抽油杆柱有限元动力方程的差分解及其收敛性

根据有杆泵抽油系统工作过程所对应的力学行为特征，建立了基于有限元理论的抽油杆柱动力控制方程；针对系统工况诊断这一非常规有限元动力求解问题，提出了适合于杆柱对角线型质量矩阵的有限元──有限差分解法；这种方法的优点在于其适应性强，可以考虑抽油杆接箍的影响并能较方便地处理级次杆连接处的力和位移连续条件．还从理论上证明了求解方法的无条件收敛性，并已经油田近２００口油井实际数据验证．最后给出了以文中方法为基础的计算机智能诊断软件对两口油井工况进行诊断的结果．     

基于任务的大学英语写作教学效率研究

任务型写作教学法比传统写作教学法有着多方面的优势,其在课堂教学实施中主要分为准备阶段、写作阶段和分析修改阶段。笔者为期一年的任务型写作教学实验表明,在大学英语教学中实施任务型写作教学不但有效提高了学生的写作成绩,而且还提高了学生的写作学习的兴趣和自信心。因此,任务型写作教学法是一种非常值得探讨和研究的课题。     

刍议广告英语中的语言特征

广告涵盖面广,语言丰富,风格多样,与现实生活结合紧密。广告的目的、宣传对象及宣传媒介要求它的语言简洁、吸引人、大众化。通过阅读欣赏英语广告,不但可以学习词汇,还可以了解句子结构、语态在不同的语境中的具体运用以及它们在广告中所起的作用,不失为一种轻松有效的学习方法。从语言特点、修辞手段、交际策略、文体风格四个方面浅议广告英语中的语言特征。     

Single-polarization single-mode hollow-core negative curvature fiber with nested U-type cladding elements

Hollow-core negative curvature fibers (HC-NCFs) have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions. In this work, a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed. To achieve the single-polarization single-mode transmission, we use two different silica tubes in thickness, which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes, respectively. Besides, the elliptical elements are introduced to achieve good single-mode performance. By studying the influences of the structure parameters on the propagation characteristics, the optimized structure parameters are obtained. The simulation results show that when the wavelength is fixed at 1550 nm, the single-polarization single-mode transmission is achieved, with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174. Furthermore, the confinement loss is only 0.0015 dB/m.