共查询到20条相似文献，搜索用时 671 毫秒
1.
Lee SB Mitchell DT Trofin L Nevanen TK Söderlund H Martin CR 《Science (New York, N.Y.)》2002,296(5576):2198-2200
Synthetic bio-nanotube membranes were developed and used to separate two enantiomers of a chiral drug. These membranes are based on alumina films that have cylindrical pores with monodisperse nanoscopic diameters (for example, 20 nanometers). Silica nanotubes were chemically synthesized within the pores of these films, and an antibody that selectively binds one of the enantiomers of the drug was attached to the inner walls of the silica nanotubes. These membranes selectively transport the enantiomer that specifically binds to the antibody, relative to the enantiomer that has lower affinity for the antibody. The solvent dimethyl sulfoxide was used to tune the antibody binding affinity. The enantiomeric selectivity coefficient increases as the inside diameter of the silica nanotubes decreases. 相似文献
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为了进一步完善植物根系固土力学机制，以神东矿区采煤塌陷区的先锋植物黑沙蒿为研究对象，采用TY8000伺服式强力机研究其含侧根分支处根段的抗拉力学特性。结果表明，随根径的增加，黑沙蒿含侧根分支处根段的抗拉力逐渐增加，抗拉强度逐渐下降；在轴向拉力反复加载下，试验根由弹性变形逐渐过渡到塑性变形，表现出明显的弹塑性特征；试验根的σ～ε曲线主要分为直线型、上凸型、多峰型、波动型4种，除σ～ε曲线外，其余3种σ～ε曲线基本均以上凸型逐渐达到第1个峰值；各径级代表性σ～ε曲线的极限弹性应力由4.62 MPa降至2.25 MPa，而极限弹性应变无变化规律。黑沙蒿含侧根分支处根段的抗拉力与根径呈幂函数正相关，抗拉强度与根径呈幂函数负相关；试验根在轴向拉力下表现出弹塑性特征；随应变的不断增加，试验根应力由快速增长过渡为缓慢增长；试验根的极限弹性应力与根径呈负相关，而极限弹性应变与根径无相关性。 相似文献
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Zheng M Jagota A Strano MS Santos AP Barone P Chou SG Diner BA Dresselhaus MS McLean RS Onoa GB Samsonidze GG Semke ED Usrey M Walls DJ 《Science (New York, N.Y.)》2003,302(5650):1545-1548
Wrapping of carbon nanotubes (CNTs) by single-stranded DNA (ssDNA) was found to be sequence-dependent. A systematic search of the ssDNA library selected a sequence d(GT)n, n = 10 to 45 that self-assembles into a helical structure around individual nanotubes in such a way that the electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic properties, enabling nanotube separation by anion exchange chromatography. Optical absorption and Raman spectroscopy show that early fractions are enriched in the smaller diameter and metallic tubes, whereas late fractions are enriched in the larger diameter and semiconducting tubes. 相似文献
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Lightly etched single-walled carbon nanotubes are chemically reacted to form rings. The rings appear to be fully closed as opposed to open coils, as ring-opening reactions did not change the structure of the observed rings. The average diameter of the rings was 540 nanometers with a narrow size distribution. The nanotubes in solution were modeled as wormlike polymer chains, yielding a persistence length of 800 nanometers. Nanotubes shorter than this length behave stiffly and stay nearly straight in solution. However, nanotubes longer than the Kuhn segment length of 1600 nanometers undergo considerable thermal fluctuation, suggesting a greater flexibility of these materials than is generally assumed. 相似文献
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本文在充分肯定了悬臂式电子皮带秤称重精度几乎不受皮带张力影响,与自动给料装置配套构成定量控制系统成功地在水泥、化工、冶金及人造板等行业中得到应用的前提下。进一步分析了它的动态特性,求得了阶跃响应及脉冲响应的数学表达式、动态误差和累积误差。指出了在皮带不停止运转的情况下,阶跃给料和阶跃停料对积累精度无影响,脉动给料不产生累积误差。动态误差产生的主要原因是秤机的结构型式。提高悬臂式电子皮带秤的动态精度,主要应从改变其秤机的结构型式入手。 相似文献
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Sekitani T Noguchi Y Hata K Fukushima T Aida T Someya T 《Science (New York, N.Y.)》2008,321(5895):1468-1472
By using an ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, we uniformly dispersed single-walled carbon nanotubes (SWNTs) as chemically stable dopants in a vinylidene fluoride-hexafluoropropylene copolymer matrix to form a composite film. We found that the SWNT content can be increased up to 20 weight percent without reducing the mechanical flexibility or softness of the copolymer. The SWNT composite film was coated with dimethyl-siloxane-based rubber, which exhibited a conductivity of 57 siemens per centimeter and a stretchability of 134%. Further, the elastic conductor was integrated with printed organic transistors to fabricate a rubberlike active matrix with an effective area of 20 by 20 square centimeters. The active matrix sheet can be uniaxially and biaxially stretched by 70% without mechanical or electrical damage. The elastic conductor allows for the construction of electronic integrated circuits, which can be mounted anywhere, including arbitrary curved surfaces and movable parts, such as the joints of a robot's arm. 相似文献
8.
Yamamoto Y Fukushima T Suna Y Ishii N Saeki A Seki S Tagawa S Taniguchi M Kawai T Aida T 《Science (New York, N.Y.)》2006,314(5806):1761-1764
Controlled self-assembly of a trinitrofluorenone-appended gemini-shaped amphiphilic hexabenzocoronene selectively formed nanotubes or microfibers with different photochemical properties. In these nanotubes, which are 16 nanometers in diameter and several micrometers long, a molecular layer of electron-accepting trinitrofluorenone laminates an electron-donating graphitic layer of pi-stacked hexabenzocoronene. The coaxial nanotubular structure allows photochemical generation of spatially separated charge carriers and a quick photoconductive response with a large on/off ratio greater than 10(4). In sharp contrast, the microfibers consist of a charge-transfer complex between the hexabenzocoronene and trinitrofluorenone parts and exhibit almost no photocurrent generation. 相似文献
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在齐穗后15 d和成熟期,分别测量了4个不同水稻品种(系)茎秆3个不同节间的弹性模量、拉伸强度极限,以及节间横截实面积、节间茎粗、节间茎壁厚,并作了差异显著性测验和相关性分析。发现同一水稻茎秆不同节间弹性模量、拉伸强度极限都随茎秆的成熟而增大,大小顺序一般为:第2节间>第3节间>第4节间,它们的差异显著性与水稻品种(系)、发育时期有关;不同的品种(系)茎秆同一节间的弹性模量和拉伸强度极限存在差异,差异显著性受品种(系)的遗传特性、节间位置和发育时期影响;节间横截面积、节间茎粗、节间茎壁厚与节间拉伸强度极限、弹性模量存在负相关。 相似文献
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Macroscopic fibers and ribbons of oriented carbon nanotubes 总被引：1，自引：0，他引：1
Vigolo B Pénicaud A Coulon C Sauder C Pailler R Journet C Bernier P Poulin P 《Science (New York, N.Y.)》2000,290(5495):1331-1334
A simple method was used to assemble single-walled carbon nanotubes into indefinitely long ribbons and fibers. The processing consists of dispersing the nanotubes in surfactant solutions, recondensing the nanotubes in the flow of a polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. Flow-induced alignment may lead to a preferential orientation of the nanotubes in the mesh that has the form of a ribbon. Unlike classical carbon fibers, the nanotube fibers can be strongly bent without breaking. Their obtained elastic modulus is 10 times higher than the modulus of high-quality bucky paper. 相似文献
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为探究轴向、径向荷载下植物根系对弹性变形的适应与抵抗特性,以水土流失地区常见植物种黑沙蒿根系为对象,采用TY8000伺服控制试验机,研究1～5 mm径级范围内黑沙蒿直根及含侧根分支处根段承受轴向、径向荷载下弹性模量与刚度的变化。结果表明:直根及含侧根分支处根段力-位移曲线(F-s曲线)承受轴向荷载时呈上凸形,承受径向荷载时呈下凹形;直根段、含侧根分支处根段的拉伸弹性模量、弯曲弹性模量均与根径幂函数负相关,抗拉刚度及抗弯刚度与根径幂函数正相关;弹性模量与刚度在轴向荷载下表现出较大的差异,在径向荷载下差异不显著。试验结果说明黑沙蒿较细根适应变形能力更强,较粗根抵抗变形能力更强,且根型影响变形性质。 相似文献
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牦牛肺脏的适应性结构 总被引：10，自引：3，他引：10
应用光镜和电镜技术，对牦牛肺脏的微细结构进行了系统观测，分析其结构特性与高原低氧环境适应性的关系。结果表明，牦牛肺小叶结构明显，肺泡I型上皮菲薄，构成肺泡壁的绝大部分。与其它动物不同，牦牛I型肺泡上皮见有间断处，为非连续型上皮。气－血屏障的算术平均厚度和调和平均厚度分别为0.53±0.10µm和0.44±0.07µm，明显比体格较小的其它家畜还要薄，这有利于气体交换时增加氧的弥散量。肺脏微动脉中膜的肌层厚度与血管外径的百分比为5.00±0.93%，与高原驼马的比值近似，而比奶牛和公牛的要小，可减少牦牛肺动脉高压的发病几率。肺胸膜、小叶间隔、肺泡隔、各级支气管管壁和血管壁内都有丰富的弹性纤维分布，并相互联系，构成一个完整的弹性系统，维持肺脏良好的扩张和回缩状态。杯状细胞不仅大量分布于各级支气管，细支气管粘膜上皮中也出现杯状细胞，其分泌的粘液有助于牦牛在干旱环境下保护呼吸道的通气量。这些结构特点是牦牛世代生活于高原低氧环境下所获得的适应性变化。 相似文献
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We report the synthesis of tubular graphite cones using a chemical vapor deposition method. The cones have nanometer-sized tips, micrometer-sized roots, and hollow interiors with a diameter ranging from about 2 to several tens of nanometers. The cones are composed of cylindrical graphite sheets; a continuous shortening of the graphite layers from the interior to the exterior makes them cone-shaped. All of the tubular graphite cones have a faceted morphology. The constituent graphite sheets have identical chiralities of a zigzag type across the entire diameter, imparting structural control to tubular-based carbon structures. The tubular graphite cones have potential for use as tips for scanning probe microscopy, but with greater rigidity and easier mounting than currently used carbon nanotubes. 相似文献
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Crystalline Ropes of Metallic Carbon Nanotubes 总被引：7，自引：0，他引：7
A Thess R Lee P Nikolaev H Dai P Petit J Robert C Xu YH Lee SG Kim AG Rinzler DT Colbert GE Scuseria D Tomanek JE Fischer RE Smalley 《Science (New York, N.Y.)》1996,273(5274):483-487
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. 相似文献
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Tang X Kleinhammes A Shimoda H Fleming L Bennoune KY Sinha S Bower C Zhou O Wu Y 《Science (New York, N.Y.)》2000,288(5465):492-494
Single-walled carbon nanotubes were studied by (13)C nuclear magnetic resonance (NMR). Two types of (13)C nuclear spins were identified with different spin-lattice relaxation rates. The fast-relaxing component, assigned to metallic tubes, followed the relaxation behavior expected in metals, and the density-of-states at the Fermi level increased with decreasing tube diameter. The slow-relaxing component has a significantly lower density-of-states at the Fermi level. Exposure to oxygen has a substantial effect on relaxation rates of both components. 相似文献
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对悬臂式电子皮带刀转换特性进行了分析，从理论上推导了悬臂秤架的数学模型即传递函数，指出了产生测量失真的主要原因是秤架具有不等灵敏度，从而使其数学模型具有二次积分特性。本文提出了一种等灵敏度秤架的方案，并改善了它的特性。 相似文献
18.
Bachilo SM Strano MS Kittrell C Hauge RH Smalley RE Weisman RB 《Science (New York, N.Y.)》2002,298(5602):2361-2366
Spectrofluorimetric measurements on single-walled carbon nanotubes (SWNTs) isolated in aqueous surfactant suspensions have revealed distinct electronic absorption and emission transitions for more than 30 different semiconducting nanotube species. By combining these fluorimetric results with resonance Raman data, each optical transition has been mapped to a specific (n,m) nanotube structure. Optical spectroscopy can thereby be used to rapidly determine the detailed composition of bulk SWNT samples, providing distributions in both tube diameter and chiral angle. The measured transition frequencies differ substantially from simple theoretical predictions. These deviations may reflect combinations of trigonal warping and excitonic effects. 相似文献
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Viscoelasticity describes the ability of a material to possess both elasticity and viscosity. Viscoelastic materials, such as rubbers, possess a limited operational temperature range (for example, for silicone rubber it is -55° to 300°C), above which the material breaks down and below which the material undergoes a glass transition and hardens. We created a viscoelastic material composed from a random network of long interconnected carbon nanotubes that exhibited an operational temperature range from -196° to 1000°C. The storage and loss moduli, frequency stability, reversible deformation level, and fatigue resistance were invariant from -140° to 600°C. We interpret that the thermal stability stems from energy dissipation through the zipping and unzipping of carbon nanotubes at contacts. 相似文献
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Raman spectra of hexagonal close-packed iron (varepsilon-Fe) have been measured from 15 to 152 gigapascals by using diamond-anvil cells with ultrapure synthetic diamond anvils. The results give a Gruneisen parameter gamma(0) = 1.68 (+/-0.20) and q = 0.7 (+/-0.5). Phenomenological modeling shows that the Raman-active mode can be approximately correlated with an acoustic phonon and thus provides direct information about the high-pressure elastic properties of iron, which have been controversial. In particular, the C(44) elastic modulus is found to be lower than previous determinations. This leads to changes of about 35% at core pressures for shear wave anisotropies. 相似文献