Improved Estimation of CSA–Dipolar Coupling Cross-Correlation Rates from Laboratory-Frame Relaxation Experiments

We have investigated the underlying assumptions in estimating cross-correlation rates between chemical shift anisotropy (CSA) and dipolar coupling mechanisms in a scalar-coupled two-spin IS system, from laboratory frame relaxation experiments. It has been shown that for an arbitrary relaxation delay, the difference in relaxation rates of the individual components of an in-phase (or antiphase) doublet is not related to the CSA–dipolar coupling cross-correlation rate in a simple way. This is especially true in the case where the difference in the decay rates of the in-phase and antiphase terms of the density matrix becomes comparable to the magnitude of the scalar coupling between the two spins. Improved means of extracting cross-correlation rates in these cases are presented.     

Improved Resolution from Double Constant-Time Evolution of 3D and 4D Triple-Resonance Experiments

Triple-resonance NMR experiments are nearly essential for performing backbone assignments of proteins larger than 15 kDa. Our work extends the double constant-time (2CT) evolution scheme to triple-resonance 3D and 4D experiments. The modifications needed to accomplish 2CT evolution in triple resonance experiments are straight forward, are completely general, and consequently, will yield increased resolution for all out-and-back experiments. We expect that the increased resolution of experiments presented here will be useful in the study of larger proteins (>30 kDa) and in the study of highly helical proteins where¹HN,¹⁵N, and¹³C dimensions are poorly dispersed.     

计算机仿真实验在物理实验教学中的作用

计算机仿真实验是近年来在多媒体教学中开辟的新领域,在物理实验中开设计算机仿真实验,可以缓解硬件资源不足,起到增强学生实验技能、提高实验教学效果的作用,并实现教学模式多样化.     

现代化的以太漂移实验

迈克耳孙-莫雷实验 在古希腊，以太（Ether）指的是青天或上层大气．17世纪时，法国科学家笛卡儿（René Descartes）最先将以太引进科学，并赋予它某种力学性质．后来，以太又在很大程度上作为光波的荷载物，同光的波动学说相联系．     

中子学积分实验

从６０年代开始,我所就开展了聚变中子积分实验,完成了造氚率、裂变率、穿透率及泄漏中子能谱测量等研究课题．１９８７年以来承担了“８６３”计划的聚变裂变混合堆包层中子学积分实验,开展了Ｂｅ、Ｐｂ的１４ＭｅＶ中子倍增率实验,其中Ｂｅ实验为中、美、日国际合作,实验误差为２．８％,实验结果为理论计算提供积分检验．新的一轮中、美、俄的更大厚度的Ｂｅ中子倍增率实验国际合作正在进行之中．现在,中美关于核聚变合作已经确定了１７个项目,我所承担了其中的“关于ＩＴＥＲ和建议的聚变堆包层及屏蔽系统的中子学积分实验”这一项目． Since 1960s, the fusion neutronics integral experiments have been carried outin our institute. Several research subjects, including the measurements of the tritium production rate,the fission rate,the leakage rate and the neutron energy spectra, have been finished. Since 1987,neutronics integral experiments of the blanket in the fusion-fission hybridreactor in the "863" project have been taken on. The experiments of 14MeV neutron multiplication in Be and Pb have been performed and the experimental error is ...     

实验并“快乐”着——让学生在物理实验选修课中感受快乐

高中实行新课程改革的目标就是要对学生实施素质教育,让学生按照自己的爱好特长和将来的发展方向,挑选自己感兴趣的课程,有选择地进行学习.     

Experiments at COSY

At the COSY cooler synchrotron several experimental facilities are in operation at internal and external target stations. The combination of a high quality low emittance proton beam with high acceptance detector systems allows precise and complete experiments. The momentum range of the COSY beam from 300 MeV/c up to about 3.5 GeV/c opens a large field of experimental studies. One main topic of the present experiments is strangeness production with emphasis to the threshold region.     

Experiments on clusters

In this contribution we discuss four different types of experiments that have been conducted at molecular beams of neutral clusters. The size of particularly stable sodium chloride clusters and their corresponding geometrical structure is inferred from intensity anomalies in mass spectra. This information is obtained either for charged or for neutral clusters depending on whether the clusters are ionized by electron impact or by multiphoton absorption. The important role of fragmentation in mass spectrometry of xenon clusters is revealed by multiphoton ionization; dissociative reactions occurring on the time scale of 10⁻⁷ s with respect to the ionizing event can be analyzed. The solvation energy of negatively charged carbon dioxide clusters as a function of cluster size is obtained from electron attachment spectra. A resonance in the ion yield close to zero eV electron energy signifies that all clusters except for the monomer feature a positive electron affinity. An analysis of the kinetic energy of fragment ions, originating from delayed dissociation of triply charged carbon dioxide clusters, reveals that the size distribution of their fission fragments is extremely symmetric.     

有效衔接基础性实验与设计性实验的探究

引导学生利用现有仪器和原理,将常规基础性实验"惠斯登单臂电桥测电阻"改进为"利用单臂电桥非平衡性测电阻"的设计探索性实验,强化对学生创新精神和研究能力的培养,为开展后面更高层次的设计性实验奠定基础,从而形成基础性实验与设计性实验合理过渡、有序衔接的实验教学体系。     

In-Situ and In-Operando Experiments

How do we learn about the electronic and atomic characteristics of novel materials for efficient solar energy conversion (photovoltaics and water-splitting), energy storage (Li-ion batteries and multivalent-ion batteries), and efficient catalytic activity and selectivity in catalysis? The fundamental scientific problems that we plan to understand and ultimately control are: (1) efficient absorption-induced electron-hole pair formation and its separation at the complex interfaces; (2) bandgap, band levels, and band structure of earth abundant materials that are of crucial importance in electrochemical and photocatalytic applications.     

物理实验的现代化

通过“计算机技术”在物理实验中的应用与实践,探索物理实验的改革之路。     

Experiments on four-nucleon reactions

The status of experimental evidence on four-nucleon reactions in the range from very low to medium energies (50 MeV) is reviewed. The recent progress of microscopic theories as well as computer capabilities, the renewed interest in astrophysical and the new fusion-energy aspects of the four-nucleon reactions, the emphasis on improved measurements of polarization observables especially at very low energies and on new types of studies such as break-up reactions with polarized projectiles prompt such a survey. The aim is to stimulate interest in the four-nucleon system. It is expected that the four-nucleon system will undergo a development similar to the three-nucleon system as a special testing ground for nuclear forces.     

Rare decays: Experiments

The experimental status of generation number violating muon and kaon decays is reviewed. We concentrate on three experiments with a large PSI contribution, neutrinoless muon-electron conversion, muonium-antimuonium conversion and the decayK ⁺→π ⁺. The SINDRUM II experiment at PSI searches for the coherent conversion of a muon into an electron in titanium. The design and construction of the SINDRUM II detector and the results of the first data-taking period in 89 are presented. In total 3.2 million events have been analyzed and no candidate for the processμ ⁻ Ti→e ⁺ Ti has been found. Using two independent determinations of the total number of muon stops an upper limit ofB _μe <4.4×10⁻¹² (90% C.L.) is obtained. The plans to lower the sensitivity by two orders of magnitude are discussed. A muonium-antimuonium conversion experiment is being set up at PSI using the refurbished SINDRUM I detector. The goal of the experiment is to improve the sensitivity for the effective coupling constant by a factor of ∼100. Finally a new proposal E865 has been accepted at BNL to improve the sensitivity for the branching ratio of the decayK ⁺→π ⁺ by a factor 70 to 3×10⁻¹². Representing the SINDRUM II Collaboration: (ETH Zürich, Univ. Zürich, Paul Scherrer Institute Villigen, RWTH Aachen, Univ. Tbilisi)     

Inconclusive Doppler Effect Experiments

The experiments of the Ives-Stilwell type, on second-order Doppler effect, are examined and shown to be inconclusive.