Toughness improvement of polyamide 11 assessed via quasistatic tensile tests on notched round bars

International audienceToughening a polymeric material by adding rubber particles is a common technique used forglassy polymers and measured by means of Charpy or Izod impact tests. These latter aredetermined under dynamic conditions, thus at high strain rate or equivalently at very lowtemperature for polymeric materials.This work is devoted to three grades of semi-crystalline PolyAmide 11 (PA11), used in alarge number of engineering components. Service conditions are close to the glass transitiontemperature. Therefore, tests with quasi-static loading are expected to be more appropriate.The aim of the study is to find a methodology allowing the quantification of toughnessimprovement. To this end, an experimental database was constituted. Three grades of PA11were involved, that enable to analyze effects of: i) aging, ii) addition of a plasticizer iii)addition of rubber particles. Tensile tests were then carried out on notched round bars.Trends of load versus notch opening displacement curves are investigated. Longitudinalcross-sections on specimens issued from interrupted tests and fracture surfaces wereexamined in order to study deformation and damage mechanisms. An attempt is made to linktoughness improvement to the increase in global fracture energy

Étude de la rétrodiffusion des surfaces d'eau en bande Ka à faible incidence

The evolution of the altimetric techniques from Ku-band to Ka-band and the wide swath al-timetry in the context of the SWOT mission (« Surface Water Ocean Topography », CNES/NASA) raises new scientific questions about the validity of the backscattering models from water sur-faces in such a frequency band and errors in estimating water heights from time-evolving water surfaces. A backscattering model (GO4) adapted to the SWOT configuration is introduced. It preserves the accuracy of the referencial Physical Optics model while maintaining the simplicity of the clas-sical Optical Geometrics model. In addition to the classical slope parameter, it introduces another parameter called as « effective curvature » (msc). This model allows the inverson of the surface slope and curvature parameters under certain conditions which are developped in this manus-cript. The joint validity of the backscattering models in Ka-band and from water surfaces is che-cked from controlled wind-wave tank radar measurements . In a last part, the temporal properties of the backscattered signal is studied, in particular the correlation time and the Doppler shift induced by waves motion. Influence of the latters on the non focused SAR synthesis is studied in the context of the SWOT system.L’évolution des techniques altimétriques de la bande Ku Nadir vers la bande Ka et l’interféro-métrie large fauchée proche Nadir dans le contexte de la mission SWOT (« Surface Water Ocean Topography », CNES/NASA) soulève de nouvelles questions scientifiques quant à la validité des modèles de rétrodiffusion des surfaces d’eau dans cette bande de fréquence et les erreurs sur les estimations de hauteurs d’eau dues aux mouvements de ces surfaces au cours du temps. Un modèle de rétrodiffusion (GO4) adapté à la configuration SWOT est présenté. Il conserve la précision du modèle de référence de l’Optique Physique tout en gardant la simplicité du modèle plus couramment employé de l’Optique Géométrique. En plus du paramètre classique de pente, il introduit un paramètre supplémentaire, dit de « courbure effective » (msc). Le modèle permet l’inversion des paramètres de pente et de courbure de la surface sous certaines conditions déve-loppées dans ce manuscrit. La validité des modèles conjoints de rétrodiffusion en bande Ka et de surface d’eau a été vérifiée sur des mesures radar effectuées en soufflerie dans un environnement contrôlé. Dans une dernière partie, les propriétés temporelles du signal rétrodiffusé ont été étudiées, en particulier le temps de corrélation et le décalage Doppler induit par le mouvement des vagues. Nous étudions l’influence de ces quantités sur les performances de la synthèse SAR non focalisée du système SWOT

An evaluation of the complete replacement of both fishmeal and fish oil in diets for juvenile Asian seabass, Lates calcarifer

An experiment was conducted to examine the potential for the complete replacement of fishmeal (FM) and fish oil (FO) in diets for barramundi,Lates calcarifer. A series of diets were formulated to the same digestible protein and energy specifications, but which were designed with FM inclusion levels at 300, 200, 100 or 0g/kg and FO at 100%, 30%, 15% or 0% of the added oil in the diets (4×4 factorial design). Ricebran oil was the alternative oil used in the growth study, while soybean meal and poultry meal were the main alternative protein sources used. For the growth study, fish of an initial weight of 154.4±1.1g were randomly allocated across 48 tanks (three replicates per treatment). After eight weeks, the average weight gain across all treatments was 187.7±2.3g/fish and feed conversion across all treatments averaged 1.04±0.01 feed/gain. A significant effect of FM on both feed intake and weight gain was observed, and this was observed as early as within the first few weeks, but no similar such effect was observed with FO. No effects were observed on protein deposition efficiency, though both lipid and energy deposition efficiencies were affected by FM level. The reduction in FO had a notable effect on the fatty acid composition of the diets and subsequently the fish fatty acid composition. Expression of key LC-PUFA metabolism genes in the liver of the fish was influenced by both FM and FO levels, but was only significant at the extremes of the treatment ranges. The results from this study demonstrate that there is clear potential to replace almost all the FM content of barramundi diets without loss of fish performance, up to and including diets with as little as 100g/kg fishmeal. Replacement of fish oil was more successful with the ability to completely replace all FO demonstrated at all but the lowest inclusion levels of FM. These results clearly demonstrate that the near complete replacement of both FM and FO in barramundi diets is a technical reality

The architectural profession: a management viewpoint.

Massachusetts Institute of Technology. Dept. of Urban Studies and Planning. Thesis. 1971. M.C.P.Bibliography: leaves 167-172.M.C.P

A comparative study on communication structures of Chinese journals in the social sciences

We argue that the communication structures in the Chinese social sciences have not yet been sufficiently reformed. Citation patterns among Chinese domestic journals in three subject areas -- political science and marxism, library and information science, and economics -- are compared with their counterparts internationally. Like their colleagues in the natural and life sciences, Chinese scholars in the social sciences provide fewer references to journal publications than their international counterparts; like their international colleagues, social scientists provide fewer references than natural sciences. The resulting citation networks, therefore, are sparse. Nevertheless, the citation structures clearly suggest that the Chinese social sciences are far less specialized in terms of disciplinary delineations than their international counterparts. Marxism studies are more established than political science in China. In terms of the impact of the Chinese political system on academic fields, disciplines closely related to the political system are less specialized than those weakly related. In the discussion section, we explore reasons that may cause the current stagnation and provide policy recommendations

Small- and medium-sized enterprises’ knowledge management systems as edifiers of new value innovations

Abstract: Background: New value innovations are organically ingrained and complementary to the process of knowledge management. However, epistemological trends highlight only limited studies to have explored how the effectiveness of knowledge management leverages new value innovations. Objectives: This research evaluates how the effectiveness of the small- and medium-sized enterprises’ (SMEs) knowledge management systems enhance new value innovations so as to identify the major paradoxes and a business model that coherently integrates knowledge management with new value innovations. Method: Using a qualitative research method, semi-structured interviews were used to explore the opinions of 20 purposively sampled managers from 20 SMEs on how knowledge management edifies new value innovations. Results: A strong culture of information utilisation was found to enhance relevant analysis and identification of new gaps in the markets that must be filled through new value innovations or modifications of the existing products. However, poor culture of knowledge utilisation, cost of knowledge management and the often poorly functional business information systems were still reiterated as major paradoxes hampering effective knowledge management as one of the determinants of new value innovations. Conclusion: The study concluded with a model highlighting a continuum of knowledge management–new value innovation pillars like a strong culture of information utilisation, and encouragement of creativity that the executives must consider to create an effective knowledge management foundation that subsequently leverages the overall effectiveness of new value innovations

What lies beneath? The role of informal and hidden networks in the management of crises

Crisis management research traditionally focuses on the role of formal communication networks in the escalation and management of organisational crises. Here, we consider instead informal and unobservable networks. The paper explores how hidden informal exchanges can impact upon organisational decision-making and performance, particularly around inter-agency working, as knowledge distributed across organisations and shared between organisations is often shared through informal means and not captured effectively through the formal decision-making processes. Early warnings and weak signals about potential risks and crises are therefore often missed. We consider the implications of these dynamics in terms of crisis avoidance and crisis management