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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Basaltic Ring Structures as an Analog for Ring Features in Athabasca Valles, Mars

Basaltic ring structures (BRSs) are enigmatic, quasi-circular landforms in eastern Washington State that were first recognized in 1965. They remained a subject of geologic scrutiny through the 1970 s and subsequently faded from the spotlight, but recent Mars Orbiter Camera (MOC) images showing morphologically similar structures in Athabasca Valles, Mars, have sparked renewed interest in BRSs. The only known BRSs occur in the Channeled Scabland, a region where catastrophic Pleistocene floods from glacial Lake Missoula eroded into the Miocene flood basalts of the Columbia Plateau. The geologic setting of the martian ring structures (MRSs) is similar; Athabasca Valles is a young channel system that formed when catastrophic aqueous floods carved into a volcanic substrate. This study investigates the formation of terrestrial BRSs and examines the extent to which they are appropriate analogs for the MRSs in Athabasca Valles.

Jaeger, W. L.↗
NASA NTRS1974

Spinning mode sound propagation in ducts with acoustic treatment

A detailed theoretical study of the acoustic propagation of spinning modes in acoustically treated open circular ducts is described. The suppressor with splitter rings was modeled by using the rectangular approximation to the annular duct. The theoretical models were used to determine optimum impedance and maximum attenuation for several spinning lobe numbers from 0 to 50. Some interesting results of the analysis are that for circular ducts the maximum possible attenuation and the optimum wall impedance are strong functions of the lobe number. For annular ducts the attenuation and optimum wall impedance are insensitive to the spinning lobe number for well cut-on modes. The above results help explain why suppressors with splitter rings were quite effective in spite of the lack of detailed information on the noise source modal structure.

Rice, E. J.↗
DOE OSTI2023

First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization

Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at the center of the M87 galaxy. EHT images in linear polarization have further identified a coherent spiral pattern around the black hole, produced from ordered magnetic fields threading the emitting plasma. Here we present the first analysis of circular polarization using EHT data, acquired in 2017, which can potentially provide additional insights into the magnetic fields and plasma composition near the black hole. Interferometric closure quantities provide convincing evidence for the presence of circularly polarized emission on event-horizon scales. We produce images of the circular polarization using both traditional and newly developed methods. All methods find a moderate level of resolved circular polarization across the image ( $\langle$| v |$\rangle$ < 3.7%), consistent with the low image-integrated circular polarization fraction measured by the Atacama Large Millimeter/submillimeter Array (| v int |< 1%). Despite this broad agreement, the methods show substantial variation in the morphology of the circularly polarized emission, indicating that our conclusions are strongly dependent on the imaging assumptions because of the limited baseline coverage, uncertain telescope gain calibration, and weakly polarized signal. We include this upper limit in an updated comparison to general relativistic magnetohydrodynamic simulation models. This analysis reinforces the previously reported preference for magnetically arrested accretion flow models. We find that most simulations naturally produce a low level of circular polarization consistent with our upper limit and that Faraday conversion is likely the dominant production mechanism for circular polarization at 230 GHz in M87*.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Torque sensor having a spoked sensor element support structure

Piezoelectric sensor devices are attached across pairs of circularly arranged spokes arrayed on the periphery of an annular ring. The sensor devices each include a preloaded steel ball mounting arrangement for mounting a piezoelectric sensor element. A first circular interface plate on one side of the sensor structure attaches to alternate one of the spokes, and a circular interface plate on the opposite side of the same diameter as the first interface plate attaches to the remaining spokes.

Lurie, Boris J.↗
DOE OSTI2023

Polarimetric Geometric Modeling for mm-VLBI Observations of Black Holes

The Event Horizon Telescope (EHT) is a millimeter very long baseline interferometry (VLBI) array that has imaged the apparent shadows of the supermassive black holes M87* and Sagittarius A*. Polarimetric data from these observations contain a wealth of information on the black hole and accretion flow properties. In this work, we develop polarimetric geometric modeling methods for mm-VLBI data, focusing on approaches that fit data products with differing degrees of invariance to broad classes of calibration errors. We establish a fitting procedure using a polarimetric “m-ring” model to approximate the image structure near a black hole. By fitting this model to synthetic EHT data from general relativistic magnetohydrodynamic models, we show that the linear and circular polarization structure can be successfully approximated with relatively few model parameters. We then fit this model to EHT observations of M87* taken in 2017. In total intensity and linear polarization, the m-ring fits are consistent with previous results from imaging methods. In circular polarization, the m-ring fits indicate the presence of event-horizon-scale circular polarization structure, with a persistent dipolar asymmetry and orientation across several days. The same structure was recovered independently of observing band, used data products, and model assumptions. Despite this broad agreement, imaging methods do not produce similarly consistent results. Our circular polarization results, which imposed additional assumptions on the source structure, should thus be interpreted with some caution. Polarimetric geometric modeling provides a useful and powerful method to constrain the properties of horizon-scale polarized emission, particularly for sparse arrays like the EHT.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Hand-held terminal antennas for personal satellite communications

This paper deals with two hand-held antenna types operating with geostationary and medium earth orbit (GEO and MEO) satellite systems. They could be applied to the low earth orbit (LEO) and highly elliptical orbit (HEO) systems respectively doing the appropriate frequency scale designs. The first one is a lambda/2 (1/2 turn) quadrifilar helix (quasi-hemispherical coverage), and the second one is a self-diplexed antenna made of a circular patch and a short-circuited ring patch in stacked configuration (zenithal coverage).

Caballero, J. E.↗
NASA NTRS2004

Approximate Solution for Choked Flow in Gas Seal Pads

Previous analyses of high pressure seals have considered adiabatic flow with friction but neglected effects of seal rotation. Most of this work analyzed a one-dimensional flow field. This works well to calculate stiffness and leakage of full circular seals, either face seals or annular ring seals. However, it cannot provide accurate results for a rectangular seal pad with its strongly two-dimensional flow field and its reliance on hydrodynamic forces to maintain a full fluid film. On the other hand, solutions of Reynolds lubrication equation have been obtained for the two-dimensional flow in a seal pad. But these solutions do not account for choking which occurs at high seal pressure ratios, nor do they consider the pressure loss that occurs in the entrance region of the flow field. The aim of the present work is to build on the Reynolds equation solution by use of an approximate choked flow analysis. This will account for the pressure losses in the flow entrance region, ensure that fluid velocities remain subsonic, and enable fluid inertial effects within the pad film to be accounted for. Results show that, in general, fluid inertia acts to decrease pad film load capacity and leakage, and increase film stiffness.

Fleming, David P.↗
DOE OSTI2020

Coherent transverse instability of bunched beams in circular accelerators

Coherent transverse oscillations of a bunch in a ring accelerator are considered. Three different models of the bunch are used: a hollow bunch in a square potential well, a square bunch in a parabolic potential well, and a parabolic bunch in a parabolic well. The bunch space-charge field, wakefield, and chromaticity are taken into account in all the cases. The bunch eigenmodes and various instabilities are studied. The results are compared and analyzed to establish the range of applicability of the models. Role of the Landau damping due to dependence of the SC field on the longitudinal coordinate is discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Accelerators for Electroweak Physics and Higgs Boson Studies

We discuss the goals, the designs, the state of technical readiness, and the critical R&D needs of the accelerators that are currently under discussion as Higgs and electroweak factories. We also address the respective staging options enabling future energy-frontier colliders. The accelerators covered are based on many different techniques and approaches. They include several circular colliders, various linear colliders, colliders based on energy recovery linacs (ERLs), ERL-ring combinations, as well as γγ colliders. The linear colliders proposed consist of options for the International Linear Collider (ILC), for the Compact Linear Collider (CLIC), for the Cold Copper Collider (C 3 ), and for the more recent Higgs-Energy Lepton Collider (HELEN). ERLs are key components of the Recycling Linear e + e - Collider (ReLiC),of the Energy Recovery Linear Collider (ERLC), and of the Circular Energy Recovery Collider (CERC). Among the more conventional ring colliders the following proposals are featured: the Future Circular Collider (FCC-ee), the Circular Electron Positron Collider (CEPC), the Electron Positron Circular Collider at Fermilab (EPCCF), and the Large Electron Positron collider #3 (LEP-3). In addition, we consider the X-ray FEL based gamma- gamma Collider Higgs Factory (XCC) and the High-Energy High-Luminosity γ-γ collider (HE&HL γγ). Finally, a Higgs factory based on a circular muon collider is mentioned for completeness.

43 PARTICLE ACCELERATORS↗
NASA NTRS1976

Multiple ring structures and the problem of correlation between lunar basins

Comparison of multi-ringed, mare-filled basins on the nearside of the moon indicates that a simple one-to-one correspondence of all rings between lunar basins does not exist. The only rings which can be correlated reasonably well between such basins are concentric systems of mare ridges and basin rims, and the frequently cited square-root-of-2 spacing relationship does not correctly describe their spacing. It is concluded that the Cordillera is the rim of the Orientale Basin and is equivalent to the 1340 km diameter ring of the Imbrium Basin and the rims of the other mare-filled basins. The area between the Rook and Cordillera rings is believed equivalent to the marginal shelf areas of the more completely mare-filled basins. A circular arc approximately 520 km diameter located just inside the outer Rook Ring would have been the most likely site for formation of a concentric system of mare ridges, had filling of the Orientale Basin been complete.

Brennan, W. J.↗
NASA NTRS1993

Yana ring structure, North-Eastern Siberia: A possible counterpart of coronae on Venus

An arch of Verkhoyansky Range in NE Siberia, Russia is considered as W and S parts of the rim of the large ring structure, referred hereafter as Yana Ring Structure (YRS). It has general appearance similar to coronae on Venus and could be considered as the terrestrial counter part of coronae. The structure is located between 63 and 70 deg N, 125 and 140 deg E. The outer diameter of YRS (between the rim feet) is 680-700 km. The rim crest diameter is 500-520 km. The inner diameters (between the inner feet of the rim) is 320-350 km. The rim of YRS consist of the following topographic features: W segment is Orulgan Range (N part of Verkhoyansky Range), SW and S segments consist of S part of Verkhoyansky Range, SE segment is Elginskoye Ploskogorye (Tableland), E segment is Chersky Range (its part W of Indigirka River), NE segment is Selennyakhsky Range, and NW segment is Kular Range. Inside this ring of mountains Yanskoye Ploskogorye (Tableland) is located. The circular outlines of YRS are marked with the large river valleys located outside: Lena River (lower of Aldan River mouth) is located W from YRS, Aldan River (lower of Amga River mouth) is from S, Indigirka River (between 64 and 67 deg N lat) is from E, and Selennyakh River (the part running N to S) is from NE. The ring patterns inside the mountaineous rim of YRS are marked with the tributaries of Yana River. The largest ring here, 300 km in diameter, consists of Bytangay (with Bellyakh) River at W, Nelgese and Derbeke Rivers at S/SE, and Tuostakh River at E. The typical altitudes of YRS mountain rim are 1000-2000 m. The maximal ones are: 2400 m in W part of the rim, 2300 m in S, 1600 m in SE, 2200-2500 m in E, and 1300-1500 m in N. The central part of YRS have typical altitudes of 400-600 m. There are lowlands with altitudes 50-200 m to the S, W, N, and NW outside YRS Oymyakonskoye Nagorye (Highland) is located SE of YRS at 500-1500 m altitudes. It should be recognized from this description YRS have a general appearance of circular highland with its central plateau located 1000-2000 m lower than surrounding mountain rim, but 300-400 m higher than plains of lowlands located outside the rim. Such topographic patterns are typical for coronae on Venus. The diameter of YRS is equal to the largest coronae on Venus. There are only 3 or 4 structures of such or larger size on the whole Venus. This calls to compare morphology and geologic evolution of YRS with morphology and models of coronae evolutions especially the largest ones, to search the similarities and/or differences in geologic histories of the structures on the Earth and Venus.

Burba, G. A.↗
NASA NTRS2004

Distribution of Large Visible and Buried Impact Basins on Mars: Comparison with Free-Air Gravity, Crustal Thickness and Magnetization Models

A comparison of the distribution of visible and buried impact basins (Quasi-Circular Depressions or QCDs) on Mars > 200 km in diameter with free air gravity, crustal thickness and magnetization models shows some QCDs have coincident gravity anomalies but most do not. Very few QCDs have closely coincident magnetization anomalies, and only the oldest of the very large impact basins have strong magnetic anomalies within their main rings. Crustal thickness data show a large number of Circular Thinned Areas (CTAs). Some of these correspond to known impact basins, while others may represent buried impact basins not always recognized as QCDs in topography data alone. If true, the buried lowlands may be even older than we have previously estimated.

Frey, H. V.↗
NASA NTRS2002

Dynamical Models of the Solar System Formation and Evolution

Mark Lewis has extended his them is work by completing a series of N-body simulations of a narrow ring that: is in the location of Saturn's F-ring and is perturbed by a single satellite comparable to Prometheus, but on a circular orbit. We had previously shown how the satellite perturbations can cause a broadly distributed sparse population of ring particles to become concentrated into narrow rings that can be maintained outside of any resonance location. For low optical depths, the collisions between ring particles are highly localized in the peaks of the satellite wakes. The inelastic collisions therefore occur at a particular orbital phase angle so as to damp the azimuthal component of the relative velocities. Since particle positions are not changed by collisions, the semimajor axes of the particles are shifted toward the actual particle positions where the collisions occur. Thus, negative radial diffusion can occur while conserving orbital angular momentum so long as the forced eccentricity is continually re-excited by the satellite. We speculated that the separation between the final ringlets was largely determined by the magnitude of the forced eccentricities induced by the satellite at closest approach. We carried out a series of simulations with a variety of different satellite masses in order to vary the magnitude of the forced eccentricity. We found that indeed the final spacing of the ringlets does increase with the magnitude of the forced eccentricity (Lewis and Stewart 2002). This occurs because neighboring eccentric ringlets drift out of phase with one another due to Keplerian shear and eventually collide with one another, leading to a smaller number of more widely spaced ringlets, The time scale required to form narrow ringlets in these simulations is much shorter than one would expect from standard theories based upon the orbit-averaged torque produced by multiple passes by the satellite. We find that the initial ringlets form in less than two synodic periods and the final state is typically reached in 10 to 20 synodic periods. These studies move us closer to understanding the significantly more complex system of Saturn's F ring, where the perturbation magnitude varies over short temporal and spatial time scales due to the orbital eccentricities of the perturbing satellite. We are currently extending the simulation to allow for an eccentric orbit of the satellite.

Stewart, Glen R.↗
NASA NTRS1976

A source array for generating higher order acoustic modes in circular ducts

A unique source array has been developed for the generation of both spinning and non-spinning higher order modes in a circular duct. The array consists of two concentric rings of sources. Through individual control of the response of each element, the array provided phase and amplitude control in the radial as well as circumferential directions. Radial modes shapes were measured in a 12-inch diameter anechoically-terminated hollow duct. These modes could be generated at their cut-off frequency and throughout a frequency range extending to the cut-off frequency for the next higher order radial mode. Comparisons are given between theory and experiment for the generation of specific modes. The radial dependence of the measured mode shapes was enhanced considerably by the design of this array. The results indicate a significant improvement over previous mode generation mechanisms. The contamination of the generated mode by additional spurious modes is also considered for variations between individual elements within the source array.

Wyerman, B. R.↗
NASA NTRS2018

Probing Supraglacial Debris on Mars 2: Crater Morphology

Lobate debris aprons (LDA), lineated valley fill (LVF), and concentric crater fill (CCF) on Mars, interpreted to bedebris-covered glaciers, possess craters with a suite of distinct interior landforms (called "ring-mold craters")that have been attributed to the presence of glacial ice at depth or surface modification processes. We testedcurrent hypotheses for the formation of ring-mold craters by conducting a comprehensive analysis of the size andmorphology of 16,457 impact craters 125m in diameter formed within glacial deposits in DeuteronilusMensae. Two major groups, bowl-shaped craters and ring-mold craters, are found, with at least nine distinctcrater types. While there is statistical difference in median diameters between these crater types, this differenceis relatively small and is within the estimated uncertainty in diameter measurements and may be related to moreenhanced erosion of the rims of ring-mold craters. Clear degradation sequences are observed, supporting a rolefor post-impact modification in producing at least some of the diversity in crater landforms. The spatial densityof ring-mold craters is also directly correlated with the development of LDA, LVF, and CCF surface textures. Flowlineations cross-cut two ring-mold crater types but they maintain their circular planforms in some cases, suggestingthat the craters initially formed completely within mantling layers deposited after glacial flow hadceased. We also find analogous craters in non-glacial units; glacial ice is therefore not required to form theobserved morphologic diversity. Our observations are most consistent with formation of crater landforms byemplacement and modification of at least two depositional episodes of icy dust (i.e., "mantle"). This mantle wasinitially tens of meters in thickness to support crater formation, and has experienced much downwasting anderosion since emplacement. Derived crater retention ages of 460 Ma for LDA, LVF, and CCF features in the regiontherefore reflect deposition of mantle units and only give a very minimum age for the formation of LDA, LVF, andCCF

Geological↗
NASA NTRS1979

Towards a theory for the Uranian rings

Interparticle collisions, radiation drag, and differential precession all tend to disrupt the rings of Uranus. The first two effects lead to radial spreading which would disrupt a free ring in less than or approximately 100,000,000 yr. It is proposed that the rings are confined in radius by gravitational torques from a series of small satellites that orbit with the ring system. Differential precession tends to destroy the apse alignment of the elliptical epsilon ring. It is suggested that apse alignment is maintained by the self-gravity of the ring. The resulting mass of the epsilon ring is approximately 5 times 10 to the 18th power g. Its radial confinement requires (for example) a pair of satellites of mass approximately 10 to the 19th power g, in circular orbits roughly 500 km away on either side of the ring

Goldreich, P.↗
NASA NTRS1991

Near-infrared observations of the Jovian ring and small satellites

The Jovian ring has been observed at 2.2 microns at a near-maximum opening angle of 3.2 deg and a phase angle of 2.2 deg. The 126,100 +/- 500 km ring radius at maximum brightness obtained is compatible with Voyager data at high phase angles. Circular orbital elements have also been obtained for the two small satellites (Metis and Adrastea) associated with the ring. A combination of these orbits with the Voyager imaging-based measurements of Synnott yields a substantial improvement in mean motion estimates.

Nicholson, Philip D.↗