Two-photon excitation imaging based on a compact scanning head

The adaptation of a confocal laser scanning microscope to a two-photon architecture for 3-D fluorescence microscopy is described     

A pumping technique using electrohydrodynamic flow inside a gel

We demonstrated a new type of electrohydrodynamic (EHD) pump that had a pair of electrodes placed inside a gel (poly(vinyl alcohol) swollen by dimethyl sulfoxide). The fluid (decahydronaphthalene) was in contact with the gel surface. During a voltage application to the electrodes, the EHD flow of dimethyl sulfoxide inside the gel caused the flow of the fluid outside the gel. An advantage of this pumping technique is that one can dissolve some chemicals in the fluid without the fear of their electrochemical decomposition because the electrodes inside the gel are not in contact with the fluid.     

低扬程大型泵站停泵动态特性计算

基于刚性水锤理论,分析和表达了低扬程大型泵装置水力特性和泵机组动力学特性,并运用最小二乘曲面拟合的方法仿真模拟了水泵的全性能曲线,建立了事故停泵动态特性计算的有限差分非线形方程组,采用了牛顿-莱福森(Newton-Raphson)迭代法对方程组进行求解。该数学模型被应用于模拟南水北调淮安三站贯流泵机组事故停泵过渡过程计算。     

PV water pumping with a peak-power tracker using a simple six-stepsquare-wave inverter

The application of photovoltaics (PVs) has been increasingly popular, especially in remote areas, where power from a utility is not available or is too costly to install. PV-powered water pumping is frequently used for agriculture and in households. Among many available schemes, the system under study consists of a PV array, a variable-frequency inverter, an induction motor, and a water pump. The inverter feeds the induction motor, which drives the water pump. To seek the optimum power output of the PV array, the inverter is operated at variable frequency, to vary the output of the water pump. The inverter is operated to generate a six-step quasi-square wave, instead of a pulsewidth modulated (PWM) voltage output, to reduce the switching losses. The inverter acts as both a variable-frequency source and a peak-power tracker of the system, thus, having the number of switches minimized. The system is a low-cost design, with a simple control strategy. The DC bus is supported by a DC capacitor; thus, a balance-of-power flow must be maintained to avoid the collapse of the DC-bus voltage. Another advantage of the system is that the current is limited to an upper limit of the PV-array current. Thus, in case a short circuit is developed, the motor winding and the power semiconductor switches can be protected against excessive current flow     

Theoretical analysis of ion-drag pumping

An improved one-dimensional theoretical model for ion-drag pumping is developed. All three components of the current density are considered, and the distributions of the charge density and electrical field under various conditions are provided. The solutions presented are in nondimensional form, while the combined effects of the controlling fluid properties and operating conditions are incorporated into three nondimensional numbers. The efficiency plots given in terms of the three nondimensional numbers play a vital role in the selection of the working fluid and design of an efficient ion-drag pump     

High-power continuous-wave intracavity frequency-doubled Nd:GdVO/sub 4/-LBO laser under diode pumping into the emitting level

The continuous-wave high power laser emission of Nd:GdVO/sub 4/ at the fundamental wavelength of 1.06 /spl mu/m and its 531-nm second harmonic obtained by intracavity frequency doubling with an LBO nonlinear crystal is investigated under pumping by diode laser at 808 nm (on the /sup 4/I/sub 9/2//spl rarr//sup 4/F/sub 5/2/ transition) and 879 nm (on the /sup 4/I/sub 9/2//spl rarr//sup 4/F/sub 3/2/ transition). It is shown that, in spite of a lower absorption at 879 nm, the infrared emission is comparable under these two wavelengths of pump. The green emission performances were, however, improved by the 879 nm pump: 5.1 W at 531 nm with M/sup 2/=1.46 and 0.31 overall optical-to-optical efficiency was obtained from a 3-mm-thick 1-at.% Nd:GdVO/sub 4/ laser medium and a 10-mm-long LBO nonlinear crystal in a Z-type cavity for 16.5 W pump power. In similar conditions, the maximum green power for the 808 nm pump was 4.4 W, with 0.26 overall optical-to-optical efficiency and M/sup 2/=3.40 beam quality; at this pump wavelength the green emission shows evident saturation for pump power in excess of 9.9 W. This behavior is connected with the enhanced heat generation under 809-nm pumping, as evidenced by the increased thermal lensing of the fundamental emission. A careful alignment of the laser enables emission almost free of chaotic intensity fluctuations.     

Control of a DC/DC converter by fuzzy controller for a solar pumping system

The exploitation of the solar energy is very significant for the very sunny countries. Moreover the dryness phenomenon in these country is imposes more and more the use of pumping plants. The storage of the water in insulated basins from the wells has a double advantage. On the one hand, it is a technical storage solution of the solar energy collected by the photovoltaic panels. On the other hand, it is a hygienic way out to supply water for the rural population.In our work, we propose a technique for the identification of the maximum power point (MPP) based on fuzzy logic. This method is used to generate the cyclic ratio to operate the switcher within the maximum power of a photovoltaic array (PVA).For simulation purpose we made a complete modeling of the entire system. The system carried out consists of a photovoltaic array supplying, through a DC converter, a direct current (DC) engine coupled to a centrifugal pump. Our experimental bench consists of two principal units. A DC converter module composed of IGBT power transistors. And a processing module connected to a PC serial port, handling the input signals delivered by photovoltaic generator and controlling the power unit.The obtained experimental results confirm the simulation result which is very satisfactory and show the utility of the fuzzy controller for the optimization of the system.     

可逆式水轮机泵工况下驼峰现象的数值模拟

本文对具有高部分负荷驼峰的水泵水轮机泵工况进行了定常数值模拟和分析,并与实验结果进行了对比.结果表明:在网格生成时考虑流道边壁y-plus分布、并采用SST k-ω湍流模型能够较准确地模拟出可逆式水轮机泵工况下扬程-流量曲线的驼峰特性.通过进一步内部流动的分析发现,转轮进出口处的两段区域的流态和驼峰的形成有密切的联系.     

泵站水泵吸水室内水动力学特性分析

取水泵站内产生漩涡和泥沙沉积是影响泵站效益发挥的两个重要问题。该文以巴基斯坦拉合尔地区南迪普电站的取水泵站为研究对象,采用物理模型试验和CFD(computational fluid dynamic)相结合的方法,研究了吸水室在设置M型防涡装置后,水泵吸水管内及进水流道内的水动力学特性。结果表明:基于CFD的模拟技术,成功重现了吸水管内涡核区的分布;当设置M型防涡装置后,吸水管内最大涡流角为4.82°,相对无防涡装置时,降低了72.69%;通过定义流速的标准差定量的表证水流均匀性,同时,解释了M型防涡装置的消涡机理。该研究为大型取水泵站的设计提供了有益的参考。     

大型泵站进水流场十字消涡板整流特性研究

为研究十字消涡板对喇叭管下方水体及进入喇叭管内部水体的整流效果,以一大型泵站为研究对象,采用CFD计算方法进行了泵站流场数值模拟。研究发现,不设置消涡装置时,进水池存在大尺度回流和旋涡,并且在喇叭管正下方存在高速度及高涡量区,从而导致水泵进口流态恶化。在设置了高宽比分别为6:8,6:15和6:24的三种十字消涡板后,进水池流场、吸水喇叭口入口断面及水泵进口断面的流速均匀性均有显著变化。相对于高宽比为6:8和6:24的方案,高宽比为6:15的方案能明显减小进水流场底面上高速区,流场变得更加均匀,使得吸水喇叭管中轴线纵剖面上的涡量分布特征值由不设置消涡装置时的0.508减小到0.101,喇叭管入口断面的涡量分布特征值由0.495减小至0.098,喇叭口入口断面的流速均匀度最大提高4.1%,水泵进口断面的均匀度最大提高3.2%。研究结果对大型泵站进水池流态控制有一定指导意义。     

光伏水泵系统的电磁兼容性设计

本文主要针对光伏水泵系统的基本构成和特点，论述了该系统中主要存在的电磁干扰问题，以及电磁兼容性设计思路和具体实现技术，并根据一个光伏水泵系统实例，给出相应的电磁干扰测试分析结果。     

明山电排站计算机监控系统

明山电排站自动化系统取消了常规的电气控制,完全参考“无人值班、少人值守”的要求进行规划设计,采用先进合理的设备、成熟的技术,综合利用自动化控制、微机保护、图像监视和计算机网络、通信技术,建立先进的自动化监视和控制保护系统。     

Innovative electrode designs for electrohydrodynamic conduction pumping

In the absence of a direct charge injection, pumping of an isothermal liquid can be achieved through the charges associated with the heterocharge layers of finite thickness in the vicinity of the electrodes. These charges are based on the process of dissociation of a neutral electrolytic species and recombination of the generated ions. This type of pumping is referred to as electrohydrodynamic (EHD) conduction pumping. The EHD conduction pumping mechanism is experimentally investigated with four innovative electrode designs, with refrigerant R-123 as the working fluid in this paper. Specifically, two different types of perforated disks and two different types of porous disks are used as the high-voltage electrode while a ring is used as the common ground electrode for the four designs. Pressures up to approximately 1400 Pa (at 18.5-kV potential with 0.23 W of power consumption) are generated with one electrode pair. Such pressure generations make the EHD conduction pumping attractive to certain applications in the presence and absence of gravity, such as capillary pumped loops and heat pipes.     

First direct implementation of a true random source on programmable hardware

True random sources are not implementable in digital hardware, so that many practical applications have historically relied on pseudo‐random generators in order to avoid the potentially long prototyping times and the costs of dedicated analog design. However, pseudo‐random sources have liabilities that make them hardly suitable for some tasks (notably security related ones). Previous attempts to conciliate security, cost‐effectiveness, and rapid development included the exploitation of the analog accessory parts often present on programmable devices. In these designs some analog blocks are used for their side effects (noise amplification) rather than for their originally intended behaviour. Conversely, here we report a direct implementation of a true random source on programmable, low‐cost, general‐purpose hardware, where all blocks are used only for their nominal function. To the best of the authors' knowledge, this is the first proposal of this sort. The design exploits an FPAA, and is based on a non‐linear system exhibiting chaotic behaviour. Measures confirm the correct operation, high throughput, and robustness of the system. Copyright © 2005 John Wiley & Sons, Ltd.     

Effective constitutive parameters of a random medium containing small chiral spheres

We have analyzed the effective constitutive parameters for a random medium containing small chiral spheres embedded in an achiral background medium by using our approach. The approach is based on an unconventional multiple scattering method by which wave scattering can be systematically treated in a medium whose dielectric particles are randomly displaced from a uniformly ordered spatial distribution. We have clarified the characteristics of the effective medium parameters by changing the volume fraction and constitutive parameters of chiral spheres. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(1): 11–18, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10294     

泵站水泵蜗形进水池的试验研究

火电厂冷却水泵进水池通常采用矩形进水池,通过分析表明矩形进水池的流态并非十分理想,水力设计尚需改进。因此提出蜗形进水池方案代替矩形进水池,并且通过模型试验来研究两类进水池水力性能的优劣。试验中采用美国进水设计标准中旋度计测量涡角检验进水性能的方法。试验结果表明蜗形进水池优于矩形进水池。研究结论和传统的泵装置性能试验结论一致,表明通过涡角检验进水性能的方法是可靠正确的。     

Scattering of Dirac electrons by a random array of magnetic flux tubes

The scattering of two-dimensional (2D) massless electrons as presented in graphene in the presence of a random array of circular magnetic flux tubes is investigated. The momentum relaxation time and the Hall factor are obtained using optical theorem techniques for scattering. Electrons with energy close to those of the Landau levels of the flux tubes exhibit resonant scattering and have a long life-time to reside inside the magnetic flux tube. These resonances appear as sharp structures in the Hall factor and the magneto-resistance.     

Unsteady and steady flow control on pumping systems

The possibility of reducing the severity of pressure transients produced during the starting and stopping of pumps by means of a gradual variation of the rotational speed of the pump driver is shown. Efficient regulation of the discharge supplied by the pump is also possible by varying the rotational speed instead of throttling. Both problems require knowing how to vary the speed; a simple PID (proportional-integral-derivative) control scheme is used to show the way rotational speed should be varied     

Subharmonic hybrid mode-locking of a monolithic semiconductor laser

Performance of a subharmonically hybrid mode-locked (SH-ML) monolithic semiconductor laser is investigated. A 33-GHz passively mode-locked distributed Bragg reflector semiconductor laser is stabilized by the injection of an electrical signal with a subharmonic frequency of the laser cavity resonance. Systematic measurements on the phase noise, timing jitter, amplitude modulation, and locking bandwidth are performed for the second- and third-order SH-ML conditions, and the results are compared with the fundamental hybrid mode-locking (FH-ML) case. Low timing jitter of less than 0.6 ps, comparable to that under the FH-ML case, is achieved for the both SH-ML cases. The amplitude modulation imposed by the subharmonic driving frequencies is found to be very small (<-24 dBc) for the second-order SH-ML because of the sufficiently low modulation response of the laser at 16.5 GHz. The third-order SH-ML is found to exhibit a very unique locking characteristics, leading to a maximum locking bandwidth of 56 MHz that is even larger than that for the FH-ML case