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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Legacy Survey of Space and Time Data Preview 1: Visit searchable catalog

The Legacy Survey of Space and Time Data Preview 1 (DP1) is the first release of data from the NSF-DOE Vera C. Rubin Observatory. It consists of raw and calibrated single-epoch images, co-adds, difference images, detection catalogs, and other derived data products. DP1 is based on 1792 science-grade optical/near-infrared exposures acquired over 48 distinct nights by the Rubin Commissioning Camera, LSSTComCam, on the Simonyi Survey Telescope at the Summit Facility on Cerro Pachón, Chile during the first on-sky commissioning campaign in late 2024. DP1 covers a total of approximately 15 sq. deg. over seven roughly equally-sized non-contiguous fields, each independently observed in six broad photometric bands, ugrizy, spanning a range of stellar densities and latitudes and overlapping with external reference datasets. This dataset is a subset of the full data release consisting of a searchable catalog named Visit. This catalog contains metadata, including dates and filters for every visit. This catalog contains 1,786 rows with 15 columns.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

EFFECT OF FILTER TEMPERATURE ON TRAPPING ZINC VAPOR

To address the {sup 65}Zn contamination issue in the TEF, a multi-task experimental program was initiated. The first experimental task was completed and is reported in Ref. 1. The results of the second experimental task are reported here. This task examined the effect of filter temperature on trapping efficiency and deposit morphology. Based on the first experimental tasks that examined filter pore size and trapping efficiency, stainless steel filter media with a 20 {micro}m pore size was selected. A series of experiments using these filters was conducted during this second task to determine the effect of filter temperature on zinc vapor trapping efficiency, adhesion and morphology. The tests were conducted with the filters heated to 60, 120, and 200 C; the zinc source material was heated to 400 C for all the experiments to provide a consistent zinc source. The samples were evaluated for mass change, deposit adhesion and morphology. As expected from the physical vapor deposition literature, a difference in deposit morphology and appearance was observed between the three filter temperatures. The filter held at 60 C had the largest average mass gain while the 120 and 200 C filters exhibited similar but lower weight gains. The standard deviations were large and suggest that all three temperatures exhibited comparable gains. No zinc was detected on the backside surface of the filters indicating high efficiency for front and internal trapping. A zinc rich deposit was formed on the surface of the 60 C filter. Based on a simple tape adhesion test, the surface zinc was readily removed from the 60 C filter while less zinc deposit was removed from the 120 and 200 C filter samples. It is surmised that the higher temperatures enable the zinc to deposit within the filter media rather than on the surface. Based on the findings that all three statistically trapped the same quantity of zinc vapor and that the higher temperatures resulted in a more adherent/better trapped product, operating the filters at 120 to 200 C is recommended.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A Bloom Filter Based Scalable Data Integrity Check Tool for Large-Scale Dataset

Large scale HPC applications are becoming increasingly data intensive. At Oak Ridge Leadership Computing Facility (OLCF), we are observing the number of files curated under individual project are reaching as high as 200 millions and project data size is exceeding petabytes. These simulation datasets, once validated, often needs to be transferred to archival system for long term storage or shared with the rest of the research community. Ensuring the data integrity of the full dataset at this scale is paramount important but also a daunting task. This is especially true considering that most conventional tools are serial and file-based, unwieldy to use and/or can't scale to meet user's demand.To tackle this particular challenge, this paper presents the design, implementation and evaluation of a scalable parallel checksumming tool, fsum, which we developed at OLCF. It is built upon the principle of parallel tree walk and work-stealing pattern to maximize parallelism and is capable of generating a single, consistent signature for the entire dataset at extreme scale. We also applied a novel bloom-filter based technique in aggregating signatures to overcome the signature ordering requirement. Given the probabilistic nature of bloom filter, we provided a detailed error and trade-off analysis. Using multiple datasets from production environment, we demonstrated that our tool can efficiently handle both very large files as well as many small-file based datasets. Our preliminary test showed that on the same hardware, it outperforms conventional tool by as much as 4×. It also exhibited near-linear scaling properties when provisioned with more compute resources.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Tunable terahertz multichannel filter based on one-dimensional superconductor-dielectric photonic crystals

By means of the transfer matrix method, the transmission properties of one-dimensional photonic crystals (PCs) consisting of superconductor and dielectric have been systematically investigated within the terahertz frequency range (0.1–10 THz). It is shown that comb-like resonant peaks in transmission band can be formed without adding any defect layer in superconductor-dielectric PCs, which means that such a one-dimensional periodic structure can serve as a tunable terahertz multichannel filter by using the PCs passband. Furthermore, the influences coming from the period of the structure, the thickness of the components, the permittivity of the dielectric layers, temperature, and the normal conducting electrons on the filtering properties are also numerically investigated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

MEASURING THE CLUMP MASS FUNCTION IN THE AGE OF SCUBA2, HERSCHEL, AND ALMA

We use simulated images of star-forming regions to explore the effects of various image acquisition techniques on the derived clump mass function. In particular, we focus on the effects of finite image angular resolution, the presence of noise, and spatial filtering. We find that, even when the image has been so heavily degraded with added noise and lowered angular resolution that the clumps it contains clearly no longer correspond to pre-stellar cores, still the clump mass function is typically consistent with the stellar initial mass function within their mutual uncertainties. We explain this result by suggesting that noise, source blending, and spatial filtering all randomly perturb the clump masses, biasing the mass function toward a lognormal form whose high-mass end mimics a Salpeter power law. We argue that this is a consequence of the central limit theorem and that it strongly limits our ability to accurately measure the true mass function of the clumps. We support this conclusion by showing that the characteristic mass scale of the clump mass function, represented by the 'break mass', scales as a simple function of the angular resolution of the image from which the clump mass function is derived. This strongly constrains our ability to use the clump mass function to derive a star formation efficiency. We discuss the potential and limitations of the current and next generation of instruments for measuring the clump mass function.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Hierarchical Inference with Bayesian Neural Networks: An Application to Strong Gravitational Lensing

In the past few years, approximate Bayesian Neural Networks (BNNs) have demonstrated the ability to produce statistically consistent posteriors on a wide range of inference problems at unprecedented speed and scale. However, any disconnect between training sets and the distribution of real-world objects can introduce bias when BNNs are applied to data. This is a common challenge in astrophysics and cosmology, where the unknown distribution of objects in our universe is often the science goal. In this work, we incorporate BNNs with flexible posterior parameterizations into a hierarchical inference framework that allows for the reconstruction of population hyperparameters and removes the bias introduced by the training distribution. We focus on the challenge of producing posterior PDFs for strong gravitational lens mass model parameters given Hubble Space Telescope–quality single-filter, lens-subtracted, synthetic imaging data. We show that the posterior PDFs are sufficiently accurate (statistically consistent with the truth) across a wide variety of power-law elliptical lens mass distributions. We then apply our approach to test data sets whose lens parameters are drawn from distributions that are drastically different from the training set. We show that our hierarchical inference framework mitigates the bias introduced by an unrepresentative training set's interim prior. Simultaneously, we can precisely reconstruct the population hyperparameters governing our test distributions. Our full pipeline, from training to hierarchical inference on thousands of lenses, can be run in a day. The framework presented here will allow us to efficiently exploit the full constraining power of future ground- and space-based surveys (https://github.com/swagnercarena/ovejero).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Filtering with Marked Point Process Observations via Poisson Chaos Expansion

We study a general filtering problem with marked point process observations. The motivation comes from modeling financial ultra-high frequency data. First, we rigorously derive the unnormalized filtering equation with marked point process observations under mild assumptions, especially relaxing the bounded condition of stochastic intensity. Then, we derive the Poisson chaos expansion for the unnormalized filter. Based on the chaos expansion, we establish the uniqueness of solutions of the unnormalized filtering equation. Moreover, we derive the Poisson chaos expansion for the unnormalized filter density under additional conditions. To explore the computational advantage, we further construct a new consistent recursive numerical scheme based on the truncation of the chaos density expansion for a simple case. The new algorithm divides the computations into those containing solely system coefficients and those including the observations, and assign the former off-line.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2010

Development of a compact tomography camera system using a multianode photomultiplier tube for compact torus experiments

A compact tomography camera system consisting of a photomultiplier tube, a multislit optical system, and a band-pass interference filter has been developed. The viewing area and spatial resolution can be configured by the arrangement of the slit system. The camera system has been specially designed for self-organized compact torus experiments having strong magnetohydrodynamics events with a submicrosecond time-scale. The developed system has been tested on a field-reversed configuration formed by the field-reversed theta-pinch. Performance evaluation of the system has been performed by comparison to the former optical system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Optical coherence tomography (OCT) leading to more insight into cochlear mechanics

Optical Coherence Tomography (OCT) was used to measure vibrations of the basilar membrane (BM) and the Reticular Lamina (RL) in the cochlea of the guinea pig, at frequencies up to 25 kHz. Because of the difficulty of the experiments the data have limited sets of parameters and are subject to high noise levels. In a viable guinea-pig cochlea, the RL moves in the region of maximum response with a larger amplitude than the BM. We cannot rule out that some of that difference is due to a geometrical factor. We also found a consistent increase of this amplitude difference with frequency, which points to a low-pass filtering process. That process might be linked to the mass of the fluid contained in the Organ of Corti channel (OoC channel)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Time-resolved biphase signatures of quadratic nonlinearity observed in coupled Alfvén eigenmodes on the DIII-D tokamak

We report the detection of nonstationary quadratic coupling between toroidicity-induced Alfvén eigenmodes (TAEs) on sub-millisecond time scales. Identification of phase coherency between multiple TAEs and nonlinearly generated modes is facilitated by wavelet-based bicoherence analysis of time-series from inductive coils, taken from a DIII-D discharge heated by neutral beam injection (NBI). Characterization of nonlinear three-wave interaction is inferred by stationary local bispectrum phase (biphase) and confirmed via bandpass filtering. Biphase dynamics associated with prominent bispectral features are well-resolved in time and consistent with transient quadratic coupling. Onset and duration of nonlinearity are correlated with enhanced amplitude of participating TAEs; coincident changes in amplitude are observed for modes at difference frequency |f TAE,1 - f TAE,2 |.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

HST/ACS IMAGING OF OMEGA CENTAURI: OPTICAL COUNTERPARTS OF CHANDRA X-RAY SOURCES

We present results of a search for optical counterparts of X-ray sources in and toward the globular cluster Omega Centauri (NGC 5139) using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The ACS data consist of a mosaic of Wide Field Channel images obtained using F625W, F435W, and F658N filters; with nine pointings we cover the central {approx}10' Multiplication-Sign 10' of the cluster and encompass 109 known Chandra sources. We find promising optical counterparts for 59 of the sources, {approx}40 of which are likely to be associated with the cluster. These include 27 candidate cataclysmic variables (CVs), 24 of which are reported here for the first time. Fourteen of the CV candidates are very faint, with absolute magnitudes in the range M {sub 625} =10.4-12.6, making them comparable in brightness to field CVs near the period minimum discovered in the Sloan Digital Sky Survey. Additional optical counterparts include three BY Dra candidates, a possible blue straggler, and a previously reported quiescent low-mass X-ray binary. We also identify 3 foreground stars and 11 probable active galactic nuclei. Finally, we report the discovery of a group of seven stars whose X-ray properties are suggestive of magnetically active binaries, and whose optical counterparts lie on or very near the metal-rich anomalous giant and subgiant branches in {omega} Cen. If the apparent association between these seven stars and the RGB/SGB-a stars is real, then the frequency of X-ray sources in this metal-rich population is enhanced by a factor of at least five relative to the other giant and subgiant populations in the cluster. If these stars are not members of the metal-rich population, then they bring the total number of red stragglers (also known as sub-subgiants) that have been identified in {omega} to Cen 20, the largest number yet known in any globular cluster.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PS1-10jh CONTINUES TO FOLLOW THE FALLBACK ACCRETION RATE OF A TIDALLY DISRUPTED STAR

We present late-time observations of the tidal disruption event candidate PS1-10jh. UV and optical imaging with Hubble Space Telescope/WFC3 localize the transient to be coincident with the host galaxy nucleus to an accuracy of 0.023 arcsec, corresponding to 66 pc. The UV flux in the F225W filter, measured 3.35 rest-frame years after the peak of the nuclear flare, is consistent with a decline that continues to follow a t{sup −5/3} power-law with no spectral evolution. Late epochs of optical spectroscopy obtained with MMT ∼ 2 and 4 years after the peak, enable a clean subtraction of the host galaxy from the early spectra, revealing broad helium emission lines on top of a hot continuum, and placing stringent upper limits on the presence of hydrogen line emission. We do not measure Balmer Hδ absorption in the host galaxy that is strong enough to be indicative of a rare, post-starburst “E+A” galaxy as reported by Arcavi et al. The light curve of PS1-10jh over a baseline of 3.5 years is best modeled by fallback accretion of a tidally disrupted star. Its strong broad helium emission relative to hydrogen (He iiλ4686/Hα > 5) could be indicative of either the hydrogen-poor chemical composition of the disrupted star, or certain conditions in the tidal debris of a solar-composition star in the presence of an optically thick, extended reprocessing envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Detecting Peer-to-Peer Botnets in SCADA Systems

Supervisory Control and Data Acquisition (SCADA) systems monitor and control critical infrastructure such as the smart grid. As SCADA systems become increasingly interconnected and adopt more and more cyber-enabled components, the risks of cyber attacks become a major concern. Due to their decentralized organization, peer-to-peer (P2P) botnets are resilient to many existing takedown measures and can be exploited as an effective way to launch cyber attacks on SCADA systems. However, little work has been done to detect P2P botnets in SCADA systems, which carry traffic flows with characteristics significantly different from the Internet. In this paper, we design a P2P-botnet detection method for SCADA systems, leveraging built-in traffic monitoring capabilities of SCADA networking devices. The proposed method consists of two stages. In the first stage, we design a simple feature test to filter out non-P2P hosts, which significantly reduces the data volume for P2P-botnet identification. In the second stage, we jointly consider flow-based and connectivity-based features that effectively set apart bots from benign hosts. We propose to use unsupervised learning for P2P-botnet identification, which not only identifies known P2P botnets but also captures newly emerged ones. Our simulation results show that the proposed system achieves high detection rates with very few false positives. Furthermore, our evaluation shows that the proposed method can detect hosts running P2P SCADA applications that are infected by P2P bots.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2013

Development and validation of a measurement-based source model for kilovoltage cone-beam CT Monte Carlo dosimetry simulations

Purpose: The purpose of this study is to adapt an equivalent source model originally developed for conventional CT Monte Carlo dose quantification to the radiation oncology context and validate its application for evaluating concomitant dose incurred by a kilovoltage (kV) cone-beam CT (CBCT) system integrated into a linear accelerator.Methods: In order to properly characterize beams from the integrated kV CBCT system, the authors have adapted a previously developed equivalent source model consisting of an equivalent spectrum module that takes into account intrinsic filtration and an equivalent filter module characterizing the added bowtie filtration. An equivalent spectrum was generated for an 80, 100, and 125 kVp beam with beam energy characterized by half-value layer measurements. An equivalent filter description was generated from bowtie profile measurements for both the full- and half-bowtie. Equivalent source models for each combination of equivalent spectrum and filter were incorporated into the Monte Carlo software package MCNPX. Monte Carlo simulations were then validated against in-phantom measurements for both the radiographic and CBCT mode of operation of the kV CBCT system. Radiographic and CBCT imaging dose was measured for a variety of protocols at various locations within a body (32 cm in diameter) and head (16 cm in diameter) CTDI phantom. The in-phantom radiographic and CBCT dose was simulated at all measurement locations and converted to absolute dose using normalization factors calculated from air scan measurements and corresponding simulations. The simulated results were compared with the physical measurements and their discrepancies were assessed quantitatively.Results: Strong agreement was observed between in-phantom simulations and measurements. For the radiographic protocols, simulations uniformly underestimated measurements by 0.54%–5.14% (mean difference =−3.07%, SD = 1.60%). For the CBCT protocols, simulations uniformly underestimated measurements by 1.35%–5.31% (mean difference =−3.42%, SD = 1.09%).Conclusions: This work demonstrates the feasibility of using a measurement-based kV CBCT source model to facilitate dose calculations with Monte Carlo methods for both the radiographic and CBCT mode of operation. While this initial work validates simulations against measurements for simple geometries, future work will involve utilizing the source model to investigate kV CBCT dosimetry with more complex anthropomorphic phantoms and patient specific models.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Technical Note: Procedure for the calibration and validation of kilo-voltage cone-beam CT models

Purpose: The aim of this work is to propose a general and simple procedure for the calibration and validation of kilo-voltage cone-beam CT (kV CBCT) models against experimental data. Methods: The calibration and validation of the CT model is a two-step procedure: the source model then the detector model. The source is described by the direction dependent photon energy spectrum at each voltage while the detector is described by the pixel intensity value as a function of the direction and the energy of incident photons. The measurements for the source consist of a series of dose measurements in air performed at each voltage with varying filter thicknesses and materials in front of the x-ray tube. The measurements for the detector are acquisitions of projection images using the same filters and several tube voltages. The proposed procedure has been applied to calibrate and assess the accuracy of simple models of the source and the detector of three commercial kV CBCT units. If the CBCT system models had been calibrated differently, the current procedure would have been exclusively used to validate the models. Several high-purity attenuation filters of aluminum, copper, and silver combined with a dosimeter which is sensitive to the range of voltages of interest were used. A sensitivity analysis of the model has also been conducted for each parameter of the source and the detector models. Results: Average deviations between experimental and theoretical dose values are below 1.5% after calibration for the three x-ray sources. The predicted energy deposited in the detector agrees with experimental data within 4% for all imaging systems. Conclusions: The authors developed and applied an experimental procedure to calibrate and validate any model of the source and the detector of a CBCT unit. The present protocol has been successfully applied to three x-ray imaging systems. The minimum requirements in terms of material and equipment would make its implementation suitable in most clinical environments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Simulating the Impact of Premixed Charge Compression Ignition on Light-Duty Diesel Fuel Economy and Emissions of Particulates and NO x

We utilize the Powertrain Systems Analysis Toolkit (PSAT) combined with transient engine and aftertreatment component models implemented in Matlab/Simulink to simulate the effect of premixed charge compression ignition (PCCI) on the fuel economy and emissions of light-duty diesel-powered conventional and hybrid electric vehicles (HEVs). Our simulated engine is capable of both conventional diesel combustion (CDC) and premixed charge compression ignition (PCCI) over real transient driving cycles. Our simulated aftertreatment train consists of a diesel oxidation catalyst (DOC), lean NOx trap (LNT), and catalyzed diesel particulate filter (DPF). The results demonstrate that, in the simulated conventional vehicle, PCCI can significantly reduce fuel consumption and emissions by reducing the need for LNT and DPF regeneration. However, the opportunity for PCCI operation in the simulated HEV is limited because the engine typically experiences higher loads and multiple stop-start transients that are outside the allowable PCCI operating range. Thus developing ways of extending the PCCI operating range combined with improved control strategies for engine and emissions control management will be especially important for realizing the potential benefits of PCCI in HEVs.

Gao, Zhiming↗
DOE OSTI2019

Equation Discovery Using Fast Function Extraction: a Deterministic Symbolic Regression Approach

Advances in machine learning (ML) coupled with increased computational power have enabled identification of patterns in data extracted from complex systems. ML algorithms are actively being sought in recovering physical models or mathematical equations from data. This is a highly valuable technique where models cannot be built using physical reasoning alone. In this paper, we investigate the application of fast function extraction (FFX), a fast, scalable, deterministic symbolic regression algorithm to recover partial differential equations (PDEs). FFX identifies active bases among a huge set of candidate basis functions and their corresponding coefficients from recorded snapshot data. This approach uses a sparsity-promoting technique from compressive sensing and sparse optimization called pathwise regularized learning to perform feature selection and parameter estimation. Furthermore, it recovers several models of varying complexity (number of basis terms). FFX finally filters out many identified models using non-dominated sorting and forms a Pareto front consisting of optimal models with respect to minimizing complexity and test accuracy. Numerical experiments are carried out to recover several ubiquitous PDEs such as wave and heat equations among linear PDEs and Burgers, Korteweg–de Vries (KdV), and Kawahara equations among higher-order nonlinear PDEs. Additional simulations are conducted on the same PDEs under noisy conditions to test the robustness of the proposed approach.

42 ENGINEERING↗
DOE OSTI2017

The Second Flight of the Sunrise Balloon-borne Solar Observatory: Overview of Instrument Updates, the Flight, the Data, and First Results

The Sunrise balloon-borne solar observatory, consisting of a 1 m aperture telescope that provides a stabilized image to a UV filter imager and an imaging vector polarimeter, carried out its second science flight in 2013 June. It provided observations of parts of active regions at high spatial resolution, including the first high-resolution images in the Mg ii k line. The obtained data are of very high quality, with the best UV images reaching the diffraction limit of the telescope at 3000 Å after Multi-Frame Blind Deconvolution reconstruction accounting for phase-diversity information. Here a brief update is given of the instruments and the data reduction techniques, which includes an inversion of the polarimetric data. Mainly those aspects that evolved compared with the first flight are described. A tabular overview of the observations is given. In addition, an example time series of a part of the emerging active region NOAA AR 11768 observed relatively close to disk center is described and discussed in some detail. The observations cover the pores in the trailing polarity of the active region, as well as the polarity inversion line where flux emergence was ongoing and a small flare-like brightening occurred in the course of the time series. The pores are found to contain magnetic field strengths ranging up to 2500 G, and while large pores are clearly darker and cooler than the quiet Sun in all layers of the photosphere, the temperature and brightness of small pores approach or even exceed those of the quiet Sun in the upper photosphere.

79 ASTRONOMY AND ASTROPHYSICS↗