Attitude estimation and angular velocity estimation are the most critical components of a spacecraft's guidance, navigation and control. Usually, an array of tightlycoupled sensors (star trackers, gyroscopes, sun sensors, magnetometers) is used to estimate these quantities. The cost (financial, mass, power, time, human resources) for the integration of these separate sub-systems is a major deterrent towards realizing the goal of smaller, cheaper and faster to launch spacecrafts/satellites. In this work, we present a novel stellar imaging system that is capable of estimating attitude and angular velocities at true update rates of greater than 100Hz, thereby eliminating the need for a separate star tracker and gyroscope sub-systems. High image acquisition rates necessitate short integration times and large optical apertures, thereby adding mass and volume to the sensor. The proposed high speed sensor overcomes these difficulties by employing light amplification technologies coupled with fiber optics. To better understand the performance of the sensor, an electro-optical model of the sensor system is developed which is then used to design a high-fidelity night sky image simulator. Novel star position estimation algorithms based on a two-dimensional Gaussian fitting to the star pixel intensity profiles are then presented. These algorithms are non-iterative, perform local background estimation in the vicinity of the star and lead to significant improvements in the star centroid determination. Further, a new attitude determination algorithm is developed that uses the inter-star angles of the identified stars as constraints to recompute the body measured vectors and provide a higher accuracy estimate of the attitude as compared to existing methods. The spectral response of the sensor is then used to develop a star catalog generation method that results in a compact on-board star catalog. Finally, the use of a fiber optic faceplate is proposed as an additional means of stray light mitigation for the system. This dissertation serves to validate the conceptual design of the high update rate star sensor through analysis, hardware design, algorithm development and experimental testing.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η διαστασιολόγηση Φ/Β πάρκου ισχύος 500 kWp στο οποίο θα γίνει χρήση ιχνηλατών – trackers. Το συγκεκριμένο Φ/Β πάρκο μελετήθηκε για την περιοχή της Λάρισας. Η εξασφάλιση μεγάλου ποσοστού απαιτούμενης ηλεκτρικής ενέργειας μέσα από Ανανεώσιμες Πηγές, όπως είναι η φωτοβολταϊκή τεχνολογία, είναι μια σημαντική κατεύθυνση προς την προστασία του περιβάλλοντος. Παράλληλα αποτελεί μία σημαντική πρόκληση τόσο για τους μηχανικούς όσο και για την παγκόσμια οικονομία. Στο πρώτο κεφάλαιο δίνονται γενικά στοιχεία για τον Ήλιο και την ακτινοβολία που εκπέμπει, ενώ γίνεται και μια αναφορά στο πως μετράται η ηλιακή ακτινοβολία. Επίσης παρουσιάζεται η κατάσταση των εγκατεστημένων Φ/Β σε Ελλάδα και Ευρώπη. Στο δεύτερο κεφάλαιο επεξηγείται η φωτοβολταϊκή ηλεκτρική ενέργεια και το φωτοβολταϊκό φαινόμενο. Επίσης γίνεται μαθηματική ανάλυση για το μοντέλο της διόδου των κυττάρου και του πλαισίου και τέλος δίνονται οι εξισώσεις που αποδίδουν τις παραμέτρους του μοντέλου. Στο τρίτο κεφάλαιο εξετάζονται τα χαρακτηριστικά των Φ/Β πλαισίων όπως είναι ο βαθμός απόδοσης τους. Επίσης περιγράφονται τα υλικά κατασκευής των πλαισίων, ενώ αναφέρονται παράγοντες οι οποίοι επηρεάζουν την απόδοση τους. Στο τέταρτο κεφάλαιο περιγράφονται γενικά στοιχεία ενός Φ/Β πάρκου. Εξετάζεται το φαινόμενο της νησιδοποίησης και αναφέρονται στοιχεία για την αδειοδότηση του έργου. Επίσης περιγράφονται τεχνικά στοιχεία όπως η γείωση και οι μετατροπείς – inverters και εξηγείται τι είναι το ποσοστό απόδοσης της εγκατάστασης και ο ευρωπαϊκός βαθμός απόδοσης. Στο πέμπτο κεφάλαιο εξηγείται η λειτουργία του ιχνηλάτη – tracker και αναφέρονται τα πλεονεκτήματα χρήσης του σε σχέση με τα φ/β σε σταθερή βάση. Ακόμη περιγράφεται η περιστροφή γύρω από έναν άξονα και δύο άξονες. Τέλος γίνεται μία μαθηματική ανάλυση ως προς την γωνία πρόσπτωσης και του ποσού της λαμβάνουσας ηλιακής ακτινοβολίας. Τέλος στο έκτο κεφάλαιο γίνεται η διαστασιολόγηση του Φ/β πάρκου. Στο συγκεκριμένο κεφάλαιο παρουσιάζεται η χωροθέτηση των ιχνηλατών στο οικόπεδο και η ενεργειακή μελέτη η οποία έγινε μέσω του προγράμματος PVSYST 5.56. Επίσης γίνεται τεχνική ανάλυση ως προς τους μετατροπείς, τη σύνδεση με το δίκτυο τις καλωδιώσεις και την αντικεραυνική προστασία και τελικά γίνεται η οικονομοτεχνική μελέτη της ανάλυσης. / The purpose of the present thesis is the design – dimensioning of a photovoltaic park with nominal power 500 kWp. In the specific park, they are going to be used sun trackers and it is located near Larisa – Greece. The aim of replacing a great percent of conventional energy sources with renewable is significant for the environment's protection, but also it is a great challenge for the engineers and the global economy. In the first chapter, there is a brief presentation of solar energy and radiation and how can be calculated. Furthermore, the pv market potential in Greece and in Europe is described. In the second chapter is explained how the pv generator works and what is photovoltaic phenomenon. Also there is a mathematical analysis about the model of pv diode. In the third chapter, there is a presentation of pv module characteristics such as performance ratio. Also, the materials that pv modules are usually made of and factors that affect their performance are mentioned. In the fourth chapter, there is a description of the general data of a pv park such as inverters, grounding. Moreover, the phenomenon of islanding is explained. In the fifth chapter, there is an explanation of how a solar tracker works. Also, the advantages of using solar tracker in comparison with fixed tilt systems are presented. Finally, in the sixth chapter , the design and dimensioning of the pv park is presented and it is shown how the trackers are located in the field. Furthermore, the PVSYT 5.56 is used to simulate the energy yield of the pv park and a technical analysis is presented which includes the pv modules, the trackers, the transformer that are used and other critical data. In the end there is an economic analysis which shows the estimated profit of the specific investment.

Photovoltaic (PV) solar panels and trackers represent one of the most common renewable energy technology which converts sunlight radiation into electrical energy. The solar trackers specifically are more complex structures because they involve mechanical devices, a supporting slender structure, and photovoltaic modules mounted and positioned on top of the supporting structure. Solar trackers are mounted on mobile supports or racks, in order to enable the rotation and tilt of the PV which thus maintains their optimum exposure to the incident sunlight. Solar trackers support structures should be designed for wind resistance during the operation and at stow position for its life span and this became a concern considering the new tendency of installing the solar trackers on the rooftop of low-rise or medium-rise buildings. The current research focused on performing site measurements of the wind-induced displacement for a dual-axis solar tracking system installed on the roof of the Mann Parking building of the University of Ottawa, for different azimuth, elevations. The supporting structure of the solar tracker was instrumented with 16 strain gauges and the strains developed in the metal truss members were measured during the months February 2015 and March 2015. The tracker was rotated and tilted at different angles through the duration of the experiment and the strains observed on each structural element were recorded. In order to estimate deflections of the supporting structure for wind speeds higher than the ones measured, a finite element (FE) model of the solar tracker was created and static analysis was performed for different inclinations using the SAP 2000 structural software. The experimental results were in agreement with the FE simulation results as the stresses obtained ranged between 1.02 × 107 Pa and 7.88 × 107 Pa. Lower attack angles between 45° and 60° were found to have significant effect on the elements of the solar tracker irrespective of the wind load magnitude. Operational attack angles between 65° and 75° were found to be safer positions as obtained displacements and stress analysis result showed that the supporting structure of the solar tracker was stable for wind speeds between 0 m/s and 33m/s in Ottawa region

Background: Objectively tracking sedentary behavior (SB) and physical activity (PA) is becoming increasingly important as research continues to show the negative effects with increasing SB and decreasing PA. Objectives: The purpose of this study was to evaluate three commercial activity trackers with young adults regarding how they accurately measure SB and PA behaviors in a laboratory setting. Methods: 50 college-aged participants wore three wrist-based activity trackers (Fitbit Surge, Apple Watch, and Basis Peak) and two ActiGraph accelerometer devices during a series of SB and PA behaviors for five-minute intervals in a laboratory setting. The activity trackers were evaluated against direct observation and the ActiGraph devices, placed on the hip and wrist, which are consistent with the National Health and Nutrition Examination Survey (NHANES) standards of measure. Results: Overall accuracy during the SBs compared to direct observation was high, with Apple (99.0%), Basis (99.0%), and Fitbit (94.9%) performing similar to the Hip ActiGraph (95.1%) and markedly better than the Wrist ActiGraph (58.6%). Overall significant correlations (p ≤ 0.05) during the PAs were higher with the Wrist ActiGraph (66.7%) than with the Hip ActiGraph (8.3%). The Wrist and Hip ActiGraphs significantly correlated in three out of four SBs, but not in any PA behaviors.Discussion: Activity trackers are reliable when determining sedentary behavior, tend to overestimate step count during light walking, and underestimate activity level when biking. Also,the Wrist ActiGraph consistently underestimated both SB and PA step count compared to the Hip ActiGraph. While some variability is seen in the validity of the activity trackers, each activity tracker studied has its strengths and weaknesses. Understanding these strengths and limitations helps healthcare professionals more accurately interpret recorded data based on the patient specific device.

Yes / The school environment is an ideal setting for promoting physical activity (PA). Wearable activity trackers (wearables) have previously been implemented, in research, as intervention tools within the school-environment. However, the large-scale use and acceptance of wearables, in schools, is unknown. This study distributed a cross-sectional survey to school staff to investigate the prevalence of child and adolescent wearable use in schools, including when and how they are used, and school staff's willingness to use them in the future (as implemented by school staff). This survey consisted of between 13 and 22 items, including closed-ended and open-ended questions. Closed-ended responses were displayed descriptively (wearable prevalence and characteristics), and open-ended qualitative responses were categorised using descriptive content analysis (how wearables are used). 1087 school staff provided valid responses. Of those, 896 (82.4%) had never used a wearable as a teaching or support tool for their students, and 120 (11%) currently used- and 71 (6.5%) had previously used- a wearable as a teaching or support tool for their students. When wearables were used, school staff implemented their use regularly and during physical education lessons or throughout the entire school day. Wearables were used to monitor or increase student's PA levels, or for student and staff educational purposes (e.g., academic learning, movement breaks). Most school staff were willing to use a wearable as a teaching or support tool to promote student's PA, and/or learning about PA, in the future. This study is the first study to explore the widescale use and acceptance of children and adolescents using wearables in the school-setting. Findings may inform the development of future school-based interventions and public health initiatives for physical activity promotion, using wearables. / This study is funded as part of a PhD studentship by the Born in Bradford study. The Born in Bradford study receives core infrastructure funding from the Wellcome Trust (WT101597MA) and the National Institute for Health Research (NIHR), under its NIHR ARC Yorkshire and Humber (NIHR200166) and Clinical Research Network (CRN) research delivery support. For this piece of work, funding from the Sport England’s Local Delivery Pilot awarded Born in Bradford funding for this PhD studentship. S.A.C is supported by the NIHR Leicester Biomedical Research Centre—Lifestyle theme.

Le suivi visuel d’objet est une fonction élémentaire de la vision par ordinateur ayant fait l’objet de nombreux travaux. La dérive au cours du temps est l'un des phénomènes les plus critiques à maîtriser, car elle aboutit à la perte définitive de la cible suivie. Malgré les nombreuses approches proposées dans la littérature pour contrer ce phénomène, aucune ne surpasse une autre en terme de robustesse face aux diverses sources de perturbations visuelles : variation d'illumination, occultation, mouvement brusque de caméra, changement d'aspect. L’objectif de cette thèse est d’exploiter la complémentarité d’un ensemble d'algorithmes de suivi, « trackers », en développant des stratégies de fusion en ligne capables de les combiner génériquement. La chaîne de fusion proposée a consisté à sélectionner les trackers à partir d'indicateurs de bon fonctionnement, à combiner leurs sorties et à les corriger. La prédiction en ligne de dérive a été étudiée comme un élément clé du mécanisme de sélection. Plusieurs méthodes sont proposées pour chacune des étapes de la chaîne, donnant lieu à 46 configurations de fusion possibles. Évaluées sur 3 bases de données, l’étude a mis en évidence plusieurs résultats principaux : une sélection performante améliore considérablement la robustesse de suivi ; une correction de mise à jour est préférable à une réinitialisation ; il est plus avantageux de combiner un petit nombre de trackers complémentaires et de performances homogènes qu'un grand nombre ; la robustesse de fusion d’un petit nombre de trackers est corrélée à la mesure d’incomplétude, ce qui permet de sélectionner la combinaison de trackers adaptée à un contexte applicatif donné. / Visual object tracking is an elementary function of computer vision that has been the subject of numerous studies. Drift over time is one of the most critical phenomena to master because it leads to the permanent loss of the target being tracked. Despite the numerous approaches proposed in the literature to counter this phenomenon, none outperforms another in terms of robustness to the various sources of visual perturbations: variation of illumination, occlusion, sudden movement of camera, change of aspect. The objective of this thesis is to exploit the complementarity of a set of tracking algorithms by developing on-line fusion strategies capable of combining them generically. The proposed fusion chain consists of selecting the trackers from indicators of good functioning, combining their outputs and correcting them. On-line drift prediction was studied as a key element of the selection mechanism. Several methods are proposed for each step of the chain, giving rise to 46 possible fusion configurations. Evaluated on 3 databases, the study highlighted several key findings: effective selection greatly improves robustness; The correction improves the robustness but is sensitive to bad selection, making updating preferable to reinitialization; It is more advantageous to combine a small number of complementary trackers with homogeneous performances than a large number; The robustness of fusion of a small number of trackers is correlated to the incompleteness measure, which makes it possible to select the appropriate combination of trackers to a given application context.

Childhood obesity is a foremost concern throughout the health care community. Approximately 17.6% of the pediatric population meet the criteria for obesity, which can lead to health disparities later in life, such as hypertension, type 2 diabetes mellitus, and metabolic syndrome. Emerging mobile and wearable lifestyle tracking devices can be a viable solution to the challenging problem of childhood obesity through behavior changes, feasibility, and adherence. The purpose of this literature review was to determine the effect that mobile and wearable activity tracking devices have on the obese pediatric population. A centralized review of the literature was conducted using various data basesand resulted in 19 articles. 5 articles were chosen to review in more detail. 13 other articles were hand searched through credible resource citations, rendering 14 articles that met all criteria. The three general themes found in this literature review suggest that wearable activity tracking devices can be designed and effectively used by the pediatric population. Also, wearable activity tracking devices are accurate in conveying information on physical activity, calories, and heart rate. Lastly, wearable activity tracking devices can initiate behavioral changes in children leading to an increase in physical activity, resulting in the prevention and treatment of pediatric obesity.While in a majority of the studies analyzed trails were short. The research suggests wearable activity tracking devices will produce the desired results of increased activity in pediatric populations when they are worn correctly, are adequately engaging, and when they are designed in a feasible manner that is appealing to children.

Η παρούσα διπλωματική εργασία πραγματεύεται την στατική ανάλυση και την ανάλυση κόπωσης διαξονικού ιχνηλάτη φωτοβολταϊκής εγκατάστασης. Η σχεδίαση της κατασκευής γίνεται στο σχεδιαστικό πακέτο Catia V5, τα στατικά φορτία υπολογίζονται με βάσει τον διεθνή κανονισμό Eurocode 1 , τα δυναμικά φορτία ανέμου υπολογίζονται βάσει το Kaimal spectrum ενώ οι αναλύσεις γίνονται στο λογισμικό πεπερασμένων στοιχείων Msc.Patran-Nastran. Η εργασία αποτελείται από επτά (7) κεφάλαια εκ των οποίων το έβδομο είναι τα συμπεράσματα. Στο κεφάλαιο 1 γίνεται μια εισαγωγή για τους τύπους στήριξης των φωτοβολταϊκών πλαισίων και για τις βασικές παραμέτρους της ηλιακής τεχνικής και της τροχιάς του ηλίου. Τέλος, υπολογίζονται οι δύο βασικές ηλιακές γωνιές αζιμούθια και ζενίθια κατά την διάρκεια του έτους ώστε να καθοριστούν οι κινήσεις της διάταξης του tracker. Στο κεφάλαιο 2 αναλύεται ο τρόπος σχεδίασης του ιχνηλάτη στο σχεδιαστικό πρόγραμμα Catia-v5. Συγκεκριμένα, προβάλλονται αναλυτικά τα βασικότερα μέρη της κατασκευής και τα τμήματα που συναρμολογήθηκαν ώστε να δημιουργηθεί η διάταξη.Tέλος, παρουσιάζονται οι σύνδεσμοι που επιτρέπουν την κίνηση του ιχνηλάτη και οι βαθμοί ελευθερίας που περιορίζονται από τον καθένα. Στο κεφάλαιο 3 αρχικά παρουσιάζονται οι μεθοδολογίες υπολογισμού των αδρανειακών φορτίων της ίδιας της κατασκευής, των αδρανειακών φορτίων των φ/β πλαισίων, των φορτίων χιονιού και των φορτίων ανέμου βάσει του Ευρωκώδικα 1. Έπειτα, παρουσιάζεται η μεθοδολογία υπολογισμού των δυναμικών φορτίων ανέμου που επιδρούν στην κατασκευή και ύστερα προβάλλονται τα αποτελέσματα των υπολογισμών. Τέλος, γίνεται μια αναφορά στις ιδιότητες και στην μηχανική συμπεριφορά των υλικών από τα οποία αποτελείται η κατασκευή του tracker. Στο κεφάλαιο 4 γίνεται μια σύντομη αναφορά στην θεωρία και στους τύπους των πεπερασμένων στοιχείων που χρησιμοποιούνται στην μοντελοποίηση του ιχνηλάτη. Και εν συνεχεία παρουσιάζονται διεξοδικά οι διαδικασίες μοντελοποίησης όλης της κατασκευής αλλά και τμημάτων της με στοιχεία δοκού, στοιχεία κελύφους και στοιχεία όγκου. Το κεφάλαιο 5 παρουσιάζει την διαδικασία υπολογισμού της ζωής σε κόπωση που ακολουθεί η υπορουτίνα του Msc.Fatigue στο πρόγραμμα των πεπερασμένων στοιχείων. Τέλος στο κεφάλαιο 6, παρουσιάζονται οι αναλύσεις που έγιναν ώστε να βρεθούν οι δυσμενέστερες καταστάσεις της κατασκευής αλλά και τα αντίστοιχα αποτελέσματα. / Current study deals with the static analysis of the double-axis solar tracker structure and the fatigue analysis of it, using finite elements techniques. The design of structure is done in the Catia V5 design software, the static loads are calculated according to Eurocode 1 Standard , the dynamic wind loads are calculated according to Kaimal Spectrum which is used to model dynamic loads in Sign structures while the analyses are carried out in the Msc. Patran-Nastran Finite Element Analysis program. The study consists of seven (7) parts and the last one refers to conclusions. In the first section, the types of PV panel support and the basic parameters of solar energy and of solar track are mentioned. Finally, the two basic solar angles such as azimuth and zenith are calculated during a year period with the purpose of determination of tracker motion. In section two, the way the sun tracker has been designed in Catia V5 is analyzed. Specifically, the main parts of steel structure and the parts that were assembled so that the order be created are presented. Finally, the connections of two main subparts of structure, which allow the movement of structure, and the degrees of freedom, which are constrained by each one, are presented. In section 3, firstly, the calculation methodology of inertial loads of the structure and of the PV panels and the calculation methodology of snow and wind loads are presented in according to Eurocode 1 Standard. Then, the calculation method of dynamic wind loads, which affect the construction, and the results of calculations are presented. In the end of this section, a report of material properties and behavior, which are used in the tracker structure, is presented. In addition, in section 4, the theory and the types of finite elements, which are used in the structure modeling, are presented. Subsequently, the procedures of structure modeling with beam, shell and 3-d finite elements are analytically presented. In section 5, the background of total-life calculation that is used by the subroutine of Msc.Fatigue in Finite Element Analysis program Msc. Patran-Nastran is reviewed. In section 6, the static and fatigue analyses, which are carried out in order to find the unfavorable load situations of structure and analyses results, are presented.

The third-party tracking ecosystem continuously evolves in scope, therefore, understanding of it is at best elusive. In this thesis, we investigate this complex ecosystem from three dimen-sions. Firstly, we examine third-party trackers from a geographical perspective. We observe a non-uniform presence of local third-party trackers between regions and countries within re-gions, with some trackers focusing on specific regions and countries. Secondly, we focus on how trackers share user-specific identifiers (IDs). We identify user-specific IDs that we suspect are used to track users. We find a significant amount of ID-sharing practices across different organ-isations providing various service categories. Our observations reveal that ID-sharing happens at a large scale regardless of the user profile size and profile condition such as logged-in and logged-out. Finally, we quantify the effect of tracker-blockers, a popular option for the users to protect their privacy, on the page-load performance. The effect of such tools on the over-all user browsing experience is questionable as the blockage of trackers can disrupt the general website loading process. The tracker-blockers we studied have a considerable negative effect on page-load performance. Unexpectedly, we find that even highly popular websites are negatively affected. This thesis points to significant gaps in our knowledge about the inner workings of this complex ecosystem. Moreover, it highlights some of the challenges that we face when attempting to preserve user's privacy by using tracker-blockers.

Tato diplomová práce se zabývá zhodnocením marketingové strategie společnosti Team Trackers. Společnost Team Trackers poskytuje asistenční služby leteckým společnostem. Tyto služby zahrnují péči o pasažéry leteckých společností od prvního telefonického kontaktu s cestujícím až po výpočet a vyplacení odškodnění pasažérovi. První část této diplomové práce obsahuje informace o společnosti Team Trackers, zhodnocení výběru umístění společnosti a okolnosti založení. Dále jsou zde informace o strategických leteckých aliancích. Další část se zabývá organizační strukturou, marketingovým mixem společnosti a SWOT analýzou firmy Team Trackers. Následuje krátké zhodnocení výzkumu potenciálu trhu a strategie v oblasti informačních technologií.