Characteristics of a 4-fold segmented clover detectore

Four high-purity germanium 4-fold segmented Clover detectors have been applied in the experiment of neutron-rich nucleus 21N. The performance of those four Clovers have been tested with radioactive sources and in-beam experiments, and the main results including energy resolution, peak-to-total ratios, the variation of the hit pattern distribution in different crystals of one Clover detector with the energy of γ ray, and absolute full energy peak detection effciency curve, were presented.     

低温压力容器补强圈的优化设计北大核心

开孔结构作为低温压力容器最薄弱的部位,对其进行优化设计十分必要。采用ANSYS有限元分析软件,对圆柱筒体上相同管径的接管补强圈进行静力模拟分析。计算内容包括:补强圈最佳径厚比(半径长与厚度的比值);最佳补偿金属量。模拟结果表明:在径厚比为8. 7时,该比例补强圈对减少应力集中的效果最为显著;补强圈金属量增加,应力峰值降低;在控制补强圈直径上限大小的规定下,补强圈金属量为等面积补偿法所计算的补偿金属量的1. 4倍时,对减少结构应力峰值的效果较好且符合行业制造标准。可为低温压力容器开孔设计及生产制造提供参考。     

Rare Decay B_c → D_s *μ~+ μ~- in a Family Non-Universal Z′ Model

Using the form factors calculated in the three-point QCD sum rules, we calculate the new physics contributions to the physical observables of B c → Ds* μ+ μ decay in a family non-universal Z′ model. Under the consideration of three cases of the new physics parameters, we find that: (a) the Z′ boson can provide large contributions to the differential decay rates; (b) the forward-backward asymmetry (FBA) can be increased by about 47%, 38%, and 110% at most in S1, S2, and extreme limit values (ELV), respectively. In addition, the zero crossing can be shifted in all the cases; (c) when s 0.08, the value of P L can be changed from 1 in the Standard Model (SM) to 0.5 in S1, 0.6 in S2, and 0 in extreme limit values, respectively; (d) the new physics corrections to P T will decrease the SM prediction about 25% for the cases of S1     

亚临界雷诺数下圆柱受迫振动的数值研究

在Navier-Stokes方程和k-ω湍流模型的基础上,利用流线迎风有限元方法结合ALE动网格技术对亚临界雷诺数下的圆柱受迫振动问题开展了数值模拟研究。本文的数值模型成功模拟了Re=5000条件下,圆柱发生受迫振动时尾迹区内的2S,2P和P+S尾流模式;对Re=10000情况下,无量纲振幅分别为0.3,0.4,0.5的圆柱受迫振动问题开展了数值模拟,分析了给定振幅条件下圆柱受力随振动频率的变化关系以及受迫振动的锁定区间。以上数值计算结果与Gopalkrishnan (1993)的实验结果基本符合。研究结果表明,二维数值模型能够基本正确地反映出圆柱发生受迫振动时的涡激振动特性以及有关的受力变化趋势,为今后进一步开展三维数值分析工作奠定了基础。     

节流阀后压力变化对液化系统参数的影响

天然气液化系统的工作参数主要是借助节流阀来调节的。针对丙烷预冷混合制冷剂循环,借助过程模拟软件HYSYS,计算了液化系统各节点的状态参数。在天然气进口状态不变的情况下,以节流阀后压力为自变量,对预冷循环流程、混合制冷循环流程、天然气液化流程三部分进行了稳态分析。结果表明:预冷节流阀的调节可以控制预冷循环与主冷循环分别承担的负荷,随着预冷节流阀后压力的升高,预冷压缩机功耗降低,主冷压缩机功耗升高;升高主冷循环中节流阀后压力可降低主冷功耗。在主冷制冷循环中,一级节流与二级节流之间温度与阀后压力有关,二级节流后温度存在极值点。当天然气出口节流阀后压力升高时,液化率也会升高。     

ESI-MS研究N-苯甲酰基-脱氢枞胺衍生物与血管紧张肽Ⅲ的相互作用

采用电喷雾质谱法,考察了4种最新合成的N-苯甲酰基-脱氢枞胺衍生物（NBDD）——N-苯甲酰基-脱氢枞胺(NBD),N-邻氯苯甲酰基-脱氢枞胺(NClBD),N-苯甲酰基-脱氢枞胺-7-酮(NBDO),N-邻氯苯甲酰基-脱氢枞胺-7-酮(NClBDO)与具有重要生理作用的血管紧张肽Ⅲ（AngⅢ）的相互作用。结果表明,这4种化合物与AngⅢ以不同的摩尔比 (1:1,3:1,5:1)混合时,均可形成非共价复合物,并主要形成+2价复合物离子。对4种NBDD:AngⅢ为1:1的+2价复合物离子[NBDD-AngⅢ+2H]2+进行了2级质谱分析,并根据相对碰撞能的大小,比较了这4种复合物离子的稳定性。对NBDD:AngⅢ为2:1的+2价复合物离子[(NBDD)2-AngⅢ+2H]2+进行了2级和3级质谱分析,并探讨了(NBDD)2-AngⅢ复合物中NBDD分子与AngⅢ的结合方式。     

Fourth generation effects in ■_s→π~-K+ decay

We study the effects of the fourth quark generation model in ■_s →π-K+decay.Combining with the up-to-date experimental measurement for B(■_s →π-K +) and A dir cp(■_s →π-K +) by the CDF Collaboration,we derive the new bound of weak phase φ bd,which are 0 < φ bd < 44,321 < φ bd < 360 and 0 < φ bd < 26,342 < φ bd < 360 for m t = 400 and 600 GeV respectively.In these regions,B(■_s →π-K +) and A dir cp(■_s →π-K +) consist with the current experimental data within errors.     

Fourth generation effects in Bs→π^-K^＋ decay

We study the effects of the fourth quark generation model in B_s → π^-K⁺ decay. Combining with the up-to-date experimental measurement for B(B_s → π^-K⁺) and A_cp^dir(B_s → π^-K⁺) by the CDF Collaboration, we derive the new bound of weak phase ø_bd, which are 0°< ø_bd <44°, 321°< ø_bd < 360° and 0°< ø_bd < 26°, 342°< ø_bd < 360° for m_t'=400 and 600 GeV respectively. In these regions, B(B_s → π^-K⁺) and A_cp^dir(B_s → π^-K⁺) consist with the current experimental data within errors.     

基于精品资源共享课建设的思考——以《中学物理教学技能与教学设计》为例

课堂是教师教学的主阵地,课程是人才培养的重要载体.文章结合《中学物理教学技能与教学设计》的建设,从课程定位、教学内容、教学模式、教学评价等方面,介绍了精品资源共享课的建设和体会.     

Probing the halo and cluster structure of exotic nuclei

The Halo and cluster structure at the ground state of unstable nuclei are among the most exciting phenomena of current nuclear physics. Probing these structures requires a careful selection of reaction tools. In the past twenty years, knockout reactions have been used intensively to investigate spectroscopically the structure of unstable nuclei. In this report we have illustrated the latest development of the knockout reaction tool and have emphasized the recoiled proton tagging method. A quantitative criteria is developed to evaluate the quasi-free feature of the knockout process. The newly discovered "towing mode" reaction tool is also outlined and its applicability at transit energies is discussed.