Polarization and valley switching in monolayer group-IV monochalcogenides

Group-IV monochalcogenides are a family of two-dimensional puckered materials with an orthorhombic structure that is comprised of polar layers. In this article, we use first principles calculations to show the multistability of monolayer SnS and GeSe, two prototype materials where the direction of the puckering can be switched by application of tensile stress or electric field. Furthermore, the two inequivalent valleys in momentum space, which are dictated by the puckering orientation, can be excited selectively using linearly polarized light, and this provides an additional tool to identify the polarization direction. Our findings suggest that SnS and GeSe monolayers may have observable ferroelectricity and multistability, with potential applications in information storage

Spin-Orbit Dirac Fermions in 2D Systems

We propose a novel model for including spin-orbit interactions in buckled two dimensional systems. Our results show that in such systems, intrinsic spin-orbit coupling leads to a formation of Dirac cones, similar to Rashba model. We explore the microscopic origins of this behaviour and confirm our results using DFT calculations

Probing the Circumnuclear Stellar Populations of Starburst Galaxies in the Near-infrared

We employ the NASA Infrared Telescope Facility's near-infrared spectrograph SpeX at 0.8-2.4$\mu$m to investigate the spatial distribution of the stellar populations (SPs) in four well known Starburst galaxies: NGC34, NGC1614, NGC3310 and NGC7714. We use the STARLIGHT code updated with the synthetic simple stellar populations models computed by Maraston (2005, M05). Our main results are that the NIR light in the nuclear surroundings of the galaxies is dominated by young/intermediate age SPs ($t \leq 2\times10^9$yr), summing from $\sim$40\% up to 100\% of the light contribution. In the nuclear aperture of two sources (NGC1614 and NGC3310) we detected a predominant old SP component ($t > 2\times10^9$yr), while for NGC34 and NGC7714 the younger component prevails. Furthermore, we found evidence of a circumnuclear star formation ring-like structure and a secondary nucleus in NGC1614, in agreement with previous studies. We also suggest that the merger/interaction experienced by three of the galaxies studied, NGC1614, NGC3310 and NGC7714 can explain the lower metallicity values derived for the young SP component of these sources. In this scenario the fresh unprocessed metal poorer gas from the destroyed/interacting companion galaxy is driven to the centre of the galaxies and mixed with the central region gas, before star formation takes place. In order to deepen our analysis, we performed the same procedure of SP synthesis using Maraston (2011, M11) EPS models. Our results show that the newer and higher resolution M11 models tend to enhance the old/intermediate age SP contribution over the younger ages

Two-dimensional square buckled Rashba lead chalcogenides

We propose the lead sulphide (PbS) monolayer as a two-dimensional semiconductor with a large Rashba-like spin-orbit effect controlled by the out-of-plane buckling. The buckled PbS conduction band is found to possess Rashba-like dispersion and spin texture at the M and Γ points, with large effective Rashba parameters of λ∼5 eV Å and λ∼1 eV Å, respectively. Using a tight-binding formalism, we show that the Rashba effect originates from the very large spin-orbit interaction and the hopping term that mixes the in-plane and out-of-plane p orbitals of Pb and S atoms. The latter, which depends on the buckling angle, can be controlled by applying strain to vary the spin texture as well as the Rashba parameter at Γ and M. Our density functional theory results together with tight-binding formalism provide a unifying framework for designing Rashba monolayers and for manipulating their spin properties.P.Z.H., H.S.P., and D.K.C. acknowledge the support of the Physics and Mechanical Engineering Department at Boston University. P.Z.H. is grateful for the hospitality of the NUS Centre for Advanced 2D Materials and Graphene Research Centre where this work was initiated. D.K.C. acknowledges the hospitality of the Aspen Center for Physics, which is supported by the US National Science Foundation Grant No. PHY-1607611. A.S.R., A.C.,and A.H.C.N. acknowledge support by the National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and CRP award "Novel 2D materials with tailored properties: Beyond graphene" (Grant No. R-144-000295-281). (Physics and Mechanical Engineering Department at Boston University; PHY-1607611 - US National Science Foundation; R-144-000295-281 - National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and CRP award "Novel 2D materials with tailored properties: Beyond graphene")Published versio

Distribution of epicenters in the Olami-Feder-Christensen model

We show that the well established Olami-Feder-Christensen (OFC) model for the dynamics of earthquakes is able to reproduce a new striking property of real earthquake data. Recently, it has been pointed out by Abe and Suzuki that the epicenters of earthquakes could be connected in order to generate a graph, with properties of a scale-free network of the Barabasi-Albert type. However, only the non conservative version of the Olami-Feder-Christensen model is able to reproduce this behavior. The conservative version, instead, behaves like a random graph. Besides indicating the robustness of the model to describe earthquake dynamics, those findings reinforce that conservative and non conservative versions of the OFC model are qualitatively different. Also, we propose a completely new dynamical mechanism that, even without an explicit rule of preferential attachment, generates a free scale network. The preferential attachment is in this case a ``by-product'' of the long term correlations associated with the self-organized critical state. The detailed study of the properties of this network can reveal new aspects of the dynamics of the OFC model, contributing to the understanding of self-organized criticality in non conserving models.Comment: 7 pages, 7 figure

Evaluation of de novo RNA-Seq assemblers in differential expression experiments.

The objective of this study is to evaluate methodologies applied on de novo transcriptomics studies, proposing criteria for ranking the data, in order to maximize the chance of correctly identifying a differentially expressed transcript.X-meeting 2015

Thermodynamic study of syngas combustion in gas microturbines with regeneration composed with metallic and ceramic materials

The objective of this research is to carry out an energetic evaluation of syngas combustion in gas microturbines with regenerators made with two different types of material: metallic or ceramic. A modified chemical equilibrium model was used to calculate syngas composition obtained from sugarcane bagasse gasification in a fluidized bed gasifier using steam as gasifying agent. For the gas microturbines with a regenerator of metallic materials, combustion temperatures of 850, 900, and 950 °C were established; and for those with a regenerator of ceramic materials, combustion temperatures of 1150, 1250, and 1350 °C were established. The range for the compression ratio was 2 to 6, and the excess air percentages employed were 400, 500, and 600%. Excellent results were obtained: maximum power ratio was 1.87 kWh/Nm3, maximum cycle efficiency was 57%, and maximum regenerator effectiveness was 100%. Thus, syngas combustion performance in the gas microturbines with regeneration was excellent

Processing and technological characterization of extruded breakfast cereal obtained with a mix of broken rice and common bean flour.

The aim of this work was to evaluate the functional technological properties of breakfast cereal obtained with a mix of broken rice and common bean flour, by the analyses of expansion index, water absorption index, water solubility index, apparent density, viscosity and instrumental texture. The product was elaborated with a rice and common bean mixed flour, using the proportion of 70% broken rice flour and 30% of broken common bean flour. The tested formulation was processed in a single-screw extruder. The extrusion parameters were set using three extrusion zones with temperatures of 40°C (1st zone), 60°C (2nd zone) e 80°C (3rd zone); mixture moisture during processing set at 14%; screw speed set at 177 rpm; feeding rate of 290g/minute and circular matrix of 3.85mm. The developed breakfast cereal was sprinkled with a sufficient quantity of a 70 ºBrix sucrose solution to make a final product with approximately 35% sugar. The processed formulation was manually collected, submitted to a forced air circulation oven drying and, afterwards, it was stored in polyethylene bags until analyses. The extruded obtained showed relatively low values for water absorption index (6.41g gel/g dry matter) and high values for water solubility index (44.50%). The expansion index of breakfast cereal was 8.89 indicating a good expansion of the final product. For apparent density it was observed the value of 0.25 and for instrumental texture evaluation, the value of 1,087.44g. The paste viscosity is an important attribute to study the functional properties of starchy food. Severe treatments destroy the starch granular structure, reducing the paste viscosity, what can be observed in this work through viscosity values below 130cP. It can be concluded that the use of broken common bean and rice mixed flour is an alternative to elaborate extruded breakfast cereal with good technological properties

Perfil de aminoácidos de sopa de arroz e feijão elaborada por extrusão.

O objetivo deste trabalho foi elaborar formulação de sopa instantânea a partir de quirera de arroz e bandinha de feijão por extrusão termoplástica e caracterizar o produto obtido quanto ao perfil de aminoácidos. A sopa instantânea foi produzida em extrusor mono-rosca, escala piloto. Os parâmetros de extrusão foram fixos, utilizando-se três zonas de aquecimento com temperaturas de 30oC, 40oC e 70oC, velocidade do parafuso 177rpm, taxa de alimentação 260g/min e matriz circular de 3,85mm. A sopa extrudada apresentou como aminoácidos limitantes, metionina, cisteína, e o triptofano. Em relação aos demais aminoácidos indispensáveis, a sopa extrudada atingiu os valores necessários para suprir as necessidades de crianças de 1 a 3 anos, com destaques para a fenilalanina e tirosina, com escores químicos de 6,05 e 2,17, respectivamente. A sopa extrudada a partir de quirera de arroz e bandinha de feijão apresenta quantidades ideais para a maioria dos aminoácidos indispensáveis à dieta humana