DNA纳米管的扭转刚度模型

刚度是衡量材料弹性变形难易程度的一个定量表征参数,与DNA纳米管静动力学特性及其结构生物功能密切相关．本文致力于研究DNA纳米管的扭转刚度．首先,在六角形均匀封装条件下,考虑到单个DNA杆件弯扭组合问题的静不定特点,我们利用平衡方程、变形协调方程和弹性本构方程,合理预测了DNA纳米管扭转实验中单个DNA杆件的弯扭组合变形,由此给出了DNA纳米管扭转刚度预测的解析模型．最后的结果表明：随着DNA杆数的增加,DNA纳米管的弯曲刚度显著增加,而其扭转刚度却几乎不变,合理解释了扭转实验中发现的现象．有关结论为DNA折叠结构的设计和应用提供了参考．     

用于枪击探测的紫外光传感器技术指标分析

利用一款标准的日盲型紫外探测传感器对枪击火焰进行了探测实验,结合紫外光传输特性,对实验数据进行分析,提出了探测枪击火焰紫外光谱的传感器技术指标。不考虑入射角度和响应时间的影响,1 km处要检测到步枪击发,传感器响应电流达到能明显检出的100 nA,则传感器的响应率和响应面积乘积至少达到0.002 AW-1m2。根据一种枪击探测装置原型方案,对紫外探测传感器的透光性、日盲特性、对紫外光的响应率、入射角和短路电流等技术指标进行了分析。采用分子束外延法制备了一种MgZnO紫外探测传感器,对其紫外光谱透光率、响应率和响应时间进行了测量,进一步优化性能后有望满足枪击探测要求。     

Hydrothermal Syntheses and Characterization of Two 1D Chain Complexes and Tetra-capped Keggin Clusters

Two new compounds, [Ni(en)₂]{[Ni(en)₂]₂[Mo^VI₆Mo^V₂V^IV₈O₄₀(SiO₄)]}[(NH₂)₂(C₂H₄)₂NH]·2H₂O(1) and [Ni(en)₂]{[Ni(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(VO₄)]}(en)·H₂O(2)(en=ethylenediamine), have been hydrothermally synthesized and characterized by elemental analysis, infrared(IR), X-ray photoelectron spectroscopy(XPS), electron spin-resonance(ESR) and thermogravimetric(TG) analysis and single-crystal X-ray diffraction(XRD) analysis. Both the compounds exhibit a 1D chain composed of bi-supporting tetra-capped Keggin clusters and nickle coordination fragments. The 1D chains are further assembled into a 3D supramolecular network with different packing modes via hydrogen bonds. The magnetic susceptibility of compound 1 demonstrates the presence of antiferromagnetic interactions.     

空间目标探测与识别的波段选择

介绍了根据目标的反射率实验测量和大气光谱特征对大气层外目标进行探测的波段选择方法.测量出样品及标准板的反射光强度,计算出样品的光谱反射率,在考虑空间目标自身的辐射强度、光谱反射率、背景大气的辐射亮度、目标-背景对比度、不同波段斜程透过率等诸多因素后进行波段选择.利用MODTRAN大气传输模型计算了目标亮度、背景大气的辐射亮度、对比度以及不同波段斜程透过率的典型光谱特征、并进行光谱特征分析,综合考虑目标的视亮度以及对比度,结果表明0.76～0.90 μm是包覆黄色镀铝聚酯薄膜的目标最佳探测波段,0.52～0.60 μm是包覆银色镀铝聚酯薄膜的目标最佳探测波段.     

新型1,3,4-噁二唑衍生物的合成与性质研究

研制高效载流子传输材料是提高有机电致发光器件性能的关键. 采用对酯对二酰氯(5)与含不同链长烷氧取代基的苯甲酰肼(2)缩合制备了一系列腰接羧基1,3,4-噁二唑衍生物, 即1,4-二[5-(4-烷氧基苯)-1,3,4-噁二唑基]-2,5-二羧基苯(7; 烷氧基＝OCnH2n＋1; n＝8, 12, 16), 并采用UV-vis吸收和荧光光谱对合成物进行了表征. 结果表明: 7的分子结构中羧基的横向引入, 对化合物的光物理性质和能带结构产生较大影响. 这些噁二唑化合物的LUMO及HOMO值分别介于－3.62与－3.58 eV之间及－6.94与－6.90 eV之间, 说明它们可能具有良好的电子传输性.     

Efficient stereoselective synthesis of benzoxazines via copper-catalyzed three-component coupling reactions

A convenient one-pot synthesis of 1,4-benzoxazines via three-component coupling and subsequent O-cyclization is reported. The present reaction provides an efficient protocol to functionalized 1,4-benzoxazine derivatives in good to high yields from aldehydes, amines and alkynes. Furthermore, the O-annulation process is completely regio- and stereoselective, only the six-membered rings and its Z-isomers were obtained.     

Calculation of the crystal-melt interfacial free energy of succinonitrile from molecular simulation

The crystal-metal interfacial free energy for a six-site model of succinonitrile [N triple bond C-(CH(2))(2)-C triple bond N] has been calculated using molecular-dynamics simulation from the power spectrum of capillary fluctuations in interface position. The orientationally averaged magnitude of the interfacial free energy is determined to be (7.0+/-0.4)x10(-3) J m(-2). This value is in agreement (within the error bars) with the experimental value [(7.9+/-0.8)x10(-3) J m(-2)] of Marasli et al. [J. Cryst. Growth 247, 613 (2003)], but is about 20% lower than the earlier experimental value [(8.9+/-0.5)x10(-3) J m(-2)] obtained by Schaefer et al. [Philos. Mag. 32, 725 (1975)]. In agreement with the experiment, the calculated anisotropy of the interfacial free energy of this body-centered-cubic material is small. In addition, the Turnbull coefficient from our simulation is also in agreement with the experiment. This work demonstrates that the capillary fluctuation method of Hoyt et al. [Phys. Rev. Lett. 86, 5530 (2001)] can be successfully applied to determine the crystal-melt interfacial free energy of molecular materials.     

Study on multiple ring-like vortex formation and small vortex generation in late flow transition on a flat plate

A high-order direct numerical simulation (DNS) of flow transition over a flat plate at a free stream Mach number 0.5 has been carried out. During the simulation, we cannot find, according to the classical theory of boundary layer transition, the “hairpin vortex breakdown to smaller structures” in the last stage of flow transition on a flat plate. However, we did discover the so-called spikes as a result of a multibridge or multiring formation. This indicated a large and stable vortex structure which can travel for a long distance. We believe that this is a result of ring heads that are located in an inviscid region. These heads of the “turbulence spot” never seem to break down and persist as a stable structure. In addition, we discovered that the U-shaped vortex is a part of an existing coherent structure instead of a newly generated one. The U-shaped vortex also provides an additional channel to transfer vorticity to the ring from the wall. During travel, the leading primary ring in the front of the spot is sloped and skewed, causing disappearance of the second sweep. As a consequence, no energy is brought down to the lower boundary layer near the vortex ring head of the spot. Thus, the small length scale structures become damped and the existing U-shaped vortex structure becomes distinguishable. So, the question is where do the turbulent small length scale vortices come from? We will address this with a new theory which states that all of small length scales (turbulence) are generated by high-shear (HS) layers rather than being produced by “vortex breakdown.” The new DNS shows that the HS layers are produced by strong positive spikes surrounded by low-speed fluids and by the interaction between the secondary and higher-level vortices and the wall surface especially near the ring neck. This multiple ring-like vortex generation also follows the first Helmholtz vortex conservation law. Furthermore, the Λ-shaped vortex is formed and rolling up, and the Λ-vortex is stretched and narrowed, and a new bridge is generated after the neck. The bridge will further become a second ring and so on. Besides the original vortex legs, there are also U-shaped vortex tubes. Finally, the multiple ring vortex structure is formed. From this process, no evidence is found to support that two consequent multiring circles are mixed to generate small vortices. The connection of downdraft/updraft motions is also studied.