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Results for “Crystal Imaging”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

A new hue capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies

A new image processing based color capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies is presented. This method is highly applicable to the surfaces exposed to convective heating in gas turbine engines. It is shown that, in the single-crystal mode, many of the colors appearing on the heat transfer surface correlate strongly with the local temperature. A very accurate quantitative approach using an experimentally determined linear hue vs temperature relation is found to be possible. The new hue-capturing process is discussed in terms of the strength of the light source illuminating the heat transfer surface, the effect of the orientation of the illuminating source with respect to the surface, crystal layer uniformity, and the repeatability of the process. The present method is more advantageous than the multiple filter method because of its ability to generate many isotherms simultaneously from a single-crystal image at a high resolution in a very time-efficient manner.

Camci, C.↗
NASA NTRS2003

Method for acquiring, storing and analyzing crystal images

A system utilizing a digital computer for acquiring, storing and evaluating crystal images. The system includes a video camera (12) which produces a digital output signal representative of a crystal specimen positioned within its focal window (16). The digitized output from the camera (12) is then stored on data storage media (32) together with other parameters inputted by a technician and relevant to the crystal specimen. Preferably, the digitized images are stored on removable media (32) while the parameters for different crystal specimens are maintained in a database (40) with indices to the digitized optical images on the other data storage media (32). Computer software is then utilized to identify not only the presence and number of crystals and the edges of the crystal specimens from the optical image, but to also rate the crystal specimens by various parameters, such as edge straightness, polygon formation, aspect ratio, surface clarity, crystal cracks and other defects or lack thereof, and other parameters relevant to the quality of the crystals.

Gester, Thomas E.↗
NASA NTRS2016

Modeling and Control of Liquid Crystal Imager

In this paper, we present some ideas regarding the modeling and the control aspects of liquid crystal-based imaging systems. We address the challenges of building and deploying a liquid crystal imager by: a) considering the dynamics and control aspects, such as pointing and wavefront error control of large lightweight apertures synthesized by liquid crystal elements, and b) conducting experimental characterization of a prototype electrically-switchable liquid crystal lens.

Quadrelli, Marco B.↗
NASA NTRS1986

Laser Schlieren Crystal-Growth Imager

Crystal observed as it grows from melt with aid of laser schlieren imaging. Observation method allows entire perimeter of growing crystal to be inspected. Isolated crystal facets examined, convection flows and temperature and concentration gradients revealed. Method does not require contact with, or proximity to, crystal.

Owen, R. B.↗
NASA NTRS1992

Wavelength tunable liquid crystal imaging filters for remote sensing from geosynchronous platforms

Recent advances in liquid crystal technology have enabled us to construct tunable birefringent filters with bandwidths between approximately 0.1 nm and 50 nm. The center wavelength of these filters can be selected electronically, in a few tens of milliseconds, with no moving parts. These liquid crystal tunable filters (LCTF's), together with existing CCD detectors, make possible a new generation of lightweight, rugged, high-resolution imaging spectrophotometers. Such instruments would be particularly interesting for remote sensing applications from geosynchronous platforms. Important advantages exist in the aperture, absence of image shift, power consumption, size, weight, and absence of high drive frequencies, compared to current instruments used or considered for multispectral scene analysis. In the present work, we have reviewed spectral requirements of planned NASA geosynchronous remote sensing missions and identified several applications of the liquid crystal tunable filter technology. We have modeled the LCTF performance in the visible and near-infrared, and carried out a literature study on space-hardening of the filter components, to evaluate the suitability of LCTF's for geosynchronous missions. We have also compared the power consumption, weight, size, reliability, and optical performance of an imaging spectrophotometer using a LCTF monochromator, to other instruments that have been put forward for remote sensing from geosynchronous platforms. We put forward some conceptual designs for LCTF's that seem to offer important reliability, over the mechanical filter wheels presently baselined for the HEPI and ALM experiments. The extremely wide acceptance angle achievable with LCTF's could also avoid the present need for large-aperture interference filters in the ALM (and LIS) experiments. Thermal vacuum testing and radiation damage analysis is required to investigate the space hardening of these new filters for geosynchronous flight.

Foukal, Peter↗
NASA NTRS1981

Cylindrical Crystal Imaging Spectrometer (CCIS) for cosmic X-ray spectroscopy

A "stigmatic" focusing, Bragg crystal spectrometer was developed and used for high spectral resolution X-ray emission line diagnostics on hot laboratory plasmas. The concept be applied at the focal plane of an orbiting X-ray telescope where it offers several advantages over conventional spectrometers, i.e., mechanical simplicity, high resolving power and sensitivity, simultaneous measurement of an extended segment of spectrum, and good imaging properties. The instrument features a simple, unambiguous, non-scanning spectrum readout that is not adversely affected by either spacecraft pointing error or source extent. The performance of the instrument is estimated in the context of the Advanced X-Ray Astrophysical Facility mission.

Schnopper, H. W.↗
NASA NTRS1988

Streaking images that appear only in the plane of diffraction in undoped GaAs single crystals: Diffraction imaging (topography) by monochromatic synchrotron radiation

Streaking images restricted to the direction of the diffraction (scattering) vector have been observed on transmission through undoped GaAs. These disruption images (caused by the reduction of diffraction in the direction of observation) appear both in the forward and in Bragg diffracted directions in monochromatic synchrontron radiation diffraction imaging. This previously unobserved phenomenon can be explained in terms of planar defects (interfaces) or platelets which affects the absorption coefficient in anomalous transmission. Such regions of the crystal look perfect despite the presence of imperfections when the scattering vector is not perpendicular to the normal of the platelets. The observed crystallographic orientation of these interfaces strongly indicates that they are antiphase boundaries.

Kuriyama, Masao↗
NASA NTRS1991

High resolution synchrotron X-radiation diffraction imaging of crystals grown in microgravity and closely related terrestrial crystals

Irregularities in three crystals grown in space and in four terrestrial crystals grown under otherwise comparable conditions have been observed in high resolution diffraction imaging. The images provide important new clues to the nature and origins of irregularities in each crystal. For two of the materials, mercuric iodide and lead tin telluride, more than one phase (an array of non-diffracting inclusions) was observed in terrestrial samples; but the formation of these multiple phases appears to have been suppressed in directly comparable crystals grown in microgravity. The terrestrial seed crystal of triglycine sulfate displayed an unexpected layered structure, which propagated during directly comparable space growth. Terrestrial Bridgman regrowth of gallium arsenide revealed a mesoscopic structure substantially different from that of the original Czochralski material. A directly comparable crystal is to be grown shortly in space.

Steiner, Bruce↗
NASA NTRS1991

High resolution diffraction imaging of crystals grown in microgravity and closely related terrestrial crystals

Irregularities found in three crystals grown in space, in four crystals grown entirely on the ground were examined and compared. Irregularities were observed in mercuric iodide, lead tin telluride, triglycine sulfate, and gallium arsenide by high resolution synchrotron x radiation diffraction imaging. Radiation detectors made from mercuric iodide crystals grown in microgravity were reported to perform far better than conventional detectors grown from the same material under full gravity. Effort is now underway to reproduce these 'space' crystals, optimize their properties, and extend comparable superiority to other types of materials.

Steiner, B.↗
NASA NTRS1999

Characterization of Optical Lenses to be Considered for the Imaging of Crystal Dendrite Growth

Dynamic fracture is a phenomenon that is extremely sensitive to small perturbations in system parameters. This phenomenon is, in some ways, similar to that of dendritic crystal growth, although it is governed by different physical principles. Crystal dendrite growth patterns are affected by parameters such as temperature, pressure, and gravity. By studying the behavior of crystal dendrites in a controlled, microgravity environment, a greater understanding of dynamic fracture could be revealed. A sealed cubical container contains four stingers, which facilitate the growth of crystal dendrites. The container has five windows and is emersed in a liquid, for thermal isolation. The tip of a dendrite can advance in any direction, therefore three-dimensional images of the process are desired. Furthermore, because of the rapid growth rate, a fast image frame rate is required for accurate tracking of dendrite tip velocity. In addition, optical parameters such as field of view, depth of focus, and resolution are examined, as well as the working distance between a lens and the target of observation.

Wing, Frank M.↗
NASA NTRS1988

Liquid-Crystal-Television Image Subtracters

Two image-subtraction systems from output images that show differences between input images of two objects. First: differences appear as bright regions in otherwise dark output image. Second: differences and similarities shown by colors. All parts of two images processed simultaneously by optical components only; digital electronic processing of data not required. Concept offers potential for rapid, inexpensive comparison of images in such applications as automatic inspection, medical diagnosis, and robotic vision.

Chao, Tien-Hsin↗
NASA NTRS2021

Absolute throughput calibration of multiple spherical crystals for the Orion High-REsolution X-ray spectrometer (OHREX)

We present absolute throughput analysis of several crystals for the Orion High-REsolution X-ray (OHREX) imaging crystal spectrometer using ray tracing and experimental measurements. The OHREX spectrometer is a high-resolution x-ray spectrometer designed to measure spectral line shapes at the Orion laser facility. The spectrometer is fielded with up to two spherical crystals simultaneously covering two independent spectral ranges. Each crystal has a nominal radius of curvature of R = 67.2 cm and is fielded at a nominal Bragg angle of 51.3°. To cover different bands of interest, several different crystals are available, including Ge (111), KAP, and several cuts of quartz, whose resolving power λ/Δλ exceeds 10 000. The calibrated response of the available crystals has previously been reported from measurements at the EBIT-I electron beam ion trap at Lawrence Livermore National Laboratory. Here, we model the absolute throughput of each crystal using ray tracing and verify the results using experimental data for the quartz (10¯11) crystal.

M. J. MacDonald↗
NASA NTRS1991

Real time quantitative imaging for semiconductor crystal growth, control and characterization

A quantitative real time image processing system has been developed which can be software-reconfigured for semiconductor processing and characterization tasks. In thermal imager mode, 2D temperature distributions of semiconductor melt surfaces (900-1600 C) can be obtained with temperature and spatial resolutions better than 0.5 C and 0.5 mm, respectively, as demonstrated by analysis of melt surface thermal distributions. Temporal and spatial image processing techniques and multitasking computational capabilities convert such thermal imaging into a multimode sensor for crystal growth control. A second configuration of the image processing engine in conjunction with bright and dark field transmission optics is used to nonintrusively determine the microdistribution of free charge carriers and submicron sized crystalline defects in semiconductors. The IR absorption characteristics of wafers are determined with 10-micron spatial resolution and, after calibration, are converted into charge carrier density.

Wargo, Michael J.↗
NASA NTRS1991

Medical Imaging System

The MD Image System, a true-color image processing system that serves as a diagnostic aid and tool for storage and distribution of images, was developed by Medical Image Management Systems, Huntsville, AL, as a "spinoff from a spinoff." The original spinoff, Geostar 8800, developed by Crystal Image Technologies, Huntsville, incorporates advanced UNIX versions of ELAS (developed by NASA's Earth Resources Laboratory for analysis of Landsat images) for general purpose image processing. The MD Image System is an application of this technology to a medical system that aids in the diagnosis of cancer, and can accept, store and analyze images from other sources such as Magnetic Resonance Imaging.

Source record↗
NASA NTRS1981

High-resolution iron-line spectroscopy

Methods of resolving the iron lines, the most common X-ray emission lines in both galactic and extragalactic X-ray sources, are reviewed. A self-focussing crystal spectrometer is shown to be the most suitable instrument, and the optimum crystal geometry is spherical (Schnopper and Taylor 1980). The principles of operation of such a spherical crystal imaging spectrometer are examined and its sensitivity is shown to be two orders of magnitude better than a focal plane crystal spectrometer on AXAF. A Spacelab version of this payload would be very cost-effective.

Griffiths, R. E.↗
NASA NTRS2016

Derivation of Physical and Optical Properties of Midlatitude Cirrus Ice Crystals for a Size-Resolved Cloud Microphysics Model

Single-crystal images collected in mid-latitude cirrus are analyzed to provide internally consistent ice physical and optical properties for a size-resolved cloud microphysics model, including single-particle mass, projected area, fall speed, capacitance, single-scattering albedo, and asymmetry parameter. Using measurements gathered during two flights through a widespread synoptic cirrus shield, bullet rosettes are found to be the dominant identifiable habit among ice crystals with maximum dimension (Dmax) greater than 100μm. Properties are therefore first derived for bullet rosettes based on measurements of arm lengths and widths, then for aggregates of bullet rosettes and for unclassified (irregular) crystals. Derived bullet rosette masses are substantially greater than reported in existing literature, whereas measured projected areas are similar or lesser, resulting in factors of 1.5-2 greater fall speeds, and, in the limit of large Dmax, near-infrared single-scattering albedo and asymmetry parameter (g) greater by approx. 0.2 and 0.05, respectively. A model that includes commonly imaged side plane growth on bullet rosettes exhibits relatively little difference in microphysical and optical properties aside from approx. 0:05 increase in mid-visible g primarily attributable to plate aspect ratio. In parcel simulations, ice size distribution, and g are sensitive to assumed ice properties.

asymmetry↗
NASA NTRS2000

Effect of Film-Hole Shape on Turbine Blade Film Cooling Performance

The detailed heat transfer coefficient and film cooling effectiveness distributions as well as tile detailed coolant jet temperature profiles on the suction side of a gas turbine blade A,ere measured using a transient liquid crystal image method and a traversing cold wire and a traversing thermocouple probe, respectively. The blade has only one row of film holes near the gill hole portion on the suction side of the blade. The hole geometries studied include standard cylindrical holes and holes with diffuser shaped exit portion (i.e. fanshaped holes and laidback fanshaped holes). Tests were performed on a five-blade linear cascade in a low-speed wind tunnel. The mainstream Reynolds number based on cascade exit velocity was 5.3 x 10(exp 5). Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. The wake Strouhal number was kept at 0 or 0.1. Coolant blowing ratio was varied from 0.4 to 1.2. Results show that both expanded holes have significantly improved thermal protection over the surface downstream of the ejection location, particularly at high blowing ratios. However, the expanded hole injections induce earlier boundary layer transition to turbulence and enhance heat transfer coefficients at the latter part of the blade suction surface. In general, the unsteady wake tends to reduce film cooling effectiveness.

Han, J. C.↗