Evidence for surface states in pristine and Co-doped ZnO nanostructures: magnetization and nonlinear optical studies

An unexpected presence of ferromagnetic (FM) ordering in nanostructured ZnO has been reported previously. Recently, from our detailed magnetization studies and ab initio calculations, we attributed this FM ordering in nanostructured ZnO to the presence of surface states, and a direct correlation between the magnetic properties and crystallinity of ZnO was observed. In this study, through a systematic sample preparation of both pristine and Co-doped ZnO nanostructures, and detailed magnetization and nonlinear optical (NLO) measurements, we confirm that the observed FM ordering is due to the presence of surface states.     

碳纳米管在水平方向上排列的研究进展

综述了近几年来碳纳米管(CNTs)在水平方向上的定向生长以及后合成排列CNTs的各种方法,如机械拉伸法、磁场法、Langmuir-Blodgett(LB)法、电场法、流体法等,系统分析和比较了各种方法的优缺点,同时展望了该领域的研究和应用前景.     

基于分子动力学的单晶硅纳米压痕过程分析

基于分子动力学角度,本文主要分析了单晶硅的纳米压痕过程,并尝试解释其瞬间原子位置、作用力变化以及其压痕过程等原理。经过笔者试验发现:磨粒的不断压入,会使单晶硅的硅晶格发生变成,且磨粒产生的能量会以应变能的形式存储在晶格之中。同时,随着硅原子势能增加到一定数值时,硅原子键就会以断裂形式变成非晶层堆积在磨粒下方。当磨粒离开单晶硅时,非晶层开始重构,释放能量,达到新的平衡状态。     

X线引导下行经皮胃造瘘术治疗口咽部肿瘤导致吞咽困难患者21例

【摘要】 目的 评价X线引导下经皮胃造瘘术（PRG）在口咽部肿瘤导致吞咽困难者中的临床应用及营养状况的改善作用。方法 对21例行PRG患者进行回顾性分析,观察患者PRG置管前、置管后1、3和6个月的营养指标,包括血红蛋白、总蛋白、白蛋白、转铁蛋白变化及体质量指数的改变,并记录置管前后并发症情况。结果 21例患者共完成PRG操作21次,成功率100%,患者术后肠内营养1、3和6个月后血红蛋白、总蛋白、白蛋白、转铁蛋白及体质指数均有不同程度的改善,置管前、后组内比较差异有统计学意义（P < 0.05）;并发症发生率14.3%（3/21）,感染发生率4.8%（1/21）。结论 PRG耐受性好,是口咽部肿瘤患者肠内营养的一种有效、简单、安全的方法,可明显改善此类患者的营养状况。
     

微波退火时间对HfO2薄膜结构和光电性能的影响

采用原子层沉积(ALD)方法在硅衬底上沉积了氧化铪(HfO₂)薄膜,对其进行不同时间的微波退火(MWA)。采用X射线衍射(XRD)、拉曼光谱(Raman)、原子力显微镜(AFM)、紫外可见光谱(UV-Vis)、椭偏仪(SE)和阻抗分析仪对薄膜的物相结构、形貌和光电性能进行表征,研究了微波退火时间对薄膜结构、光学和电学性能的影响。结果表明：沉积态的HfO₂薄膜具有非晶态性质;当微波退火时间从5 min增至20 min时,HfO₂薄膜的折射率几乎不变,结晶性增强,表面粗糙度降低,但介电常数却减小。     

Influence of parameters and optimization of EDM performance measures on MDN 300 steel using Taguchi method

Maraging steel (MDN 300) exhibits high levels of strength and hardness. Optimization of performance measures is essential for effective machining. In this paper, Taguchi method, used to determine the influence of process parameters and optimization of electrical discharge machining (EDM) performance measures on MDN 300 steel, has been discussed. The process performance criteria such as material removal rate (MRR), tool wear rate (TWR), relative wear ratio (RWR), and surface roughness (SR) were evaluated. Discharge current, pulse on time, and pulse off time have been considered the main factors affecting EDM performance. The results of the present work reveal that the optimal level of the factors for SR and TWR are same but differs from the optimum levels of the factors for MRR and RWR. Further, discharge current, pulse on time, and pulse off time have been found to play a significant role in EDM operations. Detailed analysis of structural features of machined surface was done by using scanning electron microscope (SEM) to understand the influence of parameters. SEM of electrical discharge machining surface indicates that at higher discharge current and longer pulse on duration give rougher surface with more craters, globules of debris, pockmarks or chimneys, and microcracks than that of lower discharge current and lower pulse on duration.     

气割工艺分析

对切割氧气压力、切割速度及倾角、割嘴与割件距离等对切口表面的质量的影响因素进行了分析,并提出改进质量的措施。     

双马来酰亚胺树脂改性研究

综述了采用物理法和化学法改性双马来酰亚胺树脂(BMI)的研究进展,物理法使用的材料涉及:碳纳米管,三维编织碳纤维和凯夫拉纤维混合物,空心玻璃微球,氧化铜,硅灰石,无机纳米粒子和晶须。化学法包括:二元胺改性,烯丙基化合物改性,有机硅改性,热塑性树脂改性等。