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Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η μελέτη και ο σχεδιασμός καινοτόμων αλγορίθμων φυσικού επιπέδου σε ασύρματα συστήματα επικοινωνίας που χρησιμοποιούν διαμόρφωση με πολύπλεξη συχνότητας ορθογωνίων φερουσών (Orthogonal Frequency Division Multiplexing - OFDM). Η έρευνα επικεντρώθηκε σε δύο κατηγορίες προβλημάτων, στον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης καθώς και αλγορίθμων αντιμετώπισης ισχυρού θορύβου φάσης. Αναπτύχθηκαν αλγόριθμοι εκτίμησης φάσης με γραμμική πολυπλοκότητα, μέσω ενός καινούργιου εναλλακτικού μοντέλου περιγραφής του συστήματος. Το μοντέλο αυτό επιτρέπει την επέκταση των κλασικών αλγορίθμων εκτίμησης της κοινής φάσης με στόχο την εκτίμηση του συνολικού διανύσματος θορύβου φάσης. Επιπλέον, η τεχνική διαγώνιας φόρτωσης (diagonal-loading) προσαρμόστηκε κατάλληλα για τη βελτίωση σύγκλισης της προτεινόμενης λύσης. Τέλος, προτάθηκε και αξιολογήθηκε ένα συνολικό σύστημα OFDM όπου η εκτίμηση του καναλιού, της διαταραχής φάσης και των δεδομένων βασίζονται στο κριτήριο ελαχίστων τετραγώνων, διατηρώντας έτσι τη συνολική πολυπλοκότητα σε χαμηλά επίπεδα. Στο πλαίσιο του σχεδιασμού αλγορίθμων προσαρμοστικής διαμόρφωσης προτείνεται ένα γενικό μοντέλο περιγραφής απόδοσης συστήματος ικανό να περιγράψει τα αναπτυσσόμενα πρωτόκολλα μετάδοσης. Η πρόταση αυτή εντάσσεται στην οικογένεια των τεχνικών ισοδύναμης σηματοθορυβικής απεικόνισης (Εffective SNR Μapping - ESM). Χρησιμοποιώντας τις τεχνικές ESM και κατάλληλους περιορισμούς στην παραμετροποίηση των μεταβλητών μετάδοσης, αναπτύχθηκαν αλγόριθμοι προσαρμοστικής διαμόρφωσης χαμηλής πολυπλοκότητας που ικανοποιούν διαφορετικά κριτήρια βελτιστοποίησης. Επιπρόσθετα, προτείνεται ένα γενικό πλαίσιο για τον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης, χρησιμοποιώντας προσεγγιστικά μοντέλα απόδοσης. Ορίστηκαν οι κατάλληλες μετρικές για την ποσοτικοποίηση της σπατάλης ενέργειας που επιφέρει η χρήση προσεγγιστικών μοντέλων. Μελετήθηκε η επίδραση της καθυστέρησης ανατροφοδότησης πληροφορίας καναλιού στους αλγορίθμους και παρήχθησαν κατάλληλα μοντέλα περιγραφής απόδοσης που συμπεριλαμβάνουν το χρόνο καθυστέρησης. Το συνολικό αποτέλεσμα της εργασίας είναι αλγόριθμοι που καταφέρνουν υψηλή απόδοση συστήματος, με χαμηλή πολυπλοκότητα, κάτι το οποίο τους κάνει υλοποιήσιμους σε ρεαλιστικά συστήματα. / The objective of this thesis is to study and develop novel, low complexity physical layer algorithms for Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. The study aims at two algorithmic categories, namely adaptive modulation and coding and compensation of severe phase noise (PHN) errors. A parameterized windowed least-squares (WLS) decision directed phase error estimator is proposed via proper (alternative) system modeling, applied to both channel estimation and data detection stage in OFDM systems. The window is optimized so as to minimize the post-compensation error variance (PCEV) of the residual phase, analytically computed for arbitrary PHN and frequency offset (FO) models. Closed-form expressions for near-optimal windows are derived for zero-mean FO, Wiener and first-order autoregressive PHN models, respectively. Furthermore, the diagonal-loading approach is properly employed, initially proposed for providing robustness to a general class of estimators in the presence of model mismatch, to enhance convergence of the iterative estimation scheme, in those high-SNR regions where the effect of data decision errors dominates performance. In the proposed OFDM scheme, channel, IFO estimation and data equalization are also based on the LS criterion, thus keeping the overall system complexity low. A generic performance description model is proposed and used for AMC algorithmic design, capable of describing most of current and under preparation communication protocols. This model proposition is incorporated to a larger family of performance modelling techniques named Effective SNR Mapping techniques (ESM). Using the ESM techniques and proper parameter adaptation constraints, a number of low-complexity AMC algorithms are developed under a chosen set of optimization scenarios. A framework for the design of AMC algorithms using approximate performance description models is proposed. Specific bounds are derived for quantifying the power loss when using approximate models. The effect of outdated channel state information is also studied by statistically characterizing the effective SNR at the receiver. This description allows parameter adaptation under mobility scenarios. The main value of this collective procedure is the development of low complexity- high performance algorithms, implementable on pragmatic OFDM systems.

Ce travail de recherche traite du couplage entre un liquide incompressible, irrotationnel et son contenant : une structure élastique. Cette interaction fluide-structure est traitée dans le cadre des petites déformations autour d'un état d'équilibre.Dans un premier temps, on présente une méthode d'introduction des sources dissipatives visqueuses dans le liquide à partir des équations du système couplé conservatif en s'appuyant sur une approche de type fluide potentiel généralement utilisée pour traiter les problèmes de couplage fluide-structure linéarisés non amortis. Un modèle d'amortissement diagonal est alors choisi pour le liquide et les effets dissipatifs de celui-ci sont pris en compte en calculant les coefficients d'amortissement modaux. Seuls les effets dissipatifs liées à la viscosité du liquide sont alors pris en compte. Le système couplé dissipatif obtenu possède une matrice d'amortissement non symétrique. Une résolution de ce système à amortissement non classique est alors présentée et les expressions des réponses fréquentielle et temporelle linéarisées sont données pour différents types d'excitations.Dans un deuxième temps, le liquide est supposé non visqueux et les forces de tension surfacique sont prises en compte. Cette configuration concerne principalement les satellites où le système couplé est en situation de microgravité. Une formulation du problème conservatif permettant de prendre en compte l'incompressibilité du fluide, la condition de continuité à l'interface fluide structure, les effets de capillarité du fluide ainsi que les effets éventuels de précontraintes statiques est alors établie. On se propose pour cela d'utiliser une méthode énergétique via le Principe de Moindre Action. La démarche est alors décomposée en deux étapes : une étude statique afin de déterminer la position de référence, puis une étude dynamique linéarisée autour de cette position d'équilibre. Cette formulation forme notamment une base pour l'introduction des sources dissipatives liées aux effets de capillarité via la méthode précédemment introduite. / This study deals with the coupling between an incompressible, irrotational fluid and an elastic container in the context of small amplitude vibrations.Firstly, we present a method to introduce the viscous dissipative sources in the liquid directly from the equations of the conservative coupled problem using a fluid potential approach generally used to treat linear undamped problems. A diagonal damping model is chosen for the liquid and its dissipative effects are taken into account through modal damping coefficients. Only the viscous effects are considered here. The coupled system obtained has a non symmetric damping matrix. This system with non classical damping is solved and expressions of the frequency and linearized time responses are given for different load examples.Secondly, the liquid is supposed to be inviscid and surface tension forces are considered. This configuration is related to satellite applications where the coupled system is in microgravity conditions. A unified formulation of the conservative problem taking into account the fluid incompressibility, the contact condition at the fluid structure interface, capillarity and prestress effects is given. Thus, we propose to use an energy method via the Least Action Principle. The reasoning is then divided into two parts: a static study to determine the reference state and a linearized dynamic study around this equilibrium state. This formulation is a good framework to introduce the dissipative sources associated with the capillary effects by using the method previously introduced.

Text in Afrikaans / In hierdie verhandeling word die aard van kommunikasie van die Lugmagbasis (LMB) Swartkop onder die loep geneem. Die outeur toon aan dat daar nie altyd duidelikheid is oor die aard van kommunikasie in militere instellings nie. Dit het die prikkeling gebied om die aard van kommunikasie in 'n militere installing te bepaal - in hierdie geval, LMB Swartkop. Die rede vir die studie is om kommunikasie as 'n interne organisatoriese reeling by die LMB Swartkop te ondersoek. Om die agtergrond tot die navorsing te bied, word die ekonomiese- en politieke redes vir verandering by die LMB Swartkop kortliks weergee. Die redes hoekom hierdie Lugmagbasis as fokusgebied gebruik word vir die navorsing, word ook aangevoer. Daar word met die navorsing gefokus op vertikale kommunikasie, horisontale kommunikasie, diagonale kommunikasie, asook enkele interne organisatorieseen omgewingsfaktore. Enkele aspekte ten opsigte van eksterne faktore, soos byvoorbeeld die 1994-verkiesing en die nuwe Grondwet, wat kon lei tot verbetering van kommunikasie te Lugmagbasis Swartkop en die houding van die personeel jeens kommunikasie word ook aangeraak. Die bevindinge van die navorsing wentel rondom die feit dat vertikale, horisontale en diagonale kommunikasie 'n definitiewe bydrae maak om werk op die Lugmagbasis Swartkop effektief te verrig. Hierdie kommunikasie vind hoofsaaklik plaas wanneer daar formeel en informeel oor werk gekommunikeer word. / In this dissertation, the nature of communication of the Air Force Base Swartkop is being put under the magnifying glass. The author indicates that the nature of communication in military organisations is not clear This provided the incentive to study the nature of communication of a military organisation and in this case, Air Force Base Swartkop. The reason for the study is to determine how the nature of communication as an internal organisational arrangement contributes to the effective functioning of the base. This study focuses on vertical, horizontal and diagonal communication as well as internal organisational, external and environmental factors. Aspects such as the personnel's attitude towards communication is discussed as well. The findings of the study centre on the fact that vertical, horizontal and diagonal communication make a definite contribution to the effective functioning of the base. This communication mainly occurs when personnel communicate formally and informally on work. / Public Administration and Management / M.Admin. (Public Administration)

This thesis deals with design of a multi-purpose sports hall. The aim of this work is to design a support structure with a diameter of 80.0 m at ± 0.000. Construction of a circular layout in the level of ± 0.000 of an external diameter 80.0 m. Height of the hall at the top is 20.0 m Indoors girders is solved in 36 beams which meet at the middle of the rings. Ensure the stability of bracing. Anchoring is done by pin connections located at the bottom of the strip, anchored in concrete bases through the base plate and pre-concreted anchor bolts.

The aim of the Diploma Thesis is elaboration of study of bridge crossing over the Svitava river and ČD railway track in Blansko. It concerns a five-pole steel beam road bridge with through-span which carries road of the third category. The static system of the construction is solved as solid-web beam of 1.3 meters height which is in three middle spans reinforced by truss construction with top chord and system of diagonals without verticals. The height of the main beam where reinforced by trusswork is 4.75 meters. The width of spans in the road axis is 18.5 + 30.525 + 44.4 + 30.525 + 18,5 metres. The bridge deck consists of steel cross beams bonded with reinforced concrete slab of 200 millimeters of thickness. The drive-through width of the roadway is 7.0 meters. The bridge is fitted with right-sided walkway placed on steel cantilevers. The walk-through width of the walkway is 3.0 meters. Material used is S355 Steel, C30/37 Concrete and S460 Steel which is used for marginal spans of the bridge. Load-bearing construction is assessed in compliance with current technical requirements laid down by European Directives, so called “Eurocodes”. The calculation of inner powers is performed using the Scia Engineer 2013.1 software.

M-matrices are extensively employed in numerical analysis. These matrices can be generalized by corresponding operators on a partially ordered normed space. We extend results which are well-known for M-matrices to this more general setting. We investigate two different notions of an M-operator, where we focus on two questions: 1. For which types of partially ordered normed spaces do the both notions coincide? This leads to the study of positive-off-diagonal operators. 2. Which conditions on an M-operator ensure that its (positive) inverse satisfies certain maximum principles? We deal with generalizations of the "maximum principle for inverse column entries". / M-Matrizen werden in der numerischen Mathematik vielfältig angewandt. Eine Verallgemeinerung dieser Matrizen sind entsprechende Operatoren auf halbgeordneten normierten Räumen. Bekannte Aussagen aus der Theorie der M-Matrizen werden auf diese Situation übertragen. Für zwei verschiedene Typen von M-Operatoren werden die folgenden Fragen behandelt: 1. Für welche geordneten normierten Räume sind die beiden Typen gleich? Dies führt zur Untersuchung außerdiagonal-positiver Operatoren. 2. Welche Bedingungen an einen M-Operator sichern, dass seine (positive) Inverse gewissen Maximumprinzipien genügt? Es werden Verallgemeinerungen des "Maximumprinzips für inverse Spalteneinträge" angegeben und untersucht.

<p>A large rectangular industrial duct consists of plates stiffened with parallel wide flange sections. The plates along with stiffeners acts to resist the pressure loads and to carry other loads to the supports. The behaviours of the components of large industrial ducts are significantly different from the behaviours on which the current design methods are based on. Investigation presented herein deals with the design methods for spacing stiffeners, proportioning stiffeners and calculating shear resistance of side panel.</p> <p>Current method of spacing stiffeners is based on large deflection plate theory. A parametric study was conducted on dimensionless parameters identified in order to benefit from membrane action in partially yielding plate for spacing stiffeners. Design equations were established in terms of dimensionless pressure, plate slenderness and normalized out-of-plane deflection for three cases namely; 0%, 16.5% and 33% of through thickness yielding of the plate. Results show that approximately 50% increase in stiffener spacing when yielding of 16.5% of thickness is permitted.</p> <p>Under suction type pressure load, the unsupported compression flange and restrained tension flange lead to distortional buckling of the stiffeners. The current methods do not address distortional buckling adequately. A parametric study on dimensionless parameters governing the behaviour and strength of stiffened plat panels was conducted. The study indicated that the behaviour and strength of the stiffened panels could be a function of web slenderness and overall slenderness of the stiffener. The study also identified the slenderness limit of stiffener web for which the stiffener reaches the yield moment capacity. This study demonstrated the conservatism of current method. Finally a method was established to calculate the strength of stiffened plate panel subjected lateral pressure.</p> <p>Side panels adjacent to the supports transfer large amount of shear to the supports and, in addition, resist internal pressure. Currently the design of side panels for shear is based on the methods used for the web of fabricated plate girders. The behaviour and the characteristics between the web of plate girder and the thin side panels are significantly different. A parametric study was conducted on dimensionless parameters identified. It was concluded that the plate slenderness dominates the normalized shear strength of stockier side panels. The aspect ratio and plate slenderness influence the normalized shear strength of slender side panels. Design methods to calculate the shear strength of side panels were proposed.</p> / Doctor of Philosophy (PhD)

It is the tyre that ensures the interaction between a wheel and road surface and it is the the tyre which also acts as a primary cushioning. Its construction, features and condition highly influence driving properties of a car and thus passenger safety as well. In motorsports the tyre is a key part of the vehicle and therefore it is necessary to make use of its complete potential for reaching the best results. The aim of this thesis is a device construction suitable for tyre parameter and their characteristics measurement. The next task is to design a measuring system for tyre pressure and temperature monitoring. With using of these devices a few real-tyre measurements and subsequent result evaluation will be done. The output of the thesis is an overview of construction details, overview of selected tyre parameters, design and drawing documentation of multipurpose measuring device and the results of my measurements.