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.
New efforts using helicopter-borne and ground based electromagnetics for mineral exploration
Meyer, U.; Siemon, B.; Noell, U.; Gutzmer, J.; Spitzer, K.; Becken, M.
2014-12-01
Throughout the last decades mineral resources, especially rare earth elements, gained a steadily growing importance in industry and therefore as well in exploration. New targets for mineral investigations came into focus and known sources have been and will be revisited. Since most of the mining for mineral resources in the past took place in the upper hundred metres below surface new techniques made deeper mining economically feasible. Consequently, mining engineers need the best possible knowledge about the full spatial extent of prospective geological structures, including their maximum depths. Especially in Germany and Europe, politics changed in terms not to rely only on the global mineral trade market but on national resources, if available. BGR and partners therefore started research programs on different levels to evaluate and develop new technologies on environmental friendly, non-invasive spatial exploration using airborne and partly ground-based electromagnetic methods. Mining waste heaps have been explored for valuable residual minerals (research project ROBEHA), a promising tin bearing ore body is being explored by airborne electromagnetics (research project E3) and a new airborne technology is aimed at to be able to reach investigation depths of about 1 km (research project DESMEX). First results of the projects ROBEHA and E3 will be presented and the project layout of DESMEX will be discussed.
DEFF Research Database (Denmark)
Schamper, Cyril Noel Clarence; Auken, Esben; Sørensen, Kurt Ingvard K.I.
2014-01-01
by the geometry of the transmitter loop, we denote it the 'Coil Response'. The modelling of a helicopter-borne time-domain system by an equivalent electronic circuit shows that the time decay of the coil response remains identical whatever the position of the receiver loop, which is confirmed by field......Very early times in the order of 2-3 μs from the end of the turn-off ramp for time-domain electromagnetic systems are crucial for obtaining a detailed resolution of the near-surface geology in the depth interval 0-20 m. For transient electromagnetic systems working in the off time, an electric...... current is abruptly turned off in a large transmitter loop causing a secondary electromagnetic field to be generated by the eddy currents induced in the ground. Often, however, there is still a residual primary field generated by remaining slowly decaying currents in the transmitter loop. The decay...
Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media
Schmidt, Felix; Lünenschloss, Peter; Mai, Juliane; Wagner, Norman; Töpfer, Hannes; Bumberger, Jan
2016-04-01
The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections. Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric
DEFF Research Database (Denmark)
Steuner, Annika; Siemon, Bernhard; Auken, Esben
2010-01-01
at the University of Aarhus, Denmark. For verification of and comparison with the airborne methods, ground-basedtransient electromagnetics and 2-D resistivity surveying were carried out. The target of investigation was the Cuxhaven valley in NorthernGermany, which is a significant local groundwater reservoir...... outlines a shallow conductor at about 20m depth and a deeper conductor below 40m depth inside the valley. This is confirmedby 2-D resistivity surveying and a drilling. The thickness of the deeper conductor, however, is not revealed due to the limited investigation depthof the HEM system. The SkyTEM survey...... does not resolve the shallow conductor, but it outlines the thickness of the deeper clay layer inside thevalley and reveals a conductive layer at about 180m depth outside the valley. The SkyTEM results are very consistent with ground-based transientelectromagnetic soundings.Airborne electromagnetic...
High-Performance Computational Electromagnetics in Frequency-Domain and Time-Domain
2015-03-04
aforementioned contributions, for a given 1In view of its applications to seismic wave propagation Dr. Amlani’s PhD thesis received two awards at Cal- tech, one...for wave scattering problems. PhD thesis, California Institute of Technol- ogy, 2014. Available at http://www.its.caltech.edu/~obruno/preprints...solutions for some of the most challenging scattering problems in science and engineering. Electromagnetic scattering . Frequency domain solvers. Integral
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.
Florez, H M; Martinelli, M
2016-01-01
Correlation spectroscopy has been proposed as a spectroscopic technique for measuring the coherence between the ground states in electromagnetically induced transparency (EIT). While in time domain the steep dispersion in EIT condition accounts for the robustness of the correlation linewidth against power broadening, such physical insight was not directly established in the frequency domain. We propose a perturbative approach to describe the correlation spectroscopy of two noisy lasers coupled to a $\\Lambda$-transition in cold atoms, leading to EIT. Such approach leads to an analytical expression that maps the intensity correlation directly in terms of the absorption and dispersion of the light fields. Low and high perturbative regimes are investigated and demonstrate that, for coherent light sources, the first oder term in perturbation expansion represents a sufficient description for the correlation. Sidebands resonances are also observed, showing the richness of the frequency domain approach.
DEFF Research Database (Denmark)
Schamper, Cyril Noel Clarence; Auken, Esben; Sørensen, Kurt Ingvard K.I.
2014-01-01
current is abruptly turned off in a large transmitter loop causing a secondary electromagnetic field to be generated by the eddy currents induced in the ground. Often, however, there is still a residual primary field generated by remaining slowly decaying currents in the transmitter loop. The decay...... disturbs or biases the earth response data at the very early times. These biased data must be culled, or some specific processing must be applied in order to compensate or remove the residual primary field. As the bias response can be attributed to decaying currents with its time constantly controlled...
Fast time- and frequency-domain finite-element methods for electromagnetic analysis
Lee, Woochan
Fast electromagnetic analysis in time and frequency domain is of critical importance to the design of integrated circuits (IC) and other advanced engineering products and systems. Many IC structures constitute a very large scale problem in modeling and simulation, the size of which also continuously grows with the advancement of the processing technology. This results in numerical problems beyond the reach of existing most powerful computational resources. Different from many other engineering problems, the structure of most ICs is special in the sense that its geometry is of Manhattan type and its dielectrics are layered. Hence, it is important to develop structure-aware algorithms that take advantage of the structure specialties to speed up the computation. In addition, among existing time-domain methods, explicit methods can avoid solving a matrix equation. However, their time step is traditionally restricted by the space step for ensuring the stability of a time-domain simulation. Therefore, making explicit time-domain methods unconditionally stable is important to accelerate the computation. In addition to time-domain methods, frequency-domain methods have suffered from an indefinite system that makes an iterative solution difficult to converge fast. The first contribution of this work is a fast time-domain finite-element algorithm for the analysis and design of very large-scale on-chip circuits. The structure specialty of on-chip circuits such as Manhattan geometry and layered permittivity is preserved in the proposed algorithm. As a result, the large-scale matrix solution encountered in the 3-D circuit analysis is turned into a simple scaling of the solution of a small 1-D matrix, which can be obtained in linear (optimal) complexity with negligible cost. Furthermore, the time step size is not sacrificed, and the total number of time steps to be simulated is also significantly reduced, thus achieving a total cost reduction in CPU time. The second contribution
Tantum, Stacy L.; Colwell, Kenneth A.; Scott, Waymond R.; Torrione, Peter A.; Collins, Leslie M.; Morton, Kenneth D.
2013-06-01
Frequency-domain electromagnetic induction (EMI) sensors have been shown to provide target signatures which enable discrimination of landmines from harmless clutter. In particular, frequency-domain EMI sensors are well-suited for target characterization by inverting a physics-based signal model. In many model-based signal processing paradigms, the target signatures can be decomposed into a weighted sum of parameterized basis functions, where the basis functions are intrinsic to the target under consideration and the associated weights are a function of the target sensor orientation. When sensor array data is available, the spatial diversity of the measured signals may provide more information for estimating the basis function parameters. After model inversion, the basis function parameters can form the foundation of model-based classification of the target as landmine or clutter. In this work, sparse model inversion of spatial frequency-domain EMI sensor array data followed by target classification using a statistical model is investigated. Results for data measured with a prototype frequency-domain EMI sensor at a standardized test site are presented. Preliminary results indicate that extracting physics-based features from spatial frequency-domain EMI sensor array data followed by statistical classification provides an effective approach for classifying targets as landmine or clutter.
Tantum, Stacy L.; Colwell, Kenneth A.; Morton, Kenneth D., Jr.; Scott, Waymond R., Jr.; Collins, Leslie M.; Torrione, Peter A.
2012-06-01
Frequency-domain electromagnetic induction (EMI) sensors have been shown to provide target signatures which enable discrimination of landmines from harmless clutter. In particular, frequency-domain EMI sensors are well-suited for target characterization by inverting a physics-based signal model. In many model-based signal processing paradigms, the target signatures can be decomposed into a weighted sum of parameterized basis functions, where the basis functions are intrinsic to the target under consideration and the associated weights are a function of the target sensor orientation. When spatial data is available, the diversity of the measured signals may provide more information for estimating the basis function parameters. After model inversion, the basis function parameters can be used as features for classifying the target as landmine or clutter. In this work, feature extraction from spatial frequency-domain EMI sensor data is investigated. Results for data measured with a prototype frequency-domain EMI sensor at a standardized test site are presented. Preliminary results indicate that Structured relevance vector machine (sRVM) regression model inversion using spatial data provides stable, and sparse, sets of target features.
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.
Frequency-domain electromagnetic sounding with combination wave in near-field zone
Institute of Scientific and Technical Information of China (English)
苏发; 何继善
1996-01-01
By analysing the propagation law of electromagnetic wave,the distribution pattern of the field and the theory of frequency electromagnetic sounding,the physical mechanisms that make the frequency electromagnetic sounding in near-field zone difficult are discussed.Based on the theory of near source field,a new method of dual-frequency electromagnetic sounding of combination wave in near-field zone is advanced.Meanwhile,the method of measurement of fields,the definition of apparent resistivity and the numerical algorithm are approached.
Institute of Scientific and Technical Information of China (English)
YU Shi-jian; Cheng Jiu-long; LIU Jia-qi
2007-01-01
This paper took the abnormal geological objects with high or low resistivity in the coal face as the background to establish the physical model. 2D forward numerical simulation for electromagnetic wave equation was implemented by the finite-difference scheme. According to the simulative results, the attenuation-absorption coefficient were calculated respectively based on field intensity and frequency shift parameter. Research result indicates, when coal-bed contains high electric resistivity geological abnormal object or low electric resistivity geological abnormal object, absorption attenuation function researched by frequency shift parameter of electromagnetic wave signal is more sensitive than by electromagnetic field intensity parameter.
Chave, Alan D.; Everett, Mark E.; Mattsson, Johan; Boon, James; Midgley, Jonathan
2016-11-01
In recent years, marine controlled source electromagnetics (CSEM) has found increasing use in hydrocarbon exploration due to its ability to detect thin resistive zones beneath the seafloor. It is the purpose of this paper to evaluate the physics of CSEM for an ocean whose electrical thickness is comparable to or much thinner than that of the overburden using the in-line configuration through examination of the elliptically-polarized seafloor electric field, the time-averaged energy flow depicted by the real part of the complex Poynting vector, energy dissipation through Joule heating and the Fréchet derivatives of the seafloor field with respect to the sub-seafloor conductivity that is assumed to be isotropic. The deep water (ocean layer electrically much thicker than the overburden) seafloor electromagnetic response for a model containing a resistive reservoir layer has a greater amplitude and reduced phase as a function of offset compared to that for a halfspace, or a stronger and faster response. For an ocean whose electrical thickness is comparable to or much smaller than that of the overburden, the electric field displays a greater amplitude and reduced phase at small offsets, shifting to a stronger amplitude and increased phase at intermediate offsets, and a weaker amplitude and enhanced phase at long offsets, or a stronger and faster response that first changes to stronger and slower, and then transitions to weaker and slower. These transitions can be understood by visualizing the energy flow throughout the structure caused by the competing influences of the dipole source and guided energy flow in the reservoir layer, and the air interaction caused by coupling of the entire sub-seafloor resistivity structure with the sea surface. A stronger and faster response occurs when guided energy flow is dominant, while a weaker and slower response occurs when the air interaction is dominant. However, at intermediate offsets for some models, the air interaction can
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
Chave, Alan D.; Everett, Mark E.; Mattsson, Johan; Boon, James; Midgley, Jonathan
2017-02-01
In recent years, marine controlled source electromagnetics (CSEM) has found increasing use in hydrocarbon exploration due to its ability to detect thin resistive zones beneath the seafloor. It is the purpose of this paper to evaluate the physics of CSEM for an ocean whose electrical thickness is comparable to or much thinner than that of the overburden using the in-line configuration through examination of the elliptically polarized seafloor electric field, the time-averaged energy flow depicted by the real part of the complex Poynting vector, energy dissipation through Joule heating and the Fréchet derivatives of the seafloor field with respect to the subseafloor conductivity that is assumed to be isotropic. The deep water (ocean layer electrically much thicker than the overburden) seafloor EM response for a model containing a resistive reservoir layer has a greater amplitude and reduced phase as a function of offset compared to that for a half-space, or a stronger and faster response. For an ocean whose electrical thickness is comparable to or much smaller than that of the overburden, the electric field displays a greater amplitude and reduced phase at small offsets, shifting to a stronger amplitude and increased phase at intermediate offsets and a weaker amplitude and enhanced phase at long offsets, or a stronger and faster response that first changes to stronger and slower, and then transitions to weaker and slower. These transitions can be understood by visualizing the energy flow throughout the structure caused by the competing influences of the dipole source and guided energy flow in the reservoir layer, and the air interaction caused by coupling of the entire subseafloor resistivity structure with the sea surface. A stronger and faster response occurs when guided energy flow is dominant, while a weaker and slower response occurs when the air interaction is dominant. However, at intermediate offsets for some models, the air interaction can partially or
Mata, Luz Angelica Caudillo; Schwarzbach, Christoph
2016-01-01
In order to reduce the computational cost of the simulation of electromagnetic responses in geophysical settings that involve highly heterogeneous media, we develop a multiscale finite volume method with oversampling for the quasi-static Maxwell's equations in the frequency domain. We assume a coarse mesh nested within a fine mesh that accurately discretizes the problem. For each coarse cell, we independently solve a local version of the original Maxwell's system subject to linear boundary conditions on an extended domain, which includes the coarse cell and a neighborhood of fine cells around it. The local Maxwell's system is solved using the fine mesh contained in the extended domain and the mimetic finite volume method. Next, these local solutions (basis functions) together with a weak-continuity condition are used to construct a coarse-mesh version of the global problem. The basis functions can be used to obtain the fine-mesh details from the solution of the coarse-mesh problem. Our approach leads to a sig...
Ito, Y.; Anan, S.; Okazaki, K.
2010-12-01
In recent years, many case studies with the investigation by the helicopter-borne electromagnetic method; HEM and the helicopter-borne magnetic method; HMG are reported in Japan. Both methods are suitable methods to acquire the three-dimensional information to evaluate geological features properties of the underground in promptly and over the wide area. The authors describe the applicability on the civil engineering geology fields of both methods through the confirming results of the correspondence another geological investigation results to evaluate the geological structures in the underground of road slopes situated along the coast in the east part of Hokkaido, Japan. The investigated sites were road slopes where surface collapses were caused in the past time. The geological features of the investigated site were clarified as the Neocene mudstone, fine-grained sandstone, tuffs, conglomerates and terrace deposit by the results of the geological survey. The height of the road slopes are above the sea 60m or more, and a smooth terrace spreads out their backwards. The authors carried out HEM, frequency domain, and the HMG. In addition, vertical electric soundings and the electric conductance such as the stream water of neighborhood were measured for the calibration of the resistivity by HEM and confirmation of the resistivity distribution sallow part of the site ground. As the results of HEM, the apparent resistivity distribution is high in a shallow part, and low in the depth overall. The change in resistivity distribution was thought to be caused corresponding to the difference of the rock type on this site. In general, the specimen resistivity is the order of conglomerate, sandstone, mudstone for sedimentary rocks of this site. The change in resistivity distribution was also thought to be corresponding to the moisture states balance. The resistivity is high in the unsaturated zone of shallow part, and low in the saturation zone of the deep part. As for this, the
Robust 1D inversion and analysis of helicopter electromagnetic (HEM) data
DEFF Research Database (Denmark)
Tølbøll, R.J.; Christensen, N.B.
2006-01-01
Ground-based electrical and electromagnetic methods are used systematically for quantitative hydrogeologic investigations in Denmark. In recent years, a desire for faster and more cost-efficient methods has led to growing interest in the possibility of using airborne systems, and in 2001 a number...... of test flights were performed using a frequency-domain, helicopter-borne electromagnetic (HEM) system. We perform a theoretical examination of the resolution capabilities of the applied system. Quantitative model parameter analyses show that the system only weakly resolves conductive, near-surface layers...
Energy Technology Data Exchange (ETDEWEB)
campione, salvatore; Warne, Larry K.; Schiek, Richard; Basilio, Lorena I.
2017-09-01
This report details the modeling results for the response of a finite-length dissipative conductor interacting with a conducting ground to a hypothetical nuclear device with the same output energy spectrum as the Fat Man device. We use a frequency-domain method based on transmission line theory and implemented it in a code we call ATLOG - Analytic Transmission Line Over Ground. Select results are compared to ones computed using the circuit simulator Xyce. Intentionally Left Blank
Minsley, Burke J.
2011-01-01
A meaningful interpretation of geophysical measurements requires an assessment of the space of models that are consistent with the data, rather than just a single, ‘best’ model which does not convey information about parameter uncertainty. For this purpose, a trans-dimensional Bayesian Markov chain Monte Carlo (MCMC) algorithm is developed for assessing frequencydomain electromagnetic (FDEM) data acquired from airborne or ground-based systems. By sampling the distribution of models that are consistent with measured data and any prior knowledge, valuable inferences can be made about parameter values such as the likely depth to an interface, the distribution of possible resistivity values as a function of depth and non-unique relationships between parameters. The trans-dimensional aspect of the algorithm allows the number of layers to be a free parameter that is controlled by the data, where models with fewer layers are inherently favoured, which provides a natural measure of parsimony and a signiﬁcant degree of ﬂexibility in parametrization. The MCMC algorithm is used with synthetic examples to illustrate how the distribution of acceptable models is affected by the choice of prior information, the system geometry and conﬁguration and the uncertainty in the measured system elevation. An airborne FDEM data set that was acquired for the purpose of hydrogeological characterization is also studied. The results compare favorably with traditional least-squares analysis, borehole resistivity and lithology logs from the site, and also provide new information about parameter uncertainty necessary for model assessment.
Okuma, S.; Ueda, T.; Mitsuhata, Y.; Uchida, T.
2012-12-01
The Geological Survey of Japan, AIST conducted a helicopter-borne EM and magnetic survey over tsunami invaded areas in northeast Japan 15 months after the 2011 off the Pacific coast of Tohoku Earthquake. The purpose of the survey is to map the electrical resistivity of the ground intruded by seawater during the tsunami on March 11, 2011 for its reutilization as farming lands and water assessment of the area. The survey was flown in June 2012 at an altitude of 60m above ground with a speed of 50km/h along survey and traverse lines spaced 100m and 1,000m apart, respectively. The airborne EM system (Fuguro Airborne Surveys' RESOLVE system) was installed in a bird and towed 30m below the helicopter. This is a frequency-domain system operated at five frequencies (340, 1,500, 6,900, 31,000, 140,000 Hz) in a horizontal coplanar configuration and at a frequency (3,300 Hz) in a coaxial configuration. The survey area is located at the border of Miyagi and Fukushima Prefectures along the Pacific coast in the southern part of the Sendai Plain and is divided into two sub-areas: Watari-Yamamoto-Shinchi area (area A) and Matsukawa-ura Bay area (area B). The area A is known for its production of high-quality strawberries on beach ridges and much fresh groundwater has been used for irrigation of strawberries and warming of strawberry greenhouses by water curtain. However, the salinity of groundwater from shallow irrigation wells in this area increased dramatically after the tsunami (Mori et al., 2012). Since it still remains at high level, there is an urgent need to find new water resources. Whereas, the area B is characterized by a beautiful lagoon called the Matsukawa-ura which is preserved as one of prefectural parks of Fukushima Prefecture. Rice fields occupy the areas west of the Matsukawa-ura and most of them were covered by seawater during the attack of the tsunami. Desalinization of the rice fields is being conducted intensively to resume rice farming in these fields. The
Pragmatic circuits frequency domain
Eccles, William
2006-01-01
Pragmatic Circuits: Frequency Domain goes through the Laplace transform to get from the time domain to topics that include the s-plane, Bode diagrams, and the sinusoidal steady state. This second of three volumes ends with a-c power, which, although it is just a special case of the sinusoidal steady state, is an important topic with unique techniques and terminology. Pragmatic Circuits: Frequency Domain is focused on the frequency domain. In other words, time will no longer be the independent variable in our analysis. The two other volumes in the Pragmatic Circuits series include titles on DC
Recent Ice thickness helicopter borne radar surveys in Patagonia
Rivera, Andres; Zamora, Rodrigo; Andres Uribe, Jose; Oberreuter, Jonathan; Gacitua, Guisella; Rignot, Eric
2014-05-01
The Patagonian icefields are the biggest temperate ice bodies in southern hemisphere, which have experienced important areal shrinkage and thinning in recent decades, significantly contributing to sea level rise. The main driving factor behind this retreating condition is recent decade atmospheric warming explaining higher melting rates and equilibrium line altitude upward migration. Ice dynamic is also playing an important role especially in glaciers calving into deep fjords or lakes, type of glaciers that are predominant in the Patagonian icefields. In order to better understand their ice dynamics, several recent works have measured ice velocities using feature tracking and other techniques, however, ice thickness is still barely known. In spite of several on the ground radar measurements successfully detecting several hundred of m of ice thickness at the higher plateaus, this variable remains the great missing part of the equation especially when the thickness is approximately deeper than 600 m or where the glacier surfaces are very crevassed or nearby the Equilibrium line Altitude, where on the ground measurements are logistically constrained. In order to tackle the lack of thickness data, a helicopter borne radar system was used to survey several Patagonian temperate glaciers calving into fjords (Glaciares San Rafael and Jorge Montt) or lakes (Nef, Colonia and Steffen). The radar system is comprised by a hanging bow-tie dipole antenna working at a central frequency of 20 MHz. The antenna is an aluminum structure of 7 x 5 x 1.2 m weighting near 350 kg that is hanging at 20 m below a helicopter, and is connected to the helicopter cabin by an optical fiber cable. At the antenna are installed a 3,200 Volts peak transmitter, a two channel radar receiver, and an integrated GPS registering each trace. The helicopter flying speed was kept at near 40 knots and the antenna was normally hanging at 40 m above the ice. The surveys took place along predefined tracks
Institute of Scientific and Technical Information of China (English)
陈明生; 王时文; 马韬; 吴先良
2014-01-01
Method of moments (MOM) is a common numerical method for solving electromagnetics, which is used widely owing to its high accuracy. As the traditional MOM is applied to solving electromagnetic problem in both spatial and frequency domains, the matrix equation generated from the integral equation must be solved repeatedly since small spatial increments and frequency increments are both required. To resolve problems of this kind, the compressive sensing (CS) theory combined with the asymptotic waveform evaluation (AWE) is introduced to form a new efficient computational method. Firstly, a new incident source is constructed based on CS theory, in which much spatial information is included. Secondly, illuminated by the new incident source, the new equation is solved by AWE technique, and finally a fast implement is formed for solving electromagnetic scattering characteristics in both spatial and frequency domains.%矩量法是求解目标电磁散射问题的一种常用数值方法，因其精度较高而被广泛应用。应用矩量法求解目标频空电磁散射特性时，随着入射波的角度和频率的变化，需要间隔很小的角度和频率步长反复求解矩量法生成的矩阵方程，运算量极大。为解决此类问题，本文结合压缩感知理论和渐近波形估计形成一种新的有效计算方法。首先，基于压缩感知理论引入一种富含空间信息的新型入射源，其次，在该入射源照射下应用渐近波形估计技术求解，从而快速实现目标频空电磁散射特性分析。
Helicopter-borne measurements of sea ice thickness, using a small and lightweight, digital EM system
Haas, Christian; Lobach, John; Hendricks, Stefan; Rabenstein, Lasse; Pfaffling, Andreas
2009-03-01
Sea ice is an important climate variable and is also an obstacle for marine operations in polar regions. We have developed a small and lightweight, digitally operated frequency-domain electromagnetic-induction (EM) system, a so-called EM bird, dedicated for measurements of sea ice thickness. It is 3.5 m long and weighs only 105 kg, and can therefore easily be shipped to remote places and operated from icebreakers and small helicopters. Here, we describe the technical design of the bird operating at two frequencies of f1 = 3.68 kHz and f2 = 112 kHz, and study its technical performance. On average, noise amounts to ± 8.5 ppm and ± 17.5 ppm for f1 and f2, respectively. Electrical drift amounts to 200 ppm/h and 2000 ppm/h for f1 and f2, during the first 0.5 h of operation. It is reduced by 75% after 2 h. Calibration of the Inphase and Quadrature ppm signals varies by 2 to 3%. A sensitivity study shows that all these signal variations do affect the accuracy of the ice thickness retrieval, but that it remains better than ± 0.1 m over level ice in most cases. This accuracy is also confirmed by means of comparisons of the helicopter EM data with other thickness measurements. The paper also presents the ice thickness retrieval from single-component Inphase data of f1.
Institute of Scientific and Technical Information of China (English)
何德平; 周志军; 童孝忠
2012-01-01
Based on Matlab as programming tool, the formula of 2-D forward modeling of frequency domain controlled-source electromagnetic is derived adopting the finite element method of quadratic interpolation in a rectangular element.In order to simulate the infinity border and meet the memory requirement of computer, the non-uniform gird is designed with ensuring the computation accuracy. In programm compiling, it only stored the non-zero elements of finite element matrix to reduce the forward calculation time. By numerical simulation of homogeneous half-space model and electromagnetic response of 2-D model, the corresponding curve of apparent resistivity and impendence phase is obtained, and the correctness of the forward modeling algorithm is verified.%该文以Matlab为程序编译工具,采用双二次插值的有限单元法,推导出频率域可控源电磁法二维正演的计算公式.为了模拟无穷远边界及满足计算机的内存需求,在保证计算精度的情况下设计了非均匀网格剖分.在程序编制中,只存储有限元系数矩阵的非零元素,大大减少了正演计算的时间.通过对均匀半空间和二维模型电磁响应的计算,获得了相应的视电阻率和阻抗相位曲线,验证了算法的正确性.
Frequency-Domain Optical Mammogram
2002-10-01
the tumor. * Combination of the above two points into a composite false-color breast image containing structural information (from the second...Antonangeli, A. Savoia, T. Parasassi, and N. Rosato, " Plastique : a synchrotron radiation beamline for time resolved fluorescence in the frequency domain
Development and evaluation of a helicopter-borne water-quality monitoring system
Wallace, J. W.; Jordan, R. A.; Flynn, J.; Thomas, R. W.
1978-01-01
A small, helicopter-borne water-quality monitoring package is being developed by the NASA/EPA using a combination of basic in situ water quality sensors and physical sample collector technology. The package is a lightweight system which can be carried and operated by one person as a passenger in a small helicopter typically available by rental at commercial airports. Real-time measurements are made by suspending the water quality monitoring package with a cable from the hovering helicopter. Designed primarily for use in rapidly assessing hazardous material spills in inland and coastal zone water bodies, the system can survey as many as 20 data stations up to 1.5 kilometers apart in 1 hour. The system provides several channels of sensor data and allows for the addition of future sensors. The system will also collect samples from selected sites with sample collection on command. An EPA Spill Response Team member can easily transport, deploy, and operate the water quality monitoring package to determine the distribution, movement, and concentration of the spilled material in the water body.
Mapping Saturated Areas With a Helicopter-Borne C Band Scatterometer
Brun, C.; Bernard, R.; Vidal-Madjar, D.; Gascuel-Odoux, C.; Merot, P.; Duchesne, J.; Nicolas, H.
1990-05-01
The "contributing area" concept is one of several basic concepts in modeling hydrologic processes used to explain storm runoff production. The main difficulty in using this concept of variable source areas is the identification and characterization of saturated areas according to the temporal and spatial variability during a storm event. In this experiment a helicopter-borne C band scatterometer has been used to locate the saturated areas within a small watershed. In contrast to the general results, where radar cross section increases with soil moisture, calibration shows a backscatter coefficient decreasing for the high gravimetric water contents of the saturated areas, which may be due to the increasing importance of specular reflection processes. It appears that a threshold on the backscatter coefficient may be determined which would allow the location of saturated areas, independent of the nature of the field surface (vegetation cover or slope). These experiments, which were intended partly as ERS 1 satellite simulations, show that active microwaves may be a good tool for partial hydrology.
Frequency domain FIR and IIR adaptive filters
Lynn, D. W.
1990-01-01
A discussion of the LMS adaptive filter relating to its convergence characteristics and the problems associated with disparate eigenvalues is presented. This is used to introduce the concept of proportional convergence. An approach is used to analyze the convergence characteristics of block frequency-domain adaptive filters. This leads to a development showing how the frequency-domain FIR adaptive filter is easily modified to provide proportional convergence. These ideas are extended to a block frequency-domain IIR adaptive filter and the idea of proportional convergence is applied. Experimental results illustrating proportional convergence in both FIR and IIR frequency-domain block adaptive filters is presented.
Piermattei, Livia; Hollaus, Markus; Pfeifer, Norbert; Chen, Yuwei; Karjalainen, Mika; Hakala, Teemu; Hyyppä, Juha; Wagner, Wolfgang
2017-04-01
Forests are complex ecosystems that show substantial variation with respect to climate, management regime, stand history, disturbance, and needs of local communities. The dynamic processes of growth and disturbance are reflected in the structural components of forests that include the canopy vertical structure and geometry (e.g. size, height, and form), tree position and species diversity. Current remote-sensing systems to measure forest structural attributes include passive optical sensors and active sensors. The technological capabilities of active remote sensing like the ability to penetrate the vegetation and provide information about its vertical structure has promoted an extensive use of LiDAR (Light Detection And Ranging) and radar (RAdio Detection And Ranging) system over the last 20 years. LiDAR measurements from aircraft (airborne laser scanning, ALS) currently represents the primary data source for three-dimensional information on forest vertical structure. Contrary, despite the potential of radar remote sensing, their use is not yet established in forest monitoring. In order to better understand the interaction of pulsed radar with the forest canopy, and to increase the feasibility of this system, the Finnish Geospatial Research Institute has developed a helicopter-borne profiling radar system, called TomoRadar. TomoRadar is capable of recording a canopy-penetrating profile of forests. To georeference the radar measurements the system was equipped with a global navigation satellite system and an inertial measurement unit with a centimeter level accuracy of the flight trajectory. The TomoRadar operates at Ku-band, (wave lengths λ 1.5cm) with two separated parabolic antennas providing co- and cross-polarization modes. The purpose of this work is to investigate the capability of the TomoRadar system, for estimating the forest vertical profile, terrain topography and tree height. We analysed 600 m TomoRadar crosspolarized (i.e. horizontal - vertical
Frequency Domain Image Filtering Using CUDA
Directory of Open Access Journals (Sweden)
Muhammad Awais Rajput
2014-10-01
Full Text Available In this paper, we investigate the implementation of image filtering in frequency domain using NVIDIA?s CUDA (Compute Unified Device Architecture. In contrast to signal and image filtering in spatial domain which uses convolution operations and hence is more compute-intensive for filters having larger spatial extent, the frequency domain filtering uses FFT (Fast Fourier Transform which is much faster and significantly reduces the computational complexity of the filtering. We implement the frequency domain filtering on CPU and GPU respectively and analyze the speed-up obtained from the CUDA?s parallel processing paradigm. In order to demonstrate the efficiency of frequency domain filtering on CUDA, we implement three frequency domain filters, i.e., Butterworth, low-pass and Gaussian for processing different sizes of images on CPU and GPU respectively and perform the GPU vs. CPU benchmarks. The results presented in this paper show that the frequency domain filtering with CUDA achieves significant speed-up over the CPU processing in frequency domain with the same level of (output image quality on both the processing architectures
Wideband Radar Echo Frequency-domain Simulation and Analysis for High Speed Moving Targets
Directory of Open Access Journals (Sweden)
Ning Chao
2014-04-01
Full Text Available A frequency-domain method is proposed for wideband radar echo simulation of high-speed moving targets. Based on the physical process of electromagnetic waves observing a moving target, a frequency-domain echo model of wideband radar is constructed, and the block diagram of the radar echo simulation in frequency-domain is presented. Then, the impacts of radial velocity and slant range on the matching filtering of LFM radar are analyzed, and some quantitative conclusions on the shift and expansion of the radar profiles are obtained. Simulation results illustrate the correctness and efficiency of the proposed method.
Load Estimation by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Pedersen, Ivar Chr. Bjerg; Hansen, Søren Mosegaard; Brincker, Rune;
2007-01-01
When performing operational modal analysis the dynamic loading is unknown, however, once the modal properties of the structure have been estimated, the transfer matrix can be obtained, and the loading can be estimated by inverse filtering. In this paper loads in frequency domain are estimated...... by analysis of simulated responses of a 4 DOF system, for which the exact modal parameters are known. This estimation approach entails modal identification of the natural eigenfrequencies, mode shapes and damping ratios by the frequency domain decomposition technique. Scaled mode shapes are determined by use...
System Identification A Frequency Domain Approach
Pintelon, Rik
2012-01-01
System identification is a general term used to describe mathematical tools and algorithms that build dynamical models from measured data. Used for prediction, control, physical interpretation, and the designing of any electrical systems, they are vital in the fields of electrical, mechanical, civil, and chemical engineering. Focusing mainly on frequency domain techniques, System Identification: A Frequency Domain Approach, Second Edition also studies in detail the similarities and differences with the classical time domain approach. It high??lights many of the important steps in the identi
Directory of Open Access Journals (Sweden)
L. Sold
2014-08-01
Full Text Available The spatial representation of accumulation measurements is a major limitation for current glacier mass balance monitoring approaches. Here, we present a new method for estimating annual accumulation rates on a temperate alpine glacier based on the interpretation of internal reflection horizons (IRH in helicopter-borne ground-penetrating radar (GPR data. For each individual GPR measurement, the signal traveltime is combined with a simple model for firn densification and refreezing of meltwater. The model is calibrated at locations where GPR profiles intersect in two subsequent years and the densification can be tracked over time. Two 10.5 m long firn cores provide a reference for the density and chronology of firn layers. Thereby, IRH correspond to density maxima, but not exclusively to former summer glacier surfaces. From GPR profiles across the accumulation area, we obtain spatial distributions of water equivalent for at least four annual firn layers, reaching a mean density of 0.74 g cm−3. Refreezing accounts for 9% of the density increase over time and depth. The strongest limitation to our method is the dependence on layer chronology assumptions. The uncertainties inherent to the modelling approach itself are in the same order of conventional point measurements in snow pits. We show that GPR can be used to complement existing mass balance monitoring programs on temperate alpine glaciers, but also to retrospectively extend newly initiated time series.
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, ...
Institute of Scientific and Technical Information of China (English)
朱凯光; 杨建文
2008-01-01
We present the theoretical investigations of magnetometric resistivity and frequency domain electromagnetic methods in monitoring and mapping contaminant transport in groundwater systems. Taking the uniform media conceptualized model with a contaminant source in the ground surface as an example, numerical geo-electrical models are constructed based on the hydrological simulation results of contaminant concentration evolutions. The time-lapse 2-D forward modeling of MMR and the 1-D inversion results of FEM prove that these two geophysical methods are effective in contaminant plume monitoring. Based on geophysical simulations, the instructions for instrument design are given.%本文对磁电阻率法与频率域电磁法在地下水污染监测中的应用进行了理论研究.以污染物位于地表的均匀介质模型为例,根据污染物扩散的水文地质动态仿真结果,计算出与各监测时刻对应的地下水污染地电模型.通过各地电模型的二维磁电阻率法正演模拟结果以及一维频率域电磁法的反演结果,验证了这两种地球物理方法在地下水污染物运移监测中的有效性.
Helicopter-Borne Scatterometer.
1982-10-01
averagec ret-Os: Height: 2 52 noches 64.0 r- 10" single- nerod 1100 ris resolution) Depth: 10.65 riches 270 5 rr, 10’ rerrods averaged 110 nis...unregulated voltage within the range of 22 to 30 volts. Transients of up to 80 volts in accordance with Figure 6 of MIL -STD-704-A will not normally damage
Communicating oscillatory networks: frequency domain analysis
Directory of Open Access Journals (Sweden)
Ihekwaba Adaoha EC
2011-12-01
Full Text Available Abstract Background Constructing predictive dynamic models of interacting signalling networks remains one of the great challenges facing systems biology. While detailed dynamical data exists about individual pathways, the task of combining such data without further lengthy experimentation is highly nontrivial. The communicating links between pathways, implicitly assumed to be unimportant and thus excluded, are precisely what become important in the larger system and must be reinstated. To maintain the delicate phase relationships between signals, signalling networks demand accurate dynamical parameters, but parameters optimised in isolation and under varying conditions are unlikely to remain optimal when combined. The computational burden of estimating parameters increases exponentially with increasing system size, so it is crucial to find precise and efficient ways of measuring the behaviour of systems, in order to re-use existing work. Results Motivated by the above, we present a new frequency domain-based systematic analysis technique that attempts to address the challenge of network assembly by defining a rigorous means to quantify the behaviour of stochastic systems. As our focus we construct a novel coupled oscillatory model of p53, NF-kB and the mammalian cell cycle, based on recent experimentally verified mathematical models. Informed by online databases of protein networks and interactions, we distilled their key elements into simplified models containing the most significant parts. Having coupled these systems, we constructed stochastic models for use in our frequency domain analysis. We used our new technique to investigate the crosstalk between the components of our model and measure the efficacy of certain network-based heuristic measures. Conclusions We find that the interactions between the networks we study are highly complex and not intuitive: (i points of maximum perturbation do not necessarily correspond to points of maximum
Time delay measurement in the frequency domain
Energy Technology Data Exchange (ETDEWEB)
Durbin, Stephen M., E-mail: durbin@purdue.edu; Liu, Shih-Chieh [Purdue University, West Lafayette, IN 47907 (United States); Dufresne, Eric M.; Li, Yuelin; Wen, Haidan [Argonne National Laboratory, Argonne, IL 60439 (United States)
2015-08-06
A simple frequency domain technique for determining the time delay between laser pump and X-ray probe pulses achieves 1 ps resolution even for ∼100 ps synchrotron pulses, permitting improved pump–probe characterization of ultrafast processes. Pump–probe studies at synchrotrons using X-ray and laser pulses require accurate determination of the time delay between pulses. This becomes especially important when observing ultrafast responses with lifetimes approaching or even less than the X-ray pulse duration (∼100 ps). The standard approach of inspecting the time response of a detector sensitive to both types of pulses can have limitations due to dissimilar pulse profiles and other experimental factors. Here, a simple alternative is presented, where the frequency response of the detector is monitored versus time delay. Measurements readily demonstrate a time resolution of ∼1 ps. Improved precision is possible by simply extending the data acquisition time.
Realization of Thermal Inertia in Frequency Domain
Directory of Open Access Journals (Sweden)
Boe-Shong Hong
2014-02-01
Full Text Available To realize the lagging behavior in heat conduction observed in these two decades, this paper firstly theoretically excludes the possibility that the underlying thermal inertia is a result of the time delay in heat diffusion. Instead, we verify in experiments the electro-thermal analogy, wherein the thermal inertial is parameterized by thermal inductance that formulates hyperbolic heat-conduction. The thermal hyperbolicity exhibits a special frequency response in Bode plot, wherein the amplitude ratios is kept flat after crossing some certain frequency, as opposed to Fourier heat-conduction. We apply this specialty to design an instrument that reliably identifies thermal inductances of some materials in frequency domain. The instrument is embedded with a DSP-based frequency synthesizer capable of modulating frequencies in utmost high-resolution. Thermal inertia implies a new possibility for energy storage in analogy to inductive energy storage in electricity or mechanics.
Comparison of the domain and frequency domain state feedbacks
Energy Technology Data Exchange (ETDEWEB)
Zhang, S.Y.
1986-01-01
In this paper, we present explicitly the equivalence of the time domain and frequency domain state feedbacks, as well as the dynamic state feedback and a modified frequency domain state feedback, from the closed-loop transfer function point of view. The difference of the two approaches is also shown.
Estimated Frequency Domain Model Uncertainties used in Robust Controller Design
DEFF Research Database (Denmark)
Tøffner-Clausen, S.; Andersen, Palle; Stoustrup, Jakob;
1994-01-01
This paper deals with the combination of system identification and robust controller design. Recent results on estimation of frequency domain model uncertainty are......This paper deals with the combination of system identification and robust controller design. Recent results on estimation of frequency domain model uncertainty are...
AU-FREDI - AUTONOMOUS FREQUENCY DOMAIN IDENTIFICATION
Yam, Y.
1994-01-01
The Autonomous Frequency Domain Identification program, AU-FREDI, is a system of methods, algorithms and software that was developed for the identification of structural dynamic parameters and system transfer function characterization for control of large space platforms and flexible spacecraft. It was validated in the CALTECH/Jet Propulsion Laboratory's Large Spacecraft Control Laboratory. Due to the unique characteristics of this laboratory environment, and the environment-specific nature of many of the software's routines, AU-FREDI should be considered to be a collection of routines which can be modified and reassembled to suit system identification and control experiments on large flexible structures. The AU-FREDI software was originally designed to command plant excitation and handle subsequent input/output data transfer, and to conduct system identification based on the I/O data. Key features of the AU-FREDI methodology are as follows: 1. AU-FREDI has on-line digital filter design to support on-orbit optimal input design and data composition. 2. Data composition of experimental data in overlapping frequency bands overcomes finite actuator power constraints. 3. Recursive least squares sine-dwell estimation accurately handles digitized sinusoids and low frequency modes. 4. The system also includes automated estimation of model order using a product moment matrix. 5. A sample-data transfer function parametrization supports digital control design. 6. Minimum variance estimation is assured with a curve fitting algorithm with iterative reweighting. 7. Robust root solvers accurately factorize high order polynomials to determine frequency and damping estimates. 8. Output error characterization of model additive uncertainty supports robustness analysis. The research objectives associated with AU-FREDI were particularly useful in focusing the identification methodology for realistic on-orbit testing conditions. Rather than estimating the entire structure, as is
Determination of beam coupling impedance in the frequency domain
Energy Technology Data Exchange (ETDEWEB)
Niedermayer, Uwe
2016-07-01
The concept of beam coupling impedance describes the electromagnetic interaction of uniformly moving charged particles with their surrounding structures in the Frequency Domain (FD). In synchrotron accelerators, beam coupling impedances can lead to beam induced component heating and coherent beam instabilities. Thus, in order to ensure the stable operation of a synchrotron, its impedances have to be quantified and their effects have to be controlled. Nowadays, beam coupling impedances are mostly obtained by Fourier transform of wake potentials, which are the results of Time Domain (TD) simulations. However, at low frequencies, low beam velocity, or for dispersive materials, TD simulations become unhandy. In this area, analytical calculations of beam coupling impedance in the FD, combined with geometry approximations, are still widely used. This thesis describes the development of two electromagnetic field solvers to obtain the beam coupling impedance directly in the FD, where the beam velocity is only a parameter and dispersive materials can be included easily. One solver is based on the Finite Integration Technique (FIT) on a staircase mesh. It is implemented both in 2D and 3D. However, the staircase mesh is inefficient on curved structures, which is particularly problematic for the modeling of a dipole source, that is required for the computation of the transverse beam coupling impedance. This issue is overcome by the second solver developed in this thesis, which is based on the Finite Element Method (FEM) on an unstructured triangular mesh. It is implemented in 2D and includes an optional Surface Impedance Boundary Condition (SIBC). Thus, it is well suited for the computation of longitudinal and transverse impedances of long beam pipe structures of arbitrary cross-section. Besides arbitrary frequency and beam velocity, also dispersive materials can be chosen, which is crucial for the computation of the impedance of ferrite kicker magnets. Numerical impedance
Causality between Regional Stock Markets: A Frequency Domain Approach
National Research Council Canada - National Science Library
Nikola Gradojevic; Eldin Dobardzic
2013-01-01
...), this paper presents a frequency domain analysis of a causal relationship between the returns on the CROBEX, SBITOP, CETOP and DAX indices, and the return on the major Serbian stock exchange index, BELEX 15...
Frequency Domain Electroretinography in Retinitis Pigmentosa versus Normal Eyes
Directory of Open Access Journals (Sweden)
Homa Hassan-Karimi
2012-01-01
Full Text Available Purpose: To compare electroretinogram (ERG characteristics in patients with retinitis pigmentosa (RP and normal subjects using frequency domain analysis. Methods: Five basic ERG recordings were performed in normal subjects and patients with a clinical diagnosis of RP according to the ISCEV (International Society of Clinical Electrophysiology of Vision protocol. Frequency domain analysis was performed by MATLAB software. Different frequency domain parameters were compared between the study groups. Results: Peak frequency (Fmod of flicker and oscillatory responses in RP patients showed significant (P<0.0001 high pass response as compared to normal controls. Peak frequency (Fmod of the other responses was not significantly different between the two groups. Conclusion: In addition to conventional ERG using time domain methods, frequency domain analysis may be useful for diagnosis of RP. Oscillatory and flicker responses may be analyzed in frequency domain. Fast Fourier transform may reveal two distinct high pass responses (shift to higher frequencies in Fmod. Time and frequency domain analyses may be performed simultaneously with many modern ERG machines and may therefore be recommended in RP patients.
Numerical methods for time-domain and frequency-domain analysis: applications in engineering
Tamas, R. D.
2015-11-01
Numerical methods are widely used for modeling different physical phenomena in engineering, especially when an analytic approach is not possible. Time-domain or frequency- domain type variations are generally investigated, depending on the nature of the process under consideration. Some methods originate from mechanics, although most of their applications belong to other fields, such as electromagnetism. Conversely, other methods were firstly developed for electromagnetism, but their field of application was extended to other fields. This paper presents some results that we have obtained by using a general purpose method for solving linear equations, i.e., the method of moments (MoM), and a time-domain method derived for electromagnetism, i.e., the Transmission Line Matrix method (TLM).
Institute of Scientific and Technical Information of China (English)
王世隆; 王言章; 随阳轶; 王琦; 林君
2011-01-01
The multiple instrument calibrations of flying helicopter-borne time-domain electromagnetic method (HTEM) can eliminate the environmental time-varying effect on the system during flight. Using the bird calibration device to solve the problem that the wire-loop method can't achieve, we consider the bird model of HTEM with the concentric bucking loop, propose the bird device space models and the coil circuit models, and analyze the transmitter magnetic field distribution, the bucking loop's effect and the relationship between it and the receiving coil, the space information of the calibration device and its signal detecting method. Conclusions are as follows: (1) the bucking loop that losses 0. 89% of the transmitting area can increase 44. 5 dB of the signal dynamic range. (2) The calibration device is levelly placed between the bucking loop and the transmitting coils. If it has more turns and greater radius and it is closer to the bucking loop, its signal response is stronger. (3) When the inductance of calibration coil becomes greater and its resistance is less, its exponential decay becomes slower. The signal detection time point is directly decided by damping character of receiver coil which has matching resistance. We do experiments about the calibration curve characters and the device coil displacement. The relative error about the time constant of the device characteristics is less than 1. 3%, which proves the validity of the coil circuit models and device space models. The proposed models and approaches are also applicable to the bird calibration device research about HTEM with the eccentric bucking loop and the known wire-loop static testing on the high resistance ground.%直升机间域航空电磁法(Helicopter-borne time-domain electromagnetic method,HTEM)的多次空中仪器校准可消除飞行过程中仪器系统受外界环境的时变影响.吊舱校准装置可解决地面环线方式无法实现的空中飞行过程中仪器校准问题.本文
Robust time and frequency domain estimation methods in adaptive control
Lamaire, Richard Orville
1987-01-01
A robust identification method was developed for use in an adaptive control system. The type of estimator is called the robust estimator, since it is robust to the effects of both unmodeled dynamics and an unmeasurable disturbance. The development of the robust estimator was motivated by a need to provide guarantees in the identification part of an adaptive controller. To enable the design of a robust control system, a nominal model as well as a frequency-domain bounding function on the modeling uncertainty associated with this nominal model must be provided. Two estimation methods are presented for finding parameter estimates, and, hence, a nominal model. One of these methods is based on the well developed field of time-domain parameter estimation. In a second method of finding parameter estimates, a type of weighted least-squares fitting to a frequency-domain estimated model is used. The frequency-domain estimator is shown to perform better, in general, than the time-domain parameter estimator. In addition, a methodology for finding a frequency-domain bounding function on the disturbance is used to compute a frequency-domain bounding function on the additive modeling error due to the effects of the disturbance and the use of finite-length data. The performance of the robust estimator in both open-loop and closed-loop situations is examined through the use of simulations.
Evaluation of Damping Using Frequency Domain Operational Modal Analysis Techniques
DEFF Research Database (Denmark)
Bajric, Anela; Georgakis, Christos T.; Brincker, Rune
2015-01-01
Operational Modal Analysis (OMA) techniques provide in most cases reasonably accurate estimates of structural frequencies and mode shapes. In contrast though, they are known to often produce uncertain structural damping estimates, which is mainly due to inherent random and/or bias errors...... domain techniques, the Frequency Domain Decomposition (FDD) and the Frequency Domain Polyreference (FDPR). The response of a two degree-of-freedom (2DOF) system is numerically established with specified modal parameters subjected to white noise loading. The system identification is evaluated with well...
Frequency domain simultaneous algebraic reconstruction techniques: algorithm and convergence
Wang, Jiong; Zheng, Yibin
2005-03-01
We propose a simultaneous algebraic reconstruction technique (SART) in the frequency domain for linear imaging problems. This algorithm has the advantage of efficiently incorporating pixel correlations in an a priori image model. First it is shown that the generalized SART algorithm converges to the weighted minimum norm solution of a weighted least square problem. Then an implementation in the frequency domain is described. The performance of the new algorithm is demonstrated with fan beam computed tomography (CT) examples. Compared to the traditional SART and its major alternative ART, the new algorithm offers superior image quality and potential application to other modalities.
Error Analysis in Frequency Domain for Linear Multipass Algorithms
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Error analysis methods in frequency domain are developed in this paper for determining the characteristic root and transfer function errors when the linear multipass algorithms are used to solve linear differential equations.the relation between the local truncation error in time domain and the error in frequency domain is established, which is the basis for developing the error estimation methods. The error estimation methods for the digital simulation model constructed by using the Runge-Kutta algorithms and the linear multistep predictor-corrector algorithms are also given.
Finite-Difference Frequency-Domain Method in Nanophotonics
DEFF Research Database (Denmark)
Ivinskaya, Aliaksandra
is often indispensable. This thesis presents the development of rigorous finite-difference method, a very general tool to solve Maxwell’s equations in arbitrary geometries in three dimensions, with an emphasis on the frequency-domain formulation. Enhanced performance of the perfectly matched layers...... is obtained through free space squeezing technique, and nonuniform orthogonal grids are built to greatly improve the accuracy of simulations of highly heterogeneous nanostructures. Examples of the use of the finite-difference frequency-domain method in this thesis range from simulating localized modes...
High-speed optical frequency-domain imaging
Yun, S. H.; Tearney, G. J.; Boer; Iftimia, N. V.; Bouma, B. E.
2003-01-01
We demonstrate high-speed, high-sensitivity, high-resolution optical imaging based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. We derive and show experimentally that frequency-domain ranging provides a superior signal-to-noise ratio compared with conventional time-domain ranging as used in optical coherence tomography. A high sensitivity of −110 dB was obtained with a 6 mW source at an axial resolution of 13.5 µm and an A-line rate of 15.7 kHz, rep...
An Improved Traffic Matrix Decomposition Method with Frequency Domain Regularization
Wang, Zhe; Yin, Baolin
2012-01-01
In this letter, we propose a novel network traffic matrix decomposition method named as Stable Principal Component Pursuit with Frequency Domain Regularization (SPCP-FDR). SPCP-FDR improves the Stable Principal Component Pursuit (SPCP) method by using a new noise regularization function defined in frequency domain. Compared with SPCP, SPCP-FDR is more adaptive to empirical frequency properties of diverse traffic components. The Accelerated Proximal Gradient (APG) algorithm for SPCP-FDR is presented. Our experiment results demonstrate the rationality of this new method.
Modal Identification from Ambient Responses Using Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, Lingmi; Andersen, Palle
2000-01-01
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical...
Modal Identification from Ambient Responses using Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, L.; Andersen, P.
2000-01-01
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, ie. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical...
A Frequency Domain Design Method For Sampled-Data Compensators
DEFF Research Database (Denmark)
Niemann, Hans Henrik; Jannerup, Ole Erik
1990-01-01
A new approach to the design of a sampled-data compensator in the frequency domain is investigated. The starting point is a continuous-time compensator for the continuous-time system which satisfy specific design criteria. The new design method will graphically show how the discrete...
Frequency-domain thermal modelling of power semiconductor devices
DEFF Research Database (Denmark)
Ma, Ke; Blaabjerg, Frede; Andresen, Markus
2015-01-01
to correctly predict the device temperatures, especially when considering the thermal grease and heat sink attached to the power semiconductor devices. In this paper, the frequency-domain approach is applied to the modelling of thermal dynamics for power devices. The limits of the existing RC lump...
Higher order statistical frequency domain decomposition for operational modal analysis
Nita, G. M.; Mahgoub, M. A.; Sharyatpanahi, S. G.; Cretu, N. C.; El-Fouly, T. M.
2017-02-01
Experimental methods based on modal analysis under ambient vibrational excitation are often employed to detect structural damages of mechanical systems. Many of such frequency domain methods, such as Basic Frequency Domain (BFD), Frequency Domain Decomposition (FFD), or Enhanced Frequency Domain Decomposition (EFFD), use as first step a Fast Fourier Transform (FFT) estimate of the power spectral density (PSD) associated with the response of the system. In this study it is shown that higher order statistical estimators such as Spectral Kurtosis (SK) and Sample to Model Ratio (SMR) may be successfully employed not only to more reliably discriminate the response of the system against the ambient noise fluctuations, but also to better identify and separate contributions from closely spaced individual modes. It is shown that a SMR-based Maximum Likelihood curve fitting algorithm may improve the accuracy of the spectral shape and location of the individual modes and, when combined with the SK analysis, it provides efficient means to categorize such individual spectral components according to their temporal dynamics as coherent or incoherent system responses to unknown ambient excitations.
Automated Frequency Domain Decomposition for Operational Modal Analysis
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, Palle; Jacobsen, Niels-Jørgen
2007-01-01
The Frequency Domain Decomposition (FDD) technique is known as one of the most user friendly and powerful techniques for operational modal analysis of structures. However, the classical implementation of the technique requires some user interaction. The present paper describes an algorithm for au...
The Peltier driven frequency domain approach in thermal analysis.
De Marchi, Andrea; Giaretto, Valter
2014-10-01
The merits of Frequency Domain analysis as a tool for thermal system characterization are discussed, and the complex thermal impedance approach is illustrated. Pure AC thermal flux generation with negligible DC component is possible with a Peltier device, differently from other existing methods in which a significant DC component is intrinsically attached to the generated AC flux. Such technique is named here Peltier Driven Frequency Domain (PDFD). As a necessary prerequisite, a novel one-dimensional analytical model for an asymmetrically loaded Peltier device is developed, which is general enough to be useful in most practical situations as a design tool for measurement systems and as a key for the interpretation of experimental results. Impedance analysis is possible with Peltier devices by the inbuilt Seebeck effect differential thermometer, and is used in the paper for an experimental validation of the analytical model. Suggestions are then given for possible applications of PDFD, including the determination of thermal properties of materials.
The Peltier driven frequency domain approach in thermal analysis
Marchi, Andrea De; Giaretto, Valter
2014-10-01
The merits of Frequency Domain analysis as a tool for thermal system characterization are discussed, and the complex thermal impedance approach is illustrated. Pure AC thermal flux generation with negligible DC component is possible with a Peltier device, differently from other existing methods in which a significant DC component is intrinsically attached to the generated AC flux. Such technique is named here Peltier Driven Frequency Domain (PDFD). As a necessary prerequisite, a novel one-dimensional analytical model for an asymmetrically loaded Peltier device is developed, which is general enough to be useful in most practical situations as a design tool for measurement systems and as a key for the interpretation of experimental results. Impedance analysis is possible with Peltier devices by the inbuilt Seebeck effect differential thermometer, and is used in the paper for an experimental validation of the analytical model. Suggestions are then given for possible applications of PDFD, including the determination of thermal properties of materials.
A Visible Watermarking Scheme for Digital Images in Frequency Domain
Directory of Open Access Journals (Sweden)
D.R.Denslin Brabin
2012-11-01
Full Text Available A novel method is proposed for visible watermarking of digital image in frequency domain. The method is based on DCT modification of original image with respect to watermark image. The host image pixels are transformed into frequency coefficients as well as the watermark image pixels are also transformed into frequency coefficients using DCT. The compound mapping function is used to adjust the pixel values close to those of desired visible watermarks. Thus the watermarking is done in frequency domain using compound mapping function. One who has the watermark image and mapping function parameters only can remove the watermark. Thus it enhances the security. Experimental results demonstrate the effectiveness of the proposed approach.
Microcirculation monitoring with real time spatial frequency domain imaging
Chen, Xinlin; Cao, Zili; Lin, Weihao; Zhu, Danfeng; Zhu, Xiuwei; Zeng, Bixin; Xu, M.
2017-01-01
We present a spatial frequency domain imaging (SFDI) study of local hemodynamics in the forearm of healthy volunteers performing paced breathing. Real time Single Snapshot Multiple Frequency Demodulation - Spatial Frequency Domain Imaging (SSMD-SFDI) was used to map the optical properties of the subsurface of the forearm continuously. The oscillations of the concentrations of deoxy- and oxyhemoglobin at the subsurface of the forearm induced by paced breathing are found to be close to out-of-phase, attributed to the dominance of the blood flow modulation by paced breathing. The properties of local microcirculation including the blood transit times through capillaries and venules are extracted by fitting to Simplified Hemodynamics Model. Our preliminary results suggest that the real time SSMD-SFDI platform may serve as one effective imaging modality for microcirculation monitoring.
Domain Decomposition Solvers for Frequency-Domain Finite Element Equations
Copeland, Dylan
2010-10-05
The paper is devoted to fast iterative solvers for frequency-domain finite element equations approximating linear and nonlinear parabolic initial boundary value problems with time-harmonic excitations. Switching from the time domain to the frequency domain allows us to replace the expensive time-integration procedure by the solution of a simple linear elliptic system for the amplitudes belonging to the sine- and to the cosine-excitation or a large nonlinear elliptic system for the Fourier coefficients in the linear and nonlinear case, respectively. The fast solution of the corresponding linear and nonlinear system of finite element equations is crucial for the competitiveness of this method. © 2011 Springer-Verlag Berlin Heidelberg.
Frequency domain analysis of noise in autoregulated gene circuits
Simpson, Michael L.; Cox, Chris D.; Sayler, Gary S.
2003-01-01
We describe a frequency domain technique for the analysis of intrinsic noise within negatively autoregulated gene circuits. This approach is based on the transfer function around the feedback loop (loop transmission) and the equivalent noise bandwidth of the system. The loop transmission, T, is shown to be a determining factor of the dynamics and the noise behavior of autoregulated gene circuits, and this T-based technique provides a simple and flexible method for the analysis of noise arisin...
Reduced Order Internal Models in the Frequency Domain
Laakkonen, Petteri; Paunonen, Lassi
2016-01-01
The internal model principle states that all robustly regulating controllers must contain a suitably reduplicated internal model of the signal to be regulated. Using frequency domain methods, we show that the number of the copies may be reduced if the class of perturbations in the problem is restricted. We present a two step design procedure for a simple controller containing a reduced order internal model achieving robust regulation. The results are illustrated with an example of a five tank...
Frequency domain stability criteria for fractional-order control systems
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
This paper concerns about the frequency domain stability criteria for fractional-order control systems. On the base of characteristics of the fractional-order equations solutions, we consider the Nyquist stability criterion in a wider sense and obtain a more common means to analyze the stability of fractional-order systems conveniently. Finally, this paper illustrates the generalized stability criteria with an example to show the effect of the parameters variation on the fractional-order control systems.
Spatial frequency domain spectroscopy of two layer media
Yudovsky, Dmitry; Durkin, Anthony J.
2011-10-01
Monitoring of tissue blood volume and oxygen saturation using biomedical optics techniques has the potential to inform the assessment of tissue health, healing, and dysfunction. These quantities are typically estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in superficial tissue such as the skin can be confounded by the strong absorption of melanin in the epidermis. Furthermore, epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. This study describes a technique for decoupling the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. An artificial neural network was used to map input optical properties to spatial frequency domain diffuse reflectance of two layer media. Then, iterative fitting was used to determine the optical properties from simulated spatial frequency domain diffuse reflectance. Additionally, an artificial neural network was trained to directly map spatial frequency domain reflectance to sets of optical properties of a two layer medium, thus bypassing the need for iteration. In both cases, the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis were determined independently. The accuracy and efficiency of the iterative fitting approach was compared with the direct neural network inversion.
Removal of Spectral Modulation from Echoes for Helicopter-Borne SAR Imaging%一种去除回波频谱调制的直升机SAR成像方法
Institute of Scientific and Technical Information of China (English)
张红波; 何涛; 陈德民
2012-01-01
Since radar signals are modulated by rotor blades shadowing and helicopter vibration, the helicopter-borne synthetic aperture radar (SAR) imaging is difficult. Therefore, modulation reasons are analyzed and investigated based on time-frequency method. The modulation phase errors are extracted from the dechirped data and then compensated to remove modulation. Subsequently, the phase gradient autofocus is performed to achieve a high quality SAR image. The method has great reference value to the helicopter-borne SAR imaging.%直升机机载合成孔径雷达(Synthetic aperture radar,SAR)信号受到主旋翼遮挡和直升机振动的调制,给合成孔径成像造成很大影响.本文采用时频分析方法对调制产生的原因和特征进行分析和研究,提出利用去斜后的方位相位误差作补偿,再进行相位梯度自聚焦(Phase gradient autofocus,PGA)处理,实现调制雷达回波的高质量SAR成像.实测数据表明,本方法较好地解决了回波调制情况下的成像问题,对直升机平台SAR成像具有重要的参考价值.
Hein, Annette; Larsen, Jakob Juul; Parsekian, Andrew D.
2017-02-01
Surface nuclear magnetic resonance (NMR) is a unique geophysical method due to its direct sensitivity to water. A key limitation to overcome is the difficulty of making surface NMR measurements in environments with anthropogenic electromagnetic noise, particularly constant frequency sources such as powerlines. Here we present a method of removing harmonic noise by utilizing frequency domain symmetry of surface NMR signals to reconstruct portions of the spectrum corrupted by frequency-domain noise peaks. This method supplements the existing NMR processing workflow and is applicable after despiking, coherent noise cancellation, and stacking. The symmetry based correction is simple, grounded in mathematical theory describing NMR signals, does not introduce errors into the data set, and requires no prior knowledge about the harmonics. Modelling and field examples show that symmetry based noise removal reduces the effects of harmonics. In one modelling example, symmetry based noise removal improved signal-to-noise ratio in the data by 10 per cent. This improvement had noticeable effects on inversion parameters including water content and the decay constant T2*. Within water content profiles, aquifer boundaries and water content are more accurate after harmonics are removed. Fewer spurious water content spikes appear within aquifers, which is especially useful for resolving multilayered structures. Within T2* profiles, estimates are more accurate after harmonics are removed, especially in the lower half of profiles.
Without the electromagnetic force, you would not be solid. The atoms of your body are held together by electromagnetism: negatively charged electrons are held around the positively charged nucleus. Atoms share electrons to form molecules, so building up the structure of matter. As its name suggests, electromagnetism has a double nature: a moving electric charge creates a magnetic field. This intimate connection between electricity and magnetism was described by James Maxwell in 1864. The electromagnetic force can be both positive and negative : opposite charges attract, whereas like charges repel. Electromagnetic radiation, such as radio, microwaves, light and X-rays, is emitted by charges when they are made to move. For example, an oscillating current in a wire emits radio waves. Text for the interactive: Why do the needles move when you switch on the current ?
Frequency domain analysis of lightning protection using four lightning protection rods
Directory of Open Access Journals (Sweden)
Javor Vesna
2008-01-01
Full Text Available In this paper the lightning discharge channel is modeled as a vertical monopole antenna excited by a pulse generator at its base. The lightning electromagnetic field of a nearby lightning discharge in the case of lightning protection using four vertical lightning protection rods was determined in the frequency domain. Unknown current distributions were determined by numerical solving of a system of integral equations of two potentials using the Point Matching Method and polynomial approximation of the current distributions. The influence of the real ground, treated as homogeneous loss half-space of known electrical parameters, expressed through a Sommerfeld integral kernel, was modeled using a new Two-image approximation which gives good results in both near and far fields.
A frequency domain approach to handling qualities design
Wolovich, W. A.
1978-01-01
A method for designing linear multivariable feedback control systems based on desired closed loop transfer matrix information is introduced. The technique which was employed to achieve the final design was based on a theoretical result, known as the structure theorem. The structure theorem was a frequency domain relationship which simplified the expression for the transfer matrix (matrix of transfer functions) of a linear time-invariant multivariable system. The effect of linear state variable feedback on the closed loop transfer matrix of the system was also clarified.
Statistical multiresolution analysis in amplitude-frequency domain
Institute of Scientific and Technical Information of China (English)
SUN Hong; GUAN Bao; Henri Maitre
2004-01-01
A concept of statistical multiresolution analysis in amplitude-frequency domain is proposed, which is to employ the wavelet transform on the statistical character of a signal in amplitude domain. In terms of the theorem of generalized ergodicity, an algorithm to estimate the transform coefficients based on the amplitude statistical multiresolution analysis (AMA) is presented. The principle of applying the AMA to Synthetic Aperture Radar (SAR) image processing is described, and the good experimental results imply that the AMA is an efficient tool for processing of speckled signals modeled by the multiplicative noise.
Small signal frequency domain model of an HVDC converter
Energy Technology Data Exchange (ETDEWEB)
Osauskas, C.M.; Hume, D.J.; Wood, A.R. [UnIversity of Canterbury, Christchurch (New Zealand). Dept. of Electrical and Electronic Engineering
2001-11-01
A small-signal analytic frequency domain model of a 6-pulse HVDC converter is presented. The model consists of a set of explicit algebraic equations which relate the transfer of distortion from AC voltage, DC current and firing angle modulation, to AC current and DC voltage. The equations represent the linearisation of the transfers around a base operating point, and are derived from a piecewise linear description of the AC current and DC voltage waveforms. The model provides an understanding of the transfer of distortion by the converter and is in excellent agreement with time domain simulations. (author)
Baseband feedback for SAFARI-SPICA using Frequency Domain Multiplexing
Bounab, A.; de Korte, P.; Cros, A.; van der Kuur, J.; van Leeuwen, B. J.; Monna, B.; Mossel, R.; Nieuwenhuizen, A.; Ravera, L.
We report on the performance of the digital baseband feedback circuit developed to readout and process signals from arrays of transition edge sensors for SPICA-SAFARI in frequency domain multiplexing (FDM). The standard procedure to readout the SQUID current amplifiers is to use a feedback loop (flux-locked loop: FLL). However the achievable FFL bandwidth is limited by the cable transport delay t_d, which makes standard feedback inconvenient. A much better approach is to use baseband feedback. We have developed a model of the electronic readout chain for SPICA-SAFARI instrument by using an Anlog-digital co-simulation based on Simulink-System Generator environment.
A frequency-domain derivation of shot-noise
Rice, Frank
2016-01-01
A formula for shot-noise is derived in the frequency-domain. The derivation is complete and reasonably rigorous while being appropriate for undergraduate students; it models a sequence of random pulses using Fourier sine and cosine series, and requires some basic statistical concepts. The text here may serve as a pedagogic introduction to the spectral analysis of random processes and may prove useful to introduce students to the logic behind stochastic problems. The concepts of noise power spectral density and equivalent noise bandwidth are introduced.
Frequency-domain waveform inversion using the phase derivative
Choi, Yun Seok
2013-09-26
Phase wrapping in the frequency domain or cycle skipping in the time domain is the major cause of the local minima problem in the waveform inversion when the starting model is far from the true model. Since the phase derivative does not suffer from the wrapping effect, its inversion has the potential of providing a robust and reliable inversion result. We propose a new waveform inversion algorithm using the phase derivative in the frequency domain along with the exponential damping term to attenuate reflections. We estimate the phase derivative, or what we refer to as the instantaneous traveltime, by taking the derivative of the Fourier-transformed wavefield with respect to the angular frequency, dividing it by the wavefield itself and taking the imaginary part. The objective function is constructed using the phase derivative and the gradient of the objective function is computed using the back-propagation algorithm. Numerical examples show that our inversion algorithm with a strong damping generates a tomographic result even for a high ‘single’ frequency, which can be a good initial model for full waveform inversion and migration.
Frequency domain analysis of triggered lightning return stroke luminosity velocity
Carvalho, F. L.; Uman, M. A.; Jordan, D. M.; Moore, R. C.
2017-02-01
Fourier analysis is applied to time domain return stroke luminosity signals to calculate the phase and group velocities and the amplitude of the luminosity signals as a function of frequency measured between 4 m and 115 m during 12 triggered lightning strokes. We show that pairs of time domain luminosity signals measured at different heights can be interpreted as the input and the output of a system whose frequency domain transfer function can be determined from the measured time domain signals. From the frequency domain transfer function phase we find the phase and group velocities, and luminosity amplitude as a function of triggered lightning channel height and signal frequency ranging from 50 kHz to 300 kHz. We show that higher-frequency luminosity components propagate faster than the lower frequency components and that higher-frequency luminosity components attenuate more rapidly than lower frequency components. Finally, we calculate time domain return stroke velocities as a function of channel height using two time delay techniques: (1) measurement at the 20% amplitude level and (2) cross correlation.
Frequency-domain optical mammography: edge effect corrections.
Fantini, S; Franceschini, M A; Gaida, G; Gratton, E; Jess, H; Mantulin, W W; Moesta, K T; Schlag, P M; Kaschke, M
1996-01-01
We have investigated the problem of edge effects in laser-beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency-domain measurements by employing a two-step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge-corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency-domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two-step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images.
Quantitative analysis of a frequency-domain nonlinearity indicator.
Reichman, Brent O; Gee, Kent L; Neilsen, Tracianne B; Miller, Kyle G
2016-05-01
In this paper, quantitative understanding of a frequency-domain nonlinearity indicator is developed. The indicator is derived from an ensemble-averaged, frequency-domain version of the generalized Burgers equation, which can be rearranged in order to directly compare the effects of nonlinearity, absorption, and geometric spreading on the pressure spectrum level with frequency and distance. The nonlinear effect is calculated using pressure-squared-pressure quadspectrum. Further theoretical development has given an expression for the role of the normalized quadspectrum, referred to as Q/S by Morfey and Howell [AIAA J. 19, 986-992 (1981)], in the spatial rate of change of the pressure spectrum level. To explore this finding, an investigation of the change in level for initial sinusoids propagating as plane waves through inviscid and thermoviscous media has been conducted. The decibel change with distance, calculated through Q/S, captures the growth and decay of the harmonics and indicates that the most significant changes in level occur prior to sawtooth formation. At large distances, the inviscid case results in a spatial rate of change that is uniform across all harmonics. For thermoviscous media, large positive nonlinear gains are observed but offset by absorption, which leads to a greater overall negative spatial rate of change for higher harmonics.
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 imaging for monitoring palpable breast lesions
Robbins, Constance M.; Antaki, James F.; Kainerstorfer, Jana M.
2017-02-01
We describe a novel approach for monitoring breast lesions, utilizing spatial frequency domain imaging, a diffuse optical imaging method to detect hemoglobin contrast, in combination with mechanical compression of the tissue. The project is motivated by the growing rate of unnecessary breast biopsies, caused by uncertainty in X-ray mammographic diagnoses. We believe there is a need for an alternate means of tracking the progression palpable lesions exhibiting probably benign features, that can be performed non-invasively and hence frequently: at home or in the clinic. The proposed approach capitalizes on two distinguishing properties of cancerous lesions, namely the relative stiffness with respect to surrounding tissue and the optical absorption due to the greater vascularization, hence hemoglobin concentration. The current research project is a pilot study to evaluate the principle on soft, breast tissue-mimicking phantoms containing stiffer, more highly absorbing inclusions. Spatial frequency domain imaging was performed by projecting onto the phantom a series of wide-field patterns at multiple spatial frequencies. Image analysis then was performed to map absorption and scattering properties. The results of the study demonstrate that compression significantly increases the optical contrast observed for inclusions located 10 and 15 mm beneath the surface. In the latter case, the inclusion was not detectable without compression.
Frequency-domain waveform inversion using the unwrapped phase
Choi, Yun Seok
2011-01-01
Phase wrapping in the frequency-domain (or cycle skipping in the time-domain) is the major cause of the local minima problem in the waveform inversion. The unwrapped phase has the potential to provide us with a robust and reliable waveform inversion, with reduced local minima. We propose a waveform inversion algorithm using the unwrapped phase objective function in the frequency-domain. The unwrapped phase, or what we call the instantaneous traveltime, is given by the imaginary part of dividing the derivative of the wavefield with respect to the angular frequency by the wavefield itself. As a result, the objective function is given a traveltime-like function, which allows us to smooth it and reduce its nonlinearity. The gradient of the objective function is computed using the back-propagation algorithm based on the adjoint-state technique. We apply both our waveform inversion algorithm using the unwrapped phase and the conventional waveform inversion and show that our inversion algorithm gives better convergence to the true model than the conventional waveform inversion. © 2011 Society of Exploration Geophysicists.
Frequency domain processing of on-chip biphoton frequency comb
Jaramillo-Villegas, Jose A; Odele, Ogaga D; Leaird, Daniel E; Ou, Zhe-Yu; Qi, Minghao; Weiner, Andrew M
2016-01-01
Quantum information processing (QIP) promises to improve the security of our communications as well as to solve some algorithms with exponential complexity in polynomial time. Biphotons have been demonstrated as one of the most promising platforms for real implementations of QIP systems. In particular, time-bin entangled photons have been used for implementations of quantum gates which require highly stable interferometers. On the other hand, frequency-bin entanglement has been proposed to avoid the use of interferometers and the complexity of their stabilization, which potentially makes the implementation of quantum gates highly scalable. Through Fourier transform pulse shaping and electro-optic modulation, there has been a wide range of experiments that show control of entangled photons in the frequency domain. In addition, biphoton frequency combs (BFC) have also been generated using bulk optics and frequency filtering of broadband continuous biphoton spectra. However, on-chip entangled photon pair generat...
An Improved Frequency Domain Technique for Determining Soil Water Content
Institute of Scientific and Technical Information of China (English)
SUN Yu-Rui; MA Dao-Kun; LIN Jian-Hui; P. SCHULZE LAMMERS; L. DAMEROW
2005-01-01
For many years a soil water content sensor with low cost, reliability and sufficient accuracy has been desirable. Thus,an improved measurement method based on the frequency domain (FD) principle for determining soil water content was considered. Unlike other measurement principles, a new measurable index, η, which was independent of the output impedance and the amplitude of the oscillator while relying on the electrical impedance of a multi-pin probe, was proposed. Moreover, a model for processing the impedance of the multi-pin soil probe was developed, and several important electrical parameters for establishing their operating ranges applicable to this probe were evaluated. In order to confirm the theoretical analysis, an experiment was conducted with a 4-pin probe. Using the developed model, the relationship between the proposed indexηand soil volumetric water content was shown to be linear (R2 = 0.9921). Thus, as the measurable index, ηseemed satisfactory.
Incoherent Optical Frequency Domain Reflectometry for Distributed Thermal Sensing
DEFF Research Database (Denmark)
Karamehmedovic, Emir
2006-01-01
This thesis reports the main results from an investigation of a fibre-optic distributed temperature sensor based on spontaneous Raman scattering. The technique used for spatial resolving is the incoherent optical frequency domain reflectometry, where a pump laser is sine modulated with a stepwise...... increasing frequency, after which the inverse Fourier transform is applied to the signal from the backscattered light. This technique is compared with the more conventional optical time domain reflectometry, where a short pulse is sent through the fibre, and the location of the scattering section...... is determined by the time difference from the emission to the detection of light. A temperature sensor with a range of 2-4km comprising a step-index multi-mode fibre and a high-power 980nm pump laser existed prior to the start of the PhD study. In this study, a sensor range of approximately 10km, and a spatial...
Broadband ultrasonic sensor array via optical frequency domain reflectometry
Gabai, Haniel; Steinberg, Idan; Eyal, Avishay
2015-03-01
We introduce a new approach for multiplexing fiber-based ultrasound sensors using Optical Frequency Domain Reflectometry (OFDR). In the present demonstration of the method, each sensor was a short section of Polyimide-coated single-mode fiber. One end of the sensing fiber was pigtailed to a mirror and the other end was connected, via a fiber optic delay line, to a 1X4 fiber coupler. The multiplexing was enabled by using a different delay to each sensor. Ultrasonic excitation was performed by a 1MHz transducer which transmitted 4μs tone-bursts above the sensor array. The ultrasound waves generated optical phase variations in the fibers which were detected using the OFDR method. The ultrasound field at the sensors was successfully reconstructed without any noticeable cross-talk.
Frequency domain synthesis of trajectory learning controllers for robot manipulators
Directory of Open Access Journals (Sweden)
Tom Kavli
1993-07-01
Full Text Available Trajectory learning control is a method for generating near to optimal feedforward control for systems that are controlled along a reference trajectory in repeated cycles. Iterative refinements of a stored feedforward control sequence corresponding to one cycle of the control trajectory is computed based upon the recorded trajectory error from the previous cycle. Several learning operators have been proposed in earlier work, and convergence proofs are developed for certain classes of systems, but no satisfactory method for design and analysis of learning operators under the presence of uncertainties in the system model have been presented. This article presents frequency domain methods for analysing the convergence properties and performance of the learning controller when the amplitude and phase of the system transfer function is assumed to be within specified windows. Experimental results with an industrial robot manipulator confirm the theoretical results.
Parameter Identification of Weakly Nonlinear Vibration System in Frequency Domain
Directory of Open Access Journals (Sweden)
Jiehua Peng
2004-01-01
Full Text Available A new method of identifying parameters of nonlinearly vibrating system in frequency domain is presented in this paper. The problems of parameter identification of the nonlinear dynamic system with nonlinear elastic force or nonlinear damping force are discussed. In the method, the mathematic model of parameter identification is frequency response function. Firstly, by means of perturbation method the frequency response function of weakly nonlinear vibration system is derived. Next, a parameter transformation is made and the frequency response function becomes a linear function of the new parameters. Then, based on this function and with the least square method, physical parameters of the system are identified. Finally, the applicability of the proposed technique is confirmed by numerical simulation.
Hybrid time/frequency domain modeling of nonlinear components
DEFF Research Database (Denmark)
Wiechowski, Wojciech Tomasz; Lykkegaard, Jan; Bak, Claus Leth
2007-01-01
model is used as a basis for its implementation. First, the linear network part is replaced with an ideal voltage source and a time domain (EMT) simulation is performed. During the initial oscillations, harmonic content of the converter currents is calculated at every period by a fast Fourier transform...... and the periodic steady state is identified. Obtained harmonic currents are assigned to current sources and used in the frequency domain calculation in the linear network. The obtained three-phase bus voltage is then inverse Fourier transformed and assigned to the voltage source and the time domain simulation...... is performed again. This process is repeated until the change in the magnitudes and phase angles of the fundamental and low order characteristic harmonics of the bus voltage is smaller then predefined precision indexes. The method is verified against precise time domain simulation. The convergence properties...
Research on the frequency domain ∑△-DPCA
Institute of Scientific and Technical Information of China (English)
Shen Mingwei; Zhu Daiyin; Zhu Zhaoda
2008-01-01
The frequency domain ∑△-DPCA processing (F-∑△-DPCA) is investigated in detail, and an im-proved scheme for the F-]EA-DPCA is proposed, which can significantly reduce the computational burden. In practice, because of the sum and difference beam pattern designed independently and other system errors, the clutter suppression of the time domain ∑△-DPCA processing (T-∑△-DPCA) is significantly degraded. However,the F-∑△-DPCA adaptively calculates the optimum gain ratio for motion compensation within each Doppler cell,which is robust to system errors. Theoretical analysis and simulation results are presented to validate that the F-∑△-DPCA can achieve superior performance of clutter cancellation than the time domain processing, and its performance can be significantly increased if more pulses are used for the Doppler filtering. The improved approach is efficient, and feasible for real-time application.
Accurate reconstruction of digital holography using frequency domain zero padding
Shin, Jun Geun; Kim, Ju Wan; Lee, Jae Hwi; Lee, Byeong Ha
2017-04-01
We propose an image reconstruction method of digital holography for getting more accurate reconstruction. Digital holography provides both the light amplitude and the phase of a specimen through recording the interferogram. Since the Fresenl diffraction can be efficiently implemented by the Fourier transform, zero padding technique can be applied to obtain more accurate information. In this work, we report the method of frequency domain zero padding (FDZP). Both in computer-simulation and in experiment made with a USAF 1951 resolution chart and target, the FDZD gave the more accurate rconstruction images. Even though, the FDZD asks more processing time, with the help of graphics processing unit (GPU), it can find good applications in digital holography for 3-D profile imaging.
Causality between regional stock markets: A frequency domain approach
Directory of Open Access Journals (Sweden)
Gradojević Nikola
2013-01-01
Full Text Available Using a data set from five regional stock exchanges (Serbia, Croatia, Slovenia, Hungary and Germany, this paper presents a frequency domain analysis of a causal relationship between the returns on the CROBEX, SBITOP, CETOP and DAX indices, and the return on the major Serbian stock exchange index, BELEX 15. We find evidence of a somewhat dominant effect of the CROBEX and CETOP stock indices on the BELEX 15 stock index across a range of frequencies. The results also indicate that the BELEX 15 index and the SBITOP index interact in a bi-directional causal fashion. Finally, the DAX index movements consistently drive the BELEX 15 index returns for cycle lengths between 3 and 11 days without any feedback effect.
Frequency Domain Storage Ring Method for Electric Dipole Moment Measurement
Talman, Richard
2015-01-01
Precise measurement of the electric dipole moments (EDM) of fundamental charged particles would provide a significant probe of physics beyond the standard model. Any measurably large EDM would imply violation of both time reversal and parity conservation, with implications for the matter/anti-matter imbalance of the universe, not currently understood within the standard model. A frequency domain (i.e. difference of frequencies) method is proposed for measuring the EDM of electrons or protons or, with modifications, deuterons. Anticipated precision (i.e. reproducibility) is $10^{-30}\\,$e-cm for the proton EDM, with comparable accuracy (i.e. including systematic error). This would be almost six orders of magnitude smaller than the present upper limit, and will provide a stringent test of the standard model. Resonant polarimetry, made practical by the large polarized beam charge, is the key (most novel, least proven) element of the method. Along with the phase-locked, rolling polarization "Koop spin wheel," reso...
Quantifying online visuomotor feedback utilization in the frequency domain.
de Grosbois, John; Tremblay, Luc
2016-12-01
The utilization of sensory information during activities of daily living is ubiquitous both prior to and during movements (i.e., related to planning and online control, respectively). Because of the overlapping nature of online corrective processes, the quantification of feedback utilization has proven difficult. In the present study, we primarily sought to evaluate the utility of a novel analysis in the frequency domain for identifying visuomotor feedback utilization (i.e., online control). A second goal was to compare the sensitivity of the frequency analysis to that of currently utilized measures of online control. Participants completed reaching movements to targets located 27, 30, and 33 cm from a start position. During these reaches, vision of the environment was either provided or withheld. Performance was assessed across contemporary measures of online control. For the novel frequency analysis presented in this study, the acceleration profiles of reaching movements were detrended with a 5th-order polynomial fit, and the proportional power spectra were computed from the residuals of these fits. The results indicated that the use of visual feedback during reaching movements increased the contribution of the 4.68-Hz frequency to the residuals of the acceleration profiles. Comparisons across all measures of online control showed that the most sensitive measure was the squared Fisher transform of the correlation between the positions at 75 % and 100 % of the movement time. However, because such correlational measures can be contaminated by offline control processes, the frequency-domain analysis proposed herein represents a viable and promising alternative to detect changes in online feedback utilization.
Li, Gang; Li, Yuguo
2017-01-01
We present a joint inversion method for the transmitter navigation and the seafloor resistivity for frequency domain marine controlled-source electromagnetic (CSEM) data. The inversion approach is based on the modified BFGS scheme, which has an advantage that one can update the Hessian matrix by using the BFGS scheme rather than computing the Hessian matrix itself during the inversion process. The partial derivatives of the electromagnetic field responses with respect to both the seafloor resistivity and the transmitter navigation parameters including the azimuth, dip and horizontal positions of the transmitter antenna are analytically calculated. We invert for both the navigation parameters of the towed dipole source (including antenna azimuth, dip, and horizontal positions) and seafloor resistivity by using the whole range of data instead of the near-field data (usually source-receiver offset navigation parameters can be independently resolved, and a better reconstruction can be obtained with multiple frequency data. The inversions of both the synthetical and field data sets indicate that our inversion method can simultaneously reconstruct seafloor resistivity structures and transmitter navigation parameters.
Energy Technology Data Exchange (ETDEWEB)
Guiguet, J.C. [Agence Nationale des Frequences (ANFR), 94 - Maisons Alfort (France); Dodinot, B.; Sadoul, N.; Blangy, H. [Centre Hospitalier Universitaire Nancy-Brabois, Clinique Cardiologique, 54 - Vandoeuvre Brabois (France); Nadi, M.; Hedjiedj, A.; Schmitt, P. [Universite Henri Poincare-Nancy, Lab. d' Instrumentation Electronique de Nancy, Faculte des Sciences, 54 - Vandoeuvre les Nancy (France); Joly, L.; Dodinot, B.; Aliot, E. [Centre Hospitalier Universitaire Nancy-Brabois, Service de Cardiologie, 54 - Vandoeuvre-les-Nancy (France); Silny, J. [Aachen University (Germany); Franck, R.; Himbert, C.; Hidden-Lucet, F.; Petitot, J.C.; Fontaine, G. [Hopital Pitie-Salpetriere, Institut de Cardiologie, Service de Rythmologie, 75 - Paris (France); Souques, M.; Lambrozo, J. [Electricite de France (EDF-Gaz de France), Service des Etudes Medicales, 75 - Paris (France); Magne, I.; Bailly, J.M. [Electricite de France (EDF-Gaz de France), Div. Recherche Developpement, 77 - Moret sur Loing (France); Trigano, J.A. [Centre Hospitalier Universitaire, Hopital Nord, 13 - Marseille (France); Burais, N. [CEGELY, Ecole Centrale de Lyon, 69 - Ecully (France); Gaspard, J.Y. [Magtech, 69 - Ecully (France); Andrivet, Ph. [Societe Medtronic France, 92 - Boulogne-Billancourt (France)
2004-07-01
Presentation of electromagnetic sources constituted by various radio transmitters contributing to different radio communication services in the environment. Results of a measures campaign to assess the electromagnetic field in the close neighbourhood of various stations. Analysis by frequency domains. (author)
Grant, Ian S
1990-01-01
The Manchester Physics Series General Editors: D. J. Sandiford; F. Mandl; A. C. Phillips Department of Physics and Astronomy, University of Manchester Properties of Matter B. H. Flowers and E. Mendoza Optics Second Edition F. G. Smith and J. H. Thomson Statistical Physics Second Edition F. Mandl Electromagnetism Second Edition I. S. Grant and W. R. Phillips Statistics R. J. Barlow Solid State Physics Second Edition J. R. Hook and H. E. Hall Quantum Mechanics F. Mandl Particle Physics Second Edition B. R. Martin and G. Shaw the Physics of Stars Second Edition A. C. Phillips Computing for Scient
In vivo spatial frequency domain spectroscopy of two layer media
Yudovsky, Dmitry; Nguyen, John Quan M.; Durkin, Anthony J.
2012-10-01
Monitoring of tissue blood volume and local oxygen saturation can inform the assessment of tissue health, healing, and dysfunction. These quantities can be estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in skin can be confounded by the strong absorption of melanin in the epidermis and epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. Therefore, a method is desired that decouples the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. A previously developed inverse method based on a neural network forward model was applied to simulated spatial frequency domain reflectance of skin for multiple wavelengths in the near infrared. It is demonstrated that the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis can be determined independently and with minimal coupling. Then, the same inverse method was applied to reflectance measurements from a tissue simulating phantom and in vivo human skin. Oxygen saturation and total hemoglobin concentrations were estimated from the volar forearms of weakly and strongly pigmented subjects using a standard homogeneous model and the present two layer model.
Multiscale Point Correspondence Using Feature Distribution and Frequency Domain Alignment
Directory of Open Access Journals (Sweden)
Zeng-Shun Zhao
2012-01-01
Full Text Available In this paper, a hybrid scheme is proposed to find the reliable point-correspondences between two images, which combines the distribution of invariant spatial feature description and frequency domain alignment based on two-stage coarse to fine refinement strategy. Firstly, the source and the target images are both down-sampled by the image pyramid algorithm in a hierarchical multi-scale way. The Fourier-Mellin transform is applied to obtain the transformation parameters at the coarse level between the image pairs; then, the parameters can serve as the initial coarse guess, to guide the following feature matching step at the original scale, where the correspondences are restricted in a search window determined by the deformation between the reference image and the current image; Finally, a novel matching strategy is developed to reject the false matches by validating geometrical relationships between candidate matching points. By doing so, the alignment parameters are refined, which is more accurate and more flexible than a robust fitting technique. This in return can provide a more accurate result for feature correspondence. Experiments on real and synthetic image-pairs show that our approach provides satisfactory feature matching performance.
A frequency domain based rigid motion artifact reduction algorithm
Luo, Hai; Huang, Xiaojie; Pan, Wenyu; Zhou, Heqin; Feng, Huanqing
2009-10-01
During a CT scan, patients' conscious or unconscious motions would result in motion artifacts which undermine the image quality and hamper doctors' accurate diagnosis and therapy. It is desirable to develop a precise motion estimation and artifact reduction method in order to produce high-resolution images. Rigid motion can be decomposed into two components: translational motion and rotational motion. Since considering the rotation and translation simultaneously is very difficult, most former studies on motion artifact reduction ignore rotation. The extended HLCC based method considering the rotation and translation simultaneously relies on a searching algorithm which leads to expensive computing cost. Therefore, a novel method which does not rely on searching is desirable. In this paper, we focus on parallel-beam CT. We first propose a frequency domain based method to estimate rotational motion, which is not affected by translational motion. It realizes the separation of rotation estimation and translation estimation. Then we combine this method with the HLCC based method to construct a new method for general rigid motion called separative estimation and collective correction method. Furthermore, we present numerical simulation results to show the accuracy and robustness of our approach.
Damping identification in frequency domain using integral method
Guo, Zhiwei; Sheng, Meiping; Ma, Jiangang; Zhang, Wulin
2015-03-01
A new method for damping identification of linear system in frequency domain is presented, by using frequency response function (FRF) with integral method. The FRF curve is firstly transformed to other type of frequency-related curve by changing the representations of horizontal and vertical axes. For the newly constructed frequency-related curve, integral is conducted and the area forming from the new curve is used to determine the damping. Three different methods based on integral are proposed in this paper, which are called FDI-1, FDI-2 and FDI-3 method, respectively. For a single degree of freedom (Sdof) system, the formulated relation of each method between integrated area and loss factor is derived theoretically. The numeral simulation and experiment results show that, the proposed integral methods have high precision, strong noise resistance and are very stable in repeated measurements. Among the three integral methods, FDI-3 method is the most recommended because of its higher accuracy and simpler algorithm. The new methods are limited to linear system in which modes are well separated, and for closely spaced mode system, mode decomposition process should be conducted firstly.
A Frequency Domain Steganography using Z Transform (FDSZT)
Mandal, J K
2012-01-01
Image steganography is art of hiding information onto the cover image. In this proposal a transformed domain based gray scale image authentication/data hiding technique using Z transform (ZT) termed as FDSZT, has been proposed. ZTransform is applied on 2x2 masks of the source image in row major order to transform original sub image (cover image) block to its corresponding frequency domain. One bit of the hidden image is embedded in each mask of the source image onto the fourth LSB of transformed coefficient based on median value of the mask. A delicate handle has also been performed as post embedding operation for proper decoding. Stego sub image is obtained through a reverse transform as final step of embedding in a mask. During the process of embedding, dimension of the hidden image followed by the content of the message/hidden image are embedded. Reverse process is followed during decoding. High PSNR obtained for various images conform the quality of invisible watermark of FDSZT.
Frequency domain analysis of noise in autoregulated gene circuits
Simpson, Michael L.; Cox, Chris D.; Sayler, Gary S.
2003-01-01
We describe a frequency domain technique for the analysis of intrinsic noise within negatively autoregulated gene circuits. This approach is based on the transfer function around the feedback loop (loop transmission) and the equivalent noise bandwidth of the system. The loop transmission, T, is shown to be a determining factor of the dynamics and the noise behavior of autoregulated gene circuits, and this T-based technique provides a simple and flexible method for the analysis of noise arising from any source within the gene circuit. We show that negative feedback not only reduces the variance of the noise in the protein concentration, but also shifts this noise to higher frequencies where it may have a negligible effect on the noise behavior of following gene circuits within a cascade. This predicted effect is demonstrated through the exact stochastic simulation of a two-gene cascade. The analysis elucidates important aspects of gene circuit structure that control functionality, and may provide some insights into selective pressures leading to this structure. The resulting analytical relationships have a simple form, making them especially useful as synthetic gene circuit design equations. With the exception of the linearization of Hill kinetics, this technique is general and may be applied to the analysis or design of networks of higher complexity. This utility is demonstrated through the exact stochastic simulation of an autoregulated two-gene cascade operating near instability. PMID:12671069
A new image cipher in time and frequency domains
Abd El-Latif, Ahmed A.; Niu, Xiamu; Amin, Mohamed
2012-10-01
Recently, various encryption techniques based on chaos have been proposed. However, most existing chaotic encryption schemes still suffer from fundamental problems such as small key space, weak security function and slow performance speed. This paper introduces an efficient encryption scheme for still visual data that overcome these disadvantages. The proposed scheme is based on hybrid Linear Feedback Shift Register (LFSR) and chaotic systems in hybrid domains. The core idea is to scramble the pixel positions based on 2D chaotic systems in frequency domain. Then, the diffusion is done on the scrambled image based on cryptographic primitive operations and the incorporation of LFSR and chaotic systems as round keys. The hybrid compound of LFSR, chaotic system and cryptographic primitive operations strengthen the encryption performance and enlarge the key space required to resist the brute force attacks. Results of statistical and differential analysis show that the proposed algorithm has high security for secure digital images. Furthermore, it has key sensitivity together with a large key space and is very fast compared to other competitive algorithms.
Frequency domain identification of grinding stiffness and damping
Leonesio, Marco; Parenti, Paolo; Bianchi, Giacomo
2017-09-01
As equivalent stiffness and damping of the grinding process dominate cutting stability, their identification is essential to predict and avoid detrimental chatter occurrence. The identification of these process constants is not easy in large cylindrical grinding machines, e.g. roll grinders, since there are no practical ways to measure cutting force normal component. This paper presents a novel frequency domain approach for identifying these process parameters, exploiting in-process system response, measured via impact testing. This method adopts a sub-structuring approach to couple the wheel-workpiece relative dynamic compliance with a two-dimensional grinding force model that entails both normal and tangential directions. The grinding specific energy and normal force ratio, that determine grinding stiffness and damping, are identified by fitting the closed loop FRF (Frequency Response Function) measured during specific plunge-grinding tests. The fitting quality supports the predictive capability of the model. Eventually, the soundness of the proposed identification procedure is further assessed by comparing the grinding specific energy identified through standard cutting power measurements.
Simulation of DLA grating structures in the frequency domain
Egenolf, T.; Boine-Frankenheim, O.; Niedermayer, U.
2017-07-01
Dielectric laser accelerators (DLA) driven by ultrashort laser pulses can reach orders of magnitude larger gradients than contemporary RF electron accelerators. A new implemented field solver based on the finite element method in the frequency domain allows the efficient calculation of the structure constant, i.e. the ratio of energy gain to laser peak amplitude. We present the maximization of this ratio as a parameter study looking at a single grating period only. Based on this optimized shape the entire design of a beta-matched grating is completed in an iterative process. The period length of a beta-matched grating increases due to the increasing velocity of the electron when a subrelativistic beam is accelerated. The determination of the optimal length of each grating period thus requires the knowledge of the energy gain within all so far crossed periods. Furthermore, we outline to reverse the excitation in the presented solver for beam coupling impedance calculations and an estimation of the beam loading intensity limit.
Patellofemoral pain syndrome: electromyography in a frequency domain analysis
Catelli, D. S.; Kuriki, H. U.; Polito, L. F.; Azevedo, F. M.; Negrão Filho, R. F.; Alves, N.
2011-09-01
The Patellofemoral Pain Syndrome (PFPS), has a multifactorial etiology and affects approximately 7 to 15% of the population, mostly women, youth, adults and active persons. PFPS causes anterior or retropatelar pain that is exacerbated during functional motor gestures, such as up and down stairs or spending long periods of time sitting, squatting or kneeling. As the diagnostic evaluation of this syndrome is still indirect, different mechanisms and methodologies try to make a classification that distinguishes patients with PFPS in relation to asymptomatic. Thereby, the purpose of this investigation was to determine the characteristics of the electromyographic (EMG) signal in the frequency domain of the vastus medialis oblique (VMO) and vastus lateralis (VL) in patients with PFPS, during the ascent of stairs. 33 young women (22 control group and 11 PFPS group), were evaluated by EMG during ascent of stairs. The VMO mean power frequency (MPF) and the VL frequency 95% (F95) were lower in symptomatic individuals. This may be related to the difference in muscle recruitment strategy exerted by each muscle in the PFPS group compared to the control group.
Imaging scattering orientation with spatial frequency domain imaging.
Konecky, Soren D; Rice, Tyler; Durkin, Anthony J; Tromberg, Bruce J
2011-12-01
Optical imaging techniques based on multiple light scattering generally have poor sensitivity to the orientation and direction of microscopic light scattering structures. In order to address this limitation, we introduce a spatial frequency domain method for imaging contrast from oriented scattering structures by measuring the angular-dependence of structured light reflectance. The measurement is made by projecting sinusoidal patterns of light intensity on a sample, and measuring the degree to which the patterns are blurred as a function of the projection angle. We derive a spatial Fourier domain solution to an anisotropic diffusion model. This solution predicts the effects of bulk scattering orientation on the amplitude and phase of the projected patterns. We introduce a new contrast function based on a scattering orientation index (SOI) which is sensitive to the degree to which light scattering is directionally dependent. We validate the technique using tissue simulating phantoms, and ex vivo samples of muscle and brain. Our results show that SOI is independent of the overall amount of bulk light scattering and absorption, and that isotropic versus oriented scattering structures can be clearly distinguished. We determine the orientation of subsurface microscopic scattering structures located up to 600 μm beneath highly scattering (μ(') (s) = 1.5 mm(-1)) material.
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.
Calibration of a frequency-domain reflectometer for determining soil ...
African Journals Online (AJOL)
2006-01-01
Jan 1, 2006 ... The range in soil-water content was from 0.20 to 0.42 m3·m-3. A total of 78 soil samples from ... measuring the propagation of an electromagnetic pulse along ... wave with amplitude that is a measure of the soil-water content.
MULTILOOP PI CONTROLLER FOR ACHIEVING SIMULTANEOUS TIME AND FREQUENCY DOMAIN SPECIFICATIONS
2015-01-01
Most of the controllers in control system are designed to satisfy either time domain or frequency domain specifications. This work presents the computation of a multiloop PI controller for achieving time and frequency domain specifications simultaneously. The desired time and frequency domain measures are to be specified initially to the design. To obtain the desired value of the performance measures the graphical relationship between the PI controller and the performance criteria is given. T...
Spacial and Frequency Domain Calculation of Terrain Roughness Metric Root-Mean-Square (RMS)
2014-11-01
TARDEC Technical Report No. 26042 November 2014 SPACIAL AND FREQUENCY DOMAIN CALCULATION OF TERRAIN ROUGHNESS METRIC ROOT-MEAN...DATE (DD-MM-YYYY) 11-15-2014 2. REPORT TYPE TECHNICAL 3. DATES COVERED (From - To) 2013-2014 SPACIAL AND FREQUENCY DOMAIN CALCULATION OF TERRAIN...roughness. Based on mathematics of the Fourier transform and duality, calculations are performed in the spacial and frequency domains to show equivalent
Compact optical processor for Hough and frequency domain features
Ott, Peter
1996-11-01
Shape recognition is necessary in a broad band of applications such as traffic sign or work piece recognition. It requires not only neighborhood processing of the input image pixels but global interconnection of them. The Hough transform (HT) performs such a global operation and it is well suited in the preprocessing stage of a shape recognition system. Translation invariant features can be easily calculated form the Hough domain. We have implemented on the computer a neural network shape recognition system which contains a HT, a feature extraction, and a classification layer. The advantage of this approach is that the total system can be optimized with well-known learning techniques and that it can explore the parallelism of the algorithms. However, the HT is a time consuming operation. Parallel, optical processing is therefore advantageous. Several systems have been proposed, based on space multiplexing with arrays of holograms and CGH's or time multiplexing with acousto-optic processors or by image rotation with incoherent and coherent astigmatic optical processors. We took up the last mentioned approach because 2D array detectors are read out line by line, so a 2D detector can achieve the same speed and is easier to implement. Coherent processing can allow the implementation of tilers in the frequency domain. Features based on wedge/ring, Gabor, or wavelet filters have been proven to show good discrimination capabilities for texture and shape recognition. The astigmatic lens system which is derived form the mathematical formulation of the HT is long and contains a non-standard, astigmatic element. By methods of lens transformation s for coherent applications we map the original design to a shorter lens with a smaller number of well separated standard elements and with the same coherent system response. The final lens design still contains the frequency plane for filtering and ray-tracing shows diffraction limited performance. Image rotation can be done
Characterization of static bifurcations for n-dimensional flows in the frequency domain
Institute of Scientific and Technical Information of China (English)
Li ZENG; Yi ZHAO
2006-01-01
In this paper n-dimensional flows (described by continuous-time system) with static bifurcations are considered with the aim of classification of different elementary bifurcations using the frequency domain formalism. Based on frequency domain approach, we prove some criterions for the saddle-node bifurcation, transcritical bifurcation and pitchfork bifurcation, and give an example to illustrate the efficiency of the result obtained.
某直升机机载设备印制板振动试验失效分析%PCB Vibration Test Failure Analysis for Helicopter-borne Equipment
Institute of Scientific and Technical Information of China (English)
薄玉奎
2011-01-01
文中以某机载电子设备振动试验中印制板（PCB）故障现象为研究对象,通过理论分析和ANSYS动力学计算的方法对PCB板产生故障的机理进行了分析和计算。计算结果与试验现象相符,认为谐振和PCB板设计问题是导致该试验故障的原因,并在结构接口方面对引起谐振的情况进行了分析,阐述了结构和电讯方面相应的改进措施。%The mechanism which results in the PCB failure in a vibration test for the helicopter-borne electronic equipment is described in this paper by theoretical analysis and ANSYS dynamic calculation.The calculation results agree with the test phenomenon.Resonance and defects in PCB design are determined as the reasons of the PCB failure.The structural interface problem which results in the resonance is analyzed.And the structural and electronic improvement measures are introduced,too.
Fast Frequency-domain Waveforms for Spin-Precessing Binary Inspirals
Klein, Antoine; Yunes, Nicolás
2014-01-01
The detection and characterization of gravitational wave signals from compact binary coalescence events relies on accurate waveform templates in the frequency domain. The stationary phase approximation (SPA) can be used to compute closed-form frequency-domain waveforms for non-precessing, quasi-circular binary inspirals. However, until now, no fast frequency-domain waveforms have existed for generic, spin-precessing quasi-circular compact binary inspirals. Templates for these systems have had to be computed via a discrete Fourier transform of finely sampled time-domain waveforms, which is far more computationally expensive than those constructed directly in the frequency-domain, especially for those systems that are dominated by the inspiral part. There are two obstacles to deriving frequency-domain waveforms for precessing systems: (i) the spin-precession equations do not admit closed-form solutions for generic systems; (ii) the SPA fails catastrophically. Presently there is no general solution to the first ...
On the Analysis Methods for the Time Domain and Frequency Domain Response of a Buried Objects*
Poljak, Dragan; Šesnić, Silvestar; Cvetković, Mario
2014-05-01
There has been a continuous interest in the analysis of ground-penetrating radar systems and related applications in civil engineering [1]. Consequently, a deeper insight of scattering phenomena occurring in a lossy half-space, as well as the development of sophisticated numerical methods based on Finite Difference Time Domain (FDTD) method, Finite Element Method (FEM), Boundary Element Method (BEM), Method of Moments (MoM) and various hybrid methods, is required, e.g. [2], [3]. The present paper deals with certain techniques for time and frequency domain analysis, respectively, of buried conducting and dielectric objects. Time domain analysis is related to the assessment of a transient response of a horizontal straight thin wire buried in a lossy half-space using a rigorous antenna theory (AT) approach. The AT approach is based on the space-time integral equation of the Pocklington type (time domain electric field integral equation for thin wires). The influence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The obtained results for the transient current induced along the electrode due to the transmitted plane wave excitation are compared to the numerical results calculated via an approximate transmission line (TL) approach and the AT approach based on the space-frequency variant of the Pocklington integro-differential approach, respectively. It is worth noting that the space-frequency Pocklington equation is numerically solved via the Galerkin-Bubnov variant of the Indirect Boundary Element Method (GB-IBEM) and the corresponding transient response is obtained by the aid of inverse fast Fourier transform (IFFT). The results calculated by means of different approaches agree satisfactorily. Frequency domain analysis is related to the assessment of frequency domain response of dielectric sphere using the full wave model based on the set of coupled electric field integral
Fatigue Damage Assessment by Considering Mean Value Effect in Frequency Domain
Institute of Scientific and Technical Information of China (English)
丁红岩; 朱奇; 张浦阳
2015-01-01
Fatigue damage assessment is carried out considering mean value effect by applying four criteria of failure. Three frequency domain methods, i.e., level crossing counting (LCC), range counting (RC) and a new proposed method, are applied. The core of frequency domain method is the construction of probability density function for the mean stress and stress range of the stress process. The applicability of these frequency domain methods are inspected by comparing with time domain method. Numerical simulations verify the applicability of LCC and the proposed method, while RC gives poor estimations.
Hays, J. R.
1969-01-01
Lumped parametric system models are simplified and computationally advantageous in the frequency domain of linear systems. Nonlinear least squares computer program finds the least square best estimate for any number of parameters in an arbitrarily complicated model.
Solving forward and inverse seismic problems by boundary-element method in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Xianxi, J.
1988-01-01
Solving the boundary value problem of wave equation by boundary element method in frequency domain involves these steps: 1. ID Fourier transform of time variable is made to convert the wave equation into Helmholtz equation; 2. this equation is then solved using boundary-element method in frequency domain; 3. the result is returned to time domain by making inverse Fourier transform. Compared with other formulas, the formula in this paper brings higher accuracy but less computation.
The Capability of Time- And Frequency-domain Algorithms for Bistatic SAR Processing
Vu, Viet; Sjögren, Thomas; Pettersson, Mats
2013-01-01
The paper presents a study of the capability of time- And frequency-domain algorithms for bistatic SAR processing. Two typical algorithms, Bistatic Fast Backprojection (BiFBP) and Bistatic Range Doppler (BiRDA), which are both available for general bistatic geometry, are selected as the examples of time- And frequency-domain algorithms in this study. Their capability is evaluated based on some criteria such as processing time required by the algorithms to reconstruct SAR images from bistatic ...
Time and Frequency Domain Identification and Analysis of a Gas Turbine Engine
Boaghe, O.M.; S. A. Billings; L. M. Li; Fleming, P J; Liu, J
2000-01-01
The NARMAX (Nonlinear Auto Regressive Moving Average model with eXogenous inputs) approach has been used to analyse the dynamics of a gas turbine engine. The fuel flow-shaft speed relationship is analysed by identifying both time and frequency domain models of the system. The frequency domain analysis is studied by mapping the discrete-time NARMAX models into the Generalised Frequency Response Functions (GFRF's) to reveal the nonlinear coupling between the various input spectral components an...
Frequency-domain generelaized singular peruturbation method for relative error model order reduction
Institute of Scientific and Technical Information of China (English)
Hamid Reza SHAKER
2009-01-01
A new mixed method for relative error model order reduction is proposed.In the proposed method the frequency domain balanced stochastic truncation method is improved by applying the generalized singular perturbation method to the frequency domain balanced system in the reduction procedure.The frequency domain balanced stochastic truncation method,which was proposed in [15] and [17] by the author,is based on two recently developed methods,namely frequency domain balanced truncation within a desired frequency bound and inner-outer factorization techniques.The proposed method in this paper is a carry over of the frequency-domain balanced stochastic truncation and is of interest for practical model order reduction because in this context it shows to keep the accuracy of the approximation as high as possible without sacrificing the computational efficiency and important system properties.It is shown that some important properties of the frequency domain stochastic balanced reduction technique are extended to the proposed reduction method by using the concept and properties of the reciprocal systems.Numerical results show the accuracy,simplicity and flexibility enhancement of the method.
Conversion of Dielectric Data from the Time Domain to the Frequency Domain
Directory of Open Access Journals (Sweden)
Vladimir Durman
2005-01-01
Full Text Available Polarisation and conduction processes in dielectric systems can be identified by the time domain or the frequency domain measurements. If the systems is a linear one, the results of the time domain measurements can be transformed into the frequency domain, and vice versa. Commonly, the time domain data of the absorption conductivity are transformed into the frequency domain data of the dielectric susceptibility. In practice, the relaxation are mainly evaluated by the frequency domain data. In the time domain, the absorption current measurement were prefered up to now. Recent methods are based on the recovery voltage measurements. In this paper a new method of the recovery data conversion from the time the frequency domain is proposed. The method is based on the analysis of the recovery voltage transient based on the Maxwell equation for the current density in a dielectric. Unlike the previous published solutions, the Laplace fransform was used to derive a formula suitable for practical purposes. the proposed procedure allows also calculating of the insulation resistance and separating the polarisation and conduction losses.
Spectral element method for elastic and acoustic waves in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Shi, Linlin; Zhou, Yuanguo; Wang, Jia-Min; Zhuang, Mingwei [Institute of Electromagnetics and Acoustics, and Department of Electronic Science, Xiamen, 361005 (China); Liu, Na, E-mail: liuna@xmu.edu.cn [Institute of Electromagnetics and Acoustics, and Department of Electronic Science, Xiamen, 361005 (China); Liu, Qing Huo, E-mail: qhliu@duke.edu [Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708 (United States)
2016-12-15
Numerical techniques in time domain are widespread in seismic and acoustic modeling. In some applications, however, frequency-domain techniques can be advantageous over the time-domain approach when narrow band results are desired, especially if multiple sources can be handled more conveniently in the frequency domain. Moreover, the medium attenuation effects can be more accurately and conveniently modeled in the frequency domain. In this paper, we present a spectral-element method (SEM) in frequency domain to simulate elastic and acoustic waves in anisotropic, heterogeneous, and lossy media. The SEM is based upon the finite-element framework and has exponential convergence because of the use of GLL basis functions. The anisotropic perfectly matched layer is employed to truncate the boundary for unbounded problems. Compared with the conventional finite-element method, the number of unknowns in the SEM is significantly reduced, and higher order accuracy is obtained due to its spectral accuracy. To account for the acoustic-solid interaction, the domain decomposition method (DDM) based upon the discontinuous Galerkin spectral-element method is proposed. Numerical experiments show the proposed method can be an efficient alternative for accurate calculation of elastic and acoustic waves in frequency domain.
Spectral element method for elastic and acoustic waves in frequency domain
Shi, Linlin; Zhou, Yuanguo; Wang, Jia-Min; Zhuang, Mingwei; Liu, Na; Liu, Qing Huo
2016-12-01
Numerical techniques in time domain are widespread in seismic and acoustic modeling. In some applications, however, frequency-domain techniques can be advantageous over the time-domain approach when narrow band results are desired, especially if multiple sources can be handled more conveniently in the frequency domain. Moreover, the medium attenuation effects can be more accurately and conveniently modeled in the frequency domain. In this paper, we present a spectral-element method (SEM) in frequency domain to simulate elastic and acoustic waves in anisotropic, heterogeneous, and lossy media. The SEM is based upon the finite-element framework and has exponential convergence because of the use of GLL basis functions. The anisotropic perfectly matched layer is employed to truncate the boundary for unbounded problems. Compared with the conventional finite-element method, the number of unknowns in the SEM is significantly reduced, and higher order accuracy is obtained due to its spectral accuracy. To account for the acoustic-solid interaction, the domain decomposition method (DDM) based upon the discontinuous Galerkin spectral-element method is proposed. Numerical experiments show the proposed method can be an efficient alternative for accurate calculation of elastic and acoustic waves in frequency domain.
MULTILOOP PI CONTROLLER FOR ACHIEVING SIMULTANEOUS TIME AND FREQUENCY DOMAIN SPECIFICATIONS
Directory of Open Access Journals (Sweden)
M. SENTHILKUMAR
2015-08-01
Full Text Available Most of the controllers in control system are designed to satisfy either time domain or frequency domain specifications. This work presents the computation of a multiloop PI controller for achieving time and frequency domain specifications simultaneously. The desired time and frequency domain measures are to be specified initially to the design. To obtain the desired value of the performance measures the graphical relationship between the PI controller and the performance criteria is given. Thus by using graphical method a set of PI controller parameters to meet the desired performance measures are obtained in an effective and simpler way. The coupled tank has become a classic design of control engineering for multivariable process. The proposed control strategy has been implemented in the same coupled tank process and validated through simulation studies.
Practical iterative learning control with frequency domain design and sampled data implementation
Wang, Danwei; Zhang, Bin
2014-01-01
This book is on the iterative learning control (ILC) with focus on the design and implementation. We approach the ILC design based on the frequency domain analysis and address the ILC implementation based on the sampled data methods. This is the first book of ILC from frequency domain and sampled data methodologies. The frequency domain design methods offer ILC users insights to the convergence performance which is of practical benefits. This book presents a comprehensive framework with various methodologies to ensure the learnable bandwidth in the ILC system to be set with a balance between learning performance and learning stability. The sampled data implementation ensures effective execution of ILC in practical dynamic systems. The presented sampled data ILC methods also ensure the balance of performance and stability of learning process. Furthermore, the presented theories and methodologies are tested with an ILC controlled robotic system. The experimental results show that the machines can work in much h...
The application of finite element method to forward and inverse seismic problems in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Shaoyou, J.; Xiangheng, J.; Shizhe, X.
1987-04-01
Unstable result is obtained when the boundary problem of wave equation is solved using finite element method in time domain. However, when the boundary problem of wave equation is solved by finite element method in frequency domain, not only the unstablity can be avoided but also computation is speeded up because of using FFT. The procedure for solving the boundary problem using finite element method in frequency domain is as follows: 1. the wave equation is transformed into Helmholtz equation by making one-dimensional Fourier transform with respect to time; 2. Helmholtz equation is solved using finite element method in frequency domain; 3. the obtained result is returned to time domain by making inverse Fourier transform. Both forward and inverse seismic problems can be solved by this method.
Frequency-Domain Adaptive Algorithm for Network Echo Cancellation in VoIP
Directory of Open Access Journals (Sweden)
Patrick A. Naylor
2008-05-01
Full Text Available We propose a new low complexity, low delay, and fast converging frequency-domain adaptive algorithm for network echo cancellation in VoIP exploiting MMax and sparse partial (SP tap-selection criteria in the frequency domain. We incorporate these tap-selection techniques into the multidelay filtering (MDF algorithm in order to mitigate the delay inherent in frequency-domain algorithms. We illustrate two such approaches and discuss their tradeoff between convergence performance and computational complexity. Simulation results show an improvement in convergence rate for the proposed algorithm over MDF and significantly reduced complexity. The proposed algorithm achieves a convergence performance close to that of the recently proposed, but substantially more complex improved proportionate MDF (IPMDF algorithm.
Efficiency Improvement of the frequency-domain BEM for Rapid transient elastodynamic analysis
Xiao, Jinyou; Wen, Lihua
2012-01-01
The frequency-domain fast boundary element method (BEM) combined with the exponential window technique leads to an efficient yet simple method for elastodynamic analysis. In this paper, the efficiency of this method is further enhanced by three strategies. Firstly, we propose to use exponential window with large damping parameter to improve the conditioning of the BEM matrices. Secondly, the frequency domain windowing technique is introduced to alleviate the severe Gibbs oscillations in time-domain responses caused by large damping parameters. Thirdly, a solution extrapolation scheme is applied to obtain better initial guesses for solving the sequential linear systems in the frequency domain. Numerical results of three typical examples with the problem size up to 0.7 million unknowns clearly show that the first and third strategies can significantly reduce the computational time. The second strategy can effectively eliminate the Gibbs oscillations and result in accurate time-domain responses.
Method of moments in electromagnetics
Gibson, Walton C
2007-01-01
Responding to the need for a clear, up-to-date introduction to the field, The Method of Moments in Electromagnetics explores surface integral equations in electromagnetics and presents their numerical solution using the method of moments (MOM) technique. It provides the numerical implementation aspects at a nuts-and-bolts level while discussing integral equations and electromagnetic theory at a higher level. The author covers a range of topics in this area, from the initial underpinnings of the MOM to its current applications. He first reviews the frequency-domain electromagnetic theory and t
Performance of Downlink Frequency Domain Packet Scheduling for the UTRAN Long Term Evolution
DEFF Research Database (Denmark)
Pokhariyal, Akhilesh; Kolding, Troels E.; Mogensen, Preben
2006-01-01
In this paper we investigate the potential of downlink frequency-domain packet scheduling (FDPS) for the 3GPP UTRAN long term evolution. Utilizing frequency-domain channel quality reports, the scheduler flexibly multiplexes users on different portions of the system bandwidth. Compared to frequen...... Urban channel profile, studies show that the scheduling resolution should preferably be as low as 375 kHz to yield significant FDPS gain and the std. of the error of radio state reports need to be kept within 1.5-2 dB....
The capability of time- and frequency-domain algorithms for bistatic SAR processing
Vu, Viet T.; Sjögren, Thomas K.; Pettersson, Mats I.
2013-05-01
The paper presents a study of the capability of time- and frequency-domain algorithms for bistatic SAR processing. Two typical algorithms, Bistatic Fast Backprojection (BiFBP) and Bistatic Range Doppler (BiRDA), which are both available for general bistatic geometry, are selected as the examples of time- and frequency-domain algorithms in this study. Their capability is evaluated based on some criteria such as processing time required by the algorithms to reconstruct SAR images from bistatic SAR data and the quality assessments of those SAR images.
Consensus for Linear Multiagent Systems With Time-Varying Delays: A Frequency Domain Perspective.
Chen, Yuanye; Shi, Yang
2016-07-27
This paper investigates the consensus problem for multiagent systems with time-varying delays. The bounded delays can be arbitrarily fast time-varying. The communication topology is assumed to be undirected and fixed. With general linear dynamics under average state feedback protocols, the consensus problem is then transformed into the robust control problem. Further, sufficient frequency domain criteria are established in terms of small gain theorem by analyzing the delay dependent gains for both continuous-time and discrete-time systems. The controller synthesis problems can be solved by applying the frequency domain design methods. Numerical examples are demonstrated to verify the effectiveness of the proposed approaches.
Frequency Domain Packet Scheduling Under Fractional Load for the UTRAN LTE Downlink
DEFF Research Database (Denmark)
Pokhariyal, Akhilesh; Monghal, Guillaume Damien; Pedersen, Klaus I.
2007-01-01
In this paper we investigate performance of frequency domain packet scheduling (FDPS) under fractional load (FL), based on the UTRAN Long Term Evolution downlink. FL may be regarded as an inter-cell interference (ICI) mitigation technique, which can improve the user experienced SINR. We consider...
DEFF Research Database (Denmark)
Guo, Hairun; Zeng, Xianglong; Zhou, Binbin
2013-01-01
We interpret the purely spectral forward Maxwell equation with up to third-order induced polarizations for pulse propagation and interactions in quadratic nonlinear crystals. The interpreted equation, also named the nonlinear wave equation in the frequency domain, includes quadratic and cubic...
Frequency domain probe design for high frequency sensing of soil moisture
Accurate moisture sensing is an important need for many research programs as well as in control of industrial processes. This paper covers the development of a frequency domain sensing probe for use in obtaining measurements of material properties suitable for work ranging from 0 to 6GHz. The probe ...
Frequency domain volume rendering by the wavelet X-ray transform
Westenberg, Michel A.; Roerdink, Jos B.T.M.
2000-01-01
We describe a wavelet-based X-ray rendering method in the frequency domain with a smaller time complexity than wavelet splatting. Standard Fourier volume rendering is summarized and interpolation and accuracy issues are briefly discussed. We review the implementation of the fast wavelet transform in
Molenaar, P.C.M.
1987-01-01
Outlines a frequency domain analysis of the dynamic factor model and proposes a solution to the problem of constructing a causal filter of lagged factor loadings. The method is illustrated with applications to simulated and real multivariate time series. The latter applications involve topographic a
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.
Xiao, Pei; Lin, Zihuai; Fagan, Anthony; Cowan, Colin; Vucetic, Branka; Wu, Yi
2011-12-01
In this paper, we propose a novel transceiver structure for orthogonal frequency division multiple access-based uplink multiuser multiple-input multiple-output systems. The numerical results show that the proposed frequency-domain equalization schemes significantly outperform conventional linear minimum mean square error-based equalizers in terms of bit error rate performance with moderate increase in computational complexity.
Modeling of Nanophotonic Resonators with the Finite-Difference Frequency-Domain Method
DEFF Research Database (Denmark)
Ivinskaya, Aliaksandra; Lavrinenko, Andrei; Shyroki, Dzmitry
2011-01-01
Finite-difference frequency-domain method with perfectly matched layers and free-space squeezing is applied to model open photonic resonators of arbitrary morphology in three dimensions. Treating each spatial dimension independently, nonuniform mesh of continuously varying density can be built ea...
Statistics and frequency-domain moveout for multiple-taper receiver functions
Park, J.; Levin, V.
2016-10-01
The multiple-taper correlation (MTC) algorithm for the estimation of teleseismic receiver functions (RFs) has desirable statistical properties. This paper presents several adaptations to the MTC algorithm that exploit its frequency-domain uncertainty estimates to generate stable RFs that include moveout corrections for deeper interfaces. Narrow-band frequency averaging implicit in spectral cross-correlation restricts the MTC-based RF estimates to resolve Ps converted phases only at short delay times, appropriate to the upper 100 km of Earth's lithosphere. The Ps conversions from deeper interfaces can be reconstructed by the MTC algorithm in two ways. Event cross-correlation computes a cross-correlation of single-taper spectrum estimates for a cluster of events rather than for a set of eigenspectrum estimates of a single P coda. To extend the reach of the algorithm, pre-stack moveout corrections in the frequency domain preserves the formal uncertainties of the RF estimates, which are used to weight RF stacks. Moving-window migration retains the multiple-taper approach, but cross-correlates the P-polarized motion with time-delayed SH and SV motion to focus on a Ps phase of interest. The frequency-domain uncertainties of bin-averaged RFs do not translate directly into the time domain. A jackknife over data records in each bin stack offers uncertainty estimates in the time domain while preserving uncertainty weighting in the frequency-domain RF stack.
Modal Identification of Output-Only Systems using Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, L.; Andersen, P.
2000-01-01
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, ie. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical ...
Low-Bandwidth Channel Quality Indication for OFDMA Frequency Domain Packet Scheduling
DEFF Research Database (Denmark)
Kolding, Troels E.; Frederiksen, Frank; Pokhariyal, Akhilesh
2007-01-01
In this paper, we study methods for lowering the bandwidth needed for the UE to transmit channel quality indication (CQI) for time and frequency domain scheduling (FDPS) in OFDMA. We consider smart compression methods, such as threshold based indication, to only include scheduler...
Frequency-Domain Thermal Modelling and Characterization of Power Semiconductor Devices
DEFF Research Database (Denmark)
Ma, Ke; He, Ning; Liserre, Marco
2016-01-01
their limits to correctly predict the device temperatures, especially when considering the thermal grease and heat sink attached to the power semiconductor devices. In this paper, frequency-domain approach is applied to the modelling of the thermal dynamics for power devices. The limits of the existing RC lump...
Design PID controllers for desired time-domain or frequency-domain response.
Zhang, Weidong; Xi, Yugeng; Yang, Genke; Xu, Xiaoming
2002-10-01
Practical requirements on the design of control systems, especially process control systems, are usually specified in terms of time-domain response, such as overshoot and rise time, or frequency-domain response, such as resonance peak and stability margin. Although numerous methods have been developed for the design of the proportional-integral-derivative (PID) controller, little work has been done in relation to the quantitative time-domain and frequency-domain responses. In this paper, we study the following problem: Given a nominal stable process with time delay, we design a suboptimal PID controller to achieve the required time-domain response or frequency-domain response for the nominal system or the uncertain system. An H(infinity) PID controller is developed based on optimal control theory and the parameters are derived analytically. Its properties are investigated and compared with that of two developed suboptimal controllers: an H2 PID controller and a Maclaurin PID controller. It is shown that all three controllers can provide the quantitative time-domain and frequency-domain responses.
van Munster, E.B.; Goedhart, J.; Kremers, G.J.; Manders, E.M.M.; Gadella, Th.W.J.
2007-01-01
BACKGROUND: Wide-field frequency-domain fluorescence lifetime imaging microscopy (FLIM) is an established technique to determine fluorescence lifetimes. Disadvantage of wide-field imaging is that measurements are compromised by out-of-focus blur. Conventional scanning confocal typically means long
Real-time frequency-domain fiber optic sensor for intra-arterial blood oxygen measurements
Alcala, J. R.; Scott, Ian L.; Parker, Jennifer W.; Atwater, Beauford W.; Yu, Clement; Fischer, Russell; Bellingrath, K.
1993-05-01
A real time frequency domain phosphorimeter capable of measuring precise and accurate excited state lifetimes for determining oxygen is described. This frequency domain instrument does not make use of cross correlation techniques traditionally used in frequency domain fluorometers. Instead, the electrical signal from the detector is filtered to contain only the first several harmonics. This filtered signal is then sampled and averaged over a few thousand cycles. The absolute phase and absolute modulation of each sampled harmonic of the excitation and of the luminescence is computed by employing fast Fourier transform algorithms. The phase delay and the modulation ratio is then calculated at each harmonic frequency. A least squares fit is performed in the frequency domain to obtain the lifetimes of discrete exponentials. Oxygen concentrations are computed from these lifetimes. Prototypes based on these techniques were built employing commercially available components. Results from measurements in saline solution and in the arterial blood of dogs show that oxygen concentrations can be determined reproducibly. The system drift is less than 1% in over 100 hours of continuous operation. The performance of fiber optic sensors was evaluated in dogs over a period of 10 hours. The sensors tracked changes in arterial oxygen tension over the course of the experiment without instabilities. The overall response of the system was about 90 seconds. The update time was 3 seconds.
Plastique: A synchrotron radiation beamline for time resolved fluorescence in the frequency domain
De Stasio, Gelsomina; Zema, N.; Antonangeli, F.; Savoia, A.; Parasassi, T.; Rosato, N.
1991-06-01
PLASTIQUE is the only synchrotron radiation beamline in the world that performs time resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and dynamics of molecules. We describe the beamline and some initial data.
Postural Analysis in Time and Frequency Domains in Patients with Ehlers-Danlos Syndrome
Galli, Manuela; Rigoldi, Chiara; Celletti, Claudia; Mainardi, Luca; Tenore, Nunzio; Albertini, Giorgio; Camerota, Filippo
2011-01-01
The goal of this work is to analyze postural control in Ehlers-Danlos syndrome (EDS) participants in time and frequency domain. This study considered a pathological group composed by 22 EDS participants performing a postural test consisting in maintaining standing position over a force platform for 30 s in two conditions: open eyes (OE) and closed…
DEFF Research Database (Denmark)
Jacobsen, Niels-Jørgen; Andersen, Palle; Brincker, Rune
2006-01-01
Enhanced Frequency Domain Decomposition technique for eliminating the influence of these harmonic components in the modal parameter extraction process. For various experiments, the quality of the method is assessed and compared to the results obtained using broadband stochastic excitation forces. Good...
Comparison of Frequency-Domain Array Methods for Studying Earthquake Rupture Process
Sheng, Y.; Yin, J.; Yao, H.
2014-12-01
Seismic array methods, in both time- and frequency- domains, have been widely used to study the rupture process and energy radiation of earthquakes. With better spatial resolution, the high-resolution frequency-domain methods, such as Multiple Signal Classification (MUSIC) (Schimdt, 1986; Meng et al., 2011) and the recently developed Compressive Sensing (CS) technique (Yao et al., 2011, 2013), are revealing new features of earthquake rupture processes. We have performed various tests on the methods of MUSIC, CS, minimum-variance distortionless response (MVDR) Beamforming and conventional Beamforming in order to better understand the advantages and features of these methods for studying earthquake rupture processes. We use the ricker wavelet to synthesize seismograms and use these frequency-domain techniques to relocate the synthetic sources we set, for instance, two sources separated in space but, their waveforms completely overlapping in the time domain. We also test the effects of the sliding window scheme on the recovery of a series of input sources, in particular, some artifacts that are caused by the sliding window scheme. Based on our tests, we find that CS, which is developed from the theory of sparsity inversion, has relatively high spatial resolution than the other frequency-domain methods and has better performance at lower frequencies. In high-frequency bands, MUSIC, as well as MVDR Beamforming, is more stable, especially in the multi-source situation. Meanwhile, CS tends to produce more artifacts when data have poor signal-to-noise ratio. Although these techniques can distinctly improve the spatial resolution, they still produce some artifacts along with the sliding of the time window. Furthermore, we propose a new method, which combines both the time-domain and frequency-domain techniques, to suppress these artifacts and obtain more reliable earthquake rupture images. Finally, we apply this new technique to study the 2013 Okhotsk deep mega earthquake
DEFF Research Database (Denmark)
Pittalà, Fabio; Hauske, Fabian N.; Ye, Yabin;
2011-01-01
CD and DGD monitoring from Frequency- Domain Zero-Forcing and MMSE filter functions adapted with the aid of short CAZAC training sequences is demonstrated.......CD and DGD monitoring from Frequency- Domain Zero-Forcing and MMSE filter functions adapted with the aid of short CAZAC training sequences is demonstrated....
Time and frequency domain models for multiaxial fatigue life estimation under random loading
Directory of Open Access Journals (Sweden)
Andrea Carpinteri
2015-07-01
Full Text Available Engineering structures and components are often subjected to random fatigue loading produced, for example, by wind turbulences, marine waves and vibrations. The methods available in the literature for fatigue assessment under random loading are formulated in time domain or, alternatively, in frequency domain. The former methods require the knowledge of the loading time history, and a large number of experimental tests/numerical simulations is needed to obtain statistically reliable results. The latter methods are generally more advantageous with respect to the time domain ones, allowing a rapid fatigue damage evaluation. In the present paper, a multiaxial criterion formulated in the frequency-domain is presented to estimate the fatigue lives of smooth metallic structures subjected to combined bending and torsion random loading. A comparison in terms of fatigue life prediction by employing a time domain methods, previously proposed by the authors, is also performed.
DEFF Research Database (Denmark)
Borg, Michael; Collu, M.
2015-01-01
The re-emerging interest in vertical axis wind turbines for floating offshore applications has led to a need to investigate the relatively complex dynamics of such floating offshore structures. Through the use of a coupled model of dynamics this article investigates the frequency-domain character......The re-emerging interest in vertical axis wind turbines for floating offshore applications has led to a need to investigate the relatively complex dynamics of such floating offshore structures. Through the use of a coupled model of dynamics this article investigates the frequency-domain...... characteristics of floating vertical axis wind turbine aerodynamic loads. The impact of platform induced motion on aerodynamic loads is discussed in detail, with results indicating an increase in aerodynamic loads of several orders of magnitude over the range of frequencies usually containing significant wave...
Jung, Justin; Istfan, Raeef; Roblyer, Darren
2014-07-01
Near-Infrared frequency-domain technologies, such as Diffuse Optical Spectroscopy (DOS), have demonstrated growing potential in a number of clinical applications. The broader dissemination of this technology is limited by the complexity and cost of instrumentation. We present here a simple system constructed with off-the-shelf components that utilizes undersampling for digital frequency-domain dDOS measurements. Broadband RF sweeps (50-300 MHz) were digitally sampled at 25 MSPS; amplitude, phase, and optical property extractions were within 5% of network analyzer derived values. The use of undersampling for broad bandwidth dDOS provides a significant reduction in complexity, power consumption, and cost compared with high-speed ADCs and analog techniques.
A hybrid analysis method for linear dynamic soil-structure interaction in time and frequency domain
Institute of Scientific and Technical Information of China (English)
丁海平; 廖振鹏
2001-01-01
A hybrid analysis method in time and frequency domains for linear soil-structure interaction is presented. First, the time domain solution of the system with Rayleigh damping excited by a short time impulse is obtained by the decoupling numerical simulation technique of near-field wave motion. Then, the corresponding frequency domain solution can be got by Fourier transform. According to the relationship between damping value and dynamic re-sponse of a system, the solution of the system with complex damping can be got by Taylor expansion. The hybrid method makes the best of decoupling and explicit algorithm in time domain, and increases the calculation efficien-cy for linear soil-structure interaction analysis.
Frequency domain volume rendering by the wavelet X-ray transform.
Westenberg, M A; Roerdink, J M
2000-01-01
We describe a wavelet based X-ray rendering method in the frequency domain with a smaller time complexity than wavelet splatting. Standard Fourier volume rendering is summarized and interpolation and accuracy issues are briefly discussed. We review the implementation of the fast wavelet transform in the frequency domain. The wavelet X-ray transform is derived, and the corresponding Fourier-wavelet volume rendering algorithm (FWVR) is introduced, FWVR uses Haar or B-spline wavelets and linear or cubic spline interpolation. Various combinations are tested and compared with wavelet splatting (WS). We use medical MR and CT scan data, as well as a 3-D analytical phantom to assess the accuracy, time complexity, and memory cost of both FWVR and WS. The differences between both methods are enumerated.
FILDIG: a program to filter brain electrical signals in the frequency domain.
Guevara, M A; Ramos, J; Hernández-González, M; Corsi-Cabrera, M
2005-11-01
A software program to filter brain electrical signals in the frequency domain has been developed and is presently reported. Many other filters are commercially available; however, most of them are linked to data acquisition and/or analysis programs rendering them costly. Depending on the experimental field, the full programs are not always needed. To overcome the need to obtain narrow bands in EEG research and other biological signals in an easy, fast and cheap way, we developed a computer program (FILDIG) that renders an almost ideal in-phase filter in the frequency domain and can be used in all types of personal microcomputers (PC and Mac's) and with few resources. The system uses an interactive graphic display and, with a minimum interface, it is capable of filtering multiple channels and simultaneously obtaining electrical signals (EEG, EMG, EOG, etc.) without noise or specific frequency bands.
DEFF Research Database (Denmark)
Rodrigues, J.; Brincker, Rune; Andersen, P.
2004-01-01
from the time series, are due to the noise reduction that results from the time averaging procedure of the random decrement technique, and from avoiding leakage in the spectral densities, as long as the random decrement functions are evaluated with sufficient time length to have a complete decay within......This paper explores the idea of estimating the spectral densities as the Fourier transform of the random decrement functions for the application of frequency domain output-only modal identification methods. The gains in relation to the usual procedure of computing the spectral densities directly...... that length. The idea is applied in the analysis of ambient vibration data collected in a ¼ scale model of a 4-story building. The results show that a considerable improvement is achieved, in terms of noise reduction in the spectral density functions and corresponding quality of the frequency domain modal...
Directory of Open Access Journals (Sweden)
M.I.Khalil
2017-02-01
Full Text Available Steganography is the discipline of invisible communication by hiding the exchanged secret information (message in another digital information media (image, video or audio. The existence of the message is kept indiscernible in sense that no one, other than the intended recipient, suspects the existence of the message. The majority of steganography techniques are implemented either in spatial domain or in frequency domain of the digital images while the embedded information can be in the form of plain or cipher message. Medical image steganography is classified as a distinctive case of image steganography in such a way that both the image and the embedded information have special requirements such as achieving utmost clarity reading of the medical images and the embedded messages. There is a contention between the amount of hidden information and the caused detectable distortion of image. The current paper studies the degradation of the medical image when undergoes the steganography process in the frequency domain.
Frequency domain stability analysis of nonlinear active disturbance rejection control system.
Li, Jie; Qi, Xiaohui; Xia, Yuanqing; Pu, Fan; Chang, Kai
2015-05-01
This paper applies three methods (i.e., root locus analysis, describing function method and extended circle criterion) to approach the frequency domain stability analysis of the fast tool servo system using nonlinear active disturbance rejection control (ADRC) algorithm. Root locus qualitative analysis shows that limit cycle is generated because the gain of the nonlinear function used in ADRC varies with its input. The parameters in the nonlinear function are adjustable to suppress limit cycle. In the process of root locus analysis, the nonlinear function is transformed based on the concept of equivalent gain. Then, frequency domain description of the nonlinear function via describing function is presented and limit cycle quantitative analysis including estimating prediction error is presented, which virtually and theoretically demonstrates that the describing function method cannot guarantee enough precision in this case. Furthermore, absolute stability analysis based on extended circle criterion is investigated as a complement.
Cao, Zili; Lin, Weihao; Chen, Xinlin; Zeng, Bixin; Xu, Min
2017-02-01
We have presented a novel Single Snapshot Multiple Frequency Demodulation (SSMD) method enabling single snapshot wide field imaging of optical properties of turbid media in the Spatial Frequency Domain. SSMD makes use of the orthogonality of harmonic functions and extracts the modulation transfer function (MTF) at multiple modulation frequencies and of arbitrary orientations and amplitudes simultaneously from a single structured-illuminated image at once. SSMD not only increases significantly the data acquisition speed and reduces motion artifacts but also exhibits excellent noise suppression in imaging as well. The performance of SSMD-SFDI is demonstrated with experiments on both tissue mimicking phantoms and in vivo for recovering optical properties. SSMD is ideal in the implementation of a real-time spatial frequency domain imaging platform, which will open up SFDI for vast applications in, for example, mapping the optical properties of a dynamic turbid medium or monitoring fast temporal evolutions.
USING CROSS-CORRELATION THEORY TO EXTRACT MODAL PARAMETERS IN FREQUENCY-DOMAIN
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Conventional modal parameter identifications are usually based on frequency response functions, which require measurements of both the input force and the resulting response. However, in many cases, only response data are available while the actual excitations (such as wind/wave load) are not measurable. Modal parameters estimation must base itself on response-only data. Over the past years, many time-domain modal parameter identification techniques from output-only are proposed. A poly-reference frequency-domain modal identification scheme on response-only is presented. It is based on coupling the cross-correlation theory with conventional frequency-domain modal parameter extraction. An experiment using an airplane model is performed to verify the proposed method.
Spatial and frequency domain interferometry using the MU radar - A tutorial and recent developments
Fukao, Shoichiro; Palmer, Robert D.
Fundamental notions of spatial and frequency-domain interferometry are reviewed, and a novel method is proposed for steering the antenna beam after the data are stored. Also presented is a comparison of techniques for wind-vector determination with emphasis given to a method based on the linear variation of the phase of the cross-spectra. Recent applications of spatial interferometry (SI) and frequency-domain interferometry (FDI) are listed including an implementation of FDI with MU radar. The vertical wind velocity estimated from the Doppler technique is shown to be a measure of the wind perpendicular to tilted refractivity surfaces. The bias generated by horizontal wind is found to have a significant effect on the Doppler estimate in SI. The use of MU radar in FDI can facilitate measurements of the positions of high reflectivity layers smaller than the resolution volume.
A frequency domain radar interferometric imaging (FII) technique based on high-resolution methods
Luce, H.; Yamamoto, M.; Fukao, S.; Helal, D.; Crochet, M.
2001-01-01
In the present work, we propose a frequency-domain interferometric imaging (FII) technique for a better knowledge of the vertical distribution of the atmospheric scatterers detected by MST radars. This is an extension of the dual frequency-domain interferometry (FDI) technique to multiple frequencies. Its objective is to reduce the ambiguity (resulting from the use of only two adjacent frequencies), inherent with the FDI technique. Different methods, commonly used in antenna array processing, are first described within the context of application to the FII technique. These methods are the Fourier-based imaging, the Capon's and the singular value decomposition method used with the MUSIC algorithm. Some preliminary simulations and tests performed on data collected with the middle and upper atmosphere (MU) radar (Shigaraki, Japan) are also presented. This work is a first step in the developments of the FII technique which seems to be very promising.
Fractional Fourier transform for partially coherent beam in spatial-frequency domain
Institute of Scientific and Technical Information of China (English)
Cai Yang-Jian; Lin Qiang
2004-01-01
By using Fourier transform and the tensor analysis method, the fractional Fourier transform (FRT) in the spatialfrequency domain for partially coherent beams is derived. Based on the FRT in the spatial-frequency domain, an analytical transform formula is derived for a partially coherent twisted anisotropic Gaussian-Schell model (GSM) beam passing through the FRT system. The connections between the FRT formula and the generalized diffraction integral formulae for partially coherent beams through an aligned optical system and a misaligned optical system in the spatialfrequency domain are discussed, separately. By using the derived formula, the intensity distribution of partially coherent twisted anisotropic GSM beams in the FRT plane are studied in detail. The formula derived provide a convenient tool for analysing and calculating the FRTs of the partially coherent beams in spatial-frequency domain.
The research on recognition and extraction of river feature in IKNOS based on frequency domain
Wang, Ke; Feng, Xuezhi; Xiao, Pengfeng; Wu, Guoping
2009-10-01
Because the resolution of remotely sensed imagery becomes higher, new methods are introduced to process the high-resolution remotely sensed imagery. The algorithms introduced in this paper to recognize and extract the river features based on the frequency domain. This paper uses the Gabor filter in frequency domain to enhance the texture of river and remove the noise from remotely sensed imagery. And then according to the theory of phase congruency, this paper retrieves the PC of every point such that features such as edge of river, building and farmland in the remotely sensed imagery. Lastly, the skeletal methodology is introduced to determine the edge of river within the help of the trend of river.
Directory of Open Access Journals (Sweden)
Tong Wu
2016-11-01
Full Text Available We present a spatial frequency domain multiplexing method for extending the imaging depth range of a spectral domain optical coherence tomography (SDOCT system without any expensive device. This method uses two galvo scanners with different pivot-offset distances in two independent reference arms for spatial frequency modulation and multiplexing. The spatial frequency contents corresponding to different depth regions of the sample can be shifted to different frequency bands. The spatial frequency domain multiplexing SDOCT system provides an approximately 1.9-fold increase in the effective ranging depth compared with that of a conventional full-range SDOCT system. The reconstructed images of phantom and biological tissue demonstrate the expected increase in ranging depth. The parameters choice criterion for this method is discussed.
DEFF Research Database (Denmark)
Madsen, Kristoffer Hougaard; Hansen, Lars Kai; Mørup, Morten
2009-01-01
We propose the Time Frequency Gradient Method (TFGM) which forms a framework for optimization of models that are constrained in the time domain while having efficient representations in the frequency domain. Since the constraints in the time domain in general are not transparent in a frequency...... representation we demonstrate how the class of objective functions that are separable in either time or frequency instances allow the gradient in the time or frequency domain to be converted to the opposing domain. We further demonstrate the usefulness of this framework for three different models; Shifted Non......-negative Matrix Factorization, Convolutive Sparse Coding as well as Smooth and Sparse Matrix Factorization. Matlab implementation of the proposed algorithms are available for download at www.erpwavelab.org....
Performance of Spatial Division Multiplexing MIMO with Frequency Domain Packet Scheduling
DEFF Research Database (Denmark)
Wei, Na; Pokhariyal, Akhilesh; Sørensen, Troels Bundgaard;
2008-01-01
This paper addresses the performance of Spatial Division Multiplexing (SDM) Multiple-input Multiple-output (MIMO) techniques together with Frequency Domain Packet Scheduling (FDPS) in both theory and practice. We start with a theoretical analysis under some ideal assumptions to derive the perform......This paper addresses the performance of Spatial Division Multiplexing (SDM) Multiple-input Multiple-output (MIMO) techniques together with Frequency Domain Packet Scheduling (FDPS) in both theory and practice. We start with a theoretical analysis under some ideal assumptions to derive...... is to investigate the impact of realistic factors on performance. Results confirm that the combination of SDM and FDPS can increase the spectral efficiency significantly, particularly in a micro-cell scenario, and up to 30%-60% gain is observed over 1x2 with FDPS depending on the traffic models considered. Finally...
Fast simulation approaches for power fluctuation model of wind farm based on frequency domain
DEFF Research Database (Denmark)
Lin, Jin; Gao, Wen-zhong; Sun, Yuan-zhang
2012-01-01
This paper discusses one model developed by Riso, DTU, which is capable of simulating the power fluctuation of large wind farms in frequency domain. In the original design, the “frequency-time” transformations are time-consuming and might limit the computation speed for a wind farm of large size....... is more than 300 times if all these approaches are adopted, in any low, medium and high wind speed test scenarios....
Frequency-domain photoacoustic phased array probe for biomedical imaging applications.
Telenkov, Sergey; Alwi, Rudolf; Mandelis, Andreas; Worthington, Arthur
2011-12-01
We report the development of a frequency-domain biomedical photoacoustic imaging system that utilizes a continuous-wave laser source with a custom intensity modulation pattern, ultrasonic phased array for signal detection, and processing coupled with a beam-forming algorithm for reconstruction of photoacoustic correlation images. Sensitivity to optical contrast was demonstrated using tissue-mimicking phantoms and in-vivo tissue samples.
Directory of Open Access Journals (Sweden)
Wu Yi
2011-01-01
Full Text Available Abstract In this paper, we propose a novel transceiver structure for orthogonal frequency division multiple access-based uplink multiuser multiple-input multiple-output systems. The numerical results show that the proposed frequency-domain equalization schemes significantly outperform conventional linear minimum mean square error-based equalizers in terms of bit error rate performance with moderate increase in computational complexity.
High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing
MacLachlan, Robert A.; Riviere, Cameron N.
2009-01-01
Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large ...
Design of UWB pulse radio transceiver using statistical correlation technique in frequency domain
Directory of Open Access Journals (Sweden)
M. Anis
2007-06-01
Full Text Available In this paper, we propose a new technique to extract low power UWB pulse radio signals, near to noise level, using statistical correlation technique in frequency domain. The receiver consists of many narrow bandpass filters which extract energy either from transmitted UWB signal, interfering channels or noise. Transmitted UWB data can be eliminated by statistical correlation of multiple bandpass filter outputs. Super-regenerative oscillators, tuned within UWB spectrum, are designed as bandpass filters. Summers and comparators perform statistical correlation.
Channel estimation in space and frequency domain for MIMO-OFDM systems
Institute of Scientific and Technical Information of China (English)
PAN Pei-sheng; ZHENG Bao-yu
2009-01-01
Multiple-input multiple-output (MIMO) systems can be combined with orthogonal frequency division multiplexing (OFDM) systems to improve the capacity and quality of wireless communications. In this article, a channel estimation technique in both space and frequency domain for MIMO-OFDM systems is proposed. It is shown that the proposed scheme with space-frequency pilot tones achieve optimal minimum mean square error (MMSE) channel estimation. Simulation results indicate that the proposed method achieves good performance.
BER Performance of Frequency Domain Differential Demodulation OFDM in Flat Fading Channel
Institute of Scientific and Technical Information of China (English)
SONG Lijun; TANG Youxi; LI Shaoqian; HUANG Shunji
2003-01-01
A closed form expression for the bit error rate (BER) performance of frequency domain differential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fading channel is derived. The performance is evaluated by computer simulation and compared with the time domain differential demodulation(TDDD). The results indicate that the performance of FDDD is better than that of TDDD, and the lower band of BER in the former is lower than that of the latter.
Directory of Open Access Journals (Sweden)
Fu Chin-Hua
2011-02-01
Full Text Available Abstract Background An accurate prediction of unplanned readmission (UR after discharge from hospital can facilitate physician's decision making processes for providing better quality of care in geriatric patients. The objective of this study was to explore the association of cardiac autonomic functions as measured by frequency domain heart rate variability (HRV and 14-day UR in geriatric patients. Methods Patients admitted to the geriatric ward of a regional hospital in Chiayi county in Taiwan were followed prospectively from July 2006 to June 2007. Those with invasive tubes and those who were heavy smokers, heavy alcohol drinkers, on medications that might influence HRV, or previously admitted to the hospital within 30 days were excluded. Cardiac autonomic functions were evaluated by frequency domain indices of HRV. Multiple logistic regression was used to assess the association between UR and HRV indices adjusted for age and length of hospitalization. Results A total of 78 patients met the inclusion criteria and 15 of them were readmitted within 14 days after discharge. The risk of UR was significantly higher in patients with lower levels of total power (OR = 1.39; 95% CI = 1.04-2.00, low frequency power (LF (OR = 1.22; 95% CI = 1.03-1.49, high frequency power (HF (OR = 1.27; 95% CI = 1.02-1.64, and lower ratios of low frequency power to high frequency power (LF/HF ratio (OR = 1.96; 95% CI = 1.07-3.84. Conclusion This is the first study to evaluate the association between frequency domain heart rate variability and the risk of UR in geriatric patients. Frequency domain heart rate variability indices measured on admission were significantly associated with increased risk of UR in geriatric patients. Additional studies are required to confirm the value and feasibility of using HRV indices on admission as a non-invasive tool to assist the prediction of UR in geriatric patients.
Albulescu, Claudiu Tiberiu; Daniel GOYEAU; Tiwari, Aviral Kumar
2013-01-01
International audience; The present paper analyse the relationship between the volume of transactions with futures equity index products and the return volatility of their underlying assets. The study addresses the case of five stock markets, members of the Euronext.liffe: London, Paris, Amsterdam, Brussels and Lisbon. We employ a frequency domain analysis, using monthly data for the period 2001.09 – 2010.06, which allows us to identify the direction of the causality between the derivatives v...
High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing
MacLachlan, Robert A.; Riviere, Cameron N.
2009-01-01
Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large ...
Quantifying Stability Using Frequency Domain Data from Wireless Inertial Measurement Units
Directory of Open Access Journals (Sweden)
Stephen Slaughter
2012-08-01
Full Text Available The quantification of gait stability can provide valuable information when evaluating subjects for age related and neuromuscular disease changes. Using tri-axial inertial measurement units (IMU for acceleration and rotational data provide a non-linear profile for this type of movement. As subjects traverse various surfaces representing decreasing stability, the different phasing of gait data make comparisons difficult. By converting from time to frequency domain data, the phase effects can be ignored, allowing for significant correlations. In this study, 12 subjects provided gait information over various surfaces while wearing an IMU. Instabilities were determined by comparing frequency domain data over less stable surfaces to frequency domain data of neural network (NN models representing the normal gait for any given participant. Time dependent data from 2 axes of acceleration and 2 axes of rotation were converted using a discrete Fourier transform (FFT algorithm. The data over less stable surfaces were compared to the normal gait NN model by averaging the Pearson product moment correlation (r values. This provided a method to quantify the decreased stability. Data showed progressively decreasing correlation coefficient values as subjects encountered progressively less stable surface environments. This methodology has allowed for the quantification of instability in gait situations for application in real-time fall prevention situations.
Frequency domain modeling and dynamic characteristics evaluation of existing wind turbine systems
Chiang, Chih-Hung; Yu, Chih-Peng
2016-04-01
It is quite well accepted that frequency domain procedures are suitable for the design and dynamic analysis of wind turbine structures, especially for floating offshore wind turbines, since random wind loads and wave induced motions are most likely simulated in the frequency domain. This paper presents specific applications of an effective frequency domain scheme to the linear analysis of wind turbine structures in which a 1-D spectral element was developed based on the axially-loaded member. The solution schemes are summarized for the spectral analyses of the tower, the blades, and the combined system with selected frequency-dependent coupling effect from foundation-structure interactions. Numerical examples demonstrate that the modal frequencies obtained using spectral-element models are in good agreement with those found in the literature. A 5-element mono-pile model results in less than 0.3% deviation from an existing 160-element model. It is preliminarily concluded that the proposed scheme is relatively efficient in performing quick verification for test data obtained from the on-site vibration measurement using the microwave interferometer.
Broadband Beamspace DOA Estimation: Frequency-Domain and Time-Domain Processing Approaches
Directory of Open Access Journals (Sweden)
Yan Shefeng
2007-01-01
Full Text Available Frequency-domain and time-domain processing approaches to direction-of-arrival (DOA estimation for multiple broadband far field signals using beamspace preprocessing structures are proposed. The technique is based on constant mainlobe response beamforming. A set of frequency-domain and time-domain beamformers with constant (frequency independent mainlobe response and controlled sidelobes is designed to cover the spatial sector of interest using optimal array pattern synthesis technique and optimal FIR filters design technique. These techniques lead the resulting beampatterns higher mainlobe approximation accuracy and yet lower sidelobes. For the scenario of strong out-of-sector interfering sources, our approaches can form nulls or notches in the direction of them and yet guarantee that the mainlobe response of the beamformers is constant over the design band. Numerical results show that the proposed time-domain processing DOA estimator has comparable performance with the proposed frequency-domain processing method, and that both of them are able to resolve correlated source signals and provide better resolution at lower signal-to-noise ratio (SNR and lower root-mean-square error (RMSE of the DOA estimate compared with the existing method. Our beamspace DOA estimators maintain good DOA estimation and spatial resolution capability in the scenario of strong out-of-sector interfering sources.
Directory of Open Access Journals (Sweden)
Trautmann Steffen
2004-01-01
Full Text Available We propose a zero-forcing frequency domain block equalizer for discrete multitone (DMT systems with a guard interval of insufficient length. In addition to the insufficient guard interval in the time domain, the equalizer takes advantage of frequency domain redundancy in the form of subcarriers that do not transmit any data. After deriving sufficient conditions for zero-forcing equalization, that is, complete removal of intersymbol and intercarrier interference, we calculate the noise enhancement of the equalizer by evaluating the signal-to-noise ratio (SNR for each subcarrier. The SNRs are used by an adaptive loading algorithm. It decides how many bits are assigned to each subcarrier in order to achieve a maximum data rate at a fixed error probability. We show that redundancy in the time domain can be traded off for redundancy in the frequency domain resulting in a transceiver with a lower system latency time. The derived equalizer matrix is sparse, thus resulting in a low computational complexity.
Joint AVO inversion in the time and frequency domain with Bayesian interference
Zong, Zhao-Yun; Yin, Xing-Yao; Li, Kun
2016-12-01
Amplitude variations with offset or incident angle (AVO/AVA) inversion are typically combined with statistical methods, such as Bayesian inference or deterministic inversion. We propose a joint elastic inversion method in the time and frequency domain based on Bayesian inversion theory to improve the resolution of the estimated P- and S-wave velocities and density. We initially construct the objective function using Bayesian inference by combining seismic data in the time and frequency domain. We use Cauchy and Gaussian probability distribution density functions to obtain the prior information for the model parameters and the likelihood function, respectively. We estimate the elastic parameters by solving the initial objective function with added model constraints to improve the inversion robustness. The results of the synthetic data suggest that the frequency spectra of the estimated parameters are wider than those obtained with conventional elastic inversion in the time domain. In addition, the proposed inversion approach offers stronger antinoising compared to the inversion approach in the frequency domain. Furthermore, results from synthetic examples with added Gaussian noise demonstrate the robustness of the proposed approach. From the real data, we infer that more model parameter details can be reproduced with the proposed joint elastic inversion.
Kougioumtzoglou, I. A.; Fragkoulis, V. C.; Pantelous, A. A.; Pirrotta, A.
2017-09-01
A frequency domain methodology is developed for stochastic response determination of multi-degree-of-freedom (MDOF) linear and nonlinear structural systems with singular matrices. This system modeling can arise when a greater than the minimum number of coordinates/DOFs is utilized, and can be advantageous, for instance, in cases of complex multibody systems where the explicit formulation of the equations of motion can be a nontrivial task. In such cases, the introduction of additional/redundant DOFs can facilitate the formulation of the equations of motion in a less labor intensive manner. Specifically, relying on the generalized matrix inverse theory, a Moore-Penrose (M-P) based frequency response function (FRF) is determined for a linear structural system with singular matrices. Next, relying on the M-P FRF a spectral input-output (excitation-response) relationship is derived in the frequency domain for determining the linear system response power spectrum. Further, the above methodology is extended via statistical linearization to account for nonlinear systems. This leads to an iterative determination of the system response mean vector and covariance matrix. Furthermore, to account for singular matrices, the generalization of a widely utilized formula that facilitates the application of statistical linearization is proved as well. The formula relates to the expectation of the derivatives of the system nonlinear function and is based on a Gaussian response assumption. Several linear and nonlinear MDOF structural systems with singular matrices are considered as numerical examples for demonstrating the validity and applicability of the developed frequency domain methodology.
Frequency-domain analysis of intrinsic neuronal properties using high-resistant electrodes
Directory of Open Access Journals (Sweden)
Christian Rössert
2009-08-01
Full Text Available Intrinsic cellular properties of neurons in culture or slices are usually studied by the whole cell clamp method using low-resistant patch pipettes. These electrodes allow detailed analyses with standard electrophysiological methods such as current- or voltage-clamp. However, in these preparations large parts of the network and dendritic structures may be removed, thus preventing an adequate study of synaptic signal processing. Therefore, intact in vivo preparations or isolated in vitro whole brains have been used in which intracellular recordings are usually made with sharp, high-resistant electrodes to optimize the impalement of neurons. The general non-linear resistance properties of these electrodes, however, severely limit accurate quantitative studies of membrane dynamics especially needed for precise modelling. Therefore, we have developed a frequency-domain analysis of membrane properties that uses a Piece-wise Non-linear Electrode Compensation (PNEC method. The technique was tested in second-order vestibular neurons and abducens motoneurons of isolated frog whole brain preparations using sharp potassium chloride- or potassium acetate-filled electrodes. All recordings were performed without online electrode compensation. The properties of each electrode were determined separately after the neuronal recordings and were used in the frequency-domain analysis of the combined measurement of electrode and cell. This allowed detailed analysis of membrane properties in the frequency-domain with high-resistant electrodes and provided quantitative data that can be further used to model channel kinetics. Thus, sharp electrodes can be used for the characterization of intrinsic properties and synaptic inputs of neurons in intact brains.
Institute of Scientific and Technical Information of China (English)
何艳丽; 董石麟
2002-01-01
Large span spatial lattice structures have many natural frequencies in a narrow frequency range, the conventional frequency domain method is difficult to contain all significant contribution modes. Through numerical examples, it is found that some high order modes are likely to be overlooked because of their higher positions of modal order, in spite of their significance to wind response. According to the contributions of modes to strain energy of system, the paper presented an efficient method to compensate the errors owing to missing out some significant high order modes. The effectiveness of the proposed method is verified through a numerical analysis of the wind responses of a spherical dome.
A Novel Ship Wake Detection Method of SAR Images Based on Frequency Domain
Institute of Scientific and Technical Information of China (English)
Liu Hao; Zhu Minhui
2003-01-01
Moving ships produce a set of waves of "V' pattern on the ocean. These waves can often be seen by Synthetic Aperture Radar (SAR). The detection of these wakes can provide important information for surveillance of shipping, such as ship traveling direction and speed. A novel approach to the detection of ship wakes in SAR images based on frequency domain is provided in this letter. Compared with traditional Radon-based approaches, computation is reduced by 20%-40% without losing nearly any of detection performance. The testing results using real data and simulation of synthetic SAR images test the algorithm's feasibility and robustness.
Linearized Aeroelastic Computations in the Frequency Domain Based on Computational Fluid Dynamics
Amsallem, David; Choi, Youngsoo; Farhat, Charbel
2015-01-01
An iterative, CFD-based approach for aeroelastic computations in the frequency domain is presented. The method relies on a linearized formulation of the aeroelastic problem and a fixed-point iteration approach and enables the computation of the eigenproperties of each of the wet aeroelastic eigenmodes. Numerical experiments on the aeroelastic analysis and design optimization of two wing configurations illustrate the capability of the method for the fast and accurate aeroelastic analysis of aircraft configurations and its advantage over classical time-domain approaches.
Dynamic analysis of offshore structures with non-zero initial conditions in the frequency domain
Liu, Fushun; Lu, Hongchao; Li, Huajun
2016-03-01
The state of non-zero conditions is typically treated as fact when considering the dynamic analysis of offshore structures. This article extends a newly proposed method [1] to manage the non-zero initial conditions of offshore structures in the frequency domain, including new studies on original environmental loads reconstruction, response comparisons with the commercial software ANSYS, and a demonstration using an experimental cantilever beam. The original environmental loads, such as waves, currents, and winds, that act on a structure are decomposed into multiple complex exponential components are represented by a series of poles and corresponding residues. Counter to the traditional frequency-domain method, the non-zero initial conditions of offshore structures could be solved in the frequency domain. Compared with reference [1], an improvement reported in this article is that practical issues, including the choice of model order and central-processing-unit (CPU) time consumption, are further studied when applying this new method to offshore structures. To investigate the feasibility of the representation of initial environmental loads by their poles and corresponding residues, a measured random wave force collected from a column experiment at the Lab of Ocean University of China is used, decomposed, reconstructed and then compared with the original wave force; then, a numerical offshore platform is used to study the performance of the proposed method in detail. The numerical results of this study indicate that (1) a short duration of environmental loads are required to obtain their constitutive poles and residues, which implies good computational efficiency; and (2) the proposed method has a similar computational efficiency to traditional methods due to the use of the inverse Fourier transform technique. To better understand the performance, of time consumption and accuracy of the proposed method, the commercial software ANSYS is used to determine responses
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.
Institute of Scientific and Technical Information of China (English)
Pan Jin; Wang De-yu
2006-01-01
In this paper, adaptive genetic algorithm (AGA) is applied to topology optimization of truss structure with frequency domain excitations. The optimization constraints include fundamental frequency, displacement responses under force excitations and acceleration responses under foundation acceleration excitations. The roulette wheel selection operator, adaptive crossover and mutation operators are used as genetic operators. Some heuristic strategies are put forward to direct the deletion of the extra bars and nodes on truss structures. Three examples demonstrate that the proposed method can yield the optimum structure form and the lightest weight of the given ground structure while satisfying dynamic response constraints.
Frequency-domain imaging algorithm for ultrasonic testing by application of matrix phased arrays
Directory of Open Access Journals (Sweden)
Dolmatov Dmitry
2017-01-01
Full Text Available Constantly increasing demand for high-performance materials and systems in aerospace industry requires advanced methods of nondestructive testing. One of the most promising methods is ultrasonic imaging by using matrix phased arrays. This technique allows to create three-dimensional ultrasonic imaging with high lateral resolution. Further progress in matrix phased array ultrasonic testing is determined by the development of fast imaging algorithms. In this article imaging algorithm based on frequency domain calculations is proposed. This approach is computationally efficient in comparison with time domain algorithms. Performance of the proposed algorithm was tested via computer simulations for planar specimen with flat bottom holes.
Spatial and frequency domain effects of defects in 1D photonic crystal
Rudziński, A; Szczepański, P; 10.1007/s11082-007-9095-3
2009-01-01
The aim of this paper is to present the analysis of influence of defects in 1D photonic crystal (PC) on the density of states and simultaneously spontaneous emission, in both spatial and frequency domains. In our investigations we use an analytic model of 1D PC with defects. Our analysis reveals how presence of a defect causes a defect mode to appear. We show that a defect in 1D PC has local character, being negligible in regions of PC situated far from the defected elementary cell. We also analyze the effect of multiple defects, which lead to photonic band gap splitting.
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, Palle; Zhang, Lingmi
2007-01-01
As a part of a research project co-founded by the European Community, a series of 15 damage tests were performed on a prestressed concrete highway bridge in Switzerland. The ambient response of the bridge was recorded for each damage case. A dense array of instruments allowed the identification...... of a modal model with a total of 408 degrees of freedom. Six modes were identified in the frequency range from 0 to 16.7 Hz. The objective of this paper is to demonstrate the effectiveness of the Frequency Domain Decomposition (FDD) technique for modal identification of large structures. A second objective...
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, P.; Zhang, L.
2002-01-01
As a part of a research project co-founded by the European Community, a series of 15 damage tests were performed on a prestressed concrete highway bridge in Switzerland. The ambient response of the bridge was recorded for each damage case. A dense array of instruments allowed the identification...... of a modal model with a total of 408 degrees of freedom. Six modes were identified in the frequency range from 0 to 16.7 Hz. The objective of this paper is to demonstrate the effectiveness of the Frequency Domain Decomposition (FDD) technique for modal identification of large structures. A second objective...
Functional cerebral activation detected by frequency-domain near-infrared spectroscopy
Toronov, Vladislav Y.; Webb, Andrew G.; Choi, Jee H.; Wolf, Martin; Safonova, Larisa P.; Wolf, Ursula; Gratton, Enrico
2002-07-01
The aim of our study was to explore the possibility of detecting haemodynamic changes in the brain using frequency- domain near-IR spectroscopy by exploiting the phase of the intensity modulated optical signal. To obtain optical signals with eh highest possible signal-to-noise ratio, we performed simultaneous NIRS-fMRI measurements, with subsequent correlation of the time courses of both measurements. The cognitive paradigm used arithmetic calculations, with optical signals acquired with sensors placed on the forehead. In three subjects we demonstrated correlation between the haemodynamic signals obtained using NIRS and BOLD fMRI.
SDCMA BLIND DETECTION IN FREQUENCY DOMAIN FOR MC DS-CDMA SYSTEMS
Institute of Scientific and Technical Information of China (English)
Ju Meiyan; Feng Guangzeng
2006-01-01
This paper proposes Steepest Decreasing Constant Modulus Algorithm (SDCMA) detection in frequency domain for MultiCarrier Direct Sequence-Code Division Multiple Access (MC DS-CDMA) systems.The proposed algorithm is used to equalize independent fadings of all subcarriers. At the same time we compare the SDCMA blind detection with subspace-based Minimum Mean-Squared Error (MMSE) detection. The simulation results show that the performance of SDCMA blind detection is superior to. that of subspace-based MMSE detection and the complexity of the former is much lower than that of the latter.
Simulation of power fluctuation of wind farms based on frequency domain
DEFF Research Database (Denmark)
Lin, Jin; Sun, Yuanzhang; Li, Guojie
2011-01-01
With the capacity of installed wind power generators steadily increasing in China, power fluctuation from wind farms will significantly affect the security and reliability of the power system. Traditional modeling of power fluctuation is based on the time domain or statistics methodology which...... the power spectral density of wind speed, the frequency domain model of a wind power generator and the information on weather and geography of the wind farms. The correctness and effectiveness of the model are verified by comparing the measurement data with simulation results of a certain wind farm. © 2011...
Time and Frequency-Domain Cross-Verification of SLS 6DOF Trajectory Simulations
Johnson, Matthew; McCullough, John
2017-01-01
The Space Launch System (SLS) Guidance, Navigation, and Control (GNC) team and its partners have developed several time- and frequency-based simulations for development and analysis of the proposed SLS launch vehicle. The simulations differ in fidelity and some have unique functionality that allows them to perform specific analyses. Some examples of the purposes of the various models are: trajectory simulation, multi-body separation, Monte Carlo, hardware in the loop, loads, and frequency domain stability analyses. While no two simulations are identical, many of the models are essentially six degree-of-freedom (6DOF) representations of the SLS plant dynamics, hardware implementation, and flight software. Thus at a high level all of those models should be in agreement. Comparison of outputs from several SLS trajectory and stability analysis tools are ongoing as part of the program's current verification effort. The purpose of these comparisons is to highlight modeling and analysis differences, verify simulation data sources, identify inconsistencies and minor errors, and ultimately to verify output data as being a good representation of the vehicle and subsystem dynamics. This paper will show selected verification work in both the time and frequency domain from the current design analysis cycle of the SLS for several of the design and analysis simulations. In the time domain, the tools that will be compared are MAVERIC, CLVTOPS, SAVANT, STARS, ARTEMIS, and POST 2. For the frequency domain analysis, the tools to be compared are FRACTAL, SAVANT, and STARS. The paper will include discussion of these tools including their capabilities, configurations, and the uses to which they are put in the SLS program. Determination of the criteria by which the simulations are compared (matching criteria) requires thoughtful consideration, and there are several pitfalls that may occur that can severely punish a simulation if not considered carefully. The paper will discuss these
Energy Technology Data Exchange (ETDEWEB)
Feng, Xiaobing [Univ. of Tennessee, Knoxville, TN (United States)
1996-12-31
A non-overlapping domain decomposition iterative method is proposed and analyzed for mixed finite element methods for a sequence of noncoercive elliptic systems with radiation boundary conditions. These differential systems describe the motion of a nearly elastic solid in the frequency domain. The convergence of the iterative procedure is demonstrated and the rate of convergence is derived for the case when the domain is decomposed into subdomains in which each subdomain consists of an individual element associated with the mixed finite elements. The hybridization of mixed finite element methods plays a important role in the construction of the discrete procedure.
A frequency domain design of PID controller for an AVR system
Institute of Scientific and Technical Information of China (English)
Md Nishat ANWAR; Somnath PAN
2014-01-01
We propose a new proportional-integral-derivative (PID) controller design method for an automatic voltage regula-tion (AVR) system based on approximate model matching in the frequency domain. The parameters of the PID controller are obtained by approximate frequency response matching between the closed-loop control system and a reference model with the desired specifications. Two low frequency points are required for matching the frequency response, and the design method yields linear algebraic equations, solution of which gives the controller parameters. The effectiveness of the proposed method is demonstrated through examples taken from the literature and comparison with some popular methods.
Investigation of Frequency-Domain Link Adaptation for a 5-MHz OFDMA/HSDPA system
DEFF Research Database (Denmark)
Pokhariyal, Akhilesh; Kolding, Troels E.; Frederiksen, Frank
2005-01-01
In this paper, we investigate frequency domain link adaptation (FDLA), e.g. utilizing the frequency selectivity of the channel in an OFDMA system. To make the study specific and based on realistic parameters, we re-use the specifications from a recent 3GPP 5-MHz OFDMA study item. The link...... find that optimum waterfilling power distribution only provides a marginal gain over a simpler on/off equal power distribution algorithm per sub-carrier pool when signaling imperfections are taken into account....
Time and Frequency-Domain Cross-Verification of SLS 6DOF Trajectory Simulations
VanZwieten, Tannen; Johnson, Matthew D.; McCullough, John P.; Gilligan, Eric T.
2014-01-01
The SLS GNC team and its partners have developed several time- and frequency-based simulations for development and analysis of the proposed SLS launch vehicle. The simulations differ in fidelity and some have unique functionality that allows them to perform specific analyses. Some examples of the purposes of the various models are: trajectory simulation, multi-body separation, Monte Carlo, hardware in the loop, loads, and frequency domain stability analyses. While no two simulations are identical, many of the models are essentially six degree-of-freedom (6DOF) representations of the SLS plant dynamics, hardware implementation, and flight software. Thus at a high level all of those models should be in agreement. Comparison of outputs from several SLS trajectory and stability analysis tools are ongoing as part of the program's current verification effort. The purpose of these comparisons is to highlight modeling and analysis differences, verify simulation data sources, identify inconsistencies and minor errors, and ultimately to verify output data as being a good representation of the vehicle and subsystem dynamics. This paper will show selected verification work in both the time and frequency domain from the current design analysis cycle of the SLS for several of the design and analysis simulations. In the time domain, the tools that will be compared are MAVERIC, CLVTOPS, SAVANT, STARS, ARTEMIS, and POST 2. For the frequency domain analysis, the tools to be compared are FRACTAL, SAVANT, and STARS. The paper will include discussion of these tools including their capabilities, configurations, and the uses to which they are put in the SLS program. Determination of the criteria by which the simulations are compared (matching criteria) requires thoughtful consideration, and there are several pitfalls that may occur that can severely punish a simulation if not considered carefully. The paper will discuss these considerations and will present a framework for responding to
Optical frequency domain reflectometry: principles and applications in fiber optic sensing
Kreger, Stephen T.; Rahim, Nur Aida Abdul; Garg, Naman; Klute, Sandra M.; Metrey, Daniel R.; Beaty, Noah; Jeans, James W.; Gamber, Robert
2016-05-01
Optical Frequency Domain Reflectometry (OFDR) is the basis of an emerging high-definition distributed fiber optic sensing (HD-FOS) technique that provides an unprecedented combination of resolution and sensitivity. OFDR employs swept laser interferometry to produce strain or temperature vs. sensor length with fiber Bragg gratings (FBGs) or Rayleigh scatter as the source signal. We look at the influence of HD-FOS on design and test of new, lighter weight, stronger and more fuel efficient vehicles. Examples include defect detection, model verification and structural health monitoring of composites, and temperature distribution monitoring of battery packs and inverters in hybrid and electric powertrains.
Reducing Dataset Size in Frequency Domain for Brain Computer Interface Motor Imagery Classification
Directory of Open Access Journals (Sweden)
Ch.Aparna
2010-12-01
Full Text Available Brain computer interface is an emerging area of research where the BCI system is able to detect and interpret the mental activity into computer interpretable signals opening a wide area of applications where activities can be completed without using muscular movement. In Brain Computer Interface research, for classification of EEG signals the raw signals captured has to undergo some preprocessing, to obtain the right attributes for classification. In this paper, we present a system which allows for classification of mental tasks based on a statistical data obtained in frequency domain using Discrete cosine transform and extracting useful frequencies from the same with application of decision tree algorithms for classification.
Xu, Tianhua; Popov, Sergei; Forzati, Marco; Martensson, Jonas; Mussolin, Marco; Li, Jie; Wang, Ke; Zhang, Yimo; Friberg, Ari T
2016-01-01
The frequency domain equalizers (FDEs) employing two types of overlap-add zero-padding (OLA-ZP) methods are applied to compensate the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system. Simulation results demonstrate that the OLA-ZP methods can achieve the same acceptable performance as the overlap-save method. The required minimum overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier transform length to minimize the computational complexity is also analyzed.
Frequency domain optical tomography using a conjugate gradient method without line search
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyun Keol [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, P4-3240, Chicoutimi, Quebec, G7H 2B1 (Canada); Charette, Andre [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, P4-3240, Chicoutimi, Quebec, G7H 2B1 (Canada)]. E-mail: andre_charette@uqac.ca
2007-03-15
A conjugate gradient method without line search (CGMWLS) is presented. This method is used to retrieve the local maps of absorption and scattering coefficients inside the tissue-like test medium, with the synthetic data. The forward problem is solved with a discrete-ordinates finite-difference method based on the frequency domain formulation of radiative transfer equation. The inversion results demonstrate that the CGMWLS can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by reducing cross-talk between absorption and scattering coefficients.
Nöther, Nils; Wosniok, Aleksander; Krebber, Katerina; Thiele, Elke
2008-03-01
We report on the development of a complete system for spatially resolved detection of critical soil displacement in river embankments. The system uses Brillouin frequency domain analysis (BOFDA) for distributed measurement of strain in silica optical fibers. Our development consists of the measurement unit, an adequate coating for the optical fibers and a technique to integrate the coated optical fibers into geotextiles as they are commonly used in dike construction. We present several laboratory and field tests that prove the capability of the system to detect areas of soil displacement as small as 2 meters. These are the first tests of truly distributed strain measurements on optical fibers embedded into geosynthetics.
Institute of Scientific and Technical Information of China (English)
2008-01-01
Optical frequency domain phase conjugation(FDPC) is based on phase conjuga-tion of spectrum of an input signal.It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal.The use of FDPC to con-trol polarization signal distortion in birefringent optical fiber systems is proposed.Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically.It is shown that the distortion of polariza-tion signals can be controlled effectively by FDPC.The impairments due to disper-sion and nonlinear effects can be suppressed simultaneously.
Institute of Scientific and Technical Information of China (English)
BU Yang; WANG XiangZhao
2008-01-01
Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to con-trol polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polariza-tion signals can be controlled effectively by FDPC. The impairments due to disper-sion and nonlinear effects can be suppressed simultaneously.
A perspective on single-channel frequency-domain speech enhancement
Benesty, Jacob
2010-01-01
This book focuses on a class of single-channel noise reduction methods that are performed in the frequency domain via the short-time Fourier transform (STFT). The simplicity and relative effectiveness of this class of approaches make them the dominant choice in practical systems. Even though many popular algorithms have been proposed through more than four decades of continuous research, there are a number of critical areas where our understanding and capabilities still remain quite rudimentary, especially with respect to the relationship between noise reduction and speech distortion. All exis
Zhou, Si-Da; Heylen, Ward; Sas, Paul; Liu, Li
2014-05-01
This paper investigates the problem of modal parameter estimation of time-varying structures under unknown excitation. A time-frequency-domain maximum likelihood estimator of modal parameters for linear time-varying structures is presented by adapting the frequency-domain maximum likelihood estimator to the time-frequency domain. The proposed estimator is parametric, that is, the linear time-varying structures are represented by a time-dependent common-denominator model. To adapt the existing frequency-domain estimator for time-invariant structures to the time-frequency methods for time-varying cases, an orthogonal polynomial and z-domain mapping hybrid basis function is presented, which has the advantageous numerical condition and with which it is convenient to calculate the modal parameters. A series of numerical examples have evaluated and illustrated the performance of the proposed maximum likelihood estimator, and a group of laboratory experiments has further validated the proposed estimator.
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.
Institute of Scientific and Technical Information of China (English)
Ke Xiao; Shang-Bo Zhou; Wei-Wei Zhang
2008-01-01
For a general nonlinear fractional-orderdifferential equation, the numerical solution is a goodway to approximate the trajectory of such systems. Inthis paper, a novel algorithm for numerical solution offractional-order differential equations based on thedefinition of Grunwald-Letnikov is presented. Theresults of numerical solution by using the novel methodand the frequency-domain method are compared, and the limitations of frequency-domain method arediscussed.
Institute of Scientific and Technical Information of China (English)
Ke Xiao; Shang-Bo Zhou; Wei-Wei Zhang
2008-01-01
For a general nonlinear fractional-order differential equation, the numerical solution is a good way to approximate the trajectory of such systems. In this paper, a novel algorithm for numerical solution of fractional-order differential equations based on the definition of Grunwald-Letnikov is presented. The results of numerical solution by using the novel method and the frequency-domain method are compared, and the limitations of frequency-domain method arediscussed.
Institute of Scientific and Technical Information of China (English)
蔡阳健; 林强
2002-01-01
The generalized Collins formula for partially coherent beams through axially non-symmetrical optical systems in the spatial-frequency domain is derived by means of the tensor method. Based on this formula, the tensor ABCD law in the spatial-frequency domain for partially coherent twisted anisotropic Gaussian-Schell model (GSM) beams is derived, which governs the transformation of the twisted anisotropic GSM beams in the spatialfrequency domain. An example of an application is provided.
Design of a multivariable RF control system using gain-shaping in the frequency domain
Ziomek, C. D.; Jachim, S. P.; Natter, E. F.
1991-05-01
Due to the time-varying nature of the radio-frequency (RF) accelerator, RF field amplitude and phase parameters must be precisely controlled in order to confine and accelerate the charged particle beam. Typically, a feedback control system regulates the RF field, rejects noise and disturbances, and maintains operational stability over changes in the electrical structure of the accelerator. This paper describes a multivariable control system that compensates the electrical structure of the accelerator by using gain-shaping in the frequency domain. The amplitude and phase quantities have been resolved into in-phase and quadrature (I and Q) variables. These orthogonal variables have simple mathematical relationships, and can be analyzed using linear transfer function matrices. The transfer matrix theory has been applied to the design of the multivariable control system that regulates the RF field in-phase and quadrature components. Frequency-domain controllers compensate these two signals to provide desired frequency response characteristics. A control predistorter performs an inverse coupling function, so that the I and Q components are effectively decoupled by the accelerator. Furthermore, computer interface circuitry allows the adaptive optimization of the mathematical transfer functions of the compensators.
Qi, Feng; Tavakol, Vahid; Ocket, Ilja; Xu, Peng; Schreurs, Dominique; Wang, Jinkuan; Nauwelaers, Bart
2010-01-01
Active millimeter wave imaging systems have become a promising candidate for indoor security applications and industrial inspection. However, there is a lack of simulation tools at the system level. We introduce and evaluate two modeling approaches that are applied to active millimeter wave imaging systems. The first approach originates in Fourier optics and concerns the calculation in the spatial frequency domain. The second approach is based on wave propagation and corresponds to calculation in the spatial domain. We compare the two approaches in the case of both rough and smooth objects and point out that the spatial frequency domain calculation may suffer from a large error in amplitude of 50% in the case of rough objects. The comparison demonstrates that the concepts of point-spread function and f-number should be applied with careful consideration in coherent millimeter wave imaging systems. In the case of indoor applications, the near-field effect should be considered, and this is included in the spatial domain calculation.
Directory of Open Access Journals (Sweden)
Hanus Robert
2016-01-01
Full Text Available Knowledge of the structure of a flow is really significant for the proper conduct a number of industrial processes. In this case a description of a two-phase flow regimes is possible by use of the time-series analysis e.g. in frequency domain. In this article the classical spectral analysis based on Fourier Transform (FT and Short-Time Fourier Transform (STFT were applied for analysis of signals obtained for water-air flow using gamma ray absorption. The presented method was illustrated by use data collected in experiments carried out on the laboratory hydraulic installation with a horizontal pipe of 4.5 m length and inner diameter of 30 mm equipped with two 241Am radioactive sources and scintillation probes with NaI(Tl crystals. Stochastic signals obtained from detectors for plug, bubble, and transitional plug – bubble flows were considered in this work. The recorded raw signals were analyzed and several features in the frequency domain were extracted using autospectral density function (ADF, cross-spectral density function (CSDF, and the STFT spectrogram. In result of a detail analysis it was found that the most promising to recognize of the flow structure are: maximum value of the CSDF magnitude, sum of the CSDF magnitudes in the selected frequency range, and the maximum value of the sum of selected amplitudes of STFT spectrogram.
Frequency-Domain Tomography for Single-shot, Ultrafast Imaging of Evolving Laser-Plasma Accelerators
Li, Zhengyan; Zgadzaj, Rafal; Wang, Xiaoming; Downer, Michael
2011-10-01
Intense laser pulses propagating through plasma create plasma wakefields that often evolve significantly, e.g. by expanding and contracting. However, such dynamics are known in detail only through intensive simulations. Laboratory visualization of evolving plasma wakes in the ``bubble'' regime is important for optimizing and scaling laser-plasma accelerators. Recently snap-shots of quasi-static wakes were recorded using frequency-domain holography (FDH). To visualize the wake's evolution, we have generalized FDH to frequency-domain tomography (FDT), which uses multiple probes propagating at different angles with respect to the pump pulse. Each probe records a phase streak, imprinting a partial record of the evolution of pump-created structures. We then topographically reconstruct the full evolution from all phase streaks. To prove the concept, a prototype experiment visualizing nonlinear index evolution in glass is demonstrated. Four probes propagating at 0, 0.6, 2, 14 degrees to the index ``bubble'' are angularly and temporally multiplexed to a single spectrometer to achieve cost-effective FDT. From these four phase streaks, an FDT algorithm analogous to conventional CT yields a single-shot movie of the pump's self-focusing dynamics.
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.
Simultaneous storage of medical images in the spatial and frequency domain: A comparative study
Directory of Open Access Journals (Sweden)
Acharya U Rajendra
2004-06-01
Full Text Available Abstract Background Digital watermarking is a technique of hiding specific identification data for copyright authentication. This technique is adapted here for interleaving patient information with medical images, to reduce storage and transmission overheads. Methods The patient information is encrypted before interleaving with images to ensure greater security. The bio-signals are compressed and subsequently interleaved with the image. This interleaving is carried out in the spatial domain and Frequency domain. The performance of interleaving in the spatial, Discrete Fourier Transform (DFT, Discrete Cosine Transform (DCT and Discrete Wavelet Transform (DWT coefficients is studied. Differential pulse code modulation (DPCM is employed for data compression as well as encryption and results are tabulated for a specific example. Results It can be seen from results, the process does not affect the picture quality. This is attributed to the fact that the change in LSB of a pixel changes its brightness by 1 part in 256. Spatial and DFT domain interleaving gave very less %NRMSE as compared to DCT and DWT domain. Conclusion The Results show that spatial domain the interleaving, the %NRMSE was less than 0.25% for 8-bit encoded pixel intensity. Among the frequency domain interleaving methods, DFT was found to be very efficient.
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.
Linear systems modeling of adaptive optics in the spatial-frequency domain.
Ellerbroek, Brent L
2005-02-01
Spatial-frequency domain techniques have traditionally been applied to obtain estimates for the independent effects of a variety of individual error sources in adaptive optics (AO). Overall system performance is sometimes estimated by introducing the approximation that these individual error terms are statistically independent, so that their magnitudes may be summed in quadrature. More accurate evaluation methods that account for the correlations between the individual error sources have required Monte Carlo simulations or large matrix calculations that can take much longer to compute, particularly as the order of the AO system increases beyond a few hundred degrees of freedom. We describe an approach to evaluating AO system performance in the spatial-frequency domain that is relatively computationally efficient but still accounts for many of the interactions between the fundamental error sources in AO. We exploit the fact that (in the limits of an infinite aperture and geometrical optics) all the basic wave-front propagation, sensing, and correction processes that describe the behavior of an AO system are spatial-filtering operations in the Fourier domain. Essentially all classical wave-front control algorithms and evaluation formulas are expressed in terms of these filters and may therefore be evaluated one spatial-frequency component at a time. Performance estimates for very-high-order AO systems may be obtained in 1 to 2 orders of magnitude less time than needed when detailed simulations or analytical models in the spatial domain are used, with a relative discrepancy of 5% to 10% for typical sample problems.
Suspension parameter estimation in the frequency domain using a matrix inversion approach
Thite, A. N.; Banvidi, S.; Ibicek, T.; Bennett, L.
2011-12-01
The dynamic lumped parameter models used to optimise the ride and handling of a vehicle require base values of the suspension parameters. These parameters are generally experimentally identified. The accuracy of identified parameters can depend on the measurement noise and the validity of the model used. The existing publications on suspension parameter identification are generally based on the time domain and use a limited degree of freedom. Further, the data used are either from a simulated 'experiment' or from a laboratory test on an idealised quarter or a half-car model. In this paper, a method is developed in the frequency domain which effectively accounts for the measurement noise. Additional dynamic constraining equations are incorporated and the proposed formulation results in a matrix inversion approach. The nonlinearities in damping are estimated, however, using a time-domain approach. Full-scale 4-post rig test data of a vehicle are used. The variations in the results are discussed using the modal resonant behaviour. Further, a method is implemented to show how the results can be improved when the matrix inverted is ill-conditioned. The case study shows a good agreement between the estimates based on the proposed frequency-domain approach and measurable physical parameters.
High-resolution wind profiling using combined spatial and frequency domain interferometry
Palmer, R. D.; Huang, X.; Fukao, S.; Yamamoto, M.; Nakamura, T.
1995-11-01
A novel approach to wind profiling is presented which is based on the hybrid use of spatial interferometry (SI) and frequency domain interferometry (FDI). Many algorithms exist that can be used to determine the wind field using SI. However, the imaging Doppler interferometry (IDI) technique is somewhat unique in that the wind field within the radar beam is angularly "imaged" using the Doppler sorting effect. The spatial locations of scatterers are determined by assuming a wind field across the beam and Fourier analyzing signals to sort Doppler velocities. Pulsed radar systems are limited in range resolution by the length of the transmitted pulse, and wind estimates are obtained for a discrete set of altitudes determined by sampling the continuous stream of signals. Frequency domain interferometry (FDI) can be used to determine the radial location of scattering layers within the resolution volume. Thus the combined use of FDI and IDI can provide the radial and angular location of particular scattering points. Using the Doppler sorting idea, a new wind profiling technique is presented which uses FDI to increase the altitude resolution of wind estimates obtained from IDI. Experimental data that illustrate the implementation of the algorithm are presented from the Middle and Upper (MU) Atmosphere radar.
Directory of Open Access Journals (Sweden)
Zeguang YI
2015-08-01
Full Text Available Aiming at fault diagnosis problems caused by complex machinery parts, serious background noises and the application limitations of traditional blind signal processing algorithm to the mechanical acoustic signal processing, a failure acoustic diagnosis based on reference signal frequency domain semi-blind extraction is proposed. Key technologies are introduced: Based on frequency-domain blind deconvolution algorithm, the artificial fish swarm algorithm which is good for global optimization is used to construct improved multi-scale morphological filters which is applicable to mechanical failure in order to weaken the background noises; combining the structural parameters of parts to build a reference signal, complex components blind separation is carried out on the signals after noise reduction paragraph by paragraph by reference signal unit semi-blind extraction algorithm; then the improved KL-distance of complex independent components is employed as distance measure to resolve the permutation, and finally the mechanical fault characteristic signals are extracted and separated. The actual acoustic diagnosis of rolling bearing fault in sound field environment results proves the effectiveness of this algorithm.
A critical analysis of the Mises stress criterion used in frequency domain fatigue life prediction
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Adam Niesłony
2016-10-01
Full Text Available Multiaxial fatigue failure criteria are formulated in time and frequency domain. The number of frequency domain criteria is rather small and the most popular one is the equivalent von Mises stress criterion. This criterion was elaborated by Preumont and Piefort on the basis of well-known von Mises stress concept, first proposed by Huber in 1907, and well accepted by the scientific community and engineers. It is important to know, that the criterion was developed to determine the yield stress and material effort under static load. Therefore the direct use of equivalent von Mises stress criterion for fatigue life prediction can lead to some incorrectness of theoretical and practical nature. In the present study four aspects were discussed: influence of the value of fatigue strength of tension and torsion, lack of parallelism of the SN curves, abnormal behaviour of the criterion under biaxial tensioncompression and influence of phase shift between particular stress state components. Information contained in this article will help to prevent improper use of this criterion and contributes to its better understanding
Directory of Open Access Journals (Sweden)
Pei-Chen Lin
2016-02-01
Full Text Available In the ICU, fluid therapy is conventional strategy for the patient in shock. However, only half of ICU patients have well-responses to fluid therapy, and fluid loading in non-responsive patient delays definitive therapy. Prediction of fluid responsiveness (FR has become intense topic in clinic. Most of conventional FR prediction method based on time domain analysis, and it is limited ability to indicate FR. This study proposed a method which predicts FR based on frequency domain analysis, named instantaneous pulse rate variability (iPRV. iPRV provides a new indication in very high frequency (VHF range (0.4-0.8Hz of spectrum for peripheral responses. Twenty six healthy subjects participated this study and photoplethysmography signal was recorded in supine baseline, during head-up tilt (HUT, and passive leg raising (PLR, which induces variation of venous return and helps for quantitative assessment of FR individually. The result showed the spectral power of VHF decreased during HUT (573.96±756.36 ms2 in baseline; 348.00±434.92 ms2 in HUT and increased during PLR (573.96±756.36 ms2 in baseline; 718.92±973.70 ms2 in PLR, which present the compensated regulation of venous return and FR. This study provides an effective indicator for assessing FR in frequency domain and has potential to be a reliable system in ICU.
Directory of Open Access Journals (Sweden)
Lin Wang
2010-01-01
Full Text Available Frequency-domain blind source separation (BSS performs poorly in high reverberation because the independence assumption collapses at each frequency bins when the number of bins increases. To improve the separation result, this paper proposes a method which combines two techniques by using beamforming as a preprocessor of blind source separation. With the sound source locations supposed to be known, the mixed signals are dereverberated and enhanced by beamforming; then the beamformed signals are further separated by blind source separation. To implement the proposed method, a superdirective fixed beamformer is designed for beamforming, and an interfrequency dependence-based permutation alignment scheme is presented for frequency-domain blind source separation. With beamforming shortening mixing filters and reducing noise before blind source separation, the combined method works better in reverberation. The performance of the proposed method is investigated by separating up to 4 sources in different environments with reverberation time from 100 ms to 700 ms. Simulation results verify the outperformance of the proposed method over using beamforming or blind source separation alone. Analysis demonstrates that the proposed method is computationally efficient and appropriate for real-time processing.
The PolyMAX Frequency-Domain Method: A New Standard for Modal Parameter Estimation?
Directory of Open Access Journals (Sweden)
Bart Peeters
2004-01-01
Full Text Available Recently, a new non-iterative frequency-domain parameter estimation method was proposed. It is based on a (weighted least-squares approach and uses multiple-input-multiple-output frequency response functions as primary data. This so-called “PolyMAX” or polyreference least-squares complex frequency-domain method can be implemented in a very similar way as the industry standard polyreference (time-domain least-squares complex exponential method: in a first step a stabilisation diagram is constructed containing frequency, damping and participation information. Next, the mode shapes are found in a second least-squares step, based on the user selection of stable poles. One of the specific advantages of the technique lies in the very stable identification of the system poles and participation factors as a function of the specified system order, leading to easy-to-interpret stabilisation diagrams. This implies a potential for automating the method and to apply it to “difficult” estimation cases such as high-order and/or highly damped systems with large modal overlap. Some real-life automotive and aerospace case studies are discussed. PolyMAX is compared with classical methods concerning stability, accuracy of the estimated modal parameters and quality of the frequency response function synthesis.
A Modified Normalization Technique for Frequency-Domain Full Waveform Inversion
Hwang, J.; Jeong, G.; Min, D. J.; KIM, S.; Heo, J. Y.
2016-12-01
Full waveform inversion (FWI) is a technique to estimate subsurface material properties minimizing the misfit function built with residuals between field and modeled data. To achieve computational efficiency, FWI has been performed in the frequency domain by carrying out modeling in the frequency domain, whereas observed data (time-series data) are Fourier-transformed.One of the main drawbacks of seismic FWI is that it easily gets stuck in local minima because of lacking of low-frequency data. To compensate for this limitation, damped wavefields are used, as in the Laplace-domain waveform inversion. Using damped wavefield in FWI plays a role in generating low-frequency components and help recover long-wavelength structures. With these newly generated low-frequency components, we propose a modified frequency-normalization technique, which has an effect of boosting contribution of low-frequency components to model parameter update.In this study, we introduce the modified frequency-normalization technique which effectively amplifies low-frequency components of damped wavefields. Our method is demonstrated for synthetic data for the SEG/EAGE salt model. AcknowledgementsThis work was supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20168510030830) and by the Dual Use Technology Program, granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea.
Brain connectivity study of joint attention using frequency-domain optical imaging technique
Chaudhary, Ujwal; Zhu, Banghe; Godavarty, Anuradha
2010-02-01
Autism is a socio-communication brain development disorder. It is marked by degeneration in the ability to respond to joint attention skill task, from as early as 12 to 18 months of age. This trait is used to distinguish autistic from nonautistic populations. In this study, diffuse optical imaging is being used to study brain connectivity for the first time in response to joint attention experience in normal adults. The prefrontal region of the brain was non-invasively imaged using a frequency-domain based optical imager. The imaging studies were performed on 11 normal right-handed adults and optical measurements were acquired in response to joint-attention based video clips. While the intensity-based optical data provides information about the hemodynamic response of the underlying neural process, the time-dependent phase-based optical data has the potential to explicate the directional information on the activation of the brain. Thus brain connectivity studies are performed by computing covariance/correlations between spatial units using this frequency-domain based optical measurements. The preliminary results indicate that the extent of synchrony and directional variation in the pattern of activation varies in the left and right frontal cortex. The results have significant implication for research in neural pathways associated with autism that can be mapped using diffuse optical imaging tools in the future.
On numerical methods for direct and inverse problems in electromagnetism
Zemanova, Viera
2009-01-01
This thesis is devoted to the study of processes in the propagation of electromagnetic fields. We do not aim at one particular problem, actually very different kinds of topics are analyzed here. We deal with direct problems as well as with inverse ones, low frequency electromagnetism is discussed and consequently the wave propagation problem in high frequency domain is studied. Study of electromagnetic materials and their behavior is of a huge interest for the technological world. Its impo...
Lithospheric imaging from teleseismic data by frequency-domain elastic full-waveform tomography
Pageot, D.; Operto, S.; Vallée, M.; Brossier, R.; Virieux, J.; Seiscope
2010-12-01
Teleseismic data recorded by dense multicomponent surveys are potentially amenable to multichannel processing such as full waveform inversion to develop high-resolution lithospheric models. In this study, 2D frequency-domain full waveform tomography (FWT) is tailored to suit teleseismic geometries. Frequency-domain FWT seeks to estimate the elastic properties of the Earth by minimizing a misfit function between recorded and modeled full wavefields. FWT is designed to invert few discrete frequencies by proceeding hierarchically from the low frequencies to the higher ones, following a multiscale approach useful to mitigate the inversion nonlinearity. In teleseismic framework, seismic sources are planar incident wavefields impinging the base of the lithosphere with arbitrary incidence and obliquity angles. The full wavefield is computed using a scattered-field formulation in the frequency domain. First, an analytical wavefield is computed in a homogeneous background model with free surface on the topside for an incident compressional plane wave. Then, a scattering source is formed by the product of the analytical planewave with the difference of the forward problem operators associated with the homogeneous background and lithospheric models. The scattered wavefield is then computed by performing a simulation in the lithospheric model using the scattering source, and, finally, the full wavefield is built by summation of the analytical wavefield and of the scattered wavefield. The 2D P-SV wave modeling is performed with a finite element discontinuous Galerkin method allowing for unstructured triangular meshes. Teleseismic experiments are characterized by a narrow illumination of aperture angles because of the limited number of planewave sources related to the teleseismic earthquake distribution. This narrow aperture bandwith requires the use of finely-sampled frequencies to prevent spatial aliasing in the reconstructed FWT models. Moreover, planewave propagation from
Frequency-domain elastic full waveform inversion using encoded simultaneous sources
Jeong, W.; Son, W.; Pyun, S.; Min, D.
2011-12-01
Currently, numerous studies have endeavored to develop robust full waveform inversion and migration algorithms. These processes require enormous computational costs, because of the number of sources in the survey. To avoid this problem, the phase encoding technique for prestack migration was proposed by Romero (2000) and Krebs et al. (2009) proposed the encoded simultaneous-source inversion technique in the time domain. On the other hand, Ben-Hadj-Ali et al. (2011) demonstrated the robustness of the frequency-domain full waveform inversion with simultaneous sources for noisy data changing the source assembling. Although several studies on simultaneous-source inversion tried to estimate P- wave velocity based on the acoustic wave equation, seismic migration and waveform inversion based on the elastic wave equations are required to obtain more reliable subsurface information. In this study, we propose a 2-D frequency-domain elastic full waveform inversion technique using phase encoding methods. In our algorithm, the random phase encoding method is employed to calculate the gradients of the elastic parameters, source signature estimation and the diagonal entries of approximate Hessian matrix. The crosstalk for the estimated source signature and the diagonal entries of approximate Hessian matrix are suppressed with iteration as for the gradients. Our 2-D frequency-domain elastic waveform inversion algorithm is composed using the back-propagation technique and the conjugate-gradient method. Source signature is estimated using the full Newton method. We compare the simultaneous-source inversion with the conventional waveform inversion for synthetic data sets of the Marmousi-2 model. The inverted results obtained by simultaneous sources are comparable to those obtained by individual sources, and source signature is successfully estimated in simultaneous source technique. Comparing the inverted results using the pseudo Hessian matrix with previous inversion results
Frequency-domain algorithm for the Lorenz-gauge gravitational self-force
Akcay, Sarp; Barack, Leor
2013-01-01
State-of-the-art computations of the gravitational self-force (GSF) on massive particles in black hole spacetimes involve numerical evolution of the metric perturbation equations in the time-domain, which is computationally very costly. We present here a new strategy, based on a frequency-domain treatment of the perturbation equations, which offers considerable computational saving. The essential ingredients of our method are (i) a Fourier-harmonic decomposition of the Lorenz-gauge metric perturbation equations and a numerical solution of the resulting coupled set of ordinary equations with suitable boundary conditions; (ii) a generalized version of the method of extended homogeneous solutions [Phys. Rev. D {\\bf 78}, 084021 (2008)] used to circumvent the Gibbs phenomenon that would otherwise hamper the convergence of the Fourier mode-sum at the particle's location; and (iii) standard mode-sum regularization, which finally yields the physical GSF as a sum over regularized modal contributions. We present a work...
Demonstrations of analog-to-digital conversion using a frequency domain stretched processor.
Reibel, Randy Ray; Harrington, Calvin; Dahl, Jason; Ostrander, Charles; Roos, Peter Aaron; Berg, Trenton; Mohan, R Krishna; Neifeld, Mark A; Babbitt, Wm R
2009-07-06
The first proof-of-concept demonstrations are presented for a broadband photonic-assisted analog-to-digital converter (ADC) based on spatial spectral holography (SSH). The SSH-ADC acts as a frequency-domain stretch processor converting high bandwidth input signals to low bandwidth output signals, allowing the system to take advantage of high performance, low bandwidth electronic ADCs. Demonstrations with 50 MHz effective bandwidth are shown to highlight basic performance with approximately 5 effective bits of vertical resolution. Signal capture with 1600 MHz effective bandwidth is also shown. Because some SSH materials span over 100 GHz and have large time apertures (approximately 10 micros), this technique holds promise as a candidate for the next generation of ADCs.
Ferri, A. A.; Dowell, E. H.
1985-01-01
The anticipated low damping level in large space structures (LSS) has been a major concern for the designers of these structures. Low damping degrades the free response and complicates the design of shape and attitude controllers for flexible spacecraft. Dry friction damping has been considered as a means of increasing the passive damping of LSS, by placing it in the joints and connecting junctures of structures. However, dry friction is highly nonlinear and, hence, analytical investigations are difficult to perform. Here, a multi-harmonic, frequency domain solution technique is developed and applied to a multi-DOF, dry friction damped system. It is seen that the multi-harmonic method is much more accurate than traditional, one harmonic solution methods. The method also compares well with time integration. Finally, comparisons are made with experimental results.
Spectral evolution of two-dimensional kinetic plasma turbulence in the wavenumber-frequency domain
Comişel, H; Narita, Y; Motschmann, U
2013-01-01
We present a method for studying the evolution of plasma turbulence by tracking dispersion relations in the energy spectrum in the wavenumber-frequency domain. We apply hybrid plasma simulations in a simplified two-dimensional geometry to demonstrate our method and its applicability to plasma turbulence in the ion kinetic regime. We identify four dispersion relations: ion-Bernstein waves, oblique whistler waves, oblique Alfv\\'en/ion-cyclotron waves, and a zero-frequency mode. The energy partition and frequency broadening are evaluated for these modes. The method allows us to determine the evolution of decaying plasma turbulence in our restricted geometry and shows that it cascades along the dispersion relations during the early phase with an increasing broadening around the dispersion relations.
Use of Time- and Frequency-Domain Approaches for Damage Detection in Civil Engineering Structures
Directory of Open Access Journals (Sweden)
V. H. Nguyen
2014-01-01
Full Text Available The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The methodology is based on Principal Component Analysis of the Hankel matrix built from output-only measurements and of Frequency Response Functions. Damage detection is performed using the concept of subspace angles between a current (possibly damaged state and a reference (undamaged state. The first structure is the Champangshiehl Bridge located in Luxembourg. Several damage levels were intentionally created by cutting a growing number of prestressed tendons and vibration data were acquired by the University of Luxembourg for each damaged state. The second example consists in reinforced and prestressed concrete panels. Successive damages were introduced in the panels by loading heavy weights and by cutting steel wires. The illustrations show different consequences in damage identification by the considered techniques.
Energy Technology Data Exchange (ETDEWEB)
Li Guoyu; Li Yan [Institute of Information Engineering, Handan College, Handan, 056005 (China); Zhao Peng, E-mail: guoyu_li@yahoo.cn [School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China)
2011-02-01
In optical frequency domain reflectometry (OFDR) system, the spatial resolution is obtained by using the total frequency-sweep span of the tunable laser. However, in practice, the spatial resolution is severely limited by nonlinearity in the lightwave-frequency sweep of the tunable laser. A closed-loop PZT modulated DBR linear fiber laser is proposed to improve the spatial resolution of the OFDR system. Experimental results show that the spatial resolution of OFDR system has improved greatly. When the frequency sweep excursion is 66GHz and the fiber under test (FUT) is 7 m, the OFDR system has a spatial resolution of 1.5 m with open-loop PZT modulated laser. But the spatial resolution increases to 35 cm with closed-loop PZT modulated laser.
Nelson, C. A.; Zhu, X.-Y.
2016-10-01
Optical excitations at semiconductor surfaces or interfaces are accompanied by transient interfacial electric fields due to charge redistribution or transfer. While such transient fields may be probed by time-resolved second harmonic generation (TR-SHG), it is difficult to determine the field direction, which is invaluable to unveiling the underlying physics. Here we apply a time-resolved frequency domain interferometric second harmonic (TR-FDISH) generation technique to determine the phase relationship between the SH field emitted from bulk GaAs(1 0 0) and the transient SH field from the space charge region. The interference between these two SH fields allow us to unambiguously determine the directions of transient electric fields. Since SH fields from a static bulk contribution and a changing electric field contribution are present at most semiconductor surfaces or interfaces under optical excitation, the TR-FDISH technique is of general significance to probing the dynamics of interfacial charge transfer/redistribution.
Parallel full-waveform inversion in the frequency domain by the Gauss-Newton method
Zhang, Wensheng; Zhuang, Yuan
2016-06-01
In this paper, we investigate the full-waveform inversion in the frequency domain. We first test the inversion ability of three numerical optimization methods, i.e., the steepest-descent method, the Newton-CG method and the Gauss- Newton method, for a simple model. The results show that the Gauss-Newton method performs well and efficiently. Then numerical computations for a benchmark model named Marmousi model by the Gauss-Newton method are implemented. Parallel algorithm based on message passing interface (MPI) is applied as the inversion is a typical large-scale computational problem. Numerical computations show that the Gauss-Newton method has good ability to reconstruct the complex model.
Higher-order modulations of fs laser pulses for GHz frequency domain photon migration system.
Lin, Huang-Yi; Cheng, Nanyu; Tseng, Sheng-Hao; Chan, Ming-Che
2014-02-24
Except the fundamental modulation frequency, by higher-order-harmonic modulations of mode-locked laser pulses and a simple frequency demodulation circuit, a novel approach to GHz frequency-domain-photon-migration (FDPM) system was reported. With this novel approach, a wide-band modulation frequency comb is available without any external modulation devices and the only electronics to extract the optical attenuation and phase properties at a selected modulation frequency in FDPM systems are good mixers and lock-in devices. This approach greatly expands the frequency range that could be achieved by conventional FDPM systems and suggests that our system could extract much more information from biological tissues than the conventional FDPM systems. Moreover, this demonstration will be beneficial for discerning the minute change of tissue properties.
A Frequency Domain Approach to Registration of Aliased Images with Application to Super-resolution
Directory of Open Access Journals (Sweden)
Vandewalle Patrick
2006-01-01
Full Text Available Super-resolution algorithms reconstruct a high-resolution image from a set of low-resolution images of a scene. Precise alignment of the input images is an essential part of such algorithms. If the low-resolution images are undersampled and have aliasing artifacts, the performance of standard registration algorithms decreases. We propose a frequency domain technique to precisely register a set of aliased images, based on their low-frequency, aliasing-free part. A high-resolution image is then reconstructed using cubic interpolation. Our algorithm is compared to other algorithms in simulations and practical experiments using real aliased images. Both show very good visual results and prove the attractivity of our approach in the case of aliased input images. A possible application is to digital cameras where a set of rapidly acquired images can be used to recover a higher-resolution final image.
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.
Broadband absorption spectroscopy by combining frequency-domain and steady-state techniques
Berger, Andrew J.; Bevilacqua, Frederic; Jakubowski, Dorota B.; Cerussi, Albert E.; Butler, John A.; Hsiang, D.; Tromberg, Bruce J.
2001-06-01
A technique for measuring broadband near-infrared absorption spectra of turbid media is presented using a combination of frequency-domain (FD) and steady-state (SS) reflectance methods. Most of the wavelength coverage is provided by a white-light SS measurement, while the FD data are acquired at a few selected wavelengths. Coefficients of absorption ((mu) a) and reduced scattering ((mu) s') derived from the FD data are used to intensity-calibrate the SS measurements and to estimate (mu) s' at all wavelengths in the spectral window of interest. After these steps are performed, (mu) a can be determined by comparing the SS reflectance values to the predictions of diffusion theory, wavelength by wavelength. We present an application of this method to breast tumor characterization. A case study of a fibroadenoma is shown, where different absorption spectra were found between the normal and the tumor sides.
Single carrier frequency domain equalization and diversity combining for cooperative systems
Institute of Scientific and Technical Information of China (English)
Xiong Haitao; Xu Jing; Wang Ping
2009-01-01
A low-complexity single carrier frequency-domain equalizer (SC/FDE) and diversity combining method for cooperative systems with demodulate-and-forward relaying over frequency-selective channels is proposed. At the relay nodes, linear SC/FDE is adopted and normalized correlation coefficient is introduced to derive an equivalent source-to-relay-destination (S-R-D) channel that is highlighted in this study. At the destination, a joint SC/FDE and diversity combining receiver is proposed by utilizing the equivalent S-R-D channel. Simulation results demonstrate the superiority of the proposed SC/FDE scheme over the straightforward SC/FDE which ignores the decisions errors at the intermediate relay nodes.
Adaptive eigenspace method for inverse scattering problems in the frequency domain
Grote, Marcus J.; Kray, Marie; Nahum, Uri
2017-02-01
A nonlinear optimization method is proposed for the solution of inverse scattering problems in the frequency domain, when the scattered field is governed by the Helmholtz equation. The time-harmonic inverse medium problem is formulated as a PDE-constrained optimization problem and solved by an inexact truncated Newton-type iteration. Instead of a grid-based discrete representation, the unknown wave speed is projected to a particular finite-dimensional basis of eigenfunctions, which is iteratively adapted during the optimization. Truncating the adaptive eigenspace (AE) basis at a (small and slowly increasing) finite number of eigenfunctions effectively introduces regularization into the inversion and thus avoids the need for standard Tikhonov-type regularization. Both analytical and numerical evidence underpins the accuracy of the AE representation. Numerical experiments demonstrate the efficiency and robustness to missing or noisy data of the resulting adaptive eigenspace inversion method.
Thalmayr, Florian; Hashimoto, Ken-Ya; Omori, Tatsuya; Yamaguchi, Masatsune
2010-07-01
This paper demonstrates a novel frequency domain analysis (FDA) to evaluate the scattering behavior of a waveguide mode at arbitrary scattering geometries by a time harmonic simulation based on the finite element method (FEM). To this end, we add an injection-damping mechanism (IDM) to avoid interference at the acoustic input port. The IDM can be easily constructed by a numerical operation. Our approach offers improved time consumption and calculation power necessary over the established method in the time domain. After checking the validity of the proposed method, we discuss the importance of considering wave scattering phenomena in film bulk acoustic wave resonator (FBAR) devices by applying the proposed method to two simplified models of an FBAR device.
Frequency domain wave equation forward modeling using gaussian elimination with static pivoting
Jian-Yong, Song; Xiao-Dong, Zheng; Yan, Zhang; Ji-Xiang, Xu; Zhen, Qin; Xue-Juan, Song
2011-03-01
Frequency domain wave equation forward modeling is a problem of solving large scale linear sparse systems which is often subject to the limits of computational efficiency and memory storage. Conventional Gaussian elimination cannot resolve the parallel computation of huge data. Therefore, we use the Gaussian elimination with static pivoting (GESP) method for sparse matrix decomposition and multi-source finite-difference modeling. The GESP method does not only improve the computational efficiency but also benefit the distributed parallel computation of matrix decomposition within a single frequency point. We test the proposed method using the classic Marmousi model. Both the single-frequency wave field and time domain seismic section show that the proposed method improves the simulation accuracy and computational efficiency and saves and makes full use of memory. This method can lay the basis for waveform inversion.
The three-layered mismatched media diffusion equation in frequency domain
Wang, Xichang; Wang, Shumei; Meng, Zhaokun; Yang, Shangming
2006-09-01
Near-IR radiation has great potential in medical diagnosis and therapy because of the non-invasive nature of light and the selectively poisonous effect to tumors of photodynarnic treatment. Therefore, Near-IR light propagation in highly scattering biological tissue must be understudied for basic research and clinical application of biomedical optics. A tissue is multi-layered mismatched medium, but many investigators only study the diffusion equation of matched medium. they take the tissue as the same refractive index. In order to understand the light transport in tissue, We analyze the diffusion of photons three-layered mismatched medium and set up the solution of Green's function in frequency domain, we employ the extrapolated boundary condition to set up a solution of the diffusion equation. At the same time, we utilize the diffuse equation to calculate the phase in different situation
Identification of the Swiss Z24 Highway Bridge by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, P.
2002-01-01
This paper presents the result of the modal identification of the Swiss highway bridge Z24. A series of 15 progressive damage tests were performed on the bridge before it was demolished in autumn 1998, and the ambient response of the bridge was recorded for each damage case. In this paper the modal...... properties are identified from the ambient responses by frequency domain decomposition. 6 modes were identified for all 15 damage cases. The identification was carried out for the full 3D data case i.e. including all measurements, a total of 291 channels, a reduced data case in 2D including 153 channels......, and finally, a 1D case including 20 channels. The modal properties for the different damage cases are compared with the modal properties of the undamaged bridge. Deviations for frequencies, damping ratios and MAC values are used as monitoring variables. From these results it can be concluded, that frequencies...
Frequency Domain MMSE one-tap Equalizer for FBMC-OQAM System
Directory of Open Access Journals (Sweden)
Nisha Varghese
2005-07-01
Full Text Available The need for higher data rate in the modern communication world leads to the development of multicarrier modulation. OFDM, the most popular MCM technique, has some disadvantages like inefficiency due to the insertion of cyclic prefix, spectral leakage among the subchannels due to the poor stopband attenuation of prototype filter etc. Due to these drawbacks of OFDM, a Filter Bank based Multi Carrier system with Offset Quadrature Amplitude Modulation has been proposed. The analysis and synthesis filter banks in FBMC- OQAM system is designed using exponential modulation of a single prototype filter which is designed using frequency sampling method of filter design. In the presence of fading channels, Frequency Domain MMSE one-tap equalizer is designed. Simulation results for Vehicular A and Pedestrian B channels show that the proposed equalizer gives better results for BER performance for the system.
Numerical Calculation of Beam Coupling Impedances in the Frequency Domain using FIT
Niedermayer, U
2012-01-01
The transverse impedance of kicker magnets is considered to be one of the main beam instability sources in the projected SIS-100 at FAIR and also in the SPS at CERN. The longitudinal impedance can contribute to the heat load, which is especially a concern in the cold sections of SIS-100 and LHC. In the high frequency range, commercially available time domain codes like CST Particle Studio serve to calculate the impedance but they are inapplicable at medium and low frequencies which become more important for larger size synchrotrons. We present the ongoing work of developing a Finite Integration Technique (FIT) solver in frequency domain which is based on the Parallel and Extensible Toolkit for Scientific computing (PETSc) framework in C++. Proper beam adapted boundary conditions are important to validate the concept. The code is applied to an inductive insert used to compensate the longitudinal space charge impedance in low energy machines. Another application focuses on the impedance contribution of a ferrit...
Dutta, Saibal; Chatterjee, Amitava; Munshi, Sugata
2010-12-01
The present work proposes the development of an automated medical diagnostic tool that can classify ECG beats. This is considered an important problem as accurate, timely detection of cardiac arrhythmia can help to provide proper medical attention to cure/reduce the ailment. The proposed scheme utilizes a cross-correlation based approach where the cross-spectral density information in frequency domain is used to extract suitable features. A least square support vector machine (LS-SVM) classifier is developed utilizing the features so that the ECG beats are classified into three categories: normal beats, PVC beats and other beats. This three-class classification scheme is developed utilizing a small training dataset and tested with an enormous testing dataset to show the generalization capability of the scheme. The scheme, when employed for 40 files in the MIT/BIH arrhythmia database, could produce high classification accuracy in the range 95.51-96.12% and could outperform several competing algorithms.
Copot, Cosmin; Zhong, Yu; Ionescu, Clara; Keyser, Robin
2013-06-01
In this paper, two methods to tune a fractional-order PI λ D μ controller for a mechatronic system are presented. The first method is based on a genetic algorithm to obtain the parameter values for the fractionalorder PI λ D μ controller by global optimization. The second method used to design the fractional-order PI λ D μ controller relies on an auto-tuning approach by meeting some specifications in the frequency domain. The real-time experiments are conducted using a Steward platform which consists of a table tilted by six servo-motors with a ball on the top of the table. The considered system is a 6 degrees of freedom (d.o.f.) motion platform. The feedback on the position of the ball is obtained from images acquired by a visual sensor mounted above the platform. The fractional-order controllers were implemented and the performances of the steward platform are analyzed.
Frequency-domain Model Matching PID Controller Design for Aero-engine
Liu, Nan; Huang, Jinquan; Lu, Feng
2014-12-01
The nonlinear model of aero-engine was linearized at multiple operation points by using frequency response method. The validation results indicate high accuracy of static and dynamic characteristics of the linear models. The improved PID tuning method of frequency-domain model matching was proposed with the system stability condition considered. The proposed method was applied to the design of PID controller of the high pressure rotor speed control in the flight envelope, and the control effects were evaluated by the nonlinear model. Simulation results show that the system had quick dynamic response with zero overshoot and zero steadystate error. Furthermore, a PID-fuzzy switching control scheme for aero-engine was designed, and the fuzzy switching system stability was proved. Simulations were studied to validate the applicability of the multiple PIDs fuzzy switching controller for aero-engine with wide range dynamics.
Directory of Open Access Journals (Sweden)
David O. Smallwood
1993-01-01
, that relates pairs of elements of the vector random process {X(t},−∞
Oblique frequency domain interferometry measurements using the middle and upper atmosphere radar
Palmer, R. D.; Fukao, S.; Larsen, M. F.; Yamamoto, M.; Tsuda, T.; Kato, S.
1992-09-01
First results are presented from oblique frequency domain interferometry (FDI) measurements conducted using the middle and upper atmosphere radar in Japan in October 1990. Using the idea of Doppler sorting, an equation is derived which shows a parabolic variation of the oblique FDI cross-spectral phase as a function of Doppler velocity. However, because of the small range of Doppler velocities observed with the measured cross spectra, the phase has an approximate linear variation; that is, the cross spectra sample only a small portion of the parabolic structure and are therefore approximately linear and are shown to follow the model closely. Using the oblique FDI configuration, a comparison is drawn between simultaneous measurements of signal-to-noise ratio, coherence, three-dimensional wind, and profiles of FDI cross spectra. We find that the regions that exhibit a well-defined scattering layer correspond to those regions of high aspect sensitivity. An explanation is suggested based on the anisotropy of the turbulence.
Frequency domain model for transient analysis of lightning protection systems of buildings.
Gómez, Pablo
2016-10-01
A frequency domain modeling approach for lightning protection systems (LPS) of buildings is described and validated in this paper. The model is based on a 2-port transmission line representation of each conductor, and the further assembling of a network representing the complete structure. Horizontal and vertical conductors are modeled using formulas based on the complex images method, in order to take into account frequency dependence. Variation of electrical parameters with height is also considered for vertical conductors. This is accomplished by means of a non-uniform modeling approach based on conductor subdivision and cascaded connection of chain matrices computed for each segment. The results from the model are validated by means of comparisons with measurements reported elsewhere, as well as simulations using PSCAD/EMTDC.
Rolling element bearing faults diagnosis based on kurtogram and frequency domain correlated kurtosis
Gu, Xiaohui; Yang, Shaopu; Liu, Yongqiang; Hao, Rujiang
2016-12-01
Envelope analysis is one of the most useful methods in localized fault diagnosis of rolling element bearings. However, there is a challenge in selecting the optimal resonance band. In this paper, a novel method based on kurtogram and frequency domain correlated kurtosis is proposed. To obtain the correct relationship between the node and frequency band in wavelet packet transform, a vital process named frequency ordering is conducted to solve the frequency folding problem due to down sampling. Correlated kurtosis of envelope spectrum instead of correlated kurtosis of envelope signal or kurtosis of envelope spectrum is utilized to generate the kurtogram, in which the maximum value can indicate the optimal band for envelope analysis. Several cases of experimental bearing fault signals are used to evaluate the immunity of the proposed method to strong noise interference. The improved performance has also been compared with two previous developed methods. The results demonstrate the effectiveness and robustness of the method in fault diagnosis of rolling element bearings.
An improved wave-vector frequency-domain method for nonlinear wave modeling.
Jing, Yun; Tao, Molei; Cannata, Jonathan
2014-03-01
In this paper, a recently developed wave-vector frequency-domain method for nonlinear wave modeling is improved and verified by numerical simulations and underwater experiments. Higher order numeric schemes are proposed that significantly increase the modeling accuracy, thereby allowing for a larger step size and shorter computation time. The improved algorithms replace the left-point Riemann sum in the original algorithm by the trapezoidal or Simpson's integration. Plane waves and a phased array were first studied to numerically validate the model. It is shown that the left-point Riemann sum, trapezoidal, and Simpson's integration have first-, second-, and third-order global accuracy, respectively. A highly focused therapeutic transducer was then used for experimental verifications. Short high-intensity pulses were generated. 2-D scans were conducted at a prefocal plane, which were later used as the input to the numerical model to predict the acoustic field at other planes. Good agreement is observed between simulations and experiments.
Frequency-Domain Maximum-Likelihood Estimation of High-Voltage Pulse Transformer Model Parameters
Aguglia, D
2014-01-01
This paper presents an offline frequency-domain nonlinear and stochastic identification method for equivalent model parameter estimation of high-voltage pulse transformers. Such kinds of transformers are widely used in the pulsed-power domain, and the difficulty in deriving pulsed-power converter optimal control strategies is directly linked to the accuracy of the equivalent circuit parameters. These components require models which take into account electric fields energies represented by stray capacitance in the equivalent circuit. These capacitive elements must be accurately identified, since they greatly influence the general converter performances. A nonlinear frequency-based identification method, based on maximum-likelihood estimation, is presented, and a sensitivity analysis of the best experimental test to be considered is carried out. The procedure takes into account magnetic saturation and skin effects occurring in the windings during the frequency tests. The presented method is validated by experim...
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A new method of resolving overlapped peak, Fourier self-deconvolution (FSD) using approximation CN obtained from frequency domain wavelet transform of F(ω) yielded by Fourier transform of overlapped peak signals f(t) as the linear function, was presented in this paper.Compared with classical FSD, the new method exhibits excellent resolution for different overlapped peak signals such as HPLC signals, and have some characteristics such as an extensive applicability for any overlapped peak shape signals and a simple operation because of no selection procedure of the linear function. Its excellent resolution for those different overlapped peak signals is mainly because F(ω) obtained from Fourier transform of f(t) and CN obtained from wavelet transform of F(ω) have the similar linearity and peak width. The effect of those fake peaks can be eliminated by the algorithm proposed by authors. This method has good potential in the process of different overlapped peak signals.
The frequency domain causality analysis between energy consumption and income in the United States
Directory of Open Access Journals (Sweden)
Aviral Kumar Tiwari
2014-03-01
Full Text Available We investigated Granger-causality in the frequency domain between primary energy consumption/electricity consumption and GDP for the US by employing approach of Lemmens et al. (2008 and covering the period of January, 1973 to December, 2008. We found that causal and reverse causal relations between primary energy consumption and GDP and electricity consumption and GDP vary across frequencies. Our unique contribution in the existing literature lies in decomposing the causality on the basis of time horizons and demonstrating bidirectional the short-run, the medium-run and the long-run causality between GDP and primary energy consumption/electricity consumption and thus providing evidence for the feedback hypothesis. These results have important implications for the US for planning of the short, the medium and the long run energy and economic growth related policies.
An Adaptive Steganographic Method in Frequency Domain Based on Statistical Metrics of Image
Directory of Open Access Journals (Sweden)
Seyyed Amin Seyyedi
2015-05-01
Full Text Available Steganography is a branch of information hiding. A tradeoff between the hiding payload and quality of digital image steganographic schemes is major challenge of the steganographic methods. An adaptive steganographic method for embedding secret message into gray scale images is proposed. Before embedding the secret message, the cover image is transformed into frequency domain by integer wavelet. The middle frequency band of cover image is partitioned into 4×4 non overlapping blocks. The blocks by deviation and entropy metrics are classified into three categories: smooth, edge, and texture regions. Number of bits which can be embedded in a block is defined by block features. Moreover, RC4 encryption method is used to increase secrecy protection. Experimental results denote the feasibility of the proposed method. Statistical tests were conducted to collect related data to verify the security of method.
Frequency-domain identification of aircraft structural modes from short-duration flight tests
Vayssettes, J.; Mercère, G.; Vacher, P.; De Callafon, R. A.
2014-07-01
This article presents identification algorithms dedicated to the modal analysis of civil aircraft structures during in-flight flutter tests. This particular operational framework implies several specifications for the identification procedure. To comply with these requirements, the identification problem is formulated in the frequency domain as an output-error problem. Iterative identification methods based on structured matrix fraction descriptions are used to solve this problem and to identify a continuous-time model. These iterative methods are specifically designed to deal with experiments where short-duration tests with multiple-input excitations are used. These algorithms are first discussed and then evaluated through a simulation example illustrative of the in-flight modal analysis of a civil aircraft. Based on these evaluation results, an efficient iterative algorithm is suggested and applied to real flight-test data measured on board a military aircraft.
Visco-acoustic transmission waveform inversion of velocity structure in space-frequency domain
Institute of Scientific and Technical Information of China (English)
Guihua Long; Xiaofan Li; Meigen Zhang; Tong Zhu
2009-01-01
According to the least square criterion of minimizing the misfit between modeled and observed data, this paper provides a preconditioned gradient method to invert the visco-acoustic velocity structure on the basis of using sparse matrix LU factorization technique to directly solve the visco-acoustic wave forward problem in space-frequency domain. Numerical results obtained in an inclusion model inversion and a layered homogeneous model inversion demonstrate that different scale media have their own frequency responses, and the strategy of using low-frequency inverted result as the starting model in the high-frequency inversion can greatly reduce the non-uniqueness of their solutions. It can also be observed in the experi-ments that the fast convergence of the algorithm can be achieved by using diagonal elements of Hessian matrix as the pre-conditioned operator, which fully incorporates the advantage of quadratic convergence of Gauss-Newton method.
On the convergence and causality of a frequency domain method for dynamic structural analysis
Institute of Scientific and Technical Information of China (English)
Kuifu Chen; Senwen Zhang
2006-01-01
Venanico-Filho et al.developed an elegant matrix formulation for dynamic analysis by frequency domain (FD),but the convergence,causality and extended period need further refining.In the present Paper,it was argued that:(1) under reasonable assumptions (approximating the frequency response function by the discrete Fourier transform of the discretized unitary impulse response function),the matrix formulation by FD is equivalent to a circular convolution;(2) to avoid the wraparound Interference,the excitation vector and impulse response must be padded with enough zeros:(3) provided that the zero padding requirement satisfied,the convergence and accuracy of direct time domain analysis,which is equivalent to that by FD,are guaranteed by the numerical integration scheme;(4) the imaginary part of the computational response approaching zero is due to the continuity of the impulse response functions.
Photon acceleration versus frequency-domain interferometry for laser wakefield diagnostics
Energy Technology Data Exchange (ETDEWEB)
Dias, J.M.; Oliveira e Silva, L.; Mendonca, J.T. [GoLP/Centro de Fisica de Plasmas, Inst. Superior Tecnico, Lisbon (Portugal)
1998-03-01
A detailed comparison between the photon acceleration diagnostic technique and the frequency-domain interferometric technique for laser wakefield diagnostics, by using ray-tracing equations is presented here. The dispersion effects on the probe beam and the implications of an arbitrary phase velocity of the plasma wave are discussed for both diagnostic techniques. In the presence of large amplitude plasma wave and long interaction distances significant frequency shifts can be observed. The importance of this effect on the determination of the phase and frequency shifts measurements given by each of the two diagnostic techniques, is also analyzed. The accuracy of both diagnostic techniques is discussed and some of their technical problems are reviewed. (author)
A review of time-domain and frequency-domain component mode synthesis method
Craig, R. R., Jr.
1985-01-01
Hurty (1965) has conducted a dynamic analysis of structural systems using component modes. The component mode synthesis (CMS) procedure considered by him represents a form of substructure coupling analysis which is often utilized in structural dynamics. Time-domain CMS methods employing real modes are discussed, taking into account real component modes, normal modes, redundant constraint modes, rigid-body modes, attachment modes, inertia-relief modes, statically-complete interface mode sets, dynamic component mode supersets, component modal models, the coupling of components, and the classification of methods. Attention is also given to the experimental determination of component mode synthesis parameters, time-domain CMS methods for damped systems, and frequency-domain CMS methods for damped systems.
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 fluorescence lifetime microwell-plate platform for respirometry measurements
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.
Multiobjective Optimization for Electronic Circuit Design in Time and Frequency Domains
Directory of Open Access Journals (Sweden)
J. Dobes
2013-04-01
Full Text Available The multiobjective optimization provides an extraordinary opportunity for the finest design of electronic circuits because it allows to mathematically balance contradictory requirements together with possible constraints. In this paper, an original and substantial improvement of an existing method for the multiobjective optimization known as GAM (Goal Attainment Method is suggested. In our proposal, the GAM algorithm itself is combined with a procedure that automatically provides a set of parameters -- weights, coordinates of the reference point -- for which the method generates noninferior solutions uniformly spread over an appropriately selected part of the Pareto front. Moreover, the resulting set of obtained solutions is then presented in a suitable graphic form so that the solution representing the most satisfactory tradeoff can be easily chosen by the designer. Our system generates various types of plots that conveniently characterize results of up to four-dimensional problems. Technically, the procedures of the multiobjective optimization were created as a software add-on to the CIA (Circuit Interactive Analyzer program. This way enabled us to utilize many powerful features of this program, including the sensitivity analyses in time and frequency domains. As a result, the system is also able to perform the multiobjective optimization in the time domain and even highly nonlinear circuits can be significantly improved by our program. As a demonstration of this feature, a multiobjective optimization of a C-class power amplifier in the time domain is thoroughly described in the paper. Further, a four-dimensional optimization of a video amplifier is demonstrated with an original graphic representation of the Pareto front, and also some comparison with the weighting method is done. As an example of improving noise properties, a multiobjective optimization of a low-noise amplifier is performed, and the results in the frequency domain are shown
Moghimirad, Elahe; Mahloojifar, Ali; Mohammadzadeh Asl, Babak
2016-05-01
A new frequency-domain implementation of a synthetic aperture focusing technique is presented in the paper. The concept is based on synthetic aperture radar (SAR) and sonar that is a developed version of the convolution model in the frequency domain. Compared with conventional line-by-line imaging, synthetic aperture imaging has a better resolution and contrast at the cost of more computational load. To overcome this problem, point-by-point reconstruction methods have been replaced by block-processing algorithms in radar and sonar; however, these techniques are relatively unknown in medical imaging. In this paper, we extended one of these methods called wavenumber to medical ultrasound imaging using a simple model of synthetic aperture focus. The model, derived here for monostatic mode, can be generalized to multistatic as well. The method consists of 4 steps: a 2D fast Fourier transform of the data, frequency shift of the data to baseband, interpolation to convert polar coordinates to rectangular ones, and returning the data to the spatial-domain using a 2D inverse Fourier transform. We have also used chirp pulse excitation followed by matched filtering and spotlighting algorithm to compensate the effect of differences in parameters between radar and medical imaging. Computational complexities of the two methods, wavenumber and delay-and-sum (DAS), have been calculated. Field II simulated point data have been used to evaluate the results in terms of resolution and contrast. Evaluations with simulated data show that for typical phantoms, reconstruction by the wavenumber algorithm is almost 20 times faster than classical DAS while retaining the resolution. © The Author(s) 2015.
Jing, Xingjian
2015-01-01
This book is a systematic summary of some new advances in the area of nonlinear analysis and design in the frequency domain, focusing on the application oriented theory and methods based on the GFRF concept, which is mainly done by the author in the past 8 years. The main results are formulated uniformly with a parametric characteristic approach, which provides a convenient and novel insight into nonlinear influence on system output response in terms of characteristic parameters and thus facilitate nonlinear analysis and design in the frequency domain. The book starts with a brief introduction to the background of nonlinear analysis in the frequency domain, followed by recursive algorithms for computation of GFRFs for different parametric models, and nonlinear output frequency properties. Thereafter the parametric characteristic analysis method is introduced, which leads to the new understanding and formulation of the GFRFs, and nonlinear characteristic output spectrum (nCOS) and the nCOS based analysis a...
DEFF Research Database (Denmark)
Nelson, Paul C.; Ewert, Stephan; Carney, Laurel H.;
2007-01-01
-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms=0.25) and a range of AM frequencies (4-64 Hz). In a second experiment, masked sinusoidal......In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level...
Double-grid finite-difference frequency-domain (DG-FDFD) method for scattering from chiral objects
Alkan, Erdogan; Elsherbeni, Atef
2013-01-01
This book presents the application of the overlapping grids approach to solve chiral material problems using the FDFD method. Due to the two grids being used in the technique, we will name this method as Double-Grid Finite Difference Frequency-Domain (DG-FDFD) method. As a result of this new approach the electric and magnetic field components are defined at every node in the computation space. Thus, there is no need to perform averaging during the calculations as in the aforementioned FDFD technique [16]. We formulate general 3D frequency-domain numerical methods based on double-grid
Directory of Open Access Journals (Sweden)
Jong-Seob Baek
2008-01-01
Full Text Available This paper presents a new block iterative/adaptive frequency-domain channel estimation scheme, in which a channel frequency response (CFR is estimated iteratively by the proposed weighted element-wise block adaptive frequency-domain channel estimation (WEB-CE scheme using the soft information obtained by a soft-input soft-output (SISO decoder. In the WEB-CE, an equalizer coefficient is calculated by minimizing a weighted conditional squared-norm of the a posteriori error vector with respect to its correction term. Simulation results verify the superiority of the WEB-CE in a time-varying typical urban (TU channel.
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
This letter deals with the frequency domain Blind Source Separation of Convolutive Mixtures(CMBSS).From the frequency representation of the"overlap and save",a Weighted General Discrete Fourier Transform (WGDFT) is derived to replace the traditional Discrete Fourier Transform (DFT).The mixing matrix on each frequency bin could be estimated more precisely from WGDFT coefficients than from DFT coefficients,which improves separation performance.Simulation results verify the validity of WGDFT for frequency domain blind source separation of convolutive mixtures.
Real-time frequency domain temperature and oxygen sensor with a single optical fiber.
Liao, S C; Xu, Z; Izatt, J A; Alcala, J R
1997-11-01
The combined excited-state phosphorescence life-times of an alexandrite crystal and platinum tetraphenylporphyrin Pt(TPP) in a single-fiber sensor are used to monitor temperature and oxygen concentration in the physiological range from 15-45 degrees C and 0-50% O2 with precision of 0.24 degree C and 0.15% O2 and accuracy of 0.28 degree C and 0.2% O2. A 500-micron cubic alexandrite crystal bound to the distal end of a 750-micron-diameter optical fiber core and the Pt(TPP) coated circumferentially with a length of 1 cm from the end of the same fiber are excited with pulsed super-bright blue LED light. This apparatus uses a 125-kHz sampler for data acquisition and frequency domain methods for signal processing. The instrument amplifies both the dc and ac components of the photomultiplier output and band limits the signal to 20 kHz. The fundamental frequency of the excitation is set to 488.3 Hz and the highest harmonic used is the 35th. This bandlimited signal is sampled and averaged over a few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. At least four log-spaced harmonic phases or modulations are averaged before decoding the two lifetimes of temperature and oxygen phosphorescent sensors. A component of zero lifetime is introduced to account for the excitation backscatter leakage through optical interference filters seen by the photodetector. Linear and second-order empirical polynomials are employed to compute the temperatures and oxygen concentrations from the inverse lifetimes. In the situation of constant oxygen concentration, the lifetime of Pt(TPP) changes with temperature but can be compensated using the measured temperature lifetime. The system drift is 0.24 degree C for the temperature measurement and 0.59% for the oxygen concentration measurement over 30 h of continuous operation
Hydrograph structure informed calibration in the frequency domain with time localization
Kumarasamy, K.; Belmont, P.
2015-12-01
Complex models with large number of parameters are commonly used to estimate sediment yields and predict changes in sediment loads as a result of changes in management or conservation practice at large watershed (>2000 km2) scales. As sediment yield is a strongly non-linear function that responds to channel (peak or mean) velocity or flow depth, it is critical to accurately represent flows. The process of calibration in such models (e.g., SWAT) generally involves the adjustment of several parameters to obtain better estimates of goodness of fit metrics such as Nash Sutcliff Efficiency (NSE). However, such indicators only provide a global view of model performance, potentially obscuring accuracy of the timing or magnitude of specific flows of interest. We describe an approach for streamflow calibration that will greatly reduce the black-box nature of calibration, when response from a parameter adjustment is not clearly known. Fourier Transform or the Short Term Fourier Transform could be used to characterize model performance in the frequency domain as well, however, the ambiguity of a Fourier transform with regards to time localization renders its implementation in a model calibration setting rather useless. Brief and sudden changes (e.g. stream flow peaks) in signals carry the most interesting information from parameter adjustments, which are completely lost in the transform without time localization. Wavelet transform captures the frequency component in the signal without compromising time and is applied to contrast changes in signal response to parameter adjustments. Here we employ the mother wavelet called the Mexican hat wavelet and apply a Continuous Wavelet Transform to understand the signal in the frequency domain. Further, with the use of the cross-wavelet spectrum we examine the relationship between the two signals (prior or post parameter adjustment) in the time-scale plane (e.g., lower scales correspond to higher frequencies). The non-stationarity of
Spatially-dense, multi-spectral, frequency-domain diffuse optical tomography of breast cancer
Ban, Han Yong
Diffuse optical tomography (DOT) employs near-infrared light to image the concentration of chromophores and cell organelles in tissue and thereby providing access to functional parameters that can differentiate cancerous from normal tissues. This thesis describes research at the bench and in the clinic that explores and identifies the potential of DOT breast cancer imaging. The bench and clinic instrumentation differ but share important features: they utilize a very large, spatially dense, set of source-detector pairs (10 7) for imaging in the parallel-plate geometry. The bench experiments explored three-dimensional (3D) image resolution and fidelity as a function of numerous parameters and also ascertained the effects of a chest wall phantom. The chest wall is always present but is typically ignored in breast DOT. My experiments clarified chest wall influences and developed schemes to mitigate these effects. Mostly, these schemes involved selective data exclusion, but their efficacy also depended on reconstruction approach. Reconstruction algorithms based on analytic (fast) Fourier inversion and linear algebraic techniques were explored. The clinical experiments centered around a DOT instrument that I designed, constructed, and have begun to test (in-vitro and in-vivo). This instrumentation offers many features new to the field. Specifically, the imager employs spatially-dense, multi-spectral, frequency-domain data; it possesses the world's largest optical source-detector density yet reported, facilitated by highly-parallel CCD-based frequency-domain imaging based on gain-modulation heterodyne detection. The instrument thus measures both phase and amplitude of the diffusive light waves. Other features include both frontal and sagittal breast imaging capabilities, ancillary cameras for measurement of breast boundary profiles, real-time data normalization, and mechanical improvements for patient comfort. The instrument design and construction is my most significant
Frequency domain analysis of errors in cross-correlations of ambient seismic noise
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2016-12-01
We analyse random errors (variances) in cross-correlations of ambient seismic noise in the frequency domain, which differ from previous time domain methods. Extending previous theoretical results on ensemble averaged cross-spectrum, we estimate confidence interval of stacked cross-spectrum of finite amount of data at each frequency using non-overlapping windows with fixed length. The extended theory also connects amplitude and phase variances with the variance of each complex spectrum value. Analysis of synthetic stationary ambient noise is used to estimate the confidence interval of stacked cross-spectrum obtained with different length of noise data corresponding to different number of evenly spaced windows of the same duration. This method allows estimating Signal/Noise Ratio (SNR) of noise cross-correlation in the frequency domain, without specifying filter bandwidth or signal/noise windows that are needed for time domain SNR estimations. Based on synthetic ambient noise data, we also compare the probability distributions, causal part amplitude and SNR of stacked cross-spectrum function using one-bit normalization or pre-whitening with those obtained without these pre-processing steps. Natural continuous noise records contain both ambient noise and small earthquakes that are inseparable from the noise with the existing pre-processing steps. Using probability distributions of random cross-spectrum values based on the theoretical results provides an effective way to exclude such small earthquakes, and additional data segments (outliers) contaminated by signals of different statistics (e.g. rain, cultural noise), from continuous noise waveforms. This technique is applied to constrain values and uncertainties of amplitude and phase velocity of stacked noise cross-spectrum at different frequencies, using data from southern California at both regional scale (˜35 km) and dense linear array (˜20 m) across the plate-boundary faults. A block bootstrap resampling method
Digital Frequency Domain Fluorometry and the Study of Hoechst 33258 Dye-Dna Interactions
Feddersen, Brett Andrew
Fluorescence is a powerful tool for the study of chemical and biological processes. The typical decay times of fluorescence are ideal to study events in the pico to nanosecond range. On these time scales, the motions of many biological processes can be studied. The use of frequency domain fluorometry to measure the lifetime of the excited state has been used for many years. However, the development of an acquisition system based on modern digital techniques, presented in this thesis, has opened the door to different types of experiments that previously were either too time consuming or could not be done. The use of digital techniques and the development of a method to modulate an image intensifier have made it possible to incorporate linear and matrix detectors in frequency domain fluorometry. The extension of time -resolved fluorescence measurements to linear arrays has made it possible to follow the time evolution of the emission spectra while the use of matrix detectors has permitted the measurement of the lifetime at every "pixel" of an image. The dye Hoechst 33258 has been used for many years in the study of DNA and DNA binding. However, the fluorescent properties of Hoechst 33258 are not well understood. The dye is highly quenched in aqueous solutions and becomes brightly fluorescent when bound to Acdot T rich sequences of DNA or placed in non-aqueous solutions. The fluorescence of Hoechst 33258 seems to arise from two different solvation states of the molecule. When Hoechst 33258 binds to calf thymus DNA or poly(d(A cdotT)), the molecule becomes highly fluorescent, yet the two states can still be distinguished. The two states are attributed to different binding modes of the dye. The loose binding allows access of water molecules which results in different emission properties. On the other hand, when Hoechst binds onto d(CGCGAATTCGCG) only one lifetime is observed. The single lifetime has been attributed to strong binding of the Hoechst molecule onto the AATT
Pioldi, Fabio; Rizzi, Egidio
2017-07-01
Output-only structural identification is developed by a refined Frequency Domain Decomposition ( rFDD) approach, towards assessing current modal properties of heavy-damped buildings (in terms of identification challenge), under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type II bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames (with variable structural features) are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 "Far-Field" (22 NS, 22 WE) earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.
Yngvesson, Sigfrid K.; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew; Khan, Ashraf
2012-03-01
In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This possibility of re-excision is undesirable in terms of reducing patient morbidity, emotional stress and healthcare. It has been shown that terahertz (THz) images of breast specimens can accurately differentiate between breast carcinoma, normal fibroglandular tissue, and adipose tissue. That study employed the Time-Domain Spectroscopy (TDS) technique. We are instead developing a new technique, Frequency-Domain Terahertz Imaging (FDTI). In this joint project between UMass/Amherst and UMass Medical School/Worcester (UMMS), we are investigating the feasibility of the FDTI technique for THz reflection imaging of breast cancer margins. Our system, which produces mechanically scanned images of size 2cm x 2cm, uses a THz gas laser. The system is calibrated with mixtures of water and ethanol and reflection coefficients as low as 1% have been measured. Images from phantoms and specimens cut from breast cancer lumpectomies at UMMS will be presented. Finally, there will be a discussion of a possible transition of this FDTI setup to a compact and inexpensive CMOS THz camera for use in the operating room.
On time-domain and frequency-domain MMSE-based TEQ design for DMT transmission
Vanbleu, K; Moonen, M; Ysebaert, G; 10.1109/TSP.2005.851161
2005-01-01
We reconsider the minimum mean square error (MMSE) time-domain equalizer (TEQ), bitrate maximizing TEQ (BM-TEQ), and per-tone equalizer design (PTEQ) for discrete multitone (DMT) transmission and cast them in a common least-squares (LS) based framework. The MMSE- TEQ design criterion can be formulated as a constrained linear least-squares (CLLS) criterion that minimizes a time-domain (TD) error energy. From this CLLS-based TD-MMSE-TEQ criterion, we derive two new least-squares (LS) based frequency-domain (FD) MMSE-TEQ design criteria: a CLLS-based FD-MMSE-TEQ criterion and a so-called separable nonlinear LS (SNLLS) based FD-MMSE-TEQ design. Finally, the original BM-TEQ design is shown to be equivalent to a so-called iteratively-reweighted (IR) version of the SNLLS-based FD-MMSE-TEQ design. This LS-based framework then results in the following contributions. The new, IR-SNLLS-based BM-TEQ design criterion gives rise to an elegant, iterative, fast converging, Gauss-Newton-based design algorithm that exploits th...
Osburn, Thomas; Evans, Charles; Hopper, Seth
2014-01-01
We present an algorithm for calculating the metric perturbations and gravitational self-force for extreme-mass-ratio inspirals (EMRIs) with eccentric orbits. The massive black hole is taken to be Schwarzschild and metric perturbations are computed in Lorenz gauge. The perturbation equations are solved as coupled systems of ordinary differential equations in the frequency domain. Accurate local behavior of the metric is attained through use of the method of extended homogeneous solutions and mode-sum regularization is used to find the self-force. We focus on calculating the self-force with sufficient accuracy to ensure its error contributions to the phase in a long term orbital evolution will be $\\delta\\Phi \\lesssim 10^{-2}$ radians. This requires the orbit-averaged force to have fractional errors $\\lesssim 10^{-8}$ and the oscillatory part of the self-force to have errors $\\lesssim 10^{-3}$ (a level frequently easily exceeded). Our code meets this error requirement in the oscillatory part, extending the reach...
Permutation Correction in the Frequency Domain in Blind Separation of Speech Mixtures
Directory of Open Access Journals (Sweden)
Pham DT
2006-01-01
Full Text Available This paper presents a method for blind separation of convolutive mixtures of speech signals, based on the joint diagonalization of the time varying spectral matrices of the observation records. The main and still largely open problem in a frequency domain approach is permutation ambiguity. In an earlier paper of the authors, the continuity of the frequency response of the unmixing filters is exploited, but it leaves some frequency permutation jumps. This paper therefore proposes a new method based on two assumptions. The frequency continuity of the unmixing filters is still used in the initialization of the diagonalization algorithm. Then, the paper introduces a new method based on the time-frequency representations of the sources. They are assumed to vary smoothly with frequency. This hypothesis of the continuity of the time variation of the source energy is exploited on a sliding frequency bandwidth. It allows us to detect the remaining frequency permutation jumps. The method is compared with other approaches and results on real world recordings demonstrate superior performances of the proposed algorithm.
Lakowicz, Joseph R.; Gryczynski, Ignacy; Szmacinski, Henryk; Nowaczyk, Kazimierz; Johnson, Michael L.
1992-02-01
During the past seven years, there have been remarkable advances in the frequency-domain method for measurement of time-resolved emission or light scattering. In this presentation we describe the recent extension of the frequency range to 10 GHz using a specially designed microchannel plate PMT. Experimental data will be shown for measurement of picosecond rotational diffusion and for sub-picosecond resolution of time delays. The resolution of ps to ns timescale processes is not obtained at the expense of sensitivity or is it shown by measurements on the intrinsic tryptophan emission from hemoglobin. We also describe a time- resolved reflectance imaging experiment on a scattering medium containing an absorbing object. Time-resolved imaging of the back-scattered light is realized by means of a RF-phase- sensitive camera, synchronized to the laser pulses. By processing the stored images, a final image can be created, the contrast of which is based only on time differences of the back- scattered photons. This image reveals the presence and position of the absorber within the scattering medium. And finally, we describe a new methodology, fluorescence lifetime imaging (FLIM), in which the contrast depends on the fluorescence lifetime at each point in a two-dimensional image, and not the local concentration and/or intensity of the fluorophore. We used FLIM to create lifetime images of NADH when free in solution and when bound to malate dehydrogenase. FLIM has numerous potential applications in cell biology and imaging.
Directory of Open Access Journals (Sweden)
Carlo Ruzzo
2016-10-01
Full Text Available System identification of offshore floating platforms is usually performed by testing small-scale models in wave tanks, where controlled conditions, such as still water for free decay tests, regular and irregular wave loading can be represented. However, this approach may result in constraints on model dimensions, testing time, and costs of the experimental activity. For such reasons, intermediate-scale field modelling of offshore floating structures may become an interesting as well as cost-effective alternative in a near future. Clearly, since the open sea is not a controlled environment, traditional system identification may become challenging and less precise. In this paper, a new approach based on Frequency Domain Decomposition (FDD method for Operational Modal Analysis is proposed and validated against numerical simulations in ANSYS AQWA v.16.0 on a simple spar-type structure. The results obtained match well with numerical predictions, showing that this new approach, opportunely coupled with more traditional wave tanks techniques, proves to be very promising to perform field-site identification of the model structures.
Frequency domain reduced order models for gravitational waves from aligned-spin black-hole binaries
Pürrer, Michael
2014-01-01
Black-hole binary coalescences are one of the most promising sources for the first detection of gravitational waves. Fast and accurate theoretical models of the gravitational radiation emitted from these coalescences are highly important for the detection and extraction of physical parameters. Spinning effective-one-body (EOB) models for binaries with aligned spins have been shown to be highly faithful, but are slow to generate and thus have not yet been used for parameter estimation studies. I provide a frequency-domain singular value decomposition (SVD)-based surrogate reduced order model that is thousands to hundred thousands times faster for typical system masses and has a faithfulness mismatch of better than $\\sim 0.1\\%$ with the original SEOBNRv1 model for advanced LIGO detectors. This model enables parameter estimation studies up to signal-to-noise ratios (SNRs) of 20 and even up to SNR 50 for masses below $50 M_\\odot$. This article discusses various choices for approximations and interpolation over th...
Improved free-surface expression for frequency-domain elastic optimal mixed-grid modeling
Cao, Jian; Chen, Jing-Bo; Dai, Meng-Xue
2016-07-01
An accurate and efficient forward modeling is the foundation of full-waveform inversion (FWI). In elastic wave modeling, one of the key problems is how to deal with the free-surface boundary condition appropriately. For the representation of the free-surface boundary condition, conventional displacement-based approaches and staggered-grid approaches are often used in time-domain. In frequency-domain, considering the saving of storage and CPU time, we integrate the idea of physical parameter-modified staggered-grid approach in time-domain with an elastic optimal mixed-grid modeling scheme to design an improved parameter-modified free-surface expression. Accuracy analysis shows that an elastic optimal mixed-grid modeling scheme using the parameter-modified free-surface expression can provide more accurate solutions with only 4 grid points per smallest shear wavelength than conventional displacement-based approaches and is stable for most Poisson ratios. Besides, it also yields smaller condition number of the resulting impedance matrix than conventional displacement-based approaches in laterally varying complex media. These advantages reveal great potential of this free-surface expression in big-data practical application.
Volterra series truncation and kernel estimation of nonlinear systems in the frequency domain
Zhang, B.; Billings, S. A.
2017-02-01
The Volterra series model is a direct generalisation of the linear convolution integral and is capable of displaying the intrinsic features of a nonlinear system in a simple and easy to apply way. Nonlinear system analysis using Volterra series is normally based on the analysis of its frequency-domain kernels and a truncated description. But the estimation of Volterra kernels and the truncation of Volterra series are coupled with each other. In this paper, a novel complex-valued orthogonal least squares algorithm is developed. The new algorithm provides a powerful tool to determine which terms should be included in the Volterra series expansion and to estimate the kernels and thus solves the two problems all together. The estimated results are compared with those determined using the analytical expressions of the kernels to validate the method. To further evaluate the effectiveness of the method, the physical parameters of the system are also extracted from the measured kernels. Simulation studies demonstrates that the new approach not only can truncate the Volterra series expansion and estimate the kernels of a weakly nonlinear system, but also can indicate the applicability of the Volterra series analysis in a severely nonlinear system case.
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).
Saager, Rolf B.; Dang, An N.; Huang, Samantha S.; Kelly, Kristen M.; Durkin, Anthony J.
2017-09-01
Spatial Frequency Domain Spectroscopy (SFDS) is a technique for quantifying in-vivo tissue optical properties. SFDS employs structured light patterns that are projected onto tissues using a spatial light modulator, such as a digital micromirror device. In combination with appropriate models of light propagation, this technique can be used to quantify tissue optical properties (absorption, μa, and scattering, μs', coefficients) and chromophore concentrations. Here we present a handheld implementation of an SFDS device that employs line (one dimensional) imaging. This instrument can measure 1088 spatial locations that span a 3 cm line as opposed to our original benchtop SFDS system that only collects a single 1 mm diameter spot. This imager, however, retains the spectral resolution (˜1 nm) and range (450-1000 nm) of our original benchtop SFDS device. In the context of homogeneous turbid media, we demonstrate that this new system matches the spectral response of our original system to within 1% across a typical range of spatial frequencies (0-0.35 mm-1). With the new form factor, the device has tremendously improved mobility and portability, allowing for greater ease of use in a clinical setting. A smaller size also enables access to different tissue locations, which increases the flexibility of the device. The design of this portable system not only enables SFDS to be used in clinical settings but also enables visualization of properties of layered tissues such as skin.
Frequency Domain Multi-parameter Full Waveform Inversion for Acoustic VTI Media
Djebbi, R.
2017-05-26
Multi-parameter full waveform inversion (FWI) for transversely isotropic (TI) media with vertical axis of symmetry (VTI) suffers from the trade-off between the parameters. The trade-off results in the leakage of one parameter\\'s update into the other during the inversion. It affects the accuracy and convergence of the inversion. The sensitivity analyses suggested a parameterisation using the horizontal velocity vh, epsilon and eta to reduce the trade-off for surface recorded seismic data.We test the (vh, epsilon, eta) parameterisation for acoustic VTI media using a scattering integral (SI) based inversion. The data is modeled in frequency domain and the model is updated using a preconditioned conjugate gradient method. We applied the method to the VTI Marmousi II model and in the inversion, we keep eta parameter fixed as the background initial model and we invert simultaneously for both vh and epsilon. The results show the suitability of the parameterisation for multi-parameter VTI acoustic inversion as well as the accuracy of the inversion approach.
Poggi, Valerio; Ermert, Laura; Burjanek, Jan; Michel, Clotaire; Fäh, Donat
2015-01-01
Frequency domain decomposition (FDD) is a well-established spectral technique used in civil engineering to analyse and monitor the modal response of buildings and structures. The method is based on singular value decomposition of the cross-power spectral density matrix from simultaneous array recordings of ambient vibrations. This method is advantageous to retrieve not only the resonance frequencies of the investigated structure, but also the corresponding modal shapes without the need for an absolute reference. This is an important piece of information, which can be used to validate the consistency of numerical models and analytical solutions. We apply this approach using advanced signal processing to evaluate the resonance characteristics of 2-D Alpine sedimentary valleys. In this study, we present the results obtained at Martigny, in the Rhône valley (Switzerland). For the analysis, we use 2 hr of ambient vibration recordings from a linear seismic array deployed perpendicularly to the valley axis. Only the horizontal-axial direction (SH) of the ground motion is considered. Using the FDD method, six separate resonant frequencies are retrieved together with their corresponding modal shapes. We compare the mode shapes with results from classical standard spectral ratios and numerical simulations of ambient vibration recordings.
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
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.
Mazhar, Amaan; Saggese, Steve; Pollins, Alonda C; Cardwell, Nancy L; Nanney, Lillian; Cuccia, David J
2014-08-01
The standard of care for clinical assessment of burn severity and extent lacks a quantitative measurement. In this work, spatial frequency domain imaging (SFDI) was used to measure 48 thermal burns of graded severity (superficial partial, deep partial, and full thickness) in a porcine model. Functional (total hemoglobin and tissue oxygen saturation) and structural parameters (tissue scattering) derived from the SFDI measurements were monitored over 72 h for each burn type and compared to gold standard histological measurements of burn depth. Tissue oxygen saturation (stO₂) and total hemoglobin (ctHbT) differentiated superficial partial thickness burns from more severe burn types after 2 and 72 h, respectively (p burns from all burn types immediately after injury (p burn types from each other after 24 h (p burn depth as measured by vimentin immunostain (r² > 0.89). These results show promise for the use of SFDI-derived tissue scattering as a correlation to burn depth and the potential to assess burn depth via a combination of SFDI functional and structural parameters.
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.
Single trial time-frequency domain analysis of error processing in post-traumatic stress disorder.
Clemans, Zachary A; El-Baz, Ayman S; Hollifield, Michael; Sokhadze, Estate M
2012-09-13
Error processing studies in psychology and psychiatry are relatively common. Event-related potentials (ERPs) are often used as measures of error processing, two such response-locked ERPs being the error-related negativity (ERN) and the error-related positivity (Pe). The ERN and Pe occur following committed error in reaction time tasks as low frequency (4-8 Hz) electroencephalographic (EEG) oscillations registered at the midline fronto-central sites. We created an alternative method for analyzing error processing using time-frequency analysis in the form of a wavelet transform. A study was conducted in which subjects with PTSD and healthy control completed a forced-choice task. Single trial EEG data from errors in the task were processed using a continuous wavelet transform. Coefficients from the transform that corresponded to the theta range were averaged to isolate a theta waveform in the time-frequency domain. Measures called the time-frequency ERN and Pe were obtained from these waveforms for five different channels and then averaged to obtain a single time-frequency ERN and Pe for each error trial. A comparison of the amplitude and latency for the time-frequency ERN and Pe between the PTSD and control group was performed. A significant group effect was found on the amplitude of both measures. These results indicate that the developed single trial time-frequency error analysis method is suitable for examining error processing in PTSD and possibly other psychiatric disorders.
McClatchy, David M; Rizzo, Elizabeth J; Wells, Wendy A; Cheney, Philip P; Hwang, Jeeseong C; Paulsen, Keith D; Pogue, Brian W; Kanick, Stephen C
2016-06-20
Localized measurements of scattering in biological tissue provide sensitivity to microstructural morphology but have limited utility to wide-field applications, such as surgical guidance. This study introduces sub-diffusive spatial frequency domain imaging (sd-SFDI), which uses high spatial frequency illumination to achieve wide-field sampling of localized reflectances. Model-based inversion recovers macroscopic variations in the reduced scattering coefficient [Formula: see text] and the phase function backscatter parameter (γ). Measurements in optical phantoms show quantitative imaging of user-tuned phase-function-based contrast with accurate decoupling of parameters that define both the density and the size-scale distribution of scatterers. Measurements of fresh ex vivo breast tissue samples revealed, for the first time, unique clustering of sub-diffusive scattering properties for different tissue types. The results support that sd-SFDI provides maps of microscopic structural biomarkers that cannot be obtained with diffuse wide-field imaging and characterizes spatial variations not resolved by point-based optical sampling.
Fusion of infrared and visible images based on saliency scale-space in frequency domain
Chen, Yanfei; Sang, Nong; Dan, Zhiping
2015-12-01
A fusion algorithm of infrared and visible images based on saliency scale-space in the frequency domain was proposed. Focus of human attention is directed towards the salient targets which interpret the most important information in the image. For the given registered infrared and visible images, firstly, visual features are extracted to obtain the input hypercomplex matrix. Secondly, the Hypercomplex Fourier Transform (HFT) is used to obtain the salient regions of the infrared and visible images respectively, the convolution of the input hypercomplex matrix amplitude spectrum with a low-pass Gaussian kernel of an appropriate scale which is equivalent to an image saliency detector are done. The saliency maps are obtained by reconstructing the 2D signal using the original phase and the amplitude spectrum, filtered at a scale selected by minimizing saliency map entropy. Thirdly, the salient regions are fused with the adoptive weighting fusion rules, and the nonsalient regions are fused with the rule based on region energy (RE) and region sharpness (RS), then the fused image is obtained. Experimental results show that the presented algorithm can hold high spectrum information of the visual image, and effectively get the thermal targets information at different scales of the infrared image.
The impact of monetary policy on output and inflation in India: A frequency domain analysis
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Salunkhe Bhavesh
2017-01-01
Full Text Available In the recent past, several attempts by the RBI to control inflation through tight monetary policy have ended up slowing the growth process, thereby provoking prolonged discussion among academics and policymakers about the efficacy of monetary policy in India. Against this backdrop, the present study attempts to estimate the causal relationship between monetary policy and its final objectives; i.e., growth, and controlling inflation in India. The methodological tool used is testing for Granger Causality in the frequency domain as developed by Lemmens et al. (2008, and monetary policy has been proxied by the weighted average call money rate. In view of the fact that output gap is one of the determinants of future inflation, an attempt has also been made to study the causal relationship between output gap and inflation. The results of empirical estimation show a bi-directional causality between policy rate and inflation and between policy rate and output, which implies that the monetary authorities in India were equally concerned about inflation and output growth when determining policy. Furthermore, any attempt to control inflation affects output with the same or even greater magnitude than inflation, thereby damaging the growth process. The relationship between output gap and inflation was found to be positive, as reported in earlier studies for India. Furthermore, the output gap causes inflation only in the short-tomediumrun.
Institute of Scientific and Technical Information of China (English)
Hongde Qin; Jing Shen; Xiaobo Chen
2011-01-01
The free-surface Green function method is widely used in solving the radiation or diffraction problems caused by a ship or ocean structure oscillating on the waves.In the context of inviscid potential flow,hydrodynamic problems such as multi-body interaction and tank side wall effect cannot be properly dealt with based on the traditional free-surface frequency domain Green function method,in which the water viscosity is omitted and the energy dissipation effect is absent.In this paper,an open-sea Green function with viscous dissipation was presented within the theory of visco-potential flow.Then the tank Green function with a partial reflection from the side walls in wave tanks was formulated as a formal sum of open-sea Green functions representing the infinite images between two parallel side walls of the source in the tank.The new far-field characteristics of the tank Green function is vitally important for improving the validity of side-wall effects evaluation,which can be used in supervising the tank model tests.
Estimation of tire-road friction coefficient based on frequency domain data fusion
Chen, Long; Luo, Yugong; Bian, Mingyuan; Qin, Zhaobo; Luo, Jian; Li, Keqiang
2017-02-01
Due to the noise of sensing equipment, the tire states, such as the sideslip angle and the slip ratio, cannot be accurately observed under the conditions with small acceleration, which results in the inapplicability of the time domain data based tire-road friction coefficient (TRFC) estimation method. In order to overcome this shortcoming, frequency domain data fusion is proposed to estimate the TRFC based on the natural frequencies of the steering system and the in-wheel motor driving system. Firstly, a relationship between TRFC and the steering system natural frequency is deduced by investigating its frequency response function (FRF). Then the lateral TRFC is determined by the steering natural frequency which is only identified using the information of the assist motor current and the steering speed of the column. With spectral comparison between the steering and driving systems, the data fusion is carried out to get a comprehensive TRFC result, using the different frequency information of the longitudinal and lateral value. Finally, simulations and experiments on different road surfaces validated the correctness of the steering system FRF and the effectiveness of the proposed approach.
Empirical frequency domain model for fixed-pattern noise in infrared focal plane arrays
Pérez, Francisco; Pezoa, Jorge E.; Figueroa, Miguel; Torres, Sergio N.
2014-11-01
In this paper, a new empirical model for the spatial structure of the fixed-pattern noise (FPN) observed in infrared (IR) focal-plane arrays (FPA) is presented. The model was conceived after analyzing, in the spatial frequency domain, FPN calibration data from different IR cameras and technologies. The analysis showed that the spatial patterns of the FPN are retained in the phase spectrum, while the noise intensity is determined by the magnitude spectrum. Thus, unlike traditional representations, the proposed model abstracts the FPN structure using one matrix for its magnitude spectrum and another matrix for its phase spectrum. Three applications of the model are addressed here. First, an algorithm is provided for generating random samples of the FPN with the same spatial pattern of the actual FPN. Second, the model is used to assess the performance of non-uniformity correction (NUC) algorithms in the presence of spatially correlated and uncorrelated FPN. Third, the model is used to improve the NUC capability of a method that requires, as a reference, a proper FPN sample.
Shifting of wrapped phase maps in the frequency domain using a rational number
Gdeisat, Munther A.; Burton, David R.; Lilley, Francis; Arevalillo-Herráez, Miguel; Abushakra, Ahmad; Qaddoura, Maen
2016-10-01
The number of phase wraps in an image can be either reduced, or completely eliminated, by transforming the image into the frequency domain using a Fourier transform, and then shifting the spectrum towards the origin. After this, the spectrum is transformed back to the spatial domain using the inverse Fourier transform and finally the phase is extracted using the arctangent function. However, it is a common concern that the spectrum can be shifted only by an integer number, meaning that the phase wrap reduction is often not optimal. In this paper we propose an algorithm than enables the spectrum to be frequency shifted by a rational number. The principle of the proposed method is confirmed both by using an initial computer simulation and is subsequently validated experimentally on real fringe patterns. The technique may offer in some cases the prospects of removing the necessity for a phase unwrapping process altogether and/or speeding up the phase unwrapping process. This may be beneficial in terms of potential increases in signal recovery robustness and also for use in time-critical applications.
A HYBRID TECHNIQUE FOR FREQUENCY DOMAIN IDENTIFICATION OF SERVO SYSTEM WITH FRICTION FORCE
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SHAIK.RAFI KIRAN,
2011-03-01
Full Text Available The system identification process in servo system with frictional force seems to be a complex task becauseof its non-linear nature. For such non-linear systems, a good choice is system identification in frequencydomain. However, most of the techniques are manual and are inappropriate for determination of systemparameters. This makes system identification ineffective for servo systems with frictional force. Toovercome this issue, a hybrid technique is proposed in this paper. The proposed technique exploits neuralnetwork and genetic algorithm to determine the system parameters of servo systems with friction. In theproposed technique, the target parameters are determined from the transfer function derived for thesystem. Subsequently, the system parameters are identified by a process formed by blending the neuralnetwork and genetic algorithm techniques. Prior to performing the identification procedure, backpropagation training is given to the neural network using a pre-examined dataset. Then with thecombined operation of neural network and genetic algorithm, the system parameters that are closer tothe target parameters for the servo system with frictional force are determined. The technique isimplemented and compared with the existing frequency domain identification technique. From thecomparative results, it is evident that the proposed technique outperforms the existing technique.
Bender, Amy N; de Haan, Tijmen; Dobbs, Matt A; Gilbert, Adam J; Montgomery, Joshua; Rowlands, Neil; Smecher, Graeme M; Smith, Ken; Wilson, Andrew
2014-01-01
Frequency domain multiplexing (fMux) is an established technique for the readout of transition-edge sensor (TES) bolometers in millimeter-wavelength astrophysical instrumentation. In fMux, the signals from multiple detectors are read out on a single pair of wires reducing the total cryogenic thermal loading as well as the cold component complexity and cost of a system. The current digital fMux system, in use by POLARBEAR, EBEX, and the South Pole Telescope, is limited to a multiplexing factor of 16 by the dynamic range of the Superconducting Quantum Interference Device pre-amplifier and the total system bandwidth. Increased multiplexing is key for the next generation of large format TES cameras, such as SPT-3G and POLARBEAR2, which plan to have on the of order 15,000 detectors. Here, we present the next generation fMux readout, focusing on the warm electronics. In this system, the multiplexing factor increases to 64 channels per module (2 wires) while maintaining low noise levels and detector stability. This ...
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.
Probing the disassembly of ultrafast laser heated gold using frequency domain interferometry.
Ao, Tommy; Ping, Yuan; Lee, Edward
2005-10-01
Ultrafast laser heating of a solid offers a unique approach to examine the behavior of non-equilibrium high energy density states. Initially, the electrons are optically excited while the ions in the lattice remain cold. This is followed by electron-electron and electron-phonon relaxation. Recently, experiments were performed in which ultrathin freestanding, gold foils were heated by a femtosecond pump laser to a strongly overdriven regime with energy densities reaching 20 MJ/kg. Interestingly, femtosecond laser reflectivity and transmission measurements on the heated sample revealed a quasi-steady-state behavior before the onset of hydrodynamic expansion. This led to the conjecture of the existence of a metastable, disordered state prior to the disassembly of the solid. To further examine the dynamics of ultrafast laser heated solids, frequency domain interferometry (FDI) was used to provide an independent observation. The highly sensitive change in the phase shift of the FDI probe clearly showed evidence of the quasi-steady-state behavior. The new experiment also yielded a detailed measurement of the time scale of such a quasi-steady-state phase that may help elucidate the process of electron-phonon coupling and disassembly in a strongly overdriven regime.
Gizon, Laurent; Duruflé, Marc; Hanson, Chris S; Leguèbe, Michael; Birch, Aaron C; Chabassier, Juliette; Fournier, Damien; Hohage, Thorsten; Papini, Emanuele
2016-01-01
Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equati...
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Hong eZhou
2016-06-01
Full Text Available Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid.
Pratesi, S; Donzelli, G
2000-01-01
Near infrared spectroscopy (NIRS) is a non invasive, portable, safe technique for monitoring cerebral oxygenation and haemodynamics. A new frequency-domain tissue oximeter based on a multi-distance measurement protocol is presented. The effects of apneic episodes on cerebral and peripheral arterial oxygen saturation (SatO2) in preterm newborns, as monitored by NIRS and by pulse oximetry, are reported. The study population consist of 5 preterms (26 to 30 weeks of gestational age), in the second week of postnatal age, affected by apnea of prematurity. NIRS and pulse oximetric measurements were made contemporarily for a 40-minutes period for each infant. All monitorized apneic events were associated with bradicardia, and resolved spontaneously or after tactile stimulation. As results: a) there was always cerebral deoxygenation in association with apneic events, b) the mean SatO2 as measured by NIRS was slightly lower than the pulse oximeter readings, c) cerebral SatO2 decreased faster and the absolute value of the cerebral SaO2 decrease was greater than that measured peripherally (mean value of 27 versus 13%), d) increases of cerebral deoxyhemoglobin and total hemoglobin and a decrease of oxyhemoglobin were also observed. These preliminary results show that peripheral oxygen saturation measurements as measured by pulse oximetry could not always reflect brain oxygenation.
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.
Prakash, Jaya; Chandrasekharan, Venkittarayan; Upendra, Vishwajith; Yalavarthy, Phaneendra K
2010-01-01
Diffuse optical tomographic image reconstruction uses advanced numerical models that are computationally costly to be implemented in the real time. The graphics processing units (GPUs) offer desktop massive parallelization that can accelerate these computations. An open-source GPU-accelerated linear algebra library package is used to compute the most intensive matrix-matrix calculations and matrix decompositions that are used in solving the system of linear equations. These open-source functions were integrated into the existing frequency-domain diffuse optical image reconstruction algorithms to evaluate the acceleration capability of the GPUs (NVIDIA Tesla C 1060) with increasing reconstruction problem sizes. These studies indicate that single precision computations are sufficient for diffuse optical tomographic image reconstruction. The acceleration per iteration can be up to 40, using GPUs compared to traditional CPUs in case of three-dimensional reconstruction, where the reconstruction problem is more underdetermined, making the GPUs more attractive in the clinical settings. The current limitation of these GPUs in the available onboard memory (4 GB) that restricts the reconstruction of a large set of optical parameters, more than 13,377.
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S. Radhakrishnan
2016-08-01
Full Text Available The dielectric relaxation of benzyl alcohol substitutents (benzyl alcohol, m-methylbenzyl alcohol and m-nitrobenzyl alcohol with methyl methacrylate and butyl methacrylate in dilute solution of carbon tetrachloride is measured at 9.37 GHz using Frequency domain (X-band technique. Different dielectric parameters like dielectric constant (ε׳, dielectric loss factor (ε״ at Microwave frequency, static dielectric constant (ε0 and dielectric constant at infinite dilution (ε∞ at optical frequency have been determined. From the measured dielectric data, the relaxation time (t calculated using Higasi method and activation energies (∆Ft and ∆Fη have been determined. All the dielectric parameters that are vary with the substitutent change in benzyl alcohol andchain length of acrylic esters. Suggests that, the proton donating ability is varying with the substitution of benzyl alcohol and proton accepting ability is varying with the chain length of acrylic esters. The relaxation time and molar free energy activation of 1:1 molar ratio is greater than other higher molar ratios (i.e. 3:1, 2:1, 1:2, 1:3 confirm that the existence of most likely 1:1 complex formation between the studied systems and also complex formation formed between free hydroxyl group of substituted benzyl alcohols and carbonyl group of acrylic esters (MMA and EMA.
Energy Technology Data Exchange (ETDEWEB)
Viana, Rodrigo S.S.; Tardelli, Tiago C.; Yoriyaz, Helio, E-mail: hyoriyaz@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Jackowski, Marcel P., E-mail: mjack@ime.usp.b [University of Sao Paulo (USP), SP (Brazil). Dept. of Computer Science
2011-07-01
In recent years, a new technique for in vivo spectrographic imaging of stable isotopes was presented as Neutron Stimulated Emission Computed Tomography (NSECT). In this technique, a fast neutrons beam stimulates stable nuclei in a sample, which emit characteristic gamma radiation. The photon energy is unique and is used to identify the emitting nuclei. The emitted gamma energy spectra can be used for reconstruction of the target tissue image and for determination of the tissue elemental composition. Due to the stochastic nature of photon emission process by irradiated tissue, one of the most suitable algorithms for tomographic reconstruction is the Expectation-Maximization (E-M) algorithm, once on its formulation are considered simultaneously the probabilities of photons emission and detection. However, a disadvantage of this algorithm is the introduction of noise in the reconstructed image as the number of iterations increases. This increase can be caused either by features of the algorithm itself or by the low sampling rate of projections used for tomographic reconstruction. In this work, a linear filter in the frequency domain was used in order to improve the quality of the reconstructed images. (author)
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%.
Zero-guard-interval coherent optical OFDM with overlapped frequency-domain CD and PMD equalization.
Chen, Chen; Zhuge, Qunbi; Plant, David V
2011-04-11
This paper presents a new channel estimation/equalization algorithm for coherent OFDM (CO-OFDM) digital receivers, which enables the elimination of the cyclic prefix (CP) for OFDM transmission. We term this new system as the zero-guard-interval (ZGI)-CO-OFDM. ZGI-CO-OFDM employs an overlapped frequency-domain equalizer (OFDE) to compensate both chromatic dispersion (CD) and polarization mode dispersion (PMD) before the OFDM demodulation. Despite the zero CP overhead, ZGI-CO-OFDM demonstrates a superior PMD tolerance than the previous reduced-GI (RGI)-CO-OFDM, which is verified under several different PMD conditions. Additionally, ZGI-CO-OFDM can improve the channel estimation accuracy under high PMD conditions by using a larger intra-symbol frequency-averaging (ISFA) length as compared to RGI-CO-OFDM. ZGI-CO-OFDM also enables the use of ever smaller fast Fourier transform (FFT) sizes (i.e. OFDM. We show that ZGI-CO-OFDM requires reasonably small additional computation effort (~13.6%) compared to RGI-CO-OFDM for 112-Gb/s transmission over a 1600-km dispersion-uncompensated optical link.
How to Apply a Filter Defined in the Frequency Domain by a Continuous Function
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Thibaud Briand
2016-11-01
Full Text Available We propose algorithms for filtering real-valued images, when the filter is provided as a continuous function defined in the Nyquist frequency domain. This problem is ambiguous because images are discrete entities and there is no unique way to define the filtering. We provide a theoretical framework designed to analyse the classical and computationally efficient filtering implementations based on discrete Fourier transforms (DFT. In this framework, the filtering is interpreted as the convolution of a distribution, standing for the filter, with a trigonometric polynomial interpolator of the image. The various plausible interpolations and choices of the distribution lead to three equally licit algorithms which can be seen as method variants of the same standard filtering algorithm. In general none should be preferred to the others and the choice depends on the application. In practice, the method differences, which come from the boundary DFT coefficients, are not visible to the naked eye. We demonstrate that claim on several experimental configurations by varying the input image and the considered filter. In some cases however, we discuss how the choice of the variant may affect fundamental properties of the filtering.
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Rie Saotome
2015-01-01
Full Text Available In order to explore marine natural resources using remote robotic sensor or to enable rapid information exchange between ROV (remotely operated vehicles, AUV (autonomous underwater vehicle, divers, and ships, ultrasonic underwater communication systems are used. However, if the communication system is applied to rich living creature marine environment such as shallow sea, it suffers from generated Impulsive Noise so-called Shrimp Noise, which is randomly generated in time domain and seriously degrades communication performance in underwater acoustic network. With the purpose of supporting high performance underwater communication, a robust digital communication method for Impulsive Noise environments is necessary. In this paper, we propose OFDM ultrasonic communication system with diversity receiver. The main feature of the receiver is a newly proposed Frequency Domain Diversity Combined Impulsive Noise Canceller. The OFDM receiver utilizes 20–28 KHz ultrasonic channel and subcarrier spacing of 46.875 Hz (MODE3 and 93.750 Hz (MODE2 OFDM modulations. In addition, the paper shows Impulsive Noise distribution data measured at a fishing port in Okinawa and at a barge in Shizuoka prefectures and then proposed diversity OFDM transceivers architecture and experimental results are described. By the proposed Impulsive Noise Canceller, frame bit error rate has been decreased by 20–30%.
Microwave signal processing in two-frequency domain for ROF systems implementation: training course
Morozov, Oleg G.; Morozov, Gennady A.
2014-04-01
This article is presented materials from two tutorials: "Optical two-frequency domain reflectometry1, 2" and "Microwave technologies in industry, living systems and telecommunications3". These materials were prepared for master training courses and listed in the "SPIE Optical Education Directory" for 2013/2014. The main its theme is microwave photonics. Microwave photonics has been defined as the study of photonic devices operating at microwave frequencies and their application to microwave and optical systems. Its initial rationale was to use the advantages of photonic technologies to provide functions in microwave systems that are very complex or even impossible to carry out directly in the radiofrequency domain. But microwave photonics is also succeeding in incorporating a variety of techniques used in microwave engineering to improve the performance of photonic communication networks and systems. Three parts of this chapter are devoted to applications and construction principles of systems forming microwave photonic filters, measuring instantaneous frequency of microwave heterodyne signals and characterizing stimulated Mandelstam- Brillouin scattering spectrum in ROF systems. The main emphasis is on the use of the two-frequency symmetric radiation, generated by the Il'in-Morozov's method4, in given systems. It is forming radiation for the synthesis of optical filters coefficients, it's application and processing determine the increase in the signal-to-noise ratio during heterodyne frequencies monitoring and characterization of nonlinear effects spectrum.
Qin, Hongde; Shen, Jing; Chen, Xiaobo
2011-09-01
The free-surface Green function method is widely used in solving the radiation or diffraction problems caused by a ship or ocean structure oscillating on the waves. In the context of inviscid potential flow, hydrodynamic problems such as multi-body interaction and tank side wall effect cannot be properly dealt with based on the traditional free-surface frequency domain Green function method, in which the water viscosity is omitted and the energy dissipation effect is absent. In this paper, an open-sea Green function with viscous dissipation was presented within the theory of visco-potential flow. Then the tank Green function with a partial reflection from the side walls in wave tanks was formulated as a formal sum of open-sea Green functions representing the infinite images between two parallel side walls of the source in the tank. The new far-field characteristics of the tank Green function is vitally important for improving the validity of side-wall effects evaluation, which can be used in supervising the tank model tests.
Sharma, Vikas; Parey, Anand
2017-02-01
In the purview of fluctuating speeds, gear fault diagnosis is challenging due to dynamic behavior of forces. Various industrial applications employing gearbox which operate under fluctuating speed conditions. For diagnostics of a gearbox, various vibrations based signal processing techniques viz FFT, time synchronous averaging and time-frequency based wavelet transform, etc. are majorly employed. Most of the time, theories about data or computational complexity limits the use of these methods. In order to perform fault diagnosis of a gearbox for fluctuating speeds, frequency domain averaging (FDA) of intrinsic mode functions (IMFs) after their dynamic time warping (DTW) has been done in this paper. This will not only attenuate the effect of fluctuating speeds but will also extract the weak fault feature those masked in vibration signal. Experimentally signals were acquired from Drivetrain Diagnostic Simulator for different gear health conditions i.e., healthy pinion, pinion with tooth crack, chipped tooth and missing tooth and were analyzed for the different fluctuating profiles of speed. Kurtosis was calculated for warped IMFs before DTW and after DTW of the acquired vibration signals. Later on, the application of FDA highlights the fault frequencies present in the FFT of faulty gears. The result suggests that proposed approach is more effective towards the fault diagnosing with fluctuating speed.
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.
Frequency domain interferometry mode observations of PMSE using the EISCAT VHF radar
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P. B. Chilson
Full Text Available During the summer of 1997 investigations into the nature of polar mesosphere summer echoes (PMSE were conducted using the European incoherent scatter (EISCAT VHF radar in Norway. The radar was operated in a frequency domain interferometry (FDI mode over a period of two weeks to study the frequency coherence of the returned radar signals. The operating frequencies of the radar were 224.0 and 224.6 MHz. We present the first results from the experiment by discussing two 4-h intervals of data collected over two consecutive nights. During the first of the two days an enhancement of the FDI coherence, which indicates the presence of distinct scattering layers, was found to follow the lower boundary of the PMSE. Indeed, it is not unusual to observe that the coherence values are peaked around the heights corresponding to both the lower- and upper-most boundaries of the PMSE layer and sublayers. A Kelvin-Helmholtz mechanism is offered as one possible explanation for the layering structure. Additionally, our analysis using range-time-pseudocolor plots of signal-to-noise ratios, spectrograms of Doppler velocity, and estimates of the positions of individual scattering layers is shown to be consistent with the proposition that upwardly propagating gravity waves can become steepened near the mesopause.
Key words: Ionosphere (polar ionosphere · Meteorology and Atmospheric Dynamics (middle atmosphere dynamics · Radio Science (Interferometry
Murdock, Richard J; Putnam, Shawn A; Das, Soumen; Gupta, Ankur; Chase, Elyse D Z; Seal, Sudipta
2017-01-16
A clinically relevant magneto-optical technique (fd-FRS, frequency-domain Faraday rotation spectroscopy) for characterizing proteins using antibody-functionalized magnetic nanoparticles (MNPs) is demonstrated. This technique distinguishes between the Faraday rotation of the solvent, iron oxide core, and functionalization layers of polyethylene glycol polymers (spacer) and model antibody-antigen complexes (anti-BSA/BSA, bovine serum albumin). A detection sensitivity of ≈10 pg mL(-1) and broad detection range of 10 pg mL(-1) ≲ cBSA ≲ 100 µg mL(-1) are observed. Combining this technique with predictive analyte binding models quantifies (within an order of magnitude) the number of active binding sites on functionalized MNPs. Comparative enzyme-linked immunosorbent assay (ELISA) studies are conducted, reproducing the manufacturer advertised BSA ELISA detection limits from 1 ng mL(-1) ≲ cBSA ≲ 500 ng mL(-1) . In addition to the increased sensitivity, broader detection range, and similar specificity, fd-FRS can be conducted in less than ≈30 min, compared to ≈4 h with ELISA. Thus, fd-FRS is shown to be a sensitive optical technique with potential to become an efficient diagnostic in the chemical and biomolecular sciences.
Ghaffari, A.; Klumperink, Eric A.M.; van Vliet, Frank Edward; Nauta, Bram
2014-01-01
To reject strong interference in excess of 0 dBm, a 4- element LO-phase shifting phased-array receiver with 8-phase passive mixers terminated by baseband capacitors is presented. The passive mixers upconvert both the spatial and frequency domain filtering from baseband to RF, hence realizing blocker
Electromagnetic aquametry electromagnetic wave interaction with water and moist substances
Kupfer, Klaus
2006-01-01
This book covers all aspects of Electromagnetic Aquametry. It summarizes the wide area of metrology and its applications in electromagnetic sensing of moist materials. The physical properties of water in various degrees of binding interacting with electromagnetic fields is presented by model systems. The book describes measurement methods and sensors in the frequency domain, TDR-techniques for environmental problems, methods and sensors for quality assessment of biological substances, and nuclear magnetic resonance techniques. Environmental sciences, as well as civil and geoengineering, fossil fuels, food and pharmaceutical science are the main fields of application. A very wide frequency sprectrum is used for dielectric measurement methods, but the microwave range is clearly dominant. Multiparameter methods as well as methods of principal components and artificial neural networks for density independent measurements are described.
Directory of Open Access Journals (Sweden)
Gul Ar Navi Khan
2014-08-01
Full Text Available Background: Preeclampsia is a disorder characterized by development of hypertension to the extent of 140/90 mmHg or more with proteinuria after 20th weeks of pregnancy in a previously normotensive and non proteinuric woman. Physiologically blood pressure is controlled by Autonomic Nervous System (ANS so study of ANS during pregnancy plays a significant role to extract some vital information which may be helpful to deal with Pregnancy Induced Hypertension (PIH or preeclampsia. The autonomic nervous system and changes in ANS during different pathophysiological conditions could be evaluated with heart rate variability analysis test. The modification in the autonomic control occurs during pregnancy and its evaluation through Heart Rate Variability (HRV analysis is very informative technique now a day but studied little thus the main objective of our project is to compare the maternal HRV changes between normal pregnancy and pre-eclamptic pregnancy. Methods: 48 subjects (33 of normotensive pregnant women i.e., control group and 15 pre-eclamptic pregnant women i.e, study group of more than 20 weeks pregnancy were recruited from the outpatients, antenatal unit and wards of obstetrics and gynaecology department of JNMC, AMU, Aligarh. Physical examination was done and anthropometric measurement like height and weight were taken. BMI was calculated as per Quetlet's index. Urine test was conducted to every pregnant woman for urine albumin and we designated the pregnant women as pre-eclamptic women on the basis of definition. The subject was advised to take complete bed rest in supine position for 15 minutes in a cool and calm environment. The recording of short term HRV was done according to recommendation of the task force on HRV. The data was transferred from Medicaid machine to window based computer with HRV analysis software. Frequency domain analysis of HRV was taken for further statistical analysis. Results: There was no significant difference of
Mosher, Mark
Within a wave energy converter's operational bandwidth, device operation tends to be optimal in converting mechanical energy into a more useful form at an incident wave period that is proximal to that of a power-producing mode of motion. Point absorbers, a particular classification of wave energy converters, tend to have a relative narrow optimal bandwidth. When not operating within the narrow optimal bandwidth, a point absorber's response and efficiency is attenuated. Given the wide range of sea-states that can be expected during a point absorber's operational life, these devices require a means to adjust, or control, their natural response to maximize the amount of energy absorbed in the large population of non-optimal conditions. In the field of wave energy research, there is considerable interest in the use of non-linear control techniques to this end. Non-linear control techniques introduce time-varying and state dependent control parameters into the point absorber motion equations, which usually motivates a computationally expensive numerical integration to determine the response of the device - important metrics such as gross converted power and relative travels of the device's pieces are extracted through post processing of the time series data. As an alternative, the work presented in this thesis was based on a closed form perturbation based approach for analysis of the response of a device with periodically-varying control parameters, subject to regular wave forcing, in the frequency domain. The proposed perturbation based method provides significant savings in computational time and enables the device's response to be represented in a closed form manner with a relatively small number of solution components - each component is comprised of a complex amplitude and oscillation frequency. This representation of the solution was found to be very concise and descriptive, and to lend itself to the calculation of gross absorbed power and travel constraint
Frequency domain analysis of heart rate variability in horses at rest and during exercise.
Physick-Sheard, P W; Marlin, D J; Thornhill, R; Schroter, R C
2000-05-01
The pattern of variation in heart rate on a beat-to-beat basis contains information concerning sympathetic (SNS) and parasympathetic (PNS) contributions to autonomic nervous system (ANS) modulation of heart rate (HR). In the present study, heart period (RR interval) time series data were collected at rest and during 3 different treadmill exercise protocols from 6 Thoroughbred horses. Frequency and spectral power were determined in 3 frequency bands: very low (VLF) 0-0.01-0.07-< or = 0.5 cycles/beat. Indicators of sympathetic (SNSI = LO/HI) and parasympathetic (PNSI = HI/TOTAL) activity were calculated. Power in all bands fell progressively with increasing exercise intensity from rest to trot. At the gallop VLF and LO power continued to fall but HI power rose. SNSI rose from rest to walk, then fell with increasing effort and was lowest at the gallop. PNSI fell from rest to walk, then rose and was highest at the gallop. Normalised HI power exceeded combined VLF and LO power at all gaits, with the ratio HI to LO power being lowest at the walk and highest at the gallop. ANS indicators showed considerable inter-horse variation, and varied less consistently than raw power with increasing physical effort. In the horses studied, the relationship between power and HR changed at exercise intensities associated with heart rates above approximately 120-130 beats/min. At this level, humoral and other non-neural mechanisms may become more important than autonomic modulation in influencing heart rate and heart rate variability (HRV). HRV at intense effort may be influenced by respiratory-gait entrainment, energetics of locomotion and work of breathing. HRV analysis in the frequency domain would appear to be of potential value as a noninvasive means of assessing autonomic modulation of heart rate at low exercise intensities, only. The technique may be a sensitive method for assessing exercise response to experimental manipulations and disease states.
2.5-D frequency-domain viscoelastic wave modelling using finite-element method
Zhao, Jian-guo; Huang, Xing-xing; Liu, Wei-fang; Zhao, Wei-jun; Song, Jian-yong; Xiong, Bin; Wang, Shang-xu
2017-10-01
2-D seismic modelling has notable dynamic information discrepancies with field data because of the implicit line-source assumption, whereas 3-D modelling suffers from a huge computational burden. The 2.5-D approach is able to overcome both of the aforementioned limitations. In general, the earth model is treated as an elastic material, but the real media is viscous. In this study, we develop an accurate and efficient frequency-domain finite-element method (FEM) for modelling 2.5-D viscoelastic wave propagation. To perform the 2.5-D approach, we assume that the 2-D viscoelastic media are based on the Kelvin-Voigt rheological model and a 3-D point source. The viscoelastic wave equation is temporally and spatially Fourier transformed into the frequency-wavenumber domain. Then, we systematically derive the weak form and its spatial discretization of 2.5-D viscoelastic wave equations in the frequency-wavenumber domain through the Galerkin weighted residual method for FEM. Fixing a frequency, the 2-D problem for each wavenumber is solved by FEM. Subsequently, a composite Simpson formula is adopted to estimate the inverse Fourier integration to obtain the 3-D wavefield. We implement the stiffness reduction method (SRM) to suppress artificial boundary reflections. The results show that this absorbing boundary condition is valid and efficient in the frequency-wavenumber domain. Finally, three numerical models, an unbounded homogeneous medium, a half-space layered medium and an undulating topography medium, are established. Numerical results validate the accuracy and stability of 2.5-D solutions and present the adaptability of finite-element method to complicated geographic conditions. The proposed 2.5-D modelling strategy has the potential to address modelling studies on wave propagation in real earth media in an accurate and efficient way.
Frequency-domain L2-stability conditions for time-varying linear and nonlinear MIMO systems
Institute of Scientific and Technical Information of China (English)
Zhihong HUANG; Y. V. VENKATESH; Cheng XIANG; Tong Heng LEE
2014-01-01
The paper deals with the L2-stability analysis of multi-input-multi-output (MIMO) systems, governed by integral equations, with a matrix of periodic/aperiodic time-varying gains and a vector of monotone, non-monotone and quasi-monotone nonlin-earities. For nonlinear MIMO systems that are described by differential equations, most of the literature on stability is based on an application of quadratic forms as Lyapunov-function candidates. In contrast, a non-Lyapunov framework is employed here to derive new and more general L2-stability conditions in the frequency domain. These conditions have the following features:i) They are expressed in terms of the positive definiteness of the real part of matrices involving the transfer function of the linear time-invariant block and a matrix multiplier function that incorporates the minimax properties of the time-varying linear/nonlinear block. ii) For certain cases of the periodic time-varying gain, they contain, depending on the multiplier function chosen, no restrictions on the normalized rate of variation of the time-varying gain, but, for other periodic/aperiodic time-varying gains, they do. Overall, even when specialized to periodic-coefficient linear and nonlinear MIMO systems, the stability conditions are distinct from and less restrictive than recent results in the literature. No comparable results exist in the literature for aperiodic time-varying gains. Furthermore, some new stability results concerning the dwell-time problem and time-varying gain switching in linear and nonlinear MIMO systems with periodic/aperiodic matrix gains are also presented. Examples are given to illustrate a few of the stability theorems.
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.
Gizon, Laurent; Barucq, Hélène; Duruflé, Marc; Hanson, Chris S.; Leguèbe, Michael; Birch, Aaron C.; Chabassier, Juliette; Fournier, Damien; Hohage, Thorsten; Papini, Emanuele
2017-03-01
Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims: Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods: We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results: We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions: The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.
Multimedia Traffic Queueing Analysis in High-Speed Networks: a Frequency Domain Approach
Hwang, Chia-Lin
Multimedia traffic in high speed networks possesses correlation and burstiness properties. Classical queueing theory has generally ignored such properties by making renewal assumption on message interarrival time. Developing a new traffic theory for integration of multimedia services on high speed networks becomes absolutely essential. In this dissertation, we explore a new concept of spectral characterization of wide-band input process in high speed networks. It provides us a much richer and heterogeneous input environment, while keeping the complexity of queueing analysis tractable. The correlation nature of multimedia traffic is well captured by the input spectral functions. The queue response to the power spectrum and higher order statistics has been studied. Our study shows that the input power spectrum is the most essential statistic for queueing analysis. Further, the input power in low-frequency band has dominant impact on queueing performance, whereas the high-frequency power to a large extent can be neglected. Understanding of queue response to input spectrum provides us a great deal of knowledge to develop advanced network traffic measure theory, and to introduce effective network resource allocation policies. The interrelationship between the traffic spectral statistics and link capacity allocation in high speed network has been investigated. Finally we developed a sophisticated computational tool, called SMAQ, that can integrate traffic measurement and queueing analysis for stochastic modeling. The SMAQ tool takes a unique frequency-domain approach to combine the techniques of signal processing and performance analysis. Essentially, signal processing techniques are used to obtain the steady -state and second-order statistics of a traffic stream. The focus here is on the construction of a special class of Markov chains that can statistically match with each given traffic stream (or superposition of different traffic streams). The analytical queueing
Frequency domain phase noise analysis of dual injection-locked optoelectronic oscillators.
Jahanbakht, Sajad
2016-10-01
Dual injection-locked optoelectronic oscillators (DIL-OEOs) have been introduced as a means to achieve very low-noise microwave oscillations while avoiding the large spurious peaks that occur in the phase noise of the conventional single-loop OEOs. In these systems, two OEOs are inter-injection locked to each other. The OEO with the longer optical fiber delay line is called the master OEO, and the other is called the slave OEO. Here, a frequency domain approach for simulating the phase noise spectrum of each of the OEOs in a DIL-OEO system and based on the conversion matrix approach is presented. The validity of the new approach is verified by comparing its results with previously published data in the literature. In the new approach, first, in each of the master or slave OEOs, the power spectral densities (PSDs) of two white and 1/f noise sources are optimized such that the resulting simulated phase noise of any of the master or slave OEOs in the free-running state matches the measured phase noise of that OEO. After that, the proposed approach is able to simulate the phase noise PSD of both OEOs at the injection-locked state. Because of the short run-time requirements, especially compared to previously proposed time domain approaches, the new approach is suitable for optimizing the power injection ratios (PIRs), and potentially other circuit parameters, in order to achieve good performance regarding the phase noise in each of the OEOs. Through various numerical simulations, the optimum PIRs for achieving good phase noise performance are presented and discussed; they are in agreement with the previously published results. This further verifies the applicability of the new approach. Moreover, some other interesting results regarding the spur levels are also presented.
Sauvé, Alexandre; Montier, Ludovic
2016-10-01
uc(Context): Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for ν knowledge of detector response. However bolometers have highly nonlinear characteristics, coming from their electrical and thermal coupling making them very difficult to model. uc(Goal): We present a method to build the analytical transfer function in frequency domain which describe the voltage response of an Alternative Current (AC) biased bolometer to optical excitation, based on the standard bolometer model. This model is built using the setup of the Planck/HFI instrument and offers the major improvement of being based on a physical model rather than the currently in use had-hoc model based on Direct Current (DC) bolometer theory. uc(Method): The analytical transfer function expression will be presented in matrix form. For this purpose, we build linearized versions of the bolometer electro thermal equilibrium. A custom description of signals in frequency is used to solve the problem with linear algebra. The model performances is validated using time domain simulations. uc(Results): The provided expression is suitable for calibration and data processing. It can also be used to provide constraints for fitting optical transfer function using real data from steady state electronic response and optical response. The accurate description of electronic response can also be used to improve the ADC nonlinearity correction for quickly varying optical signals.
Zhu, Kaixian; Chemla, Denis; Roisman, Gabriel; Mao, Wenyuan; Bazizi, Samir; Lefevre, Amaury; Escourrou, Pierre
2012-11-01
Heightened sympathetic activity plays a role in the cardiovascular sequelae of obstructive sleep apnoea (OSA). Cardiac autonomic function may be assessed non-invasively by studying heart rate variability (HRV). The aim of the present study was to compare overnight HRV between a control group and a group of subjects with severe OSA. The potential confounding effects of age, sex, baseline autonomic status and sleep stage distribution were taken into account. Our prospective Holter study compared overnight (0030-0530 hours) HRV in 23 controls (apnoea hypopnoea index (AHI) = 5 ± 3 /h) and 23 subjects with severe OSA (AHI = 65 ± 23 /h), matched for age and sex and with a similar percentage of rapid eye movement sleep. The mean normal-to-normal RR interval (NN) was shorter in the OSA compared with control group (903 vs 1039 ms, respectively), whereas the other time-domain indices of HRV, as well as the classic frequency-domain indices, were similar. Essentially similar results were obtained hourly and when only subjects with high mean values of the standard deviation of all NN (≥ 90 ms) were evaluated. In the 0.01-0.06 Hz range corresponding to the typical OSA pattern of bradycardia-tachycardia termed cyclic variation of heart rate (CVHR), higher power was documented hourly in OSA, with a significant correlation between overnight power and both AHI and mean oxyhaemoglobin saturation. The percentage of NN > x ms different from the previous one (pNNx family) had no diagnostic value. The results of the present study suggest that NN may be the best index to quantify the overnight sympathovagal balance in OSA and that a spectral band overlapping the apnoea-related pattern of CVHR slightly improved the characterization of the apnoea-related HRV patterns.
Theory of the time reversal cavity for electromagnetic fields.
Carminati, R; Pierrat, R; de Rosny, J; Fink, M
2007-11-01
We derive a general expression of the electric dyadic Green function in a time-reversal cavity, based on vector diffraction theory in the frequency domain. Our theory gives a rigorous framework to time-reversal experiments using electromagnetic waves and suggests a methodology to design structures generating subwavelength focusing after time reversal.
Characterization of shallow ocean sediments using the airborne electromagnetic method
Won, I. J.; Smits, K.
1986-01-01
Experimental airborne electromagnetic (AEM) survey data collected in Cape Cod Bay are used to derive continuous profiles of water depth, electrical depth, water conductivity, and bottom sediment conductivity. Through a few well-known empirical relationships, the conductivities are used, in turn, to derive density, porosity, sound speed, and acoustic reflectivity of the ocean bottom. A commercially available Dighem III AEM system was used for the survey without any significant modification. The helicopter-borne system operated at 385 and 7200 Hz; both were in a horizontal coplanar configuration. The interpreted profiles show good agreement with available ground truth data. Where no such data are available, the results appear to be very reasonable. Compared with the shipborne electrode array method, the AEM method can determine the necessary parameters at a much higher speed with a better lateral resolution over a wide range of water depths from 0 to perhaps 100 m. The bottom sediment conductivity that can be measured by the AEM method is closely related to physical properties of sediments, such as porosity, density, sound speed, and, indirectly, sediment types that might carry broad implications for various offshore activities.
Frequency domain reflectometry NDE for aging cables in nuclear power plants
Glass, S. W.; Jones, A. M.; Fifield, L. S.; Hartman, T. S.
2017-02-01
Degradation of the cable jacket, electrical insulation, and other cable components of installed cables within nuclear power plants (NPPs) is known to occur as a function of age, temperature, radiation, and other environmental factors. Although system tests verify cable function under normal loads, demonstration of some cable's ability to perform under exceptional loads associated with design-basis events is essential to assuring plant integrity. The cable's ability to perform safely over the initial 40-year planned and licensed life has generally been demonstrated and there have been very few age-related cable failures. With greater than 1000 km of power, control, instrumentation, and other cables typically found in an NPP, replacing all the cables would be a severe cost burden. Justification for life extension to 60 and 80 years requires a cable aging management program that includes condition monitoring to justify cable performance under normal operation as well as accident conditions. A variety of tests are available to assess various aspects of electrical and mechanical cable performance, but none are suitable for all cable configurations nor does any single test confirm all features of interest. One particularly promising test that is beginning to be used more and more by utilities is frequency domain reflectometry (FDR). FDR is a nondestructive electrical inspection technique used to detect and localize faults in power and communication system conductors along the length of a cable from a single connection point. FDR detects discontinuities in the electrical impedance that arise due to cable splices or similar changes along the path of the conductor pair. In addition, FDR has the potential to provide sensitivity to insulation degradation by detecting small changes in impedance between the cable conductors being examined. The technique is also sensitive to cable bends, the particular lay of the cable in tray, proximity to other cable, and other factors that
Bramhavar, Suraj
The concept of optical excitation and detection of nanoscale mechanical motion has led to a variety of tools for non-destructive materials characterization and remote sensing. These techniques, commonly referred to as laser ultrasonics, offer the benefit of high-bandwidth, highly localized measurements, and also allow for the ability to investigate nanoscale devices. The impact of laser ultrasonic systems has been felt in industries ranging from semiconductor metrology to biological and chemical sensing. In this thesis, we develop a variety of techniques utilizing a frequency domain laser ultrasonic approach, where amplitude modulated continuous wave laser light is used instead of traditional pulsed laser sources, and we apply these systems in free-space, optical fiber based, and integrated on-chip configurations. In doing so, we demonstrate the ability to efficiently transduce various types of mechanical motion including surface and bulk acoustic waves, guided acoustic waves, and resonant motion from nanomechanical systems (NEMS). First, we develop a superheterodyne free-space ultrasonic inspection system in an effort to characterize surface acoustic wave dispersion in thin-film material systems. We utilize a similar system to study negative refraction and focusing behavior of guided elastic waves in a thin metal plate, providing a novel approach for the study of negative index physics. Furthermore, we develop a near-field optical technique using optical fibers to simultaneously transduce the motion of 70 NEMS resonators using a single channel. This multiplexed approach serves as a crucial step in moving NEMS technology out of the research laboratory. Finally, we go on to study opto-mechanical interactions between optical whispering gallery mode (WGM) resonators and integrated NEMS devices on the same chip, using the enhanced interactions to study optical forces acting on the nanoscale mechanical devices. This integrated system provides a very efficient mechanical
Renormalized scattering series for frequency-domain waveform modelling of strong velocity contrasts
Jakobsen, M.; Wu, R. S.
2016-08-01
An improved description of scattering and inverse scattering processes in reflection seismology may be obtained on the basis of a scattering series solution to the Helmoltz equation, which allows one to separately model primary and multiple reflections. However, the popular scattering series of Born is of limited seismic modelling value, since it is only guaranteed to converge if the global contrast is relatively small. For frequency-domain waveform modelling of realistic contrasts, some kind of renormalization may be required. The concept of renormalization is normally associated with quantum field theory, where it is absolutely essential for the treatment of infinities in connection with observable quantities. However, the renormalization program is also highly relevant for classical systems, especially when there are interaction effects that act across different length scales. In the scattering series of De Wolf, a renormalization of the Green's functions is achieved by a split of the scattering potential operator into fore- and backscattering parts; which leads to an effective reorganization and partially re-summation of the different terms in the Born series, so that their order better reflects the physics of reflection seismology. It has been demonstrated that the leading (single return) term in the De Wolf series (DWS) gives much more accurate results than the corresponding Born approximation, especially for models with high contrasts that lead to a large accumulation of phase changes in the forward direction. However, the higher order terms in the DWS that are associated with internal multiples have not been studied numerically before. In this paper, we report from a systematic numerical investigation of the convergence properties of the DWS which is based on two new operator representations of the DWS. The first operator representation is relatively similar to the original scattering potential formulation, but more global and explicit in nature. The second
First Frequency-Domain Interferometry Observations of Large-Scale Vertical Motion in the Atmosphere.
Muschinski, Andreas; Chilson, Phillip B.; Kern, Stefan; Nielinger, Jost; Schmidt, Gerhard; Prenosil, Thomas
1999-05-01
The spatiotemporal distribution of the vertical velocity at synoptic and subsynoptic scales is key to the patterns of weather and climate on earth. On these scales, the vertical velocity is on the order of one to a few centimeters per second, typically about three orders of magnitude smaller than typical horizontal wind velocities. Because of the smallness of large-scale vertical velocities relative to typical horizontal velocities, a direct observation of the large-scale vertical air velocity is extremely difficult.In a case study on observational material obtained during a 68-h experiment using the SOUSY very high frequency (VHF) radar in the Harz Mountains in Germany, the authors present the first intercomparison between three different sources of physical information that can provide large-scale vertical wind velocities: (i) the Doppler shifts observed with a vertically pointing VHF radar; (ii) the rates of change of the altitudes of refractive-index discontinuities as identified with frequency-domain interferometry (FDI), which is still a relatively unexplored technique in meteorology; and (iii) the output of a regional numerical weather prediction model (NWPM), which has been set up to model the meteorological situation during the observational period.There are several phenomena that have been known to possibly cause significant biases in mean vertical velocities retrieved from the Doppler shifts measured with vertically pointing clear-air VHF radars: (i) stationary or nonstationary gravity waves with vertical-velocity amplitudes up to the order of 1 m s1; (ii) stationary or horizontally advected tilted refractive-index discontinuities that are aspect sensitive in the VHF regime; and (iii) a correlation between the radar-reflectivity fluctuations and the vertical-velocity fluctuations within a vertically propagating gravity wave.On the basis of an intercomparison between the vertical velocities retrieved from (i) `standard Doppler' VHF radar observations, (ii
Quantitative frequency-domain fluorescence spectroscopy in tissues and tissue-like media
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
Planar Lithographed Superconducting LC Resonators for Frequency-Domain Multiplexed Readout Systems
Rotermund, K.; Barch, B.; Chapman, S.; Hattori, K.; Lee, A.; Palaio, N.; Shirley, I.; Suzuki, A.; Tran, C.
2016-07-01
Cosmic microwave background (CMB) polarization experiments are increasing the number of transition edge sensor (TES) bolometers to increase sensitivity. In order to maintain low thermal loading of the sub-Kelvin stage, the frequency-domain multiplexing (FDM) factor has to increase accordingly. FDM is achieved by placing TES bolometers in series with inductor-capacitor (LC) resonators, which select the readout frequency. The multiplexing factor can be raised with a large total readout bandwidth and small frequency spacing between channels. The inductance is kept constant to maintain a uniform readout bandwidth across detectors, while the maximum acceptable value is determined by bolometer stability. Current technology relies on commercially available ceramic chip capacitors. These have high scatter in their capacitance thereby requiring large frequency spacing. Furthermore, they have high equivalent series resistance (ESR) at higher frequencies and are time consuming and tedious to hand assemble via soldering. A solution lies in lithographed, planar spiral inductors (currently in use by some experiments) combined with interdigitated capacitors on a silicon (Si) substrate. To maintain reasonable device dimensions, we have reduced trace and gap widths of the LCs to 4 \\upmu m. We increased the inductance from 16 to 60 \\upmu H to achieve a higher packing density, a requirement for FDM systems with large multiplexing factors. Additionally, the Si substrate yields low ESR values across the entire frequency range and lithography makes mass production of LC pairs possible. We reduced mutual inductance between inductors by placing them in a checkerboard pattern with the capacitors, thereby increasing physical distances between adjacent inductors. We also reduce magnetic coupling of inductors with external sources by evaporating a superconducting ground plane onto the backside of the substrate. We report on the development of lithographed LCs in the 1-5 MHz range for use
Comparison of misfit functions for phase-only inversion in the frequency domain
Jeong, G.; Jeong, W.; Min, D. J.
2014-12-01
Full waveform inversion suffers from non-uniqueness and non-linearity problems. By using kinematic property of wavefield rather than dynamic property, we can mitigate such problems because the phase is linear and robust (Kamei et al. 2013). For the phase-only inversion, several misfit functions were suggested. Bednar et al. (2007) compared the logarithmic phase-only inversion proposed by Shin and Min (2006) with the conventional phase-only inversion. On the other hand, Kamei et al. (2014) introduced another method that uses the exponential of phase by normalizing the wavefield with respect to the amplitude. In this study, we compare the aforementioned three phase-only inversion methods in the frequency domain: i) the logarithmic phase-only inversion, ii) the conventional phase-only inversion I (briefly conventional I method) that normalizes wavefield with respect to the amplitude variation, and iii) the conventional phase-only inversion II (briefly conventional II method) that replaces the amplitude of the modeled data with that of field data. In the cases of the logarithmic and conventional I methods, if the modeled signal function is close to 0 or becomes large, the gradients of the misfit function diverge to infinity or converge to 0, respectively. In contrast, the conventional II method does not suffer from these problems. For fair comparison, we removed extremely small or large values with Gaussian filtering to avoid the instability problem in the logarithmic and conventional I methods. In addition, we assumed that the phase of the field data is unwrapped to the same degree as the phase of the modeled data in all the cases. On the other hand, the logarithmic and conventional II methods require the additional assumption that amplitudes of the field data are the same as those of the modeled data. However, the conventional I method does not require such an assumption. Our numerical examples show that the conventional I method yields more robust and accurate
Porto, Italo; Di Vito, Luca; Burzotta, Francesco; Niccoli, Giampaolo; Trani, Carlo; Leone, Antonio M; Biasucci, Luigi M; Vergallo, Rocco; Limbruno, Ugo; Crea, Filippo
2012-02-01
Frequency-domain optical coherence tomography (FD-OCT) is easily able to define both pre- and post-stenting features of the atherosclerotic plaque that can potentially be related to periprocedural complications. We sought to examine which FD-OCT-defined characteristics, assessed both before and after stent deployment, predicted periprocedural (type IVa) myocardial infarction (MI). FD-OCT was performed before and after coronary stenting in 50 patients undergoing percutaneous coronary intervention (PCI) for either non-ST segment elevation MI (NSTEMI) or stable angina. All patients underwent single-vessel stenting, and only drug-eluting stents were implanted. Troponin T was analyzed on admission, before PCI, and at 12 and 24 hours after PCI, and type IVa MI was defined in stable angina as a rise of at least 3× upper reference limit and in NSTEMI as a pre-PCI troponin T fall, followed by post-PCI troponin T rise >20%. Type IVa MI was diagnosed in 21 patients, while the remaining 29 represented the control group. FD-OCT analysis showed that thin-cap fibroatheroma (76.2% versus 41.4%; P=0.017) prior to PCI, intrastent thrombus (61.9% versus 20.7%; P=0.04), and intrastent dissection (61.9% versus 31%; P=0.03) after PCI were significantly more frequent in type IVa MI than in the control group. Multivariate logistic regression analysis confirmed thin-cap fibroatheroma (OR 29.7, 95% CI 1.4 to 32.1), intrastent thrombus (OR 5.5, CI 1.2 to 24.9) and intrastent dissection (OR 5.3, CI 1.2 to 24.3) as independent predictors of type IVa MI. In conclusion, presence of thin-cap fibroatheroma at pre-PCI FD-OCT and of intrastent thrombus and intrastent dissection at post-PCI FD-OCT predict type IVa MI in a contemporary sample of patients treated with second-generation drug-eluting stents. Interestingly, 2 of the 3 predictors of type IVa MI were not apparent at pre-PCI FD-OCT.
Institute of Scientific and Technical Information of China (English)
Z.J.YANG; A.J.DEEKS
2008-01-01
A frequency-domain approach based on the semi-analytical scaled boundary finite element method (SBFEM) was developed to calculate dynamic stress intensity factors (DSIFs) at bimaterial interface cracks subjected to transient loading. Be-cause the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction, and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions, the mixed-mode DSIFs were calculated directly by definition. The complex frequency-response functions of DSIFs were then used by the fast Fourier transform (FFT) and the inverse FFT to calculate time histories of DSIFs. A benchmark example was modelled. Good re-sults were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM.
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.
Kierkegaard, Axel; Boij, Susann; Efraimsson, Gunilla
2010-02-01
Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.
Energy Technology Data Exchange (ETDEWEB)
Duan Zhisheng [State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics and Engineering Science, Peking University, Beijing 100871 (China)], E-mail: duanzs@pku.edu.cn; Wang Jinzhi; Yang Ying; Huang Lin [State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics and Engineering Science, Peking University, Beijing 100871 (China)
2009-04-30
This paper surveys frequency-domain and time-domain methods for feedback nonlinear systems and their possible applications to chaos control, coupled systems and complex dynamical networks. The absolute stability of Lur'e systems with single equilibrium and global properties of a class of pendulum-like systems with multi-equilibria are discussed. Time-domain and frequency-domain criteria for the convergence of solutions are presented. Some latest results on analysis and control of nonlinear systems with multiple equilibria and applications to chaos control are reviewed. Finally, new chaotic oscillating phenomena are shown in a pendulum-like system and a new nonlinear system with an attraction/repulsion function.
Nakamura, Satoshi; Goto, Hayato; Kujiraoka, Mamiko; Ichimura, Kouichi
2016-12-01
We propose a scheme for frequency-domain quantum computation (FDQC) in which the errors due to crosstalk are suppressed using extra physical systems coupled to a cavity. FDQC is a promising method to realize large-scale quantum computation, but crosstalk is a major problem. When physical systems employed as qubits satisfy specific resonance conditions, gate errors due to crosstalk increase. In our scheme, the errors are suppressed by controlling the resonance conditions using extra physical systems.
DEFF Research Database (Denmark)
Pokhariyal, Akhilesh; Pedersen, Klaus I.; Monghal, Guillaume Damien
2007-01-01
and fairness control. By dividing the packet scheduler into a time-domain and a frequency-domain part we can effectively control the fairness among users. Different algorithms are applied at each scheduler part and the combined performance is evaluated in terms of cell throughput, coverage and capacity (number...... of a 20% loss in average cell throughput in comparison to the proportional fair scheduler....
Indian Academy of Sciences (India)
Qian Lin; Xiaofeng Wu; Yun Chen
2015-12-01
This paper studies the global synchronization of non-autonomous, time-delay, chaotic power systems via linear state-error feedback control. The frequency domain criterion and the LMI criterion are proposed and applied to design the coupling matrix. Some algebraic criteria via a single-variable linear coupling are derived and formulated in simple algebraic inequalities. The effectiveness of the new criteria is illustrated with numerical examples.
GUM2DFT—a software tool for uncertainty evaluation of transient signals in the frequency domain
Eichstädt, S.; Wilkens, V.
2016-05-01
The Fourier transform and its counterpart for discrete time signals, the discrete Fourier transform (DFT), are common tools in measurement science and application. Although almost every scientific software package offers ready-to-use implementations of the DFT, the propagation of uncertainties in line with the guide to the expression of uncertainty in measurement (GUM) is typically neglected. This is of particular importance in dynamic metrology, when input estimation is carried out by deconvolution in the frequency domain. To this end, we present the new open-source software tool GUM2DFT, which utilizes closed formulas for the efficient propagation of uncertainties for the application of the DFT, inverse DFT and input estimation in the frequency domain. It handles different frequency domain representations, accounts for autocorrelation and takes advantage of the symmetry inherent in the DFT result for real-valued time domain signals. All tools are presented in terms of examples which form part of the software package. GUM2DFT will foster GUM-compliant evaluation of uncertainty in a DFT-based analysis and enable metrologists to include uncertainty evaluations in their routine work.
Decay-ratio calculation in the frequency domain with the LAPUR code using 1D-kinetics
Energy Technology Data Exchange (ETDEWEB)
Munoz-Cobo, J. L.; Escriva, A.; Garcia, C.; Berna, C. [Instituto de Ingenieria Energetica, Universitat Politecnica de Valencia, Camino de Vera s/n, Valencia 46022 (Spain); Melara, J. [IBERDROLA Ingenieria Y Construccion, C/ Jose Bardasano Baos 9, 28016 Madrid (Spain)
2012-07-01
This paper deals with the problem of computing the Decay Ratio in the frequency domain codes as the LAPUR code. First, it is explained how to calculate the feedback reactivity in the frequency domain using slab-geometry i.e. 1D kinetics, also we show how to perform the coupling of the 1D kinetics with the thermal-hydraulic part of the LAPUR code in order to obtain the reactivity feedback coefficients for the different channels. In addition, we show how to obtain the reactivity variation in the complex domain by solving the eigenvalue equation in the frequency domain and we compare this result with the reactivity variation obtained in first order perturbation theory using the 1D neutron fluxes of the base case. Because LAPUR works in the linear regime, it is assumed that in general the perturbations are small. There is also a section devoted to the reactivity weighting factors used to couple the reactivity contribution from the different channels to the reactivity of the entire reactor core in point kinetics and 1D kinetics. Finally we analyze the effects of the different approaches on the DR value. (authors)
Efficient 2D and 3D multiparameters frequency-domain full waveform inversion (Invited)
Virieux, J.; Operto, S.; Ribodetti, A.; Ben Hadj Ali, H.; Brossier, R.; Etienne, V.; Gholami, Y.; Hu, G.; Jia, Y.; Pageot, D.; Prieux, V.
2010-12-01
With the tremendous increase of the computational power provided by large-scale distributed-memory platforms and the development of dense 3D multi-component wide-aperture/wide-azimuth surveys, full waveform inversion (FWI) introduced in geophysics by Albert Tarantola has become a re-emerging technique to build high-resolution velocity models of the subsurface. Because of the cost of the forward modeling and the high dimensionality of the model space, full waveform inversion is actually a local optimization problem, the aim of which is the minimization of the misfit between the recorded and modeled seismic wavefields. Among all possible minimization criteria, the L1 norm provides the most robust and easy-to-tune criterion. With such criterion, white noise in all seismograms with outliers does not prevent the convergence to the nearly same minimum as for noise-free data. The frequency formulation of the FWI allows coarse sampling of the frequencies data over few frequencies for the reconstruction of the medium when wide-aperture geometries are considered. A preconditioned quasi-Newton L-BFGS modified algorithm provides scaled gradients of the misfit function for each class of parameters. The gradient is computed by the adjoint-state method where the forward field is stored in the core memory of the computer while computing the backpropagation of residuals for cross-correlation at each point of the medium, thanks to the frequency-domain approach. We are using a sequential multiscale hierarchical inversion algorithm with two nested levels of data preconditioning with respect to frequency and first-arrival time. We are able to reconstruct both Vp and Vs velocity structures in various offshore and onshore environments various configurations of crustal investigation where both body waves (and surface) waves are progressively included in the inversion scheme. Solving the forward problem for 2D geometry could be efficiently performed in frequency by using a direct solver
Frequency-domain photoacoustic imaging system%频率域光声成像系统的研究
Institute of Scientific and Technical Information of China (English)
杨虹; 黄远辉; 苗少峰; 宫睿; 邵晓鹏; 毕祥丽
2016-01-01
Frequency-domain photoacoustic imaging is a new imaging modality, which uses the output amplitude information periodically modulated by a continuous-wave laser as a light source to stimulate biological tissues and to produce photoacoustic signals processed at frequency-domain and used to image the tissues. Firstly, the principles, developments and research status of photoacoustic imaging and frequency-domain photoacoustic imaging were introduced, and then the specific test methods and basic reconstruction algorithms of the frequency-domain photoacoustic imaging filed were described. In order to make up for time domain photoacoustic imaging with high costs, great harmful, poor portability and so on shortcomings, two imaging modalities were proposed and two complete experimental system structure diagrams were exhibited, showing different features and developing directions of photoacoustic imaging with respect to the traditional domain-photoacoustic imaging. At last, the outlook of the frequency-domain photoacoustic imaging was made to provide some references and guidance for our research and development about photoacoustic imaging.%频率域光声成像是指使用连续波激光器输出激光光源,利用该调制后的激光信号辐射组织,在频率域对激励的光声信号进行处理并成像的方式.首先阐述光声成像和频率域光声成像的原理、发展以及研究现状,然后介绍频率域光声成像的具体实验方法和基本重建算法.为了弥补时域光声成像成本高、伤害性大、便携性差等缺点,提出了频率域光声成像的两种成像方式,给出了完整的实验系统结构图,展示其相对于传统时域光声成像不同的研究特点与方向.最后对频率域光声成像进行展望,为光声成像在国内的研究和发展提供一定的借鉴和引导.
Granet, Gérard
2013-01-01
This paper focuses on scatterometry problems arising in lithography production of periodic gratings. Namely, the paper introduces a theoretical and numerical-modeling-oriented approach to scatterometry problems and discusses its capabilities. The approach allows for reliable detection of deviations in gratings\\' critical dimensions (CDs) during the manufacturing process. The core of the approach is the one-to-one correspondence between the electromagnetic (EM) characteristics and the geometric/material properties of gratings. The approach is based on highly accurate solutions of initial boundary-value problems describing EM waves\\' interaction on periodic gratings. The advantage of the approach is the ability to perform simultaneously and interactively both in frequency and time domains under conditions of possible resonant scattering of EM waves by infinite or finite gratings. This allows a detection of CDs for a wide range of gratings, and, thus is beneficial for the applied scatterometry. (C) 2013 Optical Society of America
Koroma, S. G.; Thompson, D. J.; Hussein, M. F. M.; Ntotsios, E.
2017-07-01
This paper presents a methodology for studying ground vibration in which the railway track is modelled in the space-time domain using the finite element method (FEM) and, for faster computation, discretisation of the ground using either FEM or the boundary element method (BEM) is avoided by modelling it in the wavenumber-frequency domain. The railway track is coupled to the ground through a series of rectangular strips located at the surface of the ground; their vertical interaction is described by a frequency-dependent dynamic stiffness matrix whose elements are represented by discrete lumped parameter models. The effectiveness of this approach is assessed firstly through frequency domain analysis using as excitation a stationary harmonic load applied on the rail. The interaction forces at the ballast/ground interface are calculated using the FE track model in the space-time domain, transformed to the wavenumber domain, and used as input to the ground model for calculating vibration in the free field. Additionally, time domain simulations are also performed with the inclusion of nonlinear track parameters. Results are presented for the coupled track/ground model in terms of time histories and frequency spectra for the track vibration, interaction forces and free-field ground vibration. For the linear track model, the results from the mixed formulation are in excellent agreement with those from a semi-analytical model formulated in the wavenumber-frequency domain, particularly in the vicinity of the loading point. The accuracy of the mixed formulation away from the excitation point depends strongly on the inclusion of through-ground coupling in the lumped parameter model, which has been found to be necessary for both track dynamics and ground vibration predictions.
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
Maetzler, Walter; Karam, Marie; Berger, Monika Fruhmann; Heger, Tanja; Maetzler, Corina; Ruediger, Heinz; Bronzova, Juliana; Lobo, Patricia Pita; Ferreira, Joaquim J; Ziemssen, Tjalf; Berg, Daniela
2015-03-01
The autonomic nervous system (ANS) is regularly affected in Parkinson's disease (PD). Information on autonomic dysfunction can be derived from e.g. altered heart rate variability (HRV) and sympathetic skin response (SSR). Such parameters can be quantified easily and measured repeatedly which might be helpful for evaluating disease progression and therapeutic outcome. In this 2-center study, HRV and SSR of 45 PD patients and 26 controls were recorded. HRV was measured during supine metronomic breathing and analyzed in time- and frequency-domains. SSR was evoked by repetitive auditory stimulation. Various ANS parameters were compared (1) between patients and healthy controls, (2) to clinical scales (Unified Parkinson's disease rating scale, Mini-Mental State Examination, Becks Depression Inventory), and (3) to disease duration. Root mean square of successive differences (RMSSD) and low frequency/high frequency (LF/HF) ratio differed significantly between PD and controls. Both, HRV and SSR parameters showed low or no association with clinical scores. Time-domain parameters tended to be affected already at early PD stages but did not consistently change with longer disease duration. In contrast, frequency-domain parameters were not altered in early PD phases but tended to be lower (LF, LF/HF ratio), respectively higher (HF) with increasing disease duration. This report confirms previous results of altered ANS parameters in PD. In addition, it suggests that (1) these ANS parameters are not relevantly associated with motor, behavioral, and cognitive changes in PD, (2) time-domain parameters are useful for the assessment of early PD, and (3) frequency-domain parameters are more closely associated with disease duration.
DEFF Research Database (Denmark)
Holdyk, Andrzej; Holbøll, Joachim; Arana, Ivan;
2012-01-01
Transient voltages resulting from switching operations depend on an interaction between the breaker, the transformer, cables and a neighbourhood grid and imply a risk for the transformer and other components. In this paper the Frequency Domain Severity Factor (FDSF) is used to assess the severity...... implemented in ATP-EMTP using standard component models and further validated against measurements. The results show the range of overvoltages on the transformer terminals as well as the corresponding FSDF for all turbines under a number of varying parameters. The maximum FDSF of 1.235 and frequency of 445 k...
DEFF Research Database (Denmark)
Gil-Cacho, Jose M.; van Waterschoot, Toon; Moonen, Marc
2014-01-01
In this paper, we propose a new framework to tackle the double-talk (DT) problem in acoustic echo cancellation (AEC). It is based on a frequency-domain adaptive filter (FDAF) implementation of the so-called prediction error method adaptive filtering using row operations (PEM-AFROW) leading...... to the FDAF-PEM-AFROW algorithm. We show that FDAF-PEM-AFROW is by construction related to the best linear unbiased estimate (BLUE) of the echo path. We depart from this framework to show an improvement in performance with respect to other adaptive filters minimizing the BLUE criterion, namely the PEM...
Men, Kuo; Quan, Hong; Yang, Peipei; Cao, Ting; Li, Weihao
2010-04-01
The frequency-domain magnetic resonance spectroscopy (MRS) is achieved by the Fast Fourier Transform (FFT) of the time-domain signals. Usually we are only interested in the portion lying in a frequency band of the whole spectrum. A method based on the singular value decomposition (SVD) and frequency-selection is presented in this article. The method quantifies the spectrum lying in the interested frequency band and reduces the interference of the parts lying out of the band in a computationally efficient way. Comparative experiments with the standard time-domain SVD method indicate that the method introduced in this article is accurate and timesaving in practical situations.
Giovanneschi, F.; Gonzalez-Huici, M. A.; Uschkerat, U.
2013-06-01
In this work we present a comprehensive analysis of the scattered signals from buried landmine-like targets via accurate numerical modeling of Ground Penetrating Radar (GPR) responses considering various antenna-soil-target scenarios. Different characteristics in time and frequency domain are extracted and interpreted for each configuration. The acquired knowledge is useful to better understand the scattering mechanisms of subsurface objects and can be incorporated to target recognition procedures. A brief explanation of the results is also provided together with an overview of the most relevant temporal and spectral features encountered.
DEFF Research Database (Denmark)
Nelson, Paul C.; Ewert, Stephan; Carney, Laurel H.;
In the audio-frequency domain, the envelope apparently plays an important role in detection of intensity increments and in comodulation masking release (CMR). The current study addressed the question whether the second-order envelope ("venelope") contributes similarly for comparable experiments...... were found to be the same in conditions with a continuous (modulated) carrier and with traditional gated stimuli for AM frequencies ranging from 4 –64 Hz. The second set of experiments compared the amount of CMR in a tone-in-noise detection task when slow, regular fluctuations were imposed...
Dovlo, Edem; Lashkari, Bahman; Choi, Sung soo Sean; Mandelis, Andreas
2015-03-01
This paper demonstrates the co-registration of ultrasound (US) and frequency domain photoacoustic radar (FD-PAR) images with significant image improvement from applying image normalization, filtering and amplification techniques. Achieving PA imaging functionality on a commercial Ultrasound instrument could accelerate clinical acceptance and use. Experimental results presented demonstrate live animal testing and show enhancements in signal-to-noise ratio (SNR), contrast and spatial resolution. The co-registered image produced from the US and phase PA images, provides more information than both images independently.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In this paper, a Turbo aided Cyclic Prefix (CP) reconstruction scheme, termed Turbo-CPR, is proposed for Single-Carrier systems with Frequency-Domain Equalization (SC-FDE) that employ insufficient CP in the transmitter. In Turbo-CPR, the decoder output is incorporated in the process of equalization, i.e. Turbo equalizer is employed. It is shown in the simulation results that Turbo-CPR not only recovers the performance loss due to insufficiency of CP, but also provides extra gains over the lower bound of performance for conventional CP reconstruction schemes.
Jo, Ju-Yeon; Tanimura, Yoshitaka
2016-01-01
Frequency-domain two-dimensional Raman signals, which are equivalent to coherent two-dimensional Raman scattering (COTRAS) signals, for liquid water and carbon tetrachloride were calculated using an equilibrium-nonequilibrium hybrid MD simulation algorithm. We elucidate mechanisms governing the 2D signal pro?les involving anharmonic mode-mode coupling and the nonlinearities of the polarizability for the intermolecular and intramolecular vibrational modes. The predicted signal pro?les and intensities can be utilized to analyze recently developed single-beam 2D spectra, whose signals are generated from a coherently controlled pulse, allowing the single-beam measurement to be carried out more efficiently.
DEFF Research Database (Denmark)
This book is dedicated to various aspects of electromagnetic wave theory and its applications in science and technology. The covered topics include the fundamental physics of electromagnetic waves, theory of electromagnetic wave propagation and scattering, methods of computational analysis...
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.
Directory of Open Access Journals (Sweden)
Guo Shuixia
2010-06-01
Full Text Available Abstract Background Reverse-engineering approaches such as Bayesian network inference, ordinary differential equations (ODEs and information theory are widely applied to deriving causal relationships among different elements such as genes, proteins, metabolites, neurons, brain areas and so on, based upon multi-dimensional spatial and temporal data. There are several well-established reverse-engineering approaches to explore causal relationships in a dynamic network, such as ordinary differential equations (ODE, Bayesian networks, information theory and Granger Causality. Results Here we focused on Granger causality both in the time and frequency domain and in local and global networks, and applied our approach to experimental data (genes and proteins. For a small gene network, Granger causality outperformed all the other three approaches mentioned above. A global protein network of 812 proteins was reconstructed, using a novel approach. The obtained results fitted well with known experimental findings and predicted many experimentally testable results. In addition to interactions in the time domain, interactions in the frequency domain were also recovered. Conclusions The results on the proteomic data and gene data confirm that Granger causality is a simple and accurate approach to recover the network structure. Our approach is general and can be easily applied to other types of temporal data.
Jeon, R. J.; Mandelis, A.; Sanchez, V.; Abrams, S. H.
2005-06-01
Non-intrusive, non-contacting frequency-domain photothermal radiometry (FD-PTR or PTR) and frequency-domain luminescence (FD-LUM or LUM) have been used with 659- nm and 830-nm laser sources to detect artificial and natural sub-surface defects in human teeth. Fifty-two human teeth were examined with simultaneous measurements of PTR and LUM and compared to conventional diagnostic methods including continuous (dc) luminescence (DIAGNOdent), visual inspection and radiographs by calculating sensitivities and specificities. With the combined criteria of four PTR and LUM signals (two amplitudes and two phases), it was found that the sensitivity of this method was much higher than any of the other methods used in this study, whereas the specificity was comparable to that of dc luminescence diagnostics. Therefore, PTR and LUM, used together as a combined technique, have the potential to be a reliable tool to diagnose early pit and fissure caries and could provide detailed information about deep lesions with its depth profilometric character. Also, from experiments with natural or artificial defects, some depth profilometric characteristics were confirmed.
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.
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. © European Union 2014. New Phytologist © 2014 New Phytologist Trust.
Energy Technology Data Exchange (ETDEWEB)
Yokoi, Koki [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Raicu, Valerică, E-mail: vraicu@uwm.edu [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI (United States)
2017-06-28
Relaxation in fractal structures was investigated theoretically starting from a simple model of a Cantorian tree and kinetic equations linking the change in the number of particles (e.g., electrical charges) populating each branch of the tree and their transfer to other branches or to the ground state. We numerically solved the system of differential equations obtained and determined the so-called cumulative distribution function of particles, which, in dielectric or mechanical relaxation parlance, is the same as the relaxation function of the system. As a physical application, we studied the relationship between the dielectric relaxation in time-domain and the dielectric dispersion in the frequency-domain. Upon choosing appropriate rate constants, our model described accurately well-known non-exponential and non-Debye time- and frequency-domain functions, such as stretched exponentials, Havrilliak–Negami, and frequency power law. Our approach opens the door to applying kinetic models to describe a wide array of relaxation processes, which traditionally have posed great challenges to theoretical modeling based on first principles. - Highlights: • Relaxation was investigated for a system of particles flowing through a Cantorian tree. • A set of kinetic equations was formulated and used to compute the relaxation function of the system. • The dispersion function of the system was computed from the relaxation function. • An analytical method was used to recover the original relaxation function from the dispersion function. • This formalism was used to study dielectric relaxation and dispersion in fractal structures.
Akcay, Sarp
2010-01-01
Fast, reliable orbital evolutions of compact objects around massive black holes will be needed as input for gravitational wave search algorithms in the data stream generated by the planned Laser Interferometer Space Antenna (LISA). Currently, the state of the art is a time-domain code by [Phys. Rev. D{\\bf 81}, 084021, (2010)] that computes the gravitational self-force on a point-particle in an eccentric orbit around a Schwarzschild black hole. Currently, time-domain codes take up to a few days to compute just one point in parameter space. In a series of articles, we advocate the use of a frequency-domain approach to the problem of gravitational self-force (GSF) with the ultimate goal of orbital evolution in mind. Here, we compute the GSF for a particle in a circular orbit in Schwarzschild spacetime. We solve the linearized Einstein equations for the metric perturbation in Lorenz gauge. Our frequency-domain code reproduces the time-domain results for the GSF up to $\\sim 1000$ times faster for small orbital rad...
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.
Directory of Open Access Journals (Sweden)
Xiaodong Chen
2013-01-01
Full Text Available In this paper, the calibration factor of the superconducting gravimeter 057 (SG057 at the Lhasa station is accurately determined for the first time with a frequency-domain approach and the data recorded by the LaCoste Romberg Earth Tides No. 20 (LCR-ET20 gravimeter which is installed nearby SG057. The advantage of the frequency-domain approach is that it eliminates the influence of different gravimeter drifts on the determination of the calibration factor. The determined calibration factor of SG057 is (-77.7358 ± 0.0409 × 10-8 m s-2 V-1, and the relative accuracy is about 0.5‰. The newly determined calibration factor has been calculated with the Wuhan international tidal gravity reference values (ITGRVs based on the data recorded by LCR-ET20 at the Wuhan station before it was installed at the Lhasa station. A high-precision synthesized gravity tide is achieved at the Lhasa station with accurate tidal parameters and theoretical tidal parameters for the long tidal waves from the Dehant-Defraigne-Wahr (DDW earth tide model. The synthesized gravity tide can be used for tidal gravity corrections of future gravity measurements in the Tibetan area. The linear gravimeter drift of SG057 is estimated by gravity records without the effects of land uplift, atmosphere and polar motion yielding a rate of 6.8 × 10-8 m s-2 yr-1.
He, Fei; Wei, Hua-Liang; Billings, Stephen A.
2015-08-01
This paper introduces a new approach for nonlinear and non-stationary (time-varying) system identification based on time-varying nonlinear autoregressive moving average with exogenous variable (TV-NARMAX) models. The challenging model structure selection and parameter tracking problems are solved by combining a multiwavelet basis function expansion of the time-varying parameters with an orthogonal least squares algorithm. Numerical examples demonstrate that the proposed approach can track rapid time-varying effects in nonlinear systems more accurately than the standard recursive algorithms. Based on the identified time domain model, a new frequency domain analysis approach is introduced based on a time-varying generalised frequency response function (TV-GFRF) concept, which enables the analysis of nonlinear, non-stationary systems in the frequency domain. Features in the TV-GFRFs which depend on the TV-NARMAX model structure and time-varying parameters are investigated. It is shown that the high-dimensional frequency features can be visualised in a low-dimensional time-frequency space.
Hallacoglu, Bertan; Matulewicz, Richard S.; Paltiel, Harriet J.; Padua, Horacio; Gargollo, Patricio; Cannon, Glenn; Alomari, Ahmad; Sassaroli, Angelo; Fantini, Sergio
2009-09-01
We present a quantitative near-IR spectroscopy study of the absolute values of oxygen saturation of hemoglobin before and after surgically induced testicular torsion in adult rabbits. Unilateral testicular torsions (0, 540, or 720 deg) on experimental testes and contralateral sham surgery on control testes are performed in four adult rabbits. A specially designed optical probe for measurements at multiple source-detector distances and a commercial frequency-domain tissue spectrometer are used to measure absolute values of testicular hemoglobin saturation. Our results show: (1) a consistent baseline absolute tissue hemoglobin saturation value of 78+/-5%, (2) a comparable tissue hemoglobin saturation of 77+/-6% after sham surgery, and (3) a significantly lower tissue hemoglobin saturation of 36+/-2% after 540- and 720-deg testicular torsion surgery. Our findings demonstrate the feasibility of performing frequency-domain, multidistance near-IR spectroscopy for absolute testicular oximetry in the assessment of testicular torsion. We conclude that near-IR spectroscopy has potential to serve as a clinical diagnostic and monitoring tool for the assessment of absolute testicular hemoglobin desaturation caused by torsion, with the possibility of serving as a complement to conventional color and spectral Doppler ultrasonography.
3D linear inversion of magnetic susceptibility data acquired by frequency domain EMI
Thiesson, J.; Tabbagh, A.; Simon, F.-X.; Dabas, M.
2017-01-01
Low induction number EMI instruments are able to simultaneously measure a soil's apparent magnetic susceptibility and electrical conductivity. This family of dual measurement instruments is highly useful for the analysis of soils and archeological sites. However, the electromagnetic properties of soils are found to vary over considerably different ranges: whereas their electrical conductivity varies from ≤ 0.1 to ≥ 100 mS/m, their relative magnetic permeability remains within a very small range, between 1.0001 and 1.01 SI. Consequently, although apparent conductivity measurements need to be inverted using non-linear processes, the variations of the apparent magnetic susceptibility can be approximated through the use of linear processes, as in the case of the magnetic prospection technique. Our proposed 3D inversion algorithm starts from apparent susceptibility data sets, acquired using different instruments over a given area. A reference vertical profile is defined by considering the mode of the vertical distributions of both the electrical resistivity and of the magnetic susceptibility. At each point of the mapped area, the reference vertical profile response is subtracted to obtain the apparent susceptibility variation dataset. A 2D horizontal Fourier transform is applied to these variation datasets and to the dipole (impulse) response of each instrument, a (vertical) 1D inversion is performed at each point in the spectral domain, and finally the resulting dataset is inverse transformed to restore the apparent 3D susceptibility variations. It has been shown that when applied to synthetic results, this method is able to correct the apparent deformations of a buried object resulting from the geometry of the instrument, and to restore reliable quantitative susceptibility contrasts. It also allows the thin layer solution, similar to that used in magnetic prospection, to be implemented. When applied to field data it initially delivers a level of contrast
DEFF Research Database (Denmark)
This book is dedicated to various aspects of electromagnetic wave theory and its applications in science and technology. The covered topics include the fundamental physics of electromagnetic waves, theory of electromagnetic wave propagation and scattering, methods of computational analysis......, material characterization, electromagnetic properties of plasma, analysis and applications of periodic structures and waveguide components, etc....
Extension of the frequency-domain pFFT method for wave structure interaction in finite depth
Teng, Bin; Song, Zhi-jie
2017-06-01
To analyze wave interaction with a large scale body in the frequency domain, a precorrected Fast Fourier Transform (pFFT) method has been proposed for infinite depth problems with the deep water Green function, as it can form a matrix with Toeplitz and Hankel properties. In this paper, a method is proposed to decompose the finite depth Green function into two terms, which can form matrices with the Toeplitz and a Hankel properties respectively. Then, a pFFT method for finite depth problems is developed. Based on the pFFT method, a numerical code pFFT-HOBEM is developed with the discretization of high order elements. The model is validated, and examinations on the computing efficiency and memory requirement of the new method have also been carried out. It shows that the new method has the same advantages as that for infinite depth.
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.
Directory of Open Access Journals (Sweden)
D. Pylarinos
2013-12-01
Full Text Available A number of 387 discharge portraying waveforms recorded on 18 different 150 kV post insulators installed at two different Substations in Crete, Greece are considered in this paper. Twenty different features are extracted from each waveform and two feature selection algorithms (t-test and mRMR are employed. Genetic algorithms are used to classify waveforms in two different classes related to the portrayed discharges. Five different data sets are employed (1. the original feature vector, 2. time domain features, 3. frequency domain features, 4. t-test selected features 5. mRMR selected features. Results are discussed and compared with previous classification implementations on this particular data group.
Directory of Open Access Journals (Sweden)
Lin Shao
2016-01-01
Full Text Available This paper aims at the frequency-domain packet scheduling (FDPS problem in orthogonal frequency division multiple access (OFDMA system. Under users’ data queue size constraints, a new swap-based FDPS algorithm is proposed to achieve further improvement in system throughput. In this algorithm, the swap of physical resource blocks (PRBs between different users is introduced to give a comprehensive view of the overall scheduling process. Moreover, the proposed algorithm optimizes the choosing method of swap candidates and always tries to select the user who can maximize the throughput improvement. Simulation results demonstrate that this new algorithm can improve the system throughput significantly as well as reduce the resource waste effectively.
Farooq, Vasim; Serruys, Patrick W; Heo, Jung Ho; Gogas, Bill D; Okamura, Takayuki; Gomez-Lara, Josep; Brugaletta, Salvatore; Garcìa-Garcìa, Hector M; van Geuns, Robert Jan
2011-08-01
Coronary artery bifurcations are a common challenging lesion subset accounting for approximately 10% to 20% of all percutaneous coronary interventions. The provisional T-stenting approach is generally recommended as the first-line management of most lesions. Carina shift is suggested to be the predominant mechanism of side-branch pinching during provisional T-stenting and has been indirectly inferred from bench work and other intravascular imaging modalities. Offline 3-dimensional (3D) reconstructions of patients studied in the first-in-man trial of the high-frequency (160 frames/s) Terumo optical frequency domain imaging system were undertaken using volume-rendering software. Through a series of 3D reconstructions, several novel hypothesis-generating concepts are presented.
Yüksel, Kivilcim; Pala, Deniz
2016-06-01
This work presents a novel approach in interrogating Polarization Dependent Loss (PDL) of cascaded identical FBGs using Optical Frequency Domain Reflectometer (OFDR). The fundamentals of both polarisation properties of uniform FBGs and polarisation-sensitive OFDR are explained and the benefits of this novel approach in measuring transversal load are discussed. The numerical programs computing the spectral evolution of PDL of the FBGs in the array as a function of grating parameters (grating length and birefringence) are presented. Our simulation results show an excellent agreement with the previously reported simulation (and experimental) results in the literature obtained on a single FBG by using classical state-of-the-art measurement techniques. As an envisaged application, the proposed system shows the feasibility of measuring the residual stresses during manufacturing process of composite materials which is not straightforward by amplitude spectrum measurements and/or considering only the axial strains.
Nadeau, Kyle P.; Durkin, Anthony J.; Tromberg, Bruce J.
2014-05-01
We have developed a method for extracting spatial frequency information content from biological tissue, which is used to calculate tissue optical properties and determine tissue structural orientation. This demodulation method employs a two-dimensional Hilbert transform using a spiral phase function in Fourier space. The approach presented here allows for the determination of tissue optical properties using a single frame of data for each modulation frequency, increasing imaging speed by two to threefold versus conventional, three-phase spatial frequency domain imaging (SFDI). This new single-phase Hilbert transform approach recovers optical property and scattering orientation index values within 1% and 10% of three-phase SFDI, respectively. These results suggest that, using the Hilbert demodulation technique, SFDI data acquisition speed can be increased significantly while preserving data quality, which will help us move forward toward the implementation of a real-time SFDI platform.
Directory of Open Access Journals (Sweden)
Si-Da Zhou
2015-01-01
Full Text Available Real-time estimation of modal parameters of time-varying structures can conduct an obvious contribution to some specific applications in structural dynamic area, such as health monitoring, damage detection, and vibration control; the recursive algorithm of modal parameter estimation supplies one of fundamentals for acquiring modal parameters in real-time. This paper presents a vector multistage recursive method of modal parameter estimation for time-varying structures in hybrid time and frequency domain, including stages of recursive estimation of time-dependent power spectra, frozen-time modal parameter estimation, recursive modal validation, and continuous-time estimation of modal parameters. An experimental example validates the proposed method finally.
H2 consensus control of time-delayed multi-agent systems: A frequency-domain method.
Ye, Fei; Zhang, Weidong; Ou, Linlin
2017-01-01
An analytical H2 controller design approach of homogeneous multi-agent systems with time delays is presented to improve consensus performance. Firstly, a closed-loop multi-input multi-output framework in frequency domain is introduced, and a consensus tracking condition is given. Secondly, the decomposition method is utilized to simplify the analysis of internal stability and H2 performance index of the whole system to a set of independent optimization problems. Finally, the H2 optimal controller can be computed from all the stabilizing controllers. The contributions of the new approach are that the design procedure is conducted analytically for arbitrary delayed multi-agent systems, and a simple quantitative tuning way is developed to trade off the nominal performance and robustness. The simulation examples show the effectiveness of the proposed control strategy.
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.
Petrantonakis, Panagiotis C; Hadjileontiadis, Leontios J
2010-01-01
Emotion discrimination from electroencephalogram (EEG) has gained attention the last decade as a user-friendly and effective approach to EEG-based emotion recognition (EEG-ER) systems. Nevertheless, challenging issues regarding the emotion elicitation procedure, especially its effectiveness, raise. In this work, a novel method, which not only evaluates the degree of emotion elicitation but localizes the emotion information in the time-frequency domain, as well, is proposed. The latter, incorporates multidimensional directed information at the time-frequency EEG representation, extracted using empirical mode decomposition, and introduces an asymmetry index for adaptive emotion-related EEG segment selection. Experimental results derived from 16 subjects visually stimulated with pictures from the valence/arousal space drawn from the International Affective Picture System database, justify the effectiveness of the proposed approach and its potential contribution to the enhancement of EEG-ER systems.
Kim, J.; Mandelis, A.; Matvienko, A.; Abrams, S.; Amaechi, B. T.
2012-11-01
The ability of frequency-domain photothermal radiometry (PTR) and modulated luminescence (LUM) to detect secondary caries is presented. Signal behavior upon sequential demineralization and remineralization of a spot (diameter ~1 mm) on a vertical wall of sectioned tooth samples was investigated experimentally. From these studies, it was found that PTR-LUM signals change, showing a certain pattern upon progressive demineralization and remineralization. PTR amplitudes slightly decreased upon progressive demineralization and slightly increased upon subsequent remineralization. The PTR phase increased during both demineralization and remineralization. LUM amplitudes exhibit a decreasing trend at excitation/probe distances larger than 200 μm away from the edge for both demineralization and remineralization; however, at locations close to the edge (up to ~200 μm), LUM signals slightly decrease upon demineralization and slightly increase during subsequent remineralization.
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.
Institute of Scientific and Technical Information of China (English)
S.Ali Ghafari Oskoei; Ghyslaine McClure
2008-01-01
At present,high.speed computing capabilities and advanced nonlinear dynamic finite element procedures enable detailed dynamic analysis of cable structures.Although deterministic approaches require considerable analysis time and effort in relation to modeling,running,and data processing,they seem to be the only alternative to obtain high accuracy.Detailed dynamic analysis of cable roof networks is sophisticated and requires advanced modeling expertise.This paper presents a comparison between detailed nonlinear dynamic analysis and a simplified frequency domain approach to estimate the maximum probable response of weakly nonlinear cable roofs.The approach can be considered as alternative to detailed time-domain analysis in the preliminary design phase,or can be used to validate results obtained from more elaborated numerical models.The proposed method is illustrated with two examples of cable net roofs that were also analysed in the time domain.
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.
Directory of Open Access Journals (Sweden)
Natalie Baddour
2015-12-01
Full Text Available This paper considers the effect of an impedance mismatch between the absorber and its surroundings on the aborber reconstructions from the photoacoustic signal profile, in particular when a non-delta input pulse is used. A transfer function approach is taken, demonstrating in the case of impedance mismatch how the total response can be modeled using the sum of the mismatch-free response and its time-delayed, time-reversed replicas, which may or may not overlap. It is shown how this approach can be exploited to accommodate the effects of non-delta pulses and/or pulse-equivalent waveforms such as linear-frequency-modulated (LFM chirps, and impedance mismatches in any inversion algorithms, even in the presence of large reflection coefficients. As a consequence, for simple-absorber reconstruction algorithms that assume impulses or ‘short enough’ pulses, the compressive portion of the measured response may be used in reconstruction formulas that do not model the impedance mismatch, regardless of the size of the mismatch. For longer-duration input waveforms, it is demonstrated how existing reconstruction methods can be successfully adapted to include the effect of the impedance mismatch. Simulations are used to illustrate these ideas. The gained physical insight into how components of the generated pressure wave carry absorber information is then exploited for signal inversion and absorber reconstruction in the frequency domain when multi-frequency modulation chirps are used for photoacoustic radar pressure measurements. The foundational theoretical developments ultimately address impendance mismatch issues germane to the major photoacoustic frequency-domain imaging modality to-date, which is the photoacoustic radar.
Jeon, Raymond J.; Mandelis, Andreas; Sanchez, Victor; Abrams, Stephen H.
2004-07-01
Non-intrusive, non-contacting frequency-domain photothermal radiometry (FD-PTR or PTR) and frequency-domain luminescence (FD-LUM or LUM) have been used with 659-nm and 830-nm laser sources to detect artificial and natural sub-surface defects in human teeth. Fifty-two human teeth were examined with simultaneous measurements of PTR and LUM with the 659-nm laser and compared to conventional diagnostic methods including continuous (dc) luminescence (DIAGNOdent), visual inspection and radiographs. To compare each method, sensitivities and specificities were calculated by using histological observations as the gold standard. With the combined criteria of four PTR and LUM signals (two amplitudes and two phases), it was found that the sensitivity of this method was much higher than any of the other methods used in this study, whereas the specificity was comparable to that of dc luminescence diagnostics. Therefore, PTR and LUM, as a combined technique, has the potential to be a reliable tool to diagnose early pit and fissure caries and could provide detailed information about deep lesions with its depth profilometric character. Also, from the experiments with the teeth having natural or aritficial defect, some depth profilometric characteristics were confirmed. The major findings are (i) PTR is sensitive to very deep (>5 mm) defects at low modulation frequencies (5 Hz). Both PTR and LUM amplitudes exhibit a peak at tooth thicknesses ca. 1.4 - 2.7 mm. Furthermore the LUM amplitude exhibits a small trough at ca. 2.5~3.5 mm; (ii) PTR is sensitive to various defects such as a deep carious lesion, a demineralized area, and a crack while LUM exhibits low sensitivity and spatial resolution.
Wei, Ying-Chieh; Wei, Ying-Yu; Chang, Kai-Hsiung; Young, Ming-Shing
2012-04-01
The objective of this study is to design and develop a programmable electrocardiogram (ECG) generator with frequency domain characteristics of heart rate variability (HRV) which can be used to test the efficiency of ECG algorithms and to calibrate and maintain ECG equipment. We simplified and modified the three coupled ordinary differential equations in McSharry's model to a single differential equation to obtain the ECG signal. This system not only allows the signal amplitude, heart rate, QRS-complex slopes, and P- and T-wave position parameters to be adjusted, but can also be used to adjust the very low frequency, low frequency, and high frequency components of HRV frequency domain characteristics. The system can be tuned to function with HRV or not. When the HRV function is on, the average heart rate can be set to a value ranging from 20 to 122 beats per minute (BPM) with an adjustable variation of 1 BPM. When the HRV function is off, the heart rate can be set to a value ranging from 20 to 139 BPM with an adjustable variation of 1 BPM. The amplitude of the ECG signal can be set from 0.0 to 330 mV at a resolution of 0.005 mV. These parameters can be adjusted either via input through a keyboard or through a graphical user interface (GUI) control panel that was developed using LABVIEW. The GUI control panel depicts a preview of the ECG signal such that the user can adjust the parameters to establish a desired ECG morphology. A complete set of parameters can be stored in the flash memory of the system via a USB 2.0 interface. Our system can generate three different types of synthetic ECG signals for testing the efficiency of an ECG algorithm or calibrating and maintaining ECG equipment.
Khan, Sebastian; Husa, Sascha; Hannam, Mark; Ohme, Frank; Pürrer, Michael; Forteza, Xisco Jiménez; Bohé, Alejandro
2016-02-01
We present a new frequency-domain phenomenological model of the gravitational-wave signal from the inspiral, merger and ringdown of nonprecessing (aligned-spin) black-hole binaries. The model is calibrated to 19 hybrid effective-one-body-numerical-relativity waveforms up to mass ratios of 1 ∶18 and black-hole spins of |a /m |˜0.85 (0.98 for equal-mass systems). The inspiral part of the model consists of an extension of frequency-domain post-Newtonian expressions, using higher-order terms fit to the hybrids. The merger ringdown is based on a phenomenological ansatz that has been significantly improved over previous models. The model exhibits mismatches of typically less than 1% against all 19 calibration hybrids and an additional 29 verification hybrids, which provide strong evidence that, over the calibration region, the model is sufficiently accurate for all relevant gravitational-wave astronomy applications with the Advanced LIGO and Virgo detectors. Beyond the calibration region the model produces physically reasonable results, although we recommend caution in assuming that any merger-ringdown waveform model is accurate outside its calibration region. As an example, we note that an alternative nonprecessing model, SEOBNRv2 (calibrated up to spins of only 0.5 for unequal-mass systems), exhibits mismatch errors of up to 10% for high spins outside its calibration region. We conclude that waveform models would benefit most from a larger number of numerical-relativity simulations of high-aligned-spin unequal-mass binaries.
Directory of Open Access Journals (Sweden)
Tomi Roinila
2014-07-01
Full Text Available Silicon nanowire-based field-effect transistors (SiNW FETs have demonstrated the ability of ultrasensitive detection of a wide range of biological and chemical targets. The detection is based on the variation of the conductance of a nanowire channel, which is caused by the target substance. This is seen in the voltage–current behavior between the drain and source. Some current, known as leakage current, flows between the gate and drain, and affects the current between the drain and source. Studies have shown that leakage current is frequency dependent. Measurements of such frequency characteristics can provide valuable tools in validating the functionality of the used transistor. The measurements can also be an advantage in developing new detection technologies utilizing SiNW FETs. The frequency-domain responses can be measured by using a commercial sine-sweep-based network analyzer. However, because the analyzer takes a long time, it effectively prevents the development of most practical applications. Another problem with the method is that in order to produce sinusoids the signal generator has to cope with a large number of signal levels. This may become challenging in developing low-cost applications. This paper presents fast, cost-effective frequency-domain methods with which to obtain the responses within seconds. The inverse-repeat binary sequence (IRS is applied and the admittance spectroscopy between the drain and source is computed through Fourier methods. The methods is verified by experimental measurements from an n-type SiNW FET.
Wei, Ying-Chieh; Wei, Ying-Yu; Chang, Kai-Hsiung; Young, Ming-Shing
2012-04-01
The objective of this study is to design and develop a programmable electrocardiogram (ECG) generator with frequency domain characteristics of heart rate variability (HRV) which can be used to test the efficiency of ECG algorithms and to calibrate and maintain ECG equipment. We simplified and modified the three coupled ordinary differential equations in McSharry's model to a single differential equation to obtain the ECG signal. This system not only allows the signal amplitude, heart rate, QRS-complex slopes, and P- and T-wave position parameters to be adjusted, but can also be used to adjust the very low frequency, low frequency, and high frequency components of HRV frequency domain characteristics. The system can be tuned to function with HRV or not. When the HRV function is on, the average heart rate can be set to a value ranging from 20 to 122 beats per minute (BPM) with an adjustable variation of 1 BPM. When the HRV function is off, the heart rate can be set to a value ranging from 20 to 139 BPM with an adjustable variation of 1 BPM. The amplitude of the ECG signal can be set from 0.0 to 330 mV at a resolution of 0.005 mV. These parameters can be adjusted either via input through a keyboard or through a graphical user interface (GUI) control panel that was developed using LABVIEW. The GUI control panel depicts a preview of the ECG signal such that the user can adjust the parameters to establish a desired ECG morphology. A complete set of parameters can be stored in the flash memory of the system via a USB 2.0 interface. Our system can generate three different types of synthetic ECG signals for testing the efficiency of an ECG algorithm or calibrating and maintaining ECG equipment. © 2012 American Institute of Physics
Electromagnetic soil properties variability in a mine-field trial site in Cambodia
Gorriti, A.G.; Ranada-Shaw, A.; Schoolderman, A.J.; Rhebergen, J.B.; Slob, E.C.
2006-01-01
In this paper, the characterization of the electromagnetic soil properties of a blind lane used in a trial for a dual-sensor mine detector is presented. Several techniques are used and are compared here; Time Domain Reflectometry, gravimetric techniques and Frequency Domain Reflection and Transmissi
Stored electromagnetic energy and quality factor of radiating structures
Capek, Miloslav; Jelinek, Lukas; Vandenbosch, Guy A. E.
2016-04-01
This paper deals with the old yet unsolved problem of defining and evaluating the stored electromagnetic energy-a quantity essential for calculating the quality factor, which reflects the intrinsic bandwidth of the considered electromagnetic system. A novel paradigm is proposed to determine the stored energy in the time domain leading to the method, which exhibits positive semi-definiteness and coordinate independence, i.e. two key properties actually not met by the contemporary approaches. The proposed technique is compared with an up-to-date frequency domain method that is extensively used in practice. Both concepts are discussed and compared on the basis of examples of varying complexity.
Qiao, Yao-Bin; Qi, Hong; Zhao, Fang-Zhou; Ruan, Li-Ming
2016-12-01
Reconstructing the distribution of optical parameters in the participating medium based on the frequency-domain radiative transfer equation (FD-RTE) to probe the internal structure of the medium is investigated in the present work. The forward model of FD-RTE is solved via the finite volume method (FVM). The regularization term formatted by the generalized Gaussian Markov random field model is used in the objective function to overcome the ill-posed nature of the inverse problem. The multi-start conjugate gradient (MCG) method is employed to search the minimum of the objective function and increase the efficiency of convergence. A modified adjoint differentiation technique using the collimated radiative intensity is developed to calculate the gradient of the objective function with respect to the optical parameters. All simulation results show that the proposed reconstruction algorithm based on FD-RTE can obtain the accurate distributions of absorption and scattering coefficients. The reconstructed images of the scattering coefficient have less errors than those of the absorption coefficient, which indicates the former are more suitable to probing the inner structure. Project supported by the National Natural Science Foundation of China (Grant No. 51476043), the Major National Scientific Instruments and Equipment Development Special Foundation of China (Grant No. 51327803), and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51121004).
Angelo, Joseph P.; Bigio, Irving J.; Gioux, Sylvain
2016-03-01
Imaging technologies working in the spatial frequency domain are becoming increasingly popular for generating wide-field optical property maps, enabling further analysis of tissue parameters such as absorption or scattering. While acquisition methods have witnessed a very rapid growth and are now performing in real-time, processing methods are yet slow preventing information to be acquired and displayed in real-time. In this work, we present solutions for rapid inverse problem solving for optical properties by use of advanced look-up tables. In particular, we present methods and results from a dense, linearized look-up table and an analytical representation that currently run 100 times faster than the standard method and within 10% in both absorption and scattering. With the resulting computation time in the tens of milliseconds range, the proposed techniques enable video-rate feedback of real-time techniques such as snapshot of optical properties (SSOP) imaging, making full video-rate guidance in the clinic possible.
Directory of Open Access Journals (Sweden)
Chin Francois
2004-01-01
Full Text Available Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.
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.
Coskun, Ulas C.; Lam, Sandra; Sun, Yuansheng; Liao, Shih-Chu Jeff; George, Steven C.; Barbieri, Beniamino
2017-02-01
Phosphorescence probes can have significantly long lifetimes, on the order of micro- to milli-seconds or longer. In addition, environmental changes can affect the lifetimes of these phosphorescence probes. Thus, Phosphorescence Lifetime Imaging Microscopy (PLIM) is a very useful tool to localize the phosphorescence probes based on their lifetimes to study the variance in the lifetimes due to the micro environmental changes. Since the probes respond to the biologically relevant parameters like oxygen concentration, they can be used to study various biologically relevant processes like cellular metabolism, protein interaction etc. In this case, we study the effects of oxygen on Oxyphor G4 with PLIM. Since The Oxyphor G4 can be quenched by O2, it is a good example of such a probe and has a lifetime around 250us. Here we present the digital frequency domain PLIM technique and study the lifetime of the Oxyphor G4 as a function of the O2 concentration. The lifetime data are successfully presented in a phasor plot for various O2 concentrations and are consistent with the time domain data. Overall, we can analyze the oxygen consumption of varying cells using this technique.
Huan, Huiting; Mandelis, Andreas; Lashkari, Bahman; Liu, Lixian
2017-04-01
The evaluation of the stress-strain state of metallic materials is an important problem in the field of non-destructive testing (NDT). Prolonged cyclic loading or overloading will lead to permanent changes of material strength in an inconspicuous manner that poses threat to the safety of structures, components and products. This research focuses on gauging the mechanical strength of metallic alloys through the application of frequency-domain laser ultrasound (FDLU) based on a continuous-wave diode laser source. The goal is to develop industrial NDT procedures for fatigue monitoring in metallic substrates and coatings so that the technique can be used for mechanical strength assessment. A small-scale, non-commercial rig was fabricated to hold the sample and conduct tensile FDLU testing in parallel with an adhesive strain gauge affixed on the tested sample for independent measurement of the applied stress. Harmonic modulation and lock-in detection were used to investigate the LU signal sensitivity to the stress-strain state of ordinary aluminum alloy samples. A 1 MHz focused piezoelectric transducer was used to detect the LU signal. During the tensile procedure, both amplitude and phase signals exhibited good repeatability and sensitivity to the increasing stress-strain within the elastic regime. Signals beyond the elastic limit also revealed significant change patterns.
Dovlo, Edem; Lashkari, Bahman; Mandelis, Andreas
2016-03-01
Frequency-domain photoacoustic radar (FD-PAR) imaging of absorbers in turbid media and their comparison and/or validation as well as co-registration with their corresponding ultrasound (US) images are demonstrated in this paper. Also presented are the FD-PAR tomography and the effects of reducing the number of scan lines (or angles) on image quality, resolution, and contrast. The FD-PAR modality uses intensity-modulated (coded) continuous wave laser sources driven by frequency-swept (chirp) waveforms. The spatial cross-correlation function between the PA response and the reference signal used for laser source modulation produces the reconstructed image. Live animal testing is demonstrated, and images of comparable signal-to-noise ratio, contrast, and spatial resolution were obtained. Various image improvement techniques to further reduce absorber spread and artifacts in the images such as normalization, filtering, and amplification were also investigated. The co-registered image produced from the combined US and PA images provides more information than both images independently. The significance of this work lies in the fact that achieving PA imaging functionality on a commercial ultrasound instrument could accelerate its clinical acceptance and use. This work is aimed at functional PA imaging of small animals in vivo.
Foote, David; Lin, Yingda; Hill, Wendell T., III
2015-05-01
In a recent set of coherent control experiments, an anomalous sinusoidal variation of the ionization yield was observed in Xe when ionized by a pairs of phase-locked, many-cycle 800 nm pulses. Compared with the signal of a single transform limited pulse, both enhancement and suppression was possible, which depended on the temporal separation and relative phase of the pulses. In the time domain, the control can be viewed as a temporal Young's double slit experiment - two coherent electron wavepackets interfering. In the frequency domain, the photoelectron spectrum is given by the modulus squared of the Fourier transform of the field, which is a few-cycle squared sinusodial function. In analogy to a few-cycle pulse where the carrier phase dictates the ejection direction of rescattered electrons, enhancement (suppression) occurs when the effective carrier waveform is cos[w-w0]2 (sin[w-w0]2). The contrast decreased with increasing pulse separation and decreasing multiphoton order. Detailed results and a model simulation will be presented.
Gao, Hong; Cao, Xiuhan; Li, Jinyi; Du, Zhenhui
2016-10-01
Multi-pass cells (MPCs) are commonly used to improve the sensitivity for trace gas detection using spectroscopy technologies. The determination of Effective Optical Path Length (EOPL) of a MPC is very important and challenging in applications which aim at absolute measurements. It is well-known that the temperature changing will exercise some influence on the MPCs' spatial structure, however, measurements of the influence haven't been reported which might due to the limitation of measuring method. In this paper, we used a direct high-precision measuring method with Optical Frequency Domain Reflectometer (OFDR) to evaluate the thermal stability of a multi-pass cell. To simulate the environment with a large range of temperature changing, this paper gave a series of experiments by setting the temperature control unit in system from 25 to 175 degree Celsius, and the MPC's EOPL was measured simultaneously for the investigation of temperature response. The results showed that the effective optical path length increase monotonically along with the variation of the temperature, and the rising rate is 0.5 mm/ºC with the total length of about 3 meters which should be pay attention to when the ultra-high accuracy results are demanded. To stabilize the EOPL of the system, if it is possible, the environment temperature of gas cell can be controlled with a constant temperature. In practical applications, the real-time monitoring of EOPL with a direct measuring method may be necessary.
McClatchy, David M; Hoopes, P Jack; Pogue, Brian W; Kanick, Stephen Chad
2017-02-01
For the first time, spatially resolved quantitative metrics of light scattering recovered with sub-diffusive spatial frequency domain imaging (sd-SFDI) are shown to be sensitive to changes in intratumoral morphology and viability by direct comparison to histopathological analysis. Two freshly excised subcutaneous murine tumor cross-sections were measured with sd-SFDI, and recovered optical scatter parameter maps were co-registered to whole mount histology. Unique clustering of the optical scatter parameters μs' vs. γ (i.e. diffuse scattering vs. relative backscattering) evaluated at a single wavelength showed complete separation between regions of viable tumor, aggresive tumor with stromal growth, varying levels of necrotic tumor, and also peritumor muscle. The results suggest that with further technical development, sd-SFDI may represent a non-destructive screening tool for analysis of excised tissue or a non-invasive approach to investigate suspicious lesions without the need for exogenous labels or spectrally resolved imaging. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Yao, Yong-Sheng; Zheng, Jian-Long; Chen, Zeng-Shun; Zhang, Jun-Hui; Li, Yong
2016-06-10
This paper presents a systematic pioneering study on the use of agricultural-purpose frequency domain reflectometry (FDR) sensors to monitor temperature and moisture of a subgrade in highway extension and reconstruction engineering. The principle of agricultural-purpose FDR sensors and the process for embedding this kind of sensors for subgrade engineering purposes are introduced. Based on field measured weather data, a numerical analysis model for temperature and moisture content in the subgrade's soil is built. Comparisons of the temperature and moisture data obtained from numerical simulation and FDR-based measurements are conducted. The results show that: (1) the embedding method and process, data acquisition, and remote transmission presented are reasonable; (2) the temperature and moisture changes are coordinated with the atmospheric environment and they are also in close agreement with numerical calculations; (3) the change laws of both are consistent at positions where the subgrade is compacted uniformly. These results suggest that the data measured by the agricultural-purpose FDR sensors are reliable. The findings of this paper enable a new and effective real-time monitoring method for a subgrade's temperature and moisture changes, and thus broaden the application of agricultural-purpose FDR sensors.
Takida, Yuma; Minamide, Hiroaki
2017-05-01
The development of reliable, high-power, frequency-tunable terahertz (THz)-wave sources is crucial for a wide variety of applications, such as spectroscopy, imaging, and sensing. In order to generate frequency-tunable THz waves at room temperature, one of the most promising methods is a wavelength conversion in nonlinear optical crystals. Here, we present our recent results on high-power, widely-tunable, frequency-agile THz-wave sources based on nonlinear parametric processes in MgO:LiNbO3 crystals. By changing the noncollinear phase-matching condition in MgO:LiNbO3, the tunability of sub-nanosecond-pumped injection-seeded THz-wave parametric generators (is-TPGs) covers the 3.65-octave frequency range from 0.37 THz up to 4.65 THz. The monochromatic THz-wave output from is-TPGs is greater than 10 kW peak power with the linewidth of approximately 3 GHz and the stability of 1%. These is-TPG systems are reliable and promising high-power tunable THz-wave sources for frequency-domain spectroscopic measurements towards THz sensing and detector sensitivity calibration.
Directory of Open Access Journals (Sweden)
Salim Bahçeci
2010-01-01
Full Text Available In impulse radio ultra-wideband (IR-UWB systems where the channel lengths are on the order of a few hundred taps, conventional use of frequency-domain (FD processing for channel estimation and equalization may not be feasible because the need to add a cyclic prefix (CP to each block causes a significant reduction in the spectral efficiency. On the other hand, using no or short CP causes the interblock interference (IBI and thus degradation in the receiver performance. Therefore, in order to utilize FD receiver processing UWB systems without a significant loss in the spectral efficiency and the performance, IBI cancellation mechanisms are needed in both the channel estimation and equalization operations. For this reason, in this paper, we consider the joint FD channel estimation and equalization for IR-UWB systems with short cyclic prefix (CP and propose a novel iterative receiver employing soft IBI estimation and cancellation within both its FD channel estimator and FD equalizer components. We show by simulation results that the proposed FD receiver attains performances close to that of the full CP case in both line-of-sight (LOS and non-line-of-sight (NLOS UWB channels after only a few iterations.
Directory of Open Access Journals (Sweden)
Madhukumar A. S.
2004-01-01
Full Text Available Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.
Directory of Open Access Journals (Sweden)
Yong-Sheng Yao
2016-06-01
Full Text Available This paper presents a systematic pioneering study on the use of agricultural-purpose frequency domain reflectometry (FDR sensors to monitor temperature and moisture of a subgrade in highway extension and reconstruction engineering. The principle of agricultural-purpose FDR sensors and the process for embedding this kind of sensors for subgrade engineering purposes are introduced. Based on field measured weather data, a numerical analysis model for temperature and moisture content in the subgrade’s soil is built. Comparisons of the temperature and moisture data obtained from numerical simulation and FDR-based measurements are conducted. The results show that: (1 the embedding method and process, data acquisition, and remote transmission presented are reasonable; (2 the temperature and moisture changes are coordinated with the atmospheric environment and they are also in close agreement with numerical calculations; (3 the change laws of both are consistent at positions where the subgrade is compacted uniformly. These results suggest that the data measured by the agricultural-purpose FDR sensors are reliable. The findings of this paper enable a new and effective real-time monitoring method for a subgrade’s temperature and moisture changes, and thus broaden the application of agricultural-purpose FDR sensors.
Development of frequency domain multiplexing for the X-ray Integral Field Unit (X-IFU) on the Athena
Akamatsu, Hiroki; van der Kuur, Jan; de Vries, Cor P; Ravensberg, Kevin; Adams, Joseph S; Bandler, Simon R; Bruijn, Marcel P; Chervenak, James A; Kilbourne, Caroline A; Kiviranta, Mikko; Linden, A J van den; Jackson, Brian D; Smith, Stephen J
2016-01-01
We are developing the frequency domain multiplexing (FDM) read-out of transition-edge sensor (TES) microcalorimeters for the X-ray Integral Field Unit (X-IFU) instrument on board of the future European X-Ray observatory Athena. The X-IFU instrument consists of an array of $\\sim$3840 TESs with a high quantum efficiency ($>$90 \\%) and spectral resolution $\\Delta E$=2.5 eV $@$ 7 keV ($E/\\Delta E\\sim$2800). FDM is currently the baseline readout system for the X-IFU instrument. Using high quality factor LC filters and room temperature electronics developed at SRON and low-noise two stage SQUID amplifiers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. An integrated noise equivalent power resolution of about 2.0 eV at 1.7 MHz has been demonstrated with a pixel from a new TES array from NASA/Goddard (GSFC-A2). We have achieved X-ray energy resolutions $\\sim$2.5 eV at AC bias frequency at 1.7 MHz in the single pixel read-out. We have...
Damour, T; Nagar, A
2010-01-01
The coalescences of binary black hole (BBH) systems, here taken to be non-spinning, 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 BBHs, 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 absence of knowledge of the exact waveforms, our study assumes as fiducial, target waveforms the ones generated by the most accurate version of the effective one body (EOB) formalism. 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 t...
Luce, H.; Kubo, K.; Fukao, S.
2001-09-01
Studies of atmospheric structures and dynamics at small scales require high resolution observations in space and time. Stratosphere-troposphere radars offer high potentialities for such studies, in particular, with the dual-frequency domain interferometry (FDI) technique used for tracking thin atmospheric layers. In the present paper, attention is drawn to the performances of this technique, discussed in light of comparisons between data sets collected in different radar configurations with the middle and upper atmosphere (MU) radar (Shigaraki, Japan, 34.85°N, 136.10°E). Measurements in FDI mode with two range resolutions (300 and 600 m) and two frequency differences (0.50 and 0.25 MHz) have been conducted, interleaved with measurements in Doppler-beam-swinging mode performed at a range resolution of 150 m. From the data comparisons it is found that the thickness of the echoing layers in FDI mode strongly depends on the initial range resolution used. Thus, even if the FDI mode is believed to give a better description of the stable layers, the FDI-deduced thickness with an initial range resolution of 300 m may not be consistent with the true thickness of the atmospheric layers. It could then be misleading to use FDI observations in order to estimate the thickness of atmospheric layers. However, it is also shown that under some circumstances, FDI can provide reliable information on the characteristics of the atmospheric structures which cannot be available with "non-FDI" techniques.
Taki, Hirofumi; Sakamoto, Takuya; Taki, Kousuke; Yamakawa, Makoto; Shiina, Tsuyoshi; Kudo, Motoi; Sato, Toru
2013-01-01
We have proposed a high-range-resolution ultrasound imaging method for human carotid artery using an adaptive beamforming technique based on frequency domain interferometry (FDI). The method assumes that the received signal consists of multiple echoes of targets and noise, where the waveform of each echo is similar to that of the reference signal. In this study, we examine the dependence of the echo waveform on the target depth, and investigate the proper measurement-range for the FDI imaging method using a reference signal. Furthermore, we propose a ROI-division process, where each sub-ROI has a proper measurement-range for the application of the FDI imaging method. Simulation and experimental results show the efficiency of the ROI-division process in improving the image quality of human carotid artery acquired using the FDI imaging method. We believe that the modified FDI imaging method with the ROI-division process has the potential to facilitate significant progress in the detection of vessel stenosis and in the assessment of cardiovascular disease risk.
Luce, H.; Crochet, M.; Hanuise, C.; Yamamoto, M.; Fukao, S.
1999-09-01
The frequency domain interferometry (FDI) technique has been developed for probing thin layered structures of the atmosphere. The position and thickness of a single layer embedded within the scattering volume can be deduced from the complex normalized cross correlation (coherence) of received signals at two closely spaced frequencies. Applied in the vertical pointing direction, this technique identified layered structures ("FDI layers") of 50-200 m in thickness in the lower atmosphere. These structures are 1 order of magnitude thicker than observed temperature sheets (about 10-m thick) which are very likely responsible for the main part of the VHF radar echoes in vertical direction. In this paper, although the ambiguity of the dual FDI technique is well known, we emphasize that the FDI layers do not necessarily correspond to a single atmospheric layer; they can also be interpreted as a more complex structure of very thin atmospheric layers. A simple model, introduced as an example, shows that the FDI layer thickness can also approximately be interpreted as the vertical separation of two very thin atmospheric layers. This result can explain by itself the differences between the estimated thicknesses by balloon and FDI radar techniques. Finally, we stress that comparisons with high-resolution in situ measurements are urgently needed for interpreting the FDI layers.
Price, Stanton R.; Anderson, Derek T.; Stone, Kevin; Keller, James M.
2014-05-01
It is well-known that a pattern recognition system is only as good as the features it is built upon. In the fields of image processing and computer vision, we have numerous spatial domain and spatial-frequency domain features to extract characteristics of imagery according to its color, shape and texture. However, these approaches extract information across a local neighborhood, or region of interest, which for target detection contains both object(s) of interest and background (surrounding context). A goal of this research is to filter out as much task irrelevant information as possible, e.g., tire tracks, surface texture, etc., to allow a system to place more emphasis on image features in spatial regions that likely belong to the object(s) of interest. Herein, we outline a procedure coined soft feature extraction to refine the focus of spatial domain features. This idea is demonstrated in the context of an explosive hazards detection system using forward looking infrared imagery. We also investigate different ways to spatially contextualize and calculate mathematical features from shearlet filtered candidate image chips. Furthermore, we investigate localization strategies in relation to different ways of grouping image features to reduce the false alarm rate. Performance is explored in the context of receiver operating characteristic curves on data from a U.S. Army test site that contains multiple target and clutter types, burial depths, and times of day.
Saager, Rolf B; Balu, Mihaela; Crosignani, Viera; Sharif, Ata; Durkin, Anthony J; Kelly, Kristen M; Tromberg, Bruce J
2015-06-01
The combined use of nonlinear optical microscopy and broadband reflectance techniques to assess melanin concentration and distribution thickness in vivo over the full range of Fitzpatrick skin types is presented. Twelve patients were measured using multiphoton microscopy (MPM) and spatial frequency domain spectroscopy (SFDS) on both dorsal forearm and volar arm, which are generally sun-exposed and non-sun-exposed areas, respectively. Both MPM and SFDS measured melanin volume fractions between (skin type I non-sun-exposed) and 20% (skin type VI sun exposed). MPM measured epidermal (anatomical) thickness values ~30-65 μm, while SFDS measured melanin distribution thickness based on diffuse optical path length. There was a strong correlation between melanin concentration and melanin distribution (epidermal) thickness measurements obtained using the two techniques. While SFDS does not have the ability to match the spatial resolution of MPM, this study demonstrates that melanin content as quantified using SFDS is linearly correlated with epidermal melanin as measured using MPM (R² = 0.8895). SFDS melanin distribution thickness is correlated to MPM values (R² = 0.8131). These techniques can be used individually and/or in combination to advance our understanding and guide therapies for pigmentation-related conditions as well as light-based treatments across a full range of skin types.
Dali, Sarabjyot S; Sevick-Muraca, Eva M
2012-11-15
Isotropic scattering coefficient measurements were made of monodisperse polystyrene lattices of two different diameters of 144 nm and 223 nm and at volume fractions ranging from 0.15 to 0.22, using frequency domain photon migration measurements at wavelengths of 660, 685, 785 and 828 nm. The isotropic scattering coefficient measurements were shown to be sensitive to the changing ionic strength (0.5-4 mM, NaCl equiv.) of the dispersions exhibiting hindered scattering owing to structure at the lowest ionic strength values. Monte Carlo simulations and numerical solution of the Ornstein Zernike equations were used to compute isotropic scattering coefficients for comparison to measured values. The interaction potential was modeled as a hard sphere Yukawa potential and the Hypernetted Chain closure was used to solve the OZ equation. Effective particle charges were found after renormalization of the bare particle charge and used to predict the isotropic scattering coefficient. The model data were found to follow similar trends as experimental measurements. The refractive index of the particles has found to be an important factor for predicting experimental isotropic scattering coefficient values. Published by Elsevier Inc.
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyun Keol [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, Chicoutimi, Que., G7H 2B1 (Canada); Charette, Andre [Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, Chicoutimi, Que., G7H 2B1 (Canada)]. E-mail: andre_charette@uqac.ca
2007-03-15
The Sensitivity Function-based Conjugate Gradient Method (SFCGM) is described. This method is used to solve the inverse problems of function estimation, such as the local maps of absorption and scattering coefficients, as applied to optical tomography for biomedical imaging. A highly scattering, absorbing, non-reflecting, non-emitting medium is considered here and simultaneous reconstructions of absorption and scattering coefficients inside the test medium are achieved with the proposed optimization technique, by using the exit intensity measured at boundary surfaces. The forward problem is solved with a discrete-ordinates finite-difference method on the framework of the frequency-domain full equation of radiative transfer. The modulation frequency is set to 600 MHz and the frequency data, obtained with the source modulation, is used as the input data. The inversion results demonstrate that the SFCGM can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by significantly reducing a cross-talk between inter-parameters. It is also observed that the closer-to-detector objects are better retrieved.
Pürrer, Michael
2016-03-01
I provide a frequency domain reduced order model (ROM) for the aligned-spin effective-one-body model "SEOBNRv2" for data analysis with second- and third-generation ground-based gravitational wave (GW) detectors. SEOBNRv2 models the dominant mode of the GWs emitted by the coalescence of black hole binaries. The large physical parameter space (dimensionless spins -1 ≤χi≤0.99 and symmetric mass ratios 0.01 ≤η ≤0.25 ) requires sophisticated reduced order modeling techniques, including patching in the parameter space and in frequency. I find that the time window over which the inspiral-plunge and the merger-ringdown waveform in SEOBNRv2 are connected has a discontinuous dependence on the parameters when the spin parameter χ =0.8 or the symmetric mass ratio η ˜0.083 . This discontinuity increases resolution requirements for the ROM. The ROM can be used for compact binary systems with total masses of 2 M⊙ or higher for the Advanced LIGO design sensitivity and a 10 Hz lower cutoff frequency. The ROM has a worst mismatch against SEOBNRv2 of ˜1 %, but in general mismatches are better than ˜0.1 %. The ROM is crucial for key data analysis applications for compact binaries, such as GW searches and parameter estimation carried out within the LIGO Scientific Collaboration.
Directory of Open Access Journals (Sweden)
SARIKA TALE,
2011-04-01
Full Text Available Heart disease occurs eventually in majority of patients with diabetes mellitus and to be the outstanding factor in over all diabetes morbidity and mortality rates. Thus the timely detection of diabetic autonomic neuropathy and the use of effective means to improve autonomic nervous system function become of almost significance. In this work Electrocardiogram (ECG data of 20 Diabetes Mellitus (DM and 20 normal control volunteers were recorded and autonomic nervous system activities are quantified by means of frequency and time domainanalysis. Time domain measure ,Standard deviation of successive NN intervals (SDNN,NN intervals differing more than 50 msec.( NN50 count,Percentage value of NN50 count( pNN50 count, HRV triangular index, show a lower variation in the DM patient group compared to normal subjects and p value <0.01. The frequency domain measures indicate significant differences in very low frequency (VLF, low frequency (LF power and high frequency (HF power. Value generated from the ratio of low frequency to high frequency, (LF/HF ispretty high, with not much significance between both groups.
Rodin, David; Yee, Shannon K.
2017-01-01
Transient thermoreflectance (TTR) techniques are ubiquitous methods for measuring thermal conductivity of bulk materials and thin-films. Both through-plane thermal conductivity k⊥ and in-plane thermal conductivity k∥ should be independently measured in transversely anisotropic materials. When these properties are measured using conventional TTR techniques, the accuracy of the k∥ measurement is dependent on the accuracy of measuring k⊥ and vice versa. This is especially problematic for thin-films measurements as uncertainty in k⊥ (˜5%) can propagate and grow for uncertainty in k∥. In this paper, we present a method for the simultaneous measurement of k⊥ and k∥ using beam-offset frequency domain thermoreflectance (FDTR) with robust uncertainty estimation. The conventional diffusive heat transfer solution is analyzed to show that offset and heating frequency can independently control the sensitivity to directional thermal conductivity and extract values for k∥ and k⊥. Numerical uncertainty analyses demonstrate that sweeping both heating frequency and beam offset results in a reduction of measurement uncertainty. This modified measurement technique is demonstrated on crystalline alumina (c-Al2O3), amorphous alumina (a-Al2O3), quartz, fused silica, and highly oriented pyrolytic graphite.
Florez, H. M.; Kumar, A.; Theophilo, K.; Nussenzveig, P.; Martinelli, M.
2016-07-01
The correlation spectroscopy has been successfully employed in the measurement of the intrinsic linewidth of electromagnetically induced transparency (EIT) in time and frequency domain. We study the role of the sidebands of the intense fields in the measured spectra, analyzing the information that can be recovered working with different analysis frequencies. In this case, the nonzero one-photon detuning appears as a necessary condition for spectrally resolving the sideband resonances in the correlation coefficient. Our experimental findings are supported by the perturbative model defined in the frequency domain.
Florez, H M; Theophilo, K; Nussenzveig, P; Martinelli, M
2015-01-01
The correlation spectroscopy has been successfully employed in the measurement of the intrinsic linewidth of electromagnetically induced transparency (EIT) in time and frequency domain. We study the role of the sidebands of the intense fields in the measured spectra, analyzing the information that can be recovered working with different analysis frequencies. In this case, the non-zero one-photon detuning appears as a necessary condition for spectrally resolving the sideband resonances in the correlation coefficient. Our experimental findings are supported by the perturbative model defined in the frequency domain.
1986-12-01
Static Electricity. Paper No 17: 1-9. Fort Worth TX, June 21- 23, 1983. 40. Rustan, P.L. and J. Moreau . "Aircraft Lightning Attach- ment at Low Altitudes...John F. and Gustave L. Weinstock. Aircraft Related Lightning Mechanisms: Technical Report. Contract F33615-71-C-1581. McDonnell Aircraft Company, St
Energy Technology Data Exchange (ETDEWEB)
Sheshyekani, K. [Dept. of Electrical and Computer Engineering, Shahid Beheshti University, Tehran, 1983963113 (Iran, Islamic Republic of); Sadeghi, S.H.H.; Moini, R. [Electromagnetics Research Laboratory of Amirkabir University of Technology, 424 Hafez Ave., Tehran 15914 (Iran, Islamic Republic of); Rachidi, F. [Swiss Federal Institute of Technology, Lausanne 1015 (Switzerland)
2011-02-15
A frequency-domain method is proposed for the transient analysis of grounding systems with ionized soil. The method involves two stages. First, the grounding system is transformed into a nonlinear equivalent circuit, in which the frequency-domain circuit parameters of the grounding electrodes are extracted by the method of moment (MoM) and the nonlinear part of the equivalent circuit represents the soil ionization. Soil ionization is represented by a nonlinear load whose characteristics can be specified based on either experimental data or theoretical models, without any limitations in the order of nonlinearity. In the second stage the nonlinear equivalent circuit is treated using the arithmetic operator method (AOM). The AOM uses a linear matrix transformation of spectra to perform basic arithmetic operations in the frequency-domain. The main feature of the proposed method is its efficiency in dealing with the nonlinear behavior of soil ionization in the frequency-domain solution of grounding systems by the MoM. It also enables one to consider the actual nonlinear behavior of soil ionization specified by experimental data or appropriate theoretical models. (author)
Bahler, D. D.
1978-01-01
Procedures are presented for obtaining valid frequency-domain transfer functions of regulated reactor energy-storage dc-to-dc converters. These procedures are for measuring loop gain, closed loop gain, output impedance, and audio susceptibility. The applications of these measurements are discussed.
Velasco Soares, D.; Baesso Mauro, L.; Medina Neto, A.; Bicanic, D.D.; Koehorst, R.B.M.; Hooft, van der J.J.J.; Bento, A.C.
2011-01-01
The frequency-domain open photoacoustic cell (OPC) approach was used to determine room temperature thermal diffusivity of skins (pericarps) from the raw tomatoes (Lycopersicon esculetum Mill.) characterized by the three different stages of ripeness (from immature-green to a mature-red). Periodically
Data-Aided Frequency-Domain 2×2 MIMO Equalizer for 112 Gbit/s PDM-QPSK Coherent Transmission Systems
DEFF Research Database (Denmark)
Pittalà, Fabio; Hauske, Fabian N.; Ye, Yabin;
2012-01-01
Benefits of a low-complexity adaptive 32-tap 2×2 MIMO frequency-domain filter update by data-aided channel estimation over a time-domain filter with DD-LMS are shown. Superior stability and convergence speed is demonstrated with identical impairment tolerance....
Vajuvalli, Nithin N.; Chikkemenahally, Dharmendra Kumar K.; Nayak, Krupa N.; Bhosale, Manoj G.; Geethanath, Sairam
2016-12-01
Dynamic contrast enhancement magnetic resonance imaging (DCE-MRI) is a well-established method for non-invasive detection and therapeutic monitoring of pathologies through administration of intravenous contrast agent. Quantification of pharmacokinetic (PK) maps can be achieved through application of compartmental models relevant to the pathophysiology of the tissue under interrogation. The determination of PK parameters involves fitting of time-concentration data to these models. In this work, the Tofts model in frequency domain (TM-FD) is applied to a weakly vascularized tissue such as the breast. It is derived as a convolution-free model from the conventional Tofts model in the time domain (TM-TD). This reduces the dimensionality of the curve-fitting problem from two to one. The approaches of TM-FD and TM-TD were applied to two kinds of in silico phantoms and six in vivo breast DCE data sets with and without the addition of noise. The results showed that computational time taken to estimate PK maps using TM-FD was 16-25% less than with TM-TD. Normalized root mean square error (NRMSE) calculation and Pearson correlation analyses were performed to validate robustness and accuracy of the TM-FD and TM-TD approaches. These compared with ground truth values in the case of phantom studies for four different temporal resolutions. Results showed that NRMSE values for TM-FD were significantly lower than those of TM-TD as validated by a paired t-test along with reduced computational time. This approach therefore enables online evaluation of PK maps by radiologists in a clinical setting, aiding in the evaluation of 3D and/or increased coverage of the tissue of interest.
Development of frequency domain multiplexing for the X-ray Integral Field unit (X-IFU) on the Athena
Akamatsu, Hiroki; Gottardi, Luciano; van der Kuur, Jan; de Vries, Cor P.; Ravensberg, Kevin; Adams, Joseph S.; Bandler, Simon R.; Bruijn, Marcel P.; Chervenak, James A.; Kilbourne, Caroline A.; Kiviranta, Mikko; van der Linden, A. J.; Jackson, Brian D.; Smith, Stephen J.
2016-07-01
We are developing the frequency domain multiplexing (FDM) read-out of transition-edge sensor (TES) microcalorimeters for the X-ray Integral Field Unit (X-IFU) instrument on board of the future European X-Ray observatory Athena. The X-IFU instrument consists of an array of 3840 TESs with a high quantum efficiency (>90 %) and spectral resolution ΔE=2.5 eV @ 7 keV (E/ ΔE 2800). FDM is currently the baseline readout system for the X-IFU instrument. Using high quality factor LC filters and room temperature electronics developed at SRON and low-noise two stage SQUID amplifiers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. An integrated noise equivalent power resolution of about 2.0 eV at 1.7 MHz has been demonstrated with a pixel from a new TES array from NASA/Goddard (GSFC-A2). We have achieved X-ray energy resolutions 2.5 eV at AC bias frequency at 1.7 MHz in the single pixel read-out. We have also demonstrated for the first time an X-ray energy resolution around 3.0 eV in a 6 pixel FDM read-out with TES array (GSFC-A1). In this paper we report on the single pixel performance of these microcalorimeters under MHz AC bias, and further results of the performance of these pixels under FDM.
Chilson, Phillip B.; Muschinski, Andreas; Schmidt, Gerhard
1997-05-01
In this paper we report the first high-resolution observations of upper tropospheric Kelvin-Helmholtz billows using VHF frequency domain interferometry (FDI). The measurements were made using the sounding system VHF radar located in the German Harz Mountains operating at the frequencies of 53.25 and 53.75 MHz. Through an application of the FDI technique it has been possible to track the altitude of thin scattering layers with an accuracy of a few tens of meters and a temporal resolution of 13 s. Taking advantage of the FDI technique, we found several examples of Kelvin-Helmholtz instability (KHI) in regions coinciding with large values of wind shear. One particularly good example is presented in detail. The KHI occurred just below the axis of the jet at an altitude of 9.1 km. It produced oscillations in the vertical velocity field in the altitude range of 8-10 km. The oscillations had a local period of 90 s and persisted over a time interval of 10 min. On the basis of the magnitude of the horizontal wind at the time and height of the KHI, the billow train had a horizontal extent of about 27 km, while the horizontal length of the individual billow amounted to about 4.0 km. The 90-s oscillations were also observed in the radar signal power, the FDI-derived layer height, and the coherence between the received radar signals for the two frequencies. Using the FDI data, we were able to identify the individual billows located within the train and observe their maximum crest-to-trough amplitudes to be between 220 and 230 m. This was less than the conventional radar resolution of 300 m used during the experiment.
Chen, J.-S.; Chu, Y.-H.
2001-01-01
The thickness and position of an atmospheric layer embedded in the radar volume can be resolved by using the frequency-domain interferometry (FDI) technique in accordance with an analytical expression, in which a single layer with Gaussian shape is assumed. However, the FDI experimental results obtained from the Chung-Li VHF radar show that the layer thickness is usually dependent on the layer position. In view of this, an attempt is made in this paper to interpret the observations. With the help of numerical simulation, we examine three FDI models: (1) a non-Gaussian layer, (2) single layer in company with background scatterers, and (3) multiple layers. The analytical FDI expression derived from the Gaussian-layer model is employed in the numerical study to calculate the layer position and layer thickness on the basis of the coherence and phase estimated from the examined layer model. It shows that the resultant thickness and position of the FDI layer are dependent on each other, which is in agreement with the observed thickness-position relations shown in this paper. Moreover, the numerical results can also provide a reasonable interpretation of the observations reported by earlier scientific workers, such as the discrepancy between the vertical displacement velocity of the layer and the vertical Doppler velocity, the difference in thickness between the FDI-derived layer and in situ observed temperature//humidity sheets, etc. We finally illustrate that the range weighting effect of the radar system plays a crucial role in the FDI-derived thickness-position relations.
Directory of Open Access Journals (Sweden)
Sebastian Kempf
2017-01-01
Full Text Available We report on the first demonstration of a scalable GHz frequency-domain readout of metallic magnetic calorimeters (MMCs using a 64 pixel detector array that is read out by an integrated, on-chip microwave SQUID multiplexer. The detector array is optimized for detecting soft X-ray photons and the multiplexer is designed to provide a signal rise time τrise<400ns and an intrinsic energy sensitivity ϵ<30h. This results in an expected energy resolution ΔEFWHM<10eV. We measured a signal rise time τrise as low as 90ns and an energy resolution ΔEFWHM as low as 50eV for 5.9keV photons. The rise time is about an order of magnitude faster compared to other multiplexed low-temperature microcalorimeters and close to the intrinsic value set by the coupling between electron and spins. The energy resolution is degraded with respect to our design value due to a rather low intrinsic quality factor of the microwave resonators that is caused by the quality of the Josephson junction of the associated rf-SQUID as well as an elevated chip temperature as compared to the heat bath. Though the achieved energy resolution is not yet compatible with state-of-the-art single-channel MMCs, this demonstration of a scalable readout approach for MMCs in combination with the full understanding of the device performance showing ways how to improve represents an important milestone for the development of future large-scale MMC detector arrays.
Wang, L.; Cheaito, R.; Braun, J. L.; Giri, A.; Hopkins, P. E.
2016-09-01
The thermoreflectance-based techniques time- and frequency-domain thermoreflectance (TDTR and FDTR, respectively) have emerged as robust platforms to measure the thermophysical properties of a wide array of systems on varying length scales. Routine in the implementation of these techniques is the application of a thin metal film on the surface of the sample of interest to serve as an opto-thermal transducer ensuring the measured modulated reflectivity is dominated by the change in thermoreflectance of the sample. Here, we outline a method to directly measure the thermal conductivities of bulk materials without using a metal transducer layer using a standard TDTR/FDTR experiment. A major key in this approach is the use of a thermal model with z-dependent heat source when the optical penetration depth is comparable to the beam sizes and measuring the FDTR response at a long delay time to minimize non-thermoreflectivity contributions to the modulated reflectance signals (such as free carrier excitations). Using this approach, we demonstrate the ability to measure the thermal conductivity on three semiconductors, intrinsic Si (100), GaAs (100), and InSb (100), the results of which are validated with FDTR measurements on the same wafers with aluminum transducers. We outline the major sources of uncertainty in this approach, including frequency dependent heating and precise knowledge of the pump and probe spot sizes. As a result, we discuss appropriate pump-frequency ranges in which to implement this TDTR/FDTR approach and present a procedure to measure the effective spot sizes by fitting the FDTR data of an 80 nm Al/SiO2 sample at a time delay in which the spot size sensitivity dominates an FDTR measurement over the substrate thermal properties. Our method provides a more convenient way to directly measure the thermal conductivities of semiconductors.
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.
A framework for simulation and inversion in electromagnetics
Heagy, Lindsey J; Kang, Seogi; Rosenkjaer, Gudni K; Oldenburg, Douglas W
2016-01-01
Simulations and inversions of geophysical electromagnetic data are paramount for discerning meaningful information about the subsurface from these data. Depending on the nature of the source electromagnetic experiments may be classified as time-domain or frequency-domain. Multiple heterogeneous and sometimes anisotropic physical properties, including electrical conductivity and magnetic permeability, may need be considered in a simulation. Depending on what one wants to accomplish in an inversion, the parameters which one inverts for may be a voxel-based description of the earth or some parametric representation that must be mapped onto a simulation mesh. Each of these permutations of the electromagnetic problem has implications in a numerical implementation of the forward simulation as well as in the computation of the sensitivities, which are required when considering gradient-based inversions. This paper proposes a framework for organizing and implementing electromagnetic simulations and gradient-based inv...
Tamas, Razvan; Dumitrascu, Ana; Caruntu, George
2015-02-01
The method of moments is mostly used in electromagnetism to solve linear operator equations. In this paper, we present three different, alternative applications of this numerical technique: resolution of the integral equation of convolution i.e., deconvolution, synthesis of electromagnetic radiators optimized to yield a given time-domain or frequency-domain response, and processing of data provided by an inertial navigation system, with the aim to decompose a complex displacement into elementary movements.
Milson, James L.
1990-01-01
Three activities involving electromagnetism are presented. Discussed are investigations involving the construction of an electromagnet, the effect of the number of turns of wire in the magnet, and the effect of the number of batteries in the circuit. Extension activities are suggested. (CW)
Bosanac, Slobodan Danko
2016-01-01
This book is devoted to theoretical methods used in the extreme circumstances of very strong electromagnetic fields. The development of high power lasers, ultrafast processes, manipulation of electromagnetic fields and the use of very fast charged particles interacting with other charges requires an adequate theoretical description. Because of the very strong electromagnetic field, traditional theoretical approaches, which have primarily a perturbative character, have to be replaced by descriptions going beyond them. In the book an extension of the semi-classical radiation theory and classical dynamics for particles is performed to analyze single charged atoms and dipoles submitted to electromagnetic pulses. Special attention is given to the important problem of field reaction and controlling dynamics of charges by an electromagnetic field.
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Bosanac, Slobodan Danko [Ruder Boskovic Institute, Zagreb (Croatia). Physical Chemistry
2016-07-01
This book is devoted to theoretical methods used in the extreme circumstances of very strong electromagnetic fields. The development of high power lasers, ultrafast processes, manipulation of electromagnetic fields and the use of very fast charged particles interacting with other charges requires an adequate theoretical description. Because of the very strong electromagnetic field, traditional theoretical approaches, which have primarily a perturbative character, have to be replaced by descriptions going beyond them. In the book an extension of the semi-classical radiation theory and classical dynamics for particles is performed to analyze single charged atoms and dipoles submitted to electromagnetic pulses. Special attention is given to the important problem of field reaction and controlling dynamics of charges by an electromagnetic field.
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.
Directory of Open Access Journals (Sweden)
Maksim Alekhin
2013-01-01
Full Text Available Comparison of bioradiolocation and standard respiratory plethysmography signals during simultaneous registration of different types of the human breathing movements is performed in both time and frequency domains. For all couples of synchronized signals corresponding to bioradiolocation and respiratory plethysmography methods, the cross-correlation and spectral functions are calculated, and estimates of their generalized characteristics are defined. The obtained results consider bioradiolocation to be a reliable remote sensing technique for noncontact monitoring of breathing pattern in medical applications.
Hermann, Boris; Esmaeelpour, M.; Povazay, Boris; Hofer, Bernd; Bounaparte, F.; Sheen, Nick; North, Rachel; Drexler, Wolfgang
2009-02-01
We present in vivo frequency domain optical coherence tomography of the human retina and choroid in the 1060 nm water transmission window with 72 nm optical bandwidth (choroidal vasculature without the need of contrast agents, the choroidal-scleral interface as well as the first scleral layer, the absorbing lamina fusca sclerae. Furthermore the choroidal thickness was quantified in 30 healthy subjects and correlated with axial eye length. First results indicate an decrease in choroidal thickness with increasing axial eye length.
Grimm, W; Hoffmann, J; Knop, U; Winzenburg, J; Menz, V; Maisch, B
1996-11-01
Signal-averaged electrocardiography (SAECG) was performed in 120 consecutive patients with idiopathic dilated cardiomyopathy (IDC), and in 60 healthy controls. Time-domain analysis of SAECGs revealed ventricular late potentials in 27 of 120 patients with IDC (23%) compared to 2 of 60 controls (3%; P < 0.05). Frequency-domain analysis of SAECGs showed ventricular late potentials in 9 of 120 patients with IDC (8%) compared to none of the 60 controls (0%, P < 0.05). During a prospective follow-up of 15 +/- 7 months, serious arrhythmic events, defined as sustained ventricular tachyarrhythmias or sudden death, occurred in 17 of 120 patients with IDC (14%). The sensitivity, specificity, and positive and negative predictive values of ventricular late potentials for serious arrhythmic events were 35%, 80%, 22%, and 88% for the time-domain analysis, and 18%, 94%, 33%, and 87% for the frequency-domain analysis of SAECG, respectively. Thus, neither the time-nor the frequency-domain analysis of SAECG appears to be useful for risk stratification in the setting of IDC in view of their low sensitivity and low positive predictive value for serious arrhythmic events during follow-up.
Zimmerling, Jörn; Wei, Lei; Urbach, Paul; Remis, Rob
2016-06-01
In this paper we present a Krylov subspace model-order reduction technique for time- and frequency-domain electromagnetic wave fields in linear dispersive media. Starting point is a self-consistent first-order form of Maxwell's equations and the constitutive relation. This form is discretized on a standard staggered Yee grid, while the extension to infinity is modeled via a recently developed global complex scaling method. By applying this scaling method, the time- or frequency-domain electromagnetic wave field can be computed via a so-called stability-corrected wave function. Since this function cannot be computed directly due to the large order of the discretized Maxwell system matrix, Krylov subspace reduced-order models are constructed that approximate this wave function. We show that the system matrix exhibits a particular physics-based symmetry relation that allows us to efficiently construct the time- and frequency-domain reduced-order models via a Lanczos-type reduction algorithm. The frequency-domain models allow for frequency sweeps meaning that a single model provides field approximations for all frequencies of interest and dominant field modes can easily be determined as well. Numerical experiments for two- and three-dimensional configurations illustrate the performance of the proposed reduction method.
A framework for simulation and inversion in electromagnetics
Heagy, Lindsey J.; Cockett, Rowan; Kang, Seogi; Rosenkjaer, Gudni K.; Oldenburg, Douglas W.
2017-10-01
Simulations and inversions of electromagnetic geophysical data are paramount for discerning meaningful information about the subsurface from these data. Depending on the nature of the source electromagnetic experiments may be classified as time-domain or frequency-domain. Multiple heterogeneous and sometimes anisotropic physical properties, including electrical conductivity and magnetic permeability, may need be considered in a simulation. Depending on what one wants to accomplish in an inversion, the parameters which one inverts for may be a voxel-based description of the earth or some parametric representation that must be mapped onto a simulation mesh. Each of these permutations of the electromagnetic problem has implications in a numerical implementation of the forward simulation as well as in the computation of the sensitivities, which are required when considering gradient-based inversions. This paper proposes a framework for organizing and implementing electromagnetic simulations and gradient-based inversions in a modular, extensible fashion. We take an object-oriented approach for defining and organizing each of the necessary elements in an electromagnetic simulation, including: the physical properties, sources, formulation of the discrete problem to be solved, the resulting fields and fluxes, and receivers used to sample to the electromagnetic responses. A corresponding implementation is provided as part of the open source simulation and parameter estimation project SIMPEG (http://simpeg.xyz). The application of the framework is demonstrated through two synthetic examples and one field example. The first example shows the application of the common framework for 1D time domain and frequency domain inversions. The second is a field example that demonstrates a 1D inversion of electromagnetic data collected over the Bookpurnong Irrigation District in Australia. The final example is a 3D example which shows how the modular implementation is used to compute the
Crane, Randolph W.; Marts, Donna J.
1994-01-01
An electromagnetic fastener for manipulating objects in space uses the matic attraction of various metals. An end effector is attached to a robotic manipulating system having an electromagnet such that when current is supplied to the electromagnet, the object is drawn and affixed to the end effector, and when the current is withheld, the object is released. The object to be manipulated includes a multiplicity of ferromagnetic patches at various locations to provide multiple areas for the effector on the manipulator to become affixed to the object. The ferromagnetic patches are sized relative to the object's geometry and mass.
A Study on Frequency-domain Division Based on Channel Equalization%基于通道均衡的频域除法研究
Institute of Scientific and Technical Information of China (English)
魏文斌; 于文震; 王秀春
2011-01-01
在频域通道均衡中,一个关键技术是求解均衡滤波器的响应.文中利用循环卷积和离散傅里叶变换乘积之间的关系,研究了通道均衡中频域除法的两类求解法:一类是时域算法,包括循环矩阵伪逆求解法和循环卷积求循环反卷积算法;另一类是基于最小范数的矩阵形式的频域算法.借助于仿真数据,根据求得的均衡滤波器和待校滤波器的卷积对参考滤波器的逼近误差,验证了上述算法的有效性.实验结果表明,基于最小范数的矩阵形式的频域算法在逼近性能、实时性方面均优于上面两种时域算法.%In frequency-domain channel equalization, one of the most crucial technologies is to seek the response of an equalization filter. AccordinS to the relation between the circular convolution in the time domain and the DFT product in the frequency domain,it is referred that two classes of algorithms on frequency-domain division in channel equalization, one class is time-domain algorithms which include an algorithm to seek the pseudo-inverse of a circular matrix and another algorithm to seek the deconvolution by circular convolution , the other is a frequency-domain algorithm having the least MSRe with matrix form. Accordinfl; to the error with the convolution between the filter to be emended and the corresponding equalization filter approximating the reference filter, the validity of the above algonthms is tested. The experimemal results shows that the frequency-domain algonthm having the least MSRe with matrix form excels those two time-domain algorithms in both approximation degree and real time.
Thomas, David T; Hartnett, James P; Hughes, William F
1973-01-01
The applications involving electromagnetic fields are so pervasive that it is difficult to estimate their contribution to the industrial output: generation of electricity, power transmission lines, electric motors, actuators, relays, radio, TV and microwave transmission and reception, magnetic storage, and even the mundane little magnet used to hold a paper note on the refrigerator are all electromagnetic in nature. One would be hard pressed to find a device that works without relaying on any electromagnetic principle or effect. This text provides a good theoretical understanding of the electromagnetic field equations but also treats a large number of applications. In fact, no topic is presented unless it is directly applicable to engineering design or unless it is needed for the understanding of another topic. In electrostatics, for example, the text includes discussions of photocopying, ink-jet printing, electrostatic separation and deposition, sandpaper production, paint spraying, and powder coating. In ma...
... causes cancer. Some people worry that wireless and cellular phones cause cancer or other health problems. The phones do give off radio-frequency energy (RF), a form of electromagnetic radiation. So far, scientific evidence has not found a ...
2012-03-01
DISTRIBUTION STATEMENT A: Approved for Public Release Electromagnetic Railgun ASNE Combat System Symposium 26-29 March 2012 CAPT Mike...4. TITLE AND SUBTITLE Electromagnetic Railgun 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER...Defense 3/29/2012 Slide 5 Distribution A Naval Railgun – Key Elements Capacitors or Rotating Machines Ship Integration Launcher Projectile
DEFF Research Database (Denmark)
Cermak, Daniel; Okutsu, Ayaka; Jørgensen, Stina Marie Hasse
2015-01-01
Daniel Cermak-Sassenrath, Ayaka Okutsu, Stina Hasse. Electromagnetic Landscape - In-between Signal, Noise and Environment. Installation and artist talk. 21th International Symposium on Electronic Art (ISEA) 2015, Vancouver, CAN, Aug 14-18, 2015.......Daniel Cermak-Sassenrath, Ayaka Okutsu, Stina Hasse. Electromagnetic Landscape - In-between Signal, Noise and Environment. Installation and artist talk. 21th International Symposium on Electronic Art (ISEA) 2015, Vancouver, CAN, Aug 14-18, 2015....
Controlled source electromagnetic methods in geothermal exploration
Energy Technology Data Exchange (ETDEWEB)
Ward, S.H.
1983-04-01
The objective of this manuscript is to sketch the problems inherent in application of controlled source electromagnetic methods (CSEM) to geothermal exploration. Measurements have been made in both the time and frequency domains with time domain measurements currently enjoying an advantage over frequency domain measurements for shallow applications. Application of CSEM methods is impeded by natural field, electrification, geological, cultural, and topographic noise. Lateral resolution of parameters of adjacent steeply dipping bodies and vertical resolution of parameters of adjacent beds in a flatly dipping sequence are concerns with any CSEM method. Current channeling into a localized good conductor form a surrounding, overlying, or underlying conductor poses problems for the interpreter. In selecting a transmitter-receiver configuration for CSEM in a particular application, a compromise is usually achieved between such factors as domain of data acquisition, rejection of noise, resolution, current channeling, and depth of exploration. Not surprisingly there is only marginal agreement on the optimum selection of each of these variables. However, one of the more promising techniques for application in geothermal exploration is the controlled source audiomagnetotelluric method (CSAMT).
Institute of Scientific and Technical Information of China (English)
王保利; 张唤兰; 张庆庆
2016-01-01
Using ray tracing to carry out travel time computation on grid based 2D model, then carried out Love type channel wave trans⁃mission record synthesis. Considering frequency dispersion, adsorption attenuation impacts on wave field amplitude, phase, carried out frequency domain synthesis for thin coal belt model transmission channel wave theoretic record, and analyzed wave field characteris⁃tics. The result has shown that frequency domain synthesis channel wave transmission record is consistent with theoretical analysis on attributes of time, frequency dispersion characteristics and energy, and similar to 3D elastic wave equation simulated fundamental Love type channel wave field characteristics, but frequency domain synthesis algorithm computed velocity is quicker 1~2 orders of magni⁃tude.%利用射线追踪对网格化的二维模型进行走时计算，在频率域对Love型透射槽波记录进行了合成。在考虑了频散、吸收衰减等对波场振幅、相位影响的基础上，对含薄煤带模型的透射槽波理论记录进行了频域合成，并进行了波场特征分析。结果表明：频域合成的槽波透射记录在时间、频散特征、能量等属性上与理论分析一致，且与三维弹性波波动方程模拟的基阶Love型槽波波场特征相似，但频域合成算法的计算速度快1~2个数量级。
Energy Technology Data Exchange (ETDEWEB)
Zhang, G.; Katz, A.; Alfano, R.R. [Institute for Ultrafast Spectroscopy and Lasers and New York State Center for Advanced Technology for Ultrafast Photonic Materials and Applications Department of Electrical Engineering and Physics, The City College of the City University of New York, 138th Street and Convent Avenue, New York, NY 10031 (United States); Kofinas, A.D.; Kofinas, D.A.; Beyer, D. [Departments of Obstetrics and Gynecology and Medicine, The Brooklyn Hospital Center, The Affiliate of Weill Medical College of Cornell University, 121 De Kalb Avenue, Brooklyn, NY 11201 (United States); Stubblefield, P.G. [Department of Obstetrics and Gynecology, Boston University School of Medicine, 1 Boston Medical Center Place, Boston, MA 02118 (United States); Rosenfeld, W.; Maulik, D. [Departments of Obstetrics and Gynecology and Pediatrics, Winthrop University Hospital, State University of New York at Stony Brook, 251 First Street, Mineola, New York 11501 (United States); Stankovic, M.R. [Departments of Obstetrics and Gynecology and Medicine, The Brooklyn Hospital Center, The Affiliate of Weill Medical College of Cornell University, 121 De Kalb Avenue, Brooklyn, NY 11201 (United States); Department of Obstetrics and Gynecology, Boston University School of Medicine, 1 Boston Medical Center Place, Boston, MA 02118 (United States); Departments of Obstetrics and Gynecology and Pediatrics, Winthrop University Hospital, State University of New York at Stony Brook, 251 First Street, Mineola, New York 11501 (United States)
2000-11-01
The newborn piglet brain model was used to correlate continuous-wave (CW) and frequency-domain (FD) near-infrared spectroscopy. Six ventilated and instrumented newborn piglets were subjected to a series of manipulations in blood oxygenation with the effects on brain perfusion known to be associated with brain hypoxia-ischaemia. An excellent agreement between the CW and FD was demonstrated. This agreement improved when the scattering properties (determined by the FD device) were employed to calculate the differential pathlength factor, an important step in CW data processing. (author)
Energy Technology Data Exchange (ETDEWEB)
Signorelli, G., E-mail: giovanni.signorelli@pi.infn.it [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Baldini, A.M. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Bemporad, C. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Università di Pisa, Dipartimento di Fisica, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Biasotti, M. [INFN Sezione di Genova and Università degli studi di Genova, Via Dodecaneso 33, 16146 Genova (Italy); Cei, F. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Università di Pisa, Dipartimento di Fisica, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Ceriale, V.; Corsini, D.; Fontanelli, F. [INFN Sezione di Genova and Università degli studi di Genova, Via Dodecaneso 33, 16146 Genova (Italy); Galli, L.; Gallucci, G. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Gatti, F. [INFN Sezione di Genova and Università degli studi di Genova, Via Dodecaneso 33, 16146 Genova (Italy); Incagli, M.; Grassi, M. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Nicolò, D. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Università di Pisa, Dipartimento di Fisica, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Spinella, F. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Vaccaro, D. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Università di Pisa, Dipartimento di Fisica, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Venturini, M. [INFN Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy)
2016-07-11
We present the design, implementation and first tests of the superconducting LC filters for the frequency domain readout of spiderweb TES bolometers of the SWIPE experiment on the balloon-borne LSPE mission which aims at measuring the linear polarization of the Cosmic Microwave Background at large angular scales to find the imprint of inflation on the B-mode CMB polarization. LC filters are designed, produced and tested at the INFN sections of Pisa and Genoa where thin film deposition and cryogenic test facilities are present, and where also the TES spiderweb bolometers are being produced.
Li, Danyu; He, Jing; Tang, Jin; Chen, Ming; Chen, Lin
2014-12-01
A half cycle 64-quadrature amplitude modulation (QAM) Nyquist subcarrier modulation (SCM) polarization division multiplexing (PDM) intensity modulation direct detection optical communication system is experimentally demonstrated. At the receiver, training sequences-based channel estimation and an overlap frequency domain equalization method are proposed to enhance the system performance. The experimental results show that the half cycle 64-QAM Nyquist-SCM PDM signal can be transmitted over 43-km standard single-mode fibers with a bit error rate below the forward error coding threshold of 2.4×10-2.
Time-Domain Computation Of Electromagnetic Fields In MMICs
Lansing, Faiza S.; Rascoe, Daniel L.
1995-01-01
Maxwell's equations solved on three-dimensional, conformed orthogonal grids by finite-difference techniques. Method of computing frequency-dependent electrical parameters of monolithic microwave integrated circuit (MMIC) involves time-domain computation of propagation of electromagnetic field in response to excitation by single pulse at input terminal, followed by computation of Fourier transforms to obtain frequency-domain response from time-domain response. Parameters computed include electric and magnetic fields, voltages, currents, impedances, scattering parameters, and effective dielectric constants. Powerful and efficient means for analyzing performance of even complicated MMIC.
Two-Component Multi-Parameter Time-Frequency Electromagnetics
Institute of Scientific and Technical Information of China (English)
HuangZhou; DongWeibin; HeTiezhi
2003-01-01
The two-component multi-parameter time-frequency electromagnetic method, used for the development of oilfields,makes use of both the traditional individual conductivity parameters of oil-producing layers and the dispersion information of the conductivity, i.e., the induced polarization parameter. The frequency-domain dispersion data is used to delineate the contacts between oil and water and the time domain dBz/dt component is used to estimate the depths to the un-known reservoirs so as to offer significant data in many aspects for oil exploration and detection.
Pawlak, M.
2017-09-01
The frequency-domain expression for the photoluminescence signal SPL (the photocarrier radiometry signal which is the form of the near infrared photoluminescence) which consists of the discrete lifetimes can be written as following [1
基于频域的图像增强技术研究%Study on Image Enhancement Technique Based on Frequency Domain
Institute of Scientific and Technical Information of China (English)
关雪梅
2012-01-01
Image enhancement is a kind of basic image processing technology,the purpose of which is to process the image,to be applied to specific Visual effects for better,more useful images.Image enhancement technology currently used,according to the different processing space,can be divided into image enhancement method based on frequency domain and spatial domain method for image enhancement.This article is intended primarily for image enhancement method in frequency domain for research,including low-pass,high-pass filtering method and homomorphic filtering method.%图像增强是一类基本的图像处理技术,其目的是对图像进行加工,以得到对具体应用来说视觉效果更好、更有用的图像。目前常用的图像增强技术根据处理空间的不同,可分为基于频域的图像增强方法和基于空域的图像增强方法。文中主要针对频域图像增强方法进行研究,包括低通滤波方法、高通滤波方法和同态滤波方法。
Hu, Dong; Fu, Xiaping; He, Xueming; Ying, Yibin
2016-12-01
Spatial-frequency domain imaging (SFDI), as a noncontact, low-cost and wide-field optical imaging technique, offers great potential for agro-product safety and quality assessment through optical absorption (μa) and scattering (μ) property measurements. In this study, a laboratory-based SFDI system was constructed and developed for optical property measurement of fruits and vegetables. The system utilized a digital light projector to generate structured, periodic light patterns and illuminate test samples. The diffuse reflected light was captured by a charge coupled device (CCD) camera with the resolution of 1280 × 960 pixels. Three wavelengths (460, 527, and 630 nm) were selected for image acquisition using bandpass filters in the system. The μa and μ were calculated in a region of interest (ROI, 200 × 300 pixels) via nonlinear least-square fitting. Performance of the system was demonstrated through optical property measurement of ‘Redstar’ apples. Results showed that the system was able to acquire spatial-frequency domain images for demodulation and calculation of the μa and μ. The calculated μa of apple tissue experiencing internal browning (IB) were much higher than healthy apple tissue, indicating that the SFDI technique had potential for IB tissue characterization.
Husa, Sascha; Hannam, Mark; Pürrer, Michael; Ohme, Frank; Forteza, Xisco Jiménez; Bohé, Alejandro
2015-01-01
In this paper we discuss the anatomy of frequency-domain gravitational-wave signals from non-precessing 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 augment...