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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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NASA NTRS2004

Telescope Scientist on the Advanced X-ray Astrophysics Observatory

In this period, the Chandra X-ray Observatory continued to perform exceptionally well, with many scientific observations and spectacular results. The HRMA performance continues to be essentially identical to that predicted from ground calibration data. The Telescope Scientist Team has improved the mirror model to provide a more accurate description to the Chandra observers, enabling them to reduce the systematic errors and uncertainties in their data reduction. There also has been good progress in the scientific program. Using the Telescope Scientist GTO time, we carried out an extensive Chandra program to observe distant clusters of galaxies. The goals of this program were to use clusters to derive cosmological constraints and to investigate the physics and evolution of clusters. A total of 71 clusters were observed with ACIS-I; the last observations were completed in December 2003.

Smith, Carl M.↗
NASA NTRS2005

Current Sheet Evolution in the Aftermath of a CME Event

We report on SOHO-UVCS observations of the coronal restructuring following a Coronal Mass Ejection (CME) on November 26,2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after a CME in the NW quadrant, UVCS began taking spectra at 1.7 solar radius, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the Fe XVIII emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by Ulysses-SWICS throughout the magnetic cloud associated with the CME. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2005

Coronal Current Sheet Evolution in the Aftermath of a CME

We report on SOHO-UVCS observations of coronal restructuring following a Coronal Mass Ejection (CME) on November 26, 2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after the CME, which was directed towards Ulysses, UVCS began taking spectra at 1.7 solar radii, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6x10(6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by SWICS throughout the magnetic cloud associated with the CME, although the rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2006

Current Sheet Evolution In The Aftermath Of A CME Event

We report on SOHO UVCS observations of the coronal restructuring following a coronal mass ejection (CME) on 2002 November 26, at the time of a SOHO-Ulysses quadrature campaign. Starting about 1.5 hr after a CME in the northwest quadrant, UVCS began taking spectra at 1.7 R, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 A line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature versus time in the current sheet and estimate its density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by the Ulysses SWICS throughout the magnetic cloud associated with the CME, although its rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. The SOHO-Ulysses data set provided us with the unique opportunity of analyzing a current sheet structure from its lowest coronal levels out to its in situ properties. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2006

Lifetime Evolution of UV Jets

We report on observations acquired in May 2003 during a SOHO-Ulysses quadrature campaign. From May 25 to May 28, the SoHO LASCO Coronal Mass Ejection (CME) catalog lists a number of events which might have been observed by SOHO/UVCS, whose slit was centered along the Ulysses direction. However, because of time gaps in the observing schedule, or because of the unfavorable position of some CMEs, the most interesting events recorded by UVCS were a few short-lived ejections that represent the extension at higher altitudes of recursive EIT jets. We focus on jets occurring on May 26/27, visible also in EIT and LASCO images, which seem to propagate along the radial to Ulysses. UVCS spectra at 1.7 Rsun showed an unusually high emission in cool lines, lasting for about 10 to 25 minutes, with no evidence of hot plasma. Analysis of the cool line emission allowed us to infer the evolution of physical parameters during the jets lifetime and derive a crude estimate of the energy needed to account for their properties. We also looked for any evidence of the event in in situ data. Whether UVCS is observing jets or narrow CMEs is discussed in the contest of previous works on these classes of events and, in the last Section, we propose a scenario that accounts for our observations.

Corti, G.↗
NASA NTRS2006

Io: Loki Patera as a Magma Sea

We develop a physical model for Loki Patera as a magma sea. We calculate the total volume of magma moving through the Loki Patera volcanic system every resurfacing cycle (approx.540 days) and the resulting variation in thermal emission. The rate of magma solidification at times reaches 3 x 10(exp 6) kg per second, with a total solidified volume averaging 100 cu km per year. A simulation of gas physical chemistry evolution yields the crust porosity profile and the timescale when it will become dense enough to founder in a manner consistent with observations. The Loki Patera surface temperature distribution shows that different areas are at different life cycle stages. On a regional scale, however, there can be coordinated activity, indicated by the wave of thermal change which progresses from Loki Patera's SW quadrant toward the NE at a rate of approx.1 km per day. Using the observed surface temperature distribution, we test several mechanisms for resurfacing Loki Patera, finding that resurfacing with lava flows is not realistic. Only the crustal foundering process is consistent with observations. These tests also discovered that sinking crust has a 'heat deficit' which promotes the solidification of additional magma onto the sinking plate ("bulking up"). In the limiting case, the mass of sinking material can increase to a mass of approx.3 times that of the foundering plate. With all this solid matter sinking, there is a compensating upward motion in the liquid magma. This can be in excess of 2 m per year. In this manner, solid-liquid convection is occurring in the sea.

heat flow↗
NASA NTRS2019

The Sub-Neptune Desert and Its Dependence on Stellar Type: Controlled by Lifetime X-Ray Irradiation

Short-period sub-Neptunes with substantial volatile envelopes are among the most common type of known exoplanets. However, recent studies of the Kepler population have suggested a dearth of sub-Neptunes on highly irradiated orbits, where they are vulnerable to atmospheric photoevaporation. Physically, we expect this "photoevaporation desert" to depend on the total lifetime X-ray and extreme ultraviolet flux, the main drivers of atmospheric escape. In this work, we study the demographics of sub-Neptunes as a function of lifetime exposure to high-energy radiation and host-star mass. We find that for a given present-day insolation, planets orbiting a 0.3 solar mass star experience approximately 100 times more X-ray flux over their lifetimes versus a 1.2 solar mass star. Defining the photoevaporation desert as a region consistent with zero occurrence at 2 sigma, the onset of the desert happens for integrated X-ray fluxes greater than 1.43 times 10 (sup 22) to 8.23 times 10 (sup 20) as a function of planetary radii for 1.8 to 4 Earth radius. We also compare the location of the photoevaporation desert for different stellar types. We find much greater variability in the desert onset in the bolometric flux space compared to the integrated X-ray flux space, suggestive of photoevaporation driven by steady-state stellar X-ray emissions as the dominant control on desert location. Finally, we report tentative evidence for the sub-Neptune valley, first seen around Sun-like stars, for M&K dwarfs. The discovery of additional planets around low-mass stars from surveys such as the Transiting Exoplanet Survey Satellite (TESS) mission will enable detailed exploration of these trends.

Planets and Satellites: Gaseous Planets↗
NASA NTRS2018

New Formation Models for the Kepler-36 System

Formation of the planets in the Kepler-36 system is modeled by detailed numerical simulations according to the core-nucleated accretion scenario. The standard model is updated to include the dissolution of accreting rocky planetesimals in the gaseous envelope of the planet, leading to substantial enrichment of the envelope mass in heavy elements and a non-uniform composition with depth. For Kepler-36 c, models involving in situ formation and models involving orbital migration are considered. The results are compared with standard formation models. The calculations include the formation (accretion) phase, as well as the subsequent cooling phase, up to the age of Kepler-36 (7 Gyr). During the latter phase, mass loss induced by stellar XUV radiation is included. In all cases, the results fit the measured mass, 7.84 M, and radius, 3.68 R, of Kepler-36 c. Two parameters are varied to obtain these fits: the disk solid surface density at the formation location, and the "efficiency" factor in the XUV mass loss rate. The updated models are hotter and therefore less dense in the silicate portion of the planet and in the overlying layers of H/He, as compared with standard models. The lower densities mean that only about half as much H/He is needed to be accreted to fit the present-day mass and radius constraints. For Kepler-36 b, an updated in situ calculation shows that the entire H/He envelope is lost, early in the cooling phase, in agreement with observation.

planets and satellites:formation↗
NASA NTRS2023

JWST Observations of the Enigmatic Y Dwarf WISE 1828+2650: I. Limits to a Binary Companion

The Y-dwarf WISE 1828+2650 is one of the coldest known Brown Dwarfs with an effective temperature of ~300 K. Located at a distance of just 10 pc, previous model-based estimates suggest WISE 1828+2650 has a mass of ~5-10 M J , making it a valuable laboratory for understanding the formation, evolution and physical characteristics of gas giant planets. However, previous photometry and spectroscopy have presented a puzzle with the near-impossibility of simultaneously fitting both the short (0.9-2.0 μm) and long wavelength (3-5 μm) data. A potential solution to this problem has been the suggestion that WISE 1828+2650 is a binary system whose composite spectrum might provide a better match to the data. Alternatively, new models being developed to fit JWST/NIRSpec and MIRI spectroscopy might provide new insights. This article describes JWST/NIRCam observations of WISE 1828+2650 in 6 filters to address the binarity question and to provide new photometry to be used in model fitting. We also report Adaptive Optics imaging with the Keck 10 m telescope. We find no evidence for multiplicity for a companion beyond 0.5 AU with either JWST or Keck. Companion articles will present low and high resolution spectra of WISE 1828 obtained with both NIRSpec and MIRI.

Infrared spectroscopy↗
NASA NTRS2023

JWST Observations of the Enigmatic Y Dwarf WISE 1828+2650: I. Limits to a Binary Companion

The Y-dwarf WISE 1828+2650 is one of the coldest known brown dwarfs with an effective temperature of∼300K. Located at a distance of just 10 pc, previous model-based estimates suggest WISE1828+2650 has a mass of∼5–10MJ, making it a valuable laboratory for understanding the formation, evolution, and physical characteristics of gas giant planets. However, previous photometry and spectroscopy have presented a puzzle, with the near impossibility of simultaneously fitting both the short-(0.9–2.0μm)and long-wavelength(3–5μm)data. A potential solution to this problem has been the suggestion that WISE 1828+2650 is a binary system whose composite spectrum might provide a better match to the data. Alternatively, new models being developed to fit JWST/NIRSpec, and MIRI spectroscopy might provide new insights. This article describes JWST/NIRCam observations of WISE 1828+2650 in six filters to address the binarity question and to provide new photometry tobe used in model fitting. We also report adaptive optics imaging with the Keck I0 m telescope. We find no evidence for multiplicity for a companion beyond 0.5 au with either JWST or Keck. Companion articles will present low-and high-resolution spectra of WISE 1828 obtained with both NIRSpec and MIRI.

NIRCam↗
NASA NTRS1992

Galaxy formation and physical bias

We have supplemented our code, which computes the evolution of the physical state of a representative piece of the universe to include, not only the dynamics of dark matter (with a standard PM code), and the hydrodynamics of the gaseous component (including detailed collisional and radiative processes), but also galaxy formation on a heuristic but plausible basis. If, within a cell the gas is Jeans' unstable, collapsing, and cooling rapidly, it is transformed to galaxy subunits, which are then followed with a collisionless code. After grouping them into galaxies, we estimate the relative distributions of galaxies and dark matter and the relative velocities of galaxies and dark matter. In a large scale CDM run of 80/h Mpc size with 8 x 10 exp 6 cells and dark matter particles, we find that physical bias b is on the 8/h Mpc scale is about 1.6 and increases towards smaller scales, and that velocity bias is about 0.8 on the same scale. The comparable HDM simulation is highly biased with b = 2.7 on the 8/h Mpc scale. Implications of these results are discussed in the light of the COBE observations which provide an accurate normalization for the initial power spectrum. CDM can be ruled out on the basis of too large a predicted small scale velocity dispersion at greater than 95 percent confidence level.

Cen, Renyue↗
NASA NTRS1994

Crossflow-Vortex Breakdown on Swept Wings: Correlation of Nonlinear Physics

The spatial evolution of cross flow-vortex packets in a laminar boundary layer on a swept wing are computed by the direct numerical simulation of the incompressible Navier- Stokes equations. A wall-normal velocity distribution of steady suction and blowing at the wing surface is used to generate a strip of equally spaced and periodic disturbances along the span. Three simulations are conducted to study the effect of initial amplitude on the disturbance evolution, to determine the role of traveling cross ow modes in transition, and to devise a correlation function to guide theories of transition prediction. In each simulation, the vortex packets first enter a chordwise region of linear independent growth, then, the individual packets coalesce downstream and interact with adjacent packets, and, finally, the vortex packets nonlinearly interact to generate inflectional velocity profiles. As the initial amplitude of the disturbance is increased, the length of the evolution to breakdown decreases. For this pressure gradient, stationary modes dominate the disturbance evolution. A two-coeffcient function was devised to correlate the simulation results. The coefficients, combined with a single simulation result, provide sufficient information to generate the evolution pattern for disturbances of any initial amplitude.

Joslin, R. D.↗
NASA NTRS1987

Evolution of magnetic cataclysmic binaries

The physics of magnetic cataclysmic binary evolution is considered, and it is suggested that DQ Her stars will not evolve into AM Her stars (assuming that mu1 remains constant throughout their evolution), in contradiction to previous assertions. Four regimes that depend on mu1 values are identified, and it is suggested that the mu1 values of the known DQ Her stars are significantly less than those of the known AM Her stars (unless all known stars of both groups have M1 greater than 1 solar mass). A new way of producing ultrashort period binaries is proposed in which synchronization of the magnetic degenerate dwarfs injects angular momentum into the binary, driving the system apart and producing a synchronization-induced period gap. The secondaries in these binaries are shown to be hydrogen-rich rather than hydrogen depleted or pure helium.

Lamb, D. Q.↗
NASA NTRS2014

Landform Evolution Modeling of Sedimentary Processes on Icy Worlds: the Cases of Hyperion and Helene

Sedimentary activity (erosion, transportation and deposition) is a major landscape-shaping process on many icy worlds of the outer solar system for which an understanding of this process is central to their geologic characterizations. Several recent studies, lead by the authors, have identified the effects of sedimentary activity on icy satellite landforms and recognized the role of mass wasting and volatile loss and redistribution in the evolution of these features. We apply state of the art, physics based, landform evolution modeling to icy satellite sedimentary landforms in order to fully quantitatively characterize how their morphologies change with time, and what their present appearances imply for the initial abundance and distribution of loose material, volatiles, and refractories in original pristine landforms. We will present results of our landform evolution modeling to the development of the landscapes of the Saturnian moons of Hyperion and Helene. Our current conclusions for Hyperion are that its unique appearance can be explained in part by the loss to space of ballistic ejecta during impact events. In order to create the smooth surfaces and the reticulate, honeycomb pattern of narrow divides between old craters, appreciable subsequent modification of crater morphology must occur through mass-wasting processes accompanied by sublimation, probably facilitated by the loss of CO2 as a component of the relief-supporting matrix of the bedrock. This mass wasting effectively destroys small craters, at least in part accounting for the paucity of sub-kilometer craters on Hyperion. Helene’s unusual morphology consists of broad depressions (modified large craters) and a generally smooth surface patterned with streaks and grooves. The streaks appear to be oriented down-gradient, as are the grooves. This pattern suggests intensive mass-wasting as a dominant process. Our initial modeling of this surface suggests a Bingham-like rheological behavior for the loose down-slope moving material. Interestingly, as a Bingham flow, the models indicate that aperiodic "intermittent" behavior to be present, suggesting that periods of quiet steady landform evolution are punctuated short periods of active surface readjustment.

Saturnian moons↗
NASA NTRS1988

The evolution of the system of globular clusters

The physical processes affecting the evolution of the system of globular clusters are reviewed. Aspects of internal structure evolution discussed include evaporation, core collapse, expansion, tidal shocks, and interaction with other massive components of the Galaxy such as black holes, molecular clouds, and other clusters. The evolution of orbital parameters is examined, including dynamical friction, scattering by massive subcomponents, and interactions with nearby systems. In addition, an overview of the system evolution is presented.

Ostriker, Jeremiah P.↗
NASA NTRS1991

Effects of high pressure nitrogen on the thermal stability of SiC fibers

Polymer-derived SiC fibers were exposed to nitrogen gas pressures of 7 and 50 atm at temperatures up to 1800 C. The fiber weight loss, chemical composition, and tensile strength were then measured at room temperature in order to understand the effects of nitrogen exposure on fiber stability. High pressure nitrogen treatments limited weight loss to 3 percent or less for temperatures up to 1800 C. The bulk Si-C-O chemical composition of the fiber remained relatively constant up to 1800 C with only a slight increase in nitrogen content after treatment at 50 atm; however, fiber strength retention was significantly improved. To further understand the effects of the nitrogen atmosphere on the fiber stability, the results of previous high pressure argon treatments were compared to those of the high pressure nitrogen treatments. High pressure inert gas can temporarily maintain fiber strength by physically inhibiting the evolution of gaseous species which result from internal reactions. In addition to this physical effect, it would appear that high pressure nitrogen further improved fiber temperature capability by chemically reacting with the fiber surface, thereby reducing the rate of gas evolution. Subsequent low pressure argon treatments following the initial nitrogen treatments resulted in stronger fibers than after argon treatment alone, further supporting the chemical reaction mechanism and its beneficial effects on fiber strength.

Jaskowiak, Martha H.↗
NASA NTRS1996

Controlled Quantum Packets

We look at time evolution of a physical system from the point of view of dynamical control theory. Normally we solve motion equation with a given external potential and we obtain time evolution. Standard examples are the trajectories in classical mechanics or the wave functions in Quantum Mechanics. In the control theory, we have the configurational variables of a physical system, we choose a velocity field and with a suited strategy we force the physical system to have a well defined evolution. The evolution of the system is the 'premium' that the controller receives if he has adopted the right strategy. The strategy is given by well suited laboratory devices. The control mechanisms are in many cases non linear; it is necessary, namely, a feedback mechanism to retain in time the selected evolution. Our aim is to introduce a scheme to obtain Quantum wave packets by control theory. The program is to choose the characteristics of a packet, that is, the equation of evolution for its centre and a controlled dispersion, and to give a building scheme from some initial state (for example a solution of stationary Schroedinger equation). It seems natural in this view to use stochastic approach to Quantum Mechanics, that is, Stochastic Mechanics [S.M.]. It is a quantization scheme different from ordinary ones only formally. This approach introduces in quantum theory the whole mathematical apparatus of stochastic control theory. Stochastic Mechanics, in our view, is more intuitive when we want to study all the classical-like problems. We apply our scheme to build two classes of quantum packets both derived generalizing some properties of coherent states.

DeMartino, Salvatore↗
NASA NTRS1987

Space Station evolution

The Space Station that will be launched and made operational in the early 1990s should be viewed as a beginning, a facility that will evolve with the passing of time to better meet the needs and requirements of a diverse set of users. Evolution takes several forms, ranging from simple growth through addition of infrastructure elements to upgrading of system capability through inclusion of advanced technologies. Much of the early considerations of Space Station evolution focused on physical growth. However, a series of recent workshops have revealed that the more likely mode of Space Station evolution will not be through growth but rather through a process known as 'branching'.

Black, David C.↗