High pressure phase transitions for CdSe

The structure and pressure-induced phase transitions for CdSe are investigated using first-principles calculations. The pressure-induced phase transition sequence WZ/ZB → Rs → Cmcm → CsCl for CdSe is drawn reasonably for the fist time, the corresponding transition pressures are 3.8, 29 and 107 GPa, respectively and the intermediate states between the Cmcm structure and the CsCl structure should exist.     

扁管和百叶窗式微通道换热器空气侧阻力的实验研究

在迎面风速1~4m/s、雷诺数100~500,迎风面尺寸600mm×550mm以及环境温度20℃工况条件下,测试了微通道换热器空气侧阻力,对比分析了测试结果与不同关联式计算结果,表明现有不同关联式间预测结果相差较大,其中Davenport的关联式与实验值较为接近,但实验值也仅有其预测值的55%~66%。实验也表明微通道换热器空气阻力与换热量和迎风面积相同的平翅片圆管换热器空气阻力相当,认为独特的扁管结构和较小的换热器厚度是其减小空气阻力的有效手段。     

单面波浪平板脉动热管的传热性能

对一种单面波浪平板脉动热管的传热性能进行了实验研究,分析在空气强制对流冷却条件下充液率、加热功率、倾角等因素对其传热性能的影响。研究结果表明,除0°倾角外,脉动热管的最佳充液率为20%～30%,倾斜角度对脉动热管传热性能的影响很小,但90°时相对最好。脉动热管在0°放置时其传热性能较差,在低充液率的情况下甚至丧失脉动效果,主要是工质回流不畅的原因,与平板脉动热管的槽道设计有很大关系。此外低加热功率时热管传热性能存在波动,有时甚至不能启动。     

Co吸附二氧化硅团簇的几何结构、光电及磁学特性

基于密度泛函理论中的广义梯度近似方法,系统地研究了Co(SiO2)n(n=1-7)团簇的几何结构、光电特性和磁学性质。结果表明:受悬挂键和电子云分布影响,单个Co原子以一定倾角吸附在稳定性很好的(SiO2)n(n=1-7)链状团簇上,多个Co原子却在其上发生团聚作用;不断减小的垂直电离势和不断增大的电子亲和势使得Co(SiO2)n(n=1-7)团簇的硬度随着团簇尺寸的增大而降低;Co原子的吸附使得非磁性二氧化硅转化为磁性复合团簇,随着Co原子数目的增多磁矩不断增大,结合该团簇的近红外光吸收特性,从理论上证实了二氧化硅磁性复合材料既具有超顺磁性又可以吸收可见-近红外光,为其在医学界被用作光动力靶向治疗提供了理论依据。     

Influence of fluoride treatment on surface properties,biodegradation and cytocompatibility of Mg–Nd–Zn–Zr alloy

Fluoride treatment is a commonly used technique or pre-treatment to optimize the degradation kinetic and improve the biocompatibility of magnesium-based implant. The influence of changed surface properties and degradation kinetics on subsequent protein adsorption and cytocompatibility is critical to understand the biocompatibility of the implant. In this study, a patent magnesium alloy Mg–Nd–Zn–Zr alloy (JDBM) designed for cardiovascular stent application was treated by immersion in hydrofluoric acid. A 1.5 μm thick MgF₂ layer was prepared. The surface roughness was increased slightly while the surface zeta potential was changed to a much more negative value after the treatment. Static contact angle test was performed, showing an increase in hydrophilicity and surface energy after the treatment. The MgF₂ layer slowed down in vitro degradation rate, but lost the protection effect after 10 days. The treatment enhanced human albumin adsorption while no difference of human fibrinogen adsorption amount was observed. Direct cell adhesion test showed many more live HUVECs retained than bare magnesium alloy. Both treated and untreated JDBM showed no adverse effect on HUVEC viability and spreading morphology. The relationship between changed surface characteristics, degradation rate and protein adsorption, cytocompatibility was also discussed.     

石墨烯和硅丙乳液复合材料的制备及性能

采用化学氧化还原法和超声分散制备出石墨烯(GN),采用X射线衍射仪、红外光谱和原子力显微镜对所得石墨烯进行了分析和表征。结果表明,氧化石墨烯被较好地还原为石墨烯并且成功分散为纳米级厚度;采用溶液超声共混法制备石墨烯/硅丙乳液复合材料。对复合材料成膜进行扫描电镜表征、热重分析、导电渗流测试、力学性能以及耐水、耐腐蚀性测试,发现复合材料具有较低的渗滤阈值(质量分数0.5%),石墨烯用量大于0.9%时,体积电阻率基本稳定在103Ω·cm以下,导电性有了明显提高;石墨烯的用量为0.7%时,与硅丙乳液相比,复合材料拉伸强度提高了15.5%,断裂伸长率下降了3.6%,耐水性提高了14%,失重5%时的热分解温度提高了43℃,耐腐蚀性能也得到了极大提高。     

小管径椭圆管开缝翅片换热器的数值模拟

对小管径椭圆管开缝翅片换热器空气侧的流动与传热特性进行数值模拟,对影响其换热性能的2个主要参数椭圆管偏心率和开缝翅片开缝错列高度分布进行优化,与传统管翅式换热器换热性能进行比较。模拟结果表明:当椭圆管两轴之比Rx:Ry=2:3(偏心率),开缝高度分布为0.8 mm,0.6 mm和0.4 mm时,换热效果最好。与传统管翅式换热器相比,小管径椭圆管开缝翅片换热器换热系数提高10%~20%,而压降几乎相等,总体换热性能提高。     

芳纶表面氧化锌纳米棒的制备及表征

以硝酸锌、六亚甲基四胺为原料,通过低温水浴方法在芳纶Ⅲ表面实现氧化锌纳米棒的修饰。采用X射线衍射仪、扫描电子显微镜、能量色散X射线谱仪、紫外分光光度计和热失重仪等测试手段对所制备的样品进行了表征。结果表明,芳纶Ⅲ表面生长的氧化锌纳米棒为六方纤锌矿相结构,并且择优取向生长。借助于氧化锌纳米棒吸收紫外线的能力和耐高温的特性,氧化锌纳米棒修饰后的芳纶Ⅲ具有良好的抗紫外性和优异的热稳定性。     

Influences of temperature on mechanical properties of cement asphalt mortars

The compressive mechanical properties of cement asphalt mortars (CAMs) with varied bitumen-cement ratio (B/C) were studied under different temperatures, in order to reveal the susceptibility of mechanical properties to temperature. Results indicate that the compressive strength and the elastic modulus generally increase with a decrease in temperature for all tested CAMs. The quantitative evaluation of the temperature dependence of the strength and the elastic modulus using defined temperature-sensitivity factors is proposed and validated by the test results, which show that the mechanical properties of those CAMs with higher B/C have greater temperature sensitivity. For a given CAM, the temperature-sensitivity factor of the strength is larger than that of the elastic modulus. The temperature-sensitivity factors enable estimating the compressive strength and the elastic modulus of CAMs at selected temperatures from the tested values at a reference temperature, such as room temperature, by using the proposed equations. The relative elastic modulus is found to be in direct proportion to the square root of the relative compressive strength at a selected temperature, i.e. $ E_{\text{r}} \propto \sqrt {\sigma_{\text{pr}} } $ .