Fusion (physique) | EPFL Graph Search

thumb|Glaçons fondant à température ambiante (animation accélérée). En physique et en métallurgie, la fusion est le passage d'un corps de l'état solide vers l'état liquide. Pour un corps pur, c’est-à-dire pour une substance constituée d'atomes ou molécules tous identiques, la fusion s'effectue à température constante dite point de fusion. La température de fusion ou de solidification d'un corps pur, appelée « point de fusion », est une constante qui dépend très peu de la pression (contrairement à la température d'ébullition, voir diagramme de phase). Si la température de fusion d'un corps pur est une constante physique, sa température de solidification peut, pour sa part, varier. L'eau par exemple peut geler à des températures de l'ordre de -39 °C dans l'atmosphère (surfusion de l'eau). Par contre, la température de fusion d'un mélange de corps purs (voir Diagramme de phase > Diagramme binaire et ternaire ) s'effectue sur une plage de température (sauf pour un eutectique), et

Enhanced Electrical Conductivities of Complex Hydrides Li-2(BH4)(NH2) and Li-4(BH4)(NH2)(3) by Melting

Yu Zhou

The electrical conductivities of complex hydrides Li2(BH 4)(NH2) and Li4(BH4)(NH 2)3 consisting of (BH4)- and (NH2)- anions are investigated focusing on their low melting temperatures (365 K for Li2(BH4)(NH2) and 490K for Li4(BH4)(NH2)3). The two hydrides show lithium fast-ion conductivities of about 1 × 10 -4 S·cm-1 at room temperature. After melting, the total ion conductivities OfLi2(BH4)(NH2) and Li4 (BH 4)(NH2)3 reach 6 × 10-2 S·cm-1 (378 K) and 2 x 10-1 S·cm -1 (513 K), respectively. The crystal structure and local atomistic structures closely correlated with the lithium ion conduction before and after melting are also discussed. ©2011 The Japan Institute of Metals.

2011

Black carbon and dust in the Third Pole glaciers: revaluated concentrations, mass absorption cross-sections and contributions to glacier ablation

Yang Li, Xinyang Li, Julia Schmale, Wei Yang

In snow and ice, light-absorbing particles (LAPs), such as black carbon (BC) and dust, accelerate the melting of Third Pole glaciers (TPGs). In this study, we revaluated LAP concentrations in the snow pits of TPGs (SP-TPGs), measured LAP mass absorption cross-sections (MACs), and simulated their effects on glacier darkening and melting based on the Spectral Albedo Model for Dirty Snow and a surface energy and mass balance model. The results indicated that because of their short distances to emission sources, the average BC concentrations measured in snow pits in the periphery of Third Pole were much higher than those measured in the inland Tibetan Plateau, and the average dust concentrations generally decreased from north to south. The average MACs of BC in the SP-TPGs varied from 3.1 to 7.7 m2 g−1 at 550 nm, most of the average spectral values were comparable in the visible and near-infrared bands to those calculated by Mie theory, except those in Urumqi Glacier No. 1 (UR), Syek Zapadniy Glacier (SZ), and Laohugou Glacier No.12 (LH), while the average spectral MACs of dust in the SP-TPGs were considerably smaller in magnitude than most of the variations measured in other regions. Compared with the pure snow surfaces, BC and dust played comparable roles in reducing albedo in UR, SZ, LH, and Renlongba Glacier, whereas BC was the most prominent absorber in the other glaciers. The combined effect of BC and dust accelerated melting by 30.4–345.9 mm w.e. (19.7–45.3% of the total mass balance) through surface albedo darkening (0.06–0.17) and increased radiation absorption (25.8–65.7 W m−2) within one month of the ablation season. This study provides a new data set of LAP concentrations and MACs and helps to clarify the roles of these factors in the cryospheric environment of the Third Pole.

2021

Full Phase Diagram of Active Brownian Disks: From Melting to Motility-Induced Phase Separation

Pasquale Digregorio, Ignacio Pagonabarraga Mora

We establish the complete phase diagram of self-propelled hard disks in two spatial dimensions from the analysis of the equation of state and the statistics of local order parameters. The equilibrium melting scenario is maintained at small activities, with coexistence between active liquid and hexatic order, followed by a proper hexatic phase, and a further transition to an active solid. As activity increases, the emergence of hexatic and solid order is shifted towards higher densities. Above a critical activity and for a certain range of packing fractions, the system undergoes motility-induced phase separation and demixes into low and high density phases; the latter can be either disordered (liquid) or ordered (hexatic or solid) depending on the activity.

2018

Black carbon and dust in the Third Pole glaciers: revaluated concentrations, mass absorption cross-sections and contributions to glacier ablation

Yang Li, Xinyang Li, Julia Schmale, Wei Yang

2021