Sintering kinetics of nanometric calcium oxide in vacuum atmosphere

A recent application for nanometric CaO powder is its use as a spallation target material for the production of isotope beams at CERN. The stability of the nanostructure at high operation temperatures is a crucial feature to provide stable and improved isotope release rates. Prior to operation, sintering studies under thermal conditions similar to those of the target operation are required to establish the microstructural evolution due to coarsening and densification processes. This knowledge enables the identification of the limiting temperatures for the target operation, ensuring a stable nanostructure for higher and constant isotope release rates. In this study, nanometric CaO powder with 58 m(2) g(-1) of specific surface area was obtained from vacuum decomposition of calcium carbonate at 800 degrees C. The microstructure evolution of porous powder compacts was investigated under vacuum atmosphere, from 1000 to 1250 degrees C, for holding times from 3 to 600 min. For temperatures higher than 1000 degrees C, a significant surface area reduction was observed, accompanied by porosity decrease. The morphological analysis of the pore evolution revealed a differential sintering of the porous compacts, mainly occuning inside the aggregates. The kinetic analysis of the surface area reduction pointed to aggregate shrinkage controlled by volume diffusion with surface diffusion as an underlying mechanism for lower temperatures. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved

International buyer-supplier relationships, transfer of knowledge and local supplier's capability

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Dynamic resource allocation architecture for IEEE802.16e: Design and performance analysis

Mobile communications has witnessed an exponential increase in the amount of users, services and applications. WiMAX (Worldwide Interoperability for Microwave Access) targets to provide broadband connectivity to wide area coverage, both in fixed and in mobile environments, as well as in the provision of QoS constraints of those applications and services envisioned for Next Generation Networks (NGNs), which results in significant design challenges in the MAC (Medium Access Control) to provide the seamless transport of heterogeneous traffic in a cost-effective manner. This paper proposes a Dynamic Resource Allocation (DRA) architecture for the IEEE802.16e broadband wireless system (also known as Mobile WiMAX) that can provide operators the flexibility to deliver broadband traffic with high spectral efficiency. The proposed DRA architecture framework encompasses scheduler, Link Adaptation (LA), Resource Allocation (RA) and Hybrid Automated Repeat Request (HARQ) functional blocks which interwork seamlessly. The performance of the DRA was evaluated using commonly deployed scheduling policies: Max C/I, Proportional Fair and Round Robin schemes. Simulation results show that the proposed DRA scheme has the capacity to provide enhanced coverage and QoS provisioning for the area networks (WANs), such as the ones envisioned for B3G mobile wireless networks

In-Vacuum Projection of Nanoparticles for On-Chip Tunneling Spectroscopy

Starting with a discussion of the percolation problem applied to the trapping of conducting nanoparticles between nanometer-spaced electrodes, we show that a good strategy to trap a single nanoparticle between the electrodes is to prepare chips with low coverage of nanoparticles to avoid percolating current paths. To increase the probability of trapping a single nanoparticle, we developed a new method where nanoparticles are projected in-vacuum on the chip, followed by a measure of the tunnel current, in a cycle that is repeated up to a few thousand times until a preset threshold value is reached. A plot of the tunneling current as a function of time allows discriminating between the two possible current paths, i.e., a single nanoparticle trapped between the electrodes or a percolating path across many nanoparticles. We applied the method to prepare chip circuits with single gold nanoparticles, as demonstrated by the observation of Coulomb blockade. Furthermore, we applied the method to trap single magnetite nanoparticles for the study of electric-field-induced switching from insulator to metal In single nanoparticles

Life history of harbor porpoises (Phocoena phocoena) in Scottish (UK) waters

Life history parameters were determined for stranded and bycaught\nharbor porpoises (Phocoena phocoena) from Scottish (UK) waters (1992â 2005).\nFetal growth rate was 84.4 mm/mo and mean size at birth was 76.4\ncm (range 65â 88 cm). Males and females had a similar range of body\nlengths (65â 170 cm and 66â 173 cm, respectively), although asymptotic\nlengths were higher in females than males (approximately 158 cm and\n147 cm, respectively). Nonpregnant females were significantly lighter,\nin relation to their length than males. Maximum estimated age was\n20 yr for both sexes. Age at sexual maturity (ASM) was estimated\nas 4.35 yr in females and 5.00 yr in males. Conception occurred mainly\nin July and August although reproductively active males were recorded\nduring April to July. Gestation lasted 10â 11 mo, with calving mainly\nbetween May and July. Lactating females were recorded during June\nto November, while small calves with solid food in their stomachs\nwere found mainly during February to May. Estimated pregnancy rate\n(0.34â 0.40) is lower than recorded elsewhere, but is likely underestimated\ndue to the prevalence of mature females of poor health status in\nthe sample. Nevertheless, cetacean strandings can be an essential\nsource of data on demographic parameters

Assessment of imposex and butyltin concentrations in Gemophos viverratus (Kiener, 1834), from São Vicente, Republic of Cabo Verde (Africa)

This work constitutes the first assessment of tributyltin (TBT) pollution levels in the Republic of Cabo Verde (Africa) and proposes the marine gastropod Gemophos viverratus (Kiener, 1834) as a new bioindicator of TBT pollution in the Macaronesia and west coast of Africa. Specimens were collected between August and October 2012 along a gradient of naval traffic in São Vicente Island. The results clearly indicate an increase of imposex levels (percentage of females affected with imposex, 0-100 %; vas deferens sequence index, 0-4.1; relative penis length index, 0-54.6 %) and female TBT contamination (from 5 to 37 ngSn g(-1) dry weight (dw)) from outside to inside the harbour of Porto Grande Bay and identify this area as the focus of TBT pollution in the island. The butyltin degradation index for G. viverratus tissues ranged between 1.3 and 2.2, which being above 1 suggests that a considerable part of TBT inputs to the bay may not be very recent. Sterile females were found inside the harbour with an incidence up to 21.4 %. Considering the existence of a planktonic veliger stage in the life cycle of G. viverratus, it is expected that recruitment of newborn individuals can be supplied from unaffected breeding females inside and outside the Porto Grande Bay, resulting in a reduced impact of TBT pollution on population abundance. G. viverratus is very promising to be used as a simple, inexpensive and efficient novel tool for TBT pollution biomonitoring in the Macaronesia and west coast of Africa, a region for which there is an astonishing lack of information concerning levels and ecological impacts of TBT pollution

An identification key for the five most common species of Metastrongylus

Species of the Metastrongylus genus, the lung nematodes of pigs that require an intermediate host (earthworm) to complete their cycle, pose a potential risk to both livestock and humans. This parasite which can result in lung pathology and mixed infections with other pathogens (e.g. viruses) can be fatal to pigs. Although this genus is distributed worldwide, there are no classification keys for identifying this common parasite species. In this work, we take advantage of parasitological surveys of wild boar (Sus scrofa) in northern and central Spain and southern Poland to develop a morphological identification key for the five most common Metastrongylus species (Metastrongylus apri, Metastrongylus pudendotectus, Metastrongylus salmi, Metastrongylus confusus and Metastrongylus asymetricus). In addition, we provide the first record of M. confusus in Spain, probably unidentified until now due to the lack of appropriate identification keys. We hope that this user-friendly identification key will enable parasitologists and veterinary practitioners to avoid further misclassifications of Metastrongylus species

Effects of substituting ytterbium for scandium on corrosion behaviour of Al-Sc alloy

The localized corrosion and electrochemical behaviour of Al-0.28 wt.% Sc and Al-0.24 wt.% Sc-0.07 wt.% Yb alloys have been studied in 3.5 wt.% NaCl solution. The results showed that the impurity intermetallic phases containing Fe can act as cathodes and promote localized corrosion in the surrounding matrix. Yb had strong effect on the polarization behaviour in the anodic domain of Al-Sc alloy by improving the pitting corrosion resistance of this alloy. It has been deduced that a high number density of fully coherent nano-sized Al3Sc or Al-3(Sc, Yb) precipitates in heat treated alloys can enhance the passivation tendency of these alloys

Designing Near-Infrared and Visible Light Emitters by Postsynthetic Modification of Ln(+3)-IRMOF-3

The postsynthetic modification of metal-organic frameworks is a promising new route for engineering optical centres and tuning the light emission properties of materials. Here, the postsynthetic modification of isoreticular metal-organic framework-3 (IRMOF-3) with ethyl oxalyl monochloride and ethyl acetoacetate followed by the chelation of trivalent lanthanide ions afforded efficient near-infrared (Nd3+) and visible (Eu3+ and Tb3+) light emitters. IRMOF-3 was used as an example owing to its highly porous crystalline structure and the presence of non-coordinating amino groups on the benzenedicarboxylate (bdc) linker, which are amenable to modification. The conversion of the amino groups was 100 and 65% for ethyl oxalyl monochloride and ethyl acetoacetate, respectively. The materials were characterised by elemental analysis, powder X-ray diffraction, optical and scanning electron microscopy, Fourier transform infrared spectroscopy, and solution (H-1) and (C-13) solid-state nuclear magnetic resonance spectroscopy. The solid-state luminescence properties of Ln-modified IRMOF-3 were investigated at room temperature. The presence of the bdc aromatic ring, beta-diketonates and oxamate enhanced the Ln(3+) sensitization through ligand-to-metal energy transfer. The magnetic behaviour of all compounds was further analysed. The spin-orbit coupling and zero-field splitting parameters were evaluated by fitting the experimental magnetic susceptibility to the analytical expressions for the free Ln(3+) ions

Handbook of research on engaging digital atives in higher education settings

The concept of digital natives, firstly introduced in 2001 by Marc Prensky, refers to all who were born and who have grown up with digital technologies. Today, over the last decade, it is important to understand the technological profile of this new generation that was born in a digital world and that remains immersed. As it is believed that present and future learning environments should motivate and engage learners in reflective thinking and active knowledge construction, the potential of technology is in knowing how to help students and teachers in doing so. In other words, to find patterns of discourse to implement and accomplish the necessary interaction, mediated by technology, in the learning process. Moreover, given the intense competition in knowledge-based economies and the wide omnipresence of information and communication, it is also essential to offer different educational supports that can integrate the idea of educating students for global citizenship. Having this issue as a backdrop, the overall goal of this work is to contribute to the understanding of how HEI need to anticipate and prepare themselves for this new native generation. Thus, the Handbook of Research on Engaging Digital Natives in Higher-Education Settings aims to publish literature reviews and evaluations of good practices in higher education that support and inspire colleagues to a better understanding of how to use technology for learning and teaching activities. Although the target audience of this book is composed of academics, students, researchers, and education policy representatives, we definitely hope that the audience can act as an important anchor for all those that are committed with higher-education settings regarding the issue of engaging (digital natives) students in the learning and teaching process. The Handbook of Research on Engaging Digital Natives in Higher-Education Settings is a compilation of 20 contributions of the central concerns, challenges, opportunities, experiences, and commitment of 50 authors from 10 countries over 4 continents that really work and live side by side with today’s students. The Handbook of Research on Engaging Digital Natives in Higher-Education Settings is organized in three parts: Digital Natives, Strategies of Teaching and Learning, and Virtual Education. While the seven chapters of the first part address the nature of the concept, the seven chapters that follow report about how different methodological approaches can be designed to meet the cultural changes that derive from the concept. Finally, the last six chapters focus on the subject of education within a wider digital exploration context