基于模式转换及双峰谐振效应的薄包层镀膜长周期光纤光栅特性研究

基于耦合模理论,首先研究了镀膜长周期光纤光栅(LPFG)高阶包层模的模式转换,划分了高阶包层模的非模式转换区及模式转换区。分析了高阶包层模有效折射率随薄膜厚度增加的响应特性,包层模谐振波长在模式转换区的偏移量要大于非模式转换区。在此基础上,研究了不同包层半径下高阶包层模谐振波长随光栅周期的变化情况,结果表明,相同包层半径下模式转换区内双峰间距的偏移量大于非模式转换区;无论在模式转换区还是非模式转换区,包层半径的减小将增加双峰间距的偏移量。最后分析了不同包层半径下的高阶包层模双峰透射谱在模式转换区及非模式转换区内的折射率响应,进而提出了薄包层镀膜LPFG的优化设计方案,当选定敏感膜层厚度及折射率处于镀膜LPFG的模式转换区内,光栅周期靠近相位匹配转折点时,将得到灵敏度高于传统LPFG双峰传感器的镀膜LPFG折射率型双峰传感器;而减小包层半径,将进一步提高传感器的分辨本领。     

十氢萘/空气混合物高温着火延迟的激波管测量

在激波管上进行了气相十氢萘/空气混合物的着火延迟测量, 着火温度为950-1395 K, 着火压力为1.82×10⁵-16.56×10⁵ Pa, 化学计量比分别为0.5、1.0 和2.0. 在侧窗处利用反射激波压力和CH^*发射光来测出着火延迟时间. 系统研究了着火温度、着火压力和化学计量比对十氢萘着火延迟时间的影响. 实验结果显示着火温度和着火压力的升高均会缩短着火延迟时间. 首次在相对高和低压的条件下观察到了化学计量比对十氢萘着火延迟的影响是完全相反的. 当压力为15.15×10⁵ Pa时, 富油混合物呈现出最短的着火延迟时间, 而贫油混合物的着火延迟时间却是最长的. 相反, 当压力为2.02×10⁵ Pa时, 富油混合物的着火延迟时间最长. 着火延迟数据与已有的动力学机理的预测值进行对比, 结果显示机理在所有的实验条件下均很好地预测了实验着火延时趋势. 为了探明化学计量比对着火延迟时间影响的本质, 对高、低压条件下的着火延时进行了敏感度分析.结果显示, 压力为2.02×10⁵ Pa时, 控制着火延迟的关键反应为H+O₂=OH+O, 而涉及十氢萘及其相应自由基的反应在15.15×10⁵ Pa时对着火延迟起主要作用.     

Sensitivity of the macroscopic elasticity tensor to topological microstructural changes

A remarkably simple analytical expression for the sensitivity of the two-dimensional macroscopic elasticity tensor to topological microstructural changes of the underlying material is proposed. The derivation of the proposed formula relies on the concept of topological derivative, applied within a variational multi-scale constitutive framework where the macroscopic strain and stress at each point of the macroscopic continuum are volume averages of their microscopic counterparts over a representative volume element (RVE) of material associated with that point. The derived sensitivity—a symmetric fourth order tensor field over the RVE domain—measures how the estimated two-dimensional macroscopic elasticity tensor changes when a small circular hole is introduced at the microscale level. This information has potential use in the design and optimisation of microstructures.     

Sono-synthesis approach of reduced graphene oxide for ammonia vapour detection at room temperature

In this paper, we report the sono-synthesis of reduced graphene oxide (rGO) using polyethyleneimine (PEI), and its performance for ammonia vapour detection at room temperature. Graphene oxide (GO) and reduced graphene oxide (rGO) were prepared by sonication method by using low-frequency ultrasound under ambient condition and films were deposited by Doctor Blade method. The rGO, which has vapour accessible structure showed a good sensing response with a minimum detection limit of 1 ppm and the detection range from 1 ppm to 100 ppm. The sensing response was found to be 2% at 1 ppm and 34% at 100 ppm of ammonia and the developed sensor operated at room temperature. The sensor displays a response time of 6 s and a recovery time of 45 s towards 100 ppm of ammonia vapour. The source for the highly sensitive, selective and stable detection of ammonia with negligible interference from other vapours is discussed and reported. We believe reduced graphene oxide (rGO) could potentially be used to manufacture a new generation of low-power portable ammonia sensors.     

辅助气燃烧接口对有机化合物碳同位素测定的影响

对多种烷烃及芳香化合物采用不同类型的反应管进行了碳同位素分析, 旨在阐明燃烧接口对有机化合物色谱行为的影响. 结果表明, 在反应管中填充较少的催化剂有助于提高化合物的分离度, 这可能是由于反应管中载气具有较高的线速度, 从而减少了化合物的扩散加宽. 然而, 不同反应管对分离度的改善作用相对有限. 对于不同的反应管, 化合物的灵敏度变化主要与开口分流处分流比的变化有关, 而这种变化可能是由反应管内载气流速的变化所致.     

波长调制型表面等离子体共振的传感特性研究

表面等离子体共振(SPR)光学传感器能实现生物医学的快速、 无标记、 高精度检测,是生物化学分析的重要方法。 研制了基于波长调制型的Kretschmann结构表面等离子体共振(SPR)生物传感系统,研究了在体溶液传感方式下的传感性能。 利用不同浓度的乙醇和乙二醇溶液进行体溶液传感测试。 实验结果表明,在折射率低时共振波长对折射率变化响应的灵敏度低,但响应的线性度高;随着折射率增大,共振波长对折射率的响应变化的灵敏度提高。 在1.407 0～1.430 RIU折射率范围内,灵敏度高达11 487 nm·RIU-1。 传感器的共振波长的稳定性为0.213 8 nm,可分辨最小折射率趋近10-6 RIU。 所研制的波长调制型表面等离子共振传感器操作简单、 灵敏度高、 检测范围大,可实现浓度极低生物标记物的有效检测,在化学、 生物传感领域有重要的应用。     

Synthesis,Crystal Structure,Thermal Decomposition and Sensitive Properties of a New Complex [Cu(IMI)4](PA)2

A new coordination complex [Cu(IMI)₄](PA)₂ had been synthesized with imidazole(IMI) as ligands and picrate(PA^-) groups as outer anions, and characterized by Fourier transform infrared(FTIR) spectrum and elemental analysis. Its crystal structure was determined by single crystal X-ray diffraction(XRD) analysis. The crystallographic data show that the crystal belongs to monoclinic, C2/c space group, a=2.542(5) nm, b=0.91773(18) nm, c=1.3778(3) nm, β=107.854(3)° and Z=4. Furthermore, the central copper(II) ion is coordinated by four N atoms from four imi- dazole ligands. All the molecular units are linked into a zigzag pattern along a-axis by the hydrogen bonds, and extended to the distance regularly. Thermal decomposition mechanisms were determined based on differential scanning calorimetry(DSC) and thermogravimetry-differential thermogravimetry(TG-DTG) analysis, and kinetic parameters of the first exothermic process were studied using Kissinger’s and Ozawa-Doyle’s method, respectively. Sensitivity tests show that the title complex has low sensitivity to external stimulus, but it has a higher energy of combustion of 14.2 kJ/g due to which it may be used as the additives of energetic materials to improve the explosive performance.     

Novel High-nitrogen Energetic Compound Based on Semicarbazide-substituted Tetrazine

A novel energetic compound 3-(3,5-dimethylpyrazol-1-yl)-6-semicarbazide-1,2,4,5-tetrazine(DSTZ) was prepared and characterized by elemental analysis and Fourier transform infrared(FTIR) spectroscopy. The crystal structure was determined by X-ray single crystal diffraction technology. The crystal belongs to the monoclinic system with a P2₁/c space group, a=0.9942(7) nm, b=0.5067(3) nm, c=1.1830(8) nm, β=109.616°, Z=2 and D_c=1.475 g/cm³. With extensive hydrogen bonds, the molecules were linked together to form a three-dimensional herringbone-like pattern. Thermal analysis of the compound was carried out via differential scanning calorimetry(DSC) and thermogravimetric-derivative thermogravimetry(TG-DTG). Under a nitrogen atmosphere at a heating rate of 10 K/min, DSTZ decomposed directly in a range of 493-513 K. Only one intense exothermic process was observed and the decomposition products were all gaseous products. Conventional sensitivity properties were determined, showing that the title complex was insensitive to friction, impact and flame.     

A continuous shape sensitivity equation method for unsteady laminar flows

This paper presents the application of a general shape sensitivity equation method (SEM) to unsteady laminar flows. The formulation accounts for complex parameter dependence and is suitable for a wide range of problems. The flow and sensitivity equations are solved on 3D meshes using a Streamline-Upwind Petrov Galerkin (SUPG) finite element method. In the case of shape parameters, boundary conditions for sensitivities depend on the flow gradient at the boundary. Therefore, an accurate recovery of solution gradients is crucial to the success of shape sensitivity computations. In this work, solution gradients at boundary points are extracted using the Finite Node Displacement (FiND) method on which the finite element discretization is enriched locally via the insertion of nodes close to the boundary points. The normal derivative of the solution is then determined using finite differences. This approach to evaluate shape sensitivity boundary conditions is embedded in the continuous SEM. The methodology is applied to the flow past a cylinder in ground proximity. First, the proposed method is verified on a steady state problem. The computed sensitivity is compared to the actual change in the solution when a small perturbation is imposed to the shape parameter. Then, the study investigates the ability of the SEM to anticipate the unsteady flow response to changes in the ground to cylinder gap. A reduction of the gap causes damping of the vortex shedding while an increase amplifies the unsteadiness.     

Shape Sensitivity and Design for Fluids with Shocks

For many problems of compressible fluid dynamics it is desirable to find the sensitivity of the shock position with respect to the shape of the domain occupied by the fluid. One application is for the minimization of the sonic boom of airplanes; another is for the stability of the stream in fast-flowing rivers or canals. Classical calculus of variation is not valid for these cases because of the presence of Dirac functions appearing when a discontinuous function is differentiated, but we show here on the compressible potential flow equation how to find the equations of the derivatives and what are the linearized problems. Some numerical test cases are given for illustration.