Thermal effects on atomic friction

We model friction acting on the tip of an atomic force microscope as it is dragged across a surface at non-zero temperatures. We find that stick-slip motion occurs and that the average frictional force follows $|\ln v|^{2/3}$, where $v$ is the tip velocity. This compares well to recent experimental work (Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all microscopic parameters. We calculate the scaled form of the average frictional force's dependence on both temperature and tip speed as well as the form of the friction-force distribution function.Comment: Accepted for publication, Physical Review Letter

Early and Middle Holocene Hunter-Gatherer Occupations in Western Amazonia: The Hidden Shell Middens

We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region's past and offers a new context within which the late Holocene "Earthmovers" of the Llanos de Moxos could have emerged. © 2013 Lombardo et al

Game accessibility for visually impaired people: a review

Playing games is an important way to promote the integration, inclusion, and socialization of participants. This is especially the case of persons with disabilities, such as visually impaired people. Unfortunately, very few games are accessible to such persons. Hopefully, in many digital games, this accessibility can be enabled in principle by assistive technologies, such as screen readers. The aim of this work consists in reviewing the recent literature on game accessibility for people with visual impairment and discussing benefits, limitations, and possible improvements of currently available accessibility solutions. After providing a definition of visual impairment and describing its relationship with gaming, the work reviews general techniques for designing more accessible games. Subsequently, it focuses on specific techniques based on replacing visual stimuli with auditory stimuli (e.g., sonification and sound-source simulation), also presenting some recently proposed sonification-mapping strategies. Then, the application of machine-learning techniques to the development of accessible interfaces for online versions of board games is illustrated by a recent case study. Finally, a discussion and some conclusions are provided, with a particular focus on policy implications of improvements in game accessibility for visually impaired people

Velocity tuning of friction with two trapped atoms

Our ability to control friction remains modest, as our understanding of the underlying microscopic processes is incomplete. Atomic force experiments have provided a wealth of results on the dependence of nanofriction on structure velocity and temperature but limitations in the dynamic range, time resolution, and control at the single-atom level have hampered a description from first principles. Here, using an ion-crystal system with single-atom, single-substrate-site spatial and single-slip temporal resolution we measure the friction force over nearly five orders of magnitude in velocity, and contiguously observe four distinct regimes, while controlling temperature and dissipation. We elucidate the interplay between thermal and structural lubricity for two coupled atoms, and provide a simple explanation in terms of the Peierls–Nabarro potential. This extensive control at the atomic scale enables fundamental studies of the interaction of many-atom surfaces, possibly into the quantum regime

Salt Dependence of the Tribological Properties of a Surface-Grafted Weak Polycation in Aqueous Solution

The nanoscopic adhesive and frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with gold- or PDMAEMA-coated atomic force microscope tips in potassium halide solutions with different concentrations up to 300 mM is a strong function of salt concentration. The conformation of the polymers in the brush layer is sensitive to salt concentration, which leads to large changes in adhesive forces and the contact mechanics at the tip–sample contact, with swollen brushes (which occur at low salt concentrations) yielding large areas of contact and friction–load plots that fit JKR behaviour, while collapsed brushes (which occur at high salt concentrations) yield sliding dominated by ploughing, with conformations in between fitting DMT mechanics. The relative effect of the different anions follows the Hofmeister series, with I − collapsing the brushes more than Br − and Cl − for the same salt concentration

Evaluating hydrological and socio-economic impacts of green/blue space projects for storm water management = Evaluation des effets hydrologiques et socioéconomiques des espaces verts/bleus pour la gestion des eaux de pluie

FR: Les régions et villes européennes doivent faire face à des nombreuses questions liées à l'eau :gestion des eaux pluviales, qualité de l'eau, impact des sécheresses sur les milieux aquatiques. Pourrépondre durablement à ces questions, il est évident que l'eau doit être intégrée dans ledéveloppement urbain et dans les politiques d'aménagement du territoire. L'objectif général du projetpour la coopération interrégionale Aqua-Add (Mieux intégrer l'eau dans les projets urbains) est dedéployer le potentiel de l'eau dans les paysages urbains (potentiel économique, social etenvironnemental). Dans ce contexte, l'approche hydrologique et un modèle hédonique des prix sontintégrés et appliqués afin de vérifier les effets hydrologiques et socio-économiques des différentessolutions pour la gestion des eaux de pluie, et de faciliter le débat avec les acteurs de l'aménagement.L'objectif de cette étude est d'évaluer les effets hydrologiques et socio-économiques des espacesverts/bleus pour la gestion des eaux de pluie dans les villes moyennes. Nous présentons et étudionsici plus particulièrement l'étude de cas de Imperia (Italie)European regions and cities face important challenges related to water management, includingstorage, discharge, quality and periodic stress. To address these challenges, it is evident that watermust become an integral part of urban planning policies and their implementation. The internationalco-operation project Aqua-Add (Deploying the added value of water in local and regionaldevelopment) aims to deploy the potential of 'water' (economically, socially and environmentally) inurbanized landscapes and to improve the implementation of water measures in local and regionalurban planning. In this framework, hydrologic and hedonic-pricing simulation modelling approachesare integrated and applied in order to demonstrate the potential environmental, social and economicimpacts of different water management scenarios as well as to facilitate more informed decisionmaking across stakeholders. The objective of this paper is to assess the hydrological as well as socioeconomic implications of green/blue space projects for storm water management in medium-sizedcities. In particular, the case study of Imperia (Italy) is here presented and discussed