Use of blowing catalysts for integral skin polyurethane applications in a controlled molecular architectural environment: Synthesis and impact on ultimate physical properties

Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (T_g) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher T_g values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002     

Modelling of the pressure-velocity correlation in turbulence diffusion

Most current computations of trubulent flows with second-moment closure adopt the diffusion models which neglect the effect of pressure-velocity correlation. In the present paper the importance of this correlation effect is elucidated the neglect of this effect accounts for some major defects in the wide application of the second-moment closures. Through the relation between and , established by Lumley, we propose here a new turbulence diffusion model which takes into consideration the pressure effect. Applications of this new model in the computation of shearless turbulence mixing layer and plane and round-jet flows show that the spreading rate of these flows can be satisfactorily captured.     

Millettia ferruginea extract attenuates cisplatin-induced alterations in kidney functioning,DNA damage,oxidative stress,and renal tissue morphology

This study aimed to investigate the beneficial role of Millettia ferruginea extract (MF) in preventing cisplatin (Cisp) induced nephrotoxicity in rats. A total of 55 metabolites were identified using LC-MS analysis. The in vivo results indicated that MF pretreatment for 4 weeks (20 mg/kg b.w.) remarkably attenuated the altered renal biomarkers by decreasing the levels of plasma creatinine, urea, and uric acid when compared to the Cisp-group. The nephroprotective capacity of MF was further strengthened by histopathological observations, where Cisp + MF treated rats showed lower number of inflammatory cells and tubular degenerative changes than the Cisp-group. The harmful effects of cisplatin on renal oxidative stress indicators (MDA, SOD, CAT, and GPx), were restored by the treatment of MF. In addition, the reduction of inflammatory markers (IL-6 and TNF-α), associated with alleviating DNA fragmentation, highlighted the preventive effect of MF in kidney tissue. Additionally, MF components presented lower binding energies when docked into the active site of TNF-α and IL-6. The present findings concluded that M. ferruginea extract exhibited nephroprotective potential, which may be attributed to its antioxidant and anti-inflammatory properties. Further work is recommended to confirm the current results, explore the involved mechanism of action, and determine the therapeutic doses and time.     

Effect of Electrode Pattern on the Column Structure and Yield Stress of Electrorheological Fluids

For electrorheological (ER) suspensions, the aggregate structures of particles were observed in electric fields by the use of transparent cells with different electrode patterns. Although the suspension is dispersed to noninteracting particles without electric fields, many aggregates are formed on the electrode surface in electric fields. Since the dipole–dipole interactions cause chain structures of particles and equilibrium conformations of chains are always aligned with electric field, the aggregates indicate the presence of columns spanning the electrode gap. The particle concentration in columns which are developed between parallel-plate electrodes is about 22 vol %. In striped electrodes, the particles construct striped aggregates along the electrodes and no particles remain in the insulating region. The particle concentration in striped aggregates is about 35 vol %. The nonuniformity of electric field is responsible for the high particle concentration. The increase in particle concentration of column lead to the high yield stress of electrified suspension. Therefore, the ER performance of suspension as an overall response can be improved by the electrode design.     

论英语词与句的节奏

指出学习英语的关键是对初学者进行语言感觉训练。提出只有掌握了英语的语音语调和节奏，才能学好英语。     

金瓷修复体双材料界面断裂强度有限元分析

建立金瓷修复体双材料界面裂纹扩展的有限元计算模型．首先利用有限元计算得到平面应力条件下裂纹尖端位移场，求出裂尖附近复应力强度因子主导区域内对应点的相对位移，再辅以传统计算方法得到衡量双材料抵抗断裂能力的复应力强度因子K，并利用双材料界面断裂有关理论和基本公式，求得相关的断裂力学参量，对计算结果进行了实验验证．分析表明，金瓷层厚比对金瓷裂纹开裂具有很大的影响，为进一步分析和研究金瓷修复体断裂行为提供了研究方法。     

复合型加载下缺口前应力应变分布的有限元分析

用有限元法计算了一种低合金高强钢缺口试样在非对称四点弯曲加载(Ⅰ Ⅱ型复合加载)下缺口前端的变形和应力应变分布.研究结果表明:纯Ⅰ型加载时,缺口前端变形和塑性区形状对称分布.Ⅰ Ⅱ型复合加载下缺口前端的变形为一侧钝化,另一侧锐化,塑性区顺时针旋转一个角度θ,且θ随Ⅱ型载荷比例的增加而增大.表征缺口前端变形程度的d/b0值,随外加载荷P/Pgy的增加和Ⅱ型载荷比例的增加而增大.另外,对缺口前端最小塑性区路径上的最大切向正应力σθθ、三相应力度σm/和等效塑性应变εp的分布,以及它们随外加载荷P/Pgy和Ⅱ型载荷比例的变化规律也进行了分析,发现缺口试样的开裂遵循最大切应力判据.     

实验性免疫应激雏鸡胸腺T细胞研究

用ND（新城疫）I系疫苗大剂量肌肉注射2周龄雏鸡的方法建立实验性免疫应激模型，检测胸腺中CIM＋、CD8＋T细胞动态变化以及超微结构变化．结果显示：免疫应激前期（1—5d）表现为CIM＋T细胞数目减少，CD8＋T细胞数目增加的趋势；部分T细胞发生凋亡，并且是一个逐渐加剧的过程，呈现从凋亡到坏死的病理学变化过程．     

零上低温对甘蓝幼苗逆境指标的动态影响

以甘蓝幼苗为材料，研究了零上低温对其部分生理生化指标的影响．结果表明：随着低温(5℃)处理时间的延长，甘蓝幼苗体内的脯氨酸含量、总糖、可溶性糖含量、丙二醛含量逐渐升高．而脂肪酸、蛋白质含量逐渐降低，体内SOD，POD活性先升高再降低．     

冲击破煤过程中能量耗散的理论分析

介绍了能量在冲击式破煤过程中的产生、传递和耗散过程以及能量最终的分布范围;运用应力波的方法分析了应力波在煤体中传播过程,并得出能量在衰减过程中衰减率的计算方法;还分析了剥落厚度的计算方法,并得出正弦应力波在煤体中传播时的冲劈厚度和最大煤块尺寸的关系;根据冲击规律和能量的传递特征对能量的传递过程进行了分析,并求出冲击消耗能量和最小散逸能之间的关系,指出了要使煤块破碎必须满足冲击消耗能量要大于最小散逸能。