Pressurized Formic Acid Dehydrogenation: An Entropic Spring Replaces Hydrogen Compression Cost.

Formic acid is unique among liquid organic hydrogen carriers (LOHCs), because its dehydrogenation is highly entropically driven. This enables the evolution of high-pressure hydrogen at mild temperatures that is difficult to achieve with other LOHCs, conceptually by releasing the "spring" of energy stored entropically in the liquid carrier. Applications calling for hydrogen-on-demand, such as vehicle filling, require pressurized H2. Hydrogen compression dominates the cost for such applications, yet there are very few reports of selective, catalytic dehydrogenation of formic acid at elevated pressure. Herein, we show that homogenous catalysts with various ligand frameworks, including Noyori-type tridentate (PNP, SNS, SNP, SNPO), bidentate chelates (pyridyl)NHC, (pyridyl)phosphine, (pyridyl)sulfonamide, and their metallic precursors, are suitable catalysts for the dehydrogenation of neat formic acid under self-pressurizing conditions. Quite surprisingly, we discovered that their structural differences can be related to performance differences in their respective structural families, with some tolerant or intolerant of pressure and others that are significantly advantaged by pressurized conditions. We further find important roles for H2 and CO in catalyst activation and speciation. In fact, for certain systems, CO behaves as a healing reagent when trapped in a pressurizing reactor system, enabling extended life from systems that would be otherwise deactivated.

Imaging the itinerant-to-localized transmutation of electrons across the metal-to-insulator transition in V2O3.

In solids, strong repulsion between electrons can inhibit their movement and result in a "Mott" metal-to-insulator transition (MIT), a fundamental phenomenon whose understanding has remained a challenge for over 50 years. A key issue is how the wave-like itinerant electrons change into a localized-like state due to increased interactions. However, observing the MIT in terms of the energy- and momentum-resolved electronic structure of the system, the only direct way to probe both itinerant and localized states, has been elusive. Here we show, using angle-resolved photoemission spectroscopy (ARPES), that in V2O3, the temperature-induced MIT is characterized by the progressive disappearance of its itinerant conduction band, without any change in its energy-momentum dispersion, and the simultaneous shift to larger binding energies of a quasi-localized state initially located near the Fermi level.

Spatiotemporal characterization of the field-induced insulator-to-metal transition.

Many correlated systems feature an insulator-to-metal transition that can be triggered by an electric field. Although it is known that metallization takes place through filament formation, the details of how this process initiates and evolves remain elusive. We use in-operando optical reflectivity to capture the growth dynamics of the metallic phase with space and time resolution. We demonstrate that filament formation is triggered by nucleation at hotspots, with a subsequent expansion over several decades in time. By comparing three case studies (VO2, V3O5, and V2O3), we identify the resistivity change across the transition as the crucial parameter governing this process. Our results provide a spatiotemporal characterization of volatile resistive switching in Mott insulators, which is important for emerging technologies, such as optoelectronics and neuromorphic computing.

A quantum material spintronic resonator.

In a spintronic resonator a radio-frequency signal excites spin dynamics that can be detected by the spin-diode effect. Such resonators are generally based on ferromagnetic metals and their responses to spin torques. New and richer functionalities can potentially be achieved with quantum materials, specifically with transition metal oxides that have phase transitions that can endow a spintronic resonator with hysteresis and memory. Here we present the spin torque ferromagnetic resonance characteristics of a hybrid metal-insulator-transition oxide/ ferromagnetic metal nanoconstriction. Our samples incorporate [Formula: see text], with Ni, Permalloy ([Formula: see text]) and Pt layers patterned into a nanoconstriction geometry. The first order phase transition in [Formula: see text] is shown to lead to systematic changes in the resonance response and hysteretic current control of the ferromagnetic resonance frequency. Further, the output signal can be systematically varied by locally changing the state of the [Formula: see text] with a dc current. These results demonstrate new spintronic resonator functionalities of interest for neuromorphic computing.

Subthreshold firing in Mott nanodevices.

Resistive switching, a phenomenon in which the resistance of a device can be modified by applying an electric field1-5, is at the core of emerging technologies such as neuromorphic computing and resistive memories6-9. Among the different types of resistive switching, threshold firing10-14 is one of the most promising, as it may enable the implementation of artificial spiking neurons7,13,14. Threshold firing is observed in Mott insulators featuring an insulator-to-metal transition15,16, which can be triggered by applying an external voltage: the material becomes conducting ('fires') if a threshold voltage is exceeded7,10-12. The dynamics of this induced transition have been thoroughly studied, and its underlying mechanism and characteristic time are well documented10,12,17,18. By contrast, there is little knowledge regarding the opposite transition: the process by which the system returns to the insulating state after the voltage is removed. Here we show that Mott nanodevices retain a memory of previous resistive switching events long after the insulating resistance has recovered. We demonstrate that, although the device returns to its insulating state within 50 to 150 nanoseconds, it is possible to re-trigger the insulator-to-metal transition by using subthreshold voltages for a much longer time (up to several milliseconds). We find that the intrinsic metastability of first-order phase transitions is the origin of this phenomenon, and so it is potentially present in all Mott systems. This effect constitutes a new type of volatile memory in Mott-based devices, with potential applications in resistive memories, solid-state frequency discriminators and neuromorphic circuits.

Robust Coupling between Structural and Electronic Transitions in a Mott Material.

The interdependences of different phase transitions in Mott materials are fundamental to the understanding of the mechanisms behind them. One of the most important relations is between the ubiquitous structural and electronic transitions. Using IR spectroscopy, optical reflectivity, and x-ray diffraction, we show that the metal-insulator transition is coupled to the structural phase transition in V_{2}O_{3} films. This coupling persists even in films with widely varying transition temperatures and strains. Our findings are in contrast to recent experimental findings and theoretical predictions. Using V_{2}O_{3} as a model system, we discuss the pitfalls in measurements of the electronic and structural states of Mott materials in general, calling for a critical examination of previous work in this field. Our findings also have important implications for the performance of Mott materials in next-generation neuromorphic computing technology.

El tipo de parto, ¿podría condicionar el éxito en la lactancia materna exclusiva? / The type of childbirth, could condition success in exclusivebreastfeeding?

Fundamentos: Existen pocos trabajos que muestren factores de riesgo y protección asociados a la Lactancia Materna exclusiva (LME).El objetivo fue determinar qué factores constituyen elementos de protección o de riesgo para la instalación de LME en mujeres de distinto nivel socioeconómico y educativo, controladas en el sistema público de salud de Santiago. Métodos: Una muestra de 242 madres, atendidas en sistema público, con hijos de entre 1 y 6 meses, a quienes se les aplico una encuesta sobre LME. Resultados: Las principales causas de destete fueron "no se llena queda con hambre" 18,8%, seguida por las causas "rechazo del niño al pecho" 12%, e "inicio de actividades laborales o estudiantiles" 12%. La regresión logística mostró que el parto vaginal está asociado positivamente a la LME (OR 0,44; IC 0,24 -0,78), en cambio el no tener experiencia previa o haber tenido una mala experiencia está asociado negativamente a la LME (OR 3,82; IC 1,87 -7,78). Conclusiones: El parto vaginal es un elemento protector que está ligado a los procedimientos que le siguen y que permiten una inducción temprana de la lactancia

Background: Few studies show risk and protection factors associated with it, and although the prevalence of LME.The objective was to determine which factors constitute elements of protection or risk for the installation of LME in women of different socioeconomic and educational levels, controlled in the public health system of Santiago. Methods: A sample of 242 mothers, attended in public system, with children between 1 and 6 months. To whom a survey on LME was applied. Results: The main causes of weaning were "not filled, with hunger" "18.8%, followed by causes" rejection of the child to the breast" 12%, and" onsetof work or student activities "12%. Logistic regression showed that protective vaginal delivery (OR 0.44 IC 0.24 -0.78) and having no prior experience or having a poor experience is at risk(OR 3.82 CI 1.87 -7.78).Conclusions: Vaginal birth is a protective element that is linked to the procedures that follow and allow early induction of lactation

Diagnóstico matemático de la monitoría fetal aplicando la Ley de Zipf-Mandelbrot / Zipf-Mandelbrot law and mathematical approach in fetal cardiac monitoring diagnosis

El actual diagnóstico clínico de la monitoría fetal presenta problemas de objetividad y reproducibilidad, sin embargo el análisis físico y matemático del trazado lleva a caracterizaciones objetivas y reproducibles de la dinámica cardíaca fetal. Desarrollar una nueva metodología diagnóstica de la monitoría fetal aplicando las concepciones de la teoría de sistemas dinámicos y la ley de Zipf-Mandelbrot para evaluar la complejidad del trazado a partir de la aparición de Componentes Dinámicos del Sistema (CDS)