4 research outputs found
Study of alternations in electroencephalogram during the exposure to electromagnetic signal with third generation characteristics: Computational dosimetry assessment of study with human volunteers
163 σ.Η διπλωματική εργασία εντάσσεται στο πλαίσιο έρευνας του εργαστηρίου Βιοϊατρικών Προσομοιώσεων και Απεικονιστικής Τεχνολογίας (Biomedical Simulations and Imaging Unit - BIOSIM) του Εθνικού Μετσόβιου Πολυτεχνείου (National Technical University of Athens - NTUA) με θέμα την αποτίμηση των πιθανών αλλαγών στις καταγραφές ηλεκτροεγκεφαλογραφήματος και προκλητών δυναμικών κατά τη διάρκεια ακουστικών ερεθισμάτων, λόγω εκθεσης σε ηλεκτρομαγνητικά πεδία από τερματικές συσκευές κινητών επικοινωνιών τρίτης γενιάς (3G). Αναλυτικότερα, αφορά την προετοιμασία πειράματος εθελοντών που θα διεξαχθεί σε συνεργασία με το Ερευνητικό Πανεπιστημιακό Ινστιτούτο Ψυχικής Υγιεινής (ΕΠΙΨΥ). Το εν λόγω πείραμα αποσκοπεί στην ανάλυση του ηλεκτροεγκεφαλογραφήματος εθελοντών που λαμβάνεται σε συνθήκες έκθεσης σε ακτινοβολία ραδιοσυχνοτήτων (σήμα UMTS, 1966MHz) μέσα σε κλειστό θάλαμο που αποκλείει εξωτερικές παρεμβολές. Στο πλαίσιο της διπλωματικής εργασίας, μοντελοποιήθηκε η κάσκα ηλεκτροδίων που θα χρησιμοποιηθεί στο πείραμα και ελέγχθηκε μέσω προσομοιώσεων με ένα επίπεδο πολυστρωματικό μοντέλο βιολογικών ιστών. Πραγματοποιήθηκε αναλυτική δοσιμετρική μελέτη για μοντέλο κεφαλιού με χρήση της Μεθόδου των Πεπερασμένων Διαφορών στο Πεδίο του Χρόνου (Finite Difference Time Domain - FDTD). Εξετάστηκε η κατανομή του Ρυθμού Ειδικής Απορρόφησης (Specific Absorption Rate - SAR) και η επίδραση της παρουσίας των ηλεκτροδίων καταγραφής ΗΕΓ και της σχετικής τοποθέτησης των καλωδίων τους στην απορρόφηση ισχύος από τους εγκεφαλικούς ιστούς.This diploma thesis is part of the research work of the Biomedical Simulations and Imaging (BIOSIM) Unit of National Technical University of Athens (NTUA) aiming at the assessment of possible alternation in electroencephalogram (EEG) and event related potentials recordings during acoustic stimuli, due to exposure to electromagnetic signal with third generation (3G) characteristics. Specifically, the work concerns the preparation of a study with human volunteers, which will be carried out in collaboration with the University Research Institute of Mental Health. This study aims at the analysis of the EEG of volunteers exposed to RF radiation (UMTS signal, 1966MHz) into a chamber which excludes external interferences. In the frame of this diploma thesis, the electrode cap used in the study was modeled and checked through simulations of a flat layered model of biological tissues. Computational dosimetry was carried out for the head model using the SEMCAD-X software and the Finite Difference Time Domain (FDTD) method. The Specific Absorption Rate (SAR) distribution was calculated, while the effect of the presence of the EEG electrodes and the relative positioning of their leads on the resulting power absorption by the brain tissues was studied in detail.Ορέστης Σ. Καζασίδη
Evaluation of Rodent Hair Tubes for Activity Indices
Activity indices are used to determine the presence and activity of small mammals, such as the hair index derived from the use of hair tubes. In contrast to trapping animals, hair tubes are non-invasive and less labor-intensive, and appear to be a suitable alternative in appropriate settings. We developed a method to calculate hair density semi-automatically. In addition, hair tube data were validated with field data using wildlife cameras for the small mammal community in grassland, wheat crops, and hedges to assess how well data from hair tubes match data from wildlife cameras. Adhesive tape with hair from hair tubes was processed and scanned. The resulting images were analyzed using a newly developed computer program that enables background and adhesive tape to be automatically distinguished from hair, providing a quantitative measure of hair density. Based on validation with wildlife cameras, hair tubes seem to be a suitable tool to estimate small mammal activity at the community level in several habitats. There was a moderate-to-strong positive correlation of the hair tube index with the sum of voles and Apodemus individuals (activity index) recorded in grasslands (Spearman’s correlation coefficient 0.43), hedges (0.79), and wheat (0.44). The newly developed computer program allows the automatic calculation of hair density, making it easier to assess the activity of small mammals
Extended-image-based correction of aberrations using a deformable mirror with hysteresis
With a view to the next generation of large space telescopes, we investigate guide-starfree, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror.We designed and built a high-resolution imaging testbed to evaluate control algorithms. In this paper we use an algorithm based on the heuristic hill climbing technique and compare the correction in three different domains, namely the voltage domain, the domain of the Zernike modes, and the domain of the singular modes of the deformable mirror. Through our systematic experimental study, we found that successive control in two domains effectively counteracts uncompensated hysteresis of the deformable mirror.Numerics for Control & Identificatio