基于 MPDE-EEMD 及自适应共振解调的轴承故障特征提取方法

针对滚动轴承振动信号具有非线性、非平稳性和非高斯性,并且故障特征往往淹没于系统噪声之中而难于识别的问题, 提出了以多种群差分进化(multiple population differential evolution, MPDE) 算法来改进集合经验模式分解( ensemble empirical mode decomposition, EEMD) 的 MPDE-EEMD 消噪方法,并与自适应共振解调技术( adaptive resonance demodulation technique, ARDT)相结合实现故障特征提取。 首先,为了解决 EEMD 中加入参数依靠人工选择且难以准确获取的问题,建立极值点分布 特性评价函数,利用 MPDE 来寻优获取最佳白噪声幅值,实现 EEMD 自适应分解。 然后,采用峭度与相关性相结合的准则对分 解后的 IMF 分量进行自动筛选,将满足条件的有效信号进行重构,实现对原始振动信号的降噪处理。 最后,采用 ARDT 自动确 定对消噪信号进行带通滤波的带宽和中心频率,再通过包络解调提取出滤波信号的特征频率。 将轴承仿真故障信号与实际故 障信号用于算法的验证,结果表明 MPDE-EEMD+ARDT 能有效提取出轴承故障特征。     

Performance study of change-point detection thresholds for cumulative sum statistic in a sequential context

Sequential detection is based on a recursive statistic and a threshold it must reach to report a change. In this paper, we consider the score-based cumulative sum statistic and propose to evaluate the detection performance of some thresholds on simulated data. Three thresholds come from the literature: the Wald constant, the empirical constant, and the conditional empirical instantaneous threshold (the latter two are built by a simulation-based procedure). Two new thresholds are built by a simulation-based procedure: the first one is instantaneous, the second is a dynamical version of the previous one. The thresholds' performance measured by an estimation of the mean time between false alarm (MTBFA) and the average detection delay (ADD) are evaluated on independent and autocorrelated data for several scenario, according to the detection objective and the real change in the data. The simulations allow us to compare the difference between the thresholds' results and to see that their performances prove to be robust when a parameter of the prechange regime is misestimated or when the data independence assumption is violated. We found also that the conditional empirical threshold is the best at minimizing the detection delay while maintaining the given false alarm rate. However, on real data, we suggest to use the dynamic instantaneous threshold because it is the easiest to build for practical implementation.     

2.5 GHz城市环境电磁态势的计算与补偿

复杂城市空间的电磁态势分布可以通过电磁场数值计算的方法进行预测。文章使用矩量法(MOM)结合一致性几何绕射理论(UTD)的方法对2.5 GHz频率下某小区环境中的电磁态势进行了仿真计算以及实际测量。场景中的树木结构在此频率下显示出比较强烈的波动性,对电磁仿真计算结果产生了不可忽略的影响,文中将其对仿真计算结果的影响进行了单独建模仿真,给出其产生影响的经验值,对仿真结果进行修正。修正结果与测量结果对比证明该经验值在该频率下可以有效补偿计算结果的缺失。     

Empirical Analysis of Agricultural Cultural Resources Value Evaluation under DEA Model

Agricultural culture is a productive activity about education and management. It aims at high efficiency and high quality, uses technology as its means, and takes nature as its carrier. Agricultural cultural resources are the product of the rapid development of modern economy. It promotes the development of the national economy and profoundly affects people's production and life. DEA model, also known as data envelope analysis method, is an algorithm that uses multiple data decision units for input and output training to obtain the final model. This article explains the concept and basic characteristics of agricultural culture. Through questionnaire surveys and expert interviews, we collected development data, screened human, material, and financial data, and calculated information on economic and social resources. On this basis, this paper establishes the evaluation index of agricultural culture based on DEA model. Then, through empirical analysis from a specific perspective, it can be concluded that increasing human, material and financial input can achieve economic and social benefits. Generally speaking, cultural investment can promote the development of the industry. The research results of this paper laid a theoretical foundation for the development of agricultural culture, and put forward a development model focusing on technology development, improving investment efficiency, and investing in material resources.     

有色金属行业上市公司资本结构与企业绩效的实证分析

介绍有色金属行业及其上市公司的现状 ,应用混合数据采用TSCS分析方法 ,对有色金属行业上市公司资本结构与企业绩效的关系进行实证研究。结果表明 ,有色金属行业上市公司企业绩效与资产负债率负相关。认为理性的企业行为应当是尽可能降低企业资产负债率 ,优化企业资本结构 ,提高企业绩效     

发热量的应用及其与灰分的代数关系

从发热量的定义及其国标检测方法出发,分析了低位发热量应用时的注意事项,并推导了发热量与灰分的经验公式,列出转换表,具有一定实用性。     

A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Calibration results

To gain understanding of nutrient and phytoplankton dynamics in Lake Okeechobee, Florida, we developed and applied a deterministic, mass balance, water quality model at the whole-lake spatial scale. The model was calibrated to a comprehensive set of field data for 1985–1986, and then used to simulate the period 1973–1992. The model represented the mean behavior of in-lake total phosphorus, dissolved available phosphorus, total nitrogen and chlorophyll a concentrations reasonably well during the calibration period. The model did not represent dissolved available nitrogen concentrations very well, nor did it capture much of the observed temporal variability during the calibration period. The model results identified important information needs to improve our understanding of the nitrogen cycle including, sediment-water nitrogen fluxes, denitrification and nitrogen fixation. Results from the 1973–1992 simulation indicated that model assumptions and/or calibration parameters were not uniformly applicable over this period. Total phosphorus concentration results from this model were compared with results from two site-specific, empirical loading models for the lake. None of these models represented annual average concentrations uniformly well over the entire 20-year period, and none captured much of the observed inter-annual variability. External total phosphorus loadings and lake hydrology are not sufficient to fully describe total phosphorus dynamics in Lake Okeechobee. Other important factors are diffusive sediment-water fluxes, wind-induced sediment resuspension, and the spatial heterogeneity in the lake.     

粉煤灰陶粒混凝土的弹性模量计算

采用粉煤灰陶粒配制成的轻骨料混凝土,其弹性模量实测值低于现有的经验公式计算值。通过试验,建立了适用于粉煤灰陶粒混凝土的弹性模量经验公式,并与国内外有关规范的指标进行了比较,证明了回归公式的可用性。     

跨海公路隧道岩石覆盖厚度探讨

在特殊的地质环境条件下,建设海底隧道无疑是最安全经济、路线最短的方案。自从1936年第1条海底隧道--日本关门隧道开始建造以来,在世界各地,已有近百条海底隧道相继建设,海底隧道的设计与施工,还有许多技术问题丞待解决。结合我国拟建厦门海底隧道的工程实际,探讨了国内外海峡海底隧道工程的特点及其最小岩石覆盖层厚度的问题;结合世界上已建海底隧道的工程经验,应用经验类比法和数值分析法,研究厦门海底隧道的岩石覆盖厚度。研究成果将对我国未来的海峡海底隧道修建工程有所借鉴。     

复合地基动弹性模量和阻尼比的试验研究

通过水泥土复合试样的动力试验,着重研究掺入比、围压等因素对复合试样动弹性模量和阻尼的影响。通过回归分析,提出了计算动弹性模量和阻尼比的简单方法,并给出了考虑上述影响因素的经验公式,对水泥搅拌桩复合地基抗震设计研究提供了一些初步参考依据。