自辐射场下UN2分子的光谱研究

对铀原子和氮原子分别使用相对论有效原子实势和6-311+G(d)基组, 采用优选的密度泛函B3P86方法, 研究了铀本身产生自辐射场(-0.005–0.005 a.u.)作用下UN₂基态分子的能隙E_g和谐振频率ν. 结果表明: UN₂分子在自辐射场中反对称伸缩振动频率ν₃(σ_g)和对称伸缩振动频率σ₁(σ_g)与实验值1051.1 cm^-1和1008.3 cm^-1 基本符合; E_g随自辐射场场强的增大而趋于减少, 占据轨道的电子容易被激发至空轨道而形成激发态; UN₂分子在自辐射场中趋于不稳定, N₂, O₂等更容易扩散到表面内层而腐蚀铀表面, 加剧了铀在自辐射场中的腐蚀.     

时间频率基准装置的研制现状

时间频率基准装置——铯原子喷泉钟, 在标准时间产生和保持、基础物理研究中发挥了重要的作用. 介绍了铯原子喷泉钟的工作原理, 对影响其性能的各项噪声源和频移项给出了分析, 影响频率稳定度性能的主要因素为Dick 效应相关的原子团装载时间、微波激励源相位噪声和探测激光的频率噪声, 影响频率不确定性能主要频移项为: 黑体辐射频移、冷原子碰撞频移、腔相位分布频移和微波泄露频移; 总结和比较了当前具有先进性能的铯原子喷泉钟采用的技术; 介绍了铯原子喷泉钟的主要应用方向、空间冷原子铯钟的研制情况和光学频率原子钟进展.     

Degradation studies on segmented polyurethanes prepared with poly (d, l-lactic acid) diol, hexamethylene diisocyanate and different chain extenders

In order to investigate the effect of different chain extenders on degradation properties of segmented polyurethanes (SPUs), three types of segmented polyurethanes (SPU-P, SPU-O and SPU-A) based on poly (d, l-lactic acid) diol, hexamethylene diisocyanate (HDI), were synthesized with three chain extenders: peperazine (PP), 1, 4-butanediol (BDO) and 1, 4-butanediamine (BDA), respectively. Thermogravimetric analysis, activation energy and in vitro degradation were used to characterize the obtained polymers, quantitatively. The results revealed that chain extender played an important role in thermal degradation and biodegradation of polyurethanes. Thermogravimetric analysis and activation energy demonstrated that SPU-O, SPU-P and SPU-A presented best, second and weakest thermostability, respectively, and the thermal degradation mechanism of three SPUs was the same and regarded as a two-stage degradation. Data of hydrolytic degradation of the polymers during 12 weeks indicated that the in vitro degradation stability of SPU-A and SPU-P was similar, but both were better than that of SPU-O. The reason for the differences among three types of SPUs was discussed in this paper.     

Global decaying solution to dissipative nonlinear evolution equations with ellipticity

We establish the global existence and decaying results for the Cauchy problem of nonlinear evolution equations:

(E)     

一类逆时反问题的改进正则化方法的收敛性

1引 言 非线性反问题广泛地存在于许多科学和工程问题中,反问题求解的主要困难在于问题的不适定性,即待求函数或参量不连续依赖于观测数据.用来求解非线性不适定问题的方法主要有Tikhonov正则化方法和迭代正则化方法[1,2,3,4].Tikhonov正则化方法是通过引入正则化参数及稳定泛函,将目标泛函离散化,从而得到解的一个稳定近似,即正则化解.     

Direct Electrochemistry and Electrocatalysis of Myoglobin with Ionic Liquid through Multilayers Film on Carbon Ionic Liquid Electrode

Multilayers of myoglobin (Mb) with ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM]BF₄) was assembled on carbon ionic liquid electrode (CILE) based on the electrostatic attraction between the negatively charged Mb and the positively charged imidazolium ion of IL. The CILE was fabricated with 1‐ethyl‐3‐methylimidazolium ethylsulfate ([EMIM]EtOSO₃) as the modifier, which exhibited imidazolium ion on the electrode surface. Then Mb molecules were assembled on the surface of CILE step‐by‐step to get a {IL/Mb}_n multilayer film modified electrode. UV‐Vis adsorption and FT‐IR spectra indicated that Mb remained its native structure in the IL matrix. In deaerated phosphate buffer solution (pH 7.0) a pair of well‐defined quasi‐reversible redox peaks appeared with the apparent formal potential (E^0′) as ‐0.212 V (vs. SCE), which was the characteristic of Mb heme Fe(III)/Fe(II) redox couples. The results indicated that the direct electron transfer of Mb was realized on the modified electrode. The {IL/Mb}_n/CILE displayed excellent electrocatalytic ability to the trichloroacetic acid reduction in the concentration range from 2.0 to 22.0 mmol/L with the detection limit of 0.6 mmol/L (3σ). The proposed method provides a new platform to fabricate the third generation biosensor based on the self‐assembly of redox protein with ILs.     

Inclusion Complexes of Coenzyme Q10 with Polyamine‐Modified β‐Cyclodextrins: Characterization,Solubilization, and Inclusion Mode

The inclusion‐complexation behavior of coenzyme Q10 (CoQ10) with the three polyamine‐modified β‐cyclodextrins (CDs) 1 – 3 was investigated in both solution and the solid state by means of NMR, XRD, and FT‐IR spectroscopy. The results showed that the apparent solubility of CoQ10 increased linearly upon addition of hosts 1 – 3 , giving A_L‐type phase‐solubility curves. These hosts 1 – 3 were able to solubilize CoQ10 to high levels, up to 1.35, 1.52, and 1.44 mg/ml (calculated as CoQ10), respectively. The host 2 with a moderate‐length chain is the most suitable for inclusion complexation of CoQ10. Accroding to the ROESY experiments, the MeO groups of CoQ10 and the tether of 2 can be co‐included into the cavity of β‐CD through the induced‐fit interaction between host and guest. The binding ability of modified β‐CDs 1 – 3 upon complexation with CoQ10 are discussed from the viewpoints of the size/shape‐matching relationship and the induced‐fit concept between host CDs and guest CoQ10 molecule.     

SmI2-mediated radical cross-couplings of α-hydroxylated aza-hemiacetals and N,S-acetals with α,β-unsaturated compounds: asymmetric synthesis of (+)-hyacinthacine A2, (-)-uniflorine A, and (+)-7-epi-casuarine

The SmI(2)-mediated radical coupling reactions of β-hydroxylated pyrrolidine/piperidine aza-hemiacetals 8 and 9 and N,S-acetals 6 and 33 with α,β-unsaturated compounds are described. This method allows a rapid access to β-hydroxylated pyrrolidines, piperidines, pyrrolizidinones, and indolizidinones. Starting from N,S-acetal 33 and via a common intermediate 27, the alkaloids hyacinthacine A(2) (2), uniflorine A (3, 6-epi-casuarine), and the unnatural epimer 7-epi-casuarine (37) have been synthesized in four and five steps with overall yields of 34%, 16%, and 13%, respectively. The radical mechanism of the coupling reactions has been confirmed by controlled experiments, which also allowed deducing the anionic mechanism in the coupling between N,S-acetal 6 and carbonyl compounds. This demonstrates that the mechanisms of these SmI(2)-mediated reactions are switchable from Barbier-type anionic to radical by cooperative action of BF(3)·OEt(2) and t-BuOH.     

Convergence of Calabi–Yau manifolds

In this paper, we study the convergence of Calabi–Yau manifolds under Kähler degeneration to orbifold singularities and complex degeneration to canonical singularities (including the conifold singularities), and the collapsing of a family of Calabi–Yau manifolds.     

Microcalorimetric study on expression of foreign genes in Bacillus thuringiensis

The thermogenic curves of the aerobic metabolism of the three strains of Bacillus thuringiensis B.t. A, B.t. B and B.t. C have been determined by using an LKB-2277 BioActivity Monitor. B.t. A was the host bacterium without foreign gene. B.t. B and B.t. C were constructed by transforming different foreign genes into the host B.t. A, respectively. B.t. B expressed erythromycin resistant gene, while B.t. C expressed both erythromycin resistant gene and tyrosinase gene. The heat flow rate of these strains is B.t. A> B.t. B >B.t. C. These results indicated that there is obvious interrelation between expression of foreign genes and heat flow rate of B.t. strains. This revised version was published online in August 2006 with corrections to the Cover Date.