Micromechanical study of the dilatational response of porous solids with pressure-insensitive matrix displaying tension-compression asymmetry

In this paper, the dilatational response of porous solids with pressure-insensitive matrix displaying strength differential (SD) effects is investigated. To this end, micromechanical finite-element analyses of three-dimensional unit cells are carried out. The matrix behavior is governed by the isotropic form of Cazacu et al. (2006) criterion that accounts for SD effects through a parameter k. Simulation results are presented for axisymmetric tensile loadings corresponding to fixed values of the stress triaxiality for the two possible values of the Lode parameter, LP. For moderate and high stress triaxialities, it is shown that for materials for which the matrix tensile strength is larger than its compressive strength (k > 0), under tensile loadings corresponding at LP=1 the void growth rate is much faster than in the case of tensile loadings at LP=-1. The opposite holds true for materials with matrix tensile strength lower than its compressive strength (k< 0). This drastic difference in porosity evolution is explained by the distribution of the local plastic strain and stresses, which are markedly different than in a von Mises material (i.e. no SD effects of the matrix).info:eu-repo/semantics/publishedVersio

The role of tension-compression asymmetry of the plastic flow on ductility and damage accumulation of porous polycrystals

The influence of the tension-compression asymmetry of the plastic flow, due to intrinsic single-crystal deformation mechanisms, on porosity evolution and the overall ductility of voided metallic polycrystals is assessed. To this end, detailed micromechanical finite-element analyses of three-dimensional unit cells containing a single initially spherical cavity are carried out. The plastic flow of the matrix (fully-dense material) is described by a criterion that accounts for strength-differential effects induced by deformation twinning of the constituent grains of the metallic polycrystalline materials. The dilatational response of porous polycrystals are calculated for macroscopic axisymmetric tensile loadings corresponding to a fixed value of the stress triaxiality and the two possible values of the Lode parameter. It is shown that damage accumulation, and ultimately ductility of the porous polycrystals are markedly different as compared to the case when the matrix is governed by von Mises criterion. Most importantly, a direct correlation is established between the macroscopic material parameter k that is intimately related to the particularities of the plastic flow of the matrix and the rate of damage accumulation. (C) 2017 Portuguese Society of Materials (SPM). Published by Elsevier Espana, S.L.U.. All rights reserved.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) via the project PTDC/EMETEC/1805/2012.This work has been supported by FCT (Fundacao para a Ciencia e Tecnologia) in the scope of the project UID/EEA/04436/2013.info:eu-repo/semantics/publishedVersio

On the energy of a non-singular black hole solution satisfying the weak energy condition

The energy-momentum localization for a new four-dimensional and spherically symmetric, charged black hole solution that through a coupling of general relativity with non-linear electrodynamics is everywhere non-singular while it satisfies the weak energy condition is investigated. The Einstein and M\{o} ller energy-momentum complexes have been employed in order to calculate the energy distribution and the momenta for the aforesaid solution. It is found that the energy distribution depends explicitly on the mass and the charge of the black hole, on two parameters arising from the space-time geometry considered, and on the radial coordinate. Further, in both prescriptions all the momenta vanish.In addition, a comparison of the results obtained by the two energy-momentum complexes is made, whereby some limiting and particular cases are pointed out.Comment: 20 pages, 9 figure

On the effect of the ratio between the yield stresses in shear and in uniaxial tension on forming of isotropic materials

It is generally believed that the choice of the yield criterion used to describe the plastic behaviour of isotropic metallic materials does not affect much the accuracy of the predictions of forming operations. For this reason, the von Mises yield criterion is used for modelling the plastic behaviour. However, according to the von Mises yield criterion, irrespective of the material, the ratio between the yield stresses in simple shear and in uniaxial tension is the same. In this paper, it is presented a numerical study which reveals that even for one of the simplest deep drawing processes, namely the forming of a cylindrical cup, the yielding description influences the predictions of the plastic strains and the final profile of the part. For the description of yielding, an isotropic yield criterion which allows to differentiate between isotropic materials was used. Specifically, this yield criterion involves a parameter α which is expressible solely in terms of the ratio between the yield stresses in shear and in uniaxial tension; for α = 0 it reduces to the von Mises yield criterion. The results of the numerical study are revealing and are believed to provide a new point of view when considering material requirements for drawing performance and models to be used for prediction of the plastic behaviour in deep-drawing processes. From the analysis of the loading paths that the materials experience during the forming of the cup, it appears that the prevalent belief that the yielding properties in the tension-tension quadrant of the yield surface dictate the final profile should be reconsidered. Indeed, the simulations results indicate that for isotropic materials characterized by α > 0 (σT/τY> √ 3), the cup height is greater than for a von Mises material (α = 0), which is higher than the one obtained for materials with α < 0 (σT/τY< √ 3), i.e. lower values of the ratio between the yield stresses in shear and in uniaxial tension lead to greater cup heights. It is shown that this is mainly related to the plastic deformation of the material initially located in the flange region, which is dictated by the shape of the yield surface in the compression-tension quadrant (i.e. normal to the yield surface in the region between uniaxial compression and pure shear stress states).The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under the projects with reference PTDC/EME-EME/30592/2017 (POCI01–0145-FEDER-030592) and PTDC/EME-EME/31243/2017 (POCI01–0145-FEDER-031243) and by UE/FEDER through the program COMPETE2020 under the project MATIS (CENTRO-01–0145-FEDER000014) and UIDB/00285/2020. JLA and NC gratefully acknowledge partial support for this work from the Air Force Research Laboratory (AFRL) under contract FA8651–08-D-0108/52

Hardy's inequality for functions vanishing on a part of the boundary

We develop a geometric framework for Hardy's inequality on a bounded domain when the functions do vanish only on a closed portion of the boundary.Comment: 26 pages, 2 figures, includes several improvements in Sections 6-8 allowing to relax the assumptions in the main results. Final version published at http://link.springer.com/article/10.1007%2Fs11118-015-9463-

Point-of-care testing for disasters: needs assessment, strategic planning, and future design.

Objective evidence-based national surveys serve as a first step in identifying suitable point-of-care device designs, effective test clusters, and environmental operating conditions. Preliminary survey results show the need for point-of-care testing (POCT) devices using test clusters that specifically detect pathogens found in disaster scenarios. Hurricane Katrina, the tsunami in southeast Asia, and the current influenza pandemic (H1N1, "swine flu") vividly illustrate lack of national and global preparedness. Gap analysis of current POCT devices versus survey results reveals how POCT needs can be fulfilled. Future thinking will help avoid the worst consequences of disasters on the horizon, such as extensively drug-resistant tuberculosis and pandemic influenzas. A global effort must be made to improve POC technologies to rapidly diagnose and treat patients to improve triaging, on-site decision making, and, ultimately, economic and medical outcomes

Creating Conditions for Harnessing the Potential of Transitions to Agroecology in Europe and Requirements for Policy | Création de conditions pour exploiter le potentiel des transitions vers l'agroécologie en Europe et exigences des politiques | Schaffung von Bedingungen für die Nutzung des agrarökologischen Potenzials in Europa und Anforderungen an die Politik

The European Union’s Farm-to-Fork Strategy sets out its ambitions and approach to how European’s value food sustainability, and the accompanying opportunities for improving the environment as well as the lifestyles and health of EU citizens. It identifies the role of agroecological approaches in primary production as one of the means by which these ambitions can be achieved, through new knowledge and innovations in land management and supply chains. This article concludes the Special Issue on the EU Horizon 2020 projects LIFT and UNISECO, synthesising requirements for the realisation of transitions to agroecology in Europe. It reports the key needs identified of developing human capital, partnerships, cooperation and social capital, access to data and tools, and the links between these needs and relevant EU and national level policies.Les systèmes alimentaires doivent être réorientés pour mieux prendre en compte les interactions avec l’environnement, l’économie, la santé et la société. Les transitions vers des pratiques et des systèmes agricoles agroécologiques peuvent relier les domaines de l’action publique et permettre d'atteindre des objectifs environnementaux, économiques et sociaux. Ces transitions fournissent une perspective pour examiner les politiques, les pratiques et les comportements des acteurs des systèmes agricoles et des chaînes de valeur, l’identifi cation des obstacles à l'adoption et les domaines d’action publique auxquels ils contribuent ou qui présentent des lacunes. Le développement du capital social et humain et de structures de gouvernance qui permettent les transitions vers l’agroécologie est la clé de leurs chances de succès. L’éducation et l’apprentissage tout au long de la carrière sont essentiels pour développer les connaissances et les compétences des jeunes générations de gestionnaires fonciers et d’autres acteurs des chaînes de valeur, tout au long de leur carrière. Le résultat recherché est une compréhension partagée des avantages des pratiques et des systèmes agroécologiques, créant des opportunités pour rééquilibrer les politiques vers la neutralité climatique, inverser la perte de biodiversité et renforcer les droits des citoyens. Pour concrétiser ces opportunités, les politiques et stratégies doivent être cohérentes à tous les niveaux territoriaux et systémiques, et adaptées au lieu, au système, aux personnes et aux étapes des transitions. Dans l’ensemble, elles devraient être conçus pour garantir que tous les citoyens bénéfi cient des transitions vers des systèmes agricoles agroécologiques, sur le long terme, et que personne ni aucun lieu ne soit désavantagé par les processus de changement ou les résultats escomptés.Die Lebensmittelsysteme müssen neu ausgerichtet werden, um den Wechselwirkungen zwischen der Umwelt, der Wirtschaft, der Gesundheit und der Gesellschaft stärker Rechnung zu tragen. Die Umstellung auf agrarökologische Anbaumethoden und - systeme kann die Politikbereiche miteinander verbinden und zur Erreichung ökologischer, wirtschaftlicher und sozialer Ziele beitragen. Sie bieten einen Ansatzpunkt für die Überprüfung der Politik, der Praxis und der Verhaltensweisen der Akteure in landwirtschaftlichen Systemen und Wertschöpfungsketten. Des Weiteren helfen sie bei der Ermittlung von Umsetzungsbarrieren und von Politikbereichen, zu denen sie beitragen oder in denen es Lücken gibt. Die Entwicklung von Sozial- und Humankapital sowie von Governance- Strukturen – die den Übergang zur Agrarökologie ermöglichen – sind ein wesentlicher Erfolgsfaktor. Bildung und lebenslanges Lernen sind ein zentraler Baustein, um die Kenntnisse und Fähigkeiten der jüngeren Generationen von Landwirten und Landwirtinnen und anderen Akteuren in den Wertschöpfungsketten zu entwickeln. Das angestrebte Ergebnis ist ein gemeinsames Verständnis über die Vorteile agrarökologischer Praktiken und Systeme. Dieses schafft Möglichkeiten für eine Neuausrichtung der Politik im Hinblick auf Klimaneutralität, Umkehrung des Verlusts der biologischen Vielfalt und Stärkung der Rechte der Bürger. Zur Verwirklichung der Möglichkeiten, sollten Politiken und Strategien über territoriale und Systemebenen hinweg kohärent und auf Ort, System, Menschen und Phasen des Übergangs zugeschnitten sein. Insgesamt sollten sie so konzipiert sein, dass alle Bürgerinnen und Bürger langfristig von der Umstellung auf agrarökologische Bewirtschaftungssysteme profi tieren und dass niemand oder kein Ort durch den Veränderungsprozess oder das angestrebte Ergebnis benachteiligt wird

Endoscopic Ultrasound-Guided Fiducial Placement for Stereotactic Body Radiation Therapy in Patients with Pancreatic Cancer

Accurate delivery of stereotactic body radiotherapy (SBRT) to pancreatic tumors relies on successful EUS-guided placement of fiducial markers. The aim of this study is to report the technical feasibility and safety of EUS-guided fiducial placement and to evaluate the characteristics and technical benefit of SBRT in a cohort of patients with pancreatic cancer (PC). A retrospective chart review was performed for all (n = 82) PC patients referred for EUS-guided fiducial placement by a single endosonographer at a tertiary cancer center. Data regarding EUS-related technical details, SBRT characteristics, adverse events, and continuous visibility of fiducials were recorded and analyzed. Most patients included in the study had either locally advanced disease (32 patients, 39%) or borderline resectable disease (29 patients, 35%). Eighty-two PC patients underwent the placement of 230 fiducial markers under EUS guidance. The technical success rate of the fiducial placement was 98%. No immediate EUS-related adverse events were reported. The average time to the simulation CT after fiducial placement was 3.1 days. Of the 216 fiducial markers used for the SBRT delivery, 202 fiducial markers were visible on both the simulation CT and the cone beam CT scan. A median dose of 40cGY was given to all the patients in five fractions. Of these, 41% of the patients reported no SBRT-related toxicities during the follow-up. Fatigue and nausea were the most reported SBRT-related toxicities, which were seen in 35% of the patients post-SBRT. Our results demonstrate that EUS-guided fiducial placement is safe and effective in target volume delineation, facilitating SBRT delivery in PC patients. Further clinical trials are needed to determine the SBRT-related survival benefits in patients with pancreatic cancer