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- Bolton, Kim, et al.
(författare)
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Carbon Nanotube Growth Mechanisms
- 2007
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Ingår i: Proceedings of Diamond 2007, the 18th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide.
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Konferensbidrag (refereegranskat)abstract
- We have used a variety of computational methods to study key aspects of single-walled carbon nanotube (SWNT) growth. Molecular dynamics (MD) studies based on an empirical force field showed; for example; why SWNT growth occurs in a temperature window and why; for 1-2 nm catalyst particles; the SWNT diameter varies linearly with the size of the particle. In addition; the liquid or solid phase of the catalyst particle is strongly dependent on particle size; and smaller particles (< 1.5 nm) are liquid at typical chemical vapor deposition temperatures whereas larger particles (> 5 nm) are solid. The phase of particles of intermediate sizes depends on the exact temperature and on their carbon content. The effect of substrates on metal-carbide properties and SWNT growth has been studied by combing density functional (DFT) and MD methods. A major effect of flat; inert substrates is to flatten the catalyst particles thereby increasing their melting points. DFT has also been used to study the catalyst-SWNT interaction which is critical for the growth of long SWNTs; and is also being used to study the importance of the SWNT cap structure on its chirality. This knowledge is important; for example; when using SWNTs as seeds for the growth of longer nanotubes.
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| 4. |
- Larsson, Andreas, et al.
(författare)
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Modelling of Carbon Nanotube Catalytic Growth
- 2008
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Konferensbidrag (refereegranskat)abstract
- Carbon nanotubes (CNTs) have; due to their remarkable mechanical; electronic and thermal properties; many suggested uses; and have even been demonstrated as interconnects and nano-transistors in laboratory built devices [1-4]. The reason CNTs are not yet incorporated into electronics is due to growth control and placement issues. With present day state-of-the-art techniques it is not possible to grow CNTs with only one property (i.e. either all metallic or all semiconducting); which presents the first and principal hurdle for the utilisation of CNTs in semiconductor industry. It is; however; possible to grow CNTs of a certain type (multi-walled; double-walled; or single walled); within a rather narrow diameter distribution. It is also well understood how the orientation of the honey-comb structure relative to the CNT axis determines the property of the CNT itself. The problem lies in realizing growth of CNTs with control over this internal graphene structuring. We have performed first-principles calculations of how single-walled carbon nanotubes (SWNTs) bond with different metal nanoparticles explaining why the traditional catalysts (Fe; Co; Ni) are more successful than other metals (Cu; Pd; Au) [5]; and how this realization relates to new nanocomposite catalyst particles (Cu/Mo) [6]. We will present our contribution to understanding the mechanism of catalytic CNT growth; since it is only through better knowledge that property-controlled growth of CNTs can be achieved
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| 5. |
- Larsson, Peter O., et al.
(författare)
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A detailed look at the catalytic action of transition metal atom dopants in MgH2 nanoclusters
- 2008
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Konferensbidrag (refereegranskat)abstract
- Magnesium hydride (MgH2 ) is a candidate for solid-state hydrogen storage applications. In this work; hydrogen desorption from transition metal doped MgH2 clusters of approximately 1 nm was investigated by density functional theory (PBE functional and Gaussian basis sets). It was found that transition metals were more stable at the surface than in the center of the cluster and that desorption energies of hydrogen atoms bound to such surface doped transition metals were significantly lowered. It was furthermore observed how transition metals attract hydrogens to keep at least four hydrogen atoms coordinated even when the total hydrogen content of the cluster decreases. This effect is associated with migration of the transition metal atoms from the surface sites to the interior sites during the dehydrogenation process; releasing more hydrogen as they diffuse. This diffusion mechanism may account for the fact that a small amount of catalysts is sufficient to improve the kinetics of MgH2 .
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| 8. |
- Pikkarainen, Harri V S, et al.
(författare)
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On-line solid debris analysis of oil using vision technology on open computing platform
- 2009
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Ingår i: 6th International Conference on Condition Monitoring and Machinery Failure Prevention Technologies 2009. - 9781618390097 ; , s. 320-331
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Konferensbidrag (refereegranskat)abstract
- This article describes a case-study related to on-line condition monitoring measurements in process industry. A platform for on-line, real-time and remotely operated condition monitoring has been developed. The system consists of an open source based embedded and cost effective DSP computing platform, a machine vision sensor for solid debris analysis of oils, and interfaces for other measurement technologies (e.g. vibration analysis and/or temperature measurements). In addition, the platform is equipped with data transmission interface that enables remote operation and control. Real-time analysis of solid particles in oil is useful in many preventive condition monitoring applications, for example, in the lubrication circuit of a paper machine or with cold rolling lubrication oils. In the case of a paper machine the generated information can be used to pinpoint upcoming failures in the machine elements (e.g. bearings, gears etc.). Whereas in the case of cold rolling applications the information is useful to prevent quality problems in the rolled metal product. In the both applications the presented system enables also monitoring failures in the filtration system. Preliminary results and designs show that the system is able to detect and analyse size and shape for particles larger than 50 micrometers continuously with a frame rate of 5 Hz from the oil flow volume of 13.8 ml/s and flow speed of 60 mm/s. The system is in progress of being further developed in collaboration with the industry. Easy integration of different sensors and real-time measurements make the system a powerful tool for making maintenance decisions in process industry
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| 9. |
- Barcot, Ana, et al.
(författare)
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Stormwater Uptake in Sponge-Like Porous Bodies Surrounded by a Pond: A Fluid Mechanics Analysis
- 2023
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Ingår i: Water. - : MDPI. - 2073-4441. ; 15:18
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a previously published model for the water up take of stormwater in sponge-like porous bodies by the group is further developed. This is done by investigating the highest-performing model and considering the water uptake from the surroundings of a pond and rain-infiltrated soil. This implies that water uptake from impermeable to partially permeable surfaces is examined. Hence, the following cases are considered: (1) impervious bottom surface and no precipitation, (2) impervious bottom surface with precipitation, (3) permeable soil with no precipitation, and (4) permeable soil with precipitation. A mathematical model covering all these cases is presented, where the governing equations are the mass conservation and Darcy’s law together with an assumption of a sharp wetting front being a first-order approximation of the complete Richard’s equation. Results for the water uptake height, pond depth, and wetting front are computed numerically and plotted against time. Analytical solutions are also presented in certain cases, and critical values are obtained. The parametric study includes variations in the ratio of the model- to the surrounding ground surface area, initial pond depth, precipitation, and soil characteristics. To exemplify, the time it takes to absorb the water from the pond after a precipitation period is presented. The results are related to the Swedish rainfall data of 1 h duration with a return period of 10 years. When evaluating efficiency, the focus is on the absorption time. Results vary considerably, demonstrating a general trend that with soil infiltration, the water absorption rate is higher. For most cases, the considered water amount is absorbed completely, although depending on the parameters and conditions. These results serve to optimize the model for each of the cases. The main focus of the research lies in the theoretical aspect.
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| 10. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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A dual-lattice hydrodynamic-thermal MRT-LBM model implemented on GPU for DNS calculations of turbulent thermal flows
- 2023
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Ingår i: International journal of numerical methods for heat & fluid flow. - : Emerald Group Publishing Limited. - 0961-5539 .- 1758-6585. ; 33:5, s. 1703-1725
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Tidskriftsartikel (refereegranskat)abstract
- PurposeThe purpose of this paper is to present a fast and bare bones implementation of a numerical method for quickly simulating turbulent thermal flows on GPUs. The work also validates earlier research showing that the lattice Boltzmann method (LBM) method is suitable for complex thermal flows.Design/methodology/approachA dual lattice hydrodynamic (D3Q27) thermal (D3Q7) multiple-relaxation time LBM model capable of thermal DNS calculations is implemented in CUDA.FindingsThe model has the same computational performance compared to earlier publications of similar LBM solvers. The solver is validated against three benchmark cases for turbulent thermal flow with available data and is shown to be in excellent agreement.Originality/valueThe combination of a D3Q27 and D3Q7 stencil for a multiple relaxation time -LBM has, to the authors’ knowledge, not been used for simulations of thermal flows. The code is made available in a public repository under a free license.
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