Institute of Computer Science

FORTH, Greece

Institute of Computer Science

FORTH, Greece
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Mountantonakis M.,Institute of Computer Science | Tzitzikas Y.,University of Crete
Proceedings of the VLDB Endowment | Year: 2016

A big number of datasets has been published according to the principles of Linked Data and this number keeps in- creasing. Although the ultimate objective is linking and integration, it is not currently evident how connected the current LOD cloud is. Measurements (and indexes) that involve more than two datasets are not available although they are important: (a) for obtaining complete information about one particular URI (or set of URIs) with provenance (b) for aiding dataset discovery and selection, (c) for assess- ing the connectivity between any set of datasets for quality checking and for monitoring their evolution over time, (d) for constructing visualizations that provide more informa- tive overviews. Since it would be prohibitively expensive to perform all these measurements in a naïve way, in this paper we introduce indexes (and their construction algo- rithms) that can speedup such tasks. In brief, we introduce (i) a namespace-based prex index, (ii) a sameAs catalog for computing the symmetric and transitive closure of the owl:sameAs relationships encountered in the datasets, (iii) a semantics-aware element index (that exploits the afore- mentioned indexes), and nally (iv) two lattice-based incre- mental algorithms for speeding up the computation of the intersection of URIs of any set of datasets. We discuss the speedup obtained by the introduced indexes and algorithms through comparative results and nally we report measure- ments about connectivity of the LOD cloud that have never been carried out so far. © 2016 VLDB Endowment 2150-8097/16/08.

Bikakis A.,Institute of Computer Science | Antoniou G.,Institute of Computer Science | Hasapis P.,Athens University of Economics and Business
Knowledge and Information Systems | Year: 2011

Ambient Intelligence environments host various agents that collect, process, change and share the available context information. The imperfect nature of context, the open and dynamic nature of such environments and the special characteristics of ambient agents have introduced new research challenges in the study of Distributed Artificial Intelligence. This paper proposes a solution based on the Multi-Context Systems paradigm, according to which local knowledge of ambient agents is encoded in rule theories (contexts), and information flow between agents is achieved through mapping rules that associate concepts used by different contexts. To resolve potential inconsistencies that may arise from the interaction of contexts through their mappings (global conflicts), we use a preference ordering on the system contexts, which may express the confidence that an agent has in the knowledge imported by other agents. On top of this model, we have developed four alternative strategies for global conflicts resolution, which mainly differ in the type and extent of context and preference information that is used to resolve potential conflicts. The four strategies have been respectively implemented in four versions of a distributed algorithm for query evaluation and evaluated in a simulated P2P system. © 2010 Springer-Verlag London Limited.

Einloft J.,Institute of Computer Science | Ackermann J.,Institute of Computer Science | Nothen J.,Institute of Computer Science | Koch I.,Institute of Computer Science
Bioinformatics | Year: 2013

Structural modeling of biochemical networks enables qualitative as well as quantitative analysis of those networks. Automated network decomposition into functional modules is a crucial point in network analysis. Although there exist approaches for the analysis of networks, there is no open source tool available that combines editing, visualization and the computation of steady-state functional modules. We introduce a new tool called MonaLisa, which combines computation and visualization of functional modules as well as an editor for biochemical Petri nets. The analysis techniques allow for network decomposition into functional modules, for example t-invariants (elementary modes), maximal common transition sets, minimal cut sets and t-clusters. The graphical user interface provides various functionalities to construct and modify networks as well as to visualize the results of the analysis. © 2013 The Author. Published by Oxford University Press. All rights reserved.

Papadourakis V.,Institute of Computer Science | Argyros A.,Institute of Computer Science | Argyros A.,University of Crete
Computer Vision and Image Understanding | Year: 2010

We present a robust object tracking algorithm that handles spatially extended and temporally long object occlusions. The proposed approach is based on the concept of "object permanence" which suggests that a totally occluded object will re-emerge near its occluder. The proposed method does not require prior training to account for differences in the shape, size, color or motion of the objects to be tracked. Instead, the method automatically and dynamically builds appropriate object representations that enable robust and effective tracking and occlusion reasoning. The proposed approach has been evaluated on several image sequences showing either complex object manipulation tasks or human activity in the context of surveillance applications. Experimental results demonstrate that the developed tracker is capable of handling several challenging situations, where the labels of objects are correctly identified and maintained over time, despite the complex interactions among the tracked objects that lead to several layers of occlusions. © 2010 Elsevier Inc.

Markaki M.,University of Crete | Stylianou Y.,University of Crete | Stylianou Y.,Institute of Computer Science
IEEE Transactions on Audio, Speech and Language Processing | Year: 2011

In this paper, we explore the information provided by a joint acoustic and modulation frequency representation, referred to as modulation spectrum, for detection and discrimination of voice disorders. The initial representation is first transformed to a lower dimensional domain using higher order singular value decomposition (HOSVD). From this dimension-reduced representation a feature selection process is suggested using an information-theoretic criterion based on the mutual information between voice classes (i.e., normophonic/dysphonic) and features. To evaluate the suggested approach and representation, we conducted cross-validation experiments on a database of sustained vowel recordings from healthy and pathological voices, using support vector machines (SVMs) for classification. For voice pathology detection, the suggested approach achieved a classification accuracy of 94.1±0.28% (95% confidence interval), which is comparable to the accuracy achieved using cepstral-based features. However, for voice pathology classification the suggested approach significantly outperformed the performance of cepstral-based features. © 2010 IEEE.

Yang M.,Institute of Computer Science
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2011

For patients with Cardiovascular Implantable Electronic Devices (CIEDs), telemonitoring promises improved quality of life and safety, since events recorded by the device or observed by the patient can alert a health professional. Taking into account the latest clinical guidelines when responding to such alerts, is a topic of active research addressed by the iCARDEA project. A key technical challenge is correlating telemonitoring CIED report data in a vendor-independent format with Electronic Health Record (EHR) data collected in the hospital and Personal Health Record (PHR) data entered by the patient, in guideline-driven care processes. The iCARDEA CIED exposure service component presented in this paper employs standards specifications from ISO/IEEE 11073 (Health Informatics, Point-of-care Medical Device Communication) and HL7v2.x in the context of Integrating the Healthcare Enterprise (IHE) profiles to deliver telemonitoring CIED report data from two different CIED vendors to the adaptive care planner that implements guideline-driven care plans. Experience gained with implementation and initial component testing is discussed, while challenges and expectations for future health information standards to effectively support EHR-integrated guide-line-driven telemonitoring services are highlighted.

Kondylakis H.,Institute of Computer Science | Plexousakis D.,Institute of Computer Science
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Information systems rely more and more on semantic web ontologies to share and interpret data within and across research domains. However, an important problem when dealing with ontologies is the fact that they are living artefacts and subject to change. When ontologies evolve, queries formulated using a past ontology version might become invalid and should be redefined or adapted. In this paper we propose a solution in order to identify the impact of ontology evolution on queries and to ease query migration. We present a module that receives as input the sequence of changes between the two ontology versions along with a set of queries and automatically identifies the specific change operations that affect the input queries. Besides the automatic identification of the affecting change operations, query migration is further aided by providing an explanation for the specific invalidation. This explanation is presented graphically by means of change paths that represent the evolution of the specific parts of the ontology that invalidate the query. We evaluate the time complexity of our approach and show how it can possibly reduce the human effort spent on query redefinition/adaptation. © 2012 Springer-Verlag.

Willms J.,Institute of Computer Science
IEEE Transactions on Information Theory | Year: 2013

We analyze the connection between the autocorrelation of a binary sequence and its run structure given by the run length encoding. We show that both the periodic and the aperiodic autocorrelation of a binary sequence can be formulated in terms of the run structure. The run structure is given by the consecutive runs of the sequence. Let C=(C-0,C-1,C-n) denote the autocorrelation vector of a binary sequence and the difference operator. We prove that the k th component of ∠2(C) can be directly calculated by using the consecutive runs of total length k. In particular, this shows that the kth autocorrelation is already determined by all consecutive runs of total length l< k. In the aperiodic case, we show how the run vector R can be efficiently calculated and give a characterization of skew-symmetric sequences in terms of their run length encoding. © 2013 IEEE.

Hladek L.,Institute of Computer Science
Proceedings of Meetings on Acoustics | Year: 2013

When an auditory target is presented simultaneously with a spatially displaced visual target, the perceived auditory target location shifts towards the visual target. This effect, known as the ventriloquism effect or visual capture, has been extensively studied in the horizontal dimension, but not in distance. Here, we measured distance localization performance in a reverberant room. Stimuli were either audio-visual (AV) 300-ms broadband noise bursts presented synchronously with spatially congruent or incongruent visual stimuli/LEDs, or auditory-only (A-only) noise bursts. One of 8 speakers (distance 70 cm to 203 cm directly ahead of the listener) presented a stimulus on each trial. During adaptation runs, the AV stimuli were presented with the V-component closer or further by 30% than the A-component (displacement direction fixed within session). The ventriloquism effect was observed for both V-closer and V-further AV stimuli, with slightly stronger shifts induced by the V-closer stimuli. Ventriloquism aftereffect, assessed by presenting A-only trials interleaved with the adaptation-AV trials, was also observed, but was weaker than the ventriloquism effect. The results suggest that visual targets do capture auditory targets in the distance dimension, but visual modulation might be asymmetrical with respect to distance. © 2013 Acoustical Society of America.

Chronaki C.E.,Institute of Computer Science | Vardas P.,University of Crete
Europace | Year: 2013

AimsTo provide a European perspective on reimbursement issues surrounding remote monitoring of cardiac implantable electronic devices in view of the anticipated costs and benefits.Methods and resultsReview of recent literature addressing clinical, economic, sociocultural, and technological factors associated with remote monitoring. When healthcare transformation is urgently needed, remote monitoring offers opportunities to innovate and cope with escalating costs and constrained resources, while improving patient safety, quality, and access to care as reflected in clinical studies. The introduction of remote monitoring into daily practice requires analysis of reimbursement policies to address funding scope, payment method, payer, price and allocation, and alignment with health system objectives and goals to ensure financial and operational sustainability of resources, infrastructure, and processes. Remote monitoring policies should gradually transition from activity-based, added-value services in a care-and-cure setting, to performance and outcome-oriented highlighting prevention, surveillance, and empowerment. By encouraging and rewarding innovation and interoperability, proprietary remote monitoring technologies can open up using standards and connect to support a growing evidence base that guides clinical decision support and planning of future policies.ConclusionCareful planning, sharing of experiences, and gradual adoption of reimbursement models that focus on outcome, performance, and cost-effectiveness are key aspects of containing escalating costs and improving quality and access to healthcare. Despite differences in health systems and payment methods in Europe, policy-makers, professional societies, payers, providers, and the industry need to join forces to transform healthcare and make innovation happen. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2013.

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