锁相环中无源环路滤波器的设计与仿真

锁相环(PLL)的基本频率特性主要是由环路滤波器决定的.为了节省锁相环的设计仿真时间,提高设计效率,提出一种基于ADS仿真平台的环路滤波器系统级设计与仿真方法.分析RC无源滤波器截止频率与锁相速度之间的关系;引入滞后超前滤波器结构,提高PLL的稳定性,还分析滞后超前滤波器的幅度-频率特性,以及影响相位返回量的因素,并基...     

The effect of a secretion-enhanced heavy chain on improving intein-based dual-vector co-delivery of a full-length factor VIII gene

Treatment of hemophilia A by gene therapy is adversely affected by inefficient FVIII secretion and the large FVIII gene, which is difficult to package in the promising adeno-associated virus (AAV) vectors. Inhibited secretion of FVIII is caused mainly by inefficient secretion of its heavy chain. Previously, we have employed a protein splicing-based dual-vector to co-transfer a B-domain-deleted FVIII (BDD-FVIII) gene, suggesting that the light chain, covalently ligated to a co-expressed heavy chain can improve the secretion of spliced BDD-FVIII. However, its level of secretion was affected by inefficient secretion the heavy chain. Here, we studied the effect of a mutant heavy chain with L303E/F309S substitutions, which enhance FVIII secretion on the heavy chain itself and spliced FVIII when using a protein splicing-based split-delivery of a full-length FVIII gene. Eukaryotic vectors expressing Ssp DnaB intein-fused mutant heavy and light chains were transiently co-transfected into cultured COS-7 cells. A spliced FVIII protein was seen in co-transfected cells by Western blot analysis. The heavy chain was secreted by cells transfected with the mutant heavy chain gene alone at (39±11) ng/mL and this secretion increased to (123±13) ng/mL when cells were co-transfected with the light chain gene, which was greater than the secretion of wild-type heavy chain. The amount of spliced FVIII in the culture supernatant of co-transfected cells was (86±14) ng/mL, with an activity of (0.61±0.08) IU/mL, which was greater than that of wild-type FVIII co-transfected cells. Spliced FVIII and bioactivity were also detected in the combined culture supernatant of cells individually transfected with mutant heavy and light chain gene at a higher level than that of combined wild-type heavy and light chain transfections. This suggested that the heavy chain with improved secretion markedly increased the efficacy of protein splicing-based split delivery of the full-length FVIII gene using a dual-vector. These results encourage the transfer of this technology to an animal model using a dual-AAV vector.     

基于限时脉冲控制害虫策略的Gompertz模型

基于在限定时间内控制害虫的策略,建立具有Gompertz增长的脉冲微分方程模型,得到该模型的边值解存在的条件,给出计算最大脉冲周期的方法,解决在限定时间内将害虫密度控制在经济阈值之下的问题.     

气候变化适应研究国际发展态势分析

气候变化适应是应对气候变化的重要选择之一。利用汤森路透数据分析工具和Aureka分析平台对气候变化适应研究领域的科学论文进行了统计分析,从文献计量学角度揭示了气候变化适应研究的国际发展态势、研究主题、热点问题和发展趋势。     

Na2CO3–K2CO3熔盐电化学法除锈

The formation of a rust layer on iron and steels surfaces accelerates their degradation and eventually causes material failure. In addition to fabricating a protective layer or using a sacrificial anode, repairing or removing the rust layer is another way to reduce the corrosion rate and extend the lifespans of iron and steels. Herein, an electrochemical healing approach was employed to repair the rust layer in molten Na₂CO₃?K₂CO₃. The rusty layers on iron rods and screws were electrochemically converted to iron in only several minutes and a metallic luster appeared. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses showed that the structures of the rust layer after healing were slightly porous and the oxygen content reached a very low level. Thus, high-temperature molten-salt electrolysis may be an effective way to metalize iron rust of various shapes and structures in a short time, and could be used in the repair of cultural relics and even preparing a three-dimensional porous structures for other applications.     

基于WAP的移动学习系统的设计与实现

移动学习系统的设计,包括系统设计原则、系统设计目标、相关的支撑技术、系统体系结构设计和功能模块设计,并分别对各个功能模块加以实现．该系统主要实现了移动学习、网上教学以及教学评价等功能,主要功能分为学生模块、教师模块和管理员模块三个部分．     

基于ERP理论的煤炭企业管理系统设计与探讨

目前,ERP在国内煤炭行业的应用仍处于起步阶段,文章针对中煤能源集团公司ERP系统结构进行了探讨,并对系统中平台功能及平台中各模块间关系进行了分析,说明了ERP系统的实施对企业管理水平具有提升作用.     

曲克芦丁合成工艺研究

用碳酸钠做催化剂,以芦丁和环氧乙烷为原料,加入乙二胺四乙酸二钠对金属离子进行了络合,同时加入亚硫酸钠作为抗氧剂,加入磷酸二氢钾,控制溶液的pH值不超过9,以HPLC法进行反应监测,在75℃条件下,反应8 h,得粗品曲克芦丁含量为61.6%,用甲醇精制后,含量为94%.对曲克芦丁合成工艺进行优化,采用水做溶剂降低工业化生...     

基于多源数据分析的三峡库区抗滑工程优化与比选

针对三峡库区抗滑工程选型、多排抗滑桩位置选取与抗滑工程参数设计问题,通过分析整理三峡库区重庆段已成功治理的257组地质灾害数据,运用分类统计参数方法,分析最优支护结构形式;基于FLAC^3D软件,建立力学分析数值模型,选取多排抗滑桩合理位置;将理正软件设计参数与收集资料进行对比,确定最优桩间距与锚固深度取值,并应用于工程实例验证。研究结果表明：当滑坡剩余推力小于100 kN/m且工程设置位置处滑体厚度小于5 m时,宜采用重力式挡墙;大于100 kN/m或滑体厚度较大时建议采取抗滑桩。当设置两级抗滑桩支护滑坡时,前排桩位于反翘端点,排距占反翘端点与滑坡后缘距离为20%时,滑坡的总推力最小,为最优方案。三峡库区重庆段滑坡抗滑桩锚固深度与桩长比值推荐值为0.45,桩间距推荐值为5.5 m或6.0 m。将研究结果应用于三峡库区重庆段滑坡工程实例,对比分析得出此优化设计方法具有可行性和实用性,可为后续滑坡治理提供参考。     

亚砷酸钠对大鼠离体坐骨神经干复合动作电位的影响

应用电生理方法观察了不同浓度的亚砷酸钠对大鼠离体坐骨神经干复合动作电位的幅度、阈强度、传导速度及持续时间的影响。结果表明:亚砷酸钠溶液浸泡大鼠坐骨神经干30分钟,当浓度高于3×10-4mol/L时,复合动作电位的幅值较对照组明显降低(P<0.01)。复合动作电位的阈强度随亚砷酸钠浓度的升高而增加,差异有显著性(P<0.01)。复合动作电位的传导速度随亚砷酸钠浓度的升高而变慢,但只有亚砷酸钠浓度高于10-3mol/L时,复合动作电位传导速度与对照组相比差异才有显著性(P<0.01)。复合动作电位的持续时间随亚砷酸钠浓度增加而延长,但与对照组相比无差异(P>0.05)。这说明亚砷酸钠可影响大鼠坐骨神经干复合动作电位。