ABSTRACT
The critical point is a fixed point in finite-size scaling. To quantify the behavior of such a fixed point, we define, at a given temperature and scaling exponent ratio, the width of scaled observables for different sizes. The minimum of the width reveals the position of the fixed point, its corresponding phase transition temperature, and scaling exponent ratio. The value of this ratio tells the nature of the fixed point, which can be a critical point, a point of the first-order phase transition line, or a point of the crossover region. To demonstrate the effectiveness of this method, we apply it to three typical samples produced by the three-dimensional three-state Potts model. Results show the method to be more precise and effective than conventional methods. Finally, we discuss a possible application at the Beam Energy Scan program of the Relativistic Heavy Ion Collider.
ABSTRACT
Magnesium hydride and its compounds have a high hydrogen storage capacity and are inexpensive, and thus have been considered as one of the most promising hydrogen storage materials for on-board applications. Nevertheless, Mg/MgH2 systems suffer from great drawbacks in terms of kinetics and thermodynamics for hydrogen uptake/release. Over the past decades, although significant progress has been achieved with respect to hydrogen sorption kinetics in Mg/MgH2 systems, their high thermal stability remains the main drawback, which hinders their practical applications. Accordingly, herein, we present a brief summary of the synthetic routes and a comprehensive overview of the advantages and disadvantages of the promising strategies to effectively tune the thermodynamics of Mg-based materials, such as alloying, nanostructuring, metastable phase formation, changing reaction pathway, and nano Mg-based composites. Among them nanostructuring and metastable phase formation, which have the superiority of changing the thermodynamics without affecting the hydrogen capacity, have attracted increasing interest in this field. To further optimize the hydrogen storage performance, we specially emphasize novel nanostructured materials, which have the advantage of combining alloy engineering, nanostructuring and the synergistic effect to change the thermodynamics of Mg/MgH2 to some extent. Furthermore, the remaining challenges and the directions of further research on MgH2, including the fundamental mechanism of the Mg-H bond instability, advanced synthetic routes, stabilizing nanostructures, and predicting novel composite materials, are proposed.
ABSTRACT
Significant improvements in the hydrogen sorption properties of the Li-Mg-N-H system have been achieved by adding a small amount of LiBH4. Herein, the hydrogen storage properties of the 1.1MgH2-2LiNH2-0.1LiBH4 system are further enhanced by addition of LaNi5-based (LaNi3.8Al0.75Mn0.45, LaNi4.5Mn0.5, LaNi4Co) alloy hydrides. The refinement of the Li-Mg-B-N-H particles and the metathesis reaction are facilitated by adding LaNi5-based alloy hydrides during the ball milling process. The addition of LaNi5-based alloy hydrides can enhance the hydrogen sorption kinetics, reduce the dehydrogenation temperature and promote a more thorough dehydrogenation of the Li-Mg-B-N-H system. The LaNi5-based alloy hydrides are involved in hydrogen de/hydrogenation reaction. Among the three alloys, LaNi4.5Mn0.5 makes the most obvious improvement on the reaction kinetics, and the dehydrogenation peak temperature is reduced by 12 °C, while the activation energy is reduced by 11% with 10 wt% LaNi4.5Mn0.5 addition. The weakening of the N-H bond and the homogeneous distribution of the LaNi5-based alloy hydrides in the Li-Mg-B-N-H composite have important roles in the reduction of the desorption barrier and the kinetics enhancement.
ABSTRACT
Two spatial correlation patterns, fixed-to-arbitrary and neighboring bin correlation patterns, are suggested. It is demonstrated that these patterns present scale-independent and distinguishable measures for correlated and uncorrelated random multiplicative cascade processes. Their application to very high multiplicity events in relativistic heavy ion collisions is discussed.
