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At least 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Imaging interferometry with non-redundant arrays

The performance of a set of nonredundant arrays, that convert an existing telescope to an interferometer, was simulated. Each array is a perforated mask, placed at an image of the objective. Each pair of holes in a mask transmits a unique spatial frequency that is present in the target; hence the term nonredundant. Each mask produces a fringe I(f) in the focal plane that is the product of the Fourier transforms of the object and the optical transfer function S(f).

Zirker, J. B.↗
NASA NTRS1987

Location of planar targets in three space from monocular images

Many pieces of existing and proposed space hardware that would be targets of interest for a telerobot can be represented as planar or near-planar surfaces. Examples include the biostack modules on the Long Duration Exposure Facility, the panels on Solar Max, large diameter struts, and refueling receptacles. Robust and temporally efficient methods for locating such objects with sufficient accuracy are therefore worth developing. Two techniques that derive the orientation and location of an object from its monocular image are discussed and the results of experiments performed to determine translational and rotational accuracy are presented. Both the quadrangle projection and elastic matching techniques extract three-space information using a minimum of four identifiable target points and the principles of the perspective transformation. The selected points must describe a convex polygon whose geometric characteristics are prespecified in a data base. The rotational and translational accuracy of both techniques was tested at various ranges. This experiment is representative of the sensing requirements involved in a typical telerobot target acquisition task. Both techniques determined target location to an accuracy sufficient for consistent and efficient acquisition by the telerobot.

Cornils, Karin↗
NASA NTRS1993

Hubble Space Telescope characterized by using phase-retrieval algorithms

We describe several results characterizing the Hubble Space Telescope from measured point spread functions by using phase-retrieval algorithms. The Cramer-Rao lower bounds show that point spread functions taken well out of focus result in smaller errors when aberrations are estimated and that, for those images, photon noise is not a limiting factor. Reconstruction experiments with both simulated and real data show that the calculation of wave-front propagation by the retrieval algorithms must be performed with a multiple-plane propagation rather than a simple fast Fourier transform to ensure the high accuracy required. Pupil reconstruction was performed and indicates a misalignment of the optical axis of a camera relay telescope relative to the main telescope. After we accounted for measured spherical aberration in the relay telescope, our estimate of the conic constant of the primary mirror of the HST was - 1.0144.

Fienup, J. R.↗
NASA NTRS2001

Performance of the Wavelet Decomposition on Massively Parallel Architectures

Traditionally, Fourier Transforms have been utilized for performing signal analysis and representation. But although it is straightforward to reconstruct a signal from its Fourier transform, no local description of the signal is included in its Fourier representation. To alleviate this problem, Windowed Fourier transforms and then wavelet transforms have been introduced, and it has been proven that wavelets give a better localization than traditional Fourier transforms, as well as a better division of the time- or space-frequency plane than Windowed Fourier transforms. Because of these properties and after the development of several fast algorithms for computing the wavelet representation of any signal, in particular the Multi-Resolution Analysis (MRA) developed by Mallat, wavelet transforms have increasingly been applied to signal analysis problems, especially real-life problems, in which speed is critical. In this paper we present and compare efficient wavelet decomposition algorithms on different parallel architectures. We report and analyze experimental measurements, using NASA remotely sensed images. Results show that our algorithms achieve significant performance gains on current high performance parallel systems, and meet scientific applications and multimedia requirements. The extensive performance measurements collected over a number of high-performance computer systems have revealed important architectural characteristics of these systems, in relation to the processing demands of the wavelet decomposition of digital images.

El-Ghazawi, Tarek A.↗
DOE OSTI2020

Peculiarities of the phase transformation dynamics in bulk FeRh based alloys from magnetic and structural measurements

We analyze coexistence of antiferromagnetic and ferromagnetic phases in bulk iron-rhodium and its alloys with palladium, Fe 50,4 Rh 49,6 , Fe 49,7 Rh 47,4 Pd 2,9 and Fe 48,3 Rh 46,8 Pd 4,9 , using neutron diffraction, magnetization and scanning Hall probe imaging. Temperature dependencies of the lattice parameters, AFM and FM phase weight fractions, and Fe magnetic moment values were obtained on cooling and heating across the AFM-FM transition. Substantial thermomagnetic hysteresis for the phases’ weight fractions and a relatively narrow one for the unit cell volume has been observed on cooling-heating. Furthermore, a clear dependence of hysteretic behavior on Pd concentration has been traced. Additional direct magnetic measurements of the spatial distribution of the phase transition are acquired using scanning Hall probe microscopy, which reveals the length scale of the phase coexistence and the spatial progression of the transition in the presence of external magnetic field. Also, the magnetic phase diagram has been constructed for a series of Pd-doped FeRh alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

FFT-based model for irradiated aggregate microstructures in concrete

The concrete biological shield of light water reactors is exposed to neutron and gamma irradiation throughout its lifetime, which results in the long-term degradation of the concrete’s mechanical properties. Under neutron irradiation, the concrete’s aggregates are subjected to radiation-induced volumetric expansion (RIVE), which strongly depends on the mineral content of the aggregate and exhibits the largest expansion in silicate-bearing minerals. In this work, the authors used the fast Fourier transform-based code Microstructure-Oriented Scientific Analysis of Irradiated Concrete (MOSAIC) in 2D to model the expansion of five different aggregates provided by the Japan Concrete Aging Management Program (JCAMP). Comparable rock specimens were irradiated at the JEEP-II test reactor. The model uses realistic aggregate microstructure reconstruction based on high-resolution characterization images. The model accounts for anisotropic RIVE, thermal expansion, and the associated initiation and propagation of damage. The RIVE models are calibrated based on expansion data in the literature. The authors assume that damage occurs exclusively at interfaces between the particles that compose an aggregate and that these interfaces also exhibit swelling. Using a micromechanical model, the evolution of Young’s modulus with RIVE is calculated for each aggregate and compared with Russian irradiation data. The modeled linear expansion agrees well with the experimentally measured expansion. Furthermore, the model also predicts that anisotropic RIVE and thermal expansion result in an earlier onset of damage with neutron fluence than in the isotropic case.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction

Here, we employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescence phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α’ phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Methodology for Yield Determination of Surface Shots Over Water

Shockwave analysis is one of the few methods used to determine the yield of a nuclear detonation. It has been noted that the shockwave of these surface shots over water are asymmetric making accurate yield determination difficult. To calculate the yield of these shots more accurately, reanalysis of these films is required. Armed with the digitized replicas of the original nuclear test films and the latest image processing tools, a methodology for segmenting the shockwave from the digitized film and measuring these shockwaves is devised to quickly and accurately quantify the shape of these asymmetric shockwaves. With a two-dimensional result from these asymmetric shockwaves, several methods are discussed to transform the final shockwave contour to a scalar value which can be used in existing yield determination equations.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
NASA NTRS1992

Studies of temporal change using radar interferometry

Decorrelation of the radar signals with time, which is indicative of changes in the surface occurring during the period of time spanned by the images, is examined. It is concluded that the decorrelation effects due to thermal noise can be easily evaluated and removed, while those due to slight angular changes between flight tracks are negligible. Spatial baseline and rotation-induced decorrelation can be derived using the Fourier transform of the impulse response intensity, and increases linearly with baseline or rotation in an ideal system. Empirical results confirm that as the baseline increases, the overall correlation decreases due to spatial baseline noise.

Villasenor, John↗
NASA NTRS1994

Neural networks: Alternatives to conventional techniques for automatic docking

Automatic docking of orbiting spacecraft is a crucial operation involving the identification of vehicle orientation as well as complex approach dynamics. The chaser spacecraft must be able to recognize the target spacecraft within a scene and achieve accurate closing maneuvers. In a video-based system, a target scene must be captured and transformed into a pattern of pixels. Successful recognition lies in the interpretation of this pattern. Due to their powerful pattern recognition capabilities, artificial neural networks offer a potential role in interpretation and automatic docking processes. Neural networks can reduce the computational time required by existing image processing and control software. In addition, neural networks are capable of recognizing and adapting to changes in their dynamic environment, enabling enhanced performance, redundancy, and fault tolerance. Most neural networks are robust to failure, capable of continued operation with a slight degradation in performance after minor failures. This paper discusses the particular automatic docking tasks neural networks can perform as viable alternatives to conventional techniques.

Vinz, Bradley L.↗
NASA NTRS1994

An algorithm for extraction of periodic signals from sparse, irregularly sampled data

Temporal gaps in discrete sampling sequences produce spurious Fourier components at the intermodulation frequencies of an oscillatory signal and the temporal gaps, thus significantly complicating spectral analysis of such sparsely sampled data. A new fast Fourier transform (FFT)-based algorithm has been developed, suitable for spectral analysis of sparsely sampled data with a relatively small number of oscillatory components buried in background noise. The algorithm's principal idea has its origin in the so-called 'clean' algorithm used to sharpen images of scenes corrupted by atmospheric and sensor aperture effects. It identifies as the signal's 'true' frequency that oscillatory component which, when passed through the same sampling sequence as the original data, produces a Fourier image that is the best match to the original Fourier space. The algorithm has generally met with succession trials with simulated data with a low signal-to-noise ratio, including those of a type similar to hourly residuals for Earth orientation parameters extracted from VLBI data. For eight oscillatory components in the diurnal and semidiurnal bands, all components with an amplitude-noise ratio greater than 0.2 were successfully extracted for all sequences and duty cycles (greater than 0.1) tested; the amplitude-noise ratios of the extracted signals were as low as 0.05 for high duty cycles and long sampling sequences. When, in addition to these high frequencies, strong low-frequency components are present in the data, the low-frequency components are generally eliminated first, by employing a version of the algorithm that searches for non-integer multiples of the discrete FET minimum frequency.

Wilcox, J. Z.↗
NASA NTRS1994

Measurements of striae in CR+ doped YAG laser crystals

Striations in Czochralski (CZ) grown crystals have been observed in materials such as GaAs, silicon, photorefractive crystals used for data storage, potassium titanyl phosphate crystals and LiNbO3. Several techniques have been used for investigating these defects including electron microscopy, laser scanning tomography, selective photoetching, X-ray diffuse scattering, interference orthoscopy, laser interferometry and micro-Fourier transform infrared spectroscopy mapping. A 2mm thick sample of the material to be investigated is illuminated with light that is absorbed and non-absorbed by the ion concentration to be observed. The back surface of the sample is focused onto a solid-state image detector and images of the input beam and absorbed (and diffracted) beams are captured at two wavelengths. The variation of the coefficient of absorption asa function of distance on the sample can be derived from these measurements. A Big Sky Software Beamcode system is used to capture and display images. Software has been written to convert the Beamcode data files to a format that can be imported into a spreadsheet program such as Quatro Pro. The spreadsheet is then used to manipulate and display data. A model of the intensity map of the striae collected by the imaging system has been proposed and a data analysis procedure derived. From this, the variability of the attenuation coefficient alpha can be generated. Preliminary results show that alpha may vary by a factor of four or five over distances of 100 mu m. Potential errors and problems have been discovered and additional experiments and improvements to the experimental setup are in progress and we must now show that the measurement techniques and data analysis procedures provide 'real' information. Striae are clearly visible at all wavelengths including white light. Their basic spatial frequency does not change radically, at least when changing from blue to green to white light. Further experimental and theoretical work can be done to improve the data collection techniques and to verify the data analysis procedures.

Cady, Fredrick M.↗
NASA NTRS2023

The James Webb Space Telescope Mission: Optical Telescope Element Design, Development, and Performance

The James Webb Space Telescope (JWST) is a large, infrared space telescope that has recently started its science program which will enable breakthroughs in astrophysics and planetary science. Notably, JWST will provide the very first observations of the earliest luminous objects in the universe and start a new era of exoplanet atmospheric characterization. This transformative science is enabled by a 6.6 m telescope that is passively cooled with a 5 layer sunshield. The primary mirror is comprised of 18 controllable, low areal density hexagonal segments, that were aligned and phased relative to each other in orbit using innovative image-based wave front sensing and control algorithms. This revolutionary telescope took more than two decades to develop with a widely distributed team across engineering disciplines. We present an overview of the telescope requirements, architecture, development, superb on-orbit performance, and lessons learned. JWST successfully demonstrates a segmented aperture space telescope and establishes a path to building even larger space telescopes.

Infrared observatories↗
DOE OSTI2019

Microfluidic electrochemical device and process for chemical imaging and electrochemical analysis at the electrode-liquid interface in-situ

A microfluidic electrochemical device and process are detailed that provide chemical imaging and electrochemical analysis under vacuum at the surface of the electrode-sample or electrode-liquid interface in-situ. The electrochemical device allows investigation of various surface layers including diffuse layers at selected depths populated with, e.g., adsorbed molecules in which chemical transformation in electrolyte solutions occurs.

42 ENGINEERING↗
DOE OSTI2019

An asymmetric hybrid cryptosystem using equal modulus and random decomposition in hybrid transform domain

In this paper, an asymmetric hybrid cryptosystem with coherent superposition, equal modulus and random decomposition in hybrid transform domain is proposed. To further strengthen the security of the cryptosystem, a hyperchaotic system is used as a pixel-swapping procedure. The hybrid transform is generated by utilizing fractional Fourier transform of various orders and Walsh transform. The hyperchaotic framework’s parameters and starting conditions alongside the fractional orders of the fractional Fourier transform extend the key-space and consequently give extra strength to the proposed cryptosystem. The designed cryptosystem has an extended key-space to avoid any brute-force attack and is non-linear in nature. The scheme is validated on gray-scale images. Computer based simulations have been performed to verify the validity and the performance of the proposed cryptosystem against different types of attacks. Results demonstrate that the proposed cryptosystem not only offers higher protection against noise attacks but is also invulnerable to special attack.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

TiO2∙rGO nanocomposite as a photo catalyst for the reduction of Cr6+

Highlights: • Titania decorated reduced graphene oxide was fabricated by hydrothermal process. • TiO{sub 2} nanoparticles attached to the surfaces of the rGO are anatase. • rGO surfaces were covered with TiO{sub 2} nanoparticles whose average sizes. • Photocatalytic reduction of toxic Cr{sup 6+} is increased as x is increased. - Abstract: Titania decorated reduced graphene oxide (TiO{sub 2}∙x%rGO (x = 0, 1, 05, 10, 15, 20 and 25) nanocomposites (NC’s) were fabricated using a hydrothermal process. Scanning electron microscope (SEM) images show that the rGO surfaces were covered with TiO{sub 2} nanoparticles whose average sizes increased as x is increased. X Ray Diffraction (XRD) of all the NP’s exhibits the diffractions peaks of the anatase phase of the TiO{sub 2}. The Fourier-Transform Infrared (FT-IR) spectra of these NC’s indicate an increase in the Ti-O-C interfacial chemical bond vibration signals as x increases. A decrease in the energy of the band (energy) gap as the amount of rGO is increased is determined from the UV–vis light absorption spectra. The use of these TiO{sub 2}∙x%rGO NC’s to reduce toxic Cr{sup 6+} ions to nontoxic Cr{sup 3+} ions is studied. The photo-catalytic reduction of the toxic Cr{sup 6+} is seen in general to increase as x is increased.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Optimal 1D Ly α forest power spectrum estimation – III. DESI early data

ABSTRACT The 1D power spectrum P1D of the Ly α forest provides important information about cosmological and astrophysical parameters, including constraints on warm dark matter models, the sum of the masses of the three neutrino species, and the thermal state of the intergalactic medium. We present the first measurement of P1D with the quadratic maximum likelihood estimator (QMLE) from the Dark Energy Spectroscopic Instrument (DESI) survey early data sample. This early sample of 54 600 quasars is already comparable in size to the largest previous studies, and we conduct a thorough investigation of numerous instrumental and analysis systematic errors to evaluate their impact on DESI data with QMLE. We demonstrate the excellent performance of the spectroscopic pipeline noise estimation and the impressive accuracy of the spectrograph resolution matrix with 2D image simulations of raw DESI images that we processed with the DESI spectroscopic pipeline. We also study metal line contamination and noise calibration systematics with quasar spectra on the red side of the Ly α emission line. In a companion paper, we present a similar analysis based on the Fast Fourier Transform estimate of the power spectrum. We conclude with a comparison of these two approaches and discuss the key sources of systematic error that we need to address with the upcoming DESI Year 1 analysis.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1970

Discrete control of linear distributed systems with application to the deformable primary mirror of a large orbiting telescope

One of the more significant technological problems associated with the orbital operation of large astronomical telescope's is the fabrication and maintenance of the primary mirror surface to the tolerance required for diffraction-limited performance. An interesting approach to the solution of this problem involves continuously measuring and automatically correcting the optical surface of a thin deformable mirror by means of discrete actuators located on its rear surface: The realization of diffraction-limited performance from a telescope in space by this method rests on the ability of the designer to achieve extremely accurate control of a highly complex, interacting, multivariable system. This paper presents the results of a detailed study of the discrete control of linear distributed systems with specific application to the design of a practical controller for a plant representative of a telescope primary mirror for an orbiting astronomical observatory. The problem of controlling the distributed plant is treated by employing modal techniques to represent variations in the optical figure. Distortion of the mirror surface, which arises primarily from thermal gradients, is countered by actuators working against a backing structure to apply a corrective force distribution to the controlled surface. Each displacement actuator is in series with a spring attached to the mirror by means of a pad intentionally introduced to restrict the excitation of high-order modes. Control is then exerted over a finite number (equal.to the number of actuators) of the most significant modes. Through the application of the modal expansion technique the mirror equation of motion is transformed tb a set of uncoupled, linear, time-invariant, ordinary differential equations. The desired dynamic response and static accuracy may then be achieved by the application of classical single-variable design techniques. The formulation of a quadratic performance index which incorporates a measure of image quality permits determination of the trade-off between the-number of actuators and optical purity. A criterion for defining actuator placement and pad size is presented which minimizes the tendency of the controller to excite the unmonitored modes.

Jeremiah F Creedon↗