绿色照明光源LED的控制策略

绿色照明的第4代光源白色LED,已开始逐步在家庭照明、公路照明、移动照明、军事照明、设备照明得到应用,而由太阳电池、蓄电池、控制器和LED所组成的照明系统正越来越受到人们重视.可是由于太阳电池所产生的电能价格在目前来说是较为昂贵的,所以应对LED照明系统采用节电控制.本文主要讨论了几种LED控制方式,分析了这几种电路的工作原理,找出比较节电的控制方式,着重指出适合太阳能LED照明系统的控制方式.     

Factors affecting the hydraulic performance of infiltration based SUDS in clay

The influence of small scale soil heterogeneity on the hydraulic performance of infiltration based sustainable urban drainage systems (SUDS) was studied using field data from a clayey glacial till and groundwater simulations with the integrated surface water and groundwater model HydroGeoSphere. Simulations of homogeneous soil blocks with hydraulic properties ranging from sand to clay showed that infiltration capacities vary greatly for the different soil types observed in glacial till. The inclusion of heterogeneities dramatically increased infiltration volume by a factor of 22 for a soil with structural changes above and below the CaCO₃ boundary. Infiltration increased further by 8% if tectonic fractures were included and by another 61% if earthworm burrows were added. Comparison of HydroGeoSphere infiltration hydrographs with a simple soakaway model (Roldin et al., 2012) showed similar results for homogeneous soils but indicated that exclusion of small scale soil physical features may greatly underestimate hydraulic performance of infiltration based SUDS.     

Adaptive backward Euler time stepping with truncation error control for numerical modelling of unsaturated fluid flow

An automatic time stepping scheme with embedded error control is developed and applied to the moisture‐based Richards equation. The algorithm is based on the first‐order backward Euler scheme, and uses a numerical estimate of the local truncation error and an efficient time step selector to control the temporal accuracy of the integration. Local extrapolation, equivalent to the use of an unconditionally stable Thomas–Gladwell algorithm, achieves second‐order temporal accuracy at minimal additional costs. The time stepping algorithm also provides accurate initial estimates for the iterative non‐linear solver. Numerical tests confirm the ability of the scheme to automatically optimize the time step size to match a user prescribed temporal error tolerance. An important merit of the proposed method is its conceptual and computational simplicity. It can be directly incorporated into existing or new software based on the backward Euler scheme (currently prevalent in subsurface hydrologic modelling), and markedly improves their performance compared with simple fixed or heuristic time step selection. The generality of the approach also makes possible its use for solving PDEs in other engineering applications, where strong non‐linearity, stability or implementation considerations favour a simple and robust low‐order method, or where there is a legacy of backward Euler codes in current use. Copyright © 2001 John Wiley & Sons, Ltd.     

一种槽式回转弹仓结构设计和动力学仿真

为了合理布置自行火炮的内部空间,设计一种槽式回转异形弹仓。介绍了弹仓的基本结构和工作原理,通过改变导槽的路径,灵活改变弹仓形状,使弹仓可以布置在不太规则的空间里,充分利用了自行火炮内部有限的空间,并基于RecurDyn的动力学建模进行仿真分析。仿真结果表明:该槽式回转弹仓增强了弹仓在不规则空间里的适应性和增加了载弹数量,可为异形弹仓的设计提供参考。     

Constrained feedback control of imperfectly known singularly perturbed non-linear systems

Global attractors are investigated for a class of imperfectly known, singularly perturbed, dynamic control systems. The uncertain systems are modelled as non-linear perturbations to a known non-linear idealized system and are represented by two time-scale subsystems. The two subsystems, which depend on a scalar singular perturbation parameter, represent a singularly perturbed system which has the property that the system reduces to one of lower order when the singular perturbation parameter is set to zero. It is assumed that the full-order system is subject to constraints on the control inputs. A class of constrained feedback controllers is developed which assures global uniform attraction of a compact set, containing the state origin, for all values of the singular perturbation parameter less than some threshold value.     

Computer Control of Kaldo Oxygen Steelmaking

The Stora-Kaldo installation of Sharon Steel is equipped with a digital computer. The computer has been functioning since May, 1964. Results are outlined.     

Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption

Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.