Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “BLACK”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

( NuSTAR NuSTAR) observations of the black hole GS 1354-645: evidence of rapid black hole spin

We present the results of a NuSTAR study of the dynamically confirmed stellar-mass black hole GS 1354−645. The source was observed during its 2015 “hard” state outburst; we concentrate on spectra from two relatively bright phases. In the higher-flux observation, the broadband NuSTAR spectra reveal a clear, strong disk reflection spectrum, blurred by a degree that requires a black hole spin of a=cJ/GM{sup 2}⩾0.98 (1σ statistical limits only). The fits also require a high inclination: θ≃75(2){sup ∘}. Strong “dips” are sometimes observed in the X-ray light curves of sources viewed at such an angle; these are absent, perhaps indicating that dips correspond to flared disk structures that only manifest at higher accretion rates. In the lower flux observation, there is evidence of radial truncation of the thin accretion disk. We discuss these results in the context of spin in stellar-mass black holes, and inner accretion flow geometries at moderate accretion rates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Russian anthropogenic black carbon: Emission reconstruction and Arctic black carbon simulation

Development of reliable source emission inventories is needed to advance the understanding of the origin of Arctic haze using chemical transport modeling. This paper develops a regional anthropogenic black carbon (BC) emission inventory for the Russian Federation, the largest country by land area in the Arctic Council. Activity data from combination of local Russia information and international resources, emission factors based on either Russian documents or adjusted values for local conditions, and other emission source data are used to approximate the BC emissions. Emissions are gridded at a resolution of 0.1° × 0.1° and developed into a monthly temporal profile. Total anthropogenic BC emission of Russia in 2010 is estimated to be around 224 Gg. Gas flaring, a commonly ignored black carbon source, contributes a significant fraction of 36.2% to Russia's total anthropogenic BC emissions. Other sectors, i.e., residential, transportation, industry, and power plants, contribute 25.0%, 20.3%, 13.1%, and 5.4%, respectively. Three major BC hot spot regions are identified: the European part of Russia, the southern central part of Russia where human population densities are relatively high, and the Urals Federal District where Russia's major oil and gas fields are located but with sparse human population. BC simulations are conducted using the hemispheric version of Community Multi-scale Air Quality Model with emission inputs from a global emission database EDGAR (Emissions Database for Global Atmospheric Research)-HTAPv2 (Hemispheric Transport of Air Pollution) and EDGAR-HTAPv2 with its Russian part replaced by the newly developed Russian BC emissions, respectively. The simulation using the new Russian BC emission inventory could improve 30–65% of absorption aerosol optical depth measured at the AERONET sites in Russia throughout the whole year as compared to that using the default HTAPv2 emissions. At the four ground monitoring sites (Zeppelin, Barrow, Alert, and Tiksi) in the Arctic Circle, surface BC simulations are improved the most during the Arctic haze periods (October–March). The poor performance of Arctic BC simulations in previous studies may be partly ascribed to the Russian BC emissions built on out-of-date and/or missing information, which could result in biases to both emission rates and the spatial distribution of emissions. Finally, this study highlights that the impact of Russian emissions on the Arctic haze has likely been underestimated, and its role in the Arctic climate system needs to be reassessed. The Russian black carbon emission source data generated in this study can be obtained via http://abci.ornl.gov/download.shtml or http://acs.engr.utk.edu/Data.php.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

High-accuracy waveforms for black hole-neutron star systems with spinning black holes

The availability of accurate numerical waveforms is an important requirement for the creation and calibration of reliable waveform models for gravitational wave astrophysics. For black hole-neutron star binaries, very few accurate waveforms are however publicly available. Most recent models are calibrated to a large number of older simulations with good parameter space coverage for low-spin non-precessing binaries but limited accuracy, and a much smaller number of longer, more recent simulations limited to non-spinning black holes. In this paper, we present long, accurate numerical waveforms for three new systems that include rapidly spinning black holes, and one precessing configuration. Here, we study in detail the accuracy of the simulations, and in particular perform for the first time in the context of BHNS binaries a detailed comparison of waveform extrapolation methods to the results of Cauchy Characteristic Extraction. The new waveforms have <0.1rad phase errors during inspiral, rising to ~(0.2-0.4)rad errors at merger, and ≲1% error in their amplitude. We compute the faithfulness of recent analytical models to these numerical results, and find that models specifically designed for BHNS binaries perform well (F>0.99) for binaries seen face-on. For edge-on observations, particularly for precessing systems, disagreements between models and simulations increase, and models that include precession and/or higher-order modes start to perform better than BHNS models that currently lack these features.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Separability of the Dirac equation in the STU black hole spacetime: Pairwise-equal charge case study

We study the separability of the Dirac equation in the background of four dimensional charged rotating asymptotically flat black hole solution of supergravity and the low energy string theory known as STU black hole. In particular, we analyze in detail the separability conditions in the pairwise equal charge STU black hole space-time. While in the latter case the minimally coupled Dirac equation is not separable, the introduction of a specific torsion term ensures the separability. The source of the torsion is the Kalb-Ramond field, which is an integral part of string theory, but further aspects of its properties and coupling to fermionic fields remain to be studied. To derive the torsion, two different approaches are used in conformally related frames, showing that the torsion is not unique. The correspondingly modified Dirac equations in the Einstein and string frames are shown to be separable. Furthermore, the massless radial and angular wave equations are examined; they show close similarity with corresponding equations for the standard Kerr background. A generalization of the Teukolsky equation for the pairwise equal case is conjectured. We also briefly analyze a technically sophisticated radial equation in the massive case.

Dirac equation↗
NASA NTRS1975

Comparison under a simulated sun of two black-nickel-coated flat-plate solar collectors with a nonselective black-paint-coated collector

A performance evaluation was made of two, black nickel coated, flat plate solar collectors. Collector performance was determined under a simulated sun for a wide range of inlet temperatures, including the temperature required for solar powered absorption air conditioning. For a basis of comparison a performance test was made on a traditional, two glass, nonselective, black paint coated, flat plate collector. Performance curves and performance parameters are presented to point out the importance of the design variables which determine an efficient collector. A black nickel coated collector was found to be a good performer at the conditions expected for solar powered absorption air conditioning. This collector attained a thermal efficiency of 50 percent at an inlet temperature of 366 K (200 F) and an incident flux of 946 watts/sq m (300 Btu/hr-sq ft).

Simon, F. F.↗
NASA NTRS2016

NuSTAR Observations of the Black Hole GS 1354-645: Evidence of Rapid Black Hole Spin

We present the results of a NuSTAR study of the dynamically confirmed stellar-mass black hole GS 1354−645. The source was observed during its 2015 "hard" state outburst; we concentrate on spectra from two relatively bright phases. In the higher-flux observation, the broadband NuSTAR spectra reveal a clear, strong disk reflection spectrum, blurred by a degree that requires a black hole spin of a = cJ/ GM(sup 2) > or = 0.98 (1(sigma) statistical limits only). The fits also require a high inclination: theta approx. = 75(2)deg. Strong "dips" are sometimes observed in the X-ray light curves of sources viewed at such an angle; these are absent, perhaps indicating that dips correspond to flared disk structures that only manifest at higher accretion rates. In the lower flux observation, there is evidence of radial truncation of the thin accretion disk. We discuss these results in the context of spin in stellar-mass black holes, and inner accretion flow geometries at moderate accretion rates.

accretion disks↗
DOE OSTI2017

Black carbon emissions in Russia: A critical review

Russia has a particularly important role regarding black carbon (BC) emissions given the extent of its territory above the Arctic Circle, where BC emissions have a particularly pronounced effect on the climate. This study presents a comprehensive review of BC estimates from a range of studies. We assess underlying methodologies and data sources for each major emissions source based on their level of detail, accuracy and extent to which they represent current conditions. We then present reference values for each major emissions source. In the case of flaring, the study presents new estimates drawing on data on Russian associated petroleum gas and the most recent satellite data on flaring. We also present estimates of organic carbon (OC) for each source, either based on the reference studies or from our own calculations. In addition, the study provides uncertainty estimates for each source. Total BC emissions are estimated at 689 Gg in 2014, with an uncertainty range between (407-1,416), while OC emissions are 9,228 Gg (with uncertainty between 5,595 and 14,728). Wildfires dominated and contributed about 83% of the total BC emissions, however the effect on radiative forcing is mitigated by OC emissions. We also present an adjusted estimate of Arctic forcing from Russian OC and BC emissions. In recent years, Russia has pursued policies to reduce flaring and limit particulate emissions from on-road transport, both of which appear to significantly contribute to the lower emissions and forcing values found in this study.

Black carbon↗
DOE OSTI2015

Charged black holes in string-inspired gravity II. Mass inflation and dependence on parameters and potentials

We investigate the relation between the existence of mass inflation and model parameters of string-inspired gravity models. In order to cover various models, we investigate a Brans-Dicke theory that is coupled to a U(1) gauge field. By tuning a model parameter that decides the coupling between the Brans-Dicke field and the electromagnetic field, we can make both of models such that the Brans-Dicke field is biased toward strong or weak coupling directions after gravitational collapses. We observe that as long as the Brans-Dicke field is biased toward any (strong or weak) directions, there is no Cauchy horizon and no mass inflation. Therefore, we conclude that to induce a Cauchy horizon and mass inflation inside a charged black hole, either there is no bias of the Brans-Dicke field as well as no Brans-Dicke hair outside the horizon or such a biased Brans-Dicke field should be well trapped and controlled by a potential.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Investigation of primordial black hole bursts using interplanetary network gamma-ray bursts

The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 10 13 –10 18 cm (7–10 5 au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Furthermore, assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Orbital Evolution of Binary Black Holes in Active Galactic Nucleus Disks: A Disk Channel for Binary Black Hole Mergers?

We perform a series of high-resolution 2D hydrodynamical simulations of equal-mass binary black holes (BBHs) embedded in active galactic nucleus (AGN) accretion disks to study whether these binaries can be driven to merger by the surrounding gas. We find that the gravitational softening adopted for the BBH has a profound impact on this result. When the softening is less than 10% of the binary separation, we show that, in agreement with recent simulations of isolated equal-mass binaries, prograde BBHs expand in time rather than contract. Eventually, however, the binary separation becomes large enough that the tidal force of the central AGN disrupts them. Only when the softening is relatively large do we find that prograde BBHs harden. We determine through detailed analysis of the binary torque, that this dichotomy is due to a loss of spiral structure in the circum-single disks orbiting each black hole when the softening is a significant fraction of the binary separation. Properly resolving these spirals—both with high resolution and small softening—results in a significant source of binary angular momentum. Only for retrograde BBHs do we find consistent hardening, regardless of softening, as these BBHs lack the important spiral structure in their circum-single disks. This suggests that the gas-driven inspiral of retrograde binaries can produce a population of compact BBHs in the gravitational-wave-emitting regime in AGN disks, which may contribute a large fraction to the observed BBH mergers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Black Carbon Radiative Forcing over the Tibetan Plateau

We estimate the snow albedo forcing and direct radiative forcing (DRF) of black carbon (BC) in the Tibetan Plateau using a global chemical transport model in conjunction with a stochastic snow model and a radiative transfer model. Our best estimate of the annual BC snow albedo forcing in the Plateau is 2.9 W m-2 (uncertainty: 1.5–5.0 W m-226 ). We find that BC-snow internal mixing increases the albedo forcing by 40-60% compared with external mixing and coated BC increases the forcing by 30-50% compared with uncoated BC, whereas Koch snowflakes reduce the forcing by 20-40% relative to spherical snow grains. Our best estimate of the annual BC DRF at the top of the atmosphere is 2.3 W m-2 (uncertainty: 0.7–4.3 W m-230 ) in the Plateau after scaling the modeled BC absorption optical depth to Aerosol Robotic Network (AERONET) observations. The BC forcings are attributed to emissions from different regions.

black carbon↗
DOE OSTI2014

Using an explicit emission tagging method in global modeling of source‐receptor relationships for black carbon in the Arctic: Variations, sources, and transport pathways

Abstract We introduce an explicit emission tagging technique in the Community Atmosphere Model to quantify source‐region‐resolved characteristics of black carbon (BC), focusing on the Arctic. Explicit tagging of BC source regions without perturbing the emissions provides a physically consistent and computationally efficient approach to establish source‐receptor relationships and transport pathways. Our analysis shows that the contributions of major source regions to the global BC burden are not proportional to the respective emissions due to strong region‐dependent removal rates and lifetimes, while the contributions to BC direct radiative forcing show a near‐linear dependence on their respective contributions to the burden. Arctic BC concentrations, deposition, and source contributions all have strong seasonal variations. Eastern Asia contributes the most to the wintertime Arctic BC burden, but has much less impact on lower‐level concentrations and deposition. Northern Europe emissions are more important to both surface concentration and deposition in winter than in summer. The largest contribution to Arctic BC in the summer is from Northern Asia. Although local emissions contribute less than 10% to the annual mean BC burden and deposition within the Arctic, the per‐emission efficiency is much higher than for non‐Arctic sources. The interannual variability (1996–2005) due to meteorology is small in annual mean BC burden and radiative forcing but is significant in yearly seasonal means over the Arctic. When a slow aging treatment of BC is introduced, the increase of BC lifetime and burden is source dependent. Global BC forcing‐per‐burden efficiency also increases primarily due to changes in BC vertical distributions.

Wang, Hailong↗
DOE OSTI2021

Surface Functionalization of Black Phosphorus with Nitrenes: Identification of P=N Bonds Using Isotopic Labeling

Abstract: Surface functionalization of two-dimensional crystals is a key path to tuning their intrinsic physical and chemical properties. However, synthetic protocols and experimental strategies to directly probe chemical bonding in modified surfaces are scarce. Introduced here is a mild, surface-specific protocol for the surface functionalization of few-layer black phosphorus nanosheets using a family of photolytically generated nitrenes (RN) from the corresponding azides. By embedding spectroscopic tags in the organic backbone, a multitude of characterization techniques are employed to investigate in detail the chemical structure of the modified nanosheets, including vibrational (infrared, Raman), Xray (emission, photoelectron), CPMAS NMR, and UV-vis spectroscopy. To directly probe the functional groups introduced on the surface, R fragments were selected such that in conjunction with vibrational spectroscopy, 15N-labeling experiments, and DFT methods, diagnostic P=N vibrational modes indicative of iminophosphorane units on the nanosheet surface could be conclusively identified.

Walz, Kendall↗
DOE OSTI2017

New X-ray bound on density of primordial black holes

We set a new upper limit on the abundance of primordial black holes (PBH) based on existing X-ray data. PBH interactions with interstellar medium should result in significant fluxes of X-ray photons, which would contribute to the observed number density of compact X-ray objects in galaxies. The data constrain PBH number density in the mass range from a few M {sub ⊙} to 2× 10{sup 7} M {sub ⊙}. PBH density needed to account for the origin of black holes detected by LIGO is marginally allowed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Black Hole Entropy from Bondi-Metzner-Sachs Symmetry at the Horizon

Near the horizon, the obvious symmetries of a black hole spacetime—the horizon-preserving diffeomorphisms—are enhanced to a larger symmetry group with a BMS3 algebra. Using dimensional reduction and covariant phase space techniques, I explore this augmented symmetry, and demonstrate that it is strong enough to determine the black hole entropy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Faint cosmos AGNs at z ∼ 3.3. I. Black hole properties and constraints on early black hole growth

We present new Keck/MOSFIRE K-band spectroscopy for a sample of 14 faint, X-ray-selected active galactic nuclei (AGNs) in the COSMOS field. The data cover the spectral region surrounding the broad Balmer emission lines, which enables the estimation of black hole masses (M{sub BH}) and accretion rates (in terms of L/L{sub Edd}). We focus on 10 AGNs at z ≃ 3.3, where we observe the Hβ spectral region, while for the other four z ≃ 2.4 sources we use the Hα broad emission line. Compared with previous detailed studies of unobscured AGNs at these high redshifts, our sources are fainter by an order of magnitude, corresponding to number densities of order ∼10{sup −6}–10{sup −5} Mpc{sup −3}. The lower AGN luminosities also allow for a robust identification of the host galaxy emission, necessary to obtain reliable intrinsic AGN luminosities, BH masses and accretion rates. We find the AGNs in our sample to be powered by supermassive black holes (SMBHs) with a typical mass of M{sub BH}≃5×10{sup 8} M{sub ⊙}—significantly lower than the higher-luminosity, rarer quasars reported in earlier studies. The accretion rates are in the range L/L{sub Edd} ∼ 0.1–0.4, with an evident lack of sources with lower L/L{sub Edd} (and higher M{sub BH}), as found in several studies of faint AGNs at intermediate redshifts. Based on the early growth expected for the SMBHs in our sample, we argue that a significant population of faint z ∼ 5−6 AGNs, with M{sub BH}∼10{sup 6} M{sub ⊙}, should be detectable in the deepest X-ray surveys available, but this is not observed. We discuss several possible explanations for the apparent absence of such a population, concluding that the most probable scenario involves an evolution in source obscuration and/or radiative efficiencies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Are LIGO's black holes made from smaller black holes?

One proposed formation channel for stellar mass black holes (BHs) is through hierarchical mergers of smaller BHs. Repeated mergers between comparable mass BHs leave an imprint on the spin of the resulting BH since the final BH spin is largely determined by the orbital angular momentum of the binary. We find that for stellar mass BHs forming hierarchically the distribution of spin magnitudes is universal, with a peak at a∼0.7 and little support below a∼0.5. We show that the spin distribution is robust against changes to the mass ratio of the merging binaries, the initial spin distribution of the first generation of BHs, and the number of merger generations. While we assume an isotropic distribution of initial spin directions, spins that are preferentially aligned or antialigned do not qualitatively change our results. We also consider a “cluster catastrophe” model for BH formation in which we allow for mergers of arbitrary mass ratios and show that this scenario predicts a unique spin distribution that is similar to the universal distribution derived for major majors. We explore the ability of spin measurements from ground-based gravitational-wave (GW) detectors to constrain hierarchical merger scenarios. We apply a hierarchical Bayesian mixture model to mock GW data and argue that the fraction of BHs that formed through hierarchical mergers will be constrained with O(100) LIGO binary black hole detections, while with O(10) detections we could falsify a model in which all component BHs form hierarchically.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Implications of Binary Black Hole Detections on the Merger Rates of Double Neutron Stars and Neutron Star–Black Holes

We show that the inferred merger rate and chirp masses of binary black holes (BBHs) detected by advanced LIGO (aLIGO) can be used to constrain the rate of double neutron star (DNS) and neutron star–black hole (NSBH) mergers in the universe. We explicitly demonstrate this by considering a set of publicly available population synthesis models of Dominik et al. and show that if all the BBH mergers, GW150914, LVT151012, GW151226, and GW170104, observed by aLIGO arise from isolated binary evolution, the predicted DNS merger rate may be constrained to be 2.3–471.0 Gpc{sup −3} yr{sup −1} and that of NSBH mergers will be constrained to 0.2–48.5 Gpc{sup −3} yr{sup −1}. The DNS merger rates are not constrained much, but the NSBH rates are tightened by a factor of ∼4 as compared to their previous rates. Note that these constrained DNS and NSBH rates are extremely model-dependent and are compared to the unconstrained values 2.3–472.5 Gpc{sup −3} yr{sup −1} and 0.2–218 Gpc{sup −3} yr{sup −1}, respectively, using the same models of Dominik et al. (2012a). These rate estimates may have implications for short Gamma Ray Burst progenitor models assuming they are powered (solely) by DNS or NSBH mergers. While these results are based on a set of open access population synthesis models, which may not necessarily be the representative ones, the proposed method is very general and can be applied to any number of models, thereby yielding more realistic constraints on the DNS and NSBH merger rates from the inferred BBH merger rate and chirp mass.

79 ASTRONOMY AND ASTROPHYSICS↗