模拟退火算法在神经网络中的实现

神经网络是用于模拟人的大脑组织结构的一种网络结构。在很多技术领域存在着大量的组合优化问题．这些问题随着规模的增大,求解的时闻和空间呈指数级增长,当规模达到一定程度,在时间上,求解就变得没有可行性可言,而神经网络是近似求解的一种很好的解决方法。神经网络的实现方法有多种,例如模拟退火算法、BP算法和遗传算法,等等,其中,模拟退火算法是一种计算精度比较高、收敛速度较快的算法。     

模拟退火算法中关键参数的研究

模拟退火算法是求解组合优化问题的一个有效方法,但算法中各个参数值的选择和设置对运行的结果和效果有较大影响。因此,本文主要是利用几个具体的TSP问题对算法中 的几个重要参数做比较研究,得出了一组比较有效的参数取值,为求解与TSP问题类似的其他问题奠定了有效的参数基础。     

Fatigue crack growth prediction in nuclear piping using Markov chain Monte Carlo simulation

In this paper, we present and demonstrate a methodology to improve probabilistic fatigue crack growth (FCG) predictions by using the concept of Bayesian updating using Markov chain Monte Carlo simulations. The methodology is demonstrated on a cracked pipe undergoing fatigue loading. Initial estimates of the FCG rate are made using the Paris law. The prior probability distributions of the Paris law parameters are taken from the tests on specimen made of the same material as that of pipe. Measured data on crack depth over number of loading cycles are used to update the prior distribution using the Markov chain Monte Carlo. The confidence interval on the predicted FCG rate is also estimated. In actual piping placed in a plant, the measured data can be considered equivalent to the data received from in-service inspection. It is shown that the proposed methodology improves the fatigue life prediction. The number of observations used for updating is found to leave a significant effect on the accuracy of the updated prediction.     

Replica Exchange Light Transport

We solve the light transport problem by introducing a novel unbiased Monte Carlo algorithm called replica exchange light transport, inspired by the replica exchange Monte Carlo method in the fields of computational physics and statistical information processing. The replica exchange Monte Carlo method is a sampling technique whose operation resembles simulated annealing in optimization algorithms using a set of sampling distributions. We apply it to the solution of light transport integration by extending the probability density function of an integrand of the integration to a set of distributions. That set of distributions is composed of combinations of the path densities of different path generation types: uniform distributions in the integral domain, explicit and implicit paths in light (particle/photon) tracing, indirect paths in bidirectional path tracing, explicit and implicit paths in path tracing, and implicit caustics paths seen through specular surfaces including the delta function in path tracing. The replica‐exchange light transport algorithm generates a sequence of path samples from each distribution and samples the simultaneous distribution of those distributions as a stationary distribution by using the Markov chain Monte Carlo method. Then the algorithm combines the obtained path samples from each distribution using multiple importance sampling. We compare the images generated with our algorithm to those generated with bidirectional path tracing and Metropolis light transport based on the primary sample space. Our proposing algorithm has better convergence property than bidirectional path tracing and the Metropolis light transport, and it is easy to implement by extending the Metropolis light transport.     

大城市交通与建成环境综合规划的范式扩展与深化 — —中美案例的比较与启示

城市交通与建成环境规划是城市 综合规划的核心内容,在城市的不同发展阶 段,其社会经济条件与主要规划理念、政策 保障之间的匹配度对城市发展产生了持续影 响。在中国城市面临空间增长型向内涵提升 型转变发展的重要时期,进一步审视发达 国家大城市交通与建成环境综合规划在不 同阶段的范式变化（包括主要背景、发展理 念、规划要点、实施效果等）,对比中国大城 市发展的阶段性特征,将为中国大城市交通 与建成环境的提质发展提供有益参考。本文 通过梳理中美两国部分大城市交通与建成 环境规划的发展脉络,总结不同阶段的范式 发展特征,结合当前中国大城市空间发展趋 向,为中国大城市交通与建成环境的综合发 展提供借鉴和指导。     

Emission inventory of VOCs from mobile sources in a metropolitan region

Based on methodologies developed by US EPA, European EMEP/CORINAIR, and Australian NPI, and the former emission inventory in Korea, two methods were applied to 151 villages in northeastern Seoul, Korea to estimate emission of VOCs from line and area vehicle sources depending on vehicle types with different fuel types. A discharge coefficient method for the line source on the Eastern main road was calculated by multiplying the emission amounts per unit of mileage, and a fuel exhaust coefficient method for the area vehicle sources on other roads was determined as multiplying the emission rates by the actual consumption of excess fuel. Results indicated the methods could be adequate for estimating the amounts of mobile emissions when limited information on mobile emission is available. The methods can be used to develop the emission model for all VOCs emission sources (point and non-point sources), which provides input data of atmospheric models.     

克隆遗传算法与模拟退火算法相结合的配电网络重构

配电网重构可以提高配电网运行的安全性、经济性和供电质量,对于当前国内配电自动化系统建设和应用具有重要意义。将克隆遗传算法(CGA)与退火算法(SA)结合起来,把退火算法中的Metropolis抽样准则融入到克隆遗传算法中,形成克隆遗传退火算法(CGSA)。以网损最小为目标函数,以配电网电压降的限制、线路电流量的限制等为约束条件,在考虑配电网自身特点的基础上,以IEEE33节点为算例,利用克隆遗传退火算法求解。结果证明该优化算法具有较好的全局收敛性和收敛速度。     

一个在中国工作的欧洲建筑师

总之,在中国的建筑执业经历对我来说,既是刺激的又是失望的。刺激是因为我们在一次次将新的中国文化与住宅综合体的城市设计相结合的尝试中起了重要作用;失望是我们看来,中国效尤了西方失败的先例,坚持认为这种信念是次要的,虽然城市文化在千百年来代表了中国最高的、最悠久的传统。为了与西方消费主义的新殖民主义对抗,我们需要借助体现传统中国文明的现代建筑。只有借助不同伟大传统之间的对话,才能产生新的优秀的城市建筑。