS)
Schkolnik, Gerard S.; Orme, John S.; Hreha, Mark A.
1995-01-01
A frequency-based performance identification approach was evaluated using flight data from the NASA F-15 Highly Integrated Digital Electronic Control aircraft. The approach used frequency separation to identify the effectiveness of multiple controls simultaneously as an alternative to independent control identification methods. Fourier transformations converted measured control and response data into frequency domain representations. Performance gradients were formed using multiterm frequency matching of control and response frequency domain models. An objective function was generated using these performance gradients. This function was formally optimized to produce a coordinated control trim set. This algorithm was applied to longitudinal acceleration and evaluated using two control effectors: nozzle throat area and inlet first ramp. Three criteria were investigated to validate the approach: simultaneous gradient identification, gradient frequency dependency, and repeatability. This report describes the flight test results. These data demonstrate that the approach can accurately identify performance gradients during simultaneous control excitation independent of excitation frequency.
Inverse polynomial reconstruction method in DCT domain
NASA Astrophysics Data System (ADS)
Dadkhahi, Hamid; Gotchev, Atanas; Egiazarian, Karen
2012-12-01
The discrete cosine transform (DCT) offers superior energy compaction properties for a large class of functions and has been employed as a standard tool in many signal and image processing applications. However, it suffers from spurious behavior in the vicinity of edge discontinuities in piecewise smooth signals. To leverage the sparse representation provided by the DCT, in this article, we derive a framework for the inverse polynomial reconstruction in the DCT expansion. It yields the expansion of a piecewise smooth signal in terms of polynomial coefficients, obtained from the DCT representation of the same signal. Taking advantage of this framework, we show that it is feasible to recover piecewise smooth signals from a relatively small number of DCT coefficients with high accuracy. Furthermore, automatic methods based on minimum description length principle and cross-validation are devised to select the polynomial orders, as a requirement of the inverse polynomial reconstruction method in practical applications. The developed framework can considerably enhance the performance of the DCT in sparse representation of piecewise smooth signals. Numerical results show that denoising and image approximation algorithms based on the proposed framework indicate significant improvements over wavelet counterparts for this class of signals.
Alles, E J; Zhu, Y; van Dongen, K W A; McGough, R J
2012-10-01
The fast nearfield method, when combined with time-space decomposition, is a rapid and accurate approach for calculating transient nearfield pressures generated by ultrasound transducers. However, the standard time-space decomposition approach is only applicable to certain analytical representations of the temporal transducer surface velocity that, when applied to the fast nearfield method, are expressed as a finite sum of products of separate temporal and spatial terms. To extend time-space decomposition such that accelerated transient field simulations are enabled in the nearfield for an arbitrary transducer surface velocity, a new transient simulation method, frequency-domain time-space decomposition (FDTSD), is derived. With this method, the temporal transducer surface velocity is transformed into the frequency domain, and then each complex-valued term is processed separately. Further improvements are achieved by spectral clipping, which reduces the number of terms and the computation time. Trade-offs between speed and accuracy are established for FDTSD calculations, and pressure fields obtained with the FDTSD method for a circular transducer are compared with those obtained with Field II and the impulse response method. The FDTSD approach, when combined with the fast nearfield method and spectral clipping, consistently achieves smaller errors in less time and requires less memory than Field II or the impulse response method.
Alles, E J; Zhu, Y; van Dongen, K W A; McGough, R J
2012-10-01
The fast nearfield method, when combined with time-space decomposition, is a rapid and accurate approach for calculating transient nearfield pressures generated by ultrasound transducers. However, the standard time-space decomposition approach is only applicable to certain analytical representations of the temporal transducer surface velocity that, when applied to the fast nearfield method, are expressed as a finite sum of products of separate temporal and spatial terms. To extend time-space decomposition such that accelerated transient field simulations are enabled in the nearfield for an arbitrary transducer surface velocity, a new transient simulation method, frequency-domain time-space decomposition (FDTSD), is derived. With this method, the temporal transducer surface velocity is transformed into the frequency domain, and then each complex-valued term is processed separately. Further improvements are achieved by spectral clipping, which reduces the number of terms and the computation time. Trade-offs between speed and accuracy are established for FDTSD calculations, and pressure fields obtained with the FDTSD method for a circular transducer are compared with those obtained with Field II and the impulse response method. The FDTSD approach, when combined with the fast nearfield method and spectral clipping, consistently achieves smaller errors in less time and requires less memory than Field II or the impulse response method. PMID:23160476
An Efficient Grid Generation Method for Arbitrary Domains
NASA Astrophysics Data System (ADS)
Orme, Melissa; Huang, Changzheng
1997-11-01
This paper describes an efficient grid generation method for arbitrary or multiply connected domains. Our method, essentially based on the edge swapping techniques, combines the advantages of the Delaunay triangulation method and the advancing front method. The latter two methods are in popular use nowadays. But both suffer some limitations. Delaunay method generates high quality grid but grid may cut across the boundary in concave regions. Advancing front method works for general domain but may encounter difficulties where fronts have to be merged. The current method garantees the boundary integrity and attains the nice Delaunay features into the domain. This is achieved by carefully documenting the grid information so that each edge is readily identified to be inside or outside the domain; and (2) continuously swapping out those bad edges that destroy the Delaunay properties. The computer program built on this method allows users to control the grid density distribution by specifying typical grid sizes on a few chosen points. Interesting examples are demonstrated here. One of them is a circular domain with three letters APS inside. (see figure 1 and figure 2 ). Given a grid size for APS and another size for the circle, the program automatically generates a smooth triangular grid regardless of the complex multiply connected geometry.
High-resolution frequency-domain second-harmonic optical coherence tomography
NASA Astrophysics Data System (ADS)
Su, Jianping; Tomov, Ivan V.; Jiang, Yi; Chen, Zhongping
2007-04-01
We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain second-harmonic optical coherence tomography (SH-OCT) to 12 μm. The acquisition time was shortened by more than 2 orders of magnitude compared to the time-domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon, and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on the SH has been used to obtain polarization resolved images.
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.
An Alternative Realization of Gauss-Newton for Frequency-Domain Acoustic Waveform Inversion
NASA Astrophysics Data System (ADS)
Liu, Y.; Yang, J.; Chi, B.; Dong, L.
2014-12-01
Since FWI was studied under the least-square misfit optimization proposed by Tarantola (1984) in time domain, it has been greatly improved by many researchers. Pratt (1998) developed FWI in frequency domain using a Gauss-Newton optimization. In recent years, FWI has been widely studied under the framework of adjoint-state methods, as summarized by Plessix (2006). Preconditioning and high order gradients are important for FWI. Many researches have focused on the Newton optimization, in which the calculation of inverse Hessian is the key problem. Pseudo Hessian such as the diagonal Hessian was firstly used to approximate inverse Hessian (Choi & Shin, 2007). Then Gauss-Newton or l-BFGS method was widely studied to iteratively calculate the inverse approximate Hessian Haor full Hessian (Sheen et al., 2006). Full Hessian is the base of the exact Newton optimization. Fichtner and Trampert (2011) presented an extension of the adjoint-state method to directly compute the full Hessian; Métivier et al. (2012) proposed a general second-order adjoint-state formula for Hessian-vector product to tackle Gauss-Newton and exact Newton. Liu et al. (2014) proposed a matrix-decomposition FWI (MDFWI) based on Born kernel. They used the Born Fréchet kernel to explicitly calculate the gradient of the objective function through matrix decomposition, no full Fréchet kernel being stored in memory beforehand. However, they didn't give a method to calculate the Gauss-Newton. In this paper, We propose a method based on Born Fréchet kernel to calculate the Gauss-Newton for acoustic full waveform inversion (FWI). The Gauss-Newton is iteratively constructed without needing to store the huge approximate Hessian (Ha) or Fréchet kernel beforehand, and the inverse of Ha is not need to be calculated either. This procedure can be efficiently accomplished through matrix decomposition. More resolved result and faster convergence are obtained when this Gauss-Newton is applied in FWI based on the Born
NASA Astrophysics Data System (ADS)
Damour, Thibault; Nagar, Alessandro; Trias, Miquel
2011-01-01
The coalescences of binary black hole systems, here taken to be nonspinning, are among the most promising sources for gravitational wave (GW) ground-based detectors, such as LIGO and Virgo. To detect the GW signals emitted by binary black holes and measure the parameters of the source, one needs to have in hand a bank of GW templates that are both effectual (for detection) and accurate (for measurement). We study the effectualness and the accuracy of the two types of parametrized banks of templates that are directly defined in the frequency domain by means of closed-form expressions, namely, “post-Newtonian” (PN) and “phenomenological” models. In the absence of knowledge of the (continuous family of) exact waveforms, our study assumes as fiducial, target waveforms the ones generated by the most accurate version of the effective-one-body formalism, calibrated upon a few high-accuracy numerical-relativity (NR) waveforms. We find that, for initial GW detectors the use, at each point of parameter space, of the best closed-form template (among PN and phenomenological models) leads to an effectualness >97% over the entire mass range and >99% in an important fraction of parameter space; however, when considering advanced detectors, both of the closed-form frequency-domain models fail to be effectual enough in significant domains of the two-dimensional [total mass and mass ratio] parameter space. Moreover, we find that, for both initial and advanced detectors, the two closed-form frequency-domain models fail to satisfy the minimal required accuracy standard in a very large domain of the two-dimensional parameter space. In addition, a side result of our study is the determination, as a function of the mass ratio, of the maximum frequency at which a frequency-domain PN waveform can be “joined” onto a NR-calibrated effective-one-body waveform without undue loss of accuracy. In the case of mass ratios larger than 4∶1 this maximum frequency occurs well before the
Resonant frequency method for bearing ball inspection
Khuri-Yakub, B. T.; Hsieh, Chung-Kao
1993-01-01
The present invention provides for an inspection system and method for detecting defects in test objects which includes means for generating expansion inducing energy focused upon the test object at a first location, such expansion being allowed to contract, thereby causing pressure wave within and on the surface of the test object. Such expansion inducing energy may be provided by, for example, a laser beam or ultrasonic energy. At a second location, the amplitudes and phases of the acoustic waves are detected and the resonant frequencies' quality factors are calculated and compared to predetermined quality factor data, such comparison providing information of whether the test object contains a defect. The inspection system and method also includes means for mounting the bearing ball for inspection.
NASA Astrophysics Data System (ADS)
Jiménez, Noé; Camarena, Francisco; Redondo, Javier; Sánchez-Morcillo, Víctor; Konofagou, Elisa E.
2015-10-01
We report a numerical method for solving the constitutive relations of nonlinear acoustics, where multiple relaxation processes are included in a generalized formulation that allows the time-domain numerical solution by an explicit finite differences scheme. Thus, the proposed physical model overcomes the limitations of the one-way Khokhlov-Zabolotskaya-Kuznetsov (KZK) type models and, due to the Lagrangian density is implicitly included in the calculation, the proposed method also overcomes the limitations of Westervelt equation in complex configurations for medical ultrasound. In order to model frequency power law attenuation and dispersion, such as observed in biological media, the relaxation parameters are fitted to both exact frequency power law attenuation/dispersion media and also empirically measured attenuation of a variety of tissues that does not fit an exact power law. Finally, a computational technique based on artificial relaxation is included to correct the non-negligible numerical dispersion of the finite difference scheme, and, on the other hand, improve stability trough artificial attenuation when shock waves are present. This technique avoids the use of high-order finite-differences schemes leading to fast calculations. The present algorithm is especially suited for practical configuration where spatial discontinuities are present in the domain (e.g. axisymmetric domains or zero normal velocity boundary conditions in general). The accuracy of the method is discussed by comparing the proposed simulation solutions to one dimensional analytical and k-space numerical solutions.
Item Selection Methods for the Adolescent Domain Screening Inventory
ERIC Educational Resources Information Center
Corrigan, Matthew J.
2009-01-01
Objective: The purpose of this article is to describe the method of item selection tested in the development of the Adolescent Domain Screening Inventory. Method: The convenience sampling frame used for these analyses consisted of 26,781 Communities That Care Youth Surveys. The three item selection methods were used to assess known instrument,…
Regner, K T; Majumdar, S; Malen, J A
2013-06-01
This paper describes the instrumentation for broadband frequency domain thermoreflectance (BB-FDTR), a novel, continuous wave laser technique for measuring the thermal conductivity accumulation function. The thermal conductivity accumulation function describes cumulative contributions to the bulk thermal conductivity of a material from energy carriers with different mean free paths. It can be used to map reductions in thermal conductivity in nano-devices, which arise when the dimensions of the device are commensurate to the mean free path of energy carriers. BB-FDTR uses high frequency surface temperature modulation to generate non-diffusive phonon transport realized through a reduction in the perceived thermal conductivity. By controlling the modulation frequency it is possible to reconstruct the thermal conductivity accumulation function. A unique heterodyning technique is used to down-convert the signal, therein improving our signal to noise ratio and enabling results over a broader range of modulation frequencies (200 kHz-200 MHz) and hence mean free paths.
A Domain Decomposition Parallelization of the Fast Marching Method
NASA Technical Reports Server (NTRS)
Herrmann, M.
2003-01-01
In this paper, the first domain decomposition parallelization of the Fast Marching Method for level sets has been presented. Parallel speedup has been demonstrated in both the optimal and non-optimal domain decomposition case. The parallel performance of the proposed method is strongly dependent on load balancing separately the number of nodes on each side of the interface. A load imbalance of nodes on either side of the domain leads to an increase in communication and rollback operations. Furthermore, the amount of inter-domain communication can be reduced by aligning the inter-domain boundaries with the interface normal vectors. In the case of optimal load balancing and aligned inter-domain boundaries, the proposed parallel FMM algorithm is highly efficient, reaching efficiency factors of up to 0.98. Future work will focus on the extension of the proposed parallel algorithm to higher order accuracy. Also, to further enhance parallel performance, the coupling of the domain decomposition parallelization to the G(sub 0)-based parallelization will be investigated.
Full frequency-dependent phase-domain modelling of transmission lines and corona phenomena
NASA Astrophysics Data System (ADS)
Castellanos, Fernando
This thesis presents two main developments in the modelling of power transmission lines for the simulation of electric networks. The first one is wide bandwidth circuit corona model and the second a phase-domain multiphase full frequency-dependent line model. The latter can be easily used in connection with the former. Both models have been developed for implementation in time domain simulation computer programs, such as the ElectroMagnetic Transients Program (EMTP). Corona in overhead transmission lines is a highly nonlinear and non deterministic phenomenon. Circuit models have been developed in the past to represent its behaviour, but the response of these models is usually limited to a narrow band of frequencies. The corona model presented in this thesis overcomes this problem by: (1) matching closely the topology of the circuit to the topology of the physical system, and (2) duplicating the high-order dynamic response of the phenomenon with a high-order transient circuit response. The resulting model is valid for a wide range of frequencies and is able to represent waveshapes from switching to lightning surges. A unique set of model parameters can be obtained directly from test-cage measurements, and the same set can be used directly for an arbitrary overhead line configuration. The model uses only standard EMTP circuit elements and requires no iterations. Simulations of corona charge-voltage (q-v) curves and of travelling surges were performed and compared to existing field test measurements. The proposed new transmission line model (z-line) can be used for the representation of multicircuit transmission lines in time-domain transient solutions. The model includes a full representation of the frequency-dependent line parameters and is formulated directly in phase coordinates. The solution in phase coordinates, as opposed to modal coordinates, avoids the problems associated with the representation of the frequency-dependent transformation matrices that relate
Clinical skin imaging using color spatial frequency domain imaging (Conference Presentation)
NASA Astrophysics Data System (ADS)
Yang, Bin; Lesicko, John; Moy, Austin J.; Reichenberg, Jason; Tunnell, James W.
2016-02-01
Skin diseases are typically associated with underlying biochemical and structural changes compared with normal tissues, which alter the optical properties of the skin lesions, such as tissue absorption and scattering. Although widely used in dermatology clinics, conventional dermatoscopes don't have the ability to selectively image tissue absorption and scattering, which may limit its diagnostic power. Here we report a novel clinical skin imaging technique called color spatial frequency domain imaging (cSFDI) which enhances contrast by rendering color spatial frequency domain (SFD) image at high spatial frequency. Moreover, by tuning spatial frequency, we can obtain both absorption weighted and scattering weighted images. We developed a handheld imaging system specifically for clinical skin imaging. The flexible configuration of the system allows for better access to skin lesions in hard-to-reach regions. A total of 48 lesions from 31 patients were imaged under 470nm, 530nm and 655nm illumination at a spatial frequency of 0.6mm^(-1). The SFD reflectance images at 470nm, 530nm and 655nm were assigned to blue (B), green (G) and red (R) channels to render a color SFD image. Our results indicated that color SFD images at f=0.6mm-1 revealed properties that were not seen in standard color images. Structural features were enhanced and absorption features were reduced, which helped to identify the sources of the contrast. This imaging technique provides additional insights into skin lesions and may better assist clinical diagnosis.
NASA Astrophysics Data System (ADS)
Takahashi, Ryosuke; Okajima, Takaharu
2016-08-01
We investigated how stress relaxation mapping is quantified compared with the force modulation mapping of confluent epithelial cells using atomic force microscopy (AFM). Using a multi-frequency AFM technique, we estimated the power-law rheological behaviors of cells simultaneously in time and frequency domains. When the power-law exponent α was low (<0.1), the α values were almost the same in time and frequency domains. On the other hand, we found that at the high values (α > 0.1), α in the time domain was underestimated relative to that in the frequency domain, and the difference increased with α, whereas the cell modulus was overestimated in the time domain. These results indicate that power-law rheological parameters estimated by stress relaxation are sensitive to lag time during initial indentation, which is inevitable in time-domain AFM experiments.
NASA Astrophysics Data System (ADS)
Applegate, Matthew B.; Hariri, Lida P.; Beagle, John; Tan, Khay Ming; Chee, Chunmin; Hales, Charles A.; Suter, Melissa J.
2012-02-01
Smoke inhalation injury is a serious threat to victims of fires and explosions, however accurate diagnosis of patients remains problematic. Current evaluation techniques are highly subjective, often involving the integration of clinical findings with bronchoscopic assessment. It is apparent that new quantitative methods for evaluating the airways of patients at risk of inhalation injury are needed. Optical frequency domain imaging (OFDI) is a high resolution optical imaging modality that enables volumetric microscopy of the trachea and upper airways in vivo. We anticipate that OFDI may be a useful tool in accurately assessing the airways of patients at risk of smoke inhalation injury by detecting injury prior to the onset of symptoms, and therefore guiding patient management. To demonstrate the potential of OFDI for evaluating smoke inhalation injury, we conducted a preclinical study in which we imaged the trachea/upper airways of 4 sheep prior to, and up to 60 minutes post exposure to cooled cotton smoke. OFDI enabled the visualization of increased mucus accumulation, mucosal thickening, epithelial disruption and sloughing, and increased submucosal signal intensity attributed to polymorphonuclear infiltrates. These results were consistent with histopathology findings. Bronchoscopic inspection of the upper airways appeared relatively normal with only mild accumulation of mucus visible within the airway lumen. The ability of OFDI to not only accurately detect smoke inhalation injury, but to quantitatively assess and monitor the progression or healing of the injury over time may provide new insights into the management of patients such as guiding clinical decisions regarding the need for intubation and ventilator support.
Empirical frequency domain model for fixed-pattern noise in infrared focal plane arrays
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
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.
Frequency domain synthesis of optimal inputs for adaptive identification and control
NASA Technical Reports Server (NTRS)
Fu, Li-Chen; Sastry, Shankar
1987-01-01
The input design problem of selecting appropriate inputs for use in SISO adaptive identification and model reference adaptive control algorithms is considered. Averaging theory is used to characterize the optimal inputs in the frequency domain. The design problem is formulated as an optimization problem which maximizes the smallest eigenvalue of the average information matrix over power constrained signals, and the global optimal solution is obtained using a convergent numerical algorithm. A bound on the frequency search range required in the design algorithm has been determined in terms of the desired performance.
High speed 3D endoscopic optical frequency domain imaging probe for lung cancer diagnosis
NASA Astrophysics Data System (ADS)
Li, Jianan; Feroldi, Fabio; Mo, Jianhua; Helderman, Frank; de Groot, Mattijs; de Boer, Johannes F.
2013-06-01
We present a miniature motorized endoscopic probe for Optical Frequency Domain Imaging with an outer diameter of 1.65 mm and a rotation speed of 3,000 - 12,500 rpm. The probe has a motorized distal end which provides a significant advantage over proximally driven probes since it does not require a drive shaft to transfer the rotational torque to the distal end of the probe and functions without a fiber rotary junction. The probe has a focal Full Width at Half Maximum of 9.6 μm and a working distance of 0.47 mm. We analyzed the non-uniform rotation distortion and found a location fluctuation of only 1.87° in repeated measurements of the same object. The probe was integrated in a high-speed Optical Frequency Domain Imaging setup at 1310 nm. We demonstrated its performance with imaging ex vivo pig bronchial and in vivo goat lung.
Multi-frequency communication system and method
Carrender, Curtis Lee; Gilbert, Ronald W.
2004-06-01
A multi-frequency RFID remote communication system is provided that includes a plurality of RFID tags configured to receive a first signal and to return a second signal, the second signal having a first frequency component and a second frequency component, the second frequency component including data unique to each remote RFID tag. The system further includes a reader configured to transmit an interrogation signal and to receive remote signals from the tags. A first signal processor, preferably a mixer, removes an intermediate frequency component from the received signal, and a second processor, preferably a second mixer, analyzes the IF frequency component to output data that is unique to each remote tag.
Characterization of nonmelanoma skin cancer for light therapy using spatial frequency domain imaging
Rohrbach, Daniel J.; Zeitouni, Nathalie C.; Muffoletto, Daniel; Saager, Rolf; Tromberg, Bruce J.; Sunar, Ulas
2015-01-01
The dosimetry of light-based therapies critically depends on both optical and vascular parameters. We utilized spatial frequency domain imaging to quantify optical and vascular parameters, as well as estimated light penetration depth from 17 nonmelanoma skin cancer patients. Our data indicates that there exist substantial spatial variations in these parameters. Characterization of these parameters may inform understanding and optimization of the clinical response of light-based therapies. PMID:26137378
Nonuniform strain measurement in composite material based on optical frequency domain reflection
NASA Astrophysics Data System (ADS)
Li, Huajun; Zhang, Dongsheng; Li, Litong; Wu, Mengqi; Wen, Xiaoyan
2016-06-01
Traditional electrical sensor or traditional fiber Bragg grating sensing technology is not applicable to the measurement of nonuniform strain in composite material. Therefore, the distributed nonuniform strain in the lap plate position of composite interlining material is measured using a single fiber with optical frequency domain reflection technology in this study. The experimental results show consistency with the experiment phenomena, and the measurement accuracy could be increased to the submillimeter level.
Full field frequency domain common path optical coherence tomography with annular aperture
NASA Astrophysics Data System (ADS)
Abdulhalim, I.; Friedman, Ron; Liraz, Lior; Dadon, Ronen
2007-07-01
Theoretical and experimental results are presented using the common path Mirau interference microscope and using the Linnik microscope with annular masks to increase the depth of field. The competence between the spatial and temporal coherence was investigated theoretically and confirmed experimentally. Phase imaging of onion epidermis cells was presented showing the possibility of obtaining profiles of the cells. Frequency domain OCT was shown to be possible using full field setup.
Kim, Sang-Yoon; Lim, Woochang
2015-08-01
We are interested in characterization of synchronization transitions of bursting neurons in the frequency domain. Instantaneous population firing rate (IPFR) [Formula: see text], which is directly obtained from the raster plot of neural spikes, is often used as a realistic collective quantity describing population activities in both the computational and the experimental neuroscience. For the case of spiking neurons, a realistic time-domain order parameter, based on [Formula: see text], was introduced in our recent work to characterize the spike synchronization transition. Unlike the case of spiking neurons, the IPFR [Formula: see text] of bursting neurons exhibits population behaviors with both the slow bursting and the fast spiking timescales. For our aim, we decompose the IPFR [Formula: see text] into the instantaneous population bursting rate [Formula: see text] (describing the bursting behavior) and the instantaneous population spike rate [Formula: see text] (describing the spiking behavior) via frequency filtering, and extend the realistic order parameter to the case of bursting neurons. Thus, we develop the frequency-domain bursting and spiking order parameters which are just the bursting and spiking "coherence factors" [Formula: see text] and [Formula: see text] of the bursting and spiking peaks in the power spectral densities of [Formula: see text] and [Formula: see text] (i.e., "signal to noise" ratio of the spectral peak height and its relative width). Through calculation of [Formula: see text] and [Formula: see text], we obtain the bursting and spiking thresholds beyond which the burst and spike synchronizations break up, respectively. Consequently, it is shown in explicit examples that the frequency-domain bursting and spiking order parameters may be usefully used for characterization of the bursting and the spiking transitions, respectively.
NASA Astrophysics Data System (ADS)
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.
Frequency Domain Fluorescent Molecular Tomography and Molecular Probes for Small Animal Imaging
NASA Astrophysics Data System (ADS)
Kujala, Naresh Gandhi
Fluorescent molecular tomography (FMT) is a noninvasive biomedical optical imaging that enables 3-dimensional quantitative determination of fluorochromes distributed in biological tissues. There are three methods for imaging large volume tissues based on different light sources: (a) using a light source of constant intensity, through a continuous or constant wave, (b) using a light source that is intensity modulated with a radio frequency (RF), and (c) using ultrafast pulses in the femtosecond range. In this study, we have developed a frequency domain fluorescent molecular tomographic system based on the heterodyne technique, using a single source and detector pair that can be used for small animal imaging. In our system, the intensity of the laser source is modulated with a RF frequency to produce a diffuse photon density wave in the tissue. The phase of the diffuse photon density wave is measured by comparing the reference signal with the signal from the tissue using a phasemeter. The data acquisition was performed by using a Labview program. The results suggest that we can measure the phase change from the heterogeneous inside tissue. Combined with fiber optics and filter sets, the system can be used to sensitively image the targeted fluorescent molecular probes, allowing the detection of cancer at an early stage. We used the system to detect the tumor-targeting molecular probe Alexa Fluor 680 and Alexa Fluor 750 bombesin peptide conjugates in phantoms as well as mouse tissues. We also developed and evaluated fluorescent Bombesin (BBN) probes to target gastrin-releasing peptide (GRP) receptors for optical molecular imaging. GRP receptors are over-expressed in several types of human cancer cells, including breast, prostate, small cell lung, and pancreatic cancers. BBN is a 14 amino acid peptide that is an analogue to human gastrin-releasing peptide that binds specifically to GRPr receptors. BBN conjugates are significant in cancer detection and therapy. The
Laser noise measurement techniques and applications of femtosecond encoding in the frequency domain
NASA Astrophysics Data System (ADS)
Scott, Ryan Patrick
This dissertation investigates mode-locked laser noise measurement techniques, the concept and measurement of a laser's noise transfer function, and then two applications of spectral encoding of optical pulses. The one application is optical code division multiple access (O-CDMA) and the other is optical arbitrary waveform generation (OAWG). The relationship between source stability, encoding, and overall system performance in O-CDMA is also discussed. Techniques for making sensitive and high-dynamic-range measurements of laser amplitude and envelope phase noise (timing jitter) in the frequency domain at the shot-noise limit are described. The short term stability of a Kerr-lens modelocked (KLM) Ti:sapphire laser is shown to be close to that of the precision crystal oscillators used in its characterization. The amplitude and envelope phase noise of a KLM Ti:sapphire laser are shown to depend directly on the pump laser amplitude stability. The sensitivity of this process is described by a noise transfer function (NTF) which represents the magnitude of the amplitude-to-amplitude modulation and amplitude-to-phase modulation conversion gain of the pump-induced amplitude and phase noise, respectively. A spectral phase-encoded time-spreading (SPECTS) O-CDMA testbed is described. The testbed employs a fiber-pigtailed, bulk-optics arrangement that utilizes a two-dimensional spatial light phase modulator for encoding multiple channels. The time-gated SPECTS O-CDMA receiver is composed of a nonlinear optical loop mirror (NOLM) and a nonlinear thresholder Experimentally measured performance is compared to numerical simulations. Finally, an optical frequency comb with 20-GHz spacing is shaped by an integrated silica arrayed-waveguide grating (AWG) pair to produce optical waveforms with high fidelity. Characterization of both the intensity and phase of the crafted opitical fields is accomplished with cross-correlation frequency-resolved optical gating (XFROG) which has been
Domain identification in impedance computed tomography by spline collocation method
NASA Technical Reports Server (NTRS)
Kojima, Fumio
1990-01-01
A method for estimating an unknown domain in elliptic boundary value problems is considered. The problem is formulated as an inverse problem of integral equations of the second kind. A computational method is developed using a splice collocation scheme. The results can be applied to the inverse problem of impedance computed tomography (ICT) for image reconstruction.
Time and Frequency-Domain Cross-Verification of SLS 6DOF Trajectory Simulations
NASA Technical Reports Server (NTRS)
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
NASA Astrophysics Data System (ADS)
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.
Embedding multiple watermarks in the DFT domain using low- and high-frequency bands
NASA Astrophysics Data System (ADS)
Ganic, Emir; Dexter, Scott D.; Eskicioglu, Ahmet M.
2005-03-01
Although semi-blind and blind watermarking schemes based on Discrete Cosine Transform (DCT) or Discrete Wavelet Transform (DWT) are robust to a number of attacks, they fail in the presence of geometric attacks such as rotation, scaling, and translation. The Discrete Fourier Transform (DFT) of a real image is conjugate symmetric, resulting in a symmetric DFT spectrum. Because of this property, the popularity of DFT-based watermarking has increased in the last few years. In a recent paper, we generalized a circular watermarking idea to embed multiple watermarks in lower and higher frequencies. Nevertheless, a circular watermark is visible in the DFT domain, providing a potential hacker with valuable information about the location of the watermark. In this paper, our focus is on embedding multiple watermarks that are not visible in the DFT domain. Using several frequency bands increases the overall robustness of the proposed watermarking scheme. Specifically, our experiments show that the watermark embedded in lower frequencies is robust to one set of attacks, and the watermark embedded in higher frequencies is robust to a different set of attacks.
A compact frequency domain fluorometer with a directly modulated deuterium light source
NASA Astrophysics Data System (ADS)
Morgan, C. G.; Hua, Y.; Mitchell, A. K.; Murray, J. G.; Boardman, A. D.
1996-01-01
A phase fluorometer based on a low-cost and versatile high-frequency modulated light source and a fast gain-modulated photomultiplier is described. The apparatus is particularly well-suited to high-sensitivity frequency-domain fluorescence measurements requiring ultraviolet excitation. The system is very compact since it features a directly modulated light source, a miniature photomultiplier tube, and an rf synthesizer on a PC board. Equipped with a suitable fiber optic probe sensor, the device has potential as a portable unit for a wide range of remote sensing applications. The lamp can be modulated at frequencies up to 120 MHz and the phase fluorometer has been tested at up to 70 MHz with a range of fluorescent lifetime standards containing quinine sulfate quenched with sodium chloride.
NASA Technical Reports Server (NTRS)
Liang, Steven Y.; Dornfeld, David A.; Nickerson, Jackson A.
1987-01-01
The coloring effect on the acoustic emission signal due to the frequency response of the data acquisition/processing instrumentation may bias the interpretation of AE signal characteristics. In this paper, a frequency domain deconvolution technique, which involves the identification of the instrumentation transfer functions and multiplication of the AE signal spectrum by the inverse of these system functions, has been carried out. In this way, the change in AE signal characteristics can be better interpreted as the result of the change in only the states of the process. Punch stretching process was used as an example to demonstrate the application of the technique. Results showed that, through the deconvolution, the frequency characteristics of AE signals generated during the stretching became more distinctive and can be more effectively used as tools for process monitoring.
Tian, Hua; Luo, Shiqiang; Zhang, Rui; Yang, Gang; Huang, Hua
2009-12-01
Frequency-domain electricity properties of four objects, including bullfrog skin, bullfrog muscle, triply distilled water and 0.9% NaCl, were tested in the range of 100Hz-10MHz using home-made electrode and measuring system. The experimental results showed that the resistance of 0.9% NaCl decreased dramatically, that the amplitude frequency characteristics of bullfrog's muscle and skin were similar, but that of triply distilled water did not change significantly. The frequency dependence of 0.9% NaCl showed that the electrode had great influence on the measuring system, so a new equivalent circuit model based on the electrode system was needed. These findings suggest that the new five-parameter equivalent circuit model, which embodies considerations on the interaction between electrodes and tissues, is a reasonable equivalent circuit for studying the electrical characteristics of biological materials.
NASA Technical Reports Server (NTRS)
Eren, K.
1980-01-01
The mathematical background in spectral analysis as applied to geodetic applications is summarized. The resolution (cut-off frequency) of the GEOS 3 altimeter data is examined by determining the shortest wavelength (corresponding to the cut-off frequency) recoverable. The data from some 18 profiles are used. The total power (variance) in the sea surface topography with respect to the reference ellipsoid as well as with respect to the GEM-9 surface is computed. A fast inversion algorithm for matrices of simple and block Toeplitz matrices and its application to least squares collocation is explained. This algorithm yields a considerable gain in computer time and storage in comparison with conventional least squares collocation. Frequency domain least squares collocation techniques are also introduced and applied to estimating gravity anomalies from GEOS 3 altimeter data. These techniques substantially reduce the computer time and requirements in storage associated with the conventional least squares collocation. Numerical examples given demonstrate the efficiency and speed of these techniques.
An improved scattering-integral approach for frequency-domain full waveform inversion
NASA Astrophysics Data System (ADS)
Liu, Yuzhu; Yang, Jizhong; Chi, Benxin; Dong, Liangguo
2015-09-01
This paper proposes an improvement on the scattering-integral (SI) approach for acoustic frequency-domain full waveform inversion (FWI) based on the individual Born kernels. The main development is a method for calculating the steepest-descent direction and the pseudo-Newton direction by vector operations with definite physical meaning, without needing to store the huge Fréchet kernels in memory beforehand. The Gauss-Newton descent direction can therefore be iteratively constructed without needing to store the huge approximate Hessian matrix or to calculate its inverse. The banded pseudo-Hessian and its inverse can be obtained in this way as well. This approach is efficient and makes the traditional SI approach more practical. At the same time, it keeps the advantages of the SI approach which can generate exact gradient of the objective function, enables separation of forward and inverse computation and provides straightforward access to Gauss-Newton iteration. This approach is called Born kernel full waveform inversion (BKFWI). Its effectiveness using the steepest-descent direction has been proved through 2-D numerical experiments. More fully resolved results and faster convergence are obtained when the Gauss-Newton direction is used. Because no additional forward simulations are needed for the Gauss-Newton direction, BKFWI is a highly valid alternative to traditional adjoint-state full waveform inversion (ADFWI) when the number of source stations is more than a few percent of the number of receiver stations. Such conditions are common in controlled source exploration, OBS (Ocean Bottom Seismometer) exploration, earthquake seismology, and even certain traditional seismic explorations. This method is also shown to be a convenient way to obtain accurate Gauss-Newton directions for multiparameter FWI because kernel coupling in the Hessian matrix can be easily handled.
Noninvasive absolute cerebral oximetry with frequency-domain near-infrared spectroscopy
NASA Astrophysics Data System (ADS)
Hallacoglu, Bertan
Near-infrared spectroscopy (NIRS) measurements of absolute concentrations of oxy-hemoglobin and deoxy-hemoglobin in the human brain can provide critical information about cerebral physiology in terms of cerebral blood volume, blood flow, oxygen delivery, and metabolic rate of oxygen. We developed several frequency domain NIRS data acquisition and analysis methods aimed at absolute measurements of hemoglobin concentration and saturation in cerebral tissue of adult human subjects. Extensive experimental investigations were carried out in various homogenous and two-layered tissue-mimicking phantoms, and biological tissues. The advantages and limitations of commonly used homogenous models and inversion strategies were thoroughly investigated. Prior to human subjects, extensive studies were carried out in in vivo animal models. In rabbits, absolute hemoglobin oxygen desaturation was shown to depend strongly on surgically induced testicular torsion. Methods developed in this study were then adapted for measurements in the rat brain. Absolute values were demonstrated to discern cerebrovascular impairment in a rat model of diet-induced vascular cognitive impairment. These results facilitated the development of clinically useful optical measures of cerebrovascular health. In a large group of human subjects, employing a homogeneous model for absolute measurements was shown to be reliable and robust. However, it was also shown to be limited due to the relatively thick extracerebral tissue. The procedure we develop in this work and the thesis thereof performs a nonlinear inversion procedure with six unknown parameters with no other prior knowledge for the retrieval of the optical coefficients and top layer thickness with high accuracy on two-layered media. Our absolute measurements of cerebral hemoglobin concentration and saturation are based on the discrimination of extracerebral and cerebral tissue layers, and they can enhance the impact of NIRS for cerebral hemodynamics and
Yafi, Amr; Vetter, Thomas S; Scholz, Thomas; Patel, Sarin; Saager, Rolf B; Cuccia, David J; Evans, Gregory R; Durkin, Anthony J
2010-01-01
Background The purpose of this study is to investigate the capabilities of a novel optical wide-field imaging technology known as Spatial Frequency Domain Imaging (SFDI) to quantitatively assess reconstructive tissue status. Methods Twenty two cutaneous pedicle flaps were created on eleven rats based on the inferior epigastric vessels. After baseline measurement, all flaps underwent vascular ischemia, induced by clamping the supporting vessels for two hours (either arterio-venous or selective venous occlusions) normal saline was injected to the control flap, and hypertonic hyperoncotic saline solution to the experimental flap. Flaps were monitored for two hours after reperfusion. The SFDI system was used for quantitative assessment of flap status over the duration of the experiment. Results All flaps demonstrated a significant decline in oxy-hemoglobin and tissue oxygen saturation in response to occlusion. Total hemoglobin and deoxy-hemoglobin were markedly increased in the selective venous occlusion group. After reperfusion and the solutions were administered, oxy-hemoglobin and tissue oxygen saturation in those flaps that survived gradually returned to the baseline levels. However, flaps for which oxy-hemoglobin and tissue oxygen saturation didn’t show any signs of recovery appeared to be compromised and eventually became necrotic within 24–48 hours in both occlusion groups. Conclusion SFDI technology provides a quantitative, objective method to assess tissue status. This study demonstrates the potential of this optical technology to assess tissue perfusion in a very precise and quantitative way, enabling wide-field visualization of physiological parameters. The results of this study suggest that SFDI may provide a means for prospectively identifying dysfunctional flaps well in advance of failure. PMID:21200206
NASA Astrophysics Data System (ADS)
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
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]. PMID:26761607
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].
Hou, Da Jun; Wu, Jin-Jei; Wu, Chien-Jang; Shen, Jian Qi; Chiueh, Her-Lih; Cheng, Li-Yi; Lin, Hung-Erh
2016-04-01
In this work, based on the use of the concept of spoof surface plasmon polaritons (spoof SPPs), we propose a novel kind of microstrips to suppress the interference between bended parallel microstrips. This novel structure is implemented by introducing subwavelength periodic structures onto the sides of a conventional microstrip. We numerically analyze the transmission characteristics of such new microstrips. We also measure the suppression arising from crosstalk between the bended corrugated microstrip and the conventional microstrip in both frequency and time domains. Experimental results show that such transmission line structure has superb interference restraining properties. Additionally, transmission properties have been investigated using circuit model. It is found that the coupling effect between the corrugated microstrip and the conventional microstrip can be efficiently suppressed in high speed digital signal transmission application. PMID:27137029
NASA Astrophysics Data System (ADS)
Alcala, J. Ricardo; Yu, Clement; Yeh, Gong Jong
1993-06-01
An instrument to measure the excited-state lifetimes of phosphorescent materials in real time is described. This apparatus uses pulsed and frequency-doubled Nd:YAG solid-state laser for excitation, sampler for data acquisition, and frequency domain methods for data fitting. The instrument amplifies the ac components of the detector output and band limits the signal to 25 kHz. The fundamental frequency of the excitation is then set to obtain a desired number of harmonics. This band limited signal is sampled and averaged over few thousand 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 is then computed. Ten to a hundred values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited-state lifetimes from subpicowatt luminescent signals in 100 μm optical fibers. To monitor oxygen for biomedical applications the response time of the system is decreased by collecting only 8 or 16 harmonics. A least-squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation. The phosphorescence lifetimes measured reproducibly to three parts in a thousand are used to monitor oxygen. Oxygen concentrations are computed employing empirical polynomials. The system drift is less than 1% over 100 h of continuous operation. This instrument is used to measure oxygen concentrations in vitro and in vivo with 2 s update times and 90 s full response times. Examples of measurements in saline solutions and in dogs are presented.
NASA Astrophysics Data System (ADS)
Creusen, I. M.; Hazelhoff, L.; De With, P. H. N.
2013-10-01
In large-scale automatic traffic sign surveying systems, the primary computational effort is concentrated at the traffic sign detection stage. This paper focuses on reducing the computational load of particularly the sliding window object detection algorithm which is employed for traffic sign detection. Sliding-window object detectors often use a linear SVM to classify the features in a window. In this case, the classification can be seen as a convolution of the feature maps with the SVM kernel. It is well known that convolution can be efficiently implemented in the frequency domain, for kernels larger than a certain size. We show that by careful reordering of sliding-window operations, most of the frequency-domain transformations can be eliminated, leading to a substantial increase in efficiency. Additionally, we suggest to use the overlap-add method to keep the memory use within reasonable bounds. This allows us to keep all the transformed kernels in memory, thereby eliminating even more domain transformations, and allows all scales in a multiscale pyramid to be processed using the same set of transformed kernels. For a typical sliding-window implementation, we have found that the detector execution performance improves with a factor of 5.3. As a bonus, many of the detector improvements from literature, e.g. chi-squared kernel approximations, sub-class splitting algorithms etc., can be more easily applied at a lower performance penalty because of an improved scalability.
Analysis on the Time and Frequency Domains of the Acceleration in Front Crawl Stroke
Gil, Joaquín Madera; Moreno, Luis-Millán González; Mahiques, Juan Benavent; Muñoz, Víctor Tella
2012-01-01
The swimming involves accelerations and decelerations in the swimmer’s body. Thus, the main objective of this study is to make a temporal and frequency analysis of the acceleration in front crawl swimming, regarding the gender and the performance. The sample was composed by 31 male swimmers (15 of high-level and 16 of low-level) and 20 female swimmers (11 of high-level and 9 of low-level). The acceleration was registered from the third complete cycle during eight seconds in a 25 meters maximum velocity test. A position transducer (200Hz) was used to collect the data, and it was synchronized to an aquatic camera (25Hz). The acceleration in the temporal (root mean square, minimum and maximum of the acceleration) and frequency (power peak, power peak frequency and spectral area) domains was calculated with Fourier analysis, as well as the velocity and the spectrums distribution in function to present one or more main peaks (type 1 and type 2). A one-way ANOVA was used to establish differences between gender and performance. Results show differences between genders in all the temporal domain variables (p<0.05) and only the Spectral Area (SA) in the frequency domain (p<0.05). Between gender and performance, only the Root Mean Square (RMS) showed differences in the performance of the male swimmers (p<0.05) and in the higher level swimmers, the Maximum (Max) and the Power Peak (PP) of the acceleration showed differences between both genders (p<0.05). These results confirms the importance of knowing the RMS to determine the efficiency of the swimmers regarding gender and performance level PMID:23487001
NASA Astrophysics Data System (ADS)
Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Zhou, Xiaoxiao; Shi, Yan
2016-03-01
In this paper, a reflective metasurface is designed, fabricated, and experimentally demonstrated to generate an orbital angular momentum (OAM) vortex wave in radio frequency domain. Theoretical formula of phase-shift distribution is deduced and used to design the metasurface producing vortex radio waves. The prototype of a practical configuration is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that the vortex waves with different OAM mode numbers can be flexibly generated by using sub-wavelength reflective metasurfaces. The proposed method and metasurface pave a way to generate the OAM vortex waves for radio and microwave wireless communication applications.
NASA Technical Reports Server (NTRS)
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.
A hybrid absorbing boundary condition for frequency-domain finite-difference modelling
NASA Astrophysics Data System (ADS)
Ren, Zhiming; Liu, Yang
2013-10-01
Liu and Sen (2010 Geophysics 75 A1-6 2012 Geophys. Prospect. 60 1114-32) proposed an efficient hybrid scheme to significantly absorb boundary reflections for acoustic and elastic wave modelling in the time domain. In this paper, we extend the hybrid absorbing boundary condition (ABC) into the frequency domain and develop specific strategies for regular-grid and staggered-grid modelling, respectively. Numerical modelling tests of acoustic, visco-acoustic, elastic and vertically transversely isotropic (VTI) equations show significant absorptions for frequency-domain modelling. The modelling results of the Marmousi model and the salt model also demonstrate the effectiveness of the hybrid ABC. For elastic modelling, the hybrid Higdon ABC and the hybrid Clayton and Engquist (CE) ABC are implemented, respectively. Numerical simulations show that the hybrid Higdon ABC gets better absorption than the hybrid CE ABC, especially for S-waves. We further compare the hybrid ABC with the classical perfectly matched layer (PML). Results show that the two ABCs cost the same computation time and memory space for the same absorption width. However, the hybrid ABC is more effective than the PML for the same small absorption width and the absorption effects of the two ABCs gradually become similar when the absorption width is increased.
Renormalized scattering series for frequency-domain waveform modelling of strong velocity contrasts
NASA Astrophysics Data System (ADS)
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
A finite-difference frequency-domain code for electromagnetic induction tomography
Sharpe, R M; Berryman, J G; Buettner, H M; Champagne, N J.,II; Grant, J B
1998-12-17
We are developing a new 3D code for application to electromagnetic induction tomography and applications to environmental imaging problems. We have used the finite-difference frequency- domain formulation of Beilenhoff et al. (1992) and the anisotropic PML (perfectly matched layer) approach (Berenger, 1994) to specify boundary conditions following Wu et al. (1997). PML deals with the fact that the computations must be done in a finite domain even though the real problem is effectively of infinite extent. The resulting formulas for the forward solver reduce to a problem of the form Ax = y, where A is a non-Hermitian matrix with real values off the diagonal and complex values along its diagonal. The matrix A may be either symmetric or nonsymmetric depending on details of the boundary conditions chosen (i.e., the particular PML used in the application). The basic equation must be solved for the vector x (which represents field quantities such as electric and magnetic fields) with the vector y determined by the boundary conditions and transmitter location. Of the many forward solvers that could be used for this system, relatively few have been thoroughly tested for the type of matrix encountered in our problem. Our studies of the stability characteristics of the Bi-CG algorithm raised questions about its reliability and uniform accuracy for this application. We have found the stability characteristics of Bi-CGSTAB [an alternative developed by van der Vorst (1992) for such problems] to be entirely adequate for our application, whereas the standard Bi-CG was quite inadequate. We have also done extensive validation of our code using semianalytical results as well as other codes. The new code is written in Fortran and is designed to be easily parallelized, but we have not yet tested this feature of the code. An adjoint method is being developed for solving the inverse problem for conductivity imaging (for mapping underground plumes), and this approach, when ready, will
Domain decomposition methods for a parallel Monte Carlo transport code
Alme, H J; Rodrigue, G H; Zimmerman, G B
1999-01-27
Achieving parallelism in simulations that use Monte Carlo transport methods presents interesting challenges. For problems that require domain decomposition, load balance can be harder to achieve. The Monte Carlo transport package may have to operate with other packages that have different optimal domain decompositions for a given problem. To examine some of these issues, we have developed a code that simulates the interaction of a laser with biological tissue; it uses a Monte Carlo method to simulate the laser and a finite element model to simulate the conduction of the temperature field in the tissue. We will present speedup and load balance results obtained for a suite of problems decomposed using a few domain decomposition algorithms we have developed.
Approximation method to compute domain related integrals in structural studies
NASA Astrophysics Data System (ADS)
Oanta, E.; Panait, C.; Raicu, A.; Barhalescu, M.; Axinte, T.
2015-11-01
Various engineering calculi use integral calculus in theoretical models, i.e. analytical and numerical models. For usual problems, integrals have mathematical exact solutions. If the domain of integration is complicated, there may be used several methods to calculate the integral. The first idea is to divide the domain in smaller sub-domains for which there are direct calculus relations, i.e. in strength of materials the bending moment may be computed in some discrete points using the graphical integration of the shear force diagram, which usually has a simple shape. Another example is in mathematics, where the surface of a subgraph may be approximated by a set of rectangles or trapezoids used to calculate the definite integral. The goal of the work is to introduce our studies about the calculus of the integrals in the transverse section domains, computer aided solutions and a generalizing method. The aim of our research is to create general computer based methods to execute the calculi in structural studies. Thus, we define a Boolean algebra which operates with ‘simple’ shape domains. This algebraic standpoint uses addition and subtraction, conditioned by the sign of every ‘simple’ shape (-1 for the shapes to be subtracted). By ‘simple’ shape or ‘basic’ shape we define either shapes for which there are direct calculus relations, or domains for which their frontiers are approximated by known functions and the according calculus is carried out using an algorithm. The ‘basic’ shapes are linked to the calculus of the most significant stresses in the section, refined aspect which needs special attention. Starting from this idea, in the libraries of ‘basic’ shapes, there were included rectangles, ellipses and domains whose frontiers are approximated by spline functions. The domain triangularization methods suggested that another ‘basic’ shape to be considered is the triangle. The subsequent phase was to deduce the exact relations for the
Zhu, Lingyu; Ji, Shengchang; Shen, Qi; Liu, Yuan; Li, Jinyu; Liu, Hao
2013-01-01
The capacitors in high-voltage direct-current (HVDC) converter stations radiate a lot of audible noise which can reach higher than 100 dB. The existing noise level prediction methods are not satisfying enough. In this paper, a new noise level prediction method is proposed based on a frequency response function considering both electrical and mechanical characteristics of capacitors. The electro-mechanical frequency response function (EMFRF) is defined as the frequency domain quotient of the vibration response and the squared capacitor voltage, and it is obtained from impulse current experiment. Under given excitations, the vibration response of the capacitor tank is the product of EMFRF and the square of the given capacitor voltage in frequency domain, and the radiated audible noise is calculated by structure acoustic coupling formulas. The noise level under the same excitations is also measured in laboratory, and the results are compared with the prediction. The comparison proves that the noise prediction method is effective.
NASA Astrophysics Data System (ADS)
Oh, Ju-Won; Min, Dong-Joo
2013-07-01
To enhance the feasibility of seismic full waveform inversion (FWI) for various types of geological structures, the model parameters should be updated along directions such that both long- and short-wavelength structures can be properly resolved. These long- and short-wavelength structures are primarily influenced by the low- and high-frequency components of the gradients, respectively. In some cases, however, the gradients are not flexible to reconstruct both the long- and the short-wavelength structures. This problem can be related to the scaling method using the Hessian matrix and the effect of the source spectrum. In this study, we analyse the problems of conventional scaling methods in frequency-domain FWI and propose a weighting method to compensate for these problems. The weighting method is applied to the conventional elastic FWI, where the gradient is scaled by the diagonal of the pseudo-Hessian matrix inside the frequency loop so that the effect of the source spectrum can be removed through cancellation. The weighting factors are designed using the backpropagated wavefields incited by the deconvolved residuals, which play a role in making the descent directions appropriately reflect the spectral differences between the observed data and the initial (or the inverted) modelling responses. We analyse the characteristics of the Jacobians and residuals and compare the descent directions of the two conventional waveform inversion methods with descent directions of the weighting method for thick rectangular-shaped and thin-layers models. The results indicate that the descent directions computed using the conventional inversion methods do not reflect the characteristics of deconvolved residuals and that particular frequency components are always emphasized regardless of geological models, while the spatial resolution of the descent direction calculated using the weighting method is flexibly determined depending on the differences between the true and the assumed
NASA Astrophysics Data System (ADS)
Koirala, Shesh R.; Gentry, Randall W.; Mulholland, Patrick J.; Perfect, Edmund; Schwartz, John S.
2010-06-01
SummaryIn the realm of sustainability science, it is becoming increasingly important to understand the basal condition of a natural system as well as its long-term behavior. Research is needed to better explain the temporal scaling of water chemistry in streams and watersheds and its relationship with the hydrologic factors that influence its behavior. Persistence of dissolved chemicals in streams has been demonstrated to be linked to certain hydrologic processes, such as interaction between hydrologic units and storage in surface or sub-surface systems. In this study, spectral and wavelet analyses provided a novel theoretical basis for insights into long-term chloride behavior in an east Tennessee watershed. Temporal scaling analyses were conducted on weekly time series data of chloride collected from November 1995 to December 2005 at the West Fork of Walker Branch in Oak Ridge, Tennessee. The objectives of the study were to: evaluate chloride concentration (a conservative solute) to determine the presence of statistical persistence and the relationship of the persistence to hydrologic variables (discharge and rainfall) using time and frequency domain analyses of high-frequency hydrologic and chloride concentration data. Results demonstrated that chloride showed some level of statistical persistence that was influenced by rainfall and/or discharge. Short-term statistical persistence (less than a year) was related to the persistence of rainfall and discharge, whereas long-term statistical persistence (more than a year) was related to the persistence of discharge.
Koirala, Shesh R; Gentry, Randall W; Mulholland, Patrick J; Perfect, Edmund; Schwartz, John S
2010-01-01
In the realm of sustainability science, it is becoming increasingly important to understand the basal condition of a natural system as well as its long-term behavior. Research is needed to better explain the temporal scaling of water chemistry in streams and watersheds and its relationship with the hydrologic factors that influence its behavior. Persistence of dissolved chemicals in streams has been demonstrated to be linked to certain hydrologic processes, such as interaction between hydrologic units and storage in surface or sub-surface systems. In this study, spectral and wavelet analyses provided a novel theoretical basis for insights into long-term chloride behavior in an east Tennessee watershed. Temporal scaling analyses were conducted on weekly time series data of chloride collected from November 1995 to December 2005 at the West Fork of Walker Branch in Oak Ridge, Tennessee. The objectives of the study were to: evaluate chloride concentration (a conservative solute) to determine the presence of statistical persistence and the relationship of the persistence to hydrologic variables (discharge and rainfall) using time and frequency domain analyses of high-frequency hydrologic and chloride concentration data. Results demonstrated that chloride showed some level of statistical persistence that was influenced by rainfall and/or discharge. Short-term statistical persistence (less than a year) was related to the persistence of rainfall and discharge, whereas long-term statistical persistence (more than a year) was related to the persistence of discharge.
Frequency domain holography of laser wakefield accelerators in the nonlinear bubble regime
NASA Astrophysics Data System (ADS)
Yi, S. A.; Kalmykov, S.; Dong, P.; Reed, S. A.; Downer, M.; Shvets, G.
2009-11-01
We present the theoretical basis of frequency domain holography (FDH), a technique for single-shot visualization of laser driven plasma wakes. In FDH, the nonlinear index modulations of the plasma wake are recorded as phase shifts in a co-propagating probe pulse, and interference with a reference allows for the reconstruction of the wake structure. Earlier experimental work [N. H. Matlis et al., Nature Phys. 2, 749 (2006)] has shown that reconstruction of the probe phase is sufficient for imaging weakly nonlinear periodic wakes. In the highly nonlinear regime, the laser ponderomotive force blows out plasma electrons and forms a density ``bubble'' that strongly focuses the probe light. We show that imaging the bubble requires full (amplitude and phase) reconstruction of the probe pulse, and find reconstructions of simulated frequency domain holograms in full agreement with direct PIC modeling of the probe pulse. We also assess the sensitivity of the technique to the spectral bandwidth of the probe and reference pulses. In combination with ray-tracing techniques which help evaluate the localized frequency up- and down-shifts of the probe light (``photon acceleration''), FDH appears to be a unique tool for visualization of plasma wakes. This work is supported by the US DOE grants DE-FG02-04ER41321 and DE-FG02-07ER54945.
Comparison of geometrical and diffraction imaging in the space and frequency domains.
Mahajan, Virendra N; Díaz, José A
2016-04-20
The geometrical and diffraction point-spread functions of an optical imaging system have been reviewed and compared in the past [Proc. SPIE3729, 434 (1999)PSISDG0277-786X10.1117/12.346821]. In this paper, we review and compare corresponding optical transfer functions. While the truth lies with the diffraction optical-transfer functions (OTF), it is considered easier and quicker to calculate the geometrical OTF, especially for large aberrations. We describe the theory of the two OTFs and explore the range of spatial frequencies and the magnitude of the primary aberrations over which the geometrical OTF may provide a reasonable approximation of the diffraction OTF. Moreover, balancing of spherical aberration with defocus for optimum diffraction OTF is studied as a function of both the aberration value as well as the spatial frequency. How to gauge the progress of an optical design in the frequency domain based on the geometrical OTF is outlined as the ray spot size is used in the space domain. PMID:27140094
A microcomputer based frequency-domain processor for laser Doppler anemometry
NASA Technical Reports Server (NTRS)
Horne, W. Clifton; Adair, Desmond
1988-01-01
A prototype multi-channel laser Doppler anemometry (LDA) processor was assembled using a wideband transient recorder and a microcomputer with an array processor for fast Fourier transform (FFT) computations. The prototype instrument was used to acquire, process, and record signals from a three-component wind tunnel LDA system subject to various conditions of noise and flow turbulence. The recorded data was used to evaluate the effectiveness of burst acceptance criteria, processing algorithms, and selection of processing parameters such as record length. The recorded signals were also used to obtain comparative estimates of signal-to-noise ratio between time-domain and frequency-domain signal detection schemes. These comparisons show that the FFT processing scheme allows accurate processing of signals for which the signal-to-noise ratio is 10 to 15 dB less than is practical using counter processors.
NASA Astrophysics Data System (ADS)
Franke, S. J.; Roettger, J.; Lahoz, C.; Liu, C. H.
1992-06-01
During the polar mesosphere summer echo (PMSE) campaign in 1988 the first multiple-frequency mesospheric measurements were carried out using EISCAT 224-MHz radar. A case study of nearly simultaneous measurements of coherent backscatter, collected on two closely spaced frequencies on July 3, 1988, is presented. The data are used to investigate the frequency coherence of the radar echoes and to perform frequency domain interferometry (FDI) analysis. The FDI techniques provides precise information about the thickness and relative position of isolated scattering layers. The results indicate that scattering layers with thicknesses in the range 85-120 m are sometimes present in the polar summer mesosphere. Such a layer is shown to exist for a period of approximately 10 min, and its position is tracked as it descends over more than 1 km in altitude and transits from one range gate to the next. In addition, the FDI technique is used to study a case where a sudden frequency jump is observed in the Doppler spectrum.
Methods of detection using a cellulose binding domain fusion product
Shoseyov, O.; Shpiegl, I.; Goldstein, M.A.; Doi, R.H.
1999-01-05
A cellulose binding domain (CBD) having a high affinity for crystalline cellulose and chitin is disclosed, along with methods for the molecular cloning and recombinant production. Fusion products comprising the CBD and a second protein are likewise described. A wide range of applications are contemplated for both the CBD and the fusion products, including drug delivery, affinity separations, and diagnostic techniques. 34 figs.
Methods of use of cellulose binding domain proteins
Shoseyov, O.; Shpiegl, I.; Goldstein, M.A.; Doi, R.H.
1997-09-23
A cellulose binding domain (CBD) having a high affinity for crystalline cellulose and chitin is disclosed, along with methods for the molecular cloning and recombinant production. Fusion products comprising the CBD and a second protein are likewise described. A wide range of applications are contemplated for both the CBD and the fusion products, including drug delivery, affinity separations, and diagnostic techniques. 16 figs.
Methods of detection using a cellulose binding domain fusion product
Shoseyov, Oded; Shpiegl, Itai; Goldstein, Marc A.; Doi, Roy H.
1999-01-01
A cellulose binding domain (CBD) having a high affinity for crystalline cellulose and chitin is disclosed, along with methods for the molecular cloning and recombinant production thereof. Fusion products comprising the CBD and a second protein are likewise described. A wide range of applications are contemplated for both the CBD and the fusion products, including drug delivery, affinity separations, and diagnostic techniques.
Methods of use of cellulose binding domain proteins
Shoseyov, Oded; Shpiegl, Itai; Goldstein, Marc A.; Doi, Roy H.
1997-01-01
A cellulose binding domain (CBD) having a high affinity for crystalline cellulose and chitin is disclosed, along with methods for the molecular cloning and recombinant production thereof. Fusion products comprising the CBD and a second protein are likewise described. A wide range of applications are contemplated for both the CBD and the fusion products, including drug delivery, affinity separations, and diagnostic techniques.
Measuring frequency domain granger causality for multiple blocks of interacting time series.
Faes, Luca; Nollo, Giandomenico
2013-04-01
In the past years, several frequency-domain causality measures based on vector autoregressive time series modeling have been suggested to assess directional connectivity in neural systems. The most followed approaches are based on representing the considered set of multiple time series as a realization of two or three vector-valued processes, yielding the so-called Geweke linear feedback measures, or as a realization of multiple scalar-valued processes, yielding popular measures like the directed coherence (DC) and the partial DC (PDC). In the present study, these two approaches are unified and generalized by proposing novel frequency-domain causality measures which extend the existing measures to the analysis of multiple blocks of time series. Specifically, the block DC (bDC) and block PDC (bPDC) extend DC and PDC to vector-valued processes, while their logarithmic counterparts, denoted as multivariate total feedback [Formula: see text] and direct feedback [Formula: see text], represent into a full multivariate framework the Geweke's measures. Theoretical analysis of the proposed measures shows that they: (i) possess desirable properties of causality measures; (ii) are able to reflect either direct causality (bPDC, [Formula: see text] or total (direct + indirect) causality (bDC, [Formula: see text] between time series blocks; (iii) reduce to the DC and PDC measures for scalar-valued processes, and to the Geweke's measures for pairs of processes; (iv) are able to capture internal dependencies between the scalar constituents of the analyzed vector processes. Numerical analysis showed that the proposed measures can be efficiently estimated from short time series, allow to represent in an objective, compact way the information derived from the causal analysis of several pairs of time series, and may detect frequency domain causality more accurately than existing measures. The proposed measures find their natural application in the evaluation of directional
Measuring frequency domain granger causality for multiple blocks of interacting time series.
Faes, Luca; Nollo, Giandomenico
2013-04-01
In the past years, several frequency-domain causality measures based on vector autoregressive time series modeling have been suggested to assess directional connectivity in neural systems. The most followed approaches are based on representing the considered set of multiple time series as a realization of two or three vector-valued processes, yielding the so-called Geweke linear feedback measures, or as a realization of multiple scalar-valued processes, yielding popular measures like the directed coherence (DC) and the partial DC (PDC). In the present study, these two approaches are unified and generalized by proposing novel frequency-domain causality measures which extend the existing measures to the analysis of multiple blocks of time series. Specifically, the block DC (bDC) and block PDC (bPDC) extend DC and PDC to vector-valued processes, while their logarithmic counterparts, denoted as multivariate total feedback [Formula: see text] and direct feedback [Formula: see text], represent into a full multivariate framework the Geweke's measures. Theoretical analysis of the proposed measures shows that they: (i) possess desirable properties of causality measures; (ii) are able to reflect either direct causality (bPDC, [Formula: see text] or total (direct + indirect) causality (bDC, [Formula: see text] between time series blocks; (iii) reduce to the DC and PDC measures for scalar-valued processes, and to the Geweke's measures for pairs of processes; (iv) are able to capture internal dependencies between the scalar constituents of the analyzed vector processes. Numerical analysis showed that the proposed measures can be efficiently estimated from short time series, allow to represent in an objective, compact way the information derived from the causal analysis of several pairs of time series, and may detect frequency domain causality more accurately than existing measures. The proposed measures find their natural application in the evaluation of directional
On the implementation of a real-time information security architecture in frequency domain
NASA Astrophysics Data System (ADS)
Basu, Abhishek; Sarkar, Souvik; Sarkar, Subir Kumar
2015-12-01
This paper presents the real-time implementation of a watermarking-based information security architecture in frequency domain. The scheme emphasises on the human visual system (HVS)-supported watermarking approach using wavelet-lifting technique. In addition to HVS, image registration algorithm is also introduced in order to increase the resiliency as well as the security of the estimated recovered watermark image. The algorithmic steps with optimisation considerations about the real-time implementation on TMS320CDSK6416/6713 fixed/floating point digital signal processor are also projected.
Improvements in frequency-domain based NIRF optical tomography modality for preclinical studies
NASA Astrophysics Data System (ADS)
Darne, Chinmay D.; Sevick-Muraca, Eva M.
2014-05-01
Herein we present recent improvements in system design and performance evaluation of near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system developed for small animal fluorescence tomography and installed within a commercial micro-CT/PET scanner. We improved system performance by increasing signal-to-noise ratio (SNR) through use of high powered rf modulation, novel data collection scheme, and data discrimination based on the associated noise levels. Noise characteristics show improvement with these techniques and are currently being employed to improve 3-D fluorescence for tomographic reconstructions in phantoms before incorporating into hybrid scanner.
Automated on-orbit frequency domain identification for large space structures
NASA Technical Reports Server (NTRS)
Bayard, D. S.; Hadaegh, F. Y.; Yam, Y.; Scheid, R. E.; Mettler, E.; Milman, M. H.
1991-01-01
Recent experiences in the field of flexible structure control in space have indicated a need for on-orbit system identification to support robust control redesign to avoid in-flight instabilities and maintain high spacecraft performance. This paper highlights an automated frequency domain system identification methodology recently developed to fulfill this need. The methodology is focused to support (1) the estimation of system quantities useful for robust control analysis and design; (2) experiment design tailored to performing system identification in a typically constrained on-orbit environment; and (3) the automation of operations to reduce 'human in the loop' requirements.
Optical frequency domain reflectometry: principles and applications in fiber optic sensing
NASA Astrophysics Data System (ADS)
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.
Dynamic frequency-domain interferometer for absolute distance measurements with high resolution
Weng, Jidong; Liu, Shenggang; Ma, Heli; Tao, Tianjiong; Wang, Xiang; Liu, Cangli; Tan, Hua
2014-11-15
A unique dynamic frequency-domain interferometer for absolute distance measurement has been developed recently. This paper presents the working principle of the new interferometric system, which uses a photonic crystal fiber to transmit the wide-spectrum light beams and a high-speed streak camera or frame camera to record the interference stripes. Preliminary measurements of harmonic vibrations of a speaker, driven by a radio, and the changes in the tip clearance of a rotating gear wheel show that this new type of interferometer has the ability to perform absolute distance measurements both with high time- and distance-resolution.
Frequency-domain stimulated and spontaneous light emission signals at molecular junctions
Harbola, Upendra; Agarwalla, Bijay Kumar; Mukamel, Shaul
2014-08-21
Using a diagrammatic superoperator formalism we calculate optical signals at molecular junctions where a single molecule is coupled to two metal leads which are held at different chemical potentials. The molecule starts in a nonequilibrium steady state whereby it continuously exchanges electrons with the leads with a constant electron flux. Expressions for frequency domain optical signals measured in response to continuous laser fields are derived by expanding the molecular correlation functions in terms of its many-body states. The nonunitary evolution of molecular states is described by the quantum master equation.
Time-resolved experiments in the frequency domain using synchrotron radiation (invited)
NASA Astrophysics Data System (ADS)
De Stasio, Gelsomina; Giusti, A. M.; Parasassi, T.; Ravagnan, G.; Sapora, O.
1992-01-01
PLASTIQUE is the only synchrotron radiation beam line in the world that performs time-resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and the dynamics of molecules. This technique measures fluorescence lifetimes with picosecond resolution in the near UV spectral range. Such accurate measurements are rendered possible by taking phase and modulation data, and by the advantages of the cross-correlation technique. A successful experiment demonstrated the radiation damage induced by low doses of radiation on rabbit blood cell membranes.
Functional cerebral activation detected by frequency-domain near-infrared spectroscopy
NASA Astrophysics Data System (ADS)
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.
Hybrid Optoelectronic Bistability in Frequency-Domain and Its Potential Application in FBG Sensors
NASA Astrophysics Data System (ADS)
Ye, Hong-An; Liu, Chun-Yu; Lv, Guo-Hui; Xin, Hai-Ying; Zhu, Xiao-Liang
2008-12-01
We propose a novel optical bistable device (OBD) in frequency-domain with which we can perform optical bistable operations in a number of fibre Bragg gratings (FBGs) which are included in the same OBD. Such an OBD may bring more opportunities in applications and, as an example, we show the possibility of using it in an FBG sensor demodulating system. By use of a tunable light source, consisting of a broad band source and a scanning fibre F-P (FFP), we demonstrate the above-mentioned operations experimentally.
NASA Astrophysics Data System (ADS)
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.
Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments.
Benuzzi-Mounaix, A; Koenig, M; Boudenne, J M; Hall, T A; Batani, D; Scianitti, F; Masini, A; Di Santo, D
1999-09-01
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target approximately 5 x 10(13) W/cm(2) to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps. PMID:11970183
Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments
NASA Astrophysics Data System (ADS)
Benuzzi-Mounaix, A.; Koenig, M.; Boudenne, J. M.; Hall, T. A.; Batani, D.; Scianitti, F.; Masini, A.; di Santo, D.
1999-09-01
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target ~5×1013 W/cm2 to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps.
NASA Astrophysics Data System (ADS)
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.
Krishnan, Sunder Ram; Seelamantula, Chandra Sekhar; Bouwens, Arno; Leutenegger, Marcel; Lasser, Theo
2012-10-01
We address the problem of high-resolution reconstruction in frequency-domain optical-coherence tomography (FDOCT). The traditional method employed uses the inverse discrete Fourier transform, which is limited in resolution due to the Heisenberg uncertainty principle. We propose a reconstruction technique based on zero-crossing (ZC) interval analysis. The motivation for our approach lies in the observation that, for a multilayered specimen, the backscattered signal may be expressed as a sum of sinusoids, and each sinusoid manifests as a peak in the FDOCT reconstruction. The successive ZC intervals of a sinusoid exhibit high consistency, with the intervals being inversely related to the frequency of the sinusoid. The statistics of the ZC intervals are used for detecting the frequencies present in the input signal. The noise robustness of the proposed technique is improved by using a cosine-modulated filter bank for separating the input into different frequency bands, and the ZC analysis is carried out on each band separately. The design of the filter bank requires the design of a prototype, which we accomplish using a Kaiser window approach. We show that the proposed method gives good results on synthesized and experimental data. The resolution is enhanced, and noise robustness is higher compared with the standard Fourier reconstruction. PMID:23201655
Dielectric measurements of water in the radio microwave frequencies by time domain reflectometry
Merabet, M.; Bose, T.K.
1988-10-20
The time domain reflectometric method is used with success to measure the dielectric properties of water from 10 MHz to 8 GHz. It is shown that special precautions must be taken into account in order to determine the dielectric properties of a substance with high dielectric constant in the microwave region.
Stankovski, Tomislav; Cooke, William H.; Rudas, László; Stefanovska, Aneta
2013-01-01
We experimentally altered the timing of respiratory motoneuron activity as a means to modulate and better understand otherwise hidden human central neural and hemodynamic oscillatory mechanisms. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, tidal carbon dioxide concentrations, and muscle sympathetic nerve activity in 13 healthy supine young men who gradually increased or decreased their breathing frequencies between 0.05 and 0.25 Hz over 9-min periods. We analyzed results with traditional time- and frequency-domain methods, and also with time-frequency methods (wavelet transform, wavelet phase coherence, and directional coupling). We determined statistical significance and identified frequency boundaries by comparing measurements with randomly generated surrogates. Our results support several major conclusions. First, respiration causally modulates both sympathetic (weakly) and vagal motoneuron (strongly) oscillations over a wide frequency range—one that extends well below the frequency of actual breaths. Second, breathing frequency broadly modulates vagal baroreflex gain, with peak gains registered in the low frequency range. Third, breathing frequency does not influence median levels of sympathetic or vagal activity over time. Fourth, phase relations between arterial pressure and sympathetic and vagal motoneurons are unaffected by breathing, and are therefore likely secondary to intrinsic responsiveness of these motoneurons to other synaptic inputs. Finally, breathing frequency does not affect phase coherence between diastolic pressure and muscle sympathetic oscillations, but it augments phase coherence between systolic pressure and R-R interval oscillations over a limited portion of the usual breathing frequency range. These results refine understanding of autonomic oscillatory processes and those physiological mechanisms known as the human respiratory gate. PMID:24114700
Frequency-domain nonlinear regression algorithm for spectral analysis of broadband SFG spectroscopy.
He, Yuhan; Wang, Ying; Wang, Jingjing; Guo, Wei; Wang, Zhaohui
2016-03-01
The resonant spectral bands of the broadband sum frequency generation (BB-SFG) spectra are often distorted by the nonresonant portion and the lineshapes of the laser pulses. Frequency domain nonlinear regression (FDNLR) algorithm was proposed to retrieve the first-order polarization induced by the infrared pulse and to improve the analysis of SFG spectra through simultaneous fitting of a series of time-resolved BB-SFG spectra. The principle of FDNLR was presented, and the validity and reliability were tested by the analysis of the virtual and measured SFG spectra. The relative phase, dephasing time, and lineshapes of the resonant vibrational SFG bands can be retrieved without any preset assumptions about the SFG bands and the incident laser pulses. PMID:26974068
Schnegg, Alexander; Behrends, Jan; Lips, Klaus; Bittl, Robert; Holldack, Karsten
2009-08-21
Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool to ascertain very large zero field splittings in transition metal ion complexes. A description of the FD-FT THz-EPR at the BESSY II storage ring providing CSR in a frequency range from 5 cm(-1) up to 40 cm(-1) at external magnetic fields from -10 T to +10 T is given together with first measurements on the single molecule magnet Mn(12)Ac where we studied DeltaM(S) = +/-1 spin transition energies as a function of the external magnetic field and temperature.
EMGAN: A computer program for time and frequency domain reduction of electromyographic data
NASA Technical Reports Server (NTRS)
Hursta, W. N.
1975-01-01
An experiment in electromyography utilizing surface electrode techniques was developed for the Apollo-Soyuz test project. This report describes the computer program, EMGAN, which was written to provide first order data reduction for the experiment. EMG signals are produced by the membrane depolarization of muscle fibers during a muscle contraction. Surface electrodes detect a spatially summated signal from a large number of muscle fibers commonly called an interference pattern. An interference pattern is usually so complex that analysis through signal morphology is extremely difficult if not impossible. It has become common to process EMG interference patterns in the frequency domain. Muscle fatigue and certain myopathic conditions are recognized through changes in muscle frequency spectra.
NASA Astrophysics Data System (ADS)
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.
NASA Technical Reports Server (NTRS)
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. The standard technique for forced response analysis to assess structural integrity is to decompose a CFD generated flow field into its harmonic components, and to then perform a frequency response analysis at the problematic natural frequencies. 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. These complications suggest the question of whether frequency domain analysis is capable of capturing the excitation content sufficiently. Two studies comparing frequency response analysis with transient response analysis, therefore, have been performed. The first is of a bladed disk with each blade modeled by simple beam elements. It was hypothesized that the randomness and other variation from the standard harmonic excitation would reduce the blade structural response, but the results showed little reduction. The second study was of a realistic model of a bladed-disk excited by the same CFD used in the J2X engine program. The results showed that the transient analysis results were up to 10% higher for "clean" nodal diameter excitations and six times larger for "messy" excitations, where substantial Fourier content around the main harmonic exists.
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.
Time and frequency domain investigation of the heat transfer to a synthetic air jet
NASA Astrophysics Data System (ADS)
Rylatt, D. I.; O'Donovan, T. S.
2012-11-01
Heat transfer to a synthetic air jets is investigated experimentally. The influence of peaks in heat transfer outwith the stagnation region of the jet are of particular interest. Heat transfer to the jets is reported for experimental parameters, jet exit to impingement surface spacings, H/D = 1, Reynolds number of 3000, non-dimensional Stroke length, L0/D of 14.and an excitation frequency of 70 Hz Peaks in heat transfer outwith the stagnation region of the jet are investigated in both the time and frequency domain and a connection between the driving frequency of the jet and changes in the rate of heat transfer is outlined. It is shown that two type's changes in the rate of heat transfer outwith the stagnation region are present in synthetic jet impingement heat transfer; those associated with the jet excitation frequency and therefore attributed to interactions between the two jet flow regimes and those associated with the breakdown of coherent structures in the jet flow.
Domain decomposition methods for solving an image problem
Tsui, W.K.; Tong, C.S.
1994-12-31
The domain decomposition method is a technique to break up a problem so that ensuing sub-problems can be solved on a parallel computer. In order to improve the convergence rate of the capacitance systems, pre-conditioned conjugate gradient methods are commonly used. In the last decade, most of the efficient preconditioners are based on elliptic partial differential equations which are particularly useful for solving elliptic partial differential equations. In this paper, the authors apply the so called covering preconditioner, which is based on the information of the operator under investigation. Therefore, it is good for various kinds of applications, specifically, they shall apply the preconditioned domain decomposition method for solving an image restoration problem. The image restoration problem is to extract an original image which has been degraded by a known convolution process and additive Gaussian noise.
Parallel implementation of the biorthogonal multiresolution time-domain method
NASA Astrophysics Data System (ADS)
Zhu, Xianyang; Carin, Lawrence; Dogaru, Traian
2003-05-01
The three-dimensional biorthogonal multiresolution time-domain (Bi-MRTD) method is presented for both free-space and half-space scattering problems. The perfectly matched layer (PML) is used as an absorbing boundary condition. It has been shown that improved numerical-dispersion properties can be obtained with the use of smooth, compactly supported wavelet functions as the basis, whereas we employ the Cohen-Daubechies-Fouveau (CDF) biorthogonal wavelets. When a CDF-wavelet expansion is used, the spatial-sampling rate can be reduced considerably compared with that of the conventional finite-difference time-domain (FDTD) method, implying that larger targets can be simulated without sacrificing accuracy. We implement the Bi-MRTD on a cluster of allocated-memory machines, using the message-passing interface (MPI), such that very large targets can be modeled. Numerical results are compared with analytical ones and with those obtained by use of the traditional FDTD method.
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
Wei, Changdong; Zheng, Xuan; Cahill, David G; Zhao, Ji-Cheng
2013-07-01
A pump-probe photothermal technique - dual-frequency time-domain thermoreflectance - was developed for measuring heat capacity with a spatial resolution on the order of 10 μm. The method was validated by measuring several common materials with known heat capacity. Rapid measurement of composition-phase-property relationships was demonstrated on Ti-TiSi2 and Ni-Zr diffusion couples; experimental values of heat capacity of the intermetallic compounds in these diffusion couples were compared with literature values and CALPHAD (CALculation of PHAse Diagram) calculations. The combination of this method and diffusion multiples provides an efficient way to generate thermodynamic data for CALPHAD modeling and database construction. The limitation of this method in measuring low thermal diffusivity materials is also discussed.
Everything Hertz: methodological issues in short-term frequency-domain HRV
Heathers, James A. J.
2014-01-01
Frequency analysis of the electrocardiographic RR interval is a common method of quantifying autonomic outflow by measuring the beat-to-beat modulation of the heart (heart rate variability; HRV). This review identifies a series of problems with the methods of doing so—the interpretation of low-frequency spectral power, the multiple use of equivalent normalized low frequency (LFnu), high frequency (HFnu) and ratio (LF/HF) terms, and the lack of control over extraneous variables, and reviews research in the calendar year 2012 to determine their prevalence and severity. Results support the mathematical equivalency of ratio units across studies, a reliance on those variables to explain autonomic outflow, and insufficient control of critical experimental variables. Research measurement of HRV has a substantial need for general methodological improvement. PMID:24847279
Multi-dimensional forward modeling of frequency-domain helicopter-borne electromagnetic data
NASA Astrophysics Data System (ADS)
Miensopust, M.; Siemon, B.; Börner, R.; Ansari, S.
2013-12-01
Helicopter-borne frequency-domain electromagnetic (HEM) surveys are used for fast high-resolution, three-dimensional (3-D) resistivity mapping. Nevertheless, 3-D modeling and inversion of an entire HEM data set is in many cases impractical and, therefore, interpretation is commonly based on one-dimensional (1-D) modeling and inversion tools. Such an approach is valid for environments with horizontally layered targets and for groundwater applications but there are areas of higher dimension that are not recovered correctly applying 1-D methods. The focus of this work is the multi-dimensional forward modeling. As there is no analytic solution to verify (or falsify) the obtained numerical solutions, comparison with 1-D values as well as amongst various two-dimensional (2-D) and 3-D codes is essential. At the center of a large structure (a few hundred meters edge length) and above the background structure in some distance to the anomaly 2-D and 3-D values should match the 1-D solution. Higher dimensional conditions are present at the edges of the anomaly and, therefore, only a comparison of different 2-D and 3-D codes gives an indication of the reliability of the solution. The more codes - especially if based on different methods and/or written by different programmers - agree the more reliable is the obtained synthetic data set. Very simple structures such as a conductive or resistive block embedded in a homogeneous or layered half-space without any topography and using a constant sensor height were chosen to calculate synthetic data. For the comparison one finite element 2-D code and numerous 3-D codes, which are based on finite difference, finite element and integral equation approaches, were applied. Preliminary results of the comparison will be shown and discussed. Additionally, challenges that arose from this comparative study will be addressed and further steps to approach more realistic field data settings for forward modeling will be discussed. As the driving
High speed miniature motorized endoscopic probe for 3D optical frequency domain imaging
NASA Astrophysics Data System (ADS)
Li, Jianan; Feroldi, Fabio; Mo, Jianhua; Helderman, Frank; de Groot, Mattijs; de Boer, Johannes F.
2013-03-01
We present a miniature motorized endoscopic probe for Optical Frequency Domain Imaging with an outer diameter of 1.65 mm and a rotation speed of 3,000 - 12,500 rpm. This is the smallest motorized high speed OCT probe to our knowledge. The probe has a motorized distal end which provides a significant advantage over proximally driven probes since it does not require a drive shaft to transfer the rotational torque to the distal end of the probe and functions without a fiber rotary junction. The probe has a focal Full Width at Half Maximum of 9.6 μm and a working distance of 0.47 mm. We analyzed the non-uniform rotation distortion and found a location fluctuation of only 1.87° in repeated measurements of the same object. The probe was integrated in a high-speed Optical Frequency Domain Imaging setup at 1310 nm We demonstrated its performance with imaging ex vivo pig bronchial and in vivo goat lung.
Time and frequency-domain identification and verification of BO-105 dynamic models
NASA Technical Reports Server (NTRS)
Kaletka, Juergen; Gruenhagen, Wolfgang V.; Tischler, Mark B.; Fletcher, Jay W.
1989-01-01
Mathematical models for the dynamics of the DLR BO 105 helicopter are extracted from flight test data using two different approaches: frequency-domain and time-domain identification. Both approaches are reviewed. Results from an extensive data consistency analysis are given. Identifications for 6 degrees of freedom (DOF) rigid body models are presented and compared in detail. The extracted models compare favorably and their prediction capability is demonstrated in verification results. Approaches to extend the 6 DOF models are addressed and first results are presented. System identification is broadly defined as the deduction of system characteristics from measured data. It provides the only possibility to extract both non-parametric (e.g., frequency responses) and parametric (e.g., state space matrices) aircraft models from flight test data and therefore gives a reliable characterization of the dynamics of the actually existing aircraft. Main applications of system identification are seen in areas where higher accuracies of the mathematical models are required: Simulation validation, control system design (in particular model-following control system design for in-flight simulation), and handling qualities.
Brain connectivity study of joint attention using frequency-domain optical imaging technique
NASA Astrophysics Data System (ADS)
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.
High-resolution wind profiling using combined spatial and frequency domain interferometry
NASA Astrophysics Data System (ADS)
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.
Frequency-Domain Tomography for Single-shot, Ultrafast Imaging of Evolving Laser-Plasma Accelerators
NASA Astrophysics Data System (ADS)
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-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.
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. PMID:20428484
Simulation of ultrasound two-dimensional array transducers using a frequency domain model.
Rao, Min; Varghese, Tomy; Zagzebski, James A
2008-07-01
Ultrasound imaging with two-dimensional (2D) arrays has garnered broad interest from scanner manufacturers and researchers for real time three-dimensional (3D) applications. Previously the authors described a frequency domain B-mode imaging model applicable for linear and phased array transducers. In this paper, the authors extend this model to incorporate 2D array transducers. Further approximations can be made based on the fact that the dimensions of the 2D array element are small. The model is compared with the widely used ultrasound simulation program FIELD II, which utilizes an approximate form of the time domain impulse response function. In a typical application, errors in simulated RF waveforms are less than 4% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/35 of those incurred using FIELD II. The 2D model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, dynamic receive focusing, and 3D beam steering can also be simulated.
Improved free-surface expression for frequency-domain elastic optimal mixed-grid modeling
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
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
A hybrid method for strong low-frequency noise suppression in prestack seismic data
NASA Astrophysics Data System (ADS)
Hu, Chunhua; Lu, Wenkai
2014-09-01
Low-frequency components are important portion of seismic data in exploration geophysics, and have great effects on seismic imaging of deep subsurface and full waveform inversion. Unfortunately, seismic data usually suffers from various kinds of noises and has low signal to noise ratio (SNR) in low-frequency band, although this situation has been improved by developments of acquisition technology. In this paper, we propose a low-frequency cascade filter (LFCF) in Fourier domain for strong low-frequency noise suppression in prestack gathers. LFCF includes a 1D adaptive median filter in f-x domain and a 2D notch filter in f-k domain, which is able to process high-amplitude swell noise, random noise, and seismic interference noise. We employ traces rearrangement and spike-detection mechanisms in adaptive f-x median filter, which can handle strong noise specifically, such as wide-spreading swell noise and tug noise. And a notch filter in f-k domain is designed to separate reflection signal and random noise by different apparent velocities. Through these means, our method can effectively attenuate low-frequency random and coherent noise while simultaneously protect the signal. Experiments on synthetic example and field data are conducted, and the results demonstrate that our method is practical and effective and can preserve signal down to 2 Hz.
Dual Domain Material Point Method for Materials in Extreme
NASA Astrophysics Data System (ADS)
Zhang, Duan; Dhakal, Tilak
Dual domain material point method is the latest version of the material point method designed to overcome many numerical difficulties of the original material point method with an increased numerical accuracy. In this talk, after reviewing the numerical theory of the method, we apply this method to cases involving extreme material deformation, shock propagation, and pulverization based on continuum theories. We will compare this method to other similar particle methods, and then examine the applicability and needed modification of the continuum theory for cases involving strong thermodynamic non-equilibrium. The history of the material deformation is often important in such systems. We will explore the Lagrangian capability brought by the use of particles in the dual domain material point method and introduce a multiscale scheme taking advantages of the particle-mesh communications in the method to study history dependent thermodynamically non-equilibrium systems, caused by extreme material deformations, such as hypervelocity impact and shock loading. We will also discuss the history tracking capability, analyze numerical advantages and difficulties, and show the results obtained from this numerical scheme. Work supported by ASC project of LANL.
Domain decomposed preconditioners with Krylov subspace methods as subdomain solvers
Pernice, M.
1994-12-31
Domain decomposed preconditioners for nonsymmetric partial differential equations typically require the solution of problems on the subdomains. Most implementations employ exact solvers to obtain these solutions. Consequently work and storage requirements for the subdomain problems grow rapidly with the size of the subdomain problems. Subdomain solves constitute the single largest computational cost of a domain decomposed preconditioner, and improving the efficiency of this phase of the computation will have a significant impact on the performance of the overall method. The small local memory available on the nodes of most message-passing multicomputers motivates consideration of the use of an iterative method for solving subdomain problems. For large-scale systems of equations that are derived from three-dimensional problems, memory considerations alone may dictate the need for using iterative methods for the subdomain problems. In addition to reduced storage requirements, use of an iterative solver on the subdomains allows flexibility in specifying the accuracy of the subdomain solutions. Substantial savings in solution time is possible if the quality of the domain decomposed preconditioner is not degraded too much by relaxing the accuracy of the subdomain solutions. While some work in this direction has been conducted for symmetric problems, similar studies for nonsymmetric problems appear not to have been pursued. This work represents a first step in this direction, and explores the effectiveness of performing subdomain solves using several transpose-free Krylov subspace methods, GMRES, transpose-free QMR, CGS, and a smoothed version of CGS. Depending on the difficulty of the subdomain problem and the convergence tolerance used, a reduction in solution time is possible in addition to the reduced memory requirements. The domain decomposed preconditioner is a Schur complement method in which the interface operators are approximated using interface probing.
Domain decomposition methods for the parallel computation of reacting flows
NASA Technical Reports Server (NTRS)
Keyes, David E.
1988-01-01
Domain decomposition is a natural route to parallel computing for partial differential equation solvers. Subdomains of which the original domain of definition is comprised are assigned to independent processors at the price of periodic coordination between processors to compute global parameters and maintain the requisite degree of continuity of the solution at the subdomain interfaces. In the domain-decomposed solution of steady multidimensional systems of PDEs by finite difference methods using a pseudo-transient version of Newton iteration, the only portion of the computation which generally stands in the way of efficient parallelization is the solution of the large, sparse linear systems arising at each Newton step. For some Jacobian matrices drawn from an actual two-dimensional reacting flow problem, comparisons are made between relaxation-based linear solvers and also preconditioned iterative methods of Conjugate Gradient and Chebyshev type, focusing attention on both iteration count and global inner product count. The generalized minimum residual method with block-ILU preconditioning is judged the best serial method among those considered, and parallel numerical experiments on the Encore Multimax demonstrate for it approximately 10-fold speedup on 16 processors.
A Robust Image Watermarking in the Joint Time-Frequency Domain
NASA Astrophysics Data System (ADS)
Öztürk, Mahmut; Akan, Aydın; Çekiç, Yalçın
2010-12-01
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.
Fast multiscale Gaussian beam methods for wave equations in bounded convex domains
Bao, Gang; Lai, Jun; Qian, Jianliang
2014-03-15
Motivated by fast multiscale Gaussian wavepacket transforms and multiscale Gaussian beam methods which were originally designed for pure initial-value problems of wave equations, we develop fast multiscale Gaussian beam methods for initial boundary value problems of wave equations in bounded convex domains in the high frequency regime. To compute the wave propagation in bounded convex domains, we have to take into account reflecting multiscale Gaussian beams, which are accomplished by enforcing reflecting boundary conditions during beam propagation and carrying out suitable reflecting beam summation. To propagate multiscale beams efficiently, we prove that the ratio of the squared magnitude of beam amplitude and the beam width is roughly conserved, and accordingly we propose an effective indicator to identify significant beams. We also prove that the resulting multiscale Gaussian beam methods converge asymptotically. Numerical examples demonstrate the accuracy and efficiency of the method.
NASA Astrophysics Data System (ADS)
Yang, Jianqiang; Zhu, Yong; Luo, Yun; Jiang, Tian
2010-10-01
The frequency stabilization error is an important error source to limit the precision of four frequency differential ring laser gyro (DILAG) in navigation application. Different from the traditional technology mainly related to frequency stabilization circuits design, this paper introduces a new method to solve the problem. The method can essentially minimize the frequency stabilization sensitivity of DILAG, by applying an outer longitudinal magnetic field to the gain region of DILAG. Through adjusting the value of magnetic field to make the frequency splitting equal to the Faraday splitting, the minimum frequency stabilization sensitivity of DILAG will be available. The physics mechanism and mathematic model of this method are analyzed and set up. Concrete steps to realize the method are given in detail. Experimental results have verified its validity and it can decrease the startup drift. Hence, this new method can improve the performance of DILAG, which will be helpful to navigation application.
Quantitative frequency-domain fluorescence spectroscopy in tissues and tissue-like media
NASA Astrophysics Data System (ADS)
Cerussi, Albert Edward
1999-09-01
In the never-ending quest for improved medical technology at lower cost, modern near-infrared optical spectroscopy offers the possibility of inexpensive technology for quantitative and non-invasive diagnoses. Hemoglobin is the dominant chromophore in the 700-900 nm spectral region and as such it allows for the optical assessment of hemoglobin concentration and tissue oxygenation by absorption spectroscopy. However, there are many other important physiologically relevant compounds or physiological states that cannot be effectively sensed via optical methods because of poor optical contrast. In such cases, contrast enhancements are required. Fluorescence spectroscopy is an attractive component of optical tissue spectroscopy. Exogenous fluorophores, as well as some endogenous ones, may furnish the desperately needed sensitivity and specificity that is lacking in near-infrared optical tissue spectroscopy. The main focus of this thesis was to investigate the generation and propagation of fluorescence photons inside tissues and tissue-like media (i.e., scattering dominated media). The standard concepts of fluorescence spectroscopy have been incorporated into a diffusion-based picture that is sometimes referred to as photon migration. The novelty of this work lies in the successful quantitative recovery of fluorescence lifetimes, absolute fluorescence quantum yields, fluorophore concentrations, emission spectra, and both scattering and absorption coefficients at the emission wavelength from a tissue-like medium. All of these parameters are sensitive to the fluorophore local environment and hence are indicators of the tissue's physiological state. One application demonstrating the capabilities of frequency-domain lifetime spectroscopy in tissue-like media is a study of the binding of ethidium bromide to bovine leukocytes in fresh milk. Ethidium bromide is a fluorescent dye that is commonly used to label DNA, and hence visualize chromosomes in cells. The lifetime of
Simplified approaches to some nonoverlapping domain decomposition methods
Xu, Jinchao
1996-12-31
An attempt will be made in this talk to present various domain decomposition methods in a way that is intuitively clear and technically coherent and concise. The basic framework used for analysis is the {open_quotes}parallel subspace correction{close_quotes} or {open_quotes}additive Schwarz{close_quotes} method, and other simple technical tools include {open_quotes}local-global{close_quotes} and {open_quotes}global-local{close_quotes} techniques, the formal one is for constructing subspace preconditioner based on a preconditioner on the whole space whereas the later one for constructing preconditioner on the whole space based on a subspace preconditioner. The domain decomposition methods discussed in this talk fall into two major categories: one, based on local Dirichlet problems, is related to the {open_quotes}substructuring method{close_quotes} and the other, based on local Neumann problems, is related to the {open_quotes}Neumann-Neumann method{close_quotes} and {open_quotes}balancing method{close_quotes}. All these methods will be presented in a systematic and coherent manner and the analysis for both two and three dimensional cases are carried out simultaneously. In particular, some intimate relationship between these algorithms are observed and some new variants of the algorithms are obtained.
Kakodkar, Rohit R.; Feser, Joseph P.
2015-09-07
We present a numerical approach to the solution of elastic phonon-interface and phonon-nanostructure scattering problems based on a frequency-domain decomposition of the atomistic equations of motion and the use of perfectly matched layer (PML) boundaries. Unlike molecular dynamic wavepacket analysis, the current approach provides the ability to simulate scattering from individual phonon modes, including wavevectors in highly dispersive regimes. Like the atomistic Green's function method, the technique reduces scattering problems to a system of linear algebraic equations via a sparse, tightly banded matrix regardless of dimensionality. However, the use of PML boundaries enables rapid absorption of scattered wave energies at the boundaries and provides a simple and inexpensive interpretation of the scattered phonon energy flux calculated from the energy dissipation rate in the PML. The accuracy of the method is demonstrated on connected monoatomic chains, for which an analytic solution is known. The parameters defining the PML are found to affect the performance and guidelines for selecting optimal parameters are given. The method is used to study the energy transmission coefficient for connected diatomic chains over all available wavevectors for both optical and longitudinal phonons; it is found that when there is discontinuity between sublattices, even connected chains of equivalent acoustic impedance have near-zero transmission coefficient for short wavelengths. The phonon scattering cross section of an embedded nanocylinder is calculated in 2D for a wide range of frequencies to demonstrate the extension of the method to high dimensions. The calculations match continuum theory for long-wavelength phonons and large cylinder radii, but otherwise show complex physics associated with discreteness of the lattice. Examples include Mie oscillations which terminate when incident phonon frequencies exceed the maximum available frequency in the embedded nanocylinder, and
Phonon Mean Free Path Spectra Measured by Broadband Frequency Domain Thermoreflectance
NASA Astrophysics Data System (ADS)
Malen, Jonathan
2014-03-01
Nonmetallic crystalline materials conduct heat by the transport of quantized atomic lattice vibrations called phonons. Thermal conductivity depends on how far phonons travel between scattering events -- their mean free paths (MFPs). Due to the breadth of the phonon MFP spectrum, nanostructuring of materials and devices can reduce thermal conductivity from bulk by scattering long MFP phonons, while short MFP phonons are unaffected. We have developed a novel approach called Broadband Frequency Domain Thermoreflectance (BB-FDTR) that uses high-frequency laser heating to generate non-Fourier heat conduction that can sort phonons based on their MFPs. BB-FDTR outputs thermal conductivity as a function of heating frequency. Through non-equilibrium Boltzmann Transport Equation models this data can be converted to thermal conductivity accumulation, which describes how thermal conductivity is summed from phonons with different MFPs. Relative to alternative approaches, BB-FDTR yields order-of-magnitude improvements in the resolution and breadth of the thermal conductivity accumulation function. We will present data for GaAs, GaN, AlN, Si, and SiC that show interesting commonalities near their respective Debye temperatures and suggest that there may be a universal phonon MFP spectrum for small unit cell non-metals in the high temperature limit. At the time of this abstract submission we are also working on measurements of semiconductor alloys and select metals that will be presented if completed by the conference.
Phan, Anh-Vu; Gray, Leonard J; Salvadori, Alberto
2010-01-01
In this paper, a two-dimensional symmetric-Galerkin boundary integral formulation for elastodynamic fracture analysis in the frequency domain is described. The numerical implementation is carried out with quadratic elements, allowing the use of an improved quarter-point element for accurately determining frequency responses of the dynamic stress intensity factors (DSIFs). To deal with singular and hypersingular integrals, the formulation is decomposed into two parts: the first part is identical to that for elastostatics while the second part contains at most logarithmic singularities. The treatment of the elastostatic singular and hypersingular singular integrals employs an exterior limit to the boundary, while the weakly singular integrals in the second part are handled by Gauss quadrature. Time histories (transient responses) of the DSIFs can be obtained in a post-processing step by applying the fast Fourier transform (FFT) and inverse FFT to the frequency responses of these DSIFs. Several test examples are presented for the calculation of the DSIFs due to two types of impact loading: Heaviside step loading and blast loading. The results suggest that the combination of symmetric-Galerkin and FFT algorithms in determining transient responses of the DSIFs is robust and effective.
Frequency-domain measurement of the spin-imbalance lifetime in superconductors
NASA Astrophysics Data System (ADS)
Quay, C. H. L.; Dutreix, C.; Chevallier, D.; Bena, C.; Aprili, M.
2016-06-01
We have measured the lifetime of spin imbalances in the quasiparticle population of a superconductor (τs) in the frequency domain. A time-dependent spin imbalance is created by injecting spin-polarized electrons at finite excitation frequencies into a thin-film mesoscopic superconductor (Al) in an in-plane magnetic field (in the Pauli limit). The time-averaged value of the spin-imbalance signal as a function of excitation frequency frf shows a cutoff at frf≈1 /(2 π τs) . The spin-imbalance lifetime is relatively constant in the accessible ranges of temperatures, with perhaps a slight increase with increasing magnetic field. Taking into account sample thickness effects, τs is consistent with previous measurements and of the order of the electron-electron scattering time τe e. Our data are qualitatively well described by a theoretical model taking into account all quasiparticle tunneling processes from a normal metal into a superconductor.
Yang, Bin; Lesicko, John; Sharma, Manu; Hill, Michael; Sacks, Michael S; Tunnell, James W
2015-04-01
The measurement of soft tissue fiber orientation is fundamental to pathophysiology and biomechanical function in a multitude of biomedical applications. However, many existing techniques for quantifying fiber structure rely on transmitted light, limiting general applicability and often requiring tissue processing. Herein, we present a novel wide-field reflectance-based imaging modality, which combines polarized light imaging (PLI) and spatial frequency domain imaging (SFDI) to rapidly quantify preferred fiber orientation on soft collagenous tissues. PLI utilizes the polarization dependent scattering property of fibers to determine preferred fiber orientation; SFDI imaging at high spatial frequency is introduced to reject the highly diffuse photons and to control imaging depth. As a result, photons scattered from the superficial layer of a multi-layered sample are highlighted. Thus, fiber orientation quantification can be achieved for the superficial layer with optical sectioning. We demonstrated on aortic heart valve leaflet that, at spatial frequency of f = 1mm(-1) , the diffuse background can be effectively rejected and the imaging depth can be limited, thus improving quantification accuracy. PMID:25909033
Yang, Bin; Lesicko, John; Sharma, Manu; Hill, Michael; Sacks, Michael S.; Tunnell, James W.
2015-01-01
The measurement of soft tissue fiber orientation is fundamental to pathophysiology and biomechanical function in a multitude of biomedical applications. However, many existing techniques for quantifying fiber structure rely on transmitted light, limiting general applicability and often requiring tissue processing. Herein, we present a novel wide-field reflectance-based imaging modality, which combines polarized light imaging (PLI) and spatial frequency domain imaging (SFDI) to rapidly quantify preferred fiber orientation on soft collagenous tissues. PLI utilizes the polarization dependent scattering property of fibers to determine preferred fiber orientation; SFDI imaging at high spatial frequency is introduced to reject the highly diffuse photons and to control imaging depth. As a result, photons scattered from the superficial layer of a multi-layered sample are highlighted. Thus, fiber orientation quantification can be achieved for the superficial layer with optical sectioning. We demonstrated on aortic heart valve leaflet that, at spatial frequency of f = 1mm−1, the diffuse background can be effectively rejected and the imaging depth can be limited, thus improving quantification accuracy. PMID:25909033
Ha, Jinyong; Yoo, Hongki; Tearney, Guillermo J; Bouma, Brett E
2012-08-01
Intracoronary optical coherence tomography and optical frequency domain imaging (OFDI) have been utilized for two-dimensional and three-dimensional imaging of vascular microanatomy. Image quality and the spatial accuracy of multidimensional reconstructions, however, can be degraded due to artifacts resulting from relative motion between the intracoronary catheter and the vessel wall. To track the relative motion of a catheter with regard to the vessel, a motion tracking system was incorporated with a standard OFDI system by using wavelength division multiplexing techniques. Motion of the vessel was acquired by a frequency shift of the backscattered light caused by the Doppler effect. A single monochromatic beam was utilized for tracking the relative longitudinal displacements of a catheter-based fiber probe with regard to the vessel. Although two tracking beams are, in general, required to correct for longitudinal motion artifacts, the accurate reconstruction in a longitudinal view was achieved by the Doppler frequency information of a single beam. Our results demonstrate that the single beam based motion tracking scheme is a cost-effective, practical approach to compensating for longitudinal distortions due to cardiac dynamics, thus leading to accurate quantitative analysis of 3D intracoronary OFDI.
Improving the execution of clinical guidelines and temporal data abstraction high-frequency domains.
Seyfang, Andreas; Paesold, Michael; Votruba, Peter; Miksch, Silvia
2008-01-01
The execution of clinical guidelines and protocols (CGPs) is a challenging task in high-frequency domains such as Intensive Care Units. On the one hand, sophisticated temporal data abstraction is required to match the low-level information from monitoring devices and electronic patient records with the high-level concepts in the CGPs. On the other hand, the frequency of the data delivered by monitoring devices mandates a highly efficient implementation of the reasoning engine which handles both data abstraction and execution of the guideline. The language Asbru represents CGPs as a hierarchy of skeletal plans and integrates intelligent temporal data abstraction with plan execution to bridge the gap between measurements and concepts in CGPs. We present our Asbru interpreter, which compiles abstraction rules and plans into a network of abstraction modules by the system. This network performs the content of the plans triggered by the arriving patient data. Our approach evaluated to be efficient enough to handle high-frequency data while coping with complex guidelines and temporal data abstraction.
NASA Astrophysics Data System (ADS)
Nadeau, K. P.; Khoury, P.; Mazhar, A.; Cuccia, D.; Durkin, A. J.
2013-03-01
Recently, digital photography has become an efficient and economic method to assist dermatologists in monitoring skin characteristics. Although this technology has advanced a great deal in resolution and costs, conventional digital cameras continue to only provide qualitative recording of color information. To address this issue, we are developing a compact, quantitative skin imaging camera by employing spatial frequency domain imaging (SFDI), a non-contact approach for determining tissue optical properties over a wide field-of-view. SFDI uses knowledge of optical properties at multiple wavelengths to recover concentrations of tissue constituents such as oxy/deoxy-hemoglobin, water, and melanin. This method has been well researched and presented in laboratory and research settings. The next step in the development of SFDI systems is to make typical systems compact and cheaper using commercial components. We present our findings by performing a component-by-component analysis of key SFDI system components including light sources, projectors, and cameras.