Generation of mesoporosity in MOR zeolites synthesized under perturbation conditions

The hydrothermal synthesis of various mesoporous materials with mordenite (MOR) structures is performed under perturbation conditions involving varying-temperature crystallizations and the use of ternary organic templates, and at least three types of mesoporous materials are obtained from the same starting gel containing the ternary organic templates. The greater structural diversities of these materials are found to correlate remarkably with the second-staged crystallization temperature and time. Among these materials, the two mesoporous materials crystallized incompletely over low temperature periods are differently structural composites consisting of MOR crystallites within disordered mesoporous phases, whereas the mesoporous mordenite crystallized completely over relatively high temperature period possesses the intrinsic microporosity and hierarchical mesoporosity. TEM morphological investigations on the mesoporous mordenite crystals demonstrate the formation of intracrystalline mesopores. Furthermore, an entirely new approach to synthesize mesoporous MOR zeolites is proposed based on the pore-inducing role of MOR structure defects and the adequate perturbation towards synthesis conditions.     

Temperature effect on synthesis of different carbon nanostructures by sulfur-assisted chemical vapor deposition

The temperature effect on synthesizing different carbon nanostructures in the range of 820−1020 °C by sulfur-assisted chemical vapor deposition is investigated. When the growth temperature is no more than 900 °C (e.g. 820, 860, and 900 °C), carbon onions can be obtained, accompanying with some fishbone-like carbon nanofibers (CNFs), graphite sheet and carbon nanotubes (CNTs). When the growth temperature is increased to 940 °C or above (e.g. 980 and 1020 °C), the products are mainly CNTs. Furthermore, by comparing the nitrogen adsorption-desorption results of samples obtained with and without sulfur addition at each temperature, it is found that the specific surface area (SSA) of products can be remarkably enlarged after introducing small amount of sulfur during growth. This is favorable to their applications in areas like electrodes of supercapacitors, adsorbents, catalyst supports, and so on.     

Enhanced work hardening in Hadfield steel during explosive treatment

This paper presents results concerning Hadfield steel subjected to explosive treatment and compression, respectively, with the purpose of clarifying the difference between dynamic and static deformation behaviors. A Hadfield steel sample that was deformed to a lower strain at an exceptionally high strain rate exhibited the same hardness as a sample that was deformed to a higher strain at a low strain rate. A deformation model based on in situ deformation has been developed, whereby the enhanced work hardening during explosive treatment is attributed to the deformation of the grains being mainly accommodated by the curvature of the grain boundaries and shape change of the surrounding grains in their original positions, without obvious macroscopic deformation.     

基于CFD软件的电力电子设备强制风冷散热的数值模拟

随着电力电子技术的发展,对电力电子设备散热问题的研究日益重要。该文运用CFD软件对电力电子设备的强制风冷散热进行数值模拟研究,得出简单可行的散热方案,为设备的散热设计提供一定的依据,提高设备的可靠性。     

Improvement of resistive switching characteristics in ZrO2 film by embedding a thin TiOx layer

The stabilization of the resistive switching characteristics is important to resistive random access memory (RRAM) device development. In this paper, an alternative approach for improving resistive switching characteristics in ZrO(2)-based resistive memory devices has been investigated. Compared with the Cu/ZrO(2)/Pt structure device, by embedding a thin TiO(x) layer between the ZrO(2) and the Cu top electrode, the Cu/TiO(x)-ZrO(2)/Pt structure device exhibits much better resistive switching characteristics. The improvement of the resistive switching characteristics in the Cu/TiO(x)-ZrO(2)/Pt structure device might be attributed to the modulation of the barrier height at the electrode/oxide interfaces.     

A smart multifunctional nanocomposite for intracellular targeted drug delivery and self-release

A multifunctional 'all-in-one' nanocomposite is fabricated using a colloid, template and surface-modification method. This material encompasses magnetic induced target delivery, cell uptake promotion and controlled drug release in one system. The nanocomposite is characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, N(2) adsorption and vibrating sample magnetometry. The prepared material has a diameter of 350-400 nm, a high surface area of 420.29 m(2) g(-1), a pore size of 1.91 nm and a saturation magnetization of 32 emu g(-1). Doxorubicin (DOX) is loaded in mesopores and acid-sensitive blockers are introduced onto the orifices of the mesopores by a Schiff base linker to implement pH-dependent self-release. Folate was also introduced to improve DOX targeted delivery and endocytosis. The linkers remained intact to block pores with ferrocene valves and inhibit the diffusion of DOX at neutral pH. However, in lysosomes of cancer cells, which have a weak acidic pH, hydrolysis of the Schiff base group removes the nanovalves and allows the trapped DOX to be released. These processes are demonstrated by UV-visible absorption spectra, confocal fluorescence microscopy images and methyl thiazolyl tetrazolium assays in vitro, which suggest that the smart nanocomposite successfully integrates targeted drug delivery with internal stimulus induced self-release and is a potentially useful material for nanobiomedicine.     

The multi-domain hybrid boundary node method for 3D elasticity

In this paper, a multi-domain technique for 3D elasticity problems is derived from the hybrid boundary node method (Hybrid BNM). The Hybrid BNM is based on the modified variational principle and the Moving Least Squares (MLS) approximation. It does not require a boundary element mesh, neither for the purpose of interpolation of the solution variables nor for the integration of energy. This method can reduce the human-labor costs of meshing, especially for complex construction. This paper presents a further development of the Hybrid BNM for multi-domain analysis in 3D elasticity. Using the equilibrium and continuity conditions on the interfaces, the final algebraic equation is obtained by assembling the algebraic equation for each single sub-domain. The proposed multi-domain technique is capable to deal with interface and multi-medium problems and results in a block sparsity of the coefficient matrix. Numerical examples demonstrate the accuracy of the proposed multi-domain technique.     

Influencing factors on the size uniformity of self-assembled SiGe quantum rings grown by molecular beam epitaxy

The size uniformity of self-assembled SiGe quantum rings, which are formed by capping SiGe quantum dots with a thin Si layer, is found to be greatly influenced by the growth temperature and the areal density of SiGe quantum dots. Higher growth temperature benefits the size uniformity of quantum dots, but results in low Ge concentration as well as asymmetric Ge distribution in the dots, which induces the subsequently formed quantum rings to be asymmetric in shape or even broken somewhere in the ridge of rings. Low growth temperature degrades the size uniformity of quantum dots, and thus that of quantum rings. A high areal density results in the expansion and coalescence of neighboring quantum dots to form a chain, rather than quantum rings. Uniform quantum rings with a size dispersion of 4.6% and an areal density of 7.8×10(8) cm(-2) are obtained at the optimized growth temperature of 640°C.     

过氧化氢对质子交换膜热分解机理的影响

采用非等温热重-微分热重(TG-DTG)技术研究了燃料电池质子交换膜在过氧化氢氧化后的热分解机理,并用Achar和Coats-Redfem方法对非等温动力学数据进行了分析,得到了其热分解的反应机理函数和动力学参数.计算结果显示,第一阶段热分解过程受(D3)三维扩散机理控制,表现活化能为172.6 kJ/mol,指前因子...     

Modeling and simulation of InAs/GaAs quantum dot lasers

Based on the analysis of carrier dynamics in quantum dots (QDs), the numerical model of InAs/GaAs QD laser is developed by means of complete rate equations. The model includes four energy levels and among them three energy levels join in lasing. A simulation is conducted by MATLAB according to the rate equation model we obtain. The simulation results of PI characteristic, gain characteristic and intensity modulation response are reasonable. Also, the relations between the left facet reflectivity of laser cavity and threshold current as well as modulation bandwidth are studied. It is indicated that the left facet reflectivity increasing can result in reduced threshold current and improved modulation bandwidth, which is in accordance with experimental results. The internal mechanism of QD lasers is fully described with the rate equation model, which is helpful for QD lasers research.