Vibration-assisted upconversion of molecular luminescence induced by scanning tunneling microscopy

We investigate the effects of coupling between a molecular exciton, which consists of an electron and a hole in a molecule, and a surface plasmon (exciton-plasmon coupling) on the electron transitions of the molecule using nonequilibrium Green’s function method. Due to the exciton-plasmon coupling, excitation channels of the molecule arise in the energy range lower than the electronic excitation energy of the molecule. It is found that the electron transitions via these excitation channels give rise to the molecular luminescence and the vibrational excitations at the bias voltage lower than the electronic excitation energy of the molecule. Our results also indicate that the vibrational excitations assist the emission of photons, whose energy exceeds the product of the elementary charge and the bias voltage, (upconverted luminescence).     

高温热解法制备碳螺线管的扫描电子显微镜研究

采用高温热解法,以乙炔为碳源,在金属催化剂和促进剂的作用下,大量制备碳螺线管.利用扫描电子显微镜对二重螺旋状碳纤维的形成和碳粒子纳米结构进行了观察研究,探讨螺旋生长机制.螺旋状生长的推动力是催化剂中间体的晶面的各向异性。本文还利用扫描电子显微镜表征其拉弹性。     

Wastepaper gasification with CO2 or steam using catalysts of molten carbonates

In this paper, wastepaper gasification with carbon dioxide or steam has been investigated in the presence of molten carbonate catalysts. The reactions of wastepaper with steam or carbon dioxide have been compared. Hydrogen was the main product on the condition of steam used as reactant gas, but in the case where carbon dioxide was used, the amount of carbon monoxide generated from wastepaper gasification greatly increased via the Boudouard reaction. Different ratios of mixtures of lithium, sodium and potassium carbonates as the catalysts have been tested; the lithium carbonate was found to play a critical role. The reaction rate of carbon conversion was approximately first order for low carbon conversions. Both the rate constants and the activation energies have been calculated at different temperatures (923–1023 K). In additions, the flexibility of this technique was examined with three different types of wastepaper. The results suggest that this process can promote effective use of wastepaper and recovery of carbon dioxide. At 1023 K, a high value of cold gas efficiency of about 95% was acquired.     

Visualization of water vapour flow in a packed bed adsorber by near-infrared diffused transmittance tomography

This work presents a procedure based on spatially-resolved near-infrared imaging, in order to observe temperature and composition maps in gas–solid packed beds subjected to effects of aspect ratio and non-isothermal conditions. The technique was applied to the water vapour flow in a packed bed adsorber of low aspect ratio, filled with silica gel, using a tuneable diode laser, focal planar array detector and tomographic reconstruction. The 2D projected images from parallel scanning permitted data to be retrieved from the packing and above the packing sections of 12.0×12.0×18.2 mm³ at a volume-resolution of 0.15×0.15×0.026 mm³ and a time-resolution of less than 3 min. The technique revealed uneven temperature and composition maps in the core packed bed and in the vicinity of the wall due to flow maldistribution. In addition, the heat uptake from the packed bed and local cross-mixing were experimentally ascertained by local profiles of the water vapour composition and temperature under various aspect ratios and feed flow rates. The relative deviations in temperature and compositions were 11.1% and 9.3%, respectively. The deviation in composition, which covers the packing and above the packing sections, was slightly higher than the deviation of 8% obtained up-to-date but was limited to the exit of a packed bed adsorber.     

Various conformations of carbon nanocoils prepared by supported Ni-Fe/molecular sieve catalyst

The carbon nanocoils with various kinds of conformations were prepared by the catalytic pyrolysis of acetylene using the Ni metal catalyst supported on molecular Sieves which was prepared using Fe-containing kaolin as the raw material. There are four kinds of carbon nanocoils conformations produced by this catalyst. The influences of reaction temperature and gas conditions on the conformations of the nanocoils were investigated and the reasons of forming nano-size coils were discussed by comparison with pure Ni metal catalyst.     

Preparation of micro-coiled carbon fibres by metal powder-activated pyrolysis of acetylene containing a small amount of sulphur compounds

Micro-coiled carbon fibres were prepared by the transition metal-activated pyrolysis of acetylene containing a small amount of sulphur compounds, and the preparation conditions were examined in detail. The coiled carbon fibres grew at the reaction temperatures of 700–850 °C and thiophene gas flow rates of 0.14–0.45 standard cm³min^–1 (0.10–0.35 vol % reaction atmosphere). The optimum values depended on the type of metal catalysts used. Among the metal catalysts used, nickel, titanium and tungsten were the most effective for the growth of the coiled carbon fibres and a maximum yield of about 50%–55% was obtained. The bulk resistivity of the coiled carbon fibres decreased with increasing bulk density and was 10⁰ S^–1 cm at a bulk density of 1.     

Nuclear design of a heliotron-H fusion power reactor

Nuclear analysis was carried out for the heliotron-H fusion power reactor employing anl=2 helical heliotron field. The neutronics aspects examined were (a) tritium breeding capability, (b) shielding effectiveness for the superconducting magnet (SCM), and (c) induced activity after shutdown. In this reactor design of the heliotron-H, the space available for the blanket and shield is limited due to the reactor geometry. Thus, some parametric survey calculations were performed to satisfy the design requirements. The nucleonic design features of the heliotron-H are as follows. An adequate tritium breeding ratio of 1.17 is obtained when a 10-cm thick Pb neutron multiplier and a 40-cm thick Li₂O breeding blanket are used. In this case, the total nuclear energy deposition is 16.10 MeV per 14.06 MeV incident neutron. The performance of the SCM is assured during 2 yr of continuous operation using a 20-cm thick tungsten shield. Biological dose rate behind the SCM at 1 day after shutdown is too high for hands-on maintenance.     

Chemical vapour deposition of tantalum diboride

Tantalum diboride (TaB₂) was deposited on a quartz substrate from a gas mixture of TaCl₅, BCl₃, H₂, and Ar at a temperature between 900 and 1300° C. When the atomic ratio (B/Ta) in source gas was held above 1.0 at 1000° C, TaB₂ with a composition of between TaB_1.90 and TaB_1.95 was obtained in a single phase. The deposits grew to grain crystals with an increase in temperature and with an increase in the atomic ratio (B/Ta) in the source gas. The mass transfer of TaCl₅ was supposed to be the rate-determining step. The Vickers microhardness values for the coating deposited at 1100° C from a source gas with atomic ratio (B/Ta) above 1.0 were 3500 to 4100 kg mm^–2. Dispersing Ni or Pd on the substrate as an impurity, woolly crystals of up to 100m in length were grown in 30 min at 1050° C, and the growth mechanism was thought to be that of tip-VLS.     

Preparation of carbon micro-coils involving the decomposition of hydrocarbons using PACT (plasma and catalyst technology) reactor

Carbon micro-coils as well as carbon fibers with various morphologies were prepared by the decomposition of hydrocarbons, such as acetylene, methane, propane, ethylene, etc., at 770°C using a PACT (plasma and catalyst technology) reactor. The preparation conditions, growth mechanism and morphology of the carbon micro-coils were examined. The Ni electrode of the PACT reactor was used as the catalyst as well as a plasma source electrode. It was found that hydrocarbons, such as methane, propane and ethylene, decomposed under the plasma and catalyst atmosphere to form acetylene as the main decomposition product, and then this acetylene was further decomposed to form carbon micro-coils. Using a Ni powder catalyst dispersed on the substrate, the carbon micro-coils with a double helix structure, in which two pieces of carbon coils entwine each other in the same coiling direction, grew among the single straight carbon fibers and paired straight fibers. On the other hand, the carbon micro-coils with a single helix structure and wide coil pitch were obtained by the indirect decomposition of acetylene using the N₂ plasma formed by the PACT reactor.