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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Spectral Index and Quasi-Periodic Oscillation Frequency Correlation in Black Hole (BH) Sources: Observational Evidence of Two Phases and Phase Transition in BHs

Recent studies have shown that strong correlations are observed between the low frequencies (1-10 Hz) of quasiperiodic oscillations (QPOs) and the spectral power law index of several Black Hole (BH) candidate sources, in low hard states, steep power-law (soft) states and in transition between these states. The observations indicate that the X-ray spectrum of such state (phases) show the presence of a power-law component and are sometimes related to simultaneous radio emission indicated the probable presence of a jet. Strong QPOs (less than 20% rms) are present in the power density spectrum in the spectral range where the power-law component is dominant ( i.e. 60-90% ). This evidence contradicts the dominant long standing interpretation of QPOs as a signature of the thermal accretion disk. We present the data from the literature and our own data to illustrate the dominance of power-law index-QPO frequency correlations. We provide a model, that identifies and explains the origin of the QPOs and how they are imprinted on the properties of power-law flux component. We argue the existence of a bounded compact coronal region which is a natural consequence of the adjustment of Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central object and that ultimately leads to the formation of a transition layer (TL) between the adjustment radius and the innermost boundary. The model predicts two phases or states dictated by the photon upscattering produced in the TL: (1) hard state, in which the TL is optically thin and very hot (kT approx. greater than 50 keV) producing photon upscattering via thermal Componization; the photon spectrum index Gamma appprox.1.5 for this state is dictated by gravitational energy release and Compton cooling in an optically thin shock near the adjustment radius; (2) a soft state which is optically thick and relatively cold (approx. less than 5 keV); the index for this state, Gamma approx. 2.8 is determined by soft-photon upscattering and photon trapping in converging flow into BH. In the TL model for corona the QPO frequency vnu(sub high) is related to the gravitational (close to Keplerian) frequency nu(sub K) at the outer (adjustment) radius and nu(sub low) is related to the TL s normal mode (magnetoacoustic) oscillation frequency nu(sub MA). The observed correlations between index and low and high QPO frequencies are readily explained in terms of this model. We also suggest a new method for evaluation of the BH mass using the index-frequency correlation.

Titarchuk, Lev↗
DOE OSTI2020

Materials Data on Li(BH)5 by Materials Project

Li(BH)5 crystallizes in the hexagonal P6_422 space group. The structure is one-dimensional and consists of three Li(BH)5 ribbons oriented in the (0, 1, 0) direction. Li is bonded in a 6-coordinate geometry to six H atoms. There are a spread of Li–H bond distances ranging from 2.05–2.25 Å. There are three inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the second B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the third B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. There are three inequivalent H sites. In the first H site, H is bonded in a distorted T-shaped geometry to two equivalent Li and one B atom. In the second H site, H is bonded in a water-like geometry to one Li and one B atom. In the third H site, H is bonded in a water-like geometry to one Li and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li(BH)6 by Materials Project

Li(BH)6 crystallizes in the cubic Pa-3 space group. The structure is zero-dimensional and consists of eight Li(BH)6 clusters. Li is bonded in a distorted octahedral geometry to six H atoms. There are three shorter (2.09 Å) and three longer (2.24 Å) Li–H bond lengths. There are two inequivalent B sites. In the first B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the second B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. There are two inequivalent H sites. In the first H site, H is bonded in a distorted water-like geometry to one Li and one B atom. In the second H site, H is bonded in a water-like geometry to one Li and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BH)12 by Materials Project

CaB12H12 crystallizes in the monoclinic C2/c space group. The structure is zero-dimensional and consists of twenty-four boranediylradical molecules and four Ca(BH)6 clusters. In each Ca(BH)6 cluster, Ca2+ is bonded in a 6-coordinate geometry to six H+0.83+ atoms. There are a spread of Ca–H bond distances ranging from 2.37–2.42 Å. There are three inequivalent B1- sites. In the first B1- site, B1- is bonded in a single-bond geometry to one H+0.83+ atom. The B–H bond length is 1.21 Å. In the second B1- site, B1- is bonded in a single-bond geometry to one H+0.83+ atom. The B–H bond length is 1.21 Å. In the third B1- site, B1- is bonded in a single-bond geometry to one H+0.83+ atom. The B–H bond length is 1.20 Å. There are three inequivalent H+0.83+ sites. In the first H+0.83+ site, H+0.83+ is bonded in a water-like geometry to one Ca2+ and one B1- atom. In the second H+0.83+ site, H+0.83+ is bonded in a distorted water-like geometry to one Ca2+ and one B1- atom. In the third H+0.83+ site, H+0.83+ is bonded in a distorted water-like geometry to one Ca2+ and one B1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

B 2 H 6 splitting on catalytic surfaces and role of BH 3 towards hydrogen spillover

A fundamental understanding of the spillover mechanism is an open and challenging problem and plays an important role in catalysis. In particular, bond-exchange spillover mechanism is considered to be effective for reversible storage and release of hydrogen at near ambient conditions. For this, three critical steps are needed: finding the right support (acceptor), the right catalyst to split H 2 , and ensuring that once H 2 is split, the H atoms can migrate on the surface with the help of secondary catalysts and eventually hydrogenate the entire material. In this paper we address these challenges using density functional theory. Here we show that BH 3 , a secondary catalyst, can be produced by symmetrically splitting its stable precursor, B 2 H 6 , on doped metal-free surfaces such as graphene and h-BN as well as on MOF5. In addition, to reduce computational cost, we develop structural descriptor and predictive model equation to effectively screen potential BH 3 binding sites. Symmetrical splitting of B 2 H 6 on different types of materials can address the hydrogen spillover challenge, making efficient storage of hydrogen possible.

08 HYDROGEN↗
NASA NTRS2003

Formation of Supermassive Black Holes in Galactic Bulges: A Rotating Collapse Model Consistent with the M(sub BH-sigma) Relation

Motivated by the observed correlation between black hole masses M(sub BH) and the velocity dispersion sigma of host galaxies, we develop a theoretical model of black hole formation in galactic bulges (this paper generalizes an earlier ApJ Letter). The model assumes an initial state specified by a uniform rotation rate OMEGA and a density distribution of the form rho = a(sup 2)(sub eff)per2piGR(sup 2)(so that a(sub eff)is an effective transport speed). The black hole mass is determined when the centrifugal radius of the collapse flow exceeds the capture radius of the central black hole (for Schwarzschild geometry). This model reproduces the observed correlation between the estimated black hole masses and the velocity dispersions of galactic bulges, i.e., M(sub BH) approximately equal to 10(sup 8) solar mass(sigma per 200 kilometers per second)(sup 4) where sigma = the square root of 2a(sub eff). To obtain this normalization, the rotation rate OMEGA approximately equal to 2 x 10(exp -15) rad per second. The model also defines a bulge mass scale M(sub B). If we identify the scale M(sub B) with the bulge mass, the model determines the ratio mu(sub B) of black hole mass to the host mass: mu(sub B) approximately equal to 0.0024(sigma per 200 kilometer per second), again in reasonable agreement with observed values. In this scenario, supermassive black holes form quickly (in approximately 10(exp 5) yr) and are born rapidly rotating (with a per M approximately 0.9). This paper also shown how these results depend on the assumed initial conditions; the most important quantity is the initial distribution of specific angular momentum in the precollapse state.

Adams, Fred C.↗
NASA NTRS2010

Discovery and Monitoring of a New Black Hole Candidate XTE J1752-223 with RXTE: RMS Spectrum Evolution, BH Mass and the Source Distance

We report on the discovery and monitoring observations of a new galactic black hole candidate XTE J1752-223 by Rossi X-ray Timing Explorer (RXTE). The new source appeared on the X-ray sky on October 21 2009 and was active for almost 8 months. Phenomenologically, the source exhibited the low-hard/highsoft spectral state bi-modality and the variability evolution during the state transition that matches standard behavior expected from a stellar mass black hole binary. We model the energy spectrum throughout the outburst using a generic Comptonization model assuming that part of the input soft radiation in the form of a black body spectrum gets reprocessed in the Comptonizing medium. We follow the evolution of fractional root-mean-square (RMS) variability in the RXTE/PCA energy band with the source spectral state and conclude that broad band variability is strongly correlated with the source hardness (or Comptonized fraction). We follow changes in the energy distribution of rms variability during the low-hard state and the state transition and find further evidence that variable emission is strongly concentrated in the power-law spectral component. We discuss the implication of our results to the Comptonization regimes during different spectral states. Correlations of spectral and variability properties provide measurements of the BH mass and distance to the source. The spectral-timing correlation scaling technique applied to the RXTE observations during the hardto- soft state transition indicates a mass of the BH in XTE J1752-223 between 8 and 11 solar masses and a distance to the source about 3.5 kiloparsec.

Shaposhinikov, Nikolai↗
DOE OSTI2020

Materials Data on Tl(BH)6 by Materials Project

Tl(BH)6 crystallizes in the cubic Fm-3 space group. The structure is zero-dimensional and consists of forty-eight boranediylradical molecules and eight thallium molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K(BH)3 by Materials Project

K(BH)3 is Parent of FeAs superconductors-derived structured and crystallizes in the cubic Fm-3m space group. The structure is zero-dimensional and consists of twenty-four boranediylradical molecules and eight potassium molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(BH)3 by Materials Project

Cs(BH)3 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Cs is bonded to twelve equivalent H atoms to form a mixture of corner and face-sharing CsH12 cuboctahedra. All Cs–H bond lengths are 3.44 Å. B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. H is bonded in a single-bond geometry to four equivalent Cs and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rb(BH)6 by Materials Project

Rb(BH)6 crystallizes in the cubic Fm-3 space group. The structure is three-dimensional. Rb is bonded in a distorted q6 geometry to twelve equivalent H atoms. All Rb–H bond lengths are 3.00 Å. B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. H is bonded in a single-bond geometry to two equivalent Rb and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(BH)6 by Materials Project

Cs(BH)6 crystallizes in the cubic Fm-3 space group. The structure is three-dimensional. Cs is bonded in a distorted q6 geometry to twelve equivalent H atoms. All Cs–H bond lengths are 3.18 Å. B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. H is bonded in a single-bond geometry to two equivalent Cs and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K(BH)6 by Materials Project

K(BH)6 crystallizes in the cubic Fm-3 space group. The structure is three-dimensional. K is bonded in a distorted q6 geometry to twelve equivalent H atoms. All K–H bond lengths are 2.95 Å. B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. H is bonded in a single-bond geometry to two equivalent K and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsAg(BH)10 by Materials Project

CsAg(BH)10 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. Cs1+ is bonded in a 5-coordinate geometry to thirteen H1+ atoms. There are a spread of Cs–H bond distances ranging from 3.22–3.41 Å. Ag1+ is bonded in a 6-coordinate geometry to six H1+ atoms. There are a spread of Ag–H bond distances ranging from 2.14–2.40 Å. There are seven inequivalent B+1.20- sites. In the first B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.20 Å. In the second B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.22 Å. In the third B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.20 Å. In the fourth B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.20 Å. In the fifth B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.22 Å. In the sixth B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.20 Å. In the seventh B+1.20- site, B+1.20- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.22 Å. There are seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one Cs1+ and one B+1.20- atom. In the second H1+ site, H1+ is bonded in a distorted single-bond geometry to one Cs1+, one Ag1+, and one B+1.20- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to two equivalent Cs1+ and one B+1.20- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one Cs1+, two equivalent Ag1+, and one B+1.20- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one Cs1+ and one B+1.20- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to two equivalent Cs1+ and one B+1.20- atom. In the seventh H1+ site, H1+ is bonded in a distorted single-bond geometry to one Cs1+, one Ag1+, and one B+1.20- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BH(PbO2)2 by Materials Project

BH(PbO2)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.37–1.41 Å. There are two inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 3-coordinate geometry to three O2- atoms. There are one shorter (2.25 Å) and two longer (2.32 Å) Pb–O bond lengths. In the second Pb2+ site, Pb2+ is bonded in a 3-coordinate geometry to three O2- atoms. There are one shorter (2.28 Å) and two longer (2.34 Å) Pb–O bond lengths. H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.61 Å) H–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one B3+, one Pb2+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted water-like geometry to one B3+ and one H1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one B3+ and one Pb2+ atom. In the fourth O2- site, O2- is bonded to four Pb2+ atoms to form edge-sharing OPb4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li(BH)3 by Materials Project

Li(BH)3 crystallizes in the cubic Fm-3m space group. The structure is zero-dimensional and consists of twenty-four boranediylradical molecules and eight litio molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li(BH)6 by Materials Project

Li(BH)6 crystallizes in the cubic Fm-3 space group. The structure is zero-dimensional and consists of forty-eight boranediylradical molecules and eight lithium molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Synthesis of Cp* Terphenylamido U(III) Iodide Complexes with a Substitutable Iodide Position to Generate Terminal U(III)–(κ 3 -BH 4 ) Complexes

Reaction of Cp*UI 2 (THF) 3 (Cp* = pentamethylcyclopentadienide; THF = tetrahydrofuran) with Na R3 TerNH ( R3 Ter = 2,6(2,4,6-R 3 C 6 H 2 ) 2 C 6 H 3 ; R = Me, Et, iPr) gave the U(III) monoiodide complexes Cp*( R3 TerNH)UI (R = Me, 1-Me; R = Et, 2-Et; R = iPr, 3-iPr). These complexes contain a functionalizable iodide position which reacts favorably with NaBH4 to give the κ 3 -borohydride complexes Cp*( R3 TerNH)U(H 3 BH) (R = Me, 4-Me; R = Et, 5-Et; R = iPr, 6-iPr). All compounds were experimentally characterized by SC-XRD, 1 H and 11 B NMR spectroscopy as well as UV–vis–NIR and FTIR analyses. DFT calculations corroborate the experimental findings, confirming the 5f 3 U(III) configuration across the entire series and revealing an increased U 5f orbital contribution in the borohydride derivatives. All compounds exhibit small but non-negligible U(III)–(η 6 -arene) δ-back-bonding interactions arising from the unpaired 5f electrons. Calculated steric parameters show progressively greater shielding of the U(III) center with increasing bulk of the terphenyl substituents from Me to iPr.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗