旋转输液管动力稳定性理论分析北大核心CSCD

基于Lagrange原理和假设模态法建立了旋转输液管的动力学模型.通过降阶升维的方法求解系统的特征值问题,并分析了旋转输液管自由振动特性.得到了不同端部集中质量和转速下,系统特征值随流速升高的演变轨迹.揭示了临界流速随系统参数的变化规律.研究发现,内部流体的流动对旋转输液管动力学特性存在显著影响.在某些参数组合下,系统低阶模态能够形成不同形式的内共振关系.预示了旋转输液管模型蕴含丰富的动力学现象.     

PROPERTIES OF TEMPERATURE DEPENDENCE OF THRESHOLD IN PURE AND IMPUHITY-DOPED BLUE BRONZES

Temperature dependence of the threshold of pure and impurity-doped blue bronzes has been studied. It is found that for pare blue bronzes the threshold field near 100K has an anomalous peak, but for impurity-doped samples no anomaly is observed in the range of liquid nitrogen temperature, and the value of the threshold field gradu-ally increases with the decrease of temperature. The results show that in the high-quality pure blue bronzes, there may exist an incommensurate to quasi-commensurate transition near 100K. But for the impurity-doped or "dirty" pure samples, such an incommensurate to quasi-commensurate transition near 100K can be extensively re-strained by impurities or defects, which leads to a pure incommensurate CDW in a wide temperature range.     

利用虚拟目标值的预见控制设计(英文)

研究了预见跟踪控制问题,即控制器可利用过去、现在和未来的信息来决定所施加控制量的大小．通常的作法是通过把未来预见信息加入控制量中来实现的．提出了一种不同的作法：利用未来目标值及系统的当前状态产生一个虚拟目标值,让系统转而去跟踪这个已被事先处理过的目标值信号,从而提高了系统的控制精度同时减少了控制所需的能量．数值仿真表明了这种方法的优越性．     

M-ary 正交调制 DS/CDMA 在衰落信道中的性能分析

讨论了Ｍ－ａｒｙ正交调制ＤＳ／ＣＤＭＡ系统在瑞利及莱斯衰落下的误码性能。采用理论分析的方法,推导出了在瑞利及莱斯衰落下ＤＳ／ＣＤＭＡ系统误码率的闭式表达,理论分析与数值积分结果相符。对于实际信道功率时延曲线为指数衰减的情况,讨论了不同指数衰减率对系统性能的影响,并就分集接收方案及不同系统参数的影响也作了分析。结果表明随着指数衰减率的增加和莱斯参数的减小,误码逐渐增大;而随着分集的加入,系统误码性能可大大改善。     

计算机支持的协同工作与多媒体会议系统

计算机支持的协同工作（ＣＳＣＷ）新近发展起来的一个跨学科的新兴研究领域,多媒体会议系统是ＣＳＣＷ中一个非常重要的研究项目,本介绍ＣＳＣＷ的基本知识的发展状况,同时介绍了一个多媒体会议系统的模型和应用。     

ULTRASONICALLY DISPERSED POTASSIUM AS DEPROTONATING AND COUPLING AGENT──SYNTHESIS OF 1，6－DINITRILES IN SITU

ＵＬＴＲＡＳＯＮＩＣＡＬＬＹ　ＤＩＳＰＥＲＳＥＤ　ＰＯＴＡＳＳＩＵＭ　ＡＳ　ＤＥＰＲＯＴＯＮＡＴＩＮＧ　ＡＮＤ　ＣＯＵＰＬＩＮＧ　ＡＧＥＮＴ──ＳＹＮＴＨＥＳＩＳ　ＯＦ　１，６－ＤＩＮＩＴＲＩＬＥＳ　ＩＮ　ＳＩＴＵＵＬＴＲＡＳＯＮＩＣＡＬＬＹＤＩＳＰ...     

β沸石分子筛固体酸的制备及其在异丁烷和丁烯烷基化反应中的应用

以四乙基溴化铵(TEABr)为模板剂，硅胶为硅源，铝酸钠为铝源，采用水热晶化法合成β沸石．研究了其晶化温度、晶化时间、硅铝比、碱度、水含量等各种因素对晶化过程和产物性质的影响．得出适宜的初始凝胶组成为SiO2和Al2O3的比值在25-60之间，TEABr和SiO2的比值在0．32～0．4之间，OH^-和SiO2的比值在0．2～0．23之间，H2O和SiO2的比值在8．6～18．0之间．通过XRD，ICP，IR，SEM和NH3-TPD方法分别对样品的结构和性质进行了表征．烷基化反应的结果表明，β分子筛具有较为适宜的孔结构和反应活性．     

大孔树脂吸附法处理含苯肼工业废水的研究

以Hz-841大孔树脂为吸附剂,95%乙醇为脱附剂处理含苯肼4000~5000mg/L的工业废水,取得了理想的分离效果,苯肼吸附率>99.8%,树脂工作吸附量40~50g/L。     

SYNTHESIS OF THE POLYSTYRENE-TYPE ADSORBENTS CONTAINING POLAR GROUPS AND THEIR CAPACITIES IN THE ADSORPTION OF STEVIOSIDE AND GYPENOSIDES

Seven polystyrene-type adsorbents (Ⅰ—Ⅶ) were synthesized by the modification of styrene-divinylbenzene copolymer respectively with hydroxymethyl, aminomethyl, methoxymethyl, phenoxymethyl, (4-hydroxy phenoxy)methyl, (4-acetylphenoxy)methyl, and acetyl groups. Their structures were characterized with chemical methods and physical techniques. The adsorption capacities of the adsorbents to stevioside and gypenosides were determined via batch test in which the HPLC method was used for the analysis of Saponin concentration of solution. The results showed that all the adsorbents could adsorb these saponins to a certain extent, but Ⅵ and Ⅶ had large capacities owing to their moderate polarities.     

二碘化钐促进的硒代酯的合成

用SmI2/THF/HMPA体系在室温下使二芳基二硒醚中的Se-Se键还原断裂成硒负离子物种, 继而与酸酐作用得到硒代酯, 该反应条件温和中性, 产率良好, 提供了合成硒代酯的一个新途径。