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NASA NTRS2019

FIGS: spectral fitting constraints on the star formation history of massive galaxies since the cosmic noon

We constrain the stellar population properties of a sample of 52 massive galaxies – with stellar mass log (M(s)/M(⊙)) ≳ 10.5 – over the redshift range 0.5 < z < 2 by use of observer-frame optical and near-infrared slitless spectra from Hubble Space Telescope’s ACS and WFC3 grisms. The deep exposures (∼100 ks) allow us to target individual spectra of massive galaxies to F160W = 22.5 AB. Our spectral fitting approach uses a set of six base models adapted to the redshift and spectral resolution of each observation, and fits the weights of the base models, including potential dust attenuation, via a Markov Chain Monte Carlo method. Our sample comprises a mixed distribution of quiescent (19) and star-forming galaxies (33). We quantify the width of the age distribution (Δt) that is found to dominate the variance of the retrieved parameters according to principal component analysis. The population parameters follow the expected trend towards older ages with increasing mass, and Δt appears to weakly anticorrelate with stellar mass, suggesting a more efficient star formation at the massive end. As expected, the redshift dependence of the relative stellar age (measured in units of the age of the Universe at the source) in the quiescent sample rejects the hypothesis of a single burst (aka monolithic collapse). Radial colour gradients within each galaxy are also explored, finding a wider scatter in the star-forming subsample, but no conclusive trend with respect to the population parameters.

Ignacio Ferreras↗
NASA NTRS1994

On the determination of the number of O stars in H II regions and starburst galaxies

The hot star population in H II regions, H II galaxies, and starburst galaxies is often described in terms of the number of 'equivalent' O stars of a single representative subtype and luminosity class needed to produce the ionizing luminosity deduced from the nebular recombination lines in the optical spectra. In this paper we define conversion factors eta(sub 0), eta(sub 1), and zeta(sub 5000) with which the total number of O V stars and their flux contribution at 5000 A can be derived from the number of these 'equivalent' stars. These quantities depend primarily on three parameters: the slope and upper mass limit of the stellar mass function and the metallicity of the region. Using the latest stellar atmosphere and evolution models, we calculate eta(sub 0), eta(sub 1), and zeta(sub 5000) for a large number of values of these parameters. The results are presented in tabular as well as graphical form. We apply our results to two H II regions for which the hot star population are known and find that the predicted numbers of O stars agree well the observed counts. In addition, we describe a method by which the values of eta(sub 0) and eta(sub 1) and the observed emission-line fluxes can be used to place constraints on the allowed values of the slope and upper mass limit of the stellar mass function in a region.

Vacca, William D.↗
NASA NTRSDate not supplied

An Approach to Shape Parameterization Using Laboratory Hypervelocity Impact Experiments

NASA’s Orbital Debris Program Office relies on laboratory-based impact tests to supplement the measurement data of on-orbit events that defines the orbital debris environment. These experiments provide information that is essential to interpreting the radar and optical measurements of orbital fragmentation events into useful metrics, such as characteristic size of the debris, and to providing a better understanding of the distributions of fragment populations in terms of their masses, material constituents, fragment densities, cross-sectional areas, area-to-mass ratios, shapes, etc. The Satellite Orbital Debris Characterization Impact Test (SOCIT) was a notable laboratory impact experiment conducted in 1992 using a surplus U.S. Navy Transit navigation satellite of the 1960s. The data from this ground-based experiment were combined with on-orbit measurements to develop the NASA Standard Satellite Breakup Model (SSBM). To account for advancements in satellite design and construction since, a new impact test series – DebriSat – was conducted in 2014. This test utilized a high-fidelity mock-up spacecraft that better represents the materials and construction techniques used to design and manufacture modern spacecraft. Together, these tests offer valuable data to model an orbital debris environment composed of legacy and modern spacecraft. This paper presents an overview of the two laboratory impact tests, comparing their fragment parameter distributions with each other and with relevant distributions from the NASA SSBM. The categorization and descriptions of fragment shapes are of significant interest for future work, yet there are marked differences in the definitions of shape categories between each dataset. The categorizations of constituent materials, and the measurement techniques employed to populate these two datasets, are also different. New rubrics simplify and equate the categorizations between datasets to aid comparative analyses and to facilitate the potential use of both datasets in tandem with future environmental debris models. A preferred approach to classifying shape across disparate datasets uses the characteristic-length dimensions, and a simplified shape classification based on physical, solid-body dimensions, to mathematically construct an encapsulating right-circular cylinder that represents the fragment. The ratio of cylinder length-to-diameter (L:D) then provides a single continuum value for shape that is strongly correlated with its designated shape and size. This metric can then be used to further assess the distribution of shape with populations of other fragment characteristics within these datasets. The shape parameterization using the L:D ratios of right-circular cylinders is discussed.

John H. Seago↗
NASA NTRSDate not supplied

An Approach to Shape Parameterization Using Laboratory Hypervelocity Impact Experiments

NASA’s Orbital Debris Program Office relies on laboratory-based impact tests to supplement the measurement data of on-orbit events that defines the orbital debris environment. These experiments provide information that is essential to interpreting the radar and optical measurements of orbital fragmentation events into useful metrics, such as characteristic size of the debris, and to providing a better understanding of the distributions of fragment populations in terms of their masses, material constituents, fragment densities, cross-sectional areas, area-to-mass ratios, shapes, etc. The Satellite Orbital Debris Characterization Impact Test (SOCIT) was a notable laboratory impact experiment conducted in 1992 using a surplus U.S. Navy Transit navigation satellite of the 1960s. The data from this ground-based experiment were combined with on-orbit measurements to develop the NASA Standard Satellite Breakup Model (SSBM). To account for advancements in satellite design and construction since, a new impact test series – DebriSat – was conducted in 2014. This test utilized a high-fidelity mock-up spacecraft that better represents the materials and construction techniques used to design and manufacture modern spacecraft. Together, these tests offer valuable data to model an orbital debris environment composed of legacy and modern spacecraft. This paper presents an overview of the two laboratory impact tests, comparing their fragment parameter distributions with each other and with relevant distributions from the NASA SSBM. The categorization and descriptions of fragment shapes are of significant interest for future work, yet there are marked differences in the definitions of shape categories between each dataset. The categorizations of constituent materials, and the measurement techniques employed to populate these two datasets, are also different. New rubrics simplify and equate the categorizations between datasets to aid comparative analyses and to facilitate the potential use of both datasets in tandem with future environmental debris models. A preferred approach to classifying shape across disparate datasets uses the characteristic-length dimensions, and a simplified shape classification based on physical, solid-body dimensions, to mathematically construct an encapsulating right-circular cylinder that represents the fragment. The ratio of cylinder length-to-diameter (L:D) then provides a single continuum value for shape that is strongly correlated with its designated shape and size. This metric can then be used to further assess the distribution of shape with populations of other fragment characteristics within these datasets. The shape parameterization using the L:D ratios of right-circular cylinders is discussed.

John H Seago↗
NASA NTRSDate not supplied

CDKN1A/P21’S Role in Osteoprogenitor Fate Regulation in Response to Mechanical Loading: A Single Cell Resolution Investigation

Forces generated by gravity in load-bearing tissues such as bone marrow promote stem cell-based tissue-regenerative processes by increasing proliferation and differentiation of tissue progenitors. Conversely, in microgravity, mouse bone marrow mesenchymal and hematopoietic precursors down-regulate differentiation markers and up-regulate stemness maintenance genes. During microgravity, these transcriptomic changes are associated with Cdkn1a overexpression in osteoprogenitors, and further the homozygous deletion of the CDKN1a gene in the mouse model results in elevated stem-cell based regeneration of severed digits and ear-hole punches. In this work we sought to test the hypothesis that gravity mechanotransduction regulates mesenchymal stem cell derived osteoprogenitor based osteogenesis by modulating proliferation and differentiation fates at specific cell cycle stages via a p21/CDKN1a-regulated mechanism.. To test our hypothesis, we isolated primary mouse bone marrow osteoprogenitors from Cdkn1a-/- (null) or wildtype mice, cultured the cells for 7-days unloaded in osteogenic differentiation media, to allow commitment of the adherent cell population, and subsequently, cultured an additional 48-hours under cyclic stretch or static control loading conditions. After 48-hours of dynamic mechanical loading, we used a 10X Genomics Chromium/Single Cell controller to generate bar-coded single cell Illumina libraries and sequenced expressomes for 6,000 static control and 6,000 cyclic stretch cells for each genotype. Stage-specific single cell analyses show Cdkn1a-/- osteogenic cultures are more differentiated with fewer progenitors, and that cyclic stretch further promotes the conversion of progenitors to osteoblasts in both wildtype and Cdkn1a-/- backgrounds. The proportion of late mineralizing osteoblasts doubled in Cdkn1a-/- cultures, but is not affected by load. Finally, single cell expression of Cdkn1a, in the wildtype cells, is most strongly suppressed by cyclic stretch both in early and late osteoblasts, and minimally in the progenitor population. Collectively, our results support the hypothesis that Cdkn1a constitutively plays a mechano-reversible anti-proliferative role during stem cell-based bone tissue regeneration, and suggests a new molecular target to counter regenerative deficits caused by disuse.

Eduardo Almeida↗
NASA NTRS1981

Gravity, lignification, and land plant evolution

Vascular plants began their occupation of the wetlands interfacing both terrestrial and marine environments at some point in early Paleozoic time. Chemical differences between green algae and vascular land plants are mainly related to an abundance of lignins in the land plants. Answers to questions relating to the phylogeny and adaptive significance of the lignins must depend on experiments and observations using contemporary plant material. A summary is provided of a series of such observations. It is found that the differences between modern Chlorophyta and vascular land plants cannot be explained in full on the basis of lignification alone. Nevertheless, the data point to the emergence of the primitive land populations into an oxygen-rich terrestrial world where the need for mechanical support and water conservation could be met by a single aerobic biochemical process connected to essential aromatic amino acids likely to be found in every cell

Siegel, S. M.↗
NASA NTRS1985

Challenges in the development of the shuttle extravehicular mobility unit

The development of the Shuttle extravehicular mobility unit (EMU) has required significant technology advances in the design of the astronaut life support system and space-suit assembly. The life support system and space-suit assemblies are integrated into a single system and optimized for the primary function of supporting astronaut extravehicular operations. Rather than accommodating a limited, male-only astronaut population, the EMU must satisfy size requirements for both males and females with a minimum of sized parts. In addition, the Shuttle EMU has been designed to implement Space Shuttle Program philosophy of long operating life and mission reuse capability to minimize program lifetime cost. The advancement in life support system and space-suit technology achieved by the development of the Shuttle extravehicular mobility unit (EMU) is illustrated by comparison with the requirements for and the design features of the Apollo EMU.

Mcmann, H. J.↗
NASA NTRS1989

The effects of surface films on mechanical behavior of B2 ordered intermetallic alloys

Surface films deposited on body-centered cubic metals can greatly reduce the yield and flow stresses and increase the ductility at low homologous temperatures. This softening process is associated with the ability of the film-substrate interface to generate large populations of mobile edge dislocations. This phenomenon is extended to B2 ordered intermetallic alloys, which display many deformation characteristics of bcc metals. Single crystal NiAl coated with thermally formed oxide films and polycrystalline FeAl with electrochemically formed Fe-Al-O films display film softening at and below room temperature. The extent of film softening is shown to depend on many factors, including crystal orientation, deformation temperature, operative slip systems, film thickness, film adherence, and film and substrate properties.

Noebe, R. D.↗
NASA NTRS1993

A Darwinian approach to control-structure design

Genetic algorithms (GA's), as introduced by Holland (1975), are one form of directed random search. The form of direction is based on Darwin's 'survival of the fittest' theories. GA's are radically different from the more traditional design optimization techniques. GA's work with a coding of the design variables, as opposed to working with the design variables directly. The search is conducted from a population of designs (i.e., from a large number of points in the design space), unlike the traditional algorithms which search from a single design point. The GA requires only objective function information, as opposed to gradient or other auxiliary information. Finally, the GA is based on probabilistic transition rules, as opposed to deterministic rules. These features allow the GA to attack problems with local-global minima, discontinuous design spaces and mixed variable problems, all in a single, consistent framework.

Zimmerman, David C.↗
NASA NTRS2011

On the Effect of IMF Turning on Ion Dynamics at Mercury

We investigate the effect of a rotation of the Interplanetary Magnetic Field (IMF) on the transport of magnetospheric ion populations at Mercury. We focus on ions of planetary origin and investigate their large-scale circulation using three-dimensional single-particle simulations. We show that a nonzero Bx component of the IMF leads to a pronounced asymmetry in the overall circulation pattern . In particular, we demonstrate that the centrifugal acceleration due to curvature of the E x B drift paths is more pronounced in one hemisphere than the other, leading to filling of the magnetospheric lobes and plasma sheet with more or less energetic material depending upon the hemisphere of origin. Using a time-varying electric and magnetic field model, we investigate the response of ions to rapid (a few tens of seconds) re-orientation of the IMF. We show that, for ions with gyroperiods comparable to the field variation time scale, the inductive electric field should lead to significant nonadiabatic energization, up to several hundreds of eVs or a few keVs. It thus appears that IMP turning at Mercury should lead to localized loading of the magnetosphere with energetic material of planetary origin (e.g., Na+).

Delcourt, D. C.↗
NASA NTRS2015

The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory

The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forwardforward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given.

Parker, L. Neergaard↗
NASA NTRSDate not supplied

Enabling Single Cell Research in Hollow Hydrogel Microparticles

Studying biology at the single cell level enables novel discoveries through ultra-high throughput identification and isolation of rare cells and interesting subpopulations. Encapsulation of single cells in hollow hydrogel microparticles, or PicoShells, enables easy visualization, manipulation, and assaying of single cells. The PicoShell’s porous hydrogel shell allows diffusion of nutrients and wastes into and out of the hollow liquid core, allowing uninhibited cell growth. The porous shell also allows diffusion of assay reagents, enabling solution changes, and multi-step assays. Finally, single cells and their progeny can be tracked through time, for example to measure single cell growth rates. However, PicoShells are fabricated using microfluidic techniques, which require specialized expertise, equipment, and facilities. This limits PicoShell’s widespread utility for single cell biology. For Saccharomyces cerevisiae and other desiccation-tolerant microbes, desiccating PicoShells containing cells of interest offers a solution, enabling those without microfluidic capabilities to obtain dried, shelf-stable PicoShells containing their cells of interest from a specialized microfluidics facility. Researchers could then rehydrate the PicoShells and perform their single cell assays, bypassing the microfluidic steps. Desiccated PicoShells could also be flown in space, where desiccation is already a common practice for microbes (i.e. BioSentinel and BioNutrients), bringing single cell analysis capabilities to space. In this work, we develop a method to desiccate PicoShells containing S. cerevisiae while maintaining characteristics similar to fresh, non-desiccated PicoShells. We show good microparticle morphology and hydrogel pore size as well as high yeast viability in line with previous studies. We also demonstrate sorting of a fast-growing yeast population using size-based filtration, as S. cerevisiae in PicoShells are able to physically stretch the microparticle as they grow, increasing the PicoShell diameter. These efforts contribute to the feasibility of leveraging microparticle PicoShells for single cell space biology research on Earth and in space.

Simon Ng↗
NASA NTRS1998

Cerebellar microfolia and other abnormalities of neuronal growth, migration, and lamination in the Pit1dw-J homozygote mutant mouse

The Snell dwarf mouse (Pit1dw-J homozygote) has a mutation in the Pit1 gene that prevents the normal formation of the anterior pituitary. In neonates and adults there is almost complete absence of growth hormone (GH), prolactin (PRL), thyroxin (T4), and thyroid-stimulating hormone (TSH). Since these hormones have been suggested to play a role in normal development of the central nervous system (CNS), we have investigated the effects of the Pit1dw-J mutation on the cerebellum and hippocampal formation. In the cerebellum, there were abnormalities of both foliation and lamination. The major foliation anomalies were 1) changes in the relative size of specific folia and also the proportional sizes of the anterior vs posterior cerebellum; and 2) the presence of between one and three microfolia per half cerebellum. The microfolia were all in the medial portion of the hemisphere in the caudal part of the cerebellum. Each microfolium was just rostral to a normal fissure and interposed between the fissure and a normal gyrus. Lamination abnormalities included an increase in the number of single ectopic granule cells in the molecular layer in both cerebellar vermis (86%) and hemisphere (40%) in comparison with the wild-type mouse. In the hippocampus of the Pit1dw-J homozygote mouse, the number of pyramidal cells was decreased, although the width of the pyramidal cell layer throughout areas CA1-CA3 appeared to be normal, but less densely populated than in the wild-type mouse. Moreover, the number of granule cells that form the granule cell layer was decreased from the wild-type mouse and some ectopic granule cells (occurring both as single cells and as small clusters) were observed in the innermost portion of the molecular layer. The abnormalities observed in the Pit1dw-J homozygote mouse seem to be caused by both direct and indirect effects of the deficiency of TSH (or T4), PRL, or GH rather than by a direct effect of the deletion of Pit1.

Non-NASA Center↗
NASA NTRS2015

The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory

The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forward-forward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given.

Parker, L. Neergaard↗
NASA NTRS1973

Computer-aided communication satellite system analysis and optimization

The capabilities and limitations of the various published computer programs for fixed/broadcast communication satellite system synthesis and optimization are discussed. A satellite Telecommunication analysis and Modeling Program (STAMP) for costing and sensitivity analysis work in application of communication satellites to educational development is given. The modifications made to STAMP include: extension of the six beam capability to eight; addition of generation of multiple beams from a single reflector system with an array of feeds; an improved system costing to reflect the time value of money, growth in earth terminal population with time, and to account for various measures of system reliability; inclusion of a model for scintillation at microwave frequencies in the communication link loss model; and, an updated technological environment.

Stagl, T. W.↗
NASA NTRS1985

On the gravitational stability of the interstellar medium in spiral arms

The dynamics of self-gravitating gaseous density perturbations in the tightly wound spiral-arm model of the forcing potential (Brown 1969) is investigated. The cloud ensemble of the cold phase of the interstellar medium is regarded as a collisional gas whose 'molecules' are the clouds themselves, and the dynamical evolution of density perturbations is calculated assuming this gas obeys a polytropic pressure-density law. It is suggested that the formation of extreme Population I objects found predominantly along the arms of Sb/Sc systems is regulated by an overall energy balance in the cloud fluid. A single parameter is found which appears to characterize the flow's gravitational response to perturbations; this spiral parameter, Q-sub-sp, differs from the Toomre Q parameter by a factor of the square root of the density enhancement at the shock. It is necessary but not sufficient that Q-sub-sp be less than unity for significant growth to occur.

Balbus, S. A.↗
NASA NTRS1987

Petrogenesis of basalts from the Archean Matachewan Dike Swarm Superior Province of Canada

The Matachewan Dike swarm of eastern Ontario comprises Archean age basalts that were emplaced in the greenstone, granite-greenstone, and metasedimentary terrains of the Superior Province of Canada. The basalts are Fe-rich tholeiites, characterized by the near ubiquitos presence of large, compositionally uniform, calcic plagioclase. Major and trace element whole-rock compositions, along with microprobe analyses of constituent phases, from a group of dikes from the eastern portion of the province, were evaluated to constrain petrological processes that operated during the formation and evolution of the magmas. Three compositional groupings, were identified within the dikes. One group has compositional characteristics similar to modern abyssal tholeiites and is termed morb-type. A second group, enriched in incompatible elements and light-REE enriched, is referred to as the enriched group. The third more populated group has intermediate characteristics and is termed the main group. The observation of both morb-type and enriched compositions within a single dike strongly argues for the contemporaneous existence of magmas derived through different processes. Mixing calculations suggest that two possibilities exist. The least evolved basalts lie on a mixing line between the morb-type and enriched group, suggesting mixing of magmas derived from heterogeneous mantle. Mixing of magmas derived from a depleted mantle with heterogeneous Archean crust can duplicate certain aspects of the Matachewan dike composition array.

Nelson, Dennis O.↗
NASA NTRS2019

Space Radiation and Plasma Effects on Satellites and Aviation: Quantities and Metrics for Tracking Performance of Space Weather Environment Models

The Community Coordinated Modeling Center has been leading communitywide space science and space weather model validation projects for many years. These efforts have been broadened and extended via the newly launched International Forum for Space Weather Modeling Capabilities Assessment (https://ccmc.gsfc.nasa.gov/assessment/). Its objective is to track space weather models' progress and performance over time, a capability that is critically needed in space weather operations and different user communities in general. The Space Radiation and Plasma Effects Working Team of the afore mentioned International Forum works on one of the many focused evaluation topics and deals with five different subtopics (https://ccmc.gsfc.nasa.gov/assessment/topics/radiationall.php) and varieties of particle populations: Surface Charging from tens of eV to 50keV electrons and internal charging due to energetic electrons from hundreds keV to several MeVs. Single event effects from solar energetic particles and galactic cosmic rays (several MeV to TeV), total dose due to accumulation of doses from electrons (>100 keV) and protons (>1 MeV) in a broad energy range, and radiation effects from solar energetic particles and galactic cosmic rays at aviation altitudes. A unique aspect of the Space Radiation and Plasma Effects focus area is that it bridges the space environments, engineering, and user communities. The intent of the paper is to provide an overview of the current status and to suggest a guide for how to best validate space environment models for operational/engineering use, which includes selection of essential space environment and effect quantities and appropriate metrics.

Zheng, Yihua↗