The Dynamics of Vehicular Networks in Urban Environments

Vehicular Ad hoc NETworks (VANETs) have emerged as a platform to support intelligent inter-vehicle communication and improve traffic safety and performance. The road-constrained, high mobility of vehicles, their unbounded power source, and the emergence of roadside wireless infrastructures make VANETs a challenging research topic. A key to the development of protocols for inter-vehicle communication and services lies in the knowledge of the topological characteristics of the VANET communication graph. This paper explores the dynamics of VANETs in urban environments and investigates the impact of these findings in the design of VANET routing protocols. Using both real and realistic mobility traces, we study the networking shape of VANETs under different transmission and market penetration ranges. Given that a number of RSUs have to be deployed for disseminating information to vehicles in an urban area, we also study their impact on vehicular connectivity. Through extensive simulations we investigate the performance of VANET routing protocols by exploiting the knowledge of VANET graphs analysis.Comment: Revised our testbed with even more realistic mobility traces. Used the location of real Wi-Fi hotspots to simulate RSUs in our study. Used a larger, real mobility trace set, from taxis in Shanghai. Examine the implications of our findings in the design of VANET routing protocols by implementing in ns-3 two routing protocols (GPCR & VADD). Updated the bibliography section with new research work

Self-optimizing block transfer in web service grids

Nowadays, Web Services (WSs) play an increasingly impor-tant role in Web data management solutions, since they offer a practical solution for accessing and manipulating data sources spanning administrative domains. Neverthe-less, they are notoriously slow and transferring large data volumes across WSs becomes the main bottleneck in such WS-based applications. This paper deals with the problem of minimizing at runtime, in a self-managing way, the data transfer cost of a WS encapsulating a data source. To reduce the transfer cost, the data volume is typically divided into blocks. In this case, response time exhibits a quadratic-like, non-linear behavior with regards to the block size; as such, minimizing the transfer cost entails finding the optimum block size. This situation is encountered in several systems

A Grid-Enabled Digital Library System for Natural Disaster Metadata

Abstract. The need to organize and publish metadata about European research results in the field of natural disasters has been met with the help of two innovative technologies: the Open Grid Service Architecture (OGSA) and the Resource Description Framework (RDF). OGSA provides a common platform for sharing distributed metadata securely. RDF facilitates the creation and exchange of metadata. In this paper, we present the design and implementation of a Grid-based digital library for natural-disaster research metadata. We describe the EU-MEDIN RDF schema that we propose to standardize the description of natural-disaster resources, and the gDisDL Grid service-based architecture for storing and querying of RDF metadata in a secure and distributed manner. Finally, we describe a prototype implementation of gDisDL using the Jena RDF Library by HP and the Globus 3 toolkit

Exploring the sentiment of entrepreneurs on Twitter

Sentiment analysis is an evolving field of study that employs artificial intelligence techniques to identify the emotions and opinions expressed in a given text. Applying sentiment analysis to study the billions of messages that circulate in popular online social media platforms has raised numerous opportunities for exploring the emotional expressions of their users. In this paper we combine sentiment analysis with natural language processing and topic analysis techniques and conduct two different studies to examine whether engagement in entrepreneurship is associated with more positive emotions expressed on Twitter. In study 1, we investigate three samples with 6.717.308, 13.253.244, and 62.067.509 tweets respectively. We find that entrepreneurs express more positive emotions than non-entrepreneurs for most topics. We also find that social entrepreneurs express more positive emotions, and that serial entrepreneurs express less positive emotions than other entrepreneurs. In study 2, we use 21.491.962 tweets to explore 37.225 job-status changes by individuals who entered or quit entrepreneurship. We find that a job change to entrepreneurship is associated with a shift in the expression of emotions to more positive ones

A Theoretical Framework for Analyzing Satellite-based Web Multicasting Services

In this paper we study Web multicasting, a service offered by satellite operators to Internet Service Providers around the world. This service employs satellite connections for disseminating periodically Web content to regional and "institutional" WWW caches. We propose a theoretical framework for Web multicasting and formalize the notions of Utility and QoS perceived by customers of Web multicasting services. We explore two alternative charging schemes, Usage- and Subscription-based pricing, and propose a framework for negotiating the provision of the Web multicasting service between a satellite operator and its potential customers. We use this negotiation framework to compare theoretically the two pricing schemes at hand. We show that a given level of QoS can be guaranteed under Subscription-based pricing at a cost at least as low as under Usage-based pricing. Our theoretical framework can be used further by satellite operators and prospective customers to define the content provided through Web multicasting, estimate its quality, negotiate its price and assess its overall effectiveness

Intermediaries for the World-Wide Web Overview and Classification

Intermediaries are software entities deployed on Internet hosts of the wireline and wireless Web that intervene to the flow of information from clients to origin servers at the application level of the WWW. Intermediaries represent a useful abstraction for the design and study of emerging software infrastructures for "nextgeneration " Web services. Their importance is increasing with the increasing demand for personalization, localization, and support for ubiquitous access over different physical media and protocols. In this paper, we present an overview of a wide range of systems that can be described as intermediaries, classifying them in a number of broad categories according to their basic functionalities. Going beyond simple WWW proxies, we examine the requirements arising from the need to support personalization, mobility and ubiquity under high loads. We identify and refine a set of important properties and characteristics of intermediary systems. Based on these properties, we introduce a detailed taxonomy of characteristic systems and identify a number of key component of emerging intermediary infrastructures