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Dimitrios Sarlis, Nikolaos Papailiou, Ioannis Konstantinou, Georgios Smaragdakis, Nectarios Koziris
2015 Computer communication review  
Nikolaos Papailiou was supported by IKY fellowships of excellence for postgraduate studies in Greece -SIEMENS program.  ... 
doi:10.1145/2831347.2831351 fatcat:yd7422imkvb5valy7noimhcdcu

Uncertain Graph Sparsification [article]

Panos Parchas, Nikolaos Papailiou, Dimitris Papadias, Francesco Bonchi
2017 arXiv   pre-print
Uncertain graphs are prevalent in several applications including communications systems, biological databases and social networks. The ever increasing size of the underlying data renders both graph storage and query processing extremely expensive. Sparsification has often been used to reduce the size of deterministic graphs by maintaining only the important edges. However, adaptation of deterministic sparsification methods fails in the uncertain setting. To overcome this problem, we introduce
more » ... e first sparsification techniques aimed explicitly at uncertain graphs. The proposed methods reduce the number of edges and redistribute their probabilities in order to decrease the graph size, while preserving its underlying structure. The resulting graph can be used to efficiently and accurately approximate any query and mining tasks on the original graph. An extensive experimental evaluation with real and synthetic datasets illustrates the effectiveness of our techniques on several common graph tasks, including clustering coefficient, page rank, reliability and shortest path distance.
arXiv:1611.04308v4 fatcat:g534ej7hhrhn3f3hg2arzazzg4


Nikolaos Papailiou, Ioannis Konstantinou, Dimitrios Tsoumakos, Nectarios Koziris
2012 Proceedings of the 21st international conference companion on World Wide Web - WWW '12 Companion  
In this work we present H2RDF , a fully distributed RDF store that combines the MapReduce processing framework with a NoSQL distributed data store. Our system features two unique characteristics that enable efficient processing of both simple and multi-join SPARQL queries on virtually unlimited number of triples: Join algorithms that execute joins according to query selectivity to reduce processing; and adaptive choice among centralized and distributed (MapReduce-based) join execution for fast
more » ... uery responses. Our system efficiently answers both simple joins and complex multivariate queries and easily scales to 3 billion triples using a small cluster of 9 worker nodes. H2RDF outperforms state-of-the-art distributed solutions in multi-join and nonselective queries while achieving comparable performance to centralized solutions in selective queries. In this demonstration we showcase the system's functionality through an interactive GUI. Users will be able to execute predefined or custom-made SPARQL queries on datasets of different sizes, using different join algorithms. Moreover, they can repeat all queries utilizing a different number of cluster resources. Using real-time cluster monitoring and detailed statistics, participants will be able to understand the advantages of different execution schemes versus the input data as well as the scalability properties of H2RDF over both the data size and the available worker resources.
doi:10.1145/2187980.2188058 dblp:conf/www/PapailiouKTK12 fatcat:6vdxhwgvhje23izc5aizmqpwxu


Nikolaos Papailiou, Dimitrios Tsoumakos, Ioannis Konstantinou, Panagiotis Karras, Nectarios Koziris
2014 Proceedings of the 2014 ACM SIGMOD international conference on Management of data - SIGMOD '14  
The proliferation of data in RDF format has resulted in the emergence of a plethora of specialized management systems. While the ability to adapt to the complexity of a SPARQL query -given their inherent diversity -is crucial, current approaches do not scale well when faced with substantially complex, non-selective joins, resulting in exponential growth of execution times. In this demonstration we present H2RDF+, an RDF store that efficiently performs distributed Merge and Sort-Merge joins
more » ... a multipleindex scheme over HBase indexes. Through a greedy planner that incorporates our cost-model, it adaptively commands for either single or multi-machine query execution based on join complexity. In this paper, we present its key scientific contributions and allow participants to interact with an H2RDF+ deployment over a Cloud infrastructure. Using a web-based GUI we allow users to load different datasets (both real and synthetic), apply any query (custom or predefined) and monitor its execution. By allowing real-time inspection of cluster status, response times and committed resources the audience will evaluate the validity of H2RDF+'s claims and perform direct comparisons to two other stateof-the-art RDF stores.
doi:10.1145/2588555.2594535 dblp:conf/sigmod/PapailiouTKKK14 fatcat:hlui2tfwlrgxjcfmowkmipnvv4


Katerina Doka, Nikolaos Papailiou, Dimitrios Tsoumakos, Christos Mantas, Nectarios Koziris
2015 Proceedings of the 2015 ACM SIGMOD International Conference on Management of Data - SIGMOD '15  
Nikolaos Papailiou has received funding from IKY fellowships of excellence for postgraduate studies in Greece -SIEMENS program.  ... 
doi:10.1145/2723372.2735377 dblp:conf/sigmod/DokaPTMK15 fatcat:5dyeik3d45esje2mbqmwravm4q

PANIC: Modeling Application Performance over Virtualized Resources

Ioannis Giannakopoulos, Dimitrios Tsoumakos, Nikolaos Papailiou, Nectarios Koziris
2015 2015 IEEE International Conference on Cloud Engineering  
Nikolaos Papailiou has received funding from IKY fellowships of excellence for postgraduate studies in Greece -SIEMENS program.  ... 
doi:10.1109/ic2e.2015.27 dblp:conf/ic2e/GiannakopoulosT15 fatcat:6pcq75f7avhkpgqygafrmdmi5u

Mix 'n' match multi-engine analytics

Katerina Doka, Nikolaos Papailiou, Victor Giannakouris, Dimitrios Tsoumakos, Nectarios Koziris
2016 2016 IEEE International Conference on Big Data (Big Data)  
Papailiou has received funding from IKY fellowships of excellence for postgraduate studies in Greece -SIEMENS program.  ... 
doi:10.1109/bigdata.2016.7840605 dblp:conf/bigdataconf/DokaPGTK16 fatcat:nimpr3poqfhapgxssfoulvva6u

CELAR: Automated application elasticity platform

Ioannis Giannakopoulos, Nikolaos Papailiou, Christos Mantas, Ioannis Konstantinou, Dimitrios Tsoumakos, Nectarios Koziris
2014 2014 IEEE International Conference on Big Data (Big Data)  
Nikolaos Papailiou has received funding from IKY fellowships of excellence for postgraduate studies in Greece -SIEMENS program.  ... 
doi:10.1109/bigdata.2014.7004481 dblp:conf/bigdataconf/GiannakopoulosPMKTK14 fatcat:wlwam7xvmvfr7lamsmh5bflgoy

Graph-Aware, Workload-Adaptive SPARQL Query Caching

Nikolaos Papailiou, Dimitrios Tsoumakos, Panagiotis Karras, Nectarios Koziris
2015 Proceedings of the 2015 ACM SIGMOD International Conference on Management of Data - SIGMOD '15  
Papailiou has received funding from IKY fellowships of excellence for postgraduate studies in Greece -SIEMENS program.  ...  10 Average query response times for W1, W2, W3 and W4 Figure 11 : 11 Effectiveness of caching techniques Figure 12 : 12 Cache performance for different dataset, caching policies and cache size Nikolaos  ... 
doi:10.1145/2723372.2723714 dblp:conf/sigmod/PapailiouTKK15 fatcat:t4qgqvxt7ncu3gof4c2bsbsg7y

Morbid Obesity and Sleeve Gastrectomy: How Does It Work?

Joanna Papailiou, Konstantinos Albanopoulos, Konstantinos G. Toutouzas, Christos Tsigris, Nikolaos Nikiteas, George Zografos
2010 Obesity Surgery  
Laparoscopic sleeve gastrectomy is known to be a safe and effective procedure for treating morbid obesity and is performed with increasing frequency both in Europe and the USA. Despite its broad use, many questions about the remaining gastric tube diameter, its long-term efficacy, its effects on gastric emptying, and the hormones involved still remain to be answered. In order to use such a relatively new surgical procedure wisely, it is essential for every surgeon and physician to understand
more » ... sleeve gastrectomy acts in obesity and what its potential benefits on the patients' metabolism are. This review focuses on the most important pathophysiologic questions referred to sleeve gastrectomy on the literature so far, in an attempt to evaluate the different issues still pending on the subject.
doi:10.1007/s11695-010-0148-5 pmid:20383753 fatcat:zjsz4s7efzbojozy54fzax7xuy

AAA Rupture and Psoas Hematoma due to Type II Endoleak from Inferior Mesenteric Artery "Unusual" Collaterals

Panagiotis G. Theodoridis, Dimitrios N. Staramos, Nikolaos Ptochis, Ioannis A. Papailiou, Ilias Dodos, Nikolaos Iatrou, Anastasios G. Potouridis, Konstantinos Dervisis
2017 Case Reports in Vascular Medicine  
Although endovascular aneurysm repair (EVAR) in the abdominal aorta has reduced the perioperative mortality when compared with open repair, the need for reintervention after complications such as endoleak may be presented in up to 20% of the cases. Type II endoleak from branch vessels is often benign but can potentially be associated with progressive abdominal aortic aneurysm growth and sac expansion. We present a rare case of a patient who presented with sac expansion and psoas hematoma due to
more » ... Type II endoleak from "unusual" collaterals of IMA and was treated successfully with endoleak microembolization and percutaneous decompression of the hematoma.
doi:10.1155/2017/8607437 pmid:28634567 pmcid:PMC5467359 fatcat:43jh2grys5garixgvz2efkv7tu

Automatic scaling of selective SPARQL joins using the TIRAMOLA system

Evangelos Angelou, Nikolaos Papailiou, Ioannis Konstantinou, Dimitrios Tsoumakos, Nectarios Koziris
2012 Proceedings of the 4th International Workshop on Semantic Web Information Management - SWIM '12  
Modern cloud infrastructures based on virtual hardware provide new opportunities and challenges for developers and system administrators alike. Most notable is the promise of resource elasticity, whereby the infrastructure can increase or decrease in size based on demand. Utilizing elastic resources, applications can provide better quality of service and reduce cost by only paying for the required amount of resources. In this work, we extensively study the performance of some popular NoSQL
more » ... ases over an elastic cloud infrastructure. NoSQL databases focus on analytical processing of large scale datasets, offering increased scalability over commodity hardware. We then proceed to describe TIRA-MOLA, a cloud-enabled framework for automatic provisioning of elastic resources on any NoSQL platform. Our system administers cluster resources (VMs) according to useror application-specified constraints through an expandable monitoring and command-issuing module. Users can easily modify resizing policies, based on application-specific metrics and thus fully utilize the elasticity of the underlying infrastructure. As a realistic use-case, we apply this framework on top of a fully distributed RDF store backed by an elastic NoSQL database. Letting TIRAMOLA manage the number of committed resources results in automated cluster resize actions and throughput maximization, while application experts need only provide simple elasticity rules.
doi:10.1145/2237867.2237868 dblp:conf/sigmod/AngelouPKTK12 fatcat:emc6ulbbf5eelbo3bqsgtga6h4

Analysing and Enriching Focused Semantic Web Archives for Parliament Applications

Elena Demidova, Nicola Barbieri, Stefan Dietze, Adam Funk, Helge Holzmann, Diana Maynard, Nikolaos Papailiou, Wim Peters, Thomas Risse, Dimitris Spiliotopoulos
2014 Future Internet  
Nikolaos Papailiou has received funding from IKY fellowships of excellence for postgraduate studies in Greece, SIEMENS program. Author Contributions All authors contributed equally to the paper.  ... 
doi:10.3390/fi6030433 fatcat:jasz3i3sofhipellazgoo4cvre

Scalable Indexing and Adaptive Querying of RDF Data in the cloud

Nikolaos Papailiou, Dimitrios Tsoumakos, Ioannis Konstantinou, Panagiotis Karras, Nectarios Koziris
2014 Proceedings of Semantic Web Information Management on Semantic Web Information Management - SWIM'14  
Efficient RDF data management systems are central to the vision of the Semantic Web. The enormous increase in both user and machine generated content dictates for scalable solutions in triple data stores. Current systems manage to decentralize some or all the stages of RDF data management, scaling to arbitrarily large numbers of triples. Yet, these systems prove highly inflexible in adjusting their behavior relative to the query in hand. Queries over triple data include multiple joins with
more » ... ng degrees of selectivity and cost. In many cases, a join performed on a single centralized computer node is highly preferable. Thus, both informed query planning and adaptive join execution are necessary to gain optimal performance in both selective and non selective queries. Towards that direction, we describe H2RDF+, an RDF store that efficiently performs distributed joins over a multiple index scheme. H2RDF+ materializes 6 RDF indexes and detailed statistics using HBase. In this work, we emphasize on our novel, scalable and efficient MapReduce indexing process that allows H2RDF+ to handle arbitrarily large RDF datasets. Aggressive byte-level compression is also extensively used to reduce the storage space requirements of the system. H2RDF+ can also adaptively process both complex and selective queries by adaptively choosing the amount of resources allocated for each join, based on join complexity estimated through index statistics.
doi:10.1145/2630602.2630603 dblp:conf/sigmod/PapailiouTKKK14a fatcat:7asq5xr43fbazklagzowxyynue

Aldosterone synthase deficiency type II: an unusual presentation of the first Greek case reported with confirmed genetic analysis

Stayroula Papailiou, Elpis Athina Vlachopapadopoulou, Amalia Sertedaki, Despoina Maritsi, Nikolaos Syggelos, Angeliki Syggelou
2020 Endocrine Regulations  
AbstractObjective. Aldosterone synthase deficiency (ASD) is a rare, autosomal recessive inherited disease with an overall clinical phenotype of failure to thrive, vomiting, severe dehydration, hyperkalemia, and hyponatremia. Mutations in the CYP11B2 gene encoding aldosterone synthase are responsible for the occurrence of ASD. Defects in CYP11B2 gene have only been reported in a limited number of cases worldwide. Due to this potential life-threatening risk, comprehensive hormonal investigation
more » ... llowed by genetic confirmation is essential for the clinical management of offsprings.Case presentation. We herein describe an unusual case of ASD type II in a neonate with faltering growth as a single presenting symptom. To our knowledge, this is the first Greek case of ASD type II reported with confirmed genetic analysis. Next generation sequencing of her DNA revealed the homozygous mutation p.T185I (ACC-ATC) (c.554C>T) (g.7757C>T) in exon 3 of the CYP11B2 gene in the neonate, inherited from both parents who were heterozygotes for the mutation.Conclusions. Physicians handling neonates with faltering growth, particularly in the initial six weeks of life, should be suspicious of mineralocorticoid insufficiency either as isolated hypoaldosteronism or in the context of congenital adrenal hyperplasia. Essential investigations should be performed and appropriate treatment should be administered promptly without awaiting for the hormonal profile results. Interpretation of the clinical picture and the hormonal profile will guide the analysis of candidate genes. Primary selective hypoaldosteronism is a rare, life threatening disease, but still with an unknown overall population impact. Thus, reporting cases with confirmed gene mutations is of major importance.
doi:10.2478/enr-2020-0025 pmid:32857717 fatcat:taxbrle2wfhyri3ddm6kusmpsa
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