No description available.

The performance of building envelopes and roofing systems significantly depends on accurate knowledge of wind loads and the response of envelope components under realistic wind conditions. Wind tunnel testing is a well-established practice to determine wind loads on structures. For small structures much larger model scales are needed than for large structures, to maintain modeling accuracy and minimize Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel meaning that it is not possible to simulate the low frequency end of the turbulence spectrum. Such flows are called flows with Partial Turbulence Simulation. In this dissertation, the test procedure and scaling requirements for tests in partial turbulence simulation are discussed. A theoretical method is proposed for including the effects of low-frequency turbulences in the post-test analysis. In this theory the turbulence spectrum is divided into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in a quasi-steady manner. The joint probability of load resulting from the two processes is derived from which full-scale equivalent peak pressure coefficients can be obtained. The efficacy of the method is proved by comparing predicted data derived from tests on large-scale models of the Silsoe Cube and Texas-Tech University buildings in Wall of Wind facility at Florida International University with the available full-scale data. For multi-layer building envelopes such as rain-screen walls, roof pavers, and vented energy efficient walls not only peak wind loads but also their spatial gradients are important. Wind permeable roof claddings like roof pavers are not well dealt with in many existing building codes and standards. Large-scale experiments were carried out to investigate the wind loading on concrete pavers including wind blow-off tests and pressure measurements. Simplified guidelines were developed for design of loose-laid roof pavers against wind uplift. The guidelines are formatted so that use can be made of the existing information in codes and standards such as ASCE 7-10 on pressure coefficients on components and cladding.

Les matériaux poreux silicatés ont été mis à profit pour encapsuler différents types de molécules, clusters ou nano-objets fonctionnels, donnant lieu à des nanocomposites hybrides organiques-inorganiques à propriétés physiques, chimiques ou biologiques remarquables. Élucider l'organisation structurale à l'échelle moléculaire de tels nanocomposites est indispensable pour l'analyse et la compréhension des propriétés macroscopiques qui en découlent. Ainsi, les techniques de diffusion totale associées à la fois à l'analyse Debye et la Fonction de Distribution de Paires (PDF) sont des méthodes de choix pour la caractérisation des propriétés structurales de matériaux hybrides nano-structurés. Le principal objectif de ce travail consiste à l'utilisation des approches basées sur la diffusion totale de rayons X pour l'analyse structurale complète de molécules photoactives confinées dans des matrices silicatées amorphes avec différentes tailles de pores, afin d'étudier l'influence de l'organisation structurale sur les propriétés optiques et d'explorer également les limites de ces approches d'analyse. Nous avons étudié deux systèmes photoactifs. L'analyse structurale du premier complexe confiné, Na2[Fe(CN)5NO].2H2O (SNP), a été entreprise par une approche multi-échelle combinant la RMN du solide et l'analyse PDF. Cette approche a permis l'identification de la nature des espèces incorporées, l'arrangement des cations et des anions ainsi que la distinction des différentes phases existantes : molécules isolées et nanoparticules. Les analyses Debye et PDF sur le deuxième composé étudié, [NdCl2(H2O)6]Cl, montrent que l'organisation structurale du complexe confiné est différente de celle du matériau massif cristallin. De plus, les cations Nd3+ changent de coordination de 8 à 9 durant le processus d'imprégnation et adoptent ainsi un arrangement structural très similaire à celui en solution aqueuse. Cette modification structurale est en accord avec le changement des propriétés luminescentes de ce complexe / Silica xerogels are versatile host materials for the inclusion of molecules, clusters, or nano-objects yielding host-guest compounds with unique physical, chemical or biological properties. The knowledge of the structural organization of the guest within the host is crucial for the understanding of its properties. Total scattering methods, based on Debye function analysis (DFA) and Pair Distribution Function (PDF), have become powerful tools for structural characterization of nanostructured hybrid materials. The aim of this work is to use the X-ray total scattering method to obtain structural information on photoactive molecules embedded into amorphous silica hosts with different pore sizes, to correlate their structure with the optical properties, and to explore the limitations of the chosen method. Two different photoactive complexes have been investigated. In the first example, the combined PDF and NMR study on Na2[Fe(CN)5NO].2H2O (SNP) embedded into silica matrices allows to extract the nature of the inserted species: quasi-free isolated molecules can be distinguished from nanoparticles and in the former case a model for the arrangement of cation-anion can be proposed from the PDF analysis. In the second example, a luminescent Nd3+ complex, the PDF and DFA analysis reveal that the structural organization of the embedded Nd3+ complexes is different from that of the crystalline material. Furthermore, the Nd3+ cations change the coordination from 8 to 9 during the wet-impregnation doping and adopt very similar structural arrangement as in aqueous solution, which is in agreement with the observed change in the luminescence properties

L'objectif de cette thèse est d'étudier le comportement local d'une mesure de probabilité, notamment à l'aide d'un indice de régularité locale. Dans la première partie, nous établissons la normalité asymptotique de l'estimateur des kn plus proches voisins de la densité. Dans la deuxième, nous définissons un estimateur du mode sous des hypothèses affaiblies. Nous montrons que l'indice de régularité intervient dans ces deux problèmes. Enfin, nous construisons dans une troisième partie différents estimateurs pour l'indice de régularité à partir d'estimateurs de la fonction de répartition, dont nous réalisons une revue bibliographique. / The goal of this thesis is to study the local behavior of a probability measure, using a local regularity index. In the first part, we establish the asymptotic normality of the nearest neighbor density estimate. In the second, we define a mode estimator under weakened hypothesis. We show that the regularity index interferes in this two problems. Finally, we construct in a third part various estimators of the regularity index from estimators of the distribution function, which we achieve a review.

The result of my dissertation justifies the use of fuzzy-sets theory to make a prediction of cost risk of a PPP project, when there is not enough information available to clearly describe the project, and, when the probability distributions of the variables that characterize the project are unknown. I showed that fuzzy-sets theory and linguistic variables may be effectively used in such a case. In this thesis were classified different types of uncertainty and investigated traditional methods for estimating efficiency of a investment project in conditions of uncertainty. On the basis of the analysis were offered new ways of conducting risk analysis for PPP projects with use of fuzzy sets theory. The main goal was to create an application model for risk assessment of the PPP project which, with a high degree of reliability, suggests a general assessment of situation. The goal set in my work was met. Model of risk assessment of the project proposed by me gives more stable results in comparison with the probabilistic model. For comparison were used different types of probability distribution functions and membership functions. The following conclusions and statements describe the novelty of the work on fuzzy logic and economic theory: develops a method of cash-flow (future expenditure connected with the appearance of risk) modeling of investment project in fuzzy environment, demonstrates the use of fuzzy sets theory in projects analyses and describes how to calculate and interpret this value, demonstrates example of the use of results applied to the analysis of infrastructure development project in Moscow, Russia. The possibility of using this method is not only in the analysis of infrastructure development projects, but also in realization of non-commercial projects by social institutes and government agencies.

The task of this diploma thesis is the Lattice Boltzmann method (LBM). LBM is a mesoscopic method describing the particle motion in a fluid by the Boltzmann equation, where the distribution function is involved. The Chapman-Enskog expansion shows the connection with the macroscopic Navier-Stokes equations of conservation laws. In this process the Hermite polynoms are used. The Lattice Boltzmann equation is derived by the discretisation of velocity, space and time which is concluding to the numerical algorithm. This algorithm is applied at two problems of fluid flow: the two-dimensional square cavity and a flow arround obstacles. In both cases were the results of velocities compared to results calculated by finite volume method (FVM). The relative errors are in order of multiple 1 %.

This work will describe current distribution measurement problems along antenna conductor using a probe (coupling loop), which is attached to selective micro-voltmeter, which will indicate signal level (voltage). The signal level will be used for representing the current distribution. Subsequently, measuring workplace issues from generator to antenna conductor, probe and selective micro-voltmeter, will be discussed. Analysis of voltages of this link-up and additional study will be conducted. Other parameters, which complement this situation, will be calculated from the current distribution. A computer program, which calculates these parameters and speeds up the collected data processing, will be used for this process.

Orthogonal frequency division multiplexing (OFDM) has become a very popular method for high-data-rate communication. However, it is well known that OFDM is plagued by a large peak-to-average power ratio (PAPR) problem. This high PAPR results in overdesigned power amplifiers, which amongst other things leads to inefficient amplifier usage, which is undesirable. Various methods have been recommended to reduce the PAPR of an OFDM transmission; however, all these methods result in a number of drawbacks. In this thesis, a novel method called offset modulation (OM-OFDM) is proposed to control the PAPR of an OFDM signal. The proposed OM-OFDM method does not result in a number of the drawbacks being experienced by current methods in the field. The theoretical bandwidth occupancy and theoretical bit error rate (BER) expression for an OM-OFDM transmission is derived. A newly applied power performance decision metric is also introduced, which can be utilised throughout the PAPR field, in order to compare various methods. The proposed OM-OFDM method appears to be similar to a well-known constant envelope OFDM (CE-OFDM) transmission. The modulation, structural and performance differences between an OM-OFDM and a CE-OFDM method are discussed. By applying the power performance decision metric, the OM-OFDM method is shown to offer significant performance gains when compared to CE-OFDM and traditional OFDM transmissions. In addition, the OM-OFDM method is able to accurately control the PAPR of a transmission for a targeted BER. By applying the power performance decision metric and complementary cumulative distribution function (CCDF), the proposed OM-OFDM method is shown to offer further performance gains when compared to existing PAPR methods, under frequency selective fading conditions. In this thesis, the OM-OFDM method has been combined with an existing active constellation extended (ACE) PAPR reduction method. To introduce a novel method called offset modulation with active constellation extension (OM-ACE), to control the PAPR of an OFDM signal. The theoretical BER expression for an OM-ACE transmission is presented and validated. Thereafter, by applying the decision metric and CCDF, the OM-ACE method is shown to offer performance improvements when compared to various PAPR methods. The use of OM-OFDM for cognitive radio applications is also investigated. Cognitive radio applications require transmissions that are easily detectable. The detection characteristics of an OM-OFDM and OFDM transmission are studied by using receiver operating characteristic curves. A derivation of a simplified theoretical closed-form expression, which relates the probability of a missed detection to the probability of a false alarm, for an unknown deterministic signal, at various signal-to-noise ratio (SNR) values is derived and validated. Previous expressions have been derived, which relate the probability of a missed detection to the probability of a false alarm. However, they have not been presented in such a generic closed-form expression that can be used for any unknown deterministic signal (for instance OFDM and OM-OFDM). Thereafter, an examination of the spectrum characteristics of an OM-OFDM transmission indicates its attractive detection characteristics. The proposed OM-OFDM method is further shown to operate at a significantly lower SNR value than an OFDM transmission, while still offering better detection characteristics than that of an OFDM transmission under Rician, Rayleigh and frequency selective fading channel conditions. In addition to its attractive PAPR properties, OM-OFDM also offers good detection characteristics for cognitive radio applications. These aspects make OM-OFDM a promising candidate for future deployment. / Thesis (PhD)--University of Pretoria, 2012. / Electrical, Electronic and Computer Engineering / unrestricted

Es werden verschiedene Stetigkeitskonzepte, die in der statistischen Theorie und Methodik eine Rolle spielen, erläutert.

This PhD thesis employed high energy synchrotron x-ray radiation to reveal atomic scale structural features occurring in plastically deformed Zr52.5Ti5Cu18Ni14.5Al10 (Vit105) bulk metallic glass (BMG). The study is divided into three parts: Strain evolution during in-situ compression, strain distribution maps in mechanically-imprinted BMG, and residual strain around a single shear band. 1. Strain evolution during in-situ compression The structural rearrangements occurring during compressive deformation of a plastically deformable BMG showed that the elastic and plastic deformation of the BMG is correlated to the structural changes at short- (SRO) and medium range order (MRO). In the elastic regime, the atomic distances at SRO vary linearly with macroscopic stress. Analysis of the area under radial distribution function indicates that a small fraction of bonds in the first shell is broken in the loading direction whereas some new bonds are formed in the transverse direction. Atomic bonds at SRO appeared significantly stiffer than the MRO shells. Compared to the macroscopic values of the elastic strain, Young’s modulus and Poisson's ratio, both SRO and MRO appeared significantly stiffer, implying that the elastic behavior of the BMG is not only ruled by simple compression of the atoms/clusters but also is aided by rearrangement of atoms/clusters. The deviation of MRO atomic strain-stress correlation from linearity at the onset of plastic deformation was attributed to the activation of irreversible shear transformation zones. It was demonstrated by a strong shear strain value at the onset of yielding. This value is in good agreement with the reported value of the critical shear strain needed for activation of an irreversible STZ. The length scale of 12.5 Å indicated the largest shear strain and is probably the most effective length scale in the formation of STZs. The atomic pairs at SRO with smallest shear strain have the least contribution to the STZs. It was also indicated that the typical fracture angle of this BMG can be explained by the orientation of maximum shear strain at the onset of catastrophic shear band formation. 2. Strain distribution map in mechanically-imprinted BMG In mechanical imprinting, the BMG plate is loaded between two tools with a regular array of linear teeth and, as a result, a regular pattern of linear imprints is created on the surface of the plate. Mechanically imprinting results in considerable tensile plasticity of brittle Vit105 BMG plate. The distribution of hardness and Young’s modulus values at the transverse cross section of imprinted plate probed via nanoindentation revealed oscillating soft and hard regions beneath the surface. Spatially-resolved strain maps obtained via high-energy nano-size beam X-ray diffraction exhibited that the plastic deformation during imprinting creates a spatially heterogeneous atomic arrangement, consisting of strong compressive and tensile strain fields as well as significant shear strain fields in the cross section. It was shown that the heat treatment diminishes the heterogeneous structure resulting in brittle behavior in tension. The analysis of strain tensor components based on changes in the first diffraction maximum of the structure function, q1, revealed that Ɛx, the strain perpendicular to the loading direction, changes from the compressive at near to the surface to the tensile mode at the center of the imprinted plate. In contrast, the strain component along the loading direction, Ɛy, changes from tensile near the surface to the compressive at the center. Beneath the surface, Ɛx reaches to values about 1.5% under the imprints where there is a negligible Ɛy. The distribution map of principal strains, Ɛ1 and Ɛ2, indicated that large regions with compressive Ɛ1 and Ɛ2 exist under the imprints which can result in blocking of the propagating shear bands in agreement with microstructural observations of shear banding after uniaxial tension. Moreover, the region beneath the border of the imprinted and un-imprinted parts has the highest residual shear strain. Microstructural observations indicated that such regions can nucleate new shear bands upon tensile loading of imprinted BMG plate. 3. Residual strain around a single shear band In order to probe structural changes in the shear-induced zone around a single shear band, the distribution of residual strains at short- and medium-range order around a single shear band was determined in cold-rolled BMG plate using the nano-focused high energy x-ray diffraction. Plastic deformation results in significant residual normal and shear strains at distances of more than 15 μm around the shear band. The residual normal strains exhibit an asymmetric distribution whereas the residual shear strain is distributed symmetrically around the shear band. The large amount of residual atomic shear strain magnitude at the vicinity of the shear band triggers the nucleation of the new shear bands. The coincidence of the direction of the nucleating secondary shear bands from the main shear band with the orientation of the residual shear strain at the vicinity of the mature shear band highlight the dominant role of the shear strain in determining further plastic deformation at regions near the shear band. / Im Rahmen dieser Arbeit wird hochenergetische Synchrotron Röntgenstrahlung zum Aufzeigen der strukturellen Veränderungen in plastisch verformtem Zr52.5Ti5Cu18Ni14.5Al10 metallischen Glas verwendet. Die Arbeit gliedert sich in drei Teile: Dehnungsentwicklung während in-situ Druckversuch, Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases, und Restdehnungen in der Umgebung eines einzenen Scherbandes. 1. Dehnungsentwicklung während in-situ Druckversuch Die während der Verformung auftretende strukturelle Neuordnung eines plastisch verformbaren metallischen Glases zeigt die Korrelation der elastischen und plastischen Verformung mit den strukturellen Änderungen in den Größenordnungen der Nah- (SRO) und mittelreichweitigen Ordnung (MRO). Im elastischen Bereich verändern sich die Atomabstände in der SRO linear mit der makroskopisch anliegenden Spannung. Die Untersuchung der Fläche unter der Radialen Verteilungsfunktion (RDF) deutet auf ein Aufbrechen eines geringen Anteils der Bindungen der ersten Schale in Druckspannungsrichtung und deren Neubildung quer dazu. Die atomaren Bindungen in der SRO erscheinen wesentlich steifer als in den MRO Schalen. Vergleicht man die Werte von elastischer Dehnung, E-Modul und Querkontraktionszahl mit ihren makroskopischen Gegenstücken erscheinen beide, SRO und MRO, wesentlich steifer. Dies zeigt, dass die elastische Verformung von metallischen Gläsern nicht nur von der einfachen Stauchung der Atome bzw. Atomgruppen bestimmt, sondern auch durch deren Neuanordnung unterstützt wird. Das Abweichen der Dehnungs-Spannungs-Korrelation vom linearen Verhalten in der MRO am Beginn der plastischen Verformung wird der irreversiblen Bildung von Schertransformations-zonen (STZ) zugeschrieben. Dies zeigt sich zudem in den erhöhten Scherdehnungswerten am Beginn der Dehngrenze, welche mit den in der Literatur berichteten Werten für die kritische Scherdehnung zum Bilden einer STZ übereinstimmen. Bei einem Atomabstand von 12,5 Å tritt der höchste Wert der Scherdehnung auf und markiert den effektivsten Längenbereich der STZ Bildung. Andererseits haben die atomaren Paare in der SRO mit der geringsten Scherdehnung den geringsten Beitrag an der STZ. Es zeigt sich außerdem, dass der typische Bruchwinkel dieses metallischen Glases über die Orientierung der maximalen Scherdehnung am Beginn der kritischen Scherbandbildung erklärt werden kann. 2. Dehnungsverteilung eines mechanisch geprägten massiven metallischen Glases Eine Prägung besteht darin, eine Platte metallischen Glases mit zwei Stempel, auf denen eine regelmäßige Anordnung von geradlinigen Kerben angebracht ist, zu belasten. Dadurch wird eine ebenso regelmäßige Anordnung von geradlinigen Kerben auf der Oberfläche des metallischen Glases erzeugt. Die plastische Verformbarkeit der Vit105 Platte im Zugversuch wird durch Prägung im Vergleich zur gegossenen Probe eindeutig verbessert. Die Untersuchung der Härte und des E-Moduls über den Querschnitt der geprägten Probe zeigt die Einbringung von Abwechselnd weichen und harten Regionen an der Oberfläche. Es wurden räumlich aufgelöste Dehnungskarten des geprägten metallischen Glases durch Beugung eines hochenergetischen nanometergroßen Röntgenstrahles erzeugt. Die Ergebnisse offenbaren, dass die durch Prägung eingebrachte plastische Verformung eine räumlich heterogene Atomanordnung erzeugt, welche aus starken Druck- und Zugdehnungsfeldern besteht. Zusätzlich wird eine signifikante Scherdehnung in die Probe eingebracht. Die Wärmebehandlung beseitigt diese heterogene Struktur und führt sie fast auf den Ausgangszustand zurück. Die Analyse der Dehnungstensorkomponenten basierend auf Änderungen im erstem Maximum des Strukturfaktors, q1, zeigt, dass sich Ɛx von der Oberfläche zur Mitte der Platte hin von einer Stauchung in eine Dehnung umwandelt. Im Gegensatz dazu wandelt sich die Komponente Ɛy von der Oberfläche zur Mitte der Platte hin von einer Dehnung in eine Stauchung um. An der Oberfläche unter den Eindrücken, wo Ɛy vernachlässigbar ist, erreicht Ɛx Werte von ca. 1.5 %. Die Verteilungskarten der Hauptdehnungen zeigt, dass beide e1 und e2 unterhalb der Kerben als Stauchungen vorhanden sind. Daraus resultiert das Blockieren und Ablenken der sich ausbreitenden Scherbänder, was an Zugproben im REM beobachtet werden kann. Weiterhin hat der Bereich an der Grenze der geprägten und nicht geprägten Regionen die höchste Restscherdehnung. Mikrostrukturelle Beobachtungen deuten darauf hin, dass solche Bereiche unter Zuglast Keimstellen für neue Scherbänder sind. 3. Restdehnungen in der Umgebung eines einzenen Scherbandes Es wurde ein einzelnes Scherband einer kaltgewalzte Platte mittels Beugung eines hochenergetischen nanometergroßen Röntgenstrahles untersucht. Die strukturellen Unterschiede in der scherinduzierten Zone um ein einzelnes Scherband werden durch die Verteilung der Restdehnungen in SRO und MRO bestimmt. Plastische Verformung führt zu signifikanten Restnormal- und Restscherdehnungen in Entfernungen von mehr als 15 µm um das Scherband. Die Restnormaldehnungen zeigen eine asymmetrische Verteilung, wohingegen die Restscherdehnungen auf beiden Seiten des Scherbandes symmetrisch verteilt sind. Der große Betrag der atomaren Restscherdehnung in der Nähe des Scherbandes führt zur Bildung von neuen Scherbändern. Das Zusammenfallen der Richtung des sich bildenden sekundären Scherbandes und der Orientierung der Restscherdehnung, in der Nähe des primären Scherbandes, demonstriert die dominierende Rolle der Scherdehnung bei weiterer plastischer Verformung in der Nähe des Scherbandes.