Transient holographic grating in azo-dye-doped liquid crystals with off-resonant light

Holographic gratings in nematic liquid crystals doped with Disperse Red 1 (DR1) were investigated using a linearly polarised He–Ne laser. Although the electric transitions of the samples were almost off-resonant, the diffraction of the transient holographic grating was found to exhibit a sinusoidal feature with changing the polarisation of recording beams, and the diffraction intensities and response time of the gratings were strongly dependent on DR1 concentration. The results revealed that the diffraction of holographic grating depends on the rate of trans–cis isomerisation of DR1 molecules. Moreover, the temperature dependence of diffraction indicated that the grating formation mechanism was attributed to photoinduced reorientation of photoisomerisation effect.     

Density functional theory studies of Si36H36 and C36H36 nanocages

This work presents systematic studies of the possible classical structures of Si₃₆H₃₆ and C₃₆H₃₆ nanocages using density functional theory calculations. The computed structures, relative stabilities, and electronic properties of these silicon‐ and carbon‐based hydrides are investigated and compared. The results indicate that none of the Si₃₆H₃₆ or C₃₆H₃₆ nanocages exhibit a perfect spherical shape. Hydrogenated nanocages with higher number of adjacent pentagons are more stable and this observation is contrary to the trend of bare fullerenes. The hydrogenated small cages are energetically more favorable than large ones according to the obtained binding energies. Moreover, the energy levels, distributions, and irreducible representations of the frontier orbital for Si₃₆H₃₆ and C₃₆H₃₆ nanocages are also explored. Obvious localizations within the inner space of nanocages are detected for the lowest unoccupied molecular orbital of C₃₆H₃₆. © 2014 Wiley Periodicals, Inc.     

Synthesis of Sulfotyrosine‐Containing Peptides by Incorporating Fluorosulfated Tyrosine Using an Fmoc‐Based Solid‐Phase Strategy

Tyrosine O‐sulfation is a common protein post‐translational modification that regulates many biological processes, including leukocyte adhesion and chemotaxis. Many peptides with therapeutic potential contain one or more sulfotyrosine residues. We report a one‐step synthesis for Fmoc‐fluorosulfated tyrosine. An efficient Fmoc‐based solid‐phase peptide synthetic strategy is then introduced for incorporating the fluorosulfated tyrosine residue into peptides of interest. Standard simultaneous peptide‐resin cleavage and removal of the acid‐labile side‐chain protecting groups affords the crude peptides containing fluorosulfated tyrosine. Basic ethylene glycol, serving both as solvent and reactant, transforms the fluorosulfated tyrosine peptides into sulfotyrosine peptides in high yield.     

Photonic Modulation Enabled by Controlling the Edge Structures of Boron-Doped Molecular Carbons

Control over topological edges of molecular carbons (MCs) is of importance for achieving diverse molecular topologies and desirable physical properties. However, it remains very challenging for heteroatom-doped MCs due to the synthetic difficulty. Herein, we report control over the edge structures of boron-doped MCs (BMCs) via the sequential cyclization strategy. Three BMC molecules that feature the C₅₆B₂ or C₈₄B₂ polycyclic π-skeletons with selective cove/fjord or cove/bay edges, respectively, were synthesized through the rational combination of Mallory photoreaction and Scholl reaction. We not only obtain the largest boron-doped π-system reported so far, but also disclose that fine control of their edges and length greatly affects electronic structures and thereby photonic properties of BMCs, such as tunable aromaticity, decreased band gaps, as well as redshifted absorptions and fluorescence. Remarkably, the C₅₆B₂ molecule exhibits stimulated emission behavior and amplified spontaneous emission property, both of which have never been reported for pristine boron-doped π-systems, thus demonstrating the potential of BMCs as optical gain materials for laser cavities.     

Synthesis of a “Butterfly Cage” Based on a Double‐Decker Silsesquioxane

Novel polyhedral structures were prepared with a butterfly‐shape composed of oligosiloxane wings and a double‐decker silsesquioxane (DDSQ) body. The compounds were synthesized in two steps from commercially available alkoxysilanes, and their structures were confirmed using spectroscopic methods and X‐ray crystallography. Not like other phenyl‐substituted cage silsesquioxanes, these butterfly cages show very good solubility in common organic solvents. The crystal structures clearly showed their unique features: a larger space with longer siloxane chains and a very flexible framework. Moreover, these compounds are thermally stable with a Td₅ (5 % weight loss temperature) over 320 °C.     

移动周期载荷作用下孔隙热弹性地基的动力学响应

根据孔隙热弹性线性理论,本文首先建立了在移动周期载荷作用下孔隙热弹性地基动力学响应分析的数学模型,其中提出了在周期性边界上必须满足的6类适当的条件,即界面位移相等、应力相等、孔隙百分比相等、温度相等以及在外法线方向孔隙发展相等和温度导数相等。在此基础上,分别采用微分求积法(DQM)和有限差分法(FDM)对控制方程进行空间和时间离散,并求解。作为算例,分别研究了在移动周期载荷和极限车载作用下孔隙热弹性地基的动力学响应,考察了车速对沉降、孔隙体积百分比和温度的影响。可以看到,本文提出的处理周期性问题DQM,具有精度高、收敛性好,计算效率高等特点。     

温度对季节性冻土水分迁移的影响研究

寒区季节性冻土冻胀性质对工程实际影响很大。为了了解温度对水分迁移现象的影响,本文通过地温测试仪对野外不同深度处的土层温度进行测量,并在不同时间相应深度取土样,测其含水率,通过比较不同时间不同深度处的含水率的变化情况来分析温度变化对水分迁移现象的影响。在气温回升之前,当地表温度降低时,温度随深度的降低而升高; 随着地表温度不断降低,各深度处的温度也不断下降,温度梯度增加,各深度处地层的含水率变化大,即温度梯度的增加促进了季节性冻土区水分迁移现象的发生。     

单光子计数探测系统的线性性能研究

利用单光子计数技术对微弱光进行探测具有与其他模拟法相比的多个优势,如有好的抗漂移性、高的信噪比、较宽的线性区等。线性性能是探测器的基本性能之一,利用叠加法和距离平方反比法测量单光子计数探测系统的线性范围,当非线性因子为0.05时,利用叠加法实验测得系统线性响应计数率为3.9×10~5 Counts/s,利用距离平方反比法实验测得系统线性响应计数率为5×10~5 Counts/s。结果表明,两种方法测得响应线性度一致性较好。分析了电子学系统的漏计误差对探测器系统线性范围的影响。实验表明,通过缩短电子学系统中甄别器的死区时间(td)可以提高系统的线性范围。     

一种机械式电表读数区域的自动定位方法

针对电表读数区域自动定位这一关键技术的具体应用,提出了一种适合四种类型机械式电表的读数区域自动定位算法;采用同态滤波增加图像前景与背景之间的亮度差异,同时利用改进的Bersen算法,有效的将电表前景与背景分开;利用区域定位对图像进行粗定位,并对粗定位区域纵向投影,根据目标字符的纹理特征和先验知识对目标区域精确定位;经实验证明,该算法对其中四种电表图像的适应性良好。