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[en] A melting curve maximum in cesium which is associated with a continuous 6s to 5d electronic transition cannot be explained by conventional Lindemann model. A new melting equation which reduces to the Kennedy equation for normal melting solids when the energy gap ΔE is large has been derived. This equation places melting maximum in cesium at 15 kbar, in fair agreement with the experimental value of 17 kbar. At about 200 kbar, the metallic radius of rubidium approaches that of yttrium (4d1) supporting the prominent d-band character of rubidium at high pressures. Little is known about the change in character of the d-bonding as a function of the metallic radius. High pressure studies on alkali metals may provide valuable information in this area. (auth.)
[en] Highlights: • Hydrogen bonds break down in water adsorbed on diamond or nanodiamond, causing. • Contraction of molar volume up to 50%. • Depression of freezing point. • Depression of evaporation temperature and heat. • Blue shift of IR spectra. The molar volume of water adsorbed on the surface of micro- and nano-powders of diamond was determined from the measured densities of dry and variously hydrated diamond powders. This volume decreases near the diamond surface and in the first adsorbed monolayer can be as low as half that of bulk water. This effect can be attributed to breakdown of the hydrogen bond network, as confirmed by IR spectroscopy and calorimetrical data for crystal hydrates of diamond.
[en] Bi-22l2 tubes for fault current limiter (FCL) were fabricated by centrifugal melting process. SrSO4 (10 wt. %) was added to Bi-2212 powder to lower the melting point of Bi-22l2 and to improve the mechanical properties. The BSCCO powder was completely melted at 1300 degree C using the RF furnace and then poured into rotating steel mold. The steel mold, preheated at 450 degree C - 550 degree C for 2 hour was rotated at 1020 - 2520 RPM. The solidified BSCCO tube was cooled down to room temperature in the furnace for 48 hours and separated from the mold between Bi-2212 and the mold. ZrO2 solution was used to separate it easily from the mold and Ag tape was attached in the mold inner wall of the mold to analysis electrical property. Bi-22l2 tube was often cracked when the cooling rate was high. BSCCO tubes with 70 φ x 100 mm, 50 φ x 100 mm and 30 φ x 150 mm size were fabricated by centrifugal melting process. The Jc3 of tubes with 50 φ x 100 mm x 4.0 t and 50 φ x 100 mm x 4.0 t were 178 and 74.2 A/cm2 at 77K, respectively. The processing condition for Bi-2212 tube fabrication was investigated using XRD and SEM analyses.
[en] A key property of glass forming alloys, the anomalously small volume difference with respect to the crystal, is shown to arise as a direct consequence of the soft repulsive potentials between metals. This feature of the inter-atomic potential is demonstrated to be responsible for a significant component of the glass forming ability of alloys due to the decrease in the enthalpy of fusion and the associated depression of the freezing point.
[en] An integrated model based on bond number and bond strength in a system with a cubo-octahedral structure is developed to predict the size-dependent thermal characteristics of nanoparticles. Without any adjustable parameters, this model can be used to predict the melting point and cohesive energy of low-dimensional materials, suggesting that both depend on the size and on the atomic distance. The good agreement of the theoretical prediction with the experimental and molecular dynamic simulation results confirms the validity of the cubo-octahedron in describing the thermodynamic behaviors of nanoparticles even without considering their crystalline structures. -- Highlights: ► An united model for melting point or cohesive energy of nanoparticles is established. ► Decreased cohesive energy or melting point arises from the lowered bond number. ► Good estimation of the model is obtained even nanoparticle's structure is unknown.
[en] Key to resolving the scientific challenge of the glass transition is to understand the origin of the massive increase in viscosity of liquids cooled below their melting temperature (avoiding crystallisation). A number of competing and often mutually exclusive theoretical approaches have been advanced to describe this phenomenon. Some posit a bona fide thermodynamic phase to an ‘ideal glass’, an amorphous state with exceptionally low entropy. Other approaches are built around the concept of the glass transition as a primarily dynamic phenomenon. These fundamentally different interpretations give equally good descriptions of the data available, so it is hard to determine which—if any—is correct. Recently however this situation has begun to change. A consensus has emerged that one powerful means to resolve this longstanding question is to approach the putative thermodynamic transition sufficiently closely, and a number of techniques have emerged to meet this challenge. Here we review the results of some of these new techniques and discuss the implications for the existence—or otherwise—of the thermodynamic transition to an ideal glass. (topical review)
[en] Highlights: •Sensitivity analysis for the ULOF of the PGSFR was performed using PAPIRUS. •Uncertainty propagation was performed by mapping uncertainty bands of parameters. •Distributions for fuel centerline, cladding and coolant temperatures were determined. -- Abstract: In this research, sensitivity and uncertainty analyses for 23 parameters were performed for unprotected loss of flow (ULOF) for the prototype Gen-IV sodium-cooled fast reactor (PGSFR) by using the parallel computing platform integrated for uncertainty and sensitivity analysis (PAPIRUS). Based on the development of the phenomena and model identification and ranking table (PIRT), the relative importance of the parameters was confirmed through the sensitivity analysis. The objective of the global uncertainty analysis is to evaluate all safety parameters of the system in the combined phase space formed by the parameters and dependent variables. The uncertainty propagation was performed by mapping the uncertainty bands of the model parameters through the MARS-LMR to determine the distributions for the fuel centerline, cladding, and coolant temperatures. The results show that the uncertainty bands of the temperatures are below the melting point.