Chiral single-wall gold nanotubes

Based on first-principles calculations we show that gold atoms can form both freestanding and tip-suspended chiral single-wall nanotubes composed of helical atomic strands. The freestanding, infinite (5,5) tube is found to be energetically the most favorable. While energetically less favorable, the experimentally observed (5,3) tube stretching between two tips corresponds to a local minimum in the string tension. Similarly, the (4,3) tube is predicted as a favorable structure yet to be observed experimentally. Analysis of band structure, charge density, and quantum ballistic conductance suggests that the current on these wires is less chiral than expected, and there is no direct correlation between the numbers of conduction channels and helical strands.     

Chiral vectors-tunable electronic property of MoS2 nanotubes

It has been demonstrated that the mechanical and electronic properties of materials change significantly when the external dimension are confined to the nanoscale. Consequently, one-dimensional (1D) transition-metal dichalcogenide (TMDC) nanotubes (NTs), obtained from scrolling two-dimensional (2D) TMDC, have attracted much attentions because of their intriguing properties wherein the chirality of NTs plays a key role in affecting the electronic properties. Taking into the amount of speculations on the mechanism and the increasing needs for better device design and performance control, understanding the effect of chirality on the electronic properties is timely and relevant. Here, MoS₂ NTs are comprehensively studied by first-principles calculations. The results show that the armchair (6≤ch≤14) exhibits the indirect-band-gap and zigzag (10≤ch≤20) with direct-band-gap. Moreover, the carrier mobility is enhanced with the decrease of radial length, in accord with the smaller effective mass of hole and electron for both types NTs. Finally, the formation energy showed that the smaller the radial diameters is, the harder the NTs is to form. Moreover, the similarity of lattice parameters and formation energy implies a potential possibility of transition between two types of NTs with low index chiral vectors, such as ANT(6,6)/ZNT(10,0).     

Chiral vectors-tunable electronic property of MoS2 nanotubes

It has been demonstrated that the mechanical and electronic properties of materials change significantly when the external dimension are confined to the nanoscale. Consequently, one-dimensional (1D) transition-metal dichalcogenide (TMDC) nanotubes (NTs), obtained from scrolling 2D TMDC, have attracted much attentions because of their intriguing properties and the chirality plays a key role in affecting the electronic properties. Taking the amount of speculations on the mechanism and the increasing needs for better device design and performance control, understanding the effect of chirality on the electronic properties is timely and relevant. Here, MoS₂ NTs are comprehensively studied by first-principles calculations. The results show that the armchair (6≤ch≤14) exhibits the indirect-band-gap and zigzag (10≤ch≤20) with direct-band-gap. Moreover, the carrier mobility is enhanced with the decrease of radial length, in accord with the smaller effective mass of hole and electron for both types NTs. Finally, the formation energy showed that the smaller the radial diameters is, the harder the NTs is to form. Moreover, the similarity of lattice parameters and formation energy implies a potential possibility of transition between two types of NTs with low index chiral vectors, such as ANT(6,6)/ZNT(10,0).     

Chiral vector determination of carbon nanotubes by observation of interference patterns near the end cap

We have observed clear interference images near the end caps of semiconducting carbon nanotubes with quasiarmchair and zigzag chiral vectors, using a scanning tunneling microscope. We performed a simple tight-binding calculation to simulate the interference patterns, in which Bloch states with k and -k wave vectors were superimposed. The calculations were able to reproduce the observed interference patterns. In addition, we demonstrated that the interference patterns can be categorized by the positions of k_{min} in the Brillouin zone that yield minimum energy in the conduction band, and can give information on the chiral vector of a carbon nanotube.     

Quasiparticle conductivities in disordered d-wave superconductors

We study the quasiparticle transport coefficients in disordered d-wave superconductors. We find that spin and charge excitations are generally localized unless magnetic impurities are present. If the system is close to a nesting point in the impurity-scattering unitary limit, the tendency towards localization is reduced while the quasiparticle density of states gets enhanced by disorder. We also show that the residual repulsive interaction among quasiparticles has a delocalizing effect and increases the density of states.     

Bulk and grain boundary electrical conductivities of NASICON

The ionic conductivity of ceramic samples of NASICON was investigated by the use of the complex admittance method. Measurements were made in the frequency range 5?5×10⁵ Hz from room termparature (RT) up to 400°C. The existence of three activation energies for both the bulk and the grain boundary conductivities is reported. A diffusive Warburg-like behaviour of electrical conductivity was revealed at temperatures where the value of the bulk conductivity approaches that of the grain boundary.     

不同周期结构硅锗超晶格导热性能研究

构造了均匀、梯度、随机3种不同周期分布的硅/锗(Si/Ge)超晶格结构.采用非平衡分子动力学(NEMD)方法模拟了硅/锗超晶格在3种不同周期分布下的热导率,并研究了样本总长度和温度对热导率的影响.模拟结果表明:梯度和随机周期Si/Ge超晶格的热导率明显低于均匀周期结构超晶格;在不同的周期结构下,声子分别以波动和粒子性质...     

Chiral Magnetic Effect and Chiral Phase Transition

We study the influence of the chiral phase transition on the chiral magnetic effect. The azimuthal charge-particle correlations as functions of the temperature are calculated. It is found that there is a pronounced cusp in the correlations as the temperature reaches its critical value for the QCD phase transition. It is predicted that there will be a drastic suppression of the charge-particle correlations as the collision energy in RHIC decreases to below a critical value. We show then the azimuthal charge-particle correlations can be the signal to identify the occurrence of the QCD phase transitions in RHIC energy scan experiments.     

The Si,Ge, Sn,Pb doped (6,3) Chiral single-walled carbon nanotubes: A computational study

Electronic structure properties including bond lengths, bond angles, dipole moments (μ), energies, band gaps, NMR parameters of the isotropic and anisotropic chemical shielding parameters for the sites of various atoms were calculated using the density functional theory for Si, Ge, Sn, Pb doped (6,3) Chiral single-walled carbon nanotubes (SWCNTs). The calculations indicated that average bond lengths were as: Pb3C>Sn3C>Ge3C>Si3C>C3C. The dipole moments for Si, Ge, Sn, Pb doped (6,3) Chiral single-walled carbon nanotubes structures show fairly large changes with respect to the pristine model.     

The thermal and electrical conductivities of metals at high temperatures

A method of investigating the electrical and thermal conductivities of metals at high temperatures is described. The theory of the method depends upon the application of ideas which are fundamental in the study of electrical contact phenomena. The ratio of the thermal to the electrical conductivity of platinum has been determined from 1200° C to the melting point (1773° C) and from the melting point to 2300° C by making simultaneous observations of electrical potential and maximum temperature in a short wire through which current is passed. The wire terminates in two blocks of the same metal, and the ends of the wire are not assumed to be plane isothermal (and equipotential) surfaces. The wire remains in place when partly molten so that observations are extended well into the molten range. The method is independent of the exact geometrical configuration of the conducting system. The details of the arrangement of the apparatus and of the method of temperature measurement are given. The results are discussed in relation to the properties of the molten metal bridges formed between the electrodes of electrical contacts and to the value of theLorenz factor in theWiedemann-Franz law.     

Theoretical and experimental conductivities of silver halide-silver sulfide ISE membranes

In a previous paper, the Smith-Anderson particulate conductivity model has been extended to particulate ISE membranes. In this paper, theoretically calculated results are compared with experimentally measured results for silver halide-silver sulfide ISE membranes. Calculated and experimental ionic conductivities are in very good agreement. Calculated and experimental electronic conductivities are in poor agreement. The possible reasons for the latter are discussed.     

Chiral Bosonized Versions Hidden in Chiral Schwinger Models

The left- and right-handed chiral Schwinger models are re-examined by a modified chiral bosonization. Contrary to the usual chiral bosonization, we impose the chiral constraint on the right-handed chiral Schwinger model and the antichiral constraint on the left-handed one. The resulting chiral boson and theories are gauge-invariant and equivalent to one (free) cbiral boson and one antichiral boson respectively.     

Carbon nanotube grease with enhanced thermal and electrical conductivities

A stable and homogeneous grease based on carbon nanotubes (CNTs, single-wall and multi-wall) in polyalphaolefin oil has been produced without using a chemical surfactant. For example, for a 11 wt% (7 vol%) single-wall CNT (diameter 1–2 nm, length 0.5–40 μm) loading, the thermal conductivity (TC) of the grease shows a 60–70% increase compared to that for no nanotube loading. In addition, the grease is electrically conductive, has a high dropping point, good temperature resistance, and does not react with copper at temperatures up to 177 °C. The performance of carbon nanotube grease could be much better with the improvement of nanotube quality and purity. A possible explanation for these results is that of a high loading of CNTs (>10 wt%), they become associated with each other by van der Waals forces in the grease to form three-dimensional percolation networks. Time-dependent magnetic results demonstrate that, even under the influence of a strong outside magnetic field, the TC value remains constant. This phenomenon can be attributed to the existence of networks that makes magnetic alignment of nanotubes impossible.     

层状各向异性介质大地电磁联合反演研究

地壳和上地幔中存在的电性各向异性是地电模型、地下结构和构造模型间一个重要的联系因素. 近年来, 它引起了广泛的关注, 推动了对电性各向异性结构模型和反演理论新方法的研究. 本文在Marquardt反演理论的基础上, 引入权因子对其改进后用于大地电磁视电阻率和阻抗相位联合反演, 通过具体算例的分析, 验证了理论的正确性; 此外, 对西北某地大地电磁实测资料处理解释, 说明了程序的实用性并为今后研究深部电性构造提供了一种新的方法和途径.