6-O-羧甲基壳聚糖的乳化性能与结构的关系

研究了甲壳素核甲基化反应条件对产物结构的影响,讨论了6-O-羧甲基壳聚糖的乳化性能与结构的关系,结果表明,产物取代度在0.7～0.9之间,-NH2含量＞64％,粘度＞0.14Pa·s,产物具有良好的乳化性和水溶性,并通过响应面分析（RSA）优化了改性条件,最佳反应条件是;甲壳素用40％NaOH溶液浸4h,在破与氯乙酸重量比为1.2：1和温度40℃条件下反应2h,再在50℃时保温12h,即制备得到一种水溶性高的新型乳化剂6-O-羧甲基亮聚精。     

UMHexagonS算法的研究与改进

针对UMHexagon S算法存在的问题,提出了一种改进的UMHexagon S算法。算法充分利用运动矢量的中心偏置特性与运动同质性,采用递增数列步长的对称十字型搜索模板和多层次八边形搜索模板以减少无用的搜索点,根据运动矢量的变化趋势自适应地确定多层次八边形的搜索方向,用16点井字型搜索代替5×5全搜索,并改善了运动估计的粗定位。实验结果表明,与UMHexagon S算法相比,改进算法在保证PSNR和比特率基本不变的前提下,平均减少了18.53%的运动估计时间,尤其是对大运动视频序列的效果更好,最大可以减少25.17%的运动估计时间。     

Design and implementation of FFT/IFFT in IEEE 802.16d OFDM system

The IEEE 802.16 standard specifies the air interface of wireless metropolitan area network (WMAN), and aims to provide wireless broadband access for integrated voice and video services. This paper presents the efficient design and implementation of fast Frouier transform (FFT) and inverse fast Frouier transform (IFFT) for the application in IEEE 802.16d orthogonal frequency division multiplexing (OFDM) system. In this design, a novel pipeline structure for the branch of butterfly unit (BU) is proposed, which can improve the processing symbol rate by adding the number of branch flexibly. The symmetrical ping-pang structure of random access memory (RAM) is performed to increase the system throughput. Simulation results reveal that only with 1 branch of BU, the proposed FFT/IFFT design can almost achieve the maximum bandwidth requirement of IEEE 802.16d OFDM system. And this design has been verified by FPGA and successfully implemented in the prototype of WiMAX transceiver.     

PBL在电路课程教学中的应用

本文介绍了PBL教学方法,讨论其在电路课程中的应用基础,举证一个PBL在电路课程中的应用案例,分析PBL在电路课程中应用的关键和难点.     

Nickel silicide nanocrystal-containing magnetoceramics from the bulk pyrolysis of polysilazane and nickelocene

Nickel silicide nanocrystal containing Si–Ni–C–N multiphase ceramics were synthesized by bulk pyrolysis of the mixture of polysilazane (PSZ) and nickelocene (NiCp₂) at high temperature. The pyrolysis behavior of the precursors was investigated by TGA/DSC-Mass Spectrometry. The yield of the ceramic containing NiCp₂ precursor was increased by 8–10% compared to pure PSZ. Nickel silicide nanocrystal containing ceramics were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. The NiCp₂ in polymeric precursors induced the formation of α-Si₃N₄, SiC, graphitic carbon, and Ni₂Si at 1100 °C. Nickel silicide nanocrystals containing ceramics exhibited soft magnetism with ultralow hysteresis loss offering a convenient cost effective approach for the preparation of tunable transition metal-containing ceramics using a commercial inexpensive polymeric precursor of NiCp₂.     

Microstructure and high-temperature friction and wear behavior of WC-(W,Cr)2C-Ni coating prepared by high velocity oxy-fuel spraying

WC-(W,Cr)₂C-Ni coating was prepared by high velocity oxy-fuel spraying (HVOF). The microstructure and phase composition of the as-sprayed coating and that after oxidation at high temperature were analyzed by means of scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The oxidation behavior of as-sprayed coating and starting powders was evaluated by thermogravimetry. Dry sliding friction and wear behavior of the WC-(W,Cr)₂C-Ni coating sliding against Si₃N₄ ball at different temperatures (room temperature 20 °C and elevated temperature of 700 °C and 800 °C) was evaluated using an oscillating friction and wear tester. Besides, the microhardness and fracture toughness of the coating was also measured. Results show that sintering agglomerated WC-20 wt.%Cr-7 wt.%Ni powder is an effective method to prepare agglomerated and sintered WC-(W,Cr)₂C-Ni composite powder. The excellent oxidation resistance of WC-(W,Cr)₂C-Ni coating is mainly resulted from a double-decker shell-core microstructure formed in the coating. The composition of the outer shell is (W,Cr)₂C phase and that of the inner shell is Cr₃C₂. During high-temperature friction and wear test, well remained hard WC phase in the WC-(W,Cr)₂C-Ni coating can guarantee its good mechanical properties and wear resistance, and newly generated nano NiWO₄, CrWO₄ and Cr₂WO₆ particles can further improve these properties significantly.     

两步刻蚀多晶硅提高图形陡直度

微电子机械系统中关键工艺之一就是刻蚀出高深宽比的图形。本文对掺磷多晶硅反应离子刻蚀（ＲＩＥ）进行了研究,采用两步刻蚀工艺,ＳＦ６,ＣＦ４,Ｃｌ２ＣＦ三种气体组合,从原来４５度的各向同性刻蚀提高到７３度以上的各向异性蚀。射频功率３９０瓦时,刻蚀速率每分钟２００ｎｍ。对３．５微米厚的多晶硅,刻蚀时间在２０分钟左右,基本上达到要求。