Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Model Inference”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Confirming the existence of a quiescent galaxy population out to z = 3: A stacking analysis of mid-, far-infrared, and radio data

We performed a comprehensive stacking analysis on ∼14,200 quiescent galaxy (QG) candidates at z = 0–3 across mid-, far-infrared (MIR and FIR), and radio wavelengths. Identified via their rest-frame NUV − r and r − J colors, the QG candidates (M{sub ⋆}=10{sup 9.8--12.2} M{sub ⊙}) have drastically different IR and radio properties depending on their 24 μm emission strength. The fraction of QG candidates with strong 24 μm emission (equivalent to inferred star formation rates SFR{sub 24}⩾100 M{sub ⊙} yr{sup −1}, hereafter “IR-bright”) increases with redshift and peaks at 15%, and their stacked MIPS 24 μm, Herschel (PACS and SPIRE) and VLA emissions are consistent with being star-forming galaxies (SFGs). In contrast, the majority of QG candidates are faint or undetected at 24 μm individually (i.e., SFR{sub 24} < 100 M{sub ⊙} yr{sup −1}, hereafter “IR-faint”). Their low dust-obscured SFRs derived from Herschel stacking (SFR{sub H} ≲ 3, 15, 50 M{sub ⊙} yr{sup −1} out to z ∼ 1, 2, 3) are >2.5–12.5× lower than compared to SFGs. This is consistent with the quiescence, as expected from their low unobscured SFRs, as inferred from modeling their ultraviolet-to-NIR photometry. The discrepancy between the L{sub IR} derived from stacking Herschel and 24 μm indicates that IR-faint QGs have dust SEDs that are different from those of SFGs. For the most massive (M{sub ⋆}⩾10{sup 11} M{sub ⊙}) IR-faint QGs at z < 1.5, the stacked 1.4 GHz emission is in excess of that expected from other SFR indicators, suggesting a widespread presence of low-luminosity active galactic nuclei. Our results reaffirm the existence of a significant population of QGs out to z = 3, thus corroborating the need to quench star formation in galaxies at early epochs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

SHOCK CONNECTIVITY IN THE 2010 AUGUST AND 2012 JULY SOLAR ENERGETIC PARTICLE EVENTS INFERRED FROM OBSERVATIONS AND ENLIL MODELING

During periods of increased solar activity, coronal mass ejections (CMEs) can occur in close succession and proximity to one another. This can lead to the interaction and merger of CME ejecta as they propagate in the heliosphere. The particles accelerated in these shocks can result in complex solar energetic particle (SEP) events, as observing spacecraft form both remote and local shock connections. It can be challenging to understand these complex SEP events from in situ profiles alone. Multipoint observations of CMEs in the near-Sun environment, from the Solar Terrestrial Relations Observatory –Sun Earth Connection Coronal and Heliospheric Investigation and the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph, greatly improve our chances of identifying the origin of these accelerated particles. However, contextual information on conditions in the heliosphere, including the background solar wind conditions and shock structures, is essential for understanding SEP properties well enough to forecast their characteristics. Wang–Sheeley–Arge WSA-ENLIL + Cone modeling provides a tool to interpret major SEP event periods in the context of a realistic heliospheric model and to determine how much of what is observed in large SEP events depends on nonlocal magnetic connections to shock sources. We discuss observations of the SEP-rich periods of 2010 August and 2012 July in conjunction with ENLIL modeling. We find that much SEP activity can only be understood in the light of such models, and in particular from knowing about both remote and local shock source connections. These results must be folded into the investigations of the physics underlying the longitudinal extent of SEP events, and the source connection versus diffusion pictures of interpretations of SEP events.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

H- and Dissociation in Ultra-hot Jupiters: A Retrieval Case Study of WASP-18b

Atmospheres of a number of ultra-hot Jupiters (UHJs) with temperatures ≳2000 K have been observed recently. Many of these planets show largely featureless thermal spectra in the near-infrared observed with the HST WFC3 spectrograph (1.1–1.7 μm) even though this spectral range contains strong H{sub 2}O opacity. Recent works have proposed the possibility of H- opacity masking the H{sub 2}O feature and/or thermal dissociation of H{sub 2}O causing its apparent depletion at the high temperatures of UHJs. In this work, we test these hypotheses using observations of the exoplanet WASP-18b as a case study. We report detailed atmospheric retrievals of the planet using the HyDRA retrieval code, extended to include the effects of H- opacity and thermal dissociation. We report constraints on the H{sub 2}O, CO, and H- abundances as well as the pressure–temperature profile of the dayside atmosphere for retrievals with and without H-/dissociation for each data set. We find that the H{sub 2}O and H- abundances are relatively unconstrained given the featureless WFC3 spectra. We do not conclusively detect H- in the planet, contrary to previous studies that used equilibrium models to infer its presence. The constraint on the CO abundance depends on the combination of WFC3 and Spitzer data, ranging from solar to super-solar CO values. We additionally see signs of a thermal inversion from two of the data sets. Our study demonstrates the potential of atmospheric retrievals of UHJs, including the effects of H- and thermal dissociation of molecules.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Long-term Photometry and Orbital Period Change of the W UMa–type Binary v0599 Aur: Evidence of about 11 yr Magnetic-activity Cycle

Combining all available photometric data from various surveys and literature with our observations, we present 10 sets of light curves for the eclipsing binary V0599 Aur covering a timescale of 20 yr. During the last two decades, the O’Connell effect continuously varied and went through at least two flips between positive and negative effects. The photometric solutions from our two sets of multicolored light curves show that V0599 Aur is a W-type shallow contact binary with an active spot on the secondary. Its absolute parameters are determined by combining the Gaia distance with the photometric solutions. The period investigation reveals a secular decrease and a cyclic variation in its orbital period. The former mainly originates from the mass transfer from the more massive secondary to the less massive primary. The latter can be preferentially explained as a result of cyclic magnetic activity of the secondary, with three observational supports: (1) the existence and evolution of an active spot suggested by the long-term photometry, (2) periodic variation in both the O’Connell effect and relative luminosity, and (3) weak correlations between O’Connell effect/relative luminosity changes and cyclic period variation. Together with the cyclic period variation and its theoretical reasonability by Applegate’s mechanism, we suggest that the secondary of V0599 Aur is a solar-type magnetic-activity star with an approximately 11 yr active cycle. Furthermore, by combining the secular period decrease with the Roche-lobe model, we infer that V0599 Aur is evolving from the marginal contact state controlled by thermal relaxation oscillation theory to the overcontact state.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

RETURN OF THE KING: TIME-SERIES PHOTOMETRY OF FO AQUARII’S INITIAL RECOVERY FROM ITS UNPRECEDENTED 2016 LOW STATE

In 2016 May, the intermediate polar FO Aqr was detected in a low state for the first time in its observational history. We report time-resolved photometry of the system during its initial recovery from this faint state. Our data, which includes high-speed photometry with cadences of just 2 s, show the existence of very strong periodicities at 22.5 and 11.26 minutes, equivalent to the spin–orbit beat frequency and twice its value, respectively. A pulse at the spin frequency is also present but at a much lower amplitude than is normally observed in the bright state. By comparing our power spectra with theoretical models, we infer that a substantial amount of accretion was stream-fed during our observations, in contrast to the disk-fed accretion that dominates the bright state. In addition, we find that FO Aqr’s rate of recovery has been unusually slow in comparison to rates of recovery seen in other magnetic cataclysmic variables, with an e -folding time of 115 ± 7 days. The recovery also shows irregular variations in the median brightness of as much as 0.2 mag over a 10-day span. Finally, we show that the arrival times of the spin pulses are dependent upon the system’s overall brightness.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Observational Evidence for High Neutronization in Supernova Remnants: Implications for Type Ia Supernova Progenitors

The physical process whereby a carbon–oxygen white dwarf explodes as a Type Ia supernova (SN Ia) remains highly uncertain. The degree of neutronization in SN Ia ejecta holds clues to this process because it depends on the mass and the metallicity of the stellar progenitor, and on the thermodynamic history prior to the explosion. We report on a new method to determine ejecta neutronization using Ca and S lines in the X-ray spectra of Type Ia supernova remnants (SNRs). Applying this method to Suzaku data of Tycho, Kepler , 3C 397, and G337.2−0.7 in the Milky Way, and N103B in the Large Magellanic Cloud, we find that the neutronization of the ejecta in N103B is comparable to that of Tycho and Kepler , which suggests that progenitor metallicity is not the only source of neutronization in SNe Ia. We then use a grid of SN Ia explosion models to infer the metallicities of the stellar progenitors of our SNRs. The implied metallicities of 3C 397, G337.2−0.7, and N103B are major outliers compared to the local stellar metallicity distribution functions, indicating that progenitor metallicity can be ruled out as the origin of neutronization for these SNRs. Although the relationship between ejecta neutronization and equivalent progenitor metallicity is subject to uncertainties stemming from the {sup 12}C + {sup 16}O reaction rate, which affects the Ca/S mass ratio, our main results are not sensitive to these details.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Twelve Years of Spectroscopic Monitoring in the Galactic Center: The Closest Look at S-stars near the Black Hole

We study the young S-stars within a distance of 0.04 pc from the supermassive black hole in the center of our Galaxy. Given how inhospitable the region is for star formation, their presence is more puzzling the younger we estimate their ages. In this study, we analyze the result of 12 years of high-resolution spectroscopy within the central arcsecond of the Galactic Center (GC). By co-adding between 55 and 105 hr of spectra we have obtained high signal-to-noise H- and K-band spectra of eight stars orbiting the central supermassive black hole. Using deep H-band spectra, we show that these stars must be high surface gravity (dwarf) stars. We compare these deep spectra to detailed model atmospheres and stellar evolution models to infer the stellar parameters. Our analysis reveals an effective temperature of 21,000–28,500 K, a rotational velocity of 60–170 km s{sup −1}, and a surface gravity of 4.1–4.2. These parameters imply a spectral type of B0–B3V for these stars. The inferred masses lie within 8–14 M{sub ⊙}. We derive an age of 6.6{sub −4.7}{sup +3.4} Myr for the star S2, which is compatible with the age of the clockwise-rotating young stellar disk in the GC. We estimate the ages of all other studied S-stars to be less than 15 Myr, which is compatible with the age of S2 within the uncertainties. The relatively low ages for these S-stars favor a scenario in which the stars formed in a local disk rather than a field binary-disruption scenario that occurred over a longer period of time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Peeking Between the Pulses: The Far-UV Spectrum of the Previously Unseen White Dwarf in AR Scorpii

The compact object in the interacting binary AR Sco has widely been presumed to be a rapidly rotating, magnetized white dwarf (WD), but it has never been detected directly. Isolating its spectrum has proven difficult because the spin-down of the WD generates pulsed synchrotron radiation that far outshines the WD's photosphere. As a result, a previous study of AR Sco was unable to detect the WD in the averaged far-ultraviolet spectrum from a Hubble Space Telescope (HST) observation. In an effort to unveil the WD's spectrum, we reanalyze these HST observations by calculating the average spectrum in the troughs between synchrotron pulses. We identify weak spectral features from the previously unseen WD and estimate its surface temperature to be 11,500 ± 500 K. Additionally, during the synchrotron pulses, we detect broad Lyα absorption consistent with hot WD spectral models. We infer the presence of a pair of hotspots, with temperatures between 23,000 and 28,000 K, near the magnetic poles of the WD. As the WD is not expected to be accreting from its companion, we describe two possible mechanisms for heating the magnetic poles. Here, the Lyα absorption of the hotspots appears relatively undistorted by Zeeman splitting, constraining the WD's field strength to be ≲100 MG, but the data are insufficient to search for the subtle Zeeman splits expected at lower field strengths.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Synthesizing Stellar Populations in South Pole Telescope Galaxy Clusters. I. Ages of Quiescent Member Galaxies at 0.3 < $\textit{z}$ < 1.4

Using stellar population synthesis models to infer star formation histories (SFHs), we analyze photometry and spectroscopy of a large sample of quiescent galaxies that are members of Sunyaev–Zel'dovich (SZ)-selected galaxy clusters across a wide range of redshifts. We calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < $\textit{z}$ < 1.4 using rest-frame optical spectra and the Python-based Prospector framework, from 61 clusters in the SPT-GMOS Spectroscopic Survey (0.3 < $\textit{z}$ < 0.9) and three clusters in the SPT Hi-z cluster sample (1.25 < $\textit{z}$ < 1.4). We analyze spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. We find that quiescent galaxies in our data set sample a diversity of SFHs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, $t_{50}$) of $\textit{z}$ = 2.8 ± 0.5, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. We also report median age–stellar mass relations for the full sample (age of the universe at $t_{50}$ (Gyr) = 2.52 (±0.04)–1.66 (±0.12) log$_{10}(M/10^{11}M_⊙$)) and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate ~0.75 Gyr earlier than lower-mass galaxies. We also find marginally steeper age–mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

A Study of the Merging Dwarf Galaxy VCC322

Abstract Galaxy interactions and mergers can enhance or reduce star formation, but a complete understanding of the involved processes is still lacking. The effect of dwarf galaxy mergers is even less clear than their massive counterpart. We present a study on a dwarf merger remnant in the Virgo cluster, VCC322, which might form a triple system with VCC334 and VCC319. We identify a prominent long and straight tail-like substructure that has a size comparable to its host galaxy VCC322. By comparing the color–color (g−rversusr−H) distribution with simple stellar population models, we infer that the metallicity and stellar age of this tail areZ ⋆ ∼ 0.02Z ⊙ andt ⋆ ∼ 10 Gyr, respectively. In VCC319, we find a sign of isophotal twisting. This suggests that VCC319 may be subject to tidal interaction. An analysis of the Sloan Digital Sky Survey optical spectra of VCC322 indicates mass- and light-weighted ages of about 10 9.8 yr and 10 7.5 yr, respectively, indicating an ongoing star formation activity. However, the star formation in VCC322 seems suppressed when compared to other star-forming dwarfs of comparable stellar masses. Our finding of shock excitation of optical emission lines indicates that interaction-induced shock may contribute to the heating of cold gas and suppression of star formation.

Astronomy & Astrophysics↗
DOE OSTI2021

First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon

Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density n_e of order 10^4-7 cm-3, magnetic field strength B of order 1-30 G, and electron temperature Te of order (1-12) x 10^10 K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloidal magnetic fields in the emission region. In a quantitative comparison with a large library of simulated polarimetric images from general relativistic magnetohydrodynamic (GRMHD) simulations, we identify a subset of physical models that can explain critical features of the polarimetric EHT observations while producing a relativistic jet of sufficient power. The consistent GRMHD models are all of magnetically arrested accretion disks, where near-horizon magnetic fields are dynamically important. We use the models to infer a mass accretion rate onto the black hole in M87 of (3-20) x 10^-4 Msun yr-1.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Combination of the CDF and D0 Effective Leptonic Electroweak Mixing Angles

CDF and D0 have measured the effective leptonic weak mixing angle $sin^2 \theta^{lept}_{eff}$ , using their full Tevatron datasets. This note describes the Tevatron combination of these measurements, and the zfitter standard model-based inference of the on-shell electroweak mixing angle $sin^2 \theta_W$, or equivalently, the W-boson mass. The combination of CDF and D0 results yields: $sin^2 \theta^{lept}_ {eff}$ = 0.23179 ± 0.00035, and $sin^2 \theta_W$ = 0.22356 ± 0.00035, or equivalently, $M_W$(indirect) = 80.351 ± 0.018 GeV/$c^2$.

Source record↗
DOE OSTI2017

Reduced chemistry model calibration using unsteady flames with repetitive extinction and ignition

In this paper, combustion in a narrow channel with an imposed temperature gradient is used to calibrate a reduced chemical mechanism. The focus is placed on unsteady flames with repetitive extinction and ignition (FREI) at high pressure. The reduced mechanism follows a hybrid approach, combining a small fuel-dependent submechanism with a detailed fuel-independent submechanism for the core species chemistry. The fuel-dependent submechanism consists of three species and nine reactions describing both the low and high-temperature fuel decomposition pathways. The sensitivity of the extinction and ignition locations to the fuel-dependent reactions is assessed and multiple reactions are found to affect the FREI behavior. The sensitive reactions are calibrated following a Bayesian approach. The calibrated reduced model is compared to a detailed model and good agreement in ignition delay times and laminar flame speeds is observed. Finally, this illustrates the potential of a micro flow reactor with a controlled temperature profile to test fuels, calibrate chemical models, and infer kinetic data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Wastewater treatment plant online monitoring and control

A method of operating a waste water treatment plant (WWTP) having at least one of an aerobic digester (AD) and a membrane bioreactor (MBR) is described. The method of operating AD is comprised of monitoring and controlling AD in real-time using an online extended Kalman filter (EKF) having a online dynamic model of AD. The EKF uses real-time AD measured data, and online dynamic model of AD to update adapted model parameters and estimate model based inferred variables for AD, which are used for AD control by AD control system having supervisory and low-level control layers. The method of operating MBR is similar to that of AD. The supervisory control ensures the WWTP satisfying the effluent quality requirement while minimize the operation cost. A WWTP having at least one of AD or MBR is disclosed. The method of operating a WWTP can be implemented using a computer.

Kumar, Aditya↗
DOE OSTI2025

Lens Modeling of STRIDES Strongly Lensed Quasars Using Neural Posterior Estimation

Strongly lensed quasars can be used to constrain cosmological parameters through time-delay cosmography. Models of the lens masses are a necessary component of this analysis. To enable time-delay cosmography from a sample of $\mathcal{O}(10^3)$ lenses, which will soon become available from surveys like the Rubin Observatory’s Legacy Survey of Space and Time and the Euclid Wide Survey, we require fast and standardizable modeling techniques. To address this need, we apply neural posterior estimation (NPE) for modeling galaxy-scale strongly lensed quasars from the Strong Lensing Insights into the Dark Energy Survey (STRIDES) sample. NPE brings two advantages: speed and the ability to implicitly marginalize over nuisance parameters. We extend this method by employing sequential NPE to increase precision of mass model posteriors. We then fold individual lens models into a hierarchical Bayesian inference to recover the population distribution of lens mass parameters, accounting for out-of-distribution shift. After verifying our method using simulated analogs of the STRIDES lens sample, we apply our method to 14 Hubble Space Telescope single-filter observations. We find the population mean of the power-law elliptical mass distribution slope, γ lens , to be $\mathcal{M}_γ$ lens = 2.13 ± 0.06. Our result represents the first population-level constraint for these systems. This population-level inference from fully automated modeling is an important stepping stone toward cosmological inference with large samples of strongly lensed quasars.

79 ASTRONOMY AND ASTROPHYSICS↗