Time-optimal solutions provide us with the fastest means to regulate a system in presence of input constraints. This advantage of time-optimal control solutions is offset by the fact that their real-time implementation involves computationally intensive iterative techniques. Moreover, time-optimal controls depend on the initial state and have to be recalculated for even the slightest perturbation. Clearly time-optimal controls are not good candidates for online regulation. Consequently, the search for alternatives to time-optimal solutions is a very active area of research. The work described here is inspired by the simplicity of optimal-aim concept. The "optimal-aim strategies" provide online regulation in presence of bounded inputs with minimal computational effort. These are based purely on state-space geometry of the plant and are inherently adaptive in nature. Optimal-aim techniques involve aiming of trajectory derivative (or the state velocity vector) so as to approach the equilibrium state in the best possible manner. This thesis documents the efforts to develop an online regulation algorithm for systems with input constraints. Through a number of hypotheses focussed on trying to reproduce the exact time-optimal solution, the diffculty associated with this task is demonstrated. A modification of optimal-aim concept is employed to develop a novel regulation algorithm. In this algorithm, aim directions are chosen in a special manner to generate the time-optimal control approximately. The control scheme thus developed is shown to be globally stabilizing for systems having eigenvalues in the CLHP (closed left half-plane). It is expected that this method or its modifications can be extended to higher dimensional systems as a part of future research. An alternative control algorithm involving a simple state-space aiming concept is also developed and discussed.

Iterative rounding has been an increasingly popular approach to solving network design optimization problems ever since Jain introduced the concept in his revolutionary 2-approximation for the Survivable Network Design Problem (SNDP). This paper looks at several important iterative rounding approximation algorithms and makes improvements to some of their proofs. We generalize a matrix restatement of Nagarajan et al.'s token argument, which we can use to simplify the proofs of Jain's 2-approximation for SNDP and Fleischer et al.'s 2-approximation for the Element Connectivity (ELC) problem. Lau et al. show how one can construct a (2,2B + 3)-approximation for the degree bounded ELC problem, and this thesis provides the proof. We provide some structural results for basic feasible solutions of the Prize-Collecting Steiner Tree problem, and introduce a new problem that arises, which we call the Prize-Collecting Generalized Steiner Tree problem.

We consider the lower-bounded facility location (LBFL) problem (, also known as load-balanced facility location), which is a generalization of uncapacitated facility location (UFL) problem where each open facility is required to serve a minimum number of clients. More formally, in the LBFL problem, we are given a set of clients Ɗ , a set of facilities Ƒ, a non-negative facility-opening cost f_i for each i ∈ Ƒ, a lower bound M, and a distance metric c(i,j) on the set Ɗ ∪ Ƒ, where c(i,j) denotes the cost of assigning client j to facility i. A feasible solution S specifies the set of open facilities F_S ⊆ Ƒ and the assignment of each client j to an open facility i(j) such that each open facility serves at least M clients. Our goal is to find feasible solution S that minimizes ∑_{i ∈ F_S} f_i + ∑_j c(i,j). The current best approximation ratio for LBFL is 550. We substantially advance the state-of-the-art for LBFL by devising an approximation algorithm for LBFL that achieves a significantly-improved approximation guarantee of 83.

A comprehensive experimental study has been conducted using Particle Image Velocimetry (PIV) for a wide array of ventilation schemes and mining configurations for the purpose of examining ventilation characteristics in dead end mine headings. Flow behaviors in two basic mining sequences of box and slab cuts for 30 ft and 60 ft deep cuts were studied. The present thesis discusses the effect for various geometric and flow parameters including the variation of inlet flow velocities, entry heights, face zone widths and curtain widths on the flow behavior. The Reynolds number Re considered for this study ranges from 1 105 to 3 106 based on curtain width and exit velocity. The variation of the face zone and the curtain widths considerably affected the flow behavior, resulting in recirculation regions in the face area for critical combinations. Jet spreading angles and virtual origins have been calculated for the different geometries showing that an optimum range of face and curtain widths exists. A detailed discussion employing various scenarios for exhaust ventilation systems has also been made. Full-size measurements and comparison of the experimental data with numerical simulations is presented. Implementation of machine-mounted scrubbers in the blowing system are discussed for different values of the ventilation ratios (Qs/Qin) ranging from 14% to 53%. The scrubber system, typically introduced for dust collection, is also shown to be a useful tool in providing adequate ventilation to the immediate face area.

Prepay or pay-as-you-go programs are an increasingly popular type of rate plan offered by electric utilities. Under these plans, ratepayers must keep a positive balance at all times to avoid being automatically disconnected, they are charged daily for their usage, and they are provided with a means to monitor their consumption. One of the suggested benefits of these plans is that they allow electricity consumers to better manage their usage. Using household level monthly usage data from customers enrolled in prepay programs at two Kentucky rural electric cooperatives, we investigate whether there is a change in consumption after these customers enrolled in the program. To address this question, we employ a fixed-effects model. The results of our model indicate that prepay customers reduce their consumption by an average of 11% after enrolling in the program. We also find that this response is larger during periods of high or low temperatures than during mild weather. Furthermore, we find evidence that the prepayment effect diminishes over the length of time that a customer is enrolled in the program.

Problembakgrund & problemdiskussion: I dagens informationssamhälle finns det oändligt med möjligheter att nå information. Dels genom traditionell media i form av papperstidningar, men också genom webbaserade plattformar i mobiltelefonen, surfplattan och datorn. För investerare innebär detta att de dagligen möts av information om företag de äger och har ett intresse för. En stor del av den information som publiceras innehåller inte något fundamentalt värde. Enligt teori om en effektiv marknad och rationella investerare påverkas investerare inte av denna information. Inom beteendevetenskapen är detta däremot fullt tänkbart. Med en beteendevetenskaplig utgångspunkt önskar vi därmed undersöka om synligheten av bolagsnamnen i press påverkar likviditeten i deras aktier. Problemformulering: Påverkar synligheten av företagsnamnet i press, och i så fall hur, likviditeten i aktierna för bolagen listade på First North? Syfte: Huvudsyftet med studien är att utreda om handelsvolymen i aktierna för bolagen listade på First North påverkas av att bolagsnamnet syns i pressen. Om vi finner ett samband i huvudsyftet vill vi även som delsyfte undersöka om påverkan skiljer sig mellan tryckt och webbaserad press. Teori: Studien inkluderar teorin om den effektiva marknaden, bounded rationality samt behavioral finance teorier om övertro, social påverkan och flockbeteende, representativitet och familjaritet. Bounded rationality diskuterar människors verkliga beslutsfattande kontra de finansiella teoriernas uppfattning om effektiva marknader och rationella individer. Behavioral finance avser förklara investerarnas beteende. Grundtanken i teorin om övertro är att det finns investerare som överskattar sin egen förmåga. Social påverkan och flockbeteende är teorier om hur investerares beslut kan påverkas av omgivningen. Representativitet och familjaritet beskriver hur investerare tar investeringsbeslut utifrån sin känsla eller koppling till företaget. Metod: I utförandet av studien har en kvantitativ metod och deduktiv ansats använts. Vår studerade marknad är First North under åren 2011-2013. Urvalspopulationen består av 15 bolag listade på den svenska delen av denna. För dessa har vi samlat in data för antalet omnämnanden i tryckt och webbaserad press för årens alla dagar och finansiell information för samtliga 753 handelsdagar. Empiri/analys: Resultatet av undersökningen visar att handelsvolymen ökar vid ytterligare ett omnämnande av bolagen i den webbaserade pressen. Efter att ha inkluderat kontrollvariabler för bolagsstorlek, fundamentala nyheter, marknadssentiment med flera anser vi att ett orsakssamband styrkts. Studien visar att likviditeten i aktierna höjs vid ökad synlighet i webbaserad press. Utifrån detta har vi dragit slutsatsen att det finns investerare på First North vars beslutsprocess är betydligt mer invecklad än vad som antas i teori om effektiva marknader och rationella investerare. Investerarnas beteenden kan bättre förklaras av teorier inom behavioral finance. Slutsats: Vi anser att vi besvarat vår problemformulering och uppfyllt studiens syften. Studien har visat att likviditeten i aktierna för bolagen listade på First North påverkas av synlighet i webbaserad press.

An n-Venn diagram is defined as a collection of n finitely intersecting closed curves dividing the plane into 2^n distinct regions, where each region is in the interior of a unique subset of the curves. A Venn diagram is simple if at most two curves intersect at any point, and it is monotone if it has some embedding on the plane in which all curves are convex. An n-Venn diagram has n-fold rotational symmetry if a rotation of 180 degrees about a centre point in the plane leaves the diagram unchanged, up to a relabeling of the curves. It has been known that rotationally symmetric Venn diagrams could exist only if the number of curves is prime. Moreover, non-simple Venn diagrams with rotational symmetry have been proven to exist for any prime number of curves. However, the largest prime for which a simple rotationally symmetric Venn diagram was known prior to this, was 7. In this thesis, we are concerned with generating simple monotone Venn diagrams, especially those that have some type(s) of symmetry. Several representations of these diagrams are introduced and different backtracking search algorithms are provided based on these representations. Using these algorithms we show that there are 39,020 non-isomorphic simple monotone 6-Venn diagrams in total. In the case of drawing Venn diagrams on a sphere, we prove that there exists a simple symmetric n-Venn diagram, for any n >= 6, with the following set(s) of isometries : (a) a 4-fold rotational symmetry about the polar axis, together with an additional involutional symmetry about an axis through the equator, or (b) an involutional symmetry about the polar axis together with two reflectional symmetries about orthogonal planes that intersect at the polar axis. Finally, we introduce a new type of symmetry of Venn diagrams which leads us to the discovery of the first simple rotationally symmetric Venn diagrams of 11 and 13 curves. / Graduate / 0984 / Khalegh@GMail.com

The complicated turbulence structures in wall-bounded flows require accurate subgrid scale, SGS, modelling and realistic inlet boundary conditions for Large Eddy Simulation, LES. The present study focused on the investigation and development of transport equation SGS models and on the development of inlet conditions generation algorithms specialised for LES of wall-bounded flows. The investigation of SGS models has been carried out in two stages. In the first stage, models based on resolved scales and models based on subgrid scales were tested on a series of channel flow cases. Among the second group of models, there was a new SGS model whose development was based on the concept of dissipation calculated from the energy spectrum. The results indicated the superiority of the models based on subgrid scales, with the new model providing the most accurate flow field in general. (Continues...).

Karhunen-Lo`{e}ve decomposition is a well established tool, in areas such as signal processing, data compression and low-dimensional modeling. In computational fluid mechanics (CFD) too, KL decomposition can be used to achieve reduced storage requirements, or construction of relatively low-dimensional models. These relatively low-dimensional models, can be used to investigate the dynamics of the flow field in a qualitative manner. Employment of these reduced models is beneficial, as the they can be studied with even stringent computing resources. In addition, these models enable the identification and investigation of interactions between flowlets of different nature (the flow field is decomposed into these flowlets). However, one should not forget that, the reduced models do not necessarily capture the entire dynamics of the original flow, especially in the case of turbulent flows. In the presented study, a KL basis is used to construct reduced models of Navier-Stokes equations in the case of wall-bounded turbulent flow, using Galerkin projection. The resulting nonlinear dynamical systems are then used to investigate the dynamics of transition to turbulence in plane Poiseuille flow in a qualitative fashion. The KL basis used, is extracted from a flow filed obtained from a direct numerical simulation of plane Poiseuille flow.

Made available in DSpace on 2014-06-11T19:30:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-23Bitstream added on 2014-06-13T20:40:36Z : No. of bitstreams: 1 righetto_e_dr_ilha.pdf: 923323 bytes, checksum: f390d9baa00b45f3196dda419f801f19 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho apresenta-se uma estratégia de programação linear especializada para resolver, de forma eficiente, o problema de planejamento da expansão de sistemas de transmissão de energia elétrica usando o algoritmo de busca em vizinhança variável (VNS). O modelo matem´atico para este problema é um modelo de programação linear inteira mista. A solução deste modelo através de metaheurísticas, dependendo do sistema elétrico sob análise, pode exigir a solução de centenas de milhares de problemas de programação linear (PL) que exigem elevado esforço computacional e consomem a maior parte do tempo de CPU exigido pela metaheurística. A ideia fundamental deste artigo consiste em identificar soluções básicas adequadas para iniciar o processo de solução do problema de planejamento da transmissão e os inúmeros problemas de PL exigidos pela metaheurística, fazendo que os problemas de PL sejam resolvidos de forma eficiente computacionalmente. A solução básica adequada consiste na definição uma base dual factível específica para o problema que permite que novos problemas de PL resultantes das alterações de alguns parâmetros do problema de planejamento possam ser resolvidos usando um algoritmo dual simplex canalizado. A metodologia proposta foi validada e testada em um sistema de médio porte / This paper presents a linear programming expert strategy to solve efficiently the energy transmission network expansion planning problem using the variable neighborhood search algorithm (VNS). The mathematical model used is a mixed integer linear programming problem. Solution of this model using different metaheuristics, depending on the electrical system under analysis, may require hundreds of thousands of linear programming problems (LP) which require high computational effort and consume almost all of the CPU time required by the metaheuristic. The basic idea of this paper is to identify appropriate basic solutions which help to start the process and speed up the solution of the many subsequent subproblems generated during a typical run, solving the LP problems efficiently. The starting basic solution is defined as an appropriate dual feasible basis for the specific problem, new LP problems resulting from changes in some parameters of the planning problem are solved using a bounded dual simplex algorithm. The proposed methodology was validated and tested in a system of medium size