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We have imaged the nucleus of the nearby radio galaxy NGC 4261 (3C270) with the VLBA at 1.6, 8.4, 22, and 43 GHz. At 8.4 GHz our image reveals a narrow gap in emission just east of the core, which we interpret as absorption by an inner accretion disk seen nearly edge-on.
After completing its duty in the vacuum chamber at the High Contrast Imaging Testbed (HCIT) facility at NASA’s Jet Propulsion Laboratory, the General Purpose Coronagraph Testbed (GPCT) has been retrofitted as the In-Air Coronagraph Testbed (IACT), with the purpose of verification of Boston Micromachines (BMC) 50x50 MEMS deformable mirrors (MEMS DM) performance by contrast comparison before and after random vibration testing. The testbed is configured as a vortex coronagraph, with one MEMS DM in the pupil plane to create a half dark hole in monochromatic light. High wavefront stability is achieved using an environmentally isolating enclosure, based on the enclosure design previously used on Caltech’s High Contrast Spectroscopy Testbed (HCST). Further, a smaller enclosure has been designed which will enforce humidity conditions necessary for the MEMS DM to operate. We expect this testbed to achieve 1e-8 contrast, and will use this contrast level as a baseline to assess survival or failure of MEMS DMs during vibration testing. In this presentation, we will present an overview of the design of the IACT, commissioning results, and plans for upcoming DM tests in preparation for launch on future space telescopes with coronagraph instruments.
This paper describes an analysis of the potential of an airborne hyperspectral imaging IR instrument to infer wake vortices via turbine jet exhaust as a proxy. The goal was to determine the requirements for an imaging spectrometer or radiometer to effectively detect the exhaust plume, and by inference, the location of the wake vortices. The effort examines the gas spectroscopy of the various major constituents of turbine jet exhaust and their contributions to the modeled detectable radiance. Initially, a theoretical analysis of wake vortex proxy detection by thermal radiation was realized in a series of simulations. The first stage used the SLAB plume model to simulate turbine jet exhaust plume characteristics, including exhaust gas transport dynamics and concentrations. The second stage used these plume characteristics as input to the Line By Line Radiative Transfer Model (LBLRTM) to simulate responses from both an imaging IR hyperspectral spectrometer or radiometer. These numerical simulations generated thermal imagery that was compared with previously reported wake vortex temperature data. This research is a continuation of an effort to specify the requirements for an imaging IR spectrometer or radiometer to make wake vortex measurements. Results of the two-stage simulation will be reported, including instrument specifications for wake vortex thermal detection. These results will be compared with previously reported results for IR imaging spectrometer performance.
PixelVision, Inc., has developed a series of integrated imaging engines capable of high-resolution image capture at dynamic speeds. This technology was used originally at Jet Propulsion Laboratory in a series of imaging engines for a NASA mission to Pluto. By producing this integrated package, Charge-Coupled Device (CCD) technology has been made accessible to a wide range of users.
The twin Mars Exploration Rovers (MER) delivered an unprecedented array of image sensors to the Mars surface. These cameras were essential for operations, science, and public engagement. The Multimission Image Processing Laboratory (MIPL) at the Jet Propulsion Laboratory was responsible for the first-order processing of all of the images returned by these cameras. This processing included reconstruction of the original images, systematic and ad hoc generation of a wide variety of products derived from those images, and delivery of the data to a variety of customers, within tight time constraints. A combination of automated and manual processes was developed to meet these requirements, with significant inheritance from prior missions. This paper describes the image products generated by MIPL for MER and the processes used to produce and deliver them.
An initial experimental study of the effect of streamwise vorticity on supersonic turbulent mixing has been carried out. A Mach 3 streamwise vortex is generated using a strutmounted swirl injector and is injected into a Mach 3.5 freestream. The resulting flowfield is investigated using both five-hole angularity probe and total temperature probe surveys. The results are compared to identical experiments with a baseline, swirl-free Mach 3 jet. Laser Light Sheet (LLS) images are used to observe the mixing phenomena. The entrainment of energy and mass is used to evaluate the degree of mixing between the two streams for both the vortex and jet cases. The results reveal that streamwise vorticity does lead to a modest mixing enhancement of about 34 percent for the conditions tested.
Hubble Space Telescope imaging of HH 30 has revealed this object to be a prototype young stellar object (YSO) accretion disk system. An optically thick circumstellar absorption disk, 450 AU in diameter, is seen extending perpendicular to highly collimated bipolar jets.
Prandtl's suggested use of a doubly infinite arrangement of airfoil images in the theoretical determination of wind-tunnel jet-boundary corrections was first adapted by Glauert to the case of closed rectangular jets. More recently, Theodorsen, using the same image arrangement but a different analytical treatment, has extended this work to include not only closed but also partly closed and open tunnels. This report presents the results of wind-tunnel tests conducted at the Georgia School of Technology for the purpose of verifying the five cases analyzed by Theodorsen. The tests were conducted in a square tunnel and the results constitute a satisfactory verification of his general method of analysis. During the preparation of the data two minor errors were discovered in the theory and these have been rectified.
Empirical mode decomposition is an adaptive signal processing method that when applied to a broadband signal, such as that generated by turbulence, acts as a set of band-pass filters. This process was applied to data from time-resolved, particle image velocimetry measurements of subsonic jets prior to computing the second-order, two-point, space-time correlations from which turbulent phase velocities and length and time scales could be determined. The application of this method to large sets of simultaneous time histories is new. In this initial study, the results are relevant to acoustic analogy source models for jet noise prediction. The high frequency portion of the results could provide the turbulent values for subgrid scale models for noise that is missed in large-eddy simulations. The results are also used to infer that the cross-correlations between different components of the decomposed signals at two points in space, neglected in this initial study, are important.
Empirical mode decomposition is an adaptive signal processing method that when applied to a broadband signal, such as that generated by turbulence, acts as a set of band-pass filters. This process was applied to data from time-resolved, particle image velocimetry measurements of subsonic jets prior to computing the second-order, two-point, space-time correlations from which turbulent phase velocities and length and time scales could be determined. The application of this method to large sets of simultaneous time histories is new. In this initial study, the results are relevant to acoustic analogy source models for jet noise prediction. The high frequency portion of the results could provide the turbulent values for subgrid scale models for noise that is missed in large-eddy simulations. The results are also used to infer that the cross-correlations between different components of the decomposed signals at two points in space, neglected in this initial study, are important.
Empirical mode decomposition is an adaptive signal processing method that when applied to a broadband signal, such as that generated by turbulence, acts as a set of band-pass filters. This process was applied to data from time-resolved, particle image velocimetry measurements of subsonic jets prior to computing the second-order, two-point, space-time correlations from which turbulent phase velocities and length and time scales could be determined. The application of this method to large sets of simultaneous time histories is new. In this initial study, the results are relevant to acoustic analogy source models for jet noise prediction. The high frequency portion of the results could provide the turbulent values for subgrid scale models for noise that is missed in large-eddy simulations. The results are also used to infer that the cross-correlations between different components of the decomposed signals at two points in space, neglected in this initial study, are important.
Past variability studies of flat-spectrum, compact extra-galactic radio sources have suggested that low- and high-optically polarized quasars (LPQ/HPQ) are the same type of object, differing only in the angle their relativistic jets make to the line of sight. This view has been challenged, however, by recent millimeter-wave polarization observations which indicate intrinsic differences in the inner magnetic field properties of the two classes. The inner jets of LPQs tend to have lower fractional polarizations than HPQs, and inferred magnetic field directions that are mostly parallel to the jet. The magnetic fields of HPQs, on the other hand, lie mainly in a transverse direction. The latter configuration is a prediction of the standard shock-in-jet model, in which a portion of a jet undergoes a strong transverse compression, thereby enhancing the perpendicular components of an originally tangled magnetic field. The main goal of this study is to establish a connection between the optical polarization and magnetic field properties of the inner jets of blazars. The magnetic field orientations of several HPQs have been shown to be stable over many years, which may be due to standing shock(s) located close to the base of the jet. Since these shocks are able to produce large amounts of optically polarized synchrotron radiation, their presence may very well determine whether an object is classified as an HPQ or LPQ. We have imaged the parsec-scale jet regions and magnetic fields of 11 LPQs with the Very Long Baseline Array (VLBA) at 43 and 22 GHz, and have obtained near- simultaneous optical polarization data for the sample. We discuss correlations between the optical and radio polarization data, and compare the LPQ properties to those of a sample of HPQs presently being monitored with the VLBA and JCMT at mm and sub-mm wavelengths, respectively. This research was performed in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA.
We present and discuss visible-wavelength long-slit spectra of four low-redshift 3C galaxies obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST). The slit was aligned with near-nuclear jet-like structure seen in HST images of the galaxies, to give unprecedented spatial resolution of their inner regions. In 3C 135 and 3C 171, the spectra reveal clumpy emission-line structures that indicate outward motions of a few hundred kilometers per second within a centrally illuminated and ionized biconical region. There may also be some low-ionization, high-velocity material associated with 3C 135. In 3C 264 and 3C 78, the jets have blue featureless spectra consistent with their proposed synchrotron origin. There is weak associated line emission in the innermost part of the jets with mild outflow velocity. These jets are bright and highly collimated only within a circumnuclear region of lower galaxy luminosity, which is not dusty. We discuss the origins of these central regions and their connection with relativistic jets.
A study has been initiated to evaluate the feasibility of transmitting selected GOES images to aircraft in flight. Pertinent observations that could be made from satellite images on board aircraft include jet stream activity, cloud/wind motion, cloud temperatures, tropical storm activity, and location of severe weather. The basic features of the Satellite Aircraft Flight Environment System (SAFES) are described. This system uses East GOES and West GOES satellite images, which are interpreted, enhanced, and then retransmitted to designated aircraft.
To improve the quality of photos sent to Earth by unmanned spacecraft. NASA's Jet Propulsion Laboratory (JPL) developed a computerized image enhancement process that brings out detail not visible in the basic photo. JPL is now applying this technology to biomedical research in its Medical lrnage Analysis Facility, which employs computer enhancement techniques to analyze x-ray films of internal organs, such as the heart and lung. A major objective is study of the effects of I stress on persons with heart disease. In animal tests, computerized image processing is being used to study coronary artery lesions and the degree to which they reduce arterial blood flow when stress is applied. The photos illustrate the enhancement process. The upper picture is an x-ray photo in which the artery (dotted line) is barely discernible; in the post-enhancement photo at right, the whole artery and the lesions along its wall are clearly visible. The Medical lrnage Analysis Facility offers a faster means of studying the effects of complex coronary lesions in humans, and the research now being conducted on animals is expected to have important application to diagnosis and treatment of human coronary disease. Other uses of the facility's image processing capability include analysis of muscle biopsy and pap smear specimens, and study of the microscopic structure of fibroprotein in the human lung. Working with JPL on experiments are NASA's Ames Research Center, the University of Southern California School of Medicine, and Rancho Los Amigos Hospital, Downey, California.
ABSTRACT Blazars are active galactic nuclei (AGNs) observed at small viewing angles to the observer’s line of sight; hence most of them are compact sources in the radio regime. At low radio frequencies, we may observe additional extended structures, considered to be lobes propagating directly towards Earth. However, there are rare cases of blazars whose morphologies are interpreted in the framework of an episodic jet activity with a reorientation of the jet axis. In this paper, we aim to find other candidates for sources of this kind and present Low Frequency Array (LOFAR) observations of seven blazars with rare morphologies composed of kiloparsec-scale jets and elongated multihundred kiloparsec-scale features. Based on their radio images and physical parameters, we propose that jets could change the direction of propagation out of the sky plane during the lifetime of at least some of these sources and with such we may observe morphologically different AGN types simultaneously, similar to the previously discovered blazar SBS B1646+499. Several plausible origin scenarios are presented, including fast realignment and precession. We also derive the 144 MHz fluxes of the compact and extended structures, the total radio luminosities, the spectral indices for the diffuse haloes, and the core-dominance parameters. We also discuss the possibility that these objects are actually giant blazars with rare Fanaroff–Riley I (FR I) morphology. The previously discovered blazar SBS B1646+499 should be classified as a giant independently of its inclination with regard to the observer.
Charge-coupled devices (CCD's) were recognized for their potential as an imaging technology almost immediately following their conception in 1970. Twenty years later, they are firmly established as the technology of choice for visible imaging. While consumer applications of CCD's, especially the emerging home video camera market, dominated manufacturing activity, the scientific market for CCD imagers has become significant. Activity of the Jet Propulsion Laboratory and its industrial partners in the area of CCD imagers for space scientific instruments is described. Requirements for scientific imagers are significantly different from those needed for home video cameras, and are described. An imager for an instrument on the CRAF/Cassini mission is described in detail to highlight achieved levels of performance.
It is desired to maintain supersonic flow through the combustor of supersonic airbreathing engines to reduce static temperatures and total pressure losses inherent in reducing flow to subsonic speeds. Due to the supersonic speeds through the combustor, mixing of the fuel and air must by rapid for complete combustion to occur within a reasonable streamwise distance. It was proposed that the addition of swirl to the fuel jet prior to injection might enhance the mixing of the fuel with the air. The effects of swirl on the mixing of a 30 deg wall jet into a Mach 2 flow were experimentally investigated. Swirl was introduced into the fuel stream by tangential injection into a cylindrical swirl chamber. The flow was then accelerated through a convergent-divergent nozzle with an area ratio of two, and supersonically injected into the Mach 2 flow such that the static pressure of the fuel matched the effective back pressure of the main flow. Two different cases with swirl and one without swirl were investigated, with both helium and air simulating the fuel. Rayleigh scattering was used to visualize the flow and seeding the fuel with water allowed it to be traced through the main flow. Using histograms of the pure molecular Rayleigh scattering images, the helium concentration in the jet-mixing region of the flow was monitored and found to decrease slightly with swirl, indicating better mixing. Thresholding the water-seeded images allowed the jet-mixing region to be isolated and showed a slight increase in this area with swirl. Penetration, however, was slightly less with swirl. Rescaling the data for equal mass flow rates allowed comparison for a scramjet application of a combustor with a single injector and the desire to fuel to a specified fuel-to-oxidant ratio. These results showed a substantial increase in the spreading area with swirl, an increase in the mixing occurring in this area, and slightly better penetration.