Enhanced ferroelectric and piezoelectric properties of BCT-BZT at the morphotropic phase boundary driven by the coexistence of phases with different symmetries

The discovery of lead-free piezoelectric materials is crucial for future information and energy storage applications. Enhanced piezoelectric and other physical properties are commonly observed near the morphotropic phase boundary (MPB) composition of ferroelectric solid solutions. The (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) system exhibits a large electromechanical response around its MPB region at x=0.5. We report experimental and theoretical results of BZT-xBCT over a wide composition range (0.3=x=1.0). X-ray diffraction and Raman spectroscopy studies indicate a composition-induced structural phase transition from a rhombohedral (R3m) phase at x=0.4 to a tetragonal (P4mm) phase at x=0.6 through a multiphase coexistence region at 0.45=x=0.55 involving orthorhombic + tetragonal (Amm2+P4mm) phases. First-principles calculations elucidate the phase competition in the coexistence region. The critical composition (x= 0.5) displays enhanced dielectric, ferroelectric and piezoelectric properties, where notably d33~ 320 pC/N. This work provides clear evidence of Amm2+P4mm crystallographic phases in the MPB region, which is responsible for the improved functional properties.C. C. acknowledges support from the Spanish Ministry of Science, Innovation, and Universities under the “Ramón y Cajal” fellowship RYC2018-024947-I.Peer ReviewedPostprint (author's final draft

Quantum dot passivation of halide perovskite films with reduced defects, suppressed phase segregation, and enhanced stability

Structural defects are ubiquitous for polycrystalline perovskite films, compromising device performance and stability. Herein, a universal method is developed to overcome this issue by incorporating halide perovskite quantum dots (QDs) into perovskite polycrystalline films. CsPbBr3 QDs are deposited on four types of halide perovskite films (CsPbBr3, CsPbIBr2, CsPbBrI2, and MAPbI3) and the interactions are triggered by annealing. The ions in the CsPbBr3 QDs are released into the thin films to passivate defects, and concurrently the hydrophobic ligands of QDs self-assemble on the film surfaces and grain boundaries to reduce the defect density and enhance the film stability. For all QD-treated films, PL emission intensity and carrier lifetime are significantly improved, and surface morphology and composition uniformity are also optimized. Furthermore, after the QD treatment, light-induced phase segregation and degradation in mixed-halide perovskite films are suppressed, and the efficiency of mixed-halide CsPbIBr2 solar cells is remarkably improved to over 11% from 8.7%. Overall, this work provides a general approach to achieving high-quality halide perovskite films with suppressed phase segregation, reduced defects, and enhanced stability for optoelectronic applications.Peer ReviewedPostprint (author's final draft

Benefits of Entomophile Pollination in Crops of Brassica napus and Aspects of Plant Floral Biology

Rapeseed (Brassica napus L. var. oleifera) is an oleaginous species of the Brassicaceae family, being the third most produced oleaginous in the world. Rapeseed can produce fruits and seeds from both self-pollination and cross-pollination. However, cross-pollination rate is approximately 30% and may suffer variations due to the abundance and diversity of pollinator insects, cultivar and meteorological conditions. Different researchers have reported that pollination by insects, especially Apis mellifera honeybee, on rapeseed flowers provides an increase in productivity, improving yield and contributing to the uniformity and initial pod establishment. It is estimated that the economic value of A. mellifera honeybees for rapeseed cultivation in Brazil is US$ 8.2 million. The objective of this chapter is gathering data for a compilation of information regarding rapeseed culture and the importance of A. mellifera in Brassica napus pollination

CONSTRUINDO UM MOTOR ELETRICO DE CORRENTE CONTINUA COMO APRENDIZAGEM ATIVA DA LEI DE FARADAY

We present a teaching proposal on electromagnetic phenomena (DC motor) with a focus on practical activities according to the concept of Piaget, here extrapolated to include the objects in virtual environments. We set up in the classroom an electric DC motor to discuss concepts of electromagnetic theory. We carried out the physical modeling and its computational simulation using the Modellus educational software. In both situations, the teaching laboratory with the real object of study, and in the virtual laboratory with the simulation of the object, the participants showed an intense interest, illustrating the potential of the active learning.Apresentamos uma proposta de ensino na área de eletromagnetismo (motor de corrente continua - cc) com foco nas atividades práticas segundo a conceituação de Piaget, aqui extrapolada para incluir os objetos em ambientes virtuais. Montamos em sala de aula um motor elétrico de cc, para discutir conceitos da teoria eletromagnética. Realiza-se a modelagem física e sua simulação em computador utilizando o software educacional Modellus. Em ambas as situações, no laboratório didático com o objeto de estudo real, e no laboratório virtual com a simulação do objeto, os participantes mostram intenso interesse, ilustrando as potencialidades da aprendizagem ativa

Assessing the validity of the MyJump2 app for measuring different jumps in professional cerebral palsy football players: an experimental study

Background: Vertical jumps can be used to assess neuromuscular status in sports performance. This is particularly important in Cerebral Palsy Football (CP Football) because players are exposed to high injury risk, but it may be complicated because the gold standard for assessing jump performance is scarce in field evaluation. Thus, field techniques, such as mobile apps, have been proposed as an alternative method for solving this problem. Objective: This study aims to evaluate the reliability of the measures of the MyJump2 app to assess vertical jump performance in professional CP Football. Methods: We assessed 40 male CP Football athletes (age 28.1 [SD 1.4] years, weight 72.5 [SD 6.2] kg, and height 176 [SD 4.2] cm) through the countermovement jump (CMJ) and squat jump (SJ) using a contact mat. At the same time, we assessed the athletes using the MyJump2 app. Results: There were no significant differences between the instruments in SJ height (P=.12) and flight time (P=.15). Additionally, there were no significant differences between the instruments for CMJ in jump height (P=.16) and flight time (P=.13). In addition, it was observed that there were significant and strong intraclass correlations in all SJ variables varying from 0.86 to 0.89 (both P<.001), which was classified as "almost perfect." Similar results were observed in all variables from the CMJ, varying from 0.92 to 0.96 (both P <=.001). Conclusions: We conclude that the MyJump2 app presents high validity and reliability for measuring jump height and flight time of the SJ and CMJ in CP Football athletes.7

Influence of silver precursors on growth of metallic nanoparticles in heavy metal oxide glasses

In this work we report a systematic study on the influence of the chemical nature of silver precursors on the formation of glass-ceramics from oxide glasses. Thermal, structural and optical properties were analyzed as a function of the glass composition. Controlled crystallization was achieved by thermal treatment of the samples above glass transition. The influence of time of treatment on both nanoparticle growth and optical properties of the samples was studied by transmission electron microscopy and UV-Vis spectroscopy, respectively. Results showed that only glasses containing AgCl and AgNO3 led to glass-ceramics growth after thermal treatment.CNPqCAPESFAPESP/CEPI

The Brazilian Developments on the Regional Atmospheric Modeling System (BRAMS 5.2): An Integrated Environmental Model Tuned for Tropical Areas

We present a new version of the Brazilian developments on the Regional Atmospheric Modeling System where different previous versions for weather, chemistry and carbon cycle were unified in a single integrated software system. The new version also has a new set of state-of-the-art physical parameterizations and greater computational parallel and memory usage efficiency. Together with the description of the main features are examples of the quality of the transport scheme for scalars, radiative fluxes on surface and model simulation of rainfall systems over South America in different spatial resolutions using a scale-aware convective parameterization. Besides, the simulation of the diurnal cycle of the convection and carbon dioxide concentration over the Amazon Basin, as well as carbon dioxide fluxes from biogenic processes over a large portion of South America are shown. Atmospheric chemistry examples present model performance in simulating near-surface carbon monoxide and ozone in Amazon Basin and Rio de Janeiro megacity. For tracer transport and dispersion, it is demonstrated the model capabilities to simulate the volcanic ash 3-d redistribution associated with the eruption of a Chilean volcano. Then, the gain of computational efficiency is described with some details. BRAMS has been applied for research and operational forecasting mainly in South America. Model results from the operational weather forecast of BRAMS on 5 km grid spacing in the Center for Weather Forecasting and Climate Studies, INPE/Brazil, since 2013 are used to quantify the model skill of near surface variables and rainfall. The scores show the reliability of BRAMS for the tropical and subtropical areas of South America. Requirements for keeping this modeling system competitive regarding on its functionalities and skills are discussed. At last, we highlight the relevant contribution of this work on the building up of a South American community of model developers