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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 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Data Management as a Cluster Middleware Centerpiece

Through earth and space modeling and the ongoing launches of satellites to gather data, NASA has become one of the largest producers of data in the world. These large data sets necessitated the creation of a Data Management System (DMS) to assist both the users and the administrators of the data. Halcyon Systems Inc. was contracted by the NASA Center for Computational Sciences (NCCS) to produce a Data Management System. The prototype of the DMS was produced by Halcyon Systems Inc. (Halcyon) for the Global Modeling and Assimilation Office (GMAO). The system, which was implemented and deployed within a relatively short period of time, has proven to be highly reliable and deployable. Following the prototype deployment, Halcyon was contacted by the NCCS to produce a production DMS version for their user community. The system is composed of several existing open source or government-sponsored components such as the San Diego Supercomputer Center s (SDSC) Storage Resource Broker (SRB), the Distributed Oceanographic Data System (DODS), and other components. Since Data Management is one of the foremost problems in cluster computing, the final package not only extends its capabilities as a Data Management System, but also to a cluster management system. This Cluster/Data Management System (CDMS) can be envisioned as the integration of existing packages.

Zero, Jose↗
DOE OSTI2019

Ellipticity of brightest cluster galaxies as tracer of halo orientation and weak-lensing mass bias

Weak-lensing measurements of the masses of galaxy clusters are commonly based on the assumption of spherically symmetric density profiles. Yet, the cold dark matter model predicts the shapes of dark matter haloes to be triaxial. Halo triaxiality, and the orientation of the major axis with respect to the line of sight, are expected to be the leading cause of intrinsic scatter in weak-lensing mass measurements. The shape of central cluster galaxies (brightest cluster galaxies; BCGs) is expected to follow the shape of the dark matter halo. In this work we investigate the use of BCG ellipticity as predictor of the weak-lensing mass bias in individual clusters compared to the mean. Using weak-lensing masses $M^{\rm WL}_{500}$ from the Weighing the Giants project, and M 500 derived from gas masses as low-scatter mass proxy, we find that, on average, the lensing masses of clusters with the roundest/most elliptical 25 percent of BCGs are biased ~20 percent high/low compared to the average, as qualitatively predicted by the cold dark matter model. For cluster cosmology projects utilizing weak-lensing mass estimates, the shape of the BCG can thus contribute useful information on the effect of orientation bias in weak-lensing mass estimates as well as on cluster selection bias.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

A Model of Grain Boundary Complexion Transitions and Grain Growth in Yttria-Doped Alumina

In this work, we present a physically-parameterized microstructure evolution model for the Yttria-doped alumina system. Yttria-doped alumina is a well-known ceramic system which undergoes first-order phase-like transitions at grain boundaries, which can radically alter interface properties. The change in interfacial properties in turn can radically change microstructure outcomes during processing, including the induction of abnormal grain growth modes. In this work, we develop a simulation that evolves alumina microstructure as a function of yttria concentration and temperature. In the window studied, we achieve strong agreement with reviewed experimental results in identifying the windows for large grains, small grains, abnormal grain growth, and complexion transition kinetics. We then apply the model to study and demonstrate how the possible inclusion of second-phase particles or uneven solute distribution profiles will impact microstructure evolution. It is found that particles do not significantly affect abnormal grain growth in the window studied (but do lead to reduced grain size through pinning effects). It is found that even modest amounts of solute inhomogeneity will result in substantial changes in microstructure outcomes, frequently leading to clusters of abnormal grains. This model largely corroborates the expectations and hypotheses made from recent experimental studies in oxide-doped alumina systems. Further, it is found that there exists a peak transition fraction for the system at which abnormal grain size tends to be maximized.

Grain Growth, Grain Boundary Complexion, abnormal ↗
DOE OSTI2018

Water Oxidation Catalysis via Size-Selected Iridium Clusters

Here, the detailed mechanism and efficacy of four electron electrochemical water oxidation depend critically upon the detailed atomic structure of each catalytic site, which are numerous and diverse in most metal oxides anodes. In order to limit the diversity of sites, arrays of discrete iridium clusters with identical metal atom number (Ir 2 , Ir 4 , or Ir 8 ) were deposited in submonolayer coverage on conductive oxide supports, and the electrochemical properties and activity of each was evaluated. Exceptional electroactivity for the oxygen evolving reaction (OER) was observed for all cluster samples in acidic electrolyte. Reproducible cluster-size-dependent trends in redox behavior were also resolved. First-principles computational models of the individual discrete-size clusters allow correlation of catalytic-site structure and multiplicity with redox behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Effects of cosmic string velocities and the origin of globular clusters

With the hypothesis that cosmic string loops act as seeds for globular clusters in mind, we study the role that velocities of these strings will play in determining the mass distribution of globular clusters. Loops with high enough velocities will not form compact and roughly spherical objects and can hence not be the seeds for globular clusters. We compute the expected number density and mass function of globular clusters as a function of both the string tension and the peak loop velocity, and compare the results with the observational data on the mass distribution of globular clusters in our Milky Way. We determine the critical peak string loop velocity above which the agreement between the string loop model for the origin of globular clusters (neglecting loop velocities) and observational data is lost.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Ruprecht 147: A Paradigm of Dissolving Star Cluster

We employed recent Gaia/DR2 data to investigate the dynamical status of the nearby (300 pc), old (2.5 Gyr) open cluster Ruprecht 147. We found prominent leading and trailing tails of stars along the cluster orbit, which demonstrates that Ruprecht 147 is losing stars at fast pace. Star counts indicate the cluster has a core radius of 33.3 arcmin and a tidal radius of 137.5 arcmin. The cluster also possesses an extended corona, which cannot be reproduced by a simple King model. We computed the present-day cluster mass using its luminosity and mass function, and derived an estimate of 234 ± 52 M {sub ⊙}. We also estimated the cluster original mass using available recipes extracted from N-body simulations obtaining a mass at birth of 50,000 ± 6500 M {sub ⊙}. Therefore dynamical mass loss, mostly caused by tidal interaction with the Milky Way, reduced the cluster mass by about 99%. We then conclude that Ruprecht 147 is rapidly dissolving into the general Galactic disk.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

On the effects of cluster density and concentration on the horizontal branch morphology - The origin of the blue tails

Possible relationships between horizontal branch (HB) morphology in Galactic globular clusters and the cluster structure and dynamical evolution are investigated. New HB observables are defined and determined using a theoretical framework deduced from HB models. Data for 53 Galactic globular clusters are used to obtain correlations between the observables. It is found that the net length of the HB and the presence and extent of blue tails in particular are correlated with the cluster density and concentrations, in the sense of more concentrated or denser clusters having bluer and longer HB morphologies. This effect is especially strong for the intermediate metallicity clusters. Thus, the cluster environment can affect the stellar evolution leading to the HB and therefore the HB morphology. This result is interpreted in terms of an enhanced mass removal from the HB progenitors.

Fusi Pecci, F.↗
DOE OSTI2022

Dark Energy Survey Year 3 results: Cosmology with moments of weak lensing mass maps

We present a cosmological analysis using the second and third moments of the weak lensing mass (convergence) maps from the first three years of data (Y3) data of the Dark Energy Survey. The survey spans an effective area of 4139 square degrees and uses the images of over 100 million galaxies to reconstruct the convergence field. The second moment of the convergence as a function of smoothing scale contains information similar to standard shear 2-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The data is analyzed in the context of the Λ CDM model, varying five cosmological parameters and 19 nuisance parameters modeling astrophysical and measurement systematics. Our modeling of the observables is completely analytical, and has been tested with simulations in our previous methodology study. We obtain a 1.7% measurement of the amplitude of fluctuations parameter S 8 ≡ σ 8 ( Ω m / 0.3 ) 0.5 = 0.784 ± 0.013 . The measurements are shown to be internally consistent across redshift bins, angular scales, and between second and third moments. In particular, the measured third moment is consistent with the expectation of gravitational clustering under the Λ CDM model. The addition of the third moment improves the constraints on S 8 and Ω m by ∼ 15 % and ∼ 25 % compared to an analysis that only uses second moments. We compare our results with Planck constraints from the cosmic microwave background, finding a 2.2 – 2.8 σ tension in the full parameter space, depending on the combination of moments considered. The third moment, independently, is in 2.8 σ tension with Planck, and thus provides a cross-check on the analyses of 2-point correlations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Dark energy survey year 3 results: Cosmological constraints from cluster abundances, weak lensing, and galaxy clustering

Galaxy clusters provide a unique probe of the late-time cosmic structure and serve as a powerful independent test of the Λ⁢CDM model. This work presents the first set of cosmological constraints derived with ∼16,000 optically selected redMaPPer clusters across nearly 5000 deg 2 using DES year 3 datasets. Our analysis leverages a consistent modeling framework for galaxy cluster cosmology and DES-Y3 joint analyses of galaxy clustering and weak lensing (3 × 2⁢pt), ensuring direct comparability with the DES-Y3 3 × 2⁢pt analysis. Here, we obtain constraints of 𝑆 8 = 0.864 ± 0.035 and Ω m = $0.26⁢5^{+0.019}_{−0.031}$ from the cluster-based data vector. We find that cluster constraints and 3 × 2⁢pt constraints are consistent under the Λ⁢CDM model with a posterior predictive distribution (PPD) value of 0.53. The consistency between clusters and 3 × 2⁢pt provides a stringent test of Λ⁢CDM across different mass and spatial scales. Jointly analyzing clusters with 3 × 2⁢pt further improves cosmological constraints, yielding 𝑆 8 = $0.81⁢1^{+0.022}_{−0.020}$ and Ω m = $0.29⁢4^{+0.022}_{−0.033}$, a 24% improvement in the Ω m − 𝑆 8 figure of merit over 3 × 2⁢pt alone. Moreover, we find no significant deviation from the Planck CMB constraints with a probability to exceed (PTE) value of 0.6, significantly reducing previous 𝑆 8 tension claims. Finally, combining DES 3 × 2⁢pt, DES clusters, and Planck CMB places an upper limit on the sum of neutrino masses of ∑𝑚 𝜈 < 0.26 eV at 95% confidence under the Λ⁢CDM model. These results establish optically selected clusters as a key cosmological probe and pave the way for cluster-based analyses in upcoming stage-IV surveys such as LSST, Euclid, and Roman.

Abbott, T. M. C. [NSF’s National Optical-Infrared ↗
NASA NTRS1980

The photometric properties of brightest cluster galaxies. II - SIT and CCD surface photometry

Surface photometry of the first-ranked galaxy in 108 Abell clusters is presented. Galaxy structure, as parameterized by simple Hubble law models, is found to correlate with galaxy absolute magnitude and cluster structure. All the structure data support the dynamical friction evolution model. Twenty-eight percent of the galaxies have multiple component nuclei; the short lifetimes of such systems provide the best available evidence that ongoing evolution actually occurs. Average magnitude and structure evolution rates are derived from the data.

Hoessel, J. G.↗
DOE OSTI2011

Symmetry of nuclear Hamiltonian as an origin of clustering

It is established that the set of solutions of the Hamiltonian of the generalized Elliott SU(3) model in the space of A-fermion wave functions contains a subset of multicluster solutions {Psi}{sub {Delta}}{sup A} which can be precisely represented in terms of solutions of the Hamiltonian of the same form acting in the reduced space of certain intercluster coordinates. The conditions imposed on a multicluster partition which exhibits such properties are determined by applying the group-theory methods.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Biological Electron Transfer and Catalysis Energy Frontier Research Center

The overarching objective of the BETCy EFRC project is to investigate the mechanisms and structural basis controlling electron bifurcation, electron-ion coupling, and redox catalysis in model enzymes. This detailed understanding of how biological systems control and exploit electron flow will be used to develop modular biochemical conversions for the production of hydrocarbon and hydrogen biofuels. This project will conduct an in-depth study of metalloenzyme structure-function relationships that enable retuning of catalytic sites, electron-transfer thermodynamics, and the evolution of tailor-designed chemical reactions involving two model enzymes: hydrogenase and nitrogenase. The center is organized into three major thrust areas: Thrust 1. Energy conservation and electron flow; Thrust 2. ATP-coupled electron transfer; and Thrust 3. Atomic level determinants of enzymatic redox properties and their relationship to catalytic bias. We will develop a collective knowledge in metalloenzymes by applying physical science and computational tools to characterize biochemical reactions catalyzed specifically by multi-subunit enzymes harboring iron-sulfur clusters and flavin cofactors, as models for redox reactions throughout biology. Understanding these mechanisms is central to overcoming the key thermodynamic barriers currently limiting production of reduced products and biofuels. The research plan of the BETCy EFRC has been designed to provide the basis to exploit unique biochemical mechanisms that have yet to be explored substantively in the context of bioenergy but have the potential for game-changing advancement. The successful outcome of this research will be a collection of fundamental principles that serve as a blueprint to enable the tailored re-design of biological systems and enzymes to control matter and energy at the level of electrons and molecules to provide the foundations to create new energy technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Falicov-Kimball model extended by pair hopping of d-electrons

The effect of the pair hopping of d-electrons has been examined in an exact diagonalization techniqueon a four-site square cluster using extended Falicov-Kimball model. This hopping interaction shifts the critical f-level energy (E{sub c}) at which valence transition occurs. Sharp peaks are observed in the specific heat curves and pair hopping decreases the peak height indicating a reduction in the number of density of states. Antiferromagnetic ordering as well as Curie-like behavior has been observed in the spin susceptibility (χ) characteristics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1988

Hot gas in evolving galaxy clusters and groups - Implications for the microwave and X-ray backgrounds

A phenomenological model for the luminosity function of galaxy groups and clusters allows its evolution to be described in terms of the two-point galaxy correlation function. The observable properties of hot gas in virialized groups and clusters at high redshift have been computed. These include the spectral distortion by Comptonization of the cosmic blackbody spectrum, fluctuations in the cosmic microwave background arising by this same process, and the diffuse X-ray background and fluctuations therein arising from thermal emission by the intracluster gas.

Schaeffer, Richard↗
NASA NTRSDate not supplied

ASCoT 3: Nonlinear Principal Components Analysis and Uncertainty Quantification in Early Concept Spacecraft Flight Software Cost Estimation

For mission planners and evaluators alike, value in cost models comes from a mean or median prediction, an understanding of the uncertainty on that prediction, and an understanding of model performance. Here we apply advanced statistical and machine learning methods to spacecraft flight software cost, effort, and SLOC estimation, and present the results in the latest version of the Analogy Software Cost Tool (ASCoT). We present in- and out-of-sample performance metrics for our models, each of which incorporate some amount of epistemic uncertainty. ASCoT, hosted on the One NASA Cost Engineering (ONCE) database via the Online NASA Space Estimation Tool (ONSET), was first showcased in 2016 as a number of analogy-based models and methods (kNN and Clustering) to support early project formulation. This ASCoT update improves upon the previous analogic methods by incorporating uncertainty in the data transformations. In particular, we use a Nonlinear Principal Components Analysis (NLPCA) to deal with ordinal data.

Robotic Spacecraft↗
DOE OSTI2021

Environmental predictors of pulmonary nontuberculous mycobacteria (NTM) sputum positivity among persons with cystic fibrosis in the state of Florida

Nontuberculous mycobacteria (NTM) are opportunistic human pathogens that are commonly found in soil and water, and exposure to these organisms may cause pulmonary nontuberculous mycobacterial disease. Persons with cystic fibrosis (CF) are at high risk for developing pulmonary NTM infections, and studies have shown that prolonged exposure to certain environments can increase the risk of pulmonary NTM. It is therefore important to determine the risk associated with different geographic areas. Using annualized registry data obtained from the Cystic Fibrosis Foundation Patient Registry for 2010 through 2017, we conducted a geospatial analysis of NTM infections among persons with CF in Florida. A Bernoulli model in SaTScan was used to identify clustering of ZIP codes with higher than expected numbers of NTM culture positive individuals. Generalized linear mixed models with a binomial distribution were used to test the association of environmental variables and NTM culture positivity. We identified a significant cluster of M . abscessus and predictors of NTM sputum positivity, including annual precipitation and soil mineral levels.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Equations of state and phase transitions in stellar matter

Realistic description of core-collapsing supernovae evolution and structure of proto-neutron stars chiefly depends on microphysics input in terms of equations of state, chemical composition and weak interaction rates. At sub-saturation densities the main uncertainty comes from the symmetry energy. Within a nuclear statistical equilibrium (NSE) model with consistent treatment of clusterized and unbound components we investigate the meaning of symmetry energy in the case of dis-homogeneous systems, as the one thought to constitute the neutron star crust, and its sensitivity to the isovector properties of the effective interaction. At supra-saturation densities the situation is much more difficult because of the poor knowledge of nucleon-hyperon and hyperon-hyperon interactions and thermodynamic behavior in terms of phase transitions. Within a simple (npΛ) model we show that compressed baryonic matter with strangeness manifests a complex phase diagram with first and second order phase transitions. The fact that both are explored under strangeness chemical equilibrium and survive Coulomb suggests that they might have sizable consequences on star evolution. An example in this sense is the drastic reduction of the neutrino-mean free path in the vicinity of the critical point obtained within RPA which would lead to a less rapid star cooling.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Optimizing BAO measurements with non-linear transformations of the Lyman-α forest

We explore the effect of applying a non-linear transformation to the Lyman-α forest transmitted flux F=e{sup −τ} and the ability of analytic models to predict the resulting clustering amplitude. Both the large-scale bias of the transformed field (signal) and the amplitude of small scale fluctuations (noise) can be arbitrarily modified, but we were unable to find a transformation that increases significantly the signal-to-noise ratio on large scales using Taylor expansion up to the third order. In particular, however, we achieve a 33% improvement in signal to noise for Gaussianized field in transverse direction. On the other hand, we explore an analytic model for the large-scale biasing of the Lyα forest, and present an extension of this model to describe the biasing of the transformed fields. Using hydrodynamic simulations we show that the model works best to describe the biasing with respect to velocity gradients, but is less successful in predicting the biasing with respect to large-scale density fluctuations, especially for very nonlinear transformations.

79 ASTRONOMY AND ASTROPHYSICS↗