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Guo, Y.

Publications and source records attributed to Guo, Y..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Harmonic decomposition of three-particle azimuthal correlations at energies available at the BNL Relativistic Heavy Ion Collider

Here, we present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from √ s NN=7.7 to 200 GeV using the STAR detector. The quantity < cos(mΦ 1 +nΦ 2 –(m+n)Φ 3 ) >, with Φ being the azimuthal angles of the particles is evaluated as a function of √ s NN, collision centrality, transverse momentum, p T , pseudorapidity difference, Δη, and harmonics (m and n). These data provide detailed information on global event properties such as the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on Δη is observed for most harmonic combinations, which is consistent with breaking of longitudinal boost invariance. An interesting energy dependence is observed when one of the harmonics m,n, or m+n is equal to two, for which the correlators are dominated by the two-particle correlations relative to the second-harmonic event plane. These measurements can be used to constrain models of heavy-ion collisions over a wide range of temperature and baryon chemical potential.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Gearbox high-speed-stage bearing slip induced by electric excitation in a test facility

The goal of this paper is to investigate the behaviour of the high-speed stage of a wind turbine gearbox during transient grid-loss events triggered at different power levels in a full-scale nacelle dynamometer test. The gear mesh behaviour and the bearing roller slip during these events are characterized by strain measurements placed in the gear teeth roots and embedded in the outer rings of the tapered roller bearing locating pair. From our experiments, we conclude that the high-speed stage experiences a multidimensional loading consisting of bending and torsional deformation during the transient event. This loading propagates throughout the gearbox and results in unfavourable loading conditions at the bearing that have the potential to go beyond the preload during the torque reversals that occur during the grid-loss event. During the torque reversal, roller slip can occur in the bearings. It is observed that the slip behaviour is directly linked to the initial power level of the generator. Electrically induced excitation that typically leads to dynamic torque events can therefore cause mechanical gearbox degradation.

17 WIND ENERGY↗
DOE OSTI2018

Optimization of the Mechanical Properties and Residual Stresses in 2024 Aluminum Alloy Through Heat Treatment

Residual stresses induced during quenching of aluminum alloys cause dimensional instability and distortion. In this study, the effects of different concentrations of polyalkylene glycol (PAG) quenchants on residual stresses and mechanical properties of 2024 aluminum alloy were investigated. Surface residual stresses were measured by using hole-drilling strain-gauge method. Also, mechanical properties and microstructure of the heat-treated samples were analyzed using hardness measurements, tensile tests, and transmission electron microscopy. Results showed that quenching into a 15% polymeric solution and aging at 190 °C for 12 h cause 50% reduction in residual stress as compared with quenching in water at 20 °C and naturally aging. Moreover, tensile strength decreased by 104 MPa (~ 20%) in compared with the T6 sample.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Measurement of the H Λ 3 lifetime in Au+Au collisions at the BNL Relativistic Heavy Ion Collider [Measurement of the H Λ 3 lifetime in Au+Au collisions at the Relativistic Heavy Ion Collider]

Here, an improved measurement of the 3 Λ H lifetime is presented. In this paper, the mesonic decay modes 3 Λ H → 3 He + π – and 3 Λ H → d + p + π – are used to reconstruct the 3 Λ H from Au+Au collision data collected by the STAR collaboration at Relativistic Heavy Ion Collider (RHIC). A minimum χ2 estimation is used to determine the lifetime of τ = 142 +24 –21 (stat.) ± 29 (syst.) ps. This lifetime is about 50% shorter than the lifetime τ = 263 ± 2 ps of a free Λ, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R. ( 3 He+π – )/( B.R. ( 3 He+π – ) + B.R. (d+p+π – ) ) = 0.32 ± 0.05 (stat.) ± 0.08 (syst.). Our ratio result favors the assignment J( 3 Λ H) = 1/2 over J( 3 Λ H) = 3/2. These measurements will help to constrain models of hyperon-baryon interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗