共轴刚性双旋翼/机身干扰流场数值模拟

采用滑移网格技术求解Navier-Stokes(RANS)方程的方法,研究了共轴刚性双旋翼/机身的干扰问题。通过Caradonna-Tung旋翼、Robin直升机、Maryland直升机旋翼/机身干扰和Harrington 2共轴双旋翼等算例,验证了所提出的旋翼流场数值模拟方法的正确性。在此基础上,以Maryland机身为原型,分析了不同桨距的共轴刚性双旋翼与机身之间的干扰特性。结果表明:所提出的数值模拟方法能够很好地模拟共轴刚性双旋翼/机身的气动干扰特性;由于机身对于共轴刚性双旋翼下洗流场的阻滞作用,旋翼的悬停效率增加5%左右,并且随着拉力系数的增大使得悬停效率的增量更加明显;旋翼的悬停效率增加主要来源于下旋翼0°方位角附近的桨叶升力系数的增大,并且拉力系数的增量由桨根向桨尖方向逐渐减小

CMIP5模式对中国西北干旱区模拟能力评价/Evaluation of CMIP5 modes's simulation ability in the northwest arid areas of China[J]

气候模式是研究气候系统和气候变化的重要工具,气候模式结果是进行气候预测和气候变化风险评估的重要依据.基于中国西北干旱区78个气象站点1960-2005年的观测数据,对最新公布的CMIP5的39个模式在中国西北干旱区1960-2005年平均气温、降水的模拟能力进行评估.结果表明:多个模式模拟年平均气温与观测值的相关系数达到0.39,夏、秋季节的相关系数好于春、冬季,年平均气温模拟大多偏低2℃以上,其中MIROC4h、CCSM4和CMCC-CM对年平均气温的模拟绝对误差较小.模拟的年、季降水量与观测值的相关系数很差,均不到0.1.年降水量模拟普遍偏高100 mm以上,其中CMCC-CM、CNRM-CM5和MRI-CGCM3对年降水量模拟绝对误差较小.年际变化趋势上,模拟的平均气温升高趋势和降水量增加趋势均比观测趋势要低,模拟的冬季平均气温升高趋势偏低最明显,达-0.21℃/10 a,模拟夏季的降水量增加趋势偏低最明显,相对误差达-99％.CMIP5模式对中国西北干旱区的模拟效果整体上偏差较大,未来无论从物理过程还是模式算法都需要进一步研究和改进

Prediction of Energy Resolution in the JUNO Experiment

International audienceThis paper presents the energy resolution study in the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The study reveals an energy resolution of 2.95% at 1 MeV. Furthermore, the study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data taking. Moreover, it provides a guideline in comprehending the energy resolution characteristics of liquid scintillator-based detectors

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^