Statistical properties of a filtered Poisson process with additive random noise: distributions, correlations and moment estimation

NASA Astrophysics Data System (ADS)

Theodorsen, A.; E Garcia, O.; Rypdal, M.

2017-05-01

Filtered Poisson processes are often used as reference models for intermittent fluctuations in physical systems. Such a process is here extended by adding a noise term, either as a purely additive term to the process or as a dynamical term in a stochastic differential equation. The lowest order moments, probability density function, auto-correlation function and power spectral density are derived and used to identify and compare the effects of the two different noise terms. Monte-Carlo studies of synthetic time series are used to investigate the accuracy of model parameter estimation and to identify methods for distinguishing the noise types. It is shown that the probability density function and the three lowest order moments provide accurate estimations of the model parameters, but are unable to separate the noise types. The auto-correlation function and the power spectral density also provide methods for estimating the model parameters, as well as being capable of identifying the noise type. The number of times the signal crosses a prescribed threshold level in the positive direction also promises to be able to differentiate the noise type.

Application of multivariate autoregressive spectrum estimation to ULF waves

NASA Technical Reports Server (NTRS)

Ioannidis, G. A.

1975-01-01

The estimation of the power spectrum of a time series by fitting a finite autoregressive model to the data has recently found widespread application in the physical sciences. The extension of this method to the analysis of vector time series is presented here through its application to ULF waves observed in the magnetosphere by the ATS 6 synchronous satellite. Autoregressive spectral estimates of the power and cross-power spectra of these waves are computed with computer programs developed by the author and are compared with the corresponding Blackman-Tukey spectral estimates. The resulting spectral density matrices are then analyzed to determine the direction of propagation and polarization of the observed waves.

Practical Implementation of Multiple Model Adaptive Estimation Using Neyman-Pearson Based Hypothesis Testing and Spectral Estimation Tools

DTIC Science & Technology

1996-09-01

Generalized Likelihood Ratio (GLR) and voting techniques. The third class consisted of multiple hypothesis filter detectors, specifically the MMAE. The...vector version, versus a tensor if we use the matrix version of the power spectral density estimate. Using this notation, we will derive an...as MATLAB , have an intrinsic sample covariance computation available, which makes this method quite easy to implement. In practice, the mean for the

Improving the Accuracy of Mapping Urban Vegetation Carbon Density by Combining Shadow Remove, Spectral Unmixing Analysis and Spatial Modeling

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

Measurements of surface-pressure fluctuations on the XB-70 airplane at local Mach numbers up to 2.45

NASA Technical Reports Server (NTRS)

Lewis, T. L.; Dods, J. B., Jr.; Hanly, R. D.

1973-01-01

Measurements of surface-pressure fluctuations were made at two locations on the XB-70 airplane for nine flight-test conditions encompassing a local Mach number range from 0.35 to 2.45. These measurements are presented in the form of estimated power spectral densities, coherence functions, and narrow-band-convection velocities. The estimated power spectral densities compared favorably with wind-tunnel data obtained by other experimenters. The coherence function and convection velocity data supported conclusions by other experimenters that low-frequency surface-pressure fluctuations consist of small-scale turbulence components with low convection velocity.

Radar Investigations of Asteroids

NASA Technical Reports Server (NTRS)

Ostro, S. J.

1984-01-01

Radar investigations of asteroids, including observations during 1984 to 1985 of at least 8 potential targets and continued analyses of radar data obtained during 1980 to 1984 for 30 other asteroids is proposed. The primary scientific objectives include estimation of echo strength, polarization, spectral shape, spectral bandwidth, and Doppler shift. These measurements yield estimates of target size, shape, and spin vector; place constraints on topography, morphology, density, and composition of the planetary surface; yield refined estimates of target orbital parameters; and reveals the presence of asteroidal satellites.

Canopy reflectance modelling of semiarid vegetation

NASA Technical Reports Server (NTRS)

Franklin, Janet

1994-01-01

Three different types of remote sensing algorithms for estimating vegetation amount and other land surface biophysical parameters were tested for semiarid environments. These included statistical linear models, the Li-Strahler geometric-optical canopy model, and linear spectral mixture analysis. The two study areas were the National Science Foundation's Jornada Long Term Ecological Research site near Las Cruces, NM, in the northern Chihuahuan desert, and the HAPEX-Sahel site near Niamey, Niger, in West Africa, comprising semiarid rangeland and subtropical crop land. The statistical approach (simple and multiple regression) resulted in high correlations between SPOT satellite spectral reflectance and shrub and grass cover, although these correlations varied with the spatial scale of aggregation of the measurements. The Li-Strahler model produced estimated of shrub size and density for both study sites with large standard errors. In the Jornada, the estimates were accurate enough to be useful for characterizing structural differences among three shrub strata. In Niger, the range of shrub cover and size in short-fallow shrublands is so low that the necessity of spatially distributed estimation of shrub size and density is questionable. Spectral mixture analysis of multiscale, multitemporal, multispectral radiometer data and imagery for Niger showed a positive relationship between fractions of spectral endmembers and surface parameters of interest including soil cover, vegetation cover, and leaf area index.

Geometrical Description in Binary Composites and Spectral Density Representation

PubMed Central

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 coinciding peak locations but different heights. It is speculated that the coincidence in the peak locations is an absolute illustration of the self-similar fractal nature of the mixture topology (structure) created with the LLL expression. Consequently, the spectra are not altered significantly with increased filler concentration level—they exhibit a self-similar spectral density function for different concentration levels. Last but not least, the estimated percolation strengths also confirm the fractal nature of the systems characterized by the LLL mixture expression. It is concluded that the LLL expression is suitable for complex composite systems that have hierarchical order in their structure. These observations confirm the finding in the literature.

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 solar neighborhood, 1: Standard spectral types (K5-M8) for northern dwarfs within eight parsecs

NASA Technical Reports Server (NTRS)

Henry, Todd J.; Kirkpatrick, J. Davy; Simons, Douglas A.

1994-01-01

Spectral types on a standard system are presented for late-type dwarfs within 8 pc. All known main-sequence stars north of -25 deg and with M(sub V) greater than or = 8.00 have been observed, resulting in 92 spectra. Based upon the stellar system density to 5 pc, we estimate that approximately 35 systems in the 8 pc sample are 'missing.' In an effort to reveal these systems, we use an empirical spectral type-M(sub V) relation to estimate distances to additional stars that may lie within 8 pc.

Estimation of proportions in mixed pixels through their region characterization

NASA Technical Reports Server (NTRS)

Chittineni, C. B. (Principal Investigator)

1981-01-01

A region of mixed pixels can be characterized through the probability density function of proportions of classes in the pixels. Using information from the spectral vectors of a given set of pixels from the mixed pixel region, expressions are developed for obtaining the maximum likelihood estimates of the parameters of probability density functions of proportions. The proportions of classes in the mixed pixels can then be estimated. If the mixed pixels contain objects of two classes, the computation can be reduced by transforming the spectral vectors using a transformation matrix that simultaneously diagonalizes the covariance matrices of the two classes. If the proportions of the classes of a set of mixed pixels from the region are given, then expressions are developed for obtaining the estmates of the parameters of the probability density function of the proportions of mixed pixels. Development of these expressions is based on the criterion of the minimum sum of squares of errors. Experimental results from the processing of remotely sensed agricultural multispectral imagery data are presented.

Clinical evaluation of melanomas and common nevi by spectral imaging

PubMed Central

Diebele, Ilze; Kuzmina, Ilona; Lihachev, Alexey; Kapostinsh, Janis; Derjabo, Alexander; Valeine, Lauma; Spigulis, Janis

2012-01-01

A clinical trial on multi-spectral imaging of malignant and non-malignant skin pathologies comprising 17 melanomas and 65 pigmented common nevi was performed. Optical density data of skin pathologies were obtained in the spectral range 450–950 nm using the multispectral camera Nuance EX. An image parameter and maps capable of distinguishing melanoma from pigmented nevi were proposed. The diagnostic criterion is based on skin optical density differences at three fixed wavelengths: 540nm, 650nm and 950nm. The sensitivity and specificity of this method were estimated to be 94% and 89%, respectively. The proposed methodology and potential clinical applications are discussed. PMID:22435095

Enhancing active and passive remote sensing in the ocean using broadband acoustic transmissions and coherent hydrophone arrays

NASA Astrophysics Data System (ADS)

Tran, Duong Duy

The statistics of broadband acoustic signal transmissions in a random continental shelf waveguide are characterized for the fully saturated regime. The probability distribution of broadband signal energies after saturated multi-path propagation is derived using coherence theory. The frequency components obtained from Fourier decomposition of a broadband signal are each assumed to be fully saturated, where the energy spectral density obeys the exponential distribution with 5.6 dB standard deviation and unity scintillation index. When the signal bandwidth and measurement time are respectively larger than the correlation bandwidth and correlation time of its energy spectral density components, the broadband signal energy obtained by integrating the energy spectral density across the signal bandwidth then follows the Gamma distribution with standard deviation smaller than 5.6 dB and scintillation index less than unity. The theory is verified with broadband transmissions in the Gulf of Maine shallow water waveguide in the 300-1200 Hz frequency range. The standard deviations of received broadband signal energies range from 2.7 to 4.6 dB for effective bandwidths up to 42 Hz, while the standard deviations of individual energy spectral density components are roughly 5.6 dB. The energy spectral density correlation bandwidths of the received broadband signals are found to be larger for signals with higher center frequency. Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing using a single low-frequency (< 2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth, located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the array. The dependence of broadband energy on bandwidth and measurement time was verified employing recorded sperm whale clicks in the Gulf of Maine.

Hyperspectral Biofilm Classification Analysis for Carrying Capacity of Migratory Birds in the South Bay Salt Ponds

NASA Technical Reports Server (NTRS)

Hsu, Wei-Chen; Kuss, Amber Jean; Ketron, Tyler; Nguyen, Andrew; Remar, Alex Covello; Newcomer, Michelle; Fleming, Erich; Debout, Leslie; Debout, Brad; Detweiler, Angela;

Statistics of some atmospheric turbulence records relevant to aircraft response calculations

NASA Technical Reports Server (NTRS)

Mark, W. D.; Fischer, R. W.

1981-01-01

Methods for characterizing atmospheric turbulence are described. The methods illustrated include maximum likelihood estimation of the integral scale and intensity of records obeying the von Karman transverse power spectral form, constrained least-squares estimation of the parameters of a parametric representation of autocorrelation functions, estimation of the power spectra density of the instantaneous variance of a record with temporally fluctuating variance, and estimation of the probability density functions of various turbulence components. Descriptions of the computer programs used in the computations are given, and a full listing of these programs is included.

Improving the Curie depth estimation through optimizing the spectral block dimensions of the aeromagnetic data in the Sabalan geothermal field

NASA Astrophysics Data System (ADS)

Akbar, Somaieh; Fathianpour, Nader

2016-12-01

The Curie point depth is of great importance in characterizing geothermal resources. In this study, the Curie iso-depth map was provided using the well-known method of dividing the aeromagnetic dataset into overlapping blocks and analyzing the power spectral density of each block separately. Determining the optimum block dimension is vital in improving the resolution and accuracy of estimating Curie point depth. To investigate the relation between the optimal block size and power spectral density, a forward magnetic modeling was implemented on an artificial prismatic body with specified characteristics. The top, centroid, and bottom depths of the body were estimated by the spectral analysis method for different block dimensions. The result showed that the optimal block size could be considered as the smallest possible block size whose corresponding power spectrum represents an absolute maximum in small wavenumbers. The Curie depth map of the Sabalan geothermal field and its surrounding areas, in the northwestern Iran, was produced using a grid of 37 blocks with different dimensions from 10 × 10 to 50 × 50 km2, which showed at least 50% overlapping with adjacent blocks. The Curie point depth was estimated in the range of 5 to 21 km. The promising areas with the Curie point depths less than 8.5 km are located around Mountain Sabalan encompassing more than 90% of known geothermal resources in the study area. Moreover, the Curie point depth estimated by the improved spectral analysis is in good agreement with the depth calculated from the thermal gradient data measured in one of the exploratory wells in the region.

Gaussian model for emission rate measurement of heated plumes using hyperspectral data

NASA Astrophysics Data System (ADS)

Grauer, Samuel J.; Conrad, Bradley M.; Miguel, Rodrigo B.; Daun, Kyle J.

2018-02-01

This paper presents a novel model for measuring the emission rate of a heated gas plume using hyperspectral data from an FTIR imaging spectrometer. The radiative transfer equation (RTE) is used to relate the spectral intensity of a pixel to presumed Gaussian distributions of volume fraction and temperature within the plume, along a line-of-sight that corresponds to the pixel, whereas previous techniques exclusively presume uniform distributions for these parameters. Estimates of volume fraction and temperature are converted to a column density by integrating the local molecular density along each path. Image correlation velocimetry is then employed on raw spectral intensity images to estimate the volume-weighted normal velocity at each pixel. Finally, integrating the product of velocity and column density along a control surface yields an estimate of the instantaneous emission rate. For validation, emission rate estimates were derived from synthetic hyperspectral images of a heated methane plume, generated using data from a large-eddy simulation. Calculating the RTE with Gaussian distributions of volume fraction and temperature, instead of uniform distributions, improved the accuracy of column density measurement by 14%. Moreover, the mean methane emission rate measured using our approach was within 4% of the ground truth. These results support the use of Gaussian distributions of thermodynamic properties in calculation of the RTE for optical gas diagnostics.

Leak Detection and Location of Water Pipes Using Vibration Sensors and Modified ML Prefilter.

PubMed

Choi, Jihoon; Shin, Joonho; Song, Choonggeun; Han, Suyong; Park, Doo Il

2017-09-13

This paper proposes a new leak detection and location method based on vibration sensors and generalised cross-correlation techniques. Considering the estimation errors of the power spectral densities (PSDs) and the cross-spectral density (CSD), the proposed method employs a modified maximum-likelihood (ML) prefilter with a regularisation factor. We derive a theoretical variance of the time difference estimation error through summation in the discrete-frequency domain, and find the optimal regularisation factor that minimises the theoretical variance in practical water pipe channels. The proposed method is compared with conventional correlation-based techniques via numerical simulations using a water pipe channel model, and it is shown through field measurement that the proposed modified ML prefilter outperforms conventional prefilters for the generalised cross-correlation. In addition, we provide a formula to calculate the leak location using the time difference estimate when different types of pipes are connected.

Leak Detection and Location of Water Pipes Using Vibration Sensors and Modified ML Prefilter

PubMed Central

Shin, Joonho; Song, Choonggeun; Han, Suyong; Park, Doo Il

2017-01-01

This paper proposes a new leak detection and location method based on vibration sensors and generalised cross-correlation techniques. Considering the estimation errors of the power spectral densities (PSDs) and the cross-spectral density (CSD), the proposed method employs a modified maximum-likelihood (ML) prefilter with a regularisation factor. We derive a theoretical variance of the time difference estimation error through summation in the discrete-frequency domain, and find the optimal regularisation factor that minimises the theoretical variance in practical water pipe channels. The proposed method is compared with conventional correlation-based techniques via numerical simulations using a water pipe channel model, and it is shown through field measurement that the proposed modified ML prefilter outperforms conventional prefilters for the generalised cross-correlation. In addition, we provide a formula to calculate the leak location using the time difference estimate when different types of pipes are connected. PMID:28902154

Remote sensing investigations of wetland biomass and productivity for global biosystems research

NASA Technical Reports Server (NTRS)

Harkisky, M.; Klemas, V.

1983-01-01

Monitoring biomass of wetlands ecosystems can provide information on net primary production and on the chemical and physical status of wetland soils relative to anaerobic microbial transformation of key elements. Multispectral remote sensing techniques successfully estimated macrophytic biomass in wetlands systems. Regression models developed from ground spectral data for predicting Spartina alterniflora biomass over an entire growing season include seasonal variations in biomass density and illumination intensity. An independent set of biomass and spectral data were collected and the standing crop biomass and net primary productivity were estimated. The improved spatial, radiometric and spectral resolution of th LANDSAT-4 Thematic Mapper over the LANDSAT MSS can greatly enhance multispectral techniques for estimating wetlands biomass over large areas. These techniques can provide the biomass data necessary for global ecology studies.

Low Streamflow Forcasting using Minimum Relative Entropy

NASA Astrophysics Data System (ADS)

Cui, H.; Singh, V. P.

2013-12-01

Minimum relative entropy spectral analysis is derived in this study, and applied to forecast streamflow time series. Proposed method extends the autocorrelation in the manner that the relative entropy of underlying process is minimized so that time series data can be forecasted. Different prior estimation, such as uniform, exponential and Gaussian assumption, is taken to estimate the spectral density depending on the autocorrelation structure. Seasonal and nonseasonal low streamflow series obtained from Colorado River (Texas) under draught condition is successfully forecasted using proposed method. Minimum relative entropy determines spectral of low streamflow series with higher resolution than conventional method. Forecasted streamflow is compared to the prediction using Burg's maximum entropy spectral analysis (MESA) and Configurational entropy. The advantage and disadvantage of each method in forecasting low streamflow is discussed.

Senegalese land surface change analysis and biophysical parameter estimation using NOAA AVHRR spectral data

NASA Technical Reports Server (NTRS)

Vukovich, Fred M.; Toll, David L.; Kennard, Ruth L.

1989-01-01

Surface biophysical estimates were derived from analysis of NOAA Advanced Very High Spectral Resolution (AVHRR) spectral data of the Senegalese area of west Africa. The parameters derived were of solar albedo, spectral visible and near-infrared band reflectance, spectral vegetative index, and ground temperature. Wet and dry linked AVHRR scenes from 1981 through 1985 in Senegal were analyzed for a semi-wet southerly site near Tambacounda and a predominantly dry northerly site near Podor. Related problems were studied to convert satellite derived radiance to biophysical estimates of the land surface. Problems studied were associated with sensor miscalibration, atmospheric and aerosol spatial variability, surface anisotropy of reflected radiation, narrow satellite band reflectance to broad solar band conversion, and ground emissivity correction. The middle-infrared reflectance was approximated with a visible AVHRR reflectance for improving solar albedo estimates. In addition, the spectral composition of solar irradiance (direct and diffuse radiation) between major spectral regions (i.e., ultraviolet, visible, near-infrared, and middle-infrared) was found to be insensitive to changes in the clear sky atmospheric optical depth in the narrow band to solar band conversion procedure. Solar albedo derived estimates for both sites were not found to change markedly with significant antecedent precipitation events or correspondingly from increases in green leaf vegetation density. The bright soil/substrate contributed to a high albedo for the dry related scenes, whereas the high internal leaf reflectance in green vegetation canopies in the near-infrared contributed to high solar albedo for the wet related scenes. The relationship between solar albedo and ground temperature was poor, indicating the solar albedo has little control of the ground temperature. The normalized difference vegetation index (NDVI) and the derived visible reflectance were more sensitive to antecedent rainfall amounts and green vegetation changes than were near-infrared changes. The information in the NDVI related to green leaf density changes primarily was from the visible reflectance. The contribution of the near-infrared reflectance to explaining green vegetation is largely reduced when there is a bright substrate.

A Review of Spectral Methods for Variable Amplitude Fatigue Prediction and New Results

NASA Technical Reports Server (NTRS)

Larsen, Curtis E.; Irvine, Tom

2013-01-01

A comprehensive review of the available methods for estimating fatigue damage from variable amplitude loading is presented. The dependence of fatigue damage accumulation on power spectral density (psd) is investigated for random processes relevant to real structures such as in offshore or aerospace applications. Beginning with the Rayleigh (or narrow band) approximation, attempts at improved approximations or corrections to the Rayleigh approximation are examined by comparison to rainflow analysis of time histories simulated from psd functions representative of simple theoretical and real world applications. Spectral methods investigated include corrections by Wirsching and Light, Ortiz and Chen, the Dirlik formula, and the Single-Moment method, among other more recent proposed methods. Good agreement is obtained between the spectral methods and the time-domain rainflow identification for most cases, with some limitations. Guidelines are given for using the several spectral methods to increase confidence in the damage estimate.

Mapping surface energy balance components by combining Landsat Thematic Mapper and ground-based meteorological data

NASA Technical Reports Server (NTRS)

Moran, M. Susan; Jackson, Ray D.; Raymond, Lee H.; Gay, Lloyd W.; Slater, Philip N.

1989-01-01

Surface energy balance components were evaluated by combining satellite-based spectral data with on-site measurements of solar irradiance, air temperature, wind speed, and vapor pressure. Maps of latent heat flux density and net radiant flux density were produced using Landsat TM data for three dates. The TM-based estimates differed from Bowen-ratio and aircraft-based estimates by less than 12 percent over mature fields of cotton, wheat, and alfalfa.

Eddy covariance measurements with a new fast-response, enclosed-path analyzer: Spectral characteristics and cross-system comparisons

Treesearch

K. Novick; J. Walker; W.S. Chan; A. Schmidt; C. Sobek; J.M. Vose

2013-01-01

A new class of enclosed path gas analyzers suitable for eddy covariance applications combines the advantages of traditional closed-path systems (small density corrections, good performance in poor weather) and open-path systems (good spectral response, low power requirements), and permits estimates of instantaneous gas mixing ratio. Here, the extent to which these...

A two dimensional power spectral estimate for some nonstationary processes. M.S. Thesis

NASA Technical Reports Server (NTRS)

Smith, Gregory L.

1989-01-01

A two dimensional estimate for the power spectral density of a nonstationary process is being developed. The estimate will be applied to helicopter noise data which is clearly nonstationary. The acoustic pressure from the isolated main rotor and isolated tail rotor is known to be periodically correlated (PC) and the combined noise from the main and tail rotors is assumed to be correlation autoregressive (CAR). The results of this nonstationary analysis will be compared with the current method of assuming that the data is stationary and analyzing it as such. Another method of analysis is to introduce a random phase shift into the data as shown by Papoulis to produce a time history which can then be accurately modeled as stationary. This method will also be investigated for the helicopter data. A method used to determine the period of a PC process when the period is not know is discussed. The period of a PC process must be known in order to produce an accurate spectral representation for the process. The spectral estimate is developed. The bias and variability of the estimate are also discussed. Finally, the current method for analyzing nonstationary data is compared to that of using a two dimensional spectral representation. In addition, the method of phase shifting the data is examined.

Dolphin biosonar target detection in noise: wrap up of a past experiment.

PubMed

Au, Whitlow W L

2014-07-01

The target detection capability of bottlenose dolphins in the presence of artificial masking noise was first studied by Au and Penner [J. Acoust. Soc. Am. 70, 687-693 (1981)] in which the dolphins' target detection threshold was determined as a function of the ratio of the echo energy flux density and the estimated received noise spectral density. Such a metric was commonly used in human psychoacoustics despite the fact that the echo energy flux density is not compatible with noise spectral density which is averaged intensity per Hz. Since the earlier detection in noise studies, two important parameters, the dolphin integration time applicable to broadband clicks and the dolphin's auditory filter shape, were determined. The inclusion of these two parameters allows for the estimation of the received energy flux density of the masking noise so that the dolphin target detection can now be determined as a function of the ratio of the received energy of the echo over the received noise energy. Using an integration time of 264 μs and an auditory bandwidth of 16.7 kHz, the ratio of the echo energy to noise energy at the target detection threshold is approximately 1 dB.

Shell stability and conditions analyzed using a new method of extracting shell areal density maps from spectrally resolved images of direct-drive inertial confinement fusion implosions

DOE PAGES

Johns, H. M.; Mancini, R. C.; Nagayama, T.; ...

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. Thesemore » 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 = 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.« less

Identification and modification of dominant noise sources in diesel engines

NASA Astrophysics Data System (ADS)

Hayward, Michael D.

Determination of dominant noise sources in diesel engines is an integral step in the creation of quiet engines, but is a process which can involve an extensive series of expensive, time-consuming fired and motored tests. The goal of this research is to determine dominant noise source characteristics of a diesel engine in the near and far-fields with data from fewer tests than is currently required. Pre-conditioning and use of numerically robust methods to solve a set of cross-spectral density equations results in accurate calculation of the transfer paths between the near- and far-field measurement points. Application of singular value decomposition to an input cross-spectral matrix determines the spectral characteristics of a set of independent virtual sources, that, when scaled and added, result in the input cross spectral matrix. Each virtual source power spectral density is a singular value resulting from the decomposition performed over a range of frequencies. The complex relationship between virtual and physical sources is estimated through determination of virtual source contributions to each input measurement power spectral density. The method is made more user-friendly through use of a percentage contribution color plotting technique, where different normalizations can be used to help determine the presence of sources and the strengths of their contributions. Convolution of input measurements with the estimated path impulse responses results in a set of far-field components, to which the same singular value contribution plotting technique can be applied, thus allowing dominant noise source characteristics in the far-field to also be examined. Application of the methods presented results in determination of the spectral characteristics of dominant noise sources both in the near- and far-fields from one fired test, which significantly reduces the need for extensive fired and motored testing. Finally, it is shown that the far-field noise time history of a physically altered engine can be simulated through modification of singular values and recalculation of transfer paths between input and output measurements of previously recorded data.

Simultaneous estimation of plasma parameters from spectroscopic data of neutral helium using least square fitting of CR-model

NASA Astrophysics Data System (ADS)

Jain, Jalaj; Prakash, Ram; Vyas, Gheesa Lal; Pal, Udit Narayan; Chowdhuri, Malay Bikas; Manchanda, Ranjana; Halder, Nilanjan; Choyal, Yaduvendra

2015-12-01

In the present work an effort has been made to estimate the plasma parameters simultaneously like—electron density, electron temperature, ground state atom density, ground state ion density and metastable state density from the observed visible spectra of penning plasma discharge (PPD) source using least square fitting. The analysis is performed for the prominently observed neutral helium lines. The atomic data and analysis structure (ADAS) database is used to provide the required collisional-radiative (CR) photon emissivity coefficients (PECs) values under the optical thin plasma condition in the analysis. With this condition the estimated plasma temperature from the PPD is found rather high. It is seen that the inclusion of opacity in the observed spectral lines through PECs and addition of diffusion of neutrals and metastable state species in the CR-model code analysis improves the electron temperature estimation in the simultaneous measurement.

Vortex dynamics in superconducting transition edge sensors

NASA Astrophysics Data System (ADS)

Ezaki, S.; Maehata, K.; Iyomoto, N.; Asano, T.; Shinozaki, B.

2018-02-01

The temperature dependence of the electrical resistance (R-T) and the current-voltage (I-V) characteristics has been measured and analyzed in a 40 nm thick Ti thin film, which is used as a transition edge sensor (TES). The analyses of the I-V characteristics with the vortex-antivortex pair dissociation model indicate the possible existence of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional superconducting Ti thin films. We investigated the noise due to the vortices' flow in TESs. The values of the current noise spectral density in the TESs were estimated by employing the vortex dynamics caused by the BKT transition in the Ti thin films. The estimated values of the current noise spectral density induced by the vortices' flow were in respectable agreement with the values of excess noise experimentally observed in the TESs with Ti/Au bilayer.

Internal Characteristics of Phobos and Deimos from Spectral Properties and Density: Relationship to Landforms and Comparison with Asteroids

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.

Setting up a proper power spectral density (PSD) and autocorrelation analysis for material and process characterization

NASA Astrophysics Data System (ADS)

Rutigliani, Vito; Lorusso, Gian Francesco; De Simone, Danilo; Lazzarino, Frederic; Rispens, Gijsbert; Papavieros, George; Gogolides, Evangelos; Constantoudis, Vassilios; Mack, Chris A.

2018-03-01

Power spectral density (PSD) analysis is playing more and more a critical role in the understanding of line-edge roughness (LER) and linewidth roughness (LWR) in a variety of applications across the industry. It is an essential step to get an unbiased LWR estimate, as well as an extremely useful tool for process and material characterization. However, PSD estimate can be affected by both random to systematic artifacts caused by image acquisition and measurement settings, which could irremediably alter its information content. In this paper, we report on the impact of various setting parameters (smoothing image processing filters, pixel size, and SEM noise levels) on the PSD estimate. We discuss also the use of PSD analysis tool in a variety of cases. Looking beyond the basic roughness estimate, we use PSD and autocorrelation analysis to characterize resist blur[1], as well as low and high frequency roughness contents and we apply this technique to guide the EUV material stack selection. Our results clearly indicate that, if properly used, PSD methodology is a very sensitive tool to investigate material and process variations

Resolution Measurement from a Single Reconstructed Cryo-EM Density Map with Multiscale Spectral Analysis.

PubMed

Yang, Yu-Jiao; Wang, Shuai; Zhang, Biao; Shen, Hong-Bin

2018-06-25

As a relatively new technology to solve the three-dimensional (3D) structure of a protein or protein complex, single-particle reconstruction (SPR) of cryogenic electron microscopy (cryo-EM) images shows much superiority and is in a rapidly developing stage. Resolution measurement in SPR, which evaluates the quality of a reconstructed 3D density map, plays a critical role in promoting methodology development of SPR and structural biology. Because there is no benchmark map in the generation of a new structure, how to realize the resolution estimation of a new map is still an open problem. Existing approaches try to generate a hypothetical benchmark map by reconstructing two 3D models from two halves of the original 2D images for cross-reference, which may result in a premature estimation with a half-data model. In this paper, we report a new self-reference-based resolution estimation protocol, called SRes, that requires only a single reconstructed 3D map. The core idea of SRes is to perform a multiscale spectral analysis (MSSA) on the map through multiple size-variable masks segmenting the map. The MSSA-derived multiscale spectral signal-to-noise ratios (mSSNRs) reveal that their corresponding estimated resolutions will show a cliff jump phenomenon, indicating a significant change in the SSNR properties. The critical point on the cliff borderline is demonstrated to be the right estimator for the resolution of the map.

Three-dimensional dominant frequency mapping using autoregressive spectral analysis of atrial electrograms of patients in persistent atrial fibrillation.

PubMed

Salinet, João L; Masca, Nicholas; Stafford, Peter J; Ng, G André; Schlindwein, Fernando S

2016-03-08

Areas with high frequency activity within the atrium are thought to be 'drivers' of the rhythm in patients with atrial fibrillation (AF) and ablation of these areas seems to be an effective therapy in eliminating DF gradient and restoring sinus rhythm. Clinical groups have applied the traditional FFT-based approach to generate the three-dimensional dominant frequency (3D DF) maps during electrophysiology (EP) procedures but literature is restricted on using alternative spectral estimation techniques that can have a better frequency resolution that FFT-based spectral estimation. Autoregressive (AR) model-based spectral estimation techniques, with emphasis on selection of appropriate sampling rate and AR model order, were implemented to generate high-density 3D DF maps of atrial electrograms (AEGs) in persistent atrial fibrillation (persAF). For each patient, 2048 simultaneous AEGs were recorded for 20.478 s-long segments in the left atrium (LA) and exported for analysis, together with their anatomical locations. After the DFs were identified using AR-based spectral estimation, they were colour coded to produce sequential 3D DF maps. These maps were systematically compared with maps found using the Fourier-based approach. 3D DF maps can be obtained using AR-based spectral estimation after AEGs downsampling (DS) and the resulting maps are very similar to those obtained using FFT-based spectral estimation (mean 90.23 %). There were no significant differences between AR techniques (p = 0.62). The processing time for AR-based approach was considerably shorter (from 5.44 to 5.05 s) when lower sampling frequencies and model order values were used. Higher levels of DS presented higher rates of DF agreement (sampling frequency of 37.5 Hz). We have demonstrated the feasibility of using AR spectral estimation methods for producing 3D DF maps and characterised their differences to the maps produced using the FFT technique, offering an alternative approach for 3D DF computation in human persAF studies.

Fine Structures of Solar Radio Type III Bursts and Their Possible Relationship with Coronal Density Turbulence

NASA Astrophysics Data System (ADS)

Chen, Xingyao; Kontar, Eduard P.; Yu, Sijie; Yan, Yihua; Huang, Jing; Tan, Baolin

2018-03-01

Solar radio type III bursts are believed to be the most sensitive signatures of near-relativistic electron beam propagation in the corona. A solar radio type IIIb-III pair burst with fine frequency structures, observed by the Low Frequency Array (LOFAR) with high temporal (∼10 ms) and spectral (12.5 kHz) resolutions at 30–80 MHz, is presented. The observations show that the type III burst consists of many striae, which have a frequency scale of about 0.1 MHz in both the fundamental (plasma) and the harmonic (double plasma) emission. We investigate the effects of background density fluctuations based on the observation of striae structure to estimate the density perturbation in the solar corona. It is found that the spectral index of the density fluctuation spectrum is about ‑1.7, and the characteristic spatial scale of the density perturbation is around 700 km. This spectral index is very close to a Kolmogorov turbulence spectral index of ‑5/3, consistent with a turbulent cascade. This fact indicates that the coronal turbulence may play the important role of modulating the time structures of solar radio type III bursts, and the fine structure of radio type III bursts could provide a useful and unique tool to diagnose the turbulence in the solar corona.

Peripheral transverse densities of the baryon octet from chiral effective field theory and dispersion analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alarcón, J. M.; Hiller Blin, A. N.; Vicente Vacas, M. J.

2017-05-08

The baryon electromagnetic form factors are expressed in terms of two-dimensional densities describing the distribution of charge and magnetization in transverse space at fixed light-front time. In this paper, we calculate the transverse densities of the spin-1/2 flavor-octet baryons at peripheral distances b=O(Mmore » $$-1\\atop{π}$$) using methods of relativistic chiral effective field theory (χ EFT) and dispersion analysis. The densities are represented as dispersive integrals over the imaginary parts of the form factors in the timelike region (spectral functions). The isovector spectral functions on the two-pion cut t > 4 M$$2\\atop{π}$$ are calculated using relativistic χEFT including octet and decuplet baryons. The χEFT calculations are extended into the ρ meson mass region using an N/D method that incorporates the pion electromagnetic form factor data. The isoscalar spectral functions are modeled by vector meson poles. We compute the peripheral charge and magnetization densities in the octet baryon states, estimate the uncertainties, and determine the quark flavor decomposition. Finally, the approach can be extended to baryon form factors of other operators and the moments of generalized parton distributions.« less

Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

NASA Astrophysics Data System (ADS)

Wurl, D.; Grainger, R. G.; McDonald, A. J.; Deshler, T.

2010-05-01

Stratospheric aerosol particles under non-volcanic conditions are typically smaller than 0.1 μm. Due to fundamental limitations of the scattering theory in the Rayleigh limit, these tiny particles are hard to measure by satellite instruments. As a consequence, current estimates of global aerosol properties retrieved from spectral aerosol extinction measurements tend to be strongly biased. Aerosol surface area densities, for instance, are observed to be about 40% smaller than those derived from correlative in situ measurements (Deshler et al., 2003). An accurate knowledge of the global distribution of aerosol properties is, however, essential to better understand and quantify the role they play in atmospheric chemistry, dynamics, radiation and climate. To address this need a new retrieval algorithm was developed, which employs a nonlinear Optimal Estimation (OE) method to iteratively solve for the monomodal size distribution parameters which are statistically most consistent with both the satellite-measured multi-wavelength aerosol extinction data and a priori information. By thus combining spectral extinction measurements (at visible to near infrared wavelengths) with prior knowledge of aerosol properties at background level, even the smallest particles are taken into account which are practically invisible to optical remote sensing instruments. The performance of the OE retrieval algorithm was assessed based on synthetic spectral extinction data generated from both monomodal and small-mode-dominant bimodal sulphuric acid aerosol size distributions. For monomodal background aerosol, the new algorithm was shown to fairly accurately retrieve the particle sizes and associated integrated properties (surface area and volume densities), even in the presence of large extinction uncertainty. The associated retrieved uncertainties are a good estimate of the true errors. In the case of bimodal background aerosol, where the retrieved (monomodal) size distributions naturally differ from the correct bimodal values, the associated surface area (A) and volume densities (V) are, nevertheless, fairly accurately retrieved, except at values larger than 1.0 μm2 cm-3 (A) and 0.05 μm3 cm-3 (V), where they tend to underestimate the true bimodal values. Due to the limited information content in the SAGE II spectral extinction measurements this kind of forward model error cannot be avoided here. Nevertheless, the retrieved uncertainties are a good estimate of the true errors in the retrieved integrated properties, except where the surface area density exceeds the 1.0 μm2 cm-3 threshold. When applied to near-global SAGE II satellite extinction measured in 1999 the retrieved OE surface area and volume densities are observed to be larger by, respectively, 20-50% and 10-40% compared to those estimates obtained by the SAGE~II operational retrieval algorithm. An examination of the OE algorithm biases with in situ data indicates that the new OE aerosol property estimates tend to be more realistic than previous estimates obtained from remotely sensed data through other retrieval techniques. Based on the results of this study we therefore suggest that the new Optimal Estimation retrieval algorithm is able to contribute to an advancement in aerosol research by considerably improving current estimates of aerosol properties in the lower stratosphere under low aerosol loading conditions.

Ocean wavenumber estimation from wave-resolving time series imagery

USGS Publications Warehouse

Plant, N.G.; Holland, K.T.; Haller, M.C.

2008-01-01

We review several approaches that have been used to estimate ocean surface gravity wavenumbers from wave-resolving remotely sensed image sequences. Two fundamentally different approaches that utilize these data exist. A power spectral density approach identifies wavenumbers where image intensity variance is maximized. Alternatively, a cross-spectral correlation approach identifies wavenumbers where intensity coherence is maximized. We develop a solution to the latter approach based on a tomographic analysis that utilizes a nonlinear inverse method. The solution is tolerant to noise and other forms of sampling deficiency and can be applied to arbitrary sampling patterns, as well as to full-frame imagery. The solution includes error predictions that can be used for data retrieval quality control and for evaluating sample designs. A quantitative analysis of the intrinsic resolution of the method indicates that the cross-spectral correlation fitting improves resolution by a factor of about ten times as compared to the power spectral density fitting approach. The resolution analysis also provides a rule of thumb for nearshore bathymetry retrievals-short-scale cross-shore patterns may be resolved if they are about ten times longer than the average water depth over the pattern. This guidance can be applied to sample design to constrain both the sensor array (image resolution) and the analysis array (tomographic resolution). ?? 2008 IEEE.

Bearing failure detection of micro wind turbine via power spectral density analysis for stator current signals spectrum

NASA Astrophysics Data System (ADS)

Mahmood, Faleh H.; Kadhim, Hussein T.; Resen, Ali K.; Shaban, Auday H.

2018-05-01

The failure such as air gap weirdness, rubbing, and scrapping between stator and rotor generator arise unavoidably and may cause extremely terrible results for a wind turbine. Therefore, we should pay more attention to detect and identify its cause-bearing failure in wind turbine to improve the operational reliability. The current paper tends to use of power spectral density analysis method of detecting internal race and external race bearing failure in micro wind turbine by estimation stator current signal of the generator. The failure detector method shows that it is well suited and effective for bearing failure detection.

Correlation techniques and measurements of wave-height statistics

NASA Technical Reports Server (NTRS)

Guthart, H.; Taylor, W. C.; Graf, K. A.; Douglas, D. G.

1972-01-01

Statistical measurements of wave height fluctuations have been made in a wind wave tank. The power spectral density function of temporal wave height fluctuations evidenced second-harmonic components and an f to the minus 5th power law decay beyond the second harmonic. The observations of second harmonic effects agreed very well with a theoretical prediction. From the wave statistics, surface drift currents were inferred and compared to experimental measurements with satisfactory agreement. Measurements were made of the two dimensional correlation coefficient at 15 deg increments in angle with respect to the wind vector. An estimate of the two-dimensional spatial power spectral density function was also made.

Hyperfine Sublevel Correlation (HYSCORE) Spectra for Paramagnetic Centers with Nuclear Spin I = 1 Having Isotropic Hyperfine Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maryasov, Alexander G.; Bowman, Michael K.

2004-07-08

It is shown that HYSCORE spectra of paramagnetic centers having nuclei of spin I=1 with isotropic hfi and arbitrary NQI consist of ridges having zero width. A parametric presentation of these ridges is found which shows the range of possible frequencies in the HYSCORE spectrum and aids in spectral assignments and rapid estimation of spin Hamiltonian parameters. An alternative approach for the spectral density calculation is presented that is based on spectral decomposition of the Hamiltonian. Only the eigenvalues of the Hamiltonian are needed in this approach. An atlas of HYSCORE spectra is given in the Supporting Information. This approachmore » is applied to the estimation of the spin Hamiltonian parameters of the oxovanadium-EDTA complex.« less

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.

Fluorescent Fe K Emission from High Density Accretion Disks

NASA Astrophysics Data System (ADS)

Bautista, Manuel; Mendoza, Claudio; Garcia, Javier; Kallman, Timothy R.; Palmeri, Patrick; Deprince, Jerome; Quinet, Pascal

2018-06-01

Iron K-shell lines emitted by gas closely orbiting black holes are observed to be grossly broadened and skewed by Doppler effects and gravitational redshift. Accordingly, models for line profiles are widely used to measure the spin (i.e., the angular momentum) of astrophysical black holes. The accuracy of these spin estimates is called into question because fitting the data requires very high iron abundances, several times the solar value. Meanwhile, no plausible physical explanation has been proffered for why these black hole systems should be so iron rich. The most likely explanation for the super-solar iron abundances is a deficiency in the models, and the leading candidate cause is that current models are inapplicable at densities above 1018 cm-3. We study the effects of high densities on the atomic parameters and on the spectral models for iron ions. At high densities, Debye plasma can affect the effective atomic potential of the ions, leading to observable changes in energy levels and atomic rates with respect to the low density case. High densities also have the effec of lowering energy the atomic continuum and reducing the recombination rate coefficients. On the spectral modeling side, high densities drive level populations toward a Boltzman distribution and very large numbers of excited atomic levels, typically accounted for in theoretical spectral models, may contribute to the K-shell spectrum.

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.

Performance limitations of a white light extrinsic Fabry-Perot interferometric displacement sensor

NASA Astrophysics Data System (ADS)

Moro, Erik A.; Todd, Michael D.; Puckett, Anthony D.

2012-06-01

Non-contacting interferometric fiber optic sensors offer a minimally invasive, high-accuracy means of measuring a structure's kinematic response to loading. The performance of interferometric sensors is often dictated by the technique employed for demodulating the kinematic measurand of interest from phase in the observed optical signal. In this paper a white-light extrinsic Fabry-Perot interferometer is implemented, offering robust displacement sensing performance. Displacement data is extracted from an estimate of the power spectral density, calculated from the interferometer's received optical power measured as a function of optical transmission frequency, and the sensor's performance is dictated by the details surrounding the implementation of this power spectral density estimation. One advantage of this particular type of interferometric sensor is that many of its control parameters (e.g., frequency range, frequency sampling density, sampling rate, etc.) may be chosen to so that the sensor satisfies application-specific performance needs in metrics such as bandwidth, axial displacement range, displacement resolution, and accuracy. A suite of user-controlled input values is investigated for estimating the spectrum of power versus wavelength data, and the relationships between performance metrics and input parameters are described in an effort to characterize the sensor's operational performance limitations. This work has been approved by Los Alamos National Laboratory for unlimited public release (LA-UR 12-01512).

Estimation of beam material random field properties via sensitivity-based model updating using experimental frequency response functions

NASA Astrophysics Data System (ADS)

Machado, M. R.; Adhikari, S.; Dos Santos, J. M. C.; Arruda, J. R. F.

2018-03-01

Structural parameter estimation is affected not only by measurement noise but also by unknown uncertainties which are present in the system. Deterministic structural model updating methods minimise the difference between experimentally measured data and computational prediction. Sensitivity-based methods are very efficient in solving structural model updating problems. Material and geometrical parameters of the structure such as Poisson's ratio, Young's modulus, mass density, modal damping, etc. are usually considered deterministic and homogeneous. In this paper, the distributed and non-homogeneous characteristics of these parameters are considered in the model updating. The parameters are taken as spatially correlated random fields and are expanded in a spectral Karhunen-Loève (KL) decomposition. Using the KL expansion, the spectral dynamic stiffness matrix of the beam is expanded as a series in terms of discretized parameters, which can be estimated using sensitivity-based model updating techniques. Numerical and experimental tests involving a beam with distributed bending rigidity and mass density are used to verify the proposed method. This extension of standard model updating procedures can enhance the dynamic description of structural dynamic models.

Gauging Metallicity of Diffuse Gas under an Uncertain Ionizing Radiation Field

NASA Astrophysics Data System (ADS)

Chen, Hsiao-Wen; Johnson, Sean D.; Zahedy, Fakhri S.; Rauch, Michael; Mulchaey, John S.

2017-06-01

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically enriched outflows or in more chemically pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities. Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.

Gauging Metallicity of Diffuse Gas under an Uncertain Ionizing Radiation Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Hsiao-Wen; Zahedy, Fakhri S.; Johnson, Sean D.

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically enriched outflows or in more chemically pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition tomore » gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities. Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.« less

Propane spectral resolution enhancement by the maximum entropy method

NASA Technical Reports Server (NTRS)

Bonavito, N. L.; Stewart, K. P.; Hurley, E. J.; Yeh, K. C.; Inguva, R.

1990-01-01

The Burg algorithm for maximum entropy power spectral density estimation is applied to a time series of data obtained from a Michelson interferometer and compared with a standard FFT estimate for resolution capability. The propane transmittance spectrum was estimated by use of the FFT with a 2 to the 18th data sample interferogram, giving a maximum unapodized resolution of 0.06/cm. This estimate was then interpolated by zero filling an additional 2 to the 18th points, and the final resolution was taken to be 0.06/cm. Comparison of the maximum entropy method (MEM) estimate with the FFT was made over a 45/cm region of the spectrum for several increasing record lengths of interferogram data beginning at 2 to the 10th. It is found that over this region the MEM estimate with 2 to the 16th data samples is in close agreement with the FFT estimate using 2 to the 18th samples.

Comparison of Fatigue Life Estimation Using Equivalent Linearization and Time Domain Simulation Methods

NASA Technical Reports Server (NTRS)

Mei, Chuh; Dhainaut, Jean-Michel

2000-01-01

The Monte Carlo simulation method in conjunction with the finite element large deflection modal formulation are used to estimate fatigue life of aircraft panels subjected to stationary Gaussian band-limited white-noise excitations. Ten loading cases varying from 106 dB to 160 dB OASPL with bandwidth 1024 Hz are considered. For each load case, response statistics are obtained from an ensemble of 10 response time histories. The finite element nonlinear modal procedure yields time histories, probability density functions (PDF), power spectral densities and higher statistical moments of the maximum deflection and stress/strain. The method of moments of PSD with Dirlik's approach is employed to estimate the panel fatigue life.

Estimations of Mo X-pinch plasma parameters on QiangGuang-1 facility by L-shell spectral analyses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Jian; Qiu, Aici; State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024

2013-08-15

Plasma parameters of molybdenum (Mo) X-pinches on the 1-MA QiangGuang-1 facility were estimated by L-shell spectral analysis. X-ray radiation from X-pinches had a pulsed width of 1 ns, and its spectra in 2–3 keV were measured with a time-integrated X-ray spectrometer. Relative intensities of spectral features were derived by correcting for the spectral sensitivity of the spectrometer. With an open source, atomic code FAC (flexible atomic code), ion structures, and various atomic radiative-collisional rates for O-, F-, Ne-, Na-, Mg-, and Al-like ionization stages were calculated, and synthetic spectra were constructed at given plasma parameters. By fitting the measured spectramore » with the modeled, Mo X-pinch plasmas on the QiangGuang-1 facility had an electron density of about 10{sup 21} cm{sup −3} and the electron temperature of about 1.2 keV.« less

Different techniques of multispectral data analysis for vegetation fraction retrieval

NASA Astrophysics Data System (ADS)

Kancheva, Rumiana; Georgiev, Georgi

2012-07-01

Vegetation monitoring is one of the most important applications of remote sensing technologies. In respect to farmlands, the assessment of crop condition constitutes the basis of growth, development, and yield processes monitoring. Plant condition is defined by a set of biometric variables, such as density, height, biomass amount, leaf area index, and etc. The canopy cover fraction is closely related to these variables, and is state-indicative of the growth process. At the same time it is a defining factor of the soil-vegetation system spectral signatures. That is why spectral mixtures decomposition is a primary objective in remotely sensed data processing and interpretation, specifically in agricultural applications. The actual usefulness of the applied methods depends on their prediction reliability. The goal of this paper is to present and compare different techniques for quantitative endmember extraction from soil-crop patterns reflectance. These techniques include: linear spectral unmixing, two-dimensional spectra analysis, spectral ratio analysis (vegetation indices), spectral derivative analysis (red edge position), colorimetric analysis (tristimulus values sum, chromaticity coordinates and dominant wavelength). The objective is to reveal their potential, accuracy and robustness for plant fraction estimation from multispectral data. Regression relationships have been established between crop canopy cover and various spectral estimators.

Aortic endothelium detection using spectral estimation optical coherence tomography (Conference Presentation)

NASA Astrophysics Data System (ADS)

Liu, Xinyu; Chen, Si; Luo, Yuemei; Bo, En; Wang, Nanshuo; Yu, Xiaojun; Liu, Linbo

2016-02-01

The evaluation of the endothelium coverage on the vessel wall is most wanted by cardiologists. Arterial endothelial cells play a crucial role in keeping low-density lipoprotein and leukocytes from entering into the intima. The damage of endothelial cells is considered as the first step of atherosclerosis development and the presence of endothelial cells is an indicator of arterial healing after stent implantation. Intravascular OCT (IVOCT) is the highest-resolution coronary imaging modality, but it is still limited by an axial resolution of 10-15 µm. This limitation in axial resolution hinders our ability to visualize cellular level details associated with coronary atherosclerosis. Spectral estimation optical coherence tomography (SE-OCT) uses modern spectral estimation techniques and may help reveal the microstructures underlying the resolution limit. In this presentation, we conduct an ex vivo study using SE-OCT to image the endothelium cells on the fresh swine aorta. We find that in OCT images with an axial resolution of 10 µm, we may gain the visibility of individual endothelium cells by applying the autoregressive spectral estimation techniques to enhance the axial resolution. We believe the SE-OCT can provide a potential to evaluate the coverage of endothelium cells using current IVOCT with a 10-µm axial resolution.

Spectral Analysis of Vector Magnetic Field Profiles

NASA Technical Reports Server (NTRS)

Parker, Robert L.; OBrien, Michael S.

1997-01-01

We investigate the power spectra and cross spectra derived from the three components of the vector magnetic field measured on a straight horizontal path above a statistically stationary source. All of these spectra, which can be estimated from the recorded time series, are related to a single two-dimensional power spectral density via integrals that run in the across-track direction in the wavenumber domain. Thus the measured spectra must obey a number of strong constraints: for example, the sum of the two power spectral densities of the two horizontal field components equals the power spectral density of the vertical component at every wavenumber and the phase spectrum between the vertical and along-track components is always pi/2. These constraints provide powerful checks on the quality of the measured data; if they are violated, measurement or environmental noise should be suspected. The noise due to errors of orientation has a clear characteristic; both the power and phase spectra of the components differ from those of crustal signals, which makes orientation noise easy to detect and to quantify. The spectra of the crustal signals can be inverted to obtain information about the cross-track structure of the field. We illustrate these ideas using a high-altitude Project Magnet profile flown in the southeastern Pacific Ocean.

Rangeland biomass estimation demonstration. [Texas Experimenta Ranch

NASA Technical Reports Server (NTRS)

Newton, R. W. (Principal Investigator); Boyd, W. E.; Clark, B. V.

1982-01-01

Because of their sensitivity to chlorophyll density, green leaf density, and leaf water density, two hand-held radiometers which have sensor bands coinciding with thematic mapper bands 3, 4, and 5 were used to calibrate green biomass to LANDSAT spectral ratios as a step towards using portable radiometers to speed up ground data acquisition. Two field reflectance panels monitored incoming radiation concurrently with sampling. Software routines were developed and used to extract data from uncorrected tapes of MSS data provided in NASA LANDSAT universal format. A LANDSAT biomass calibration curve estimated the range biomass over a four scene area and displayed this information spatially as a product in a format of use to ranchers. The regional biomass contour map is discussed.

Eastern US crustal thickness estimates from spectral analysis and inversion of onshore Bouguer gravity anaomalies

NASA Astrophysics Data System (ADS)

Dybus, W.; Benoit, M. H.; Ebinger, C. J.

2011-12-01

The crustal thickness beneath much of the eastern half of the US is largely unconstrained. Though there have been several controlled source seismic surveys of the region, many of these studies suffer from rays that turn in the crust above the Moho, resulting in somewhat ambiguous crustal thickness values. Furthermore, the broadband seismic station coverage east of the Mississippi has been limited, and most of the region remains largely understudied. In this study, we estimated the depth to the Moho using both spectral analysis and inversion of Bouguer gravity anomalies. We systematically estimated depths to lithospheric density contrasts from radial power spectra of Bouguer gravity within 100 km X 100 km windows eastward from the Mississippi River to the Atlantic Coast, and northward from North Carolina to Maine. The slopes and slope breaks in the radial power spectra were computed using an automated algorithm. The slope values for each window were visually inspected and then used to estimate the depth to the Moho and other lithospheric density contrasts beneath each windowed region. Additionally, we performed a standard Oldenburg-Parker inversion for lithospheric density contrasts using various reference depths and density contrasts that are realistic for the different physiographic provinces in the Eastern US. Our preliminary results suggest that the gravity-derived Moho depths are similar to those found using seismic data, and that the crust is relatively thinner (~28-33 km) than expected in beneath the Piedmont region (~35-40 km). Given the relative paucity of seismic data in the eastern US, analysis of onshore gravity data is a valuable tool for interpolating between seismic stations.

Improved canopy reflectance modeling and scene inference through improved understanding of scene pattern

NASA Technical Reports Server (NTRS)

Franklin, Janet; Simonett, David

1988-01-01

The Li-Strahler reflectance model, driven by LANDSAT Thematic Mapper (TM) data, provided regional estimates of tree size and density within 20 percent of sampled values in two bioclimatic zones in West Africa. This model exploits tree geometry in an inversion technique to predict average tree size and density from reflectance data using a few simple parameters measured in the field (spatial pattern, shape, and size distribution of trees) and in the imagery (spectral signatures of scene components). Trees are treated as simply shaped objects, and multispectral reflectance of a pixel is assumed to be related only to the proportions of tree crown, shadow, and understory in the pixel. These, in turn, are a direct function of the number and size of trees, the solar illumination angle, and the spectral signatures of crown, shadow and understory. Given the variance in reflectance from pixel to pixel within a homogeneous area of woodland, caused by the variation in the number and size of trees, the model can be inverted to give estimates of average tree size and density. Because the inversion is sensitive to correct determination of component signatures, predictions are not accurate for small areas.

Arbitrary-order Hilbert Spectral Analysis and Intermittency in Solar Wind Density Fluctuations

NASA Astrophysics Data System (ADS)

Carbone, Francesco; Sorriso-Valvo, Luca; Alberti, Tommaso; Lepreti, Fabio; Chen, Christopher H. K.; Němeček, Zdenek; Šafránková, Jana

2018-05-01

The properties of inertial- and kinetic-range solar wind turbulence have been investigated with the arbitrary-order Hilbert spectral analysis method, applied to high-resolution density measurements. Due to the small sample size and to the presence of strong nonstationary behavior and large-scale structures, the classical analysis in terms of structure functions may prove to be unsuccessful in detecting the power-law behavior in the inertial range, and may underestimate the scaling exponents. However, the Hilbert spectral method provides an optimal estimation of the scaling exponents, which have been found to be close to those for velocity fluctuations in fully developed hydrodynamic turbulence. At smaller scales, below the proton gyroscale, the system loses its intermittent multiscaling properties and converges to a monofractal process. The resulting scaling exponents, obtained at small scales, are in good agreement with those of classical fractional Brownian motion, indicating a long-term memory in the process, and the absence of correlations around the spectral-break scale. These results provide important constraints on models of kinetic-range turbulence in the solar wind.

Field dynamics inference via spectral density estimation

NASA Astrophysics Data System (ADS)

Frank, Philipp; Steininger, Theo; Enßlin, Torsten A.

2017-11-01

Stochastic differential equations are of utmost importance in various scientific and industrial areas. They are the natural description of dynamical processes whose precise equations of motion are either not known or too expensive to solve, e.g., when modeling Brownian motion. In some cases, the equations governing the dynamics of a physical system on macroscopic scales occur to be unknown since they typically cannot be deduced from general principles. In this work, we describe how the underlying laws of a stochastic process can be approximated by the spectral density of the corresponding process. Furthermore, we show how the density can be inferred from possibly very noisy and incomplete measurements of the dynamical field. Generally, inverse problems like these can be tackled with the help of Information Field Theory. For now, we restrict to linear and autonomous processes. To demonstrate its applicability, we employ our reconstruction algorithm on a time-series and spatiotemporal processes.

Field dynamics inference via spectral density estimation.

PubMed

Frank, Philipp; Steininger, Theo; Enßlin, Torsten A

2017-11-01

Stochastic differential equations are of utmost importance in various scientific and industrial areas. They are the natural description of dynamical processes whose precise equations of motion are either not known or too expensive to solve, e.g., when modeling Brownian motion. In some cases, the equations governing the dynamics of a physical system on macroscopic scales occur to be unknown since they typically cannot be deduced from general principles. In this work, we describe how the underlying laws of a stochastic process can be approximated by the spectral density of the corresponding process. Furthermore, we show how the density can be inferred from possibly very noisy and incomplete measurements of the dynamical field. Generally, inverse problems like these can be tackled with the help of Information Field Theory. For now, we restrict to linear and autonomous processes. To demonstrate its applicability, we employ our reconstruction algorithm on a time-series and spatiotemporal processes.

A new approach for the calculation of response spectral density of a linear stationary random multidegree of freedom system

NASA Astrophysics Data System (ADS)

Sharan, A. M.; Sankar, S.; Sankar, T. S.

1982-08-01

A new approach for the calculation of response spectral density for a linear stationary random multidegree of freedom system is presented. The method is based on modifying the stochastic dynamic equations of the system by using a set of auxiliary variables. The response spectral density matrix obtained by using this new approach contains the spectral densities and the cross-spectral densities of the system generalized displacements and velocities. The new method requires significantly less computation time as compared to the conventional method for calculating response spectral densities. Two numerical examples are presented to compare quantitatively the computation time.

Characterizing Complexity of Containerized Cargo X-ray Images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Guangxing; Martz, Harry; Glenn, Steven

X-ray imaging can be used to inspect cargos imported into the United States. In order to better understand the performance of X-ray inspection systems, the X-ray characteristics (density, complexity) of cargo need to be quantified. In this project, an image complexity measure called integrated power spectral density (IPSD) was studied using both DNDO engineered cargos and stream-of-commerce (SOC) cargos. A joint distribution of cargo density and complexity was obtained. A support vector machine was used to classify the SOC cargos into four categories to estimate the relative fractions.

Coded DS-CDMA Systems with Iterative Channel Estimation and no Pilot Symbols

DTIC Science & Technology

2010-08-01

ar X iv :1 00 8. 31 96 v1 [ cs .I T ] 1 9 A ug 2 01 0 1 Coded DS - CDMA Systems with Iterative Channel Estimation and no Pilot Symbols Don...sequence code-division multiple-access ( DS - CDMA ) systems with quadriphase-shift keying in which channel estimation, coherent demodulation, and decoding...amplitude, phase, and the interference power spectral density (PSD) due to the combined interference and thermal noise is proposed for DS - CDMA systems

A Fourier approach to cloud motion estimation

NASA Technical Reports Server (NTRS)

Arking, A.; Lo, R. C.; Rosenfield, A.

1977-01-01

A Fourier technique is described for estimating cloud motion from pairs of pictures using the phase of the cross spectral density. The method allows motion estimates to be made for individual spatial frequencies, which are related to cloud pattern dimensions. Results obtained are presented and compared with the results of a Fourier domain cross correlation scheme. Using both artificial and real cloud data show that the technique is relatively sensitive to the presence of mixtures of motions, changes in cloud shape, and edge effects.

Study of the effect of low-power pulse laser on arc plasma and magnesium alloy target in hybrid welding by spectral diagnosis technique

NASA Astrophysics Data System (ADS)

Liu, Liming; Hao, Xinfeng

2008-10-01

In order to study the effect of laser pulses on arc plasma and target metal in the hybrid welding process, the spectra of the plasmas in the welding process of magnesium alloys are analysed in this paper. The acquisition system of plasma spectra is set up and the spectral lines of welding plasma are acquired. Compared with tungsten-inert gas (TIG) welding, the intensities of the spectral lines of magnesium increase sharply while those of Ar decrease for strong evaporation and ionization of magnesium alloys in low-power laser/arc hybrid welding. The electron temperature and density are estimated by the Boltzmann plot method and the Stark broadening effect. The result shows that the electron temperature of arc plasma in the hybrid welding process is much lower than that in TIG welding, especially in the laser beam-affected zone. In contrast, the electron density of the plasma is enhanced. The influences of laser parameters on electron temperature are also studied. The changes in electron temperature and density indicate that the effect of laser pulse on the target metal is the dominant factor influencing the electron temperature and density in low-power laser/arc hybrid welding.

Statistical analysis of modal parameters of a suspension bridge based on Bayesian spectral density approach and SHM data

NASA Astrophysics Data System (ADS)

Li, Zhijun; Feng, Maria Q.; Luo, Longxi; Feng, Dongming; Xu, Xiuli

2018-01-01

Uncertainty of modal parameters estimation appear in structural health monitoring (SHM) practice of civil engineering to quite some significant extent due to environmental influences and modeling errors. Reasonable methodologies are needed for processing the uncertainty. Bayesian inference can provide a promising and feasible identification solution for the purpose of SHM. However, there are relatively few researches on the application of Bayesian spectral method in the modal identification using SHM data sets. To extract modal parameters from large data sets collected by SHM system, the Bayesian spectral density algorithm was applied to address the uncertainty of mode extraction from output-only response of a long-span suspension bridge. The posterior most possible values of modal parameters and their uncertainties were estimated through Bayesian inference. A long-term variation and statistical analysis was performed using the sensor data sets collected from the SHM system of the suspension bridge over a one-year period. The t location-scale distribution was shown to be a better candidate function for frequencies of lower modes. On the other hand, the burr distribution provided the best fitting to the higher modes which are sensitive to the temperature. In addition, wind-induced variation of modal parameters was also investigated. It was observed that both the damping ratios and modal forces increased during the period of typhoon excitations. Meanwhile, the modal damping ratios exhibit significant correlation with the spectral intensities of the corresponding modal forces.

Land use, forest density, soil mapping, erosion, drainage, salinity limitations

NASA Technical Reports Server (NTRS)

Yassoglou, N. J. (Principal Investigator)

1973-01-01

The author has identified the following significant results. The results of analyses show that it is possible to obtain information of practical significance as follows: (1) A quick and accurate estimate of the proper use of the valuable land can be made on the basis of temporal and spectral characteristics of the land features. (2) A rather accurate delineation of the major forest formations in the test areas was achieved on the basis of spatial and spectral characteristics of the studied areas. The forest stands were separated into two density classes; dense forest, and broken forest. On the basis of ERTS-1 data and the existing ground truth information a rather accurate mapping of the major vegetational forms of the mountain ranges can be made. (3) Major soil formations are mapable from ERTS-1 data: recent alluvial soils; soil on quarternary deposits; severely eroded soil and lithosol; and wet soils. (4) An estimation of cost benefits cannot be made accurately at this stage of the investigation. However, a rough estimate of the ratio of the cost for obtaining the same amount information from ERTS-1 data and from conventional operations would be approximately 1:6 to 1:10, in favor of the ERTS-1.

Spectral lines and characteristic of temporal variations in photoionized plasmas induced with laser-produced plasma extreme ultraviolet source

NASA Astrophysics Data System (ADS)

Saber, I.; Bartnik, A.; Wachulak, P.; Skrzeczanowski, W.; Jarocki, R.; Fiedorowicz, H.

2017-11-01

Spectral lines for Kr/Ne/H2 photoionized plasma in the ultraviolet and visible (UV/Vis) wavelength ranges have been created using a laser-produced plasma (LPP) EUV source. The source is based on a double-stream gas puff target irradiated with a commercial Nd:YAG laser. The laser pulses were focused onto a gas stream, injected into a vacuum chamber synchronously with the EUV pulses. Spectral lines from photoionization in neutral Kr/Ne/H2 and up to few charged states were observed. The intense emission lines were associated with the Kr transition lines. Experimental and theoretical investigations on intensity variations for some ionic lines are presented. A decrease in the intensity with the delay time between the laser pulse and the spectrum acquisition was revealed. Electron temperature and electron density in the photoionized plasma have been estimated from the characteristic emission lines. Temperature was obtained using Boltzmann plot method, assuming that the population density of atoms and ions are considered in a local thermodynamic equilibrium (LTE). Electron density was calculated from the Stark broadening profile. The temporal evaluation of the plasma and the way of optimizing the radiation intensity of LPP EUV sources is discussed.

MRI Proton Density Fat Fraction Is Robust Across the Biologically Plausible Range of Triglyceride Spectra in Adults With Nonalcoholic Steatohepatitis

PubMed Central

Hong, Cheng William; Mamidipalli, Adrija; Hooker, Jonathan C.; Hamilton, Gavin; Wolfson, Tanya; Chen, Dennis H.; Dehkordy, Soudabeh Fazeli; Middleton, Michael S.; Reeder, Scott B.; Loomba, Rohit; Sirlin, Claude B.

2017-01-01

Background Proton density fat fraction (PDFF) estimation requires spectral modeling of the hepatic triglyceride (TG) signal. Deviations in the TG spectrum may occur, leading to bias in PDFF quantification. Purpose To investigate the effects of varying six-peak TG spectral models on PDFF estimation bias. Study Type Retrospective secondary analysis of prospectively acquired clinical research data. Population Forty-four adults with biopsy-confirmed nonalcoholic steatohepatitis. Field Strength/Sequence Confounder-corrected chemical-shift-encoded 3T MRI (using a 2D multiecho gradient-recalled echo technique with magnitude reconstruction) and MR spectroscopy. Assessment In each patient, 61 pairs of colocalized MRI-PDFF and MRS-PDFF values were estimated: one pair used the standard six-peak spectral model, the other 60 were six-peak variants calculated by adjusting spectral model parameters over their biologically plausible ranges. MRI-PDFF values calculated using each variant model and the standard model were compared, and the agreement between MRI-PDFF and MRS-PDFF was assessed. Statistical Tests MRS-PDFF and MRI-PDFF were summarized descriptively. Bland–Altman (BA) analyses were performed between PDFF values calculated using each variant model and the standard model. Linear regressions were performed between BA biases and mean PDFF values for each variant model, and between MRI-PDFF and MRS-PDFF. Results Using the standard model, mean MRS-PDFF of the study population was 17.9±8.0% (range: 4.1–34.3%). The difference between the highest and lowest mean variant MRI-PDFF values was 1.5%. Relative to the standard model, the model with the greatest absolute BA bias overestimated PDFF by 1.2%. Bias increased with increasing PDFF (P < 0.0001 for 59 of the 60 variant models). MRI-PDFF and MRS-PDFF agreed closely for all variant models (R2=0.980, P < 0.0001). Data Conclusion Over a wide range of hepatic fat content, PDFF estimation is robust across the biologically plausible range of TG spectra. Although absolute estimation bias increased with higher PDFF, its magnitude was small and unlikely to be clinically meaningful. Level of Evidence 3 Technical Efficacy Stage 2 PMID:28851124

Spectral density method to Anderson-Holstein model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chebrolu, Narasimha Raju, E-mail: narasimharaju.phy@gmail.com; Chatterjee, Ashok

Two-parameter spectral density function of a magnetic impurity electron in a non-magnetic metal is calculated within the framework of the Anderson-Holstein model using the spectral density approximation method. The effect of electron-phonon interaction on the spectral function is investigated.

Quantitative contrast-enhanced spectral mammography based on photon-counting detectors: A feasibility study.

PubMed

Ding, Huanjun; Molloi, Sabee

2017-08-01

To investigate the feasibility of accurate quantification of iodine mass thickness in contrast-enhanced spectral mammography. A computer simulation model was developed to evaluate the performance of a photon-counting spectral mammography system in the application of contrast-enhanced spectral mammography. A figure-of-merit (FOM), which was defined as the decomposed iodine signal-to-noise ratio (SNR) with respect to the square root of the mean glandular dose (MGD), was chosen to optimize the imaging parameters, in terms of beam energy, splitting energy, and prefiltrations for breasts of various thicknesses and densities. Experimental phantom studies were also performed using a beam energy of 40 kVp and a splitting energy of 34 keV with 3 mm Al prefiltration. A two-step calibration method was investigated to quantify the iodine mass thickness, and was validated using phantoms composed of a mixture of glandular and adipose materials, for various breast thicknesses and densities. Finally, the traditional dual-energy log-weighted subtraction method was also studied as a comparison. The measured iodine signal from both methods was compared to the known value to characterize the quantification accuracy and precision. The optimal imaging parameters, which lead to the highest FOM, were found at a beam energy between 42 and 46 kVp with a splitting energy at 34 keV. The optimal tube voltage decreased as the breast thickness or the Al prefiltration increased. The proposed quantification method was able to measure iodine mass thickness on phantoms of various thicknesses and densities with high accuracy. The root-mean-square (RMS) error for cm-scale lesion phantoms was estimated to be 0.20 mg/cm 2 . The precision of the technique, characterized by the standard deviation of the measurements, was estimated to be 0.18 mg/cm 2 . The traditional weighted subtraction method also predicted a linear correlation between the measured signal and the known iodine mass thickness. However, the correlation slope and offset values were strongly dependent on the total breast thickness and density. The results of this study suggest that iodine mass thickness for cm-scale lesions can be accurately quantified with contrast-enhanced spectral mammography. The quantitative information can potentially improve the differential power for malignancy. © 2017 American Association of Physicists in Medicine.

Feasibility of estimating volumetric breast density from mammographic x-ray spectra using a cadmium telluride photon-counting detector.

PubMed

Ghammraoui, Bahaa; Badal, Andreu; Glick, Stephen J

2018-06-03

Mammographic density of glandular breast tissue has a masking effect that can reduce lesion detection accuracy and is also a strong risk factor for breast cancer. Therefore, accurate quantitative estimation of breast density is clinically important. In this study, we investigate experimentally the feasibility of quantifying volumetric breast density with spectral mammography using a CdTe-based photon-counting detector. To demonstrate proof-of-principle, this study was carried out using the single pixel Amptek XR-100T-CdTe detector. The total number of x rays recorded by the detector from a single pencil-beam projection through 50%/50% of adipose/glandular mass fraction-equivalent phantoms was measured. Material decomposition assuming two, four, and eight energy bins was then applied to characterize the inspected phantom into adipose and glandular using log-likelihood estimation, taking into account the polychromatic source, the detector response function, and the energy-dependent attenuation. Measurement tests were carried out for different doses, kVp settings, and different breast sizes. For dose of 1 mGy and above, the percent relative root mean square (RMS) errors of the estimated breast density was measured below 7% for all three phantom studies. It was also observed that some decrease in RMS errors was achieved using eight energy bins. For 3 and 4 cm thick phantoms, performance at 40 and 45 kVp showed similar performance. However, it was observed that 45 kVp showed better performance for a phantom thickness of 6 cm at low dose levels due to increased statistical variation at lower photon count levels with 40 kVp. The results of the current study suggest that photon-counting spectral mammography systems using CdTe detectors have the potential to be used for accurate quantification of volumetric breast density on a pixel-to-pixel basis, with an RMS error of less than 7%. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Amplitude of primeval fluctuations from cosmological mass density reconstructions

NASA Technical Reports Server (NTRS)

Seljak, Uros; Bertschinger, Edmund

1994-01-01

We use the POTENT reconstruction of the mass density field in the nearby universe to estimate the amplitude of the density fluctuation power spectrum for various cosmological models. We find that sigma(sub 8) Omega(sub m sup 0.6) = 1.3(sub -0.3 sup +0.4), almost independently of the power spectrum. This value agrees well with the Cosmic Background Explorer (COBE) normalization for the standard cold dark matter model, while alternative models predict an excessive amplitude compared with COBE. Flat, low Omega(sub m) models and tilted models with spectral index n less than 0.8 are particularly discordant.

Narrow Quasar Absorption Lines and the History of the Universe

NASA Astrophysics Data System (ADS)

Liebscher, Dierck-Ekkehard

In order to get an estimation of the parameters of the cosmological model the statistics of narrow absorption lines in quasar spectra is evaluated. To this end a phenomenological model of the evolution of the corresponding absorbers in density, size, number and dimension is presented and compared with the observed evolution in the spectral density of the lines and their column density seen in the equivalent width. In spite of the wide range of possible models, the Einstein-deSitter model is shown to be unlikely because of the implied fast evolution in mass.

Temporal variations of electron density and temperature in Kr/Ne/H2 photoionized plasma induced by nanosecond pulses from extreme ultraviolet source

NASA Astrophysics Data System (ADS)

Saber, I.; Bartnik, A.; Wachulak, P.; Skrzeczanowski, W.; Jarocki, R.; Fiedorowicz, H.

2017-06-01

Spectral investigations of low-temperature photoionized plasmas created in a Kr/Ne/H2 gas mixture were performed. The low-temperature plasmas were generated by gas mixture irradiation using extreme ultraviolet pulses from a laser-plasma source. Emission spectra in the ultraviolet/visible range from the photoionized plasmas contained lines that mainly corresponded to neutral atoms and singly charged ions. Temporal variations in the plasma electron temperature and electron density were studied using different characteristic emission lines at various delay times. Results, based on Kr II lines, showed that the electron temperature decreased from 1.7 to 0.9 eV. The electron densities were estimated using different spectral lines at each delay time. In general, except for the Hβ line, in which the electron density decreased from 3.78 × 1016 cm-3 at 200 ns to 5.77 × 1015 cm-3 at 2000 ns, most of the electron density values measured from the different lines were of the order of 1015 cm-3 and decreased slightly while maintaining the same order when the delay time increased. The time dependences of the measured and simulated intensities of a spectral line of interest were also investigated. The validity of the partial or full local thermodynamic equilibrium (LTE) conditions in plasma was explained based on time-resolved electron density measurements. The partial LTE condition was satisfied for delay times in the 200 ns to 1500 ns range. The results are summarized, and the dominant basic atomic processes in the gas mixture photoionized plasma are discussed.

Acoustic detection, tracking, and characterization of three tornadoes.

PubMed

Frazier, William Garth; Talmadge, Carrick; Park, Joseph; Waxler, Roger; Assink, Jelle

2014-04-01

Acoustic data recorded at 1000 samples per second by two sensor arrays located at ranges of 1-113 km from three tornadoes that occurred on 24 May 2011 in Oklahoma are analyzed. Accurate bearings to the tornadoes have been obtained using beamforming methods applied to the data at infrasonic frequencies. Beamforming was not viable at audio frequencies, but the data demonstrate the ability to detect significant changes in the shape of the estimated power spectral density in the band encompassing 10 Hz to approximately 100 Hz at distances of practical value from the sensors. This suggests that arrays of more closely spaced sensors might provide better bearing accuracy at practically useful distances from a tornado. Additionally, a mathematical model, based on established relationships of aeroacoustic turbulence, is demonstrated to provide good agreement to the estimated power spectra produced by the tornadoes at different times and distances from the sensors. The results of this analysis indicate that, qualitatively, an inverse relationship appears to exist between the frequency of an observed peak of the power spectral density and the reported tornado intensity.

Spectral density of mixtures of random density matrices for qubits

NASA Astrophysics Data System (ADS)

Zhang, Lin; Wang, Jiamei; Chen, Zhihua

2018-06-01

We derive the spectral density of the equiprobable mixture of two random density matrices of a two-level quantum system. We also work out the spectral density of mixture under the so-called quantum addition rule. We use the spectral densities to calculate the average entropy of mixtures of random density matrices, and show that the average entropy of the arithmetic-mean-state of n qubit density matrices randomly chosen from the Hilbert-Schmidt ensemble is never decreasing with the number n. We also get the exact value of the average squared fidelity. Some conjectures and open problems related to von Neumann entropy are also proposed.

Assessing a learning process with functional ANOVA estimators of EEG power spectral densities.

PubMed

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.

Inversion of H/V in layered media from seismic ambient noise based on the diffuse field theory and on improved calculation of Green functions

NASA Astrophysics Data System (ADS)

Sánchez-Sesma, Francisco J.; Piña, José; García-Jerez, Antonio; Luzón, Francisco; Perton, Mathieu

2014-05-01

The microtremor H/V spectral ratio (MHVSR) is widely used to assess the dominant frequency of soil sites. Measurements are relatively simple as only one station is needed. It has been recently proposed a theoretical basis linking ambient noise vibrations with diffuse field theory. In this theory the directional energy density computed as the average spectral density of motion at a point, is proportional to the imaginary part of Green function at the observation point. Appropriate normalization is crucial to make the experimental spectral ratios closer to the theoretical counterpart. According to this theory the square of H/V is twice the ratio ImG11 / ImG33, where ImG11 and ImG33 are the imaginary part of Green functions at the load point for horizontal and vertical components, respectively. In order to efficiently compute the imaginary part of Green's functions in a layered medium we start from an integral on the complex k plane and, using Harkrider's nomenclature, separate formulae for body-, Rayleigh-, and Love-wave components to the spectral densities are obtained. Then the poles allow for integration using the Cauchy residue theorem plus some contributions from branch integrals. It is possible to isolate pseudo reflections from ImG11 and thus constrain the inversion of soil profile. We assess ImG11 removing the influence of illumination spectrum using the H/V spectral ratio and an estimate of ImG33 (from an a priori model) by means of ImG11=0.5(H/V )2*ImG33. It has been found that ImG33 is less sensitive to details of stratigraphy. In fact, the Poisson ratio of the uppermost layer controls the slope in high frequency. With the obtained model ImG33 can be updated and the estimate of ImG11 will be improved. ACKNOWLEDGEMENTS. This research has been partially supported by DGAPA-UNAM under Project IN104712, by the MINECO research project CGL2010-16250, Spain, by the EU with FEDER, and the AXA Research Fund.

Real-time spectral analysis of HRV signals: an interactive and user-friendly PC system.

PubMed

Basano, L; Canepa, F; Ottonello, P

1998-01-01

We present a real-time system, built around a PC and a low-cost data acquisition board, for the spectral analysis of the heart rate variability signal. The Windows-like operating environment on which it is based makes the computer program very user-friendly even for non-specialized personnel. The Power Spectral Density is computed through the use of a hybrid method, in which a classical FFT analysis follows an autoregressive finite-extension of data; the stationarity of the sequence is continuously checked. The use of this algorithm gives a high degree of robustness of the spectral estimation. Moreover, always in real time, the FFT of every data block is computed and displayed in order to corroborate the results as well as to allow the user to interactively choose a proper AR model order.

Random vibration analysis of space flight hardware using NASTRAN

NASA Technical Reports Server (NTRS)

Thampi, S. K.; Vidyasagar, S. N.

1990-01-01

During liftoff and ascent flight phases, the Space Transportation System (STS) and payloads are exposed to the random acoustic environment produced by engine exhaust plumes and aerodynamic disturbances. The analysis of payloads for randomly fluctuating loads is usually carried out using the Miles' relationship. This approximation technique computes an equivalent load factor as a function of the natural frequency of the structure, the power spectral density of the excitation, and the magnification factor at resonance. Due to the assumptions inherent in Miles' equation, random load factors are often over-estimated by this approach. In such cases, the estimates can be refined using alternate techniques such as time domain simulations or frequency domain spectral analysis. Described here is the use of NASTRAN to compute more realistic random load factors through spectral analysis. The procedure is illustrated using Spacelab Life Sciences (SLS-1) payloads and certain unique features of this problem are described. The solutions are compared with Miles' results in order to establish trends at over or under prediction.

Investigation of mixed ionospheric and fround scatter using high spectral content pulse sequences for SuperDARN radars

NASA Astrophysics Data System (ADS)

Spaleta, J.; Bristow, W. A.

2013-12-01

SuperDARN radars estimate plasma drift velocities from the Doppler shift observed on signals scattered from field-aligned density irregularities. These field-aligned density irregularities are embedded in the ionospheric plasma, and move at the same velocity as background plasma. As a result, the electromagnetic signals scattered from these irregularities are Doppler shifted. The SuperDARN radars routinely observe ionospheric scatter Doppler velocities ranging from zero to thousands of meters per second. The radars determine the Doppler shift of the ionospheric scatter by linear fitting the phase of an auto correlation function derived from the radar pulse sequence. The phase fitting technique employed assumes a single dominant velocity is present in the signal. In addition, the SuperDARN radars can also observe signals scattered from the ground. Once refracted by the ionospheric plasma and bent earthward, the radar pulses eventually reach the ground where they scatter, sending signal back to the radar. This ground-scatter signal is characterized as having a low Doppler shift and low spectral width. The SuperDARN radars are able to use these signal characteristics to discriminate the ground scatter signal from the ionospheric scatter, when regions of ground scatter are isolated from ionospheric scatter returns. The phase fitting assumption of a single dominate target can easily be violated at ranges where ground and ionospheric scatter mix together. Due to the wide elevation angle extent of the SuperDARN radar design, ground and ionospheric scatter from different propagation paths can mix together in the return signal. When this happens, the fitting algorithm attempts to fit to the dominant signal, and if ground scatter dominates, information about the ionospheric scatter at that range can be unresolved. One way to address the mix scatter situation is to use a high spectral content pulse sequence together with a spectral estimation technique. The high spectral content pulse sequence consists of twice as many pulses and five times as many distinct lags over which to calculate the auto correlation function. This additional spectral information makes it possible to use spectral estimator techniques, that are robust against aperiodic time series data, to calculate the existence of multiple scatter modes in the signal. A comparison of the operation of the traditional SuperDARN pulse sequence and high spectral content pulse sequence will be presented for both synthetic examples and real SuperDARN radar mixed scatter situation.

Temporal scaling of hydraulic head and river base flow and its implication for groundwater recharge

USGS Publications Warehouse

Zhang, You‐Kuan; Schilling, Keith

2004-01-01

Spectral analyses were conducted for hourly hydraulic head (h) data observed over a 4‐year period at seven monitoring wells in the Walnut Creek watershed, Iowa. The log power spectral density of the hydraulic head fluctuations versus log frequency (f) at all seven wells is shown to have a distinct slope or fractal dimension (D), indicating temporal scaling in the time series of water level fluctuations. The fractal dimension of the time series varies from well to well, and the spectrum for the average h over all seven wells has a fractal dimension of 1.46 and Hurst coefficient of 0.54. The log power spectral density of estimated base flow in the Walnut Creek and four other watersheds versus log f is shown to have two distinct slopes with a break in scaling at about 30 days. It is shown that the groundwater recharge process in a basin can be estimated from a head spectrum based on existing theoretical results. Hydraulic head in an aquifer may fluctuate as a fractal in time in response to either a white noise or fractal recharge process, depending on physical parameters (i.e., transmissivity and specific yield) of the aquifer. The recharge process at the Walnut Creek watershed is shown to have a white noise spectrum based on the observed head spectrum.

Calibration and evaluation of CCD spectroradiometers for ground-based and airborne measurements of spectral actinic flux densities

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), resulting in estimated detection limits of 5 × 10-7 and 1 × 10-7 s-1, respectively, derived from nighttime measurements on the ground (0.3 s integration time, 10 s averages). For j(O1D) the detection limit could be further reduced by setting spectral actinic flux densities to zero below atmospheric cutoff wavelengths. The accuracies of photolysis frequencies were determined from linear regressions with data from the double-monochromator reference instrument. The agreement was typically within ±5 %. Because optical-receiver aspects are not specific for the CCD spectroradiometers, they were widely excluded in this work and will be treated in a separate paper, in particular with regard to airborne applications.

Interpreting The Unresolved Intensity Of Cosmologically Redshifted Line Radiation

NASA Technical Reports Server (NTRS)

Switzer, E. R.; Chang, T.-C.; Masui, K. W.; Pen, U.-L.; Voytek, T. C.

2016-01-01

Intensity mapping experiments survey the spectrum of diffuse line radiation rather than detect individual objects at high signal-to-noise ratio. Spectral maps of unresolved atomic and molecular line radiation contain three-dimensional information about the density and environments of emitting gas and efficiently probe cosmological volumes out to high redshift. Intensity mapping survey volumes also contain all other sources of radiation at the frequencies of interest. Continuum foregrounds are typically approximately 10(sup 2)-10(Sup 3) times brighter than the cosmological signal. The instrumental response to bright foregrounds will produce new spectral degrees of freedom that are not known in advance, nor necessarily spectrally smooth. The intrinsic spectra of fore-grounds may also not be well known in advance. We describe a general class of quadratic estimators to analyze data from single-dish intensity mapping experiments and determine contaminated spectral modes from the data themselves. The key attribute of foregrounds is not that they are spectrally smooth, but instead that they have fewer bright spectral degrees of freedom than the cosmological signal. Spurious correlations between the signal and foregrounds produce additional bias. Compensation for signal attenuation must estimate and correct this bias. A successful intensity mapping experiment will control instrumental systematics that spread variance into new modes, and it must observe a large enough volume that contaminant modes can be determined independently from the signal on scales of interest.

Remote Sensing of Parasitic Nematodes in Plants

NASA Technical Reports Server (NTRS)

Lawrence, Gary W.; King, Roger; Kelley, Amber T.; Vickery, John

2007-01-01

A method and apparatus for remote sensing of parasitic nematodes in plants, now undergoing development, is based on measurement of visible and infrared spectral reflectances of fields where the plants are growing. Initial development efforts have been concentrated on detecting reniform nematodes (Rotylenchulus reniformis) in cotton plants, because of the economic importance of cotton crops. The apparatus includes a hand-held spectroradiometer. The readings taken by the radiometer are processed to extract spectral reflectances at sixteen wavelengths between 451 and 949 nm that, taken together, have been found to be indicative of the presence of Rotylenchulus reniformis. The intensities of the spectral reflectances are used to estimate the population density of the nematodes in an area from which readings were taken.

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.

Optimizing Radiometric Processing and Feature Extraction of Drone Based Hyperspectral Frame Format Imagery for Estimation of Yield Quantity and Quality of a Grass Sward

NASA Astrophysics Data System (ADS)

Näsi, R.; Viljanen, N.; Oliveira, R.; Kaivosoja, J.; Niemeläinen, O.; Hakala, T.; Markelin, L.; Nezami, S.; Suomalainen, J.; Honkavaara, E.

2018-04-01

Light-weight 2D format hyperspectral imagers operable from unmanned aerial vehicles (UAV) have become common in various remote sensing tasks in recent years. Using these technologies, the area of interest is covered by multiple overlapping hypercubes, in other words multiview hyperspectral photogrammetric imagery, and each object point appears in many, even tens of individual hypercubes. The common practice is to calculate hyperspectral orthomosaics utilizing only the most nadir areas of the images. However, the redundancy of the data gives potential for much more versatile and thorough feature extraction. We investigated various options of extracting spectral features in the grass sward quantity evaluation task. In addition to the various sets of spectral features, we used photogrammetry-based ultra-high density point clouds to extract features describing the canopy 3D structure. Machine learning technique based on the Random Forest algorithm was used to estimate the fresh biomass. Results showed high accuracies for all investigated features sets. The estimation results using multiview data provided approximately 10 % better results than the most nadir orthophotos. The utilization of the photogrammetric 3D features improved estimation accuracy by approximately 40 % compared to approaches where only spectral features were applied. The best estimation RMSE of 239 kg/ha (6.0 %) was obtained with multiview anisotropy corrected data set and the 3D features.

Calibrated simulations of Z opacity experiments that reproduce the experimentally measured plasma conditions

DOE PAGES

Nagayama, T.; Bailey, J. E.; Loisel, G.; ...

2016-02-05

Recently, frequency-resolved iron opacity measurements at electron temperatures of 170–200 eV and electron densities of (0.7 – 4.0) × 10 22 cm –3 revealed a 30–400% disagreement with the calculated opacities [J. E. Bailey et al., Nature (London) 517, 56 (2015)]. The discrepancies have a high impact on astrophysics, atomic physics, and high-energy density physics, and it is important to verify our understanding of the experimental platform with simulations. Reliable simulations are challenging because the temporal and spatial evolution of the source radiation and of the sample plasma are both complex and incompletely diagnosed. In this article, we describe simulationsmore » that reproduce the measured temperature and density in recent iron opacity experiments performed at the Sandia National Laboratories Z facility. The time-dependent spectral irradiance at the sample is estimated using the measured time- and space-dependent source radiation distribution, in situ source-to-sample distance measurements, and a three-dimensional (3D) view-factor code. The inferred spectral irradiance is used to drive 1D sample radiation hydrodynamics simulations. The images recorded by slit-imaged space-resolved spectrometers are modeled by solving radiation transport of the source radiation through the sample. We find that the same drive radiation time history successfully reproduces the measured plasma conditions for eight different opacity experiments. These results provide a quantitative physical explanation for the observed dependence of both temperature and density on the sample configuration. Simulated spectral images for the experiments without the FeMg sample show quantitative agreement with the measured spectral images. The agreement in spectral profile, spatial profile, and brightness provides further confidence in our understanding of the backlight-radiation time history and image formation. Furthermore, these simulations bridge the static-uniform picture of the data interpretation and the dynamic-gradient reality of the experiments, and they will allow us to quantitatively assess the impact of effects neglected in the data interpretation.« less

Bounding filter - A simple solution to lack of exact a priori statistics.

NASA Technical Reports Server (NTRS)

Nahi, N. E.; Weiss, I. M.

1972-01-01

Wiener and Kalman-Bucy estimation problems assume that models describing the signal and noise stochastic processes are exactly known. When this modeling information, i.e., the signal and noise spectral densities for Wiener filter and the signal and noise dynamic system and disturbing noise representations for Kalman-Bucy filtering, is inexactly known, then the filter's performance is suboptimal and may even exhibit apparent divergence. In this paper a system is designed whereby the actual estimation error covariance is bounded by the covariance calculated by the estimator. Therefore, the estimator obtains a bound on the actual error covariance which is not available, and also prevents its apparent divergence.

GEOS-2 C-band radar system project. Spectral analysis as related to C-band radar data analysis

NASA Technical Reports Server (NTRS)

1972-01-01

Work performed on spectral analysis of data from the C-band radars tracking GEOS-2 and on the development of a data compaction method for the GEOS-2 C-band radar data is described. The purposes of the spectral analysis study were to determine the optimum data recording and sampling rates for C-band radar data and to determine the optimum method of filtering and smoothing the data. The optimum data recording and sampling rate is defined as the rate which includes an optimum compromise between serial correlation and the effects of frequency folding. The goal in development of a data compaction method was to reduce to a minimum the amount of data stored, while maintaining all of the statistical information content of the non-compacted data. A digital computer program for computing estimates of the power spectral density function of sampled data was used to perform the spectral analysis study.

Determining density of maize canopy. 1: Digitized photography

NASA Technical Reports Server (NTRS)

Stoner, E. R.; Baumgardner, M. F.; Swain, P. H.

1972-01-01

The relationship between different densities of maize (Zea mays L.) canopies and the energy reflected by these canopies was studied. Field plots were laid out, representing four growth stages of maize, on a dark soil and on a very light colored surface soil. Spectral and spatial data were obtained from color and color infrared photography taken from a vertical distance of 10 m above the maize canopies. Estimates of ground cover were related to field measurements of leaf area index. Ground cover was predicted from leaf area index measurements by a second order equation. Color infrared photography proved helpful in determining the density of maize canopy on dark soils. Color photography was useful for determining canopy density on light colored soils. The near infrared dye layer is the most valuable in canopy density determinations.

Initial Results in Using a Self-Coherence Method for Detecting Sustained Oscillations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Ning; Dagle, Jeffery E.

2015-01-01

This paper develops a self-coherence method for detecting sustained oscillations using phasor measurement unit (PMU) data. Sustained oscillations decrease system performance and introduce potential reliability issues. Timely detection of the oscillations at an early stage provides the opportunity for taking remedial reaction. Using high-speed time-synchronized PMU data, this paper details a self-coherence method for detecting sustained oscillation, even when the oscillation amplitude is lower than ambient noise. Simulation and field measurement data are used to evaluate the proposed method’s performance. It is shown that the proposed method can detect sustained oscillations and estimate oscillation frequencies with a low signal-to-noise ratio.more » Comparison with a power spectral density method also shows that the proposed self-coherence method performs better. Index Terms—coherence, power spectral density, phasor measurement unit (PMU), oscillations, power system dynamics« less

High spatial resolution three-dimensional mapping of vegetation spectral dynamics using computer vision and hobbyist unmanned aerial vehicles

NASA Astrophysics Data System (ADS)

Dandois, J. P.; Ellis, E. C.

2013-12-01

High spatial resolution three-dimensional (3D) measurements of vegetation by remote sensing are advancing ecological research and environmental management. However, substantial economic and logistical costs limit this application, especially for observing phenological dynamics in ecosystem structure and spectral traits. Here we demonstrate a new aerial remote sensing system enabling routine and inexpensive aerial 3D measurements of canopy structure and spectral attributes, with properties similar to those of LIDAR, but with RGB (red-green-blue) spectral attributes for each point, enabling high frequency observations within a single growing season. This 'Ecosynth' methodology applies photogrammetric ''Structure from Motion'' computer vision algorithms to large sets of highly overlapping low altitude (< 130 m) aerial photographs acquired using off-the-shelf digital cameras mounted on an inexpensive (< USD$4000), lightweight (< 2 kg), hobbyist-grade unmanned aerial system (UAS). Ecosynth 3D point clouds with densities of 30 - 67 points m-2 were produced using commercial computer vision software from digital photographs acquired repeatedly by UAS over three 6.25 ha (250 m x 250 m) Temperate Deciduous forest sites in Maryland USA. Ecosynth canopy height maps (CHMs) were strong predictors of field-measured tree heights (R2 0.63 to 0.84) and were highly correlated with a LIDAR CHM (R 0.87) acquired 4 days earlier, though Ecosynth-based estimates of aboveground biomass densities included significant errors (31 - 36% of field-based estimates). Repeated scanning of a 0.25 ha forested area at six different times across a 16 month period revealed ecologically significant dynamics in canopy color at different heights and a structural shift upward in canopy density, as demonstrated by changes in vertical height profiles of point density and relative RGB brightness. Changes in canopy relative greenness were highly correlated (R2 = 0.88) with MODIS NDVI time series for the same area and vertical differences in canopy color revealed the early green up of the dominant canopy species, Liriodendron tulipifera, strong evidence that Ecosynth time series measurements capture vegetation structural and spectral dynamics at the spatial scale of individual trees. Observing canopy phenology in 3D at high temporal resolutions represents a breakthrough in forest ecology. Inexpensive user-deployed technologies for multispectral 3D scanning of vegetation at landscape scales (< 1 km2) heralds a new era of participatory remote sensing by field ecologists, community foresters and the interested public.

O2 on ganymede: Spectral characteristics and plasma formation mechanisms

USGS Publications Warehouse

Calvin, W.M.; Johnson, R.E.; Spencer, J.R.

1996-01-01

Weak absorption features in the visible reflectance spectrum of Jupiter's satellite Ganymede have been correlated to those observed in the spectrum of molecular oxygen. We examine the spectral characteristics of these absorption features in all phases of O2 and conclude that the molecular oxygen is most likely present at densities similar to the liquid or solid ??-phase. The contribution of O2 to spectral features observed on Ganymede in the near-infrared wavelength region affects the previous estimates of photon pathlength in ice. The concentration of the visible absorption features on the trailing hemisphere of Ganymede suggests an origin due to bombardment by magneto-spheric ions. We derive an approximate O2 formation rate from this mechanism and consider the state of O2 within the surface.

Mapping surface energy balance components by combining landsat thematic mapper and ground-based meteorological data

USGS Publications Warehouse

Moran, M.S.; Jackson, R. D.; Raymond, L.H.; Gay, L.W.; Slater, P.N.

1989-01-01

Surface energy balance components were evaluated by combining satellite-based spectral data with on-site measurements of solar irradiance, air temperature, wind speed, and vapor pressure. Maps of latent heat flux density (??E) and net radiant flux density (Rn) were produced using Landsat Thematic Mapper (TM) data for three dates: 23 July 1985, 5 April 1986, and 24 June 1986. On each date, a Bowen-ratio apparatus, located in a vegetated field, was used to measure ??E and Rn at a point within the field. Estimates of ??E and Rn were also obtained using radiometers aboard an aircraft flown at 150 m above ground level. The TM-based estimates differed from the Bowen-ratio and aircraft-based estimates by less than 12 % over mature fields of cotton, wheat, and alfalfa, where ??E and Rn ranged from 400 to 700 Wm-2. ?? 1989.

A sparse matrix-vector multiplication based algorithm for accurate density matrix computations on systems of millions of atoms

NASA Astrophysics Data System (ADS)

Ghale, Purnima; Johnson, Harley T.

2018-06-01

We present an efficient sparse matrix-vector (SpMV) based method to compute the density matrix P from a given Hamiltonian in electronic structure computations. Our method is a hybrid approach based on Chebyshev-Jackson approximation theory and matrix purification methods like the second order spectral projection purification (SP2). Recent methods to compute the density matrix scale as O(N) in the number of floating point operations but are accompanied by large memory and communication overhead, and they are based on iterative use of the sparse matrix-matrix multiplication kernel (SpGEMM), which is known to be computationally irregular. In addition to irregularity in the sparse Hamiltonian H, the nonzero structure of intermediate estimates of P depends on products of H and evolves over the course of computation. On the other hand, an expansion of the density matrix P in terms of Chebyshev polynomials is straightforward and SpMV based; however, the resulting density matrix may not satisfy the required constraints exactly. In this paper, we analyze the strengths and weaknesses of the Chebyshev-Jackson polynomials and the second order spectral projection purification (SP2) method, and propose to combine them so that the accurate density matrix can be computed using the SpMV computational kernel only, and without having to store the density matrix P. Our method accomplishes these objectives by using the Chebyshev polynomial estimate as the initial guess for SP2, which is followed by using sparse matrix-vector multiplications (SpMVs) to replicate the behavior of the SP2 algorithm for purification. We demonstrate the method on a tight-binding model system of an oxide material containing more than 3 million atoms. In addition, we also present the predicted behavior of our method when applied to near-metallic Hamiltonians with a wide energy spectrum.

Modeling the Response of Anopheles gambiae (Diptera: Culicidae) Populations in the Kenya Highlands to a Rise in Mean Annual Temperature.

PubMed

Wallace, Dorothy; Prosper, Olivia; Savos, Jacob; Dunham, Ann M; Chipman, Jonathan W; Shi, Xun; Ndenga, Bryson; Githeko, Andrew

2017-03-01

A dynamical model of Anopheles gambiae larval and adult populations is constructed that matches temperature-dependent maturation times and mortality measured experimentally as well as larval instar and adult mosquito emergence data from field studies in the Kenya Highlands. Spectral classification of high-resolution satellite imagery is used to estimate household density. Indoor resting densities collected over a period of one year combined with predictions of the dynamical model give estimates of both aquatic habitat and total adult mosquito densities. Temperature and precipitation patterns are derived from monthly records. Precipitation patterns are compared with average and extreme habitat estimates to estimate available aquatic habitat in an annual cycle. These estimates are coupled with the original model to produce estimates of adult and larval populations dependent on changing aquatic carrying capacity for larvae and changing maturation and mortality dependent on temperature. This paper offers a general method for estimating the total area of aquatic habitat in a given region, based on larval counts, emergence rates, indoor resting density data, and number of households.Altering the average daily temperature and the average daily rainfall simulates the effect of climate change on annual cycles of prevalence of An. gambiae adults. We show that small increases in average annual temperature have a large impact on adult mosquito density, whether measured at model equilibrium values for a single square meter of habitat or tracked over the course of a year of varying habitat availability and temperature. © The Authors 2016. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Cosine-Gaussian Schell-model sources.

PubMed

Mei, Zhangrong; Korotkova, Olga

2013-07-15

We introduce a new class of partially coherent sources of Schell type with cosine-Gaussian spectral degree of coherence and confirm that such sources are physically genuine. Further, we derive the expression for the cross-spectral density function of a beam generated by the novel source propagating in free space and analyze the evolution of the spectral density and the spectral degree of coherence. It is shown that at sufficiently large distances from the source the degree of coherence of the propagating beam assumes Gaussian shape while the spectral density takes on the dark-hollow profile.

A novel multireceiver communications system configuration based on optimal estimation theory

NASA Technical Reports Server (NTRS)

Kumar, R.

1990-01-01

A multireceiver configuration for the purpose of carrier arraying and/or signal arraying is presented. Such a problem arises for example, in the NASA Deep Space Network where the same data-modulated signal from a spacecraft is received by a number of geographically separated antennas and the data detection must be efficiently performed on the basis of the various received signals. The proposed configuration is arrived at by formulating the carrier and/or signal arraying problem as an optimal estimation problem. Two specific solutions are proposed. The first solution is to simultaneously and optimally estimate the various phase processes received at different receivers with coupled phase locked loops (PLLs) wherein the individual PLLs acquire and track their respective receivers' phase processes, but are aided by each other in an optimal manner. However, when the phase processes are relatively weakly correlated, and for the case of relatively high values of symbol energy-to-noise spectral density ratio, a novel configuration for combining the data modulated, loop-output signals is proposed. The scheme can be extended to the case of low symbol energy-to-noise case by performing the combining/detection process over a multisymbol period. Such a configuration results in the minimization of the effective radio loss at the combiner output, and thus a maximization of energy per bit to noise-power spectral density ration is achieved.

47 CFR 90.1215 - Power limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... peak power spectral density of 21 dBm per one MHz. High power devices using channel bandwidths other than those listed above are permitted; however, they are limited to peak power spectral density of 21 d... conducted output power and the peak power spectral density should be reduced by the amount in decibels that...

Quantification of breast density with spectral mammography based on a scanned multi-slit photon-counting detector: a feasibility study.

PubMed

Ding, Huanjun; Molloi, Sabee

2012-08-07

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. 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 of the dual energy image with respect to the square root of mean glandular dose, 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. For an average sized 4.5 cm thick breast, the FOM was maximized with a tube voltage of 46 kVp 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 approximately 1.54% using standard calibration function. The results from the modified fitting function, which integrated the tube voltage as a variable in the calibration, indicated a RMS error of approximately 1.35% for all four studies. The results of the current study suggest that photon-counting spectral mammography systems may potentially be implemented for an accurate quantification of volumetric breast density, with an RMS error of less than 2%, using the proposed dual energy imaging technique.

Diffraction of cosine-Gaussian-correlated Schell-model beams.

PubMed

Pan, Liuzhan; Ding, Chaoliang; Wang, Haixia

2014-05-19

The expression of spectral density of cosine-Gaussian-correlated Schell-model (CGSM) beams diffracted by an aperture is derived, and used to study the changes in the spectral density distribution of CGSM beams upon propagation, where the effect of aperture diffraction is emphasized. It is shown that, comparing with that of GSM beams, the spectral density distribution of CGSM beams diffracted by an aperture has dip and shows dark hollow intensity distribution when the order-parameter n is big enough. The central intensity increases with increasing truncation parameter of aperture. The comparative study of spectral density distributions of CGSM beams with aperture and that of without aperture is performed. Furthermore, the effect of order-parameter n and spatial coherence of CGSM beams on the spectral density distribution is discussed in detail. The results obtained may be useful in optical particulate manipulation.

Estimation of Ice Surface Scattering and Acoustic Attenuation in Arctic Sediments from Long-Range Propagation Data

DTIC Science & Technology

1984-01-01

frequencies over the calculation at 1 meter. This was corrected by +60 dB to obtain the signature at I meter, and then by -160 dB to obtain the voltage...FFT with appropriate corrections for one-sided energy spectral density re . 1 V2/Hz. The spectrum was then smeared over a 4 Hz band by a running...after correcting the array estimated slownesses for slight bathymetric dip local to the receiving array. A preliminary inversion of this type is given by

Nonlinear damping model for flexible structures. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Zang, Weijian

1990-01-01

The study of nonlinear damping problem of flexible structures is addressed. Both passive and active damping, both finite dimensional and infinite dimensional models are studied. In the first part, the spectral density and the correlation function of a single DOF nonlinear damping model is investigated. A formula for the spectral density is established with O(Gamma(sub 2)) accuracy based upon Fokker-Planck technique and perturbation. The spectral density depends upon certain first order statistics which could be obtained if the stationary density is known. A method is proposed to find the approximate stationary density explicitly. In the second part, the spectral density of a multi-DOF nonlinear damping model is investigated. In the third part, energy type nonlinear damping model in an infinite dimensional setting is studied.

A Novel Time-Varying Spectral Filtering Algorithm for Reconstruction of Motion Artifact Corrupted Heart Rate Signals During Intense Physical Activities Using a Wearable Photoplethysmogram Sensor

PubMed Central

Salehizadeh, Seyed M. A.; Dao, Duy; Bolkhovsky, Jeffrey; Cho, Chae; Mendelson, Yitzhak; Chon, Ki H.

2015-01-01

Accurate estimation of heart rates from photoplethysmogram (PPG) signals during intense physical activity is a very challenging problem. This is because strenuous and high intensity exercise can result in severe motion artifacts in PPG signals, making accurate heart rate (HR) estimation difficult. In this study we investigated a novel technique to accurately reconstruct motion-corrupted PPG signals and HR based on time-varying spectral analysis. The algorithm is called Spectral filter algorithm for Motion Artifacts and heart rate reconstruction (SpaMA). The idea is to calculate the power spectral density of both PPG and accelerometer signals for each time shift of a windowed data segment. By comparing time-varying spectra of PPG and accelerometer data, those frequency peaks resulting from motion artifacts can be distinguished from the PPG spectrum. The SpaMA approach was applied to three different datasets and four types of activities: (1) training datasets from the 2015 IEEE Signal Process. Cup Database recorded from 12 subjects while performing treadmill exercise from 1 km/h to 15 km/h; (2) test datasets from the 2015 IEEE Signal Process. Cup Database recorded from 11 subjects while performing forearm and upper arm exercise. (3) Chon Lab dataset including 10 min recordings from 10 subjects during treadmill exercise. The ECG signals from all three datasets provided the reference HRs which were used to determine the accuracy of our SpaMA algorithm. The performance of the SpaMA approach was calculated by computing the mean absolute error between the estimated HR from the PPG and the reference HR from the ECG. The average estimation errors using our method on the first, second and third datasets are 0.89, 1.93 and 1.38 beats/min respectively, while the overall error on all 33 subjects is 1.86 beats/min and the performance on only treadmill experiment datasets (22 subjects) is 1.11 beats/min. Moreover, it was found that dynamics of heart rate variability can be accurately captured using the algorithm where the mean Pearson’s correlation coefficient between the power spectral densities of the reference and the reconstructed heart rate time series was found to be 0.98. These results show that the SpaMA method has a potential for PPG-based HR monitoring in wearable devices for fitness tracking and health monitoring during intense physical activities. PMID:26703618

A Novel Time-Varying Spectral Filtering Algorithm for Reconstruction of Motion Artifact Corrupted Heart Rate Signals During Intense Physical Activities Using a Wearable Photoplethysmogram Sensor.

PubMed

Salehizadeh, Seyed M A; Dao, Duy; Bolkhovsky, Jeffrey; Cho, Chae; Mendelson, Yitzhak; Chon, Ki H

2015-12-23

Accurate estimation of heart rates from photoplethysmogram (PPG) signals during intense physical activity is a very challenging problem. This is because strenuous and high intensity exercise can result in severe motion artifacts in PPG signals, making accurate heart rate (HR) estimation difficult. In this study we investigated a novel technique to accurately reconstruct motion-corrupted PPG signals and HR based on time-varying spectral analysis. The algorithm is called Spectral filter algorithm for Motion Artifacts and heart rate reconstruction (SpaMA). The idea is to calculate the power spectral density of both PPG and accelerometer signals for each time shift of a windowed data segment. By comparing time-varying spectra of PPG and accelerometer data, those frequency peaks resulting from motion artifacts can be distinguished from the PPG spectrum. The SpaMA approach was applied to three different datasets and four types of activities: (1) training datasets from the 2015 IEEE Signal Process. Cup Database recorded from 12 subjects while performing treadmill exercise from 1 km/h to 15 km/h; (2) test datasets from the 2015 IEEE Signal Process. Cup Database recorded from 11 subjects while performing forearm and upper arm exercise. (3) Chon Lab dataset including 10 min recordings from 10 subjects during treadmill exercise. The ECG signals from all three datasets provided the reference HRs which were used to determine the accuracy of our SpaMA algorithm. The performance of the SpaMA approach was calculated by computing the mean absolute error between the estimated HR from the PPG and the reference HR from the ECG. The average estimation errors using our method on the first, second and third datasets are 0.89, 1.93 and 1.38 beats/min respectively, while the overall error on all 33 subjects is 1.86 beats/min and the performance on only treadmill experiment datasets (22 subjects) is 1.11 beats/min. Moreover, it was found that dynamics of heart rate variability can be accurately captured using the algorithm where the mean Pearson's correlation coefficient between the power spectral densities of the reference and the reconstructed heart rate time series was found to be 0.98. These results show that the SpaMA method has a potential for PPG-based HR monitoring in wearable devices for fitness tracking and health monitoring during intense physical activities.

Fluorescence lifetime spectroscopy: potential for in-vivo estimation of skin fluorophores changes after low power laser treatment

NASA Astrophysics Data System (ADS)

Ferulova, Inesa; Lihachev, Alexey; Spigulis, Janis

2013-11-01

The impact of visible cwlaser irradiation on skin autofluorescence lifetimes was investigated in spectral range from 450 nm to 600 nm. Skin optical provocations were performed during 1 min by 405 nm low power cw laser with power density up to 20 mW/cm2. Autofluorescence lifetimes were measured before and immediately after the optical provocation.

A Software Toolbox for Systematic Evaluation of Seismometer-Digitizer System Responses

DTIC Science & Technology

2011-09-01

characteristics (e.g., borehole vs. surface installation) instead of the actual seismic noise characteristics. Their results suggest that our best...Administration Award No. DE-FG02-09ER85548 ABSTRACT Measurement of the absolute amplitudes of a seismic signal requires accurate knowledge of...estimates seismic noise power spectral densities, and NOISETRAN, which generates a pseudo-amplitude response (PAR) for a seismic station, based on

Very High-Frequency (VHF) ionospheric scintillation fading measurements at Lima, Peru

NASA Technical Reports Server (NTRS)

Blank, H. A.; Golden, T. S.

1972-01-01

During the spring equinox of 1970, scintillating signals at VHF (136.4 MHz) were observed at Lima, Peru. The transmission originated from ATS 3 and was observed through a pair of antennas spaced 1200 feet apart on an east-west baseline. The empirical data were digitized, reduced, and analyzed. The results include amplitude probability density and distribution functions, time autocorrelation functions, cross correlation functions for the spaced antennas, and appropriate spectral density functions. Results show estimates of the statistics of the ground diffraction pattern to gain insight into gross ionospheric irregularity size, and irregularity velocity in the antenna planes.

Twenty-five years of maximum-entropy principle

NASA Astrophysics Data System (ADS)

Kapur, J. N.

1983-04-01

The strengths and weaknesses of the maximum entropy principle (MEP) are examined and some challenging problems that remain outstanding at the end of the first quarter century of the principle are discussed. The original formalism of the MEP is presented and its relationship to statistical mechanics is set forth. The use of MEP for characterizing statistical distributions, in statistical inference, nonlinear spectral analysis, transportation models, population density models, models for brand-switching in marketing and vote-switching in elections is discussed. Its application to finance, insurance, image reconstruction, pattern recognition, operations research and engineering, biology and medicine, and nonparametric density estimation is considered.

AGN neutrino flux estimates for a realistic hybrid model

NASA Astrophysics Data System (ADS)

Richter, S.; Spanier, F.

2018-07-01

Recent reports of possible correlations between high energy neutrinos observed by IceCube and Active Galactic Nuclei (AGN) activity sparked a burst of publications that attempt to predict the neutrino flux of these sources. However, often rather crude estimates are used to derive the neutrino rate from the observed photon spectra. In this work neutrino fluxes were computed in a wide parameter space. The starting point of the model was a representation of the full spectral energy density (SED) of 3C 279. The time-dependent hybrid model that was used for this study takes into account the full pγ reaction chain as well as proton synchrotron, electron-positron-pair cascades and the full SSC scheme. We compare our results to estimates frequently used in the literature. This allows to identify regions in the parameter space for which such estimates are still valid and those in which they can produce significant errors. Furthermore, if estimates for the Doppler factor, magnetic field, proton and electron densities of a source exist, the expected IceCube detection rate is readily available.

Estimation of wood density and chemical composition by means of diffuse reflectance mid-infrared Fourier transform (DRIFT-MIR) spectroscopy.

PubMed

Nuopponen, Mari H; Birch, Gillian M; Sykes, Rob J; Lee, Steve J; Stewart, Derek

2006-01-11

Sitka spruce (Picea sitchensis) samples (491) from 50 different clones as well as 24 different tropical hardwoods and 20 Scots pine (Pinus sylvestris) samples were used to construct diffuse reflectance mid-infrared Fourier transform (DRIFT-MIR) based partial least squares (PLS) calibrations on lignin, cellulose, and wood resin contents and densities. Calibrations for density, lignin, and cellulose were established for all wood species combined into one data set as well as for the separate Sitka spruce data set. Relationships between wood resin and MIR data were constructed for the Sitka spruce data set as well as the combined Scots pine and Sitka spruce data sets. Calibrations containing only five wavenumbers instead of spectral ranges 4000-2800 and 1800-700 cm(-1) were also established. In addition, chemical factors contributing to wood density were studied. Chemical composition and density assessed from DRIFT-MIR calibrations had R2 and Q2 values in the ranges of 0.6-0.9 and 0.6-0.8, respectively. The PLS models gave residual mean squares error of prediction (RMSEP) values of 1.6-1.9, 2.8-3.7, and 0.4 for lignin, cellulose, and wood resin contents, respectively. Density test sets had RMSEP values ranging from 50 to 56. Reduced amount of wavenumbers can be utilized to predict the chemical composition and density of a wood, which should allow measurements of these properties using a hand-held device. MIR spectral data indicated that low-density samples had somewhat higher lignin contents than high-density samples. Correspondingly, high-density samples contained slightly more polysaccharides than low-density samples. This observation was consistent with the wet chemical data.

Maximum likelihood method for estimating airplane stability and control parameters from flight data in frequency domain

NASA Technical Reports Server (NTRS)

Klein, V.

1980-01-01

A frequency domain maximum likelihood method is developed for the estimation of airplane stability and control parameters from measured data. The model of an airplane is represented by a discrete-type steady state Kalman filter with time variables replaced by their Fourier series expansions. The likelihood function of innovations is formulated, and by its maximization with respect to unknown parameters the estimation algorithm is obtained. This algorithm is then simplified to the output error estimation method with the data in the form of transformed time histories, frequency response curves, or spectral and cross-spectral densities. The development is followed by a discussion on the equivalence of the cost function in the time and frequency domains, and on advantages and disadvantages of the frequency domain approach. The algorithm developed is applied in four examples to the estimation of longitudinal parameters of a general aviation airplane using computer generated and measured data in turbulent and still air. The cost functions in the time and frequency domains are shown to be equivalent; therefore, both approaches are complementary and not contradictory. Despite some computational advantages of parameter estimation in the frequency domain, this approach is limited to linear equations of motion with constant coefficients.

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.

Spatiotemporal Built-up Land Density Mapping Using Various Spectral Indices in Landsat-7 ETM+ and Landsat-8 OLI/TIRS (Case Study: Surakarta City)

NASA Astrophysics Data System (ADS)

Risky, Yanuar S.; Aulia, Yogi H.; Widayani, Prima

2017-12-01

Spectral indices variations support for rapid and accurate extracting information such as built-up density. However, the exact determination of spectral waves for built-up density extraction is lacking. This study explains and compares the capabilities of 5 variations of spectral indices in spatiotemporal built-up density mapping using Landsat-7 ETM+ and Landsat-8 OLI/TIRS in Surakarta City on 2002 and 2015. The spectral indices variations used are 3 mid-infrared (MIR) based indices such as the Normalized Difference Built-up Index (NDBI), Urban Index (UI) and Built-up and 2 visible based indices such as VrNIR-BI (visible red) and VgNIR-BI (visible green). Linear regression statistics between ground value samples from Google Earth image in 2002 and 2015 and spectral indices for determining built-up land density. Ground value used amounted to 27 samples for model and 7 samples for accuracy test. The classification of built-up density mapping is divided into 9 classes: unclassified, 0-12.5%, 12.5-25%, 25-37.5%, 37.5-50%, 50-62.5%, 62.5-75%, 75-87.5% and 87.5-100 %. Accuracy of built-up land density mapping in 2002 and 2015 using VrNIR-BI (81,823% and 73.235%), VgNIR-BI (78.934% and 69.028%), NDBI (34.870% and 74.365%), UI (43.273% and 64.398%) and Built-up (59.755% and 72.664%). Based all spectral indices, Surakarta City on 2000-2015 has increased of built-up land density. VgNIR-BI has better capabilities for built-up land density mapping on Landsat-7 ETM + and Landsat-8 OLI/TIRS.

Investigating the effect of characteristic x-rays in cadmium zinc telluride detectors under breast computerized tomography operating conditions

PubMed Central

Glick, Stephen J.; Didier, Clay

2013-01-01

A number of research groups have been investigating the use of dedicated breast computerized tomography (CT). Preliminary results have been encouraging, suggesting an improved visualization of masses on breast CT as compared to conventional mammography. Nonetheless, there are many challenges to overcome before breast CT can become a routine clinical reality. One potential improvement over current breast CT prototypes would be the use of photon counting detectors with cadmium zinc telluride (CZT) (or CdTe) semiconductor material. These detectors can operate at room temperature and provide high detection efficiency and the capability of multi-energy imaging; however, one factor in particular that limits image quality is the emission of characteristic x-rays. In this study, the degradative effects of characteristic x-rays are examined when using a CZT detector under breast CT operating conditions. Monte Carlo simulation software was used to evaluate the effect of characteristic x-rays and the detector element size on spatial and spectral resolution for a CZT detector used under breast CT operating conditions. In particular, lower kVp spectra and thinner CZT thicknesses were studied than that typically used with CZT based conventional CT detectors. In addition, the effect of characteristic x-rays on the accuracy of material decomposition in spectral CT imaging was explored. It was observed that when imaging with 50-60 kVp spectra, the x-ray transmission through CZT was very low for all detector thicknesses studied (0.5–3.0 mm), thus retaining dose efficiency. As expected, characteristic x-ray escape from the detector element of x-ray interaction increased with decreasing detector element size, approaching a 50% escape fraction for a 100 μm size detector element. The detector point spread function was observed to have only minor degradation with detector element size greater than 200 μm and lower kV settings. Characteristic x-rays produced increasing distortion in the spectral response with decreasing detector element size. If not corrected for, this caused a large bias in estimating tissue density parameters for material decomposition. It was also observed that degradation of the spectral response due to characteristic x-rays caused worsening precision in the estimation of tissue density parameters. It was observed that characteristic x-rays do cause some degradation in the spatial and spectral resolution of thin CZT detectors operating under breast CT conditions. These degradations should be manageable with careful selection of the detector element size. Even with the observed spectral distortion from characteristic x-rays, it is still possible to correctly estimate tissue parameters for material decomposition using spectral CT if accurate modeling is used. PMID:24187383

Children with Heavy Prenatal Alcohol Exposure have Different Frequency Domain Signal Characteristics when Producing Isometric Force

PubMed Central

Nguyen, Tanya T.; Ashrafi, Ashkan; Thomas, Jennifer D.; Riley, Edward P.; Simmons, Roger W.

2013-01-01

To extend our current understanding of the teratogenic effects of prenatal alcohol exposure on the control of isometric force, the present study investigated the signal characteristics of power spectral density functions resulting from sustained control of isometric force by children with and without heavy prenatal exposure to alcohol. It was predicted that the functions associated with the force signals would be fundamentally different for the two groups. Twenty-five children aged between 7 and 17 years with heavy prenatal alcohol exposure and 21 non-alcohol exposed control children attempted to duplicate a visually represented target force by pressing on a load cell. The level of target force (5 and 20% of maximum voluntary contraction) and the time interval between visual feedback (20ms, 320ms and 740ms) were manipulated. A multivariate spectral estimation method with sinusoidal windows was applied to individual isometric force-time signals. Analysis of the resulting power spectral density functions revealed that the alcohol-exposed children had a lower mean frequency, less spectral variability, greater peak power and a lower frequency at which peak power occurred. Furthermore, mean frequency and spectral variability produced by the alcohol-exposed group remained constant across target load and visual feedback interval, suggesting that these children were limited to making long-time scale corrections to the force signal. In contrast, the control group produced decreased mean frequency and spectral variability as target force and the interval between visual feedback increased, indicating that when feedback was frequently presented these children used the information to make short-time scale adjustments to the ongoing force signal. Knowledge of these differences could facilitate the design of motor rehabilitation exercises that specifically target isometric force control deficits in alcohol-exposed children. PMID:23238099

EVOLUTION OF GALAXIES AND THEIR ENVIRONMENTS AT z = 0.1-3 IN COSMOS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scoville, N.; Benson, A.; Fu, Hai

2013-05-01

Large-scale structures (LSSs) out to z < 3.0 are measured in the Cosmic Evolution Survey (COSMOS) using extremely accurate photometric redshifts (photoz). The K{sub s} -band-selected sample (from Ultra-Vista) is comprised of 155,954 galaxies. Two techniques-adaptive smoothing and Voronoi tessellation-are used to estimate the environmental densities within 127 redshift slices. Approximately 250 statistically significant overdense structures are identified out to z = 3.0 with shapes varying from elongated filamentary structures to more circularly symmetric concentrations. We also compare the densities derived for COSMOS with those based on semi-analytic predictions for a {Lambda}CDM simulation and find excellent overall agreement between themore » mean densities as a function of redshift and the range of densities. The galaxy properties (stellar mass, spectral energy distributions (SEDs), and star formation rates (SFRs)) are strongly correlated with environmental density and redshift, particularly at z < 1.0-1.2. Classifying the spectral type of each galaxy using the rest-frame b - i color (from the photoz SED fitting), we find a strong correlation of early-type galaxies (E-Sa) with high-density environments, while the degree of environmental segregation varies systematically with redshift out to z {approx} 1.3. In the highest density regions, 80% of the galaxies are early types at z = 0.2 compared to only 20% at z = 1.5. The SFRs and the star formation timescales exhibit clear environmental correlations. At z > 0.8, the SFR density is uniformly distributed over all environmental density percentiles, while at lower redshifts the dominant contribution is shifted to galaxies in lower density environments.« less

Enhanced Radio Frequency (RF) Collection With Distributed Wireless Sensor Networks

DTIC Science & Technology

2007-06-01

48 4. Controlling the Size of the Beamwidth ............................................50 C. SPECTRAL ESTIMATION...55 Figure 35. Spectral Estimation results 157 MHz. .............................................................58 Figure 36. Spectral ...Estimation results 800 MHz. .............................................................59 Figure 37. Spectral Estimation results 2.4 GHz

Parameterization of spectral baseline directly from short echo time full spectra in 1 H-MRS.

PubMed

Lee, Hyeong Hun; Kim, Hyeonjin

2017-09-01

To investigate the feasibility of parameterizing macromolecule (MM) resonances directly from short echo time (TE) spectra rather than pre-acquired, T 1 -weighted, metabolite-nulled spectra in 1 H-MRS. Initial line parameters for metabolites and MMs were set for rat brain spectra acquired at 9.4 Tesla upon a priori knowledge. Then, MM line parameters were optimized over several steps with fixed metabolite line parameters. The proposed method was tested by estimating metabolite T 1 . The results were compared with those obtained with two existing methods. Furthermore, subject-specific, spin density-weighted, MM model spectra were generated according to the MM line parameters from the proposed method for metabolite quantification. The results were compared with those obtained with subject-specific, T 1 -weighted, metabolite-nulled spectra. The metabolite T 1 were largely in close agreement among the three methods. The spin density-weighted MM resonances from the proposed method were in good agreement with the T 1 -weighted, metabolite-nulled spectra except for the MM resonance at ∼3.2 ppm. The metabolite concentrations estimated by incorporating these two different spectral baselines were also in good agreement except for several metabolites with resonances at ∼3.2 ppm. The MM parameterization directly from short-TE spectra is feasible. Further development of the method may allow for better representation of spectral baseline with negligible T 1 -weighting. Magn Reson Med 78:836-847, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

A Search for Fast Radio Bursts with the GBNCC Pulsar Survey

NASA Astrophysics Data System (ADS)

Chawla, P.; Kaspi, V. M.; Josephy, A.; Rajwade, K. M.; Lorimer, D. R.; Archibald, A. M.; DeCesar, M. E.; Hessels, J. W. T.; Kaplan, D. L.; Karako-Argaman, C.; Kondratiev, V. I.; Levin, L.; Lynch, R. S.; McLaughlin, M. A.; Ransom, S. M.; Roberts, M. S. E.; Stairs, I. H.; Stovall, K.; Swiggum, J. K.; van Leeuwen, J.

2017-08-01

We report on a search for fast radio bursts (FRBs) with the Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey at 350 MHz. Pointings amounting to a total on-sky time of 61 days were searched to a dispersion measure (DM) of 3000 pc cm-3, while the rest (23 days; 29% of the total time) were searched to a DM of 500 pc cm-3. No FRBs were detected in the pointings observed through 2016 May. We estimate a 95% confidence upper limit on the FRB rate of 3.6× {10}3 FRBs sky-1 day-1 above a peak flux density of 0.63 Jy at 350 MHz for an intrinsic pulse width of 5 ms. We place constraints on the spectral index α by running simulations for different astrophysical scenarios and cumulative flux density distributions. The nondetection with GBNCC is consistent with the 1.4 GHz rate reported for the Parkes surveys for α > +0.35 in the absence of scattering and free-free absorption and α > -0.3 in the presence of scattering, for a Euclidean flux distribution. The constraints imply that FRBs exhibit either a flat spectrum or a spectral turnover at frequencies above 400 MHz. These constraints also allow estimation of the number of bursts that can be detected with current and upcoming surveys. We predict that CHIME may detect anywhere from several to ˜50 FRBs per day (depending on model assumptions), making it well suited for interesting constraints on spectral index, the log N-log S slope, and pulse profile evolution across its bandwidth (400-800 MHz).

WE-DE-207B-04: Quantitative Contrast-Enhanced Spectral Mammography Based On Photon-Counting Detectors: A Feasibility Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, H; Zhou, B; Beidokhti, D

Purpose: To investigate the feasibility of accurate quantification of iodine mass thickness in contrast-enhanced spectral mammography. Methods: Experimental phantom studies were performed on a spectral mammography system based on Si strip photon-counting detectors. Dual-energy images were acquired using 40 kVp and a splitting energy of 34 keV with 3 mm Al pre-filtration. The initial calibration was done with glandular and adipose tissue equivalent phantoms of uniform thicknesses and iodine disk phantoms of various concentrations. A secondary calibration was carried out using the iodine signal obtained from the dual-energy decomposed images and the known background phantom thicknesses and densities. The iodinemore » signal quantification method was validated using phantoms composed of a mixture of glandular and adipose materials, for various breast thicknesses and densities. Finally, the traditional dual-energy weighted subtraction method was also studied as a comparison. The measured iodine signal from both methods was compared to the known iodine concentrations of the disk phantoms to characterize the quantification accuracy. Results: There was good agreement between the iodine mass thicknesses measured using the proposed method and the known values. The root-mean-square (RMS) error was estimated to be 0.2 mg/cm2. The traditional weighted subtraction method also predicted a linear correlation between the measured signal and the known iodine mass thickness. However, the correlation slope and offset values were strongly dependent on the total breast thickness and density. Conclusion: The results of the current study suggest that iodine mass thickness can be accurately quantified with contrast-enhanced spectral mammography. The quantitative information can potentially improve the differentiation between benign and malignant legions. Grant funding from Philips Medical Systems.« less

Power-law statistics of neurophysiological processes analyzed using short signals

NASA Astrophysics Data System (ADS)

Pavlova, Olga N.; Runnova, Anastasiya E.; Pavlov, Alexey N.

2018-04-01

We discuss the problem of quantifying power-law statistics of complex processes from short signals. Based on the analysis of electroencephalograms (EEG) we compare three interrelated approaches which enable characterization of the power spectral density (PSD) and show that an application of the detrended fluctuation analysis (DFA) or the wavelet-transform modulus maxima (WTMM) method represents a useful way of indirect characterization of the PSD features from short data sets. We conclude that despite DFA- and WTMM-based measures can be obtained from the estimated PSD, these tools outperform the standard spectral analysis when characterization of the analyzed regime should be provided based on a very limited amount of data.

Indices of refraction for the HITRAN compilation

NASA Technical Reports Server (NTRS)

Massie, S. T.

1994-01-01

Indices of refraction of sulfuric acid solutions, water, and ice, which will become part of the HITRAN database, are discussed. Representative calculations are presented for the sulfate aerosol, to illustrate the broadband spectral features of i.r. aerosol extinction spectra. Values of the sulfuric acid mass density are used in an application of the Lorentz-Lorenz equation, which is used to estimate the sensitivity of extinction coefficients to temperature dependent refractive indices.

Vector and Axial-Vector Current Correlators Within the Instanton Model of QCD Vacuum

NASA Astrophysics Data System (ADS)

Dorokhov, A. E.

2005-08-01

The pion electric polarizability, α {π ^ ± }E , the leading order hadronic contribution to the muon anomalous magnetic moment, aμ hvp(1) , and the ratio of the V - A and V + A correlators are found within the instanton model of QCD vacuum. The results are compared with phenomenological estimates of these quantities from the ALEPH and OPAL data on vector and axial-vector spectral densities.

The Seismic Tool-Kit (STK): an open source software for seismology and signal processing.

NASA Astrophysics Data System (ADS)

Reymond, Dominique

2016-04-01

We present an open source software project (GNU public license), named STK: Seismic ToolKit, that is dedicated mainly for seismology and signal processing. The STK project that started in 2007, is hosted by SourceForge.net, and count more than 19 500 downloads at the date of writing. The STK project is composed of two main branches: First, a graphical interface dedicated to signal processing (in the SAC format (SAC_ASCII and SAC_BIN): where the signal can be plotted, zoomed, filtered, integrated, derivated, ... etc. (a large variety of IFR and FIR filter is proposed). The estimation of spectral density of the signal are performed via the Fourier transform, with visualization of the Power Spectral Density (PSD) in linear or log scale, and also the evolutive time-frequency representation (or sonagram). The 3-components signals can be also processed for estimating their polarization properties, either for a given window, or either for evolutive windows along the time. This polarization analysis is useful for extracting the polarized noises, differentiating P waves, Rayleigh waves, Love waves, ... etc. Secondly, a panel of Utilities-Program are proposed for working in a terminal mode, with basic programs for computing azimuth and distance in spherical geometry, inter/auto-correlation, spectral density, time-frequency for an entire directory of signals, focal planes, and main components axis, radiation pattern of P waves, Polarization analysis of different waves (including noize), under/over-sampling the signals, cubic-spline smoothing, and linear/non linear regression analysis of data set. A MINimum library of Linear AlGebra (MIN-LINAG) is also provided for computing the main matrix process like: QR/QL decomposition, Cholesky solve of linear system, finding eigen value/eigen vectors, QR-solve/Eigen-solve of linear equations systems ... etc. STK is developed in C/C++, mainly under Linux OS, and it has been also partially implemented under MS-Windows. Usefull links: http://sourceforge.net/projects/seismic-toolkit/ http://sourceforge.net/p/seismic-toolkit/wiki/browse_pages/

Carrier-density dependence of photoluminescence from localized states in InGaN/GaN quantum wells in nanocolumns and a thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimosako, N., E-mail: n-shimosako@sophia.jp; Inose, Y.; Satoh, H.

2015-11-07

We have measured and analyzed the carrier-density dependence of photoluminescence (PL) spectra and the PL efficiency of InGaN/GaN multiple quantum wells in nanocolumns and in a thin film over a wide excitation range. The localized states parameters, such as the tailing parameter, density and size of the localized states, and the mobility edge density are estimated. The spectral change and reduction of PL efficiency are explained by filling of the localized states and population into the extended states around the mobility edge density. We have also found that the nanocolumns have a narrower distribution of the localized states and amore » higher PL efficiency than those of the film sample although the In composition of the nanocolumns is higher than that of the film.« less

Assessing NIR & MIR Spectral Analysis as a Method for Soil C Estimation Across a Network of Sampling Sites

NASA Astrophysics Data System (ADS)

Spencer, S.; Ogle, S.; Borch, T.; Rock, B.

2008-12-01

Monitoring soil C stocks is critical to assess the impact of future climate and land use change on carbon sinks and sources in agricultural lands. A benchmark network for soil carbon monitoring of stock changes is being designed for US agricultural lands with 3000-5000 sites anticipated and re-sampling on a 5- to10-year basis. Approximately 1000 sites would be sampled per year producing around 15,000 soil samples to be processed for total, organic, and inorganic carbon, as well as bulk density and nitrogen. Laboratory processing of soil samples is cost and time intensive, therefore we are testing the efficacy of using near-infrared (NIR) and mid-infrared (MIR) spectral methods for estimating soil carbon. As part of an initial implementation of national soil carbon monitoring, we collected over 1800 soil samples from 45 cropland sites in the mid-continental region of the U.S. Samples were processed using standard laboratory methods to determine the variables above. Carbon and nitrogen were determined by dry combustion and inorganic carbon was estimated with an acid-pressure test. 600 samples are being scanned using a bench- top NIR reflectance spectrometer (30 g of 2 mm oven-dried soil and 30 g of 8 mm air-dried soil) and 500 samples using a MIR Fourier-Transform Infrared Spectrometer (FTIR) with a DRIFT reflectance accessory (0.2 g oven-dried ground soil). Lab-measured carbon will be compared to spectrally-estimated carbon contents using Partial Least Squares (PLS) multivariate statistical approach. PLS attempts to develop a soil C predictive model that can then be used to estimate C in soil samples not lab-processed. The spectral analysis of soil samples either whole or partially processed can potentially save both funding resources and time to process samples. This is particularly relevant for the implementation of a national monitoring network for soil carbon. This poster will discuss our methods, initial results and potential for using NIR and MIR spectral approaches to either replace or augment traditional lab-based carbon analyses of soils.

Estimation of the radial diffusion coefficient using REE-associated ground Pc 5 pulsations

NASA Astrophysics Data System (ADS)

Fujimoto, A.; Yumoto, K.

2010-12-01

Pc 5 pulsations with frequencies between 1.67 and 6.67 mHz are believed to contribute to the REE in the outer radiation belt during magnetic storms, by means of the observations [Baker et al., 1998; Rostoker et al., 1998; Mathie and Mann, 2000; O'Brien et al., 2001, 2003] and several theoretical studies. The latter studies are roughly categorized into two themes: in-situ acceleration at L lower than 6.6 by wave-particle interactions [Liu et al., 199 9; Summers et al., 1999; Summers and Ma, 2000] and acceleration by radial diffusion from the outer to the inner magnetosphere [Elkington et al., 1999, 2003; Hudson et al., 2000; Kim et al., 2001]. One possible acceleration mechanism is the resonant interaction with Pc 5 toroidal and poloidal pulsations, referred as the radial diffusion mechanism. One of unsolved problems is where and which Pc 5 pulsation mode (toroidal and/or poloidal) play effective role in the radial diffusion process. In order to verify Pc 5 pulsation as the major roles for REEs, we have to examine the time variation of electron phase space density (cf. Green et al., 2004). Electron phase space density is not directly measured, but we can estimate radial diffusion coefficients which determine the electron transportation efficiency, using ground-based magnetic field data. We estimated the radial diffusion coefficient of ground Pc 5 pulsations associated with the Relativistic Electron Enhancement (REE) in the geosynchronous orbit. In order to estimate the radial diffusion coefficient D_LL, we need the value of in-situ Pc 5 electric field power spectral density. In this paper, however, we estimated the equatorial electric field mapped from Pc 5 pulsations power spectral density on the ground. Reciprocal of radial diffusion coefficient describes the timescale T_LL for an electron to diffuse 1 Re. Applying a superposed epoch analysis about timescales T_LL of the radial diffusion for 12 REE events in 2008, we found that when the relativistic electron enhancements occur, T_LL at higher latitude (L larger than 5) is predominantly diffusional, whereas T_LL at lower latitude (L less than 4) is mainly convectional. We concluded that higher-latitude Pc 5 pulsations play more effective roles than lower latitude Pc 5 pulsations in the radial diffusion process.

Estimating maximum instantaneous distortion from inlet total pressure rms and PSD measurements. [Root Mean Square and Power Spectral Density methods

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.

Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

PubMed

Almeida, G F B; Martins, R J; Otuka, A J G; Siqueira, J P; Mendonca, C R

2015-10-19

We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring.

Electron-boson spectral density function of correlated multiband systems obtained from optical data: Ba0.6K0.4Fe2As2 and LiFeAs.

PubMed

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.

Effect of manmade pixels on the inherent dimension of natural material distributions

NASA Astrophysics Data System (ADS)

Schlamm, Ariel; Messinger, David; Basener, William

2009-05-01

The inherent dimension of hyperspectral data may be a useful metric for discriminating between the presence of manmade and natural materials in a scene without reliance on spectral signatures take from libraries. Previously, a simple geometric method for approximating the inherent dimension was introduced along with results from application to single material clusters. This method uses an estimate of the slope from a graph based on the point density estimation in the spectral space. Other information can be gathered from the plot which may aid in the discrimination between manmade and natural materials. In order to use these measures to differentiate between the two material types, the effect of the inclusion of manmade pixels on the phenomenology of the background distribution must be evaluated. Here, a procedure for injecting manmade pixels into a natural region of a scene is discussed. The results of dimension estimation on natural scenes with varying amounts of manmade pixels injected are presented here, indicating that these metrics can be sensitive to the presence of manmade phenomenology in an image.

Preliminary comparison between real-time in-vivo spectral and transverse oscillation velocity estimates

NASA Astrophysics Data System (ADS)

Pedersen, Mads Møller; Pihl, Michael Johannes; Haugaard, Per; Hansen, Jens Munk; Lindskov Hansen, Kristoffer; Bachmann Nielsen, Michael; Jensen, Jørgen Arendt

2011-03-01

Spectral velocity estimation is considered the gold standard in medical ultrasound. Peak systole (PS), end diastole (ED), and resistive index (RI) are used clinically. Angle correction is performed using a flow angle set manually. With Transverse Oscillation (TO) velocity estimates the flow angle, peak systole (PSTO), end diastole (EDTO), and resistive index (RITO) are estimated. This study investigates if these clinical parameters are estimated equally good using spectral and TO data. The right common carotid arteries of three healthy volunteers were scanned longitudinally. Average TO flow angles and std were calculated { 52+/-18 ; 55+/-23 ; 60+/-16 }°. Spectral angles { 52 ; 56 ; 52 }° were obtained from the B-mode images. Obtained values are: PSTO { 76+/-15 ; 89+/-28 ; 77+/-7 } cm/s, spectral PS { 77 ; 110 ; 76 } cm/s, EDTO { 10+/-3 ; 14+/-8 ; 15+/-3 } cm/s, spectral ED { 18 ; 13 ; 20 } cm/s, RITO { 0.87+/-0.05 ; 0.79+/-0.21 ; 0.79+/-0.06 }, and spectral RI { 0.77 ; 0.88 ; 0.73 }. Vector angles are within +/-two std of the spectral angle. TO velocity estimates are within +/-three std of the spectral estimates. RITO are within +/-two std of the spectral estimates. Preliminary data indicates that the TO and spectral velocity estimates are equally good. With TO there is no manual angle setting and no flow angle limitation. TO velocity estimation can also automatically handle situations where the angle varies over the cardiac cycle. More detailed temporal and spatial vector estimates with diagnostic potential are available with the TO velocity estimation.

Underwater Sound Radiation from Large Raindrops

DTIC Science & Technology

1991-09-01

decreasing shape of the impact spectrum, one must pick a reference point rather that a peak value to compare one drop with another. For comparison of...34 1. Type I Bubble Spectral Density and Peak Pressure ............... 34 2. Type II Bubble Average Spectral Densities at 1 m on Axis (20 C...32 Table 4. TYPE II BUBBLE AVERAGE PEAK SPECTRAL DENSITY SU M M A RY ............................................. 39 Table 5. SUMMARY

A Novel Technique Applying Spectral Estimation to Johnson Noise Thermometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ezell, N. Dianne Bull; Britton, Chuck; Ericson, Nance

Johnson noise thermometry is one of many important measurement techniques used to monitor the safety levels and stability in a nuclear reactor. However, this measurement is very dependent on the minimal electromagnetic environment. Properly removing unwanted electromagnetic interference (EMI) is critical for accurate drift-free temperature measurements. The two techniques developed by Oak Ridge National Laboratory (ORNL) to remove transient and periodic EMI are briefly discussed here. Spectral estimation is a key component in the signal processing algorithm used for EMI removal and temperature calculation. The cross-power spectral density is a key component in the Johnson noise temperature computation. Applying eithermore » technique requires the simple addition of electronics and signal processing to existing resistive thermometers. With minimal installation changes, the system discussed here can be installed on existing nuclear power plants. The Johnson noise system developed is tested at three locations: ORNL, Sandia National Laboratory, and the Tennessee Valley Authority’s Kingston Fossil Plant. Each of these locations enabled improvement on the EMI removal algorithm. Finally, the conclusions made from the results at each of these locations is discussed, as well as possible future work.« less

A Novel Technique Applying Spectral Estimation to Johnson Noise Thermometry

DOE PAGES

Ezell, N. Dianne Bull; Britton, Chuck; Ericson, Nance; ...

2018-03-30

Johnson noise thermometry is one of many important measurement techniques used to monitor the safety levels and stability in a nuclear reactor. However, this measurement is very dependent on the minimal electromagnetic environment. Properly removing unwanted electromagnetic interference (EMI) is critical for accurate drift-free temperature measurements. The two techniques developed by Oak Ridge National Laboratory (ORNL) to remove transient and periodic EMI are briefly discussed here. Spectral estimation is a key component in the signal processing algorithm used for EMI removal and temperature calculation. The cross-power spectral density is a key component in the Johnson noise temperature computation. Applying eithermore » technique requires the simple addition of electronics and signal processing to existing resistive thermometers. With minimal installation changes, the system discussed here can be installed on existing nuclear power plants. The Johnson noise system developed is tested at three locations: ORNL, Sandia National Laboratory, and the Tennessee Valley Authority’s Kingston Fossil Plant. Each of these locations enabled improvement on the EMI removal algorithm. Finally, the conclusions made from the results at each of these locations is discussed, as well as possible future work.« less

Wavelet Based Characterization of Low Radio Frequency Solar Emissions

NASA Astrophysics Data System (ADS)

Suresh, A.; Sharma, R.; Das, S. B.; Oberoi, D.; Pankratius, V.; Lonsdale, C.

2016-12-01

Low-frequency solar radio observations with the Murchison Widefield Array (MWA) have revealed the presence of numerous short-lived, narrow-band weak radio features, even during quiet solar conditions. In their appearance in in the frequency-time plane, they come closest to the solar type III bursts, but with much shorter spectral spans and flux densities, so much so that they are not detectable with the usual swept frequency radio spectrographs. These features occur at rates of many thousand features per hour in the 30.72 MHz MWA bandwidth, and hence necessarily require an automated approach to determine robust statistical estimates of their properties, e.g., distributions of spectral widths, temporal spans, flux densities, slopes in the time-frequency plane and distribution over frequency. To achieve this, a wavelet decomposition approach has been developed for feature recognition and subsequent parameter extraction from the MWA dynamic spectrum. This work builds on earlier work by the members of this team to achieve a reliable flux calibration in a computationally efficient manner. Preliminary results show that the distribution of spectral span of these features peaks around 3 MHz, most of them last for less than two seconds and are characterized by flux densities of about 60% of the background solar emission. In analogy with the solar type III bursts, this non-thermal emission is envisaged to arise via coherent emission processes. There is also an exciting possibility that these features might correspond to radio signatures of nanoflares, hypothesized (Gold, 1964; Parker, 1972) to explain coronal heating.

A Fiber-Optic System Generating Pulses of High Spectral Density

NASA Astrophysics Data System (ADS)

Abramov, A. S.; Zolotovskii, I. O.; Korobko, D. A.; Fotiadi, A. A.

2018-03-01

A cascade fiber-optic system that generates pulses of high spectral density by using the effect of nonlinear spectral compression is proposed. It is demonstrated that the shape of the pulse envelope substantially influences the degree of compression of its spectrum. In so doing, maximum compression is achieved for parabolic pulses. The cascade system includes an optical fiber exhibiting normal dispersion that decreases along the fiber length, thereby ensuring that the pulse envelope evolves toward a parabolic shape, along with diffraction gratings and a fiber spectral compressor. Based on computer simulation, we determined parameters of cascade elements leading to maximum spectral density of radiation originating from a subpicosecond laser pulse of medium energy.

Review of Quantitative Ultrasound: Envelope Statistics and Backscatter Coefficient Imaging and Contributions to Diagnostic Ultrasound.

PubMed

Oelze, Michael L; Mamou, Jonathan

2016-02-01

Conventional medical imaging technologies, including ultrasound, have continued to improve over the years. For example, in oncology, medical imaging is characterized by high sensitivity, i.e., the ability to detect anomalous tissue features, but the ability to classify these tissue features from images often lacks specificity. As a result, a large number of biopsies of tissues with suspicious image findings are performed each year with a vast majority of these biopsies resulting in a negative finding. To improve specificity of cancer imaging, quantitative imaging techniques can play an important role. Conventional ultrasound B-mode imaging is mainly qualitative in nature. However, quantitative ultrasound (QUS) imaging can provide specific numbers related to tissue features that can increase the specificity of image findings leading to improvements in diagnostic ultrasound. QUS imaging can encompass a wide variety of techniques including spectral-based parameterization, elastography, shear wave imaging, flow estimation, and envelope statistics. Currently, spectral-based parameterization and envelope statistics are not available on most conventional clinical ultrasound machines. However, in recent years, QUS techniques involving spectral-based parameterization and envelope statistics have demonstrated success in many applications, providing additional diagnostic capabilities. Spectral-based techniques include the estimation of the backscatter coefficient (BSC), estimation of attenuation, and estimation of scatterer properties such as the correlation length associated with an effective scatterer diameter (ESD) and the effective acoustic concentration (EAC) of scatterers. Envelope statistics include the estimation of the number density of scatterers and quantification of coherent to incoherent signals produced from the tissue. Challenges for clinical application include correctly accounting for attenuation effects and transmission losses and implementation of QUS on clinical devices. Successful clinical and preclinical applications demonstrating the ability of QUS to improve medical diagnostics include characterization of the myocardium during the cardiac cycle, cancer detection, classification of solid tumors and lymph nodes, detection and quantification of fatty liver disease, and monitoring and assessment of therapy.

Review of quantitative ultrasound: envelope statistics and backscatter coefficient imaging and contributions to diagnostic ultrasound

PubMed Central

Oelze, Michael L.; Mamou, Jonathan

2017-01-01

Conventional medical imaging technologies, including ultrasound, have continued to improve over the years. For example, in oncology, medical imaging is characterized by high sensitivity, i.e., the ability to detect anomalous tissue features, but the ability to classify these tissue features from images often lacks specificity. As a result, a large number of biopsies of tissues with suspicious image findings are performed each year with a vast majority of these biopsies resulting in a negative finding. To improve specificity of cancer imaging, quantitative imaging techniques can play an important role. Conventional ultrasound B-mode imaging is mainly qualitative in nature. However, quantitative ultrasound (QUS) imaging can provide specific numbers related to tissue features that can increase the specificity of image findings leading to improvements in diagnostic ultrasound. QUS imaging techniques can encompass a wide variety of techniques including spectral-based parameterization, elastography, shear wave imaging, flow estimation and envelope statistics. Currently, spectral-based parameterization and envelope statistics are not available on most conventional clinical ultrasound machines. However, in recent years QUS techniques involving spectral-based parameterization and envelope statistics have demonstrated success in many applications, providing additional diagnostic capabilities. Spectral-based techniques include the estimation of the backscatter coefficient, estimation of attenuation, and estimation of scatterer properties such as the correlation length associated with an effective scatterer diameter and the effective acoustic concentration of scatterers. Envelope statistics include the estimation of the number density of scatterers and quantification of coherent to incoherent signals produced from the tissue. Challenges for clinical application include correctly accounting for attenuation effects and transmission losses and implementation of QUS on clinical devices. Successful clinical and pre-clinical applications demonstrating the ability of QUS to improve medical diagnostics include characterization of the myocardium during the cardiac cycle, cancer detection, classification of solid tumors and lymph nodes, detection and quantification of fatty liver disease, and monitoring and assessment of therapy. PMID:26761606

Resolvent estimates in homogenisation of periodic problems of fractional elasticity

NASA Astrophysics Data System (ADS)

Cherednichenko, Kirill; Waurick, Marcus

2018-03-01

We provide operator-norm convergence estimates for solutions to a time-dependent equation of fractional elasticity in one spatial dimension, with rapidly oscillating coefficients that represent the material properties of a viscoelastic composite medium. Assuming periodicity in the coefficients, we prove operator-norm convergence estimates for an operator fibre decomposition obtained by applying to the original fractional elasticity problem the Fourier-Laplace transform in time and Gelfand transform in space. We obtain estimates on each fibre that are uniform in the quasimomentum of the decomposition and in the period of oscillations of the coefficients as well as quadratic with respect to the spectral variable. On the basis of these uniform estimates we derive operator-norm-type convergence estimates for the original fractional elasticity problem, for a class of sufficiently smooth densities of applied forces.

Analysis and prediction of ocean swell using instrumented buoys

NASA Technical Reports Server (NTRS)

Mettlach, Theodore; Wang, David; Wittmann, Paul

1994-01-01

During the period 20-23 September 1990, the remnants of Supertyphoon Flo moved into the central North Pacific Ocean with sustained wind speeds of 28 m/s. The strong wind and large fetch area associated with this storm generated long-period swell that propagated to the west coast of North America. National Data Buoy Center moored-buoy stations, located in a network that ranged from the Gulf of Alaska to the California Bight, provided wave spectral estimates of the swell from this storm. The greatest dominant wave periods measured were approximately 20-25 s, and significant wave heights measured ranged from 3 to 8 m. Wave spectra from an array of three nondirectional buoys are used to find the source of the long-period swell. Directional wave spectra from a heave-pitch-roll buoy are also used to make an independent estimate of the source of the swell. The ridge-line method, using time-frequency contour plots of wave spectral energy density, is used to determine the time of swell generation, which is used with the appropriate surface pressure analysis to infer the swell generation area. The diagnosed sources of the swell are also compared with nowcasts from the Global Spectral Ocean Wave Model of the Fleet Numerical Oceanography Center. A simple method of predicting the propagation of ocean swell, by applying a simple kinematic model of wave propagation to the estimated point and time source, is demonstrated.

Quantification of breast density with spectral mammography based on a scanned multi-slit photon-counting detector: A feasibility study

PubMed Central

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 approximately 1.54% using standard calibration function. The results from the modified fitting function, which integrated the tube voltage as a variable in the calibration, indicated a RMS error of approximately 1.35% for all four studies. Conclusions The results of the current study suggest that photon-counting spectral mammography systems may potentially be implemented for an accurate quantification of volumetric breast density, with an RMS error of less than 2%, using the proposed dual energy imaging technique. PMID:22771941

Predicting Anthropogenic Noise Contributions to US Waters.

PubMed

Gedamke, Jason; Ferguson, Megan; Harrison, Jolie; Hatch, Leila; Henderson, Laurel; Porter, Michael B; Southall, Brandon L; Van Parijs, Sofie

2016-01-01

To increase understanding of the potential effects of chronic underwater noise in US waters, the National Oceanic and Atmospheric Administration (NOAA) organized two working groups in 2011, collectively called "CetSound," to develop tools to map the density and distribution of cetaceans (CetMap) and predict the contribution of human activities to underwater noise (SoundMap). The SoundMap effort utilized data on density, distribution, acoustic signatures of dominant noise sources, and environmental descriptors to map estimated temporal, spatial, and spectral contributions to background noise. These predicted soundscapes are an initial step toward assessing chronic anthropogenic noise impacts on the ocean's varied acoustic habitats and the animals utilizing them.

Predicting stem borer density in maize using RapidEye data and generalized linear models

NASA Astrophysics Data System (ADS)

Abdel-Rahman, Elfatih M.; Landmann, Tobias; Kyalo, Richard; Ong'amo, George; Mwalusepo, Sizah; Sulieman, Saad; Ru, Bruno Le

2017-05-01

Average maize yield in eastern Africa is 2.03 t ha-1 as compared to global average of 6.06 t ha-1 due to biotic and abiotic constraints. Amongst the biotic production constraints in Africa, stem borers are the most injurious. In eastern Africa, maize yield losses due to stem borers are currently estimated between 12% and 21% of the total production. The objective of the present study was to explore the possibility of RapidEye spectral data to assess stem borer larva densities in maize fields in two study sites in Kenya. RapidEye images were acquired for the Bomet (western Kenya) test site on the 9th of December 2014 and on 27th of January 2015, and for Machakos (eastern Kenya) a RapidEye image was acquired on the 3rd of January 2015. Five RapidEye spectral bands as well as 30 spectral vegetation indices (SVIs) were utilized to predict per field maize stem borer larva densities using generalized linear models (GLMs), assuming Poisson ('Po') and negative binomial ('NB') distributions. Root mean square error (RMSE) and ratio prediction to deviation (RPD) statistics were used to assess the models performance using a leave-one-out cross-validation approach. The Zero-inflated NB ('ZINB') models outperformed the 'NB' models and stem borer larva densities could only be predicted during the mid growing season in December and early January in both study sites, respectively (RMSE = 0.69-1.06 and RPD = 8.25-19.57). Overall, all models performed similar when all the 30 SVIs (non-nested) and only the significant (nested) SVIs were used. The models developed could improve decision making regarding controlling maize stem borers within integrated pest management (IPM) interventions.

Parameters of the flare and surrounding medium and their evolution during 20 January 2005 solar event

NASA Astrophysics Data System (ADS)

Troitskaia, E.; Arkhangelskaja, I.; Arkhangelsky, A.; Gan, W.

2013-02-01

Basing on the data of AVS-F apparatus from SONG-D detector onboard CORONAS-F satellite, we have studied the extreme solar event of January 20, 2005 used the 2.223 MeV, 4.44 MeV and 6.13 MeV γ-lines temporal profiles. By the statistical modeling method we calculated the temporal profile of 2.223 MeV line too. Calculations have been performed in assumption of Bessel type of accelerated particles energy spectrum, different 3He content in the region of nuclear reactions and several density models of the solar atmosphere. Comparisons of the results of modeling with observational 2.223 MeV AVS-F/SONG-D data reveal the increasing of the ratio of 3He concentration to 1H one during the flare from 2× 10-5 at the rise phase of the gamma-ray flux up to 2× 10--4 at the decay one. During the same period the spectrum became harder and the density of solar atmosphere increased too. Averaged over full time of 2.223 MeV γ-emission concentration ratio of 3He/1H is equal to (1.40±0.15)×10--4, also the density model with enlarged density up to 2×1017 cm-3 in the lower chromosphere and through the whole photosphere is realized. Besides, we have estimated the spectral index αT that is close to 0.1 for accelerated protons in the range of 1-100 MeV. Using the AVS-F gamma-rays spectral data in the wide range up to 140 MeV, we have obtained the spectral index of s=2.5±0.1 in the case of power law spectrum for energies more than 300 MeV.

[The sawtooth oscillation phenomenon of visible spectral signal in HT-6M Tokamak].

PubMed

Xu, W; Fang, Z; Wan, B; Li, J; Luo, J; Yin, F

1997-02-01

The sawtooth oscillation phenomenon of visible spectral signal in HT-6M Tokamak is presented. The influences of electron temperature, electron density and atomic ground density on the spectral signal discussed. This phenomenon results mainly from the change of electron temperature at the edge.

Combined natural gamma ray spectral/litho-density measurements applied to complex lithologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quirein, J.A.; Gardner, J.S.; Watson, J.T.

1982-09-01

Well log data has long been used to provide lithological descriptions of complex formations. Historically, most of the approaches used have been restrictive because they assumed fixed, known, and distinct lithologies for specified zones. The approach described in this paper attempts to alleviate this restriction by estimating the ''probability of a model'' for the models suggested as most likely by the reservoir geology. Lithological variables are simultaneously estimated from response equations for each model and combined in accordance with the probability of each respective model. The initial application of this approach has been the estimation of calcite, quartz, and dolomitemore » in the presence of clays, feldspars, anhydrite, or salt. Estimations were made by using natural gamma ray spectra, photoelectric effect, bulk density, and neutron porosity information. For each model, response equations and parameter selections are obtained from the thorium vs potassium crossplot and the apparent matrix density vs apparent volumetric photoelectric cross section crossplot. The thorium and potassium response equations are used to estimate the volumes of clay and feldspar. The apparent matrix density and volumetric cross section response equations can then be corrected for the presence of clay and feldspar. A test ensures that the clay correction lies within the limits for the assumed lithology model. Results are presented for varying lithologies. For one test well, 6,000 feet were processed in a single pass, without zoning and without adjusting more than one parameter pick. The program recognized sand, limestone, dolomite, clay, feldspar, anhydrite, and salt without analyst intervention.« less

A Software Toolbox for Systematic Evaluation of Seismometer-Digitizer System Responses

DTIC Science & Technology

2010-09-01

characteristics (e.g., borehole vs. surface installation) than the actual seismic noise characteristics. These results suggest that our best results of NOISETRAN...Award No. DE-FG02-09ER85548/Phase_I ABSTRACT Measurement of the absolute amplitudes of a seismic signal requires accurate knowledge of...power spectral density (PSD) estimator for background noise spectra at a seismic station. SACPSD differs from the current PSD used by NEIC and IRIS

Remote sensing of coastal wetlands biomass using Thematic Mapper wavebands

NASA Technical Reports Server (NTRS)

Hardisky, M. A.; Klemas, V.

1985-01-01

Spectral data, simulating thematic mapper bands 3, 4 and 5 are gathered in salt and brackish marshes using a hand-held radiometer. Simple regression models are developed equating spectral radiance indices with total live biomass for S. alterniflora in a salt marsh and for a variety of plant species in a brackish marsh. Models are then tested using an independent set of data and compared to harvest estimates of biomass. In the salt marsh, biomass estimates from spectral data are similar to harvest biomass estimates during most of the growing season. Estimates of annual net aerial primary productivity calculated from spectral data are within 21% of production estimated from harvest data. During August, biomass estimates from spectral data in the brackish marsh are similar to biomass estimated by harvesting techniques. At other times during the growing season, spectral data estimates of biomass are not always comparable to harvest biomass estimates. Reasonable estimates of wetlands biomass are possible during the peak of the growing season (August) using spectral data similar to thematic mapper bands 3, 4 and 5 gathered with hand-held radiometers.

Preliminary Observations of Noise Spectra at the SRO and ASRO Stations

USGS Publications Warehouse

Peterson, Jon

1980-01-01

Introduction The seismic noise spectra presented in this report were derived from SRO and ASRO station data for the purpose of evaluating the performance of the seismic instruments. They are also useful for constructing a spectral estimate of earth noise at a quiet site based on noise samples obtained from a network of globally distributed sites. It is hoped that the spectra will be usefull for other purposes as well. The term 'noise' is used here to describe the ambient signals recorded during a quiet period when earthquake signals have not been detected by visual inspectino of the analog seismogram. The total recorded noise is the sum of instrumental noise, environmental noise (such as effects of temperature, pressure, wind), earth background noise from both natural and cultural sources, and very possibly low-level signals from earthquakes that cannot be visually identified. It is not possible to separate and quantify the signals generated by these independent noise sources using a single sample of station data, although instrumental problems may be indicated by gross changes of noise levels, if the changes are not in the microseismic bands. Since seismic data at the SRO and ASRO stations are recorded in a digital format, spectral computations can be automated so that station noise levels can be monitored as part of data-review procedures. The noise spectra presented in this study are intended to serve as an initial baseline against which relative changes in noise levels can be measured. Total noise power was computed separately for the short- and long-period bands, which are recorded separately at the stations. Power spectral densities were derived by averaging the spectral estimates of a number of contiguous dat segments. The mean value and slope were removed from each segment, cosine-tapered windows were applied, and the estimates were obtained using a fast Fourier transform. In the short-period analyses 16 segments were used, each segment being 1024 samples in length. Because the sampling interval is .05 seconds, the total record length is nearly 13.7 minutes. Normally, the short-period SRO and ASRO data are recorded in an event-only mode. However, several days of continuous short-period data were acquired from most stations for the purpose of this study. Where there was appreciable diurnal variation in short-period noise, spectral data were computed for both day and night intervals. In most cases the long-period spectral densities were obtained by averagin the estimates from 16 data segments, each segment having a length of 2048 samples. Since the long-period sampling interval in 1 second, the total record length used was nearly 9.1 hours. In a few instances, a smaller number of segments was averaged. Spectral data were computed from the vertical-component short-period signals and all three components of long-period signals. All of the spectral plots have been corrected for known instrument response and presented in units of earth displacement. With a few exceptions, the samples of noise data used were acquired during the early months of 1980, winter at some of the stations and summer at others. The starting times for the intervals analyzed are listed in Table 1. A seasonal variation of noise levels in microseismic bands is to be expected. However, none of the stations were experiencing a noticeably high level of microseisms during the intervals analyzed. Weltman and others (1979) have studied and reported daily and seasonal RMS (root-mean-square) noise trends at the SRO and ASRO stations.

Parametric Power Spectral Density Analysis of Noise from Instrumentation in MALDI TOF Mass Spectrometry

PubMed Central

Shin, Hyunjin; Mutlu, Miray; Koomen, John M.; Markey, Mia K.

2007-01-01

Noise in mass spectrometry can interfere with identification of the biochemical substances in the sample. For example, the electric motors and circuits inside the mass spectrometer or in nearby equipment generate random noise that may distort the true shape of mass spectra. This paper presents a stochastic signal processing approach to analyzing noise from electrical noise sources (i.e., noise from instrumentation) in MALDI TOF mass spectrometry. Noise from instrumentation was hypothesized to be a mixture of thermal noise, 1/f noise, and electric or magnetic interference in the instrument. Parametric power spectral density estimation was conducted to derive the power distribution of noise from instrumentation with respect to frequencies. As expected, the experimental results show that noise from instrumentation contains 1/f noise and prominent periodic components in addition to thermal noise. These periodic components imply that the mass spectrometers used in this study may not be completely shielded from the internal or external electrical noise sources. However, according to a simulation study of human plasma mass spectra, noise from instrumentation does not seem to affect mass spectra significantly. In conclusion, analysis of noise from instrumentation using stochastic signal processing here provides an intuitive perspective on how to quantify noise in mass spectrometry through spectral modeling. PMID:19455245

Spectral Characteristics of VLF Sferics Associated With RHESSI TGFs

NASA Astrophysics Data System (ADS)

Mezentsev, Andrew; Lehtinen, Nikolai; Østgaard, Nikolai; Pérez-Invernón, F. J.; Cummer, Steven A.

2018-01-01

We compared the modeled energy spectral density of very low frequency (VLF) radio emissions from terrestrial gamma ray flashes (TGFs) with the energy spectral density of VLF radio sferics recorded by Duke VLF receiver simultaneously with those TGFs. In total, six events with world wide lightning location network (WWLLN) defined locations were analyzed to exhibit a good fit between the modeled and observed energy spectral densities. In VLF range the energy spectral density of the TGF source current moment is found to be dominated by the contribution of secondary low-energy electrons and independent of the relativistic electrons which play their role in low-frequency (LF) range. Additional spectral modulation by the multiplicity of TGF peaks was found and demonstrated a good fit for two TGFs whose VLF sferics consist of two overlapping pulses each. The number of seeding pulses in TGF defines the spectral shape in VLF range, which allows to retrieve this number from VLF sferics, assuming they were radiated by TGFs. For two events it was found that the number of seeding pulses is small, of the order of 10. For the rest of the events the lower boundary of the number of seeding pulses was found to be between 10 to 103.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smallwood, D.O.

In a previous paper Smallwood and Paez (1991) showed how to generate realizations of partially coherent stationary normal time histories with a specified cross-spectral density matrix. This procedure is generalized for the case of multiple inputs with a specified cross-spectral density function and a specified marginal probability density function (pdf) for each of the inputs. The specified pdfs are not required to be Gaussian. A zero memory nonlinear (ZMNL) function is developed for each input to transform a Gaussian or normal time history into a time history with a specified non-Gaussian distribution. The transformation functions have the property that amore » transformed time history will have nearly the same auto spectral density as the original time history. A vector of Gaussian time histories are then generated with the specified cross-spectral density matrix. These waveforms are then transformed into the required time history realizations using the ZMNL function.« less

Estimate of the Coulomb correlation energy in CeAg2Ge2 from inverse photoemission and high resolution photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Banik, Soma; Arya, A.; Bendounan, Azzedine; Maniraj, M.; Thamizhavel, A.; Vobornik, I.; Dhar, S. K.; Deb, S. K.

2014-08-01

The occupied and the unoccupied electronic structure of CeAg2Ge2 single crystal has been studied using high resolution photoemission and inverse photoemission spectroscopy, respectively. High resolution photoemission reveals the clear signature of Ce 4f states in the occupied electronic structure which was not observed clearly in our earlier studies. The Coulomb correlation energy in this system has been determined experimentally from the position of the 4f states above and below the Fermi level. Theoretically, the correlation energy has been determined by using the first principles density functional calculations within the generalized gradient approximations taking into account the strong intra-atomic (on-site) interaction Hubbard Ueff term. The calculated valence band shows minor changes in the spectral shape with increasing Ueff due to the fact that the density of Ce 4f state is narrow in the occupied part and is hybridized with the Ce 5d, Ag 4d and Ge 4p states. On the other hand, substantial changes are observed in the spectral shape of the calculated conduction band with increasing Ueff since the density of Ce 4f state is very large in the unoccupied part, compared to other states. The estimated value of correlation energy for CeAg2Ge2 from the experiment and the theory is ≈ 4.2 eV. The resonant photoemission data are analyzed in the framework of the single-impurity Anderson model which further confirms the presence of the Coulomb correlation energy and small hybridization in this system.

Methods for Multiloop Identification of Visual and Neuromuscular Pilot Responses.

PubMed

Olivari, Mario; Nieuwenhuizen, Frank M; Venrooij, Joost; Bülthoff, Heinrich H; Pollini, Lorenzo

2015-12-01

In this paper, identification methods are proposed to estimate the neuromuscular and visual responses of a multiloop pilot model. A conventional and widely used technique for simultaneous identification of the neuromuscular and visual systems makes use of cross-spectral density estimates. This paper shows that this technique requires a specific noninterference hypothesis, often implicitly assumed, that may be difficult to meet during actual experimental designs. A mathematical justification of the necessity of the noninterference hypothesis is given. Furthermore, two methods are proposed that do not have the same limitations. The first method is based on autoregressive models with exogenous inputs, whereas the second one combines cross-spectral estimators with interpolation in the frequency domain. The two identification methods are validated by offline simulations and contrasted to the classic method. The results reveal that the classic method fails when the noninterference hypothesis is not fulfilled; on the contrary, the two proposed techniques give reliable estimates. Finally, the three identification methods are applied to experimental data from a closed-loop control task with pilots. The two proposed techniques give comparable estimates, different from those obtained by the classic method. The differences match those found with the simulations. Thus, the two identification methods provide a good alternative to the classic method and make it possible to simultaneously estimate human's neuromuscular and visual responses in cases where the classic method fails.

An evaluation of random analysis methods for the determination of panel damping

NASA Technical Reports Server (NTRS)

Bhat, W. V.; Wilby, J. F.

1972-01-01

An analysis is made of steady-state and non-steady-state methods for the measurement of panel damping. Particular emphasis is placed on the use of random process techniques in conjunction with digital data reduction methods. The steady-state methods considered use the response power spectral density, response autocorrelation, excitation-response crosspower spectral density, or single-sided Fourier transform (SSFT) of the response autocorrelation function. Non-steady-state methods are associated mainly with the use of rapid frequency sweep excitation. Problems associated with the practical application of each method are evaluated with specific reference to the case of a panel exposed to a turbulent airflow, and two methods, the power spectral density and the single-sided Fourier transform methods, are selected as being the most suitable. These two methods are demonstrated experimentally, and it is shown that the power spectral density method is satisfactory under most conditions, provided that appropriate corrections are applied to account for filter bandwidth and background noise errors. Thus, the response power spectral density method is recommended for the measurement of the damping of panels exposed to a moving airflow.

Granger causality revisited

PubMed Central

Friston, Karl J.; Bastos, André M.; Oswal, Ashwini; van Wijk, Bernadette; Richter, Craig; Litvak, Vladimir

2014-01-01

This technical paper offers a critical re-evaluation of (spectral) Granger causality measures in the analysis of biological timeseries. Using realistic (neural mass) models of coupled neuronal dynamics, we evaluate the robustness of parametric and nonparametric Granger causality. Starting from a broad class of generative (state-space) models of neuronal dynamics, we show how their Volterra kernels prescribe the second-order statistics of their response to random fluctuations; characterised in terms of cross-spectral density, cross-covariance, autoregressive coefficients and directed transfer functions. These quantities in turn specify Granger causality — providing a direct (analytic) link between the parameters of a generative model and the expected Granger causality. We use this link to show that Granger causality measures based upon autoregressive models can become unreliable when the underlying dynamics is dominated by slow (unstable) modes — as quantified by the principal Lyapunov exponent. However, nonparametric measures based on causal spectral factors are robust to dynamical instability. We then demonstrate how both parametric and nonparametric spectral causality measures can become unreliable in the presence of measurement noise. Finally, we show that this problem can be finessed by deriving spectral causality measures from Volterra kernels, estimated using dynamic causal modelling. PMID:25003817

Multi-wavelength campaign on NGC 7469. II. Column densities and variability in the X-ray spectrum

NASA Astrophysics Data System (ADS)

Peretz, U.; Behar, E.; Kriss, G. A.; Kaastra, J.; Arav, N.; Bianchi, S.; Branduardi-Raymont, G.; Cappi, M.; Costantini, E.; De Marco, B.; Di Gesu, L.; Ebrero, J.; Kaspi, S.; Mehdipour, M.; Middei, R.; Paltani, S.; Petrucci, P. O.; Ponti, G.; Ursini, F.

2018-01-01

We have investigated the ionic column density variability of the ionized outflows associated with NGC 7469, to estimate their location and power. This could allow a better understanding of galactic feedback of AGNs to their host galaxies. Analysis of seven XMM-Newton grating observations from 2015 is reported. We used an individual-ion spectral fitting approach, and compared different epochs to accurately determine variability on timescales of years, months, and days. We find no significant column density variability in a ten-year period implying that the outflow is far from the ionizing source. The implied lower bound on the ionization equilibrium time, ten years, constrains the lower limit on the distance to be at least 12 pc, and up to 31 pc, much less but consistent with the 1 kpc wide starburst ring. The ionization distribution of column density is reconstructed from measured column densities, nicely matching results of two 2004 observations, with one large high ionization parameter (ξ) component at 2 < log ξ< 3.5, and one at 0.5 < log ξ< 1 in cgs units. The strong dependence of the expression for kinetic power, ∝ 1 /ξ, hampers tight constraints on the feedback mechanism of outflows with a large range in ionization parameter, which is often observed and indicates a non-conical outflow. The kinetic power of the outflow is estimated here to be within 0.4 and 60% of the Eddington luminosity, depending on the ion used to estimate ξ.

New Methods of Spectral-Density Based Graph Construction and Their Application to Hyperspectral Image Analysis

NASA Astrophysics Data System (ADS)

Stevens, Jeffrey

The past decade has seen the emergence of many hyperspectral image (HSI) analysis algorithms based on graph theory and derived manifold-coordinates. Yet, despite the growing number of algorithms, there has been limited study of the graphs constructed from spectral data themselves. Which graphs are appropriate for various HSI analyses--and why? This research aims to begin addressing these questions as the performance of graph-based techniques is inextricably tied to the graphical model constructed from the spectral data. We begin with a literature review providing a survey of spectral graph construction techniques currently used by the hyperspectral community, starting with simple constructs demonstrating basic concepts and then incrementally adding components to derive more complex approaches. Throughout this development, we discuss algorithm advantages and disadvantages for different types of hyperspectral analysis. A focus is provided on techniques influenced by spectral density through which the concept of community structure arises. Through the use of simulated and real HSI data, we demonstrate density-based edge allocation produces more uniform nearest neighbor lists than non-density based techniques through increasing the number of intracluster edges, facilitating higher k-nearest neighbor (k-NN) classification performance. Imposing the common mutuality constraint to symmetrify adjacency matrices is demonstrated to be beneficial in most circumstances, especially in rural (less cluttered) scenes. Many complex adaptive edge-reweighting techniques are shown to slightly degrade nearest-neighbor list characteristics. Analysis suggests this condition is possibly attributable to the validity of characterizing spectral density by a single variable representing data scale for each pixel. Additionally, it is shown that imposing mutuality hurts the performance of adaptive edge-allocation techniques or any technique that aims to assign a low number of edges (<10) to any pixel. A simple k bias addresses this problem. Many of the adaptive edge-reweighting techniques are based on the concept of codensity, so we explore codensity properties as they relate to density-based edge reweighting. We find that codensity may not be the best estimator of local scale due to variations in cluster density, so we introduce and compare two inherently density-weighted graph construction techniques from the data mining literature: shared nearest neighbors (SNN) and mutual proximity (MP). MP and SNN are not reliant upon a codensity measure, hence are not susceptible to its shortcomings. Neither has been used for hyperspectral analyses, so this presents the first study of these techniques on HSI data. We demonstrate MP and SNN can offer better performance, but in general none of the reweighting techniques improve the quality of these spectral graphs in our neighborhood structure tests. As such, these complex adaptive edge-reweighting techniques may need to be modified to increase their effectiveness. During this investigation, we probe deeper into properties of high-dimensional data and introduce the concept of concentration of measure (CoM)--the degradation in the efficacy of many common distance measures with increasing dimensionality--as it relates to spectral graph construction. CoM exists in pairwise distances between HSI pixels, but not to the degree experienced in random data of the same extrinsic dimension; a characteristic we demonstrate is due to the rich correlation and cluster structure present in HSI data. CoM can lead to hubness--a condition wherein some nodes have short distances (high similarities) to an exceptionally large number of nodes. We study hub presence in 49 HSI datasets of varying resolutions, altitudes, and spectral bands to demonstrate hubness effects are negligible in a k-NN classification example (generalized counting scenarios), but we note its impact on methods that use edge weights to derive manifold coordinates or splitting clusters based on spectral graph theory requires more investigation. Many of these new graph-related quantities can be exploited to demonstrate new techniques for HSI classification and anomaly detection. We present an initial exploration into this relatively new and exciting field based on an enhanced Schroedinger Eigenmap classification example and compare results to the current state-of-the-art approach. We produce equivalent results, but demonstrate different types of misclassifications, opening the door to combine the best of both approaches to achieve truly superior performance. A separate less mature hubness-assisted anomaly detector (HAAD) is also presented.

Running of the spectral index in deformed matter bounce scenarios with Hubble-rate-dependent dark energy

NASA Astrophysics Data System (ADS)

Arab, M.; Khodam-Mohammadi, A.

2018-03-01

As a deformed matter bounce scenario with a dark energy component, we propose a deformed one with running vacuum model (RVM) in which the dark energy density ρ _{Λ } is written as a power series of H^2 and \\dot{H} with a constant equation of state parameter, same as the cosmological constant, w=-1. Our results in analytical and numerical point of views show that in some cases same as Λ CDM bounce scenario, although the spectral index may achieve a good consistency with observations, a positive value of running of spectral index (α _s) is obtained which is not compatible with inflationary paradigm where it predicts a small negative value for α _s. However, by extending the power series up to H^4, ρ _{Λ }=n_0+n_2 H^2+n_4 H^4, and estimating a set of consistent parameters, we obtain the spectral index n_s, a small negative value of running α _s and tensor to scalar ratio r, which these reveal a degeneracy between deformed matter bounce scenario with RVM-DE and inflationary cosmology.

Integrated spectral photocurrent density and reproducibility analyses of excitonic ZnO/NiO heterojunction.

PubMed

Patel, Malkeshkumar; Kim, Joondong

2017-12-01

In this data article, the excitonic ZnO/NiO heterojunction device (Patel et al., 2017) [1] was measured for the integrated photocurrent density and reproducibility. Photograph of the prepared devices of ZnO/NiO on the FTO/glass is presented. Integrated photocurrent density as a function of photon energy from the sunlight is presented. Quantum efficiency measurement system (McScienceK3100, Korea) compliance with International Measurement System was employed to measure ZnO/NIO devices. These data are shown for the 300-440 nm of segment of the sunlight (AM1.5G, http://rredc.nrel.gov/solar/spectra/am1.5/). Reproducibility measure of ZnO/NiO device was presented for nine devices with the estimated device performance parameters including the open circuit voltage, short circuit current density, fill factor and power conversion efficiency.

An HF and lower VHF spectrum assessment system exploiting instantaneously wideband capture

NASA Astrophysics Data System (ADS)

Barnes, Rod I.; Singh, Malkiat; Earl, Fred

2017-09-01

We report on a spectral environment evaluation and recording (SEER) system, for instantaneously wideband spectral capture and characterization in the HF and lower VHF band, utilizing a direct digital receiver coupled to a data recorder. The system is designed to contend with a wide variety of electromagnetic environments and to provide accurately calibrated spectral characterization and display from very short (ms) to synoptic scales. The system incorporates a novel RF front end involving automated gain and equalization filter selection which provides an analogue frequency-dependent gain characteristic that mitigates the high dynamic range found across the HF and lower VHF spectrum. The system accurately calibrates its own internal noise and automatically subtracts this from low variance, external spectral estimates, further extending the dynamic range over which robust characterization is possible. Laboratory and field experiments demonstrate that the implementation of these concepts has been effective. Sensitivity to varying antenna load impedance of the internal noise reduction process has been examined. Examples of software algorithms to provide extraction and visualization of spectral behavior over narrowband, wideband, short, and synoptic scales are provided. Application in HF noise spectral density monitoring, spectral signal strength assessment, and electromagnetic interference detection is possible with examples provided. The instantaneously full bandwidth collection provides some innovative applications, and this is demonstrated by the collection of discrete lightning emissions, which form fast ionograms called "flashagrams" in power-delay-frequency plots.

Multi-material decomposition of spectral CT images

NASA Astrophysics Data System (ADS)

Mendonça, Paulo R. S.; Bhotika, Rahul; Maddah, Mahnaz; Thomsen, Brian; Dutta, Sandeep; Licato, Paul E.; Joshi, Mukta C.

2010-04-01

Spectral Computed Tomography (Spectral CT), and in particular fast kVp switching dual-energy computed tomography, is an imaging modality that extends the capabilities of conventional computed tomography (CT). Spectral CT enables the estimation of the full linear attenuation curve of the imaged subject at each voxel in the CT volume, instead of a scalar image in Hounsfield units. Because the space of linear attenuation curves in the energy ranges of medical applications can be accurately described through a two-dimensional manifold, this decomposition procedure would be, in principle, limited to two materials. This paper describes an algorithm that overcomes this limitation, allowing for the estimation of N-tuples of material-decomposed images. The algorithm works by assuming that the mixing of substances and tissue types in the human body has the physicochemical properties of an ideal solution, which yields a model for the density of the imaged material mix. Under this model the mass attenuation curve of each voxel in the image can be estimated, immediately resulting in a material-decomposed image triplet. Decomposition into an arbitrary number of pre-selected materials can be achieved by automatically selecting adequate triplets from an application-specific material library. The decomposition is expressed in terms of the volume fractions of each constituent material in the mix; this provides for a straightforward, physically meaningful interpretation of the data. One important application of this technique is in the digital removal of contrast agent from a dual-energy exam, producing a virtual nonenhanced image, as well as in the quantification of the concentration of contrast observed in a targeted region, thus providing an accurate measure of tissue perfusion.

Inverting a dispersive scene's side-scanned image

NASA Technical Reports Server (NTRS)

Harger, R. O.

1983-01-01

Consideration is given to the problem of using a remotely sensed, side-scanned image of a time-variant scene, which changes according to a dispersion relation, to estimate the structure at a given moment. Additive thermal noise is neglected in the models considered in the formal treatment. It is shown that the dispersion relation is normalized by the scanning velocity, as is the group scanning velocity component. An inversion operation is defined for noise-free images generated by SAR. The method is extended to the inversion of noisy imagery, and a formulation is defined for spectral density estimation. Finally, the methods for a radar system are used for the case of sonar.

Radio-frequency capacitive discharge with flowing liquid electrodes at reduced gas pressures

NASA Astrophysics Data System (ADS)

Gaisin, Al. F.; Son, E. E.; Petryakov, S. Yu.

2017-07-01

Results are presented from experimental studies of the electrophysical and spectral characteristics of the low-temperature plasma of a radio-frequency capacitive discharge excited between two flowing liquid electrodes at gas pressures of 103-105 Pa. The plasma composition, the electron density, and the vibrational and rotational temperatures of gas molecules are estimated. The types and shapes of discharge are described, and the thermal and gas-hydrodynamic processes in the discharge zone are analyzed.

Comparison of the surface ion density of silica gel evaluated via spectral induced polarization versus acid-base titration

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.

Investigating the Role of Gravity Wave on Equatorial Ionospheric Irregularities using SABER and C/NOFS Satellites Observations

NASA Astrophysics Data System (ADS)

Nigussie, M.; Damtie, B.; Moldwin, M.; Yizengaw, E.; Tesema, F.; Tebabal, A.

2017-12-01

Theoretical simulations have shown that gravity wave (GW) seeded perturbations amplified by Rayleigh-Taylor Instability (RTI) results in ESF (equatorial spread F); however, there have been limited observational studies using simultaneous observations of GW and ionospheric parameters. In this paper, for the fist time, simultaneous atmospheric temperature perturbation profiles that are due to GWs obtained from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on-board the TIMED satellite and equatorial in -situ ion density and vertical plasma drift velocity observations with and without ESF activity obtained from C/NOFS satellites are used to investigate the effect of GW on the generation of ESF. The horizontal and vertical wavelengths of ionospheric oscillations and GWs respectively have been estimated applying wavelet transforms. Cross wavelet analysis has also been applied between two closely observed profiles of temperature perturbations to estimate the horizontal wavelength of the GWs. Moreover, vertically propagating GWs that dissipate energy at the upper atmosphere have been investigated using spectral analysis compared with theoretical results. The analysis show that when the ion density shows strong post sunset irregularity between 20 and 24 LT, vertically upward drift velocities increase between 17 and 19 LT, but it becomes vertically downward when the ion density shows smooth variation. The horizontal wavelengths estimated from C/NOFS and SABER observations show excellent agreement when ion density observations show strong fluctuations; otherwise, they have poor agreement. It is also found that altitude profiles of potential energy of GW increases up to 90 km and then decreases significantly. It is found that the vertical wavelength of GW, corresponding to the dominant spectral power, ranges from about 7 km to 20 km regardless of the situation of the ionosphere; however, GWs with vertical wavelengths between 100 m to 1 km are found to be saturated between 90 and 110 km whether the ionosphere exhibits irregularity or not. The above results imply that ESF is due to the amplification of perturbations as a result of energy dissipation from GW with vertical wavelength 100 m to 1 km by the RTI that is mainly controlled by Pre-Reversal Enhancement of the zonal electric field.

Spectral Characteristics of VLF Sferics Associated With RHESSI TGFs.

PubMed

Mezentsev, Andrew; Lehtinen, Nikolai; Østgaard, Nikolai; Pérez-Invernón, F J; Cummer, Steven A

2018-01-16

We compared the modeled energy spectral density of very low frequency (VLF) radio emissions from terrestrial gamma ray flashes (TGFs) with the energy spectral density of VLF radio sferics recorded by Duke VLF receiver simultaneously with those TGFs. In total, six events with world wide lightning location network (WWLLN) defined locations were analyzed to exhibit a good fit between the modeled and observed energy spectral densities. In VLF range the energy spectral density of the TGF source current moment is found to be dominated by the contribution of secondary low-energy electrons and independent of the relativistic electrons which play their role in low-frequency (LF) range. Additional spectral modulation by the multiplicity of TGF peaks was found and demonstrated a good fit for two TGFs whose VLF sferics consist of two overlapping pulses each. The number of seeding pulses in TGF defines the spectral shape in VLF range, which allows to retrieve this number from VLF sferics, assuming they were radiated by TGFs. For two events it was found that the number of seeding pulses is small, of the order of 10. For the rest of the events the lower boundary of the number of seeding pulses was found to be between 10 to 10 3 .

Specific features of the cathodoluminescence spectra of AlInGaN QWs, caused by the influence of phase separation and internal electric fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuznetsova, Ya. V., E-mail: yana@mail.ioffe.ru; Jmerik, V. N.; Nechaev, D. V.

2016-07-15

The specific features of the cathodoluminescence (CL) spectra in AlInGaN heterostructures, caused by the influence of phase separation and internal electric fields, observed at varied CL excitation density, are studied. It is shown that the evolution of the CL spectrum and the variation in the spectral position of emission lines of nanoscale layers with current density in the primary electron beam makes it possible to identify the occurrence of phase separation in the layer and, in the absence of this separation, to estimate the electric-field strength in the active region of the structure.

Quantitative Doppler Analysis Using Conventional Color Flow Imaging Acquisitions.

PubMed

Karabiyik, Yucel; Ekroll, Ingvild Kinn; Eik-Nes, Sturla H; Lovstakken, Lasse

2018-05-01

Interleaved acquisitions used in conventional triplex mode result in a tradeoff between the frame rate and the quality of velocity estimates. On the other hand, workflow becomes inefficient when the user has to switch between different modes, and measurement variability is increased. This paper investigates the use of power spectral Capon estimator in quantitative Doppler analysis using data acquired with conventional color flow imaging (CFI) schemes. To preserve the number of samples used for velocity estimation, only spatial averaging was utilized, and clutter rejection was performed after spectral estimation. The resulting velocity spectra were evaluated in terms of spectral width using a recently proposed spectral envelope estimator. The spectral envelopes were also used for Doppler index calculations using in vivo and string phantom acquisitions. In vivo results demonstrated that the Capon estimator can provide spectral estimates with sufficient quality for quantitative analysis using packet-based CFI acquisitions. The calculated Doppler indices were similar to the values calculated using spectrograms estimated on a commercial ultrasound scanner.

A New Method of Assessing Uncertainty of the Cross-Convolution Method of Shear Wave Splitting Measurement

NASA Astrophysics Data System (ADS)

Schutt, D.; Breidt, J.; Corbalan Castejon, A.; Witt, D. R.

2017-12-01

Shear wave splitting is a commonly used and powerful method for constraining such phenomena as lithospheric strain history or asthenospheric flow. However, a number of challenges with the statistics of shear wave splitting have been noted. This creates difficulties in assessing whether two separate measurements are statistically similar or are indicating real differences in anisotropic structure, as well as for created proper station averaged sets of parameters for more complex situations such as multiple or dipping layers of anisotropy. We present a new method for calculating the most likely splitting parameters using the Menke and Levin [2003] method of cross-convolution. The Menke and Levin method is used because it can more readily be applied to a wider range of anisotropic scenarios than the commonly used Silver and Chan [1991] technique. In our approach, we derive a formula for the spectral density of a function of the microseismic noise and the impulse response of the correct anisotropic model that holds for the true anisotropic model parameters. This is compared to the spectral density of the observed signal convolved with the impulse response for an estimated set of anisotropic parameters. The most likely parameters are found when the former and latter spectral densities are the same. By using the Whittle likelihood to compare the two spectral densities, a likelihood grid for all possible anisotropic parameter values is generated. Using bootstrapping, the uncertainty and covariance between the various anisotropic parameters can be evaluated. We will show this works with a single layer of anisotropy and a vertically incident ray, and discuss the usefulness for a more complex case. The method shows great promise for calculating multiple layer anisotropy parameters with proper assessment of uncertainty. References: Menke, W., and Levin, V. 2003. The cross-convolution method for interpreting SKS splitting observations, with application to one and two-layer anisotropic earth models. Geophysical Journal International, 154: 379-392. doi:10.1046/j.1365-246X.2003.01937.x. Silver, P.G., and Chan, W.W. 1991. Shear Wave Splitting and Sub continental Mantle Deformation. Journal of Geophysical Research, 96: 429-454. doi:10.1029/91JB00899.

Spectral function from Reduced Density Matrix Functional Theory

NASA Astrophysics Data System (ADS)

Romaniello, Pina; di Sabatino, Stefano; Berger, Jan A.; Reining, Lucia

2015-03-01

In this work we focus on the calculation of the spectral function, which determines, for example, photoemission spectra, from reduced density matrix functional theory. Starting from its definition in terms of the one-body Green's function we derive an expression for the spectral function that depends on the natural occupation numbers and on an effective energy which accounts for all the charged excitations. This effective energy depends on the two-body as well as higher-order density matrices. Various approximations to this expression are explored by using the exactly solvable Hubbard chains.

Comparison of Background Parenchymal Enhancement at Contrast-enhanced Spectral Mammography and Breast MR Imaging.

PubMed

Sogani, Julie; Morris, Elizabeth A; Kaplan, Jennifer B; D'Alessio, Donna; Goldman, Debra; Moskowitz, Chaya S; Jochelson, Maxine S

2017-01-01

Purpose To assess the extent of background parenchymal enhancement (BPE) at contrast material-enhanced (CE) spectral mammography and breast magnetic resonance (MR) imaging, to evaluate interreader agreement in BPE assessment, and to examine the relationships between clinical factors and BPE. Materials and Methods This was a retrospective, institutional review board-approved, HIPAA-compliant study. Two hundred seventy-eight women from 25 to 76 years of age with increased breast cancer risk who underwent CE spectral mammography and MR imaging for screening or staging from 2010 through 2014 were included. Three readers independently rated BPE on CE spectral mammographic and MR images with the ordinal scale: minimal, mild, moderate, or marked. To assess pairwise agreement between BPE levels on CE spectral mammographic and MR images and among readers, weighted κ coefficients with quadratic weights were calculated. For overall agreement, mean κ values and bootstrapped 95% confidence intervals were calculated. The univariate and multivariate associations between BPE and clinical factors were examined by using generalized estimating equations separately for CE spectral mammography and MR imaging. Results Most women had minimal or mild BPE at both CE spectral mammography (68%-76%) and MR imaging (69%-76%). Between CE spectral mammography and MR imaging, the intrareader agreement ranged from moderate to substantial (κ = 0.55-0.67). Overall agreement on BPE levels between CE spectral mammography and MR imaging and among readers was substantial (κ = 0.66; 95% confidence interval: 0.61, 0.70). With both modalities, BPE demonstrated significant association with menopausal status, prior breast radiation therapy, hormonal treatment, breast density on CE spectral mammographic images, and amount of fibroglandular tissue on MR images (P < .001 for all). Conclusion There was substantial agreement between readers for BPE detected on CE spectral mammographic and MR images. © RSNA, 2016.

Novel multireceiver communication systems configurations based on optimal estimation theory

NASA Technical Reports Server (NTRS)

Kumar, Rajendra

1992-01-01

A novel multireceiver configuration for carrier arraying and/or signal arraying is presented. The proposed configuration is obtained by formulating the carrier and/or signal arraying problem as an optimal estimation problem, and it consists of two stages. The first stage optimally estimates various phase processes received at different receivers with coupled phase-locked loops wherein the individual loops acquire and track their respective receivers' phase processes but are aided by each other in an optimal manner via LF error signals. The proposed configuration results in the minimization of the the effective radio loss at the combiner output, and thus maximization of energy per bit to noise power spectral density ratio is achieved. A novel adaptive algorithm for the estimator of the signal model parameters when these are not known a priori is also presented.

Spectral effects in the propagation of chirped laser pulses in uniform underdense plasma

NASA Astrophysics Data System (ADS)

Pathak, Naveen; Zhidkov, Alexei; Hosokai, Tomonao; Kodama, Ryosuke

2018-01-01

Propagation of linearly chirped and linearly polarized, powerful laser pulses in uniform underdense plasma with their duration exceeding the plasma wave wavelength is examined via 3D fully relativistic particle-in-cell simulations. Spectral evolution of chirped laser pulses, determined by Raman scattering, essentially depends on the nonlinear electron evacuation from the first wake bucket via modulation of the known parameter /n e ( r ) ω0 2 γ . Conversely, the relative motion of different spectral components inside a pulse changes the evolution of the pulse length and, therefore, the ponderomotive forces at the pulse rear. Such longitudinal dynamics of the pulse length provoke a parametric resonance in the laser wake with continuous electron self-injection for any chirped pulses. However, the total charge of accelerated electrons and their energy distribution essentially depends on the chirp. Besides, negatively chirped laser pulses are shown to be useful for spatially resolved measurements of the plasma density profiles and for rough estimations of the laser pulse intensity evolution in underdense plasma.

Open Systems with Error Bounds: Spin-Boson Model with Spectral Density Variations.

PubMed

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.

Two-point spectral model for variable density homogeneous turbulence

NASA Astrophysics Data System (ADS)

Pal, Nairita; Kurien, Susan; Clark, Timothy; Aslangil, Denis; Livescu, Daniel

2017-11-01

We present a comparison between a two-point spectral closure model for buoyancy-driven variable density homogeneous turbulence, with Direct Numerical Simulation (DNS) data of the same system. We wish to understand how well a suitable spectral model might capture variable density effects and the transition to turbulence from an initially quiescent state. Following the BHRZ model developed by Besnard et al. (1990), the spectral model calculation computes the time evolution of two-point correlations of the density fluctuations with the momentum and the specific-volume. These spatial correlations are expressed as function of wavenumber k and denoted by a (k) and b (k) , quantifying mass flux and turbulent mixing respectively. We assess the accuracy of the model, relative to a full DNS of the complete hydrodynamical equations, using a and b as metrics. Work at LANL was performed under the auspices of the U.S. DOE Contract No. DE-AC52-06NA25396.

Spectral decompositions of multiple time series: a Bayesian non-parametric approach.

PubMed

Macaro, Christian; Prado, Raquel

2014-01-01

We consider spectral decompositions of multiple time series that arise in studies where the interest lies in assessing the influence of two or more factors. We write the spectral density of each time series as a sum of the spectral densities associated to the different levels of the factors. We then use Whittle's approximation to the likelihood function and follow a Bayesian non-parametric approach to obtain posterior inference on the spectral densities based on Bernstein-Dirichlet prior distributions. The prior is strategically important as it carries identifiability conditions for the models and allows us to quantify our degree of confidence in such conditions. A Markov chain Monte Carlo (MCMC) algorithm for posterior inference within this class of frequency-domain models is presented.We illustrate the approach by analyzing simulated and real data via spectral one-way and two-way models. In particular, we present an analysis of functional magnetic resonance imaging (fMRI) brain responses measured in individuals who participated in a designed experiment to study pain perception in humans.

Advanced Receiver tracking of Voyager 2 near solar conjunction

NASA Technical Reports Server (NTRS)

Brown, D. H.; Hurd, W. J.; Vilnrotter, V. A.; Wiggins, J. D.

1988-01-01

The Advanced Receiver (ARX) was used to track the Voyager 2 spacecraft at low Sun-Earth-Probe (SEP) angles near solar conjunction in December of 1987. The received carrier signal exhibited strong fluctuations in both phase and amplitude. The ARX used spectral estimation and mathematical modeling of the phase and receiver noise processes to set an optimum carrier tracking bandwidth. This minimized the mean square phase error in tracking carrier phase and thus minimized the loss in the telemetry signal-to-noise ratio due to the carrier loop. Recovered symbol SNRs and errors in decoded engineering data for the ARX are compared with those for the current Block 3 telemetry stream. Optimum bandwidths are plotted against SEP angle. Measurements of the power spectral density of the solar phase and amplitude fluctuations are also given.

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.

Spectrotemporal Modulation Sensitivity as a Predictor of Speech Intelligibility for Hearing-Impaired Listeners

PubMed Central

Bernstein, Joshua G.W.; Mehraei, Golbarg; Shamma, Shihab; Gallun, Frederick J.; Theodoroff, Sarah M.; Leek, Marjorie R.

2014-01-01

Background A model that can accurately predict speech intelligibility for a given hearing-impaired (HI) listener would be an important tool for hearing-aid fitting or hearing-aid algorithm development. Existing speech-intelligibility models do not incorporate variability in suprathreshold deficits that are not well predicted by classical audiometric measures. One possible approach to the incorporation of such deficits is to base intelligibility predictions on sensitivity to simultaneously spectrally and temporally modulated signals. Purpose The likelihood of success of this approach was evaluated by comparing estimates of spectrotemporal modulation (STM) sensitivity to speech intelligibility and to psychoacoustic estimates of frequency selectivity and temporal fine-structure (TFS) sensitivity across a group of HI listeners. Research Design The minimum modulation depth required to detect STM applied to an 86 dB SPL four-octave noise carrier was measured for combinations of temporal modulation rate (4, 12, or 32 Hz) and spectral modulation density (0.5, 1, 2, or 4 cycles/octave). STM sensitivity estimates for individual HI listeners were compared to estimates of frequency selectivity (measured using the notched-noise method at 500, 1000measured using the notched-noise method at 500, 2000, and 4000 Hz), TFS processing ability (2 Hz frequency-modulation detection thresholds for 500, 10002 Hz frequency-modulation detection thresholds for 500, 2000, and 4000 Hz carriers) and sentence intelligibility in noise (at a 0 dB signal-to-noise ratio) that were measured for the same listeners in a separate study. Study Sample Eight normal-hearing (NH) listeners and 12 listeners with a diagnosis of bilateral sensorineural hearing loss participated. Data Collection and Analysis STM sensitivity was compared between NH and HI listener groups using a repeated-measures analysis of variance. A stepwise regression analysis compared STM sensitivity for individual HI listeners to audiometric thresholds, age, and measures of frequency selectivity and TFS processing ability. A second stepwise regression analysis compared speech intelligibility to STM sensitivity and the audiogram-based Speech Intelligibility Index. Results STM detection thresholds were elevated for the HI listeners, but only for low rates and high densities. STM sensitivity for individual HI listeners was well predicted by a combination of estimates of frequency selectivity at 4000 Hz and TFS sensitivity at 500 Hz but was unrelated to audiometric thresholds. STM sensitivity accounted for an additional 40% of the variance in speech intelligibility beyond the 40% accounted for by the audibility-based Speech Intelligibility Index. Conclusions Impaired STM sensitivity likely results from a combination of a reduced ability to resolve spectral peaks and a reduced ability to use TFS information to follow spectral-peak movements. Combining STM sensitivity estimates with audiometric threshold measures for individual HI listeners provided a more accurate prediction of speech intelligibility than audiometric measures alone. These results suggest a significant likelihood of success for an STM-based model of speech intelligibility for HI listeners. PMID:23636210

The Seismic Tool-Kit (STK): An Open Source Software For Learning the Basis of Signal Processing and Seismology.

NASA Astrophysics Data System (ADS)

Reymond, D.

2016-12-01

We present an open source software project (GNU public license), named STK: Seismic Tool-Kit, that is dedicated mainly for learning signal processing and seismology. The STK project that started in 2007, is hosted by SourceForge.net, and count more than 20000 downloads at the date of writing.The STK project is composed of two main branches:First, a graphical interface dedicated to signal processing (in the SAC format (SAC_ASCII and SAC_BIN): where the signal can be plotted, zoomed, filtered, integrated, derivated, ... etc. (a large variety of IFR and FIR filter is proposed). The passage in the frequency domain via the Fourier transform is used to introduce the estimation of spectral density of the signal , with visualization of the Power Spectral Density (PSD) in linear or log scale, and also the evolutive time-frequency representation (or sonagram). The 3-components signals can be also processed for estimating their polarization properties, either for a given window, or either for evolutive windows along the time. This polarization analysis is useful for extracting the polarized noises, differentiating P waves, Rayleigh waves, Love waves, ... etc. Secondly, a panel of Utilities-Program are proposed for working in a terminal mode, with basic programs for computing azimuth and distance in spherical geometry, inter/auto-correlation, spectral density, time-frequency for an entire directory of signals, focal planes, and main components axis, radiation pattern of P waves, Polarization analysis of different waves (including noise), under/over-sampling the signals, cubic-spline smoothing, and linear/non linear regression analysis of data set. STK is developed in C/C++, mainly under Linux OS, and it has been also partially implemented under MS-Windows. STK has been used in some schools for viewing and plotting seismic records provided by IRIS, and it has been used as a practical support for teaching the basis of signal processing. Useful links:http://sourceforge.net/projects/seismic-toolkit/http://sourceforge.net/p/seismic-toolkit/wiki/browse_pages/

On the mixing time in the Wang-Landau algorithm

NASA Astrophysics Data System (ADS)

Fadeeva, Marina; Shchur, Lev

2018-01-01

We present preliminary results of the investigation of the properties of the Markov random walk in the energy space generated by the Wang-Landau probability. We build transition matrix in the energy space (TMES) using the exact density of states for one-dimensional and two-dimensional Ising models. The spectral gap of TMES is inversely proportional to the mixing time of the Markov chain. We estimate numerically the dependence of the mixing time on the lattice size, and extract the mixing exponent.

Automated Method of Frequency Determination in Software Metric Data Through the Use of the Multiple Signal Classification (MUSIC) Algorithm

DTIC Science & Technology

1998-06-26

METHOD OF FREQUENCY DETERMINATION 4 IN SOFTWARE METRIC DATA THROUGH THE USE OF THE 5 MULTIPLE SIGNAL CLASSIFICATION ( MUSIC ) ALGORITHM 6 7 STATEMENT OF...graph showing the estimated power spectral 12 density (PSD) generated by the multiple signal classification 13 ( MUSIC ) algorithm from the data set used...implemented in this module; however, it is preferred to use 1 the Multiple Signal Classification ( MUSIC ) algorithm. The MUSIC 2 algorithm is

Remote Sensing of Coastal Wetlands Biomass Using Thematic Mapper Wavebands. [Lewes, Delaware

NASA Technical Reports Server (NTRS)

Hardisky, M. A.; Klemas, V.

1985-01-01

Spectral data, simulating thematic mapper bands 3, 4 and 5 were gathered in salt and brackish marshes using a hand-held radiometer. Simple regression models were developed equating spectral radiance indicies with total live biomass for S. alterniflora in a salt marsh and for a variety of plant species in a brackish marsh. Models were then tested and compared to harvest estimates of biomass. In the salt marsh, biomass estimates from spectral data were similar to harvest biomass estimates during most of the growing season. Estimates of annual net aerial primary productivity calculated from spectral data were within 21% of production estimated from harvest data. During August, biomass estimates from spectral data in the brackish marsh were similar to biomass estimated by harvesting techniques but not always comparable at other times in the growing season.

Spectral Estimation: An Overdetermined Rational Model Equation Approach.

DTIC Science & Technology

1982-09-15

A-A123 122 SPECTRAL ESTIMATION: AN OVERDETERMINEO RATIONAL MODEL 1/2 EQUATION APPROACH..(U) ARIZONA STATE UNIV TEMPE DEPT OF ELECTRICAL AND COMPUTER...2 0 447,_______ 4. TITLE (mAd Sabile) S. TYPE or REPORT a PEP40D COVERED Spectral Estimation; An Overdeteruined Rational Final Report 9/3 D/8 to...andmmd&t, by uwek 7a5 4 Rational Spectral Estimation, ARMA mo~Ie1, AR model, NMA Mdle, Spectrum, Singular Value Decomposition. Adaptivb Implementatlan

9C spectral-index distributions and source-count estimates from 15 to 93 GHz - a re-assessment

NASA Astrophysics Data System (ADS)

Waldram, E. M.; Bolton, R. C.; Riley, J. M.; Pooley, G. G.

2018-01-01

In an earlier paper (2007), we used follow-up observations of a sample of sources from the 9C survey at 15.2 GHz to derive a set of spectral-index distributions up to a frequency of 90 GHz. These were based on simultaneous measurements made at 15.2 GHz with the Ryle telescope and at 22 and 43 GHz with the Karl G. Jansky Very Large Array (VLA). We used these distributions to make empirical estimates of source counts at 22, 30, 43, 70 and 90 GHz. In a later paper (2013), we took data at 15.7 GHz from the Arcminute Microkelvin Imager (AMI) and data at 93.2 GHz from the Combined Array for Research in Millimetre-wave Astronomy (CARMA) and estimated the source count at 93.2 GHz. In this paper, we re-examine the data used in both papers and now believe that the VLA flux densities we measured at 43 GHz were significantly in error, being on average only about 70 per cent of their correct values. Here, we present strong evidence for this conclusion and discuss the effect on the source-count estimates made in the 2007 paper. The source-count prediction in the 2013 paper is also revised. We make comparisons with spectral-index distributions and source counts from other telescopes, in particular with a recent deep 95 GHz source count measured by the South Pole Telescope. We investigate reasons for the problem of the low VLA 43-GHz values and find a number of possible contributory factors, but none is sufficient on its own to account for such a large deficit.

Variability of daily UV index in Jokioinen, Finland, in 1995-2015

NASA Astrophysics Data System (ADS)

Heikkilä, A.; Uusitalo, K.; Kärhä, P.; Vaskuri, A.; Lakkala, K.; Koskela, T.

2017-02-01

UV Index is a measure for UV radiation harmful for the human skin, developed and used to promote the sun awareness and protection of people. Monitoring programs conducted around the world have produced a number of long-term time series of UV irradiance. One of the longest time series of solar spectral UV irradiance in Europe has been obtained from the continuous measurements of Brewer #107 spectrophotometer in Jokioinen (lat. 60°44'N, lon. 23°30'E), Finland, over the years 1995-2015. We have used descriptive statistics and estimates of cumulative distribution functions, quantiles and probability density functions in the analysis of the time series of daily UV Index maxima. Seasonal differences in the estimated distributions and in the trends of the estimated quantiles are found.

Radiative characteristics of a thin solid fuel at discrete levels of pyrolysis: Angular, spectral, and thermal dependencies

NASA Astrophysics Data System (ADS)

Pettegrew, Richard Dale

Numerical models of solid fuel combustion rely on accurate radiative property values to properly account for radiative heat transfer to and from the surface. The spectral properties can change significantly over the temperature range from ambient to burnout temperature. The variations of these properties are due to mass loss (as the sample pyrolyzes), chemical changes, and surface finish changes. In addition, band-integrated properties can vary due to the shift in the peak of the Planck curve as the temperature increases, which results in differing weightings of the spectral values. These effects were quantified for a thin cellulosic fuel commonly used in microgravity combustion studies (KimWipesRTM). Pyrolytic effects were simulated by heat-treating the samples in a constant temperature oven for varying times. Spectral data was acquired using a Fourier Transform Infrared (FTIR) spectrometer, along with an integrating sphere. Data was acquired at different incidence angles by mounting the samples at different angles inside the sphere. Comparisons of samples of similar area density created using different heat-treatment regimens showed that thermal history of the samples was irrelevant in virtually all spectral regions, with overall results correlating well with changes in area density. Spectral, angular, and thermal dependencies were determined for a representative data set, showing that the spectral absorptance decreases as the temperature increases, and decreases as the incidence angle varies from normal. Changes in absorptance are primarily offset by corresponding changes in transmittances, with reflectance values shown to be low over the tested spectral region of 2.50 mum to 24.93 mum. Band-integrated values were calculated as a function of temperature for the entire tested spectral region, as well as limited bands relevant for thermal imaging applications. This data was used to demonstrate the significant error that is likely if incorrect emittance values are used in heat transfer calculations. The pyrolyzed samples were also used to determine the activation energy and pre-exponential factor needed in the zeroth-order Arrhenius reaction, sometimes used to model the mass loss from the surface in numerical models. The values determined were used to calculate an estimated peak surface temperature, which agrees well with experimentally determined values.

Optical depth estimates and effective critical densities of dense gas tracers in the inner parts of nearby galaxy discs

NASA Astrophysics Data System (ADS)

Jiménez-Donaire, M. J.; Bigiel, F.; Leroy, A. K.; Cormier, D.; Gallagher, M.; Usero, A.; Bolatto, A.; Colombo, D.; García-Burillo, S.; Hughes, A.; Kramer, C.; Krumholz, M. R.; Meier, D. S.; Murphy, E.; Pety, J.; Rosolowsky, E.; Schinnerer, E.; Schruba, A.; Tomičić, N.; Zschaechner, L.

2017-04-01

High critical density molecular lines like HCN (1-0) or HCO+ (1-0) represent our best tool to study currently star-forming, dense molecular gas at extragalactic distances. The optical depth of these lines is a key ingredient to estimate the effective density required to excite emission. However, constraints on this quantity are even scarcer in the literature than measurements of the high-density tracers themselves. Here, we combine new observations of HCN, HCO+ and HNC (1-0) and their optically thin isotopologues H13CN, H13CO+ and HN13C (1-0) to measure isotopologue line ratios. We use IRAM 30-m observations from the large programme EMPIRE and new Atacama Large Millimetre/submillimetre Array observations, which together target six nearby star-forming galaxies. Using spectral stacking techniques, we calculate or place strong upper limits on the HCN/H13CN, HCO+/H13CO+ and HNC/HN13C line ratios in the inner parts of these galaxies. Under simple assumptions, we use these to estimate the optical depths of HCN (1-0) and HCO+ (1-0) to be τ ˜ 2-11 in the active, inner regions of our targets. The critical densities are consequently lowered to values between 5 and 20 × 105 cm-3, 1 and 3 × 105 cm-3 and 9 × 104 cm-3 for HCN, HCO+ and HNC, respectively. We study the impact of having different beam-filling factors, η, on these estimates and find that the effective critical densities decrease by a factor of η _{12}/η _{13} τ_{12}. A comparison to existing work in NGC 5194 and NGC 253 shows the HCN/H13CN and HCO+/H13CO+ ratios in agreement with our measurements within the uncertainties. The same is true for studies in other environments such as the Galactic Centre or nuclear regions of active galactic nucleus dominated nearby galaxies.

A Steady-State Kalman Predictor-Based Filtering Strategy for Non-Overlapping Sub-Band Spectral Estimation

PubMed Central

Li, Zenghui; Xu, Bin; Yang, Jian; Song, Jianshe

2015-01-01

This paper focuses on suppressing spectral overlap for sub-band spectral estimation, with which we can greatly decrease the computational complexity of existing spectral estimation algorithms, such as nonlinear least squares spectral analysis and non-quadratic regularized sparse representation. Firstly, our study shows that the nominal ability of the high-order analysis filter to suppress spectral overlap is greatly weakened when filtering a finite-length sequence, because many meaningless zeros are used as samples in convolution operations. Next, an extrapolation-based filtering strategy is proposed to produce a series of estimates as the substitutions of the zeros and to recover the suppression ability. Meanwhile, a steady-state Kalman predictor is applied to perform a linearly-optimal extrapolation. Finally, several typical methods for spectral analysis are applied to demonstrate the effectiveness of the proposed strategy. PMID:25609038

Nonstationary Transient Vibroacoustic Response of a Beam Structure

NASA Technical Reports Server (NTRS)

Caimi, R. E.; Margasahayam, R. N.; Nayfeh, Jamal F.

1997-01-01

This study consists of an investigation into the nonstationary transient response of the Verification Test Article (VETA) when subjected to random acoustic excitation. The goal is to assess excitation models that can be used in the design of structures and equipment when knowledge of the structure and the excitation is limited. The VETA is an instrumented cantilever beam that was exposed to acoustic loading during five Space Shuttle launches. The VETA analytical structural model response is estimated using the direct averaged power spectral density and the normalized pressure spectra methods. The estimated responses are compared to the measured response of the VETA. These comparisons are discussed with a focus on prediction conservatism and current design practice.

Examination of P/S Spectral Ratios for Small Explosions at Local Distances and Interpretation of Moment Tensors Estimated from Near-Source Data

DTIC Science & Technology

2010-09-01

EXAMINATION OF P/S SPECTRAL RATIOS FOR SMALL EXPLOSIONS AT LOCAL DISTANCES AND INTERPRETATION OF MOMENT TENSORS ESTIMATED FROM NEAR-SOURCE DATA...and particle motion. We then estimated smoothed spectra for the P- and S-waves and formed P/S spectral ratios. The signal quality and difficulty in...4. TITLE AND SUBTITLE Examination of P/S Spectral Ratios for Small Explosions at Local Distances and Interpretation of Moment Tensors Estimated from

The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets

NASA Astrophysics Data System (ADS)

Rackham, Benjamin V.; Apai, Dániel; Giampapa, Mark S.

2018-02-01

Transmission spectra are differential measurements that utilize stellar illumination to probe transiting exoplanet atmospheres. Any spectral difference between the illuminating light source and the disk-integrated stellar spectrum due to starspots and faculae will be imprinted in the observed transmission spectrum. However, few constraints exist for the extent of photospheric heterogeneities in M dwarfs. Here we model spot and faculae covering fractions consistent with observed photometric variabilities for M dwarfs and the associated 0.3–5.5 μm stellar contamination spectra. We find that large ranges of spot and faculae covering fractions are consistent with observations and corrections assuming a linear relation between variability amplitude, and covering fractions generally underestimate the stellar contamination. Using realistic estimates for spot and faculae covering fractions, we find that stellar contamination can be more than 10× larger than the transit depth changes expected for atmospheric features in rocky exoplanets. We also find that stellar spectral contamination can lead to systematic errors in radius and therefore the derived density of small planets. In the case of the TRAPPIST-1 system, we show that TRAPPIST-1's rotational variability is consistent with spot covering fractions {f}{spot}={8}-7+18 % and faculae covering fractions {f}{fac}={54}-46+16 % . The associated stellar contamination signals alter the transit depths of the TRAPPIST-1 planets at wavelengths of interest for planetary atmospheric species by roughly 1–15× the strength of planetary features, significantly complicating JWST follow-up observations of this system. Similarly, we find that stellar contamination can lead to underestimates of the bulk densities of the TRAPPIST-1 planets of {{Δ }}(ρ )=-{8}-20+7 % , thus leading to overestimates of their volatile contents.

Inertial Range Turbulence of Fast and Slow Solar Wind at 0.72 AU and Solar Minimum

NASA Astrophysics Data System (ADS)

Teodorescu, Eliza; Echim, Marius; Munteanu, Costel; Zhang, Tielong; Bruno, Roberto; Kovacs, Peter

2015-05-01

We investigate Venus Express observations of magnetic field fluctuations performed systematically in the solar wind at 0.72 Astronomical Units (AU), between 2007 and 2009, during the deep minimum of solar cycle 24. The power spectral densities (PSDs) of the magnetic field components have been computed for time intervals that satisfy the data integrity criteria and have been grouped according to the type of wind, fast and slow, defined for speeds larger and smaller, respectively, than 450 km s-1. The PSDs show higher levels of power for the fast wind than for the slow. The spectral slopes estimated for all PSDs in the frequency range 0.005-0.1 Hz exhibit a normal distribution. The average value of the trace of the spectral matrix is -1.60 for fast solar wind and -1.65 for slow wind. Compared to the corresponding average slopes at 1 AU, the PSDs are shallower at 0.72 AU for slow wind conditions suggesting a steepening of the solar wind spectra between Venus and Earth. No significant time variation trend is observed for the spectral behavior of both the slow and fast wind.

Spectral X-ray Radiography for Safeguards at Nuclear Fuel Fabrication Facilities: A Feasibility Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbert, Andrew J.; McDonald, Benjamin S.; Smith, Leon E.

The methods currently used by the International Atomic Energy Agency to account for nuclear materials at fuel fabrication facilities are time consuming and require in-field chemistry and operation by experts. Spectral X-ray radiography, along with advanced inverse algorithms, is an alternative inspection that could be completed noninvasively, without any in-field chemistry, with inspections of tens of seconds. The proposed inspection system and algorithms are presented here. The inverse algorithm uses total variation regularization and adaptive regularization parameter selection with the unbiased predictive risk estimator. Performance of the system is quantified with simulated X-ray inspection data and sensitivity of the outputmore » is tested against various inspection system instabilities. Material quantification from a fully-characterized inspection system is shown to be very accurate, with biases on nuclear material estimations of < 0.02%. It is shown that the results are sensitive to variations in the fuel powder sample density and detector pixel gain, which increase biases to 1%. Options to mitigate these inaccuracies are discussed.« less

Assessing the performance of aerial image point cloud and spectral metrics in predicting boreal forest canopy cover

NASA Astrophysics Data System (ADS)

Melin, M.; Korhonen, L.; Kukkonen, M.; Packalen, P.

2017-07-01

Canopy cover (CC) is a variable used to describe the status of forests and forested habitats, but also the variable used primarily to define what counts as a forest. The estimation of CC has relied heavily on remote sensing with past studies focusing on satellite imagery as well as Airborne Laser Scanning (ALS) using light detection and ranging (lidar). Of these, ALS has been proven highly accurate, because the fraction of pulses penetrating the canopy represents a direct measurement of canopy gap percentage. However, the methods of photogrammetry can be applied to produce point clouds fairly similar to airborne lidar data from aerial images. Currently there is little information about how well such point clouds measure canopy density and gaps. The aim of this study was to assess the suitability of aerial image point clouds for CC estimation and compare the results with those obtained using spectral data from aerial images and Landsat 5. First, we modeled CC for n = 1149 lidar plots using field-measured CCs and lidar data. Next, this data was split into five subsets in north-south direction (y-coordinate). Finally, four CC models (AerialSpectral, AerialPointcloud, AerialCombi (spectral + pointcloud) and Landsat) were created and they were used to predict new CC values to the lidar plots, subset by subset, using five-fold cross validation. The Landsat and AerialSpectral models performed with RMSEs of 13.8% and 12.4%, respectively. AerialPointcloud model reached an RMSE of 10.3%, which was further improved by the inclusion of spectral data; RMSE of the AerialCombi model was 9.3%. We noticed that the aerial image point clouds managed to describe only the outermost layer of the canopy and missed the details in lower canopy, which was resulted in weak characterization of the total CC variation, especially in the tails of the data.

Multisource Data Classification Using A Hybrid Semi-supervised Learning Scheme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vatsavai, Raju; Bhaduri, Budhendra L; Shekhar, Shashi

2009-01-01

In many practical situations thematic classes can not be discriminated by spectral measurements alone. Often one needs additional features such as population density, road density, wetlands, elevation, soil types, etc. which are discrete attributes. On the other hand remote sensing image features are continuous attributes. Finding a suitable statistical model and estimation of parameters is a challenging task in multisource (e.g., discrete and continuous attributes) data classification. In this paper we present a semi-supervised learning method by assuming that the samples were generated by a mixture model, where each component could be either a continuous or discrete distribution. Overall classificationmore » accuracy of the proposed method is improved by 12% in our initial experiments.« less

Spectroscopic results in helium from the NASA Lewis Bumpy Torus plasma. [ion heating by Penning discharge in confinement geometry

NASA Technical Reports Server (NTRS)

Richardson, R. W.

1974-01-01

Spectroscopic measurements were carried out on the NASA Lewis Bumpy Torus experiment in which a steady state ion heating method based on the modified Penning discharge is applied in a bumpy torus confinement geometry. Electron temperatures in pure helium are measured from the ratio of spectral line intensities. Measured electron temperatures range from 10 to 100 eV. Relative electron densities are also measured over the range of operating conditions. Radial profiles of temperature and relative density are measured in the two basic modes of operation of the device called the low and high pressure modes. The electron temperatures are used to estimate particle confinement times based on a steady state particle balance.

Low frequency critical current noise and two level system defects in Josephson junctions

NASA Astrophysics Data System (ADS)

Nugroho, Christopher Daniel

The critical current in a Josephson junction is known to exhibit a 1/falpha low frequency noise. Implemented as a superconducting qubit, this low frequency noise can lead to decoherence. While the 1/f noise has been known to arise from an ensemble of two level systems connected to the tunnel barrier, the precise microscopic nature of these TLSs remain a mystery. In this thesis we will present measurements of the 1/f alpha low frequency noise in the critical current and tunneling resistance of Al-AlOx-Al Josephson junctions. Measurements in a wide range of resistively shunted and unshunted junctions confirm the equality of critical current and tunneling resistance noise. That is the critical current fluctuation corresponds to fluctuations of the tunneling resistance. In not too small Al-AlOx-Al junctions we have found that the fractional power spectral density scales linearly with temperature. We confirmed that the 1/falpha power spectrum is the result of a large number of two level systems modulating the tunneling resistance. At small junction areas and low temperatures, the number of thermally active TLSs is insufficient to integrate out a featureless 1/ f spectral shape. By analyzing the spectral variance in small junction areas, we have been able to deduce the TLS defect density, n ≈ 2.53 per micrometer squared per Kelvin spread in the TLS energy per factor e in the TLS lifetimes. This density is consistent with the density of tunneling TLSs found in glassy insulators, as well as the density deduced from coherent TLSs interacting at qubit frequencies. The deduced TLS density combined with the magnitude of the 1/f power spectral density in large area junctions, gives an average TLS effective area, A ˜ 0.3 nanometer squared. In ultra small tunnel junctions, we have studied the time-domain dynamics of isolated TLSs. We have found a TLS whose dynamics is described by the quantum tunneling between the two localized wells, and a one-phonon absorption/emission switching rate. From the quantum limiting rate and the WKB approximation, we estimated that the TLS has a mass and tunneling distance product consistent with an atomic mass tunneling through crystal lattice distances. At higher temperatures TLSs have been found that obey a simple thermal activation dynamics. By analyzing the TLS response to an external electric field, we have deduced that the TLS electric dipole is in the order of, P ˜ 1 electron-Angstrom, consistent with the TLS having the charge of one electron tunneling through a disorder potential of distances, d ˜ 1 Angstrom.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Ramanpreet; Kaper, Lex; Ellerbroek, Lucas E.

We present the optical to near-infrared spectrum of MAXI J1659-152 during the onset of its 2010 X-ray outburst. The spectrum was obtained with X-shooter on the ESO Very Large Telescope early in the outburst simultaneous with high-quality observations at both shorter and longer wavelengths. At the time of the observations, the source was in the low-hard state. The X-shooter spectrum includes many broad ({approx}2000 km s{sup -1}), double-peaked emission profiles of H, He I, and He II, characteristic signatures of a low-mass X-ray binary during outburst. We detect no spectral signatures of the low-mass companion star. The strength of themore » diffuse interstellar bands results in a lower limit to the total interstellar extinction of A{sub V} {approx_equal} 0.4 mag. Using the neutral hydrogen column density obtained from the X-ray spectrum we estimate A{sub V} {approx_equal} 1 mag. The radial velocity structure of the interstellar Na I D and Ca II H and K lines results in a lower limit to the distance of {approx}4 {+-} 1 kpc, consistent with previous estimates. With this distance and A{sub V} , the dereddened spectral energy distribution represents a flat disk spectrum. The two 10 minute X-shooter spectra show significant variability in the red wing of the emission-line profiles, indicating a global change in the density structure of the disk, though on a timescale much shorter than the typical viscous timescale of the disk.« less

Time-Average Molecular Rayleigh Scattering Technique for Measurement of Velocity, Denisty, Temperature, and Turbulence Intensity in High Speed Nozzle Flows

NASA Technical Reports Server (NTRS)

Mielke, Amy F.; Seasholtz, Richard G.; Elam, Kristie A.; Panda, Jayanta

2004-01-01

A molecular Rayleigh scattering based flow diagnostic is developed to measure time average velocity, density, temperature, and turbulence intensity in a 25.4-mm diameter nozzle free jet facility. The spectrum of the Rayleigh scattered light is analyzed using a Fabry-Perot interferometer operated in the static imaging mode. The resulting fringe pattern containing spectral information of the scattered light is recorded using a low noise CCD camera. Nonlinear least squares analysis of the fringe pattern using a kinetic theory model of the Rayleigh scattered light provides estimates of density, velocity, temperature, and turbulence intensity of the gas flow. Resulting flow parameter estimates are presented for an axial scan of subsonic flow at Mach 0.95 for comparison with previously acquired pitot tube data, and axial scans of supersonic flow in an underexpanded screeching jet. The issues related to obtaining accurate turbulence intensity measurements using this technique are discussed.

Modeling SMAP Spacecraft Attitude Control Estimation Error Using Signal Generation Model

NASA Technical Reports Server (NTRS)

Rizvi, Farheen

2016-01-01

Two ground simulation software are used to model the SMAP spacecraft dynamics. The CAST software uses a higher fidelity model than the ADAMS software. The ADAMS software models the spacecraft plant, controller and actuator models, and assumes a perfect sensor and estimator model. In this simulation study, the spacecraft dynamics results from the ADAMS software are used as CAST software is unavailable. The main source of spacecraft dynamics error in the higher fidelity CAST software is due to the estimation error. A signal generation model is developed to capture the effect of this estimation error in the overall spacecraft dynamics. Then, this signal generation model is included in the ADAMS software spacecraft dynamics estimate such that the results are similar to CAST. This signal generation model has similar characteristics mean, variance and power spectral density as the true CAST estimation error. In this way, ADAMS software can still be used while capturing the higher fidelity spacecraft dynamics modeling from CAST software.

Pervasive randomness in physics: an introduction to its modelling and spectral characterisation

NASA Astrophysics Data System (ADS)

Howard, Roy

2017-10-01

An introduction to the modelling and spectral characterisation of random phenomena is detailed at a level consistent with a first exposure to the subject at an undergraduate level. A signal framework for defining a random process is provided and this underpins an introduction to common random processes including the Poisson point process, the random walk, the random telegraph signal, shot noise, information signalling random processes, jittered pulse trains, birth-death random processes and Markov chains. An introduction to the spectral characterisation of signals and random processes, via either an energy spectral density or a power spectral density, is detailed. The important case of defining a white noise random process concludes the paper.

Characterization of electrical noise limits in ultra-stable laser systems.

PubMed

Zhang, J; Shi, X H; Zeng, X Y; Lü, X L; Deng, K; Lu, Z H

2016-12-01

We demonstrate thermal noise limited and shot noise limited performance of ultra-stable diode laser systems. The measured heterodyne beat linewidth between such two independent diode lasers reaches 0.74 Hz. The frequency instability of one single laser approaches 1.0 × 10 -15 for averaging time between 0.3 s and 10 s, which is close to the thermal noise limit of the reference cavity. Taking advantage of these two ultra-stable laser systems, we systematically investigate the ultimate electrical noise contributions, and derive expressions for the closed-loop spectral density of laser frequency noise. The measured power spectral density of the beat frequency is compared with the theoretically calculated closed-loop spectral density of the laser frequency noise, and they agree very well. It illustrates the power and generality of the derived closed-loop spectral density formula of the laser frequency noise. Our result demonstrates that a 10 -17 level locking in a wide frequency range is feasible with careful design.

Cryogenic terahertz spectrum of (+)-methamphetamine hydrochloride and assignment using solid-state density functional theory.

PubMed

Hakey, Patrick M; Allis, Damian G; Ouellette, Wayne; Korter, Timothy M

2009-04-30

The cryogenic terahertz spectrum of (+)-methamphetamine hydrochloride from 10.0 to 100.0 cm(-1) is presented, as is the complete structural analysis and vibrational assignment of the compound using solid-state density functional theory. This cryogenic investigation reveals multiple spectral features that were not previously reported in room-temperature terahertz studies of the title compound. Modeling of the compound employed eight density functionals utilizing both solid-state and isolated-molecule methods. The results clearly indicate the necessity of solid-state simulations for the accurate assignment of solid-state THz spectra. Assignment of the observed spectral features to specific atomic motions is based on the BP density functional, which provided the best-fit solid-state simulation of the experimental spectrum. The seven experimental spectral features are the result of thirteen infrared-active vibrational modes predicted at a BP/DNP level of theory with more than 90% of the total spectral intensity associated with external crystal vibrations.

Fine structure of Galactic foreground ISM towards high-redshift AGN - utilizing Herschel PACS and SPIRE data

NASA Astrophysics Data System (ADS)

Perger, K.; Pinter, S.; Frey, S.; Tóth, L. V.

2018-05-01

One of the most certain ways to determine star formation rate in galaxies is based on far infrared (FIR) measurements. To decide the origin of the observed FIR emission, subtracting the Galactic foreground is a crucial step. We utilized Herschel photometric data to determine the hydrogen column densities in three galactic latitude regions, at b = 27°, 50° and -80°. We applied a pixel-by-pixel fit to the spectral energy distribution (SED) for the images aquired from parallel PACS-SPIRE observations in all three sky areas. We determined the column densities with resolutions 45'' and 6', and compared the results with values estimated from the IRAS dust maps. Column densities at 27° and 50° galactic latitudes determined from the Herschel data are in a good agreement with the literature values. However, at the highest galactic latitude we found that the column densities from the Herschel data exceed those derived from the IRAS dust map.

Effects of the density and homogeneity in NIRS crop moisture estimation

NASA Astrophysics Data System (ADS)

Lenzini, Nicola; Rovati, Luigi; Ferrari, Luca

2017-06-01

Near-infrared spectroscopy (NIRS) is widely used in fruits and vegetables quality evaluation. This technique is also used for the analysis of alfalfa, a crop that occupies a position of great importance in the agricultural field. In particular for the storage, moisture content is a key parameter for the crops and for this reason its monitoring is very important during the harvesting phase. Usually optical methods like NIRS are well suitable in laboratory frameworks where the specimen is properly prepared, while their application during the harvesting phase presents several diffculties. A lot of influencing factors, such as density and degree of homogeneity can affect the moisture evaluation. In this paper we present the NIRS analysis of alfalfa specimens with different values of moisture and density, as well as the obtained results. To study scattering and absorption phenomena, the forward and backward scattered light from the sample have been spectrally analyzed.

Random laser illumination: an ideal source for biomedical polarization imaging?

NASA Astrophysics Data System (ADS)

Carvalho, Mariana T.; Lotay, Amrit S.; Kenny, Fiona M.; Girkin, John M.; Gomes, Anderson S. L.

2016-03-01

Imaging applications increasingly require light sources with high spectral density (power over spectral bandwidth. This has led in many cases to the replacement of conventional thermal light sources with bright light-emitting diodes (LEDs), lasers and superluminescent diodes. Although lasers and superluminescent diodes appear to be ideal light sources due to their narrow bandwidth and power, however, in the case of full-field imaging, their spatial coherence leads to coherent artefacts, such as speckle, that corrupt the image. LEDs, in contrast, have lower spatial coherence and thus seem the natural choice, but they have low spectral density. Random Lasers are an unconventional type of laser that can be engineered to provide low spatial coherence with high spectral density. These characteristics makes them potential sources for biological imaging applications where specific absorption and reflection are the characteristics required for state of the art imaging. In this work, a Random Laser (RL) is used to demonstrate speckle-free full-field imaging for polarization-dependent imaging in an epi-illumination configuration. We compare LED and RL illumination analysing the resulting images demonstrating that the RL illumination produces an imaging system with higher performance (image quality and spectral density) than that provided by LEDs.

Effect of non-Poisson samples on turbulence spectra from laser velocimetry

NASA Technical Reports Server (NTRS)

Sree, Dave; Kjelgaard, Scott O.; Sellers, William L., III

1994-01-01

Spectral analysis of laser velocimetry (LV) data plays an important role in characterizing a turbulent flow and in estimating the associated turbulence scales, which can be helpful in validating theoretical and numerical turbulence models. The determination of turbulence scales is critically dependent on the accuracy of the spectral estimates. Spectral estimations from 'individual realization' laser velocimetry data are typically based on the assumption of a Poisson sampling process. What this Note has demonstrated is that the sampling distribution must be considered before spectral estimates are used to infer turbulence scales.

FLARES ON A-TYPE STARS: EVIDENCE FOR HEATING OF SOLAR CORONA BY NANOFLARES?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Švanda, Michal; Karlický, Marian, E-mail: michal@astronomie.cz

We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler . We found that the histogram of occurrence frequencies of stellar flares is systematically shifted toward a high-energy tail for A-type stars compared to stars of cooler spectral types. We extrapolated the fitted power laws toward flares with smaller energies (nanoflares) and made estimates for total energy flux to stellar atmospheres by flares. We found that, for A-type stars, the total energy flux density was at least four-times smaller than for G stars. We speculate that this deficit in energymore » supply may explain the lack of hot coronae on A-type stars. Our results indicate the importance of nanoflares for heating and formation of the solar corona.« less

Higher-order cumulants and spectral kurtosis for early detection of subterranean termites

NASA Astrophysics Data System (ADS)

de la Rosa, Juan José González; Moreno Muñoz, Antonio

2008-02-01

This paper deals with termite detection in non-favorable SNR scenarios via signal processing using higher-order statistics. The results could be extrapolated to all impulse-like insect emissions; the situation involves non-destructive termite detection. Fourth-order cumulants in time and frequency domains enhance the detection and complete the characterization of termite emissions, non-Gaussian in essence. Sliding higher-order cumulants offer distinctive time instances, as a complement to the sliding variance, which only reveal power excesses in the signal; even for low-amplitude impulses. The spectral kurtosis reveals non-Gaussian characteristics (the peakedness of the probability density function) associated to these non-stationary measurements, specially in the near ultrasound frequency band. Contrasted estimators have been used to compute the higher-order statistics. The inedited findings are shown via graphical examples.

Object-oriented recognition of high-resolution remote sensing image

NASA Astrophysics Data System (ADS)

Wang, Yongyan; Li, Haitao; Chen, Hong; Xu, Yuannan

2016-01-01

With the development of remote sensing imaging technology and the improvement of multi-source image's resolution in satellite visible light, multi-spectral and hyper spectral , the high resolution remote sensing image has been widely used in various fields, for example military field, surveying and mapping, geophysical prospecting, environment and so forth. In remote sensing image, the segmentation of ground targets, feature extraction and the technology of automatic recognition are the hotspot and difficulty in the research of modern information technology. This paper also presents an object-oriented remote sensing image scene classification method. The method is consist of vehicles typical objects classification generation, nonparametric density estimation theory, mean shift segmentation theory, multi-scale corner detection algorithm, local shape matching algorithm based on template. Remote sensing vehicles image classification software system is designed and implemented to meet the requirements .

Demonstration of zero bias responsivity in MBE grown β-Ga2O3 lateral deep-UV photodetector

NASA Astrophysics Data System (ADS)

Singh Pratiyush, Anamika; Krishnamoorthy, Sriram; Kumar, Sandeep; Xia, Zhanbo; Muralidharan, Rangarajan; Rajan, Siddharth; Nath, Digbijoy N.

2018-06-01

We demonstrate zero-bias spectral responsivity in MBE-grown β-Ga2O3 planar UV-C detector with good linearity up to optical power density of 4.6 mW cm‑2. Devices with asymmetrical metal contacts were realized on 150 nm thick β-Ga2O3 films on sapphire. The device exhibited a spectral responsivity of 1.4 mA W‑1 at 255 nm under zero-bias condition, dark current <10 nA at 15 V and UV-to-visible rejection ratio ∼105 at 5 V. The demonstrated UV-C detector exhibited an estimated high detectivity of 2.0 × 1012 Jones at 1 V and were found to be very stable and repeatable, suggesting its potential use for focal plane arrays.

Radial diffusion of relativistic electrons into the radiation belt slot region during the 2003 Halloween geomagnetic storms

NASA Astrophysics Data System (ADS)

Loto'Aniu, T. M.; Mann, I. R.; Ozeke, L. G.; Chan, A. A.; Dent, Z. C.; Milling, D. K.

2006-04-01

A study was undertaken to estimate the radial diffusion timescale, τLL, for relativistic electrons (2-6 MeV) to diffuse into the slot region due to drift-resonance with Pc5 ULF waves (2-10 mHz) on 29 October 2003. Large amplitude ULF waves were observed by ground-based magnetometer arrays to penetrate deep into the slot region (L ≃ 2-3) starting at 0600 UT and maximising (˜200 nT p-p) between 0930-1630 UT. Around the same time, the SAMPEX PET instrument measured an over two orders of magnitude increase in relativistic (2-6 MeV) electron flux levels in ˜24 hours within the slot region. The ground-based D-component magnetic power spectral densities (PSDδB) for 29 October were estimated for six latitudinally spaced ground stations covering L ˜ 2.3-4.3 for an observed ULF wave with central frequency ˜4 mHz. The PSDδB values were used to calculate the in situ equatorial poloidal wave electric field power spectral densities (PSDδEm) using a standing Alfvén wave model. The radial diffusion coefficients, DLL, were estimated using the PSDδEm values. The fastest τLL were 3-5 hours at L > 4, while τLL initially increased with decreasing L-value below L ≃ 4; peaking at L ≃ 3 with τLL ˜ 12-24 hours with PSDδEm estimated using a wave frequency bandwidth between Δf = 1 mHz and Δf = 2.5 mHz. The τLL over the L-range L ˜ 2.3-3.3 were consistent with the timescales observed by SAMPEX for the increase in relativistic fluxes in the slot region on 29 October. The authors believe that this is the first example of the ULF wave drift-resonance with relativistic electrons explaining a radiation belt slot region filling event.

Ocean Surface Wave Optical Roughness - Innovative Measurement and Modeling

DTIC Science & Technology

2007-09-30

whitecap crest length spectral density (Phillips et al, 2001, Gemmrich, 2005) and microscale breaker crest length spectral density (Jessup and Phadnis ...open sea, Journal of Physical Oceanography, 16, 290-297. Jessup, A.T. & Phadnis , K.R. 2005 Measurement of the geometric and kinematic properties of

Ocean Surface Wave Optical Roughness - Innovative Measurement and Modeling

DTIC Science & Technology

2006-09-30

length spectral density (eg. Phillips et al, 2001, Gemmrich, 2005) and microscale breaker crest length spectral density (eg. Jessup and Phadnis , 2005...Oceanography, 16, 290-297. Jessup, A.T. & Phadnis , K.R. 2005 Measurement of the geometric and kinematic properties of microsacle breaking waves from

Ocean Surface Wave Optical Roughness - Innovative Measurement and Modeling

DTIC Science & Technology

2006-09-30

crest length spectral density (eg. Phillips et al, 2001, Gemmrich, 2005) and microscale breaker crest length spectral density (eg. Jessup and Phadnis ...Jessup, A.T. & Phadnis , K.R. 2005 Measurement of the geometric and kinematic properties of microsacle breaking waves from infrared imagery using a

Spectroscopic Evidence of Alfvén Wave Damping in the Off-limb Solar Corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, G. R., E-mail: girjesh@iucaa.in

We investigate the off-limb active-region and quiet-Sun corona using spectroscopic data. The active region is clearly visible in several spectral lines formed in the temperature range of 1.1–2.8 MK. We derive the electron number density using the line ratio method, and the nonthermal velocity in the off-limb region up to the distance of 140 Mm. We compare density scale heights derived from several spectral line pairs with expected scale heights per the hydrostatic equilibrium model. Using several isolated and unblended spectral line profiles, we estimate nonthermal velocities in the active region and quiet Sun. Nonthermal velocities obtained from warm linesmore » in the active region first show an increase and then later either a decrease or remain almost constant with height in the far off-limb region, whereas nonthermal velocities obtained from hot lines show consistent decrease. However, in the quiet-Sun region, nonthermal velocities obtained from various spectral lines show either a gradual decrease or remain almost constant with height. Using these obtained parameters, we further calculate Alfvén wave energy flux in both active and quiet-Sun regions. We find a significant decrease in wave energy fluxes with height, and hence provide evidence of Alfvén wave damping. Furthermore, we derive damping lengths of Alfvén waves in the both regions and find them to be in the range of 25–170 Mm. Different damping lengths obtained at different temperatures may be explained as either possible temperature-dependent damping or by measurements obtained in different coronal structures formed at different temperatures along the line of sight. Temperature-dependent damping may suggest some role of thermal conduction in the damping of Alfvén waves in the lower corona.« less

UAV hyperspectral and lidar data analysis for vegetation applications

NASA Astrophysics Data System (ADS)

Sankey, Temuulen; Sankey, Joel; Donager, Jonathon

2017-04-01

High spatial and spectral resolution remote sensing data are critically needed to classify forest vegetation and measure their structure at the level of individual species and canopies. Here we test high-resolution lidar and hyperspectral data from unmanned aerial vehicles (UAV) and demonstrate a lidar-hyperspectral image fusion method in treated and control forests with varying tree density and canopy cover as well as in an ecotone with a gradient of vegetation and topography in northern Arizona, USA. The fusion performs better (88% overall accuracy) than either data type alone, particularly for species with similar spectral signature, but different canopy sizes. The lidar data provides estimates of individual tree height (R2=0.90; RMSE=2.3m) and crown diameter (R2=0.72; RMSE=0.71m) as well as total tree canopy cover (R2=0.87; RMSE=9.5%) and tree density (R2=0.77; RMSE=0.69 trees/cell) in 10 m cells across thin only, burn only, thin-and-burn, and control treatments, where tree cover and density ranged between 22-50% and 1-3.5 trees/cell, respectively. The lidar data also produces high accuracy DEM (R2=0.95; RMSE=0.43m). The lidar and hyperspectral sensors and methods demonstrated here can be widely applied across a gradient of vegetation and topography for monitoring ecosystem changes.

Computed lateral rate and acceleration power spectral response of conventional and STOL airplanes to atmospheric turbulence

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.

Spatially unresolved SED fitting can underestimate galaxy masses: a solution to the missing mass problem

NASA Astrophysics Data System (ADS)

Sorba, Robert; Sawicki, Marcin

2018-05-01

We perform spatially resolved, pixel-by-pixel Spectral Energy Distribution (SED) fitting on galaxies up to z ˜ 2.5 in the Hubble eXtreme Deep Field (XDF). Comparing stellar mass estimates from spatially resolved and spatially unresolved photometry we find that unresolved masses can be systematically underestimated by factors of up to 5. The ratio of the unresolved to resolved mass measurement depends on the galaxy's specific star formation rate (sSFR): at low sSFRs the bias is small, but above sSFR ˜ 10-9.5 yr-1 the discrepancy increases rapidly such that galaxies with sSFRs ˜ 10-8 yr-1 have unresolved mass estimates of only one-half to one-fifth of the resolved value. This result indicates that stellar masses estimated from spatially unresolved data sets need to be systematically corrected, in some cases by large amounts, and we provide an analytic prescription for applying this correction. We show that correcting stellar mass measurements for this bias changes the normalization and slope of the star-forming main sequence and reduces its intrinsic width; most dramatically, correcting for the mass bias increases the stellar mass density of the Universe at high redshift and can resolve the long-standing discrepancy between the directly measured cosmic SFR density at z ≳ 1 and that inferred from stellar mass densities (`the missing mass problem').

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.

Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources

DOE PAGES

Nesci, R.; Tosti, G.; Pursimo, T.; ...

2013-06-18

Context. We present that spectral energy distribution and its variability are basic tools for understanding the physical processes operating in active galactic nuclei (AGN). Aims. In this paper we report the results of a one-year near-infrared (NIR) and optical monitoring of a sample of 22 AGN known to be gamma-ray emitters, aimed at discovering correlations between optical and gamma-ray emission. Methods. We observed our objects with the Rapid Eye Mount (REM) telescope in J,H,K, and R bands nearly twice every month during their visibility window and derived light curves and spectral indexes. We also analyzed the gamma-ray data from themore » Fermi gamma-ray Space Telescope, making weekly averages. Results. Six sources were never detected during our monitoring, proving to be fainter than their historical Two micron all sky survey (2MASS) level. All of the sixteen detected sources showed marked flux density variability, while the spectral indexes remained unchanged within our sensitivity limits. Steeper sources showed, on average, a larger variability. From the NIR light curves we also computed a variability speed index for each detected source. Only one source (PKS 0208-512) underwent an NIR flare during our monitoring. Half of the sources showed a regular flux density trend on a one-year time scale, but do not show any other peculiar characteristic. The broadband spectral index α ro appears to be a good proxy of the NIR spectral index only for BL Lac objects. No clear correlation between NIR and gamma-ray data is evident in our data, save for PKS 0537-441, PKS 0521-360, PKS 2155-304, and PKS 1424-418. In conclusion, the gamma-ray/NIR flux ratio showed a large spread, QSO being generally gamma-louder than BL Lac, with a marked correlation with the estimated peak frequency (ν peak) of the synchrotron emission.« less

Speech Enhancement, Gain, and Noise Spectrum Adaptation Using Approximate Bayesian Estimation

PubMed Central

Hao, Jiucang; Attias, Hagai; Nagarajan, Srikantan; Lee, Te-Won; Sejnowski, Terrence J.

2010-01-01

This paper presents a new approximate Bayesian estimator for enhancing a noisy speech signal. The speech model is assumed to be a Gaussian mixture model (GMM) in the log-spectral domain. This is in contrast to most current models in frequency domain. Exact signal estimation is a computationally intractable problem. We derive three approximations to enhance the efficiency of signal estimation. The Gaussian approximation transforms the log-spectral domain GMM into the frequency domain using minimal Kullback–Leiber (KL)-divergency criterion. The frequency domain Laplace method computes the maximum a posteriori (MAP) estimator for the spectral amplitude. Correspondingly, the log-spectral domain Laplace method computes the MAP estimator for the log-spectral amplitude. Further, the gain and noise spectrum adaptation are implemented using the expectation–maximization (EM) algorithm within the GMM under Gaussian approximation. The proposed algorithms are evaluated by applying them to enhance the speeches corrupted by the speech-shaped noise (SSN). The experimental results demonstrate that the proposed algorithms offer improved signal-to-noise ratio, lower word recognition error rate, and less spectral distortion. PMID:20428253

Ocean Surface Wave Optical Roughness - Innovative Measurement and Modeling

DTIC Science & Technology

2006-01-01

spectral density (eg. Phillips et al, 2001, Gemmrich, 2005) and microscale breaker crest length spectral density (eg. Jessup and Phadnis , 2005) have...observed as whitecaps in the open sea, Journal of Physical Oceanography, 16, 290-297. Jessup, A.T. & Phadnis , K.R. 2005 Measurement of the geometric

Crustal structure of the Dabie orogenic belt (eastern China) inferred from gravity and magnetic data

NASA Astrophysics Data System (ADS)

Yang, Yu-shan; Li, Yuan-yuan

2018-01-01

In order to better characterize the crustal structure of the Dabie orogen and its tectonic history, we present a crustal structure along a 500 km long profile across the Dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data. Source depth estimations from the spectral analysis by continuous wavelet transform (CWT) provide better constraints for constructing the initial density model. The calculated gravity effects from the initial model show great discrepancy with the observed data, especially at the center of the profile. More practical factors are then incorporated into the gravity modeling. First, we add a high density body right beneath the high pressure metamorphic (HPM) and ultrahigh pressure metamorphic (UHPM) belt considering the exposed HPM and UHPM rocks in the mid of our profile. Then, the anomalous bodies A, B, and C inferred from the CWT-based spectral analysis results are fixed in the model geometry. In the final crustal density structure, two anomalous bodies B and C with high density and low magnetization could possibly be attributed to metasomatised mantle materials by SiO2-rich melt derived from the foundering subducted mafic lower crust. Under the extensional environment in the early Cretaceous, the upwelling metasomatised mantle was partially melted to produce the parental magma of the post-collisional mafic-ultramafic intrusive rocks. As for the low density body A with strong magnetization located in the lower crust right beneath the HP and UHP metamorphic belt, it is more likely to be composed of serpentinized mantle peridotite (SMP). This serpentinized mantle peridotite body (SMPB) represents the emplacement of mantle-derived peridotites in the crust, accompanying the exhumation of the UHP metamorphic rocks.

Reduced quantum dynamics with arbitrary bath spectral densities: hierarchical equations of motion based on several different bath decomposition schemes.

PubMed

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.

High level white noise generator

DOEpatents

Borkowski, Casimer J.; Blalock, Theron V.

1979-01-01

A wide band, stable, random noise source with a high and well-defined output power spectral density is provided which may be used for accurate calibration of Johnson Noise Power Thermometers (JNPT) and other applications requiring a stable, wide band, well-defined noise power spectral density. The noise source is based on the fact that the open-circuit thermal noise voltage of a feedback resistor, connecting the output to the input of a special inverting amplifier, is available at the amplifier output from an equivalent low output impedance caused by the feedback mechanism. The noise power spectral density level at the noise source output is equivalent to the density of the open-circuit thermal noise or a 100 ohm resistor at a temperature of approximately 64,000 Kelvins. The noise source has an output power spectral density that is flat to within 0.1% (0.0043 db) in the frequency range of from 1 KHz to 100 KHz which brackets typical passbands of the signal-processing channels of JNPT's. Two embodiments, one of higher accuracy that is suitable for use as a standards instrument and another that is particularly adapted for ambient temperature operation, are illustrated in this application.

Reduced quantum dynamics with arbitrary bath spectral densities: Hierarchical equations of motion based on several different bath decomposition schemes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Hao; Zhu, Lili; Bai, Shuming

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 inmore » 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.« less

Inherent length-scales of periodic solar wind number density structures

NASA Astrophysics Data System (ADS)

Viall, N. M.; Kepko, L.; Spence, H. E.

2008-07-01

We present an analysis of the radial length-scales of periodic solar wind number density structures. We converted 11 years (1995-2005) of solar wind number density data into radial length series segments and Fourier analyzed them to identify all spectral peaks with radial wavelengths between 72 (116) and 900 (900) Mm for slow (fast) wind intervals. Our window length for the spectral analysis was 9072 Mm, approximately equivalent to 7 (4) h of data for the slow (fast) solar wind. We required that spectral peaks pass both an amplitude test and a harmonic F-test at the 95% confidence level simultaneously. From the occurrence distributions of these spectral peaks for slow and fast wind, we find that periodic number density structures occur more often at certain radial length-scales than at others, and are consistently observed within each speed range over most of the 11-year interval. For the slow wind, those length-scales are L ˜ 73, 120, 136, and 180 Mm. For the fast wind, those length-scales are L ˜ 187, 270 and 400 Mm. The results argue for the existence of inherent radial length-scales in the solar wind number density.

Spectral algorithm for non-destructive damage localisation: Application to an ancient masonry arch model

NASA Astrophysics Data System (ADS)

Masciotta, Maria-Giovanna; Ramos, Luís F.; Lourenço, Paulo B.; Vasta, Marcello

2017-02-01

Structural monitoring and vibration-based damage identification methods are fundamental tools for condition assessment and early-stage damage identification, especially when dealing with the conservation of historical constructions and the maintenance of strategic civil structures. However, although the substantial advances in the field, several issues must still be addressed to broaden the application range of such tools and to assert their reliability. This study deals with the experimental validation of a novel method for non-destructive damage identification purposes. This method is based on the use of spectral output signals and has been recently validated by the authors through a numerical simulation. After a brief insight into the basic principles of the proposed approach, the spectral-based technique is applied to identify the experimental damage induced on a masonry arch through statically increasing loading. Once the direct and cross spectral density functions of the nodal response processes are estimated, the system's output power spectrum matrix is built and decomposed in eigenvalues and eigenvectors. The present study points out how the extracted spectral eigenparameters contribute to the damage analysis allowing to detect the occurrence of damage and to locate the target points where the cracks appear during the experimental tests. The sensitivity of the spectral formulation to the level of noise in the modal data is investigated and discussed. As a final evaluation criterion, the results from the spectrum-driven method are compared with the ones obtained from existing non-model based damage identification methods.

A comparative study of microwave radiometer observations over snowfields with radiative transfer model calculations. [for water runoff estimation

NASA Technical Reports Server (NTRS)

Chang, A. T. C.; Shiue, J. C.

1979-01-01

Truck mounted microwave instrumentation was used to study the microwave emission characteristics of the Colorado Rocky Mountain snowpack in the vicinity of Fraser, Colorado during the winter of 1978. The spectral signatures of 5.0, 10.7, 18, and 37 GHz radiometers with dual polarization were used to measure the snowpack density and temperature profiles, rain profile, and free water content. These data were compared with calculated results based on microscopic scattering models for dry, surface melting, and very wet snowpacks.

Identification of modal parameters including unmeasured forces and transient effects

NASA Astrophysics Data System (ADS)

Cauberghe, B.; Guillaume, P.; Verboven, P.; Parloo, E.

2003-08-01

In this paper, a frequency-domain method to estimate modal parameters from short data records with known input (measured) forces and unknown input forces is presented. The method can be used for an experimental modal analysis, an operational modal analysis (output-only data) and the combination of both. A traditional experimental and operational modal analysis in the frequency domain starts respectively, from frequency response functions and spectral density functions. To estimate these functions accurately sufficient data have to be available. The technique developed in this paper estimates the modal parameters directly from the Fourier spectra of the outputs and the known input. Instead of using Hanning windows on these short data records the transient effects are estimated simultaneously with the modal parameters. The method is illustrated, tested and validated by Monte Carlo simulations and experiments. The presented method to process short data sequences leads to unbiased estimates with a small variance in comparison to the more traditional approaches.

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

Pc 5 magnetic pulsations with frequencies between 1.67 and 6.67 mHz, are believed to contribute to the Relativistic Electron Enhancement (REE) in the outer radiation belt during magnetic storms. Ground-based observations suggested that high-speed solar wind and large-amplitude Pc 5 waves with a long duration during the storm recovery phase are closely associated with the production of relativistic electrons [Baker et al., 1998; Rostoker et al., 1998; Mathie and Mann, 2000; O’Brien et al., 2001, 2003]. On the other hand, many relativistic electron acceleration mechanisms have been proposed theoretically. They are separated roughly into two themes: in situ acceleration at L lower than 6.6 by wave particle interactions (as internal source acceleration mechanisms) [Liu et al., 1999; Summers et al., 1999; Summers and Ma, 2000] and acceleration by radial diffusion to transport and accelerate a source population of electrons from the outer to the inner magnetosphere (as external source acceleration mechanisms) [Elkington et al., 1999, 2003; Hudson et al., 2000; Kim et al., 2001]. One possible external source acceleration mechanism is the resonant interaction with ULF toroidal and poloidal waves. In order to verify which of the two mechanisms is more effective for the REE, we have to examine the time variation of electron phase space density. Electron phase space density is not directly measured, but we can estimate radial diffusion coefficients using observational electric and magnetic data. The goal of this paper is to get more reliable radial diffusion coefficient from ground-based observational magnetic field and to show reasonability of it for radial diffusion model. We use the global magnetometer data obtained from ULTIMA (Ultra Large Terrestrial International Magnetic Array, see http://www.serc.kyushu-u.ac.jp/ultima/ultima.html) stations, to precisely define the radial diffusion timescales. The ULTIMA includes McMAC, CARISAM, 210MM and MAGDAS/CPMN magnetometer 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.

Comparison of Background Parenchymal Enhancement at Contrast-enhanced Spectral Mammography and Breast MR Imaging

PubMed Central

Morris, Elizabeth A.; Kaplan, Jennifer B.; D’Alessio, Donna; Goldman, Debra; Moskowitz, Chaya S.

2017-01-01

Purpose To assess the extent of background parenchymal enhancement (BPE) at contrast material–enhanced (CE) spectral mammography and breast magnetic resonance (MR) imaging, to evaluate interreader agreement in BPE assessment, and to examine the relationships between clinical factors and BPE. Materials and Methods This was a retrospective, institutional review board–approved, HIPAA-compliant study. Two hundred seventy-eight women from 25 to 76 years of age with increased breast cancer risk who underwent CE spectral mammography and MR imaging for screening or staging from 2010 through 2014 were included. Three readers independently rated BPE on CE spectral mammographic and MR images with the ordinal scale: minimal, mild, moderate, or marked. To assess pairwise agreement between BPE levels on CE spectral mammographic and MR images and among readers, weighted κ coefficients with quadratic weights were calculated. For overall agreement, mean κ values and bootstrapped 95% confidence intervals were calculated. The univariate and multivariate associations between BPE and clinical factors were examined by using generalized estimating equations separately for CE spectral mammography and MR imaging. Results Most women had minimal or mild BPE at both CE spectral mammography (68%–76%) and MR imaging (69%–76%). Between CE spectral mammography and MR imaging, the intrareader agreement ranged from moderate to substantial (κ = 0.55–0.67). Overall agreement on BPE levels between CE spectral mammography and MR imaging and among readers was substantial (κ = 0.66; 95% confidence interval: 0.61, 0.70). With both modalities, BPE demonstrated significant association with menopausal status, prior breast radiation therapy, hormonal treatment, breast density on CE spectral mammographic images, and amount of fibroglandular tissue on MR images (P < .001 for all). Conclusion There was substantial agreement between readers for BPE detected on CE spectral mammographic and MR images. © RSNA, 2016 PMID:27379544

An analytic technique for statistically modeling random atomic clock errors in estimation

NASA Technical Reports Server (NTRS)

Fell, P. J.

1981-01-01

Minimum variance estimation requires that the statistics of random observation errors be modeled properly. If measurements are derived through the use of atomic frequency standards, then one source of error affecting the observable is random fluctuation in frequency. This is the case, for example, with range and integrated Doppler measurements from satellites of the Global Positioning and baseline determination for geodynamic applications. An analytic method is presented which approximates the statistics of this random process. The procedure starts with a model of the Allan variance for a particular oscillator and develops the statistics of range and integrated Doppler measurements. A series of five first order Markov processes is used to approximate the power spectral density obtained from the Allan variance.

47 CFR 25.212 - Narrowband analog transmissions and digital transmissions in the GSO Fixed Satellite Service.

Code of Federal Regulations, 2013 CFR

2013-10-01

... kHz if the maximum input power spectral density into the antenna does not exceed −8 dBW/4 kHz and the maximum transmitted satellite carrier EIRP density does not exceed 17 dBW/4 kHz. (2) In the 14.0... services, if the maximum input spectral power density into the antenna does not exceed −14 dBW/4 kHz, and...

Time scale variation of NV resonance line profiles of HD203064

NASA Astrophysics Data System (ADS)

Strantzalis, A.

2012-01-01

Hot emission star, such as Be and Oe, present many spectral lines with very complex and peculiar profiles. Therefore, we cannot find a classical distribution to fit theoretically those physical line profiles. So, many physical parameters of the regions, where spectral lines are created, are difficult to estimate. Here, in this poster paper we study the UV NV (λλ 1238.821, 1242.804 A) resonance lines of the Be star HD203064 at three different dates. We using the Gauss-Rotation model, that proposed the idea that these complex profiles consist of a number of independent Discrete or Satellite Absorption Components (DACs, SACs). Our purpose is to calculate the values of a group of physical parameters as the apparent rotational, radial, and random velocities of the thermal motions of the ions. Also the Full Width at Half Maximum (FWHM) and the column density, as well as the absorbed energy of the independent regions of matter, which produce the main and the satellite components of the studied spectral lines. In addition, we determine the time scale variations of the above physical parameters.

Raman spectral evidence of methyl rotation in liquid toluene.

PubMed

Kapitán, Josef; Hecht, Lutz; Bour, Petr

2008-02-21

In order to rationalize subtle details in the liquid phase toluene Raman backscattering spectra, an analysis was performed based on a quantum-mechanical Hamiltonian operator comprising rotation of the methyl group and the angular dependence of vibrational frequencies and polarizability derivatives. The separation of the methyl torsion from the other vibrational motions appears to be necessary in order to explain relative intensity ratios of several bands and an anomalous broadening of spectral intensity observed at 1440 cm(-1). These results suggest that the CH3 group in the liquid phase rotates almost freely, similarly as in the gaseous phase, and that the molecule consequently exhibits effectively C(2v) point group symmetry. A classical description and an adiabatic separation of the methyl rotation from other molecular motion previously used in peptide models is not applicable to toluene because of a strong coupling with other vibrational motions. Density functional computations, particularly the BPW91 functional, provide reasonable estimates of harmonic frequencies and spectral intensities, as well as qualitatively correct fourth-order anharmonic corrections to the vibrational potential.

Single-particle spectral density of the unitary Fermi gas: Novel approach based on the operator product expansion, sum rules and the maximum entropy method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gubler, Philipp, E-mail: pgubler@riken.jp; RIKEN Nishina Center, Wako, Saitama 351-0198; Yamamoto, Naoki

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.

Saturn Ring Rain: New Observations and Estimates of Water Influx

NASA Astrophysics Data System (ADS)

Moore, L.; O'Donoghue, J.; Mueller-Wodarg, I.; Galand, M.; Mendillo, M.

2014-04-01

We estimate the maximum rates of water influx from Saturn's rings based on ionospheric model reproductions of derived H3+ column densities. On 17 April 2011 over two hours of near-infrared spectral data were obtained of Saturn using the Near InfraRed Spectrograph (NIRSPEC) instrument on the 10-m Keck II telescope. Two bright H3+ rotationalvibrational emission lines were visible nearly from pole to pole, allowing low-latitude ionospheric emissions to be studied for the first time, and revealing significant latitudinal structure, with local extrema in one hemisphere being mirrored at magnetically conjugate latitudes in the opposite hemisphere. In addition, those minima and maxima mapped to latitudes of increased or decreased density, respectively, in Saturn's rings, implying a direct ringatmosphere connection in which charged water group particles from the rings are guided by magnetic field lines as they "rain" down upon the atmosphere. Water products act to quench the local ionosphere, and therefore modify the H3+ densities and their observed emissions. Using the Saturn Thermosphere Ionosphere Model (STIM), a 3-D model of Saturn's upper atmosphere, we derive the maximum rates of water influx required from the rings in order to reproduce the H3+ column densities observed on 17 April 2011. We estimate the globally averaged maximum ringderived water influx to be (1.6-12)x105 cm-2 sec-1, which represents a maximum total global influx of water from Saturn's rings to its atmosphere of (1.0-6.8)x1026 sec-1. We will also present the initial findings of Keck ring rain observing campaigns from April 2013 and May 2014.

Saturn’s Ring Rain: Initial Estimates of Ring Mass Loss Rates

NASA Astrophysics Data System (ADS)

Moore, Luke; O'Donoghue, J.; Mueller-Wodarg, I.; Mendillo, M.

2013-10-01

We estimate rates of mass loss from Saturn’s rings based on ionospheric model reproductions of derived H3+ column densities. On 17 April 2011 over two hours of near-infrared spectral data were obtained of Saturn using the Near InfraRed Spectrograph (NIRSPEC) instrument on the 10-m Keck II telescope. The intensity of two bright H3+ rotational-vibrational emission lines was visible from nearly pole to pole, allowing low-latitude ionospheric emissions to be studied for the first time, and revealing significant latitudinal structure, with local extrema in one hemisphere being mirrored at magnetically conjugate latitudes in the opposite hemisphere. Even more striking, those minima and maxima mapped to latitudes of increased or increased density in Saturn’s rings, implying a direct ring-atmosphere connection in which charged water group particles from the rings are guided by magnetic field lines as they “rain” down upon the atmosphere. Water products act to quench the local ionosphere, and therefore modify the observed H3+ densities. Using the Saturn Thermosphere Ionosphere Model (STIM), a 3-D model of Saturn’s upper atmosphere, we derive the rates of water influx required from the rings in order to reproduce the observed H3+ column densities. As a unique pair of conjugate latitudes map to a specific radial distance in the ring plane, the derived water influxes can equivalently be described as rates of ring mass erosion as a function of radial distance in the ring plane, and therefore also allow for an improved estimate of the lifetime of Saturn’s rings.

Application of MODIS GPP to Forecast Risk of Hantavirus Pulmonary Syndrome Based on Fluctuations in Reservoir Population Density

NASA Astrophysics Data System (ADS)

Loehman, R.; Heinsch, F. A.; Mills, J. N.; Wagoner, K.; Running, S.

2003-12-01

Recent predictive models for hantavirus pulmonary syndrome (HPS) have used remotely sensed spectral reflectance data to characterize risk areas with limited success. We present an alternative method using gross primary production (GPP) from the MODIS sensor to estimate the effects of biomass accumulation on population density of Peromyscus maniculatus (deer mouse), the principal reservoir species for Sin Nombre virus (SNV). The majority of diagnosed HPS cases in North America are attributed to SNV, which is transmitted to humans through inhalation of excretions and secretions from infected rodents. A logistic model framework is used to evaluate MODIS GPP, temperature, and precipitation as predictors of P. maniculatus density at established trapping sites across the western United States. Rodent populations are estimated using monthly minimum number alive (MNA) data for 2000 through 2002. Both local meteorological data from nearby weather stations and 1.25 degree x 1 degree gridded data from the NASA DAO were used in the regression model to determine the spatial sensitivity of the response. MODIS eight-day GPP data (1-km resolution) were acquired and binned to monthly average and monthly sum GPP for 3km x 3km grids surrounding each rodent trapping site. The use of MODIS GPP to forecast HPS risk may result in a marked improvement over past reflectance-based risk area characterizations. The MODIS GPP product provides a vegetation dynamics estimate that is unique to disease models, and targets the fundamental ecological processes responsible for increased rodent density and amplified disease risk.

Comparison of three methods for long-term monitoring of boreal lake area using Landsat TM and ETM+ imagery

USGS Publications Warehouse

Roach, Jennifer K.; Griffith, Brad; Verbyla, David

2012-01-01

Programs to monitor lake area change are becoming increasingly important in high latitude regions, and their development often requires evaluating tradeoffs among different approaches in terms of accuracy of measurement, consistency across multiple users over long time periods, and efficiency. We compared three supervised methods for lake classification from Landsat imagery (density slicing, classification trees, and feature extraction). The accuracy of lake area and number estimates was evaluated relative to high-resolution aerial photography acquired within two days of satellite overpasses. The shortwave infrared band 5 was better at separating surface water from nonwater when used alone than when combined with other spectral bands. The simplest of the three methods, density slicing, performed best overall. The classification tree method resulted in the most omission errors (approx. 2x), feature extraction resulted in the most commission errors (approx. 4x), and density slicing had the least directional bias (approx. half of the lakes with overestimated area and half of the lakes with underestimated area). Feature extraction was the least consistent across training sets (i.e., large standard error among different training sets). Density slicing was the best of the three at classifying small lakes as evidenced by its lower optimal minimum lake size criterion of 5850 m2 compared with the other methods (8550 m2). Contrary to conventional wisdom, the use of additional spectral bands and a more sophisticated method not only required additional processing effort but also had a cost in terms of the accuracy and consistency of lake classifications.

Detailed spectral and morphological analysis of the shell type supernova remnant RCW 86

NASA Astrophysics Data System (ADS)

H.E.S.S. Collaboration; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Angüner, E. O.; Backes, M.; Balzer, A.; Becherini, Y.; Becker Tjus, J.; Berge, D.; Bernhard, S.; Bernlöhr, K.; Birsin, E.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Bulik, T.; Carr, J.; Casanova, S.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Chrétien, M.; Colafrancesco, S.; Cologna, G.; Condon, B.; Conrad, J.; Couturier, C.; Cui, Y.; Davids, I. D.; Degrange, B.; Deil, C.; deWilt, P.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O.'C.; Dubus, G.; Dutson, K.; Dyks, J.; Dyrda, M.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Espigat, P.; Farnier, C.; Fegan, S.; Feinstein, F.; Fernandes, M. V.; Fernandez, D.; Fiasson, A.; Fontaine, G.; Förster, A.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Grudzińska, M.; Hadasch, D.; Häffner, S.; Hahn, J.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hillert, A.; Hinton, J. A.; Hofmann, W.; Hofverberg, P.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, F.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kerszberg, D.; Khélifi, B.; Kieffer, M.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Krayzel, F.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lefaucheur, J.; Lefranc, V.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Lohse, T.; Lopatin, A.; Lorentz, M.; Lu, C.-C.; Lui, R.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Menzler, U.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Morå, K.; Moulin, E.; Murach, T.; de Naurois, M.; Niemiec, J.; Oakes, L.; Odaka, H.; Öttl, S.; Ohm, S.; Opitz, B.; Ostrowski, M.; Oya, I.; Panter, M.; Parsons, R. D.; Paz Arribas, M.; Pekeur, N. W.; Pelletier, G.; Petrucci, P.-O.; Peyaud, B.; Pita, S.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reichardt, I.; Reimer, A.; Reimer, O.; Renaud, M.; de los Reyes, R.; Rieger, F.; Romoli, C.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seyffert, A. S.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tluczykont, M.; Trichard, C.; Tuffs, R.; Valerius, K.; van der Walt, J.; van Eldik, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; Weidinger, M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Żywucka, N.

2018-04-01

Aim. We aim for an understanding of the morphological and spectral properties of the supernova remnant RCW 86 and for insights into the production mechanism leading to the RCW 86 very high-energy γ-ray emission. Methods: We analyzed High Energy Spectroscopic System (H.E.S.S.) data that had increased sensitivity compared to the observations presented in the RCW 86 H.E.S.S. discovery publication. Studies of the morphological correlation between the 0.5-1 keV X-ray band, the 2-5 keV X-ray band, radio, and γ-ray emissions have been performed as well as broadband modeling of the spectral energy distribution with two different emission models. Results: We present the first conclusive evidence that the TeV γ-ray emission region is shell-like based on our morphological studies. The comparison with 2-5 keV X-ray data reveals a correlation with the 0.4-50 TeV γ-ray emission. The spectrum of RCW 86 is best described by a power law with an exponential cutoff at Ecut = (3.5 ± 1.2stat) TeV and a spectral index of Γ ≈ 1.6 ± 0.2. A static leptonic one-zone model adequately describes the measured spectral energy distribution of RCW 86, with the resultant total kinetic energy of the electrons above 1 GeV being equivalent to 0.1% of the initial kinetic energy of a Type Ia supernova explosion (1051 erg). When using a hadronic model, a magnetic field of B ≈ 100 μG is needed to represent the measured data. Although this is comparable to formerly published estimates, a standard E-2 spectrum for the proton distribution cannot describe the γ-ray data. Instead, a spectral index of Γp ≈ 1.7 would be required, which implies that ˜7 × 1049/ncm-3 has been transferred into high-energy protons with the effective density ncm-3 = n/1 cm-3. This is about 10% of the kinetic energy of a typical Type Ia supernova under the assumption of a density of 1 cm-3.

Reconstructing Spectral Scenes Using Statistical Estimation to Enhance Space Situational Awareness

DTIC Science & Technology

2006-12-01

simultane- ously spatially and spectrally deblur the images collected from ASIS. The algorithms are based on proven estimation theories and do not...collected with any system using a filtering technology known as Electronic Tunable Filters (ETFs). Previous methods to deblur spectral images collected...spectrally deblurring then the previously investigated methods. This algorithm expands on a method used for increasing the spectral resolution in gamma-ray

Influence of aerosols on surface reaching spectral irradiance and introduction to a new technique of estimating aerosol radiative forcing from high resolution spectral flux measurements

NASA Astrophysics Data System (ADS)

Rao, Roshan

2016-04-01

Aerosol radiative forcing estimates with high certainty are required in climate change studies. The approach in estimating the aerosol radiative forcing by using the chemical composition of aerosols is not effective as the chemical composition data with radiative properties are not widely available. We look into the approach where ground based spectral radiation flux measurement is made and along with an Radtiative transfer (RT) model, radiative forcing is estimated. Measurements of spectral flux were made using an ASD spectroradiometer with 350 - 1050 nm wavelength range and a 3nm resolution during around 54 clear-sky days during which AOD range was around 0.01 to 0.7. Simultaneous measurements of black carbon were also made using Aethalometer (Magee Scientific) which ranged from around 1.5 ug/m3 to 8 ug/m3. The primary study involved in understanding the sensitivity of spectral flux due to change in individual aerosol species (Optical properties of Aerosols and Clouds (OPAC) classified aerosol species) using the SBDART RT model. This made us clearly distinguish the influence of different aerosol species on the spectral flux. Following this, a new technique has been introduced to estimate an optically equivalent mixture of aerosol species for the given location. The new method involves matching different combinations of aerosol species in OPAC model and RT model as long as the combination which gives the minimum root mean squared deviation from measured spectral flux is obtained. Using the optically equivalent aerosol mixture and RT model, aerosol radiative forcing is estimated. Also an alternate method to estimate the spectral SSA is discussed. Here, the RT model, the observed spectral flux and spectral AOD is used. Spectral AOD is input to RT model and SSA is varied till the minimum root mean squared difference between observed and simulated spectral flux from RT model is obtained. The methods discussed are limited to clear sky scenes and its accuracy to derive an optically equivalent aerosol mixture reduces when diffuse component of flux increases. In our analysis, RT model clearly shows that direct component of spectral flux is more sensitive to different aerosol species than total spectral flux which is also supported by our observed data.

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.

The Power Spectrum of Ionic Nanopore Currents: The Role of Ion Correlations.

PubMed

Zorkot, Mira; Golestanian, Ramin; Bonthuis, Douwe Jan

2016-04-13

We calculate the power spectrum of electric-field-driven ion transport through nanometer-scale membrane pores using both linearized mean-field theory and Langevin dynamics simulations. Remarkably, the linearized mean-field theory predicts a plateau in the power spectral density at low frequency ω, which is confirmed by the simulations at low ion concentration. At high ion concentration, however, the power spectral density follows a power law that is reminiscent of the 1/ω(α) dependence found experimentally at low frequency. On the basis of simulations with and without ion-ion interactions, we attribute the low-frequency power-law dependence to ion-ion correlations. We show that neither a static surface charge density, nor an increased pore length, nor an increased ion valency have a significant effect on the shape of the power spectral density at low frequency.

Quasi-stellar objects in the intergalactic medium: Source for the cosmic X-ray background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sherman, R.D.

1980-06-15

QSOs are regarded as sources of both electromagnetic radiation and ejected matter that heat and ionize a dense intergalactic medium (IGM). Using current estimates of QSO luminosity, number density, evolution, and spectral index, we study three viable models: the diffuse cosmic X-ray background is (1) due entirely to thermal Bremsstrahlung of the IGM, (2) completely supplied by QSO X-radiation, (3) or a combination of both. The upper limits on an IGM fractional density with respect to closure are ..cap omega..=0.26, 0.24, and 0.21 for pure collisional, photo/collisional mixture, and pure photoionization, respectively. These calculations give emission spectra, Compton distortion ofmore » the cosmic microwave background, and optical depths to distant OSOs for comparison with relevant data.« less

A robust pseudo-inverse spectral filter applied to the Earth Radiation Budget Experiment (ERBE) scanning channels

NASA Technical Reports Server (NTRS)

Avis, L. M.; Green, R. N.; Suttles, J. T.; Gupta, S. K.

1984-01-01

Computer simulations of a least squares estimator operating on the ERBE scanning channels are discussed. The estimator is designed to minimize the errors produced by nonideal spectral response to spectrally varying and uncertain radiant input. The three ERBE scanning channels cover a shortwave band a longwave band and a ""total'' band from which the pseudo inverse spectral filter estimates the radiance components in the shortwave band and a longwave band. The radiance estimator draws on instantaneous field of view (IFOV) scene type information supplied by another algorithm of the ERBE software, and on a priori probabilistic models of the responses of the scanning channels to the IFOV scene types for given Sun scene spacecraft geometry. It is found that the pseudoinverse spectral filter is stable, tolerant of errors in scene identification and in channel response modeling, and, in the absence of such errors, yields minimum variance and essentially unbiased radiance estimates.

Sound Transmission through Cylindrical Shell Structures Excited by Boundary Layer Pressure Fluctuations

NASA Technical Reports Server (NTRS)

Tang, Yvette Y.; Silcox, Richard J.; Robinson, Jay H.

1996-01-01

This paper examines sound transmission into two concentric cylindrical sandwich shells subject to turbulent flow on the exterior surface of the outer shell. The interior of the shells is filled with fluid medium and there is an airgap between the shells in the annular space. The description of the pressure field is based on the cross-spectral density formulation of Corcos, Maestrello, and Efimtsov models of the turbulent boundary layer. The classical thin shell theory and the first-order shear deformation theory are applied for the inner and outer shells, respectively. Modal expansion and the Galerkin approach are used to obtain closed-form solutions for the shell displacements and the radiation and transmission pressures in the cavities including both the annular space and the interior. The average spectral density of the structural responses and the transmitted interior pressures are expressed explicitly in terms of the summation of the cross-spectral density of generalized force induced by the boundary layer turbulence. The effects of acoustic and hydrodynamic coincidences on the spectral density are observed. Numerical examples are presented to illustrate the method for both subsonic and supersonic flows.

A novel recursive Fourier transform for nonuniform sampled signals: application to heart rate variability spectrum estimation.

PubMed

Holland, Alexander; Aboy, Mateo

2009-07-01

We present a novel method to iteratively calculate discrete Fourier transforms for discrete time signals with sample time intervals that may be widely nonuniform. The proposed recursive Fourier transform (RFT) does not require interpolation of the samples to uniform time intervals, and each iterative transform update of N frequencies has computational order N. Because of the inherent non-uniformity in the time between successive heart beats, an application particularly well suited for this transform is power spectral density (PSD) estimation for heart rate variability. We compare RFT based spectrum estimation with Lomb-Scargle Transform (LST) based estimation. PSD estimation based on the LST also does not require uniform time samples, but the LST has a computational order greater than Nlog(N). We conducted an assessment study involving the analysis of quasi-stationary signals with various levels of randomly missing heart beats. Our results indicate that the RFT leads to comparable estimation performance to the LST with significantly less computational overhead and complexity for applications requiring iterative spectrum estimations.

Individual spectral densities and molecular motion in polycrystalline hexamethylbenzene-d18

NASA Astrophysics Data System (ADS)

Hoatson, Gina L.; Vold, Robert L.; Tse, Tak Y.

1994-04-01

Methods are described for obtaining the orientation dependence of individual motional spectral densities, J1(ω0) and J2(2ω0), from deuterium spin relaxation experiments on polycrystalline materials. Spectral density measurements provide detailed information in a motional regime too fast to be studied by the two-dimensional (2D) exchange method. Their potential as a source of detailed kinetic and geometric information is illustrated for hexamethylbenzene-d18 (HMB). The relaxation behavior of HMB cannot be explained exclusively by six-site jumps around the C6v axis. Agreement between the experimentally determined spectral densities and simulations is improved if the methyl rotation is explicitly included. At ambient temperature the experimental data are best fitted with the simultaneous jump rates, k6=3.85×108 s-1 and k3=5.0×1011 s-1. This is significantly different from the rate determined using a simple six-site jump model, k6=3.9×109 s-1. Geometric distortions of the methyl rotation axes can account for the observed motionally averaged electric field gradient tensor. When these distortions are included in analysis of the spectral density data, there is a small, but significant, improvement in the fit. k3 is unchanged and the best fit k6 is reduced to 2.2×108 s-1, with distortions out of plane by δ=2.5° and in plane ɛ=ɛ'=1.202.

Estimation of spectral distribution of sky radiance using a commercial digital camera.

PubMed

Saito, Masanori; Iwabuchi, Hironobu; Murata, Isao

2016-01-10

Methods for estimating spectral distribution of sky radiance from images captured by a digital camera and for accurately estimating spectral responses of the camera are proposed. Spectral distribution of sky radiance is represented as a polynomial of the wavelength, with coefficients obtained from digital RGB counts by linear transformation. The spectral distribution of radiance as measured is consistent with that obtained by spectrometer and radiative transfer simulation for wavelengths of 430-680 nm, with standard deviation below 1%. Preliminary applications suggest this method is useful for detecting clouds and studying the relation between irradiance at the ground and cloud distribution.

The Flare Irradiance Spectral Model (FISM) and its Contributions to Space Weather Research, the Flare Energy Budget, and Instrument Design

NASA Technical Reports Server (NTRS)

Chamberlin, Phillip

2008-01-01

The Flare Irradiance Spectral Model (FISM) is an empirical model of the solar irradiance spectrum from 0.1 to 190 nm at 1 nm spectral resolution and on a 1-minute time cadence. The goal of FISM is to provide accurate solar spectral irradiances over the vacuum ultraviolet (VUV: 0-200 nm) range as input for ionospheric and thermospheric models. The seminar will begin with a brief overview of the FISM model, and also how the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) will contribute to improving FISM. Some current studies will then be presented that use FISM estimations of the solar VUV irradiance to quantify the contributions of the increased irradiance from flares to Earth's increased thermospheric and ionospheric densites. Initial results will also be presented from a study looking at the electron density increases in the Martian atmosphere during a solar flare. Results will also be shown quantifying the VUV contributions to the total flare energy budget for both the impulsive and gradual phases of solar flares. Lastly, an example of how FISM can be used to simplify the design of future solar VUV irradiance instruments will be discussed, using the future NOAA GOES-R Extreme Ultraviolet and X-Ray Sensors (EXIS) space weather instrument.

Go Long! Identifying Distant Brown Dwarfs in HST/WFC3 Parallel Field

NASA Astrophysics Data System (ADS)

Aganze, Christian; Burgasser, Adam J.; Malkan, Matthew Arnold; Masters, Daniel C.; Mercado, Gretel; Suarez, Adrian; Tamiya, Tomoki

2016-01-01

The spatial distribution of brown dwarfs beyond the local Solar Neighborhood is crucial for understanding their Galactic formation, dynamical and evolutionary history. Wide-field red optical and infrared surveys (e.g., 2MASS, SDSS, WISE) have enabled measures of the local density of brown dwarfs, but probe a relatively shallow (˜100 parsecs) volume; few constraints exist for the scale height or radial distributions of these low mass and low luminosity objects. We have searched ~1400 square arcminutes of WFC3 Infrared Spectroscopic Parallel Survey (WISPS) data to identify distant brown dwarfs (d > 300 pc) with near-infrared grism spectra from the the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3). Using spectral indices to identify candidates, measure spectral types and estimate distances, and comparing the WFC3 spectra to spectral templates in the SpeX Prism Library, we report our first results from this work, the discovery of ~50 late-M, L and T dwarfs with distances of 30 - 1000+ pc. We compare the distance and spectral type distribution to population simulations, and discuss current selection biases.The material presented here is based on work supported by the National Aeronautics and Space Administration under Grant No. NNX15AI75G

A Skew-t space-varying regression model for the spectral analysis of resting state brain activity.

PubMed

Ismail, Salimah; Sun, Wenqi; Nathoo, Farouk S; Babul, Arif; Moiseev, Alexader; Beg, Mirza Faisal; Virji-Babul, Naznin

2013-08-01

It is known that in many neurological disorders such as Down syndrome, main brain rhythms shift their frequencies slightly, and characterizing the spatial distribution of these shifts is of interest. This article reports on the development of a Skew-t mixed model for the spatial analysis of resting state brain activity in healthy controls and individuals with Down syndrome. Time series of oscillatory brain activity are recorded using magnetoencephalography, and spectral summaries are examined at multiple sensor locations across the scalp. We focus on the mean frequency of the power spectral density, and use space-varying regression to examine associations with age, gender and Down syndrome across several scalp regions. Spatial smoothing priors are incorporated based on a multivariate Markov random field, and the markedly non-Gaussian nature of the spectral response variable is accommodated by the use of a Skew-t distribution. A range of models representing different assumptions on the association structure and response distribution are examined, and we conduct model selection using the deviance information criterion. (1) Our analysis suggests region-specific differences between healthy controls and individuals with Down syndrome, particularly in the left and right temporal regions, and produces smoothed maps indicating the scalp topography of the estimated differences.

Effect of musical training on static and dynamic measures of spectral-pattern discrimination.

PubMed

Sheft, Stanley; Smayda, Kirsten; Shafiro, Valeriy; Maddox, W Todd; Chandrasekaran, Bharath

2013-06-01

Both behavioral and physiological studies have demonstrated enhanced processing of speech in challenging listening environments attributable to musical training. The relationship, however, of this benefit to auditory abilities as assessed by psychoacoustic measures remains unclear. Using tasks previously shown to relate to speech-in-noise perception, the present study evaluated discrimination ability for static and dynamic spectral patterns by 49 listeners grouped as either musicians or nonmusicians. The two static conditions measured the ability to detect a change in the phase of a logarithmic sinusoidal spectral ripple of wideband noise with ripple densities of 1.5 and 3.0 cycles per octave chosen to emphasize either timbre or pitch distinctions, respectively. The dynamic conditions assessed temporal-pattern discrimination of 1-kHz pure tones frequency modulated by different lowpass noise samples with thresholds estimated in terms of either stimulus duration or signal-to-noise ratio. Musicians performed significantly better than nonmusicians on all four tasks. Discriminant analysis showed that group membership was correctly predicted for 88% of the listeners with the structure coefficient of each measure greater than 0.51. Results suggest that enhanced processing of static and dynamic spectral patterns defined by low-rate modulation may contribute to the relationship between musical training and speech-in-noise perception. [Supported by NIH.].

Stochastic chaos induced by diffusion processes with identical spectral density but different probability density functions.

PubMed

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.

Some characteristics of the international space channel

NASA Technical Reports Server (NTRS)

Noack, T. L.; Poland, W. B., Jr.

1975-01-01

Some physical characteristics of radio transmission links and the technology of PCM modulation combine with the Radio Regulations of the International Telecommunications Union to define a communications channel having a determinable channel capacity, error rate, and sensitivity to interference. These characteristics and the corresponding limitations on EIRP, power flux density, and power spectral density for space service applications are described. The ITU regulations create a critical height of 1027 km where some parameters of the limitation rules change. The nature of restraints on power spectral density are discussed and an approach to a standardized representation of Necessary Bandwidth for the Space Services is described. It is shown that, given the PFD (power flux density) and PSD (power spectral density) limitations of radio regulations, the channel performance is determined by the ratio of effective receiving antenna aperture to system noise temperature. Based on this approach, the method for a quantitative trade-off between spectrum spreading and system performance is presented. Finally, the effects of radio frequency interference between standard systems is analyzed.

Terrain Classification on Venus from Maximum-Likelihood Inversion of Parameterized Models of Topography, Gravity, and their Relation

NASA Astrophysics Data System (ADS)

Eggers, G. L.; Lewis, K. W.; Simons, F. J.; Olhede, S.

2013-12-01

Venus does not possess a plate-tectonic system like that observed on Earth, and many surface features--such as tesserae and coronae--lack terrestrial equivalents. To understand Venus' tectonics is to understand its lithosphere, requiring a study of topography and gravity, and how they relate. Past studies of topography dealt with mapping and classification of visually observed features, and studies of gravity dealt with inverting the relation between topography and gravity anomalies to recover surface density and elastic thickness in either the space (correlation) or the spectral (admittance, coherence) domain. In the former case, geological features could be delineated but not classified quantitatively. In the latter case, rectangular or circular data windows were used, lacking geological definition. While the estimates of lithospheric strength on this basis were quantitative, they lacked robust error estimates. Here, we remapped the surface into 77 regions visually and qualitatively defined from a combination of Magellan topography, gravity, and radar images. We parameterize the spectral covariance of the observed topography, treating it as a Gaussian process assumed to be stationary over the mapped regions, using a three-parameter isotropic Matern model, and perform maximum-likelihood based inversions for the parameters. We discuss the parameter distribution across the Venusian surface and across terrain types such as coronoae, dorsae, tesserae, and their relation with mean elevation and latitudinal position. We find that the three-parameter model, while mathematically established and applicable to Venus topography, is overparameterized, and thus reduce the results to a two-parameter description of the peak spectral variance and the range-to-half-peak variance (in function of the wavenumber). With the reduction the clustering of geological region types in two-parameter space becomes promising. Finally, we perform inversions for the JOINT spectral variance of topography and gravity, in which the INITIAL loading by topography retains the Matern form but the FINAL topography and gravity are the result of flexural compensation. In our modeling, we pay explicit attention to finite-field spectral estimation effects (and their remedy via tapering), and to the implementation of statistical tests (for anisotropy, for initial-loading process correlation, to ascertain the proper density contrasts and interface depth in a two-layer model), robustness assessment and uncertainty quantification, as well as to algorithmic intricacies related to low-dimensional but poorly scaled maximum-likelihood inversions. We conclude that Venusian geomorphic terrains are well described by their 2-D topographic and gravity (cross-)power spectra, and the spectral properties of distinct geologic provinces on Venus are worth quantifying via maximum-likelihood-based methods under idealized three-parameter Matern distributions. Analysis of fitted parameters and the fitted-data residuals reveals natural variability in the (sub)surface properties on Venus, as well as some directional anisotropy. Geologic regions tend to cluster according to terrain type in our parameter space, which we analyze to confirm their shared geologic histories and utilize for guidance in ongoing mapping efforts of Venus and other terrestrial bodies.

Testing methods for using high-resolution satellite imagery to monitor polar bear abundance and distribution

USGS Publications Warehouse

LaRue, Michelle A.; Stapleton, Seth P.; Porter, Claire; Atkinson, Stephen N.; Atwood, Todd C.; Dyck, Markus; Lecomte, Nicolas

2015-01-01

High-resolution satellite imagery is a promising tool for providing coarse information about polar species abundance and distribution, but current applications are limited. With polar bears (Ursus maritimus), the technique has only proven effective on landscapes with little topographic relief that are devoid of snow and ice, and time-consuming manual review of imagery is required to identify bears. Here, we evaluated mechanisms to further develop methods for satellite imagery by examining data from Rowley Island, Canada. We attempted to automate and expedite detection via a supervised spectral classification and image differencing to expedite image review. We also assessed what proportion of a region should be sampled to obtain reliable estimates of density and abundance. Although the spectral signature of polar bears differed from nontarget objects, these differences were insufficient to yield useful results via a supervised classification process. Conversely, automated image differencing—or subtracting one image from another—correctly identified nearly 90% of polar bear locations. This technique, however, also yielded false positives, suggesting that manual review will still be required to confirm polar bear locations. On Rowley Island, bear distribution approximated a Poisson distribution across a range of plot sizes, and resampling suggests that sampling >50% of the site facilitates reliable estimation of density (CV <15%). Satellite imagery may be an effective monitoring tool in certain areas, but large-scale applications remain limited because of the challenges in automation and the limited environments in which the method can be effectively applied. Improvements in resolution may expand opportunities for its future uses.

Using satellite remote sensing to model and map the distribution of Bicknell's thrush (Catharus bicknelli) in the White Mountains of New Hampshire

NASA Astrophysics Data System (ADS)

Hale, Stephen Roy

Landsat-7 Enhanced Thematic Mapper satellite imagery was used to model Bicknell's Thrush (Catharus bicknelli) distribution in the White Mountains of New Hampshire. The proof-of-concept was established for using satellite imagery in species-habitat modeling, where for the first time imagery spectral features were used to estimate a species-habitat model variable. The model predicted rising probabilities of thrush presence with decreasing dominant vegetation height, increasing elevation, and decreasing distance to nearest Fir Sapling cover type. To solve the model at all locations required regressor estimates at every pixel, which were not available for the dominant vegetation height and elevation variables. Topographically normalized imagery features Normalized Difference Vegetation Index and Band 1 (blue) were used to estimate dominant vegetation height using multiple linear regression; and a Digital Elevation Model was used to estimate elevation. Distance to nearest Fir Sapling cover type was obtained for each pixel from a land cover map specifically constructed for this project. The Bicknell's Thrush habitat model was derived using logistic regression, which produced the probability of detecting a singing male based on the pattern of model covariates. Model validation using Bicknell's Thrush data not used in model calibration, revealed that the model accurately estimated thrush presence at probabilities ranging from 0 to <0.40 and from 0.50 to <0.60. Probabilities from 0.40 to <0.50 and greater than 0.60 significantly underestimated and overestimated presence, respectively. Applying the model to the study area illuminated an important implication for Bicknell's Thrush conservation. The model predicted increasing numbers of presences and increasing relative density with rising elevation, with which exists a concomitant decrease in land area. Greater land area of lower density habitats may account for more total individuals and reproductive output than higher density less abundant land area. Efforts to conserve areas of highest individual density under the assumption that density reflects habitat quality could target the smallest fraction of the total population.

Bayesian parameter estimation in spectral quantitative photoacoustic tomography

NASA Astrophysics Data System (ADS)

Pulkkinen, Aki; Cox, Ben T.; Arridge, Simon R.; Kaipio, Jari P.; Tarvainen, Tanja

2016-03-01

Photoacoustic tomography (PAT) is an imaging technique combining strong contrast of optical imaging to high spatial resolution of ultrasound imaging. These strengths are achieved via photoacoustic effect, where a spatial absorption of light pulse is converted into a measurable propagating ultrasound wave. The method is seen as a potential tool for small animal imaging, pre-clinical investigations, study of blood vessels and vasculature, as well as for cancer imaging. The goal in PAT is to form an image of the absorbed optical energy density field via acoustic inverse problem approaches from the measured ultrasound data. Quantitative PAT (QPAT) proceeds from these images and forms quantitative estimates of the optical properties of the target. This optical inverse problem of QPAT is illposed. To alleviate the issue, spectral QPAT (SQPAT) utilizes PAT data formed at multiple optical wavelengths simultaneously with optical parameter models of tissue to form quantitative estimates of the parameters of interest. In this work, the inverse problem of SQPAT is investigated. Light propagation is modelled using the diffusion equation. Optical absorption is described with chromophore concentration weighted sum of known chromophore absorption spectra. Scattering is described by Mie scattering theory with an exponential power law. In the inverse problem, the spatially varying unknown parameters of interest are the chromophore concentrations, the Mie scattering parameters (power law factor and the exponent), and Gruneisen parameter. The inverse problem is approached with a Bayesian method. It is numerically demonstrated, that estimation of all parameters of interest is possible with the approach.

Analytical approaches to modelling panspermia - beyond the mean-field paradigm

NASA Astrophysics Data System (ADS)

Lingam, Manasvi

2016-01-01

We model the process of panspermia by adopting two different approaches. The first method conceives it as a self-replication process, endowed with non-local creation and extinction. We show that some features suggestive of universal behaviour emerge, such as exponential decay or growth, and a power spectral density that displays a power-law behaviour in a particular regime. We also present a special case wherein the number density of the planets seeded through panspermia approaches a finite asymptotic distribution. The power spectral density for the independent and spontaneous emergence of life is investigated in conjunction with its counterpart for panspermia. The former exhibits attributes characteristic of a noise spectrum, including the resemblance to white noise in a certain regime. These features are absent in panspermia, suggesting that the power spectral density could be utilized as a future tool for differentiating between the two processes. Our second approach adopts the machinery of Markov processes and diffusion, and we show that the power spectral density exhibits a power-law tail in some domains, as earlier, suggesting that this behaviour may be fairly robust. We comment on a generalization of the diffusive model, and also indicate how the methods and results developed herein could be used to analyse other phenomena.

Nonlinear GARCH model and 1 / f noise

NASA Astrophysics Data System (ADS)

Kononovicius, A.; Ruseckas, J.

2015-06-01

Auto-regressive conditionally heteroskedastic (ARCH) family models are still used, by practitioners in business and economic policy making, as a conditional volatility forecasting models. Furthermore ARCH models still are attracting an interest of the researchers. In this contribution we consider the well known GARCH(1,1) process and its nonlinear modifications, reminiscent of NGARCH model. We investigate the possibility to reproduce power law statistics, probability density function and power spectral density, using ARCH family models. For this purpose we derive stochastic differential equations from the GARCH processes in consideration. We find the obtained equations to be similar to a general class of stochastic differential equations known to reproduce power law statistics. We show that linear GARCH(1,1) process has power law distribution, but its power spectral density is Brownian noise-like. However, the nonlinear modifications exhibit both power law distribution and power spectral density of the 1 /fβ form, including 1 / f noise.

Investigation of Techniques for Inventorying Forested Regions. Volume 1: Reflectance Modeling and Empirical Multispectral Analysis of Forest Canopy Components

NASA Technical Reports Server (NTRS)

Nalepka, R. F. (Principal Investigator); Sadowski, F. G.; Malila, W. A.

1977-01-01

The author has identified the following significant results. Effects of vegetation density on overall canopy reflectance differed dramatically, depending on spectral band, base material, and vegetation type. For example, reflectance changes caused by variations in vegetation density were hardly apparant for a simulated burned surface in LANDSAT band 5, while large changes occurred in band 7. When increasing densities of tree overstory were placed over understories, intermediate to dense overstories effectively masked the understories and dominated the spectral signatures. Dramatic changes in reflectance occurred for canopies placed on a number of varying topographic positions. Such changes were seen to result in the spectral overlap of some nonforested with densely forested situations.

Asymmetries in the spectral density of an interaction-quenched Luttinger liquid

NASA Astrophysics Data System (ADS)

Calzona, A.; Gambetta, F. M.; Carrega, M.; Cavaliere, F.; Sassetti, M.

2018-03-01

The spectral density of an interaction-quenched one-dimensional system is investigated. Both direct and inverse quench protocols are considered and it is found that the former leads to stronger effects on the spectral density with respect to the latter. Such asymmetry is directly reflected on transport properties of the system, namely the charge and energy current flowing to the system from a tunnel coupled biased probe. In particular, the injection of particles from the probe to the right-moving channel of the system is considered. The resulting fractionalization phenomena are strongly affected by the quench protocol and display asymmetries in the case of direct and inverse quench. Transport properties therefore emerge as natural probes for the observation of this quench-induced behavior.

Estimating structural attributes of Douglas-fir/western hemlock forest stands from Landsat and SPOT imagery

NASA Technical Reports Server (NTRS)

Cohen, Warren B.; Spies, Thomas A.

1992-01-01

Relationships between spectral and texture variables derived from SPOT HRV 10 m panchromatic and Landsat TM 30 m multispectral data and 16 forest stand structural attributes is evaluated to determine the utility of satellite data for analysis of hemlock forests west of the Cascade Mountains crest in Oregon and Washington, USA. Texture of the HRV data was found to be strongly related to many of the stand attributes evaluated, whereas TM texture was weakly related to all attributes. Data analysis based on regression models indicates that both TM and HRV imagery should yield equally accurate estimates of forest age class and stand structure. It is concluded that the satellite data are a valuable source for estimation of the standard deviation of tree sizes, mean size and density of trees in the upper canopy layers, a structural complexity index, and stand age.

Color reproduction of human skin by spectral reflectance using RGB images and the Wiener estimation method

NASA Astrophysics Data System (ADS)

Sato, Kiyomi; Miyazawa, Shota; Funamizu, Hideki; Yuasa, Tomonori; Nishidate, Izumi; Aizu, Yoshihisa

2017-04-01

Skin measurements based on spectral reflectance are widely studied in the fields of medical care and cosmetics. It has the advantage that several skin properties can be estimated in the non-invasive and non-contacting manner. In this study, we demonstrate the color reproduction of human skin by spectral reflectance using RGB images and the Wiener estimation method.

Tidally induced turbulence in the Bermuda underwater cave-system

NASA Astrophysics Data System (ADS)

Molodtsov, S.; Anis, A.; Iliffe, T. M.

2016-02-01

This study presents results from field measurements of turbulence made in Bermuda's underwater cave-system. To the best of our knowledge, this is the first time that turbulence velocity measurements have been taken in an underwater cave-system. Water currents in caves are unaffected by surface waves and thus provide a unique opportunity to obtain clear signals of tidally induced turbulence. An acoustic Doppler velocimeter and acoustic Doppler current profiler were deployed in several cave locations during a period of six days. Power spectral density (PSD) of velocity fluctuations was estimated using the multitaper power spectral method. Turbulence kinetic energy dissipation rates, ɛ, were calculated based on the PSD and were found to exhibit a clear -5/3 slope within the inertial subrange. Measurement periods covered full diurnal cycles and estimates of ɛ showed a strong correlation with the tide phase with values up to 10-3 W/kg during peak ebb and flood (horizontal velocities up to 0.35 m/s). Furthermore, ɛ was found to closely follow the wall boundary layer parametrization, ɛ = u*3/(ᴋz), where u* is the friction velocity, ᴋ is von Karman's constant, and z is the height above the bed.

Spectral ratio method for measuring emissivity

USGS Publications Warehouse

Watson, K.

1992-01-01

The spectral ratio method is based on the concept that although the spectral radiances are very sensitive to small changes in temperature the ratios are not. Only an approximate estimate of temperature is required thus, for example, we can determine the emissivity ratio to an accuracy of 1% with a temperature estimate that is only accurate to 12.5 K. Selecting the maximum value of the channel brightness temperatures is an unbiased estimate. Laboratory and field spectral data are easily converted into spectral ratio plots. The ratio method is limited by system signal:noise and spectral band-width. The images can appear quite noisy because ratios enhance high frequencies and may require spatial filtering. Atmospheric effects tend to rescale the ratios and require using an atmospheric model or a calibration site. ?? 1992.

Evaluating the utility of the medium-spatial resolution Landsat 8 multispectral sensor in quantifying aboveground biomass in uMgeni catchment, South Africa

NASA Astrophysics Data System (ADS)

Dube, Timothy; Mutanga, Onisimo

2015-03-01

Aboveground biomass estimation is critical in understanding forest contribution to regional carbon cycles. Despite the successful application of high spatial and spectral resolution sensors in aboveground biomass (AGB) estimation, there are challenges related to high acquisition costs, small area coverage, multicollinearity and limited availability. These challenges hamper the successful regional scale AGB quantification. The aim of this study was to assess the utility of the newly-launched medium-resolution multispectral Landsat 8 Operational Land Imager (OLI) dataset with a large swath width, in quantifying AGB in a forest plantation. We applied different sets of spectral analysis (test I: spectral bands; test II: spectral vegetation indices and test III: spectral bands + spectral vegetation indices) in testing the utility of Landsat 8 OLI using two non-parametric algorithms: stochastic gradient boosting and the random forest ensembles. The results of the study show that the medium-resolution multispectral Landsat 8 OLI dataset provides better AGB estimates for Eucalyptus dunii, Eucalyptus grandis and Pinus taeda especially when using the extracted spectral information together with the derived spectral vegetation indices. We also noted that incorporating the optimal subset of the most important selected medium-resolution multispectral Landsat 8 OLI bands improved AGB accuracies. We compared medium-resolution multispectral Landsat 8 OLI AGB estimates with Landsat 7 ETM + estimates and the latter yielded lower estimation accuracies. Overall, this study demonstrates the invaluable potential and strength of applying the relatively affordable and readily available newly-launched medium-resolution Landsat 8 OLI dataset, with a large swath width (185-km) in precisely estimating AGB. This strength of the Landsat OLI dataset is crucial especially in sub-Saharan Africa where high-resolution remote sensing data availability remains a challenge.

Spectral Discrete Probability Density Function of Measured Wind Turbine Noise in the Far Field

PubMed Central

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

UV spectral shift of benzene in sub- and supercritical water

NASA Astrophysics Data System (ADS)

Kometani, Noritsugu; Takemiya, Koji; Yonezawa, Yoshiro; Amita, Fujitsugu; Kajimoto, Okitsugu

2004-08-01

UV absorption spectra of benzene have been measured over the wide range of temperature and pressure from the ambient state to the supercritical state ( T = 400 °C and P = 40 MPa). The analysis of the spectral shift of benzene in water relative to that in the gas indicates that at T = 380 and 390 °C the local solvent density around benzene is likely to be depressed below the bulk density for densities near the critical density. It is found that π-hydrogen bond between benzene and water becomes evident with lowering temperature below T = 340 °C.

Snow Water Equivalent estimation based on satellite observation

NASA Astrophysics Data System (ADS)

Macchiavello, G.; Pesce, F.; Boni, G.; Gabellani, S.

2009-09-01

The availability of remotely sensed images and them analysis is a powerful tool for monitoring the extension and typology of snow cover over territory where the in situ measurements are often difficult. Information on snow are fundamental for monitoring and forecasting the available water above all in regions at mid latitudes as Mediterranean where snowmelt may cause floods. The hydrological model requirements and the daily acquisitions of MODIS (Moderate Resolution Imaging Spectroradiometer), drove, in previous research activities, to the development of a method to automatically map the snow cover from multi-spectral images. But, the major hydrological parameter related to the snow pack is the Snow Water Equivalent (SWE). This represents a direct measure of stored water in the basin. Because of it, the work was focused to the daily estimation of SWE from MODIS images. But, the complexity of this aim, based only on optical data, doesn’t find any information in literature. Since, from the spectral range of MODIS data it is not possible to extract a direct relation between spectral information and the SWE. Then a new method, respectful of the physic of the snow, was defined and developed. Reminding that the snow water equivalent is the product of the three factors as snow density, snow depth and the snow covered areas, the proposed approach works separately on each of these physical behaviors. Referring to the physical characteristic of snow, the snow density is function of the snow age, then it was studied a new method to evaluate this. Where, a module for snow age simulation from albedo information was developed. It activates an age counter updated by new snow information set to estimate snow age from zero accumulation status to the end of melting season. The height of the snow pack, can be retrieved by adopting relation between vegetation and snow depth distributions. This computes snow height distribution by the relation between snow cover fraction and the forest canopy density. Finally, the SWE has to be calculated for the snow covered areas, detected by means of a previously developed decision tree classifier able to classify snow cover by self selecting rules in a statistically optimum way. The advantages introduced from this work are many. Firstly, applying a suitable method with data features, it is possible to automatically obtain snow cover description with high frequency. Moreover, the advantages of the modularity in the proposed approach allows to improve the three factors estimation in an independent way. Limitations lie into clouds problem that affects results by obscuring the observed territory, that is bounded by fusing temporal and spatial information. Then the spatial resolution of data, satisfactory with the scale of hydrological models, mismatch with the available in situ point information, causing difficulties for a method validation or calibration. However this working flow results computationally cost-effectiveness, robust to the radiometric noise of the original data, provides spatially extended and frequent information.

Comparison of spectral estimators for characterizing fractionated atrial electrograms

PubMed Central

2013-01-01

Background Complex fractionated atrial electrograms (CFAE) acquired during atrial fibrillation (AF) are commonly assessed using the discrete Fourier transform (DFT), but this can lead to inaccuracy. In this study, spectral estimators derived by averaging the autocorrelation function at lags were compared to the DFT. Method Bipolar CFAE of at least 16 s duration were obtained from pulmonary vein ostia and left atrial free wall sites (9 paroxysmal and 10 persistent AF patients). Power spectra were computed using the DFT and three other methods: 1. a novel spectral estimator based on signal averaging (NSE), 2. the NSE with harmonic removal (NSH), and 3. the autocorrelation function average at lags (AFA). Three spectral parameters were calculated: 1. the largest fundamental spectral peak, known as the dominant frequency (DF), 2. the DF amplitude (DA), and 3. the mean spectral profile (MP), which quantifies noise floor level. For each spectral estimator and parameter, the significance of the difference between paroxysmal and persistent AF was determined. Results For all estimators, mean DA and mean DF values were higher in persistent AF, while the mean MP value was higher in paroxysmal AF. The differences in means between paroxysmals and persistents were highly significant for 3/3 NSE and NSH measurements and for 2/3 DFT and AFA measurements (p<0.001). For all estimators, the standard deviation in DA and MP values were higher in persistent AF, while the standard deviation in DF value was higher in paroxysmal AF. Differences in standard deviations between paroxysmals and persistents were highly significant in 2/3 NSE and NSH measurements, in 1/3 AFA measurements, and in 0/3 DFT measurements. Conclusions Measurements made from all four spectral estimators were in agreement as to whether the means and standard deviations in three spectral parameters were greater in CFAEs acquired from paroxysmal or in persistent AF patients. Since the measurements were consistent, use of two or more of these estimators for power spectral analysis can be assistive to evaluate CFAE more objectively and accurately, which may lead to improved clinical outcome. Since the most significant differences overall were achieved using the NSE and NSH estimators, parameters measured from their spectra will likely be the most useful for detecting and discerning electrophysiologic differences in the AF substrate based upon frequency analysis of CFAE. PMID:23855345

Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

NASA Astrophysics Data System (ADS)

McFarlane, S. A.; Gaustad, K. L.; Mlawer, E. J.; Long, C. N.; Delamere, J.

2011-09-01

We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

NASA Astrophysics Data System (ADS)

McFarlane, S. A.; Gaustad, K. L.; Mlawer, E. J.; Long, C. N.; Delamere, J.

2011-05-01

We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

Model Order Reduction Algorithm for Estimating the Absorption Spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Beeumen, Roel; Williams-Young, David B.; Kasper, Joseph M.

The ab initio description of the spectral interior of the absorption spectrum poses both a theoretical and computational challenge for modern electronic structure theory. Due to the often spectrally dense character of this domain in the quantum propagator’s eigenspectrum for medium-to-large sized systems, traditional approaches based on the partial diagonalization of the propagator often encounter oscillatory and stagnating convergence. Electronic structure methods which solve the molecular response problem through the solution of spectrally shifted linear systems, such as the complex polarization propagator, offer an alternative approach which is agnostic to the underlying spectral density or domain location. This generality comesmore » at a seemingly high computational cost associated with solving a large linear system for each spectral shift in some discretization of the spectral domain of interest. In this work, we present a novel, adaptive solution to this high computational overhead based on model order reduction techniques via interpolation. Model order reduction reduces the computational complexity of mathematical models and is ubiquitous in the simulation of dynamical systems and control theory. The efficiency and effectiveness of the proposed algorithm in the ab initio prediction of X-ray absorption spectra is demonstrated using a test set of challenging water clusters which are spectrally dense in the neighborhood of the oxygen K-edge. On the basis of a single, user defined tolerance we automatically determine the order of the reduced models and approximate the absorption spectrum up to the given tolerance. We also illustrate that, for the systems studied, the automatically determined model order increases logarithmically with the problem dimension, compared to a linear increase of the number of eigenvalues within the energy window. Furthermore, we observed that the computational cost of the proposed algorithm only scales quadratically with respect to the problem dimension.« less

Antiproton signatures from astrophysical and dark matter sources at the galactic center

NASA Astrophysics Data System (ADS)

Cembranos, J. A. R.; Gammaldi, V.; Maroto, A. L.

2015-03-01

The center of our Galaxy is a complex region characterized by extreme phenomena. The presence of the supermassive Sagittarius A* black hole, a high dark matter density and an even higher baryonic density are able to produce very energetic processes. Indeed, high energetic gamma-rays have been observed by different telescopes, although their origin is not clear. In this work, we estimate the possible antiproton flux component associated with this signal. The expected secondary astrophysical antiproton background already saturates the observed data. It implies that any other important astrophysical source leads to an inconsistent excess. We estimate the sensitivity of PAMELA to this new primary antiproton source, which depends on the diffusion model and its spectral features. In particular, we consider antiproton spectra described by a power-law, a monochromatic signal and a Standard Model particle-antiparticle channel production. This latter spectrum is typical in the production from annihilating or decaying dark matter. We pay particular attention to the case of a heavy dark matter candidate, which could be associated with the High Energy Stereoscopic System (HESS) data observed from the J1745-290 source.

Spectral fitting inversion of low-frequency normal modes with self-coupling and cross-coupling of toroidal and spheroidal multiplets: numerical experiments to estimate the isotropic and anisotropic velocity structures

NASA Astrophysics Data System (ADS)

Oda, Hitoshi

2016-06-01

The aspherical structure of the Earth is described in terms of lateral heterogeneity and anisotropy of the P- and S-wave velocities, density heterogeneity, ellipticity and rotation of the Earth and undulation of the discontinuity interfaces of the seismic wave velocities. Its structure significantly influences the normal mode spectra of the Earth's free oscillation in the form of cross-coupling between toroidal and spheroidal multiplets and self-coupling between the singlets forming them. Thus, the aspherical structure must be conversely estimated from the free oscillation spectra influenced by the cross-coupling and self-coupling. In the present study, we improve a spectral fitting inversion algorithm which was developed in a previous study to retrieve the global structures of the isotropic and anisotropic velocities of the P and S waves from the free oscillation spectra. The main improvement is that the geographical distribution of the intensity of the S-wave azimuthal anisotropy is represented by a nonlinear combination of structure coefficients for the anisotropic velocity structure, whereas in the previous study it was expanded into a generalized spherical harmonic series. Consequently, the improved inversion algorithm reduces the number of unknown parameters that must be determined compared to the previous inversion algorithm and employs a one-step inversion method by which the structure coefficients for the isotropic and anisotropic velocities are directly estimated from the fee oscillation spectra. The applicability of the improved inversion is examined by several numerical experiments using synthetic spectral data, which are produced by supposing a variety of isotropic and anisotropic velocity structures, earthquake source parameters and station-event pairs. Furthermore, the robustness of the inversion algorithm is investigated with respect to the back-ground noise contaminating the spectral data as well as truncating the series expansions by finite terms to represent the three-dimensional velocity structures. As a result, it is shown that the improved inversion can estimate not only the isotropic and anisotropic velocity structures but also the depth extent of the anisotropic regions in the Earth. In particular, the cross-coupling modes are essential to correctly estimate the isotropic and anisotropic velocity structures from the normal mode spectra. In addition, we argue that the effect of the seismic anisotropy is not negligible when estimating only the isotropic velocity structure from the spheroidal mode spectra.

Laser-induced plasmas in air studied using two-color interferometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zefeng; Wu, Jian, E-mail: jxjawj@mail.xjtu.edu.cn; Li, Xingwen

2016-08-15

Temporally and spatially resolved density profiles of Cu atoms, electrons, and compressed air, from laser-induced copper plasmas in air, are measured using fast spectral imaging and two-color interferometry. From the intensified CCD images filtered by a narrow-band-pass filter centered at 515.32 nm, the Cu atoms expansion route is estimated and used to determine the position of the fracture surface between the Cu atoms and the air. Results indicate that the Cu atoms density at distances closer to the target (0–0.4 mm) is quite low, with the maximum density appearing at the edge of the plasma's core being ∼4.6 × 10{sup 24 }m{sup −3} at 304 ns.more » The free electrons are mainly located in the internal region of the plume, which is supposed to have a higher temperature. The density of the shock wave is (4–6) × 10{sup 25 }m{sup −3}, corresponding to air compression of a factor of 1.7–2.5.« less

Diagnosis of high-temperature implosions using low- and high-opacity Krypton lines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yaakobi, B.; Epstein, R.; Hooper, C.F. Jr.

1996-04-01

High-temperature laser target implosions can be achieved by using relatively thin-shell targets, and they can be. diagnosed by doping the fuel with krypton and measuring K-shell and L-shell lines. Electron temperatures of up to 5 keV at modest compressed densities ({approximately}1-5g/cm{sup 3}) are predicted for such experiments, with ion temperatures peaking above 10 keV at the center. It is found that the profiles of low-opacity (optically thin) lines in the expected density range are dominated by the Doppler broadening and can provide a measurement of the ion temperature if spectrometers of spectral resolution {Delta}{lambda}/{lambda} {ge} 1000 are used. For high-opacitymore » lines, obtained with a higher krypton fill pressure, the measurement of the escape factor can yield the {rho}R of the compressed fuel. At higher densities, Stark broadening of low-opacity lines becomes important and can provide a density measurement, whereas lines of higher opacity can be used to estimate the extent of mixing.« less

VizieR Online Data Catalog: Spectral properties of 441 radio pulsars (Jankowski+, 2018)

NASA Astrophysics Data System (ADS)

Jankowski, F.; van Straten, W.; Keane, E. F.; Bailes, M.; Barr, E. D.; Johnston, S.; Kerr, M.

2018-03-01

We present spectral parameters for 441 radio pulsars. These were obtained from observations centred at 728, 1382 and 3100MHz using the 10-50cm and the 20cm multibeam receiver at the Parkes radio telescope. In particular, we list the pulsar names (J2000), the calibrated, band-integrated flux densities at 728, 1382 and 3100MHz, the spectral classifications, the frequency ranges the spectral classifications were performed over, the spectral indices for pulsars with simple power-law spectra and the robust modulation indices at all three centre frequencies for pulsars of which we have at least six measurement epochs. The flux density uncertainties include scintillation and a systematic contribution, in addition to the statistical uncertainty. Upper limits are reported at the 3σ level and all other uncertainties at the 1σ level. (1 data file).

[Quantitative relationships between hyper-spectral vegetation indices and leaf area index of rice].

PubMed

Tian, Yong-Chao; Yang, Jie; Yao, Xia; Zhu, Yan; Cao, Wei-Xing

2009-07-01

Based on field experiments with different rice varieties under different nitrogen application levels, the quantitative relationships of rice leaf area index (LAI) with canopy hyper-spectral parameters at different growth stages were analyzed. Rice LAI had good relationships with several hyper-spectral vegetation indices, the correlation coefficient being the highest with DI (difference index), followed by with RI (ratio index), and NI (normalized index), based on the spectral reflectance or the first derivative spectra. The two best spectral indices for estimating LAI were the difference index DI (854, 760) (based on two spectral bands of 850 nm and 760 nm) and the difference index DI (D676, D778) (based on two first derivative bands of 676 nm and 778 nm). In general, the hyper-spectral vegetation indices based on spectral reflectance performed better than the spectral indices based on the first derivative spectra. The tests with independent dataset suggested that the rice LAI monitoring models with difference index DI (854,760) as the variable could give an accurate LAI estimation, being available for estimation of rice LAI.

Seismic noise level variation in South Korea

NASA Astrophysics Data System (ADS)

Sheen, D.; Shin, J.

2008-12-01

The variations of seismic background noise in South Korea have been investigated by means of power spectral analysis. The Korea Institute of Geoscience and Mineral Resources (KIGAM) and the Korea Meteorological Administation (KMA) have national wide seismic networks in South Korea, and, in the end of 2007, there are 30 broadband stations which have been operating for more than a year. In this study, we have estimated the power spectral density of seismic noise for 30 broadband stations from 2005 to 2007. Since we estimate PSDs from a large dataset of continuous waveform in this study, a robust PSD estimate of McNamara and Buland (2004) is used. In the frequency range 1-5 Hz, the diurnal variations of noise are observed at most of stations, which are especially larger at coastal stations and at insular than at inland. Some stations shows daily difference of diurnal variations, which represents that cultural activities contribute to the noise level of a station. The variation of number of triggered stations, however, shows that cultural noise has little influence on the detection capability of seismic network in South Korea. Seasonal variations are observed well in the range 0.1-0.5 Hz, while much less found in the frequency range 1-5 Hz. We observed that strong peaks in the range 0.1-0.5 Hz occur at the summer when Pacific typhoons are close to the Korean Peninsula.

Power strain imaging based on vibro-elastography techniques

NASA Astrophysics Data System (ADS)

Wen, Xu; Salcudean, S. E.

2007-03-01

This paper describes a new ultrasound elastography technique, power strain imaging, based on vibro-elastography (VE) techniques. With this method, tissue is compressed by a vibrating actuator driven by low-pass or band-pass filtered white noise, typically in the 0-20 Hz range. Tissue displacements at different spatial locations are estimated by correlation-based approaches on the raw ultrasound radio frequency signals and recorded in time sequences. The power spectra of these time sequences are computed by Fourier spectral analysis techniques. As the average of the power spectrum is proportional to the squared amplitude of the tissue motion, the square root of the average power over the range of excitation frequencies is used as a measure of the tissue displacement. Then tissue strain is determined by the least squares estimation of the gradient of the displacement field. The computation of the power spectra of the time sequences can be implemented efficiently by using Welch's periodogram method with moving windows or with accumulative windows with a forgetting factor. Compared to the transfer function estimation originally used in VE, the computation of cross spectral densities is not needed, which saves both the memory and computational times. Phantom experiments demonstrate that the proposed method produces stable and operator-independent strain images with high signal-to-noise ratio in real time. This approach has been also tested on a few patient data of the prostate region, and the results are encouraging.

Estimating economic thresholds for site-specific weed control using manual weed counts and sensor technology: an example based on three winter wheat trials.

PubMed

Keller, Martina; Gutjahr, Christoph; Möhring, Jens; Weis, Martin; Sökefeld, Markus; Gerhards, Roland

2014-02-01

Precision experimental design uses the natural heterogeneity of agricultural fields and combines sensor technology with linear mixed models to estimate the effect of weeds, soil properties and herbicide on yield. These estimates can be used to derive economic thresholds. Three field trials are presented using the precision experimental design in winter wheat. Weed densities were determined by manual sampling and bi-spectral cameras, yield and soil properties were mapped. Galium aparine, other broad-leaved weeds and Alopecurus myosuroides reduced yield by 17.5, 1.2 and 12.4 kg ha(-1) plant(-1)  m(2) in one trial. The determined thresholds for site-specific weed control with independently applied herbicides were 4, 48 and 12 plants m(-2), respectively. Spring drought reduced yield effects of weeds considerably in one trial, since water became yield limiting. A negative herbicide effect on the crop was negligible, except in one trial, in which the herbicide mixture tended to reduce yield by 0.6 t ha(-1). Bi-spectral cameras for weed counting were of limited use and still need improvement. Nevertheless, large weed patches were correctly identified. The current paper presents a new approach to conducting field trials and deriving decision rules for weed control in farmers' fields. © 2013 Society of Chemical Industry.

Mid-IR hyperspectral imaging of laminar flames for 2-D scalar values.

PubMed

Rhoby, Michael R; Blunck, David L; Gross, Kevin C

2014-09-08

This work presents a new emission-based measurement which permits quantification of two-dimensional scalar distributions in laminar flames. A Michelson-based Fourier-transform spectrometer coupled to a mid-infrared camera (1.5 μm to 5.5 μm) obtained 256 × 128pixel hyperspectral flame images at high spectral (δν̃ = 0.75cm(−1)) and spatial (0.52 mm) resolutions. The measurements revealed line and band emission from H2O, CO2, and CO. Measurements were collected from a well-characterized partially-premixed ethylene (C2H4) flame produced on a Hencken burner at equivalence ratios, Φ, of 0.8, 0.9, 1.1, and 1.3. After describing the instrument and novel calibration methodology, analysis of the flames is presented. A single-layer, line-by-line radiative transfer model is used to retrieve path-averaged temperature, H2O, CO2 and CO column densities from emission spectra between 2.3 μm to 5.1 μm. The radiative transfer model uses line intensities from the latest HITEMP and CDSD-4000 spectroscopic databases. For the Φ = 1.1 flame, the spectrally estimated temperature for a single pixel 10 mm above burner center was T = (2318 ± 19)K, and agrees favorably with recently reported laser absorption measurements, T = (2348 ± 115)K, and a NASA CEA equilibrium calculation, T = 2389K. Near the base of the flame, absolute concentrations can be estimated, and H2O, CO2, and CO concentrations of (12.5 ± 1.7) %, (10.1 ± 1.0) %, and (3.8 ± 0.3) %, respectively, compared favorably with the corresponding CEA values of 12.8%, 9.9% and 4.1%. Spectrally-estimated temperatures and concentrations at the other equivalence ratios were in similar agreement with measurements and equilibrium calculations. 2-D temperature and species column density maps underscore the Φ-dependent chemical composition of the flames. The reported uncertainties are 95% confidence intervals and include both statistical fit errors and the propagation of systematic calibration errors using a Monte Carlo approach. Systematic errors could warrant a factor of two increase in reported uncertainties. This work helps to establish IFTS as a valuable combustion diagnostic tool.

Chromophore-Dependent Intramolecular Exciton-Vibrational Coupling in the FMO Complex: Quantification and Importance for Exciton Dynamics.

PubMed

Padula, Daniele; Lee, Myeong H; Claridge, Kirsten; Troisi, Alessandro

2017-11-02

In this paper, we adopt an approach suitable for monitoring the time evolution of the intramolecular contribution to the spectral density of a set of identical chromophores embedded in their respective environments. We apply the proposed method to the Fenna-Matthews-Olson (FMO) complex, with the objective to quantify the differences among site-dependent spectral densities and the impact of such differences on the exciton dynamics of the system. Our approach takes advantage of the vertical gradient approximation to reduce the computational demands of the normal modes analysis. We show that the region of the spectral density that is believed to strongly influence the exciton dynamics changes significantly in the timescale of tens of nanoseconds. We then studied the impact of the intramolecular vibrations on the exciton dynamics by considering a model of FMO in a vibronic basis and neglecting the interaction with the environment to isolate the role of the intramolecular exciton-vibration coupling. In agreement with the assumptions in the literature, we demonstrate that high frequency modes at energy much larger than the excitonic energy splitting have negligible influence on exciton dynamics despite the large exciton-vibration coupling. We also find that the impact of including the site-dependent spectral densities on exciton dynamics is not very significant, indicating that it may be acceptable to apply the same spectral density on all sites. However, care needs to be taken for the description of the exciton-vibrational coupling in the low frequency part of intramolecular modes because exciton dynamics is more susceptible to low frequency modes despite their small Huang-Rhys factors.

Characterization and modelling of the spatially- and spectrally-varying point-spread function in hyperspectral imaging systems for computational correction of axial optical aberrations

NASA Astrophysics Data System (ADS)

Špiclin, Žiga; Bürmen, Miran; Pernuš, Franjo; Likar, Boštjan

2012-03-01

Spatial resolution of hyperspectral imaging systems can vary significantly due to axial optical aberrations that originate from wavelength-induced index-of-refraction variations of the imaging optics. For systems that have a broad spectral range, the spatial resolution will vary significantly both with respect to the acquisition wavelength and with respect to the spatial position within each spectral image. Variations of the spatial resolution can be effectively characterized as part of the calibration procedure by a local image-based estimation of the pointspread function (PSF) of the hyperspectral imaging system. The estimated PSF can then be used in the image deconvolution methods to improve the spatial resolution of the spectral images. We estimated the PSFs from the spectral images of a line grid geometric caliber. From individual line segments of the line grid, the PSF was obtained by a non-parametric estimation procedure that used an orthogonal series representation of the PSF. By using the non-parametric estimation procedure, the PSFs were estimated at different spatial positions and at different wavelengths. The variations of the spatial resolution were characterized by the radius and the fullwidth half-maximum of each PSF and by the modulation transfer function, computed from images of USAF1951 resolution target. The estimation and characterization of the PSFs and the image deconvolution based spatial resolution enhancement were tested on images obtained by a hyperspectral imaging system with an acousto-optic tunable filter in the visible spectral range. The results demonstrate that the spatial resolution of the acquired spectral images can be significantly improved using the estimated PSFs and image deconvolution methods.

New generation aircraft design problems relative to turbulence stability, aeroelastic loads and gust alleviation

NASA Technical Reports Server (NTRS)

Heimbaugh, Richard M.

1987-01-01

Past history, present status, and future of discrete gusts are schematically presented. It is shown that there are two approaches to the gust analysis: discrete and spectral density. The role of these two approaches to gust analysis are discussed. The idea of using power spectral density (PSD) in the analysis of gusts is especially detailed.

Estimation of optimum density and temperature for maximum efficiency of tin ions in Z discharge extreme ultraviolet sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masnavi, Majid; Nakajima, Mitsuo; Hotta, Eiki

Extreme ultraviolet (EUV) discharge-based lamps for EUV lithography need to generate extremely high power in the narrow spectrum band of 13.5{+-}0.135 nm. A simplified collisional-radiative model and radiative transfer solution for an isotropic medium were utilized to investigate the wavelength-integrated light outputs in tin (Sn) plasma. Detailed calculations using the Hebrew University-Lawrence Livermore atomic code were employed for determination of necessary atomic data of the Sn{sup 4+} to Sn{sup 13+} charge states. The result of model is compared with experimental spectra from a Sn-based discharge-produced plasma. The analysis reveals that considerably larger efficiency compared to the so-called efficiency of amore » black-body radiator is formed for the electron density {approx_equal}10{sup 18} cm{sup -3}. For higher electron density, the spectral efficiency of Sn plasma reduces due to the saturation of resonance transitions.« less

Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

NASA Technical Reports Server (NTRS)

Cox, D. P.; Anderson, P. R.

1981-01-01

An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

Use of ground-based remotely sensed data for surface energy balance evaluation of a semiarid rangeland

USGS Publications Warehouse

Moran, M.S.; Kustas, William P.; Vidal, A.; Stannard, D.I.; Blanford, J.H.; Nichols, W.D.

1994-01-01

An interdisciplinary field experiment was conducted to study the water and energy balance of a semiarid rangeland watershed in southeast Arizona during the summer of 1990. Two subwatersheds, one grass dominated and the other shrub dominated, were selected for intensive study with ground-based remote sensing systems and hydrometeorological instrumentation. Surface energy balance was evaluated at both sites using direct and indirect measurements of the turbulent fluxes (eddy correlation, variance, and Bowen ratio methods) and using an aerodynamic approach based on remote measurements of surface reflectance and temperature and conventional meteorological information. Estimates of net radiant flux density (Rn), derived from measurements of air temperature, incoming solar radiation, and surface temperature and radiance compared well with values measured using a net radiometer (mean absolute difference (MAD) ≃ 50 W/m2 over a range from 115 to 670 W/m2). Soil heat flux density (G) was estimated using a relation between G/Rn and a spectral vegetation index computed from the red and near-infrared surface reflectance. These G estimates compared well with conventional measurements of G using buried soil heat flux plates (MAD ≃ 20 W/m2 over a range from −13 to 213 W/m2). In order to account for the effects of sparse vegetation, semiempirical adjustments to the single-layer bulk aerodynamic resistance approach were required for evaluation of sensible heat flux density (H). This yielded differences between measurements and remote estimates of H of approximately 33 W/m2 over a range from 13 to 303 W/m2. The resulting estimates of latent heat flux density, LE, were of the same magnitude and trend as measured values; however, a significant scatter was still observed: MAD ≃ 40 W/m2 over a range from 0 to 340 W/m2. Because LE was solved as a residual, there was a cumulative effect of errors associated with remote estimates of Rn, G, and H.

Core shift effect in blazars

NASA Astrophysics Data System (ADS)

Agarwal, A.; Mohan, P.; Gupta, Alok C.; Mangalam, A.; Volvach, A. E.; Aller, M. F.; Aller, H. D.; Gu, M. F.; Lähteenmäki, A.; Tornikoski, M.; Volvach, L. N.

2017-07-01

We studied the pc-scale core shift effect using radio light curves for three blazars, S5 0716+714, 3C 279 and BL Lacertae, which were monitored at five frequencies (ν) between 4.8 and 36.8 GHz using the University of Michigan Radio Astronomical Observatory (UMRAO), the Crimean Astrophysical Observatory (CrAO) and Metsähovi Radio Observatory for over 40 yr. Flares were Gaussian fitted to derive time delays between observed frequencies for each flare (Δt), peak amplitude (A) and their half width. Using A ∝ να, we infer α in the range of -16.67-2.41 and using Δ t ∝ ν ^{1/k_r}, we infer kr ∼ 1, employed in the context of equipartition between magnetic and kinetic energy density for parameter estimation. From the estimated core position offset (Ωrν) and the core radius (rcore), we infer that opacity model may not be valid in all cases. The mean magnetic field strengths at 1 pc (B1) and at the core (Bcore) are in agreement with previous estimates. We apply the magnetically arrested disc model to estimate black hole spins in the range of 0.15-0.9 for these blazars, indicating that the model is consistent with expected accretion mode in such sources. The power-law-shaped power spectral density has slopes -1.3 to -2.3 and is interpreted in terms of multiple shocks or magnetic instabilities.

Equatorial Density Irregularity Structures at Intermediate Scales and Their Temporal Evolution

NASA Technical Reports Server (NTRS)

Kil, Hyosub; Heelis, R. A.

1998-01-01

We examine high resolution measurements of ion density in the equatorial ionosphere from the AE-E satellite during the years 1977-1981. Structure over spatial scales from 18 km to 200 m is characterized by the spectrum of irregularities at larger and smaller scales and at altitudes above 350 km and below 300 km. In the low-altitude region, only small amplitude large-scale (lambda greater than 5 km) density modulations are often observed, and thus the power spectrum of these density structures exhibits a steep spectral slope at kilometer scales. In the high-altitude region, sinusoidal density fluctuations, characterized by enhanced power near 1-km scale, are frequently observed during 2000-0200 LT. However, such fluctuations are confined to regions at the edges of larger bubble structures where the average background density is high. Small amplitude irregularity structures, observed at early local time hours, grow rapidly to high-intensity structures in about 90 min. Fully developed structures, which are observed at late local time hours, decay very slowly producing only-small differences in spectral characteristics even 4 hours later. The local time evolution of irregularity structure is investigated by using average statistics for low-(1% less than sigma less than 5%) and high-intensity (sigma greater than 10%) structures. At lower altitudes, little chance in the spectral slope is seen as a function of local time, while at higher attitudes the growth and maintenance of structures near 1 km scales dramatically affects the spectral slope.

Influence UHF radiation on the process of self-assembly and lethal effect of bacterial lipopolysaccharide

NASA Astrophysics Data System (ADS)

Brill, G. E.; Egorova, A. V.; Bugaeva, I. O.; Postnov, D. E.; Melnikov, A. G.; Ushakova, O. V.

2018-04-01

The influence of low-intensity electromagnetic radiation on the process of self-assembly, spectral-fluorescent characteristics and lethal effect of bacterial lipopolysaccharide (endotoxin) was performed. A solution of bacterial lipopolysaccharide exposed to electromagnetic waves with a frequency of 1 GHz, the power density of 0.1 μW/cm2 for 10 min. In experiments on a large group of control and irradiated mice, a comparative analysis of the estimated lethal dose of endotoxin was performed. It was proved that UHF radiation of certain parameters reduces the lethal effects of bacterial lipopolysaccharide on 26%.

Solution-Processable High-Purity Semiconducting SWCNTs for Large-Area Fabrication of High-Performance Thin-Film Transistors.

PubMed

Gu, Jianting; Han, Jie; Liu, Dan; Yu, Xiaoqin; Kang, Lixing; Qiu, Song; Jin, Hehua; Li, Hongbo; Li, Qingwen; Zhang, Jin

2016-09-01

For the large-area fabrication of thin-film transistors (TFTs), a new conjugated polymer poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl] is developed to harvest ultrahigh-purity semiconducting single-walled carbon nanotubes. Combined with spectral and nanodevice characterization, the purity is estimated up to 99.9%. High density and uniform network formed by dip-coating process is liable to fabricate high-performance TFTs on a wafer-scale and the as-fabricated TFTs exhibit a high degree of uniformity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of radiometric signal in sedimentating suspension flow in open channel

NASA Astrophysics Data System (ADS)

Zych, Marcin; Hanus, Robert; Petryka, Leszek; Świsulski, Dariusz; Doktor, Marek; Mastej, Wojciech

2015-05-01

The article discusses issues related to the estimation of the sedimentating solid particles average flow velocity in an open channel using radiometric methods. Due to the composition of the compound, which formed water and diatomite, received data have a very weak signal to noise ratio. In the process analysis the known determining of the solid phase transportation time delay the classical cross-correlation function is the most reliable method. The use of advanced frequency analysis based on mutual spectral density function and wavelet transform of recorded signals allows a reduction of the noise contribution.

Rocket observations of the precipitation of electrons by ground VLF transmitters

NASA Technical Reports Server (NTRS)

Arnoldy, Roger L.; Kintner, Paul M.

1989-01-01

Recent results obtained with electric and magnetic receivers aboard a NASA sounding rocket launched on July 31, 1987 are presented which relate multiple electron spectral peaks observed in the bounce loss cone fluxes to the resonant interaction of electrons with VLF waves from ground transmitters. The correlation of transmitter signals passing through the ionosphere with the precipitated electrons was investigated. The analysis of these in situ wave and particle data addresses the propagation of waves through the ionosphere, and, through an application of the resonant theory, enables an estimation of the cold plasma density in the interaction region.

Correlated perturbations from inflation and the cosmic microwave background.

PubMed

Amendola, Luca; Gordon, Christopher; Wands, David; Sasaki, Misao

2002-05-27

We compare the latest cosmic microwave background data with theoretical predictions including correlated adiabatic and cold dark matter (CDM) isocurvature perturbations with a simple power-law dependence. We find that there is a degeneracy between the amplitude of correlated isocurvature perturbations and the spectral tilt. A negative (red) tilt is found to be compatible with a larger isocurvature contribution. Estimates of the baryon and CDM densities are found to be almost independent of the isocurvature amplitude. The main result is that current microwave background data do not exclude a dominant contribution from CDM isocurvature fluctuations on large scales.

FIVE YEARS OF SYNTHESIS OF SOLAR SPECTRAL IRRADIANCE FROM SDID/SISA AND SDO /AIA IMAGES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fontenla, J. M.; Codrescu, M.; Fedrizzi, M.

In this paper we describe the synthetic solar spectral irradiance (SSI) calculated from 2010 to 2015 using data from the Atmospheric Imaging Assembly (AIA) instrument, on board the Solar Dynamics Observatory spacecraft. We used the algorithms for solar disk image decomposition (SDID) and the spectral irradiance synthesis algorithm (SISA) that we had developed over several years. The SDID algorithm decomposes the images of the solar disk into areas occupied by nine types of chromospheric and 5 types of coronal physical structures. With this decomposition and a set of pre-computed angle-dependent spectra for each of the features, the SISA algorithm ismore » used to calculate the SSI. We discuss the application of the basic SDID/SISA algorithm to a subset of the AIA images and the observed variation occurring in the 2010–2015 period of the relative areas of the solar disk covered by the various solar surface features. Our results consist of the SSI and total solar irradiance variations over the 2010–2015 period. The SSI results include soft X-ray, ultraviolet, visible, infrared, and far-infrared observations and can be used for studies of the solar radiative forcing of the Earth’s atmosphere. These SSI estimates were used to drive a thermosphere–ionosphere physical simulation model. Predictions of neutral mass density at low Earth orbit altitudes in the thermosphere and peak plasma densities at mid-latitudes are in reasonable agreement with the observations. The correlation between the simulation results and the observations was consistently better when fluxes computed by SDID/SISA procedures were used.« less

Evaluation of spatial, radiometric and spectral Thematic Mapper performance for coastal studies

NASA Technical Reports Server (NTRS)

Klemas, V. (Principal Investigator)

1984-01-01

The effect different wetland plant canopies have upon observed reflectance in Thematic Mapper bands is studied. The three major vegetation canopy types (broadleaf, gramineous and leafless) produce unique spectral responses for a similar quantity of live biomass. The spectral biomass estimate of a broadleaf canopy is most similar to the harvest biomass estimate when a broadleaf canopy radiance model is used. All major wetland vegetation species can be identified through TM imagery. Simple regression models are developed equating the vegetation index and the infrared index with biomass. The spectral radiance index largely agreed with harvest biomass estimates.

Multitaper scan-free spectrum estimation using a rotational shear interferometer.

PubMed

Lepage, Kyle; Thomson, David J; Kraut, Shawn; Brady, David J

2006-05-01

Multitaper methods for a scan-free spectrum estimation that uses a rotational shear interferometer are investigated. Before source spectra can be estimated the sources must be detected. A source detection algorithm based upon the multitaper F-test is proposed. The algorithm is simulated, with additive, white Gaussian detector noise. A source with a signal-to-noise ratio (SNR) of 0.71 is detected 2.9 degrees from a source with a SNR of 70.1, with a significance level of 10(-4), approximately 4 orders of magnitude more significant than the source detection obtained with a standard detection algorithm. Interpolation and the use of prewhitening filters are investigated in the context of rotational shear interferometer (RSI) source spectra estimation. Finally, a multitaper spectrum estimator is proposed, simulated, and compared with untapered estimates. The multitaper estimate is found via simulation to distinguish a spectral feature with a SNR of 1.6 near a large spectral feature. The SNR of 1.6 spectral feature is not distinguished by the untapered spectrum estimate. The findings are consistent with the strong capability of the multitaper estimate to reduce out-of-band spectral leakage.

Multitaper scan-free spectrum estimation using a rotational shear interferometer

NASA Astrophysics Data System (ADS)

Lepage, Kyle; Thomson, David J.; Kraut, Shawn; Brady, David J.

2006-05-01

Multitaper methods for a scan-free spectrum estimation that uses a rotational shear interferometer are investigated. Before source spectra can be estimated the sources must be detected. A source detection algorithm based upon the multitaper F-test is proposed. The algorithm is simulated, with additive, white Gaussian detector noise. A source with a signal-to-noise ratio (SNR) of 0.71 is detected 2.9° from a source with a SNR of 70.1, with a significance level of 10-4, ˜4 orders of magnitude more significant than the source detection obtained with a standard detection algorithm. Interpolation and the use of prewhitening filters are investigated in the context of rotational shear interferometer (RSI) source spectra estimation. Finally, a multitaper spectrum estimator is proposed, simulated, and compared with untapered estimates. The multitaper estimate is found via simulation to distinguish a spectral feature with a SNR of 1.6 near a large spectral feature. The SNR of 1.6 spectral feature is not distinguished by the untapered spectrum estimate. The findings are consistent with the strong capability of the multitaper estimate to reduce out-of-band spectral leakage.

Utilizing the ratio and the summation of two spectral lines for estimation of optical depth: Focus on thick plasmas

NASA Astrophysics Data System (ADS)

Rezaei, Fatemeh; Tavassoli, Seyed Hassan

2016-11-01

In this paper, a study is performed on the spectral lines of plasma radiations created from focusing of the Nd:YAG laser on Al standard alloys at atmospheric air pressure. A new theoretical method is presented to investigate the evolution of the optical depth of the plasma based on the radiative transfer equation, in LTE condition. This work relies on the Boltzmann distribution, lines broadening equations, and as well as the self-absorption relation. Then, an experimental set-up is devised to extract some of plasma parameters such as temperature from modified line ratio analysis, electron density from Stark broadening mechanism, line intensities of two spectral lines in the same order of ionization from similar species, and the plasma length from the shadowgraphy section. In this method, the summation and the ratio of two spectral lines are considered for evaluation of the temporal variations of the plasma parameters in a LIBS homogeneous plasma. The main advantage of this method is that it comprises the both of thin and thick laser induced plasmas without straight calculation of self-absorption coefficient. Moreover, the presented model can also be utilized for evaluation the transition of plasma from the thin condition to the thick one. The results illustrated that by measuring the line intensities of two spectral lines at different evolution times, the plasma cooling and the growth of the optical depth can be followed.

Python Radiative Transfer Emission code (PyRaTE): non-LTE spectral lines simulations

NASA Astrophysics Data System (ADS)

Tritsis, A.; Yorke, H.; Tassis, K.

2018-05-01

We describe PyRaTE, a new, non-local thermodynamic equilibrium (non-LTE) line radiative transfer code developed specifically for post-processing astrochemical simulations. Population densities are estimated using the escape probability method. When computing the escape probability, the optical depth is calculated towards all directions with density, molecular abundance, temperature and velocity variations all taken into account. A very easy-to-use interface, capable of importing data from simulations outputs performed with all major astrophysical codes, is also developed. The code is written in PYTHON using an "embarrassingly parallel" strategy and can handle all geometries and projection angles. We benchmark the code by comparing our results with those from RADEX (van der Tak et al. 2007) and against analytical solutions and present case studies using hydrochemical simulations. The code will be released for public use.

Electric-field noise from carbon-adatom diusion on a Au(110) surface: first-principles calculations and experiments

NASA Astrophysics Data System (ADS)

Sadeghpour, Hossein; Kim, Eunja; Safavi-Naini, Arghavan; Weck, Philippe; Hite, Dustin; McKay, Kyle; Pappas, David

2017-04-01

The decoherence of trapped-ion quantum gates due to heating of their motional modes is a fundamental science and engineering challenge. Mitigating this noise, is fundamental to efficient and scalable operations in ion microtraps. To understand heating at the trap-electrode surfaces, we investigate the possible source of noise by focusing on the diffusion of carbon-containing adsorbates onto the Au(110) surface. Using density functional theory and detailed scanning probe microscopy, we show that the diffusive motion of carbon adatom on gold surface significantly affect the energy landscape and adatom dipole moment variation. A model for the diffusion noise, which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values.

A low-frequency noise model with carrier generation-recombination process for pentacene organic thin-film transistor

NASA Astrophysics Data System (ADS)

Han, C. Y.; Qian, L. X.; Leung, C. H.; Che, C. M.; Lai, P. T.

2013-07-01

By including the generation-recombination process of charge carriers in conduction channel, a model for low-frequency noise in pentacene organic thin-film transistors (OTFTs) is proposed. In this model, the slope and magnitude of power spectral density for low-frequency noise are related to the traps in the gate dielectric and accumulation layer of the OTFT for the first time. The model can well fit the measured low-frequency noise data of pentacene OTFTs with HfO2 or HfLaO gate dielectric, which validates this model, thus providing an estimate on the densities of traps in the gate dielectric and accumulation layer. It is revealed that the traps in the accumulation layer are much more than those in the gate dielectric, and so dominate the low-frequency noise of pentacene OTFTs.

Quantifying the influences of spectral resolution on uncertainty in leaf trait estimates through a Bayesian approach to RTM inversion

DOE PAGES

Shiklomanov, Alexey N.; Dietze, Michael C.; Viskari, Toni; ...

2016-06-09

The remote monitoring of plant canopies is critically needed for understanding of terrestrial ecosystem mechanics and biodiversity as well as capturing the short- to long-term responses of vegetation to disturbance and climate change. A variety of orbital, sub-orbital, and field instruments have been used to retrieve optical spectral signals and to study different vegetation properties such as plant biochemistry, nutrient cycling, physiology, water status, and stress. Radiative transfer models (RTMs) provide a mechanistic link between vegetation properties and observed spectral features, and RTM spectral inversion is a useful framework for estimating these properties from spectral data. However, existing approaches tomore » RTM spectral inversion are typically limited by the inability to characterize uncertainty in parameter estimates. Here, we introduce a Bayesian algorithm for the spectral inversion of the PROSPECT 5 leaf RTM that is distinct from past approaches in two important ways: First, the algorithm only uses reflectance and does not require transmittance observations, which have been plagued by a variety of measurement and equipment challenges. Second, the output is not a point estimate for each parameter but rather the joint probability distribution that includes estimates of parameter uncertainties and covariance structure. We validated our inversion approach using a database of leaf spectra together with measurements of equivalent water thickness (EWT) and leaf dry mass per unit area (LMA). The parameters estimated by our inversion were able to accurately reproduce the observed reflectance (RMSE VIS = 0.0063, RMSE NIR-SWIR = 0.0098) and transmittance (RMSE VIS = 0.0404, RMSE NIR-SWIR = 0.0551) for both broadleaved and conifer species. Inversion estimates of EWT and LMA for broadleaved species agreed well with direct measurements (CV EWT = 18.8%, CV LMA = 24.5%), while estimates for conifer species were less accurate (CV EWT = 53.2%, CV LMA = 63.3%). To examine the influence of spectral resolution on parameter uncertainty, we simulated leaf reflectance as observed by ten common remote sensing platforms with varying spectral configurations and performed a Bayesian inversion on the resulting spectra. We found that full-range hyperspectral platforms were able to retrieve all parameters accurately and precisely, while the parameter estimates of multispectral platforms were much less precise and prone to bias at high and low values. We also observed that variations in the width and location of spectral bands influenced the shape of the covariance structure of parameter estimates. Lastly, our Bayesian spectral inversion provides a powerful and versatile framework for future RTM development and single- and multi-instrumental remote sensing of vegetation.« less

Quantifying the influences of spectral resolution on uncertainty in leaf trait estimates through a Bayesian approach to RTM inversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shiklomanov, Alexey N.; Dietze, Michael C.; Viskari, Toni

The remote monitoring of plant canopies is critically needed for understanding of terrestrial ecosystem mechanics and biodiversity as well as capturing the short- to long-term responses of vegetation to disturbance and climate change. A variety of orbital, sub-orbital, and field instruments have been used to retrieve optical spectral signals and to study different vegetation properties such as plant biochemistry, nutrient cycling, physiology, water status, and stress. Radiative transfer models (RTMs) provide a mechanistic link between vegetation properties and observed spectral features, and RTM spectral inversion is a useful framework for estimating these properties from spectral data. However, existing approaches tomore » RTM spectral inversion are typically limited by the inability to characterize uncertainty in parameter estimates. Here, we introduce a Bayesian algorithm for the spectral inversion of the PROSPECT 5 leaf RTM that is distinct from past approaches in two important ways: First, the algorithm only uses reflectance and does not require transmittance observations, which have been plagued by a variety of measurement and equipment challenges. Second, the output is not a point estimate for each parameter but rather the joint probability distribution that includes estimates of parameter uncertainties and covariance structure. We validated our inversion approach using a database of leaf spectra together with measurements of equivalent water thickness (EWT) and leaf dry mass per unit area (LMA). The parameters estimated by our inversion were able to accurately reproduce the observed reflectance (RMSE VIS = 0.0063, RMSE NIR-SWIR = 0.0098) and transmittance (RMSE VIS = 0.0404, RMSE NIR-SWIR = 0.0551) for both broadleaved and conifer species. Inversion estimates of EWT and LMA for broadleaved species agreed well with direct measurements (CV EWT = 18.8%, CV LMA = 24.5%), while estimates for conifer species were less accurate (CV EWT = 53.2%, CV LMA = 63.3%). To examine the influence of spectral resolution on parameter uncertainty, we simulated leaf reflectance as observed by ten common remote sensing platforms with varying spectral configurations and performed a Bayesian inversion on the resulting spectra. We found that full-range hyperspectral platforms were able to retrieve all parameters accurately and precisely, while the parameter estimates of multispectral platforms were much less precise and prone to bias at high and low values. We also observed that variations in the width and location of spectral bands influenced the shape of the covariance structure of parameter estimates. Lastly, our Bayesian spectral inversion provides a powerful and versatile framework for future RTM development and single- and multi-instrumental remote sensing of vegetation.« less

Development and application of the maximum entropy method and other spectral estimation techniques

NASA Astrophysics Data System (ADS)

King, W. R.

1980-09-01

This summary report is a collection of four separate progress reports prepared under three contracts, which are all sponsored by the Office of Naval Research in Arlington, Virginia. This report contains the results of investigations into the application of the maximum entropy method (MEM), a high resolution, frequency and wavenumber estimation technique. The report also contains a description of two, new, stable, high resolution spectral estimation techniques that is provided in the final report section. Many examples of wavenumber spectral patterns for all investigated techniques are included throughout the report. The maximum entropy method is also known as the maximum entropy spectral analysis (MESA) technique, and both names are used in the report. Many MEM wavenumber spectral patterns are demonstrated using both simulated and measured radar signal and noise data. Methods for obtaining stable MEM wavenumber spectra are discussed, broadband signal detection using the MEM prediction error transform (PET) is discussed, and Doppler radar narrowband signal detection is demonstrated using the MEM technique. It is also shown that MEM cannot be applied to randomly sampled data. The two new, stable, high resolution, spectral estimation techniques discussed in the final report section, are named the Wiener-King and the Fourier spectral estimation techniques. The two new techniques have a similar derivation based upon the Wiener prediction filter, but the two techniques are otherwise quite different. Further development of the techniques and measurement of the technique spectral characteristics is recommended for subsequent investigation.

Spectral likelihood expansions for Bayesian inference

NASA Astrophysics Data System (ADS)

Nagel, Joseph B.; Sudret, Bruno

2016-03-01

A spectral approach to Bayesian inference is presented. It pursues the emulation of the posterior probability density. The starting point is a series expansion of the likelihood function in terms of orthogonal polynomials. From this spectral likelihood expansion all statistical quantities of interest can be calculated semi-analytically. The posterior is formally represented as the product of a reference density and a linear combination of polynomial basis functions. Both the model evidence and the posterior moments are related to the expansion coefficients. This formulation avoids Markov chain Monte Carlo simulation and allows one to make use of linear least squares instead. The pros and cons of spectral Bayesian inference are discussed and demonstrated on the basis of simple applications from classical statistics and inverse modeling.

Photopigment self-screening and the determination of macular pigment absorbance using heterochromatic flicker photometry.

PubMed

Smollon, William E; Wooten, Billy R; Hammond, Billy R

2015-11-01

Heterochromatic flicker photometry (HFP) is commonly used to determine macular pigment optical density (MPOD). Since HFP in this application is a locus comparison method, an identical relative spectral response at each locus is required for a perfect measure. We know this requirement cannot be strictly true since the optical density of photopigments increases as the foveal center is approached. Thus, the self-screening effect would result in an underestimate of MPOD. An earlier study concluded that the underestimate is on the order of 30%. We examined this issue by manipulating photopigment optical density, and consequently the degree of selfscreening. A continuously exposed, 470 nm, background bleached cone photopigments over a range from 0 to 80%. MPOD was determined 10' and 30' from the foveal center. Two subjects were used in the main experiment. Five additional subjects were studied with just the 0% and 80% bleach levels. Spectral measures were obtained at 0% and 70% bleach levels for the two primary subjects. Subjects in the main experiment showed MPOD estimates that increased with increasing bleaching. The effect, however, was small: one observer's MPOD increased 0.08 and 0.02 for the 10' and 30' loci, respectively; the other observer's values were 0.04 and 0.01 for the same loci. Comparable values were obtained for the other five subjects using the 0% and 80% bleach conditions. Spectral measures were consistent with the findings of the main experiment. When self-screening is nearly abolished (80% bleach), a relatively small underestimation is revealed for the unbleached state. For the 1° target we show about 2-3% underestimation. Our 20' target reveals a larger underestimate (8-9%), consistent with longer photoreceptor outer-segments nearer the foveal center. We conclude that HFP yields values essentially independent of self-screening for targets of 1° diameter or greater. Smaller targets are less than 10% underestimated for near-zero bleach conditions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spectral estimates of intercepted solar radiation by corn and soybean canopies

NASA Technical Reports Server (NTRS)

Gallo, K. P.; Brooks, C. C.; Daughtry, C. S. T.; Bauer, M. E.; Vanderbilt, V. C.

1982-01-01

Attention is given to the development of methods for combining spectral and meteorological data in crop yield models which are capable of providing accurate estimates of crop condition and yields throughout the growing season. The present investigation is concerned with initial tests of these concepts using spectral and agronomic data acquired in controlled experiments. The data were acquired at the Purdue University Agronomy Farm, 10 km northwest of West Lafayette, Indiana. Data were obtained throughout several growing seasons for corn and soybeans. Five methods or models for predicting yields were examined. On the basis of the obtained results, it is concluded that estimating intercepted solar radiation using spectral data is a viable approach for merging spectral and meteorological data in crop yield models.

Detecting leafy spurge in native grassland using hyperspectral image analysis

NASA Astrophysics Data System (ADS)

Kloppenburg, Catherine

Leafy spurge (Euphoria esula L.) is a perennial noxious weed that has been encroaches on the native grassland regions of North America resulting in biological and economic impacts. Leafy spurge growth is most prevalent along river banks and in pasture areas. Due to poor accessibility and the cost and labour associated with data collection, estimates of number and size of leafy spurge infestations is poor. Remote sensing has the ability to cover large areas, providing an alternate means to ground surveys and will allow for the capability to create an accurate baseline of infestations. Airborne hyperspectral data were collected over the two test sites selected on the Blood Reserve in Southern Alberta using a combined Airborne Imaging Spectrometer for different Applications (AISA) Eagle and Hawk sensor systems in July, 2010. This study used advanced analysis tools, including spectral mixture analysis, spectral angle mapper and mixture-tuned matched filter techniques to evaluate the ability to detect leafy spurge patches. The results show that patches of leafy spurge with flowering stem density >40 stems m-2 were identified with 85 % accuracy while identification of lower density stems were less accurate (10 - 40 %). The results are promising with respect to quantifying areas of significant leafy spurge infestation and targeting biological control and potential insect release sites.

Investigating ChaMPlane X-Ray Sources in the Galactic Bulge with Magellan LDSS2 Spectra

NASA Astrophysics Data System (ADS)

Koenig, Xavier; Grindlay, Jonathan E.; van den Berg, Maureen; Laycock, Silas; Zhao, Ping; Hong, JaeSub; Schlegel, Eric M.

2008-09-01

We have carried out optical and X-ray spectral analyses on a sample of 136 candidate optical counterparts of X-ray sources found in five Galactic bulge fields included in our Chandra Multiwavelength Plane Survey. We use a combination of optical spectral fitting and quantile X-ray analysis to obtain the hydrogen column density toward each object, and a three-dimensional dust model of the Galaxy to estimate the most probable distance in each case. We present the discovery of a population of stellar coronal emission sources, likely consisting of pre-main-sequence, young main-sequence, and main-sequence stars, as well as a component of active binaries of RS CVn or BY Dra type. We identify one candidate quiescent low-mass X-ray binary with a subgiant companion; we note that this object may also be an RS CVn system. We report the discovery of three new X-ray-detected cataclysmic variables (CVs) in the direction of the Galactic center (at distances lesssim2 kpc). This number is in excess of predictions made with a simple CV model based on a local CV space density of lesssim10-5 pc-3, and a scale height ~200 pc. We discuss several possible reasons for this observed excess.

Infrared dust bubble CS51 and its interaction with the surrounding interstellar medium

NASA Astrophysics Data System (ADS)

Das, Swagat R.; Tej, Anandmayee; Vig, Sarita; Liu, Hong-Li; Liu, Tie; Ishwara Chandra, C. H.; Ghosh, Swarna K.

2017-12-01

A multiwavelength investigation of the southern infrared dust bubble CS51 is presented in this paper. We probe the associated ionized, cold dust, molecular and stellar components. Radio continuum emission mapped at 610 and 1300 MHz, using the Giant Metrewave Radio Telescope, India, reveals the presence of three compact emission components (A, B, and C) apart from large-scale diffuse emission within the bubble interior. Radio spectral index map shows the co-existence of thermal and non-thermal emission components. Modified blackbody fits to the thermal dust emission using Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver data is performed to generate dust temperature and column density maps. We identify five dust clumps associated with CS51 with masses and radius in the range 810-4600 M⊙ and 1.0-1.9 pc, respectively. We further construct the column density probability distribution functions of the surrounding cold dust which display the impact of ionization feedback from high-mass stars. The estimated dynamical and fragmentation time-scales indicate the possibility of collect and collapse mechanism in play at the bubble border. Molecular line emission from the Millimeter Astronomy Legacy Team 90 GHz survey is used to understand the nature of two clumps which show signatures of expansion of CS51.

Processing Raman Spectra of High-Pressure Hydrogen Flames

NASA Technical Reports Server (NTRS)

Nguyen, Quang-Viet; Kojima, Jun

2006-01-01

The Raman Code automates the analysis of laser-Raman-spectroscopy data for diagnosis of combustion at high pressure. On the basis of the theory of molecular spectroscopy, the software calculates the rovibrational and pure rotational Raman spectra of H2, O2, N2, and H2O in hydrogen/air flames at given temperatures and pressures. Given a set of Raman spectral data from measurements on a given flame and results from the aforementioned calculations, the software calculates the thermodynamic temperature and number densities of the aforementioned species. The software accounts for collisional spectral-line-broadening effects at pressures up to 60 bar (6 MPa). The line-broadening effects increase with pressure and thereby complicate the analysis. The software also corrects for spectral interference ("cross-talk") among the various chemical species. In the absence of such correction, the cross-talk is a significant source of error in temperatures and number densities. This is the first known comprehensive computer code that, when used in conjunction with a spectral calibration database, can process Raman-scattering spectral data from high-pressure hydrogen/air flames to obtain temperatures accurate to within 10 K and chemical-species number densities accurate to within 2 percent.

Influence of Laser Radiation Power Density on the Intensity of Spectral Lines for Main Components in a Clay Laser-Induced Plasma

NASA Astrophysics Data System (ADS)

Anufrik, S. S.; Kurian, N. N.; Znosko, K. F.; Belkov, M. V.

2018-05-01

We have studied the intensity of the spectral lines for the main components in clay: Al I 309.4 nm, Al II 358.7 nm, Mg II 279.6 nm, Ti II 323.6 nm vs. the position of the object relative to the focus of the optical system when the samples are exposed to single laser pulses from a YAG:Nd3+ laser. We have determined the permissible ranges for positioning the object relative to the focus of the optical system (positive and negative defocusing) for which there is practically no change in the reproducibility of the intensity for the spectral lines for red and white clay samples. We show that the position of the object relative to the focus of the optical system should be within the range ΔZ ±1.5 mm for optimal laser pulse energies for the analyte spectral lines. We have calculated the radiation flux density for different laser pulse energies and different distances from the focus to the object. We have shown experimentally that reducing the radiation flux density leads to a decrease in the intensity of the analyte spectral lines.

Fundamental limits to frequency estimation: a comprehensive microscopic perspective

NASA Astrophysics Data System (ADS)

Haase, J. F.; Smirne, A.; Kołodyński, J.; Demkowicz-Dobrzański, R.; Huelga, S. F.

2018-05-01

We consider a metrology scenario in which qubit-like probes are used to sense an external field that affects their energy splitting in a linear fashion. Following the frequency estimation approach in which one optimizes the state and sensing time of the probes to maximize the sensitivity, we provide a systematic study of the attainable precision under the impact of noise originating from independent bosonic baths. Specifically, we invoke an explicit microscopic derivation of the probe dynamics using the spin-boson model with weak coupling of arbitrary geometry. We clarify how the secular approximation leads to a phase-covariant (PC) dynamics, where the noise terms commute with the field Hamiltonian, while the inclusion of non-secular contributions breaks the PC. Moreover, unless one restricts to a particular (i.e., Ohmic) spectral density of the bath modes, the noise terms may contain relevant information about the frequency to be estimated. Thus, by considering general evolutions of a single probe, we study regimes in which these two effects have a non-negligible impact on the achievable precision. We then consider baths of Ohmic spectral density yet fully accounting for the lack of PC, in order to characterize the ultimate attainable scaling of precision when N probes are used in parallel. Crucially, we show that beyond the semigroup (Lindbladian) regime the Zeno limit imposing the 1/N 3/2 scaling of the mean squared error, recently derived assuming PC, generalises to any dynamics of the probes, unless the latter are coupled to the baths in the direction perfectly transversal to the frequency encoding—when a novel scaling of 1/N 7/4 arises. As our microscopic approach covers all classes of dissipative dynamics, from semigroup to non-Markovian ones (each of them potentially non-phase-covariant), it provides an exhaustive picture, in which all the different asymptotic scalings of precision naturally emerge.

Diagnosis of skin cancer using image processing

NASA Astrophysics Data System (ADS)

Guerra-Rosas, Esperanza; Álvarez-Borrego, Josué; Coronel-Beltrán, Ángel

2014-10-01

In this papera methodology for classifying skin cancerin images of dermatologie spots based on spectral analysis using the K-law Fourier non-lineartechnique is presented. The image is segmented and binarized to build the function that contains the interest area. The image is divided into their respective RGB channels to obtain the spectral properties of each channel. The green channel contains more information and therefore this channel is always chosen. This information is point to point multiplied by a binary mask and to this result a Fourier transform is applied written in nonlinear form. If the real part of this spectrum is positive, the spectral density takeunit values, otherwise are zero. Finally the ratio of the sum of the unit values of the spectral density with the sum of values of the binary mask are calculated. This ratio is called spectral index. When the value calculated is in the spectral index range three types of cancer can be detected. Values found out of this range are benign injure.

Estimation of Soil Moisture Content from the Spectral Reflectance of Bare Soils in the 0.4–2.5 μm Domain

PubMed Central

Fabre, Sophie; Briottet, Xavier; Lesaignoux, Audrey

2015-01-01

This work aims to compare the performance of new methods to estimate the Soil Moisture Content (SMC) of bare soils from their spectral signatures in the reflective domain (0.4–2.5 μm) in comparison with widely used spectral indices like Normalized Soil Moisture Index (NSMI) and Water Index SOIL (WISOIL). Indeed, these reference spectral indices use wavelengths located in the water vapour absorption bands and their performance are thus very sensitive to the quality of the atmospheric compensation. To reduce these limitations, two new spectral indices are proposed which wavelengths are defined using the determination matrix tool by taking into account the atmospheric transmission: Normalized Index of Nswir domain for Smc estimatiOn from Linear correlation (NINSOL) and Normalized Index of Nswir domain for Smc estimatiOn from Non linear correlation (NINSON). These spectral indices are completed by two new methods based on the global shape of the soil spectral signatures. These methods are the Inverse Soil semi-Empirical Reflectance model (ISER), using the inversion of an existing empirical soil model simulating the soil spectral reflectance according to soil moisture content for a given soil class, and the convex envelope model, linking the area between the envelope and the spectral signature to the SMC. All these methods are compared using a reference database built with 32 soil samples and composed of 190 spectral signatures with five or six soil moisture contents. Half of the database is used for the calibration stage and the remaining to evaluate the performance of the SMC estimation methods. The results show that the four new methods lead to similar or better performance than the one obtained by the reference indices. The RMSE is ranging from 3.8% to 6.2% and the coefficient of determination R2 varies between 0.74 and 0.91 with the best performance obtained with the ISER model. In a second step, simulated spectral radiances at the sensor level are used to analyse the sensitivity of these methods to the sensor spectral resolution and the water vapour content knowledge. The spectral signatures of the database are then used to simulate the signal at the top of atmosphere with a radiative transfer model and to compute the integrated incident signal representing the spectral radiance measurements of the HYMAP airborne hyperspectral instrument. The sensor radiances are then corrected from the atmosphere by an atmospheric compensation tool to retrieve the surface reflectances. The SMC estimation methods are then applied on the retrieve spectral reflectances. The adaptation of the spectral index wavelengths to the HyMap sensor spectral bands and the application of the convex envelope and ISER models to boarder spectral bands lead to an error on the SMC estimation. The best performance is then obtained with the ISER model (RMSE of 2.9% and R2 of 0.96) while the four other methods lead to quite similar RMSE (from 6.4% to 7.8%) and R2 (between 0.79 and 0.83) values. In the atmosphere compensation processing, an error on the water vapour content is introduced. The most robust methods to water vapour content variations are WISOIL, NINSON, NINSOL and ISER model. The convex envelope model and NSMI index require an accurate estimation of the water vapour content in the atmosphere. PMID:25648710

Analysis of multi-layered films. [determining dye densities by applying a regression analysis to the spectral response of the composite transparency

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.

ERTS evaluation for land use inventory

NASA Technical Reports Server (NTRS)

Hardy, E. E. (Principal Investigator)

1973-01-01

The author has identified the following significant results. The feasibility of accomplishing a general inventory of any given region based on spectral categories from satellite data has been demonstrated in a pilot study for an area of 6300 square kilometers in central New York State. This was accomplished by developing special processing techniques to improve and balance contrast and density for each spectral band of an image scene to compare with a standard range of density and contrast found to be acceptable for interpretation of the scene. Diazo film transparencies were made from enlarged black and white transparencies of each spectral band. Color composites were constructed from these diazo films in combinations of hue and spectral bands to enhance different spectral features in the scene. Interpretation and data takeoff was accomplished manually by translating interpreted areas onto an overlay to construct a spectral map. The minimum area interpreted was 25 hectares. The minimum area geographically referenced was one square kilometer. The interpretation and referencing of data from ERTS-1 was found to be about 88% accurate for eight primary spectral categories.

Generation of Stationary Non-Gaussian Time Histories with a Specified Cross-spectral Density

DOE PAGES

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

Comparative Analysis of the Clinical Significance of Oscillatory Components in the Rhythmic Structure of Pulse Signal in the Diagnostics of Psychosomatic Disorders in School Age Children.

PubMed

Desova, A A; Dorofeyuk, A A; Anokhin, A M

2017-01-01

We performed a comparative analysis of the types of spectral density typical of various parameters of pulse signal. The experimental material was obtained during the examination of school age children with various psychosomatic disorders. We also performed a typological analysis of the spectral density functions corresponding to the time series of different parameters of a single oscillation of pulse signals; the results of their comparative analysis are presented. We determined the most significant spectral components for two disordersin children: arterial hypertension and mitral valve prolapse.

Influence of defects on the absorption edge of InN thin films: The band gap value

NASA Astrophysics Data System (ADS)

Thakur, J. S.; Danylyuk, Y. V.; Haddad, D.; Naik, V. M.; Naik, R.; Auner, G. W.

2007-07-01

We investigate the optical-absorption spectra of InN thin films whose electron density varies from ˜1017tõ1021cm-3 . The low-density films are grown by molecular-beam-epitaxy deposition while highly degenerate films are grown by plasma-source molecular-beam epitaxy. The optical-absorption edge is found to increase from 0.61to1.90eV as the carrier density of the films is increased from low to high density. Since films are polycrystalline and contain various types of defects, we discuss the band gap values by studying the influence of electron degeneracy, electron-electron, electron-ionized impurities, and electron-LO-phonon interaction self-energies on the spectral absorption coefficients of these films. The quasiparticle self-energies of the valence and conduction bands are calculated using dielectric screening within the random-phase approximation. Using one-particle Green’s function analysis, we self-consistently determine the chemical potential for films by coupling equations for the chemical potential and the single-particle scattering rate calculated within the effective-mass approximation for the electron scatterings from ionized impurities and LO phonons. By subtracting the influence of self-energies and chemical potential from the optical-absorption edge energy, we estimate the intrinsic band gap values for the films. We also determine the variations in the calculated band gap values due to the variations in the electron effective mass and static dielectric constant. For the lowest-density film, the estimated band gap energy is ˜0.59eV , while for the highest-density film, it varies from ˜0.60tõ0.68eV depending on the values of electron effective mass and dielectric constant.

Remote estimation of crown size and tree density in snowy areas

NASA Astrophysics Data System (ADS)

Kishi, R.; Ito, A.; Kamada, K.; Fukita, T.; Lahrita, L.; Kawase, Y.; Murahashi, K.; Kawamata, H.; Naruse, N.; Takahashi, Y.

2017-12-01

Precise estimation of tree density in the forest leads us to understand the amount of carbon dioxide fixed by plants. Aerial photographs have been used to measure the number of trees. Campaign using aircraft, however, is expensive ( $50,000/1 campaign flight) and the research area is limited in drone. In addition, previous studies estimating the density of trees from aerial photographs have been performed in the summer, so there was a gap of 15% in the estimation due to the overlapping of the leaves. Here, we have proposed a method to accurately estimate the number of forest trees from the satellite images of snow-covered deciduous forest area, using the ratio of branches to snow. The advantages of our method are as follows; 1) snow area could be excluded easily due to the high reflectance, 2) tree branches are small overlapping compared to leaves. Although our method can use only in the snowfall region, the area covered with snow in the world becomes more than 12,800,000 km2. Our proposition should play an important role in discussing global warming. As a test area, we have chosen the forest near Mt. Amano in Iwate prefecture in Japan. First, we made a new index of (Band1-Band5)/(Band1+Band5), which will be suitable to distinguish between the snow and the tree trunk using the corresponding spectral reflection data. Next, the index values of changing the ratio in 1% increments were listed. From the satellite image analysis at 4 points, the ratio of snow to tree trunk showed the following values, I:61%, II:65%, III:66% and IV:65%. To confirm the estimation, we used the aerial photograph from Google earth; the rate was I:42.05%, II:48.89%, III:50.64%, IV:49.05%, respectively. There is a correlation between the numerical values of both, but there are differences. We will discuss in detail at this point, focusing on the effect of shadows.

Contribution of strong discontinuities to the power spectrum of the solar wind.

PubMed

Borovsky, Joseph E

2010-09-10

Eight and a half years of magnetic field measurements (2(22) samples) from the ACE spacecraft in the solar wind at 1 A.U. are analyzed. Strong (large-rotation-angle) discontinuities in the solar wind are collected and measured. An artificial time series is created that preserves the timing and amplitudes of the discontinuities. The power spectral density of the discontinuity series is calculated and compared with the power spectral density of the solar-wind magnetic field. The strong discontinuities produce a power-law spectrum in the "inertial subrange" with a spectral index near the Kolmogorov -5/3 index. The discontinuity spectrum contains about half of the power of the full solar-wind magnetic field over this "inertial subrange." Warnings are issued about the significant contribution of discontinuities to the spectrum of the solar wind, complicating interpretation of spectral power and spectral indices.

Photocatalytic Active Radiation Measurements and Use

NASA Technical Reports Server (NTRS)

Davis, Bruce A.; Underwood, Lauren W.

2011-01-01

Photocatalytic materials are being used to purify air, to kill microbes, and to keep surfaces clean. A wide variety of materials are being developed, many of which have different abilities to absorb various wavelengths of light. Material variability, combined with both spectral illumination intensity and spectral distribution variability, will produce a wide range of performance results. The proposed technology estimates photocatalytic active radiation (PcAR), a unit of radiation that normalizes the amount of light based on its spectral distribution and on the ability of the material to absorb that radiation. Photocatalytic reactions depend upon the number of electron-hole pairs generated at the photocatalytic surface. The number of electron-hole pairs produced depends on the number of photons per unit area per second striking the surface that can be absorbed and whose energy exceeds the bandgap of the photocatalytic material. A convenient parameter to describe the number of useful photons is the number of moles of photons striking the surface per unit area per second. The unit of micro-einsteins (or micromoles) of photons per m2 per sec is commonly used for photochemical and photoelectric-like phenomena. This type of parameter is used in photochemistry, such as in the conversion of light energy for photosynthesis. Photosynthetic response correlates with the number of photons rather than by energy because, in this photochemical process, each molecule is activated by the absorption of one photon. In photosynthesis, the number of photons absorbed in the 400 700 nm spectral range is estimated and is referred to as photosynthetic active radiation (PAR). PAR is defined in terms of the photosynthetic photon flux density measured in micro-einsteins of photons per m2 per sec. PcAR is an equivalent, similarly modeled parameter that has been defined for the photocatalytic processes. Two methods to measure the PcAR level are being proposed. In the first method, a calibrated spectrometer with a cosine receptor is used to measure the spectral irradiance. This measurement, in conjunction with the photocatalytic response as a function of wavelength, is used to estimate the PcAR. The photocatalytic response function is determined by measuring photocatalytic reactivity as a function of wavelength. In the second method, simple shaped photocatalytic response functions can be simulated with a broad-band detector with a cosine receptor appropriately filtered to represent the spectral response of the photocatalytic material. This second method can be less expensive than using a calibrated spectrometer.

Evaluating the portability of satellite derived chlorophyll-a algorithms for temperate inland lakes using airborne hyperspectral imagery and dense surface observations.

PubMed

Johansen, Richard; Beck, Richard; Nowosad, Jakub; Nietch, Christopher; Xu, Min; Shu, Song; Yang, Bo; Liu, Hongxing; Emery, Erich; Reif, Molly; Harwood, Joseph; Young, Jade; Macke, Dana; Martin, Mark; Stillings, Garrett; Stumpf, Richard; Su, Haibin

2018-06-01

This study evaluated the performances of twenty-nine algorithms that use satellite-based spectral imager data to derive estimates of chlorophyll-a concentrations that, in turn, can be used as an indicator of the general status of algal cell densities and the potential for a harmful algal bloom (HAB). The performance assessment was based on making relative comparisons between two temperate inland lakes: Harsha Lake (7.99 km 2 ) in Southwest Ohio and Taylorsville Lake (11.88 km 2 ) in central Kentucky. Of interest was identifying algorithm-imager combinations that had high correlation with coincident chlorophyll-a surface observations for both lakes, as this suggests portability for regional HAB monitoring. The spectral data utilized to estimate surface water chlorophyll-a concentrations were derived from the airborne Compact Airborne Spectral Imager (CASI) 1500 hyperspectral imager, that was then used to derive synthetic versions of currently operational satellite-based imagers using spatial resampling and spectral binning. The synthetic data mimics the configurations of spectral imagers on current satellites in earth's orbit including, WorldView-2/3, Sentinel-2, Landsat-8, Moderate-resolution Imaging Spectroradiometer (MODIS), and Medium Resolution Imaging Spectrometer (MERIS). High correlations were found between the direct measurement and the imagery-estimated chlorophyll-a concentrations at both lakes. The results determined that eleven out of the twenty-nine algorithms were considered portable, with r 2 values greater than 0.5 for both lakes. Even though the two lakes are different in terms of background water quality, size and shape, with Taylorsville being generally less impaired, larger, but much narrower throughout, the results support the portability of utilizing a suite of certain algorithms across multiple sensors to detect potential algal blooms through the use of chlorophyll-a as a proxy. Furthermore, the strong performance of the Sentinel-2 algorithms is exceptionally promising, due to the recent launch of the second satellite in the constellation, which will provide higher temporal resolution for temperate inland water bodies. Additionally, scripts were written for the open-source statistical software R that automate much of the spectral data processing steps. This allows for the simultaneous consideration of numerous algorithms across multiple imagers over an expedited time frame for the near real-time monitoring required for detecting algal blooms and mitigating their adverse impacts. Copyright © 2018 Elsevier B.V. All rights reserved.

Can We Estimate Injected Carbon Dioxide Prior to the Repeat Survey in 4D Seismic Monitoring Scheme?

NASA Astrophysics Data System (ADS)

Sakai, A.

2005-12-01

To mitigate global climate change, the geologic sequestration by injecting carbon dioxide in the aquifer and others is one of the most promising scenarios. Monitoring is required to verify the long-term safe storage of carbon dioxide in the subsurface. As evidenced in the oil industry, monitoring by time-lapse 3D seismic survey is the most effective to spatially detect fluid movements and change of pore pressure. We have conducted 3D seismic survey onshore Japan surrounding RITE/METI Iwanohara carbon dioxide injection test site. Target aquifer zone is at 1100m deep in the Pleistocene layer with 60m thick and most permeable zone is approx. 12m thick. Baseline 3D seismic survey was conducted in July-August 2003 and a monitor 3D seismic survey was in July-August 2005 by vibrating source with 10-120Hz sweep frequency band. Prior to the monitor survey, we evaluated seismic data with integrating wireline logging data. As target carbon dioxide injection layer is thin, high-resolution seismic data is required to estimate potential spreading of injected carbon dioxide. To increase seismic resolution, spectrally enhancing method was in use. The procedure is smoothing number of seismic spectral amplitude, computing well log spectrum, and constructing matching filter between seismic and well spectrum. Then it was applied to the whole seismic traces after evaluating test traces. Synthetic seismograms from logging data were computed with extracting optimal wavelets. Fitting between spectrally enhanced seismic traces and synthetic seismograms was excellent even for deviated monitor wells. Acoustic impedance was estimated by inversion of these 3D seismic traces. In analyzing logging data of sonic, density, CMR, and others, the elastic wave velocity was reconstructed by rock physics approach after estimating compositions. Based on models, velocity changes by carbon dioxide injection was evaluated. The correlation of acoustic impedance with porosity and logarithmic permeability was good and relying on this relation and geological constraints with inversion techniques, porosity and permeability was estimated in 3D volume. If the carbon dioxide movement was solely controlled by permeability, estimated permeability volume might predict the time-lapse seismic data prior to a repeat survey. We compare the estimate with the actual 4D changes and discuss related variations.

A spectral reflectance estimation technique using multispectral data from the Viking lander camera

NASA Technical Reports Server (NTRS)

Park, S. K.; Huck, F. O.

1976-01-01

A technique is formulated for constructing spectral reflectance curve estimates from multispectral data obtained with the Viking lander camera. The multispectral data are limited to six spectral channels in the wavelength range from 0.4 to 1.1 micrometers and most of these channels exhibit appreciable out-of-band response. The output of each channel is expressed as a linear (integral) function of the (known) solar irradiance, atmospheric transmittance, and camera spectral responsivity and the (unknown) spectral responsivity and the (unknown) spectral reflectance. This produces six equations which are used to determine the coefficients in a representation of the spectral reflectance as a linear combination of known basis functions. Natural cubic spline reflectance estimates are produced for a variety of materials that can be reasonably expected to occur on Mars. In each case the dominant reflectance features are accurately reproduced, but small period features are lost due to the limited number of channels. This technique may be a valuable aid in selecting the number of spectral channels and their responsivity shapes when designing a multispectral imaging system.

47 CFR 25.223 - Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 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 frequency...

47 CFR 25.223 - Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 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 frequency...

47 CFR 25.223 - Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 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 frequency...

47 CFR 25.223 - Off-axis EIRP spectral density limits for feeder link earth stations in the 17/24 GHz BSS.

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 frequency...

Study on the spectral characteristics of the damaged rice under brown planthopper, Nilaparvata lugens

NASA Astrophysics Data System (ADS)

Wu, Xiuju; Cheng, Qian

2010-11-01

The spectra of healthy leaves and leaves damaged by the rice brown planthopper (BPH, Nilaparvata lugens) were measured using a Spectroradiometer with spectral range of 350-1050 nm and resolution of 3 nm. The data was analyzed using the method of red edge methods. In the range of 430-530 nm and 560-730cnm, the band depth and slope were calculated. The damage degrees of rice plants caused by the BPH nymphae with different numbers were measured well by the spectral reflectance. The spectral characteristics of damaged rice under brown Planthopper, Nilaparvata lugenswere analyzed, and the reflectance was significantly negatively correlated with the number of BPHs. The red edge slope and edge area of the reflectance also significance correlated with the number of nymphae. The estimation models were constructed to estimate the BPHs using the spectral reflectance at the wavelengths of 550 nm and 760 nm and the red edge index. The results showed that accuracy of the estimation models were 66-81% and the spectral reflectance at R755 was efficient for estimating the number of BPHs.

Galactic cosmic ray spectral index: the case of Forbush decreases of March 2012

NASA Astrophysics Data System (ADS)

Livada, M.; Mavromichalaki, H.; Plainaki, C.

2018-01-01

During the burst of solar activity in March 2012, close to the maximum of solar cycle 24, a number of X-class and M-class flares and halo CMEs with velocity up to 2684 km/s were recorded. During a relatively short period (7-21 March 2012) two Forbush decreases were registered in the ground-level neutron monitor data. In this work, after a short description of the solar and geomagnetic background of these Forbush decreases, we deduce the cosmic ray density and anisotropy variations based on the daily cosmic ray data of the neutron monitor network (http://www.nmdb.eu; http://cosray.phys.uoa.gr). Applying to our data two different coupling functions methods, the spectral index of these Forbush decreases was calculated following the technique of Wawrzynczak and Alania (Adv. Space Res. 45:622-631, 2010). We pointed out that the estimated values of the spectral index γ of these events are almost similar for both cases following the fluctuation of the Forbush decrease. The study and the calculation of the cosmic ray spectrum during such cosmic ray events are very important for Space Weather applications.

Broadband spectral fitting of blazars using XSPEC

NASA Astrophysics Data System (ADS)

Sahayanathan, Sunder; Sinha, Atreyee; Misra, Ranjeev

2018-03-01

The broadband spectral energy distribution (SED) of blazars is generally interpreted as radiation arising from synchrotron and inverse Compton mechanisms. Traditionally, the underlying source parameters responsible for these emission processes, like particle energy density, magnetic field, etc., are obtained through simple visual reproduction of the observed fluxes. However, this procedure is incapable of providing confidence ranges for the estimated parameters. In this work, we propose an efficient algorithm to perform a statistical fit of the observed broadband spectrum of blazars using different emission models. Moreover, we use the observable quantities as the fit parameters, rather than the direct source parameters which govern the resultant SED. This significantly improves the convergence time and eliminates the uncertainty regarding initial guess parameters. This approach also has an added advantage of identifying the degenerate parameters, which can be removed by including more observable information and/or additional constraints. A computer code developed based on this algorithm is implemented as a user-defined routine in the standard X-ray spectral fitting package, XSPEC. Further, we demonstrate the efficacy of the algorithm by fitting the well sampled SED of blazar 3C 279 during its gamma ray flare in 2014.

Simulating the effect of high column density absorbers on the one-dimensional Lyman α forest flux power spectrum

NASA Astrophysics Data System (ADS)

Rogers, Keir K.; Bird, Simeon; Peiris, Hiranya V.; Pontzen, Andrew; Font-Ribera, Andreu; Leistedt, Boris

2018-03-01

We measure the effect of high column density absorbing systems of neutral hydrogen (H I) on the one-dimensional (1D) Lyman α forest flux power spectrum using cosmological hydrodynamical simulations from the Illustris project. High column density absorbers (which we define to be those with H I column densities N(H I) > 1.6 × 10^{17} atoms cm^{-2}) cause broadened absorption lines with characteristic damping wings. These damping wings bias the 1D Lyman α forest flux power spectrum by causing absorption in quasar spectra away from the location of the absorber itself. We investigate the effect of high column density absorbers on the Lyman α forest using hydrodynamical simulations for the first time. We provide templates as a function of column density and redshift, allowing the flexibility to accurately model residual contamination, i.e. if an analysis selectively clips out the largest damping wings. This flexibility will improve cosmological parameter estimation, for example, allowing more accurate measurement of the shape of the power spectrum, with implications for cosmological models containing massive neutrinos or a running of the spectral index. We provide fitting functions to reproduce these results so that they can be incorporated straightforwardly into a data analysis pipeline.

Smoothness of In vivo Spectral Baseline Determined by Mean Squared Error

PubMed Central

Zhang, Yan; Shen, Jun

2013-01-01

Purpose A nonparametric smooth line is usually added to spectral model to account for background signals in vivo magnetic resonance spectroscopy (MRS). The assumed smoothness of the baseline significantly influences quantitative spectral fitting. In this paper, a method is proposed to minimize baseline influences on estimated spectral parameters. Methods In this paper, the non-parametric baseline function with a given smoothness was treated as a function of spectral parameters. Its uncertainty was measured by root-mean-squared error (RMSE). The proposed method was demonstrated with a simulated spectrum and in vivo spectra of both short echo time (TE) and averaged echo times. The estimated in vivo baselines were compared with the metabolite-nulled spectra, and the LCModel-estimated baselines. The accuracies of estimated baseline and metabolite concentrations were further verified by cross-validation. Results An optimal smoothness condition was found that led to the minimal baseline RMSE. In this condition, the best fit was balanced against minimal baseline influences on metabolite concentration estimates. Conclusion Baseline RMSE can be used to indicate estimated baseline uncertainties and serve as the criterion for determining the baseline smoothness of in vivo MRS. PMID:24259436

Use of spectral analysis with iterative filter for voxelwise determination of regional rates of cerebral protein synthesis with L-[1-11C]leucine PET.

PubMed

Veronese, Mattia; Schmidt, Kathleen C; Smith, Carolyn Beebe; Bertoldo, Alessandra

2012-06-01

A spectral analysis approach was used to estimate kinetic parameters of the L-[1-(11)C]leucine positron emission tomography (PET) method and regional rates of cerebral protein synthesis (rCPS) on a voxel-by-voxel basis. Spectral analysis applies to both heterogeneous and homogeneous tissues; it does not require prior assumptions concerning number of tissue compartments. Parameters estimated with spectral analysis can be strongly affected by noise, but numerical filters improve estimation performance. Spectral analysis with iterative filter (SAIF) was originally developed to improve estimation of leucine kinetic parameters and rCPS in region-of-interest (ROI) data analyses. In the present study, we optimized SAIF for application at the voxel level. In measured L-[1-(11)C]leucine PET data, voxel-level SAIF parameter estimates averaged over all voxels within a ROI (mean voxel-SAIF) generally agreed well with corresponding estimates derived by applying the originally developed SAIF to ROI time-activity curves (ROI-SAIF). Region-of-interest-SAIF and mean voxel-SAIF estimates of rCPS were highly correlated. Simulations showed that mean voxel-SAIF rCPS estimates were less biased and less variable than ROI-SAIF estimates in the whole brain and cortex; biases were similar in white matter. We conclude that estimation of rCPS with SAIF is improved when the method is applied at voxel level than in ROI analysis.

Magnetic field power density spectra during 'scatter-free' solar particle events

NASA Technical Reports Server (NTRS)

Tan, L. C.; Mason, G. M.

1993-01-01

We have examined interplanetary magnetic field power spectral density during four previously identified 3He-rich flare periods when the about 1 MeV nucleon-1 particles exhibited nearly scatter-free transport from the sun to 1 AU. Since the scattering mean free path A was large, it might be expected that interplanetary turbulence was low, yet the spectral density value was low only for one of the four periods. For the other three, however, the spectral index q of the power density spectrum was near 2.0, a value at which quasi-linear theories predict an increase in the scattering mean free path. Comparing the lambda values from the energetic particles with that computed from a recent quasi-linear theory which includes helicity and the propagation direction of waves, we find lambda(QLT)/lambda(SEP) = 0.08 +/- 0.03 for the four events. Thus, the theory fits the q-dependence of lambda; however, as found for previous quasi-linear theories, the absolute value is low.

Solar-Cycle Variability of Magnetosheath Fluctuations at Earth and Venus

NASA Astrophysics Data System (ADS)

Dwivedi, N. K.; Narita, Y.; Kovacs, P.

2014-12-01

The magnetosheath is a region between the bow-shock and magnetopause and the magnetosheath plasma is mostly in the turbulent state. In the present investigation we put an effort to closely examine the magnetosheath fluctuations dependency on the solar-cycles (solar-maximum and solar minimum) at the magnetized planetary body (Earth) and their comparison with the un-magnetized planetary body (Venus) for the solar minimum. We use the CLUSTER FGM data for the solar-maximum (2001-2002), solar-minimum (2006-2008) and Venus fluxgate magnetometer data for the solar-minimum (2006-2008) to perform a comparative statistical study on the energy spectra and probability density function (PDF) and asses the spectral features of the magnetic fluctuations of the both planetary bodies. In the comparison we study the relation between the inertial ranges of the spectra and the temporal scales of non-Gaussian magnetic fluctuations derived from PDF analyses. The first can refer to turbulent cascade dynamics, while the latter may indicate intermittency. We first transformed the magnetic field data into mean field aligned coordinate system with respect to the large-scale magnetic field direction and then after we compute the power spectral density with the help of Welch algorithm. The computed energy spectra of Earth's magnetosheath show a moderate variability with the solar-cycles and have a broader inertial range. However the estimated energy spectra for the solar-minimum at Venus give the clear evidence of the existence of the break point in the vicinity of the ion gyroradius. After the break-point the energy spectra become steeper and show a distinctive spectral scales which is interpreted as the realization of the begging of the energy cascade. We also briefly address the influence of turbulence on the plasma transport and wave dynamics responsible for the spectral break and predict spectral features of the energy spectra for the solar-maximum at Venus based on the results obtained for the solar-minimum. The research leading to these results has received funding from the European Community's Seventh Framework Programme ([FP7/2007-2013]) under grant agreement number 313038/STORM.

A real-time spectral mapper as an emerging diagnostic technology in biomedical sciences.

PubMed

Epitropou, George; Kavvadias, Vassilis; Iliou, Dimitris; Stathopoulos, Efstathios; Balas, Costas

2013-01-01

Real time spectral imaging and mapping at video rates can have tremendous impact not only on diagnostic sciences but also on fundamental physiological problems. We report the first real-time spectral mapper based on the combination of snap-shot spectral imaging and spectral estimation algorithms. Performance evaluation revealed that six band imaging combined with the Wiener algorithm provided high estimation accuracy, with error levels lying within the experimental noise. High accuracy is accompanied with much faster, by 3 orders of magnitude, spectral mapping, as compared with scanning spectral systems. This new technology is intended to enable spectral mapping at nearly video rates in all kinds of dynamic bio-optical effects as well as in applications where the target-probe relative position is randomly and fast changing.

Evaluation of spatial, radiometric and spectral thematic mapper performance for coastal studies

NASA Technical Reports Server (NTRS)

Klemas, V.

1985-01-01

The main emphasis of the research was to determine what effect different wetland plant canopies would have upon observed reflectance in Thematic Mapper bands. The three major vegetation canopy types (broadleaf, gramineous and leafless) produce unique spectral responses for a similar quantity of live biomass. Biomass estimates computed from spectral data were most similar to biomass estimates determined from harvest data when models developed for a specific canopy were used. In other words, the spectral biomass estimate of a broadleaf canopy was most similar to the harvest biomass estimate when a broadleaf canopy radiance model was used. Work is continuing to more precisely determine regression coefficients for each canopy type and to model the change in the coefficients with various combinations of canopy types. Researchers suspect that textural and spatial considerations can be used to identify canopy types and improve biomass estimates from Thematic Mapper data.

Dosimetry in MARS spectral CT: TOPAS Monte Carlo simulations and ion chamber measurements.

PubMed

Lu, Gray; Marsh, Steven; Damet, Jerome; Carbonez, Pierre; Laban, John; Bateman, Christopher; Butler, Anthony; Butler, Phil

2017-06-01

Spectral computed tomography (CT) is an up and coming imaging modality which shows great promise in revealing unique diagnostic information. Because this imaging modality is based on X-ray CT, it is of utmost importance to study the radiation dose aspects of its use. This study reports on the implementation and evaluation of a Monte Carlo simulation tool using TOPAS for estimating dose in a pre-clinical spectral CT scanner known as the MARS scanner. Simulated estimates were compared with measurements from an ionization chamber. For a typical MARS scan, TOPAS estimated for a 30 mm diameter cylindrical phantom a CT dose index (CTDI) of 29.7 mGy; CTDI was measured by ion chamber to within 3% of TOPAS estimates. Although further development is required, our investigation of TOPAS for estimating MARS scan dosimetry has shown its potential for further study of spectral scanning protocols and dose to scanned objects.

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.

Spectral Index Properties of millijansky Radio Sources in ATLAS

NASA Astrophysics Data System (ADS)

Randall, Kate; Hopkins, A. M.; Norris, R. P.; Zinn, P.; Middelberg, E.; Mao, M. Y.; Sharp, R. G.

2012-01-01

At the faintest radio flux densities (S1.4GHz < 10 milliJansky (mJy)), the spectral index properties of radio sources are not well constrained. The bright radio source population (S1.4GHz > 10 mJy) is well studied and is predominantly comprised of AGN. At fainter flux densities, particularly into the microJansky regime, star-forming galaxies begin to dominate the radio source population. Understanding these faint radio source populations is essential for understanding galaxy evolution, and the link between AGN and star formation. Conflicting results have recently arisen regarding whether there is a flattening of the average spectral index between a low radio frequency (325 or 610 MHz) and 1.4 GHz at these faint flux densities. To explore this issue, we have investigated the spectral index properties of a new catalogue of 843 MHz radio sources in the ELAIS-S1 (the European Large Area ISO Survey - South 1 Region) field. Our results support previous work showing a tendency towards flatter radio spectra at fainter flux densities. This catalogue is cross-matched to the Australia Telescope Large Area Survey (ATLAS), the widest deep radio survey to date at 1.4 GHz, with complementary 2.3 GHz, optical and infrared Spitzer Wide-area Infra-Red Extragalactic data. The variation of spectral index properties have been explored as a function of redshift, luminosity and flux density. [These new measurements have been used to identify a population of faint Compact Steep Spectrum sources, thought to be one of the earliest stages of the AGN life-cycle. Exploring this population will aid us in understanding the evolution of AGN as a whole.

Background Noise of the Aldeia da Serra Region (Portugal) from a temporary broad band network

NASA Astrophysics Data System (ADS)

Wachilala, Piedade; Borges, José; Caldeira, Bento; Bezzeghoud, Mourad

2017-04-01

In this study, we analyse seismic background noise to assess the effect of noise based on the detectability of a temporary network constituted by DOCTAR (Deep Ocean Test Array), who have been deployed in a period between 2011 and 2012 in Portugal mainland, and the Évora permanent seismic station. This network is constituted by 14 digital broadband stations (14 CMG-3ESP and one STS2 sensors) with a flat response between the 60 sec to 50 Hz, 24-bit and 120s to 60Hz respectively. The temporary network was operated in continuous recording mode (three-components) in a region located in the north of the region of Évora, within a radius of about 30 km around the village of Aldeia da Serra, region in which there is an important seismic activity in the context of Portugal mainland. We calculated power spectral densities of background noise for each station/component and compare them with high-noise model and low-noise model of Peterson (1993). We consider different for day and night local and for different periods of the year. Power spectral density estimates show moderate noise levels with all stations falling within the high and low bounds of Peterson (1993). Considering the results of the noise, we estimate the detection limit of each station and consequently the detectability of the network. From this information and taking in attention the events recorded during the period of DOCTAR operation we analyse the improvement promoted by this temporary network regarding the existent seismic networks to the local seismicity study. This work was partially supported by COMPETE 2020 program (POCI-01-0145-FEDER-007690 project). We acknowledge GFZ Potsdam for providing part of the data used in this study.

Identification of the subthalamic nucleus in deep brain stimulation surgery with a novel wavelet-derived measure of neural background activity.

PubMed

Snellings, André; Sagher, Oren; Anderson, David J; Aldridge, J Wayne

2009-10-01

The authors developed a wavelet-based measure for quantitative assessment of neural background activity during intraoperative neurophysiological recordings so that the boundaries of the subthalamic nucleus (STN) can be more easily localized for electrode implantation. Neural electrophysiological data were recorded in 14 patients (20 tracks and 275 individual recording sites) with dopamine-sensitive idiopathic Parkinson disease during the target localization portion of deep brain stimulator implantation surgery. During intraoperative recording, the STN was identified based on audio and visual monitoring of neural firing patterns, kinesthetic tests, and comparisons between neural behavior and the known characteristics of the target nucleus. The quantitative wavelet-based measure was applied offline using commercially available software to measure the magnitude of the neural background activity, and the results of this analysis were compared with the intraoperative conclusions. Wavelet-derived estimates were also compared with power spectral density measurements. The wavelet-derived background levels were significantly higher in regions encompassed by the clinically estimated boundaries of the STN than in the surrounding regions (STN, 225 +/- 61 microV; ventral to the STN, 112 +/- 32 microV; and dorsal to the STN, 136 +/- 66 microV). In every track, the absolute maximum magnitude was found within the clinically identified STN. The wavelet-derived background levels provided a more consistent index with less variability than measurements with power spectral density. Wavelet-derived background activity can be calculated quickly, does not require spike sorting, and can be used to identify the STN reliably with very little subjective interpretation required. This method may facilitate the rapid intraoperative identification of STN borders.

Identification of the subthalamic nucleus in deep brain stimulation surgery with a novel wavelet-derived measure of neural background activity

PubMed Central

Snellings, André; Sagher, Oren; Anderson, David J.; Aldridge, J. Wayne

2016-01-01

Object A wavelet-based measure was developed to quantitatively assess neural background activity taken during surgical neurophysiological recordings to localize the boundaries of the subthalamic nucleus during target localization for deep brain stimulator implant surgery. Methods Neural electrophysiological data was recorded from 14 patients (20 tracks, n = 275 individual recording sites) with dopamine-sensitive idiopathic Parkinson’s disease during the target localization portion of deep brain stimulator implant surgery. During intraoperative recording the STN was identified based upon audio and visual monitoring of neural firing patterns, kinesthetic tests, and comparisons between neural behavior and known characteristics of the target nucleus. The quantitative wavelet-based measure was applied off-line using MATLAB software to measure the magnitude of the neural background activity, and the results of this analysis were compared to the intraoperative conclusions. Wavelet-derived estimates were compared to power spectral density measures. Results The wavelet-derived background levels were significantly higher in regions encompassed by the clinically estimated boundaries of the STN than in surrounding regions (STN: 225 ± 61 μV vs. ventral to STN: 112 ± 32 μV, and dorsal to STN: 136 ± 66 μV). In every track, the absolute maximum magnitude was found within the clinically identified STN. The wavelet-derived background levels provided a more consistent index with less variability than power spectral density. Conclusions The wavelet-derived background activity assessor can be calculated quickly, requires no spike sorting, and can be reliably used to identify the STN with very little subjective interpretation required. This method may facilitate rapid intraoperative identification of subthalamic nucleus borders. PMID:19344225

Estimates of effective elastic thickness of oceanic lithosphere using model including surface and subsurface loads and effective elastic thickness of subduction zones

NASA Astrophysics Data System (ADS)

Yang, A.; Yongtao, F.

2016-12-01

The effective elastic thickness (Te) is an important parameter that characterizes the long term strength of the lithosphere, which has great significance on understanding the mechanical properties and evolution of the lithosphere. In contrast with many controversies regarding elastic thickness of continent lithosphere, the Te of oceanic lithosphere is thought to be in a simple way that is dependent on the age of the plate. However, rescent studies show that there is no simple relationship between Te and age at time of loading for both seamounts and subduction zones. As subsurface loading is very importand and has large influence in the estimate of Te for continent lithosphere, and many oceanic features such as subduction zones also have considerable subsurface loading. We introduce the method to estimate the effective elastic thickness of oceanic lithosphere using model including surface and subsurface loads by using free-air gravity anomaly and bathymetric data, together with a moving window admittance technique (MWAT). We use the multitaper spectral estimation method to calculate the power spectral density. Through tests with synthetic subduction zone like bathymetry and gravity data show that the Te can be recovered in an accurance similar to that in the continent and there is also a trade-off between spatial resolution and variance for different window sizes. We estimate Te of many subduction zones (Peru-Chile trench, Middle America trench, Caribbean trench, Kuril-Japan trench, Mariana trench, Tonga trench, Java trench, Ryukyu-Philippine trench) with an age range of 0-160 Myr to reassess the relationship between elastic thickness and the age of the lithosphere at the time of loading. The results do not show a simple relationship between Te and age.

TP89 - SIRZ Decomposition Spectral Estimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seetho, Isacc M.; Azevedo, Steve; Smith, Jerel

2016-12-08

The primary objective of this test plan is to provide X-ray CT measurements of known materials for the purposes of generating and testing MicroCT and EDS spectral estimates. These estimates are to be used in subsequent Ze/RhoE decomposition analyses of acquired data.

Finite entanglement entropy and spectral dimension in quantum gravity

NASA Astrophysics Data System (ADS)

Arzano, Michele; Calcagni, Gianluca

2017-12-01

What are the conditions on a field theoretic model leading to a finite entanglement entropy density? We prove two very general results: (1) Ultraviolet finiteness of a theory does not guarantee finiteness of the entropy density; (2) If the spectral dimension of the spatial boundary across which the entropy is calculated is non-negative at all scales, then the entanglement entropy cannot be finite. These conclusions, which we verify in several examples, negatively affect all quantum-gravity models, since their spectral dimension is always positive. Possible ways out are considered, including abandoning the definition of the entanglement entropy in terms of the boundary return probability or admitting an analytic continuation (not a regularization) of the usual definition. In the second case, one can get a finite entanglement entropy density in multi-fractional theories and causal dynamical triangulations.

Relationship between behavioral and physiological spectral-ripple discrimination.

PubMed

Won, Jong Ho; Clinard, Christopher G; Kwon, Seeyoun; Dasika, Vasant K; Nie, Kaibao; Drennan, Ward R; Tremblay, Kelly L; Rubinstein, Jay T

2011-06-01

Previous studies have found a significant correlation between spectral-ripple discrimination and speech and music perception in cochlear implant (CI) users. This relationship could be of use to clinicians and scientists who are interested in using spectral-ripple stimuli in the assessment and habilitation of CI users. However, previous psychoacoustic tasks used to assess spectral discrimination are not suitable for all populations, and it would be beneficial to develop methods that could be used to test all age ranges, including pediatric implant users. Additionally, it is important to understand how ripple stimuli are processed in the central auditory system and how their neural representation contributes to behavioral performance. For this reason, we developed a single-interval, yes/no paradigm that could potentially be used both behaviorally and electrophysiologically to estimate spectral-ripple threshold. In experiment 1, behavioral thresholds obtained using the single-interval method were compared to thresholds obtained using a previously established three-alternative forced-choice method. A significant correlation was found (r = 0.84, p = 0.0002) in 14 adult CI users. The spectral-ripple threshold obtained using the new method also correlated with speech perception in quiet and noise. In experiment 2, the effect of the number of vocoder-processing channels on the behavioral and physiological threshold in normal-hearing listeners was determined. Behavioral thresholds, using the new single-interval method, as well as cortical P1-N1-P2 responses changed as a function of the number of channels. Better behavioral and physiological performance (i.e., better discrimination ability at higher ripple densities) was observed as more channels added. In experiment 3, the relationship between behavioral and physiological data was examined. Amplitudes of the P1-N1-P2 "change" responses were significantly correlated with d' values from the single-interval behavioral procedure. Results suggest that the single-interval procedure with spectral-ripple phase inversion in ongoing stimuli is a valid approach for measuring behavioral or physiological spectral resolution.

Influence of aerosols on surface reaching spectral irradiance and introduction to a new technique for estimating aerosol radiative forcing from spectral flux measurements

NASA Astrophysics Data System (ADS)

Rao, R. R.

2015-12-01

Aerosol radiative forcing estimates with high certainty are required in climate change studies. The approach in estimating the aerosol radiative forcing by using the chemical composition of aerosols is not effective as the chemical composition data with radiative properties are not widely available. In this study we look into the approach where ground based spectral radiation flux measurements along with an RT model is used to estimate radiative forcing. Measurements of spectral flux were made using an ASD spectroradiometer with 350 - 1050 nm wavelength range and 3nm resolution for around 54 clear-sky days during which AOD range was around 0.1 to 0.7. Simultaneous measurements of black carbon were also made using Aethalometer (Magee Scientific) which ranged from around 1.5 ug/m3 to 8 ug/m3. All the measurements were made in the campus of Indian Institute of Science which is in the heart of Bangalore city. The primary study involved in understanding the sensitivity of spectral flux to change in the mass concentration of individual aerosol species (Optical properties of Aerosols and Clouds -OPAC classified aerosol species) using the SBDART RT model. This made us clearly distinguish the region of influence of different aerosol species on the spectral flux. Following this, a new technique has been introduced to estimate an optically equivalent mixture of aerosol species for the given location. The new method involves an iterative process where the mixture of aerosol species are changed in OPAC model and RT model is run as long as the mixture which mimics the measured spectral flux within 2-3% deviation from measured spectral flux is obtained. Using the optically equivalent aerosol mixture and RT model aerosol radiative forcing is estimated. The new method is limited to clear sky scenes and its accuracy to derive an optically equivalent aerosol mixture reduces when diffuse component of flux increases. Our analysis also showed that direct component of spectral flux is more sensitive to different aerosol species than total spectral flux which was also supported by our observed data.

Models and methods to characterize site amplification from a pair of records

USGS Publications Warehouse

Safak, E.

1997-01-01

The paper presents a tutorial review of the models and methods that are used to characterize site amplification from the pairs of rock- and soil-site records, and introduces some new techniques with better theoretical foundations. The models and methods discussed include spectral and cross-spectral ratios, spectral ratios for downhole records, response spectral ratios, constant amplification factors, parametric models, physical models, and time-varying filters. An extensive analytical and numerical error analysis of spectral and cross-spectral ratios shows that probabilistically cross-spectral ratios give more reliable estimates of site amplification. Spectral ratios should not be used to determine site amplification from downhole-surface recording pairs because of the feedback in the downhole sensor. Response spectral ratios are appropriate for low frequencies, but overestimate the amplification at high frequencies. The best method to be used depends on how much precision is required in the estimates.

Estimation of canopy carotenoid content of winter wheat using multi-angle hyperspectral data

NASA Astrophysics Data System (ADS)

Kong, Weiping; Huang, Wenjiang; Liu, Jiangui; Chen, Pengfei; Qin, Qiming; Ye, Huichun; Peng, Dailiang; Dong, Yingying; Mortimer, A. Hugh

2017-11-01

Precise estimation of carotenoid (Car) content in crops, using remote sensing data, could be helpful for agricultural resources management. Conventional methods for Car content estimation were mostly based on reflectance data acquired from nadir direction. However, reflectance acquired at this direction is highly influenced by canopy structure and soil background reflectance. Off-nadir observation is less impacted, and multi-angle viewing data are proven to contain additional information rarely exploited for crop Car content estimation. The objective of this study was to explore the potential of multi-angle observation data for winter wheat canopy Car content estimation. Canopy spectral reflectance was measured from nadir as well as from a series of off-nadir directions during different growing stages of winter wheat, with concurrent canopy Car content measurements. Correlation analyses were performed between Car content and the original and continuum removed spectral reflectance. Spectral features and previously published indices were derived from data obtained at different viewing angles and were tested for Car content estimation. Results showed that spectral features and indices obtained from backscattering directions between 20° and 40° view zenith angle had a stronger correlation with Car content than that from the nadir direction, and the strongest correlation was observed from about 30° backscattering direction. Spectral absorption depth at 500 nm derived from spectral data obtained from 30° backscattering direction was found to reduce the difference induced by plant cultivars greatly. It was the most suitable for winter wheat canopy Car estimation, with a coefficient of determination 0.79 and a root mean square error of 19.03 mg/m2. This work indicates the importance of taking viewing geometry effect into account when using spectral features/indices and provides new insight in the application of multi-angle remote sensing for the estimation of crop physiology.

Evaluation of the robustness of estimating five components from a skin spectral image

NASA Astrophysics Data System (ADS)

Akaho, Rina; Hirose, Misa; Tsumura, Norimichi

2018-04-01

We evaluated the robustness of a method used to estimate five components (i.e., melanin, oxy-hemoglobin, deoxy-hemoglobin, shading, and surface reflectance) from the spectral reflectance of skin at five wavelengths against noise and a change in epidermis thickness. We also estimated the five components from recorded images of age spots and circles under the eyes using the method. We found that noise in the image must be no more 0.1% to accurately estimate the five components and that the thickness of the epidermis affects the estimation. We acquired the distribution of major causes for age spots and circles under the eyes by applying the method to recorded spectral images.

Microstructure measurements in natural waters: Methodology and applications

NASA Astrophysics Data System (ADS)

Roget, Elena; Lozovatsky, Iossif; Sanchez, Xavier; Figueroa, Manuel

2006-08-01

Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding. A new analytical approximation for the 1D Panchev-Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations. Statistical analysis of eddy Kb and thermal Kθ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between Kb and Kθ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged Kb and Kθ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χθ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.

Deep, Broadband Spectral Line Surveys of Molecule-rich Interstellar Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Widicus Weaver, Susanna L.; Laas, Jacob C.; Zou, Luyao

2017-09-01

Spectral line surveys are an indispensable tool for exploring the physical and chemical evolution of astrophysical environments due to the vast amount of data that can be obtained in a relatively short amount of time. We present deep, broadband spectral line surveys of 30 interstellar clouds using two broadband λ  = 1.3 mm receivers at the Caltech Submillimeter Observatory. This information can be used to probe the influence of physical environment on molecular complexity. We observed a wide variety of sources to examine the relative abundances of organic molecules as they relate to the physical properties of the source (i.e., temperature,more » density, dynamics, etc.). The spectra are highly sensitive, with noise levels ≤25 mK at a velocity resolution of ∼0.35 km s{sup −1}. In the initial analysis presented here, column densities and rotational temperatures have been determined for the molecular species that contribute significantly to the spectral line density in this wavelength regime. We present these results and discuss their implications for complex molecule formation in the interstellar medium.« less

Distributions and motions of nearby stars defined by objective prism surveys and Hipparcos data

NASA Technical Reports Server (NTRS)

Hemenway, P. D.; Lee, J. T.; Upgren, A. R.

1997-01-01

Material and objective prism spectral classification work is used to determine the space density distribution of nearby common stars to the limits of objective prism spectral surveys. The aim is to extend the knowledge of the local densities of specific spectral types from a radius of 25 pc from the sun, as limited in the Gliese catalog of nearby stars, to 50 pc or more. Future plans for the application of these results to studies of the kinematic and dynamical properties of stars in the solar neighborhood as a function of their physical properties and ages are described.

Estimating the Error of an Analog Quantum Simulator by Additional Measurements

NASA Astrophysics Data System (ADS)

Schwenk, Iris; Zanker, Sebastian; Reiner, Jan-Michael; Leppäkangas, Juha; Marthaler, Michael

2017-12-01

We study an analog quantum simulator coupled to a reservoir with a known spectral density. The reservoir perturbs the quantum simulation by causing decoherence. The simulator is used to measure an operator average, which cannot be calculated using any classical means. Since we cannot predict the result, it is difficult to estimate the effect of the environment. Especially, it is difficult to resolve whether the perturbation is small or if the actual result of the simulation is in fact very different from the ideal system we intend to study. Here, we show that in specific systems a measurement of additional correlators can be used to verify the reliability of the quantum simulation. The procedure only requires additional measurements on the quantum simulator itself. We demonstrate the method theoretically in the case of a single spin connected to a bosonic environment.

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.

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.

Mechanical behaviour of the lithosphere beneath the Adamawa uplift (Cameroon, West Africa) based on gravity data

NASA Astrophysics Data System (ADS)

Poudjom Djomani, Y. H.; Diament, M.; Albouy, Y.

1992-07-01

The Adamawa massif in Central Cameroon is one of the African domal uplifts of volcanic origin. It is an elongated feature, 200 km wide. The gravity anomalies over the Adamawa uplift were studied to determine the mechanical behaviour of the lithosphere. Two approaches were used to analyse six gravity profiles that are 600 km long and that run perpendicular to the Adamawa trend. Firstly, the coherence function between topography and gravity was interpreted; secondly, source depth estimations by spectral analysis of the gravity data was performed. To get significant information for the interpretation of the experimental coherence function, the length of the profiles was varied from 320 km to 600 km. This treatment allows one to obtain numerical estimates of the coherence function. The coherence function analysis points out that the lithosphere is deflected and thin beneath the Adamawa uplift, and the Effective Elastic Thickness is of about 20 km. To fit the coherence, a load from below needs to be taken into account. This result on the Adamawa massif is of the same order of magnitude as those obtained on other African uplifts such as Hoggar, Darfur and Kenya domes. For the depth estimation, three major density contrasts were found: the shallowest depth (4-15 km) can be correlated to shear zone structures and the associated sedimentary basins beneath the uplift; the second density contrast (18-38 km) corresponds to the Moho; and finally, the last depth (70-90 km) would be the top of the upper mantle and demotes the low density zone beneath the Adamawa uplift.

A new catalogue of Galactic novae: investigation of the MMRD relation and spatial distribution

NASA Astrophysics Data System (ADS)

Özdönmez, Aykut; Ege, Ergün; Güver, Tolga; Ak, Tansel

2018-05-01

In this study, a new Galactic novae catalogue is introduced collecting important parameters of these sources such as their light-curve parameters, classifications, full width half-maximum (FWHM) of Hα line, distances and interstellar reddening estimates. The catalogue is also published on a website with a search option via a SQL query and an online tool to re-calculate the distance/reddening of a nova from the derived reddening-distance relations. Using the novae in the catalogue, the existence of a maximum magnitude-rate of decline (MMRD) relation in the Galaxy is investigated. Although an MMRD relation was obtained, a significant scattering in the resulting MMRD distribution still exists. We suggest that the MMRD relation likely depends on other parameters in addition to the decline time, as FWHM Hα, the light-curve shapes. Using two different samples depending on the distances in the catalogue and from the derived MMRD relation, the spatial distributions of Galactic novae as a function of their spectral and speed classes were studied. The investigation on the Galactic model parameters implies that best estimates for the local outburst density are 3.6 and 4.2 × 10-10 pc-3 yr-1 with a scale height of 148 and 175 pc, while the space density changes in the range of 0.4-16 × 10-6 pc-3. The local outburst density and scale height obtained in this study infer that the disc nova rate in the Galaxy is in the range of ˜20 to ˜100 yr-1 with an average estimate 67^{+21}_{-17} yr-1.

Electric-field noise from carbon-adatom diffusion on a Au(110) surface: First-principles calculations and experiments

DOE PAGES

Kim, E.; Safavi-Naini, A.; Hite, D. A.; ...

2017-03-01

The decoherence of trapped-ion quantum bits due to heating of their motional modes is a fundamental science and engineering problem. This heating is attributed to electric-field noise arising from processes on the trap-electrode surfaces. In this work, we address the source of this noise by focusing on the diffusion of carbon-containing adsorbates on the surface of Au(110). We show by detailed scanned probe microscopy and density functional theory how the carbon adatom diffusion on the gold surface changes the energy landscape, and how the adatom dipole moment varies with the diffusive motion. Lastly, a simple model for the diffusion noise,more » which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values.« less

Correction of scatter in megavoltage cone-beam CT

NASA Astrophysics Data System (ADS)

Spies, L.; Ebert, M.; Groh, B. A.; Hesse, B. M.; Bortfeld, T.

2001-03-01

The role of scatter in a cone-beam computed tomography system using the therapeutic beam of a medical linear accelerator and a commercial electronic portal imaging device (EPID) is investigated. A scatter correction method is presented which is based on a superposition of Monte Carlo generated scatter kernels. The kernels are adapted to both the spectral response of the EPID and the dimensions of the phantom being scanned. The method is part of a calibration procedure which converts the measured transmission data acquired for each projection angle into water-equivalent thicknesses. Tomographic reconstruction of the projections then yields an estimate of the electron density distribution of the phantom. It is found that scatter produces cupping artefacts in the reconstructed tomograms. Furthermore, reconstructed electron densities deviate greatly (by about 30%) from their expected values. The scatter correction method removes the cupping artefacts and decreases the deviations from 30% down to about 8%.

Electric-field noise from carbon-adatom diffusion on a Au(110) surface: First-principles calculations and experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, E.; Safavi-Naini, A.; Hite, D. A.

The decoherence of trapped-ion quantum bits due to heating of their motional modes is a fundamental science and engineering problem. This heating is attributed to electric-field noise arising from processes on the trap-electrode surfaces. In this work, we address the source of this noise by focusing on the diffusion of carbon-containing adsorbates on the surface of Au(110). We show by detailed scanned probe microscopy and density functional theory how the carbon adatom diffusion on the gold surface changes the energy landscape, and how the adatom dipole moment varies with the diffusive motion. Lastly, a simple model for the diffusion noise,more » which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values.« less

Prior-knowledge-based spectral mixture analysis for impervious surface mapping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jinshui; He, Chunyang; Zhou, Yuyu

2014-01-03

In this study, we developed a prior-knowledge-based spectral mixture analysis (PKSMA) to map impervious surfaces by using endmembers derived separately for high- and low-density urban regions. First, an urban area was categorized into high- and low-density urban areas, using a multi-step classification method. Next, in high-density urban areas that were assumed to have only vegetation and impervious surfaces (ISs), the Vegetation-Impervious model (V-I) was used in a spectral mixture analysis (SMA) with three endmembers: vegetation, high albedo, and low albedo. In low-density urban areas, the Vegetation-Impervious-Soil model (V-I-S) was used in an SMA analysis with four endmembers: high albedo, lowmore » albedo, soil, and vegetation. The fraction of IS with high and low albedo in each pixel was combined to produce the final IS map. The root mean-square error (RMSE) of the IS map produced using PKSMA was about 11.0%, compared to 14.52% using four-endmember SMA. Particularly in high-density urban areas, PKSMA (RMSE = 6.47%) showed better performance than four-endmember (15.91%). The results indicate that PKSMA can improve IS mapping compared to traditional SMA by using appropriately selected endmembers and is particularly strong in high-density urban areas.« less

Remote sensing investigations of wetland biomass and productivity for global biosystems research

NASA Technical Reports Server (NTRS)

Klemas, V.

1986-01-01

The relationship between spectral radiance and plant canopy biomass was studied in wetlands. Spectroradiometer data was gathered on Thematic Mapper wavebands 3, 4, and 5, and correlated with canopy and edaphic factors determined by harvesting. The relationship between spectral radiance and plant canopy biomass for major salt and brackish canopy types was determined. Algorithms were developed for biomass measurement in mangrove swamps. The influence of latitudinal variability in canopy structure on biomass assessment of selected plants was investigated. Brackish marsh biomass estimates were obtained from low altitude aircraft and compared with ground measurements. Annual net aerial primary productivity estimates computed from spectral radiance data were compiled for a Spartina alterniflora marsh. Spectral radiance data were expressed as vegetation or infrared index values. Biomass estimates computed from models were in close agreement with biomass estimates determined from harvests.

Simulation of Ge Dopant Emission in Indirect-Drive ICF Implosion Experiments

NASA Astrophysics Data System (ADS)

Macfarlane, J. J.; Golovkin, I.; Kulkarni, S.; Regan, S.; Epstein, R.; Mancini, R.; Peterson, K.; Suter, L. J.

2013-10-01

We present results from simulations performed to study the radiative properties of dopants used in inertial confinement fusion indirect-drive capsule implosion experiments on NIF. In Rev5 NIF ignition capsules, a Ge dopant is added to an inner region of the CH ablator to absorb hohlraum x-ray preheat. Spectrally resolved emission from ablator dopants can be used to study the degree of mixing of ablator material into the ignition hot spot. Here, we study the atomic processes that affect the radiative characteristics of these elements using a set of simulation tools to first estimate the evolution of plasma conditions in the compressed target, and then to compute the atomic kinetics of the dopant and the resultant radiative emission. Using estimates of temperature and density profiles predicted by radiation-hydrodynamics simulations, we set up simple 2-D plasma grids where we allow dopant material to be embedded in the fuel, and perform multi-dimensional collisional-radiative simulations using SPECT3D to compute non-LTE atomic level populations and spectral signatures from the dopant. Recently improved Stark-broadened line shape modeling for Ge K-shell lines has been included. The goal is to study the radiative and atomic processes that affect the emergent spectra, including the effects of inner-shell photoabsorption and K α reemission from the dopant.

The ISO Long Wavelength Spectrometer line spectrum of VY Canis Majoris and other oxygen-rich evolved stars

NASA Astrophysics Data System (ADS)

Polehampton, E. T.; Menten, K. M.; van der Tak, F. F. S.; White, G. J.

2010-02-01

Context. The far-infrared spectra of circumstellar envelopes around various oxygen-rich stars were observed using the ISO Long Wavelength Spectrometer (LWS). These have been shown to be spectrally rich, particularly in water lines, indicating a high H2O abundance. Aims: We have examined high signal-to-noise ISO LWS observations of the luminous supergiant star, VY CMa, with the aim of identifying all of the spectral lines. By paying particular attention to water lines, we aim to separate the lines due to other species, in particular, to prepare for forthcoming observations that will cover the same spectral range using Herschel PACS and at higher spectral resolution using Herschel HIFI and SOFIA. Methods: We have developed a fitting method to account for blended water lines using a simple weighting scheme to distribute the flux. We have used this fit to separate lines due to other species which cannot be assigned to water. We have applied this approach to several other stars which we compare with VY CMa. Results: We present line fluxes for the unblended H2O and CO lines, and present detections of several possible ν2=1 vibrationally excited water lines. We also identify blended lines of OH, one unblended and several blended lines of NH3, and one possible detection of H3O+. Conclusions: The spectrum of VY CMa shows a detection of emission from virtually every water line up to 2000 K above the ground state, as well as many additional higher energy and some vibrationally excited lines. A simple rotation diagram analysis shows large scatter (probably due to some optically thick lines). The fit gives a rotational temperature of 670+210-130 K, and lower limit on the water column density of (7.0±1.2) × 1019 cm-2. We estimate a CO column density ~100 times lower, showing that water is the dominant oxygen carrier. The other stars that we examined have similar rotation temperatures, but their H2O column densities are an order of magnitude lower (as are the mass loss rates). Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.Current address: Space Science Department, Rutherford Appleton Laboratory, UK

Limits on radio emission from meteors using the MWA

NASA Astrophysics Data System (ADS)

Zhang, Xiang; Hancock, Paul; Devillepoix, Hadrien A. R.; Wayth, Randall B.; Beardsley, A.; Crosse, B.; Emrich, D.; Franzen, T. M. O.; Gaensler, B. M.; Horsley, L.; Johnston-Hollitt, M.; Kaplan, D. L.; Kenney, D.; Morales, M. F.; Pallot, D.; Steele, K.; Tingay, S. J.; Trott, C. M.; Walker, M.; Williams, A.; Wu, C.; Ji, Jianghui; Ma, Yuehua

2018-04-01

Recently, low frequency, broadband radio emission has been observed accompanying bright meteors by the Long Wavelength Array (LWA). The broadband spectra between 20 and 60 MHz were captured for several events, while the spectral index (dependence of flux density on frequency, with Sν∝να) was estimated to be -4 ± 1 during the peak of meteor afterglows. Here we present a survey of meteor emission and other transient events using the Murchison Widefield Array (MWA) at 72-103 MHz. In our 322-hour survey, down to a 5σ detection threshold of 3.5 Jy/beam, no transient candidates were identified as intrinsic emission from meteors. We derived an upper limit of -3.7 (95% confidence limit) on the spectral index in our frequency range. We also report detections of other transient events, like reflected FM broadcast signals from small satellites, conclusively demonstrating the ability of the MWA to detect and track space debris on scales as small as 0.1 m in low Earth orbits.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagayama, T.; Bailey, J. E.; Loisel, G. P.

Iron opacity calculations presently disagree with measurements at an electron temperature of ~180–195 eV and an electron density of (2–4)×10 22cm –3, conditions similar to those at the base of the solar convection zone. The measurements use x rays to volumetrically heat a thin iron sample that is tamped with low-Z materials. The opacity is inferred from spectrally resolved x-ray transmission measurements. Plasma self-emission, tamper attenuation, and temporal and spatial gradients can all potentially cause systematic errors in the measured opacity spectra. In this article we quantitatively evaluate these potential errors with numerical investigations. The analysis exploits computer simulations thatmore » were previously found to reproduce the experimentally measured plasma conditions. The simulations, combined with a spectral synthesis model, enable evaluations of individual and combined potential errors in order to estimate their potential effects on the opacity measurement. Lastly, the results show that the errors considered here do not account for the previously observed model-data discrepancies.« less

The embedded young stars in the Taurus-Auriga molecular cloud. I - Models for spectral energy distributions

NASA Technical Reports Server (NTRS)

Kenyon, Scott J.; Calvet, Nuria; Hartmann, Lee

1993-01-01

We describe radiative transfer calculations of infalling, dusty envelopes surrounding pre-main-sequence stars and use these models to derive physical properties for a sample of 21 heavily reddened young stars in the Taurus-Auriga molecular cloud. The density distributions needed to match the FIR peaks in the spectral energy distributions of these embedded sources suggest mass infall rates similar to those predicted for simple thermally supported clouds with temperatures about 10 K. Unless the dust opacities are badly in error, our models require substantial departures from spherical symmetry in the envelopes of all sources. These flattened envelopes may be produced by a combination of rotation and cavities excavated by bipolar flows. The rotating infall models of Terebey et al. (1984) models indicate a centrifugal radius of about 70 AU for many objects if rotation is the only important physical effect, and this radius is reasonably consistent with typical estimates for the sizes of circumstellar disks around T Tauri stars.

Spectral weight of excitations in Bose Hubbard model

NASA Astrophysics Data System (ADS)

Alavani, Bhargav K.; Pai, Ramesh V.

2017-05-01

We obtain excitation spectra in the superfluid and the Mott Insulator phases of Bose Hubbard model near unit filling within Random Phase Approximation (RPA) and calculate its spectral weight. This gives a transparent description of contribution of each excitation towards the total Density of States (DOS) which we calculate from these spectral weights.

Hybrid least squares multivariate spectral analysis methods

DOEpatents

Haaland, David M.

2002-01-01

A set of hybrid least squares multivariate spectral analysis methods in which spectral shapes of components or effects not present in the original calibration step are added in a following estimation or calibration step to improve the accuracy of the estimation of the amount of the original components in the sampled mixture. The "hybrid" method herein means a combination of an initial classical least squares analysis calibration step with subsequent analysis by an inverse multivariate analysis method. A "spectral shape" herein means normally the spectral shape of a non-calibrated chemical component in the sample mixture but can also mean the spectral shapes of other sources of spectral variation, including temperature drift, shifts between spectrometers, spectrometer drift, etc. The "shape" can be continuous, discontinuous, or even discrete points illustrative of the particular effect.

Determination of seasonals using wavelets in terms of noise parameters changeability

NASA Astrophysics Data System (ADS)

Klos, Anna; Bogusz, Janusz; Figurski, Mariusz

2015-04-01

The reliable velocities of GNSS-derived observations are becoming of high importance nowadays. The fact on how we determine and subtract the seasonals may all cause the time series autocorrelation and affect uncertainties of linear parameters. The periodic changes in GNSS time series are commonly assumed as the sum of annual and semi-annual changes with amplitudes and phases being constant in time and the Least-Squares Estimation (LSE) is used in general to model these sine waves. However, not only seasonals' time-changeability, but also their higher harmonics should be considered. In this research, we focused on more than 230 globally distributed IGS stations that were processed at the Military University of Technology EPN Local Analysis Centre (MUT LAC) in Bernese 5.0 software. The network was divided into 7 different sub-networks with few of overlapping stations and processed separately with newest models. Here, we propose a wavelet-based trend and seasonals determination and removal of whole frequency spectrum between Chandler and quarter-annual periods from North, East and Up components and compare it with LSE-determined values. We used a Meyer symmetric, orthogonal wavelet and assumed nine levels of decomposition. The details from 6 up to 9 were analyzed here as periodic components with frequencies between 0.3-2.5 cpy. The characteristic oscillations for each of frequency band were pointed out. The details lower than 6 summed together with detrended approximation were considered as residua. The power spectral densities (PSDs) of original and decomposed data were stacked for North, East and Up components for each of sub-networks so as to show what power was removed with each of decomposition levels. Moreover, the noises that the certain frequency band follows (in terms of spectral indices of power-law dependencies) were estimated here using a spectral method and compared for all processed sub-networks. It seems, that lowest frequencies up to 0.7 cpy are characterized by lower spectral indices in comparison to higher ones being close to white noise. Basing on the fact, that decomposition levels overlap each other, the frequency-window choice becomes a main point in spectral index estimation. Our results were compared with those obtained by Maximum Likelihood Estimation (MLE) and possible differences as well as their impact on velocity uncertainties pointed out. The results show that the spectral indices estimated in time and frequency domains differ of 0.15 in maximum. Moreover, we compared the removed power basing on wavelet decomposition levels with the one subtracted with LSE, assuming the same periodicities. In comparison to LSE, the wavelet-based approach leaves the residua being closer to white noise with lower power-law amplitudes of them, what strictly reduces velocity uncertainties. The last approximation was analyzed here as long-term trend, being the non-linear and compared with LSE-determined linear one. It seems that these two trends differ at the level of 0.3 mm/yr in the most extreme case, what makes wavelet decomposition being useful for velocity determination.

Image enhancement by spectral-error correction for dual-energy computed tomography.

PubMed

Park, Kyung-Kook; Oh, Chang-Hyun; Akay, Metin

2011-01-01

Dual-energy CT (DECT) was reintroduced recently to use the additional spectral information of X-ray attenuation and aims for accurate density measurement and material differentiation. However, the spectral information lies in the difference between low and high energy images or measurements, so that it is difficult to acquire accurate spectral information due to amplification of high pixel noise in the resulting difference image. In this work, an image enhancement technique for DECT is proposed, based on the fact that the attenuation of a higher density material decreases more rapidly as X-ray energy increases. We define as spectral error the case when a pixel pair of low and high energy images deviates far from the expected attenuation trend. After analyzing the spectral-error sources of DECT images, we propose a DECT image enhancement method, which consists of three steps: water-reference offset correction, spectral-error correction, and anti-correlated noise reduction. It is the main idea of this work that makes spectral errors distributed like random noise over the true attenuation and suppressed by the well-known anti-correlated noise reduction. The proposed method suppressed noise of liver lesions and improved contrast between liver lesions and liver parenchyma in DECT contrast-enhanced abdominal images and their two-material decomposition.

A high-order 3-D spectral-element method for the forward modelling and inversion of gravimetric data—Application to the western Pyrenees

NASA Astrophysics Data System (ADS)

Martin, Roland; Chevrot, Sébastien; Komatitsch, Dimitri; Seoane, Lucia; Spangenberg, Hannah; Wang, Yi; Dufréchou, Grégory; Bonvalot, Sylvain; Bruinsma, Sean

2017-04-01

We image the internal density structure of the Pyrenees by inverting gravity data using an a priori density model derived by scaling a Vp model obtained by full waveform inversion of teleseismic P-waves. Gravity anomalies are computed via a 3-D high-order finite-element integration in the same high-order spectral-element grid as the one used to solve the wave equation and thus to obtain the velocity model. The curvature of the Earth and surface topography are taken into account in order to obtain a density model as accurate as possible. The method is validated through comparisons with exact semi-analytical solutions. We show that the spectral-element method drastically accelerates the computations when compared to other more classical methods. Different scaling relations between compressional velocity and density are tested, and the Nafe-Drake relation is the one that leads to the best agreement between computed and observed gravity anomalies. Gravity data inversion is then performed and the results allow us to put more constraints on the density structure of the shallow crust and on the deep architecture of the mountain range.

Virtual Sensors: Using Data Mining Techniques to Efficiently Estimate Remote Sensing Spectra

NASA Technical Reports Server (NTRS)

Srivastava, Ashok N.; Oza, Nikunj; Stroeve, Julienne

2004-01-01

Various instruments are used to create images of the Earth and other objects in the universe in a diverse set of wavelength bands with the aim of understanding natural phenomena. These instruments are sometimes built in a phased approach, with some measurement capabilities being added in later phases. In other cases, there may not be a planned increase in measurement capability, but technology may mature to the point that it offers new measurement capabilities that were not available before. In still other cases, detailed spectral measurements may be too costly to perform on a large sample. Thus, lower resolution instruments with lower associated cost may be used to take the majority of measurements. Higher resolution instruments, with a higher associated cost may be used to take only a small fraction of the measurements in a given area. Many applied science questions that are relevant to the remote sensing community need to be addressed by analyzing enormous amounts of data that were generated from instruments with disparate measurement capability. This paper addresses this problem by demonstrating methods to produce high accuracy estimates of spectra with an associated measure of uncertainty from data that is perhaps nonlinearly correlated with the spectra. In particular, we demonstrate multi-layer perceptrons (MLPs), Support Vector Machines (SVMs) with Radial Basis Function (RBF) kernels, and SVMs with Mixture Density Mercer Kernels (MDMK). We call this type of an estimator a Virtual Sensor because it predicts, with a measure of uncertainty, unmeasured spectral phenomena.

Gigahertz-peaked spectra pulsars in Pulsar Wind Nebulae

NASA Astrophysics Data System (ADS)

Basu, R.; RoŻko, K.; Kijak, J.; Lewandowski, W.

2018-04-01

We have carried out a detailed study of the spectral nature of six pulsars surrounded by pulsar wind nebulae (PWNe). The pulsar flux density was estimated using the interferometric imaging technique of the Giant Metrewave Radio Telescope at three frequencies 325, 610, and 1280 MHz. The spectra showed a turnover around gigahertz frequency in four out of six pulsars. It has been suggested that the gigahertz-peaked spectrum (GPS) in pulsars arises due to thermal absorption of the pulsar emission in surrounding medium like PWNe, H II regions, supernova remnants, etc. The relatively high incidence of GPS behaviour in pulsars surrounded by PWNe imparts further credence to this view. The pulsar J1747-2958 associated with the well-known Mouse nebula was also observed in our sample and exhibited GPS behaviour. The pulsar was detected as a point source in the high-resolution images. However, the pulsed emission was not seen in the phased-array mode. It is possible that the pulsed emission was affected by extreme scattering causing considerable smearing of the emission at low radio frequencies. The GPS spectra were modelled using the thermal free-free absorption and the estimated absorber properties were largely consistent with PWNe. The spatial resolution of the images made it unlikely that the point source associated with J1747-2958 was the compact head of the PWNe, but the synchrotron self-absorption seen in such sources was a better fit to the estimated spectral shape.

LIDAR TS for ITER core plasma. Part III: calibration and higher edge resolution

NASA Astrophysics Data System (ADS)

Nielsen, P.; Gowers, C.; Salzmann, H.

2017-12-01

Calibration, after initial installation, of the proposed two wavelength LIDAR Thomson Scattering System requires no access to the front end and does not require a foreign gas fill for Raman scattering. As already described, the variation of solid angle of collection with scattering position is a simple geometrical variation over the unvignetted region. The additional loss over the vignetted region can easily be estimated and in the case of a small beam dump located between the Be tiles, it is within the specified accuracy of the density. The only additional calibration is the absolute spectral transmission of the front-end optics. Over time we expect the transmission of the two front-end mirrors to suffer a deterioration mainly due to depositions. The reduction in transmission is likely to be worse towards the blue end of the scattering spectrum. It is therefore necessary to have a method to monitor such changes and to determine its spectral variation. Standard methods use two lasers at different wavelength with a small time separation. Using the two-wavelength approach, a method has been developed to determine the relative spectral variation of the transmission loss, using simply the measured signals in plasmas with peak temperatures of 4-6 keV . Comparing the calculated line integral of the fitted density over the full chord to the corresponding interferometer data we also have an absolute calibration. At the outer plasma boundary, the standard resolution of the LIDAR Thomson Scattering System is not sufficient to determine the edge gradient in an H-mode plasma. However, because of the step like nature of the signal here, it is possible to carry out a deconvolution of the scattered signals, thereby achieving an effective resolution of ~ 1-2 cm in the outer 10-20 cm.

The Atacama Cosmology Telescope: Extragalactic Sources at 148 GHz in the 2008 Survey

NASA Technical Reports Server (NTRS)

Marriage, T. A.; Juin, J. B.; Lin, Y. T.; Marsden, D.; Nolta, M. R.; Partridge, B.; Ade, P. A. R.; Aguirre, P.; Amiri, M.; Appel, J. W.;

The Class 0 Protostar BHR71: Herschel Observations and Dust Continuum Models

NASA Astrophysics Data System (ADS)

Yang, Yao-Lun; Evans, Neal J., II; Green, Joel D.; Dunham, Michael M.; Jørgensen, Jes K.

2017-02-01

We use Herschel spectrophotometry of BHR71, an embedded Class 0 protostar, to provide new constraints on its physical properties. We detect 645 (non-unique) spectral lines among all spatial pixels. At least 61 different spectral lines originate from the central region. A CO rotational diagram analysis shows four excitation temperature components, 43, 197, 397, and 1057 K. Low-J CO lines trace the outflow while the high-J CO lines are centered on the infrared source. The low-excitation emission lines of {{{H}}}2{{O}} trace the large-scale outflow, while the high-excitation emission lines trace a small-scale distribution around the equatorial plane. We model the envelope structure using the dust radiative transfer code, hyperion, incorporating rotational collapse, an outer static envelope, outflow cavity, and disk. The evolution of a rotating collapsing envelope can be constrained by the far-infrared/millimeter spectral energy distribution along with the azimuthally averaged radial intensity profile, and the structure of the outflow cavity plays a critical role at shorter wavelengths. Emission at 20-40 μm requires a cavity with a constant-density inner region and a power-law density outer region. The best-fit model has an envelope mass of 19 {M}⊙ inside a radius of 0.315 pc and a central luminosity of 18.8 {L}⊙ . The time since collapse began is 24,630-44,000 years, most likely around 36,000 years. The corresponding mass infall rate in the envelope (1.2 × 10-5 {M}⊙ {{yr}}-1) is comparable to the stellar mass accretion rate, while the mass-loss rate estimated from the CO outflow is 20% of the stellar mass accretion rate. We find no evidence for episodic accretion.

LOOKING FOR GRANULATION AND PERIODICITY IMPRINTS IN THE SUNSPOT TIME SERIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopes, Ilídio; Silva, Hugo G., E-mail: ilidio.lopes@tecnico.ulisboa.pt, E-mail: hgsilva@uevora.pt

2015-05-10

The sunspot activity is the end result of the cyclic destruction and regeneration of magnetic fields by the dynamo action. We propose a new method to analyze the daily sunspot areas data recorded since 1874. By computing the power spectral density of daily data series using the Mexican hat wavelet, we found a power spectrum with a well-defined shape, characterized by three features. The first term is the 22 yr solar magnetic cycle, estimated in our work to be 18.43 yr. The second term is related to the daily volatility of sunspots. This term is most likely produced by themore » turbulent motions linked to the solar granulation. The last term corresponds to a periodic source associated with the solar magnetic activity, for which the maximum power spectral density occurs at 22.67 days. This value is part of the 22–27 day periodicity region that shows an above-average intensity in the power spectra. The origin of this 22.67 day periodic process is not clearly identified, and there is a possibility that it can be produced by convective flows inside the star. The study clearly shows a north–south asymmetry. The 18.43 yr periodical source is correlated between the two hemispheres, but the 22.67 day one is not correlated. It is shown that toward the large timescales an excess occurs in the northern hemisphere, especially near the previous two periodic sources. To further investigate the 22.67 day periodicity, we made a Lomb–Scargle spectral analysis. The study suggests that this periodicity is distinct from others found nearby.« less

Preliminary evaluation of the Environmental Research Institute of Michigan crop calendar shift algorithm for estimation of spring wheat development stage. [North Dakota, South Dakota, Montana, and Minnesota

NASA Technical Reports Server (NTRS)

Phinney, D. E. (Principal Investigator)

1980-01-01

An algorithm for estimating spectral crop calendar shifts of spring small grains was applied to 1978 spring wheat fields. The algorithm provides estimates of the date of peak spectral response by maximizing the cross correlation between a reference profile and the observed multitemporal pattern of Kauth-Thomas greenness for a field. A methodology was developed for estimation of crop development stage from the date of peak spectral response. Evaluation studies showed that the algorithm provided stable estimates with no geographical bias. Crop development stage estimates had a root mean square error near 10 days. The algorithm was recommended for comparative testing against other models which are candidates for use in AgRISTARS experiments.

Diffusion spectral imaging modules correlate with EEG LORETA neuroimaging modules.

PubMed

Thatcher, Robert W; North, Duane M; Biver, Carl J

2012-05-01

The purpose of this study was to test the hypothesis that the highest temporal correlations between 3-dimensional EEG current source density corresponds to anatomical Modules of high synaptic connectivity. Eyes closed and eyes open EEG was recorded from 19 scalp locations with a linked ears reference from 71 subjects age 13-42 years. LORETA was computed from 1 to 30 Hz in 2,394 cortical gray matter voxels that were grouped into six anatomical Modules corresponding to the ROIs in the Hagmann et al.'s [2008] diffusion spectral imaging (DSI) study. All possible cross-correlations between voxels within a DSI Module were compared with the correlations between Modules. The Hagmann et al. [ 2008] Module correlation structure was replicated in the correlation structure of EEG three-dimensional current source density. EEG Temporal correlation between brain regions is related to synaptic density as measured by diffusion spectral imaging. Copyright © 2011 Wiley-Liss, Inc.

High-Energy Density science at the Linac Coherent Light Source

NASA Astrophysics Data System (ADS)

Glenzer, S. H.; Fletcher, L. B.; Hastings, J. B.

2016-03-01

The Matter in Extreme Conditions end station at the Linac Coherent Light Source holds great promise for novel pump-probe experiments to make new discoveries in high- energy density science. In recent experiments we have demonstrated the first spectrally- resolved measurements of plasmons using a seeded 8-keV x-ray laser beam. Forward x-ray Thomson scattering spectra from isochorically heated solid aluminum show a well-resolved plasmon feature that is down-shifted in energy by 19 eV from the incident 8 keV elastic scattering feature. In this spectral range, the simultaneously measured backscatter spectrum shows no spectral features indicating observation of collective plasmon oscillations on a scattering length comparable to the screening length. This technique is a prerequisite for Thomson scattering measurements in compressed matter where the plasmon shift is a sensitive function of the free electron density and where the plasmon intensity provides information on temperature.

Low frequency noise in p-InAsSbP/n-InAs infrared photodiodes

NASA Astrophysics Data System (ADS)

Dyakonova, N.; Karandashev, S. A.; Levinshtein, M. E.; Matveev, B. A.; Remennyi, M. A.

2018-06-01

We report the first experimental study of low-frequency noise in p-InAsSbP/n-InAs infrared photodiodes. For forward bias, experiments have been carried out at 300 and 77 K, in the photovoltaic regime the measurements have been done at 300 K. At room temperature the current noise spectral density, SI , exhibits the ∼1/f frequency dependence. For low currents, I ≤ I 0 ∼ 4 × 10‑5 A, S I is proportional to I 2, at higher currents this dependence changes to S I ∼ I. At 77 K the noise spectral density is significantly higher than at 300 K, and Lorentzian contributions to noise are observed. The current dependences of spectral noise density can be approximately described as S I ∼ I 1.5 and show particularities suggesting the contribution of defects.

Modeling Electronic-Nuclear Interactions for Excitation Energy Transfer Processes in Light-Harvesting Complexes.

PubMed

Lee, Mi Kyung; Coker, David F

2016-08-18

An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation.

High-Energy Density science at the Linac Coherent Light Source

DOE PAGES

Glenzer, S. H.; Fletcher, L. B.; Hastings, J. B.

2016-04-01

The Matter in Extreme Conditions end station at the Linac Coherent Light Source holds great promise for novel pump-probe experiments to make new discoveries in high- energy density science. Recently, our experiments have demonstrated the first spectrally- resolved measurements of plasmons using a seeded 8-keV x-ray laser beam. Forward x-ray Thomson scattering spectra from isochorically heated solid aluminum show a well-resolved plasmon feature that is down-shifted in energy by 19 eV from the incident 8 keV elastic scattering feature. In this spectral range, the simultaneously measured backscatter spectrum shows no spectral features indicating observation of collective plasmon oscillations on amore » scattering length comparable to the screening length. Moreover, this technique is a prerequisite for Thomson scattering measurements in compressed matter where the plasmon shift is a sensitive function of the free electron density and where the plasmon intensity provides information on temperature.« less

Scaling within the spectral function approach

NASA Astrophysics Data System (ADS)

Sobczyk, J. E.; Rocco, N.; Lovato, A.; Nieves, J.

2018-03-01

Scaling features of the nuclear electromagnetic response functions unveil aspects of nuclear dynamics that are crucial for interpreting neutrino- and electron-scattering data. In the large momentum-transfer regime, the nucleon-density response function defines a universal scaling function, which is independent of the nature of the probe. In this work, we analyze the nucleon-density response function of 12C, neglecting collective excitations. We employ particle and hole spectral functions obtained within two distinct many-body methods, both widely used to describe electroweak reactions in nuclei. We show that the two approaches provide compatible nucleon-density scaling functions that for large momentum transfers satisfy first-kind scaling. Both methods yield scaling functions characterized by an asymmetric shape, although less pronounced than that of experimental scaling functions. This asymmetry, only mildly affected by final state interactions, is mostly due to nucleon-nucleon correlations, encoded in the continuum component of the hole spectral function.

Alternate Implosion Models for the Plane Parallel Diode.

DTIC Science & Technology

1982-04-02

higher density regions, perhaps altering the spectral mix of line and continuum radiation. 3) Examine the effect of the chemical potential (properly...inclusion of previous time levels (i-i, i-2...) in an estimate of AF would be a means of filtering the noise that might develop in this variable, and...NN’N NO G~l-0NNV . OO’)N aQ.’)4Ŕ N 4 . * .~ 0 I’) MMIs )NN4 P).N 44 NN 4 0. 00(0 0-0 NN 1 OWEI) ~4N Vi N 0 vm -N 0. 0N0 M a 40 0 I.) 0.0. N Nflmwo ONNOM

A parameter identification method for the rotordynamic coefficients of a high Reynolds number hydrostatic bearing

NASA Technical Reports Server (NTRS)

Rouvas, C.; Childs, D. W.

1993-01-01

In identifying the rotordynamic coefficients of a high-Reynolds-number hydrostatic bearing, fluid-flow induced forces present a unique problem, in that they provide an unmeasureable and uncontrollable excitation to the bearing. An analysis method is developed that effectively eliminates the effects of fluid-flow induced excitation on the estimation of the bearing rotordynamic coefficients, by using power spectral densities. In addition to the theoretical development, the method is verified experimentally by single-frequency testing, and repeatability tests. Results obtained for a bearing are the twelve rotordynamic coefficients (stiffness, damping, and inertia coefficients) as functions of eccentricity ratio, speed, and supply pressure.

On the abundance of planetary water and exo-life after Kepler

NASA Astrophysics Data System (ADS)

Wandel, Amri

2015-08-01

Combining the recent results of the Kepler mission on the abundance of small planets within the Habitable Zone with a Drake-equation formalism I derive the space density of planets with surface water and biotic planets as a function of the yet unknown probabilities for the evolution of an Earthlike atmosphere and biosphere, respectively. I describe how these probabilities may be estimated by future spectral observations of exoplanet biomarkers such as atmospheric oxygen and water. I find that planets with surface liquid water may be expected within 10 light years and biotic planets within 10 -- 100 light years from Earth. ArXiv 1412.1302.

Lithospheric structure in the Pacific geoid

NASA Technical Reports Server (NTRS)

Marsh, B. D.

1984-01-01

In order that sub-lithospheric density variations be revealed with the geoid, the regional geoid anomalies associated with bathymetric variations must first be removed. Spectral techniques were used to generate a synthetic geoid by filtering the residual bathymetry assuming an Airy-type isostatic compensation model. An unbiased estimated of the admittances show that for region under study, no single compensation mechanism will explain all of the power in the geoid. Nevertheless, because topographic features are mainly coherent with the geoid, to first order an isostationally compensated lithosphere cut by major E-W fracture zones accounts for most of the power in the high degree and other SEASAT geoid in the Pacific.

Evaluation of spatial, radiometric and spectral Thematic Mapper performance for coastal studies

NASA Technical Reports Server (NTRS)

Klemas, V. (Principal Investigator)

1984-01-01

The effect different wetland plant canopies have upon observed reflectance in Thematic Mapper bands is examined. The three major vegetation canopy types (broadleaf, gramineous and leafless) produce unique spectral responses for a similar quantity of live biomass. Biomass estimates computed from spectral data were most similar to biomass estimates determined from harvest data when models developed for a specific canopy were used. Precise determination of regression coefficients for each canopy type and modeling changes in the coefficients with various combinations of canopy types are being tested. The multispectral band scanner vegetation index estimates are very similar to the vegetation index estimates.

Effect of non-Poisson samples on turbulence spectra from laser velocimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sree, D.; Kjelgaard, S.O.; Sellers, W.L. III

1994-12-01

Spectral estimations from LV data are typically based on the assumption of a Poisson sampling process. It is demonstrated here that the sampling distribution must be considered before spectral estimates are used to infer turbulence scales. A non-Poisson sampling process can occur if there is nonhomogeneous distribution of particles in the flow. Based on the study of a simulated first-order spectrum, it has been shown that a non-Poisson sampling process causes the estimated spectrum to deviate from the true spectrum. Also, in this case the prefiltering techniques do not improve the spectral estimates at higher frequencies. 4 refs.

Fast and accurate spectral estimation for online detection of partial broken bar in induction motors

NASA Astrophysics Data System (ADS)

Samanta, Anik Kumar; Naha, Arunava; Routray, Aurobinda; Deb, Alok Kanti

2018-01-01

In this paper, an online and real-time system is presented for detecting partial broken rotor bar (BRB) of inverter-fed squirrel cage induction motors under light load condition. This system with minor modifications can detect any fault that affects the stator current. A fast and accurate spectral estimator based on the theory of Rayleigh quotient is proposed for detecting the spectral signature of BRB. The proposed spectral estimator can precisely determine the relative amplitude of fault sidebands and has low complexity compared to available high-resolution subspace-based spectral estimators. Detection of low-amplitude fault components has been improved by removing the high-amplitude fundamental frequency using an extended-Kalman based signal conditioner. Slip is estimated from the stator current spectrum for accurate localization of the fault component. Complexity and cost of sensors are minimal as only a single-phase stator current is required. The hardware implementation has been carried out on an Intel i7 based embedded target ported through the Simulink Real-Time. Evaluation of threshold and detectability of faults with different conditions of load and fault severity are carried out with empirical cumulative distribution function.

Irreducible Green's functions method for a quantum dot coupled to metallic and superconducting leads

NASA Astrophysics Data System (ADS)

Górski, Grzegorz; Kucab, Krzysztof

2017-05-01

Using irreducible Green's functions (IGF) method we analyse the Coulomb interaction dependence of the spectral functions and the transport properties of a quantum dot coupled to isotropic superconductor and metallic leads (SC-QD-N). The irreducible Green's functions method is the modification of classical equation of motion technique. The IGF scheme is based on differentiation of double-time Green's functions, both over the primary and secondary times. The IGF method allows to obtain the spectral functions for equilibrium and non-equilibrium impurity Anderson model used for SC-QD-N system. By the numerical computations, we show the change of spectral and the anomalous densities under the influence of the Coulomb interactions. The observed sign change of the anomalous spectral density can be used as the criterion of the SC singlet-Kondo singlet transition.

Spectrotemporal modulation sensitivity for hearing-impaired listeners: dependence on carrier center frequency and the relationship to speech intelligibility.

PubMed

Mehraei, Golbarg; Gallun, Frederick J; Leek, Marjorie R; Bernstein, Joshua G W

2014-07-01

Poor speech understanding in noise by hearing-impaired (HI) listeners is only partly explained by elevated audiometric thresholds. Suprathreshold-processing impairments such as reduced temporal or spectral resolution or temporal fine-structure (TFS) processing ability might also contribute. Although speech contains dynamic combinations of temporal and spectral modulation and TFS content, these capabilities are often treated separately. Modulation-depth detection thresholds for spectrotemporal modulation (STM) applied to octave-band noise were measured for normal-hearing and HI listeners as a function of temporal modulation rate (4-32 Hz), spectral ripple density [0.5-4 cycles/octave (c/o)] and carrier center frequency (500-4000 Hz). STM sensitivity was worse than normal for HI listeners only for a low-frequency carrier (1000 Hz) at low temporal modulation rates (4-12 Hz) and a spectral ripple density of 2 c/o, and for a high-frequency carrier (4000 Hz) at a high spectral ripple density (4 c/o). STM sensitivity for the 4-Hz, 4-c/o condition for a 4000-Hz carrier and for the 4-Hz, 2-c/o condition for a 1000-Hz carrier were correlated with speech-recognition performance in noise after partialling out the audiogram-based speech-intelligibility index. Poor speech-reception and STM-detection performance for HI listeners may be related to a combination of reduced frequency selectivity and a TFS-processing deficit limiting the ability to track spectral-peak movements.

Remote sensing estimation of isoprene and monoterpene emissions generated by natural vegetation in Monterrey, Mexico.

PubMed

Gastelum, Sandra L; Mejía-Velázquez, G M; Lozano-García, D Fabián

2016-06-01

In addition to oxygen, hydrocarbons are the most reactive chemical compounds produced by plants into the atmosphere. These compounds are part of the family of volatile organic compounds (VOCs) and are discharged in a great variety of forms. Among the VOCs produced by natural sources such as vegetation, the most studied until today are the isoprene and monoterpene. These substances can play an important role in the chemical balance of the atmosphere of a region. In this project, we develop a methodology to estimate the natural (vegetation) emission of isoprene and monoterpenes and applied it to the Monterrey Metropolitan Area, Mexico and its surrounding areas. Landsat-TM data was used to identify the dominant vegetation communities and field work to determine the foliage biomass density of key species. The studied communities were submontane scrub, oak, and pine forests and a combination of both. We carried out the estimation of emissions for isoprene and monoterpenes compounds in the different plant communities, with two different criteria: (1) taking into account the average foliage biomass density obtained from the various sample point in each vegetation community, and (2) using the foliage biomass density obtained for each transect, associated to an individual spectral class within a particular vegetation type. With this information, we obtained emission maps for each case. The results show that the main producers of isoprene are the communities that include species of the genus Quercus, located mainly on the Sierra Madre Oriental and Sierra de Picachos, with average isoprene emissions of 314.6 ton/day and 207.3 ton/day for the two methods utilized. The higher estimates of monoterpenes were found in the submontane scrub areas distributed along the valley of the metropolitan zone, with an estimated average emissions of 47.1 ton/day and 181.4 tons for the two methods respectively.

Electron-density-sensitive Line Ratios of Fe XIII– XVI from Laboratory Sources Compared to CHIANTI

NASA Astrophysics Data System (ADS)

Weller, M. E.; Beiersdorfer, P.; Soukhanovskii, V. A.; Scotti, F.; LeBlanc, B. P.

2018-02-01

We present electron-density-sensitive line ratios for Fe XIII– XVI measured in the spectral wavelength range of 200–440 Å and an electron density range of (1–4) × 1013 cm‑3. The results provide a test at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 Å, i.e., high resolution across the broad wavelength range. The response of the instrument was relatively calibrated using spectroscopic techniques in order to improve accuracy. The line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.

Characterization of Electron Temperature and Density Profiles of Plasmas Produced by Nike KrF Laser for Laser Plasma Instability (LPI) Research

NASA Astrophysics Data System (ADS)

Oh, Jaechul; Weaver, J. L.; Phillips, L.; Obenschain, S. P.; Schmitt, A. J.; Kehne, D. M.; Chan, L.-Y.; Serlin, V.

2011-10-01

Previous experiments with Nike KrF laser (λ = 248 nm , Δν ~ 1 THz) observed LPI signatures near quarter critical density (nc / 4) in CH plasmas, however, detailed measurement of the temperature (Te) and density (ne) profiles was missing. The current Nike LPI campaign will perform experimental determination of the plasma profiles. A side-on grid imaging refractometer (GIR) is the main diagnostic to resolve Te and ne in space taking 2D snapshots of probe laser (λ = 266 nm , Δt = 8 psec) beamlets (50 μm spacing) refracted by the plasma at laser peak time. Ray tracing of the beamlets through hydrodynamically simulated (FASTRAD3D) plasma profiles estimates the refractometer may access densities up to ~ 0 . 2nc . With the measured Te and ne profiles in the plasma corona, we will discuss analysis of light data radiated from the plasmas in spectral ranges relevant to two plasmon decay and convective Raman instabilities. Validity of the (Te ,ne) data will also be discussed for the thermal transport study. Work supported by DoE/NNSA and ONR and performed at NRL.

Proton exchange membrane fuel cell diagnosis by spectral characterization of the electrochemical noise

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.

Many-Body Spectral Functions from Steady State Density Functional Theory.

PubMed

Jacob, David; Kurth, Stefan

2018-03-14

We propose a scheme to extract the many-body spectral function of an interacting many-electron system from an equilibrium density functional theory (DFT) calculation. To this end we devise an ideal scanning tunneling microscope (STM) setup and employ the recently proposed steady-state DFT formalism (i-DFT) which allows one to calculate the steady current through a nanoscopic region coupled to two biased electrodes. In our setup, one of the electrodes serves as a probe ("STM tip"), which is weakly coupled to the system we want to measure. In the ideal STM limit of vanishing coupling to the tip, the system is restored to quasi-equilibrium and the normalized differential conductance yields the exact equilibrium many-body spectral function. Calculating this quantity from i-DFT, we derive an exact relation expressing the interacting spectral function in terms of the Kohn-Sham one. As illustrative examples, we apply our scheme to calculate the spectral functions of two nontrivial model systems, namely the single Anderson impurity model and the Constant Interaction Model.

Enhancement of low-temperature thermometry by strong coupling

NASA Astrophysics Data System (ADS)

Correa, Luis A.; Perarnau-Llobet, Martí; Hovhannisyan, Karen V.; Hernández-Santana, Senaida; Mehboudi, Mohammad; Sanpera, Anna

2017-12-01

We consider the problem of estimating the temperature T of a very cold equilibrium sample. The temperature estimates are drawn from measurements performed on a quantum Brownian probe strongly coupled to it. We model this scenario by resorting to the canonical Caldeira-Leggett Hamiltonian and find analytically the exact stationary state of the probe for arbitrary coupling strength. In general, the probe does not reach thermal equilibrium with the sample, due to their nonperturbative interaction. We argue that this is advantageous for low-temperature thermometry, as we show in our model that (i) the thermometric precision at low T can be significantly enhanced by strengthening the probe-sampling coupling, (ii) the variance of a suitable quadrature of our Brownian thermometer can yield temperature estimates with nearly minimal statistical uncertainty, and (iii) the spectral density of the probe-sample coupling may be engineered to further improve thermometric performance. These observations may find applications in practical nanoscale thermometry at low temperatures—a regime which is particularly relevant to quantum technologies.

A Muscle Fibre Conduction Velocity Tracking ASIC for Local Fatigue Monitoring.

PubMed

Koutsos, Ermis; Cretu, Vlad; Georgiou, Pantelis

2016-12-01

Electromyography analysis can provide information about a muscle's fatigue state by estimating Muscle Fibre Conduction Velocity (MFCV), a measure of the travelling speed of Motor Unit Action Potentials (MUAPs) in muscle tissue. MFCV better represents the physical manifestations of muscle fatigue, compared to the progressive compression of the myoelectic Power Spectral Density, hence it is more suitable for a muscle fatigue tracking system. This paper presents a novel algorithm for the estimation of MFCV using single threshold bit-stream conversion and a dedicated application-specified integrated circuit (ASIC) for its implementation, suitable for a compact, wearable and easy to use muscle fatigue monitor. The presented ASIC is implemented in a commercially available AMS 0.35 [Formula: see text] CMOS technology and utilizes a bit-stream cross-correlator that estimates the conduction velocity of the myoelectric signal in real time. A test group of 20 subjects was used to evaluate the performance of the developed ASIC, achieving good accuracy with an error of only 3.2% compared to Matlab.

Yield estimation of sugarcane based on agrometeorological-spectral models

NASA Technical Reports Server (NTRS)

Rudorff, Bernardo Friedrich Theodor; Batista, Getulio Teixeira

1990-01-01

This work has the objective to assess the performance of a yield estimation model for sugarcane (Succharum officinarum). The model uses orbital gathered spectral data along with yield estimated from an agrometeorological model. The test site includes the sugarcane plantations of the Barra Grande Plant located in Lencois Paulista municipality in Sao Paulo State. Production data of four crop years were analyzed. Yield data observed in the first crop year (1983/84) were regressed against spectral and agrometeorological data of that same year. This provided the model to predict the yield for the following crop year i.e., 1984/85. The model to predict the yield of subsequent years (up to 1987/88) were developed similarly, incorporating all previous years data. The yield estimations obtained from these models explained 69, 54, and 50 percent of the yield variation in the 1984/85, 1985/86, and 1986/87 crop years, respectively. The accuracy of yield estimations based on spectral data only (vegetation index model) and on agrometeorological data only (agrometeorological model) were also investigated.

Antiproton signatures from astrophysical and dark matter sources at the galactic center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cembranos, J.A.R.; Gammaldi, V.; Maroto, A.L., E-mail: cembra@ucm.es, E-mail: vivigamm@ucm.es, E-mail: maroto@fis.ucm.es

2015-03-01

The center of our Galaxy is a complex region characterized by extreme phenomena. The presence of the supermassive Sagittarius A* black hole, a high dark matter density and an even higher baryonic density are able to produce very energetic processes. Indeed, high energetic gamma-rays have been observed by different telescopes, although their origin is not clear. In this work, we estimate the possible antiproton flux component associated with this signal. The expected secondary astrophysical antiproton background already saturates the observed data. It implies that any other important astrophysical source leads to an inconsistent excess. We estimate the sensitivity of PAMELAmore » to this new primary antiproton source, which depends on the diffusion model and its spectral features. In particular, we consider antiproton spectra described by a power-law, a monochromatic signal and a Standard Model particle-antiparticle channel production. This latter spectrum is typical in the production from annihilating or decaying dark matter. We pay particular attention to the case of a heavy dark matter candidate, which could be associated with the High Energy Stereoscopic System (HESS) data observed from the J1745-290 source.« less

Multispectral imaging of absorption and scattering properties of in vivo exposed rat brain using a digital red-green-blue camera.

PubMed

Yoshida, Keiichiro; Nishidate, Izumi; Ishizuka, Tomohiro; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu

2015-05-01

In order to estimate multispectral images of the absorption and scattering properties in the cerebral cortex of in vivo rat brain, we investigated spectral reflectance images estimated by the Wiener estimation method using a digital RGB camera. A Monte Carlo simulation-based multiple regression analysis for the corresponding spectral absorbance images at nine wavelengths (500, 520, 540, 560, 570, 580, 600, 730, and 760 nm) was then used to specify the absorption and scattering parameters of brain tissue. In this analysis, the concentrations of oxygenated hemoglobin and that of deoxygenated hemoglobin were estimated as the absorption parameters, whereas the coefficient a and the exponent b of the reduced scattering coefficient spectrum approximated by a power law function were estimated as the scattering parameters. The spectra of absorption and reduced scattering coefficients were reconstructed from the absorption and scattering parameters, and the spectral images of absorption and reduced scattering coefficients were then estimated. In order to confirm the feasibility of this method, we performed in vivo experiments on exposed rat brain. The estimated images of the absorption coefficients were dominated by the spectral characteristics of hemoglobin. The estimated spectral images of the reduced scattering coefficients had a broad scattering spectrum, exhibiting a larger magnitude at shorter wavelengths, corresponding to the typical spectrum of brain tissue published in the literature. The changes in the estimated absorption and scattering parameters during normoxia, hyperoxia, and anoxia indicate the potential applicability of the method by which to evaluate the pathophysiological conditions of in vivo brain due to the loss of tissue viability.

Submillimeter, millimeter, and microwave spectral line catalogue

NASA Technical Reports Server (NTRS)

Poynter, R. L.; Pickett, H. M.

1980-01-01

A computer accessible catalogue of submillimeter, millimeter, and microwave spectral lines in the frequency range between O and 3000 GHz (such as; wavelengths longer than 100 m) is discussed. The catalogue was used as a planning guide and as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue was constructed by using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances.

Covariance propagation in spectral indices

DOE PAGES

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

Dual ant colony operational modal analysis parameter estimation method

NASA Astrophysics Data System (ADS)

Sitarz, Piotr; Powałka, Bartosz

2018-01-01

Operational Modal Analysis (OMA) is a common technique used to examine the dynamic properties of a system. Contrary to experimental modal analysis, the input signal is generated in object ambient environment. Operational modal analysis mainly aims at determining the number of pole pairs and at estimating modal parameters. Many methods are used for parameter identification. Some methods operate in time while others in frequency domain. The former use correlation functions, the latter - spectral density functions. However, while some methods require the user to select poles from a stabilisation diagram, others try to automate the selection process. Dual ant colony operational modal analysis parameter estimation method (DAC-OMA) presents a new approach to the problem, avoiding issues involved in the stabilisation diagram. The presented algorithm is fully automated. It uses deterministic methods to define the interval of estimated parameters, thus reducing the problem to optimisation task which is conducted with dedicated software based on ant colony optimisation algorithm. The combination of deterministic methods restricting parameter intervals and artificial intelligence yields very good results, also for closely spaced modes and significantly varied mode shapes within one measurement point.

Conceptual DFT analysis of the fragility spectra of atoms along the minimum energy reaction coordinate.

PubMed

Ordon, Piotr; Komorowski, Ludwik; Jedrzejewski, Mateusz

2017-10-07

Theoretical justification has been provided to the method for monitoring the sequence of chemical bonds' rearrangement along a reaction path, by tracing the evolution of the diagonal elements of the Hessian matrix. Relations between the divergences of Hellman-Feynman forces and the energy and electron density derivatives have been demonstrated. By the proof presented on the grounds of the conceptual density functional theory formalism, the spectral amplitude observed on the atomic fragility spectra [L. Komorowski et al., Phys. Chem. Chem. Phys. 18, 32658 (2016)] reflects selectively the electron density modifications in bonds of an atom. In fact the spectral peaks for an atom reveal changes of the electron density occurring with bonds creation, breaking, or varying with the reaction progress.

Conceptual DFT analysis of the fragility spectra of atoms along the minimum energy reaction coordinate

NASA Astrophysics Data System (ADS)

Ordon, Piotr; Komorowski, Ludwik; Jedrzejewski, Mateusz

2017-10-01

Theoretical justification has been provided to the method for monitoring the sequence of chemical bonds' rearrangement along a reaction path, by tracing the evolution of the diagonal elements of the Hessian matrix. Relations between the divergences of Hellman-Feynman forces and the energy and electron density derivatives have been demonstrated. By the proof presented on the grounds of the conceptual density functional theory formalism, the spectral amplitude observed on the atomic fragility spectra [L. Komorowski et al., Phys. Chem. Chem. Phys. 18, 32658 (2016)] reflects selectively the electron density modifications in bonds of an atom. In fact the spectral peaks for an atom reveal changes of the electron density occurring with bonds creation, breaking, or varying with the reaction progress.

Pseudo-spectral methodology for a quantitative assessment of the cover of in-stream vegetation in small streams

NASA Astrophysics Data System (ADS)

Hershkovitz, Yaron; Anker, Yaakov; Ben-Dor, Eyal; Schwartz, Guy; Gasith, Avital

2010-05-01

In-stream vegetation is a key ecosystem component in many fluvial ecosystems, having cascading effects on stream conditions and biotic structure. Traditionally, ground-level surveys (e.g. grid and transect analyses) are commonly used for estimating cover of aquatic macrophytes. Nonetheless, this methodological approach is highly time consuming and usually yields information which is practically limited to habitat and sub-reach scales. In contrast, remote-sensing techniques (e.g. satellite imagery and airborne photography), enable collection of large datasets over section, stream and basin scales, in relatively short time and reasonable cost. However, the commonly used spatial high resolution (1m) is often inadequate for examining aquatic vegetation on habitat or sub-reach scales. We examined the utility of a pseudo-spectral methodology, using RGB digital photography for estimating the cover of in-stream vegetation in a small Mediterranean-climate stream. We compared this methodology with that obtained by traditional ground-level grid methodology and with an airborne hyper-spectral remote sensing survey (AISA-ES). The study was conducted along a 2 km section of an intermittent stream (Taninim stream, Israel). When studied, the stream was dominated by patches of watercress (Nasturtium officinale) and mats of filamentous algae (Cladophora glomerata). The extent of vegetation cover at the habitat and section scales (100 and 104 m, respectively) were estimated by the pseudo-spectral methodology, using an airborne Roli camera with a Phase-One P 45 (39 MP) CCD image acquisition unit. The swaths were taken in elevation of about 460 m having a spatial resolution of about 4 cm (NADIR). For measuring vegetation cover at the section scale (104 m) we also used a 'push-broom' AISA-ES hyper-spectral swath having a sensor configuration of 182 bands (350-2500 nm) at elevation of ca. 1,200 m (i.e. spatial resolution of ca. 1 m). Simultaneously, with every swath we used an Analytical Spectral Device (ASD) to measure hyper-spectral signatures (2150 bands configuration; 350-2500 nm) of selected ground-level targets (located by GPS) of soil, water; vegetation (common reed, watercress, filamentous algae) and standard EVA foam colored sheets (red, green, blue, black and white). Processing and analysis of the data were performed over an ITT ENVI platform. The hyper-spectral image underwent radiometric calibration according to the flight and sensor calibration parameters on CALIGEO platform and the raw DN scale was converted into radiance scale. Ground level visual survey of vegetation cover and height was applied at the habitat scale (100 m) by placing a 1m2 netted grids (10x10cm cells) along 'bank-to-bank' transect (in triplicates). Estimates of plant cover obtained by the pseudo-spectral methodology at the habitat scale were 35-61% for the watercress, 0.4-25% for the filamentous algae and 27-51% for plant-free patches. The respective estimates by ground level visual survey were 26-50, 14-43% and 36-50%. The pseudo-spectral methodology also yielded estimates for the section scale (104 m) of ca. 39% for the watercress, ca. 32% for the filamentous algae and 6% for plant-free patches. The respective estimates obtained by hyper-spectral swath were 38, 26 and 8%. Validation against ground-level measurements proved that pseudo-spectral methodology gives reasonably good estimates of in-stream plant cover. Therefore, this methodology can serve as a substitute for ground level estimates at small stream scales and for the low resolution hyper-spectral methodology at larger scales.

The stationary non-equilibrium plasma of cosmic-ray electrons and positrons

NASA Astrophysics Data System (ADS)

Tomaschitz, Roman

2016-06-01

The statistical properties of the two-component plasma of cosmic-ray electrons and positrons measured by the AMS-02 experiment on the International Space Station and the HESS array of imaging atmospheric Cherenkov telescopes are analyzed. Stationary non-equilibrium distributions defining the relativistic electron-positron plasma are derived semi-empirically by performing spectral fits to the flux data and reconstructing the spectral number densities of the electronic and positronic components in phase space. These distributions are relativistic power-law densities with exponential cutoff, admitting an extensive entropy variable and converging to the Maxwell-Boltzmann or Fermi-Dirac distributions in the non-relativistic limit. Cosmic-ray electrons and positrons constitute a classical (low-density high-temperature) plasma due to the low fugacity in the quantized partition function. The positron fraction is assembled from the flux densities inferred from least-squares fits to the electron and positron spectra and is subjected to test by comparing with the AMS-02 flux ratio measured in the GeV interval. The calculated positron fraction extends to TeV energies, predicting a broad spectral peak at about 1 TeV followed by exponential decay.

X-ray imaging spectroscopic diagnostics on Nike

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Karasik, M.; Serlin, V.; Weaver, J. L.; Oh, J.; Obenschain, S. P.; Ralchenko, Yu.

2017-10-01

Electron temperature and density diagnostics of the laser plasma produced within the focal spot of the NRL's Nike laser are being explored with the help of X-ray imaging spectroscopy. Spectra of He-like and H-like ions were taken by Nike focusing spectrometers in a range of lower (1.8 kev, Si XIV) and higher (6.7 kev, Fe XXV) x-ray energies. Data that were obtained with spatial resolution were translated into the temperature and density as functions of distance from the target. As an example electron density was determined from He-like satellites to Ly-alpha in Si XIV. The dielectronic satellites with intensity ratios that are sensitive to collisional transfer of population between different triplet groups of double-excited states 2l2l' in Si XIII were observed with high spatial and spectral resolution Lineouts taken at different axial distances from the planar Si target show changing spectral shapes due to the different electron densities as determined by supporting non-LTE simulations. These shapes are relatively insensitive to the plasma temperature which was measured using different spectral lines. This work was supported by the US DOE/NNSA.

Spectral estimates of solar radiation intercepted by corn canopies

NASA Technical Reports Server (NTRS)

Bauer, M. E. (Principal Investigator); Daughtry, C. S. T.; Gallo, K. P.

1982-01-01

Reflectance factor data were acquired with a Landsat band radiometer throughout two growing seasons for corn (Zea mays L.) canopies differing in planting dates, populations, and soil types. Agronomic data collected included leaf area index (LAI), biomass, development stage, and final grain yields. The spectral variable, greenness, was associated with 78 percent of the variation in LAI over all treatments. Single observations of LAI or greenness have limited value in predicting corn yields. The proportions of solar radiation intercepted (SRI) by these canopies were estimated using either measured LAI or greenness. Both SRI estimates, when accumulated over the growing season, accounted for approximately 65 percent of the variation in yields. Models which simulated the daily effects of weather and intercepted solar radiation on growth had the highest correlations to grain yields. This concept of estimating intercepted solar radiation using spectral data represents a viable approach for merging spectral and meteorological data for crop yield models.

Passive acoustic measurement of bedload grain size distribution using self-generated noise

NASA Astrophysics Data System (ADS)

Petrut, Teodor; Geay, Thomas; Gervaise, Cédric; Belleudy, Philippe; Zanker, Sebastien

2018-01-01

Monitoring sediment transport processes in rivers is of particular interest to engineers and scientists to assess the stability of rivers and hydraulic structures. Various methods for sediment transport process description were proposed using conventional or surrogate measurement techniques. This paper addresses the topic of the passive acoustic monitoring of bedload transport in rivers and especially the estimation of the bedload grain size distribution from self-generated noise. It discusses the feasibility of linking the acoustic signal spectrum shape to bedload grain sizes involved in elastic impacts with the river bed treated as a massive slab. Bedload grain size distribution is estimated by a regularized algebraic inversion scheme fed with the power spectrum density of river noise estimated from one hydrophone. The inversion methodology relies upon a physical model that predicts the acoustic field generated by the collision between rigid bodies. Here we proposed an analytic model of the acoustic energy spectrum generated by the impacts between a sphere and a slab. The proposed model computes the power spectral density of bedload noise using a linear system of analytic energy spectra weighted by the grain size distribution. The algebraic system of equations is then solved by least square optimization and solution regularization methods. The result of inversion leads directly to the estimation of the bedload grain size distribution. The inversion method was applied to real acoustic data from passive acoustics experiments realized on the Isère River, in France. The inversion of in situ measured spectra reveals good estimations of grain size distribution, fairly close to what was estimated by physical sampling instruments. These results illustrate the potential of the hydrophone technique to be used as a standalone method that could ensure high spatial and temporal resolution measurements for sediment transport in rivers.

Regional comparisons of Vs30 and Spectral Ratio Methods

NASA Astrophysics Data System (ADS)

McNamara, D. E.; Gee, L. S.; Stephenson, W. J.; Odum, J. K.; Williams, R. A.; Hartzell, S.

2013-12-01

Earthquake damage is often increased due to local ground-motion amplification in soft soils and thick basin sediments with factors such as topographic effects and water saturation. Seismic hazard assessments depend on detailed information on local site response and many different methods have been developed to estimate site response. Based on numerous empirical studies, the average shear-wave velocity in the upper 30 m (Vs30) has become the most common means of classifying site conditions and has been adopted in the NEHRP design provisions for new buildings. In general, higher Vs30 values are associated with firm, dense rock and lower levels of ground shaking while lower Vs30 values are associated with softer soils and high site amplification. Vs30 is commonly computed by measuring the time it takes for shear-waves to travel from 30m depth to the surface using either active sources such as explosions or passive ambient noise microtremor sources. Since this approach is limited to locations where active measurements are undertaken, recent methods have sought to approximate Vs30 regionally, such as using topographic slope as a proxy. In this presentation, we compute a standard site response, horizontal-to-vertical spectral ratio (HVSR) using long-term power spectral density statistics of both ambient noise and earthquake signals at permanent and temporary seismic stations. We compare the HVSR results to surface observations of Vs30 and approximations using topographic slope in several different regions including the Eastern United States, St. Louis and the Los Angeles basin. In our comparison of the HVSR results to Vs30, we find that HVSR peak frequency can be used as a proxy for Vs30. Relationships between surface measured Vs30 and HVSR are less scattered than with Vs30 estimated using topographic approximations. In general, higher Vs30 is associated with higher HVSR peak frequency with variations in slope for different regions. We use these regional relationships to estimate NEHRP soil class at over 200 seismic stations in the US.

Relationship of red and photographic infrared spectral radiances to alfalfa biomass, forage water content, percentage canopy cover, and severity of drought stress

NASA Technical Reports Server (NTRS)

Tucker, C. J.; Elgin, J. H., Jr.; Mcmurtrey, J. E., III

1979-01-01

Red and photographic infrared spectral data were collected using a handheld radiometer for two cuttings of alfalfa. Significant linear and non-linear correlation coefficients were found between the spectral variables and plant height, biomass, forage water content, and estimated canopy cover for the earlier alfalfa cutting. The alfalfa of later cutting experienced a period of severe drought stress which limited growth. The spectral variables were found to be highly correlated with the estimated drought scores for this alfalfa cutting.

Understanding How Kurtosis Is Transferred from Input Acceleration to Stress Response and Its Influence on Fatigue Llife

NASA Technical Reports Server (NTRS)

Kihm, Frederic; Rizzi, Stephen A.; Ferguson, Neil S.; Halfpenny, Andrew

2013-01-01

High cycle fatigue of metals typically occurs through long term exposure to time varying loads which, although modest in amplitude, give rise to microscopic cracks that can ultimately propagate to failure. The fatigue life of a component is primarily dependent on the stress amplitude response at critical failure locations. For most vibration tests, it is common to assume a Gaussian distribution of both the input acceleration and stress response. In real life, however, it is common to experience non-Gaussian acceleration input, and this can cause the response to be non-Gaussian. Examples of non-Gaussian loads include road irregularities such as potholes in the automotive world or turbulent boundary layer pressure fluctuations for the aerospace sector or more generally wind, wave or high amplitude acoustic loads. The paper first reviews some of the methods used to generate non-Gaussian excitation signals with a given power spectral density and kurtosis. The kurtosis of the response is examined once the signal is passed through a linear time invariant system. Finally an algorithm is presented that determines the output kurtosis based upon the input kurtosis, the input power spectral density and the frequency response function of the system. The algorithm is validated using numerical simulations. Direct applications of these results include improved fatigue life estimations and a method to accelerate shaker tests by generating high kurtosis, non-Gaussian drive signals.

The Far-Infrared Luminosity Function and Star Formation Rate Density for Dust Obscured Galaxies in the Bootes Field

NASA Astrophysics Data System (ADS)

Calanog, Jae Alyson; Wardlow, J. L.; Fu, H.; Cooray, A. R.; HerMES

2013-01-01

We present the far-Infrared (FIR) luminosity function (LF) and the star-formation rate density (SFRD) for dust-obscured galaxies (DOGs) in the Bootes field at redshift 2. These galaxies are selected by having a large rest frame mid-IR to UV flux density ratio ( > 1000) and are expected to be some of the most luminous and heavily obscured galaxies in the Universe at this epoch. Photometric redshifts for DOGs are estimated from optical and mid-IR data using empirically derived low resolution spectral templates for AGN and galaxies. We use HerMES Herschel-SPIRE data to fit a modified blackbody to calculate the FIR luminosity (LFIR) and dust temperature (Td) for all DOGs individually detected in SPIRE maps. A stacking analyses was implemented to measure a median sub-mm flux of undetected DOGs. We find that DOGs have LIR and Td that are similar with the sub-millimeter galaxy (SMG) population, suggesting these two populations are related. The DOG LF and SFRD at 2 are calculated and compared to SMGs.

Spectral and temperature-dependent infrared emissivity measurements of painted metals for improved temperature estimation during laser damage testing

NASA Astrophysics Data System (ADS)

Baumann, Sean M.; Keenan, Cameron; Marciniak, Michael A.; Perram, Glen P.

2014-10-01

A database of spectral and temperature-dependent emissivities was created for painted Al-alloy laser-damage-testing targets for the purpose of improving the uncertainty to which temperature on the front and back target surfaces may be estimated during laser-damage testing. Previous temperature estimates had been made by fitting an assumed gray-body radiance curve to the calibrated spectral radiance data collected from the back surface using a Telops Imaging Fourier Transform Spectrometer (IFTS). In this work, temperature-dependent spectral emissivity measurements of the samples were made from room temperature to 500 °C using a Surface Optics Corp. SOC-100 Hemispherical Directional Reflectometer (HDR) with Nicolet FTS. Of particular interest was a high-temperature matte-black enamel paint used to coat the rear surfaces of the Al-alloy samples. The paint had been assumed to have a spectrally flat and temperatureinvariant emissivity. However, the data collected using the HDR showed both spectral variation and temperature dependence. The uncertainty in back-surface temperature estimation during laser-damage testing made using the measured emissivities was improved from greater than +10 °C to less than +5 °C for IFTS pixels away from the laser burn-through hole, where temperatures never exceeded those used in the SOC-100 HDR measurements. At beam center, where temperatures exceeded those used in the SOC-100 HDR, uncertainty in temperature estimates grew beyond those made assuming gray-body emissivity. Accurate temperature estimations during laser-damage testing are useful in informing a predictive model for future high-energy-laser weapon applications.

Single-Trial Normalization for Event-Related Spectral Decomposition Reduces Sensitivity to Noisy Trials

PubMed Central

Grandchamp, Romain; Delorme, Arnaud

2011-01-01

In electroencephalography, the classical event-related potential model often proves to be a limited method to study complex brain dynamics. For this reason, spectral techniques adapted from signal processing such as event-related spectral perturbation (ERSP) – and its variant event-related synchronization and event-related desynchronization – have been used over the past 20 years. They represent average spectral changes in response to a stimulus. These spectral methods do not have strong consensus for comparing pre- and post-stimulus activity. When computing ERSP, pre-stimulus baseline removal is usually performed after averaging the spectral estimate of multiple trials. Correcting the baseline of each single-trial prior to averaging spectral estimates is an alternative baseline correction method. However, we show that this method leads to positively skewed post-stimulus ERSP values. We eventually present new single-trial-based ERSP baseline correction methods that perform trial normalization or centering prior to applying classical baseline correction methods. We show that single-trial correction methods minimize the contribution of artifactual data trials with high-amplitude spectral estimates and are robust to outliers when performing statistical inference testing. We then characterize these methods in terms of their time–frequency responses and behavior compared to classical ERSP methods. PMID:21994498

Raman spectral signatures as conformational probes of gas phase flexible molecules

NASA Astrophysics Data System (ADS)

Golan, Amir; Mayorkas, Nitzan; Rosenwaks, Salman; Bar, Ilana

2009-07-01

A novel application of ionization-loss stimulated Raman spectroscopy (ILSRS) for monitoring the spectral features of four conformers of a gas phase flexible molecule is reported. The Raman spectral signatures of four conformers of 2-phenylethylamine are well matched by the results of density functional theory calculations, showing bands uniquely identifying the structures. The measurement of spectral signatures by ILSRS in an extended spectral range, with a conventional laser source, is instrumental in facilitating the unraveling of intra- and intermolecular interactions that are significant in biological structure and activity.

Multi-octave supercontinuum generation from mid-infrared filamentation in a bulk crystal

PubMed Central

Silva, F.; Austin, D.R.; Thai, A.; Baudisch, M.; Hemmer, M.; Faccio, D.; Couairon, A.; Biegert, J.

2012-01-01

In supercontinuum generation, various propagation effects combine to produce a dramatic spectral broadening of intense ultrashort optical pulses. With a host of applications, supercontinuum sources are often required to possess a range of properties such as spectral coverage from the ultraviolet across the visible and into the infrared, shot-to-shot repeatability, high spectral energy density and an absence of complicated pulse splitting. Here we present an all-in-one solution, the first supercontinuum in a bulk homogeneous material extending from 450 nm into the mid-infrared. The spectrum spans 3.3 octaves and carries high spectral energy density (2 pJ nm−1–10 nJ nm−1), and the generation process has high shot-to-shot reproducibility and preserves the carrier-to-envelope phase. Our method, based on filamentation of femtosecond mid-infrared pulses in the anomalous dispersion regime, allows for compact new supercontinuum sources. PMID:22549836

Spectral Estimation Model Construction of Heavy Metals in Mining Reclamation Areas

PubMed Central

Dong, Jihong; Dai, Wenting; Xu, Jiren; Li, Songnian

2016-01-01

The study reported here examined, as the research subject, surface soils in the Liuxin mining area of Xuzhou, and explored the heavy metal content and spectral data by establishing quantitative models with Multivariable Linear Regression (MLR), Generalized Regression Neural Network (GRNN) and Sequential Minimal Optimization for Support Vector Machine (SMO-SVM) methods. The study results are as follows: (1) the estimations of the spectral inversion models established based on MLR, GRNN and SMO-SVM are satisfactory, and the MLR model provides the worst estimation, with R2 of more than 0.46. This result suggests that the stress sensitive bands of heavy metal pollution contain enough effective spectral information; (2) the GRNN model can simulate the data from small samples more effectively than the MLR model, and the R2 between the contents of the five heavy metals estimated by the GRNN model and the measured values are approximately 0.7; (3) the stability and accuracy of the spectral estimation using the SMO-SVM model are obviously better than that of the GRNN and MLR models. Among all five types of heavy metals, the estimation for cadmium (Cd) is the best when using the SMO-SVM model, and its R2 value reaches 0.8628; (4) using the optimal model to invert the Cd content in wheat that are planted on mine reclamation soil, the R2 and RMSE between the measured and the estimated values are 0.6683 and 0.0489, respectively. This result suggests that the method using the SMO-SVM model to estimate the contents of heavy metals in wheat samples is feasible. PMID:27367708

Spectral Estimation Model Construction of Heavy Metals in Mining Reclamation Areas.

PubMed

Dong, Jihong; Dai, Wenting; Xu, Jiren; Li, Songnian

2016-06-28

The study reported here examined, as the research subject, surface soils in the Liuxin mining area of Xuzhou, and explored the heavy metal content and spectral data by establishing quantitative models with Multivariable Linear Regression (MLR), Generalized Regression Neural Network (GRNN) and Sequential Minimal Optimization for Support Vector Machine (SMO-SVM) methods. The study results are as follows: (1) the estimations of the spectral inversion models established based on MLR, GRNN and SMO-SVM are satisfactory, and the MLR model provides the worst estimation, with R² of more than 0.46. This result suggests that the stress sensitive bands of heavy metal pollution contain enough effective spectral information; (2) the GRNN model can simulate the data from small samples more effectively than the MLR model, and the R² between the contents of the five heavy metals estimated by the GRNN model and the measured values are approximately 0.7; (3) the stability and accuracy of the spectral estimation using the SMO-SVM model are obviously better than that of the GRNN and MLR models. Among all five types of heavy metals, the estimation for cadmium (Cd) is the best when using the SMO-SVM model, and its R² value reaches 0.8628; (4) using the optimal model to invert the Cd content in wheat that are planted on mine reclamation soil, the R² and RMSE between the measured and the estimated values are 0.6683 and 0.0489, respectively. This result suggests that the method using the SMO-SVM model to estimate the contents of heavy metals in wheat samples is feasible.

Detecting anthropogenic footprints in sea level rise: the role of complex colored noise

NASA Astrophysics Data System (ADS)

Dangendorf, Sönke; Marcos, Marta; Müller, Alfred; Zorita, Eduardo; Jensen, Jürgen

2015-04-01

While there is scientific consensus that global mean sea level (MSL) is rising since the late 19th century, it remains unclear how much of this rise is due to natural variability or anthropogenic forcing. Uncovering the anthropogenic contribution requires profound knowledge about the persistence of natural MSL variations. This is challenging, since observational time series represent the superposition of various processes with different spectral properties. Here we statistically estimate the upper bounds of naturally forced centennial MSL trends on the basis of two separate components: a slowly varying volumetric (mass and density changes) and a more rapidly changing atmospheric component. Resting on a combination of spectral analyses of tide gauge records, ocean reanalysis data and numerical Monte-Carlo experiments, we find that in records where transient atmospheric processes dominate, the persistence of natural volumetric changes is underestimated. If each component is assessed separately, natural centennial trends are locally up to ~0.5 mm/yr larger than in case of an integrated assessment. This implies that external trends in MSL rise related to anthropogenic forcing might be generally overestimated. By applying our approach to the outputs of a centennial ocean reanalysis (SODA), we estimate maximum natural trends in the order of 1 mm/yr for the global average. This value is larger than previous estimates, but consistent with recent paleo evidence from periods in which the anthropogenic contribution was absent. Comparing our estimate to the observed 20th century MSL rise of 1.7 mm/yr suggests a minimum external contribution of at least 0.7 mm/yr. We conclude that an accurate detection of anthropogenic footprints in MSL rise requires a more careful assessment of the persistence of intrinsic natural variability.

Comparison of Calibration Methods for Tristimulus Colorimeters.

PubMed

Gardner, James L

2007-01-01

Uncertainties in source color measurements with a tristimulus colorimeter are estimated for calibration factors determined, based on a known source spectral distribution or on accurate measurements of the spectral responsivities of the colorimeter channels. Application is to the National Institute of Standards and Technology (NIST) colorimeter and an International Commission on Illumination (CIE) Illuminant A calibration. Detector-based calibration factors generally have lower uncertainties than source-based calibration factors. Uncertainties are also estimated for calculations of spectral mismatch factors. Where both spectral responsivities of the colorimeter channels and the spectral power distributions of the calibration and test sources are known, uncertainties are lowest if the colorimeter calibration factors are recalculated for the test source; this process also avoids correlations between the CIE Source A calibration factors and the spectral mismatch factors.

Comparison of Calibration Methods for Tristimulus Colorimeters

PubMed Central

Gardner, James L.

2007-01-01

Uncertainties in source color measurements with a tristimulus colorimeter are estimated for calibration factors determined, based on a known source spectral distribution or on accurate measurements of the spectral responsivities of the colorimeter channels. Application is to the National Institute of Standards and Technology (NIST) colorimeter and an International Commission on Illumination (CIE) Illuminant A calibration. Detector-based calibration factors generally have lower uncertainties than source-based calibration factors. Uncertainties are also estimated for calculations of spectral mismatch factors. Where both spectral responsivities of the colorimeter channels and the spectral power distributions of the calibration and test sources are known, uncertainties are lowest if the colorimeter calibration factors are recalculated for the test source; this process also avoids correlations between the CIE Source A calibration factors and the spectral mismatch factors. PMID:27110460

Time-Varying Delay Estimation Applied to the Surface Electromyography Signals Using the Parametric Approach

NASA Astrophysics Data System (ADS)

Luu, Gia Thien; Boualem, Abdelbassit; Duy, Tran Trung; Ravier, Philippe; Butteli, Olivier

Muscle Fiber Conduction Velocity (MFCV) can be calculated from the time delay between the surface electromyographic (sEMG) signals recorded by electrodes aligned with the fiber direction. In order to take into account the non-stationarity during the dynamic contraction (the most daily life situation) of the data, the developed methods have to consider that the MFCV changes over time, which induces time-varying delays and the data is non-stationary (change of Power Spectral Density (PSD)). In this paper, the problem of TVD estimation is considered using a parametric method. First, the polynomial model of TVD has been proposed. Then, the TVD model parameters are estimated by using a maximum likelihood estimation (MLE) strategy solved by a deterministic optimization technique (Newton) and stochastic optimization technique, called simulated annealing (SA). The performance of the two techniques is also compared. We also derive two appropriate Cramer-Rao Lower Bounds (CRLB) for the estimated TVD model parameters and for the TVD waveforms. Monte-Carlo simulation results show that the estimation of both the model parameters and the TVD function is unbiased and that the variance obtained is close to the derived CRBs. A comparison with non-parametric approaches of the TVD estimation is also presented and shows the superiority of the method proposed.

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.

Sensitivity of spectral reflectance values to different burn and vegetation ratios: A multi-scale approach applied in a fire affected area

NASA Astrophysics Data System (ADS)

Pleniou, Magdalini; Koutsias, Nikos

2013-05-01

The aim of our study was to explore the spectral properties of fire-scorched (burned) and non fire-scorched (vegetation) areas, as well as areas with different burn/vegetation ratios, using a multisource multiresolution satellite data set. A case study was undertaken following a very destructive wildfire that occurred in Parnitha, Greece, July 2007, for which we acquired satellite images from LANDSAT, ASTER, and IKONOS. Additionally, we created spatially degraded satellite data over a range of coarser resolutions using resampling techniques. The panchromatic (1 m) and multispectral component (4 m) of IKONOS were merged using the Gram-Schmidt spectral sharpening method. This very high-resolution imagery served as the basis to estimate the cover percentage of burned areas, bare land and vegetation at pixel level, by applying the maximum likelihood classification algorithm. Finally, multiple linear regression models were fit to estimate each land-cover fraction as a function of surface reflectance values of the original and the spatially degraded satellite images. The main findings of our research were: (a) the Near Infrared (NIR) and Short-wave Infrared (SWIR) are the most important channels to estimate the percentage of burned area, whereas the NIR and red channels are the most important to estimate the percentage of vegetation in fire-affected areas; (b) when the bi-spectral space consists only of NIR and SWIR, then the NIR ground reflectance value plays a more significant role in estimating the percent of burned areas, and the SWIR appears to be more important in estimating the percent of vegetation; and (c) semi-burned areas comprising 45-55% burned area and 45-55% vegetation are spectrally closer to burned areas in the NIR channel, whereas those areas are spectrally closer to vegetation in the SWIR channel. These findings, at least partially, are attributed to the fact that: (i) completely burned pixels present low variance in the NIR and high variance in the SWIR, whereas the opposite is observed in completely vegetated areas where higher variance is observed in the NIR and lower variance in the SWIR, and (ii) bare land modifies the spectral signal of burned areas more than the spectral signal of vegetated areas in the NIR, while the opposite is observed in SWIR region of the spectrum where the bare land modifies the spectral signal of vegetation more than the burned areas because the bare land and the vegetation are spectrally more similar in the NIR, and the bare land and burned areas are spectrally more similar in the SWIR.

High Frequency Radio Observations of the Reactivated Magnetar PSR J1622-4950

NASA Astrophysics Data System (ADS)

Pearlman, Aaron B.; Majid, Walid A.; Prince, Thomas A.; Horiuchi, Shinji; Kocz, Jonathon; Lazio, T. J. W.; Naudet, Charles J.

2017-07-01

Radio emission from the magnetar PSR J1622-4950 was recently reported to have resumed (Camilo et al., ATel #10346). We have carried out Target of Opportunity (ToO) radio observations of PSR J1622-4950 at S-band (2.3 GHz) and X-band (8.4 GHz) using the 70-m diameter Deep Space Network (DSN) radio dish (DSS-43) in Canberra, Australia. We report on our single polarization mode observations of PSR J1622-4950 spanning 5 hours on 23 May 2017 starting at 16:03:32 UTC. Pulsations were detected at a period of 4.327308(1) s. We measure a mean flux density of 3.8(8)/0.41(8) mJy at S/X-band, from which we derive a spectral index of -1.7(2). We note that PSR J1622-4950's spectral behavior is now consistent with the majority of pulsars, which have a mean spectral index of -1.8(2) (Maron et al. (2000)). The result by Maron et al. (2000) is used here because they included more high frequency pulsar spectra than other studies to characterize the underlying spectral index distribution over a wide frequency range. The mean flux density at S-band has now increased by an order of magnitude compared to previous flux density measurements by Scholz et al. (2017) during the magnetar's quiescent state. Furthermore, the spectral index has steepened compared to a nearly flat spectral index from flux density measurements between 1.4 and 24 GHz prior to the disappearance of the radio emission (Levin et al. (2010); Keith et al. (2011); Levin et al. (2012); Anderson et al. (2012); Scholz et al. (2017)). We are continuing to monitor changes in PSR J1622-4950's radio spectrum at both S-band and X-band. We thank the DSN (Deep Space Network) and Canberra Deep Space Communication Complex (CDSCC) teams for scheduling these observations.

Quantifying uncertainty in soot volume fraction estimates using Bayesian inference of auto-correlated laser-induced incandescence measurements

NASA Astrophysics Data System (ADS)

Hadwin, Paul J.; Sipkens, T. A.; Thomson, K. A.; Liu, F.; Daun, K. J.

2016-01-01

Auto-correlated laser-induced incandescence (AC-LII) infers the soot volume fraction (SVF) of soot particles by comparing the spectral incandescence from laser-energized particles to the pyrometrically inferred peak soot temperature. This calculation requires detailed knowledge of model parameters such as the absorption function of soot, which may vary with combustion chemistry, soot age, and the internal structure of the soot. This work presents a Bayesian methodology to quantify such uncertainties. This technique treats the additional "nuisance" model parameters, including the soot absorption function, as stochastic variables and incorporates the current state of knowledge of these parameters into the inference process through maximum entropy priors. While standard AC-LII analysis provides a point estimate of the SVF, Bayesian techniques infer the posterior probability density, which will allow scientists and engineers to better assess the reliability of AC-LII inferred SVFs in the context of environmental regulations and competing diagnostics.

Laser ablated copper plasmas in liquid and gas ambient

NASA Astrophysics Data System (ADS)

Kumar, Bhupesh; Thareja, Raj K.

2013-05-01

The dynamics of copper ablated plasma plumes generated using laser ablation of copper targets in both liquid (de-ionized water) and gas (air) ambients is reported. Using time and space resolved visible emission spectroscopy (450-650 nm), the plasma plumes parameters are investigated. The electron density (ne) determined using Stark broadening of the Cu I (3d104d1 2D3/2-3d104p1 2P3/2 at 521.8 nm) line is estimated and compared for both plasma plumes. The electron temperature (Te) was estimated using the relative line emission intensities of the neutral copper transitions. Field emission scanning electron microscopy and energy dispersive x-ray spectral analysis of the ablated copper surface indicated abundance of spherical nanoparticles in liquid while those in air are amalgamates of irregular shapes. The nanoparticles suspended in the confining liquid form aggregates and exhibit a surface plasmon resonance at ˜590 nm.

Leaf and canopy reflectance spectrometry applied to the estimation of angular leaf spot disease severity of common bean crops

PubMed Central

Martínez-Martínez, Víctor; Machado, Marley L.; Pinto, Francisco A. C.

2018-01-01

This study is aimed at (i) estimating the angular leaf spot (ALS) disease severity in common beans crops in Brazil, caused by the fungus Pseudocercospora griseola, employing leaf and canopy spectral reflectance data, (ii) evaluating the informative spectral regions in the detection, and (iii) comparing the estimation accuracy when the reflectance or the first derivative reflectance (FDR) is employed. Three data sets of useful spectral reflectance measurements in the 440 to 850 nm range were employed; measurements were taken over the leaves and canopy of bean crops with different levels of disease. A system based in Principal Component Analysis (PCA) and Artificial Neural Networks (ANN) was developed to estimate the disease severity from leaf and canopy hyperspectral reflectance spectra. Levels of disease to be taken as true reference were determined from the proportion of the total leaf surface covered by necrotic lesions on RGB images. When estimating ALS disease severity in bean crops by using hyperspectral reflectance spectrometry, this study suggests that (i) successful estimations with coefficients of determination up to 0.87 can be achieved if the spectra is acquired by the spectroradiometer in contact with the leaves, (ii) unsuccessful estimations are obtained when the spectra are acquired by the spectroradiometer from one or more meters above the crop, (iii) the red to near-infrared spectral region (630–850 nm) offers the same precision in the estimation as the blue to near-infrared spectral region (440–850), and (iv) neither significant improvements nor significant detriments are achieved when the input data to the estimation processing system are the FDR spectra, instead of the reflectance spectra. PMID:29698420

Spectral Estimation Techniques for time series with Long Gaps: Applications to Paleomagnetism and Geomagnetic Depth Sounding

NASA Astrophysics Data System (ADS)

Smith-Boughner, Lindsay

Many Earth systems cannot be studied directly. One cannot measure the velocities of convecting fluid in the Earth's core but can measure the magnetic field generated by these motions on the surface. Examining how the magnetic field changes over long periods of time, using power spectral density estimation provides insight into the dynamics driving the system. The changes in the magnetic field can also be used to study Earth properties - variations in magnetic fields outside of Earth like the ring-current induce currents to flow in the Earth, generating magnetic fields. Estimating the transfer function between the external changes and the induced response characterizes the electromagnetic response of the Earth. From this response inferences can be made about the electrical conductivity of the Earth. However, these types of time series, and many others have long breaks in the record with no samples available and limit the analysis. Standard methods require interpolation or section averaging, with associated problems of introducing bias or reducing the frequency resolution. Extending the methods of Fodor and Stark (2000), who adapt a set of orthogonal multi-tapers to compensate for breaks in sampling- an algorithm and software package for applying these techniques is developed. Methods of empirically estimating the average transfer function of a set of tapers and confidence intervals are also tested. These methods are extended for cross-spectral, coherence and transfer function estimation in the presence of noise. With these methods, new analysis of a highly interrupted ocean sediment core from the Oligocene (Hartl et al., 1993) reveals a quasi-periodic signal in the calibrated paleointensity time series at 2.5 cpMy. The power in the magnetic field during this period appears to be dominated by reversal rate processes with less overall power than the early Oligocene. Previous analysis of the early Oligocene by Constable et al. (1998) detected a signal near 8 cpMy. These results suggest that a strong magnetic field inhibits reversals and has more variability in shorter term field changes. Using over 9 years of data from the CHAMP low-Earth orbiting magnetic satellite and the techniques developed here, more robust estimates of the electromagnetic response of the Earth can be made. The tapers adapted for gaps provide flexibility to study the effects of local time, storm conditions on Earth's 1-D electromagnetic response as well as providing robust estimates of the C-response at longer periods than previous satellite studies.

QEEG Spectral and Coherence Assessment of Autistic Children in Three Different Experimental Conditions

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…

Spectrotemporal modulation sensitivity for hearing-impaired listeners: Dependence on carrier center frequency and the relationship to speech intelligibility

PubMed Central

Mehraei, Golbarg; Gallun, Frederick J.; Leek, Marjorie R.; Bernstein, Joshua G. W.

2014-01-01

Poor speech understanding in noise by hearing-impaired (HI) listeners is only partly explained by elevated audiometric thresholds. Suprathreshold-processing impairments such as reduced temporal or spectral resolution or temporal fine-structure (TFS) processing ability might also contribute. Although speech contains dynamic combinations of temporal and spectral modulation and TFS content, these capabilities are often treated separately. Modulation-depth detection thresholds for spectrotemporal modulation (STM) applied to octave-band noise were measured for normal-hearing and HI listeners as a function of temporal modulation rate (4–32 Hz), spectral ripple density [0.5–4 cycles/octave (c/o)] and carrier center frequency (500–4000 Hz). STM sensitivity was worse than normal for HI listeners only for a low-frequency carrier (1000 Hz) at low temporal modulation rates (4–12 Hz) and a spectral ripple density of 2 c/o, and for a high-frequency carrier (4000 Hz) at a high spectral ripple density (4 c/o). STM sensitivity for the 4-Hz, 4-c/o condition for a 4000-Hz carrier and for the 4-Hz, 2-c/o condition for a 1000-Hz carrier were correlated with speech-recognition performance in noise after partialling out the audiogram-based speech-intelligibility index. Poor speech-reception and STM-detection performance for HI listeners may be related to a combination of reduced frequency selectivity and a TFS-processing deficit limiting the ability to track spectral-peak movements. PMID:24993215

Determining the von Mises stress power spectral density for frequency domain fatigue analysis including out-of-phase stress components

NASA Astrophysics Data System (ADS)

Bonte, M. H. A.; de Boer, A.; Liebregts, R.

2007-04-01

This paper provides a new formula to take into account phase differences in the determination of an equivalent von Mises stress power spectral density (PSD) from multiple random inputs. The obtained von Mises PSD can subsequently be used for fatigue analysis. The formula was derived for use in the commercial vehicle business and was implemented in combination with Finite Element software to predict and analyse fatigue failure in the frequency domain.

Dynamics of a spin-boson model with structured spectral density

NASA Astrophysics Data System (ADS)

Kurt, Arzu; Eryigit, Resul

2018-05-01

We report the results of a study of the dynamics of a two-state system coupled to an environment with peaked spectral density. An exact analytical expression for the bath correlation function is obtained. Validity range of various approximations to the correlation function for calculating the population difference of the system is discussed as function of tunneling splitting, oscillator frequency, coupling constant, damping rate and the temperature of the bath. An exact expression for the population difference, for a limited range of parameters, is derived.

Similar Spectral Power Densities Within the Schumann Resonance and a Large Population of Quantitative Electroencephalographic Profiles: Supportive Evidence for Koenig and Pobachenko

PubMed Central

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

Similar Spectral Power Densities Within the Schumann Resonance and a Large Population of Quantitative Electroencephalographic Profiles: Supportive Evidence for Koenig and Pobachenko.

PubMed

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.

Height Dependence of Plasma Properties of a Dark Lane and a Cool Loop in a Solar Limb Active Region Observed by Hinode/EIS

NASA Astrophysics Data System (ADS)

Lee, K.; Imada, S.; Moon, Y.; Lee, J.

2013-12-01

We investigate spectral properties of a cool loop and a dark lane over a limb active region on 2007 March 14 by the Hinode/EUV Imaging Spectrometer. The cool loop is clearly seen in the spectral lines formed at the transition region temperature. The dark lane is characterized by an elongated faint structure in coronal spectral lines and rooted on a bright point. We determine their electron densities, Doppler velocities, and non-thermal velocities with height over the limb. We derived electron densities using the density sensitive line pairs of Mg VII, Si X, Fe XII, Fe XIII and Fe XIV spectra. Under the hydrostatic equilibrium and isothermal assumption, we determine their temperatures from the density scale height. Comparing the scale height temperatures to the peak formation temperatures of the spectral lines, we note that the scale height temperature of the cool loop is consistent with a peak formation temperature of the Fe XII and the scale height temperatures of the dark lane from each spectral lines are much lower than their peak formation temperatures. The non-thermal velocity in the cool loop slightly decreases along the loop while that in the dark lane sharply falls off with height. The variation of non-thermal velocity with height in the cool loop and the dark lane is contrast to that in off-limb polar coronal holes which are considered as source of the solar wind. Such a decrease in the non-thermal velocity may be explained by wave damping near the solar surface or turbulence due to magnetic reconnection near the bright point.

Coupling BCI and cortical stimulation for brain-state-dependent stimulation: methods for spectral estimation in the presence of stimulation after-effects

PubMed Central

Walter, Armin; Murguialday, Ander R.; Rosenstiel, Wolfgang; Birbaumer, Niels; Bogdan, Martin

2012-01-01

Brain-state-dependent stimulation (BSDS) combines brain-computer interfaces (BCIs) and cortical stimulation into one paradigm that allows the online decoding for example of movement intention from brain signals while simultaneously applying stimulation. If the BCI decoding is performed by spectral features, stimulation after-effects such as artefacts and evoked activity present a challenge for a successful implementation of BSDS because they can impair the detection of targeted brain states. Therefore, efficient and robust methods are needed to minimize the influence of the stimulation-induced effects on spectral estimation without violating the real-time constraints of the BCI. In this work, we compared four methods for spectral estimation with autoregressive (AR) models in the presence of pulsed cortical stimulation. Using combined EEG-TMS (electroencephalography-transcranial magnetic stimulation) as well as combined electrocorticography (ECoG) and epidural electrical stimulation, three patients performed a motor task using a sensorimotor-rhythm BCI. Three stimulation paradigms were varied between sessions: (1) no stimulation, (2) single stimulation pulses applied independently (open-loop), or (3) coupled to the BCI output (closed-loop) such that stimulation was given only while an intention to move was detected using neural data. We found that removing the stimulation after-effects by linear interpolation can introduce a bias in the estimation of the spectral power of the sensorimotor rhythm, leading to an overestimation of decoding performance in the closed-loop setting. We propose the use of the Burg algorithm for segmented data to deal with stimulation after-effects. This work shows that the combination of BCIs controlled with spectral features and cortical stimulation in a closed-loop fashion is possible when the influence of stimulation after-effects on spectral estimation is minimized. PMID:23162436

Broadband radio jet emission and variability of γ-ray blazars

NASA Astrophysics Data System (ADS)

Nestoras, Ioannis

2015-07-01

AGN (Active Galactic Nuclei) and in particular their subclass blazars, are among the most energetic objects observed in the universe, featuring extreme phenomenological characteristics such as rapid broadband flux density and polarization variability, fast super--luminal motion, high degree of polarization and a broadband, double-humped spectral energy distribution (SED). The details of the emission processes and violent variability of blazars are still poorly understood. Variability studies give important clues about the size, structure, physics and dynamics of the emitting region making AGN/blazar monitoring programs of uttermost importance in providing the necessary constraints for understanding the origin of energy production. In this framework the F-gamma program was initiated, monitoring monthly 60 fermi detected AGN/blazars at 12 frequencies between 2.6 and 345GHz since 2007. For the thesis in hand observations and data analysis were performed within the realms of the F-gamma program, using the Effelsberg (EB) 100m and Pico Veleta (PV) 30m telescopes at 10 frequency bands ranging from 2.64 to 142GHz. The cm to short-mm variability/spectral characteristics are monitored for a sample of 59 sources for a period of five years enabling for the first time a detailed study of the observed flaring activity in both the light curve and spectral domains for such a large number of sources and such high cadence. Also the observing systems and methods are introduced as well as the data reduction techniques. The thesis at hand is structured as follows: Chapter 3 presents the reduction methods and post measurement corrections applied to the data such as pointing offsets, gain--elevation and sensitivity corrections as well as specific corrections applied for each of the Effelsberg and Pico Veleta observing systems respectively. Chapter 4 presents the analysis tools and methods that were used such as: variability characteristics, flare amplitudes with a new method for estimating the intrinsic standard deviation, flare time scales using Structure Function analysis, spectral indices and spectral peak estimations. Chapter 5 presents the results of the analysis performed upon the five year light curves. The significance of variability through a x^2 test is estimated as well as the flare amplitudes using the intrinsic variability of the light curves along with a new proposed k--index. The introduction of the k--index enables the characterization of the observed variability amplitudes across frequency, thus permitting us to limit the parameter space of various physical models. Also flare time scales, brightness temperatures and Doppler factors are reported. Chapter 6 presents the corresponding analysis in the spectral domain, including results for spectral indices and an S_max - v_max analysis. By determining the spectral peak of every spectra for a selected number of sources, it is possible to track the evolution of the flaring activity in the S_max - v_max plane, enabling us to discriminate between different underlying physical mechanisms that are in action. Finally Chapter 7 includes the overall discussion and a summary of results obtained.

Planck intermediate results. VII. Statistical properties of infrared and radio extragalactic sources from the Planck Early Release Compact Source Catalogue at frequencies between 100 and 857 GHz

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Argüeso, F.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bethermin, M.; Bhatia, R.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Cabella, P.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Chamballu, A.; Chary, R.-R.; Chen, X.; Chiang, L.-Y.; Christensen, P. R.; Clements, D. L.; Colafrancesco, S.; Colombi, S.; Colombo, L. P. L.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davis, R. J.; de Bernardis, P.; de Gasperis, G.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Fosalba, P.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Harrison, D.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Jaffe, T. R.; Jaffe, A. H.; Jagemann, T.; Jones, W. C.; Juvela, M.; Keihänen, E.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurinsky, N.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lawrence, C. R.; Leonardi, R.; Lilje, P. B.; López-Caniego, M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Mazzotta, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Mitra, S.; Miville-Deschènes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sajina, A.; Sandri, M.; Savini, G.; Scott, D.; Smoot, G. F.; Starck, J.-L.; Sudiwala, R.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Türler, M.; Valenziano, L.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; White, M.; Yvon, D.; Zacchei, A.; Zonca, A.

2013-02-01

We make use of the Planck all-sky survey to derive number counts and spectral indices of extragalactic sources - infrared and radio sources - from the Planck Early Release Compact Source Catalogue (ERCSC) at 100 to 857 GHz (3 mm to 350 μm). Three zones (deep, medium and shallow) of approximately homogeneous coverage are used to permit a clean and controlled correction for incompleteness, which was explicitly not done for the ERCSC, as it was aimed at providing lists of sources to be followed up. Our sample, prior to the 80% completeness cut, contains between 217 sources at 100 GHz and 1058 sources at 857 GHz over about 12 800 to 16 550 deg2 (31 to 40% of the sky). After the 80% completeness cut, between 122 and 452 and sources remain, with flux densities above 0.3 and 1.9 Jy at 100 and 857 GHz. The sample so defined can be used for statistical analysis. Using the multi-frequency coverage of the Planck High Frequency Instrument, all the sources have been classified as either dust-dominated (infrared galaxies) or synchrotron-dominated (radio galaxies) on the basis of their spectral energy distributions (SED). Our sample is thus complete, flux-limited and color-selected to differentiate between the two populations. We find an approximately equal number of synchrotron and dusty sources between 217 and 353 GHz; at 353 GHz or higher (or 217 GHz and lower) frequencies, the number is dominated by dusty (synchrotron) sources, as expected. For most of the sources, the spectral indices are also derived. We provide for the first time counts of bright sources from 353 to 857 GHz and the contributions from dusty and synchrotron sources at all HFI frequencies in the key spectral range where these spectra are crossing. The observed counts are in the Euclidean regime. The number counts are compared to previously published data (from earlier Planck results, Herschel, BLAST, SCUBA, LABOCA, SPT, and ACT) and models taking into account both radio or infrared galaxies, and covering a large range of flux densities. We derive the multi-frequency Euclidean level - the plateau in the normalised differential counts at high flux-density - and compare it to WMAP, Spitzer and IRAS results. The submillimetre number counts are not well reproduced by current evolution models of dusty galaxies, whereas the millimetre part appears reasonably well fitted by the most recent model for synchrotron-dominated sources. Finally we provide estimates of the local luminosity density of dusty galaxies, providing the first such measurements at 545 and 857 GHz. Appendices are available in electronic form at http://www.aanda.orgCorresponding author: herve.dole@ias.u-psud.fr

Numerical investigation of the spreading of self-excited stratified jets

NASA Technical Reports Server (NTRS)

Batcho, P. F.; Karniadakis, G. E.; Orszag, S. A.

1990-01-01

The structure and evolution of self-excited subsonic periodic arrays of jets of constant and variable density are studied using spectral-element direct numerical simulations. The governing equation of motion is presented, and a method based on spectral element discretizations appropriate for simulating arbitrarily complex geometry jets and large density variations for subsonic flows is developed. Variable density fields are found to be more unstable than the corresponding uniform density fields with much higher rms values; as a result, their spreading is also considerably larger. There is a dramatic increase in spreading after a few pairings occur. Findings presented for low and high side-momentum flux reveal a shifting of the origin of instability from the near-field to the far-field, respectively, and suggest possible routes of stabilization.

Quantile regression applied to spectral distance decay

USGS Publications Warehouse

Rocchini, D.; Cade, B.S.

2008-01-01

Remotely sensed imagery has long been recognized as a powerful support for characterizing and estimating biodiversity. Spectral distance among sites has proven to be a powerful approach for detecting species composition variability. Regression analysis of species similarity versus spectral distance allows us to quantitatively estimate the amount of turnover in species composition with respect to spectral and ecological variability. In classical regression analysis, the residual sum of squares is minimized for the mean of the dependent variable distribution. However, many ecological data sets are characterized by a high number of zeroes that add noise to the regression model. Quantile regressions can be used to evaluate trend in the upper quantiles rather than a mean trend across the whole distribution of the dependent variable. In this letter, we used ordinary least squares (OLS) and quantile regressions to estimate the decay of species similarity versus spectral distance. The achieved decay rates were statistically nonzero (p < 0.01), considering both OLS and quantile regressions. Nonetheless, the OLS regression estimate of the mean decay rate was only half the decay rate indicated by the upper quantiles. Moreover, the intercept value, representing the similarity reached when the spectral distance approaches zero, was very low compared with the intercepts of the upper quantiles, which detected high species similarity when habitats are more similar. In this letter, we demonstrated the power of using quantile regressions applied to spectral distance decay to reveal species diversity patterns otherwise lost or underestimated by OLS regression. ?? 2008 IEEE.

Spectral distance decay: Assessing species beta-diversity by quantile regression

USGS Publications Warehouse

Rocchinl, D.; Nagendra, H.; Ghate, R.; Cade, B.S.

2009-01-01

Remotely sensed data represents key information for characterizing and estimating biodiversity. Spectral distance among sites has proven to be a powerful approach for detecting species composition variability. Regression analysis of species similarity versus spectral distance may allow us to quantitatively estimate how beta-diversity in species changes with respect to spectral and ecological variability. In classical regression analysis, the residual sum of squares is minimized for the mean of the dependent variable distribution. However, many ecological datasets are characterized by a high number of zeroes that can add noise to the regression model. Quantile regression can be used to evaluate trend in the upper quantiles rather than a mean trend across the whole distribution of the dependent variable. In this paper, we used ordinary least square (ols) and quantile regression to estimate the decay of species similarity versus spectral distance. The achieved decay rates were statistically nonzero (p < 0.05) considering both ols and quantile regression. Nonetheless, ols regression estimate of mean decay rate was only half the decay rate indicated by the upper quantiles. Moreover, the intercept value, representing the similarity reached when spectral distance approaches zero, was very low compared with the intercepts of upper quantiles, which detected high species similarity when habitats are more similar. In this paper we demonstrated the power of using quantile regressions applied to spectral distance decay in order to reveal species diversity patterns otherwise lost or underestimated by ordinary least square regression. ?? 2009 American Society for Photogrammetry and Remote Sensing.

Constrained signal reconstruction from wavelet transform coefficients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brislawn, C.M.

1991-12-31

A new method is introduced for reconstructing a signal from an incomplete sampling of its Discrete Wavelet Transform (DWT). The algorithm yields a minimum-norm estimate satisfying a priori upper and lower bounds on the signal. The method is based on a finite-dimensional representation theory for minimum-norm estimates of bounded signals developed by R.E. Cole. Cole`s work has its origins in earlier techniques of maximum-entropy spectral estimation due to Lang and McClellan, which were adapted by Steinhardt, Goodrich and Roberts for minimum-norm spectral estimation. Cole`s extension of their work provides a representation for minimum-norm estimates of a class of generalized transformsmore » in terms of general correlation data (not just DFT`s of autocorrelation lags, as in spectral estimation). One virtue of this great generality is that it includes the inverse DWT. 20 refs.« less

Preliminary evaluation of spectral, normal and meteorological crop stage estimation approaches

NASA Technical Reports Server (NTRS)

Cate, R. B.; Artley, J. A.; Doraiswamy, P. C.; Hodges, T.; Kinsler, M. C.; Phinney, D. E.; Sestak, M. L. (Principal Investigator)

1980-01-01

Several of the projects in the AgRISTARS program require crop phenology information, including classification, acreage and yield estimation, and detection of episodal events. This study evaluates several crop calendar estimation techniques for their potential use in the program. The techniques, although generic in approach, were developed and tested on spring wheat data collected in 1978. There are three basic approaches to crop stage estimation: historical averages for an area (normal crop calendars), agrometeorological modeling of known crop-weather relationships agrometeorological (agromet) crop calendars, and interpretation of spectral signatures (spectral crop calendars). In all, 10 combinations of planting and biostage estimation models were evaluated. Dates of stage occurrence are estimated with biases between -4 and +4 days while root mean square errors range from 10 to 15 days. Results are inconclusive as to the superiority of any of the models and further evaluation of the models with the 1979 data set is recommended.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hudgins, L.H.

After a brief review of the elementary properties of Fourier Transforms, the Wavelet Transform is defined in Part I. Basic results are given for admissable wavelets. The Multiresolution Analysis, or MRA (a mathematical structure which unifies a large class of wavelets with Quadrature Mirror Filters) is then introduced. Some fundamental aspects of wavelet design are then explored. The Discrete Wavelet Transform is discussed and, in the context of an MRA, is seen to supply a Fast Wavelet Transform which competes with the Fast Fourier Transform for efficiency. In Part II, the Wavelet Transform is developed in terms of the scalemore » number variable s instead of the scale length variable a where a = 1/s. Basic results such as the admissibility condition, conservation of energy, and the reconstruction theorem are proven in this context. After reviewing some motivation for the usual Fourier power spectrum, a definition is given for the wavelet power spectrum. This `spectral density` is then intepreted in the context of spectral estimation theory. Parseval`s theorem for Wavelets then leads naturally to the Wavelet Cross Spectrum, Wavelet Cospectrum, and Wavelet Quadrature Spectrum. Wavelet Transforms are then applied in Part III to the analysis of atmospheric turbulence. Data collected over the ocean is examined in the wavelet transform domain for underlying structure. A brief overview of atmospheric turbulence is provided. Then the overall method of applying Wavelet Transform techniques to time series data is described. A trace study is included, showing some of the aspects of choosing the computational algorithm, and selection of a specific analyzing wavelet. A model for generating synthetic turbulence data is developed, and seen to yield useful results in comparing with real data for structural transitions. Results from the theory of Wavelet Spectral Estimation and Wavelength Cross-Transforms are applied to studying the momentum transport and the heat flux.« less

Probing the Physical Properties of High Redshift Optically Obscured Galaxies in the Bootes NOAO Deep Wide Field Survey using the Infrared Spectrograph on Spitzer

NASA Astrophysics Data System (ADS)

Higdon, S. J. U.; Weedman, D.; Higdon, J. L.; Houck, J. R.; Soifer, B. T.; Armus, L.; Charmandaris, V.; Herter, T. L.; Brandl, B. R.; Brown, M. J. I.; Dey, A.; Jannuzi, B.; Le Floc'h, E.; Rieke, M.

2004-12-01

We have surveyed a field covering 8.4 degrees2 within the NOAO Deep Wide Field Survey region in Boötes with the Multiband Imaging Photometer on the Spitzer Space Telescope to a limiting 24 um flux density of 0.3 mJy, identifying ˜ 22,000 point sources. Thirty one sources from this survey with F(24 um) > 0.75 mJy , which are optically ``invisible'' (R > 26) or very faint (I > 24) have been observed with the low-resolution modules of the Infrared Spectrograph on SST. The spectra were extracted using the IRS SMART spectral analysis package in order to optimize their signal to noise. A suite of mid-IR spectral templates of well known galaxies, observed as part of the IRS GTO program, is used to perform formal fits to the spectral energy distribution of the Boötes sources. These fits enable us to measure their redshift, to calculate the depth of the 9.7 um silicate feature along with the strength of 7.7 um PAH, as well as to estimate their bolometric luminosities. We compare the mid-IR slope, the measured PAH luminosity, and the optical depth of these sources with those of galaxies in the local Universe. As a result we are able to estimate the contribution of a dust enshrouded active nucleus to the mid-IR and bolometric luminosity of these systems. This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through Contract Number 1257184 issued by JPL/Caltech.

Investigation of spectral analysis techniques for randomly sampled velocimetry data

NASA Technical Reports Server (NTRS)

Sree, Dave

1993-01-01

It is well known that velocimetry (LV) generates individual realization velocity data that are randomly or unevenly sampled in time. Spectral analysis of such data to obtain the turbulence spectra, and hence turbulence scales information, requires special techniques. The 'slotting' technique of Mayo et al, also described by Roberts and Ajmani, and the 'Direct Transform' method of Gaster and Roberts are well known in the LV community. The slotting technique is faster than the direct transform method in computation. There are practical limitations, however, as to how a high frequency and accurate estimate can be made for a given mean sampling rate. These high frequency estimates are important in obtaining the microscale information of turbulence structure. It was found from previous studies that reliable spectral estimates can be made up to about the mean sampling frequency (mean data rate) or less. If the data were evenly samples, the frequency range would be half the sampling frequency (i.e. up to Nyquist frequency); otherwise, aliasing problem would occur. The mean data rate and the sample size (total number of points) basically limit the frequency range. Also, there are large variabilities or errors associated with the high frequency estimates from randomly sampled signals. Roberts and Ajmani proposed certain pre-filtering techniques to reduce these variabilities, but at the cost of low frequency estimates. The prefiltering acts as a high-pass filter. Further, Shapiro and Silverman showed theoretically that, for Poisson sampled signals, it is possible to obtain alias-free spectral estimates far beyond the mean sampling frequency. But the question is, how far? During his tenure under 1993 NASA-ASEE Summer Faculty Fellowship Program, the author investigated from his studies on the spectral analysis techniques for randomly sampled signals that the spectral estimates can be enhanced or improved up to about 4-5 times the mean sampling frequency by using a suitable prefiltering technique. But, this increased bandwidth comes at the cost of the lower frequency estimates. The studies further showed that large data sets of the order of 100,000 points, or more, high data rates, and Poisson sampling are very crucial for obtaining reliable spectral estimates from randomly sampled data, such as LV data. Some of the results of the current study are presented.

Quantitative methods and detection techniques in hyperspectral imaging involving medical and other applications

NASA Astrophysics Data System (ADS)

Roy, Ankita

2007-12-01

This research using Hyperspectral imaging involves recognizing targets through spatial and spectral matching and spectral un-mixing of data ranging from remote sensing to medical imaging kernels for clinical studies based on Hyperspectral data-sets generated using the VFTHSI [Visible Fourier Transform Hyperspectral Imager], whose high resolution Si detector makes the analysis achievable. The research may be broadly classified into (I) A Physically Motivated Correlation Formalism (PMCF), which places both spatial and spectral data on an equivalent mathematical footing in the context of a specific Kernel and (II) An application in RF plasma specie detection during carbon nanotube growing process. (III) Hyperspectral analysis for assessing density and distribution of retinopathies like age related macular degeneration (ARMD) and error estimation enabling the early recognition of ARMD, which is treated as an ill-conditioned inverse imaging problem. The broad statistical scopes of this research are two fold-target recognition problems and spectral unmixing problems. All processes involve experimental and computational analysis of Hyperspectral data sets is presented, which is based on the principle of a Sagnac Interferometer, calibrated to obtain high SNR levels. PMCF computes spectral/spatial/cross moments and answers the question of how optimally the entire hypercube should be sampled and finds how many spatial-spectral pixels are required precisely for a particular target recognition. Spectral analysis of RF plasma radicals, typically Methane plasma and Argon plasma using VFTHSI has enabled better process monitoring during growth of vertically aligned multi-walled carbon nanotubes by instant registration of the chemical composition or density changes temporally, which is key since a significant correlation can be found between plasma state and structural properties. A vital focus of this dissertation is towards medical Hyperspectral imaging applied to retinopathies like age related macular degeneration targets taken with a Fundus imager, which is akin to the VFTHSI. Detection of the constituent components in the diseased hyper-pigmentation area is also computed. The target or reflectance matrix is treated as a highly ill-conditioned spectral un-mixing problem, to which methodologies like inverse techniques, principal component analysis (PCA) and receiver operating curves (ROC) for precise spectral recognition of infected area. The region containing ARMD was easily distinguishable from the spectral mesh plots over the entire band-pass area. Once the location was detected the PMCF coefficients were calculated by cross correlating a target of normal oxygenated retina with the deoxygenated one. The ROCs generated using PMCF shows 30% higher detection probability with improved accuracy than ROCs based on Spectral Angle Mapper (SAM). By spectral unmixing methods, the important endmembers/carotenoids of the MD pigment were found to be Xanthophyl and lutein, while beta-carotene which showed a negative correlation in the unconstrained inverse problem is a supplement given to ARMD patients to prevent the disease and does not occur in the eye. Literature also shows degeneration of meso-zeaxanthin. Ophthalmologists may assert the presence of ARMD and commence the diagnosis process if the Xanthophyl pigment have degenerated 89.9%, while the lutein has decayed almost 80%, as found deduced computationally. This piece of current research takes it to the next level of precise investigation in the continuing process of improved clinical findings by correlating the microanatomy of the diseased fovea and shows promise of an early detection of this disease.

Time domain simulation of the response of geometrically nonlinear panels subjected to random loading

NASA Technical Reports Server (NTRS)

Moyer, E. Thomas, Jr.

1988-01-01

The response of composite panels subjected to random pressure loads large enough to cause geometrically nonlinear responses is studied. A time domain simulation is employed to solve the equations of motion. An adaptive time stepping algorithm is employed to minimize intermittent transients. A modified algorithm for the prediction of response spectral density is presented which predicts smooth spectral peaks for discrete time histories. Results are presented for a number of input pressure levels and damping coefficients. Response distributions are calculated and compared with the analytical solution of the Fokker-Planck equations. RMS response is reported as a function of input pressure level and damping coefficient. Spectral densities are calculated for a number of examples.

Sh2-138: physical environment around a small cluster of massive stars

NASA Astrophysics Data System (ADS)

Baug, T.; Ojha, D. K.; Dewangan, L. K.; Ninan, J. P.; Bhatt, B. C.; Ghosh, S. K.; Mallick, K. K.

2015-12-01

We present a multiwavelength study of the Sh2-138, a Galactic compact H II region. The data comprise of optical and near-infrared (NIR) photometric and spectroscopic observations from the 2-m Himalayan Chandra Telescope, radio observations from the Giant Metrewave Radio Telescope (GMRT), and archival data covering radio through NIR wavelengths. A total of 10 Class I and 54 Class II young stellar objects (YSOs) are identified in a 4.6 arcmin×4.6 arcmin area of the Sh2-138 region. Five compact ionized clumps, with four lacking of any optical or NIR counterparts, are identified using the 1280 MHz radio map, and correspond to sources with spectral type earlier than B0.5. Free-free emission spectral energy distribution fitting of the central compact H II region yields an electron density of ˜2250 ± 400 cm-3. With the aid of a wide range of spectra, from 0.5-15 μm, the central brightest source - previously hypothesized to be the main ionizing source - is characterized as a Herbig Be type star. At large scale (15 arcmin ×15 arcmin), the Herschel images (70-500 μm) and the nearest neighbour analysis of YSOs suggest the formation of an isolated cluster at the junction of filaments. Furthermore, using a greybody fit to the dust spectrum, the cluster is found to be associated with the highest column density (˜3 × 1022 cm-2) and high temperature (˜35 K) regime, as well as with the radio continuum emission. The mass of the central clump seen in the column density map is estimated to be ˜3770 M⊙.

On oscillating flows in randomly heterogeneous porous media.

PubMed

Trefry, M G; McLaughlin, D; Metcalfe, G; Lester, D; Ord, A; Regenauer-Lieb, K; Hobbs, B E

2010-01-13

The emergence of structure in reactive geofluid systems is of current interest. In geofluid systems, the fluids are supported by a porous medium whose physical and chemical properties may vary in space and time, sometimes sharply, and which may also evolve in reaction with the local fluids. Geofluids may also experience pressure and temperature conditions within the porous medium that drive their momentum relations beyond the normal Darcy regime. Furthermore, natural geofluid systems may experience forcings that are periodic in nature, or at least episodic. The combination of transient forcing, near-critical fluid dynamics and heterogeneous porous media yields a rich array of emergent geofluid phenomena that are only now beginning to be understood. One of the barriers to forward analysis in these geofluid systems is the problem of data scarcity. It is most often the case that fluid properties are reasonably well known, but that data on porous medium properties are measured with much less precision and spatial density. It is common to seek to perform an estimation of the porous medium properties by an inverse approach, that is, by expressing porous medium properties in terms of observed fluid characteristics. In this paper, we move toward such an inversion for the case of a generalized geofluid momentum equation in the context of time-periodic boundary conditions. We show that the generalized momentum equation results in frequency-domain responses that are governed by a second-order equation which is amenable to numerical solution. A stochastic perturbation approach demonstrates that frequency-domain responses of the fluids migrating in heterogeneous domains have spatial spectral densities that can be expressed in terms of the spectral densities of porous media properties. This journal is © 2010 The Royal Society

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.

Novel plasma source for safe beryllium spectral line studies in the presence of beryllium dust

NASA Astrophysics Data System (ADS)

Stankov, B. D.; Vinić, M.; Gavrilović Božović, M. R.; Ivković, M.

2018-05-01

Plasma source for beryllium spectral line studies in the presence of beryllium dust particles was realised. The guideline during construction was to prevent exposure to formed dust, considering the toxicity of beryllium. Plasma source characterization through determination of optimal working conditions is described. The necessary conditions for Be spectral line appearance and optimal conditions for line shape measurements are found. It is proven experimentally that under these conditions dust appears coincidently with the second current maximum. The electron density measured after discharge current maximum is determined from the peak separation of the hydrogen Balmer beta spectral line, and the electron temperature is determined from the ratios of the relative intensities of Be spectral lines emitted from successive ionized stages of atoms. Maximum values of electron density and temperature are measured to be 9.3 × 1022 m-3 and 16 800 K, respectively. Construction details and testing of the BeO discharge tube in comparison with SiO2 and Al2O3 discharge tubes are also presented in this paper.