A variable band universal flux/charge modulator for VSI and CSImodulation

This paper presents an integrated approach for closed-loop control of the output voltage of a voltage-source inverter and the output current of a current-source inverter, using hysteresis with a rectangular bounding box in the synchronous d-q reference frame and a simple set of switching rules. The modulator is constrained to only select from the two nearest active space vectors to the target reference, and hence achieves a significantly improved harmonic performance compared to Sigma-Delta and other stationary frame hysteresis modulators. A further refinement then adjusts the dimensions of the bounding box to restrict the switching process to two active space vectors (and null vectors) only within a constant switching period. This achieves a harmonic performance similar to open-loop space-vector modulation. Discontinuous modulation can also be implemented using an alternative dimension-varying strategy and, since the modulator is a closed-loop system, it exhibits excellent robustness to parameter variations and other system disturbances. The practicability and performance of the modulator under various modulation conditions have been verified both in simulation and experimentally     

Superconducting Microcomposites by Oxidation of Metallic Precursors

Applications of high-temperature superconducting oxides will be severely limited unless they exhibit sufficient mechanical properties (flexibility, fracture toughness, etc.) and electrical properties (low contact resistance, low a.c. losses, etc.), in addition to having sufficiently high critical temperatures, current densities and magnetic fields. Metal/superconducting oxide microcomposites appear to be on form in which these new materials can meet service requirements.     

Constraint-Based Fuzzy Models for an Environment with Heterogeneous Information-Granules

A novel framework for fuzzy modeling and model-based control design is described. Based on the theory of fuzzy constraint processing, the fuzzy model can be viewed as a generalized Takagi-Sugeno （TS） fuzzy model with fuzzy functional consequences. It uses multivariate antecedent membership functions obtained by granular-prototype fuzzy clustering methods and consequent fuzzy equations obtained by fuzzy regression techniques. Constrained optimization is used to estimate the consequent parameters, where the constraints are based on control-relevant a priori knowledge about the modeled process. The fuzzy-constraint-based approach provides the following features. 1） The knowledge base of a constraint-based fuzzy model can incorporate information with various types of fuzzy predicates. Consequently, it is easy to provide a fusion of different types of knowledge. The knowledge can be from data-driven approaches and/or from controlrelevant physical models. 2） A corresponding inference mechanism for the proposed model can deal with heterogeneous information granules. 3） Both numerical and linguistic inputs can be accepted for predicting new outputs. The proposed techniques are demonstrated by means of two examples： a nonlinear function-fitting problem and the well-known Box-Jenkins gas furnace process. The first example shows that the proposed model uses fewer fuzzy predicates achieving similar results with the traditional rule-based approach, while the second shows the performance can be significantly improved when the control-relevant constraints are considered.     

Synthesis of poly(2,3-dimethyl-1,3-butadiene) and its hydrogenation using a metallocene/n-butyllithium catalyst system

Poly(2,3-Dimethyl-1,3-butadiene) (PDMB) with varying contents of 1,4-and 1,2-structures has been anionically synthesized using either n-butyllithium or sec-butyllithium as an initiator. The addition of tetrahydrofuran could enhance the rate of synthesis and effect the microstructure. The T_m was higher for PDMB with a lower content of 1,2-structure, and the T_g was lower. This PDMB was then hydrogenated with a nickelocene/n-butyllithium catalyst system leading to the formation of HPDMB. The trans 1,4-structure unit was more difficult to hydrogenate due to its steric hindrance. Repetitive hydrogenation was necessary in order to achieve a high degree of hydrogenation. The hydrogenated PDMB is an amorphous elastomeric material. The T_g’s were found to decrease with an increase in the degree of hydrogenation, concurrent with a gradual disappearance of the T_m’s. Since a HPDMS with a low content of 1,2-structure resembles a head-to-head polypropylene, our data suggest that the T_g of an atactic head-to-head polypropylene lie between −30 and −35 °C.     

面向老年人的地铁空间用户需求研究

目的香港老龄化日益加剧,香港城市生活将面临巨大的挑战。从用户研究的角度,研究老年人地铁日常生活与需求,从而发掘老年人地铁生活中的设计机会,为提升老年人地铁生活体验提供路径。方法以香港地铁为例,通过观察、调查问卷、采访,用户旅程地图等用户研究方法,对老年人在地铁日常生活中的需求进行了研究,对影响老年人地铁生活质量的因素进行了重要性排序,建立老年人地铁需求金字塔。结论获得了15个影响老年人地铁生活的要素,同时获得了这15个要素的重要性排序,从而建立了老年人地铁需求金字塔。提出了提升老年人的地铁使用体验要从生理性需求,独立性需求和娱乐性需求3个层面入手,并逐层递进。     

Current Development,Obstacle and Futural Direction of Induced Pluripotent Stem Cell and Mesenchymal Stem Cell Treatment in Degenerative Retinal Disease

Degenerative retinal disease is one of the major causes of vision loss around the world. The past several decades have witnessed emerging development of stem cell treatment for retinal disease. Nevertheless, sourcing stem cells remains controversial due to ethical concerns and their rarity. Furthermore, induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs) are both isolated from patients’ mature tissues; thus, issues such as avoiding moral controversy and adverse events related to immunosuppression and obtaining a large number of cells have opened a new era in regenerative medicine. This review focuses on the current application and development, clinical trials, and latest research of stem cell therapy, as well as its limitations and future directions.     

Investigations of thin films on GaAs using the proton resonant scattering technique

We have characterized a number of thermally stable thin film/GaAs systems including thin films of refractory metal suicides and nitrides as well as dielectric films on GaAs substrates using a MeV proton scattering technique. Thin films of tungsten suicides, zirconium nitride and silicon dioxide on GaAs substrates are investigated. The enhanced proton scattering cross sections of nitrogen, silicon and oxygen at their corresponding resonant energies enable us to accurately measure the compositions of these films. The advantages and disadvantages of this technique regarding depth resolution, accessible depth, and mass resolution compared to the conventional Rutherford backscattering spectrometry for thin film analysis are discussed.     

Hydrogenation of natural rubber using nickel 2-ethylhexanoate catalyst in combination with triisobutylaluminum

Kinetic studies for the homogeneous hydrogenation of natural rubber, in the presence of nickel 2-ethylhexanoate and triisobutylaluminum, have been carried out by monitoring the change in hydrogen pressure in a Parr reactor of fixed volume. ¹H-NMR spectroscopy provides the measurements of the extent of hydrogenation. The reaction kinetics, in the presence of a fixed amount of catalyst, showed an overall second-order kinetic with respect to [H₂] and [CC]. The reaction has a relatively low apparent activation energy of 26.0 kJ mol^-1 and is therefore suitable for the hydrogenation of natural rubber at ambient conditions to minimize side reactions. The impurities in commercial rubbers have a slight effect on the catalyst activity. © 1996 John Wiley & Sons, Inc.     

Multi-scaled polymersomes from self-assembly of octadecanol-modified dextrans

Lipid-conjugated polysaccharide vesicles in nano- and micro-scale were developed from amphiphilic octadecanol-modified dextrans (OMD) prepared by partial esterification of dextran with activated octadecanol-carbamate imidazole in a well-controlled manner. The critical aggregation concentration (CAC) of OMD adducts in aqueous phase varies, depending mainly on their octadecanol contents. Through supramolecular assembly of the OMD adducts comprising either 17 or 28 mol% octadecanol residues with respect to the anhydroglucopyranose units by the partial solvent displacement technique with the initial water content of DMSO/H₂O solutions beyond a critical point, stable nano-scaled OMD assemblies were developed and characterized by the vesicle-like morphology. The dimension of polymersomes can be effectively controlled by the OMD composition as well as the initial water content. On the other hand, micro-scaled OMD polymersomes can be achieved by the double emulsion technique in a water/oil/water (w₁/o/w₂) manner. Both the contents of NaCl in aqueous solution as the w₁ phase and of DMSO in DMSO/CHCl₃ co-solvents as the organic phase, in which OMD was dissolved, are of great importance in controlling the polymersome morphology and size. These micro-scaled OMD polymersome walls are characterized by size-selective permeability capable of encapsulating large water-soluble cargoes while allowing transport of small polar species across the membrane, thereby rendering these unique colloidal particles of potential applications in biomedical technologies.