基于粒子群优化反向传播神经网络的铁路路基沉降量预测

铁路路基沉降规律复杂、沉降量难以预测,因此提出一种粒子群优化反向传播神经网络的路基沉降量预测模型。传统神经网络建模时存在收敛速度慢、易陷入局部极小值等不足。因此,通过粒子群算法修正网络的初始权/阈值,提高全局收敛性,建立基于粒子群优化的反向传播神经网络预测模型。通过对宝中线实测数据进行仿真实验,结果显示：经粒子群优化的神经网络可避免局部极小问题,加快网络收敛速度,提高了对铁路路基沉降量的预测精度。     

Low Mortgage Rates and Securitization: A Distinct Perspective on the US Housing Boom*

In this paper, we analyse the impacts of low interest rates and lax underwriting standards on the US housing boom around the beginning of the new millennium. We suggest a time-varying mean of the log price-to-rent ratio (PtR) to capture the persistent changes in housing prices. We show that the increasing latent trend in the PtR was significantly affected by the increased securitization of residential mortgage loans and decreasing interest rates, with the former effect being about three times larger than the latter. In the absence of securitization, negative interest rates would have been needed to reproduce an equally large housing boom since 2003.     

Household behavior with respect to meat consumption in the presence of BSE and CWD

In this study, Canadian household meat consumption behavior in exotic (deer and elk meat) and traditional meats (beef, pork, chicken, turkey, bison, and seafood) is examined. This research introduces some differences in public response to transmissible spongiform encephalopathies (TSE) risks across consumer segments from different sources of meat supply, including hunted meat. The analysis uses a combination of survey and household meat purchase data that include a balanced household panel of 2,393 households per year across time. A two-step estimation procedure is used with a probit model in the first step (consume or not) and a doublelog–translog two-stage demand system in the second step (level of consumption). It is assumed and tested that household sociodemographics, consumers’ risk perceptions/attitudes, and media coverage of bovine spongiform encephalopathy (BSE) and chronic wasting disease (CWD) are underlying demand shifters in consumers’ daily meat purchase decision. The results suggest that households who obtain venison from hunting show the highest confidence in venison safety. Exotic meat preferences negatively affect traditional meat consumption in the daily diets of households who purchase traditional meats from stores and obtain venison from hunting. In response to the media coverage of BSE and CWD, exotic meat eaters are less sensitive to animal disease media information than the general population.     

Estimating the Weight Undersize Distribution for the Wicksell problem

In Wicksell's corpuscle problem one is interested in estimating the distribution of sphere diameters from the diameters of circle profiles obtained by a random section of the body containing the sphericle particles. The problem is known to be an ill posed inverse problem. Several regularization techniques have been applied to find solutions. We will review some of these in this article. In practical situations one often is more interested in the distribution of weight rather than the distribution of diameters. In estimating the weight undersite distribution similar problems are encountered. We will consider an estimator that is obtained by smoothing the distribution function of the circle diameters locally. It will be shown how the bandwidth must be chosen to obtain consistency and mean square error optirnality. Also asymptotic normality will be shown.     

基于混合粒子群算法的车辆路径优化问题研究

设计了一种引入了量子和遗传算法思想的粒子群算法．该算法结合了粒子群优化算法的快速寻优能力和量子算法可以同时处理多个目标的优点．避免了基本粒子群算法易陷入局部最优的缺点,提高了求解速度。该算法用于解决车辆路径问题。通过实验表明了这种算法具有较好的性能。     

具有模糊加工时间的偏柔性作业车间调度问题研究

研究了以最小化制造跨度为目标的,具有模糊加工时间的偏柔性作业车间调度问题。针对该问题,采用三角模糊数来表征时间参数;并采用预处理算法,将偏柔性作业车间调度问题转化为更容易处理的完全柔性作业车间调度问题,给出了基于粒子群优化的调度模型;最后通过实例验证了模型的有效性。     

基于粒子群算法的土石方装运机械配备方案优化

土石方工程中,合理的制定机械配备方案将直接影响工程的进展与造价。针对该问题构造时间一费用评价函数,引入一种改进后的粒子群算法,利用该算法具有多个可行解同时寻优并能以较大概率收敛到全局最优的特性,在综合考虑时间和费用的基础上,实现了土石方装运系统的机械配备方案仿真优化,有一定的实用价值。     

动态助词“过”的语法化历程

动态助词＂过＂一般分为＂过1＂和其中＂过2＂,＂过1＂表示动作的完结,＂过2＂表示曾然。其语法化历程为：一般动词＂过＂→趋向动词＂过＂→动态助词＂过1＂→动态助词＂过2＂。动态助词＂过1＂和＂过2＂的演变又可分别区分为两个阶段,即演变发生和演变扩散。就形成机制而言,＂过1＂的产生主要是受隐喻、类推以及重新分析的作用,趋向动词＂过＂的形成是＂过1＂产生的关键;而＂过2＂是＂过1＂吸收了助词＂来＂及其经常出现的句法环境的语法意义而产生的,可以说是＂过1＂在特殊语境下的产物。     

浅谈普通混凝土用天然砂的筛分析试验

规范化试验、检测工作的内容,程序,和相关管理方法,并指出砂的筛分析试验是既常用又重要的试验参数,必须提供准确可靠的数据, 用以评定混凝土用砂的质量.     

基于摄像机位置的大规模粒子云绘制加速算法

粒子云团作为一种场景仿真的重要元素,具有数量大、分布不均匀、覆盖面广的特点,实时模拟很困难。为解决现有算法绘制速度慢的问题,提出了一种基于摄像机的非均匀分层加速算法,降低了冗余粒子数。在一个场景仿真程序中对算法进行效用测试,实践证明此算法在保证画面效果的同时提高了绘制速度。