Thermal and dynamic mechanical behavior of epoxy composites reinforced with post-consumed yerba mate

Yerba mate (YM) is widely consumed in Latin American countries, and its residues can be used as bio-resources such as reinforced in epoxy composites. The present work aims to produce epoxy resin composites and evaluate the influence of post-consumed YM as reinforcement. The concentrations of YM used were 5, 10, and 20% (wt/wt). Chemical, thermal, morphological, and dynamic mechanical behaviors were explored. The YM incorporation did not influence chemically on the epoxy structure and a pull-out phenomenon was observed as YM content increased. The YM at lower concentrations (5 and 10%) led to higher values of activation energies calculated from model-free isoconversional methods. On the other hand, the composite e/YM 20 wt% improved all dynamic-mechanical properties. YM proved to be a suitable and cheap reinforcement for epoxy resin.     

In Situ Phase Evolution of Ni/Ti Reactive Multilayers

Joining shape-memory alloys (SMA) to other materials is strongly required in order to enlarge their fields of application. Fusion welding induces strong compositional and microstructural changes that significantly affect the shape-memory effect and the superelastic behavior of these alloys. The exothermic and in some cases self-propagating character of some nano-multilayer reactions is explored in this study as an alternative for joining SMA. To follow these very fast reactions, high brilliance sources, such as synchrotron radiation, are required. In situ high-resolution x-ray diffraction data, giving the phase evolution sequence with temperature of the Ni/Ti multilayer thin films under study, are presented. A correlation between the multilayer design and the tendency for the sequence of phase formation is established.     

Medium wave DRM field trials in Brazil – Some daytime and nighttime results in urban environment

The Digital Radio Mondiale (DRM) system broadcasts audio in the frequency band below 174 MHz  and . In this experiment in urban areas in Brazil, a hybrid signal composed of an analog AM signal and a digital DRM30 signal, with the same content, were broadcasted in diurnal and nocturnal transmissions. This paper describes the experimental setup, which employs the spectral shaping technique in simulcast transmission [14], and presents some results of medium wave propagation measurements campaigns that are being carried out in Brazil. The experiment is part of a series of field trials that are being conducted by the Brazilian Government which includes campaigns at MW, HF and VHF frequency bands.     

The Influence of the Rare Earth Element Ce on the High-Temperature Oxidation Kinetics of Low-Cr Steels

The oxidation behavior of steels containing low-Cr concentrations (0.5-2.25 wt.%) has been studied in laboratory air in the temperature range of 400-550 °C. The oxidation rate of the steels was lower than that of pure iron, but higher than that of pure iron when a small amount of rare earth element cerium (0.03 wt.%) is added to the 2.25Cr1Mo steel. The mass change follows a nearly parabolic law for the case of pure iron and the steel without Ce addition, while linear behavior describes the oxygen uptake for the case of the 2.25Cr1Mo+0.03Ce steel. SEM cross-section observations and thermodynamic calculations confirm that there is no wustite (FeO) formation during oxidation of pure iron and low-Cr steels at 550 °C, whereas FeO might be formed in the oxide scale of 2.25Cr1Mo+0.03Ce at the same oxidation conditions (temperature, atmosphere, and exposure time). By investigating the temperature for FeO stability, this study reveals that the temperature for FeO formation on pure iron is 568 °C, for the 2.25Cr1Mo steel 589 °C, and 471 °C for the 2.25Cr1Mo+0.03Ce. This low value for the FeO stability temperature found for the steel 2.25Cr1Mo+0.03Ce steel explains why this steel oxidizes very fast at 550 °C.     

The SciCryo Project and Cryogenic Scintillation of Al2O3 for Dark Matter

We discuss cryogenic scintillation of Al₂O₃. Room-temperature measurements with α particles are first carried out to study effect of Ti concentration on response. Measurements under X-rays between room temperature and 10 K confirm a doubling of light output. The integration of a scintillation-phonon detector into an ionization-phonon dark matter search is underway, and the quenching factor for neutrons has been verified.      

Contextual web searches in Facebook using learning materials and discussion messages

The web is nowadays one of the main information sources, and information search is an important area in which many advances have been registered. One approach to improve web search results is to consider contextual information. Usually, information about context has been provided through user logs on previous searches or the monitoring of clicks on first results, but different approaches can be used in specific environments. In a web based learning environment, existing documents and exchanged messages could provide contextual information. So, the main goal of this work is to provide a contextual web search engine based on shared documents and messages posted in a social network used for collaborative learning. Contextual search is provided through query expansion using learning documents (material provided by the teacher) and discussion messages (posts, links and comments that result from the participants’ interactions). A prototype was implemented and used in a learning scenario to acquire the context in a learning community. The proposed approach makes the context acquisition faster and more dynamic as it considers an automatic approach over text processing of documents and discussions. In addition, the results of the query engine with and without the contextual information were compared and the proposed approach using contextual information showed improvements in the precision of the results.     

A semi-automatic strategy for achieving learning content and practice repurposing

The development of instructional content using Information Technologies is an expensive, time-consuming and complex process that requires new methodologies. It was in this context that the concept of Learning Objects (LOs) was proposed in order to promote reuse. However, this goal is not yet fully attained and new contributions to increase reuse are still welcome. Besides, if content is conveyed in LOs that are easier to reuse, they must be combined and sequenced in order to build more elaborated and complex content. This paper presents a strategy to deal with these problems based on the definition of small LOs here called Component Objects (COs). These COs are structured and combined according to a conceptual metamodel, which is the basis for the definition of conceptual schemas representing the existing material, including not only content but also practice. This strategy for searching, extracting, and sequencing COs, supports a teacher to better control the implementation of complex content, reducing errors in the authoring process. This approach includes a specification language and an algorithm for semi-automatic sequencing learning content and practice. Finally, a case study that shows the proposed approach and some results of using the algorithm are presented.