共查询到20条相似文献,搜索用时 31 毫秒
1.
The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged singlewalled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels. 相似文献
2.
依据磁场中Boltzmann输运方程及单层磁纳米管(SWNTs)的能量色散关系,对单个SWNTs中轴向磁场诱发的低温磁阻进行了数值计算.分析表明:当电子以低能输运时,SWNTs的磁阻有明显的Aharonov-Bohn(A-B)效应,与并SWNTs的能隙相对应. 相似文献
3.
Freely suspended metallic single-walled carbon nanotubes (SWNTs) exhibit reduced current carrying ability compared to those lying on substrates, and striking negative differential conductance at low electric fields. Theoretical analysis reveals significant self-heating effects including electron scattering by hot nonequilibrium optical phonons. Electron transport characteristics under strong self-heating are exploited for the first time to probe the thermal conductivity of individual SWNTs (approximately 3600 W m-1 K-1 at T=300 K) up to approximately 700 K, and reveal a 1/T dependence expected for umklapp phonon scattering at high temperatures. 相似文献
4.
Arun Tej Mallajosyula S. Sundar Kumar Iyer Baquer Mazhari 《Current Applied Physics》2013,13(4):677-683
P3HT:PCBM bulk heterojunction devices incorporating SWNTs, which are predominantly metallic in character, have been analyzed using impedance spectroscopy to understand the effect of SWNTs on their charge carrier transport properties. SWNTs reduce the effective lifetime of injected charge carriers. Frequency dependence of capacitance and conductance of P3HT:PCBM devices show monotonic variations without any clear peak positions. Simulations of the complex admittance of the P3HT:PCBM devices under trap free space charge limited current within the framework of Scher–Montrol theory are used to qualitatively show that such characteristics are a signature of charge transport which is highly dispersive in nature. The position of peak τpeak in the imaginary part of impedance Im(Z), which is essentially same as the first transition frequency of Cole–Cole plot, has a direct relation with the effective dc mobility of charge carriers which varies with dispersion parameters. Using the dc mobility values and the voltage variation of peak frequency of Im(Z), the ratio of τdc to τpeak has been calculated. The magnitude of this ratio is indicative of the degree of dispersiveness in transport. It has been shown that, SWNTs at low concentrations tend to reduce the dispersiveness in charge transport. 相似文献
5.
Sand particles blown by wind cause serious environmental problems and many researchers are trying to understand the dynamic
properties of blown sand better. But the existing numerical approaches have not been able to simulate many important characteristics
of wind-sand flow. In this paper, the evolution and fluctuation properties of blown sand at a dynamic steady state are investigated
by using a more effective method. Using the LES (large eddy simulation) method for air phase movement and the DEM (discrete
element method) for solid phase movement along with the existing particle-bed splashing function, we have characterized the
whole movement property of the wind-sand system. The results indicate that the saturation time decreases with the inlet friction
velocity, and it gradually reaches the shortest saturation time of about 1s; the saturation length, which is about 14 m at
the usual wind velocity, first increases with wind velocity and then reaches a plateau; within the saturation length, the
sand transport rate at different positions varies with time; the sand transport rate of the stable wind-sand flow is non-uniform
with distance downwind and time, and has a notable correlation with the inflow friction velocity. 相似文献
6.
《Journal of Physics and Chemistry of Solids》2003,64(4):571-581
Singlewall carbon nanotubes (SWNTs) produced by electric-arc and laser ablation methods were characterized by X-ray diffraction before and after the reaction with alkali metals (M=K, Rb, and Cs). Reaction with annealed SWNTs gave MC8 composition at saturation. The alkali metal lattice showed short range order incommensurate with graphene cylinders of SWNTs. X-ray diffractogram simulations have enabled the study of the influence of SWNTs structure on that of intercalation compounds. Chemically-purified bundles, constituted of open SWNTs, can be intercalated inside and between the tubes forming disordered structures. Annealed or pristine bundles were intercalated only between the tubes leading to short or long range ordered structure depending on host crystallinity and alkali metal (K, Rb or Cs). The expansion of the 2D SWNTs lattice after intercalation is comparable to graphite intercalation compounds. Some 2D arrangements of SWNTs and K atoms are proposed and discussed to reproduce XRD results. 13C NMR and ESR studies of annealed doped SWNTs emphasize the fact that the intercalation compounds of SWNTs are metallic. 相似文献
7.
8.
In the previous multiscale finite-volume (MSFV) method, an efficient and accurate multiscale approach was proposed to solve the elliptic flow equation. The reconstructed fine-scale velocity field was then used to solve the nonlinear hyperbolic transport equation for the fine-scale saturations using an overlapping Schwarz scheme. A coarse-scale system for the transport equations was not derived because of the hyperbolic character of the governing equations and intricate nonlinear interactions between the saturation field and the underlying heterogeneous permeability distribution. In this paper, we describe a sequential implicit multiscale finite-volume framework for coupled flow and transport with general prolongation and restriction operations for both pressure and saturation, in which three adaptive prolongation operators for the saturation are used. In regions with rapid pressure and saturation changes, the original approach, with full reconstruction of the velocity field and overlapping Schwarz, is used to compute the saturations. In regions where the temporal changes in velocity or saturation can be represented by asymptotic linear approximations, two additional approximate prolongation operators are proposed. The efficiency and accuracy are evaluated for two-phase incompressible flow in two- and three-dimensional domains. The new adaptive algorithm is tested using various models with homogeneous and heterogeneous permeabilities. It is demonstrated that the multiscale results with the adaptive transport calculation are in excellent agreement with the fine-scale solutions. Furthermore, the adaptive multiscale scheme of flow and transport is much more computationally efficient compared with the previous MSFV method and conventional fine-scale reservoir simulation methods. 相似文献
9.
Mohamed Zakari 《Physica A》1997,240(3-4):676-684
A hierarchy of evolution equations for higher-order moments of the velocity distribution function is generalized by including the effects of an external field. The use of continued-fraction techniques yields generalized transport coefficients including not only memory effects but also non-linear effects leading to a saturation in the corresponding flux. The ensuing corrections to the Einstein transport relation far from equilibrium are also studied. 相似文献
10.
In this work, the influence factors, namely chirality, temperature, radius and surface chemical modification, of the interaction energy for polyethylene (PE) molecule encapsulated into single-walled carbon nanotubes (SWNTs) had been investigated by molecular mechanics (MM) and molecular dynamics (MD) simulation. The results showed that all these factors would influence the interaction energy between PE and SWNTs. The interaction energy between PE molecule and the armchair SWNTs is largest among eight kinds of chiral SWNTs. The interaction energy decreases with the increase of temperature or the SWNT radius. The methyl, phenyl, hydroxyl, carboxyl, -F, and amino groups, have been introduced onto the surface of the SWNTs by the simulation software and the influence of SWNT chemical modification has also been investigated. The interaction energy between PE and chemically modified SWNTs is larger than that between PE and pristine SWNTs, and increases with increasing the concentration of the modified groups monotonously. In addition, the group electronegativity and van der Waals force will affect the interaction energy between PE and chemically modified SWNTs greatly, which can be attributed to the electronic structures of the chemically modified groups. This study can provide some useful suggestions for the composite material design and drug transport. 相似文献
11.
Synthesis, integration, and electrical properties of individual single-walled carbon nanotubes 总被引:4,自引:0,他引:4
J. Kong C. Zhou A. Morpurgo H.T. Soh C.F. Quate C. Marcus H. Dai 《Applied Physics A: Materials Science & Processing》1999,69(3):305-308
High-quality single-walled carbon nanotubes (SWNTs) are synthesized by chemical vapor deposition (CVD) of methane on silicon-dioxide
substrates at controlled locations using patterned catalytic islands. With the synthesized nanotube chips, microfabrication
techniques are used to reliably contact individual SWNTs and obtain low contact resistance. The combined chemical synthesis
and microfabrication approaches enable systematic characterization of electron transport properties of a large number of individual
SWNTs. Results of electrical properties of representative semiconducting and metallic SWNTs are presented. The lowest two-terminal
resistance for individual metallic SWNTs (≈5 μm long) is ≈16.5 kΩ measured at 4.2 K.
Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 14 July 1999 相似文献
12.
Maeda A Matsumoto S Kishida H Takenobu T Iwasa Y Shiraishi M Ata M Okamoto H 《Physical review letters》2005,94(4):047404
We measured third-order nonlinear susceptibility (chi(3)) spectra in semiconducting single-walled carbon nanotubes (SWNTs) by the Z-scan method. |Imchi(3)| is remarkably enhanced under resonant excitation to the lowest interband transition, reaching 4.2 x 10(-6) esu and 1.5 x 10(-7) esu in SWNTs grown by the laser ablation and HiPco methods, respectively. A comparison of the transient absorption changes evaluated by degenerate and nondegenerate pump-probe measurements suggests that the resonant enhancement of |Imchi(3)| is dominated by a coherent process rather than by saturation of absorption. 相似文献
13.
14.
Ya. Yu. Volkova P. S. Zelenovskiy D. N. Sokolovskiy A. N. Babushkin 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(4):285-287
Single-wall carbon nanotubes (SWNTs) under high pressure exhibit high structural stability and a series of structural transitions up to 35 GPa. As theoretically predicted, the irreversible transformation of SWNTs in the pressure range of 10–30 GPa can be attributed to the polymerization of nanotubes. The electrical conductivity of SWNTs is studied at high pressures up to 35 GPa using a diamond anvil cell (DAC) with electrically conductive anvils of the “rounded cone-plane” type made of synthetic carbonado-type diamonds. SWNTs are studied before and after the application of high pressure using the Raman confocal microscopy technique. Analysis of Raman spectra and pressure dependences of the SWNT resistance shows that the observed structural changes in SWNTs are reversible and no polymerization or collapse are observed. 相似文献
15.
《Physica E: Low-dimensional Systems and Nanostructures》2009,41(10):3179-3182
Based on the theory of thermal elasticity mechanics, an elastic Bernoulli–Euler beam model is developed for vibration and instability analysis of fluid-conveying single-walled carbon nanotubes (SWNTs) considering the thermal effect. Results are demonstrated for the dependence of natural frequencies on the flow velocity as well as temperature change. The influence of temperature change on the critical flow velocity at which buckling instability occurs is investigated. It is concluded that the effect of temperature change on the instability of SWNTs conveying fluid is significant. 相似文献
16.
The induced motion of vortex chains (helical waves) is studied in a system consisting of a Josephson junction coupled magnetically to a waveguide. The relation between the transport current density and the chain velocity is established. 相似文献
17.
用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率,发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时,单壁纳米碳管的管间孔也会成为有效的氢吸附位.
关键词:
Monte Carlo方法
单壁纳米碳管
储氢
微孔 相似文献
18.
A. V. Okotrub L. G. Bulusheva A. V. Gusel’nikov 《Journal of Experimental and Theoretical Physics》2004,99(6):1244-1252
A carbonaceous material containing single-wall carbon nanotubes (SWNTs) has been synthesized by arc-discharge evaporation of graphite with a catalytic additive of nickel and cobalt powders. The synthesized SWNTs were purified from an amorphous carbon component (soot) and the catalyst particles by boiling in nitric acid. A comparison of the X-ray fluorescence spectra measured before and after this treatment showed that acid etching significantly decreased the content of soot in the material. The material enriched with SWNTs is characterized by a reduced threshold for the appearance of the field emission current, which is explained by a decrease in the screening effect of soot. The current-voltage characteristics of SWNTs exhibit a hysteresis, which is suggested to be due to the adsorption of molecules and radicals on the surface and at the ends of carbon nanotubes. 相似文献
19.
Latham P.E. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(3):273-285
The effects of AC space charge on multicavity gyroklystron amplifiers are studied. It is found that when AC space charge is included in the analysis of weakly relativistic multicavity gyroklystron amplifiers, the optimized nonlinear efficiency becomes a function of beam current. For a cold beam (no velocity spread), the efficiency is maximum at zero current and decreases monotonically as the current increases. The zero current limit of the optimized efficiency when AC space-charge effects are included is not the same as the optimized efficiency with no space charge; it is significantly higher. This behavior is regularized when velocity spread is taken into account; in that case, the nonlinear efficiency increases with beam current until it reaches a maximum, then falls off slowly. The increase in efficiency is attributed to enhanced bunching associated with the saturation of the space-charge instability in the drift region; the reduction in efficiency at high current occurs because space charge induces an additional velocity spread in the beam 相似文献
20.
Y. Zhang M. Han 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(2):277-282
Using the π orbital tight-binding model and the
multi-channel Laudauer-Büttiker formula, the combined effect of
Aharonov-Bohm effect (induced by an axial magnetic field) and uniaxial
strain on quantum conductance oscillations of the electronic Fabry-Perot
resonators composed of armchair and metallic zigzag single-walled carbon
nanotubes (SWNTs) has been studied. It is found that, for the case of the
armchair SWNT, conductance oscillations near the band gap are dominated by
Aharonov-Bohm effect, while the conductance oscillations in other regions
are dominated by the uniaxial strains. The combined effect of Aharonov-Bohm
effect and uniaxial strains on quantum conductance oscillations is not
obvious. But, for the case of the metallic zigzag SWNTs, obvious
single-channel transport and one or two conductance oscillations existing in
two different gate voltage ranges were found by the combined effect of
uniaxial strain and axial magnetic field. 相似文献