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Tuesday 14 May 2019 16:00 – 17:00 A. Payatakes Seminar Room

” Intense THz sources: upscaling the power ”

Dr. Anastasios D. Koulouklidis Institute of Electronic Structure and Laser (IESL)

Abstract
The terahertz (THz) frequency range is one of the most interesting regions of the electromagnetic spectrum and lies between the far-infrared and the microwave region, in a frequency interval from 0.1 THz to 30 THz. Historically, this part of the spectrum was known as the “THz gap” due to the lack of coherent sources in this frequency range. Nevertheless, during the last two decades numerous works have been done on coherent sources, making it possible to access the THz frequency region of the electromagnetic spectrum and reveal its unique properties. Despite this rapid development, the power of available THz sources remains rather low, limiting the interactions of THz radiation with matter mostly in the realm of linear optics, while nonlinear free space THz optics stays largely out of reach. Here we discuss our advances towards the generation of intense, broadband THz pulses. We focus on the generation scheme based on two-color filamentation in air, under which the fundamental and the second harmonic of an ultrashort pulsed laser are combined and focused into air forming a filament, which produces intense THz pulses in the far field. Novel approaches to enhance the THz emission and further upscale the efficiency of these THz sources will be presented. These include, firstly the use of abruptly autofocusing beams for generating strong THz pulses at well-defined remote locations. Secondly, the THz emission through filamentation in liquids and finally the use of mid-infrared two-color laser pulses to drive the filamentation in air. Further improvement of these sources can increase the emitted THz energy at the multi-millijoule level with peak electric and magnetic fields at the gigavolt per centimeter and kilotesla level respectively. Quasi-static ultrashort electric and magnetic bursts at these intensities will be enabling free space extreme nonlinear and relativistic science.

Tuesday 2 April 2019 16:00 – 17:00 A. Payatakes Seminar Room

” Path-space variational inference in coarse-graining molecular systems”

Dr. Evangelia Kalligiannaki Institute of Applied and Computational Mathematics (IACM)

Abstract
A standard methodology to overcome problems of long relaxation times of complex systems is to abandon the chemical detail and describe the molecular system by fewer degrees of freedom. Such particle-based, systematic coarse-grained models of molecular systems are developed by averaging out the details at the molecular level, and by representing groups of atoms by a single coarse particle. The challenge though is to find coarse models that represent the structural and dynamic properties of the all-atom system adequately. In this talk, we will firstly give a short overview of best-fit procedures to predict parameterized families of CG models at equilibrium. Then, we will present in more detail the use of information-theoretic tools, the minimization of the relative entropy for systems out of equilibrium, and the reduction to the path-space force-matching method. Finally, we will introduce the parametrized stochastic dynamics for a system of liquid methane (at equilibrium and transient time regimes), infer the model parameters with the path-space force-matching minimization approach.

Tuesday 26 March 2019 16:00 – 17:00 A. Payatakes Seminar Room

” Biodiversity and Environmental Heterogeneity Surrogates in Systematic Conservation Planning ”

Dr. Aggeliki Doxa Institute of Applied and Computational Mathematics (IACM)

Abstract
Systematic conservation planning tools have been recently broadly used to spatially identify management priorities and help minimize potential impacts from surrounding human activities. Fine-filter approaches that focus on specific species are most commonly used for setting nature conservation priorities worldwide. Alternatively, instead of using species as biodiversity surrogates, coarse-filter approaches focus on preserving environmental characteristics and have recently gained increasing attention yet their connection to conservation planning still remains limited. I will present examples from the two approaches based on my previous and present work. The case studies will focus on how and which biodiversity and environmental surrogates are useful and how to select them. They will also illustrate how combining conservation with land use (ex. urban) planning may provide guidelines to avoid losing irreplaceable, high nature value areas and give concrete management tools to evaluate the efficiency of the existing protected areas network and set future conservation priorities.

Τρίτη 19 Μαρτίου 2019 16:00 – 17:00 Αίθουσα Παγιατάκη

“Μεταξύ Ύπαρξης και Ανυπαρξίας: Αναζητώντας Κοιτάσματα Πετρελαίου στον Ελληνικό Μεσοπόλεμο”

Δρ. Χρήστος Καραμπάτσος ,Ινστιτούτο Μεσογειακών Σπουδών (IMΣ)

Περίληψη
Λίγο μετά το ξέσπασμα της «ελληνικής κρίσης», η συζήτηση περί της εξεύρεσης των ελληνικών υδρογονανθράκων αναδύθηκε εκ νέου «μετά από χρόνια σιωπής». Είναι μια συζήτηση που χαρακτηρίζεται από πυκνότητα, περιπλοκότητα και σχεδόν πλήρη απουσία της ιστοριογραφικής διάστασης. Αυτή η απουσία καθίσταται ακόμη πιο ενδιαφέρουσα αν λάβουμε υπ’ όψη ότι ο εντοπισμός υδρογονανθράκων στην Ελλάδα επιχειρείται ήδη από το δεύτερο μισό του 19ου αιώνα.
Ακόμη και αν υπήρξαν εν πολλοίς «ατελέσφορες», οι προπολεμικές έρευνες για τους ελληνικούς υδρογονάνθρακες αποδείχθηκαν παραγωγικές από άλλες απόψεις. Για παράδειγμα, διαμόρφωσαν ένα νέο είδος ειδημόνων, που αποτέλεσαν τους πρώτους φορείς πετρελαϊκής γνώσης στην Ελλάδα. Ήταν γεωλόγοι και μηχανικοί, αξιωματικοί του στρατού και επιχειρηματίες, ακόμη και «ανεξάρτητοι» κυνηγοί πετρελαίου. Οι εργασίες τους, τουλάχιστον από τους βαλκανικούς πολέμους και μετά, οδήγησαν στην ανάδυση μιας νέας έννοιας της ελληνικής επικράτειας, ενός «κάθετου χαρακτήρα», η παραγωγή του οποίου αποτελεί τμήμα των διαδικασιών «αστικού εκσυγχρονισμού» που απαντώνται στον μεσοπόλεμο.
Ταυτόχρονα, οι ελπίδες και οι λογαριασμοί γύρω από τα ελληνικά κοιτάσματα πετρελαίου, αναδύονταν και διαψεύδονταν διαδοχικά επί δεκαετίες. Το αντίστοιχο σώμα δημόσιου λόγου
κυμαινόταν από την άκρατη ευφορία μέχρι την πρόβλεψη επικείμενων καταστροφών, ως είθισται για τους λόγους περί πετρελαίου παγκοσμίως. Αυτοί οι λόγοι αντηχούν στη σημερινή δημόσια συζήτηση περί πετρελαίων, προσδίδοντάς της ένα ενδιαφέρον, φαινομενικά «ιστορικό», στην πραγματικότητα όμως μυθολογικό υπόβαθρο.
Τόσο οι ειδικοί του πετρελαίου, όσο και οι λόγοι περί πετρελαίου βρίσκονται διαχρονικά στην τομή ενός σύνθετου τεχνοκοινωνικού συστήματος που περιλαμβάνει τα κράτη και τις πολιτικές τους, τις διεθνείς και εγχώριες εταιρείες εκμετάλλευσης, τους εργαζόμενους σε αυτές τις εταιρείες και τις τοπικές κοινότητες που βρίσκονται κοντά ή και εντός των προς εκμετάλλευση περιοχών. Κατ’ αυτόν τον τρόπο, η ιστοριογραφική εστίαση στους ειδικούς του πετρελαίου και τους λόγους περί «κοιτασμάτων πετρελαίου» στην Ελλάδα, δεν αφορά αποκλειστικά τις έρευνες πετρελαίου. Αφορά επίσης τις σχέσεις μεταξύ του ελληνικού κράτους και μεγάλων διεθνών επιχειρήσεων, τη διαμόρφωση της ελληνικής επικράτειας, την εισαγωγή τεχνολογίας και επιστημονικής γνώσης στην Ελλάδα και βέβαια την ιστορία συγκεκριμένων τοπικών κοινωνιών. Δεδομένου δηλαδή ότι πρόκειται για «ατελέσφορα» εγχειρήματα, τα οφέλη αποδεικνύονται διόλου αμελητέα.

Tuesday 12 March 2019 16:00 – 17:00 A. Payatakes Seminar Room

” Metamaterial modification of optical chirality with bilayer chiral metasurfaces and sensing evaluation ”

Dr. Nikos Vasilantonakis Institute of Electronic Structure and Laser (IESL)

Abstract
Chirality is a ubiquitous property of materials providing unique functionalities on a molecular basis. This results in a wide variety of applications from image display and data storage to biomolecular chiral sensing and enantioselective catalysis. However, the inherently weak light-matter interaction leads to weak chiroptical signals, a term that is known as optical chirality. Here, the metamaterial modification of optical chirality with bilayer metasurfaces under single polarization excitation is examined. It is shown that the designed bilayer metasurfaces provide more than an order of magnitude higher optical chirality compared to single layer counterparts and the overall enhancement of superchiral fields is found to be more efficient when the inner bilayer distance is in the 200-300 nm range. Furthermore, the linear connection of the change of transmittance with the mean optical chirality, directly connects these two components allowing the determination of the near-field behavior by measuring the far-field response. The present results would allow the design and fabrication of large-scale and cheap chiral bilayers at the nanoscale, which could be applied for a plethora of applications such as ultra-efficient chiral sensing, enantioselective catalysis or stereoscopic displays among others.

Tuesday 5 March 2019 16:00 – 17:00 A. Payatakes Seminar Room

” Aerial approach between Archaeology, History and Ethnography on Cretan Mountains ”

Dr. Gialuca Cantoro Institute of Mediterranean Studies (IMS)

Abstract
Aerial archaeology in Greece is still an exceptional and uncommon practice. Archaeological or historical projects making use of historical or modern aerial photographs can be counted in half dozen so far. The project “Crete from Above” brings prominently the bird eye view in the complex and pluri-stratified Cretan archaeological and historical context. The approach aims at identifying and mapping abandoned and forgotten historical and modern artefacts on the mountainous landscape of the major Greek island. The project originates from the consideration that the space which surrounds us and with which we continuously interact, is not a static entity. It is the result of the complex relations and influences of humans (and their cultures), animals and landscapes. Material and tangible results of such interactions (which often involve many more variables than the above outlined) are normally reshaped, repurposed, obliterated, damaged or endangered in view of the “development” of certain areas. However, sometimes, past standing structures become iconic elements of the landscape of which they are part, in a certain spontaneous monumentalisation process, as almost fossil or fossilized built landscapes. Main goal of the project is therefore to “tag” abandoned and collapsing artifact with archaeological and historical facts, promoting at once the involvement of local communities and (oftentimes) contemporary users of such artefacts (or what remains of them).
The paper will present “views” of the Cretan mountainous landscape through historical and modern aerial photography, highlighting the difficulties of working in such a challenging context and the ongoing activities for community engagement in an attractive and expanding touristic destination.

Tuesday 26 February 2019 16:00 – 17:00 A. Payatakes Seminar Room

“Algorithm development for the study of 3D optimum data of electrical resistivity tomographies”

Dr. Simyrdanis Kleanthis Institute of Mediterranean Studies (IMS)

Abstract
Electrical Resistivity Tomography (ERT) is a widely used geophysical method for near ground surface investigation for geological, archaeological and geotechnical applications. The ERT initially was used with 2D data that were collected on straight survey lines. Later, multiple parallel lines were used for a pseudo-3D results in order to define more realistically the 3D resistivity distribution of the subsurface. Nowadays, due to the computer development and the software updates, a fully 3D data acquisition is possible. However, the exponentially increased amount of data, which in turn is increasing the acquisition time and the power of the computer processing renders its practical implementation quite difficult. Hence, the necessity of 3D data optimisation leads to studies for decreasing the amount of data without compromising the resolving capabilities of the inversion results. The optimisation technique is based on the sensitivity matrix (Jacobian) and the results are tested with synthetic and field data verification.

Tuesday 19 February 2019 16:00 – 17:00 Seminar Room 1

Dr. Nasos Argyriou Institute of Mediterranean Studies (IMS)

Abstract
The determination of geomorphology plays an important role in archaeological landscape research. Several landform types can be distinguished by characteristic geomorphic attributes that portray the surrounding landscape of a settlement and evaluate its geographical importance in terms of its ability to sustain a population. Various geoinformatic approaches are acknowledged, by using the freely available ASTER G-DEM, to provide valuable knowledge regarding the interfered processes shaping landscapes. The locations of archaeological settlements and the characterization of the dominant surrounding landscape geomorphometrics can reveal insights into the development of settlements and provide a better understanding of human behavior, with regard the landscape characteristics over time, such as the water management. In order to assess the best routes for water resources reaching the major settlements a multi-disciplinary approach within a Geographical Information Systems (GIS) environment is acknowledged by using integrated Multi-Criteria Decision Analysis (MCDA) and Least-Cost Path Analysis (LCPA). Such an approach proves to be a valuable tool for archaeologists to determine and evaluate the sustainability of the settlements and the water management planning in ancient periods.