Analysis of elastic functionally graded materials under large displacements via high-order tetrahedral elements

The purpose of this study is to present a position based tetrahedral finite element method of any order to accurately predict the mechanical behavior of solids constituted by functionally graded elastic materials and subjected to large displacements. The application of high-order elements makes it possible to overcome the volumetric and shear locking that appears in usual homogeneous isotropic situations or even in non-homogeneous cases developing small or large displacements. The use of parallel processing to improve the computational efficiency, allows employing high-order elements instead of low-order ones with reduced integration techniques or strain enhancements. The Green-Lagrange strain is adopted and the constitutive relation is the functionally graded Saint Venant-Kirchhoff law. The equilibrium is achieved by the minimum total potential energy principle. Examples of large displacement problems are presented and results confirm the locking free behavior of high-order elements for non-homogeneous materials. (C) 2011 Elsevier B.V. All rights reserved.

Contribution of the cashew gum (Anacardium occidentale L.) for development of layer-by-layer films with potential application in nanobiomedical devices

The search for bioactive molecules to be employed as recognition elements in biosensors has stimulated researchers to pore over the rich Brazilian biodiversity. In this sense, we introduce the use of natural cashew gum (Anacardium occidentale L) as an active biomaterial to be used in the form of layer-by-layer films, in conjunction with phthalocyanines, which were tested as electrochemical sensors for dopamine detection. We investigated the effects of chemical composition of cashew gum from two different regions of Brazil (Piaui and Ceara states) on the physico-chemical characteristics of these nanostructures. The morphology of the nanostructures containing cashew gum was studied by atomic force microscopy which indicates that smooth films punctuated by globular features were formed that showed low roughness values. The results indicate that, independent of the origin, cashew gum stands out as an excellent film forming material with potential application in nanobiomedical devices as electrochemical sensors. (c) 2012 Elsevier B.V. All rights reserved.

Synthesis and Characterization of Gold/Alanine Nanocomposites with Potential Properties for Medical Application as Radiation Sensors

Radiation dose assessment is essential for several medical treatments and diagnostic procedures. In this context, nanotechnology has been used in the development of improved radiation sensors, with higher sensitivity as well as smaller sizes and energy dependence. This paper deals with the synthesis and characterization of gold/alanine nanocomposites with varying mass percentage of gold, for application as radiation sensors. Alanine is an excellent stabilizing agent for gold nanoparticles because the size of the nanoparticles does not augment with increasing mass percentage of gold, as evidenced by UV-vis spectroscopy, dynamic light scattering, and transmission electron microscopy. X-ray diffraction patterns suggest that the alanine crystalline orientation undergoes alterations upon the addition of gold nanoparticles. Fourier transform infrared spectroscopy indicates that there is interaction between the gold nanoparticles and the amine group of the alanine molecules, which may be the reason for the enhanced stability of the nanocomposite. The application of the nanocomposites as radiation detectors was evaluated by the electron spin resonance technique. The sensitivity is improved almost 3 times in the case of the nanocomposite containing 3% (w/w) gold, so it can be easily tuned by changing the amount of gold nanoparticles in the nanocomposites, without the size of the nanoparticles influencing the radiation absorption. In conclusion, the featured properties, such as homogeneity, nanoparticle size stability, and enhanced sensitivity, make these nanocomposites potential candidates for the construction of small-sized radiation sensors with tunable sensitivity for application in several medical procedures.

Rare-earth impurities in gallium nitride: The role of the Hubbard potential

We performed a first principles investigation on the electronic properties of 4f-rare earth substitutional impurities in zincblende gallium nitride (GaN:REGa, with RE=Eu, Gd, Tb, Dy, Ho, Er and Tm). The calculations were performed within the all electron methodology and the density functional theory. We investigated how the introduction of the on-site Hubbard U potential (GGA + U) corrects the electronic properties of those impurities. We showed that a self-consistent procedure to compute the Hubbard potential provides a reliable description on the position of the 4f-related energy levels with respect of the GaN valence band top. The results were compared to available data coming from a recent phenomenological model. (C) 2012 Elsevier B.V. All rights reserved.