A theoretical evaluation of the effect of water on the electronic properties of low density amorphous carbon nanoparticles

Monte Carlo simulations combined with first-principles calculations were carried out to investigate the structure and electronic properties of amorphous carbon nanoparticles containing between 287 and 467 atoms, isolated and in an aqueous environment. Carbon interactions were described in terms of the semiemperical Tersoff potential and the interactions of the nanoparticles with water were described by an all-atom Lennard–Jones potential. The nanostructures were generated from low mass density amorphous carbon phases simulated under ambient conditions. Our study has indicated that the formation energy of these nanomaterials is slightly affected by the initial configuration of the amorphous phase. The large number of dangling bonds present in the nanostructures leads to huge magnetic moments, in a 31–42 μ_B range, calculated for the amorphous nanostructures containing distinct sp²/sp³ ratios. Also, these nanoparticles exhibit strong interaction energies with the aqueous environment, which are in agreement with the high reactivity expected for these amorphous systems. Most importantly, the calculated magnetism appears to be reduced between 1% and 14% in the presence of water, depending on both the nanoparticle density and surface.     

Response of Corn Seedlings (Zea mays L.) to Different Concentrations of Nitrogen in Absence and Presence of Silicon

Silicon - Corn plants are highly demanding of nitrogen and the application of silicon has been studied because it minimizes stress from different natures, and for the better utilization of some...     

Crowd simulation: applying mobile grids to the social force model

The social force model (SF) is able to reproduce many emergent phenomena observed in real crowds. Unfortunately, in some situations, such as low density environments, SF may produce counterintuitive results where the trajectories simulated look more like particles than to real people. We modify the SF model through the use of a mobile grid to allow the simulated pedestrians to change the direction of their desired velocity at reasonable times, thus avoiding nearby blocked or crowded areas smoothly. Our experiments focus on qualitative behavior, and verify that our model produces the desired trajectories of the pedestrians, achieving softer and more coherent trajectories when compared to the pure SF model solution. Like SF, our model reproduces the “faster-is-slower” and the arching underlying the clogging effects. Finally, we examine the occupation rates of the space when pedestrians were submitted to narrowed corridors and observe the “edge effect.”     

Brazilian scientific production in science education

In the present study we analyzed the Brazilian scientific production in the area of science education. The study was structured on: data by research groups registered in Conselho Nacional de Desenvolvimento Científico e Tecnológico; analysis of the post-graduate strictu sensu programs; analysis of theses and dissertations linked to post-graduate programs; and papers in international databases. Our research was conducted strictly via world wide web, from December 2009 to September 2010. It was found that both number of research groups, researchers, post-graduate programs, thesis, dissertations and papers presented a marked increase, especially in the last decade (from 2000 onwards). The major research centers were found to be located in public universities from Brazilian southeast and south regions. However, it was observed a tendency of decentralization, due to a recent investment in new public universities in the other Brazilian regions. So, this study sought to present an overview of the scientific production about science education and we expect that this information can help to expand the vision about the development of this research area in Brazil.     

Highly translucent nanostructured glass-ceramic

Transparent and translucent glass-ceramics (GCs) are found in an increasing number of domestic and high-technology applications. In this paper, we evaluated and optimized the effects of two-stage heat treatments on the resulting crystalline phases and microstructure of a glass of the SiO₂–Li₂O–P₂O₅–TiO₂–CaO–ZnO–Al₂O₃ system. The objective was to develop a transparent nanostructured glass-ceramic (GC). After numerous heat treatment trials, we found that a long nucleation period of 72 h at 455 °C followed by a crystal growth treatment at 660 °C for 2 h resulted in a highly translucent GC having homogenously distributed nanocrystals. The relatively high amount of P₂O₅ (2.5 mol%) induced the formation of lithium disilicate as the main crystal phase. We thus developed a GC having crystals under 50 nm, with a high crystallized fraction (52%vol. Li₂Si₂O₅ and 26% vol Li₂SiO₃), transmittance of approximately 80% in the visible spectrum for 1.2 mm thick specimens, nano hardness of 8.7 ± 0.1 GPa (load of 400 mN), a high elastic modulus of 138 ± 3 GPa as measured by nanoindentation, and good flexural strength (350 ± 40 MPa) as measured by ball-on-3 balls tests. Due to its high content of Li⁺, this GC has the potential to be chemically strengthened and can be further developed to be used in a number of applications, such as on displays of electronic devices.     

Shrimp processing residue as an alternative ingredient for new product development

Shrimp residues were dried (65 °C), grounded, and posteriorly used as an ingredient to the production of ‘spiced shrimp flour’ and ‘shrimp flavoured biscuits’. Both products were packed in modified atmosphere (100% N₂) and stored for 180 days (25 °C) for shelf life evaluation. The centesimal composition, physicochemical, microbiological and sensory analyses were carried out in triplicate. The microbiological analysis (residue and shrimp flour) was within the limits of the legislation, confirming the hygienic–sanitary care during processing. The protein content was the most outstanding (40.13% for the spiced shrimp flour and 20.52% for the shrimp flavoured biscuits). The microbiological evaluation for the ‘spiced shrimp flour’ and ‘shrimp flavoured biscuits’ was below the legal limit, and both products were accepted by sensory analysis. The shelf life evaluation demonstrated stability for 6 months. Thus, we concluded that the Litopenaeus vannamei shrimp residue is a promising ingredient in the food industry.     

Processing and properties of tape-cast alumina/zirconia laminates composites

In the present work, laminar ceramic structures formed by layers of alumina and partially stabilized zirconia were fabricated by water-based tape casting. Rheological, physical and mechanical properties of slurries and laminates were evaluated. The laminates consisted of stacked alumina and zirconia green tapes produced by thermopressing. Pyrolysis was carried out at 450 °C and sintering at 1500 °C. The alumina/zirconia laminates were studied for a better understanding of the formation behavior and crack propagation at the laminate interface. The flexural strength values of laminates depend on the stress state on their surface. The laminates with the highest amount of zirconia layers presented low strength values (6.7 MPa), while the laminates with more alumina layers had a higher strength level (57.7 MPa). This is because these laminates have alumina layers on the surface which are in a state of residual compressive stress.