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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 685 records · Page 38

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NASA NTRS2003

Integrated Optical Design Analysis (IODA): New Test Data and Modeling Features

A general overview of the capabilities of the IODA ("Integrated Optical Design Analysis") exchange of data and modeling results between thermal, structures, optical design, and testing engineering disciplines. This presentation focuses on new features added to the software that allow measured test data to be imported into the IODA environment for post processing or comparisons with pretest model predictions. software is presented. IODA promotes efficient

Moore, Jim↗

NASA NTRS1982

A statistical model of the photomultiplier gain process with applications to optical pulse detection

A Markov diffusion model was used to determine an approximate probability density for the random gain. This approximate density preserves the correct second-order statistics and appears to be in reasonably good agreement with experimental data. The receiver operating curve for a pulse counter detector of PMT cathode emission events was analyzed using this density. The error performance of a simple binary direct detection optical communication system was also derived.

Tan, H. H.↗

NASA NTRS1982

A statistical model of the photomultiplier gain process with applications to optical pulse detection

Tan, H. H.↗

DOE OSTI2026

Development Fiber Optic Distributed System for Direct Detection of Subsurface Gases Leakages

Carbon, natural gas, and hydrogen gas storage is an emerging solution to safeguard us against pollution, support goals of negative carbon emission, and protect sources of renewable energy. Properly constructed storage wells provide a virtually impervious barrier to any unintended subsurface transmission. The ability to ensure the long-term integrity of such wells is vital to the success of any storage operation and be successful in the public eyes. Therefore, robust monitoring of any gas migration into the subsurface is highly sought. A fiber-optic distributed chemical sensor (DCS) enables monitoring of long-term well integrity along its depth, ensuring the success of any storage operation and bolsters public acceptance of the safety of the reservoir via leak early detection. The same technique can be applied to gas monitoring in pipeline networks and nuclear stockpile monitoring applications. Fiber based Raman spectroscopy enables DCS, as optical fibers can be deployed in virtually any environment and relay spectroscopic information over long distances back to the user. Hollow core fibers (HCF) make excellent DCSs as the air core of the fiber allows gas from the environment to diffuse into the core, which interacts with the laser signal that is carried in the air core. This work builds upon the previous LDRD project, Fiber Optic System for Direct Detection of Carbon Dioxide Leakage in Carbon Storage Wells (21-FS-003), in which the feasibility of Raman spectroscopy detection of Carbon Dioxide (CO2) in HCF detection was demonstrated. We mitigated the risk of this DCS technology by establishing and completing five objectives. The first objective was to model and optically characterize HCF uptake of CO2, establishing the relationship between HCF length, gas diffusion time, detectable gas concentration, and measured Raman intensity. In objective two, we developed a fiber core drilling recipe to enable additional diffusion ports in the fiber core and established a method for maintaining fiber strength and integrity post drilling. Objective three characterized the drilled fibers against the undrilled fibers, establishing the differences in the gas mechanics and optical properties and provided parameters to iterate the drilling process. In objective four, a fusion splicing technique was developed to join the HCF to conventional single-mode fibers, localizing the gas detection point at the drilled HCF hole, emulating a DCS. Lastly, objective five was the testing of the sensor in Edgar Mines at Colorado School of Mines on a CO2 pipeline with a simulated leak, to showcase the ability to detect CO2 leaks. This capstone result showed CO2 leak detection in < 10 minutes, raising the technology readiness level of HCF segments as deployable DCS.

organic↗

NASA NTRS1991

Optical polarimetry of PKS 2155 - 304 and constraints on accretion disk models for BL Lacertae objects

Optical broad-band polarimetry and photometry of the BL Lacertae object PKS 2155 - 304 during late 1990 are presented. Variability in both flux and linear polarization was moderate during this period. The optical polarization ranged from 2 to 7 percent while photometric variations were within 0.2 mag (V = 13.2-13.4). Accurate multicolor measurements were made to study any wavelength dependence of the polarization with an eye to using these data to test the model of Wandel and Urry (1991) which proposes that the UV to soft X-ray continuum of this object arises from an accretion disk. Wavelength-dependent polarization (WDP) is observed in PKS 2155 - 304. However, the polarization is always seen to decrease with wavelength when WDP is observed. This is opposite to the expected sense of WDP if the UV continuum is dominated by an accretion disk.

Smith, Paul S.↗

NASA NTRS1983

The relationship between the X-ray and optical luminosities for QSOs

A study of simple models for the optical and X-ray luminosities of QSOs shows that a thick accretion disk around a black hole is consistent with the observed dependence of the X-ray luminosity L(x) on the optical luminosity L(opt) to the bth power, with b roughly in the range 0.5-0.8. The disk is expected to be thick since the sources are accreting at rates near the Edington limit. Using the model of McMillan, Lightman, and Cohn (1981) for the gas supply rate, the evolution of L(opt) is predicted to be proportional to t/t(0) to the -8/3 and that of L(x) is predicted to be proportional to t/t(0) to the -2.

Tucker, W. H.↗

NASA NTRS1990

Microwave structure of the quiet sun at 8.5 GHz

Multifrequency VLA observations of the quiet sun near 8.5 GHz are presented. Two regions of the sun were observed, one dominated by an enhanced network corresponding to a decayed active region, and the other corresponding to an enhanced network with no active features. The full-day synthesis maps for both show nearly perfect correspondence to H-alpha images, and to longitudinal magnetograms. The coronal loops were observed to appear as regions of radio emission with no underlying longitudinal magnetic fields, being aligned with H-alpha fibrils in the photosphere, and connecting regions of opposite magnetic polarity. The emission can be modeled as optically thin free-free emission from a coronal loop with a peak axial density of approximately 2.4-2.8 x 10 to the 9th/cu cm, for an assumed coronal temperature of 1-2 x 10 to the 6th K. The quiet chromosphere sources are measured, and the significance of these measurements for existing chromospheric models is discussed.

Gary, Dale E.↗

DOE OSTI2021

Machine Learning Predictions of Transition Probabilities in Atomic Spectra

Forward modeling of optical spectra with absolute radiometric intensities requires knowledge of the individual transition probabilities for every transition in the spectrum. In many cases, these transition probabilities, or Einstein A-coefficients, quickly become practically impossible to obtain through either theoretical or experimental methods. Complicated electronic orbitals with higher order effects will reduce the accuracy of theoretical models. Experimental measurements can be prohibitively expensive and are rarely comprehensive due to physical constraints and sheer volume of required measurements. Due to these limitations, spectral predictions for many element transitions are not attainable. In this work, we investigate the efficacy of using machine learning models, specifically fully connected neural networks (FCNN), to predict Einstein A-coefficients using data from the NIST Atomic Spectra Database. For simple elements where closed form quantum calculations are possible, the data-driven modeling workflow performs well but can still have lower precision than theoretical calculations. For more complicated nuclei, deep learning emerged more comparable to theoretical predictions, such as Hartree–Fock. Unlike experiment or theory, the deep learning approach scales favorably with the number of transitions in a spectrum, especially if the transition probabilities are distributed across a wide range of values. It is also capable of being trained on both theoretical and experimental values simultaneously. In addition, the model performance improves when training on multiple elements prior to testing. The scalability of the machine learning approach makes it a potentially promising technique for estimating transition probabilities in previously inaccessible regions of the spectral and thermal domains on a significantly reduced timeline.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS2000

BOREAS TE-18 Landsat TM Physical Classification Image of the NSA

The BOREAS TE-18 team focused its efforts on using remotely sensed data to characterize the successional and disturbance dynamics of the boreal forest for use in carbon modeling. The objective of this classification is to provide the BOREAS investigators with a data product that characterizes the land cover of the NSA. A Landsat-5 TM image from 21-Jun-1995 was used to derive the classification. A technique was implemented that uses reflectances of various land cover types along with a geometric optical canopy model to produce spectral trajectories. These trajectories are used in a way that is similar to training data to classify the image into the different land cover classes. The data are provided in a binary, image file format. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hall, Forrest G.↗

NASA NTRS2000

BOREAS TE-18 Landsat TM Physical Classification Image of the SSA

The BOREAS TE-18 team focused its efforts on using remotely sensed data to characterize the successional and disturbance dynamics of the boreal forest for use in carbon modeling. The objective of this classification is to provide the BOREAS investigators with a data product that characterizes the land cover of the SSA. A Landsat-5 TM image from 02-Sep-1994 was used to derive the classification. A technique was implemented that uses reflectances of various land cover types along with a geometric optical canopy model to produce spectral trajectories. These trajectories are used as training data to classify the image into the different land cover classes. These data are provided in a binary image file format. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

Hall, Forrest G.↗

NASA NTRS2000

BOREAS TE-18 Landsat TM Maximum Likelihood Classification Image of the SSA

The BOREAS TE-18 team focused its efforts on using remotely sensed data to characterize the successional and disturbance dynamics of the boreal forest for use in carbon modeling. The objective of this classification is to provide the BOREAS investigators with a data product that characterizes the land cover of the SSA. A Landsat-5 TM image from 02-Sep- 1994 was used to derive the classification. A technique was implemented that uses reflectances of various land cover types along with a geometric optical canopy model to produce spectral trajectories. These trajectories are used as training data to classify the image into the different land cover classes. These data are provided in a binary image file format. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Center (DAAC).

Hall, Forrest G.↗

NASA NTRS1982

Mid-latitude model analysis of solar radiation, the upper layers of the sea, and seasonal climate

A simplified, time-dependent energy balance climate model is run at the latitude belt 40-50 deg N. The model solves for the temperatures of the land, air, and 12 vertical oceanic layers, and it includes a wind stirred mixed layer. A change in model ocean optical turbidity from relatively clear (Jerlov 1) to particle rich (Jerlov III) conditions decreases the effective thickness of the oceanic layer in which heat is stored seasonally and increases the seasonal variation of sea surface temperature by 2-3 C. A decrease in the liquid water content of clouds by a factor of 4 warms the model climate and increases the seasonal variation of sea surface temperatures by 2-3 C. A 2-3 C change in the seasonal variation of sea surface temperature is also obtained by varying oceanic mixing through a factor of 2 change in the surface wind speed.

Charlock, T. P.↗

NASA NTRS1992

Model of an axially strained weakly guiding optical fiber modal pattern

Axial strain can be determined by monitoring the modal pattern variation of an optical fiber. The results of a numerical model developed to calculate the modal pattern variation at the end of a weakly guiding optical fiber under axial strain is presented. Whenever an optical fiber is under stress, the optical path length, the index of refraction, and the propagation constants of each fiber mode change. In consequence, the modal phase term for the fields and the fiber output pattern are also modified. For multimode fibers, very complicated patterns result. The predicted patterns are presented, and an expression for the phase variation with strain is derived.

Egalon, Claudio O.↗

NASA NTRSDate not supplied

Assessment of Sensor Data Accuracy within Gazebo/ROS for High-Precision Autonomous In-Space Robotic Operations

Modeling high-precision in-space servicing, assembly, and manufacturing operations in a simulated environment is a critical step in the development of robotic systems that will be used to autonomously assemble large-scale structures in space. Limited facility size and high costs for manufacturing prototypes make it challenging to conduct full-scale operational testing under appropriate environmental conditions; therefore, testing in a modular, high-fidelity simulation environment is necessary for verification and validation of technology and architecture designs prior to launch. Several modeling and simulation environments exist both within NASA and industry that can be used to test robotic system design and operations, including the widely used commercial tool Gazebo integrated with Robotic Operating System software. Because the performance of autonomous robotic systems relies heavily on the quality of sensor input data, this paper focuses on assessing the accuracy of pose data from an optical sensor model in the Gazebo environment against the behavior of real hardware. The results of the tests will help developers using Gazebo for large-scale, high-precision simulation to account for modeling inaccuracies within their robotic control system algorithms.

simulation↗

DOE OSTI2020

In situ temperature profile measurements with high-energy X-rays as a probe of optical floating zone crystal growth environment

The ability of optical floating zone (OFZ) furnaces to rapidly produce large single crystals of complex emerging materials has had a transformative effect on many scientific fields that require samples of this type. However, the crystal growth process within the OFZ furnace is not well understood owing to the challenges involved in monitoring the high-temperature crystal growth process. Novel beamline-compatible optical furnaces that approximate the inhomogeneous growth environment within an OFZ furnace have been fabricated and tested in high-energy synchrotron beamlines. In this paper, it is demonstrated that temperature profiles can be effectively extracted from powder diffraction data collected on polycrystalline ceramic rods heated at their tip. Furthermore, these measured temperature profiles can be accurately reproduced using a heat-transfer model that accounts for solid-state thermal conduction, partial sample lamp power absorption, convective air cooling and radiative cooling, allowing key thermal parameters such as thermal conductivity to be extracted from experimental data.

36 MATERIALS SCIENCE↗

NASA NTRS2016

H2RG Detector Characterization for RIMAS and Instrument Efficiencies

The Rapid infrared IMAger-Spectrometer (RIMAS) is a near-infrared (NIR) imager and spectrometer that will quickly follow up gamma-ray burst afterglows on the 4.3-meter Discovery Channel Telescope (DCT). RIMAS has two optical arms which allows simultaneous coverage over two bandpasses (YJ and HK) in either imaging or spectroscopy mode. RIMAS utilizes two Teledyne HgCdTe H2RG detectors controlled by Astronomical Research Cameras, Inc. (ARC/Leach) drivers. We report the laboratory characterization of RIMAS's detectors: conversion gain, read noise, linearity, saturation, dynamic range, and dark current. We also present RIMAS's instrument efficiency from atmospheric transmission models and optics data (both telescope and instrument) in all three observing modes.

Toy, Vicki L.↗

DOE OSTI2022

Frequency-Domain Spectroscopic Study of the Photosystem I Supercomplexes, Isolated IsiA Monomers, and the Intact IsiA Ring

The PSI 3 -IsiA 18 supercomplex is one of the largest and most complicated assemblies in photosynthesis. The IsiA ring, composed of 18 IsiA monomers (IsiA 18 ) surrounding the PSI trimer (PSI 3 ), forms under iron-deficient condition in cyanobacteria and acts as a peripheral antenna. Based on the supercomplex structure recently determined via cryo-EM imaging, we model various optical spectra of the IsiA monomers and IsiA 18 ring. Comparison of the absorption and emission spectra of the isolated IsiA monomers and the full ring reveals that about 2.7 chlorophylls (Chls) are lost in the isolated IsiA monomers. The best fits for isolated monomers spectra are obtained assuming the absence of Chl 508, Chl 517 and 70% loss of Chl 511. The best model describing all three hexamers and the entire ring suggests that the lowest energy pigments are Chls 511, 514 and 517. Based on the modeling results presented in this work we conclude that there are most likely three entry points for EET from the IsiA6 hexamer to the PSI core monomer, with two of these entry points likely being located next to each other (i.e. nine entry points from IsiA 18 to the PSI 3 trimer). Lastly, we show that excitation energy transfer inside individual monomers is fast (< 2 ps at T = 5 K) and at least 20 times faster than inter-monomer energy transfer.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS2024

Modeling Atmospheric Brown Carbon in the GISS ModelE Earth System Model

Brown carbon (BrC) is an absorbing organic aerosol (OA), primarily emitted through biomass burning (BB), which exhibits light absorption unique to both black carbon (BC) and other organic aerosols. Despite many field and laboratory studies seeking to constrain BrC properties, the radiative forcing (RF) of BrC is still highly uncertain. To better understand its climate impact, we introduced BrC to the One-Moment Aerosol (OMA) module of the GISS ModelE Earth system model (ESM). We assessed ModelE sensitivity to primary BrC processed through a novel chemical aging scheme and to secondary BrC formed from biogenic volatile organic compounds (BVOCs). Initial results show that BrC typically contributes a top-of-the-atmosphere (TOA) radiative effect of 0.04 W m −2 . Sensitivity tests indicate that explicitly simulating BrC (separating it from other OAs), including secondary BrC, and simulating chemical bleaching of BrC contribute distinguishable radiative effects and should be accounted for in BrC schemes. This addition of prognostic BrC to ModelE allows greater physical and chemical complexity in OA representation with no apparent trade-off in model performance, as the evaluation of ModelE aerosol optical depth against Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectroradiometer (MODIS) retrieval data, with and without the BrC scheme, reveals similar skill in both cases. Thus, BrC should be explicitly simulated to allow more physically based chemical composition, which is crucial for more detailed OA studies like comparisons to in situ measurement campaigns. We include a summary of best practices for BrC representation within ModelE at the end of this paper.

brown carbon aerosols↗