Facile preparation of amphiphilic oxyethylene-oxypropylene block copolymers by selective triazine coupling

A novel synthetic route for preparing high molecular weight poly(oxyalkylene) block copolymers has been developed by using 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride, cc) as the coupling core. The coupling reaction involves the selective substitutions of oligo(oxyalkylene)-amines onto three chlorides of the triazine ring in a stepwise manner at 0, 25 and 130 °C. By judiciously selecting the starting amines and reaction conditions, one can tailor the copolymer structures with different block configurations (tri-block, multi-block, random and alternating block). The prepared copolymers can have a high molecular weight, up to 25,600 g/mol (GPC polydispersity=1.48), and also high thermal stability due to the presence of triazine functionalities. The copolymers with hydrophilic and hydrophobic oligo(oxyalkylene) blocks are of versatile properties in solubility (water soluble or water insoluble) and morphology (crystalline or amorphous). With a specific structure of alternating oligo(oxyethylene)/oligo(oxypropylene) blocks (2000 g/mol each block), the copolymer exhibits the property of self-association. It reduces the interfacial tension of toluene/water as low as 0.5 dyne/cm at the critical micelle concentration of 0.01 wt%.     

Preparation of Titanium Nitride/Alumina Laminate Composites

A preparation route for TiN/Al₂O₃ laminate composites has been described. A water-based process using Al₂O₃ and TiN slurries with solids contents of 40 and 35 vol%, respectively, was used to make TiN and Al₂O₃ tapes. The removal of the binder was monitored by weight-loss measurements in a thermogravimetry unit. Bodies composed of Al₂O₃ and TiN tapes were densified at temperatures of 1400° and 1500°C using the Spark Plasma Sintering^® (SPS) technique. Densities of >98% of the theoretical densities were approached. Crack-free and almost fully densified TiN/Al₂O₃ compacts were prepared by heating the burned-out green bodies to the final sintering temperature (1500°C) at a rate of 100°C/min, and with a holding time of 5–10 min, under a pressure of 75 MPa. The microstructures of the obtained compacts were studied using scanning electron microscopy. Grain sizes in the sintered Al₂O₃ and TiN compacts were similar to those of the precursor powders. Hardness and indentation fracture toughness were measured at room temperature, and the monolithic compacts as well as the laminate composites exhibited anisotropic mechanical behavior; i.e., the cracks propagated much more easily in a direction parallel to the laminas than perpendicular to them.     

Stability analysis and controller synthesis for discrete uncertain singular fuzzy systems with distinct difference matrices in the rules

This paper mainly studies an extended discrete singular fuzzy model incorporating the multiple difference matrices in the rules and discusses its stability and design issues. By embracing additional algebraic constraint, traditional discrete Takagi-Sugeno (T-S) fuzzy model can be extended to a generalised discrete singular Takagi-Sugeno (GDST-S) model with individual difference matrices E_i in the locally singular models, where it can describe a larger class of physical or non-linear systems. Based on the linear matrix inequality (LMI) approach, we focus on deriving some explicit stability and design criteria expressed by the LMIs for the regarded system. Thus, the stability verification and controller synthesis can be performed by the current LMI tools. Finally, some illustrative examples are given to illustrate the effectiveness and validity of the proposed approach.     

A generalized method for correcting instrument spreading in gel permeation chromatography

A general method of chromatogram correction for skewed instrument spreading in gel permeation chromatography is presented. The correction method is so general that there is no restriction on the shape of the spreading function. It admits nonsymmetric, non-Gaussian as well as nonconvolution type. Aspects of solution techniques are discussed and an illustrative example is given to elucidate the method.     

射流流化床内流体力学行为的模拟研究

以流化床应用为代表的气固流动系统是许多化工过程中的重要组成部分 ,CFD( computational fluid dynamics)方法能够为其优化设计和放大提供所需要的信息 .本文采用双欧拉模型 ,与 Gidaspow等的实验结果进行了对比 ,模拟了二维射流流化床内气泡的形成规律 ,得到了带锥型分布器的流化床内瞬时空隙率和气固相速度分布等流体力学参数 .对锥型分布器流化床的实验结果表明 ,模拟得到的气泡的形状与实验现象相接近 .     

Studies of microhardness and mar resistance using a scanning probe microscope

Scanning probe microscopy (SPM) is in a period of rapid development. It shows great promise for characterizing coating surfaces. This paper describes modification of an SPM so that it can be used to mar the surfaces of coatings under controlled conditions and to characterize the mars. Mar resistance of coatings is analyzed in terms of a ‘three response, two mechanism model.' The three responses (fracture, elastic, and plastic) can be measured quantitatively using the SPM. Of the three responses, only two (fracture and plastic deformation) are marring mechanisms – elastic deformations recover instantaneously. In some cases mars resulting from plastic deformation may recover slowly with time or with immersion in water; this phenomenon is attributed to viscoelastic creep. Microhardness is also measured with the modified SPM. Some thermoset coatings appear to be substantially harder near their surfaces than in the mass of material, and such materials may respond quite differently to stress applied at different levels near the surface. This finding has important implications for all coating properties that are strongly influenced by the surface. A quantity called ‘micro mar resistance' is defined. It may be useful for comparing different coatings under specified conditions of marring. However, there can be no single quantity that expresses ‘mar resistance' of a coating under all conditions.     

New polyimide–silica organic–inorganic hybrids

A series of polyimide–silica hybrid films with silica contents up to 30 wt % were successfully prepared by the sol‐gel reaction of tetraethoxysiliane in the presence of poly(amic acid) containing pendent hydroxyl groups. The films were yellow and transparent when the silica content was less than 11 wt %. The chemical structure of the films was characterized by Fourier transform infrared spectroscopy, and the morphology of the films was investigated by scanning electronic microscopy and atomic force microscopy. Thermogravimetric analysis, differential scanning calorimetry, and stress–strain tests were used to measure the performance of the films. The results indicate that the glass‐transition temperatures and decomposition temperatures of the hybrid films increased with increasing silica content, whereas the tensile strength had a maximum with the variety of silica contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2210–2214, 2003     

A parallel image encryption method based on compressive sensing

Recently, compressive sensing-based encryption methods which combine sampling, compression and encryption together have been proposed. However, since the quantized measurement data obtained from linear dimension reduction projection directly serve as the encrypted image, the existing compressive sensing-based encryption methods fail to resist against the chosen-plaintext attack. To enhance the security, a block cipher structure consisting of scrambling, mixing, S-box and chaotic lattice XOR is designed to further encrypt the quantized measurement data. In particular, the proposed method works efficiently in the parallel computing environment. Moreover, a communication unit exchanges data among the multiple processors without collision. This collision-free property is equivalent to optimal diffusion. The experimental results demonstrate that the proposed encryption method not only achieves the remarkable confusion, diffusion and sensitivity but also outperforms the existing parallel image encryption methods with respect to the compressibility and the encryption speed.     

A noisy-smoothing relevance feedback method for content-based medical image retrieval

In this paper, we address a new problem of noisy images which present in the procedure of relevance feedback for medical image retrieval. We concentrate on the noisy images, caused by the users mislabeling some irrelevant images as relevant ones, and a noisy-smoothing relevance feedback (NS-RF) method is proposed. In NS-RF, a two-step strategy is proposed to handle the noisy images. In step 1, a noisy elimination algorithm is adopted to identify and eliminate the noisy images. In step 2, to further alleviate the influence of noisy images, a fuzzy membership function is employed to estimate the relevance probabilities of retained relevant images. After noisy handling, the fuzzy support vector machine, which can take into account different relevant images with different relevance probabilities, is adopted to re-rank the images. The experimental results on the IRMA medical image collection demonstrate that the proposed method can deal with the noisy images effectively.     

高职院校特色专业监控体系建设研究

近年来,高职院校都比较注重特色专业的建设。其中,特色专业建设的监控体系也受到了高职院校的重视,并取得了一定的效果,同时,也给其他院校提供了有价值的参考和借鉴。但由于在认识水平、管理水平和教学水平等方面仍有一些问题,导致在监控过程和措施实施方面还存在许多疏漏,有待完善。