基于应变能均化指标和云模型的结构损伤识别

为了解决测量噪声等引起的损伤识别不确定问题,提出了基于应变能均化指标和云模型相结合的识别方法。分析了结构的模态应变能以及两种损伤指标,并考虑到模态应变能耗散率指标和等效指标之间的互补性质,通过均化方法建立了模态应变能均化指标;给出了云模型的基本理论,分析了云模型的数字特征、云处理算法以及确定度计算方法;结合随机测量噪声等引起的不确定性问题,建立了基于应变能均化指标和云模型的损伤识别方法。数值计算结果表明,应变能均化指标的识别结果略优于应变能耗散率指标和应变能等效指标,当考虑随机测量噪声时,云模型与应变能均化指标相结合的方法可以较好地进行含噪数据的损伤识别。     

Effect of interfacial interaction between graphene oxide derivatives and poly(vinyl chloride) upon the mechanical properties of their nanocomposites

In this work, graphene oxide (GO) and poly(methyl methacrylate) (PMMA) grafted GO reduced by dopamine (rGO@PDA-g-PMMA) were employed to determine the key factor responsible for the improved mechanical properties of poly(vinyl chloride) (PVC). Dopamine was utilized to reduce GO and simultaneous coating of polydopamine (PDA) on the GO surface. rGO@PDA-g-PMMA was prepared by a combination of mussel-inspired chemistry and surface-initiated atom transfer radical polymerization techniques. The resulting derivatives were characterized by thermogravimetric analysis, Fourier transforms infrared spectroscopy, X-ray diffraction, and Raman spectroscopy. PVC nanocomposites containing GO derivatives were prepared by solution blend and the nanocomposite films were obtained using a casting method. The mechanical properties of the nanocomposites were studied using both dynamic mechanical thermal analysis and tensile testing. The results revealed that the vital components responsible for the improved mechanical properties and thermal stability of rGO@PDA-g-PMMA/PVC nanocomposites compared to pure PVC are the interfacial interactions between the GO derivatives and the PVC matrix.     

High-pressure structural and electronic behaviors of superhard BC5: Density functional calculations

The structural and electronic properties of the recently synthesized superhard BC₅ are studied by using density functional theory within the generalized gradient approximation (GGA). P3m1-II structure is confirmed as the most stable state of BC₅ by comparing three potential structures. The high-pressure effect on superhard BC₅ is also successfully calculated. The obtained pressure dependence of structural property shows that the compressibility along three cell vectors is very close to each other. Based on the density of states (DOS), we find high pressure hardly change the DOS at Fermi level (E_F) which is related closely to the transition temperature T_c. The result is useful to further study the superconductivity of BC₅.     

Effects of sputtering parameters on the performance of electrodes fabricated for proton exchange membrane fuel cells

One way to alleviate the emission of air pollutants and CO₂ due to burning fossil fuels is the use of fuel cells. Sputter deposition techniques are good candidates for the fabrication of electrodes used for proton exchange membrane fuel cells (PEMFCs). Input power and sputtering-gas pressure are two important parameters in a sputtering process. However, little is known about the effects of these sputtering parameters on the performance of PEMFC electrodes. Therefore, this study applied a radio frequency (RF) magnetron sputter deposition process to prepare PEMFC electrodes and investigated the effects of RF power and sputtering-gas pressure in electrode fabrication on electrode/cell performance. At a Pt loading of 0.1 mg cm⁻², the electrode fabricated at 100 W, 10⁻³ Torr was found to exhibit the best performance mainly due to its lowest kinetic (activation) resistance (dominating the cell performance) in comparison to those fabricated by 50 and 150 W at 10⁻³ Torr, as well as by 10⁻⁴ and 10⁻² Torr at 100 W. In the tested ranges, the control of sputtering-gas pressure seems to be more critical than that of RF power for the activation loss. In addition to electrochemically active surface area, electrode microstructure should also be responsible for electrode/cell polarization, particularly the activation polarization.     

Highly selective electrocatalytic hydrogenation of cinnamaldehyde over tin dioxide-supported palladium nanocatalysts

Selective hydrogenation of α, β-unsaturated aldehydes has always been a hot research topic owing to favorable thermodynamics in CC hydrogenation. In this work, a series of Pd/SnO₂ nanocatalysts were facilely synthesized under mild conditions, via the reduction of Na₂PdCl₄ by dimethylaminoborane. Under galvanostatic electrolysis at 3.33 mA cm^?2 for 8 h, the selective conversion of cinnamaldehyde (CAL) was achieved over Pd/SnO₂-coated carbon fiber in neutral phosphate buffer, giving the cinnamyl alcohol (COL) selectivity of 78.85% at the conversion of 84.88%. The Pd/SnO₂ nanocatalysts outperform commercial Pd/C catalysts, showing high COL selectivity and faradaic efficiency. The cathodic reduction potential of CAL over Pd_4·3/SnO₂ occurs at ?0.92 V. The SnO₂ support is beneficial to promote the CO adsorption of CAL and lower the HER activity of Pd nanocatalysts, thereby contributing to superior activity of Pd_4·3/SnO₂ for selective hydrogenation of CAL.     

天然沥青对基质沥青低温改性研究

为了提高基质沥青的低温性能,采用新疆地产的天然沥青来改性基质沥青,以克拉玛依90#和110#2种基质沥青为例,通过在5℃和10℃的测力延度实验,计算了2种基质沥青在改性前后应力、断裂做功、温度敏感系数的变化,并通过改性前后玻璃化温度的变化来证实低温改性效果.实验结果表明,天然沥青对克拉玛依110#基质沥青的最佳掺比为5%,天然沥青对克拉玛依90#基质沥青的最佳掺比为7%,改性沥青表现出较好的低温性能.     

MSCT血管成像技术在门静脉高压症中的临床应用价值

目的探讨多层螺旋CT（MSCT）血管成像技术（MSCT angiography,MSCTA）在门静脉高压症（portal hy-pertension,PHT）诊断及临床治疗中的价值。方法对50例PHT患者者行MSCTA,观察患者门静脉系统的解剖学类型、门静脉主干及其分支侧支循环显示情况;观察食管胃底静脉曲张的形态、位置及血供类型。结果 50例门静脉高压症患者门静脉及侧支循环显影包括：食管下段静脉曲张94.0%,胃底静脉曲张90.0%,胃左静脉曲张90.0%,食管旁静脉曲张72.0%,胃短、胃后静脉曲张32.0%,脾/胃-肾静脉分流28.0%,副脐静脉、腹壁静脉曲张26.0%,腹膜后-椎旁静脉曲张22.0%。对21例患者施行手术,手术与影像学诊断完全符合。MSCTA检出胃静脉曲张（gastric varices,GV）阳性49例所见的病状与胃镜下所见病状对比一致性较好。结论 MSCTA能为PHT患者判断病变程度、预测其并发症及选择治疗方案提供可靠的依据。     

新疆地区既有居住建筑节能改造的技术研究

寒冷地区既有居住建筑能耗在建筑总能耗中所占比例最大,浪费特别严重,也是节能潜力最大的部分。结合新疆目前既有居住建筑节能改造的现状,从建筑外围护结构、供热管网和热源系统等方面研究了主要的节能改造技术,针对既有居住建筑的改造工程,探讨合理的改造方案,为即将到来的大规模既有居住建筑节能改造提供参考。     

有机膨润土处理葡萄酒废水的试验研究

以新疆乌兰林格有机膨润土处理葡萄酒废水,在单因素吸附试验的基础上,采用L9(34)正交试验法确定有机膨润土吸附处理葡萄酒废水的最佳工艺条件为:当废水用量为50mL时,有机膨润土用量1.2g、废水pH值5、吸附时间60min、振荡速度为190r/min。葡萄酒废水经有机膨润土处理后,水质清澈透明,CODCr、BOD5的去除率分别为60%和79%,各项指标达到国家规定的城镇污水二级排放标准。     

粘结层对不同形状叠层压电振子发电性能影响

针对悬臂梁叠层压电振子,利用ANSYS软件仿真分析了其自由端尺寸的改变对于压电振子的输出电压及其固有频率的影响,并得到了叠层压电振子在结合面上的切应力的变化关系。研究表明,在相同条件下,随着自由端尺寸的减小,压电振子的开路电压、基频均有不同程度的增加,但其结合面上的切应力却有较大程度的增幅(最大为74%),这种变化易使叠层结构发生抗剪强度不足的破坏。