No abstract

No abstract

No abstract

No abstract

Carbon nanotube arrays were prepared by chemical vapor deposition (CVD) of hydrocarbon gas on various substrates. The effect of substrates on the growth, morphology and structure of carbon nanotubes were investigated. Aligned carbon nanotubes with high density and purity were achieved by CVD on bulk silica substrate. On the film-like substrates, very long carbon nanotubes of length ∼ 2 mm were produced, which is an order of magnitude longer (1 mm vs. 100 µm) than that described in most previous reports. Highresolution transmission electron microscopy (HRTEM) investigation illustrates that these carbon nanotubes are well graphitized and very pure. The tubes are typically consist of several to tens of concentric shells of carbon sheets with spacing about 0.34 nm. Micro-Raman spectroscopy has been carried out to detect the microstructures of CNT. The observed ratio of the integrated intensity of D and G band was found different from that of carbon nanotubes produced by arc-discharge method and pyrolytic graphite (PG). The resonance properties and higher order Raman bands are also different from other forms of carbon. With the help of the results of SEM and HRTEM the origination of the broader band structure were discussed.PACS. 68.65.+g Low dimensional structures (superlattices, quantum well structures, multilayers): structure, and nanoelectronic properties -81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD etc.) -81.20.Fw Sol-gel processing, precipitation -61.16.Bg Transmission, reflection and scanning electron microscopy (including EBIC)

No abstract

High-field magnetization process of General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 07 Jun 2019Journal of Magnetism and Magnetic Materials 140-144 (1995) The high-field magnetization process of Sm2(Fe 1 xGax)17 compounds (x = 0-0.5) has been investigated. Substitution of Ga for Fe leads to an increase of the spin reorientation temperature. A tentative spin phase diagram is proposed. The magnetization of magnetically aligned samples was measured at 4.2 K in quasi-static fields up to 21 T.

The anode recirculation mode is increasingly being adopted in today’s fuel cell systems. The recycling of hydrogen gas can effectively improve fuel utilization and the wider economy. However, using the purge strategy for the recirculation exhaust has a significant impact on the operational performance and economic efficiency of fuel cell systems.Experiments have shown that, when the purge interval increases from 6 s to 10 s, the recirculation pump power increases by about 20%, the nitrogen content in the exhaust gas increases, and the stack voltage shows a 10 V attenuation. The accumulation of nitrogen permeation in the anode circuit leads to the degradation of the fuel cell performance. Therefore, it is necessary to discharge the accumulated nitrogen through the purge valve in a timely manner. However, opening the exhaust valve with excessively high frequency can result in the unreacted hydrogen being discharged, which reduces the economic efficiency of the fuel cell. This paper is based on the principle of mass conservation and models each subsystem of the anode circuit in the recirculation pump mode of the fuel cell separately, including the proportional valve model, the hydrogen consumption model of the fuel cell, the nitrogen permeation model of the fuel cell, the neural network model of the circulating pump, and the purge valve model. These submodels are integrated to construct a nitrogen content observer for the hydrogen circuit, which can estimate the nitrogen content. The accuracy of the model is validated through experimental data. The estimation error is less than 5.5%. The nitrogen content in the anode circuit can be effectively estimated, providing a model reference for purge operations and improving hydrogen utilization.