The mean flow field generated by a pitched blade turbine: Changes in the circulation pattern due to impeller geometry

The mean flow field in a tank stirred with a pitched blade turbine was measured using a two-component Laser Doppler Anemometer system (LDA). The effects of impeller clearances and impeller geometries (number of blades, blade angle and blade size) on the mean flow field have been studied. The primary pumping number, induced pumping number of the primary circulation loop and the induced pumping number of the secondary circulation loop, which often has been ignored, are reported. The flow patterns and circulation loops are more complex than those traditional ones, which vary with the geometries of the PTD and the clearances.     

Personal Trusted Devices for Web Services: Revisiting Multilevel Security

In this paper we revisit the concept of mandatory access control and investigate its potential with personal digital assistants (PDA). Only if applications are clearly separated and Trojans cannot leak personal information can these PDAs become personal trusted devices. Limited processing power and memory can be overcome by using Web services instead of full-fledged applications – a trend also in non-mobile computing. Web services, however, introduce additional security risks, some of them specific for mobile users. We propose an identification scheme that can be effectively used to protect privacy and show how this system builds upon a light-weight version of mandatory access control.     

EGFP-Arg7融合蛋白表达及在HeLa细胞中的转导活性

目的 构建pET-28a-EGFP-Arg7重组子,观察表达的融合蛋EGFP-Arg7在细胞内的转导活性.方法 构建EGFP-Arg7(阴性对照为EGFP)序列,与pET-28a连接后,转化Ecoli BL21(DE3),IPTG诱导表达,并经Ni2+.NTA纯化.纯化产物作用于HeLa细胞后用荧光显微镜观察其转导活性.结果 重组pET-28a-EGFP-Arg7经酶切鉴定和序列分析,证明构建正确.转化E.coil BL21(DE3)后,重组蛋白获得可溶性表达.纯化后的融合蛋白纯度达90%以上.重组蛋白EGFP-Arg7作用于HeLa细胞后用荧光显微镜可观察到强绿色荧光.结论 Arg7具有很好的转导活性,能携带与其连接的蛋白质穿过HeLa细胞膜.     

融合蛋白PTD-SOD对豚鼠UVB损伤的预防效应

本研究建立了体外豚鼠皮肤一次性中波紫外（UVB）损伤和多次性UVB损伤模型，以超氧化物歧化酶（SOD）为对照，探讨两种融合了蛋白转导域的超氧化物歧化酶（PTD—SOD）PTD—SOD1和PTD—SOD2对豚鼠UVB损伤的预防效应，动物实验利用数码相机拍摄豚鼠背部相关区域皮肤的颜色变化，再利用PHOTOSHOP软件通过测量a^＊值，分析产生红斑程度来衡量辐射损伤的程度。结果表明，对于一次性辐射损伤，SOD基本没有预防效果，两种PTD—SOD均有较好的预防效果，PTD—SOD2的预防效果优于PTD—SOD1，两种蛋白的剂量与其保护效果均呈钟形曲线关系。其最佳给药时间均为辐射前0．5h，使用量为2000U，超过则保护效果减弱。对于多次性辐射损伤，也是SOD基本没有预防效果，两种PTD，SOD均有较好的预防效果，而PTD-SOD2的预防效果优于PTD-SOD1；皮肤切片结果也表明，两种PTD—SOD都能有效减轻豚鼠皮肤表皮层因多次性UVB辐射引起的肿胀。     

The Modulated Spectra Analysis of Backscattered Field Caused by Rotating Metal Airscrew

High-frequency asymptotic technique is currently the most effective method to work out the electromagnetic scattering of rotating objects. In this letter, the backscattered field of the rotating metal airscrew is investigated based on Physical optics （PO） and Physical theory of diffraction （PTD）, in conjunction with the quasistationary method. Using the Fourier transforms, theory predicted model of the Doppler spectra of the radar return from rotating objects can be founded, so as to predict variety rule of the modulated spectra of radar return signal. Taking the φ -φ polarization as an example, the time and frequency domain responses of radar echo from rotating objects are predicted. By comparing the radar modulated spectra of a rotating target with that of a relatively fixed or nonrotational moving target, some important information can be obtained. These will help to identify targets.     

光电化学方法现场监测模拟海水中铜腐蚀及缓蚀剂PTD的缓蚀行为

采用光电化学方法现场测量铜电极的开路光电压,研究铜在模拟海水3%NaCl溶液中的腐蚀行为及缓蚀剂PTD对铜的缓蚀行为.实验发现,在3%NaCl溶液中铜电极随浸泡时间的延长其开路光电压由正变负即光响应由p型光响应转变为n型光响应,这表明铜表面受到Cl-的严重侵蚀.加入缓蚀剂PTD后,当PTD的浓度小于6×10-5%时,铜电极的光响应转型时间较不加PTD时提前.当PTD的浓度大于6×10-5%时,铜电极的光响应不存在转型情况,表明PTD产生了良好的缓蚀作用.在本文条件下,PTD产生缓蚀作用的最佳浓度为1×10     

基于DDM技术的FEM/PO-PTD方法在深腔导体目标RCS分析中的应用

采用一种基于区域分解法(DDM)的混合方法——FEM/PO—PTD法，分析带有深腔的三维电大尺寸导体目标的电磁散射特性。应用DDM将原有深腔分成若干个较小的子域。对于腔体开口面所在子域，应用等效原理，结合物理光学法(PO)与物理绕射理论(PTD)，得到腔体开口面的边界积分方程；对于其它子域，通过传输条件实现各子域间的耦合。在各子域内推导出此边值问题的等价泛函。应用基于棱边的有限元法(Edge—based FEM)进行分析。理论分析与计算结果表明，该混合方法与其它计算同类问题的方法相比，有较高的计算精度，同时能减少对计算机内存的需求     

无刷直流电机双闭环控制系统的建模与仿真

在分析无刷直流电机数学模型的基础上,提出了一种无刷直流电机控制系统仿真建模的新方法。在Matlab/Simulink中按功能进行模块化建模,用M文件和S函数来编写功能模块,实现了电流滞环和转速单神经元PID控制的双闭调速系统仿真。仿真结果与理论分析一致,验证了该控制系统设计的合理性。此仿真模型可用以验证各种控制算法,为无刷直流电机控制系统的分析和设计提供了有效的途径。     

PTD和PTDEEC算式的奇异点处理

将计算劈型目标电磁散射的ＰＴＤ绕射系统通过简单的三角变换写成另一种表达式，提高它们在奇异点邻域的数值稳定性，数值结果表明本文给出的公式在奇异点附近比原始的表达式要好。     

预测反射面天线馈源毁伤效应的混合算法

提出了一种预测反射面天线系统在馈源毁伤状态下辐射特性的混合算法.采用时域有限差分法(FDTD)分析了波导开口辐射器馈源穿孔毁伤时的初级辐射特性,利用物理光学法(PO)和物理绕射理论(PTD)分析了反射面天线的次级辐射特性.并采用非场分裂式完全匹配层(UPML)吸收边界条件、共形网格(Conformalmesh)技术提高计算精度和效率,取得了良好的效果,充分验证了混合算法的有效性.