Carbon nanotube quantum resistors

The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum G0 = 2e2/h = (12.9 kilohms)-1. The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities, J > 10(7) amperes per square centimeter, have been attained.     

Imaging electron wave functions of quantized energy levels in carbon nanotubes

Carbon nanotubes provide a unique system for studying one-dimensional quantization phenomena. Scanning tunneling microscopy was used to observe the electronic wave functions that correspond to quantized energy levels in short metallic carbon nanotubes. Discrete electron waves were apparent from periodic oscillations in the differential conductance as a function of the position along the tube axis, with a period that differed from that of the atomic lattice. Wave functions could be observed for several electron states at adjacent discrete energies. The measured wavelengths are in good agreement with the calculated Fermi wavelength for armchair nanotubes.     

Conductance-controlled point functionalization of single-walled carbon nanotubes

We used covalent attachments to single-walled carbon nanotubes (SWNTs) to fabricate single-molecule electronic devices. The technique does not rely on submicrometer lithography or precision mechanical manipulation, but instead uses circuit conductance to monitor and control covalent attachment to an electrically connected SWNT. Discrete changes in the circuit conductance revealed chemical processes happening in real time and allowed the SWNT sidewalls to be deterministically broken, reformed, and conjugated to target species. By controlling the chemistry through electronically controlled electrochemical potentials, we were able to achieve single chemical attachments. We routinely functionalized pristine, defect-free SWNTs at one, two, or more sites and demonstrated three-terminal devices in which a single attachment controls the electronic response.     

Electrowetting in carbon nanotubes

We demonstrate reversible wetting and filling of open single-wall carbon nanotubes with mercury by means of electrocapillary pressure originating from the application of a potential across an individual nanotube in contact with a mercury drop. Wetting improves the conductance in both metallic and semiconducting nanotube probes by decreasing contact resistance and forming a mercury nanowire inside the nanotube. Molecular dynamics simulations corroborate the electrocapillarity-driven filling process and provide estimates for the imbibition speed and electrocapillary pressure.     

打捆机草捆后捆绳张力的测试研究

捆草机工作时,捆绳张力是破坏捆绳并导致散捆和形不成草捆的主要原因之一。我们根据国产９ＫＧ－３５０型高密度捆草机捆草的实际情况,研制了测定捆绳张力的应变式传感器,并用所设计的传感器测取了打捆后捆绳张力的变化。这对高密度捆草机捆绳的选择和捆绳标准的制定提供了重要依据。     

水稻种绳播放机的设计

研制了一种水稻种绳播放机,该机主要由悬挂机构、防堵机构、播放机构、开沟机构、覆土机构、镇压机构6部分组成。直播时,将卷好稻种的种绳盘挂在研制的种绳播放器上,将绳的端部固定在地头,然后由拖拉机悬挂带动前进,实现开沟、放种绳、覆土一次完成。试验结果表明,样机种绳顺利播放到田地,种绳播放深度达到了农艺要求。     

种绳直播机覆土深度测试系统的设计研究

利用动态模拟试验方法,设计种绳直播机覆土深度的动态测试系统。模仿大田情况,利用该系统对设计的样机进行测试,由测试结果及分析可知样机铺放种绳的均匀性较好,播种深度符合作业要求。在此基础上建立、修正种绳覆土深度的数学模型,为测试田间播放的种绳覆土深度提供一种新的思路,并为其测试带来极大的方便,同时也为其它农业机具的动态测试提供参考。     

基于动力学的钢丝绳断丝数检测方法初探

钢丝绳是由许多优质碳素钢丝捻制成股,再由若干股围绕绳芯捻制成绳。由于钢丝绳结构的特殊性决定了它具有较好的力学性能,同时在工作可靠性和结构多样性等方面也表现出独特的优点,被广泛应用于众多工程领域。钢丝绳的设计、制造、使用和维护等方面还存在着相当多的技术难题,甚至还不能给出钢丝绳在使用过程中真正意义上的安全系数．以至于钢丝绳工程结构时常出现意外安全事故。针对钢丝绳无损检测问题展开了研究．用弦振动方程建立钢丝绳断丝数检测方程。利用该方程对悬索钢丝绳的断丝数进行了探索性试验研究。结果表明,钢丝绳断丝数较少．负载较小时,对基频的影响较小;当钢丝绳断丝数较多,负载较大时,对基频的影响较为明显。因此。该方法为钢丝绳无损检测技术提供了一种的新的检测手段．具备一定的可行性。图4表1参11     

Covalently bridging gaps in single-walled carbon nanotubes with conducting molecules

Molecular electronics is often limited by the poorly defined nature of the contact between the molecules and the metal surface. We describe a method to wire molecules into gaps in single-walled carbon nanotubes (SWNTs). Precise oxidative cutting of a SWNT produces carboxylic acid-terminated electrodes separated by gaps of 相似文献   

Solid-state thermal rectifier

We demonstrated nanoscale solid-state thermal rectification. High-thermal-conductivity carbon and boron nitride nanotubes were mass-loaded externally and inhomogeneously with heavy molecules. The resulting nanoscale system yields asymmetric axial thermal conductance with greater heat flow in the direction of decreasing mass density. The effect cannot be explained by ordinary perturbative wave theories, and instead we suggest that solitons may be responsible for the phenomenon. Considering the important role of electrical rectifiers (diodes) in electronics, thermal rectifiers have substantial implications for diverse thermal management problems, ranging from nanoscale calorimeters to microelectronic processors to macroscopic refrigerators and energy-saving buildings.     

滑索的悬索设计数学模型

从悬链线理论出发,利用牛顿迭代数值解法建立滑索的悬索设计数学模型,便于滑索的安装架设,提高其安全性能,为滑索的悬索设计提供科学理论依据.     

基于方向信息测度的钢丝绳表面缺陷检测

提出了一种基于方向信息测度的钢丝绳表面缺陷检测方法.根据钢丝绳表面的纹理特点,设计了一种新的空域同态滤波器,可增强缺陷纹理图像和消除不均匀光照对缺陷纹理检测的干扰;改进方向信息测度方法,实现了钢丝绳纹路与背景的分离;提取钢丝绳纹路的纹理特征并使用神经网络进行缺陷识别.结果表明,该算法能快速、准确完成对钢丝绳表面缺陷的自动检测.     

水稻种绳直播机关键工作部件的设计研究

针对目前水稻直播机存在结构复杂、笨重、造价高、机具下陷量大、能耗高、机具转弯半径大、开沟器容易堵塞、每穴粒数调整困难等问题,提出了水稻种绳直播技术并介绍了其基本原理,重点对种绳直播机的种绳播放装置及防堵装置进行了分析计算与结构设计,为水稻种绳直播机的研制开发及有效解决播种机使用过程中存在的问题提供了依据.     

单跨索道闭合牵引索拉力分析

本文阐明闭合牵引索拉力与载荷位置有关，分析了在索道任意点处荷重提升时闭合牵引索拉力的计算方法，所得结果能有效地指导闭合牵引索的安装、架设及索道的安全生产．     

Ⅲ索43型索道的磨损问题及对策

通过对SJ—0.4／2遥控索道闭合牵引索和摩擦卷筒的力学分析，探讨其磨损机理，提出工程上适用的减磨设计方法．     

林用起重机起吊木捆偏摆系统的动力学模型与仿真

建立了林用起重机木捆偏摆系统的动力学模型,并经过线性简化得出木捆在垂直方向的摆角主要与其同向的小车加(减)速度和绳长,以及木捆升降速度有关,而水平摆角与自身的转动惯量和钢丝绳的扭转系数有关.建立了小车制动后木捆匀速下降过程的二自由度木捆摆振微分方程,最后采用Simulink对振动微分方程进行仿真,结果表明绳索长度、木捆...     

水稻精播绳制造设备的设计及大田试验

水稻种植机械化是一个尚未完全解决的难题,为此设计一种水稻直播用精播绳制造机械设备。该设备主要由送纸机构、排种机构、加捻机构和种绳卷绕成形机构等组成。在工厂内该设备将水稻种子以精确的穴距和每穴粒数卷在4~7 cm宽的纸带内并捻制成种绳,供大田播放;对该设备生产的种绳进行大田栽培试验。结果表明:该设备工作性能稳定,种绳直播水稻用种量为常规机械直播的1/2~1/3,产量超过10 t/hm2,高于对照的常规方式直播水稻约1 t/hm2。     

陕京输气管道跨越黄河施工

陕西京输气管道在黄河跨越中采用悬索跨越形式,钢索采用密封式厚镀锌钢丝索,可３０年不维护,塔架整体竖起采用先进的连续顶推穿心式千斤顶,安装采用空中发送方案。     

促花措施对日光温室甜樱桃幼树成花及坐果的影响

日光温室中甜樱桃采用刻芽、环剥、绞缢、PP333等促花措施处理，促花效果以环剥后不包伤口、绞缢、短梢停长期低浓度PP333喷布和中长梢停长期高浓度PP333蘸尖效果较好。日光温室中甜樱桃可多次分化花芽，中后期形成的花芽坐果率明显高于前期。     

浮绳式网箱框架纲波浪力特性的初步试验研究

结合生产的实际需要,沿海浮绳式网箱生产的作用日益突出,因而研究其水动力特性非常重要。根据这一需要,采用预加张力的直交系泊方法,依据目前柔性浮绳式网箱尺寸和渔具模型试验方法设计、制作了一个柔性浮绳式网箱模型（1 m×1 m×1 m）,并进行了水槽试验。试验工况为规则波,周期为0.8～2.0 s（间隔0.2 s）,波高为50～250 mm（间隔40 mm）。在不同波浪周期、波高下,根据测量数据,分析研究作用在浮绳式网箱框架纲上波浪力的特性。试验结果表明：波浪力的变化与波浪特性相似,呈周期性、不对称变化,垂直于波浪方向的2根框架纲的波浪力峰值比与波浪方向平行的2根框架纲的稍小。框架纲上的波浪力不是同步变化的,存在一定相位差,但由于框架纲是柔性绳索制成的,因而能承受由于不同相位波浪力产生的扭矩剪切作用,证明了波浪作用下HDPE网箱常受到破坏而浮绳式网箱安然无恙的事实。最后,就水流和波浪共同作用下的网箱水动力学进行了试验研究,发现波流共同作用下的水动力值并不是单独在纯流和纯波下的水动力的值的简单相加,而存在一修正项。