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Establish data tracks on periphery of rotating drum and axially displace entire drum to place given track in alignment with either fixed or rotating read/record head. Accurate control of speed drum and rotating head can be accomplished by using separate synchronous motors driven by digitally-set oscillators to provide required difference in speed.
We present OVRO interferometric observations of linearly polarized emission from magnetically aligned dust grains which allow the magnetic field geometry in nearby star formation regions to be probed on scales ranging from 100 to 3000 AU. Current results include observations of the young stellar objects NGC1333/IRAS 4A, IRAS 16293-2422 and Orion IRc2-KL.
Purpose: Grids are often not used in mobile chest radiography, and when used, they have a low ratio and are often inaccurately aligned. Recently, a mobile radiography automatic grid alignment system (MRAGA) was developed that accurately and automatically aligns the focal spot with the grid. The objective of this study is to investigate high-ratio grid tradeoffs in mobile chest radiography at fixed patient dose when the focal spot lies on the focal axis of the grid. Methods: The chest phantoms (medium and large) used in this study were modifications of the ANSI (American National Standards Institute) chest phantom and consisted of layers of Lucite Trade-Mark-Sign , aluminum, and air. For the large chest phantom, the amount of Lucite and aluminum was increased by 50% over the medium phantom. Further modifications included a mediastinum insert and the addition of contrast targets in the lung and mediastinum regions. Five high-ratio grids were evaluated and compared to the nongrid results at x-ray tube potentials of 80, 90, 100, and 110 kVp for both phantoms. The grids investigated were from two manufacturers: 12:1 and 15:1 aluminum interspace grids from one and 10:1, 13:1, and 15:1 fiber interspace grids from another. MRAGA was employed to align the focal spot with the grid. All exposures for a given kVp and phantom size were made using the same current-time product (CTP). The phantom images were acquired using computed radiography, and contrast-to-noise ratios (CNR) and CNR improvement factors (k{sub CNR}) were determined from the resultant images. The noise in the targets and the contrast between the targets and their backgrounds were calculated using a local detrending correction, and the CNR was calculated as the ratio of the target contrast to the background noise. k{sub CNR} was defined as the ratio of the CNR imaged with the grid divided by the CNR imaged without a grid. Results: The CNR values obtained with a high-ratio grid were 4%-65% higher than those obtained without a grid at the same phantom dose. The improvement was greater for the large chest phantom than the medium chest phantom and greater for the mediastinum targets than for the lung targets. In general, the fiber interspace grids performed better than the aluminum interspace grids. In the lung, k{sub CNR} for both types of grids exhibited little dependence on kVp or grid ratio. In the mediastinum, k{sub CNR} decreased 4%-10% with increasing kVp, and varied up to 5.3% with grid ratio. Conclusions: When the focal spot is accurately aligned with the grid, the use of a high-ratio grid in mobile chest radiography improves image quality with no increase in dose to the phantom. For the grids studied, the performance of the fiber interspace grids was superior to the performance of the aluminum interspace grids, with the fiber interspace 13:1 grid producing the best overall results for the medium chest phantom and the fiber interspace 15:1 producing the best overall results for the large chest phantom.
The extended flight of the Airborne Ionospheric Observatory during the Geospace Environment Modeling (GEM) Pilot program on January 16, 1990, allowed continuous all-sky monitoring of the two-dimensional ionospheric footprint of the northward interplanetary magnetic field (IMF) cusp in several wavelengths. Especially important in determining the locus of magnetosheath electron precipitation was the 630.0-nm red line emission. The most striking morphological change in the images was the transient appearance of zonally elongated regions of enhanced 630.0-nm emission which resembled 'rays' emanating from the centroid of the precipitation. The appearance of these rays was strongly correlated with the Y component of the IMF: when the magnitude of B(sub y) was large compared to B(sub z), the rays appeared; otherwise, the distribution was relatively unstructured. Late in the flight the field of view of the imager included the field of view of flow measurements from the European incoherent scatter radar (EISCAT). The rays visible in 630.0-nm emission exactly aligned with the position of strong flow jets observed by EISCAT. We attribute this correspondence to the requirement of quasi-neutrality; namely, the soft electrons have their largest precipitating fluxes where the bulk of the ions precipitate. The ions, in regions of strong convective flow, are spread out farther along the flow path than in regions of weaker flow. The occurrence and direction of these flow bursts are controlled by the IMF in a manner consistent with newly opened flux tubes; i.e., when absolute value of B(sub y) greater than absolute value of B(sub z), tension in the reconnected field lines produce east-west flow regions downstream of the ionospheric projection of the x line. We interpret the optical rays (flow bursts), which typically last between 5 and 15 min, as evidence of periods of enhanced dayside (or lobe) reconnection when absolute value of B(sub y) greater than absolute value of B(sub z). The length of the reconnection pulse is difficult to determine, however, since strong zonal flows would be expected to persist until the tension force in the field line has decayed, even if the duration of the enhanced reconnection was relatively short.
The presence of oxyanions, such as nitrate (NO 3 – ) and phosphate (PO 4 3– ), regulates the nucleation and growth of goethite (Gt) and hematite (Hm) during the transformation of ferrihydrite (Fh). Our previous studies showed that oxyanion surface complexes control the rate and pathway of Fh transformation to Gt and Hm. However, how oxyanion surface complexes control the mechanism of Gt and Hm nucleation and growth during the Fh transformation is still unclear. Here, we used synchrotron scattering methods and cryogenic transmission electron microscopy to investigate the effects of NO 3 – outer-sphere complexes and PO 4 3– inner-sphere complexes on the mechanism of Gt and Hm formation from Fh. Our TEM results indicated that Gt particles form through a two-step model in which Fh particles first transform to Gt nanoparticles and then crystallographically align and grow to larger particles by oriented attachment (OA). In contrast, for the formation of Hm, imaging shows that Fh particles first aggregate and then transform to Hm through interface nucleation. This is consistent with our X-ray scattering results, which demonstrate that NO 3 – outer-sphere and PO 4 3– inner-sphere complexes promote the formation of Gt and Hm, respectively. These results have implications for understanding the coupled interactions of oxyanions and iron oxy-hydroxides in Earth-surface environments.
Minor mergers are thought to be important for the buildup and structural evolution of massive elliptical galaxies. In this work, we report the discovery of a system of four shell features in NGC 4889, one of the brightest members of the Coma cluster, using optical images taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The shells are well aligned with the major axis of the host and are likely to have been formed by the accretion of a small satellite galaxy. We have performed a detailed two-dimensional photometric decomposition of NGC 4889 and of the many overlapping nearby galaxies in its vicinity. This comprehensive model allows us not only to firmly detect the low-surface brightness shells, but, crucially, also to accurately measure their luminosities and colors. The shells are bluer than the underlying stars at the same radius in the main galaxy. We make use of the colors of the shells and the color-magnitude relation of the Coma cluster to infer the luminosity (or mass) of the progenitor galaxy. The shells in NGC 4889 appear to have been produced by the minor merger of a moderate-luminosity (M{sub I} Almost-Equal-To -18.7 mag) disk (S0 or spiral) galaxy with a luminosity (mass) ratio of {approx}90:1 with respect to the primary galaxy. The novel methodology presented in this work can be exploited to decode the fossil record imprinted in the photometric substructure of other nearby early-type galaxies.
Purpose: X-ray/light field alignment is a test described in many guidelines for the routine quality control of clinical linear accelerators (LINAC). Currently, the gold standard method for measuring alignment is through utilization of radiographic film. However, many modern LINACs are equipped with an electronic portal imaging device (EPID) that may be used to perform this test and thus subsequently reducing overall cost, processing, and analysis time, removing operator dependency and the requirement to sustain the departmental film processor. Methods: This work describes a novel method of utilizing the EPID together with a custom inhouse designed jig and automatic image processing software allowing measurement of the light field size, x-ray field size, and congruence between them. The authors present results of testing the method for aS1000 and aS500 Varian EPID detectors for six LINACs at a range of energies (6, 10, and 15 MV) in comparison with the results obtained from the use of radiographic film. Results: Reproducibility of the software in fully automatic operation under a range of operating conditions for a single image showed a congruence of 0.01 cm with a coefficient of variation of 0. Slight variation in congruence repeatability was noted through semiautomatic processing by four independent operators due to manual marking of positions on the jig. Testing of the methodology using the automatic method shows a high precision of 0.02 mm compared to a maximum of 0.06 mm determined by film processing. Intraindividual examination of operator measurements of congruence was shown to vary as much as 0.75 mm. Similar congruence measurements of 0.02 mm were also determined for a lower resolution EPID (aS500 model), after rescaling of the image to the aS1000 image size. Conclusions: The designed methodology was proven to be time efficient, cost effective, and at least as accurate as using the gold standard radiographic film. Additionally, congruence testing can be easily performed for all four cardinal gantry angles which can be difficult when using radiographic film. Therefore, the authors propose it can be used as an alternative to the radiographic film method allowing decommissioning of the film processor.
Electronic and optical excitations in two-dimensional systems are distinctly sensitive to the presence of a moiré superlattice. Here we used cryogenic transmission electron microscopy and spectroscopy to simultaneously image the structural reconstruction and associated localization of the lowest-energy intralayer exciton in a rotationally aligned WS 2 -WSe 2 moiré superlattice. In conjunction with optical spectroscopy and ab initio calculations, we determined that the exciton center-of-mass wave function is confined to a radius of approximately 2 nanometers around the highest-energy stacking site in the moiré unit cell. Our results provide direct evidence that atomic reconstructions lead to the strongly confining moiré potentials and that engineering strain at the nanoscale will enable new types of excitonic lattices.
Gas filter correlation (GFC) radiometry is a technique for detecting and measuring a specific gas or a small suite of gases. The GFC approach combines extremely high spectral resolution with high optical throughput (or etendue) while avoiding the stringent alignment and mechanical stability requirements imposed by interferometric measurements. The GFC approach is well matched to staring imagers and is very efficient in terms of data volume and bandwidth. A primary limitation to GFC for atmospheric remote sensing is the fact that it works best with gases that have strong absorption features but that are present in small concentrations. This report describes a software model that was developed to predict the performance of GFC sensors. This report presents a design for an airborne GFC sensor and predicts the ability of this sensor and a hypothetical satellite sensor to measure methane in the atmosphere.
The widely used transverse parameters characterizing particle beams are the Twiss parameters. These parameters can be measured experimentally but they do not fully characterize the beam since they do not account for possible correlations in particle distribution between two transverse coordinates. These correlations may occur due to uncompensated magnetic field at the cathode or misalignment of focusing quadrupoles in the transport beamline. We test a novel diagnostic for diagnosing full 4D beam matrix which may be used to identify such imperfections. The diagnostic is based on transporting the beam through the beamline which includes a quadrupole and a skew quadrupole magnets and measuring the resulting 2D beam distribution at the screen downstream. Such a measurement can be viewed as measuring a 2D projection of the 4D distribution. Different settings of the quads provide measurements of different slices of the phase space. The reconstruction of the original beam matrix from a number of measurements is done using machine learning algorithm, which provides a fast and reliable way of reconstruction for an arbitrary configuration of the scanning beamline. In August 2024, we set up the diagnostic beamline to perform a quadrupole scan of the beam. The setup includes a skew quadrupole, a regular quadrupole, and a screen. The images on the screen were post-processed to remove experimental artifacts and enhance contrast by eliminating background noise outside the core of the distribution=. The rms parameters of the distribution were then calculated and used as inputs for the reconstruction algorithm. This algorithm attempts to determine the initial beam matrix that produces expected images on the screen closely matching the observed images across all quadrupole settings. The algorithm found a solution in which the expected rms parameters closely align with the observations. Validation of the results is planned for FY25.
Remote sensing, high resolution FTS instruments often contain three primary optical subsystems: Fore-Optics, Interferometer Optics, and Post, or Detector Optics. We discuss the alignment of a double-pass FTS containing a cat's-eye retro-reflector. Also, the alignment of fore-optics containing confocal paraboloids with a reflecting field stop which relays a field image onto a camera is discussed.
Methods for improving the light grasp by an order of magnitude for earth-based observations of astrophysical objects are reviewed. Noting that the atmosphere is opaque below 0.3 micron and that techniques have been developed to make corrections for the atmospheric distortion, fully diffraction limited IR performance at 10 microns is asserted to be practicable. The use of mirror-seeing with metal mirrors with thin faceplates and air cooling is outlined as a means to achieve subarcsec resolution. Designs are considered which involve multiple sections to gain effective large aperture viewing for spectroscopy, using Si CCD detectors, and heterodyne IR interferometry, but not for direct interferometry or certain IR measurements. The Multiple Mirror Telescope is described, including designs for four 7.5 m honeycomb glass primaries co-aligned in a single mount. Further discussion is devoted to the fabrication of mirror elements and electronic image stabilization.
Direct observation of the film thickness, molecular structure and individual fluorine atoms from highly oriented poly(tetrafluoroethylene) (PTFE) films were achieved using atomic force microscopy (AFM). A thin PTFE film is mechanically deposited onto a smooth glass substrate at specific temperatures by a friction transfer technique. Atomic resolution images of these films show that the chain-like helical structures of the PTFE macromolecules are aligned parallel to each other with an intermolecular spacing of 5.72 A, and individual fluorine atoms are clearly observed along these twisted molecular chains with an interatomic spacing of 2.75 A. Furthermore, the first direct AFM measurements for the radius of the fluorine-helix, and of the carbon-helix in sub-angstrom scale are reported as 1.70 A and 0.54 A respectively.
Direct observation of the film thickness, molecular structure, and individual fluorine atoms from highly oriented poly(tetrafluoroethylene) (PTFE) films were achieved using atomic force microscopy (AFM). A thin PTFE film is mechanically deposited onto a smooth glass substrate at specific temperatures by a friction-transfer technique. Atomic resolution images of these films show that the chain-like helical structures of the PTFE macromolecules are aligned parallel to each other with an intermolecular spacing of 5.72 A, and individual fluorine atoms are clearly observed along these twisted molecular chains with an interatomic spacing of 2.75 A. Furthermore, the first direct AFM measurements for the radius of the fluorine-helix, and of the carbon-helix in sub-angstrom scale are reported as 1.7 and 0.54 A respectively.
An optical design is presented for a measurement system used to assess the impact of surface errors originating from diamond turning artifacts. Diamond turning artifacts are common by-products of optical surface shaping using the diamond turning process (a diamond-tipped cutting tool used in a lathe configuration). Assessing and evaluating the errors imparted by diamond turning (including other surface errors attributed to optical manufacturing techniques) can be problematic and generally requires the use of an optical interferometer. Commercial interferometers can be expensive when compared to the simple optical setup developed here, which is used in combination with an image-based sensing technique (phase retrieval). Phase retrieval is a general term used in optics to describe the estimation of optical imperfections or aberrations. This turnkey system uses only image-based data and has minimal hardware requirements. The system is straightforward to set up, easy to align, and can provide nanometer accuracy on the measurement of optical surface defects.
This report demonstrates empirically that couplings between magnetically conjugate medium-scale traveling ionospheric disturbances (MSTIDs) are electromagnetic in nature. This is accomplished by comparing plasma density, electric, and magnetic perturbations sampled simultaneously by sensors on the Communication Navigation Outage Forecasting System (CNOFS) satellite. During the period of interest on 17 February 2010, CNOFS made three consecutive orbits while magnetically conjugate to the field of view of an all-sky imager located at El Leoncito, Argentina (31.8degS, 69.3degW). Imaged 630.0 nm airglow was characterized by alternating bands of relatively bright and dark emissions that were aligned from northeast to southwest and propagated toward the northwest, characteristic of MSTIDs in the southern hemisphere. Measurable Poynting fluxes flow along the Earths magnetic field (S) from generator to load hemispheres. While S was predominantly away from the ionosphere above El Leoncito, interhemispheric energy flows were not one-way streets. Measured Poynting flux intensities diminished with time over the three CNOFS passes, suggesting that source mechanisms of MSTIDs were absent or that initial impedance mismatches between the two hemispheres approached an equilibrium status.
This paper presents experimental work conducted in the Icing Research Tunnel at NASA Glenn Research Center to characterize the velocity of large drops in the test section. Some icing spray clouds with large drops were generated with Mod1 nozzles at low nozzle air pressure of 2 to 4 psig for various tunnel air speeds. Drop diameters and drop velocities were measured via high-resolution imaging with a Particle Imaging Particle Tracking Velocimetry probe developed by Artium Technologies. The probe was mounted at four different locations aligned with the centerline of the test section from near the end of the contraction to the constant height test section part of the tunnel. CFD analyses were performed. It showed that the probe head geometry affects the local air flow in the measurement area of the probe between the prongs and in front of the probe. Initial analysis of the air velocity data during the test also indicated that the probe mounting stand has blockage effect on the local tunnel air velocity measurement by a pitot-static probe affixed on the mounting plate next to the stand. Those findings were later verified in the Icing Research Tunnel using a new pitot-static probe design with a linear motion system to measure the local tunnel air velocity with and without the probe. As a result, additional drop trajectory simulations were performed with the airflow moving towards the probe head with a Langmuir-D 7-bin distribution cloud containing large drops. The simulation results helped identify a critical drop-size threshold of 300 μm above which the velocities of larger drops are negligibly affected by the adverse pressure gradient generated by the probe head due to their large drop inertia. From the dimensional analysis of the drop velocity measurement data obtained, it showed that at the tunnel test section reference location a generalized empirical correlation was developed for the non-dimensional drop velocity as a function of the non-dimensional corrected drop diameter independent of the actual spraybar pressure settings and the tunnel air speeds. The generalized curve-fit correlation showed that the drop velocity was universally asymptotic to about 86 percent of the corresponding tunnel air speed at the test section reference location for the largest drop diameter captured by the probe. Further evaluation of this correlation is recommended to assess its applicability for Supercooled Large Drop icing scaling applications in the Icing Research Tunnel.
This presentation presents experimental work conducted in the Icing Research Tunnel at NASA Glenn Research Center to characterize the velocity of large drops in the tunnel test section. Some icing spray clouds with large-sized drops were generated with Mod1 nozzles at low nozzle air pressure of 2 to 4 psig for various tunnel air speeds. Drop diameters and drop velocities were measured via high-resolution imaging with a Particle Imaging Particle Tracking Velocimetry probe developed by Artium Technologies. The probe was mounted at four different locations aligned with the centerline of the test section from near the end of the contraction to the constant height test section part of the tunnel. CFD analyses were performed. It showed that the probe head geometry affects the local air flow between the prongs and in front of the probe. Initial analysis of the air velocity data during the test also indicated that the probe mounting stand has blockage effect on the local tunnel air velocity measurement by a Pitot static probe affixed on the mounting plate. Those findings were later verified in the Icing Research Tunnel using a new Pitot probe design with a linear motion system to measure the local tunnel air velocity with and without the probe. As a result, additional drop trajectory simulations as airflow moving towards the probe head were run for a Langmuir-D 7-bin drop size distribution of a spray cloud with a nominally large value of medium volumetric diameter. The simulation results helped identify a critical drop-size threshold of 300 µm above which the velocities of larger drops are not affected by the adverse pressure gradient generated by the probe head due to their large drop inertia. From the dimensional analysis of the drop velocity measurement data obtained, it showed that at the tunnel test section reference location a generalized empirical correlation was developed for the non-dimensional drop velocity as a function of the non-dimensional corrected drop diameter independent of the actual spraybar pressure settings and the tunnel air speeds. The generalized curve-fit correlation showed that the drop velocity was universally asymptotic to about 86 percent of the corresponding tunnel air speed at the test section reference location for the largest drop diameter captured by the probe. Further evaluation of this correlation is recommended to assess its applicability for Supercooled Large Drop icing scaling applications in the Icing Research Tunnel.