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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Evidence for Different Disk Mass Distributions between Early- and Late-type Be Stars in the BeSOS Survey

The circumstellar disk density distributions for a sample of 63 Be southern stars from the BeSOS survey were found by modeling their H α emission line profiles. These disk densities were used to compute disk masses and disk angular momenta for the sample. Average values for the disk mass are 3.4 × 10{sup −9} and 9.5 × 10{sup −10} M {sub ⋆} for early (B0–B3) and late (B4–B9) spectral types, respectively. We also find that the range of disk angular momentum relative to the star is (150–200) J {sub ⋆}/ M {sub ⋆} and (100–150) J {sub ⋆}/ M {sub ⋆}, again for early- and late-type Be stars, respectively. The distributions of the disk mass and disk angular momentum are different between early- and late-type Be stars at a 1% level of significance. Finally, we construct the disk mass distribution for the BeSOS sample as a function of spectral type and compare it to the predictions of stellar evolutionary models with rapid rotation. The observed disk masses are typically larger than the theoretical predictions, although the observed spread in disk masses is typically large.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Investigation of photoelectron spectroscopy

The problem of obtaining true and meaningful branching ratios from the photoelectron spectra is investigated. The problem consists of understanding the transmission of an electron energy analyzer for electrons with different energies, understanding the effects of using partially polarized radiation from different vacuum monochromators, and in understanding the effects of the angular distribution of photoelectrons ejected from different orbitals. An analysis of the degree of polarization of monochromatic radiation and of the problem of varying angular distributions led to the construction of a cylindrical mirror electron energy analyzer set at the special angle of 54 deg 44 min so that no discrimination would occur for electrons of different angular distributions. With the analyzer properly calibrated for transmission of electrons of different energies, data were taken at several wavelengths and for several atmospheric gases.

Samson, J. A. R.↗
NASA NTRS2016

Convection from Hemispherical and Conical Model Ice Roughness Elements in Stagnation Region Flows

To improve ice accretion prediction codes, more data regarding ice roughness and its effects on convective heat transfer are required. The Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research was used to model realistic ice roughness in the stagnation region of a NACA 0012 airfoil. In the VIST, a test plate representing the leading 2% chord of the airfoil was subjected to flows of 7.62 m/s (25 ft/s), 12.19 m/s (40 ft/s), and 16.76 m/s (55 ft/s). The test plate was fitted with multiple surfaces or sets of roughness panels, each with a different representation of ice roughness. The sets of roughness panels were constructed using two element distribution patterns that were created based on a laser scan of an iced airfoil acquired in the Icing Research Tunnel at NASA Glenn. For both roughness patterns, surfaces were constructed using plastic hemispherical elements, plastic conical elements, and aluminum conical elements. Infrared surface thermometry data from tests run in the VIST were used to calculate area averaged heat transfer coefficient values. The values from the roughness surfaces were compared to the smooth control surface, showing convective enhancement as high as 400% in some cases. The data gathered during this study will ultimately be used to improve the physical modeling in LEWICE or other ice accretion codes and produce predictions of in-flight ice accretion on aircraft surfaces with greater confidence.

Icing Physics↗
DOE OSTI2024

Phasor-Domain Modeling of Inverter Based Resources Considering Unbalanced Grid Faults

A significant increase in inverter-based distributed energy resources (DERs) is expected in distribution systems of the near future. The latest phasor modeling approach of DERs with emerging control technologies can capture relevant dynamics in large-scale three-phase distribution systems with unbalanced construction. However, there is a lack of appropriate phasor models to deal with unbalanced fault scenarios. As such, this paper describes per-phase phasor modeling approach appropriate for unbalanced grid disturbance studies in distribution systems with high penetration of DERs. The overall modeling performance of representative DERs is simulated in phasor domain GridLAB-D environment and validated against controller hardware-in-the loop (CHIL) testing or electromagnetic transient (EMT) based switching model simulation in PSCAD with test cases including different unbalanced grid faults. The high accuracy retained from the simulation verifies the effectiveness of the proposed phasor modeling approach considering interactions between positive and negative sequence signals.

Chen, Zhe↗
DOE OSTI2019

The evolution of galaxy shapes in CANDELS: from prolate to discy

In this study, we model the projected b/a – log a distributions of CANDELS star-forming main-sequence galaxies, where a (b) is the half-light semimajor (semiminor) axis of the galaxy images measured by GALFIT . We find that smaller a galaxies are rounder at all stellar masses M* and redshifts, so we include a when analysing b/a distributions. Approximating intrinsic shapes of the galaxies as triaxial ellipsoids and assuming a multivariate normal distribution of galaxy size and two shape parameters, we construct their intrinsic shape and size distributions to obtain the fractions of elongated (prolate), discy (oblate), and spheroidal galaxies in each redshift and mass bin. We find that galaxies tend to be prolate at low M* and high redshifts, and discy at high M* and low redshifts, qualitatively consistent with van der Wel et al., implying that galaxies tend to evolve from prolate to discy. These results are consistent with the predictions from simulations that the transition from prolate to oblate is caused by a compaction event at a characteristic mass range, making the galaxy centre baryon dominated. We give probabilities of a galaxy’s being elongated, discy, or spheroidal as a function of its M* , redshift, and projected b/a and a , which can facilitate target selections of galaxies with specific shapes at high redshifts.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

The dynamical evolution of poor clusters of galaxies: Growth and properties of the first-ranked galaxy

We report N-body simulations of the dynamical evolution of isolated clusters of 50 galaxies containing a dark matter component that comprises 90% of the cluster mass. For our adopted physical scaling, the line-of-sight velocity dispersion of the cluster is 310 km/s and the initial core radius is 250 kpc. Our results are applicable to (1) present-day poor clusters, (2) the small systems that may have merged to produce present-day rich clusters, and (3) virialized subclumps within larger systems, in between major substructure merger events. We have evolved a total of 10 cluster models, using N = 40,000 particles per model. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the gravitational potential arises from the particles alone. Dark matter is apportioned between the galaxy halos and a smoothly distributed common group halo, the intracluster background (ICB). The percentage of cluster mass initially in the ICB, Beta, is chosen to be 50, 75, or 90. Increasing Beta has the effect of removing mass from dark halos around galaxies and distributing it throughout the cluster. The initial conditions were constructed by randomly sampling a King distribution with W(sub 0) = 6. The galaxies are also King models; the masses of the galaxies follow a Schechter distribution function.

Bode, Paul W.↗
NASA NTRS1985

Studies of hot B subdwarfs. Part 2: Energy distributions of three bright sdB/sdOB stars in the 950-5500 angstrom range

Voyager ultraviolet spectrometer observations of the subdwarf B or OB stars HD 205805, UV 1758+36 and Feige 66 are presented. All three objects display the H I Layman series in absorption. These observations are combined with low dispersion IUE spectrophotometry and with Stroemgren photometry to construct virtually complete energy distributions, which extend over the range 950-5500 angstroms. Effective temperatures based on model atmosphere calculations for high gravity, hydrogen rich stars are determined. Our analyses yield T Sub e 28,200 + or - 1300 K for HD 205805, T sub e 31, 800 + or - 1100 K for UV 1758+36, and T sub e 35,700 + or - 1500 K for Feige 66. The importance of far ultraviolet observations below L sub alpha in reducing the uncertainties associated with the interstellar extinction and the degradation of the IUE sensitivity is emphasized.

Wesemael, F.↗
NASA NTRS1985

Studies of hot B subdwarfs. II - Energy distributions of three bright sdB/sdOB stars in the 950-5500 A range

Voyager ultraviolet spectrometer observations of the subdwarf B or OB stars HD 205805, UV 1758+36 and Feige 66 are presented. All three objects display the H I Layman series in absorption. These observations are combined with low dispersion IUE spectrophotometry and with Stromgren photometry to construct virtually complete energy distributions, which extend over the range 950-5500 angstroms. Effective temperatures based on model atmosphere calculations for high gravity, hygrogen rich stars are determined. Our analyses yield T sub e 28,200 + or - 1300 K for HD 205805, T sub e 31, 800 + or - 1100 K for UV 1758+36, and T sub e 35,700 + or 1500 K for Feige 66. The importance of far ultraviolet observations below L sub alpha in reducing the uncertainties associated with the interstellar extinction and the degradation of the IUE sensitivity is emphasized.

Wesemael, F.↗
DOE OSTI2024

Per-phase Phasor Modeling of GFL and GFM Inverters for Distribution System Dynamic Studies

A significant increase in inverter-based distributed energy resources (DERs) is expected in the near future. Existing electromagnetic models and sequential electromechanical models of DERs supporting dynamic analysis cannot be extended to largescale three-phase distribution systems usually with unbalanced construction. As such, there is a need for appropriate industry models that can support distribution system dynamic studies. This paper describes the latest phasor models of grid-following (GFL) and grid-forming (GFM) inverters that can capture distribution system dynamics under grid disturbances. The overall modeling performance is examined and compared with results from other platforms such as controller hardware-in-the-loop (CHIL), MATLAB/Simulink and PSCAD with electromagnetic transient (EMT) and/or phasor simulation capabilities under balanced and unbalanced faults.

Distribution system, Grid modelling, GridLAB-D, Po↗
DOE OSTI2018

Classification of Complete Proteomes of Different Organisms and Protein Sets Based on Their Protein Distributions in Terms of Some Key Attributes of Proteins

The existence of complete genome sequences makes it important to develop different approaches for classification of large-scale data sets and to make extraction of biological insights easier. Here, we propose an approach for classification of complete proteomes/protein sets based on protein distributions on some basic attributes. We demonstrate the usefulness of this approach by determining protein distributions in terms of two attributes: protein lengths and protein intrinsic disorder contents (ID). The protein distributions based on L and ID are surveyed for representative proteome organisms and protein sets from the three domains of life. The two-dimensional maps (designated as fingerprints here) from the protein distribution densities in the LD space defined by ln( L ) and ID are then constructed. The fingerprints for different organisms and protein sets are found to be distinct with each other, and they can therefore be used for comparative studies. As a test case, phylogenetic trees have been constructed based on the protein distribution densities in the fingerprints of proteomes of organisms without performing any protein sequence comparison and alignments. The phylogenetic trees generated are biologically meaningful, demonstrating that the protein distributions in the LD space may serve as unique phylogenetic signals of the organisms at the proteome level.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1981

Computer simulation of random variables and vectors with arbitrary probability distribution laws

Assume that there is given an arbitrary n-dimensional probability distribution F. A recursive construction is found for a sequence of functions x sub 1 = f sub 1 (U sub 1, ..., U sub n), ..., x sub n = f sub n (U sub 1, ..., U sub n) such that if U sub 1, ..., U sub n are independent random variables having uniform distribution over the open interval (0,1), then the joint distribution of the variables x sub 1, ..., x sub n coincides with the distribution F. Since uniform independent random variables can be well simulated by means of a computer, this result allows one to simulate arbitrary n-random variables if their joint probability distribution is known.

Bogdan, V. M.↗
DOE OSTI2024

Site Characterization of the Highest-Priority Geologic Formations for CO2 Storage in Wyoming

The project Site Characterization of the Highest-Priority Geologic Formations for CO2 Storage in Wyoming is one of 9 site characterization projects that were implemented as part of ARRA (American Recovery and Reinvestment Act). Data from this project was used to improve resolution of data in NATCARB in the area of study. Data related to this study has already been incorporated in NATCARB Atlas. The Wyoming Carbon Underground Storage Project (WY-CUSP) consisted of CO2 storage site characterization and evaluation, focusing on Wyoming’s most promising CO2 storage reservoirs (the Pennsylvanian Weber/Tensleep Sandstone and Mississippian Madison Limestone) and premier CO2 storage site (Rock Springs Uplift). Results from the WY-CUSP project suggest the two reservoirs could store up to 17,000 million tons of CO2. The WY-CUSP team drilled a stratigraphic test well and acquired a 3-D seismic survey covering 25 square miles of the Rock Springs Uplift site. The team retrieved 916 feet of core from the 12,810-foot-deep well, along with a complete log suite, borehole images, fluid samples, and other data. Project partners (1) provided continuous visual documentation of the core, including grain size, mineralogy, facies distribution, and porosity; (2) performed continuous permeability and velocity scans of selected reservoir intervals; and (3) chemically analyzed the fluid samples. WY-CUSP scientists integrated seismic attributes with observations from log suites, a VSP survey, core, fluid samples, and laboratory analyses, including continuous permeability scans. From these integrations, researchers constructed 3-D spatial distribution volumes of reservoir and seal properties that represent geological heterogeneity at the targeted CO2 storage site. The WY-CUSP team used this data to perform new CO2 plume migration simulations. Baker Hughes, Inc., completed a series of small-scale, in-situ water injectivity measurements. A database was formed when observations, analyses, and experiments from the stratigraphic test well were integrated. Correlation of these data allowed petrophysical parameters to be extrapolated from the test well out into the storage domain (5x5 mile 3-D seismic survey volume). This resulted in an improved, realistic understanding of performance assessments for potential CO2 storage scenarios. The WY-CUSP team worked on (1) improving CO2 storage resource estimates, (2) establishing long-term integrity and permanence of confining layers, (3) designing a profitable strategy for pressure management, and (4) evaluating the utilization of stored CO2 at the Rock Spring Uplift. Finally, Baker Hughes developed a microseismic baseline for the test site using in-bore geophones to complete field operations.

3-D seismic↗
NASA NTRS1994

'Spherical' disks: Moving toward a unified source model for L1551

To predict the effects of a disk on the spectral energy distribution of a deeply embedded protostar, we construct disk models with power-law temperature distributions T is proportional to r(exp -q). We then use the spherically averaged disk emission as the central source for a spherical envelope, hence the term, 'spherical' disk. We then calculate the predicted spectral energy distribution of the disk and envelope, using a spherically symmetric radiative transport code. Applying this procedure to L1551 IRS 5, we find that the predicted far-infrared flux is not very sensitive to the nature of the central source. The best source model is consistent with the far-infrared emission arising from the infalling region in an 'inside-out' collapse model, independent of the nature of the central source. Disk models are superior to the star-only model when we try to match millimeter interferometer data. While disks with various q can reproduce the observed 2.7 mm interferometer flux, only an active disk (q = 0.5) can produce enough emission in a region small enough to match the observed 2.7 mm visibilities. However, if the disk is backwarmed by the envelope, even purely reprocessing disks can meet this constraint. All types of backwarmed disks are virtually in distinguishable in their millimeter properties. We find that all reasonable envelope models are sufficiently opaque in the mid-infrared to attenuate any disk model to a level well below the observations, unless the ratio of the mid-infrared to far-infrared dust opacities is similar to that of the dust opacities advocated by Mathis, Mezger, & Panagia (1983).

Butner, Harold M.↗
NASA NTRS2006

Understanding X-Ray Source Motions in a Solar Flare Loop

RHESSI images of a solar flare on 2002 November 28 showed a 3-6 keV hard X-ray source that was initially located at the flare loop top, split and propagated to the foot points of the loop during the flare rise phase, and then propagated back up to the loop top during the declining phase of the flare (Sai, Holman, & Dennis 2006). Higher energy X-ray sources were located lower in the legs of the loop during this period of source evolution, with X-rays above 25 keV seen only at the foot points. Sui, Holman, & Dennis suggested that this spatial evolution reflected the evolution of the spectral index and low-energy cutoff to the distribution of accelerated electrons in the flare. We construct a model flare loop and electron distribution injected at the top of this loop to reproduce the source evolution of the November 28 flare. We determine the constraints on the loop model and the evolution of the accelerated electron distribution. We also study the implications of the model for energy deposition into the loop plasma, and the integrated and imaged X-ray spectra. This work is supported in part by the RHESSI Project and the NASA Guest Investigator Program.

Holman, Gordon D.↗
NASA NTRS1978

Methods for calculating the transonic boundary layer separation for V/STOL inlets at high incidence angles

A semi-empirical scheme for the prediction of transonic pressure distribution on the surface of V/STOL inlets at high incidence angles has been developed. The investigation is intended to improve the boundary layer calculation and separation prediction by including the effects of shock wave-boundary layer interaction into the Lewis Inlet Viscous Computer Program. Wind-tunnel results and theoretical pressure calculation for critical cases are used in constructing the transonic pressure distribution. The program, which describes the development of the boundary layer and predicts the possible flow separation, can handle the cases of inlets at high incidence angles where local supersonic region may occur in the flow.

Chou, D. C.↗
DOE OSTI2017

The seasonal climate niche predicts phenology and distribution of an ephemeral annual plant, Mollugo verticillata

Many short-lived species complete their life cycles during brief seasonal windows of favourable environmental conditions. Such species may persist in the face of climate warming by migration to track their seasonal climate niche in space and/or by phenological shifts to track favourable conditions in time within the year. To describe the seasonal climate niche of the short-lived annual Mollugo verticillata in California, we used data from herbarium specimens and historic climate records to estimate environmental conditions at the location, month and year of each collection. We used these data in a MaxEnt framework to construct a seasonal species distribution model (SDM) of the species’ climate niche within the total climate space available across all seasons and locations in California. The model provides fine-scale spatial and temporal predictions of habitat suitability, predicting both where and when the species should be observed. We compared the predictions of the model to those from a conventional SDM based on mean annual climate data. Both models showed that M. verticillata is limited to warm environments within California. However, the seasonal SDM also predicted phenology by mapping climate suitability across the state for each month of the year. Mollugo verticillata is limited to warm months, and its seasonal climate niche shifts in space across California in the course of the year. We used the seasonal SDM to map the predicted future species distribution for each month of the year under three warming scenarios. The species is predicted to expand its range and occur earlier in the year in most locations; in the warmest locations, seasonal suitability is predicted to decline in the warmest months, which may result in bimodal phenology with a mid-summer gap. Synthesis. We developed a novel species distribution model using herbarium records and monthly weather data, which predicts not only where a short-lived species should be found but also when during the year it is predicted to occur in those areas. Furthermore, this model can be used to predict how climate change will affect the species distribution in space as well as seasonal phenology across the landscape.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1994

Kinetic and thermodynamic properties of a convecting plasma in a two-dimensional dipole field

Charged particle guiding center motion is considered in the magnetic field of a two-dimensional ('line') dipole on which is superimposed a small, static, perpendicular electric field. The parallel equation of motion is that of a simple harmonic oscillator for cos theta, the cosine of magnetic colatitude theta. Equations for the perpendicular electric and magnetic drifts are derived as well as their bounce-averaged forms. The latter are solved to yield a bounce-averaged guiding center trajectory, which is the same as that obtained from conversation of magnetic moment mu, longitudinal invariant J, and total (kinetic plus electrostatic) energy K. The algebraic simplicity of the trajectory equations is also manifest in the forms of the invariants. An interesting result is that guiding centers drift in such a way that they preserve the values of their equatorial pitch angles and (equivalently) mirror latitudes. The most general Maxwellian form of the equilibrium one-particle distribution function f is constructed from the invariants, and spatially varying density and pressure moments, parallel and perpendicular to the magnetic field, are identified. Much of the paper deals with the more restricted problem in which f is specified as a bi-Maxwellian over a straight line of finite length in the equatorial plane of the dipole and perpendicular to field lines. This might be thought of as specifying a cross-tail ion injection source; our formalism then describes the subsequent spatial development. The distribution away from the source is a scaled bi-Maxwellian but one that is cut off at large and small kinetic energies, which depend on position. Density and pressure components are reduced from the values they would have if the total content of individual flux tubes convected intact. The equatorial and meridional variations of density and pressure components are examined and compared systematically for the isotropic and highly anisotropic situations. There appears to be little qualitative difference due to anisotropy. An anisotropy measure is defined, and its spatial variation determined as a signature of possible MHD instability. Extreme values are found, larger than at the source, but the plasma beta in such regions is probably so low as to render the effect inconsequential energetically. Finally, the possible consequence of 'nonadia- batic' pressure profiles on electrostatic interchanges is considered, and a boundary delineating stabilizing and destabilizing regions determined.

Huang, T. S.↗