Intensification of hemicellulose hot-water extraction from spruce wood by parameter tuning

The growing population on earth along with diminishing fossil deposits and the climate change debate calls out for a better utilization of renewable, bio-based materials. In a biorefinery perspective, the renewable biomass is converted into many different products such as fuels, chemicals, and materials, quite similar to the petroleum refinery industry. Since forests cover about one third of the land surface on earth, ligno-cellulosic biomass is the most abundant renewable resource available. The natural first step in a biorefinery is separation and isolation of the different compounds the biomass is comprised of. The major components in wood are cellulose, hemicellulose, and lignin, all of which can be made into various end-products. Today, focus normally lies on utilizing only one component, e.g., the cellulose in the Kraft pulping process. It would be highly desirable to utilize all the different compounds, both from an economical and environmental point of view. The separation process should therefore be optimized. Hemicelluloses can partly be extracted with hot-water prior to pulping. Depending in the severity of the extraction, the hemicelluloses are degraded to various degrees. In order to be able to choose from a variety of different end-products, the hemicelluloses should be as intact as possible after the extraction. The main focus of this work has been on preserving the hemicellulose molar mass throughout the extraction at a high yield by actively controlling the extraction pH at the high temperatures used. Since it has not been possible to measure pH during an extraction due to the high temperatures, the extraction pH has remained a “black box”. Therefore, a high-temperature in-line pH measuring system was developed, validated, and tested for hot-water wood extractions. One crucial step in the measurements is calibration, therefore extensive efforts was put on developing a reliable calibration procedure. Initial extractions with wood showed that the actual extraction pH was ~0.35 pH units higher than previously believed. The measuring system was also equipped with a controller connected to a pump. With this addition it was possible to control the extraction to any desired pH set point. When the pH dropped below the set point, the controller started pumping in alkali and by that the desired set point was maintained very accurately. Analyses of the extracted hemicelluloses showed that less hemicelluloses were extracted at higher pH but with a higher molar-mass. Monomer formation could, at a certain pH level, be completely inhibited. Increasing the temperature, but maintaining a specific pH set point, would speed up the extraction without degrading the molar-mass of the hemicelluloses and thereby intensifying the extraction. The diffusion of the dissolved hemicelluloses from the wood particle is a major part of the extraction process. Therefore, a particle size study ranging from 0.5 mm wood particles to industrial size wood chips was conducted to investigate the internal mass transfer of the hemicelluloses. Unsurprisingly, it showed that hemicelluloses were extracted faster from smaller wood particles than larger although it did not seem to have a substantial effect on the average molar mass of the extracted hemicelluloses. However, smaller particle sizes require more energy to manufacture and thus increases the economic cost. Since bark comprises 10 – 15 % of a tree, it is important to also consider it in a biorefinery concept. Spruce inner and outer bark was hot-water extracted separately to investigate the possibility to isolate the bark hemicelluloses. It was showed that the bark hemicelluloses comprised mostly of pectic material and differed considerably from the wood hemicelluloses. The bark hemicelluloses, or pectins, could be extracted at lower temperatures than the wood hemicelluloses. A chemical characterization, done separately on inner and outer bark, showed that inner bark contained over 10 % stilbene glucosides that could be extracted already at 100 °C with aqueous acetone.

Alkavan yrityksen strategiset vaihtoehdot ja selviytyminen

Työn tavoitteena on soveltaa yrityksen perustamiseen, innovaation diffuusioon ja strategiseen suunnitteluun liittyvää teoriaa Delitaz Oy:n kehitykseen liiketoimintamahdollisuuden havaitsemisesta uudeksi yritykseksi. Työssä etsitään keinoja yrityksen kehittämän innovatiivisen tuotteen saamiseksi nopeammin markkinoille ja lähtökohtia tulevaa liiketoimintasuunnitelman päivitystä varten. Työssä kootaan yhteen uuden yrityksen perustamisen vaiheisiin, selviytymiseen ja menestymiseen liittyvää teoriaa liiketoimintamahdollisuuden havaitsemisesta uuden inno-vatiivisen tuotteen markkinoille tuomiseen ja yrityksen strategiseen suunnitteluun. Tapaus-osiossa perehdytään kohdeyrityksen perustamisen vaiheisiin, toimintaympäristöön, tuotteeseen ja liiketoimintaan. Työn menetelmänä on tapaus- kehittämis- ja toimintatutkimuksen yhdistelmä. Kehittämis- tai toimintatutkimuksen varsinainen käytännön testaamisvaihe jää työn ulkopuolelle, sillä haluttuja muutoksia lähdetään vasta toteuttamaan. Johtopäätöksinä kuvataan yhden liiketoimintamahdollisuuden kehittyminen ideasta tuotteeksi ja teknologiayritykseksi yrityksen perustamisen teoriaan verrattuna ja esitetään keinoja tuotteen markkinoille saamisen nopeuttamiseksi ja mahdollisia strategisia vaihtoehtoja liiketoimintasuunnitelman päivittämiseksi.

Study of the advancement of innovations in communications industry. Case study: Russian Post Company

This study attempted to provide a project based on the already tested and successful results of foreign business which can help to contain the final price of innovation on desired levels. The research will attempt to dig out most of available information related to aforementioned definitions and thus completing theoretical background. Next author will explain used methodology and the process of evidence collection. After that the study will show the analysis of collected data in order to obtain results which are going to be compared with stated objectives in the final part. The conclusion of the research and proposed possibilities for additional work will be given in the last part. For this study author has chosen the qualitative model because it performs very well for analysis of small scale of data. The case study method was used because it gave author an opportunity to make an in-depth analysis of the collected information about particular organization so it became possible to analyze system's details in comparison. The results have been early considered valid and applicable to other studies. As the result thesis has proposed undertakings which reflect researches aimed on solving problems with provision of services and development of communications. In addition thesis has proposed formulation of database of postal service for Russian Post when (by request) customer possess an account where he or she can access postal services via PC or info table in postal office and order delivery of postal products which will be given private identification code. Project's payoff period has been calculated as well.

Innovation process development and business process integration - a multiple case study

The main objective of this study was to find out the bases for innovation model formulation in an existing organization based on cases. Innovation processes can be analyzed based on their needs and based on their emphasis on the business model development or R&D. The research was conducted in energy sector within one company by utilizing its projects as cases for the study. It is typical for the field of business that development is slow, although the case company has put emphasis on its innovation efforts. Analysis was done by identifying the cases’ needs and comparing them. The results were that because of the variances in the needs of the cases, the applicability of innovation process models varies. It was discovered that by dividing the process into two phases, a uniform model could be composed. This model would fulfill the needs of the cases and potential future projects as well.

Gearing Towards Omnichannel Grocery Retail Through Business Model Innovation

Technological innovations and the advent of digitalization have led retail business into one of its biggest transformations of all time. Consumer behaviour has changed rapidly and the customers are ever more powerful, demanding, tech-savvy and moving on various plat-forms. These attributes will continue to drive the development and robustly restructure the architecture of value creation in the retail business. The largest retail category, grocery yet awaits for a real disruption, but the signals for major change are already on the horizon. The first wave of online grocery retail was introduced in the mid 1990’s and it throve until millennium. Many overreactions, heavy investments and the burst IT-bubble almost stag-nated the whole industry for a long period of time. The second wave started with a venge-ance around 2010. Some research was carried out during the first wave from a single-viewpoint of online grocery retail, but without a comprehensive approach to online-offline business model integration. Now the accelerating growth of e-business has initiated an increased interest to examine the transformation from traditional business models towards e-business models and their integration on the companies’ traditional business models. This research strove to examine how can we recognize and analyze how digitalization and online channels are affecting the business models of grocery retail, by using business mod-el canvas as an analysis tool. Furthermore business model innovation and omnichannel retail were presented and suggested as potential solutions for these changes. 21 experts in online grocery industry were being interviewed. The thoughts of the informants were being qualitatively analysed by using an analysis tool called the business model canvas. The aim of this research was to portray a holistic view on the Omnichannel grocery retail business model, and the value chain, in which the case company Arina along with its partners are operating. The key conclusions exhibited that online grocery retail business model is not an alterna-tive model nor a substitute for the traditional grocery retail business model, though all of the business model elements are to some extent affected by it, but rather a complementary business model that should be integrated into the prevailing, conventional grocery retail business model. A set of business model elements, such as value proposition and distribu-tion channels were recognized as the most important ones and sources of innovation within these components were being illustrated. Segments for online grocery retail were empiri-cally established as polarized niche markets in contrast of the segmented mass-market of the conventional grocery retail. Business model innovation was proven to be a considera-ble method and a conceptual framework, by which to come across with new value proposi-tions that create competitive advantage for the company in the contemporary, changing business environment. Arina as a retailer can be considered as a industry model innovator, since it has initiated an entire industry in its market area, where other players have later on embarked on, and in which the contributors of the value chain, such as Posti depend on it to a great extent. Consumer behaviour clearly affects and appears everywhere in the digi-talized grocery trade and it drives customers to multiple platforms where retailers need to be present. Omnichannel retail business model was suggested to be the solution, in which the new technologies are being utilized, contemporary consumer behaviour is embedded in decision-making and all of the segments and their value propositions are being served seamlessly across the channels.

Innovation Ecosystem Perspectives on Financial Services Innovation

The context of financial services has been characterised by changes in the regulatory, technological and societal landscape. Consumers are increasingly interested in mobile payments, crowdfunding and microfinance services, either for themselves or because collaborative consumption is viewed as a more sustainable. Retail branches are re-organised to further meet the expectations of customers, start-ups focusing on technology for financial services (i.e. Fintech) are ever growing and financial services companies reinforce their own innovation practices (e.g. creation of innovation labs or venture capital investment funds). The innovation ecosystem around financial services companies represents the many actors with whom they can co-create and co-produce innovative new services for their customers (or for themselves). The innovation process is no longer a closed internal effort but needs to include external actors from the innovation ecosystem. This topic is especially interesting in a small and open economy where the financial centre takes a prominent place in the economy. The research question is therefore “How does the innovation ecosystem influence the innovation process within financial services companies?”. The influence of the innovation ecosystem on the innovation process within financial service companies mainly comes from its social capital and value creation efforts. However learning to work and exchange in an innovation ecosystem is also expected to influence the innovation process in place. Realizing the potential of the innovation ecosystem requires sufficient capabilities to manage new information coming from the innovation ecosystem. The professional associations provide the necessary coordination among actors in the innovation ecosystem to co-create and appropriate value, while fostering co-evolution within the innovation ecosystem.

Critical elements underpinning the emergence of the medical game ecosystem: gamifying traumatic brain injury rehabilitation in Finland

The healthcare sector is currently in the verge of a reform and thus, the medical game research provide an interesting area of research. The aim of this study is to explore the critical elements underpinning the emergence of the medical game ecosystem with three sub-objectives: (1) to seek who are the key actors involved in the medical game ecosystem and identify their needs, (2) to scrutinise what types of resources are required in medical game development and what types of relationships are needed to secure those resources, and (3) to identify the existing institutions (‘the rules of the game’) affecting the emergence of the medical game ecosystem. The theoretical background consists of service ecosystems literature. The empirical study conducted is based on the semi-structured theme interviews of 25 experts in three relevant fields: games and technology, health and funding. The data was analysed through a theoretical framework that was designed based upon service ecosystems literature. The study proposes that the key actors are divided into five groups: medical game companies, customers, funders, regulatory parties and complementors. Their needs are linked to improving patient motivation and enhancing the healthcare processes resulting in lower costs. Several types of resources, especially skills and knowledge, are required to create a medical game. To gain access to those resources, medical game companies need to build complex networks of relationships. Proficiency in managing those value networks is crucial. In addition, the company should take into account the underlying institutions in the healthcare sector affecting the medical game ecosystem. Three crucial institutions were identified: validation, lack of innovation supporting structures in healthcare and the rising consumerisation. Based on the findings, medical games cannot be made in isolation. A developmental trajectory model of the emerging medical game ecosystem was created based on the empirical data. The relevancy of relationships and resources is dependent on the trajectory that the medical game company at that time resides. Furthermore, creating an official and documented database for clinically valdated medical games was proposed to establish the medical game market and ensure an adequate status for the effective medical games. Finally, ecosystems approach provides interesting future opportunities for research on medical game ecosystems.

Critical elements underpinning the emergence of the medical game ecosystem:gamifying traumatic brain injury rehabilitation in Finland

The healthcare sector is currently in the verge of a reform and thus, the medical game research provide an interesting area of research. The aim of this study is to explore the critical elements underpinning the emergence of the medical game ecosystem with three sub-objectives: (1) to seek who are the key actors involved in the medical game ecosystem and identify their needs, (2) to scrutinise what types of resources are required in medical game development and what types of relationships are needed to secure those resources, and (3) to identify the existing institutions (‘the rules of the game’) affecting the emergence of the medical game ecosystem. The theoretical background consists of service ecosystems literature. The empirical study conducted is based on the semi-structured theme interviews of 25 experts in three relevant fields: games and technology, health and funding. The data was analysed through a theoretical framework that was designed based upon service ecosystems literature. The study proposes that the key actors are divided into five groups: medical game companies, customers, funders, regulatory parties and complementors. Their needs are linked to improving patient motivation and enhancing the healthcare processes resulting in lower costs. Several types of resources, especially skills and knowledge, are required to create a medical game. To gain access to those resources, medical game companies need to build complex networks of relationships. Proficiency in managing those value networks is crucial. In addition, the company should take into account the underlying institutions in the healthcare sector affecting the medical game ecosystem. Three crucial institutions were identified: validation, lack of innovation supporting structures in healthcare and the rising consumerisation. Based on the findings, medical games cannot be made in isolation. A developmental trajectory model of the emerging medical game ecosystem was created based on the empirical data. The relevancy of relationships and resources is dependent on the trajectory that the medical game company at that time resides. Furthermore, creating an official and documented database for clinically validated medical games was proposed to establish the medical game market and ensure an adequate status for the effective medical games. Finally, ecosystems approach provides interesting future opportunities for research on medical game ecosystems

The Role of HR Management in the Corporate Matrix System

The successful performance of company in the market relates to the quality management of human capital aiming to improve the company's internal performance and external implementation of the core business strategy. Companies with matrix structure focusing on realization and development of innovation and technologies for the uncertain market need to select thoroughly the approach to HR management system. Human resource management has a significant impact on the organization and use a variety of instruments such as corporate information systems to fulfill their functions and objectives. There are three approaches to strategic control management depending on major impact on the major interference in employee decision-making, development of skills and his integration into the business strategy. The mainstream research has focus only on the framework of strategic planning of HR and general productivity of firm, but not on features of organizational structure and corporate software capabilities for human capital. This study tackles the before mentioned challenges, typical for matrix organization, by using the HR control management tools and corporate information system. The detailed analysis of industry producing and selling electromotor and heating equipment in this master thesis provides the opportunity to improve system for HR control and displays its application in the ERP software. The results emphasize the sustainable role of matrix HR input control for creating of independent project teams for matrix structure who are able to respond to various uncertainties of the market and use their skills for improving performance. Corporate information systems can be integrated into input control system by means of output monitoring to regulate and evaluate the processes of teams, using key performance indicators and reporting systems.

BP BLOGGER: DESCRIPTIVE STUDY OF ELECTRONIC KNOWLEDGE DISSEMINATION IN LONG TERM CARE

Little is known of the uptake and use of knowledge disseminated in electronic formats, especially in Long Term Care (LTC) settings. The purpose of this descriptive study was to examine the dissemination of the BP Bloggers, a series of brief, evidence summaries designed to meet the knowledge needs of LTC staff. Guided by Rogers’ (2003) Diffusion of Innovations theory, the study documents dissemination of the BP Blogger and examines factors affecting dissemination, awareness, perceptions and its use. The survey of BP Blogger recipients was conducted electronically (n=114) online (n=10), by telephone (n=55), and print (n=144). Managers usually received the newsletter electronically while staff in LTC were more likely to receive printed copies. Participants disseminated the newsletter through paper, email, or posting in the workplace. Most participants rated the content, format, and usefulness of the BP Blogger as good or excellent. Time and lack of email access were barriers to dissemination.

Vertical R&D Sprillovers, Cooperation, Market Structure, and Innovation.

This paper studies vertical R&D spillovers between upstream and downstream firms. The model incorporates two vertically related industries, with horizontal spillovers within each industry and vertical spillovers between the two industries. Four types of R&D cooperation are studied : no cooperation, horizontal cooperation, vertical cooperation, and simultaneous horizontal and vertical cooperation. Vertical spillovers always increase R&D and welfare, while horizontal spillovers may increase or decrease them. The comparison of cooperative settings in terms of R&D shows that no setting uniformly dominates the others. Which type of cooperation yields more R&D depends on horizontal and vertical spillovers, and market structure. The ranking of cooperative structures hinges on the signs and magnitudes of three competitive externalities (vertical, horizontal, and diagonal) which capture the effect of the R&D of a firm on the profits of other firms. One of the basic results of the strategic investment literature is that cooperation between competitors increases (decreases) R&D when horizontal spillovers are high (low); the model shows that this result does not necessarily hold when vertical spillovers and vertical cooperation are taken into account. The paper proposes a theory of innovation and market structure, showing that the relation between innovation and competition depends on horizontal spillovers, vertical spillovers, and cooperative settings. The private incentives for R&D cooperation are addressed. It is found that buyers and sellers have divergent interests regarding the choice of cooperative settings and that spillovers increase the likelihood of the emergence of cooperation in a decentralized equilibrium.

Innover en politique : les acteurs internationaux, régionaux et nationaux en stratégies de développement économique en Afrique

Pourquoi, comment et quand y a-t-il changement institutionnel et politique en Afrique ? En examinant les stratégies de développement économique de l’Afrique postcoloniale et en s’intéressant à l’évolution du rôle de l’État – État comme acteur central du développement, tentative du retrait de l’État, interventionnisme limité au social, retour de l’État dans la sphère économique –, la présente thèse se propose d’expliquer le changement sous l’angle original des innovations politiques et institutionnelles. En effet, derrière l’apparente continuité que la plupart des auteurs tant analytiques que normatifs fustigent, il se produit des innovations dont nous proposons de rendre compte par le biais des variables idéationnelles, stratégiques, temporelles et institutionnelles. Cette thèse propose ainsi une analyse comparative inédite du rôle des acteurs nationaux (élites, États, administrations publiques du Bénin, Burkina Faso, Cameroun, Côte d’Ivoire, Congo, Sénégal, Mali, Niger, Togo), des institutions internationales (FMI, Banque mondiale, ONU) et des organisations d’intégration régionale (Union africaine, NEPAD) dans l’émergence et les trajectoires des stratégies de développement en Afrique. Les contextes temporels favorables, les crises des modèles précédents, les configurations et héritages institutionnels structurants, les stratégies instrumentales des acteurs intéressés, l’apprentissage politique, les dimensions cognitives et normatives des idées permettent d’expliquer la diffusion, la sédimentation et la conversion institutionnelles comme processus privilégiés d’innovation en Afrique. La critique de ces concepts permet de développer des outils mieux adaptés pour expliquer certaines innovations, soit l’inclusion et l’intrusion institutionnelles. L’inclusion institutionnelle est un processus mi-stratégique et mi-idéationnel à travers lequel les acteurs nationaux ou régionaux incluent intentionnellement des stratégies (ou solutions) internationales déjà existantes dans une nouvelle institution ou politique dans le but d’accroître la probabilité d’acceptation (reconnaissance, convenance sociale, partage réel ou supposé des mêmes valeurs) ou de succès (pour faire valoir les intérêts) de cette dernière dans un environnement politique structuré. Les idées sont constitutives des intérêts dans ce processus. L’intrusion institutionnelle renvoie à un processus mi-stratégique et mi-structurel par lequel les acteurs nationaux se font relativement imposer de nouvelles institutions ou politiques qu’ils n’acceptent qu’en raison de l’asymétrie de pouvoir, de la contrainte structurelle (structure), ou des gains escomptés (stratégies) des acteurs internationaux, alors que des solutions de rechange pertinentes et non contraignantes sont quasi inexistantes. Ceci n’exclut pas l’existence d’une marge de manœuvre des acteurs nationaux. Inspirés de spécialistes comme Nicolas van de Walle, Kathleen Thelen, Robert Bates, Barry Weingast, Alexander Wendt, Peter Hall, Theda Skocpol et Paul Pierson, ces concepts d’intrusion et d’inclusion institutionnelles que nous proposons réconcilient des approches parfois jugées contradictoires en intégrant les dimensions stratégiques, institutionnelles, historiques et idéationnelles à l’analyse d’un même objet scientifique. Au niveau empirique, la présente thèse permet d’avoir une meilleure compréhension des processus d’émergence des stratégies de développement économique en Afrique, ainsi qu’une meilleure connaissance des relations entre les acteurs internationaux, régionaux et nationaux en ce qui concerne l’émergence et le développement des institutions et des politiques publiques relatives au développement. Une attention particulière est accordée à la dynamique entre différents acteurs et variables (idées, intérêts, institution, temps) pour expliquer les principales stratégies des trois dernières décennies : les stratégies nationales de développement du Bénin, Burkina Faso, Cameroun, Côte d’Ivoire, Congo, Sénégal, Mali, Niger, Togo, le Plan d’action de Lagos, les programmes d’ajustement structurel, le Nouveau Partenariat pour le Développement de l’Afrique, les Documents de stratégie pour la réduction de la pauvreté et certaines interventions du Fonds monétaire international, de Banque mondiale et de l’ONU. En s’intéressant à la question de l’innovation délaissée à tort par la plupart des analyses sérieuses, la présente thèse renouvelle la discussion sur le changement et l’innovation politiques et institutionnels en Afrique et en science politique.

Un protocole de diffusion des messages dans les réseaux véhiculaires

De nos jours, la voiture est devenue le mode de transport le plus utilisé, mais malheureusement, il est accompagné d’un certain nombre de problèmes (accidents, pollution, embouteillages, etc.), qui vont aller en s’aggravant avec l’augmentation prévue du nombre de voitures particulières, malgré les efforts très importants mis en œuvre pour tenter de les réduire ; le nombre de morts sur les routes demeure très important. Les réseaux sans fil de véhicules, appelés VANET, qui consistent de plusieurs véhicules mobiles sans infrastructure préexistante pour communiquer, font actuellement l’objet d'une attention accrue de la part des constructeurs et des chercheurs, afin d’améliorer la sécurité sur les routes ou encore les aides proposées aux conducteurs. Par exemple, ils peuvent avertir d’autres automobilistes que les routes sont glissantes ou qu’un accident vient de se produire. Dans VANET, les protocoles de diffusion (broadcast) jouent un rôle très important par rapport aux messages unicast, car ils sont conçus pour transmettre des messages de sécurité importants à tous les nœuds. Ces protocoles de diffusion ne sont pas fiables et ils souffrent de plusieurs problèmes, à savoir : (1) Tempête de diffusion (broadcast storm) ; (2) Nœud caché (hidden node) ; (3) Échec de la transmission. Ces problèmes doivent être résolus afin de fournir une diffusion fiable et rapide. L’objectif de notre recherche est de résoudre certains de ces problèmes, tout en assurant le meilleur compromis entre fiabilité, délai garanti, et débit garanti (Qualité de Service : QdS). Le travail de recherche de ce mémoire a porté sur le développement d’une nouvelle technique qui peut être utilisée pour gérer le droit d’accès aux médias (protocole de gestion des émissions), la gestion de grappe (cluster) et la communication. Ce protocole intègre l'approche de gestion centralisée des grappes stables et la transmission des données. Dans cette technique, le temps est divisé en cycles, chaque cycle est partagé entre les canaux de service et de contrôle, et divisé en deux parties. La première partie s’appuie sur TDMA (Time Division Multiple Access). La deuxième partie s’appuie sur CSMA/CA (Carrier Sense Multiple Access / Collision Avoidance) pour gérer l’accès au medium. En outre, notre protocole ajuste d’une manière adaptative le temps consommé dans la diffusion des messages de sécurité, ce qui permettra une amélioration de la capacité des canaux. Il est implanté dans la couche MAC (Medium Access Control), centralisé dans les têtes de grappes (CH, cluster-head) qui s’adaptent continuellement à la dynamique des véhicules. Ainsi, l’utilisation de ce protocole centralisé nous assure une consommation efficace d’intervalles de temps pour le nombre exact de véhicules actifs, y compris les nœuds/véhicules cachés; notre protocole assure également un délai limité pour les applications de sécurité, afin d’accéder au canal de communication, et il permet aussi de réduire le surplus (overhead) à l’aide d’une propagation dirigée de diffusion.

The Technology of Copper Alloys, Particularly Leaded Bronze, in Greece, its Colonies, and in Etruria during the Iron Age

L’objet de la présente étude est le développement, l’application et la diffusion de la technologie associée à divers types d’alliages de cuivre, en particulier l’alliage du plomb-bronze, en Grèce ancienne, dans ses colonies, ainsi qu’en Étrurie. Le plomb-bronze est un mélange de diverses proportions d’étain, de cuivre et de plomb. Le consensus général chez les archéométallurgistes est que le plomb-bronze n’était pas communément utilisé en Grèce avant la période hellénistique; par conséquent, cet alliage a reçu très peu d’attention dans les documents d’archéologie. Cependant, les analyses métallographiques ont prouvé que les objets composés de plomb ajouté au bronze ont connu une distribution étendue. Ces analyses ont aussi permis de différencier la composition des alliages utilisés dans la fabrication de divers types de bronzes, une preuve tangible que les métallurgistes faisaient la distinction entre les propriétés du bronze d’étain et celles du plomb-bronze. La connaissance de leurs différentes caractéristiques de travail permettait aux travailleurs du bronze de choisir, dans bien des cas, l’alliage approprié pour une utilisation particulière. L’influence des pratiques métallurgiques du Proche-Orient a produit des variations tant dans les formes artistiques que dans les compositions des alliages de bronze grecs durant les périodes géométrique tardive et orientalisante. L’utilisation du plomb-bronze dans des types particuliers d’objets coulés montre une tendance à la hausse à partir de la période orientalisante, culminant dans la période hellénistique tardive, lorsque le bronze à teneur élevée en plomb est devenu un alliage commun. La présente étude analyse les données métallographiques de la catégorie des objets coulés en bronze et en plomb-bronze. Elle démontre que, bien que l’utilisation du plomb-bronze n’était pas aussi commune que celle du bronze d’étain, il s’agissait néanmoins d’un mélange important d’anciennes pratiques métallurgiques. Les ères couvertes sont comprises entre les périodes géométrique et hellénistique.

Quantifying diffusion in biofilms : from model hydrogels to living biofilms

Les biofilms sont des communautés de microorganismes incorporés dans une matrice exo-polymérique complexe. Ils sont reconnus pour jouer un rôle important comme barrière de diffusion dans les systèmes environnementaux et la santé humaine, donnant lieu à une résistance accrue aux antibiotiques et aux désinfectants. Comme le transfert de masse dans un biofilm est principalement dû à la diffusion moléculaire, il est primordial de comprendre les principaux paramètres influençant les flux de diffusion. Dans ce travail, nous avons étudié un biofilm de Pseudomonas fluorescens et deux hydrogels modèles (agarose et alginate) pour lesquels l’autodiffusion (mouvement Brownien) et les coefficients de diffusion mutuels ont été quantifiés. La spectroscopie par corrélation de fluorescence a été utilisée pour mesurer les coefficients d'autodiffusion dans une volume confocal de ca. 1 m3 dans les gels ou les biofilms, tandis que les mesures de diffusion mutuelle ont été faites par cellule de diffusion. En outre, la voltamétrie sur microélectrode a été utilisée pour évaluer le potentiel de Donnan des gels afin de déterminer son impact sur la diffusion. Pour l'hydrogel d'agarose, les observations combinées d'une diminution du coefficient d’autodiffusion et de l’augmentation de la diffusion mutuelle pour une force ionique décroissante ont été attribuées au potentiel de Donnan du gel. Des mesures de l'effet Donnan (différence de -30 mV entre des forces ioniques de 10-4 et 10-1 M) et l'accumulation correspondante d’ions dans l'hydrogel (augmentation d’un facteur de 13 par rapport à la solution) ont indiqué que les interactions électrostatiques peuvent fortement influencer le flux de diffusion de cations, même dans un hydrogel faiblement chargé tel que l'agarose. Curieusement, pour un gel plus chargé comme l'alginate de calcium, la variation de la force ionique et du pH n'a donné lieu qu'à de légères variations de la diffusion de sondes chargées dans l'hydrogel. Ces résultats suggèrent qu’en influençant la diffusion du soluté, l'effet direct des cations sur la structure du gel (compression et/ou gonflement induits) était beaucoup plus efficace que l'effet Donnan. De même, pour un biofilm bactérien, les coefficients d'autodiffusion étaient pratiquement constants sur toute une gamme de force ionique (10-4-10-1 M), aussi bien pour des petits solutés chargés négativement ou positivement (le rapport du coefficient d’autodiffusion dans biofilm sur celui dans la solution, Db/Dw ≈ 85 %) que pour des nanoparticules (Db/Dw≈ 50 %), suggérant que l'effet d'obstruction des biofilms l’emporte sur l'effet de charge. Les résultats de cette étude ont montré que parmi les divers facteurs majeurs qui affectent la diffusion dans un biofilm environnemental oligotrophe (exclusion stérique, interactions électrostatiques et hydrophobes), les effets d'obstruction semblent être les plus importants lorsque l'on tente de comprendre la diffusion du soluté. Alors que les effets de charge ne semblaient pas être importants pour l'autodiffusion de substrats chargés dans l'hydrogel d'alginate ou dans le biofilm bactérien, ils ont joué un rôle clé dans la compréhension de la diffusion à travers l’agarose. L’ensemble de ces résultats devraient être très utiles pour l'évaluation de la biodisponibilité des contaminants traces et des nanoparticules dans l'environnement.