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Mazzucato, E.,Bell, R.E.,Ethier, S.,Hosea, J.C.,Kaye, S.M.,LeBlanc, B.P.,Lee, W.W.,Ryan, P.M.,Smith, D.R.,Wang, W.X.,Wilson, J.R.,Yuh, H. International Atomic Energy Agency 2009 Nuclear fusion Vol.49 No.5
<P>Various theories and numerical simulations support the conjecture that the ubiquitous problem of anomalous electron transport in tokamaks may arise from a short-scale turbulence driven by the electron temperature gradient. To check whether this turbulence is present in plasmas of the National Spherical Torus Experiment, measurements of turbulent fluctuations were performed with coherent scattering of electromagnetic waves. Results from plasmas heated by high harmonic fast waves show the existence of density fluctuations in the range of wave numbers <I>k</I><SUB>⊥</SUB>ρ<SUB>e</SUB> = 0.1–0.4, corresponding to a turbulence scale length of the order of the collisionless skin depth. Experimental observations and agreement with numerical results from the linear gyro-kinetic GS2 code indicate that the observed turbulence is driven by the electron temperature gradient. These turbulent fluctuations were not observed at the location of an internal transport barrier driven by a negative magnetic shear.</P>
Alessandro Carrozza,Federico Mazzucato,Alberta Aversa,Mariangela Lombardi,Federica Bondioli,Sara Biamino,Anna Valente,Paolo Fino 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9
Directed energy deposition is an additive manufacturing technology which usually relies on prototype machines or hybridsystems, assembled with parts from different producers. Because of this lack of standardization, the optimization of the processparameters is often a mandatory step in order to develop an efficient building process. Although, this preliminary phaseis usually expensive both in terms of time and cost. The single scan approach allows to drastically reduce deposition time andmaterial usage, as in fact only a stripe per parameters combination is deposited. These specimens can then be investigated,for example in terms of geometrical features (e.g. growth, width) and microstructure to assess the most suitable processwindow. In this work, Ti-6Al-4V single scans, produced by means of directed energy deposition, corresponding to a total of50 different parameters combinations, were analyzed, focusing on several geometrical features and relative parameters correlations. Moreover, considering the susceptibility of the material to oxygen pick-up, the necessity of an additional shieldinggas system was also evaluated, by comparing the specimens obtained with and without using a supplementary argon flow. A process window, which varies according to the user needs, was found together with a relationship between microstructureand process parameters, in both shielding scenarios.
Saeed Khademzadeh,Nader Parvin,Paolo F. Bariani,Federico Mazzucato 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.6
Micro laser sintering is a promising additive manufacturing process for production of parts with micro features and complicated geometries. Micro laser sintering of mechanically alloyed NiTi was performed in the present work. The effects of powder and laser defocusing distances and also process parameters on the surface quality of single tracks and thin walls were investigated by scanning electron microscopy and optical profilometry. A modified model was described in this research to calculate the height of thin walls produced by micro laser sintering. The experimental results showed that a high melting efficiency can be obtained when the focal point of the laser is situated 200 μm above the working plane of the specimen. Optical profilometry revealed a good agreement between the proposed model for thin wall’s height estimation and experimental results.