Structural phase transitions in Ruddlesden-Popper phases of strontium titanate: {\em ab initio} and inhomogeneous Ginzburg-Landau approaches

We present the first systematic {\em ab initio} study of anti-ferrodistortive (AFD) order in Ruddlesden-Popper (RP) phases of strontium titanate, Sr$_{1+n}$Ti$_n$O$_{3n+1}$, as a function of both compressive epitaxial strain and phase number $n$. We find all RP phases to exhibit AFD order under a significant range of strains, recovering the bulk AFD order as $\sim 1/n^2$. A Ginzburg-Landau Hamiltonian generalized to include inter-octahedral interactions reproduces our {\em ab initio} results well, opening a pathway to understanding other nanostructured perovskite systems

A fully ab initio approach to inelastic atom-surface scattering

We introduce a universal and fully ab initio theory for inelastic scattering of any atom from any surface, and apply the theory to helium scattering from Nb(100). The key aspect making our approach universal is a direct first-principles evaluation of the scattering atom-electron vertex. By correcting misleading results from current state-of-the-art theories, this fully ab initio approach will be critical in guiding and interpreting experiments that adopt next-generation, non-destructive atomic beam scattering.Comment: 6 pages, 5 figure

Framework for solvation in quantum Monte Carlo

Employing a classical density-functional description of liquid environments, we introduce a rigorous method for the diffusion quantum Monte Carlo calculation of free energies and thermodynamic averages of solvated systems that requires neither thermodynamic sampling nor explicit solvent electrons. We find that this method yields promising results and small convergence errors for a set of test molecules. It is implemented readily and is applicable to a range of challenges in condensed matter, including the study of transition states of molecular and surface reactions in liquid environments.Comment: 5 pages, 3 figures, accepted for publication in Physical Review B Rapid Communication

Accelerating Correlated Quantum Chemistry Calculations Using Graphical Processing Units

Graphical processing units are now being used with dramatic effect to accelerate quantum chemistry calculations. However, early work exposed challenges involving memory bottlenecks and insufficient numerical precision. This research effort addresses those issues, proposing two new tools for accelerating matrix multiplications of arbitrary size where single-precision accuracy is not enough.Chemistry and Chemical Biolog

Positivismo jurídico, Estado de Derecho y libertad: una propuesta de formulación = Legal Positivism, Rule of Law and Freedom: A Proposal for Formulating

Resumen: En el presente trabajo se exploran las posibles vías de conexión entre el positivismo jurídico, el liberalismo clásico y el Estado de Derecho, tarea que siempre se ha visto dificultada por la visión antipositivista de los autores liberales. En tal sentido, se analizan y responden las críticas antipositivistas con el propósito de mostrar la compatibilidad entre el positivismo jurídico y el ideal del Estado de Derecho. Palabras clave: Liberalismo clásico, positivismo jurídico, Estado de Derecho, separación entre derecho y moral, fuentes sociales del derecho.Abstract: This article explores possible connections between legal positivism, classical liberalism and the rule of law, a task that has been obstructed by the anti-positivist vision of liberal authors. In that sense, anti-positivists critics are analyzed and contested with the purpose of showing the compatibility between legal positivism and the rule of law ideal. Keywords: Classical liberalism, legal positivism, rule of law, separation between law and morals, social sources of the law.

The Oxygen Reduction Pathway for Spinel Metal Oxides in Alkaline Media: An Experimentally Supported Ab Initio Study

Precious-metal-free spinel oxide electrocatalysts are promising candidates for catalyzing the oxygen reduction reaction (ORR) in alkaline fuel cells. In this theory-driven study, we use joint density-functional theory in tandem with supporting electrochemical measurements to identify a novel theoretical pathway for the ORR on cubic Co3O4 nanoparticle electrocatalysts. This pathway aligns more closely with experimental results than previous models. The new pathway employs the cracked adsorbates *(OH)(O) and *(OH)(OH), which, through hydrogen bonding, induce spectator surface *H. This results in an onset potential closely matching experimental values, in stark contrast to the traditional ORR pathway, which keeps adsorbates intact and overestimates the onset potential by 0.7 V. Finally, we introduce electrochemical strain spectroscopy (ESS), a groundbreaking strain analysis technique. ESS combines ab initio calculations with experimental measurements to validate proposed reaction pathways and pinpoint rate-limiting steps

Acute Physiological and Performance Responses to High-Intensity Resistance Circuit Training in Hypoxic and Normoxic Conditions.

The aim of this study was to analyze physical performance and physiological variables during high-intensity resistance circuit training (HRC) with the addition of 2 levels (moderate and high) of systemic hypoxia. Twelve resistance-trained young male subjects participated in the study. After a 6 repetition maximum testing session, participants performed 3 randomized trials of HRC: normoxia (NORM: fraction of inspired oxygen [FiO2] = 0.21; ∼0 m altitude), moderate hypoxia (MH: FiO2 = 0.16; ∼2.100 m altitude), or high hypoxia (HH: FiO2 = 0.13; ∼3.800 m altitude), as controlled by a hypoxic generator. Bench press force, heart rate and heart rate variability, rating of perceived exertion, resting metabolic rate, energy cost, and countermovement jump were assessed in each session. Heart rate variability in HH was significantly lower (standard deviation of all normal NN intervals [intervals between two "normal" beats] = 111.9 vs. 86.7 milliseconds; standard deviation of the difference between consecutive NN intervals = 19.5 vs. 17.0 milliseconds; p ≤ 0.05) in comparison with NORM. There were significant differences in rating of perceived exertion between NORM and HH (11.6 vs. 13.8 points). Peak and mean force on the bench press were significantly lower (p ≤ 0.05) in HH when compared with MH (peak: 725 vs. 488 N; mean: 574 vs. 373 N). Energy cost was significantly higher (p ≤ 0.01) in both hypoxic conditions compared with NORM (NORM: 10.4; MH: 11.7; HH: 13.3 kJ·min). There were no differences between conditions in heart rate and countermovement jump variables. These results indicate that hypoxic stimuli during HRC exercise alter physical performance and physiological variables and affect how strenuous the exercise is perceived to be. High-intensity resistance circuit training in hypoxia increases the stress on the performance and physiological responses, and these differences must be taken into account to avoid an excessive overload.Actividad Física y Deport