Multi-agent systems have been used in a wide range of applications from computer-based simulations and mobile robots to agent-oriented programming and intelligent systems in real environments. However, the largest environment in which software agents can interact is, without any doubt, the World Wide Web and ever since its birth agents have been used in various applications such as search engines, e-commerce, and most recently the semantic web. However, agents have yet to be used on the Web in a way that leverages the full power of artificial intelligence and multi-agent systems, which have the potential of making life much easier for humans. This thesis investigates how this can be changed, and how agents can be brought to the core of the online experience in the sense that we want people to talk and interact with agents instead of "just using yet another application or website". We analyze what makes it hard to develop intelligent agents on the web and we propose a web agent model (WAM) inspired by recent results in multi-agent systems. Nowadays, a simple conceptual model is the key for widespread adoption of new technologies and this is why we have chosen the MASQ meta-model as the basis for our approach, which provides the best compromise in terms of simplicity of concepts, generality and applicability to the web. Since until now the model was introduced only in an informal way, we also provide a clear formalization of the MASQ meta-model.Next, we identify the three main challenges that need to be addressed when building web agents: integration of bodies, web semantics and user friendliness. We focus our attention on the first two and we propose a set of principles to guide the development of what we call strong web agents. Finally, we validate our proposal through the implementation of an award winning platform called Kleenk. Our work is just a step towards fulfilling the vision of having intelligent web agents mediate the interaction with the increasingly complex World Wide Web. / Multi-agent systems have been used in a wide range of applications from computer-based simulations and mobile robots to agent-oriented programming and intelligent systems in real environments. However, the largest environment in which software agents can interact is, without any doubt, the World Wide Web and ever since its birth agents have been used in various applications such as search engines, e-commerce, and most recently the semantic web. However, agents have yet to be used on the Web in a way that leverages the full power of artificial intelligence and multi-agent systems, which have the potential of making life much easier for humans. This thesis investigates how this can be changed, and how agents can be brought to the core of the online experience in the sense that we want people to talk and interact with agents instead of "just using yet another application or website". We analyze what makes it hard to develop intelligent agents on the web and we propose a web agent model (WAM) inspired by recent results in multi-agent systems. Nowadays, a simple conceptual model is the key for widespread adoption of new technologies and this is why we have chosen the MASQ meta-model as the basis for our approach, which provides the best compromise in terms of simplicity of concepts, generality and applicability to the web. Since until now the model was introduced only in an informal way, we also provide a clear formalization of the MASQ meta-model.Next, we identify the three main challenges that need to be addressed when building web agents: integration of bodies, web semantics and user friendliness. We focus our attention on the first two and we propose a set of principles to guide the development of what we call strong web agents. Finally, we validate our proposal through the implementation of an award winning platform called Kleenk. Our work is just a step towards fulfilling the vision of having intelligent web agents mediate the interaction with the increasingly complex World Wide Web.

Internet computing enables the construction of large-scale and complex applications by aggregating and sharing computational, data and other resources across institutional boundaries. The agent model can address the ever-increasing challenges of scalability and complexity, driven by the prevalence of Internet computing, by its intrinsic properties of autonomy and reactivity, which support the flexible management of application execution in distributed, open, and dynamic environments. However, the non-deterministic behaviour of autonomous agents leads to a lack of control, which complicates exception management in the system, thus threatening the robustness and reliability of the system, because improperly handled exceptions may cause unexpected system failure and crashes. / In this dissertation, we investigate and develop mechanisms to integrate intrinsic support for concurrency control, exception handling, recoverability, and robustness into multi-agent systems. The research covers agent specification, planning and scheduling, execution, and overall coordination, in order to reduce the impact of environmental uncertainty. Simulation results confirm that our model can improve the robustness and performance of the system, while relieving developers from dealing with the low level complexity of exception handling. / A survey, along with a taxonomy, of existing proposals and approaches for building robust multi-agent systems is provided first. In addition, the merits and limitations of each category are highlighted. / Next, we introduce the ARTS (Agent-Oriented Robust Transactional System) platform which allows agent developers to compose recursively-defined, atomically-handled tasks to specify scoped and hierarchically-organized exception-handling plans for a given goal. ARTS then supports automatic selection, execution, and monitoring of appropriate plans in a systematic way, for both normal and recovery executions. Moreover, we propose multiple-step backtracking, which extends the existing step-by-step plan reversal, to serve as the default exception handling and recovery mechanism in ARTS. This mechanism utilizes previous planning results in determining the response to a failure, and allows a substitutable path to start, prior to, or in parallel with, the compensation process, thus allowing an agent to achieve its goals more directly and efficiently. ARTS helps developers to focus on high-level business logic and relaxes them from considering low-level complexity of exception management. / One of the reasons for the occurrence of exceptions in a multi-agent system is that agents are unable to adhere to their commitments. We propose two scheduling algorithms for minimising such exceptions when commitments are unreliable. The first scheduling algorithm is trust-based scheduling, which incorporates the concept of trust, that is, the probability that an agent will comply with its commitments, along with the constraints of system budget and deadline, to improve the predictability and stability of the schedule. Trust-based scheduling supports the runtime adaptation and evolvement of the schedule by interleaving the processes of evaluation, scheduling, execution, and monitoring in the life cycle of a plan. The second scheduling algorithm is commitment-based scheduling, which focuses on the interaction and coordination protocol among agents, and augments agents with the ability to reason about and manipulate their commitments. Commitment-based scheduling supports the refactoring and parallel execution of commitments to maximize the system's overall robustness and performance. While the first scheduling algorithm needs to be performed by a central coordinator, the second algorithm is designed to be distributed and embedded into the individual agent. / Finally, we discuss the integration of our approaches into Internet-based applications, to build flexible but robust systems. Specifically, we discuss the designs of an adaptive business process management system and of robust scientific workflow scheduling.

Les pathologies du foie représentent une des causes les plus fréquentes de mortalité. Ceci provient sans doute de la difficulté de poser le diagnostic à un stade précoce de leur développement malgré les très bonnes performances de l'échographie et de la tomographie de rayons X. On espère que l'IRM dont les résultats spectaculaires dans le diagnostic des tumeurs cérébrales sont aujourd'hui incontestés améliorera la situation. Malheureusement, comme les autres techniques et en dépit de son excellent contraste inhérent, l'IRM se heurte aussi au problème de la mise en évidence des maladies hépatiques. Afin de remédier à cette situation, la recherche s'est orientée vers l'élaboration de produits de contraste spécifiques. La stratégie suivie jusqu'ici est double: d'une part, des complexes d'ions paramagnétiques sont développés pour favoriser leur incorporation par les hépatocytes, et, d'autre part, des nanoparticules superparamagnétiques sont synthétisées afin de cibler les cellules de Kupffer, les macrophages fixes du foie.

Tracer based MRI perfusion measurements is a clinically useful tool to assess regional distributions of tissue blood flow and volume. The method may be based on any of the three relaxation mechanisms T1, T1 and T2*, the latter denoted DSC-MRI being the most common. The primary aim of this work was to study the feasibility of obtaining quantitative estimates using these methods. 1) Feasibility of DSC-MRI for kidneys using an iron oxide based contrast agent and the influence of secondary relaxation effects on the results, part of a clinical phase II trial: The method proved feasible and the underestimation induced by secondary relaxation can be corrected for by using a double echo sequence. 2) Influence of blood flow rate on risk factors for developing cerebral ischemia during cardio pulmonary bypass, measurements in pig with gadolinium based DSC-MRI: The results indicated an ischemic threshold level at a blood flow rate of approximately 6 ml/kg/min. 3) The ability of gadolinium based DSC-MRI to detect changes in global blood flow, experimental measurements in pig and numerical simulations: The results support that DSC-MRI can discriminate between global flow levels in the same subject given that all other parameters are kept constant. The results also indicate that calculated perfusion values are highly sensitive to the arterial deconvolution procedure. 4) Influence of differences in blood/tissue relaxivity and secondary relaxation for a gadolinium based contrast agent, measurements in pig and numerical simulations: The blood/tissue relaxivity ratio is not unity and the situation is complicated by secondary relaxation effects. Deconvolution regularization appears to partly counteract the overestimation induced by difference in blood/tissue relaxivity for DSC-MRI. In summary, the fundamental assumption of equal blood and tissue relaxivity is experimentally shown to be invalid and the influence of this discrepancy is substantial. Several factors contribute to measurement errors, a combination of these factors can incidentally lead to additive errors or error cancellation based on a variety of experimental and analysis conditions. Given that the differences in blood/tissue relaxivity cannot readily be accounted for in a clinical setting, absolute perfusion quantification by tracer based MRI remains challenging if not impossible.

none

The focus of this thesis is to better explore and understand the effects of agent interactions, information feedback, and adaptive learning in a repeated game of bidding in farmland auction markets. This thesis will develop a multi-agent model of farm-land auction markets based on data from the Saskatchewan Dark Brown Soil Zone of the Canadian Prairies. Several auction types will be modeled and data will be gathered on land transactions between farm agents to ascertain which auction type (if any) is best suited for farmland markets. Specifically, the model gathers information for 3 types of sealed-bid auctions, and 1 English auction and compares them on the basis of efficiency, price information revelation, stability, and with respect to repeated bidding and agent learning. The effects of auction choice on macro-level indicators, such as farm exits, retirement, financial stability, average productivity, farm size, and participation were unknown at the outset of this thesis because of the complex dynamic nature of the environment. I find that the chosen learning mechanism employed here affects both price and variance of prices in all auctions. I also find that the second-price-sealed-bid auction generates the most perceived surplus, most equitable share of surplus, and also decreases uncertainty in the common-value element of prices. A priori it was believed that auction choice would have an impact on pricing efficiency, price levels, and shares of surplus generated from auctions as predicted by theoretical works. Surprisingly, auction choice does not influence market structure or evolution.

Along with the development of the economy and technology, the network has become more important in people's work and life than before. More and more people take advantage of network to improve the quality of their work and life. The network applications are based on the database visiting, and the database visiting is almost based on the Distributed database. The Distributed data service can be widely used in the corporation and many important fields. More technology and solutions are proposed, including the Mobile Agent technology. Mobile Agent is a code segment that can migration in the network, carrying the task code, using network and computers' resource, cooperating with other MAs, finishing one or more designated tasks. Compared with other mobile code, the MA technology can use less network resource, carry less information, and operate with higher efficiency. Using the technology to solve distributed problems is a hot research topic currently. In this paper, we first review the current research status in the Mobile Agent and distributed data service fields. After that, based on the current issues in the Distributed data service fields, we propose a complete solution using the Mobile Agent technology. Last, with the proposed solution, we construct a complete distributed data service model. In our solution, the traditional Distributed data-retrieving procedure is investigated and enhanced with the Mobile Agent technology to achieve high efficiency. The Mobile Agent related technology, such as MA communication, MA security, and MA cooperation technology are also used to improve the model 's efficiency and reduce the network's cost. We have used a project management system as a sub-model. Compared with the traditional approaches, the model works more efficiently with larger number of stations and large amount of the data-request. Finally, detailed analyzing of one instance is presented to show the characteristic of the model.

The focus of this thesis is to better explore and understand the effects of agent interactions, information feedback, and adaptive learning in a repeated game of bidding in farmland auction markets. This thesis will develop a multi-agent model of farm-land auction markets based on data from the Saskatchewan Dark Brown Soil Zone of the Canadian Prairies. Several auction types will be modeled and data will be gathered on land transactions between farm agents to ascertain which auction type (if any) is best suited for farmland markets. Specifically, the model gathers information for 3 types of sealed-bid auctions, and 1 English auction and compares them on the basis of efficiency, price information revelation, stability, and with respect to repeated bidding and agent learning. The effects of auction choice on macro-level indicators, such as farm exits, retirement, financial stability, average productivity, farm size, and participation were unknown at the outset of this thesis because of the complex dynamic nature of the environment. I find that the chosen learning mechanism employed here affects both price and variance of prices in all auctions. I also find that the second-price-sealed-bid auction generates the most perceived surplus, most equitable share of surplus, and also decreases uncertainty in the common-value element of prices. A priori it was believed that auction choice would have an impact on pricing efficiency, price levels, and shares of surplus generated from auctions as predicted by theoretical works. Surprisingly, auction choice does not influence market structure or evolution.

Begreppet ansvarsredovisning har många olika meningar, och har fått en allt större betydelse för företagens kommunikation. Samhället ställer krav på organisationernas och företagens etik, sociala ansvar och miljöansvar enligt litteraturen. Trots dessa krav är företagens och organisationernas ansvarsredovisning till stor del frivillig. Den lågkonjunktur som råder i Sverige och i övriga världen kan också antas ha påverkat kraven på företagen, att ta ett större samhälligt ansvar. Allmänheten ställer också större krav på att informationen redovisas på ett korrekt sätt, och att informationen är tillförlitlig. Syftet med denna uppsats är att utifrån studiens frågor beskriva innebörden av begreppet ansvarsredovisning. Resultatet visar att ansvar har en teknisk innebörd som kräver tekniska färdigheter och kommunikation, men har även en social dimension som blir allt viktigare. Hur kan ansvarsredovisning beskrivas i ett organisatoriskt sammanhang, samt den tekniska dimensionen av ansvarsredovisningen? Vi har studerat organisationen ur ett organisatoriskt perspektiv. Studiens resultat karakteriseras genom två olika former, den sociala och den tekniska. Studien är baserad på det induktiva perspektivet. Undersökningsstrategin är deskriptiv och explorativ. Vi använder en multipel teoretisk referensram för att berika analysen av insamlade materialet. Tillämpning av multipla teorier resulterade i en i en klar koppling mellan teori och praktik. Företag och organisationer vill framstå i ”god dager” i media som en ansvarsfull enhet.Ansvarsredovisning balanserar förhållandet mellan intressenters krav och företagens och organisationernas ansvar.Ansvarsredovisningens betydelse ökar stadigt, trots att lagkravet för ansvarsredovisning är minimalt. Vi tror att ansvarsredovisningen har kommit för att stanna.

none