Influence of Coherent Flow Structures on the Dynamics of Suspended Sediment Transport in Open-Channel Flow

The influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components of the instantaneous velocity vector and the instantaneous suspended particle concentration with an acoustic particle flux profiler. The measurements were carried out in clear water and in particle-laden open-channel flows. In both cases, they clearly show the predominance of ejection and sweep phases that are part of a burst cycle. The analysis further demonstrates the importance of the ejection and sweep phases in sediment resuspension and transport. Ejections pick up the sediment at the bed and carry it up through the water column close to the surface. It is shown that ejections and sweeps are in near equality in the near-bottom layer, whereas ejections clearly dominate in the remaining water column. The implications of these results for sediment transport dynamics are discussed.     

Formation of low-resistivity poly-Si and SiNx films by Cat-CVD for ULSI application

In this paper, bulk-Si metal–oxide–semiconductor field effect transistors (MOSFETs) are fabricated using the catalytic chemical vapor deposition (Cat-CVD) method as an alternative technology to the conventional high-temperature thermal chemical vapor deposition. Particularly, formation of low-resistivity phosphorus (P)-doped poly-Si films is attempted by using Cat-CVD-deposited amorphous silicon (a-Si) films and successive rapid thermal annealing (RTA) of them. Even after RTA processes, neither peeling nor bubbling are observed, since hydrogen contents in Cat-CVD a-Si films can be as low as 1.1%. Both the crystallization and low resistivity of 0.004 Ω·cm are realized by RTA at 1000 °C for only 5 s. It is also revealed that Cat-CVD SiN_x films prepared at 250 °C show excellent oxidation resistance, when the thickness of films is larger than approximately 10 nm for wet O₂ oxidation at 1100 °C. It is found that the thickness required to stop oxygen penetration is equivalent to that for thermal CVD SiN_x prepared at 750 °C. Finally, complementary MOSFETs (CMOSs) of single-crystalline Si were fabricated by using Cat-CVD poly-Si for gate electrodes and SiN_x films for masks of local oxidation of silicon (LOCOS). At 3.3 V operation, less than 1.0 pA μm⁻¹ of OFF leakage current and ON/OFF ratio of 10⁷–10⁸ are realized, i.e. the devices can operate similarly to conventional thermal CVD process.     

Energy Dissipation at the Slug Nose and the Modeling of Solids Transport in Intermittent Flow

It is shown, by means of Lagrangian momentum and power balances across the slug nose in slug flow, that the power dissipated due to sudden expansion of the fluid in the film immediately downstream of the slug nose is greater than the power lost due to viscous action at the pipe wall but that it may not be large enough to materially aid particle transport. This has the implication that sand transport in intermittent flow may be considered as transport in a hybrid flow of hydraulic conveying and stratified flow when the length of the mixing section at the slug nose is short compared to the length of the slug body.     

Reactor modelling for electrochemical processes

This paper presents a relatively straightforward approach to the modelling of electrochemical reactors operated in batch or continuous modes. The models are based on ideal flow assumptions of either well-mixed or plug flow and incorporate reaction rate models based on electrochemical kinetics and mass transport at one electrode. General characteristics of the reactor models are described, particularly with regard to the need for good mass transport in metal recovery applications. An example is given on the use of the model in the recovery of a heavy metal (Cd²⁺) from an acidified solution containing Cd(II) and Fe(III) ions. The reaction rate model is based on experimental data.     

Possible tactics to improve the growth of single-walled carbon nanotubes by chemical vapor deposition

The growth time, growth mode and the method of preparing the supported catalysts play an important role in the growth of single-walled nanotubes (SWNTs). Their effects on the chemical vapor deposition (CVD) growth of SWNTs with MgO-supported catalysts were investigated in this study. It is shown that the growth rate of SWNTs was large during the initial few minutes of growth, however the quality of the tubes was low owing to the formation of many defects. Long term growth may favor the formation of tubes with high quality and high yield, but the introduction of other forms of carbon (impurities) is also unavoidable. There was a balance between the increase in yield and quality and sacrifice of the purity during growth of SWNTs. MgO-supported catalysts prepared by the co-precipitation method were found to be more effective for the synthesis of SWNTs than those prepared by the widely used impregnation method. The size and dispersion state of the catalyst were found to be crucial in enhancing the growth of SWNTs. In addition, growth on the surface of SWNTs over nanosized catalyst films was shown to be more favorable for the synthesis of tube products with higher quality, yield and purity.     

High‐Tg Carbazole Derivatives as Blue‐Emitting Hole‐Transporting Materials for Electroluminescent Devices

A series of dicarbazolyl derivatives bridged by various aromatic spacers and decorated with peripheral diarylamines were synthesized using Ullmann and Pd‐catalyzed C–N coupling procedures. These derivatives emit blue light in solution. In general, they possess high glass‐transition temperatures (T_g > 125 °C) which vary with the bridging segment and methyl substitution on the peripheral amine. Double‐layer organic light‐emitting devices were successfully fabricated using these molecules as hole‐transporting and emitting materials. Devices of the configuration ITO/HTL/TPBI/Mg:Ag (ITO: indium tin oxide; HTL: hole‐transporting layer; TPBI: 1,3,5‐tris(N‐phenylbenzimidazol‐2‐yl)benzene) display blue emission from the HTL layer. The EL spectra of these devices appear slightly distorted due to the exciplex formation at the interfaces. However, for the devices of the configuration ITO/HTL/Alq₃/Mg:Ag (Alq₃ = tris(8‐hydroxyquinoline)aluminum) a bright green light from the Alq₃ layer was observed. This clearly demonstrates the facile hole‐transporting property of the materials described here.