Frequency domain nonlinear optics
NASA Astrophysics Data System (ADS)
Legare, Francois
2016-05-01
The universal dilemma of gain narrowing occurring in fs amplifiers prevents ultra-high power lasers from delivering few-cycle pulses. This problem is overcome by a new amplification concept: Frequency domain Optical Parametric Amplification - FOPA. It enables simultaneous up-scaling of peak power and amplified spectral bandwidth and can be performed at any wavelength range of conventional amplification schemes, however, with the capability to amplify single cycles of light. The key idea for amplification of octave-spanning spectra without loss of spectral bandwidth is to amplify the broad spectrum ``slice by slice'' in the frequency domain, i.e. in the Fourier plane of a 4f-setup. The striking advantages of this scheme, are its capability to amplify (more than) one octave of bandwidth without shorting the corresponding pulse duration. This is because ultrabroadband phase matching is not defined by the properties of the nonlinear crystal employed but the number of crystals employed. In the same manner, to increase the output energy one simply has to increase the spectral extension in the Fourier plane and to add one more crystal. Thus, increasing pulse energy and shortening its duration accompany each other. A proof of principle experiment was carried out at ALLS on the sub-two cycle IR beam line and yielded record breaking performance in the field of few-cycle IR lasers. 100 μJ two-cycle pulses from a hollow core fibre compression setup were amplified to 1.43mJ without distorting spatial or temporal properties. Pulse duration at the input of FOPA and after FOPA remains the same. Recently, we have started upgrading this system to be pumped by 250 mJ to reach 40 mJ two-cycle IR few-cycle pulses and latest results will be presented at the conference. Furthermore, the extension of the concept of FOPA to other nonlinear optical processes will be discussed. Frequency domain nonlinear optics.
Frequency domain optical parametric amplification
NASA Astrophysics Data System (ADS)
Schmidt, Bruno E.; Thiré, Nicolas; Boivin, Maxime; Laramée, Antoine; Poitras, François; Lebrun, Guy; Ozaki, Tsuneyuki; Ibrahim, Heide; Légaré, François
2014-05-01
Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43 mJ two-cycle pulses at 1.8 μm wavelength.
Frequency domain optical parametric amplification
Schmidt, Bruno E.; Thiré, Nicolas; Boivin, Maxime; Laramée, Antoine; Poitras, François; Lebrun, Guy; Ozaki, Tsuneyuki; Ibrahim, Heide; Légaré, François
2014-01-01
Today’s ultrafast lasers operate at the physical limits of optical materials to reach extreme performances. Amplification of single-cycle laser pulses with their corresponding octave-spanning spectra still remains a formidable challenge since the universal dilemma of gain narrowing sets limits for both real level pumped amplifiers as well as parametric amplifiers. We demonstrate that employing parametric amplification in the frequency domain rather than in time domain opens up new design opportunities for ultrafast laser science, with the potential to generate single-cycle multi-terawatt pulses. Fundamental restrictions arising from phase mismatch and damage threshold of nonlinear laser crystals are not only circumvented but also exploited to produce a synergy between increased seed spectrum and increased pump energy. This concept was successfully demonstrated by generating carrier envelope phase stable, 1.43 mJ two-cycle pulses at 1.8 μm wavelength. PMID:24805968
NASA Astrophysics Data System (ADS)
Gu, Xuejun; Kim, Hyun K.; Masciotti, James; Hielscher, Andreas H.
2009-02-01
Computational speed and available memory size on a single processor are two limiting factors when using the frequency-domain equation of radiative transport (FD-ERT) as a forward and inverse model to reconstruct three-dimensional (3D) tomographic images. In this work, we report on a parallel, multiprocessor reducedspace sequential quadratic programming (RSQP) approach to improve computational speed and reduce memory requirement. To evaluate and quantify the performance of the code, we performed simulation studies employing a 3D numerical mouse model. Furthermore, we tested the algorithm with experimental data obtained from tumor bearing mice.
Culver, J P; Choe, R; Holboke, M J; Zubkov, L; Durduran, T; Slemp, A; Ntziachristos, V; Chance, B; Yodh, A G
2003-02-01
Three-dimensional diffuse optical tomography (DOT) of breast requires large data sets for even modest resolution (1 cm). We present a hybrid DOT system that combines a limited number of frequency domain (FD) measurements with a large set of continuous wave (cw) measurements. The FD measurements are used to quantitatively determine tissue averaged absorption and scattering coefficients. The larger cw data sets (10(5) measurements) collected with a lens coupled CCD, permit 3D DOT reconstructions of a 1-liter tissue volume. To address the computational complexity of large data sets and 3D volumes we employ finite difference based reconstructions computed in parallel. Tissue phantom measurements evaluate imaging performance. The tests include the following: point spread function measures of resolution, characterization of the size and contrast of single objects, field of view measurements and spectral characterization of constituent concentrations. We also report in vivo measurements. Average tissue optical properties of a healthy breast are used to deduce oxy- and deoxy-hemoglobin concentrations. Differential imaging with a tumor simulating target adhered to the surface of a healthy breast evaluates the influence of physiologic fluctuations on image noise. This tomography system provides robust, quantitative, full 3D image reconstructions with the advantages of high data throughput, single detector-tissue coupling path, and large (1L) imaging domains. In addition, we find that point spread function measurements provide a useful and comprehensive representation of system performance.
Optical wire guided lumpectomy: frequency domain measurements
NASA Astrophysics Data System (ADS)
Dayton, A. L.; Keränen, V. T.; Prahl, S. A.
2009-02-01
In practice, complete removal of the tumor during a lumpectomy is difficult; the published rates of positive margins range from 10% to 50%. A spherical lumpectomy specimen with tumor directly in the middle may improve the success rate. A light source placed within the tumor may accomplish this goal by creating a sphere surrounding the tumor that can serve as a guide for resection. In an optical phantom and a prophylactic mastectomy specimen, sinusoidally modulated light within the medium was collected by optical fiber(s) at fixed distance(s) from the source and used to measure the optical properties. These optical properties were then used to calculate the distance the light had traveled through the medium. The fiber was coupled to an 830nm diode laser that was modulated at 100, 200 and 300 MHz. A handheld optical probe collected the modulated light and a network analyzer measured the phase lag. This data was used to calculate the distance the light traveled from the emitting fiber tip to the probe. The optical properties were μa = 0.004mm-1 and μ1s = 0.38mm-1 in the phantom. The optical properties for the tissue were μa = 0.005mm-1 and μ1s = 0.20mm-1. The prediction of distance from the source was within 4mm of the actual distance at 30mm in the phantom and within 3mm of the actual distance at 25mm in the tissue. The feasibility of a frequency domain system that makes measurements of local optical properties and then extrapolates those optical properties to make measurements of distance with a separate probe was demonstrated.
Frequency Domain Optical Coherence Tomography Techniques in Eye Imaging
NASA Astrophysics Data System (ADS)
Wojtkowski, M.; Kowalczyk, A.; Targowski, P.; Gorczyñska, I.
2000-12-01
This contribution presents an application of frequency-domain optical tomography to ophthalmology. Essential theoretical foundations of time-domain and frequency-domain optical tomography are presented. Images of sections through the anterior chamber, the corneo-scleral angle and fundus of the eye are reconstructed from the spectral fringes. The morphological information gained by tomograms is important for diagnosing and planning of a treatment of glaucoma.
Frequency domain optical tomography using a Monte Carlo perturbation method
NASA Astrophysics Data System (ADS)
Yamamoto, Toshihiro; Sakamoto, Hiroki
2016-04-01
A frequency domain Monte Carlo method is applied to near-infrared optical tomography, where an intensity-modulated light source with a given modulation frequency is used to reconstruct optical properties. The frequency domain reconstruction technique allows for better separation between the scattering and absorption properties of inclusions, even for ill-posed inverse problems, due to cross-talk between the scattering and absorption reconstructions. The frequency domain Monte Carlo calculation for light transport in an absorbing and scattering medium has thus far been analyzed mostly for the reconstruction of optical properties in simple layered tissues. This study applies a Monte Carlo calculation algorithm, which can handle complex-valued particle weights for solving a frequency domain transport equation, to optical tomography in two-dimensional heterogeneous tissues. The Jacobian matrix that is needed to reconstruct the optical properties is obtained by a first-order "differential operator" technique, which involves less variance than the conventional "correlated sampling" technique. The numerical examples in this paper indicate that the newly proposed Monte Carlo method provides reconstructed results for the scattering and absorption coefficients that compare favorably with the results obtained from conventional deterministic or Monte Carlo methods.
Distributed dynamic strain measurement using optical frequency-domain reflectometry.
Zhou, Da-Peng; Chen, Liang; Bao, Xiaoyi
2016-08-20
Distributed dynamic strain measurement based on optical frequency-domain reflectometry is proposed. The technique makes use of the wide scanning range of a tunable laser source in a short sweeping time, and subdivides the overall spectrum into narrower frequency windows. The advantage of subdividing the laser spectral range is to improve the measurement uncertainty induced by the laser wavelength difference between repeated scans. The noise-limited dynamic strain resolution is investigated experimentally, indicating that a minimum detectable strain is less than 200 nε for a spatial resolution of 20 cm. By measuring the subdivided spectral shifts in the time sequence along the sensing fiber, the dynamic strain can be properly quantified over a 30 m measurement range for a highest sampling rate of up to 50 Hz. PMID:27556996
Optical Frequency Domain Visualization of Electron Beam Driven Plasma Wakefields
NASA Astrophysics Data System (ADS)
Zgadzaj, Rafal; Downer, M. C.; Muggli, Patric; Yakimenko, Vitaly; Babzien, Marcus; Kusche, Karl; Fedurin, Mikhail
2010-11-01
Beam-driven plasma wakefield accelerators (PWFA), such as the ``plasma afterburner,'' are a promising approach for significantly increasing the particle energies of conventional accelerators. The study and optimization of PWFA would benefit from an experimental correlation between the parameters of the drive bunch, the accelerated bunch and the corresponding, accelerating plasma wave structure. However, the plasma wave structure has not yet been observed directly in PWFA. We will report our current work on noninvasive optical Frequency Domain Interferometric (FDI) and Holographic (FDH) visualization of beam-driven plasma waves. Both techniques employ two laser pulses (probe and reference) co-propagating with the particle drive-beam and its plasma wake. The reference pulse precedes the drive bunch, while the probe overlaps the plasma wave and maps its longitudinal and transverse structure. The experiment is being developed at the BNL/ATF Linac to visualize wakes generated by two and multi-bunch drive beams.
Optical Frequency Domain Visualization of Electron Beam Driven Plasma Wakefields
NASA Astrophysics Data System (ADS)
Zgadzaj, Rafal; Downer, Michael C.; Muggli, Patric; Yakimenko, Vitaly; Kusche, Karl; Fedurin, Michhail; Babzien, Marcus
2010-11-01
Bunch driven plasma wakefield accelerators (PWFA), such as the "plasma afterburner," are a promising emerging method for significantly increasing the energy output of conventional particle accelerators [1]. The study and optimization of this method would benefit from an experimental correlation of the drive bunch parameters and the accelerated particle parameters with the corresponding plasma wave structure. However, the plasma wave structure has not been observed directly so far. We will report ongoing development of a noninvasive optical Frequency Domain Interferometric (FDI) [2] and Holographic (FDH) [3] diagnostics of bunch driven plasma wakes. Both FDI and FDH have been previously demonstrated in the case of laser driven wakes. These techniques employ two laser pulses co-propagating with the drive particle bunch and the trailing plasma wave. One pulse propagates ahead of the drive bunch and serves as a reference, while the second is overlapped with the plasma wave and probes its structure. The multi-shot FDI and single-shot FDH diagnostics permit direct noninvasive observation of longitudinal and transverse structure of the plasma wakes. The experiment is being developed at the 70 MeV Linac in the Accelerator Test Facility at Brookhaven National Laboratory to visualize wakes generated by two [4] and multi-bunch [5] drive beams.
Polarization sensitive optical frequency domain imaging system for endobronchial imaging.
Li, Jianan; Feroldi, Fabio; de Lange, Joop; Daniels, Johannes M A; Grünberg, Katrien; de Boer, Johannes F
2015-02-01
A polarization sensitive endoscopic optical frequency domain imaging (PS-OFDI) system with a motorized distal scanning catheter is demonstrated. It employs a passive polarization delay unit to multiplex two orthogonal probing polarization states in depth, and a polarization diverse detection unit to detect interference signal in two orthogonal polarization channels. Per depth location four electro-magnetic field components are measured that can be represented in a complex 2x2 field matrix. A Jones matrix of the sample is derived and the sample birefringence is extracted by eigenvalue decomposition. The condition of balanced detection and the polarization mode dispersion are quantified. A complex field averaging method based on the alignment of randomly pointing field phasors is developed to reduce speckle noise. The variation of the polarization states incident on the tissue due to the circular scanning and catheter sheath birefringence is investigated. With this system we demonstrated imaging of ex vivo chicken muscle, in vivo pig lung and ex vivo human lung specimens. PMID:25836196
Broad bandwidth frequency domain instrument for quantitative tissue optical spectroscopy
Pham, Tuan H.; Coquoz, Olivier; Fishkin, Joshua B.; Anderson, Eric; Tromberg, Bruce J.
2000-06-01
Near-infrared (NIR) optical properties of turbid media, e.g., tissue, can be accurately quantified noninvasively using methods based on diffuse reflectance or transmittance, such as frequency domain photon migration (FDPM). Factors which govern the accuracy and sensitivity of FDPM-measured optical properties include instrument performance, the light propagation model, and fitting algorithms used to calculate optical properties from measured data. In this article, we characterize instrument, model, and fitting uncertaintics of an FDPM system designed for clinical use and investigate how each of these factors affects the quantification of NIR absorption ({mu}{sub a}) and reduced scattering ({mu}{sub s}{sup '}) parameters in tissue phantoms. The instrument is based on a 500 MHz, multiwavelength platform that sweeps through 201 discrete frequencies in as little as 675 ms. Phase and amplitude of intensity modulated light launched into tissue, i.e., diffuse photon density waves (PDW), are measured with an accuracy of {+-}0.30 degree sign and {+-}3.5%, while phase and amplitude precision are {+-}0.025 degree sign and {+-}0.20%, respectively. At this level of instrument uncertainty, simultaneous fitting of frequency-dependent phase and amplitude nonlinear model functions derived from a photon diffusion approximation provides an accurate and robust strategy for determining optical properties from FDPM data, especially for media with high absorption. In an optical property range that is characteristic of most human tissues in the NIR (5x10{sup -3}<{mu}{sub a}<5x10{sup -2} mm{sup -1}, 0.5<{mu}{sub s}{sup '}<2 mm{sup -1}), we theoretically and experimentally demonstrate that the multifrequency, simultaneous-fit approach allows {mu}{sub a} and {mu}{sub s}{sup '} to be quantified with an accuracy of {+-}5% and {+-}3%, respectively. Although exceptionally high levels of precision can be obtained using this approach (<1% of the estimated absorption and scattering values), we show
High-resolution frequency domain second harmonic optical coherence tomography
NASA Astrophysics Data System (ADS)
Su, Jianping; Tomov, I. V.; Jiang, Yi; Chen, Zhongping
2007-02-01
We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain SH-OCT to 12μm. The acquisition time was shortened by more than two orders of magnitude compared to time domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on second harmonic has been used to obtain polarization resolved images.
Quantum theory of optical coherence of nonstationary light in the space-frequency domain
Lahiri, Mayukh; Wolf, Emil
2010-10-15
Classical theories of coherence for statistically stationary, as well as, nonstationary optical fields are frequently discussed both in the space-time and in the space-frequency domains. However, the quantum treatment of coherence theory is generally carried out in the space-time domain. In this paper, we present a quantum-mechanical theory of first-order coherence for statistically nonstationary light in the space-frequency domain.
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.
Parallel full-waveform inversion in the frequency domain by the Gauss-Newton method
NASA Astrophysics Data System (ADS)
Zhang, Wensheng; Zhuang, Yuan
2016-06-01
In this paper, we investigate the full-waveform inversion in the frequency domain. We first test the inversion ability of three numerical optimization methods, i.e., the steepest-descent method, the Newton-CG method and the Gauss- Newton method, for a simple model. The results show that the Gauss-Newton method performs well and efficiently. Then numerical computations for a benchmark model named Marmousi model by the Gauss-Newton method are implemented. Parallel algorithm based on message passing interface (MPI) is applied as the inversion is a typical large-scale computational problem. Numerical computations show that the Gauss-Newton method has good ability to reconstruct the complex model.
Optical frequency domain reflectometry: principles and applications in fiber optic sensing
NASA Astrophysics Data System (ADS)
Kreger, Stephen T.; Rahim, Nur Aida Abdul; Garg, Naman; Klute, Sandra M.; Metrey, Daniel R.; Beaty, Noah; Jeans, James W.; Gamber, Robert
2016-05-01
Optical Frequency Domain Reflectometry (OFDR) is the basis of an emerging high-definition distributed fiber optic sensing (HD-FOS) technique that provides an unprecedented combination of resolution and sensitivity. OFDR employs swept laser interferometry to produce strain or temperature vs. sensor length with fiber Bragg gratings (FBGs) or Rayleigh scatter as the source signal. We look at the influence of HD-FOS on design and test of new, lighter weight, stronger and more fuel efficient vehicles. Examples include defect detection, model verification and structural health monitoring of composites, and temperature distribution monitoring of battery packs and inverters in hybrid and electric powertrains.
Spatially-dense, multi-spectral, frequency-domain diffuse optical tomography of breast cancer
NASA Astrophysics Data System (ADS)
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
High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing.
Maclachlan, Robert A; Riviere, Cameron N
2009-06-01
Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm × 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-μm peak-to-peak resolution at 1-kHz sampling.
High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing.
Maclachlan, Robert A; Riviere, Cameron N
2009-06-01
Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm × 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-μm peak-to-peak resolution at 1-kHz sampling. PMID:20428484
Removing the depth-degeneracy in optical frequency domain imaging with frequency shifting
Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Bouma, B. E.
2009-01-01
A novel technique using an acousto-optic frequency shifter in optical frequency domain imaging (OFDI) is presented. The frequency shift eliminates the ambiguity between positive and negative differential delays, effectively doubling the interferometric ranging depth while avoiding image cross-talk. A signal processing algorithm is demonstrated to accommodate nonlinearity in the tuning slope of the wavelength-swept OFDI laser source. PMID:19484034
Frequency-domain single-shot optical frequency comb tomography using VIPA
NASA Astrophysics Data System (ADS)
Miyaoka, Takumi; Shioda, Tatsutoshi
2016-03-01
Novel two-dimensional single-shot imaging optical system based on Frequency-domain interferometry using a virtually imaged phased array is proposed. The VIPA simultaneously outputs incoherent optical frequency combs (OFCs) whose teeth interval are scanned as a function of its output angle. Teeth intervals of the OFCs only in a reference are spatially swept by using of a VIPA whose advantage compared to an optical resonator. Thus, the single-shot imaging system can be realized with the FSR scanned frequency-domain OFC interference monitored by CCD. This system enable high speed 2-dimensional tomographic image without mechanical moving part. And the axial measurement range is not limited by using multi-order interference that is generated by OFCs interferometry. We will present the operation principle with its confirmed results in terms of both simulation and experiment.
Real-time frequency-domain fiber optic sensor for intra-arterial blood oxygen measurements
NASA Astrophysics Data System (ADS)
Alcala, J. R.; Scott, Ian L.; Parker, Jennifer W.; Atwater, Beauford W.; Yu, Clement; Fischer, Russell; Bellingrath, K.
1993-05-01
A real time frequency domain phosphorimeter capable of measuring precise and accurate excited state lifetimes for determining oxygen is described. This frequency domain instrument does not make use of cross correlation techniques traditionally used in frequency domain fluorometers. Instead, the electrical signal from the detector is filtered to contain only the first several harmonics. This filtered signal is then sampled and averaged over a few thousand cycles. The absolute phase and absolute modulation of each sampled harmonic of the excitation and of the luminescence is computed by employing fast Fourier transform algorithms. The phase delay and the modulation ratio is then calculated at each harmonic frequency. A least squares fit is performed in the frequency domain to obtain the lifetimes of discrete exponentials. Oxygen concentrations are computed from these lifetimes. Prototypes based on these techniques were built employing commercially available components. Results from measurements in saline solution and in the arterial blood of dogs show that oxygen concentrations can be determined reproducibly. The system drift is less than 1% in over 100 hours of continuous operation. The performance of fiber optic sensors was evaluated in dogs over a period of 10 hours. The sensors tracked changes in arterial oxygen tension over the course of the experiment without instabilities. The overall response of the system was about 90 seconds. The update time was 3 seconds.
High speed 3D endoscopic optical frequency domain imaging probe for lung cancer diagnosis
NASA Astrophysics Data System (ADS)
Li, Jianan; Feroldi, Fabio; Mo, Jianhua; Helderman, Frank; de Groot, Mattijs; de Boer, Johannes F.
2013-06-01
We present a miniature motorized endoscopic probe for Optical Frequency Domain Imaging with an outer diameter of 1.65 mm and a rotation speed of 3,000 - 12,500 rpm. The probe has a motorized distal end which provides a significant advantage over proximally driven probes since it does not require a drive shaft to transfer the rotational torque to the distal end of the probe and functions without a fiber rotary junction. The probe has a focal Full Width at Half Maximum of 9.6 μm and a working distance of 0.47 mm. We analyzed the non-uniform rotation distortion and found a location fluctuation of only 1.87° in repeated measurements of the same object. The probe was integrated in a high-speed Optical Frequency Domain Imaging setup at 1310 nm. We demonstrated its performance with imaging ex vivo pig bronchial and in vivo goat lung.
Nonuniform strain measurement in composite material based on optical frequency domain reflection
NASA Astrophysics Data System (ADS)
Li, Huajun; Zhang, Dongsheng; Li, Litong; Wu, Mengqi; Wen, Xiaoyan
2016-06-01
Traditional electrical sensor or traditional fiber Bragg grating sensing technology is not applicable to the measurement of nonuniform strain in composite material. Therefore, the distributed nonuniform strain in the lap plate position of composite interlining material is measured using a single fiber with optical frequency domain reflection technology in this study. The experimental results show consistency with the experiment phenomena, and the measurement accuracy could be increased to the submillimeter level.
NASA Astrophysics Data System (ADS)
Lin, Alexander J.; Konecky, Soren D.; Rice, Tyler B.; Green, Kim N.; Choi, Bernard; Durkin, Anthony J.; Tromberg, Bruce J.
2012-02-01
Early neurovascular coupling (NVC) changes in Alzheimer's disease can potentially provide imaging biomarkers to assist with diagnosis and treatment. Previous efforts to quantify NVC with intrinsic signal imaging have required assumptions of baseline optical pathlength to calculate changes in oxy- and deoxy-hemoglobin concentrations during evoked stimuli. In this work, we present an economical spatial frequency domain imaging (SFDI) platform utilizing a commercially available LED projector, camera, and off-the-shelf optical components suitable for imaging dynamic optical properties. The fast acquisition platform described in this work is validated on silicone phantoms and demonstrated in neuroimaging of a mouse model.
Brain connectivity study of joint attention using frequency-domain optical imaging technique
NASA Astrophysics Data System (ADS)
Chaudhary, Ujwal; Zhu, Banghe; Godavarty, Anuradha
2010-02-01
Autism is a socio-communication brain development disorder. It is marked by degeneration in the ability to respond to joint attention skill task, from as early as 12 to 18 months of age. This trait is used to distinguish autistic from nonautistic populations. In this study, diffuse optical imaging is being used to study brain connectivity for the first time in response to joint attention experience in normal adults. The prefrontal region of the brain was non-invasively imaged using a frequency-domain based optical imager. The imaging studies were performed on 11 normal right-handed adults and optical measurements were acquired in response to joint-attention based video clips. While the intensity-based optical data provides information about the hemodynamic response of the underlying neural process, the time-dependent phase-based optical data has the potential to explicate the directional information on the activation of the brain. Thus brain connectivity studies are performed by computing covariance/correlations between spatial units using this frequency-domain based optical measurements. The preliminary results indicate that the extent of synchrony and directional variation in the pattern of activation varies in the left and right frontal cortex. The results have significant implication for research in neural pathways associated with autism that can be mapped using diffuse optical imaging tools in the future.
Motion artifacts in optical coherence tomography with frequency-domain ranging
Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Bouma, B. E.
2009-01-01
We describe results of theoretical and experimental investigations of artifacts that can arise in spectral-domain optical coherence tomography (SD-OCT) and optical frequency domain imaging (OFDI) as a result of sample or probe beam motion. While SD-OCT and OFDI are based on similar spectral interferometric principles, the specifics of motion effects are quite different because of distinct signal acquisition methods. These results provide an understanding of motion artifacts such as signal fading, spatial distortion and blurring, and emphasize the need for fast image acquisition in biomedical applications. PMID:19483816
Ha, Jinyong; Yoo, Hongki; Tearney, Guillermo J; Bouma, Brett E
2012-08-01
Intracoronary optical coherence tomography and optical frequency domain imaging (OFDI) have been utilized for two-dimensional and three-dimensional imaging of vascular microanatomy. Image quality and the spatial accuracy of multidimensional reconstructions, however, can be degraded due to artifacts resulting from relative motion between the intracoronary catheter and the vessel wall. To track the relative motion of a catheter with regard to the vessel, a motion tracking system was incorporated with a standard OFDI system by using wavelength division multiplexing techniques. Motion of the vessel was acquired by a frequency shift of the backscattered light caused by the Doppler effect. A single monochromatic beam was utilized for tracking the relative longitudinal displacements of a catheter-based fiber probe with regard to the vessel. Although two tracking beams are, in general, required to correct for longitudinal motion artifacts, the accurate reconstruction in a longitudinal view was achieved by the Doppler frequency information of a single beam. Our results demonstrate that the single beam based motion tracking scheme is a cost-effective, practical approach to compensating for longitudinal distortions due to cardiac dynamics, thus leading to accurate quantitative analysis of 3D intracoronary OFDI.
Feasibility of direct digital sampling for diffuse optical frequency domain spectroscopy in tissue
NASA Astrophysics Data System (ADS)
Roblyer, Darren; O'Sullivan, Thomas D.; Warren, Robert V.; Tromberg, Bruce J.
2013-04-01
Frequency domain optical spectroscopy in the diffusive regime is currently being investigated for biomedical applications including tumor detection, therapy monitoring, exercise metabolism and others. Analog homodyne or heterodyne detection of sinusoidally modulated signals has been the predominant method for measuring phase and amplitude of photon density waves that have traversed through tissue. Here we demonstrate the feasibility of utilizing direct digital sampling of modulated signals using a 3.6 gigasample/second 12 bit analog to digital converter. Digitally synthesized modulated signals between 50 MHz and 400 MHz were measured on tissue-simulating phantoms at six near-infrared wavelengths. An amplitude and phase precision of 1% and 0.6° were achieved during drift tests. Amplitude, phase, scattering and absorption values were compared with a well-characterized network analyzer-based diffuse optical device. Optical properties measured with both systems were within 3.6% for absorption and 2.8% for scattering over a range of biologically relevant values. Direct digital sampling represents a viable method for frequency domain diffuse optical spectroscopy and has the potential to reduce system complexity, size and cost.
High-resolution frequency-domain second-harmonic optical coherence tomography
NASA Astrophysics Data System (ADS)
Su, Jianping; Tomov, Ivan V.; Jiang, Yi; Chen, Zhongping
2007-04-01
We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain second-harmonic optical coherence tomography (SH-OCT) to 12 μm. The acquisition time was shortened by more than 2 orders of magnitude compared to the time-domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon, and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on the SH has been used to obtain polarization resolved images.
NASA Astrophysics Data System (ADS)
Xu, T.; Jacobsen, G.; Popov, S.; Forzati, M.; Mårtensson, J.; Mussolin, M.; Li, J.; Wang, K.; Zhang, Y.; Friberg, A. T.
2011-06-01
The frequency domain equalizers (FDEs) employing two types of overlap-add zero-padding (OLA-ZP) methods are applied to compensate the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system. Simulation results demonstrate that the OLA-ZP methods can achieve the same acceptable performance as the overlapsave method. The required minimum overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier transform length to minimize the computational complexity is also analyzed.
Multipixel system for gigahertz frequency-domain optical imaging of finger joints
NASA Astrophysics Data System (ADS)
Netz, Uwe J.; Beuthan, Jürgen; Hielscher, Andreas H.
2008-03-01
Frequency-domain optical imaging systems have shown great promise for characterizing blood oxygenation, hemodynamics, and other physiological parameters in human and animal tissues. However, most of the frequency domain systems presented so far operate with source modulation frequencies below 150MHz. At these low frequencies, their ability to provide accurate data for small tissue geometries such as encountered in imaging of finger joints or rodents is limited. Here, we present a new system that can provide data up to 1GHz using an intensity modulated charged coupled device camera. After data processing, the images show the two-dimensional distribution of amplitude and phase of the light modulation on the finger surface. The system performance was investigated and test measurements on optical tissue phantoms were taken to investigate whether higher frequencies yield better signal-to-noise ratios (SNRs). It could be shown that local changes in optical tissue properties, as they appear in the initial stages of rheumatoid arthritis in a finger joint, are detectable by simple image evaluation, with the range of modulation frequency around 500MHz proving to yield the highest SNR.
Radiation effects on optical frequency domain reflectometry fiber-based sensor.
Rizzolo, S; Marin, E; Cannas, M; Boukenter, A; Ouerdane, Y; Périsse, J; Macé, J-R; Bauer, S; Marcandella, C; Paillet, P; Girard, S
2015-10-15
We investigate the radiation effects on germanosilicate optical fiber acting as the sensing element of optical frequency domain reflectometry devices. Thanks to a new setup permitting to control temperature during irradiation, we evaluate the changes induced by 10 keV x rays on their Rayleigh response up to 1 MGy in a temperature range from -40°C up to 75°C. Irradiation at fixed temperature points out that its measure is reliable during both irradiation and the recovery process. Mixed temperature and radiation measurements show that changing irradiation temperature leads to an error in distributed measurements that depends on the calibration procedure. These results demonstrate that Rayleigh-based optical fiber sensors are very promising for integration in harsh environments. PMID:26469566
High speed miniature motorized endoscopic probe for 3D optical frequency domain imaging
NASA Astrophysics Data System (ADS)
Li, Jianan; Feroldi, Fabio; Mo, Jianhua; Helderman, Frank; de Groot, Mattijs; de Boer, Johannes F.
2013-03-01
We present a miniature motorized endoscopic probe for Optical Frequency Domain Imaging with an outer diameter of 1.65 mm and a rotation speed of 3,000 - 12,500 rpm. This is the smallest motorized high speed OCT probe to our knowledge. The probe has a motorized distal end which provides a significant advantage over proximally driven probes since it does not require a drive shaft to transfer the rotational torque to the distal end of the probe and functions without a fiber rotary junction. The probe has a focal Full Width at Half Maximum of 9.6 μm and a working distance of 0.47 mm. We analyzed the non-uniform rotation distortion and found a location fluctuation of only 1.87° in repeated measurements of the same object. The probe was integrated in a high-speed Optical Frequency Domain Imaging setup at 1310 nm We demonstrated its performance with imaging ex vivo pig bronchial and in vivo goat lung.
Weng, Jidong; Tao, Tianjiong; Liu, Shenggang; Ma, Heli; Wang, Xiang; Liu, Cangli; Tan, Hua
2013-11-01
A new optical-fiber frequency domain interferometer (OFDI) device for accurate measurement of the absolute distance between two stationary objects, with centimeter measuring range and nanometer resolution, has been developed. Its working principle and on-line data processing method were elaborated. The new OFDI instrument was constructed all with currently available commercial communication products. It adopted the wide-spectrum amplified spontaneous emission light as the light source and optical-fiber tip as the test probe. Since this device consists of only fibers or fiber coupled components, it is very compact, convenient to operate, and easy to carry. By measuring the single-step length of a translation stage and the thickness of standard gauge blocks, its ability in implementing nanometer resolution and centimeter measuring range on-line measurements was validated.
Miniature swept source for point of care Optical Frequency Domain Imaging
Goldberg, Brian D.; Nezam, S.M. Reza Motaghian; Jillella, Priyanka; Bouma, Brett E.; Tearney, Guillermo J.
2009-01-01
Point of care (POC) medical technologies require portable, small, robust instrumentation for practical implementation. In their current embodiment, optical frequency domain imaging (OFDI) systems employ large form-factor wavelength-swept lasers, making them impractical in the POC environment. Here, we describe a first step toward a POC OFDI system by demonstrating a miniaturized swept-wavelength source. The laser is based on a tunable optical filter using a reflection grating and a miniature resonant scanning mirror. The laser achieves 75 nm of bandwidth centered at 1340 nm, a 0.24 nm instantaneous line width, a 15.3 kHz repetition rate with 12 mW peak output power, and a 30.4 kHz A-line rate when utilizing forward and backward sweeps. The entire laser system is approximately the size of a deck of cards and can operate on battery power for at least one hour. PMID:19259202
Compensation of motion artifacts in catheter-based optical frequency domain imaging
Ha, J. Y.; Shishkov, M.; Colice, M.; Oh, W. Y.; Yoo, H.; Liu, L.; Tearney, G. J.; Bouma, B. E.
2010-01-01
A novel heterodyne Doppler interferometer method for compensating motion artifacts caused by cardiac motion in intracoronary optical frequency domain imaging (OFDI) is demonstrated. To track the relative motion of a catheter with regard to the vessel, a motion tracking system is incorporated with a standard OFDI system by using wavelength division multiplexing (WDM) techniques. Without affecting the imaging beam, dual WDM monochromatic beams are utilized for tracking the relative radial and longitudinal velocities of a catheter-based fiber probe. Our results demonstrate that tracking instantaneous velocity can be used to compensate for distortion in the images due to motion artifacts, thus leading to accurate reconstruction and volumetric measurements with catheter-based imaging. PMID:20589002
Athanasiou, L S; Bourantas, C V; Siogkas, P K; Sakellarios, A I; Exarchos, T P; Naka, K K; Papafaklis, M I; Michalis, L K; Prati, F; Fotiadis, D I
2012-01-01
The aim of this study is to describe a new method for three-dimensional (3D) reconstruction of coronary arteries using Frequency Domain Optical Coherence Tomography (FD-OCT) images. The rationale is to fuse the information about the curvature of the artery, derived from biplane angiographies, with the information regarding the lumen wall, which is produced from the FD-OCT examination. The method is based on a three step approach. In the first step the lumen borders in FD-OCT images are detected. In the second step a 3D curve is produced using the center line of the vessel from the two biplane projections. Finally in the third step the detected lumen borders are placed perpendicularly onto the path based on the centroid of each lumen border. The result is a 3D reconstructed artery produced by all the lumen borders of the FD-OCT pullback representing the 3D arterial geometry of the vessel.
NASA Astrophysics Data System (ADS)
Sampathkumar, Ashwin
2015-05-01
In this paper, we describe a narrow-bandwidth generation and detection of photoacoustic (PA) signals in biological specimens using frequency-domain photoacoustics. An intensity-modulated laser was used for PA generation, and a homodyne Michelson interferometer coupled to a lock-in amplifier was used for optical PA detection. The amplitude and phase of the PA signal were measured at the modulation frequency as the frequency was swept over the bandwidth of interest. A synthesized pulse response was obtained using time-domain reconstruction and the absorber map was estimated using k-space reconstruction methods. Experimental results obtained from 500-μm graphite rods embedded in tissue-mimicking phantoms and slide-mounted tissue samples are presented along with their respective time-domain and time-reversal reconstruction maps.
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-01-01
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10−3 m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination. PMID:27146550
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry.
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-05-05
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10(-3) m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination.
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.
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry.
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-01-01
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10(-3) m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination. PMID:27146550
Real-time locating and speed measurement of fibre fuse using optical frequency-domain reflectometry
NASA Astrophysics Data System (ADS)
Jiang, Shoulin; Ma, Lin; Fan, Xinyu; Wang, Bin; He, Zuyuan
2016-05-01
We propose and experimentally demonstrate real-time locating and speed measurement of fibre fuse by analysing the Doppler shift of reflected light using optical frequency-domain reflectometry (OFDR). Our method can detect the start of a fibre fuse within 200 ms which is equivalent to a propagation distance of about 10 cm in standard single-mode fibre. We successfully measured instantaneous speed of propagating fibre fuses and observed their subtle fluctuation owing to the laser power instability. The resolution achieved for speed measurement in our demonstration is 1 × 10‑3 m/s. We studied the fibre fuse propagation speed dependence on the launched power in different fibres. Our method is promising for both real time fibre fuse monitoring and future studies on its propagation and termination.
Frequency-Domain Intravascular Optical Coherence Tomography of the Femoropopliteal Artery
Karnabatidis, Dimitris Katsanos, Konstantinos; Paraskevopoulos, Ioannis; Diamantopoulos, Athanasios; Spiliopoulos, Stavros; Siablis, Dimitris
2011-12-15
Purpose: Optical coherence tomography (OCT) is a catheter-based imaging method that employs near-infrared light to produce high-resolution intravascular images. The authors report the safety and feasibility and illustrate common imaging findings of frequency-domain OCT (FD-OCT) imaging of the femoropopliteal artery in a series of 20 patients who underwent infrainguinal angioplasty. Methods: After crossing the lesion of interest, OCT was performed with a dextrose saline flush technique with simultaneous obstructive manual groin compression. An automatic pullback FD-OCT device was employed (each scan acquiring 54 mm of vessel lumen in 271 consecutive frames). OCT images were acquired before and after balloon dilatation and following provisional stenting if necessary and were evaluated for baseline characteristics of plaque or in-stent restenosis (ISR), vessel wall trauma after angioplasty, presence of thrombus, stent apposition, and tissue prolapse. Imaging follow-up was not included in this study's protocol. Results: Twenty-seven obstructive lesions (18 cases of de novo atherosclerosis and 9 of ISR) of the femoropopliteal artery were imaged and 148 acquisitions were analyzed in total. High-resolution intravascular OCT imaging with effective blood clearance was achieved in 93.9%. Failure was mainly attributed to preocclusive proximal lesions and/or collateral flow. Mixed features of lipid pool areas, calcium deposits, necrotic core, and fibrosis were identified in all of the imaged atherosclerotic lesions, whereas ISR was purely fibrotic. After balloon angioplasty, OCT identified extensive intimal tears in all cases and one case of severe dissection that biplane subtraction angiography failed to identify. Conclusions: Infrainguinal frequency-domain optical coherence tomography is safe and feasible and may provide intravascular high-resolution imaging of the femoropopliteal artery during infrainguinal angioplasty procedures.
High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing.
Oh, W Y; Yun, S H; Vakoc, B J; Shishkov, M; Desjardins, A E; Park, B H; de Boer, J F; Tearney, G J; Bouma, B E
2008-01-21
Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm.
Frequency-domain elastic full-waveform multiscale inversion method based on dual-level parallelism
NASA Astrophysics Data System (ADS)
Li, Yuan-Yuan; Li, Zhen-Chun; Zhang, Kai; Zhang, Xuan
2015-12-01
The complexity of an elastic wavefield increases the nonlinearity of inversion. To some extent, multiscale inversion decreases the nonlinearity of inversion and prevents it from falling into local extremes. A multiscale strategy based on the simultaneous use of frequency groups and layer stripping method based on damped wave field improves the stability of inversion. A dual-level parallel algorithm is then used to decrease the computational cost and improve practicability. The seismic wave modeling of a single frequency and inversion in a frequency group are computed in parallel by multiple nodes based on multifrontal massively parallel sparse direct solver and MPI. Numerical tests using an overthrust model show that the proposed inversion algorithm can effectively improve the stability and accuracy of inversion by selecting the appropriate inversion frequency and damping factor in lowfrequency seismic data.
NASA Astrophysics Data System (ADS)
Applegate, Matthew B.; Hariri, Lida P.; Beagle, John; Tan, Khay Ming; Chee, Chunmin; Hales, Charles A.; Suter, Melissa J.
2012-02-01
Smoke inhalation injury is a serious threat to victims of fires and explosions, however accurate diagnosis of patients remains problematic. Current evaluation techniques are highly subjective, often involving the integration of clinical findings with bronchoscopic assessment. It is apparent that new quantitative methods for evaluating the airways of patients at risk of inhalation injury are needed. Optical frequency domain imaging (OFDI) is a high resolution optical imaging modality that enables volumetric microscopy of the trachea and upper airways in vivo. We anticipate that OFDI may be a useful tool in accurately assessing the airways of patients at risk of smoke inhalation injury by detecting injury prior to the onset of symptoms, and therefore guiding patient management. To demonstrate the potential of OFDI for evaluating smoke inhalation injury, we conducted a preclinical study in which we imaged the trachea/upper airways of 4 sheep prior to, and up to 60 minutes post exposure to cooled cotton smoke. OFDI enabled the visualization of increased mucus accumulation, mucosal thickening, epithelial disruption and sloughing, and increased submucosal signal intensity attributed to polymorphonuclear infiltrates. These results were consistent with histopathology findings. Bronchoscopic inspection of the upper airways appeared relatively normal with only mild accumulation of mucus visible within the airway lumen. The ability of OFDI to not only accurately detect smoke inhalation injury, but to quantitatively assess and monitor the progression or healing of the injury over time may provide new insights into the management of patients such as guiding clinical decisions regarding the need for intubation and ventilator support.
NASA Astrophysics Data System (ADS)
Adler, Desmond C.; Xu, Chenyang; Petersen, Christopher; Schmitt, Joseph M.
2010-02-01
We report on the design of a frequency domain optical coherence tomography (FD-OCT) system, fiber optic imaging catheter, and image processing algorithms for in vivo clinical use in the human coronary arteries. This technology represents the third generation of commercially-available OCT system developed at LightLab Imaging Inc. over the last ten years, enabling three-dimensional (3D) intravascular imaging at unprecedented speeds and resolutions for a commercial system. The FD-OCT engine is designed around an exclusively licensed micro-cavity swept laser that was co-developed with AXSUN Technologies Ltd. The laser's unique combination of high sweep rates, broad tuning ranges, and narrow linewidth enable imaging at 50,000 axial lines/s with an axial resolution of < 16 μm in tissue. The disposable 2.7 French (0.9 mm) imaging catheter provides a spot size of < 30 μm at a working distance of 2 mm. The catheter is rotated at 100 Hz and pulled back 50 mm at 20 mm/s to conduct a high-density spiral scan in 2.5 s. Image processing algorithms have been developed to provide clinically important measurements of vessel lumen dimensions, stent malapposition, and neointimal thickness. This system has been used in over 2000 procedures since August 2007 at over 40 clinical sites, providing cardiologists with an advanced tool for 3D assessment of the coronary arteries.
Combined spectrally encoded confocal microscopy and optical frequency domain imaging system
NASA Astrophysics Data System (ADS)
Kang, DongKyun; Suter, Melissa J.; Boudoux, Caroline; Yachimski, Patrick S.; Bouma, Brett E.; Nishioka, Norman S.; Tearney, Guillermo J.
2009-02-01
Spectrally encoded confocal microscopy (SECM) and optical frequency domain imaging (OFDI) are two reflectancebased imaging technologies that may be utilized for high-resolution microscopic screening of internal organs. SECM provides en face images of tissues with a high lateral resolution of 1-2 μm, and a penetration depth of up to 300 μm. OFDI generates cross-sectional images of tissue architecture with a resolution of 10-20 μm and a penetration depth of 1- 2 mm. Since the two technologies yield complementary microscopic information on two different size scales (SECM-cellular and OFDI-architectural) that are commonly used for histopathologic evaluation, their combination may allow for more accurate optical diagnosis. Here, we report the integration of these two imaging modalities in a single bench top system. SECM images of swine small intestine showed the presence of goblet cells, and OFDI images revealed the finger-shaped villous architecture. In clinical study of 9 gastroesophageal biopsies from 8 patients, a diverse set of architectural and cellular features was observed, including squamous mucosa with mild hyperplasia and gastric antral mucosa with gastric pits and crypts. The capability of this multimodality device to enable the visualization of microscopic features on these two size scales supports our hypothesis that improved diagnostic accuracy may be obtained by merging these two technologies into a single instrument.
NASA Astrophysics Data System (ADS)
Zhou, Kenneth J.; Pu, Yang; Chen, Jun
2014-03-01
It is well-known that light transport can be well described using Maxwell's electromagnetic theory. In biological tissue, the scattering particles cause the interaction of scattered waves from neighboring particles. Since such interaction cannot be ignored, multiple scattering occurs. The theoretical solution of multiple scattering is complicated. A suitable description is that the wavelike behavior of light is ignored and the transport of an individual photon is considered to be absorbed or scattered. This is known as the Radiative Transfer Equation (RTE) theory. Analytical solutions to the RTE that explicitly describes photon migration can be obtained by introducing some proper approximations. One of the most popular models used in the field of tissue optics is the Diffusion Approximation (DA). In this study, we report on the results of our initial study of optical properties of ex vivo normal and cancerous prostate tissues and how tissue parameters affect the near infrared light transporting in the two types of tissues. The time-resolved transport of light is simulated as an impulse isotropic point source of energy within a homogeneous unbounded medium with different absorption and scattering properties of cancerous and normal prostate tissues. Light source is also modulated sinusoidally to yield a varied fluence rate in frequency domain at a distant observation point within the cancerous and normal prostate tissues. Due to difference of the absorption and scattering coefficients between cancerous and normal tissues, the expansion of light pulse, intensity, phase are found to be different.
NASA Astrophysics Data System (ADS)
Parent, Francois; Kanti Mandal, Koushik; Loranger, Sebastien; Watanabe Fernandes, Eric Hideki; Kashyap, Raman; Kadoury, Samuel
2016-03-01
We propose here a new alternative to provide real-time device tracking during minimally invasive interventions using a truly-distributed strain sensor based on optical frequency domain reflectometry (OFDR) in optical fibers. The guidance of minimally invasive medical instruments such as needles or catheters (ex. by adding a piezoelectric coating) has been the focus of extensive research in the past decades. Real-time tracking of instruments in medical interventions facilitates image guidance and helps the user to reach a pre-localized target more precisely. Image-guided systems using ultrasound imaging and shape sensors based on fiber Bragg gratings (FBG)-embedded optical fibers can provide retroactive feedback to the user in order to reach the targeted areas with even more precision. However, ultrasound imaging with electro-magnetic tracking cannot be used in the magnetic resonance imaging (MRI) suite, while shape sensors based on FBG embedded in optical fibers provides discrete values of the instrument position, which requires approximations to be made to evaluate its global shape. This is why a truly-distributed strain sensor based on OFDR could enhance the tracking accuracy. In both cases, since the strain is proportional to the radius of curvature of the fiber, a strain sensor can provide the three-dimensional shape of medical instruments by simply inserting fibers inside the devices. To faithfully follow the shape of the needle in the tracking frame, 3 fibers glued in a specific geometry are used, providing 3 degrees of freedom along the fiber. Near real-time tracking of medical instruments is thus obtained offering clear advantages for clinical monitoring in remotely controlled catheter or needle guidance. We present results demonstrating the promising aspects of this approach as well the limitations of using the OFDR technique.
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. <128), while maintaining the zero CP overhead. Finally, we provide an analytical comparison of the computation complexity between the conventional, RGI- and ZGI- CO-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. PMID:21503054
Performance of reduced bit-depth acquisition for optical frequency domain imaging.
Goldberg, Brian D; Vakoc, Benjamin J; Oh, Wang-Yuhl; Suter, Melissa J; Waxman, Sergio; Freilich, Mark I; Bouma, Brett E; Tearney, Guillermo J
2009-09-14
High-speed optical frequency domain imaging (OFDI) has enabled practical wide-field microscopic imaging in the biological laboratory and clinical medicine. The imaging speed of OFDI, and therefore the field of view, of current systems is limited by the rate at which data can be digitized and archived rather than the system sensitivity or laser performance. One solution to this bottleneck is to natively digitize OFDI signals at reduced bit depths, e.g., at 8-bit depth rather than the conventional 12-14 bit depth, thereby reducing overall bandwidth. However, the implications of reduced bit-depth acquisition on image quality have not been studied. In this paper, we use simulations and empirical studies to evaluate the effects of reduced depth acquisition on OFDI image quality. We show that image acquisition at 8-bit depth allows high system sensitivity with only a minimal drop in the signal-to-noise ratio compared to higher bit-depth systems. Images of a human coronary artery acquired in vivo at 8-bit depth are presented and compared with images at higher bit-depth acquisition.
NASA Astrophysics Data System (ADS)
Petersen, Christopher; Adler, Desmond; Schmitt, Joseph
2010-02-01
We report clinical study results of three-dimensional (3D) in vivo imaging of human coronary arteries using frequency domain optical coherence tomography (FD-OCT). At the time of this report, over 2000 patients in over 10 countries have been imaged using FD-OCT systems and disposable fiberoptic catheters developed by LightLab Imaging Inc. The first commercial versions of the systems were introduced in Europe in May 2009. The system operates at 50,000 axial lines/s, performing a 50 mm spiral pullback in 2.5 seconds with a rotational frame rate of 100 Hz. The commercial system employs a proprietary micro-cavity swept laser, allowing imaging of vessel diameters up to 10 mm. Data compiled from early studies indicate that FD-OCT is being used for post-intervention imaging of deployed coronary stents in over 40% of cases. High-resolution 3D imaging of stent geometry immediately following deployment enables detection of stent malapposition, which can increase the risk of thrombosis. Longer term follow-up imaging of stented vessels can detect thrombus formation, which can be treated pharmacologically, and excessive neointimal growth, which may require angioplasty or re-stenting. FD-OCT is also being used for pre-intervention imaging of stenotic lesions in about 60% of cases. Here FD-OCT is used to measure the minimum lumen area and to identify calcified deposits, side branches, or other vascular structures that could interfere with the stenting procedure. Overall, FD-OCT continues to be adopted at an increasing rate and has provided interventional cardiologists with a powerful tool for pre- and postintervention assessment of the coronary arteries.
Full field frequency domain common path optical coherence tomography with annular aperture
NASA Astrophysics Data System (ADS)
Abdulhalim, I.; Friedman, Ron; Liraz, Lior; Dadon, Ronen
2007-07-01
Theoretical and experimental results are presented using the common path Mirau interference microscope and using the Linnik microscope with annular masks to increase the depth of field. The competence between the spatial and temporal coherence was investigated theoretically and confirmed experimentally. Phase imaging of onion epidermis cells was presented showing the possibility of obtaining profiles of the cells. Frequency domain OCT was shown to be possible using full field setup.
NASA Astrophysics Data System (ADS)
Fantini, Sergio; Hueber, Dennis; Franceschini, Maria Angela; Gratton, Enrico; Rosenfeld, Warren; Stubblefield, Phillip G.; Maulik, Dev; Stankovic, Miljan R.
1999-06-01
We have used continuous-wave (CW) and frequency-domain spectroscopy to investigate the optical properties of the newborn piglet brain in vivo and non-invasively. Three anaesthetized, intubated, ventilated and instrumented newborn piglets were placed into a stereotaxic instrument for optimal experimental stability, reproducible probe-to-scalp optical contact and 3D adjustment of the optical probe. By measuring the absolute values of the brain absorption and reduced scattering coefficients at two wavelengths (758 and 830 nm), frequency-domain spectroscopy provided absolute readings (in contrast to the relative readings of CW spectroscopy) of cerebral haemoglobin concentration and saturation during experimentally induced perturbations in cerebral haemodynamics and oxygenation. Such perturbations included a modulation of the inspired oxygen concentration, transient brain asphyxia, carotid artery occlusion and terminal brain asphyxia. The baseline cerebral haemoglobin saturation and concentration, measured with frequency-domain spectroscopy, were about 60% and 42 µM respectively. The cerebral saturation values ranged from a minimum of 17% (during transient brain asphyxia) to a maximum of 80% (during recovery from transient brain asphyxia). To analyse the CW optical data, we have (a) derived a mathematical relationship between the cerebral optical properties and the differential pathlength factor and (b) introduced a method based on the spatial dependence of the detected intensity (dc slope method). The analysis of the cerebral optical signals associated with the arterial pulse and with respiration demonstrates that motion artefacts can significantly affect the intensity recorded from a single optode pair. Motion artefacts can be strongly reduced by combining data from multiple optodes to provide relative readings in the dc slope method. We also report significant biphasic changes (initial decrease and successive increase) in the reduced scattering coefficient measured
Improvements in frequency-domain based NIRF optical tomography modality for preclinical studies
NASA Astrophysics Data System (ADS)
Darne, Chinmay D.; Sevick-Muraca, Eva M.
2014-05-01
Herein we present recent improvements in system design and performance evaluation of near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system developed for small animal fluorescence tomography and installed within a commercial micro-CT/PET scanner. We improved system performance by increasing signal-to-noise ratio (SNR) through use of high powered rf modulation, novel data collection scheme, and data discrimination based on the associated noise levels. Noise characteristics show improvement with these techniques and are currently being employed to improve 3-D fluorescence for tomographic reconstructions in phantoms before incorporating into hybrid scanner.
Oh, Wang-Yuhl; Vakoc, Benjamin J; Shishkov, Milen; Tearney, Guillermo J; Bouma, Brett E
2010-09-01
We demonstrate a high-speed wavelength-swept laser with a tuning range of 104 nm (1228-1332 nm) and a repetition rate of 403 kHz. The design of the laser utilizes a high-finesse polygon-based wavelength-scanning filter and a short-length unidirectional ring resonator. Optical frequency domain imaging of the human skin in vivo is presented using this laser, and the system shows sensitivity of higher than 98 dB with single-side ranging depth of 1.7 mm over 4 dB sensitivity roll-off.
Nadeau, Kyle P.; Durkin, Anthony J.; Tromberg, Bruce J.
2014-01-01
Abstract. We have developed a method for extracting spatial frequency information content from biological tissue, which is used to calculate tissue optical properties and determine tissue structural orientation. This demodulation method employs a two-dimensional Hilbert transform using a spiral phase function in Fourier space. The approach presented here allows for the determination of tissue optical properties using a single frame of data for each modulation frequency, increasing imaging speed by two to threefold versus conventional, three-phase spatial frequency domain imaging (SFDI). This new single-phase Hilbert transform approach recovers optical property and scattering orientation index values within 1% and 10% of three-phase SFDI, respectively. These results suggest that, using the Hilbert demodulation technique, SFDI data acquisition speed can be increased significantly while preserving data quality, which will help us move forward toward the implementation of a real-time SFDI platform. PMID:24858131
NASA Astrophysics Data System (ADS)
Klose, C. D.; Kim, H. K.; Netz, U.; Blaschke, S.; Zwaka, P. A.; Mueller, G. A.; Beuthan, J.; Hielscher, A. H.
2009-02-01
Novel methods that can help in the diagnosis and monitoring of joint disease are essential for efficient use of novel arthritis therapies that are currently emerging. Building on previous studies that involved continuous wave imaging systems we present here first clinical data obtained with a new frequency-domain imaging system. Three-dimensional tomographic data sets of absorption and scattering coefficients were generated for 107 fingers. The data were analyzed using ANOVA, MANOVA, Discriminant Analysis DA, and a machine-learning algorithm that is based on self-organizing mapping (SOM) for clustering data in 2-dimensional parameter spaces. Overall we found that the SOM algorithm outperforms the more traditional analysis methods in terms of correctly classifying finger joints. Using SOM, healthy and affected joints can now be separated with a sensitivity of 0.97 and specificity of 0.91. Furthermore, preliminary results suggest that if a combination of multiple image properties is used, statistical significant differences can be found between RA-affected finger joints that show different clinical features (e.g. effusion, synovitis or erosion).
Jun, Changsu; Villiger, Martin; Oh, Wang-Yuhl; Bouma, Brett E
2014-10-20
Innovations in laser engineering have yielded several novel configurations for high repetition rate, broad sweep range, and long coherence length wavelength swept lasers. Although these lasers have enabled high performance frequency-domain optical coherence tomography, they are typically complicated and costly and many require access to proprietary materials or devices. Here, we demonstrate a simplified ring resonator configuration that is straightforward to construct from readily available materials at a low total cost. It was enabled by an insight regarding the significance of isolation against bidirectional operation and by configuring the sweep range of the intracavity filter to exceed its free spectral range. The design can easily be optimized to meet a range of operating specifications while yielding robust and stable performance. As an example, we demonstrate 240 kHz operation with 125 nm sweep range and >70 mW of average output power and demonstrate high quality frequency domain OCT imaging. The complete component list and directions for assembly of the laser are posted on-line at www.octresearch.org.
Jun, Changsu; Villiger, Martin; Oh, Wang-Yuhl; Bouma, Brett E.
2014-01-01
Innovations in laser engineering have yielded several novel configurations for high repetition rate, broad sweep range, and long coherence length wavelength swept lasers. Although these lasers have enabled high performance frequency-domain optical coherence tomography, they are typically complicated and costly and many require access to proprietary materials or devices. Here, we demonstrate a simplified ring resonator configuration that is straightforward to construct from readily available materials at a low total cost. It was enabled by an insight regarding the significance of isolation against bidirectional operation and by configuring the sweep range of the intracavity filter to exceed its free spectral range. The design can easily be optimized to meet a range of operating specifications while yielding robust and stable performance. As an example, we demonstrate 240 kHz operation with 125 nm sweep range and >70 mW of average output power and demonstrate high quality frequency domain OCT imaging. The complete component list and directions for assembly of the laser are posted on-line at www.octresearch.org. PMID:25401614
Jun, Changsu; Villiger, Martin; Oh, Wang-Yuhl; Bouma, Brett E
2014-10-20
Innovations in laser engineering have yielded several novel configurations for high repetition rate, broad sweep range, and long coherence length wavelength swept lasers. Although these lasers have enabled high performance frequency-domain optical coherence tomography, they are typically complicated and costly and many require access to proprietary materials or devices. Here, we demonstrate a simplified ring resonator configuration that is straightforward to construct from readily available materials at a low total cost. It was enabled by an insight regarding the significance of isolation against bidirectional operation and by configuring the sweep range of the intracavity filter to exceed its free spectral range. The design can easily be optimized to meet a range of operating specifications while yielding robust and stable performance. As an example, we demonstrate 240 kHz operation with 125 nm sweep range and >70 mW of average output power and demonstrate high quality frequency domain OCT imaging. The complete component list and directions for assembly of the laser are posted on-line at www.octresearch.org. PMID:25401614
Spirou, Gloria M.; Mandelis, Andreas; Vitkin, I. Alex; Whelan, William M
2008-05-10
Photoacoustic (more precisely, photothermoacoustic) signals generated by the absorption of photons can be related to the incident laser fluence rate. The dependence of frequency domain photoacoustic (FD-PA) signals on the optical absorption coefficient ({mu}a) and the effective attenuation coefficient ({mu}eff) of a turbid medium [polyvinyl chloride-plastisol (PVCP)] with tissuelike optical properties was measured, and empirical relationships between these optical properties and the photoacoustic (PA) signal amplitude and the laser fluence rate were derived for the water (PVCP system with and without optical scatterers). The measured relationships between these sample optical properties and the PA signal amplitude were found to be linear, consistent with FD-PA theory: {mu}a=a(A/{phi})-b and {mu}eff=c(A/{phi})+d, where {phi} is the laser fluence, A is the FD-PA amplitude, and a,...,d are empirical coefficients determined from the experiment using linear frequency-swept modulation and a lock-in heterodyne detection technique. This quantitative technique can easily be used to measure the optical properties of general turbid media using FD-PAs.
Furukawa, Hiroyuki; Hiro-Oka, Hideaki; Satoh, Nobuyuki; Yoshimura, Reiko; Choi, Donghak; Nakanishi, Motoi; Igarashi, Akihito; Ishikawa, Hitoshi; Ohbayashi, Kohji; Shimizu, Kimiya
2010-01-01
We describe a high-speed long-depth range optical frequency domain imaging (OFDI) system employing a long-coherence length tunable source and demonstrate dynamic full-range imaging of the anterior segment of the eye including from the cornea surface to the posterior capsule of the crystalline lens with a depth range of 12 mm without removing complex conjugate image ambiguity. The tunable source spanned from 1260 to 1360 nm with an average output power of 15.8 mW. The fast A-scan rate of 20,000 per second provided dynamic OFDI and dependence of the whole anterior segment change on time following abrupt relaxation from the accommodated to the relaxed status, which was measured for a healthy eye and that with an intraocular lens. PMID:21258564
Lippok, Norman; Villiger, Martin; Jun, Changsu; Bouma, Brett E
2015-05-01
Fiber-based polarization-sensitive optical frequency domain imaging is more challenging than free-space implementations. Using multiple input states, fiber-based systems provide sample birefringence information with the benefit of a flexible sample arm but come at the cost of increased system and acquisition complexity, and either reduce acquisition speed or require increased acquisition bandwidth. Here we show that with the calibration of a single polarization state, fiber-based configurations can approach the conceptual simplicity of traditional free-space configurations. We remotely control the polarization state of the light incident at the sample using the eigenpolarization states of a wave plate as a reference, and determine the Jones matrix of the output fiber. We demonstrate this method for polarization-sensitive imaging of biological samples. PMID:25927775
NASA Astrophysics Data System (ADS)
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.
Lippok, Norman; Villiger, Martin; Jun, Changsu; Bouma, Brett E
2015-05-01
Fiber-based polarization-sensitive optical frequency domain imaging is more challenging than free-space implementations. Using multiple input states, fiber-based systems provide sample birefringence information with the benefit of a flexible sample arm but come at the cost of increased system and acquisition complexity, and either reduce acquisition speed or require increased acquisition bandwidth. Here we show that with the calibration of a single polarization state, fiber-based configurations can approach the conceptual simplicity of traditional free-space configurations. We remotely control the polarization state of the light incident at the sample using the eigenpolarization states of a wave plate as a reference, and determine the Jones matrix of the output fiber. We demonstrate this method for polarization-sensitive imaging of biological samples.
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.
Tauke-Pedretti, Anna; Skogen, Erik J; Vawter, Gregory A
2014-05-20
An optical sampler includes a first and second 1.times.n optical beam splitters splitting an input optical sampling signal and an optical analog input signal into n parallel channels, respectively, a plurality of optical delay elements providing n parallel delayed input optical sampling signals, n photodiodes converting the n parallel optical analog input signals into n respective electrical output signals, and n optical modulators modulating the input optical sampling signal or the optical analog input signal by the respective electrical output signals, and providing n successive optical samples of the optical analog input signal. A plurality of output photodiodes and eADCs convert the n successive optical samples to n successive digital samples. The optical modulator may be a photodiode interconnected Mach-Zehnder Modulator. A method of sampling the optical analog input signal is disclosed.
Frequency-domain nonlinear optics in two-dimensionally patterned quasi-phase-matching media.
Phillips, C R; Mayer, B W; Gallmann, L; Keller, U
2016-07-11
Advances in the amplification and manipulation of ultrashort laser pulses have led to revolutions in several areas. Examples include chirped pulse amplification for generating high peak-power lasers, power-scalable amplification techniques, pulse shaping via modulation of spatially-dispersed laser pulses, and efficient frequency-mixing in quasi-phase-matched nonlinear crystals to access new spectral regions. In this work, we introduce and demonstrate a new platform for nonlinear optics which has the potential to combine these separate functionalities (pulse amplification, frequency transfer, and pulse shaping) into a single monolithic device that is bandwidth- and power-scalable. The approach is based on two-dimensional (2D) patterning of quasi-phase-matching (QPM) gratings combined with optical parametric interactions involving spatially dispersed laser pulses. Our proof of principle experiment demonstrates this technique via mid-infrared optical parametric chirped pulse amplification of few-cycle pulses. Additionally, we present a detailed theoretical and numerical analysis of such 2D-QPM devices and how they can be designed. PMID:27410862
NASA Astrophysics Data System (ADS)
Alcala, J. Ricardo; Yu, Clement; Yeh, Gong Jong
1993-06-01
An instrument to measure the excited-state lifetimes of phosphorescent materials in real time is described. This apparatus uses pulsed and frequency-doubled Nd:YAG solid-state laser for excitation, sampler for data acquisition, and frequency domain methods for data fitting. The instrument amplifies the ac components of the detector output and band limits the signal to 25 kHz. The fundamental frequency of the excitation is then set to obtain a desired number of harmonics. This band limited signal is sampled and averaged over few thousand cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic is then computed. Ten to a hundred values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited-state lifetimes from subpicowatt luminescent signals in 100 μm optical fibers. To monitor oxygen for biomedical applications the response time of the system is decreased by collecting only 8 or 16 harmonics. A least-squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation. The phosphorescence lifetimes measured reproducibly to three parts in a thousand are used to monitor oxygen. Oxygen concentrations are computed employing empirical polynomials. The system drift is less than 1% over 100 h of continuous operation. This instrument is used to measure oxygen concentrations in vitro and in vivo with 2 s update times and 90 s full response times. Examples of measurements in saline solutions and in dogs are presented.
Transformation Optics: A Time- and Frequency-Domain Analysis of Electron-Energy Loss Spectroscopy.
Kraft, Matthias; Luo, Yu; Pendry, J B
2016-08-10
Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) play a pivotal role in many of the cutting edge experiments in plasmonics. EELS and CL experiments are usually supported by numerical simulations, which-though accurate-may not provide as much physical insight as analytical calculations do. Fully analytical solutions to EELS and CL systems in plasmonics are rare and difficult to obtain. This paper aims to narrow this gap by introducing a new method based on transformation optics that allows to calculate the quasistatic frequency- and time-domain response of plasmonic particles under electron beam excitation. We study a nonconcentric annulus (and ellipse in the Supporting Information ) as an example.
NASA Astrophysics Data System (ADS)
Mastanduno, Michael A.; Davis, Scott C.; Jiang, Shudong; diFlorio-Alexander, Roberta; Pogue, Brian W.; Paulsen, Keith D.
2012-03-01
Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) is used to image high-risk patients for breast cancer because of its higher sensitivity to tumors (approaching 100%) than traditional x-ray mammography. We focus on Near Infrared Spectroscopy (NIRS) as an emerging functional and molecular imaging technique that non-invasively quantifies optical properties of total hemoglobin, oxygen saturation, water content, scattering, and lipid concentration to increase the relatively low specificity of DCE-MRI. Our optical imaging system combines six frequency domain wavelengths, measured using PMT detectors with three continuous wave wavelengths measured using CCD/spectrometers. We present methods on combining the synergistic attributes of DCE-MR and NIRS for in-vivo imaging of breast cancer in three dimensions using a custom optical MR breast coil and diffusion based light modeling software, NIRFAST. We present results from phantom studies, healthy subjects, and breast cancer patients. Preliminary results show contrast recovery within 10% in phantoms and spatial resolution less than 5mm. Images from healthy subjects were recovered with properties similar to literature values and previous studies. Patient images have shown elevated total hemoglobin values and water fraction, agreeing with histology and previous results. The additional information gained from NIRS may improve the ability to distinguish between malignant and benign lesions during MR imaging. These dual modality instruments will provide complex anatomical and molecular prognostic information, and may decrease the number of biopsies, thereby improving patient care.
Krishnan, Sunder Ram; Seelamantula, Chandra Sekhar; Bouwens, Arno; Leutenegger, Marcel; Lasser, Theo
2012-10-01
We address the problem of high-resolution reconstruction in frequency-domain optical-coherence tomography (FDOCT). The traditional method employed uses the inverse discrete Fourier transform, which is limited in resolution due to the Heisenberg uncertainty principle. We propose a reconstruction technique based on zero-crossing (ZC) interval analysis. The motivation for our approach lies in the observation that, for a multilayered specimen, the backscattered signal may be expressed as a sum of sinusoids, and each sinusoid manifests as a peak in the FDOCT reconstruction. The successive ZC intervals of a sinusoid exhibit high consistency, with the intervals being inversely related to the frequency of the sinusoid. The statistics of the ZC intervals are used for detecting the frequencies present in the input signal. The noise robustness of the proposed technique is improved by using a cosine-modulated filter bank for separating the input into different frequency bands, and the ZC analysis is carried out on each band separately. The design of the filter bank requires the design of a prototype, which we accomplish using a Kaiser window approach. We show that the proposed method gives good results on synthesized and experimental data. The resolution is enhanced, and noise robustness is higher compared with the standard Fourier reconstruction. PMID:23201655
NASA Astrophysics Data System (ADS)
Zafar, Haroon; Sharif, Faisal; Leahy, Martin J.
2014-03-01
Quantitative coronary angiography (QCA) has been used as a standard technique for the evaluation of coronary artery disease for many years. Intracoronary optical coherence tomography (OCT) offers higher resolution, faster image acquisition speeds and greater sensitivity than the intravascular ultrasound (IVUS). Recently developed frequency domain OCT (FD-OCT) systems overcome many technical limitations of conventional time domain OCT systems (TDOCT). The main objective of this study was to compare the FD-OCT and QCA measurements for the assessment of coronary lesions. A total of 21 stenoses in 18 patients were analysed using QCA and FD-OCT. The average minimum lumen diameter (MLD) and percent lumen area stenosis (%AS) by QCA were 1.52+/-0.44 mm and 68+/-9% respectively. The average MLD and %AS by FD-OCT were 1.32+/-0.38 mm and 63+/-14% respectively. There was a moderate but significant correlation between QCA and FD-OCT measured MLD (r = 0.5, p < 0.01) and %AS (r = 0.56, p < 0.01). Bland-Altman analysis showed that the mean differences between the QCA and FD-OCT measurements were 0.18+/-0.81 (limits of agreement: -0.63 to 0.99) for MLD and 4.4+/-22.8 (limits of agreement: -18.4 to 27.2) for %AS. The root mean square error (RMSE) between the QCA and FD-OCT measured MLD and %AS was +/-0.44 mm and +/-12.1% respectively.
NASA Astrophysics Data System (ADS)
Sourbier, Florent; Operto, Stéphane; Virieux, Jean; Amestoy, Patrick; L'Excellent, Jean-Yves
2009-03-01
This is the first paper in a two-part series that describes a massively parallel code that performs 2D frequency-domain full-waveform inversion of wide-aperture seismic data for imaging complex structures. Full-waveform inversion methods, namely quantitative seismic imaging methods based on the resolution of the full wave equation, are computationally expensive. Therefore, designing efficient algorithms which take advantage of parallel computing facilities is critical for the appraisal of these approaches when applied to representative case studies and for further improvements. Full-waveform modelling requires the resolution of a large sparse system of linear equations which is performed with the massively parallel direct solver MUMPS for efficient multiple-shot simulations. Efficiency of the multiple-shot solution phase (forward/backward substitutions) is improved by using the BLAS3 library. The inverse problem relies on a classic local optimization approach implemented with a gradient method. The direct solver returns the multiple-shot wavefield solutions distributed over the processors according to a domain decomposition driven by the distribution of the LU factors. The domain decomposition of the wavefield solutions is used to compute in parallel the gradient of the objective function and the diagonal Hessian, this latter providing a suitable scaling of the gradient. The algorithm allows one to test different strategies for multiscale frequency inversion ranging from successive mono-frequency inversion to simultaneous multifrequency inversion. These different inversion strategies will be illustrated in the following companion paper. The parallel efficiency and the scalability of the code will also be quantified.
NASA Astrophysics Data System (ADS)
Sourbier, F.; Operto, S.; Virieux, J.
2006-12-01
We present a distributed-memory parallel algorithm for 2D visco-acoustic full-waveform inversion of wide-angle seismic data. Our code is written in fortran90 and use MPI for parallelism. The algorithm was applied to real wide-angle data set recorded by 100 OBSs with a 1-km spacing in the eastern-Nankai trough (Japan) to image the deep structure of the subduction zone. Full-waveform inversion is applied sequentially to discrete frequencies by proceeding from the low to the high frequencies. The inverse problem is solved with a classic gradient method. Full-waveform modeling is performed with a frequency-domain finite-difference method. In the frequency-domain, solving the wave equation requires resolution of a large unsymmetric system of linear equations. We use the massively parallel direct solver MUMPS (http://www.enseeiht.fr/irit/apo/MUMPS) for distributed-memory computer to solve this system. The MUMPS solver is based on a multifrontal method for the parallel factorization. The MUMPS algorithm is subdivided in 3 main steps: a symbolic analysis step that performs re-ordering of the matrix coefficients to minimize the fill-in of the matrix during the subsequent factorization and an estimation of the assembly tree of the matrix. Second, the factorization is performed with dynamic scheduling to accomodate numerical pivoting and provides the LU factors distributed over all the processors. Third, the resolution is performed for multiple sources. To compute the gradient of the cost function, 2 simulations per shot are required (one to compute the forward wavefield and one to back-propagate residuals). The multi-source resolutions can be performed in parallel with MUMPS. In the end, each processor stores in core a sub-domain of all the solutions. These distributed solutions can be exploited to compute in parallel the gradient of the cost function. Since the gradient of the cost function is a weighted stack of the shot and residual solutions of MUMPS, each processor
Frequency domain photoacoustic and fluorescence microscopy.
Langer, Gregor; Buchegger, Bianca; Jacak, Jaroslaw; Klar, Thomas A; Berer, Thomas
2016-07-01
We report on simultaneous frequency domain optical-resolution photoacoustic and fluorescence microscopy with sub-µm lateral resolution. With the help of a blood smear, we show that photoacoustic and fluorescence images provide complementary information. Furthermore, we compare theoretically predicted signal-to-noise ratios of sinusoidal modulation in frequency domain with pulsed excitation in time domain. PMID:27446698
Frequency domain photoacoustic and fluorescence microscopy.
Langer, Gregor; Buchegger, Bianca; Jacak, Jaroslaw; Klar, Thomas A; Berer, Thomas
2016-07-01
We report on simultaneous frequency domain optical-resolution photoacoustic and fluorescence microscopy with sub-µm lateral resolution. With the help of a blood smear, we show that photoacoustic and fluorescence images provide complementary information. Furthermore, we compare theoretically predicted signal-to-noise ratios of sinusoidal modulation in frequency domain with pulsed excitation in time domain.
Frequency domain photoacoustic and fluorescence microscopy
Langer, Gregor; Buchegger, Bianca; Jacak, Jaroslaw; Klar, Thomas A.; Berer, Thomas
2016-01-01
We report on simultaneous frequency domain optical-resolution photoacoustic and fluorescence microscopy with sub-µm lateral resolution. With the help of a blood smear, we show that photoacoustic and fluorescence images provide complementary information. Furthermore, we compare theoretically predicted signal-to-noise ratios of sinusoidal modulation in frequency domain with pulsed excitation in time domain. PMID:27446698
Ding, Zhenyang; Liu, Tiegen; Meng, Zhuo; Liu, Kun; Chen, Qinnan; Du, Yang; Li, Dingjie; Yao, X Steve
2012-06-01
We propose using non-uniform FFT to minimize the degrading effect of frequency tuning nonlinearity of a tunable laser source (TLS) in an optical frequency-domain reflectometry (OFDR) system. We use an auxiliary interferometer to obtain the required instantaneous optical frequency of the TLS and successfully demonstrate 100 times enhancement in spatial resolution of OFDR with only a 20% increase in computation time. The corresponding measurement reflectivity sensitivity is better than -80 dB, sufficient to detect bending induced index changes in an optical fiber. PMID:22755676
NASA Astrophysics Data System (ADS)
Ding, Zhenyang; Liu, Tiegen; Meng, Zhuo; Liu, Kun; Chen, Qinnan; Du, Yang; Li, Dingjie; Yao, X. Steve
2012-06-01
We propose using non-uniform FFT to minimize the degrading effect of frequency tuning nonlinearity of a tunable laser source (TLS) in an optical frequency-domain reflectometry (OFDR) system. We use an auxiliary interferometer to obtain the required instantaneous optical frequency of the TLS and successfully demonstrate 100 times enhancement in spatial resolution of OFDR with only a 20% increase in computation time. The corresponding measurement reflectivity sensitivity is better than -80 dB, sufficient to detect bending induced index changes in an optical fiber.
Ahn, Tae-Jung; Jung, Yongmin; Oh, Kyunghwan; Kim, Dug Young
2005-12-12
We propose a new chromatic dispersion measurement method for the higher-order modes of an optical fiber using optical frequency modulated continuous-wave (FMCW) interferometry. An optical fiber which supports few excited modes was prepared for our experiments. Three different guiding modes of the fiber were identified by using far-field spatial beam profile measurements and confirmed with numerical mode analysis. By using the principle of a conventional FMWC interferometry with a tunable external cavity laser, we have demonstrated that the chromatic dispersion of a few-mode optical fiber can be obtained directly and quantitatively as well as qualitatively. We have also compared our measurement results with those of conventional modulation phase-shift method. PMID:19503215
Optical parallel selectionist systems
NASA Astrophysics Data System (ADS)
Caulfield, H. John
1993-01-01
There are at least two major classes of computers in nature and technology: connectionist and selectionist. A subset of connectionist systems (Turing Machines) dominates modern computing, although another subset (Neural Networks) is growing rapidly. Selectionist machines have unique capabilities which should allow them to do truly creative operations. It is possible to make a parallel optical selectionist system using methods describes in this paper.
NASA Astrophysics Data System (ADS)
Furukawa, Hiroyuki; Hiro-Oka, Hideaki; Yoshimura, Reiko; Choi, Dong-Hak; Nakanishi, Motoi; Igarashi, Akihito; Ohbayashi, Kohji; Shimizu, Kimiya
2011-03-01
We describe a high-speed long-depth range optical frequency domain imaging (OFDI) system employing a long-coherence length tunable source and demonstrate dynamic full-range imaging of the anterior segment of the eye including from the cornea surface to the posterior capsule of the crystalline lens with a depth range of 12 mm without removing complex conjugate image ambiguity. The dependence of the whole anterior segment change on time following abrupt relaxation from the accommodated to the relaxed status was measured for a healthy eye and that with an intraocular lens.
Trajectories in parallel optics.
Klapp, Iftach; Sochen, Nir; Mendlovic, David
2011-10-01
In our previous work we showed the ability to improve the optical system's matrix condition by optical design, thereby improving its robustness to noise. It was shown that by using singular value decomposition, a target point-spread function (PSF) matrix can be defined for an auxiliary optical system, which works parallel to the original system to achieve such an improvement. In this paper, after briefly introducing the all optics implementation of the auxiliary system, we show a method to decompose the target PSF matrix. This is done through a series of shifted responses of auxiliary optics (named trajectories), where a complicated hardware filter is replaced by postprocessing. This process manipulates the pixel confined PSF response of simple auxiliary optics, which in turn creates an auxiliary system with the required PSF matrix. This method is simulated on two space variant systems and reduces their system condition number from 18,598 to 197 and from 87,640 to 5.75, respectively. We perform a study of the latter result and show significant improvement in image restoration performance, in comparison to a system without auxiliary optics and to other previously suggested hybrid solutions. Image restoration results show that in a range of low signal-to-noise ratio values, the trajectories method gives a significant advantage over alternative approaches. A third space invariant study case is explored only briefly, and we present a significant improvement in the matrix condition number from 1.9160e+013 to 34,526.
NASA Astrophysics Data System (ADS)
Kato, Ryozo; Xu, Yibin; Goto, Masahiro
2011-10-01
In this paper, we describe the development of a new frequency-domain (FD) method using completely optical techniques for determining the interfacial thermal resistance between a metal film and its substrate. The 3ω method, which is a FD method based on the technique of photolithography to define a metal-film heater/thermometer pattern, has been most widely used so far. The 2ω method implemented a thermoreflectance technique for measuring ac temperature. In this study we additionally implement a laser technique for periodic heating. Our new method can provide the absolute value of interfacial thermal resistance between a film and its substrate, using the known thermophysical properties of the substrate material, even though the optical power of the pump laser and the optical properties of the metal film are unknown. To verify the method, we measure the thermal resistance of interfaces such as, Au-Al2O3, Bi-Al2O3, Au-SiO2 (thermally oxidized), and Bi-SiO2 (thermally oxidized). The results of the measurements show good agreement with the data obtained by the 2ω method and with the data theoretically predicted using the diffusion mismatch model (DMM).
Berger, Andrew J.; Venugopalan, Vasan; Durkin, Anthony J.; Pham, Tuan; Tromberg, Bruce J.
2000-04-01
Frequency-domain photon migration (FDPM) is a widely used technique for measuring the optical properties (i.e., absorption, {mu}{sub a}, and reduced scattering, {mu}{sub s}{sup '}, coefficients) of turbid samples. Typically, FDPM data analysis is performed with models based on a photon diffusion equation; however, analytical solutions are difficult to obtain for many realistic geometries. Here, we describe the use of models based instead on representative samples and multivariate calibration (chemometrics). FDPM data at seven wavelengths (ranging from 674 to 956 nm) and multiple modulation frequencies (ranging from 50 to 600 MHz) were gathered from turbid samples containing mixtures of three absorbing dyes. Values for {mu}{sub a} and {mu}{sub s}{sup '} were extracted from the FDPM data in different ways, first with the diffusion theory and then with the chemometric technique of partial least squares. Dye concentrations were determined from the FDPM data by three methods, first by least-squares fits to the diffusion results and then by two chemometric approaches. The accuracy of the chemometric predictions was comparable or superior for all three dyes. Our results indicate that chemometrics can recover optical properties and dye concentrations from the frequency-dependent behavior of photon density waves, without the need for diffusion-based models. Future applications to more complicated geometries, lower-scattering samples, and simpler FDPM instrumentation are discussed. (c) 2000 Optical Society of America.
Ohno, Shingo; Iida, Daisuke; Toge, Kunihiro; Manabe, Tetsuya
2016-08-22
Long-range C-OFDR measurement of fiber Rayleigh scatter signature is described. The Rayleigh scatter signature, which is an interference pattern of backscatters from the random refractive indices in fibers, is known to be applicable to fiber identification and temperature or strain sensing by measuring its repeatability and its spectral shift. However, these applications have not been realized at ranges beyond the laser coherence length since laser phase noise degrades its repeatability. This paper proposes and demonstrates a method for analyzing the optical power spectrum of local Rayleigh backscatter to overcome the limitation imposed by laser phase noise. The measurable range and spatial performance are also investigated experimentally with respect to the remaining phase noise and noise reduction by signal averaging with the proposed method. The feasibility of Rayleigh scatter signature measurement for long-range applications is confirmed. PMID:27557243
Tromberg, B.J.; Tsay, T.T.; Berns, M.W.; Svaasand, L.O.; Haskell, R.C.
1995-06-13
Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid. 14 figs.
Tromberg, Bruce J.; Tsay, Tsong T.; Berns, Michael W.; Svaasand, Lara O.; Haskell, Richard C.
1995-01-01
Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid.
Dehaes, Mathieu; Grant, P. Ellen; Sliva, Danielle D.; Roche-Labarbe, Nadège; Pienaar, Rudolph; Boas, David A.; Franceschini, Maria Angela; Selb, Juliette
2011-01-01
The near infrared spectroscopy (NIRS) frequency-domain multi-distance (FD-MD) method allows for the estimation of optical properties in biological tissue using the phase and intensity of radiofrequency modulated light at different source-detector separations. In this study, we evaluated the accuracy of this method to retrieve the absorption coefficient of the brain at different ages. Synthetic measurements were generated with Monte Carlo simulations in magnetic resonance imaging (MRI)-based heterogeneous head models for four ages: newborn, 6 and 12 month old infants, and adult. For each age, we determined the optimal set of source-detector separations and estimated the corresponding errors. Errors arise from different origins: methodological (FD-MD) and anatomical (curvature, head size and contamination by extra-cerebral tissues). We found that the brain optical absorption could be retrieved with an error between 8–24% in neonates and infants, while the error increased to 19–44% in adults over all source-detector distances. The dominant contribution to the error was found to be the head curvature in neonates and infants, and the extra-cerebral tissues in adults. PMID:21412461
NASA Astrophysics Data System (ADS)
Dehaes, Mathieu; Grant, P. Ellen; Sliva, Danielle D.; Roche-Labarbe, Nadège; Pienaar, Rudolph; Boas, David A.; Franceschini, Maria Angela; Selb, Juliette
2011-03-01
NIRS is safe, non-invasive and offers the possibility to record local hemodynamic parameters at the bedside, avoiding the transportation of neonates and critically ill patients. In this work, we evaluate the accuracy of the frequency-domain multi-distance (FD-MD) method to retrieve brain optical properties from neonate to adult. Realistic measurements are simulated using a 3D Monte Carlo modeling of light propagation. Height different ages were investigated: a term newborn of 38 weeks gestational age, two infants of 6 and 12 months of age, a toddler of 2 year (yr.) old, two children of 5 and 10 years of age, a teenager of 14 yr. old, and an adult. Measurements are generated at multiple distances on the right parietal area of head models and fitted to a homogeneous FD-MD model to estimate the brain optical properties. In the newborn, infants, toddler and 5 yr. old child models, the error was dominated by the head curvature, while the superficial layer in the 10 yr. old child, teenager and adult heads. The influence of the CSF is also evaluated. In this case, absorption coefficients suffer from an additional error. In all cases, measurements at 5 mm provided worse estimation because of the diffusion approximation.
NASA Astrophysics Data System (ADS)
Sibai, Mira; Veilleux, Israel; Elliott, Jonathan T.; Leblond, Frederic; Roberts, David W.; Wilson, Brian C.
2015-03-01
Intraoperative fluorescence guidance enables maximum safe resection of, for example, glioblastomas by providing surgeons with real-time tumor optical contrast. Specifically, 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence guided resection can improve surgical outcomes by better defining tumor margins and identifying satellite tumor foci. However, visual assessment of PpIX fluorescence is subjective and limited by the distorting effects of light attenuation (absorption and scattering) by tissue and background tissue autofluorescence. We have previously shown, using a point fluorescence-reflectance fiberoptic probe, that non-invasive measurement of the absolute PpIX concentration, [PpIX], further improves sensitivity and specificity, leading to the demonstration that the technique can also detect low-grade gliomas as well as otherwise undetectable residual tumor foci in high-grade disease. Here, we extend this approach to wide-field quantitative fluorescence imaging (qFI) by implementing spatial frequency domain imaging (SFDI) to recover the tissue optical absorption and transport scattering coefficients across the field of view. We report on the performance of this approach to determine the intrinsic fluorescence intensity in tissue-simulating phantoms in both the fully diffusive (i.e. scatter-dominated) and sub-diffusive (low transport albedo) regimes, for which higher spatial frequencies are used. The performance of qFI is compared to a Born- normalization correction scheme, as well as to the values obtained using the fiberoptic probe on homogeneous tissue phantoms containing PpIX.
Lo, William C. Y.; Villiger, Martin; Golberg, Alexander; Broelsch, G. Felix; Khan, Saiqa; Lian, Christine G.; Austen, William G.; Yarmush, Martin; Bouma, Brett E.
2016-01-01
Hypertrophic scars (HTS), frequently seen after traumatic injuries and surgery, remain a major clinical challenge due to the limited success of existing therapies. A significant obstacle to understanding HTS etiology is the lack of tools to monitor scar remodeling longitudinally and non-invasively. We present an in vivo, label-free technique using polarization-sensitive optical frequency domain imaging (PS-OFDI) for the 3D, longitudinal assessment of collagen remodeling in murine HTS. In this study, HTS was induced with a mechanical tension device for 4 to 10 days on incisional wounds and imaged up to one month after device removal; an excisional HTS model was also imaged at 6 months after injury to investigate deeper and more mature scars. We showed that local retardation (LR) and degree of polarization (DOP) provide a robust signature for HTS. Compared to normal skin with heterogeneous LR and low DOP, HTS was characterized by an initially low LR, which increased as collagen fibers remodeled, and a persistently high DOP. This study demonstrates that PS-OFDI offers a powerful tool to gain significant biological insights into HTS remodeling by enabling longitudinal assessment of collagen in vivo, which is critical to elucidating HTS etiology and developing more effective HTS therapies. PMID:26763427
Kubota, Shuji; Okazaki, Toru; Hara, Hisao; Hiroi, Yukio
2016-01-01
Objectives The aims of this study are (1) to evaluate the safety and feasibility of using optical frequency domain imaging (OFDI) during balloon pulmonary angioplasty (BPA) procedures, (2) to assess the correlations between the vessel area (VA) and luminal area (LA) obtained by OFDI and intravascular ultrasound (IVUS), and (3) to compare inter‐ and intra‐observer variability among measurements taken from OFDI and IVUS images. Background The BPA in patients with chronic thromboembolic pulmonary hypertension (CTEPH) is an evolving procedure. Methods Twenty‐three consecutive attempts of pair of OFDI and IVUS during BPA were evaluated. All complications that occurred during‐BPA and up to 48 hr post‐BPA were recorded. Using side branches as landmarks, 48 pairs of regions were chosen to compare measurements of VA and LA. Results OFDI images can be obtained without any procedurally related complications. Although the VA and LA measurements obtained by OFDI were smaller than those obtained by IVUS, high correlations were found (VA: r = 0.78, P < 0.0001 and LA: r = 0.75, P < 0.0001). Less inter‐ and intra‐observer variability was found when using measurements taken from OFDI versus IVUS images. Conclusions OFDI during BPA was safe and feasible. The reproducibility of OFDI imaging was excellent and offered a favorable addition to the BPA procedures. © 2016 The Authors Catheterization and Cardiovascular Interventions Published by Wiley Periodicals, Inc. PMID:26991798
NASA Astrophysics Data System (ADS)
Hsieh, Yi-Da; Kimura, Hiroto; Hayashi, Kenta; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Yasui, Takeshi
2016-09-01
A terahertz (THz) frequency synthesizer based on photomixing of two near-infrared lasers with a sub-THz to THz frequency offset is a powerful tool for spectroscopy of polar gas molecules due to its broad spectral coverage; however, its frequency accuracy and resolution are relatively low. To tune the output frequency continuously and widely while maintaining its traceability to a frequency standard, we developed a photomixing THz synthesizer phase-locked to dual optical frequency combs (OFCs). While the phase-locking to dual OFCs ensured continuous tuning within a spectral range of 120 GHz, in addition to the traceability to the frequency standard, use of a broadband uni-traveling carrier photodiode for photomixing enabled the generation of CW-THz radiation within a frequency range from 0.2 to 1.5 THz. We demonstrated THz frequency-domain spectroscopy of gas-phase acetonitrile CH3CN and its isotope CH3 13CN in the frequency range of 0.600-0.720 THz using this THz synthesizer. Their rotational transitions were assigned with a frequency accuracy of 8.42 × 10-8 and a frequency resolution of 520 kHz. Furthermore, the concentration of the CH3CN gas at 20 Pa was determined to be (5.41 ± 0.05) × 1014 molecules/cm3 by curve fitting analysis of the measured absorbance spectrum, and the mixture ratio of the mixed CH3CN/CH3 13CN gas was determined to be 1:2.26 with a gas concentration of 1014-1015 molecules/cm3. The developed THz synthesizer is highly promising for high-precision THz-FDS of low-pressure molecular gases and will enable the qualitative and quantitative analyses of multiple gases.
NASA Technical Reports Server (NTRS)
Parker, Jr., Allen R (Inventor); Chan, Hon Man (Inventor); Piazza, Anthony (Nino) (Inventor); Richards, William Lance (Inventor)
2014-01-01
A method and system for multiplexing a network of parallel fiber Bragg grating (FBG) sensor-fibers to a single acquisition channel of a closed Michelson interferometer system via a fiber splitter by distinguishing each branch of fiber sensors in the spatial domain. On each branch of the splitter, the fibers have a specific pre-determined length, effectively separating each branch of fiber sensors spatially. In the spatial domain the fiber branches are seen as part of one acquisition channel on the interrogation system. However, the FBG-reference arm beat frequency information for each fiber is retained. Since the beat frequency is generated between the reference arm, the effective fiber length of each successive branch includes the entire length of the preceding branch. The multiple branches are seen as one fiber having three segments where the segments can be resolved. This greatly simplifies optical, electronic and computational complexity, and is especially suited for use in multiplexed or branched OFS networks for SHM of large and/or distributed structures which need a lot of measurement points.
NASA Astrophysics Data System (ADS)
Sahin, Gökhan
The influence of the illumination wavelength on the electrical parameters of a vertical parallel junction silicon solar cell by its rear side is theoretically analyzed. Based on the excess minority carrier's density, the photocurrent density and photovoltage across the junction were determined. From both photocurrent and the photovoltage, the series and shunt resistance expressions are deduced and the solar cell associated capacitance and conversion efficiency are calculated. The aim of this study is to show the influence of the illumination wavelength on the electrical parameters of the cell and the behavior of both parasitic resistances and capacitance versus operating point.
In vivo mouse imaging using frequency domain optoacoustic tomography
NASA Astrophysics Data System (ADS)
Kellnberger, Stephan; Deliolanis, Nikolaos C.; Queirós, Daniel; Sergiadis, George; Ntziachristos, Vasilis
2013-06-01
Frequency domain optoacoustics relates to stimulation of optoacoustic signals using intensity modulated continuous wave light instead of pulsed laser light employed in time domain optoacoustic imaging. We present a method to generate frequency domain tomographic images of optical absorbers and cross sectional in-vivo mouse images, showing the changes of optical absorption before and after injection of indocyanine green (ICG). OCIS codes: 170.6960, 170.3880, 170.5220
NASA Astrophysics Data System (ADS)
Demel, Anja; Feilke, Katharina; Wolf, Martin; Poets, Christian F.; Franz, Axel R.
2014-01-01
Near-infrared spectroscopy (NIRS) is increasingly used in neonatal intensive care. We investigated the impact of skin, bone, and cerebrospinal fluid (CSF) layer thickness in term and preterm infants on absorption-(μa) and/or reduced scattering coefficients (μs‧) measured by multidistance frequency-domain (FD)-NIRS. Transcranial ultrasound was performed to measure the layer thicknesses. Correlations were only statistically significant for μa at 692 nm with bone thickness and μs‧ at 834 nm with skin thickness. There is no evidence that skin, bone, or CSF thickness have an important effect on μa and μs‧. Layer thicknesses of skin, bone, and CSF in the range studied do not seem to affect cerebral oxygenation measurements by multidistance FD-NIRS significantly.
Radiative Transport Based Frequency Domain Fluorescence Tomography
Joshi, Amit; Rasmussen, John C.; Sevick-Muraca, Eva M.; Wareing, Todd A.; McGhee, John
2011-01-01
We report the development of radiative transport model based fluorescence optical tomography from frequency domain boundary measurements. The coupled radiative transport model for describing NIR fluorescence propagation in tissue is solved by a novel software based on the established Attila™ particle transport simulation platform. The proposed scheme enables the prediction of fluorescence measurements with non-contact sources and detectors at minimal computational cost. An adjoint transport solution based fluorescence tomography algorithm is implemented on dual grids to efficiently assemble the measurement sensitivity Jacobian matrix. Finally, we demonstrate fluorescence tomography on a realistic computational mouse model to locate nM to μM fluorophore concentration distributions in simulated mouse organs. PMID:18364555
Parallel optical memories for very large databases
NASA Astrophysics Data System (ADS)
Mitkas, Pericles A.; Berra, P. B.
1993-02-01
The steady increase in volume of current and future databases dictates the development of massive secondary storage devices that allow parallel access and exhibit high I/O data rates. Optical memories, such as parallel optical disks and holograms, can satisfy these requirements because they combine high recording density and parallel one- or two-dimensional output. Several configurations for database storage involving different types of optical memory devices are investigated. All these approaches include some level of optical preprocessing in the form of data filtering in an attempt to reduce the amount of data per transaction that reach the electronic front-end.
Frequency-domain prediction of turbofan noise radiation
NASA Astrophysics Data System (ADS)
Özyörük, Y.; Alpman, E.; Ahuja, V.; Long, L. N.
2004-03-01
This paper describes a frequency-domain numerical method for predicting noise radiation from ducted fans, including acoustic treatment and non-uniform background flow effects. The method solves the Euler equations linearized about a mean flow in the frequency domain. A pseudo-time derivative term is added to the frequency-domain equations so that a time marching technique can be employed to drive the acoustic field to steady state explicitly. This approach makes distributed parallel computing more viable for equations of this type and will allow for future use of well-known convergence acceleration techniques, such as multigrid, to obtain the solutions efficiently. Simulations of the JT15D static test inlet are performed including the effects of liners, and the results are compared with experimental data. A generic engine geometry is used for demonstrating further the prediction capability of the code, calculating the attenuation effects of different liner impedances and liner installation locations on the radiated sound fields.
Frequency domain FIR and IIR adaptive filters
NASA Technical Reports Server (NTRS)
Lynn, D. W.
1990-01-01
A discussion of the LMS adaptive filter relating to its convergence characteristics and the problems associated with disparate eigenvalues is presented. This is used to introduce the concept of proportional convergence. An approach is used to analyze the convergence characteristics of block frequency-domain adaptive filters. This leads to a development showing how the frequency-domain FIR adaptive filter is easily modified to provide proportional convergence. These ideas are extended to a block frequency-domain IIR adaptive filter and the idea of proportional convergence is applied. Experimental results illustrating proportional convergence in both FIR and IIR frequency-domain block adaptive filters is presented.
Correia, Carlos M; Teixeira, Joel
2014-12-01
Computationally efficient wave-front reconstruction techniques for astronomical adaptive-optics (AO) systems have seen great development in the past decade. Algorithms developed in the spatial-frequency (Fourier) domain have gathered much attention, especially for high-contrast imaging systems. In this paper we present the Wiener filter (resulting in the maximization of the Strehl ratio) and further develop formulae for the anti-aliasing (AA) Wiener filter that optimally takes into account high-order wave-front terms folded in-band during the sensing (i.e., discrete sampling) process. We employ a continuous spatial-frequency representation for the forward measurement operators and derive the Wiener filter when aliasing is explicitly taken into account. We further investigate and compare to classical estimates using least-squares filters the reconstructed wave-front, measurement noise, and aliasing propagation coefficients as a function of the system order. Regarding high-contrast systems, we provide achievable performance results as a function of an ensemble of forward models for the Shack-Hartmann wave-front sensor (using sparse and nonsparse representations) and compute point-spread-function raw intensities. We find that for a 32×32 single-conjugated AOs system the aliasing propagation coefficient is roughly 60% of the least-squares filters, whereas the noise propagation is around 80%. Contrast improvements of factors of up to 2 are achievable across the field in the H band. For current and next-generation high-contrast imagers, despite better aliasing mitigation, AA Wiener filtering cannot be used as a standalone method and must therefore be used in combination with optical spatial filters deployed before image formation actually takes place.
NASA Astrophysics Data System (ADS)
Choe, Regine; Durduran, Turgut; Yu, Guoqiang; Nijland, Mark J. M.; Nathanielsz, Peter W.; Chance, Britton; Yodh, Arjun G.; Ramanujam, Nirmala
2003-07-01
A study using pregnant sheep was designed to simulate fetal hypoxia in order to investigate the ability of near-infrared spectroscopy (NIRS) to detect and quantify fetal hypoxia in utero. The near-infrared spectroscopic probe consisted of two detectors and six source positions. It was placed on the maternal ewe abdomen above the fetal head. The light sources were modulated at 70 MHz and frequency-encoded so that simultaneous measurements at 675, 786, 830 nm for each source position were possible. After the baseline measurements, fetal hypoxia was induced by blocking the aorta of pregnant ewe and thus compromising the blood supply to the uterus. Blood gas samples were concurrently drawn from the fetal brachial artery and jugular veins. Analysis of the diffuse optical data used a two-layer model to separate the maternal layer from the fetal head. The analysis also employed a priori spectral information about tissue chromophores. This approach provided good quantification of blood oxygenation changes, which correlated well with the blood gas analyses. By contrast the homogeneous model underestimated oxygenation changes during hypoxia.
Wang, Yuanquan; Shi, Jianyang; Yang, Chao; Wang, Yiguang; Chi, Nan
2014-05-01
We propose and experimentally demonstrate a novel integrated passive optical network (PON) and indoor visible light communication (VLC) system based on Nyquist single carrier frequency domain equalization (N-SC-FDE) modulation with direct detection. In this system, a directly modulated laser and a commercially available red light emitting diode are served as the transmitters of the PON and VLC, respectively. To enable high spectral efficiency, high-speed transmission, and flexible multiple access with simplified optical network unit-side digital signal processing, multilevel, multiband quadrature amplitude modulations 128/64/16 are implemented here. VLC N-SC-FDE signals are successfully delivered a further 30 cm indoor distance after transmitting over a span of 40 km single mode fiber (SMF) together with 3 sub-band PON signals. As a proof of concept, a 10 Gb/s PON and 500 Mb/s VLC integrated system for three wired users and one wireless user is successfully achieved, which shows the promising potential and feasibility of this proposal to extend multiple services from metropolitan to suburban areas.
Substructure coupling in the frequency domain
NASA Technical Reports Server (NTRS)
1985-01-01
Frequency domain analysis was found to be a suitable method for determining the transient response of systems subjected to a wide variety of loads. However, since a large number of calculations are performed within the discrete frequency loop, the method loses it computational efficiency if the loads must be represented by a large number of discrete frequencies. It was also discovered that substructure coupling in the frequency domain work particularly well for analyzing structural system with a small number of interface and loaded degrees of freedom. It was discovered that substructure coupling in the frequency domain can lead to an efficient method of obtaining natural frequencies of undamped structures. It was also found that the damped natural frequencies of a system may be determined using frequency domain techniques.
Spatial frequency domain spectroscopy of two layer media
Yudovsky, Dmitry; Durkin, Anthony J.
2011-01-01
Monitoring of tissue blood volume and oxygen saturation using biomedical optics techniques has the potential to inform the assessment of tissue health, healing, and dysfunction. These quantities are typically estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in superficial tissue such as the skin can be confounded by the strong absorption of melanin in the epidermis. Furthermore, epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. This study describes a technique for decoupling the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. An artificial neural network was used to map input optical properties to spatial frequency domain diffuse reflectance of two layer media. Then, iterative fitting was used to determine the optical properties from simulated spatial frequency domain diffuse reflectance. Additionally, an artificial neural network was trained to directly map spatial frequency domain reflectance to sets of optical properties of a two layer medium, thus bypassing the need for iteration. In both cases, the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis were determined independently. The accuracy and efficiency of the iterative fitting approach was compared with the direct neural network inversion. PMID:22029367
Frequency-domain analysis of absolute gravimeters
NASA Astrophysics Data System (ADS)
Svitlov, S.
2012-12-01
An absolute gravimeter is analysed as a linear time-invariant system in the frequency domain. Frequency responses of absolute gravimeters are derived analytically based on the propagation of the complex exponential signal through their linear measurement functions. Depending on the model of motion and the number of time-distance coordinates, an absolute gravimeter is considered as a second-order (three-level scheme) or third-order (multiple-level scheme) low-pass filter. It is shown that the behaviour of an atom absolute gravimeter in the frequency domain corresponds to that of the three-level corner-cube absolute gravimeter. Theoretical results are applied for evaluation of random and systematic measurement errors and optimization of an experiment. The developed theory agrees with known results of an absolute gravimeter analysis in the time and frequency domains and can be used for measurement uncertainty analyses, building of vibration-isolation systems and synthesis of digital filtering algorithms.
Optics Program Modified for Multithreaded Parallel Computing
NASA Technical Reports Server (NTRS)
Lou, John; Bedding, Dave; Basinger, Scott
2006-01-01
A powerful high-performance computer program for simulating and analyzing adaptive and controlled optical systems has been developed by modifying the serial version of the Modeling and Analysis for Controlled Optical Systems (MACOS) program to impart capabilities for multithreaded parallel processing on computing systems ranging from supercomputers down to Symmetric Multiprocessing (SMP) personal computers. The modifications included the incorporation of OpenMP, a portable and widely supported application interface software, that can be used to explicitly add multithreaded parallelism to an application program under a shared-memory programming model. OpenMP was applied to parallelize ray-tracing calculations, one of the major computing components in MACOS. Multithreading is also used in the diffraction propagation of light in MACOS based on pthreads [POSIX Thread, (where "POSIX" signifies a portable operating system for UNIX)]. In tests of the parallelized version of MACOS, the speedup in ray-tracing calculations was found to be linear, or proportional to the number of processors, while the speedup in diffraction calculations ranged from 50 to 60 percent, depending on the type and number of processors. The parallelized version of MACOS is portable, and, to the user, its interface is basically the same as that of the original serial version of MACOS.
Koyama, Kohei; Yoneyama, Kihei; Mitarai, Takanobu; Kuwata, Shingo; Kongoji, Ken; Harada, Tomoo; Akashi, Yoshihiro J
2015-08-01
Longitudinal measurement using intravascular ultrasound is limited because the motorized pullback device assumes no cardiac motion. A newly developed intracoronary imaging modality, optical frequency domain imaging (OFDI), has higher resolution and an increased auto-pullback speed with presumably lesser susceptibility to cardiac motion artifacts during pullback for longitudinal measurement; however, it has not been fully investigated. We aimed to clarify the influence of cardiac motion on the accuracy and reproducibility of longitudinal measurements obtained using OFDI and to determine the optimal pullback speed. This ex vivo study included 31 stents deployed in the mid left anterior descending artery under phantom heartbeat and coronary flow simulation. Longitudinal stent lengths were measured twice using OFDI at three pullback speeds. Differences in stent lengths between OFDI and microscopy and between two repetitive pullbacks were assessed to determine accuracy and reproducibility. Furthermore, three-dimensional (3D) reconstruction was used for evaluating image quality. With regard to differences in stent length between OFDI and microscopy, the intraclass correlation coefficient values were 0.985, 0.994, and 0.995 at 10, 20, and 40 mm/s, respectively. With regard to reproducibility, the values were 0.995, 0.996, and 0.996 at 10, 20, and 40 mm/s, respectively. 3D reconstruction showed a superior image quality at 10 and 20 mm/s compared with that at 40 mm/s. OFDI demonstrated high accuracy and reproducibility for longitudinal stent measurements. Moreover, its accuracy and reproducibility were remarkable at a higher pullback speed. A 20-mm/s pullback speed may be optimal for clinical and research purposes.
Parallel algorithms for optical digital computers
Huang, A.
1983-01-01
Conventional computers suffer from several communication bottlenecks which fundamentally limit their performance. These bottlenecks are characterised by an address-dependent sequential transfer of information which arises from the need to time-multiplex information over a limited number of interconnections. An optical digital computer based on a classical finite state machine can be shown to be free of these bottlenecks. Such a processor would be unique since it would be capable of modifying its entire state space each cycle while conventional computers can only alter a few bits. New algorithms are needed to manage and use this capability. A technique based on recognising a particular symbol in parallel and replacing it in parallel with another symbol is suggested. Examples using this parallel symbolic substitution to perform binary addition and binary incrementation are presented. Applications involving Boolean logic, functional programming languages, production rule driven artificial intelligence, and molecular chemistry are also discussed. 12 references.
Compact parallel optical interface built with optical fiber tips
NASA Astrophysics Data System (ADS)
Kopp, Christophe; Gilbert, Karen; Bernabe, Stéphane; Albert, Blandine
2006-09-01
MultiChip Module approach and the use of micro-optics offer determinant solutions to reach the mechanical compactness required by most applications for high rate data communications transmitters and receivers. Such a miniaturization often leads to develop very challenging assembling processes when fiber coupling is needed. In this paper we present an original fabrication process to build very small parallel optical interface with optical fiber tips. This fabrication process is based on common fiber ribbon mounting into wet etched V shaped holder into silicon and a dicing-polishing step to create small pieces with optical quality considering flatness and roughness. The dicing-polishing principle is well-known in integrated waveguides technology. An example of realization is presented to connect a parallel optical subassembly transmitter with a MPO/MTP connector. The results show that the dicing-polishing step allows to obtain a diced-polished face with a roughness about 5 to 10nm onto the fiber. Such an optical quality is as good as a cleaved fiber when measuring light coupling performances. Thus, such micro-optical components offer a new building block for designers to extract the light from their photonic devices. Moreover, the fabrication process appears to be low cost and compatible with mass production.
Diagnosis of colon cancer using frequency domain fluorescence imaging technique
NASA Astrophysics Data System (ADS)
Dinish, U. S.; Gulati, P.; Murukeshan, V. M.; Seah, L. K.
2007-03-01
Early detection and treatment of colon cancer has been associated with better disease prognosis. Conventional and reported optical techniques have limitations in detecting early stages of colon cancer growth. In this paper, a homodyne signal processing assisted frequency domain (FD) fluorescence imaging methodology is proposed for the early diagnosis of colon cancer. Simulated phantom tissues representing the biopsy samples at different stages of colon cancer growth are prepared and used for the imaging study. Selective imaging of healthy and diseased sites simulated in the samples was achieved even for fluorescence emissions having close lifetimes and wavelength values. Possible extension of the methodology for in vivo investigations is also discussed.
Detecting structural information of scatterers using spatial frequency domain imaging.
Bodenschatz, Nico; Krauter, Philipp; Nothelfer, Steffen; Foschum, Florian; Bergmann, Florian; Liemert, André; Kienle, Alwin
2015-11-01
We demonstrate optical phantom experiments on the phase function parameter γ using spatial frequency domain imaging. The incorporation of two different types of scattering particles allows for control of the optical phantoms’ microscopic scattering properties. By laterally structuring areas with either TiO2 or Al2O3 scattering particles, we were able to obtain almost pure subdiffusive scattering contrast in a single optical phantom. Optical parameter mapping was then achieved using an analytical radiative transfer model revealing the microscopic structural contrast on a macroscopic field of view. As part of our study, we explain several correction and referencing techniques for high spatial frequency analysis and experimentally study the sampling depth of the subdiffusive parameter γ.
Detecting structural information of scatterers using spatial frequency domain imaging.
Bodenschatz, Nico; Krauter, Philipp; Nothelfer, Steffen; Foschum, Florian; Bergmann, Florian; Liemert, André; Kienle, Alwin
2015-11-01
We demonstrate optical phantom experiments on the phase function parameter γ using spatial frequency domain imaging. The incorporation of two different types of scattering particles allows for control of the optical phantoms’ microscopic scattering properties. By laterally structuring areas with either TiO2 or Al2O3 scattering particles, we were able to obtain almost pure subdiffusive scattering contrast in a single optical phantom. Optical parameter mapping was then achieved using an analytical radiative transfer model revealing the microscopic structural contrast on a macroscopic field of view. As part of our study, we explain several correction and referencing techniques for high spatial frequency analysis and experimentally study the sampling depth of the subdiffusive parameter γ. PMID:26590206
Method of parallel switching of optical channels
Kompanets, I N; Neevina, T A; Kompanets, S I
2012-12-31
The possibility of creating parallel-type switches for N Multiplication-Sign N optical waveguide channel communication is studied. A method based on bit-by-bit channel addressing is proposed and one of its possible implementations using the photorefractive effect in the waveguide material is considered. The method is modelled by the example of switching of 8 Multiplication-Sign 8 channels, controlled by reconfigurable matrix of light signals. (special issue devoted to the 90th anniversary of n.g. basov)
Studies in optical parallel processing. [All optical and electro-optic approaches
NASA Technical Reports Server (NTRS)
Lee, S. H.
1978-01-01
Threshold and A/D devices for converting a gray scale image into a binary one were investigated for all-optical and opto-electronic approaches to parallel processing. Integrated optical logic circuits (IOC) and optical parallel logic devices (OPA) were studied as an approach to processing optical binary signals. In the IOC logic scheme, a single row of an optical image is coupled into the IOC substrate at a time through an array of optical fibers. Parallel processing is carried out out, on each image element of these rows, in the IOC substrate and the resulting output exits via a second array of optical fibers. The OPAL system for parallel processing which uses a Fabry-Perot interferometer for image thresholding and analog-to-digital conversion, achieves a higher degree of parallel processing than is possible with IOC.
HDMI optical extender based on parallel optical transmitter and receiver
NASA Astrophysics Data System (ADS)
Luo, Zhixiang; Zhu, Zhishi; Zhang, Hailiang
2009-08-01
High-Definition Multimedia Interface(HDMI) can carry high quality multi-channel audio data and can carry all standard and highdefinition video formats. To send the information form video source to the display unit, the HDMI cable which carries four differential pairs is used. Now HDMI 1.3 increases its single-link bandwidth from 165MHz (4.95 gigabits per second) to 340 MHz (10.2 Gbps) to support the demands of future high definition display devices, so the traditional copper wire cable imposes limits on signal transmission distance and signal quality at so high speed. Optical fiber is of low dispersion, which in turn has the strength of longer signal transmission distance and better signal transmission quality in comparison to the traditional copper wire cable. So the optical extender consisting of two modules - one transmitter and one receiver- is developed. The transmitter connects to a computer/DVD player etc. The receiver connects to a display. Between the two modules, four-core ribbon fibre is used to transmit the video and audio signals. HDMI needs four differential pairs, so we design the parallel optical transmitter based on VCSEL array and VCSEL driver chip HXT3404 from Gigoptix and the parallel optical receiver based on PIN array and transimpedance amplifier chip HXR3404. Each channel can reach 3.125Gbps, so the data speed of the optical extender is 12.5Gbps. The experiment shows that the optical extender can transfer the video and audio data to the display uint 100 meter away.
Parallel reservoir computing using optical amplifiers.
Vandoorne, Kristof; Dambre, Joni; Verstraeten, David; Schrauwen, Benjamin; Bienstman, Peter
2011-09-01
Reservoir computing (RC), a computational paradigm inspired on neural systems, has become increasingly popular in recent years for solving a variety of complex recognition and classification problems. Thus far, most implementations have been software-based, limiting their speed and power efficiency. Integrated photonics offers the potential for a fast, power efficient and massively parallel hardware implementation. We have previously proposed a network of coupled semiconductor optical amplifiers as an interesting test case for such a hardware implementation. In this paper, we investigate the important design parameters and the consequences of process variations through simulations. We use an isolated word recognition task with babble noise to evaluate the performance of the photonic reservoirs with respect to traditional software reservoir implementations, which are based on leaky hyperbolic tangent functions. Our results show that the use of coherent light in a well-tuned reservoir architecture offers significant performance benefits. The most important design parameters are the delay and the phase shift in the system's physical connections. With optimized values for these parameters, coherent semiconductor optical amplifier (SOA) reservoirs can achieve better results than traditional simulated reservoirs. We also show that process variations hardly degrade the performance, but amplifier noise can be detrimental. This effect must therefore be taken into account when designing SOA-based RC implementations.
Frequency domain laser velocimeter signal processor
NASA Technical Reports Server (NTRS)
Meyers, James F.; Murphy, R. Jay
1991-01-01
A new scheme for processing signals from laser velocimeter systems is described. The technique utilizes the capabilities of advanced digital electronics to yield a signal processor capable of operating in the frequency domain maximizing the information obtainable from each signal burst. This allows a sophisticated approach to signal detection and processing, with a more accurate measurement of the chirp frequency resulting in an eight-fold increase in measurable signals over the present high-speed burst counter technology. Further, the required signal-to-noise ratio is reduced by a factor of 32, allowing measurements within boundary layers of wind tunnel models. Measurement accuracy is also increased up to a factor of five.
Optical interconnects: the Parallel Optical Link Organization (POLO) approach
NASA Astrophysics Data System (ADS)
Ishak, Waguih S.; Hahn, Kenneth H.; Booth, Bruce L.; Mueller, Ervin H.; Levi, Anthony F. J.; Craig, Richard R.
1995-04-01
The Parallel Optical Link Organization (POLO) is an industry consortium of Hewlett-Packard, Du Pont, AMP, University of Southern California, and SDL, supported by ARPA and will operate between August 1994 and August 1997. The POLO Consortium was formed to leverage the individual strengths of its members to develop low-cost, high-performance optical interconnect modules for applications in workstation clusters, high-speed switching systems, and multimedia. The goal of the program is to demonstrate the manufacturability of affordable optoelectronic transceiver modules and to provide application platforms that show a clear advantage over copper-wire interconnections. The technical objective of the program is to provide a 10 - 20 Gb/s parallel channel optical interconnect module with a projected manufacturing cost of about $10 per channel. In addition, the POLO Consortium provides a complete solution to the end user, including a programmable host interface module and software interface. The POLO Consortium has formed a User Group consisting of seven world-leading computer, telecommunication, and optoelectronic subsystem manufacturers. Regular meetings with the User Group are planned and at the first meeting, a full set of POLO Module specifications have been discussed and generated. The POLO Consortium will provide the User Group members with hardware for evaluation and feedback.
Materials characterization using frequency domain photoacoustic microscopy
NASA Astrophysics Data System (ADS)
Balogun, Oluwaseyi Oladeinde
A frequency domain photoacoustic microscopy system is developed for the characterization of micro- and nanoscale materials. An amplified, intensity modulated continuous wave (CW) laser source is used to generate narrow-bandwidth acoustic waves through the thermoelastic effect. The displacement resulting from acoustic wave interaction with material boundaries is measured using a path-stabilized Michelson interferometer. The signal from the interferometer is coupled to a RF lock-in amplifier or vector network analyzer, allowing for the bandwidth of the detection system to be matched to that of the acoustic signals. Measurements are made over an extremely narrow bandwidth by modulating the excitation laser source on the sample surface over a long time interval and selecting a corresponding integration time for the detection system. An analysis of the signal-to-noise ratio (SNR) of this system indicates that it offers substantial improvements over existing systems that incorporate pulsed laser sources to generate broad bandwidth acoustic waves. Using a bandwidth of 1.0 Hz, for instance, experimental results show a minimum detectable displacement of 3.1 fm. Extracting quantitative material parameters from the complex acoustic spectrum can be difficult when multiple acoustic modes are excited, or in the presence of reflections from sample boundaries. Two techniques are used to process the measured signals. In the first technique, the modulation frequency of the excitation laser is scanned over the bandwidth of interest, and a transient sample response is constructed from the frequency domain data. Acoustic arrivals that are separated in the time domain are time gated for further analysis. In the second approach, the modulation frequency of the excitation laser is fixed, but the source to receiver distance is varied. The spatial frequencies of the acoustic modes are found by analyzing the spatial variation of the phase, allowing for the velocity of each mode generated at
Parallel Optical and Electrochemical DNA Detection
NASA Astrophysics Data System (ADS)
Knoll, Wolfgang; Liu, Jianyun; Niu, Lifang; Nielsen, Peter Eigil; Tiefenauer, Louis
This contribution introduces strategies for the sensitive detection of oligonucleotides as bio-analytes binding from solution to a variety of probe architectures assembled at the (Au-) sensor surface. Detection principles based on surface plasmon optics and electrochemical techniques are compared. In particular, cyclic- and square wave voltammetry (SWV) are applied for the read-out of ferrocene redox labels conjugated to streptavidin that binds to the (biotinylated) DNA targets after hybridizing to the interfacial probe matrix of either DNA or peptide nucleic acid (PNA) strands. By employing streptavidin modified with fluorophores the identical sensor architecture can be used for the recording of hybridization reactions by surface plasmon fluorescence spectroscopy (SPFS). The Langmuir isotherms determined by both techniques, i.e., by SWV and SPFS, give virtually identical affinity constants KA, confirming that the mode of detection has no influence on the hybridization reaction. By using semiconducting nanoparticles as luminescence labels that can be tuned in their bandgap energies over a wide range of emission wavelengths surface plasmon fluorescence microscopy allows for the parallel read-out of multiple analyte binding events simultaneously.
Frequency Domain Sampling Using Biomedical Imaging Physics
NASA Astrophysics Data System (ADS)
Seo, Gun Ha; Chung, Minji; Kyung, Richard
2015-04-01
In magnetic resonance image analysis using physical and computational method, the process of transformation from frequency domain to image domain requires significant amount time because Inverse Fourier Transformation (IFT) takes every frequency points to determine the final output image. This paper shows the mechanisms and physics of image formation using the selectivity of proper k-space by removing different amounts of high or low frequencies to create the most optimal magnetic resonance image of a human tibial bone. Originally, square unit step function, N/2-N/10:N/2 + N/10 = 1, was used during the Fourier Transformations. And Gaussian filter, y = exp(-t2/40n) , where t = h-L/2, h = [0,M], L =2*7*N/40, the size of frequency matrix (M, N) = (365,557) was tested. Also circle equations as a filter, r = sqrt((x-M/2)2 + (y-N/2)2) , were tested in creating the images of the human tibial bone to find an efficient filter. The best efficiency occurred when the exponent n in the proposed Gaussian filter equation is in between 3 and 8, and therefore, a new algorithm is needed to find the exact number since the number is not only an integer.
Frequency Domain Calculations Of Acoustic Propagation
NASA Technical Reports Server (NTRS)
Lockard, David P.
2004-01-01
Two complex geometry problems are solved using the linearized Euler equations. The impedance mismatch method1 is used to impose the solid surfaces without the need to use a body-fitted grid. The problem is solved in the frequency domain to avoid long run times. Although the harmonic assumption eliminates all time dependence, a pseudo-time term is added to allow conventional iterative methods to be employed. A Jameson type, Runge-Kutta scheme is used to advance the solution in pseudo time. The spatial operator is based on a seven-point, sixth-order finite difference. Constant coefficient, sixth-derivative artificial dissipation is used throughout the domain. A buffer zone technique employing a complex frequency to damp all waves near the boundaries is used to minimize reflections. The results show that the method is capable of capturing the salient features of the scattering, but an excessive number of grid points are required to resolve the phenomena in the vicinity of the solid bodies because the wavelength of the acoustics is relatively short compared with the size of the bodies. Smoothly transitioning into the immersed boundary condition alleviates the difficulties, but a fine mesh is still required.
Thermal property microscopy with frequency domain thermoreflectance.
Yang, Jia; Maragliano, Carlo; Schmidt, Aaron J
2013-10-01
A thermal property microscopy technique based on frequency domain thermoreflectance (FDTR) is presented. In FDTR, a periodically modulated laser locally heats a sample while a second probe beam monitors the surface reflectivity, which is related to the thermal properties of the sample with an analytical model. Here, we extend FDTR into an imaging technique capable of producing micrometer-scale maps of several thermophysical properties simultaneously. Thermal phase images are recorded at multiple frequencies chosen for maximum sensitivity to thermal properties of interest according to a thermal model of the sample. The phase versus frequency curves are then fit point-by-point to obtain quantitative thermal property images of various combinations of thermal properties in multilayer samples, including the in-plane and cross-plane thermal conductivities, heat capacity, thermal interface conductance, and film thickness. An FDTR microscope based on two continuous-wave lasers is described, and a sensitivity analysis of the technique to different thermal properties is carried out. As a demonstration, we image ~3 nm of patterned titanium under 100 nm of gold on a silicon substrate, and simultaneously create maps of the thermal interface conductance and substrate thermal conductivity. Results confirm the potential of our technique for imaging and quantifying thermal properties of buried layers, indicating its utility for mapping thermal properties in integrated circuits.
Thermal property microscopy with frequency domain thermoreflectance
NASA Astrophysics Data System (ADS)
Yang, Jia; Maragliano, Carlo; Schmidt, Aaron J.
2013-10-01
A thermal property microscopy technique based on frequency domain thermoreflectance (FDTR) is presented. In FDTR, a periodically modulated laser locally heats a sample while a second probe beam monitors the surface reflectivity, which is related to the thermal properties of the sample with an analytical model. Here, we extend FDTR into an imaging technique capable of producing micrometer-scale maps of several thermophysical properties simultaneously. Thermal phase images are recorded at multiple frequencies chosen for maximum sensitivity to thermal properties of interest according to a thermal model of the sample. The phase versus frequency curves are then fit point-by-point to obtain quantitative thermal property images of various combinations of thermal properties in multilayer samples, including the in-plane and cross-plane thermal conductivities, heat capacity, thermal interface conductance, and film thickness. An FDTR microscope based on two continuous-wave lasers is described, and a sensitivity analysis of the technique to different thermal properties is carried out. As a demonstration, we image ˜3 nm of patterned titanium under 100 nm of gold on a silicon substrate, and simultaneously create maps of the thermal interface conductance and substrate thermal conductivity. Results confirm the potential of our technique for imaging and quantifying thermal properties of buried layers, indicating its utility for mapping thermal properties in integrated circuits.
Frequency domain analysis of knock images
NASA Astrophysics Data System (ADS)
Qi, Yunliang; He, Xin; Wang, Zhi; Wang, Jianxin
2014-12-01
High speed imaging-based knock analysis has mainly focused on time domain information, e.g. the spark triggered flame speed, the time when end gas auto-ignition occurs and the end gas flame speed after auto-ignition. This study presents a frequency domain analysis on the knock images recorded using a high speed camera with direct photography in a rapid compression machine (RCM). To clearly visualize the pressure wave oscillation in the combustion chamber, the images were high-pass-filtered to extract the luminosity oscillation. The luminosity spectrum was then obtained by applying fast Fourier transform (FFT) to three basic colour components (red, green and blue) of the high-pass-filtered images. Compared to the pressure spectrum, the luminosity spectra better identify the resonant modes of pressure wave oscillation. More importantly, the resonant mode shapes can be clearly visualized by reconstructing the images based on the amplitudes of luminosity spectra at the corresponding resonant frequencies, which agree well with the analytical solutions for mode shapes of gas vibration in a cylindrical cavity.
NASA Astrophysics Data System (ADS)
El-Ghussein, Fadi; Mastanduno, Michael A.; Jiang, Shudong; Pogue, Brian W.; Paulsen, Keith D.
2014-01-01
A new optical parallel detection system of hybrid frequency and continuous-wave domains was developed to improve the data quality and accuracy in recovery of all breast optical properties. This new system was deployed in a previously existing system for magnetic resonance imaging (MRI)-guided spectroscopy, and allows incorporation of additional near-infrared wavelengths beyond 850 nm, with interlaced channels of photomultiplier tubes (PMTs) and silicon photodiodes (PDs). The acquisition time for obtaining frequency-domain data at six wavelengths (660, 735, 785, 808, 826, and 849 nm) and continuous-wave data at three wavelengths (903, 912, and 948 nm) is 12 min. The dynamic ranges of the detected signal are 105 and 106 for PMT and PD detectors, respectively. Compared to the previous detection system, the SNR ratio of frequency-domain detection was improved by nearly 103 through the addition of an RF amplifier and the utilization of programmable gain. The current system is being utilized in a clinical trial imaging suspected breast cancer tumors as detected by contrast MRI scans.
El-Ghussein, Fadi; Mastanduno, Michael A; Jiang, Shudong; Pogue, Brian W; Paulsen, Keith D
2014-01-01
A new optical parallel detection system of hybrid frequency and continuous-wave domains was developed to improve the data quality and accuracy in recovery of all breast optical properties. This new system was deployed in a previously existing system for magnetic resonance imaging (MRI)-guided spectroscopy, and allows incorporation of additional near-infrared wavelengths beyond 850 nm, with interlaced channels of photomultiplier tubes (PMTs) and silicon photodiodes (PDs). The acquisition time for obtaining frequency-domain data at six wavelengths (660, 735, 785, 808, 826, and 849 nm) and continuous-wave data at three wavelengths (903, 912, and 948 nm) is 12 min. The dynamic ranges of the detected signal are 105 and 106 for PMT and PD detectors, respectively. Compared to the previous detection system, the SNR ratio of frequency-domain detection was improved by nearly 103 through the addition of an RF amplifier and the utilization of programmable gain. The current system is being utilized in a clinical trial imaging suspected breast cancer tumors as detected by contrast MRI scans. PMID:23979460
Mastanduno, Michael A.; Jiang, Shudong; Pogue, Brian W.; Paulsen, Keith D.
2013-01-01
Abstract. A new optical parallel detection system of hybrid frequency and continuous-wave domains was developed to improve the data quality and accuracy in recovery of all breast optical properties. This new system was deployed in a previously existing system for magnetic resonance imaging (MRI)-guided spectroscopy, and allows incorporation of additional near-infrared wavelengths beyond 850 nm, with interlaced channels of photomultiplier tubes (PMTs) and silicon photodiodes (PDs). The acquisition time for obtaining frequency-domain data at six wavelengths (660, 735, 785, 808, 826, and 849 nm) and continuous-wave data at three wavelengths (903, 912, and 948 nm) is 12 min. The dynamic ranges of the detected signal are 105 and 106 for PMT and PD detectors, respectively. Compared to the previous detection system, the SNR ratio of frequency-domain detection was improved by nearly 103 through the addition of an RF amplifier and the utilization of programmable gain. The current system is being utilized in a clinical trial imaging suspected breast cancer tumors as detected by contrast MRI scans. PMID:23979460
Experimental free-space optical network for massively parallel computers
NASA Astrophysics Data System (ADS)
Araki, S.; Kajita, M.; Kasahara, K.; Kubota, K.; Kurihara, K.; Redmond, I.; Schenfeld, E.; Suzaki, T.
1996-03-01
A free-space optical interconnection scheme is described for massively parallel processors based on the interconnection-cached network architecture. The optical network operates in a circuit-switching mode. Combined with a packet-switching operation among the circuit-switched optical channels, a high-bandwidth, low-latency network for massively parallel processing results. The design and assembly of a 64-channel experimental prototype is discussed, and operational results are presented.
Comparison of the domain and frequency domain state feedbacks
Zhang, S.Y.
1986-01-01
In this paper, we present explicitly the equivalence of the time domain and frequency domain state feedbacks, as well as the dynamic state feedback and a modified frequency domain state feedback, from the closed-loop transfer function point of view. The difference of the two approaches is also shown.
Laser Safety Method For Duplex Open Loop Parallel Optical Link
Baumgartner, Steven John; Hedin, Daniel Scott; Paschal, Matthew James
2003-12-02
A method and apparatus are provided to ensure that laser optical power does not exceed a "safe" level in an open loop parallel optical link in the event that a fiber optic ribbon cable is broken or otherwise severed. A duplex parallel optical link includes a transmitter and receiver pair and a fiber optic ribbon that includes a designated number of channels that cannot be split. The duplex transceiver includes a corresponding transmitter and receiver that are physically attached to each other and cannot be detached therefrom, so as to ensure safe, laser optical power in the event that the fiber optic ribbon cable is broken or severed. Safe optical power is ensured by redundant current and voltage safety checks.
AU-FREDI - AUTONOMOUS FREQUENCY DOMAIN IDENTIFICATION
NASA Technical Reports Server (NTRS)
Yam, Y.
1994-01-01
The Autonomous Frequency Domain Identification program, AU-FREDI, is a system of methods, algorithms and software that was developed for the identification of structural dynamic parameters and system transfer function characterization for control of large space platforms and flexible spacecraft. It was validated in the CALTECH/Jet Propulsion Laboratory's Large Spacecraft Control Laboratory. Due to the unique characteristics of this laboratory environment, and the environment-specific nature of many of the software's routines, AU-FREDI should be considered to be a collection of routines which can be modified and reassembled to suit system identification and control experiments on large flexible structures. The AU-FREDI software was originally designed to command plant excitation and handle subsequent input/output data transfer, and to conduct system identification based on the I/O data. Key features of the AU-FREDI methodology are as follows: 1. AU-FREDI has on-line digital filter design to support on-orbit optimal input design and data composition. 2. Data composition of experimental data in overlapping frequency bands overcomes finite actuator power constraints. 3. Recursive least squares sine-dwell estimation accurately handles digitized sinusoids and low frequency modes. 4. The system also includes automated estimation of model order using a product moment matrix. 5. A sample-data transfer function parametrization supports digital control design. 6. Minimum variance estimation is assured with a curve fitting algorithm with iterative reweighting. 7. Robust root solvers accurately factorize high order polynomials to determine frequency and damping estimates. 8. Output error characterization of model additive uncertainty supports robustness analysis. The research objectives associated with AU-FREDI were particularly useful in focusing the identification methodology for realistic on-orbit testing conditions. Rather than estimating the entire structure, as is
Polarized spatial frequency domain imaging of heart valve fiber structure
NASA Astrophysics Data System (ADS)
Goth, Will; Yang, Bin; Lesicko, John; Allen, Alicia; Sacks, Michael S.; Tunnell, James W.
2016-03-01
Our group previously introduced Polarized Spatial Frequency Domain Imaging (PSFDI), a wide-field, reflectance imaging technique which we used to empirically map fiber direction in porcine pulmonary heart valve leaflets (PHVL) without optical clearing or physical sectioning of the sample. Presented is an extended analysis of our PSFDI results using an inverse Mueller matrix model of polarized light scattering that allows additional maps of fiber orientation distribution, along with instrumentation permitting increased imaging speed for dynamic PHVL fiber measurements. We imaged electrospun fiber phantoms with PSFDI, and then compared these measurements to SEM data collected for the same phantoms. PHVL was then imaged and compared to results of the same leaflets optically cleared and imaged with small angle light scattering (SALS). The static PHVL images showed distinct regional variance of fiber orientation distribution, matching our SALS results. We used our improved imaging speed to observe bovine tendon subjected to dynamic loading using a biaxial stretching device. Our dynamic imaging experiment showed trackable changes in the fiber microstructure of biological tissue under loading. Our new PSFDI analysis model and instrumentation allows characterization of fiber structure within heart valve tissues (as validated with SALS measurements), along with imaging of dynamic fiber remodeling. The experimental data will be used as inputs to our constitutive models of PHVL tissue to fully characterize these tissues' elastic behavior, and has immediate application in determining the mechanisms of structural and functional failure in PHVLs used as bio-prosthetic implants.
Ultrasound breast imaging using frequency domain reverse time migration
NASA Astrophysics Data System (ADS)
Roy, O.; Zuberi, M. A. H.; Pratt, R. G.; Duric, N.
2016-04-01
Conventional ultrasonography reconstruction techniques, such as B-mode, are based on a simple wave propagation model derived from a high frequency approximation. Therefore, to minimize model mismatch, the central frequency of the input pulse is typically chosen between 3 and 15 megahertz. Despite the increase in theoretical resolution, operating at higher frequencies comes at the cost of lower signal-to-noise ratio. This ultimately degrades the image contrast and overall quality at higher imaging depths. To address this issue, we investigate a reflection imaging technique, known as reverse time migration, which uses a more accurate propagation model for reconstruction. We present preliminary simulation results as well as physical phantom image reconstructions obtained using data acquired with a breast imaging ultrasound tomography prototype. The original reconstructions are filtered to remove low-wavenumber artifacts that arise due to the inclusion of the direct arrivals. We demonstrate the advantage of using an accurate sound speed model in the reverse time migration process. We also explain how the increase in computational complexity can be mitigated using a frequency domain approach and a parallel computing platform.
Characterization of nonmelanoma skin cancer for light therapy using spatial frequency domain imaging
Rohrbach, Daniel J.; Zeitouni, Nathalie C.; Muffoletto, Daniel; Saager, Rolf; Tromberg, Bruce J.; Sunar, Ulas
2015-01-01
The dosimetry of light-based therapies critically depends on both optical and vascular parameters. We utilized spatial frequency domain imaging to quantify optical and vascular parameters, as well as estimated light penetration depth from 17 nonmelanoma skin cancer patients. Our data indicates that there exist substantial spatial variations in these parameters. Characterization of these parameters may inform understanding and optimization of the clinical response of light-based therapies. PMID:26137378
Frequency domain optoacoustic tomography using amplitude and phase
Mohajerani, Pouyan; Kellnberger, Stephan; Ntziachristos, Vasilis
2014-01-01
We introduce optoacoustic tomographic imaging using intensity modulated light sources and collecting amplitude and phase information in the frequency domain. Imaging is performed at multiple modulation frequencies. The forward modeling uses the Green's function solution to the pressure wave equation in frequency domain and the resulting inverse problem is solved using regularized least squares minimization. We study the effect of the number of frequencies and of the bandwidth employed on the image quality achieved. The possibility of employing an all-frequency domain optoacoustic imaging for experimental measurements is studied as a function of noise. We conclude that frequency domain optoacoustic tomography may evolve to a practical experimental method using light intensity modulated sources, with advantages over time-domain optoacoustics. PMID:25431755
In vivo spatial frequency domain spectroscopy of two layer media
NASA Astrophysics Data System (ADS)
Yudovsky, Dmitry; Nguyen, John Quan M.; Durkin, Anthony J.
2012-10-01
Monitoring of tissue blood volume and local oxygen saturation can inform the assessment of tissue health, healing, and dysfunction. These quantities can be estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in skin can be confounded by the strong absorption of melanin in the epidermis and epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. Therefore, a method is desired that decouples the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. A previously developed inverse method based on a neural network forward model was applied to simulated spatial frequency domain reflectance of skin for multiple wavelengths in the near infrared. It is demonstrated that the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis can be determined independently and with minimal coupling. Then, the same inverse method was applied to reflectance measurements from a tissue simulating phantom and in vivo human skin. Oxygen saturation and total hemoglobin concentrations were estimated from the volar forearms of weakly and strongly pigmented subjects using a standard homogeneous model and the present two layer model.
Multifrequency frequency-domain spectrometer for tissue analysis.
Spichtig, Sonja; Hornung, René; Brown, Derek W; Haensse, Daniel; Wolf, Martin
2009-02-01
In this paper we describe the modification and assessment of a standard multidistance frequency-domain near infrared spectroscopy (NIRS) instrument to perform multifrequency frequency-domain NIRS measurements. The first aim of these modifications was to develop an instrument that enables measurement of small volumes of tissue such as the cervix, which is too small to be measured using a multidistance approach. The second aim was to enhance the spectral resolution to be able to determine the absolute concentrations of oxy-, deoxy- and total hemoglobin, water, and lipids. The third aim was to determine the accuracy and error of measurement of this novel instrument in both in vitro and in vivo environments. The modifications include two frequency synthesizers with variable, freely adjustable frequency, broadband high-frequency amplifiers, the development of a novel avalanche photodiode (APD) detector and demodulation circuit, additional laser diodes with additional wavelengths, and a respective graphic user interface to analyze the measurements. To test the instrument and algorithm, phantoms with optical properties similar to those of biological tissue were measured and analyzed. The results show that the absorption coefficient can be determined with an error of <10%. The error of the scattering coefficient was <31%. Since the accuracy of the chromophore concentrations depends on the absorption coefficient and not on the scattering coefficient, the <10% error is the clinically relevant parameter. In addition, the new APD had similar accuracy as the standard photomultiplier tubes. To determine the accuracy of chromophore concentration measurements we employed liquid Intralipid(R) phantoms that contained 99% water, 1% lipid, and an increasing concentration of hemoglobin in steps of 0.010 mM. Water concentration was measured with an accuracy of 6.5% and hemoglobin concentration with an error of 0.0024 mM independent of the concentration. The measured lipid concentration
Dynamically reconfigurable optical interconnect architecture for parallel multiprocessor systems
NASA Astrophysics Data System (ADS)
Girard, Mary M.; Husbands, Charles R.; Antoszewska, Reza
1991-12-01
The progress in parallel processing technology in recent years has resulted in increased requirements to process large amounts of data in real time. The massively parallel architectures proposed for these applications require the use of a high speed interconnect system to achieve processor-to-processor connectivity without incurring excessive delays. The characteristics of optical components permit high speed operation while the nonconductive nature of the optical medium eliminates ground loop and transmission line problems normally associated with a conductive medium. The MITRE Corp. is evaluating an optical wavelength division multiple access interconnect network design to improve interconnectivity within parallel processor systems and to allow reconfigurability of processor communication paths. This paper describes the architecture and control of and highlights the results from an 8- channel multiprocessor prototype with effective throughput of 3.2 Gigabits per second (Gbps).
Parallel processor simulator for multiple optic channel architectures
NASA Astrophysics Data System (ADS)
Wailes, Tom S.; Meyer, David G.
1992-12-01
A parallel processing architecture based on multiple channel optical communication is described and compared with existing interconnection strategies for parallel computers. The proposed multiple channel architecture (MCA) uses MQW-DBR lasers to provide a large number of independent, selectable channels (or virtual buses) for data transport. Arbitrary interconnection patterns as well as machine partitions can be emulated via appropriate channel assignments. Hierarchies of parallel architectures and simultaneous execution of parallel tasks are also possible. Described are a basic overview of the proposed architecture, various channel allocation strategies that can be utilized by the MCA, and a summary of advantages of the MCA compared with traditional interconnection techniques. Also describes is a comprehensive multiple processor simulator that has been developed to execute parallel algorithms using the MCA as a data transport mechanism between processors and memory units. Simulation results -- including average channel load, effective channel utilization, and average network latency for different algorithms and different transmission speeds -- are also presented.
Robust time and frequency domain estimation methods in adaptive control
NASA Technical Reports Server (NTRS)
Lamaire, Richard Orville
1987-01-01
A robust identification method was developed for use in an adaptive control system. The type of estimator is called the robust estimator, since it is robust to the effects of both unmodeled dynamics and an unmeasurable disturbance. The development of the robust estimator was motivated by a need to provide guarantees in the identification part of an adaptive controller. To enable the design of a robust control system, a nominal model as well as a frequency-domain bounding function on the modeling uncertainty associated with this nominal model must be provided. Two estimation methods are presented for finding parameter estimates, and, hence, a nominal model. One of these methods is based on the well developed field of time-domain parameter estimation. In a second method of finding parameter estimates, a type of weighted least-squares fitting to a frequency-domain estimated model is used. The frequency-domain estimator is shown to perform better, in general, than the time-domain parameter estimator. In addition, a methodology for finding a frequency-domain bounding function on the disturbance is used to compute a frequency-domain bounding function on the additive modeling error due to the effects of the disturbance and the use of finite-length data. The performance of the robust estimator in both open-loop and closed-loop situations is examined through the use of simulations.
Analysis of stimulated Raman photoacoustics in frequency domain: A feasibility study
NASA Astrophysics Data System (ADS)
Li, Gaoming; Gao, Fei; Feng, Xiaohua; Zheng, Yuanjin
2016-08-01
The frequency domain analysis of stimulated Raman Photoacoustic (PA) induced by laser pulses with Gaussian and rectangular temporal profiles is presented. Utilizing the pulsed laser with nanosecond and microsecond pulse width with Gaussian temporal profile, the frequency component of the PA signals cannot be differentiated between the stimulated Raman PA and the linear optical absorption PA, which is limited by the response bandwidth of biological tissue. When the laser pulses with rectangular temporal profile are used, we deduced the PA expression and numerically derived its frequency spectrum. The frequency components of PA signal induced by the stimulated Raman phonons is more than that induced by optical absorption in some low frequency ranges, which is inside the bandwidth of tissue system. Therefore, stimulated Raman PA signal can be distinguished from the linear optical absorption PA signal in frequency domain. Numerical simulations were conducted in this paper to demonstrate the proposition and feasibility of stimulated Raman PA in frequency domain, which will be experimentally validated in future work.
Real-Time Reconfigurable Interconnections for Parallel Optical Processing
NASA Astrophysics Data System (ADS)
McArdle, Neil; Taghizadeh, Mohammad R.
1995-06-01
In this letter we describe the advantages of a dynamic optical interconnection system for parallel information processing applications. The system is based on a liquid crystal television which acts as a binary phase-only spatial light modulator. We describe example algorithms where reconfigurable interconnects would be useful and present results of several interconnection topologies which have been implemented.
Adaptive optics parallel near-confocal scanning ophthalmoscopy.
Lu, Jing; Gu, Boyu; Wang, Xiaolin; Zhang, Yuhua
2016-08-15
We present an adaptive optics parallel near-confocal scanning ophthalmoscope (AOPCSO) using a digital micromirror device (DMD). The imaging light is modulated to be a line of point sources by the DMD, illuminating the retina simultaneously. By using a high-speed line camera to acquire the image and using adaptive optics to compensate the ocular wave aberration, the AOPCSO can image the living human eye with cellular level resolution at the frame rate of 100 Hz. AOPCSO has been demonstrated with improved spatial resolution in imaging of the living human retina compared with adaptive optics line scan ophthalmoscopy.
Adaptive optics parallel near-confocal scanning ophthalmoscopy.
Lu, Jing; Gu, Boyu; Wang, Xiaolin; Zhang, Yuhua
2016-08-15
We present an adaptive optics parallel near-confocal scanning ophthalmoscope (AOPCSO) using a digital micromirror device (DMD). The imaging light is modulated to be a line of point sources by the DMD, illuminating the retina simultaneously. By using a high-speed line camera to acquire the image and using adaptive optics to compensate the ocular wave aberration, the AOPCSO can image the living human eye with cellular level resolution at the frame rate of 100 Hz. AOPCSO has been demonstrated with improved spatial resolution in imaging of the living human retina compared with adaptive optics line scan ophthalmoscopy. PMID:27519106
Parallel optics technology assessment for the versatile link project
Chramowicz, J.; Kwan, S.; Rivera, R.; Prosser, A.; /Fermilab
2011-01-01
This poster describes the assessment of commercially available and prototype parallel optics modules for possible use as back end components for the Versatile Link common project. The assessment covers SNAP12 transmitter and receiver modules as well as optical engine technologies in dense packaging options. Tests were performed using vendor evaluation boards (SNAP12) as well as custom evaluation boards (optical engines). The measurements obtained were used to compare the performance of these components with single channel SFP+ components operating at a transmission wavelength of 850 nm over multimode fibers.
Radiation-hard/high-speed parallel optical links
NASA Astrophysics Data System (ADS)
Gan, K. K.; Buchholz, P.; Heidbrink, S.; Kagan, H. P.; Kass, R. D.; Moore, J.; Smith, D. S.; Vogt, M.; Ziolkowski, M.
2016-09-01
We have designed and fabricated a compact parallel optical engine for transmitting data at 5 Gb/s. The device consists of a 4-channel ASIC driving a VCSEL (Vertical Cavity Surface Emitting Laser) array in an optical package. The ASIC is designed using only core transistors in a 65 nm CMOS process to enhance the radiation-hardness. The ASIC contains an 8-bit DAC to control the bias and modulation currents of the individual channels in the VCSEL array. The performance of the optical engine up at 5 Gb/s is satisfactory.
Functional cerebral activation detected by frequency-domain near-infrared spectroscopy
NASA Astrophysics Data System (ADS)
Toronov, Vladislav Y.; Webb, Andrew G.; Choi, Jee H.; Wolf, Martin; Safonova, Larisa P.; Wolf, Ursula; Gratton, Enrico
2002-07-01
The aim of our study was to explore the possibility of detecting haemodynamic changes in the brain using frequency- domain near-IR spectroscopy by exploiting the phase of the intensity modulated optical signal. To obtain optical signals with eh highest possible signal-to-noise ratio, we performed simultaneous NIRS-fMRI measurements, with subsequent correlation of the time courses of both measurements. The cognitive paradigm used arithmetic calculations, with optical signals acquired with sensors placed on the forehead. In three subjects we demonstrated correlation between the haemodynamic signals obtained using NIRS and BOLD fMRI.
Feasibility of optically interconnected parallel processors using wavelength division multiplexing
Deri, R.J.; De Groot, A.J.; Haigh, R.E.
1996-03-01
New national security demands require enhanced computing systems for nearly ab initio simulations of extremely complex systems and analyzing unprecedented quantities of remote sensing data. This computational performance is being sought using parallel processing systems, in which many less powerful processors are ganged together to achieve high aggregate performance. Such systems require increased capability to communicate information between individual processor and memory elements. As it is likely that the limited performance of today`s electronic interconnects will prevent the system from achieving its ultimate performance, there is great interest in using fiber optic technology to improve interconnect communication. However, little information is available to quantify the requirements on fiber optical hardware technology for this application. Furthermore, we have sought to explore interconnect architectures that use the complete communication richness of the optical domain rather than using optics as a simple replacement for electronic interconnects. These considerations have led us to study the performance of a moderate size parallel processor with optical interconnects using multiple optical wavelengths. We quantify the bandwidth, latency, and concurrency requirements which allow a bus-type interconnect to achieve scalable computing performance using up to 256 nodes, each operating at GFLOP performance. Our key conclusion is that scalable performance, to {approx}150 GFLOPS, is achievable for several scientific codes using an optical bus with a small number of WDM channels (8 to 32), only one WDM channel received per node, and achievable optoelectronic bandwidth and latency requirements. 21 refs. , 10 figs.
Frequency Domain Tomography Of Evolving Laser-Plasma Accelerator Structures
Dong Peng; Reed, Stephen; Kalmykov, Serguei; Shvets, Gennady; Downer, Mike
2009-01-22
Frequency Domain Holography (FDH), a technique for visualizing quasistatic objects propagating near the speed of light, has produced 'snapshots' of laser wakefields, but they are averaged over structural variations that occur during propagation through the plasma medium. Here we explore via simulations a generalization of FDH--that we call Frequency Domain Tomography (FDT)--that can potentially record a time sequence of quasistatic snapshots, like the frames of a movie, of the wake structure as it propagates through the plasma. FDT utilizes a several probe-reference pulse pairs that propagate obliquely to the drive pulse and wakefield, along with tomographic reconstruction algorithms similar to those used in medical CAT scans.
Frequency domain analysis of spreading-constriction thermal impedance
NASA Astrophysics Data System (ADS)
Casalegno, Francesco; De Marchi, Andrea; Giaretto, Valter
2013-02-01
Spreading-constriction effects are analyzed in the frequency domain. The existence of a half-pole altering the steady state solution at high frequencies is pointed out. Application to the case of thermoelectric devices allows direct comparison with experimental data because thermal quantities can be measured as electrical signals at the very spot where spreading takes place. Good agreement with theory is shown here for a thermoelectric device in which the particular constriction geometry enhances its effect, making easily observable the difference between frequency domain and the steady state approaches.
Frequency domain analysis of spreading-constriction thermal impedance.
Casalegno, Francesco; De Marchi, Andrea; Giaretto, Valter
2013-02-01
Spreading-constriction effects are analyzed in the frequency domain. The existence of a half-pole altering the steady state solution at high frequencies is pointed out. Application to the case of thermoelectric devices allows direct comparison with experimental data because thermal quantities can be measured as electrical signals at the very spot where spreading takes place. Good agreement with theory is shown here for a thermoelectric device in which the particular constriction geometry enhances its effect, making easily observable the difference between frequency domain and the steady state approaches.
High-performance parallel interface to synchronous optical network gateway
St. John, Wallace B.; DuBois, David H.
1996-01-01
A system of sending and receiving gateways interconnects high speed data interfaces, e.g., HIPPI interfaces, through fiber optic links, e.g., a SONET network. An electronic stripe distributor distributes bytes of data from a first interface at the sending gateway onto parallel fiber optics of the fiber optic link to form transmitted data. An electronic stripe collector receives the transmitted data on the parallel fiber optics and reforms the data into a format effective for input to a second interface at the receiving gateway. Preferably, an error correcting syndrome is constructed at the sending gateway and sent with a data frame so that transmission errors can be detected and corrected in a real-time basis. Since the high speed data interface operates faster than any of the fiber optic links the transmission rate must be adapted to match the available number of fiber optic links so the sending and receiving gateways monitor the availability of fiber links and adjust the data throughput accordingly. In another aspect, the receiving gateway must have sufficient available buffer capacity to accept an incoming data frame. A credit-based flow control system provides for continuously updating the sending gateway on the available buffer capacity at the receiving gateway.
High-performance parallel interface to synchronous optical network gateway
St. John, W.B.; DuBois, D.H.
1996-12-03
Disclosed is a system of sending and receiving gateways interconnects high speed data interfaces, e.g., HIPPI interfaces, through fiber optic links, e.g., a SONET network. An electronic stripe distributor distributes bytes of data from a first interface at the sending gateway onto parallel fiber optics of the fiber optic link to form transmitted data. An electronic stripe collector receives the transmitted data on the parallel fiber optics and reforms the data into a format effective for input to a second interface at the receiving gateway. Preferably, an error correcting syndrome is constructed at the sending gateway and sent with a data frame so that transmission errors can be detected and corrected in a real-time basis. Since the high speed data interface operates faster than any of the fiber optic links the transmission rate must be adapted to match the available number of fiber optic links so the sending and receiving gateways monitor the availability of fiber links and adjust the data throughput accordingly. In another aspect, the receiving gateway must have sufficient available buffer capacity to accept an incoming data frame. A credit-based flow control system provides for continuously updating the sending gateway on the available buffer capacity at the receiving gateway. 7 figs.
A frequency-domain channel model and emulator for aeronautical communications
NASA Astrophysics Data System (ADS)
Yang, Xiaopeng; Liang, Jun; Yao, Kun; Shi, Haoshan
2005-11-01
In this paper, we propose a frequency domain simulation structure for aeronautical wideband frequency-selective channel, which features ground-air and air-air wireless links. With appropriate channel parameters, the emulator can model the parking, taxi and en-route scenarios. The wideband frequency-selective channel consists of some parallel sub-channels in frequency domain, which are assumed to be independent to each other and have Rayleigh-distributed envelopes. The sub-channel models and emulators are based on a simple structure and characterized by flat fading. Through such decomposition approach, a frequency domain frequency-selective channel model can be achieved, which is suitable for an implementation of orthogonal frequency-division multiplexing (OFDM) or multi-carrier code-division multi-access (MC-CDMA) channel emulator on computer. Some appropriate emulator parameters have been proposed through channel sounding data collected for different scenarios. Particularly, in order to emulate the time-varying fading model well, the parameter sets are generated from time to time before the simulation with the same statistics.
Frequency Domain Detection of Biomolecules using Silicon Nanowire Biosensors
Zheng, Gengfeng; Gao, Xuan P. A.; Lieber, Charles M.
2010-01-01
We demonstrate a new protein detection methodology based upon frequency domain electrical measurement using silicon nanowire field-effect transistor (SiNW FET) biosensors. The power spectral density of voltage from a current-biased SiNW FET shows 1/f-dependence in frequency domain for measurements of antibody functionalized SiNW devices in buffer solution or in the presence of protein not specific to the antibody receptor. In the presence of protein (antigen) recognized specifically by the antibody-functionalized SiNW FET, the frequency spectrum exhibits a Lorentzian shape with a characteristic frequency of several kHz. Frequency and conventional time domain measurements carried out with the same device as a function of antigen concentration show more than 10-fold increase in detection sensitivity in the frequency domain data. These concentration dependent results together with studies of antibody receptor density effect further address possible origins of the Lorentzian frequency spectrum. Our results show that frequency domain measurements can be used as a complementary approach to conventional time domain measurements for ultra-sensitive electrical detection of proteins and other biomolecules using nanoscale FETs. PMID:20698634
Frequency-Domain Methods for Characterization of Pulsed Power Diagnostics
White, A D; Anderson, R A; Ferriera, T J; Goerz, D A
2009-07-27
This paper discusses methods of frequency-domain characterization of pulsed power sensors using vector network analyzer and spectrum analyzer techniques that offer significant simplification over time-domain methods, while mitigating or minimizing the effect of the difficulties present in time domain characterization. These methods are applicable to characterization of a wide variety of sensors.
Robust frequency-domain elastic Full Waveform Inversion: which norm?
NASA Astrophysics Data System (ADS)
Brossier, R.; Operto, S. O.; Virieux, J.
2009-12-01
Full waveform inversion (FWI) is becoming a powerful and efficient tool to derive high resolution models of subsurface visco-elastic parameters at different scales. In the frequency-domain (FD), 2D FWI is computationally affordable from both modeling and inversion viewpoints, because the inversion can be limited to few discrete frequencies when applied to wide-aperture acquisition geometries. However, FWI is an ill-posed data-fitting procedure that is sensitive to noise, inaccuracies of the starting model and definition of multi-parameter classes. The impact of the noise in FD FWI, when applied to decimated data sets, has been marginally illustrated in the past. We investigate here the sensitivities and performances of different minimization functionals, such as the least-square norm (L2), the least-absolute-values norm (L1), and some combinations of both (the Huber and the so-called Hybrid criteria), using realistic onshore and offshore synthetic case studies. The minimization functionals are implemented in a massively-parallel, 2D elastic FD FWI algorithm for imaging P- and S-wave velocities (VP and VS). Results show that the L1 norm provides the most reliable models, even when only few discrete frequencies are used in the inversion and when outliers pollute the data. The L2 norm can provide reliable results in the presence of uniform white noise if the data redundancy is increased by refining the frequency sampling interval in the inversion, at the expense of the computational efficiency. The Huber and the Hybrid criteria are shown to be sensitive to a threshold, which controls the transition between the L1 and L2 behaviors, and which requires tedious trial-and-error investigations for reliable estimation. The L1 norm provides a robust alternative to the L2 norm for the inversion of decimated data sets in the framework of efficient FD FWI. Synthetic onshore SEG/EAGE overthrust model experiment. Body and surface waves are jointly inverted. (a-b) true VP and VS
POLO: a gigabyte/s parallel optical link
NASA Astrophysics Data System (ADS)
Hahn, Kenneth H.; Dolfi, David W.
1996-01-01
The Parallel Optical Link Organization (POLO) is an ARPA sponsored industry consortium consisting of four companies and one university. The members are Hewlett-Packard, AMP, Du Pont, SDL, and the University of Southern California. The consortium's goal is to develop a high speed (1 Gbyte/s) parallel optical interconnect module for applications in central office switching environments and clustered computing. Previous reports have described the general layout of the POLO interconnect module and reported preliminary results. In this paper, we discuss further progress to date on the POLO module and show results for a 10 channel module operating at 622 Mb/s per channel. In addition, we discuss the current performance limitations of the module, packaging issues associated with assembly, a testbed which utilizes the POLO interconnect for the transmission of high resolution images between workstations, and plans for the second generation POLO module.
SERODS optical data storage with parallel signal transfer
Vo-Dinh, Tuan
2003-06-24
Surface-enhanced Raman optical data storage (SERODS) systems having increased reading and writing speeds, that is, increased data transfer rates, are disclosed. In the various SERODS read and write systems, the surface-enhanced Raman scattering (SERS) data is written and read using a two-dimensional process called parallel signal transfer (PST). The various embodiments utilize laser light beam excitation of the SERODS medium, optical filtering, beam imaging, and two-dimensional light detection. Two- and three-dimensional SERODS media are utilized. The SERODS write systems employ either a different laser or a different level of laser power.
SERODS optical data storage with parallel signal transfer
Vo-Dinh, Tuan
2003-09-02
Surface-enhanced Raman optical data storage (SERODS) systems having increased reading and writing speeds, that is, increased data transfer rates, are disclosed. In the various SERODS read and write systems, the surface-enhanced Raman scattering (SERS) data is written and read using a two-dimensional process called parallel signal transfer (PST). The various embodiments utilize laser light beam excitation of the SERODS medium, optical filtering, beam imaging, and two-dimensional light detection. Two- and three-dimensional SERODS media are utilized. The SERODS write systems employ either a different laser or a different level of laser power.
Parallel approach to MEMS and micro-optics interferometric testing
NASA Astrophysics Data System (ADS)
Kujawińska, M.; Beer, S.; Gastinger, K.; Gorecki, C.; Haugholt, K. H.; Józwik, M.; Lambelet, P.; Paris, R.; Styk, A.; Zeitner, U.
2011-08-01
The paper presents the novel approach to an interferometric, quantitative, massive parallel inspection of MicroElectroMechanicalSystems (MEMS), MicroOptoElectroMechanical Systems (MOEMS) and microoptics arrays. The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing wafer is exchangeable and contains one of the micro-optical interferometer arrays based on: (1) a low coherent interferometer array based on a Mirau configuration or (2) a laser interferometer array based on a Twyman-Green configuration. The optical, mechanical, and electro-optical design of the system and data analysis concept based on this approach is presented. The interferometer arrays are developed and integrated at a standard test station for micro-fabrication together with the illumination and imaging modules and special mechanics which includes scanning and electrostatic excitation systems. The smart-pixel approach is applied for massive parallel electro-optical detection and data reduction. The first results of functional tests of the system are presented. The concept is discussed in reference to the future M(O)EMS and microoptics manufacturers needs and requirements.
Frequency-domain stimulated and spontaneous light emission signals at molecular junctions
Harbola, Upendra; Agarwalla, Bijay Kumar; Mukamel, Shaul
2014-08-21
Using a diagrammatic superoperator formalism we calculate optical signals at molecular junctions where a single molecule is coupled to two metal leads which are held at different chemical potentials. The molecule starts in a nonequilibrium steady state whereby it continuously exchanges electrons with the leads with a constant electron flux. Expressions for frequency domain optical signals measured in response to continuous laser fields are derived by expanding the molecular correlation functions in terms of its many-body states. The nonunitary evolution of molecular states is described by the quantum master equation.
Hybrid Optoelectronic Bistability in Frequency-Domain and Its Potential Application in FBG Sensors
NASA Astrophysics Data System (ADS)
Ye, Hong-An; Liu, Chun-Yu; Lv, Guo-Hui; Xin, Hai-Ying; Zhu, Xiao-Liang
2008-12-01
We propose a novel optical bistable device (OBD) in frequency-domain with which we can perform optical bistable operations in a number of fibre Bragg gratings (FBGs) which are included in the same OBD. Such an OBD may bring more opportunities in applications and, as an example, we show the possibility of using it in an FBG sensor demodulating system. By use of a tunable light source, consisting of a broad band source and a scanning fibre F-P (FFP), we demonstrate the above-mentioned operations experimentally.
High-resolution parallel optical coherence tomography in scattering samples
NASA Astrophysics Data System (ADS)
Laubscher, M.; Ducros, Mathieu G.; Karamata, Boris; Bourquin, Stephane; Lasser, Theo
2001-11-01
Parallel optical coherence tomography in scattering samples is demonstrated using a 58 by 58 smart-pixel detector array. A femtosecond mode-locked Ti:Sapphire laser in combination with a free space Michelson interferometer was employed to achieve 4micrometers longitudinal resolution and 9mm transverse resolution on a 260x260 micrometers 2 field of view. We imaged a resolution target covered by an intralipid solution with different scattering coefficients as well as onion cells.
Parallel optical interconnects utilizing VLSI/FLC spatial light modulators
NASA Astrophysics Data System (ADS)
Genco, Sheryl M.
1991-12-01
Interconnection architectures are a cornerstone of parallel computing systems. However, interconnections can be a bottleneck in conventional computer architectures because of queuing structures that are necessary to handle the traffic through a switch at very high data rates and bandwidths. These issues must find new solutions to advance the state of the art in computing beyond the fundamental limit of silicon logic technology. Today's optoelectronic (OE) technology in particular VLSI/FLC spatial light modulators (SLMs) can provide a unique and innovative solution to these issues. This paper reports on the motivations for the system, describes the major areas of architectural requirements, discusses interconnection topologies and processor element alternatives, and documents an optical arbitration (i.e., control) scheme using `smart' SLMs and optical logic gates. The network topology is given in section 2.1 `Architectural Requirements -- Networks,' but it should be noted that the emphasis is on the optical control scheme (section 2.4) and the system.
1060-nm VCSEL-based parallel-optical modules for optical interconnects
NASA Astrophysics Data System (ADS)
Nishimura, N.; Nagashima, K.; Kise, T.; Rizky, A. F.; Uemura, T.; Nekado, Y.; Ishikawa, Y.; Nasu, H.
2015-03-01
The capability of mounting a parallel-optical module onto a PCB through solder-reflow process contributes to reduce the number of piece parts, simplify its assembly process, and minimize a foot print for both AOC and on-board applications. We introduce solder-reflow-capable parallel-optical modules employing 1060-nm InGaAs/GaAs VCSEL which leads to the advantages of realizing wider modulation bandwidth, longer transmission distance, and higher reliability. We demonstrate 4-channel parallel optical link performance operated at a bit stream of 28 Gb/s 231-1 PRBS for each channel and transmitted through a 50-μm-core MMF beyond 500 m. We also introduce a new mounting technology of paralleloptical module to realize maintaining good coupling and robust electrical connection during solder-reflow process between an optical module and a polymer-waveguide-embedded PCB.
Biwavelength transceiver module for parallel simultaneous bidirectional optical interconnections
NASA Astrophysics Data System (ADS)
Nguyen, Nga T. H.; Ukaegbu, Ikechi A.; Sangirov, Jamshid; Cho, Mu-Hee; Lee, Tae-Woo; Park, Hyo-Hoon
2013-12-01
The design of a biwavelength transceiver (TRx) module for parallel simultaneous bidirectional optical interconnects is described. The TRx module has been implemented using two different wavelengths, 850 and 1060 nm, to send and receive signals simultaneously through a common optical interface while optimizing cost and performance. Filtering mirrors are formed in the optical fibers which are embedded on a V-grooved silicon substrate for reflecting and filtering optical signals from/to vertical-cavity surface-emitting laser (VCSEL)/photodiode (PD). The VCSEL and PD are flip-chip bonded on individual silicon optical benches, which are attached on the silicon substrate for optical signal coupling from the VCSEL to fiber and from fiber to the PD. A high-speed and low-loss ceramic printed circuit board, which has a compact size of 0.033 cc, has been designed to carry transmitter and receiver chips for easy packaging of the TRx module. Applied for quad small form-factor pluggable applications at 40-Gbps operation, the four-channel biwavelength TRx module showed clear eye diagrams with a bit error rate (BER) of 10-12 at input powers of -5 and -5.8 dBm for 1060 and 850 nm operation modes, respectively.
A cost-efficient frequency-domain photoacoustic imaging system
NASA Astrophysics Data System (ADS)
LeBoulluec, Peter; Liu, Hanli; Yuan, Baohong
2013-09-01
Photoacoustic (PA) imaging techniques have recently attracted much attention and can be used for noninvasive imaging of biological tissues. Most PA imaging systems in research laboratories use the time domain method with expensive nanosecond pulsed lasers that are not affordable for most educational laboratories. Using an intensity modulated light source to excite PA signals is an alternative technique, known as the frequency domain method, with a much lower cost. In this paper, we describe a simple frequency domain PA system and demonstrate its imaging capability. The system provides opportunities not only to observe PA signals in tissue phantoms but also to acquire hands-on skills in PA signal detection. It also provides opportunities to explore the underlying mechanisms of the PA effect.
A cost-efficient frequency-domain photoacoustic imaging system
LeBoulluec, Peter; Liu, Hanli; Yuan, Baohong
2013-01-01
Photoacoustic (PA) imaging techniques have recently attracted much attention and can be used for noninvasive imaging of biological tissues. Most PA imaging systems in research laboratories use the time domain method with expensive nanosecond pulsed lasers that are not affordable for most educational laboratories. Using an intensity modulated light source to excite PA signals is an alternative technique, known as the frequency domain method, with a much lower cost. In this paper, we describe a simple frequency domain PA system and demonstrate its imaging capability. The system provides opportunities not only to observe PA signals in tissue phantoms, but also to acquire hands-on skills in PA signal detection. It also provides opportunities to explore the underlying mechanisms of the PA effect. PMID:24659823
Asymptotic Waveform Evaluation (AWE) Technique for Frequency Domain Electromagnetic Analysis
NASA Technical Reports Server (NTRS)
Cockrell, C. R.; Beck, F. B.
1996-01-01
The Asymptotic Waveform Evaluation (AWE) technique is applied to a generalized frequency domain electromagnetic problem. Most of the frequency domain techniques in computational electromagnetics result in a matrix equation, which is solved at a single frequency. In the AWE technique, the Taylor series expansion around that frequency is applied to the matrix equation. The coefficients of the Taylor's series are obtained in terms of the frequency derivatives of the matrices evaluated at the expansion frequency. The coefficients hence obtained will be used to predict the frequency response of the system over a frequency range. The detailed derivation of the coefficients (called 'moments') is given along with an illustration for electric field integral equation (or Method of Moments) technique. The radar cross section (RCS) frequency response of a square plate is presented using the AWE technique and is compared with the exact solution at various frequencies.
Parallel multithread computing for spectroscopic analysis in optical coherence tomography
NASA Astrophysics Data System (ADS)
Trojanowski, Michal; Kraszewski, Maciej; Strakowski, Marcin; Pluciński, Jerzy
2014-05-01
Spectroscopic Optical Coherence Tomography (SOCT) is an extension of Optical Coherence Tomography (OCT). It allows gathering spectroscopic information from individual scattering points inside the sample. It is based on time-frequency analysis of interferometric signals. Such analysis requires calculating hundreds of Fourier transforms while performing a single A-scan. Additionally, further processing of acquired spectroscopic information is needed. This significantly increases the time of required computations. During last years, application of graphical processing units (GPU's) was proposed to reduce computation time in OCT by using parallel computing algorithms. GPU technology can be also used to speed-up signal processing in SOCT. However, parallel algorithms used in classical OCT need to be revised because of different character of analyzed data. The classical OCT requires processing of long, independent interferometric signals for obtaining subsequent A-scans. The difference with SOCT is that it requires processing of multiple, shorter signals, which differ only in a small part of samples. We have developed new algorithms for parallel signal processing for usage in SOCT, implemented with NVIDIA CUDA (Compute Unified Device Architecture). We present details of the algorithms and performance tests for analyzing data from in-house SD-OCT system. We also give a brief discussion about usefulness of developed algorithm. Presented algorithms might be useful for researchers working on OCT, as they allow to reduce computation time and are step toward real-time signal processing of SOCT data.
Autonomous Frequency-Domain System-Identification Program
NASA Technical Reports Server (NTRS)
Yam, Yeung; Mettler, Edward; Bayard, David S.; Hadaegh, Fred Y.; Milman, Mark H.; Scheid, Robert E.
1993-01-01
Autonomous Frequency Domain Identification (AU-FREDI) computer program implements system of methods, algorithms, and software developed for identification of parameters of mathematical models of dynamics of flexible structures and characterization, by use of system transfer functions, of such models, dynamics, and structures regarded as systems. Software considered collection of routines modified and reassembled to suit system-identification and control experiments on large flexible structures.
Frequency-domain multiscale quantum mechanics/electromagnetics simulation method
Meng, Lingyi; Yin, Zhenyu; Yam, ChiYung E-mail: ghc@everest.hku.hk; Koo, SiuKong; Chen, GuanHua E-mail: ghc@everest.hku.hk; Chen, Quan; Wong, Ngai
2013-12-28
A frequency-domain quantum mechanics and electromagnetics (QM/EM) method is developed. Compared with the time-domain QM/EM method [Meng et al., J. Chem. Theory Comput. 8, 1190–1199 (2012)], the newly developed frequency-domain QM/EM method could effectively capture the dynamic properties of electronic devices over a broader range of operating frequencies. The system is divided into QM and EM regions and solved in a self-consistent manner via updating the boundary conditions at the QM and EM interface. The calculated potential distributions and current densities at the interface are taken as the boundary conditions for the QM and EM calculations, respectively, which facilitate the information exchange between the QM and EM calculations and ensure that the potential, charge, and current distributions are continuous across the QM/EM interface. Via Fourier transformation, the dynamic admittance calculated from the time-domain and frequency-domain QM/EM methods is compared for a carbon nanotube based molecular device.
Three-dimensional phantoms for curvature correction in spatial frequency domain imaging
Nguyen, Thu T. A.; Le, Hanh N. D.; Vo, Minh; Wang, Zhaoyang; Luu, Long; Ramella-Roman, Jessica C.
2012-01-01
The sensitivity to surface profile of non-contact optical imaging, such as spatial frequency domain imaging, may lead to incorrect measurements of optical properties and consequently erroneous extrapolation of physiological parameters of interest. Previous correction methods have focused on calibration-based, model-based, and computation-based approached. We propose an experimental method to correct the effect of surface profile on spectral images. Three-dimensional (3D) phantoms were built with acrylonitrile butadiene styrene (ABS) plastic using an accurate 3D imaging and an emergent 3D printing technique. In this study, our method was utilized for the correction of optical properties (absorption coefficient μa and reduced scattering coefficient μs′) of objects obtained with a spatial frequency domain imaging system. The correction method was verified on three objects with simple to complex shapes. Incorrect optical properties due to surface with minimum 4 mm variation in height and 80 degree in slope were detected and improved, particularly for the absorption coefficients. The 3D phantom-based correction method is applicable for a wide range of purposes. The advantages and drawbacks of the 3D phantom-based correction methods are discussed in details. PMID:22741068
A Simple Physical Optics Algorithm Perfect for Parallel Computing
NASA Technical Reports Server (NTRS)
Imbriale, W. A.; Cwik, T.
1993-01-01
One of the simplest reflector antenna computer programs is based upon a discrete approximation of the radiation integral. This calculation replaces the actual reflector surface with a triangular facet representation so that the reflector resembles a geodesic dome. The Physical Optics (PO) current is assumed to be constant in magnitude and phase over each facet so the radiation integral is reduced to a simple summation. This program has proven to be surprisingly robust and useful for the analysis of arbitrary reflectors, particularly when the near-field is desired and surface derivatives are not known. Because of its simplicity, the algorithm has proven to be extremely easy to adapt to the parallel computing architecture of a modest number of large-grain computing elements such as are used in the Intel iPSC and Touchstone Delta parallel machines.
Massively parallel processor networks with optical express channels
Deri, R.J.; Brooks, E.D. III; Haigh, R.E.; DeGroot, A.J.
1999-08-24
An optical method for separating and routing local and express channel data comprises interconnecting the nodes in a network with fiber optic cables. A single fiber optic cable carries both express channel traffic and local channel traffic, e.g., in a massively parallel processor (MPP) network. Express channel traffic is placed on, or filtered from, the fiber optic cable at a light frequency or a color different from that of the local channel traffic. The express channel traffic is thus placed on a light carrier that skips over the local intermediate nodes one-by-one by reflecting off of selective mirrors placed at each local node. The local-channel-traffic light carriers pass through the selective mirrors and are not reflected. A single fiber optic cable can thus be threaded throughout a three-dimensional matrix of nodes with the x,y,z directions of propagation encoded by the color of the respective light carriers for both local and express channel traffic. Thus frequency division multiple access is used to hierarchically separate the local and express channels to eliminate the bucket brigade latencies that would otherwise result if the express traffic had to hop between every local node to reach its ultimate destination. 3 figs.
Massively parallel processor networks with optical express channels
Deri, Robert J.; Brooks, III, Eugene D.; Haigh, Ronald E.; DeGroot, Anthony J.
1999-01-01
An optical method for separating and routing local and express channel data comprises interconnecting the nodes in a network with fiber optic cables. A single fiber optic cable carries both express channel traffic and local channel traffic, e.g., in a massively parallel processor (MPP) network. Express channel traffic is placed on, or filtered from, the fiber optic cable at a light frequency or a color different from that of the local channel traffic. The express channel traffic is thus placed on a light carrier that skips over the local intermediate nodes one-by-one by reflecting off of selective mirrors placed at each local node. The local-channel-traffic light carriers pass through the selective mirrors and are not reflected. A single fiber optic cable can thus be threaded throughout a three-dimensional matrix of nodes with the x,y,z directions of propagation encoded by the color of the respective light carriers for both local and express channel traffic. Thus frequency division multiple access is used to hierarchically separate the local and express channels to eliminate the bucket brigade latencies that would otherwise result if the express traffic had to hop between every local node to reach its ultimate destination.
Implementation of an LED-based clinical spatial frequency domain imaging system
NASA Astrophysics Data System (ADS)
Mazhar, Amaan; Sharif, Seyed A.; Saggese, Steve; Choi, Bernard; Cuccia, David J.; Durkin, Anthony J.
2012-03-01
Spatial Frequency Domain Imaging (SFDI) is a non-contact imaging method that uses multiple frequency spatial illumination to generate two dimensional maps of tissue optical properties (absorption and reduced scattering) and chromophore concentrations. We present phantom validation and pilot clinical data of a deployed light-emitting diode (LED) based system. The system employs four LED wavelengths (658 nm, 730 nm, 850 nm, 970 nm) to quantitatively assess tissue health by measurement of common tissue constituents. Phantom validation results and maps of oxyhemoglobin, deoxy-hemoglobin, water content, reduced scattering, and surface topography will be presented for pilot studies assessing burn severity and efficacy of port wine stain treatment.
Lu, Yujie; Darne, Chinmay D; Tan, I-Chih; Zhu, Banghe; Rightmer, Ryan; Rasmussen, John C; Sevick-Muraca, Eva M
2015-06-01
The performance evaluation of a variety of small animal tomography measurement approaches and algorithms for recovery of fluorescent absorption cross section has not been conducted. Herein, we employed an intensified CCD system installed in a commercial small animal CT (Computed Tomography) scanner to compare image reconstructions from time-independent, continuous wave (CW) measurements and from time-dependent, frequency domain (FD) measurements in a series of physical phantoms specifically designed for evaluation. Comparisons were performed as a function of (1) number of projections, (2) the level of preprocessing filters used to improve the signal-to-noise ratio (SNR), (3) endogenous heterogeneity of optical properties, as well as in the cases of (4) two fluorescent targets and (5) a mouse-shaped phantom. Assessment of quantitative recovery of fluorescence absorption cross section was performed using a fully parallel, regularization-free, linear reconstruction algorithm with diffusion approximation (DA) and high order simplified spherical harmonics ( SPN) approximation to the radiative transport equation (RTE). The results show that while FD measurements may result in superior image reconstructions over CW measurements, data acquisition times are significantly longer, necessitating further development of multiple detector/source configurations, improved data read-out rates, and detector technology. FD measurements with SP3 reconstructions enabled better quantitative recovery of fluorescent target strength, but required increased computational expense. Despite the developed parallel reconstruction framework being able to achieve more than 60 times speed increase over sequential implementation, further development in faster parallel acceleration strategies for near-real time and real-time image recovery and more precise forward solution is necessary. PMID:25438307
Klapp, Iftach; Mendlovic, David
2009-07-01
The problem of image restoration of space variant blur is common and important. One of the most useful descriptions of this problem is in its algebraic form I=H*O, where O is the object represented as a column vector, I is the blur image represented as a column vector and H is the PSF matrix that represents the optical system. When inverting the problem to restore the geometric object from the blurred image and the known system matrix, restoration is limited in speed and quality by the system condition. Current optical design methods focus on image quality, therefore if additional image processing is needed the matrix condition is taken "as is". In this paper we would like to present a new optical approach which aims to improve the system condition by proper optical design. In this new method we use Singular Value Decomposition (SVD) to define the weak parts of the matrix condition. We design a second optical system based on those weak SVD parts and then we add the second system parallel to the first one. The original and second systems together work as an improved parallel optics system. Following that, we present a method for designing such a "parallel filter" for systems with a spread SVD pattern. Finally we present a study case in which by using our new method we improve a space variant image system with an initial condition number of 8.76e4, down to a condition number of 2.29e3. We use matrix inversion to simulate image restoration. Results show that the new parallel optics immunity to Additive White Gaussian Noise (AWGN) is much better then that of the original simple lens. Comparing the original and the parallel optics systems, the parallel optics system crosses the MSEIF=0 [db] limit in SNR value which is more than 50db lower then the SNR value in the case of the original simple lens. The new parallel optics system performance is also compared to another method based on the MTF approach.
Fast Fourier backprojection for frequency-domain optoacoustic tomography.
Mohajerani, Pouyan; Kellnberger, Stephan; Ntziachristos, Vasilis
2014-09-15
We present a time-efficient backprojection image reconstruction approach applied to frequency-domain (FD) optoacoustic tomography based on tissue illumination at multiple, discrete frequencies. The presented method estimates the Fourier transform of a spatial, circular profile of the underlying image using the amplitude and phase data. These data are collected over multiple frequencies using an acoustic transducer positioned at several locations around the sample. Fourier-transform values for absent frequencies are estimated using interpolation based on low-pass filtering in the image domain. Reconstruction results are presented for synthetic measurements using numerical phantoms, and the results are compared with FD model-based reconstructions.
A frequency-domain derivation of shot-noise
NASA Astrophysics Data System (ADS)
Rice, Frank
2016-01-01
A formula for shot-noise is derived in the frequency-domain. The derivation is complete and reasonably rigorous while being appropriate for undergraduate students; it models a sequence of random pulses using Fourier sine and cosine series, and requires some basic statistical concepts. The text here may serve as a pedagogic introduction to the spectral analysis of random processes and may prove useful to introduce students to the logic behind stochastic problems. The concepts of noise power spectral density and equivalent noise bandwidth are introduced.
Design sensitivity analysis of mechanical systems in frequency domain
NASA Astrophysics Data System (ADS)
Nalecz, A. G.; Wicher, J.
1988-02-01
A procedure for determining the sensitivity functions of mechanical systems in the frequency domain by use of a vector-matrix approach is presented. Two examples, one for a ground vehicle passive front suspension, and the second for a vehicle active suspension, illustrate the practical applications of parametric sensitivity analysis for redesign and modification of mechanical systems. The sensitivity functions depend on the frequency of the system's oscillations. They can be easily related to the system's frequency characteristics which describe the dynamic properties of the system.
Frequency domain multiplexing for large-scale bolometer arrays
Spieler, Helmuth
2002-05-31
The development of planar fabrication techniques for superconducting transition-edge sensors has brought large-scale arrays of 1000 pixels or more to the realm of practicality. This raises the problem of reading out a large number of sensors with a tractable number of connections. A possible solution is frequency-domain multiplexing. I summarize basic principles, present various circuit topologies, and discuss design trade-offs, noise performance, cross-talk and dynamic range. The design of a practical device and its readout system is described with a discussion of fabrication issues, practical limits and future prospects.
Pole-zero form fractional model identification in frequency domain
Mansouri, R.; Djamah, T.; Djennoune, S.; Bettayeb, M.
2009-03-05
This paper deals with system identification in the frequency domain using non integer order models given in the pole-zero form. The usual identification techniques cannot be used in this case because of the non integer orders of differentiation which makes the problem strongly nonlinear. A general identification method based on Levenberg-Marquardt algorithm is developed and allows to estimate the (2n+2m+1) parameters of the model. Its application to identify the ''skin effect'' of a squirrel cage induction machine modeling is then presented.
Frequency domain, waveform inversion of laboratory crosswell radar data
Ellefsen, Karl J.; Mazzella, Aldo T.; Horton, Robert J.; McKenna, Jason R.
2010-01-01
A new waveform inversion for crosswell radar is formulated in the frequency-domain for a 2.5D model. The inversion simulates radar waves using the vector Helmholtz equation for electromagnetic waves. The objective function is minimized using a backpropagation method suitable for a 2.5D model. The inversion is tested by processing crosswell radar data collected in a laboratory tank. The estimated model is consistent with the known electromagnetic properties of the tank. The formulation for the 2.5D model can be extended to inversions of acoustic and elastic data.
Transient stability assessment by pattern recognition in the frequency domain
Ostojic, D.R. ); Heydt, G.T. . School of Electrical Engineering)
1991-02-01
This paper presents pattern recognition methodology which utilizes spectral monitoring of electromechanical oscillations to assess the transient stability of interconnected power systems. The proposed frequency domain approach permits definitive recognition of unstable dynamic modes. This is used to design an adaptive linear classifier which, in the developmental implementation virtually eliminates both false dismissals, and false alarms. The result is an accurate and reliable decision-making system which performs transient stability monitoring and assessment in real-time. Production computer code has not yet been implemented, but it is expected that the cited performance in developmental tests will be duplicated.
Spectrally encoded common-path fiber-optic-based parallel optical coherence tomography.
Lee, Kye-Sung; Hur, Hwan; Sung, Ha-Young; Kim, I Jong; Kim, Geon-Hee
2016-09-15
We demonstrate a fiber-optic-based parallel optical coherence tomography (OCT) using spectrally encoded extended illumination with a common-path handheld probe, where the flexibility and robustness of the system are significantly improved, which is critical in the clinical environment. To the best of our knowledge, we present the first parallel OCT based on fiber optics including a fiber coupler with a sensitivity of 94 dB, which is comparable to that of point-scanning OCT. We also investigated the effect of the phase stability of the fiber-based interferometry on the parallel OCT system by comparing the common-path OCT with two-arm OCT. Using the homemade common-path handheld probe based on a Mirau interferometer, the phase stability was 32 times better than that of the two-arm OCT. The axial resolution of the common-path OCT was measured as 5.1±0.3 μm. To demonstrate the in vivo imaging performance of the fiber-optic-based parallel OCT, human skin was imaged. PMID:27628367
Spectrally encoded common-path fiber-optic-based parallel optical coherence tomography.
Lee, Kye-Sung; Hur, Hwan; Sung, Ha-Young; Kim, I Jong; Kim, Geon-Hee
2016-09-15
We demonstrate a fiber-optic-based parallel optical coherence tomography (OCT) using spectrally encoded extended illumination with a common-path handheld probe, where the flexibility and robustness of the system are significantly improved, which is critical in the clinical environment. To the best of our knowledge, we present the first parallel OCT based on fiber optics including a fiber coupler with a sensitivity of 94 dB, which is comparable to that of point-scanning OCT. We also investigated the effect of the phase stability of the fiber-based interferometry on the parallel OCT system by comparing the common-path OCT with two-arm OCT. Using the homemade common-path handheld probe based on a Mirau interferometer, the phase stability was 32 times better than that of the two-arm OCT. The axial resolution of the common-path OCT was measured as 5.1±0.3 μm. To demonstrate the in vivo imaging performance of the fiber-optic-based parallel OCT, human skin was imaged.
Parametric Study of the Frequency-Domain Thermoreflectance Technique
C. Xing; C. Jensen; Z. Hua; H. Ban; D. H. Hurley; M. Khafizov; J. Rory Kennedy
2012-11-01
Without requiring regression for parameter determination, one-dimensional (1D) analytical models are used by many research groups to extract the thermal properties in frequency-domain thermoreflectance measurements. Experimentally, this approach involves heating the sample with a pump laser and probing the temperature response with spatially coincident probe laser. Micron order lateral resolution can be obtained by tightly focusing the pump and probe lasers. However, small laser beam spot sizes necessarily bring into question the assumptions associated with 1D analytical models. In this study, we analyzed the applicability of 1D analytical models by comparing to 2D analytical and fully numerical models. Specifically, we considered a generic nlayer two-dimensional (2D), axisymmetric analytical model including effects of volumetric heat absorption, contact resistance, and anisotropic properties. In addition, a finite element numerical model was employed to consider nonlinear effects caused by temperature dependent thermal conductivity. Nonlinearity is of germane importance to frequency domain approaches because the experimental geometry is such that the probe is always sensing the maximum temperature fluctuation. To quantify the applicability of the 1D model, parametric studies were performed considering the effects of: film thickness, heating laser size, probe laser size, substrate-to-film effusivity ratio, interfacial thermal resistance between layers, volumetric heating, substrate thermal conductivity, nonlinear boundary conditions, and anisotropic and temperature dependent thermal conductivity.
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.
Frequency-domain seismic-wave modeling, migration, and full-waveform inversion
NASA Astrophysics Data System (ADS)
Xu, Kun
In the dissertation, I have proposed and developed new approaches for seismic modeling, migration, and full-waveform inversion in the frequency domain. For 3D scalar-wave simulations in the frequency-space domain, we develop a fourth-order compact finite-difference (FD) form with a high-order spatial accuracy (4-5 grid points per shortest wavelength), and optimal one-way wave-equation (OWWE) absorbing boundary conditions (ABCs) with only one outer layer; these strategies greatly reduce the total number of the model grid points, and thus the overall computational cost. For reverse-time migration (RTM) using the cross-correlation imaging condition in the time domain, extra disk storage or wavefield simulations are required to make the forward propagated source and backward-propagated receiver wavefields available at the same time. We propose a new method to implement RTM in the frequency domain. Using virtual sources for the backward propagation of the receiver wavefield, we can straightforwardly implement the excitation-time and cross-correlation imaging conditions at each frequency without any disk storage or I/O and with complete spatial coverage of the migrated images. As both time and frequency domains have their own advantages for the inversion, we implement a hybrid scheme to combine both advantages in elastic full-waveform inversion (FWI). We simulate the wavefields using a time-domain high-precision finite-element (FE) modeling parallelized over shots with the message passing interface (MPI), and implement the inversion in the frequency domain via Fourier transform. Thus, we can easily apply both frequency-selection and time-windowing techniques to reduce the nonlinearity in inversion. To decouple different parameters in elastic FWI, we propose a new multi-steplength gradient approach to assign individual weights separately for each parameter gradient, and search for an optimal steplength along the composite gradient direction. As variations in the results
3D micro profile measurement with the method of spatial frequency domain analysis
NASA Astrophysics Data System (ADS)
Xu, Yongxiang
2015-10-01
3D micro profiles are often needed for measurement in many fields, e.g., binary optics, electronic industry, mechanical manufacturing, aeronautic and space industry, etc. In the case where height difference between two neighboring points of a test profile is equal to or greater than λ / 4, microscopic interferometry based on laser source will no longer be applicable because of the uncertainty in phase unwrapping. As white light possesses the characteristic of interference length approximate to zero, applying it for micro profilometry can avoid the trouble and can yield accurate results. Using self-developed Mirau-type scanning interference microscope, a step-like sample was tested twice, with 128 scanning interferograms recorded for each test. To process each set of the interferograms, the method of spatial frequency domain analysis was adopted. That is, for each point, by use of Furrier transform, white-light interference intensities were decomposed in spatial frequency domain, thus obtaining phase values corresponding to different wavenumbers; by using least square fitting on phases and wave numbers, a group-velocity OPD was gained for the very point; and finally in terms of the relation between relative height and the group-velocity OPD, the profile of the test sample was obtained. Two tests yielded same profile result for the sample, and step heights obtained were 50.88 nm and 50.94 nm, respectively. Meantime, the sample was also measured with a Zygo Newview 7200 topography instrument, with same profile result obtained and step height differing by 0.9 nm. In addition, data processing results indicate that chromatic dispersion equal to and higher than 2nd order is negligible when applying spatial frequency domain analysis method.
Scalable multiplexing for parallel imaging with interleaved optical coherence tomography
Lee, Hee Yoon; Marvdashti, Tahereh; Duan, Lian; Khan, Saara A.; Ellerbee, Audrey K.
2014-01-01
We demonstrate highly parallel imaging with interleaved optical coherence tomography (iOCT) using an in-house-fabricated, air-spaced virtually-imaged phased array (VIPA). The air-spaced VIPA performs spectral encoding of the interferograms from multiple lateral points within a single sweep of the source and allows us to tune and balance several imaging parameters: number of multiplexed points, ranging depth, and sensitivity. In addition to a thorough discussion of the parameters and operating principles of the VIPA, we experimentally demonstrate the effect of different VIPA designs on the multiplexing potential of iOCT. Using a 200-kHz light source, we achieve an effective A-scan rate of 3.2-MHz by multiplexing 16 lateral points onto a single wavelength sweep. The improved sensitivity of this system is demonstrated for 3D imaging of biological samples such as a human finger and a fruit fly. PMID:25401031
Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media
NASA Astrophysics Data System (ADS)
Schmidt, Felix; Lünenschloss, Peter; Mai, Juliane; Wagner, Norman; Töpfer, Hannes; Bumberger, Jan
2016-04-01
The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections. Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric
Blurred and noisy image pairs in parallel optics.
Klapp, Iftach; Sochen, Nir; Mendlovic, David
2014-11-01
In previous works we have shown that parallel optics (PO) architecture can be used to improve the system matrix condition, which results in improving its immunity to additive noise in the image restoration process. PO is composed of a "main" system and an "auxiliary" system. Previously, we suggested the "trajectories" method to realize PO. In that method, a required auxiliary system is composed from auxiliary optics with a pixel confined response, followed by signal processing. In this paper, we emphasize the important secondary effects of the trajectories method. We show that in such a system, where the postprocessing comes after the detection, the postprocessing acts as a noise filter, hence allowing us to work with noisy data in the auxiliary channel. Roughly speaking, the SNR of an imaging system depends on the numerical aperture (NA). It follows that the main system, which typically has a higher NA, also has a higher SNR. Hence in the PO system, the ratio between the NA values of the main and auxiliary systems is expected to dictate the gap between their SNR values. In this paper, we show that when the system is implemented by the trajectories method, this expectation is too conservative. It is shown that due to the noise filtering, the auxiliary system can be noisier than expected. This claim is proved analytically and verified and exemplified by using experimental measurements.
Angle correction for small animal tumor imaging with spatial frequency domain imaging (SFDI).
Zhao, Yanyu; Tabassum, Syeda; Piracha, Shaheer; Nandhu, Mohan Sobhana; Viapiano, Mariano; Roblyer, Darren
2016-06-01
Spatial frequency domain imaging (SFDI) is a widefield imaging technique that allows for the quantitative extraction of tissue optical properties. SFDI is currently being explored for small animal tumor imaging, but severe imaging artifacts occur for highly curved surfaces (e.g. the tumor edge). We propose a modified Lambertian angle correction, adapted from the Minnaert correction method for satellite imagery, to account for tissue surface angles up to 75°. The method was tested in a hemisphere phantom study as well as a small animal tumor model. The proposed method reduced µa and µs` extraction errors by an average of 64% and 16% respectively compared to performing no angle correction, and provided more physiologically agreeable optical property and chromophore values on tumors. PMID:27375952
Angle correction for small animal tumor imaging with spatial frequency domain imaging (SFDI)
Zhao, Yanyu; Tabassum, Syeda; Piracha, Shaheer; Nandhu, Mohan Sobhana; Viapiano, Mariano; Roblyer, Darren
2016-01-01
Spatial frequency domain imaging (SFDI) is a widefield imaging technique that allows for the quantitative extraction of tissue optical properties. SFDI is currently being explored for small animal tumor imaging, but severe imaging artifacts occur for highly curved surfaces (e.g. the tumor edge). We propose a modified Lambertian angle correction, adapted from the Minnaert correction method for satellite imagery, to account for tissue surface angles up to 75°. The method was tested in a hemisphere phantom study as well as a small animal tumor model. The proposed method reduced µa and µs` extraction errors by an average of 64% and 16% respectively compared to performing no angle correction, and provided more physiologically agreeable optical property and chromophore values on tumors. PMID:27375952
NASA Astrophysics Data System (ADS)
Fishkin, Joshua B.; So, Peter T. C.; Cerussi, Albert E.; Gratton, Enrico; Fantini, Sergio; Franceschini, Maria Angela
1995-03-01
We have measured the optical absorption and scattering coefficient spectra of a multiple-scattering medium (i.e., a biological tissue-simulating phantom comprising a lipid colloid) containing methemoglobin by using frequency-domain techniques. The methemoglobin absorption spectrum determined in the multiple-scattering medium is in excellent agreement with a corrected methemoglobin absorption spectrum obtained from a steady-state spectrophotometer measurement of the optical density of a minimally scattering medium. The determination of the corrected methemoglobin absorption spectrum takes into account the scattering from impurities in the methemoglobin solution containing no lipid colloid. Frequency-domain techniques allow for the separation of the absorbing from the scattering properties of multiple-scattering media, and these techniques thus provide an absolute
Real-Time Parameter Estimation in the Frequency Domain
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
2000-01-01
A method for real-time estimation of parameters in a linear dynamic state-space model was developed and studied. The application is aircraft dynamic model parameter estimation from measured data in flight. Equation error in the frequency domain was used with a recursive Fourier transform for the real-time data analysis. Linear and nonlinear simulation examples and flight test data from the F-18 High Alpha Research Vehicle were used to demonstrate that the technique produces accurate model parameter estimates with appropriate error bounds. Parameter estimates converged in less than one cycle of the dominant dynamic mode, using no a priori information, with control surface inputs measured in flight during ordinary piloted maneuvers. The real-time parameter estimation method has low computational requirements and could be implemented
Frequency domain compensation of a DYNGEN turbofan engine model
NASA Technical Reports Server (NTRS)
Schafer, R. M.; Gejji, R. R.; Hoppner, P. W.; Longenbaker, W. E.; Sain, M. K.
1977-01-01
Following Rosenbrock's ideas regarding the advantages of dominance in linear multivariable control systems, a new graphical technique is used for the design of compensators that achieve dominance. The technique is illustrated with an application to the problem of designing compensators for a linear turbofan-engine model. The resulting design is put into perspective by examining it in the light of two other multivariable frequency-domain methods. One, MacFarlane's method of characteristic loci, is used to realize a final design for stability and low interaction. The other is a direct technique based upon the algebraic expansion of the determinant of the return difference in terms of it's elements. Results from simulations carried out on the NASA DYNGEN software are included.
Ion mobility spectrometer using frequency-domain separation
Martin, S.J.; Butler, M.A.; Frye, G.C.; Schubert, W.K.
1998-08-04
An apparatus and method are provided for separating and analyzing chemical species in an ion mobility spectrometer using a frequency-domain technique wherein the ions generated from the chemical species are selectively transported through an ion flow channel having a moving electrical potential therein. The moving electrical potential allows the ions to be selected according to ion mobility, with certain of the ions being transported to an ion detector and other of the ions being effectively discriminated against. The apparatus and method have applications for sensitive chemical detection and analysis for monitoring of exhaust gases, hazardous waste sites, industrial processes, aerospace systems, non-proliferation, and treaty verification. The apparatus can be formed as a microelectromechanical device (i.e. a micromachine). 6 figs.
Real-Time Parameter Estimation in the Frequency Domain
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
1999-01-01
A method for real-time estimation of parameters in a linear dynamic state space model was developed and studied. The application is aircraft dynamic model parameter estimation from measured data in flight for indirect adaptive or reconfigurable control. Equation error in the frequency domain was used with a recursive Fourier transform for the real-time data analysis. Linear and nonlinear simulation examples and flight test data from the F-18 High Alpha Research Vehicle HARV) were used to demonstrate that the technique produces accurate model parameter estimates with appropriate error bounds. Parameter estimates converged in less than 1 cycle of the dominant dynamic mode natural frequencies, using control surface inputs measured in flight during ordinary piloted maneuvers. The real-time parameter estimation method has low computational requirements, and could be implemented aboard an aircraft in real time.
Frequency domain stress intensity calibration of damped cracked panels
NASA Technical Reports Server (NTRS)
Doyle, James F.; Rizzi, Stephen A.
1993-01-01
This paper discusses two schemes for doing finite element K calibration in the frequency domain. The baseline scheme uses the definition of K as a limit toward the crack tip. The limiting process requires using a very fine mesh around the crack tip making the scheme computationally very expensive. It is shown that the behavior of K as a function of frequency is very similar to a modal response. Taking advantage of this, a more efficient scheme involves a modal analysis of the cracked sheet and scaling the response to that of the static stress intensity. In this way, only a static K calibration need be performed. All the examples shown are for a frequency range spanning multiple resonances and with two levels of damping.
Frequency domain fluorimetry using a mercury vapor lamp
NASA Astrophysics Data System (ADS)
Bohn, Matthew J.; Lundin, Michael A.; Marciniak, Michael A.
2009-04-01
Frequency Domain (FD) fluorimetry, capitalizes on the frequency response function of a fluorophore and offers independence from light scatter and excitation/emission intensity variations in order to extract the sample's fluorescent lifetime. Mercury vapor lamps, a common source of industrial facility lighting, emit radiation that overlaps the UV/blue absorption spectrum of many fluorophores and may be used as an efficient and portable excitation source. The AC power modulation of mercury vapor lamps modulates the lamp's intensity at 120 Hz (in the United States) and higher harmonics. The fluorescent lifetimes for 3 different materials (willemite, uranium doped glass and U3O8) are measured with conventional techniques and compared with the FD technique using the power harmonics from a mercury vapor lamp. The mercury lamp measurements agree to within 25% of the conventional methods.
Critical comparison between time- and frequency-domain relaxation functions
NASA Astrophysics Data System (ADS)
Snyder, Chad R.; Mopsik, Frederick I.
1999-07-01
Considerable work has been performed on providing a theoretical basis for the Kohlrausch-Williams-Watts (KWW) and Havriliak-Negami (HN) relaxation functions. Because of this, several papers have examined the ``interconnection'' of these two functions. In this paper, we demonstrate that, with achievable instrumental sensitivity, these two functions are distinguishable. We further address the issue of the ``universal'' limiting power laws and the ability to obtain the exponents associated with them. Finally, the stability and accuracy of our numerical Laplace transform is demonstrated by comparison between functions with known analytical time and frequency solutions. The stability of our algorithm indicates that the method of Alvarez and co-workers [F. Alvarez, A. Alegría, and J. Colmenero, Phys. Rev. B 44, 7306 (1991)] is an unnecessary approximation for converting between the time and frequency domain.
Frequency domain identification for robust large space structure control design
NASA Technical Reports Server (NTRS)
Yam, Y.; Bayard, D. S.; Scheid, R. E.
1991-01-01
A methodology is demonstrated for frequency domain identification of large space structures which systematically transforms experimental raw data into a form required for synthesizing H(infinity) controllers using modern robust control design software (e.g., Matlab Toolboxes). A unique feature of this approach is that the additive uncertainty is characterized to a specified statistic confidence rather than with hard bounds. In this study, the difference in robust performance is minimal between the two levels of confidence. In general cases, the present methodology provides a tool for performance/confidence level tradeoff studies. For simplicity, the additive uncertainty on a frequency grid is considered and the interpolation error in between grid points is neglected.
Frequency domain identification experiment on a large flexible structure
NASA Technical Reports Server (NTRS)
Bayard, D. S.; Hadaegh, F. Y.; Yam, Y.; Scheid, R. E.; Mettler, E.; Milman, M. H.
1989-01-01
Recent experiences in the field of flexible structure control in space have indicated a need for on-orbit system identification to support robust control redesign to avoid in-flight instabilities and maintain high spacecraft performance. The authors highlight an automated frequency domain system identification methodology recently developed to fill this need. The methodology supports (1) the estimation of system quantities useful for robust control analysis and design, (2) experiment design tailored to performing system identification in a typically constrained on-orbit environment, and (3) the automation of operations to reduce human-in-the-loop requirements. A basic overview of the methodology is presented first, followed by an experimental verification of the approach performed on the JPL/AFAL testbed facility.
Frequency-domain ultrasound waveform tomography breast attenuation imaging
NASA Astrophysics Data System (ADS)
Sandhu, Gursharan Yash Singh; Li, Cuiping; Roy, Olivier; West, Erik; Montgomery, Katelyn; Boone, Michael; Duric, Neb
2016-04-01
Ultrasound waveform tomography techniques have shown promising results for the visualization and characterization of breast disease. By using frequency-domain waveform tomography techniques and a gradient descent algorithm, we have previously reconstructed the sound speed distributions of breasts of varying densities with different types of breast disease including benign and malignant lesions. By allowing the sound speed to have an imaginary component, we can model the intrinsic attenuation of a medium. We can similarly recover the imaginary component of the velocity and thus the attenuation. In this paper, we will briefly review ultrasound waveform tomography techniques, discuss attenuation and its relations to the imaginary component of the sound speed, and provide both numerical and ex vivo examples of waveform tomography attenuation reconstructions.
Ion mobility spectrometer using frequency-domain separation
Martin, Stephen J.; Butler, Michael A.; Frye, Gregory C.; Schubert, W. Kent
1998-01-01
An apparatus and method is provided for separating and analyzing chemical species in an ion mobility spectrometer using a frequency-domain technique wherein the ions generated from the chemical species are selectively transported through an ion flow channel having a moving electrical potential therein. The moving electrical potential allows the ions to be selected according to ion mobility, with certain of the ions being transported to an ion detector and other of the ions being effectively discriminated against. The apparatus and method have applications for sensitive chemical detection and analysis for monitoring of exhaust gases, hazardous waste sites, industrial processes, aerospace systems, non-proliferation, and treaty verification. The apparatus can be formed as a microelectromechanical device (i.e. a micromachine).
EEG time and frequency domain analyses of primary insomnia.
Hamida, Sana Tmar-Ben; Penzel, Thomas; Ahmed, Beena
2015-08-01
In this work, we present a range of electroencephalographic (EEG) time and frequency domain features that can be used to characterize patients suffering with primary insomnia. When evaluated using 10 insomniacs and 10 healthy subjects, we found significant differences in the feature values between the two groups. Participants with primary insomnia were observed to have significantly elevated Hjorth's parameters particularly complexity, high zero crossing rates specifically during wake and sleep stage 1 and high gamma power in all sleep stages. Given the significant differences between the two groups, these features can be used to better understand the sleep dynamics of insomniacs and accurately discriminate insomniac EEG data from that of healthy subjects. PMID:26737710
Remote Strain Sensing of CFRP Using Microwave Frequency Domain Reflectometry
NASA Technical Reports Server (NTRS)
Wilson, William C.; Moore, Jason P.; Juarez, Peter D.
2016-01-01
NASA's Advanced Composites Project is investigating technologies that increase automated remote inspection of aircraft composite structures. Therefore, microwave Frequency Domain Reflectometry (FDR) is being investigated as a method of enabling rapid remote measurement of strain occurring at the first ply of a composite fiber reinforced polymer (CFRP) structure using Radio Frequency (RF) Electro-Magnetic (EM) radiation. While microwave reflectometry has been used to detect disbonds in CFRP structures, its use in detecting strain has been limited. This work will present data demonstrating the measurement of the reactance changes due to loading conditions that are indicative of strain in a CFRP structure. In addition, the basic EM signature will be presented along with an analysis of temperature and humidity effects.
Frequency-domain approaches to quantitative brain SPECT
NASA Astrophysics Data System (ADS)
Cheng, Jui-Hsi
1997-12-01
Quantitative SPECT (Single Photon Emission Computed Tomography) has been limited mainly by (1) inadequate numbers of detected photons which are contaminated by Poisson noise in projections, (2) photon attenuation in the body, (3) inclusion of scattered photons in the projections, and (4) depth-dependent blurring due to the finite size of collimator holes. Various methods to compensate for the above effects via either spatial- domain approaches or frequency-domain approaches have been proposed. However, most of the proposed methods focus only on individual effects. A reconstruction method which can compensate for all of the effects simultaneously is necessary. We have developed an algorithm to compensate for all of the effects simultaneously using frequency-domain approaches. For noise suppression, a method to convert the signal-dependent Poisson noise into signal- independent Gaussian white noise was first applied. Then the Wiener filter with a designed butterfly window was used. For scatter-photon removal, a subtraction technique based on multiple energy-window acquisitions was employed. For collimation deblurring, a direct inverse filter was designed via stationary phase condition (depth-frequency relationship). For attenuation compensation, an exact analytical solution was derived by Fourier analysis. Our algorithm was executed on a HP/730 workstation. An improvement was shown in computing time, noise suppression, recognition of phantom features, and quantification of concentrations of regions of interest (ROI). In addition to simulation, we performed a series of experiments to verify our models and test our algorithm. These include (1) investigation of the characteristics of Poisson noise of SPECT, (2) comparison of the performance of dual-energy window and triple-energy window methods for scatter correction, (3) measurement of a depth- dependent PSF, (4) reconstruction of the attenuation map using scatter-window data, and (5) implementation of a simultaneous
Clinical skin imaging using color spatial frequency domain imaging (Conference Presentation)
NASA Astrophysics Data System (ADS)
Yang, Bin; Lesicko, John; Moy, Austin J.; Reichenberg, Jason; Tunnell, James W.
2016-02-01
Skin diseases are typically associated with underlying biochemical and structural changes compared with normal tissues, which alter the optical properties of the skin lesions, such as tissue absorption and scattering. Although widely used in dermatology clinics, conventional dermatoscopes don't have the ability to selectively image tissue absorption and scattering, which may limit its diagnostic power. Here we report a novel clinical skin imaging technique called color spatial frequency domain imaging (cSFDI) which enhances contrast by rendering color spatial frequency domain (SFD) image at high spatial frequency. Moreover, by tuning spatial frequency, we can obtain both absorption weighted and scattering weighted images. We developed a handheld imaging system specifically for clinical skin imaging. The flexible configuration of the system allows for better access to skin lesions in hard-to-reach regions. A total of 48 lesions from 31 patients were imaged under 470nm, 530nm and 655nm illumination at a spatial frequency of 0.6mm^(-1). The SFD reflectance images at 470nm, 530nm and 655nm were assigned to blue (B), green (G) and red (R) channels to render a color SFD image. Our results indicated that color SFD images at f=0.6mm-1 revealed properties that were not seen in standard color images. Structural features were enhanced and absorption features were reduced, which helped to identify the sources of the contrast. This imaging technique provides additional insights into skin lesions and may better assist clinical diagnosis.
Parallel processing using an optical delay-based reservoir computer
NASA Astrophysics Data System (ADS)
Van der Sande, Guy; Nguimdo, Romain Modeste; Verschaffelt, Guy
2016-04-01
Delay systems subject to delayed optical feedback have recently shown great potential in solving computationally hard tasks. By implementing a neuro-inspired computational scheme relying on the transient response to optical data injection, high processing speeds have been demonstrated. However, reservoir computing systems based on delay dynamics discussed in the literature are designed by coupling many different stand-alone components which lead to bulky, lack of long-term stability, non-monolithic systems. Here we numerically investigate the possibility of implementing reservoir computing schemes based on semiconductor ring lasers. Semiconductor ring lasers are semiconductor lasers where the laser cavity consists of a ring-shaped waveguide. SRLs are highly integrable and scalable, making them ideal candidates for key components in photonic integrated circuits. SRLs can generate light in two counterpropagating directions between which bistability has been demonstrated. We demonstrate that two independent machine learning tasks , even with different nature of inputs with different input data signals can be simultaneously computed using a single photonic nonlinear node relying on the parallelism offered by photonics. We illustrate the performance on simultaneous chaotic time series prediction and a classification of the Nonlinear Channel Equalization. We take advantage of different directional modes to process individual tasks. Each directional mode processes one individual task to mitigate possible crosstalk between the tasks. Our results indicate that prediction/classification with errors comparable to the state-of-the-art performance can be obtained even with noise despite the two tasks being computed simultaneously. We also find that a good performance is obtained for both tasks for a broad range of the parameters. The results are discussed in detail in [Nguimdo et al., IEEE Trans. Neural Netw. Learn. Syst. 26, pp. 3301-3307, 2015
Refined method of frequency domain interferometry for the MST radar
NASA Astrophysics Data System (ADS)
Pan, C. J.; Liu, C. H.; Roettger, J.
1993-08-01
The frequency domain interferometry (FDI) technique consists of transmitting a series of pulses with alternative carrier frequencies f1 and f2. From the resulting data, two different time series V1(t) and V2(t) can be formed corresponding to the carrier frequencies f1 and f2, respectively. Processing V1(t) and V2(t) in the frequency domain, the normalized cross-spectrum S(sub 12)(f) can be obtained by the equation S(sub 12)(f) = (*V1(f) V2(f)*) / (*V1(f)(exp 2)* *V2(f)(exp 2)*)(exp 1/2), where V1(f) and V2(f) represent the Fourier transforms of V1(t) and V2(t), respectively, and * * indicates the ensemble mean of periodograms necessary to estimate the auto and cross spectrum. Then, the amplitude and phase of S(sub 12)(f), the coherence function, are both functions of the doppler frequency f. As the beamwidth of the Chung-Li VHF radar is about 7.4 deg, the beam broadening effect is significant. According to the simple model pointed out by Woodman and Chu, the doppler frequency is related to angle of arrival given by theta = (f - fm)lambda/2U, where U is the mean wind speed, theta is the angle of arrival, lambda is the wavelength, and fm is the mean doppler frequency. Combining these two ideas, the coherence function S(sub 12)(f) is a function of doppler frequency f and each f corresponds to an angle of arrival. Therefore, the layer's thickness and positions can be estimated from different angles of arrival. This is the so called refined FDI method. An experiment has been carried out to implement this idea. Two frequencies f1 = 52 MHz and f2 = 52.5 MHz were employed at Chung-Li VHF radar to carry out the FDI observations with a 300 meter range resolution. By using the refined FDI method, it is shown that more information is obtained than the traditional FDI method to look inside the fine structure of the layer.
Development and qualification of a mechanical-optical interface for parallel optics links
NASA Astrophysics Data System (ADS)
Chuang, S.; Schoellner, D.; Ugolini, A.; Wakjira, J.; Wolf, G.
2015-03-01
As parallel optics applications continue to expand, there remains a need for an effective coupling interface between the board-level active components and the passive components of the network. While mid-board level photonic turn connectors are available, coupling interfaces are generally not available outside of proprietary solutions. Development of a general mechanical-optical coupling interface opens the door for broader parallel optics implementation. An interface for use between the optical transmitter and the photonic turn connector is introduced. The interface is a monolithic injection molded component with an array of collimating lenses to couple efficiently with common VCSEL/PD designs. The component has precise epoxy control features to manage epoxy bond-line thickness and strength. Suitable UV and thermal epoxies have been qualified for effective die bond placement of the component in the VCSEL/PD environment. Environmental and mechanical performance of the component to industry-standard qualification requirements are reviewed, and tensile force testing and durability results validate the mechanical characteristics of the interface.
A compact frequency domain fluorometer with a directly modulated deuterium light source
NASA Astrophysics Data System (ADS)
Morgan, C. G.; Hua, Y.; Mitchell, A. K.; Murray, J. G.; Boardman, A. D.
1996-01-01
A phase fluorometer based on a low-cost and versatile high-frequency modulated light source and a fast gain-modulated photomultiplier is described. The apparatus is particularly well-suited to high-sensitivity frequency-domain fluorescence measurements requiring ultraviolet excitation. The system is very compact since it features a directly modulated light source, a miniature photomultiplier tube, and an rf synthesizer on a PC board. Equipped with a suitable fiber optic probe sensor, the device has potential as a portable unit for a wide range of remote sensing applications. The lamp can be modulated at frequencies up to 120 MHz and the phase fluorometer has been tested at up to 70 MHz with a range of fluorescent lifetime standards containing quinine sulfate quenched with sodium chloride.
Frequency-domain fluorescence spectroscopy of human stratum corneum
NASA Astrophysics Data System (ADS)
Garrison, Michael D.; Potts, Russell O.; Abraham, William
1994-08-01
The intercellular lipid lamellae of mammalian stratum corneum (SC) constitute the major barrier to percutaneous penetration of drugs and other solute molecules. In order to understand the barrier property of skin on a molecular level, we have initiated fluorescence spectroscopic investigation of the membranous structures of the SC and related model systems using the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Incorporated into distearoylphosphatidylcholine and stratum corneum bilayers, DPH fluorescence reflected the change in lipid structure under thermal and chemical perturbations. Using a multiharmonic frequency approach, we measured the fluorescence lifetime and rotational correlation times for DPH in these systems. Our data indicated that a biexponential decay ((tau) 1 approximately equals 9 ns, (tau) 2 approximately equals 1.5 ns) described the intensity decay, while a hindered rotor model ((phi) approximately equals 5 ns, r(infinity ) approximately equals 0.3) described the anisotropy decay. These parameters reported the known thermotropic phase transition in porcine stratum corneum, and the influence of the penetration enhancer oleic acid in human epidermis. Thus, we have shown frequency- domain fluorescence spectroscopy to be a facile and powerful tool for monitoring the permeability of a solid tissue such as the SC.
An analog filter approach to frequency domain fluorescence spectroscopy
Trainham, Clifford P.; O'Neill, Mary D.; McKenna, Ian J.
2015-10-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modeled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as Spicea can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modeling of the entiremore » system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. Furthermore, the techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response.« less
A Frequency-Domain Substructure System Identification Algorithm
NASA Technical Reports Server (NTRS)
Blades, Eric L.; Craig, Roy R., Jr.
1996-01-01
A new frequency-domain system identification algorithm is presented for system identification of substructures, such as payloads to be flown aboard the Space Shuttle. In the vibration test, all interface degrees of freedom where the substructure is connected to the carrier structure are either subjected to active excitation or are supported by a test stand with the reaction forces measured. The measured frequency-response data is used to obtain a linear, viscous-damped model with all interface-degree of freedom entries included. This model can then be used to validate analytical substructure models. This procedure makes it possible to obtain not only the fixed-interface modal data associated with a Craig-Bampton substructure model, but also the data associated with constraint modes. With this proposed algorithm, multiple-boundary-condition tests are not required, and test-stand dynamics is accounted for without requiring a separate modal test or finite element modeling of the test stand. Numerical simulations are used in examining the algorithm's ability to estimate valid reduced-order structural models. The algorithm's performance when frequency-response data covering narrow and broad frequency bandwidths is used as input is explored. Its performance when noise is added to the frequency-response data and the use of different least squares solution techniques are also examined. The identified reduced-order models are also compared for accuracy with other test-analysis models and a formulation for a Craig-Bampton test-analysis model is also presented.
Damping identification in frequency domain using integral method
NASA Astrophysics Data System (ADS)
Guo, Zhiwei; Sheng, Meiping; Ma, Jiangang; Zhang, Wulin
2015-03-01
A new method for damping identification of linear system in frequency domain is presented, by using frequency response function (FRF) with integral method. The FRF curve is firstly transformed to other type of frequency-related curve by changing the representations of horizontal and vertical axes. For the newly constructed frequency-related curve, integral is conducted and the area forming from the new curve is used to determine the damping. Three different methods based on integral are proposed in this paper, which are called FDI-1, FDI-2 and FDI-3 method, respectively. For a single degree of freedom (Sdof) system, the formulated relation of each method between integrated area and loss factor is derived theoretically. The numeral simulation and experiment results show that, the proposed integral methods have high precision, strong noise resistance and are very stable in repeated measurements. Among the three integral methods, FDI-3 method is the most recommended because of its higher accuracy and simpler algorithm. The new methods are limited to linear system in which modes are well separated, and for closely spaced mode system, mode decomposition process should be conducted firstly.
Patellofemoral pain syndrome: electromyography in a frequency domain analysis
NASA Astrophysics Data System (ADS)
Catelli, D. S.; Kuriki, H. U.; Polito, L. F.; Azevedo, F. M.; Negrão Filho, R. F.; Alves, N.
2011-09-01
The Patellofemoral Pain Syndrome (PFPS), has a multifactorial etiology and affects approximately 7 to 15% of the population, mostly women, youth, adults and active persons. PFPS causes anterior or retropatelar pain that is exacerbated during functional motor gestures, such as up and down stairs or spending long periods of time sitting, squatting or kneeling. As the diagnostic evaluation of this syndrome is still indirect, different mechanisms and methodologies try to make a classification that distinguishes patients with PFPS in relation to asymptomatic. Thereby, the purpose of this investigation was to determine the characteristics of the electromyographic (EMG) signal in the frequency domain of the vastus medialis oblique (VMO) and vastus lateralis (VL) in patients with PFPS, during the ascent of stairs. 33 young women (22 control group and 11 PFPS group), were evaluated by EMG during ascent of stairs. The VMO mean power frequency (MPF) and the VL frequency 95% (F95) were lower in symptomatic individuals. This may be related to the difference in muscle recruitment strategy exerted by each muscle in the PFPS group compared to the control group.
Development of a frequency-domain electromagnetic scattering measurement system
NASA Astrophysics Data System (ADS)
Oh, Kenneth K.
1993-12-01
This thesis describes the development of a system for measuring frequency-domain scattered fields in the Transient Electromagnetic Scattering Range at the Naval Postgraduate School. The new system employs a stepped-frequency CW waveform and utilizes an HP-8510B network analyzer as an RF front-end and a coherent receiver. A pair of AEL H1498 antennas was installed to cover a frequency range of 2 GHz to 18 GHz. An HP-82300C BASIC Language Processor was installed on a COMPAQ Deskpro-386 PC, and an HP-BASIC program was developed for remote control of the HP-8510B with data acquisition over the HPIB bus. A post-processing algorithm was created using MatLab for background subtraction, calibration, and deconvolution. A set of RCS measurements was made using various size spheres, and the postprocessing outputs were compared to computed values. Good agreement between these measurements and computed data indicates excellent accuracy of the measurement system and valid operations of the postprocessing algorithm.
A frequency-domain transient stability criterion for normal contingencies
Marceau, R.J.; Rizzi, J.C.; Mailhot, R.
1995-08-01
In a previous paper, a simple frequency-domain stability criterion was proposed for networks near the stability limit subjected to a 3-phase fault with no loss of line. The criterion can be summarized as follows: if a system is stable, the phase angle of the Fourier transform of a network`s transient voltage response exhibits a clockwise polar plot behavior at all buses (i.e. for increasing frequency); if the system is unstable, it exhibits a counterclockwise behavior in at least one location. Though these results are of interest, the criterion would be of greater practical use in mechanizing dynamic security analysis if it could be extended to the types of contingencies actually used in security analysis, namely normal contingencies. Normal contingencies are commonly defined as the loss of any element in a power system, either spontaneously or preceded by a fault, and such changes in topology impact post-contingency steady-state voltages in addition to their transient behavior. The present paper shows how such cases can be treated, thereby extending the applicable range of the criterion to normal contingencies.
An Analog Filter Approach to Frequency Domain Fluorescence Spectroscopy.
Trainham, R; O'Neill, M; McKenna, I J
2015-11-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modelled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as SPICE can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modelling of the entire system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. The techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response. The simplification of the analysis mathematics, and the ability to model the entire detection chain, make it possible to develop more compact instruments for remote sensing applications. PMID:26429345
An analog filter approach to frequency domain fluorescence spectroscopy
Trainham, Clifford P.; O'Neill, Mary D.; McKenna, Ian J.
2015-10-01
The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modeled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as Spicea can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modeling of the entire system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. Furthermore, the techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response.
A simple method for converting frequency domain aerodynamics to the time domain
NASA Technical Reports Server (NTRS)
Dowell, E. H.
1980-01-01
A simple, direct procedure was developed for converting frequency domain aerodynamics into indicial aerodynamics. The data required for aerodynamic forces in the frequency domain may be obtained from any available (linear) theory. The method retains flexibility for the analyst and is based upon the particular character of the frequency domain results. An evaluation of the method was made for incompressible, subsonic, and transonic two dimensional flows.
Microwave signal processing in two-frequency domain for ROF systems implementation: training course
NASA Astrophysics Data System (ADS)
Morozov, Oleg G.; Morozov, Gennady A.
2014-04-01
This article is presented materials from two tutorials: "Optical two-frequency domain reflectometry1, 2" and "Microwave technologies in industry, living systems and telecommunications3". These materials were prepared for master training courses and listed in the "SPIE Optical Education Directory" for 2013/2014. The main its theme is microwave photonics. Microwave photonics has been defined as the study of photonic devices operating at microwave frequencies and their application to microwave and optical systems. Its initial rationale was to use the advantages of photonic technologies to provide functions in microwave systems that are very complex or even impossible to carry out directly in the radiofrequency domain. But microwave photonics is also succeeding in incorporating a variety of techniques used in microwave engineering to improve the performance of photonic communication networks and systems. Three parts of this chapter are devoted to applications and construction principles of systems forming microwave photonic filters, measuring instantaneous frequency of microwave heterodyne signals and characterizing stimulated Mandelstam- Brillouin scattering spectrum in ROF systems. The main emphasis is on the use of the two-frequency symmetric radiation, generated by the Il'in-Morozov's method4, in given systems. It is forming radiation for the synthesis of optical filters coefficients, it's application and processing determine the increase in the signal-to-noise ratio during heterodyne frequencies monitoring and characterization of nonlinear effects spectrum.
Comparison of geometrical and diffraction imaging in the space and frequency domains.
Mahajan, Virendra N; Díaz, José A
2016-04-20
The geometrical and diffraction point-spread functions of an optical imaging system have been reviewed and compared in the past [Proc. SPIE3729, 434 (1999)PSISDG0277-786X10.1117/12.346821]. In this paper, we review and compare corresponding optical transfer functions. While the truth lies with the diffraction optical-transfer functions (OTF), it is considered easier and quicker to calculate the geometrical OTF, especially for large aberrations. We describe the theory of the two OTFs and explore the range of spatial frequencies and the magnitude of the primary aberrations over which the geometrical OTF may provide a reasonable approximation of the diffraction OTF. Moreover, balancing of spherical aberration with defocus for optimum diffraction OTF is studied as a function of both the aberration value as well as the spatial frequency. How to gauge the progress of an optical design in the frequency domain based on the geometrical OTF is outlined as the ray spot size is used in the space domain. PMID:27140094
Frequency Domain Magnetic Measurements from Kilohertz to Gigahertz
NASA Astrophysics Data System (ADS)
Gregg, John F.
"......we applied much prolonged labor on investigating the magnetical forces; so wonderful indeed are they, compared with the forces in all other minerals, surpassing even the virtues of all bodies around us. Nor have we found this labor idle or unfruitful; since daily in our experimenting new unexpected properties came to light."William Gilbert, De Magnete, 1600Abstract. This review deals with practical aspects of making frequency-domain measurements of magnetic susceptibility and magnetic losses from 200 kHz up to 10 GHz. It sets out the types of measurement concerned, distinguishing resonant from nonresonant phenomena. The techniques available are categorized according to suitability for the different frequency regimes and types of investigation. Practical recipes are provided for undertaking such experiments across the entire frequency range. Marginal oscillator spectrometry is discussed which is applicable across the whole frequency range. Different instruments are presented, and particular emphasis is placed on designs which function on the Robinson principle. Analysis of oscillation condition and signal-to-noise performance is dealt with, also sample considerations such as filling factor. Practical circuits are presented and their merits and demerits evaluated. Layout and radio-frequency design considerations are dealt with. Ultrahigh/microwave frequency marginal oscillator spectrometry is given special treatment and several practical designs are given. The essentials of good microwave design are emphasized. A general discussion of resonant structures is included which treats multiple layer coil design, slow wave line structures, stripline and cavities. Unusual cavity designs such as the rhumbatron are treated. Use of striplines with microwave marginal spectrometry is described and compared with conventional network-analysis techniques. The use of parameter matrices for high-frequency analysis is alluded to. Some details of good construction practice are
A Simple Physical Optics Algorithm Perfect for Parallel Computing Architecture
NASA Technical Reports Server (NTRS)
Imbriale, W. A.; Cwik, T.
1994-01-01
A reflector antenna computer program based upon a simple discreet approximation of the radiation integral has proven to be extremely easy to adapt to the parallel computing architecture of the modest number of large-gain computing elements such as are used in the Intel iPSC and Touchstone Delta parallel machines.
Frequency domain fluorescence lifetime microwell-plate platform for respirometry measurements
NASA Astrophysics Data System (ADS)
Chatni, M. R.; Yale, G.; Van Ryckeghem, A.; Porterfield, D. M.
2010-04-01
Traditionally micro-well plate based platforms used in biology utilize fluorescence intensity based methods to measure processes of biological relevance. However, fluorescence intensity measurements suffer from calibration drift due to a variety of factors. Photobleaching and self-quenching of the fluorescent dyes cause the intensity signal to drop over the lifetime of sensor immobilized inside the well. Variation in turbidity of the sample during the course of the measurement affects the measured fluorescence intensity. In comparison, fluorescence lifetime measurements are not significantly affected by these factors because fluorescence lifetime is a physico-chemical property of the fluorescent dye. Reliable and inexpensive frequency domain fluorescence lifetime instrumentation platforms are possible because the greater tolerance for optical alignment, and because they can be performed using inexpensive light sources such as LEDs. In this paper we report the development of a frequency domain fluorescence lifetime well-plate platform utilizing an oxygen sensitive transition-metal ligand complex fluorophore with a lifetime in the microsecond range. The fluorescence lifetime dye is incorporated in a polymer matrix and immobilized on the base of micro-well of a 60 well micro-well plate. Respiration measurements are performed in both aqueous and non-aqueous environment. Respirometry measurements were recorded from single Daphnia magna egg in hard water. Daphnia is an aquatic organism, important in environmental toxicology as a standard bioassay and early warning indicator for water quality monitoring. Also respirometry measurements were recorded from Tribolium castaneum eggs, which are common pests in the processed flour industry. These eggs were subjected to mitochondrial electron transport chain inhibitor such as potassium cyanide (KCN) and its effects on egg respiration were measured in real-time.
Spatial Frequency Domain Imaging: Applications in Preclinical Models of Alzheimer's Disease
NASA Astrophysics Data System (ADS)
Lin, Alexander Justin
A clinical challenge in Alzheimer's disease (AD) is diagnosing and treating patients earlier, before symptoms of cognitive dysfunction occur. A good screening test would be sensitive to the AD brain pathology, safe, and cost-effective. Diffuse optical imaging, which measures how non-ionizing light is absorbed and scattered in tissue, may fulfill these three parameters. We imaged the brains of transgenic AD mouse models in vivo with a quantitative, camera-based, diffuse optical imaging technology called spatial frequency domain imaging (SFDI) to characterize near-infrared (650-970nm) optical biomarkers of AD. Compared to age-matched control mice, we found a decrease in light absorption --- due to lower oxygenated and total hemoglobin concentrations in the brain --- correlating to decreased blood vessel volume and density in histology. Light scattering also increased in AD mice, correlating to brain structural changes caused by neuron loss and activation of inflammatory cells. Furthermore, inhaled gas challenges revealed brain vascular function was diminished. To investigate how AD affects the small changes in blood perfusion caused by increased brain activity, we built a new SFDI system from a commercial light-emitting diode microprojector and off-the-shelf optical components and cameras to measure optical properties in the visible range (460-632nm). Our measurements showed a reduced amplitude and duration of blood vessel dilation to increased brain activity in the AD mice. Altogether, this work increased our understanding of AD pathogenesis, explored optical biomarkers of AD, and improved technology access to other research labs. These results and technologies can further be used to facilitate longitudinal drug therapy trials in mice and provide a roadmap to diffuse optical spectroscopy studies in humans.
Chahl, J S
2014-01-20
This paper describes an application for arrays of narrow-field-of-view sensors with parallel optical axes. These devices exhibit some complementary characteristics with respect to conventional perspective projection or angular projection imaging devices. Conventional imaging devices measure rotational egomotion directly by measuring the angular velocity of the projected image. Translational egomotion cannot be measured directly by these devices because the induced image motion depends on the unknown range of the viewed object. On the other hand, a known translational motion generates image velocities which can be used to recover the ranges of objects and hence the three-dimensional (3D) structure of the environment. A new method is presented for computing egomotion and range using the properties of linear arrays of independent narrow-field-of-view optical sensors. An approximate parallel projection can be used to measure translational egomotion in terms of the velocity of the image. On the other hand, a known rotational motion of the paraxial sensor array generates image velocities, which can be used to recover the 3D structure of the environment. Results of tests of an experimental array confirm these properties.
Analysis of frequency domain frame detection and synchronization in OQAM-OFDM systems
NASA Astrophysics Data System (ADS)
Thein, Christoph; Schellmann, Malte; Peissig, Jürgen
2014-12-01
For future communication systems, filter bank multicarrier schemes offer the flexibility to increase spectrum utilization in heterogeneous wireless environments by good separation of signals in the frequency domain. To fully exploit this property for frame detection and synchronization, the advantage of the filter bank should be taken at the receiver side. In this work, the concept of frequency domain processing for frame detection and synchronization is analyzed and a suitable preamble design as well as corresponding estimation algorithms is discussed. The theoretical performance of the detection and estimation schemes is derived and compared with simulation-based assessments. The results show that, even though the frequency domain algorithms are sensitive to carrier frequency offsets, satisfactory frame detection and synchronization can be achieved in the frequency domain. In comparison to time domain synchronization methods, the computational complexity increases; however, enhanced robustness in shared spectrum access scenarios is gained in case the described frequency domain approach is utilized.
Visual saliency: a biologically plausible contourlet-like frequency domain approach
Bian, Peng
2010-01-01
In this paper we propose a fast frequency domain saliency detection method that is also biologically plausible, referred to as frequency domain divisive normalization (FDN). We show that the initial feature extraction stage, common to all spatial domain approaches, can be simplified to a Fourier transform with a contourlet-like grouping of coefficients, and saliency detection can be achieved in frequency domain. Specifically, we show that divisive normalization, a model of cortical surround inhibition, can be conducted in frequency domain. Since Fourier coefficients are global in space, we extend to this model by conducting piecewise FDN (PFDN) using overlapping local patches to provide better biological plausibility. Not only do FDN and PFDN outperform current state-of-the-art methods in eye fixation prediction, they are also faster. Speed and simplicity are advantages of our frequency domain approach, and its biological plausibility is the main contribution of our paper. PMID:21886671
Parallelized unscented Kalman filters for carrier recovery in coherent optical communication.
Jignesh, Jokhakar; Corcoran, Bill; Lowery, Arthur
2016-07-15
We show that unscented Kalman filters can be used to mitigate local oscillator phase noise and to compensate carrier frequency offset in coherent single-carrier optical communication systems. A parallel processing architecture implementing the unscented Kalman filter is proposed, improving upon a previous parallelized linear Kalman filter (LKF) implementation. PMID:27420508
Parallelized unscented Kalman filters for carrier recovery in coherent optical communication.
Jignesh, Jokhakar; Corcoran, Bill; Lowery, Arthur
2016-07-15
We show that unscented Kalman filters can be used to mitigate local oscillator phase noise and to compensate carrier frequency offset in coherent single-carrier optical communication systems. A parallel processing architecture implementing the unscented Kalman filter is proposed, improving upon a previous parallelized linear Kalman filter (LKF) implementation.
NASA Astrophysics Data System (ADS)
Sauvé, Alexandre; Montier, Ludovic
2016-10-01
uc(Context): Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for ν < 1 Hz, and secondly the Analog To digital Converter (ADC) component had been insufficiently characterized on-ground. These two problems require an exquisite knowledge of detector response. However bolometers have highly nonlinear characteristics, coming from their electrical and thermal coupling making them very difficult to model. uc(Goal): We present a method to build the analytical transfer function in frequency domain which describe the voltage response of an Alternative Current (AC) biased bolometer to optical excitation, based on the standard bolometer model. This model is built using the setup of the Planck/HFI instrument and offers the major improvement of being based on a physical model rather than the currently in use had-hoc model based on Direct Current (DC) bolometer theory. uc(Method): The analytical transfer function expression will be presented in matrix form. For this purpose, we build linearized versions of the bolometer electro thermal equilibrium. A custom description of signals in frequency is used to solve the problem with linear algebra. The model performances is validated using time domain simulations. uc(Results): The provided expression is suitable for calibration and data processing. It can also be used to provide constraints for fitting optical transfer function using real data from steady state electronic response and optical response. The accurate description of electronic response can also be used to improve the ADC nonlinearity correction for quickly varying optical signals.
Miyazaki, J; Kawasumi, K; Kobayashi, T
2014-09-01
We present a scheme for time-resolved pump-probe microscopy using intensity modulated laser diodes. The modulation frequencies of the pump and probe beams are varied up to 500 MHz with fixed frequency detuning typically set at 15 kHz. The frequency response of the pump-probe signal is detected using a lock-in amplifier referenced at the beat frequency. This frequency domain method is capable of characterizing the nanosecond to picosecond relaxation dynamics of sample species without the use of a high speed detector or a high frequency lock-in amplifier. Furthermore, as the pump-probe signal is based on the nonlinear interaction between the two laser beams and the sample, our scheme provides better spatial resolution than the conventional diffraction-limited optical microscopes. Time-resolved pump-probe imaging of fluorescence beads and aggregates of quantum dots demonstrates that this method is useful for the microscopic analysis of optoelectronic devices. The system is implemented using compact and low-cost laser diodes, and thus has a broad range of applications in the fields of photochemistry, optical physics, and biological imaging.
Spatial frequency domain imaging of burn wounds in a preclinical model of graded burn severity
Nguyen, John Quan; Crouzet, Christian; Mai, Tuan; Riola, Kathleen; Uchitel, Daniel; Liaw, Lih-Huei; Bernal, Nicole; Ponticorvo, Adrien; Choi, Bernard
2013-01-01
Abstract. Frequent monitoring of early-stage burns is necessary for deciding optimal treatment and management. Both superficial and full thickness burns are relatively easy to diagnose based on clinical observation. In between these two extremes are superficial-partial thickness and deep-partial thickness burns. These burns, while visually similar, differ dramatically in terms of clinical treatment and are known to progress in severity over time. The objective of this study was to determine the potential of spatial frequency domain imaging (SFDI) for noninvasively mapping quantitative changes in chromophore and optical properties that may be an indicative of burn wound severity. A controlled protocol of graded burn severity was developed and applied to 17 rats. SFDI data was acquired at multiple near-infrared wavelengths over a course of 3 h. Burn severity was verified using hematoxylin and eosin histology. From this study, we found that changes in water concentration (edema), deoxygenated hemoglobin concentration, and optical scattering (tissue denaturation) to be statistically significant at differentiating superficial partial-thickness burns from deep-partial thickness burns. PMID:23764696
Spatial frequency domain imaging of burn wounds in a preclinical model of graded burn severity
NASA Astrophysics Data System (ADS)
Nguyen, John Quan; Crouzet, Christian; Mai, Tuan; Riola, Kathleen; Uchitel, Daniel; Liaw, Lih-Huei; Bernal, Nicole; Ponticorvo, Adrien; Choi, Bernard; Durkin, Anthony J.
2013-06-01
Frequent monitoring of early-stage burns is necessary for deciding optimal treatment and management. Both superficial and full thickness burns are relatively easy to diagnose based on clinical observation. In between these two extremes are superficial-partial thickness and deep-partial thickness burns. These burns, while visually similar, differ dramatically in terms of clinical treatment and are known to progress in severity over time. The objective of this study was to determine the potential of spatial frequency domain imaging (SFDI) for noninvasively mapping quantitative changes in chromophore and optical properties that may be an indicative of burn wound severity. A controlled protocol of graded burn severity was developed and applied to 17 rats. SFDI data was acquired at multiple near-infrared wavelengths over a course of 3 h. Burn severity was verified using hematoxylin and eosin histology. From this study, we found that changes in water concentration (edema), deoxygenated hemoglobin concentration, and optical scattering (tissue denaturation) to be statistically significant at differentiating superficial partial-thickness burns from deep-partial thickness burns.
Resource parallel provisioning scheme for collaborating service in optical grid network
NASA Astrophysics Data System (ADS)
Wu, Runze; Ji, Yuefeng
2008-11-01
Divisible loads can be divided into any number independent sub-tasks, and map them on different platform to be processed in parallel jobs. Divisible load theory is introduced into parallel and distributed computing system to obtain available resources distributing on different locations for reaching processing efficiency, which can be extended to distributing multimedia and application system based grid. Light path scheduling algorithm based on DLT is proposed to realize optical resource scheduling on demand in optical grid under the requirement of intensive data applications, especially facing to parallel and distributed system. The proposed algorithm introduces the Divisible Load Theory as load distributing method and is extended for the distributed algorithm of divisible load scheduling to match multichannel application requirement of optical grid network. The proposed method deploys multiple wavelengths for original node, and builds parallel lightpaths to transmit independent divisible loads to collaborating nodes for a big task.
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.
Laser noise measurement techniques and applications of femtosecond encoding in the frequency domain
NASA Astrophysics Data System (ADS)
Scott, Ryan Patrick
This dissertation investigates mode-locked laser noise measurement techniques, the concept and measurement of a laser's noise transfer function, and then two applications of spectral encoding of optical pulses. The one application is optical code division multiple access (O-CDMA) and the other is optical arbitrary waveform generation (OAWG). The relationship between source stability, encoding, and overall system performance in O-CDMA is also discussed. Techniques for making sensitive and high-dynamic-range measurements of laser amplitude and envelope phase noise (timing jitter) in the frequency domain at the shot-noise limit are described. The short term stability of a Kerr-lens modelocked (KLM) Ti:sapphire laser is shown to be close to that of the precision crystal oscillators used in its characterization. The amplitude and envelope phase noise of a KLM Ti:sapphire laser are shown to depend directly on the pump laser amplitude stability. The sensitivity of this process is described by a noise transfer function (NTF) which represents the magnitude of the amplitude-to-amplitude modulation and amplitude-to-phase modulation conversion gain of the pump-induced amplitude and phase noise, respectively. A spectral phase-encoded time-spreading (SPECTS) O-CDMA testbed is described. The testbed employs a fiber-pigtailed, bulk-optics arrangement that utilizes a two-dimensional spatial light phase modulator for encoding multiple channels. The time-gated SPECTS O-CDMA receiver is composed of a nonlinear optical loop mirror (NOLM) and a nonlinear thresholder Experimentally measured performance is compared to numerical simulations. Finally, an optical frequency comb with 20-GHz spacing is shaped by an integrated silica arrayed-waveguide grating (AWG) pair to produce optical waveforms with high fidelity. Characterization of both the intensity and phase of the crafted opitical fields is accomplished with cross-correlation frequency-resolved optical gating (XFROG) which has been
Evaluation of emerging parallel optical link technology for high energy physics
Chramowicz, J.; Kwan, S.; Prosser, A.; Winchell, M.; /Fermilab
2012-01-01
Modern particle detectors utilize optical fiber links to deliver event data to upstream trigger and data processing systems. Future detector systems can benefit from the development of dense arrangements of high speed optical links emerging from industry advancements in transceiver technology. Supporting data transfers of up to 120 Gbps in each direction, optical engines permit assembly of the optical transceivers in close proximity to ASICs and FPGAs. Test results of some of these parallel components will be presented including the development of pluggable FPGA Mezzanine Cards equipped with optical engines to provide to collaborators on the Versatile Link Common Project for the HI-LHC at CERN.
Parallel optical information, concept, and response evolver: POINCARE
NASA Astrophysics Data System (ADS)
Caulfield, H. John; Caulfield, Kimberly
1991-08-01
It is now possible to build a nonlinear adaptive system which will incorporate many of the properties of the human mind, such as true originality in such skills as reasoning by analogy and reasoning by retrodiction, including literally unpredictable thoughts; and development of individual styles, personalities, expertise, etc. Like humans, these optical processors will have a rich `subconscious'' experience. Like humans, they will be clonable, but clones will develop differently as they experience the world differently, make different decisions, develop different habits, etc. In short, powerful optical processors with some of the properties normally associated with human intelligence can be made. This approach can result in a powerful optical processor with those properties. A demonstration chosen for simplicity of implementation is suggested. This could be the first computer of any type which uses quantum indeterminacy in an integral and important way.
Singh-Moon, Rajinder P; Roblyer, Darren M; Bigio, Irving J; Joshi, Shailendra
2014-09-01
We present an application of spatial frequency-domain imaging (SFDI) to the wide-field imaging of drug delivery to brain tissue. Measurements were compared with values obtained by a previously validated variation of diffuse reflectance spectroscopy, the method of optical pharmacokinetics (OP). We demonstrate a crosscorrelation between the two methods for absorption extraction and drug concentration determination in both experimental tissue phantoms and freshly extracted rodent brain tissue. These methods were first used to assess intra-arterial (IA) delivery of cationic liposomes to brain tissue in Sprague Dawley rats under transient cerebral hypoperfusion. Results were found to be in agreement with previously published experimental data and pharmacokinetic models of IA drug delivery. We then applied the same scheme to evaluate IA mitoxantrone delivery to glioma-bearing rats. Good correlation was seen between OP and SFDI determined concentrations taken from normal and tumor averaged sites. This study shows the feasibility of mapping drug/tracer distributions and encourages the use of SFDI for spatial imaging of tissues for drug/tracer-tagged carrier deposition and pharmacokinetic studies.
NASA Astrophysics Data System (ADS)
Singh-Moon, Rajinder P.; Roblyer, Darren M.; Bigio, Irving J.; Joshi, Shailendra
2014-09-01
We present an application of spatial frequency-domain imaging (SFDI) to the wide-field imaging of drug delivery to brain tissue. Measurements were compared with values obtained by a previously validated variation of diffuse reflectance spectroscopy, the method of optical pharmacokinetics (OP). We demonstrate a cross-correlation between the two methods for absorption extraction and drug concentration determination in both experimental tissue phantoms and freshly extracted rodent brain tissue. These methods were first used to assess intra-arterial (IA) delivery of cationic liposomes to brain tissue in Sprague Dawley rats under transient cerebral hypoperfusion. Results were found to be in agreement with previously published experimental data and pharmacokinetic models of IA drug delivery. We then applied the same scheme to evaluate IA mitoxantrone delivery to glioma-bearing rats. Good correlation was seen between OP and SFDI determined concentrations taken from normal and tumor averaged sites. This study shows the feasibility of mapping drug/tracer distributions and encourages the use of SFDI for spatial imaging of tissues for drug/tracer-tagged carrier deposition and pharmacokinetic studies.
Zhang, Yide; Khan, Aamir A; Vigil, Genevieve D; Howard, Scott S
2016-07-01
Multiphoton microscopy (MPM) combined with fluorescence lifetime imaging microscopy (FLIM) has enabled three-dimensional quantitative molecular microscopy in vivo. The signal-to-noise ratio (SNR), and thus the imaging rate of MPM-FLIM, which is fundamentally limited by the shot noise and fluorescence saturation, has not been quantitatively studied yet. In this paper, we investigate the SNR performance of the frequency-domain (FD) MPM-FLIM with two figures of merit: the photon economy in the limit of shot noise, and the normalized SNR in the limit of saturation. The theoretical results and Monte Carlo simulations find that two-photon FD-FLIM requires 50% fewer photons to achieve the same SNR as conventional one-photon FLIM. We also analytically show that the MPM-FD-FLIM can exploit the DC and higher harmonic components generated by nonlinear optical mixing of the excitation light to improve SNR, reducing the required number of photons by an additional 50%. Finally, the effect of fluorophore saturation on the experimental SNR performance is discussed. PMID:27409702
Probing the disassembly of ultrafast laser heated gold using frequency domain interferometry.
NASA Astrophysics Data System (ADS)
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.
Yang, Bin; Lesicko, John; Sharma, Manu; Hill, Michael; Sacks, Michael S; Tunnell, James W
2015-04-01
The measurement of soft tissue fiber orientation is fundamental to pathophysiology and biomechanical function in a multitude of biomedical applications. However, many existing techniques for quantifying fiber structure rely on transmitted light, limiting general applicability and often requiring tissue processing. Herein, we present a novel wide-field reflectance-based imaging modality, which combines polarized light imaging (PLI) and spatial frequency domain imaging (SFDI) to rapidly quantify preferred fiber orientation on soft collagenous tissues. PLI utilizes the polarization dependent scattering property of fibers to determine preferred fiber orientation; SFDI imaging at high spatial frequency is introduced to reject the highly diffuse photons and to control imaging depth. As a result, photons scattered from the superficial layer of a multi-layered sample are highlighted. Thus, fiber orientation quantification can be achieved for the superficial layer with optical sectioning. We demonstrated on aortic heart valve leaflet that, at spatial frequency of f = 1mm(-1) , the diffuse background can be effectively rejected and the imaging depth can be limited, thus improving quantification accuracy. PMID:25909033
Yang, Bin; Lesicko, John; Sharma, Manu; Hill, Michael; Sacks, Michael S.; Tunnell, James W.
2015-01-01
The measurement of soft tissue fiber orientation is fundamental to pathophysiology and biomechanical function in a multitude of biomedical applications. However, many existing techniques for quantifying fiber structure rely on transmitted light, limiting general applicability and often requiring tissue processing. Herein, we present a novel wide-field reflectance-based imaging modality, which combines polarized light imaging (PLI) and spatial frequency domain imaging (SFDI) to rapidly quantify preferred fiber orientation on soft collagenous tissues. PLI utilizes the polarization dependent scattering property of fibers to determine preferred fiber orientation; SFDI imaging at high spatial frequency is introduced to reject the highly diffuse photons and to control imaging depth. As a result, photons scattered from the superficial layer of a multi-layered sample are highlighted. Thus, fiber orientation quantification can be achieved for the superficial layer with optical sectioning. We demonstrated on aortic heart valve leaflet that, at spatial frequency of f = 1mm−1, the diffuse background can be effectively rejected and the imaging depth can be limited, thus improving quantification accuracy. PMID:25909033
A method for efficient fractional sample delay generation for real-time frequency-domain beamformers
Breeding, J.E.; Karnowski, T.P.
1995-07-01
This paper presents an efficient method for fractional delay filter generation for frequency-domain beamformers. A common misunderstanding regarding frequency-domain beamforming is that any fractional time shift can be achieved using the delay property of the discrete Fourier transform (DFT). Blind application of the DFT delay property introduces circular convolution errors that may adversely affect the beam`s time series. The method presented avoids these errors while enabling real-time processing.
NASA Technical Reports Server (NTRS)
Book, W. J.; Majett, M.
1982-01-01
The potential benefits of the ability to control more flexible mechanical arms are discussed. A justification is made in terms of speed of movement. A new controller design procedure is then developed to provide this capability. It uses both a frequency domain representation and a state variable representation of the arm model. The frequency domain model is used to update the modal state variable model to insure decoupled states. The technique is applied to a simple example with encouraging results.
Applications of Emerging Parallel Optical Link Technology to High Energy Physics Experiments
Chramowicz, J.; Kwan, S.; Prosser, A.; Winchell, M.; /Fermilab
2011-09-01
Modern particle detectors depend upon optical fiber links to deliver event data to upstream trigger and data processing systems. Future detector systems can benefit from the development of dense arrangements of high speed optical links emerging from the telecommunications and storage area network market segments. These links support data transfers in each direction at rates up to 120 Gbps in packages that minimize or even eliminate edge connector requirements. Emerging products include a class of devices known as optical engines which permit assembly of the optical transceivers in close proximity to the electrical interfaces of ASICs and FPGAs which handle the data in parallel electrical format. Such assemblies will reduce required printed circuit board area and minimize electromagnetic interference and susceptibility. We will present test results of some of these parallel components and report on the development of pluggable FPGA Mezzanine Cards equipped with optical engines to provide to collaborators on the Versatile Link Common Project for the HI-LHC at CERN.
NASA Astrophysics Data System (ADS)
Tatsuura, Satoshi; Wada, Osamu; Furuki, Makoto; Tian, Minquan; Sato, Yasuhiro; Iwasa, Izumi; Pu, Lyong Sun
2001-04-01
In this study, we introduce a new concept of all-optical two-dimensional serial-to-parallel pulse converters. Femtosecond optical pulses can be understood as thin plates of light traveling in space. When a femtosecond signal-pulse train and a single gate pulse were fed onto a material with a finite incident angle, each signal-pulse plate met the gate-pulse plate at different locations in the material due to the time-of-flight effect. Meeting points can be made two-dimensional by adding a partial time delay to the gate pulse. By placing a nonlinear optical material at an appropriate position, two-dimensional serial-to-parallel conversion of a signal-pulse train can be achieved with a single gate pulse. We demonstrated the detection of parallel outputs from a 1-Tb/s optical-pulse train through the use of a BaB2O4 crystal. We also succeeded in demonstrating 1-Tb/s serial-to-parallel operation through the use of a novel organic nonlinear optical material, squarylium-dye J-aggregate film, which exhibits ultrafast recovery of bleached absorption.
High-performance parallel interface to synchronous optical network gateway
St. John, Wallace B.; DuBois, David H.
1998-08-11
A digital system provides sending and receiving gateways for HIPPI interfaces. Electronic logic circuitry formats data signals and overhead signals in a data frame that is suitable for transmission over a connecting fiber optic link. Multiplexers route the data and overhead signals to a framer module. The framer module allocates the data and overhead signals to a plurality of 9-byte words that are arranged in a selected protocol. The formatted words are stored in a storage register for output through the gateway.
Neural mapping and parallel optical flow computation for autonomous navigation
Bulthoff, H.H.; Little, J.J.; Mallot, H.A.
1988-09-01
In this paper, the authors present information processing strategies, derived from neurobiology, which facilitate the evaluation of optical flow data considerably. In most previous approaches, the extraction of motion data from varying image intensities is complicated by the so-called aperture and correspondence problems. The correspondence problem arises if motion detection is based on image features that have to be identified in subsequent frames. If this problem is avoided by continuously registering image intensity changes not necessarily corresponding to features, the motion signal obtained becomes ambiguous due to the aperture problem. Recently a new algorithm for the computation of optical flow has been developed that produces dense motion data which are not subject to the aperture problem. Once the velocity vector field is established, optical flow analysis has to deal with the global space-variance of this field which carries much of the information. Local detectors for divergence (looming) and curl, that can be used in tasks such as obstacle avoidance, produce space-variant results even in the absence of obstacles. Also, motion detection itself could be restricted to just one direction per site for certain information processing tasks, were it not for the space-variance of that direction. For observer motion on a planar surface, these problems can be overcome by a retinotopic mapping, or transform, applied to image coordinates which inverts the perspective for points on this surface.
NASA Astrophysics Data System (ADS)
Li, Y.; Han, B.; Métivier, L.; Brossier, R.
2016-09-01
We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions.
Characterization of an intraluminal differential frequency-domain photoacoustics system
NASA Astrophysics Data System (ADS)
Lashkari, Bahman; Son, Jungik; Liang, Simon; Castelino, Robin; Foster, F. Stuart; Courtney, Brian; Mandelis, Andreas
2016-03-01
Cardiovascular related diseases are ranked as the second highest cause of death in Canada. Among the most important cardiovascular diseases is atherosclerosis. Current methods of diagnosis of atherosclerosis consist of angiography, intravascular ultrasound (IVUS) and optical coherence tomography (OCT). None of these methods possesses adequate sensitivity, as the ideal technique should be capable of both depth profiling, as well as functional imaging. An alternative technique is photoacoustics (PA) which can perform deep imaging and spectroscopy. The presented study explores the application of wavelength-modulated differential photoacoustic radar (WM-DPAR) for characterizing arterial vessels. The wavelength-modulated differential photoacoustic technique was shown to be able to substantially increase the dynamic range and sensitivity of hemoglobin oxygenation level detection. In this work the differential PA technique was used with a very high frequency modulation range. To perform spectroscopic PA imaging, at least two wavelengths are required. The selected wavelengths for this work are 1210 nm and 980 nm. 1210 nm corresponds to the maximum optical absorption coefficient of cholesterol and cholesteryl esters which are the main constituents of plaques. Since water, elastin and collagen also have high absorption coefficients at 1210 nm, this wavelength alone cannot provide very high sensitivity and specificity. The additional wavelength, 980 nm corresponds to high absorption coefficient of those constituents of healthy artery tissue. The simultaneous application of the abovementioned wavelengths can provide higher sensitivity and improved specificity in detecting lipids in the arterial vessels.
Optical coupling and splitting with two parallel waveguide tapers.
Tao, S H
2011-01-17
A coupling and splitting device comprising a width taper and a spatial-modulated subwavelength grating waveguide (SSGW) is proposed. The width taper is a waveguide with increasing width and the SSGW is a waveguide grating whose width and thickness are constant but the filling factor increases along the light propagation. Thus, the effective index of the subwavelength grating increases according to the effective medium theory. Light of orthogonal polarizations from a single-mode fiber can be coupled efficiently with the two parallel tapers. Furthermore, the coupled lights of orthogonal polarizations in the two tapers can be further split with connecting bent waveguides. Fabrication of the device is fully compatible with current complementary metal oxide semiconductor technology.
2D multi-parameter elastic seismic imaging by frequency-domain L1-norm full waveform inversion
NASA Astrophysics Data System (ADS)
Brossier, Romain; Operto, Stéphane; Virieux, Jean
2010-05-01
Full waveform inversion (FWI) is becoming a powerful and efficient tool to derive high-resolution quantitative models of the subsurface. In the frequency-domain, computationally efficient FWI algorithms can be designed for wide-aperture acquisition geometries by limiting inversion to few discrete frequencies. However, FWI remains an ill-posed and highly non-linear data-fitting procedure that is sensitive to noise, inaccuracies of the starting model and definition of multiparameter classes. The footprint of the noise in seismic imaging is conventionally mitigated by stacking highly redundant multifold data. However, when the data redundancy is decimated in the framework of efficient frequency-domain FWI, it is essential to assess the sensitivity of the inversion to noise. The impact of the noise in FWI, when applied to decimated data sets, has been marginally illustrated in the past and least-squares minimisation has remained the most popular approach. We investigate in this study the sensitivity of frequency-domain elastic FWI to noise for realistic onshore and offshore synthetic data sets contaminated by ambient random white noise. Four minimisation functionals are assessed in the framework of frequency domain FWI of decimated data: the classical least-square norm (L2), the least-absolute-values norm (L1), and some combinations of both (the Huber and the so-called Hybrid criteria). These functionals are implemented in a massively-parallel, 2D elastic frequency-domain FWI algorithm. A two-level hierarchical algorithm is implemented to mitigate the non-linearity of the inversion in complex environments. The first outer level consists of successive inversions of frequency groups of increasing high-frequency content. This level defines a multi-scale approach while preserving some data redundancy by means of simultaneous inversion of multiple frequencies. The second inner level used complex-valued frequencies for data preconditioning. This preconditioning controls the
Konishi, Tsuyoshi; Takahashi, Koji; Matsui, Hideki; Satoh, Takema; Itoh, Kazuyoshi
2011-08-15
We report the attempt of optical quantization and coding in 5-bit parallel format for photonic A/D conversion. The proposed system is designed to realize generation of 32 different optical codes in proportion to the corresponding signal levels when fed a certain range of amplitude-varied input pulses to the setup. Optical coding in a bit-parallel format made it possible, that provides 5 bit optical codes from 32 optical quantized pulses. The 5-bit parallel operation of an optical quantization and coding module with 5 multi-ports was tested in our experimental setup.
Quantitative frequency-domain fluorescence spectroscopy in tissues and tissue-like media
NASA Astrophysics Data System (ADS)
Cerussi, Albert Edward
1999-09-01
In the never-ending quest for improved medical technology at lower cost, modern near-infrared optical spectroscopy offers the possibility of inexpensive technology for quantitative and non-invasive diagnoses. Hemoglobin is the dominant chromophore in the 700-900 nm spectral region and as such it allows for the optical assessment of hemoglobin concentration and tissue oxygenation by absorption spectroscopy. However, there are many other important physiologically relevant compounds or physiological states that cannot be effectively sensed via optical methods because of poor optical contrast. In such cases, contrast enhancements are required. Fluorescence spectroscopy is an attractive component of optical tissue spectroscopy. Exogenous fluorophores, as well as some endogenous ones, may furnish the desperately needed sensitivity and specificity that is lacking in near-infrared optical tissue spectroscopy. The main focus of this thesis was to investigate the generation and propagation of fluorescence photons inside tissues and tissue-like media (i.e., scattering dominated media). The standard concepts of fluorescence spectroscopy have been incorporated into a diffusion-based picture that is sometimes referred to as photon migration. The novelty of this work lies in the successful quantitative recovery of fluorescence lifetimes, absolute fluorescence quantum yields, fluorophore concentrations, emission spectra, and both scattering and absorption coefficients at the emission wavelength from a tissue-like medium. All of these parameters are sensitive to the fluorophore local environment and hence are indicators of the tissue's physiological state. One application demonstrating the capabilities of frequency-domain lifetime spectroscopy in tissue-like media is a study of the binding of ethidium bromide to bovine leukocytes in fresh milk. Ethidium bromide is a fluorescent dye that is commonly used to label DNA, and hence visualize chromosomes in cells. The lifetime of
NASA Astrophysics Data System (ADS)
Yusuf, Yusril; Kusumasari, Ervanggis Minggar; Ula, Nur Mufidatul; Jahidah, Khannah; Triyana, Kuwat; Sosiati, Harini; Harsojo
2016-04-01
Optical properties of two nematic liquid crystals, i.e., 4-methoxybenzylidene-4-butylaniline (MBBA) and 4-cyano-4'-pentylbiphenyl (5 CB) which are parallel oriented by nanofibers has been successfully performed. Planar samples of liquid crystals were made using polyvinyl alcohol (PVA) nanofiber from electrospinning process. Electrospinning method was modified using copper (Cu) as gap collector. These planar samples area are 15 mm x 25 mm. Optical characteristic of these samples were studied by using optical polarizing microscope. The optical intensity changes by a rotationof crossed polarizers is observed. The sinusoidal intensity change was observedin these samples as such as in the planar sample prepared by the rubbing method.
Parallel lensless optical correlator based on two phase-only spatial light modulators.
Zeng, Xu; Inoue, Takashi; Fukuchi, Norihiro; Bai, Jian
2011-06-20
In this paper, we proposed a parallel phase-only lensless optical correlator based on two pieces of Liquid Crystal on Silicon Spatial Light Modulators. Phase Fresnel Lens Array and specialized grating are implemented to realize multi-channel and multiplexed LOC. Experimental results of Chinese characters' recognitions are given as demonstration of proposed technique. High uniformity of processing channels has been verified by autocorrelation process of four same Chinese characters. The technique is programmable and adjustment of optical path could be realized without changing of optical setup. The implementations could be performed on the same configuration as single channel optical correlator without mechanical alternation. PMID:21716500
MT-compatible red VCSEL module for parallel optical interconnections
NASA Astrophysics Data System (ADS)
Van Hove, An; Van de Putte, Koen; Naessens, Kris; Dhoedt, Bart; Baets, Roel G.; Van Daele, Peter
2000-04-01
In this paper we present the design, fabrication and characterization of a module which directly connectorizes a 1 by 8 red VCSEL array to a small diameter polymer optical fiber array, using a standard MT ferrule. The facets of the POF are prepared by a hot knife cutting, followed by a short polishing step. First coupling results show total losses in the range of 1.1 dB/channel for a 30 cm POF link. Optical crosstalk between adjacent channels is below -45 dB. Plastic micromachined parts surrounding the VCSEL chip ensure the correct alignment of the connector, using the connector, using the connector guiding points. The parts themselves are aligned to the chip with a n index-alignment technique, using an excimer laser ablated mastertool. In a deconnectorizable version of the module, a thin, flat glue layer on the chip acts as a window between the VCSEL chip and the MT terminated POF array. Integrated in a standard ceramic package, clear eye diagrams have been measured at 150 MHz for a 10m POF link, coupled to the VCSEL array. Further efforts on higher speed measurements using dedicated drivers, will also be presented.
Signal post processing in frequency domain OCT and OCM using a filter bank approach
NASA Astrophysics Data System (ADS)
Hofer, Bernd; Považay, Boris; Hermann, Boris; Unterhuber, Angelika; Matz, Gerald; Hlawatsch, Franz; Drexler, Wolfgang
2007-02-01
Current signal post processing in spectrally encoded frequency domain (FD) optical coherence microscopy (OCM) and optical coherence tomography (OCT) uses Fourier transforms in combination with non-uniform resampling strategies to map the k-space data acquired by the spectrometer to spatial domain signals which are necessary for tomogram generation. We propose to use a filter bank (FB) framework for the remapping process. With our new approach, the spectrometer is modeled as a critically sampled analysis FB, whose outputs are quantized subband signals that constitute the k-space spectroscopic data. The optimal procedure to map this data to the spatial domain is via a suitably designed synthesis FB which has low complexity. FB theory additionally states that 1) it is possible to find a synthesis FB such that the overall system has the perfect reconstruction (PR) property; 2) any processing on critically sampled subband signals (as done in current schemes) results in aliasing artifacts. These perspectives are evaluated both theoretically and experimentally. We determine the analysis FB corresponding to our FD-OCM system by using a tunable laser and show that for our grating-based spectrometer - employing a CCD-line camera - the non-uniform resampling together with FFT indeed causes aliasing terms and depth dependent signal attenuation. Furthermore, we compute a finite impulse response based synthesis FB and assess the desired PR property by means of layered samples. The resulting images exhibit higher resolution and improved SNR compared to the common FFT-based approach. The potential of the proposed FB approach opens a new perspective also for other spectroscopic applications.
Noninvasive absolute cerebral oximetry with frequency-domain near-infrared spectroscopy
NASA Astrophysics Data System (ADS)
Hallacoglu, Bertan
Near-infrared spectroscopy (NIRS) measurements of absolute concentrations of oxy-hemoglobin and deoxy-hemoglobin in the human brain can provide critical information about cerebral physiology in terms of cerebral blood volume, blood flow, oxygen delivery, and metabolic rate of oxygen. We developed several frequency domain NIRS data acquisition and analysis methods aimed at absolute measurements of hemoglobin concentration and saturation in cerebral tissue of adult human subjects. Extensive experimental investigations were carried out in various homogenous and two-layered tissue-mimicking phantoms, and biological tissues. The advantages and limitations of commonly used homogenous models and inversion strategies were thoroughly investigated. Prior to human subjects, extensive studies were carried out in in vivo animal models. In rabbits, absolute hemoglobin oxygen desaturation was shown to depend strongly on surgically induced testicular torsion. Methods developed in this study were then adapted for measurements in the rat brain. Absolute values were demonstrated to discern cerebrovascular impairment in a rat model of diet-induced vascular cognitive impairment. These results facilitated the development of clinically useful optical measures of cerebrovascular health. In a large group of human subjects, employing a homogeneous model for absolute measurements was shown to be reliable and robust. However, it was also shown to be limited due to the relatively thick extracerebral tissue. The procedure we develop in this work and the thesis thereof performs a nonlinear inversion procedure with six unknown parameters with no other prior knowledge for the retrieval of the optical coefficients and top layer thickness with high accuracy on two-layered media. Our absolute measurements of cerebral hemoglobin concentration and saturation are based on the discrimination of extracerebral and cerebral tissue layers, and they can enhance the impact of NIRS for cerebral hemodynamics and
Yafi, Amr; Vetter, Thomas S; Scholz, Thomas; Patel, Sarin; Saager, Rolf B; Cuccia, David J; Evans, Gregory R; Durkin, Anthony J
2010-01-01
Background The purpose of this study is to investigate the capabilities of a novel optical wide-field imaging technology known as Spatial Frequency Domain Imaging (SFDI) to quantitatively assess reconstructive tissue status. Methods Twenty two cutaneous pedicle flaps were created on eleven rats based on the inferior epigastric vessels. After baseline measurement, all flaps underwent vascular ischemia, induced by clamping the supporting vessels for two hours (either arterio-venous or selective venous occlusions) normal saline was injected to the control flap, and hypertonic hyperoncotic saline solution to the experimental flap. Flaps were monitored for two hours after reperfusion. The SFDI system was used for quantitative assessment of flap status over the duration of the experiment. Results All flaps demonstrated a significant decline in oxy-hemoglobin and tissue oxygen saturation in response to occlusion. Total hemoglobin and deoxy-hemoglobin were markedly increased in the selective venous occlusion group. After reperfusion and the solutions were administered, oxy-hemoglobin and tissue oxygen saturation in those flaps that survived gradually returned to the baseline levels. However, flaps for which oxy-hemoglobin and tissue oxygen saturation didn’t show any signs of recovery appeared to be compromised and eventually became necrotic within 24–48 hours in both occlusion groups. Conclusion SFDI technology provides a quantitative, objective method to assess tissue status. This study demonstrates the potential of this optical technology to assess tissue perfusion in a very precise and quantitative way, enabling wide-field visualization of physiological parameters. The results of this study suggest that SFDI may provide a means for prospectively identifying dysfunctional flaps well in advance of failure. PMID:21200206
NASA Astrophysics Data System (ADS)
Nadeau, K. P.; Khoury, P.; Mazhar, A.; Cuccia, D.; Durkin, A. J.
2013-03-01
Recently, digital photography has become an efficient and economic method to assist dermatologists in monitoring skin characteristics. Although this technology has advanced a great deal in resolution and costs, conventional digital cameras continue to only provide qualitative recording of color information. To address this issue, we are developing a compact, quantitative skin imaging camera by employing spatial frequency domain imaging (SFDI), a non-contact approach for determining tissue optical properties over a wide field-of-view. SFDI uses knowledge of optical properties at multiple wavelengths to recover concentrations of tissue constituents such as oxy/deoxy-hemoglobin, water, and melanin. This method has been well researched and presented in laboratory and research settings. The next step in the development of SFDI systems is to make typical systems compact and cheaper using commercial components. We present our findings by performing a component-by-component analysis of key SFDI system components including light sources, projectors, and cameras.
NASA Astrophysics Data System (ADS)
Nicolaides, Lena; Garcia, Jose A.; Mandelis, Andreas; Abrams, Stephen H.
2001-04-01
Frequency-domain IR photothermal radiometry is introduced as a dynamic dental diagnostic tool and its main features are compared with modulated laser luminescence for quantifying sound and carious enamel or dentin. Dental caries found in the fissures or grooves of teeth is very difficult to diagnose or quantify with the present clinical techniques. Visual examination and dental radiographs do not detect the presence of decay until there has been significant carious destruction of the tooth. A high-spatial-resolution dynamic experimental imaging set-up, which can provide simultaneous measurements of laser-induced frequency-domain IR photothermal radiometric and luminescence signals form defects in teeth, was developed. Following optical absorption of laser photons, the new set-up can monitor simultaneously and independently the non-radiative conversion, and the radiative de-excitation in turbid media such as hard dental tissue. This work is intended to show the complementarity between modulated luminescence and photothermal frequency scans in detecting carious lesions in teeth. A sound extracted molar with a dentin-enamel interface was introduced to examine the depth profilometric abilities of the method. Occlusal surfaces of teeth with potential areas of demineralization or carious destruction in the fissures were examined and compared to the signals produced by the sound enamel establishing the depth profilometric abilities of the method. The significance to clinical dentistry lies in the potential of this technique to detect and monitor early carious lesions in the pits and fissures of teeth.
NASA Astrophysics Data System (ADS)
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.
Frequency Domain Fluorescent Molecular Tomography and Molecular Probes for Small Animal Imaging
NASA Astrophysics Data System (ADS)
Kujala, Naresh Gandhi
Fluorescent molecular tomography (FMT) is a noninvasive biomedical optical imaging that enables 3-dimensional quantitative determination of fluorochromes distributed in biological tissues. There are three methods for imaging large volume tissues based on different light sources: (a) using a light source of constant intensity, through a continuous or constant wave, (b) using a light source that is intensity modulated with a radio frequency (RF), and (c) using ultrafast pulses in the femtosecond range. In this study, we have developed a frequency domain fluorescent molecular tomographic system based on the heterodyne technique, using a single source and detector pair that can be used for small animal imaging. In our system, the intensity of the laser source is modulated with a RF frequency to produce a diffuse photon density wave in the tissue. The phase of the diffuse photon density wave is measured by comparing the reference signal with the signal from the tissue using a phasemeter. The data acquisition was performed by using a Labview program. The results suggest that we can measure the phase change from the heterogeneous inside tissue. Combined with fiber optics and filter sets, the system can be used to sensitively image the targeted fluorescent molecular probes, allowing the detection of cancer at an early stage. We used the system to detect the tumor-targeting molecular probe Alexa Fluor 680 and Alexa Fluor 750 bombesin peptide conjugates in phantoms as well as mouse tissues. We also developed and evaluated fluorescent Bombesin (BBN) probes to target gastrin-releasing peptide (GRP) receptors for optical molecular imaging. GRP receptors are over-expressed in several types of human cancer cells, including breast, prostate, small cell lung, and pancreatic cancers. BBN is a 14 amino acid peptide that is an analogue to human gastrin-releasing peptide that binds specifically to GRPr receptors. BBN conjugates are significant in cancer detection and therapy. The
An optical leveling technique for parallel near-field photolithography system
NASA Astrophysics Data System (ADS)
Liu, Zhuming; Chen, Xinyong; Zhang, Yuan; Weaver, John; Roberts, Clive J.
2012-10-01
An optical leveling technique is reported for a compact parallel (multi-cantilever) scanning near-field photolithography (SNP) prototype. This instrument operates in liquid and was designed to overcome the challenge of low sample throughput of previous serial scanning SNPs. A combination of zone plate lens array, probe array, and standard atomic force microscope feedback technique are employed to deliver parallel probe operation in the current SNP. Compared to the commonly used two-end or multi-end "force feedback" alignment techniques, the optical levelling technique applied provides a simple solution to maintaining all levers in an array within the near-field region. As a proof-of-principle experiment, the operation of the prototype was demonstrated by producing nano-scale patterns in parallel using scanning near-field photolithography.
User`s guide for the frequency domain algorithms in the LIFE2 fatigue analysis code
Sutherland, H.J.; Linker, R.L.
1993-10-01
The LIFE2 computer code is a fatigue/fracture analysis code that is specialized to the analysis of wind turbine components. The numerical formulation of the code uses a series of cycle count matrices to describe the cyclic stress states imposed upon the turbine. However, many structural analysis techniques yield frequency-domain stress spectra and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the analysis of this class of data, a Fourier analysis is used to transform a frequency-domain spectrum to an equivalent time series suitable for rainflow counting by other modules in the code. This paper describes the algorithms incorporated into the code and their numerical implementation. Example problems are used to illustrate typical inputs and outputs.
Adaptive multidirectional frequency domain filter for noise removal in wrapped phase patterns.
Liu, Guixiong; Chen, Dongxue; Peng, Yanhua; Zeng, Qilin
2016-08-01
In order to avoid the detrimental effects of excessive noise in the phase fringe patterns of a laser digital interferometer over the accuracy of phase unwrapping and the successful detection of mechanical fatigue defects, an effective method of adaptive multidirectional frequency domain filtering is introduced based on the characteristics of the energy spectrum of localized wrapped phase patterns. Not only can this method automatically set the cutoff frequency, but it can also effectively filter out noise while preserving the image edge information. Compared with the sine and cosine transform filtering and the multidirectional frequency domain filtering, the experimental results demonstrate that the image filtered by our method has the fewest number of residues and is the closest to the noise-free image, compared to the two aforementioned methods, demonstrating the effectiveness of this adaptive multidirectional frequency domain filter. PMID:27505376
Demultiplexing based on frequency-domain joint decision MMA for MDM system
NASA Astrophysics Data System (ADS)
Caili, Gong; Li, Li; Guijun, Hu
2016-06-01
In this paper, we propose a demultiplexing method based on frequency-domain joint decision multi-modulus algorithm (FD-JDMMA) for mode division multiplexing (MDM) system. The performance of FD-JDMMA is compared with frequency-domain multi-modulus algorithm (FD-MMA) and frequency-domain least mean square (FD-LMS) algorithm. The simulation results show that FD-JDMMA outperforms FD-MMA in terms of BER and convergence speed in the cases of mQAM (m=4, 16 and 64) formats. And it is also demonstrated that FD-JDMMA achieves better BER performance and converges faster than FD-LMS in the cases of 16QAM and 64QAM. Furthermore, FD-JDMMA maintains similar computational complexity as the both equalization algorithms.
NASA Astrophysics Data System (ADS)
Shi, Sheng-bing; Chen, Zhen-xing; Qin, Shao-gang; Song, Chun-yan; Jiang, Yun-hong
2014-09-01
With the development of science and technology, photoelectric equipment comprises visible system, infrared system, laser system and so on, integration, information and complication are higher than past. Parallelism and jumpiness of optical axis are important performance of photoelectric equipment,directly affect aim, ranging, orientation and so on. Jumpiness of optical axis directly affect hit precision of accurate point damage weapon, but we lack the facility which is used for testing this performance. In this paper, test system which is used fo testing parallelism and jumpiness of optical axis is devised, accurate aim isn't necessary and data processing are digital in the course of testing parallelism, it can finish directly testing parallelism of multi-axes, aim axis and laser emission axis, parallelism of laser emission axis and laser receiving axis and first acuualizes jumpiness of optical axis of optical sighting device, it's a universal test system.
High-Precise and Robust Face-Recognition System Based on Optical Parallel Correlator
NASA Astrophysics Data System (ADS)
Kodate, Kashiko
2005-10-01
Facial recognition is applied in a wide range of security systems, and has been studied since the 1970s, with extensive research into and development of digital processing. However, there is only available a 1:1 verification system combined with ID card identification, or an ID-less system with a small number of images in the database. The number of images that can be stored is limited, and recognition has to be improved to account for photos taken at different angles. Commercially available facial recognition systems for the most part utilize digital computers performing electronic pattern recognition. In contrast, optical analog operations can process two-dimensional images instantaneously in parallel using a lens-based Fourier transform function. In the 1960s two methods were proposed, the Vanderlugt correlator and the joint transform correlator (JTC). We present a new scheme using a multi-channel parallel JTC to make better use of spatial parallelism, through the use of a diffraction-type multi-level zone-plate array to extend a single-channel JTC. Our project's objectives were: (i) to design a matched filter which equips the system with high recognition capability at a faster calculation speed by analyzing the spatial frequency of facial image elements, and (ii) to create a four-channel Vanderlugt correlator with super-high-speed (1000 frame/s) optical parallel facial recognition system, robust enough for 1:N identification, for a large database with 4000 images. Automation was also achieved for the entire process via a practical controlling system. The achieved super-high-speed facial recognition system based on optical parallelism is faster in its processing time than the JTC optical correlator.
Heath, Robert M. Tanner, Michael G.; Casaburi, Alessandro; Hadfield, Robert H.; Webster, Mark G.; San Emeterio Alvarez, Lara; Jiang, Weitao; Barber, Zoe H.; Warburton, Richard J.
2014-02-10
The device physics of parallel-wire superconducting nanowire single photon detectors is based on a cascade process. Using nano-optical techniques and a parallel wire device with spatially separate pixels, we explicitly demonstrate the single- and multi-photon triggering regimes. We develop a model for describing efficiency of a detector operating in the arm-trigger regime. We investigate the timing response of the detector when illuminating a single pixel and two pixels. We see a change in the active area of the detector between the two regimes and find the two-pixel trigger regime to have a faster timing response than the one-pixel regime.
Practical Realization of Massively Parallel Fiber -Free-Space Optical Interconnects
NASA Astrophysics Data System (ADS)
Gruber, Matthias; Jahns, Jürgen; El Joudi, El Mehdi; Sinzinger, Stefan
2001-06-01
We propose a novel approach to realizing massively parallel optical interconnects based on commercially available multifiber ribbons with MT-type connectors and custom-designed planar-integrated free-space components. It combines the advantages of fiber optics, that is, a long range and convenient and flexible installation, with those of (planar-integrated) free-space optics, that is, a wide range of implementable functions and a high potential for integration and parallelization. For the interface between fibers and free-space optical systems a low-cost practical solution is presented. It consists of using a metal connector plate that was manufactured on a computer-controlled milling machine. Channel densities are of the order of 100 /mm2 between optoelectronic VLSI chips and the free-space optical systems and 1 /mm2 between the free-space optical systems and MT-type fiber connectors. Experiments in combination with specially designed planar-integrated test systems prove that multiple one-to-one and one-to-many interconnects can be established with not more than 10% uniformity error.
NASA Technical Reports Server (NTRS)
Athale, R. A.; Lee, S. H.
1978-01-01
The paper describes the fabrication and operation of an optical parallel logic (OPAL) device which performs Boolean algebraic operations on binary images. Several logic operations on two input binary images were demonstrated using an 8 x 8 device with a CdS photoconductor and a twisted nematic liquid crystal. Two such OPAL devices can be interconnected to form a half-adder circuit which is one of the essential components of a CPU in a digital signal processor.
NASA Astrophysics Data System (ADS)
Li, Zhengyan; Zgadzaj, Rafal; Wang, Xiaoming; Reed, Stephen; Dong, Peng; Downer, Michael C.
2010-11-01
We demonstrate a prototype Frequency Domain Streak Camera (FDSC) that can capture the picosecond time evolution of the plasma accelerator structure in a single shot. In our prototype Frequency-Domain Streak Camera, a probe pulse propagates obliquely to a sub-picosecond pump pulse that creates an evolving nonlinear index "bubble" in fused silica glass, supplementing a conventional Frequency Domain Holographic (FDH) probe-reference pair that co-propagates with the "bubble". Frequency Domain Tomography (FDT) generalizes Frequency-Domain Streak Camera by probing the "bubble" from multiple angles and reconstructing its morphology and evolution using algorithms similar to those used in medical CAT scans. Multiplexing methods (Temporal Multiplexing and Angular Multiplexing) improve data storage and processing capability, demonstrating a compact Frequency Domain Tomography system with a single spectrometer.
Postural Analysis in Time and Frequency Domains in Patients with Ehlers-Danlos Syndrome
ERIC Educational Resources Information Center
Galli, Manuela; Rigoldi, Chiara; Celletti, Claudia; Mainardi, Luca; Tenore, Nunzio; Albertini, Giorgio; Camerota, Filippo
2011-01-01
The goal of this work is to analyze postural control in Ehlers-Danlos syndrome (EDS) participants in time and frequency domain. This study considered a pathological group composed by 22 EDS participants performing a postural test consisting in maintaining standing position over a force platform for 30 s in two conditions: open eyes (OE) and closed…
Collins, Kimberlee C; Maznev, Alexei A; Cuffe, John; Nelson, Keith A; Chen, Gang
2014-12-01
Laser-based time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance (FDTR) techniques are widely used for investigating thermal transport at micro- and nano-scales. We demonstrate that data obtained in TDTR measurements can be represented in a frequency-domain form equivalent to FDTR, i.e., in the form of a surface temperature amplitude and phase response to time-harmonic heating. Such a representation is made possible by using a large TDTR delay time window covering the entire pulse repetition interval. We demonstrate the extraction of frequency-domain data up to 1 GHz from TDTR measurements on a sapphire sample coated with a thin layer of aluminum, and show that the frequency dependencies of both the amplitude and phase responses agree well with theory. The proposed method not only allows a direct comparison of TDTR and FDTR data, but also enables measurements at high frequencies currently not accessible to FDTR. The frequency-domain representation helps uncover aspects of the measurement physics which remain obscured in a traditional TDTR measurement, such as the importance of modeling the details of the heat transport in the metal transducer film for analyzing high frequency responses.
NASA Astrophysics Data System (ADS)
Collins, Kimberlee C.; Maznev, Alexei A.; Cuffe, John; Nelson, Keith A.; Chen, Gang
2014-12-01
Laser-based time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance (FDTR) techniques are widely used for investigating thermal transport at micro- and nano-scales. We demonstrate that data obtained in TDTR measurements can be represented in a frequency-domain form equivalent to FDTR, i.e., in the form of a surface temperature amplitude and phase response to time-harmonic heating. Such a representation is made possible by using a large TDTR delay time window covering the entire pulse repetition interval. We demonstrate the extraction of frequency-domain data up to 1 GHz from TDTR measurements on a sapphire sample coated with a thin layer of aluminum, and show that the frequency dependencies of both the amplitude and phase responses agree well with theory. The proposed method not only allows a direct comparison of TDTR and FDTR data, but also enables measurements at high frequencies currently not accessible to FDTR. The frequency-domain representation helps uncover aspects of the measurement physics which remain obscured in a traditional TDTR measurement, such as the importance of modeling the details of the heat transport in the metal transducer film for analyzing high frequency responses.
Attenuation-corrected fluorescence extraction for image-guided surgery in spatial frequency domain
Yang, Bin; Sharma, Manu
2013-01-01
Abstract. A new approach to retrieve the attenuation-corrected fluorescence using spatial frequency-domain imaging is demonstrated. Both in vitro and ex vivo experiments showed the technique can compensate for the fluorescence attenuation from tissue absorption and scattering. This approach has potential in molecular image-guided surgery. PMID:23955392
Attenuation-corrected fluorescence extraction for image-guided surgery in spatial frequency domain.
Yang, Bin; Sharma, Manu; Tunnell, James W
2013-08-01
A new approach to retrieve the attenuation-corrected fluorescence using spatial frequency-domain imaging is demonstrated. Both in vitro and ex vivo experiments showed the technique can compensate for the fluorescence attenuation from tissue absorption and scattering. This approach has potential in molecular image-guided surgery. PMID:23955392
Applying an FSK Based Transmission Scheme to Broadband Channels Using Frequency Domain Equalization
NASA Astrophysics Data System (ADS)
Georgi, Sebastian, Dr.; Peissig, Dr. Jürgen, Prof.
2012-05-01
Equalization of broadband signals can be efficiently realized in frequency domain. One prominent example is the orthogonal frequency division multiplexing (OFDM) transmission technique. With the introduction of a cyclic prefix and a modulation onto orthogonal subcarriers the equalization can be performed in frequency domain with one tap only. However the extremely high peak to average power ratio of OFDM modulated transmit signals and the demand of linearity inside the signal transmission chain results in a poor energy efficiency at the power amplifier. This paper claims, that as long as a cyclic prefix exists, any receive signal can be equalized in frequency domain. In this paper a transmission scheme with constant envelope is chosen for energy efficiency reasons. Therefore an FSK modulation and gaussian pulse shaping is used to create the transmit signal. Equalization at the receiver is done in frequency domain as known in OFDM. To simplify the equalization, a cyclic prefix is added to the transmit signal as well. This transmission scheme is introduced and evaluated in terms of spectral efficiency and bit error rate (BER) performance in this paper. The comparison is done with a typical OFDM system. In particular the characteristics of a nonlinear power amplifier are considered. It will be shown, that signals with constant envelope such as FSK modulated signals can also make use of an OFDM like equalization procedure with comparable BER performance and spectral requirements.
Plastique: A synchrotron radiation beamline for time resolved fluorescence in the frequency domain
NASA Astrophysics Data System (ADS)
De Stasio, Gelsomina; Zema, N.; Antonangeli, F.; Savoia, A.; Parasassi, T.; Rosato, N.
1991-06-01
PLASTIQUE is the only synchrotron radiation beamline in the world that performs time resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and dynamics of molecules. We describe the beamline and some initial data.
Statistics and frequency-domain moveout for multiple-taper receiver functions
NASA Astrophysics Data System (ADS)
Park, J.; Levin, V.
2016-10-01
The multiple-taper correlation (MTC) algorithm for the estimation of teleseismic receiver functions (RFs) has desirable statistical properties. This paper presents several adaptations to the MTC algorithm that exploit its frequency-domain uncertainty estimates to generate stable RFs that include moveout corrections for deeper interfaces. Narrow-band frequency averaging implicit in spectral cross-correlation restricts the MTC-based RF estimates to resolve Ps converted phases only at short delay times, appropriate to the upper 100 km of Earth's lithosphere. The Ps conversions from deeper interfaces can be reconstructed by the MTC algorithm in two ways. Event cross-correlation computes a cross-correlation of single-taper spectrum estimates for a cluster of events rather than for a set of eigenspectrum estimates of a single P coda. To extend the reach of the algorithm, pre-stack moveout corrections in the frequency domain preserves the formal uncertainties of the RF estimates, which are used to weight RF stacks. Moving-window migration retains the multiple-taper approach, but cross-correlates the P-polarized motion with time-delayed SH and SV motion to focus on a Ps phase of interest. The frequency-domain uncertainties of bin-averaged RFs do not translate directly into the time domain. A jackknife over data records in each bin stack offers uncertainty estimates in the time domain while preserving uncertainty weighting in the frequency-domain RF stack.
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, ...
A finite-difference frequency-domain code for electromagnetic induction tomography
Sharpe, R M; Berryman, J G; Buettner, H M; Champagne, N J.,II; Grant, J B
1998-12-17
We are developing a new 3D code for application to electromagnetic induction tomography and applications to environmental imaging problems. We have used the finite-difference frequency- domain formulation of Beilenhoff et al. (1992) and the anisotropic PML (perfectly matched layer) approach (Berenger, 1994) to specify boundary conditions following Wu et al. (1997). PML deals with the fact that the computations must be done in a finite domain even though the real problem is effectively of infinite extent. The resulting formulas for the forward solver reduce to a problem of the form Ax = y, where A is a non-Hermitian matrix with real values off the diagonal and complex values along its diagonal. The matrix A may be either symmetric or nonsymmetric depending on details of the boundary conditions chosen (i.e., the particular PML used in the application). The basic equation must be solved for the vector x (which represents field quantities such as electric and magnetic fields) with the vector y determined by the boundary conditions and transmitter location. Of the many forward solvers that could be used for this system, relatively few have been thoroughly tested for the type of matrix encountered in our problem. Our studies of the stability characteristics of the Bi-CG algorithm raised questions about its reliability and uniform accuracy for this application. We have found the stability characteristics of Bi-CGSTAB [an alternative developed by van der Vorst (1992) for such problems] to be entirely adequate for our application, whereas the standard Bi-CG was quite inadequate. We have also done extensive validation of our code using semianalytical results as well as other codes. The new code is written in Fortran and is designed to be easily parallelized, but we have not yet tested this feature of the code. An adjoint method is being developed for solving the inverse problem for conductivity imaging (for mapping underground plumes), and this approach, when ready, will
Parallel processing demonstrator with plug-on-top free-space interconnect optics
NASA Astrophysics Data System (ADS)
Berger, Christoph; Wang, Xiaoqing; Ekman, Jeremy T.; Marchand, Philippe J.; Spaanenburg, Henk; Wang, Mark M.; Kiamilev, Fouad E.; Esener, Sadik C.
2001-05-01
We demonstrate a setup with 10 optically interconnected chips,k which can perform a distributed radix-2-butterfly calculation for fast Fourier transformation. The setup consists of a motherboard, five multi-chip-modules (MCMs, with processor/transceiver chips and laser/detector chips), four plug-on-top optics modules that provide the bi- directional optical links between the MCMs, and external control electronics. The design of the optics and optomechanics satisfies numerous real-world constraints, such as compact size (< 1 inch thick), suitability for mass-production, suitability for large arrays (up to 103 parallel channels), compatibility with standard electronics fabrication and packaging technology, and potential for active misalignment compensation by integrating MEMS technology.
Constant-time parallel sorting algorithm and its optical implementation using smart pixels
NASA Astrophysics Data System (ADS)
Louri, Ahmed; Hatch, James A., Jr.; Na, Jongwhoa
1995-06-01
Sorting is a fundamental operation that has important implications in a vast number of areas. For instance, sorting is heavily utilized in applications such as database machines, in which hashing techniques are used to accelerate data-processing algorithms. It is also the basis for interprocessor message routing and has strong implications in video telecommunications. However, high-speed electronic sorting networks are difficult to implement with VLSI technology because of the dense, global connectivity required. Optics eliminates this bottleneck by offering global interconnects, massive parallelism, and noninterfering communications. We present a parallel sorting algorithm and its efficient optical implementation. The algorithm sorts n data elements in few steps, independent of the number of elements to be sorted. Thus it is a constant-time sorting algorithm [i.e., O(1) time]. We also estimate the system's performance to show that the proposed sorting algorithm can provide at least 2 orders of magnitude improvement in execution time over conventional electronic algorithms.
Sasoglu, F Mert; Bohl, Andrew J; Allen, Kathleen B; Layton, Bradley E
2009-01-01
An image analysis method and its validation are presented for tracking the displacements of parallel mechanical force sensors. Force is measured using a combination of beam theory, optical microscopy, and image analysis. The primary instrument is a calibrated polymeric microbeam array mounted on a micromanipulator with the intended purpose of measuring traction forces on cell cultures or cell arrays. One application is the testing of hypotheses involving cellular mechanotransduction mechanisms. An Otsu-based image analysis code calculates displacement and force on cellular or other soft structures by using edge detection and image subtraction on digitally captured optical microscopy images. Forces as small as 250+/-50 nN and as great as 25+/-2.5 microN may be applied and measured upon as few as one or as many as hundreds of structures in parallel. A validation of the method is provided by comparing results from a rigid glass surface and a compliant polymeric surface.
Time and frequency-domain measurement of ground-state recovery times in red fluorescent proteins.
Manna, Premashis; Jimenez, Ralph
2015-04-16
The field of bioimaging and biosensors has been revolutionized by the discovery of fluorescent proteins (FPs) and their use in live cells. FPs are characterized with rich photodynamics due to the presence of nonfluorescent or dark states which are responsible for fluorescence intermittency or "blinking", which has been exploited in several localization-based super-resolution techniques that surpass the diffraction-limited resolution of conventional microscopy. Molecules that convert to these dark states recover to the ground states either spontaneously or upon absorption of another photon, depending on the particular FP and the structural transition that is involved. In this work, we demonstrate time- and frequency-domain methods for the measurement of the ground-state recovery (GSR) times of FPs both in live cells and in solutions. In the time-domain method, we excited the sample with millisecond pulses at varying dark times to obtain percent-recovery. In the frequency-domain method, dark-state hysteresis was employed to obtain the positive phase shift or "phase advance". We extracted the GSR time constants from our measurements using calculations and simulations based on a three-state model system. The GSR time constants of the red FPs studied in these experiments fall in the range from μs to msec time-scales. We find that the time- and frequency-domain techniques are complementary to each other. While accurate GSR times can be extracted from the time-domain technique, frequency-domain measurements are primarily sensitive to the rates of dark-state conversion (DSC) processes. A correlation between GSR times, DSC, and photobleaching rates for the red FPs mCherry, TagRFP-T, and Kriek were observed. These time- and frequency-domain methods can be used in high-throughput screening and sorting of FPs clones based on GSR time constant and photostability and will therefore be valuable for the development of new photoswitchable or photoactivatable FPs.
Comparison of Frequency-Domain Array Methods for Studying Earthquake Rupture Process
NASA Astrophysics Data System (ADS)
Sheng, Y.; Yin, J.; Yao, H.
2014-12-01
Seismic array methods, in both time- and frequency- domains, have been widely used to study the rupture process and energy radiation of earthquakes. With better spatial resolution, the high-resolution frequency-domain methods, such as Multiple Signal Classification (MUSIC) (Schimdt, 1986; Meng et al., 2011) and the recently developed Compressive Sensing (CS) technique (Yao et al., 2011, 2013), are revealing new features of earthquake rupture processes. We have performed various tests on the methods of MUSIC, CS, minimum-variance distortionless response (MVDR) Beamforming and conventional Beamforming in order to better understand the advantages and features of these methods for studying earthquake rupture processes. We use the ricker wavelet to synthesize seismograms and use these frequency-domain techniques to relocate the synthetic sources we set, for instance, two sources separated in space but, their waveforms completely overlapping in the time domain. We also test the effects of the sliding window scheme on the recovery of a series of input sources, in particular, some artifacts that are caused by the sliding window scheme. Based on our tests, we find that CS, which is developed from the theory of sparsity inversion, has relatively high spatial resolution than the other frequency-domain methods and has better performance at lower frequencies. In high-frequency bands, MUSIC, as well as MVDR Beamforming, is more stable, especially in the multi-source situation. Meanwhile, CS tends to produce more artifacts when data have poor signal-to-noise ratio. Although these techniques can distinctly improve the spatial resolution, they still produce some artifacts along with the sliding of the time window. Furthermore, we propose a new method, which combines both the time-domain and frequency-domain techniques, to suppress these artifacts and obtain more reliable earthquake rupture images. Finally, we apply this new technique to study the 2013 Okhotsk deep mega earthquake
Architecture design of virtual-optics data security using parallel hardware and software
NASA Astrophysics Data System (ADS)
Peng, Xiang; Zhang, Peng; Niu, Hanben
In this paper, we present an approach of high-efficiency implementation of data security based on virtual-optics imaging methodology (VOIM) with the aid of parallel hardware and parallel software (PHPS) strategy. With this approach, we are able to greatly strengthen the performance of the VOIM through exploiting parallel architecture of the digital signal processor (DSP) and parallel software design. In order to achieve high performance, we build up Master-Slave design architecture with the aid of TMS320C6701-DSP to construct a PHPS implementation scheme for the multimedia data encryption and decryption based on the framework of virtual-optics. In addition, we also adopt software pipelines and other optimization techniques to further strengthen the performance of such a strategy. This approach makes it possible for the VOIM to be realized in real-time applications in embedded systems for multimedia data security. Experiment results with digital image and digital audio signals show the validity of proposed approach.
NASA Astrophysics Data System (ADS)
Louri, Ahmed; Sung, Hongki
1995-10-01
The interconnection network structure can be the deciding and limiting factor in the cost and the performance of parallel computers. One of the most popular point-to-point interconnection networks for parallel computers today is the hypercube. The regularity, logarithmic diameter, symmetry, high connectivity, fault tolerance, simple routing, and reconfigurability (easy embedding of other network topologies) of the hypercube make it a very attractive choice for parallel computers. Unfortunately the hypercube possesses a major drawback, which is the links per node increases as the network grows in size. As an alternative to the hypercube, the binary de Bruijn (BdB) network has recently received much attention. The BdB not only provides a logarithmic diameter, fault tolerance, and simple routing but also requires fewer links than the hypercube for the same network size. Additionally, a major advantage of the BdB edges per node is independent of the network size. This makes it very desirable for large-scale parallel systems. However, because of its asymmetrical nature and global connectivity, it poses a major challenge for VLSI technology. Optics, owing to its three-dimensional and global-connectivity nature, seems to be very suitable for implementing BdB networks. We present an implementation methodology for optical BdB networks. The distinctive feature of the proposed implementation methodology is partitionability of the network into a few primitive operations that can be implemented efficiently. We further show feasibility of the
A lower bound for routing on a completely connected optical communication parallel computer
Goldberg, L.A.; Jerrum, M.; MacKenzie, P.D.
1993-08-03
The task of routing a 2-relation on an n-processor completely connected optical communication parallel computer (OCPC) is considered. A lower bound is presented that applies to any randomized distributed algorithm for this task: specifically, it is shown that the expected number of steps required to route a 2-relation is {Omega}({radical} log log n) in the worst case. For comparison, the best upper bound known is O(log log n).
NASA Astrophysics Data System (ADS)
Zimmermann, Bernhard B.; Fang, Qianqian; Boas, David A.; Carp, Stefan A.
2016-01-01
Frequency domain near-infrared spectroscopy (FD-NIRS) has proven to be a reliable method for quantification of tissue absolute optical properties. We present a full-sampling direct analog-to-digital conversion FD-NIR imager. While we developed this instrument with a focus on high-speed optical breast tomographic imaging, the proposed design is suitable for a wide-range of biophotonic applications where fast, accurate quantification of absolute optical properties is needed. Simultaneous dual wavelength operation at 685 and 830 nm is achieved by concurrent 67.5 and 75 MHz frequency modulation of each laser source, respectively, followed by digitization using a high-speed (180 MS/s) 16-bit A/D converter and hybrid FPGA-assisted demodulation. The instrument supports 25 source locations and features 20 concurrently operating detectors. The noise floor of the instrument was measured at <1.4 pW/√Hz, and a dynamic range of 115+ dB, corresponding to nearly six orders of magnitude, has been demonstrated. Titration experiments consisting of 200 different absorption and scattering values were conducted to demonstrate accurate optical property quantification over the entire range of physiologically expected values.
Van Munster, E B; Gadella, T W J
2004-01-01
In conventional wide-field frequency-domain fluorescence lifetime imaging microscopy (FLIM), excitation light is intensity-modulated at megahertz frequencies. Emitted fluorescence is recorded by a CCD camera through an image intensifier, which is modulated at the same frequency. From images recorded at various phase differences between excitation and intensifier gain modulation, the phase and modulation depth of the emitted light is obtained. The fluorescence lifetime is determined from the delay and the decrease in modulation depth of the emission relative to the excitation. A minimum of three images is required, but in this case measurements become susceptible to aliasing caused by the presence of higher harmonics. Taking more images to avoid this is not always possible owing to phototoxicity or movement. A method is introduced, phiFLIM, requiring only three recordings that is not susceptible to aliasing. The phase difference between the excitation and the intensifier is scanned over the entire 360 degrees range following a predefined phase profile, during which the image produced by the intensifier is integrated onto the CCD camera, yielding a single image. Three different images are produced following this procedure, each with a different phase profile. Measurements were performed with a conventional wide-field frequency-domain FLIM system based on an acousto-optic modulator for modulation of the excitation and a microchannel-plate image intensifier coupled to a CCD camera for the detection. By analysis of the harmonic content of measured signals it was found that the third harmonic was effectively the highest present. Using the conventional method with three recordings, phase errors due to aliasing of up to +/- 29 degrees and modulation depth errors of up to 30% were found. Errors in lifetimes of YFP-transfected HeLa cells were as high as 100%. With phiFLIM, using the same specimen and settings, systematic errors due to aliasing did not occur.
FOCEX: A fiber-optic extender for a high speed parallel RS485 data cable
Meadows, J.T.; Anderson, J.T.; Cooper, P.S.; Engelfried, J.; Franzen, J.W.; Forster, B.G.; Levinson, F.; Rawls, J.; Haber, S.
1995-05-01
For longer-distant, high speed data links, optical fibre becomes most cost-effective than copper or other hard wire cable systems. Fermilab supplied to Finisar Corp. of Menlo Park, CA., a set of specifications for card functions, sizes and interconnector pin assignments. Finisar designed and assembled a set of fiber optical P.C. cards using 100 megabyte/sec commercial optoelectronics and a serialization and deserialization HOT-ROD chipset designed by GAZELLE Microcircuits, Inc. (A Tri Quint Semiconductors company). The cooperative effort between Fermilab and Finisar has allowed Fermilab to created a reliable 50 Megabytes/sec (40 bit parallel RS485 DART data bus) cable to cable extender using a virtually invisible Fiber Channel point-to-point(FC-0) fiber optical single-simplex system. The system is easily capable of sustaining a 50 megabytes/sec of data, control and status line throughput at distances of 1625 feet (500 meters) using standard multi-mode fiber.
Deri, Robert J.; DeGroot, Anthony J.; Haigh, Ronald E.
2002-01-01
As the performance of individual elements within parallel processing systems increases, increased communication capability between distributed processor and memory elements is required. There is great interest in using fiber optics to improve interconnect communication beyond that attainable using electronic technology. Several groups have considered WDM, star-coupled optical interconnects. The invention uses a fiber optic transceiver to provide low latency, high bandwidth channels for such interconnects using a robust multimode fiber technology. Instruction-level simulation is used to quantify the bandwidth, latency, and concurrency required for such interconnects to scale to 256 nodes, each operating at 1 GFLOPS performance. Performance scales have been shown to .apprxeq.100 GFLOPS for scientific application kernels using a small number of wavelengths (8 to 32), only one wavelength received per node, and achievable optoelectronic bandwidth and latency.
FOCEX: A fiber-optic extender for a high speed parallel RS485 data cable
NASA Astrophysics Data System (ADS)
Meadows, J. T.; Anderson, J. T.; Cooper, P. S.; Engelfried, J.; Franzen, J. W.; Forster, B. G.; Levinson, F.; Rawls, J.; Haber, S.
1995-05-01
For longer-distant, high speed data links, optical fiber becomes most cost-effective than copper or other hard wire cable systems. Fermilab supplied to Finisar Corp. of Menlo Park, CA, a set of specifications for card functions, sizes and interconnector pin assignments. Finisar designed and assembled a set of fiber optical P.C. cards using 100 megabyte/sec commercial optoelectronics and a serialization and deserialization HOT-ROD chipset designed by GAZELLE Microcircuits, Inc. (A Tri Quint Semiconductors company). The cooperative effort between Fermilab and Finisar has allowed Fermilab to created a reliable 50 Megabytes/sec (40 bit parallel RS485 DART data bus) cable to cable extender using a virtually invisible Fiber Channel point-to-point(FC-0) fiber optical single-simplex system. The system is easily capable of sustaining a 50 megabytes/sec of data, control and status line throughput at distances of 1625 feet (500 meters) using standard multi-mode fiber.
Morozov, A N; Turchin, I V
2013-12-31
The method of optical coherence tomography with the scheme of parallel reception of the interference signal (P-OCT) is developed on the basis of spatial paralleling of the reference wave by means of a phase diffraction grating producing the appropriate time delay in the Mach–Zehnder interferometer. The absence of mechanical variation of the optical path difference in the interferometer essentially reduces the time required for 2D imaging of the object internal structure, as compared to the classical OCT that uses the time-domain method of the image construction, the sensitivity and the dynamic range being comparable in both approaches. For the resulting field of the interfering object and reference waves an analytical expression is derived that allows the calculation of the autocorrelation function in the plane of photodetectors. For the first time a method of linear phase modulation by 2π is proposed for P-OCT systems, which allows the use of compact high-frequency (a few hundred kHz) piezoelectric cell-based modulators. For the demonstration of the P-OCT method an experimental setup was created, using which the images of the inner structure of biological objects at the depth up to 1 mm with the axial spatial resolution of 12 μm were obtained. (optical coherence tomography)
Focusing optics of a parallel beam CCD optical tomography apparatus for 3D radiation gel dosimetry.
Krstajić, Nikola; Doran, Simon J
2006-04-21
Optical tomography of gel dosimeters is a promising and cost-effective avenue for quality control of radiotherapy treatments such as intensity-modulated radiotherapy (IMRT). Systems based on a laser coupled to a photodiode have so far shown the best results within the context of optical scanning of radiosensitive gels, but are very slow ( approximately 9 min per slice) and poorly suited to measurements that require many slices. Here, we describe a fast, three-dimensional (3D) optical computed tomography (optical-CT) apparatus, based on a broad, collimated beam, obtained from a high power LED and detected by a charged coupled detector (CCD). The main advantages of such a system are (i) an acquisition speed approximately two orders of magnitude higher than a laser-based system when 3D data are required, and (ii) a greater simplicity of design. This paper advances our previous work by introducing a new design of focusing optics, which take information from a suitably positioned focal plane and project an image onto the CCD. An analysis of the ray optics is presented, which explains the roles of telecentricity, focusing, acceptance angle and depth-of-field (DOF) in the formation of projections. A discussion of the approximation involved in measuring the line integrals required for filtered backprojection reconstruction is given. Experimental results demonstrate (i) the effect on projections of changing the position of the focal plane of the apparatus, (ii) how to measure the acceptance angle of the optics, and (iii) the ability of the new scanner to image both absorbing and scattering gel phantoms. The quality of reconstructed images is very promising and suggests that the new apparatus may be useful in a clinical setting for fast and accurate 3D dosimetry. PMID:16585845
Focusing optics of a parallel beam CCD optical tomography apparatus for 3D radiation gel dosimetry
NASA Astrophysics Data System (ADS)
Krstajic, Nikola; Doran, Simon J.
2006-04-01
Optical tomography of gel dosimeters is a promising and cost-effective avenue for quality control of radiotherapy treatments such as intensity-modulated radiotherapy (IMRT). Systems based on a laser coupled to a photodiode have so far shown the best results within the context of optical scanning of radiosensitive gels, but are very slow (~9 min per slice) and poorly suited to measurements that require many slices. Here, we describe a fast, three-dimensional (3D) optical computed tomography (optical-CT) apparatus, based on a broad, collimated beam, obtained from a high power LED and detected by a charged coupled detector (CCD). The main advantages of such a system are (i) an acquisition speed approximately two orders of magnitude higher than a laser-based system when 3D data are required, and (ii) a greater simplicity of design. This paper advances our previous work by introducing a new design of focusing optics, which take information from a suitably positioned focal plane and project an image onto the CCD. An analysis of the ray optics is presented, which explains the roles of telecentricity, focusing, acceptance angle and depth-of-field (DOF) in the formation of projections. A discussion of the approximation involved in measuring the line integrals required for filtered backprojection reconstruction is given. Experimental results demonstrate (i) the effect on projections of changing the position of the focal plane of the apparatus, (ii) how to measure the acceptance angle of the optics, and (iii) the ability of the new scanner to image both absorbing and scattering gel phantoms. The quality of reconstructed images is very promising and suggests that the new apparatus may be useful in a clinical setting for fast and accurate 3D dosimetry.
Rice, Tyler B.; Konecky, Soren D.; Owen, Christopher; Choi, Bernard; Tromberg, Bruce J.
2012-01-01
Laser Speckle Imaging (LSI) is fast, noninvasive technique to image particle dynamics in scattering media such as biological tissue. While LSI measurements are independent of the overall intensity of the laser source, we find that spatial variations in the laser source profile can impact measured flow rates. This occurs due to differences in average photon path length across the profile, and is of significant concern because all lasers have some degree of natural Gaussian profile in addition to artifacts potentially caused by projecting optics. Two in vivo measurement are performed to show that flow rates differ based on location with respect to the beam profile. A quantitative analysis is then done through a speckle contrast forward model generated within a coherent Spatial Frequency Domain Imaging (cSFDI) formalism. The model predicts remitted speckle contrast as a function of spatial frequency, optical properties, and scattering dynamics. Comparison with experimental speckle contrast images were done using liquid phantoms with known optical properties for three common beam shapes. cSFDI is found to accurately predict speckle contrast for all beam shapes to within 5% root mean square error. Suggestions for improving beam homogeneity are given, including a widening of the natural beam Gaussian, proper diffusing glass spreading, and flat top shaping using microlens arrays. PMID:22741080
NASA Astrophysics Data System (ADS)
Doronina-Amitonova, L. V.; Fedotov, I. V.; Ivashkina, O. I.; Zots, M. A.; Fedotov, A. B.; Anokhin, K. V.; Zheltikov, A. M.
2013-11-01
Seeing the big picture of functional responses within large neural networks in a freely functioning brain is crucial for understanding the cellular mechanisms behind the higher nervous activity, including the most complex brain functions, such as cognition and memory. As a breakthrough toward meeting this challenge, implantable fiber-optic interfaces integrating advanced optogenetic technologies and cutting-edge fiber-optic solutions have been demonstrated, enabling a long-term optogenetic manipulation of neural circuits in freely moving mice. Here, we show that a specifically designed implantable fiber-optic interface provides a powerful tool for parallel long-term optical interrogation of distinctly separate, functionally different sites in the brain of freely moving mice. This interface allows the same groups of neurons lying deeply in the brain of a freely behaving mouse to be reproducibly accessed and optically interrogated over many weeks, providing a long-term dynamic detection of genome activity in response to a broad variety of pharmacological and physiological stimuli.
10-channel fiber array fabrication technique for parallel optical coherence tomography system
NASA Astrophysics Data System (ADS)
Arauz, Lina J.; Luo, Yuan; Castillo, Jose E.; Kostuk, Raymond K.; Barton, Jennifer
2007-02-01
Optical Coherence Tomography (OCT) shows great promise for low intrusive biomedical imaging applications. A parallel OCT system is a novel technique that replaces mechanical transverse scanning with electronic scanning. This will reduce the time required to acquire image data. In this system an array of small diameter fibers is required to obtain an image in the transverse direction. Each fiber in the array is configured in an interferometer and is used to image one pixel in the transverse direction. In this paper we describe a technique to package 15μm diameter fibers on a siliconsilica substrate to be used in a 2mm endoscopic probe tip. Single mode fibers are etched to reduce the cladding diameter from 125μm to 15μm. Etched fibers are placed into a 4mm by 150μm trench in a silicon-silica substrate and secured with UV glue. Active alignment was used to simplify the lay out of the fibers and minimize unwanted horizontal displacement of the fibers. A 10-channel fiber array was built, tested and later incorporated into a parallel optical coherence system. This paper describes the packaging, testing, and operation of the array in a parallel OCT system.
Determining XV-15 aeroelastic modes from flight data with frequency-domain methods
NASA Technical Reports Server (NTRS)
Acree, C. W., Jr.; Tischler, Mark B.
1993-01-01
The XV-15 tilt-rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier transformed). All spectral data were computed using chirp z-transforms. Modal frequencies and damping were determined by fitting curves to frequency-response magnitude and phase data. The results given in this report are for the XV-15 with its original metal rotor blades. Also, frequency and damping values are compared with theoretical predictions made using two different programs, CAMRAD and ASAP. The frequency-domain data-analysis method proved to be very reliable and adequate for tracking aeroelastic modes during flight-envelope expansion. This approach required less flight-test time and yielded mode estimations that were more repeatable, compared with the exponential-decay method previously used.
A Frequency Domain Approach for Controlling Fast-Scale Instabilities in Switching Power Converters
NASA Astrophysics Data System (ADS)
Rodriguez, E.; Alarcón, E.; Iu, H. H. C.; El Aroudi, A.
This paper deals with controllers of fast-scale instabilities in DC-DC switching power converters from a frequency domain standpoint with the aim of understanding their working principle and hence simplifying their design. Some approaches for controlling fast-scale instabilities and their limitations are revisited. Considering the frequency domain transfer function of already existing controllers, a simple and extended notch filter centered at half of the switching frequency is proposed to avoid these instabilities. However, a switching converter under this controller may still exhibit the undesired slow-scale instability. Accordingly, the paper explores an alternative approach based on amplifying the harmonic at the switching frequency. Numerical simulations show that the new proposed controller can concurrently improve both fast-scale and slow-scale stability margins. The results from the different controllers are contrasted in terms of stability boundaries, indicating that the last one presents a wider stability range.
The research on recognition and extraction of river feature in IKNOS based on frequency domain
NASA Astrophysics Data System (ADS)
Wang, Ke; Feng, Xuezhi; Xiao, Pengfeng; Wu, Guoping
2009-10-01
Because the resolution of remotely sensed imagery becomes higher, new methods are introduced to process the high-resolution remotely sensed imagery. The algorithms introduced in this paper to recognize and extract the river features based on the frequency domain. This paper uses the Gabor filter in frequency domain to enhance the texture of river and remove the noise from remotely sensed imagery. And then according to the theory of phase congruency, this paper retrieves the PC of every point such that features such as edge of river, building and farmland in the remotely sensed imagery. Lastly, the skeletal methodology is introduced to determine the edge of river within the help of the trend of river.
Spatial and frequency domain interferometry using the MU radar - A tutorial and recent developments
NASA Astrophysics Data System (ADS)
Fukao, Shoichiro; Palmer, Robert D.
Fundamental notions of spatial and frequency-domain interferometry are reviewed, and a novel method is proposed for steering the antenna beam after the data are stored. Also presented is a comparison of techniques for wind-vector determination with emphasis given to a method based on the linear variation of the phase of the cross-spectra. Recent applications of spatial interferometry (SI) and frequency-domain interferometry (FDI) are listed including an implementation of FDI with MU radar. The vertical wind velocity estimated from the Doppler technique is shown to be a measure of the wind perpendicular to tilted refractivity surfaces. The bias generated by horizontal wind is found to have a significant effect on the Doppler estimate in SI. The use of MU radar in FDI can facilitate measurements of the positions of high reflectivity layers smaller than the resolution volume.
A frequency domain radar interferometric imaging (FII) technique based on high-resolution methods
NASA Astrophysics Data System (ADS)
Luce, H.; Yamamoto, M.; Fukao, S.; Helal, D.; Crochet, M.
2001-01-01
In the present work, we propose a frequency-domain interferometric imaging (FII) technique for a better knowledge of the vertical distribution of the atmospheric scatterers detected by MST radars. This is an extension of the dual frequency-domain interferometry (FDI) technique to multiple frequencies. Its objective is to reduce the ambiguity (resulting from the use of only two adjacent frequencies), inherent with the FDI technique. Different methods, commonly used in antenna array processing, are first described within the context of application to the FII technique. These methods are the Fourier-based imaging, the Capon's and the singular value decomposition method used with the MUSIC algorithm. Some preliminary simulations and tests performed on data collected with the middle and upper atmosphere (MU) radar (Shigaraki, Japan) are also presented. This work is a first step in the developments of the FII technique which seems to be very promising.
NASA Astrophysics Data System (ADS)
Zhao, Liang; Ge, Jian-Hua
2012-12-01
Single-carrier (SC) transmission with frequency-domain equalization (FDE) is today recognized as an attractive alternative to orthogonal frequency-division multiplexing (OFDM) for communication application with the inter-symbol interference (ISI) caused by multi-path propagation, especially in shallow water channel. In this paper, we investigate an iterative receiver based on minimum mean square error (MMSE) decision feedback equalizer (DFE) with symbol rate and fractional rate samplings in the frequency domain (FD) and serially concatenated trellis coded modulation (SCTCM) decoder. Based on sound speed profiles (SSP) measured in the lake and finite-element ray tracking (Bellhop) method, the shallow water channel is constructed to evaluate the performance of the proposed iterative receiver. Performance results show that the proposed iterative receiver can significantly improve the performance and obtain better data transmission than FD linear and adaptive decision feedback equalizers, especially in adopting fractional rate sampling.
Motion estimation in the frequency domain using fuzzy c-planes clustering.
Erdem, C E; Karabulut, G Z; Yanmaz, E; Anarim, E
2001-01-01
A recent work explicitly models the discontinuous motion estimation problem in the frequency domain where the motion parameters are estimated using a harmonic retrieval approach. The vertical and horizontal components of the motion are independently estimated from the locations of the peaks of respective periodogram analyses and they are paired to obtain the motion vectors using a procedure proposed. In this paper, we present a more efficient method that replaces the motion component pairing task and hence eliminates the problems of the pairing method described. The method described in this paper uses the fuzzy c-planes (FCP) clustering approach to fit planes to three-dimensional (3-D) frequency domain data obtained from the peaks of the periodograms. Experimental results are provided to demonstrate the effectiveness of the proposed method.
NASA Astrophysics Data System (ADS)
Florez, H. M.; González, C.; Martinelli, M.
2016-07-01
Correlation spectroscopy has been proposed as a spectroscopic technique for measuring the coherence between the ground states in electromagnetically induced transparency (EIT). While in the time domain the steep dispersion in the EIT condition accounts for the robustness of the correlation linewidth against power broadening, such physical insight was not directly established in the frequency domain. We propose a perturbative approach to describe the correlation spectroscopy of two noisy lasers coupled to a Λ transition in cold atoms, leading to EIT. Such approach leads to an analytical expression that maps the intensity correlation directly in terms of the absorption and dispersion of the light fields. Low and high perturbative regimes are investigated and demonstrate that, for coherent light sources, the first-order term in perturbation expansion represents a sufficient description for the correlation. Sideband resonances are also observed, showing the richness of the frequency domain approach.
Identification and verification of frequency-domain models for XV-15 tilt-rotor aircraft dynamics
NASA Technical Reports Server (NTRS)
Tischler, M. B.; Leung, J. G. M.; Dugan, D. C.
1984-01-01
Frequency-domain methods are used to extract the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight test data for the cruise condition (V = 170 knots). The frequency responses are numerically fitted with transfer-function forms to identify equivalent model characteristics. The associated handling quality parameters meet or exceed Level 2, Category A, requirements for fixed-wing military aircraft. Step response matching is used to verify the time-domain fidelity of the transfer-function models for the cruise and hover flight conditions. The transient responses of the model and aircraft are in close agreement in all cases, except for the normal acceleration response to elevator deflection in cruise. This discrepancy is probably due to the unmodeled rotor rpm dynamics. The utility of the frequency-domain approach for dynamics identification and analysis is clearly demonstrated.
NASA Technical Reports Server (NTRS)
Seidel, R. C.; Lehtinen, B.
1974-01-01
A technique is described for designing feedback control systems using frequency domain models, a quadratic cost function, and a parameter optimization computer program. FORTRAN listings for the computer program are included. The approach is applied to the design of shock position controllers for a supersonic inlet. Deterministic or random system disturbances, and the presence of random measurement noise are considered. The cost function minimization is formulated in the time domain, but the problem solution is obtained using a frequency domain system description. A scaled and constrained conjugate gradient algorithm is used for the minimization. The approach to a supersonic inlet included the calculations of the optimal proportional-plus integral (PI) and proportional-plus-integral-plus-derivative controllers. A single-loop PI controller was the most desirable of the designs considered.
Frequency-domain localization of alpha rhythm in humans via a maximum entropy approach
NASA Astrophysics Data System (ADS)
Patel, Pankaj; Khosla, Deepak; Al-Dayeh, Louai; Singh, Manbir
1997-05-01
Generators of spontaneous human brain activity such as alpha rhythm may be easier and more accurate to localize in frequency-domain than in time-domain since these generators are characterized by a specific frequency range. We carried out a frequency-domain analysis of synchronous alpha sources by generating equivalent potential maps using the Fourier transform of each channel of electro-encephalographic (EEG) recordings. SInce the alpha rhythm recorded by EEG scalp measurements is probably produced by several independent generators, a distributed source imaging approach was considered more appropriate than a model based on a single equivalent current dipole. We used an imaging approach based on a Bayesian maximum entropy technique. Reconstructed sources were superposed on corresponding anatomy form magnetic resonance imaging. Results from human studies suggest that reconstructed sources responsible for alpha rhythm are mainly located in the occipital and parieto- occipital lobes.
Frequency domain interferometry using the 1290 MHz Soendre Stromfjord radar: First results
NASA Astrophysics Data System (ADS)
Palmer, Robert D.; Larsen, Miguel F.; Heinselman, C. J.; Mikkelsen, I. S.
1993-08-01
First results from the implementation of frequency domain interferometry (FDI) using an L-band frequency of 1290 MHz are presented. The experiment was conducted in September 1991 using the radar facility located in Soendre Stromford, Greenland. The spectra and the correlation functions obtained from the FDI data are compared to previous results at other frequencies. The data show the Soendre Stromford radar is providing reliable wind measurements in the lower atmosphere and that FDI can be implemented at L-band.
Nonlinear dynamics of internet congestion control: A frequency-domain approach
NASA Astrophysics Data System (ADS)
Gentile, Franco S.; Moiola, Jorge L.; Paolini, Eduardo E.
2014-04-01
In this paper a fluid-flow model for TCP congestion avoidance combined with different AQM schemes is analyzed. The conditions for the appearance of Hopf bifurcations are stated analytically using frequency-domain techniques. The proposed methodology allows the characterization of the emerging periodic orbits, providing approximations of their amplitude and frequency. In addition, multiple oscillations and limit cycle bifurcations are found via numerical tools.
NASA Astrophysics Data System (ADS)
Wang, W.; Wen, L.
2013-12-01
Back projection is a method to back project the seismic energy recorded in a seismic array back to the earthquake source region and determine the rupture process of a large earthquake. The method takes advantage of the coherence of seismic energy in a seismic array and is quick in determining some important properties of earthquake source. The method can be performed in both time and frequency domains. In time domain, the most conventional procedure is beam forming with some measures of suppressing the noise, such as the Nth root stacking, etc. In the frequency domain, the multiple signal classification method (MUSIC) estimates the direction of arrivals of multiple waves propagating through an array using the subspace method. The advantage of this method is the ability to study rupture properties at various frequencies and to resolve simultaneous arrivals making it suitable for detecting biliteral rupture of an earthquake source. We present a comparison of back projection results on some large earthquakes between the methods in time domain and frequency domain. The time-domain procedure produces an image that is smeared and exhibits some artifacts, although some enhancing stacking methods can at some extent alleviate the problem. On the other hand, the MUSIC method resolves clear multiple arrivals and provides higher resolution of rupture imaging.
Frequency domain response of a parametrically excited riser under random wave forces
NASA Astrophysics Data System (ADS)
Lei, Song; Zhang, Wen-Shou; Lin, Jia-Hao; Yue, Qian-Jin; Kennedy, D.; Williams, F. W.
2014-01-01
Floating Production, Drilling, Storage and Offloading units represent a new technology with a promising future in the offshore oil industry. An important role is played by risers, which are installed between the subsea wellhead and the Tension Leg Deck located in the middle of the moon-pool in the hull. The inevitable heave motion of the floating hull causes a time-varying axial tension in the riser. This time dependent tension may have an undesirable influence on the lateral deflection response of the riser, with random wave forces in the frequency domain. To investigate this effect, a riser is modeled as a Bernoulli-Euler beam. The axial tension is expressed as a static part, along with a harmonic dynamic part. By linearizing the wave drag force, the riser's lateral deflection is obtained through a partial differential equation containing a time-dependent coefficient. Applying the Galerkin method, the equation is reduced to an ordinary differential equation that can be solved using the pseudo-excitation method in the frequency domain. Moreover, the Floquet-Liapunov theorem is used to estimate the stability of the vibration system in the space of parametric excitation. Finally, stability charts are obtained for some numerical examples, the correctness of the proposed method is verified by comparing with Monte-Carlo simulation and the influence of the parametric excitation on the frequency domain responses of the riser is discussed.
Frequency-domain correction of sensor dynamic error for step response.
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly. PMID:23206091
NASA Technical Reports Server (NTRS)
Baumeister, K. J.; Kreider, K. L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in ducts. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
NASA Technical Reports Server (NTRS)
Baumeister, Kenneth J.; Kreider, Kevin L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Testing for Granger Causality in the Frequency Domain: A Phase Resampling Method.
Liu, Siwei; Molenaar, Peter
2016-01-01
This article introduces phase resampling, an existing but rarely used surrogate data method for making statistical inferences of Granger causality in frequency domain time series analysis. Granger causality testing is essential for establishing causal relations among variables in multivariate dynamic processes. However, testing for Granger causality in the frequency domain is challenging due to the nonlinear relation between frequency domain measures (e.g., partial directed coherence, generalized partial directed coherence) and time domain data. Through a simulation study, we demonstrate that phase resampling is a general and robust method for making statistical inferences even with short time series. With Gaussian data, phase resampling yields satisfactory type I and type II error rates in all but one condition we examine: when a small effect size is combined with an insufficient number of data points. Violations of normality lead to slightly higher error rates but are mostly within acceptable ranges. We illustrate the utility of phase resampling with two empirical examples involving multivariate electroencephalography (EEG) and skin conductance data.
Flight testing and frequency domain analysis for rotorcraft handling qualities characteristics
NASA Technical Reports Server (NTRS)
Ham, Johnnie A.; Gardner, Charles K.; Tischler, Mark B.
1993-01-01
A demonstration of frequency domain flight testing techniques and analyses was performed on a U.S. Army OH-58D helicopter in support of the OH-58D Airworthiness and Flight Characteristics Evaluation and the Army's development and ongoing review of Aeronautical Design Standard 33C, Handling Qualities Requirements for Military Rotorcraft. Hover and forward flight (60 knots) tests were conducted in 1 flight hour by Army experimental test pilots. Further processing of the hover data generated a complete database of velocity, angular rate, and acceleration frequency responses to control inputs. A joint effort was then undertaken by the Airworthiness Qualification Test Directorate (AQTD) and the U.S. Army Aeroflightdynamics Directorate (AFDD) to derive handling qualities information from the frequency response database. A significant amount of information could be extracted from the frequency domain database using a variety of approaches. This report documents numerous results that have been obtained from the simple frequency domain tests; in many areas, these results provide more insight into the aircraft dynamics that affect handling qualities than to traditional flight tests. The handling qualities results include ADS-33C bandwidth and phase delay calculations, vibration spectral determinations, transfer function models to examine single axis results, and a six degree of freedom fully coupled state space model. The ability of this model to accurately predict aircraft responses was verified using data from pulse inputs. This report also documents the frequency-sweep flight test technique and data analysis used to support the tests.
Flight-testing and frequency-domain analysis for rotorcraft handling qualities
NASA Technical Reports Server (NTRS)
Ham, Johnnie A.; Gardner, Charles K.; Tischler, Mark B.
1995-01-01
A demonstration of frequency-domain flight-testing techniques and analysis was performed on a U.S. Army OH-58D helicopter in support of the OH-58D Airworthiness and Flight Characteristics Evaluation and of the Army's development and ongoing review of Aeronautical Design Standard 33C, Handling Qualities Requirements for Military Rotorcraft. Hover and forward flight (60 kn) tests were conducted in 1 flight hour by Army experimental test pilots. Further processing of the hover data generated a complete database of velocity, angular-rate, and acceleration-frequency responses to control inputs. A joint effort was then undertaken by the Airworthiness Qualification Test Dirtectorate and the U.S. Army Aeroflightdynamics Directorate to derive handling-quality information from the frequency-domain database using a variety of approaches. This report documents numerous results that have been obtained from the simple frequency-domain tests; in many areas, these results provide more insight into the aircraft dynmamics that affect handling qualities than do traditional flight tests. The handling-quality results include ADS-33C bandwidth and phase-delay calculations, vibration spectral determinations, transfer-function models to examine single-axis results, and a six-degree-of-freedom fully coupled state-space model. The ability of this model to accurately predict responses was verified using data from pulse inputs. This report also documents the frequency-sweep flight-test technique and data analysis used to support the tests.
Visualization of evolving laser-generated structures by frequency domain tomography
NASA Astrophysics Data System (ADS)
Chang, Yenyu; Li, Zhengyan; Wang, Xiaoming; Zgadzaj, Rafal; Downer, Michael
2011-10-01
We introduce frequency domain tomography (FDT) for single-shot visualization of time-evolving refractive index structures (e.g. laser wakefields, nonlinear index structures) moving at light-speed. Previous researchers demonstrated single-shot frequency domain holography (FDH), in which a probe-reference pulse pair co- propagates with the laser-generated structure, to obtain snapshot-like images. However, in FDH, information about the structure's evolution is averaged. To visualize an evolving structure, we use several frequency domain streak cameras (FDSCs), in each of which a probe-reference pulse pair propagates at an angle to the propagation direction of the laser-generated structure. The combination of several FDSCs constitutes the FDT system. We will present experimental results for a 4-probe FDT system that has imaged the whole-beam self-focusing of a pump pulse propagating through glass in a single laser shot. Combining temporal and angle multiplexing methods, we successfully processed data from four probe pulses in one spectrometer in a single-shot. The output of data processing is a multi-frame movie of the self- focusing pulse. Our results promise the possibility of visualizing evolving laser wakefield structures that underlie laser-plasma accelerators used for multi-GeV electron acceleration.
Frequency domain modeling and dynamic characteristics evaluation of existing wind turbine systems
NASA Astrophysics Data System (ADS)
Chiang, Chih-Hung; Yu, Chih-Peng
2016-04-01
It is quite well accepted that frequency domain procedures are suitable for the design and dynamic analysis of wind turbine structures, especially for floating offshore wind turbines, since random wind loads and wave induced motions are most likely simulated in the frequency domain. This paper presents specific applications of an effective frequency domain scheme to the linear analysis of wind turbine structures in which a 1-D spectral element was developed based on the axially-loaded member. The solution schemes are summarized for the spectral analyses of the tower, the blades, and the combined system with selected frequency-dependent coupling effect from foundation-structure interactions. Numerical examples demonstrate that the modal frequencies obtained using spectral-element models are in good agreement with those found in the literature. A 5-element mono-pile model results in less than 0.3% deviation from an existing 160-element model. It is preliminarily concluded that the proposed scheme is relatively efficient in performing quick verification for test data obtained from the on-site vibration measurement using the microwave interferometer.
Frequency-domain correction of sensor dynamic error for step response.
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.
Frequency-domain correction of sensor dynamic error for step response
NASA Astrophysics Data System (ADS)
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.
A 10-Gbps × 12-Channel Pluggable Parallel Optical Transceiver Based on CXP Interface Specifications
NASA Astrophysics Data System (ADS)
Yang, Kun; Li, Zhihua; Li, Baoxia; Gao, Wei; Liu, Fengman; Song, Jian; Wan, Lixi
2012-06-01
A novel 10-Gbps × 12-channel pluggable parallel optical transceiver is designed and fabricated. Compared with other optical transceivers, this transceiver emphasizes small size, high-density, low power consumption, and high transmission speed. Most importantly, its optical coupling structure is simplified to promote cost-effective large-scale production. This transceiver is electrically pluggable and consists of transmitter and receiver modules linked by parallel multi-mode fibers. Each module consists of a six-layered high-speed, high-density printed circuit board, the size of which is 30 mm × 18 mm × 1 mm, packaged with optoelectronic devices and corresponding control chips. The printed circuit boards not only provide a high-speed electrical connection between the I/O interfaces and high-speed chips, but they also supply power and ground planes to those chips. End-to-end error-free transmission at 10.3125 Gbps was obtained for a 231 - 1 non-return-to-zero pseudo-random bit sequence.
An FPGA-based High Speed Parallel Signal Processing System for Adaptive Optics Testbed
NASA Astrophysics Data System (ADS)
Kim, H.; Choi, Y.; Yang, Y.
In this paper a state-of-the-art FPGA (Field Programmable Gate Array) based high speed parallel signal processing system (SPS) for adaptive optics (AO) testbed with 1 kHz wavefront error (WFE) correction frequency is reported. The AO system consists of Shack-Hartmann sensor (SHS) and deformable mirror (DM), tip-tilt sensor (TTS), tip-tilt mirror (TTM) and an FPGA-based high performance SPS to correct wavefront aberrations. The SHS is composed of 400 subapertures and the DM 277 actuators with Fried geometry, requiring high speed parallel computing capability SPS. In this study, the target WFE correction speed is 1 kHz; therefore, it requires massive parallel computing capabilities as well as strict hard real time constraints on measurements from sensors, matrix computation latency for correction algorithms, and output of control signals for actuators. In order to meet them, an FPGA based real-time SPS with parallel computing capabilities is proposed. In particular, the SPS is made up of a National Instrument's (NI's) real time computer and five FPGA boards based on state-of-the-art Xilinx Kintex 7 FPGA. Programming is done with NI's LabView environment, providing flexibility when applying different algorithms for WFE correction. It also facilitates faster programming and debugging environment as compared to conventional ones. One of the five FPGA's is assigned to measure TTS and calculate control signals for TTM, while the rest four are used to receive SHS signal, calculate slops for each subaperture and correction signal for DM. With this parallel processing capabilities of the SPS the overall closed-loop WFE correction speed of 1 kHz has been achieved. System requirements, architecture and implementation issues are described; furthermore, experimental results are also given.
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.
NASA Astrophysics Data System (ADS)
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 ˜5% (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.
Saager, Rolf B.; Balu, Mihaela; Crosignani, Viera; Sharif, Ata; Durkin, Anthony J.; Kelly, Kristen M.; Tromberg, Bruce J.
2015-01-01
Abstract. 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 ∼5% (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. PMID:26065839
Rice, Tyler B.; Kwan, Elliott; Hayakawa, Carole K.; Durkin, Anthony J.; Choi, Bernard; Tromberg, Bruce J.
2013-01-01
Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown impact from several variables that affect speckle contrast. These variables may include optical absorption and scattering coefficients, multi-layer dynamics including static, non-ergodic regions, and systematic effects such as laser coherence length. In order to account for these effects and move toward quantitative, depth-resolved LSI, we have developed a method that combines Monte Carlo modeling, multi-exposure speckle imaging (MESI), spatial frequency domain imaging (SFDI), and careful instrument calibration. Monte Carlo models were used to generate total and layer-specific fractional momentum transfer distributions. This information was used to predict speckle contrast as a function of exposure time, spatial frequency, layer thickness, and layer dynamics. To verify with experimental data, controlled phantom experiments with characteristic tissue optical properties were performed using a structured light speckle imaging system. Three main geometries were explored: 1) diffusive dynamic layer beneath a static layer, 2) static layer beneath a diffuse dynamic layer, and 3) directed flow (tube) submerged in a dynamic scattering layer. Data fits were performed using the Monte Carlo model, which accurately reconstructed the type of particle flow (diffusive or directed) in each layer, the layer thickness, and absolute flow speeds to within 15% or better. PMID:24409388
Hielscher, Andreas H; Bartel, Sebastian
2004-02-01
Optical tomography (OT) is a fast developing novel imaging modality that uses near-infrared (NIR) light to obtain cross-sectional views of optical properties inside the human body. A major challenge remains the time-consuming, computational-intensive image reconstruction problem that converts NIR transmission measurements into cross-sectional images. To increase the speed of iterative image reconstruction schemes that are commonly applied for OT, we have developed and implemented several parallel algorithms on a cluster of workstations. Static process distribution as well as dynamic load balancing schemes suitable for heterogeneous clusters and varying machine performances are introduced and tested. The resulting algorithms are shown to accelerate the reconstruction process to various degrees, substantially reducing the computation times for clinically relevant problems.
Parallel distributed free-space optoelectronic computer engine using flat plug-on-top optics package
NASA Astrophysics Data System (ADS)
Berger, Christoph; Ekman, Jeremy T.; Wang, Xiaoqing; Marchand, Philippe J.; Spaanenburg, Henk; Kiamilev, Fouad E.; Esener, Sadik C.
2000-05-01
We report about ongoing work on a free-space optical interconnect system, which will demonstrate a Fast Fourier Transformation calculation, distributed among six processor chips. Logically, the processors are arranged in two linear chains, where each element communicates optically with its nearest neighbors. Physically, the setup consists of a large motherboard, several multi-chip carrier modules, which hold the processor/driver chips and the optoelectronic chips (arrays of lasers and detectors), and several plug-on-top optics modules, which provide the optical links between the chip carrier modules. The system design tries to satisfy numerous constraints, such as compact size, potential for mass-production, suitability for large arrays (up to 1024 parallel channels), compatibility with standard electronics fabrication and packaging technology, potential for active misalignment compensation by integration MEMS technology, and suitability for testing different imaging topologies. We present the system architecture together with details of key components and modules, and report on first experiences with prototype modules of the setup.
Simulation of optical devices using parallel finite-difference time-domain method
NASA Astrophysics Data System (ADS)
Li, Kang; Kong, Fanmin; Mei, Liangmo; Liu, Xin
2005-11-01
This paper presents a new parallel finite-difference time-domain (FDTD) numerical method in a low-cost network environment to stimulate optical waveguide characteristics. The PC motherboard based cluster is used, as it is relatively low-cost, reliable and has high computing performance. Four clusters are networked by fast Ethernet technology. Due to the simplicity nature of FDTD algorithm, a native Ethernet packet communication mechanism is used to reduce the overhead of the communication between the adjacent clusters. To validate the method, a microcavity ring resonator based on semiconductor waveguides is chosen as an instance of FDTD parallel computation. Speed-up rate under different division density is calculated. From the result we can conclude that when the decomposing size reaches a certain point, a good parallel computing speed up will be maintained. This simulation shows that through the overlapping of computation and communication method and controlling the decomposing size, the overhead of the communication of the shared data will be conquered. The result indicates that the implementation can achieve significant speed up for the FDTD algorithm. This will enable us to tackle the larger real electromagnetic problem by the low-cost PC clusters.
NASA Astrophysics Data System (ADS)
Chen, Zhiyan; Zhao, Chen; Shen, Yi; Li, Peng; Wang, Xiaoping; Ding, Zhihua
2015-04-01
Aiming at the requirements of real-time inspection in material industry, an ultrawide-field parallel SD-OCT system capable of visualizing cross-sectional image of internal structures by a single shot of a 2-D CMOS camera is developed. To achieve ultrawide-field parallel detection, one meniscus lens with negative dioptric is introduced as an additional relay lens and imaging optics including sample arm, relay lenses and spectrometer are optimized as a whole for desirable imaging quality. The developed system has an ultrawide-field of 35 mm and an axial range of 8 mm in air. The maximum on-axis sensitivity and the axial resolution are experimentally determined to be 65 dB and 17.7 μm, respectively. The on-axis lateral resolution is measured to be 44 μm in parallel direction and 22 μm in scanning direction. The system is applied to obtain 3-D volume images of a set of glass-samples covering an area of about 28 mm by 15 mm with thicknesses ranging between 2.1 mm and 4 mm, from which defects such as solid inclusion, micro-deformation and bubble are identified either on the surfaces or inside the samples.
NASA Astrophysics Data System (ADS)
Sylwestrzak, Marcin; Szlag, Daniel; Szkulmowski, Maciej; Targowski, Piotr
2011-06-01
In this contribution we describe a specialised data processing system for Spectral Optical Coherence Tomography (SOCT) biomedical imaging which utilises massively parallel data processing on a low-cost, Graphics Processing Unit (GPU). One of the most significant limitations of SOCT is the data processing time on the main processor of the computer (CPU), which is generally longer than the data acquisition. Therefore, real-time imaging with acceptable quality is limited to a small number of tomogram lines (A-scans). Recent progress in graphics cards technology gives a promising solution of this problem. The newest graphics processing units allow not only for a very high speed three dimensional (3D) rendering, but also for a general purpose parallel numerical calculations with efficiency higher than provided by the CPU. The presented system utilizes CUDATM graphic card and allows for a very effective real time SOCT imaging. The total imaging speed for 2D data consisting of 1200 A-scans is higher than refresh rate of a 120 Hz monitor. 3D rendering of the volume data build of 10 000 A-scans is performed with frame rate of about 9 frames per second. These frame rates include data transfer from a frame grabber to GPU, data processing and 3D rendering to the screen. The software description includes data flow, parallel processing and organization of threads. For illustration we show real time high resolution SOCT imaging of human skin and eye.
NASA Technical Reports Server (NTRS)
Golomidov, Y. V.; Li, S. K.; Popov, S. A.; Smolov, V. B.
1986-01-01
After a classification and analysis of electronic and optoelectronic switching devices, the design principles and structure of a matrix optical switch is described. The switching and pair-exclusion operations in this type of switch are examined, and a method for the optical switching of communication channels is elaborated. Finally, attention is given to the structural organization of a parallel computer system with a matrix optical switch.
Frequency-Domain Analysis of Intrinsic Neuronal Properties using High-Resistant Electrodes.
Rössert, Christian; Straka, Hans; Glasauer, Stefan; Moore, Lee E
2009-01-01
Intrinsic cellular properties of neurons in culture or slices are usually studied by the whole cell clamp method using low-resistant patch pipettes. These electrodes allow detailed analyses with standard electrophysiological methods such as current- or voltage-clamp. However, in these preparations large parts of the network and dendritic structures may be removed, thus preventing an adequate study of synaptic signal processing. Therefore, intact in vivo preparations or isolated in vitro whole brains have been used in which intracellular recordings are usually made with sharp, high-resistant electrodes to optimize the impalement of neurons. The general non-linear resistance properties of these electrodes, however, severely limit accurate quantitative studies of membrane dynamics especially needed for precise modelling. Therefore, we have developed a frequency-domain analysis of membrane properties that uses a Piece-wise Non-linear Electrode Compensation (PNEC) method. The technique was tested in second-order vestibular neurons and abducens motoneurons of isolated frog whole brain preparations using sharp potassium chloride- or potassium acetate-filled electrodes. All recordings were performed without online electrode compensation. The properties of each electrode were determined separately after the neuronal recordings and were used in the frequency-domain analysis of the combined measurement of electrode and cell. This allowed detailed analysis of membrane properties in the frequency-domain with high-resistant electrodes and provided quantitative data that can be further used to model channel kinetics. Thus, sharp electrodes can be used for the characterization of intrinsic properties and synaptic inputs of neurons in intact brains. PMID:20582288
Water content evaluation in unsaturated soil using GPR signal analysis in the frequency domain
NASA Astrophysics Data System (ADS)
Benedetto, Andrea
2010-05-01
The evaluation of the water content of unsaturated soil is important for many applications, such as environmental engineering, agriculture and soil science. This study is applied to pavement engineering, but the proposed approach can be utilized in other applications as well. There are various techniques currently available which measure the soil moisture content and some of these techniques are non-intrusive. Herein, a new methodology is proposed that avoids several disadvantages of existing techniques. In this study, ground-coupled Ground Penetrating Radar (GPR) techniques are used to non-destructively monitor the volumetric water content. The signal is processed in the frequency domain; this method is based on Rayleigh scattering according to the Fresnel theory. The scattering produces a non-linear frequency modulation of the electromagnetic signal, where the modulation is a function of the water content. To test the proposed method, five different types of soil were wetted in laboratory under controlled conditions and the samples were analyzed using GPR. The GPR data were processed in the frequency domain, demonstrating a correlation between the shift of the frequency spectrum of the radar signal and the moisture content. The techniques also demonstrate the potential for detecting clay content in soils. This frequency domain approach gives an innovative method that can be applied for an accurate and non-invasive estimation of the water content of soils - particularly, in sub-asphalt aggregate layers - and assessing the bearing capacity and efficacy of the pavement drainage layers. The main benefit of this method is that no preventive calibration is needed.
Measuring frequency domain granger causality for multiple blocks of interacting time series.
Faes, Luca; Nollo, Giandomenico
2013-04-01
In the past years, several frequency-domain causality measures based on vector autoregressive time series modeling have been suggested to assess directional connectivity in neural systems. The most followed approaches are based on representing the considered set of multiple time series as a realization of two or three vector-valued processes, yielding the so-called Geweke linear feedback measures, or as a realization of multiple scalar-valued processes, yielding popular measures like the directed coherence (DC) and the partial DC (PDC). In the present study, these two approaches are unified and generalized by proposing novel frequency-domain causality measures which extend the existing measures to the analysis of multiple blocks of time series. Specifically, the block DC (bDC) and block PDC (bPDC) extend DC and PDC to vector-valued processes, while their logarithmic counterparts, denoted as multivariate total feedback [Formula: see text] and direct feedback [Formula: see text], represent into a full multivariate framework the Geweke's measures. Theoretical analysis of the proposed measures shows that they: (i) possess desirable properties of causality measures; (ii) are able to reflect either direct causality (bPDC, [Formula: see text] or total (direct + indirect) causality (bDC, [Formula: see text] between time series blocks; (iii) reduce to the DC and PDC measures for scalar-valued processes, and to the Geweke's measures for pairs of processes; (iv) are able to capture internal dependencies between the scalar constituents of the analyzed vector processes. Numerical analysis showed that the proposed measures can be efficiently estimated from short time series, allow to represent in an objective, compact way the information derived from the causal analysis of several pairs of time series, and may detect frequency domain causality more accurately than existing measures. The proposed measures find their natural application in the evaluation of directional
Measuring frequency domain granger causality for multiple blocks of interacting time series.
Faes, Luca; Nollo, Giandomenico
2013-04-01
In the past years, several frequency-domain causality measures based on vector autoregressive time series modeling have been suggested to assess directional connectivity in neural systems. The most followed approaches are based on representing the considered set of multiple time series as a realization of two or three vector-valued processes, yielding the so-called Geweke linear feedback measures, or as a realization of multiple scalar-valued processes, yielding popular measures like the directed coherence (DC) and the partial DC (PDC). In the present study, these two approaches are unified and generalized by proposing novel frequency-domain causality measures which extend the existing measures to the analysis of multiple blocks of time series. Specifically, the block DC (bDC) and block PDC (bPDC) extend DC and PDC to vector-valued processes, while their logarithmic counterparts, denoted as multivariate total feedback [Formula: see text] and direct feedback [Formula: see text], represent into a full multivariate framework the Geweke's measures. Theoretical analysis of the proposed measures shows that they: (i) possess desirable properties of causality measures; (ii) are able to reflect either direct causality (bPDC, [Formula: see text] or total (direct + indirect) causality (bDC, [Formula: see text] between time series blocks; (iii) reduce to the DC and PDC measures for scalar-valued processes, and to the Geweke's measures for pairs of processes; (iv) are able to capture internal dependencies between the scalar constituents of the analyzed vector processes. Numerical analysis showed that the proposed measures can be efficiently estimated from short time series, allow to represent in an objective, compact way the information derived from the causal analysis of several pairs of time series, and may detect frequency domain causality more accurately than existing measures. The proposed measures find their natural application in the evaluation of directional
Kim, Sang-Yoon; Lim, Woochang
2015-08-01
We are interested in characterization of synchronization transitions of bursting neurons in the frequency domain. Instantaneous population firing rate (IPFR) [Formula: see text], which is directly obtained from the raster plot of neural spikes, is often used as a realistic collective quantity describing population activities in both the computational and the experimental neuroscience. For the case of spiking neurons, a realistic time-domain order parameter, based on [Formula: see text], was introduced in our recent work to characterize the spike synchronization transition. Unlike the case of spiking neurons, the IPFR [Formula: see text] of bursting neurons exhibits population behaviors with both the slow bursting and the fast spiking timescales. For our aim, we decompose the IPFR [Formula: see text] into the instantaneous population bursting rate [Formula: see text] (describing the bursting behavior) and the instantaneous population spike rate [Formula: see text] (describing the spiking behavior) via frequency filtering, and extend the realistic order parameter to the case of bursting neurons. Thus, we develop the frequency-domain bursting and spiking order parameters which are just the bursting and spiking "coherence factors" [Formula: see text] and [Formula: see text] of the bursting and spiking peaks in the power spectral densities of [Formula: see text] and [Formula: see text] (i.e., "signal to noise" ratio of the spectral peak height and its relative width). Through calculation of [Formula: see text] and [Formula: see text], we obtain the bursting and spiking thresholds beyond which the burst and spike synchronizations break up, respectively. Consequently, it is shown in explicit examples that the frequency-domain bursting and spiking order parameters may be usefully used for characterization of the bursting and the spiking transitions, respectively.
Dynamic analysis of offshore structures with non-zero initial conditions in the frequency domain
NASA Astrophysics Data System (ADS)
Liu, Fushun; Lu, Hongchao; Li, Huajun
2016-03-01
The state of non-zero conditions is typically treated as fact when considering the dynamic analysis of offshore structures. This article extends a newly proposed method [1] to manage the non-zero initial conditions of offshore structures in the frequency domain, including new studies on original environmental loads reconstruction, response comparisons with the commercial software ANSYS, and a demonstration using an experimental cantilever beam. The original environmental loads, such as waves, currents, and winds, that act on a structure are decomposed into multiple complex exponential components are represented by a series of poles and corresponding residues. Counter to the traditional frequency-domain method, the non-zero initial conditions of offshore structures could be solved in the frequency domain. Compared with reference [1], an improvement reported in this article is that practical issues, including the choice of model order and central-processing-unit (CPU) time consumption, are further studied when applying this new method to offshore structures. To investigate the feasibility of the representation of initial environmental loads by their poles and corresponding residues, a measured random wave force collected from a column experiment at the Lab of Ocean University of China is used, decomposed, reconstructed and then compared with the original wave force; then, a numerical offshore platform is used to study the performance of the proposed method in detail. The numerical results of this study indicate that (1) a short duration of environmental loads are required to obtain their constitutive poles and residues, which implies good computational efficiency; and (2) the proposed method has a similar computational efficiency to traditional methods due to the use of the inverse Fourier transform technique. To better understand the performance, of time consumption and accuracy of the proposed method, the commercial software ANSYS is used to determine responses
Feng, Xiaobing
1996-12-31
A non-overlapping domain decomposition iterative method is proposed and analyzed for mixed finite element methods for a sequence of noncoercive elliptic systems with radiation boundary conditions. These differential systems describe the motion of a nearly elastic solid in the frequency domain. The convergence of the iterative procedure is demonstrated and the rate of convergence is derived for the case when the domain is decomposed into subdomains in which each subdomain consists of an individual element associated with the mixed finite elements. The hybridization of mixed finite element methods plays a important role in the construction of the discrete procedure.
NASA Astrophysics Data System (ADS)
Damour, Thibault; Nagar, Alessandro; Trias, Miquel
2011-01-01
The coalescences of binary black hole systems, here taken to be nonspinning, are among the most promising sources for gravitational wave (GW) ground-based detectors, such as LIGO and Virgo. To detect the GW signals emitted by binary black holes and measure the parameters of the source, one needs to have in hand a bank of GW templates that are both effectual (for detection) and accurate (for measurement). We study the effectualness and the accuracy of the two types of parametrized banks of templates that are directly defined in the frequency domain by means of closed-form expressions, namely, “post-Newtonian” (PN) and “phenomenological” models. In the absence of knowledge of the (continuous family of) exact waveforms, our study assumes as fiducial, target waveforms the ones generated by the most accurate version of the effective-one-body formalism, calibrated upon a few high-accuracy numerical-relativity (NR) waveforms. We find that, for initial GW detectors the use, at each point of parameter space, of the best closed-form template (among PN and phenomenological models) leads to an effectualness >97% over the entire mass range and >99% in an important fraction of parameter space; however, when considering advanced detectors, both of the closed-form frequency-domain models fail to be effectual enough in significant domains of the two-dimensional [total mass and mass ratio] parameter space. Moreover, we find that, for both initial and advanced detectors, the two closed-form frequency-domain models fail to satisfy the minimal required accuracy standard in a very large domain of the two-dimensional parameter space. In addition, a side result of our study is the determination, as a function of the mass ratio, of the maximum frequency at which a frequency-domain PN waveform can be “joined” onto a NR-calibrated effective-one-body waveform without undue loss of accuracy. In the case of mass ratios larger than 4∶1 this maximum frequency occurs well before the
On the implementation of a real-time information security architecture in frequency domain
NASA Astrophysics Data System (ADS)
Basu, Abhishek; Sarkar, Souvik; Sarkar, Subir Kumar
2015-12-01
This paper presents the real-time implementation of a watermarking-based information security architecture in frequency domain. The scheme emphasises on the human visual system (HVS)-supported watermarking approach using wavelet-lifting technique. In addition to HVS, image registration algorithm is also introduced in order to increase the resiliency as well as the security of the estimated recovered watermark image. The algorithmic steps with optimisation considerations about the real-time implementation on TMS320CDSK6416/6713 fixed/floating point digital signal processor are also projected.
Time domain and frequency domain design techniques for model reference adaptive control systems
NASA Technical Reports Server (NTRS)
Boland, J. S., III
1971-01-01
Some problems associated with the design of model-reference adaptive control systems are considered and solutions to these problems are advanced. The stability of the adapted system is a primary consideration in the development of both the time-domain and the frequency-domain design techniques. Consequentially, the use of Liapunov's direct method forms an integral part of the derivation of the design procedures. The application of sensitivity coefficients to the design of model-reference adaptive control systems is considered. An application of the design techniques is also presented.
Automated on-orbit frequency domain identification for large space structures
NASA Technical Reports Server (NTRS)
Bayard, D. S.; Hadaegh, F. Y.; Yam, Y.; Scheid, R. E.; Mettler, E.; Milman, M. H.
1991-01-01
Recent experiences in the field of flexible structure control in space have indicated a need for on-orbit system identification to support robust control redesign to avoid in-flight instabilities and maintain high spacecraft performance. This paper highlights an automated frequency domain system identification methodology recently developed to fulfill this need. The methodology is focused to support (1) the estimation of system quantities useful for robust control analysis and design; (2) experiment design tailored to performing system identification in a typically constrained on-orbit environment; and (3) the automation of operations to reduce 'human in the loop' requirements.
Dynamic frequency-domain interferometer for absolute distance measurements with high resolution
Weng, Jidong; Liu, Shenggang; Ma, Heli; Tao, Tianjiong; Wang, Xiang; Liu, Cangli; Tan, Hua
2014-11-15
A unique dynamic frequency-domain interferometer for absolute distance measurement has been developed recently. This paper presents the working principle of the new interferometric system, which uses a photonic crystal fiber to transmit the wide-spectrum light beams and a high-speed streak camera or frame camera to record the interference stripes. Preliminary measurements of harmonic vibrations of a speaker, driven by a radio, and the changes in the tip clearance of a rotating gear wheel show that this new type of interferometer has the ability to perform absolute distance measurements both with high time- and distance-resolution.
Aero-acoustics source separation with sparsity inducing priors in the frequency domain
NASA Astrophysics Data System (ADS)
Schwander, Olivier; Picheral, José; Gac, Nicolas; Mohammad-Djafari, Ali; Blacodon, Daniel
2015-01-01
The characterization of acoustic sources is of great interest in many industrial applications, in particular for the aeronautic or automotive industry for the development of new products. While localization of sources using observations from a wind tunnel is a well-known subject, the characterization and separation of the sources still needs to be explored. We present here a Bayesian approach for sources separation. Two prior modeling of the sources are considered: a sparsity inducing prior in the frequency domain and an autoregressive model in the time domain. The proposed methods are evaluated on synthetic data simulating noise sources emitting from an airfoil inside a wind tunnel.
NASA Astrophysics Data System (ADS)
André, Frédéric; Lambot, Sébastien
2015-04-01
Accurate knowledge of the shallow soil properties is of prime importance in agricultural, hydrological and environmental engineering. During the last decade, numerous geophysical techniques, either invasive or resorting to proximal or remote sensing, have been developed and applied for quantitative characterization of soil properties. Amongst them, time domain reflectrometry (TDR) and frequency domain reflectometry (FDR) are recognized as standard techniques for the determination of soil dielectric permittivity and electrical conductivity, based on the reflected electromagnetic waves from a probe inserted into the soil. TDR data were first commonly analyzed in the time domain using methods considering only a part of the waveform information. Later, advancements have led to the possibility of analyzing the TDR signal through full-wave inverse modeling either in the time or the frequency domains. A major advantage of FDR compared to TDR is the possibility to increase the bandwidth, thereby increasing the information content of the data and providing more detailed characterization of the medium. Amongst the recent works in this field, Minet et al. (2010) developed a modeling procedure for processing FDR data based on an exact solution of Maxwell's equations for wave propagation in one-dimensional multilayered media. In this approach, the probe head is decoupled from the medium and is fully described by characteristic transfer functions. The authors successfully validated the method for homogeneous sand subject to a range of water contents. In the present study, we further validated the modelling approach using reference liquids with well-characterized frequency-dependent electrical properties. In addition, the FDR model was coupled with a dielectric mixing model to investigate the ability of retrieving water content, pore water electrical conductivity and sand porosity from inversion of FDR data acquired in sand subject to different water content levels. Finally, the
Time-resolved experiments in the frequency domain using synchrotron radiation (invited)
NASA Astrophysics Data System (ADS)
De Stasio, Gelsomina; Giusti, A. M.; Parasassi, T.; Ravagnan, G.; Sapora, O.
1992-01-01
PLASTIQUE is the only synchrotron radiation beam line in the world that performs time-resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and the dynamics of molecules. This technique measures fluorescence lifetimes with picosecond resolution in the near UV spectral range. Such accurate measurements are rendered possible by taking phase and modulation data, and by the advantages of the cross-correlation technique. A successful experiment demonstrated the radiation damage induced by low doses of radiation on rabbit blood cell membranes.
Time and Frequency-Domain Cross-Verification of SLS 6DOF Trajectory Simulations
NASA Technical Reports Server (NTRS)
VanZwieten, Tannen; Johnson, Matthew D.; McCullough, John P.; Gilligan, Eric T.
2014-01-01
The SLS GNC team and its partners have developed several time- and frequency-based simulations for development and analysis of the proposed SLS launch vehicle. The simulations differ in fidelity and some have unique functionality that allows them to perform specific analyses. Some examples of the purposes of the various models are: trajectory simulation, multi-body separation, Monte Carlo, hardware in the loop, loads, and frequency domain stability analyses. While no two simulations are identical, many of the models are essentially six degree-of-freedom (6DOF) representations of the SLS plant dynamics, hardware implementation, and flight software. Thus at a high level all of those models should be in agreement. Comparison of outputs from several SLS trajectory and stability analysis tools are ongoing as part of the program's current verification effort. The purpose of these comparisons is to highlight modeling and analysis differences, verify simulation data sources, identify inconsistencies and minor errors, and ultimately to verify output data as being a good representation of the vehicle and subsystem dynamics. This paper will show selected verification work in both the time and frequency domain from the current design analysis cycle of the SLS for several of the design and analysis simulations. In the time domain, the tools that will be compared are MAVERIC, CLVTOPS, SAVANT, STARS, ARTEMIS, and POST 2. For the frequency domain analysis, the tools to be compared are FRACTAL, SAVANT, and STARS. The paper will include discussion of these tools including their capabilities, configurations, and the uses to which they are put in the SLS program. Determination of the criteria by which the simulations are compared (matching criteria) requires thoughtful consideration, and there are several pitfalls that may occur that can severely punish a simulation if not considered carefully. The paper will discuss these considerations and will present a framework for responding to
Identification of XV-15 aeroelastic modes using frequency-domain methods
NASA Technical Reports Server (NTRS)
Acree, Cecil W., Jr.; Tischler, Mark B.
1989-01-01
The XV-15 Tilt-Rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier transformed) with cross spectral and transfer function methods. Modal frequencies and damping were determined by performing curve fits to transfer function magnitude and phase data and to cross spectral magnitude data. Results are given for the XV-15 with its original metal rotor blades. Frequency and damping values are also compared with earlier predictions.
Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments.
Benuzzi-Mounaix, A; Koenig, M; Boudenne, J M; Hall, T A; Batani, D; Scianitti, F; Masini, A; Di Santo, D
1999-09-01
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target approximately 5 x 10(13) W/cm(2) to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps. PMID:11970183
Chirped pulse reflectivity and frequency domain interferometry in laser driven shock experiments
NASA Astrophysics Data System (ADS)
Benuzzi-Mounaix, A.; Koenig, M.; Boudenne, J. M.; Hall, T. A.; Batani, D.; Scianitti, F.; Masini, A.; di Santo, D.
1999-09-01
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target ~5×1013 W/cm2 to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps.
Chládek, J; Brázdil, M; Halámek, J; Plešinger, F; Jurák, P
2013-01-01
We present an off-line analysis procedure for exploring brain activity recorded from intra-cerebral electroencephalographic data (SEEG). The objective is to determine the statistical differences between different types of stimulations in the time-frequency domain. The procedure is based on computing relative signal power change and subsequent statistical analysis. An example of characteristic statistically significant event-related de/synchronization (ERD/ERS) detected across different frequency bands following different oddball stimuli is presented. The method is used for off-line functional classification of different brain areas. PMID:24109865
Frequency domain synthesis of optimal inputs for adaptive identification and control
NASA Technical Reports Server (NTRS)
Fu, Li-Chen; Sastry, Shankar
1987-01-01
The input design problem of selecting appropriate inputs for use in SISO adaptive identification and model reference adaptive control algorithms is considered. Averaging theory is used to characterize the optimal inputs in the frequency domain. The design problem is formulated as an optimization problem which maximizes the smallest eigenvalue of the average information matrix over power constrained signals, and the global optimal solution is obtained using a convergent numerical algorithm. A bound on the frequency search range required in the design algorithm has been determined in terms of the desired performance.
Tromberg, Bruce J.; Berger, Andrew J.; Cerussi, Albert E.; Bevilacqua, Frederic; Jakubowski, Dorota
2008-09-23
A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain and steady-state reflectance methods. Most of the wavelength coverage is provided by a white-light steady-state measurement, whereas the frequency-domain data are acquired at a few selected wavelengths. Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest. The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values.
NASA Technical Reports Server (NTRS)
Sreenivas, Kidambi; Whitfield, David L.
1995-01-01
Two linearized solvers (time and frequency domain) based on a high resolution numerical scheme are presented. The basic approach is to linearize the flux vector by expressing it as a sum of a mean and a perturbation. This allows the governing equations to be maintained in conservation law form. A key difference between the time and frequency domain computations is that the frequency domain computations require only one grid block irrespective of the interblade phase angle for which the flow is being computed. As a result of this and due to the fact that the governing equations for this case are steady, frequency domain computations are substantially faster than the corresponding time domain computations. The linearized equations are used to compute flows in turbomachinery blade rows (cascades) arising due to blade vibrations. Numerical solutions are compared to linear theory (where available) and to numerical solutions of the nonlinear Euler equations.
Lin, Zhuchong; Liu, Kun; Zhang, Li; Zeng, Delin
2016-09-01
Maglev dual-stage inertially stabilization (MDIS) system is a newly proposed system which combines a conventional two-axis gimbal assembly and a 5-DOF (degree of freedom) magnetic bearing with vernier tilting capacity to perform dual-stage stabilization for the LOS of the suspended optical instrument. Compared with traditional dual-stage system, maglev dual-stage system exhibits different characteristics due to the negative position stiffness of the magnetic forces, which introduces additional coupling in the dual stage control system. In this paper, the coupling effect on the system performance is addressed based on frequency-domain analysis, including disturbance rejection, fine stage saturation and coarse stage structural resonance suppression. The difference between various control strategies is also discussed, including pile-up(PU), stabilize-follow (SF) and stabilize-compensate (SC). A number of principles for the design of a maglev dual stage system are proposed. A general process is also suggested, which leads to a cost-effective design striking a balance between high performance and complexity. At last, a simulation example is presented to illustrate the arguments in the paper.
Wave-Propagation Modeling and Inversion Using Frequency-Domain Integral Equation Methods
NASA Astrophysics Data System (ADS)
Strickland, Christopher E.
Full waveform inverse methods describe the full physics of wave propagation and can potentially overcome the limitations of ray theoretic methods. This work explores the use of integral equation based methods for simulation and inversion and illustrates their potential for computationally demanding problems. A frequency-domain integral equation approach to simulate wave-propagation in heterogeneous media and solve the inverse wave-scattering problem will be presented for elastic, acoustic, and electromagnetic systems. The method will be illustrated for georadar (ground- or ice-penetrating radar) applications and compared to results obtained using ray theoretic methods. In order to tackle the non-linearity of the problem, the inversion incorporates a broad range of frequencies to stabilize the solution. As with most non-linear inversion methods, a starting model that reasonably approximates the true model is critical to convergence of the algorithm. To improve the starting model, a variable reference inversion technique is developed that allows the background reference medium to vary for each source-receiver data pair and is less restrictive than using a single reference medium for the entire dataset. The reference medium can be assumed homogeneous (although different for each data point) to provide a computationally efficient, single-step, frequency-domain inversion approach that incorporates finite frequency effects not captured by ray based methods. The inversion can then be iterated on to further refine the solution.
Frequency domain holography of laser wakefield accelerators in the nonlinear bubble regime
NASA Astrophysics Data System (ADS)
Yi, S. A.; Kalmykov, S.; Dong, P.; Reed, S. A.; Downer, M.; Shvets, G.
2009-11-01
We present the theoretical basis of frequency domain holography (FDH), a technique for single-shot visualization of laser driven plasma wakes. In FDH, the nonlinear index modulations of the plasma wake are recorded as phase shifts in a co-propagating probe pulse, and interference with a reference allows for the reconstruction of the wake structure. Earlier experimental work [N. H. Matlis et al., Nature Phys. 2, 749 (2006)] has shown that reconstruction of the probe phase is sufficient for imaging weakly nonlinear periodic wakes. In the highly nonlinear regime, the laser ponderomotive force blows out plasma electrons and forms a density ``bubble'' that strongly focuses the probe light. We show that imaging the bubble requires full (amplitude and phase) reconstruction of the probe pulse, and find reconstructions of simulated frequency domain holograms in full agreement with direct PIC modeling of the probe pulse. We also assess the sensitivity of the technique to the spectral bandwidth of the probe and reference pulses. In combination with ray-tracing techniques which help evaluate the localized frequency up- and down-shifts of the probe light (``photon acceleration''), FDH appears to be a unique tool for visualization of plasma wakes. This work is supported by the US DOE grants DE-FG02-04ER41321 and DE-FG02-07ER54945.
Comparison of frequency-domain and time-domain rotorcraft vibration control methods
NASA Technical Reports Server (NTRS)
Gupta, N. K.
1984-01-01
Active control of rotor-induced vibration in rotorcraft has received significant attention recently. Two classes of techniques have been proposed. The more developed approach works with harmonic analysis of measured time histories and is called the frequency-domain approach. The more recent approach computes the control input directly using the measured time history data and is called the time-domain approach. The report summarizes the results of a theoretical investigation to compare the two approaches. Five specific areas were addressed: (1) techniques to derive models needed for control design (system identification methods), (2) robustness with respect to errors, (3) transient response, (4) susceptibility to noise, and (5) implementation difficulties. The system identification methods are more difficult for the time-domain models. The time-domain approach is more robust (e.g., has higher gain and phase margins) than the frequency-domain approach. It might thus be possible to avoid doing real-time system identification in the time-domain approach by storing models at a number of flight conditions. The most significant error source is the variation in open-loop vibrations caused by pilot inputs, maneuvers or gusts. The implementation requirements are similar except that the time-domain approach can be much simpler to implement if real-time system identification were not necessary.
A Unified Frequency Domain Model to Study the Effect of Demyelination on Axonal Conduction.
Chaubey, Saurabh; Goodwin, Shikha J
2016-01-01
Multiple sclerosis is a disease caused by demyelination of nerve fibers. In order to determine the loss of signal with the percentage of demyelination, we need to develop models that can simulate this effect. Existing time-based models does not provide a method to determine the influences of demyelination based on simulation results. Our goal is to develop a system identification approach to generate a transfer function in the frequency domain. The idea is to create a unified modeling approach for neural action potential propagation along the length of an axon containing number of Nodes of Ranvier (N). A system identification approach has been used to identify a transfer function of the classical Hodgkin-Huxley equations for membrane voltage potential. Using this approach, we model cable properties and signal propagation along the length of the axon with N node myelination. MATLAB/Simulink platform is used to analyze an N node-myelinated neuronal axon. The ability to transfer function in the frequency domain will help reduce effort and will give a much more realistic feel when compared to the classical time-based approach. Once a transfer function is identified, the conduction as a cascade of each linear time invariant system-based transfer function can be modeled. Using this approach, future studies can model the loss of myelin in various parts of nervous system. PMID:27103847
A hybrid absorbing boundary condition for frequency-domain finite-difference modelling
NASA Astrophysics Data System (ADS)
Ren, Zhiming; Liu, Yang
2013-10-01
Liu and Sen (2010 Geophysics 75 A1-6 2012 Geophys. Prospect. 60 1114-32) proposed an efficient hybrid scheme to significantly absorb boundary reflections for acoustic and elastic wave modelling in the time domain. In this paper, we extend the hybrid absorbing boundary condition (ABC) into the frequency domain and develop specific strategies for regular-grid and staggered-grid modelling, respectively. Numerical modelling tests of acoustic, visco-acoustic, elastic and vertically transversely isotropic (VTI) equations show significant absorptions for frequency-domain modelling. The modelling results of the Marmousi model and the salt model also demonstrate the effectiveness of the hybrid ABC. For elastic modelling, the hybrid Higdon ABC and the hybrid Clayton and Engquist (CE) ABC are implemented, respectively. Numerical simulations show that the hybrid Higdon ABC gets better absorption than the hybrid CE ABC, especially for S-waves. We further compare the hybrid ABC with the classical perfectly matched layer (PML). Results show that the two ABCs cost the same computation time and memory space for the same absorption width. However, the hybrid ABC is more effective than the PML for the same small absorption width and the absorption effects of the two ABCs gradually become similar when the absorption width is increased.
NASA Astrophysics Data System (ADS)
Hanus, Robert; Zych, Marcin; Petryka, Leszek; Jaszczur, Marek; Hanus, Paweł
2016-03-01
Knowledge of the structure of a flow is really significant for the proper conduct a number of industrial processes. In this case a description of a two-phase flow regimes is possible by use of the time-series analysis e.g. in frequency domain. In this article the classical spectral analysis based on Fourier Transform (FT) and Short-Time Fourier Transform (STFT) were applied for analysis of signals obtained for water-air flow using gamma ray absorption. The presented method was illustrated by use data collected in experiments carried out on the laboratory hydraulic installation with a horizontal pipe of 4.5 m length and inner diameter of 30 mm equipped with two 241Am radioactive sources and scintillation probes with NaI(Tl) crystals. Stochastic signals obtained from detectors for plug, bubble, and transitional plug - bubble flows were considered in this work. The recorded raw signals were analyzed and several features in the frequency domain were extracted using autospectral density function (ADF), cross-spectral density function (CSDF), and the STFT spectrogram. In result of a detail analysis it was found that the most promising to recognize of the flow structure are: maximum value of the CSDF magnitude, sum of the CSDF magnitudes in the selected frequency range, and the maximum value of the sum of selected amplitudes of STFT spectrogram.
High-resolution wind profiling using combined spatial and frequency domain interferometry
NASA Astrophysics Data System (ADS)
Palmer, R. D.; Huang, X.; Fukao, S.; Yamamoto, M.; Nakamura, T.
1995-11-01
A novel approach to wind profiling is presented which is based on the hybrid use of spatial interferometry (SI) and frequency domain interferometry (FDI). Many algorithms exist that can be used to determine the wind field using SI. However, the imaging Doppler interferometry (IDI) technique is somewhat unique in that the wind field within the radar beam is angularly "imaged" using the Doppler sorting effect. The spatial locations of scatterers are determined by assuming a wind field across the beam and Fourier analyzing signals to sort Doppler velocities. Pulsed radar systems are limited in range resolution by the length of the transmitted pulse, and wind estimates are obtained for a discrete set of altitudes determined by sampling the continuous stream of signals. Frequency domain interferometry (FDI) can be used to determine the radial location of scattering layers within the resolution volume. Thus the combined use of FDI and IDI can provide the radial and angular location of particular scattering points. Using the Doppler sorting idea, a new wind profiling technique is presented which uses FDI to increase the altitude resolution of wind estimates obtained from IDI. Experimental data that illustrate the implementation of the algorithm are presented from the Middle and Upper (MU) Atmosphere radar.
Image blurring and deblurring using two biased photorefractive crystals in the frequency domain
NASA Astrophysics Data System (ADS)
Gan, Haiyong; Ma, Chong; Sun, Zhixu; Xu, Tao; Li, Jianwei; Xu, Nan; Wang, Jinjin; Song, Feng; Sheng, Chuanxiang; Sun, Ming; Li, Li
2014-11-01
In an imaging system based on a coherent source of moderate power density, images can be blurred when a biased photorefractive crystal is applied at the focal point of the imaging lens. In the frequency domain of the original images, the intensity patterns are diffracted through the photorefractive crystal with varied bias voltage. The high intensity region, which is usually the center or low frequency region of the intensity patterns, is more readily focused or defocused, resulting in blurred images in perception. Such blurred images could not be simply recovered by defocusing methods, which can only indistinguishably focus or defocus the whole intensity patterns. However, the blurred images may be deblurred to certain extent for recovery if a second photorefractive crystal with bias voltage is employed at the focal point of a tandem imaging system. The mechanism of deblurring is similar to that of blurring: the blurred images are transferred through the frequency domain again using an imaging lens, where the second biased photorefractive crystal diffracts the intensity patterns to revert the sensitive region where previously gets focused or defocused. In this work, theoretical analyses are presented in detail to explain the blurring-deblurring mechanism using two biased photorefractive crystals and compatible experimental results are obtained and illustrated. Considering the blurring and deblurring function subgroups of the experiment setup can be potentially developed into encryption and decryption units compatible with far field propagation, the technology presented herein may be promising to find applications in secure laser-based free-space communication systems.
Frequency-Domain Tomography for Single-shot, Ultrafast Imaging of Evolving Laser-Plasma Accelerators
NASA Astrophysics Data System (ADS)
Li, Zhengyan; Zgadzaj, Rafal; Wang, Xiaoming; Downer, Michael
2011-10-01
Intense laser pulses propagating through plasma create plasma wakefields that often evolve significantly, e.g. by expanding and contracting. However, such dynamics are known in detail only through intensive simulations. Laboratory visualization of evolving plasma wakes in the ``bubble'' regime is important for optimizing and scaling laser-plasma accelerators. Recently snap-shots of quasi-static wakes were recorded using frequency-domain holography (FDH). To visualize the wake's evolution, we have generalized FDH to frequency-domain tomography (FDT), which uses multiple probes propagating at different angles with respect to the pump pulse. Each probe records a phase streak, imprinting a partial record of the evolution of pump-created structures. We then topographically reconstruct the full evolution from all phase streaks. To prove the concept, a prototype experiment visualizing nonlinear index evolution in glass is demonstrated. Four probes propagating at 0, 0.6, 2, 14 degrees to the index ``bubble'' are angularly and temporally multiplexed to a single spectrometer to achieve cost-effective FDT. From these four phase streaks, an FDT algorithm analogous to conventional CT yields a single-shot movie of the pump's self-focusing dynamics.
NASA Technical Reports Server (NTRS)
Wu, Andy
1995-01-01
Allan Deviation computations of linear frequency synthesizer systems have been reported previously using real-time simulations. Even though it takes less time compared with the actual measurement, it is still very time consuming to compute the Allan Deviation for long sample times with the desired confidence level. Also noises, such as flicker phase noise and flicker frequency noise, can not be simulated precisely. The use of frequency domain techniques can overcome these drawbacks. In this paper the system error model of a fictitious linear frequency synthesizer is developed and its performance using a Cesium (Cs) atomic frequency standard (AFS) as a reference is evaluated using frequency domain techniques. For a linear timing system, the power spectral density at the system output can be computed with known system transfer functions and known power spectral densities from the input noise sources. The resulting power spectral density can then be used to compute the Allan Variance at the system output. Sensitivities of the Allan Variance at the system output to each of its independent input noises are obtained, and they are valuable for design trade-off and trouble-shooting.
Simultaneous storage of medical images in the spatial and frequency domain: A comparative study
Nayak, Jagadish; Bhat, P Subbanna; Acharya U, Rajendra; UC, Niranjan
2004-01-01
Background Digital watermarking is a technique of hiding specific identification data for copyright authentication. This technique is adapted here for interleaving patient information with medical images, to reduce storage and transmission overheads. Methods The patient information is encrypted before interleaving with images to ensure greater security. The bio-signals are compressed and subsequently interleaved with the image. This interleaving is carried out in the spatial domain and Frequency domain. The performance of interleaving in the spatial, Discrete Fourier Transform (DFT), Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT) coefficients is studied. Differential pulse code modulation (DPCM) is employed for data compression as well as encryption and results are tabulated for a specific example. Results It can be seen from results, the process does not affect the picture quality. This is attributed to the fact that the change in LSB of a pixel changes its brightness by 1 part in 256. Spatial and DFT domain interleaving gave very less %NRMSE as compared to DCT and DWT domain. Conclusion The Results show that spatial domain the interleaving, the %NRMSE was less than 0.25% for 8-bit encoded pixel intensity. Among the frequency domain interleaving methods, DFT was found to be very efficient. PMID:15180899
Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation
Jing, Yun; Tao, Molei; Clement, Greg T.
2011-01-01
A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green’s function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed. PMID:21302985
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.
Suspension parameter estimation in the frequency domain using a matrix inversion approach
NASA Astrophysics Data System (ADS)
Thite, A. N.; Banvidi, S.; Ibicek, T.; Bennett, L.
2011-12-01
The dynamic lumped parameter models used to optimise the ride and handling of a vehicle require base values of the suspension parameters. These parameters are generally experimentally identified. The accuracy of identified parameters can depend on the measurement noise and the validity of the model used. The existing publications on suspension parameter identification are generally based on the time domain and use a limited degree of freedom. Further, the data used are either from a simulated 'experiment' or from a laboratory test on an idealised quarter or a half-car model. In this paper, a method is developed in the frequency domain which effectively accounts for the measurement noise. Additional dynamic constraining equations are incorporated and the proposed formulation results in a matrix inversion approach. The nonlinearities in damping are estimated, however, using a time-domain approach. Full-scale 4-post rig test data of a vehicle are used. The variations in the results are discussed using the modal resonant behaviour. Further, a method is implemented to show how the results can be improved when the matrix inverted is ill-conditioned. The case study shows a good agreement between the estimates based on the proposed frequency-domain approach and measurable physical parameters.
A Unified Frequency Domain Model to Study the Effect of Demyelination on Axonal Conduction
Chaubey, Saurabh; Goodwin, Shikha J.
2016-01-01
Multiple sclerosis is a disease caused by demyelination of nerve fibers. In order to determine the loss of signal with the percentage of demyelination, we need to develop models that can simulate this effect. Existing time-based models does not provide a method to determine the influences of demyelination based on simulation results. Our goal is to develop a system identification approach to generate a transfer function in the frequency domain. The idea is to create a unified modeling approach for neural action potential propagation along the length of an axon containing number of Nodes of Ranvier (N). A system identification approach has been used to identify a transfer function of the classical Hodgkin–Huxley equations for membrane voltage potential. Using this approach, we model cable properties and signal propagation along the length of the axon with N node myelination. MATLAB/Simulink platform is used to analyze an N node-myelinated neuronal axon. The ability to transfer function in the frequency domain will help reduce effort and will give a much more realistic feel when compared to the classical time-based approach. Once a transfer function is identified, the conduction as a cascade of each linear time invariant system-based transfer function can be modeled. Using this approach, future studies can model the loss of myelin in various parts of nervous system. PMID:27103847
Frequency-domain Monte Carlo method for linear oscillatory gas flows
NASA Astrophysics Data System (ADS)
Ladiges, Daniel R.; Sader, John E.
2015-03-01
Gas flows generated by resonating nanoscale devices inherently occur in the non-continuum, low Mach number regime. Numerical simulations of such flows using the standard direct simulation Monte Carlo (DSMC) method are hindered by high statistical noise, which has motivated the development of several alternate Monte Carlo methods for low Mach number flows. Here, we present a frequency-domain low Mach number Monte Carlo method based on the Boltzmann-BGK equation, for the simulation of oscillatory gas flows. This circumvents the need for temporal simulations, as is currently required, and provides direct access to both amplitude and phase information using a pseudo-steady algorithm. The proposed method is validated for oscillatory Couette flow and the flow generated by an oscillating sphere. Good agreement is found with an existing time-domain method and accurate numerical solutions of the Boltzmann-BGK equation. Analysis of these simulations using a rigorous statistical approach shows that the frequency-domain method provides a significant improvement in computational speed.
Ramírez-Miquet, Evelio E; Perchoux, Julien; Loubière, Karine; Tronche, Clément; Prat, Laurent; Sotolongo-Costa, Oscar
2016-01-01
Optical feedback interferometry (OFI) is a compact sensing technique with recent implementation for flow measurements in microchannels. We propose implementing OFI for the analysis at the microscale of multiphase flows starting with the case of parallel flows of two immiscible fluids. The velocity profiles in each phase were measured and the interface location estimated for several operating conditions. To the authors knowledge, this sensing technique is applied here for the first time to multiphase flows. Theoretical profiles issued from a model based on the Couette viscous flow approximation reproduce fairly well the experimental results. The sensing system and the analysis presented here provide a new tool for studying more complex interactions between immiscible fluids (such as liquid droplets flowing in a microchannel). PMID:27527178
Electro-optic directed XOR logic circuits based on parallel-cascaded micro-ring resonators.
Tian, Yonghui; Zhao, Yongpeng; Chen, Wenjie; Guo, Anqi; Li, Dezhao; Zhao, Guolin; Liu, Zilong; Xiao, Huifu; Liu, Guipeng; Yang, Jianhong
2015-10-01
We report an electro-optic photonic integrated circuit which can perform the exclusive (XOR) logic operation based on two silicon parallel-cascaded microring resonators (MRRs) fabricated on the silicon-on-insulator (SOI) platform. PIN diodes embedded around MRRs are employed to achieve the carrier injection modulation. Two electrical pulse sequences regarded as two operands of operations are applied to PIN diodes to modulate two MRRs through the free carrier dispersion effect. The final operation result of two operands is output at the Output port in the form of light. The scattering matrix method is employed to establish numerical model of the device, and numerical simulator SG-framework is used to simulate the electrical characteristics of the PIN diodes. XOR operation with the speed of 100Mbps is demonstrated successfully.
Ramírez-Miquet, Evelio E; Perchoux, Julien; Loubière, Karine; Tronche, Clément; Prat, Laurent; Sotolongo-Costa, Oscar
2016-08-04
Optical feedback interferometry (OFI) is a compact sensing technique with recent implementation for flow measurements in microchannels. We propose implementing OFI for the analysis at the microscale of multiphase flows starting with the case of parallel flows of two immiscible fluids. The velocity profiles in each phase were measured and the interface location estimated for several operating conditions. To the authors knowledge, this sensing technique is applied here for the first time to multiphase flows. Theoretical profiles issued from a model based on the Couette viscous flow approximation reproduce fairly well the experimental results. The sensing system and the analysis presented here provide a new tool for studying more complex interactions between immiscible fluids (such as liquid droplets flowing in a microchannel).
Ramírez-Miquet, Evelio E.; Perchoux, Julien; Loubière, Karine; Tronche, Clément; Prat, Laurent; Sotolongo-Costa, Oscar
2016-01-01
Optical feedback interferometry (OFI) is a compact sensing technique with recent implementation for flow measurements in microchannels. We propose implementing OFI for the analysis at the microscale of multiphase flows starting with the case of parallel flows of two immiscible fluids. The velocity profiles in each phase were measured and the interface location estimated for several operating conditions. To the authors knowledge, this sensing technique is applied here for the first time to multiphase flows. Theoretical profiles issued from a model based on the Couette viscous flow approximation reproduce fairly well the experimental results. The sensing system and the analysis presented here provide a new tool for studying more complex interactions between immiscible fluids (such as liquid droplets flowing in a microchannel). PMID:27527178
Mazhar, Amaan; Sharif, Seyed A.; Cuccia, J. David; Nelson, J. Stuart; Kelly, Kristen M.; Durkin, Anthony J.
2012-01-01
Background and Objective Objective methods to assess port wine stain (PWS) response to laser treatment have been the subject of various research efforts for several years. Herein, we present a pilot study using a newly developed, light emitting diode (LED) based spatial frequency domain imaging (SFDI) device to record quantitatively biochemical compositional changes in PWS after laser therapy. Study Design/Patients and Methods A SFDI system was used to image before, and after, five PWS treatment sessions [n = 4 subjects (one subject was imaged before and after two consecutive laser treatments)]. SFDI derived wide-field optical properties (absorption and scattering) and tissue chromophore concentrations including oxy-hemoglobin (ctO2Hb), deoxy-hemoglobin (ctHHb), total hemoglobin (ctTHb), and tissue oxygen saturation (stO2) are presented for skin imaged prior to and immediately after laser treatment. The SFDI derived images were analyzed by comparing the above measurements in PWS to those of normal skin and tracking changes immediately after laser exposure. Results Elevated oxy-hemoglobin (>20%) and tissue oxygen saturation (>5%) were measured in all PWS lesions and compared to values for normal skin prior to treatment. Laser treatment resulted in an increase in deoxy-hemoglobin (>100%), decrease in tissue oxygen saturation (>10%), and reduced scattering (>15%) in all PWS lesions. One subject was followed before and after two consecutive laser treatments and the overall improvement in PWS lesion blanching was quantitatively assessed by measuring a 45% decrease in dermal blood volume. Conclusion SFDI is a rapid non-contact wide-field optical technique that shows potential as an imaging device that can be used to quantify biochemical compositional changes in PWS after laser therapy. Future work will investigate the potential of SFDI to provide intra-operative guidance for laser therapy of PWS lesions on an individual patient basis. PMID:22911574
Frequency-domain elastic full waveform inversion using encoded simultaneous sources
NASA Astrophysics Data System (ADS)
Jeong, W.; Son, W.; Pyun, S.; Min, D.
2011-12-01
Currently, numerous studies have endeavored to develop robust full waveform inversion and migration algorithms. These processes require enormous computational costs, because of the number of sources in the survey. To avoid this problem, the phase encoding technique for prestack migration was proposed by Romero (2000) and Krebs et al. (2009) proposed the encoded simultaneous-source inversion technique in the time domain. On the other hand, Ben-Hadj-Ali et al. (2011) demonstrated the robustness of the frequency-domain full waveform inversion with simultaneous sources for noisy data changing the source assembling. Although several studies on simultaneous-source inversion tried to estimate P- wave velocity based on the acoustic wave equation, seismic migration and waveform inversion based on the elastic wave equations are required to obtain more reliable subsurface information. In this study, we propose a 2-D frequency-domain elastic full waveform inversion technique using phase encoding methods. In our algorithm, the random phase encoding method is employed to calculate the gradients of the elastic parameters, source signature estimation and the diagonal entries of approximate Hessian matrix. The crosstalk for the estimated source signature and the diagonal entries of approximate Hessian matrix are suppressed with iteration as for the gradients. Our 2-D frequency-domain elastic waveform inversion algorithm is composed using the back-propagation technique and the conjugate-gradient method. Source signature is estimated using the full Newton method. We compare the simultaneous-source inversion with the conventional waveform inversion for synthetic data sets of the Marmousi-2 model. The inverted results obtained by simultaneous sources are comparable to those obtained by individual sources, and source signature is successfully estimated in simultaneous source technique. Comparing the inverted results using the pseudo Hessian matrix with previous inversion results
Ruh, Dominic; Tränkle, Benjamin; Rohrbach, Alexander
2011-10-24
Multi-dimensional, correlated particle tracking is a key technology to reveal dynamic processes in living and synthetic soft matter systems. In this paper we present a new method for tracking micron-sized beads in parallel and in all three dimensions - faster and more precise than existing techniques. Using an acousto-optic deflector and two quadrant-photo-diodes, we can track numerous optically trapped beads at up to tens of kHz with a precision of a few nanometers by back-focal plane interferometry. By time-multiplexing the laser focus, we can calibrate individually all traps and all tracking signals in a few seconds and in 3D. We show 3D histograms and calibration constants for nine beads in a quadratic arrangement, although trapping and tracking is easily possible for more beads also in arbitrary 2D arrangements. As an application, we investigate the hydrodynamic coupling and diffusion anomalies of spheres trapped in a 3 × 3 arrangement. PMID:22109012
Yedvab, Y.; Reiss, I.; Bettan, M.; Harari, R.; Grober, A.; Ettedgui, H.; Caspi, E. N.
2006-07-01
A method for determining delayed neutrons source in the frequency domain based on measuring power oscillations in a non-critical reactor is presented. This method is unique in the sense that the delayed neutrons source is derived from the dynamic behavior of the reactor, which serves as the measurement system. An algorithm for analyzing power oscillation measurements was formulated, which avoids the need for a multi-parameter non-linear fit process used by other methods. Using this algorithm results of two sets of measurements performed in IRR-I and IRR-II (Israeli Research Reactors I and II) are presented. The agreement between measured values from both reactors and calculated values based on Keepin (and JENDL-3.3) group parameters is very good. (authors)
NASA Technical Reports Server (NTRS)
Weissman, David E.; Staton, Leo D.
1991-01-01
A novel approach to the reduction of scattered, interfering signals that corrupt measurements of the signal backscattered from radar targets of interest is being developed. It is being explored with sphere measurements in an indoor microwave radar range. This method is based on the concept of Wiener filtering (which minimizes the difference between the signal plus noise and the desired signal in the time domain). In contrast to the traditional Wiener filter, in which the time domain error between two sequences are minimized, the approach reported uses the frequency domain phasor amplitudes of a swept frequency signal. It minimizes the difference (least-mean-square-magnitude) between the signal-plus-noise and the signal complex phasors, across the entire spectrum.
Fast frequency domain method to detect skew in a document image
NASA Astrophysics Data System (ADS)
Mehta, Sunita; Walia, Ekta; Dutta, Maitreyee
2015-12-01
In this paper, a new fast frequency domain method based on Discrete Wavelet Transform and Fast Fourier Transform has been implemented for the determination of the skew angle in a document image. Firstly, image size reduction is done by using two-dimensional Discrete Wavelet Transform and then skew angle is computed using Fast Fourier Transform. Skew angle error is almost negligible. The proposed method is experimented using a large number of documents having skew between -90° and +90° and results are compared with Moments with Discrete Wavelet Transform method and other commonly used existing methods. It has been determined that this method works more efficiently than the existing methods. Also, it works with typed, picture documents having different fonts and resolutions. It overcomes the drawback of the recently proposed method of Moments with Discrete Wavelet Transform that does not work with picture documents.
Frequency-domain identification of aircraft structural modes from short-duration flight tests
NASA Astrophysics Data System (ADS)
Vayssettes, J.; Mercère, G.; Vacher, P.; De Callafon, R. A.
2014-07-01
This article presents identification algorithms dedicated to the modal analysis of civil aircraft structures during in-flight flutter tests. This particular operational framework implies several specifications for the identification procedure. To comply with these requirements, the identification problem is formulated in the frequency domain as an output-error problem. Iterative identification methods based on structured matrix fraction descriptions are used to solve this problem and to identify a continuous-time model. These iterative methods are specifically designed to deal with experiments where short-duration tests with multiple-input excitations are used. These algorithms are first discussed and then evaluated through a simulation example illustrative of the in-flight modal analysis of a civil aircraft. Based on these evaluation results, an efficient iterative algorithm is suggested and applied to real flight-test data measured on board a military aircraft.
NASA Astrophysics Data System (ADS)
Zhang, Shengli; Tang, Jiong
2016-04-01
Gearbox is one of the most vulnerable subsystems in wind turbines. Its healthy status significantly affects the efficiency and function of the entire system. Vibration based fault diagnosis methods are prevalently applied nowadays. However, vibration signals are always contaminated by noise that comes from data acquisition errors, structure geometric errors, operation errors, etc. As a result, it is difficult to identify potential gear failures directly from vibration signals, especially for the early stage faults. This paper utilizes synchronous averaging technique in time-frequency domain to remove the non-synchronous noise and enhance the fault related time-frequency features. The enhanced time-frequency information is further employed in gear fault classification and identification through feature extraction algorithms including Kernel Principal Component Analysis (KPCA), Multilinear Principal Component Analysis (MPCA), and Locally Linear Embedding (LLE). Results show that the LLE approach is the most effective to classify and identify different gear faults.
A frequency-domain thermoreflectance method for the characterization of thermal properties.
Schmidt, Aaron J; Cheaito, Ramez; Chiesa, Matteo
2009-09-01
A frequency-domain thermoreflectance method for measuring the thermal properties of homogenous materials and submicron thin films is described. The method can simultaneously determine the thermal conductivity and heat capacity of a sample, provided the thermal diffusivity is greater, similar3x10(-6) m(2)/s, and can also simultaneously measure in-plane and cross-plane thermal conductivities, as well the thermal boundary conductance between material layers. Two implementations are discussed, one based on an ultrafast pulsed laser system and one based on continuous-wave lasers. The theory of the method and an analysis of its sensitivity to various thermal properties are given, along with results from measurements of several standard materials over a wide range of thermal diffusivities. We obtain specific heats and thermal conductivities in good agreement with literature values, and also obtain the in-plane and cross-plane thermal conductivities for crystalline quartz.
Regner, K T; Majumdar, S; Malen, J A
2013-06-01
This paper describes the instrumentation for broadband frequency domain thermoreflectance (BB-FDTR), a novel, continuous wave laser technique for measuring the thermal conductivity accumulation function. The thermal conductivity accumulation function describes cumulative contributions to the bulk thermal conductivity of a material from energy carriers with different mean free paths. It can be used to map reductions in thermal conductivity in nano-devices, which arise when the dimensions of the device are commensurate to the mean free path of energy carriers. BB-FDTR uses high frequency surface temperature modulation to generate non-diffusive phonon transport realized through a reduction in the perceived thermal conductivity. By controlling the modulation frequency it is possible to reconstruct the thermal conductivity accumulation function. A unique heterodyning technique is used to down-convert the signal, therein improving our signal to noise ratio and enabling results over a broader range of modulation frequencies (200 kHz-200 MHz) and hence mean free paths.
Effect of bird maneuver on frequency-domain helicopter EM response
Fitterman, D.V.; Yin, C.
2004-01-01
Bird maneuver, the rotation of the coil-carrying instrument pod used for frequency-domain helicopter electromagnetic surveys, changes the nominal geometric relationship between the bird-coil system and the ground. These changes affect electromagnetic coupling and can introduce errors in helicopter electromagnetic, (HEM) data. We analyze these effects for a layered half-space for three coil configurations: vertical coaxial, vertical coplanar, and horizontal coplanar. Maneuver effect is shown to have two components: one that is purely geometric and another that is inductive in nature. The geometric component is significantly larger. A correction procedure is developed using an iterative approach that uses standard HEM inversion routines. The maneuver effect correction reduces inversion misfit error and produces laterally smoother cross sections than obtained from uncorrected data. ?? 2004 Society of Exploration Geophysicists. All rights reserved.
Oblique frequency domain interferometry measurements using the middle and upper atmosphere radar
NASA Astrophysics Data System (ADS)
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.
Wavelet-transform-based time-frequency domain reflectometry for reduction of blind spot
NASA Astrophysics Data System (ADS)
Lee, Sin Ho; Park, Jin Bae; Choi, Yoon Ho
2012-06-01
In this paper, wavelet-transform-based time-frequency domain reflectometry (WTFDR) is proposed to reduce the blind spot in reflectometry. TFDR has a blind spot problem when the time delay between the reference signal and the reflected signal is short enough compared with the time duration of the reference signal. To solve the blind spot problem, the wavelet transform (WT) is used because the WT has linearity. Using the characteristics of the WT, the overlapped reference signal at the measured signal can be separated and the blind spot is reduced by obtaining the difference of the wavelet coefficients for the reference and reflected signals. In the proposed method, the complex wavelet is utilized as a mother wavelet because the reference signal in WTFDR has a complex form. Finally, the computer simulations and the real experiments are carried out to confirm the effectiveness and accuracy of the proposed method.
Frequency-domain nonlinear regression algorithm for spectral analysis of broadband SFG spectroscopy.
He, Yuhan; Wang, Ying; Wang, Jingjing; Guo, Wei; Wang, Zhaohui
2016-03-01
The resonant spectral bands of the broadband sum frequency generation (BB-SFG) spectra are often distorted by the nonresonant portion and the lineshapes of the laser pulses. Frequency domain nonlinear regression (FDNLR) algorithm was proposed to retrieve the first-order polarization induced by the infrared pulse and to improve the analysis of SFG spectra through simultaneous fitting of a series of time-resolved BB-SFG spectra. The principle of FDNLR was presented, and the validity and reliability were tested by the analysis of the virtual and measured SFG spectra. The relative phase, dephasing time, and lineshapes of the resonant vibrational SFG bands can be retrieved without any preset assumptions about the SFG bands and the incident laser pulses. PMID:26974068
A Fast Method of Transforming Relaxation Functions Into the Frequency Domain
Mopsik, Frederick I.
1999-01-01
The limits to the error due to truncation of the numeric integration of the one-sided Laplace transform of a relaxation function in the time domain into its equivalent frequency domain are established. Separate results are given for large and small ω. These results show that, for a given ω, only a restricted range of time samples is needed to perform the computation to a given accuracy. These results are then combined with a known error estimate for integration by cubic splines to give a good estimate for the number of points needed to perform the computation to a given accuracy. For a given data window between t1 and t2, the computation time is shown to be proportional to ln(t1/t2).
NASA Technical Reports Server (NTRS)
Liang, Steven Y.; Dornfeld, David A.; Nickerson, Jackson A.
1987-01-01
The coloring effect on the acoustic emission signal due to the frequency response of the data acquisition/processing instrumentation may bias the interpretation of AE signal characteristics. In this paper, a frequency domain deconvolution technique, which involves the identification of the instrumentation transfer functions and multiplication of the AE signal spectrum by the inverse of these system functions, has been carried out. In this way, the change in AE signal characteristics can be better interpreted as the result of the change in only the states of the process. Punch stretching process was used as an example to demonstrate the application of the technique. Results showed that, through the deconvolution, the frequency characteristics of AE signals generated during the stretching became more distinctive and can be more effectively used as tools for process monitoring.
NASA Astrophysics Data System (ADS)
Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Shi, Yan
2016-06-01
In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effective way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.
Frequency-Domain Analysis of Diffusion-Cooled Hot-Electron Bolometer Mixers
NASA Technical Reports Server (NTRS)
Skalare, A.; McGrath, W. R.; Bumble, B.; LeDuc, H. G.
1998-01-01
A new theoretical model is introduced to describe heterodyne mixer conversion efficiency and noise (from thermal fluctuation effects) in diffusion-cooled superconducting hot-electron bolometers. The model takes into account the non-uniform internal electron temperature distribution generated by Wiedemann-Franz heat conduction, and accepts for input an arbitrary (analytical or experimental) superconducting resistance-versus- temperature curve. A non-linear large-signal solution is solved iteratively to calculate the temperature distribution, and a linear frequency-domain small-signal formulation is used to calculate conversion efficiency and noise. In the small-signal solution the device is discretized into segments, and matrix algebra is used to relate the heating modulation in the segments to temperature and resistance modulations. Matrix expressions are derived that allow single-sideband mixer conversion efficiency and coupled noise power to be directly calculated. The model accounts for self-heating and electrothermal feedback from the surrounding bias circuit.
Frequency-domain bridging multiscale method for wave propagation simulations in damaged structures
NASA Astrophysics Data System (ADS)
Casadei, F.; Ruzzene, M.
2010-03-01
Efficient numerical models are essential for the simulation of the interaction of propagating waves with localized defects. Classical finite elements may be computationally time consuming, especially when detailed discretizations are needed around damage regions. A multi-scale approach is here propose to bridge a fine-scale mesh defined on a limited region around the defect and a coarse-scale discretization of the entire domain. This "bridging" method is formulated in the frequency domain in order to further reduce the computational cost and provide a general framework valid for different types of structures. Numerical results presented for propagating elastic waves in 1D and 2D damaged waveguides illustrate the proposed technique and its advantages.
Monitoring Protein Fouling on Polymeric Membranes Using Ultrasonic Frequency-Domain Reflectometry
Kujundzic, Elmira; Greenberg, Alan R.; Fong, Robin; Hernandez, Mark
2011-01-01
Novel signal-processing protocols were used to extend the in situ sensitivity of ultrasonic frequency-domain reflectometry (UFDR) for real-time monitoring of microfiltration (MF) membrane fouling during protein purification. Different commercial membrane materials, with a nominal pore size of 0.2 μm, were challenged using bovine serum albumin (BSA) and amylase as model proteins. Fouling induced by these proteins was observed in flat-sheet membrane filtration cells operating in a laminar cross-flow regime. The detection of membrane-associated proteins using UFDR was determined by applying rigorous statistical methodology to reflection spectra of ultrasonic signals obtained during membrane fouling. Data suggest that the total power reflected from membrane surfaces changes in response to protein fouling at concentrations as low as 14 μg/cm2, and results indicate that ultrasonic spectra can be leveraged to detect and monitor protein fouling on commercial MF membranes. PMID:24957732
Design of PI controllers for achieving time and frequency domain specifications simultaneously.
Hamamci, Serdar Ethem; Tan, Nusret
2006-10-01
This paper deals with the design of PI controllers which achieve the desired frequency and time domain specifications simultaneously. A systematic method, which is effective and simple to apply, is proposed. The required values of the frequency domain performance measures namely the gain and phase margins and the time domain performance measures such as settling time and overshoot are defined prior to the design. Then, to meet these desired performance values, a method which presents a graphical relation between the required performance values and the parameters of the PI controller is given. Thus, a set of PI controllers which attain desired performances can be found using the graphical relations. Illustrative examples are given to demonstrate the benefits of the method presented.
Tian, Hua; Luo, Shiqiang; Zhang, Rui; Yang, Gang; Huang, Hua
2009-12-01
Frequency-domain electricity properties of four objects, including bullfrog skin, bullfrog muscle, triply distilled water and 0.9% NaCl, were tested in the range of 100Hz-10MHz using home-made electrode and measuring system. The experimental results showed that the resistance of 0.9% NaCl decreased dramatically, that the amplitude frequency characteristics of bullfrog's muscle and skin were similar, but that of triply distilled water did not change significantly. The frequency dependence of 0.9% NaCl showed that the electrode had great influence on the measuring system, so a new equivalent circuit model based on the electrode system was needed. These findings suggest that the new five-parameter equivalent circuit model, which embodies considerations on the interaction between electrodes and tissues, is a reasonable equivalent circuit for studying the electrical characteristics of biological materials.
A microcomputer based frequency-domain processor for laser Doppler anemometry
NASA Technical Reports Server (NTRS)
Horne, W. Clifton; Adair, Desmond
1988-01-01
A prototype multi-channel laser Doppler anemometry (LDA) processor was assembled using a wideband transient recorder and a microcomputer with an array processor for fast Fourier transform (FFT) computations. The prototype instrument was used to acquire, process, and record signals from a three-component wind tunnel LDA system subject to various conditions of noise and flow turbulence. The recorded data was used to evaluate the effectiveness of burst acceptance criteria, processing algorithms, and selection of processing parameters such as record length. The recorded signals were also used to obtain comparative estimates of signal-to-noise ratio between time-domain and frequency-domain signal detection schemes. These comparisons show that the FFT processing scheme allows accurate processing of signals for which the signal-to-noise ratio is 10 to 15 dB less than is practical using counter processors.
Schnegg, Alexander; Behrends, Jan; Lips, Klaus; Bittl, Robert; Holldack, Karsten
2009-08-21
Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool to ascertain very large zero field splittings in transition metal ion complexes. A description of the FD-FT THz-EPR at the BESSY II storage ring providing CSR in a frequency range from 5 cm(-1) up to 40 cm(-1) at external magnetic fields from -10 T to +10 T is given together with first measurements on the single molecule magnet Mn(12)Ac where we studied DeltaM(S) = +/-1 spin transition energies as a function of the external magnetic field and temperature.
NASA Astrophysics Data System (ADS)
Copot, Cosmin; Zhong, Yu; Ionescu, Clara; Keyser, Robin
2013-06-01
In this paper, two methods to tune a fractional-order PI λ D μ controller for a mechatronic system are presented. The first method is based on a genetic algorithm to obtain the parameter values for the fractionalorder PI λ D μ controller by global optimization. The second method used to design the fractional-order PI λ D μ controller relies on an auto-tuning approach by meeting some specifications in the frequency domain. The real-time experiments are conducted using a Steward platform which consists of a table tilted by six servo-motors with a ball on the top of the table. The considered system is a 6 degrees of freedom (d.o.f.) motion platform. The feedback on the position of the ball is obtained from images acquired by a visual sensor mounted above the platform. The fractional-order controllers were implemented and the performances of the steward platform are analyzed.
EMGAN: A computer program for time and frequency domain reduction of electromyographic data
NASA Technical Reports Server (NTRS)
Hursta, W. N.
1975-01-01
An experiment in electromyography utilizing surface electrode techniques was developed for the Apollo-Soyuz test project. This report describes the computer program, EMGAN, which was written to provide first order data reduction for the experiment. EMG signals are produced by the membrane depolarization of muscle fibers during a muscle contraction. Surface electrodes detect a spatially summated signal from a large number of muscle fibers commonly called an interference pattern. An interference pattern is usually so complex that analysis through signal morphology is extremely difficult if not impossible. It has become common to process EMG interference patterns in the frequency domain. Muscle fatigue and certain myopathic conditions are recognized through changes in muscle frequency spectra.
NASA Technical Reports Server (NTRS)
Eren, K.
1980-01-01
The mathematical background in spectral analysis as applied to geodetic applications is summarized. The resolution (cut-off frequency) of the GEOS 3 altimeter data is examined by determining the shortest wavelength (corresponding to the cut-off frequency) recoverable. The data from some 18 profiles are used. The total power (variance) in the sea surface topography with respect to the reference ellipsoid as well as with respect to the GEM-9 surface is computed. A fast inversion algorithm for matrices of simple and block Toeplitz matrices and its application to least squares collocation is explained. This algorithm yields a considerable gain in computer time and storage in comparison with conventional least squares collocation. Frequency domain least squares collocation techniques are also introduced and applied to estimating gravity anomalies from GEOS 3 altimeter data. These techniques substantially reduce the computer time and requirements in storage associated with the conventional least squares collocation. Numerical examples given demonstrate the efficiency and speed of these techniques.
Frequency-domain Model Matching PID Controller Design for Aero-engine
NASA Astrophysics Data System (ADS)
Liu, Nan; Huang, Jinquan; Lu, Feng
2014-12-01
The nonlinear model of aero-engine was linearized at multiple operation points by using frequency response method. The validation results indicate high accuracy of static and dynamic characteristics of the linear models. The improved PID tuning method of frequency-domain model matching was proposed with the system stability condition considered. The proposed method was applied to the design of PID controller of the high pressure rotor speed control in the flight envelope, and the control effects were evaluated by the nonlinear model. Simulation results show that the system had quick dynamic response with zero overshoot and zero steadystate error. Furthermore, a PID-fuzzy switching control scheme for aero-engine was designed, and the fuzzy switching system stability was proved. Simulations were studied to validate the applicability of the multiple PIDs fuzzy switching controller for aero-engine with wide range dynamics.
Roudot, Philippe; Kervrann, Charles; Blouin, Cedric M; Waharte, Francois
2015-10-01
Fluorescence lifetime is usually defined as the average nanosecond-scale delay between excitation and emission of fluorescence. It has been established that lifetime measurements yield numerous indications on cellular processes such as interprotein and intraprotein mechanisms through fluorescent tagging and Förster resonance energy transfer. In this area, frequency-domain fluorescence lifetime imaging microscopy is particularly appropriate to probe a sample noninvasively and quantify these interactions in living cells. The aim is then to measure the fluorescence lifetime in the sample at each location in space from fluorescence variations observed in a temporal sequence of images obtained by phase modulation of the detection signal. This leads to a sensitivity of lifetime determination to other sources of fluorescence variations such as intracellular motion. In this paper, we propose a robust statistical method for lifetime estimation for both background and small moving structures with a focus on intracellular vesicle trafficking. PMID:26479936
NASA Astrophysics Data System (ADS)
Li, Xuan; Zhao, Shanghong; Zhu, Zihang; Gong, Bing; Chu, Xingchun; Li, Yongjun; Zhao, Jing; Liu, Yun
2015-10-01
A novel filterless optical millimeter-wave signal generation scheme is proposed. In the scheme, the undesired sidebands are suppressed using two parallel dual-parallel Mach-Zehnder modulators (MZMs) with different modulation indexes and polarization multiplexing, and frequency multiplication factor as high as 16 can be achieved. Simulation results show that 80, 120, and 160 GHz signals are generated through a 10 GHz RF signal using the proposed method, and the performance of the generated signals is good when commercially available MZMs with extinction ratio of 20-30 dB are used. The scheme has large tunability of modulation index for frequency octupling and 12-tupling signals generation and high stability against the RF driving voltage deviation for frequency 16-tupling generation.
Hao, Guang-You; Wheeler, James K.; Holbrook, N. Michele; Goldstein, Guillermo
2013-01-01
Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves, and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn, concurrently with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short- and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of ‘vulnerability segmentation’ between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidence from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous, and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate. PMID:23585669
Frequency Domain Analysis of Errors in Cross-Correlations of Ambient Seismic Noise
NASA Astrophysics Data System (ADS)
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2016-09-01
We analyze random errors (variances) in cross-correlations of ambient seismic noise in the frequency domain, which differ from previous time domain methods. Extending previous theoretical results on ensemble averaged cross-spectrum, we estimate confidence interval of stacked cross-spectrum of finite amount of data at each frequency using non-overlapping windows with fixed length. The extended theory also connects amplitude and phase variances with the variance of each complex spectrum value. Analysis of synthetic stationary ambient noise is used to estimate the confidence interval of stacked cross-spectrum obtained with different length of noise data corresponding to different number of evenly spaced windows of the same duration. This method allows estimating Signal/Noise Ratio (SNR) of noise cross-correlation in the frequency domain, without specifying filter bandwidth or signal/noise windows that are needed for time domain SNR estimations. Based on synthetic ambient noise data, we also compare the probability distributions, causal part amplitude and SNR of stacked cross-spectrum function using one-bit normalization or pre-whitening with those obtained without these preprocessing steps. Natural continuous noise records contain both ambient noise and small earthquakes that are inseparable from the noise with the existing preprocessing steps. Using probability distributions of random cross-spectrum values based on the theoretical results provides an effective way to exclude such small earthquakes, and additional data segments (outliers) contaminated by signals of different statistics (e.g. rain, cultural noise), from continuous noise waveforms. This technique is applied to constrain values and uncertainties of amplitude and phase velocity of stacked noise cross-spectrum at different frequencies, using data from southern California at both regional scale (˜ 35 km) and dense linear array (˜ 20 m) across the plate-boundary faults. A block bootstrap resampling method
Frequency Domain Ultrasound Waveform Tomography: Breast Imaging Using a Ring Transducer
Sandhu, G Y; Li, C; Roy, O; Schmidt, S; Duric, N
2016-01-01
Application of the frequency domain acoustic wave equation on data acquired from ultrasound tomography scans is shown to yield high resolution sound speed images on the order of the wavelength of the highest reconstructed frequency. Using a signal bandwidth of 0.4–1 MHz and an average sound speed of 1500 m/s, the resolution is approximately 1.5 mm. The quantitative sound speed values and morphology provided by these images have the potential to inform diagnosis and classification of breast disease. In this study, we present the formalism, practical application, and in vivo results of waveform tomography applied to breast data gathered by two different ultrasound tomography scanners that utilize ring transducers. The formalism includes a review of frequency domain modeling of the wave equation using finite difference operators as well as a review of the gradient descent method for the iterative reconstruction scheme. It is shown that the practical application of waveform tomography requires an accurate starting model, careful data processing, and a method to gradually incorporate higher frequency information into the sound speed reconstruction. Following these steps resulted in high resolution quantitative sound speed images of the breast. These images show marked improvement relative to commonly used ray tomography reconstruction methods. The robustness of the method is demonstrated by obtaining similar results from two different ultrasound tomography devices. We also compare our method to MRI to demonstrate concordant findings. The clinical data used in this work was obtained from a HIPAA compliant clinical study (IRB 040912M1F). PMID:26110909
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.
Kiyono, Ken; Tsujimoto, Yutaka
2016-07-01
We develop a general framework to study the time and frequency domain characteristics of detrending-operation-based scaling analysis methods, such as detrended fluctuation analysis (DFA) and detrending moving average (DMA) analysis. In this framework, using either the time or frequency domain approach, the frequency responses of detrending operations are calculated analytically. Although the frequency domain approach based on conventional linear analysis techniques is only applicable to linear detrending operations, the time domain approach presented here is applicable to both linear and nonlinear detrending operations. Furthermore, using the relationship between the time and frequency domain representations of the frequency responses, the frequency domain characteristics of nonlinear detrending operations can be obtained. Based on the calculated frequency responses, it is possible to establish a direct connection between the root-mean-square deviation of the detrending-operation-based scaling analysis and the power spectrum for linear stochastic processes. Here, by applying our methods to DFA and DMA, including higher-order cases, exact frequency responses are calculated. In addition, we analytically investigate the cutoff frequencies of DFA and DMA detrending operations and show that these frequencies are not optimally adjusted to coincide with the corresponding time scale.
NASA Astrophysics Data System (ADS)
Quirce, A.; Pérez, P.; Popp, A.; Valle, A.; Pesquera, L.; Hong, Y.; Thienpont, H.; Panajotov, K.
2016-04-01
We report a theoretical and experimental analysis of the polarization switching found in a single-transverse mode VCSEL when subject to parallel optical injection. We have found a novel situation in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. Analytical expressions for the power of both linear polarizations in the previous steady state are determined. We show that considering two linear polarization modes in a model of a VCSEL subject to parallel optical injection leads to simpler expressions than those found for a VCSEL with only a single linear polarization. We show that the power emitted in both linear polarizations depend linearly on the injected power. The stability region of this solution is measured in the plane injected power versus frequency detuning.
NASA Astrophysics Data System (ADS)
Schmalz, Mark S.
1992-08-01
A novel parallel model of natural language (NL) understanding is presented which can realize high levels of semantic abstraction, and is designed for implementation on synchronous SIMD architectures and optical processors. Theory is expressed in terms of the Image Algebra (IA), a rigorous, concise, inherently parallel notation which unifies the design, analysis, and implementation of image processing algorithms. The IA has been implemented on numerous parallel architectures, and IA preprocessors and interpreters are available for the FORTRAN and Ada languages. In a previous study, we demonstrated the utility of IA for mapping MEA- conformable (Multiple Execution Array) algorithms to optical architectures. In this study, we extend our previous theory to map serial parsing algorithms to the synchronous SIMD paradigm. We initially derive a two-dimensional image that is based upon the adjacency matrix of a semantic graph. Via IA template mappings, the operations of bottom-up parsing, semantic disambiguation, and referential resolution are implemented as image-processing operations upon the adjacency matrix. Pixel-level operations are constrained to Hadamard addition and multiplication, thresholding, and row/column summation, which are available in magnitude-only optics. Assuming high parallelism in the parse rule base, the parsing of n input symbols with a grammar consisting of M rules of arity H, on an N-processor architecture, could exhibit time complexity of T(n)
NASA Astrophysics Data System (ADS)
Weber, Jessie R.; Cuccia, David J.; Johnson, William R.; Bearman, Gregory H.; Durkin, Anthony J.; Hsu, Mike; Lin, Alexander; Binder, Devin K.; Wilson, Dan; Tromberg, Bruce J.
2011-01-01
We present an approach for rapidly and quantitatively mapping tissue absorption and scattering spectra in a wide-field, noncontact imaging geometry by combining multifrequency spatial frequency domain imaging (SFDI) with a computed-tomography imaging spectrometer (CTIS). SFDI overcomes the need to spatially scan a source, and is based on the projection and analysis of periodic structured illumination patterns. CTIS provides a throughput advantage by simultaneously diffracting multiple spectral images onto a single CCD chip to gather spectra at every pixel of the image, thus providing spatial and spectral information in a single snapshot. The spatial-spectral data set was acquired 30 times faster than with our wavelength-scanning liquid crystal tunable filter camera, even though it is not yet optimized for speed. Here we demonstrate that the combined SFDI-CTIS is capable of rapid, multispectral imaging of tissue absorption and scattering in a noncontact, nonscanning platform. The combined system was validated for 36 wavelengths between 650-1000 nm in tissue simulating phantoms over a range of tissue-like absorption and scattering properties. The average percent error for the range of absorption coefficients (μa) was less than 10% from 650-800 nm, and less than 20% from 800-1000 nm. The average percent error in reduced scattering coefficients (μs') was less than 5% from 650-700 nm and less than 3% from 700-1000 nm. The SFDI-CTIS platform was applied to a mouse model of brain injury in order to demonstrate the utility of this approach in characterizing spatially and spectrally varying tissue optical properties.
NASA Astrophysics Data System (ADS)
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.
Kakodkar, Rohit R.; Feser, Joseph P.
2015-09-07
We present a numerical approach to the solution of elastic phonon-interface and phonon-nanostructure scattering problems based on a frequency-domain decomposition of the atomistic equations of motion and the use of perfectly matched layer (PML) boundaries. Unlike molecular dynamic wavepacket analysis, the current approach provides the ability to simulate scattering from individual phonon modes, including wavevectors in highly dispersive regimes. Like the atomistic Green's function method, the technique reduces scattering problems to a system of linear algebraic equations via a sparse, tightly banded matrix regardless of dimensionality. However, the use of PML boundaries enables rapid absorption of scattered wave energies at the boundaries and provides a simple and inexpensive interpretation of the scattered phonon energy flux calculated from the energy dissipation rate in the PML. The accuracy of the method is demonstrated on connected monoatomic chains, for which an analytic solution is known. The parameters defining the PML are found to affect the performance and guidelines for selecting optimal parameters are given. The method is used to study the energy transmission coefficient for connected diatomic chains over all available wavevectors for both optical and longitudinal phonons; it is found that when there is discontinuity between sublattices, even connected chains of equivalent acoustic impedance have near-zero transmission coefficient for short wavelengths. The phonon scattering cross section of an embedded nanocylinder is calculated in 2D for a wide range of frequencies to demonstrate the extension of the method to high dimensions. The calculations match continuum theory for long-wavelength phonons and large cylinder radii, but otherwise show complex physics associated with discreteness of the lattice. Examples include Mie oscillations which terminate when incident phonon frequencies exceed the maximum available frequency in the embedded nanocylinder, and
Elder, A D; Frank, J H; Swartling, J; Dai, X; Kaminski, C F
2006-11-01
High brightness light emitting diodes are an inexpensive and versatile light source for wide-field frequency-domain fluorescence lifetime imaging microscopy. In this paper a full calibration of an LED based fluorescence lifetime imaging microscopy system is presented for the first time. A radio-frequency generator was used for simultaneous modulation of light emitting diode (LED) intensity and the gain of an intensified charge coupled device (CCD) camera. A homodyne detection scheme was employed to measure the demodulation and phase shift of the emitted fluorescence, from which phase and modulation lifetimes were determined at each image pixel. The system was characterized both in terms of its sensitivity to measure short lifetimes (500 ps to 4 ns), and its capability to distinguish image features with small lifetime differences. Calibration measurements were performed in quenched solutions containing Rhodamine 6G dye and the results compared to several independent measurements performed with other measurement methodologies, including time correlated single photon counting, time gated detection, and acousto optical modulator (AOM) based modulation of excitation sources. Results are presented from measurements and simulations. The effects of limited signal-to-noise ratios, baseline drifts and calibration errors are discussed in detail. The implications of limited modulation bandwidth of high brightness, large area LED devices ( approximately 40 MHz for devices used here) are presented. The results show that phase lifetime measurements are robust down to sub ns levels, whereas modulation lifetimes are prone to errors even at large signal-to-noise ratios. Strategies for optimizing measurement fidelity are discussed. Application of the fluorescence lifetime imaging microscopy system is illustrated with examples from studies of molecular mixing in microfluidic devices and targeted drug delivery research. PMID:17204064
Wang Bingbing; Gao Lianghui; Li Xiaofeng; Fu Panming; Guo Dongsheng
2007-06-15
High-order above-threshold ionization (ATI) is investigated in the frequency domain, based on a nonperturbative quantum electrodynamics theoretical approach. The transition matrix element of high-order ATI is expressed as a superposition of products of generalized Bessel functions, which represent probability amplitudes of finding electrons with given energies. From the frequency-domain viewpoint the high-order ATI can be described simply as an ATI followed by laser-assisted collision (LAC), and the features of high-order ATI reflect mainly the characteristics of LAC. We investigate thoroughly the LAC, finding that the plateau can be simulated by a simple classical model. We also discuss the correspondence between the time- and frequency-domain pictures of rescattering ATI.
Wang, Longbao; Tao, Jun; Zheng, Yahong Rosa
2012-12-01
A frequency-domain turbo equalization (FDTE) scheme without cyclic prefix (CP) or zero padding is proposed for single-carrier, multiple-input-multiple-output underwater acoustic communication. In the first iteration of the FDTE, the received continuous data stream is divided into consecutive blocks and a combined inter-block-interference (IBI) cancellation and overlapped windowing scheme is used to diagonalize each data block for low-complexity detection in the frequency domain. Since the second iteration, IBI cancellation and CP reconstruction are applied on each block to enable effective symbol detection. This work extends the authors' previous work on frequency-domain hard-decision equalization to soft-decision turbo equalization so that it not only retains high data transmission efficiency, but also improves the bit error rate performance with slightly increased complexity due to multiple iterations. Its feasibility and effectiveness have been tested by field trial data from the ACOMM09 underwater communication experiment. PMID:23231110
Wang, Longbao; Tao, Jun; Zheng, Yahong Rosa
2012-12-01
A frequency-domain turbo equalization (FDTE) scheme without cyclic prefix (CP) or zero padding is proposed for single-carrier, multiple-input-multiple-output underwater acoustic communication. In the first iteration of the FDTE, the received continuous data stream is divided into consecutive blocks and a combined inter-block-interference (IBI) cancellation and overlapped windowing scheme is used to diagonalize each data block for low-complexity detection in the frequency domain. Since the second iteration, IBI cancellation and CP reconstruction are applied on each block to enable effective symbol detection. This work extends the authors' previous work on frequency-domain hard-decision equalization to soft-decision turbo equalization so that it not only retains high data transmission efficiency, but also improves the bit error rate performance with slightly increased complexity due to multiple iterations. Its feasibility and effectiveness have been tested by field trial data from the ACOMM09 underwater communication experiment.
NASA Astrophysics Data System (ADS)
Chang, Edward S.
1996-09-01
The multimedia communication needs high-performance, cost- effective communication techniques to transport data for the fast-growing multimedia traffic resulting from the recent deployment of World Wide Web (WWW), media-on-demand , and other multimedia applications. To transport a large volume, of multimedia data, high-performance servers are required to perform media processing and transfer. Typically, the high- performance multimedia server is a massively parallel processor with a high number of I/O ports, high storage capacity, fast signal processing, and excellent cost- performance. The parallel I/O ports of the server are connected to multiple clients through a network switch which uses parallel links in both switch-to-server and switch-to- client connections. In addition to media processing and storage, media communication is also a major function of the multimedia system. Without a high-performance communication network, a high-performance server can not deliver its full capacity of service to clients. Fortunately, there are many advanced communication technologies developed for networking, which can be adopted by the multimedia communication to economically deliver the full capacity of a high-performance multimedia service to clients. The VCSEL array technology has been developed for gigabit-rate parallel optical interconnections because of its high bandwidth, small-size, and easy-fabrication advantages. Several firms are developing multifiber, low-skew, low-cost ribbon cables to transfer signals form a VCSEL array. The OC12 SONET data-rate is widely used by high-performance multimedia communications for its high-data-rate and cost- effectiveness. Therefore, the OC12 VCSEL parallel optical interconnection is the ideal technology to meet the high- performance low-cost requirements for delivering affordable multimedia services to mass users. This paper describes a multimedia OC12 parallel optical interconnection using a VCSEL array transceiver, a multifiber
Goldberg, L.A.; Jerrum, M.; Leighton, T.; Rao, S.
1993-01-20
In this paper we consider the problem of interprocessor communication on a Completely Connected Optical Communication Parallel Computer (OCPC). The particular problem we study is that of realizing an h-relation. In this problem, each processor has at most h messages to send and at most h messages to receive. It is clear that any 1-relation can be realized in one communication step on an OCPC. However, the best known p-processor OCPC algorithm for realizing an arbitrary h-relation for h > 1 requires {Theta}(h + log p) expected communication steps. (This algorithm is due to Valiant and is based on earlier work of Anderson and Miller.) Valiant`s algorithm is optimal only for h = {Omega}(log p) and it is an open question of Gereb-Graus and Tsantilas whether there is a faster algorithm for h = o(log p). In this paper we answer this question in the affirmative by presenting a {Theta} (h + log log p) communication step algorithm that realizes an arbitrary h-relation on a p-processor OCPC. We show that if h {le} log p then the failure probability can be made as small as p{sup -{alpha}} for any positive constant {alpha}.
On the Analysis Methods for the Time Domain and Frequency Domain Response of a Buried Objects*
NASA Astrophysics Data System (ADS)
Poljak, Dragan; Šesnić, Silvestar; Cvetković, Mario
2014-05-01
There has been a continuous interest in the analysis of ground-penetrating radar systems and related applications in civil engineering [1]. Consequently, a deeper insight of scattering phenomena occurring in a lossy half-space, as well as the development of sophisticated numerical methods based on Finite Difference Time Domain (FDTD) method, Finite Element Method (FEM), Boundary Element Method (BEM), Method of Moments (MoM) and various hybrid methods, is required, e.g. [2], [3]. The present paper deals with certain techniques for time and frequency domain analysis, respectively, of buried conducting and dielectric objects. Time domain analysis is related to the assessment of a transient response of a horizontal straight thin wire buried in a lossy half-space using a rigorous antenna theory (AT) approach. The AT approach is based on the space-time integral equation of the Pocklington type (time domain electric field integral equation for thin wires). The influence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The obtained results for the transient current induced along the electrode due to the transmitted plane wave excitation are compared to the numerical results calculated via an approximate transmission line (TL) approach and the AT approach based on the space-frequency variant of the Pocklington integro-differential approach, respectively. It is worth noting that the space-frequency Pocklington equation is numerically solved via the Galerkin-Bubnov variant of the Indirect Boundary Element Method (GB-IBEM) and the corresponding transient response is obtained by the aid of inverse fast Fourier transform (IFFT). The results calculated by means of different approaches agree satisfactorily. Frequency domain analysis is related to the assessment of frequency domain response of dielectric sphere using the full wave model based on the set of coupled electric field integral
To Err is Normable: The Computation of Frequency-Domain Error Bounds from Time-Domain Data
NASA Technical Reports Server (NTRS)
Hartley, Tom T.; Veillette, Robert J.; DeAbreuGarcia, J. Alexis; Chicatelli, Amy; Hartmann, Richard
1998-01-01
This paper exploits the relationships among the time-domain and frequency-domain system norms to derive information useful for modeling and control design, given only the system step response data. A discussion of system and signal norms is included. The proposed procedures involve only simple numerical operations, such as the discrete approximation of derivatives and integrals, and the calculation of matrix singular values. The resulting frequency-domain and Hankel-operator norm approximations may be used to evaluate the accuracy of a given model, and to determine model corrections to decrease the modeling errors.
Hydrograph structure informed calibration in the frequency domain with time localization
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Kodama, Kazuto; An, Zhisheng; Chang, Hong; Qiang, Xiaoke
2015-04-01
Measurement of low-field magnetic susceptibility over a wide band of frequencies spanning four orders of magnitude is a useful method for the assessment of the grain size distribution of ultrafine magnetic particles smaller than the SP/SSD boundary. This method has been applied to a loess/paleosol sequence at Luochuan in the Chinese Loess Plateau. The studied succession consists of sequences from the latest paleosol unit to the upper part of the loess unit, spanning the last glacial-interglacial cycle. Reconstructed grain size distributions (GSDs) consist of volume fractions on the order of 10-24 m3, and the mean GSDs are modal but with distinctive skewness among the loess, the weakly developed paleosol (weak paleosol), and the mature paleosol. This indicates that the mean volume of SP particles in this sequence tends to increase during the transition from the loess to the paleosol. An index, defined as the difference between χ130 at the lowest (130 Hz) and χ500k at the highest (500 kHz) frequencies normalized to χ130, is judged to be a more suitable index than previous frequency dependence parameters for the concentration of SP particles. This index has a strong correlation with χ130, showing a continuous 'growth curve' with the rate of increase being highest for the loess, moderate for the weak paleosol, and saturated for the paleosol. The characteristic curve suggests that smaller SP particles are preferentially formed in the earlier stage of pedogenesis rather than the later phase when even larger particles are formed in the mature paleosol. These results demonstrate that the broad-band-frequency susceptibility measurement will be useful for the quantitative assessment of magnetic nanoparticles in soils and sediments. Additionally, we point out that the measurement in the frequency domain generally requires time and may not be most suitable to routine measurements. We thus propose an alternative manner, the measurement in the time domain that can be
MC-CDMA with frequency domain diversity reception for sectored indoor wireless cellular networks
NASA Astrophysics Data System (ADS)
Sibanda, Andrew; Dlodlo, Mqhele E.
2001-07-01
A Monte Carlo simulation was conducted to assess the performance of Multi-Carrier Code Division Multiple Access (MC-CDMA) in a sectored cell, in an indoor environment. In each sector, terminal schedule packet transmission using slotted p-persistent Inhibit Sense Multiple Access, while the packets themselves are transmitted using MC-CDMA. The simulated bit error rate performance of MC-CDMA with combining strategies maximal ratio combining (MRC) and equal gain combining (EGC) used in the frequency domain are presented. A comparison is made between analytically determined bit error probability for a single user in an additive white Gaussian noise channel using binary phase shift keying (BPSK), and simulated bit error rate for a single user using MC-CDMA with MRC and EGC. The determination of the number of sectors in a cell is also given. MC-CDMA with diversity combining outperforms BPSK in a non-fading AWGN channel. Further, as the user-number increases, EGC performs better than MRC if these combining strategies are used with MC-CDMA. Finally, the results show the basis for determining the number of sectors in a cell. When using slotted p-persistent ISMA, it is envisaged that only a single user will transmit at a time in a sector.
NASA Astrophysics Data System (ADS)
Zhou, Haigen; Lin, Jun; Liu, Changsheng; Kang, Lili; Li, Gang; Zeng, Xinsen
2016-03-01
Multi-source and multi-frequency emission method can make full use of the valuable and short flight time in frequency domain semi-airborne electromagnetic (FSAEM) exploration, which has potential to investigate the deep earth structure in complex terrain region. Because several sources are adjacent in multi-source emission method, the interaction of different sources should be considered carefully. An equivalent circuit model of dual-source is established in this paper to assess the interaction between two individual sources, where the parameters are given with the typical values based on the practical instrument system and its application. By simulating the output current of two sources in different cases, the influence from the adjacent source is observed clearly. The current waveforms show that the mutual resistance causes the fluctuation and drift in another source and that the mutual inductance causes transient peaks. A field test with dual-source was conducted to certify the existence of interaction between adjacent sources. The simulation of output current also shows that current errors at low frequency are mainly caused by the mutual resistance while those at high frequency are mainly due to the mutual inductance. Increasing the distance between neighboring sources is a proposed measure to reduce the emission signal errors with designed ones. The feasible distance is discussed in the end. This study gives a useful guidance to lay multi sources to meet the requirement of measurement accuracy in FSAEM survey.
An Efficient Audio Watermarking Algorithm in Frequency Domain for Copyright Protection
NASA Astrophysics Data System (ADS)
Dhar, Pranab Kumar; Khan, Mohammad Ibrahim; Kim, Cheol-Hong; Kim, Jong-Myon
Digital Watermarking plays an important role for copyright protection of multimedia data. This paper proposes a new watermarking system in frequency domain for copyright protection of digital audio. In our proposed watermarking system, the original audio is segmented into non-overlapping frames. Watermarks are then embedded into the selected prominent peaks in the magnitude spectrum of each frame. Watermarks are extracted by performing the inverse operation of watermark embedding process. Simulation results indicate that the proposed watermarking system is highly robust against various kinds of attacks such as noise addition, cropping, re-sampling, re-quantization, MP3 compression, and low-pass filtering. Our proposed watermarking system outperforms Cox's method in terms of imperceptibility, while keeping comparable robustness with the Cox's method. Our proposed system achieves SNR (signal-to-noise ratio) values ranging from 20 dB to 28 dB, in contrast to Cox's method which achieves SNR values ranging from only 14 dB to 23 dB.
NASA Technical Reports Server (NTRS)
Brown, Andrew M.; Schmauch, Preston
2012-01-01
Turbine blades in rocket and jet engine turbomachinery experience enormous harmonic loading conditions. These loads result from the integer number of upstream and downstream stator vanes as well as the other turbine stages. The standard technique for forced response analysis to assess structural integrity is to decompose a CFD generated flow field into its harmonic components, and to then perform a frequency response analysis at the problematic natural frequencies. Recent CFD analysis and water-flow testing at NASA/MSFC, though, indicates that this technique may miss substantial harmonic and non-harmonic excitation sources that become present in complex flows. These complications suggest the question of whether frequency domain analysis is capable of capturing the excitation content sufficiently. Two studies comparing frequency response analysis with transient response analysis, therefore, have been performed. The first is of a bladed disk with each blade modeled by simple beam elements. It was hypothesized that the randomness and other variation from the standard harmonic excitation would reduce the blade structural response, but the results showed little reduction. The second study was of a realistic model of a bladed-disk excited by the same CFD used in the J2X engine program. The results showed that the transient analysis results were up to 10% higher for "clean" nodal diameter excitations and six times larger for "messy" excitations, where substantial Fourier content around the main harmonic exists.
Empirical frequency domain model for fixed-pattern noise in infrared focal plane arrays
NASA Astrophysics Data System (ADS)
Pérez, Francisco; Pezoa, Jorge E.; Figueroa, Miguel; Torres, Sergio N.
2014-11-01
In this paper, a new empirical model for the spatial structure of the fixed-pattern noise (FPN) observed in infrared (IR) focal-plane arrays (FPA) is presented. The model was conceived after analyzing, in the spatial frequency domain, FPN calibration data from different IR cameras and technologies. The analysis showed that the spatial patterns of the FPN are retained in the phase spectrum, while the noise intensity is determined by the magnitude spectrum. Thus, unlike traditional representations, the proposed model abstracts the FPN structure using one matrix for its magnitude spectrum and another matrix for its phase spectrum. Three applications of the model are addressed here. First, an algorithm is provided for generating random samples of the FPN with the same spatial pattern of the actual FPN. Second, the model is used to assess the performance of non-uniformity correction (NUC) algorithms in the presence of spatially correlated and uncorrelated FPN. Third, the model is used to improve the NUC capability of a method that requires, as a reference, a proper FPN sample.
Phonon Mean Free Path Spectra Measured by Broadband Frequency Domain Thermoreflectance
NASA Astrophysics Data System (ADS)
Malen, Jonathan
2014-03-01
Nonmetallic crystalline materials conduct heat by the transport of quantized atomic lattice vibrations called phonons. Thermal conductivity depends on how far phonons travel between scattering events -- their mean free paths (MFPs). Due to the breadth of the phonon MFP spectrum, nanostructuring of materials and devices can reduce thermal conductivity from bulk by scattering long MFP phonons, while short MFP phonons are unaffected. We have developed a novel approach called Broadband Frequency Domain Thermoreflectance (BB-FDTR) that uses high-frequency laser heating to generate non-Fourier heat conduction that can sort phonons based on their MFPs. BB-FDTR outputs thermal conductivity as a function of heating frequency. Through non-equilibrium Boltzmann Transport Equation models this data can be converted to thermal conductivity accumulation, which describes how thermal conductivity is summed from phonons with different MFPs. Relative to alternative approaches, BB-FDTR yields order-of-magnitude improvements in the resolution and breadth of the thermal conductivity accumulation function. We will present data for GaAs, GaN, AlN, Si, and SiC that show interesting commonalities near their respective Debye temperatures and suggest that there may be a universal phonon MFP spectrum for small unit cell non-metals in the high temperature limit. At the time of this abstract submission we are also working on measurements of semiconductor alloys and select metals that will be presented if completed by the conference.
Weighted least-squares algorithm for phase unwrapping based on confidence level in frequency domain
NASA Astrophysics Data System (ADS)
Wang, Shaohua; Yu, Jie; Yang, Cankun; Jiao, Shuai; Fan, Jun; Wan, Yanyan
2015-12-01
Phase unwrapping is a key step in InSAR (Synthetic Aperture Radar Interferometry) processing, and its result may directly affect the accuracy of DEM (Digital Elevation Model) and ground deformation. However, the decoherence phenomenon such as shadows and layover, in the area of severe land subsidence where the terrain is steep and the slope changes greatly, will cause error transmission in the differential wrapped phase information, leading to inaccurate unwrapping phase. In order to eliminate the effect of the noise and reduce the effect of less sampling which caused by topographical factors, a weighted least-squares method based on confidence level in frequency domain is used in this study. This method considered to express the terrain slope in the interferogram as the partial phase frequency in range and azimuth direction, then integrated them into the confidence level. The parameter was used as the constraints of the nonlinear least squares phase unwrapping algorithm, to smooth the un-requirements unwrapped phase gradient and improve the accuracy of phase unwrapping. Finally, comparing with interferometric data of the Beijing subsidence area obtained from TerraSAR verifies that the algorithm has higher accuracy and stability than the normal weighted least-square phase unwrapping algorithms, and could consider to terrain factors.
Zhou, Hong; Melloni, Lucia; Poeppel, David; Ding, Nai
2016-01-01
Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid. PMID:27375465
NASA Astrophysics Data System (ADS)
Bender, Amy N.; Cliche, Jean-François; de Haan, Tijmen; Dobbs, Matt A.; Gilbert, Adam J.; Montgomery, Joshua; Rowlands, Neil; Smecher, Graeme M.; Smith, Ken; Wilson, Andrew
2014-07-01
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 is achieved by increasing the system bandwidth, reducing the dynamic range requirements though active feedback, and digital synthesis of voltage biases with a novel polyphase filter algorithm. In addition, a version of the new fMux readout includes features such as low power consumption and radiation-hard components making it viable for future space-based millimeter telescopes such as the LiteBIRD satellite.
Time and frequency-domain identification and verification of BO-105 dynamic models
NASA Technical Reports Server (NTRS)
Kaletka, Juergen; Gruenhagen, Wolfgang V.; Tischler, Mark B.; Fletcher, Jay W.
1989-01-01
Mathematical models for the dynamics of the DLR BO 105 helicopter are extracted from flight test data using two different approaches: frequency-domain and time-domain identification. Both approaches are reviewed. Results from an extensive data consistency analysis are given. Identifications for 6 degrees of freedom (DOF) rigid body models are presented and compared in detail. The extracted models compare favorably and their prediction capability is demonstrated in verification results. Approaches to extend the 6 DOF models are addressed and first results are presented. System identification is broadly defined as the deduction of system characteristics from measured data. It provides the only possibility to extract both non-parametric (e.g., frequency responses) and parametric (e.g., state space matrices) aircraft models from flight test data and therefore gives a reliable characterization of the dynamics of the actually existing aircraft. Main applications of system identification are seen in areas where higher accuracies of the mathematical models are required: Simulation validation, control system design (in particular model-following control system design for in-flight simulation), and handling qualities.
Frequency-Domain Models for Nonlinear Microwave Devices Based on Large-Signal Measurements
Jargon, Jeffrey A.; DeGroot, Donald C.; Gupta, K. C.
2004-01-01
In this paper, we introduce nonlinear large-signal scattering ( S) parameters, a new type of frequency-domain mapping that relates incident and reflected signals. We present a general form of nonlinear large-signal S-parameters and show that they reduce to classic S-parameters in the absence of nonlinearities. Nonlinear large-signal impedance ( Z) and admittance ( D) parameters are also introduced, and equations relating the different representations are derived. We illustrate how nonlinear large-signal S-parameters can be used as a tool in the design process of a nonlinear circuit, specifically a single-diode 1 GHz frequency-doubler. For the case where a nonlinear model is not readily available, we developed a method of extracting nonlinear large-signal S-parameters obtained with artificial neural network models trained with multiple measurements made by a nonlinear vector network analyzer equipped with two sources. Finally, nonlinear large-signal S-parameters are compared to another form of nonlinear mapping, known as nonlinear scattering functions. The nonlinear large-signal S-parameters are shown to be more general. PMID:27366621
Pham, Audrey S.; Reinhart, Gregory D.
2003-01-01
The allosteric properties of the wild-type Escherichia coli phosphofructokinase were compared to the E187A mutant by using frequency-domain techniques. Tryptophan-shifted mutants comprising of double (W311Y/Y55W and W/311F/F188W) and triple (W311Y/Y55W/E187A and W311F/F188W/E187A) amino acid residue changes, which allowed for better fluorescence probing at targeted sites, were also compared to the wild-type and E187A. The additive nature of multiple mutations allowed one to partition the net effect of modifying residue 187. In general, the mutant enzymes displayed greater heterogeneity in sub-state population than did the wild-type enzyme. The semi-cone angle model was used to quantify the extent of depolarization of the fluorophore. Use of the model presupposes that the extent of depolarization directly correlates with the degree of flexibility of the fluorophore. A relationship has been established between the values determined from the semi-cone angle calculations and the thermodynamic components responsible for the allosteric linkage between the regulatory and substrate binding. Coupling interactions giving rise to positive entropy components are manifested by increasing flexibility of the ternary complexes rather than the binary complexes. PMID:12829519
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
Shifting of wrapped phase maps in the frequency domain using a rational number
NASA Astrophysics Data System (ADS)
Gdeisat, Munther A.; Burton, David R.; Lilley, Francis; Arevalillo-Herráez, Miguel; Abushakra, Ahmad; Qaddoura, Maen
2016-10-01
The number of phase wraps in an image can be either reduced, or completely eliminated, by transforming the image into the frequency domain using a Fourier transform, and then shifting the spectrum towards the origin. After this, the spectrum is transformed back to the spatial domain using the inverse Fourier transform and finally the phase is extracted using the arctangent function. However, it is a common concern that the spectrum can be shifted only by an integer number, meaning that the phase wrap reduction is often not optimal. In this paper we propose an algorithm than enables the spectrum to be frequency shifted by a rational number. The principle of the proposed method is confirmed both by using an initial computer simulation and is subsequently validated experimentally on real fringe patterns. The technique may offer in some cases the prospects of removing the necessity for a phase unwrapping process altogether and/or speeding up the phase unwrapping process. This may be beneficial in terms of potential increases in signal recovery robustness and also for use in time-critical applications.
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.
NASA Astrophysics Data System (ADS)
Franke, S. J.; Roettger, J.; Lahoz, C.; Liu, C. H.
1992-06-01
During the polar mesosphere summer echo (PMSE) campaign in 1988 the first multiple-frequency mesospheric measurements were carried out using EISCAT 224-MHz radar. A case study of nearly simultaneous measurements of coherent backscatter, collected on two closely spaced frequencies on July 3, 1988, is presented. The data are used to investigate the frequency coherence of the radar echoes and to perform frequency domain interferometry (FDI) analysis. The FDI techniques provides precise information about the thickness and relative position of isolated scattering layers. The results indicate that scattering layers with thicknesses in the range 85-120 m are sometimes present in the polar summer mesosphere. Such a layer is shown to exist for a period of approximately 10 min, and its position is tracked as it descends over more than 1 km in altitude and transits from one range gate to the next. In addition, the FDI technique is used to study a case where a sudden frequency jump is observed in the Doppler spectrum.
Smallwood, D.O.; Paez, T.L.
1991-01-01
A procedure for generating vectors of time domain signals which are partially coherent in a prescribed manner is described. The procedure starts with the spectral density matrix, (G{sub xx}(f)), that relates pairs of elements of the vector random process (x(t), {minus}{infinity} < t < {infinity}). The spectral density matrix is decomposed into the form (G{sub xx}(f)) = (U(f)) (S(f)) (U(f)){prime} where (U(f)) is a matrix of complex frequency response functions, and (S(f)) is a diagonal matrix of real functions which can vary with frequency. The factors of the spectral density matrix, (U(f)) and (S(f)), are then used to generate a frame of random data in the frequency domain. The data is transformed into the time domain using an inverse FFT to generate a frame of data in the time domain. Successive frames of data are then windowed, overlapped, and added to form a vector of normal stationary sampled time histories, (x(t)), of arbitrary length. 11 refs., 4 figs., 1 tab.
Phan, Anh-Vu; Gray, Leonard J; Salvadori, Alberto
2010-01-01
In this paper, a two-dimensional symmetric-Galerkin boundary integral formulation for elastodynamic fracture analysis in the frequency domain is described. The numerical implementation is carried out with quadratic elements, allowing the use of an improved quarter-point element for accurately determining frequency responses of the dynamic stress intensity factors (DSIFs). To deal with singular and hypersingular integrals, the formulation is decomposed into two parts: the first part is identical to that for elastostatics while the second part contains at most logarithmic singularities. The treatment of the elastostatic singular and hypersingular singular integrals employs an exterior limit to the boundary, while the weakly singular integrals in the second part are handled by Gauss quadrature. Time histories (transient responses) of the DSIFs can be obtained in a post-processing step by applying the fast Fourier transform (FFT) and inverse FFT to the frequency responses of these DSIFs. Several test examples are presented for the calculation of the DSIFs due to two types of impact loading: Heaviside step loading and blast loading. The results suggest that the combination of symmetric-Galerkin and FFT algorithms in determining transient responses of the DSIFs is robust and effective.
Frequency-domain measurement of the spin-imbalance lifetime in superconductors
NASA Astrophysics Data System (ADS)
Quay, C. H. L.; Dutreix, C.; Chevallier, D.; Bena, C.; Aprili, M.
2016-06-01
We have measured the lifetime of spin imbalances in the quasiparticle population of a superconductor (τs) in the frequency domain. A time-dependent spin imbalance is created by injecting spin-polarized electrons at finite excitation frequencies into a thin-film mesoscopic superconductor (Al) in an in-plane magnetic field (in the Pauli limit). The time-averaged value of the spin-imbalance signal as a function of excitation frequency frf shows a cutoff at frf≈1 /(2 π τs) . The spin-imbalance lifetime is relatively constant in the accessible ranges of temperatures, with perhaps a slight increase with increasing magnetic field. Taking into account sample thickness effects, τs is consistent with previous measurements and of the order of the electron-electron scattering time τe e. Our data are qualitatively well described by a theoretical model taking into account all quasiparticle tunneling processes from a normal metal into a superconductor.
Mazhar, Amaan; Saggese, Steve; Pollins, Alonda C.; Cardwell, Nancy L.; Nanney, Lillian; Cuccia, David J.
2014-01-01
Abstract. 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<0.01), but were unable to differentiate deep partial from full thickness wounds in the first 72 h. Tissue scattering parameters separated superficial burns from all burn types immediately after injury (p<0.01), and separated all three burn types from each other after 24 h (p<0.01). Tissue scattering parameters also showed a strong negative correlation to histological 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. PMID:25147961
Improved free-surface expression for frequency-domain elastic optimal mixed-grid modeling
NASA Astrophysics Data System (ADS)
Cao, Jian; Chen, Jing-Bo; Dai, Meng-Xue
2016-07-01
An accurate and efficient forward modeling is the foundation of full-waveform inversion (FWI). In elastic wave modeling, one of the key problems is how to deal with the free-surface boundary condition appropriately. For the representation of the free-surface boundary condition, conventional displacement-based approaches and staggered-grid approaches are often used in time-domain. In frequency-domain, considering the saving of storage and CPU time, we integrate the idea of physical parameter-modified staggered-grid approach in time-domain with an elastic optimal mixed-grid modeling scheme to design an improved parameter-modified free-surface expression. Accuracy analysis shows that an elastic optimal mixed-grid modeling scheme using the parameter-modified free-surface expression can provide more accurate solutions with only 4 grid points per smallest shear wavelength than conventional displacement-based approaches and is stable for most Poisson ratios. Besides, it also yields smaller condition number of the resulting impedance matrix than conventional displacement-based approaches in laterally varying complex media. These advantages reveal great potential of this free-surface expression in big-data practical application.
Two-dimensional frequency-domain acoustic full-waveform inversion with rugged topography
NASA Astrophysics Data System (ADS)
Zhang, Qian-Jiang; Dai, Shi-Kun; Chen, Long-Wei; Li, Kun; Zhao, Dong-Dong; Huang, Xing-Xing
2015-09-01
We studied finite-element-method-based two-dimensional frequency-domain acoustic FWI under rugged topography conditions. The exponential attenuation boundary condition suitable for rugged topography is proposed to solve the cutoff boundary problem as well as to consider the requirement of using the same subdivision grid in joint multifrequency inversion. The proposed method introduces the attenuation factor, and by adjusting it, acoustic waves are sufficiently attenuated in the attenuation layer to minimize the cutoff boundary effect. Based on the law of exponential attenuation, expressions for computing the attenuation factor and the thickness of attenuation layers are derived for different frequencies. In multifrequency-domain FWI, the conjugate gradient method is used to solve equations in the Gauss-Newton algorithm and thus minimize the computation cost in calculating the Hessian matrix. In addition, the effect of initial model selection and frequency combination on FWI is analyzed. Examples using numerical simulations and FWI calculations are used to verify the efficiency of the proposed method.
Frequency Domain Response at Pacific Coast Harbors to Major Tsunamis of 2005-2011
NASA Astrophysics Data System (ADS)
Xing, Xiuying; Kou, Zhiqing; Huang, Ziyi; Lee, Jiin-Jen
2013-06-01
Tsunamis waves caused by submarine earthquake or landslide might contain large wave energy, which could cause significant human loss and property damage locally as well as in distant region. The response of three harbors located at the Pacific coast (i.e. Crescent City Harbor, Los Angeles/Long Beach Port, and San Diego Harbor) to six well-known tsunamis events generated (both near-field and far-field) between 2005 and 2011 are examined and simulated using a hybrid finite element numerical model in frequency domain. The model incorporated the effects of wave refraction, wave diffraction, partial wave reflection from boundaries, entrance and bottom energy dissipation. It can be applied to harbor regions with arbitrary shapes and variable water depth. The computed resonant periods or modes of oscillation for three harbors are in good agreement with the energy spectral analysis of the time series of water surface elevations recorded at tide gauge stations inside three harbors during the six tsunamis events. The computed wave induced currents based on the present model are also in qualitative agreement with some of the reported eye-witness accounts absence of reliable current data. The simulated results show that each harbor responded differently and significantly amplified certain wave period(s) of incident wave trains according to the shape, topography, characteristic dimensions and water depth of the harbor basins.
Frequency domain mediolateral balance assessment using a center of pressure tracking task.
Cofré Lizama, L Eduardo; Pijnappels, Mirjam; Reeves, N Peter; Verschueren, Sabine M P; van Dieën, Jaap H
2013-11-15
Since impaired mediolateral balance can increase fall risk, especially in the elderly, its quantification and training might be a powerful preventive tool. We propose a visual tracking task (VTT) with increasing frequencies (.3-2.0Hz) and with center of pressure as visual feedback as an assessment method. This mediolateral balance assessment (MELBA) consists of two tasks, tracking a predictable target signal to determine physical capacity and tracking an unpredictable target signal to determine sensorimotor integration limitations. Within and between sessions learning effects and reliability in balance performance descriptors in both tasks were studied in 20 young adults. Balance performance was expressed as the phase-shift (PS) and gain (G) between the target and CoP in the frequency domain and cut-off frequencies at which the performance dropped. Results showed significant differences between the MELBA tasks in PS and G indicating a lower delay and higher accuracy in tracking the predictable target. Significant within and between sessions learning effects for the same measures were found only for the unpredictable task. Reliability of the cut-off frequencies at which PS and G performance declined and the average values within cut-off frequencies was fair to good (ICC .46-.66) for the unpredictable task and fair to excellent for the predictable task (ICC .68-.87). In conclusion, MELBA can reliably quantify balance performance using a predictable VTT. Additionally, the unpredictable tasks can give insight into the visuomotor integration mechanisms controlling balance and highlights MELBA's potential as a training tool.
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%.
3D seismic data reconstruction based on complex-valued curvelet transform in frequency domain
NASA Astrophysics Data System (ADS)
Zhang, Hua; Chen, Xiaohong; Li, Hongxing
2015-02-01
Traditional seismic data sampling must follow the Nyquist Sampling Theorem. However, the field data acquisition may not meet the sampling criteria due to missing traces or limits in exploration cost, causing a prestack data reconstruction problem. Recently researchers have proposed many useful methods to regularize the seismic data. In this paper, a 3D seismic data reconstruction method based on the Projections Onto Convex Sets (POCS) algorithm and a complex-valued curvelet transform (CCT) has been introduced in the frequency domain. In order to improve reconstruction efficiency and reduce the computation time, the seismic data are transformed from the t-x-y domain to the f-x-y domain and the data reconstruction is processed for every frequency slice during the reconstruction process. The selection threshold parameter is important for reconstruction efficiency for each iteration, therefore an exponential square root decreased (ESRD) threshold is proposed. The experimental results show that the ESRD threshold can greatly reduce iterations and improve reconstruction efficiency compared to the other thresholds for the same reconstruction result. We also analyze the antinoise ability of the CCT-based POCS reconstruction method. The example studies on synthetic and real marine seismic data showed that our proposed method is more efficient and applicable.
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.
Zhou, Haigen; Lin, Jun; Liu, Changsheng; Kang, Lili; Li, Gang; Zeng, Xinsen
2016-03-01
Multi-source and multi-frequency emission method can make full use of the valuable and short flight time in frequency domain semi-airborne electromagnetic (FSAEM) exploration, which has potential to investigate the deep earth structure in complex terrain region. Because several sources are adjacent in multi-source emission method, the interaction of different sources should be considered carefully. An equivalent circuit model of dual-source is established in this paper to assess the interaction between two individual sources, where the parameters are given with the typical values based on the practical instrument system and its application. By simulating the output current of two sources in different cases, the influence from the adjacent source is observed clearly. The current waveforms show that the mutual resistance causes the fluctuation and drift in another source and that the mutual inductance causes transient peaks. A field test with dual-source was conducted to certify the existence of interaction between adjacent sources. The simulation of output current also shows that current errors at low frequency are mainly caused by the mutual resistance while those at high frequency are mainly due to the mutual inductance. Increasing the distance between neighboring sources is a proposed measure to reduce the emission signal errors with designed ones. The feasible distance is discussed in the end. This study gives a useful guidance to lay multi sources to meet the requirement of measurement accuracy in FSAEM survey. PMID:27036795
Time and frequency domain investigation of the heat transfer to a synthetic air jet
NASA Astrophysics Data System (ADS)
Rylatt, D. I.; O'Donovan, T. S.
2012-11-01
Heat transfer to a synthetic air jets is investigated experimentally. The influence of peaks in heat transfer outwith the stagnation region of the jet are of particular interest. Heat transfer to the jets is reported for experimental parameters, jet exit to impingement surface spacings, H/D = 1, Reynolds number of 3000, non-dimensional Stroke length, L0/D of 14.and an excitation frequency of 70 Hz Peaks in heat transfer outwith the stagnation region of the jet are investigated in both the time and frequency domain and a connection between the driving frequency of the jet and changes in the rate of heat transfer is outlined. It is shown that two type's changes in the rate of heat transfer outwith the stagnation region are present in synthetic jet impingement heat transfer; those associated with the jet excitation frequency and therefore attributed to interactions between the two jet flow regimes and those associated with the breakdown of coherent structures in the jet flow.
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
Signal generation and mixing electronics for frequency-domain lifetime and spectral fluorometry
NASA Technical Reports Server (NTRS)
Cruce, Tommy Clay (Inventor); Hallidy, William H. (Inventor); Chin, Robert C. (Inventor)
2007-01-01
The present invention additionally comprises a method and apparatus for generating and mixing signals for frequency-domain lifetime and spectral fluorometry. The present invention comprises a plurality of signal generators that generate a plurality of signals where the signal generators modulate the amplitude and/or the frequency of the signals. The present invention uses one of these signals to drive an excitation signal that the present invention then directs and transmits at a target mixture, which absorbs the energy from the excitation signal. The property of fluorescence causes the target mixture to emit an emitted signal that the present invention detects with a signal detector. The present invention uses a plurality of mixers to produce a processor reference signal and a data signal. The present invention then uses a processor to compare the processor reference signal with the data signal by analyzing the differences in the phase and the differences in the amplitude between the two signals. The processor then extracts the fluorescence lifetime and fluorescence spectrum of the emitted signal from the phase and amplitude information using a chemometric analysis.
Signal generation and mixing electronics for frequency-domain lifetime and spectral fluorometry
NASA Technical Reports Server (NTRS)
Cruce, Tommy C. (Inventor); Hallidy, William H. (Inventor); Chin, Robert C. (Inventor)
1999-01-01
The present invention additionally comprises a method and apparatus for generating and mixing signals for frequency-domain lifetime and spectral fluorometry. The present invention comprises a plurality of signal generators that generate a plurality of signals where the signal generators modulate the amplitude and/or the frequency of the signals. The present invention uses one of these signals to drive an excitation signal that the present invention then directs and transmits at a target mixture, which absorbs the energy from the excitation signal. The property of fluorescence causes the target mixture to emit an emitted signal that the present invention detects with a signal detector. The present invention uses a plurality of mixers to produce a processor reference signal and a data signal. The present invention then uses a processor to compare the processor reference signal with the data signal by analyzing the differences in the phase and the differences in the amplitude between the two signals. The processor then extracts the fluorescence lifetime and fluorescence spectrum of the emitted signal from the phase and amplitude information using a chemometric analysis.
First-in-human pilot study of a spatial frequency domain oxygenation imaging system
NASA Astrophysics Data System (ADS)
Gioux, Sylvain; Mazhar, Amaan; Lee, Bernard T.; Lin, Samuel J.; Tobias, Adam M.; Cuccia, David J.; Stockdale, Alan; Oketokoun, Rafiou; Ashitate, Yoshitomo; Kelly, Edward; Weinmann, Maxwell; Durr, Nicholas J.; Moffitt, Lorissa A.; Durkin, Anthony J.; Tromberg, Bruce J.; Frangioni, John V.
2011-08-01
Oxygenation measurements are widely used in patient care. However, most clinically available instruments currently consist of contact probes that only provide global monitoring of the patient (e.g., pulse oximetry probes) or local monitoring of small areas (e.g., spectroscopy-based probes). Visualization of oxygenation over large areas of tissue, without a priori knowledge of the location of defects, has the potential to improve patient management in many surgical and critical care applications. In this study, we present a clinically compatible multispectral spatial frequency domain imaging (SFDI) system optimized for surgical oxygenation imaging. This system was used to image tissue oxygenation over a large area (16×12 cm) and was validated during preclinical studies by comparing results obtained with an FDA-approved clinical oxygenation probe. Skin flap, bowel, and liver vascular occlusion experiments were performed on Yorkshire pigs and demonstrated that over the course of the experiment, relative changes in oxygen saturation measured using SFDI had an accuracy within 10% of those made using the FDA-approved device. Finally, the new SFDI system was translated to the clinic in a first-in-human pilot study that imaged skin flap oxygenation during reconstructive breast surgery. Overall, this study lays the foundation for clinical translation of endogenous contrast imaging using SFDI.
NASA Astrophysics Data System (ADS)
Siemon, Bernhard; Steuer, Annika; Ullmann, Angelika; Vasterling, Margarete; Voß, Wolfgang
Airborne geophysical methods have been used successfully in groundwater exploration over the last decades. Particularly airborne electromagnetics is appropriate for large-scale and efficient groundwater surveying. Due to the dependency of the electrical conductivity on both the clay content of the host material and the mineralisation of the water, airborne electromagnetics is suitable for providing information on groundwater resources, water quality, aquifer conditions and protection levels. Frequency-domain helicopter-borne electromagnetic systems are used to investigate near-surface groundwater occurrences in detail even in rough terrain and populated areas. In order to reveal the subsurface conductivity distribution, the quantities measured, the secondary magnetic fields, are generally inverted into resistivity-depth models. Due to the skin-effect the penetration depths of the electromagnetic fields depend on the system characteristics used: high-frequency data describe the shallower parts of the conducting subsurface and the low-frequency data the deeper parts. Typical maximum investigation depths range from some ten metres (highly conductive saltwater saturated sediments) to several hundred metres (resistive hard rocks). In urban areas there are a number of man-made sources affecting the electromagnetic measurements. These effects on the secondary field values are discussed on the basis of synthetic data as well as uncorrected and corrected field data. The case histories of different hydrogeological setups in Indonesia, The Netherlands and Germany demonstrate that airborne electromagnetics can be applied to groundwater exploration purposes even in urban areas.
NASA Astrophysics Data System (ADS)
Ji, Yongzhen; Yuan, Sanyi; Wang, Shangxu; Deng, Li
2016-10-01
The prestack amplitude variation with angle (AVA) inversion method utilising angle information to obtain the elastic parameters estimation of subsurface rock is vital to reservoir characterisation. Under the assumption of blocky layered media, an AVA inversion algorithm combining prestack spectral reflectivity inversion with sparse Bayesian learning (SBL) is presented. Prior information of the model parameters is involved in the inversion through the hierarchical Gaussian distribution where each parameter has a unique variance instead of sharing a common one. The frequency-domain prestack SBL inversion method retrieves sparse P- and S-wave impedance reflectivities by sequentially adding, deleting or re-estimating hyper-parameters without pre-setting the number of non-zero P- and S-wave reflectivity spikes. The selection of frequency components can help get rid of noise outside the selected frequency band. The precondition of the parameters helps to balance the weight of different parameters and incorporate the relationship between those parameters into the inversion process, thus improves the inversion result. Synthetic and real data examples illustrate the effectiveness of the method.
Frequency-Domain Equalization in Single-Carrier Transmission: Filter Bank Approach
NASA Astrophysics Data System (ADS)
Yang, Yuan; Ihalainen, Tero; Rinne, Mika; Renfors, Markku
2007-12-01
This paper investigates the use of complex-modulated oversampled filter banks (FBs) for frequency-domain equalization (FDE) in single-carrier systems. The key aspect is mildly frequency-selective subband processing instead of a simple complex gain factor per subband. Two alternative low-complexity linear equalizer structures with MSE criterion are considered for subband-wise equalization: a complex FIR filter structure and a cascade of a linear-phase FIR filter and an allpass filter. The simulation results indicate that in a broadband wireless channel the performance of the studied FB-FDE structures, with modest number of subbands, reaches or exceeds the performance of the widely used FFT-FDE system with cyclic prefix. Furthermore, FB-FDE can perform a significant part of the baseband channel selection filtering. It is thus observed that fractionally spaced processing provides significant performance benefit, with a similar complexity to the symbol-rate system, when the baseband filtering is included. In addition, FB-FDE effectively suppresses narrowband interference present in the signal band.
A frequency domain model for the spatial fixed-pattern noise in infrared focal plane arrays
NASA Astrophysics Data System (ADS)
Medina, Osvaldo J.; Pezoa, Jorge E.; Torres, Sergio N.
2011-10-01
The multiplicative and additive components of the fixed-pattern noise (FPN) in infrared (IR) focal plane arrays (FPAs) are typically modeled as time-stationary, spatially unstructured random processes. Even though the latter assumption is convenient, it is also inaccurate due to FPN is indeed observed as a spatial pattern, with random intensity values, superimposed over the true images. In this paper, the spatial structure in both the multiplicative and the additive components of the FPN has been modeled in the frequency domain. The key observation in the proposed models is that regular spatial patterns manifest themselves as narrowband components in the magnitude spectrum of an image. Thus, the spatial structure of FPN can be abstracted in a straightforward manner by approximating the spectral response of the FPN. Moreover, the random intensity of the FPN has been also modeled by matching the empirically estimated distributions of the intensity values of both multiplicative and additive components of the FPN. Experimental characterization of FPN has been conducted using black-body radiator sources, and the theoretical as well as practical applicability of the proposed models has been illustrated by both synthesizing FPN from three different IR cameras and by proposing a simple yet effective metric to assess the amount of FPN in FPA-based cameras.
Improving the execution of clinical guidelines and temporal data abstraction high-frequency domains.
Seyfang, Andreas; Paesold, Michael; Votruba, Peter; Miksch, Silvia
2008-01-01
The execution of clinical guidelines and protocols (CGPs) is a challenging task in high-frequency domains such as Intensive Care Units. On the one hand, sophisticated temporal data abstraction is required to match the low-level information from monitoring devices and electronic patient records with the high-level concepts in the CGPs. On the other hand, the frequency of the data delivered by monitoring devices mandates a highly efficient implementation of the reasoning engine which handles both data abstraction and execution of the guideline. The language Asbru represents CGPs as a hierarchy of skeletal plans and integrates intelligent temporal data abstraction with plan execution to bridge the gap between measurements and concepts in CGPs. We present our Asbru interpreter, which compiles abstraction rules and plans into a network of abstraction modules by the system. This network performs the content of the plans triggered by the arriving patient data. Our approach evaluated to be efficient enough to handle high-frequency data while coping with complex guidelines and temporal data abstraction.
NASA Astrophysics Data System (ADS)
Ball, Keenan R.; Buck, John R.
2003-04-01
Correlating the acoustic and physical behavior of marine mammals is an ongoing challenge for scientists studying the links between acoustic communication and social behavior of these animals. This talk describes a system to record and correlate the physical and acoustical behavior of dolphins. A sparse, short baseline audio/video array consisting of 16 hydrophones and an underwater camera was constructed in a cross configuration to measure the acoustic signals of vocalizing dolphins. The bearings of vocalizing dolphins were estimated using the broadband frequency domain beamforming algorithm for sparse arrays to suppress grating lobes of Thode et al. [J. Acoust. Soc. Am. 107 (2000)]. The estimated bearings from the acoustic signals were then converted to video image coordinates and a marker was placed on the video image. The system was calibrated both at an indoor tank and from an outdoor dock at UMass Dartmouth prior to field tests in a natural lagoon at the Dolphin Connection on Duck Key, FL. These tests confirmed that the system worked well within the limits of underwater visibility by consistently placing the marker on or near the whistling or echolocating dolphin. [Work supported by NSF Ocean Sciences.
Yngvesson, Sigfrid K.; St. Peter, Benjamin; Siqueira, Paul; Kelly, Patrick; Glick, Stephen; Karellas, Andrew; Khan, Ashraf
2013-01-01
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 × 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. PMID:24353380
Zhou, Hong; Melloni, Lucia; Poeppel, David; Ding, Nai
2016-01-01
Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid. PMID:27375465
An implicit and adaptive nonlinear frequency domain approach for periodic viscous flows
NASA Astrophysics Data System (ADS)
Mosahebi, A.; Nadarajah, S.
2014-12-01
An implicit nonlinear Lower-Upper symmetric Gauss-Seidel (LU-SGS) solver has been extended to the adaptive Nonlinear Frequency Domain method (adaptive NLFD) for periodic viscous flows. The discretized equations are linearized in both spatial and temporal directions, yielding an innovative segregate approach, where the effects of the neighboring cells are transferred to the right-hand-side and are updated iteratively. This property of the solver is aligned with the adaptive NLFD concept, in which different cells have different number of modes; hence, should be treated individually. The segregate analysis of the modal equations prevents assembling and inversion of a large left-hand-side matrix, when high number of modes are involved. This is an important characteristic for a selected flow solver of the adaptive NLFD method, where a high modal content may be required in highly unsteady parts of the flow field. The implicit nonlinear LU-SGS solver has demonstrated to be both robust and computationally efficient as the number of modes is increased. The developed solver is thoroughly validated for the laminar vortex shedding behind a stationary cylinder, high angle of attack NACA0012 airfoil, and a plunging NACA0012 airfoil. An order of magnitude improvement in the computational time is observed through the developed implicit approach over the classical modified 5-stage Runge-Kutta method.
Simulation of ultrasound two-dimensional array transducers using a frequency domain model.
Rao, Min; Varghese, Tomy; Zagzebski, James A
2008-07-01
Ultrasound imaging with two-dimensional (2D) arrays has garnered broad interest from scanner manufacturers and researchers for real time three-dimensional (3D) applications. Previously the authors described a frequency domain B-mode imaging model applicable for linear and phased array transducers. In this paper, the authors extend this model to incorporate 2D array transducers. Further approximations can be made based on the fact that the dimensions of the 2D array element are small. The model is compared with the widely used ultrasound simulation program FIELD II, which utilizes an approximate form of the time domain impulse response function. In a typical application, errors in simulated RF waveforms are less than 4% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/35 of those incurred using FIELD II. The 2D model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, dynamic receive focusing, and 3D beam steering can also be simulated.