Water Splitting Reaction at Polar Lithium Niobate Surfaces

Water splitting is a highly promising, environmentally friendly approach for hydrogen production. It is often discussed in the context of carbon dioxide free combustion and storage of electrical energy after conversion to chemical energy. Since the oxidation and reduction reactions are related to significant overpotentials, the search for suitable catalysts is of particular importance. Ferroelectric materials, for example, lithium niobate, attracted considerable interest in this respect. Indeed, the presence of surfaces with different polarizations and chemistries leads to spatial separation of reduction and oxidation reactions, which are expected to be boosted by the electrons and holes available at the positive and negative surfaces, respectively. Employing the density functional theory and a simplified thermodynamic approach, we estimate the overpotentials related to the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on both polar LiNbO3 (0001) surfaces. Our calculations performed for ideal surfaces in vacuum predict the lowest overpotential for the hydrogen evolution reaction (0.4 V) and for the oxygen evolution reaction (1.2 V) at the positive and at the negative surfaces, respectively, which are lower than (or comparable with) commonly employed catalysts. However, calculations performed to model the aqueous solution in which the reactions occur reveal that the presence of water substantially increases the required overpotential for the HER, even inverting the favorable polarization direction for oxidation and reduction reactions. In aqueous solution, we predict an overpotential of 1.2 V for the HER at the negative surface and 1.1 V for the OER at the positive surface

Cluster Abundance in f(R) Gravity Models

As one of the most powerful probes of cosmological structure formation, the abundance of massive galaxy clusters is a sensitive probe of modifications to gravity on cosmological scales. In this paper, we present results from N-body simulations of a general class of f(R) models, which self-consistently solve the non-linear field equation for the enhanced forces. Within this class we vary the amplitude of the field, which controls the range of the enhanced gravitational forces, both at the present epoch and as a function of redshift. Most models in the literature can be mapped onto the parameter space of this class. Focusing on the abundance of massive dark matter halos, we compare the simulation results to a simple spherical collapse model. Current constraints lie in the large-field regime, where the chameleon mechanism is not important. In this regime, the spherical collapse model works equally well for a wide range of models and can serve as a model-independent tool for placing constraints on f(R) gravity from cluster abundance. Using these results, we show how constraints from the observed local abundance of X-ray clusters on a specific f(R) model can be mapped onto other members of this general class of models.Comment: 8 pages, 6 figure

Optimal Phonon-to-Spin Mapping in a system of a trapped ion

We propose a protocol for measurement of the phonon number distribution of a harmonic oscillator based on selective mapping to a discrete spin-1/2 degree of freedom. We consider a system of a harmonically trapped ion, where a transition between two long lived states can be driven with resolved motional sidebands. The required unitary transforms are generated by amplitude-modulated polychromatic radiation fields, where the time-domain ramps are obtained from numerical optimization by application of the Chopped RAndom Basis (CRAB) algorithm. We provide a detailed analysis of the scaling behavior of the attainable fidelities and required times for the mapping transform with respect to the size of the Hilbert space. As one application we show how the mapping can be employed as a building block for experiments which require measurement of the work distribution of a quantum process

The crossroads of organizational learning: a multiparadigmatic view

A literatura sobre Aprendizagem Organizacional [AO] tem avançado não somente no volume de publicações, mas apontando outras dimensões do tema. Envolve diversos campos teóricos: psicológicos, sociológicos, culturais, históricos e metodológicos, além da gestão propriamente dita. Assim, pergunta-se: Quais questões e características básicas fazem a AO peculiar e a separa de outros conceitos relacionados? Para responder a este questionamento são apresentadas as diversas perspectivas teóricas que abordam AO, algumas questões e reflexões relacionadas às teorias, assim como definições e estudos desenvolvidos no campo. Utilizando-se uma análise de inspiração multiparadigmática, as contribuições identificadas foram agrupadas em cinco campos que apresentam alguns temas e questões recorrentes. Esta análise aponta quatro questões (relacionadas ao nível de análise, resultados da aprendizagem, mudanças e processos de aprendizagem), que o conceito de AO deve superar para tornar-ser significativo. Visando superar estes desafios, sugere-se a adoção de uma perspectiva baseada em práticas.The literature on Organizational Learning [OL] has been moving forward not only in the volume of publications but also by pointing to other dimensions of the theme. The debate involves several theoretical fields psychological, sociological, cultural, historical and methodological - in addition to management itself. A question emerges: which issues and basic characteristics make OL different and separated from the other related concepts? In order to answer this question a number of theoretical perspectives of OL are presented and discussed, along with some inquiries and reflections related to these theories, as well as definitions and studies developed in this field. Using the multiparadigmatic approach, the literature on OL was organized and grouped into five fields. This analysis pointed to four questions (related to the level of learning, learning results, changes and learning processes) that the concept of OL has to overcome to become significant. It is suggested that a possible way to overcome these challenges is to adopt a perspective based on practices

Developmental Increase of Neocortical Presynaptic Efficacy via Maturation of Vesicle Replenishment

The efficacy of neocortical synapses to transmit during bursts of action potentials (APs) increases during development but the underlying mechanisms are largely unclear. We investigated synaptic efficacy at synapses between layer 5 pyramidal neurons (L5PNs) during development, using paired recordings, presynaptic two-photon Ca2+ imaging, and numerical simulations. Our data confirm a developmental increase in paired-pulse ratios (PPRs). Independent of age, Ca2+ imaging revealed no AP invasion failures and linear summation of presynaptic Ca2+ transients, making differences in Ca2+ signaling an unlikely reason for developmental changes in PPR. Cumulative excitatory postsynaptic current (EPSC) amplitudes indicate that neither the size of the readily-releasable pool (RRP) nor replenishment rates were different between age groups, while the time-courses of depression differed significantly. At young synapses, EPSCs depressed rapidly to near steady-state during the first four APs, and synaptic failures (Fsyn) increased from 0 to 30%. At mature synapses this drop was significantly slower and strongly biphasic, such that near steady-state depression was reached not before 18 APs with Fsyn remaining between 0 and 5%. While young synapses reliably transmitted during pairs of APs, albeit with strong depression, mature synapses maintained near 100% transfer efficacy with significantly less depression during high-frequency bursts of APs. Our analysis indicates that at mature synapses a replenishment pool (RepP) is responsible for their high efficacy during bursting activity, while this RepP is functionally immature at young synapses. Hence, our data provide evidence that the functional maturation of a RepP underlies increasing synaptic efficacy during the development of an excitatory cortical synapse

De volta pra casa ou o caminho sem volta em duas narrativas do Brasil

O artigo discute a representação do corpo feminino subalterno em dois romances brasileiros: As mulheres de Tijucopapo, de Marilene Felinto, e Ponciá Vicêncio, de Conceição Evaristo. A leitura se propõe a enfocar esse corpo como lócus em que se desdobram as tensões resultantes das relações desiguais de gênero, raça e classe no Brasil, corpo colonizado e verdadeiro campo de batalha, em cujos movimentos ainda se enfrentam a casa grande e a senzala. Tomando como motes o tema da estrada e o motivo do exílio, pretende-se também abordar os deslocamentos efetuados pelas personagens femininas nos dois romances, como percursos formadores de sua identidade

Erwerbstätigkeit im Mikrozensus: Konzepte, Definition, Umsetzung

'Im Mikrozensus werden unterschiedliche Konzepte und Definitionen zur Messung von Erwerbstätigkeit angewandt. Zu unterscheiden ist das Labour-Force-Konzept und das Unterhaltskonzept. Die Vergleichbarkeit von Ergebnissen und Eckzahlen aus unterschiedlichen nationalen und internationalen Quellen erweist sich aufgrund der Verwendung unterschiedlicher Konzepte und Definitionen als Problem. Im Hinblick auf die Verbesserung der Vergleichbarkeit von Daten wird in dieser Arbeit eine Übersicht über die Abgrenzung und Definition von Erwerbstätigkeit, Arbeits- bzw. Erwerbslosigkeit entlang der unterschiedlichen Konzepte gegeben. Es werden die Besonderheiten der Konzeption ausgehend vom Mikrozensus 1996 genannt, und auf Abweichungen und Gemeinsamkeiten der Umsetzung von 1957 bis 1996 hingewiesen. Besonderes Gewicht liegt dabei auf der Betrachtung der beim Zentrum für Umfragen, Methoden und Analysen (ZUMA) verfügbaren Mikrozensen. Die Beschreibung der Anwendungsmöglichkeiten wird mit Auswertungsbeispielen illustriert. Abschließend werden Aspekte der nationalen und internationalen Vergleichbarkeit der Messung von Erwerbsbeteiligung diskutiert.' (Autorenreferat

Editorial: Case reports in neuroimaging and stimulation: [case report]

The brain, a remarkable and intricate system, plays a fundamental role in shaping our behavior, encompassing cognitive and emotional processes (1–3). Understanding its structural and functional organization has been greatly enhanced through the utilization of neuroimaging and brain stimulation techniques. These powerful tools not only provide insights into the complex workings of the brain but also hold promise as potential therapeutic interventions for mental disorders (4)