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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Compact laser diode array based on epitaxially integrated AlGaAs/GaAs heterostructures

The main results of the development of compact laser diode mini-arrays operating under 875-nm pulsed pumping are presented and the instrumental characteristics of these arrays are studied. Specific features of these sources, in addition to a high output power (∼1.5 kW), are a narrow directional pattern (angular divergence 21° × 8°) and a small emitting area (less than 1 mm{sup 2}). The use of serially integrated AlGaAs/GaAs MOCVD heterostructures with three emitting regions to develop laser diode arrays allowed us to improve their working parameters. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Vertical-cavity surface-emitting lasers with intracavity contacts and a rhomboidal current aperture for compact atomic clocks

Single-mode vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts, composite distributed Bragg reflectors, and a rhomboidal selectively-oxidised current aperture are studied. It is shown that the use of a rhomboidal current aperture allows the light output polarisation to be fixed without using a special surface relief and leads to efficient narrowing of the emission line with retaining a high slope efficiency. The developed VCSELs have a high output power (exceeding 1 mW), a threshold current below 1 mA, an effective modulation frequency exceeding 5 GHz, and a linewidth smaller than 60 MHz at increased (65 – 75 °C) temperatures and are promising for application in compact Cs vapour cell atomic clocks. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Ergodic decomposition for measures quasi-invariant under a Borel action of an inductively compact group

The aim of this paper is to prove ergodic decomposition theorems for probability measures which are quasi-invariant under Borel actions of inductively compact groups as well as for σ-finite invariant measures. For infinite measures the ergodic decomposition is not unique, but the measure class of the decomposing measure on the space of projective measures is uniquely defined by the initial invariant measure. Bibliography: 21 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Extension of transformation groups of compact solvmanifolds

We indicate a way to extend connected simply connected soluble Lie groups acting transitively and locally effectively on a given compact solvmanifold. In 1973, Auslander posed the problem of describing all groups of this kind. The results obtained here lead to the conclusion that it is unlikely that this problem has an exhaustive solution. Bibliography: 10 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Compact noncontraction semigroups of affine operators

We analyze compact multiplicative semigroups of affine operators acting in a finite-dimensional space. The main result states that every such semigroup is either contracting, that is, contains elements of arbitrarily small operator norm, or all its operators share a common invariant affine subspace on which this semigroup is contracting. The proof uses functional difference equations with contraction of the argument. We look at applications to self-affine partitions of convex sets, the investigation of finite affine semigroups and the proof of a criterion of primitivity for nonnegative matrix families. Bibliography: 32 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

A novel compact end-loaded piston cylinder cell for high pressure neutron scattering up to 5 GPa

Here, a miniature sized end-loaded piston cylinder cell with radial side windows for neutron scattering experiments is described. The principle of the bicone-shaped cylinders used was first presented by McWhan in 1974. The present cell is of compact portable design yet significantly enlarges the scattering angles. Its small size allows neutron scattering experiments at low temperatures. The bicone-shaped cylinders are made from various ceramics or a highly neutron-transmissive Ni-free Cr–Mo–V steel. Successful neutron scattering experiments up to 5 GPa have been demonstrated on the CORELLI single-crystal diffractometer and the VISION vibrational spectrometer of the Spallation Neutron Source at the Oak Ridge National Laboratory.

Neutrons↗
DOE OSTI2013

THE STAR FORMATION HISTORY OF THE VERY METAL-POOR BLUE COMPACT DWARF I Zw 18 FROM HST/ACS DATA

We have derived the star formation history (SFH) of the blue compact dwarf galaxy I Zw 18 through comparison of deep HST/ACS data with synthetic color-magnitude diagrams (CMDs). A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We confirm that I Zw 18 is not a truly young galaxy, having started forming stars earlier than ∼1 Gyr ago, and possibly at epochs as old as a Hubble time. In I Zw 18's main body we infer a lower limit of ≈2 × 10{sup 6} M {sub ☉} for the mass locked up in old stars. I Zw 18's main body has been forming stars very actively during the last ∼10 Myr, with an average star formation rate (SFR) as high as ≈1 M {sub ☉} yr{sup –1} (or ≈2 × 10{sup –5} M {sub ☉} yr{sup –1} pc{sup –2}). On the other hand, the secondary body was much less active at these epochs, in agreement with the absence of significant nebular emission. The high current SFR can explain the very blue colors and the high ionized gas content in I Zw 18, resembling primeval galaxies in the early universe. Detailed chemical evolution models are required to quantitatively check whether the SFH from the synthetic CMDs can explain the low measured element abundances, or if galactic winds with loss of metals are needed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HATS9-b and HATS10-b: Two compact hot jupiters in field 7 of the K2 mission

We report the discovery of two transiting extrasolar planets by the HATSouth survey. HATS-9b orbits an old (10.8 ± 1.5 Gyr) V = 13.3 G dwarf star with a period P≈1.9153 days. The host star has a mass of 1.03 M{sub ⊙}, radius of 1.503 R{sub ⊙} , and effective temperature 5366 ± 70 K. The planetary companion has a mass of 0.837 M{sub J} and radius of 1.065 R{sub J}, yielding a mean density of 0.85 g cm{sup −3}. HATS-10b orbits a V = 13.1 G dwarf star with a period P≈3.3128 days. The host star has a mass of 1.1 M{sub ⊙}, radius of 1.11 R{sub ⊙} , and effective temperature 5880 ± 120 K. The planetary companion has a mass of 0.53 M{sub J} and radius of 0.97 R{sub J}, yielding a mean density of 0.7 g cm{sup −3}. Both planets are compact in comparison with planets receiving similar irradiation from their host stars and lie in the nominal coordinates of Field 7 of K2, but only HATS-9b falls on working silicon. Future characterization of HATS-9b with the exquisite photometric precision of the Kepler telescope may provide measurements of its reflected light signature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY

The Kepler space telescope has opened new vistas in exoplanet discovery space by revealing populations of Earth-sized planets that provide a new context for understanding planet formation. Approximately 70% of all stars in the Galaxy belong to the diminutive M dwarf class, several thousand of which lie within Kepler's field of view, and a large number of these targets show planet transit signals. The Kepler M dwarf sample has a characteristic mass of 0.5 M {sub Sun} representing a stellar population twice as common as Sun-like stars. Kepler-32 is a typical star in this sample that presents us with a rare opportunity: five planets transit this star, giving us an expansive view of its architecture. All five planets of this compact system orbit their host star within a distance one-third the size of Mercury's orbit, with the innermost planet positioned a mere 4.3 stellar radii from the stellar photosphere. New observations limit possible false positive scenarios, allowing us to validate the entire Kepler-32 system making it the richest known system of transiting planets around an M dwarf. Based on considerations of the stellar dust sublimation radius, a minimum mass protoplanetary nebula, and the near period commensurability of three adjacent planets, we propose that the Kepler-32 planets formed at larger orbital radii and migrated inward to their present locations. The volatile content inferred for the Kepler-32 planets and order of magnitude estimates for the disk migration rates suggest that these planets may have formed beyond the snow line and migrated in the presence of a gaseous disk. If true, then this would place an upper limit on their formation time of {approx}10 Myr. The Kepler-32 planets are representative of the full ensemble of planet candidates orbiting the Kepler M dwarfs for which we calculate an occurrence rate of 1.0 {+-} 0.1 planet per star. The formation of the Kepler-32 planets therefore offers a plausible blueprint for the formation of one of the largest known populations of planets in our Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A STUDY ON THE CHEMICAL PROPERTIES OF BLUE COMPACT DWARF GALAXIES

In this paper, we report our studies on the gaseous and chemical properties of a relatively large sample (53 members) of blue compact dwarf galaxies (BCDs). The results of correlations among the oxygen abundance, stellar mass, gas mass, baryonic mass, and gas fraction are present both for E- and I-type BCDs, which are classified according to Loose and Thuan and show elliptical and irregular outer haloes, respectively. These correlations of I-type BCDs show slopes similar to those of E-type ones. However, in general, E-type BCDs are more gas-poor and metal-rich than I-type ones at a given baryonic mass. Based on these results, we suggest that E-type BCDs, at least a part of them, and I-type ones might be likely at different evolutionary phases and/or having different progenitors. Our investigation of the correlation between oxygen abundance and gas fraction shows that BCDs appear to have not evolved as isolated systems, but to have experienced some gas flows and/or mergers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE SPIN-DOWN OF PSR J0821-4300 AND PSR J1210-5226: CONFIRMATION OF CENTRAL COMPACT OBJECTS AS ANTI-MAGNETARS

Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of central compact objects (CCOs) in supernova remnants, proving that these young neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821-4300 in Puppis A, P-dot = (9.28{+-}0.36) Multiplication-Sign 10{sup -18}. Its proper motion, {mu} = 61 {+-} 9 mas yr{sup -1}, was also measured using Chandra. This contributes a kinematic term to the period derivative via the Shklovskii effect, which is subtracted from P-dot to derive dipole B{sub s} = 2.9 Multiplication-Sign 10{sup 10} G, a value similar to that of the first measured CCO, PSR J1852+0040 in Kes 79, which has B{sub s} = 3.1 Multiplication-Sign 10{sup 10} G. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. Paradoxically, such nonuniform surface temperature appears to require strong crustal magnetic fields, probably toroidal or quadrupolar components much stronger than the external dipole. A spectral feature, consisting of either an emission line at Almost-Equal-To 0.75 keV or an absorption line at Almost-Equal-To 0.46 keV, is modulated in strength with the rotation. It may be due to a cyclotron process in a magnetic field on the surface that is slightly stronger than the dipole deduced from the spin-down. We also timed anew the 424 ms PSR J1210-5226, resolving previous ambiguities about its spin-down rate. Its P-dot is (2.22 {+-} 0.02) Multiplication-Sign 10{sup -17}, corresponding to B{sub s} = 9.8 Multiplication-Sign 10{sup 10} G. This is also compatible with a cyclotron resonance interpretation of its prominent absorption line at 0.7 keV and its harmonics. These results deepen the mystery of the origin and evolution of CCOs: Why are their numerous descendants not evident?.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE MASS-LOSS-INDUCED ECCENTRIC KOZAI MECHANISM: A NEW CHANNEL FOR THE PRODUCTION OF CLOSE COMPACT OBJECT-STELLAR BINARIES

Over a broad range of initial inclinations and eccentricities, an appreciable fraction of hierarchical triple star systems with similar masses are essentially unaffected by the Kozai-Lidov mechanism (KM) until the primary in the central binary evolves into a compact object. Once it does, it may be much less massive than the other components in the ternary, enabling the 'eccentric Kozai mechanism (EKM)': the mutual inclination between the inner and outer binaries can flip signs driving the inner binary to very high eccentricity, leading to a close binary or collision. We demonstrate this 'mass-loss-induced eccentric Kozai' (MIEK) mechanism by considering an example system and defining an ad hoc minimal separation between the inner two members at which tidal effects become important. For fixed initial masses and semimajor axes, but uniform distributions of eccentricity and cosine of the mutual inclination, {approx}10% of systems interact tidally or collide while the primary is on the main sequence (MS) due to the KM or EKM. Those affected by the EKM are not captured by earlier quadrupole-order secular calculations. We show that fully {approx}30% of systems interact tidally or collide for the first time as the primary swells to AU scales, mostly as a result of the KM. Finally, {approx}2% of systems interact tidally or collide for the first time after the primary sheds most of its mass and becomes a white dwarf (WD), mostly as a result of the MIEK mechanism. These findings motivate a more detailed study of mass loss in triple systems and the formation of close neutron star (NS)/WD-MS and NS/WD-NS/WD binaries without an initial common envelope phase.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

COMPACT OBJECT COALESCENCE RATE ESTIMATION FROM SHORT GAMMA-RAY BURST OBSERVATIONS

Recent observational and theoretical results suggest that short-duration gamma-ray bursts (SGRBs) originate from the merger of compact binary systems of two neutron stars or a neutron star and a black hole. The observation of SGRBs with known redshifts allows astronomers to infer the merger rate of these systems in the local universe. We use data from the SWIFT satellite to estimate this rate to be in the range {approx}500-1500 Gpc{sup -3} yr{sup -1}. This result is consistent with earlier published results which were obtained through alternative approaches. We estimate the number of coincident observations of gravitational-wave signals with SGRBs in the advanced gravitational-wave detector era. By assuming that all SGRBs are created by neutron star-neutron star (neutron star-black hole) mergers, we estimate the expected rate of coincident observations to be in the range {approx_equal} 0.2-1 ({approx_equal} 1-3) yr{sup -1}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A STATE TRANSITION OF THE LUMINOUS X-RAY BINARY IN THE LOW-METALLICITY BLUE COMPACT DWARF GALAXY I Zw 18

We present a measurement of the X-ray spectrum of the luminous X-ray binary in I Zw 18, the blue compact dwarf galaxy with the lowest known metallicity. We find the highest flux yet observed, corresponding to an intrinsic luminosity near 1 Multiplication-Sign 10{sup 40} erg s{sup -1} establishing it as an ultraluminous X-ray source (ULX). The energy spectrum is dominated by disk emission with a weak or absent Compton component and there is no significant timing noise; both are indicative of the thermal state of stellar-mass black hole X-ray binaries and inconsistent with the Compton-dominated state typical of most ULX spectra. A previous measurement of the X-ray spectrum shows a harder spectrum that is well described by a power law. Thus, the binary appears to exhibit spectral states similar to those observed from stellar-mass black hole binaries. If the hard state occurs in the range of luminosities found for the hard state in stellar-mass black hole binaries, then the black hole mass must be at least 85 M{sub Sun }. Spectral fitting of the thermal state shows that disk luminosities for which thin disk models are expected to be valid are produced only for relatively high disk inclinations, {approx}> 60 Degree-Sign , and rapid black hole spins. We find a{sub *} > 0.98 and M > 154 M{sub Sun} for a disk inclination of 60 Degree-Sign . Higher inclinations produce higher masses and somewhat lower spins.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

IONIZED OUTFLOWS FROM COMPACT STEEP SPECTRUM SOURCES

Massive outflows are known to exist, in the form of extended emission-line regions (EELRs), around about one-third of powerful FR II radio sources. We investigate the origin of these EELRs by studying the emission-line regions around compact-steep-spectrum (CSS) radio galaxies that are younger (10{sup 3}-10{sup 5} yr old) versions of the FR II radio galaxies. We have searched for and analyzed the emission-line regions around 11 CSS sources by taking integral field spectra using Gemini Multi-Object Spectrograph on Gemini North. We fit the [O III] {lambda}5007 line and present the velocity maps for each detected emission-line region. We find, in most cases, that the emission-line regions have multi-component velocity structures with different velocity dispersions and/or flux distributions for each component. The velocity gradients of the emission-line gas are mostly well aligned with the radio axis, suggesting a direct causal link between the outflowing gas and the radio jets. The complex velocity structure may be a result of different driving mechanisms related to the onset of the radio jets. We also present the results from the line-ratio diagnostics we used to analyze the ionization mechanism of the extended gas, which supports the scenario where the emission-line regions are ionized by a combination of active galactic nucleus radiation and shock excitation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE COMPACT, TIME-VARIABLE RADIO SOURCE PROJECTED INSIDE W3(OH): EVIDENCE FOR A PHOTOEVAPORATED DISK?

We present new Karl G. Jansky Very Large Array (VLA) observations of the compact ({approx}0.''05), time-variable radio source projected near the center of the ultracompact H II region W3(OH). The analysis of our new data as well as of VLA archival observations confirms the variability of the source on timescales of years and for a given epoch indicates a spectral index of {alpha} = 1.3 {+-} 0.3 (S{sub {nu}}{proportional_to}{nu}{sup {alpha}}). This spectral index and the brightness temperature of the source ({approx}6500 K) suggest that we are most likely detecting partially optically thick free-free radiation. The radio source is probably associated with the ionizing star of W3(OH), but an interpretation in terms of an ionized stellar wind fails because the detected flux densities are orders of magnitude larger than expected. We discuss several scenarios and tentatively propose that the radio emission could arise in a static ionized atmosphere around a fossil photoevaporated disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

X-RAY OBSERVATIONS OF DISRUPTED RECYCLED PULSARS: NO REFUGE FOR ORPHANED CENTRAL COMPACT OBJECTS

We present a Chandra X-ray survey of the disrupted recycled pulsars (DRPs), isolated radio pulsars with P > 20 ms and B{sub s} < 3 Multiplication-Sign 10{sup 10} G. These observations were motivated as a search for the immediate descendants of the Almost-Equal-To 10 central compact objects (CCOs) in supernova remnants (SNRs), 3 of which have similar timing and magnetic properties as the DRPs, but are bright, thermal X-ray sources consistent with minimal neutron star (NS) cooling curves. Since none of the DPRs were detected in this survey, there is no evidence that they are ''orphaned'' CCOs, NSs whose SNRs has dissipated. Upper limits on their thermal X-ray luminosities are in the range of log L{sub x} [erg s{sup -1}] = 31.8-32.8, which implies cooling ages >10{sup 4}-10{sup 5} yr, roughly 10 times the ages of the Almost-Equal-To 10 known CCOs in a similar volume of the Galaxy. The order of a hundred CCO descendants that could be detected by this method are thus either intrinsically radio quiet or occupy a different region of (P, B{sub s} ) parameter space from the DRPs. This motivates a new X-ray search for orphaned CCOs among radio pulsars with larger B-fields, which could verify the theory that their fields are buried by the fall-back of supernova ejecta, but quickly regrow to join the normal pulsar population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ULTRA-COMPACT HIGH VELOCITY CLOUDS AS MINIHALOS AND DWARF GALAXIES

We present dark matter minihalo models for the Ultra-Compact, High-Velocity H I Clouds (UCHVCs) recently discovered in the 21 cm ALFALFA survey. We assume gravitational confinement of 10{sup 4} K H I gas by flat-cored dark-matter subhalos within the Local Group. We show that for flat cores, typical (median) tidally stripped cosmological subhalos at redshift z = 0 have dark-matter masses of ∼10{sup 7} M{sub ☉} within the central 300 pc (independent of total halo mass), consistent with the 'Strigari mass scale' observed in low-luminosity dwarf galaxies. Flat-cored subhalos also resolve the mass discrepancy between simulated and observed satellites around the Milky Way. For the UCHVCs, we calculate the photoionization-limited hydrostatic gas profiles for any distance-dependent total observed H I mass and predict the associated (projected) H I half-mass radii, assuming the clouds are embedded in distant (d ∼> 300 kpc) and unstripped subhalos. For a typical UCHVC (0.9 Jy km s{sup –1}), we predict physical H I half-mass radii of 0.18 to 0.35 kpc (or angular sizes of 0.'6 to 2.'1) for distances ranging from 300 kpc to 2 Mpc. As a consistency check, we model the gas-rich dwarf galaxy Leo T, for which there is a well-resolved H I column density profile and a known distance (420 kpc). For Leo T, we find that a subhalo with M{sub 300} = 8 (± 0.2) × 10{sup 6} M{sub ☉} best fits the observed H I profile. We derive an upper limit of P{sub HIM} ∼< 150 cm{sup –3} K for the pressure of any enveloping hot intergalactic medium gas at the distance of Leo T. Our analysis suggests that some of the UCHVCs may in fact constitute a population of 21 cm-selected but optically faint dwarf galaxies in the Local Group.

79 ASTRONOMY AND ASTROPHYSICS↗