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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 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Radiation of charged particle bunches in corrugated waveguides with small period

Bunch radiation in periodical waveguides was mainly analyzed for situations when wavelengths are comparable to the structure period (Smith-Purcell emission). However, it is also interesting to study long wave radiation with wavelengths which are much greater than the structure period. In this paper, the electromagnetic field is analyzed using the method of equivalent boundary conditions. According to this approach, the exact boundary conditions on the complex periodic surface are replaced with certain equivalent conditions which must be fulfilled on the smooth surface. We consider a vacuum circular waveguide with a corrugated conductive wall (corrugation has rectangular form). The charge moves along the waveguide axis. The period and the depth of corrugation are much less than the waveguide radius and wavelengths under consideration. Expressions for the full field components and the wave field components are obtained. It is established that radiation consists of the only one TM waveguide mode which is excited if the charge velocity is more than certain limit value. Dependencies of the frequency and amplitude of the mode on the charge velocity and parameters of corrugation are analyzed. It is demonstrated that typical amplitude of waveguide mode from the ultra relativistic bunch has the same order as one in the ordinary regular waveguides with dielectric filling. In order to verify the method applied in this work we have simulated the electromagnetic field using the CST Particle Studio. For this purpose, we have considered the charged particle bunch with negligible thickness and Gaussian longitudinal distribution. It has been shown that the coincidence between theoretical and simulated results is good. This fact confirms that the theory based on the equivalent boundary conditions adequately describe the radiation process in the situation under consideration. The obtained results can be useful for development of methods of the electromagnetic radiation generation and technique of the wakefield acceleration of charged particles.

Cherenkov and transition radiation↗
DOE OSTI2015

TU-F-CAMPUS-I-05: Parameterization of the Noise Power Spectrum in X-Ray Computed Tomography

Purpose: The purpose of this work was to develop a method so that the noise power spectrum (NPS) can be approximated for arbitrary levels of mAs, from a single determination in CT. Methods: The NPS is factorized into 2 components, 1) a parameterized function representing the 1D normalized spatial frequency distribution and 2) a function to scale the magnitude of 1) for arbitrary values of mAs. The 1D NPS, normalized by image variance (NNPS), was determined for 2 FBP reconstruction kernels (smoothing and edge enhancing) for 400 mAs. The NNPS were fit to the parameterized function and a scaling function was established to approximate the image variance at arbitrary values of mAs. Using the root mean square error normalized by the maximum value (NRMSE), the NPS approximated with the factorization method was compared to the NPS determined at 5 different mAs levels. Results: The factorization resulted in a set of 7 coefficients that can be used to approximate the 1D NPS, for arbitrary levels of mAs, for the convolution kernels studied in this work. The approximated NPS (factorization) agreed well with the determined NPS for all mAs levels. The greatest NRMSE was 0.02 and was observed for the edge enhancing kernel. Conclusion: The proposed factorization method has been demonstrated as applicable for FBP reconstruction. It can be used to approximate the 1D NPS for arbitrary levels of mAs, from a single NPS determination. Furthermore, approximations of the 1D NPS can conveniently be distributed since the factorization method only used 7 coefficients in the approximation.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2015

Three-Dimensional Piecewise-Continuous Class-Shape Transformation of Wings

Class-Shape Transformation (CST) is a popular method for creating analytical representations of the surface coordinates of various components of aerospace vehicles. A wide variety of two- and three-dimensional shapes can be represented analytically using only a modest number of parameters, and the surface representation is smooth and continuous to as fine a degree as desired. This paper expands upon the original two-dimensional representation of airfoils to develop a generalized three-dimensional CST parametrization scheme that is suitable for a wider range of aircraft wings than previous formulations, including wings with significant non-planar shapes such as blended winglets and box wings. The method uses individual functions for the spanwise variation of airfoil shape, chord, thickness, twist, and reference axis coordinates to build up the complete wing shape. An alternative formulation parameterizes the slopes of the reference axis coordinates in order to relate the spanwise variation to the tangents of the sweep and dihedral angles. Also discussed are methods for fitting existing wing surface coordinates, including the use of piecewise equations to handle discontinuities, and mathematical formulations of geometric continuity constraints. A subsonic transport wing model is used as an example problem to illustrate the application of the methodology and to quantify the effects of piecewise representation and curvature constraints.

Olson, Erik D.↗
DOE OSTI2014

Modeling of transport phenomena in tokamak plasmas with neural networks

A new transport model that uses neural networks (NNs) to yield electron and ion heat ux pro les has been developed. Given a set of local dimensionless plasma parameters similar to the ones that the highest delity models use, the NN model is able to efficiently and accurately predict the ion and electron heat transport pro les. As a benchmark, a NN was built, trained, and tested on data from the 2012 and 2013 DIII-D experimental campaigns. It is found that NN can capture the experimental behavior over the majority of the plasma radius and across a broad range of plasma regimes. Although each radial location is calculated independently from the others, the heat ux pro les are smooth, suggesting that the solution found by the NN is a smooth function of the local input parameters. This result supports the evidence of a well-de ned, non-stochastic relationship between the input parameters and the experimentally measured transport uxes. Finally, the numerical efficiency of this method, requiring only a few CPU-μs per data point, makes it ideal for scenario development simulations and real-time plasma control.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Two-step fabrication technique of gold tips for use in point-contact spectroscopy

For a successful point-contact spectroscopy (PCS) measurement, metallic tips of proper shape and smoothness are essential to ensure the ballistic nature of a point-contact junction. Until recently, the fabrication of Au tips suitable for use in point-contact spectroscopy has remained more of an art involving a trial and error method rather than an automated scientific process. To address these issues, we have developed a technique with which one can prepare high quality Au tips reproducibly and systematically. It involves an electronic control of the driving voltages used for an electrochemical etching of a gold wire in a HCl-glycerol mixture or a HCl solution. We find that a stopping current, below which the circuit is set to shut off, is a single very important parameter to produce an Au tip of desired shape. We present detailed descriptions for a two-step etching process for Au tips and also test results from PCS measurements using them.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Choroidal vasculature characteristics based choroid segmentation for enhanced depth imaging optical coherence tomography images

Purpose: In clinical research, it is important to measure choroidal thickness when eyes are affected by various diseases. The main purpose is to automatically segment choroid for enhanced depth imaging optical coherence tomography (EDI-OCT) images with five B-scans averaging. Methods: The authors present an automated choroid segmentation method based on choroidal vasculature characteristics for EDI-OCT images with five B-scans averaging. By considering the large vascular of the Haller’s layer neighbor with the choroid-sclera junction (CSJ), the authors measured the intensity ascending distance and a maximum intensity image in the axial direction from a smoothed and normalized EDI-OCT image. Then, based on generated choroidal vessel image, the authors constructed the CSJ cost and constrain the CSJ search neighborhood. Finally, graph search with smooth constraints was utilized to obtain the CSJ boundary. Results: Experimental results with 49 images from 10 eyes in 8 normal persons and 270 images from 57 eyes in 44 patients with several stages of diabetic retinopathy and age-related macular degeneration demonstrate that the proposed method can accurately segment the choroid of EDI-OCT images with five B-scans averaging. The mean choroid thickness difference and overlap ratio between the authors’ proposed method and manual segmentation drawn by experts were −11.43 μm and 86.29%, respectively. Conclusions: Good performance was achieved for normal and pathologic eyes, which proves that the authors’ method is effective for the automated choroid segmentation of the EDI-OCT images with five B-scans averaging.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1996

A Full Multi-Grid Method for the Solution of the Cell Vertex Finite Volume Cauchy-Riemann Equations

The system of inhomogeneous Cauchy-Riemann equations defined on a square domain and subject to Dirichlet boundary conditions is considered. This problem is discretised by using the cell vertex finite volume method on quadrilateral meshes. The resulting algebraic problem is overdetermined and the solution is defined in a least squares sense. By this approach a consistent algebraic problem is obtained which differs from the original one by O(h(exp 2)) perturbations of the right-hand side. A suitable cell-based convergent smoothing iteration is presented which is naturally linked to the least squares formulation. Hence, a standard multi-grid algorithm is reported which combines the given smoother and cell-based transfer operators. Some remarkable reduction properties of these operators are shown. A full multi-grid method is discussed which solves the discrete problem to the level of truncation error by employing one multi-grid cycle at each current level of discretisation. Experiments and applications of the full multi-grid scheme are presented.

Borzi, A.↗
DOE OSTI2016

Facile solution-precipitation assisted synthesis and luminescence property of greenish-yellow emitting Ca{sub 6}Ba(PO{sub 4}){sub 4}O:Eu{sup 2+} phosphor

Highlights: • Ca{sub 6}Ba(PO{sub 4}){sub 4}O:Eu{sup 2+} phosphor was prepared by the solution-precipitation assisted route. • The phosphors have satisfactory smooth grain surface and particle size. • It shows greenish-yellow color emission (maximum at 540 nm) upon blue light excitation. • Eu{sup 2+} is coordinated with isolated oxygen atoms and those from PO{sub 4} polyhedra. - Abstract: Greenish-yellow emitting microcrystalline Ca{sub 6}Ba(PO{sub 4}){sub 4}O:Eu{sup 2+} phosphor was successfully prepared by a solution-precipitation assisted high temperature reaction method. Phase structure, morphology and/or luminescence properties of the precursor and the as-prepared phosphors were characterized. The phase-pure Ca{sub 6}Ba(PO{sub 4}){sub 4}O:Eu{sup 2+} phosphors were obtained with smooth grain surface and particle size of 2–8 μm. Ca{sub 6}Ba(PO{sub 4}){sub 4}O:Eu{sup 2+} exhibits bright greenish-yellow color emission with its maximum at 540 nm upon UV-blue light excitation. The maximum position of the broad emission band is independent on the calcination temperature. The emission intensity increases with increasing calcination temperature due to improved crystallinity. Besides, the presence of two Eu{sup 2+} emission centers in the Ca{sub 6}Ba(PO{sub 4}){sub 4}O crystal lattice was confirmed and the coordination effects are considered concerning the roles of isolated O atoms and those from the PO{sub 4} tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Aliased tidal errors in TOPEX/POSEIDON sea surface height data

Alias periods and wavelengths for the M(sub 2, S(sub 2), N(sub 2), K(sub 1), O(sub 1), and P(sub 1) tidal constituents are calculated for TOPEX/POSEIDON. Alias wavelenghts calculated in previous studies are shown to be in error, and a correct method is presented. With the exception of the K(sub 1) constituent, all of these tidal aliases for TOPEX/POSEIDON have periods shorter than 90 days and are likely to be confounded with long-period sea surface height signals associated with real ocean processes. In particular, the correspondence between the periods and wavelengths of the M(sub 2) alias and annual baroclinic Rossby waves that plagued Geosat sea surface height data is avoided. The potential for aliasing residual tidal errors in smoothed estimates of sea surface height is calculated for the six tidal constituents. The potential for aliasing the lunar tidal constituents M(sub 2), N(sub 2) and O(sub 1) fluctuates with latitude and is different for estimates made at the crossovers of ascending and descending ground tracks than for estimates at points midway between crossovers. The potential for aliasing the solar tidal constituents S(sub 2), K(sub 1) and P(sub 1) varies smoothly with latitude. S(sub 2) is strongly aliased for latitudes within 50 degress of the equator, while K(sub 1) and P(sub 1) are only weakly aliased in that range. A weighted least squares method for estimating and removing residual tidal errors from TOPEX/POSEIDON sea surface height data is presented. A clear understanding of the nature of aliased tidal error in TOPEX/POSEIDON data aids the unambiguous identification of real propagating sea surface height signals. Unequivocal evidence of annual period, westward propagating waves in the North Atlantic is presented.

Schlax, Michael G.↗
DOE OSTI2018

A Positive-Definite, WENO-Limited, High-Order Finite Volume Solver for 2-D Transport on the Cubed Sphere Using an ADER Time Discretization

Modern computer architectures reward added computation if it reduces algorithmic dependence, reduces data movement, increases accuracy/robustness, and improves memory accesses. The driving motive for this study is to develop a numerical algorithm that respects these constraints while improving accuracy and robustness. This study introduces the ADER-DT (Arbitrary DERivatives in time and space-differential transform) time discretization to positive-definite, weighted essentially nonoscillatory (WENO)-limited, finite volume transport on the cubed sphere in lieu of semidiscrete integrators. The cost of the ADER-DT algorithm is significantly improved from previous implementations without affecting accuracy. A new function-based WENO implementation is also detailed for use with the ADER-DT time discretization. While ADER-DT costs about 1.5 times more than a fourth-order, five-stage strong stability preserving Runge-Kutta (SSPRK4) method, it is far more computationally dense (which is advantageous on accelerators such as graphics processing units), and it has a larger effective maximum stable time step. ADER-DT errors converge more quickly with grid refinement than SSPRK4, giving 6.5 times less error in the L ∞ norm than SSPRK4 at the highest refinement level for smooth data. For nonsmooth data, ADER-DT resolves C 0 discontinuities more sharply. For a complex flow field, ADER exhibits less phase error than SSPRK4. In conclusion, improving both accuracy and robustness as well as better respecting modern computational efficiency requirements, we believe the method presented herein is competitive for efficiently transporting tracers over the sphere for applications targeting modern computing architectures.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1983

Equivalent absorption coefficients generated from frequency probability distributions

A flexible and computationally accurate method of treating aerosol scattering in spectral regions in which gaseous absorption is important is described. In the method, line-by-line absorption coefficients are computed as a function of pressure, temperature, and absorber gas for the spectral region of interest. The coefficients are sorted into a probability distribution which is converted into a cumulative probability distribution, which in turn can be inverted due to its monotonic nature. The inverted distribution is a smooth curve giving the absorption coefficient as a function of an independent variable on the domain. The frequency integration of the radiative transfer equation can then be performed by a quadrature technique with values of the absorption coefficient determined from the inverted distribution curve. The method is illustrated by applying it to the 9.6 micron band of ozone.

Ackerman, T. P.↗
DOE OSTI2019

Polyvinyl Alcohol (PVA)–Azadirachta indica (Neem) Nanofibrous Mat for Biomedical Application: Formation and Characterization

The present study provides credence to the formation of polyvinyl alcohol (PVA)–Azadirachta indica (neem) nanofibrous mat (PNNM) under optimum processing conditions of electrospinning technique from a mixer of PVA and neem extract to utilize the inherent medicinal properties of this herb for biomedical application. The bonding behavior, orientation of fibers, thermal behavior, and moisture management properties were evaluated by Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermo gravimetric analysis (TGA) and moisture management tester (MMT) reports respectively. The antibacterial activity of the developed sample at the maximum mixing ratio of neem extract (80%) was tested against Gram-positive (S. aureus) bacteria using agar disc diffusion method. The results reveal that the prepared nanofibrous mat exhibited better thermal and moisture management properties in comparison with PVA nanofiber alone. The formation of smooth fibers was confirmed by SEM images having average diameter of 185 nm under 5k, 10k and 15k magnifications. The characteristic peaks of PVA and neem constituents in FTIR spectra of the developed mat confirmed the presence of both components. Bacterial resistance was reached up to 20 mm due to the antibacterial constituents of neem extract. Thus the developed mat could be used as a biocompatible and bio based in biomedical applications. Graphic Abstract: .

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural and optical properties of ZnO thin films grown by rapid atmospheric mist chemical vapor technique

In this work, the effect of deposition time on the structural and optical properties of ZnO films deposited by Ultrasonic Spray Mist-CVD was studied aiming the application in perovskite solar cells, as holes blocking layer. Crystallinity, surface morphology and optical properties of the ZnO films were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), conventional and Photoluminescence (PL) spectroscopies, respectively. The XRD measurement proves the existence of the hexagonal wurtzite phase and a high degree of crystallinity with [001] preferential orientation. The SEM study shows that the films possess a compact structure. Smooth and homogenous surface was confirmed also by AFM. The obtained results indicate that ZnO films deposited by a simple, safe and cost-effective method present a great potential for application in perovskite solar cells.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

SUBTRACTING FOREGROUNDS FROM INTERFEROMETRIC MEASUREMENTS OF THE REDSHIFTED 21 cm EMISSION

The ability to subtract foreground contamination from low-frequency observations is crucial to reveal the underlying 21 cm signal. The traditional line-of-sight methods can deal with the removal of diffuse emission and unresolved point sources, but not bright point sources. In this paper, we introduce a foreground cleaning technique in Fourier space, which allows us to handle all such foregrounds simultaneously and thus sidestep any special treatments to bright point sources. Its feasibility is tested with a simulated data cube for the 21 CentiMeter Array experiment. This data cube includes more realistic models for the 21 cm signal, continuum foregrounds, detector noise, and frequency-dependent instrumental response. We find that a combination of two weighting schemes can be used to protect the frequency coherence of foregrounds: the uniform weighting in the uv plane and the inverse-variance weighting in the spectral fitting. The visibility spectrum is therefore well approximated by a quartic polynomial along the line of sight. With this method, we demonstrate that the huge foreground contamination can be cleaned out effectively with residuals on the order of {approx}10 mK, while the spectrally smooth component of the cosmological signal is also removed, bringing about a systematic underestimate in the extracted power spectrum primarily on large scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Treating quarks within neutron stars

Neutron star interiors provide the opportunity to probe properties of cold dense matter in the QCD phase diagram. Utilizing models of dense matter in accord with nuclear systematics at nuclear densities, we investigate the compatibility of deconfined quark cores with current observational constraints on the maximum mass and tidal deformability of neutron stars. Here we explore various methods of implementing the hadron-to-quark phase transition, specifically, first-order transitions with sharp (Maxwell construction) and soft (Gibbs construction) interfaces, and smooth crossover transitions. We find that within the models we apply, hadronic matter has to be stiff for a first-order phase transition and soft for a crossover transition. In both scenarios and for the equations of state we employed, quarks appear at the center of premerger neutron stars in the mass range ≈ 1.0 – 1.6 M ⊙ , with a squared speed of sound $c^2_{QM}$ ≳ 0.4 characteristic of strong repulsive interactions required to support the recently discovered neutron star masses ≥ 2 M ⊙ . We also identify equations of state and phase transition scenarios that are consistent with the bounds placed on tidal deformations of neutron stars in the recent binary merger event GW170817. We emphasize that distinguishing hybrid stars with quark cores from normal hadronic stars is very difficult from the knowledge of masses and radii alone, unless drastic sharp transitions induce distinctive disconnected hybrid branches in the mass-radius relation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

WE-G-18A-03: Cone Artifacts Correction in Iterative Cone Beam CT Reconstruction

Purpose: For iterative reconstruction (IR) in cone-beam CT (CBCT) imaging, data truncation along the superior-inferior (SI) direction causes severe cone artifacts in the reconstructed CBCT volume images. Not only does it reduce the effective SI coverage of the reconstructed volume, it also hinders the IR algorithm convergence. This is particular a problem for regularization based IR, where smoothing type regularization operations tend to propagate the artifacts to a large area. It is our purpose to develop a practical cone artifacts correction solution. Methods: We found it is the missing data residing in the truncated cone area that leads to inconsistency between the calculated forward projections and measured projections. We overcome this problem by using FDK type reconstruction to estimate the missing data and design weighting factors to compensate the inconsistency caused by the missing data. We validate the proposed methods in our multi-GPU low-dose CBCT reconstruction system on multiple patients' datasets. Results: Compared to the FDK reconstruction with full datasets, while IR is able to reconstruct CBCT images using a subset of projection data, the severe cone artifacts degrade overall image quality. For head-neck case under a full-fan mode, 13 out of 80 slices are contaminated. It is even more severe in pelvis case under half-fan mode, where 36 out of 80 slices are affected, leading to inferior soft-tissue delineation. By applying the proposed method, the cone artifacts are effectively corrected, with a mean intensity difference decreased from ∼497 HU to ∼39HU for those contaminated slices. Conclusion: A practical and effective solution for cone artifacts correction is proposed and validated in CBCT IR algorithm. This study is supported in part by NIH (1R01CA154747-01)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

WE-AB-202-06: Correlating Lung CT HU with Transformation-Based and Xe-CT Derived Ventilation

Purpose: Regional lung ventilation is useful to reduce radiation-induced function damage during lung cancer radiation therapy. Recently a new direct HU (Hounsfield unit)-based method was proposed to estimate the ventilation potential without image registration. The purpose of this study is to examine if there is a functional dependence between HU values and transformation-based or Xe-CT derived ventilation. Methods: 4DCT images acquired from 13 patients prior to radiation therapy and 4 mechanically ventilated sheep subjects which also have associated Xe-CT images were used for this analysis. Transformation-based ventilation was computed using Jacobian determinant of the transformation field between peak-exhale and peak-inhale 4DCT images. Both transformation and Xe-CT derived ventilation was computed for each HU bin. Color scatter plot and cumulative histogram were used to compare and validate the direct HU-based method. Results: There was little change of the center and shape of the HU histograms between free breathing CT and 4DCT average, with or without smoothing, and between the repeated 4DCT scans. HU of −750 and −630 were found to have the greatest transformation-based ventilation for human and sheep subjects, respectively. Maximum Xe-CT derived ventilation was found to locate at HU of −600 in sheep subjects. The curve between Xe-CT ventilation and HU was noisy for tissue above HU −400, possibly due to less intensity change of Xe gas during wash-out and wash-in phases. Conclusion: Both transformation-based and Xe-CT ventilation demonstrated that lung tissues with HU values in the range of (-750, −600) HU have the maximum ventilation potential. The correlation between HU and ventilation suggests that HU might be used to help guide the ventilation calculation and make it more robust to noise and image registration errors. Research support from NIH grants CA166703 and CA166119 and a gift from Roger Koch.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

A nonsmooth nonconvex optimization algorithm for two-stage optimization problems

An optimization algorithm for a group of nonsmooth nonconvex problems inspired by two-stage stochastic programming problems is proposed. The main challenges for these problems include (1) the problems lack the popular lower-type properties such as prox-regularity assumed in many nonsmooth nonconvex optimization algorithms, (2) the objective can not be analytically expressed and (3) the evaluation of function values and subgradients are computationally expensive. To address these challenges, this report first examines the properties that exist in many two-stage problems, specifically upper-C 2 objectives. Then, we show that quadratic penalty method for securityconstrained alternating current optimal power flow (SCACOPF) contingency problems can make the contingency solution functions upper-C 2 . Based on these observations, a simplified bundle algorithm that bears similarity to sequential quadratic programming (SQP) method is proposed. It is more efficient in implementation and computation compared to conventional bundle methods. Global convergence analysis of the algorithm is presented under novel and reasonable assumptions. The proposed algorithm therefore fills the gap of theoretical convergence for smoothed SCACOPF problems. The inconsistency that might arise in our treatment of the constraints are addressed through a penalty algorithm whose convergence analysis is also provided. Finally, theoretical capabilities and numerical performance of the algorithm are demonstrated through numerical examples.

97 MATHEMATICS AND COMPUTING↗