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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SN 2013ej: A type IIL supernova with weak signs of interaction

We present optical photometric and spectroscopic observations of SN 2013ej. It is one of the brightest Type II supernovae (SNe II) exploded in a nearby (∼10 Mpc) galaxy, NGC 628. The light-curve characteristics are similar to SNe II, but with a relatively shorter (∼85 days) and steeper (∼1.7 mag (100 days){sup −1} in V) plateau phase. The SN shows a large drop of 2.4 mag in V-band brightness during the plateau-to-nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV-plateau trend extending up to 85 days. The radioactive {sup 56}Ni mass estimated from the tail luminosity is 0.02 M{sub ⊙}, which is significantly lower than typical SNe IIP. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a Type II event. However, light-curve characteristics and some spectroscopic features provide strong support in classifying it as a Type IIL event. A detailed synow modeling of spectra indicates the presence of some high-velocity components in Hα and Hβ profiles, implying a possible ejecta–circumstellar medium interaction. The nebular phase spectrum shows an unusual notch in the Hα emission, which may indicate bipolar distribution of {sup 56}Ni. Modeling of the bolometric light curve yields a progenitor mass of ∼14 M{sub ⊙} and a radius of ∼450 R{sub ⊙}, with a total explosion energy of ∼2.3×10{sup 51} erg.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Evaluating the Feasibility of Isolated Pancreatic Perfusion for Chemotherapy Using Computed Tomography: An Experimental Study in Pig Models

PurposePercutaneous isolated pancreatic perfusion (PIPP) is performed along with interventional radiology techniques to obtain high drug concentration by occluding the arterial inlet and venous outlet of the pancreas. The experimental study aimed to evaluate the contrast distribution in PIPP under different flow rates with or without anterior mesenteric artery (AMA) occlusion.Materials and MethodsThis study was approved by a local animal experiment ethics committee. Nine pigs were divided into Groups 1, 2, and 3, by infusion rates of 12, 24, and 36 mL/min. Groups 4 and 5 (3 pigs each) and Group 6 (2 pigs) underwent PIPP at the same respective infusion rates with and without AMA occlusion. Computed tomography (CT) arteriography was performed during PIPP with nonionic contrast media. The enhanced volume was calculated by adding the enhanced area in each slice using 1.25-mm axial images. The percent enhanced volume to the whole pancreas (%eV) was used to simulate drug distribution; the result was compared among groups.ResultsWithout AMA occlusion, a larger %eV was obtained with high infusion rates (P = 0.039). The median %eV in Groups 1, 2, and 3 were 57.7, 74.2, and 90.5%, respectively. With AMA occlusion, CT demonstrated duodenal enhancement at an infusion rate of 36 mL/min, and the median %eV in Groups 4, 5, and 6 were 92.8, 95.4, and 98.5%, respectively. A significantly larger %eV was obtained after AMA occlusion (P = 0.031).ConclusionA higher infusion rate or AMA occlusion increases the enhanced volume in PIPP in pig models. Level of evidence: No level of evidence.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

The physical properties of Li-doped g-C{sub 3}N{sub 4} monolayer sheet investigated by the first-principles

Highlights: • Systematically research on Li-doped g-C{sub 3}N{sub 4} monolayer sheets by first-principles calculation. • Optimal dopant concentration for optical absorption is 7.12%. • Thermodynamics stability of the doped substrate g-C{sub 3}N{sub 4} decreased with Li dopant concentration increasing. • The values of work function Φ decreased monotonously with the increasing of Li dopant concentration. - Abstract: The geometric, electronic, optical properties, thermodynamic stability, and work function of Li-doped g-C{sub 3}N{sub 4} monolayer were investigated by the first-principles calculation. It was found that the Li atoms were preferentially substituted the open-hollow sites of g-C{sub 3}N{sub 4}. Interestingly, the “odd” number of Li doped g-C{sub 3}N{sub 4} showed metallic properties, while the “even” number of Li atoms widened the band gap of g-C{sub 3}N{sub 4}. The HOMO and LUMO distributions reveal that the active sites located at edge N and C atoms for both pristine and the Li-doped g-C{sub 3}N{sub 4}. In addition, thermodynamic analysis showed that the doped Li atoms reduced the thermodynamic stability of g-C{sub 3}N{sub 4} monolayer sheets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

STELLAR POPULATION SYNTHESIS BASED MODELING OF THE MILKY WAY USING ASTEROSEISMOLOGY OF 13,000 KEPLER RED GIANTS

With current space-based missions it is now possible to obtain age-sensitive asteroseismic information for tens of thousands of red giants. This provides a promising opportunity to study the Galactic structure and evolution. We use asteroseismic data of red giants, observed by Kepler, to test the current theoretical framework of modeling the Galaxy based on population synthesis modeling and the use of asteroseismic scaling relations for giants. We use the open source code Galaxia to model the Milky Way and find the distribution of the masses predicted by Galaxia to be systematically offset with respect to the seismically inferred observed masses. The Galactic model overestimates the number of low-mass stars, and these stars are predominantly old and of low metallicity. Using corrections to the Δν scaling relation suggested by stellar models significantly reduces the disagreement between predicted and observed masses. For a few cases where non-seismic mass estimates are available, the corrections to Δν also improve the agreement between seismic and non-seismic mass estimates. The disagreement between predictions of the Galactic model and the observations is most pronounced for stars with [Fe/H]<−0.5 and [Fe/H]>0 or for T{sub eff}>4700 K. Altering the star formation rate in order to suppress stars older than 10 Gyr improves the agreement for mass but leads to inconsistent color distributions. We also tested the predictions of the TRILEGAL Galactic model. However, unlike Galaxia, it had difficulties in reproducing the photometric properties of the Kepler Input Catalog because it overestimates the number of blue stars. We conclude that either the scaling relations and/or the Galactic models need to be revised to reconcile predictions of theory with asteroseismic observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Calculation of Transfer Functions of Multilayer Biotissues in the Problems of Correction of Their Fluorescence Spectra

A method for rapid calculation of a flux of stimulated fluorescence of a multilayer optically dense medium with inhomogeneous distribution of the fluorophore has been developed. The light field in the medium at the excitation wavelength of fluorescence is represented by a superposition of incident collimated, incident diffuse, and reflected diffuse fluxes. A two-stream approximation is used to describe the light field in the medium at the wavelength of emission of the fluorescence. Fluxes in adjacent elementary layers of the medium and on its surface are connected by simple matrix operators that are obtained using a combination of engineering approaches of radiation-transfer theory and single-scattering approximation. The calculations of fluorescence fluxes of a four-layer biotissue that are excited and recorded at 400–800 nm are compared with their Monte Carlo simulation with a discrepancy of 1%. The effect of the propagation medium on the fluorescence spectra of 5-ALA-induced protoporphyrin IX that are recorded from human skin was studied, and a technique for their correction that is based on measurements and quantitative analysis of the diffuse reflectance spectrum of skin was proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Surface donor states distribution post SiN passivation of AlGaN/GaN heterostructures

In this paper, we present a physics based analytical model to describe the effect of SiN passivation on two-dimensional electron gas density and surface barrier height in AlGaN/GaN heterostructures. The model is based on an extraction technique to calculate surface donor density and surface donor level at the SiN/AlGaN interface. The model is in good agreement with the experimental results and promises to become a useful tool in advanced design and characterization of GaN based heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Emission of photons by positrons channeled in single crystals near an energy of 100 GeV

Emission by 120-GeV positrons in the channeling regime in the (011) plane of a silicon single crystal has been considered. Trajectories of positrons under different initial conditions have been calculated within the theory of nonlinear oscillations. The amplitude distribution function of channeled particles has been determined taking into account the nonlinearity of their motion. The intensity of radiation under various initial conditions has been calculated by two different methods. These results can be useful for comparison with experimental data at energies of positrons beginning with 100 GeV and higher.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Simulating PV System Performance with Component Reliability Distributions

A feature developed by Sandia National Laboratories (SNL) for simulating PV system component reliability has been integrated into the National Renewable Energy Laboratory's System Advisor Model (SAM). The PV Reliability Performance Model (PV-RPM) uses fault/failure and repair distributions to estimate impacts to power, energy production and operational costs. Realization results include the number of failures per component, failure rate, O&M costs incurred based on maintenance strategies, and energy lost based on the failure estimates. As the inputs are inherently uncertain and based on probability distributions, the model realizations include statistical confidence intervals to help bracket the probability that the sample interval contains the true mean value of the variable in question. This paper presents the current validation efforts and provides detail on how this feature is utilized in a PV performance model.

14 SOLAR ENERGY↗
DOE OSTI2011

NONLINEAR COLOR-METALLICITY RELATIONS OF GLOBULAR CLUSTERS. II. A TEST ON THE NONLINEARITY SCENARIO FOR COLOR BIMODALITY USING THE u-BAND COLORS: THE CASE OF M87 (NGC 4486)

The optical color distributions of globular clusters (GCs) in most large elliptical galaxies are bimodal. Based on the assumed linear relationship between GC colors and their metallicities, the bimodality has been taken as evidence of two GC subsystems with different metallicities in each galaxy and has led to a number of theories in the context of galaxy formation. More recent observations and modeling of GCs, however, suggests that the color-metallicity relations (CMRs) are inflected, and thus colors likely trace metallicities in a nonlinear manner. The nonlinearity could produce bimodal color distributions from a broad underlying metallicity spread, even if it is unimodal. Despite the far-reaching implications, whether CMRs are nonlinear and whether the nonlinearity indeed causes the color bimodality are still open questions. Given that the spectroscopic refinement of CMRs is still very challenging, we here propose a new photometric technique to probe the possible nonlinear nature of CMRs. In essence, a color distribution of GCs is a 'projected' distribution of their metallicities. Since the form of CMRs hinges on which color is used, the shape of color distributions varies depending significantly on the colors. Among other optical colors, the u-band related colors (e.g., u - g and u - z) are theoretically predicted to exhibit significantly less inflected CMRs than other preferred CMRs (e.g., for g - z). As a case study, we performed the Hubble Space Telescope (HST)/WFPC2 archival u-band photometry for the M87 (NGC 4486) GC system with confirmed color bimodality. We show that the u-band color distributions are significantly different from that of g - z and consistent with our model predictions. With more u-band measurements, this method will support or rule out the nonlinear CMR scenario for the origin of GC color bimodality with high confidence. The HST/WFC3 observations in F336W for nearby large elliptical galaxies are highly anticipated in this regard.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

GASP. IV. A Muse View of Extreme Ram-pressure-stripping in the Plane of the Sky: The Case of Jellyfish Galaxy JO204

In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP) survey, we present the characterization of JO204, a jellyfish galaxy in A957, a relatively low-mass cluster with M=4.4×10{sup 14} M{sub ⊙}. This galaxy shows a tail of ionized gas that extends up to 30 kpc from the main body in the opposite direction of the cluster center. No gas emission is detected in the galaxy outer disk, suggesting that gas-stripping is proceeding outside-in. The stellar component is distributed as a regular disk galaxy; the stellar kinematics shows a symmetric rotation curve with a maximum radial velocity of 200 km s{sup −1} out to 20 kpc from the galaxy center. The radial velocity of the gas component in the central part of the disk follows the distribution of the stellar component; the gas kinematics in the tail retains the rotation of the galaxy disk, indicating that JO204 is moving at high speed in the intracluster medium. Both the emission and radial-velocity maps of the gas and stellar components indicate ram-pressure as the most likely primary mechanism for gas-stripping, as expected given that JO204 is close to the cluster center and it is likely at the first infall in the cluster. The spatially resolved star formation history of JO204 provides evidence that the onset of ram-pressure-stripping occurred in the last 500 Myr, quenching the star formation activity in the outer disk, where the gas has been already completely stripped. Our conclusions are supported by a set of hydrodynamic simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

The role of precipitation size distributions in km-scale NWP simulations of intense precipitation: Evaluation of cloud properties and surface precipitation

We investigate the sensitivity of simulated cloud properties and surface precipitation to assumptions regarding the size distributions of the precipitating hydrometeors in a one-moment bulk microphysics scheme. Three sensitivity experiments were applied to two composites of 15 convective and 15 frontal stratiform intense precipitation events observed in a coastal midlatitude region (Belgium), which were evaluated against satellite-retrieved cloud properties and radar-rain-gauge derived surface precipitation. It is found that the cloud optical thickness distribution was well captured by all experiments, although a significant underestimation of cloudiness occurred in the convective composite. The cloud-top-pressure distribution was improved most by more realistic snow size distributions (including a temperature-dependent intercept parameter and non-spherical snow for the calculation of the slope parameter), due to increased snow depositional growth at high altitudes. Surface precipitation was far less sensitive to whether graupel or hail was chosen as the rimed ice species, as compared to previous idealized experiments. This smaller difference in sensitivity could be explained by the stronger updraught velocities and higher freezing levels in the idealized experiments compared to typical coastal midlatitude environmental conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame from which the unmodulated signal descends. Then we describe a mathematically-sound profile likelihood analysis in which the likelihood is profiled over a continuum of nuisance parameters (namely, the WIMP velocity distribution). As a first application of the method, which is very general and valid for any class of velocity distributions, we restrict the analysis to velocity distributions that are isotropic in the Galactic frame. In this way we obtain halo-independent maximum-likelihood estimates and confidence intervals for the DAMA unmodulated signal. We find that the estimated unmodulated signal is in line with expectations for a WIMP-induced modulation and is compatible with the DAMA background+signal rate. Specifically, for the isotropic case we find that the modulated amplitude ranges between a few percent and about 25% of the unmodulated amplitude, depending on the WIMP mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Forward modeling of reduced power spectra from three-dimensional K-space

We present results from a numerical forward model to evaluate one-dimensional reduced power spectral densities (PSDs) from arbitrary energy distributions in k-space. In this model, we can separately calculate the diagonal elements of the spectral tensor for incompressible axisymmetric turbulence with vanishing helicity. Given a critically balanced turbulent cascade with k{sub ∥}∼k{sub ⊥}{sup α} and α<1, we explore the implications on the reduced PSD as a function of frequency. The spectra are obtained under the assumption of Taylor’s hypothesis. We further investigate the functional dependence of the spectral index κ on the field-to-flow angle θ between plasma flow and background magnetic field from MHD to electron kinetic scales. We show that critically balanced turbulence asymptotically develops toward θ-independent spectra with a slope corresponding to the perpendicular cascade. This occurs at a transition frequency f{sub 2D}(L,α,θ), which is analytically estimated and depends on outer scale L, critical balance exponent α, and field-to-flow angle θ. We discuss anisotropic damping terms acting on the k-space distribution of energy and their effects on the PSD. Further, we show that the spectral anisotropies κ(θ) as found by Horbury et al. and Chen et al. in the solar wind are in accordance with a damped critically balanced cascade of kinetic Alfvén waves. We also model power spectra obtained by Papen et al. in Saturn’s plasma sheet and find that the change of spectral indices inside 9 R{sub s} can be explained by damping on electron scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

SDSS IV MaNGA: Discovery of an Hα Blob Associated with a Dry Galaxy Pair—Ejected Gas or a “Dark” Galaxy Candidate?

We report the discovery of a mysterious giant Hα blob that is ∼8 kpc away from the main MaNGA target 1-24145, one component of a dry galaxy merger, and has been identified in the first-year SDSS-IV MaNGA data. The size of the Hα blob is ∼3–4 kpc in radius, and the Hα distribution is centrally concentrated. However, there is no optical continuum counterpart in the deep broadband images reaching ∼26.9 mag arcsec{sup −2} in surface brightness. We estimate that the masses of the ionized and cold gases are 3.3×10{sup 5} M{sub ⊙} and <1.3×10{sup 9} M{sub ⊙}, respectively. The emission-line ratios indicate that the Hα blob is photoionized by a combination of massive young stars and AGNs. Furthermore, the ionization line ratio decreases from MaNGA 1-24145 to the Hα blob, suggesting that the primary ionizing source may come from MaNGA 1-24145, likely a low-activity AGN. Possible explanations for this Hα blob include the AGN outflow, the gas remnant being tidally or ram-pressure stripped from MaNGA 1-24145, or an extremely low surface brightness galaxy. However, the stripping scenario is less favored according to galaxy merger simulations and the morphology of the Hα blob. With the current data, we cannot distinguish whether this Hα blob is ejected gas due to a past AGN outburst, or a special category of “ultra-diffuse galaxy” interacting with MaNGA 1-24145 that further induces the gas inflow to fuel the AGN in MaNGA 1-24145.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

HELIOS: AN OPEN-SOURCE, GPU-ACCELERATED RADIATIVE TRANSFER CODE FOR SELF-CONSISTENT EXOPLANETARY ATMOSPHERES

We present the open-source radiative transfer code named HELIOS, which is constructed for studying exoplanetary atmospheres. In its initial version, the model atmospheres of HELIOS are one-dimensional and plane-parallel, and the equation of radiative transfer is solved in the two-stream approximation with nonisotropic scattering. A small set of the main infrared absorbers is employed, computed with the opacity calculator HELIOS-K and combined using a correlated-k approximation. The molecular abundances originate from validated analytical formulae for equilibrium chemistry. We compare HELIOS with the work of Miller-Ricci and Fortney using a model of GJ 1214b, and perform several tests, where we find: model atmospheres with single-temperature layers struggle to converge to radiative equilibrium; k-distribution tables constructed with ≳0.01 cm{sup −1} resolution in the opacity function (≲10{sup 3} points per wavenumber bin) may result in errors ≳1%–10% in the synthetic spectra; and a diffusivity factor of 2 approximates well the exact radiative transfer solution in the limit of pure absorption. We construct “null-hypothesis” models (chemical equilibrium, radiative equilibrium, and solar elemental abundances) for six hot Jupiters. We find that the dayside emission spectra of HD 189733b and WASP-43b are consistent with the null hypothesis, while the latter consistently underpredicts the observed fluxes of WASP-8b, WASP-12b, WASP-14b, and WASP-33b. We demonstrate that our results are somewhat insensitive to the choice of stellar models (blackbody, Kurucz, or PHOENIX) and metallicity, but are strongly affected by higher carbon-to-oxygen ratios. The code is publicly available as part of the Exoclimes Simulation Platform (exoclime.net).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

AN INTEGRAL FIELD STUDY OF ABUNDANCE GRADIENTS IN NEARBY LUMINOUS INFRARED GALAXIES

We present for the first time metallicity maps generated using data from the Wide Field Spectrograph on the ANU 2.3 m of 10 luminous infrared galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low-metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models that trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

An Investigation of Blazars without Redshifts: Not a Missing Population at High Redshift

We investigate a sample of 622 blazars with measured fluxes at 12 wavebands across the radio-to-gamma-ray spectrum but without spectroscopic or photometric redshifts. This sample includes hundreds of sources with newly analyzed X-ray spectra reported here. From the synchrotron peak frequencies, estimated by fitting the broadband spectral energy distributions (SEDs), we find that the fraction of high-synchrotron-peaked blazars in these 622 sources is roughly the same as in larger samples of blazars that do have redshifts. We characterize the no-redshift blazars using their infrared colors, which lie in the distinct locus called the WISE blazar strip, then estimate their redshifts using a KNN regression based on the redshifts of the closest blazars in the WISE color–color plot. Finally, using randomly drawn values from plausible redshift distributions, we simulate the SEDs of these blazars and compare them to known blazar SEDs. Based on all these considerations, we conclude that blazars without redshift estimates are unlikely to be high-luminosity, high-synchrotron-peaked objects, which had been suggested in order to explain the “blazar sequence”—an observed trend of SED shape with luminosity—as a selection effect. Instead, the observed properties of no-redshift blazars are compatible with a causal connection between jet power and electron cooling, i.e., a true blazar sequence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Statistical Analysis of the First Passage Path Ensemble of Jump Processes

The transition mechanism of jump processes between two different subsets in state space reveals important dynamical information of the processes and therefore has attracted considerable attention in the past years. In this paper, we study the first passage path ensemble of both discrete-time and continuous-time jump processes on a finite state space. The main approach is to divide each first passage path into nonreactive and reactive segments and to study them separately. The analysis can be applied to jump processes which are non-ergodic, as well as continuous-time jump processes where the waiting time distributions are non-exponential. In the particular case that the jump processes are both Markovian and ergodic, our analysis elucidates the relations between the study of the first passage paths and the study of the transition paths in transition path theory. We provide algorithms to numerically compute statistics of the first passage path ensemble. The computational complexity of these algorithms scales with the complexity of solving a linear system, for which efficient methods are available. Several examples demonstrate the wide applicability of the derived results across research areas.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗