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Li, S.

Publications and source records attributed to Li, S..

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

History of chemically and radiatively important atmospheric gases from the Advanced Global Atmospheric Gases Experiment (AGAGE)

In the ALE/GAGE/AGAGE global network program, continuous high frequency gas chromatographic measurements of four biogenic/anthropogenic gases (methane, CH4; nitrous oxide, N2O; hydrogen, H; and carbon monoxide, CO) and several anthropogenic gases that contribute to stratospheric ozone destruction and/or to the greenhouse effect have been carried out at five globally distributed sites for several years. The program, which began in 1978, is divided into three parts associated with three changes in instrumentation: the Atmospheric Lifetime Experiment (ALE), which used Hewlett Packard HP5840 gas chromatographs; the Global Atmospheric Gases Experiment (GAGE), which used HP5880 gas chromatographs; and the present Advanced GAGE (AGAGE). AGAGE uses two types of instruments: a gas chromatograph with multiple detectors (GC-MD), and a gas chromatograph with mass spectrometric analysis (GC-MS). Beginning in January 2004, an improved cryogenic preconcentration system (Medusa) replaced the absorption-desorption module in the GC-MS systems at Mace Head and Cape Grim; this provided improved capability to measure a broader range of volatile perfluorocarbons with high global warming potentials. More information may be found at the AGAGE home page: https://agage.mit.edu/instruments.In the latest update (Agage_gcmd_gcms_data_2020_07_04_tar.gz), all AGAGE data up to Sep. 2019 is included. A new compound, PFC-318, is also included in this update. For all released compounds and scales used by the AGAGE network, please see the "AGAGE_scale_2020_v2.pdf" file (included in "Agage_gcmd_gcms_data_2020_07_04_tar.gz").

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Searches for double beta decay of Xe 134 with EXO-200

Searches for double beta decay of 134 Xe were performed with EXO-200, a single-phase liquid xenon detector designed to search for neutrinoless double beta decay of 136 Xe. Using an exposure of 29.6 kg ∙ yr , the lower limits of T$2νββ\atop{1/2}$ > 8.7 × 10 20 yr and T$0νββ\atop{1/2}$ > 1.1 × 10 23 yr at 90% confidence level were derived, with corresponding half-life sensitivities of 1.2 × 10 21 yr and 1.9 × 10 23 yr . In conclusion, these limits exceed those in the literature for 134 Xe , improving by factors of nearly 10 5 and 2 for the two antineutrino and neutrinoless modes, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Random On-Board Pixel Sampling (ROPS) X-Ray Camera

Recent advances in compressed sensing theory and algorithms offer new possibilities for high-speed X-ray camera design. In many CMOS cameras, each pixel has an independent on-board circuit that includes an amplifier, noise rejection, signal shaper, an analog-to-digital converter (ADC), and optional in-pixel storage. When X-ray images are sparse, i.e., when one of the following cases is true: (a.) The number of pixels with true X-ray hits is much smaller than the total number of pixels; (b.) The X-ray information is redundant; or (c.) Some prior knowledge about the X-ray images exists, sparse sampling may be allowed. Here we first illustrate the feasibility of random on-board pixel sampling (ROPS) using an existing set of X-ray images, followed by a discussion about signal to noise as a function of pixel size. Next, we describe a possible circuit architecture to achieve random pixel access and in-pixel storage. The combination of a multilayer architecture, sparse on-chip sampling, and computational image techniques, is expected to facilitate the development and applications of high-speed X-ray camera technology.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Noise Characterization and Filtering in the MicroBooNE Liquid Argon TPC

The low-noise operation of readout electronics in a liquid argon time projection chamber (LArTPC) is critical to properly extract the distribution of ionization charge deposited on the wire planes of the TPC, especially for the induction planes. This paper describes the characteristics and mitigation of the observed noise in the MicroBooNE detector. The MicroBooNE's single-phase LArTPC comprises two induction planes and one collection sense wire plane with a total of 8256 wires. Current induced on each TPC wire is amplified and shaped by custom low-power, low-noise ASICs immersed in the liquid argon. The digitization of the signal waveform occurs outside the cryostat. Using data from the first year of MicroBooNE operations, several excess noise sources in the TPC were identified and mitigated. The residual equivalent noise charge (ENC) after noise filtering varies with wire length and is found to be below 400 electrons for the longest wires (4.7 m). The response is consistent with the cold electronics design expectations and is found to be stable with time and uniform over the functioning channels. This noise level is significantly lower than previous experiments utilizing warm front-end electronics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

A New Limit on CMB Circular Polarization from SPIDER

We present a new upper limit on cosmic microwave background (CMB) circular polarization from the 2015 flight of Spider, a balloon-borne telescope designed to search for B-mode linear polarization from cosmic inflation. Although the level of circular polarization in the CMB is predicted to be very small, experimental limits provide a valuable test of the underlying models. By exploiting the nonzero circular-to-linear polarization coupling of the half-wave plate polarization modulators, data from Spider's 2015 Antarctic flight provide a constraint on Stokes V at 95 and 150 GHz in the range 33<ℓ<307. No other limits exist over this full range of angular scales, and Spider improves on the previous limit by several orders of magnitude, providing 95% C.L. constraints on ℓ(ℓ+1)C{sub ℓ}{sup VV}/(2π) ranging from 141 to 255 μK{sup 2} at 150 GHz for a thermal CMB spectrum. As linear CMB polarization experiments become increasingly sensitive, the techniques described in this paper can be applied to obtain even stronger constraints on circular polarization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Probing the magnetic profile of diluted magnetic semiconductors using polarized neutron reflectivity

Room temperature ferromagnetism has been observed in the Cu doped ZnO films deposited under an oxygen partial pressure of 10 -3 and 10 -5 torr on Pt (200 nm)/Ti (45 nm)/Si (001) substrates using pulsed laser deposition. Due to the deposition at relatively high temperature (873 K), Cu and Ti atoms diffuse to the surface and interface, which significantly affects the magnetic properties. Depth sensitive polarized neutron reflectometry method provides the details of the composition and magnetization profiles and shows that an accumulation of Cu on the surface leads to an increase in the magnetization near the surface. Our results reveal that the presence of the copper at Zn sites induces ferromagnetism at room temperature, confirming intrinsic ferromagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay

Here, the Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW th reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective 239 Pu fission fractions F 239 from 0.25 to 0.35, Daya Bay measures an average IBD yield ¯σf of (5.90±0.13)×10 –43 cm 2 /fission and a fuel-dependent variation in the IBD yield, dσ f /dF 239 , of (–1.86±0.18)×10 –43 cm 2 /fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the 239 Pu fission fraction at 10 standard deviations. The variation in IBD yield is found to be energy dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1σ. This discrepancy indicates that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes 235 U, 239 Pu, 238 U, and 241 Pu. Based on measured IBD yield variations, yields of (6.17±0.17) and (4.27±0.26)×10 –43 cm 2 /fission have been determined for the two dominant fission parent isotopes 235 U and 239 Pu. A 7.8% discrepancy between the observed and predicted 235 U yields suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Trace radioactive impurities in final construction materials for EXO-200

Here, we report results from a systematic measurement campaign conducted to identify low radioactivity materials for the construction of the EXO-200 double beta decay experiment. Partial results from this campaign have already been reported in a 2008 paper by the EXO collaboration. Here we release the remaining data, collected since 2007, to the public. The data reported were obtained using a variety of analytic techniques. The measurement sensitivities are among the best in the field. We concluded the construction of the EXO-200 detector and Phase-I data was taken from 2011 to 2014. The detector’s extremely low background implicitly verifies the measurements and the analysis assumptions made during construction and reported in this paper.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment

Here, a measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GWth nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of ¯ν e ’s. Comparison of the ¯ν e rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (~1500–1950 m) relative to detectors near the reactors (~350–600 m) allowed a precise measurement of ¯ν e disappearance. More than 2.5 million ¯ν e inverse beta-decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (December, 2011–July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012–July, 2015). The ¯ν e rate observed at the far detectors relative to the near detectors showed a significant deficit, R = 0.949 ± 0.002(stat) ± 0.002(syst). The energy dependence of ¯ν e disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle sin 2 2θ 13 = 0.0841 ± 0.0027(stat) ± 0.0019(syst) and the effective neutrino mass-squared difference of |Δm 2 ee | = (2.50 ± 0.06(stat) ± 0.06(syst)) × 10 –3 eV 2 . Analysis using the exact three-flavor probability found Δm 2 32 = (2.45 ± 0.06(stat) ± 0.06(syst)) × 10 –3 eV 2 assuming the normal neutrino mass hierarchy and Δm 2 32 = (–2.56 ± 0.06(stat) ± 0.06(syst)) × 10 –3 eV 2 for the inverted hierarchy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Extended Calculations of Spectroscopic Data: Energy Levels, Lifetimes, and Transition Rates for O-like Ions from Cr xvii to Zn xxiii

Employing two state-of-the-art methods, multiconfiguration Dirac–Hartree–Fock and second-order many-body perturbation theory, the excitation energies and lifetimes for the lowest 200 states of the 2s{sup 2}2p{sup 4}, 2s2p{sup 5}, 2p{sup 6}, 2s{sup 2}2p{sup 3}3s, 2s{sup 2}2p{sup 3}3p, 2s{sup 2}2p{sup 3}3d, 2s2p{sup 4}3s, 2s2p{sup 4}3p, and 2s2p{sup 4}3d configurations, and multipole (electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2)) transition rates, line strengths, and oscillator strengths among these states are calculated for each O-like ion, from Cr xvii to Zn xxiii. Our two data sets are compared with the National Institute of Standards and Technology and CHIANTI compiled values, and previous calculations. The data are accurate enough for identification and deblending of new emission lines from the Sun and other astrophysical sources. The amount of high-accuracy data is significantly increased for the n = 3 states of several O-like ions of astrophysical interest, where experimental data are very scarce.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Improved measurement of the reactor antineutrino flux and spectrum at Daya Bay

Here, a new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GW th nuclear reactors and detected by eight antineutrino detectors deployed in two near (560 m and 600 m flux-weighted baselines) and one far (1640 m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946 ± 0.020 (0.992 ± 0.021) for the Huber+Mueller (ILL+Vogel) model. A 2.9σ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4$-$6 MeV was found in the measured spectrum, with a local significance of 4.4σ. Finally, a reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Nonlocal correlations in the orbital selective Mott phase of a one-dimensional multiorbital Hubbard model

Here, we study nonlocal correlations in a three-orbital Hubbard model defined on an extended one-dimensional chain using determinant quantum Monte Carlo and density matrix renormalization group methods. We focus on a parameter regime with robust Hund's coupling, which produces an orbital selective Mott phase (OSMP) at intermediate values of the Hubbard U , as well as an orbitally ordered ferromagnetic insulating state at stronger coupling. An examination of the orbital- and spin-correlation functions indicates that the orbital ordering occurs before the onset of magnetic correlations in this parameter regime as a function of temperature. In the OSMP, we find that the self-energy for the itinerant electrons is momentum dependent, indicating a degree of nonlocal correlations while the localized electrons have largely momentum independent self-energies. These nonlocal correlations also produce relative shifts of the holelike and electronlike bands within our model. The overall momentum dependence of these quantities is strongly suppressed in the orbitally ordered insulating phase.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Extended calculations with spectroscopic accuracy: Energy levels and transition properties for the fluorine-like isoelectronic sequence with Z = 24–30

We have performed extensive multiconfiguration Dirac–Hartree–Fock calculations and second-order many-body perturbation calculations for F-like ions with Z = 24–30. Energy levels and transition rates for electric dipole (E1), electric-quadrupole (E2), electric-octupole (E3), magnetic dipole (M1), and magnetic-quadrupole (M2) transitions, as well as radiative lifetimes, are provided for the lowest 200 levels belonging to the 1s{sup 2}2s{sup 2}2p{sup 5}, 1s{sup 2}2s2p{sup 6}, 1s{sup 2}2s{sup 2}2p{sup 4}3l, 1s{sup 2}2s2p{sup 5}3l, 1s{sup 2}2p{sup 6}3l, and 1s{sup 2}2s{sup 2}2p{sup 4}4l configurations of each ion. The results from the two sets of calculations are in excellent agreement. Extensive comparisons are also made with other theoretical results and observed data from the CHIANTI and NIST databases. The present energies and wavelengths are believed to be accurate enough to aid line identifications involving the n = 3 and n = 4 configurations, for which observations are largely missing. The calculated wavelengths and transition data will be useful in the modeling and diagnostics of astrophysical and fusion plasmas.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment

Here this Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the 2 x 10 -4 $\lesssim$| Δ$2\atop{41}$| $\lesssim$ 0.3 eV 2 . The resulting limits on sin 2 $2\theta$ 14 are improved by approximately a factor of two over previous results and constitute the most stringent constraints to date in the |Δm$2\atop{41}$| $\lesssim$ 0.2 eV 2 region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Extended relativistic configuration interaction and many-body perturbation calculations of spectroscopic data for the N ≤ 6 configurations in Ne-like ions between Cr xv and Kr xxvii

Level energies, wavelengths, electric dipole, magnetic dipole, electric quadrupole, and magnetic quadrupole transition rates, oscillator strengths, and line strengths from combined relativistic configuration interaction and many-body perturbation calculations are reported for the 201 fine-structure states of the 2s{sup 2}2p{sup 6}, 2s{sup 2}2p{sup 5}3l, 2s2p{sup 6}3l, 2s{sup 2}2p{sup 5}4l, 2s2p{sup 6}4l, 2s{sup 2}2p{sup 5}5l, and 2s{sup 2}2p{sup 5}6l configurations in all Ne-like ions between Cr xv and Kr xxvii. Calculated level energies and transition data are compared with experiments from the National Institute of Standards and Technology (NIST) and CHIANTI databases, and other recent benchmark calculations. The mean energy difference with the NIST experiments is only 0.05%. The present calculations significantly increase the amount of accurate spectroscopic data for the n > 3 states in a number of Ne-like ions of astrophysical interest. A complete data set should be helpful for analyzing new observations from solar and other astrophysical sources, and is also likely to be useful for modeling and diagnosing a variety of plasmas, including astronomical and fusion plasma.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Invited Article: A precise instrument to determine the Planck constant, and the future kilogram

A precise instrument, called a watt balance, compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and the Planck constant is established by the practical realization of the electrical units derived from the Josephson and the quantum Hall effects. We describe in this paper the fourth-generation watt balance at the National Institute of Standards and Technology (NIST), and report our initial determination of the Planck constant obtained from data taken in late 2015 and the beginning of 2016. A comprehensive analysis of the data and the associated uncertainties led to the SI value of the Planck constant, h = 6.626 069 83(22) × 10{sup −34} J s. The relative standard uncertainty associated with this result is 34 × 10{sup −9}.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗