Μελέτη επιδράσεων τεχνικών έργων στο υδροδυναμικό καθεστώς παράκτιας περιοχής.

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Ναυτική και Θαλάσσια Τεχνολογία και Επιστήμη

On the Availability of Negative Exponential Turbulent FSO Links with Time Dispersion

In this work, we investigate the influence of the group velocity dispersion effect along with the atmospheric turbulence on the performance of a terrestrial free space optical communication system which is using the atmosphere as propagation path. We assume that the examined wireless optical link employs longitudinal Gaussian pulses in order to transmit the information signal from the nonlinear laser diode of the transmitter to receiver’s photo detector. The atmospheric conditions are modelled through the negative exponential distribution model, which is a very accurate model for the signal’s irradiance estimation over strong turbulence conditions. Thus, taking into account these effects we obtain closed form mathematical expressions of the probability of fade of the link. Additionally, we evaluate specific parameters, such as the chirp, which can reduce the probability of fade and as a result they can improve the optical system’s characteristics. The influence of the time dispersion effect on chirped pulse’s propagation is further investigated. Finally, by using the derived mathematical expressions, we present several numerical results which demonstrate our suggestions for the improvement of the system’s performanc

Estimation of Outage Capacity for Free Space Optical Links Over I-K and K Turbulent Channels

The free space optical communication systems are attracting great research and commercial interest due to their capability of transferring data, over short distances, with high rate and security, low cost demands and without licensing fees. However, their performance depends strongly on the atmospheric conditions in the link’s area. In this work, we investigate the influence of the turbulence on the outage capacity of such a system for weak to strong turbulence channels modeled by the I-K and the K-distribution and we derive closed-form expressions for its estimation. Finally, using these expressions we present numerical results for various link cases with different turbulence conditions

Chord Recognition using Deep Learning Techniques

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) "Επιστήμη Δεδομένων και Μηχανική Μάθηση

Non-cell autonomous and non-catalytic activities of ATX in the developing brain

The intricate formation of the cerebral cortex requires a well-coordinated series of events, which are regulated at the level of cell-autonomous and non-cell autonomous mechanisms. Whereas cell-autonomous mechanisms that regulate cortical development are well-studied, the non cell-autonomous mechanisms remain poorly understood. A non-biased screen allowed us to identify Autotaxin (ATX) as a non cell-autonomous regulator of neural stem cell proliferation. ATX (also known as ENPP2) is best known to catalyze lysophosphatidic acid (LPA) production. Our results demonstrate that ATX affects the localization and adhesion of neuronal progenitors in a cell autonomous and non-cell autonomous manner, and strikingly, this activity is independent from its catalytic activity in producing LPA

Integrating transposable elements in the 3D genome

Chromosome organisation is increasingly recognised as an essential component of genome regulation, cell fate and cell health. Within the realm of transposable elements (TEs) however, the spatial information of how genomes are folded is still only rarely integrated in experimental studies or accounted for in modelling. Whilst polymer physics is recognised as an important tool to understand the mechanisms of genome folding, in this commentary we discuss its potential applicability to aspects of TE biology. Based on recent works on the relationship between genome organisation and TE integration, we argue that existing polymer models may be extended to create a predictive framework for the study of TE integration patterns. We suggest that these models may offer orthogonal and generic insights into the integration profiles (or "topography") of TEs across organisms. In addition, we provide simple polymer physics arguments and preliminary molecular dynamics simulations of TEs inserting into heterogeneously flexible polymers. By considering this simple model, we show how polymer folding and local flexibility may generically affect TE integration patterns. The preliminary discussion reported in this commentary is aimed to lay the foundations for a large-scale analysis of TE integration dynamics and topography as a function of the three-dimensional host genome

Phonemes, morphemes and literacy development : evidence from Greek

It has been proposed that literacy development follows a sequence from simple to complex rules: children acquire simple phonological rules before they learn more complex orthographic rules such as conditional rules or morphological rules. I hypothesise that Greek children start reading and spelling by using a simple phonological strategy and later develop more complex phonological and morphological strategies. The hypothesis that young children fail to use complex phonological and morphological rules, the processes involved in reading words with complex phonological rules, the predictors of children's use of morphological strategies in spelling and the relations between different instances of morphological spellings were investigated in six studies.\ud In the first three studies the hypothesis that young children fail to use complex phonological strategies in reading and the processes involved in reading words which involve complex rules were examined. Children (6-8 years) were asked to read words and non-words (analogous and not-analogous to real words) either in isolation or in the context of a sentence, assigned to three categories in tenns of the rules involved in reading them. The children - especially the younger ones - performed better in words and non-words that involve constant relations between graphemes and phonemes than in words and non-words that involve variant relations between graphemes and phonemes. All the age groups performed better in the analogous nonwords that involve complex phonological rules than in the not-analogous non-words.\ud Children and adults read words that involve variant but predictable spelling patterns either by establishing connections to whole words or segments of known words. Younger children benefited more from context than the older ones and the effect was bigger for more difficult words.\ud In the fourth study the hypothesis that younger children fail to use morphological strategies in spelling was tested. Children (7-10 years) were given a task involving three instances of spelling of the final morpheme. Young children spelled the final morpheme using phonological strategies while older children used morphological ones. In the last two studies, children (7-10 years) were given oral measures of grammatical awareness, a standardised verbal ability test, measures of grammatical spelling knowledge and a measure of their ability to interpret novel words. Significant correlations between grammatical awareness, different instances of morphological spelling and children's ability to interpret novel words were found even after age and verbal ability were partialled out.\ud I conclude that even in a language that is transparent (at least from spelling to phonology) a stage model of simple rules first, complex rules later still holds. In reading, complex phonological strategies must be acquired for the reading of words that involve conditional rules. Morphological spelling strategies are important for correct spelling in Greek (which is not transparent from phonology to spelling) \u

Improving the bandwidth of microstructured multimode W-type POFs in the visible light range

The bandwidth of multimode W-type microstructured plastic optical fibers (mPOFs) is analyzed using the time-dependent power flow equation (TD PFE). The results demonstrate that increasing the wavelength enhances the bandwidth in W-type mPOFs, depending on the inner cladding width and the launch beam distribution width. We observed that bandwidth improves with thinner and shallower inner cladding, as well as a narrower centrally launched beam. This characterization aligns with the fibers’ effectiveness in increasing bandwidth, allowing for the customization of various W-type optical fibers for specific applications at different wavelengths

The relationship between listening and reading comprehension of different types of text in primary school children

Η σχέση της ακουστικής και της αναγνωστικής κατανόησης έχει αποτελέσει αντικείμενο πολλών ερευνών και έχει βρεθεί, κυρίως σε έρευνες με ενήλικες, ότι υπάρχουν σημαντικές και υψηλές συσχετίσεις ανάμεσα στις δύο μορφές κατανόησης. Σκοπός της παρούσας εργασίας είναι να διερευνήσει την ικανότητα ακουστικής και αναγνωστικής κατανόησης παιδιών διαφορετικών τάξεων του Δημοτικού Σχολείου συσχετίζοντάς τη με το κειμενικό είδος, αφηγηματικό και μη αφηγηματικό. Στην έρευνα συμμετείχαν 136 παιδιά από την τρίτη (Ν=68) και την έκτη (Ν=68) τάξη του Δημοτικού Σχολείου. Για τη μέτρηση της ακουστικής και της αναγνωστικής κατανόησης χρησιμοποιήθηκαν 6 κείμενα, 3 αφηγηματικά και 3 μη αφηγηματικά, τα δύο εκ των οποίων (ένα αφηγηματικό και ένα μη αφηγηματικό) ήταν κοινά και για τις δύο ηλικιακές ομάδες, ενώ χρησιμοποιήθηκαν 2 κείμενα, ένα αφηγηματικό και ένα μη αφηγηματικό, μόνο για τα παιδιά. της τρίτης τάξης και αντίστοιχα 2 κείμενα, ένα αφηγηματικό και ένα μη αφηγηματικό, μεγαλύτερης δυσκολίας μόνο για τα παιδιά της έκτης τάξης. Τα παιδιά της κάθε τάξης κλήθηκαν να διαβάσουν ή να ακούσουν τέσσερα κείμενα, δύο αφηγηματικά και δύο μη αφηγηματικά, και να απαντήσουν σε 8 ερωτήσεις κατανόησης για κάθε κείμενο που απαιτούσαν είτε πληροφορίες που υπήρχαν στο κείμενο, είτε συνδυασμό πληροφοριών που υπήρχαν στο κείμενο είτε συναγωγή συμπερασμών με βάση πληροφορίες που υπήρχαν στο κείμενο. Τα αποτελέσματα έδειξαν ότι οι διαφορές ανάμεσα στην ακουστική και την αναγνωστική κατανόηση δεν είναι σταθερές και σχετίζονται τόσο με το είδος του κειμένου όσο και με τον τύπο της ερώτησης Τα ευρήματα αυτά σχολιάζονται στη βάση των θεωριών για την ανάπτυξη της κατανόησης.The relationship between oral and reading comprehension has been studied by a number of studies and it has been found, especially in adult research, that there are significant and high correlations between the two types of comprehension. The aim of the present study was to examine oral and reading comprehension skills in relation to text type, either narrative or not. 136 children participated in the study from third and sixth grade of primary school. For different authentic texts were used to measure comprehension, three narrative and three non narrative. On of the narrative and on of the expository texts was given to both third and sixth grade children whereas on narrative and on expository text was given only to third graders and one narrative and one expository text was given only to sixth graders. All the children were examined in two narrative and two expository texts either in oral or reading comprehension. Children had to answer into 8 questions, 2 of them required information that could be found in a part of the text, three of them required bridging inferences and three of them required elaboration inferences. Results showed that differences between oral and reading comprehension are not constant and they depend on text type and question type. Keywords: reading comprehension, oral comprehension, narrative, expository text, inferences