Encapsulation and Ostwald Ripening of Au and Au–Cl Complex Nanostructures in Silica Shells

We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle‐mediated self‐assembly. We have also used the as‐prepared multicore Au–silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au–Cl complex is formed inside the shell, and is found to be very active under in situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in situ studies of confined crystal growth.     

Experimental and modeling approaches of MR behaviors under large step strains

Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior.     

差分跳频通信系统的特点及性能

文章介绍了一种新型的短波跳频通信技术——差分跳频,分析了差分跳频技术区别于常规跳频技术的主要特点。针对按序列检测的信号接收方法,对差分跳频通信系统在AWGN信道下的性能进行了理论分析,同时做出相应的计算机仿真,证实了差分跳频通信技术和按序列检测方法的结合,使通信系统在AWGN信道下的性能得到了比较显著的提升。     

Na+、K+离子交换对Co-Mo/MCM-41加氢脱硫催化剂的影响

 用偏硅酸钠和正硅酸乙酯作硅源制备了MCM-41（分别记作MCM-41(S)和MCM-41(T)）分子筛，并用Na₂C₂O₄和K₂C₂O₄对MCM-41(S)进行了碱金属离子交换改性。以质量分数0.8 %的二苯并噻吩（DBT）的十氢萘溶液为模型化合物，考察了不同MCM-41担载的Co-Mo硫化物催化剂对DBT的加氢脱硫反应性能。结果表明，MCM-41担载的Co-Mo催化剂加氢活性较低，DBT主要通过直接脱硫反应路径脱硫。其活性顺序为：Co-Mo/MCM-41(T)>Co-Mo/MCM-41(S)>Co-Mo/MCM-41(K)>Co-Mo/MCM-41(Na)。UV-Vis结果表明，部分Co与MCM-41(S)中少量Al发生相互作用，生成了CoAl₂O₄，是造成Co-Mo/MCM-41(S)活性降低的重要因素。而在Co-Mo/MCM-41(K)和Co-Mo/MCM-41(Na)中，除CoAl₂O₄物种之外，碱金属的引入还促进了Co₃O₄物种的形成，使其活性进一步降低。     

光纤光栅感温火灾探测报警系统在原油罐区的应用

通过对现有罐区火灾自动报警技术的认真考察、对比,在石西集中处理站原油罐区安装了光纤光栅感温火灾探测报警系统.该报警系统的传感信号是光的波长变化,传感器及其探测系统是靠光缆连接而进入被测现场,它具有高安全性、高可靠性、高绝缘性、高抗电磁干扰性、防潮耐蚀、寿命长等其他传统火灾探测报警系统无法比拟的优越性能.阐述了其系统构成和运行效果.该系统在石西集中处理站运用效果良好.     

相关条件下基于N-P准则的分布式检测理论研究

本文针对并行网络、二元局部判决的情况,研究了在相关条件下基于N-P准则的分布式检测融合算法,给出了在联合概率密度已知和未知两种情况下的最优融合规则的理论推导及相应的解决方案,并在实验仿真的基础上,得到了部分有益的结论。     

一种的四进制CPM调制器的设计与FPGA实现

设计并实现了一种基于FPGA的四进制连续相位调制器（PCM）。该调制器的基带调制模块通过查表法实现，复杂度较低。仿真结果验证了设计的正确性。     

On the Feasibility of Growing Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Single Crystals

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg_1/3‐Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d₃₃, in the range of 1800–2200 pC N^–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states.     

Fabrication of Schottky barrier MOSFETs using self-assembly CoSi2 nanopatterning and spacer gate technologies

A self-assembly patterning method for generation of epitaxial CoSi₂ nanostructures was used to fabricate 50 nm channel-length MOSFETs. The transistors have either a symmetric structure with Schottky source and drain or an asymmetric structure with n⁺-source and Schottky drain. The patterning technique is based on anisotropic diffusion of Co/Si atoms in a strain field during rapid thermal oxidation. The strain field is generated along the edges of a mask consisting of 20 nm SiO₂ and 300 nm Si₃N₄. During rapid thermal oxinitridation (RTON) of the masked silicide structure, a well-defined separation of the silicide layer forms along the edge of the mask. These highly uniform gaps define the channel region of the fabricated device. The separated silicide layers act as metal source and drain. A poly-Si spacer was used as the gate contact. The asymmetric transistor was fabricated by ion implantation into the unprotected CoSi₂ layer and a subsequent out-diffusion process to form the n⁺-source. I–V characteristics of both the symmetric and asymmetric transistor structures have been investigated.     

Pack cementation process for the formation of refractory metal modified aluminide coatings on nickel-base superalloys

The vapour phase compositions of a series of pack powder mixtures containing elemental Al and Hf or W powders as depositing sources and CrCl₃·6H₂O or AlF₃or CrF₃as activators were analysed in an attempt to further develop the pack cementation process to codeposit Al and Hf or W to form diffusion coatings on nickel base superalloys. The results suggested that Al could be codeposited with Hf, but not with W, from the vapour phase. Compared with both AlF₃and CrF₃, CrCl₃·6H₂O has been shown to be a more suitable activator for codepositing Al with Hf. The optimum coating temperature was identified to be in the range of 1050°C to 1150°C. Based on the thermochemical analysis, a series of coating deposition studies were undertaken, which confirmed that codeposition of Al and Hf could be achieved at a deposition temperature of 1100°C in the CrCl₃·6H₂O activated packs containing elemental Al and Hf powders. The coating obtained had a multilayer structure consisting of a Ni₇Hf₆Al₁₆top layer and a NiAl layer underneath, followed by a diffusion zone, which revealed that the coating was formed by the outward Ni diffusion. It is suggested that the compositions suitable for codeposition of Al and Hf could be effectively identified by comparing the vapour pressures of HfCl₄and HfCl₃with that of AlCl in the packs activated by chloride salts. It has also been experimentally demonstrated that, although W could not be deposited from the vapour phase, a high volume of fine W particles can be entrapped into the outer NiAl coating layer formed by the outward Ni diffusion using a modified pack configuration. This leads to the formation of a composite coating layer with W particles evenly distributed in a matrix of NiAl. It is suggested that this modified pack process could be similarly applied to develop nickel aluminide coatings containing other refractory metals that may not be codeposited with Al from the vapour phase.