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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Contour advection with surgery: A technique for investigating finescale structure in tracer transport

We present a trajectory technique, contour advection with surgery (CAS), for tracing the evolution of material contours in a specified (including observed) evolving flow. CAS uses the algorithms developed by Dritschel for contour dynamics/surgery to trace the evolution of specified contours. The contours are represented by a series of particles, which are advected by a specified, gridded, wind distribution. The resolution of the contours is preserved by continually adjusting the number of particles, and finescale features are produced that are not present in the input data (and cannot easily be generated using standard trajectory techniques). The reliability, and dependence on the spatial and temporal resolution of the wind field, of the CAS procedure is examined by comparisons with high-resolution numerical data (from contour dynamics calculations and from a general circulation model), and with routine stratospheric analyses. These comparisons show that the large-scale motions dominate the deformation field and that CAS can accurately reproduce small scales from low-resolution wind fields. The CAS technique therefore enables examination of atmospheric tracer transport at previously unattainable resolution.

Waugh, Darryn W.↗
NASA NTRS1995

Ion distributions in the Earth's foreshock upstream from the bow shock

A variety of suprathermal and energetic ion distributions are found upstream from shocks. Some distributions, such as field-aligned beams, are generated directly at the shock either through reflection processes or through leakage from the hotter downstream region. Other distributions, such as intermediate distributions, evolve from these parent distributions through wave-particle interactions. This paper reviews our current understanding of the creation and evolution of suprathermal distributions at shocks. Examples of suprathermal ion distributions are taken from observations at the Earth's bow shock. Particular emphasis is placed on the creation of field-aligned beams and specularly reflected ion distributions and on the evolution of these distributions in the Earth's ion foreshock. However, the results from this heavily studied region are applicable to interplanetary shocks, bow shocks at other planets, and comets.

Fuselier, S. A.↗
NASA NTRS2019

Search for Subsolar Mass Ultracompact Binaries in Advanced LIGO’s Second Observing Run

We present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO’s second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between 0.2 𝑀 ⊙ –1.0 𝑀 ⊙ . We use the null result to constrain the binary merger rate of (0.2 𝑀 ⊙ , 0.2 𝑀 ⊙ ) binaries to be less than 3.7×10 5 Gpc −3 yr −1 and the binary merger rate of (1.0 𝑀 ⊙ , 1.0 𝑀 ⊙ ) binaries to be less than 5.2×10 3 Gpc −3 yr −1 . Subsolar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with subsolar masses. Assuming a particular primordial black hole (PBH) formation model, we constrain a population of merging 0.2 𝑀 ⊙ black holes to account for less than 16% of the dark matter density and a population of merging 1.0 𝑀 ⊙ black holes to account for less than 2% of the dark matter density. We discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict subsolar mass binaries.

B. P. Abbott↗
NASA NTRS2000

The Spectral Evolution of Solar Flare Hard X-Ray Emission Observed with BATSE

We present a more detailed characterization of spectral evolution in solar flare hard X-ray emission than has been previously described. Our characterization is consistent with some earlier results but utilizes higher time resolution data and reveals nuances in spectral evolution that have never been reported. We employ an underutilized data set, the Burst and Transient Source Experiment (BATSE) solar flare catalog, for our investigation and different methodology than previous studies. Our findings support the conclusion that properties of the particle Abstract: acceleration mechanism in flares, such as the acceleration rate or efficiency, are indeed important to understanding spectral evolution. On the other hand, time-of-flight models, which assume accelerator properties to be negligible, cannot explain the observed detailed spectral evolution, and correlations that we would expect to exist between spectral evolution patterns and parameters derived from time-of-flight model inversions are not supported by the data. In this fashion, we establish an observational context in which to interpret future High Energy Solar Spectroscopic Imager (HESSI) observations and delineate some constraints for theoretical models of particle acceleration.

Newton, Elizabeth K.↗
NASA NTRS2022

Interplanetary Mesoscale Observatory (InterMeso): A Mission to Untangle Dynamic Mesoscale Structures Throughout the Heliosphere

Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities.

solar wind↗
NASA NTRS2022

Interplanetary Mesoscale Observatory (InterMeso): A mission to untangle dynamic mesoscale structures throughout the heliosphere

Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities.

solar wind↗
NASA NTRS1985

Microdunes and Other Aeolian Bedforms on Venus: Wind Tunnel Simulations

The development of aeolian bedforms in the simulated Venusian environment has been experimentally studied in the Venus Wind tunnel. It is found that the development of specific bedforms, including ripples, dunes, and waves, as well as their geometry, are controlled by a combination of factors including particle size, wind speed, and atmospheric density. Microdunes are formed which are analogous to full-size terrestrial dunes and are characterized by the development of slip faces, internal cross-bedding, a low ratio of saltation path length to dune length, and a lack of particle-size sorting. They begin to develop at wind speeds just above saltation threshold and evolve into waves at higher velocities. At wind speeds of about 1.5 m/sec and higher, the bed is flat and featureless. This evolution is explained by a model based on the interaction of alternating zones of erosion and deposition and particle saltation distances.

Greeley, R.↗
NASA NTRS1984

Microdunes and other aeolian bedforms on Venus - Wind Tunnel simulations

The development of aeolian bedforms in the simulated Venusian environment has been experimentally studied in the Venus Wind Tunnel. It is found that the development of specific bedforms, including ripples, dunes, and 'waves', as well as their geometry, are controlled by a combination of factors including particle size, wind speed, and atmospheric density. Microdunes are formed which are analogous to full-size terrestrial dunes and are characterized by the development of slip faces, internal cross-bedding, a low ratio of saltation path length to dune length, and a lack of particle-size sorting. They begin to develop at wind speeds just above saltation threshold and evolve into waves at higher velocities. At wind speeds of about 1.5 m/sec and higher, the bed is flat and featureless. This evolution is explained by a model based on the interaction of alternating zones of erosion and deposition and particle saltation distances.

Greeley, R.↗
NASA NTRS1996

Workshop on Evolution of Martian Volatiles

This volume contains papers that were presented on February 12-14, 1996 at the Evolution for Martian Volatiles Workshop. Topics in this volume include: returned Martian samples; acidic volatiles and the Mars soil; solar EUV Radiation; the ancient Mars Thermosphere; primitive methane atmospheres on Earth and Mars; the evolution of Martian water; the role of SO2 for the climate history of Mars; impact crater morphology; the formation of the Martian drainage system; atmospheric dust-water ice Interactions; volatiles and volcanos; accretion of interplanetary dust particles; Mars' ionosphere; simulations with the NASA Ames Mars General Circulation Model; modeling the Martian water cycle; the evolution of Martian atmosphere; isotopic composition; solar occultation; magnetic fields; photochemical weathering; NASA's Mars Surveyor Program; iron formations; measurements of Martian atmospheric water vapor; and the thermal evolution Models of Mars.

Jakosky, B.↗
NASA NTRS1994

Heavy-ion induced genetic changes and evolution processes

On Moon and Mars, there will be more galactic cosmic rays and higher radiation doses than on Earth. Our experimental studies showed that heavy ion radiation can effectively cause mutation and chromosome aberrations and that high Linear Energy Transfer (LET) heavy-ion induced mutants can be irreversible. Chromosome translocations and deletions are common in cells irradiated by heavy particles, and ionizing radiations are effective in causing hyperploidy. The importance of the genetic changes in the evolution of life is an interesting question. Through evolution, there is an increase of DNA content in cells from lower forms of life to higher organisms. The DNA content, however, reached a plateau in vertebrates. By increasing DNA content, there can be an increase of information in the cell. For a given DNA content, the quality of information can be changed by rearranging the DNA. Because radiation can cause hyperploidy, an increase of DNA content in cells, and can induce DNA rearrangement, it is likely that the evolution of life on Mars will be effected by its radiation environment. A simple analysis shows that the radiation level on Mars may cause a mutation frequency comparable to that of the spontaneous mutation rate on Earth. To the extent that mutation plays a role in adaptation, radiation alone on Mars may thus provide sufficient mutation for the evolution of life.

Yang, C. H.↗
NASA NTRS1975

A lunar soil evolution model

Comminution, agglutination, and replenishment processes in a lunar soil are modeled by a system of time-dependent linear differential equations. In the model, a soil is subdivided into coarse-particle, fine-particle, and agglutinate fractions. The relative mass abundance of each component in a mature soil is found to be proportional to rates for the reworking processes. Evolution of the grain-size distribution from a fresh ejecta blanket to a mature soil is described quantitatively in terms of the changing proportions of the three soil constituents. If size data are available for an immature soil and a mature soil of the same system, rates for the various processes can be calculated under certain simplifying assumptions.

Mendell, W. W.↗
NASA NTRS2004

Analysis of RXTE data on Clusters of Galaxies

This grant provided support for the reduction, analysis and interpretation of of hard X-ray (HXR, for short) observations of the cluster of galaxies RXJO658--5557 scheduled for the week of August 23, 2002 under the RXTE Cycle 7 program (PI Vahe Petrosian, Obs. ID 70165). The goal of the observation was to search for and characterize the shape of the HXR component beyond the well established thermal soft X-ray (SXR) component. Such hard components have been detected in several nearby clusters. distant cluster would provide information on the characteristics of this radiation at a different epoch in the evolution of the imiverse and shed light on its origin. We (Petrosian, 2001) have argued that thermal bremsstrahlung, as proposed earlier, cannot be the mechanism for the production of the HXRs and that the most likely mechanism is Compton upscattering of the cosmic microwave radiation by relativistic electrons which are known to be present in the clusters and be responsible for the observed radio emission. Based on this picture we estimated that this cluster, in spite of its relatively large distance, will have HXR signal comparable to the other nearby ones. The planned observation of a relatively The proposed RXTE observations were carried out and the data have been analyzed. We detect a hard X-ray tail in the spectrum of this cluster with a flux very nearly equal to our predicted value. This has strengthen the case for the Compton scattering model. We intend the data obtained via this observation to be a part of a larger data set. We have identified other clusters of galaxies (in archival RXTE and other instrument data sets) with sufficiently high quality data where we can search for and measure (or at least put meaningful limits) on the strength of the hard component. With these studies we expect to clarify the mechanism for acceleration of particles in the intercluster medium and provide guidance for future observations of this intriguing phenomenon by instrument on GLAST. The details of the nonthermal particle population has important implications for the theories of cluster formation, mergers and evolution. The results of this work were first presented at the High Energy Division meeting of the American astronomical Society at Mt. Tremblene, Canada (Petrosian et al. 2003). and in an invited review talk at the General Assembly of the International Astronomical Union at Sydney, Australia (Petrosian, 2003). A paper describe the observations, the data analysis and its implication is being prepared for publication in the Astrophysical Journal.

Petrosian, Vahe↗
NASA NTRS1996

The delivery of organic matter from asteroids and comets to the early surface of Mars

Carbon delivered to the Earth by interplanetary dust particles may have been an important source of pre-biotic organic matter (Anders, 1989). Interplanetary dust is shown to deliver an order-of-magnitude higher surface concentration of carbon onto Mars than onto Earth, suggesting interplanetary dust may be an important source of carbon on Mars as well.

NASA Discipline Exobiology↗
NASA NTRS2017

MATRIX-VBS (v1.0): Implementing an Evolving Organic Aerosol Volatility in an Aerosol Microphysics Model

The gas-particle partitioning and chemical aging of semi-volatile organic aerosol are presented in a newly developed box model scheme, where its effect on the growth, composition, and mixing state of particles is examined. The volatility-basis set (VBS) framework is implemented into the aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state), which resolves mass and number aerosol concentrations and in multiple mixing-state classes. The new scheme, MATRIX-VBS, has the potential to significantly advance the representation of organic aerosols in Earth system models by improving upon the conventional representation as non-volatile particulate organic matter, often also with an assumed fixed size distribution. We present results from idealized cases representing Beijing, Mexico City, a Finnish forest, and a southeastern US forest, and investigate the evolution of mass concentrations and volatility distributions for organic species across the gas and particle phases, as well as assessing their mixing state among aerosol populations. Emitted semi-volatile primary organic aerosols evaporate almost completely in the intermediate-volatility range, while they remain in the particle phase in the low-volatility range. Their volatility distribution at any point in time depends on the applied emission factors, oxidation by OH radicals, and temperature. We also compare against parallel simulations with the original scheme, which represented only the particulate and non-volatile component of the organic aerosol, examining how differently the condensed-phase organic matter is distributed across the mixing states in the model. The results demonstrate the importance of representing organic aerosol as a semi-volatile aerosol, and explicitly calculating the partitioning of organic species between the gas and particulate phases.

volatility-basis set↗
NASA NTRSDate not supplied

Hydrated Interplanetary Dust Particles: Implications for Oxygen Reservoirs in the Outer Solar System

A re-evaluation of solar energetic particle (SEP) track densities in interplanetary dust particles (IDPs) show that many are derived from outer solar system parent bodies such as Kuiper belt objects (KBOs) or beyond. Kuiper belt objects are widely believed to represent the frozen remnants from the birth of the solar system. The population of track-rich IDPs include members from both the anhydrous chondritic-porous and hydrated chondritic-smooth classes and earlier work suggested that the hydrated IDPs may represent anhydrous IDP material that was aqueously altered. We are performing systematic studies of the mineralogy, chemistry and isotopic compositions of track-rich IDPs to gain a fuller understanding of the origin and evolution of KBOs. Here, we focus on the identification of hydrated Kuiper belt dust particles that allows for the direct evaluation of their O isotopic compositions and the implications for the oxygen isotopic composition of outer solar system ices.

L. P. Keller↗
NASA NTRS2008

The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution

The 'Supercritical Pile' is a very economical gamma ray burst (GRB) model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at an energy sim 1 MeV. We extend this model to include also the evolution of the RBW Lorentz factor Gamma and thus follow the spectral and temporal features of this model into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model can be the sources of rich time evolution which we have begun to explore. In particular, one can this way obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the nu F spectra. Furthermore, the existence of a kinematic threshold in this model provides for a operational distinction of the prompt and afterglow GRB stages; in fact, the afterglow stage sets in when the RBW Lorentz factor cannot anymore fulfill the kinematic condition for pair formation in the photon - proton pair production reactions that constitute the fundamental process for the dissipation of the blast wave kinetic energy. We present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

Kazanas, Demosthenes↗
NASA NTRS1996

The 29 July 1994 Merritt Island, Fl Microburst: A Case Study Intercomparing Kennedy Space Center Three-Dimensional Lightning Data (LDAR) and WSR-88D Radar Data

Many researchers have shown that the development and evolution of electrical discharges within convective clouds is fundamentally related to the growth and dynamics of precipitation particles aloft. In the presence of strong updrafts above the freezing level collisions among mixed-phase particles (i.e., hail. ice, supercooled water) promote the necessary charge separation needed to initiate intra-cloud lightning. A precipitation core that descends below the freezing level is often accompanied by a change in the electrical structure of the cloud. Consequently, more Cloud-to-Ground (CG) than Intra-Cloud (IC) lightning flashes appear. Descending precipitation cores can also play a significant role in the evolution of mesoscale features at the surface (e.g., microbursts, downbursts) because of latent heat and mass loading effects of water and ice. For this reason, some believe that lightning and microbursts are fundamentally linked by the presence of ice particles in thunderstorms. Several radar and lightning studies of microburst thunderstorms from COHMEX in 1986 showed that the peak IC lightning systematically occurred ten minutes before the onset of a microburst. In contrast, most CG lightning occurred at the time of the microburst. Many of the preceding studies have been done using high-resolution research radars and experimental lightning detection systems in focused field projects. In addition, these studies could only determine the vertical origin or occurrence of IC lightning, and not a true three-dimensional representation. Currently, the WSR-88D radar system and a real-time, state-of-the-art lightning system (LDAR) at the Kennedy Space Center (KSC) in Florida provide an opportunity to extend these kinds of studies in a more meaningful operational setting.

Hoffert, Steven G.↗
NASA NTRS1994

Exobiology experiments for Earth-orbital platforms

Low-gravity (microgravity) studies relevant to prebiotic evolution and the history of the biogenic elements (C, H, N, O, P, S) are particularly suited to orbital platforms. Relevant to these topics are phenomena such as gas-particle interactions (e.g., formation of organic aerosols via photolytic reactions) including nucleation, condensation, evaporation, adsorption, and catalytic reactions on surfaces; and, small-particle or grain interactions (e.g., growth of interstellar dust particles and planetesimals) including processes such as aggregation (or coagulation), scavenging, and collisions. Both gas-particle and grain (i.e., dust, crystals, organic aerosols, etc.) interactions studies can benefit from microgravity and are pertinent to studies in the areas of chemical evolution in the solar nebula, the interstellar medium, and planetary atmospheres; growth of planetesimals; and prebiotic evolution. In general, the microgravity environment allows for long duration and controlled simulations of processes occurring in exobiologically significant systems such as Titan's atmosphere, interstellar dust clouds, and the solar nebula in which gas-particle or particle-particle interactions play a significant role.

Huntington, J. L.↗