Fabrication of microdevices with integrated nanowires for investigating low-dimensional phonon transport

Phonons in low-dimensional structures with feature sizes on the order of the phonon wavelength may be coherently scattered by the boundary. This may give rise to a new regime of heat conduction, which can impact thermal energy transport and conversion. Traditional methods used to investigate phonon transport in one-dimensional structures suffer from uncertainty due to contact resistance, defects, and limited control over sample dimensions. We have developed a new batch-fabrication technique for suspended microdevices with integrated silicon nanowires from silicon-on-insulator (SOI) wafers. The nanowires are defect-free and have extremely high aspect ratios (length/critical dimension >2000). The nanowire dimensions (length and critical dimension) can be precisely controlled during fabrication. With these novel devices, phonon transport in silicon nanowires is systematically investigated. The room temperature thermal conductivity of nanowires with critical width around 80 nm is about 20 W/(m K) and much lower than that in smooth VLS wires. This suggests that the surface morphology of the structures has a significant effect on the thermal conductivity, but this phenomenon is not currently understood. This fabrication technique can also be used for thermal transport investigation in a wide-range of low-dimensional structures.     

2.4GHz无线技术标准及ZigBee抗干扰性能

介绍了ZigBee和其他几种工作于2.4GHz ISM频段的短距离无线通信技术标准,Wi-Fi、蓝牙和无线USB,对ZigBee本身的抗干扰性能以及与其他无线技术的共存进行了分析,讨论了如何保证ZigBee避免干扰和改善其共存性能.     

海洋环境下储油罐的防腐探究

通过对舟山地区油库的实地调查,分析海洋环境下温度湿度、大气中的盐类颗粒及微生物共同作用下的腐蚀环境的特点。舟山地区储油罐外腐蚀主要集中在底板区域和保温罐易积水部位,且底板外腐蚀情况较为常见。根据舟山地区储油罐外腐蚀的处理方法,探究得出适合海洋环境的防腐措施,主要有:选用合适的储油罐材料、构建合理的防腐涂料体系、合理利用阴极保护法以及建立完善的定期维护和日常保养制度等。     

金沙江溪洛渡水电站坝址选择

溪洛渡水电站是以发电为主，兼有拦沙、防洪、漂木、航运等综合利用效益的巨型水电站；担负着西电东送，实现国家能源战略平衡，充分发挥三峡工程效益等具有重要意义的水电工程。几年来，经过大量的地质勘探和设计工作，通过对坝段、坝址的地形地质条件的比较，并结合水工枢纽布置的研究，选定河道顺直，谷坡陡峻，基岩裸露的玄武岩坝段及其中坝址作为溪洛渡水电站坝址。     

快速浇筑情况下随机因素对混凝土坝开裂影响分析

混凝土坝厚浇筑层、短间歇期、均匀连续快速施工方法的应用对加快混凝土坝建设进度、施工节资意义重大,但采用快速施工方法引起的混凝土坝仓面裂缝问题值得重视.以某在建混凝土重力坝为例,分析与探讨了低温浇筑及长间歇、气温骤降等随机因素下,快速浇筑混凝土坝仓面的应力特性和裂缝机理,对早龄期混凝土坝仓面开裂风险进行了深入分析研究,提出以温度的空间梯度和时间梯度作为混凝土开裂风险的判别指标更为合理.     

溪洛渡高拱坝深孔预应力次锚索优化研究

溪洛渡拱坝深孔闸墩结构复杂,出口悬臂长24.7 m,承受水推力达81 283 kN,需在闸墩悬臂上布置预应力锚索以满足强度要求,除环形主锚索外,次锚索的布置对支铰大梁的应力影响也十分显著。参考以往工程经验,溪洛渡深孔闸墩拟定了2排次锚索、总锚应力26 500 kN和3排次锚索、总锚应力39 000 kN两种次锚索布置方案,以最大拉应力为控制标准,采用三维有限元法对这两种方案下支铰大梁运行期的应力状态进行了对比分析。计算结果表明:相比方案一,方案二中大梁拉应力量值和范围都显著减小,拉应力极值由-3.3 MPa降至-1.7 MPa,大梁跨中剖面的受拉面积由10.603 m2降至5.516 m2。可见,方案二大梁受力状态更好,符合设计要求。     

P_(350)萃取树脂分离稀土元素的性能研究

研究了以 P_(350)树脂作固定相,硝酸、高氯酸为流动相的萃取柱色谱法分离稀土元素,其平均分离因素为:β_(HNO)_3(1.04)>■_(HC1O)_4(0.99)。分配比 K_d 的顺序为:HNO_3>HC1O_4。硝酸作流动相好。     

An Efficient Lagrangian Interpolation Scheme for Computing Flow Maps and Line Integrals using Discrete Velocity Data

We propose a new class of Lagrangian approaches for constructing the flow maps of given dynamical systems. In the case when only discrete velocity data at mesh points is available, an interpolation step will be required. However, in our proposed approaches all particle trajectories share a common global interpolation at each time step and therefore interpolation operations will not increase the overall computational complexity. The old Lagrangian approaches propose to solve the corresponding ordinary differential equations (ODEs) backward in time to obtain the backward flow map. It is inconvenient and not natural, especially when incorporated with certain computational fluid dynamic solvers, because the velocity field needs to be loaded from the terminal time backward to the initial time. In contrast, our proposed approaches for computing the backward flow map propose to solve the corresponding ODEs forward in time which is more practical. We will also extend the proposed approaches to compute line integrals along any particle trajectory. This paper gives a detailed analysis on the computational complexity and error estimate of the proposed Lagrangian approach. Finally, a wide range of applications of our approaches will be given, including the so-called coherent ergodic partition and the high frequency wave propagations based on geometric optic.     

我国特高拱坝的建设成就与技术发展综述

结合二滩、溪洛渡、锦屏一级、大岗山、小湾等一系列特高拱坝的建设实践,总结了我国特高拱坝的建设成就,阐述了我国特高拱坝建设关键技术的研究进展,包括建基面的研究与确定、体形优化设计、应力分析与强度设计、拱座抗滑稳定、整体稳定、抗震设计、混凝土材料、混凝土温控防裂、基础处理、施工技术等10个方面的内容。认为我国混凝土拱坝建设技术已处于国际领先水平,指出我国特高拱坝建设需深化研究的4个问题,即特高拱坝安全评价体系建设、特高拱坝风险设计、特高拱坝抗震研究以及特高拱坝安全运行健康诊断技术研究。     

基于Pro/Engineer的齿轮自动化造型

介绍在Pro/Engineer环境下设计了一种多功能的参数化渐开线圆柱齿轮。利用它只需要输入参数就可以直接生成直齿轮，左旋斜齿轮，右旋斜齿轮或变位齿轮。并利用其开发工具Program实现齿轮的完全自动化造型。