CS2团簇增强的激光多价电离现象的质谱研究

利用脉宽为25ns的脉冲Nd:YAG 532 nm的激光,在8×1010W/cm2的强度下,用飞行时间质谱对CS2的激光电离过程进行了研究.观察到了较强的C2+和S2+高价离子信号,这些高价离子C2+,S2+的最可几平动能高达144eV,112 eV.不同进样方式,激光延迟以及束源压力的实验结果表明,这些高价离子可能来源于CS2团簇的库仑爆炸过程.多光子电离引发,逆韧致吸收加热-电子碰撞电离模型可能是高价离子产生的机理.     

Determination of /Vub/ from measurements of the inclusive charmless semileptonic partial rates of B mesons using full reconstruction tags

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element /Vub/, based on 253 fb(-1) of data collected by the Belle detector at the KEKB e+ e- asymmetric collider. Events are tagged by fully reconstructing one of the B mesons, produced in pairs from Gamma(4S). The signal for b --> u semileptonic decay is distinguished from the b --> c background using the hadronic mass Mx, the leptonic invariant mass squared q2 and the variable P+ [triple bond] Ex - /px/. The results are obtained for events with p(l)* > or = 1 GeV/c, in three kinematic regions (1) Mx < 1.7 GeV/c2, (2) Mx < 1.7 GeV/c2 combined with q2 > 8 GeV2/c2, and by (3) P+ < 0.66 GeV/c. The matrix element /Vub/ is found to be (4.09 +/- 0.19 +/- 0.20(+0.14) -0.15 +/- 0.18) x 10(-3), where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively.     

Evidence for B0 --> D+ D- and observation of B- --> D0D- and B- -->D0D*- decays

We report evidence for B(0) --> D(0)D(-) and the first observation of the decay modes B(-) --> D(0)D(-) and B(-) --> D(0)D(*-) based on a sample of 152 x 10(6) BB events collected by the Belle detector at KEKB. The branching fractions for B(0) --> D(+) D(-), B--->D(0)D(-), and B--> D(0)D(*-) are found to be (1.91 +/- 0.51 +/- 0.30) x10(-4), (4.83 +/- 0.78 +/- 0.58) x 10(-4), and (4.57 +/- 0.71 +/- 0.56) x 10(-4), respectively. Charge asymmetries in the B---> D(0)D(-) and B(-) --> D(0)D(*-) channels are consistent with zero.     

Observation of B0-->pi0pi0

We report the observation of the decay B0-->pi(0)pi(0), using a 253 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. The measured branching fraction is B(B0-->pi(0)pi(0))=(2.3(+0.4+0.2)(-0.5-0.3))x10(-6), with a significance of 5.8 standard deviations including systematic uncertainties. We also make a measurement of the direct CP violating asymmetry in this mode.     

液态金属Ga急冷凝固中微观结构转变的模拟研究

采用分子动力学方法对液态金属Ga的快速凝固过程进行计算机模拟跟踪研究,运用HA键型指数法和原子团类型指数法分析了金属原子Ga的成键类型和形成的基本原子团结构.发现:与通常的液态金属(如Al)相反,随着温度的降低,二十面体及与二十面体相关的1551, 1541键型数目明显下降;与立方体(fcc,bcc),六角密集结构相关的1421,1422键型数目明显增加;而与菱面体相关的1321,1311键型的数目却显著增加,逐渐占据优势.最后形成一种新型的以菱面体结构为主、夹杂着立方体(fcc,bcc)、六角密集(hcp)等团簇结构所组成的非晶态结构.这正是非晶态金属Ga的g(r)曲线分裂的第二峰的顺序为前低后高,而与非晶态金属Al的g(r)曲线(其分裂的第二峰的顺序为前高后低)明显不同的微观结构上的物理根源.     

30M-35kV/2000A高温超导电缆制冷系统

本文介绍了我国新研制成的首条并网运行的热绝缘型30M-35KV/2000A高温超导电缆制冷系统。该制冷系统主要有液氮泵箱、过冷箱、高真空输液管道、液氮贮槽、辅助减压抽空系统、泵箱及气动阀门供气系统、监控系统所组成。冷却方式是过冷液氮循环,制冷方式是G-M制冷机和减压抽空(备用)。给出了制冷系统的运行结果。     

Measurements of branching fractions for B --> K pi and B --> pi pi decays

We report measurements of branching fractions for B --> K pi and B --> pi pi decays based on a data sample of 449 x 10(6) BB[over] pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We also measure the ratios of partial widths for B-->Kpi decays, namely R(c) identical with 2Gamma(B(+) --> K(+) pi(0))/Gamma(B(+) --> K(0) pi(+)) = 1.08+/-0.06+/-0.08 and R(n) identical with Gamma(B(0) --> K(+) pi(-))/2 Gamma(B(0) --> K(0) pi(0)) = 1.08+/-0.08+/-0.08, where the first and the second errors are statistical and systematic, respectively. These ratios are sensitive to enhanced electroweak penguin contributions from new physics; the new measurements are, however, consistent with standard model expectations.     

Measurement of inclusive Ds, D0, and J/psi rates and determination of the Bs(*)Bs(*) production fraction in bb Events at the Upsilon(5S) resonance

The inclusive production of D(s), D(0), and J/psi mesons is studied using a 1.86 fb(-1) data sample collected on the Upsilon(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The number of bb events in this Upsilon(5S) data sample is determined. We measure the branching fractions B(Upsilon(5S)-->D(s)X)/2=(23.6+/-1.2+/-3.6)%, B(Upsilon(5S)-->D(0)X)/2=(53.8+/-2.0+/-3.4)%, and B(Upsilon(5S)-->J/psiX)/2=(1.030+/-0.080+/-0.067)%. From the D(s) and D(0) inclusive branching fractions the ratio f(s)=(18.0+/-1.3+/-3.2)% of B(s)(*)B(s)(*) to the total bb quark pair production at the Upsilon(5S) energy is obtained in a model-dependent way.     

A simulation study of microstructure evolution during solidification process of liquid metal Ni

A molecular dynamics simulation study has been performed for the microstructure evolution in a liquid metal Ni system during crystallization process at two cooling rates by adopting the embedded atom method (EAM) model potential. The bond-type index method of Honeycutt--Andersen (HA) and a new cluster-type index method (CTIM-2) have been used to detect and analyse the microstructures in this system. It is demonstrated that the cooling rate plays a critical role in the microstructure evolution: below the crystallization temperature $T_{\rm c}$, the effects of cooling rate are very remarkable and can be fully displayed. At different cooling rates of $2.0\times10^{13}$\,K\,$\cdot$\,s$^{-1}$ and $1.0\times10^{12}$\,K\,$\cdot$\,s$^{-1}$, two different kinds of crystal structures are obtained in the system. The first one is the coexistence of the hcp (expressed by (12 0 0 0 6 6) in CTIM-2) and the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 and 1422 bond-types, and the hcp basic cluster becomes the dominant one with decreasing temperature, the second one is mainly the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 bond-type, and their crystallization temperatures $T_{\rm c}$ would be 1073 and 1173\,K, respectively.