Dielectric relaxation analysis of starch oligomers and polymers with respect to their chain length

Starch belongs to the polyglucan group. This type of polysaccharide shows a broad β-relaxation process in dielectric spectra at low temperatures, which has its molecular origin in orientational motions of sugar rings via glucosidic linkages. This chain dynamic was investigated for α(1,4)-linked starch oligomers with well-defined chain lengths of 2, 3, 4, 6, and 7 anhydroglucose units (AGUs) and for α(1,4)-polyglucans with average degrees of polymerization of 5, 10, 56, 70, and so forth (up to 3000; calculated from the mean molecular weight). The activation energy (E_a) of the segmental chain motion was lowest for dimeric maltose (E_a = 49.4 ± 1.3 kJ/mol), and this was followed by passage through a maximum at a degree of polymerization of 6 (E_a = 60.8 ± 1.8 kJ/mol). Subsequently, E_a leveled off at a value of about 52 ± 1.5 kJ/mol for chains containing more than 100 repeating units. The results were compared with the values of cellulose-like oligomers and polymers bearing a β(1,4)-linkage. Interestingly, the shape of the E_a dependency on the chain length of the molecules was qualitatively the same for both systems, whereas quantitatively the starch-like substances generally showed higher E_a values. Additionally, and for comparison, three cyclodextrins were measured by dielectric relaxation spectroscopy. The ringlike molecules, with 6, 7, and 8 α(1,4)-linked AGUs, showed moderately different types of dielectric spectra. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 188–197, 2004     

高压增氧T′相R_2CuO_(4+δ)(R=Nd～Tm)低温磁性研究

T′相R2CuO4稀土铜氧化合物由于尺度效应而产生弱铁磁性行为已经被人们关注,报导了通过高温高氧压(6GPa,1000℃)合成稀土T′相R2CuO4(R=Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er和Tm)化合物的结构和磁学性能。磁化率曲线显示,在低温下所有的高压增氧R2CuO4样品都出现新的低温弱铁磁性反常行为,转变温度在28K附近。新的低温弱铁磁性行为是由于CuO2面上微量氧空穴的掺入,使处于反铁磁有序CuO2面形成局域化的铁磁性团簇造成。实验证明新发现的低温弱铁磁性行为与尺度效应产生弱铁磁性行为属于完全不同的物理机制。结果还预示T′相R2CuO4稀土铜氧化合物很难通过空穴掺杂而实现超导。     

Synthesis of New 13-O-Acylavermectin Bl Aglycones

Six new 13-O-acylavermectin Bl aglycones(3-8) were synthesized from avermectin B1 aglycone and their bioactivities were evaluated against Spodoptera exigua, Spodoptera eridania, Tetranychus urticae and Aphis fabae.     

Crystal Structures of Two Potential Tumor Imaging Agents and Therapeutic Agents Copper（Ⅱ） Ternary Complexes with Salicylidene-tyrosinato Schiff Base and Nitrogen-donor Chelating Lewis Base

The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents.     

用楔形柱面光纤微透镜耦合的1.3μm SOA组件

运用激光模式耦合理论分析了半导体光放大器(SOA)与单模通信光纤的连接损耗,并设计制作了楔形柱面光纤微透镜用来实现两者的模斑匹配,有效地降低了器件的光耦合损耗.本文介绍了楔形柱面光纤微透镜耦合的1.3 μm半导体光放大器(SOA)组件及其制作方法.该组件的最大增益不小于14 dB,其偏振灵敏度小于1 dB,增益波动不大于0.5 dB.     

硅基两维光子晶体的制备和光子带隙特性

利用反应离子束刻蚀设备制备了硅基的两维空气柱光子晶体，并用红外显微镜测试了样品的 反射谱. 理论上用时域有限差分(FDTD)方法计算了样品的光子带隙，从测试结果看光子带隙 和理论计算的光子带隙符合得很好.  关键词： 光子晶体 光子带隙 反射谱 时域有限差方法     

透镜空间L~1(p)上向量丛的示性类

本文讨论了透镜空间 L1( p)的上同调环中生成元的运算性质 ,进而利用 L1( p)的 KO -结构得到了L1( p)上任一向量丛的全 Stiefel-Whitney类     

Polling systems in heavy traffic: Exhaustiveness of service policies

We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is excellent for practical heavy-traffic scenarios. This revised version was published online in June 2006 with corrections to the Cover Date.     

四（对-羟基苯基）卟啉氧合配合物的室温固相合成，表征及氧合能力

采用固相反应合成了四羟基苯基卟啉与与Fe^2＋,Co^2＋金属离子的配合物,在室温下,将其与分子O2作用,提纯后得到两种固态氧合配合物．通过元素分析、红外光谱（IR）、核磁共振氢谱（^1HNMR）、电导、热分析（TG／DTA）、紫外光谱（UV）等测试手段确定了氧合配合物的组成为[Co·THPP·O2]（NO3）2·2H2O、[Fe·THPP·O2]Cl2·2H2O]，可知1mol配合物吸收了1molO2,采用失重法测定了氧合配合物中的配位氧,确定1mol金属配合物吸收1molO2形成超氧配合物．     

Effect of nitrogen surface doping on the work function and field emission of hydrogenated amorphous carbon films

The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc