Recoverable deformation and morphology after uniaxial elongation of a polystyrene/linear low density polyethylene blend

The transient recoverable deformation ratio after melt elongation at various elongational rates and maximum elongations was investigated for pure polystyrene and for a 85 wt.% polystyrene/15 wt.% linear low density polyethylene (PS/LLDPE 85:15) blend at a temperature of 170 ^oC. The ratio p of the zero shear rate viscosity of LLDPE to that of PS is p = 0.059 ≈ 1:17. Retraction of the elongated LLDPE droplets back to spheres and end-pinching is observed during recovery. A simple additive rule is applied in order to extract the contribution of the recovery of the elongated droplets from the total recovery of the blend. In that way, the recoverable portion of the PS/LLDPE blend induced by the interfacial tension is determined and compared with the results of a theory based on an effective medium approximation. The effective medium approximation reproduces well the time scale of the experimental data. In addition, the trends that the recoverable deformation increases with elongational rate and maximum elongation are captured by the theoretical approach.     

如何教好大学英语听力

听力教学一直是大学英语教学中的一个薄弱环节.由于课时有限,听力课如何才能上好,无论是对学生还是教师,都是一个重要的、值得深思和探讨的问题.本文从教师的角度从如何备课,怎样安排课堂教学,教学中应该教给学生什么方面的技能,培养学生那些方面的能力,如何对学生的听课效果进行检查,课后教师还应再做些什么等方面进行了认真的研究、探讨.希望能为广大师生提供一些参考.     

钻孔灌注桩后压浆处理工艺及单桩受荷性状

本文以太原安静花园1#楼单桩静载试验为依据，论述桩端侧后压浆工艺及单桩处理后受荷特性，说明本工程单桩极限承载力基本可以提高100%，并提出了这类桩基在太原应用的有关设计建议。     

《夸父逐日》新解

文章依据中外人类新成果之一--美洲印第安入主要来自亚洲和中国,暗合神话--原型批评理论,对神话进行史的研究尝试,对前人和袁珂先生关于<夸父逐日>的传说解释提出了大相径庭的解读.     

兰州高校学生参加课外体育活动情况的调查分析

着重调查研究分析了兰州高校大学生课外体育活动兴趣、动机与规律,旨在探索提高高校学生课外体育活动的主动性和自觉性,增强课外活动的效果.     

课外阅读在英语教学中的意义和方法探析

本结合教学实践重点阐述了课外阅读在英语教学中的重要意义、课外阅读的范围与读物的选择、课外阅读的方法与技巧及阅读能力的培养等。     

Effect of cyclic stress on structural changes in polycarbonate as probed by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) is used to probe structural changes in glassy polycarbonate in terms of changes in the hole volume and the number density of holes during fatigue (cyclic stress) aging. The ortho-positronium (o-Ps) pickoff annihilation lifetime τ₃, as well as the intensity I₃, were measured as a function of cyclic stresses and various previous thermophysical aging histories. It is found that τ₃, the longest of the three lifetime components resolved in the PALS of glassy polycarbonate, increases when a cyclic stress is applied. These results indicate that there is a structural change during fatigue aging. The “holes” where o-Ps can localize become larger upon fatigue aging. These results also suggest that a significant distinction exists between structural changes induced by thermophysical aging and fatigue aging. The o-Ps annihilation intensity, which is a relative measure of the hole density in a material, showed a continuous decrease upon fatigue aging, indicating the possibility of hole coalescence, which could be a precursor of crazing. The interaction between thermophysical aging and fatigue aging corresponds very well with the enthalpy relaxation behavior as reported previously, viz., a well-aged sample is much more sensitive to cyclic stress. More importantly, it is hypothesized that fatigue failure initiation is probably closely related to hole size and density fluctuation.     

镀锌钢丝干式拉拔工艺参数探讨

对镀锌钢丝干式拉拔时采用不同总压缩率和拉丝模工作锥角度生产的产品力学性能和锌层质量进行试验研究,获得最佳工艺参数:总压缩率应小于52%,拉丝模工作锥角度应使钢丝与模具的实际接触长度大于4.00 mm.     

Magnetic disaccommodation in Sr hexagonal ferrites with X-phase (2SrO·15Fe2O3) initial composition

The relaxation of the initial permeability has been measured in polycrystalline Sr hexaferrites with the initial composition of X-phase (2SrO·15Fe₂O₃) in the temperature range between 80 and 500 K. The time decay of the initial permeability after sample demagnetization is represented by means of isochronal disaccommodation curves which show the presence of different disaccommodation processes whose maxima lie at 380, 300 and 160 K (resp. A, B and D peaks). This behaviour is explained regarding the spectra corresponding to barium ferrites in order to ascribe the different relaxation processes found for ionic transitions in the cationic sites within the hexagonal structure.     

浮选精煤脱水研究与实践

通过对淮南望峰岗选煤厂浮选精煤的特性分析和对国内采用的脱水设备的技术和经济分析,论述了采用加压过滤机对浮选精煤进行脱水,可保证浮选精煤产品的水分(小于22%),能有效降低生产成本,为安徽两淮矿区选煤厂浮选精煤脱水设备的选择提供了更为切实可行的办法.