Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: See full text for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

published_or_final_version / Statistics and Actuarial Science / Master / Master of Philosophy

No description available.

Pagrindinis šio darbo tikslas susipažinti su steganografijos mokslu bei statistiniais stegoanalizės metodais, kurių dėka slepiama ir atrandama informacija įvairiuose failuose. Šitame magistro darbe išnagrinėti, aprašyti bei įgyvendinti du steganografijos ir du stegoanalizės metodai. Visi metodai realizuoti JAVA programavimo kalba, daliai matematiniams skaičiavimams atlikti panaudota MAPLE programa. Darbo pabaigoje pateikta metodų analizė. / The main goal of the thesis is to review the methods of steganography and steganalysis and to experiment with them. Steganography helps to embed hidden messages in such way that anyone except the intended recipient is unaware of the existence of the message but with the use of statistical steganalysis methods those hidden messages can be detected. This thesis consists of two steganography (LSB and LSBH) and two steganalysis methods (RS and PoV) description and implementation. All methods were implemented with JAVA code. Thesis is concluded with a comparison of these methods' quality.

Le modèle de Patterson et Capaldi (1990) stipule que les problèmes de comportement extériorisés (PCE) chez les enfants entrainent des échecs sociaux et scolaires qui, ensuite, augmentent le risque de dépression. Ce modèle a seulement été testé auprès d’enfants qui n’avaient pas nécessairement de PCE. La présente étude teste ce modèle auprès de 281 enfants (48 % de filles) dont le niveau de PCE atteint un seuil clinique. Les symptômes dépressifs ont été mesurés à l’entrée dans l’étude puis trois ans plus tard. Les prédicteurs sont la coercition parentale, les conflits avec l’enseignant, la victimisation par les pairs et les compétences scolaires. Les résultats des analyses de régression montrent que seules les compétences scolaires prédisent une hausse du score de dépression. Ce lien n’est pas modéré par le genre. Ces résultats suggèrent d’accorder une importance aux compétences scolaires pour la prévention ou la réduction des symptômes dépressifs.

This thesis describes the activation of small molecules using frustrated Lewis pairs, in particular investigating their use to reduce CO₂ to methanol, thus producing a new route towards a renewable fuel. Chapter One summarises the requirement for a renewable fuel source, the alternative methods currently available and previous research conducted into converting CO₂ to methanol using FLPs and other reducing agents. Chapter Two describes the synthesis of a new family of electron-deficient tris(aryl)boranes, B(C₆F₅)_3-x(C₆Cl₅)_x (x = 1-3), allowing the electronic effects, resulting from the gradual replacement of C₆F₅ with C₆Cl₅ ligands, to be studied. The novel Lewis acids have been fully characterised and their Lewis acidities have been determined using NMR spectroscopy, electrochemistry and DFT studies. Chapter Three discusses the synthesis of nine novel FLPs and their use to successfully split H2. Each borohydride salt has been spectroscopically fully characterised and five of the salts have been characterised using single crystal X-ray diffraction. To determine the exact positions of the H atoms, single crystal neutron diffraction and DFT experiments were carried out on [1-H][H-TMP]. Chapter Four details attempts to use the borohydride salts, synthesised in Chapter Three, to reduce CO₂ to methanol. Each experiment was been fully investigated and their catalytic viability was determined. The X-ray crystal structure of [1-OCHO][H-TMP] is described and each formatoborate and methoxyborate salt were fully characterised. Chapter Five describes experimental procedures and characterisation data.

The Bogoliubov theory of excitations in superfluid helium is used to study collective modes at zero temperature. A repulsive delta function shell potential is used in the quasiparticle excitation energy spectrum to fit the observed elementary excitation spectrum, except in the plateau region. The linearized equation of motion method is used to obtain the secular equation for a collective mode consisting of a linear combination of one and two free quasiparticles of zero total momentum. It is shown that in this case for high-lying collective modes, vertices involving three quasiparticles cancel, and only vertices involving four quasiparticles are important. A decomposition into various angular momentum states is then made. Bound roton pairs in the angular momentum D-state observed in light-scattering experiments exist only for an attractive coupling between helium atoms in this oversimplified model. Thus, the interaction between particles can be reinterpreted as a phenomenological attractive coupling between quasiparticles, in order to explain the Raman scattering from bound roton pairs in superfluid helium.

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Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

This thesis analyzes the performance and process of constructing portfolios of cryptocurrency pairs based on cointegrated relationships indicated by the Augmented Dickey-Fuller test, Johansen’s test and Phillips Peron’s test. Pairs are tested for cointegration over a 3-month and a 6-month window and then traded over a trading window of the same length. The cryptocurrencies included in the study are 14 cryptocurrencies with the highest market capitalization on April 24th 2019. One trading strategy has been applied on every portfolio following the 3-month and the 6-month methodology with thresholds at 1.75 and stop-losses at 4 standard deviations. The performance of each portfolio is compared with their corresponding buy and hold benchmark. All portfolios outperformed their buy and hold benchmark, with and without transaction costs set to 2%. Following the 3-month methodology was superior to the 6- month method and the portfolios formed through Phillips Peron’s test had the highest return for both window methods.