型钢翼缘狗骨式削弱在型钢混凝土节点的作用

为了防止地震时型钢混凝土节点核心区发生剪切破坏以及梁柱连接焊缝发生脆性断裂,提出对型钢混凝土节点核心区附近梁端型钢的上、下翼缘采取狗骨式削弱,并系统研究翼缘削弱对提高型钢混凝土节点抗震性能的作用.研究表明,由于在梁端型钢翼缘采取狗骨式削弱,不仅能够将塑性铰控制在梁型钢削弱的位置,从而有效地降低了节点核心区所受的剪力以及梁柱连接焊缝的应力;而且能够改善节点塑性铰区的转动能力和抗剪性能,提高节点的延性和耗能能力.     

Prevention and forecasting of rock burst hazards in coal mines

Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure of coal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established. We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suitable for roadways subject to hazards from rockbursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.     

In Situ Deformation Topology of COFs with Shortened Channels and High Redox Properties for Li–S Batteries

Covalent organic frameworks (COFs) with various topologies are typically synthesized by selecting and designing connecting units with rich shapes. However, this process is time-consuming and labour-intensive. Besides, the tight stacking of COFs layers greatly restrict their structural advantages. It is crucial to effectively exploit the high porosity and active sites of COFs by topological design. Herein, for the first time, inducing in situ topological changes in sub-chemometric COFs by adding graphene oxide (GO) without replacing the monomer, is proposed. Surprisingly, GO can slow down the intermolecular stacking and induce rearrangement of COFs nanosheets. The channels of D- [4+3] COFs are significantly altered while the stacking of periodically expanded framework is weakened. This not only maximizes the exposure of pore area and polar groups, but also shortens the channels and increases the redox activity, which enables high loading while enhancing host-guest interactions. This topological transformation to exhibit the structural features of COFs for efficient application is an innovative molecular design strategy.     

表面贴装式永磁同步电机弱磁控制策略的研究

研究表面贴装式永磁同步电机的弱磁控制策略,提出了一种修正电流设定值的方法.该方法由两部分组成:弱磁区域的确定和设定电流修正值的计算.电机运行所在的弱磁区域由恒转矩曲线方向和电流调节器输出电压递减方向之间的夹角来确定,输出电压的递减方向信息通过梯度下降法计算得到.设定电流修正值的大小根据该弱磁区域内转矩、电压变化量的方向...     

The mechanical behaviour of coal with respect to CO2 sequestration in deep coal seams

Carbon dioxide displays a strong affinity for coal due to its propensity to adsorb to the coal surface. The process of CO₂ adsorption on coal causes lowering of surface energy and, it is hypothesised that an associated decrease in surface film confinement results in a decrease in material tensile resistance. Following the results of work carried out on the mechanical influence of CO₂ on brown coal under in situ conditions [Viete DR, Ranjith PG. The effect of CO₂ on the geomechanical and permeability behaviour of brown coal: implications for coal seam CO₂ sequestration. Int J Coal Geol 2006;66(3):204–16], a theoretical explanation is proposed for the perceived lack of a weakening effect with the adsorption of CO₂ to coal at significant confining pressures. We propose that at significant hydrostatic stresses, resistance to failure is otherwise provided (by external confinement) and the effects of adsorptive weakening are concealed. Our model predicts that adsorptive weakening, fracturing under in situ stresses, and associated permeability increases are not an issue for coal seam CO₂ sequestration for sufficiently deep target seams. Lowering of the elastic modulus of coal upon introduction of CO₂ may proceed by means other than surface energy lowering and could well occur irrespective of the depth of sequestration. The effect of elastic modulus lowering under in situ conditions would be beneficial for the long-term retention of sequestered gases.     

基于单调初等函数的缓冲算子构造

在灰色系统缓冲算子公理体系下,将缓冲算子的构建和函数联系起来,利用基本初等函数(指数函数和余切函数)构造了2大类新的缓冲算子,并研究了其特性,最后通过实例验证了所构造的缓冲算子的实用性.解决了冲击扰动系统数据序列建模预测过程中常常出现的定量预测结果与定性分析结论不符的问题.     

低转矩磁链脉动型电励磁同步电机直接转矩驱动系统的研究

电励磁同步电动机定子电感通常较小,转子阻尼绕组的存在使得电机暂态电感更小。若采用转矩及磁链滞环型直接转矩控制(基本DTC)策略电机电磁转矩及定子磁链脉动较大。针对电励磁同步电动机引入一种空间矢量调制型直接转矩控制(SVM-DTC)策略。它基于电励磁同步电动机中转矩角控制电磁转矩原理,利用空间电压矢量合成出最佳电压矢量实时补偿定子磁链矢量误差,以达到减小电动机在运行中电磁转矩及定子磁链脉动量之目的,同时又能基本维持开关频率恒定。仿真和实验结果证明,与基本DTC相比较,SVM-DTC电磁转矩和定子磁链脉动大幅度降低;电机起动电流峰值大大减小,稳态电流畸变较小;同时系统能够平稳地由恒转矩区过渡到弱磁区运行。     

孔隙演化与C/C复合材料的疲劳行为

孔隙是C/C复合材料结构中重要的组成部分,它直接影响着材料的疲劳行为,因此,在研究C/C复合材料的疲劳行为时,考察基体以及界面中孔隙的变化具有重要的意义.综述了C/C复合材料原始孔隙结构的特点,分析了在疲劳加载过程中碳/碳复合材料孔隙结构的演化规律,强调了孔隙结构变化对碳/碳复合材料疲劳强化所作出的积极贡献,进而为其疲劳机理的研究提供依据.     

高等院校师生道德失范的成因及对策

近几年来，由于社会环境因素和高等院校内部自身的原因，在部分教师和学生中存在着道德失范问题。要解决高等院校师生的道德失范问题，必须从内、外两个方面着手，紧紧抓住以德育人这一中心，加强法制建设和思想政治教育，从制度上规范广大师生的道德行为，使高等院校的道德建设取得令人满意的成果。     

电动汽车用异步电机弱磁运行的最大转矩控制

对异步电机的弱磁运行作了深入分析,给出了弱磁运行时最大转矩控制的实现方法,可满足电动汽车对电机驱动系统的高转矩输出要求,实现方法简单可靠。理论分析和仿真结果都验证了该方法的正确性和可行性。