Analysis of the fluorescence of the ion Eu in fluoroborate glasses containing silver particles

We have studied theoretically and experimentally the fluorescence enhancement in fluoroborate glasses, doped with the ion Eu³⁺, containing small silver particles. The model developed shows that the gain coefficient has quenching and enhancement regions. The absorption peak of the metallic particles occurs at 425 nm, which is not in resonance with the ⁵L₆ level of the ion Eu³⁺. For this reason it is not possible to make a complete comparison between theoretical and experimental results, but the structure of the absorption spectra allows us to check some crucial aspects of the problem, such as energy transfer, enhancement of the local field and the high absorption by the particle system. Results of electronic microscopy have revealed non-uniformity of the particle distribution with average radii of approximately 20 Å and 35 Å and a measured localized mean filling factor of 0.02.     

Development of a virtual reality laboratory stressor

Virtual Reality - This research report describes the development of a virtual reality (VR) laboratory stressor to study the effects of exposure to stressful events. The aim of the research was to...     

Calculation of the ligand–lanthanide ion energy transfer rate in coordination compounds: contributions of exchange interactions

Recently, one of us (O.L.M.) developed a theoretical approach to the energy transfer process between a ligand and a lanthanide ion in luminescent compounds. This approach takes into account the direct Coulomb interaction only. Here we present further calculations which also include the exchange Coulomb interaction (isotropic and anisotropic). The selection rules on the total angular momentum, J, of the lanthanide 4f states, derived from each interaction are different. They are in fact complementary. We discuss the case of energy transfer to the ⁵D₁ manifold of the Eu³⁺ ion, which is forbidden when only the direct Coulomb interaction is considered but becomes allowed through the exchange interaction. In this case numerical estimates show that, depending on resonance conditions and the nature of the ligand donor state, the transfer rate may assume very high values. It is also emphasised that, according to the present approach, energy transfer to the ⁵D₀ level of the Eu³⁺ ion is forbidden by both mechanisms, provided J-mixing between the ⁷F₀ and ⁷F₂ manifolds is neglected.     

Investigating Strategies of an Irrigation Conflict

The understanding and modeling of human behavior in conflict situations is a challenge that researches investigate by developing, modifying and applying computational models. This paper aims to analyze how changes in the strategies of the various groups involved in a water use conflict can influence the decision process. The case study is an irrigation system supplied by a main canal in Rio de Janeiro State, Southeastern Brazil. Conflicts arise due to hydraulic constraints of the canal, resulting in water unavailability for some irrigators or damage to potentially irrigable lands caused by adjacent floods. The investigation strategy has been developed, considering three groups of irrigators. They can be geographically identified over the main canal’s hydrographical limits. Six different scenarios are considered to analyze the conflict. These scenarios are built taking into account six different policies of water conveyance. Additionally, the decision of the state government related to water charging has been considered. The final decision is taken by the management institution of the canal which also has two different tendencies: to opt for the scenarios providing highest net profits or to be impartial in the final decision. The Graph Model for Conflict Resolution, which solves non-cooperative games based on graph theory, was adopted to evaluate all these strategies. The results show that, according to the level of exigency of irrigator groups, state government and management institution, the conflict can in fact, be resolved.     

Evaluation of the Antioxidant Properties of the Brazilian Cerrado Fruit Annona crassiflora (Araticum)

Annona crassiflora, known commonly as araticum, is an exotic tropical fruit consumed mainly by native people of the Brazilian Cerrado (2nd biggest biome of Brazil). In this study, pulp, seed, and peel of slight ripe and overripe fruits were extracted using ethanol and water. The extracts showed high content of total phenols and were screening for their potential as antioxidants using the in vitro model 1,1‐ dipheniyl‐2‐picryl hydrazyl (DPPH). The ethanol extracts of peel and seeds showed IC50 of 48.82 μg/mL and 31.14 μg/mL, respectively, for the slightly ripe fruits. As the ethanolic fractions of araticum showed the highest antioxidant activity, they were selected for testing of its effect on lipid peroxidation. The ethanolic extracts of slightly ripe fruits showed IC₅₀ of 4.44 μg/mL, 1.72 μg/mL, and 8.62 μg/mL for the peel, seed, and pulp, respectively. This is the 1st report on the antioxidant properties of the extracts of araticum. Owing to these properties, the studies can be further extending to exploit them for their possible application as natural antioxidant for cosmetic, supplements, and functional ingredients for food products.     

Palladium on Calcium Carbonate Combined to 2‐Hydroxypropyl‐α/β‐cyclodextrins: A Selective Catalytic System for Aqueous Heck Coupling and Hydroarylation

An efficient, selective and recoverable catalytic system for ligand‐free aqueous Heck reactions using hydroxypropylated cyclodextrins (HPCDs) and palladium on calcium carbonate (Pd/CaCO₃) is highlighted. Remarkably, stereo‐ and chemoselectivities could be tuned by the cavity size of cyclodextrins, exploiting the relevance of host‐guest interactions. UV‐Vis experiments have led to strong evidence concerning an interplay between Pd(II) and α‐HPCD, possibly ascribed to a reduction/stabilization effect of CDs. Unexpectedly, hydroarylation was the favored pathway with acrylonitrile which provided access to 3‐phenylpropionitrile derivatives without usual hydride donors. Finally, determination of soluble Pd(0/II) via AAS enabled the definition of a predominant homogeneous mechanism in which TONs over 5000 were observed.     

Storage of green coffee in hermetic packaging injected with CO2

The objective of this study was to evaluate the physical, chemical, and sensory qualities of green coffee beans (Coffea arabica L.) during storage in different types of packaging. Coffee was stored from October 2008 to September 2009 in a warehouse of the Agriculture Society Ltda. (SAAG) in Santana da Vargem, southern Minas Gerais State, Brazil. The treatments in the factorial design consisted of two types of packaging (hermetic big bags with the injection of up to 60% CO₂ in a controlled atmosphere; similar bags but without the injection of CO₂ in a modified atmosphere) and three sampling positions in the bags (high, medium, and low). At 3-month intervals during a 12-month period, grains were analyzed to determine their water content, color, electrical conductivity, potassium lixiviation, and content of sugars. Sensory analysis was also conducted at these sampling times. The storage of green coffee beans in hermetic big bags on a commercial scale under modified and controlled atmospheric conditions is viable over a 12-month period. The coffee packed in big bags maintained its quality and exhibited an intensification of the green coloration of the grains during storage. Sensory analysis of coffee beans stored in a controlled atmosphere showed that the medium sampling position yielded the best ratings. The results of this analysis demonstrated that this storage technique can potentially increase the effectiveness of methods used to preserve the sensory quality of coffee beans.     

Mechanical properties of amorphous nanosprings

Helical amorphous nanosprings have attracted particular interest due to their special mechanical properties. In this work we present a simple model, within the framework of the Kirchhoff rod model, for investigating the structural properties of nanosprings having asymmetric cross section. We have derived expressions that can be used to obtain the Young's modulus and Poisson's ratio of the nanospring material composite. We also address the importance of the presence of a catalyst in the growth process of amorphous nanosprings in terms of the stability of helical rods.