校准百万年的时钟

放射性核素铁-60(60Fe)产生于大质量恒星超新星爆发时的核心,其半衰期大约百万年,因此它的丰度可用于追溯百万年前的天体物理事件。例如,科学家们已经根据少量的沉积在深海地壳内的60Fe追踪历史上太阳系附近的超新星,而这些事件可能曾影响过地球的气候。之前两次最好的60Fe半衰期测量结果分别发表于1984年和2009年,但相差近两倍。如今,一个新的实验解决了这一问题,并促使更多的相关     

稳态微聚束加速器光源

稳态微聚束(steady-state micro-bunching, SSMB)原理采用激光操控储存环中的电子,可形成具有精微纵向/时间结构的电子束团,即微聚束.通过有机结合微聚束辐射的强相干特性以及储存环内电子束的高回旋频率特性, SSMB光源可提供高平均功率、窄带宽的相干辐射,波段可覆盖从太赫兹到软X射线,具有巨大的科学及产业应用前景.本文在对现有加速器光源—同步辐射光源和自由电子激光简要介绍的基础上,对SSMB的概念及潜力、原理验证实验进展、核心物理及关键技术挑战、清华SSMB-EUV光源方案及其对科学研究和芯片光刻潜在的变革性影响进行总结论述.所综述的工作是在我国自己创新性工作基础上进行的,对于国内读者了解该领域的工作及发展具有一定的帮助.     

大尺寸YVO4晶体的自动控径提拉法生长

本文报道了在自动控制直径条件下大尺寸YVO₄晶体的提拉法生长研究。利用改进的上称重法生长大尺寸YVO₄晶体,在提拉法单晶生长过程中,晶体扩肩部分采用斜率积分模式,转肩部分采用斜率积分过渡到直径积分模式,等径部分采用直径积分模式,应用这种分段控制方式成功地实现了YVO₄晶体的自动化生长。采用4台50型自动化生长炉对YVO₄晶体自动化生长工艺进行了长达一年的可靠性验证,预设技术目标为晶体直径大于40 mm,等径部分长度大于30 mm,B级晶体质量达 80%以上,采用自动控制方法生长晶体毛坯共计138个,晶体直径达标率为99.3%,等径部分长度达标率为53.6%,晶体生长良品率为88.4%。本文还讨论了影响晶体等径部分长度达标率的若干工艺因素。     

Evolutionary Prisoner＇s Dilemma Game Based on Division of Work

We propose a new two-type-player prisoner＇s dilemma game based on the division of work on a square lattice, in which a fraction of the population μ are assigned type A and the rest B. In a one-shot two-player game, we let both of their original payoffs be scaled by a same multiplicative factor α 〉 1, if two neighboring players are of different types; however we leave the payoffs unchanged if they are of the same type. Then we show that combined with the two-type setup, the square lattice can assist to induce different social ranks according to players＇ abilities to collect payoffs. Simulation results show that the density of cooperation is significantly promoted for a wide range of the temptation to defection parameters and that there are optimal values for both α and μ leading to the maximal cooperation level. We reach these results by analyzing the distribution of the players in the social ranks and we also show some typical snapshots of the system.     

S波段2MeV轴耦合驻波加速管参数冷测调试

介绍了用于工业CT的S波段2MeV驻波电子直线加速管的微波冷测及调整,并详细描述了加速管频率的测量与调谐,加速管与矩形波导匹配,加速管品质因数及加速管整管场分布的测量,给出了加速管微波调试及调整的结果.结果如下:加速管的频率一致性达到±0.3MHz以内,过饱和状态下的耦合度为1.14,加速管单腔的品质因数约为120004-200,场分布的比值1:2.2:2.结果表明微波调试满足物理设计的要求.     

高阶线性微分方程解的角域增长性

假设A0,A1,…,Ak-1在某个角域内解析,讨论高阶线性微分方程,f(k) Ak-1f (k-1) … A1f' A0f=0在特定角域内解的增长性和渐近性,改进了一些结果.     

半微量蒸馏法测定复混肥中的总氮

复混肥料含多种营养元素,具有养分配比较合理,物理性好(颗粒状)等特点.复混肥料不仅能节省包装、运输、贮存等费用,在使用中可减少施肥次数,并适合机械施肥作业,避免重复机械行走所带来的土壤压板、环境污染等副作用,有利于提高社会效益、经济效益,保护生态环境,是农作物生长必需的肥料[1].     

First and Second Sound Modes in a Uniform Fermi Gas

First and second sound modes in a uniform fermionic atom gas with Feshbaeh resonance are investigated in the frame of a two-fluid model at finite temperature. All thermodynamic quantities axe calculated for a given thermodynamic potential. The analytical results for thermodynamic quantities and sound velocities in BCS and BEC limits are obtained. The numerical results show that there exists a continuous interpolation for sound velocities of the first and second sound modes at fixed T/Tc between BCS and BEC limits. The existence of the second sound mode indicates the existence of superfluidity.     

Rare Decay Process K→πvv^- in Three-Site Higgsless Model]

Rare decay processes K→πvv^- and KL→π^0vv^- are considered in the framework of three-site Higgsless model. The contributions of this new physics model to these two decay processes come from the new heavy gauge bosons and the correction terms for the couplings of the ordinary gauge bosons with fermions. Our numerical results show that the branching ratios of these two decay processes can be enhanced by 40% and 50% relative to those predicted by the standard model.     

固定床活性炭吸附元素态汞的试验研究

燃煤烟气中汞排放引起的污染越来越受到人们的关注，主要的原因则是其中的元素态汞（Hg^0）由于其低熔点、高平衡蒸汽压以及低水溶性而难以在传统的烟气净化装置中去除．本试验采用固定床活性炭（AC）吸附元素态汞，结果表明，活性炭对汞的吸附取决于活性炭的量、活性炭颗粒大小、汞初始浓度、反应温度以及氯化物浸泡等因素的影响．