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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR θ CYG, THE BRIGHTEST STAR OBSERVED BY THE KEPLER MISSION

θ Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star that was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were first obtained during Quarter 6 (2010 June–September) and subsequently in Quarters 8 and 12–17. We present analyses of solar-like oscillations based on Q6 and Q8 data, identifying angular degree l = 0, 1, and 2 modes with frequencies of 1000–2700 μ Hz, a large frequency separation of 83.9 ± 0.4 μ Hz, and maximum oscillation amplitude at frequency ν {sub max} = 1829 ± 54 μ Hz. We also present analyses of new ground-based spectroscopic observations, which, combined with interferometric angular diameter measurements, give T {sub eff} = 6697 ± 78 K, radius 1.49 ± 0.03 R {sub ⊙}, [Fe/H] = -0.02 ± 0.06 dex, and log g = 4.23 ± 0.03. We calculate stellar models matching these constraints using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses of 1.35–1.39 M {sub ⊙} and ages of 1.0–1.6 Gyr. θ Cyg’s T {sub eff} and log g place it cooler than the red edge of the γ Doradus instability region established from pre- Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show γ Dor gravity modes driven by the convective blocking mechanism, with frequencies of 1–3 cycles per day (11 to 33 μ Hz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 μ Hz) may be attributable to a faint, possibly background, binary.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Analysis of Sunyaev–Zel'dovich effect mass–observable relations using South Pole Telescope observations of an X-ray selected sample of low-mass galaxy clusters and groups

We use microwave observations from the South Pole Telescope (SPT) to examine the Sunyaev-Zel'dovich effect (SZE) signatures of a sample of 46 X-ray selected groups and clusters drawn from similar to 6 deg(2) of the XMM-Newton Blanco Cosmology Survey. These systems extend to redshift z = 1.02 and probe the SZE signal to the lowest X-ray luminosities (>= 10(42) erg s(-1)) yet; these sample characteristics make this analysis complementary to previous studies. We develop an analysis tool, using X-ray luminosity as a mass proxy, to extract selection-bias-corrected constraints on the SZE significance and Y-500 mass relations. The former is in good agreement with an extrapolation of the relation obtained from high-mass clusters. However, the latter, at low masses, while in good agreement with the extrapolation from the high-mass SPT clusters, is in tension at 2.8 sigma with the Planck constraints, indicating the low-mass systems exhibit lower SZE signatures in the SPT data. We also present an analysis of potential sources of contamination. For the radio galaxy point source population, we find 18 of our systems have 843 MHz Sydney University Molonglo Sky Survey sources within 2 arcmin of the X-ray centre, and three of these are also detected at significance >4 by SPT. Of these three, two are associated with the group brightest cluster galaxies, and the third is likely an unassociated quasar candidate. We examine the impact of these point sources on our SZE scaling relation analyses and find no evidence of biases. We also examine the impact of dusty galaxies using constraints from the 220 GHz data. The stacked sample provides 2.8 sigma significant evidence of dusty galaxy flux, which would correspond to an average underestimate of the SPT Y-500 signal that is (17 +/- 9) per cent in this sample of low-mass systems. Finally, we explore the impact of future data from SPTpol and XMM-XXL, showing that it will lead to a factor of 4 to 5 tighter constraints on these SZE mass-observable relations.

Liu, J.↗
DOE OSTI2011

Observation and studies of jet quenching in PbPb collisions at {radical}(s{sub NN})=2.76 TeV

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the Compact Muon Solenoid (CMS) detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 {mu}b{sup -1}. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cutoff used in this study (jet p{sub T}=120 GeV/c) up to the statistical limit of the available data sample (jet p{sub T}{approx_equal}210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Observation of a narrow mass state decaying into Υ(1S)+γ in pp̄ collisions at √s=1.96 TeV

Using data corresponding to an integrated luminosity of 1.3 fb⁻¹, we observe a narrow mass state decaying into Υ(1S)+γ, where the Υ(1S) meson is detected by its decay into a pair of oppositely charged muons, and the photon is identified through its conversion into an electron-positron pair. The significance of this observation is 5.6 standard deviations. The mass of the state is centered at 10.551±0.014(stat)±0.017(syst) GeV/c², which is consistent with that of the state recently observed by the ATLAS Collaboration.

Abazov, V. M.↗
DOE OSTI2011

First observation of radiative B⁰ → ΦK⁰γ decays and measurements of their time-dependent CP violation

We report the first observation of the radiative decay B⁰→ ΦK⁰γ using a data sample of 772 × 10⁶ BB¯ pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e⁻ collider. We observe a signal of 37 ± 8 events with a significance of 5.4 standard deviations including systematic uncertainties. The measured branching fraction is B(B⁰→ ΦK⁰γ) = (2.74±0.60±0.32)×10⁻⁶, where the uncertainties are statistical and systematic, respectively. We also report the first measurements of time-dependent CP-violation parameters: S ΦK⁰ S γ = +0.74 ⁺0.72 –1.05 (stat) +0.10 –0.24 (syst) and A ΦK⁰ S γ = +0.35 ± 0.58(stat) +0.23 –0.10 (syst). Furthermore, we measure B(B⁺ → ΦK⁺γ) = (2.48 ± 0.30 ± 0.24) × 10⁻⁶, ACP = –0.03 ± 0.11 ± 0.08 and find that the signal is concentrated in the M ΦK mass region near threshold.

Sahoo, Himansu B.↗
DOE OSTI2011

Observation of B - →$\bar{p}$ΛD 0 at Belle

We study B- meson decays to $\bar{p}$ΛD (*)0 final states using a sample of 657×10 6 B$\bar{B}$ events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. The observed branching fraction for B - →$\bar{p}$ΛD 0 is (1.43$+0.28\atop{-0.25}$±0.18)×10 -5 with a significance of 8.1 standard deviations, where the uncertainties are statistical and systematic, respectively. Most of the signal events have the $\bar{p}$ Λ mass peaking near threshold. No significant signal is observed for $\bar{p}$ΛD (*)0 and the corresponding upper limit on the branching fraction is 4.8×10 -5 at the 90% confidence level.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Correlations between jet-quenching observables at energies available at the BNL Relativistic Heavy Ion Collider

Focusing on four types of correlation plots, R{sub AA} versus v{sub 2}, R{sub AA} versus I{sub AA}, I{sub AA} versus v{sub 2}{sup I{sub AA}}, and v{sub 2} versus v{sub 2}{sup I{sub AA}}, we demonstrate how the centrality dependence of correlations between multiple jet quenching observables provide valuable insight into the energy loss mechanism in a quark-gluon plasma. In particular, we find that a qualitative energy loss model gives a good description of R{sub AA} versus v{sub 2} only when we take {Delta}E-I{sup 3} and a medium geometry generated by a model of the color glass condensate. This same {Delta}E-I{sup 3} model also qualitatively describes the trigger p{sub T} dependence of R{sub AA} versus I{sub AA} data and makes novel predictions for the centrality dependence for this R{sub AA} versus I{sub AA} correlation. Current data suggest, albeit with extremely large uncertainty, that v{sub 2}{sup I{sub AA}} >> v{sub 2}, a correlation that is difficult to reproduce in current energy loss models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Observation of the Baryonic B decay B0bar to Lambda_c^+ anti-Lambda K-

The authors report the observation of the baryonic B decay {bar B}{sup 0} {yields} {Lambda}{sub c}{sup +} {bar {Lambda}}K{sup -} with a significance larger than 7 standard deviations based on 471 x 10{sup 6} B{bar B} pairs collected with the BABAR detector at the PEP-II storage ring at SLAC. They measure the branching fraction for the decay {bar B}{sup 0} {yields} {Lambda}{sub c}{sup +} {bar {Lambda}}K{sup -} to be (3.8 {+-} 0.8{sub stat} {+-} 0.2{sub sys} {+-} 1.0 {sub {Lambda}{sub c}{sup +}}) x 10{sup -5}. The uncertainties are statistical, systematic, and due to the uncertainty in the {Lambda}{sub c}{sup +} branching fraction. They find that the {Lambda}{sub c}{sup +} K{sup -} invariant mass distribution shows an enhancement above 3.5 GeV/c{sup 2}.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Observation of the Rare Decay B+ \to K+pi0pi0 and Measurement of the Quasi-two Body Contributions B+ \to K*(892)+pi0, B+ \to f0(980)K+ and B+ \to chic0K+

We report an analysis of charmless hadronic decays of charged B mesons to the final state K{sup +}{pi}{sup 0}{pi}{sup 0}, using a data sample of (470.9 {+-} 2.8) x 10{sup 6} B{bar B} events collected with the BABAR detector at the {Gamma}(4S) resonance. We observe an excess of signal events, with a significance above 10 standard deviations including systematic uncertainties, and measure the branching fraction and CP asymmetry to be {Beta}(B{sup +} {yields} K{sup +}{pi}{sup 0}{pi}{sup 0}) = (16.2 {+-} 1.2 {+-} 1.5) x 10{sup -6} and A{sub CP}(B{sup +} {yields} K{sup +}{pi}{sup 0}{pi}{sup 0}) = -0.06 {+-} 0.06 {+-} 0.04, where the uncertainties are statistical and systematic, respectively. Additionally, we study the contributions of the B{sup +} {yields} K{sup +}(892){sup +}{pi}{sup 0}, B{sup +} {yields} f{sub 0}(980)K{sup +}, and B{sup +} {yields} {chi}{sub c0}K{sup +} quasi-two-body decays. We report the world's best measurements of the branching fraction and CP asymmetry of the B{sup +} {yields} K{sup +}{pi}{sup 0}{pi}{sup 0} and B{sup +} {yields} K{sup +}(892){sup +}{pi}{sup 0} channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Correlation between human observer performance and model observer performance in differential phase contrast CT

Purpose: With the recently expanding interest and developments in x-ray differential phase contrast CT (DPC-CT), the evaluation of its task-specific detection performance and comparison with the corresponding absorption CT under a given radiation dose constraint become increasingly important. Mathematical model observers are often used to quantify the performance of imaging systems, but their correlations with actual human observers need to be confirmed for each new imaging method. This work is an investigation of the effects of stochastic DPC-CT noise on the correlation of detection performance between model and human observers with signal-known-exactly (SKE) detection tasks.Methods: The detectabilities of different objects (five disks with different diameters and two breast lesion masses) embedded in an experimental DPC-CT noise background were assessed using both model and human observers. The detectability of the disk and lesion signals was then measured using five types of model observers including the prewhitening ideal observer, the nonprewhitening (NPW) observer, the nonprewhitening observer with eye filter and internal noise (NPWEi), the prewhitening observer with eye filter and internal noise (PWEi), and the channelized Hotelling observer (CHO). The same objects were also evaluated by four human observers using the two-alternative forced choice method. The results from the model observer experiment were quantitatively compared to the human observer results to assess the correlation between the two techniques.Results: The contrast-to-detail (CD) curve generated by the human observers for the disk-detection experiments shows that the required contrast to detect a disk is inversely proportional to the square root of the disk size. Based on the CD curves, the ideal and NPW observers tend to systematically overestimate the performance of the human observers. The NPWEi and PWEi observers did not predict human performance well either, as the slopes of their CD curves tended to be steeper. The CHO generated the best quantitative agreement with human observers with its CD curve overlapping with that of human observer. Statistical equivalence between CHO and humans can be claimed within 11% of the human observer results, including both the disk and lesion detection experiments.Conclusions: The model observer method can be used to accurately represent human observer performance with the stochastic DPC-CT noise for SKE tasks with sizes ranging from 8 to 128 pixels. The incorporation of the anatomical noise remains to be studied.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Direct observations of crystal defects in polycrystalline diamond

Highlights: • Electron channeling contrast imaging of crystal defects in polycrystalline diamond • Introducing acid etching as a novel protocol for diamond surface preparation • Characterization of {111} twins, {111} stacking faults and {111} helical dislocations in diamond using ECCI and EBSD - Abstract: Crystal defects are abundant in synthetic diamond produced by chemical vapor deposition (CVD). We present the first images of crystal defects in a bulk polycrystalline CVD diamond sample using general electron channeling contrast imaging (ECCI) in a field emission scanning electron microscope (FE-SEM). For enhancement of channeling contrast of this material, we introduce a novel protocol for diamond surface preparation that involves acid etching. Using this protocol, we imaged three types of crystal defects including twins, stacking faults and dislocations. Each defect was identified based on its appearance in electron channeling contrast (ECC) micrographs. We analyzed grains containing twins and dislocations using electron backscatter diffraction (EBSD) crystal orientation mapping. We found a large population of grains that contained Σ3 type twins on {111} planes with a 60°<111> angle–axis pair of misorientation for twin boundaries. In addition, we identified {111} stacking faults and {111} helical dislocations. These observations are in agreement with reports of crystal defects in CVD diamond thin foils studied by a transmission electron microscope (TEM).

36 MATERIALS SCIENCE↗
DOE OSTI2014

A method to determine fault vectors in 4H-SiC from stacking sequences observed on high resolution transmission electron microscopy images

A new method has been developed to determine the fault vectors associated with stacking faults in 4H-SiC from their stacking sequences observed on high resolution TEM images. This method, analogous to the Burgers circuit technique for determination of dislocation Burgers vector, involves determination of the vectors required in the projection of the perfect lattice to correct the deviated path constructed in the faulted material. Results for several different stacking faults were compared with fault vectors determined from X-ray topographic contrast analysis and were found to be consistent. This technique is expected to applicable to all structures comprising corner shared tetrahedra.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K{sub 2}CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K{sub 2}CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

36 MATERIALS SCIENCE↗