分类: 物理学 >> 核物理学 提交时间: 2023-06-09 合作期刊: 《Nuclear Science and Techniques》
摘要: Core axial power distribution is an essential topic in pressurized water reactor (PWR) reactivity control. Traditional PWRs limit stability against axial core power oscillations at a high-cycle burnup. Because the “camel” peak power shape typically occurs with increasing depletion, the approaches used for the axial power control deserve special attention. This study aims to investigate the performance of different gadolinium rod design schemes in core axial power control during power operation based on the reactivity balance strategy, and to propose new multi-concentration gadolinium rod design schemes. In the new design schemes, low-concentration gadolinium pellets are filled in the axial hump part of the gadolinium rod, and high-concentration gadolinium pellets are filled in the other parts. The impact of different gadolinium rod design schemes on the main core characteristics was evaluated using the nuclear design code package PCM developed by CGN. The results show that the new gadolinium rod design significantly impacts the core axial power shape. The new design schemes can efficiently improve the core axial power distribution along the entire cycle by reducing the core axial power peak at the end of a cycle, enhancing the reactor operation stability, and achieving a better core safety margin, revealing a sizeable potential application.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present ALMA Band-3/7 observations towards "the Heart" of a massive hub-filament system (HFS) SDC335, to investigate its fragmentation and accretion. At a resolution of $\sim0.03$ pc, 3 mm continuum emission resolves two massive dense cores MM1 and MM2, with $383(^{+234}_{-120})$ $M_\odot$ (10-24% mass of "the Heart") and $74(^{+47}_{-24})$ $M_\odot$, respectively. With a resolution down to 0.01 pc, 0.87 mm continuum emission shows MM1 further fragments into six condensations and multi-transition lines of H$_2$CS provide temperature estimation. The relation between separation and mass of condensations at a scale of 0.01 pc favors turbulent Jeans fragmentation where the turbulence seems to be scale-free rather than scale-dependent. We use the H$^{13}$CO$^+$ (1-0) emission line to resolve the complex gas motion inside "the Heart" in position-position-velocity space. We identify four major gas streams connected to large-scale filaments, inheriting the anti-clockwise spiral pattern. Along these streams, gas feeds the central massive core MM1. Assuming an inclination angle of $45(\pm15)^{\circ}$ and a H$^{13}$CO$^+$ abundance of $5(\pm3)\times10^{-11}$, the total mass infall rate is estimated to be $2.40(\pm0.78)\times10^{-3}$ $M_\odot$ yr$^{-1}$, numerically consistent with the accretion rates derived from the clump-scale spherical infall model and the core-scale outflows. The consistency suggests a continuous, near steady-state, and efficient accretion from global collapse, therefore ensuring core feeding. Our comprehensive study of SDC335 showcases the detailed gas kinematics in a prototypical massive infalling clump and calls for further systematic and statistical analyses in a large sample.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present ALMA Band-3/7 observations towards "the Heart" of a massive hub-filament system (HFS) SDC335, to investigate its fragmentation and accretion. At a resolution of $\sim0.03$ pc, 3 mm continuum emission resolves two massive dense cores MM1 and MM2, with $383(^{+234}_{-120})$ $M_\odot$ (10-24% mass of "the Heart") and $74(^{+47}_{-24})$ $M_\odot$, respectively. With a resolution down to 0.01 pc, 0.87 mm continuum emission shows MM1 further fragments into six condensations and multi-transition lines of H$_2$CS provide temperature estimation. The relation between separation and mass of condensations at a scale of 0.01 pc favors turbulent Jeans fragmentation where the turbulence seems to be scale-free rather than scale-dependent. We use the H$^{13}$CO$^+$ (1-0) emission line to resolve the complex gas motion inside "the Heart" in position-position-velocity space. We identify four major gas streams connected to large-scale filaments, inheriting the anti-clockwise spiral pattern. Along these streams, gas feeds the central massive core MM1. Assuming an inclination angle of $45(\pm15)^{\circ}$ and a H$^{13}$CO$^+$ abundance of $5(\pm3)\times10^{-11}$, the total mass infall rate is estimated to be $2.40(\pm0.78)\times10^{-3}$ $M_\odot$ yr$^{-1}$, numerically consistent with the accretion rates derived from the clump-scale spherical infall model and the core-scale outflows. The consistency suggests a continuous, near steady-state, and efficient accretion from global collapse, therefore ensuring core feeding. Our comprehensive study of SDC335 showcases the detailed gas kinematics in a prototypical massive infalling clump and calls for further systematic and statistical analyses in a large sample.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: Within the factorization-assisted topological-amplitude approach, we studied the 33 charmless B(s) → VV decays, where V stands for a light vector meson. According to the flavor flows, the amplitude of each process can be decomposed into 8 different topologies. In contrast to the conventional flavor diagrammatic approach, we further factorize each topological amplitude into decay constant, form factors and unknown universal parameters. By χ2 fitting 46 experimental observables, we extracted 10 theoretical parameters with χ2 per degree of freedom around 2. Using the fitted parameters, we calculated the branching fractions, polarization fractions, CP asymmetries and relative phases between polarization amplitudes of each decay mode. The decay channels dominated by tree diagram have large branching fractions and large longitudinal polarization fraction. The branching fractions and longitudinal polarization fractions of color-suppressed decays become smaller. Current experimental data of large transverse polarization fractions in the penguin dominant decay channels can be explained by only one transverse amplitude of penguin annihilation dia-gram. Our predictions of those not yet measured channels can be tested in the ongoing LHCb experiment and the Belle-II experiment in future.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: From the overlap lattice quark propagator calculated in the Landau gauge, we determine the quark chiral condensate by fitting operator product expansion formulas to the lattice data. The quark propagators are computed on domain wall fermion configurations generated by the RBC-UKQCD Col-laborations with Nf = 2 + 1 flavors. Three ensembles with different light sea quark masses are used at one lattice spacing 1/a = 1.75(4) GeV. We obtain ψ¯ψMS(2 GeV) = (−305(15)(21) MeV)3 in the SU(2) chiral limit.