基于神经网络的同步发电机励磁反步控制

针对同步发电机励磁系统严重的非线性以及参数非精确可知的特点，提出了一种基于神经网络的反步(Backstepping)控制方法，实现了多目标量的励磁控制。神经网络的运用解决了反步控制与励磁系统不满足匹配条件的矛盾。系统设计采用了特殊的在线权值修正算法，不需要离线学习阶段。由稳定性证明可知：控制算法中各参数的设计并不要求被控对象参数精确可知，系统具有较好的鲁棒性。仿真结果表明：该控制方法与PID控制相比具有超调量小、调节速度快等优点。     

The effect of pitch and collimation on radiation dose in spiral CT

1 Introduction Spiral computed tomography (CT) was intro- duced in clinical practice in 1980s. Its distinctive characteristic is continuous data acquisition and con- tinuous tube rotation with high speed while simulta- neously translating the patient through the gantry.[1] Owing to these functions the spiral CT possesses the ability to scan an entire organ volume within a single breathhold. Thus, the anatomical section is contiguous and therefore the reliable demonstration of small le- sions…     

A prediction-error estimation algorithm for the reconstruction of linear and nonlinear continuous time models from frequency response data

A prediction error estimation algorithm is derived for the estimation of complex number systems. The algorithm is applied to reconstruct both linear and nonlinear differential equation models from frequency response data. A simulation study is included to illustrate the algorithm.     

Pressure analysis of the hydromechanical fracture behaviour in stimulated tight sedimentary geothermal reservoirs

Hydromechanical phenomena in fractured sediments are complex. They control the flow in stimulated tight sediments and are crucial for the exploitation of geothermal energy from such rocks. We present the analysis of a cyclic water injection/production (huff–puff) process, a promising method to extract geothermal energy from tight sedimentary reservoirs. It uses a single borehole, which considerably reduces investment costs. A huff–puff test was performed in a 3800-m deep sedimentary formation (borehole Horstberg Z1, Lower Saxony, Germany). The analysis presented herein explains the downhole pressure measurements by a simplified reservoir model containing a single vertical fracture. The model addresses the flow behaviour between the fracture and the rock matrix in a layered formation, and the coupling between fluid flow and the mechanical deformation of the fracture. The latter aspect is relevant to predict the efficiency of the geothermal reservoir because cooled regions resulting from a particular injection/production scheme can be identified. The analysis methods include: (1) the curve-fitting code ODA used for a determination of different flow regimes (radial or linear), (2) an analytical solution for the calculation of the injection pressure, assuming a time-dependent fracture area, and (3) the simulator ROCMAS, which numerically solves the coupling between fluid flow and fracture deformation. Whereas each single approach is insufficient to explain the complete test data, a combination of the results yields an understanding of the flow regimes taking place during the test.     

混合使用中心矩与累加量的电力系统概率特征根分析方法

在现有电力系统概率特征根分析方法的基础上,依据特征根各阶矩阵影响程度,将随机变量的中心矩与累加量混合使用,以求达到计算精度与计算量需求之间的协调。文中所考虑的不确定因素为：基于节点功率运行曲线的系统多运行方式,利用不心程度的特征根１阶及２阶灵敏度算式,从节点电压或节上的概率特性计算也特征根的各阶数字特征,然后由Ｇｒａｍ－Ｃｈａｒｌｉｅｒ级数确定临界特征根的概率和稳定概率。在该混合算法中,既不限制随     

A new approach to auto-tuning of PID controllers

Delayed state variable filters are implemented for the estimation of parameters of monotone open-loop processes that can be approximated by a first-order lag coupled with a time delay. Based on the delayed filtered step output response, and the first and second-order derivatives, a new estimation procedure has been derived for on-line estimation of the corresponding static process gain, the apparent dead time and the apparent time constant. A new PID tuning formula is formed that is based on the placement of the open-loop zeros related to the apparent time constant and time delay, to give a controlled system with a damping of 0-5 or a maximum overshoot of approximately 16-3%. Extensive simulation studies have also been carried out to relate the controlled output step response to the open-loop system parameters, which could then be re-applied in closed loop retuning of PID controllers. Efforts have also been made to apply the tuning technique to the control of multivariable systems. Simulations are included to illustrate the concepts.     

Dynamic Routing with Security Considerations

Security has become one of the major issues for data communication over wired and wireless networks. Different from the past work on the designs of cryptography algorithms and system infrastructures, we aim at the proposing of a dynamic routing algorithm that could randomize delivery paths for data transmission. The algorithm is easy to implement and compatible with popular routing protocols, such as Routing Information Protocol in wired networks and Destination-Sequenced Distance Vector protocol in wireless networks, without introducing extra control messages. An analytic study on the proposed algorithm is presented, and a series of simulation experiments are conducted to verify the analytic results and to show the capability of the proposed algorithm.     

Poly[2-(hydroxyethyl methacrylate)-co-(sulfobetaine)]s hydrogels: 1. Synthesis and swelling behaviors of the 2-(hydroxyethyl methacrylate)-co-2-(vinyl-1-pyridinium propane sulfonate) hydrogels

A series of the 2-hydroxyethyl methacrylate/2-vinyl-l-pyridinium propane sulfonate (HEMA/VPPS) copolymeric gels have been prepared from HEMA and zwitterionic monomer VPPS of various molar ratios. The influence of the amount of VPPS in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures was investigated. Results indicate that the PHEMA hydrogels exhibit an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreases with increasing temperature. The same results are also shown for the lower VPPS content HEMA/VPPS copolymeric gels. In the equilibrium swelling ratio, the PHEMA hydrogel exhibits a minimum swelling ratio at 55 °C. Then, the minimum swelling ratio disappears gradually with increasing VPPS content in HEMA/VPPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/VPPS copolymeric gels increase rapidly with increasing salt concentration, for salts with a smaller ratio of charge/radius.     

Poly(2-hydroxyethyl methacrylate-co-sulfobetaine) hydrogels. II. Synthesis and swelling behaviors of the [2-hydroxyethyl methacrylate-co-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate] hydrogels

A series of the 2-hydroxyethyl methacrylate/3-dimethyl-(methacryloyloxyethyl)ammonium propane sulfonate (HEMA/DMAPS) copolymeric gels was prepared from various molar ratios of HEMA and the zwitterionic monomer DMAPS. The influence of the amount of the zwitterionic monomer in the copolymeric gels on the swelling behaviors in water, various saline solutions, and temperature was investigated. The results indicate that the PHEMA hydrogel (D0) and lower DMAPS content of the HEMA/DMAPS copolymeric gel (D1) exhibit overshooting phenomena in the dynamic swelling behavior. The maximum overshooting value decreases with increase in temperature. In the equilibrium swelling ratio, the PHEMA hydrogel exhibits a minimum swelling ratio at 55°C. Then, the minimum swelling ratio diminishes gradually with increasing of the DMAPS content in the HEMA/DMAPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/DMAPS copolymeric gels increase rapidly with increasing of concentration of the salt with a smaller ratio of the charge/radius. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2021–2034, 1998     

层式通风——高温空调下的出路

节能减排是当前全球性的呼声。作为回应,东亚区域的若干个政府都提倡采用更高的夏季空调温度。要推广高温空调,就必须使公众相信,这样做不会降低室内环境品质,尤其是不会降低热舒适性。要实施高温空调,就必须筛选出在这样的非常规工况下性能良好的通风系统。因其在较高室温下的良好性能,本文以数间香港办公室为例,介绍并分析一种新型通风系统——层式通风。实验和模拟计算的结果显示,如果送风速度,送风量和送、排风口的设计正确,层式通风具有热舒适性好（具体表现为头脚温差小）、能耗低、特别是呼吸区空气品质好的特点。下一步的工作将对上述优点进行定量研究。