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DOE OSTI2020

Dark Lock-in Thermography Identifies Solder Bond Failure as the Root Cause of Series Resistance Increase in Fielded Solar Modules

Correlating the electrical performance of photovoltaic modules to the spatially resolved photoluminescence, electroluminescence, and dark lock-in thermography (DLIT) images is an important long-term goal for developing solar cell technology. These images offer highly sophisticated and detailed information about the spatial distribution and (if imaged at successive time intervals) temporal degradation of local series and shunt resistances. There have been extensive studies to correlate these imaging techniques to local characteristics at the cell level. However, it has been difficult to extract and quantify module-level information from the techniques. In this study, we interpret module current-voltage (I-V) measurements along with corresponding DLIT images within a module-scale simulation framework, demonstrating that series resistance degradation of the module I-V characteristics, in this case, can be attributed to solder bond failures. Our simulations highlight how current crowding associated with a failed solder joint (or a section of the solder pad) translates to the characteristic point-like (asymmetric doublet) heating pattern in neighboring solder joints (or the neighboring regions of the solder pad). Overall, the correlation between series resistance and solder joint degradation could inform expedited diagnosis of field degradation of solar modules.

42 ENGINEERING↗

DOE OSTI2024

Prospects for Antiferromagnetic Spintronic Devices

This article examines recent advances in the field of antiferromagnetic spintronics from the perspective of potential device realization and applications. We discuss advances in the electrical control of antiferromagnetic order by current-induced spin–orbit torques, particularly in antiferromagnetic thin films interfaced with heavy metals. We also review possible scenarios for using voltage-controlled magnetic anisotropy as a more efficient mechanism to control antiferromagnetic order in thin films with perpendicular magnetic anisotropy. Next, we discuss the problem of electrical detection (i.e., readout) of antiferromagnetic order and highlight recent experimental advances in realizing anomalous Hall and tunneling magnetoresistance effects in thin films and tunnel junctions, respectively, which are based on noncollinear antiferromagnets. Understanding the domain structure and dynamics of antiferromagnetic materials is essential for engineering their properties for applications. For this reason, we then provide an overview of imaging techniques as well as micromagnetic simulation approaches for antiferromagnets. Finally, we present a perspective on potential applications of antiferromagnets for magnetic memory devices, terahertz sources, and detectors.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Algorithms for Forward and Inverse Problem Solutions in Phase Contrast Tomography

PhaseTorch is a python package that implements algorithms for forward and inverse problem solutions in X-ray phase contrast tomography (XPCT). XPCT is useful to reconstruct the 3D distribution of the refractive index decrement and absorption index of an imaged object. PhaseTorch implements algorithms for simulation, reconstruction, and analysis of XPCT data. PhaseTorch provides algorithms for simulation of XPCT data of an object with known refractive and absorption indices. It contains algorithms for reconstructing the projections of the absorption index and refractive index decrement.

Sridhar, Venkatesh↗

DOE OSTI2020

The Dark Energy Spectrographic Instrument (DESI) Corrector Assembly

The specific research of the DESI project is to study in detail the expansion history of the Universe over the past 10 billion years. In order to do this, the project designed, fabricated, tested and commissioned the DESI instrument which has been deployed at the Mayall Telescope at the Kitt Peak National Observatory near Tucson, Arizona. The DESI project was conducted by approximately 30 US and foreign national laboratories. Our CRADA with University College London (UCL) involved both research planning for eventual observing on the DESI telescope; and in the build of the optical corrector, a major part of the instrument. The key major goals of this CRADA were achieved. For survey planning, Drs. Lahav, Abdalla, Peiris, Pontzen and Dr. Farihi were all important contributors to the working groups to which they were assigned. Their modelling efforts, cosmological simulations, target selection and analyses of imaging surveys have been vital in the early planning for targets during commissioning. The major role UCL played in the development of the instrument was performed by Drs. Doel and Brooks. The optical corrector components were developed by scientists and engineers at Lawrence Berkeley National Laboratory and at Fermi National Accelerator Laboratory. UCL was assigned the arduous responsibility for creating the instrumentation necessary to take all the separate components (lenses, cells, rings) and incorporate them, while precisely aligning the optics. Following that, they installed the corrector inside the barrel and shipped everything to the Mayall. It was a great success that the optical barrel arrived safely in good condition. Drs. Doel and Brooks were involved in every step of the fabrication and kept in constant contact with the LBNL DESI Project Manager and Project Director. They were extremely successful in their alignment, which was proved by early observations. First light on the telescope was achieved on October 22, 2020. The first spectrum was taken of a random star at zenith. Shortly thereafter, the telescope slewed to M33 and several spectra were taken there and later in the Persus nebula. It was a major accomplishment for the project.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1973

A new vegetation map of the western Seward Peninsula, Alaska, based on ERTS-1 imagery

The author has identified the following significant results. A reconstituted, simulated color-infrared ERTS-1 image covering the western Seward Peninsula was prepared and it is used for identifying and mapping vegetation types by direct visual examination. The image, NASA ERTS E-1009-22095, was obtained approximately at 1110 hours, 165 degrees WMT on August 1, 1972. Seven major colors are identified. Four of these are matched with units on existing vegetation maps: bright red - shrub thicket; light gray-red - upland tundra; medium gray-red - coastal coastal wet tundra; gray - alpine barrens. The three colors having no map equivalents are tentatively interpreted as follows: pink - grassland tundra; dark gray-red - burn scars; light orange-red - senescent vegetation. A vegetation map, drawn by tracing on an acetate overlay of the image is presented. Significantly more information is depicted than on existing maps with regards to vegetation types and their areal distribution. Furthermore the preparation of the new map from ERTS-1 imagery required little time relative to conventional methods and extent of areal coverage.

Anderson, J. H.↗

NASA NTRS1976

Multiplane binocular visual display system

Electro-optic system is interfaced with digital computer in flight simulator to generate simultaneous multiple-image planes in real time. System may have applications with other display and remote-control systems.

Chase, W. D.↗

NASA NTRS1978

Effect of weighting on time sidelobe suppression

Weighting simulations in the time domain were considered to shape the time-compressed pulse waveform. The digital input radar data were 32 bit I,Q, and simulated data from a point target, imaged by a Seasat-A type system. Weighting functions tested include stepped-amplitude distributions, (with 1 through 5 steps), and the cosine-squared plus pedestal distribution. Effects treated include mainlobe ratio, signal to noise ratio, and nearest sidelobe suppression.

Dicenzo, A.↗

NASA NTRS1979

AXAF optical technology analysis

A grazing incidence telescope with six nested subsystems is investigated through the effects of misalignment and surface deformations on it's image quality. The axial rms-spot size serves as measure for the image quality. The surface deformations are simulated by ellipsoidal and sinusoidal deviation elements. Each type of defect is analyzed in the single two-element system. The full nested system is then analyzed in the presence of all possible defects on all twelve elements, whereby the magnitude of the defects is randomized within a given upper limit.

Korsch, D.↗

NASA NTRS1979

Influence of alignment and surface defects on the performance of X-ray telescopes

The effects of misalignment and surface deformations on the image quality of a grazing incidence telescope with six nested subsystems are investigated. The axial rms-spot size serves as a measure for the image quality. The surface deformations are simulated by ellipsoidal and sinusoidal deviations from the ideal surface. Misalignments are tilts, decenters, and despaces of the individual elements. The effects of each type of defect are analyzed in a single two-element system. The full nested system is then analyzed in the presence of all possible defects on all 12 elements, whereby the magnitude of the defects is randomized within a given upper limit.

Korsch, D.↗

NASA NTRS1981

An experimental study of the concatenated Reed-Solomon/Viterbi channel coding system performance and its impact on space communications

The need for efficient space communication at very low bit error probabilities to the specification and implementation of a concatenated coding system using an interleaved Reed-Solomon code as the outer code and a Viterbi-decoded convolutional code as the inner code. Experimental results of this channel coding system are presented under an emulated S-band uplink and X-band downlink two-way space communication channel, where both uplink and downlink have strong carrier power. This work was performed under the NASA End-to-End Data Systems program at JPL. Test results verify that at a bit error probability of 10 to the -6 power or less, this concatenated coding system does provide a coding gain of 2.5 dB or more over the Viterbi-decoded convolutional-only coding system. These tests also show that a desirable interleaving depth for the Reed-Solomon outer code is 8 or more. The impact of this "virtually" error-free space communication link on the transmission of images is discussed and examples of simulation results are given.

Liu, K. Y.↗

NASA NTRS1983

An example of the performance of the space telescope planetary camera

A ground-based CCD picture of the relatively local dwarf irregular galaxy Sextans B is used to simulate a Space Telescope Planetary Camera image of a similar galaxy at the distance of the Virgo cluster. The gains to be had with the Space Telescope are discussed graphically.

Hoessel, J. G.↗

NASA NTRS1983

The Information Adaptive System - A demonstration of real-time onboard image processing

The Information Adaptive System (IAS) program has the objective to develop and demonstrate, at the brassboard level, an architecture which can be used to perform advanced signal procesing functions on board the spacecraft. Particular attention is given to the processing of high-speed multispectral imaging data in real-time, and the development of advanced technology which could be employed for future space applications. An IAS functional description is provided, and questions of radiometric correction are examined. Problems of data packetization are considered along with data selection, a distortion coefficient processor, an adaptive system controller, an image processing demonstration system, a sensor simulator and output data buffer, a test support and demonstration controller, and IAS demonstration operating modes.

Thomas, G. L.↗

NASA NTRS1984

Programmable Real-Time Acousto-Optic/CCD SAR processor

The theory of operation of the Real-Time Acousto-Optic SAR Processor is reviewed and recent experimental results are presented. The results include a demonstration of the real-time imaging capability of the processor with simulated radar signals. An advanced version of this processor is then described in which a programmable reference function is entered via a second acousto-optic device to eliminate the need for a 2-D SLM. In this implementation the reference function is updated by electronic means to give the processor the flexibility to adapt rapidly to changes in the parameters of the radar/target geometry.

Haney, M.↗

NASA NTRS1985

Land use mapping using edge density texture measures on Thematic Mapper simulator data

Texture analysis was performed as part of an investigation of the information content of Thematic Mapper (TM) imagery. High altitude aircraft scanner imagery from the Airborne Thematic Mapper (ATM) instrument was acquired over central California and used to simulate TM data. Edge density texture images were constructed by computation of proportions of edge pixels in a 31 x 31 moving window on a near infrared ATM band. A training technique was employed to select computational parameters to maximize the difference between edge density measurements in urban and in rural areas. The results of classification of the texture images showed that urban and rural areas could be distinguished with texture alone, indicating that inclusion of texture in automated classification procedures could significantly improve their accuracy.

Hlavka, C. A.↗

NASA NTRS1985

The Caltech Concurrent Computation Program - Project description

The Caltech Concurrent Computation Program wwhich studies basic issues in computational science is described. The research builds on initial work where novel concurrent hardware, the necessary systems software to use it and twenty significant scientific implementations running on the initial 32, 64, and 128 node hypercube machines have been constructed. A major goal of the program will be to extend this work into new disciplines and more complex algorithms including general packages that decompose arbitrary problems in major application areas. New high-performance concurrent processors with up to 1024-nodes, over a gigabyte of memory and multigigaflop performance are being constructed. The implementations cover a wide range of problems in areas such as high energy and astrophysics, condensed matter, chemical reactions, plasma physics, applied mathematics, geophysics, simulation, CAD for VLSI, graphics and image processing. The products of the research program include the concurrent algorithms, hardware, systems software, and complete program implementations.

Fox, G.↗

NASA NTRS1986

Upgrading telescopes by active pupil wavefront correction

Exit pupil correction of the Large Deployable Reflector's (a proposed IR to sub-mm space telescope) segmented primary can be done by reimaging it onto a like segmented surface at the exit pupil. This allows the primary to be more flexible, the adaptive element to be smaller, and the supporting structure to be cheaper than if all correction were performed at a stiffly supported primary. Piston, tilt, and decenter errors of an annulus of the primary and the equations for the required corrections are considered. To verify these, the perturbations with spline functions in the lens design program are simulated. Strehl ratios used to measure image quality show that a piston error of 1 mm is fully corrected over a 5 arcmin field for an f/10 system with a 0.7 n.a. primary at 30 micrometers. Limits of correction are also shown for tilt and decenter errors of segments. Tolerances are given for tilt and decenter errors of the remaining optics also.

Stacy, J. E.↗

NASA NTRS1989

Knowledge-based machine vision systems for space station automation

Computer vision techniques which have the potential for use on the space station and related applications are assessed. A knowledge-based vision system (expert vision system) and the development of a demonstration system for it are described. This system implements some of the capabilities that would be necessary in a machine vision system for the robot arm of the laboratory module in the space station. A Perceptics 9200e image processor, on a host VAXstation, was used to develop the demonstration system. In order to use realistic test images, photographs of actual space shuttle simulator panels were used. The system's capabilities of scene identification and scene matching are discussed.

Ranganath, Heggere S.↗

NASA NTRS1989

Limex'87 ice surface characteristics and their effect upon C-band SAR sigantures

Ice surface characterization data were recorded during March 1987 in the Labrador Sea marginal ice zone, at the onset of spring melt. Measured data are used as input parameters in a simple scattering model to simulate the effects of temporal variations in material properties upon C-band scattering signatures. Snow moisture and surface roughness have a significant effect upon sigma(0)HH and large differences are predicted between undeformed floe surfaces and deformed or rubbled ice areas. The model reproduces a calibrated synthetic-aperture-radar (SAR)-derived signature obtained during the experiment with a reasonable degree of certainty. Predictions also simulate a trend observed in SAR images of increasing backscatter contrast between deformed and undeformed ice over period of surface warming.

Drinkwater, Mark R.↗