利用18O(6Li,d)22Ne反应研究22Ne Eα=470 keV共振态的性质

慢速中子俘获过程（s过程）是合成比铁重元素的重要途径之一。22Ne（α,n）25Mg反应是大质量AGB星中s过程主要的中子源,其中的22Ne主要通过14N（α,γ）18F（β+）18O（α,γ）22Ne反应链合成。该反应链中关键反应18O（α,γ）22Ne在天体物理感兴趣能区的截面非常低,其天体反应率主要来自于22Ne α分离阈附近低能共振态的贡献,但目前相关能级的共振参数严重缺失。在HI-13串列加速器的Q3D磁谱仪上,通过测量18O（6Li,d）22Ne反应的角分布,利用DWBA分析确定了22Ne分离阈附近共振能级E_α=470 keV的自旋宇称为0+,为后续计算18O（α,γ）22Ne的天体反应率打下了基础。About a half of the abundances of elements heavier than iron comes from the so-called slowneutron capture process (s-process) in Asymptotic Giant Branch (AGB) stars, with the 22Ne(α, n)25Mg reaction as one of the main neutron sources. In the beginning phase of AGB thermal pulse, 22Ne is produced by the 14N(α, γ)18F(β+)18O(α, γ)22Ne reaction sequence, in which the 18O(α, γ)22Ne reaction plays a key role. While the reaction rate of the 18O(α, γ)22Ne is mainly affected by several resonant states lying closely to the α threshold in 22Ne, up to now, the relevant 22Ne parameters are fragmentary in the energy region corresponding to the typical temperatures of s-process. The direct measurement of the 18O(α, γ)22Ne reaction rate is extremely difficult due to the very low cross section. In this work, we investigated the 22Ne resonant states via the 18O(6Li, d)22Ne reaction at the Beijing HI-13 tandem accelerator of China Institute of Atomic Energy. Based on the DWBA analysis, preliminary results showed that the spin-parity of 22Ne E_α=470 keV resonant states was assigned as 0+, which would make contributions to subsequent calculation for the reaction rate of the 18O(α, γ)22Ne.     

Ethylene Glycol Electrooxidation Based on Pentangle‐Like PtCu Nanocatalysts

The research of active and stable electrocatalysts toward liquid‐fuel oxidation reaction is of great significance for the large‐scale commercialization of fuel cells. Although extensive efforts have been devoted to pursuing high‐performance nanocatalysts for fuel cells, both the high cost and sluggish reaction kinetics have been two major drawbacks that limited its commercial development. In this regard, we demonstrated a facile solvothermal method for the syntheses of an advanced class of PtCu nanocatalysts with a unique pentangle‐like shape. By combining the merits of a highly active surface area as well as the synergistic and electronic effects, the as‐prepared pentangle‐like Pt₃Cu nanocatalysts showed superior electrocatalytic activity towards ethylene glycol oxidation with a mass and specific activities of 5162.6 mA mg^?1 and 9.7 mA cm^?2, approximately 5.0 and 5.1 times higher than the commercial Pt/C, respectively. More significantly, the Pt₃Cu pentangle also showed excellent long‐term stability with less activity decay and negligible changes in structure after 500 cycles, indicating another class of anode catalysts for fuel cells and beyond.     

非线性双曲型方程的混合元方法

1　引　　言考虑下述非线性双曲型方程的混合问题:c(x,u)utt-.(a(x,u)u)=f(x,u,t),　　x∈Ω,t∈J,(1.1)u(x,0)=u0(x),　　x∈Ω,(1.2)ut(x,0)=u1(x),　　x∈Ω,(1.3)u(x,t)=-g(x,t),　　(x,t)∈Ω×J,(1.4)其中ΩR2是一具有Lipschitz边界Ω的有界区域,J=[0,T],0相似文献   

含水合物沉积物的弹塑性本构模型

土的密度对其力学特性具有明显影响.水合物以一种固相赋存于沉积物的孔隙中,使得水合物的含量和其赋存形式都会影响含水合物沉积物(GHBS)的密度,因此在研究和描述含水合物沉积物的力学性质时应考虑水合物含量和赋存形式对其密度的影响.本文基于黏土和砂土统一的本构模型(CSUH模型),首先建立水合物体积分数与压硬性参量的关系式来反映水合物对沉积物压缩规律的影响.其次,为了合理考虑水合物含量和赋存形式对沉积物密度的影响,建立了可以描述有效初始孔隙的计算式,并将其引入到状态参量中来描述水合物对沉积物剪胀性和峰值强度的影响.最后,结合CSUH模型中水滴形屈服面,建立了一个含水合物沉积物的弹塑性本构模型.通过与室内试验结果比较,验证了该模型不仅能够合理地描述不同赋存形式、不同水合物含量下含水合物沉积物的应力应变关系,而且在描述具有相同赋存形式含水合物沉积物的力学特性时,不同的水合物含量只需采用一组参数.      

Voltammetric determination of catechin using single-walled carbon nanotubes/poly(hydroxymethylated-3,4-ethylenedioxythiophene) composite modified electrode

Ionics - A simple, sensitive, and reliable carboxylic group functionalized single-walled carbon nanotubes (f-SWCNTs)/poly(hydroxymethylated-3,4-ethylenedioxythiophene) (PEDOTM) modified glassy...     

Pulsed ESR dipolar spectroscopy for distance measurements in immobilized spin labeled proteins in liquid solution

Pulsed electron spin resonance (ESR) dipolar spectroscopy (PDS) in combination with site-directed spin labeling is unique in providing nanometer-range distances and distributions in biological systems. To date, most of the pulsed ESR techniques require frozen solutions at cryogenic temperatures to reduce the rapid electron spin relaxation rate and to prevent averaging of electron-electron dipolar interaction due to the rapid molecular tumbling. To enable measurements in liquid solution, we are exploring a triarylmethyl (TAM)-based spin label with a relatively long relaxation time where the protein is immobilized by attachment to a solid support. In this preliminary study, TAM radicals were attached via disulfide linkages to substituted cysteine residues at positions 65 and 80 or 65 and 76 in T4 lysozyme immobilized on Sepharose. Interspin distances determined using double quantum coherence (DQC) in solution are close to those expected from models, and the narrow distance distribution in each case indicates that the TAM-based spin label is relatively localized.     

微波辐射下6-烷氧基大黄酸的合成及抑菌活性研究

以大黄素为起始原料经过Williamson醚合成,乙酰基保护,氧化,脱乙酰保护合成5个新型的6-烷氧基大黄酸4a～4e.对比研究了微波反应和常规反应对中间体3-烷氧基大黄素合成产率的影响.比较了在合成关键中间产物3a～3e时不同氧化体系对反应产率的影响,找到了最佳的氧化条件.所有目标化合物的结构都通过IR,1HNMR,MS和HRMS进行了表征.对目标化合物4a～4e进行了抑菌活性测试,结果表明随着取代烷氧基链的增长,抑菌活性呈规律性变化.     

Efficient Dynamic Nuclear Polarization at 800 MHz/527 GHz with Trityl‐Nitroxide Biradicals

Cross‐effect (CE) dynamic nuclear polarization (DNP) is a rapidly developing technique that enhances the signal intensities in magic‐angle spinning (MAS) NMR spectra. We report CE DNP experiments at 211, 600, and 800 MHz using a new series of biradical polarizing agents referred to as TEMTriPols, in which a nitroxide (TEMPO) and a trityl radical are chemically tethered. The TEMTriPol molecule with the optimal performance yields a record ¹H NMR signal enhancement of 65 at 800 MHz at a concentration of 10 mM in a glycerol/water solvent matrix. The CE DNP enhancement for the TEMTriPol biradicals does not decrease as the magnetic field is increased in the manner usually observed for bis‐nitroxides. Instead, the relatively strong exchange interaction between the trityl and nitroxide moieties determines the magnetic field at which the optimum enhancement is observed.     

无限迭代函数系统的遍历性质

研究了定义在完备的可分度量空间上具有概率的无限迭代函数系统的遍历性质,证明了该系统的惟一遍历性,推广了Elton的遍历定理。其证明初等简洁,不依赖于鞅论中的较为深刻的极限定理和Banach极限技术。