多室正交异性板箱形梁桥剪滞的半解析法

将带有纵向加劲肋的多室梯形箱形梁桥作为正交异性板折板结构考虑,采用艾瑞应力函数法给出了平面应力状态时正交异性板一般边界条件下的二维应力及位移的解析表达式一般形式。然后根据板梁在二者连接处的纵向线应变与侧向曲率两个形变协调条件解出了多室正交异性板箱形梁桥的应力分布与剪力滞后的半解析公式,使用时采用类似于有限条法的步骤计算,但输入数据和运算时间却很少。该方法兼有解析法精确条理与数值法方便灵活的特点,可推广应用于高层筒体结构和带有曲线预应力钢索的箱形梁桥等。     

简支及悬臂箱梁在角隅轴向荷载作用下的翼板纵向应力

基于能量变分原理,拟定轴向荷载作用下箱梁的纵向位移函数,得到关于翼板剪切变形引起的位移差函数的基本微分方程,继而推导出箱梁翼板纵向应力表达式,并首次得出角隅轴向荷载作用下翼板出现应力不均匀分布的荷载及边界条件。通过对一模型箱梁进行计算,并与通用有限元软件ANSYS壳单元计算结果进行比较,验证了该方法和所推导公式的正确性。研究结果表明,当作用于简支箱梁截面角隅处的轴向荷载（合力无偏心）为集中或分布荷载时,翼板不产生纵向应力不均匀现象;当作用于悬臂箱梁截面角隅处的轴向荷载（合力无偏心）为集中荷载时,翼板不产生纵向应力不均匀现象,而当荷载轴向分布时,翼板将产生纵向应力不均匀现象。实际工程中,横力弯曲使悬臂箱梁产生剪力滞效应,这种效应会与轴向分布荷载产生的效应叠加,设计时对此应予以充分考虑。     

Short duration gamma ray bursts

After a short review of gamma ray bursts (GRBs), we discuss the physical implications of strong statistical correlations seen among some of the parameters of short duration bursts (T ₉₀ < 2 s). Finally, we conclude with a brief sketch of a new unified model for long and short GRBs.     

滞后序列分析视域下的高中化学高端备课师生互动行为研究*

为揭示“高端备课”项目下教师与学生行为互动的关键特征,研究采用视频分析法及滞后序列分析法(LSA)对2019年高端备课项目中“离子反应”课堂中的师生交互行为、比率、教师语言、师生操作技术以及教师与学生之间的交互行为等进行量化与质性分析。研究发现,高端备课更加关注学生对于本源性认识问题的科学认识逻辑,以传授核心观念建构以及基于学生认识发展为本为理念,由知识解析为本向促进学生认识发展转变,通过师生思维不断碰撞的过程促进学生知识迁移与应用,为常态化课堂优化提供了参考路径。     

Thermal Gradients in TMDSC Samples: A comparison of theory and experimental data

Until recently, the issue of the thermal gradients within TMDSC samples remained mostly a subject of theory and mathematical models — only the phase lag was subject to experimental verification, as this information is readily available from the analysis software of most instruments. There was no method to verify the transient behaviour and temperature gradients within a sample without making costly and intensive modifications to the equipment. Recently, however, a group of researchers were able to experimentally measure thermal profiles as a function of sample thickness with a high-speed, high-resolution infrared camera mounted on the TMDSC cell. Therefore, this paper is dedicated to comparing the predictions of our three-dimensional model with this newly available data.This revised version was published online in November 2005 with corrections to the Cover Date.     

Optimization of instrument response and resolution of standard- and high-speed power compensation DSC

Normally, for Standard DSC, the PerkinElmer power-compensation setting is the low dynamic range mode (LDRM). In this mode, a noise filter is applied to decrease the noise-to-signal ratio, which concomitantly gives rise to a delay in time of the signal measured. In case the signal is expected to be of high intensity — experienced for instance at high scan rates using High Performance DSC (HPer DSC) — the noise filtering could be diminished by which the associated delay in time would be less, leading to a faster response of the instrument, also resulting in an improved resolution. In fact, such can be realized using the faster noise filter of the high dynamic range mode (HDRM) available for the Pyris 1 and Diamond DSCs, which DSCs are both equipped with the HyperDSC^TM technique (HyperDSC being the commercial version of HPer DSC). The improvement in response is maximal for high rates like 100–500°C min⁻¹ but even at low rates like 10°C min⁻¹ it is still significant. Thus, taking advantage of HDRM, low-molar substances like indium and 4,4′-azoxyanisole show appreciable increasing height-to-width ratios for signals caused by crystallization, melting and the crystal <>liquid crystal transition respectively. Another advantage, the faster realization of steady state after the starting of the DSC, is of help in case of overlapping starting and transition signals during dynamic crystallization and melting, and during isothermal crystallization as elucidated for a HDPE. For 4,4′-azoxyanisole and for an ethylene-propylene copolymer having a broad melting range, it is shown that such faster response leads to a still better resolution with respect to temperature, even at high scan rates. Thus, the peaks belonging to the crystal-to-liquid crystal and the liquid crystal-to-isotropic liquid transitions of 4,4′-azoxyanisole were completely resolved while a thermal fractionation of the copolymer by the successive self-nucleation and annealing (SSA) technique with good resolution has been realized, both using rates as high as 200°C min⁻¹.     

带式输送机弯曲变形阻力理论研究

为了减小带式输送机的弯曲阻力,基于黏弹性材料在动载荷下的能耗理 论,对输送带运行时的弯曲变形能耗机理进行了分析,推导出输送带弯曲变形阻力系数的近似理 论公式,并通过试验验证了公式的正确性. 利用公式对各因素对弯曲阻力系数 的影响规律进行了探讨,结果表明可以通过选配合适的输送带橡胶材料获得合适的 输送带黏弹性参数,并结合调整输送带、输送机的结构参数达到降低输送机弯曲阻力的目的.     

Lag synchronization for fuzzy chaotic system based on fuzzy observer

A new fuzzy observer for lag synchronization is given in this paper. By investi- gating synchronization of chaotic systems, the structure of drive-response lag synchronization for fuzzy chaos system based on fuzzy observer is proposed. A new lag synchronization criterion is derived using the Lyapunov stability theorem, in which control gains are obtained under the LMI condition. The proposed approach is applied to the well-known Chen＇s systems. A simulation example is presented to illustrate its effectiveness.     

变宽截面箱梁剪力滞效应研究

将变宽度截面箱梁的剪力滞翘曲位移函数定义为三次抛物线形式,用能量变分原理建立了分析变宽截面箱梁剪力滞效应的控制微分方程,并用差分法求解此方程。分别计算了简支箱梁在集中荷载和均布荷载作用下的正应力,并用有限元法作了验证。将计算结果与等截面箱梁的应力进行对比,总结变宽箱梁剪力滞效应的分布规律。结果表明,均布荷载作用下,相对于等截面梁,变宽箱梁的顶板应力变化幅度更大,峰值更高,箱梁的顶板宽度变化对剪力滞效应影响较大;在集中荷载作用下,等截面与变宽度箱梁跨中截面的应力相近,应力分布曲线吻合较好,说明顶板宽度变化对剪力滞效应影响较小;分别在集中和均布荷载作用下,箱梁跨中截面应力均为正剪力滞分布状态。当箱梁顶板、底板和悬臂板宽度相等时,剪力滞效应控制微分方程也适用于等截面箱梁。