大型商圈安全评价体系及案例研究*

为整体评价大型商圈的安全性,结合公共安全科技三角形理论,从突发事件的危险性、承灾载体的脆弱性、应急能力3方面构建大型商圈安全评价指标体系,通过网络分析法和模糊综合评价法确定指标间权重系数,对大型商圈进行安全风险评价。结果表明:体系全面考虑了大型商圈安全风险影响因素及其内在关系,可为大型商圈安全评价体系构建和定量评估提供参考。     

The shaped blasting experimental study on damage and crack evolution of high stress coal seam

In the deep high stress coal and rock mass, the efficiency of the ordinary blasting method is constantly affected by the high pressure. This study investigates the shaped blasting technology with increased blasting efficiency, develops a mechanical model for coal crack expansion during shaped blasting, and examines the force-energy action of energy-gathering jets during coal splitting. The established model was combined with experiments and simulations to reveal the damage and evolution of cracks in coal and rock masses. Experiments demonstrate that shaped blasting can create an energy-gathering jet that causes a directional fracture in the test block. The peak of compressive strain in the energy-gathering direction is 1.12 times greater than that of ordinary blasting, and the static action period of the explosive gas is prolonged by 1.3 μs according to the stress curve. Moreover, the peak pressure strain increased 3.2 times, and the pull strain peak increased 3.92 times. The damage amount was represented by the resistivity and ultrasonic wave speed, and shaped blasting causes 1.2 and 1.5 times greater damage than ordinary blasting. The research results provide technical methods for safe and rapid penetration blasting in deep high-ground stressed coal mines.     

流域生态过程与水环境效应研究进展

以Web of Science数据库及CNKI(中国知网)的文献资料为数据源,利用CiteSpace文献计量工具,对流域生态过程和水环境效应研究领域的相关文献从发文量、发文期刊、关键词、作者及论文被引频次等方面进行分析,以此探讨国内外该领域研究现状、研究热点及未来发展趋势.结果 表明,流域生态过程和水环境效应研究文献数...     

An improved grey wolf optimizer algorithm for identification and location of gas emission

Identification of the leakage of hazardous gases plays an important role in the environment protection, human health and safety of industry production. However, lots of current optimization algorithms, such as particle swarm optimization (PSO) and Grey Wolf Optimizer (GWO), suffer from poor global optimization capability and estimation accuracy. In this work, a hybrid differential evolutionary and GWO (DE-GWO) algorithm is proposed. Tested by simulation cases and Prairie Grass emission experimental data, DE-GWO shows higher estimation accuracy than GWO. Compared with the other four optimization algorithms, DE-GWO exhibits finer robust stability under different population sizes, fewer iterations, as well as higher estimation accuracy with fewer search agents. Importantly, simulation results demonstrate that DE-GWO is more suitable to apply in the scene with a small number of sensors. Therefore, the proposed in this paper outperforms other optimization algorithms for the gas emission inverse problem. DE-GWO can provide reliable estimation towards gas emission identification and positioning, which shows huge potential as the data analysis module of real-time monitoring and early warning system.     

Age and spatial distribution of the world's oldest trees

Extremely old trees have important roles in providing insights about historical climatic events and supporting cultural values, yet there has been limited work on their global distribution and conservation. We extracted information on 197,855 tree cores from 4854 sites and combined it with other tree age (e.g., the OLDLIST) data from a further 156 sites to determine the age of the world's oldest trees and quantify the factors influencing their global distribution. We found that extremely old trees >1000 years were rare. Among 30 individual trees that exceeded 2000 years old, 27 occurred in high mountains. We modeled maximum tree age with climatic, soil topographic, and anthropogenic variables, and our regression models demonstrated that elevation, human population density, soil carbon content, and mean annual temperature were key determinants of the distribution of the world's oldest trees. Specifically, our model predicted that many of the oldest trees will occur in high-elevation, cold, and arid mountains with limited human disturbance. This pattern was markedly different from that of the tallest trees, which were more likely to occur in relatively more mesic and productive locations. Global warming and expansion of human activities may induce rapid population declines of extremely old trees. New strategies, including targeted establishment of conservation reserves in remote regions, especially those in western parts of China and the United States, are required to protect these trees.