Knowledge-based approach to risk analysis in the customs domain

The aim of this PhD project is to develop a fuzzy knowledge-based approach in support of risk analysis in the Customs domain. Focusing upon risk management and risk analysis in the Customs domain, this thesis explores the relationship of risk with uncertainty, fuzziness, vagueness, and imprecise knowledge and it analyses state of the art detection techniques for fraud and risk. Special focus is given to fuzzy logic, ontological engineering, and semantic modelling considering aspects such as the importance of human knowledge and semantic knowledge in the context of risk analysis for the Customs domain. An approach is presented combining the fuzzy modelling and reasoning with semantic modelling and ontologies. Fuzzy modelling and reasoning is explored in the context of risk analysis and detection in order to examine approximate human reasoning based on human knowledge. Ontologies and semantic modelling are explored as an approach to represent domain knowledge and concepts. The purpose is to enable easier communication and understanding as well as interoperability. Risk management is broader, multi-dimensional process involving a number of task, activities, and practises. The presented approach is focused on examining the analysis and detection of the risk, based on the outputs of the risk management process with the use of ontologies and fuzzy rule-based reasoning. An ontological architecture is developed in the context of the presented approach. It is considered that such architecture is possible to enable modularity, maintainability, re-usability, and extensibility and can also be extended or integrated with other ontologies. In addition, examples are discussed to illustrate representation of concepts at various levels (generic or specific) and the modelling of various semantics. Furthermore, fuzzy modelling and reasoning are investigated. This investigation consists of literature research and the use of a generic research prototype (examination of Mamdani and Sugeno model types). From theoretical research, fuzzy logic enables the expression of human knowledge with linguistic terms and it could simulate human reasoning in the context of risk analysis and detection. In addition, Hierarchical Fuzzy Systems (HFS) or Hybrid Hierarchical Fuzzy Controllers (HHFC) approaches can be used to manage complexity especially for complex domains. Linguistic fuzzy modelling (LFM) is an aspect that should be considered during fuzzy modelling. From the generic research prototype, fuzzy modelling with the use of ontologies is demonstrated together with their integration in the context of fuzzy rule-based reasoning. It is also considered that Mamdani type of fuzzy models is easier to express human knowledge since the output can be expressed with linguistic terms. However, Sugeno type of fuzzy model could be used from adaptive techniques for optimisation purposes

Porosity-moderated ultrafast electron transport in Au nanowire networks

We demonstrate for first time the ultrafast properties of a newly formed porous Au nanostructure. The properties of the porous nanostructure are compared with those of a solid gold film using time-resolved optical spectroscopy.The experiments suggest that under the same excitation conditions the relaxation dynamics are slower in the former. Our observations are evaluated by simulations based on a phenomenological rate equation model. The impeded dynamics has been attributed to the porous nature of the structure in the networks, which results in reduced efficiency during the dissipation of the laser-deposited energy. Importantly,the porosity of the complex three-dimensional nanostructure is introduced as a geometrical control parameter of its ultrafast electron transport

The influence of structure on ultrafast electron dynamics in non-stoichiometric III - V semiconductors and metallic nano-composites

Ultrafast pump and probe spectroscopy has been utilized in order to study the electronic trapping behavior in nonstoichiometric GaAs and AlGaAs and to study the effect of the size reduction of nanometer sized Au particles on the kinetics of the confined electron population. The dynamics of conduction band electrons of Low-Temperature-Grown GaAs and AlGaAs is studied by exciting electrons in the vicinity of the conduction band bottom and by probing the induced transient changes in the absorption from the top of the valence to the bottom of the conduction band of the semiconductor. The nonstoichiometric semiconductors, that we examine, contain As precipitates. The electron trapping behavior is found to depend on both the average As precipitate radius α and spacing R. The interplay of these parameters is for the first time experimentally determined to be governed by the law τ ∝ R3/α which can be predicted theoretically by assuming diffusion mediated trapping of electrons on the surfaces of the As precipitates. The kinetics of the confined electrons in Au nanoparticles is studied by perturbing the electron population in the vicinity of the Fermi energy and by probing the transient interband 3 transition from the d-bands to the Fermi surface. The mechanism of the internal electron energy re-distribution is experimentally found to accelerate with the reduction (enhancement) of the nanoparticle size (confinement). The results show an independency of the surrounding dielectric host and are in good agreement with a numerical model based on the reduction of the Coulomb screening interaction. The mechanism of the cooling of the thermalized electron population to the lattice is also found to accelerate with size reduction.Η τεχνική της υπερταχείας φασματοσκοπίας άντλησης–ανίχνευσης χρησιμοποιήθηκε ώστε να μελετηθεί η ηλεκτρονιακή συμπεριφορά παγίδευσης σε μη-στοιχειομετρικό GaAs και AlGaAs και για να μελετηθεί η επίδραση της μείωσης του μεγέθους νανοσωματιδίων Au στην κινητική κατάσταση του ηλεκτρονιακού πληθυσμού τους. Η δυναμική κατάσταση των ηλεκτρονίων της ζώνης αγωγιμότητας σε Χαμηλής-Θερμοκρασίας-Ανάπτυξης GaAs και AlGaAs μελετάται μέσω διέγερσης ηλεκτρονίων στην περιοχή του πυθμένα της ζώνης αγωγιμότητας και ανίχνευσης των επαγώμενων μεταβατικών αλλαγών στην απορρόφηση από την κορυφή της ζώνης σθένους προς τον πυθμένα της ζώνης αγωγιμότητας του ημιαγωγού. Οι μη-στοιχειομετρικοί ημιαγωγοί που εξετάζουμε περιέχουν συσσωματώματα As. Η συμπεριφορά παγίδευσης των ηλεκτρονίων βρίσκεται να εξαρτάται από τη μέση ακτίνα α και τη μέση απόσταση R των συσσωματωμάτων As. Η αλληλοσυσχέτιση αυτών των δύο παραμέτρων για πρώτη φορά προκύπτει πειραματικά να καθορίζεται από το νόμο τ ∝ R3/α, οποίος μπορεί να προβλεφθεί θεωρητικά υποθέτοντας παγίδευση των ηλεκτρονίων στις επιφάνειες των συσσωματωμάτων As εν μέσω διάχυσης. Η κινητική κατάσταση των περιορισμένων, μέσα σε νανοσωματίδια Au, ηλεκτρονίων μελετάται μέσω διατάραξης του ηλεκτρονιακού πληθυσμού στην περιοχή της ενέργειας Fermi και ανίχνευσης των μεταβατικών διαζωνικών μεταβάσεων από τις ζώνες-d προς την επιφάνεια Fermi. Από την πειραματική μελέτη προκύπτει μία επιτάχυνση του μηχανισμού της εσωτερικής ηλεκτρονιακής ανακατομής της ενέργειας με τη μείωση (αύξηση) του μεγέθους του νανοσωματιδίου (περιορισμού). Τα αποτελέσματα δείχνουν μία ανεξαρτησία από τον περιβάλλοντα διηλεκτρικό ξενιστή και βρίσκεται σε συμφωνία με ένα αριθμητικό πρότυπο βασισμένο στην μείωση της θωρακισμένης αλληλεπίδρασης Coulomb. Ομοίως, ο μηχανισμός της ψύξης του θερμοποιημένου ηλεκτρονιακού πληθυσμού προς το πλέγμα επιταχύνεται με τη μείωση του μεγέθους

Electrodeposited laser – nanostructured electrodes for increased hydrogen production

PL, MF, AK, NP acknowledge financial support from the European Union’s Horizon 2020 research and innovation program under grant agreement no 871124 Laserlab-Europe. The authors would like to acknowledge the HELLAS-CH national infrastructure (MIS 5002735) implemented under “Action for Strengthening Research and Innovation Infrastructures,” funded by the “Operational Programme Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund).Περίληψη: In the present work, a novel approach has been employed to effectively enlarge the electrocatalytic area of the electrodes in an alkaline electrolysis setup. This approach consists of a two-step electrode fabrication process: In the first step, ultrashort laser pulses have been used to nanostructure the electrode surface. In the second step, electrodeposition of nickel particles was performed in a modified Watt's bath. The resulting electrodes have been found to exhibit a significantly increased hydrogen evolution reaction (HER) activity. Compared to the laser-nanostructured electrode (LN) and an untreated (i.e., flat) electrode, the electrodeposited-laser-nanostructured (ELN) electrode provides (i) enhanced electrochemical values (ii) a significant increase of double-layer capacitance (CDL) (values up to 1945 μF cm−2) compared to that of an LN electrode (288 μF cm−2) (iii) higher Jpeaks at CVs sweeps and (iv) lower Tafel slopes (−121 mV dec−1 compared to −157 mv dec−1). The ELN electrode provides an overpotential value of |η|100 = 264 mV, which shows a noteworthy 34% decrease compared to a flat Ni electrode and a 15% decrease to an (LN) electrode. Scanning electron microscopy (SEM) revealed that the electrodeposition of nickel on the LN nickel electrodes results in a dendrite-like morphology of the surface. Thus, the enhancement of the HER has been attributed to the dendrite-like geometry and the concomitant enlargement of the electrocatalytic area of the electrode, which presents an electrochemical active surface area (ECSA) = 97 cm−2 compared to 2.8 cm−2 of the flat electrode. The electrodes have also been tested in actual hydrogen production condition, and it was found that the ELN electrode produces 4.5 times more hydrogen gas than a flat Ni electrode and 20% more hydrogen gas than an LN electrode (i.e. without the extra nickel electrodeposition).Presented on: International Journal of Hydrogen Energ

Enhanced hydrogen production through alkaline electrolysis using laser-nanostructured nickel electrodes

Summarization: This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher Jpeaks, lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%.Presented on: International Journal of Hydrogen Energ