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Computer Simulation of Particle Rearrangement in the Presence of Liquid
Lee, S . M .,Chaix, J . M .,Martin, C . L .,Allibert, C . H .,Kang, S . J . L . 대한금속재료학회(대한금속학회) 1999 METALS AND MATERIALS International Vol.5 No.2
A model was developed to describe the motion of particles which are connected by liquid bridges. The model takes into account capillary force, particles inertia, viscous drag of liquid, and elastic collision. Below a critical thickness of the liquid film between particles, the liquid is assumed to be in a visco-elastic state and follows the Maxwell model. For a single pair of particles, the model predicts that, as viscosity increases, the first particle contact occurs later, and subsequent particle bounce is weaker. In the case of planar arrays of 5000 particles, the particles agglomerate, generating pores between particle clusters during the rearrangement. The final density obtainable by particle rearrangement increases as viscosity increases. This result is attributed to the suppression of fast local densification in the case of high viscosity. The implications and limitations of the present analysis are also presented and discussed.
Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser
Gerber, S.,Yang, S.-L.,Zhu, D.,Soifer, H.,Sobota, J. A.,Rebec, S.,Lee, J. J.,Jia, T.,Moritz, B.,Jia, C.,Gauthier, A.,Li, Y.,Leuenberger, D.,Zhang, Y.,Chaix, L.,Li, W.,Jang, H.,Lee, J.-S.,Yi, M.,Dakovs American Association for the Advancement of Scienc 2017 Science Vol.357 No.6346
<P><B>A deeper look into iron selenide</B></P><P>In the past 10 years, iron-based superconductors have created more puzzles than they have helped resolve. Some of the most fundamental outstanding questions are how strong the interactions are and what the electron pairing mechanism is. Now two groups have made contributions toward resolving these questions in the intriguing compound iron selenide (FeSe) (see the Perspective by Lee). Gerber <I>et al.</I> used photoemission spectroscopy coupled with x-ray diffraction to find that FeSe has a very sizable electron-phonon interaction. Quasiparticle interference imaging helped Sprau <I>et al.</I> determine the shape of the superconducting gap and find that the electron pairing in FeSe is orbital-selective.</P><P><I>Science</I>, this issue p. 71, p. 75; see also p. 32</P><P>The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a “coherent lock-in” measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure. Comparison with theory reveals a strong enhancement of the coupling strength in FeSe owing to correlation effects. Given that the electron-phonon coupling affects superconductivity exponentially, this enhancement highlights the importance of the cooperative interplay between electron-electron and electron-phonon interactions.</P>
Ozer O.,Missiaen J.M.,Pascal C.,Lay S.,Chaix J.M.,Mitteau R. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Processing of W-Cu graded materials from attritor-milled W-CuO mixtures is described. The powder reduction steps are investigated by TG and XRD analyses and by microstructural observations (SEM, TEM). Sintering of reduced powder with different compositions is analysed by dilatometry. Sintering behaviour of the graded component processed by co-compaction of a 10/20/30wt%Cu multi-layer material is briefly discussed. Liquid Cu migration is observed and smooths the composition gradient. Perspectives to control this migration are discussed.