On quaternion based parametrization of orientation in computer vision and robotics

The problem of orientation parameterization for applications in computer vision and robotics is examined in detail herein. The necessary intuition and formulas are provided for direct practical use in any existing algorithm that seeks to minimize a cost function in an iterative fashion. Two distinct schemes of parameterization are analyzed: The first scheme concerns the traditional axis-angle approach, while the second employs stereographic projection from unit quaternion sphere to the 3D real projective space. Performance measurements are taken and a comparison is made between the two approaches. Results suggests that there exist several benefits in the use of stereographic projection that include rational expressions in the rotation matrix derivatives, improved accuracy, robustness to random starting points and accelerated convergence

Οptimization of adiabatic analysis for stirling engines - factors effecting efficiency

250 σ.Η παρούσα διπλωματική εργασία έχει διαιρεθεί σε 7 κεφάλαια. Αρχίζει με μια ιστορική αναδρομή στην ιστορία των μηχανών Stirling και έπειτα προχωράει στην ανάλυση του θεωρητικού κύκλου Stirling και αναλύει τα πλεονεκτήματα του τα μειονεκτήματα του και τις εφαρμογές του. Στο επόμενο κεφάλαιο έχουμε την μοντελοποίηση του κύκλου Stirling στο αδιαβατικό μοντέλο, όπου ακολουθείται η θεωρητική ανάλυση του αδιαβατικού μοντέλου και έπειτα παρουσιάζονται τα αποτελέσματα που έχει το μοντέλο για την μηχανή GPU-3. Στην ίδια ενότητα έχουμε και την βελτιστοποίηση του αδιαβατικού μοντέλου όπου κάνουμε σύγκριση αποτελεσμάτων του νέου κώδικα με τον παλιό και στην οποία σύγκριση έχουμε την ταύτιση των αποτελεσμάτων των δύο διαφορετικών εκδόσεων. Έπειτα γίνεται μια μελέτη για τους διαφορετικούς βαθμούς απόδοσης μιας μηχανής Stirling , στην οποία γίνεται μια κατηγοριοποίηση των βαθμών απόδοσης και στος τέλος έχουμε και κάποια υπολογιστικά παραδείγματα. Μετά ανάλυεται ο θερμοδυναμικός κύκλος Stirling με βάση τους επιζήμιους όγκους και την αποτελεσματικότητα του αναγεννητή και εξετάζουμε τον βαθμό απόδοσης του κύκλου και την παραγόμενη ισχύ συναρτήσει των δύο παραπάνω μεταβλητών. Έπειτα γίνεται μια παρουσίαη των σύγχρονων τεχνολογιών Stirling και παρουσιάζεται μια γενική εικόνα για την πρόοδο των μηχανών Stirling ανά τον κόσμο τα τελευταία 60 χρόνια. Τέλος, γίνεται η παρουσίαση της μηχανής Solo Stirling 161 CHP.This essay is divided into 7chapters. It starts with the history of Stirling engines and it continues with the theoritical analysis of the Stirling thermodynamic cycle. In the next chapter we can see the modelization of adiabatic model and its optimization. At the same time we have some examples with the GPU-3 and the P-40. After there is a study for the efficiency factors of the stirling engines with some arithmetic examples. In the next chapter there is an analysis of the Stirling Cycle using dead volumes and the efficiency factor of the regenarator. After there isa presentatation of the nowadays technology for Stirling engines all over the world. And final there is the presentatation of the Solo Stirling 161 CHP.Κωνσταντίνος Σ. Τερζάκη

EEG correlates of cerebral engagement in reading tasks

This study evaluated the utility of electroencephalographic (EEG) measures as indices of regional cerebral engagement activation during reading in neurologically intact adult volunteers. EEG was recorded from 16 scalp locations as participants performed four visual detection tasks designed to tap into increasingly more complex operations regularly involved in reading, namely visual-spatial, orthographic, phonological, and semantic. EEG records were quantified using power spectrum measures in four frequency bands (delta, theta, alpha, beta1, and beta2), in addition to a non-linear estimate of signal complexity (prediction error). Results showed that (1) changes in spectral power between pairs of reading tasks, and (2) regional variations in EEG measures for each task, were restricted to signals recorded over the left hemisphere. These findings are in agreement with knowledge regarding left hemisphere involvement in higher level component processes of reading

Usefulness of non-linear EEG analysis

Spectral analysis methods are useful for the evaluation of EEG signals. Nevertheless, they refer only to the frequency domain and ignore any potentially interesting phase information. Analytical methods based upon the theory of nonlinear dynamics provides this and additional information. We used both methods to evaluate the EEG signals of volunteers performing two distinct mental arithmetic tasks. We extracted the power spectrum, the coherence and nonlinear parameters (dimension, the first Lyapunov exponent, the Kolmogorov entropy, the mutual dimension and the dimensions based upon spatial embedding of the original data as well as their surrogates). We found that 1) the spatial embedding dimension differed from that of the surrogates, indicating nonlinearity, 2) there were differences between the two arithmetic tasks, and 3) the spectral and nonlinear methods differ in terms of the information they provide. Our results indicate that nonlinear analysis methods can be useful despite the fact that they are still at an early stage of development