Asymmetric Photochemical Reaction of 5-Methylbicyclo[1.1.1]-pentanyl Ketone

The density functional theory(DFT) calculations were performed to investigate a typical Norrish/Yang type II photoreaction of 5-methylbicyclo[1.1.1]-pentanyl ketone. The results reveal the essential correlation between structures on the one hand and energies, on the other hand, of the reactants, transition states and products based on both singlet ground(S₀) and triplet excited(T₁) potential energy surfaces. The feasible mechanism indicates that an intramolecular Norrish/Yang cyclization reaction takes place via H-abstraction to obtain the sole chiral cyclobutanol photoproduct. The located crossing point plays an important role in the cyclization process, which permits intersystem crossing(ISC) from T₁ to S₀ state. The rate-determining step may be to experience ISC between two different potential energy surfaces, requiring sufficient time for electron spin reversion, i.e., spin multiplicity alteration. These conclusions are further confirmed by the second-order M鴏ler-Plesset perturbation theory(MP2) calculations.     

宋元海洋知识中的“海”与“洋”

宋元时期随着航海实践的空前发展,海洋地理空间认知中“九州—四海”的“天下”格局的知识框架逐步被航海实践突破和“遗忘”,在海洋地理认知上抽象的“海”向具象的“洋”的转变,海洋被以多种方式划分和命名为不同的“洋”。宋元对“洋”的划分和命名仍表现为区域性知识,但其基于航海实践的知识生成路径奠定了不同朝代、不同国家形成共同海洋知识和海洋观念的逻辑基础。在中国接受和融入世界共同海洋知识和海洋观念的过程中,宋元海洋实践的空前发展开启了具有重要转折意义的新阶段。     

From De Sitter Special Relativity and Snyder＇s Model to Complete Yang Model

The de Sitter special relativity on the Beltrami-de Sitter-spacetime and Snyder＇s model in the momentum space can be combined together with an IR-UV duality to get the complete Yang model at both classical and quantum levels, which are related by the proposed Killing quantization. It is actually a special relativity based on the principle of relativity of three universal constants （c, ρp, R）.     

“阳”加速器上的Z箍缩诊断技术

概述了为开展Z箍缩实验物理研究而建立的一些诊断技术和方法。这些诊断技术已成功应用于"阳"加速器(负载电流1.2 MA,上升时间85 ns)喷气和丝阵Z箍缩物理研究中,其中软X光8通道Dante谱仪和软X光闪烁体功率计主要用于软X光能段的辐射功率、能量和低能辐射能谱测量;椭圆弯晶谱仪、凸圆柱晶体谱仪和透射光栅谱主要用于X光辐射线谱和连续谱的测量,以获取等离子体密度、电子和离子温度等信息;X光八分幅针孔相机、分能段6通道X光掠入射针孔积分相机和激光差分干涉测量系统主要用于研究Z箍缩内爆动力学过程及等离子体参数等,并给出了这些诊断系统获取的典型实验结果,包括X光辐射功率、辐射能谱、等离子体内爆图像和密度分布等。     

单壳层喷气Z箍缩内爆特性分析

在“阳”加速器（电流峰值为500—850 kA,上升时间约为85 ns）上利用单壳层喷气负载开展了Z箍缩等离子体内爆实验,获得了等离子体的辐射产额、X光辐射图像等诊断结果.利用相应的诊断结果,定义了内爆时间,对内爆过程的主要阶段进行了划分,研究了等离子体位形、辐射强度分布等实验现象,同时对等离子体的内爆轨迹、内爆质量、径向收缩比、磁流体不稳定性等进行了初步分析. 关键词： Z箍缩')" href="#">喷气负载Z箍缩 等离子体内爆 X光辐射功率 “阳”加速器     

The relationship between four-dimensional θ=π Yang－Mills theory and the two-dimensional Wess－Zumino－Novikov－Witten model

Used the dimensional reduction in the sense of Parisi and Sourlas, the gauge fixing term of the four-dimensional Yang－Mills field without the theta term is reduced to a two-dimensional principal chiral model. By adding the θ term (θ=π), the two-dimensional principal chiral model changes into the two-dimensional level 1 Wess－Zumino－Novikov－Witten model. The non-trivial fixed point indicates that Yang－Mills theory at θ=π is a critical theory without mass gap and confinement.     

科技创新添华彩 居里风范传后人——记著名放射化学家杨承宗教授

杨承宗教授是我国放射化学的奠基人。他早年在法国巴黎大学居里镭学研究所师从约里奥.居里研究放射化学。1951年获得博士学位后,他婉谢高薪聘请,毅然回国,以期早日报效祖国。建国初期,在十分困难的条件下,他领导开展了放射化学基础研究和应用研究。杨承宗在我国核能事业发展中最为突出的贡献是组织并领导了用于核试验的燃料铀的制备和培育了我国新一代放射化学工作者。他是一位德高望重成绩卓著的科学家和教育家。本文是他科研和教学生涯的简要记述,将给我们以教育和启迪。     

Modification of black‐body radiance at low temperatures and frequencies

In contrast to earlier reports, where the spectrum of the energy density of photonic black‐body radiation modified by SU(2) effects was discussed, we discuss the low‐frequency spectrum of the radiance at temperatures ranging between 5 and 20 Kelvin. We conclude that compared to the conventional theory the only observable effect is associated with the spectral gap (total screening) which for T≥ 4.3 K scales with temperature T as ν^*(T)}/GHz = 42.70 (T/K)^‐0.53 + 0.21. We also discuss how a low‐temperature black body cavity under the influence of a sufficiently strong static electric field is forced to emit according to Planck's radiation law (pure U(1) theory) even at low frequencies and how this effect can be utilized to measure SU(2) induced deviations.     

阳加速器新磁绝缘传输线的设计与检验

 介绍了阳加速器新磁绝缘传输线(MITL)的物理设计及实验检验。在缩短MITL整体长度及绝缘环宽度的同时,将原结构改成以共顶点同轴圆锥段为主体的新结构,使阴极表面、绝缘环及三相点满足电场设计要求,最小磁绝缘电流较原结构有所降低,将结构电感从原来的70.9 nH减小到31.7 nH。利用短路实验及丝阵内爆实验对新MITL进行了检验,结果表明新MITL的性能指标有所提高。