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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.

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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Lifetime statistics of quantum chaos studied by a multiscale analysis

In a series of pump and probe experiments, we study the lifetime statistics of a quantum chaotic resonator when the number of open channels is greater than one. Our design embeds a stadium billiard into a two dimensional photonic crystal realized on a silicon-on-insulator substrate. We calculate resonances through a multiscale procedure that combines energy landscape analysis and wavelet transforms. Experimental data is found to follow the universal predictions arising from random matrix theory with an excellent level of agreement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Measurement of fast-changing low velocities by photonic Doppler velocimetry

Despite the increasing popularity of photonic Doppler velocimetry (PDV) in shock wave experiments, its capability of capturing low particle velocities while changing rapidly is still questionable. The paper discusses the performance of short time Fourier transform (STFT) and continuous wavelet transform (CWT) in processing fringe signals of fast-changing low velocities measured by PDV. Two typical experiments are carried out to evaluate the performance. In the laser shock peening test, the CWT gives a better interpretation to the free surface velocity history, where the elastic precursor, main plastic wave, and elastic release wave can be clearly identified. The velocities of stress waves, Hugoniot elastic limit, and the amplitude of shock pressure induced by laser can be obtained from the measurement. In the Kolsky-bar based tests, both methods show validity of processing the longitudinal velocity signal of incident bar, whereas CWT improperly interprets the radial velocity of the shocked sample at the beginning period, indicating the sensitiveness of the CWT to the background noise. STFT is relatively robust in extracting waveforms of low signal-to-noise ratio. Data processing method greatly affects the temporal resolution and velocity resolution of a given fringe signal, usually CWT demonstrates a better local temporal resolution and velocity resolution, due to its adaptability to the local frequency, also due to the finer time-frequency product according to the uncertainty principle.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Electron cyclotron maser emission mode coupling to the z-mode on a longitudinal density gradient in the context of solar type III bursts

A beam of super-thermal, hot electrons was injected into maxwellian plasma with a density gradient along a magnetic field line. 1.5D particle-in-cell simulations were carried out which established that the EM emission is produced by the perpendicular component of the beam injection momentum. The beam has a positive slope in the distribution function in perpendicular momentum phase space, which is the characteristic feature of a cyclotron maser. The cyclotron maser in the overdense plasma generates emission at the electron cyclotron frequency. The frequencies of generated waves were too low to propagate away from the injection region, hence the wavelet transform shows a pulsating wave generation and decay process. The intensity pulsation frequency is twice the relativistic cyclotron frequency. Eventually, a stable wave packet formed and could mode couple on the density gradient to reach frequencies of the order of the plasma frequency that allowed for propagation. The emitted wave is likely to be a z-mode wave. The total electromagnetic energy generated is of the order of 0.1% of the initial beam kinetic energy. The proposed mechanism is of relevance to solar type III radio bursts, as well as other situations, when the injected electron beam has a non-zero perpendicular momentum, e.g., magnetron.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Accurate quantum dynamics calculations using symmetrized Gaussians on a doubly dense Von Neumann lattice

In a series of earlier articles [B. Poirier, J. Theor. Comput. Chem. 2, 65 (2003); B. Poirier and A. Salam, J. Chem. Phys. 121, 1690 (2004); and ibid. 121, 1704 (2004)], a new method was introduced for performing exact quantum dynamics calculations. The method uses a 'weylet' basis set (orthogonalized Weyl-Heisenberg wavelets) combined with phase space truncation, to defeat the exponential scaling of CPU effort with system dimensionality-the first method ever able to achieve this long-standing goal. Here, we develop another such method, which uses a much more convenient basis of momentum-symmetrized Gaussians. Despite being non-orthogonal, symmetrized Gaussians are collectively local, allowing for effective phase space truncation. A dimension-independent code for computing energy eigenstates of both coupled and uncoupled systems has been created, exploiting massively parallel algorithms. Results are presented for model isotropic uncoupled harmonic oscillators and coupled anharmonic oscillators up to 27 dimensions. These are compared with the previous weylet calculations (uncoupled harmonic oscillators up to 15 dimensions), and found to be essentially just as efficient. Coupled system results are also compared to corresponding exact results obtained using a harmonic oscillator basis, and also to approximate results obtained using first-order perturbation theory up to the maximum dimensionality for which the latter may be feasibly obtained (four dimensions).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Development of frequency modulation reflectometer for Korea Superconducting Tokamak Advanced Research tokamak

Frequency modulation reflectometer has been developed to measure the plasma density profile of the Korea Superconducting Tokamak Advanced Research tokamak. Three reflectometers are operating in extraordinary polarization mode in the frequency range of Q band (33.6–54 GHz), V band (48–72 GHz), and W band (72–108 GHz) to measure the density up to 7 × 10{sup 19} m{sup −3} when the toroidal magnetic field is 2 T on axis. The antenna is installed inside of the vacuum vessel. A new vacuum window is developed by using 50 μm thick mica film and 0.1 mm thick gold gasket. The filter bank of low pass filter, notch filter, and Faraday isolator is used to reject the electron cyclotron heating high power at attenuation of 60 dB. The full frequency band is swept in 20 μs. The mixer output is directly digitized with sampling rate of 100 MSamples/s. The phase is obtained by using wavelet transform. The whole hardware and software system is described in detail and the measured density profile is presented as a result.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Intelligent feature selection techniques for pattern classification of Lamb wave signals

Lamb wave interaction with flaws is a complex, three-dimensional phenomenon, which often frustrates signal interpretation schemes based on mode arrival time shifts predicted by dispersion curves. As the flaw severity increases, scattering and mode conversion effects will often dominate the time-domain signals, obscuring available information about flaws because multiple modes may arrive on top of each other. Even for idealized flaw geometries the scattering and mode conversion behavior of Lamb waves is very complex. Here, multi-mode Lamb waves in a metal plate are propagated across a rectangular flat-bottom hole in a sequence of pitch-catch measurements corresponding to the double crosshole tomography geometry. The flaw is sequentially deepened, with the Lamb wave measurements repeated at each flaw depth. Lamb wave tomography reconstructions are used to identify which waveforms have interacted with the flaw and thereby carry information about its depth. Multiple features are extracted from each of the Lamb wave signals using wavelets, which are then fed to statistical pattern classification algorithms that identify flaw severity. In order to achieve the highest classification accuracy, an optimal feature space is required but it’s never known a priori which features are going to be best. For structural health monitoring we make use of the fact that physical flaws, such as corrosion, will only increase over time. This allows us to identify feature vectors which are topologically well-behaved by requiring that sequential classes “line up” in feature vector space. An intelligent feature selection routine is illustrated that identifies favorable class distributions in multi-dimensional feature spaces using computational homology theory. Betti numbers and formal classification accuracies are calculated for each feature space subset to establish a correlation between the topology of the class distribution and the corresponding classification accuracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Wave-wave interactions in solar type III radio bursts

The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at f{sub pe}, 2f{sub pe} and 3 f{sub pe} (f{sub pe} is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Accurate modeling of switched reluctance machine based on hybrid trained WNN

According to the strong nonlinear electromagnetic characteristics of switched reluctance machine (SRM), a novel accurate modeling method is proposed based on hybrid trained wavelet neural network (WNN) which combines improved genetic algorithm (GA) with gradient descent (GD) method to train the network. In the novel method, WNN is trained by GD method based on the initial weights obtained per improved GA optimization, and the global parallel searching capability of stochastic algorithm and local convergence speed of deterministic algorithm are combined to enhance the training accuracy, stability and speed. Based on the measured electromagnetic characteristics of a 3-phase 12/8-pole SRM, the nonlinear simulation model is built by hybrid trained WNN in Matlab. The phase current and mechanical characteristics from simulation under different working conditions meet well with those from experiments, which indicates the accuracy of the model for dynamic and static performance evaluation of SRM and verifies the effectiveness of the proposed modeling method.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

A note on the relationship between turbulent coherent structures and phase correlation

Various definitions of coherent structures exist in turbulence research, but a common assumption is that coherent structures have correlated spectral phases. As a result, randomization of phases is believed, generally, to remove coherent structures from the measured data. Here, we reexamine these assumptions using atmospheric turbulence measurements. Small-scale coherent structures are detected in the usual way using the wavelet transform. A considerable percentage of the detected structures are not phase correlated, although some of them are clearly organized in space and time. At larger scales, structures have even higher degree of spatiotemporal coherence but are also associated with weak phase correlation. A series of specific examples are shown to demonstrate this. These results warn about the vague terminology and assumptions around coherent structures, particularly for complex real-world turbulence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Interface nano-confined acoustic waves in polymeric surface phononic crystals

The impulsive acoustic dynamics of soft polymeric surface phononic crystals is investigated here in the hypersonic frequency range by near-IR time-resolved optical diffraction. The acoustic response is analysed by means of wavelet spectral methods and finite element modeling. An unprecedented class of acoustic modes propagating within the polymer surface phononic crystal and confined within 100 nm of the nano-patterned interface is revealed. The present finding opens the path to an alternative paradigm for characterizing the mechanical properties of soft polymers at interfaces and for sensing schemes exploiting polymers as embedding materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tipping point analysis of atmospheric oxygen concentration

We apply tipping point analysis to nine observational oxygen concentration records around the globe, analyse their dynamics and perform projections under possible future scenarios, leading to oxygen deficiency in the atmosphere. The analysis is based on statistical physics framework with stochastic modelling, where we represent the observed data as a composition of deterministic and stochastic components estimated from the observed data using Bayesian and wavelet techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Polychromatic sparse image reconstruction and mass attenuation spectrum estimation via B-spline basis function expansion

We develop a sparse image reconstruction method for polychromatic computed tomography (CT) measurements under the blind scenario where the material of the inspected object and the incident energy spectrum are unknown. To obtain a parsimonious measurement model parameterization, we first rewrite the measurement equation using our mass-attenuation parameterization, which has the Laplace integral form. The unknown mass-attenuation spectrum is expanded into basis functions using a B-spline basis of order one. We develop a block coordinate-descent algorithm for constrained minimization of a penalized negative log-likelihood function, where constraints and penalty terms ensure nonnegativity of the spline coefficients and sparsity of the density map image in the wavelet domain. This algorithm alternates between a Nesterov’s proximal-gradient step for estimating the density map image and an active-set step for estimating the incident spectrum parameters. Numerical simulations demonstrate the performance of the proposed scheme.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Radioisotope identification method for poorly resolved gamma-ray spectrum of nuclear security concern

Gamma-ray signal can be used as a fingerprint for radioisotope identification. In the context of radioactive and nuclear materials security at the border control point, the detection task can present a significant challenge due to various constraints such as the limited measurement time, the shielding conditions, and the noise interference. This study proposes a novel method to identify the signal of one or several radioisotopes from a poorly resolved gamma-ray spectrum. In this method, the noise component in the raw spectrum is reduced by the wavelet decomposition approach, and the removal of the continuum background is performed using the baseline determination algorithm. Finally, the identification of radioisotope is completed using the matrix linear regression method. The proposed method has been verified by experiments using the poorly resolved gamma-ray signals from various scenarios including single source, mixing of natural uranium with five of the most common industrial radioactive sources (57Co, 60Co, 133Ba, 137Cs, and 241Am). The preliminary results show that the proposed algorithm is comparable with the commercial method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Mathematical approaches in deriving hydrocarbons expressions from seismic data

Defining and understanding hydrocarbon expressions in seismic expression is main concern of geoscientists in oil and gas exploration and production. Over the last decades several mathematical approaches have been developed in this regard. Most of approaches have addressed information in amplitude of seismic data. Recently, more attention has been drawn towards frequency related information in order to extract frequency behaviors of hydrocarbons bearing sediments. Spectrally decomposing seismic data into individual frequencies found to be an excellent tool for investigating geological formations and their pore fluids. To accomplish this, several mathematical approaches have been invoked. Continuous wavelet transform and Short Time Window Fourier transform are widely used techniques for this purpose. This paper gives an overview of some widely used mathematical technique in hydrocarbon reservoir detection and mapping. This is followed by an application on real data from Boonsville field.

58 GEOSCIENCES↗
DOE OSTI2016

Passive microrheology of normal and cancer cells after ML7 treatment by atomic force microscopy

Mechanical properties of living cancer and normal thyroidal cells were investigated by atomic force microscopy (AFM). Cell mechanics was compared before and after treatment with ML7, which is known to reduce myosin activity and induce softening of cell structures. We recorded force curves with extended dwell time of 6 seconds in contact at maximum forces from 500 pN to 1 nN. Data were analyzed within different frameworks: Hertz fit was applied in order to evaluate differences in Young’s moduli among cell types and conditions, while the fluctuations of the cantilever in contact with cells were analyzed with both conventional algorithms (probability density function and power spectral density) and multifractal detrended fluctuation analysis (MF-DFA). We found that cancer cells were softer than normal cells and ML7 had a substantial softening effect on normal cells, but only a marginal one on cancer cells. Moreover, we observed that all recorded signals for normal and cancer cells were monofractal with small differences between their scaling parameters. Finally, the applicability of wavelet-based methods of data analysis for the discrimination of different cell types is discussed.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Hybrid grid/basis set discretizations of the Schrödinger equation

We present a new kind of basis function for discretizing the Schrödinger equation in electronic structure calculations, called a gausslet, which has wavelet-like features but is composed of a sum of Gaussians. Gausslets are placed on a grid and combine advantages of both grid and basis set approaches. They are orthogonal, infinitely smooth, symmetric, polynomially complete, and with a high degree of locality. Because they are formed from Gaussians, they are easily combined with traditional atom-centered Gaussian bases. As a result, we also introduce diagonal approximations that dramatically reduce the computational scaling of two-electron Coulomb terms in the Hamiltonian.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

A detailed examination of laser-ion acceleration mechanisms in the relativistic transparency regime using tracers

Here we present a particle-in-cell study of linearly polarized laser-ion acceleration systems, in which we use both two-dimensional (2D) and three-dimensional (3D) simulations to characterize the ion acceleration mechanisms in targets which become transparent to the laser pulse during irradiation. First, we perform a target length scan to optimize the peak ion energies in both 2D and 3D, and the predictive capabilities of 2D simulations are discussed. Tracer analysis allows us to isolate the acceleration into stages of target normal sheath acceleration (TNSA), hole boring (HB), and break-out afterburner (BOA) acceleration, which vary in effectiveness based on the simulation parameters. The thinnest targets reveal that enhanced TNSA is responsible for accelerating the most energetic ions, whereas the thickest targets have ions undergoing successive phases of HB and TNSA (in 2D) or BOA and TNSA (in 3D); HB is not observed to be a dominant acceleration mechanism in the 3D simulations. It is in the intermediate optimal regime, both when the laser breaks through the target with appreciable amplitude and when there is enough plasma to form a sustained high density flow, that BOA is most effective and is responsible for the most energetic ions. Eliminating the transverse laser spot size effects by performing a plane wave simulation, we can isolate with greater confidence the underlying physics behind the ion dynamics we observe. Specifically, supplemented by wavelet and FFT analyses, we match the post-transparency BOA acceleration with a wave-particle resonance with a high-amplitude low-frequency electrostatic wave of increasing phase velocity, consistent with that predicted by the Buneman instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

A novel use of frequency-banded synthetic aperture focusing technique for reconstructions of alkali-silica reaction in thick-reinforced concrete structures

As they degrade and age, concrete structures are susceptible to the development of multiple defects, such as alkali-silica reaction (ASR). ASR forms a gel that occurs over time between alkaline cement paste and reactive, noncrystalline silica in aggregates [1]. With the continuing extension of the life span of nuclear power plants, it is important to monitor the structural integrity of concrete structures after 40+ years. Compression strength, modulus of elasticity, flexural stiffness, shear strength, and tensile strength are performance characteristics susceptible to the development of ASR. Current methods for monitoring for defects and degradation within thick concrete structures require damaging the concrete. Oak Ridge National Laboratory, in collaboration with the University of Pittsburgh, has developed a nondestructive evaluation (NDE) and reconstruction technique that enables deep-image reconstruction of damaged concrete. The frequency-banded synthetic aperture focusing technique (FB-SAFT) is an augmented SAFT reconstruction that segments the time-series data into different frequency bands using wavelets immediately before performing SAFT reconstructions [2]. This paper presents the NDE instrumentation and reconstruction techniques applied to thick-reinforced concrete structures and concludes with preliminary results.

Ezell, N Dianne↗