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          • KCI등재

            Molecular Dynamics Simulations of Plastic Material Deformation in Machining with a Round Cutting Edge

            김창주,Rhett,Mayor,Jun,Ni 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

            This paper reviews the application of the molecular dynamics simulation approach to the high-resolution visualization of the plastic material flow at the tool/workpiece interface during orthogonal cutting. MD simulation techniques have been applied to nano-scale processes, but due to restrictions in the model size and computational time, they have not been utilized to investigate processes occurring at the micro-scale. Techniques employed to extend the MD simulation techniques to the micro-scale are discussed. Preferred ranges for model parameters that provide for sufficient resolution in order to adequately describe the characteristic features of the plastic material flow, yet achieve significant reduction in the model computational times, are identified. An investigation of the plastic material flow at the tool/workpiece interface as the uncut chip thickness increases from 10% to 90% of the edge radius of the tool was undertaken. A key observation is that there is a marked variation in the geometry of the observed characteristic features, most notable being the rotation and growth of the stable built-up edge as the uncut chip thickness increases. Furthermore, the transition between the plowing and cutting regimes is observed.

          • KCI등재SCIESCOPUS

            Computational Tools and Nuclear Data for Radioprotection Studies in Low Energy Light Ions Accelerators

            P.,Sauvan,A.,Mayoral,J.,Sanz,F.,Ogando,M.,Garcia,D.,Lopez 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

            Some of the current accelerator programs such as TechnoFusion, Spiral2 or EVEDA/IFMIF will use low energy particles such as proton, deuteron and alpha. For these projects, the radioprotection studies require a more reliable prediction of the neutron and photon generated by interaction of these charged particles. In this paper, some developments to address this issue are presented. Except for proton, Monte Carlo codes such MCNPX or PHITS use built-in semi-empirical nuclear models to deal with charged particles interactions. Such models, applied to the above mentioned accelerators beam characteristics (particle type and energy), lead to unreliable prediction of secondary particle production. Consequently, there is a need to both generate accurate evaluated data libraries for light ion nuclear reactions and extend MCNPX to handle the evaluated charged particle nuclear data. The MCNPX code has been extended by the authors to handle proton, deuteron, triton and alpha nuclear data libraries. This tool is here presented and applied to analyse the reliability of available evaluated nuclear data for incident deuterons of energies those used in the abovementioned facilities (up to 40 MeV). Deuteron-induced reactions have been chosen because this particle is expected to be used in all these facilities. Concerning target material, copper has been selected as it is one the main constituents of accelerating components and beam dumps. The evaluated nuclear data are provided by the TENDL library, which is the only one available for deuterons with a wide range of target elements, including those of concern for the accelerators here considered. The testing of the TENDL nuclear data is carried out by comparing existing experimental data on thick target neutron yields for the given materials with those computed by the modified MCNPX code using TENDL cross sections. As a result, the assessment of its applicability to radioprotection studies of those accelerators is discussed.

          • SCOPUS

            UV-B absorbing compounds in present-day and fossil pollen, spores, cuticles, seed coats and wood: evaluation of a proxy for solar UV radiation

            Rozema,,J.,Blokker,,P.,Fuertes,,M.A.Mayoral,Broekman,,R. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.9

            UV-B absorbing compounds (UACs) in present-day and fossil pollen, spores, cuticles, seed coats and wood have been evaluated as a proxy for past UV. This proxy may not only provide information on variation of stratospheric ozone and solar UV in the period preceding and during the Antarctic ozone hole (1974-present day), but also on the development and variation of the stratospheric ozone layer and solar surface UV during the evolution of life on Earth. Sporopollenin and cutin are highly resistant biopolymers, preserving well in the geological record and contain the phenolic acids p-coumaric (pCA) and ferulic acid (FA). pCA and FA represent a good perspective for a plant-based proxy for past surface UV radiation since they are induced by solar UV-B via the phenylpropanoid pathway (PPP). UV-B absorption by these monomers in the wall of pollen and spores and in cuticles may prevent damage to the cellular metabolism. Increased pCAand FA in pollen of Vicia faba exposed to enhanced UV-B was found in greenhouse experiments. Further correlative evidence comes from UV-absorbing compounds in spores from 1960.2000 comparing exposure of land plants (Lycopodium species) to solar UV before and during ozone depletion and comparing plants from Antarctica (severe ozone depletion), Arctic, and other latitudes with less or negligible ozone depletion. Wood-derived compounds guaiacyl (G), syringyl (S), and p-hydroxyphenyl (P) are produced via the PPP. The proportions of P, G, and S in the lignin differ between various plant groups (e.g. dicotyledons/monocotyledons, gymnosperms/angiosperms). It is hypothesized that this lignin composition and derived physiological and physical properties of lignin (such as tree-ring wood density) has potential as a proxy for palaeo-UV climate. However validation by exposure of trees to enhanced UV is lacking. pCAand FA also form part of cutin polymers and are found in extant and fossil Ginkgo leaf cuticles as shown by thermally-assisted hydrolysis and methylation (THM)-pyrolysis-GC-MS. Potentially, the time scale for reconstruction of ozone column thickness and UV-B based on the UAC UV proxy may be decadal, centennial, millennial and possibly billenial. For further development of the UACs and pCA and FA-based UV proxy, it is necessary to obtain the UV dose.response (content of UACs, pCA and FA in sporopollenin and cutin) relationships for validation, based on outdoor UV radiation manipulations experiments with plants, and comparative analysis of stored plants (herbaria) or fossil material of the same or related plant species.

          • KCI등재

            Pursuit of optimal synthetic conditions for obtaining colloidal zero-valent iron nanoparticles by scanning pulsed laser ablation in liquids

            Ruth,Lahoz,Eva,Natividad,Álvaro,Mayoral,Christian,Rentenberger,Daniel,Díaz-Fernández,Eduardo,J.,Félix,Leonardo,Soriano,Wolfgang,Kautek,Oscar,Bomati-Miguel 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-

            Liquid-Assisted Pulsed Laser Ablation (LA-PLA) is a promising top-down method to directly synthesizecolloidal dispersions of nanoparticles in a eco-friendly manner. However, the role of LA-PLA synthesisparameters is not yet fully agreed. This work seeks to optimize the production of nanoscale zero-valentiron (nZVI) particles suitable for biomedical or environmental applications using nanosecond LA-PLA oniron targets with different ablation media, laser and target scanning parameters. The use of alcohols assolvents produces iron-iron oxide core-shell nanoparticles with amorphous cores, except for a smallcrystalline fraction corresponding to the biggest core sizes. Decreasing carbon chain length andcomplexity leads to a thinning of the carbonaceous material coatings and an increase of the colloidalstability and the nanoparticle productivity. Moreover, a decrease of solvent density and surface tensionallows obtaining reduced sizes and polydispersity values. Among, laser and scanning parameters, thepulse accumulation per spot displayed a clear effect in boosting size and productivity. As main outcome,aqueous dispersions with suitable colloidal properties are obtained, either by transferring to water ofoptimized nZVI particles produced in ethanol, or by direct formation of nZVI particles and in situ coatingwith hydrophilic molecules in aqueous solutions of these molecules.

          • SCIESCOPUSKCI등재

            EVOLUTION OF THE GALACTIC DISK: FOCUS ON THE SOLAR NEIGHBOURHOOD

            ANDERSEN,J.,NORDSTROM,B.,OLSEN,E.,H.,MAYOR,M.,PONT,F. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1

            The solar neighbourhood is the starting point for studies of the structure and evolution of the Galactic disk. Yet, our knowledge of the relative frequencies, distances, ages, chemical abundances, velocities, and birthplaces of the nearby stars is severely incomplete. We have determined complete, homogeneous, and precise such data for a kinematically unbiased sample of $\~$12,000 local F and G dwarf stars and describe a first, significant result from it.

          • KCI등재SCOPUS
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