University of the Aegean
  • Mytilene, Greece
Recent publications
The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.
Consider an insurer with d lines of business and the freedom to make risk-free and risky investments. The investment portfolio price process is described as a general càdlàg process. It is assumed that the claim sizes from different lines of business and their common inter-arrival times form a sequence of independent and identically distributed (i.i.d.) random pairs, each pair obeying a particular dependence structure. With this dependence structure, claim sizes from different lines of business are distributed according to the multivariate regular variation. This paper proposes conditions that can be satisfied by several important stochastic processes, including the Lévy process, Vasicek interest rate model, Cox-Ingersoll-Ross interest rate model, Heston model, and Stochastic volatility model. Under these conditions, the uniform asymptotic expansions of ruin probabilities are derived, which hold uniformly for the entire time horizon. Numerical examples are provided as a means of illustrating the main results.
In this work, 38 different organic emerging contaminants (ECs), belonging to various chemical classes such as pharmaceuticals (PhCs), endocrine-disrupting chemicals (EDCs), benzotriazoles (BTRs), benzothiazoles (BTHs), and perfluorinated compounds (PFCs), were initially identified and quantified in the biologically treated wastewater collected from Athens’ (Greece) Sewage Treatment Plant (STP). Processes already used in existing STPs such as microfiltration (MF), nanofiltration (NF), ultrafiltration (UF), UV radiation, and powdered activated carbon (PAC) were assessed for ECs’ removal, under the conditions that represent their actual application for disinfection or advanced wastewater treatment. The results indicated that MF removed only one out of the 38 ECs and hence it was selected as pretreatment step for the other processes. UV radiation in the studied conditions showed low to moderate removal for 5 out of the 38 ECs. NF showed better results than UF due to the smaller pore sizes of the filtration system. However, this enhancement was observed mainly for 8 compounds originating from the classes of PhCs and PFCs, while the removal of EDCs was not statistically significant. Among the various studied technologies, PAC stands out due to its capability to sufficiently remove most ECs. In particular, removal rates higher than 70% were observed for 9 compounds, 22 were partially removed, while 7 demonstrated low removal rates. Based on our screening experiments, future research should focus on scaling-up PAC in actual conditions, combining PAC with other processes, and conduct a complete economic and environmental assessment of the treatment.
The advancement of Circular Economy practices has accelerated the development of recovery operations in waste management. Moreover, novel Waste-to-Energy (WtE) plants go well beyond the conventional framework of Combined Heat and Power (CHP) production and have also focused on the recovery of metals or the secondary production of other products. Thus, an integrated methodology needs to be utilised for the holistic assessment of novel WtE plants. The previously introduced 3T Method is a thermodynamic approach that assesses not only the CHP efficiency but also the quality of the recovered materials/products. Nonetheless, this method operates optimally in net energy producing facilities. This study introduces an outranking multicriteria decision analysis (MCDA) method that incorporates the 3T method and can be used for the assessment of WtE plants that produce valuable materials (like gasification plants) and biorefineries. The thermodynamic parameters that are used in the 3T Method were integrated in a MCDA tool based on the PROMETHEE-GAIA methods and five WtE plants were analysed. The proposed tool successfully assessed the production of materials from Plant D with Phi flows of 0.4583 and 0.3682 for scenarios 1 & 2, while also evaluating positively the high CHP efficiency of Plant C with Phi flows of 0.0417 and 0.0864, respectively. Overall, the PROMETHEE-GAIA MCDA tool kept most of the positive attributes of the 3T Method, while enhancing at the same time the role of materials in the assessment process. This proposed tool can develop to be a useful method for assessment for biorefineries.
Sentinel-2 (S2) images have been used in several projects to detect large accumulations of marine litter and plastic targets. Their limited spatial resolution though hinders the detection of relatively small floating accumulations of marine debris. Thus, this study aims at overcoming this limit through the exploration of fusion with very high-resolution WorldView-2/3 (WV-2/3) images. Various state-of-the-art approaches (component substitution, spectral unmixing, deep learning) were applied on data collected in synchronized acquisitions of plastic targets of various sizes and materials in seawater. The fused images were evaluated for spectral and spatial distortions, as well as their ability to spectrally discriminate plastics from water. Several WV-2/3 band combinations were investigated and five litter indexes were applied. Results showed that: a) the VNIR combination is the optimal one, b) the smallest observable plastic target is 0.6 × 0.6 m² and c) SWIR bands are important for marine litter detection.
We review studies on the singularity structure and asymptotic analysis of a 3-brane (flat or curved) embedded in a five-dimensional bulk filled with a ‘perfect fluid’ with an equation of state p = γ ρ , where p is the ‘pressure’ and ρ is the ‘density’ of the fluid, depending on the fifth space coordinate. Regular solutions satisfying positive energy conditions in the bulk exist only in the cases of a flat brane for γ = − 1 or of AdS branes for γ ∈ [ − 1 , − 1 / 2 ) . More cases can be found by gluing two regular brunches of solutions at the position of the brane. However, only a flat brane for γ = − 1 leads to finite Planck mass on the brane and thus localizes gravity. In a more recent work, we showed that a way to rectify the previous findings and obtain a solution for a flat brane and a range of γ , which is both free from finite-distance singularities and compatible with the physical conditions of energy and finiteness of four-dimensional Planck mass, is by introducing a bulk fluid component that satisfies a nonlinear equation of state of the form p = γ ρ λ with γ < 0 and λ > 1 . This article is part of the theme issue ‘The future of mathematical cosmology, Volume 2’.
The exponential growth of internet connected devices in this past year has led to a significant increase in IoT targeted attacks. The lack of proper integration of security in IoT development life cycle along with a plethora of different protocols (e.g., Zigbee, LoRa, MQTT, etc.) have greatly impacted the resilience of such devices against cyber-attacks, a fact also exacerbated by the size and physical hardware structure of these devices. Thus, it is imperative to develop effective and efficient countermeasures that can also be applied post-production to help build resilience in modern IoT systems. Honeypots are prime example of this notion. Being designed to act as vulnerable computer components or systems, they provide useful intelligence regarding potential attackers. Nevertheless, honeypots have seen little use in protection IoT systems and their underlying protocols, especially in cases where honeypots can leverage the decentralized nature of IoT. In this research, we enhance the HosTaGe honeypot to build an IoT protocol honeypot that runs over mobile devices. The purpose of this paper is to introduce a honeypot specifically for IoT communication protocols over public networks that is easy-to-use and utilizes Android devices. The protocol honeypot utilizes the cellular network to establish decentralized, simulated infrastructures of IoT systems over different types of IoT network protocols. We test four IoT network implementations, one for each of the newly implemented MQTT, CoAP and AMQP protocols. Additionally, we upgrade existing Telnet and SSH protocols used in IoT systems to work over the simulated mobile honeypot. We use the virtualized honeypot networks to capture log, and analyze real-world public attacks on these protocols from the internet and provide an interface for interaction with the implemented honeypot.
The aim of the study is to investigate mitochondrial diversity in Neolithic Greece and its relation to hunter-gatherers and farmers who populated the Danubian Neolithic expansion axis. We sequenced 42 mitochondrial palaeogenomes from Greece and analysed them together with European set of 328 mtDNA sequences dating from the Early to the Final Neolithic and 319 modern sequences. To test for population continuity through time in Greece, we use an original structured population continuity test that simulates DNA from different periods by explicitly considering the spatial and temporal dynamics of populations. We explore specific scenarios of the mode and tempo of the European Neolithic expansion along the Danubian axis applying spatially explicit simulations coupled with Approximate Bayesian Computation. We observe a striking genetic homogeneity for the maternal line throughout the Neolithic in Greece whereas population continuity is rejected between the Neolithic and present-day Greeks. Along the Danubian expansion axis, our best-fitting scenario supports a substantial decrease in mobility and an increasing local hunter-gatherer contribution to the gene-pool of farmers following the initial rapid Neolithic expansion. Οur original simulation approach models key demographic parameters rather than inferring them from fragmentary data leading to a better understanding of this important process in European prehistory.
ABSTRACT This paper examines the relationship between young individuals that are Not in Employment, Education or Training (NEETs) and regional resilience across the Mediterranean European Union South. It attempts a significant contribution to the literature since academic readings on youth studies have partly overlooked potential interlinkages with regional resilience, while regional studies have neglected to assess the resilience of the young cohorts of the labour force. The paper builds on a geographical political economy approach and employs a mixed-research method, calculating regional resistance and recovery indices and drawing upon informed expert interviews. It scrutinises labour market resilience in terms of youth employment and NEETs against the 2007/08 crisis and documents which regions have been (less) resistant to youth unemployment and inactivity. Thereupon, it locates four factors of low resilience in regional youth labour markets, namely structural deficiencies, pathdependence, labour market segmentation and informal practices.
In this paper the REACT-DECARB energy planning platform, designed to assist with the assessment of decarbonisation scenarios for islands’ electricity grids, is fully presented and applied to eight (8) EU islands. The scenarios were developed in the context of a Horizon 2020 EU project employing a renewable energy production forecasting and an optimisation mixed-integer linear programming model. The platform employs energy and economic modules, life-cycle assessment and multi-criteria decision analysis to facilitate the integrated evaluation of scenarios and enables decision makers to fully grasp the technical, environmental, economic and social aspects of energy systems’ decarbonisation. Results indicate that island electrical autonomy should be considered with caution and can be a valid option only if cost criteria are not prioritised. Further, it was determined that seeking autonomy in countries with low carbon costs for electricity production may be not be environmentally beneficial. A number of inter-island comparisons have been made and have shown that the REACT-DECARB platform can assist planners and decision-makers to identify the best available scenarios, define the sensitivity issues with respect to the criteria weights and, together with local communities, come to a common ground in order to establish a roadmap for the transition towards a decarbonised energy future for islands.
Social Economy (SE) has been praised for contributing to a humane and sustainable economic growth, whilst effectively tackling the detrimental effects of economic, ecological , and other types of crises. With many of its member states experiencing a heap of such problems, the EU has actively facilitated the setting up and operation of social enterprises. The paper at hand offers a theoretically-grounded empirical analysis of SE in four South EU countries (Spain, Italy, Greece, and Cyprus), and specifically, it examines the pertinent policies and their post-implementation impact. To do so, it employs a mixed-methods approach comprising a critical scrutiny of national policy frameworks, a quantitative analysis of secondary regional data on SE workforce and enterprises, and an interview-based fieldwork focused on SE stakeholders and experts. Highlighting the crucial differences among national policy frameworks lays the groundwork for deciphering the uneven dynamics in SE development across the study regions. Our analysis underlines that, albeit SE is often presented as a viable alternative to neoliberalism, it is bound by the latter's intrinsic characteristics. Specifically, not only SE fails to limit (youth) unemployment and inactivity drastically, but on the contrary, it often becomes a fertile ground for labor practices that are exceedingly precarious.
Purpose - This study aims to identify the extent to which different motivational elements can support strong bonds and good cooperation between front-line employees and hotels’ leadership in times of crisis and work suspension. Design - The views of a sample of employees working in 4 and 5 star hotels in Heraklion Prefecture were studied in May 2020, when hotel operations were suspended. Methodology - Two hundred and one completed questionnaires were collected, consisting of 31 six-point Likert scales, whose data were analysed using the Exploratory and Confirmatory Factor Analysis (CFA). Approach - The Exploratory Factor Analysis (EFA) followed the principal component method of extraction based on a varimax rotation, while the CFA adοpted the method of Structural Equation Modeling, that was based on the maximum likelihood method of estimation. Results - In times of crisis, front-line employees of hotels consider that the creation of strong bonds and a good spirit of cooperation and communication between them and the leadership of the hotels is strongly based on the exploitation of their skills and the developmental opportunities offered. Originality of the research - The research identified motivational factors that can support the creation of strong bonds and a good spirit of cooperation and communication between front-line employees and hotel management in times of crisis. On a practical level, the findings can help hotel managers gain strategic advantage and experience for the future, should they need to deal with similar situations.
To effectively future-proof the management of the European Union fishing fleets we have explored a suite of case studies encompassing the northeast and tropical Atlantic, the Mediterranean, Baltic and Black Seas. This study shows that European Union (EU) fisheries are likely resilient to climate-driven short-term stresses, but may be negatively impacted by long-term trends in climate change. However, fisheries’ long-term stock resilience can be improved (and therefore be more resilient to increasing changes in climate) by adopting robust and adaptive fisheries management, provided such measures are based on sound scientific advice which includes uncertainty. Such management requires regular updates of biological reference points. Such updates will delineate safe biological limits for exploitation, providing both high long-term yields with reduced risk of stock collapse when affected by short-term stresses, and enhanced compliance with advice to avoid higher than intended fishing mortality. However, high resilience of the exploited ecosystem does not necessarily lead to the resilience of the economy of EU fisheries from suffering shocks associated with reduced yields, neither to a reduced carbon footprint if fuel use increases from lower stock abundances. Fuel consumption is impacted by stock development, but also by changes in vessel and gear technologies, as well as fishing techniques. In this respect, energy-efficient fishing technologies already exist within the EU, though implementing them would require improving the uptake of innovations and demonstrating to stakeholders the potential for both reduced fuel costs and increased catch rates. A transition towards reducing fuel consumption and costs would need to be supported by the setup of EU regulatory instruments. Overall, to effectively manage EU fisheries within a changing climate, flexible, adaptive, well-informed and well-enforced management is needed, with incentives provided for innovations and ocean literacy to cope with the changing conditions, while also reducing the dependency of the capture fishing industry on fossil fuels. To support such management, we provide 10 lessons to characterize ‘win-win’ fishing strategies for the European Union, which develop leverages in which fishing effort deployed corresponds to Maximum Sustainable Yield targets and Common Fisheries Policy minimal effects objectives. In these strategies, higher catch is obtained in the long run, less fuel is spent to attain the catch, and the fisheries have a higher resistance and resilience to shock and long-term factors to face climate-induced stresses.
We argue that cognitive functions are not reducible to biological functionality. Since only neural animals can develop complex forms of agency, we assume that genuinely cognitive processes are deeply related with the activity of the nervous system. We first analyze the significance of the appearance of the nervous system in certain multicellular organisms (i.e., eumetazoa), arguing that it has changed the logic of their biological organization. Then, we focus on the appearance of specifically cognitive capacities within the nervous system. Considering a case of a minimal form of perceptual representation (as it happens in the visual system of cubozoan medusae), we analyze the specific functional role of this minimal form of (cognitive) activity in relatively earlier nervous systems, arguing that though this role is only understandable within a biological organization, yet it is not reducible to the underlying biological functionality. Finally, we conclude that the appearance of cognition is in turn linked to the emergence of an autonomous neurodynamic domain and a qualitative change in body complexity.
Worldwide regulatory agencies should (re)examine the consideration of: (i) sub-threshold responses, (ii) non-linear dose-response models able to detect sub-threshold responses of both a beneficial and detrimental nature, and (iii) abandoning the use of default dose-response models for their risk assessment. Mounting evidence for significant sub-threshold responses has been accumulated for a plethora of pollutants and in all sorts of organisms, and this issue should no longer be ignored in regulatory and other contexts. The regulatory risk assessment should not be based upon obsolete science, but conform to the most up-to-date scientific findings. Failure to comply with its own standards propagates a huge and inappropriate uncertainty in risk assessment, which would undercut human and environmental health actions. [note: this is not the abstract of the publication, and the reader is referred to the publication itself]
Hybrid physical-digital installations in museums are interactive systems or exhibits that seamlessly combine physical (tangible) artifacts with virtual environments. In the museum, hybrid installations offer direct, hands-on experiences to visitors and thus may enhance their interest and engagement. Moreover, the entanglement of tangible and virtual interfaces may reinforce learning about the respective heritage. This paper reports on the design, implementation, and evaluation of an interactive installation that promotes the heritage of Tinian marble crafts that is included in the representative list of intangible heritage by UNESCO and resides in the Museum of Marble Crafts in Tinos, Greece. The installation puts the museum visitor in the role of a crane operator in a virtual reconstruction of a historic quarry and requires them to operate the crane and move marble volumes with safety in cooperation with NPCs (non-playable characters). Our design approach aimed to engage visitors in a playful learning experience, incorporating aspects of the two museum's exhibits (crane, quarry). The empirical evaluation took place at the lab and the museum with promising results on UX and learning. In addition, we identify and discuss several prospects and drawbacks of designing playful tangible interfaces for other practitioners to consider in similar applications.
Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015–2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change. During the 2015‐2019 period, the Mediterranean Sea has experienced exceptional marine heatwaves conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m depth, across a range of marine habitats and taxa (50 taxa across 8 phyla). By assessing and integrating temperature data with mass mortality records across the basin, our study provides the most up‐to‐date account of the impacts of extreme warming events on Mediterranean marine organisms and ecosystems.
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4,880 members
Gerasimos Pavlogeorgatos
  • Department of Cultural Technology and Communication
Manolis Maragoudakis
  • Department of Information and Communication Systems Engineering
Vassilis C. Moulianitis
  • Department of Product and Systems Design Engineering
Thomas Tscheulin
  • Department of Geography
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