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NASA NTRS1999

Effects of Buoyancy in Hydrogen Jet Diffusion Flames

This project was carried out to understand the effects of heat release and buoyancy on the flame structure of diffusion flames. Experiments were conducted at atmospheric pressure in both normal gravity and microgravity conditions in the NASA LeRC 2.2 s drop tower. Experiments were also conducted in a variable pressure combustion facility in normal gravity to scale buoyancy and thus, to supplement the drop tower experiments. Pure H2 or H2 mixed with He was used as the jet fluid to avoid the complexities associated with soot formation. Fuel jet burning in quiescent air was visualized and quantified by the Rainbow Schlieren Deflectometry (RSD) to obtain scalar profiles (temperature, oxygen concentration) within the flame. Burner tube diameter (d) was varied from 0.3 to 1.19 mm producing jet exit Reynolds numbers ranging from 40 to 1900, and generating flames encompassing laminar and transitional (laminar to turbulent) flow structure. Some experiments were also complemented with the CFD analysis. In a previous paper, we have presented details of the RSD technique, comparison of computed and measured scalar distributions, and effects of buoyancy on laminar and transitional H2 gas-jet diffusion flames. Results obtained from the RSD technique, variable pressure combustion chamber, and theoretical models have been published. Subsequently, we have developed a new drop rig with improved optical and image acquisition. In this set up, the schlieren images are acquired in real time and stored digitally in RAM of an onboard computer. This paper deals with laminar diffusion flames of pure H2 in normal and microgravity.

Agrawal, A. K.↗

NASA NTRS2022

Superclustering with the Atacama Cosmology Telescope and Dark Energy Survey. I. Evidence for Thermal Energy Anisotropy Using Oriented Stacking

The cosmic web contains filamentary structure on a wide range of scales. On the largest scales, superclustering aligns multiple galaxy clusters along intercluster bridges, visible through their thermal Sunyaev–Zel'dovich signal in the cosmic microwave background. We demonstrate a new, flexible method to analyze the hot gas signal from multiscale extended structures. We use a Compton y-map from the Atacama Cosmology Telescope (ACT) stacked on redMaPPer cluster positions from the optical Dark Energy Survey (DES). Cutout images from the y-map are oriented with large-scale structure information from DES galaxy data such that the superclustering signal is aligned before being overlaid. We find evidence of an extended quadrupole moment of the stacked y signal at the 3.5σ level, demonstrating that the large-scale thermal energy surrounding galaxy clusters is anisotropically distributed. We compare our ACT × DES results with the Buzzard simulations, finding broad agreement. Using simulations, we highlight the promise of this novel technique for constraining the evolution of anisotropic, non-Gaussian structure using future combinations of microwave and optical surveys.

M. Lokken↗

NASA NTRSDate not supplied

Using Polarized PCRTM-Solar Model to Validate EMIT Surface Reflectance L2A Product

Using the vector linearized discrete ordinate radiative transfer model (VLIDORT), a multiple-scattering multi-layer scattering code, coupled with a fast principal component (PC) radiative transfer model (PCRTM), we can simulate hyperspectral radiation fields from visible to shortwave infrared (VSWIR), i.e., 250 nm to 2500 nm. Since only limited accurate line-by-line calculation using VLIDORT is needed, this coupled PCRTM-VLIDORT approach is very efficient for simulating hyperspectral VSWIR spectra. These simulations incorporate accurately defined optical properties (gas absorptions, molecular and aerosol/cloud particle scattering) and detailed surface reflectance inputs. In this study we used the current L2A products of the Earth Surface Mineral Dust Source Investigation (EMIT) imaging spectrometer as the inputs to PCRTM-VLIDORT to simulate EMIT spectra. Comparing the simulated spectra with EMIT measurements provides an efficient method to validate the current EMIT product.

Xiaozhen Xiong↗

NASA NTRS2000

The Ionization Source in the Nucleus of M84

We have obtained new Hubble Space Telescope (HST) observations of M84, a nearby massive elliptical galaxy whose nucleus contains a approximately 1.5 X 10(exp 9) solar mass dark compact object, which presumably is a supermassive black hole. Our Space Telescope Imaging Spectrograph (STIS) spectrum provides the first clear detection of emission lines in the blue (e.g., [0 II] lambda 3727, HBeta and [0 III] lambda lambda4959,5007), which arise from a compact region approximately 0".28 across centered on the nucleus. Our Near Infrared Camera and MultiObject Spectrometer (NICMOS) images exhibit the best view through the prominent dust lanes evident at optical wavelengths and provide a more accurate correction for the internal extinction. The relative fluxes of the emission lines we have detected in the blue together with those detected in the wavelength range 6295 - 6867 A by Bower et al. indicate that the gas at the nucleus is photoionized by a nonstellar process, instead of hot stars. Stellar absorption features from cool stars at the nucleus are very weak. We update the spectral energy distribution of the nuclear point source and find that although it is roughly flat in most bands, the optical to UV continuum is very red, similar to the spectral energy distribution of BL Lac. Thus, the nuclear point source seen in high-resolution optical images is not a star cluster but is instead a nonstellar source. Assuming isotropic emission from this source, we estimate that the ratio of bolometric luminosity to Eddington luminosity is about 5 x 10(exp -7). However, this could be underestimated if this source is a misaligned BL Lac object, which is a possibility suggested by the spectral energy distribution and the evidence of optical variability we describe.

Bower, G. A.↗

NASA NTRS2007

Validation of Ozone Profiles Retrieved from SAGE III Limb Scatter Measurements

Ozone profiles retrieved from Stratospheric Aerosol and Gas Experiment (SAGE III) limb scatter measurements are compared with correlative measurements made by occultation instruments (SAGE II, SAGE III and HALOE [Halogen Occultation Experiment]), a limb scatter instrument (Optical Spectrograph and InfraRed Imager System [OSIRIS]) and a series of ozonesondes and lidars, in order to ascertain the accuracy and precision of the SAGE III instrument in limb scatter mode. The measurement relative accuracy is found to be 5-10% from the tropopause to about 45km whereas the relative precision is found to be less than 10% from 20 to 38km. The main source of error is height registration uncertainty, which is found to be Gaussian with a standard deviation of about 350m.

Rault, Didier F.↗

NASA NTRS1991

Molecular clouds in starburst galaxy nuclei

New CO observations of a complete sample of starburst galaxies are presented in order to determine the range of molecular gas masses and star-formation efficiencies that characterize these systems. The properties of the galaxies in the sample are given, and the H-alpha and R-band CCD images for six of the galaxies are shown. The novel feature of this study is that the galaxies in this study are infrared selected as opposed to optically selected. They exhibit levels of nuclear star formation activity which are comparable to the starburst galaxies M82 and NGC 253. A subset of galaxies with unusually narrow CO line widths, high star-formation efficiencies, and compact 10-micron distributions is revealed. It is proposed that, if gas distributions in these galaxies are also compact, as the narrow linewidths suggest, the high yields of massive stars per unit mass of molecular gas may be attributed to a star-formation mechanism which becomes more efficient as the gas density increases.

Young, Judith S.↗

DOE OSTI2023

Disentangling the Hadronic Components in NGC 1068

The recent detection of high-energy neutrinos by IceCube in the direction of the nearby Seyfert/starburst galaxy NGC 1068 implies that radio-quiet active galactic nuclei can accelerate cosmic-ray ions. Dedicated multimessenger analyses suggest that the interaction of these high-energy ions with ambient gas or photons happens in a region of the galaxy that is highly opaque for GeV–TeV gamma rays. Otherwise, the GeV–TeV emission would violate existing constraints provided by the Fermi Large Area Telescope (LAT) and the Major Atmospheric Gamma Imaging Cherenkov. The conditions of high optical depth are realized near the central supermassive black hole (SMBH). At the same time, the GeV emission detected by the Fermi LAT is likely related to the galaxy’s sustained star formation activity. In this work, we derive a 20 MeV–1 TeV spectrum of NGC 1068 using 14 yr of Fermi LAT observations. We find that the starburst hadronic component is responsible for NGC 1068's emission above ~500 MeV. However, below this energy, an additional component is required. In the 20–500 MeV range, the Fermi LAT data are consistent with hadronic emission initiated by non-thermal ions interacting with gas or photons in the vicinity of the central SMBH. This highlights the importance of the MeV band to discover hidden cosmic-ray accelerators.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1992

Reanalysis of x ray emission from M87 II: Multiphase models

In a previous paper by the authors (hereafter TB), it was shown that the hot intracluster gas around M87 could not be adequately explained in terms of a spherically symmetric, single phase model. It was found that although data from the Einstein satellite High Resolution Imager (HRI), Imaging Proportional Counter (IPC), and Focal Point Crystal Spectrometer (FPCS) could indeed be simultaneously explained by a single phase model, data from the Solid State Spectrometer (SSS) and optically determined mass estimates could not be similarly explained. A qualitative discussion was then given to indicate how the adoption of a specific multiphase model could plausibly improve upon the single phase model, but a detailed discussion was delayed until now. The x ray data is reanalyzed for the gas around M87 in the same spirit as the work in TB. That is, by assuming several cooling flow models, the shortcomings are improved upon. The procedure of TB was adopted and the data reanalyzed in the following manner: a multiphase model is assumed which can compute the surface brightness as seen by HRI and IPC. Also, the line fluxes can be computed of the lines seen by the FPCS and the mass profile after assuming hydrostatic equilibrium. The parameters of the model are then adjusted to fit the data. A check is then made to see whether the resulting model is consistent with the SSS spectrum and the equivalent width of the 7 keV complex of Fe lines as seen by large field of view instruments.

Tsai, John C.↗

NASA NTRS2013

Hydrometeor Size Distribution Measurements by Imaging the Attenuation of a Laser Spot

The optical extinction of a laser due to scattering of particles is a well-known phenomenon. In a laboratory environment, this physical principle is known as the Beer-Lambert law, and is often used to measure the concentration of scattering particles in a fluid or gas. This method has been experimentally shown to be a usable means to measure the dust density from a rocket plume interaction with the lunar surface. Using the same principles and experimental arrangement, this technique can be applied to hydrometeor size distributions, and for launch-pad operations, specifically as a passive hail detection and measurement system. Calibration of a hail monitoring system is a difficult process. In the past, it has required comparison to another means of measuring hydrometeor size and density. Using a technique recently developed for estimating the density of surface dust dispersed during a rocket landing, measuring the extinction of a laser passing through hail (or dust in the rocket case) yields an estimate of the second moment of the particle cloud, and hydrometeor size distribution in the terrestrial meteorological case. With the exception of disdrometers, instruments that measure rain and hail fall make indirect measurements of the drop-size distribution. Instruments that scatter microwaves off of hydrometeors, such as the WSR-88D (Weather Surveillance Radar 88 Doppler), vertical wind profilers, and microwave disdrometers, measure the sixth moment of the drop size distribution (DSD). By projecting a laser onto a target, changes in brightness of the laser spot against the target background during rain and hail yield a measurement of the DSD's second moment by way of the Beer-Lambert law. In order to detect the laser attenuation within the 8-bit resolution of most camera image arrays, a minimum path length is required. Depending on the intensity of the hail fall rate for moderate to heavy rainfall, a laser path length of 100 m is sufficient to measure variations in optical extinction using a digital camera. For hail fall only, the laser path may be shorter because of greater scattering due to the properties of hailstones versus raindrops. A photodetector may replace the camera in automated installations. Laser-based rain and hail measurement systems are available, but they are based on measuring the interruption of a thin laser beam, thus counting individual hydrometeors. These systems are true disdrometers since they also measure size and velocity. The method reported here is a simple method, requiring far less processing, but it is not a disdrometer.

Lane, John↗

NASA NTRS2010

NASA Tech Briefs, April 2010

Topics covered include: Active and Passive Hybrid Sensor; Quick-Response Thermal Actuator for Use as a Heat Switch; System for Hydrogen Sensing; Method for Detecting Perlite Compaction in Large Cryogenic Tanks; Using Thin-Film Thermometers as Heaters in Thermal Control Applications; Directional Spherical Cherenkov Detector; AlGaN Ultraviolet Detectors for Dual-Band UV Detection; K-Band Traveling-Wave Tube Amplifier; Simplified Load-Following Control for a Fuel Cell System; Modified Phase-meter for a Heterodyne Laser Interferometer; Loosely Coupled GPS-Aided Inertial Navigation System for Range Safety; Sideband-Separating, Millimeter-Wave Heterodyne Receiver; Coaxial Propellant Injectors With Faceplate Annulus Control; Adaptable Diffraction Gratings With Wavefront Transformation; Optimizing a Laser Process for Making Carbon Nanotubes; Thermogravimetric Analysis of Single-Wall Carbon Nanotubes; Robotic Arm Comprising Two Bending Segments; Magnetostrictive Brake; Low-Friction, Low-Profile, High-Moment Two-Axis Joint; Foil Gas Thrust Bearings for High-Speed Turbomachinery; Miniature Multi-Axis Mechanism for Hand Controllers; Digitally Enhanced Heterodyne Interferometry; Focusing Light Beams To Improve Atomic-Vapor Optical Buffers; Landmark Detection in Orbital Images Using Salience Histograms; Efficient Bit-to-Symbol Likelihood Mappings; Capacity Maximizing Constellations; Natural-Language Parser for PBEM; Policy Process Editor for P(sup 3)BM Software; A Quality System Database; Trajectory Optimization: OTIS 4; and Computer Software Configuration Item-Specific Flight Software Image Transfer Script Generator.

Source record↗

NASA NTRS1990

The Hawaii Imaging Fabry-Perot Interferometer (HIFI)

At Mauna Kea Observatory, researchers conducted optical, imaging spectrophotometric studies of selected active galaxies using both the Canada-France-Hawaii 3.6m and University of Hawaii 2.2m telecopes (Tully, Bland and Cecil 1988). To maximize spatial resolution, researchers select galaxies independent of luminosity but known to possess interesting morphologies or high-velocity, extranuclear ionized gas (Walker 1968; Rubin and Ford 1968). They study both the large-scale patterns produced in IR-luminous, starburst systems (e.g., M82, NGC 253, NGC 6240) and those with compact, but spatially extended, circumnuclear, narrow line regions (e.g., M51, NGC 1068, NGC 4151). Current studies are restricted to the optical (SII), (NII) and (OIII) lines and the brightest Balmer recombination lines. These lines are, in principle, sufficient to constrain the dynamical structure and dominant excitation mechanism of the ionized component.

Bland, Jonathan↗

NASA NTRS1988

The twin-nucleus merging galaxy Markarian 266 (NGC 5256)

Optical imaging in continuum and line wavelengths, spatially resolved optical spectroscopy, and 21 cm radio imaging of Markarian 266 are presented. The galaxy has faint extended plumes of luminosity, which indicate that it is a recent merger. There are extended regions of blue luminosity suggestive of recent star formation, and remarkable structure in forbidden O III line emission. Spectroscopic data show the velocities and densities in the ionized gas. Radio observations taken with the VLA show that both nuclei are resolved radio sources, and that there is a third radio source between them which has no optical counterpart; 21-cm absorption is seen against the brighter optical nucleus, indicating possible infall. These results are discussed in terms of galaxy mergers, nuclear activation, and ionized gas. Mkn 266 has many similarities to Arp 220 and appears to be a somewhat lower-luminosity version of the IRAS ultraluminous galaxies.

Hutchings, J. B.↗

DOE OSTI2022

Ducted fuel injection with Low-Net-Carbon fuels as a solution for meeting future emissions regulations

Several studies have proven how ducted fuel injection (DFI) reduces soot emissions for compression-ignition engines. Nevertheless, no comprehensive study has investigated how DFI performs over a load range in combination with low-net-carbon fuels. In this study, optical-engine experiments were performed with four different fuels—conventional diesel and three low-net-carbon fuels—at low and moderate load, to measure emissions levels and performance. The 1.7-liter single-cylinder optical engine was equipped with a high-speed camera to capture natural luminosity images of the combustion event. Conventional diesel and DFI combustion were investigated at four different dilution levels (to simulate exhaust-gas recirculation effects), from 14 to 21 mol% oxygen in the intake. At a given dilution level, with commercial diesel fuel, DFI reduced soot by 82% at medium load, and 75% at low load without increasing NO x . The results further show how DFI with dilution reduces soot and NO x without compromising engine performance or other emission types, especially when combined with low-net-carbon fuels. DFI with the oxygenated low-net-carbon blend HEA67 simultaneously reduced soot and NO x by as much as 93 % and 82 %, respectively, relative to conventional diesel combustion with commercial diesel fuel. These soot and NO x reductions occurred while lifecycle CO 2 was reduced by at least 70 % when using low-net-carbon fuels instead of conventional diesel. All emissions changes were compared with future emissions regulations for different vehicle sectors to investigate how DFI can be used to facilitate achievement of the regulations. Finally, the results show how the DFI cases fall below several future emissions regulation levels, rendering less need for aftertreatment systems and giving a possible lower cost of ownership.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2021

Dynamics of filaments during the edge-localized mode crash on NSTX

Edge localized modes (ELMs) are routinely observed in H-mode plasma regimes of the National Spherical Torus Experiment (NSTX). Due to the explosive nature of the instability, only diagnostics with high temporal and spatial resolution could provide a detailed insight into the dynamics associated with the ELMs. Gas-puff imaging at NSTX provides 2D measurements of the magnetic field aligned fluctuations (e.g., ELM filaments) in the scrape-off layer and at the plasma edge with 2.5 μs temporal and 10 mm optical resolution. A novel analysis technique was developed to estimate the frame-by-frame velocities and the spatial parameters of the dominant structures associated with the ELMs. The analysis was applied to single ELM events to characterize the ELM crash dynamics and then extended to a database of 159 ELM events. Statistical analysis was performed in order to find the characterizing dynamics of the ELM crash. The results show that on average, an ELM crash consists of a filament with a circular cross section, which is propelled outward with a characterizing peak radial velocity of ~3.3 km/s. The radial velocity was found to be linearly dependent on the distance of the filament from the separatrix, which has never been seen before. The ELM filament is characterized by propagation in the ion-diamagnetic direction poloidally with a peak velocity of 11.4 km/s. The ELM crash lasts for approximately 100 μs until the radial propulsion settles back to the pre-ELM level. Furthermore, the experimental findings were compared with analytical theory. Two possible mechanisms were identified for explaining the observations: the curvature interchange model and the current–filament interaction model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1981

Pioneer fly-by of Saturn and its rings

Results acquired by the imaging photopolarimeter on board Pioneer 11 during the spacecraft fly-by of Saturn and its rings on September 1, 1979 are reviewed. Analysis of the broadband photometry and polarimetry obtained of the Saturn atmosphere has been used to determine a cloud top height of 300 mb and a scale height of the aerosol distribution about 1/4 that of the ambient gas, and to point out differences between the forward scattering and belt and zone characteristics of the Saturn and Jupiter atmospheres. Images of Saturn's rings have been used to derive a profile of ring optical depth between 1.22 and 2.35 Saturn radii, and reveal new divisions and thin rings and azimuthal variations in the brightness of the A ring not observable from earth. Linear polarization observations of Titan in red and blue light reveal that the aerosols near the top of the atmosphere have radii less than about 0.09 micron and that the optical thickness of the small aerosol layer is about 0.6 above an effectively depolarizing surface, and indicate radii of 2845 + or - 25 km and 2880 + or - 22 km in red and blue light, respectively. Earth-based and spacecraft data are consistent with the formation of rings structures as a result of Poynting-Robertson drag and gravitational satellite resonances with the original ice and rock particles.

Gehrels, T.↗

NASA NTRS1986

Advanced high temperature static strain sensor development

An examination was made into various techniques to be used to measure static strain in gas turbine liners at temperatures up to 1150 K (1600 F). The methods evaluated included thin film and wire resistive devices, optical fibers, surface acoustic waves, the laser speckle technique with a heterodyne readout, optical surface image and reflective approaches and capacitive devices. A preliminary experimental program to develop a thin film capacitive device was dropped because calculations showed that it would be too sensitive to thermal gradients. In a final evaluation program, the laser speckle technique appeared to work well up to 1150 K when it was used through a relatively stagnant air path. The surface guided acoustic wave approach appeared to be interesting but to require too much development effort for the funds available. Efforts to develop a FeCrAl resistive strain gage system were only partially successful and this part of the effort was finally reduced to a characterization study of the properties of the 25 micron diameter FeCrAl (Kanthal A-1) wire. It was concluded that this particular alloy was not suitable for use as the resistive element in a strain gage above about 1000 K.

Hulse, C. O.↗

NASA NTRS1987

Near-nucleus optical observations of P/Halley

The Near-Nucleus Studies Net of the International Halley Watch has obtained an extensive series of high resolution optical images of P/Halley during its most active phases in 1985-86 which may be useful in interpreting radio observations of Comet Halley. They often show coma structure resulting from anisotropic emission of dust and gas from the inhomogeneous nucleus. Images were obtained in broadband spectral regions to study dust coma morphology, and in medium to narrow spectral bands to isolate the principal emissions of CN, C3, C2, CO+ and H2O+. The goals and methods of near-nucleus studies are discussed and recent studies of 1910 images are briefly reviewed. The role of dust jets and cometary activity in P/Halley is discussed and several examples of anisotropic emission of dust during the current apparition are shown.

Larson, Stephen M.↗

NASA NTRSDate not supplied

Tunable Mid-wave Infrared Fabry-Perot Bandpass Filters Using Phase-Change GeSbTe

Tunable mid-wave infrared (MWIR) filters are highly desirable in a wide variety of imaging and sensing, as the MWIR contains numerous spectral signatures. We fabricated spectrally-tunable Fabry-Perot bandpass filters operating across the MWIR by utilizing the phase-change material GeSbTe (GST) as a tunable cavity medium between distributed Bragg reflectors. The induced refractive index modulation of the GST increases the cavity’s optical path length, tuning the passband. Our filters have 300-nm spectral tunability, 60-75% transmission efficiencies, and 50-65 nm narrowband FWHMs (Q-factor 70-90). We demonstrate multispectral thermal imaging and dynamic gas sensing by matching the filter’s passband (~ 4.25μm) to a CO2 vibrational-absorption mode.

Tunable filter↗