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NASA NTRS1973

Microwave radiation hazards around large microwave antenna.

The microwave radiation hazards associated with the use of large antennas become increasingly more dangerous to personnel as the transmitters go to ever higher powers. The near-field area is of the greatest concern. It has spill over from subreflector and reflections from nearby objects. Centimeter waves meeting in phase will reinforce each other and create hot spots of microwave energy. This has been measured in front of and around several 26-meter antennas. Hot spots have been found and are going to be the determining factor in delineating safe areas for personnel to work. Better techniques and instruments to measure these fields are needed for the evaluation of hazard areas.

Klascius, A.↗

NASA NTRS1993

Two-dimensional thermal-hydraulics analyses of the Pellet Bed Reactor for Nuclear Thermal Propulsion

Thermal-hydraulics design and analyses of the Pellet Bed Reactor for nuclear thermal propulsion are performed using the nuclear propulsion thermal-hydraulic analysis model to determine the 2D steady-state temperature, pressure, and flow fields in the core and optimize the orificing in the hot-frit to avoid hot spots in the core at full power operation. Results show that by properly adjusting the axial porosity profile in the hot frit, hot spots in the core can be essentially eliminated during full power operation. This important accomplishment is achieved at the expense of slightly larger pressure losses in the core because of flow restriction at the hot frit. However, the overall pressure losses is only about 11 percent of the propellant inlet pressure.

Morley, Nicholas J.↗

DOE OSTI2021

A multi-institution collaboration to study copper wire hybrid and laser-cut foil X-pinches

X-pinches are a pulsed power wire-array configuration that produce nanosecond and micron-scale X-ray sources with numerous applications. The earliest embodiment of the X-pinch inspired its name, as it is typically composed of two or more fine (5-50 µm) wires crossed into the shape of an X (Fig. 1a). The ‘X’ ablates when subjected to large (10 1 -10 4 kA), fast-rising (~1 kA/ns) currents, and extreme magnetic pressure at the cross-point constricts the ablated plasma, which develops instabilities and then pinches to near-zero radius, localized ‘hot spots’, emitting X-rays from a sub-nanosecond and 1 µm scale source characteristic of a hot (~1 keV), dense (10% solid density) plasma. A subsequent gap forms where the hot spot(s) occurred, across which substantial potential accelerates electron beams (e-beams) that generate larger, longer-lasting X-ray bursts composed of harder X-rays.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1970

Eclipse cooling of selected lunar features

Thermal measurements were made in the 10 to 12 micron band of the lunar surface during the total eclipse of December19, 1964. A normalized differential thermal contour map is included, showing the location of the thermal anomalies or hot spots on the disk and the eclipse cooling curves of 400 sites, of which more than 300 were hot spots. The eclipse cooling data is compared to a particulate thermophysical model of the soil.

Shorthill, R. W.↗

NASA NTRS1993

Photometric and spectroscopic monitoring of AA Tau, DN Tau, UX Tau A, T Tau, RY Tau, Lk Ca 4, and Lk Ca 7

We report the results of a UBVRI photometric monitoring campaign for three classical T Tauri stars (AA Tau, DN Tau, and UX Tau A) and two weak emission line T Tauri stars (Lk Ca 4 and Lk Ca 7). Observations were obtained at three sites during a core observing period spanning UT 1985 October 14 through UT 1985 December 25, with additional observations continuing until UT 1986 April 6. Concurrent spectrophotometric observations were obtained for all main program stars except Lk Ca 7 and additionally for T Tau, RW Aur, and RY Tau. Periodic photometric variability, assumed to be the stars' rotation periods, were found for AA Tau, DN Tau, Lk Ca 4, and Lk Ca 7, respectively, as 8.2, 6.3, 3.4, and 5.7 days. Several U-filter flares were observed for Lk Ca 4 and Lk Ca 7, which are strongly concentrated toward phases of minimum light. Correlations are found between H-alpha line strengths and V magnitudes for AA Tau and RY Tau. An analysis of absolute color variations of classical T Tauri stars confirms that hot spots are the predominant cause of these stars' variability. Our overall results are consistent with earlier findings that long-lived cool spots are responsible for most of the variability found for weak-emission T Tauri stars, while temporal hot spots are primarily responsible for the observed variability found in classical T Tauri stars.

Vrba, F. J.↗

DOE OSTI2025

Modeling the microplastic distribution along the Delaware River Estuary: Accumulation patterns and hydrodynamic influences

Microplastic pollution is an escalating environmental concern, particularly in densely populated estuary regions, where it poses significant threats to aquatic life and human health. The dispersion patterns of microplastic particles along estuaries are influenced and complicated by multiple environmental factors such as river flow, tidal mixing, salt intrusion, and estuarine circulation. This study examines the accumulation and dispersion patterns by modeling three typical classes of microplastics in the Delaware River Estuary: synthetic fibers, sinking plastic films, and rising plastic pellets. Our findings reveal specific areas with high microplastic accumulation for each type. Notably, the upper estuary regions exhibit significant retention of rising microplastics, associated with a region with reduced along-thalweg velocities downstream of Trenton, NJ and upstream of Philadelphia, PA. Conversely, synthetic fibers and sinking plastic films accumulate in the flow convergence zone near the bottom salinity front, typically downstream of Philadelphia. All of the microplastic accumulation hot spot locations are controlled by the balance of river discharge and salinity intrusions. During the dry season, microplastic accumulation hot spots shift upstream in the estuary, whereas in the wet season, the strong river discharge pushes them downstream. Furthermore, on the other hand, tidal mixing, settling, and resuspension processes strongly impact the spreading of microplastics along the river.

Delaware River Estuary↗

NASA NTRS1988

Collisionless shock formation and the prompt acceleration of solar flare ions

The formation mechanisms of collisionless shocks in solar flare plasmas are investigated. The priamry flare energy release is assumed to arise in the coronal portion of a flare loop as many small regions or 'hot spots' where the plasma beta locally exceeds unity. One dimensional hybrid numerical simulations show that the expansion of these 'hot spots' in a direction either perpendicular or oblique to the ambient magnetic field gives rise to collisionless shocks in a few Omega(i), where Omega(i) is the local ion cyclotron frequency. For solar parameters, this is less than 1 second. The local shocks are then subsequently able to accelerate particles to 10 MeV in less than 1 second by a combined drift-diffusive process. The formation mechanism may also give rise to energetic ions of 100 keV in the shock vicinity. The presence of these energetic ions is due either to ion heating or ion beam instabilities and they may act as a seed population for further acceleration. The prompt acceleration of ions inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission can thus be explained by this mechanism.

Cargill, P. J.↗

NASA NTRS2002

Insights into Corona Formation Through Statistical Analyses

Statistical analysis of an expanded database of coronae on Venus indicates that the populations of Type 1 (with fracture annuli) and 2 (without fracture annuli) corona diameters are statistically indistinguishable, and therefore we have no basis for assuming different formation mechanisms. Analysis of the topography and diameters of coronae shows that coronae that are depressions, rimmed depressions, and domes tend to be significantly smaller than those that are plateaus, rimmed plateaus, or domes with surrounding rims. This is consistent with the model of Smrekar and Stofan and inconsistent with predictions of the spreading drop model of Koch and Munga. The diameter range for domes, the initial stage of corona formation, provides a broad constraint on the buoyancy of corona-forming plumes. Coronae are only slightly more likely to be topographically raised than depressions, with Type 1 coronae most frequently occurring as rimmed depressions and Type 2 coronae most frequently occurring with flat interiors and raised rims. Most Type 1 coronae are located along chasmata systems or fracture belts, while Type 2 coronae are found predominantly as isolated features in the plains. Coronae at hot spot rises tend to be significantly lager than coronae in other settings, consistent with a hotter upper mantle at hot spot rises and their active state.

Glaze, L. S.↗

NASA NTRS1981

Spectral evolution of the 5 March 1979 gamma burst

The spectral development of the intense gamma-ray burst observed on March 5, 1979 by nine spacecraft spaced on an interplanetary scale is discussed. As observed by the Pioneer Venus Orbiter detector, the hardness ratio of the burst, defined as the ratio between counts in the 100-1000 keV channels to those in the 50-100 keV channel, decreases during the very fast rise and subsequent 75 msec of the burst, consistent with a decrease in black-body temperature from 30 to 26 keV, and then increases during the shoulder on the gamma-ray burst light curve. Following the burst, the source was observed to exhibit many of the characteristics of a hard X-ray pulsar with a period of 8.0 sec and a hardness ratio varying in phase with the intensity. The observed characteristics of the pulsations are interpreted in terms of hot spots at the magnetic poles of a rotating neutron star, although it is shown that the simple cooling of residual hot spots does not completely explain the pulsations. Alternative explanations for the pulsation include accretion or an effect of beam geometry.

Fenimore, E. E.↗

NASA NTRS2005

Jet-Intracluster Medium Interactions of the Head Tail Radio Galaxy 3C 129

The 50 ksec XMM observations of the galaxy cluster 3C 129 were taken as scheduled, and the data are of good quality. We analyzed the data in the following way. After standard cleaning, we flat-fielded the XMM surface brightness maps. Combining the data from the EPIC MOS and PN Camera CCDs, we performed a cross-correlation analysis of the X-ray surface brightness distribution with the 1.4 GHz VLA radio map. We found evidence for cavities in the X-ray emitting Intra-Cluster Medium (ICM) associated with the radio tail of the head-tail radio galaxy 3C 129. This discovery is very interesting as it excludes the presence of a large fraction of thermal plasma in the radio tail. Together with the observation of an apparent pressure mismatch between the radio plasma and the ICM, and an upper limit on the magnetic field inside the radio tail (from the radio spectral indices map) the observation implies that the tail pressure is dominated either by low-energy electrons/positrons, or, by relativistic protons. Furthermore, we studied the energy spectrum of an X-ray "hot-spot" associated with the head of the radio galaxy 3C 129. It seems likely that the X-ray hot-spot originates from shocked gas in front of the radio galaxy. , The analysis turned out to be much more difficult than anticipated. The main reason is the lack of a comprehensive, publicly available background model that is key for the analysis of extended sources. Small groups like our do not have the man-power to come up with a background model themselves. We used the model from Read & Ponman (A&A 409, 395, 2003). However, the background subtracted X-ray surface brightness maps show a bright ring in the outer 20% of the camera. We tried to get rid of this ring and contacted the XMM helpdesk and Read & Ponman, the authors of the background paper. However, up to this day, we did not entirely succeed to remove the brightness enhancement at the outer parts of the camera. Unfortunately, our results are somewhat sensitive to the uncertainty, as the radio galaxy 3C 129 is very large and occupies a rather large fraction of the XMM field of view. We are now working on a paper describing the results. The paper will include a detailed discussion of the uncertainties associated with the non- perfect background subtraction.

Krawczynski, Henric S. W.↗

NASA NTRS1999

Lateral and Vertical Heterogeneity of Thorium in the Procellarum KREEP Terrane: As Reflected in the Ejecta Deposits of Post-Imbrium Craters

The Procellarum KREEP Terrane displays the highest concentrations of Th on the Moon. However, locations of elevated Th in this region appear to be random. As observed in the 5 deg per pixel equal-area Th data, and made more evident in the preliminary 2 deg data, Th is enhanced around the craters Aristillus, Aristarchus, Kepler, Mairan, the Apennine Bench formation, and the Fra Mauro region, while noticeably and unexpectedly lower in other locations (e.g., Archimedes, Copernicus, Eratosthenes, and Plato). We have examined the composition of the materials present in these regions with the goal of understanding the patchy nature to the distribution of Th and ultimately to decipher the geologic processes that have concentrated the Th. At present time, the published resolution of the Lunar Prospector Th gamma-ray data is low (5 deg per pixel), but this will soon be superceded by significantly higher-resolution data (2 deg per pixel). Even at this improved resolution, however, it is difficult to resolve the units that are the major source of Th. In an attempt to circumvent this problem, we employ the higher-resolution Clementine multispectral data for those regions mentioned above. We use the UV-VIS-derived compositional information and the spectral properties of craters, and their ejecta as drill holes through the mare-basalt surface to investigate the thickness and composition of underlying material. With this information we attempt to piece together the stratigraphy and geologic history of the Imbrium-Procellanim region. We processed the five-band multispectral data from the Clementine Mission (415, 750,900,950, and 1000nm) using ISIS software and calibration parameters developed by the USGS, Flagstaff, Arizona. Final image mosaics are in equal-area sinusoidal projection, and have a resolution of 250 m/pixel. Using the method of we produced maps of FeO and Ti02 composition. Here we examine the Th, FeO, and Ti02 composition and spectral properties of the craters discussed above and their ejecta, with the goal of describing the materials they excavate. One interpretation for the origin of the high-Th material is that subsurface KREEPy materials have been excavated by impact craters. The material excavated may be either volcanic KREEP (e,g., Apennine Bench Formation), KREEPy impact-melt breccia formed by the Imbrium impact (e.g., Fra Mauro Formation), or other KREEP-rich crustal material. Determining which type of material is responsible for the elevated Th and its extent is important to understanding the premare and possibly the prebasin stratigraphy of the Imbrium-Procellarum Region. Merging the 5 deg. Th data with the shaded relief map, we observe that the highest Th concentrations are not related to pre-Imbrium upper crustal materials. The Apennines, Alpes, and Caucasus Mountains represent the pre-Imbrian highlands material and do not express concentrations of Th, FeO, and TiO2 as high as the most Th-fich materials exposed within the Procellarum KREEP Terrane. We observe that, in general, these massifs contain 10-14 wt% FeO and 4-7 ppm Th. Determining whether the Th signal is from KREEP basalts or KREEPy impact-melt breccias cannot be done with the Clementine data because the two rock types are compositionally and mineralogically too similar (e.g., the Th-rich, mafic impact-melt breccias in the Apollo sample collection are dominated by a KREEP-basalt like component. Mapping-the distribution and sizes of craters and whether they display elevated Th concentrations or not, should reveal the depth and thickness of the KREEP-rich materials, and whether they are ubiquitous (i.e., impact-melt breccia) or more randomly distributed; this might be taken as an indicator of localized KREEP-basalt flows. Within the southeastern region of the Imbrium basin, there are two Th hot spots. The first is associated with the crater Aristillus, and the latter with the Apennine Bench Formation. Adjacent to these two hot spots are craters with a lower Th signature: Archimedes and Autolycus. We observe in the ejecta of Aristillus, a region of significantly lower FeO (10-14 wt%) relative to the surrounding mare basalt. The crater Autolycus, 50 km to the south, did not excavate similar low-FeO material. We suggest that the lower-FeO material in the ejecta of Aristillus corresponds to Th-rich material; the FeO content observed in Aristillus ejecta is comparable to that of KREEP basalt or mafic impact melt breccia (10-12 wt% FeO). We determine that this low FeO, Th-rich material is volcanic KREEP, as opposed to Imbrium impact melt, on the basis that the low-Fe material is exposed more prominently in ejecta in the northern portion of Aristillus. Our assumption is that if the layer underlying Aristillus was continuous, a more widespread and uniform low-Fe signature wouldbe observed in the ejecta deposit. Archimedes, 110 km southwest of Aristillus, impacted the northern portion of the Apennine Bench prior to the eruption of KREEP basalt. Archimedes rim material is not as enriched in Th as the Apennine Bench, and there are differences between the two in FeO concentration and in their continuum slope. Archimedes exhibits a much steeperor "redder" continuum slope than the Apennine Bench. This steepslope suggests the presence of glassy material. The glassy material is concentrated around an unnamed crater on the southern rim of Archimedes (4.5W, 28.2N) and along the northern rim of Archimedes. We suggest two possibilities, or a combination of the two, to explain the low-Th signal from Archimedes: (1) The Apennine Bench prior to KREEP basalt eruption was lower in Th (4-7 ppm, e.g., similar to the Apennine massifs) and KREEP basalts are absent in the rim of Archimedes; or (2) the glassy (possibly pyroclastic) material layering the rim of the Archimedes, dilutes any high-Th material present with low-Th material. (Additional information is contained in the original)

Gillis, J. J.↗

DOE OSTI2023

Bringing 2D Eclipse Mapping out of the Shadows with Leave-one-out Cross Validation

Abstract Eclipse mapping is a technique for inferring 2D brightness maps of transiting exoplanets from the shape of an eclipse light curve. With JWST’s unmatched precision, eclipse mapping is now possible for a large number of exoplanets. However, eclipse mapping has only been applied to two planets, and the nuances of fitting eclipse maps are not yet fully understood. Here, we use Leave-one-out Cross Validation (LOO-CV) to investigate eclipse mapping, with application to a JWST NIRISS/SOSS observation of the ultrahot Jupiter WASP-18b. LOO-CV is a technique that provides insight into the out-of-sample predictive power of models on a data-point-by-data-point basis. We show that constraints on planetary brightness patterns behave as expected, with large-scale variations driven by the phase-curve variation in the light curve and smaller-scale structures constrained by the eclipse ingress and egress. For WASP-18b we show that the need for higher model complexity (smaller-scale features) is driven exclusively by the shape of the eclipse ingress and egress. We use LOO-CV to investigate the relationship between planetary brightness map components when mapping under a positive-flux constraint to better understand the need for complex models. Finally, we use LOO-CV to understand the degeneracy between the competing “hot spot” and “plateau” brightness map models of WASP-18b, showing that the plateau model is driven by the ingress shape and the hot spot model is driven by the egress shape, but preference for neither model is due to outliers or unmodeled signals. Based on this analysis, we make recommendations for the use of LOO-CV in future eclipse-mapping studies.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1990

Rapid mix concepts for low emission combustors in gas turbine engines

NASA LeRC has identified the Rich burn/Quick mix/Lean burn (RQL) combustor as a potential gas turbine combustor concept to reduce NOx emissions in High Speed Civil Transport (HSCT) aircraft. To demonstrate reduced NOx levels, NASA LeRC soon will test a flametube version of an RQL combustor. The critical technology needed for the RQL combustor is a method of quickly mixing combustion air with rich burn gases. Two concepts were proposed to enhance jet mixing in a circular cross-section: the Asymmetric Jet Penetration (AJP) concept; and the Lobed Mixer (LM) concept. In Phase 1, two preliminary configurations of the AJP concept were compared with a conventional 12-jet radial-inflow slot design. The configurations were screened using an advanced 3-D Computational Fluid Dynamics (CFD) code named REFLEQS. Both non-reacting and reacting analyses were performed. For an objective comparison, the conventional design was optimized by parametric variation of the jet-to-mainstream momentum flux (J) ratio. The optimum J was then employed in the AJP simulations. Results showed that the three-jet AJP configuration was superior in overall mixedness compared to the conventional design. However, in regards to NOx emissions, the AJP configuration was inferior. The higher emission level for AJP was caused by a single hot spot located in the wake of the central jet as it entered the combustor. Ways of maintaining good mixedness while eliminating the hot spot were identified for Phase 2 study. Overall, Phase 1 showed the viability of using CFD analyses to evaluate quick-mix concepts. A high probability exists that advancing mixing concepts will reduce NOx emissions in RQL combustors, and should be explored in Phase 2, by parallel numerical and experimental work.

Talpallikar, Milind V.↗

NASA NTRS1941

Preignition Characteristics of Several Fuels Under Simulated Engine Conditions

The preignition characteristics of a number of fuels have been studied under conditions similar to those encountered in an engine. These conditions were simulated by suddenly compressing a fuel-air mixture in contact with an electrically heated hot spot in the cylinder head of the NACA combustion apparatus. Schlieren photographs and indicator cards were taken of the burning, and the hot-spot temperatures necessary to cause ignition under various conditions were determined.

Spencer, R C↗

NASA NTRS2001

Chandra Observations of X-Rays from Jupiter During the Cassini Flyby

"Observations of jovian x-rays made with the Earth-orbiting Chandra x-ray observatory on 18 December 2000 in support of the Cassini flyby of Jupiter demonstrate that most of Jupiters northern auroral x-rays come from a hot spot located poleward of the main auroral oval and magnetically connected to a region in the outer magnetosphere beyond 30 jovian radii. The hot spot is fixed in magnetic latitude and longitude and occurs in a region where anomalous infrared1-5and ultraviolet6 emissions have been observed. The auroral x-ray emissions were observed to pulsate with an approximately 40-minute period, a period similar to that reported for high-latitude radio and energetic electron bursts observed by Ulysses7, and by Galileo and Cassini.8 These results call into question the prevailing view that the jovian x-ray emissions are excited by the steady precipitation of energetic heavy ions from the outer edge of the Io plasma torus and are forcing a reconsideration of our understanding of the source mechanisms and energetics of the jovian x-ray aurora."

Gladstone, G. R.↗

NASA NTRS2001

Chandra Observations of X-Rays from Jupiter During the Cassini Flyby

Observations of jovian x-rays made with the Earth-orbiting Chandra x-ray observatory on 18 December 2000 in support of the Cassini flyby of Jupiter demonstrate that most of Jupiters northern auroral x-rays come from a hot spot located poleward of the main auroral oval and magnetically connected to a region in the outer magnetosphere beyond 30 jovian radii. The hot spot is fixed in magnetic latitude and longitude and occurs in a region where anomalous infrared1-5and ultraviolet6 emissions have been observed. The auroral x-ray emissions were observed to pulsate with an approximately 40-minute period, a period similar to that reported for high-latitude radio and energetic electron bursts observed by Ulysses7, and by Galileo and Cassini8. These results call into question the prevailing view that the jovian x-ray emissions are excited by the steady precipitation of energetic heavy ions from the outer edge of the Io plasma torus and are forcing a reconsideration of our understanding of the source mechanisms and energetics of the jovian x-ray aurora.

Gladstone, G. R.↗

NASA NTRS1984

Euro-african MAGSAT Anomaly-tectonic Observations

Preliminary satellite (MAGSAT) scalar magnetic anomaly data are compiled and differentially reduced to radial polarization by equivalent point source inversion for comparison with tectonic data of Africa, Europe and adjacent marine areas. A number of associations are evident to constrain analyses of the tectonic features and history of the region. The Precambrian shields of Africa and Europe exhibit varied magnetic signatures. All shields are not magnetic highs and, in fact, the Baltic shield is a marked minimum. The reduced-to-the-pole magnetic map shows a marked tendency for northeasterly striking anomalies in the eastern Atlantic and adjacent Africa, which is coincident to the track of several hot spots for the past 100 million years. However, there is little consistency in the sign of the magnetic anomalies and the track of the hot spots. Comparison of the radially polarized anomalies of Africa and Europe with other reduced-to-the-pole magnetic satellite anomaly maps of the Western Hemisphere support the reconstruction of the continents prior to the origin of the present-day Atlantic Ocean in the Mesozoic Era.

Hinze, W. J.↗

NASA NTRS1985

Euro-African MAGSAT anomaly-tectonic observations

Hinze, W. J.↗