壳聚糖超细微粉的制备及其微观形态结构变化的研究

圆盘式粉碎机在常温下粉碎片状壳聚糖 ,制备平均粒径为 7.6 5μm,粒径分布范围为 0 .4— 32μm的壳聚糖超细粉末。以扫描电镜、粒度分析、红外光谱、分子量测定和 X射线衍射等测试技术 ,研究粉碎过程中壳聚糖形貌、粒径、分子结构和结晶结构等变化。结果表明 ,壳聚糖超细粉末具有粒径小、粒度分布窄、分子量较高等特点 ;除了结晶度由 5 7.9%下降为 34.6 %而导致其水溶性显著提高外 ,化学结构未因粉碎过程的机械作用而显著变化。     

射频感应等离子体制备球形钨粉的工艺研究

 采用射频感应等离子体球化颗粒形状不规则的钨粉（平均粒度尺寸5～12 μm）,研究了加料速率、物料分散方式、钨粉颗粒大小等因素对球化率的影响。当加料速率大于95 g/min时,粉体的球化率随着加料速率的增大急剧减小,加料速率增大到135.75 g/min时,样品钨粉球化率仅为30%。当携带气量为0.12 m3/h 时,分散效果较佳,其球形度相应也较好,球化率几乎达到100%;随着钨粉球化率提高,其松装密度有所增大。通过对不同粒度分布的原粉进行球化处理,得出结论：钨粉原粉粒度分布均匀,则相应制备出的球形钨粉的粒度分布也比较均匀。     

等离子体中的颗粒成长模型

研究等离子体环境下的带电微小颗粒的成长过程．在收集离子和颗粒间凝合两种成长机制中,后者起主要作用,使生成的颗粒粒度接近．基于能量均分定理提出一个简化的模型,推导出颗粒粒度分布函数的动力方程．初步的数值模拟结果证实了上述成长机制的设想. 关键词：     

窄筛分水洗沙的气测和水测渗透率实验

为证实随粒度变细无因次渗透率变大是气测渗透率的特有规律,对粒度100-450μm范围内的五种窄筛分水洗沙的渗透率进行了实验测量对比。实验结果表明,随粒度变细,气测无因次渗透率规律变大是固有的,是流动滑移增强的结果。平均粒度402．5μm筛分沙形成的孔隙尺度不是受流动滑移影响的终结尺度。流动滑移影响远比认定的强,不限于Kn>10-3。同粒度范围内水测渗透率受流动滑移影响不明显,五种筛分沙的无因次渗透率-孔隙率数据几乎都落在曲线K~(1/2)／d=0．283Φ2.67的±4．1％以内。出人预料的是,不受流动滑移的水测渗透率并不比受流动滑移影响的气测渗透率低。平均粒度402．5μm筛分沙的气测渗透率比水测渗透率低近46％,远大于渗透率,孔隙率测量误差之和。数表气体粘度系数包括流动滑移成分,数值偏低是可能的。     

CeO_2掺杂对单畴GdBCO超导块材性能的影响

本文采用顶部籽晶熔融织构方法(TSMTG),分别制备出了直径为17mm的掺杂和未掺杂CeO2的单畴GdBCO超导块材,其中样品中CeO2的掺杂量为1wt%,并且研究了CeO2的掺杂对样品形貌、微观结构、磁悬浮力、以及捕获磁通的影响.研究表明了CeO2的掺杂影响超导块材的生长速率,在微观形貌上,CeO2的掺杂使样品中Gd2BaCuO5(Gd211)粒子的分布更加均匀且粒度明显变小,其平均粒径约从原来未掺杂的5.49μm减小到1.32μm,并且块材中的气孔也明显减小,从而使样品的磁悬浮力从23.06N增加到31.42N,捕获磁通从0.288T增加到0.354T.这对进一步提高超导块材的性能具有重要的指导意义     

超声场强化溶液结晶研究进展

溶液结晶技术在很多领域有着广泛的应用，超声强化溶液结晶不仅可刺激结晶成核，而且也可提高结晶生长速率，控制晶体粒径的分布，提高产品的质量和结晶设备的生产能力，具有重要的理论和实际意义，本文论述了这方面的研究进展情况，并提出了存在的问题和展望。     

氟磷共掺杂二氧化硅光纤预制棒的表面晶化

对F、P共掺杂光纤预制棒退火后的表面晶化行为进行了研究．由改进的化学汽相沉淀法制备的氟和磷共掺杂二氧化硅光纤预制棒玻璃样品在6h的115℃控温加热处理后，其表面发生晶化．用X-射线衍射仪观测其晶相，主要为旷方石英，可使玻璃具有二阶光学非线性；用光学显微镜观察了其表面形貌并对结晶微粒的大小进行测量，知晶粒大小在十几到几十μm之间，会造成散射损耗的增加．实验结果，还显示氟对结晶过程有很大的影响．     

多碱光电阴极层状——铯处理多碱光电阴极的附加厚度

根据多碱光电阴极制备过程中的光谱响应在0．4－0．5μm之间光电流减少这一事实，分析了Cs处理多碱光电极的厚度。结果表明，经第一次Cs处理，4μm处的光电流由6mA／W下降到3．8mA／W，第二次处理又进一步降低到1．6mA／W。其主要原因是Cs处理形成的K2CsSb具有一定厚度，光电子在输运过程中由于厚度增加导致散射几率增加，逸出几率下降，从而使光电发射下降。     

钢质薄壁气缸套超声珩磨的研究

作者作用自行研制的立式超声珩磨装置对钢质薄壁气缸套本体进行了超声珩磨试验，分别以表面粗糙度和珩磨效率为指标对超声珩磨油石进行了正交试验，确定了超硬磨料，粒度和结合剂对表面粗糙度和珩磨效率的影响顺序，试验结果表明，超声珩磨钢质薄壁气缸套可提高珩磨效率１－３倍，表面粗糙度Ｒａ可达０．５－２．１μｍ，超声珩磨解决了钢质薄壁气缸的加工难题，开辟了一条高效率珩磨加工软钢的途径。     

薄铝埋点等离子体K线光谱半定量诊断

高温等离子体系统中存在等离子体流体力学运动演化过程、离子的离化分布演化动力学过程、高剥离态离子谱发射过程及发射芬光辐射输运过程等，而且高温等离子体系统通常是非平衡系统，所以定量研究高温等离子体系统的发射X光谱和高温等离子体对X光的吸收是一个非常复杂的问题。为了模拟和解释实验测得的激光等离子体发射光谱，提出了一种薄埋点靶：直径为φ200μm厚度为0．1μm的铝点埋在20μm厚的CH膜底衬中，表面再覆盖0．1μm厚CH膜。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.