Interaction Driven Quantum Hall Wedding cake-like Structures in Graphene Quantum Dots

Quantum-relativistic matter is ubiquitous in nature; however it is notoriously difficult to probe. The ease with which external electric and magnetic fields can be introduced in graphene opens a door to creating a table-top prototype of strongly confined relativistic matter. Here, through a detailed spectroscopic mapping, we provide a spatial visualization of the interplay between spatial and magnetic confinement in a circular graphene resonator. We directly observe the development of a multi-tiered "wedding cake"-like structure of concentric regions of compressible/incompressible quantum Hall states, a signature of electron interactions in the system. Solid-state experiments can therefore yield insights into the behaviour of quantum-relativistic matter under extreme conditions

Analysis of Error in the Estimation of the Temporal ACF of Ergodic Sum-of-Cisoids Simulators for Mobile Fading Channels

Abstract-Mobile fading channel simulators based on ergodic sum-of-cisoids (SOC) processes have been proposed in several papers as a solution to accurately approximate the channel's autocorrelation function (ACF) in a single simulation run. However, despite the encouraging results presented in the literature, it is not clear whether the ergodicity of this type of simulators is meaningful in practice, where in contrast to what theory assumes, the waveforms generated by the simulator have finite lengths. To clarifying this issue, we present in this paper a comprehensive analysis of the random error observed when the temporal ACF (TACF) of ergodic SOC processes is estimated from waveforms of finite duration. We start by computing the instantaneous error produced by three different estimators, namely the biased, the unbiased, and the half-interval estimators. We then derive compact expressions for some insightful statistical quantities of the estimation error, such as the mean, the variance, and the mean-squared value. Based on the obtained results, we discuss the conditions under which an ergodic SOC simulator can be considered to perform similarly in theory and practice. The analysis presented in this paper can be used as a framework for testing, calibration, and performance validation of new ergodic SOC channel simulators

The conversion of CO2 to methanol on orthorhombic β-Mo2C and Cu/β-Mo2C catalysts: mechanism for admetal induced change in the selectivity and activity

The conversion of CO2 into methanol catalyzed by β-Mo2C and Cu/β-Mo2C surfaces has been investigated by means of a combined experimental and theoretical study. Experiments have shown the direct activation and dissociation of the CO2 molecule on bare β-Mo2C, whereas on Cu/β-Mo2C, CO2 must be assisted by hydrogen for its conversion. Methane and CO are the main products on the clean surface and methanol production is lower. However, the deposition of Cu clusters avoids methane formation and increases methanol production even above that corresponding to a model of the technical catalyst. DFT calculations on surface models of both possible C- and Mo-terminations, corroborate the experimental observations. Calculations for the clean Mo-terminated surface reveal the existence of two possible routes for methane production (C + 4H → CH4; CH3O + 3H → CH4 + H2O) which are competitive with methanol synthesis, displaying slightly lower energy barriers. On the other hand, a model for Cu deposited clusters on the Mo- terminated surface points towards a new route for methanol and CO production avoiding methane formation. The new route is a direct consequence of the generation of a Mo2C-Cu interface. The present experimental and theoretical results entail the interesting catalytic properties of Mo2C as an active support of metallic nanoparticles, and also illustrate how the deposition of a metal can drastically change the activity and selectivity of a carbide substrate for CO2 hydrogenation

Boosting the activity of transition metal carbides towards methane activation by nanostructuring

The interaction of methane with pristine surfaces of bulk MoC and Mo2C is known to be weak. In contrast, a series of X-ray photoelectron spectroscopy (XPS) experiments, combined with thermal desorption mass spectroscopy (TDS), for MoCy (y = 0.5-1.3) nanoparticles supported on Au(111)¿which is completely inert towards CH4¿show that these systems adsorb and dissociate CH4 at room temperature and low CH4 partial pressure. This industrially-relevant finding has been further investigated with accurate density functional theory (DFT) based calculations on a variety of MoCy supported model systems. The DFT calculations reveal that the MoCy/Au(111) systems can feature low C-H bond scission energy barriers, smaller than the CH4 adsorption energy. Our theoretical results for bulk surfaces of Mo2C and MoC show that a simple Brønsted-Evans-Polanyi (BEP) relationship holds for C-H bond scission on these systems. However, this is not the case for methane activation on the MoCy nanoparticles as a consequence of their unique electronic and chemical properties. The discovery that supported molybdenum carbide nanoparticles are able to activate methane at room temperature paves the road towards the design of a new family of active carbide catalysts for methane activation and valorisation, with important implications in climate change mitigation and carbon cycle closure

Guía para el desarrollo de un CubeSat

Este documento plasma el trabajo del equipo, integrado por los estudiantes de ingeniería electrónica, para este periodo PAP. De esta manera se guía al lector a través de fragmentos de información del documento generado, describiendo los datos obtenidos. En el documento generado, se busca que el lector pueda adquirir un entendimiento sobre el tema de los nano satélites y fundamentos para el diseño, fabricación y certificación de un CubeSat.ITESO, A.C

Interaction-driven quantum Hall wedding cake–like structures in graphene quantum dots

Quantum-relativistic matter is ubiquitous in nature; however, it is notoriously difficult to probe. The ease with which external electric and magnetic fields can be introduced in graphene opens a door to creating a tabletop prototype of strongly confined relativistic matter. Here, through a detailed spectroscopic mapping, we directly visualize the interplay between spatial and magnetic confinement in a circular graphene resonator as atomic-like shell states condense into Landau levels. We directly observe the development of a “wedding cake”–like structure of concentric regions of compressible-incompressible quantum Hall states, a signature of electron interactions in the system. Solid-state experiments can, therefore, yield insights into the behavior of quantum-relativistic matter under extreme conditions.United States. National Science Foundation. STC Center for Integrated Quantum Materials (Award 1231319)United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001

Logistic map driven by dichotomous noise

Bifurcation diagrams and invariant densities are computed and interpreted for a logistic map driven by dichotomous noise. Two deterministic limits are analyzed. Changes in the stability of such a system, when varying the correlation time of the noise, are numerically studied. The peaks of the invariant density in the white-noise case are identified as originating from the most stable attractors among those appearing in the deterministic limits

Resonant phenomena in extended chaotic systems subject to external noise: the Lorenz'96 model case

We investigate the effects of a time-correlated noise on an extended chaotic system. The chosen model is the Lorenz'96, a kind of "toy" model used for climate studies. Through the analysis of the system's time evolution and its time and space correlations, we have obtained numerical evidence for two stochastic resonance-like behavior. Such behavior is seen when both, the usual and a generalized signal-to-noise ratio function are depicted as a function of the external noise intensity or the system size. The underlying mechanism seems to be associated to a "noise-induced chaos reduction". The possible relevance of these and other findings for an "optimal" climate prediction are discussed.Comment: Submitted to Europhysics Letters (LaTex, 12 pgs, 5 figures

Horn fragments of the Halpern-Shoham Interval Temporal Logic

We investigate the satisfiability problem for Horn fragments of the Halpern-Shoham interval temporal logic depending on the type (box or diamond) of the interval modal operators, the type of the underlying linear order (discrete or dense), and the type of semantics for the interval relations (reflexive or irreflexive). For example, we show that satisfiability of Horn formulas with diamonds is undecidable for any type of linear orders and semantics. On the contrary, satisfiability of Horn formulas with boxes is tractable over both discrete and dense orders under the reflexive semantics and over dense orders under the irreflexive semantics but becomes undecidable over discrete orders under the irreflexive semantics. Satisfiability of binary Horn formulas with both boxes and diamonds is always undecidable under the irreflexive semantics

Influencia de pretratamientos con ozono gaseoso y luz UV-C en la conservación de rúcula cortada

El objetivo de este trabajo fue determinar el efecto de pretratamientos con luz UV-C y ozono gaseoso en la calidad de hojas de rúcula mínimamente procesada. Hojas cortadas se irradiaron con las siguientes dosis de luz UV-C: 0,5; 1,0; 1,5 y 2,0 J/cm² y con ozono gaseoso con las siguientes concentraciones 0,5; 1,0; 1,5 y 2,0 mg/L. El producto acondicionado en bandejas y recubierto con Polipropileno se almacenó a 5ºC durante 12 días. Periódicamente se evaluó: características organolépticas (apariencia, marchitamiento, desarrollo de podredumbres y pérdida de color y olor característico), color (L*, a* y b*), sólidos solubles, acidez y acido ascórbico (AA). Al analizar en conjunto los descriptores analizados a través del análisis sensorial se determinó que las dosis de UV-C más adecuadas serian 1,5 y 1,0 J/cm² y para ozono 1,0; 1,5 y 2,0 mg/L. En las muestras tratadas con 0,5 J/cm² el nivel de AA disminuyó en aproximadamente un 12%, con 1 J/cm² un 19%, con 1,5 J/cm² 30% y en las tratadas con 2,0 J/cm² hasta un 40%. En el caso del ozono para la concentración de 0,5 y 1,0 mg/L el nivel de AA disminuyó aproximadamente un 10% y para las concentraciones de 1,5 y 2,0 mg/L un 5%. En función de los parámetros evaluados se podrían aplicar las dosis de UV-C de 1,0 y 1,5 J/cm² y concentraciones de ozono de 1,5 y 2,0 mg/L en estudios posteriores, a fin de diseñar un proceso de elaboración para rúcula precortada con el fin de prolongar su vida útil con cargas microbianas lo más bajas posibles y acordes a este tipo de producto.Centro de Investigación y Desarrollo en Criotecnología de Alimento