Ioannis Antoniou

Aristotle University of Thessaloniki | AUTH · School of Mathematics

We investigate whether it is possible to distinguish chaotic time series from random time series using network theory. In this perspective, we selected four methods to generate graphs from time series: the natural, the horizontal, the limited penetrable horizontal visibility graph, and the phase space reconstruction method. These methods claim that...

We extend network analysis to directed criminal networks in the context of asymmetric links. We computed selected centralities, centralizations and the assortativity of a drug trafficking network with 110 nodes and 295 edges. We also monitored the centralizations of eleven temporal networks corresponding to successive stages of investigation during...

The early intervention of law enforcement authorities to prevent an impending terrorist attack is of utmost importance to ensuring economic, financial, and social stability. From our previously published research, the key individuals who play a vital role in terrorist organizations can be timely revealed. The problem now is to identify which attack...

The global economy operates as a complex and interconnected system, necessitating the application of sophisticated network methods for analysis. This study examines economic data from all countries across the globe, representing each country as a node and its exports as links, covering the period from 2008 to 2019. Through the computation of releva...

The aim of this paper is to use network analysis as a monitoring tool for the competitive conditions and the behavior of the contracting authorities and companies in the public procurement market. The proposed method examines the market using network entropy and conditional network entropy, along with each agent's metrics. Network entropy offers in...

The more complex and globalized social structures become, the greater the need for new ways of exchanging information and knowledge. Legal science is a field that needs to be codified to allow the interoperability between people and states, as well as between humans and machines. The objective of this work is to develop an ontology in order to desc...

Co-evolutionary networks are mathematical graphs which are not passive media of communication channels, simply supporting the spread of information. The channels are actually redefined according to the spread of information among the nodes. Co-evolutionary networks are learning. We report results on both passive spread and active co-evolution in re...

Law enforcement authorities deal with terrorism in two ways: prevention and legal procedures to establish the offence of forming a terrorist organization. Setting up the offence of a terrorist organization requires proof that the members of the organization acquire distinct roles in the organization. Until today, this procedure has been based on un...

The COVID-19 pandemic caused a boom in demand for personal protective equipment, or so-called “COVID-19 goods”, around the world. We investigate three key sectoral global value chain networks, namely, “chemicals”, “rubber and plastics”, and “textiles”, involved in the production of these goods. First, we identify the countries that export a higher...

In recent years, law enforcement authorities have increasingly used mathematical tools to support criminal investigations, such as those related to terrorism. In this work, two relevant questions are discussed: “How can the different roles of members of a terrorist organization be recognized?” and “are there early signs of impending terrorist acts?...

DIDSON acoustic cameras provide a way to collect temporally dense, high-resolution imaging data, similar to videos. Detection of fish targets on those videos takes place in a manual or semi-automated manner, typically assisted by specialised software. Exploiting the visual nature of the recordings, tools and techniques from the field of computer vi...

We extend the agent-based models for knowledge diffusion in networks, restricted to random mindless interactions and to “frozen” (static) networks, in order to take into account intelligent agents and network co-evolution. Intelligent agents make decisions under bounded rationality. This is the key distinction of intelligent interacting agents comp...

Red Flags in fiscal projects are warning signs that may indicate underlying problems with their implementation. In this paper, we present how National Strategic Reference Framework Open Data can be used to take full advantage of semantic web technologies and data mining techniques to build a knowledge-based system that identifies Red Flags. We coll...

The social adoption of change is usually hard because in reality, forces opposing the social adoption of change manifest. This situation of organizational conflict corresponds to the case where two competing groups of influential agents (“promoters” versus “adversaries” of change) operate concurrently within the same organizational network. We mode...

We investigated competitive conditions in global value chains (GVCs) for a period of fifteen years (2000–2014), focusing on sector structure, countries’ dominance and diversification. For this purpose, we used data from the World Input–Output Database (WIOD) and examined GVCs as weighted directed networks, where countries are the nodes and value ad...

Water buffaloes are considered social animals and perform several activities on pasture, such as grazing, moving, standing, ruminating, wallowing, lying, and drinking. However, the way these animals form their social structure in the herd during each one of these activities is still unknown. Literature for water buffaloes has focused mainly on thei...

The adoption of change in organizational networks is conditioned by the engagement of the so-called “change agents” initiating “cascades of change”, as well as by the internal communication among the members of the network. We investigate how the dynamics of the adoption of change is influenced by the engagement policy of the change agents and by t...

Density-based clustering is an effective clustering approach that groups together dense patterns in low- and high-dimensional vectors, especially when the number of clusters is unknown. Such vectors are obtained for example when computer scientists represent unstructured data and then groups them into clusters in an unsupervised way. Another facet...

Social Network Analysis (SNA) is used for the first time to investigate the relations between plant functional groups and social structure of grazing sheep. The research was conducted on a grassland in Crete's island Lefka Ori, Greece during 2016. A flock of 20 sheep of Sfakion race was analysed as a network and the sheep as nodes. The focal sampli...

Ontology matching is an essential problem in the world of Semantic Web and other distributed, open world applications. Heterogeneity occurs as a result of diversity in tools, knowledge, habits, language, interests and usually the level of detail. Automated applications have been developed, implementing diverse aligning techniques and similarity mea...

Nowadays, a large amount of text documents are produced on a daily basis, so we need efficient and effective access to their content. News articles, blogs and technical reports are often lengthy, so the reader needs a quick overview of the underlying content. To that end we present graph-based models for keyword extraction, in order to compare the...

Ontology matching is a crucial problem in the world of Semantic Web and other distributed, open world applications. Diversity in tools, knowledge, habits, language, interests and usually level of detail may drive in heterogeneity. Thus, many automated applications have been developed, implementing a large variety of matching techniques and similari...

Faster knowledge attainment within organizations leads to improved innovation, and therefore competitive advantage. Interventions on the organizational network may be risky or costly or time-demanding. We investigate several communication policies in knowledge networks, which reduce the knowledge attainment time without interventions. We examine th...

Accurate power output forecasting is a critical credibility factor for both conventional and renewable modern power systems. Renewable power systems, like photovoltaic (PV) systems, could be severely affected by alternating weather conditions, and this is an important issue relative to accurate fore-casts. In this paper a comparative analysis betwe...

Bot Assistants can be an efficient and low-cost solution to Patient Care. One important aspect of Assistant Bots is successful Communication and Socialization with the patient. A new Conditional Entropy Retrieval Based model is proposed and also an Attitude Modeling based on Popitz Powers. The algorithm successfully retrieves the suitable answer wi...

The aims of this work are: (1) to extend knowledge dynamics analysis in order to assess the influence of false beliefs and unreliable communication channels, (2) to investigate the impact of selection policy for knowledge acquisition, (3) to investigate the impact of targeted link attacks (“breaks” or “infections”) of certain “healthy” communicatio...

We describe the Public Library of Veroia dataset. This dataset was created by transforming the bibliographic records of the Public Library of Veroia catalogue into Linked Open Data. We present the data model that is used, consisting of a mix of well-established vocabularies such as BIBO, RDA, DC, FOAF between others. We developed a new tool for the...

The Time Operator and Internal Age are intrinsic features of Entropy producing Innovation Processes. The innovation spaces at each stage are the eigenspaces of the Time Operator. The internal Age is the average innovation time, analogous to lifetime computation. Time Operators were originally introduced for Quantum Systems and highly unstable Dynam...

Cryptography with Chaos was proposed by Shannon in his classic 1949 paper, although the word chaos was not mentioned. This idea has been extended and realized by Chaotic i.e. Entropy producing Torus Automorphisms. The corresponding algorithms and the software have been developed for any Torus Automorphism, adapted to be applicable for encryption in...

We extend the Time Operator and Age to Network Evolution models. Internal Age formulas and the distribution of innovations are computed for Erdős–Rényi Random Networks, for Markov Networks and Barabási–Albert preferential Attachment Networks. The innovation probabilities are found to be proportional to the quadratic entropy (which coincides with th...

The time operator and internal age are intrinsic features of entropy producing innovation processes. The innovation spaces at each stage are the eigenspaces of the time operator. The internal age is the average innovation time, analogous to lifetime computation. Time operators were originally introduced for quantum systems and highly unstable dynam...

We extend the notion of Time Operator from Kolmogorov Dynamical Systems and Bernoulli processes to Markov processes. The general methodology is presented and illustrated in the simple case of binary processes. We present a method to compute the eigenfunctions of the Time Operator. Internal Ages are related to other characteristic times of Markov ch...

We identify and explore the incompatibility of the application DBpedia Spotlight with languages with non-Latin alphabets such as the Greek language. After exploring the technical issues, we provide a series of solutions. We also present a fully functional realization of the Greek DBpedia Spotlight. Our modifications revealed the modularity and scal...

Brain function during mathematical thinking is a common concern of scientists from different research fields. The study of functional brain networks extracted from electroencephalographic (EEG) signals using graph theory seems to meet the challenge of neuroscience to understand brain functioning in terms of dynamic flow of information among brain r...

Based on previous work on non-equilibrium statistical mechanics, and the recent extensions of Time Operators to observations and financial processes, we construct a general Time Operator for non-stationary Bernoulli Processes. The Age and the innovation probabilities are defined and discussed in detail and a formula is presented for the special cas...

The two core systems of mathematical processing (subitizing and retrieval) as well as their functionality are already known and published. In this study we have used graph theory to compare the brain network organization of these two core systems in the cortical layer during difficult calculations. We have examined separately all the EEG frequency...

The hemispheric differences for Alpha1 and Alpha2 Bands. (TIF)

The hemispheric differences for Delta and Theta Bands. (TIF)

Node Strength among all tasks. This figure was extracted like the Figures 5 and 6 in the manuscript. The size of green nodes is inversely proportional to the significant (<.05) p-values: the larger the node the more significant the effect is. (TIF)

Boxplots of the distribution of the edges’ weights. (TIF)

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The world's financial system exhibits all of the properties of a complex system: irreversibility, unpredictability, and innovations. Moreover, it implements an exquisite set of durations such as tick time, execute time, time slicing, time-weighted averaging, sampling time, trade duration, position-holding time, option termination time, among others...

Gender differences in mathematical thinking is a common concern of scientists from different research fields. Both parents and teachers report that males seem to perform better in complex mathematics compared to females. This study comes to shed light in the different organization of the underlying functional networks, in order to investigate the a...

This paper describes the deployment of the Greek DBpedia and the contribution to the DBpedia information extraction framework with regard to internationalization (I18n) and multilingual support. I18n filters are proposed as pluggable components in order to address issues when extracting knowledge from non-English Wikipedia editions. We report on ou...

The Mathematics Subject Classification (MSC), maintained by the American Mathematical Society’s Mathematical Reviews (MR) and FIZ Karlsruhe’s Zentralblatt für Mathematik (Zbl), is a scheme for classifying publications in mathematics. While it is widely used, its traditional, idiosyncratic conceptualization and representation did not encourage wide...

The Mathematics Subject Classification (MSC) is a widely used scheme for classifying documents in mathematics by subject. Its traditional, idiosyncratic conceptualization and representation makes the scheme hard to maintain and requires custom implementations of search, query and annotation support. This limits uptake e.g. in semantic web technolog...

Although interoperability has always been a priority in e-learning, conventional Learning Management Systems are mostly geared towards the Standards for Learning Objects exchange and the integration among systems. The contingency for integration with other web applications and data is hardly foreseen. This prevents them, nowadays, from being flexib...

Recent web advances and progress in technology enhanced pedagogies have outlined the important role of gaming within education. The advent of SemanticWeb and Linked Data, as well as, the availability of initiatives and infrastructures like that of DBpedia have facilitated the incorporation of gaming within educational knowledge bases. This paper pr...

We propose a general framework of the combined description of a classical system with a quantum system by representing the quantum system as a Hamiltonian field and defined the evolution of the whole system as Hamiltonian flow. We illustrate the general formalism in two cases, namely the classical particle coupled with a quantum oscillator and clas...

The work of the Brussels–Austin groups over the last six years has demonstrated that for unstable systems, classical or quantum, there exist spectral decompositions of the evolution In terms of resonances and resonance states which appear as eigenvalues and eigenprojections of the evolution operator. These new spectral decompositions are non-trivia...

We provide an explicit formula which gives natural extensions of piecewise monotonic Markov maps defined on an interval of the real line. These maps are exact endomorphisms and define chaotic discrete dynamical systems.

We study the spectral properties of the evolution operator of densities of the one-dimensional version of a Markov model for instrumental conditioning proposed by Bush and Mosteller in the early '50s. The model is a probabilistic combination of dynamical systems with phase space dependent probability distribution. The spectral properties are derive...

This paper presents the first steps towards a Greek Linked Open Data (LOD) cloud, initially as a collection of exposed interlinked datasets and a Greek DBpedia core hub. It is a joint effort to become part of the wider, global linked data cloud and aims to contribute in the overall cloud informational value. During the project and while forming and...

Wikis are nowadays a mature technology and further well established as successful eLearning approaches that promote collaboration, fulfill the requirements of new trends in education and follow the theory of constructivism. Semantic Wikis on the other hand, are not yet thoroughly explored, but differentiate by offering an increased overall added va...

The Web is the largest human information construct in history transforming our society. How can we understand, measure and model the Web evolution in order to design effective policies and optimize its social benefit? Early measurements of the Internet traffic and the Web graph indicated the scale-free structure of the Web and other Complex Network...

The purpose of this paper is to assess the statistical characterization of weighted networks in terms of the generalization of the relevant parameters, namely, average path length, degree distribution, and clustering coefficient. Although the degree distribution and the average path length admit straightforward generalizations, for the clustering c...

Let 𝔐 be the Banach space of σ-additive complex-valued measures on an abstract measurable space. We prove that any closed, with respect to absolute continuity norm-closed, linear subspace L of 𝔐 is complemented and describe the unique complement, projection onto L along which has norm 1. Using this fact we prove a decomposition theorem, which inclu...

Resonance processes are often considered to be a particular case of irreversible processes both at classical and quantum level. Based upon this idea, in this review we present different approaches to resonances in nonrelativistic Quantum Mechanics as well as the relations among them. In particular, we show how the properties of quantum resonance ph...

Introduction Liouville Spaces and Quantum Liouville Operator Resolvent and Spectral Resolution of Liouville Operators The Spectrum of a; Liouville Operator Rigged Liouville Spaces

We answer qualitatively the inverse coarse-graining problem of statistical physics, namely: which microscopic dynamics give rise to a given physically observed Markov semigroup as a result of exact coarse graining? We show in particular that all measure preserving stationary Markov processes arise as projections of Kolmogorov dynamical systems. Thi...

The above discussion demonstrates that the question of the equivalence of resonances defined through the poles of a continuation of the scattering matrix and through the poles of an extended resolvent is meaningful only if one specifies an appropriate rigged Hilbert space for the extended resolvent. This means that the test space Φ with an appropri...

The purpose of this paper is to assess the statistical characterization of weighted networks in terms of the generalization of the relevant parameters, namely average path length, degree distribution and clustering coefficient. Although the degree distribution and the average path length admit straightforward generalizations, for the clustering coe...

The work of the Brussels-Austin group on irreversibility over the last years has shown that quantum large Poincaré systems lead to states and observables with diagonal singularity. States with diagonal singularity include microcanonical equilibrium and they provide the natural framework for the discussion of quantum irreversible processes. This for...

For the Friedrichs model, obtained as a one-dimensional ε-perturbation of the orthogonal sum of the momentum and a finite Hermitian matrix: , the scattering matrix is presented as Sε(p) = [I + iεM(p)]−1[I − iεM(p)]. The rational Nevanlinna-class Krein–Weyl function M is associated with the operator A and has poles at the eigenvalues of A. It is pro...

The plague of 541–542 ad started in Pelusium, a town in Egypt, and reached Constantinople in 542 ad . The following series summarizes the event and its repeated appearance until 746 ad .

We propose a Hamiltonian approach to fluid mechanics based on the dynamics formulated in terms of Lagrangian variables. The construction of the canonical variables of the fluid elucidates the origin of the Clebsch variables, introduced in the 19th century. The developed formalism permits relating the circulation conservation law (Thompson theorem)...

We applied a nonlinear analysis to traffic measurements obtained at the input of a medium size local area network. The reliable values of the time lag and embedding dimension provided the application of a layered neural network for identification and reconstruction of the underlying dynamical system. The trained neural network reproduced the statis...