Silica glass interaction with calcium hydroxide: a surface chemistry approach     

Lidia Armelao  Arianna Bassan  Renzo Bertoncello  Guido Biscontin  Sergio Daolio  Antonella Glisenti 《Journal of Cultural Heritage》2000,1(4)

The study of the interaction between silica glass and saturated Ca(OH)₂ solutions can be a useful approach to resolve the problem of the adhesion between lime-sand mortar and clay bricks. Since it is reasonable that the silica–calcium hydroxide system well simulates a brick–mortar system, experimental observations concerning the interaction of silica glass and this strong basic solution should be of value for the comprehension of the chemical reactions that could take place at the mortar–brick interface, maybe affecting the adhesion between the two building materials. We demonstrated the effects of saturated Ca(OH)₂ solutions on commercial pure silica glass (fused silica) and on silica films obtained via a sol–gel process by means of dip-coating. Silica samples were dipped in the solutions at different temperatures (room temperature, 60 and 80 °C) and at different time intervals (1 and 21 h) and then they were analysed by means of surface techniques: X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and atomic force microscopy (AFM). It has been shown that Ca(OH)₂ reacts with the silica glass network. The experimental results clearly show a very different behaviour of sol–gel silica with respect to fused silica, probably because of their different nanostructure. Many problems concerning the interaction of silica and Ca(OH)₂ are still to be solved, but the results of this research strengthen the idea that adhesion between lime-sand mortar and clay bricks is caused not only by carbonation of calcium hydroxide contained in the mortar, but even by some chemical reactions involving the brick constituents and calcium hydroxide itself. The final products, calcium silicates, may induce a chemical continuity between lime-sand mortar and clay bricks.  相似文献   

Learning design and learning analytics in mobile and ubiquitous learning: A systematic review     

Gerti Pishtari  María J. Rodríguez-Triana  Edna M. Sarmiento-Márquez  Mar Pérez-Sanagustín  Adolfo Ruiz-Calleja  Patricia Santos  Luis P. Prieto  Sergio Serrano-Iglesias  Terje Väljataga 《British journal of educational technology : journal of the Council for Educational Technology》2020,51(4):1078-1100

Mobile and Ubiquitous Learning (m/u-learning) are finding an increasing adoption in education. They are often distinguished by hybrid learning environments that encompass elements of formal and informal learning, in activities that happen in distributed settings (indoors and outdoors), across physical and virtual spaces. Despite their purported benefits, these environments imply additional complexity in the design, monitoring and evaluation of learning activities. The research literature on learning design (LD) and learning analytics (LA) has started to deal with these issues. This paper presents a systematic literature review of LD and LA, in m/u-learning. Apart from providing an overview of the current research in the field, this review elicits elements of common ground between both communities, as shown by the similar learning contexts and complementary research contributions, and based on the research gaps, proposes to: address m/u-learning beyond higher education settings, reinforce the connection between physical and virtual learning spaces, and more systematically align LD and LA processes.  相似文献   

Argumentative abilities in metacognition and in metalinguistics: a study on university students     

Maria Antonietta Pinto  Paolo Iliceto  Sergio Melogno 《European Journal of Psychology of Education - EJPE》2012,27(1):35-58

The article presents a study on metalinguistic, cognitive and metacognitive abilities in university students. A sample of 353 students was recruited; 178 of which from scientific and 175 from humanistic Faculties, with gender balance (M = 178; F = 175) whose age range was between 20 and 25 years old. They were administered a metalinguistic ability test that assesses metalinguistic awareness at implicit and explicit levels (L and ML scores) and the Raven’s Standard Progressive Matrices 38 (SPM38). In addition to the usual nonverbal administration of the matrices, candidates were asked to justify in written form the reasons for the solution indicated in each item. Three scores were considered for the SPM38: the ordinary score based on the number of correct nonverbal solutions (O.S.), a 7-point scale for assessing the argumentation of the correct solutions (C.ARG.S.) and a 6-point scale for assessing the argumentation of the incorrect solutions (I.ARG.S.). Significant gender and curriculum effects were found, with males and scientific students dominating at the nonverbal level while females and humanistic students dominated in the argumentative abilities related to the matrices and in all the scores of the metalinguistic test. A number of significant correlations were found between all the metalinguistic, cognitive and metacognitive abilities considered, with a prominent role of the metalinguistic abilities at the explicit level (ML score) that show a clear argumentative structure very similar to the C.ARG.S. argumentations in the matrices test.  相似文献   

Understanding risks,benefits, and strategic alternatives of social media applications in the public sector     

Sergio Picazo-Vela  Isis Gutiérrez-Martínez  Luis Felipe Luna-Reyes 《Government Information Quarterly》2012

Social media such as blogs, microblogs or electronic social networks can transform the ways in which we relate to other people and organizations. Government organizations are experimenting with social media to communicate with their constituents, and many analysts see in these media a powerful set of tools to reinvent government–citizen relationships. In this paper, we present the perceptions of risks, benefits and strategic guidelines about social media applications gathered from 250 public servants from Central Mexico, most of them working in information technology, as web masters or responding to Freedom of Information Act requests. The conclusions of the analysis are 1) that governments' participation in social media may result in improved communication and citizen participation, more transparency, and transfer of best practices among government agencies; 2) that a good implementation strategy is necessary to realize these benefits and to avoid risks; and 3) that the implementation of social media highlights the importance of updating laws and regulations, and of promoting changes in government culture and organizational practices.  相似文献   

Mental Representation of Literary Characters as a Distinct Aspect of Response to Literature     

Sergio Morra  Guðný Guðbjörnsdóttir 《Scandinavian Journal of Educational Research》2013,57(6):591-615

This article investigates mental representations of literary characters and their relations with other aspects of response to literature and age, gender, and expertise. A Saga chapter and the beginning of a contemporary novel were presented to 16 participants from each of three age groups (13 years, 17 years, adults) equally divided by gender and expertise level. After having evaluated the texts with rating scales, participants were interviewed on the main character of each text. The similarity between participants’ answers was computed and used for a cluster analysis. Four clusters (representation types) were identified for one character and five for the other. Character representation was affected by age but not by expertise and gender, and was unrelated to other aspects of response to literary text. Explicit ratings of the texts, instead, were affected by expertise. Theoretical and educational implications are discussed.  相似文献   

Ranking dynamics and volatility     

Carlos Garcia-Zorita  Ronald Rousseau  Sergio Marugan-Lazaro  Elias Sanz-Casado 《Journal of Informetrics》2018,12(3):567-578

Scientific journals are ordered by their impact factor while countries, institutions or researchers can be ranked by their scientific production, impact or by other simple or composite indicators as in the case of university rankings. In this paper, the theoretical framework proposed in Criado, R., Garcia, E., Pedroche, F. & Romance, M. (2013). A new method for comparing rankings through complex networks: Model and analysis of competitiveness of major European soccer leagues. Chaos, 23, 043114 for football competitions is used as a starting point to define a general index describing the dynamics or its opposite, stability, of rankings. Some characteristics to study rankings, ranking dynamics measures and axioms for such indices are presented. Furthermore, the notion of volatility of elements in rankings is introduced. Our study includes rankings with ties, entrants and leavers. Finally, some worked out examples are shown.  相似文献   

Gaze pursuit and arm control of adolescent males diagnosed with attention deficit hyperactivity disorder (ADHD) and normal controls: evidence of a dissociation in processing visual information of short and long duration     

Vickers JN  Rodrigues ST  Brown LN 《Journal of sports sciences》2002,20(3):201-216

Three-dimensional kinematic analysis of line of gaze, arm and ball was used to describe the visual and motor behaviour of male adolescents diagnosed with attention deficit hyperactivity disorder (ADHD). The ADHD participants were tested when both on (ADHD-On) and off (ADHD-Off) their medication and compared to age-matched normal controls in a modified table tennis task that required tracking the ball and hitting to cued right and left targets. Long-duration information was provided by a pre-cue, in which the target was illuminated approximately 2 s before the serve, and short-duration information by an early-cue illuminated about 350 ms after the serve, leaving approximately 500 ms to select the target and perform the action. The ADHD groups differed significantly from the control group in both the pre-cue and early-cue conditions in being less accurate, in having a later onset and duration of pursuit tracking, and a higher frequency of gaze on and off the ball. The use of medication significantly reduced the gaze frequency of the ADHD participants, but surprisingly this did not lead to an increase in pursuit tracking, suggesting a barrier was reached beyond which ball flight information could not be processed. The control and ADHD groups did not differ in arm movement onset, duration and velocity in the short-duration early-cue condition; in the long-duration pre-cue condition, however, the ADHD group's movement time onset and arm velocity differed significantly from controls. The results show that the ADHD groups were able to process short-duration information without experiencing adverse effects on their motor behaviour; however, long-duration information contributed to irregular movement control.  相似文献   

Dominant–non-dominant asymmetry of kicking a stationary and rolling ball in a futsal context     

Fabio Augusto Barbieri  Lilian Teresa Bucken Gobbi  Paulo Roberto Pereira Santiago  Sergio Augusto Cunha 《Journal of sports sciences》2015,33(13):1411-1419

The aim of this study was to analyse the characteristics of the asymmetries in the dominant and non-dominant limbs when kicking stationary and rolling balls. Ten experienced Brazilian amateur futsal players participated in this study. Each participant performed kicks under two conditions (stationary ball vs. rolling ball) with the dominant and non-dominant limbs (five kicks per condition per limb). We analysed the kicking accuracy, ball and foot velocities, angular joint displacement and velocity. The asymmetry between the dominant and non-dominant limbs was analysed by symmetry index and two-way repeated measures ANOVA. The results did not reveal any interaction between the condition and limb for ball velocity, foot velocity and accuracy. However, kicking with the dominant limb in both kicks showed higher ball velocity (stationary ball: dominant – 24.27 ± 2.21 m · s^?1 and non-dominant – 21.62 ± 2.26 m · s^?1; rolling ball: dominant – 23.88 ± 2.71 m · s^?1 and non-dominant – 21.42 ± 2.25 m · s^?1), foot velocity (stationary ball: dominant – 17.61 ± 1.87 m · s^?1 and non-dominant – 15.58 ± 2.69 m · s^?1; rolling ball: dominant – 17.25 ± 2.26 m · s^?1 and non-dominant – 14.77 ± 2.35 m · s^?1) and accuracy (stationary ball: dominant – 1.17 ± 0.84 m and non-dominant – 1.56 ± 1.30 m; rolling ball: dominant – 1.31 ± 0.91 m and non-dominant – 1.97 ± 1.44 m). In addition, the angular joint adjustments were dependent on the limb in both kicks (the kicks with non-dominant limb showed lower hip external rotation than the kicks with the dominant limb), indicating that the hip joint is important in kick performance. In conclusion, the kicks with the non-dominant limb showed different angular adjustments in comparison to kicks with the dominant limb. In addition, kicking a rolling ball with the non-dominant limb showed higher asymmetry for accuracy, indicating that complex kicks are more asymmetric.  相似文献   

Boccioni's coin     

Giuntini S  Teja A 《国际体育史杂志》2011,28(3-4):393-409

The Ardito was a fighter as well as a competitor whose status as a 'warrior' was based on courage and superior physical performance: a superior man. In addition, his exuberant conduct, both on and off the battlefield, introduced a significant new sub-culture into post-war Italian society, contributing to the attachment of notable value to virility and Mussolini's cult of the 'strong man'. The purpose of this research is to analyse the impact of this 'arditismo' (spirit of daring) on the early post-war period in particular, including the different 'male image' of the Italian citizen, and to study the sense of virility in the transition from the liberal, easy-going 'Little Italy' of Giovanni Giolitti (1842-1928) to a manly, combative, and ambitious nation. Together with some of the vitalistic tendencies in the Futurist movement, the main characteristics and mentality of the ex-Ardito (former Special Forces) would thus be significantly influential in the ideology of nascent Fascism. Indeed, the 'arditismo' influence, together with the article and social movement known as Futurism would constitute the two most highly structured foundations of early Fascist culture, bringing a political and social revolution necessary to create a 'new man'. It was as if the Arditi and the new method of military training had transferred their experience from the military into civilian life, contributing to a renewal of the image of the Italian male in the collective imagination. Indirectly, the image of women would also begin to absorb and adapt to new sports models imported from abroad, which would create for the Italian Ardito, a grudgingly tolerated rival. The main sources for this paper are the archives of the Historical Office of the Army, advertising and manuals from the late nineteenth to the early twentieth century, placards and graphic publicity from books and journals or private collections, and exhibition catalogues.  相似文献   

克隆人偏执狂?     

SergioPistoi  刘永军 《科学中国》2002,(6):20-21

本刊今年第4、5期连续报道了世界上首例人类克隆胚胎的消息及引起的广泛议论.4月初的互联网与大众媒体争相报道了意大利生育专家安蒂诺里宣称利用克隆技术成功让一名不育妇女怀孕8周的消息,这一消息同样在全球掀起了轩然大波及广泛议论.  相似文献