Mechanical heterogeneity characterization of coal materials based on nano-indentation experiments

To investigate the complex macro-mechanical properties of coal from a micro-mechanical perspective,we have conducted a series of micro-mechanical experiments on coal using a nano-indentation instrument.These experiments were conducted under both dynamic and static loading conditions,allowing us to gather the micro-mechanical parameters of coal for further analysis of its micro-mechanical heterogeneity using the box counting statistical method and the Weibull model.The research findings indicate that the load–displacement curves of the coal mass under the two different loading modes exhibit noticeable discreteness.This can be attributed to the stress concentration phenomenon caused by variations in the mechanical properties of the micro-units during the loading process of the coal mass.Consequently,there are significant fluctuations in the micro-mechanical parameters of the coal mass.Moreover,the mechanical heterogeneity of the coal at the nanoscale was confirmed based on the calculation results of the standard deviation coefficient and Weibull modulus of the coal body’s micromechanical parameters.These results reveal the influence of microstructural defects and minerals on the uniformity of the stress field distribution within the loaded coal body,as well as on the ductility characteristics of the micro-defect structure.Furthermore,there is a pronounced heterogeneity in the micromechanical parameters.Furthermore,we have established a relationship between the macro and micro elastic modulus of coal by applying the Mori-Tanaka homogenization method.This relationship holds great significance for revealing the micro-mechanical failure mechanism of coal.

美国高校本科应急管理人才培养方案

我国应急管理教育处于起步阶段,培养大多挂靠在相关学科和专业,美国具有成熟的应急管理教育培训体系和教学经验,对美国应急管理人才培养方案的研究可以为我国培养该领域人才提供良好的参考。调查了美国高校应急管理教育现状及培养目标,同时以美国10所开设应急管理本科专业的高校为样本,对其课程体系以及文、理学士的课程内容进行系统梳理和分析。发现美国应急管理教育范围广,涉及国土安全、国际减灾及公共卫生等;文理类课程差异小,系统性强,注重实用性。最后根据当前我国高校应急管理培养的薄弱之处,提出我国未来应急管理专业的发展路线,弥补我国应急管理人才不足的缺口。

极低浓度甲烷、二甲醚掺混燃烧数值模拟

在煤炭开采过程中,低浓度瓦斯涌出后一般直接排放至大气中,造成了严重的资源浪费和环境污染。为了提高极低浓度瓦斯的利用率,以极低浓度的甲烷(体积分数小于5%)作为模拟气体,向其中掺混易燃易爆的二甲醚气体促进其燃烧,借助CHEMKIN模拟软件,对掺混气体燃烧过程进行模拟分析,研究了不同当量比对混合气体燃烧后压力及生成物的影响。结果表明,二甲醚能够促进极低浓度甲烷燃烧,且燃烧后最大压力随当量比增加逐渐增大并趋于稳定。同时,当量比对于掺混燃烧气体产物成分的影响较大,在甲烷初始体积分数相同的条件下,掺混燃烧产生的尾气中CO体积分数随当量比(Φ)增加而增加,当Φ<0.8时,燃烧产物主要是CO2,当Φ>0.8时,燃烧产物主要是CO;CO2体积分数随当量比增大先增大后减小,存在峰值点,初始甲烷体积分数越大,CO2体积分数峰值越小。在当量比小于1.2时,燃烧产物中剩余甲烷体积分数很小;在当量比大于1.2时,燃烧产物中剩余甲烷体积分数随当量比增加而迅速增加。在当量比相同时,甲烷的转化率随初始甲烷体积分数增加而增加。

中文开放域问答系统的问题分类研究

中文问答系统通常由问题分析、信息检索、答案抽取组成。其中,问题分析中的问题的分类是否准确会直接关系到提取答案的准确度,所以在问答系统中起到关键性作用。本文主要介绍了中文问答系统的结构、问题分类体系以及方法,并提出结合基于规则的模式匹配与基于统计的机器学习的方法对问题进行分类,从而提高分类的准确度。

Chaotic characteristics of electromagnetic emission signals during deformation and fracture of coal

Electromagnetic emission(EME) is a kind of physical phenomenon accompanying the process of deformation and fracture of loaded coal and rock and it is of importance in quantitatively analyzing its characteristics.This will reveal the process of deformation and fracture of coal and predicting dynamic disasters in coal mines.In this study,the G-P(Grassberger and Procaccia) algorithm,calculation steps of the(if only 1 dimension) correlation dimension of time series and the identification standards of chaotic signals are introduced.Furthermore,the correlation dimensions of EME and the acoustic emission(AE) signals of time series during deformation and fracture of coal bodies are calculated and analyzed.The results show that the time series of pulses number of EME and the time series of AE count rate are chaotic and that the saturation embedding dimensions of a K3 coal sample are,respectively,5 and 6.The results can be used to provide basic parameters for predicting of EME and AE time series.

磁场对乙烯预混气体爆炸自由基影响机理

为探究磁场对预混气体爆炸特征的影响及机理,以乙烯为例,通过自行研制的实验系统研究磁场对预混乙烯/空气爆炸压力、火焰传播速度等爆炸特征的影响,利用Chemkin‑Pro模拟了乙烯爆炸链式反应过程,研究了乙烯爆炸链式反应的关键自由基,理论计算了磁场对自由基粒子的作用力,探讨了磁场影响预混气体爆炸的自由基机理。结果表明,在最大磁场强度3300 Gs作用下,6.5%乙烯最大爆炸压力降低18.18%、爆炸压力上升速率降低17.33%,沿着火焰传播方向,磁场对乙烯爆炸火焰传播速度呈现先促进后抑制的效应,抑制效果大于促进效果,总体呈现抑制效应。乙烯爆炸过程中的关键自由基为·H、·O、·CH_(2)。自由基在磁场作用下的受力与自由基的磁化强度成正比,乙烯爆炸关键自由基的磁化强度各不相同,在磁场作用下,自由基出现分层现象,减少了不同自由基之间的碰撞,降低基元反应速率,从而抑制乙烯爆炸。