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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Autocorrelation and Multifractal Detrended Fluctuation Analyses Reveal Superdiffusive Mass Transport in Solvent-Filled Nanoporous Media

Fluorescence fluctuation spectroscopy experiments were conducted to better understand the complex mass transport dynamics of organic molecules in liquid-filled nanoporous media. Anodic aluminum oxide (AAO) membranes incorporating 10 and 20 nm diameter cylindrical pores were employed as model materials. Nile red (NR) dye was used as a fluorescent tracer. The dye was dissolved separately in ethanol and toluene at a concentration of 20 nM and used to fill the membrane nanopores. Confocal fluorescence microscopy was employed to capture photon intensity time series data reflecting apparent diffusion of the dye within the pores. Autocorrelation of these data revealed that NR diffusion within the membranes occurred over a broad range of time scales. The autocorrelation decays were fit to a model for one-dimensional diffusion incorporating both fast and slow components having apparent diffusion coefficients, D f and D s , differing by a factor of ∼100. The fast mechanism was attributed to hindered bulk-like diffusion in the central pore cavity, while slow diffusion likely involved absorption of the dye to the pore surfaces. Unfortunately, important evidence of diffusion anomalies is lost in the broad autocorrelation decays obtained. The method of multifractal detrended fluctuation analysis (MF-DFA) was applied to the same data as a means to overcome this limitation. MF-DFA revealed that time series acquired from within the nanopores were multifractal and exhibited evidence of anomalous superdiffusion, likely resulting from the participation of a desorption-mediated diffusion mechanism. Monte Carlo simulations of time series modeling desorption-mediated diffusion in cylindrical nanopores provided support for this assignment. Here, the new knowledge gained affords an improved understanding of hydrocarbon dynamics within nanoporous oil and gas shales.

Diffusion↗
DOE OSTI2024

A Generative Model for Realistic Galaxy Cluster X-Ray Morphologies

Abstract The X-ray morphologies of clusters of galaxies display significant variations, reflecting their dynamical histories and the nonlinear dependence of X-ray emissivity on the density of the intracluster gas. Qualitative and quantitative assessments of X-ray morphology have long been considered a proxy for determining whether clusters are dynamically active or “relaxed.” Conversely, the use of circularly or elliptically symmetric models for cluster emission can be complicated by the variety of complex features realized in nature, spanning scales from megaparsecs down to the resolution limit of current X-ray observatories. In this work, we use mock X-ray images from simulated clusters from The Three Hundred project to define a basis set of cluster image features. We take advantage of the clusters’ approximate self-similarity to minimize the differences between images before encoding the remaining diversity through a distribution of high-order polynomial coefficients. Principal component analysis then provides an orthogonal basis for this distribution, corresponding to natural perturbations from an average model. This representation allows novel, realistically complex X-ray cluster images to be easily generated, and we provide code to do so. The approach provides a simple way to generate training data for cluster image analysis algorithms and could be straightforwardly adapted to generate clusters displaying specific types of features or selected by physical characteristics available in the original simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study

Field observations show that individual aerosol particles are a complex mixture of a wide variety of species, reflecting different sources and physico-chemical transformations. The impacts of individual aerosol morphology and mixing characteristics on the Earth system are not yet fully understood. Here we present a sensitivity study on climate-relevant aerosols optical properties to various approximations. Based on aerosol samples collected in various geographical locations, we have observationally constrained size, morphology and mixing, and accordingly simulated, using the discrete dipole approximation model (DDSCAT), optical properties of three aerosols types: (1) bare black carbon (BC) aggregates, (2) bare mineral dust, and (3) an internal mixture of a BC aggregate laying on top of a mineral dust particle, also referred to as polluted dust. DDSCAT predicts optical properties and their spectral dependence consistently with observations for all the studied cases. Predicted values of mass absorption, scattering and extinction coefficients (MAC, MSC, MEC) for bare BC show a weak dependence on the BC aggregate size, while the asymmetry parameter ( g ) shows the opposite behavior. The simulated optical properties of bare mineral dust present a large variability depending on the modeled dust shape, confirming the limited range of applicability of spheroids over different types and size of mineral dust aerosols, in agreement with previous modeling studies. The polluted dust cases show a strong decrease in MAC values with the increase in dust particle size (for the same BC size) and an increase of the single scattering albedo (SSA). Furthermore, particles with a radius between 180 and 300 nm are characterized by a decrease in SSA values compared to bare dust, in agreement with field observations.This paper demonstrates that observationally constrained DDSCAT simulations allow one to better understand the variability of the measured aerosol optical properties in ambient air and to define benchmark biases due to different approximations in aerosol parametrization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

On the Band Structure of Bi 2 Te 3

For p-Bi 2 Te 3 crystals grown by the Czochralski method, the temperature dependences of the conductivity, Hall coefficient, thermoelectric power (α), and transverse Nernst–Ettingshausen coefficient are obtained experimentally in the temperature range 77–450 K. The transmittance spectrum in the range 400–5250 cm -1 is recorded at room temperature. It is shown that, to interpret the temperature dependences of the scattering parameter r and the ratio of the thermoelectric power to temperature (α/T), it is essential to take into account the complex valence-band structure and the contribution of heavy holes to transport phenomena. Estimations of the energy band parameters in the context of the two-band model give a hole effective mass close to the free electron mass and the energy gap between nonequivalent extrema at a level of several hundredths of eV. In the absorption spectrum derived from the transmittance spectrum, a sharp increase in absorption defined by indirect interband transitions with the band gap E g ≈ 0.14 eV is observed in the region of frequencies ν ≥ 1000 cm -1 . The absorption spectrum calculated from the reflectance data using the Kramers–Kronig relations is in agreement with the experimental absorption spectrum.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Application of Linear Additive Conditions for Near-Infrared Diffuse Reflectance Absorption Spectroscopy

Determining the homogeneity of material mixing in real time during product processing is critical for quality control. According to the Kubelka–Munk (K-M) function of diffuse reflectance absorption spectrum, absorbance (A) is approximately linear with the content of the components when the sample scattering coefficient (S) is in a certain range. The S is determined by the particle size of powder samples. Therefore, this study determined particle size ranges that satisfy linear additivity in near-infrared diffuse reflectance spectroscopy (NIRDRS). Thus, the proposed NIRDRS analysis technique can be used to determine the homogeneity of material mixes or analyze the percentages of the components in the mixture. In this study, vitamin B3 and vitamin C were used for preparing mixed samples with varying percentages. The experimental results revealed that linear additivity is satisfied when the powder particle size is in the range of less than 280, 280–450, and 450–900 μm. When the confidence level is 0.01, the actual mixed spectra are not significantly different from the “simulated mixed spectra” constructed by linear addition, with their relative deviations less than 1.08%. The absolute errors of the actual and analytic percentages were within 2.98% for each component in the mixtures. The above conclusions also hold for sorghum, which has a complex material composition. Statistical models cannot analyze the percentages of components in the mixture. In contrast, linear addition and direct calibration approach avoids the use of a large number of samples for statistical modeling and analyze the percentages of mixed samples. Meanwhile, it can be used to discriminate and analyze the material mixing uniformity by building a mechanistic model.

Feng, Zhiyue↗
DOE OSTI2018

New scattering features in non-Hermitian space fractional quantum mechanics

Highlights: • Space fraction quantum mechanics (SFQM) has been investigated with complex delta and barrier potentials. • New scattering features due to these potentials are obtained in SFQM. • Spectral Singular (SS) points are blue/red shifted when Levy index is decreased. • The oscillations in scattering coefficients around SS have interesting behaviors in SFQM. • Deeper relations between the scattering properties in standard QM and those of in SFQM are observed. - Abstract: The spectral singularity (SS) and coherent perfect absorption (CPA) have been extensively studied over the last one and half decade for different non-Hermitian potentials in non-Hermitian standard quantum mechanics (SQM) governed by Schrödinger equation. In the present work we explore these scattering features in the domain of non-Hermitian space fractional quantum mechanics (SFQM) governed by fractional Schrödinger equation which is characterized by Levy index α (1<α≤2). We observe that non-Hermitian SFQM systems have more flexibility for SS and CPA and display some new features of scattering. For the delta potential V(x)=iρδ(x−x{sub 0}), ρ>0, the SS energy, E{sub ss}, is blue or red shifted with decreasing α depending on the strength of the potential. For complex rectangular barrier in non-Hermitian SQM, it is known that the reflection and transmission amplitudes are oscillatory near the spectral singular point. It is found that these oscillations eventually develop SS in non-Hermitian SFQM. The similar features are also reported for the case of CPA phenomena from complex rectangular barrier in non-Hermitian SFQM. These observations suggest a deeper relation between scattering features of non-Hermitian SQM and non-Hermitian SFQM.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Berkeley Lab WINDOW

WINDOW features include: - Microsoft Windows TM interface - algorithms for the calculation of total fenestration product U-values and Solar Heat Gain Coefficient consistent with ASHRAE SPC 142, ISO 15099, and the National Fenestration Rating Council - a Condensation Resistance Index in accordance with the NFRC 500 Standard - and integrated database of properties - imports data from other LBNL window analysis software: - Import THERM file into the Frame Library - Import records from IGDB and OPtics5 into the Glass Library for the optical properties of coated and uncoated glazings, laminates, and applied films. Program Capabilities WINDOW 7.2 offers the following features: The ability to analyze products made from any combination of glazing layers, gas layers, frames, spacers, and dividers under any environmental conditions and at any tilt; The ability to model complex glazing systems such as venetian blinds and roller shades. Directly accessible libraries of window system components, (glazing systems, glazing layers, gas fills, frame and divider elements), and environmental conditions; The choice of working in English (IP), or Systeme International (SI) units; The ability to specify the dimensions and thermal properties of each frame element (header, sills, jamb, mullion) in a window; A multi-band (wavelength-by-wavelength) spectral model; A Glass Library which can access spectral data files for many common glazing materials from the Optics5database; A night-sky radiative model; A link with the DOE-2.1E and Energy Plus building energy analysis program. Performance Indices and Other Results For a user-defined fenestration system and user-defined environmental conditions, WINDOW calculates: The U-value, solar heat gain coefficient, shading coefficient, and visible transmittance for the complete window system; The U-value, solar heat gain coefficient, shading coefficient, and visible transmittance for the glazing system (center-of-glass values); The U-values of the frame and divider elements and corresponding edge-of-glass areas (based on generic correlations); The total solar and visible transmittance and reflectances of the glazing system. Color properties, i.e. L*, a*, and b* color coordinates, dominant wavelength, and purity for transmitted and reflected (outdoor) solar radiation; The damage-weighted transmittance of the glazing system between 0.3 an 0.38 microns; The angular dependence of the solar and visible transmittances, solar and visible reflectances, solar absorptance, and solar heat gain coefficient of the glazing system; The percent relative humidity of the inside and outside air for which condensation will occur on the interior and exterior glazing surfaces respectively; The center-of-glass temperature distribution.

Curcija, DraganCharlie↗
DOE OSTI2018

Soft x-ray optical constants of sputtered chromium thin films with improved accuracy in the L and M absorption edge regions

In this paper, we determine with improved accuracy the complex index of refraction n = 1 - δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. Finally, an additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B 4 C multilayer mirror near the Cr-L 2,3 edge.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A novel software and conceptual design of the hardware platform for intensity modulated radiation therapy

Purpose: To deliver high quality intensity modulated radiotherapy (IMRT) using a novel generalized sparse orthogonal collimators (SOCs), the authors introduce a novel direct aperture optimization (DAO) approach based on discrete rectangular representation. Methods: A total of seven patients—two glioblastoma multiforme, three head & neck (including one with three prescription doses), and two lung—were included. 20 noncoplanar beams were selected using a column generation and pricing optimization method. The SOC is a generalized conventional orthogonal collimators with N leaves in each collimator bank, where N = 1, 2, or 4. SOC degenerates to conventional jaws when N = 1. For SOC-based IMRT, rectangular aperture optimization (RAO) was performed to optimize the fluence maps using rectangular representation, producing fluence maps that can be directly converted into a set of deliverable rectangular apertures. In order to optimize the dose distribution and minimize the number of apertures used, the overall objective was formulated to incorporate an L2 penalty reflecting the difference between the prescription and the projected doses, and an L1 sparsity regularization term to encourage a low number of nonzero rectangular basis coefficients. The optimization problem was solved using the Chambolle–Pock algorithm, a first-order primal–dual algorithm. Performance of RAO was compared to conventional two-step IMRT optimization including fluence map optimization and direct stratification for multileaf collimator (MLC) segmentation (DMS) using the same number of segments. For the RAO plans, segment travel time for SOC delivery was evaluated for the N = 1, N = 2, and N = 4 SOC designs to characterize the improvement in delivery efficiency as a function of N. Results: Comparable PTV dose homogeneity and coverage were observed between the RAO and the DMS plans. The RAO plans were slightly superior to the DMS plans in sparing critical structures. On average, the maximum and mean critical organ doses were reduced by 1.94% and 1.44% of the prescription dose. The average number of delivery segments was 12.68 segments per beam for both the RAO and DMS plans. The N = 2 and N = 4 SOC designs were, on average, 1.56 and 1.80 times more efficient than the N = 1 SOC design to deliver. The mean aperture size produced by the RAO plans was 3.9 times larger than that of the DMS plans. Conclusions: The DAO and dose domain optimization approach enabled high quality IMRT plans using a low-complexity collimator setup. The dosimetric quality is comparable or slightly superior to conventional MLC-based IMRT plans using the same number of delivery segments. The SOC IMRT delivery efficiency can be significantly improved by increasing the leaf numbers, but the number is still significantly lower than the number of leaves in a typical MLC.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Particle-image Velocimetry Sensitivity through Automatic Differentiation

A commonly encountered difficulty in modern experimental fluid dynamics experiments is the need for full-flow visualization and measurement; traditional techniques such as hot-wire probes and laser Doppler velocimetry cannot provide such information without difficult scanning procedures. Particle-image velocimetry (PIV) is a measurement technique which can overcome this spatial limitation to provide real-time three-dimensional fluid velocity vectors for an entire plane within the flow, as opposed to a single point that is provided by other measurement techniques. To accomplish this, a PIV system seeds the fluid flow with tracer particles; these must have nearly the same density as that of the fluid and a high drag coefficient to ensure that they follow the fluid flow without deviation. A laser is sent through optics to expand its beam into a sheet which illuminates the plane of interest in the fluid. The particles reflect more light than the fluid, and their image is recorded using a high speed camera. Due to limitations in bandwidth, video cannot be taken fast enough to be useful, and instead pairs of images are captured with a known separation in time. The illuminated particles will move between the two images taken by the camera, and their relative motion can be used to compute the fluid velocity at that point. When a single camera is used, only two-dimensional velocity vectors can be computed, but with the addition of another camera this can be improved to full three-dimensional vectors. The flow's time evolution can be measured by taking series of image pairs and processing each pair to get the velocity field at the time between each image pair. Only the two-dimensional version will be considered in this work. To compute the velocity vectors of the flow, the images are broken up into interrogation regions, usually in a uniform grid. In the most basic PIV algorithm, corresponding regions in the image pairs are cross-correlated to compute the most likely displacement from one image to the next. This is used since the cross correlation will achieve a maximum value when the two interrogation regions line up the best. The location of the peak in the correlation map and scaling information for the optical setup is used to compute the particle displacement from one image to the next. This process is similar to holding two semi-transparent images and moving one until they match as well as possible. Sub-pixel displacements between images can be obtained by fitting a Gaussian function to the correlation peak. Knowing the displacement vector for each set of interrogation regions in the image pair, it is a simple matter to divide by the time gap between the two images to compute the fluid velocity at the point in time and space. Since there are many interrogation regions in each image pair, the velocity field for a sheet is sampled according to the arrangement of the interrogation regions. The sensitivity of the final computed vector to the input images is difficult to compute, and has led most considerations of uncertainty in the PIV field to apply Monte Carlo methods and correlations to quantify the systematic and random errors which result from application of various PIV algorithms. In this work, automatic differentiation (AD) has been used to trace the dependence of velocity vectors computed using the correlation-peak PIV algorithm back to the input values given to an artificial image generator. These initial results form the foundation for continued work in the application of AD to algorithms in PIV. They demonstrate that AD methods can be successfully applied to PIV algorithms without undue complexity. The derivatives of each individual vector with regard to the coefficients of the velocity field used to create the artificial images can be computed and the statistics of them considered collectively, or correlated between each other to quantify the effectiveness of a PIV algorithm. With the initial implementation complete, adding extra algorithms is relatively simple and considerable data can be generated for analysis. It is hoped that application of these methods can lead to improved PIV algorithms which demonstrate better sensitivity to small variations in particle displacement. While these methods can be used as an analysis tool for refinement of new algorithms, computation of actual resultant vector sensitivities to input images' individual pixels is the next logical step of this work. Such information will be analyzed with experimental data to produce a better understanding of how output vectors' uncertainty relates to the actual image pairs, and lead to automatic bad vector removal. (authors)

42 ENGINEERING↗
DOE OSTI2019

Electron Cloud Studies at Fermilab

The presence of unwanted electrons in an accelerator vacuum chamber, known as E-cloud (E-cloud) can potentially cause operational problems in the Fermilab Main Injector (MI) and Recycler Ring (RR). E-cloud has caused instability in the RR in the past, and although it is not currently a problem, there is measurable E-cloud in the MI accelerator. There are planned beam intensity increases due to upgrades of the Fermilab accelerator complex, so E-cloud could become a problem. Some work has been done by others previously to understand how low SEY (Secondary Electron Yield coefficient) coatings might mitigate production of E-cloud, and to model the mechanism whereby E-cloud causes beam instability. Using previous studies as a base, this research took several approaches toward understanding the risk of E-cloud at Fermilab. The evolution of the SEY of the SS316L (stainless steel), TiN coated SS316L, and amorphous carbon coated SS316L were measured in-situ using a SEY meas urement station in the MI tunnel. The SEY of these materials change over time either due to bombardment of the E-cloud, or disruption of vacuum conditions. The SEY evolution was tracked over a several year period to find out how long it takes for the SEY of each material to reach its lowest level, and how much the SEY rises during deconditioning periods of poor vacuum. The SEY measurement results can be used to determine whether the SS316L will be a problem at upgrade intensities, and if so, whether or not TiN and A-Carbon coatings can mitigate E-cloud related problems sufficiently. Direct measurements of the E-cloud were done as well, and compared to simulation. The E-cloud bombardment rate was measured at different beam intensities and bunch lengths. It was possible to get detailed information on how the E-cloud varies over the acceleration cycle, where sensitivity to bunch length is reflected in the evolution of the E-cloud. The Retarding Field Analyzer (RFA) measuring th e E-cloud bombardment rate was near the instrument that is u! sed to measure the SEY of the beam pipe material. This proximity provided an accurate SEY value for simulations, so that the simulated E-cloud bombardment rate could be better compared to measurement. Bunch length measurements and computations generated accurate bunch length information also needed as input for simulations. After this careful control of the input parameters, the POSINST simulations of E-cloud were a good match to direct measurements. This gave confidence that predictions could be made concerning the E-cloud densities at upgrade intensities. These densities were compared against corresponding proton densities to predict the SEY required to avoid instabilities. That prediction and the information provided by the SEY measurements provide helpful information regarding the risks of E-cloud effects at future beam intensities at Fermilab.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Methods for Determining the Infrared Complex Refractive Indices n (λ) and k (λ) from Organic Solid Powders: Comparison of a Sucrose Single Crystal and a Pressed Pellet

There exists a need to measure optical constants n and k for many materials, especially organic solids in the infrared spectral region, but at present, there are only two established methods for making such measurements: single-angle (SA) reflectance and infrared spectroscopic ellipsometry (IRSE). The former derives the n/k vectors via measurement of the change in the amplitude of light reflected from the sample and then uses the Kramers–Kronig transform, while the latter measures the change in polarization of the reflected light from the sample to derive n/k. Here we make a direct comparison between the n/k vectors derived from SA measurements of a sucrose single crystal and the n/k values obtained after the crystal had been crushed, ground to powder, and pressed into a pellet form. The pellet was measured not only by SA but also via the IRSE method, and we found that pressing specular-quality pellets was critical, especially for the SA data. The n/k values of this typical organic molecule all agree to within 0.04 root-mean-square error, confirming that a pressed pellet can be used instead of a crystal to derive the intrinsic n/k vectors. In conclusion, this result is important for the many organic materials that, unlike sugar, do not have centimeter-sized crystals readily available.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗