历史中心区复兴中的地域性问题与对策

本文以上海思南路47～48街坊改造为例,探讨城市形态更新与居民外迁问题,并期待相关地域性社会对策的出现。     

Closed-loop automatic tuning of PID controller for nonlinear systems

In this paper, a robust control system is first proposed which is suitable for the control of a class of nonlinear systems. A parallel connection of a relay to a proportional integral derivative (PID) controller collectively forms the robust controller. The relay ensures robust control by providing a high feedback gain, but it also induces a control chattering phenomenon. Instead of viewing chattering as an undesirable yet inevitable feature, the chattering signals are used as natural excitation signals for identifying an equivalent PID controller using the recursive least squares algorithm. No other explicit input signal is required. Analysis is provided on the stability properties of the control scheme. Simulation results for the level control of fluid in a spherical tank using the scheme are presented.     

Systematic analysis of neutron yields from thick targets bombarded by heavy ions and protons with moving source model

A simple phenomenological analysis using the moving source model has been performed on the neutron energy spectra produced by bombarding thick targets with high energy heavy ions which have been systematically measured at the Heavy-Ion Medical Accelerator (HIMAC) facility (located in Chiba, Japan) of the National Institute of Radiological Sciences (NIRS). For the bombardment of both heavy ions and protons in the energy region of 100–500 MeV per nucleon, the moving source model incorporating the knock-on process could be generally successful in reproducing the measured neutron spectra within a factor of two margin of accuracy. This phenomenological analytical equation is expressed having several parameters as functions of atomic number Z_p, mass number A_p, energy per nucleon E_p for projectile, and atomic number Z_T, mass number A_T for target. By inputting these basic data for projectile and target into this equation we can easily estimate the secondary neutron energy spectra at an emission angle of 0–90° for bombardment with heavy ions and protons in the aforementioned energy region. This method will be quite useful to estimate the neutron source term in the neutron shielding design of high energy proton and heavy ion accelerators.     

Dynamic response of a Mindlin elastic rectangular plate under a distributed moving mass

The elastodynamic response of a rectangular Mindlin plate subjected to a distributed moving mass is investigated. The set of governing characteristic partial differential equations that include the effects of shear deformation and rotary inertia is expressed in its dimensionless form. A finite difference algorithm is employed to transform the differential equations into a set of linear algebraic equations. Simply supported edge conditions were used as an illustrative example. The analysis is also valid for other edge conditions. It is found that the maximum shearing forces, bending and twisting moments occur almost the same time. Also, the values of the maximum deflections are higher for Mindlin plates than for non-Mindlin plates.     

圆筒形铸件缩松缩孔的产生原因及解决方法

针对圆筒形铸铁辊体冒口端面产生的缩松、缩孔缺陷，进行了举例说明、系统分析，找到了缺陷产生的原因及影响因素。通过解决措施的应用与实施，有效地克服了圆筒形辊体铸件冒口端面产生的缩松、缩孔缺陷，同时应用到其它大型圆筒形铸件中，都得到了良好效果。     

Relation between microstructure, properties and spark plasma sintering (SPS) parameters of pure ultrafine WC powder

A combined experimental/numerical methodology is developed to fully consolidate pure ultrafine WC powder under a current-control mode. Three applied currents, 1900, 2100 and 2700 A, and a constant pressure of 20 MPa were employed as process conditions. The developed spark plasma sintering (SPS) finite-element model includes a moving-mesh technique to account for the contact resistance change due to sintering shrinkage and punch sliding. The effects of the heating rate on the microstructure and hardness were investigated in detail along the sample radius from both experimental and modeling points of view. The maximum hardness (2700 HV10) was achieved for a current of 1900 A at the core sample, while the maximum densification was achieved for 2100 and 2700 A. A direct relationship between the compact microstructure and both the sintering temperature and the heating rate was established.     

CXFTV2: A Fortran subroutine for the discrete least squares convex approximation

A Fortan subroutine calculates the least squares approximation to n data values containing random errors subject to non-negative second divided differences (convexity). The method employs a dual active set quadratic programming technique that allows several concavities of an iterate to be corrected simultaneously, which is a distinctive feature of this calculation. A B-spline representation of the iterates reduces each active set calculation to an unconstrained minimization with fewer variables that requires only O(n) computer operations. Details in these techniques including the data structure that establishes the implementation of the method are specified. Numerical testing on a variety of data sets indicates that the subroutine is particularly efficient, terminating after a small number of active set changes, the subroutine being suitable for large numbers of data. A numerical example and its output is provided to help the use of the software.     

用最小二乘法恢复逐行倒相副载波

介绍ＰＡＬ制彩色全电视信号中色同步信号编码原理及恢复逐行倒相副载波的过程中，两种计算色同步信号相位角的方法。并且在实验的基础上得出：最小二乘法在ＰＡＬ制电视信号的副载波相位角计算中不仅可以满足精度要求，而且简便灵活。     

折反光学系统最佳红外像面位置的研究

较深入地研究了折反光学系统的红外像面,为确定实际的红外像面提出了一个新方法—计算从可见光边缘无色的弥散圆到红外最佳像面的距离。实践证明,这是确定这类光学系统最佳像面的一个方便、可靠的方法。