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- Andres, Britta, et al.
(author)
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Characterization of nanographite and graphene produced in a high-pressure homogenizer
- 2014
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In: Graphene Week 2014.
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Conference paper (peer-reviewed)abstract
- Supercapacitor electrodes are often made of porous carbon materials such as activated carbon, but also graphene was frequently used as active electrode material. Graphene can be produced by mechanical exfoliation, chemical exfoliation, chemical vapor deposition or other elaborate methods. These techniques are relatively expensive and produce small quantities only. Recently we presented a method to produce nanographite and graphene by mechanical exfoliation of graphite in a high-pressure homogenizer. In our contribution “Large-scale production of graphene” by Nicklas Blomquist we suggest to optimize the geometry of the shear zone and increase the feeding pressure to obtain a higher yield.In this study we evaluated the influence of these process optimizations on the structural and electrical properties of the nanographite-graphene mixture. The produced dispersions were characterized in terms of particle size and shape by using a particle size analyzer, a transmission electron microscope (TEM) and an atomic force microscope (AFM). In order to analyze the performance of the produced material as electrodes for supercapacitors, electrodes were produced by vacuum filtration. The electrodes were studied by sheet-resistance and capacitance measurements. Furthermore, the structure of the electrode surface and the cross section of the electrode were visualized by using a scanning electron microscope (SEM).Comparisons with previously produced nanographite-graphene dispersions showed an increase in yield of the exfoliated nanomaterials. The optimized shear zone increased the production of nanosized particles and flakes and enhanced the material quality.
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- Antona, Jacobo, 1981, et al.
(author)
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Correlation of Global Head and Brain Tissue Injury Criteria to Experimental Concussion derived from Monkey Head Trauma Experiments
- 2013
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In: IRCOBI Conference. - 2235-3151. ; :IRC-13-55, s. 509-522
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Conference paper (peer-reviewed)abstract
- A series of 24 frontal head traumatic impacts on macaques carried out in the past were simulatedwith a validated finite element model of the specimens. From these simulations, brain tissue response and headaccelerations were extracted. Based on the accelerations, global head injury criteria were calculated.Correlation between the brain tissue mechanical parameters, the global head injury criteria and the concussionscored in the experiments were analyzed. Based on this analysis, global head injury criteria that best correlatewith concussion score for frontal impacts were identified and injury risk functions for brain tissue that can beused for human FE models are proposed. In addition, the new results were compared to a previous study basedon simulations of 19 occipital head impacts from the same data source.
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- Bark, Göran, 1941, et al.
(author)
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On some physics to consider in numerical simulation of erosive cavitation
- 2009
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In: 7th International Symposium on Cavitation.
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Conference paper (peer-reviewed)abstract
- This paper discusses some hydrodynamic mechanisms in erosive cavitation, which are all important to capture, and consider, when assessing the risk of erosion, by numerical simulations or model tests in a cavitation tunnel. Focus is put on the visual appearance and underlying physics of the mechanisms with the aim to explain main developments towards erosive cavitation. From this knowledge it is possible to conclude about requirements on numerical and experimental prediction or analysis methods to be used in assessment of erosion risk, and to elucidate links between small-scale erosive collapses and global flow, the latter described by engineering parameters as pressure distributions etc. Based on physics as well as practical engineering aspects a decomposition of the cavitation process is discussed and in particular we introduce the concept of primary and secondary cavitation in order to put emphasis on a particular class of mechanisms: cavitation created in the secondary flow field, governed by e.g. a shedding or collapse of the primarily created cavity, typically in interaction with the global flow. These secondary cavities are usually erosive and have previously not been generally described in the literature. A basic example of secondary cavitation is a rebound controlled by compression of cavity content and liquid. Occurring in a flow close to a body asymmetry typically appears and the simple rebound becomes disturbed by vortex formation and a “generalized” rebound develops. An example of a generalized rebound is the “vortex group cavitation” for which a hypothesis is suggested. Viscous shear is assumed to redistribute vortex motion initiated by collapse asymmetry and acoustic interaction is assumed to control part of the development. The role of cloud cavitation is partly reconsidered. Despite the fact that cloud cavitation is demonstrated, by theory as well as experiments, including the present, to be able to generate the highest single collapse pulses, the focusing of collapse energy is often rather dispersed in space as well as time and the erosion is correspondingly reduced. In a number of cases it is demonstrated that the most severe erosion occurs when a small cloud is synchronized, and thus gains collapse energy, by the collapse of a mainly glassy sheet. Account of the glassy collapse seems very important. An underlying part of the discussion is how the described cavitation mechanisms influence numerical simulation of cavitation nuisance. Different numerical approaches, as LES, RANS or Euler may generate adequate results, a crucial factor being high resolutions.
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