Power Spectral Density and Hilbert Transform
2016-12-01
there is 1.3 W of power. How much bandwidth does a pure sine wave require? The bandwidth of an ideal sine wave is 0 Hz. How do you represent a 1-W... sine wave source (power concentrated in a single frequency) on a power spectral density graph (power per frequency, watts per hertz)? The Dirac delta...represent the power contained in a sine wave (zero bandwidth) on a power spectral density graph. Fig. 1 Dirac delta function () =
Density Wave Signatures In VIMS Spectral Data
NASA Astrophysics Data System (ADS)
Nicholson, Philip D.; Hedman, M. M.; Cassini VIMS Team
2012-10-01
Spectral scans of Saturn's rings by the Cassini VIMS instrument have revealed both regional and local variations in the depths of the water ice bands at 1.5 and 2.0 microns, which have been interpreted in terms of variations in regolith grain size and the amount of non-icy "contaminants" (Filacchione et al. 2012; Hedman et al. 2012). Noteworthy among the local variations are distinctive patterns associated with the four strong density waves in the A ring. Within each wavetrain there is a peak in band strength relative to the surrounding material, while extending on both sides of the wave is a "halo" of reduced band strength. The typical width of these haloes is 400-500 km, about 2-3 times the visible extent of the density waves. The origin of these features is unknown, but may involve enhanced collisional erosion in the wave zones and transport of the smaller debris into nearby regions. A similar pattern of band depth variations is also seen at several locations in the more opaque B ring in association with the strong 3:2 ILRs of Janus, Pandora and Prometheus. The former shows a pattern just like its siblings in the A ring, while the latter two resonances show haloes, but without central peaks. In each case, the radial widths of the halo approaches 1000 km, but stellar occultation profiles show no detectable density wavetrain. We suggest that this spectral signature may be a useful diagnostic for the presence of strong density waves in regions where the rings are too opaque for occultations to reveal a typical wave profile. More speculatively, the displacement of the haloes' central radii from the calculated ILR locations of 600-700 km could imply a surface density in the central B ring in excess of 500 g/cm^2. This research was supported by the Cassini/Huygens project.
Power spectral density of 3D noise
NASA Astrophysics Data System (ADS)
Haefner, David P.
2017-05-01
When evaluated with a spatially uniform irradiance, an imaging sensor exhibits both spatial and temporal variations, which can be described as a three-dimensional (3D) random process considered as noise. In the 1990s, NVESD engineers developed an approximation to the 3D power spectral density (PSD) for noise in imaging systems known as 3D noise. This correspondence describes the decomposition of the full 3D PSD into the familiar components from the 3D Noise model. The standard 3D noise method assumes spectrally (spatio-temporal) white random processes, which is demonstrated to be atypically in the case with complex modern imaging sensors. Using the spectral shape allows for more appropriate analysis of the impact of the noise of the sensor. The processing routines developed for this work consider finite memory constraints and utilize Welch's method for unbiased PSD estimation. In support of the reproducible research effort, the Matlab functions associated with this work can be found on the Mathworks file exchange [1].
Spectral density measurements of gyro noise
NASA Technical Reports Server (NTRS)
Truncale, A.; Koenigsberg, W.; Harris, R.
1972-01-01
Power spectral density (PSD) was used to analyze the outputs of several gyros in the frequency range from 0.01 to 200 Hz. Data were accumulated on eight inertial quality instruments. The results are described in terms of input angle noise (arcsec 2/Hz) and are presented on log-log plots of PSD. These data show that the standard deviation of measurement noise was 0.01 arcsec or less for some gyros in the passband from 1 Hz down 10 0.01 Hz and probably down to 0.001 Hz for at least one gyro. For the passband between 1 and 100 Hz, uncertainties in the 0.01 and 0.05 arcsec region were observed.
A method of determining spectral analytical dye densities
NASA Technical Reports Server (NTRS)
Scarpace, F. L.; Friederichs, G. A.
1978-01-01
A straightforward method for the user of color imagery to determine the spectral analytical density of dyes present in the processed imagery is presented. The method involves exposing a large number of different color patches on the film which span the gamut of the film's imaging capabilities. From integral spectral density measurements at 16 to 19 different wavelengths, the unit spectral dye curves for each of the three dyes present were determined in two different types of color films. A discussion of the use of these spectral dye densities to determine the transformation between integral density measurements and analytical density is presented.
Spectral densities and nuclear spin relaxation in solids
NASA Astrophysics Data System (ADS)
Beckmann, Peter A.
1988-12-01
We investigate the properties of ten spectral densities relevant for nuclear spin relaxation studies in solids. This is preceded by a brief review of nuclear spin relaxation in solids which includes a discussion of the appropriate spin-dependent interactions and the various relaxation rates which can be measured. Also, the link between nuclear spin relaxation and dielectric relaxation is discussed. Where possible and/or appropriate each of the spectral densities is expressed as a continuous distribution of Bloembergen-Purcell-Pound (or Debye) spectral densities 2ξ /(1 + ξ 2 ω 2) for nuclear Larmor angular frequency ω and correlation time ξ. The spectral densities are named after their originators or the shape of the distributions of correlation times or both and are (1) Bloembergen-Purcell-Pound or δ-function, (2) Havriliak-Negami, (3) Cole-Cole, (4) Davidson-Cole, (5) Fang, (6) Fuoss-Kirkwood, (7) Bryn Mawr, (8) Wagner or log-Gaussian, (9) log-Lorentzian, and (10) Fröhlich or energy box. The Havriliak-Negami spectral density is related to the Dissado-Hill theory for dielectric relaxation. The spectral densities are expressed in a way which makes them easy to compare with each other and with experimental data. Many plots of the distributions of correlation times and of the spectral densities vs. various correlation times characterizing the distributions are given.
A method of determining spectral dye densities in color films
NASA Technical Reports Server (NTRS)
Friederichs, G. A.; Scarpace, F. L.
1977-01-01
A mathematical analysis technique called characteristic vector analysis, reported by Simonds (1963), is used to determine spectral dye densities in multiemulsion film such as color or color-IR imagery. The technique involves examining a number of sets of multivariate data and determining linear transformations of these data to a smaller number of parameters which contain essentially all of the information contained in the original set of data. The steps involved in the actual procedure are outlined. It is shown that integral spectral density measurements of a large number of different color samples can be accurately reconstructed from the calculated spectral dye densities.
A method of determining spectral dye densities in color films
NASA Technical Reports Server (NTRS)
Friederichs, G. A.; Scarpace, F. L.
1977-01-01
A mathematical analysis technique called characteristic vector analysis, reported by Simonds (1963), is used to determine spectral dye densities in multiemulsion film such as color or color-IR imagery. The technique involves examining a number of sets of multivariate data and determining linear transformations of these data to a smaller number of parameters which contain essentially all of the information contained in the original set of data. The steps involved in the actual procedure are outlined. It is shown that integral spectral density measurements of a large number of different color samples can be accurately reconstructed from the calculated spectral dye densities.
Direct experimental determination of spectral densities of molecular complexes
Pachón, Leonardo A.; Brumer, Paul
2014-11-07
Determining the spectral density of a molecular system immersed in a proteomic scaffold and in contact to a solvent is a fundamental challenge in the coarse-grained description of, e.g., electron and energy transfer dynamics. Once the spectral density is characterized, all the time scales are captured and no artificial separation between fast and slow processes need to be invoked. Based on the fluorescence Stokes shift function, we utilize a simple and robust strategy to extract the spectral density of a number of molecular complexes from available experimental data. Specifically, we show that experimental data for dye molecules in several solvents, amino acid proteins in water, and some photochemical systems (e.g., rhodopsin and green fluorescence proteins), are well described by a three-parameter family of sub-Ohmic spectral densities that are characterized by a fast initial Gaussian-like decay followed by a slow algebraic-like decay rate at long times.
Spectral Density Matrix of a Single Photon Measured
NASA Astrophysics Data System (ADS)
Wasilewski, Wojciech; Kolenderski, Piotr; Frankowski, Robert
2007-09-01
We propose and demonstrate a method for measuring the spectral density matrix of a single photon pulse. The method is based on registering Hong-Ou-Mandel interference between a photon to be measured and a pair of attenuated and suitably delayed laser pulses described by a known spectral amplitude. The density matrix is retrieved from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I down-conversion source, pumped by ultrashort laser pulses. The experimental results agree well with a theoretical model which takes into account the temporal as well as spatial effects in the source.
Spectral density matrix of a single photon measured.
Wasilewski, Wojciech; Kolenderski, Piotr; Frankowski, Robert
2007-09-21
We propose and demonstrate a method for measuring the spectral density matrix of a single photon pulse. The method is based on registering Hong-Ou-Mandel interference between a photon to be measured and a pair of attenuated and suitably delayed laser pulses described by a known spectral amplitude. The density matrix is retrieved from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I down-conversion source, pumped by ultrashort laser pulses. The experimental results agree well with a theoretical model which takes into account the temporal as well as spatial effects in the source.
Breast density estimation from high spectral and spatial resolution MRI.
Li, Hui; Weiss, William A; Medved, Milica; Abe, Hiroyuki; Newstead, Gillian M; Karczmar, Gregory S; Giger, Maryellen L
2016-10-01
A three-dimensional breast density estimation method is presented for high spectral and spatial resolution (HiSS) MR imaging. Twenty-two patients were recruited (under an Institutional Review Board--approved Health Insurance Portability and Accountability Act-compliant protocol) for high-risk breast cancer screening. Each patient received standard-of-care clinical digital x-ray mammograms and MR scans, as well as HiSS scans. The algorithm for breast density estimation includes breast mask generating, breast skin removal, and breast percentage density calculation. The inter- and intra-user variabilities of the HiSS-based density estimation were determined using correlation analysis and limits of agreement. Correlation analysis was also performed between the HiSS-based density estimation and radiologists' breast imaging-reporting and data system (BI-RADS) density ratings. A correlation coefficient of 0.91 ([Formula: see text]) was obtained between left and right breast density estimations. An interclass correlation coefficient of 0.99 ([Formula: see text]) indicated high reliability for the inter-user variability of the HiSS-based breast density estimations. A moderate correlation coefficient of 0.55 ([Formula: see text]) was observed between HiSS-based breast density estimations and radiologists' BI-RADS. In summary, an objective density estimation method using HiSS spectral data from breast MRI was developed. The high reproducibility with low inter- and low intra-user variabilities shown in this preliminary study suggest that such a HiSS-based density metric may be potentially beneficial in programs requiring breast density such as in breast cancer risk assessment and monitoring effects of therapy.
Spectral density of a Wishart model for nonsymmetric correlation matrices.
Vinayak
2013-10-01
The Wishart model for real symmetric correlation matrices is defined as W=AA^{t}, where matrix A is usually a rectangular Gaussian random matrix and A^{t} is the transpose of A. Analogously, for nonsymmetric correlation matrices, a model may be defined for two statistically equivalent but different matrices A and B as AB^{t}. The corresponding Wishart model, thus, is defined as C=AB^{t}BA^{t}. We study the spectral density of C for the case when A and B are not statistically independent. The ensemble average of such nonsymmetric matrices, therefore, does not simply vanishes to a null matrix. In this paper we derive a Pastur self-consistent equation which describes spectral density of C at large matrix dimension. We complement our analytic results with numerics.
Spectral density of a Wishart model for nonsymmetric correlation matrices
NASA Astrophysics Data System (ADS)
Vinayak
2013-10-01
The Wishart model for real symmetric correlation matrices is defined as W=AAt, where matrix A is usually a rectangular Gaussian random matrix and At is the transpose of A. Analogously, for nonsymmetric correlation matrices, a model may be defined for two statistically equivalent but different matrices A and B as ABt. The corresponding Wishart model, thus, is defined as C=ABtBAt. We study the spectral density of C for the case when A and B are not statistically independent. The ensemble average of such nonsymmetric matrices, therefore, does not simply vanishes to a null matrix. In this paper we derive a Pastur self-consistent equation which describes spectral density of C at large matrix dimension. We complement our analytic results with numerics.
Spectral density of the noncentral correlated Wishart ensembles.
Vinayak
2014-10-01
Wishart ensembles of random matrix theory have been useful in modeling positive definite matrices encountered in classical and quantum chaotic systems. We consider nonzero means for the entries of the constituting matrix A which defines the correlated Wishart matrix as W=AA(†), and refer to the ensemble of such Wishart matrices as the noncentral correlated Wishart ensemble (nc-CWE). We derive the Pastur self-consistent equation which describes the spectral density of nc-CWE at large matrix dimension.
Spectral density in the resonance region and analytic confinement
Kalloniatis, Alex C.; Nedelko, Sergei N.; Smekal, Lorenz von
2004-11-01
We study the role of finite widths of resonances in a nonlocal version of the Wick-Cutkosky model. The spectrum of bound states is known analytically in this model and forms linear Regge tragectories. We compute the widths of resonances, calculate the spectral density in an extension of the Breit-Wigner ansatz and discuss a mechanism for the damping of unphysical exponential growth of observables at high energy due to finite widths of resonances.
Power Spectral Densities of Atmospheric Aerosol Particle Counts
2010-01-01
Power Spectral Densities of Atmospheric Aerosol Particle Counts by Chatt C. Williamson, Steven C. Hill, Dennis M. Garvey, Michael L. Larsen...Williamson, Steven C. Hill, Dennis M. Garvey, Michael L. Larsen, and Chrryl L. Klopp Computational and Information Sciences Directorate, ARL...6. AUTHOR(S) Chatt C. Williamson, Steven C. Hill, Dennis M. Garvey, Michael L. Larsen, and Cheryl L. Klipp 5d. PROJECT NUMBER 5e. TASK NUMBER
Effective dielectric constants and spectral density analysis of plasmonic nanocomposites
NASA Astrophysics Data System (ADS)
Lu, Jin You; Raza, Aikifa; Fang, Nicholas X.; Chen, Gang; Zhang, TieJun
2016-10-01
Cermet or ceramic-metal composite coatings promise great potentials in light harvesting, but the complicated composite structure at the nanoscale induces a design challenge to predict their optical properties. We find that the effective dielectric constants of nanocomposites predicted by finite-difference-time-domain (FDTD) simulation results match those of different classical effective medium theories in their respective validity range. However, a precise prediction of the fabricated nanocomposite properties for different filling factors is very challenging. In this work, we extract the spectral density functions in the Bergman representation from the analytical models, numerical simulations, and experimental data of plasmonic nanocomposites. The spectral density functions, which only depend on geometry of the nanocomposite material, provide a unique measure on the contribution of individual and percolated particles inside the nanocomposite. According to the spectral density analysis of measured dielectric constants, the material properties of nanocomposites fabricated by the co-sputtering approach are dominated by electromagnetic interaction among individual metallic particles. While in the case of the nanocomposites fabricated by the multilayer thin film approach, the material properties are dominated by percolated metallic particles inside the dielectric host, as indicated by our FDTD simulation results. This understanding provides new physical insight into the interaction between light and plasmonic nanocomposites.
Rates, flux densities, and spectral indices of meteor radio afterglows
NASA Astrophysics Data System (ADS)
Obenberger, K. S.; Dowell, J. D.; Hancock, P. J.; Holmes, J. M.; Pedersen, T. R.; Schinzel, F. K.; Taylor, G. B.
2016-07-01
Using the narrowband all-sky imager mode of the Long Wavelength Array (LWA1), we have now detected 30 transients at 25.6 MHz, 1 at 34 MHz, and 93 at 38.0 MHz. While we have only optically confirmed that 37 of these events are radio afterglows from meteors, evidence suggests that most, if not all, are. Using the beam-forming mode of the LWA1, we have also captured the broadband spectra between 22.0 and 55.0 MHz of four events. We compare the smooth, spectral components of these four events and fit the frequency-dependent flux density to a power law, and find that the spectral index is time variable, with the spectrum steepening over time for each meteor afterglow. Using these spectral indices along with the narrowband flux density measurements of the 123 events at 25.6 and 38 MHz, we predict the expected flux densities and rates for meteor afterglows potentially observable by other low-frequency radio telescopes.
Geometrical Description in Binary Composites and Spectral Density Representation
Tuncer, Enis
2010-01-01
In this review, the dielectric permittivity of dielectric mixtures is discussed in view of the spectral density representation method. A distinct representation is derived for predicting the dielectric properties, permittivities ε, of mixtures. The presentation of the dielectric properties is based on a scaled permittivity approach, ξ=(εe-εm)(εi-εm)-1, where the subscripts e, m and i denote the dielectric permittivities of the effective, matrix and inclusion media, respectively [Tuncer, E. J. Phys.: Condens. Matter 2005, 17, L125]. This novel representation transforms the spectral density formalism to a form similar to the distribution of relaxation times method of dielectric relaxation. Consequently, I propose that any dielectric relaxation formula, i.e., the Havriliak-Negami empirical dielectric relaxation expression, can be adopted as a scaled permittivity. The presented scaled permittivity representation has potential to be improved and implemented into the existing data analyzing routines for dielectric relaxation; however, the information to extract would be the topological/morphological description in mixtures. To arrive at the description, one needs to know the dielectric properties of the constituents and the composite prior to the spectral analysis. To illustrate the strength of the representation and confirm the proposed hypothesis, the Landau-Lifshitz/Looyenga (LLL) [Looyenga, H. Physica 1965, 31, 401] expression is selected. The structural information of a mixture obeying LLL is extracted for different volume fractions of phases. Both an in-house computational tool based on the Monte Carlo method to solve inverse integral transforms and the proposed empirical scaled permittivity expression are employed to estimate the spectral density function of the LLL expression. The estimated spectral functions for mixtures with different inclusion concentration compositions show similarities; they are composed of a couple of bell-shaped distributions, with
Gemstone spectral imaging for measuring adult bone mineral density
Shao, Wei-Guang; Liu, Dian-Mei
2016-01-01
The present study aimed to detect the bone Ca2+ content of L3 vertebrae in adults by gemstone spectral computed tomography. In total, 235 patients were selected and divided into age groups of 10 years each. The scanning data were used to detect the water-based and Ca2+-based substance levels on the L3 vertebral cancellous bone images. The results indicated that there were significant differences in vertebral Ca2+-water and water-Ca2+ densities determined by gemstone spectral imaging (GSI) between males and females in subjects aged 50–59 years, 60–69 years, 70–79 years and ≥80 years (P<0.05). The ages of male and female participants were negatively correlated with vertebral Ca2+-water density (P<0.01) and water-Ca2+ density (P<0.01). In conclusion, GSI may be used as a novel method of measuring the vertebral adult bone mineral density. PMID:27703518
More systematic errors in the measurement of power spectral density
NASA Astrophysics Data System (ADS)
Mack, Chris A.
2015-07-01
Power spectral density (PSD) analysis is an important part of understanding line-edge and linewidth roughness in lithography. But uncertainty in the measured PSD, both random and systematic, complicates interpretation. It is essential to understand and quantify the sources of the measured PSD's uncertainty and to develop mitigation strategies. Both analytical derivations and simulations of rough features are used to evaluate data window functions for reducing spectral leakage and to understand the impact of data detrending on biases in PSD, autocovariance function (ACF), and height-to-height covariance function measurement. A generalized Welch window was found to be best among the windows tested. Linear detrending for line-edge roughness measurement results in underestimation of the low-frequency PSD and errors in the ACF and height-to-height covariance function. Measuring multiple edges per scanning electron microscope image reduces this detrending bias.
Determining Ionospheric Irregularity Spectral Density Function from Japan GEONET
NASA Astrophysics Data System (ADS)
Lay, E. H.; Light, M. E.; Parker, P. A.; Carrano, C. S.; Haaser, R. A.
2015-12-01
Japan's GEONET GPS network is the densest GPS monitoring network in the world, with 1200+ receivers over the area of Japan. Measuring and calibrating the integrated total electron content (TEC) from each station has been done in many cases to provide detailed maps of ionospheric disturbances over Japan. We use TEC measurements from Japan's GEONET array to determine an empirically derived description of the 2-dimensional scale sizes of spatial irregularities above Japan. The contributions from various scale sizes will be included in a statistical description for the irregularity spectral density (ISD) function. We will compare the statistics of the spatial irregularities between calm and moderately scintillated conditions.
Lei, Youming; Zheng, Fan
2016-12-01
Stochastic chaos induced by diffusion processes, with identical spectral density but different probability density functions (PDFs), is investigated in selected lightly damped Hamiltonian systems. The threshold amplitude of diffusion processes for the onset of chaos is derived by using the stochastic Melnikov method together with a mean-square criterion. Two quasi-Hamiltonian systems, namely, a damped single pendulum and damped Duffing oscillator perturbed by stochastic excitations, are used as illustrative examples. Four different cases of stochastic processes are taking as the driving excitations. It is shown that in such two systems the spectral density of diffusion processes completely determines the threshold amplitude for chaos, regardless of the shape of their PDFs, Gaussian or otherwise. Furthermore, the mean top Lyapunov exponent is employed to verify analytical results. The results obtained by numerical simulations are in accordance with the analytical results. This demonstrates that the stochastic Melnikov method is effective in predicting the onset of chaos in the quasi-Hamiltonian systems.
NASA Astrophysics Data System (ADS)
Lei, Youming; Zheng, Fan
2016-12-01
Stochastic chaos induced by diffusion processes, with identical spectral density but different probability density functions (PDFs), is investigated in selected lightly damped Hamiltonian systems. The threshold amplitude of diffusion processes for the onset of chaos is derived by using the stochastic Melnikov method together with a mean-square criterion. Two quasi-Hamiltonian systems, namely, a damped single pendulum and damped Duffing oscillator perturbed by stochastic excitations, are used as illustrative examples. Four different cases of stochastic processes are taking as the driving excitations. It is shown that in such two systems the spectral density of diffusion processes completely determines the threshold amplitude for chaos, regardless of the shape of their PDFs, Gaussian or otherwise. Furthermore, the mean top Lyapunov exponent is employed to verify analytical results. The results obtained by numerical simulations are in accordance with the analytical results. This demonstrates that the stochastic Melnikov method is effective in predicting the onset of chaos in the quasi-Hamiltonian systems.
PSD computations using Welch's method. [Power Spectral Density (PSD)
Solomon, Jr, O M
1991-12-01
This report describes Welch's method for computing Power Spectral Densities (PSDs). We first describe the bandpass filter method which uses filtering, squaring, and averaging operations to estimate a PSD. Second, we delineate the relationship of Welch's method to the bandpass filter method. Third, the frequency domain signal-to-noise ratio for a sine wave in white noise is derived. This derivation includes the computation of the noise floor due to quantization noise. The signal-to-noise ratio and noise flood depend on the FFT length and window. Fourth, the variance the Welch's PSD is discussed via chi-square random variables and degrees of freedom. This report contains many examples, figures and tables to illustrate the concepts. 26 refs.
Characterization of high density through silicon vias with spectral reflectometry.
Ku, Yi-Sha; Huang, Kuo Cheng; Hsu, Weite
2011-03-28
Measurement and control is an important step for production-worthy through silicon vias etch. We demonstrate the use and enhancement of an existing wafer metrology tool, spectral reflectometer by implementing novel theoretical model and measurement algorithm for high density through-silicon via (HDTSV) inspection. It is capable of measuring depth and depth variations of array vias by Discrete Fourier Transform (DFT) analysis in one shot measurement. Surface roughness of via bottom can also be extracted by scattering model fitting. Our non-destructive solution can measure TSV profile diameters as small as 5 μm and aspect ratios greater than 13:1. The measurement precision is in the range of 0.02 μm. Metrology results from actual 3D interconnect processing wafers are presented.
Laser line shape and spectral density of frequency noise
Stephan, G.M.; Blin, S.; Besnard, P.; Tam, T.T.; Tetu, M.
2005-04-01
Published experimental results show that single-mode laser light is characterized in the microwave range by a frequency noise which essentially includes a white part and a 1/f (flicker) part. We theoretically show that the spectral density (the line shape) which is compatible with these results is a Voigt profile whose Lorentzian part or homogeneous component is linked to the white noise and the Gaussian part to the 1/f noise. We measure semiconductor laser line profiles and verify that they can be fit with Voigt functions. It is also verified that the width of the Lorentzian part varies like 1/P where P is the laser power while the width of the Gaussian part is more of a constant. Finally, we theoretically show from first principles that laser line shapes are also described by Voigt functions where the Lorentzian part is the laser Airy function and the Gaussian part originates from population noise.
NASA Astrophysics Data System (ADS)
Cavallo, A.; Cosenza, F.; de Cesare, L.
2001-12-01
The two-time retarded and advanced Green's function technique is formulated in nonextensive classical statistical mechanics within the optimal Lagrange multiplier framework. The main spectral properties are presented and a spectral decomposition for the spectral density is obtained. Finally, the nonextensive version of the spectral density method is given and its effectiveness is tested by exploring the equilibrium properties of a classical ferromagnetic spin chain.
Specification of optical components using the power spectral density function
Lawson, J.K.; Wolfe, C.R.; Manes, K.R.; Trenholme, J.B.; Aikens, D.M.; English, R.E. Jr.
1995-06-20
This paper describes the use of Fourier techniques to characterize the wavefront of optical components, specifically, the use of the power spectral density, (PSD), function. The PSDs of several precision optical components will be shown. Many of the optical components of interest to us have square, rectangular or irregularly shaped apertures with major dimensions up-to 800 mm. The wavefronts of components with non-circular apertures cannot be analyzed with Zernicke polynomials since these functions are an orthogonal set for circular apertures only. Furthermore, Zernicke analysis is limited to treating low frequency wavefront aberrations; mid-spatial scale and high frequency error are expressed only as ``residuals.`` A more complete and powerful representation of the optical wavefront can be obtained by Fourier analysis in 1 or 2 dimensions. The PSD is obtained from the amplitude of frequency components present in the Fourier spectrum. The PSD corresponds to the scattered intensity as a function of scattering angle in the wavefront and can be used to describe the intensity distribution at focus. The shape of a resultant wavefront or the focal spot of a complex multi-component laser system can be calculated and optimized using the PSDs of individual optical components which comprise it.
Power spectral density specifications for high-power laser systems
Lawson, J.K.; Aikens, D.A.; English, R.E. Jr.; Wolfe, C.R.
1996-04-22
This paper describes the use of Fourier techniques to characterize the transmitted and reflected wavefront of optical components. Specifically, a power spectral density, (PSD), approach is used. High power solid-state lasers exhibit non-linear amplification of specific spatial frequencies. Thus, specifications that limit the amplitude of these spatial frequencies are necessary in the design of these systems. Further, NIF optical components have square, rectangular or irregularly shaped apertures with major dimensions up-to 800 mm. Components with non-circular apertures can not be analyzed correctly with Zernicke polynomials since these functions are an orthogonal set for circular apertures only. A more complete and powerful representation of the optical wavefront can be obtained by Fourier analysis in 1 or 2 dimensions. The PSD is obtained from the amplitude of frequency components present in the Fourier spectrum. The shape of a resultant wavefront or the focal spot of a complex multicomponent laser system can be calculated and optimized using PSDs of the individual optical components which comprise the system. Surface roughness can be calculated over a range of spatial scale-lengths by integrating the PSD. Finally, since the optical transfer function (OTF) of the instruments used to measure the wavefront degrades at high spatial frequencies, the PSD of an optical component is underestimated. We can correct for this error by modifying the PSD function to restore high spatial frequency information. The strengths of PSD analysis are leading us to develop optical specifications incorporating this function for the planned National Ignition Facility (NIF).
An overview of power spectral density (PSD) calculations
NASA Astrophysics Data System (ADS)
Youngworth, Richard N.; Gallagher, Benjamin B.; Stamper, Brian L.
2005-09-01
Specifications for optical surfaces have traditionally been given in terms of low frequency and high frequency components, often with a separate classification for surface slope. Low spatial frequency components are commonly referred to as figure errors and can be described by the standard 37-term Zernike polynomial set. High spatial frequency errors are commonly referred to as finish and are quantified using rms roughness. Specification with the qualitative scratch and dig classification is done usually for cosmetic or aesthetic purposes. Mid-spatial frequency errors such as waviness, ripple, and quilting can be important and are not explicitly covered by such traditional figure and finish specifications. In order to bridge the gap to cover mid-spatial frequencies, in terms of quantifying surface characteristics, Power Spectral Density (PSD) can be utilized. For such usage, it is important for the greater optics community to understand the metric, how to calculate it, and how to use it. The purpose of this paper is to provide an overview of PSD, its application in optics, and an outline of calculations needed to effectively apply it to specify optical surfaces.
On the joint spectral density of bivariate random sequences. Thesis Technical Report No. 21
NASA Technical Reports Server (NTRS)
Aalfs, David D.
1995-01-01
For univariate random sequences, the power spectral density acts like a probability density function of the frequencies present in the sequence. This dissertation extends that concept to bivariate random sequences. For this purpose, a function called the joint spectral density is defined that represents a joint probability weighing of the frequency content of pairs of random sequences. Given a pair of random sequences, the joint spectral density is not uniquely determined in the absence of any constraints. Two approaches to constraining the sequences are suggested: (1) assume the sequences are the margins of some stationary random field, (2) assume the sequences conform to a particular model that is linked to the joint spectral density. For both approaches, the properties of the resulting sequences are investigated in some detail, and simulation is used to corroborate theoretical results. It is concluded that under either of these two constraints, the joint spectral density can be computed from the non-stationary cross-correlation.
Generation of time histories with a specified auto spectral density and probability density function
Smallwood, D.O.
1996-08-01
It is recognized that some dynamic and noise environments are characterized by time histories which are not Gaussian. An example is high intensity acoustic noise. Another example is some transportation vibration. A better simulation of these environments can be generated if a zero mean non-Gaussian time history can be reproduced with a specified auto (or power) spectral density (ASD or PSD) and a specified probability density function (pdf). After the required time history is synthesized, the waveform can be used for simulation purposes. For example, modem waveform reproduction techniques can be used to reproduce the waveform on electrodynamic or electrohydraulic shakers. Or the waveforms can be used in digital simulations. A method is presented for the generation of realizations of zero mean non-Gaussian random time histories with a specified ASD, and pdf. First a Gaussian time history with the specified auto (or power) spectral density (ASD) is generated. A monotonic nonlinear function relating the Gaussian waveform to the desired realization is then established based on the Cumulative Distribution Function (CDF) of the desired waveform and the known CDF of a Gaussian waveform. The established function is used to transform the Gaussian waveform to a realization of the desired waveform. Since the transformation preserves the zero-crossings and peaks of the original Gaussian waveform, and does not introduce any substantial discontinuities, the ASD is not substantially changed. Several methods are available to generate a realization of a Gaussian distributed waveform with a known ASD. The method of Smallwood and Paez (1993) is an example. However, the generation of random noise with a specified ASD but with a non-Gaussian distribution is less well known.
Spectral density of the correlation matrix of factor models: a random matrix theory approach.
Lillo, F; Mantegna, R N
2005-07-01
We studied the eigenvalue spectral density of the correlation matrix of factor models of multivariate time series. By making use of the random matrix theory, we analytically quantified the effect of statistical uncertainty on the spectral density due to the finiteness of the sample. We considered a broad range of models, ranging from one-factor models to hierarchical multifactor models.
Effects of impurity location on the impurity bands and their spectral densities in quantum wells
NASA Astrophysics Data System (ADS)
Gold, A.; Ghazali, A.; Serre, J.
1989-09-01
The electronic density of states and the spectral density of quantum wells are calculated as functions of the impurity position zi. A multiple-scattering method which accounts for the formation of impurity bands is used. The study of the spectral densities provides us with the behavior of the averaged wave functions of the ground- and excited-state impurity bands in the k space. We demonstrate that our approach can be used to study hybridization effects between different bands.
Power Spectral Density Error Analysis of Spectral Subtraction Type of Speech Enhancement Methods
NASA Astrophysics Data System (ADS)
Händel, Peter
2006-12-01
A theoretical framework for analysis of speech enhancement algorithms is introduced for performance assessment of spectral subtraction type of methods. The quality of the enhanced speech is related to physical quantities of the speech and noise (such as stationarity time and spectral flatness), as well as to design variables of the noise suppressor. The derived theoretical results are compared with the outcome of subjective listening tests as well as successful design strategies, performed by independent research groups.
Characterizing Intra-Die Spatial Correlation Using Spectral Density Fitting Method
NASA Astrophysics Data System (ADS)
Fu, Qiang; Luk, Wai-Shing; Tao, Jun; Yan, Changhao; Zeng, Xuan
In this paper, a spectral domain method named the SDF (Spectral Density Fitting) method for intra-die spatial correlation function extraction is presented. Based on theoretical analysis of random field, the spectral density, as the spectral domain counterpart of correlation function, is employed to estimate the parameters of the correlation function effectively in the spectral domain. Compared with the existing extraction algorithm in the original spatial domain, the SDF method can obtain the same quality of results in the spectral domain. In actual measurement process, the unavoidable measurement error with arbitrary frequency components would greatly confound the extraction results. A filtering technique is further developed to diminish the high frequency components of the measurement error and recover the data from noise contamination for parameter estimation. Experimental results have shown that the SDF method is practical and stable.
Spectral density of generalized Wishart matrices and free multiplicative convolution
NASA Astrophysics Data System (ADS)
Młotkowski, Wojciech; Nowak, Maciej A.; Penson, Karol A.; Życzkowski, Karol
2015-07-01
We investigate the level density for several ensembles of positive random matrices of a Wishart-like structure, W =X X† , where X stands for a non-Hermitian random matrix. In particular, making use of the Cauchy transform, we study the free multiplicative powers of the Marchenko-Pastur (MP) distribution, MP⊠s, which for an integer s yield Fuss-Catalan distributions corresponding to a product of s -independent square random matrices, X =X1⋯Xs . New formulas for the level densities are derived for s =3 and s =1 /3 . Moreover, the level density corresponding to the generalized Bures distribution, given by the free convolution of arcsine and MP distributions, is obtained. We also explain the reason of such a curious convolution. The technique proposed here allows for the derivation of the level densities for several other cases.
Spectral density of generalized Wishart matrices and free multiplicative convolution.
Młotkowski, Wojciech; Nowak, Maciej A; Penson, Karol A; Życzkowski, Karol
2015-07-01
We investigate the level density for several ensembles of positive random matrices of a Wishart-like structure, W=XX(†), where X stands for a non-Hermitian random matrix. In particular, making use of the Cauchy transform, we study the free multiplicative powers of the Marchenko-Pastur (MP) distribution, MP(⊠s), which for an integer s yield Fuss-Catalan distributions corresponding to a product of s-independent square random matrices, X=X(1)⋯X(s). New formulas for the level densities are derived for s=3 and s=1/3. Moreover, the level density corresponding to the generalized Bures distribution, given by the free convolution of arcsine and MP distributions, is obtained. We also explain the reason of such a curious convolution. The technique proposed here allows for the derivation of the level densities for several other cases.
Valleau, Stephanie; Aspuru-Guzik, Alan; Eisfeld, Alexander
2012-12-14
We investigate on the procedure of extracting a 'spectral density' from mixed QM/MM calculations and employing it in open quantum systems models. In particular, we study the connection between the energy gap correlation function extracted from ground state QM/MM and the bath spectral density used as input in open quantum system approaches. We introduce a simple model which can give intuition on when the ground state QM/MM propagation will give the correct energy gap. We also discuss the role of higher order correlators of the energy-gap fluctuations which can provide useful information on the bath. Further, various semiclassical corrections to the spectral density, are applied and investigated. Finally, we apply our considerations to the photosynthetic Fenna-Matthews-Olson complex. For this system, our results suggest the use of the Harmonic prefactor for the spectral density rather than the Standard one, which was employed in the simulations of the system carried out to date.
Kinetic equations for a density matrix describing nonlinear effects in spectral line wings
Parkhomenko, A. I. Shalagin, A. M.
2011-11-15
Kinetic quantum equations are derived for a density matrix with collision integrals describing nonlinear effects in spectra line wings. These equations take into account the earlier established inequality of the spectral densities of Einstein coefficients for absorption and stimulated radiation emission by a two-level quantum system in the far wing of a spectral line in the case of frequent collisions. The relationship of the absorption and stimulated emission probabilities with the characteristics of radiation and an elementary scattering event is found.
[Estimation of Hunan forest carbon density based on spectral mixture analysis of MODIS data].
Yan, En-ping; Lin, Hui; Wang, Guang-xing; Chen, Zhen-xiong
2015-11-01
With the fast development of remote sensing technology, combining forest inventory sample plot data and remotely sensed images has become a widely used method to map forest carbon density. However, the existence of mixed pixels often impedes the improvement of forest carbon density mapping, especially when low spatial resolution images such as MODIS are used. In this study, MODIS images and national forest inventory sample plot data were used to conduct the study of estimation for forest carbon density. Linear spectral mixture analysis with and without constraint, and nonlinear spectral mixture analysis were compared to derive the fractions of different land use and land cover (LULC) types. Then sequential Gaussian co-simulation algorithm with and without the fraction images from spectral mixture analyses were employed to estimate forest carbon density of Hunan Province. Results showed that 1) Linear spectral mixture analysis with constraint, leading to a mean RMSE of 0.002, more accurately estimated the fractions of LULC types than linear spectral and nonlinear spectral mixture analyses; 2) Integrating spectral mixture analysis model and sequential Gaussian co-simulation algorithm increased the estimation accuracy of forest carbon density to 81.5% from 74.1%, and decreased the RMSE to 5.18 from 7.26; and 3) The mean value of forest carbon density for the province was 30.06 t · hm(-2), ranging from 0.00 to 67.35 t · hm(-2). This implied that the spectral mixture analysis provided a great potential to increase the estimation accuracy of forest carbon density on regional and global level.
Spectral densities for Frenkel exciton dynamics in molecular crystals: A TD-DFTB approach
NASA Astrophysics Data System (ADS)
Plötz, Per-Arno; Megow, Jörg; Niehaus, Thomas; Kühn, Oliver
2017-02-01
Effects of thermal fluctuations on the electronic excitation energies and intermonomeric Coulomb couplings are investigated for a perylene-tetracarboxylic-diimide crystal. To this end, time dependent density functional theory based tight binding (TD-DFTB) in the linear response formulation is used in combination with electronic ground state classical molecular dynamics. As a result, a parametrized Frenkel exciton Hamiltonian is obtained, with the effect of exciton-vibrational coupling being described by spectral densities. Employing dynamically defined normal modes, these spectral densities are analyzed in great detail, thus providing insight into the effect of specific intramolecular motions on excitation energies and Coulomb couplings. This distinguishes the present method from approaches using fixed transition densities. The efficiency by which intramolecular contributions to the spectral density can be calculated is a clear advantage of this method as compared with standard TD-DFT.
Spectral densities for Frenkel exciton dynamics in molecular crystals: A TD-DFTB approach.
Plötz, Per-Arno; Megow, Jörg; Niehaus, Thomas; Kühn, Oliver
2017-02-28
Effects of thermal fluctuations on the electronic excitation energies and intermonomeric Coulomb couplings are investigated for a perylene-tetracarboxylic-diimide crystal. To this end, time dependent density functional theory based tight binding (TD-DFTB) in the linear response formulation is used in combination with electronic ground state classical molecular dynamics. As a result, a parametrized Frenkel exciton Hamiltonian is obtained, with the effect of exciton-vibrational coupling being described by spectral densities. Employing dynamically defined normal modes, these spectral densities are analyzed in great detail, thus providing insight into the effect of specific intramolecular motions on excitation energies and Coulomb couplings. This distinguishes the present method from approaches using fixed transition densities. The efficiency by which intramolecular contributions to the spectral density can be calculated is a clear advantage of this method as compared with standard TD-DFT.
Spectral Density of Laser Beam Scintillation in Wind Turbulence. Part 1; Theory
NASA Technical Reports Server (NTRS)
Balakrishnan, A. V.
1997-01-01
The temporal spectral density of the log-amplitude scintillation of a laser beam wave due to a spatially dependent vector-valued crosswind (deterministic as well as random) is evaluated. The path weighting functions for normalized spectral moments are derived, and offer a potential new technique for estimating the wind velocity profile. The Tatarskii-Klyatskin stochastic propagation equation for the Markov turbulence model is used with the solution approximated by the Rytov method. The Taylor 'frozen-in' hypothesis is assumed for the dependence of the refractive index on the wind velocity, and the Kolmogorov spectral density is used for the refractive index field.
Alekseev, A E; Potapov, V T
2013-10-31
Spectral characteristics of the noise intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of noise is one of the main factors limiting sensitivity of interferometric sensors. For the first time, to our knowledge, the expression is obtained for the average noise power spectral density at the interferometer output versus the degree of a light source coherence and length of the scattering segment. Also, the approximate expressions are considered which determine the power spectral density in the low-frequency range (up to 200 kHz) and in the limiting case of extended scattering segments. The expression obtained for the noise power spectral density agrees with experimental normalised power spectra with a high accuracy. (interferometry of radiation)
Non Destructive Defect Detection by Spectral Density Analysis
Krejcar, Ondrej; Frischer, Robert
2011-01-01
The potential nondestructive diagnostics of solid objects is discussed in this article. The whole process is accomplished by consecutive steps involving software analysis of the vibration power spectrum (eventually acoustic emissions) created during the normal operation of the diagnosed device or under unexpected situations. Another option is to create an artificial pulse, which can help us to determine the actual state of the diagnosed device. The main idea of this method is based on the analysis of the current power spectrum density of the received signal and its postprocessing in the Matlab environment with a following sample comparison in the Statistica software environment. The last step, which is comparison of samples, is the most important, because it is possible to determine the status of the examined object at a given time. Nowadays samples are compared only visually, but this method can’t produce good results. Further the presented filter can choose relevant data from a huge group of data, which originate from applying FFT (Fast Fourier Transform). On the other hand, using this approach they can be subjected to analysis with the assistance of a neural network. If correct and high-quality starting data are provided to the initial network, we are able to analyze other samples and state in which condition a certain object is. The success rate of this approximation, based on our testing of the solution, is now 85.7%. With further improvement of the filter, it could be even greater. Finally it is possible to detect defective conditions or upcoming limiting states of examined objects/materials by using only one device which contains HW and SW parts. This kind of detection can provide significant financial savings in certain cases (such as continuous casting of iron where it could save hundreds of thousands of USD). PMID:22163742
Spectral density of Cooper pairs in two level quantum dot-superconductors Josephson junction
NASA Astrophysics Data System (ADS)
Dhyani, A.; Rawat, P. S.; Tewari, B. S.
2016-09-01
In the present paper, we report the role of quantum dot energy levels on the electronic spectral density for a two level quantum dot coupled to s-wave superconducting leads. The theoretical arguments in this work are based on the Anderson model so that it necessarily includes dot energies, single particle tunneling and superconducting order parameter for BCS superconductors. The expression for single particle spectral function is obtained by using the Green's function equation of motion technique. On the basis of numerical computation of spectral function of superconducting leads, it has been found that the charge transfer across such junctions can be controlled by the positions and availability of the dot levels.
Generation of time histories with a specified auto spectral density, skewness, and kurtosis
Smallwood, D.O.
1996-02-01
Some dynamic environments are characterized by time histories that are not Gaussian. A more accurate simulation of these environments can be generated if a realization of a non Gaussian time history can be reproduced which has a specified auto spectral density (also called power spectral density) and a specified skewness and kurtosis (not necessarily the skewness and kurtosis of a Gaussian time history). The mean square of the waveform is reproduced if the spectrum is reproduced. Modern waveform reproduction techniques can be used to reproduce the realized waveform on an electrodynamic or electrohydraulic shaker. A method is presented for the generation of realizations of zero mean non Gaussian random time histories with a specified auto spectral density, skewness, and kurtosis. Kurtosis, defined in this paper as E[{chi}{sup 4}]/E{sup 2}[{chi}{sup 2}], greater than 3 can be realized. Realizations of the random process are generated with a generalization of shot noise.
Open Systems with Error Bounds: Spin-Boson Model with Spectral Density Variations
NASA Astrophysics Data System (ADS)
Mascherpa, F.; Smirne, A.; Huelga, S. F.; Plenio, M. B.
2017-03-01
In the study of open quantum systems, one of the most common ways to describe environmental effects on the reduced dynamics is through the spectral density. However, in many models this object cannot be computed from first principles and needs to be inferred on phenomenological grounds or fitted to experimental data. Consequently, some uncertainty regarding its form and parameters is unavoidable; this in turn calls into question the accuracy of any theoretical predictions based on a given spectral density. Here, we focus on the spin-boson model as a prototypical open quantum system, find two error bounds on predicted expectation values in terms of the spectral density variation considered, and state a sufficient condition for the strongest one to apply. We further demonstrate an application of our result, by bounding the error brought about by the approximations involved in the hierarchical equations of motion resolution method for spin-boson dynamics.
Open Systems with Error Bounds: Spin-Boson Model with Spectral Density Variations.
Mascherpa, F; Smirne, A; Huelga, S F; Plenio, M B
2017-03-10
In the study of open quantum systems, one of the most common ways to describe environmental effects on the reduced dynamics is through the spectral density. However, in many models this object cannot be computed from first principles and needs to be inferred on phenomenological grounds or fitted to experimental data. Consequently, some uncertainty regarding its form and parameters is unavoidable; this in turn calls into question the accuracy of any theoretical predictions based on a given spectral density. Here, we focus on the spin-boson model as a prototypical open quantum system, find two error bounds on predicted expectation values in terms of the spectral density variation considered, and state a sufficient condition for the strongest one to apply. We further demonstrate an application of our result, by bounding the error brought about by the approximations involved in the hierarchical equations of motion resolution method for spin-boson dynamics.
Smallwood, D. O.
1996-01-01
It is shown that the usual method for estimating the coherence functions (ordinary, partial, and multiple) for a general multiple-input! multiple-output problem can be expressed as a modified form of Cholesky decomposition of the cross-spectral density matrix of the input and output records. The results can be equivalently obtained using singular value decomposition (SVD) of the cross-spectral density matrix. Using SVD suggests a new form of fractional coherence. The formulation as a SVD problem also suggests a way to order the inputs when a natural physical order of the inputs is absent.
Multi-angle/Multi-spectral Mapping of Snow Covered Area and Vegetation Density Using MISR
NASA Astrophysics Data System (ADS)
Nolin, A. W.; Selkowitz, D.
2004-12-01
Vegetation structure and density affect the dynamics of snow accumulation and ablation. The presence of vegetation also affects our ability to accurately estimate snow-covered area (SCA) from satellite-based sensors. The objective of this case study is to simultaneously retrieve subpixel estimates of snow covered area and vegetation density from multi-angle imagery. Imagery from the Multi-angle Imaging SpectroRadiometer (MISR) was acquired over Glacier National Park and a portion of the Colorado Rocky Mountains. Vegetation density can be related to the shape of the angular signature for a pixel. Here, we invert the Rahman-Pinty-Verstraete (RPV) model to compute values of a semi-empirical parameter (the k-parameter) that is statistically correlated with vegetation density. For the same pixels, we perform linear spectral unmixing using the four-band multi-spectral data at each of the nine MISR viewing angles. In areas with a mixture of vegetation and snow, SCA estimates vary as a function of viewing angle and vegetation density. Using both the multi-angle and multi-spectral data from MISR, we are able formulate corrections for SCA estimates based on the vegetation density. Moreover, the vegetation density information itself is an important retrieved parameter that can be used in snowmelt/runoff models.
NASA Technical Reports Server (NTRS)
Garber, Donald P.
1993-01-01
A probability density function for the variability of ensemble averaged spectral estimates from helicopter acoustic signals in Gaussian background noise was evaluated. Numerical methods for calculating the density function and for determining confidence limits were explored. Density functions were predicted for both synthesized and experimental data and compared with observed spectral estimate variability.
Road simulation for four-wheel vehicle whole input power spectral density
NASA Astrophysics Data System (ADS)
Wang, Jiangbo; Qiang, Baomin
2017-05-01
As the vibration of running vehicle mainly comes from road and influence vehicle ride performance. So the road roughness power spectral density simulation has great significance to analyze automobile suspension vibration system parameters and evaluate ride comfort. Firstly, this paper based on the mathematical model of road roughness power spectral density, established the integral white noise road random method. Then in the MATLAB/Simulink environment, according to the research method of automobile suspension frame from simple two degree of freedom single-wheel vehicle model to complex multiple degrees of freedom vehicle model, this paper built the simple single incentive input simulation model. Finally the spectrum matrix was used to build whole vehicle incentive input simulation model. This simulation method based on reliable and accurate mathematical theory and can be applied to the random road simulation of any specified spectral which provides pavement incentive model and foundation to vehicle ride performance research and vibration simulation.
Nonperturbative spectral-density function for the Anderson model at arbitrary temperatures
NASA Technical Reports Server (NTRS)
Neal, Henry L.
1991-01-01
Using a nonperturbative self-energy solution for the nondegenerate Anderson model, the temperature-dependent spectral-density function is calculated in the symmetric limit. The function is found to give reliable results for all values of the parameter u and inverse temperature beta.
Cavallo, A; Cosenza, F; De Cesare, L
2008-05-01
We extend the formalism of the thermodynamic two-time Green's functions to nonextensive quantum statistical mechanics. Working in the optimal Lagrangian multiplier representation, the q -spectral properties and the methods for a direct calculation of the two-time q Green's functions and the related q -spectral density ( q measures the nonextensivity degree) for two generic operators are presented in strict analogy with the extensive (q=1) counterpart. Some emphasis is devoted to the nonextensive version of the less known spectral density method whose effectiveness in exploring equilibrium and transport properties of a wide variety of systems has been well established in conventional classical and quantum many-body physics. To check how both the equations of motion and the spectral density methods work to study the q -induced nonextensivity effects in nontrivial many-body problems, we focus on the equilibrium properties of a second-quantized model for a high-density Bose gas with strong attraction between particles for which exact results exist in extensive conditions. Remarkably, the contributions to several thermodynamic quantities of the q -induced nonextensivity close to the extensive regime are explicitly calculated in the low-temperature regime by overcoming the calculation of the q grand-partition function.
Power Spectral Density plots inside MRF spots made with a polishing abrasive-free MR fluid
DeGroote, J.E.; Marino, A.E.; Spencer, K.E.; Jacobs, S.D.
2005-05-31
We present power spectral density (PSD) data measured inside magnetorheological finishing (MRF) spots in orthogonal directions. MRF spots exhibit a distinct grooving pattern that varies for each fluid/material combination. This spot analysis may provide new insights on the material removal process. Issues associated with taking orthogonal PSD measurements are also discussed.
Analytical spectral density of the Sachdev-Ye-Kitaev model at finite N
NASA Astrophysics Data System (ADS)
García-García, Antonio M.; Verbaarschot, Jacobus J. M.
2017-09-01
We derive an approximate analytical formula for the spectral density of the q -body Sachdev-Ye-Kitaev (SYK) model obtained by summing a class of diagrams representing leading intersecting contractions. This expression agrees with that of Q -Hermite polynomials, with Q a nontrivial function of q ≥2 and the number of Majorana fermions N . Numerical results, obtained by exact diagonalization, are in excellent agreement with this approximate analytical spectral density even for relatively small N ˜8 . For N ≫1 and not close to the edge of the spectrum, we find that the approximate analytical spectral density simplifies to ρasym(E )=exp [2 arcsin2(E /E0)/log η ] , where η (N ,q ) is the suppression factor of the contribution of intersecting Wick contractions relative to nested contractions and E0 is the ground-state energy per particle. This spectral density reproduces the known result for the free energy in the large-q and large-N limit at arbitrary values of the temperature. In the infrared region, where the SYK model is believed to have a gravity dual, the analytical spectral density is given by ρ (E )˜sinh [2 π √{2 }√{(1 -E /E0)/(-log η ) }] . It therefore has a square-root edge, as in random matrix ensembles, followed by an exponential growth, a distinctive feature of black holes and also of low-energy nuclear excitations. Results for level statistics in this region confirm the agreement with random matrix theory. Physically this is a signature that, for sufficiently long times, the SYK model and its gravity dual evolve to a fully ergodic state whose dynamics only depends on the global symmetry of the system. Our results strongly suggest that random matrix correlations are a universal feature of quantum black holes and that the SYK model, combined with holography, may be relevant to modeling certain aspects of the nuclear dynamics.
Spectral Discrete Probability Density Function of Measured Wind Turbine Noise in the Far Field
Ashtiani, Payam; Denison, Adelaide
2015-01-01
Of interest is the spectral character of wind turbine noise at typical residential set-back distances. In this paper, a spectral statistical analysis has been applied to immission measurements conducted at three locations. This method provides discrete probability density functions for the Turbine ONLY component of the measured noise. This analysis is completed for one-third octave sound levels, at integer wind speeds, and is compared to existing metrics for measuring acoustic comfort as well as previous discussions on low-frequency noise sources. PMID:25905097
Spectral discrete probability density function of measured wind turbine noise in the far field.
Ashtiani, Payam; Denison, Adelaide
2015-01-01
Of interest is the spectral character of wind turbine noise at typical residential set-back distances. In this paper, a spectral statistical analysis has been applied to immission measurements conducted at three locations. This method provides discrete probability density functions for the Turbine ONLY component of the measured noise. This analysis is completed for one-third octave sound levels, at integer wind speeds, and is compared to existing metrics for measuring acoustic comfort as well as previous discussions on low-frequency noise sources.
Daniell method for power spectral density estimation in atomic force microscopy
Labuda, Aleksander
2016-03-15
An alternative method for power spectral density (PSD) estimation—the Daniell method—is revisited and compared to the most prevalent method used in the field of atomic force microscopy for quantifying cantilever thermal motion—the Bartlett method. Both methods are shown to underestimate the Q factor of a simple harmonic oscillator (SHO) by a predictable, and therefore correctable, amount in the absence of spurious deterministic noise sources. However, the Bartlett method is much more prone to spectral leakage which can obscure the thermal spectrum in the presence of deterministic noise. By the significant reduction in spectral leakage, the Daniell method leads to a more accurate representation of the true PSD and enables clear identification and rejection of deterministic noise peaks. This benefit is especially valuable for the development of automated PSD fitting algorithms for robust and accurate estimation of SHO parameters from a thermal spectrum.
Quark spectral density and a strongly-coupled quark-gluon plasma.
Qin, S.; Chang, L.; Liu, Y.; Roberts, C. D.
2011-07-13
The maximum entropy method is used to compute the dressed-quark spectral density from the self-consistent numerical solution of a rainbow truncation of QCD's gap equation at temperatures above that for which chiral symmetry is restored. In addition to the normal and plasmino modes, the spectral function also exhibits an essentially nonperturbative zero mode for temperatures extending to 1.4-1.8 times the critical temperature, T{sub c}. In the neighborhood of T{sub c}, this long-wavelength mode contains the bulk of the spectral strength and as long as this mode persists, the system may fairly be described as a strongly-coupled state of matter.
Application of spectral line shapes to the study of high density ICF plasmas
Keane, C.J.; Hammel, B.A.; Langer, S.H.; Lee, R.W.; Calisti, A.; Godbert, L.; Stamm, R.; Talin, B.
1994-09-01
Spectral line broadening manifests itself in the study of high density inertial confinement fusion (ICF) plasmas in two important ways. First, comparison between measured and calculated lineshapes of individual spectral lines or groups of lines is used to diagnose plasma conditions in dense ICF plasmas, particularly in implosions. Secondly, through the emission and absorption coefficients spectral lineshapes serve as important inputs to plasma spectroscopy simulation codes which calculate simulated spectra from ICF targets. We discuss recent results from each of these areas. With regard to lineshape diagnostics, the advent of generalized line broadening codes has allowed the line profiles of complex multielectron emitters to be considered for diagnostic purposes. Particular example of this is the use of Ar He-{beta} and its associated dielectronic satellites as a diagnostic of T{sub e} and N{sub e}, as well as the development of Ne-like Xe line broadening as a density diagnostic. With respect to simulation codes, the implementation of detailed lineshapes in calculations of this type is in many ways in its infancy. We present here examples of cases where effects related to spectral lineshapes such as continuum lowering and line transfer of Stark broadened lines are important so as to provide a stimulus for future work in this field. 34 refs., 9 figs., 1 tab.
Wen, Xiaotong; Rangarajan, Govindan; Ding, Mingzhou
2013-08-28
Granger causality is increasingly being applied to multi-electrode neurophysiological and functional imaging data to characterize directional interactions between neurons and brain regions. For a multivariate dataset, one might be interested in different subsets of the recorded neurons or brain regions. According to the current estimation framework, for each subset, one conducts a separate autoregressive model fitting process, introducing the potential for unwanted variability and uncertainty. In this paper, we propose a multivariate framework for estimating Granger causality. It is based on spectral density matrix factorization and offers the advantage that the estimation of such a matrix needs to be done only once for the entire multivariate dataset. For any subset of recorded data, Granger causality can be calculated through factorizing the appropriate submatrix of the overall spectral density matrix.
Single-particle spectral density of a Bose gas in the two-fluid hydrodynamic regime
Arahata, Emiko; Nikuni, Tetsuro; Griffin, Allan
2011-11-15
In Bose superfluids, the single-particle Green's function can be directly related to the superfluid velocity-velocity correlation function in the hydrodynamic regime. An explicit expression for the single-particle spectral density was originally written down by Hohenberg and Martin in 1965, starting from the two-fluid equations for a superfluid. We give a simple derivation of their results. Using these results, we calculate the relative weights of first and second sound modes in the single-particle spectral density as a function of temperature in a uniform Bose gas. We show that the second sound mode makes a dominant contribution to the single-particle spectrum in a relatively high-temperature region. We also discuss the possibility of experimental observation of the second sound mode in a Bose gas by photoemission spectroscopy.
Smallwood, D.O.
1995-08-07
It is shown that the usual method for computing the coherence functions (ordinary, partial, and multiple) for a general multiple-input/multiple-output problem can be expressed as a modified form of Cholesky decomposition of the cross spectral density matrix of the inputs and outputs. The modified form of Cholesky decomposition used is G{sub zz} = LCL{prime}, where G is the cross spectral density matrix of inputs and outputs, L is a lower; triangular matrix with ones on the diagonal, and C is a diagonal matrix, and the symbol {prime} denotes the conjugate transpose. If a diagonal element of C is zero, the off diagonal elements in the corresponding column of L are set to zero. It is shown that the results can be equivalently obtained using singular value decomposition (SVD) of G{sub zz}. The formulation as a SVD problem suggests a way to order the inputs when a natural physical order of the inputs is absent.
NASA Astrophysics Data System (ADS)
Ritschel, Gerhard; Eisfeld, Alexander
2014-09-01
We present a scheme to express a bath correlation function (BCF) corresponding to a given spectral density (SD) as a sum of damped harmonic oscillations. Such a representation is needed, for example, in many open quantum system approaches. To this end we introduce a class of fit functions that enables us to model ohmic as well as superohmic behavior. We show that these functions allow for an analytic calculation of the BCF using pole expansions of the temperature dependent hyperbolic cotangent. We demonstrate how to use these functions to fit spectral densities exemplarily for cases encountered in the description of photosynthetic light harvesting complexes. Finally, we compare absorption spectra obtained for different fits with exact spectra and show that it is crucial to take properly into account the behavior at small frequencies when fitting a given SD.
Ritschel, Gerhard; Eisfeld, Alexander
2014-09-07
We present a scheme to express a bath correlation function (BCF) corresponding to a given spectral density (SD) as a sum of damped harmonic oscillations. Such a representation is needed, for example, in many open quantum system approaches. To this end we introduce a class of fit functions that enables us to model ohmic as well as superohmic behavior. We show that these functions allow for an analytic calculation of the BCF using pole expansions of the temperature dependent hyperbolic cotangent. We demonstrate how to use these functions to fit spectral densities exemplarily for cases encountered in the description of photosynthetic light harvesting complexes. Finally, we compare absorption spectra obtained for different fits with exact spectra and show that it is crucial to take properly into account the behavior at small frequencies when fitting a given SD.
Sum rules and spectral density flow in QCD and in superconformal theories
NASA Astrophysics Data System (ADS)
Costantini, Antonio; Delle Rose, Luigi; Serino, Mirko
2014-11-01
We discuss the signature of the anomalous breaking of the superconformal symmetry in N = 1 super Yang Mills theory and its manifestation in the form of anomaly poles. Moreover, we describe the massive deformations of the N = 1 theory and the spectral densities of the corresponding anomaly form factors. These are characterized by spectral densities which flow with the mass deformation and turn the continuum contributions from the two-particle cuts of the intermediate states into poles, with a single sum rule satisfied by each component. The poles can be interpreted as signaling the exchange of a composite axion/dilaton/dilatino (ADD) multiplet in the effective Lagrangian. We conclude that global anomalous currents characterized by a single flow in the perturbative picture always predict the existence of composite interpolating fields.
Spectral densities for hot QCD plasmas in a leading-log approximation
Hong, Juhee; Teaney, Derek
2010-10-15
We compute the spectral densities of T{sup {mu}{nu}}and J{sup {mu}}in high-temperature QCD plasmas at small frequency and momentum, {omega},k{approx}g{sup 4}T. The leading log Boltzmann equation is reformulated as a Fokker-Planck equation with nontrivial boundary conditions, and the resulting partial differential equation is solved numerically in momentum space. The spectral densities of the current, shear, sound, and bulk channels exhibit a smooth transition from free-streaming quasiparticles to ideal hydrodynamics. This transition is analyzed with conformal and nonconformal second-order hydrodynamics and a second-order diffusion equation. We determine all of the second-order transport coefficients that characterize the linear response in the hydrodynamic regime.
The power spectral density of digital modulations transmitted over nonlinear channels
NASA Technical Reports Server (NTRS)
Divsalar, D.; Simon, M. K.
1982-01-01
This paper examines by analytical methods the power spectral densities of digital modulations (in particular, staggered and unstaggered quadrature modulations) passed through band-limited nonlinear channels. Previously observed (by computer simulation or hardware measurement) behavior of such spectra with regard to the suppression or restoration of its sidelobes after passing through the nonlinearity is verified analytically. Several examples corresponding to specific quadrature modulations and filter-nonlinearity combinations are presented as illustrations of the general results.
Spectral density mapping at multiple magnetic fields suitable for (13)C NMR relaxation studies.
Kadeřávek, Pavel; Zapletal, Vojtěch; Fiala, Radovan; Srb, Pavel; Padrta, Petr; Přecechtělová, Jana Pavlíková; Šoltésová, Mária; Kowalewski, Jozef; Widmalm, Göran; Chmelík, Josef; Sklenář, Vladimír; Žídek, Lukáš
2016-05-01
Standard spectral density mapping protocols, well suited for the analysis of (15)N relaxation rates, introduce significant systematic errors when applied to (13)C relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and (13)C frequencies can be obtained from data acquired at three magnetic fields for uniformly (13)C-labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions. Copyright © 2016 Elsevier Inc. All rights reserved.
Spectral density mapping at multiple magnetic fields suitable for 13C NMR relaxation studies
NASA Astrophysics Data System (ADS)
Kadeřávek, Pavel; Zapletal, Vojtěch; Fiala, Radovan; Srb, Pavel; Padrta, Petr; Přecechtělová, Jana Pavlíková; Šoltésová, Mária; Kowalewski, Jozef; Widmalm, Göran; Chmelík, Josef; Sklenář, Vladimír; Žídek, Lukáš
2016-05-01
Standard spectral density mapping protocols, well suited for the analysis of 15N relaxation rates, introduce significant systematic errors when applied to 13C relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and 13C frequencies can be obtained from data acquired at three magnetic fields for uniformly 13C -labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions.
NASA Astrophysics Data System (ADS)
Wang, Ziyue; Zhuang, Pengfei
2017-07-01
The pion superfluid and the corresponding Goldstone and soft modes are investigated in a two-flavor quark-meson model with a functional renormalization group. By solving the flow equations for the effective potential and the meson two-point functions at finite temperature and isospin density, the critical temperature for the superfluid increases sizeably in comparison with solving the flow equation for the potential only. The spectral function for the soft mode shows clearly a transition from meson gas to quark gas with increasing temperature and a crossover from Bose-Einstein condensation to Bardeen-Cooper-Schrieffer pairing of quarks with increasing isospin density.
Gas temperature and density measurements based on spectrally resolved Rayleigh-Brillouin scattering
NASA Technical Reports Server (NTRS)
Seasholtz, Richard G.; Lock, James A.
1992-01-01
The use of molecular Rayleigh scattering for measurements of gas density and temperature is evaluated. The technique used is based on the measurement of the spectrum of the scattered light, where both temperature and density are determined from the spectral shape. Planar imaging of Rayleigh scattering from air using a laser light sheet is evaluated for ambient conditions. The Cramer-Rao lower bounds for the shot-noise limited density and temperature measurement uncertainties are calculated for an ideal optical spectrum analyzer and for a planar mirror Fabry-Perot interferometer used in a static, imaging mode. With this technique, a single image of the Rayleigh scattered light can be analyzed to obtain density (or pressure) and temperature. Experimental results are presented for planar measurements taken in a heated air stream.
NASA Astrophysics Data System (ADS)
EL Sherbini, Ashraf M.; Aboulfotouh, Abdelnasser M.; Parigger, Christian G.
2016-11-01
Spectrally broadened, singly ionized nitrogen emission lines are monitored to determine electron number densities in laser-induced plasma from aluminum, nano- and bulk-zinc monoxide, as well as hydrogen-rich plastic and wood targets. The optical emission spectra for N II at the average wavelength of 500.33 nm are recorded in standard ambient temperature and pressure environments. For time delays of 25 to 450 ns from the onset of the 1064-nm Nd:YAG radiation induced optical breakdown, the electron number densities in the range of 5.1 ±1 ×1019 to 0.22 ±0.04 ×1019 cm-3 are inferred from the continuum and the nitrogen spectral line analysis. In addition, the corresponding electron temperatures of 10.1 ±0.6 eV to 1 ±0.2 eV are determined from the calculated absolute spectral radiance values in the near infrared region. At the early stages of plasma emission, Balmer series hydrogen lines are embedded in free electron radiation yet the broadening of the N II lines yields reliable electron number density values.
Eclipsing and density effects on the spectral behavior of Beta Lyrae binary system in the UV
NASA Astrophysics Data System (ADS)
Sanad, M. R.
2010-01-01
We analyze both long and short high resolution ultraviolet spectrum of Beta Lyrae eclipsing binary system observed with the International Ultraviolet Explorer (IUE) between 1980 and 1989. The main spectral features are P Cygni profiles originating from different environments of Beta Lyrae. A set of 23 Mg II k&h spectral lines at 2800 Å, originating from the extended envelope [Hack, M., 1980. IAUS, 88, 271H], have been identified and measured to determine their fluxes and widths. We found that there is spectral variability for these physical parameters with phase, similar to that found for the light curve [Kondo, Y., McCluskey, G.E., Jeffery, M.M.S., Ronald, S.P., Carolina, P.S. McCluskey, Joel, A.E., 1994. ApJ, 421, 787], which we attribute to the eclipse effects [Ak, H., Chadima, P., Harmanec, P., Demircan, O., Yang, S., Koubský, P., Škoda, P., Šlechta, M., Wolf, M., Božić, H., 2007. A&A, 463, 233], in addition to the changes of density and temperature of the region from which these lines are coming, as a result of the variability of mass loss from the primary star to the secondary [Hoffman, J.L., Nordsieck, K.H., Fox, G.K., 1998. AJ, 115, 1576; Linnell, A.P., Hubeny, I., Harmanec, P., 1998. ApJ, 509, 379]. Also we present a study of Fe II spectral line at 2600 Å, originating from the atmosphere of the primary star [Hack, M., 1980. IAUS, 88, 271H]. We found spectral variability of line fluxes and line widths with phase similar to that found for Mg II k&h lines. Finally we present a study of Si IV spectral line at 1394 Å, originating from the extended envelope [Hack, M., 1980. IAUS, 88, 271H]. A set of 52 Si IV spectral line at 1394 Å have been identified and measured to determine their fluxes and widths. Also we found spectral variability of these physical parameters with phase similar to that found for Mg II k&h and Fe II spectral lines.
Empirical relaxation function and spectral density for underdamped vibrations at low temperatures
NASA Astrophysics Data System (ADS)
Toutounji, Mohamad
2009-03-01
A new relaxation function which accounts for electronic dephasing (electronic phase loss and excited state lifetime) is presented, whose applicability for underdamped motion at low temperatures is examined in detail. This new empirical relaxation function φ(t ) yields linear and nonlinear spectral/temporal profiles that render accurate dephasing time in the underdamped regime. The relaxation function φ(t ) is normally expressed in terms of the coupling functions Mj' and Mj″ on which the time evolution of the vibrational modes in question depends. The corresponding spectral density, which is a central quantity in probing dynamics, is derived and compared to that of the multimode Brownian oscillator model. Derivation and discussion of the new position and momentum autocorrelation functions in terms of our new spectral density are presented. While the position autocorrelation function plays a key role in representing solvation structure in polar or nonpolar medium, the momentum correlation function projects out the molecular vibrational motion. The Liouville space generating function (LGF) for harmonic and anharmonic systems is expressed in terms of our new empirical φ(t ) and spectral density, leading to more physical observation. Several statistical quantities are derived from the position and momentum correlation function, which in turn contribute to LGF. Model calculations reflecting the infinite population decay in the low temperature limit in linear and nonlinear spectroscopic signals are presented. The herein quantum dipole moment correlation function is compared to that derived in [M. Toutounji, J. Chem. Phys. 118, 5319 (2003)] using mixed quantum-classical dynamics framework, yielding reasonable results, in fact identical at higher temperatures. The results herein are found to be informative, useful, and consistent with experiments.
Generation of Stationary Non-Gaussian Time Histories with a Specified Cross-spectral Density
Smallwood, David O.
1997-01-01
The paper reviews several methods for the generation of stationary realizations of sampled time histories with non-Gaussian distributions and introduces a new method which can be used to control the cross-spectral density matrix and the probability density functions (pdfs) of the multiple input problem. Discussed first are two methods for the specialized case of matching the auto (power) spectrum, the skewness, and kurtosis using generalized shot noise and using polynomial functions. It is then shown that the skewness and kurtosis can also be controlled by the phase of a complex frequency domain description of the random process. The general casemore » of matching a target probability density function using a zero memory nonlinear (ZMNL) function is then covered. Next methods for generating vectors of random variables with a specified covariance matrix for a class of spherically invariant random vectors (SIRV) are discussed. Finally the general case of matching the cross-spectral density matrix of a vector of inputs with non-Gaussian marginal distributions is presented.« less
Kula, M; Kalaji, H M; Skoczowski, A
2017-02-01
A density in algal suspension causes a significant change in the intensity and spectral composition of light reaching individual cells. Measurements of chlorophyll fluorescence allow us to observe any general changes in the bioenergetic status of photosynthesis. The aim of the study was to determine the effect of cultivation density on the PSII photochemical efficiency of three species of algae (Chlorella vulgaris, Botryococcus braunii and Chlorella emersonii), each with a different rate of growth - high, medium and low - respectively. The cell density of algae in suspension differentiated through the cultivation time (2, 4, and 8days) and the spectral composition of light. The results showed that the density of cultivation led to change in the photosynthetic apparatus of algae. The differences described between each day of cultivation (2, 4, and 8) in the kinetics of chlorophyll a fluorescence intensity in cells of the algal strains under study probably resulted from the different phases of growth of these cultures. In addition the results showed the beneficial effect of far red light on the photosynthetic apparatus and the growth of biomass in investigated algal strains.
Spectral broadening of parametric instability in lower hybrid current drive at a high density
NASA Astrophysics Data System (ADS)
Cesario, R.; Amicucci, L.; Cardinali, A.; Castaldo, C.; Marinucci, M.; Napoli, F.; Paoletti, F.; De Arcangelis, D.; Ferrari, M.; Galli, A.; Gallo, G.; Pullara, E.; Schettini, G.; Tuccillo, A. A.
2014-04-01
The important goal of adding to the bootstrap current a more flexible tool, capable of producing and controlling steady-state profiles with a high fraction of non-inductive plasma current, could be reached using the lower hybrid current drive (LHCD) effect. Experiments performed on FTU (Frascati Tokamak Upgrade) demonstrated that LHCD can occur at reactor-graded high plasma density, provided that the parametric instability (PI)-produced broadening of the spectrum launched by the antenna is reduced under proper operating conditions, capable of producing relatively high temperature in the outer region of plasma column. This condition was produced by operations that reduce particle recycling from the vessel walls, and enhance the gas fuelling in the core by means of fast pellet. New results of FTU experiments are presented documenting that the useful effect of temperature at the periphery, which reduces the LH spectral broadening and enhances the LH-induced hard-x ray emission level, occurs in a broader range of plasma parameters than in previous work. Modelling results show that a further tool for helping LHCD at a high density would be provided by electron cyclotron resonant heating of plasma periphery. New information is provided on the modelling, able determining frequencies, growth rates and LH spectral broadening produced by PI, which allowed assessing the new method for enabling LHCD at high densities. Further robustness is provided to theoretical and experimental fundaments of the method for LHCD at a high density.
NASA Astrophysics Data System (ADS)
Nocera, A.; Alvarez, G.
2016-11-01
Frequency-dependent correlations, such as the spectral function and the dynamical structure factor, help illustrate condensed matter experiments. Within the density matrix renormalization group (DMRG) framework, an accurate method for calculating spectral functions directly in frequency is the correction-vector method. The correction vector can be computed by solving a linear equation or by minimizing a functional. This paper proposes an alternative to calculate the correction vector: to use the Krylov-space approach. This paper then studies the accuracy and performance of the Krylov-space approach, when applied to the Heisenberg, the t-J, and the Hubbard models. The cases studied indicate that the Krylov-space approach can be more accurate and efficient than the conjugate gradient, and that the error of the former integrates best when a Krylov-space decomposition is also used for ground state DMRG.
None, None
2016-11-21
Frequency-dependent correlations, such as the spectral function and the dynamical structure factor, help illustrate condensed matter experiments. Within the density matrix renormalization group (DMRG) framework, an accurate method for calculating spectral functions directly in frequency is the correction-vector method. The correction vector can be computed by solving a linear equation or by minimizing a functional. Our paper proposes an alternative to calculate the correction vector: to use the Krylov-space approach. This paper also studies the accuracy and performance of the Krylov-space approach, when applied to the Heisenberg, the t-J, and the Hubbard models. The cases we studied indicate that themore » Krylov-space approach can be more accurate and efficient than the conjugate gradient, and that the error of the former integrates best when a Krylov-space decomposition is also used for ground state DMRG.« less
None, None
2016-11-21
Frequency-dependent correlations, such as the spectral function and the dynamical structure factor, help illustrate condensed matter experiments. Within the density matrix renormalization group (DMRG) framework, an accurate method for calculating spectral functions directly in frequency is the correction-vector method. The correction vector can be computed by solving a linear equation or by minimizing a functional. Our paper proposes an alternative to calculate the correction vector: to use the Krylov-space approach. This paper also studies the accuracy and performance of the Krylov-space approach, when applied to the Heisenberg, the t-J, and the Hubbard models. The cases we studied indicate that the Krylov-space approach can be more accurate and efficient than the conjugate gradient, and that the error of the former integrates best when a Krylov-space decomposition is also used for ground state DMRG.
Freudenberger, J.; Genz, H.; Morokhovskii, V.V.; Richter, A.; Morokhovskii, V.L.; Nething, U.; Zahn, R.; Sellschop, J.P.
1997-01-01
Applying an absorber technique, the experimental shape and width of a parametric x-radiation line has been determined. The 9 keV radiation was produced by bombarding a diamond crystal of 55 {mu}m thickness with electrons of 6.8 MeV. The variance of the spectral line distribution was found to depend on the tilt angle of the crystal and to have a magnitude of {sigma}=51 eV. Simulations based on a Monte Carlo method exhibit that the observed variance is mainly influenced by multiple scattering of electrons passing through the crystal ({approx}43 eV) and the finite detector opening ({approx}18 eV), leaving for the intrinsic linewidth a value of the order of 1 eV. The spectral density of the line was found to be J{approx}10{sup {minus}7} photons/(electron{times}sr{times}eV). {copyright} {ital 1997 American Institute of Physics.}
Nocera, A; Alvarez, G
2016-11-01
Frequency-dependent correlations, such as the spectral function and the dynamical structure factor, help illustrate condensed matter experiments. Within the density matrix renormalization group (DMRG) framework, an accurate method for calculating spectral functions directly in frequency is the correction-vector method. The correction vector can be computed by solving a linear equation or by minimizing a functional. This paper proposes an alternative to calculate the correction vector: to use the Krylov-space approach. This paper then studies the accuracy and performance of the Krylov-space approach, when applied to the Heisenberg, the t-J, and the Hubbard models. The cases studied indicate that the Krylov-space approach can be more accurate and efficient than the conjugate gradient, and that the error of the former integrates best when a Krylov-space decomposition is also used for ground state DMRG.
Ramon, C; Holmes, M; Freeman, Walter J; Gratkowski, Maciej; Eriksen, K J; Haueisen, Jens
2009-01-01
Our objective was to study changes in EEG time-domain power spectral density (PSDt) and localization of language areas during covert object naming tasks in human subjects with epilepsy. EEG data for subjects with epilepsy were acquired during the covert object naming tasks using a net of 256 electrodes. The trials required each subject to provide the names of common objects presented every 4 seconds on slides. Each trial comprised the 1.0 second before and 3.0 seconds after initial object presentation. PSDt values at baseline and during tasks were calculated in the theta, alpha, beta, low gamma, and high gamma bands. The spatial contour plots reveal that PSDt values during object naming were 10-20% higher than the baseline values for different bands. Language was lateralized to left frontal or temporal areas. In all cases, the Wada test disclosed language lateralization to the left hemisphere as well.
IR spectral density of weak H-bonded complexes involving damped Fermi resonances. I. Quantum theory
NASA Astrophysics Data System (ADS)
Henri-Rousseau, Olivier; Chamma, Didier
1998-03-01
The IR spectral density of the high frequency stretching mode of weak H-bonded complexes involving Fermi resonances is studied within the linear response theory from a full quantum mechanical point of view: the anharmonic coupling between the high frequency X-H and the low frequency X-H⋯Y modes is treated inside the strong anharmonic coupling theory. Following Witkowski and Wójcik [A. Witkowski, M. Wójcik, Chem. Phys. 1 (1973) 9.], the Fermi resonance between the first excited state of the fast mode and the first harmonic of single or several bending modes is introduced. Besides, the direct relaxation involved by the fast and bending modes are incorporated, in the spirit of the reduced Green formalism, by aid of imaginary damping terms. The spectral density is obtained by the Fourier transform of the autocorrelation function of the dipole moment operator of the fast mode, in which time dependent terms appear that are solution of a set of coupled linear differential equations. It reduces in the special situation where the Fermi coupling is ignored to that obtained by Rösch and Ratner [N. Rösch, M. Ratner, J. Chem. Phys. 61 (1974) 3344.]. Furthermore, when the anharmonic coupling between the slow and fast modes is neglected, it reduces to the spectral density that may be obtained in the framework of the Giry et al. [M. Giry, B. Boulil, O. Henri-Rousseau, C.R. Acad. Sci. Paris 316 s.II (1993) 455; B. Boulil, M. Giry, O. Henri-Rousseau, Phys. status solidi (b) 158 (1990) 629.] approach. At last, it reduces to the Witkowski and Wójcik [A. Witkowski, M. Wójcik, Chem. Phys. 1 (1973) 9.] approach, when the relaxation disappears. A generalization to several Fermi resonances is also proposed. Numerical tests of the theory and physical discussions are reported in the following paper [D. Chamma, O. Henri-Rousseau, Chem. Phys. 229 (1998) 51].
Lugo, J. E.
2015-01-01
Background The relationship between muscle anatomy and physiology and its corresponding electromyography activity (EMGA) is complex and not well understood. EMGA models may be broadly divided in stochastic and motor-unit-based models. For example, these models have successfully described many muscle physiological variables such as the value of the muscle fiber velocity and the linear relationship between median frequency and muscle fiber velocity. However they cannot explain the behavior of many of these variables with changes in intramuscular temperature, or muscle PH acidity, for instance. Here, we propose that the motor unit action potential can be treated as an electromagnetic resonant mode confined at thermal equilibrium inside the muscle. The motor units comprising the muscle form a system of standing waves or modes, where the energy of each mode is proportional to its frequency. Therefore, the power spectral density of the EMGA is well described and fit by Planck’s law and from its distribution we developed theoretical relationships that explain the behavior of known physiological variables with changes in intramuscular temperature or muscle PH acidity, for instance. Methods EMGA of the calf muscle was recorded during posture maintenance in seven participants and during controlled isometric contractions in two participants. The power spectral density of the EMGA was then fit with the Planckian distribution. Then, we inferred nine theoretical relationships from the distribution and compared the theoretically derived values with experimentally obtained values. Results The power spectral density of EMGA was fit by Planckian distributions and all the theoretical relationships were validated by experimental results. Conclusions Only by considering the motor unit action potentials as electromagnetic resonant modes confined at thermal equilibrium inside the muscle suffices to predict known or new theoretical relationships for muscle physiological variables that
Difference of two Gaussian Schell-model cross-spectral densities.
Gori, Franco; Santarsiero, Massimo
2014-05-01
We present a number of results relating to the difference of two Gaussian Schell-model cross-spectral densities (CSDs). They allow us to specify conditions under which such a difference represents itself in a valid CSD. In particular, a sufficient condition is derived for the non-negative definiteness of the resulting CSD, for any admissible choice of the involved parameters, while a necessary and sufficient condition is obtained for the case of CSDs endowed with the property of being shape-invariant upon propagation.
Tera-scalable Algorithms for Variable-Density Elliptic Hydrodynamics with Spectral Accuracy
Cook, A W; Cabot, W H; Welcome, M L; Williams, P L; Miller, B J; de Supinski, B R; Yates, R K
2005-04-13
A hybrid spectral/compact solver for variable-density viscous incompressible flow is described. Parallelization strategies for the FFTs and band-diagonal matrices are discussed and compared. Transpose methods are found to be highly competitive with direct block parallel methods when the problem is scaled to tens of thousands of processors. Various mapping strategies for the IBM BlueGene/L torus configuration of processors are explored. By optimizing the communication, we have achieved virtually perfect scaling to 32768 nodes. Furthermore, communication rates come very close to the theoretical peak speed of the BlueGene/L network with sustained computation in the TeraFLOPS range.
Plasma density characterization at SPARC_LAB through Stark broadening of Hydrogen spectral lines
NASA Astrophysics Data System (ADS)
Filippi, F.; Anania, M. P.; Bellaveglia, M.; Biagioni, A.; Chiadroni, E.; Cianchi, A.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Mostacci, A.; Palumbo, L.; Pompili, R.; Shpakov, V.; Vaccarezza, C.; Villa, F.; Zigler, A.
2016-09-01
Plasma-based acceleration techniques are of great interest for future, compact accelerators due to their high accelerating gradient. Both particle-driven and laser-driven Plasma Wakefield Acceleration experiments are foreseen at the SPARC_LAB Test Facility (INFN National Laboratories of Frascati, Italy), with the aim to accelerate high-brightness electron beams. In order to optimize the efficiency of the acceleration in the plasma and preserve the quality of the accelerated beam, the knowledge of the plasma electron density is mandatory. The Stark broadening of the Hydrogen spectral lines is one of the candidates used to characterize plasma density. The implementation of this diagnostic for plasma-based experiments at SPARC_LAB is presented.
A numerical spectral approach to solve the dislocation density transport equation
NASA Astrophysics Data System (ADS)
Djaka, K. S.; Taupin, V.; Berbenni, S.; Fressengeas, C.
2015-09-01
A numerical spectral approach is developed to solve in a fast, stable and accurate fashion, the quasi-linear hyperbolic transport equation governing the spatio-temporal evolution of the dislocation density tensor in the mechanics of dislocation fields. The approach relies on using the Fast Fourier Transform algorithm. Low-pass spectral filters are employed to control both the high frequency Gibbs oscillations inherent to the Fourier method and the fast-growing numerical instabilities resulting from the hyperbolic nature of the transport equation. The numerical scheme is validated by comparison with an exact solution in the 1D case corresponding to dislocation dipole annihilation. The expansion and annihilation of dislocation loops in 2D and 3D settings are also produced and compared with finite element approximations. The spectral solutions are shown to be stable, more accurate for low Courant numbers and much less computation time-consuming than the finite element technique based on an explicit Galerkin-least squares scheme.
Hwang, Jungseek
2016-03-31
We investigate temperature smearing effects on the electron-boson spectral density function (I(2)χ(ω)) obtained from optical data using a maximum entropy inversion method. We start with two simple model input I(2)χ(ω), calculate the optical scattering rates at selected temperatures using the model input spectral density functions and a generalized Allen's formula, then extract back I(2)χ(ω) at each temperature from the calculated optical scattering rate using the maximum entropy method (MEM) which has been used for analysis of optical data of high-temperature superconductors including cuprates, and finally compare the resulting I(2)χ(ω) with the input ones. From this approach we find that the inversion process can recover the input I(2)χ(ω) almost perfectly when the quality of fits is good enough and also temperature smearing (or thermal broadening) effects appear in the I(2)χ(ω) when the quality of fits is not good enough. We found that the coupling constant and the logarithmically averaged frequency are robust to the temperature smearing effects and/or the quality of fits. We use these robust properties of the two quantities as criterions to check whether experimental data have intrinsic temperature-dependent evolutions or not. We carefully apply the MEM to two material systems (one optimally doped and the other underdoped cuprates) and conclude that the I(2)χ(ω) extracted from the optical data contain intrinsic temperature-dependent evolutions.
On the power spectral density of quadrature modulated signals. [satellite communication
NASA Technical Reports Server (NTRS)
Yan, T. Y.
1981-01-01
The conventional (no-offset) quadriphase modulation technique suffers from the fact that hardlimiting will restore the frequency sidelobes removed by proper filtering. Thus, offset keyed quadriphase modulation techniques are often proposed for satellite communication with bandpass hardlimiting. A unified theory is developed which is capable of describing the power spectral density before and after the hardlimiting process. Using the in-phase and the quadrature phase channel with arbitrary pulse shaping, analytical results are established for generalized quadriphase modulation. In particular MSK, OPSK or the recently introduced overlapped raised cosine keying all fall into this general category. It is shown that for a linear communication channel, the power spectral density of the modulated signal remains unchanged regardless of the offset delay. Furthermore, if the in phase and the quadrature phase channel have identical pulse shapes without offset, the spectrum after bandpass hardlimiting will be identical to that of the conventional QPSK modulation. Numerical examples are given for various modulation techniques. A case of different pulse shapes in the in phase and the quadrature phase channel is also considered.
Water model tuning for improved reproduction of rotational diffusion and NMR spectral density.
Takemura, Kazuhiro; Kitao, Akio
2012-06-07
A water model for molecular simulation was optimized to improve the reproduction of translational and rotational diffusion of pure water and proteins. The SPC/E(b) model was developed from the original SPC/E model with a slight increase of the O-H bond length of 1%. This tuning has significantly improved the translational and rotational diffusion when compared to the experimental values, whereas only small changes were observed in the other thermodynamic properties examined. The overall tumbling correlation times (τ(p)) from ubiquitin, protein G, bovine pancreatic trypsin inhibitor, and barstar C42/80A were successfully reproduced using the SPC/E(b) model. Calculated site-specific spectral densities of the main chain amide bond rotation in ubiquitin and protein G were in good agreement with those derived from nuclear magnetic resonance reduced spectral density mapping. The SPC/E(bT) model was also developed with temperature-dependent bond-length tuning to facilitate reproduction of the experimental τ(p) around room temperature.
Spectral Characteristics of Ionospheric Plasma Density and Tilt Variations from the Dynasonde Data
NASA Astrophysics Data System (ADS)
Negrea, Catalin; Zabotin, Nikolay; Bullett, Terence
2013-04-01
Unique capabilities of the Dynasonde technique of ionospheric radio sounding allow measuring echo ranges and angles of arrival with high precision. The inversion algorithm NeXtYZ, which is a part of the Dynasonde data analysis package, uses this information to restore parameters of a three-dimensional plasma density distribution over the sounder location, including its vertical cross-section (vertical profile) and tilts of constant electron density surfaces as functions of the true altitude. With a month-long data series from a state-of-the-art Dynasonde installation at Wallops Island, VA, we demonstrate how results of this analysis can be used to study temporal spectral characteristics of the wave disturbances at a wide range of mesospheric and thermospheric altitudes. Spectra describing dominant activity at low frequencies are determined from observations over large time periods. Also, the time evolution of high-frequency (up to 4 mHz) components is studied using a short (~2 hours) sliding window spectral calculation technique. The procedure has a relatively high sensitivity level and an estimate of it is provided. Possible sources of variability at all frequencies are investigated. Some spectral features have clear sources, such as tidal effects. Both the diurnal peak and its higher harmonics are clearly visible in our results. Other parts of the spectra have less obvious sources that may include interactions of a wind with orography and a coupling with wave motions in the ocean and/or seismic activity in the crust. We discuss likely causes for features such as the increased activity in the East-West direction compared to activity in the North-South direction at the Wallops location.
X-ray Fluctuation Power Spectral Density Survey of Six Seyfert 1 Galaxies
NASA Astrophysics Data System (ADS)
Markowitz, A.
2002-05-01
By combining low-density RXTE long- and medium-term monitoring with high-density, short-term monitoring from XMM and Chandra long-looks, we have constructed X-ray fluctuation power spectral densities (PSDs) for six Seyfert 1 galaxies. These PSDs cover unprecedented dynamic ranges, continuously spanning up to or beyond 4 orders of magnitude in temporal frequency. The PSDs of four targets show significant flattening towards lower frequencies and bear remarkable similarity to X-ray Binary PSDs, strengthening the argument that similar emission processes occur in both types of compact accreting systems, spanning a factor of ~106-7 in luminosity and putative black hole mass. Assuming a linear mass-timescale relation, the resulting PSD break frequencies imply black hole masses which generally agree with reverberation-mapped mass estimates. If the geometric origin of the variability is close to the X-ray corona, then the physical timescales associated with thermal and acoustic disk variations may be relevant.
Mariappan, G; Sundaraganesan, N
2014-01-03
A comprehensive screening of the more recent DFT theoretical approach to structural analysis is presented in this section of theoretical structural analysis. The chemical name of 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide is usually called as Flutamide (In the present study it is abbreviated as FLT) and is an important and efficacious drug in the treatment of anti-cancer resistant. The molecular geometry, vibrational spectra, electronic and NMR spectral interpretation of Flutamide have been studied with the aid of density functional theory method (DFT). The vibrational assignments of the normal modes were performed on the basis of the PED calculations using the VEDA 4 program. Comparison of computational results with X-ray diffraction results of Flutamide allowed the evaluation of structure predictions and confirmed B3LYP/6-31G(d,p) as accurate for structure determination. Application of scaling factors for IR and Raman frequency predictions showed good agreement with experimental values. This is supported the assignment of the major contributors of the vibration modes of the title compound. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. NMR chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The comparison of measured FTIR, FT-Raman, and UV-Visible data to calculated values allowed assignment of major spectral features of the title molecule. Besides, Frontier molecular orbital analyze was also investigated using theoretical calculations.
NASA Astrophysics Data System (ADS)
Mariappan, G.; Sundaraganesan, N.
2014-01-01
A comprehensive screening of the more recent DFT theoretical approach to structural analysis is presented in this section of theoretical structural analysis. The chemical name of 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide is usually called as Flutamide (In the present study it is abbreviated as FLT) and is an important and efficacious drug in the treatment of anti-cancer resistant. The molecular geometry, vibrational spectra, electronic and NMR spectral interpretation of Flutamide have been studied with the aid of density functional theory method (DFT). The vibrational assignments of the normal modes were performed on the basis of the PED calculations using the VEDA 4 program. Comparison of computational results with X-ray diffraction results of Flutamide allowed the evaluation of structure predictions and confirmed B3LYP/6-31G(d,p) as accurate for structure determination. Application of scaling factors for IR and Raman frequency predictions showed good agreement with experimental values. This is supported the assignment of the major contributors of the vibration modes of the title compound. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. NMR chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The comparison of measured FTIR, FT-Raman, and UV-Visible data to calculated values allowed assignment of major spectral features of the title molecule. Besides, Frontier molecular orbital analyze was also investigated using theoretical calculations.
Holographic vector mesons from spectral functions at finite baryon or isospin density
Erdmenger, Johanna; Kaminski, Matthias; Rust, Felix
2008-02-15
We consider gauge/gravity duality with flavor for the finite-temperature field theory dual of the AdS-Schwarzschild black hole background with embedded D7-brane probes. In particular, we investigate spectral functions at finite baryon density in the black hole phase. We determine the resonance frequencies corresponding to meson-mass peaks as function of the quark mass over temperature ratio. We find that these frequencies have a minimum for a finite value of the quark mass. If the quotient of quark mass and temperature is increased further, the peaks move to larger frequencies. At the same time the peaks narrow, in agreement with the formation of nearly stable vector meson states which exactly reproduce the meson-mass spectrum found at zero temperature. We also calculate the diffusion coefficient, which has finite value for all quark mass to temperature ratios, and exhibits a first-order phase transition. Finally we consider an isospin chemical potential and find that the spectral functions display a resonance peak splitting, similar to the isospin meson-mass splitting observed in effective QCD models.
Gómez, Carlos M; Rodríguez-Martínez, Elena I; Fernández, Alberto; Maestú, Fernando; Poza, Jesús; Gómez, Carlos
2017-01-01
The aim of this study was to define the pattern of reduction in absolute power spectral density (PSD) of magnetoencephalography (MEG) signals throughout development. Specifically, we wanted to explore whether the human skull's high permeability for electromagnetic fields would allow us to question whether the pattern of absolute PSD reduction observed in the human electroencephalogram is due to an increase in the skull's resistive properties with age. Furthermore, the topography of the MEG signals during maturation was explored, providing additional insights about the areas and brain rhythms related to late maturation in the human brain. To attain these goals, spontaneous MEG activity was recorded from 148 sensors in a sample of 59 subjects divided into three age groups: children/adolescents (7-14 years), young adults (17-20 years) and adults (21-26 years). Statistical testing was carried out by means of an analysis of variance (ANOVA), with "age group" as between-subject factor and "sensor group" as within-subject factor. Additionally, correlations of absolute PSD with age were computed to assess the influence of age on the spectral content of MEG signals. Results showed a broadband PSD decrease in frontal areas, which suggests the late maturation of this region, but also a mild increase in high frequency PSD with age in posterior areas. These findings suggest that the intensity of the neural sources during spontaneous brain activity decreases with age, which may be related to synaptic pruning.
Computation of the spectral density of two-point functions: Complex masses, cut rules, and beyond
Dudal, David; Guimaraes, Marcelo S.
2011-02-15
We present a steepest descent calculation of the Kaellen-Lehmann spectral density of two-point functions involving complex conjugate masses in Euclidean space. This problem occurs in studies of (gauge) theories with Gribov-like propagators. As the presence of complex masses and the use of Euclidean space brings the theory outside of the strict validity of the Cutkosky cut rules, we discuss an alternative method based on the Widder inversion operator of the Stieltjes transformation. It turns out that the results coincide with those obtained by naively applying the cut rules. We also point out the potential usefulness of the Stieltjes (inversion) formalism when nonstandard propagators are used, in which case cut rules are not available at all.
NASA Astrophysics Data System (ADS)
Lemonik, Yonah; Mitra, Aditi
2017-09-01
Results are presented for the time evolution of fermions initially in a nonzero temperature normal phase, following the switch on of an attractive interaction. The dynamics are studied in the disordered phase close to the critical point, where the superfluid fluctuations are large. The analysis is conducted within a two-particle irreducible, large N approximation. The system is considered from the perspective of critical quenches where it is shown that the fluctuations follow universal model A dynamics. A signature of this universality is found in a singular correction to the fermion lifetime, given by a scaling form t(3 -d )/2Sd(ɛ2t ) , where d is the spatial dimension, t is the time since the quench, and ɛ is the fermion energy. The singular behavior of the spectral density is interpreted as arising due to incoherent Andreev reflections off superfluid fluctuations.
NASA Astrophysics Data System (ADS)
Lee, Jinyong; Lee, Hyun Sook; Kim, Sunghyun; Hwang, Do Guwn
2012-05-01
We have compared the aging index of the second derivatives of photoplethysmography (PPG) with the power spectral density (PSD) from PPG signals to investigate the effect of a strong pulsed electromagnetic field (PEMF) on the improvement of vascularization in the capillary vessels of the finger. The PEMF stimulator was composed of an elliptical coil of 10 turns and 12 cm × 5 cm, and its maximum field and transition time were 0.48 T and 0.102 ms, respectively. It is not easy to analyze the stimulus effect of blood vessel from raw signals of PPG, and aging index of vascularization from the second derivatives of PPG. A PSD analysis in the frequency domain was introduced to reduce artifacts due to change in the posture of the subjects, the environment, acoustic noise, etc. For ages in the 50s, the PSD analysis before and after PEMF stimulus was rather more reliable than the second derivatives of the PPG.
NASA Astrophysics Data System (ADS)
Pedram, Masoud; Esfandiari, Akbar; Khedmati, Mohammad Reza
2017-06-01
This paper investigates the viability of damage detection using power spectral density (PSD) of structural response both numerically and experimentally. The paper establishes a sensitivity based damage detection method to use PSD. The advantages of PSD as a model updating metric are explained and its challenges are addressed. An approximate frequency response function of damaged model is used to redeem the method for the effect of incomplete measurement. The robust solution of the developed sensitivity equation is achieved through a least-squares error minimization scheme, and the challenging issues are discussed. The ability of the method in localizing and quantifying the damage and its robustness against measurement and modeling errors is investigated by a numerical example. Experimental vibration test data of a laboratory concrete beam with various level of distributed damage is used to probe the method in practical conditions. The results show that PSD of response can be used to detect damages in lower frequency ranges with acceptable accuracy.
Güven, Sertaç; Kesebir, Sermin; Demirer, R Murat; Bilici, Mustafa
2015-06-01
Our aim in this study was to investigate spectral power density (PSD) in first-episode mania and subsequent remission period and to evaluate their difference. Sixty-nine consecutive cases referring to our hospital within the previous 1 year, who were evaluated as bipolar disorder manic episode according to The Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) at the first episode and had the informed consent form signed by first degree relatives, were included in this study. Exclusion criteria included having previous depressive episode, using drugs which could influence electroencephalographic activity before electroencephalography (EEG), and having previous neurological disease, particularly epilepsy, head trauma, and/or loss of consciousness. EEG records were obtained using a digital device in 16 channels; 23 surface electrodes were placed according to the International 10-20 system. Spectral power density (dbμV/Hz) of EEG signal provided information on the power carried out by EEG waves in defined frequancy range per unit frequency in the present study. A peak power value detected on the right with FP2P4 and on the left with F7T3 electrodes were found to be higher in the manic episode than in the remission period (p=0.018 and 0.025). In the remission period, in cases with psychotic symptoms during the manic period, F4C4 peak power value was found to be lower than that in cases with no psychotic findings during the manic period (p=0.027). There was no relation was found between YMRS scores and peak power scores. Electrophysiological corollary of mood episode is present from the onset of the disease, and it differs between the manic and remission periods of bipolar disorder. In the remission period, peak power values of PSD distinguish cases with psychotic findings from cases without psychotic findings when they were manic.
GÜVEN, Sertaç; KESEBİR, Sermin; DEMİRER, R. Murat; BİLİCİ, Mustafa
2015-01-01
Introduction Our aim in this study was to investigate spectral power density (PSD) in first-episode mania and subsequent remission period and to evaluate their difference. Methods Sixty-nine consecutive cases referring to our hospital within the previous 1 year, who were evaluated as bipolar disorder manic episode according to The Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) at the first episode and had the informed consent form signed by first degree relatives, were included in this study. Exclusion criteria included having previous depressive episode, using drugs which could influence electroencephalographic activity before electroencephalography (EEG), and having previous neurological disease, particularly epilepsy, head trauma, and/or loss of consciousness. EEG records were obtained using a digital device in 16 channels; 23 surface electrodes were placed according to the International 10–20 system. Spectral power density (dbμV/Hz) of EEG signal provided information on the power carried out by EEG waves in defined frequancy range per unit frequency in the present study. Results A peak power value detected on the right with FP2P4 and on the left with F7T3 electrodes were found to be higher in the manic episode than in the remission period (p=0.018 and 0.025). In the remission period, in cases with psychotic symptoms during the manic period, F4C4 peak power value was found to be lower than that in cases with no psychotic findings during the manic period (p=0.027). There was no relation was found between YMRS scores and peak power scores. Conclusion Electrophysiological corollary of mood episode is present from the onset of the disease, and it differs between the manic and remission periods of bipolar disorder. In the remission period, peak power values of PSD distinguish cases with psychotic findings from cases without psychotic findings when they were manic.
NASA Astrophysics Data System (ADS)
Rekik, Najeh
2014-03-01
Despite the considerable progress made in quantum theory and computational methods, detailed descriptions of the potential energy surfaces of hydrogen-bonded systems have not yet been achieved. In addition, the hydrogen bond (H-bond) itself is still so poorly understood at the fundamental level that it remains unclear exactly what geometry constitutes a “real” H-bond. Therefore, in order to investigate features essential for hydrogen bonded complexes, a simple, efficient, and general method for calculating matrix elements of vibrational operators capable of describing the stretching modes and the H-bond bridges of hydrogen-bonded systems is proposed. The derived matrix elements are simple and computationally easy to evaluate, which makes the method suitable for vibrational studies of multiple-well potentials. The method is illustrated by obtaining potential energy surfaces for a number of two-dimensional systems with repulsive potentials chosen to be in Gaussian form for the stretching mode and of the Morse-type for the H-bond bridge dynamics. The forms of potential energy surfaces of weak and strong hydrogen bonds are analyzed by varying the asymmetry of the Gaussian potential. Moreover, the choice and applicability of the selected potential for the stretching mode and comparison with other potentials used in the area of hydrogen bond research are discussed. The approach for the determination of spectral density has been constructed in the framework of the linear response theory for which spectral density is obtained by Fourier transform of the autocorrelation function of the dipole moment operator of the fast mode. The approach involves anharmonic coupling between the high frequency stretching vibration (double well potential) and low-frequency donor-acceptor stretching mode (Morse potential) as well as the electrical anharmonicity of the dipole moment operator of the fast mode. A direct relaxation mechanism is incorporated through a time decaying exponential
Pc 5 Spectral Density at ULTIMA stataions and its Radial Diffusion Coefficients for REE
NASA Astrophysics Data System (ADS)
Fujimoto, A.; Tokunaga, T.; Abe, S.; Uozumi, T.; Yoshikawa, A.; Mann, I. R.; Chi, P. J.; Engebretson, M. J.; Yumoto, K.
2009-12-01
arrays. The radial diffusion coefficient can be given from the magnetic field power spectral density as a function of L, frequency (f) and m-number (m) in the Pc 5 frequency range during the REE related magnetic storms [see Brautigam et al., 2005]. We can fit Pc 5 power spectral density (L, f, m) using the ULTIMA data. The m-number of global Pc 5 pulsation on the ground is found to be almost less than 5. This is consistent with m-number required in the radial diffusion theory by Elkington et al. [1999, 2003]. We will compare the observationally estimated diffusion coefficient with theoretical diffusion coefficient [e.g. Elkington et al., 2006], and discuss adequacy of our diffusion coefficient.
Spectral factorization-based current source density analysis of ongoing neural oscillations.
Chand, Ganesh B; Dhamala, Mukesh
2014-03-15
Current source density (CSD) analysis is widely used in neurophysiological investigations intended to reveal the patterns of localized neuronal activity in terms of current sources and sinks. CSD is based on the second spatial derivatives of multi-electrode electrophysiological recordings, and can be applied to brain activity related to repeated external stimulations (evoked brain activity) or ongoing (spontaneous) brain activity. In evoked brain activity, event-related time-series averages of ensembles are used to compute CSD patterns. However, for ongoing neural activity, the lack of external events requires a different approach other than ensemble averaging. Here, we propose a new spectral factorization-based current source density (SF-CSD) analysis method for ongoing neural oscillations. We validated this new SF-CSD analysis method using simulated data and demonstrated its effectiveness by applying to experimental intra-cortical local field potentials recorded on multi-contact depth electrodes from monkeys performing selective visual attention tasks. The proposed method gives space-unbiased estimates since it does not rely on a reference for CSD calculation in the frequency-domain. The proposed SF-CSD method is expected to be a useful tool for systematic analysis of neural sources and oscillations from multi-site electrophysiological recordings. Copyright © 2013 Elsevier B.V. All rights reserved.
NASA Astrophysics Data System (ADS)
Moran, Andrew M.; Nome, Rene A.; Scherer, Norbert F.
2007-11-01
The experimental design and theoretical description of a novel five-pulse laser spectroscopy is presented with an application to a pyridinium charge transfer complex in acetonitrile and methanol. In field-resolved polarizability response spectroscopy (PORS), an electronically resonant laser pulse first excites a solvated chromophore (reactant) and off-resonant Raman spectra of the resulting nuclear motions are measured as a function of the reaction time. The present apparatus differs from our earlier design by performing the Raman probe measurement (with fixed pulse delays) in the frequency domain. In addition, the full electric fields of the signals are measured by spectral interferometry to separate nonresonant and Raman responses. Our theoretical model shows how the PORS signal arises from nuclear motions that are displaced/driven by the photoinduced reaction. The field-resolved off-resonant (of the solute's electronic transitions) probing favors detection of solvent (as opposed to solute) dynamics coupled to the reaction. The sign of the signal represents the relative strengths of polarization responses associated with the ground and photoexcited solutions. Signatures of nonresonant and PORS signal contributions to the experimental results are analyzed with numerical calculations based on a theoretical model we have developed for reaction-induced PORS. Our model identifies two mechanisms of PORS signal generation: (i) structural relaxation induced resonance; (ii) dephasing induced resonance. In the charge transfer reaction investigated, the solvent-dependent and time-evolving (solvent) polarizability spectral density (PSD) is readily obtained. The general trend of an initial broadband inertial nuclear response followed by a decrease in the linewidth of the PSD establishes that the measured PSD is inconsistent with the approximation of a linear response. Furthermore, the explicit time evolution of the PSD is important for properly describing solvent control of
NASA Technical Reports Server (NTRS)
Tomei, B. A.; Smith, L. G.
1986-01-01
Sounding rockets equipped to monitor electron density and its fine structure were launched into the auroral and equatorial ionosphere in 1980 and 1983, respectively. The measurement electronics are based on the Langmuir probe and are described in detail. An approach to the spectral analysis of the density irregularities is addressed and a software algorithm implementing the approach is given. Preliminary results of the analysis are presented.
Comparison of the STA/LTA and power spectral density methods for microseismic event detection
NASA Astrophysics Data System (ADS)
Vaezi, Yoones; Van der Baan, Mirko
2015-12-01
Robust event detection and picking is a prerequisite for reliable (micro-) seismic interpretations. Detection of weak events is a common challenge among various available event detection algorithms. In this paper we compare the performance of two event detection methods, the short-term average/long-term average (STA/LTA) method, which is the most commonly used technique in industry, and a newly introduced method that is based on the power spectral density (PSD) measurements. We have applied both techniques to a 1-hr long segment of the vertical component of some raw continuous data recorded at a borehole geophone in a hydraulic fracturing experiment. The PSD technique outperforms the STA/LTA technique by detecting a higher number of weak events while keeping the number of false alarms at a reasonable level. The time-frequency representations obtained through the PSD method can also help define a more suitable bandpass filter which is usually required for the STA/LTA method. The method offers thus much promise for automated event detection in industrial, local, regional and global seismological data sets.
A comparison of the power spectral density of scalp EEG and subjacent electrocorticograms.
Petroff, Ognen A; Spencer, Dennis D; Goncharova, Irina I; Zaveri, Hitten P
2016-02-01
Our study investigated the effects of the intact skull on background EEG rhythms recorded simultaneously by subdural electrocorticography (ECoG) and scalp EEG. We performed a retrospective analysis of twenty patients undergoing intracranial EEG monitoring. EEG and ECoG were recorded simultaneously from the central and occipital scalp and subjacent subdural electrodes removed (median 46 mm, interquartile 27-65) from the craniotomy. The power spectral density (PSD) of artifact-free EEG and ECoG segments and ratio of the scalp EEG to subjacent ECoG PSD was calculated. Overall both ECoG and scalp EEG power decreased by over three orders of magnitude from delta to gamma frequency band with an empirical inverse power relationship. The ratio of scalp EEG to ECoG PSD decreased across the delta and theta frequency bands, remained the same across the alpha, beta and low gamma bands, but increased at the higher frequency bands. EEG PSD mirrored changes in ECoG PSD across the frequency bands. As ECoG power continued to decrease above 42 Hz, extracranial voltage sources contributed to a greater fraction of scalp EEG power. Monitoring the gamma frequency band using scalp EEG was limited by low power on ECoG and masking by extracranial voltage sources. Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Gandhimathi, S; Balakrishnan, C; Theetharappan, M; Neelakantan, M A; Venkataraman, R
2017-03-15
Two Schiff bases were prepared by the condensation of o-allyl substituted 2,4-dihydroxy acetophenone with 1,2-diaminopropane (L1) and ethanediamine (L2) and characterized by elemental analysis, and ESI-MS, IR, UV-Vis, (1)H and (13)C NMR spectral techniques. The effect of solvents with respect to different polarities on UV-Vis and emission spectra of L1 and L2 was investigated at room temperature show that the compounds exist in keto and enol forms in solution and may be attributed to the intramolecular proton transfer in the ground state. The solute-solvent interactions, change in dipole moment and solvatochromic properties of the compounds were studied based on the solvent polarity parameters. For L1 and L2, the ground and excited state electronic structure calculations were carried out by DFT and TD-DFT at B3LYP/6-311G (d,p) level, respectively. The IR, NMR and electronic absorption spectra computed were compared with the experimental observations. The intramolecular charge transfer within the molecule is evidenced from the HOMO and LUMO energy levels and surface analysis. The noncovalent interactions like hydrogen bonding and van der Waals interactions were identified from the molecular geometry and electron localization function. These interactions in molecules have been studied by using reduced density gradient and graphed by Multiwfn.
NASA Astrophysics Data System (ADS)
Gandhimathi, S.; Balakrishnan, C.; Theetharappan, M.; Neelakantan, M. A.; Venkataraman, R.
2017-03-01
Two Schiff bases were prepared by the condensation of o-allyl substituted 2,4-dihydroxy acetophenone with 1,2-diaminopropane (L1) and ethanediamine (L2) and characterized by elemental analysis, and ESI-MS, IR, UV-Vis, 1H and 13C NMR spectral techniques. The effect of solvents with respect to different polarities on UV-Vis and emission spectra of L1 and L2 was investigated at room temperature show that the compounds exist in keto and enol forms in solution and may be attributed to the intramolecular proton transfer in the ground state. The solute-solvent interactions, change in dipole moment and solvatochromic properties of the compounds were studied based on the solvent polarity parameters. For L1 and L2, the ground and excited state electronic structure calculations were carried out by DFT and TD-DFT at B3LYP/6-311G (d,p) level, respectively. The IR, NMR and electronic absorption spectra computed were compared with the experimental observations. The intramolecular charge transfer within the molecule is evidenced from the HOMO and LUMO energy levels and surface analysis. The noncovalent interactions like hydrogen bonding and van der Waals interactions were identified from the molecular geometry and electron localization function. These interactions in molecules have been studied by using reduced density gradient and graphed by Multiwfn.
Yashchuk, Valeriy V.; Irick, Steve C.; Gullikson, Eric M.; Howells, Malcolm R.; MacDowell, Alastair A.; McKinney, Wayne R.; Salmassi, Farhad; Warwick, Tony
2005-07-12
The consistency of different instruments and methods for measuring two-dimensional (2D) power spectral density (PSD) distributions are investigated. The instruments are an interferometric microscope, an atomic force microscope (AFM) and the X-ray Reflectivity and Scattering experimental facility, all available at Lawrence Berkeley National Laboratory. The measurements were performed with a gold-coated mirror with a highly polished stainless steel substrate. It was shown that these three techniques provide essentially consistent results. For the stainless steel mirror, an envelope over all measured PSD distributions can be described with an inverse power-law PSD function. It is also shown that the measurements can be corrected for the specific spatial frequency dependent systematic errors of the instruments. The AFM and the X-ray scattering measurements were used to determine the modulation transfer function of the interferometric microscope. The corresponding correction procedure is discussed in detail. Lower frequency investigation of the 2D PSD distribution was also performed with a long trace profiler and a ZYGO GPI interferometer. These measurements are in some contradiction, suggesting that the reliability of the measurements has to be confirmed with additional investigation. Based on the crosscheck of the performance of all used methods, we discuss the ways for improving the 2D PSD characterization of X-ray optics.
X-Ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
NASA Technical Reports Server (NTRS)
Markowitz, A.; Edelson, R.; Vaughan, S.; Uttley, P.; George, I. M.; Griffiths, R. E.; Kaspi, S.; Lawrence, A.; McHandy, I.; Nandra, K.
2003-01-01
By combining complementary monitoring observations spanning long, medium and short time scales, we have constructed power spectral densities (PSDs) of six Seyfert 1 galaxies. These PSDs span approx. greater than 4 orders of magnitude in temporal frequency, sampling variations on time scales ranging from tens of minutes to over a year. In at least four cases, the PSD shows a "break," a significant departure from a power law, typically on time scales of order a few days. This is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass compact systems with breaks on time scales of seconds. NGC 3783 shows tentative evidence for a doubly-broken power law, a feature that until now has only been seen in the (much better-defined) PSDs of low-state XRBs. It is also interesting that (when one previously-observed object is added to make a small sample of seven), an apparently significant correlation is seen between the break time scale T and the putative black hole mass M(sub BH), while none is seen between break time scale and luminosity. The data are consistent with the linear relation T = M(sub BH) /10(exp 6.5) solar mass; extrapolation over 6-7 orders of magnitude is in reasonable agreement with XRBs. All of this strengthens the case for a physical similarity between Seyfert 1s and XRBs.
X-Ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
NASA Technical Reports Server (NTRS)
Markowitz, A.; Edelson, R.; Vaughan, S.; Uttley, P.; George, I. M.; Griffiths, R. E.; Kaspi, S.; Lawrence, A.; McHandy, I.; Nandra, K.
2003-01-01
By combining complementary monitoring observations spanning long, medium and short time scales, we have constructed power spectral densities (PSDs) of six Seyfert 1 galaxies. These PSDs span approx. greater than 4 orders of magnitude in temporal frequency, sampling variations on time scales ranging from tens of minutes to over a year. In at least four cases, the PSD shows a "break," a significant departure from a power law, typically on time scales of order a few days. This is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass compact systems with breaks on time scales of seconds. NGC 3783 shows tentative evidence for a doubly-broken power law, a feature that until now has only been seen in the (much better-defined) PSDs of low-state XRBs. It is also interesting that (when one previously-observed object is added to make a small sample of seven), an apparently significant correlation is seen between the break time scale T and the putative black hole mass M(sub BH), while none is seen between break time scale and luminosity. The data are consistent with the linear relation T = M(sub BH) /10(exp 6.5) solar mass; extrapolation over 6-7 orders of magnitude is in reasonable agreement with XRBs. All of this strengthens the case for a physical similarity between Seyfert 1s and XRBs.
Using the power spectral density method to characterise the surface topography of optical surfaces
NASA Astrophysics Data System (ADS)
Alcock, Simon G.; Ludbrook, Geoff D.; Owen, Tommy; Dockree, Richard
2010-08-01
Power Spectral Density (PSD) is an alternative method for specifying optical surfaces, and quantifies the contribution of each spatial regime to the total surface error. This approach naturally includes mid-range spatial frequency errors, which are often overlooked. The PSD method has recently been adopted by the Space and Astronomy industries, but has not yet received general acceptance within the synchrotron community. To assess the suitability for specifying synchrotron optics using PSD, Fast Fourier Transforms were performed on topography data from a range of optical surfaces of varying quality and manufacturing techniques. For each grade of optic, the entire regime ({100nm to {50mm) of surface errors was measured, with overlapping bandwidths, using a micro-interferometer and a Fizeau interferometer. From this heuristic information, root-mean square "roughness" can be predicted over any desired spatial range, thus allowing direct comparison of metrology data obtained by instruments with different spatial bandwidths. We present an efficient approach for calculating 1-D and 2-D PSDs using MATLAB algorithms, and discuss analysis considerations, including "field of view" effects and instrument calibration.
Evaluation of localized muscle fatigue using power spectral density analysis of the electromyogram
NASA Technical Reports Server (NTRS)
Lafevers, E. V.
1974-01-01
Surface electromyograms (EMGs) taken from three upper torso muscles during a push-pull task were analyzed by a power spectral density technique to determine the operational feasibility of the technique for identifying changes in the EMGs resulting from muscular fatigue. The EMGs were taken from four subjects under two conditions (1) in shirtsleeves and (2) in a pressurized space suit. This study confirmed that frequency analysis of dynamic muscle activity is capable of providing reliable data for many industrial applications where fatigue may be of practical interest. The results showed significant effects of the pressurized space suit on the pattern of shirtsleeve fatigue responses of the muscles. The data also revealed (1) reliable differences between muscles in fatigue-induced responses to various locations in the reach envelope at which the subjects were required to perform the push-pull exercise and (2) the differential sensitivity of muscles to the various reach positions in terms of fatigue-related shifts in EMG power.
THE FIRST HARD X-RAY POWER SPECTRAL DENSITY FUNCTIONS OF ACTIVE GALACTIC NUCLEUS
Shimizu, T. Taro; Mushotzky, Richard F.
2013-06-10
We present results of our power spectral density (PSD) analysis of 30 active galactic nuclei (AGNs) using the 58 month light curves from Swift's Burst Alert Telescope (BAT) in the 14-150 keV band. PSDs were fit using a Monte Carlo based algorithm to take into account windowing effects and measurement error. All but one source were found to be fit very well using an unbroken power law with a slope of {approx} - 1, consistent at low frequencies with previous studies in the 2-10 keV band, with no evidence of a break in the PSD. For five of the highest signal-to-noise ratio sources, we tested the energy dependence of the PSD and found no significant difference in the PSD at different energies. Unlike previous studies of X-ray variability in AGNs, we do not find any significant correlations between the hard X-ray variability and different properties of the AGN including luminosity and black hole mass. The lack of break frequencies and correlations seem to indicate that AGNs are similar to the high state of Galactic black holes.
Assessing a learning process with functional ANOVA estimators of EEG power spectral densities.
Gutiérrez, David; Ramírez-Moreno, Mauricio A
2016-04-01
We propose to assess the process of learning a task using electroencephalographic (EEG) measurements. In particular, we quantify changes in brain activity associated to the progression of the learning experience through the functional analysis-of-variances (FANOVA) estimators of the EEG power spectral density (PSD). Such functional estimators provide a sense of the effect of training in the EEG dynamics. For that purpose, we implemented an experiment to monitor the process of learning to type using the Colemak keyboard layout during a twelve-lessons training. Hence, our aim is to identify statistically significant changes in PSD of various EEG rhythms at different stages and difficulty levels of the learning process. Those changes are taken into account only when a probabilistic measure of the cognitive state ensures the high engagement of the volunteer to the training. Based on this, a series of statistical tests are performed in order to determine the personalized frequencies and sensors at which changes in PSD occur, then the FANOVA estimates are computed and analyzed. Our experimental results showed a significant decrease in the power of [Formula: see text] and [Formula: see text] rhythms for ten volunteers during the learning process, and such decrease happens regardless of the difficulty of the lesson. These results are in agreement with previous reports of changes in PSD being associated to feature binding and memory encoding.
NASA Astrophysics Data System (ADS)
Meng, Kai; Wan, Yongjian; Wu, Fan; Shen, Lijun; Wu, Hsing-Yu
2017-02-01
Mid to high spatial frequency error (MSFR and HSFR) should be strictly controlled in modern optical systems. Pitch tool polishing (PTP) is an effective ultra-smoothing surface manufacturing method to control MSFR and HSFR. But it is difficult to control because it is affected by a lot of factors. The present paper describes the pitch tool polishing study based on eighteen well-planned orthogonal experiments (OA18 matrix). Five main process factors (abrasive particle size, slurry concentration, pad rotation speed, acidity and polishing time) in pitch tool polishing process were investigated. In this study, power spectral density (PSD) based on Fourier analysis of surface topography data obtained by white light interferometer was used as the results of orthogonal experiments instead of material removal rate and surface roughness. A normalization method of PSD was proposed as the range analysis rule. Three parts of spatial frequency bandwidth were selected and discussed. Acidity is the most important factor in part 1 and slurry concentration is the most significant one in part 2; while acidity is the least influenced one in part 3. The result in each part was explained by two-step material removal mechanism. At last, suggestions in low and high spatial frequency are given for pitch tool polishing.
NASA Astrophysics Data System (ADS)
Stilbs, Peter; Söderman, Olle; Walderhaug, harald
The motional spectral densities, J( ω0) and J(2 ω0) are extracted directly from a bandshape analysis of the 13C signal of a deuterated methylene group of a surfactant, Li dodecyl sulfate, residing in a micelle. The extracted spectral densities are then compared with spectral densities calculated using a motional model, the so-called "two-step model," for methylene segments of aggregated surfactants. The two sets of spectral densities agree within the experimental uncertainty. Thus, the two-step model is a reasonable description of NMR relaxation in micellar systems.
Power spectral density and scaling exponent of high frequency global solar radiation sequences
NASA Astrophysics Data System (ADS)
Calif, Rudy; Schmitt, François G.; Huang, Yongxiang
2013-04-01
invariance: Iq(f) ~ f-?(q) , ?(q) is the scaling exponent. This allows to characterize the scaling behavior of a process: fractal or multifractal with intermittent properties. For q = 2, the Hilbert spectrum is defined. In this work, The data are collected at the University site of Guadeloupe, an island in the West Indies, located at 16°15 N latitude 60°30 W longitude. Our measurements sampled at 1 Hz were performed during one year period. The analyzed data present a power spectral density E(f) displaying a power law of the form E(f) ~ f-β with 1.6 ˜ β ˜ 2.2 for frequencies f ˜ 0.1 Hz, corresponding to time scales T × 10 s. Furthermore, global solar radiation data possesses multifractal properties. For comparison, other multifractal analysis techniques such as structure functions, MDFA, wavelet leaders are also used. This preliminary work set the basis for further investigation dedicated to simulate and forecast a sequence of solar energy fluctuation under different meteorological conditions, in the multifractal framework.
Chhablani, Jay; Barteselli, Giulio; Bartsch, Dirk-Uwe; Kozak, Igor; Wang, Haiyan; El-Emam, Sharif; Doede, Aubrey L; Cheng, Lingyun; Freeman, William R
2012-01-01
BACKGROUND To evaluate the impact of scanning density on macular choroidal volume measurement using spectral-domain optical coherence tomography (SD-OCT). METHODS Thirty eyes of normal subjects underwent consecutive raster choroidal scanning protocols using SD-OCT in enhanced-depth imaging mode. Manual choroidal segmentation was performed using the built-in automated retinal segmentation software to obtain five analyses with different inter-scan distances including inter-scan distances of 30 microns, 60 microns, 120 microns, 240 microns, and 480 microns. The built-in software of the device automatically generated the choroidal thickness and volume map in the similar manner as for retinal volume map, using the standardized Early Treatment Diabetic Retinopathy Study (ETDRS) grid. For each raster scan, mean absolute difference and relative difference of mean foveal choroidal thickness (FCT), foveal choroidal volume (FCV) and total macular choroidal volume (TCV) in comparison to “true value” (i.e., 30-micron inter-scan distance) were calculated. RESULTS The maximum relative differences were 10% and 16% for TCV and FCV, respectively. For mean FCT, the maximum absolute difference was 31 microns, and maximum relative difference was 12.7%. No statistically significant differences were found in measurements of mean foveal choroidal thickness (p=0.912) and volume (p=0.944), as well as macular choroidal volume (p=0.912), with varying inter-scan distance. CONCLUSIONS Our study shows that approximately 16 scans over the macula with a inter-scans distance of 480 microns is sufficient to provide clinically relevant and reliable choroidal thickness/volume map. This information could be useful in design of choroidal scanning protocols for future clinical trials. PMID:23142990
NASA Astrophysics Data System (ADS)
Rekik, Najeh; Issaoui, Noureddine; Ghalla, Houcine; Oujia, Brahim; Wójcik, Marek J.
2007-11-01
The IR spectral density (SD) of the high frequency stretching mode of H-bonded complexes involving both the intrinsic anharmonicity of the fast and slow mode, together with direct and indirect relaxations is studied within the linear response theory. For this aim, we extend a quantum non-adiabatic treatment of H-bonds involving intrinsic anharmonicity of the fast mode [N. Rekik, A. Velescu, P. Blaise, O. Henri-Rousseau, Chem. Phys. 273 (2001) 11.] which is described by an asymmetric double well potential by accounting for the anharmonicity of the slow mode and the indirect relaxation. In addition, the repulsive potential intervening in the asymmetric double well potential is described by the sum of three Gaussian whereas in the previous model, only one Gaussian was taken into account. The anharmonic coupling between the high frequency X-H→…Y and the low frequency X←-H…Y→ modes is treated inside the strong anharmonic coupling theory. The relaxation of the fast mode (direct damping) and of the H-bond bridge (indirect damping) is incorporated by aid of our previous results [N. Rekik, B.Ouari, P. Blaise, O. Henri-Rousseau, J. Mol. Struc. (Theochem.) 687 (2004) 125-133.]. The IR SD is obtained by Fourier transform of the autocorrelation function of the dipole moment operator of the fast mode. The numerical calculation shows that the indirect damping plays a specific role in the features of the lineshapes of hydrogen bonds systems by favouring more the fine structure of the low frequency tail than that of the high frequency one.
Ozgokmen, T.; Fischer, P.; Duan, J.; Iliescu, T.; Mathematics and Computer Science; Univ. of Miami; IIT; Virginia Polytechnic Inst. and State Univ.
2004-09-01
Overflows are bottom gravity currents that supply dense water masses generated in high-latitude and marginal seas into the general circulation. Oceanic observations have revealed that mixing of overflows with ambient water masses takes place over small spatial and time scales. Studies with ocean general circulation models indicate that the strength of the thermohaline circulation is strongly sensitive to representation of overflows in these models. In light of these results, overflow-induced mixing emerges as one of the prominent oceanic processes. In this study, as a continuation of an effort to develop appropriate process models for overflows, nonhydrostatic 3D simulations of bottom gravity are carried out that would complement analysis of dedicated observations and large-scale ocean modeling. A parallel high-order spectral-element Navier-Stokes solver is used as the basis of the simulations. Numerical experiments are conducted in an idealized setting focusing on the startup phase of a dense water mass released at the top of a sloping wedge. Results from 3D experiments are compared with results from 2D experiments and laboratory experiments, based on propagation speed of the density front, growth rate of the characteristic head at the leading edge, turbulent overturning length scales, and entrainment parameters. Results from 3D experiments are found to be in general agreement with those from laboratory tank experiments. In 2D simulations, the propagation speed is approximately 20% slower than that of the 3D experiments and the head growth rate is 3 times as large, Thorpe scales are 1.3-1.5 times as large, and the entrainment parameter is up to 2 times as large as those in the 3D experiments. The differences between 2D and 3D simulations are entirely due to internal factors associated with the truncation of the Navier-Stokes equations for 2D approximation.
Parkhomenko, A I; Shalagin, Anatolii M
2011-11-30
Using the eikonal approximation, we have calculated effective collision frequencies in density-matrix kinetic equations describing nonlinear effects in the wings of spectral lines. We have established the relation between the probabilities of absorption and stimulated emission and the characteristics of the radiation and elementary scattering event. The example of the power interaction potential shows that quantum mechanical calculation of the collision frequencies in the eikonal approximation and previously known spectral line wing theory give similar results for the probability of radiation absorption.
Liu, Hao; Zhu, Lili; Bai, Shuming; Shi, Qiang
2014-04-07
We investigated applications of the hierarchical equation of motion (HEOM) method to perform high order perturbation calculations of reduced quantum dynamics for a harmonic bath with arbitrary spectral densities. Three different schemes are used to decompose the bath spectral density into analytical forms that are suitable to the HEOM treatment: (1) The multiple Lorentzian mode model that can be obtained by numerically fitting the model spectral density. (2) The combined Debye and oscillatory Debye modes model that can be constructed by fitting the corresponding classical bath correlation function. (3) A new method that uses undamped harmonic oscillator modes explicitly in the HEOM formalism. Methods to extract system-bath correlations were investigated for the above bath decomposition schemes. We also show that HEOM in the undamped harmonic oscillator modes can give detailed information on the partial Wigner transform of the total density operator. Theoretical analysis and numerical simulations of the spin-Boson dynamics and the absorption line shape of molecular dimers show that the HEOM formalism for high order perturbations can serve as an important tool in studying the quantum dissipative dynamics in the intermediate coupling regime.
Liu, Hao; Zhu, Lili; Bai, Shuming; Shi, Qiang
2014-04-07
We investigated applications of the hierarchical equation of motion (HEOM) method to perform high order perturbation calculations of reduced quantum dynamics for a harmonic bath with arbitrary spectral densities. Three different schemes are used to decompose the bath spectral density into analytical forms that are suitable to the HEOM treatment: (1) The multiple Lorentzian mode model that can be obtained by numerically fitting the model spectral density. (2) The combined Debye and oscillatory Debye modes model that can be constructed by fitting the corresponding classical bath correlation function. (3) A new method that uses undamped harmonic oscillator modes explicitly in the HEOM formalism. Methods to extract system-bath correlations were investigated for the above bath decomposition schemes. We also show that HEOM in the undamped harmonic oscillator modes can give detailed information on the partial Wigner transform of the total density operator. Theoretical analysis and numerical simulations of the spin-Boson dynamics and the absorption line shape of molecular dimers show that the HEOM formalism for high order perturbations can serve as an important tool in studying the quantum dissipative dynamics in the intermediate coupling regime.
NASA Astrophysics Data System (ADS)
Bohn, Birger; Lohse, Insa
2017-09-01
The properties and performance of charge-coupled device (CCD) array spectroradiometers for the measurement of atmospheric spectral actinic flux densities (280-650 nm) and photolysis frequencies were investigated. These instruments are widely used in atmospheric research and are suitable for aircraft applications because of high time resolutions and high sensitivities in the UV range. The laboratory characterization included instrument-specific properties like the wavelength accuracy, dark signal, dark noise and signal-to-noise ratio (SNR). Spectral sensitivities were derived from measurements with spectral irradiance standards. The calibration procedure is described in detail, and a straightforward method to minimize the influence of stray light on spectral sensitivities is introduced. From instrument dark noise, minimum detection limits ≈ 1 × 1010 cm-2 s-1 nm-1 were derived for spectral actinic flux densities at wavelengths around 300 nm (1 s integration time). As a prerequisite for the determination of stray light under field conditions, atmospheric cutoff wavelengths were defined using radiative transfer calculations as a function of the solar zenith angle (SZA) and total ozone column (TOC). The recommended analysis of field data relies on these cutoff wavelengths and is also described in detail taking data from a research flight on HALO (High Altitude and Long Range Research Aircraft) as an example. An evaluation of field data was performed by ground-based comparisons with a double-monochromator-based, highly sensitive reference spectroradiometer. Spectral actinic flux densities were compared as well as photolysis frequencies j(NO2) and j(O1D), representing UV-A and UV-B ranges, respectively. The spectra expectedly revealed increased daytime levels of stray-light-induced signals and noise below atmospheric cutoff wavelengths. The influence of instrument noise and stray-light-induced noise was found to be insignificant for j(NO2) and rather limited for j(O1D
NASA Astrophysics Data System (ADS)
Zhang, Jin; Zhu, Chaoyuan; Liang, WanZhen
2017-08-01
The spectral densities of diagonal and nondiagonal exciton-phonon (e-p) coupling for tetracene crystal have been calculated by the harmonic oscillator (HO) model and ground-state MD-based approaches. We find that classical MD-based approaches overestimate the coupling of exciton with high-frequency vibrational modes and predict the strongest e-p coupling appeared above 1500 cm-1 whereas HO model and AIMD-based approach predict it appeared at ∼ 1400 cm-1. Additionally, the calculated spectral densities of nondiagonal e-p coupling for three different dimers show that they are continuously distributed in the range of 0-150 cm-1 and are 2-3 order of magnitude smaller than the maxima of diagonal e-p coupling.
A search for X-ray reprocessing echoes in the power spectral density functions of AGN
NASA Astrophysics Data System (ADS)
Emmanoulopoulos, D.; Papadakis, I. E.; Epitropakis, A.; Pecháček, T.; Dovčiak, M.; McHardy, I. M.
2016-09-01
We present the results of a detailed study of the X-ray power spectral density (PSD) functions of 12 X-ray bright AGN, using almost all the archival XMM-Newton data. The total net exposure of the EPIC-pn light curves is larger than 350 ks in all cases (and exceeds 1 Ms in the case of 1H 0707-497). In a physical scenario in which X-ray reflection occurs in the inner part of the accretion disc of AGN, the X-ray reflection component should be a filtered echo of the X-ray continuum signal and should be equal to the convolution of the primary emission with the response function of the disc. Our primary objective is to search for these reflection features in the 5-7 keV (iron line) and 0.5-1 keV (soft) bands, where the X-ray reflection fraction is expected to be dominant. We fit to the observed periodograms two models: a simple bending power-law model (BPL) and a BPL model convolved with the transfer function of the accretion disc assuming the lamp-post geometry and X-ray reflection from a homogeneous disc. We do not find any significant features in the best-fitting BPL model residuals either in individual PSDs in the iron band, soft and full band (0.3-10 keV) or in the average PSD residuals of the brightest and more variable sources (with similar black hole mass estimates). The typical amplitude of the soft and full-band residuals is around 3-5 per cent. It is possible that the expected general relativistic effects are not detected because they are intrinsically lower than the uncertainty of the current PSDs, even in the strong relativistic case in which X-ray reflection occurs on a disc around a fast rotating black hole having an X-ray source very close above it. However, we could place strong constrains to the X-ray reflection geometry with the current data sets if we knew in advance the intrinsic shape of the X-ray PSDs, particularly its high-frequency slope.
Liu, Delian; Zhang, Jianqi; Wang, Xiaorui
2016-04-04
Reference spectral signature selection is a fundamental work for automatic oil spill detection. To address this issue, a new approach is proposed here, which employs the density-based cluster to select a specific spectral signature from a hyperspectral image. This paper first introduces the framework of oil spill detection from hyperspectral images, indicating that detecting oil spill requires a reference spectral signature of oil spill, parameters of background, and a target detection algorithm. Based on the framework, we give the new reference spectral signature selection approach in details. Then, we demonstrate the estimation of background parameters according to the reflectance of seawater in the infrared bands. Next, the conventional adaptive cosine estimator (ACE) algorithm is employed to achieve oil spill detection. Finally, the proposed approach is tested via several practical hyperspectral images that are collected during the Horizon Deep water oil spill. The experimental results show that this new approach can automatically select the reference spectral signature of oil spills from hyperspectral images and has high detection performance.
NASA Astrophysics Data System (ADS)
Suess, P.; Shaw, J. H.; Komatitsch, D.; Tromp, J.
2001-12-01
We present a 3D velocity model and a 3D density model of the LA basin. The LA basin velocity model was constructed using sonic log and stacking velocity information, provided by oil industry sources and not previously incorporated into southern California velocity models. The density model is based upon a new database of approximately 300 oil industry density logs from across the Los Angeles basin. These logs use gamma ray emissions to determine formation density at samples of about one meter. We have developed an empirical relation between sonic velocity and density by comparing data from approximately 30 wells in which we have both sonic and density logs. For the remaining wells, we have derived relationships between depth and density, and characterized this relationship for the three main stratigraphic sub-divisions of the SCEC Phase 2 model (Quaternary to base Pico Fm., top Repetto Fm. to top Mohnian, and top Mohnian to basement). The density-depth and density-velocity relations will provide independent rules that can be employed to define density and velocity structure in areas where data does not exist, or in other areas with similar lithology to the Los Angeles basin. We use a spectral element method (SEM) for simulation of seismic wave propagation which is currently being implemented on a 156-node Pentium PC cluster at Cal Tech. Preliminary work shows that SEM results using a 1D velocity model for southern California compare very well to discrete-wavenumber results. Both the density structure and velocity structure must be defined in a 3D model for its use in simulations of seismic wave propagation with a spectral element method, to predict the distribution of hazardous ground shaking during large events. Previous work has typically used density values which were predicted by the sonic velocity values; use of our measured density values should provide more accurate ground shaking predictions, and comparison to previous results will provide a useful
NASA Astrophysics Data System (ADS)
Nagy, Z.; Choi, Y.; Ossenkopf-Okada, V.; van der Tak, F. F. S.; Bergin, E. A.; Gerin, M.; Joblin, C.; Röllig, M.; Simon, R.; Stutzki, J.
2017-02-01
Context. Photon dominated regions (PDRs) are interfaces between the mainly ionized and mainly molecular material around young massive stars. Analysis of the physical and chemical structure of such regions traces the impact of far-ultraviolet radiation of young massive stars on their environment. Aims: We present results on the physical and chemical structure of the prototypical high UV-illumination edge-on Orion Bar PDR from an unbiased spectral line survey with a wide spectral coverage which includes lines of many important gas coolants such as [Cii], [Ci], and CO and other key molecules such as H2CO, H2O, HCN, HCO+, and SO. Methods: A spectral scan from 480-1250 GHz and 1410-1910 GHz at 1.1 MHz resolution was obtained by the HIFI instrument on board the Herschel Space Observatory. We obtained physical parameters for the observed molecules. For molecules with multiple transitions we used rotational diagrams to obtain excitation temperatures and column densities. For species with a single detected transition we used an optically thin LTE approximation. In the case of species with available collisional rates, we also performed a non-LTE analysis to obtain kinetic temperatures, H2 volume densities, and column densities. Results: About 120 lines corresponding to 29 molecules (including isotopologues) have been detected in the Herschel/HIFI line survey, including 11 transitions of CO, 7 transitions of 13CO, 6 transitions of C18O, 10 transitions of H2CO, and 6 transitions of H2O. The rotational temperatures are in the range between 22 and 146 K and the column densities are in the range between 1.8 × 1012 cm-2 and 4.5 × 1017 cm-2. For species with at least three detected transitions and available collisional excitation rates we derived a best fit kinetic temperature and H2 volume density. Most species trace kinetic temperatures in the range between 100 and 150 K and H2 volume densities in the range between 105 and 106 cm-3. The species with temperatures and
Crowley, Mary Ellen; Hegarty, Avril; McAuliffe, Michael A P; O'Mahony, Graham E; Kiernan, Luke; Hayes, Kevin; Crean, Abina M
2017-05-01
The aim of this study was to highlight how variability in roller compacted ribbon quality can impact on NIR spectral measurement and to propose a simple method of data selection to remove erroneous spectra. The use of NIR spectroscopy for monitoring ribbon envelope density has been previously demonstrated, however to date there has been limited discussion as to how spectral data sets can contain erroneous outliers due to poor sample presentation to the NIR probes. In this study compacted ribbon of variable quality was produced from three separate blends of microcrystalline cellulose (MCC)/lactose/magnesium stearate at 8 Roll Force settings (2-16kN/cm). The three blends differed only in the storage conditions of MCC prior to blending and compaction. MCC sublots were stored at ambient (41% RH/20°C), low humidity (11% RH/20°C) and high humidity (75% RH/40°C) conditions prior to blending. Ribbon envelope density was measured and ribbon NIR spectral data was acquired at line using a multi-probe spectrometer (MultiEye™ NIR). Initial inspection of the at-line NIR spectral data set showed a large degree of variability which indicated that some form of data cleaning was required. The source of variability in spectral measurements was investigated by subjective visual examination and by statistical analysis. Spectral variability was noted due to the storage conditions of MCC prior to compaction, Roll Force settings and between individual ribbon samples sampled at a set Roll Force/Blend combination. Variability was also caused by ribbon presentation to probes, such as differences in the presentation of broken, curved and flat intact ribbons. Based on the subjective visual examination of data, a Visual Discard method was applied and was found to be particularly successful for blends containing MCC stored at ambient and low humidity. However the Visual Discard method of spectra cleaning is subjective and therefore a non-subjective method capable of screening for erroneous
NASA Astrophysics Data System (ADS)
Bernatskiy, A. V.; Ochkin, V. N.; Afonin, O. N.; Antipenkov, A. B.
2015-09-01
A novel method for measuring the number density of water molecules in low-temperature plasma is developed. The absolute intensities of rotational lines of the (0,0) band of the OH( A 2Σ- X 2П) transition are used. Lines with sufficiently large rotational quantum numbers referring to the so-called "hot" group of molecules produced by electron-impact dissociative excitation of water molecules are chosen for measurements. The excitation rate of a process with a known cross section is determined by measuring the parameters of plasma electrons by means of the probe method. The measured number densities of molecules are compared with those in the initial plasma-forming mixture. The time evolution of the particle densities in plasma is investigated. The problems of the sensitivity and applicability of the absolute spectral method are considered.
Electron density deformations provide new insights into the spectral shift of rhodopsins.
Hernández-Rodríguez, Erix Wiliam; Montero-Alejo, Ana Lilian; López, Rafael; Sánchez-García, Elsa; Montero-Cabrera, Luis Alberto; de la Vega, José Manuel García
2013-10-30
Spectral shifts of rhodopsin, which are related to variations of the electron distribution in 11-cis-retinal, are investigated here using the method of deformed atoms in molecules. We found that systems carrying the M207R and S186W mutations display large perturbations of the π-conjugated system with respect to wild-type rhodopsins. These changes agree with the predicted behavior of the bond length alternation (BLA) and the blue shifts of vertical excitation energies of these systems. The effect of the planarity of the central and Schiff-base regions of retinal chain on the electronic structure of the chromophore is also investigated. By establishing nonlinear polynomial relations between BLA, chain distortions, and vertical excitation energies, we are also able to provide a semiquantitative approach for the understanding of the mechanisms regulating spectral shifts in rhodopsin and its mutants.
Flores, Mathieu; Debellemanière, Guillaume; Bully, Alois; Meillat, Mathieu; Tumahai, Perle; Delbosc, Bernard; Saleh, Maher
2015-09-01
To investigate the relationship between outer retinal reflectivity on spectral-domain optical coherence tomography and cone density in the corresponding area. Prospective cross-sectional observational study. In this institutional-based study, 20 eyes of 10 patients presenting maculopathies with various degrees of impairment of the photoreceptor layer (central serous chorioretinopathy, chronic central serous chorioretinopathy, maculopathy associated with hydroxychloroquine, and healthy eyes) were studied. Selection criteria were intended to ensure good image quality. Inner segment ellipsoid band reflectivity, global retinal reflectivity, and relative inner segment ellipsoid reflectivity (defined as the ratio of inner segment ellipsoid band reflectivity on overall retinal reflectivity) were measured on a longitudinal reflectance profile extracted from the spectral-domain optical coherence tomography B-scan. The cone metrics were measured in the same region of interest, located in the perifoveal area, using an adaptive optics retinal camera. Inner segment ellipsoid and relative ellipsoid reflectivity were closely correlated with cone density (Pearson r: 0.72 and 0.70, respectively, P < .01). Outer retinal reflectivity on the transversal optical coherence tomography scan can be correlated to adaptive optics in terms of photoreceptor density. This quantitative approach using optical coherence tomography images could have important implications in the management of maculopathies. Copyright © 2015 Elsevier Inc. All rights reserved.
Chen, Xin; Cao, Jianshu; Silbey, Robert J
2013-06-14
The recent experimental discoveries about excitation energy transfer (EET) in light harvesting antenna (LHA) attract a lot of interest. As an open non-equilibrium quantum system, the EET demands more rigorous theoretical framework to understand the interaction between system and environment and therein the evolution of reduced density matrix. A phonon is often used to model the fluctuating environment and convolutes the reduced quantum system temporarily. In this paper, we propose a novel way to construct complex-valued Gaussian processes to describe thermal quantum phonon bath exactly by converting the convolution of influence functional into the time correlation of complex Gaussian random field. Based on the construction, we propose a rigorous and efficient computational method, the covariance decomposition and conditional propagation scheme, to simulate the temporarily entangled reduced system. The new method allows us to study the non-Markovian effect without perturbation under the influence of different spectral densities of the linear system-phonon coupling coefficients. Its application in the study of EET in the Fenna-Matthews-Olson model Hamiltonian under four different spectral densities is discussed. Since the scaling of our algorithm is linear due to its Monte Carlo nature, the future application of the method for large LHA systems is attractive. In addition, this method can be used to study the effect of correlated initial condition on the reduced dynamics in the future.
Vorticity alignment and spectral statistics in a variable-density turbulent flow
NASA Astrophysics Data System (ADS)
Gat, Ilana; Matheou, Georgios; Chung, Daniel; Dimotakis, Paul
2016-11-01
Turbulent flows with high density gradients subject to an externally imposed acceleration field, such as gravity, occur in many phenomena, ranging from geophysics to astrophysics. This study investigates turbulence in fluids over a range of density ratios, from small (R=1.005) to large (R=10). The investigation relies on direct numerical simulation using the incompressible variable-density Navier-Stokes equations, in a triply periodic domain. The flow is initialized with density gradients perpendicular to the acceleration field. This configuration induces baroclinic torques with shear and buoyancy contributing to the evolution of turbulence and turbulent mixing. Of interest in fluid modeling is vorticity alignment, which is presented for the broad density ratio range studied. Prominent variable-density contributions to the vorticity field such as baroclinic torques are discussed. Kinetic-energy spectra are compared to specific kinetic energy spectra to illustrate aspects of variable-density effects. This material is based upon work supported by the DOE, AFOSR, NSF GRFP, and Caltech.
NASA Astrophysics Data System (ADS)
Qie, G.; Wang, G.; Wang, M.
2016-12-01
Mixed pixels and shadows due to buildings in urban areas impede accurate estimation and mapping of city vegetation carbon density. In most of previous studies, these factors are often ignored, which thus result in underestimation of city vegetation carbon density. In this study we presented an integrated methodology to improve the accuracy of mapping city vegetation carbon density. Firstly, we applied a linear shadow remove analysis (LSRA) on remotely sensed Landsat 8 images to reduce the shadow effects on carbon estimation. Secondly, we integrated a linear spectral unmixing analysis (LSUA) with a linear stepwise regression (LSR), a logistic model-based stepwise regression (LMSR) and k-Nearest Neighbors (kNN), and utilized and compared the integrated models on shadow-removed images to map vegetation carbon density. This methodology was examined in Shenzhen City of Southeast China. A data set from a total of 175 sample plots measured in 2013 and 2014 was used to train the models. The independent variables statistically significantly contributing to improving the fit of the models to the data and reducing the sum of squared errors were selected from a total of 608 variables derived from different image band combinations and transformations. The vegetation fraction from LSUA was then added into the models as an important independent variable. The estimates obtained were evaluated using a cross-validation method. Our results showed that higher accuracies were obtained from the integrated models compared with the ones using traditional methods which ignore the effects of mixed pixels and shadows. This study indicates that the integrated method has great potential on improving the accuracy of urban vegetation carbon density estimation. Key words: Urban vegetation carbon, shadow, spectral unmixing, spatial modeling, Landsat 8 images
Evaluation of periodgrams as a tool to study spectral densities of heterodyne signals
NASA Astrophysics Data System (ADS)
Alvarado, Jose Manuel; Stern, Catalina
2002-11-01
The use of periodgrams as a tool to study heterodyne signals is evaluated. The heterodyne signal carries information about density fluctuations from light scattered by a turbulent jet. The goal of the analysis is to be able to separate the information about density fluctuations of acoustics origin (peaked at about 2 MHz) from fluctuations in the density due to entropy irregularities (wide peak centered at the origin). There are frequency regions where both overlap. Various methods are compared: Bartlett, Welch, Yule-Walker, Burg and others. (To be presented in Spanish.)
NASA Astrophysics Data System (ADS)
Watabe, Ken-ichi; Yanagimachi, Shinya; Ikegami, Takeshi; Iida, Hitoshi; Shimada, Yozo
2012-01-01
We have realized a phase noise standard of a signal with a -100 dBc/Hz flat phase noise at 10 MHz for Fourier frequencies of 1 Hz to 100 kHz, which ensures traceability to the International System of Units (SI). The flat phase noise signal is produced using a carrier combined with white noise. To ensure traceability, both the flat phase noise signal power and the power spectral density of white noise are determined with a calibrated power meter and the noise standard, respectively. The flatness of the phase noise standard is within ±0.7 dB.
NASA Technical Reports Server (NTRS)
Perry, Boyd, III; Pototzky, Anthony S.; Woods, Jessica A.
1989-01-01
The results of a NASA investigation of a claimed Overlap between two gust response analysis methods: the Statistical Discrete Gust (SDG) Method and the Power Spectral Density (PSD) Method are presented. The claim is that the ratio of an SDG response to the corresponding PSD response is 10.4. Analytical results presented for several different airplanes at several different flight conditions indicate that such an Overlap does appear to exist. However, the claim was not met precisely: a scatter of up to about 10 percent about the 10.4 factor can be expected.
NASA Astrophysics Data System (ADS)
Hirose, Misa; Akaho, Rina; Maita, Chikashi; Sugawara, Mai; Tsumura, Norimichi
2016-06-01
In this paper, the spectral sensitivities of a mosaic five-band camera were optimized using a numerical skin phantom to perform the separation of chromophore densities, shading and surface reflection. To simulate the numerical skin phantom, the spectral reflectance of skin was first calculated by Monte Carlo simulation of photon migration for different concentrations of melanin, blood and oxygen saturation levels. The melanin and hemoglobin concentration distributions used in the numerical skin phantom were obtained from actual skin images by independent component analysis. The calculated components were assigned as concentration distributions. The spectral sensitivities of the camera were then optimized using a nonlinear technique to estimate the spectral reflectance for skin separation. In this optimization, the spectral sensitivities were assumed to be normally distributed, and the sensor arrangement was identical to that of a conventional mosaic five-band camera. Our findings demonstrated that spectral estimation could be significantly improved by optimizing the spectral sensitivities.
Power spectral density estimation by spline smoothing in the frequency domain.
NASA Technical Reports Server (NTRS)
De Figueiredo, R. J. P.; Thompson, J. R.
1972-01-01
An approach, based on a global averaging procedure, is presented for estimating the power spectrum of a second order stationary zero-mean ergodic stochastic process from a finite length record. This estimate is derived by smoothing, with a cubic smoothing spline, the naive estimate of the spectrum obtained by applying Fast Fourier Transform techniques to the raw data. By means of digital computer simulated results, a comparison is made between the features of the present approach and those of more classical techniques of spectral estimation.-
Power spectral density estimation by spline smoothing in the frequency domain
NASA Technical Reports Server (NTRS)
Defigueiredo, R. J. P.; Thompson, J. R.
1972-01-01
An approach, based on a global averaging procedure, is presented for estimating the power spectrum of a second order stationary zero-mean ergodic stochastic process from a finite length record. This estimate is derived by smoothing, with a cubic smoothing spline, the naive estimate of the spectrum obtained by applying FFT techniques to the raw data. By means of digital computer simulated results, a comparison is made between the features of the present approach and those of more classical techniques of spectral estimation.
NASA Astrophysics Data System (ADS)
Schäfer, J.; Sing, M.; Claessen, R.; Rotenberg, Eli; Zhou, X. J.; Thorne, R. E.; Kevan, S. D.
2003-08-01
Low-temperature electronic properties of the charge-density-wave system NbSe3 are reported from angle-resolved photoemission at 15K. The effect of two instabilities q1 and q2 on the k-resolved spectral function is observed for the first time. With a pseudogap background, the gap spectra exhibit maxima at Δ*1˜110 meV and Δ*2˜45 meV. Imperfectly nested sections of the Fermi surface lack a Fermi-Dirac edge, and show the signature of a dispersion that is modified by self-energy effects. The energy scale is of the order of the effective gap 2Δ*2. The effect disappears above T2, suggesting a correlation with the charge-density-wave state.
Schaffer, Thorsten; Hensel, Bernhard; Weigand, Christian; Schüttler, Jürgen; Jeleazcov, Christian
2014-10-01
Heart rate variability (HRV) analysis is increasingly used in anaesthesia and intensive care monitoring of spontaneous breathing and mechanical ventilated patients. In the frequency domain, different estimation methods of the power spectral density (PSD) of RR-intervals lead to different results. Therefore, we investigated the PSD estimates of fast Fourier transform (FFT), autoregressive modeling (AR) and Lomb-Scargle periodogram (LSP) for 25 young healthy subjects subjected to metronomic breathing. The optimum method for determination of HRV spectral parameters under paced respiration was identified by evaluating the relative error (RE) and the root mean square relative error (RMSRE) for each breathing frequency (BF) and spectral estimation method. Additionally, the sympathovagal balance was investigated by calculating the low frequency/high frequency (LF/HF) ratio. Above 7 breaths per minute, all methods showed a significant increase in LF/HF ratio with increasing BF. On average, the RMSRE of FFT was lower than for LSP and AR. Therefore, under paced respiration conditions, estimating RR-interval PSD using FFT is recommend.
A spectral scheme for Kohn-Sham density functional theory of clusters
NASA Astrophysics Data System (ADS)
Banerjee, Amartya S.; Elliott, Ryan S.; James, Richard D.
2015-04-01
Starting from the observation that one of the most successful methods for solving the Kohn-Sham equations for periodic systems - the plane-wave method - is a spectral method based on eigenfunction expansion, we formulate a spectral method designed towards solving the Kohn-Sham equations for clusters. This allows for efficient calculation of the electronic structure of clusters (and molecules) with high accuracy and systematic convergence properties without the need for any artificial periodicity. The basis functions in this method form a complete orthonormal set and are expressible in terms of spherical harmonics and spherical Bessel functions. Computation of the occupied eigenstates of the discretized Kohn-Sham Hamiltonian is carried out using a combination of preconditioned block eigensolvers and Chebyshev polynomial filter accelerated subspace iterations. Several algorithmic and computational aspects of the method, including computation of the electrostatics terms and parallelization are discussed. We have implemented these methods and algorithms into an efficient and reliable package called ClusterES (Cluster Electronic Structure). A variety of benchmark calculations employing local and non-local pseudopotentials are carried out using our package and the results are compared to the literature. Convergence properties of the basis set are discussed through numerical examples. Computations involving large systems that contain thousands of electrons are demonstrated to highlight the efficacy of our methodology. The use of our method to study clusters with arbitrary point group symmetries is briefly discussed.
A spectral scheme for Kohn–Sham density functional theory of clusters
Banerjee, Amartya S. Elliott, Ryan S. James, Richard D.
2015-04-15
Starting from the observation that one of the most successful methods for solving the Kohn–Sham equations for periodic systems – the plane-wave method – is a spectral method based on eigenfunction expansion, we formulate a spectral method designed towards solving the Kohn–Sham equations for clusters. This allows for efficient calculation of the electronic structure of clusters (and molecules) with high accuracy and systematic convergence properties without the need for any artificial periodicity. The basis functions in this method form a complete orthonormal set and are expressible in terms of spherical harmonics and spherical Bessel functions. Computation of the occupied eigenstates of the discretized Kohn–Sham Hamiltonian is carried out using a combination of preconditioned block eigensolvers and Chebyshev polynomial filter accelerated subspace iterations. Several algorithmic and computational aspects of the method, including computation of the electrostatics terms and parallelization are discussed. We have implemented these methods and algorithms into an efficient and reliable package called ClusterES (Cluster Electronic Structure). A variety of benchmark calculations employing local and non-local pseudopotentials are carried out using our package and the results are compared to the literature. Convergence properties of the basis set are discussed through numerical examples. Computations involving large systems that contain thousands of electrons are demonstrated to highlight the efficacy of our methodology. The use of our method to study clusters with arbitrary point group symmetries is briefly discussed.
Spectral properties of reduced fermionic density operators and parity superselection rule
NASA Astrophysics Data System (ADS)
Amosov, Grigori G.; Filippov, Sergey N.
2017-01-01
We consider pure fermionic states with a varying number of quasiparticles and analyze two types of reduced density operators: one is obtained via tracing out modes, the other is obtained via tracing out particles. We demonstrate that spectra of mode-reduced states are not identical in general and fully characterize pure states with equispectral mode-reduced states. Such states are related via local unitary operations with states satisfying the parity superselection rule. Thus, valid purifications for fermionic density operators are found. To get particle-reduced operators for a general system, we introduce the operation \\varPhi (\\varrho ) = sum _i a_i \\varrho a_i^{dag }. We conjecture that spectra of \\varPhi ^p(\\varrho ) and conventional p-particle reduced density matrix \\varrho _p coincide. Non-trivial generalized Pauli constraints are derived for states satisfying the parity superselection rule.
NASA Astrophysics Data System (ADS)
Daswani, Ujla; Sharma, Pratibha; Kumar, Ashok
2015-01-01
Benzothiazole moiety is found to play an important role in medicinal chemistry with a wide range of pharmacological activities. Herein, a simple, benzothiazole derivative viz., 2-chlorobenzothiazole (2CBT) has been analyzed. The spectroscopic properties of the target compound were examined by FT-IR (4400-450 cm-1), FT-Raman (4000-50 cm-1), and NMR techniques. The 1H and 13C NMR spectra were recorded in DMSO. Theoretical calculations were performed by ab initio Hartree Fock and Density Functional Theory (DFT)/B3LYP method using varied basis sets combination. The scaled B3LYP/6-311++G(d,p) results precisely complements with the experimental findings. Electronic absorption spectra along with energy and oscillator strength were obtained by TDDFT method. Atomic charges have also been reported. Total density isosurface and total density mapped with electrostatic potential surface (MESP) has been shown.
Spectral density analysis of the optical properties of Ni-Al2O3 nano-composite films
NASA Astrophysics Data System (ADS)
Niklasson, Gunnar A.; Boström, Tobias K.; Tuncer, Enis
2011-09-01
Thin films consisting of transition metal nanoparticles in an insulating oxide exhibit a high solar absorptance together with a low thermal emittance and are used as coatings on solar collector panels. In order to optimise the nanocomposites for this application a more detailed understanding of their optical properties is needed. Here we use a highly efficient recently developed numerical method to extract the spectral density function of nickel-aluminum oxide (Ni-Al2O3) composites from experimental data on the dielectric permittivity in the visible and near-infrared wavelength ranges. Thin layers of Ni-Al2O3 were produced by a sol-gel technique. Reflectance and transmittance spectra were measured by spectrophotometry in the wavelength range 300 to 2500 nm for films with thicknesses in the range 50 to 100 nm. Transmission electron microscopy showed crystalline Ni particles with sizes in the 3 to 10 nm range. The spectral density function shows a multi-peak structure with three or four peaks clearly visible. The peak positions are influenced by particle shape, local volume fraction distributions and particle-particle interactions giving rise to structural resonances in the response of the composite to an electromagnetic field.
Palaniappan, Rajkumar; Sundaraj, Kenneth; Sundaraj, Sebastian; Huliraj, N; Revadi, S S
2016-07-01
Monitoring respiration is important in several medical applications. One such application is respiratory rate monitoring in patients with sleep apnoea. The respiratory rate in patients with sleep apnoea disorder is irregular compared with the controls. Respiratory phase detection is required for a proper monitoring of respiration in patients with sleep apnoea. To develop a model to detect the respiratory phases present in the pulmonary acoustic signals and to evaluate the performance of the model in detecting the respiratory phases. Normalised averaged power spectral density for each frame and change in normalised averaged power spectral density between the adjacent frames were fuzzified and fuzzy rules were formulated. The fuzzy inference system (FIS) was developed with both Mamdani and Sugeno methods. To evaluate the performance of both Mamdani and Sugeno methods, correlation coefficient and root mean square error (RMSE) were calculated. In the correlation coefficient analysis in evaluating the fuzzy model using Mamdani and Sugeno method, the strength of the correlation was found to be r = 0.9892 and r = 0.9964, respectively. The RMSE for Mamdani and Sugeno methods are RMSE = 0.0853 and RMSE = 0.0817, respectively. The correlation coefficient and the RMSE of the proposed fuzzy models in detecting the respiratory phases reveals that Sugeno method performs better compared with the Mamdani method. © 2014 John Wiley & Sons Ltd.
A power law power spectral density model of total electron content structure in the polar region
NASA Astrophysics Data System (ADS)
Nickisch, L. J.
2004-02-01
Measurements by the early warning radar at Thule, Greenland, together with GPS measurements from the Air Force Research Laboratory (AFRL) Ionospheric Measurement System (IMS) receiver, have been analyzed to develop a model for the structure of the total electron content (TEC) of the polar ionosphere. For the model the TEC measurements are related to the Wide Band Model (WBMOD), a climatological model of small-scale ionization structure. The TEC data agree very well with the predictions of a simple extension of WBMOD to larger scales, where a slightly steeper spectral slope (p ≈ 3) is used for the TEC structure (compared to p = 2.7 for the small-scale structure of WBMOD's polar region model). The benefit of this approach is that the TEC model subsumes the climatology of WBMOD, which is built upon two solar cycles of ionospheric measurements.
Patsourakos, S.; Klimchuk, J. A.; Young, P. R. E-mail: james.a.klimchuk@nasa.gov
2014-02-01
Recent solar spectroscopic observations have shown that coronal spectral lines can exhibit asymmetric profiles, with enhanced emissions at their blue wings. These asymmetries correspond to rapidly upflowing plasmas at speeds exceeding ≈50 km s{sup –1}. Here, we perform a study of the density of the rapidly upflowing material and compare it with that of the line core that corresponds to the bulk of the plasma. For this task, we use spectroscopic observations of several active regions taken by the Extreme Ultraviolet Imaging Spectrometer of the Hinode mission. The density sensitive ratio of the Fe XIV lines at 264.78 and 274.20 Å is used to determine wing and core densities. We compute the ratio of the blue wing density to the core density and find that most values are of order unity. This is consistent with the predictions for coronal nanoflares if most of the observed coronal mass is supplied by chromospheric evaporation driven by the nanoflares. However, much larger blue wing-to-core density ratios are predicted if most of the coronal mass is supplied by heated material ejected with type II spicules. Our measurements do not rule out a spicule origin for the blue wing emission, but they argue against spicules being a primary source of the hot plasma in the corona. We note that only about 40% of the pixels where line blends could be safely ignored have blue wing asymmetries in both Fe XIV lines. Anticipated sub-arcsecond spatial resolution spectroscopic observations in future missions could shed more light on the origin of blue, red, and mixed asymmetries.
Yadav, Vivek Kumar; Chandra, Amalendu
2013-06-14
A first principles study of the dynamics of supercritical methanol is carried out by means of ab initio molecular dynamics simulations. In particular, the fluctuation dynamics of hydroxyl stretch frequencies, hydrogen bonds, dangling hydroxyl groups, and orientation of methanol molecules are investigated for three different densities at 523 K. Apart from the dynamical properties, various equilibrium properties of supercritical methanol such as the local density distributions and structural correlations, hydrogen bonding aspects, frequency-structure correlations, and dipole distributions of methanol molecules are also investigated. In addition to the density dependence of various equilibrium and dynamical properties, their dependencies on dispersion interactions are also studied by carrying out additional simulations using a dispersion corrected density functional for all the systems. It is found that the hydrogen bonding between methanol molecules decreases significantly as we move to the supercritical state from the ambient one. The inclusion of dispersion interactions is found to increase the number of hydrogen bonds to some extent. Calculations of the frequency-structure correlation coefficient reveal that a statistical correlation between the hydroxyl stretch frequency and the nearest hydrogen-oxygen distance continues to exist even at supercritical states of methanol, although it is weakened with increase of temperature and decrease of density. In the supercritical state, the frequency time correlation function is found to decay with two time scales: One around or less than 100 fs and the other in the region of 250-700 fs. It is found that, for supercritical methanol, the times scales of vibrational spectral diffusion are determined by an interplay between the dynamics of hydrogen bonds, dangling OD groups, and inertial rotation of methanol molecules and the roles of these various components are found to vary with density of the supercritical solvent. Effects
NASA Technical Reports Server (NTRS)
Patsourakos, S.; Klimchuk, J. A.; Young, P. R.
2014-01-01
Recent solar spectroscopic observations have shown that coronal spectral lines can exhibit asymmetric profiles, with enhanced emissions at their blue wings. These asymmetries correspond to rapidly upflowing plasmas at speeds exceeding approximately equal to 50 km per sec. Here, we perform a study of the density of the rapidly upflowing material and compare it with that of the line core that corresponds to the bulk of the plasma. For this task, we use spectroscopic observations of several active regions taken by the Extreme Ultraviolet Imaging Spectrometer of the Hinode mission. The density sensitive ratio of the Fe(sub XIV) lines at 264.78 and 274.20 Angstroms is used to determine wing and core densities.We compute the ratio of the blue wing density to the core density and find that most values are of order unity. This is consistent with the predictions for coronal nanoflares if most of the observed coronal mass is supplied by chromospheric evaporation driven by the nanoflares. However, much larger blue wing-to-core density ratios are predicted if most of the coronal mass is supplied by heated material ejected with type II spicules. Our measurements do not rule out a spicule origin for the blue wing emission, but they argue against spicules being a primary source of the hot plasma in the corona. We note that only about 40% of the pixels where line blends could be safely ignored have blue wing asymmetries in both Fe(sub XIV) lines. Anticipated sub-arcsecond spatial resolution spectroscopic observations in future missions could shed more light on the origin of blue, red, and mixed asymmetries.
Measurements of the low wavenumber wall pressure spectral density during transition on a flat plate
NASA Astrophysics Data System (ADS)
Gedney, C. J.; Leehey, P.
1984-04-01
Experimental measurements of the low-Mach number wall pressure spectra density in the transition region are currently carried out in our laboratory. The six element (B&K Model No. 4144) microphone array used by Farabee and Geib was used as the wavenumber filtering apparatus and flush mounted on an open test section identical to that used by Jameson. A technique of conditional sampling on signals was used to determine the characteristics of the transitional flow. The frequency spectrum of the microphone array output was computed for uniform shading, Chebyshev shading and binomial shading. A detailed update on our progress is enclosed. The preliminary results indicate that there is no significant measurable difference in the low wavenumber wall pressure spectrum density for a transitional boundary layer as compared to a fully turbulent boundary layer.
Spectral Emission of fast non-Maxwellian Atoms at metallic Surfaces in low density Plasmas
NASA Astrophysics Data System (ADS)
Dickheuer, Sven; Marchuk, Oleksandr; Brandt, Christian; Pospieszczyk, Albrecht
2016-09-01
We have observed Doppler shifted components of the Balmer-lines emitted by fast non-Maxwellian atoms using different targets in a linear magnetized plasma in the PSI-2 device. In a pure hydrogen plasma the Doppler shifted components of the Balmer emission lines cannot be detected above the signal-to-noise-ratio. However, in a mixed H/Ar plasma with composition of 1:1 the Doppler red- and blue-shifted components can be clearly observed. The Balmer-lines are analyzed by optical emission spectroscopy at observations angles of 35° and 90°. For target materials we use Ag, Pd, Fe and C. An acceleration potential can be applied to the target to change the kinetic energy of the incoming ions between 40 and 200 eV enabling the observation of the Doppler shifted components. The emission mechanism is discussed in details and is probably due to excitation transfer from metastable argon atoms to the fast hydrogen atoms. The Doppler shifted signal can be used to determine the properties of the surfaces, e.g., the energy and angular distribution of reflected atoms. Also the spectral reflectance of the target surface can be obtained and tested against the reference data and measurements with light calibration sources.
Spectral Signal Density of Carotid Plaque Using Dual-Energy Computed Tomography.
Reynoso, Exequiel; Rodriguez-Granillo, Gastón A; Capunay, Carlos; Deviggiano, Alejandro; Meli, Francisco; Carrascosa, Patricia
2017-09-01
Plaque characterization using virtual monochromatic imaging derived from dual-energy computed tomography (CT) angiography requires the determination of normal signal density values of each plaque component. We sought to explore the signal density values of carotid plaque components using dual-energy compared to conventional single-energy CT angiography (CTA), and to establish the energy level with the largest differences between plaque components. The present prospective study involved consecutive patients referred for carotid artery evaluation by CTA. Two scans (single-energy and dual-energy CTA) were performed in all patients, and a single radiologist analyzed the data. Single-source dual-energy CTA allowed the generation of virtual monochromatic images from 40 to 140 keV. A total of 35 internal carotid artery lesions were examined in 20 symptomatic patients. The mean age was 72.3 ± 6.7 years, and 9 (45%) patients were male. Internal carotid artery geometrical variables including lumen area (P = .96), vessel area (P = .97), and percent area stenosis (P = .99) did not differ between groups (single-energy CTA, and dual-energy CTA at 40, 70, 100, and 140 keV). Differences between signal densities of different tissues were largest at 40 keV (calcium/lumen, P < .0001; fat/noncalcified, P < .0001). In the present pilot investigation, virtual monochromatic imaging at low-energy levels derived from dual-energy CTA allowed the largest differences in attenuation levels between tissues, without affecting vessel or plaque geometry. Copyright © 2017 by the American Society of Neuroimaging.
Akhmediev, N; Soto-Crespo, J M; Devine, N
2016-08-01
Turbulence in integrable systems exhibits a noticeable scientific advantage: it can be expressed in terms of the nonlinear modes of these systems. Whether the majority of the excitations in the system are breathers or solitons defines the properties of the turbulent state. In the two extreme cases we can call such states "breather turbulence" or "soliton turbulence." The number of rogue waves, the probability density functions of the chaotic wave fields, and their physical spectra are all specific for each of these two situations. Understanding these extreme cases also helps in studies of mixed turbulent states when the wave field contains both solitons and breathers, thus revealing intermediate characteristics.
NASA Astrophysics Data System (ADS)
Akhmediev, N.; Soto-Crespo, J. M.; Devine, N.
2016-08-01
Turbulence in integrable systems exhibits a noticeable scientific advantage: it can be expressed in terms of the nonlinear modes of these systems. Whether the majority of the excitations in the system are breathers or solitons defines the properties of the turbulent state. In the two extreme cases we can call such states "breather turbulence" or "soliton turbulence." The number of rogue waves, the probability density functions of the chaotic wave fields, and their physical spectra are all specific for each of these two situations. Understanding these extreme cases also helps in studies of mixed turbulent states when the wave field contains both solitons and breathers, thus revealing intermediate characteristics.
NASA Astrophysics Data System (ADS)
Corianò, Claudio; Costantini, Antonio; Rose, Luigi Delle; Serino, Mirko
2014-06-01
We discuss the signature of the anomalous breaking of the superconformal symmetry in = 1 super Yang Mills theory, mediated by the Ferrara-Zumino hypercurrent () with two vector () supercurrents () and its manifestation in the anomaly action, in the form of anomaly poles. This allows to investigate in a unified way both conformal and chiral anomalies. The analysis is performed in parallel to the Standard Model, for comparison. We investigate, in particular, massive deformations of the = 1 theory and the spectral densities of the anomaly form factors which are extracted from the components of this correlator. In this extended framework it is shown that all the anomaly form factors are characterized by spectral densities which flow with the mass deformation. In particular, the continuum contributions from the two-particle cuts of the intermediate states turn into poles in the zero mass limit, with a single sum rule satisfied by each component. Non anomalous form factors, instead, in the same anomalous correlators, are characterized by non-integrable spectral densities. These tend to uniform distributions as one moves towards the conformal point, with a clear dual behaviour. As in a previous analysis of the dilaton pole of the Standard Model, also in this case the poles can be interpreted as signaling the exchange of a composite dilaton/axion/dilatino (ADD) multiplet in the effective Lagrangian. The pole-like behaviour of the anomaly form factors is shown to be a global feature of the correlators, present at all energy scales, due to the sum rules. A similar behaviour is shown to be present in the Konishi current, which identifies additional composite states. We conclude that global anomalous currents characterized by a single flow in the perturbative picture always predict the existence of composite interpolating fields. In case of gauging of these currents, as in superconformal theories coupled to gravity, we show that the cancellation of the corresponding anomalies
Ma, Junshui; Svetnik, Vladimir; Snyder, Ellen; Lines, Christopher; Roth, Thomas; Herring, W. Joseph
2014-01-01
Study Objectives: Suvorexant, an orexin receptor antagonist, improves sleep in healthy subjects (HS) and patients with insomnia. We compared the electroencephalographic (EEG) power spectral density (PSD) profile of suvorexant with placebo using data from a phase 2 trial in patients with insomnia. We also compared suvorexant's PSD profile with the profiles of other insomnia treatments using data from 3 HS studies Design: Phase 2 trial—randomized, double-blind, two-period (4 w per period) crossover. HS studies—randomized, double-blind, crossover. Setting: Sleep laboratories. Participants: Insomnia patients (n = 229) or HS (n = 124). Interventions: Phase 2 trial—suvorexant 10 mg, 20 mg, 40 mg, 80 mg, placebo; HS study 1—suvorexant 10 mg, 50 mg, placebo; HS study 2— gaboxadol 15 mg, zolpidem 10 mg, placebo; HS study 3—trazodone 150 mg, placebo. Measurements and Results: The PSD of the EEG signal at 1–32 Hz of each PSG recording during nonrapid eye movement (NREM) and rapid eye movement (REM) sleep were calculated. The day 1 and day 28 PSD profiles of suvorexant at all four doses during NREM and REM sleep in patients with insomnia were generally flat and close to 1.0 (placebo) at all frequencies. The day 1 PSD profile of suvorexant in HS was similar to that in insomnia patients. In contrast, the other three drugs had distinct PSD profiles in HS that differed from each other. Conclusions: Suvorexant at clinically effective doses had limited effects on power spectral density compared with placebo in healthy subjects and in patients with insomnia, in contrast to the three comparison insomnia treatments. These findings suggest the possibility that antagonism of the orexin pathway might lead to improvements in sleep without major changes in the patient's neurophysiology as assessed by electroencephalographic. Citation: Ma J, Svetnik V, Snyder E, Lines C, Roth T, Herring WJ. Electroencephalographic power spectral density profile of the orexin receptor antagonist
NASA Astrophysics Data System (ADS)
Michaelsen, Kelly E.; Krishnaswamy, Venkataramanan; Shi, Linxi; Vedantham, Srinivasan; Karellas, Andrew; Pogue, Brian W.; Paulsen, Keith D.; Poplack, Steven P.
2016-09-01
Optically derived tissue properties across a range of breast densities and the effects of breast compression on estimates of hemoglobin, oxygen metabolism, and water and lipid concentrations were obtained from a coregistered imaging system that integrates near-infrared spectral tomography (NIRST) with digital breast tomosynthesis (DBT). Image data were analyzed from 27 women who underwent four IRB approved NIRST/DBT exams that included fully and mildly compressed breast acquisitions in two projections-craniocaudal (CC) and mediolateral-oblique (MLO)-and generated four data sets per patient (full and moderate compression in CC and MLO views). Breast density was correlated with HbT (r=0.64, p=0.001), water (r=0.62, p=0.003), and lipid concentrations (r=-0.74, p<0.001), but not oxygen saturation. CC and MLO views were correlated for individual subjects and demonstrated no statistically significant differences in grouped analysis. Comparison of compressed and uncompressed imaging demonstrated a significant decrease in oxygen saturation under compression (58% versus 50%, p=0.04). Mammographic breast density categorization was correlated with measured optically derived properties.
Chandrasekaran, Suryanarayanan; Aghtar, Mortaza; Valleau, Stéphanie; Aspuru-Guzik, Alán; Kleinekathöfer, Ulrich
2015-08-06
Studies on light-harvesting (LH) systems have attracted much attention after the finding of long-lived quantum coherences in the exciton dynamics of the Fenna-Matthews-Olson (FMO) complex. In this complex, excitation energy transfer occurs between the bacteriochlorophyll a (BChl a) pigments. Two quantum mechanics/molecular mechanics (QM/MM) studies, each with a different force-field and quantum chemistry approach, reported different excitation energy distributions for the FMO complex. To understand the reasons for these differences in the predicted excitation energies, we have carried out a comparative study between the simulations using the CHARMM and AMBER force field and the Zerner intermediate neglect of differential orbital (ZINDO)/S and time-dependent density functional theory (TDDFT) quantum chemistry methods. The calculations using the CHARMM force field together with ZINDO/S or TDDFT always show a wider spread in the energy distribution compared to those using the AMBER force field. High- or low-energy tails in these energy distributions result in larger values for the spectral density at low frequencies. A detailed study on individual BChl a molecules in solution shows that without the environment, the density of states is the same for both force field sets. Including the environmental point charges, however, the excitation energy distribution gets broader and, depending on the applied methods, also asymmetric. The excitation energy distribution predicted using TDDFT together with the AMBER force field shows a symmetric, Gaussian-like distribution.
Wang, RuLin; Zheng, Xiao; Kwok, YanHo; Xie, Hang; Chen, GuanHua; Yam, ChiYung
2015-04-14
Understanding electronic dynamics on material surfaces is fundamentally important for applications including nanoelectronics, inhomogeneous catalysis, and photovoltaics. Practical approaches based on time-dependent density functional theory for open systems have been developed to characterize the dissipative dynamics of electrons in bulk materials. The accuracy and reliability of such approaches depend critically on how the electronic structure and memory effects of surrounding material environment are accounted for. In this work, we develop a novel squared-Lorentzian decomposition scheme, which preserves the positive semi-definiteness of the environment spectral matrix. The resulting electronic dynamics is guaranteed to be both accurate and convergent even in the long-time limit. The long-time stability of electronic dynamics simulation is thus greatly improved within the current decomposition scheme. The validity and usefulness of our new approach are exemplified via two prototypical model systems: quasi-one-dimensional atomic chains and two-dimensional bilayer graphene.
Wang, RuLin; Zheng, Xiao; Kwok, YanHo; Xie, Hang; Chen, GuanHua; Yam, ChiYung
2015-04-14
Understanding electronic dynamics on material surfaces is fundamentally important for applications including nanoelectronics, inhomogeneous catalysis, and photovoltaics. Practical approaches based on time-dependent density functional theory for open systems have been developed to characterize the dissipative dynamics of electrons in bulk materials. The accuracy and reliability of such approaches depend critically on how the electronic structure and memory effects of surrounding material environment are accounted for. In this work, we develop a novel squared-Lorentzian decomposition scheme, which preserves the positive semi-definiteness of the environment spectral matrix. The resulting electronic dynamics is guaranteed to be both accurate and convergent even in the long-time limit. The long-time stability of electronic dynamics simulation is thus greatly improved within the current decomposition scheme. The validity and usefulness of our new approach are exemplified via two prototypical model systems: quasi-one-dimensional atomic chains and two-dimensional bilayer graphene.
Power spectral density analysis of wind-shear turbulence for related flight simulations. M.S. Thesis
NASA Technical Reports Server (NTRS)
Laituri, Tony R.
1988-01-01
Meteorological phenomena known as microbursts can produce abrupt changes in wind direction and/or speed over a very short distance in the atmosphere. These changes in flow characteristics have been labelled wind shear. Because of its adverse effects on aerodynamic lift, wind shear poses its most immediate threat to flight operations at low altitudes. The number of recent commercial aircraft accidents attributed to wind shear has necessitated a better understanding of how energy is transferred to an aircraft from wind-shear turbulence. Isotropic turbulence here serves as the basis of comparison for the anisotropic turbulence which exists in the low-altitude wind shear. The related question of how isotropic turbulence scales in a wind shear is addressed from the perspective of power spectral density (psd). The role of the psd in related Monte Carlo simulations is also considered.
NASA Technical Reports Server (NTRS)
Harrison, D. A., III; Chladek, J. T.
1983-01-01
A real-time signal processor was developed for the NASA/JSC L-and C-band airborne radar scatterometer sensor systems. The purpose of the effort was to reduce ground data processing costs. Conversion of two quadrature channels of data (like and cross polarized) was made to obtain Power Spectral Density (PSD) values. A chirp-z transform (CZT) approach was used to filter the Doppler return signal and improved high frequency and angular resolution was realized. The processors have been tested with record signals and excellent results were obtained. CZT filtering can be readily applied to scatterometers operating at other wavelengths by altering the sample frequency. The design of the hardware and software and the results of the performance tests are described in detail.
NASA Astrophysics Data System (ADS)
Wang, RuLin; Zheng, Xiao; Kwok, YanHo; Xie, Hang; Chen, GuanHua; Yam, ChiYung
2015-04-01
Understanding electronic dynamics on material surfaces is fundamentally important for applications including nanoelectronics, inhomogeneous catalysis, and photovoltaics. Practical approaches based on time-dependent density functional theory for open systems have been developed to characterize the dissipative dynamics of electrons in bulk materials. The accuracy and reliability of such approaches depend critically on how the electronic structure and memory effects of surrounding material environment are accounted for. In this work, we develop a novel squared-Lorentzian decomposition scheme, which preserves the positive semi-definiteness of the environment spectral matrix. The resulting electronic dynamics is guaranteed to be both accurate and convergent even in the long-time limit. The long-time stability of electronic dynamics simulation is thus greatly improved within the current decomposition scheme. The validity and usefulness of our new approach are exemplified via two prototypical model systems: quasi-one-dimensional atomic chains and two-dimensional bilayer graphene.
NASA Technical Reports Server (NTRS)
Murchie, S. L.; Fraeman, A. A.; Arvidson, R. E.; Rivkin, A. S.; Morris, R. V.
2013-01-01
Compositional interpretations of new spectral measurements of Phobos and Deimos from Mars Express/OMEGA and MRO/CRISM and density measurements from encounters by multiple spacecraft support refined estimates of the moons' porosity and internal structure. Phobos' estimated macroporosity of 12-20% is consistent with a fractured but coherent interior; Deimos' estimated macroporosity of 23-44% is more consistent with a loosely consolidated interior. These internal differences are reflected in differences in surface morphology: Phobos exhibits a globally coherent pattern of grooves, whereas Deimos has a surface dominated instead by fragmental debris. Comparison with other asteroids .110 km in diameter shows that this correspondence between landforms and inferred internal structure is part of a pervasive pattern: asteroids interpreted to have coherent interiors exhibit pervasive, organized ridge or groove systems, whereas loosely consolidated asteroids have landforms dominated by fragmental debris and/or retain craters >1.3 body radii in diameter suggesting a porous, compressible interior.
NASA Technical Reports Server (NTRS)
Melick, H. C., Jr.; Ybarra, A. H.; Bencze, D. P.
1975-01-01
An inexpensive method is developed to determine the extreme values of instantaneous inlet distortion. This method also provides insight into the basic mechanics of unsteady inlet flow and the associated engine reaction. The analysis is based on fundamental fluid dynamics and statistical methods to provide an understanding of the turbulent inlet flow and quantitatively relate the rms level and power spectral density (PSD) function of the measured time variant total pressure fluctuations to the strength and size of the low pressure regions. The most probable extreme value of the instantaneous distortion is then synthesized from this information in conjunction with the steady state distortion. Results of the analysis show the extreme values to be dependent upon the steady state distortion, the measured turbulence rms level and PSD function, the time on point, and the engine response characteristics. Analytical projections of instantaneous distortion are presented and compared with data obtained by a conventional, highly time correlated, 40 probe instantaneous pressure measurement system.
Power spectral density analysis of wind-shear turbulence for related flight simulations. M.S. Thesis
NASA Technical Reports Server (NTRS)
Laituri, Tony R.
1988-01-01
Meteorological phenomena known as microbursts can produce abrupt changes in wind direction and/or speed over a very short distance in the atmosphere. These changes in flow characteristics have been labelled wind shear. Because of its adverse effects on aerodynamic lift, wind shear poses its most immediate threat to flight operations at low altitudes. The number of recent commercial aircraft accidents attributed to wind shear has necessitated a better understanding of how energy is transferred to an aircraft from wind-shear turbulence. Isotropic turbulence here serves as the basis of comparison for the anisotropic turbulence which exists in the low-altitude wind shear. The related question of how isotropic turbulence scales in a wind shear is addressed from the perspective of power spectral density (psd). The role of the psd in related Monte Carlo simulations is also considered.
Charles Reece, Hui Tian, Michael Kelley, Chen Xu
2012-04-01
Microroughness is viewed as a critical issue for attaining optimum performance of superconducting radio frequency accelerator cavities. The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions derived from topography of BCP and EP with different controlled starting conditions and durations have been fitted with a combination of power law, K correlation, and shifted Gaussian models to extract characteristic parameters at different spatial harmonic scales. While the simplest characterizations of these data are not new, the systematic tracking of scale-specific roughness as a function of processing is new and offers feedback for tighter process prescriptions more knowledgably targeted at beneficial niobium topography for superconducting radio frequency applications.
Minimum data requirement for neural networks based on power spectral density analysis.
Deng, Jiamei; Maass, Bastian; Stobart, Richard
2012-04-01
One of the most critical challenges ahead for diesel engines is to identify new techniques for fuel economy improvement without compromising emissions regulations. One technique is the precise control of air/fuel ratio, which requires the measurement of instantaneous fuel consumption. Measurement accuracy and repeatability for fuel rate is the key to successfully controlling the air/fuel ratio and real-time measurement of fuel consumption. The volumetric and gravimetric measurement principles are well-known methods for measurement of fuel consumption in internal combustion engines. However, the fuel flow rate measured by these methods is not suitable for either real-time control or real-time measurement purposes because of the intermittent nature of the measurements. This paper describes a technique that can be used to find the minimum data [consisting of data from just 2.5% of the non-road transient cycle (NRTC)] to solve the problem concerning discontinuous data of fuel flow rate measured using an AVL 733S fuel meter for a medium or heavy-duty diesel engine using neural networks. Only torque and speed are used as the input parameters for the fuel flow rate prediction. Power density analysis is used to find the minimum amount of the data. The results show that the nonlinear autoregressive model with exogenous inputs could predict the particulate matter successfully with R(2) above 0.96 using 2.5% NRTC data with only torque and speed as inputs.
Peerannawar, Swarada R; Gejji, Shridhar P
2013-11-01
Electronic structure, (1)H NMR and infrared spectra of diquat (6,7-dihydrodipyrido[1,2-b:1',2'-e] pyrazine-5,8-diium or DQ(2+)) encapsulated by cucurbit[n]uril (n = 7,8) hosts are obtained using the density functional theory. Theoretical calculations have shown that both CB[7] or CB[8] host possesses strong affinity toward DQ(2+) compared to its reduced cation or neutral species. Calculated (1)H NMR spectra reveal that Hα protons on bi-pyridinium rings of DQ(2+)@CB[8] complex are de-shielded owing to C=O⋯H interactions. On the other hand aromatic (Hβ and Hδ) of DQ(2+) within the CB[8] cavity exhibit significant shielding. The complexation of CB[8] with DQ(2+) splits the carbonyl stretching vibration (1788 cm(-1)) into two distinct vibrations which correspond to 1765 cm(-1) arising from hydrogen bonded carbonyls and the 1792 cm(-1) band from non-interacting ones. Further, the CN stretching vibration in DQ(2+) exhibits a frequency blue-shift of 6 cm(-1) on its encapsulation within the CB[8] cavity. The direction of frequency shift has been explained on the basis of natural bond orbital analyses.
NASA Astrophysics Data System (ADS)
Hemalatha, P.; Kumaresan, S.; Veeravazhuthi, V.; Gunasekaran, S.
2013-05-01
S-benzyl isothiouronium nitrate (SBTN), was synthesized and characterized by X-ray diffraction, FTIR, UV-Vis and NMR spectra. The Centro-symmetric single crystal of S-benzyl isothiouronium nitrate (SBTN), which crystallizes in monoclinic crystal system with space group P21/C, exhibits second order non-linear optical (NLO) susceptibility, due to intermolecular charge transfer. S-benzyl isothiouronium ion forms well defined charge transfer (CT) salt with anion nitrate through N-H⋯O and C-H⋯O hydrogen bonds. It is to identify the direction of specific N-H⋯O hydrogen bond between the -NH2 group and O- in the anion and also sacking in the solid state responsible for NLO activity in this crystal. The SHG technique confirms the non-linear optical property of the grown crystals. Density functional theory (DFT) calculation has been carried out to study the nature of hydrogen involved in the SBTN crystal. The bond lengths and bond angles of the structure of SBTN crystal calculated using B3LYP method with 6-311+(2d,2p) basis set. These calculations are compared with experimental values to provide deep insight into its electronic structure and property of grown crystal.
NASA Astrophysics Data System (ADS)
Hipp, Martin; Fliesser, Walter; Neger, Theo
1999-08-01
An optimization of the discharge parameters of high pressure mercury lamps with respect to improved emission properties and longer lifetimes has to be performed using results of advanced model calculations. However, the reliability of these models critically depends on the availability of accurate experimental data. The aim of this work was to provide spatially resolved particle densities of neutral mercury atoms by side-on spectral interferometry. The main challenge was to find an optical arrangement that enables one to compensate for the strong wavefront distortion in the object arm caused by the extreme curvature of the bulb of the discharge lamp, a general problem in classical interferometry. The interferograms could be taken with a time-resolution of 150 microsecond(s) at any phase of the discharge current that varied with 50 Hz. The applied spectro- interferometric technique was a phase method developed at the institute. It supplies a highly resolved phase of the light wavefronts passing the plasma using FFT algorithms. By an Abel-inversion of the side-on data mercury density profiles could be presented for cross-sections ranging up to 10 mm as consequence of the specially designed test and reference beams in the used Mach-Zehnder interferometer.
Zhang, Hong; Zapol, Peter; Dixon, David A.; Wagner, Albert F.; Keceli, Murat
2015-11-17
The Shift-and-invert parallel spectral transformations (SIPs), a computational approach to solve sparse eigenvalue problems, is developed for massively parallel architectures with exceptional parallel scalability and robustness. The capabilities of SIPs are demonstrated by diagonalization of density-functional based tight-binding (DFTB) Hamiltonian and overlap matrices for single-wall metallic carbon nanotubes, diamond nanowires, and bulk diamond crystals. The largest (smallest) example studied is a 128,000 (2000) atom nanotube for which ~330,000 (~5600) eigenvalues and eigenfunctions are obtained in ~190 (~5) seconds when parallelized over 266,144 (16,384) Blue Gene/Q cores. Weak scaling and strong scaling of SIPs are analyzed and the performance of SIPs is compared with other novel methods. Different matrix ordering methods are investigated to reduce the cost of the factorization step, which dominates the time-to-solution at the strong scaling limit. As a result, a parallel implementation of assembling the density matrix from the distributed eigenvectors is demonstrated.
Zhang, Hong; Zapol, Peter; Dixon, David A.; ...
2015-11-17
The Shift-and-invert parallel spectral transformations (SIPs), a computational approach to solve sparse eigenvalue problems, is developed for massively parallel architectures with exceptional parallel scalability and robustness. The capabilities of SIPs are demonstrated by diagonalization of density-functional based tight-binding (DFTB) Hamiltonian and overlap matrices for single-wall metallic carbon nanotubes, diamond nanowires, and bulk diamond crystals. The largest (smallest) example studied is a 128,000 (2000) atom nanotube for which ~330,000 (~5600) eigenvalues and eigenfunctions are obtained in ~190 (~5) seconds when parallelized over 266,144 (16,384) Blue Gene/Q cores. Weak scaling and strong scaling of SIPs are analyzed and the performance of SIPsmore » is compared with other novel methods. Different matrix ordering methods are investigated to reduce the cost of the factorization step, which dominates the time-to-solution at the strong scaling limit. As a result, a parallel implementation of assembling the density matrix from the distributed eigenvectors is demonstrated.« less
Gubler, Philipp; Yamamoto, Naoki; Hatsuda, Tetsuo; Nishida, Yusuke
2015-05-15
Making use of the operator product expansion, we derive a general class of sum rules for the imaginary part of the single-particle self-energy of the unitary Fermi gas. The sum rules are analyzed numerically with the help of the maximum entropy method, which allows us to extract the single-particle spectral density as a function of both energy and momentum. These spectral densities contain basic information on the properties of the unitary Fermi gas, such as the dispersion relation and the superfluid pairing gap, for which we obtain reasonable agreement with the available results based on quantum Monte-Carlo simulations.
Saito, Masatoshi
2009-08-01
Dual-energy computed tomography (DECT) has the potential for measuring electron density distribution in a human body to predict the range of particle beams for treatment planning in proton or heavy-ion radiotherapy. However, thus far, a practical dual-energy method that can be used to precisely determine electron density for treatment planning in particle radiotherapy has not been developed. In this article, another DECT technique involving a balanced filter method using a conventional x-ray tube is described. For the spectral optimization of DECT using balanced filters, the author calculates beam-hardening error and air kerma required to achieve a desired noise level in electron density and effective atomic number images of a cylindrical water phantom with 50 cm diameter. The calculation enables the selection of beam parameters such as tube voltage, balanced filter material, and its thickness. The optimized parameters were applied to cases with different phantom diameters ranging from 5 to 50 cm for the calculations. The author predicts that the optimal combination of tube voltages would be 80 and 140 kV with Tb/Hf and Bi/Mo filter pairs for the 50-cm-diameter water phantom. When a single phantom calibration at a diameter of 25 cm was employed to cover all phantom sizes, maximum absolute beam-hardening errors were 0.3% and 0.03% for electron density and effective atomic number, respectively, over a range of diameters of the water phantom. The beam-hardening errors were 1/10 or less as compared to those obtained by conventional DECT, although the dose was twice that of the conventional DECT case. From the viewpoint of beam hardening and the tube-loading efficiency, the present DECT using balanced filters would be significantly more effective in measuring the electron density than the conventional DECT. Nevertheless, further developments of low-exposure imaging technology should be necessary as well as x-ray tubes with higher outputs to apply DECT coupled with the
Hernández-Hernández, Miguel A; Fernández-Torre, José L
2016-01-01
to describe the characteristics of the color density spectral array (CDSA) of bilateral bispectral index (b-BIS) monitoring system in patients with comatose nonconvulsive status epilepticus (NCSE). We hypothesized that CDSA could be helpful for monitoring NCSE in critically subjects if continuous EEG (cEEG) is not available. we retrospectively analyzed comatose patients admitted to our neurological intensive care unit (NICU) from 2011 to 2014 with a diagnosis of definitive NCSE that underwent b-BIS monitoring for at least 24h to guide anesthetic sedation. Clinical, electroencephalography and neuroimaging findings were analyzed. Moreover, all parameters from the b-BIS data including the CDSA were reviewed during periods of NCSE (NCSE pattern) and profound sedation (sedation pattern). 15 NCSE patients were included. The delay from the diagnosis of NCSE to the onset of b-BIS monitoring was 8 (0.5-31)h and total time of b-BIS monitoring 7.8±6.5 days. CDSA during NCSE pattern was characterized by continuous or intermittent red and dark red tones, spectral edge frequency (SEF) in the delta-theta range, with or without asymmetry and BIS number trend with significant variability. In contrast, CDSA during sedation revealed predominance of orange, yellow, green and occasionally blue tones, SEF in the alpha-beta range, absence of asymmetry and stability of BIS number. b-BIS monitoring system and, in particular, CDSA used by nonexpert NICU personnel may be helpful to follow-up episodes of NCSE, to detect recurrences of nonconvulsive seizures (NCSzs), and to monitor profound anesthetic therapy in comatose patients when cEEG is not available. Copyright © 2015 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Rekik, Najeh; Oujia, Brahim; Wójcik, Marek J.
2008-09-01
The main purpose of the present paper is to show how both anharmonicities of the fast and the slow modes, multiple Fermi resonances and damping mechanisms introduced within the strong anharmonic coupling theory, are susceptible to explain some analogies in the infrared spectra of hydrogen bonded systems, when passing from the condensed to the gas phase. The high-frequency mode X-H→⋯Y described by double well potential is supposed to be anharmonically coupled to the H-bond stretching mode X←-H⋯Y→ described by Morse potential and to first overtones of some bending modes through Fermi resonances. The relaxation of the fast and bending modes and of the H-bond bridge is incorporated by aid of previous results [N. Rekik, B. Ouari, P. Blaise, O. Henri-Rousseau, J. Mol. Struct. 687 (2004) 125]. The spectral density is obtained as the Fourier transform of the autocorrelation function of the dipole moment operator within linear response theory. Numerical results show that mixing of all these effects results in a broad and complicated structure and expects to provide efficient energy relaxation pathways by using large dampings parameters for the condensed phase and weaker dampings for the gas one.
Topjian, Alexis A; Fry, Michael; Jawad, Abbas F.; Herman, Susan T; Nadkarni, Vinay M.; Ichord, Rebecca; Berg, Robert A; Dlugos, Dennis J.; Abend, Nicholas S.
2014-01-01
Objective To determine the accuracy and reliability of electroencephalographic seizure detection by critical care providers using color density spectral array (CDSA) electroencephalography (EEG). Participants Critical care providers (attending physicians, fellow trainees and nurses.) Interventions A standardized powerpoint CDSA tutorial followed by classification of 200 CDSA images as displaying seizures or not displaying seizures. Measurements and Main Results Using conventional EEG recordings obtained from patients who underwent EEG monitoring after cardiac arrest, we created 100 CDSA images, 30% of which displayed seizures. The gold standard for seizure category was electroencephalographer determination from the full montage conventional EEG. Participants did not have access to the conventional EEG tracings. After completing a standardized CDSA tutorial, images were presented to participants in duplicate and in random order. Twenty critical care physicians (12 attendings and 8 fellows) and 19 critical care nurses classified the CDSA images as having any seizure(s) or no seizures. The 39 critical care providers had a CDSA seizure detection sensitivity of 70% [95% CI: 67%, 73%], specificity of 68% [95% CI: 67%, 70%], positive predictive value of 46%, and negative predictive value of 86%. The sensitivity of CDSA detection of status epilepticus was 72% [95% CI: 69%, 74%]. Conclusion Determining which post-cardiac arrest patients experience electrographic seizures by critical care providers is feasible after a brief training. There is moderate sensitivity for seizure and status epilepticus detection and a high negative predictive value. PMID:25651050
The Double-Peak Spectral Energy Density of Gamma-Ray Bursts and the True Identity of GRB 031203
NASA Astrophysics Data System (ADS)
Dado, Shlomo; Dar, Arnon
2005-07-01
A double-peak spectral energy density of prompt γ-rays, similar to that observed in blazars, is expected in the cannonball (CB) model of gamma-ray bursts (GRBs) produced in supernova (SN) explosions. The first sub-MeV ordinary peak is formed by inverse Compton scattering (ICS) of the ambient SN light by the CBs' electrons, while the second peak at GeV-TeV energies is formed by ICS of interstellar medium electrons accelerated by the jetted CBs from the SN explosion. Usually the second peak is in the GeV-TeV range. However, in X-ray flashes with a low peak energy, which in the CB model are normal GRBs viewed far off-axis, the second peak energy moves to the MeV range. In far off-axis GRBs, such as 980425 and 031203, the second peak may have been confused with the normal GRB peak. In most GRBs that have been observed so far, the γ-ray detectors ran out of statistics far below the second peak. However, in bright GRBs, the two peaks may be resolved by simultaneous measurements with Swift, INTEGRAL, and GLAST.
Vecchiato, Giovanni; Susac, Ana; Margeti, Stavroula; De Vico Fallani, Fabrizio; Maglione, Anton Giulio; Supek, Selma; Planinic, Maja; Babiloni, Fabio
2013-04-01
Proportional reasoning is very important logical skill required in mathematics and science problem solving as well as in everyday life decisions. However, there is a lack of studies on neurophysiological correlates of proportional reasoning. To explore the brain activity of healthy adults while performing a balance scale task, we used high-resolution EEG techniques and graph-theory based connectivity analysis. After unskilled subjects learned how to properly solve the task, their cortical power spectral density (PSD) maps revealed an increased parietal activity in the beta band. This indicated that subjects started to perform calculations. In addition, the number of inter-hemispheric connections decreased after learning, implying a rearrangement of the brain activity. Repeated performance of the task led to the PSD decrease in the beta and gamma bands among parietal and frontal regions along with a synchronization of lower frequencies. These findings suggest that repetition led to a more automatic task performance. Subjects were also divided in two groups according to their scores on the test of logical thinking (TOLT). Although no group differences in the accuracy and reaction times were found, EEG data showed higher activity in the beta and gamma bands for the group that scored better on TOLT. Learning and repetition induced changes in the pattern of functional connectivity were evident for all frequency bands. Overall, the results indicated that higher frequency oscillations in frontal and parietal regions are particularly important for proportional reasoning.
Chang, Zhiwei; Halle, Bertil
2015-12-21
A system of three dipole-coupled spins exhibits a surprisingly intricate relaxation behavior. Following Hubbard’s pioneering 1958 study, many authors have investigated different aspects of this problem. Nevertheless, on revisiting this classic relaxation problem, we obtain several new results, some of which are at variance with conventional wisdom. Most notably from a fundamental point of view, we find that the odd-valued spectral density function influences longitudinal relaxation. We also show that the effective longitudinal relaxation rate for a non-isochronous three-spin system can exhibit an unusual inverted dispersion step. To clarify these and other issues, we present a comprehensive theoretical treatment of longitudinal relaxation in a three-spin system of arbitrary geometry and with arbitrary rotational dynamics. By using the Liouville-space formulation of Bloch-Wangsness-Redfield theory and a basis of irreducible spherical tensor operators, we show that the number of relaxation components in the different cases can be deduced from symmetry arguments. For the isochronous case, we present the relaxation matrix in analytical form, whereas, for the non-isochronous case, we employ a computationally efficient approach based on the stochastic Liouville equation.
2012-01-01
In this study, we show that the correct determination of surface morphology using scanning force microscopy (SFM) imaging and power spectral density (PSD) analysis of the surface roughness is an extremely demanding task that is easily affected by experimental parameters such as scan speed and feedback parameters. We present examples were the measured topography data is significantly influenced by the feedback response of the SFM system and the PSD curves calculated from this experimental data do not correspond to that of the true topography. Instead, either features are "lost" due to low pass filtering or features are "created" due to oscillation of the feedback loop. In order to overcome these serious problems we show that the interaction signal (error signal) can be used not only to quantitatively control but also to significantly improve the quality of the topography raw data used for the PSD analysis. In particular, the calibrated error signal image can be used in combination with the topography image in order to obtain a correct representation of surface morphology ("true" topographic image). From this "true" topographic image a faithful determination of the PSD of surface morphology is possible. The corresponding PSD curve is not affected by the fine-tuning of feedback parameters, and allows for much faster image acquisition speeds without loss of information in the PSD curve. PMID:22397728
Code of Federal Regulations, 2010 CFR
2010-10-01
... feeder link earth stations in the 17/24 GHz BSS. 25.223 Section 25.223 Telecommunication FEDERAL....223 Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS. (a) This section applies to all applications for earth station licenses in the 17/24 GHz BSS...
NASA Astrophysics Data System (ADS)
Hao, Na; Moysey, Stephen M. J.; Powell, Brian A.; Ntarlagiannis, Dimitrios
2016-12-01
Surface complexation models are widely used with batch adsorption experiments to characterize and predict surface geochemical processes in porous media. In contrast, the spectral induced polarization (SIP) method has recently been used to non-invasively monitor in situ subsurface chemical reactions in porous media, such as ion adsorption processes on mineral surfaces. Here we compare these tools for investigating surface site density changes during pH-dependent sodium adsorption on a silica gel. Continuous SIP measurements were conducted using a lab scale column packed with silica gel. A constant inflow of 0.05 M NaCl solution was introduced to the column while the influent pH was changed from 7.0 to 10.0 over the course of the experiment. The SIP measurements indicate that the pH change caused a 38.49 ± 0.30 μS cm- 1 increase in the imaginary conductivity of the silica gel. This increase is thought to result from deprotonation of silanol groups on the silica gel surface caused by the rise in pH, followed by sorption of Na+ cations. Fitting the SIP data using the mechanistic model of Leroy et al. (Leroyet al., 2008), which is based on the triple layer model of a mineral surface, we estimated an increase in the silica gel surface site density of 26.9 × 1016 sites m- 2. We independently used a potentiometric acid-base titration data for the silica gel to calibrate the triple layer model using the software FITEQL and observed a total increase in the surface site density for sodium sorption of 11.2 × 1016 sites m- 2, which is approximately 2.4 times smaller than the value estimated using the SIP model. By simulating the SIP response based on the calibrated surface complexation model, we found a moderate association between the measured and estimated imaginary conductivity (R2 = 0.65). These results suggest that the surface complexation model used here does not capture all mechanisms contributing to polarization of the silica gel captured by the SIP data.
Jeon, Jonggu; Cho, Minhaeng
2011-12-07
The vibrational energy transfer from the excited carbonyl stretch mode in N-deuterated N-methylacetamide (NMA-d), both in isolation and in a heavy water cluster, is studied with nonequilibrium molecular dynamics (NEMD) simulations, employing a quantum mechanical/molecular mechanical (QM∕MM) force field at the semiempirical PM3 level. The nonequilibrium ensemble of vibrationally excited NMA-d is prepared by perturbing the positions and velocities of the carbonyl C and O atoms and its NEMD trajectories are obtained with a leap-frog algorithm properly modified for the initial perturbation. In addition to the time-domain analysis of the kinetic and potential energies, a novel method for the spectral analysis of the atomic kinetic energies is developed, in terms of the spectral density of kinetic energy, which provides the time-dependent changes of the frequency-resolved kinetic energies without the complications of normal mode analysis at every MD time step. Due to the QM description of the solute electronic structure, the couplings among the normal modes are captured more realistically than with classical force fields. The energy transfer in the isolated NMA-d is found to proceed first from the carbonyl bond to other modes with time scales of 3 ps or less, and then among the other modes over 3-21 ps. In the solvated NMA-d, most of the excess energy is first transferred to other intramolecular modes within 5 ps, which is subsequently dissipated to solvent with 7-19 ps time scales. The contribution of the direct energy transfer from the carbonyl bond to solvent was only 5% with ~7 ps time scale. Solvent reorganization that leads to destabilization of the electrostatic interactions is found to be crucial in the long time relaxation of the excess energy, while the water intramolecular modes do not contribute significantly. Detailed mode-specific energy transfer pathways are deduced for the isolated and solvated NMA-d and they show that the energy transfer in NMA-d is a
NASA Astrophysics Data System (ADS)
Jeon, Jonggu; Cho, Minhaeng
2011-12-01
The vibrational energy transfer from the excited carbonyl stretch mode in N-deuterated N-methylacetamide (NMA-d), both in isolation and in a heavy water cluster, is studied with nonequilibrium molecular dynamics (NEMD) simulations, employing a quantum mechanical/molecular mechanical (QM/MM) force field at the semiempirical PM3 level. The nonequilibrium ensemble of vibrationally excited NMA-d is prepared by perturbing the positions and velocities of the carbonyl C and O atoms and its NEMD trajectories are obtained with a leap-frog algorithm properly modified for the initial perturbation. In addition to the time-domain analysis of the kinetic and potential energies, a novel method for the spectral analysis of the atomic kinetic energies is developed, in terms of the spectral density of kinetic energy, which provides the time-dependent changes of the frequency-resolved kinetic energies without the complications of normal mode analysis at every MD time step. Due to the QM description of the solute electronic structure, the couplings among the normal modes are captured more realistically than with classical force fields. The energy transfer in the isolated NMA-d is found to proceed first from the carbonyl bond to other modes with time scales of 3 ps or less, and then among the other modes over 3-21 ps. In the solvated NMA-d, most of the excess energy is first transferred to other intramolecular modes within 5 ps, which is subsequently dissipated to solvent with 7-19 ps time scales. The contribution of the direct energy transfer from the carbonyl bond to solvent was only 5% with ˜7 ps time scale. Solvent reorganization that leads to destabilization of the electrostatic interactions is found to be crucial in the long time relaxation of the excess energy, while the water intramolecular modes do not contribute significantly. Detailed mode-specific energy transfer pathways are deduced for the isolated and solvated NMA-d and they show that the energy transfer in NMA-d is a
NASA Technical Reports Server (NTRS)
Scarpace, F. L.; Voss, A. W.
1973-01-01
Dye densities of multi-layered films are determined by applying a regression analysis to the spectral response of the composite transparency. The amount of dye in each layer is determined by fitting the sum of the individual dye layer densities to the measured dye densities. From this, dye content constants are calculated. Methods of calculating equivalent exposures are discussed. Equivalent exposures are a constant amount of energy over a limited band-width that will give the same dye content constants as the real incident energy. Methods of using these equivalent exposures for analysis of photographic data are presented.
McKinney, Wayne R.; Howells, M. R.; Yashchuk, V. V.
2008-09-30
An implementation of the two-dimensional statistical scattering theory of Church and Takacs for the prediction of scattering from x-ray mirrors is presented with a graphical user interface. The process of this development has clarified several problems which are of significant interest to the synchrotron community. These problems have been addressed to some extent, for example, for large astronomical telescopes, and at the National Ignition Facility for normal incidence optics, but not in the synchrotron community for grazing incidence optics. Since it is based on the Power Spectral Density (PSD) to provide a description of the deviations from ideal shape of the surface, accurate prediction of the scattering requires an accurate estimation of the PSD. Specifically, the spatial frequency range of measurement must be the correct one for the geometry of use of the optic--including grazing incidence and coherence effects, and the modifications to the PSD of the Optical Transfer Functions (OTF) of the measuring instruments must be removed. A solution for removal of OTF effects has been presented previously, the Binary Pseudo-Random Grating. Typically, the frequency range of a single instrument does not cover the range of interest, requiring the stitching together of PSD estimations. This combination generates its own set of difficulties in two dimensions. Fitting smooth functions to two dimensional PSDs, particularly in the case of spatial non-isotropy of the surface, which is often the case for optics in synchrotron beam lines, can be difficult. The convenient, and physically accurate fractal for one dimension does not readily transfer to two dimensions. Finally, a completely statistical description of scattering must be integrated with a deterministic low spatial frequency component in order to completely model the intensity near the image. An outline for approaching these problems, and our proposed experimental program is given.
NASA Astrophysics Data System (ADS)
Bedir, Islam
The methods are developed of two-loop calculation of spectral density for the 3-point correlation function of an electromagnetic current and two axial currents which are the basis of the pion form factor analysis within the framework of QCD sum rules and local quark-hadron duality approach. The nature of various types of contributions is established which are related to particular regions of momentum integrations inside Feynman integrals. The trace factors accompanying all six two-loop diagrams are calculated and classified. To regularize particular loop integrals, the dimensional regularization technique has been used. The calculation involves such methods as infinite-momentum frame approach, alpha-representation method, Sudakov parametrization of the integration momentum and covariant calculation in momentum space. It is shown that final results of integration are given by logarithms and di-logarithm functions. For the diagram with the gluon correction to the electromagnetic vertex, it is shown that its large momentum transfer behavior is dominated by the Feynman mechanism, in which the active quark carries the bulk of the hadron momentum both before and after collision with virtual photon. For this diagram, the Sudakov double logarithmic terms were obtained that are known to convert into the Sudakov form factor after summation over all orders. Another type of double-logarithmic term was found in the contribution of the diagrams with the gluon correction to the axial-current vertices. This term appears as a power correction to the leading power behavior of this diagram governed by a short-distance re-scattering subprocess in which the exchanged gluon has large virtuality. This subprocess corresponds to the asymptotic perturbative QCD contribution. This observation shows that the two double-logarithmic terms have different nature. The methods developed in this dissertation may be applied to other two-loop calculations within the QCD sum rule method.
Hwang, J; Schachinger, E; Carbotte, J P; Gao, F; Tanner, D B; Timusk, T
2008-04-04
We use optical spectroscopy to investigate the excitations responsible for the structure in the optical self-energy of thin epitaxial films of La(1.83)Sr(0.17)CuO(4). Using Eliashberg's formalism to invert the optical spectra we extract the electron-boson spectral function and find that at low temperature it has a two component structure closely matching the spin excitation spectrum recently measured by magnetic neutron scattering. We contrast the temperature evolution of the spectral density and the two-peak behavior in La(2-Sr(x)CuO(4) with another high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+delta). The bosonic spectral functions of the two materials account for the low T(c) of LSCO as compared to Bi-2212.
NASA Astrophysics Data System (ADS)
Jacobs, Verne
2015-05-01
The frequency-dependent transition rates for multi-photon processes in quantized many-electron systems are evaluated using a reduced-density-matrix approach. A fundamental foundation, based on quantum electrodynamics, is provided for systematic spectral simulations for electromagnetic interactions in quantized many-electron systems, including atomic, molecular, and solid-state systems. A perturbation expansion of the frequency-domain Liouville-space self-energy operator is employed in detailed evaluations of the spectral-line shapes. The self-energy contributions associated with environmental electron-photon and electron-phonon interactions are systematically taken into account. Detailed evaluations have been carried out for the spectral-line widths and shifts in the diagonal-resolvent, lowest order (Born), and short-memory-time (Markov) approximations. Work supported by the Office of Naval Research through the Basic Research Program at The Naval Research Laboratory.
SU-D-204-01: Dual-Energy Calibration for Breast Density Measurement Using Spectral Mammography
Ding, H; Cho, H; Kumar, N; Sennung, D; Molloi, S
2015-06-15
Purpose: To investigate the feasibility of minimizing the systematic errors in dual-energy breast density quantification induced by the use of tissue-equivalent plastic phantoms as the calibration basis materials. Methods: Dual-energy calibration using tissue-equivalent plastic phantoms was performed on a spectral mammography system based on scanning multi-slit Si strip photon-counting detectors. The plastic phantom calibration used plastic water and adipose-equivalent phantoms as the basis materials, which have different x-ray attenuation properties compared to water and lipid in actual breast tissue. Two methods were used to convert the dual-energy decomposition measurements in plastic phantom thicknesses into true water and lipid basis. The first method was based entirely on the theoretical x-ray attenuation coefficients of the investigated materials in the mammographic energy range. The conversion matrix was determined from least-squares fitting of the target material using the reported attenuation coefficients of water and lipid. The second method was developed based on experimental calibrations, which measured the low-and high-energy signals of pure water and lipid of known thicknesses. A non-linear rational function was used to correlate the decomposed thicknesses to the known values, so that the conversion coefficients can be determined. Both methods were validated using independent measurements of water and lipid mixture phantoms. The correlation of the dual-energy decomposition measurements and the known values were studied with linear regression analysis. Results: There was an excellent linear correlation between the converted water thicknesses and the known values. The slopes of the linear fits were determined to be 0.63 and 1.03 for the simulation and experimental results, respectively. The non-linear fitting in the experimental approach reduced the root-mean-square (RMS) errors from approximately 3.4 mm to 1.5 mm. Conclusion: The results suggested
NASA Astrophysics Data System (ADS)
Rekik, Najeh; Velcescu, Adina; Blaise, Paul; Henri-Rousseau, Olivier
2001-11-01
A quantum theoretical 2-D approach of the IR νX-H spectral density (SD) for symmetric or asymmetric intermediate or strong H-bonds is proposed. The presented model is based on the linear response theory; the strong anharmonic coupling theory (SACT) beyond the adiabatic approximation is used. The fast mode potential is described by an asymmetric double-well potential, whereas the slow mode is assumed to be harmonic. The slow and fast modes are assumed to be anharmonically coupled as in the SACT. The intrinsic anharmonicity of the fast mode and the anharmonicity related to the coupling between the slow and the fast modes are taken in an equal foot within quantum mechanics, without any semiclassical assumption. The relaxation is supposed given by a direct damping mechanism. When the barrier of the double-well asymmetric fast mode potential is very high, i.e. when the H-bond becomes weak, the computed theoretical SD reduces, as required, to that obtained in one of our precedent more simple approaches, dealing with weak H-bonds and working beyond the adiabatic approximation [Chem. Phys. 243 (1999) 229]. It reduces, within the adiabatic approximation, to the Franck-Condon progression of Rösch-Ratner (RR) [J. Chem. Phys. 61 (1974) 3444], and, in turn, to that of Maréchal-Witkowski (MW) [J. Chem. Phys. 48 (1968) 2697] when in this adiabatic approximation the damping is missing. When the anharmonic coupling between the slow and fast mode is missing, the behavior of the SDs is in good agreement with that which may be waited for a situation involving a 1-D asymmetric double well and thus the possibility of tunnelling. When the barrier is low, and the asymmetry is missing or weak, the changes induced by the asymmetric potential in the features of the Franck-Condon progression of the RR and MW model are more important than those in which the Fermi resonances or the Davydov coupling are acting. The model reproduces satisfactorily the increase in low frequency shift when
Johns, H. M.; Mancini, R. C.; Nagayama, T.; ...
2016-01-25
In warm target direct-drive ICF implosion experiments performed at the OMEGA laser facility, plastic microballoons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. These 2-D space-resolvedmore » titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, ρL(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (Te) = 400±28eV, electron number density (Ne) = 8.5x1024±2.5x1024 cm-3, and average areal density <ρR> = 86±7mg/cm2. Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2-9, dominated by l = 2. We extract a target breakup fraction of 7.1±1.5% from our Fourier analysis. A new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5±1μm.« less
Saroka, Kevin S.; Vares, David E.; Persinger, Michael A.
2016-01-01
In 1954 and 1960 Koenig and his colleagues described the remarkable similarities of spectral power density profiles and patterns between the earth-ionosphere resonance and human brain activity which also share magnitudes for both electric field (mV/m) and magnetic field (pT) components. In 2006 Pobachenko and colleagues reported real time coherence between variations in the Schumann and brain activity spectra within the 6–16 Hz band for a small sample. We examined the ratios of the average potential differences (~3 μV) obtained by whole brain quantitative electroencephalography (QEEG) between rostral-caudal and left-right (hemispheric) comparisons of 238 measurements from 184 individuals over a 3.5 year period. Spectral densities for the rostral-caudal axis revealed a powerful peak at 10.25 Hz while the left-right peak was 1.95 Hz with beat-differences of ~7.5 to 8 Hz. When global cerebral measures were employed, the first (7–8 Hz), second (13–14 Hz) and third (19–20 Hz) harmonics of the Schumann resonances were discernable in averaged QEEG profiles in some but not all participants. The intensity of the endogenous Schumann resonance was related to the ‘best-of-fitness’ of the traditional 4-class microstate model. Additional measurements demonstrated real-time coherence for durations approximating microstates in spectral power density variations between Schumann frequencies measured in Sudbury, Canada and Cumiana, Italy with the QEEGs of local subjects. Our results confirm the measurements reported by earlier researchers that demonstrated unexpected similarities in the spectral patterns and strengths of electromagnetic fields generated by the human brain and the earth-ionospheric cavity. PMID:26785376
Saroka, Kevin S; Vares, David E; Persinger, Michael A
2016-01-01
In 1954 and 1960 Koenig and his colleagues described the remarkable similarities of spectral power density profiles and patterns between the earth-ionosphere resonance and human brain activity which also share magnitudes for both electric field (mV/m) and magnetic field (pT) components. In 2006 Pobachenko and colleagues reported real time coherence between variations in the Schumann and brain activity spectra within the 6-16 Hz band for a small sample. We examined the ratios of the average potential differences (~3 μV) obtained by whole brain quantitative electroencephalography (QEEG) between rostral-caudal and left-right (hemispheric) comparisons of 238 measurements from 184 individuals over a 3.5 year period. Spectral densities for the rostral-caudal axis revealed a powerful peak at 10.25 Hz while the left-right peak was 1.95 Hz with beat-differences of ~7.5 to 8 Hz. When global cerebral measures were employed, the first (7-8 Hz), second (13-14 Hz) and third (19-20 Hz) harmonics of the Schumann resonances were discernable in averaged QEEG profiles in some but not all participants. The intensity of the endogenous Schumann resonance was related to the 'best-of-fitness' of the traditional 4-class microstate model. Additional measurements demonstrated real-time coherence for durations approximating microstates in spectral power density variations between Schumann frequencies measured in Sudbury, Canada and Cumiana, Italy with the QEEGs of local subjects. Our results confirm the measurements reported by earlier researchers that demonstrated unexpected similarities in the spectral patterns and strengths of electromagnetic fields generated by the human brain and the earth-ionospheric cavity.
Ding, Huanjun; Molloi, Sabee
2012-01-01
Purpose A simple and accurate measurement of breast density is crucial for the understanding of its impact in breast cancer risk models. The feasibility to quantify volumetric breast density with a photon-counting spectral mammography system has been investigated using both computer simulations and physical phantom studies. Methods A computer simulation model involved polyenergetic spectra from a tungsten anode x-ray tube and a Si-based photon-counting detector has been evaluated for breast density quantification. The figure-of-merit (FOM), which was defined as the signal-to-noise ratio (SNR) of the dual energy image with respect to the square root of mean glandular dose (MGD), was chosen to optimize the imaging protocols, in terms of tube voltage and splitting energy. A scanning multi-slit photon-counting spectral mammography system has been employed in the experimental study to quantitatively measure breast density using dual energy decomposition with glandular and adipose equivalent phantoms of uniform thickness. Four different phantom studies were designed to evaluate the accuracy of the technique, each of which addressed one specific variable in the phantom configurations, including thickness, density, area and shape. In addition to the standard calibration fitting function used for dual energy decomposition, a modified fitting function has been proposed, which brought the tube voltages used in the imaging tasks as the third variable in dual energy decomposition. Results For an average sized breast of 4.5 cm thick, the FOM was maximized with a tube voltage of 46kVp and a splitting energy of 24 keV. To be consistent with the tube voltage used in current clinical screening exam (~ 32 kVp), the optimal splitting energy was proposed to be 22 keV, which offered a FOM greater than 90% of the optimal value. In the experimental investigation, the root-mean-square (RMS) error in breast density quantification for all four phantom studies was estimated to be
NASA Astrophysics Data System (ADS)
Kumar, Arbind; S. Roy, P. N.; Das, L. K.
2016-07-01
Power spectrum analysis of Complete Bouguer Anomaly (CBA) map of Eastern Ghat Mobile Belt (EGMB) and its surroundings in India through Two Dimensional (2D) spectral analysis has provided estimates of the ensemble average depths for the density discontinuities which represent crustal inhomogeneities. The spectral analysis method has helped to estimate the depths of a perturbing body sources which are obtained from the negative slopes of the linear relationship between the logarithmic power spectrum and the wave-numbers of the gravity field. The detailed analysis reveals three horizontal discontinuities (i) Phanerozoic sediment thickness (ii) Basement depth and (iii) Conrad discontinuity. The average thickness of Phanerozoic sediments is estimated to be 3 km whereas depth of basement and Conrad discontinuity are at 7 km and 14.5 km respectively. Additionally Mohorovicic discontinuity also estimated at a depth of 32.8 km in the study region.
NASA Technical Reports Server (NTRS)
Lafevers, E. V.
1974-01-01
Surface electromyograms (EMG) taken from three upper torso muscles during a push-pull task were analyzed by a power spectral density technique to determine the utility of the spectral analysis for identifying changes in the EMG caused by muscular fatigue. The results confirmed the value of the frequency analysis for identifying fatigue producing muscular performance. Data revealed reliable differences between muscles in fatigue induced responses to various locations in the reach envelope at which the subjects were required to perform the push-pull exercise, and the differential sensitivity of individual muscles to the various reach positions; i.e., certain reach positions imposed more fatigue related shifts in EMG power than did others. It was found that a pressurized space suit changed the pattern of normal shirtsleeve muscle fatigue responses in all three of the muscles.
Aoki, Masahiko; Hirose, Katsumi; Sato, Mariko; Akimoto, Hiroyoshi; Kawaguchi, Hideo; Hatayama, Yoshiomi; Fujioka, Ichitaro; Tanaka, Mitsuki; Ono, Shuichi; Takai, Yoshihiro
2016-01-01
The purpose of this study was to investigate the prognostic significance of average iodine density as assessed by dual-energy computed tomography (DE-CT) for lung tumors treated with stereotactic body radiotherapy (SBRT). From March 2011 to August 2014, 93 medically inoperable patients with 74 primary lung cancers and 19 lung metastases underwent DE-CT prior to SBRT of a total dose of 45–60 Gy in 5–10 fractions. Of these 93 patients, nine patients had two lung tumors. Thus, 102 lung tumors were included in this study. DE-CT was performed for pretreatment evaluation. Regions of interest were set for the entire tumor, and average iodine density was obtained using a dedicated imaging software and evaluated with regard to local control. The median follow-up period was 23.4 months (range, 1.5–54.5 months). The median value of the average iodine density was 1.86 mg/cm3 (range, 0.40–9.27 mg/cm3). Two-year local control rates for the high and low average iodine density groups divided by the median value of the average iodine density were 96.9% and 75.7% (P = 0.006), respectively. Tumors with lower average iodine density showed a worse prognosis, possibly reflecting a hypoxic cell population in the tumor. The average iodine density exhibited a significant impact on local control. Our preliminary results indicate that iodine density evaluated using dual-energy spectral CT may be a useful, noninvasive and quantitative assessment of radio-resistance caused by presumably hypoxic cell populations in tumors. PMID:26826198
Aoki, Masahiko; Hirose, Katsumi; Sato, Mariko; Akimoto, Hiroyoshi; Kawaguchi, Hideo; Hatayama, Yoshiomi; Fujioka, Ichitaro; Tanaka, Mitsuki; Ono, Shuichi; Takai, Yoshihiro
2016-07-01
The purpose of this study was to investigate the prognostic significance of average iodine density as assessed by dual-energy computed tomography (DE-CT) for lung tumors treated with stereotactic body radiotherapy (SBRT). From March 2011 to August 2014, 93 medically inoperable patients with 74 primary lung cancers and 19 lung metastases underwent DE-CT prior to SBRT of a total dose of 45-60 Gy in 5-10 fractions. Of these 93 patients, nine patients had two lung tumors. Thus, 102 lung tumors were included in this study. DE-CT was performed for pretreatment evaluation. Regions of interest were set for the entire tumor, and average iodine density was obtained using a dedicated imaging software and evaluated with regard to local control. The median follow-up period was 23.4 months (range, 1.5-54.5 months). The median value of the average iodine density was 1.86 mg/cm(3) (range, 0.40-9.27 mg/cm(3)). Two-year local control rates for the high and low average iodine density groups divided by the median value of the average iodine density were 96.9% and 75.7% (P = 0.006), respectively. Tumors with lower average iodine density showed a worse prognosis, possibly reflecting a hypoxic cell population in the tumor. The average iodine density exhibited a significant impact on local control. Our preliminary results indicate that iodine density evaluated using dual-energy spectral CT may be a useful, noninvasive and quantitative assessment of radio-resistance caused by presumably hypoxic cell populations in tumors.
Code of Federal Regulations, 2012 CFR
2012-10-01
... 47 Telecommunication 2 2012-10-01 2012-10-01 false Off-axis EIRP spectral density limits for... following values, within ±3° of the GSO arc, under clear sky conditions: 32.5-25log(θ) dBW/MHz for 2° ≤ θ ≤ 7° 11.4 dBW/MHz for 7° ≤ θ ≤ 9.2° 35.5-25log(θ) dBW/MHz for 9.2° ≤ θ ≤ 48° 3.5 dBW/MHz for 48° ≤ θ...
Code of Federal Regulations, 2013 CFR
2013-10-01
... 47 Telecommunication 2 2013-10-01 2013-10-01 false Off-axis EIRP spectral density limits for... following values, within ±3° of the GSO arc, under clear sky conditions: 32.5-25log(θ) dBW/MHz for 2° ≤θ ≤7° 11.4 dBW/MHz for 7° ≤θ ≤9.2° 35.5-25log(θ) dBW/MHz for 9.2° ≤θ ≤48° 3.5 dBW/MHz for 48° ≤θ ≤180...
Code of Federal Regulations, 2011 CFR
2011-10-01
... 47 Telecommunication 2 2011-10-01 2011-10-01 false Off-axis EIRP spectral density limits for... following values, within ±3° of the GSO arc, under clear sky conditions: 32.5-25log(θ) dBW/MHz for 2° ≤ θ ≤ 7° 11.4 dBW/MHz for 7° ≤ θ ≤ 9.2° 35.5-25log(θ) dBW/MHz for 9.2° ≤ θ ≤ 48° 3.5 dBW/MHz for 48° ≤ θ...
Hwang, Jungseek
2016-03-31
We introduce an approximate method which can be used to simulate the optical conductivity data of correlated multiband systems for normal and superconducting cases by taking advantage of a reversed process in comparison to a usual optical data analysis, which has been used to extract the electron-boson spectral density function from measured optical spectra of single-band systems, like cuprates. We applied this method to optical conductivity data of two multiband pnictide systems (Ba0.6K0.4Fe2As2 and LiFeAs) and obtained the electron-boson spectral density functions. The obtained electron-boson spectral density consists of a sharp mode and a broad background. The obtained spectral density functions of the multiband systems show similar properties as those of cuprates in several aspects. We expect that our method helps to reveal the nature of strong correlations in the multiband pnictide superconductors.
Johns, H. M.; Mancini, R. C.; Nagayama, T.; Mayes, D. C.; Tommasini, R.; Smalyuk, V. A.; Regan, S. P.; Delettrez, J. A.
2016-01-25
In warm target direct-drive inertial confinement fusion implosion experiments performed at the OMEGA laser facility, plastic micro-balloons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. These 2-D space-resolved titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, ρL(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (Te) = 400 ± 28 eV, electron number density (N_{e}) = 8.5 × 10^{24} ± 2.5 × 10^{24} cm^{–3}, and average areal density <ρR> = 86 ± 7 mg/cm^{2}. Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2–9, dominated by l = 2. We extract a target breakup fraction of 7.1 ± 1.5% from our Fourier analysis. Furthermore, a new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5 ±1 μm.
2016-01-01
Absorption and emission in the ultraviolet, visible, and infrared spectral range are usually mediated by the electric-field component of light. Only some electronic transitions have significant “magnetic-dipole” character, meaning that they couple to the magnetic field of light. Nanophotonic control over magnetic-dipole emission has recently been demonstrated, and magnetic-dipole transitions have been used to probe the magnetic-field profiles of photonic structures. However, the library of available magnetic-dipole emitters is currently limited to red or infrared emitters and mostly doped solids. Here, we show that NaYF4 nanocrystals doped with Eu3+ have various electric- and magnetic-dipole emission lines throughout the visible spectral range from multiple excited states. At the same time, the colloidal nature of the nanocrystals allows easy handling. We demonstrate the use of these nanocrystals as probes for the radiative electric and magnetic local density of optical states in a planar mirror geometry. A single emission spectrum can reveal enhancement or suppression of the density of optical states at multiple frequencies simultaneously. Such nanocrystals may find application in the characterization of nanophotonic structures or as model emitters for studies into magnetic light–matter interaction at optical frequencies. PMID:27786490
Rosnik, Andreana M; Curutchet, Carles
2015-12-08
Over the past decade, both experimentalists and theorists have worked to develop methods to describe pigment-protein coupling in photosynthetic light-harvesting complexes in order to understand the molecular basis of quantum coherence effects observed in photosynthesis. Here we present an improved strategy based on the combination of quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations and excited-state calculations to predict the spectral density of electronic-vibrational coupling. We study the water-soluble chlorophyll-binding protein (WSCP) reconstituted with Chl a or Chl b pigments as the system of interest and compare our work with data obtained by Pieper and co-workers from differential fluorescence line-narrowing spectra (Pieper et al. J. Phys. Chem. B 2011, 115 (14), 4042-4052). Our results demonstrate that the use of QM/MM MD simulations where the nuclear positions are still propagated at the classical level leads to a striking improvement of the predicted spectral densities in the middle- and high-frequency regions, where they nearly reach quantitative accuracy. This demonstrates that the so-called "geometry mismatch" problem related to the use of low-quality structures in QM calculations, not the quantum features of pigments high-frequency motions, causes the failure of previous studies relying on similar protocols. Thus, this work paves the way toward quantitative predictions of pigment-protein coupling and the comprehension of quantum coherence effects in photosynthesis.
Zavaglia, Melissa; Astolfi, Laura; Babiloni, Fabio; Ursino, Mauro
2008-01-01
In the present work, a neural mass model consisting of four interconnected neural groups (pyramidal neurons, excitatory interneurons, inhibitory interneurons with slow synaptic kinetics, and inhibitory interneurons with fast synaptic kinetics) is used to investigate the mechanisms which cause the appearance of multiple rhythms in EEG spectra, and to assess how these rhythms can be affected by connectivity among different populations. In particular, we analyze a circuit, composed of three interconnected populations, each with a different synaptic kinetics (hence, with a different intrinsic rhythm). Results demonstrate that a single population can exhibit many different simultaneous rhythms, provided that some of these come from external sources (for instance, from remote regions). Analysis of coherence, and of the position of peaks in power spectral density, reveals important information on the possible connections among populations, especially useful to follow temporal changes in connectivity. Subsequently, the model is validated by comparing the power spectral density simulated in one population with that computed in the controlateral cingulated cortex (a region involved in motion preparation) during a right foot movement task in four normal subjects. The model is able to simulate real spectra quite well with only moderate parameter changes within the subject. In perspective, the results may be of value for a deeper comprehension of mechanism causing EEGs rhythms, for the study of brain connectivity and for the test of neurophysiological hypotheses.
Welch, William R W; Kubelka, Jan; Keiderling, Timothy A
2013-09-12
Infrared (IR), Raman, and vibrational circular dichroism (VCD) spectral variations for different β-sheet structures were studied using simulations based on density functional theory (DFT) force field and intensity computations. The DFT vibrational parameters were obtained for β-sheet fragments containing nine-amides and constrained to a variety of conformations and strand arrangements. These were subsequently transferred onto corresponding larger β-sheet models, normally consisting of five strands with ten amides each, for spectral simulations. Further extension to fibril models composed of multiple stacked β-sheets was achieved by combining the transfer of DFT parameters for each sheet with dipole coupling methods for interactions between sheets. IR spectra of the amide I show different splitting patterns for parallel and antiparallel β-sheets, and their VCD, in the absence of intersheet stacking, have distinct sign variations. Isotopic labeling by (13)C of selected residues yields spectral shifts and intensity changes uniquely sensitive to relative alignment of strands (registry) for antiparallel sheets. Stacking of multiple planar sheets maintains the qualitative spectral character of the single sheet but evidences some reduction in the exciton splitting of the amide I mode. Rotating sheets with respect to each other leads to a significant VCD enhancement, whose sign pattern and intensity is dependent on the handedness and degree of rotation. For twisted β-sheets, a significant VCD enhancement is computed even for sheets stacked with either the same or opposite alignments and the inter-sheet rotation, depending on the sense, can either further increase or weaken the enhanced VCD intensity. In twisted, stacked structures (without rotation), similar VCD amide I patterns (positive couplets) are predicted for both parallel and antiparallel sheets, but different IR intensity distributions still enable their differentiation. Our simulation results prove useful
NASA Astrophysics Data System (ADS)
Motamarri, Phani; Gavini, Vikram
2014-09-01
We present a subspace projection technique to conduct large-scale Kohn-Sham density functional theory calculations using higher-order spectral finite-element discretization. The proposed method treats both metallic and insulating materials in a single framework and is applicable to both pseudopotential as well as all-electron calculations. The key ideas involved in the development of this method include: (i) employing a higher-order spectral finite-element basis that is amenable to mesh adaption; (ii) using a Chebyshev filter to construct a subspace, which is an approximation to the occupied eigenspace in a given self-consistent field iteration; (iii) using a localization procedure to construct a nonorthogonal localized basis spanning the Chebyshev filtered subspace; and (iv) using a Fermi-operator expansion in terms of the subspace-projected Hamiltonian represented in the nonorthogonal localized basis to compute relevant quantities like the density matrix, electron density, and band energy. We demonstrate the accuracy and efficiency of the proposed approach on benchmark systems involving pseudopotential calculations on aluminum nanoclusters up to 3430 atoms and on alkane chains up to 7052 atoms, as well as all-electron calculations on silicon nanoclusters up to 3920 electrons. The benchmark studies revealed that accuracies commensurate with chemical accuracy can be obtained with the proposed method, and a subquadratic-scaling with system size was observed for the range of materials systems studied. In particular, for the alkane chains—representing an insulating material—close to linear scaling is observed, whereas, for aluminum nanoclusters—representing a metallic material—the scaling is observed to be O (N1.46). For all-electron calculations on silicon nanoclusters, the scaling with the number of electrons is computed to be O (N1.75). In all the benchmark systems, significant computational savings have been realized with the proposed approach, with
NASA Astrophysics Data System (ADS)
Rudnick, Gregory; Labbé, Ivo; Förster Schreiber, Natascha M.; Wuyts, Stijn; Franx, Marijn; Finlator, Kristian; Kriek, Mariska; Moorwood, Alan; Rix, Hans-Walter; Röttgering, Huub; Trujillo, Ignacio; van der Wel, Arjen; van der Werf, Paul; van Dokkum, Pieter G.
2006-10-01
We present the evolution of the volume-averaged properties of the rest-frame optically luminous (LV>3×1010 h-270 Lsolar) galaxy population to z~3, determined from four disjoint deep fields. We characterize their rest-frame UV through optical properties via the mean SED. To measure evolution, we apply the selection criteria to a sample of galaxies from the SDSS and COMBO-17 survey. The mean rest-frame 2200 Å through V-band SED becomes steadily bluer with increasing redshift, but at all redshifts z<3 the mean SED falls within the range defined by ``normal'' galaxies in the nearby universe. We measure the mean stellar mass-to-light ratios (M*/L) and stellar mass densities (ρ*) by fitting models to the mean rest-frame UV-optical SEDs. The ρ* in galaxies selected at a fixed luminosity has increased by a factor of 3.5-7.9 from z=3 to 0.1. If we instead use our observed M*/LV evolution to select galaxies at a fixed mass, ρ* evolves by a factor of 5.3-16.7. After correcting to total, the measured ρ* at z<2 lie below the integral of the star formation rate density as a function of redshift as derived from UV-selected samples after a standard correction for extinction. We find large discrepancies between recent model predictions for the evolution of ρ* and our results, even when our observational selection is applied to the models. Finally, we determine that distant red galaxies (selected to have Js-Ks>2.3) in our LrestV-selected samples contribute 30% and 64% of the stellar mass budget at z~2 and z~2.8, respectively. These galaxies are largely absent from UV surveys, and this result highlights the need for mass selection of high-redshift galaxies. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. Also based on observations collected at the European Southern Observatories on
NASA Astrophysics Data System (ADS)
Suresh, M.; Syed Ali Padusha, M.; Bharanidharan, S.; Saleem, H.; Dhandapani, A.; Manivarman, S.
2015-06-01
The experimental and theoretical vibrational frequencies of a newly synthesized compound, namely 1-(quinolin-3-yl)piperidin-2-ol (QPPO) are analyzed. The experimental FT-IR (4000-400 cm-1) and FT-Raman (4000-100 cm-1) of the molecule in solid phase have been recorded. The optimized molecular structure, vibrational assignments of QPPO have been investigated experimentally and theoretically using Gaussian03W software package. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The first order hyperpolarizability (β0) is calculated to find its character in non-linear optics. Gauge including atomic orbital (GIAO) method is used to calculate 1H NMR chemical shift calculations were carried out and compared with experimental data. The electronic properties like UV-Visible spectral analysis and HOMO-LUMO energies were reported. The energy gap shows that the charge transfer occurs within the molecule. Thermodynamic parameters of the title compound were calculated at various temperatures.
Suresh, M; Padusha, M Syed Ali; Bharanidharan, S; Saleem, H; Dhandapani, A; Manivarman, S
2015-06-05
The experimental and theoretical vibrational frequencies of a newly synthesized compound, namely 1-(quinolin-3-yl)piperidin-2-ol (QPPO) are analyzed. The experimental FT-IR (4000-400 cm(-1)) and FT-Raman (4000-100 cm(-1)) of the molecule in solid phase have been recorded. The optimized molecular structure, vibrational assignments of QPPO have been investigated experimentally and theoretically using Gaussian03W software package. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The first order hyperpolarizability (β0) is calculated to find its character in non-linear optics. Gauge including atomic orbital (GIAO) method is used to calculate (1)H NMR chemical shift calculations were carried out and compared with experimental data. The electronic properties like UV-Visible spectral analysis and HOMO-LUMO energies were reported. The energy gap shows that the charge transfer occurs within the molecule. Thermodynamic parameters of the title compound were calculated at various temperatures.
NASA Astrophysics Data System (ADS)
Ito, Fumiyuki
2010-12-01
The supermolecule approach has been used to model molecules embedded in solid argon matrix, wherein interaction between the guest and the host atoms in the first solvation shell is evaluated with the use of density functional calculations. Structural stability and simulated spectra have been obtained for formic acid dimer (FAD)-Arn (n = 21-26) clusters. The calculations at the B971/6-31++G(3df,3pd) level have shown that the tetrasubstitutional site on Ar(111) plane is likely to incorporate FAD most stably, in view of consistency with the matrix shifts available experimentally.
NASA Technical Reports Server (NTRS)
Carrier, J.; Land, S.; Buysse, D. J.; Kupfer, D. J.; Monk, T. H.
2001-01-01
The effects of age and gender on sleep EEG power spectral density were assessed in a group of 100 subjects aged 20 to 60 years. We propose a new statistical strategy (mixed-model using fixed-knot regression splines) to analyze quantitative EEG measures. The effect of gender varied according to frequency, but no interactions emerged between age and gender, suggesting that the aging process does not differentially influence men and women. Women had higher power density than men in delta, theta, low alpha, and high spindle frequency range. The effect of age varied according to frequency and across the night. The decrease in power with age was not restricted to slow-wave activity, but also included theta and sigma activity. With increasing age, the attenuation over the night in power density between 1.25 and 8.00 Hz diminished, and the rise in power between 12.25 and 14.00 Hz across the night decreased. Increasing age was associated with higher power in the beta range. These results suggest that increasing age may be related to an attenuation of homeostatic sleep pressure and to an increase in cortical activation during sleep.
NASA Technical Reports Server (NTRS)
Carrier, J.; Land, S.; Buysse, D. J.; Kupfer, D. J.; Monk, T. H.
2001-01-01
The effects of age and gender on sleep EEG power spectral density were assessed in a group of 100 subjects aged 20 to 60 years. We propose a new statistical strategy (mixed-model using fixed-knot regression splines) to analyze quantitative EEG measures. The effect of gender varied according to frequency, but no interactions emerged between age and gender, suggesting that the aging process does not differentially influence men and women. Women had higher power density than men in delta, theta, low alpha, and high spindle frequency range. The effect of age varied according to frequency and across the night. The decrease in power with age was not restricted to slow-wave activity, but also included theta and sigma activity. With increasing age, the attenuation over the night in power density between 1.25 and 8.00 Hz diminished, and the rise in power between 12.25 and 14.00 Hz across the night decreased. Increasing age was associated with higher power in the beta range. These results suggest that increasing age may be related to an attenuation of homeostatic sleep pressure and to an increase in cortical activation during sleep.
Chandrasekaran, Suryanarayanan; Aghtar, Mortaza; Valleau, Stéphanie; Aspuru-Guzik, Alán; Kleinekathöfer, Ulrich
2015-08-06
Studies on light-harvesting (LH) systems have attracted much attention after the finding of long-lived quantum coherences in the exciton dynamics of the Fenna–Matthews–Olson (FMO) complex. In this complex, excitation energy transfer occurs between the bacteriochlorophyll a (BChl a) pigments. Two quantum mechanics/molecular mechanics (QM/MM) studies, each with a different force-field and quantum chemistry approach, reported different excitation energy distributions for the FMO complex. To understand the reasons for these differences in the predicted excitation energies, we have carried out a comparative study between the simulations using the CHARMM and AMBER force field and the Zerner intermediate neglect of differential orbital (ZINDO)/S and time-dependent density functional theory (TDDFT) quantum chemistry methods. The calculations using the CHARMM force field together with ZINDO/S or TDDFT always show a wider spread in the energy distribution compared to those using the AMBER force field. High- or low-energy tails in these energy distributions result in larger values for the spectral density at low frequencies. A detailed study on individual BChl a molecules in solution shows that without the environment, the density of states is the same for both force field sets. Including the environmental point charges, however, the excitation energy distribution gets broader and, depending on the applied methods, also asymmetric. The excitation energy distribution predicted using TDDFT together with the AMBER force field shows a symmetric, Gaussian-like distribution.
Suresh, M; Syed Ali Padusha, M; Govindarasu, K; Kavitha, E
2015-03-05
The organic compound 1-(pyrazin-2-yl) piperidin-2-ol (abbreviated as PPOL) has been synthesized and characterized by IR, Raman, (1)H NMR and UV-Vis spectroscopy. The Fourier-transform Raman (3500-50cm(-1)) and infrared spectra (4000-400cm(-1)) were recorded in the solid state and interpreted by comparison with theoretical spectra derived from density functional theory (DFT) calculations. The optimized geometry, frequency and intensity of the vibrational bands of the compound was obtained by the density functional theory using 6-31G(d,p) basis set. In the optimized geometry results shows that geometry parameters are good agreement with XRD values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. (1)H NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. (1)H NMR analysis is evident for O-H⋯O intermolecular interaction of the title molecule. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp,m), standard entropies (Sm) and standard enthalpy changes (Hm) increase with rise in temperature. In addition, HOMO and LUMO energies and the first-order hyperpolarizability have been computed.
NASA Astrophysics Data System (ADS)
Govindasamy, P.; Gunasekaran, S.; Ramkumaar, G. R.
2014-09-01
The Fourier transform infrared (FT-IR) and FT-Raman spectra of N-(4-hydroxy phenyl) acetamide (N4HPA) of painkiller agent were recorded in the region 4000-450 cm-1 and 4000-50 cm-1 respectively. Density functional theory (DFT) has been used to calculate the optimized geometrical parameter, atomic charges, and vibrational wavenumbers and intensity of the vibrational bands. The computed vibrational wave numbers were compared with the FT-IR and FT-Raman experimental data. The computational calculations at DFT/B3LYP level with 6-31G(d,p), 6-31++G(d,p), 6-311G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes calculated using Vibrational energy distribution analysis (VEDA 4) program. The oscillator’s strength calculated by TD-DFT and N4HPA is approach complement with the experimental findings. The NMR chemical shifts 13C and 1H were recorded and calculated using the gauge independent atomic orbital (GIAO) method. The molecular electrostatic potential (MESP) and electron density surfaces of the molecule were constructed. The Natural charges and intermolecular contacts have been interpreted using Natural Bond orbital (NBO) analysis the HOMO-LUMO energy gap has been calculated. The thermodynamic properties like entropy, heat capacity and zero vibrational energy have been calculated.
Govindasamy, P; Gunasekaran, S; Ramkumaar, G R
2014-09-15
The Fourier transform infrared (FT-IR) and FT-Raman spectra of N-(4-hydroxy phenyl) acetamide (N4HPA) of painkiller agent were recorded in the region 4000-450 cm(-1) and 4000-50 cm(-1) respectively. Density functional theory (DFT) has been used to calculate the optimized geometrical parameter, atomic charges, and vibrational wavenumbers and intensity of the vibrational bands. The computed vibrational wave numbers were compared with the FT-IR and FT-Raman experimental data. The computational calculations at DFT/B3LYP level with 6-31G(d,p), 6-31++G(d,p), 6-311G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes calculated using Vibrational energy distribution analysis (VEDA 4) program. The oscillator's strength calculated by TD-DFT and N4HPA is approach complement with the experimental findings. The NMR chemical shifts 13C and 1H were recorded and calculated using the gauge independent atomic orbital (GIAO) method. The molecular electrostatic potential (MESP) and electron density surfaces of the molecule were constructed. The Natural charges and intermolecular contacts have been interpreted using Natural Bond orbital (NBO) analysis the HOMO-LUMO energy gap has been calculated. The thermodynamic properties like entropy, heat capacity and zero vibrational energy have been calculated.
NASA Astrophysics Data System (ADS)
Suresh, M.; Syed Ali Padusha, M.; Govindarasu, K.; Kavitha, E.
2015-03-01
The organic compound 1-(pyrazin-2-yl) piperidin-2-ol (abbreviated as PPOL) has been synthesized and characterized by IR, Raman, 1H NMR and UV-Vis spectroscopy. The Fourier-transform Raman (3500-50 cm-1) and infrared spectra (4000-400 cm-1) were recorded in the solid state and interpreted by comparison with theoretical spectra derived from density functional theory (DFT) calculations. The optimized geometry, frequency and intensity of the vibrational bands of the compound was obtained by the density functional theory using 6-31G(d,p) basis set. In the optimized geometry results shows that geometry parameters are good agreement with XRD values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. 1H NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. 1H NMR analysis is evident for O-H⋯O intermolecular interaction of the title molecule. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp,m), standard entropies (Sm) and standard enthalpy changes (Hm) increase with rise in temperature. In addition, HOMO and LUMO energies and the first-order hyperpolarizability have been computed.
Krishnakumar, V; Jayamani, N; Mathammal, R
2011-09-01
In this work, the experimental and theoretical vibrational spectra of pyrazole (PZ) and 3,5-dimethyl pyrazole (DMP) have been studied. FTIR and FT-Raman spectra of the title compounds in the solid phase are recorded in the region 4000-400 cm(-1) and 4000-50 cm(-1), respectively. The structural and spectroscopic data of the molecules in the ground state are calculated using density functional methods (B3LYP) with 6-311+G** basis set. The vibrational frequencies are calculated and scaled values are compared with experimental FTIR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete vibrational assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SM) method. 13C and 1H NMR chemical shifts results are compared with the experimental values.
NASA Technical Reports Server (NTRS)
Kunc, Joseph A.
1988-01-01
A novel approach for calculating the populations of the excited Li-like ions C IV, N V, O VI, and Ne VIII is presented. The populations of the 2(2P), 3(2S), 3(2P), and 3(2D) electronic levels in these ions in optically thin plasmas with a broad range of electron density, N(e), and temperature, T(e), are determined from the collisional-radiative model by solving the system of rate equations for the production of excited ions; the equations are linear with respect to the excited ion populations, and the N(e) and T(e) are taken as independent variables. These populations are used to determine the ratios of line intensities for dipole allowed transitions between various energy levels. This approach can be applied to impurities other than the lithiumlike ions and is especially useful for diagnostics of systems where nonintrusive spectroscopic techniques must be used.
NASA Astrophysics Data System (ADS)
Lago, A.; Alves, L. R.; Braga, C. R.; Mendonca, R. R. S.; Jauer, P. R.; Medeiros, C.; Souza, V. M. C. E. S.; Mendes, O., Jr.; Marchezi, J.; da Silva, L.; Vieira, L.; Rockenbach, M.; Sibeck, D. G.; Kanekal, S. G.; Baker, D. N.; Wygant, J. R.; Kletzing, C.
2016-12-01
The solar wind incident upon the Earth's magnetosphere can produce either enhancement, depletion or no change in the flux of relativistic electrons at the outer radiation belt. During geomagnetic storms progress, solar wind parameters may change significantly, and occasionally relativistic electron fluxes at the outer radiation belt show dropouts in a range of energy and L-shells. Wave-particle interactions observed within the Van Allen belts have been claimed to play a significant role in energetic particle flux changes. The relation between changes on the solar wind parameters and the radiation belt is still a hot topic nowadays, particularly the role played by the solar wind on sudden electron flux decreases. The twin satellite Van Allen Probes measured a relativistic electron flux dropout concurrent to broad band Ultra-low frequency (ULF) waves, i.e. from 1 mHz to 10 Hz, on October 2, 2013. Magnetic field and plasma data from both ACE and WIND satellites allowed the characterization of this event as being an interplanetary coronal mass ejection in conjunction with shock. The interaction of this event with the Earth's magnetosphere was modeled using a global magnetohydrodynamic simulation and the magnetic field perturbation deep in magnetosphere could be analyzed from the model outputs. Results show the contribution of time-varying solar wind parameters to the generation of ULF waves. The power spectral densities, as a function of L-shell, were evaluated considering changes in the input parameters, e.g. magnitude and duration of dynamic pressure and magnetic field. The modeled power spectral densities are compared with Van Allen Probes data. The results provide us a clue on the solar wind characteristics that might be able to drive ULF waves in the inner magnetosphere, and also which wave modes are expected to be excited under a specific solar wind driving.
NASA Astrophysics Data System (ADS)
Gorgas, T. J.; Tada, R.; Irino, T.; Clemens, S. C.; Ziegler, M.; Holbourn, A. E.; Murray, R. W.; Alvarez Zarikian, C. A.
2014-12-01
Sedimentation Rates (SRs) for IODP Site U1424 in the Japan Basin (40o11.40'N, 138o13.90'E) were calculated by performing spectral analysis in the depth domain on both RGB color and Gamma-Ray-Attenuation (GRA) bulk density data. Inversion and integration of SRs versus depth from spectral analysis yielded detailed SR profiles in both time and depth domains. Our results show a greater variability in calculated SR's, which differed from those established through coarse-scaled biostratigraphic and paleomagnetic data. SR profiles from our analysis exhibit similar excursions and features in both depth and age domains, with GRA representing a smoothed version of the SR profile derived from RGB data while exhibiting slight offsets in high-to-low SRs downhole versus those observed in RBG data. Both GRA and RGB profiles show a distinct periodicity in the waveband of Milankovitch cycles. The pronounced Milankovitch cyclicity suggests that climate variability and trends in SRs at Site U1424 was responding to insolation patterns during the past 4.5 Myr. A dominance of the 100 ky cycle (eccentricity) throughout the entire normalized spectral amplitude profile might be observed; however, for the purpose of fine-tuning our high-resolution Age-Depth model to fit the low-resolution Age-Depth model from biostratigraphic and paleomagnetic data, choosing obliquity (41 ky) and precession (19-23 ky) cycles as tuning-frequency produced a closer fit between high-and-low-resolution models than using the prominent eccentricity cycles (100 and 400 ky). Relatively low SRs are found when evolutive amplitude spectra are dominated by obliquity and eccentricity periods. In contrast, significant SR peaks at Site U1424 often occur when strong precessional amplitudes coexist with obliquity and eccentricity cycles. Lower SR values at Site U1424 are interpreted to reflect a decrease in diatom flux and relative increase in detrital fraction. By contrast moderate to higher SRs were associated with lower
NASA Astrophysics Data System (ADS)
Islam, Nasarul; Niaz, Saba; Manzoor, Taniya; Pandith, Altaf Hussain
2014-10-01
The density functional theoretical (DFT) computations were performed at the B3LYP/6-311G++(d, p) level to calculate the equilibrium geometry, vibrational wave numbers, intensities, and various other molecular properties of brucine and strychnine, which were found in satisfactory agreement with the experimental data. The out-of-phase stretching modes of aromatic rings and carbonyl stretching modes in combination with CH stretching modes at stereogenic centers generate VCD signals, which are remarkably efficient configuration markers for these chiral molecular systems. NBOs analysis reveals that the large values of second order perturbation energy (47.24 kcal/mol for brucine and 46.93 kcal/mol for strychnine) confirms strong hyperconjugative interaction between the orbital containing the lone pair of electron of nitrogen and the neighboring Cdbnd O antibonding orbital. The molecular electrostatic potential map of strychnine molecule, with no polar groups other than the lone keto group, shows less polarization, which accounts for its lower susceptibility towards electrophilic attack as compared to brucine.
Islam, Nasarul; Niaz, Saba; Manzoor, Taniya; Pandith, Altaf Hussain
2014-10-15
The density functional theoretical (DFT) computations were performed at the B3LYP/6-311G++(d, p) level to calculate the equilibrium geometry, vibrational wave numbers, intensities, and various other molecular properties of brucine and strychnine, which were found in satisfactory agreement with the experimental data. The out-of-phase stretching modes of aromatic rings and carbonyl stretching modes in combination with CH stretching modes at stereogenic centers generate VCD signals, which are remarkably efficient configuration markers for these chiral molecular systems. NBOs analysis reveals that the large values of second order perturbation energy (47.24kcal/mol for brucine and 46.93kcal/mol for strychnine) confirms strong hyperconjugative interaction between the orbital containing the lone pair of electron of nitrogen and the neighboring CO antibonding orbital. The molecular electrostatic potential map of strychnine molecule, with no polar groups other than the lone keto group, shows less polarization, which accounts for its lower susceptibility towards electrophilic attack as compared to brucine.
Jone Pradeepa, S; Sundaraganesan, N
2014-05-05
In this present investigation, the collective experimental and theoretical study on molecular structure, vibrational analysis and NBO analysis has been reported for 2-aminofluorene. FT-IR spectrum was recorded in the range 4000-400 cm(-1). FT-Raman spectrum was recorded in the range 4000-50 cm(-1). The molecular geometry, vibrational spectra, and natural bond orbital analysis (NBO) were calculated for 2-aminofluorene using Density Functional Theory (DFT) based on B3LYP/6-31G(d,p) model chemistry. (13)C and (1)H NMR chemical shifts of 2-aminofluorene were calculated using GIAO method. The computed vibrational and NMR spectra were compared with the experimental results. The total energy distribution (TED) was derived to deepen the understanding of different modes of vibrations contributed by respective wavenumber. The experimental UV-Vis spectra was recorded in the region of 400-200 nm and correlated with simulated spectra by suitably solvated B3LYP/6-31G(d,p) model. The HOMO-LUMO energies were measured with time dependent DFT approach. The nonlinearity of the title compound was confirmed by hyperpolarizabilty examination. Using theoretical calculation Molecular Electrostatic Potential (MEP) was investigated.
Wu, Xiaomeng; Gao, Simin; Wang, Jia-Sheng; Wang, Hongyan; Huang, Yao-Wen; Zhao, Yiping
2012-09-21
High-quality surface-enhanced Raman scattering (SERS) spectra of aflatoxin (AF) B(1), B(2), G(1) and G(2) have been acquired using silver nanorod (AgNR) array substrates fabricated by oblique angle deposition method. Significant vibrational peaks are identified on the argon plasma-cleaned substrates, and those peaks agree very well with the Raman spectra calculated by density function theory (DFT). The concentration-dependent SERS detection is also explored. The relationship between the concentration (C) of different AFs and the SERS intensity (I) of the Raman peak at Δν = 1592 cm(-1) is found to follow the general relationship I = AC(α), with α ranging from 0.32 to 0.46 for the four AFs. The limits of detection (LODs) reach 5 × 10(-5) mol L(-1) for AFB(1), 1 × 10(-4) mol L(-1) for AFB(2), and 5 × 10(-6) mol L(-1) for both AFG(1) and AFG(2) in bulk solution, or 6.17 × 10(-16) mol/1.93 × 10(-4) ng of AFB(1), 1.23 × 10(-15) mol/3.88 × 10(-4) ng for AFB(2), 6.17 × 10(-17) mol/2.03 × 10(-5) ng for AFG(1), and 6.17 × 10(-17) mol/2.04 × 10(-5) ng for AFG(2) per laser spot. Principal component analysis (PCA) is used to successfully differentiate these four different kinds of AFs at different concentrations up to their detection limits. The LODs obtained from PCA agree with the LODs obtained by using peak fitting method. With such a low detection limit and outstanding differentiation ability, we prove the possibility of utilizing the SERS detection system as a platform for highly sensitive mycotoxin detection.
Murakami, Keach; Matsuda, Ryo; Fujiwara, Kazuhiro
2016-10-01
The net photosynthetic rate of a leaf becomes acclimated to the plant's environment during growth. These rates are often measured, evaluated and compared among leaves of plants grown under different light conditions. In this study, we compared net photosynthetic rates of cucumber leaves grown under white light-emitting diode (LED) light without and with supplemental far-red (FR) LED light (W- and WFR-leaves, respectively) under three different measuring light (ML) conditions: their respective growth light (GL), artificial sunlight (AS) and blue and red (BR) light. The difference in the measured photosynthetic rates between W- and WFR-leaves was greater under BR than under GL and AS. In other words, an interaction between supplemental FR light during growth and the spectral photon flux density distribution (SPD) of ML affected the measured net photosynthetic rates. We showed that the comparison and evaluation of leaf photosynthetic rates and characteristics can be biased depending on the SPD of ML, especially for plants grown under different photon flux densities in the FR waveband. We also investigated the mechanism of the interaction. We confirmed that the distribution of excitation energy between the two photosystems (PSs) changed in response to the SPD of GL, and that this change resulted in the interaction, as suggested in previous reports. However, changes in PS stoichiometry could not completely explain the adjustment in excitation energy distribution observed in this study, suggesting that other mechanisms may be involved in the interaction.
Martinez-Gonzalez, Dolores; Lesku, John A; Rattenborg, Niels C
2008-06-01
Birds provide a unique opportunity to evaluate current theories for the function of sleep. Like mammalian sleep, avian sleep is composed of two states, slow-wave sleep (SWS) and rapid eye-movement (REM) sleep that apparently evolved independently in mammals and birds. Despite this resemblance, however, it has been unclear whether avian SWS shows a compensatory response to sleep loss (i.e., homeostatic regulation), a fundamental aspect of mammalian sleep potentially linked to the function of SWS. Here, we prevented pigeons (Columba livia) from taking their normal naps during the last 8 h of the day. Although time spent in SWS did not change significantly following short-term sleep deprivation, electroencephalogram (EEG) slow-wave activity (SWA; i.e., 0.78-2.34 Hz power density) during SWS increased significantly during the first 3 h of the recovery night when compared with the undisturbed night, and progressively declined thereafter in a manner comparable to that observed in similarly sleep-deprived mammals. SWA was also elevated during REM sleep on the recovery night, a response that might reflect increased SWS pressure and the concomitant 'spill-over' of SWS-related EEG activity into short episodes of REM sleep. As in rodents, power density during SWS also increased in higher frequencies (9-25 Hz) in response to short-term sleep deprivation. Finally, time spent in REM sleep increased following sleep deprivation. The mammalian-like increase in EEG spectral power density across both low and high frequencies, and the increase in time spent in REM sleep following sleep deprivation suggest that some aspects of avian and mammalian sleep are regulated in a similar manner.
NASA Astrophysics Data System (ADS)
Gorgas, Thomas; Irino, Tomohisa; Tada, Ryuji
2016-04-01
Sedimentation Rates (SRs) for IODP Sites U1424 (lat/lon coordinates: 40o11.40'N, 138o13.90'E; water depth: 2808 mbsl) and U1427 (lat/lon coordinates: 35o57.92'N, 134o26.06'E; water depth: 330 mbsl) were calculated by performing spectral analysis in the depth domain on both RGB color and Gamma-Ray-Attenuation (GRA) bulk density data. Inversion and integration of SRs versus depth from spectral analysis yielded detailed SR profiles in both time and depth domains. Our results show a greater variability in calculated SRs and differed from those established through coarse-scaled biostratigraphy and paleo-magnetic data. Our data analyses produces pulses of distinct high SRs for certain depth/age intervals at both sites, with time lags for such features possibly due to variable oceanographic conditions near-shore for Site U1427 versus those at Site U1424 further offshore. Both GRA and RGB profiles reveal a distinct periodicity in the waveband of Milankovitch cycles and other prominent periodicities in the 10-to-1ky period range. This observation suggests climate variabilities and trends in SRs responding to insolation patterns during the past 1 Myr at both sites and extending to 4.5 Myr for Site U1424. With only few identified eccentricity (100ky) cycle segments throughout the entire normalized spectral amplitude profile, our high-resolution Age-Depth model was tuned to obliquity (41ky) and precessional (19-23ky) cycles to achieving a strong fit with corresponding low-resolution models based on biostratigraphy, paleo-magnetic and, at least for Site U1424, augmenting volcanostratigraphy data. According to our Age-Depth models, relatively low SRs occur when evolutive amplitude spectra are dominated by periods in the range of obliquity and eccentricity. In contrast, significant SR peaks at both sites often occur when strong precessional amplitudes coexist with all other cycles. Lower SRs at Site U1424 have been interpreted to reflect a decrease in diatom flux and relative
NASA Astrophysics Data System (ADS)
Trevelyan, Alexander; Corwin, Eric
2014-03-01
We explore the response of a model statistical system to strong, non-linear perturbations to its state variables. Specifically, we work with a tunable model of Johnson-Nyquist noise, designed to permit a driving of both the drift and diffusion terms in the associated White Noise Langevin Equation. We achieve a simultaneous measurement of both sides of the Fluctuation Dissipation Theorem (FDT) by driving the circuit with digitally generated white noise and measuring the output. This allows us to calculate a frequency-dependent effective temperature for the driven system, which for an equilibrium system should be set by the energy scale of the input white noise. Comparison of the two sides of FDT-the circuit's transfer function and the power spectral density of the voltage fluctuations-across frequency-space proves non-trivial, and methods are discussed for achieving the most reliable estimate. After comparing the response for a series of functional signals, we find that FDT, measured in this simultaneous fashion, remains intact even while the system is being actively driven out of equilibrium.
NASA Astrophysics Data System (ADS)
Gupta, S.; Vierkant, G. P.
2014-09-01
The evolution of the surface roughness of growing metal or semiconductor thin films provides much needed information about their growth kinetics and corresponding mechanism. While some systems show stages of nucleation, coalescence, and growth, others exhibit varying microstructures for different process conditions. In view of these classifications, we report herein detailed analyses based on atomic force microscopy (AFM) characterization to extract the surface roughness and growth kinetics exponents of relatively low boron-doped diamond (BDD) films by utilizing the analytical power spectral density (PSD) and autocorrelation function (ACF) as mathematical tools. The machining industry has applied PSD for a number of years for tool design and analysis of wear and machined surface quality. Herein, we present similar analyses at the mesoscale to study the surface morphology as well as quality of BDD films grown using the microwave plasma-assisted chemical vapor deposition technique. PSD spectra as a function of boron concentration (in gaseous phase) are compared with those for samples grown without boron. We find that relatively higher boron concentration yields higher amplitudes of the longer-wavelength power spectral lines, with amplitudes decreasing in an exponential or power-law fashion towards shorter wavelengths, determining the roughness exponent ( α ≈ 0.16 ± 0.03) and growth exponent ( β ≈ 0.54), albeit indirectly. A unique application of the ACF, which is widely used in signal processing, was also applied to one-dimensional or line analyses (i.e., along the x- and y-axes) of AFM images, revealing surface topology datasets with varying boron concentration. Here, the ACF was used to cancel random surface "noise" and identify any spatial periodicity via repetitive ACF peaks or spatially correlated noise. Periodicity at shorter spatial wavelengths was observed for no doping and low doping levels, while smaller correlations were observed for relatively
NASA Astrophysics Data System (ADS)
Zhang, Zu-Quan; Li, Shuai; Lü, Jing-Tao; Gao, Jin-Hua
2017-08-01
Recently, the existence of local magnetic moment in a hydrogen adatom on graphene was confirmed experimentally [González-Herrero et al., Science 352, 437 (2016), 10.1126/science.aad8038]. Inspired by this breakthrough, we theoretically investigate the top-site adatom on trilayer graphene (TLG) by solving the Anderson impurity model via self-consistent mean field method. The influence of the stacking order, the adsorption site, and external electric field are carefully considered. We find that, due to its unique electronic structure, the situation of TLG is drastically different from that of the monolayer graphene. First, the adatom on rhombohedral stacked TLG (r-TLG) can have a Fano-shaped impurity spectral density, instead of the normal Lorentzian-like one, when the impurity level is around the Fermi level. Second, the impurity level of the adatom on r-TLG can be tuned into an in-gap state by an external electric field, which strongly depends on the direction of the applied electric field and can significantly affect the local magnetic moment formation. Finally, we systematically calculate the impurity magnetic phase diagrams, considering various stacking orders, adsorption sites, doping, and electric field. We show that, because of the in-gap state, the impurity magnetic phase of r-TLG will obviously depend on the direction of the applied electric field as well. All our theoretical results can be readily tested in experiment, and may give a comprehensive understanding about the local magnetic moment of an adatom on TLG.
Pettersen, Klas H; Lindén, Henrik; Tetzlaff, Tom; Einevoll, Gaute T
2014-11-01
Power laws, that is, power spectral densities (PSDs) exhibiting 1/f(α) behavior for large frequencies f, have been observed both in microscopic (neural membrane potentials and currents) and macroscopic (electroencephalography; EEG) recordings. While complex network behavior has been suggested to be at the root of this phenomenon, we here demonstrate a possible origin of such power laws in the biophysical properties of single neurons described by the standard cable equation. Taking advantage of the analytical tractability of the so called ball and stick neuron model, we derive general expressions for the PSD transfer functions for a set of measures of neuronal activity: the soma membrane current, the current-dipole moment (corresponding to the single-neuron EEG contribution), and the soma membrane potential. These PSD transfer functions relate the PSDs of the respective measurements to the PSDs of the noisy input currents. With homogeneously distributed input currents across the neuronal membrane we find that all PSD transfer functions express asymptotic high-frequency 1/f(α) power laws with power-law exponents analytically identified as α∞(I) = 1/2 for the soma membrane current, α∞(p) = 3/2 for the current-dipole moment, and α∞(V) = 2 for the soma membrane potential. Comparison with available data suggests that the apparent power laws observed in the high-frequency end of the PSD spectra may stem from uncorrelated current sources which are homogeneously distributed across the neural membranes and themselves exhibit pink (1/f) noise distributions. While the PSD noise spectra at low frequencies may be dominated by synaptic noise, our findings suggest that the high-frequency power laws may originate in noise from intrinsic ion channels. The significance of this finding goes beyond neuroscience as it demonstrates how 1/f(α) power laws with a wide range of values for the power-law exponent α may arise from a simple, linear partial differential equation.
Pettersen, Klas H.; Lindén, Henrik; Tetzlaff, Tom; Einevoll, Gaute T.
2014-01-01
Power laws, that is, power spectral densities (PSDs) exhibiting behavior for large frequencies f, have been observed both in microscopic (neural membrane potentials and currents) and macroscopic (electroencephalography; EEG) recordings. While complex network behavior has been suggested to be at the root of this phenomenon, we here demonstrate a possible origin of such power laws in the biophysical properties of single neurons described by the standard cable equation. Taking advantage of the analytical tractability of the so called ball and stick neuron model, we derive general expressions for the PSD transfer functions for a set of measures of neuronal activity: the soma membrane current, the current-dipole moment (corresponding to the single-neuron EEG contribution), and the soma membrane potential. These PSD transfer functions relate the PSDs of the respective measurements to the PSDs of the noisy input currents. With homogeneously distributed input currents across the neuronal membrane we find that all PSD transfer functions express asymptotic high-frequency power laws with power-law exponents analytically identified as for the soma membrane current, for the current-dipole moment, and for the soma membrane potential. Comparison with available data suggests that the apparent power laws observed in the high-frequency end of the PSD spectra may stem from uncorrelated current sources which are homogeneously distributed across the neural membranes and themselves exhibit pink () noise distributions. While the PSD noise spectra at low frequencies may be dominated by synaptic noise, our findings suggest that the high-frequency power laws may originate in noise from intrinsic ion channels. The significance of this finding goes beyond neuroscience as it demonstrates how power laws with a wide range of values for the power-law exponent α may arise from a simple, linear partial differential equation. PMID:25393030
Alderman, Oliver L G; Iuga, Dinu; Howes, Andrew P; Pike, Kevin J; Holland, Diane; Dupree, Ray
2013-06-07
High-resolution, solid-state (11)B NMR spectra have been obtained at high magnetic fields for a range of polycrystalline borates using double-rotation (DOR), multiple-quantum magic angle spinning and isotopic dilution. DOR linewidths can be less than 0.2 ppm in isotopically diluted samples, allowing highly accurate values for the isotropic chemical shift, δiso, and electric field gradient to be obtained. The experimental values are used as a test of density functional calculations using both projector augmented wave based CASTEP and WIEN2k. The CASTEP calculations of δiso are generally in very good agreement with experiment, having r.m.s. deviation 0.40 ppm. WIEN2k calculations of electric field gradient magnitude, CQ, and asymmetry, η, are also in excellent agreement with experiment, with r.m.s. deviations 0.038 MHz and 0.042 respectively. However, whilst CASTEP gives a similar deviation for η (0.043) it overestimates CQ by ∼15%. After scaling of the calculated electric field gradient by 0.842 the deviation in CQ is practically identical to that of the WIEN2k calculations. The spectral assignments that follow from the experimental and computational results allow identification of correlations between δiso and (a) the average B-O-B bond angle, θ[combining overline], for both three and four coordinated boron, giving δiso(B(III)) = (185.1 -θ[combining overline])/3.42 ppm and δiso(B(IV)) = (130.2 -θ[combining overline])/5.31 ppm; and (b) the ring-site T(3) unit trigonal planar angular deviation, Stri, giving δiso(T(3)(ring)) = (1.642 × 10(-2)-Stri)/(8.339 × 10(-4)) ppm.
NASA Astrophysics Data System (ADS)
Chatterjee, Monish R.; Mohamed, Fathi H. A.
2014-10-01
In recent research, propagation of plane electromagnetic (EM) waves through a turbulent medium with modified von Karman phase characteristics was modeled and numerically simulated using transverse planar apertures representing narrow phase turbulence along the propagation path. The case for extended turbulence was also studied by repeating the planar phase screens multiple times over the propagation path and incorporating diffractive effects via a split-step algorithm. The goal of the research reported here is to examine two random phenomena: (a) atmospheric turbulence due to von Karman-type phase fluctuations, and (b) chaos generated in an acousto-optic (A-O) Bragg cell under hybrid feedback. The latter problem has been thoroughly examined for its nonlinear dynamics and applications in secure communications. However, the statistical characteristics (such as the power spectral density (PSD)) of the chaos have not been estimated in recent work. To that end, treating the chaos phenomena as a random process, the time waveforms of the chaos intensity and their spectra are numerically evaluated over a (large) number of time iterations. These spectra are then averaged to derive the equivalent PSD of the A-O chaos. For the turbulence problem, an optical beam passing through an input pinhole is propagated through a random phase screen (placed at different locations) to a desired distance (typically near-field) under different levels of turbulence strength. The resulting spatial intensity profile is then averaged and the process repeated over a (large) number of pre-specified time intervals. From this data, once again, the turbulence PSD is calculated via the Fourier spectra of the average intensity snapshots. The results for the two systems are compared.
Mladenović, D; Hrnčić, D; Rašić-Marković, A; Macut, Dj; Stanojlović, O
Liver failure is associated with a neuropsychiatric syndrome, known as hepatic encephalopathy (HE). Finasteride, inhibitor of neurosteroid synthesis, may improve the course of HE. The aim of our study was to investigate the influence of finasteride on mean and relative power density of EEG bands, determined by spectral analysis, in rat model of thioacetamide-induced HE. Male Wistar rats were divided into groups: (1) control; (2) thioacetamide-treated group, TAA (900 mg/kg); (3) finasteride-treated group, FIN (150 mg/kg); and (4) group treated with finasteride (150 mg/kg) and thioacetamide (900 mg/kg), FIN + TAA. Daily doses of FIN (50 mg/kg) and TAA (300 mg/kg) were administered during 3 subsequent days, and in FIN + TAA group FIN was administered 2 h before every dose of TAA. EEG was recorded 22-24 h after treatment and analyzed by fast Fourier transformation. While TAA did not induce significant changes in the beta band, mean and relative power in this band were significantly higher in FIN + TAA versus control group (p < 0.01). TAA caused a significant decline in mean power in alpha, theta, and delta band, and in FIN + TAA group the mean power in these bands was significantly higher compared with control. While in TAA group relative power was significantly decreased in theta (p < 0.01) and increased in delta band (p < 0.01) versus control, the opposite changes were found in FIN + TAA group: an increase in theta (p < 0.01) and a decrease in delta relative power (p < 0.01). In this study, finasteride pretreatment caused EEG changes that correspond to mild TAA-induced HE.
Kropf, Pascal; Shmuel, Amir
2016-07-01
Estimation of current source density (CSD) from the low-frequency part of extracellular electric potential recordings is an unstable linear inverse problem. To make the estimation possible in an experimental setting where recordings are contaminated with noise, it is necessary to stabilize the inversion. Here we present a unified framework for zero- and higher-order singular-value-decomposition (SVD)-based spectral regularization of 1D (linear) CSD estimation from local field potentials. The framework is based on two general approaches commonly employed for solving inverse problems: quadrature and basis function expansion. We first show that both inverse CSD (iCSD) and kernel CSD (kCSD) fall into the category of basis function expansion methods. We then use these general categories to introduce two new estimation methods, quadrature CSD (qCSD), based on discretizing the CSD integral equation with a chosen quadrature rule, and representer CSD (rCSD), an even-determined basis function expansion method that uses the problem's data kernels (representers) as basis functions. To determine the best candidate methods to use in the analysis of experimental data, we compared the different methods on simulations under three regularization schemes (Tikhonov, tSVD, and dSVD), three regularization parameter selection methods (NCP, L-curve, and GCV), and seven different a priori spatial smoothness constraints on the CSD distribution. This resulted in a comparison of 531 estimation schemes. We evaluated the estimation schemes according to their source reconstruction accuracy by testing them using different simulated noise levels, lateral source diameters, and CSD depth profiles. We found that ranking schemes according to the average error over all tested conditions results in a reproducible ranking, where the top schemes are found to perform well in the majority of tested conditions. However, there is no single best estimation scheme that outperforms all others under all tested
2013-01-01
Background Observation of the signals recorded from the extremities of Parkinson’s disease patients showing rest and/or action tremor reveal a distinct high power resonance peak in the frequency band corresponding to tremor. The aim of the study was to investigate, using quantitative measures, how clinically effective and less effective deep brain stimulation protocols redistribute movement power over the frequency bands associated with movement, pathological and physiological tremor, and whether normal physiological tremor may reappear during those periods that tremor is absent. Methods The power spectral density patterns of rest and action tremor were studied in 7 Parkinson’s disease patients treated with (bilateral) deep brain stimulation of the subthalamic nucleus. Two tests were carried out: 1) the patient was sitting at rest; 2) the patient performed a hand or foot tapping movement. Each test was repeated four times for each extremity with different stimulation settings applied during each repetition. Tremor intermittency was taken into account by classifying each 3-second window of the recorded angular velocity signals as a tremor or non-tremor window. Results The distribution of power over the low frequency band (<3.5 Hz – voluntary movement), tremor band (3.5-7.5 Hz) and high frequency band (>7.5 Hz – normal physiological tremor) revealed that rest and action tremor show a similar power-frequency shift related to tremor absence and presence: when tremor is present most power is contained in the tremor frequency band; when tremor is absent lower frequencies dominate. Even under resting conditions a relatively large low frequency component became prominent, which seemed to compensate for tremor. Tremor absence did not result in the reappearance of normal physiological tremor. Conclusion Parkinson’s disease patients continuously balance between tremor and tremor suppression or compensation expressed by power shifts between the low frequency band and
Gubin, Mikhail A; Kireev, A N; Kozlovskii, Vladimir I; Korostelin, Yurii V; Pnev, A B; Podmar'kov, Yu P; Tyurikov, D A; Frolov, M P; Shelestov, D A; Shelkovnikov, Aleksandr S
2012-06-30
An optically pumped cw laser on a Cr{sup 2+} : ZnSe crystal with a tunable (in the range of 2.3 - 2 .6 mm) wavelength, operating with generation of two axial modes, has been developed. It is shown that the minimum laser frequency-noise spectral density does not exceed 0.03 Hz Hz{sup -1/2}. Application of this laser in problems of Doppler and Doppler-free spectroscopy makes it possible to detect spectral absorption lines of gases with sensitivities of 5 Multiplication-Sign 10{sup -12} and 2 Multiplication-Sign 10{sup -10} cm{sup -1}, respectively (averaging time {tau} = 1 s). Having stabilised this laser with respect to the Doppler-free resonances of saturated dispersion of methane molecule, one can obtain a short-term frequency stability of 10{sup -15} - 10{sup -16} ({tau} = 1 s).
W. J. Massman
2004-01-01
Atmospheric trace gas fluxes measured with an eddy covariance sensor that detects a constituent's density fluctuations within the in situ air need to include terms resulting from concurrent heat and moisture fluxes, the so called 'density' or 'WPL corrections' (Webb et al. 1980). The theory behind these additional terms is well established. But...
NASA Astrophysics Data System (ADS)
Gómez, J. M. Rodríguez; Vieira, L. E. Antunes; Lago, A. Dal; Palacios, J.; Balmaceda, L. A.; Stekel, T.
2017-10-01
Some key physical processes that impact the evolution of Earth's atmosphere on time-scale from days to millennia, such as the EUV emissions, are determined by the solar magnetic field. However, observations of the solar spectral irradiance are restricted to the last few solar cycles and are subject to large uncertainties. We present a physics-based model to reconstruct short-term solar spectral irradiance (SSI) variability. The coronal magnetic field is estimated to employ the Potential Field Source Surface extrapolation (PFSS) based on observational synoptic charts and magnetic flux transport model. The emission is estimated to employ the CHIANTI atomic database 8.0. The performance of the model is compared to the emission observed by TIMED/SORCE.
NASA Astrophysics Data System (ADS)
Ng, R.; Polet, J.
2016-12-01
Site response in sedimentary basins has been a topic of research interest for many decades due to the increased likelihood of earthquake damage from site amplification and resonance. We will present the results of our investigation of site response within the Los Angeles Basin through the application of the microtremor Horizontal-to-Vertical (H/V) spectral ratio method using the Geopsy software. This method was applied to 3-component broadband waveforms from the Los Angeles Syncline Seismic Interferometry Experiment (LASSIE). LASSIE is a collaborative, temporary, and dense array of 73 broadband seismometers that were active for a two-month period from October until November 2014, transecting the Los Angeles basin from Long Beach to La Puente. The data from this array enabled us to make measurements of small-scale lateral variations in the fundamental frequency, amplitude, and directional dependency of the H/V spectral ratio across this highly populated sedimentary basin. Data analysis and interpretation were conducted in accordance with the Site Effects Assessment Using Ambient Excitations (SESAME) guidelines. Our results show an average fundamental period at the basin center of 6-9.5 s and additional peaks in the spectral ratio curves at much shorter periods for sites at the basin edge. Long period H/V ratio peak amplitudes range from 2 - 5.5, with the highest values measured for the greater Long Beach area. We observe directional dependency in the frequency and amplitude of the long period peaks in the spectral ratio in proximity to the basin edge, which appears to correlate with the strike of the basin structure. We will show profiles of the H/V amplitudes and peak frequencies across the LA Basin and interpret our results in the context of site response results from other studies, as well as models of shallow and deeper basin structure.
Estimation of spectral kurtosis
NASA Astrophysics Data System (ADS)
Sutawanir
2017-03-01
Rolling bearings are the most important elements in rotating machinery. Bearing frequently fall out of service for various reasons: heavy loads, unsuitable lubrications, ineffective sealing. Bearing faults may cause a decrease in performance. Analysis of bearing vibration signals has attracted attention in the field of monitoring and fault diagnosis. Bearing vibration signals give rich information for early detection of bearing failures. Spectral kurtosis, SK, is a parameter in frequency domain indicating how the impulsiveness of a signal varies with frequency. Faults in rolling bearings give rise to a series of short impulse responses as the rolling elements strike faults, SK potentially useful for determining frequency bands dominated by bearing fault signals. SK can provide a measure of the distance of the analyzed bearings from a healthy one. SK provides additional information given by the power spectral density (psd). This paper aims to explore the estimation of spectral kurtosis using short time Fourier transform known as spectrogram. The estimation of SK is similar to the estimation of psd. The estimation falls in model-free estimation and plug-in estimator. Some numerical studies using simulations are discussed to support the methodology. Spectral kurtosis of some stationary signals are analytically obtained and used in simulation study. Kurtosis of time domain has been a popular tool for detecting non-normality. Spectral kurtosis is an extension of kurtosis in frequency domain. The relationship between time domain and frequency domain analysis is establish through power spectrum-autocovariance Fourier transform. Fourier transform is the main tool for estimation in frequency domain. The power spectral density is estimated through periodogram. In this paper, the short time Fourier transform of the spectral kurtosis is reviewed, a bearing fault (inner ring and outer ring) is simulated. The bearing response, power spectrum, and spectral kurtosis are plotted to
Spectral and Spread Spectral Teleportation
Humble, Travis S
2010-01-01
We report how quantum information encoded into the spectral degree of freedom of a single-photon state is teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of a teleported waveform can be controllably and coherently dilated using a spread spectral variant of teleportation. We present analytical fidelities for spectral and spread spectral teleportation when complex-valued Gaussian states are prepared using a proposed experimental approach, and we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.
Senthil kumar, J; Jeyavijayan, S; Arivazhagan, M
2015-02-05
The FT-IR and FT-Raman spectra of 3,5-dichlorobenzonitrile and m-bromobenzonitrile have been recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The optimized geometry, wave numbers and intensity of vibrational bonds of title molecules are obtained by ab initio and DFT level of theory with complete relaxation in the potential energy surface using 6-311++G(d, p) basis set. A complete vibrational assignments aided by the theoretical harmonic frequency, analysis have been proposed. The harmonic vibrational frequencies calculated have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The UV-Vis spectral analysis of the molecules has also been done which confirms the charge transfer of the molecules. Furthermore, the first hyperpolarizability and total dipole moment of the molecules have been calculated.
Thermophotovoltaic Spectral Control
DM DePoy; PM Fourspring; PF Baldasaro; JF Beausang; EJ Brown; MW Dashiel; KD Rahner; TD Rahmlow; JE Lazo-Wasem; EJ Gratrix; B Wemsman
2004-06-09
Spectral control is a key technology for thermophotovoltaic (TPV) direct energy conversion systems because only a fraction (typically less than 25%) of the incident thermal radiation has energy exceeding the diode bandgap energy, E{sub g}, and can thus be converted to electricity. The goal for TPV spectral control in most applications is twofold: (1) Maximize TPV efficiency by minimizing transfer of low energy, below bandgap photons from the radiator to the TPV diode. (2) Maximize TPV surface power density by maximizing transfer of high energy, above bandgap photons from the radiator to the TPV diode. TPV spectral control options include: front surface filters (e.g. interference filters, plasma filters, interference/plasma tandem filters, and frequency selective surfaces), back surface reflectors, and wavelength selective radiators. System analysis shows that spectral performance dominates diode performance in any practical TPV system, and that low bandgap diodes enable both higher efficiency and power density when spectral control limitations are considered. Lockheed Martin has focused its efforts on front surface tandem filters which have achieved spectral efficiencies of {approx}83% for E{sub g} = 0.52 eV and {approx}76% for E{sub g} = 0.60 eV for a 950 C radiator temperature.
Tofani, S.; Anglesio, L.; Ossola, P.; d`Amore, G.
1995-12-31
Magnetic fields emitted by electric appliances such as razors, hair dryers, and drills were measured in the frequency domain. Results show the presence of high-frequency components (up to 96 kHz for razors, up to 3.4 kHz for hair dryers, and up to 8.6 kHz for drills) in the harmonic content of the fields. The measured fields were used to calculate the induced current densities in an anatomically based model of the human head (resolution 1.31 cm) by using the impedance method. The harmonic field contribution to the current density was higher than that from the carrier frequency for all the tested appliances.
NASA Technical Reports Server (NTRS)
Longmire, M. S.; Bartoe, J.-D. F.; Brown, C. M.; Brueckner, G. E.; Tousey, R.
1979-01-01
Atmospheric transmittances integrated over wavelength intervals corresponding approximately to the (15-0) through (4-0) Schumann-Runge bands of O2 have been determined from EUV solar spectra (wavelengths between 1768 and 1948 A) photographed at seven altitudes between 102 and 76 km with a rocket-borne spectrograph having a resolution of 0.07 A. The observed transmittances are compared with atmospheric transmittances predicted from three models of the O2 absorption cross section. The predicted transmittances have also been used to derive column densities of atmospheric O2 from the observations. The results are compared with values calculated from the U.S. Standard Atmosphere (1976) and with oxygen column densities determined by Prinz and Brueckner (1977) from EUV solar spectra of the Schumann-Runge continuum (wavelength below 1750 A) and of the H-Lyman alpha line (1216 A) recorded on the same films used in the present research. The comparisons test the utility of the models for studies of atmospheric photochemistry, suggest which models may be best for this purpose, and indicate how the models can be improved.
Tsikata, Edem; Lee, Ramon; Shieh, Eric; Simavli, Huseyin; Que, Christian J.; Guo, Rong; Khoueir, Ziad; de Boer, Johannes; Chen, Teresa C.
2016-01-01
Purpose To describe spectral-domain optical coherence tomography (OCT) methods for quantifying neuroretinal rim tissue in glaucoma and to compare these methods to the traditional retinal nerve fiber layer thickness diagnostic parameter. Methods Neuroretinal rim parameters derived from three-dimensional (3D) volume scans were compared with the two-dimensional (2D) Spectralis retinal nerve fiber layer (RNFL) thickness scans for diagnostic capability. This study analyzed one eye per patient of 104 glaucoma patients and 58 healthy subjects. The shortest distances between the cup surface and the OCT-based disc margin were automatically calculated to determine the thickness and area of the minimum distance band (MDB) neuroretinal rim parameter. Traditional 150-μm reference surface–based rim parameters (volume, area, and thickness) were also calculated. The diagnostic capabilities of these five parameters were compared with RNFL thickness using the area under the receiver operating characteristic (AUROC) curves. Results The MDB thickness had significantly higher diagnostic capability than the RNFL thickness in the nasal (0.913 vs. 0.818, P = 0.004) and temporal (0.922 vs. 0.858, P = 0.026) quadrants and the inferonasal (0.950 vs. 0.897, P = 0.011) and superonasal (0.933 vs. 0.868, P = 0.012) sectors. The MDB area and the three neuroretinal rim parameters based on the 150-μm reference surface had diagnostic capabilities similar to RNFL thickness. Conclusions The 3D MDB thickness had a high diagnostic capability for glaucoma and may be of significant clinical utility. It had higher diagnostic capability than the RNFL thickness in the nasal and temporal quadrants and the inferonasal and superonasal sectors. PMID:27768203
Adaptive spectral doppler estimation.
Gran, Fredrik; Jakobsson, Andreas; Jensen, Jørgen Arendt
2009-04-01
In this paper, 2 adaptive spectral estimation techniques are analyzed for spectral Doppler ultrasound. The purpose is to minimize the observation window needed to estimate the spectrogram to provide a better temporal resolution and gain more flexibility when designing the data acquisition sequence. The methods can also provide better quality of the estimated power spectral density (PSD) of the blood signal. Adaptive spectral estimation techniques are known to provide good spectral resolution and contrast even when the observation window is very short. The 2 adaptive techniques are tested and compared with the averaged periodogram (Welch's method). The blood power spectral capon (BPC) method is based on a standard minimum variance technique adapted to account for both averaging over slow-time and depth. The blood amplitude and phase estimation technique (BAPES) is based on finding a set of matched filters (one for each velocity component of interest) and filtering the blood process over slow-time and averaging over depth to find the PSD. The methods are tested using various experiments and simulations. First, controlled flow-rig experiments with steady laminar flow are carried out. Simulations in Field II for pulsating flow resembling the femoral artery are also analyzed. The simulations are followed by in vivo measurement on the common carotid artery. In all simulations and experiments it was concluded that the adaptive methods display superior performance for short observation windows compared with the averaged periodogram. Computational costs and implementation details are also discussed.
NASA Technical Reports Server (NTRS)
Lang, Harold R.
1991-01-01
A new approach to stratigraphic analysis is described which uses photogeologic and spectral interpretation of multispectral remote sensing data combined with topographic information to determine the attitude, thickness, and lithology of strata exposed at the surface. The new stratigraphic procedure is illustrated by examples in the literature. The published results demonstrate the potential of spectral stratigraphy for mapping strata, determining dip and strike, measuring and correlating stratigraphic sequences, defining lithofacies, mapping biofacies, and interpreting geological structures.
Siva Priya, M; Usha Rani, N; James, C
2013-04-15
FT-IR and FT-Raman spectra of 2-methyl-4-nitrophenol (PNOC) and 3-methyl-4-nitrophenol (PNMC) were recorded and analyzed in the solid phase in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Molecular modeling of the compounds PNOC and PNMC were done by the density functional theoretical (DFT) method using Becke's three parameter exchange functional combined with the Lee-Yang-Parr correlation functional with 6-31G(d) as basis set. Vibrational assignments of the two compounds have been carried out with the help of Normal coordinate analyses (NCA) followed by the Scaled Quantum Mechanical Force Field calculations (SQMFF). Intra-molecular charge transfer and delocalization within the molecule is confirmed with the aid of natural bond orbital analysis (NBO). PNOC and PNMC are similar compounds with same functional groups, only the position of the methyl group is different. The effect of the position change of the methyl group was interpreted with the vibrational spectra.
Li, Xianchang; Li, Wei; Li, Zhong'an; Zhou, Xiaodong; Li, Zhen; Qin, Jingui; Hu, Jiming
2011-09-01
In this work, four-second order nonlinear optical (NLO) azobenzene-containing materials are studied in-depth by using vibrational spectra and density functional theory (DFT). The Fourier transform infrared (FT-IR) spectra and FT-Raman spectra are recorded in the range of 50-4000 and 100-3600cm(-1), respectively. Meanwhile, the DFT computations are performed at B3LYP/6-31G (d, p) level to derive equilibrium geometry, vibrational wavenumbers and intensities, and first hyperpolarizability, and the scaled theoretical wavenumbers are also shown to be in good agreement with experimental data. The calculated results show that these four azobenzene-containing compounds are good materials and the compound with nitro substituent groups possesses a larger first molecular hyperpolarizability (β) value. Moreover, the simultaneous infrared and Raman activation of R1 group and CC stretching suggest that the charge transfer interaction might occur between the R1 group and phenyl ring, and the HOMO-LUMO gap analysis also supports this viewpoint. Copyright © 2011 Elsevier B.V. All rights reserved.
Ibarria, L; Lindstrom, P; Rossignac, J
2006-11-17
Many scientific, imaging, and geospatial applications produce large high-precision scalar fields sampled on a regular grid. Lossless compression of such data is commonly done using predictive coding, in which weighted combinations of previously coded samples known to both encoder and decoder are used to predict subsequent nearby samples. In hierarchical, incremental, or selective transmission, the spatial pattern of the known neighbors is often irregular and varies from one sample to the next, which precludes prediction based on a single stencil and fixed set of weights. To handle such situations and make the best use of available neighboring samples, we propose a local spectral predictor that offers optimal prediction by tailoring the weights to each configuration of known nearby samples. These weights may be precomputed and stored in a small lookup table. We show that predictive coding using our spectral predictor improves compression for various sources of high-precision data.
NASA Astrophysics Data System (ADS)
Jaschek, C.
Taxonomic classification of astronomically observed stellar objects is described in terms of spectral properties. Stars receive a classification containing a letter, number, and a Roman numeral, which relates the star to other stars of higher or lower Roman numerals. The citation indicates the stellar chromatic emission in relation to the wavelengths of other stars. Standards are chosen from the available objects detected. Various classification schemes such as the MK, HD, and the Barbier-Chalonge-Divan systems are defined, including examples of indexing differences. Details delineating the separations between classifications are discussed with reference to the information content in spectral and in photometric classification schemes. The parameters usually used for classification include the temperature, luminosity, reddening, binarity, rotation, magnetic field, and elemental abundance or composition. The inclusion of recently discovered extended wavelength characteristics in nominal classifications is outlined, together with techniques involved in automated classification.
Milovanovic, Petar; Djuric, Marija; Rakocevic, Zlatko
2012-01-01
There is an increasing interest in bone nano-structure, the ultimate goal being to reveal the basis of age-related bone fragility. In this study, power spectral density (PSD) data and fractal dimensions of the mineralized bone matrix were extracted from atomic force microscope topography images of the femoral neck trabeculae. The aim was to evaluate age-dependent differences in the mineralized matrix of human bone and to consider whether these advanced nano-descriptors might be linked to decreased bone remodeling observed by some authors and age-related decline in bone mechanical competence. The investigated bone specimens belonged to a group of young adult women (n = 5, age: 20–40 years) and a group of elderly women (n = 5, age: 70–95 years) without bone diseases. PSD graphs showed the roughness density distribution in relation to spatial frequency. In all cases, there was a fairly linear decrease in magnitude of the power spectra with increasing spatial frequencies. The PSD slope was steeper in elderly individuals (−2.374 vs. −2.066), suggesting the dominance of larger surface morphological features. Fractal dimension of the mineralized bone matrix showed a significant negative trend with advanced age, declining from 2.467 in young individuals to 2.313 in the elderly (r = 0.65, P = 0.04). Higher fractal dimension in young women reflects domination of smaller mineral grains, which is compatible with the more freshly remodeled structure. In contrast, the surface patterns in elderly individuals were indicative of older tissue age. Lower roughness and reduced structural complexity (decreased fractal dimension) of the interfibrillar bone matrix in the elderly suggest a decline in bone toughness, which explains why aged bone is more brittle and prone to fractures. PMID:22946475
NASA Astrophysics Data System (ADS)
Sprouse, James F.
1985-12-01
Infrared Spectral Searching has progressed rapidly over the past two years since the last FT-IR Conference in Durham, England. In addition, if we compare the searching capabilities available to the Infrared Spectroscopist today with those that were available a short four years ago at the last North American Conference held in Columbia, South Carolina, then the advancements are even more impressive. In retrospect, I would describe the state-of-the-art in Spectral Searching at the 1981 FT-IR Conference as "Level 1 Searching", where the spectroscopist was limited to measuring a spectrum for his unknown material, and automatically searching it against very limited libraries at that time to obtain a search report. The report generally provided an ordered ranking of the best matches, chemical name, and a spectrum number so the reference spectrum could be located and reviewed in books. In 1981, there existed a total of three commercially available infrared search packages at the instrument level. Two of the packages were available for FT-IR instruments and the third was available on a dispersive instrument. Only the FT-IR packages allowed viewing the reference spectra on the CRT along with the unknown spectrum by automated spectral retrieval from the reference libraries stored on disk. However, the primary source of reference spectra was still predominantly hard copy.
Random sources for rotating spectral densities.
Mei, Zhangrong; Korotkova, Olga
2017-01-15
The propagating modes of a wide-sense stationary Schell-like source with arbitrary coherence state and a twist factor are determined. This suggests a convenient practical method for modeling novel classes of twisted partially coherent beam-like fields. The first example discusses the previously introduced twisted anisotropic Gaussian Schell-model source and verifies the feasibility of this method. As a second example, we introduce a new type of twisted partially coherent beam in which a radiated flat-top average intensity pattern remains invariant in shape (but not size) while it twists around the axis upon propagation.
NASA Astrophysics Data System (ADS)
Litvak, M. L.; Mitrofanov, I. G.; Nuzhdin, I. O.; Vostrukhin, A. V.; Golovin, D. V.; Kozyrev, A. S.; Malakhov, A. V.; Mokrousov, M. I.; Sanin, A. B.; Tretyakov, V. I.; Fedosov, F. S.
2017-03-01
Results of measurements of neutron-flux spectral density in the vicinity of the International Space Station (ISS) based on BTN-Neutron space experimental data acquired in 2007-2014 have been presented in this paper. It has been shown that, during the flight of the ISS over different regions of the Earth's surface, neutron flux in the energy range of 0.4 eV-15 MeV varies from 0.1 n/sm2/s in equatorial regions to 50 n/sm2/s in the South Atlantic anomaly region. The measurements were used to estimate the contribution of the neutron component to the overall exposure dose rate. The total contribution of fast neutrons is about 0.1-0.4 μ Zv/h above the equator area and more than 50 μ Zv/h above the South Atlantic anomaly region. A data analysis of BTN-Neutron data also showed that the time profile of neutron flux has long-periodic variations. It was found that, under the influence of Galactic cosmic rays (GCRs), modulation during 24th solar cycle neutron flux changed almost twofold (above high latitude regions). Maximum values of neutron flux were observed in January 2010 and minimum values were observed in January 2014.
Intensity Conserving Spectral Fitting
NASA Astrophysics Data System (ADS)
Klimchuk, J. A.; Patsourakos, S.; Tripathi, D.
2016-01-01
The detailed shapes of spectral-line profiles provide valuable information about the emitting plasma, especially when the plasma contains an unresolved mixture of velocities, temperatures, and densities. As a result of finite spectral resolution, the intensity measured by a spectrometer is the average intensity across a wavelength bin of non-zero size. It is assigned to the wavelength position at the center of the bin. However, the actual intensity at that discrete position will be different if the profile is curved, as it invariably is. Standard fitting routines (spline, Gaussian, etc.) do not account for this difference, and this can result in significant errors when making sensitive measurements. We have developed an iterative procedure that corrects for this effect. It converges rapidly and is very flexible in that it can be used with any fitting function. We present examples of cubic-spline and Gaussian fits and give special attention to measurements of blue-red asymmetries of coronal emission lines.
Spectral simulations of reacting turbulent flows
NASA Technical Reports Server (NTRS)
Mcmurtry, Patrick A.; Givi, Peyman
1991-01-01
Spectral methods for simulating flows are reviewed, emphasizing their recent applications to reacting flow problems. Various classifications of spectral methods and their convergence properties are described and the 'spectral element' method is presented, highlighting its flexibility in dealing with complex flow geometries. The applications considered include chemical reactions in homogeneous turbulence, temporally evolving mixing layers, variable-density simulations, nonequilibrium chemistry, and spatially evolving mixing layers.
Spectral characterization of lithographic sources
NASA Astrophysics Data System (ADS)
Cerjan, C.
1993-06-01
Spectral data collected in recent laser-plasma experiments at LLNL for Sn are compared to simulation results in order to more fully characterize the plasma properties, especially electron temperature and density. These plasma conditions determine the ionization states achieved by the material and the consequent radiative emission. Synthetic spectra are produced using very detailed radiating line positions and oscillator strengths calculated from extensive multi-configuration Dirac-Fock computations. Better quantitative agreement with experimental conversion efficiencies in the laser intensity regime of interest to projection soft x-ray lithography is obtained using this atomic database. The spectral characterization thus validates the general reliability of the simulations.
Turbulent magnetohydrodynamic density fluctuations
NASA Technical Reports Server (NTRS)
Shebalin, John V.; Montgomery, David
1988-01-01
A spectral-method numerical code is used to compute mass-density fluctuation spectra in turbulent magnetofluids. The computations are used to test and extend the analytical theory of density variations in slightly compressible magnetofluids given by Montgomery, et al. (1987) and used to infer inertial-range density-fluctuation spectra for the nearby interstellar medium and solar wind. A local equation of state is assumed, relating density to pressure. Constant, scalar resistivities and viscosities are used. In the limit of low Mach numbers and high mechanical-to-magnetic pressure ratios, the fit of the computations to the analytical theory is seen to be close.
Spectral and spread-spectral teleportation
Humble, Travis S.
2010-06-15
We report how quantum information encoded into the spectral degree of freedom of a single-photon state may be teleported using a finite spectrally entangled biphoton state. We further demonstrate how the bandwidth of the teleported wave form can be controllably and coherently dilated using a spread-spectral variant of teleportation. We calculate analytical expressions for the fidelities of spectral and spread-spectral teleportation when complex-valued Gaussian states are transferred using a proposed experimental approach. Finally, we discuss the utility of these techniques for integrating broad-bandwidth photonic qubits with narrow-bandwidth receivers in quantum communication systems.
The pulsar spectral index distribution
NASA Astrophysics Data System (ADS)
Bates, S. D.; Lorimer, D. R.; Verbiest, J. P. W.
2013-05-01
The flux-density spectra of radio pulsars are known to be steep and, to first order, described by a power-law relationship of the form Sν ∝ να, where Sν is the flux density at some frequency ν and α is the spectral index. Although measurements of α have been made over the years for several hundred pulsars, a study of the intrinsic distribution of pulsar spectra has not been carried out. From the result of pulsar surveys carried out at three different radio frequencies, we use population synthesis techniques and a likelihood analysis to deduce what underlying spectral index distribution is required to replicate the results of these surveys. We find that in general the results of the surveys can be modelled by a Gaussian distribution of spectral indices with a mean of -1.4 and unit standard deviation. We also consider the impact of the so-called gigahertz-peaked spectrum pulsars proposed by Kijak et al. The fraction of peaked-spectrum sources in the population with any significant turnover at low frequencies appears to be at most 10 per cent. We demonstrate that high-frequency (>2 GHz) surveys preferentially select flatter spectrum pulsars and the converse is true for lower frequency (<1 GHz) surveys. This implies that any correlations between α and other pulsar parameters (for example age or magnetic field) need to carefully account for selection biases in pulsar surveys. We also expect that many known pulsars which have been detected at high frequencies will have shallow, or positive, spectral indices. The majority of pulsars do not have recorded flux density measurements over a wide frequency range, making it impossible to constrain their spectral shapes. We also suggest that such measurements would allow an improved description of any populations of pulsars with `non-standard' spectra. Further refinements to this picture will soon be possible from the results of surveys with the Green Bank Telescope and LOFAR.
Different approaches of spectral analysis
NASA Technical Reports Server (NTRS)
Lacoume, J. L.
1977-01-01
Several approaches to the problem of the calculation of spectral power density of a random function from an estimate of the autocorrelation function were studied. A comparative study was presented of these different methods. The principles on which they are based and the hypothesis implied were pointed out. Some indications on the optimization of the length of the estimated correlation function was given. An example of application of the different methods discussed in this paper was included.
NASA Astrophysics Data System (ADS)
Hamhalter, Jan; Turilova, Ekaterina
2017-02-01
Quantum symmetries of spectral lattices are studied. Basic properties of spectral order on A W ∗-algebras are summarized. Connection between projection and spectral automorphisms is clarified by showing that, under mild conditions, any spectral automorphism is a composition of function calculus and Jordan ∗-automorphism. Complete description of quantum spectral symmetries on Type I and Type II A W ∗-factors are completely described.
Nikamanon, Pornpat; Pun, Elroy; Chou, Wayne; Koter, Marek D; Gershon, Paul D
2008-01-01
Background Protein-amide proton hydrogen-deuterium exchange (HDX) is used to investigate protein conformation, conformational changes and surface binding sites for other molecules. To our knowledge, software tools to automate data processing and analysis from sample fractionating (LC-MALDI) mass-spectrometry-based HDX workflows are not publicly available. Results An integrated data pipeline (Solvent Explorer/TOF2H) has been developed for the processing of LC-MALDI-derived HDX data. Based on an experiment-wide template, and taking an ab initio approach to chromatographic and spectral peak finding, initial data processing is based on accurate mass-matching to fully deisotoped peaklists accommodating, in MS/MS-confirmed peptide library searches, ambiguous mass-hits to non-target proteins. Isotope-shift re-interrogation of library search results allows quick assessment of the extent of deuteration from peaklist data alone. During raw spectrum editing, each spectral segment is validated in real time, consistent with the manageable spectral numbers resulting from LC-MALDI experiments. A semi-automated spectral-segment editor includes a semi-automated or automated assessment of the quality of all spectral segments as they are pooled across an XIC peak for summing, centroid mass determination, building of rates plots on-the-fly, and automated back exchange correction. The resulting deuterium uptake rates plots from various experiments can be averaged, subtracted, re-scaled, error-barred, and/or scatter-plotted from individual spectral segment centroids, compared to solvent exposure and hydrogen bonding predictions and receive a color suggestion for 3D visualization. This software lends itself to a "divorced" HDX approach in which MS/MS-confirmed peptide libraries are built via nano or standard ESI without source modification, and HDX is performed via LC-MALDI using a standard MALDI-TOF. The complete TOF2H package includes additional (eg LC analysis) modules. Conclusion
The Spectral Shift Function and Spectral Flow
NASA Astrophysics Data System (ADS)
Azamov, N. A.; Carey, A. L.; Sukochev, F. A.
2007-11-01
At the 1974 International Congress, I. M. Singer proposed that eta invariants and hence spectral flow should be thought of as the integral of a one form. In the intervening years this idea has lead to many interesting developments in the study of both eta invariants and spectral flow. Using ideas of [24] Singer’s proposal was brought to an advanced level in [16] where a very general formula for spectral flow as the integral of a one form was produced in the framework of noncommutative geometry. This formula can be used for computing spectral flow in a general semifinite von Neumann algebra as described and reviewed in [5]. In the present paper we take the analytic approach to spectral flow much further by giving a large family of formulae for spectral flow between a pair of unbounded self-adjoint operators D and D + V with D having compact resolvent belonging to a general semifinite von Neumann algebra {mathcal{N}} and the perturbation V in {mathcal{N}} . In noncommutative geometry terms we remove summability hypotheses. This level of generality is made possible by introducing a new idea from [3]. There it was observed that M. G. Krein’s spectral shift function (in certain restricted cases with V trace class) computes spectral flow. The present paper extends Krein’s theory to the setting of semifinite spectral triples where D has compact resolvent belonging to {mathcal{N}} and V is any bounded self-adjoint operator in {mathcal{N}} . We give a definition of the spectral shift function under these hypotheses and show that it computes spectral flow. This is made possible by the understanding discovered in the present paper of the interplay between spectral shift function theory and the analytic theory of spectral flow. It is this interplay that enables us to take Singer’s idea much further to create a large class of one forms whose integrals calculate spectral flow. These advances depend critically on a new approach to the calculus of functions of non
[Modern spectral estimation of ICP-AES].
Zhang, Z; Jia, Q; Liu, S; Guo, L; Chen, H; Zeng, X
2000-06-01
The inductively coupled plasma atomic emission spectrometry (ICP-AES) and its signal characteristics were discussed using modern spectral estimation technique. The power spectra density (PSD) was calculated using the auto-regression (AR) model of modern spectra estimation. The Levinson-Durbin recursion method was used to estimate the model parameters which were used for the PSD computation. The results obtained with actual ICP-AES spectra and measurements showed that the spectral estimation technique was helpful for the better understanding about spectral composition and signal characteristics.
General spectral utility metric for spectral imagery
NASA Astrophysics Data System (ADS)
Simmons, Rulon E.; Elder, Timothy D.; Stewart, David J.; Cincotta, Eric J.; Kennedy, Carolyn S.; Van Nostrand, R. Craig
2005-06-01
Published approaches to assessing and predicting spectral image utility are generally based on regression methods which fit coefficients to an equation with terms representing spatial scale, spectral fidelity, and signal-to-noise. Such approaches are patterned after the National Imagery Interpretability Rating Scale General Image Quality Equation (NIIRS GIQE) designed for use with remotely-sensed panchromatic imagery. Preliminary testing of these approaches suggests that they will work for some subsets of spectral imagery applications but are not generally applicable to all spectral imaging problems. We present here an approach that gets at the heart of the general problem-assessing the confidence of an image analyst in performing a specified task with a specific spectral image. While applicable in other areas such as health imaging, our approach to spectral utility assessment is presented in this paper from a remote sensing point of view. Our approach allows trade-offs in tasking and system design across the "spectrum" of imagers including panchromatic, multispectral, hyperspectral, and even ultraspectral. Our approach is based on a fusion concept called "semantic transformation." We assume that spectral and spatial information are largely separable with both contributing to the overall utility of the image. The "semantic transformation" combines the spatial and spectral information in a common term (in our case confidence) to give an overall confidence in performing the specified task. Addressing the spatial and spectral information separately allows us the freedom to assess the information contained in each in ways that the information is actually assimilated (i.e., usually spatial information in exploited visually while spectral information consisting of more than three or four bands is usually exploited by computer algorithms). For the spectral information, we can use either generic exploitation algorithms or the specific algorithms that the image analyst
Spectral Deception: Understanding Misleading Spectral Features Using Simulations
NASA Astrophysics Data System (ADS)
Hummels, Cameron B.; Silvia, Devin W.; Smith, Britton
2016-01-01
Quasar absorption line studies are our primary source of information for revealing the state of the intergalactic and circumgalacic media (IGM and CGM). Using quasars as bright background sources, tenuous intervening gas clouds imprint absorption features in the resulting spectra providing clues to the clouds' density, temperature, metallicity, and ionization state. Correctly interpreting these spectra is crucial to understanding the distribution of baryons in the universe.Using the Trident code to generate synthetic spectra from high-resolution cosmological hydrodynamical simulations, we examine how spectral noise, instrument smoothing, and certain configurations of gas can mask the true nature of gas absorbers. We demonstrate how cold gas filaments can create broad spectral features mimicking hot absorbers, and chimneys of hot gas viewed side-on appear as narrow, cold absorbers. Understanding how commonly these conditions occur is critical for correctly characterizing the physical conditions in the media galactic.
Multidimensional spectral load balancing
Hendrickson, B.; Leland, R.
1993-01-01
We describe an algorithm for the static load balancing of scientific computations that generalizes and improves upon spectral bisection. Through a novel use of multiple eigenvectors, our new spectral algorithm can divide a computation into 4 or 8 pieces at once. These multidimensional spectral partitioning algorithms generate balanced partitions that have lower communication overhead and are less expensive to compute than those produced by spectral bisection. In addition, they automatically work to minimize message contention on a hypercube or mesh architecture. These spectral partitions are further improved by a multidimensional generalization of the Kernighan-Lin graph partitioning algorithm. Results on several computational grids are given and compared with other popular methods.
Agile dual-channel spectral imaging with spectral zooming.
Chen, Bing; Wang, Michael R; Yang, Jame J
2008-08-10
A dual-channel spectral imaging system with agile spectral band access and spectral bandwidth tuning capability is presented. A diffractive grating and an acousto-optic tunable filter (AOTF) are respectively used as spectral dispersion and spectral filtering elements for the two channels. A 4f spectral filtering channel using an adjustable slit is set up at the first diffraction order of the grating to realize coarse spectral band selection. The AOTF selectively filters the spectrum of the nondispersed zero order to realize fine spectral imaging. The spectral zooming function is achieved without increasing spectral frame number facilitating real-time spectral imaging operation. Feasibility of the spectral imaging has been demonstrated through preliminary experiments. Minimum 6 nm spectral resolution and 1.2 degrees field of view have been achieved. The real-time spectral imaging capable of wide spectral band operation without loosing desired fine spectral capability is particularly useful for a variety of defense, medical, and environmental monitoring applications.
Spectral Hounsfield units: a new radiological concept.
Hurrell, Michael Anthony; Butler, Anthony Philip Howard; Cook, Nicholas James; Butler, Philip Howard; Ronaldson, J Paul; Zainon, Rafidah
2012-05-01
Computed tomography (CT) uses radiographical density to depict different materials; although different elements have different absorption fingerprints across the range of diagnostic X-ray energies, this spectral absorption information is lost in conventional CT. The recent development of dual energy CT (DECT) allows extraction of this information to a useful but limited extent. However, the advent of new photon counting chips that have energy resolution capabilities has put multi-energy or spectral CT (SCT) on the clinical horizon. This paper uses a prototype SCT system to demonstrate how CT density measurements vary with kilovoltage. While radiologists learn about linear attenuation curves during radiology training, they do not usually need a detailed understanding of this phenomenon in their clinical practice. However SCT requires a paradigm shift in how radiologists think about CT density. Because radiologists are already familiar with the Hounsfield Unit (HU), it is proposed that a modified HU be used that includes the mean energy used to obtain the image, as a conceptual bridge between conventional CT and SCT. A suggested format would be: HU(keV). • Spectral computed tomography uses K-edge and slope effects to identify element signatures. • New visualisation tools will be required to efficiently display spectral CT information. • This paper demonstrates HU variation with keV using the Medipix3 chip. • HU ( keV ) is a suggested format when stating spectral HU measurements.
Evaluating Spectral Signals to Identify Spectral Error
Bazar, George; Kovacs, Zoltan; Tsenkova, Roumiana
2016-01-01
Since the precision and accuracy level of a chemometric model is highly influenced by the quality of the raw spectral data, it is very important to evaluate the recorded spectra and describe the erroneous regions before qualitative and quantitative analyses or detailed band assignment. This paper provides a collection of basic spectral analytical procedures and demonstrates their applicability in detecting errors of near infrared data. Evaluation methods based on standard deviation, coefficient of variation, mean centering and smoothing techniques are presented. Applications of derivatives with various gap sizes, even below the bandpass of the spectrometer, are shown to evaluate the level of spectral errors and find their origin. The possibility for prudent measurement of the third overtone region of water is also highlighted by evaluation of a complex data recorded with various spectrometers. PMID:26731541
NASA Technical Reports Server (NTRS)
Zang, Thomas A.; Streett, Craig L.; Hussaini, M. Yousuff
1989-01-01
One of the objectives of these notes is to provide a basic introduction to spectral methods with a particular emphasis on applications to computational fluid dynamics. Another objective is to summarize some of the most important developments in spectral methods in the last two years. The fundamentals of spectral methods for simple problems will be covered in depth, and the essential elements of several fluid dynamical applications will be sketched.
NASA Astrophysics Data System (ADS)
Bardakçı, Tayyibe; Altun, Ahmet; Golcuk, Kurtulus; Kumru, Mustafa
2015-11-01
Transition metal complexes of the form MBr2L2, where M = Mn(II), Co(II) and Ni(II); L = p-methylaniline, were prepared and characterized by elemental and thermogravimetric analyses, magnetic moment measurements, and UV-vis, FT-IR and FT-Raman spectral studies. Geometries, spin-state energetics, and vibrational spectra of the complexes were obtained at the B3LYP/def2-TZVP level. The present experimental and theoretical data suggest 5-coordinate polymeric bromide bridged structure for the Mn complex, distorted tetrahedral structure for the Co complex, and distorted octahedral coordination site for the Ni complex. The experimental FT-IR and FT-Raman bands of the complexes were assigned based on the computational results expressed in terms of internal coordinates with percent potential energy distributions. The vibrational spectra suggest that the coordination occurs via nitrogen atom of p-methylaniline. The thermal characteristics of the complexes indicate that their decompositions start through p-methylaniline.
Spectral separation of optical spin based on antisymmetric Fano resonances
Piao, Xianji; Yu, Sunkyu; Hong, Jiho; Park, Namkyoo
2015-01-01
We propose a route to the spectral separation of optical spin angular momentum based on spin-dependent Fano resonances with antisymmetric spectral profiles. By developing a spin-form coupled mode theory for chiral materials, the origin of antisymmetric Fano spectra is clarified in terms of the opposite temporal phase shift for each spin, which is the result of counter-rotating spin eigenvectors. An analytical expression of a spin-density Fano parameter is derived to enable quantitative analysis of the Fano-induced spin separation in the spectral domain. As an application, we demonstrate optical spin switching utilizing the extreme spectral sensitivity of the spin-density reversal. Our result paves a path toward the conservative spectral separation of spins without any need of the magneto-optical effect or circular dichroism, achieving excellent purity in spin density superior to conventional approaches based on circular dichroism. PMID:26561372
National Institute of Standards and Technology Data Gateway
SRD 117 Triatomic Spectral Database (Web, free access) All of the rotational spectral lines observed and reported in the open literature for 55 triatomic molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty and reference are given for each transition reported.
National Institute of Standards and Technology Data Gateway
SRD 114 Diatomic Spectral Database (Web, free access) All of the rotational spectral lines observed and reported in the open literature for 121 diatomic molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty, and reference are given for each transition reported.
National Institute of Standards and Technology Data Gateway
SRD 115 Hydrocarbon Spectral Database (Web, free access) All of the rotational spectral lines observed and reported in the open literature for 91 hydrocarbon molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty and reference are given for each transition reported.
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.; Kopriva, D. A.; Patera, A. T.
1987-01-01
This review covers the theory and application of spectral collocation methods. Section 1 describes the fundamentals, and summarizes results pertaining to spectral approximations of functions. Some stability and convergence results are presented for simple elliptic, parabolic, and hyperbolic equations. Applications of these methods to fluid dynamics problems are discussed in Section 2.
NASA Astrophysics Data System (ADS)
Yalçın, Şerife Pınar; Ceylan, Ümit; Sarıoğlu, Ahmet Oral; Sönmez, Mehmet; Aygün, Muhittin
2015-10-01
The title compound, C22H16N2O5, was synthesized and characterized by experimental techniques (FT-IR, 1H NMR, 13C NMR, UV-Vis and X-Ray single crystal determination) and theoretical calculations. The molecular geometry, vibrational frequencies, molecular electrostatic potential (MEP), thermodynamic properties, the dipole moments, HOMO-LUMO energy has been calculated by using the Density Functional Theory (DFT) method with 6-311G(d,p) and 6-311++G(d,p) basis sets. 1H and 13C NMR chemical shifts show good agreement with experimental values. According to calculated results, the 6-311G(d,p) and 6-311++G(d,p) basis sets have showed similar results. The optimized geometry can well reproduce the crystal structure parameters.
Propagation of spectral functions and dilepton production at SIS energies
Wolf, Gy.; Kaempfer, B.; Zetenyi, M.
2012-06-15
The time evolution of vector meson spectral functions is studied within a BUU-type transport model. Applications focus on {rho} and {omega} mesons being important pieces for the interpretation of the dielectron invariant mass spectrum. Since the evolution of the spectral functions is driven by the local density, the inmedium modifications turn out to compete, in this approach, with the known vacuum contributions.
Acoustic emission spectral analysis of fiber composite failure mechanisms
NASA Technical Reports Server (NTRS)
Egan, D. M.; Williams, J. H., Jr.
1978-01-01
The acoustic emission of graphite fiber polyimide composite failure mechanisms was investigated with emphasis on frequency spectrum analysis. Although visual examination of spectral densities could not distinguish among fracture sources, a paired-sample t statistical analysis of mean normalized spectral densities did provide quantitative discrimination among acoustic emissions from 10 deg, 90 deg, and plus or minus 45 deg, plus or minus 45 deg sub s specimens. Comparable discrimination was not obtained for 0 deg specimens.
John F. Caratti
2006-01-01
The FIREMON Density (DE) method is used to assess changes in plant species density and height for a macroplot. This method uses multiple quadrats and belt transects (transects having a width) to sample within plot variation and quantify statistically valid changes in plant species density and height over time. Herbaceous plant species are sampled with quadrats while...
Spectral Redundancy in Tissue Characterization
NASA Astrophysics Data System (ADS)
Varghese, Tomy
1995-01-01
Ultrasonic backscattered signals from material comprised of quasi-periodic scatterers exhibit redundancy over both its phase and magnitude spectra. This dissertation addresses the problem of estimating the mean scatterer spacing and scatterer density from the backscattered ultrasound signal using spectral redundancy characterized by the spectral autocorrelation (SAC) function. The SAC function exploits characteristic differences between the phase spectrum of the resolvable quasi-periodic (regular) scatterers and the unresolvable uniformly distributed (diffuse) scatterers to improve estimator performance over other estimators that operate directly on the magnitude spectrum. Analytical, simulation, and experimental results (liver and breast tissue) indicate the potential of utilizing phase information using the SAC function. A closed form analytical expression for the SAC function is derived for gamma distributed scatterer spacings. The theoretical expression for the SAC function demonstrate the increased regular-to-diffuse scatterer signal ratio in the off-diagonal components of the SAC function, since the diffuse component contributes only to the diagonal components (power spectrum). The A-scan is modelled as a cyclostationary signal whose statistical parameters vary in time with single or multiple periodicities. A-scan models consist of a collection of regular scatterers with gamma distributed spacings embedded in diffuse scatterers with uniform distributed spacings. The model accounts for attenuation by convolving the frequency dependent backscatter coefficients of the scatterer centers with a time-varying system response. Simulation results show that SAC-based estimates converge more reliably over smaller amounts of data than previously used cepstrum-based estimates. A major reason for the performance advantage is the use of phase information by the SAC function, while the cepstnun uses a phaseless power spectral density, that is directly affected by the system
Universal fermionic spectral functions from string theory.
Gauntlett, Jerome P; Sonner, Julian; Waldram, Daniel
2011-12-09
We carry out the first holographic calculation of a fermionic response function for a strongly coupled d=3 system with an explicit D=10 or D=11 supergravity dual. By considering the supersymmetry current, we obtain a universal result applicable to all d=3 N=2 SCFTs with such duals. Surprisingly, the spectral function does not exhibit a Fermi surface, despite the fact that the system is at finite charge density. We show that it has a phonino pole and at low frequencies there is a depletion of spectral weight with a power-law scaling which is governed by a locally quantum critical point.
Temporal Lorentzian spectral triples
NASA Astrophysics Data System (ADS)
Franco, Nicolas
2014-09-01
We present the notion of temporal Lorentzian spectral triple which is an extension of the notion of pseudo-Riemannian spectral triple with a way to ensure that the signature of the metric is Lorentzian. A temporal Lorentzian spectral triple corresponds to a specific 3 + 1 decomposition of a possibly noncommutative Lorentzian space. This structure introduces a notion of global time in noncommutative geometry. As an example, we construct a temporal Lorentzian spectral triple over a Moyal-Minkowski spacetime. We show that, when time is commutative, the algebra can be extended to unbounded elements. Using such an extension, it is possible to define a Lorentzian distance formula between pure states with a well-defined noncommutative formulation.
Commission 45: Spectral Classification
NASA Astrophysics Data System (ADS)
Giridhar, Sunetra; Gray, Richard O.; Corbally, Christopher J.; Bailer-Jones, Coryn A. L.; Eyer, Laurent; Irwin, Michael J.; Kirkpatrick, J. Davy; Majewski, Steven; Minniti, Dante; Nordström, Birgitta
This report gives an update of developments (since the last General Assembly at Prague) in the areas that are of relevance to the commission. In addition to numerous papers, a new monograph entitled Stellar Spectral Classification with Richard Gray and Chris Corbally as leading authors will be published by Princeton University Press as part of their Princeton Series in Astrophysics in April 2009. This book is an up-to-date and encyclopedic review of stellar spectral classification across the H-R diagram, including the traditional MK system in the blue-violet, recent extensions into the ultraviolet and infrared, the newly defined L-type and T-type spectral classes, as well as spectral classification of carbon stars, S-type stars, white dwarfs, novae, supernovae and Wolf-Rayet stars.
1998-08-01
Spectrally selective glazing is window glass that permits some portions of the solar spectrum to enter a building while blocking others. This high-performance glazing admits as much daylight as possible while preventing transmission of as much solar heat as possible. By controlling solar heat gains in summer, preventing loss of interior heat in winter, and allowing occupants to reduce electric lighting use by making maximum use of daylight, spectrally selective glazing significantly reduces building energy consumption and peak demand. Because new spectrally selective glazings can have a virtually clear appearance, they admit more daylight and permit much brighter, more open views to the outside while still providing the solar control of the dark, reflective energy-efficient glass of the past. This Federal Technology Alert provides detailed information and procedures for Federal energy managers to consider spectrally selective glazings. The principle of spectrally selective glazings is explained. Benefits related to energy efficiency and other architectural criteria are delineated. Guidelines are provided for appropriate application of spectrally selective glazing, and step-by-step instructions are given for estimating energy savings. Case studies are also presented to illustrate actual costs and energy savings. Current manufacturers, technology users, and references for further reading are included for users who have questions not fully addressed here.
Nonlinear spectral correlation for fatigue crack detection under noisy environments
NASA Astrophysics Data System (ADS)
Liu, Peipei; Sohn, Hoon; Jeon, Ikgeun
2017-07-01
When ultrasonic waves at two distinct frequencies are applied to a structure with a fatigue crack, crack-induced nonlinearity creates nonlinear ultrasonic modulations at the sum and difference of the two input frequencies. The amplitude of the nonlinear modulation components is typically one or two orders of magnitude smaller than that of the primary linear components. Therefore, the modulation components can be easily buried under noise levels and it becomes difficult to extract the nonlinear modulation components under noisy environments using a conventional spectral density function. In this study, nonlinear spectral correlation, which calculates the spectral correlation between nonlinear modulation components, is proposed to isolate the nonlinear modulation components from noisy environments and used for fatigue crack detection. The proposed nonlinear spectral correlation offers the following benefits: (1) Stationary noises have little effect on nonlinear spectral correlation; (2) By using a wideband high-frequency input and a single low-frequency input, the contrast of nonlinear spectral correlation between damage and intact conditions can be enhanced; and (3) The test efficiency can be also improved via reducing the data collection time. Validation tests are performed on aluminum plates and scaled steel shafts with real fatigue cracks. The experimental results demonstrate that the proposed nonlinear spectral correlation owns a higher sensitivity to fatigue crack than the classical nonlinear coefficient estimated from the spectral density function, and the usage of nonlinear spectral correlation allows the detection of fatigue crack even using noncontact air-coupled transducers with a low signal-to-noise ratio.
ERIC Educational Resources Information Center
Keiter, Richard L.; Puzey, Whitney L.; Blitz, Erin A.
2006-01-01
Metal rods of high purity for many elements are now commercially available and may be used to construct a display of relative densities. We have constructed a display with nine metal rods (Mg, Al, Ti, V, Fe, Cu, Ag, Pb, and W) of equal mass whose densities vary from 1.74 to 19.3 g cm[superscript -3]. The relative densities of the metals may be…
ERIC Educational Resources Information Center
Keiter, Richard L.; Puzey, Whitney L.; Blitz, Erin A.
2006-01-01
Metal rods of high purity for many elements are now commercially available and may be used to construct a display of relative densities. We have constructed a display with nine metal rods (Mg, Al, Ti, V, Fe, Cu, Ag, Pb, and W) of equal mass whose densities vary from 1.74 to 19.3 g cm[superscript -3]. The relative densities of the metals may be…
Spectral representation theory of graded composite materials
NASA Astrophysics Data System (ADS)
Chan, K. L.; Kwok, C. M.; Yu, K. W.
2008-03-01
In graded composite materials, the physical properties can vary continuously in space and it may give different physical phenomena when compared with homogeneous materials. The Bergman-Milton spectral representation is a rigorous mathematical formalism to express the effective dielectric constant of nongraded composite materials [1]. In this study, we consider a material (rather than microsture [2]) graded composites, and generalize the Bergman-Milton spectral representation to extract the spectral density function for the effective dielectric constant of this graded composite material in the frequency domain [3]. Analytic and numerical solution will be presented for graded films and graded spheres. [1] D. J. Bergman, Phys. Rev. B 14, 4304 (1976). [2] J. P. Huang, K. W. Yu, G. Q. Gu, M. Karttunen, Phys. Rev. E 67, 051405 (2003). [3] L. Gao, J. P. Huang, K.W. Yu, Eur. Phys. J. B 36, 475 (2003).
NASA Astrophysics Data System (ADS)
Sigernes, Fred; Lorentzen, Dag Arne; Heia, Karsten; Svenøe, Trond
2000-06-01
A small spectral imaging system is presented that images static or moving objects simultaneously as a function of wavelength. The main physical principle is outlined and demonstrated. The instrument is capable of resolving both spectral and spatial information from targets throughout the entire visible region. The spectral domain has a bandpass of 12 . One can achieve the spatial domain by rotating the system s front mirror with a high-resolution stepper motor. The spatial resolution range from millimeters to several meters depends mainly on the front optics used and whether the target is fixed (static) or movable relative to the instrument. Different applications and examples are explored, including outdoor landscapes, industrial fish-related targets, and ground-level objects observed in the more traditional way from an airborne carrier (remote sensing). Through the examples, we found that the instrument correctly classifies whether a shrimp is peeled and whether it can disclose the spectral and spatial microcharacteristics of targets such as a fish nematode (parasite). In the macroregime, we were able to distinguish a marine vessel from the surrounding sea and sky. A study of the directional spectral albedo from clouds, mountains, snow cover, and vegetation has also been included. With the airborne experiment, the imager successfully classified snow cover, leads, and new and rafted ice, as seen from 10.000 ft (3.048 m).
NASA Astrophysics Data System (ADS)
Teutsch, Jason
2007-01-01
It is possible to enumerate all computer programs. In particular, for every partial computable function, there is a shortest program which computes that function. f-MIN is the set of indices for shortest programs. In 1972, Meyer showed that f-MIN is Turing equivalent to 0'', the halting set with halting set oracle. This paper generalizes the notion of shortest programs, and we use various measures from computability theory to describe the complexity of the resulting "spectral sets." We show that under certain Godel numberings, the spectral sets are exactly the canonical sets 0', 0'', 0''', ... up to Turing equivalence. This is probably not true in general, however we show that spectral sets always contain some useful information. We show that immunity, or "thinness" is a useful characteristic for distinguishing between spectral sets. In the final chapter, we construct a set which neither contains nor is disjoint from any infinite arithmetic set, yet it is 0-majorized and contains a natural spectral set. Thus a pathological set becomes a bit more friendly. Finally, a number of interesting open problems are left for the inspired reader.
Parametric Explosion Spectral Model
Ford, S R; Walter, W R
2012-01-19
Small underground nuclear explosions need to be confidently detected, identified, and characterized in regions of the world where they have never before occurred. We develop a parametric model of the nuclear explosion seismic source spectrum derived from regional phases that is compatible with earthquake-based geometrical spreading and attenuation. Earthquake spectra are fit with a generalized version of the Brune spectrum, which is a three-parameter model that describes the long-period level, corner-frequency, and spectral slope at high-frequencies. Explosion spectra can be fit with similar spectral models whose parameters are then correlated with near-source geology and containment conditions. We observe a correlation of high gas-porosity (low-strength) with increased spectral slope. The relationship between the parametric equations and the geologic and containment conditions will assist in our physical understanding of the nuclear explosion source.
Photovoltaic spectral responsivity measurements
Emery, K.; Dunlavy, D.; Field, H.; Moriarty, T.
1998-09-01
This paper discusses the various elemental random and nonrandom error sources in typical spectral responsivity measurement systems. The authors focus specifically on the filter and grating monochrometer-based spectral responsivity measurement systems used by the Photovoltaic (PV) performance characterization team at NREL. A variety of subtle measurement errors can occur that arise from a finite photo-current response time, bandwidth of the monochromatic light, waveform of the monochromatic light, and spatial uniformity of the monochromatic and bias lights; the errors depend on the light source, PV technology, and measurement system. The quantum efficiency can be a function of he voltage bias, light bias level, and, for some structures, the spectral content of the bias light or location on the PV device. This paper compares the advantages and problems associated with semiconductor-detector-based calibrations and pyroelectric-detector-based calibrations. Different current-to-voltage conversion and ac photo-current detection strategies employed at NREL are compared and contrasted.
Infrared transform spectral imager
NASA Astrophysics Data System (ADS)
Vujkovic-Cvijin, Pajo; Lee, Jamine; Gregor, Brian; Goldstein, Neil; Panfili, Raphael; Fox, Marsha
2012-10-01
A dispersive transform spectral imager named FAROS (FAst Reconfigurable Optical Sensor) has been developed for high frame rate, moderate-to-high resolution hyperspectral imaging. A programmable digital micromirror array (DMA) modulator makes it possible to adjust spectral, temporal and spatial resolution in real time to achieve optimum tradeoff for dynamic monitoring requirements. The system's F/2.8 collection optics produces diffraction-limited images in the mid-wave infrared (MWIR) spectral region. The optical system is based on a proprietary dual-pass Offner configuration with a single spherical mirror and a confocal spherical diffraction grating. FAROS fulfills two functions simultaneously: one output produces two-dimensional polychromatic imagery at the full focal plane array (FPA) frame rate for fast object acquisition and tracking, while the other output operates in parallel and produces variable-resolution spectral images via Hadamard transform encoding to assist in object discrimination and classification. The current version of the FAROS spectral imager is a multispectral technology demonstrator that operates in the MWIR with a 320 x 256 pixel InSb FPA running at 478 frames per second resulting in time resolution of several tens of milliseconds per hypercube. The instrument has been tested by monitoring small-scale rocket engine firings in outdoor environments. The instrument has no macro-scale moving parts, and conforms to a robust, small-volume and lightweight package, suitable for integration with small surveillance vehicles. The technology is also applicable to multispectral/hyperspectral imaging applications in diverse areas such as atmospheric contamination monitoring, agriculture, process control, and biomedical imaging, and can be adapted for use in any spectral domain from the ultraviolet (UV) to the LWIR region.
On Summability of Distributions and Spectral Geometry
NASA Astrophysics Data System (ADS)
Estrada, R.; Gracia-Bondía, J. M.; Várilly, J. C.
Modulo the moment asymptotic expansion, the Cesáro and parametric behaviours of distributions at infinity are equivalent. On the strength of this result, we construct the asymptotic analysis for spectral densities arising from elliptic pseudodifferential operators. We show how Cesáro developments lead to efficient calculations of the expansion coefficients of counting number functionals and Green functions. The bosonic action functional proposed by Chamseddine and Connes can more generally be validated as a Cesáro asymptotic development.
Artifacts Of Spectral Analysis Of Instrument Readings
NASA Technical Reports Server (NTRS)
Wise, James H.
1995-01-01
Report presents experimental and theoretical study of some of artifacts introduced by processing outputs of two nominally identical low-frequency-reading instruments; high-sensitivity servo-accelerometers mounted together and operating, in conjunction with signal-conditioning circuits, as seismometers. Processing involved analog-to-digital conversion with anti-aliasing filtering, followed by digital processing including frequency weighting and computation of different measures of power spectral density (PSD).
NASA Astrophysics Data System (ADS)
Longhi, Pietro; Park, Chan Y.
2016-08-01
We introduce a new perspective and a generalization of spectral networks for 4d {N} = 2 theories of class S associated to Lie algebras {g} = A n , D n , E6, and E7. Spectral networks directly compute the BPS spectra of 2d theories on surface defects coupled to the 4d theories. A Lie algebraic interpretation of these spectra emerges naturally from our construction, leading to a new description of 2d-4d wall-crossing phenomena. Our construction also provides an efficient framework for the study of BPS spectra of the 4d theories. In addition, we consider novel types of surface defects associated with minuscule ccrepresentations of {g}.
Chromatic confocal spectral interferometry
Papastathopoulos, Evangelos; Koerner, Klaus; Osten, Wolfgang
2006-11-10
Chromatic confocal spectral interferomertry (CCSI) is a novel scheme for topography measurements that combines the techniques of spectral interferometry and chromatic confocal microscopy. This hybrid method allows for white-light interferometric detection with a high NA in a single-shot manner. To the best of our knowledge, CCSI is the first interferometric method that utilizes a confocally filtered and chromatically dispersed focus for detection and simultaneously allows for retrieval of the depth position of reflecting or scattering objects utilizing the phase (modulation frequency) of the interferometric signals acquired. With the chromatically dispersed focus, the depth range of the sensor is decoupled from the NA of the microscope objective.
Temporal and spectral properties of Comptonized radiation
NASA Technical Reports Server (NTRS)
Kazanas, Demos; Hua, Xin-Min; Titarchuk, Lev
1997-01-01
Relationships are found between the temporal and spectral properties of radiation Compontonized in an extended atmosphere associated with compact accreting sources. It is demonstrated that the power spectrum density imposes constraints on the atmosphere's scale and profile. It is indicated that the slope and low frequency break of the power spectrum density are related to the Thomson depth of the atmosphere and the radius of its physical size, respectively. This relationship allows an independent estimate to be made of the accreting matter Thomson depth. The temporal properties of the high and low state of black hole sources are discussed.
NASA Astrophysics Data System (ADS)
Britt, D. T.; Yeomans, D.; Housen, K.; Consolmagno, G.
2005-01-01
This data set contains a tabulation of asteroid masses, diameters, and bulk densities compiled by D. T. Britt and published in Table 1 of Britt, et al. (2002) [BRITTETAL2002] in the 'Asteroids III' volume.
Analysis of the Power Spectral Density of Tape Recorder Flutter
1976-03-26
NAVAL AIR SYSTEMS COMMAND IRA N. SCHWARZ, CAPT USN Commander W. L. MILLER Technical Director This report describes work performed under...CONTROLLING OFFICE NAME AND ADDRESS Naval Air Systems Command Washington, DC 20361 (% 14. MONITORING AGENCY NAME » AODRESSfil äillrrenl (mm...19. KEY WORDS fConfinue on rev«r»« aide If necessary «nd identity by block number) Analog tape recorders Flutter Interchannel time displacement
NASA Technical Reports Server (NTRS)
Mccord, T. B.; Charette, M. P.; Johnson, T. V.; Lebofsky, L. A.; Pieters, C.; Adams, J. B.
1972-01-01
Results of observations of the spectral reflectance properties (0.3 to 1.1 micron) of a number of lunar mare, upland, and bright crater areas with the use of ground-based telescopes. These new data are discussed in view of earlier studies in an attempt to provide a basis for more detailed interpretation. The spectral reflectivity curves (0.3 to 1.1 micron) for all lunar areas studied consist of a positive sloping continuum with a superimposed symmetric absorption band centered at 0.95 micron. Upland, mare, and bright crater materials can be identified by their spectral curves. The curves for upland and mare regions show a range of shapes from fresh, bright craters to progressively darker background material that correlates with the apparent age of the surface features. The observed upland material has uniform spectral properties, but the mare material shows some variety, probably due to Ti(3+) dispersed in lunar-soil glass. Copernicus and Aristarchus appear to have exposed upland material from beneath the mare but Kepler has not. This observation suggests that the mare is no deeper than about 15 km in the Copernicus area and about 6 km deep in the Aristarchus area, but in the Kepler area the mare must be at least about 5 km deep.
Large Spectral Library Problem
Chilton, Lawrence K.; Walsh, Stephen J.
2008-10-03
Hyperspectral imaging produces a spectrum or vector at each image pixel. These spectra can be used to identify materials present in the image. In some cases, spectral libraries representing atmospheric chemicals or ground materials are available. The challenge is to determine if any of the library chemicals or materials exist in the hyperspectral image. The number of spectra in these libraries can be very large, far exceeding the number of spectral channels collected in the ¯eld. Suppose an image pixel contains a mixture of p spectra from the library. Is it possible to uniquely identify these p spectra? We address this question in this paper and refer to it as the Large Spectral Library (LSL) problem. We show how to determine if unique identi¯cation is possible for any given library. We also show that if p is small compared to the number of spectral channels, it is very likely that unique identi¯cation is possible. We show that unique identi¯cation becomes less likely as p increases.
Microwave spectral line listing
NASA Technical Reports Server (NTRS)
White, W. F., Jr.
1975-01-01
The frequency, intensity, and identification of 9615 spectral lines belonging to 75 molecules are tabulated in order of increasing frequency. Measurements for all 75 molecules were made in the frequency range from 26500 to 40000 MHz by a computer controlled spectrometer. Measurements were also made in the 18000 to 26500 MHz range for some of the molecules.
NASA Technical Reports Server (NTRS)
Mccord, T. B.; Charette, M. P.; Johnson, T. V.; Lebofsky, L. A.; Pieters, C.; Adams, J. B.
1972-01-01
Results of observations of the spectral reflectance properties (0.3 to 1.1 micron) of a number of lunar mare, upland, and bright crater areas with the use of ground-based telescopes. These new data are discussed in view of earlier studies in an attempt to provide a basis for more detailed interpretation. The spectral reflectivity curves (0.3 to 1.1 micron) for all lunar areas studied consist of a positive sloping continuum with a superimposed symmetric absorption band centered at 0.95 micron. Upland, mare, and bright crater materials can be identified by their spectral curves. The curves for upland and mare regions show a range of shapes from fresh, bright craters to progressively darker background material that correlates with the apparent age of the surface features. The observed upland material has uniform spectral properties, but the mare material shows some variety, probably due to Ti(3+) dispersed in lunar-soil glass. Copernicus and Aristarchus appear to have exposed upland material from beneath the mare but Kepler has not. This observation suggests that the mare is no deeper than about 15 km in the Copernicus area and about 6 km deep in the Aristarchus area, but in the Kepler area the mare must be at least about 5 km deep.
Spectral-collocation variational integrators
NASA Astrophysics Data System (ADS)
Li, Yiqun; Wu, Boying; Leok, Melvin
2017-03-01
Spectral methods are a popular choice for constructing numerical approximations for smooth problems, as they can achieve geometric rates of convergence and have a relatively small memory footprint. In this paper, we introduce a general framework to convert a spectral-collocation method into a shooting-based variational integrator for Hamiltonian systems. We also compare the proposed spectral-collocation variational integrators to spectral-collocation methods and Galerkin spectral variational integrators in terms of their ability to reproduce accurate trajectories in configuration and phase space, their ability to conserve momentum and energy, as well as the relative computational efficiency of these methods when applied to some classical Hamiltonian systems. In particular, we note that spectrally-accurate variational integrators, such as the Galerkin spectral variational integrators and the spectral-collocation variational integrators, combine the computational efficiency of spectral methods together with the geometric structure-preserving and long-time structural stability properties of symplectic integrators.
Ultraviolet Spectral Diagnostics
NASA Technical Reports Server (NTRS)
Heap, Sally; Lindler, Don
2009-01-01
At redshifts, z>l, the rest-frame mid-UV is brought into view of large, ground-based telescopes. Here, we report on a study of the potential of the rest-frame UV spectrum for deriving the age since the last major episode of star formation in a galaxy. We base this investigation on wide-band (0.2-1.0 microns), low-resolution (R-1000) spectra of single stars in Hubble's Next Generation Spectral Library (NGSL). We find that a combination of mid-UV spectral indices and colors can indeed yield the age of a stellar population, but only if light from the stellar population is unreddened.
Power spectral estimation algorithms
NASA Technical Reports Server (NTRS)
Bhatia, Manjit S.
1989-01-01
Algorithms to estimate the power spectrum using Maximum Entropy Methods were developed. These algorithms were coded in FORTRAN 77 and were implemented on the VAX 780. The important considerations in this analysis are: (1) resolution, i.e., how close in frequency two spectral components can be spaced and still be identified; (2) dynamic range, i.e., how small a spectral peak can be, relative to the largest, and still be observed in the spectra; and (3) variance, i.e., how accurate the estimate of the spectra is to the actual spectra. The application of the algorithms based on Maximum Entropy Methods to a variety of data shows that these criteria are met quite well. Additional work in this direction would help confirm the findings. All of the software developed was turned over to the technical monitor. A copy of a typical program is included. Some of the actual data and graphs used on this data are also included.
Fault Detection of Rotating Machinery using the Spectral Distribution Function
NASA Technical Reports Server (NTRS)
Davis, Sanford S.
1997-01-01
The spectral distribution function is introduced to characterize the process leading to faults in rotating machinery. It is shown to be a more robust indicator than conventional power spectral density estimates, but requires only slightly more computational effort. The method is illustrated with examples from seeded gearbox transmission faults and an analytical model of a defective bearing. Procedures are suggested for implementation in realistic environments.
The nature of spectral signatures in native arid plant communities
NASA Technical Reports Server (NTRS)
Conn, J. S.; Foster, K. E.; Mcginnies, W. G.
1976-01-01
Radiometric data in ERTS bands 5 and 7 of spectral signature components were compared to the overall signatures obtained from an airborne radiometric data collection system flown at low altitude. Results indicate that due to the low density and low vigor of the vegetation, vegetation has little effect on the overall signature, thus making differentiation of desert plant communities on the basis of spectral signature extremely difficult.
Fault Detection of Rotating Machinery using the Spectral Distribution Function
NASA Technical Reports Server (NTRS)
Davis, Sanford S.
1997-01-01
The spectral distribution function is introduced to characterize the process leading to faults in rotating machinery. It is shown to be a more robust indicator than conventional power spectral density estimates, but requires only slightly more computational effort. The method is illustrated with examples from seeded gearbox transmission faults and an analytical model of a defective bearing. Procedures are suggested for implementation in realistic environments.
Hybrid spectral CT reconstruction
Clark, Darin P.
2017-01-01
Current photon counting x-ray detector (PCD) technology faces limitations associated with spectral fidelity and photon starvation. One strategy for addressing these limitations is to supplement PCD data with high-resolution, low-noise data acquired with an energy-integrating detector (EID). In this work, we propose an iterative, hybrid reconstruction technique which combines the spectral properties of PCD data with the resolution and signal-to-noise characteristics of EID data. Our hybrid reconstruction technique is based on an algebraic model of data fidelity which substitutes the EID data into the data fidelity term associated with the PCD reconstruction, resulting in a joint reconstruction problem. Within the split Bregman framework, these data fidelity constraints are minimized subject to additional constraints on spectral rank and on joint intensity-gradient sparsity measured between the reconstructions of the EID and PCD data. Following a derivation of the proposed technique, we apply it to the reconstruction of a digital phantom which contains realistic concentrations of iodine, barium, and calcium encountered in small-animal micro-CT. The results of this experiment suggest reliable separation and detection of iodine at concentrations ≥ 5 mg/ml and barium at concentrations ≥ 10 mg/ml in 2-mm features for EID and PCD data reconstructed with inherent spatial resolutions of 176 μm and 254 μm, respectively (point spread function, FWHM). Furthermore, hybrid reconstruction is demonstrated to enhance spatial resolution within material decomposition results and to improve low-contrast detectability by as much as 2.6 times relative to reconstruction with PCD data only. The parameters of the simulation experiment are based on an in vivo micro-CT experiment conducted in a mouse model of soft-tissue sarcoma. Material decomposition results produced from this in vivo data demonstrate the feasibility of distinguishing two K-edge contrast agents with a spectral
Spectral Analysis of Radioxenon
2008-09-01
reasons for spectral fitting being a supplement to the standard energy spectrum ROI method. Fermi- Kurie plot Given the difficulty in fitting a beta...continuum, it is important to find an alternative method. A Fermi- Kurie plot (Krane 1988) is one method, which allows a beta spectrum to be plotted ...corrective function takes into account the initial and final spin and polarity states. A rb itr ar y un its Figure 6. Fermi- Kurie plot . T (MeV
Hybrid spectral CT reconstruction.
Clark, Darin P; Badea, Cristian T
2017-01-01
Current photon counting x-ray detector (PCD) technology faces limitations associated with spectral fidelity and photon starvation. One strategy for addressing these limitations is to supplement PCD data with high-resolution, low-noise data acquired with an energy-integrating detector (EID). In this work, we propose an iterative, hybrid reconstruction technique which combines the spectral properties of PCD data with the resolution and signal-to-noise characteristics of EID data. Our hybrid reconstruction technique is based on an algebraic model of data fidelity which substitutes the EID data into the data fidelity term associated with the PCD reconstruction, resulting in a joint reconstruction problem. Within the split Bregman framework, these data fidelity constraints are minimized subject to additional constraints on spectral rank and on joint intensity-gradient sparsity measured between the reconstructions of the EID and PCD data. Following a derivation of the proposed technique, we apply it to the reconstruction of a digital phantom which contains realistic concentrations of iodine, barium, and calcium encountered in small-animal micro-CT. The results of this experiment suggest reliable separation and detection of iodine at concentrations ≥ 5 mg/ml and barium at concentrations ≥ 10 mg/ml in 2-mm features for EID and PCD data reconstructed with inherent spatial resolutions of 176 μm and 254 μm, respectively (point spread function, FWHM). Furthermore, hybrid reconstruction is demonstrated to enhance spatial resolution within material decomposition results and to improve low-contrast detectability by as much as 2.6 times relative to reconstruction with PCD data only. The parameters of the simulation experiment are based on an in vivo micro-CT experiment conducted in a mouse model of soft-tissue sarcoma. Material decomposition results produced from this in vivo data demonstrate the feasibility of distinguishing two K-edge contrast agents with a spectral
Brager, H.R.; Schenter, R.E.; Carter, L.L.; Karnesky, R.A.
1987-08-05
A spectral tailoring device for altering the neutron energy spectra and flux of neutrons in a fast reactor thereby selectively to enhance or inhibit the transmutation rate of a target metrical to form a product isotope. Neutron moderators, neutron filters, neutron absorbers and neutron reflectors may be used as spectral tailoring devices. Depending on the intended use for the device, a member from each of these four classes of materials could be used singularly, or in combination, to provide a preferred neutron energy spectra and flux of the neutrons in the region of the target material. In one embodiment of the invention, an assembly is provided for enhancing the production of isotopes, such as cobalt 60 and gadolinium 153. In another embodiment of the invention, a spectral tailoring device is disposed adjacent a target material which comprises long lived or volatile fission products and the device is used to shift the neutron energy spectra and flux of neutrons in the region of the fission products to preferentially transmute them to produce a less volatile fission product inventory. 6 figs.
Spectral methods for discontinuous problems
NASA Technical Reports Server (NTRS)
Abarbanel, S.; Gottlieb, D.; Tadmor, E.
1985-01-01
Spectral methods yield high-order accuracy even when applied to problems with discontinuities, though not in the sense of pointwise accuracy. Two different procedures are presented which recover pointwise accurate approximations from the spectral calculations.
NASA Technical Reports Server (NTRS)
Lustman, L.
1984-01-01
An outline for spectral methods for partial differential equations is presented. The basic spectral algorithm is defined, collocation are emphasized and the main advantage of the method, the infinite order of accuracy in problems with smooth solutions are discussed. Examples of theoretical numerical analysis of spectral calculations are presented. An application of spectral methods to transonic flow is presented. The full potential transonic equation is among the best understood among nonlinear equations.
Quark Spectral Function above T{sub c}
Qin Sixue; Chang Lei; Liu Yuxin; Roberts, Craig D.
2011-05-24
The maximum entropy method is used to calculate the dressed-quark spectral density from the self-consistent solution of the rainbow-truncated gap equation of QCD at temperatures above T{sub c}, the critical temperature for chiral symmetry restoration. We find that, besides the normal and plasmino modes, the spectral function exhibits an essentially nonperturbative zero mode at the temperatures above but near T{sub c}. In the vicinity of T{sub c}, this long-wavelength mode contains the bulk of the spectral strength. So long as this mode persists, the system may reasonably be described as a strongly-coupled state of matter.
Theory of spatially and spectrally partially coherent pulses.
Lajunen, Hanna; Vahimaa, Pasi; Tervo, Jani
2005-08-01
A coherent-mode representation for spatially and spectrally partially coherent pulses is derived both in the space-frequency domain and in the space-time domain. It is shown that both the cross-spectral density and the mutual coherence function of partially coherent pulses can be expressed as a sum of spatially and spectrally and temporally completely coherent modes. The concept of the effective degree of coherence for nonstationary fields is introduced. As an application of the theory, the propagation of Gaussian Schell-model pulsed beams in the space-frequency domain is considered and their coherent-mode representation is presented.
Spectral analysis of deformed random networks
NASA Astrophysics Data System (ADS)
Jalan, Sarika
2009-10-01
We study spectral behavior of sparsely connected random networks under the random matrix framework. Subnetworks without any connection among them form a network having perfect community structure. As connections among the subnetworks are introduced, the spacing distribution shows a transition from the Poisson statistics to the Gaussian orthogonal ensemble statistics of random matrix theory. The eigenvalue density distribution shows a transition to the Wigner’s semicircular behavior for a completely deformed network. The range for which spectral rigidity, measured by the Dyson-Mehta Δ3 statistics, follows the Gaussian orthogonal ensemble statistics depends upon the deformation of the network from the perfect community structure. The spacing distribution is particularly useful to track very slight deformations of the network from a perfect community structure, whereas the density distribution and the Δ3 statistics remain identical to the undeformed network. On the other hand the Δ3 statistics is useful for the larger deformation strengths. Finally, we analyze the spectrum of a protein-protein interaction network for Helicobacter, and compare the spectral behavior with those of the model networks.
Shear spectral sum rule in a nonconformal gravity dual
Springer, Todd; Gale, Charles; Jeon, Sangyong; Lee, Su Houng
2010-11-15
A sum rule which relates a stress-energy tensor correlator to thermodynamic functions is examined within the context of a simple nonconformal gravity dual. Such a sum rule was previously derived using AdS/CFT for conformal N=4 supersymmetric Yang-Mills theory, but we show that it does not generalize to the nonconformal theory under consideration. We provide a generalized sum rule and numerically verify its validity. A useful by-product of the calculation is the computation of the spectral density in a strongly coupled nonconformal theory. Qualitative features of the spectral densities and implications for lattice measurements of transport coefficients are discussed.
NASA Astrophysics Data System (ADS)
Erard, Stéphane
2015-04-01
Older ground-based observations are reprocessed in order to assess the spectral variability of Ceres surface before the beginning of observations by the Dawn spacecraft. Ceres was observed with NACO on the VLT in 2004 and 2005, producing resolved spectra of the disk under different attitudes. The data cover the range from 0.91-3.80 µm (J, H, K, and L bands), except in the telluric regions. They consist in spectral scans of the dayside, typically with 15 lines of 20 samples, an actual resolution of ~ 100 km, and a spectral resolution R~500 to 1500. A specific calibration scheme has been applied to preprocess the data and to evidence small compositional variations at the surface of Ceres. The major signatures observed are two bands centered at 3.06 and 3.30 µm, which exhibit significant spatial variations at this scale (5 to 10%). These features are best fit by ammoniated minerals (phyllosilicates or feldspars), although the lack of secondary hydration bands seems to rule out phyllosilicates. No significant absorption or variation is observed in J, H and K bands, consistently with [1]. No presence of ices (H2O, C02…) is detected, even at the poles. If Ceres was once rich in ices (e.g., [2]), this suggests a global resurfacing with melting of ices in the subsurface, and alteration under the influence of H2O and perhaps NH3, with reduced production of phyllosilicates. References [1] Carry et al (2012) Icarus 217, 20 [2] McCord, T. B. and C. Sotin (2005) JGR 110, 05009.
High-Resolution Broadband Spectral Interferometry
Erskine, D J; Edelstein, J
2002-08-09
We demonstrate solar spectra from a novel interferometric method for compact broadband high-resolution spectroscopy. The spectral interferometer (SI) is a hybrid instrument that uses a spectrometer to externally disperse the output of a fixed-delay interferometer. It also has been called an externally dispersed interferometer (EDI). The interferometer can be used with linear spectrometers for imaging spectroscopy or with echelle spectrometers for very broad-band coverage. EDI's heterodyning technique enhances the spectrometer's response to high spectral-density features, increasing the effective resolution by factors of several while retaining its bandwidth. The method is extremely robust to instrumental insults such as focal spot size or displacement. The EDI uses no moving parts, such as purely interferometric FTS spectrometers, and can cover a much wider simultaneous bandpass than other internally dispersed interferometers (e.g. HHS or SHS).
Theoretical Studies of Spectral Properties of Plutonium
Zhu, Jian-Xin; Durakiewicz, T.; Joyce, J.J.; Wills, J.M.; Albers, R.C.; McMahan, A.K.; Jones, M.D.
2008-07-01
By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of {delta}-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We show the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the 'open shell' 5f{sup 5} configuration gives the best agreement, resolving the controversy over 5f 'open shell' versus 'close shell' atomic configurations in {delta}-Pu. (authors)
Femtosecond spectral holography
Weiner, A.M.; Leaird, D.E.; Reitze, D.H.; Paek, E.G. )
1992-10-01
Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding, and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain. 44 refs.
Spectrally encoded confocal microscopy
Tearney, G.J.; Webb, R.H.; Bouma, B.E.
1998-08-01
An endoscope-compatible, submicrometer-resolution scanning confocal microscopy imaging system is presented. This approach, spectrally encoded confocal microscopy (SECM), uses a quasi-monochromatic light source and a transmission diffraction grating to detect the reflectivity simultaneously at multiple points along a transverse line within the sample. Since this method does not require fast spatial scanning within the probe, the equipment can be miniaturized and incorporated into a catheter or endoscope. Confocal images of an electron microscope grid were acquired with SECM to demonstrate the feasibility of this technique. {copyright} {ital 1998} {ital Optical Society of America}
NASA Technical Reports Server (NTRS)
Gottlieb, D.; Turkel, E.
1985-01-01
After detailing the construction of spectral approximations to time-dependent mixed initial boundary value problems, a study is conducted of differential equations of the form 'partial derivative of u/partial derivative of t = Lu + f', where for each t, u(t) belongs to a Hilbert space such that u satisfies homogeneous boundary conditions. For the sake of simplicity, it is assumed that L is an unbounded, time-independent linear operator. Attention is given to Fourier methods of both Galerkin and pseudospectral method types, the Galerkin method, the pseudospectral Chebyshev and Legendre methods, the error equation, hyperbolic partial differentiation equations, and time discretization and iterative methods.
Femtosecond spectral holography
NASA Astrophysics Data System (ADS)
Weiner, Andrew M.; Leaird, Daniel E.; Reitze, David H.; Paek, Eung G.
1992-10-01
Storage, recall, and processing of shaped femtosecond waveforms are achieved by performing spectral holography within a femtosecond pulse shaping apparatus. Time reversal, as well as correlation and convolution, of femtosecond temporal signals is demonstrated. Applications of this technique to matched filtering, dispersion compensation, encryption and decoding, and femtosecond waveform synthesis are also discussed. The work extends the powerful principles of holographic signal processing, which have been used extensively for pattern recognition and filtering of two-dimensional spatial signals, to the femtosecond time domain.
Spectral albedos of midlatitude snowpacks
NASA Technical Reports Server (NTRS)
Choudhury, B.
1981-01-01
Spectral albedos of impure-nonhomogeneous snowpacks, typical of midlatitudes, from 400 to 2200 nm were modeled through a numerical solution of the radiative transfer equation in the two-stream approximation. Discrete depth-dependent values of density, grain size and impurity concentration were used to characterize the snowpacks. The model is for diffuse incident radiation, and the numerical method is based on doubling and invariant imbedding. The effect of soot impurities on snowpack albedos is illustrated when a snowpack is several centimeters deep and soot reduces the albedos at visible wavelengths, however, when a snowpack is only a few centimeters deep, soot may increase the albedos at visible wavelengths. By adjusting soot content and snow grain size, good quantitative agreement with some observations at the Cascade Mountains (Washington) and at Point Barrow (Alaska) are obtained; however, the model grain sizes are found to be fifty to four hundred percent larger than the measured values. For satellite snowcover observations, a model for effective albedo of partially snow-covered areas was developed and compared with some NOAA-2 observations of the southeastern United States.
Spectral partitioning in equitable graphs
NASA Astrophysics Data System (ADS)
Barucca, Paolo
2017-06-01
Graph partitioning problems emerge in a wide variety of complex systems, ranging from biology to finance, but can be rigorously analyzed and solved only for a few graph ensembles. Here, an ensemble of equitable graphs, i.e., random graphs with a block-regular structure, is studied, for which analytical results can be obtained. In particular, the spectral density of this ensemble is computed exactly for a modular and bipartite structure. Kesten-McKay's law for random regular graphs is found analytically to apply also for modular and bipartite structures when blocks are homogeneous. An exact solution to graph partitioning for two equal-sized communities is proposed and verified numerically, and a conjecture on the absence of an efficient recovery detectability transition in equitable graphs is suggested. A final discussion summarizes results and outlines their relevance for the solution of graph partitioning problems in other graph ensembles, in particular for the study of detectability thresholds and resolution limits in stochastic block models.
The dynamics of variable-density turbulence
Sandoval, D.L.
1995-11-01
The dynamics of variable-density turbulent fluids are studied by direct numerical simulation. The flow is incompressible so that acoustic waves are decoupled from the problem, and implying that density is not a thermodynamic variable. Changes in density occur due to molecular mixing. The velocity field, is in general, divergent. A pseudo-spectral numerical technique is used to solve the equations of motion. Three-dimensional simulations are performed using a grid size of 128{sup 3} grid points. Two types of problems are studied: (1) the decay of isotropic, variable-density turbulence, and (2) buoyancy-generated turbulence in a fluid with large density fluctuations. In the case of isotropic, variable-density turbulence, the overall statistical decay behavior, for the cases studied, is relatively unaffected by the presence of density variations when the initial density and velocity fields are statistically independent. The results for this case are in quantitative agreement with previous numerical and laboratory results. In this case, the initial density field has a bimodal probability density function (pdf) which evolves in time towards a Gaussian distribution. The pdf of the density field is symmetric about its mean value throughout its evolution. If the initial velocity and density fields are statistically dependent, however, the decay process is significantly affected by the density fluctuations. For the case of buoyancy-generated turbulence, variable-density departures from the Boussinesq approximation are studied. The results of the buoyancy-generated turbulence are compared with variable-density model predictions. Both a one-point (engineering) model and a two-point (spectral) model are tested against the numerical data. Some deficiencies in these variable-density models are discussed and modifications are suggested.
OSSE spectral analysis techniques
NASA Technical Reports Server (NTRS)
Purcell, W. R.; Brown, K. M.; Grabelsky, D. A.; Johnson, W. N.; Jung, G. V.; Kinzer, R. L.; Kroeger, R. A.; Kurfess, J. D.; Matz, S. M.; Strickman, M. S.
1992-01-01
Analysis of the spectra from the Oriented Scintillation Spectrometer Experiment (OSSE) is complicated because of the typically low signal to noise (approx. 0.1 percent) and the large background variability. The OSSE instrument was designed to address these difficulties by periodically offset-pointing the detectors from the source to perform background measurements. These background measurements are used to estimate the background during each of the source observations. The resulting background-subtracted spectra can then be accumulated and fitted for spectral lines and/or continua. Data selection based on various environmental parameters can be performed at various stages during the analysis procedure. In order to achieve the instrument's statistical sensitivity, however, it will be necessary for investigators to develop a detailed understanding of the instrument operation, data collection, and the background spectrum and its variability. A brief description of the major steps in the OSSE spectral analysis process is described, including a discussion of the OSSE background spectrum and examples of several observational strategies.
Spectral quantification of Southern Baltic seabed roughness
NASA Astrophysics Data System (ADS)
Szefler, K.; Tegowski, J.; Nowak, J.
2012-12-01
The work presents the fast and efficient tool for seafloor classification, where scales and shapes of geomorphological forms were taken into account. The precise bathymetry and seafloor texture was developed with multibeam echosounder at six different areas of size up to 10 by 20 km. This areas demonstrate typical geomorphological seafloor features of bottom relief at the southern Baltic Sea coastal waters. The acoustical measurements were accompanied by geological sampling and video inspection. High resolution mosaic maps were obtained as a result of multi-survey measurements with maximal spatial resolution of 0.05m. Such accuracy of the measurements allows to observe small geomorphologic forms as ripplemarks or pebbles. The most investigated polygons have bottom relief of polygenetic origin with relicts of periglacial forms together with contemporary forms of marine origin. In the studied areas different forms of sand accumulation were found, beginning with small ripplemarks ending at big sandy waves. In the seabed erosion zones the bottom surface is rough and varied with clearly formed embankments, abrasive platforms, inselbergs and stony gravely abrasive pavements on the bottom surface. Such geomorphic diversity of the bottom surface has allowed for development of consistent geomorphological classification system based mainly on spectral properties of seafloor roughness. Each analysed area was divided into squares (200 by 200 m) with an overlap between adjacent subareas of 75% a square size. Next, subdivided areas were spectrally transformed using a two dimensional fast Fourier transform (2D FFT). The spectral parameters as maximal value of spectral density function, spectral exponent and strength, spectral moments, mean frequency, spectral width and skewness for each characteristic type of bottom surface were determined relaying on the calculated 2D spectra. Moreover, other features characterised the corrugated surface as fractal dimension, radius of
Stark broadening of Kr UV spectral lines
Cirisan, M.; Djurovic, S.; Pelaez, R. J.; Aparicio, J. A.; Mar, S.
2011-01-15
This work reports new data for the Stark parameters of doubly ionized krypton spectral lines. Stark widths and shifts of Kr iii lines belonging to the UV region (245-300 nm) have been measured. A low-pressure pulsed arc, containing a mixture of 8% krypton and 92% helium, was used as a plasma source. Measured electron densities and electron temperatures were in the range (0.7-2.0)x10{sup 23} m{sup -3} and 16 000-20 000 K, respectively. Experimentally obtained data were compared to theoretical results calculated using simplified modified semiempirical formulas.
Information theory, spectral geometry, and quantum gravity.
Kempf, Achim; Martin, Robert
2008-01-18
We show that there exists a deep link between the two disciplines of information theory and spectral geometry. This allows us to obtain new results on a well-known quantum gravity motivated natural ultraviolet cutoff which describes an upper bound on the spatial density of information. Concretely, we show that, together with an infrared cutoff, this natural ultraviolet cutoff beautifully reduces the path integral of quantum field theory on curved space to a finite number of ordinary integrations. We then show, in particular, that the subsequent removal of the infrared cutoff is safe.
SHJAR Jet Noise Data and Power Spectral Laws
NASA Technical Reports Server (NTRS)
Khavaran, Abbas; Bridges, James
2009-01-01
High quality jet noise spectral data measured at the Aeroacoustic Propulsion Laboratory at the NASA Glenn Research Center is used to examine a number of jet noise scaling laws. Configurations considered in the present study consist of convergent and convergent-divergent axisymmetric nozzles. The measured spectral data are shown in narrow band and cover 8193 equally spaced points in a typical Strouhal number range of 0.0 to 10.0. The measured data are reported as lossless (i.e., atmospheric attenuation is added to measurements), and at 24 equally spaced angles (50deg to 165deg) on a 100-diameter (200-in.) arc. Following the work of Viswanathan, velocity power factors are evaluated using a least squares fit on spectral power density as a function of jet temperature and observer angle. The goodness of the fit and the confidence margins for the two regression parameters are studied at each angle, and alternative relationships are proposed to improve the spectral collapse when certain conditions are met. As an immediate application of the velocity power laws, spectral density in shockcontaining jets are decomposed into components attributed to jet mixing noise and shock noise. From this analysis, jet noise prediction tools can be developed with different spectral components derived from different physics.
Miniature spectrally selective dosimeter
NASA Technical Reports Server (NTRS)
Adams, R. R.; Macconochie, I. O.; Poole, B. D., Jr. (Inventor)
1980-01-01
A miniature spectrally selective dosimeter capable of measuring selected bandwidths of radiation exposure on small mobile areas is described. This is achieved by the combination of photovoltaic detectors, electrochemical integrators (E-cells) and filters in a small compact case which can be easily attached in close proximity to and substantially parallel to the surface being measured. In one embodiment two photovoltaic detectors, two E-cells, and three filters are packaged in a small case with attaching means consisting of a safety pin. In another embodiment, two detectors, one E-cell, three filters are packaged in a small case with attaching means consisting of a clip to clip over a side piece of an eye glass frame.
Miniature spectrally selective dosimeter
NASA Astrophysics Data System (ADS)
Adams, R. R.; MacConochie, I. O.; Poole, B. D., Jr.
1980-10-01
A miniature spectrally selective dosimeter capable of measuring selected bandwidths of radiation exposure on small mobile areas is described. This is achieved by the combination of photovoltaic detectors, electrochemical integrators (E-cells) and filters in a small compact case which can be easily attached in close proximity to and substantially parallel to the surface being measured. In one embodiment two photovoltaic detectors, two E-cells, and three filters are packaged in a small case with attaching means consisting of a safety pin. In another embodiment, two detectors, one E-cell, three filters are packaged in a small case with attaching means consisting of a clip to clip over a side piece of an eye glass frame.
Spectral disentangling with Spectangular
NASA Astrophysics Data System (ADS)
Sablowski, Daniel P.; Weber, Michael
2017-01-01
The paper introduces the software Spectangular for spectral disentangling via singular value decomposition with global optimisation of the orbital parameters of the stellar system or radial velocities of the individual observations. We will describe the procedure and the different options implemented in our program. Furthermore, we will demonstrate the performance and the applicability using tests on artificial data. Additionally, we use high-resolution spectra of Capella to demonstrate the performance of our code on real-world data. The novelty of this package is the implemented global optimisation algorithm and the graphical user interface (GUI) for ease of use. We have implemented the code to tackle SB1 and SB2 systems with the option of also dealing with telluric (static) lines. Based in part on data obtained with the STELLA robotic telescope in Tenerife, an AIP facility jointly operated by AIP and IAC.
NASA Technical Reports Server (NTRS)
Spiering, Bruce A. (Inventor)
1999-01-01
An optical imaging system provides automatic co-registration of a plurality of multi spectral images of an object which are generated by a plurality of video cameras or other optical detectors. The imaging system includes a modular assembly of beam splitters, lens tubes, camera lenses and wavelength selective filters which facilitate easy reconfiguration and adjustment of the system for various applications. A primary lens assembly generates a real image of an object to be imaged on a reticle which is positioned at a fixed length from a beam splitter assembly. The beam splitter assembly separates a collimated image beam received from the reticle into multiple image beams, each of which is projected onto a corresponding one of a plurality of video cameras. The lens tubes which connect the beam splitter assembly to the cameras are adjustable in length to provide automatic co-registration of the images generated by each camera.
Method of multivariate spectral analysis
Keenan, Michael R.; Kotula, Paul G.
2004-01-06
A method of determining the properties of a sample from measured spectral data collected from the sample by performing a multivariate spectral analysis. The method can include: generating a two-dimensional matrix A containing measured spectral data; providing a weighted spectral data matrix D by performing a weighting operation on matrix A; factoring D into the product of two matrices, C and S.sup.T, by performing a constrained alternating least-squares analysis of D=CS.sup.T, where C is a concentration intensity matrix and S is a spectral shapes matrix; unweighting C and S by applying the inverse of the weighting used previously; and determining the properties of the sample by inspecting C and S. This method can be used to analyze X-ray spectral data generated by operating a Scanning Electron Microscope (SEM) with an attached Energy Dispersive Spectrometer (EDS).
Accurate spectral color measurements
NASA Astrophysics Data System (ADS)
Hiltunen, Jouni; Jaeaeskelaeinen, Timo; Parkkinen, Jussi P. S.
1999-08-01
Surface color measurement is of importance in a very wide range of industrial applications including paint, paper, printing, photography, textiles, plastics and so on. For a demanding color measurements spectral approach is often needed. One can measure a color spectrum with a spectrophotometer using calibrated standard samples as a reference. Because it is impossible to define absolute color values of a sample, we always work with approximations. The human eye can perceive color difference as small as 0.5 CIELAB units and thus distinguish millions of colors. This 0.5 unit difference should be a goal for the precise color measurements. This limit is not a problem if we only want to measure the color difference of two samples, but if we want to know in a same time exact color coordinate values accuracy problems arise. The values of two instruments can be astonishingly different. The accuracy of the instrument used in color measurement may depend on various errors such as photometric non-linearity, wavelength error, integrating sphere dark level error, integrating sphere error in both specular included and specular excluded modes. Thus the correction formulas should be used to get more accurate results. Another question is how many channels i.e. wavelengths we are using to measure a spectrum. It is obvious that the sampling interval should be short to get more precise results. Furthermore, the result we get is always compromise of measuring time, conditions and cost. Sometimes we have to use portable syste or the shape and the size of samples makes it impossible to use sensitive equipment. In this study a small set of calibrated color tiles measured with the Perkin Elmer Lamda 18 and the Minolta CM-2002 spectrophotometers are compared. In the paper we explain the typical error sources of spectral color measurements, and show which are the accuracy demands a good colorimeter should have.
ATR neutron spectral characterization
Rogers, J.W.; Anderl, R.A.
1995-11-01
The Advanced Test Reactor (ATR) at INEL provides intense neutron fields for irradiation-effects testing of reactor material samples, for production of radionuclides used in industrial and medical applications, and for scientific research. Characterization of the neutron environments in the irradiation locations of the ATR has been done by means of neutronics calculations and by means of neutron dosimetry based on the use of neutron activation monitors that are placed in the various irradiation locations. The primary purpose of this report is to present the results of an extensive characterization of several ATR irradiation locations based on neutron dosimetry measurements and on least-squares-adjustment analyses that utilize both neutron dosimetry measurements and neutronics calculations. This report builds upon the previous publications, especially the reference 4 paper. Section 2 provides a brief description of the ATR and it tabulates neutron spectral information for typical irradiation locations, as derived from the more historical neutron dosimetry measurements. Relevant details that pertain to the multigroup neutron spectral characterization are covered in section 3. This discussion includes a presentation on the dosimeter irradiation and analyses and a development of the least-squares adjustment methodology, along with a summary of the results of these analyses. Spectrum-averaged cross sections for neutron monitoring and for displacement-damage prediction in Fe, Cr, and Ni are given in section 4. In addition, section4 includes estimates of damage generation rates for these materials in selected ATR irradiation locations. In section 5, the authors present a brief discussion of the most significant conclusions of this work and comment on its relevance to the present ATR core configuration. Finally, detailed numerical and graphical results for the spectrum-characterization analyses in each irradiation location are provided in the Appendix.
[Study on the arc spectral information for welding quality diagnosis].
Li, Zhi-Yong; Gu, Xiao-Yan; Li, Huan; Yang, Li-Jun
2009-03-01
Through collecting the spectral signals of TIG and MIG welding arc with spectrometer, the arc light radiations were analyzed based on the basic theory of plasma physics. The radiation of welding arc distributes over a broad range of frequency, from infrared to ultraviolet. The arc spectrum is composed of line spectra and continuous spectra. Due to the variation of metal density in the welding arc, there is great difference between the welding arc spectra of TIG and MIG in both their intensity and distribution. The MIG welding arc provides more line spectra of metal and the intensity of radiation is greater than TIG. The arc spectrum of TIG welding is stable during the welding process, disturbance factors that cause the spectral variations can be reflected by the spectral line related to the corresponding element entering the welding arc. The arc spectrum of MIG welding will fluctuate severely due to droplet transfer, which produces "noise" in the line spectrum aggregation zone. So for MIG welding, the spectral zone lacking spectral line is suitable for welding quality diagnosis. According to the characteristic of TIG and MIG, special spectral zones were selected for welding quality diagnosis. For TIG welding, the selected zone is in ultraviolet zone (230-300 nm). For MIG welding, the selected zone is in visible zone (570-590 nm). With the basic theory provided for welding quality diagnosis, the integral intensity of spectral signal in the selected zone of welding process with disturbing factor was studied to prove the theory. The results show that the welding quality and disturbance factors can be diagnosed with good signal to noise ratio in the selected spectral zone compared with signal in other spectral zone. The spectral signal can be used for real-time diagnosis of the welding quality.
Spectral distribution of solar radiation
NASA Technical Reports Server (NTRS)
Mecherikunnel, A. T.; Richmond, J.
1980-01-01
Available quantitative data on solar total and spectral irradiance are examined in the context of utilization of solar irradiance for terrestrial applications of solar energy. The extraterrestrial solar total and spectral irradiance values are also reviewed. Computed values of solar spectral irradiance at ground level for different air mass values and various levels of atmospheric pollution or turbidity are presented. Wavelengths are given for computation of solar, absorptance, transmittance and reflectance by the 100 selected-ordinate method and by the 50 selected-ordinate method for air mass 1.5 and 2 solar spectral irradiance for the four levels of atmospheric pollution.
Design of visible/infrared double-band spectral imager
NASA Astrophysics Data System (ADS)
Tianjin, Tang; Zhuo, Zhang; Bao-hua, Wang
2016-01-01
OFFNER hyperspectral imager using convex grating as spectral splitting component has many merits including large relative aperture, no smile, small key stone, compact construction and easier assembly and etc, has widely used in many occasions of various fields. Design of double-band hyperspectral imager using OFFNER structure is presented in this paper. SHAFER fore telescope system and convex grating imaging are adopted, groove etching density is different in different region on the same substrate for different spectral band, and different diffractive order is used respectively to split the two spectral bands. The optical system achieves good image quality in wide spectral range, compact construction and small volume. And all the reflective curved face are sphere, moderate tolerances are good for the processing and alignment.
Soybean Aphid (Hemiptera: Aphididae) Affects Soybean Spectral Reflectance
Alves, Tavvs M.; Macrae, Ian V.; Koch, Robert L.
2015-01-01
Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is the most economically important insect pest of soybean in the north central United States. Scouting-based integrated pest management (IPM) programs could become more efficient and more widely adopted by using plant spectral reflectance to estimate soybean aphid injury. Our objective was to determine whether plant spectral reflectance is affected by soybean aphid feeding. Field trials were conducted in 2013 and 2014 using caged plots. Early-, late-, and noninfested treatments were established to create a gradient of soybean aphid pressure. Whole-plant soybean aphid densities were recorded weekly. Measurements of plant spectral reflectance occurred on two sample dates per year. Simple linear regression models were used to test the effect of cumulative aphid-days (CAD) on plant spectral reflectance at 680 nm (RED) and 800 nm (NIR), normalized difference vegetation index (NDVI), and relative chlorophyll content. Data indicated that CAD had no effect on canopy-level RED reflectance, but CAD decreased canopy-level NIR reflectance and NDVI. Canopy- and leaf-level measurements typically indicated similar plant spectral response to increasing CAD. CAD generally had no effect on relative chlorophyll content. The present study provides the first documentation that remote sensing holds potential for detecting changes in plant spectral reflectance induced by soybean aphid. The use of plant spectral reflectance in soybean aphid management may assist future IPM programs to reduce sampling costs and prevent prophylactic insecticide sprays. PMID:26470392
Dual-channel spectrally encoded endoscopic probe.
Engel, Guy; Genish, Hadar; Rosenbluh, Michael; Yelin, Dvir
2012-08-01
High quality imaging through sub-millimeter endoscopic probes provides clinicians with valuable diagnostics capabilities in hard to reach locations within the body. Spectrally encoded endoscopy (SEE) has been shown promising for such task; however, challenging probe fabrication and high speckle noise had prevented its testing in in vivo studies. Here we demonstrate a novel miniature SEE probe which incorporates some of the recent progress in spectrally encoded technology into a compact and robust endoscopic system. A high-quality miniature diffraction grating was fabricated using automated femtosecond laser cutting from a large bulk grating. Using one spectrally encoded channel for imaging and a separate channel for incoherent illumination, the new system has large depth of field, negligible back reflections and well controlled speckle noise which depends on the core diameter of the illumination fiber. Moreover, by using a larger imaging channel, higher groove density grating, shorter wavelength and broader spectrum, the new endoscopic system now allow significant improvements in almost all imaging parameter compared to previous systems, through an ultra-miniature endoscopic probe.
Dual-channel spectrally encoded endoscopic probe
Engel, Guy; Genish, Hadar; Rosenbluh, Michael; Yelin, Dvir
2012-01-01
High quality imaging through sub-millimeter endoscopic probes provides clinicians with valuable diagnostics capabilities in hard to reach locations within the body. Spectrally encoded endoscopy (SEE) has been shown promising for such task; however, challenging probe fabrication and high speckle noise had prevented its testing in in vivo studies. Here we demonstrate a novel miniature SEE probe which incorporates some of the recent progress in spectrally encoded technology into a compact and robust endoscopic system. A high-quality miniature diffraction grating was fabricated using automated femtosecond laser cutting from a large bulk grating. Using one spectrally encoded channel for imaging and a separate channel for incoherent illumination, the new system has large depth of field, negligible back reflections and well controlled speckle noise which depends on the core diameter of the illumination fiber. Moreover, by using a larger imaging channel, higher groove density grating, shorter wavelength and broader spectrum, the new endoscopic system now allow significant improvements in almost all imaging parameter compared to previous systems, through an ultra-miniature endoscopic probe. PMID:22876349
Quantum spectral dimension in quantum field theory
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca; Modesto, Leonardo; Nardelli, Giuseppe
2016-03-01
We reinterpret the spectral dimension of spacetimes as the scaling of an effective self-energy transition amplitude in quantum field theory (QFT), when the system is probed at a given resolution. This picture has four main advantages: (a) it dispenses with the usual interpretation (unsatisfactory in covariant approaches) where, instead of a transition amplitude, one has a probability density solving a nonrelativistic diffusion equation in an abstract diffusion time; (b) it solves the problem of negative probabilities known for higher-order and nonlocal dispersion relations in classical and quantum gravity; (c) it clarifies the concept of quantum spectral dimension as opposed to the classical one. We then consider a class of logarithmic dispersion relations associated with quantum particles and show that the spectral dimension dS of spacetime as felt by these quantum probes can deviate from its classical value, equal to the topological dimension D. In particular, in the presence of higher momentum powers it changes with the scale, dropping from D in the infrared (IR) to a value dSUV ≤ D in the ultraviolet (UV). We apply this general result to Stelle theory of renormalizable gravity, which attains the universal value dSUV = 2 for any dimension D.
Spectral reconstruction of protein contact networks
NASA Astrophysics Data System (ADS)
Maiorino, Enrico; Rizzi, Antonello; Sadeghian, Alireza; Giuliani, Alessandro
2017-04-01
In this work, we present a method for generating an adjacency matrix encoding a typical protein contact network. This work constitutes a follow-up to our recent work (Livi et al., 2015), whose aim was to estimate the relative contribution of different topological features in discovering of the unique properties of protein structures. We perform a genetic algorithm based optimization in order to modify the matrices generated with the procedures explained in (Livi et al., 2015). Our objective here is to minimize the distance with respect to a target spectral density, which is elaborated using the normalized graph Laplacian representation of graphs. Such a target density is obtained by averaging the kernel-estimated densities of a class of experimental protein maps having different dimensions. This is possible given the bounded-domain property of the normalized Laplacian spectrum. By exploiting genetic operators designed for this specific problem and an exponentially-weighted objective function, we are able to reconstruct adjacency matrices representing networks of varying size whose spectral density is indistinguishable from the target. The topological features of the optimized networks are then compared to the real protein contact networks and they show an increased similarity with respect to the starting networks. Subsequently, the statistical properties of the spectra of the newly generated matrices are analyzed by employing tools borrowed from random matrix theory. The nearest neighbors spacing distribution of the spectra of the generated networks indicates that also the (short-range) correlations of the Laplacian eigenvalues are compatible with those of real proteins.
Multiple Point Dynamic Gas Density Measurements Using Molecular Rayleigh Scattering
NASA Technical Reports Server (NTRS)
Seasholtz, Richard; Panda, Jayanta
1999-01-01
A nonintrusive technique for measuring dynamic gas density properties is described. Molecular Rayleigh scattering is used to measure the time-history of gas density simultaneously at eight spatial locations at a 50 kHz sampling rate. The data are analyzed using the Welch method of modified periodograms to reduce measurement uncertainty. Cross-correlations, power spectral density functions, cross-spectral density functions, and coherence functions may be obtained from the data. The technique is demonstrated using low speed co-flowing jets with a heated inner jet.
Preussler, Stefan; Zadok, Avi; Wiatrek, Andrzej; Tur, Moshe; Schneider, Thomas
2012-06-18
High-resolution, wide-bandwidth optical spectrum analysis is essential to the measuring and monitoring of advanced optical, millimeter-wave, and terahertz communication systems, sensing applications and device characterization. One category of high-resolution spectrum analyzers reconstructs the power spectral density of a signal under test by scanning a Brillouin gain line across its spectral extent. In this work, we enhance both the resolution and the optical rejection ratio of such Brillouin-based spectrometers using a combination of two techniques. First, two Brillouin loss lines are superimposed upon a central Brillouin gain to reduce its bandwidth. Second, the vector attributes of stimulated Brillouin scattering amplification in standard, weakly birefringent fibers are used to change the signal state of polarization, and a judiciously aligned output polarizer discriminates between amplified and un-amplified spectral contents. A frequency resolution of 3 MHz, or eight orders of magnitude below the central optical frequency, is experimentally demonstrated. In addition, a weak spectral component is resolved in the presence of a strong adjacent signal, which is 30 dB stronger and detuned by only 60 MHz. The measurement method involves low-bandwidth direct detection, and does not require heterodyne beating. The measurement range of the proposed method is scalable to cover the C + L bands, depending on the tunable pump source. The accuracy of the measurements requires that the pump frequencies are well calibrated.
Critical density of a soliton gas
El, G. A.
2016-02-15
We quantify the notion of a dense soliton gas by establishing an upper bound for the integrated density of states of the quantum-mechanical Schrödinger operator associated with the Korteweg–de Vries soliton gas dynamics. As a by-product of our derivation, we find the speed of sound in the soliton gas with Gaussian spectral distribution function.
Spectral methods on arbitrary grids
NASA Technical Reports Server (NTRS)
Carpenter, Mark H.; Gottlieb, David
1995-01-01
Stable and spectrally accurate numerical methods are constructed on arbitrary grids for partial differential equations. These new methods are equivalent to conventional spectral methods but do not rely on specific grid distributions. Specifically, we show how to implement Legendre Galerkin, Legendre collocation, and Laguerre Galerkin methodology on arbitrary grids.
ENVIRONMENTAL APPLICATIONS OF SPECTRAL IMAGING
The utility of remote sensing using spectral imaging is just being realized through the investigation to a wide variety of environmental issues. Improved spectral and spatial resolution is very important to the detection of effects once regarded as unobservable. A current researc...
Spectral multidimensional scaling
Aflalo, Yonathan; Kimmel, Ron
2013-01-01
An important tool in information analysis is dimensionality reduction. There are various approaches for large data simplification by scaling its dimensions down that play a significant role in recognition and classification tasks. The efficiency of dimension reduction tools is measured in terms of memory and computational complexity, which are usually a function of the number of the given data points. Sparse local operators that involve substantially less than quadratic complexity at one end, and faithful multiscale models with quadratic cost at the other end, make the design of dimension reduction procedure a delicate balance between modeling accuracy and efficiency. Here, we combine the benefits of both and propose a low-dimensional multiscale modeling of the data, at a modest computational cost. The idea is to project the classical multidimensional scaling problem into the data spectral domain extracted from its Laplace–Beltrami operator. There, embedding into a small dimensional Euclidean space is accomplished while optimizing for a small number of coefficients. We provide a theoretical support and demonstrate that working in the natural eigenspace of the data, one could reduce the process complexity while maintaining the model fidelity. As examples, we efficiently canonize nonrigid shapes by embedding their intrinsic metric into , a method often used for matching and classifying almost isometric articulated objects. Finally, we demonstrate the method by exposing the style in which handwritten digits appear in a large collection of images. We also visualize clustering of digits by treating images as feature points that we map to a plane. PMID:24108352
Spectral imagery collection experiment
NASA Astrophysics Data System (ADS)
Romano, Joao M.; Rosario, Dalton; Farley, Vincent; Sohr, Brian
2010-04-01
The Spectral and Polarimetric Imagery Collection Experiment (SPICE) is a collaborative effort between the US Army ARDEC and ARL for the collection of mid-wave and long-wave infrared imagery using hyperspectral, polarimetric, and broadband sensors. The objective of the program is to collect a comprehensive database of the different modalities over the course of 1 to 2 years to capture sensor performance over a wide variety of adverse weather conditions, diurnal, and seasonal changes inherent to Picatinny's northern New Jersey location. Using the Precision Armament Laboratory (PAL) tower at Picatinny Arsenal, the sensors will autonomously collect the desired data around the clock at different ranges where surrogate 2S3 Self-Propelled Howitzer targets are positioned at different viewing perspectives at 549 and 1280m from the sensor location. The collected database will allow for: 1) Understand of signature variability under the different weather conditions; 2) Development of robust algorithms; 3) Development of new sensors; 4) Evaluation of hyperspectral and polarimetric technologies; and 5) Evaluation of fusing the different sensor modalities. In this paper, we will present the SPICE data collection objectives, the ongoing effort, the sensors that are currently deployed, and how this work will assist researches on the development and evaluation of sensors, algorithms, and fusion applications.
Covariance propagation in spectral indices
Griffin, P. J.
2015-01-09
In this study, the dosimetry community has a history of using spectral indices to support neutron spectrum characterization and cross section validation efforts. An important aspect to this type of analysis is the proper consideration of the contribution of the spectrum uncertainty to the total uncertainty in calculated spectral indices (SIs). This study identifies deficiencies in the traditional treatment of the SI uncertainty, provides simple bounds to the spectral component in the SI uncertainty estimates, verifies that these estimates are reflected in actual applications, details a methodology that rigorously captures the spectral contribution to the uncertainty in the SI, and provides quantified examples that demonstrate the importance of the proper treatment the spectral contribution to the uncertainty in the SI.
Covariance propagation in spectral indices
Griffin, P. J.
2015-01-09
In this study, the dosimetry community has a history of using spectral indices to support neutron spectrum characterization and cross section validation efforts. An important aspect to this type of analysis is the proper consideration of the contribution of the spectrum uncertainty to the total uncertainty in calculated spectral indices (SIs). This study identifies deficiencies in the traditional treatment of the SI uncertainty, provides simple bounds to the spectral component in the SI uncertainty estimates, verifies that these estimates are reflected in actual applications, details a methodology that rigorously captures the spectral contribution to the uncertainty in the SI, andmore » provides quantified examples that demonstrate the importance of the proper treatment the spectral contribution to the uncertainty in the SI.« less
ERIC Educational Resources Information Center
Machado, Calixto; Estévez, Mario; Leisman, Gerry; Melillo, Robert; Rodríguez, Rafael; DeFina, Phillip; Hernández, Adrián; Pérez-Nellar, Jesús; Naranjo, Rolando; Chinchilla, Mauricio; Garófalo, Nicolás; Vargas, José; Beltrán, Carlos
2015-01-01
We studied autistics by quantitative EEG spectral and coherence analysis during three experimental conditions: basal, watching a cartoon with audio (V-A), and with muted audio band (VwA). Significant reductions were found for the absolute power spectral density (PSD) in the central region for delta and theta, and in the posterior region for sigma…
ERIC Educational Resources Information Center
Machado, Calixto; Estévez, Mario; Leisman, Gerry; Melillo, Robert; Rodríguez, Rafael; DeFina, Phillip; Hernández, Adrián; Pérez-Nellar, Jesús; Naranjo, Rolando; Chinchilla, Mauricio; Garófalo, Nicolás; Vargas, José; Beltrán, Carlos
2015-01-01
We studied autistics by quantitative EEG spectral and coherence analysis during three experimental conditions: basal, watching a cartoon with audio (V-A), and with muted audio band (VwA). Significant reductions were found for the absolute power spectral density (PSD) in the central region for delta and theta, and in the posterior region for sigma…
ULTRAVIOLET RAMAN SPECTRAL SIGNATURE ACQUISITION: UV RAMAN SPECTRAL FINGERPRINTS.
SEDLACEK,III, A.J.FINFROCK,C.
2002-09-01
As a member of the science-support part of the ITT-lead LISA development program, BNL is tasked with the acquisition of UV Raman spectral fingerprints and associated scattering cross-sections for those chemicals-of-interest to the program's sponsor. In support of this role, the present report contains the first installment of UV Raman spectral fingerprint data on the initial subset of chemicals. Because of the unique nature associated with the acquisition of spectral fingerprints for use in spectral pattern matching algorithms (i.e., CLS, PLS, ANN) great care has been undertaken to maximize the signal-to-noise and to minimize unnecessary spectral subtractions, in an effort to provide the highest quality spectral fingerprints. This report is divided into 4 sections. The first is an Experimental section that outlines how the Raman spectra are performed. This is then followed by a section on Sample Handling. Following this, the spectral fingerprints are presented in the Results section where the data reduction process is outlined. Finally, a Photographs section is included.
Interferometric and nonlinear-optical spectral-imaging techniques for outer space and live cells
NASA Astrophysics Data System (ADS)
Itoh, Kazuyoshi
2015-12-01
Multidimensional signals such as the spectral images allow us to have deeper insights into the natures of objects. In this paper the spectral imaging techniques that are based on optical interferometry and nonlinear optics are presented. The interferometric imaging technique is based on the unified theory of Van Cittert-Zernike and Wiener-Khintchine theorems and allows us to retrieve a spectral image of an object in the far zone from the 3D spatial coherence function. The retrieval principle is explained using a very simple object. The promising applications to space interferometers for astronomy that are currently in progress will also be briefly touched on. An interesting extension of interferometric spectral imaging is a 3D and spectral imaging technique that records 4D information of objects where the 3D and spectral information is retrieved from the cross-spectral density function of optical field. The 3D imaging is realized via the numerical inverse propagation of the cross-spectral density. A few techniques suggested recently are introduced. The nonlinear optical technique that utilizes stimulated Raman scattering (SRS) for spectral imaging of biomedical targets is presented lastly. The strong signals of SRS permit us to get vibrational information of molecules in the live cell or tissue in real time. The vibrational information of unstained or unlabeled molecules is crucial especially for medical applications. The 3D information due to the optical nonlinearity is also the attractive feature of SRS spectral microscopy.
Hudson, James G.
2009-02-27
Detailed aircraft measurements were made of cloud condensation nuclei (CCN) spectra associated with extensive cloud systems off the central California coast in the July 2005 MASE project. These measurements include the wide supersaturation (S) range (2-0.01%) that is important for these polluted stratus clouds. Concentrations were usually characteristic of continental/anthropogenic air masses. The most notable feature was the consistently higher concentrations above the clouds than below. CCN measurements are so important because they provide a link between atmospheric chemistry and cloud-climate effects, which are the largest climate uncertainty. Extensive comparisons throughout the eleven flights between two CCN spectrometers operated at different but overlapping S ranges displayed the precision and accuracy of these difficult spectral determinations. There are enough channels of resolution in these instruments to provide differential spectra, which produce more rigorous and precise comparisons than traditional cumulative presentations of CCN concentrations. Differential spectra are also more revealing than cumulative spectra. Only one of the eleven flights exhibited typical maritime concentrations. Average below cloud concentrations over the two hours furthest from the coast for the 8 flights with low polluted stratus was 614?233 at 1% S, 149?60 at 0.1% S and 57?33 at 0.04% S cm-3. Immediately above cloud average concentrations were respectively 74%, 55%, and 18% higher. Concentration variability among those 8 flights was a factor of two. Variability within each flight excluding distances close to the coast ranged from 15-56% at 1% S. However, CN and probably CCN concentrations sometimes varied by less than 1% over distances of more than a km. Volatility and size-critical S measurements indicated that the air masses were very polluted throughout MASE. The aerosol above the clouds was more polluted than the below cloud aerosol. These high CCN concentrations from
Spectrally-encoded color imaging
Kang, DongKyun; Yelin, Dvir; Bouma, Brett E.; Tearney, Guillermo J.
2010-01-01
Spectrally-encoded endoscopy (SEE) is a technique for ultraminiature endoscopy that encodes each spatial location on the sample with a different wavelength. One limitation of previous incarnations of SEE is that it inherently creates monochromatic images, since the spectral bandwidth is expended in the spatial encoding process. Here we present a spectrally-encoded imaging system that has color imaging capability. The new imaging system utilizes three distinct red, green, and blue spectral bands that are configured to illuminate the grating at different incident angles. By careful selection of the incident angles, the three spectral bands can be made to overlap on the sample. To demonstrate the method, a bench-top system was built, comprising a 2400-lpmm grating illuminated by three 525-μm-diameter beams with three different spectral bands. Each spectral band had a bandwidth of 75 nm, producing 189 resolvable points. A resolution target, color phantoms, and excised swine small intestine were imaged to validate the system's performance. The color SEE system showed qualitatively and quantitatively similar color imaging performance to that of a conventional digital camera. PMID:19688002
spectral-cube: Read and analyze astrophysical spectral data cubes
NASA Astrophysics Data System (ADS)
Robitaille, Thomas; Ginsburg, Adam; Beaumont, Chris; Leroy, Adam; Rosolowsky, Erik
2016-09-01
Spectral-cube provides an easy way to read, manipulate, analyze, and write data cubes with two positional dimensions and one spectral dimension, optionally with Stokes parameters. It is a versatile data container for building custom analysis routines. It provides a uniform interface to spectral cubes, robust to the wide range of conventions of axis order, spatial projections, and spectral units that exist in the wild, and allows easy extraction of cube sub-regions using physical coordinates. It has the ability to create, combine, and apply masks to datasets and is designed to work with datasets too large to load into memory, and provide basic summary statistic methods like moments and array aggregates.
K-shell spectroscopy uncertainty due to spectral models
NASA Astrophysics Data System (ADS)
Nagayama, Taisuke; Bailey, J. E.; Loisel, G.; Rochau, G. A.; Hansen, S. B.; Blancard, C.; Cosse, Ph.; Iglesias, C. A.; Colgan, J.; Fontes, C.; Kilcrease, D.; Macfarlane, J. J.; Golovkin, I.; Florido, R.; Mancini, R. C.
2015-11-01
In high energy density plasma physics, K-shell spectra from H-, He-, and Li-like ions are often used to diagnose plasma conditions. Line ratios and line broadening of the measured spectra are sensitive to the electron temperature and density of the source plasma, respectively. Thus, plasma electron temperature, Te, and electron density, ne, can be uniquely and precisely determined by reproducing the measured spectra with a spectral model. However, the different spectral models do not perfectly agree with each other and the diagnostic results depend on the selection of spectral models. Here, we investigate the level of disagreement in inferred Te and ne due to differences in spectral models. Models in the study are ABAKO, ATOMIC, FLYCHK, OPAL, OPAS, PrismSPECT, and SCRAM. As an example, we selected Mg K-shell spectroscopy used for Fe opacity experiments [Bailey et al, Nature 517, 56 (2015)] where Fe plasma conditions are inferred from K-shell spectra of a Mg dopant. The Te and ne diagnostics using different models agree within 5% and 30%. We discuss the main source of discrepancies. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
Compact Airborne Spectral Sensor (COMPASS)
NASA Astrophysics Data System (ADS)
Simi, Christopher G.; Winter, Edwin M.; Williams, Mary M.; Driscoll, David C.
2001-08-01
The COMPACT Airborne Spectral Sensor (COMPASS) design is intended to demonstrate a new design concept for solar reflective hyper spectral systems for the Government. Capitalizing from recent focal plane developments, the COMPASS system utilizes a single FPA to cover the 0.4-2.35micrometers spectral region. This system also utilizes an Offner spectrometer design as well as an electron etched lithography curved grating technology pioneered by NASA/JPL. This paper also discusses the technical trades, which drove the design selection of COMPASS. When completed, the core COMPASS spectrometer design could be used in a large variety of configurations on a variety of aircraft.
Spectral Sensitivity of the ctenid spider Cupiennius salei Keys
Zopf, Lydia M.; Schmid, Axel; Fredman, David; Eriksson, Bo Joakim
2014-01-01
Summary The spectral sensitivity of adult male Cupiennius salei Keys, a nocturnal hunting spider, was studied in a behavioural test. As known from earlier behavioural tests, C. salei walks towards a black target presented in front of a white background. In this study a black target (size 42 × 70 cm) was presented in a white arena illuminated by monochromatic light in the range of 365 to 695 nm using 19 monochromatic filters (HW in the range of 6 – 10 nm). In the first trial, the transmission of the optical filters was between 40 % and 80%. In a second trial the transmission was reduced to 5%, using a neutral density filter. At the high intensity the spiders showed a spectral sensivity in the range from 380 to 670 nm. In the second trial the animals only showed directed walks if the illumination was in the range of 449 to 599 nm, indicating a lower sensitivity at the margins of the spectral sensitivity. In previous intracellular recordings, the measured spectral sensitivity was between 320 and 620 nm. Interestingly, these results do not completely match the behaviourally tested spectral sensitivity of the photoreceptors, where the sensitivity range is shifted to longer wavelengths. In order to investigate the molecular background of spectral sensitivity, we searched for opsin genes in C. salei. We found three visual opsins that correspond to UV and middle to long wavelength sensitive opsins as described for jumping spiders. PMID:23948480
Dynamic critical phenomena from spectral functions on the lattice
NASA Astrophysics Data System (ADS)
Berges, Jürgen; Schlichting, Sören; Sexty, Dénes
2010-06-01
We investigate spectral functions in the vicinity of the critical temperature of a second-order phase transition. Since critical phenomena in quantum field theories are governed by classical dynamics, universal properties can be computed using real-time lattice simulations. For the example of a relativistic single-component scalar field theory in 2+1 dimensions, we compute the spectral function described by universal scaling functions and extract the dynamic critical exponent z. Together with exactly known static properties of this theory, we obtain a verification from first principles that the relativistic theory is well described by the dynamic universality class of relaxational models with conserved density (Model C).
Self-induced spectral splits in supernova neutrino fluxes
Raffelt, Georg G.; Smirnov, Alexei Yu.
2007-10-15
In the dense-neutrino region above the neutrino sphere of a supernova (r < or approx. 400 km), neutrino-neutrino refraction causes collective flavor transformations. They can lead to 'spectral splits' where an energy E{sub split} splits the transformed spectrum sharply into parts of almost pure but different flavors. Unless there is an ordinary MSW resonance in the dense-neutrino region, E{sub split} is determined by flavor-lepton number conservation alone. Spectral splits are created by an adiabatic transition between regions of large and small neutrino density. We solve the equations of motion in the adiabatic limit explicitly and provide analytic expressions for a generic example.
Millimeter-wave spectral line radiation from a powerful explosion
Kotov, Yu. B.; Popov, V. D.; Semenova, T. A.; Fedorov, V. F.
2012-01-15
Millimeter-wave spectral line radiation from a powerful air explosion accompanied by neutron, X-ray, and gamma emission is considered. It is shown that the main contribution to the line radiation in the frequency window of air near the wavelength of 2.3 mm is made by nitric oxide molecules. The set of kinetic equations for a partially ionized plasma near the explosion is solved by the Runge-Kutta method. It is shown that the density of nitrogen oxide molecules increases in time to a certain steady-state level. The spectral power of radiation in the NO lines is estimated.
Spectral functions of scalar mesons
NASA Astrophysics Data System (ADS)
Giacosa, Francesco; Pagliara, Giuseppe
2007-12-01
In this work we study the spectral functions of scalar mesons in one- and two-channel cases by using nonlocal interaction Lagrangian(s). When the propagators satisfy the Källen-Lehman representation, a normalized spectral function is obtained, allowing one to take into account finite-width effects in the evaluation of decay rates. In the one-channel case, suitable to the light σ and k mesons, the spectral function can deviate consistently from a Breit-Wigner shape. In the two-channel case with one subthreshold channel, the evaluated spectral function is well approximated by a Flatté distribution; when applying the study to the a0(980) and f0(980) mesons, the tree-level forbidden KK decay is analyzed.
1982-05-01
correlation function and is equivalent to an en-transformation [11] of the same function. Gray, Houston and Morgan ( GHM ) noted the estimator to have some...satis- factory way of selecting the proper value n in the en-transform. GHM went on to conclude that an ARMA spectral estimator would probably have...which will be seen to avoid the difficulties noted by GHM , and will in fact, be shown to be equivalent to a method of moments ARMA spectral estimator
Compressive spectroscopy by spectral modulation
NASA Astrophysics Data System (ADS)
Oiknine, Yaniv; August, Isaac; Stern, Adrian
2017-05-01
We review two compressive spectroscopy techniques based on modulation in the spectral domain that we have recently proposed. Both techniques achieve a compression ratio of approximately 10:1, however each with a different sensing mechanism. The first technique uses a liquid crystal cell as a tunable filter to modulate the spectral signal, and the second technique uses a Fabry-Perot etalon as a resonator. We overview the specific properties of each of the techniques.
Radiometric and Spectral Measurement Instruments
1992-03-18
NSWCCR/RDTN-92/0003 AD-A250 771LI~ llliii11l li l l iillt111 RADIOMETRIC AND SPECTRAL MEASUREMENT INSTRUMENTS CRANE DIVISION NAVAL SURFACE WARFARE... INSTRUMENTS 6. AUTHOR(S) B. E. DOUDA H. A. WEBSTER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) a. PERFORMING ORGANIZATION REPORT NIJMBER...Maxiry-um 200 w ords) THIS IS A DESCRIPTION OF AN ASSORTMENT OF RADIOMETRIC AND SPECTRAL INSTRUMENTATION USED FOR MEASUREMENT OF THE RADIATIVE OUTPUT OF
Density: An Extended Investigation.
ERIC Educational Resources Information Center
Rieck, William
1996-01-01
Presents a complete set of laboratory experiences on density. Includes establishing a density table, identifying an unknown, determining the density of irregular solids, and expanding the density table. Activities can be augmented with discussions about other applications. (DDR)
A bone density scan measures the density of bone in a person. The lower the density of a bone the ... and whether any preventative treatment is needed. A bone density scan has the advantage of being painless and ...
Undecidability of the spectral gap.
Cubitt, Toby S; Perez-Garcia, David; Wolf, Michael M
2015-12-10
The spectral gap--the energy difference between the ground state and first excited state of a system--is central to quantum many-body physics. Many challenging open problems, such as the Haldane conjecture, the question of the existence of gapped topological spin liquid phases, and the Yang-Mills gap conjecture, concern spectral gaps. These and other problems are particular cases of the general spectral gap problem: given the Hamiltonian of a quantum many-body system, is it gapped or gapless? Here we prove that this is an undecidable problem. Specifically, we construct families of quantum spin systems on a two-dimensional lattice with translationally invariant, nearest-neighbour interactions, for which the spectral gap problem is undecidable. This result extends to undecidability of other low-energy properties, such as the existence of algebraically decaying ground-state correlations. The proof combines Hamiltonian complexity techniques with aperiodic tilings, to construct a Hamiltonian whose ground state encodes the evolution of a quantum phase-estimation algorithm followed by a universal Turing machine. The spectral gap depends on the outcome of the corresponding 'halting problem'. Our result implies that there exists no algorithm to determine whether an arbitrary model is gapped or gapless, and that there exist models for which the presence or absence of a spectral gap is independent of the axioms of mathematics.
Spectral imaging: principles and applications.
Garini, Yuval; Young, Ian T; McNamara, George
2006-08-01
Spectral imaging extends the capabilities of biological and clinical studies to simultaneously study multiple features such as organelles and proteins qualitatively and quantitatively. Spectral imaging combines two well-known scientific methodologies, namely spectroscopy and imaging, to provide a new advantageous tool. The need to measure the spectrum at each point of the image requires combining dispersive optics with the more common imaging equipment, and introduces constrains as well. The principles of spectral imaging and a few representative applications are described. Spectral imaging analysis is necessary because the complex data structure cannot be analyzed visually. A few of the algorithms are discussed with emphasis on the usage for different experimental modes (fluorescence and bright field). Finally, spectral imaging, like any method, should be evaluated in light of its advantages to specific applications, a selection of which is described. Spectral imaging is a relatively new technique and its full potential is yet to be exploited. Nevertheless, several applications have already shown its potential. (c) 2006 International Society for Analytical Cytology.
The Simple Spectral Access protocol
NASA Astrophysics Data System (ADS)
Dolensky, Markus; Tody, Doug
2004-09-01
The goal of the Simple Spectral Access (SSA) specification is to define a uniform interface to spectral data including spectral energy distributions (SEDs), 1D spectra, and time series data. In contrast to 2D images, spectra are stored in a wide variety of formats and there is no widely used standard in astronomy for representing spectral data, hence part of the challenge of specifying SSA was defining a general spectrophotometric data model as well as definitions of standard serializations in a variety of data formats including XML and FITS. Access is provided to both atlas (pre-computed) data and to virtual data which is computed on demand. The term simple in Simple Spectrum Access refers to the design goal of simplicity in both implementing spectral data services and in retrieving spectroscopic data from distributed data collections. SSA is a product of the data access layer (DAL) working group of the International Virtual Observatory Alliance (IVOA). The requirements were derived from a survey among spectral data providers and data consumers and were further refined in a broad discussion in meetings and electronic forums as well as by prototyping efforts within the European Astrophysical Virtual Observatory (AVO) and the US National Virtual Observatory (NVO).
[Optimized Spectral Indices Based Estimation of Forage Grass Biomass].
An, Hai-bo; Li, Fei; Zhao, Meng-li; Liu, Ya-jun
2015-11-01
As an important indicator of forage production, aboveground biomass will directly illustrate the growth of forage grass. Therefore, Real-time monitoring biomass of forage grass play a crucial role in performing suitable grazing and management in artificial and natural grassland. However, traditional sampling and measuring are time-consuming and labor-intensive. Recently, development of hyperspectral remote sensing provides the feasibility in timely and nondestructive deriving biomass of forage grass. In the present study, the main objectives were to explore the robustness of published and optimized spectral indices in estimating biomass of forage grass in natural and artificial pasture. The natural pasture with four grazing density (control, light grazing, moderate grazing and high grazing) was designed in desert steppe, and different forage cultivars with different N rate were conducted in artificial forage fields in Inner Mongolia. The canopy reflectance and biomass in each plot were measured during critical stages. The result showed that, due to the influence in canopy structure and biomass, the canopy reflectance have a great difference in different type of forage grass. The best performing spectral index varied in different species of forage grass with different treatments (R² = 0.00-0.69). The predictive ability of spectral indices decreased under low biomass of desert steppe, while red band based spectral indices lost sensitivity under moderate-high biomass of forage maize. When band combinations of simple ratio and normalized difference spectral indices were optimized in combined datasets of natural and artificial grassland, optimized spectral indices significant increased predictive ability and the model between biomass and optimized spectral indices had the highest R² (R² = 0.72) compared to published spectral indices. Sensitive analysis further confirmed that the optimized index had the lowest noise equivalent and were the best performing index in
Density Wave Dispersion Behavior in Saturn's A Ring
NASA Astrophysics Data System (ADS)
Spilker, L. J.
1999-09-01
Wave dispersion profiles were generated for approximately 30 spiral density waves observed in the Voyager photopolarimeter stellar occultation data of Saturn's A ring. The majority of these density waves disperse linearly over the bulk of the wave. Some of the strongest density waves, however, do not begin to disperse linearly until well past the resonance location. An algorithm based on an autoregressive power spectral technique, Burg 2, generated the dispersion profiles. The dispersion behavior was then used to calculate local surface mass densities in the vicinity of each wave. Surface mass densities for the strongest density waves, when calculated using the region where the waves begin to disperse linearly, are in good agreement with surface mass densities calculated for nearby, weaker density waves. Some of the Prometheus density waves external to the Encke gap exhibit unusual spectral structure in the first part of the wave as the frequency increases by 60-70 radial interval. The nearby, related second-order resonances may produce density waves that distort the beginning of the first-order density waves. The separation distance between these first- and second-order resonances is only 0.4 to 1.5 km in this region of the rings. When the early part of each wave is systematically omitted in the surface mass density estimates, lower surface mass densities result for all of these density waves. This work was done at JPL/Caltech under contract with NASA.
Spectrally based mapping of riverbed composition
Legleiter, Carl; Stegman, Tobin K.; Overstreet, Brandon T.
2016-01-01
Remote sensing methods provide an efficient means of characterizing fluvial systems. This study evaluated the potential to map riverbed composition based on in situ and/or remote measurements of reflectance. Field spectra and substrate photos from the Snake River, Wyoming, USA, were used to identify different sediment facies and degrees of algal development and to quantify their optical characteristics. We hypothesized that accounting for the effects of depth and water column attenuation to isolate the reflectance of the streambed would enhance distinctions among bottom types and facilitate substrate classification. A bottom reflectance retrieval algorithm adapted from coastal research yielded realistic spectra for the 450 to 700 nm range; but bottom reflectance-based substrate classifications, generated using a random forest technique, were no more accurate than classifications derived from above-water field spectra. Additional hypothesis testing indicated that a combination of reflectance magnitude (brightness) and indices of spectral shape provided the most accurate riverbed classifications. Convolving field spectra to the response functions of a multispectral satellite and a hyperspectral imaging system did not reduce classification accuracies, implying that high spectral resolution was not essential. Supervised classifications of algal density produced from hyperspectral data and an inferred bottom reflectance image were not highly accurate, but unsupervised classification of the bottom reflectance image revealed distinct spectrally based clusters, suggesting that such an image could provide additional river information. We attribute the failure of bottom reflectance retrieval to yield more reliable substrate maps to a latent correlation between depth and bottom type. Accounting for the effects of depth might have eliminated a key distinction among substrates and thus reduced discriminatory power. Although further, more systematic study across a broader
Spectrally based mapping of riverbed composition
NASA Astrophysics Data System (ADS)
Legleiter, Carl J.; Stegman, Tobin K.; Overstreet, Brandon T.
2016-07-01
Remote sensing methods provide an efficient means of characterizing fluvial systems. This study evaluated the potential to map riverbed composition based on in situ and/or remote measurements of reflectance. Field spectra and substrate photos from the Snake River, Wyoming, USA, were used to identify different sediment facies and degrees of algal development and to quantify their optical characteristics. We hypothesized that accounting for the effects of depth and water column attenuation to isolate the reflectance of the streambed would enhance distinctions among bottom types and facilitate substrate classification. A bottom reflectance retrieval algorithm adapted from coastal research yielded realistic spectra for the 450 to 700 nm range; but bottom reflectance-based substrate classifications, generated using a random forest technique, were no more accurate than classifications derived from above-water field spectra. Additional hypothesis testing indicated that a combination of reflectance magnitude (brightness) and indices of spectral shape provided the most accurate riverbed classifications. Convolving field spectra to the response functions of a multispectral satellite and a hyperspectral imaging system did not reduce classification accuracies, implying that high spectral resolution was not essential. Supervised classifications of algal density produced from hyperspectral data and an inferred bottom reflectance image were not highly accurate, but unsupervised classification of the bottom reflectance image revealed distinct spectrally based clusters, suggesting that such an image could provide additional river information. We attribute the failure of bottom reflectance retrieval to yield more reliable substrate maps to a latent correlation between depth and bottom type. Accounting for the effects of depth might have eliminated a key distinction among substrates and thus reduced discriminatory power. Although further, more systematic study across a broader range
Dekemper, Emmanuel; Loodts, Nicolas; Van Opstal, Bert; Maes, Jeroen; Vanhellemont, Filip; Mateshvili, Nina; Franssens, Ghislain; Pieroux, Didier; Bingen, Christine; Robert, Charles; De Vos, Lieve; Aballea, Ludovic; Fussen, Didier
2012-09-01
We describe a new spectral imaging instrument using a TeO(2) acousto-optical tunable filter (AOTF) operating in the visible domain (450-900 nm). It allows for fast (~1 second), monochromatic (FWHM ranges from 0.6 nm at 450 nm to 3.5 nm at 800 nm) picture acquisition with good spatial resolution. This instrument was designed as a breadboard of the visible channel of a new satellite-borne atmospheric limb spectral imager, named the Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere (ALTIUS), that is currently being developed. We tested its remote sensing capabilities by observing the dense, turbulent plume exhausted by a waste incinerator stack at two wavelengths sensitive to NO(2). An average value of 6.0±0.4×10(17) molecules cm(-2) has been obtained for the NO(2) slant column density within the plume, close to the stack outlet. Although this result was obtained with a rather low accuracy, it demonstrates the potential of spectral imaging by using AOTFs in remote sensing.
The spectral index and its running in axionic curvaton
Takahashi, Fuminobu
2013-06-01
We show that a sizable running spectral index suggested by the recent SPT data can be explained in the axionic curvaton model with a potential that consists of two sinusoidal contributions of different height and period. We find that the running spectral index is generically given by dn{sub s}/dln k ∼ 2π/ΔN (n{sub s}−1), where ΔN is the e-folds during one period of modulations. In the string axiverse, axions naturally acquire a mass from multiple contributions, and one of the axions may be responsible for the density perturbations with a sizable running spectral index via the curvaton mechanism. We note that the axionic curvaton model with modulations can also accommodate the red-tilted spectrum with a negligible running, without relying on large-field inflation.
Spectral analysis of the turbulent mixing of two fluids
Steinkamp, M.J.
1996-02-01
The authors describe a spectral approach to the investigation of fluid instability, generalized turbulence, and the interpenetration of fluids across an interface. The technique also applies to a single fluid with large variations in density. Departures of fluctuating velocity components from the local mean are far subsonic, but the mean Mach number can be large. Validity of the description is demonstrated by comparisons with experiments on turbulent mixing due to the late stages of Rayleigh-Taylor instability, when the dynamics become approximately self-similar in response to a constant body force. Generic forms for anisotropic spectral structure are described and used as a basis for deriving spectrally integrated moment equations that can be incorporated into computer codes for scientific and engineering analyses.
Cosmic Microwave Background spectral distortions from cosmic string loops
Anthonisen, Madeleine; Brandenberger, Robert; Laguë, Alex; Morrison, Ian A.; Xia, Daixi E-mail: rhb@physics.mcgill.ca E-mail: imorrison@physics.mcgill.ca
2016-02-01
Cosmic string loops contain cusps which decay by emitting bursts of particles. A significant fraction of the released energy is in the form of photons. These photons are injected non-thermally and can hence cause spectral distortions of the Cosmic Microwave Background (CMB). Under the assumption that cusps are robust against gravitational back-reaction, we compute the fractional energy density released as photons in the redshift interval where such non-thermal photon injection causes CMB spectral distortions. Whereas current constraints on such spectral distortions are not strong enough to constrain the string tension, future missions such as the PIXIE experiment will be able to provide limits which rule out a range of string tensions between G μ ∼ 10{sup −15} and G μ ∼ 10{sup −12}, thus ruling out particle physics models yielding these kind of intermediate-scale cosmic strings.
Volumetric sub-surface imaging using spectrally encoded endoscopy.
Yelin, D; Bouma, B E; Tearney, G J
2008-02-04
Endoscopic imaging below tissue surfaces and through turbid media may provide improved diagnostic capabilities and visibility in surgical settings. Spectrally encoded endoscopy (SEE) is a recently developed method that utilizes a single optical fiber, miniature optics and a diffractive grating for high-speed imaging through small diameter, flexible endoscopic probes. SEE has also been shown to provide three-dimensional topological imaging capabilities. In this paper, we have configured SEE to additionally image beneath tissue surfaces, by increasing the system's sensitivity and acquiring the complex spectral density for each spectrally resolved point on the sample. In order to demonstrate the capability of SEE to obtain subsurface information, we have utilized the system to image a resolution target through intralipid solution, and conduct volumetric imaging of a mouse embryo and excised human middle-ear ossicles. Our results demonstrate that real-time subsurface imaging is possible with this miniature endoscopy technique.
A novel variable resolution global spectral method on the sphere
NASA Astrophysics Data System (ADS)
Janakiraman, S.; Nanjundiah, Ravi S.; Vasudeva Murthy, A. S.
2012-04-01
A variable resolution global spectral method is created on the sphere using High resolution Tropical Belt Transformation (HTBT). HTBT belongs to a class of map called reparametrisation maps. HTBT parametrisation of the sphere generates a clustering of points in the entire tropical belt; the density of the grid point distribution decreases smoothly in the domain outside the tropics. This variable resolution method creates finer resolution in the tropics and coarser resolution at the poles. The use of FFT procedure and Gaussian quadrature for the spectral computations retains the numerical efficiency available with the standard global spectral method. Accuracy of the method for meteorological computations are demonstrated by solving Helmholtz equation and non-divergent barotropic vorticity equation on the sphere.
AOTF microscope for imaging with increased speed and spectral versatility.
Wachman, E S; Niu, W; Farkas, D L
1997-01-01
We have developed a new fluorescence microscope that addresses the spectral and speed limitations of current light microscopy instrumentation. In the present device, interference and neutral density filters normally used for fluorescence excitation and detection are replaced by acousto-optic tunable filters (AOTFs). Improvements are described, including the use of a dispersing prism in conjunction with the imaging AOTF and an oblique-illumination excitation scheme, which together enable the AOTF microscope to produce images comparable to those obtained with conventional fluorescence instruments. The superior speed and spectral versatility of the AOTF microscope are demonstrated by a ratio image pair acquired in 3.5 ms and a micro-spectral absorbance measurement of hemoglobin through a cranial window in a living mouse. Images FIGURE 1 FIGURE 2 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 PMID:9284289
Spectral analysis of the turbulent mixing of two fluids
Steinkamp, Michael James
1995-01-01
We describe a spectral approach to the investigation of fluid instability, generalized turbulence, and the interpenetration of fluids across an interface. The Technique also applies to a single fluid with large variations in density. Departures of fluctuating velocity components from the local mean are far subsonic, but the mean Mach number can be large. Validity of the description is demonstrated by comparisons with experiments on turbulent mixing due to the late stages of Rayleigh-Taylor instability, when the dynamics become approximately self-similar in response to a constant body force. Generic forms for anisotropic spectral structure are described and used as a basis for deriving spectrally integrated moment equations that can be incorporated into computer codes for scientific and engineering analyses.
Power spectral analysis of mammographic parenchymal patterns
NASA Astrophysics Data System (ADS)
Li, Hui; Giger, Maryellen L.; Olopade, Olufunmilayo I.
2006-03-01
Mammographic density and parenchymal patterns have been shown to be associated with the risk of developing breast cancer. Two groups of women: gene-mutation carriers and low-risk women were included in this study. Power spectral analysis was performed within parenchymal regions of 172 digitized craniocaudal normal mammograms of the BRCA1/BRCA2 gene-mutation carriers and those of women at low-risk of developing breast cancer. The power law spectrum of the form, P(f)=B/f β was evaluated for the mammographic patterns. Receiver Operating Characteristic (ROC) analysis was used to assess the performance of exponent β as a decision variable in the task of distinguishing between high and low-risk subjects. Power spectral analysis of mammograms demonstrated that mammographic parenchymal patterns have a power-law spectrum of the form, P(f)=B/f β where f is radial spatial frequency, with the average β values of 2.92 and 2.47 for the gene-mutation carriers and for the low-risk women, respectively. A z values of 0.90 and 0.89 were achieved in distinguishing between the gene-mutation carriers and the low-risk women with the individual image β value as the decision variable in the entire database and the age-matched group, respectively.
SHIELD II: WSRT HI Spectral Line Observations
NASA Astrophysics Data System (ADS)
Gordon, Alex Jonah Robert; Cannon, John M.; Adams, Elizabeth A.; SHIELD II Team
2016-01-01
The "Survey of HI in Extremely Low-mass Dwarfs II" ("SHIELD II") is a multiwavelength, legacy-class observational campaign that is facilitating the study of both internal and global evolutionary processes in low-mass dwarf galaxies discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We present new results from WSRT HI spectral line observations of 22 galaxies in the SHIELD II sample. We explore the morphology and kinematics by comparing images of the HI surface densities and the intensity weighted velocity fields with optical images from HST, SDSS, and WIYN. In most cases the HI and stellar populations are cospatial; projected rotation velocities range from less than 10 km/s to roughly 30 km/s.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College, and by NASA through grant GO-13750 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.
SHIELD II: VLA HI Spectral Line Observations
NASA Astrophysics Data System (ADS)
Lee, Eojin; Cannon, John M.; McNichols, Andrew; Teich, Yaron; SHIELD II Team
2016-01-01
The "Survey of HI in Extremely Low-mass Dwarfs II" ("SHIELD II") is a multiwavelength, legacy-class observational campaign that is facilitating the study of both internal and global evolutionary processes in low-mass dwarf galaxies discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We present new results from low-resolution D-configuration VLA HI spectral line observations of 6 galaxies in the SHIELD II sample. We explore the morphology and kinematics by comparing images of the HI surface densities and the intensity weighted velocity fields with optical images from SDSS and WIYN. These data allow us to localize the HI gas and to study the bulk neutral gas kinematics.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College.
Spectral signature of Egyptian crude oils
NASA Astrophysics Data System (ADS)
Ghatass, Z. F.; Nashed, A. W.; Saleh, I. H.; Mohmed, M. M.
2014-11-01
Crude petroleum oils are complex mixtures of diverse hydrocarbons, in widely varying compositions, that originate from a variety of geological sources. Fluorescence emission spectra have been measured for two types of Egyptian crude petroleum oil, its light and heavy products over a broad range of excitation and emission wavelengths. Both types of crude oil products are characterized by spectral signatures with a differing topography: the number of fluorescent peaks, their coordinates (λex, λem) on the plane of the three dimensions spectrum, and the shape of the bands formed by the contour line density, changeable in either direction. The refined light oil shows emission spectra at λmax between 350 and 500 nm according to the excitation wavelength. The refined heavy oil shows very broad unstructured emission spectra with λmax > 400 nm. As a group, they could certainly be distinguished from the light oil samples and most of the crude oil.
Spectral filtering for plant production
Young, R.E.; McMahon, M.J.; Rajapakse, N.C.; Becoteau, D.R.
1994-12-31
Research to date suggests that spectral filtering can be an effective alternative to chemical growth regulators for altering plant development. If properly implemented, it can be nonchemical and environmentally friendly. The aqueous CuSO{sub 4}, and CuCl{sub 2} solutions in channelled plastic panels have been shown to be effective filters, but they can be highly toxic if the solutions contact plants. Some studies suggest that spectral filtration limited to short EOD intervals can also alter plant development. Future research should be directed toward confirmation of the influence of spectral filters and exposure times on a broader range of plant species and cultivars. Efforts should also be made to identify non-noxious alternatives to aqueous copper solutions and/or to incorporate these chemicals permanently into plastic films and panels that can be used in greenhouse construction. It would also be informative to study the impacts of spectral filters on insect and microbal populations in plant growth facilities. The economic impacts of spectral filtering techniques should be assessed for each delivery methodology.
Spectral backbone of excitation transport in ultracold Rydberg gases
NASA Astrophysics Data System (ADS)
Scholak, Torsten; Wellens, Thomas; Buchleitner, Andreas
2014-12-01
The spectral structure underlying excitonic energy transfer in ultracold Rydberg gases is studied numerically, in the framework of random matrix theory, and via self-consistent diagrammatic techniques. Rydberg gases are made up of randomly distributed, highly polarizable atoms that interact via strong dipolar forces. Dynamics in such a system is fundamentally different from cases in which the interactions are of short range, and is ultimately determined by the spectral and eigenvector structure. In the energy levels' spacing statistics, we find evidence for a critical energy that separates delocalized eigenstates from states that are localized at pairs or clusters of atoms separated by less than the typical nearest-neighbor distance. We argue that the dipole blockade effect in Rydberg gases can be leveraged to manipulate this transition across a wide range: As the blockade radius increases, the relative weight of localized states is reduced. At the same time, the spectral statistics, in particular, the density of states and the nearest-neighbor level-spacing statistics, exhibits a transition from approximately a 1-stable Lévy to a Gaussian orthogonal ensemble. Deviations from random matrix statistics are shown to stem from correlations between interatomic interaction strengths that lead to an asymmetry of the spectral density and profoundly affect localization properties. We discuss approximations to the self-consistent Matsubara-Toyozawa locator expansion that incorporate these effects.
Spectral tomography of three-dimensional objects
Bulygin, F.V.; Levin, G.G.
1995-12-01
Spectral tomography is a new field in optical tomography concerned with studies of the internal space-spectral structure of polychromatic objects. In this paper, methods for obtaining projections spectral structure of three-dimensional objects and algorithms for its reconstruction are proposed and described. The results of the spectral-tomography reconstruction of the object structure are presented. 6 refs., 4 figs.
Infrared spectral profiles in liquids and atom-diatom interactions
NASA Astrophysics Data System (ADS)
Medina, A.; Roco, J. M. M.; Calvo Hernández, A.; Velasco, S.
2004-10-01
Molecular dynamics simulations of the infrared spectrum of a generic simple polar diatomic in a liquid nonpolar solvent allow to reproduce the different prototypical experimental line shapes of this kind of systems. This is feasible by using different solute-solvent anisotropic potentials at fixed thermodynamic conditions. In the limit cases, the rotation of the diatomic is explained in terms of a quasifree motion or a rotational diffusion evolution and the spectra show a doublet structure formed by P and R branches or a unique collapsed branch, respectively. When the profile contains three branches, including an intense Q branch in the vicinity of the center of the band, rotational evolution presents a particular hindering that can be understood by studying the influence on rotational spectral densities of the different time scales involved in rotational relaxation. Cancellation/enhancement effects among spectral density terms arising from intermediate and long times (0.4-1 ps) are essential to understand rotational hindering.
Spectral characteristics of Shuttle glow
NASA Technical Reports Server (NTRS)
Viereck, R. A.; Mende, S. B.; Murad, E.; Swenson, G. R.; Pike, C. P.; Culbertson, F. L.; Springer, R. C.
1992-01-01
The glowing cloud near the ram surfaces of the Space Shuttle was observed with a hand-held, intensified spectrograph operated by the astronauts from the aft-flight-deck of the Space Shuttle. The spectral measurements were made between 400 and 800 nm with a resolution of 3 nm. Analysis of the spectral response of the instrument and the transmission of the Shuttle window was performed on orbit using earth-airglow OH Meinel bands. This analysis resulted in a correction of the Shuttle glow intensity in the spectral region between 700 and 800 nm. The data presented in this report is in better agreement with laboratory measurements of the NO2 continuum.
Maximum entropy spectral analysis for streamflow forecasting
NASA Astrophysics Data System (ADS)
Cui, Huijuan; Singh, Vijay P.
2016-01-01
Configurational entropy spectral analysis (CESAS) is developed with spectral power as a random variable for streamflow forecasting. It is found that the CESAS derived by maximizing the configurational entropy yields the same solution as by the Burg entropy spectral analysis (BESA). Comparison of forecasted streamflows by CESAS and BESA shows less than 0.001% difference between the two analyses and thus the two entropy spectral analyses are concluded to be identical. Thus, the Burg entropy spectral analysis and two configurational entropy spectral analyses form the maximum entropy spectral analysis.
Time frequency analysis of Jovian and Saturnian radio spectral patterns
NASA Astrophysics Data System (ADS)
Boudjada, Mohammed Y.; Galopeau, Patrick H. M.; Al-Haddad, Emad; Lammer, Helmut
2016-04-01
Prominent radio spectral patterns were observed by the Cassini Radio and Plasma Wave Science experiment (RPWS) principally at Jupiter and Saturn. The spectral shapes are displayed in the usual dynamic spectra showing the flux density versus the time and the frequency. Those patterns exhibit well-organized shapes in the time-frequency plane connected with the rotation of the planet. We consider in this analysis the auroral emissions which occurred in the frequency range between 10 kHz and approximately 3 MHz. It concerns the Jovian hectometric emission (HOM) and the Saturnian kilometric radiation (SKR). We show in the case of Jupiter's HOM that the spectral patterns are well-arranged arc structures with curvatures depending on the Jovian rotation. Regarding the SKR emission, the spectral shapes exhibit generally complex patterns, and only sometimes arc structures are observed. We emphasize the curve alterations from vertex-early to vertex-late arcs (and vice versa) and we study their dependences, or not, on the planetary rotations. We also discuss the common physical process at the origin of the HOM and SKR emissions, specifically the spectral patterns created by the interaction between planetary satellites (e.g. Io or Dione) and the Jovian and Saturnian magnetospheres.
Dual spectrally resolved interferometry to improve measurement range
NASA Astrophysics Data System (ADS)
Seo, Y. B.; Kim, B. K.; Joo, K.-N.
2015-05-01
In this investigation, a simple optical configuration and technique to improve the performance of spectrally-resolved interferometry (SRI) is proposed and experimentally verified. SRI has the fundamental limitation in the measurement range caused by the spectral bandwidth of an optical source and the spectral resolution of a spectrometer to detect the spectral interference density. Especially, the minimum measurable range of SRI is determined by the bandwidth of the source and this minimum measurable range becomes a dead zone in SRI. The proposed method can eliminate the dead zone without the minimum measurable distance and extend the measurable range of spectrally resolved interferometry (SRI) twice based on the bandwidth separation by a dichroic beam splitter (DBS). The benefit of this dichroic SRI is that it can be simply implemented with a DBS and another reference mirror from the typical SRI. Feasibility experiments were performed to verify the principle of the dichroic SRI and the result confirmed the effectiveness of this method as the extended measuring range.
The spectral-element method, Beowulf computing, and global seismology.
Komatitsch, Dimitri; Ritsema, Jeroen; Tromp, Jeroen
2002-11-29
The propagation of seismic waves through Earth can now be modeled accurately with the recently developed spectral-element method. This method takes into account heterogeneity in Earth models, such as three-dimensional variations of seismic wave velocity, density, and crustal thickness. The method is implemented on relatively inexpensive clusters of personal computers, so-called Beowulf machines. This combination of hardware and software enables us to simulate broadband seismograms without intrinsic restrictions on the level of heterogeneity or the frequency content.
Spectral Line Shapes as a Diagnostic Tool in Magnetic Fusion
Stamm, R; Capes, H; Demura, A; Godbert-Mouret, L; Koubiti, M; Marandet, Y; Mattioli, M; Rosato, J; Rosmej, F; Fournier, K B
2006-07-22
Spectral line shapes and intensities are used for obtaining information on the various regions of magnetic fusion devices. Emission from low principal quantum numbers of hydrogen isotopes is analyzed for understanding the complex recycling mechanism. Lines emitted from high principal quantum numbers of hydrogen and helium are dominated by Stark effect, allowing an electronic density diagnostic in the divertor. Intensities of lines emitted by impurities are fitted for a better knowledge of ion transport in the confined plasma.
Spectral effects in quantum teleportation
Humble, Travis S.; Grice, Warren P.
2007-02-15
We use a multimode description of polarization-encoded qubits to analyze the quantum teleportation protocol. Specifically, we investigate how the teleportation fidelity depends on the spectral correlations inherent to polarization-entangled photons generated by type-II spontaneous parametric down conversion. We find that the maximal obtainable fidelity depends on the spectral entanglement carried by the joint probability amplitude, a result which we quantify for the case of a joint spectrum approximated by a correlated Gaussian function. We contrast these results with a similar analysis of the visibility obtained in a polarization-correlation experiment.
Spectral Effects in Quantum Teleportation
Humble, Travis S; Grice, Warren P
2007-01-01
We use a multimode description of polarization-encoded qubits to analyze the quantum teleportation protocol. Specifically, we investigate how the teleportation fidelity depends on the spectral correlations inherent to polarization-entangled photons generated by type-II spontaneous parametric down conversion. We find that the maximal obtainable fidelity depends on the spectral entanglement carried by the joint probability amplitude, a result which we quantify for the case of a joint spectrum approximated by a correlated Gaussian function. We contrast these results with a similar analysis of the visibility obtained in a polarization-correlation experiment.
Radar spectral measurements of vegetation
NASA Technical Reports Server (NTRS)
Ulaby, F. T.; Moore, R. K.
1973-01-01
Spectral data of 4-8 GHz radar backscatter were gathered during the 1972 growing season at look angles between 0 and 70 deg and for all four possible polarization linear combinations. The data covers four crop types (corn, milo, alfalfa, and soybeans) and a wide range of soil moisture content. To insure statistical representation of the results, measurements were conducted over 128 fields corresponding to a total of about 40,000 data points. The use of spectral response signatures to separate different crop types and to separate healthy corn from blighted corn was investigated.
Spectral moments of fullerene cages
NASA Astrophysics Data System (ADS)
Zhang, Hongxing; Balasubramanian, K.
Based on the symmetric method, analytical expression or recursive relations for the spectral moments of the C20, C24, C26, C28, C30, C32, C36, C38, C40, C42, C44, C50 and C60 fullerene cage clusters are obtained by factoring the original graphs and the corresponding characteristic polynomials into their smaller subgraphs and subpolynomials. We also give numerical results for the spectral moments. It is demonstrated that the symmetric method is feasible in enumerating the moments as well as factoring the characteristic polynomials for fullerene cages.
Spectral methods in fluid dynamics
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.; Zang, T. A.
1986-01-01
Fundamental aspects of spectral methods are introduced. Recent developments in spectral methods are reviewed with an emphasis on collocation techniques. Their applications to both compressible and incompressible flows, to viscous as well as inviscid flows, and also to chemically reacting flows are surveyed. The key role that these methods play in the simulation of stability, transition, and turbulence is brought out. A perspective is provided on some of the obstacles that prohibit a wider use of these methods, and how these obstacles are being overcome.
Stingray: Spectral-timing software
NASA Astrophysics Data System (ADS)
Huppenkothen, Daniela; Bachetti, Matteo; Stevens, Abigail L.; Migliari, Simone; Balm, Paul
2016-08-01
Stingray is a spectral-timing software package for astrophysical X-ray (and more) data. The package merges existing efforts for a (spectral-)timing package in Python and is composed of a library of time series methods (including power spectra, cross spectra, covariance spectra, and lags); scripts to load FITS data files from different missions; a simulator of light curves and event lists that includes different kinds of variability and more complicated phenomena based on the impulse response of given physical events (e.g. reverberation); and a GUI to ease the learning curve for new users.
MEASUREMENTS OF RAPID DENSITY FLUCTUATIONS IN THE SOLAR WIND
Malaspina, D. M.; Ergun, R. E.; Kellogg, P. J.; Bale, S. D.
2010-03-01
The power spectrum of density fluctuations in the solar wind is inferred by tracking small timescale changes in the electron plasma frequency during periods of strong Langmuir wave activity. STEREO electric field waveform data are used to produce time profiles of plasma density from which the density power spectrum is derived. The power spectra obtained by this method extend the observed frequency range by an order of magnitude while remaining consistent with previous results near a few Hertz. Density power spectral indices are found to be organized by the angle between the local magnetic field and the solar wind direction, indicating significant anisotropy in solar wind high-frequency density turbulence.
High Precision 2-D Grating Groove Density Measurement
NASA Astrophysics Data System (ADS)
Zhang, Ningxiao; McEntaffer, Randall; Tedesco, Ross
2017-08-01
Our research group at Penn State University is working on producing X-ray reflection gratings with high spectral resolving power and high diffraction efficiency. To estimate our fabrication accuracy, we apply a precise 2-D grating groove density measurement to plot groove density distributions of gratings on 6-inch wafers. In addition to plotting a fixed groove density distribution, this method is also sensitive to measuring the variation of the groove density simultaneously. This system can reach a measuring accuracy (ΔN/N) of 10-3. Here we present this groove density measurement and some applications.
Doschek, G.A.; Cowan, R.D.
1984-09-01
A spectral line list for the 10--200 A range is developed from existing solar spectra for application to high spectral resolution measurements of astrophysical plasmas. The solar spectral line lists are merged into a single comprehensive list. the effect of the solar emission measure distribution is removed from the line intensities, which results in a set of emission rates for the lines that can be applied to many optically thin, low density high temperature plasmas in ionization equilibrium. In addition to the measured solar lines, approx.250 theoretical lines are added to this list. These lines fall in wavelength regions where the existing solar lists have few lines because of limitations in instrumental sensitivity. Also, some lines have been added because the Sun has very little plasma at temperatures of approx.10/sup 5/ K, and consequently these lines are weak or absent in solar spectra. The entire list contains approx.600 lines. Finally, predicted spectra of the two RS CVn stars, ..cap alpha.. Aur (Capella) and UX Ari, are presented at 1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at 1 A resolution, and the emission rate spectrum (spectrum not modified by an emission measure distribution) is shown at very high spectral resolution.
Density: A Discovery Approach.
ERIC Educational Resources Information Center
Rieck, William
1994-01-01
Describes an activity that allows students to discover the concept of density and that density is a determining physical property of a pure substance. Makes suggestions to further enhance students' understanding of density. (ZWH)
A CO Spectral Analysis of Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Vannah, Sara; Salyk, Colette
2017-01-01
We present a spectral analysis describing the absorbing components of four stars with known protoplanetary disks: V1057 Cygni, W3 IRS5, LkHα 225S, and IRAS 19110+1045. Keck NIRSPEC observations of the M-band of the four sources allowed for the analysis of the P- and R-branch fundamental rovibrational absorption lines of carbon monoxide, as well as the H I Pfund-β emission line when present. These lines act as tracers of disk evolution and accretion, respectively, and allow us to determine the structure and physical features of the absorbing components. We find high temperatures, column densities and intense blueshifts in the spectra of V1057 Cygni, W3 IRS5, and LkHα 225S, which we tentatively determine to be indicative of absorption through polar outflows. IRAS 19110+11045 presents a lower column density, small redshift, moderate temperature, and high accretion rate. We surmise that the absorption spectrum in IRAS 19110+1045 is due to the disk itself as it is heated by accretion.
Spectral Methods for Numerical Relativity.
Grandclément, Philippe; Novak, Jérôme
2009-01-01
Equations arising in general relativity are usually too complicated to be solved analytically and one must rely on numerical methods to solve sets of coupled partial differential equations. Among the possible choices, this paper focuses on a class called spectral methods in which, typically, the various functions are expanded in sets of orthogonal polynomials or functions. First, a theoretical introduction of spectral expansion is given with a particular emphasis on the fast convergence of the spectral approximation. We then present different approaches to solving partial differential equations, first limiting ourselves to the one-dimensional case, with one or more domains. Generalization to more dimensions is then discussed. In particular, the case of time evolutions is carefully studied and the stability of such evolutions investigated. We then present results obtained by various groups in the field of general relativity by means of spectral methods. Work, which does not involve explicit time-evolutions, is discussed, going from rapidly-rotating strange stars to the computation of black-hole-binary initial data. Finally, the evolution of various systems of astrophysical interest are presented, from supernovae core collapse to black-hole-binary mergers.
Torn, Margaret; Serbin, Shawn
2015-06-10
Visible to near-infrared (350-1100nm) vegetation spectral reflectance data collected on the BEO automated tram measurement platform during the 2014 growing season. The spectra were collected using a PP Systems UniSpec-DC instrument and was processed to at-surface reflectance and interpolated to 1nm.
Asymptotics of thermal spectral functions
NASA Astrophysics Data System (ADS)
Caron-Huot, S.
2009-06-01
We use operator product expansion (OPE) techniques to study the spectral functions of currents and stress tensors at finite temperature, in the high-energy timelike region ω≫T. The leading corrections to these spectral functions are proportional to ˜T4 expectation values in general, and the leading corrections ˜g2T4 are calculated at weak coupling, up to an undetermined coefficient in the shear viscosity channel. Spectral functions are shown to be infrared safe, in the deeply virtual regime, up to order g8T4. The convergence of (vacuum subtracted) sum rules in the shear and bulk viscosity channels is established in QCD to all orders in perturbation theory, though numerically significant tails ˜T4/(logω)3 are shown to exist in the bulk viscosity channel. We argue that the spectral functions of currents and stress tensors in infinitely coupled N=4 super Yang-Mills theory do not receive any medium-dependent power correction.
Spectral ophthalmoscopy based on supercontinuum
NASA Astrophysics Data System (ADS)
Cheng, Yueh-Hung; Yu, Jiun-Yann; Wu, Han-Hsuan; Huang, Bo-Jyun; Chu, Shi-Wei
2010-02-01
Confocal scanning laser ophthalmoscope (CSLO) has been established to be an important diagnostic tool for retinopathies like age-related macular degeneration, glaucoma and diabetes. Compared to a confocal laser scanning microscope, CSLO is also capable of providing optical sectioning on retina with the aid of a pinhole, but the microscope objective is replaced by the optics of eye. Since optical spectrum is the fingerprint of local chemical composition, it is attractive to incorporate spectral acquisition into CSLO. However, due to the limitation of laser bandwidth and chromatic/geometric aberration, the scanning systems in current CSLO are not compatible with spectral imaging. Here we demonstrate a spectral CSLO by combining a diffraction-limited broadband scanning system and a supercontinuum laser source. Both optical sectioning capability and sub-cellular resolution are demonstrated on zebrafish's retina. To our knowledge, it is also the first time that CSLO is applied onto the study of fish vision. The versatile spectral CSLO system will be useful to retinopathy diagnosis and neuroscience research.
Rayleigh imaging in spectral mammography
NASA Astrophysics Data System (ADS)
Berggren, Karl; Danielsson, Mats; Fredenberg, Erik
2016-03-01
Spectral imaging is the acquisition of multiple images of an object at different energy spectra. In mammography, dual-energy imaging (spectral imaging with two energy levels) has been investigated for several applications, in particular material decomposition, which allows for quantitative analysis of breast composition and quantitative contrast-enhanced imaging. Material decomposition with dual-energy imaging is based on the assumption that there are two dominant photon interaction effects that determine linear attenuation: the photoelectric effect and Compton scattering. This assumption limits the number of basis materials, i.e. the number of materials that are possible to differentiate between, to two. However, Rayleigh scattering may account for more than 10% of the linear attenuation in the mammography energy range. In this work, we show that a modified version of a scanning multi-slit spectral photon-counting mammography system is able to acquire three images at different spectra and can be used for triple-energy imaging. We further show that triple-energy imaging in combination with the efficient scatter rejection of the system enables measurement of Rayleigh scattering, which adds an additional energy dependency to the linear attenuation and enables material decomposition with three basis materials. Three available basis materials have the potential to improve virtually all applications of spectral imaging.
Spectral clustering with epidemic diffusion
NASA Astrophysics Data System (ADS)
Smith, Laura M.; Lerman, Kristina; Garcia-Cardona, Cristina; Percus, Allon G.; Ghosh, Rumi
2013-10-01
Spectral clustering is widely used to partition graphs into distinct modules or communities. Existing methods for spectral clustering use the eigenvalues and eigenvectors of the graph Laplacian, an operator that is closely associated with random walks on graphs. We propose a spectral partitioning method that exploits the properties of epidemic diffusion. An epidemic is a dynamic process that, unlike the random walk, simultaneously transitions to all the neighbors of a given node. We show that the replicator, an operator describing epidemic diffusion, is equivalent to the symmetric normalized Laplacian of a reweighted graph with edges reweighted by the eigenvector centralities of their incident nodes. Thus, more weight is given to edges connecting more central nodes. We describe a method that partitions the nodes based on the componentwise ratio of the replicator's second eigenvector to the first and compare its performance to traditional spectral clustering techniques on synthetic graphs with known community structure. We demonstrate that the replicator gives preference to dense, clique-like structures, enabling it to more effectively discover communities that may be obscured by dense intercommunity linking.
Nonuniform sampling and spectral aliasing
NASA Astrophysics Data System (ADS)
Maciejewski, Mark W.; Qui, Harry Z.; Rujan, Iulian; Mobli, Mehdi; Hoch, Jeffrey C.
2009-07-01
The Nyquist theorem stipulates the largest sampling interval sufficient to avoid aliasing is the reciprocal of the spectral bandwidth. When data are not sampled uniformly, the Nyquist theorem no longer applies, and aliasing phenomena become more complex. For samples selected from an evenly spaced grid, signals that are within the nominal bandwidth of the grid can give rise to aliases. The effective bandwidth afforded by a set of nonuniformly sampled evolution times does not necessarily correspond to spacing of the grid from which the samples are selected, but instead depends on the actual distribution of sample times. For conventional uniform sampling there is no distinction between the grid spacing and the sampling interval. For nonuniform sampling, an effective bandwidth can be inferred from the greatest common divisor of the sample times, provided that none of the sample times are irrational. A simple way to increase the effective bandwidth for a set of nonuniformly spaced samples is to randomly select them from an oversampled grid. For a given grid spacing, "bursty" sampling helps to minimize aliasing artifacts. We show that some spectral artifacts arising from nonuniform sampling are aliases, and that increasing the effective bandwidth shifts these artifacts out of the spectral window and improves spectral quality. An advantage of nonuniform sampling is that some of the benefits of oversampling can be realized without incurring experiment time or resolution penalties. We illustrate the improvements that can be obtained with nonuniform sampling in the indirect dimension of a SOFAST-HMQC experiment.
Data analysis techniques: Spectral processing
NASA Technical Reports Server (NTRS)
Strauch, R. G.
1983-01-01
The individual steps in the data processing scheme applied to most radars used for wind sounding are analyzed. This processing method uses spectral analysis and assumes a pulse Doppler radar. Improvement in the signal to noise ratio of some radars is discussed.
AN ACCURATE FLUX DENSITY SCALE FROM 1 TO 50 GHz
Perley, R. A.; Butler, B. J. E-mail: BButler@nrao.edu
2013-02-15
We develop an absolute flux density scale for centimeter-wavelength astronomy by combining accurate flux density ratios determined by the Very Large Array between the planet Mars and a set of potential calibrators with the Rudy thermophysical emission model of Mars, adjusted to the absolute scale established by the Wilkinson Microwave Anisotropy Probe. The radio sources 3C123, 3C196, 3C286, and 3C295 are found to be varying at a level of less than {approx}5% per century at all frequencies between 1 and 50 GHz, and hence are suitable as flux density standards. We present polynomial expressions for their spectral flux densities, valid from 1 to 50 GHz, with absolute accuracy estimated at 1%-3% depending on frequency. Of the four sources, 3C286 is the most compact and has the flattest spectral index, making it the most suitable object on which to establish the spectral flux density scale. The sources 3C48, 3C138, 3C147, NGC 7027, NGC 6542, and MWC 349 show significant variability on various timescales. Polynomial coefficients for the spectral flux density are developed for 3C48, 3C138, and 3C147 for each of the 17 observation dates, spanning 1983-2012. The planets Venus, Uranus, and Neptune are included in our observations, and we derive their brightness temperatures over the same frequency range.
Shock capturing by the spectral viscosity method
NASA Technical Reports Server (NTRS)
Tadmor, Eitan
1989-01-01
A main disadvantage of using spectral methods for nonlinear conservation laws lies in the formation of Gibbs phenomenon, once spontaneous shock discontinuities appear in the solution. The global nature of spectral methods than pollutes the unstable Gibbs oscillations overall the computational domain, and the lack of entropy dissipation prevents convergences in these cases. The Spectral Viscosity method, which is based on high frequency dependent vanishing viscosity regularization of the classical spectral methods is discussed. It is shown that this method enforces the convergence of nonlinear spectral approximations without sacrificing their overall spectral accuracy.
NASA Astrophysics Data System (ADS)
Maizia, R.; Dib, A.; Thomas, A.; Martemianov, S.
2017-02-01
Electrochemical noise analysis (ENA) has been performed for the diagnosis of proton-exchange membrane fuel cell (PEMFC) under various operating conditions. Its interest is related with the possibility of a non-invasive on-line diagnosis of a commercial fuel cell. A methodology of spectral analysis has been developed and an evaluation of the stationarity of the signal has been proposed. It has been revealed that the spectral signature of fuel cell, is a linear slope with a fractional power dependence 1/fα where α = 2 for different relative humidities and current densities. Experimental results reveal that the electrochemical noise is sensitive to the water management, especially under dry conditions. At RHH2 = 20% and RHair = 20%, spectral analysis shows a three linear slopes signature on the spectrum at low frequency range (f < 100 Hz). This results indicates that power spectral density, calculated thanks to FFT, can be used for the detection of an incorrect fuel cell water balance.
Spectral analyses of the dual polarization Doppler weather radar data
NASA Astrophysics Data System (ADS)
Bachmann, Svetlana Monakhova
2007-12-01
Echoes in clear air from biological scatterers mixed within the resolution volumes over a large region are presented. These echoes were observed with the polarimetric prototype of the forthcoming WSR-88D weather radar. The study case occurred in the evening of September 7, 2004, at the beginning of the bird migrating season. Novel polarimetric spectral analyses are used for distinguishing signatures of birds and insects in multimodal spectra. These biological scatterers were present at the same time in the radar resolution volumes over a large area. Spectral techniques for (1) data censoring, (2) wind retrieval and (3) estimation of intrinsic values/functions of polarimetric variables for different types of scatterers are presented. The technique for data censoring in the frequency domain allows detection of weak signals. Censoring is performed on the level of spectral densities, allowing exposure of contributions to the spectrum from multiple types of scatterers. The spectral techniques for wind retrieval allow simultaneous estimation of wind from the data that are severely contaminated by migrating birds, and assessment of bird migration parameters. The intrinsic polarimetric signatures associated with the variety of scatterers can be evaluated using presented methodology. Algorithms for echo classification can be built on these. The possibilities of spectral processing using parametric estimation techniques are explored for resolving contributions to the Doppler spectrum from the three types of scatterers: passive wind tracers, actively flying insects and birds. A combination of parametric and non-parametric polarimetric spectral analyses is used to estimate the small bias introduced to the wind velocity by actively flying insects.
Rapid spectral-domain localization
van Dijk, Thomas; Mayerich, David; Bhargava, Rohit; Carney, P. Scott
2013-01-01
We present a method to dynamically image structures at nanometer spatial resolution with far-field instruments. We propose the use of engineered nanoprobes with distinguishable spectral responses and the measurement of coherent scattering, rather than fluorescence. Approaches such as PALM/STORM have relied on the rarity of emission events in time to distinguish signals from distinct probes. By distinguishing signals in the spectral domain, we enable the acquisition of data in a multiplex fashion and thus circumvent the fundamental problem of slow data acquisition of current techniques. The described method has the potential to image dynamic systems with a spatial resolution only limited to the size of the scattering probes. PMID:23736501
Spectral Variability of Romano's Star
NASA Astrophysics Data System (ADS)
Maryeva, O.; Abolmasov, P.
2010-10-01
We combine archival spectral observations of the LBV star V532 (Romano's star) together with existing photometric data in the B band. Spectroscopic data cover 15 years of observations (from 1992 to 2007). We show that the object in maximum of brightness behaves as an emission line supergiant while in minimum V532 moves along the sequence of late WN stars. In this sense, the object behaves similarly to the well-known Luminous Blue Variable (LBV) stars AG Car and R127, but is somewhat hotter at the minima. We identify about 100 spectral lines in the 3700-7300Å range. As of today, our spectroscopy is the most comprehensive for this object. The velocity of the wind is derived using the He I triplet lines (360±30 km s(-1) ). Physical parameters of the nebula around V532 are estimated.
Spectral solar radiation: new data
Hulstrom, R
1983-06-01
Several areas of solar research require an accurate knowledge (data) of the spectral content of solar radiation at the earth's surface for various atmospheric conditions, times during the day (air masses), geographic locations, and for the various seasons (monthly). Areas of solar research include photovoltaics, biomass, materials studies, and solar simulation. As one of its major research thrusts, the Renewable Resource Assessment and Instrumentation Branch of the Solar Energy Research Institute, has been developing improved analytical models, instrumentation, and data sets to meet the various needs for such by the previously mentioned areas of solar energy conversion research. A brief summary of selected results of such research is presented. References are given for detailed descriptions of the various individual areas of effort/research and new spectral solar radiation data sets.
On the Evolution of the Spectral Break in the Afterglow of Gamma-Ray Bursts
NASA Astrophysics Data System (ADS)
Dado, Shlomo; Dar, Arnon
2012-02-01
The temporal evolution of the spectral break in the time-resolved spectral energy density of the broadband afterglow of gamma-ray bursts (GRBs) 091127 and 080319B was shown recently to be inconsistent with that expected for the cooling break in the standard fireball model of GRBs. Here we show that it is, however, in good agreement with the predicted temporal evolution of the smooth injection break/bend in the cannonball model of GRBs.
ON THE EVOLUTION OF THE SPECTRAL BREAK IN THE AFTERGLOW OF GAMMA-RAY BURSTS
Dado, Shlomo; Dar, Arnon
2012-02-20
The temporal evolution of the spectral break in the time-resolved spectral energy density of the broadband afterglow of gamma-ray bursts (GRBs) 091127 and 080319B was shown recently to be inconsistent with that expected for the cooling break in the standard fireball model of GRBs. Here we show that it is, however, in good agreement with the predicted temporal evolution of the smooth injection break/bend in the cannonball model of GRBs.
Highly Spectral Dependent Enhancement of Upconversion Emission with Sputtered Gold Island Films†
Zhang, Hua; Xu, Di; Huang, Yu
2011-01-01
We report an five-fold overall enhacement of upconvertion emission in NaYF4:Yb/Er nanocryatals when coupled with gold island films. Spectroscopic studies show that the enhancement factors are hlighly depdent on the exact spectral positions and excitation power density, with a largest enhancement factor more than 12 observed at slected spectral position, which may be attributed to different upconversion processes involved. PMID:21079884
Dense Spectral Beam Combining with Volume Bragg Gratings in PTR Glass
2006-01-01
194. [8] A. E. Siegman, Lasers (University Science, Mill Valley, Calif.,1986). [9] ISO 11146 :1999, “Lasers and laser-related equipment – Test methods...Andrusyak - SSDLTR 2006 BC- 3 Dense spectral beam combining with volume Bragg gratings in PTR glass Oleksiy Andrusyak, Igor Ciapurin, Vasile...density SBC with narrow separation between channels [2, 3 ]. Spectral beam combining by means of VBGs is based on the fact that diffraction efficiency
NASA Technical Reports Server (NTRS)
Rhyne, R. H.; Murrow, H. N.; Sidwell, K.
1976-01-01
Use of power spectral design techniques for supersonic transports requires accurate definition of atmospheric turbulence in the long wavelength region below the knee of the power spectral density function curve. Examples are given of data obtained from a current turbulence flight sampling program. These samples are categorized as (1) convective, (2) wind shear, (3) rotor, and (4) mountain-wave turbulence. Time histories, altitudes, root-mean-square values, statistical degrees of freedom, power spectra, and integral scale values are shown and discussed.
Waltner, Daniel; Gnutzmann, Sven; Tanner, Gregor; Richter, Klaus
2013-05-01
We study the implications of unitarity for pseudo-orbit expansions of the spectral determinants of quantum maps and quantum graphs. In particular, we advocate to group pseudo-orbits into subdeterminants. We show explicitly that the cancellation of long orbits is elegantly described on this level and that unitarity can be built in using a simple subdeterminant identity which has a nontrivial interpretation in terms of pseudo-orbits. This identity yields much more detailed relations between pseudo-orbits of different lengths than was known previously. We reformulate Newton identities and the spectral density in terms of subdeterminant expansions and point out the implications of the subdeterminant identity for these expressions. We analyze furthermore the effect of the identity on spectral correlation functions such as the autocorrelation and parametric cross-correlation functions of the spectral determinant and the spectral form factor.
Solar Energetic Particle Spectral Breaks
NASA Astrophysics Data System (ADS)
Mewaldt, R.; Cohen, C.; Mason, G.; Desai, M.; Labrador, A.; Lee, M.; Li, G.
2008-05-01
A new generation of instruments during solar cycle 23 made it possible to measure solar energetic particle (SEP) energy spectra for many species over a broad energy interval (~0.1 to ~100 MeV/nucleon). These observations revealed that most large SEP events have power-law spectra below a few MeV/nucleon with rather hard spectral indices, followed by spectral steepening at higher energies. These spectral breaks are ordered by species - the spectra of lighter elements break at higher energy/nucleon than those for heavier species. To understand the charge-to-mass (Q/M) dependence of these spectral breaks, we have located the breaks for a range of species (e.g., H, He, C, N, O, Ne, Mg, Si, and Fe) and correlated the break locations with either measured or average Q/M ratios. As of this writing there are results for 13 large SEP events, based on data from ACE, GOES, SAMPEX, and STEREO, and charge state data from SAMPEX and ACE. We find that the location of the breaks is generally well-represented by a power-law in Q/M. This power-law fit can be related to the Q/M- dependence of the interplanetary diffusion coefficient and to the turbulence spectrum of the interplanetary magnetic field. We find that the slope of the deduced turbulence spectra are correlated with Fe/O and the proton fluence. These results support the idea that proton-amplified Alfven waves are generated in large SEP events, as expected for acceleration at parallel shocks.
Dynamics, Spectral Geometry and Topology
Burghelea, Dan
2011-02-10
The paper is an informal report on joint work with Stefan Haller on Dynamics in relation with Topology and Spectral Geometry. By dynamics one means a smooth vector field on a closed smooth manifold; the elements of dynamics of concern are the rest points, instantons and closed trajectories. One discusses their counting in the case of a generic vector field which has some additional properties satisfied by a still very large class of vector fields.
Remote application for spectral collection
NASA Astrophysics Data System (ADS)
Cone, Shelli R.; Steele, R. J.; Tzeng, Nigel H.; Firpi, Alexer H.; Rodriguez, Benjamin M.
2016-05-01
In the area of collecting field spectral data using a spectrometer, it is common to have the instrument over the material of interest. In certain instances it is beneficial to have the ability to remotely control the spectrometer. While several systems have the ability to use a form of connectivity to capture the measurement it is essential to have the ability to control the settings. Additionally, capturing reference information (metadata) about the setup, system configuration, collection, location, atmospheric conditions, and sample information is necessary for future analysis leading towards material discrimination and identification. This has the potential to lead to cumbersome field collection and a lack of necessary information for post processing and analysis. The method presented in this paper describes a capability to merge all parts of spectral collection from logging reference information to initial analysis as well as importing information into a web-hosted spectral database. This allows the simplification of collecting, processing, analyzing and storing field spectra for future analysis and comparisons. This concept is developed for field collection of thermal data using the Designs and Prototypes (D&P) Hand Portable FT-IR Spectrometer (Model 102). The remote control of the spectrometer is done with a customized Android application allowing the ability to capture reference information, process the collected data from radiance to emissivity using a temperature emissivity separation algorithm and store the data into a custom web-based service. The presented system of systems allows field collected spectra to be used for various applications by spectral analysts in the future.
The interpretation of spectral data
NASA Technical Reports Server (NTRS)
Holter, M. R.
1972-01-01
The characteristics and extent of data which is obtainable by electromagnetic spectrum sensing and the application to earth resources survey are discussed. The wavelength and frequency ranges of operation for various remote sensors are tabulated. The spectral sensitivities of various sensing instruments are diagrammed. Examples of aerial photography to show the effects of lighting and seasonal variations on earth resources data are provided. Specific examples of multiband photography and multispectral imagery to crop analysis are included.
Active constrained clustering by examining spectral Eigenvectors
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri L.; desJardins, Marie; Xu, Qianjun
2005-01-01
This work focuses on the active selection of pairwise constraints for spectral clustering. We develop and analyze a technique for Active Constrained Clustering by Examining Spectral eigenvectorS (ACCESS) derived from a similarity matrix.
Argentina spectral-agronomic multitemporal data set
NASA Technical Reports Server (NTRS)
Helmer, D.; Kinzler, C.; Tomppkins, M. A.; Badhwar, G. D.
1983-01-01
A multitemporal LANDSAT spectral data set was created. The data set is over five 5 nm-by-6 nm areas over Argentina and contains by field, the spectral data, vegetation type and cloud cover information.
Active constrained clustering by examining spectral Eigenvectors
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri L.; desJardins, Marie; Xu, Qianjun
2005-01-01
This work focuses on the active selection of pairwise constraints for spectral clustering. We develop and analyze a technique for Active Constrained Clustering by Examining Spectral eigenvectorS (ACCESS) derived from a similarity matrix.
Spectral analysis of multiple time series
NASA Technical Reports Server (NTRS)
Dubman, M. R.
1972-01-01
Application of spectral analysis for mathematically determining relationship of random vibrations in structures and concurrent events in electric circuits, physiology, economics, and seismograms is discussed. Computer program for performing spectral analysis of multiple time series is described.
Spectral Methods in General Relativistic MHD Simulations
NASA Astrophysics Data System (ADS)
Garrison, David
2012-03-01
In this talk I discuss the use of spectral methods in improving the accuracy of a General Relativistic Magnetohydrodynamic (GRMHD) computer code. I introduce SpecCosmo, a GRMHD code developed as a Cactus arrangement at UHCL, and show simulation results using both Fourier spectral methods and finite differencing. This work demonstrates the use of spectral methods with the FFTW 3.3 Fast Fourier Transform package integrated with the Cactus Framework to perform spectral differencing using MPI.
Spectral methods for exterior elliptic problems
NASA Technical Reports Server (NTRS)
Canuto, C.; Hariharan, S. I.; Lustman, L.
1984-01-01
Spectral approximations for exterior elliptic problems in two dimensions are discussed. As in the conventional finite difference or finite element methods, the accuracy of the numerical solutions is limited by the order of the numerical farfield conditions. A spectral boundary treatment is introduced at infinity which is compatible with the infinite order interior spectral scheme. Computational results are presented to demonstrate the spectral accuracy attainable. Although a simple Laplace problem is examined, the analysis covers more complex and general cases.
Canopy Spectral Invariants. Part 1: A New Concept in Remote Sensing of Vegetation
NASA Technical Reports Server (NTRS)
Knyazikhin, Yuri; Schull, Mitchell A.; Xu, Liang; Myneni, Ranga B.; Samanta, Arindam
2011-01-01
The concept of canopy spectral invariants expresses the observation that simple algebraic combinations of leaf and canopy spectral reflectance become wavelength independent and determine two canopy structure specific variables the recollision and escape probabilities. These variables specify an accurate relationship between the spectral response of a vegetation canopy to incident solar radiation at the leaf and the canopy scale. They are sensitive to important structural features of the canopy such as forest cover, tree density, leaf area index, crown geometry, forest type and stand age. This paper presents the mathematical basis of the concept which is linked to eigenvalues and eigenvectors of the three-dimensional radiative transfer equation.
Enhanced spectral sensitivity of a chip-scale photonic-crystal slow-light interferometer.
Magaña-Loaiza, Omar S; Gao, Boshen; Schulz, Sebastian A; Awan, Kashif M; Upham, Jeremy; Dolgaleva, Ksenia; Boyd, Robert W
2016-04-01
We experimentally demonstrate that the spectral sensitivity of a Mach-Zehnder (MZ) interferometer can be enhanced through structural slow light. We observe a 20-fold resolution enhancement by placing a dispersion-engineered, slow-light, photonic-crystal waveguide in one arm of a fiber-based MZ interferometer. The spectral sensitivity of the interferometer increases roughly linearly with the group index, and we have quantified the resolution in terms of the spectral density of interference fringes. These results show promise for the use of slow-light methods for developing novel tools for optical metrology and, specifically, for compact high-resolution spectrometers.
Chaotic maps and flows: exact Riemann-Siegel lookalike for spectral fluctuations
NASA Astrophysics Data System (ADS)
Braun, Petr; Haake, Fritz
2012-10-01
To treat the spectral statistics of quantum maps and flows that are fully chaotic classically, we use the rigorous Riemann-Siegel lookalike available for the spectral determinant of unitary time evolution operators F. Concentrating on dynamics without time reversal invariance, we get the exact two-point correlator of the spectral density for finite dimension N of the matrix representative of F, as phenomenologically given by random matrix theory. In the limit N → ∞, the correlator of the Gaussian unitary ensemble is recovered. Previously conjectured cancellations of contributions of pseudo-orbits with periods beyond half the Heisenberg time are shown to be implied by the Riemann-Siegel lookalike.
USGS Spectral Library Version 7
Kokaly, Raymond F.; Clark, Roger N.; Swayze, Gregg A.; Livo, K. Eric; Hoefen, Todd M.; Pearson, Neil C.; Wise, Richard A.; Benzel, William M.; Lowers, Heather A.; Driscoll, Rhonda L.; Klein, Anna J.
2017-04-10
We have assembled a library of spectra measured with laboratory, field, and airborne spectrometers. The instruments used cover wavelengths from the ultraviolet to the far infrared (0.2 to 200 microns [μm]). Laboratory samples of specific minerals, plants, chemical compounds, and manmade materials were measured. In many cases, samples were purified, so that unique spectral features of a material can be related to its chemical structure. These spectro-chemical links are important for interpreting remotely sensed data collected in the field or from an aircraft or spacecraft. This library also contains physically constructed as well as mathematically computed mixtures. Four different spectrometer types were used to measure spectra in the library: (1) Beckman™ 5270 covering the spectral range 0.2 to 3 µm, (2) standard, high resolution (hi-res), and high-resolution Next Generation (hi-resNG) models of Analytical Spectral Devices (ASD) field portable spectrometers covering the range from 0.35 to 2.5 µm, (3) Nicolet™ Fourier Transform Infra-Red (FTIR) interferometer spectrometers covering the range from about 1.12 to 216 µm, and (4) the NASA Airborne Visible/Infra-Red Imaging Spectrometer AVIRIS, covering the range 0.37 to 2.5 µm. Measurements of rocks, soils, and natural mixtures of minerals were made in laboratory and field settings. Spectra of plant components and vegetation plots, comprising many plant types and species with varying backgrounds, are also in this library. Measurements by airborne spectrometers are included for forested vegetation plots, in which the trees are too tall for measurement by a field spectrometer. This report describes the instruments used, the organization of materials into chapters, metadata descriptions of spectra and samples, and possible artifacts in the spectral measurements. To facilitate greater application of the spectra, the library has also been convolved to selected spectrometer and imaging spectrometers sampling and
Tethys - Geological and Spectral Properties
NASA Astrophysics Data System (ADS)
Stephan, Katrin; Jaumann, Ralf; Wagner, Roland; Clark, Roger N.; Cruikshank, Dale P.; Dalle Ore, Cristina; Brown, Robert H.; Giese, Bernd; Roatsch, Thomas; Matson, Dennis; Baines, Kevin H.; Filacchione, Gianrico; Capaccione, Fabrizio; Burratti, Bonnie J.; Nicholson, Phil D.; Rodriguez, Sebastian
2015-04-01
Despite the spectral dominance of H2O ice on Tethys' surface, distinct spectral variations derived by the Cassini VIMS instrument could be detected. The ice infrared absorption strengths are very different from what was expected from the visible albedo derived from Voyager and Cassini camera data. Although on Tethys, the major ice absorptions at 1.5 and 2µm are general stronger on the leading hemisphere of the satellite similar to that seen on the neighboring satellites Dione and Rhea, the detailed mapping shows a more complex pattern. Two relatively narrow N/S trending bands enriched in H2O ice of relatively large particle size separate the Saturn-facing and the anti-Saturnian hemisphere. The largest impact crater Odysseus (33°N/129°W) is included in the N/S trending band of deeper H2O absorptions on the leading hemisphere, whereas the geologically older and fourth largest impact crater Penelope (11°S/249°W) is excluded from the 'icy' band on the trailing hemisphere - supporting an exogenic origin of these bands. The oval shaped dark albedo unit observed by Voyager in the equatorial region of Tethys' leading hemisphere, which could be related to magnetospheric 'dust' impacting the surface, exhibits slightly surpressed H2O ice absorptions compared to their surrounding regions. Variations in the spectral slope from the visible to the ultra-violet wavelength range are similar to the variations observed by Cassini ISS. The spectral slope is steepest (i.e. the effect of an ultra-violet absorber other than H2O ice is strongest) on the leading as well on the trailing hemisphere. No spectral properties could be exclusively associated with Tethys' extended graben system Ithaca Chasma. Local variations, i.e. local deepening of H2O ice absorptions, are mostly related to several probably fresh impact craters and to locations where topographic slope is high like crater walls. However, only a few such fresh impact craters could be observed.
NASA Technical Reports Server (NTRS)
Lichtenstein, J. H.
1975-01-01
Power-spectral-density calculations were made of the lateral responses to atmospheric turbulence for several conventional and short take-off and landing (STOL) airplanes. The turbulence was modeled as three orthogonal velocity components, which were uncorrelated, and each was represented with a one-dimensional power spectrum. Power spectral densities were computed for displacements, rates, and accelerations in roll, yaw, and sideslip. In addition, the power spectral density of the transverse acceleration was computed. Evaluation of ride quality based on a specific ride quality criterion was also made. The results show that the STOL airplanes generally had larger values for the rate and acceleration power spectra (and, consequently, larger corresponding root-mean-square values) than the conventional airplanes. The ride quality criterion gave poorer ratings to the STOL airplanes than to the conventional airplanes.
Studies on spectral analysis of randomly sampled signals: Application to laser velocimetry data
NASA Technical Reports Server (NTRS)
Sree, David
1992-01-01
Spectral analysis is very useful in determining the frequency characteristics of many turbulent flows, for example, vortex flows, tail buffeting, and other pulsating flows. It is also used for obtaining turbulence spectra from which the time and length scales associated with the turbulence structure can be estimated. These estimates, in turn, can be helpful for validation of theoretical/numerical flow turbulence models. Laser velocimetry (LV) is being extensively used in the experimental investigation of different types of flows, because of its inherent advantages; nonintrusive probing, high frequency response, no calibration requirements, etc. Typically, the output of an individual realization laser velocimeter is a set of randomly sampled velocity data. Spectral analysis of such data requires special techniques to obtain reliable estimates of correlation and power spectral density functions that describe the flow characteristics. FORTRAN codes for obtaining the autocorrelation and power spectral density estimates using the correlation-based slotting technique were developed. Extensive studies have been conducted on simulated first-order spectrum and sine signals to improve the spectral estimates. A first-order spectrum was chosen because it represents the characteristics of a typical one-dimensional turbulence spectrum. Digital prefiltering techniques, to improve the spectral estimates from randomly sampled data were applied. Studies show that the spectral estimates can be increased up to about five times the mean sampling rate.
NASA Astrophysics Data System (ADS)
Wang, Haiyan; Qian, Xianmei
2013-03-01
Based on the extended Huygens-Fresnel principle, we introduced the analytic expression of a random electromagnetic partially coherent flat-topped (PCFT) vortex beam propagating in Kolmogorov atmospheric turbulence. The spectral properties of the random electromagnetic PCFT vortex beam are explored by using the unified theory of coherence and polarization. It is demonstrated by numerical results and found that after propagating through turbulent atmosphere, the spectral density, the spectral degree of polarization as well as the spectral degree of coherence of the random electromagnetic PCFT vortex beam vary. The variations of the spectral properties depend closely on the strength of atmospheric turbulence and the properties of the source beam, i.e. the topological charges, the order of flatness, the waist width as well as the initial spatial coherence. In addition, the distributions of the spectral density and the spectral degree of polarization undergo several stages of evolution and finally tend to Gaussian profile at the receiver plane. Some possible explanations have also been given for these interesting physical phenomena.
Palenik, Mark C.; Dunlap, Brett I.
2015-07-28
Despite the fundamental importance of electron density in density functional theory, perturbations are still usually dealt with using Hartree-Fock-like orbital equations known as coupled-perturbed Kohn-Sham (CPKS). As an alternative, we develop a perturbation theory that solves for the perturbed density directly, removing the need for CPKS. This replaces CPKS with a true Hohenberg-Kohn density perturbation theory. In CPKS, the perturbed density is found in the basis of products of occupied and virtual orbitals, which becomes ever more over-complete as the size of the orbital basis set increases. In our method, the perturbation to the density is expanded in terms of a series of density basis functions and found directly. It is possible to solve for the density in such a way that it makes the total energy stationary even if the density basis is incomplete.
Prostate cancer spectral multifeature analysis using TRUS images.
Mohamed, S S; Salama, M A
2008-04-01
This paper focuses on extracting and analyzing different spectral features from transrectal ultrasound (TRUS) images for prostate cancer recognition. First, the information about the images' frequency domain features and spatial domain features are combined using a Gabor filter and then integrated with the expert radiologist's information to identify the highly suspicious regions of interest (ROIs). The next stage of the proposed algorithm is to scan each identified region in order to generate the corresponding 1-D signal that represents each region. For each ROI, possible spectral feature sets are constructed using different new geometrical features extracted from the power spectrum density (PSD) of each region's signal. Next, a classifier-based algorithm for feature selection using particle swarm optimization (PSO) is adopted and used to select the optimal feature subset from the constructed feature sets. A new spectral feature set for the TRUS images using estimation of signal parameters via rotational invariance technique (ESPRIT) is also constructed, and its ability to represent tissue texture is compared to the PSD-based spectral feature sets using the support vector machines (SVMs) classifier. The accuracy obtained ranges from 72.2% to 94.4%, with the best accuracy achieved by the ESPRIT feature set.
Temporary spectral analysis of a laser plasma of mineral coal
NASA Astrophysics Data System (ADS)
Rebolledo, P.; Pacheco, P.; Sarmiento, R.; Cabanzo, R.; Mejía-Ospino, E.
2013-11-01
In this work we present results of the temporal spectral study of a plasma laser of mineral coal using the Laser-induced Breakdown Spectroscopy (LIBS) technique. The plasma was generated by focusing a laser beam of Nd:YAG laser emitting at 532 nm with energy per pulse of 35 mJ on coal target pellets. The plasma radiation was conducted by an optical fiber to the entrance slit of a spectrograph of 0.5 m, equipped with a 1200 and 2400 grooves/mm diffraction grating and an ICCD camera for registration with different delay times of the spectra in the spectral range from 250 nm to 900 nm. The temporal spectral analysis allowed the identification of the elements Al, Fe, Ca, Mg, K, and Si, and CN and C2 molecules present in natural coals. The characteristics of the spectral lines and bands were studied at different delay times obtaining the calculation of the evolution of electron temperature, electron density, and vibrational temperature of plasmas in the time. The delay times used were between 0.5 μs and 5 μs, calculating the electron temperature ranged between 5 000 K and 1 000 K.
Spectral feature variations in x-ray diffraction imaging systems
NASA Astrophysics Data System (ADS)
Wolter, Scott D.; Greenberg, Joel A.
2016-05-01
Materials with different atomic or molecular structures give rise to unique scatter spectra when measured by X-ray diffraction. The details of these spectra, though, can vary based on both intrinsic (e.g., degree of crystallinity or doping) and extrinsic (e.g., pressure or temperature) conditions. While this sensitivity is useful for detailed characterizations of the material properties, these dependences make it difficult to perform more general classification tasks, such as explosives threat detection in aviation security. A number of challenges, therefore, currently exist for reliable substance detection including the similarity in spectral features among some categories of materials combined with spectral feature variations from materials processing and environmental factors. These factors complicate the creation of a material dictionary and the implementation of conventional classification and detection algorithms. Herein, we report on two prominent factors that lead to variations in spectral features: crystalline texture and temperature variations. Spectral feature comparisons between materials categories will be described for solid metallic sheet, aqueous liquids, polymer sheet, and metallic, organic, and inorganic powder specimens. While liquids are largely immune to texture effects, they are susceptible to temperature changes that can modify their density or produce phase changes. We will describe in situ temperature-dependent measurement of aqueous-based commercial goods in the temperature range of -20°C to 35°C.
Aron, Miles; Browning, Richard; Carugo, Dario; Sezgin, Erdinc; Bernardino de la Serna, Jorge; Eggeling, Christian; Stride, Eleanor
2017-05-12
Spectral imaging with polarity-sensitive fluorescent probes enables the quantification of cell and model membrane physical properties, including local hydration, fluidity, and lateral lipid packing, usually characterized by the generalized polarization (GP) parameter. With the development of commercial microscopes equipped with spectral detectors, spectral imaging has become a convenient and powerful technique for measuring GP and other membrane properties. The existing tools for spectral image processing, however, are insufficient for processing the large data sets afforded by this technological advancement, and are unsuitable for processing images acquired with rapidly internalized fluorescent probes. Here we present a MATLAB spectral imaging toolbox with the aim of overcoming these limitations. In addition to common operations, such as the calculation of distributions of GP values, generation of pseudo-colored GP maps, and spectral analysis, a key highlight of this tool is reliable membrane segmentation for probes that are rapidly internalized. Furthermore, handling for hyperstacks, 3D reconstruction and batch processing facilitates analysis of data sets generated by time series, z-stack, and area scan microscope operations. Finally, the object size distribution is determined, which can provide insight into the mechanisms underlying changes in membrane properties and is desirable for e.g. studies involving model membranes and surfactant coated particles. Analysis is demonstrated for cell membranes, cell-derived vesicles, model membranes, and microbubbles with environmentally-sensitive probes Laurdan, carboxyl-modified Laurdan (C-Laurdan), Di-4-ANEPPDHQ, and Di-4-AN(F)EPPTEA (FE), for quantification of the local lateral density of lipids or lipid packing. The Spectral Imaging Toolbox is a powerful tool for the segmentation and processing of large spectral imaging datasets with a reliable method for membrane segmentation and no ability in programming required. The
Development of Jet Noise Power Spectral Laws Using SHJAR Data
NASA Technical Reports Server (NTRS)
Khavaran, Abbas; Bridges, James
2009-01-01
High quality jet noise spectral data measured at the Aeroacoustic Propulsion Laboratory at the NASA Glenn Research Center is used to examine a number of jet noise scaling laws. Configurations considered in the present study consist of convergent and convergent-divergent axisymmetric nozzles. Following the work of Viswanathan, velocity power factors are estimated using a least squares fit on spectral power density as a function of jet temperature and observer angle. The regression parameters are scrutinized for their uncertainty within the desired confidence margins. As an immediate application of the velocity power laws, spectral density in supersonic jets are decomposed into their respective components attributed to the jet mixing noise and broadband shock associated noise. Subsequent application of the least squares method on the shock power intensity shows that the latter also scales with some power of the shock parameter. A modified shock parameter is defined in order to reduce the dependency of the regression factors on the nozzle design point within the uncertainty margins of the least squares method.
Spectral sum rules for conformal field theories in arbitrary dimensions
NASA Astrophysics Data System (ADS)
Chowdhury, Subham Dutta; David, Justin R.; Prakash, Shiroman
2017-07-01
We derive spectral sum rules in the shear channel for conformal field theories at finite temperature in general d ≥ 3 dimensions. The sum rules result from the OPE of the stress tensor at high frequency as well as the hydrodynamic behaviour of the theory at low frequencies. The sum rule states that a weighted integral of the spectral density over frequencies is proportional to the energy density of the theory. We show that the proportionality constant can be written in terms the Hofman-Maldacena variables t 2 , t 4 which determine the three point function of the stress tensor. For theories which admit a two derivative gravity dual this proportionality constant is given by d/2(d+1) . We then use causality constraints and obtain bounds on the sum rule which are valid in any conformal field theory. Finally we demonstrate that the high frequency behaviour of the spectral function in the vector and the tensor channel are also determined by the Hofman-Maldacena variables.
Spectral Behavior of Weakly Compressible Aero-Optical Distortions
NASA Astrophysics Data System (ADS)
Mathews, Edwin; Wang, Kan; Wang, Meng; Jumper, Eric
2016-11-01
In classical theories of optical distortions by atmospheric turbulence, an appropriate and key assumption is that index-of-refraction variations are dominated by fluctuations in temperature and the effects of turbulent pressure fluctuations are negligible. This assumption is, however, not generally valid for aero-optical distortions caused by turbulent flow over an optical aperture, where both temperature and pressures fluctuations may contribute significantly to the index-of-refraction fluctuations. A general expression for weak fluctuations in refractive index is derived using the ideal gas law and Gladstone-Dale relation and applied to describe the spectral behavior of aero-optical distortions. Large-eddy simulations of weakly compressible, temporally evolving shear layers are then used to verify the theoretical results. Computational results support theoretical findings and confirm that if the log slope of the 1-D density spectrum in the inertial range is -mρ , the optical phase distortion spectral slope is given by - (mρ + 1) . The value of mρ is then shown to be dependent on the ratio of shear-layer free-stream densities and bounded by the spectral slopes of temperature and pressure fluctuations. Supported by HEL-JTO through AFOSR Grant FA9550-13-1-0001 and Blue Waters Graduate Fellowship Program.
Iterative spectral methods and spectral solutions to compressible flows
NASA Technical Reports Server (NTRS)
Hussaini, M. Y.; Zang, T. A.
1982-01-01
A spectral multigrid scheme is described which can solve pseudospectral discretizations of self-adjoint elliptic problems in O(N log N) operations. An iterative technique for efficiently implementing semi-implicit time-stepping for pseudospectral discretizations of Navier-Stokes equations is discussed. This approach can handle variable coefficient terms in an effective manner. Pseudospectral solutions of compressible flow problems are presented. These include one dimensional problems and two dimensional Euler solutions. Results are given both for shock-capturing approaches and for shock-fitting ones.
Self-spectral calibration for spectral domain optical coherence tomography
NASA Astrophysics Data System (ADS)
Zhang, Xianling; Gao, Wanrong; Bian, Haiyi; Chen, Chaoliang; Liao, Jiuling
2013-06-01
A different real-time self-wavelength calibration method for spectral domain optical coherence tomography is presented in which interference spectra measured from two arbitrary points on the tissue surface are used for calibration. The method takes advantages of two favorable conditions of optical coherence tomography (OCT) signal. First, the signal back-scattered from the tissue surface is generally much stronger than that from positions in the tissue interior, so the spectral component of the surface interference could be extracted from the measured spectrum. Second, the tissue surface is not a plane and a phase difference exists between the light reflected from two different points on the surface. Compared with the zero-crossing automatic method, the introduced method has the advantage of removing the error due to dispersion mismatch or the common phase error. The method is tested experimentally to demonstrate the improved signal-to-noise ratio, higher axial resolution, and slower sensitivity degradation with depth when compared to the use of the zero-crossing method and applied to two-dimensional cross-sectional images of human finger skin.
Planar-waveguide integrated spectral comparator.
Mossberg, T W; Iazikov, D; Greiner, C
2004-06-01
A cost-effective yet robust and versatile dual-channel spectral comparator is presented. The silica-on-silicon planar-waveguide integrated device includes two holographic Bragg-grating reflectors (HBRs) with complementary spectral transfer functions. Output comprises projections of input signal spectra onto the complementary spectral channels. Spectral comparators may be useful in optical code-division multiplexing, optical packet decoding, spectral target recognition, and the identification of molecular spectra. HBRs may be considered to be mode-specific photonic crystals.
1982-04-01
anticonvulsant drugs produced a specific pattern of spectral density change localized to sensorimotor cortex, bilater- ally. This consisted of a sharp...0102 LF 014 6601 SECURITY CLASSIFICATION OF THIS PAGE (M~en Deie bIofed ) 20 (continued) in the 12-15 Hz band. A seund ;dentlLal test series was...with pyridoxine and di- azepain but not with vaiproic dLid o’" Cdr*bd111dzep1nre. Reference to the spectral density changes produced by these groups of
ERIC Educational Resources Information Center
Shaw, Mike
2003-01-01
Integrates story telling into a science activity on the density of liquids in order to increase student interest. Shows the relationship between mass and volume ratio and how they determine density. Includes teacher notes. (YDS)