Carbon nanotube (CNT)–epoxy nanocomposites: a systematic investigation of CNT dispersion

A systematic investigation of the dispersion of carbon nanotubes (CNTs), 1–6 nm in diameter and a few microns in length, in a bisphenol F-based epoxy resin has been presented. Several dispersing techniques including high-speed dissolver, ultrasonic bath/horn, 3-roll mill, etc. have been employed. Optical microscopy has been extensively used to systematically characterise the state of CNT dispersion in the epoxy resin during the entire processing cycle from mixing CNT with resin to adding and curing with hardener. Complimentary viscosity measurements were also performed at various stages of nanocomposite processing. A method to produce a good CNT dispersion in resin was established, but the state of CNT dispersion was found to be extremely sensitive to its physical and chemical environments. The cured nanocomposites were further tested for their thermo-mechanical properties by dynamic mechanical thermal analysis (DMTA), and for flexural and compressive mechanical properties. The measured properties of various nanocomposite plates were then discussed in view of the corresponding CNT dispersion.     

DFT studies of CNT–functionalized uracil-acetate hybrids

Calculations based on density functional theory (DFT) have been performed to investigate the stabilities and properties of hybrid structures consisting of a molecular carbon nanotube (CNT) and uracil acetate (UA) counterparts. The investigated models have been relaxed to minimum energy structures and then various physical properties and nuclear magnetic resonance (NMR) properties have been evaluated. The results indicated the effects of functionalized CNT on the properties of hybrids through comparing the results of hybrids and individual structures. The oxygen atoms of uracil counterparts have been seen as the detection points of properties for the CNT–UA hybrids.     

Electrochemical synthesis and lithium storage properties of three-dimensional porous Sn–Co alloy/CNT composite

Three-dimensional (3-D) porous copper with stable pore structure is prepared by electroless plating. 3-D porous Sn–Co alloy/carbon nanotube (CNT) composite is synthesized by electrodeposition using 3-D porous copper as the substrate. The scanning electron microscope results indicate that 3-D porous Sn–Co alloy/CNT composite contains a large amount of interconnected pores with the diameter size of ~3 μm. Upon cycling, the pore structure gradually disappears, but no serious exfoliation appears due to porous structure and reinforcement by CNT. The charge/discharge results demonstrate that the 3-D porous Sn–Co alloy/CNT composite electrode delivers high first reversible specific capacity of 490 mAh g^?1, and remains 441 mAh g^?1 after 60 cycles tested at different current densities. Even at the current density of 3,200 mA g^?1, the reversible specific capacity remains 319 mAh g^?1, which is 65 % of the first specific capacity cycled at the current density of 100 mA g^?1.     

Electrical transport properties of a CNT/C<Subscript>60</Subscript>/CNT hybrid junction with closed end CNT leads using Green’s function method

We investigate transport properties of an all-carbon molecular device consisting of a CNT/C₆₀/CNT hybrid system with closed end (5,5) CNT leads. Two different ways of coupling are considered for C₆₀ molecule through one and five atoms to the cap-edges of CNTs. Our calculations are based on the Green’s function method in the nearest neighbor tight-binding approximation in the coherent regime. In this paper, the sensitivity of electron transport on the geometry of the CNT electrodes-C₆₀ interface is shown. Within the framework of the Landauer-Buttiker formalism, the electrical transmission and current-voltage characteristic are calculated at room temperature. We have investigated the effect of a gate voltage on the current in the considered geometry. In the considered structure, the appearance of the conductance resonances is a manifestation of resonant states of CNT caps, which lie within the HOMO-LUMO gap.     

CNT界面水分子动力学特性研究

采用非平衡态分子动力学模拟方法研究了碳纳米管(CNT)入口界面的水分子输运特性,分析了不同CNT直径下,水分子动力学特性的变化规律。结果表明,随着CNT直径的增大,水分子流入CNT的通量逐渐增大;界面处水分子密度沿轴向分布更加均匀且逐渐趋近于体相区域的水分子密度。由于大管径CNT对水分子热运动的约束减弱,水分子间相互扰动增强,使得CNT内部的氢键寿命逐渐缩短,有效降低界面传质能量壁垒并改善了水分子输运特性。本文的研究有助于深化对纳米多孔介质入口界面流体的输运特性理解,并为纳米多孔材料的优化设计提供基础理论指导。     

Structure and stability of various states of the EuC and EuC2 molecules

B3LYP level density functional theory （DFT） and multiconfiguration self-consistent-field （MCSCF） level ab initio method calculations have been performed on the basis of relativistic effective core potentials to investigate the nature of EuC and EuC2 molecules. The computed results indicate that the ground states of EuC and EuC2 are ^12∑^＋ and SA2, respectively. Dissociation potential energy curves of the low-lying electronic states of EuC have been calculated using the MCSCF method, and the same level calculation on EuC2 indicates that the dissociation energy of EuC2 of ground state compares well with the available experimental data. The bond characteristic is also discussed using Mulliken populations.     

Calculation and interpretation of vibronic absorption and fluorescence spectra of the first electronic nπ* transitions of pyridine and pyrimidine

We have calculated vibronic spectra of the first electronic nπ* transitions of pyridine and pyrimidine in the isolated state using the DFT method in the Franck-Condon approximation. Vibrational spectra for the ground and excited states have been calculated in the anharmonic approximation, which allowed us to refine the assignment of normal vibrations of pyridine and pyrimidine. We have done a complete interpretation of the vibrational structure of the absorption and fluorescence spectra of pyridine and pyrimidine. It has been shown that Fermi resonances between fundamental and combination vibrations and overtones 12 and 16b + 4, 6a and 2 × 16b affect the formation of the vibrational structure of electronic spectra of pyrimidine. Good agreement between calculated and experimental spectra confirms the correctness of the models of the two molecules in their ground and excited states, which makes it possible to use the models in further investigations of various properties of these molecules in electronically excited states, e.g., tautomerism of pyrimidine bases of nucleic acids.     

Pressure Shifts and Pressure Broadening of the B and γ Bands of Oxygen

Measurements of pressure shift and pressure broadening in molecular oxygen have been made for rotational transitions in the B (1←0) and γ (2←0) vibrational bands of the b¹Σ⁺_g←X³Σ⁻_g visible electronic transition. The absorption features were measured simultaneously in two cells by photoacoustic spectroscopy using a scanning dye laser. The measurements were made with background gases of both pure oxygen and air at room temperature. The pressure shifts were all negative. The measurements show the magnitude of the pressure shift increasing with vibrational quantum number when compared with existing data for the A (0←0) band. The shifts also increase with rotational number within each vibrational band. The shifts in air are larger than in oxygen although the difference gets smaller with vibrational number. The average shifts in air for the A, B, and γ bands were 36, 11, and 0.2% higher, respectively, than in pure oxygen. The pressure broadening of the rotational lines does not change significantly with vibrational number and in general decreases with rotational number within a band. The pressure shift measurements were used by the high-resolution Doppler imager (on the Upper Atmospheric Research Satellite) to correct the Doppler wind measurements.     

Hadroproduction of ψ and Υ

We show that inclusive ψ hadroproduction cross sections andx _F -distributions are quantitatively consistent with calculations based on the lowest order \(q\bar q \to c\bar c\) andgg→ \(c\bar c\) QCD subprocesses using a duality ansatz. Data in the πN, KN, NN and \(\bar NN\) channels are considered. They provide determinations of the gluon distributions within the nucleon, the pion, and the kaon at the ψ mass scale. AvailableNN→ΥX data aty=0 are consistent with the same model, using gluon distributions appropriate to the Υ mass: predictions ofx _F -distributions are made.     

The Young’s Modulus of a Zigzag CNT/Graphene Composite by Tension along the Graphene Direction

Physics of the Solid State - The Young’s modulus of a finite-sized zigzag carbon nanotube-based ribbon-like columnar graphene is theoretically studied. The dependence of elastic...     

ZA27/CNT界面特性电子理论研究

依据原子结合能定义了界面结合能. 采用递归法计算了纳米管增强锌铝基复合材料中ZA27/CNT界面电子结构，揭示了纳米管在ZA27合金晶界分布的微观物理本质，及其ZA27/CNT弱界面结合的电子层面的原因. 研究发现：金属基体对纳米管增强相上的碳原子态密度影响很大，而纳米管对基体金属中的铝、锌原子影响很小. 碳原子态密度与基体金属原子趋于同化，使纳米管与基体金属结合，但因同化程度不高导致界面结合较弱，影响强化效果. 如果在纳米管装饰或镀上与基体金属性质相近的原子层，会极大改善复合材料的界面结合强度，提高复合材料性能. 关键词： 复合材料 纳米管 电子结构 界面     

Evaluation of the Mn Lα and Lβ Spectra of Mn Metal and of Various Mn-Oxides

The Mn Lα and Lβ spectra of Mn, MnO, Mn₃O₄, Mn₂O₃, and MnO₂ have been measured. Each Mn La spectrum has been deconvoluted into two bands, Lα_A and Lα_B, and the integrated Lα_A/Lα_B intensity ratio was found to be inversely proportional to the Mn-0 inter-atomic distance, but proportional to the oxidation number. This finding tends to indicate the likelihood of crossover transition from oxygen to manganese. The intensity ratio Lβ/Lα_B of the pure metal was found to coincide closely with the statistically predicted value of 0.5. Furthermore, for Mn-metal, as well as for the oxides, the shift of the Lα_A band from the Lα_B band was found to agree with the change in the Lβ/Lα peak intensity ratio as a function of oxidation number.     

Experimental and Theoretical Study of the Electrochemical Behavior of o‐Benzoquinone and Pyrocatechol

The geometric parameters, vibrational frequencies, and the thermochemical values of o‐benzoquinone (o‐BQ), p‐benzoquinone (p‐BQ), pyrocatechol (PC), and p‐hydroquinone (p‐HQ) were computed using ab initio calculation (HF) and density functional theory (DFT) with the 6‐31G (d) and 6‐31G (d, p) basis sets, respectively. Cyclic voltammetry with a gold electrode of PC solutions in phosphate buffers at pH 7.30 showed that the standard electrode potential of half reaction for o‐BQ and PC is 0.813 V. The standard electrode potential of half reaction for o‐BQ and PC with a p‐BQ, H⁺/p‐hydroquinone (p‐HQ) reference electrode, using the solvation energies and the sum of electronic and thermal free energies of o‐BQ and PC, is consistent with the experimental one.     

Model of grain-boundary self-diffusion in α- and β-phases of titanium and zirconium

A model of the grain-boundary self-diffusion process in metals undergoing phase transitions in the solid state is proposed. The model is based on the ideas and approaches of the theory of nonequilibrium grain boundaries. It is shown that the range of application of basic relations of this theory can be extended, and they can be used to calculate the parameters of grain-boundary self-diffusion in high-temperature and low-temperature phases of metals with phase transition. Based on the constructed model, activation energies of grainboundary self-diffusion in titanium and zirconium are calculated, and their anomalously low values in the low-temperature phase are explained. The calculated activation energies of grain-boundary self-diffusion are in good agreement with experimental data.     

Preparation and Luminescent Properties of ZnO Microrods and Microtubes

Hexagonal ZnO microrods and sub-microrods have been prepared through thermal decomposition of an equimolar (0.1 M) aqueous solution of Zn(NO3)2.4H20 and (CH2)6N4 a~t 90~C for different times (10-46h). The microrods were transformed into hollow hexagonal ZnO microtubes when the growth time reached 46 h. The Raman spectra and the photoluminescent (PL) spectra were measured. The PL spectra of microrods consist of two strong narrow near-UV bands at 380 nm and 400 nm assigned to free exciton emission and exciton-exciton collision, respectively.The PL spectrum of ZnO microtubes show only one peak in the near-UV region with peak located at 380nm with FWHM of about 20nm assigned to free exciton emission. When the growth time increased, the peak intensity of near-UV band decreased.     

Research and Development of SWITRIM Code and Its Applications

The ftrst numerical simulation code package WITRIM has been developed to calculate the tritium inventory distribution and time-evolution in all sub-systems of FEB fusion reactor. The applications during recent six years indicate that it is reasonable and fully admitted by colleagues abroad. Some creative papers with new concept are published. For instance, we first time pointed out a new phenomenon of ＂tritium well depth and tritium well time＂ during the fusion reactor start-up phase. This is somewhat similar to, but quite different from the ＂iodine well depth and iodine well time＂ poisoning problem during restart-up process of a fission reactor. The authors not only proposed but also numerically solved this new phenomenon. The combination of the SWITRIM code package, user＇s guide, and application example are briefly introduced in this article.