Demand-Orientated Power Production from Biogas: Modeling and Simulations under Swedish Conditions

The total share of intermittent renewable electricity is increasing, intensifying the need for power balancing in future electricity systems. Demand-orientated combined heat and power (CHP) production from biogas has potential for this purpose. An agricultural biogas plant, using cattle manure and sugar beet for biogas and CHP production, was analyzed here. The model Dynamic Biogas plant Model (DyBiM) was developed and connected to the Anaerobic Digestion Model No. 1 (ADM1). Flexible scenarios were simulated and compared against a reference scenario with continuous production, to evaluate the technical requirements and economic implications of demand-orientated production. The study was set in Swedish conditions regarding electricity and heat price, and the flexibility approaches assessed were increased CHP and gas storage capacity and feeding management. The results showed that larger gas storage capacity was needed for demand-orientated CHP production but that feeding management reduced the storage requirement because of fast biogas production response to feeding. Income from electricity increased by 10%, applying simple electricity production strategies to a doubled CHP capacity. However, as a result of the currently low Swedish diurnal electricity price variation and lack of subsidies for demand-orientated electricity production, the increase in income was too low to cover the investment costs. Nevertheless, DyBiM proved to be a useful modeling tool for assessing the economic outcome of different flexibility scenarios for demand-orientated CHP production

E-services interoperability analysis and roadmap actions

e-Services are the building blocks for loosely-coupled, distributed applications based on the Service Oriented Architecture's principles. One of the major benefits they offer is interoperability both between components of Service Oriented systems and between different systems. Still, the variety and diversity of implementations and interpretations of SOA and the vast amount of emerging standards hinder interoperability. This paper examines the interoperability requirements and related issues for each one of the major e-Services categories: Web, Grid and P2P services. Our aim is to provide the basis for a roadmap towards improving interoperability of e-Services which will enable the successful formation of service-based distributed applications. © 2005 by International Federation for Information Processing

Reputation-based trust systems for P2P applications: Design issues and comparison framework

In Peer-to-Peer (P2P) computing area trust issues have gained focus as a result of the decentralized nature of P2P systems where autonomous peers interact with each other without relying on any central authority. There is, thus, the need of a trust system to ensure a level of robustness against malicious nodes. Various reputation-based trust models have been proposed for P2P systems which use similar concepts but focus on different aspects and address different set of design issues. As a result, there is a clear need to investigate the design aspects of reputation-based trust systems that could be deployed in P2P applications. In this paper we present the basic elements and design issues of such systems and compare representative approaches, aiming at supporting the design of reputation systems suitable for particular P2P applications. © Springer-Verlag Berlin Heidelberg 2006

Credible reputation metric for P2P e-communities

Peer-to-Peer (P2P) systems and applications are attracting a lot of attention nowadays, as they mimic human communities and support useful community. Due to their social and decentralized nature, trust plays an essential role for their functionality. P2P reputation systems have emerged in order to satisfy this need for trust. However, reputation systems themselves are targets of multiple kinds of attacks which should be taken into consideration during the design of the former in order to be effective. In this paper we propose a reputation mechanism for P2P e-communities of entities which offer services to each other. The focus is on the reputation inference algorithm (reputation metric) which integrates various credibility factors. © 2010 Springer-Verlag Berlin Heidelberg

Taxonomy of attacks and defense mechanisms in P2P reputation systems-Lessons for reputation system designers

Robust and credible reputation systems are essential for the functionality of Peer-to-Peer (P2P) applications. However, they themselves are susceptible to various types of attacks. Since most current efforts lack an exploration of a comprehensive adversary model, we try to fill in this gap by providing a thorough view of the various credibility threats against a decentralized reputation system and the respective defense mechanisms. Therefore, we explore and classify the types of potential attacks against reputation systems for P2P applications. We also study and classify the defense mechanisms which have been proposed for each type of attack and identify conflicts between defense mechanisms and/or desirable characteristics of credible reputations systems. We finally propose a roadmap for reputation system designers on how to use the results of our survey for the design of robust reputation systems for P2P applications. © 2012 Elsevier Inc

Reputation systems evaluation survey

Various reputation systems have been proposed for a broad range of distributed applications, such as peer-topeer, ad-hoc, and multiagent systems. Their evaluation has been mostly based on proprietary methods due to the lack of widely acceptable evaluation measures and methodologies. Differentiating factors in various evaluation approaches include the evaluation metrics, the consideration of the dynamic behavior of peers, the use of social networks, or the study of resilience to specific threat scenarios. The lack of a generally accepted common evaluation framework hinders the objective evaluation and comparison of different reputation systems. Aiming at narrowing the gap in the research area of objective evaluation of reputation systems, in this article, we study the various approaches to evaluating and comparing reputation systems, present them in a taxonomy, and analyze their strengths and limitations, with special focus on works suggesting a Common Evaluation Framework (CEF). We identify the challenges for a widely accepted CEF that enables testing and benchmarking of reputation systems, and we present the required properties for such a CEF; we also present an analysis of current CEF-related works in the context of the identified properties and our related proposals. © 2015 ACM

Modeling and evaluating a robust feedback-based reputation system for e-commerce platforms

Despite the steady growth of e-commerce communities in the past two decades, little has changed in the way these communities manage reputation for building trust and for protecting their member's financial interests against fraud. As these communities mature and the defects of their reputation systems are revealed, further potential for deception against their members is created, that pushes the need for novel reputation mechanisms. Although a high volume of research works has explored the concepts of reputation and trust in e-communities, most of the proposed reputation systems target decentralized e-communities, focusing on issues related with the decentralized reputationmanagement; they have not thus been integrated in e-commerce platforms. This work's objective is to provide an attackresilient feedback-based reputation system for modern e-commerce platforms, while minimizing the incurred financial burden of potent security schemes. Initially, we discuss a series of attacks and issues in reputation systems and study the different approaches of these problems from related works, while also considering the structural properties, defense mechanisms and policies of existing platforms. Then we present our proposition for a robust reputation system which consists of a novel reputation metric and attack prevention mechanisms. Finally, we describe the simulation framework and tool that we have implemented for thoroughly testing and evaluating the metric's resilience against attacks and present the evaluation experiments and their results. We consider the presented simulation framework as the second contribution of our article, aiming at facilitating the simulation and elaborate evaluation of reputation systems which specifically target e-commerce platforms by thoroughly presenting it, exhibiting its usage and making it available to the research community. © 2017 ACM

Finding Topic-Specific Trends and Influential Users in Social Networks

Social networks (SNs) have become an integral part of contemporary life, as they are increasingly used as a basic means for communication with friends, sharing of opinions and staying up to date with news and current events. The general increase in the usage and popularity of social media has led to an explosion of available data, which creates opportunities for various kinds of utilization, such as predicting, finding or even creating trends. We are thus interested in exploring the following questions: (a) Which are the most influential - popular internet publications posted in SNs, for a specific topic? (b) Which members of SNs are experts or influential regarding a specific topic? Our approach towards answering the above questions is based on the functionality of hashtags, which we use as topic indicators for posts, and on the assumption that a specific topic is represented by multiple hashtags. We present a neighborhood-based recommender system, which we have implemented using collaborative filtering algorithms in order to (a) identify hashtags, urls and users related with a specific topic, and (b) combine them with SN-based metrics in order to address the aforementioned questions in Twitter. The recommender system is built on top of Apache Spark framework in order to achieve optimal scaling and efficiency. For the verification of our system we have used data sets mined from Twitter and tested the extracted results for influential users and urls concerning specific topics in comparison with the influence scores produced by a state of the art influence estimation tool for SNs. Finally, we present and discuss the results regarding two distinct topics and also discuss the offered and potential utility of our system. © 2018, Springer Nature Switzerland AG