[EN] The scope of this thesis is the abstract finite group theory. All the groups we will consider will be finite. hence, the word "group" will be understood as a synonimous of "finite group". We say that a subgroup H of a group G is solitary when no other subgroup of G is isomorphic to H. A normal subgroup H of a group G is said to be normal solitary when no other normal subgroup of G is isomorphic to H. A normal subgroup N of a group G is said to be quotient solitary when no other normal subgroup K of G gives a quotient isomorphic to G/N. Solitary subgroups, normal solitary subgroups, and quotient solitary subgroups have been recently studied by authors like Thévenaz, who named the solitary subgroups as strongly characteristic subgroups, Kaplan and Levy, Tarnauceanu, and Atanasov and Foguel. The aim of this PhD thesis project is to deepen into the analysis of these subgroup embedding properties, by refining the knowledge of their lattice properties, by obtaining general properties related to classes of groups, and by analysing groups in which the members of some distinguished families of subgroups satisfy these embedding properties. The basic results of group theory that will be used in the memoir appear in Chapter 1. Among them, we comment on some results about soluble groups, supersoluble groups, nilpotent groups, classes of groups, and p-soluble and p-nilpotent groups for a prime p. In Chapter 2, we present the basic concepts about these embedding properties, as well as some basic results satisfied by them. Chapter 3 is devoted to the study of lattice properties of these types of subgroups. In this chapter we deepen into the study of the lattices of solitary subgroups and quotient solitary subgroups developed by Kaplan and Levy and by Tarnauceanu and we check that, even though these lattices consist of normal subgroups, they are not sublattices of the lattice of normal subgroups. We also check that the set of all normal solitary subgroups does not constitute a lattice, which motivates the introduction of the concept of subnormal solitary subgroup as a more suitable tool to deal with lattice properties. In Chapter 4, we study in depth the relations between these embedding properties and classes of groups. We observe that the subnormal solitary subgroups behave well with respect to radicals for Fitting classes and that the residuals for formations are quotient solitary subgroups. We also study conditions under which the radicals with respect to Fitting classes are quotient solitary subgroups and the residuals with respect to formations are solitary subgroups. To finish, we state the natural question of whether the solitary or subnormal solitary subgroups can be regarded as radicals for suitable Fitting classes or whether the quotient solitary subgroups are residuals for suitable Fitting classes. We give a negative answer to this question. Chapter 5 is devoted to the study of groups whose minimal subgroups are solitary, that is, groups with a unique subgroup of order p for each prime p dividing its order. We give a complete classification of these groups and we make some remarks about related problems. Our contributions to this research line have been accepted for their publication in two papers in Communications in Algebra and in Journal of Algebra and its Applications. / [ES] El ámbito de esta tesis es el de la teoría abstracta de grupos finitos. Todos los grupos que consideremos serán finitos. Por ello, la palabra «grupo» se entenderá como sinónima de «grupo finito». Decimos que un subgrupo H de un grupo G es solitario cuando ningún otro subgrupo de G es isomorfo a H. Un subgrupo normal H de un grupo G se dice normal solitario cuando ningún otro subgrupo normal de G es isomorfo a H. Un subgrupo normal N de un grupo G se dice que es solitario para cocientes cuando ningún otro subgrupo normal K de G da un cociente isomorfo a G/N. Los subgrupos solitarios, los subgrupos normales solitarios y los subgrupos solitarios para cocientes han sido recientemente estudiados por autores como Thévenaz, quien bautizó los subgrupos solitarios como subgrupos fuertemente característicos, Kaplan y Levy, Tarnauceanu y Atanasov y Foguel. El objeto de este proyecto de tesis doctoral es el de profundizar en el análisis de estas propiedades de inmersión de subgrupos, afinando en el conocimiento de sus propiedades reticulares, obteniendo propiedades generales en relación con clases de grupos y analizando grupos en los que los miembros de algunas familias destacadas de subgrupos satisfacen estas propiedades de inmersión. Los resultados básicos de teoría de grupos que se utilizan en la memoria aparecen en el capítulo 1. Entre ellos, comentamos algunos resultados sobre grupos resolubles, superresolubles, nilpotentes, clases de grupos y grupos p-resolubles y p-nilpotentes para un primo p. En el capítulo 2 presentamos los conceptos básicos sobre estas propiedades de inmersión, así como algunos resultados básicos que satisfacen. El capítulo 3 está dedicado al estudio de propiedades reticulares de estos tipos de subgrupos. En este capítulo se profundiza en el estudio de los retículos de subgrupos solitarios y solitarios para cocientes llevado a cabo por Kaplan y Levy y por Tarnauceanu y se comprueba que, a pesar de que estos retículos constan de subgrupos normales, no son subretículos del retículo de subgrupos normales. También comprobamos que el conjunto de subgrupos normales solitarios no constituye un retículo, lo que motiva la introducción del concepto de subgrupo subnormal solitario como herramienta más adecuada para tratar propiedades reticulares. En el capítulo 4 estudiamos con profundidad las relaciones entre estas propiedades de inmersión y clases de grupos. Observamos que los subgrupos subnormales solitarios se comportan bien respecto de radicales de clases de Fitting y que los residuales para formaciones son subgrupos solitarios para cocientes. Esto permite mejorar algunos resultados sobre subgrupos solitarios para cocientes. También estudiamos condiciones en que los radicales respecto de clases de Fitting son subgrupos solitarios para cocientes y los residuales respecto de formaciones son subgrupos solitarios. Por último, nos planteamos la cuestión natural de si los subgrupos solitarios o subnormales solitarios pueden verse como radicales para clases de Fitting adecuadas o si los subgrupos solitarios para cocientes son residuales para clases de Fitting adecuadas. Damos una respuesta negativa a esta cuestión. El capítulo 5 está dedicado al estudio de grupos cuyos subgrupos minimales son solitarios, es decir, grupos con un único subgrupo de orden p para cada primo p divisor de su orden. Damos una clasificación completa de estos grupos y hacemos algunas observaciones sobre problemas relacionados. Nuestras aportaciones a esta línea de investigación han sido aceptadas para su publicación en dos artículos en Communications in Algebra y en Journal of Algebra and its Applications. / [CA] L'àmbit d'aquesta tesi és el de la teoria abstracta de grups finits. Tots els grups que hi considerem seran finits. Per això, la paraula «grup» s'entendrà com a sinònima de «grup finit». Direm que un subgrup H d'un grup G és solitari quan cap altre subgrup de G no és isomorf a H. Un subgrup normal H d'un grup G es diu normal solitari quan cap altre subgrup normal de G no és isomorf a H. Un subgrup normal N d'un grup G es diu que és solitari per a quocients quan cap altre subgrup normal K de G no dóna un quocient isomorf a G/N. Els subgrups solitaris, els subgrups solitaris normals i els subgrups solitaris per a quocients han sigut recentment estudiats per autors com Thévenaz, qui batejà els subgrups solitaris com a subgrups fortament característics, Kaplan i Levy, Tarnauceanu i Atanasov i Foguel. L'objecte d'aquest projecte de tesi doctoral és el d'aprofundir en l'anàlisi d'aquestes propietats d'immersió de subgrups, afinant en el coneixement de les seues propietats reticulars, obtenint propietats generals en relació amb classes de grups i analitzant grups en què els membres d'algunes famílies destacades de subgrups satisfan aquestes propietats d'immersió. Els resultats bàsics de teoria de grups que es fan servir en la memòria apareixen al capítol 1. Entre ells, comentem alguns resultats sobre grups resolubles, superresolubles, nilpotents, classes de grups i grups p-resolubles i p-nilpotents per a un primer p. Al capítol 2 presentem els conceptes bàsics sobre aquestes propietats d'immersió, així com alguns resultats bàsics que satisfan. El capítol 3 està dedicat a l'estudi de propietats reticulars d'aquests tipus de subgrups. En aquest capítol s'aprofundeix en l'estudi dels reticles de subgrups solitaris i solitaris per a quocients dut a terme per Kaplan i Levy i per Tarnauceanu i es comprova que, encara que aquests subgrups consten de subgrups normals, no són subreticles del reticle de subgrups normals. També comprovem que el conjunt de subgrups normals solitaris no constitueix un reticle, la qual cosa motiva la introducció del concepte de subgrup subnormal solitari com a eina més adient per tractar propietats reticulars. Al capítol 4 estudiem amb profunditat les relacions entre aquestes propietats d'immersió i classes de grups. Observem que els subgrups subnormals solitaris es comporten bé respecte de radicals de classes de Fitting i que els residuals per a formacions són subgrups solitaris per a quocients. Açò permet millorar alguns resultats sobre subgrups solitaris per a quocients. També estudien condicions en què els radicals respecte de classes de Fitting són subgrups solitaris per a quocients i els residuals respecte de formacions són subgrups solitaris. Per acabar, ens plantegem la qüestió natural de si els subgrups solitaris o subnormals solitaris poden veure's com a radicals per a classes de Fitting adients o si els subgrups solitaris per a quocients són residuals per a classes de Fitting adients. Donem una resposta negativa a aquesta qüestió. El capítol 5 està dedicat a l'estudi de grups els subgrups minimals dels quals són solitaris, és a dir, grups amb un únic subgrup d'ordre p per a cada primer p divisor del seu ordre. Donem una classificació completa d'aquests grups i fem algunes observacions sobre problemes relacionats. Les nostres aportacions a aquesta línia de recerca han sigut acceptades per a llur publicació a dos articles a Communications in Algebra i a Journal of Algebra and its Applications. / Liriano Castro, ODCDJ. (2015). Subgrupos solitarios de grupos finitos [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59397

In Abhängigkeit von der Suspensionszusammensetzung und der jeweiligen Scherrate können konzentrierte Kaolinsuspensionen ungewöhnliche rheologische Phänomene wie Oszillationen der scheinbaren Viskosität oder eine negative 1.~Normalspannungsdifferenz zeigen. In dieser Arbeit wurde die Abhängigkeit der 1.~Normalspannungsdifferenz, des Speicher- und des Verlustmoduls im linear-viskoelastischen Bereich sowie der Fließgrenze von der Oberflächenbeladung des Kaolins, von der Kaolinfeststoffkonzentration, vom pH-Wert und von der Ionenstärke untersucht. Weiterhin wurde eine Methode entwickelt, die die Fixierung der scherinduzierten Mikrostruktur der Suspensionen und deren anschließende Charakterisierung mittels Röntgenbeugung gestattet. Außerdem wurde ein rheologisches Modell abgeleitet, das den Zusammenhang zwischen den Aussagen zur scherinduzierten Mikrostruktur und dem Auftreten negativer 1.~Normalspannungsdifferenzen herstellt.

Idiopathic normal pressure hydrocephalus (INPH) is a dementia treatable by insertion of a cerebrospinal fluid shunt. It has been suggested that INPH has similar pathophysiological mechanisms as cerebrovascular disease, but the vascular risk factor (VRF) profile of INPH patients has not been assessed using a modern epidemiological approach. The cognitive symptoms of INPH resemble the symptoms of depression, but the prevalence of depression among INPH patients is unknown. In addition, few studies investigate the impact of shunting on the quality of life (QoL), and no study has investigated the impact of comorbidity on QoL in INPH patients. The objective of this dissertation was to present the VRF profile of INPH and to investigate the hypothesis that INPH may be a subgroup of vascular dementia. Additional objectives were to assess the prevalence of depression in INPH patients and to investigate the impact of shunting and comorbidities on QoL in INPH. In the first cohort, the prevalence of possible INPH was assessed through clinical and radiological examinations in patients with a transient ischemic attack (TIA), consecutively admitted to the same hospital during 2006-2008. In the second cohort, VRFs, vascular disease and QoL were analysed in INPH patients consecutively shunted 2008-2010 in five out of six neurosurgical centres in Sweden. Patients remaining after inclusion (n=176, within the age-span 60-85 years and not having dementia) were compared to population-based age- and gender-matched controls (n=368, same inclusion criteria as for the INPH patients). Assessed VRFs were: hypertension, diabetes, obesity, hyperlipidemia, psychosocial factors (stress and depression), smoking, alcohol intake, physical activity and, dietary pattern. Cardiovascular, cerebrovascular and peripheral vascular disease as well as QoL were also assessed. Parameters were assessed through questionnaires, clinical examinations, measurements, ECG and, blood samples. In the first cohort, 4% of the TIA patients had clinically and radiologically verified INPH. In the second cohort, VRFs were overrepresented among the INPH patients compared with the controls. The VRFs independently associated with INPH were: hyperlipidemia (Odds ratio (OR): 2.4, 95%CI: 1.4-4.0), diabetes (OR: 2.2, 95%CI: 1.2-3.9), obesity (OR: 5.4, 95%CI: 2.5-11.8) and, psychosocial factors (OR: 5.3, 95%CI: 3.2-8.9). When adding the VRFs that were overrepresented in INPH, although not independently (physical inactivity and hypertension), these six VRFs accounted for 24% of the INPH cases in the elderly population (population attributable risk %: 24). Depression was overrepresented in shunted INPH patients compared to the controls (46% vs. 13%, p<0.001) and the main predictor for low QoL was a coexisting depression (p<0.001). In conclusion, the results of the INPH-CRasH study are consistent with a vascular pathophysiological component of INPH and indicate that INPH may be subgroup of vascular dementia. In clinical care and research, a complete risk factor analysis as well as screening for depression and a measurement for quality of life should be included in the work-up of INPH patients. The effect of targeted interventions against modifiable VRFs and anti-depressant treatment in INPH patients should be evaluated. / Idiopatisk normaltryckshydrocefalus (INPH, från engelskans ”idiopathic normal pressure hydrocephalus”) är en neurokirurgiskt behandlingsbar demens. Behandlingen är att operera in en shunt som dränerar cerebrospinalvätska från ventriklarna. Det har föreslagits att INPH skulle kunna orsakas av liknande patofysiologiska mekanismer som vid cerebrovaskulär sjukdom, men den vaskulära riskfaktorprofilen hos INPH-patienter har aldrig undersökts i en modern epidemiologisk studie. De kognitiva symtomen vid INPH påminner om symtomen vid depression, men prevalensen av depression hos INPH-patienter är okänd. Få studier undersöker hur shuntning påverkar livskvalitet och ingen studie har undersökt hur komorbiditet påverkar livskvaliteten vid INPH. Syftet med den här avhandlingen var att undersöka den vaskulära riskfaktorprofilen hos INPH-patienter samt att utforska hypotesen att INPH skulle kunna vara en undergrupp till vaskulär demens. Ytterligare ett syfte med avhandlingen var att undersöka hur många INPH-patienter som har depression samt undersöka hur shunting och komorbiditet påverkar livskvalitet vid INPH. I den första kohorten undersöktes kliniska och radiologiska fynd som tydde på INPH hos de patienter som blivit diagnostiserade med en TIA (från engelskans: transient ischemic attack) 2006-2008 på Norrlands Universitetssjukhus i Umeå. I den andra kohorten undersöktes konsekutivt shuntade INPH-patienter 2008-2010 från fem av sex neurokirurgiska kliniker i Sverige. De patienter som inkluderades i studien (n=176, ålder: 60-85 år, ej dementa) jämfördes med köns- och åldersmatchade kontroller från normalpopulationen (n=368, samma inklusionskriterier som för INPH-patienterna). De riskfaktorer som undersöktes var: hypertension, hyperlipidemi, diabetes, fetma, psykosociala faktorer (stress och depression), rökning, alkohol, fysisk aktivitet och diet. Även kardiovaskulära och cerebrovaskulära sjukdomar undersöktes, liksom perifer vaskulär sjukdom samt livskvalitet. Datainsamling skedde genom frågeformulär, kliniska undersökningar, mätningar, EKG och blodprov. I den första kohorten hade 4% av TIA-patienterna kliniskt och radiologiskt verifierad INPH. I den andra kohorten var vaskulära riskfaktorer överrepresenterade hos INPH-patienterna jämfört med iv normalpopulationen. Hyperlipidemi (OR: 2.4, 95%CI: 1.4-4.0), diabetes (OR: 2.2, 95%CI: 1.2-3.9), fetma (OR: 5.4, 95%CI: 2.5-11.8) och psykosociala faktorer (OR: 5.3, 95%CI: 3.2-8.9) var associerade med INPH oberoende av kön, ålder och de andra riskfaktorerna. Hypertension och fysisk inaktivitet var också associerade med INPH, dock inte oberoende av övriga riskfaktorer. Sammanlagd PAR% (från engelskans: population attributable risk %) för de här sex riskfaktorerna var 24%. INPH-patienterna hade depression i högre utsträckning än kontrollerna (46% vs. 13%, p<0.001), och depression var den viktigaste prediktorn för låg livskvalitet. Resultaten tyder på att vaskulär sjukdom och vaskulära riskfaktorer är involverade i den patofysiologiska mekanismen vid INPH. INPH kan vara en undergrupp till vaskulär demens. En fullständig riskfaktoranalys och screening för depression bör ingå i den preoperativa utvärderingen såväl som i forskning på INPH-patienter, och ett mått på livskvalitet bör införas. Effekten av riktade insatser mot såväl vaskulära riskfaktorer som depression vid INPH bör utvärderas.

Insolvenzprognosen und Ratings sind wichtige Aufgaben der Finanzbranche und dienen der Kreditwürdigkeitsprüfung von Unternehmen. Eine Möglichkeit dieses Aufgabenfeld anzugehen, ist maschinelles Lernen. Dabei werden Vorhersagemodelle aufgrund von Beispieldaten aufgestellt. Methoden aus diesem Bereich sind aufgrund Ihrer Automatisierbarkeit vorteilhaft. Dies macht menschliche Expertise in den meisten Fällen überflüssig und bietet dadurch einen höheren Grad an Objektivität. Allerdings sind auch diese Ansätze nicht perfekt und können deshalb menschliche Expertise nicht gänzlich ersetzen. Sie bieten sich aber als Entscheidungshilfen an und können als solche von Experten genutzt werden, weshalb interpretierbare Modelle wünschenswert sind. Leider bieten nur wenige Lernalgorithmen interpretierbare Modelle. Darüber hinaus sind einige Aufgaben wie z.B. Rating häufig Mehrklassenprobleme. Mehrklassenklassifikationen werden häufig durch Meta-Algorithmen erreicht, welche mehrere binäre Algorithmen trainieren. Die meisten der üblicherweise verwendeten Meta-Algorithmen eliminieren jedoch eine gegebenenfalls vorhandene Interpretierbarkeit. In dieser Dissertation untersuchen wir die Vorhersagegenauigkeit von interpretierbaren Modellen im Vergleich zu nicht interpretierbaren Modellen für Insolvenzprognosen und Ratings. Wir verwenden disjunktive Normalformen und Entscheidungsbäume mit Schwellwerten von Finanzkennzahlen als interpretierbare Modelle. Als nicht interpretierbare Modelle werden Random Forests, künstliche Neuronale Netze und Support Vector Machines verwendet. Darüber hinaus haben wir einen eigenen Lernalgorithmus Thresholder entwickelt, welcher disjunktive Normalformen und interpretierbare Mehrklassenmodelle generiert. Für die Aufgabe der Insolvenzprognose zeigen wir, dass interpretierbare Modelle den nicht interpretierbaren Modellen nicht unterlegen sind. Dazu wird in einer ersten Fallstudie eine in der Praxis verwendete Datenbank mit Jahresabschlüssen von 5152 Unternehmen verwendet, um die Vorhersagegenauigkeit aller oben genannter Modelle zu messen. In einer zweiten Fallstudie zur Vorhersage von Ratings demonstrieren wir, dass interpretierbare Modelle den nicht interpretierbaren Modellen sogar überlegen sind. Die Vorhersagegenauigkeit aller Modelle wird anhand von drei in der Praxis verwendeten Datensätzen bestimmt, welche jeweils drei Ratingklassen aufweisen. In den Fallstudien vergleichen wir verschiedene interpretierbare Ansätze bezüglich deren Modellgrößen und der Form der Interpretierbarkeit. Wir präsentieren exemplarische Modelle, welche auf den entsprechenden Datensätzen basieren und bieten dafür Interpretationsansätze an. Unsere Ergebnisse zeigen, dass interpretierbare, schwellwertbasierte Modelle den Klassifikationsproblemen in der Finanzbranche angemessen sind. In diesem Bereich sind sie komplexeren Modellen, wie z.B. den Support Vector Machines, nicht unterlegen. Unser Algorithmus Thresholder erzeugt die kleinsten Modelle während seine Vorhersagegenauigkeit vergleichbar mit den anderen interpretierbaren Modellen bleibt. In unserer Fallstudie zu Rating liefern die interpretierbaren Modelle deutlich bessere Ergebnisse als bei der zur Insolvenzprognose (s. o.). Eine mögliche Erklärung dieser Ergebnisse bietet die Tatsache, dass Ratings im Gegensatz zu Insolvenzen menschengemacht sind. Das bedeutet, dass Ratings auf Entscheidungen von Menschen beruhen, welche in interpretierbaren Regeln, z.B. logischen Verknüpfungen von Schwellwerten, denken. Daher gehen wir davon aus, dass interpretierbare Modelle zu den Problemstellungen passen und diese interpretierbaren Regeln erkennen und abbilden.

Consider a network which consists of noiseless point to point channels. In this network, the source node wants to send messages to a specific set of sink nodes. If an intermediate node v has just one input channel then the received symbol by that node can be replicated and sent to the outgoing channels from v. If v has at least two incoming channels then it has two options. It can either send the received symbols one-by-one, one symbol in each time unit, or v can transmit a combination of the received symbols. The former choice takes more time compared to the latter option, which is called network coding. In the literature, it has been shown that in a single source finite acyclic network the maximum throughput can be achieved by using linear network codes. Significant effort has been made to efficiently construct good network codes. In addition, a polynomial time algorithm for constructing a linear network code on a given network was introduced. Also an algorithm for constructing a linear multicast code on an acyclic network was introduced. Finally, a method for finding a representation matrix for the network matroid of a given network G was also introduced. This matrix can be used to construct a generic code. In this thesis we first provide a review of some known methods for constructing linear multicast, broadcast and dispersion codes for cyclic and acyclic networks. We then give a method for normalization of a non-normal code, and also give a new algorithm for constructing a linear multicast code on a cyclic network. The construction of generic network codes is also addressed. / Graduate / 0984 / 0544 / esmaeili@uvic.ca

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Different types of live loading due to traffic may act on bridges. The focus of this study is on normal traffic loading according to the South African specification of TMH7. Heavy vehicles are not included in normal traffic loading. TMH7 represents the code of practice for the design of highway bridges and culverts in South Africa. The aim of the study is to provide an insight into the flexural analysis of skew bridges, under the effects of normal traffic loading. The need for the study arose since the specification of TMH7 does not explicitly specify application patterns for normal traffic loading. Only the intensity of normal traffic loading is specified and it should be applied to yield the most adverse effects. For these reasons, a set of so-called standard application patterns are investigated and developed through the course of this study. The envelope of the values from the standard application patterns are compared to the most adverse application pattern for flexural effects in certain design regions of the bridge deck. Flexure, as in the context of this study, translates into the bending and twisting of the bridge deck under loads. A number of numerical experiments are performed for typical single span and multi-span continuous carriageways, where the standard application patterns are compared to the most adverse application patterns. The results from the numerical experiments are documented and compared as the angle of skew of the bridge deck increases in plan-view. For this purpose, the development of effective and specialized software was necessary. It was found that the set of standard application patterns can be used as a preliminary approximation for the most adverse effects of normal traffic loading, for specific flexural resultants in certain design regions of a bridge deck. However, for a large number of secondary flexural effects, the set of standard application patterns did not represent a good approximation for the most adverse values. / AFRIKAANSE OPSOMMING: Verskillende tipes lewendige belasting, as gevolg van verkeer, kan op brûe inwerk. Die fokus van die studie is op normale verkeers-belasting volgens die Suid-Afrikaanse spesifikasie van TMH7. Swaar-voertuie word nie ingesluit by normale verkeers-belasting nie. TMH7 verteenwoordig die kode vir die ontwerp van padbrûe en duikers in Suid-Afrika. Die doel van die studie is om insig te verskaf in die buig-analise van skewe brûe, as gevolg van die werking van normale verkeers-belasting. Die rede vir hierdie studie ontstaan aangesien die spesifikasie van TMH7 nie eksplisiet aanwendingspatrone vir normale verkeers-belasting voorskryf nie. Slegs die intensiteit van normale verkeersbelasting word voorgeskryf en dit moet aangewend word om die negatiefste effekte te verkry. Vir hierdie redes word 'n versameling van sogenaamde standaard aanwendings-patrone deur die loop van die studie ondersoek en ontwikkel. Die omhullings-kurwe van die waardes wat deur die standaard patrone gelewer word, word vergelyk met die waarde van die aanwendings-patroon wat die negatiefste buig-effek in sekere ontwerp-areas van die brugdek veroorsaak. Buig-effekte, soos van toepassing op hierdie studie, verwys na buig en wring van die brugdek as gevolg van belastings. 'n Aantal numeriese eksperimente, vir enkel-span sowel as multi-span deurlopende brugdekke, word uitgevoer en die standaard aanwendings-patrone word vergelyk met die aanwendings-patrone wat die negatiefste waardes lewer. Die resultate van die numeriese eksperimente word gedokumenteer en vergelyk soos die hoek van skeefheid van die brugdek in plan-aansig toeneem. Vir hierdie doel is die ontwikkeling van effektiewe en gespesialiseerde sagteware dus nodig. Daar is gevind dat die standaard aanwendings-patrone, vir spesifieke buig-resultante in sekere ontwerp-areas van die brugdek, as 'n voorlopige benadering vir die negatiefste effekte van normale verkeers-belasting gebruik kan word. Dit was egter verder gevind dat vir 'n groot aantal sekondêre buig-effkte, die versameling standaard aanwendings-patrone nie as 'n goeie benadering vir die negatiefste waardes dien nie.

<p>In 1998 the Swedish mathematician Warwick Tucker used rigorous interval arithmetic and normal form theory to prove the existence of a strange attractor in the Lorenz system. In large parts, that proof consists of computations implemented and performed on a computer. This thesis is an independent numerical verification of the result obtained by Warwick Tucker, as well as a study of a higher-dimensional system of ordinary differential equations introduced by the Swedish physicist Lennart Stenflo.</p><p>The same type of mapping data as Warwick Tucker obtained is calculated here via a combination of numerical integration, solving optimisation problems and a coordinate change that brings the system to a normal form around the stationary point in the origin. This data is collected in a graph and the problem of determining the existence of a strange attractor is translated to a few graph theoretical problems. The end result, after the numerical study, is a support for the conclusion that the attractor set of the Lorenz system is a strange attractor and also for the conclusion that the Lorenz-Stenflo system possesses a strange attractor.</p>

For repeated transient solutions of geometrically nonlinear structures the numerical effort often poses a major obstacle. Thus, the introduction of a reduced order model, which takes the nonlinear effects into account and accelerates the calculations considerably, is often necessary.This work yields a method that allows for rapid, accurate and parameterisable solutions by means of a reduced model of the original structure. The structure is discretised and its dynamic equilibrium described by a matrix equation. The projection on a reduced basis is introduced to obtain the reduced model. A comprehensive numerical study on several common reduced bases shows that the simple introduction of a constant basis is not sufficient to account for the nonlinear behaviour. Three requirements for an rapid, accurate and parameterisable solution are derived. The solution algorithm has to take into account the nonlinear evolution of the solution, the solution has to be independent of the nonlinear finite element terms and the basis has to be adapted to external parameters.Three approaches are provided, each responding to one requirement. These approaches are assembled to the integrated method. The approaches are the update and augmentation of the basis, the polynomial formulation of the nonlinear terms and the interpolation of the basis. A Newmark-type time-marching algorithm provides the frame of the integrated method. The application of the integrated method on test-cases with geometrically nonlinear finite elements confirms that this method leads to the initial aim of a rapid, accurate and parameterisable transient solution.

This thesis examines the impact of urban water infrastructure on the Ottawa River through an exploration of the City of Ottawa's historical development from the early modern period to the present. The primary aim is to explain how the Ottawa River came to be removed or ignored from the City of Ottawa's urban development strategy. The thesis focuses on the periods of 1910-1920 (early modernity) and 1999-2012 (present). The theories applied are risk, risk management, normal accident theory and the politics of infrastructure. The data and information for this thesis were primarily retrieved from the City of Ottawa website as well as from the archives of the City of Ottawa. The thesis identifies several factors explaining why the Ottawa River has been mistreated over time, as well as the challenges involved in reforming present-day practices and infrastructure. Several recommendations to fix the situation are advanced.

With the advent of quantum computers, the security of number-theoretic cryptography has been compromised. Consequently, new cryptosystems have been suggested in the field of non-commutative group theory. In this thesis, we provide all the necessary background to understand and work with the Artin groups. We then show that Artin groups of finite type and Artin groups of large type possess an easily-computable normal form by explicitly writing the algorithms. This solution to the word problem makes these groups candidates to be cryptographic platforms. Finally, we present some combinatorial problems that can be used in group-based cryptography and we conjecture, through empirical evidence, that the conjugacy problem in Artin groups of large type is not a hard problem.