如何确定高加速寿命试验的应力极限

气锤驱动的高加速寿命试验,主要目的是确定试验样品的应力极限(包括工作极限和破坏极限),并通过改进试验所暴露的缺陷,按预期目标拓宽产品的应力极限。本文对一些应力极限的名词术语作了解释性说明,并具体论述了如何确定应力极限及快速温变循环试验的高低温温度极值。     

我们只有一个地球

2010年《地球生命力报告》和《中国生态足迹报告2010》近期先后公布,有专家据此提醒,人类生态耗竭已超五成,如果继续以超出地球资源极限的方式生活,到2030年,人类＂将需要两个地球来满足需求＂。     

由极限概念的教学谈数学再创造

从在教学中对极限概念的表述方式的改造出发,提出了数学的再创造。通过再创造活动,寻求数学理论的最佳反映方式,形成最优化的教学过程,从而达到最好的教学效果。     

深海动物之谜

神秘的深海是一个至今不大为人类所知的世界。自古以来,渔民们和海员们都想象着在大洋的深处有着各种希奇古怪的庞然大物：大章鱼、巨大的蟒蛇等等。但海洋科学家们曾通过对生命极限的研究得出结论：在黑暗无底的大洋深处,终年水温不会超过2摄氏度,食物稀缺而压力巨大,一般来说,在大洋深处没有生物存在。然而生命的存在能力有时是令人难以想象的,甚至是难以置信的。深海鱼类以及动物群的存在就是一例。     

榆林气田污水回注井极限注入能力预测分析

气田生产为了减少气田采出水对地表环境的污染，及补充气藏能量，将污水进行沉淀、过滤等处理后，常回注至废弃气井或专门的回注井。文章以容积法和渗流法两种方法，分别建立模型，对气田回注井的 极限注入量、剩余可注入量、可回注年限进行预测，以榆林气田某区块两口污水回注井为例，选用回注井储层物 性、回注井回注动态数据，进行计算和验证，并对比了两种预测结果。研究结果明确了气田污水回注井回注特征与规律，为提升回注工艺的应用效果提供了相应的理论依据。     

基于实测资料的京津冀地区地表总辐射最优估算模型研究

地表总辐射（solar radiation, Rs）是一种对人类发展及其重要的新能源，同时也是影响区域环境变化的主要因素，Rs的准确估算对区域新能源发展及环境保护政策制定意义重大。故找出适用于京津冀地区辐射Rs模拟的标准方法是十分重要的，基于机器学习模型、辐射法和温度法共9种不同模型，分别计算了Rs在日值和月值尺度的精度，并计算了不同精度指标，结果表明：3种类型方法精度由高到低依次为机器学习模型>辐射法>温度法，其中极限学习机模型ELM在日值和月值尺度精度最高。     

大美无言

有人说,来到西藏就像遭遇一场艳遇,它带给我们的,是一种狂喜和眩晕。可我觉得,西藏更适合暗恋,内心狂跳却不能形于声色,否则,太容易超越自己的生理极限。     

基于向量加权算法优化ELM的变压器故障诊断

针对变压器设备,传统故障诊断方法的准确率与诊断效率难以满足当前的需求。本文提出了一种基于向量加权算法（INFO）优化极限学习机（ELM）的变压器故障诊断算法。在标准测试函数中选择3个测试函数对INFO算法进行寻优性能的测试,并与粒子群优化算法（PSO）、万有引力优化算法（GSA）、正余弦优化算法（SCA）和灰狼优化算法（GWO）进行了对比,经过测试验证INFO算法相较于其他优化算法具有更高的寻优性能。并使用INFO算法对ELM中初始输入权值和偏置进行优化,搭建基于油中溶解气体分析（DGA）的INFO-ELM变压器故障诊断分类模型,并与SVM、ELM、PSO-ELM、SSA-ELM、GWO-ELM故障诊断模型进行对比。结果表明,INFO-ELM故障诊断模型的综合准确率为98.71%,相对于上述对比模型分别提高了21.61%、16.87%、11.65%、10.36%和11.06%,本文提出的INFO-ELM变压器故障诊断模型具有更优良的故障诊断能力。     

天然地基基础可靠度分析方法

文章初步探讨天然地基基础可靠度分析的原理及方法,认为天然地基基础可靠度指标为地基基础状态函数的平均值除状态函数标准差的商。若C、φ、SG服从正态分布,SQ服从极限Ⅰ分布,可用极限状态方程求总安全系数下可靠指数β值.     

资源环境承载力研究方法综述

资源环境承载力是区域发展战略决策的基础,对指导区域可持续发展和服务国家战略需求具有重要意义。本文系统梳理了资源环境承载力评价从土地资源承载力向水资源承载力、环境承载力和生态承载力发展,再到近年来以土地开发强度为特征,以及基于供给能力的资源环境承载力评价兴起的历程。资源环境承载力评价从单一资源走向各类主要自然资源、环境要素及综合要素的承载力评价,研究方法不断完善。但目前资源环境承载力研究仍存在更多地关注承载的极限容量,对发展容量的关注不足;缺乏具有普适性、可推广的资源环境承载力评价理论及方法体系等问题,其研究仍面临严峻的挑战。未来资源环境承载力研究仍需在承载力从极限容量向发展容量转变,形成具有广泛指导意义的资源环境承载力评价方法体系,强化以空间开发利用为特征的资源环境承载力评价等方面的研究,以此深化资源环境承载力理论及实践应用研究,为区域可持续发展及服务国家战略提供支撑。     

湖北省荆沙区域国土资源优势与制约因素探讨

本文探讨了湖北省荆沙市的区域资源优势和发展经济的制约因素，对推动湖北省农村经济的持续发展将起到积极的作用．     

解读GB19606-2004《家用和类似用途电器噪声限值》

本文从多角度对GB 19606-2004标准进行了较为深入的分析,同时详细地比较了该标准与现行家电产品标准中的噪声限值的差异,从而指出生产厂商必须对家电产品噪声限值的变化引起足够的重视,提高产品的噪声水平以满足该强制性标准的要求.     

USING UNCENSORED TRACE-LEVEL MEASUREMENTS TO DETECT TRENDS IN GROUND WATER CONTAMINATION1

ABSTRACT: Environmental decision making involving trace-levels of contaminants can be complicated by censoring, the practice of reporting concentrations either as less than the limit of detection (LOD) or as not detected (ND) when a test result is less than the LOD. Censoring can result in data series that are difficult to meaningfully summarize, graph, and analyze through traditional statistical methods. In spite of the relatively large measurement errors associated with test results below the LOD, simple and meaningful analyses can be carried out that provide valuable information not available if data are censored. For example, an indication of increasing levels of contamination at the fringe of a plume can act as an early warning signal to trigger further study, an increased sampling frequency, or a higher level of remediation at the source. This paper involves the application of nonparametric trend analyses to uncensored trace-level groundwater monitoring data collected between March 1991 and August 1994 on dissolved arsenic and chromium for seven wells at an industrial site in New York.     

NON-ZERO LOWER LIMIT IN LOW FLOW FREQUENCY ANALYSIS?1

ABSTRACT: The implications of fitting distributions with non-zero lower limits to low flow data are examined. The 3-parameter Weibull distribution is fitted to annual minimum flow series from 60 long term stations in Canada. The relations between the estimated lower limit and three sampling variables (skewness, smallest, and largest observations) were investigated. The lower limit strongly depends on the sample skewness; it varies directly with the sample skewness, which in turn is highly influenced by the largest observation. For a given skewness, the value of the estimated lower limit is determined by the value of the smallest observation. Therefore, the lower limit cannot be accurately determined, and the resulting low flow estimates will be either too small or too high.     

原子吸收法测定铜检出限的测量不确定度评估

对原子吸收法测定铜检出限的测量不确定度进行分析探讨,建立了不确定度的评估方法。影响铜检出限测量不确定度的主要因素包括标准溶液不确定度;拟合曲线不确定度;检测仪器不确定度;吸光值量化误差不确定度等,提供了上述各因素的计算方法及过程。     

A TAU-LIKE TEST FOR TREND IN THE PRESENCE OF MULTIPLE CENSORING POINTS1

ABSTRACT: A common problem arises in testing for trends in water quality when observations are reported as “less than detection limit.” If a single detection limit is used for the entire study, existing non-parametric statistical methods, modified for ties, are applicable. If, however, the detection limit varies during the course of the study, resulting in multiple detection limits, then the commonly used trend detection methods are not appropriate. A statistic similar to Kendall's tau, but based on expected ranks, is proposed. Monte Carlo simulations show that the normal approximation to the distribution of this statistic is quite good, even for small samples and a large proportion of censored observations. The statistic is also shown to have greater power than the ad-hoc method of treating all observations less than the target censored observation as tied.     

Thermoeconomic installation limit of PV/WT hybrid energy systems for Off-grid islands

An ideal off-grid island can become 100% energy-sufficient if one installs renewable energy systems such as solar photovoltaic (PV) and wind turbine (WT) systems. However, the intermittent and uncertain nature of the power supply from renewable energy systems hinders a 100% autonomy level (AL) without an infinite energy storage capacity. The thermoeconomic installation limit (TEIL) of a PV/WT hybrid energy system was studied using hourly weather data and the energy demand profile for off-grid islands. An appropriate battery size for the TEIL was also determined. Given the current installation cost of the hybrid energy system and the battery unit, the AL for a PV/WT hybrid energy system at the TEIL is calculated to be approximately 70%. Above the limit, the size of the energy storage unit and, correspondingly, the total annual cost of the PV/WT hybrid energy system increase sharply.