Lumped Parameter Mass Flow Rate and Pressure Control Characteristics Model for High-Speed Pneumatic PWM on/off Valve

Aiming at solving the problem of strong coupling characteristic of the key parameters of high-speed pneumatic pulse width modulation（ PWM） on / off valve, a general lumped parameter mathematical model based on the valves time periods was well developed. With this model,the mass flow rate and dynamic pressure characteristics of constant volumes controlled by high-speed pneumatic PWM on /off valves was well described. A variable flow rate coefficient model was proposed to substitute for the constant one used in most of the prior works to investigate PWM on /off valves＇ dynamical pressure response, and a formula for disclosing the inherent relationship among the PWM command signal,static mass flow rate,and sonic conductance of the valve was newly derived.Finally,an extensive set of analytical experimental comparisons were implemented to verify the validity of the proposed mathematica model. With the proposed model, PWM on /off valves＇ characteristics,such as mass flow rate,step pressure response of the valve control system,mean pressure and ripple amplitude,not only in the linear range,but also in the nonlinear range can be wel predicted; Good agreement between measured and calculated results was obtained,which proved that the model is helpful for designing a control strategy in a closed loop control system.     

老年性痴呆模型大鼠学习记忆功能障碍的实验探讨

目的:探索D-半乳糖-Aβ复合模型大鼠学习记忆功能的改变,研究老年性痴呆(AD)的发病机制.方法:(1)采用1.25%D-半乳糖腹腔注射(50mg/kg·d,连续6周)致衰老,结合双侧海马齿状回背侧注射10g/1μL凝聚态β-淀粉样肽1-40(β-amyloid peptide,Aβ1-40)的复合造模方法,拟建立AD样学习记忆功能障碍的动物模型.实验动物随机分成3组:AD模型组、假造模对照组和正常对照组.(2)以单位时间逃避潜伏期(s/3min)及其逃生错误频率(次/3min)为观察指标,进行水迷宫行为学试验测定大鼠学习记忆功能的改变.结果:AD大鼠安全逃避潜伏期明显延长,逃生错误频率高,与两对照组比较差异有统计学意义(P<0.01).结论:D-半乳糖-A复合造模致AD大鼠模型具有较好的老年性痴呆的仿真特性.水迷宫行为学试验能准确反映动物学习记忆功能.     

三阶非线性微分方程两点边值问题解的存在性

利用Schuder不动点定理,给出了两类三阶非线性微分方程的两点边值问题存在解的充分条件.     

工程机群的通信与GPS定位装置的设计与实现

智能化工程机械的GPS定位与监控中心的通信装置是实现工程机械机群化管理的关键装置 .根据工程机械机群工作的特殊性 ,设计了具有WLAN方式和GSM方式相结合的双模无线通信网络 .利用嵌入式计算机作为硬件平台 ,开发了采集GPS数据和工程机械上重要数据的硬件设备 ,并利用嵌入式Linux系统作为软件平台 ,开发了一套能够根据网络情况自由选择的利用WLAN网络或GSM网络通信的软件 .利用上述网络和软硬件 ,实现了单个工程机械向监控中心的数据传输 .     

柠檬酸对Ca(NO3)2-P2O5体系合成羟基磷灰石粉体的影响

采用Ca(NO3)2·4H2O和P2O5为主要原料,柠檬酸为螯合剂,利用溶胶-凝胶法合成了纳米羟基磷灰石粉体.通过DSC,XRD和SEM等手段,分析了纳米HA粉体的形成历程,系统地研究了柠檬酸对粉体形成过程、产物杂质相及粉体粒度的影响,并对其影响机理进行了初步探讨.结果表明:柠檬酸的加入提高了胶体的稳定性,通过螯合作用...     

蟒河自然保护区金翅雀的繁殖生态学研究

１９９８上４月至８月在山西蟒河自然保护区对金翅雀的繁殖生态进行了考察，并应用回归分析研究了体重，体长，嘴峰，尾长，翼长与时间的关系，结果表明，金翅雀主要栖息在松柏和以路两侧的杨树林。每窝卵数３枚－５枚，７月以前每窝卵数可达４枚－５枚，７月以后每窝卵数以３枚居多。     

L-抗坏血酸在锂-对苯二甲酸修饰电极上的电化学行为及其测定

利用电沉积法制备了1种[Li-BDC]/GC修饰电极,并用循环伏安法和交流阻抗法研究了L-抗坏血酸（AA）在修饰电极上的电化学行为.结果表明,与裸玻碳电极相比,该修饰电极对AA具有更高的电催化活性,其氧化峰电流增大了约1.6倍.探讨了不同实验条件对电极性能的影响,在最佳实验条件下,检测AA药物浓度的线性范围为3.0×10-7～2.5×10-3 mol·L-1,线性相关系数为0.9990,检出限为6.0×10-8 mol·L-1（信噪比为3∶1）,回收率为97.2%～100.4%.该修饰电极具有较好的稳定性和重复性,并用于维生素C片剂中AA的含量测定,结果与药典方法一致.     

北京市生活垃圾重金属元素调查及污染特性分析

采用现场调研取样和理化分析检测的方法对北京市城区垃圾中重金属含量水平 ,主要污染元素和主要污染物进行测定 ,并在调查基础上提出北京市城区垃圾重金属污染的防治对策 ,为废弃物减量化、无害化与资源化治理提供依据     

Low Complexity MMSE-SQRD Signal Detection Based on Iteration

Aiming at the problem of high computational complexity of Vertical-BLAST(V-BLAST) algorithm in Multiple-Input Multiple-Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM) system signal detection, this paper first uses Sorted QR Decomposition(SQRD) iterative operation instead of matrix inversion to reduce the computational complexity of the algorithm, and then considering that the algorithm is greatly affected by noise, Minimum Mean Square Error(MMSE) criterion is used to weaken the noise effect. At the same time, in order to reduce the noise and computational complexity, MMSE and SQRD are combined, which can not only reduce the noise and computational complexity, but also obtain the sub-optimal detection order, thus improving the detection performance of the MIMO-OFDM system. Finally, the numerical simulation of the MMSE-SQRD detection algorithm is carried out. The results show that the Eb/No of MMSE-SQRD algorithm is 2 dB greater than that of the MMSE algorithm and the computational complexity is O(N_T~3) under the conditions that N_T =N_R=2 and the BER is 10~(–2). The detection algorithm satisfies the demand of short wave and wideband wireless communication.     

凝胶化改性壳聚糖膜预防感染性腹膜粘连的对比研究

目的对比研究凝胶化改性壳聚糖膜和透明质酸钠对感染性腹膜粘连的预防作用。方法SD大鼠80只,随机分成四组:假手术对照组(A组),感染对照组(B组),凝胶化改性壳聚糖膜组(C组),透明质酸钠组(D组)。利用大鼠蚓突盲端制造感染性腹膜粘连模型,然后每组分别用相应的方法处理污染面,处理后2、4周打开腹腔,以Bha-tia分级法评定蚓突盲端的粘连程度,并对盲端组织行羟脯胺酸(OHP)水平测定和病理学检查。结果术后2周和4周,C组的粘连程度显著轻于B组(P=0.000),OHP水平显著低于B组(P=0.000);D组的粘连程度、OHP水平和B组无显著性差异(P>0.05)。病理学检查:B组术后2周局部组织以急性化脓性炎症为主,4周时以肉芽组织增生和纤维组织形成的慢性炎症反应为主;C、D组的病理改变类型同B组相同,但C组的上述改变较B组明显减轻,而D组和B组间则无明显差异。结论凝胶化改性壳聚糖膜具有明显的预防感染性腹膜粘连的作用,而透明质酸钠的作用则不明显。