Dielectric breakdown strength (E-bd) defines the reliability and energy density of functional oxide ceramics in high-field applications. Here, we demonstrate that Spark Plasma Texturing (SPT) dramatically enhances E-bd in Ba0.6Sr0.4TiO3 (BST) ceramics. Dynamic thermo-mechanical coupling during SPT produces a near-fully dense, highly homogeneous microstructure with ultra-fine grains (0.44 mu m), resulting in E-bd of up to 515 kV & centerdot;cm(-1), which is more than twice higher than 200 kV & centerdot;cm(-1) for conventionally sintered ceramics and one third higher than 384 kV & centerdot;cm(-1) for ceramics prepared by standard Spark Plasma Sintering. This enhancement is of extrinsic origin and grain-boundary-controlled: impedance spectroscopy reveals elevated activation energies and resistive grain-boundary barriers that suppress long-range charge migration, while the intrinsic electronic structure with bandgap similar to 3.0 eV remains unchanged. SPT is thus established as an effective route for grain-boundary engineering in functional oxides, enabling high-reliability energy storage and tunable radio-frequency devices.
We examine the relationship between fiscal rules and capital controls across 100 countries spanning 1995 to 2019. Employing entropy balancing and alternative estimation techniques, our findings show that the adoption of fiscal rules is significantly associated with reduced reliance on capital control measures. The estimated association is notably stronger in developed countries. These results remain robust when addressing potential omitted variable bias, employing alternative estimation approaches, and accounting for structural factors. A heterogeneity analysis reveals that fiscal rules are associated with reduced controls on both capital inflows and outflows. From a dynamic perspective, fiscal rules are also associated with reduced capital controls across short, medium, and long-term horizons. Investigating the underlying mechanisms, the results indicate that fiscal rule adoption is associated with reduced capital control practices through three channels: enhancing sovereign credit ratings, containing inflation, and strengthening fiscal balances. Overall, these findings suggest that implementing stringent fiscal rules may facilitate the reduction of capital controls, thereby potentially fostering greater economic freedom and deepening international financial integration.
Composite materials are promising magnetic materials for achieving the challenges of magnetic cooling, offering a broader range of properties compared to single-phase materials. In this study we investigate the magnetocaloric properties of composite materials with the general formula (La0.67Ca(0.33-x)SrₓMn0.98Ni0.02O3)1-y/(La0.67Ca0.33MnO3)y (with y values of 1/3 and 1/2, where the Sr-doped manganite phase is a 50/50 mixture of x = 0.1 and x = 0.2), synthesised using the sol–gel Pechini method. These composites exhibit broad magnetic entropy changes (ΔS) due to the synergistic interaction between their constituent phases, which is an essential characteristic for efficient magnetic refrigeration. To quantitatively assess and optimise their magnetocaloric performance, artificial neural network (ANN) modelling was employed. This offers a novel computational approach for predicting and tuning ΔS in such complex material systems. The model performed exceptionally well, achieving a coefficient of determination (R2) ranging from 0.990 to 0.996 around the magnetic transition temperature for the composition with y = 1/3, and from 0.990 to 0.995 for the composition with y = 1/2. This demonstrates strong agreement with experimental data across the 1–5 T magnetic field range. Furthermore, the model produced remarkably low values for the mean squared error (MSE), mean absolute error (MAE), and root mean square error (RMSE). This underscores its precision in identifying optimal parameters with minimal deviation. The predicted ΔS values were found to align closely with experimental measurements, highlighting the potential of AI-driven modelling to accelerate the development of advanced materials for solid-state refrigeration. This study therefore provides a standardised framework for applying machine learning techniques to the design and characterisation of magnetocaloric materials, paving the way for more efficient and environmentally sustainable cooling technologies.
Hydrogen is gaining increasing global interest as a sustainable energy vector due to its ecological advantages and its potential to support the energy transition. However, despite its promising potential, several technical challenges remain, particularly concerning storage technologies. In this study, we explored the structural, mechanical, thermodynamic, electronic, and hydrogen storage properties of the complex hydrides Li3XH8 (X = Al, Ti and Zr) using first-principles calculations. The obtained negative formation enthalpies indicate favorable thermodynamic stability for these materials. The analysis of mechanical properties highlights a ductile character for Li3AlH8 and Li3ZrH8 , while Li3TiH8 exhibits a more fragile behavior, as confirmed by the B/G ratio values. The study of the Poisson's ratio and the nature of the bonds reveals a predominantly ionic interaction in Li3AlH8 and Li3ZrH8, whereas Li3TiH8 shows a covalent characteristic. The Born stability criteria as well as the phonon dispersion curves confirm that these hydrides are both dynamically and mechanically stable. On the electronic front, all three materials exhibit a metallic behavior, which could positively influence their hydrogen storage performance. In terms of storage capacity, these materials display remarkable values: Li3AlH8 has a gravimetric capacity of 12.53 wt%, while Li3TiH8 and Li3ZrH8 present 9.44 wt% and 6.24 wt%, respectively. The desorption temperatures obtained are 583.23 K for Li3AlH8, 693.97 K for Li3TiH8, and 695.44 K for Li3ZrH8, Although these desorption temperatures exceed the operational range recommended by the DOE (233-333 K), strategies such as controlled doping, strain engineering, or composite formation could help lower the release temperature to more practical levels. Overall, these results suggest that Li3AlH8 stands out as a promising candidate for solid-state hydrogen storage, owing to its high capacity and favorable thermodynamic properties.
We develop a covariant Hamiltonian formulation of the Mathisson-Papapetrou-Tulczyjew-Dixon dynamics at quadratic order in spin under the Tulczyjew-Dixon spin supplementary condition (TD SSC). In four-dimensional, type-D Einstein (vacuum/Λ-vacuum) spacetimes admitting a non-degenerate Killing-Yano (KY) tensor, we reduce via a Dirac bracket to the 10-dimensional physical phase space and model the quadratic sector with a spin-induced quadrupole characterized by a deformability κ (κ=1 for black-hole–like; κ≠ 1 for material or exotic compact objects). For κ=1, we construct five independent first integrals – an autonomous Hamiltonian, two KY-generated Killing invariants, a linear Rüdiger constant, and a quadratic Carter-Rüdiger constant – establishing Liouville-Arnold integrability at quadratic order in spin. For κ≠ 1, the symmetry-generated invariants are not conserved in general and integrability does not persist at this order. The proof proceeds via covariant Poisson-bracket computations using a null bivector decomposition; Kerr is recovered as a special case. These results show that integrability can persist beyond Kerr and beyond the linear-in-spin regime, laying groundwork for symmetry-based, beyond-Kerr modelling of asymmetric-mass, spinning compact binaries.
