Engineering carbon nanotubes and nanotube circuits using electrical breakdown

Carbon nanotubes display either metallic or semiconducting properties. Both large, multiwalled nanotubes (MWNTs), with many concentric carbon shells, and bundles or "ropes" of aligned single-walled nanotubes (SWNTs), are complex composite conductors that incorporate many weakly coupled nanotubes that each have a different electronic structure. Here we demonstrate a simple and reliable method for selectively removing single carbon shells from MWNTs and SWNT ropes to tailor the properties of these composite nanotubes. We can remove shells of MWNTs stepwise and individually characterize the different shells. By choosing among the shells, we can convert a MWNT into either a metallic or a semiconducting conductor, as well as directly address the issue of multiple-shell transport. With SWNT ropes, similar selectivity allows us to generate entire arrays of nanoscale field-effect transistors based solely on the fraction of semiconducting SWNTs.     

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。     

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。     

波流作用下双体组合式网箱水动力特性研究

运用刚体运动学原理及集中质量方法,建立了双体组合式网箱浮架、网衣、锚绳及浮子的受力运动方程数学模型,利用物理模型试验对数学模型进行了验证.结果表明,所建立的数学模型具有较好的可靠性及准确性.在此基础上运用数学模型,计算了在不同波流工况下,双体组合式网箱的锚绳受力、浮架运动及网衣变形.计算结果表明:在相同工况下,三类锚绳相比,连接锚绳受力最大,锚碇锚绳受力次之,网格锚绳受力最小;各种工况下,三类锚绳的受力随流速、波高的增加有不同程度的增加,随周期的增加有一定程度的减小;浮架中心点水平方向运动幅度总体表现为随流速的增加有一定程度的增加,竖直方向运动幅度总体表现为随流速的增加略有减小,浮架中心点水平、竖直方向运动幅度随波高、周期的增加均有一定程度的增加;浮架倾角随流速的变化不明显,随波高的增加有一定程度的增加,随周期的增加有一定程度的减小;网衣体积损失率总体上表现为随流速的增加有一定程度的增加,波高、周期变化对网衣变形影响较小.     

防绿潮藻固着和生长的初步研究

选用3种不同材质的缆绳和5种不同涂料,采用海上现场模拟实验的方法开展了防绿潮藻固着和生长的研究。实验结果表明,3种材质缆绳上绿潮藻幼苗的密度和长度总体随着时间的延长而增多,第4周左右固着密度能达到最大,随后呈现下降的趋势。从材质上看,聚丙烯绳上的绿潮藻幼苗平均生长长度较其他2种材质略长。所选涂料能有效地抑制绿潮藻固着、萌发和生长,涂有涂料的缆绳上的绿潮藻幼苗固着个数和生长长度明显低于对照组,其中有机氟涂料的防固着效果最好,涂在缆绳上既稳定又能有效地防止绿潮藻幼苗的固着生长。     

Crystalline Ropes of Metallic Carbon Nanotubes

Fullerene single-wall nanotubes (SWNTs) were produced in yields of more than 70 percent by condensation of a laser-vaporized carbon-nickel-cobalt mixture at 1200degreesC. X-ray diffraction and electron microscopy showed that these SWNTs are nearly uniform in diameter and that they self-organize into "ropes," which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice with a lattice constant of 17 angstroms. The x-ray form factor is consistent with that of uniformly charged cylinders 13.8 +/- 0.2 angstroms in diameter. The ropes were metallic, with a single-rope resistivity of <10(-4) ohm-centimeters at 300 kelvin. The uniformity of SWNT diameter is attributed to the efficient annealing of an initial fullerene tubelet kept open by a few metal atoms; the optimum diameter is determined by competition between the strain energy of curvature of the graphene sheet and the dangling-bond energy of the open edge, where growth occurs. These factors strongly favor the metallic (10,10) tube with C5v symmetry and an open edge stabilized by triple bonds.     

Initial pioneer venus magnetic field results: dayside observations

Initial observations by the Pioneer Venus mangnetometer in the sunlit ionosphere reveal a dynamic ionosphere, very responsive to external solar-wind conditions. The localtions of the bow shock and ionosphere are variable. The strength of the magnetic field just olutside the ionopause is in approximate pressure balance with the thermal plasma of the ionosphere and changes markedly from day, to day in response to changes in solar wind pressure. The field strength in the ionosphere is also variable from day to day. The field is often weak, at most a few gammas, but reaching many tens of gammas for periods of the order of seconds. These field enchantments are interpreted as due to the passage of spacecraft through flux ropes consisting of bundles of twisted field lines surrounded by the ionospheric plasma. The helicity of the flux varies through the flux tube, with lows pitch angles on the inside and very lage angles in the low-field outer edges of the ropes. These ropes may have external or internal sources. Consistent with previous results, the average position of the bow shock is much closer to the planet than would be expected if the solar wnd were completely deflected by the planet. In total, these observations indicate that the solar wind plays a significant role in the physics of the Venus ionosphere.     

粘虫室内饲养方法的改进

为了提高粘虫室内饲养的效率,满足实验室用虫需求,在传统饲养粘虫方法的基础上,对粘虫卵、幼虫、蛹和成虫的饲养器具以及操作方法进行了简化与改进：将产于塑料绳上的卵消毒晾干后,直接放于塑料保鲜袋中孵化;初孵幼虫置于33 cm×33 cm的100目锦纶纱养虫袋中饲养,3龄前用天然饲料饲喂,3龄后用人工饲料饲喂,直至幼虫老熟;将老熟幼虫放到35 cm×25 cm×10 cm的化蛹盒中化蛹,以吸水纸替代沙土作为化蛹介质。比较了饲养方法改进前后粘虫的卵孵化率,低龄幼虫存活率,粘虫生长发育和繁殖,以及化蛹效果。结果表明：与改进前的饲养技术相比,采用改进后的饲养技术饲养粘虫不仅操作简单、省工省时、工作效率提高,而且能够显著提高卵的孵化率和低龄幼虫的存活率。改进前用塑料盒饲养,每盒饲养20头比较适宜,而改进后每个养虫袋可以饲养幼虫50～70头,且粘虫的发育和生殖参数与改进前相当。利用改进后的粘虫室内饲养方法,能够实现室内粘虫的继代繁殖和批量饲养。     

浙江舟山虾拖网桁杆及叉纲的力学计算

桁杆虾拖网作业是东海区海洋捕捞中的主要作业方式。通过模型试验和数值计算的方法,对虾拖网的主要构件桁杆、叉纲进行理论力学分析,从而求得桁杆所受的弯矩、剪力、轴力及叉纲的拉力,桁杆与虾拖网下纲相连的吊纲和上纲网片对桁杆的张力。还进一步探索了弯矩和剪力沿桁杆的分布规律,最大拖速时桁杆所受最大拉压应力情况。为今后虾拖网的使用提出建议。     

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     

Single-Electron Transport in Ropes of Carbon Nanotubes

The electrical properties of individual bundles, or "ropes," of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.     

轻型遥控人工林集材索道力学分析及线路设计

通过对轻型遥控人工林集材索道沿线路各区段起重提升工序中牵引索紧边、松边的力学分析,探明索道在接近下支点线路区段,牵引索在绞盘机摩擦卷筒上打滑的机理;通过对大倾角集材索道重载顺坡或逆坡运行条件下的力学分析,阐明跑车在接近上支点及接近索道最低点时,摩擦卷筒制动失效、吊运木材落钩的机理。提出符合免滑条件、运载安全可靠的轻型遥控人工林集材索道线路设计方案。在人工林伐区生产试验基础上,对索道配重问题进行研究,优化索道技术参数,确保集材索道科学合理地安装架设,经济高效及安全可靠地营运。     

Band gap fluorescence from individual single-walled carbon nanotubes

Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light.     

广州市绿地园林植物挂牌现状调查与分析

对广州市24处园林绿地的植物挂牌情况进行调查,归纳总结不同绿地类型的植物标牌内容、不同生活型的挂牌方式和标牌材料等。结果显示,植物标牌内容包括中文名、学名、科名和属名,字数一般在20~100字/牌,挂牌方式有铁钉钉牌、支柱、套绳牵牌、置石等。从外形设计、悬挂方式、材质、内容等方面,提出一套植物挂牌的优选方案。     

Diameter-Selective Raman Scattering from Vibrational Modes in Carbon Nanotubes

Single wall carbon nanotubes (SWNTs) that are found as close-packed arrays in crystalline ropes have been studied by using Raman scattering techniques with laser excitation wavelengths in the range from 514.5 to 1320 nanometers. Numerous Raman peaks were observed and identified with vibrational modes of armchair symmetry (n, n) SWNTs. The Raman spectra are in good agreement with lattice dynamics calculations based on C-C force constants used to fit the two-dimensional, experimental phonon dispersion of a single graphene sheet. Calculated intensities from a nonresonant, bond polarizability model optimized for sp2 carbon are also in qualitative agreement with the Raman data, although a resonant Raman scattering process is also taking place. This resonance results from the one-dimensional quantum confinement of the electrons in the nanotube.     

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.     

杂交小麦种子生产中不同辅助授粉技术研究

[目的]研究杂交小麦制种工作中辅助授粉措施对异交结实和制种产量的影响。[方法]以京麦6号为试验材料,通过对竹竿、绳子、汽油喷药器和施药直升机等措施进行对比,评价各种措施在实施效果、工作效率和费用成本方面的优势。[结果]竹竿和直升机效果最佳,在混播制种田中异交结实达到20粒/穗以上,同时在行比制种中受父本距离变化影响较小。绳子和直升机效率最高,竹竿和汽油喷雾器的效率相对较低。费用成本方面,绳子辅助授粉方式成本最低,是目前大面积制种生产采取的主要措施;竹竿辅助授粉费用较高,但便于操作、效果好,适用于小面积生产和中试制种,在行比制种中优势更加明显;直升机辅助授粉目前有多方面优势,是解决规模化制种降低人工使用和减少制种田踩踏浪费的重要途径。[结论]该研究可为杂交小麦辅助授粉措施的选择提供参考。     

Scaling in tensile "skeletons": structures with scale-independent length dimensions

Skeletal structures that resist only tensile forces can scale differently than compression resisting structures that fail in bending or buckling. The tensile structures examined scalelike simple ropes: length and diameter of the structure are not correlated, and in three of four cases, length is independent of scale or load, but diameter is dependent on scale. These relations suggest that similarity in stress rather than strain, or deformational behavior, is the basis for mechanical adaptation in the gross dimensions of these tensile structures.     

Rheology and microscopic topology of entangled polymeric liquids

The viscoelastic properties of high molecular weight polymeric liquids are dominated by topological constraints on a molecular scale. In a manner similar to that of entangled ropes, polymer chains can slide past but not through each other. Tube models of polymer dynamics and rheology are based on the idea that entanglements confine a chain to small fluctuations around a primitive path that follows the coarse-grained chain contour. Here we provide a microscopic foundation for these highly successful phenomenological models. We analyze the topological state of polymeric liquids in terms of primitive paths and obtain parameter-free, quantitative predictions for the plateau modulus, which agree with experiment for all major classes of synthetic polymers.     

铁矿浆管道大中型跨越工程地质勘察方法

尖山铁矿－－太钢矿浆输送管道是国内最长的铁矿浆输送管道。无论是工程地质勘察、管道设计还是施工建设，在我国同长度各类管道中其难度都是最大的。对该管道大中型跨越工程中的支墩及斜拉索跨越段、悬索跨越段的工程地质勘察方法进行了论述，对各支墩及斜拉索跨越段卵石地段中所夹饱和砂土的液化判别简捷灵活。对各悬索跨越段隧洞口岩壁边坡的稳定性进行了分析，同时对区域地应力场、悬索跨越岩固墩抗力体的边界与受力条件提出了见