Influence of resonance tube geometry shape on performance of thermoacoustic engine

Based on the linear thermoacoustics, a symmetrical standing-wave thermoacoustic engine is simulated with a cylindrical tube and a tapered one as the resonance tube, respectively. The experiments with both cylindrical and tapered tubes are carried out. The suppression of nonlinear effects due to tapered tube as the resonance tube is discussed. Both simulation and experimental results show that the performance of the tapered tube is better than cylindrical one as the resonance tube.     

Progress of nanoscience in China

Fast evolving nanoseienees and nanotechnology in China has made it one of the front countries of nanotechnology development. Ill this review, we summarize some most recent progresses in nanoseienee research and nanotechnology development in China. The topics we selected in this article include llano-fabrication, nanocatalysis, bioinspired nanoteehnology, green printing nanotechnology, nanoplasmonics, nanomedicine, nanomaterials and their applications, energy and environmental nanoteehnology, nano EHS （nanosafety）, etc. Most of them have great potentials in applications or application-related key issues in future.     

不同润湿性纳米通道内库埃特流动的模拟

利用非平衡分子动力学模拟方法, 模拟了两无限大平行平板组成的纳米通道内的库埃特流动, 并给出了壁面润湿性和速度对流场密度、速度分布及壁面滑移的影响规律.数值模拟中, 统计系综采用微正则系综, 势能函数选用LJ/126模型, 壁面设为刚性原子壁面, 温度校正使用速度定标法, 牛顿运动方程的求解则采用文莱特算法.结果表明, 纳米通道内流体密度呈对称的衰减振荡分布, 且随壁面润湿性的降低, 振荡幅度减小, 振荡周期保持不变;滑移量随壁面润湿性的提高而降低, 甚至在亲水壁面时出现负滑移现象;随壁面速度的增加滑移速度逐渐增大, 且在流体呈现非线性流动阶段其增幅显著加大.另外, 还发现当壁面设置为超疏水性时, 壁面滑移呈现出随润湿性降低而减小的反常现象, 并基于杨氏方程对其进行了解释.     

热机载荷作用下三维界面裂纹问题的权函数法分析

热机载荷共同作用下双材料和复合材料中的裂纹扩展往往发生在界面处,并且工程中实际遇到的裂纹大多数是三维裂纹.由于通用权函数仅仅与裂纹体的几何形状有关,与载荷、时间无关,因此在求解复杂冲击载荷下界面裂纹应力强度因子随时间的变化过程时,避免了反复的应力分析,计算效率得到提高.根据Betti互易原理,论文推导出三维界面裂纹问题通用权函数法的普遍表达式,并给出了热机载荷共同作用下三维界面Ⅰ型、Ⅱ型和Ⅲ型裂纹问题通用权函数法的有限元格式.通过与实例计算比较,表明此方法得到的结果可以达到满意的工程应用精度.     

A novel block cryptosystem based on the coupled chaotic map lattice

In this paper, the authors propose a novel block cryptographic scheme based on the coupled chaotic map lattice. A pseudorandom number generator is constructed with the coupled spatiotemporal chaotic map lattice, which depends on the plaintext. The plaintext block is then encrypted by the classical chaotic masking technique. The pseudorandom sequences produced by the generator have excellent statistical properties; therefore, they are suitable for encrypting messages. Moreover, it can be easily implemented in parallel by hardware. Both theoretical analysis and numerical simulation prove the block cryptographic scheme secure and practical.     

基于荧光共轭聚合物的金属离子传感研究

设计合成了一系列结构相似的共轭主链含5%苯并噻二唑结构单元及侧链带胺类金属离子螯合基团的阴离子型水溶性共轭聚合物PFA, PFBTA和PFBTNA, 并对它们在不同极性溶剂中的光物理性质进行了研究. 利用分子主链含适量苯并噻二唑共聚单元的聚芴衍生物聚集态不同荧光光谱及颜色发生显著变化这一特性, 研究了这一系列水溶性聚芴衍生物在水/甲醇(9/1)溶液中对金属离子的荧光响应过程. 结果表明, 金属离子不仅能通过能量及电荷转移猝灭聚合物荧光, 还可以通过静电相互作用力使聚合物聚集态发生改变, 进而影响聚合物的光学性质. 同时分子链上引入金属离子螯合基团能够显著提高体系的检测灵敏度, 聚合物PFBTA和PFBTNA可以特异性识别Cu²⁺离子, 并且可做为其它金属离子的广谱型比色法检测材料.     

P3HT与CdTe纳米枝晶p-n异质结敏化ZnO纳米管阵列的光电化学研究

采用电化学方法首先在ITO导电玻璃上制备了一维有序ZnO纳米管阵列,然后在ZnO纳米管阵列上采用电化学方法沉积纳米枝状CdTe,形成了纳米枝状CdTe包覆ZnO纳米管的CdTe@ZnO壳核式复合结构,最后在上述复合结构中旋涂一层P3HT薄膜形成P3HT包覆的P3HT@CdTe@ZnO复合薄膜. 以此复合薄膜为光活性层组装成半导体敏化太阳电池,研究了该类电池的光电转换性能,对该电池的工作原理进行初步研究,所得太阳电池能量转换效率最高达到1.38%.     

Structures of Pt clusters on graphene doped with nitrogen, boron, and silicon: a theoretical study

The structures of Pt clusters on nitrogen-,boron-,silicon-doped graphenes are theoretically studied using densityfunctional theory.These dopants(nitrogen,boron and silicon) each do not induce a local curvature in the graphene and the doped graphenes all retain their planar form.The formation energy of the silicon-graphene system is lower than those of the nitrogen-,boron-doped graphenes,indicating that the silicon atom is easier to incorporate into the graphene.All the substitutional impurities enhance the interaction between the Pt atom and the graphene.The adsorption energy of a Pt adsorbed on the silicon-doped graphene is much higher than those on the nitrogen-and boron-doped graphenes.The doped silicon atom can provide more charges to enhance the Pt-graphene interaction and the formation of Pt clusters each with a large size.The stable structures of Pt clusters on the doped-graphenes are dimeric,triangle and tetrahedron with the increase of the Pt coverage.Of all the studied structures,the tetrahedron is the most stable cluster which has the least influence on the planar surface of doped-graphene.     

Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy

The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz--Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS₂) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS₂-lithium grease than that of lithium grease.     

Dynamic control of retrieval contrast in a Λ-type atomic system

We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in Λ configuration. The memory procedure consists of write-in, storage, and retrieval phases. By applying a weak microwave field in the storage stage, additional phase-dependent terms are included, and the contrast of the output signal pulses can be dynamically controlled (enhanced or suppressed) through manipulating the relative phase φ between optical and microwave fields. Our numerical analysis shows that the contrast is enhanced to the most extent when φ=1.5π. In addition, the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.