Quenching-assisted actuation mechanisms in core-shell structured BiFeO3-BaTiO3 piezoceramics

Electromechanical actuation in piezoceramics is usually enhanced by creating chemically homogeneous materials with structurally heterogeneous morphotropic phase boundaries, leading to abrupt changes in ion displacement directions within the perovskite unit cell. In the present study, an alternative mechanism to enhance electromechanical coupling is found in both chemically and structurally heterogeneous BiFeO3-BaTiO3 lead-free piezoceramics. Such a mechanism is observed in a composition exhibiting core-shell type microstructure, associated with donor-type substitution of Ti4+ for Fe3+, and is primarily activated by thermal quenching treatment. Here, we describe the use of in situ high-energy synchrotron X-ray powder diffraction upon the application of a high electric field to directly monitor the ferroelectric and elastic interactions between these composite-like components, formed as core and shell regions within grains. Translational short or long-range ordering is observed in the BiFeO3-depleted shell regions which undergo significant structural alterations from pseudocubic Pm3m relaxor-ferroelectric in slow-cooled ceramics to rhombohedral R3c or R3m with long-range ferroelectric order in the quenched state. The strain contributions from each component are calculated, leading to the conclusion that the total macroscopic strain arises predominantly from the transformed shell after quenching. Such observations are also complemented by investigations of microstructure and electrical properties, including ferroelectric behaviour and temperature-dependent dielectric properties

Hypermedia learning and prior knowledge: Domain expertise vs. system expertise

Prior knowledge is often argued to be an important determinant in hypermedia learning, and may be thought of as including two important elements: domain expertise and system expertise. However, there has been a lack of research considering these issues together. In an attempt to address this shortcoming, this paper presents a study that examines how domain expertise and system expertise influence students’ learning performance in, and perceptions of, a hypermedia system. The results indicate that participants with lower domain knowledge show a greater improvement in their learning performance than those with higher domain knowledge. Furthermore, those who enjoy using the Web more are likely to have positive perceptions of non-linear interaction. Discussions on how to accommodate the different needs of students with varying levels of prior knowledge are provided based on the results

Post-Traumatic Pneumocele of the Frontal Sinus

A pneumocele is an abnormal dilatation of a paranasal sinus, most commonly affecting the frontal sinus. Although the etiology of pneumocele is not entirely known, several causative factors have been suggested including trauma, surgery, tumor and infection. We report here a case of post-traumatic pneumocele of the frontal sinus following a head trauma

Uneven Transformation of Traditional Agricultural Producers into Hybrid Peasant-Entrepreneurs through Social Media

The role and importance of Information and Communication Technologies (ICT) in agricultural production and rural development have been gradually increasing. Internet usage has rapidly been becoming an important part of the farmers’ daily lives globally and in Turkey. Even though the literature on ICT usage in rural areas and farmers has also been growing, certain influences have remained underresearched. To contribute to the literature that aims to fulfill this gap, this study aims at finding answers for three main questions. The first question examines the extent to which ICT in general and the internet in particular are used by the peasant farmers whose main economic activity is traditionally agricultural production. The second question explores the internet usage purposes of them, and the third question investigates in-depth the farmers’ social media usage as e-commerce platforms by focusing on the market coverage, customer characteristics, and its influences on farmers’ production, capital accumulation, and labor force relations. We conducted 297 open-ended questionnaires for the first question, 198 for the second, and 23 semi-structured interviews for the third with participants from randomly selected villages located in the Province of Kayseri in Turkey. Our study finds that social media provides farmers with opportunities of alternative markets. They paved themselves a new way of economic survival, which triggered an uneven emergence of hybrid peasant-entrepreneurs who are neither peasants nor entrepreneurs but rather seem to be stuck in between. They hold on to their lands and operate their family farms but tend to maintain their traditional production relations. Their production relies on unpaid family workers, and the traditional dominance of the family over production and accumulation relations still remains. We also find that this hybrid adaptation paves the way for uneven development in rural settlements that are located within the proximate areas of regional cities. Keywords: social media; agricultural production; hybrid peasant-entrepreneurs; uneven rural development; Turke

The concept of european citizenship in the european union and a common view on the problem of democracy deficit

This study addresses the question of democratic legitimacy between the European Union and the member states and a general assessment is made on the causes and dimensions of this problem of democracy deficit. The phenomenon of European citizenship emerged in the 1970s as a part and tool of the process of creating European identity. European citizenship is different from nation-state citizenship in classical meaning. The problem of democratic legitimacy is approached from an institutional and social perspective. Debate over the existence of European People's support for integration process and the size of sovereignty between the country's constitutions and the founding treaties of the European Union; It has brought debate about which European people and countries would prefer, and caused great disagreements. “The European Union represents both the greatest hope and the greatest threat to 21st century European democracy”