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Li, Y.

Publications and source records attributed to Li, Y..

At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Polarization Transfer in Wide-Angle Compton Scattering and Single-Pion Photoproduction from the Proton

Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of theta(p)(cm) cm = 70 degrees. The longitudinal transfer K-LL, measured to be 0.645 +/- 0.059 +/- 0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton. However, the observed value is similar to 3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

CHROMOSPHERIC EVAPORATION IN AN X1.0 FLARE ON 2014 MARCH 29 OBSERVED WITH IRIS AND EIS

Chromospheric evaporation refers to dynamic mass motions in flare loops as a result of rapid energy deposition in the chromosphere. These motions have been observed as blueshifts in X-ray and extreme-ultraviolet (EUV) spectral lines corresponding to upward motions at a few tens to a few hundreds of km s{sup −1}. Past spectroscopic observations have also revealed a dominant stationary component, in addition to the blueshifted component, in emission lines formed at high temperatures (∼10 MK). This is contradictory to evaporation models predicting predominant blueshifts in hot lines. The recently launched Interface Region Imaging Spectrograph (IRIS) provides high-resolution imaging and spectroscopic observations that focus on the chromosphere and transition region in the UV passband. Using the new IRIS observations, combined with coordinated observations from the EUV Imaging Spectrometer, we study the chromospheric evaporation process from the upper chromosphere to the corona during an X1.0 flare on 2014 March 29. We find evident evaporation signatures, characterized by Doppler shifts and line broadening, at two flare ribbons that are separating from each other, suggesting that chromospheric evaporation takes place in successively formed flaring loops throughout the flare. More importantly, we detect dominant blueshifts in the high-temperature Fe xxi line (∼10 MK), in agreement with theoretical predictions. We also find that, in this flare, gentle evaporation occurs at some locations in the rise phase of the flare, while explosive evaporation is detected at some other locations near the peak of the flare. There is a conversion from gentle to explosive evaporation as the flare evolves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Conducting mechanisms of forming-free TiW/Cu{sub 2}O/Cu memristive devices

P-type Cu{sub 2}O is a promising CMOS-compatible candidate to fabricate memristive devices for next-generation memory, logic and neuromorphic computing. In this letter, the microscopic switching and conducting mechanisms in TiW/Cu{sub 2}O/Cu memristive devices have been thoroughly investigated. The bipolar resistive switching behaviors without an electro-forming process are ascribed to the formation and rupture of the conducting filaments composed of copper vacancies. In the low resistive state, the transport of electrons in the filaments follows Mott's variable range hopping theory. When the devices switch back to high resistive state, the coexistence of Schottky emission at the Cu/Cu{sub 2}O interface and electron hopping between the residual filaments is found to dominate the conducting process. Our results will contribute to the further understanding and optimization of p-type memristive materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Reduced carbon emission estimates from fossil fuel combustion and cement production in China

Nearly three-quarters of the growth in global carbon emissions from the burning of fossil fuels and cement production between 2010 and 2012 occurred in China. Yet estimates of Chinese emissions remain subject to large uncertainty; inventories of China’s total fossil fuel carbon emissions in 2008 differ by 0.3 gigatonnes of carbon, or 15 per cent. The primary sources of this uncertainty are conflicting estimates of energy consumption and emission factors, the latter being uncertain because of very few actual measurements representative of the mix of Chinese fuels. Here we re-evaluate China’s carbon emissions using updated and harmonized energy consumption and clinker production data and two new and comprehensive sets of measured emission factors for Chinese coal. We find that total energy consumption in China was 10 per cent higher in 2000–2012 than the value reported by China’s national statistics, that emission factors for Chinese coal are on average 40 per cent lower than the default values recommended by the Intergovernmental Panel on Climate Change, and that emissions from China’s cement production are 45 per cent less than recent estimates. Altogether, our revised estimate of China’s CO 2 emissions from fossil fuel combustion and cement production is 2.49 gigatonnes of carbon (2 standard deviations = ±7.3 per cent) in 2013, which is 14 per cent lower than the emissions reported by other prominent inventories. Over the full period 2000 to 2013, our revised estimates are 2.9 gigatonnes of carbon less than previous estimates of China’s cumulative carbon emissions. Our findings suggest that overestimation of China’s emissions in 2000–2013 may be larger than China’s estimated total forest sink in 1990–2007 (2.66 gigatonnes of carbon) or China’s land carbon sink in 2000–2009 (2.6 gigatonnes of carbon).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

GaAs quantum dot solar cell under concentrated radiation

Effects of concentrated solar radiation on photovoltaic performance are investigated in well-developed GaAs quantum dot (QD) solar cells with 1-Sun efficiencies of 18%–19%. In these devices, the conversion processes are enhanced by nanoscale potential barriers and/or AlGaAs atomically thin barriers around QDs, which prevent photoelectron capture to QDs. Under concentrated radiation, the short circuit current increases proportionally to the concentration and the open circuit voltage shows the logarithmic increase. In the range up to hundred Suns, the contributions of QDs to the photocurrent are proportional to the light concentration. The ideality factors of 1.1–1.3 found from the V{sub OC}-Sun characteristics demonstrate effective suppression of recombination processes in barrier-separated QDs. The conversion efficiency shows the wide maximum in the range of 40–90 Suns and reaches 21.6%. Detailed analysis of I-V-Sun characteristics shows that at low intensities, the series resistance decreases inversely proportional to the concentration and, at ∼40 Suns, reaches the plateau determined mainly by the front contact resistance. Improvement of contact resistance would increase efficiency to above 24% at thousand Suns.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Multipactor threshold calculation of coaxial transmission lines in microwave applications with nonstationary statistical theory

This paper presents a statistical theory for the initial onset of multipactor breakdown in coaxial transmission lines, taking both the nonuniform electric field and random electron emission velocity into account. A general numerical method is first developed to construct the joint probability density function based on the approximate equation of the electron trajectory. The nonstationary dynamics of the multipactor process on both surfaces of coaxial lines are modelled based on the probability of various impacts and their corresponding secondary emission. The resonant assumption of the classical theory on the independent double-sided and single-sided impacts is replaced by the consideration of their interaction. As a result, the time evolutions of the electron population for exponential growth and absorption on both inner and outer conductor, in response to the applied voltage above and below the multipactor breakdown level, are obtained to investigate the exact mechanism of multipactor discharge in coaxial lines. Furthermore, the multipactor threshold predictions of the presented model are compared with experimental results using measured secondary emission yield of the tested samples which shows reasonable agreement. Finally, the detailed impact scenario reveals that single-surface multipactor is more likely to occur with a higher outer to inner conductor radius ratio.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases

Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of transition-group d-metals and main-group p-elements. Here, we report the realization of FSMAs in Heusler phases that completely consist of d metals. By introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is obtained and the martensitic transformation temperature is decreased efficiently. Strong ferromagnetism is established by further doping Co atoms into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the magnetic-field-induced martensitic transformations, collective multifunctional properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only facilitate the formation of B2-type Heusler phases but also establish strong ferromagnetic coupling and offer the possibility to tune the martensitic transformation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Top-off Safety Analysis for XFP (17BM) Beamline

The purpose of this report is to analyze the top off safety of XFP beamline, which was not covered by the top off design report issued in 2014. XFP beamline has a mirror in front end (FE) to provide a vertical offset on the ratchet wall collimator aperture. This report will only be used as a basis to approve the topoff operation of XFP beamline. The topoff operation of new beamlines and the approval process is guarded by procedure PS-C-ASD-PRC-183. The primary radiological safety concern for the top-off injection, with the FE safety shutters open, is the scenario where injected electrons could be conveyed down to the beam line through the front end. With the mirror offset, the electrons can never escape FE to reach the first optical enclosure (FOE). So the worst scenario will be the electrons propagating to farthest downstream in FE, and the radiological effect of this fault condition is discussed in this note.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Evidence for the decay B 0 → η π 0

In this work, we report a search for the charmless hadronic decay B 0 → η π 0 with a data sample corresponding to an integrated luminosity of 694 fb - 1 containing 753 × 1 0 6 B B ¯ pairs. The data were collected by the Belle experiment running on the Υ ( 4 S ) resonance at the KEKB e + e - collider. We measure a branching fraction B ( B 0 → η π 0 ) = ( 4. 1 - 1.5 - 0.7 + 1.7 + 0.5 ) × 1 0 - 7 , where the first uncertainty is statistical and the second is systematic. Our measurement gives an upper limit of B ( B 0 → η π 0 ) < 6.5 × 1 0 - 7 at 90% confidence level. Finally, the signal has a significance of 3.0 standard deviations and constitutes the first evidence for this decay mode.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Complex structural dynamics of nanocatalysts revealed in Operando conditions by correlated imaging and spectroscopy probes

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions. Here by a correlated use of synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy in operando conditions, we quantitatively describe the complex structural dynamics of supported Pt catalysts exhibited during an exemplary catalytic reaction—ethylene hydrogenation. This work exploits a microfabricated catalytic reactor compatible with both probes. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans a broad size range throughout changing reaction conditions. Lastly, this method is generalizable to quantitative operando studies of complex systems using a wide variety of X-ray and electron-based experimental probes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2015

Three-Dimensional Vibration Isolator for Suppressing High-Frequency Responses for Sage III Contamination Monitoring Package (CMP)

The Stratospheric Aerosol and Gas Experiment (SAGE) III - International Space Station (ISS) instrument will be used to study ozone, providing global, long-term measurements of key components of the Earth's atmosphere for the continued health of Earth and its inhabitants. SAGE III is launched into orbit in an inverted configuration on SpaceX;s Falcon 9 launch vehicle. As one of its four supporting elements, a Contamination Monitoring Package (CMP) mounted to the top panel of the Interface Adapter Module (IAM) box experiences high-frequency response due to structural coupling between the two structures during the SpaceX launch. These vibrations, which were initially observed in the IAM Engineering Development Unit (EDU) test and later verified through finite element analysis (FEA) for the SpaceX launch loads, may damage the internal electronic cards and the Thermoelectric Quartz Crystal Microbalance (TQCM) sensors mounted on the CMP. Three-dimensional (3D) vibration isolators were required to be inserted between the CMP and IAM interface in order to attenuate the high frequency vibrations without resulting in any major changes to the existing system. Wire rope isolators were proposed as the isolation system between the CMP and IAM due to the low impact to design. Most 3D isolation systems are designed for compression and roll, therefore little dynamic data was available for using wire rope isolators in an inverted or tension configuration. From the isolator FEA and test results, it is shown that by using the 3D wire rope isolators, the CMP high-frequency responses have been suppressed by several orders of magnitude over a wide excitation frequency range. Consequently, the TQCM sensor responses are well below their qualification environments. It is indicated that these high-frequency responses due to the typical instrument structural coupling can be significantly suppressed by a vibration passive control using the 3D vibration isolator. Thermal and contamination issues were also examined during the isolator selection period for meeting the SAGE III-ISS instrument requirements.

Li, Y.↗
DOE OSTI2015

Measurement of e + e - → π + π - ψ ( 2 S ) via initial state radiation at Belle

We report here measurement of the cross section of e + e - → π + π - ψ ( 2 S ) between 4.0 and 5.5 GeV, based on an analysis of initial state radiation events in a 980 fb - 1 data sample recorded with the Belle detector. The properties of the Y ( 4360 ) and Y ( 4660 ) states are determined. Fitting the mass spectrum of π + π - ψ ( 2 S ) with two coherent Breit-Wigner functions, we discover two solutions with identical mass and width but different couplings to electron-positron pairs: M Y ( 4360 ) = ( 4347 ± 6 ± 3 ) MeV / c 2 , Γ Y ( 4360 ) = ( 103 ± 9 ± 5 ) MeV , M Y ( 4660 ) = ( 4652 ± 10 ± 8 ) MeV / c 2 , Γ Y ( 4660 ) = ( 68 ± 11 ± 1 ) MeV ; and B [ Y ( 4360 ) → π + π - ψ ( 2 S ) ] · Γ Y ( 4360 ) e + e - = ( 10.9 ± 0.6 ± 0.7 ) eV and B [ Y ( 4660 ) → π + π - ψ ( 2 S ) ] · Γ Y ( 4660 ) e + e - = ( 8.1 ± 1.1 ± 0.5 ) eV for one solution; or B [ Y ( 4360 ) → π + π - ψ ( 2 S ) ] · Γ Y ( 4360 ) e + e - = ( 9.2 ± 0.6 ± 0.6 ) eV and B [ Y ( 4660 ) → π + π = ψ ( 2 S ) ] · Γ Y ( 4660 ) e + e - = ( 2.0 ± 0.3 ± 0.2 ) eV for the other. Here, the first errors are statistical and the second systematic. Evidence for a charged charmoniumlike structure at 4.05 GeV / c 2 is observed in the π ± ψ ( 2 S ) intermediate state in the Y ( 4360 ) decays. decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

New model of calculating the energy transfer efficiency for the spherical theta-pinch device

Ion-beam-plasma-interaction plays an important role in the field of warm dense matter and inertial confinement fusion. A spherical theta pinch is proposed to act as a plasma target in various applications including a plasma stripper cell. One key parameter for such applications is the free electron density. A linear dependency of this density to the amount of energy transferred into the plasma from an energy storage was found by Teske. Since the amount of stored energy is known, the energy transfer efficiency is a reliable parameter for the design of a spherical theta pinch device. As the main assumption of a constant reflected plasma resistance is contradictory by the measured data, the traditional two models of energy transfer efficiency will lead to wrong results. From measurements, the parasitic resistance is derived as constant. Based on this key parameter, a new model is proposed. Due to no assumption, the new model is considered as exact. Further, a comparison of these three different models is given at a fixed operation voltage for the full range of working gas pressures. Due to the inappropriate assumptions included in the traditional models, one owns a tendency to overestimate the energy transfer efficiency whereas the other leads to an underestimation. Applying our new model to a wide spread set of operation voltages and gas pressures, an overall picture of the energy transfer efficiency results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Thickness-dependent charge ordering state in Bi{sub 0.4}Sr{sub 0.28}Ca{sub 0.32}MnO{sub 3} thin films under the anisotropic strain

We have achieved clear charge ordering (CO) state in Ca doped Bi{sub 0.4}Sr{sub 0.6−x}Ca{sub x}MnO{sub 3} (BSCMO) films on (110)-orientated SrTiO{sub 3}. The BSCMO film's CO transition temperature (T{sub CO}) was tuned to room temperature (RT) by optimum doping Ca (x = 0.32). Asymmetric x-ray reciprocal space mapping was used to determine the structure evolution of the films with thickness, in detail, under the anisotropic stress in films. We found that the CO phase only appears in thicker films, accompanied by an unique distortion in structure, in which twin-domains structure occurs with the [110] axis slightly tilting toward [1–10] and [−110] directions. The results demonstrate the effects of anisotropic stress on the structure and electronic phases in BSCMO films as thickness increases. Our works are valuable for allowing a RT study in the CO film and further operation of the devices for a practical use.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural transitions, magnetic properties, and electronic structures of Co(Fe)-doped MnNiSi compounds

The structural transitions, magnetic properties, and electronic structures of Co(Fe)-doped MnNiSi compounds are investigated by x-ray powder diffraction, differential scanning calorimetry (DSC), magnetic measurements, and first-principles calculations. Results indicate that all samples undergo a martensitic transition from the Ni{sub 2}In-type parent phase to TiNiSi-type orthorhombic phase at high temperatures. The substitution of Co(Fe) for Mn in Mn{sub 1−x}Co{sub x}NiSi (x = 0.2, 0.3, and 0.4) and Mn{sub 1−y}Fe{sub y}NiSi (y = 0.26, 0.30, 0.36, 0.46, and 0.55) samples decreases the structural transition temperature and Curie temperature of martensite. The martensite phases show a typical ferromagnetic behavior with saturation field being basically unchanged with increasing Co(Fe) content, while the saturation magnetization shows a decreasing tendency. The theoretically calculated moments are in good agreement with the experimentally measured results. The orbital hybridizations between different 3d elements are analyzed from the distribution of density of states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

NSLS-II injector commissioning and initial operation

The injector for the National Synchrotron Light Source II (NSLS-II) storage ring consists of a 3 GeV booster synchrotron and a 200 MeV S-band linac. The linac was designed to produce either a single bunch with a charge of 0.5 nC of electrons or a train of bunches up to 300 ns long containing a total charge of 15 nC. The booster was designed to accelerate up to 15 nC each cycle in a train of bunches up to 300 ns long. Linac commissioning was completed in April 2012. Booster commissioning was started in November 2013 and completed in March 2014. All of the significant design goals were satisfied including beam emittance, energy spread, and transport efficiency. While the maximum booster charge accelerated was only 10 nC, this has proven to be more than sufficient for storage ring commissioning and operation. The injector has operated reliably during storage ring operation since then. Results will be presented showing measurements of linac and booster operating parameters achieved during commissioning and initial operation. Operating experience and reliability during the first year of NSLS-II operation will be discussed.

43 PARTICLE ACCELERATORS↗