Search NASA⌕ Search

SEARCH · Search NASA

Results for “Spectrum analysis”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Machine learning framework for predicting uranium enrichments from M400 CZT gamma spectra

A machine learning framework was developed for predicting uranium enrichments from M400 CZT gamma spectra. This framework leverages the availability of a large amount of measured M400 gamma spectra and uses a recently updated version of Gamma Detector Response and Analysis Software (GADRAS) for gamma spectrum analysis and generation. It also leverages the existing machine learning modules in Python for gamma spectrum data processing, curation, model training, benchmarking, and optimization of the deep machine learning models. The framework is used to develop a deep learning model to analyze gamma spectra from a set of U 3 O 8 samples with enrichments ranging from 0.31 to 93.17% and UF 6 cylinders with enrichments ranging from 0.2 to 4.95%, and the model performance is tested using a set of measured spectra and the respective declared enrichment values. Results show that the model can correctly classify 99.35% of the U 3 O 8 sample enrichments, and can predict the samples’ enrichments within an average absolute error of 0.099% (in percentage points of enrichment). For the UF 6 cylinders, the average absolute error was approximately 0.03%, with an accuracy of 98% in classifying discrete enrichment values of UF 6 samples. Finally, the results also show that the model has performed significantly better in terms of predicting enrichments in UF 6 cylinders based on measured gamma spectra than the GEM code, with a standard deviation (of the relative errors) of 2.23% (compared with the 11.51% value for the GEM code) based on results from a set of test data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1969

Fast Fourier Transform Spectral Analysis Program

Fast Fourier Transform Spectral Analysis Program is used in frequency spectrum analysis of postflight, space vehicle telemetered trajectory data. This computer program with a digital algorithm can calculate power spectrum rms amplitudes and cross spectrum of sampled parameters at even time increments.

Daniel, J. A., Jr.↗
NASA NTRS1990

Enhanced vasomotion of cerebral arterioles in spontaneously hypertensive rats

Intrinsic rhythmic changes in the diameter of pial cerebral arterioles (30-70 microns) in anesthetized normotensive and hypertensive rats were assessed in vivo to determine if any significant differences exist between the two strains. All diameter measurements were analyzed using a traditional graphic analysis technique and a new frequency spectrum analysis technique known as the Prony Spectral Line Estimator. Graphic analysis of the data revealed that spontaneously hypertensive rats (SHR) possess a significantly greater fundamental frequency (5.57 +/- 0.28 cycles/min) of vasomotion compared to the control Wistar-Kyoto normotensive rats (WKY) (1.95 +/- 0.37 cycles/min). Furthermore, the SHR cerebral arterioles exhibited a significantly greater amplitude of vasomotion (10.07 +/- 0.70 microns) when compared to the WKY cerebral arterioles of the same diameter (8.10 +/- 0.70 microns). Diameter measurements processed with the Prony technique revealed that the fundamental frequency of vasomotion in SHR cerebral arterioles (6.14 +/- 0.39 cycles/min) was also significantly greater than that of the WKY cerebral arterioles (2.99 +/- 0.42 cycles/min). The mean amplitudes of vasomotion in the SHR and WKY strains obtained by the Prony analysis were found not to be statistically significant in contrast to the graphic analysis of the vasomotion amplitude of the arterioles. In addition, the Prony system was able to consistently uncover a very low frequency of vasomotion in both strains of rats that was typically less than 1 cycle/min and was not significantly different between the two strains. The amplitude of this slow frequency was also not significantly different between the two strains. The amplitude of the slow frequency of vasomotion (less than 1 cycle/min) was not different from the amplitude of the higher frequency (2-6 cycles/min) vasomotion by Prony or graphic analysis. These data suggest that a fundamental intrinsic defect exists in the spontaneously hypertensive rat that may contribute to the pathogenesis of hypertension in these animals.

NASA Discipline Cardiopulmonary↗
NASA NTRS1975

Stepwise Iterative Fourier Transform: The SIFT

A program, designed specifically to study the respective effects of some common data problems on results obtained through stepwise iterative Fourier transformation of synthetic data with known waveform composition, was outlined. Included in this group were the problems of gaps in the data, different time-series lengths, periodic but nonsinusoidal waveforms, and noisy (low signal-to-noise) data. Results on sinusoidal data were also compared with results obtained on narrow band noise with similar characteristics. The findings showed that the analytic procedure under study can reliably reduce data in the nature of (1) sinusoids in noise, (2) asymmetric but periodic waves in noise, and (3) sinusoids in noise with substantial gaps in the data. The program was also able to analyze narrow-band noise well, but with increased interpretational problems. The procedure was shown to be a powerful technique for analysis of periodicities, in comparison with classical spectrum analysis techniques. However, informed use of the stepwise procedure nevertheless requires some background of knowledge concerning characteristics of the biological processes under study.

Benignus, V. A.↗
NASA NTRS1995

Variability of accretion disks surrounding black holes: The role of inertial-acoustic mode instabilities

The global nonlinear time-dependent evolution of the inertial-acoustic mode instability in accretion disks surrounding black holes has been investigated. The viscous stress is assumed to be proportional to the gas pressure only, i.e., tau = alphap(sub g). It is found that an oscillatory nonsteady behavior exists in the inner regions of disks (r is less than 10r(sub g) where r(sub g) is the Schwarzschild radius) for sufficiently large alpha(greater than or approximately equal to 0.2) and for mass accretion rates less than about 0.3 times the Eddington value. The variations of the integrated bolometric luminosity from the disk, Delta L/L, are less than 3%. A power spectrum analysis of these variations reveals a power spectrum which can be fitted to a power-law function of the frequency Pis proportional to f(exp -gamma), with index gamma = 1.4-2.3 and a low-frequency feature at about 4 Hz in one case. In addition, a narrow peak centered at a frequency corresponding to the maximum epicyclic frequency of the disk at approximately 100-130 Hz and its first harmonic is also seen. The low-frequency modulations are remarkably similar to those observed in black hole candidate systems. The possible existence of a scattering corona in the inner region of the disk and/or other processes contributing to the power at high frequencies in the inner region of the accretion disk may make the detection of the high-frequency component difficult.

Chen, Xingming↗
DOE OSTI2024

Harmonic analysis of discrete tracers of large-scale structure

It is commonplace in cosmology to analyze fields projected onto the celestial sphere, and in particular density fields that are defined by a set of points e.g. galaxies. When performing an harmonic-space analysis of such data (e.g. an angular power spectrum) using a pixelized map one has to deal with aliasing of small-scale power and pixel window functions. We compare and contrast the approaches to this problem taken in the cosmic microwave background and large-scale structure communities, and advocate for a direct approach that avoids pixelization. We describe a method for performing a pseudo-spectrum analysis of a galaxy data set and show that it can be implemented efficiently using well-known algorithms for special functions that are suited to acceleration by graphics processing units (GPUs). The method returns the same spectra as the more traditional map-based approach if in the latter the number of pixels is taken to be sufficiently large and the mask is well sampled. The method is readily generalizable to cross-spectra and higher-order functions. It also provides a convenient route for distributing the information in a galaxy catalog directly in harmonic space, as a complement to releasing the configuration-space positions and weights, and a route to spectral apodization. Finally, we make public a code enabling the application of our method to existing and upcoming datasets.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Statistical Evaluation of Time Series Analysis Techniques

The performance of a modified version of NASA's multivariate spectrum analysis program is discussed. A multiple regression model was used to make the revisions. Performance improvements were documented and compared to the standard fast Fourier transform by Monte Carlo techniques.

Benignus, V. A.↗
NASA NTRS1984

The MST Radar Technique

The coherent radar technique is reviewed with special emphasis to mesosphere-stratosphere-troposphere (MST) radars operating in the VHF band. Some basic introduction to Doppler radar measurements and the radar equation is followed by an outline of the characteristics of atmospheric turbulence, viewed from the scattering and reflection processes of radar signals. Radar signal acquisition and preprocessing, namely coherent detection, digital sampling, pre-integration and coding, is briefly discussed. The data analysis is represented in terms of the correlation and spectrum analysis, yielding the essential parameters: power, signal-to-noise ratio, average and fluctuating velocity and persistency. The techniques to measure wind velocities, viz. the different modes of the Doppler method as well as the space antenna method are surveyed and the feasibilities of the MST radar interferometer technique are elucidated. A general view on the criteria to design phased array antennas is given. An outline of the hardware of a typical MST radar system is presented.

Roettger, J.↗
NASA NTRS1989

Spectroscopic analysis of transition state energy levels - Bending-rotational spectrum and lifetime analysis of H3 quasibound states

Converged quantum mechanical calculations of scattering matrices and transition probabilities are reported for the reaction of H with H2 with total angular momentum 0, 1, and 4 as functions of total energy in the range 0.85-1.15 eV on an accurate potential energy surface. The resonance structure is illustrated with Argand diagrams. State-to-state reactive collision delay times and lifetimes are presented. For J = 0, 1, and 4, the lowest-energy H3 resonance is at total energies of 0.983, 0.985, and 1.01 eV, respectively, with lifetimes of about 16-17 fs. For J = 1 and 4 there is a higher-energy resonance at 1.10-1.11 eV. For J = 1 the lifetime is about 4 fs and for J = 4 it is about 1 fs.

Zhao, Meishan↗
DOE OSTI2026

MapsTorch : automatic differentiation for X-ray fluorescence data analysis

X-ray fluorescence (XRF) is a popular spectroscopy technique for elemental analysis. Spectrum fitting and parameter tuning are at the core of XRF analysis and are conventionally manually intensive, especially for synchrotron experiments involving large amounts of diverse samples. This work introduces the automatic differentiation (AD) technique to XRF and an open-source package called MapsTorch. By transforming an analytical model of the XRF spectrum into a differentiable computation graph with AD, MapsTorch enables robust optimization of parameters and elemental intensities. We evaluate MapsTorch by conducting computational experiments on a large number of historical synchrotron XRF datasets and compare its performance with the currently practiced fitting tool NLopt. The results show that MapsTorch consistently achieves high-quality fits and often leads to better fitting quality than NLopt, particularly in tasks such as initial spectrum fitting and elemental intensity refinement. The robust performance of MapsTorch paves the way for developing automated and high-throughput XRF data analysis workflows to handle the increasing data volumes expected from next-generation synchrotron facilities.

X-ray fluorescence↗
NASA NTRS2020

The Advanced Spectral Library (ASTRAL): Abundance Analysis of the Chemically Peculiar Star HR 465

This paper presents the results of the spectrum analysis of the B-type magnetic chemically peculiar star HR 465. HR 465 shows unusual abundance patterns that vary with a period of 21.5 yr. Our observations are recorded at ϕ = 0.45, 0.68, and 0.85 of the spectroscopic period, where ϕ = 0 represents the phase of maximum flux in the photometric y-band. Synthetic spectra, computed using an LTE atmosphere model, are fit to high-resolution ultraviolet Hubble Space Telescope (ϕ = 0.45) spectra obtained as part of the Advanced Spectral Library Project: Hot Stars program. The ultraviolet data are supplemented by high-resolution optical spectra (ϕ = 0.68 and 0.85) recorded at the Nordic Optical Telescope with the SOFIN spectrograph. The optical data are used as a complement to the high line-density ultraviolet spectrum to derive accurate abundances for elements without spectral lines in the ultraviolet and to improve the abundance phase coverage for many atoms/ions. This analysis presents abundance results for more than 70 atoms/ions and confirms parts of the abundance characteristics previously reported where elements with high mass numbers show significant abundance enhancements compared with solar values while some of the lighter elements show abundance deficiencies. In addition, our measured abundances are consistent with the periodic variability for chromium and rare-earth elements. Our results are compared with earlier investigations of this peculiar object to constrain stellar abundance and diffusion.

Krister E. Nielsen↗
NASA NTRS2012

Temporal Variability of Observed and Simulated Hyperspectral Earth Reflectance

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a climate observation system designed to study Earth's climate variability with unprecedented absolute radiometric accuracy and SI traceability. Observation System Simulation Experiments (OSSEs) were developed using GCM output and MODTRAN to simulate CLARREO reflectance measurements during the 21st century as a design tool for the CLARREO hyperspectral shortwave imager. With OSSE simulations of hyperspectral reflectance, Feldman et al. [2011a,b] found that shortwave reflectance is able to detect changes in climate variables during the 21st century and improve time-to-detection compared to broadband measurements. The OSSE has been a powerful tool in the design of the CLARREO imager and for understanding the effect of climate change on the spectral variability of reflectance, but it is important to evaluate how well the OSSE simulates the Earth's present-day spectral variability. For this evaluation we have used hyperspectral reflectance measurements from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY), a shortwave spectrometer that was operational between March 2002 and April 2012. To study the spectral variability of SCIAMACHY-measured and OSSE-simulated reflectance, we used principal component analysis (PCA), a spectral decomposition technique that identifies dominant modes of variability in a multivariate data set. Using quantitative comparisons of the OSSE and SCIAMACHY PCs, we have quantified how well the OSSE captures the spectral variability of Earth?s climate system at the beginning of the 21st century relative to SCIAMACHY measurements. These results showed that the OSSE and SCIAMACHY data sets share over 99% of their total variance in 2004. Using the PCs and the temporally distributed reflectance spectra projected onto the PCs (PC scores), we can study the temporal variability of the observed and simulated reflectance spectra. Multivariate time series analysis of the PC scores using techniques such as Singular Spectrum Analysis (SSA) and Multichannel SSA will provide information about the temporal variability of the dominant variables. Quantitative comparison techniques can evaluate how well the OSSE reproduces the temporal variability observed by SCIAMACHY spectral reflectance measurements during the first decade of the 21st century. PCA of OSSE-simulated reflectance can also be used to study how the dominant spectral variables change on centennial scales for forced and unforced climate change scenarios. To have confidence in OSSE predictions of the spectral variability of hyperspectral reflectance, it is first necessary for us to evaluate the degree to which the OSSE simulations are able to reproduce the Earth?s present-day spectral variability.

Roberts, Yolanda↗