Catálogo de publicaciones - libros

Extraction of the media and plaque boundaries from the intravascular Ultrasound (IVUS) images is gaining popularity as a biomedical application. This paper presents a novel system for the fully automatic extraction of the boundaries of the media and the plaque visible in the IVUS images. The system utilizes an enhanced level set technique to derive the evolution of two coupled contours as the zero level sets of a single higher dimensional surface. Moreover, the system utilizes the surface features to impose the expected media thickness. By using the single surface as a communication path between the contours, the system carries all the advantages of using two evolving surfaces and it becomes more efficient, less complex, easily extensible, and faster. Additionally, the capability of using different dynamic behaviors for the segmentation of the inner and outer walls makes our system even more flexible. The derived surface evolution equations capture the domain dependent information in an elegant and effective manner and address many practical issues, such as the missing wall sections or very weak boundary contrast. We have verified the accuracy and effectiveness of our system on synthetic and real data.

Recent advances in wireless sensors and position technology provide us with unprecedent amount of moving object data. The volume of geospatial data gathered from moving objects defies human ability to analyze the stream of input data. Therefore, new methods for mining and digesting of moving object data are urgently needed. One of the popular services available for moving objects is the prediction of the unknown location of an object. In this paper we present a new method for predicting the location of a moving object. Our method uses the past trajectory of the object and combines it with movement rules discovered in the moving objects database. Our original contribution includes the formulation of the location prediction model, the design of an efficient algorithm for mining movement rules, the proposition of four strategies for movement rule matching with respect to a given object trajectory, and the experimental evaluation of the proposed model.

Association mining is one of the most used data mining techniques due to interpretable and actionable results. In this study we propose a framework to visualize the association mining results, specifically frequent itemsets and association rules, as graphs. We demonstrate the applicability and usefulness of our approach through a Market Basket Analysis (MBA) case study where we visually explore the data mining results for a supermarket data set. In this case study we derive several interesting insights regarding the relationships among the items and suggest how they can be used as basis for decision making in retailing.

XML has been widely adopted for Web data representation under various applications (such as DBMSs, Digital Libraries etc). Therefore, access to XML data sources has become a crucial issue. In this paper we introduce a credential-based access control framework for protecting XML resources. Under this framework, we propose the use of access policy files containing policies concerning a specific credentials type. Moreover, we propose the reorganization of the policies in these files based on their frequency of use (the more frequently it is used the higher in the file it is placed). Our main goal is to improve request servicing times. Several experiments have been conducted which are carried out either on single request or on multiple requests base. The proposed framework is proven quite beneficial for protecting XML-based frameworks such as digital libraries or any other data resources whose format is expressed in XML.

Negotiation is a crucial stage of Web Services interaction lifecycle. By exchanging a sequence of proposals in the negotiation stage, a service provider and a consumer try to establish a formal contract, to specify agreed terms on the service, particularly terms on non-functional aspects. In this paper, we propose an approach for proposal evaluation, one of the key decisions in negotiation that determines the acceptability of a proposal. Fuzzy truth propositions are employed to represent the restrictions attached to a service, and a utility function is used to capture the negotiator’s preferences over service attributes. The overall acceptability of the proposal can be determined by the restriction obedience and the utility of values for service attributes, collectively. Based on the acceptability of a proposal, a negotiator can decide whether to accept it as a contract, then enact with the party that offers the proposal.

We introduce a nested bitemporal relational data model that allows arbitrary levels of nesting. Bitemporal data is attached to attributes. The fundamental construct for representing temporal data is a bitemporal atom that consists of three parts: transaction time, valid time and a value. We have defined algebra for the nested bitemporal relational model. The algebra includes operations to manipulate bitemporal data, to restructure nested bitemporal relations and to rollback database to a designated state in the past. We have also defined the concept of ‘context’ for using temporal data. Bitemporal context is for auditing purposes and rollback context is for querying past states of a bitemporal database.

We describe a recovery protocol which boosts availability, fault tolerance and performance by enabling failed network nodes to resume an active role immediately after they start recovering. The protocol is designed to work in tandem with middleware-based eager update-everywhere strategies and related group communication systems. The latter provide view synchrony, i.e., knowledge about currently reachable nodes and about the status of messages delivered by faulty and alive nodes. That enables a fast replay of missed updates which defines dynamic database recovery partition. Thus, speeding up the recovery of failed nodes which, together with the rest of the network, may seamlessly continue to process transactions even before their recovery has completed. We specify the protocol in terms of the procedures executed with every message and event of interest and outline a correctness proof.

We present a case study where a mission-critical legacy hierarchical database, EWIRDB (Electronic Warfare Integrated Reprogramming Database), and its application software are migrated onto a service-oriented web architecture that is based on an XML-based database. EWIRDB stores its data in an extensible tree structure and serves many purposes of supporting EW systems reprogramming, research, development, test, and evaluation; modeling, and simulation, acquisition; and training. We present the historical stages of this migration that helped us to understand the issues and converge to the most appropriate solution eventually. We conclude that recently emerging web service technologies together with native XML database support meet the unique migration requirements of the EWIRDB and its legacy database application. We believe that the proposed solution addresses an almost 20-year old problem in the EW domain problem and forms an appropriate base for porting some other applications with similar requirements in other domains.

Today, wireless sensor networks (WSNs) enable us to run a new range of applications from habitat monitoring, to military and medical applications. A typical WSN node is composed of several sensors, a radio communication interface, a microprocessor, and a limited power supply. In many WSN applications, such as forest fire monitoring or intruder detection, user intervention and battery replenishment is not possible. Since the battery lifetime is directly related to the amount of processing and communication involved in these nodes, optimal resource usage becomes a major issue. A typical WSN application may sense and process very close or constant data values for long durations, when the environmental conditions are stable. This is a common behavior that can be exploited to reduce the power consumption of WSN nodes. This study combines two orthogonal techniques to reduce the energy dissipation of the processor component of the sensor nodes. First, we briefly discuss silent-store filtering MoteCache . Second, we utilize Content-Aware Data MAnagement (CADMA) on top of MoteCache architecture to achieve further energy savings and performance improvements. The complexity increase introduced by CADMA is also compensated by further complexity reduction in MoteCache. Our optimal configuration reduces the total node energy, and hence increases the node lifetime, by 19.4% on the average across a wide variety of simulated sensor benchmarks. Our complexity-aware configuration with a minimum MoteCache size achieves not only energy savings up to 16.2% but also performance improvements up to 4.3%, on the average.

In this study, we analyze the effects of asynchronism and neighborhood size on the collective motion of multi-agent systems. Many studies performed on the collective motion of self propelled particle systems or basically a class of multi-agent systems are modeled to be synchronous. However, in nature and in robotic applications the autonomous agents mostly act asynchronously. Therefore, a model based on the asynchronous actions of agents is developed. The agents/particles are assumed to move with constant speed and asynchronously update their direction of motion based on a nearest-neighbors rule. Based on these rules simulations are performed and the effects of asynchronism and neighborhood size on the clustering performance are investigated.