Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts

Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is usually explained using adhesion models. Here we show that quantitative agreement with recent high-load experiments can be obtained, with no adjustable parameter, using a non-adhesive model, provided that finite deformations are taken into account. Analysis of the model uncovers the basic mechanisms underlying shear-induced area reduction, local contact lifting being the dominant one. We confirm experimentally the relevance of all those mechanisms, by tracking the shear-induced evolution of tracers inserted close to the surface of a smooth elastomer sphere in contact with a smooth glass plate. Our results suggest that finite deformations are an alternative to adhesion, when interpreting a variety of sheared contact experiments involving soft materials.Comment: Version accepted at J. Mech. Phys. Solids. It includes Supplementary Informatio

Knowledge assessment and sharing on sustainable agriculture. Main lessons.

1 CD-ROM. Projeto DG-Research - Contract nº GOCE-CT-2004-505582

Knowledge assessment and sharing on sustainable agriculture. Main results, gaps in knowledge and challenges in the Latin American platform.

1 CD-ROM. Projeto DG-Research - Contract nº GOCE-CT-2004-505582

Electrocaloric effect in Ba(0.2)Ca(0.8)Ti(0.95)Ge(0.05)O(3) determined by a new pyroelectric method

The present letter explores the electrocaloric effect (ECE) in the lead free oxide Ba0.8Ca0.2Ti0.95Ge0.05O3 ceramics (BCTG). The electrocaloric responsivity (dT/dE) was determined by two different methods using the Maxwell relationship (dT/dE)~(dP/dT)_E. In a first well-known indirect method, P-E hysteresis loops were measured in a wide temperature range from which the pyroelectric coefficient p_E=(dP/dT)_E and thus (dT/dE) were determined by derivation of P(T,E) data. In the second novel method the pyroelectric coefficient p_E and consequently the electrocaloric responsivity was determined by direct measurements of the pyroelectric currents under different applied electric fields. Within the experimental error good agreement was obtained between two methods with an electrocaloric responsivity equal to 0.18 +/- 0.05 10-6 K.m.V-1 was obtained at about 410 KComment: 5 pages, 4 figure

Under threes' play with tablets

This paper outlines the key findings of a study developed in collaboration between academics, teachers and children’s media companies. The project was co-produced in that all project partners contributed to the development of the project aims and objectives and were involved in data collection, analysis and dissemination. The aim of the study was to identify children's uses of and responses to apps in terms of their play and creativity. This paper focuses on the digital play with tablets of children aged from birth to three. Ofcom (2019:4) has reported that six in ten of three- and four-year-olds in the UK use any device to go online, with 49% using a tablet for this purpose. This is a large, and growing, market that deserves the attention of researchers (Kucirkova and Radesky, 2017). Given that technology is embedded in children’s lives, playing an important part in their ‘multimodal lifeworlds’ (Arnott and Yelland, 2020), it is timely to consider what value this use has in relation to play and creativity, as both are highly significant to children’s development (Broadhead, Howard and Wood, 2010)

Under threes’ play with tablets

This paper outlines the findings from a study that examined the tablet and app use of children aged from birth to three. The aim of the study was to examine how far use of tablets and apps promoted play and creativity. A total of 954 UK parents of children aged from birth to three who had access to a tablet in the home completed an online survey that explored the children’s use of apps. Ethnographic case studies of four children aged from birth to three were undertaken in homes in order to explore in greater depth issues that emerged in the survey. The paper reports on the way in which the use of tablets promoted play and creativity across cognitive, physical social and cultural domains. The implications for policy and research are outlined

Wigner's Dynamical Transition State Theory in Phase Space: Classical and Quantum

A quantum version of transition state theory based on a quantum normal form (QNF) expansion about a saddle-centre-...-centre equilibrium point is presented. A general algorithm is provided which allows one to explictly compute QNF to any desired order. This leads to an efficient procedure to compute quantum reaction rates and the associated Gamov-Siegert resonances. In the classical limit the QNF reduces to the classical normal form which leads to the recently developed phase space realisation of Wigner's transition state theory. It is shown that the phase space structures that govern the classical reaction d ynamicsform a skeleton for the quantum scattering and resonance wavefunctions which can also be computed from the QNF. Several examples are worked out explicitly to illustrate the efficiency of the procedure presented.Comment: 132 pages, 31 figures, corrected version, Nonlinearity, 21 (2008) R1-R11

Addressing the ‘whys’ of UK children’s YouTube use: a purposes approach

Despite the widespread use of YouTube by children, there has been limited research undertaken on the “why” questions of their use. Past theoretical approaches have framed these questions in terms of broader individual needs and their relation to media use, though this work has mainly focused on adults and adolescents. This article presents relevant findings from a mixed methods study of children’s (aged 0–16) uses of social media in the United Kingdom to consider instead the “purposes” of children’s YouTube use, drawing on: (1) an online family survey; (2) family case studies; (3) child focus groups; and (4) child telephone interviews. “Purpose” is theorized in the article in relation to the ways children themselves make sense of and articulate the reasons they use YouTube or, in the case of parents and carers, for allowing, facilitating, or encouraging their children to use YouTube. Parents tended to frame the purposes of children’s YouTube use more instrumentally, focusing on perceived educational benefits and their own convenience needs. While sharing a focus on instrumental purposes, children sometimes emphasized broader dimensions of purpose, with an increased focus on humor, sensory, and hedonic dimensions. Children’s responses also emphasized the autotelic nature of play. The study foregrounded the extent to which the purposes of others (such as commercial entities) are served by children’s YouTube use. Seven child-centered, parent-centered, and “other” purposes for children’s YouTube use are discussed: cognitive, corporeal, cultural, collaborative, creative, commercial, and convenience